Trailer target monitoring system and method

[0001] This patent application is a continuation-in-part of co-pending U.S. patent application Ser. No. 14/059,835 which was filed on Oct. 22, 2013, entitled “TRAILER BACKUP ASSIST SYSTEM,” which is a continuation-in-part of U.S. patent application Ser. No. 13/443,743 which was filed on Apr. 10, 2012, entitled “DETECTION OF AND COUNTERMEASURES FOR JACKKNIFE ENABLING CONDITIONS DURING TRAILER BACKUP ASSIST,” which is a continuation-in-part of co-pending U.S. patent application Ser. No. 13/336,060, which was filed on Dec. 23, 2011, entitled “TRAILER PATH CURVATURE CONTROL FOR TRAILER BACKUP ASSIST,” which claims priority from co-pending U.S. Provisional Patent Application No. 61/477,132, which was filed on Apr. 19, 2011, entitled “TRAILER BACKUP ASSIST CURVATURE CONTROL,” which have a common Applicant herewith and are being incorporated herein in their entirety by reference.

[0002] The disclosure made herein relates generally to driver assist and active safety technologies in vehicles, and more particularly to a trailer backup assist system.

[0003] Reversing a vehicle while towing a trailer is very challenging for many drivers. This is particularly true for drivers that are unskilled at backing vehicles with attached trailers which may include those that drive with a trailer on an infrequent basis (e.g., have rented a trailer, use a personal trailer on an infrequent basis, etc.). One reason for such difficulty is that backing a vehicle with an attached trailer requires steering inputs that are opposite to normal steering when backing the vehicle without a trailer attached and/or requires braking to stabilize the vehicle-trailer combination before a jackknife condition occurs. Another reason for such difficulty is that small errors in steering while backing a vehicle with an attached trailer are amplified thereby causing the trailer to depart from a desired path.

[0004] To assist the driver in steering a vehicle with a trailer attached, a trailer backup assist system needs to know the driver's intention. One common assumption with known trailer backup assist systems is that a driver of a vehicle with an attached trailer wants to backup straight and the system either implicitly or explicitly assumes a zero curvature path for the vehicle-trailer combination. Unfortunately most of the real-world use cases of backing a trailer involve a curved path and, thus, assuming a path of zero curvature would significantly limit usefulness of the system. Some known systems assume that a path is known from a map or path planner. To this end, some known trailer backup assist systems operate under a requirement that a trailer backup path is known before backing of the trailer commences such as, for example, from a map or a path-planning algorithm. Undesirably, such implementations of the trailer backup assist systems are known to have a relatively complex human machine interface (HMI) device to specify the path, obstacles and/or goal of the backup maneuver. Furthermore, such systems also require some way to determine how well the desired path is being followed and to know when the desired goal, or stopping point and orientation, has been met, using approaches such as cameras, inertial navigation, or high precision global positioning system (GPS). These requirements lead to a relatively complex and costly system.

[0005] Another reason backing a trailer can prove to be difficult is the need to control the vehicle in a manner that limits the potential for a jackknife condition to occur. A trailer has attained a jackknife condition when a hitch angle cannot be reduced (i.e., made less acute) while continuously backing up a trailer by application of a maximum steering input for the vehicle such as, for example, by moving steered front wheels of the vehicle to a maximum steered angle at a maximum rate of steering angle change. In the case of the jackknife angle being achieved, the vehicle must be pulled forward to relieve the hitch angle in order to eliminate the jackknife condition and, thus, allow the hitch angle to be controlled via manipulation of the steered wheels of the vehicle. However, in addition to the jackknife condition creating the inconvenient situation where the vehicle must be pulled forward, it can also lead to damage to the vehicle and/or trailer if certain operating conditions of the vehicle relating to its speed, engine torque, acceleration, and the like are not detected and counteracted. For example, if the vehicle is travelling at a suitably high speed in reverse and/or subjected to a suitably high longitudinal acceleration when the jackknife condition is achieved, the relative movement of the vehicle with respect to the trailer can lead to contact between the vehicle and trailer thereby damaging the trailer and/or the vehicle.

[0006] According to one aspect of the present invention, a method of determining location of a trailer is provided. The method includes the steps of acquiring with a camera a first image of a feature of a trailer connected to a vehicle and acquiring with the camera a second image of the feature of a trailer. The method also includes the steps of comparing the first and second images and prompting entry of trailer information when the first and second images are different.

[0007] According to another aspect of the present invention, a method of determining location of a trailer target is provided. The method includes the steps of acquiring a first image of a target on a trailer and acquiring a second image of the target on the trailer. The method also includes the steps of comparing pixel sizes of the first and second images and prompting entry of trailer information when the pixel sizes in the first and second images are different.

[0008] According to a further aspect of the present invention, a trailer target monitoring system is provided. The trailer target monitoring system includes a camera mounted on a vehicle and arranged to generate images of a trailer connected to the vehicle and an image processor for processing a first image of a feature on the trailer and a second image of the feature and comparing pixel sizes of the first and second images. The trailer target monitoring system also includes a user interface for prompting a user to enter trailer information to the vehicle when the pixel sizes of the first and second images are different.

[0009] These and other aspects, objects, and features of the present invention will be understood and appreciated by those skilled in the art upon studying the following specification, claims, and appended drawings.

[0036] While various aspects of the inventive subject matter are described with reference to a particular illustrative embodiment, the inventive subject matter is not limited to such embodiments, and additional modifications, applications, and embodiments may be implemented without departing from the inventive subject matter. In the figures, like reference numbers will be used to illustrate the same components. Those skilled in the art will recognize that the various components set forth herein may be altered without varying from the scope of the inventive subject matter.

[0037] The disclosed subject matter is directed to providing trailer backup assist functionality in a manner that is relatively low cost and that offers an intuitive user interface. In particular, such trailer backup assist functionality provides for controlling curvature of a path of travel of a trailer attached to a vehicle (i.e., trailer path curvature control) by allowing a driver of the vehicle to specify a desired path of the trailer by inputting a desired trailer path curvature as the backup maneuver of the vehicle and trailer progresses. Although a control knob, a set of virtual buttons, or a touch screen can each be implemented for enabling trailer path curvature control, the disclosed subject matter is not unnecessarily limited to any particular configuration of interface through which a desired trailer path curvature is inputted. Furthermore, in the case where a steering wheel can be mechanically decoupled from steered wheels of the vehicle, the steering wheel can also be used as an interface through which a desired trailer path curvature is inputted. As will be discussed herein in greater detail, kinematical information of a system defined by the vehicle and the trailer are used to calculate a relationship (i.e., kinematics) between the trailer's curvature and the steering angle of the vehicle for determining steering angle changes of the vehicle for achieving the specified trailer path. Steering commands corresponding to the steering angle changes are used for controlling a steering system of the tow vehicle (e.g., electric power assisted steering (EPAS) system) for implementing steering angle changes of steered wheels of the vehicle to achieve (e.g., to approximate) the specified path of travel of the trailer. The trailer backup assist system automatically steers the vehicle-trailer combination as a driver uses the vehicle transmission, accelerator and brake to reverse the vehicle-trailer combination. The driver inputs a desired trailer curvature command by using an input device such as a trailer steering knob.

[0038] Trailer backup assist functionality is directed to implementing one or more countermeasures for limiting the potential of a jackknife condition being attained between a vehicle and a trailer being towed by the vehicle while backing up. In certain embodiments, curvature of a path of travel of the trailer (i.e., trailer path curvature control) can be controlled by allowing a driver of the vehicle to specify a desired path of the trailer by inputting a desired trailer path curvature as the backup maneuver of the vehicle and trailer progresses. Although a control knob, a set of virtual buttons, or a touch screen can each be implemented for enabling trailer path curvature control, the disclosed subject matter is not unnecessarily limited to any particular configuration of interface through which a desired trailer path curvature is inputted. Furthermore, in the case where a steering wheel can be mechanically decoupled from steered wheels of the vehicle, the steering wheel can also be used as an interface through which a desired trailer path curvature is inputted. As will be discussed herein in greater detail, kinematical information of a system defined by the vehicle and the trailer are used to calculate a relationship (i.e., kinematics) between the trailer's curvature and the steering angle of the vehicle for determining steering angle changes of the vehicle for achieving the specified trailer path. Steering commands corresponding to the steering angle changes are used for controlling a steering system of the tow vehicle (e.g., electric power assisted steering (EPAS) system) for implementing steering angle changes of steered wheels of the vehicle to achieve (e.g., to approximate) the specified path of travel of the trailer.

[0039] Embodiments of the disclosed subject matter are directed to trailer backup assist functionality that provides for a user interface for a system that controls curvature of a path of a trailer being backed by a vehicle. More specifically, trailer backup assist functionality configured in accordance with embodiments of the disclosed subject matter provide for such trailer path curvature control by allowing a driver of the vehicle to specify a desired path of the trailer by inputting a desired trailer path curvature as the backup maneuver of the vehicle and trailer progresses. In response to such path of the trailer being specified by the driver, embodiments of the disclosed subject matter control a power assisted steering system (e.g., electric power assisted steering (EPAS) system) of the vehicle for implementing steering angle changes of steered wheels of the vehicle to achieve the specified trailer path. Kinematics of the vehicle and the trailer are used to determine the steering angle changes that are required for achieving the specified trailer path. Accordingly, embodiments of the disclosed subject matter provide for implementation of trailer backup assist functionality in a manner that is relatively simple and that enables use of an intuitive vehicle operator interface for specifying trailer path curvature control.

[0040] Trailer Backup Assist System

[0041] Referring to FIG. 1, an embodiment of a vehicle 100 configured for performing trailer backup assist functionality is shown. A trailer backup assist system 105 of the vehicle 100 controls the curvature of path of travel of a trailer 110 that is attached to the vehicle 100. Such control is accomplished through interaction of a power assisted steering system 115 of the vehicle 100 and the trailer backup assist system 105. During operation of the trailer backup assist system 105 while the vehicle 100 is being reversed, a driver of the vehicle 100 is sometimes limited in the manner in which he/she can make steering inputs via a steering wheel of the vehicle 100. This is because in certain vehicles the trailer backup assist system 105 is in control of the power assisted steering system 115 and the power assisted steering system 115 is directly coupled to the steering wheel (i.e., the steering wheel of the vehicle 100 moves in concert with steered wheels of the vehicle 100). As is discussed below in greater detail, a human machine interface (HMI) device of the backup assist system 105 is used for commanding changes in curvature of a path of the trailer 110 such as a knob, thereby decoupling such commands from being made at the steering wheel of the vehicle 100. However, some vehicles configured to provide trailer backup assist functionality in accordance with the disclosed subject matter will have the capability to selectively decouple steering movement from movement of steerable wheels of the vehicle, thereby allowing the steering wheel to be used for commanding changes in curvature of a path of a trailer during such trailer backup assist.

[0042] The trailer backup assist system 105 includes a trailer backup assist control module 120, a trailer backup steering input apparatus 125, and a hitch angle detecting apparatus 130. The trailer backup assist control module 120 is connected to the trailer backup steering input apparatus 125 and the hitch angle detecting apparatus 130 for allowing communication of information therebetween. It is disclosed herein that the trailer backup steering input apparatus can be coupled to the trailer backup assist control module 120 in a wired or wireless manner. The trailer backup assist system control module 120 is attached to a power steering assist control module 135 of the power steering assist system 115 for allowing information to be communicated therebetween. A steering angle detecting apparatus 140 of the power steering assist system 115 is connected to the power steering assist control module 135 for providing information thereto. The trailer backup assist system is also attached to a brake system control module 145 and a powertrain control module 150 for allowing communication of information therebetween. Jointly, the trailer backup assist system 105, the power steering assist system 115, the brake system control module 145, the powertrain control module 150, and the gear selection device (PRNDL), define a trailer backup assist architecture configured in accordance with an embodiment.

[0043] The trailer backup assist control module 120 is configured for implementing logic (i.e., instructions) for receiving information from the trailer backup steering input apparatus 125, the hitch angle detecting apparatus 130, the power steering assist control module 135, the brake system control module 145, and the powertrain control module 150. The trailer backup assist control module 120 (e.g., a trailer curvature algorithm thereof) generates vehicle steering information as a function of all or a portion of the information received from the trailer backup steering input apparatus 125, the hitch angle detecting apparatus 130, the power steering assist control module 135, the brake system control module 145, and the powertrain control module 150. Thereafter, the vehicle steering information is provided to the power steering assist control module 135 for affecting steering of the vehicle 100 by the power steering assist system 115 to achieve a commanded path of travel for the trailer 110.

[0044] The trailer backup steering input apparatus 125 provides the trailer backup assist control module 120 with information defining the commanded path of travel of the trailer 110 to the trailer backup assist control module 120 (i.e., trailer steering information). The trailer steering information can include information relating to a commanded change in the path of travel (e.g., a change in radius of path curvature) and information relating to an indication that the trailer is to travel along a path defined by a longitudinal centerline axis of the trailer (i.e., along a substantially straight path of travel). As will be discussed below in detail, the trailer backup steering input apparatus 125 preferably includes a rotational control input device for allowing a driver of the vehicle 100 to interface with the trailer backup steering input apparatus 125 to command desired trailer steering actions (e.g., commanding a desired change in radius of the path of travel of the trailer and/or commanding that the trailer travel along a substantially straight path of travel as defined by a longitudinal centerline axis of the trailer). In a preferred embodiment, the rotational control input device is a knob rotatable about a rotational axis extending through a top surface/face of the knob. In other embodiments, the rotational control input device is a knob rotatable about a rotational axis extending substantially parallel to a top surface/face of the knob.

[0045] Some vehicles (e.g., those with active front steer) have a power steering assist system configuration that allows a steering wheel to be partially decoupled from movement of the steered wheels of such a vehicle. Accordingly, the steering wheel can be rotated independent of the manner in which the power steering assist system of the vehicle controls the steered wheels (e.g., as commanded by vehicle steering information provided by a power steering assist system control module from a trailer backup assist system control module configured in accordance with one embodiment). As such, in these types of vehicles where the steering wheel can be selectively decoupled from the steered wheels to allow independent operation thereof, trailer steering information of a trailer backup assist system configured in accordance with the disclosed subject matter can be provided through rotation of the steering wheel. Accordingly, it is disclosed herein that in certain embodiments, the steering wheel is an embodiment of a rotational control input device in the context of the disclosed subject matter. In such embodiments, the steering wheel would be biased (e.g., by an apparatus that is selectively engagable/activatable) to an at-rest position between opposing rotational ranges of motion.

[0046] The hitch angle detecting apparatus 130, which operates in conjunction with a hitch angle detection component 155 of the trailer 110, provides the trailer backup assist control module 120 with information relating to an angle between the vehicle 100 and the trailer 110 (i.e., hitch angle information). In a preferred embodiment, the hitch angle detecting apparatus 130 is a camera-based apparatus such as, for example, an existing rear view camera of the vehicle 100 that images (i.e., visually monitors) a target (i.e., the hitch angle detection component 155) attached the trailer 110 as the trailer 110 is being backed by the vehicle 100. Preferably, but not necessarily, the hitch angle detection component 155 is a dedicated component (e.g., an item attached to/integral with a surface of the trailer 110 for the express purpose of being recognized by the hitch angle detecting apparatus 130). Alternatively, the hitch angle detecting apparatus 130 can be a device that is physically mounted on a hitch component of the vehicle 100 and/or a mating hitch component of the trailer 110 for determining an angle between centerline longitudinal axes of the vehicle 100 and the trailer 110. The hitch angle detecting apparatus 130 can be configured for detecting a jackknife enabling condition and/or related information (e.g., when a hitch angle threshold has been met).

[0047] The power steering assist control module 135 provides the trailer backup assist control module 120 with information relating to a rotational position (e.g., angle) of the steering wheel angle and/or a rotational position (e.g., turning angle(s)) of steered wheels of the vehicle 100. In certain embodiments, the trailer backup assist control module 120 can be an integrated component of the power steering assist system 115. For example, the power steering assist control module 135 can include a trailer backup assist algorithm for generating vehicle steering information as a function of all or a portion of information received from the trailer backup steering input apparatus 125, the hitch angle detecting apparatus 130, the power steering assist control module 135, the brake system control module 145, and the powertrain control module 150.

[0048] The brake system control module 145 provides the trailer backup assist control module 120 with information relating to vehicle speed. Such vehicle speed information can be determined from individual wheel speeds as monitored by the brake system control module 145 or may be provided by an engine control module with signal plausibility. Vehicle speed may also be determined from an engine control module. In some instances, individual wheel speeds can also be used to determine a vehicle yaw rate and such yaw rate can be provided to the trailer backup assist control module 120 for use in determining the vehicle steering information. In certain embodiments, the trailer backup assist control module 120 can provide vehicle braking information to the brake system control module 145 for allowing the trailer backup assist control module 120 to control braking of the vehicle 100 during backing of the trailer 110. For example, using the trailer backup assist control module 120 to regulate speed of the vehicle 100 during backing of the trailer 110 can reduce the potential for unacceptable trailer backup conditions. Examples of unacceptable trailer backup conditions include, but are not limited to, a vehicle over speed condition, a high hitch angle rate, trailer angle dynamic instability, a calculated theoretical trailer jackknife condition (defined by a maximum vehicle steering angle, drawbar length, tow vehicle wheelbase and an effective trailer length), or physical contact jackknife limitation (defined by an angular displacement limit relative to the vehicle 100 and the trailer 110), and the like. It is disclosed herein that the backup assist control module 120 can issue a signal corresponding to a notification (e.g., a warning) of an actual, impending, and/or anticipated unacceptable trailer backup condition.

[0049] The powertrain control module 150 interacts with the trailer backup assist control module 120 for regulating speed and acceleration of the vehicle 100 during backing of the trailer 110. As mentioned above, regulation of the speed of the vehicle 100 is necessary to limit the potential for unacceptable trailer backup conditions such as, for example, jackknifing and trailer angle dynamic instability. Similar to high-speed considerations as they relate to unacceptable trailer backup conditions, high acceleration and high dynamic driver curvature requests can also lead to such unacceptable trailer backup conditions.

[0050] Steering Input Apparatus

[0051] Referring now to FIG. 2, an embodiment of the trailer backup steering input apparatus 125 discussed in reference to FIG. 1 is shown. A rotatable control element in the form of a knob 170 is coupled to a movement sensing device 175. The knob 170 is biased (e.g., by a spring return) to an at-rest position P(AR) between opposing rotational ranges of motion R(R), R(L). A first one of the opposing rotational ranges of motion R(R) is substantially equal to a second one of the opposing rotational ranges of motion R(L), R(R). To provide a tactile indication of an amount of rotation of the knob 170, a force that biases the knob 170 toward the at-rest position P(AR) can increase (e.g., non-linearly) as a function of the amount of rotation of the knob 170 with respect to the at-rest position P(AR). Additionally, the knob 170 can be configured with position indicating detents such that the driver can positively feel the at-rest position P(AR) and feel the ends of the opposing rotational ranges of motion R(L), R(R) approaching (e.g., soft end stops).

[0052] The movement sensing device 175 is configured for sensing movement of the knob 170 and outputting a corresponding signal (i.e., movement sensing device signal) to the trailer assist backup input apparatus 125 shown in FIG. 1. The movement sensing device signal is generated as a function of an amount of rotation of the knob 170 with respect to the at-rest position P(AR), a rate movement of the knob 170, and/or a direction of movement of the knob 170 with respect to the at-rest position P(AR). As will be discussed below in greater detail, the at-rest position P(AR) of the knob 170 corresponds to a movement sensing device signal indicating that the vehicle 100 should be steered such that the trailer 100 is backed along a substantially straight path (zero trailer curvature request from the driver) as defined by a centerline longitudinal axis of the trailer 110 when the knob 170 was returned to the at-rest position P(AR) and a maximum clockwise and anti-clockwise position of the knob 170 (i.e., limits of the opposing rotational ranges of motion R(R), R(L)) each correspond to a respective movement sensing device signal indicating a tightest radius of curvature (i.e., most acute trajectory) of a path of travel of the trailer 110 that is possible without the corresponding vehicle steering information causing a jackknife condition. In this regard, the at-rest position P(AR) is a zero curvature commanding position with respect to the opposing rotational ranges of motion R(R), R(L). It is disclosed herein that a ratio of a commanded curvature of a path of a trailer (e.g., radius of a trailer trajectory) and a corresponding amount of rotation of the knob can vary (e.g., non-linearly) over each one of the opposing rotational ranges of motion P(L), P(R) of the knob 170. It is also disclosed therein that the ratio can be a function of vehicle speed, trailer geometry, vehicle geometry, hitch geometry and/or trailer load.

[0053] Use of the knob 170 decouples trailer steering inputs from being made at a steering wheel of the vehicle 100. In use, as a driver of the vehicle 100 backs the trailer 110, the driver can turn the knob 170 to indicate a desired curvature of a path of the trailer 110 to follow and returns the knob 170 to the at-rest position P(AR) for causing the trailer 110 to be backed along a straight line. Accordingly, in embodiments of trailer backup assist systems where the steering wheel remains physically coupled to the steerable wheels of a vehicle during backup of an attached trailer, a rotatable control element configured in accordance with the disclosed subject matter (e.g., the knob 170) provides a simple and user-friendly means of allowing a driver of a vehicle to input trailer steering commands.

[0054] It is disclosed herein that a rotational control input device configured in accordance with embodiments of the disclosed subject matter (e.g., the knob 170 and associated movement sensing device) can omit a means for being biased to an at-rest position between opposing rotational ranges of motion. Lack of such biasing allows a current rotational position of the rotational control input device to be maintained until the rotational control input device is manually moved to a different position. Preferably, but not necessarily, when such biasing is omitted, a means is provided for indicating that the rotational control input device is positioned in a zero curvature commanding position (e.g., at the same position as the at-rest position in embodiments where the rotational control input device is biased). Examples of means for indicating that the rotational control input device is positioned in the zero curvature commanding position include, but are not limited to, a detent that the rotational control input device engages when in the zero curvature commanding position, a visual marking indicating that the rotational control input device is in the zero curvature commanding position, an active vibratory signal indicating that the rotational control input device is in or approaching the zero curvature commanding position, an audible message indicating that the rotational control input device is in of approaching the zero curvature commanding position, and the like.

[0055] It is also disclosed herein that embodiments of the disclosed subject matter can be configured with a control input device that is not rotational (i.e., a non-rotational control input device). Similar to a rotational control input device configured in accordance with embodiments of the disclosed subject matter (e.g., the knob 170 and associated movement sensing device), such a non-rotational control input device is configured to selectively provide a signal causing a trailer to follow a path of travel segment that is substantially straight and to selectively provide a signal causing the trailer to follow a path of travel segment that is substantially curved. Examples of such a non-rotational control input device include, but are not limited to, a plurality of depressible buttons (e.g., curve left, curve right, and travel straight), a touch screen on which a driver traces or otherwise inputs a curvature for path of travel commands, a button that is translatable along an axis for allowing a driver to input path of travel commands, or joystick type input and the like.

[0056] The trailer backup steering input apparatus 125 can be configured to provide various feedback information to a driver of the vehicle 100. Examples of situation that such feedback information can include, but are not limited to, a status of the trailer backup assist system 105 (e.g., active, in standby (e.g., when driving forward to reduce the trailer angle and zero trailer angle to remove bias), faulted, inactive, etc.), that a curvature limit has been reached (i.e., maximum commanded curvature of a path of travel of the trailer 110), and/or a graphical representation of the vehicle and trailer orientation state. To this end, the trailer backup steering input apparatus 125 can be configured to provide a tactile feedback signal (e.g., a vibration through the knob 170) as a warning if any one of a variety of conditions occur. Examples of such conditions include, but are not limited to, the trailer 110 approaching jackknife, the trailer backup assist system 105 has had a failure, the trailer backup assist system 105 has detected a fault, the trailer backup assist system 105 or other system of the vehicle 100 has predicted a collision on the present path of travel of the trailer 110, the trailer backup system 105 has restricted a commanded curvature of a trailer's path of travel (e.g., due to excessive speed or acceleration of the vehicle 100), and the like. Still further, it is disclosed that the trailer backup steering input apparatus 125 can use illumination (e.g., an LED 180) and/or an audible signal output (e.g., an audible output device 185 or through attached vehicle audio speakers) to provide certain feedback information (e.g., notification/warning of an unacceptable trailer backup condition).

[0057] Referring now to FIGS. 2 and 3, an example of using the trailer backup steering input apparatus 125 for dictating a curvature of a path of travel (POT) of a trailer (i.e., the trailer 110 shown in FIG. 1) while backing up the trailer with a vehicle (i.e., the vehicle 100 in FIGS. 1 and 2) is shown. In preparation of backing the trailer 110, the driver of the vehicle 100 drives the vehicle 100 forward along a pull-thru path (PTP) to position the vehicle 100 and trailer 110 at a first backup position B1. In the first backup position B1, the vehicle 100 and trailer 110 are longitudinally aligned with each other such that a longitudinal centerline axis L1 of the vehicle 100 is aligned with (e.g., parallel with or coincidental with) a longitudinal centerline axis L2 of the trailer 110. It is disclosed herein that such alignment of the longitudinal axes L1, L2 at the onset of an instance of trailer backup functionality is not a requirement for operability of a trailer backup assist system configured in accordance with the disclosed subject matter.

[0058] After activating the trailer backup assist system 105 (e.g., before, after, or during the pull-thru sequence), the driver begins to back the trailer 110 by reversing the vehicle 100 from the first backup position B1. So long as the knob 170 of the trailer backup steering input apparatus 125 remains in the at-rest position P(AR), the trailer backup assist system 105 will steer the vehicle 100 as necessary for causing the trailer 110 to be backed along a substantially straight path of travel as defined by the longitudinal centerline axis L2 of the trailer 110 at the time when backing of the trailer 110 began. When the trailer reaches the second backup position B2, the driver rotates the knob 170 to command the trailer 110 to be steered to the right (i.e., a knob position R(R) clockwise rotation). Accordingly, the trailer backup assist system 105 will steer the vehicle 100 for causing the trailer 110 to be steered to the right as a function of an amount of rotation of the knob 170 with respect to the at-rest position P(AR), a rate movement of the knob 170, and/or a direction of movement of the knob 170 with respect to the at-rest position P(AR). Similarly, the trailer 110 can be commanded to steer to the left by rotating the knob 170 to the left. When the trailer reaches backup position B3, the driver allows the knob 170 to return to the at-rest position P(AR) thereby causing the trailer backup assist system 105 to steer the vehicle 100 as necessary for causing the trailer 110 to be backed along a substantially straight path of travel as defined by the longitudinal centerline axis L2 of the trailer 110 at the time when the knob 170 was returned to the at-rest position P(AR). Thereafter, the trailer backup assist system 105 steers the vehicle 100 as necessary for causing the trailer 110 to be backed along this substantially straight path to the fourth backup position B4. In this regard, arcuate portions of a path of travel POT of the trailer 110 are dictated by rotation of the knob 170 and straight portions of the path of travel POT are dictated by an orientation of the centerline longitudinal axis L2 of the trailer when the knob 170 is in/returned to the at-rest position P(AR).

[0059] In order to activate the trailer backup assist system described above in FIGS. 1-3, the driver interacts with the trailer backup assist system and the trailer backup assist system interacts with the vehicle environment. The trailer backup assist system automatically steers as the driver reverses the vehicle. As discussed above, the driver controls the trailer trajectory by using a steering knob to input desired trailer curvature. The trailer backup assist algorithm determines the vehicle steering angle to achieve the desired trailer curvature, and the driver controls the throttle and brake while the trailer backup assist system controls the steering.

[0060] FIG. 4 shows a method 200 for implementing trailer backup assist functionality in accordance with one embodiment. In a preferred embodiment, the method 200 for implementing trailer backup assist functionality can be carried out using the trailer backup assist architecture discussed above in reference to the vehicle 100 and trailer 110 of FIG. 1. Accordingly, trailer steering information is provided through use of a rotational control input device (e.g., the knob 170 discussed in reference to FIG. 2).

[0061] An operation 202 is performed for receiving a trailer backup assist request. Examples of receiving the trailer backup assist request include activating the trailer backup assist system and providing confirmation that the vehicle and trailer are ready to be backed. After receiving a trailer backup assist request (i.e., while the vehicle is being reversed), an operation 204 is performed for receiving a trailer backup information signal. Examples of information carried by the trailer backup information signal include, but are not limited to, information from the trailer backup steering input apparatus 125, information from the hitch angle detecting apparatus 130, information from the power steering assist control module 135, information from the brake system control module 145, and information from the powertrain control module 150. It is disclosed herein that information from the trailer backup steering input apparatus 125 preferably includes trailer path curvature information characterizing a desired curvature for the path of travel of the trailer, such as provided by the trailer backup steering input apparatus 125 discussed above in reference to FIGS. 1 and 2. In this manner, the operation 204 for receiving the trailer backup information signal can include receiving trailer path curvature information characterizing the desired curvature for the path of travel of the trailer.

[0062] If the trailer backup information signal indicates that a change in curvature of the trailer's path of travel is requested (i.e., commanded via the knob 170), an operation 206 is performed for determining vehicle steering information for providing the requested change in curvature of the trailer's path of travel. Otherwise, an operation 208 is performed for determining vehicle steering information for maintaining a current straight-line heading of the trailer (i.e., as defined by the longitudinal centerline axis of the trailer). Thereafter, an operation 210 is performed for providing the vehicle steering information to a power steering assist system of the vehicle, followed by an operation 212 being performed for determining the trailer backup assist status. If it is determined that trailer backup is complete, an operation 214 is performed for ending the current trailer backup assist instance. Otherwise the method 200 returns to the operation 204 for receiving trailer backup information. Preferably, the operation for receiving the trailer backup information signal, determining the vehicle steering information, providing the vehicle steering information, and determining the trailer backup assist status are performed in a monitoring fashion (e.g., at a high rate of speed of a digital data processing device). Accordingly, unless it is determined that reversing of the vehicle for backing the trailer is completed (e.g., due to the vehicle having been successfully backed to a desired location during a trailer backup assist instance, the vehicle having to be pulled forward to begin another trailer backup assist instance, etc.), the method 200 will continually be performing the operations for receiving the trailer backup information signal, determining the vehicle steering information, providing the vehicle steering information, and determining the trailer backup assist status.

[0063] It is disclosed herein that the operation 206 for determining vehicle steering information for providing the requested change in curvature of the trailer's path of travel preferably includes determining vehicle steering information as a function of trailer path curvature information contained within the trailer backup information signal. As will be discussed below in greater detail, determining vehicle steering information can be accomplished through a low order kinematic model defined by the vehicle and the trailer. Through such a model, a relationship between the trailer path curvature and commanded steering angles of steered wheels of the vehicle can be generated for determining steering angle changes of the steered wheels for achieving a specified trailer path curvature. In this manner, the operation 206 for determining vehicle steering information can be configured for generating information necessary for providing trailer path curvature control in accordance with the disclosed subject matter.

[0064] In some embodiments of the disclosed subject matter, the operation 210 for providing the vehicle steering information to the power steering assist system of the vehicle causes the steering system to generate a corresponding steering command as a function of the vehicle steering information. The steering command is interpretable by the steering system and is configured for causing the steering system to move steered wheels of the steering system for achieving a steered angle as specified by the vehicle steering information. Alternatively, the steering command can be generated by a controller, module or computer external to the steering system (e.g., a trailer backup assist control module) and be provided to the steering system.

[0065] In parallel with performing the operations for receiving the trailer backup information signal, determining the vehicle steering information, providing the vehicle steering information, and determining the trailer backup assist status, the method 200 performs an operation 216 for monitoring the trailer backup information for determining if an unacceptable trailer backup condition exists. Examples of such monitoring include, but are not limited to assessing a hitch angle to determine if a hitch angle threshold is exceeded, assessing a backup speed to determine if a backup speed threshold is exceeded, assessing vehicle steering angle to determine if a vehicle steering angle threshold is exceeded, assessing other operating parameters (e.g., vehicle longitudinal acceleration, throttle pedal demand rate and hitch angle rate) for determining if a respective threshold value is exceeded, and the like. Backup speed can be determined from wheel speed information obtained from one or more wheel speed sensors of the vehicle. If it is determined that an unacceptable trailer backup condition exists, an operation 218 is performed for causing the current path of travel of the trailer to be inhibited (e.g., stopping motion of the vehicle), followed by the operation 214 being performed for ending the current trailer backup assist instance. It is disclosed herein that prior to and/or in conjunction with causing the current trailer path to be inhibited, one or more actions (e.g., operations) can be implemented for providing the driver with feedback (e.g., a warning) that such an unacceptable trailer angle condition is impending or approaching. In one example, if such feedback results in the unacceptable trailer angle condition being remedied prior to achieving a critical condition, the method can continue with providing trailer backup assist functionality in accordance with operations 204-212. Otherwise, the method can proceed to operation 214 for ending the current trailer backup assist instance. In conjunction with performing the operation 214 for ending the current trailer backup assist instance, an operation can be performed for controlling movement of the vehicle to correct or limit a jackknife condition (e.g., steering the vehicle, decelerating the vehicle, limiting magnitude and/or rate of driver requested trailer curvature input, limiting magnitude and/or rate of the steering command, and/or the like to preclude the hitch angle from being exceeded).

[0066] Curvature Control Algorithm

[0067] Turning now to a discussion of a kinematic model used to calculate a relationship between a curvature of a path of travel of a trailer and the steering angle of a vehicle towing the trailer, a low order kinematic model can be desirable for a trailer backup assist system configured in accordance with some embodiments. To achieve such a low order kinematic model, certain assumptions are made with regard to parameters associated with the vehicle/trailer system. Examples of such assumptions include, but are not limited to, the trailer being backed by the vehicle at a relatively low speed, wheels of the vehicle and the trailer having negligible (e.g., no) slip, tires of the vehicle having negligible (e.g., no) lateral compliance, tires of the vehicle and the trailer having negligible (e.g., no) deformation, actuator dynamics of the vehicle being negligible, the vehicle and the trailer exhibiting negligible (e.g., no) roll or pitch motions.

[0068] As shown in FIG. 5, for a system defined by a vehicle 302 and a trailer 304, the kinematic model 300 is based on various parameters associated with the vehicle 302 and the trailer 304. These kinematic model parameters include:

[0069] δ: steering angle at steered front wheels 306 of the vehicle 302;

[0070] α: yaw angle of the vehicle 302;

[0071] β: yaw angle of the trailer 304;

[0072] γ: hitch angle (γ=β−α);

[0073] W: wheel base of the vehicle 302;

[0074] L: length between hitch point 308 and rear axle 310 of the vehicle 302;

[0075] D: length between hitch point 308 and axle length 312 of the trailer 304 (axle length 312 may be an effective, or equivalent, axle length for a trailer having a multiple axle configuration; and

[0076] r₂: curvature radius for the trailer 304.

[0077] The kinematic model 300 of FIG. 5 reveals a relationship between trailer path radius of curvature r₂ at the midpoint 314 of an axle 312 of the trailer 304, steering angle δ of the steered wheels 306 of the vehicle 302, and the hitch angle γ. As shown in the equation below, this relationship can be expressed to provide the trailer path curvature κ₂ such that, if γ is given, the trailer path curvature κ₂ can be controlled based on regulating the steering angle δ (where {dot over (β)} is trailer yaw rate and {dot over (η)} is trailer velocity).

[0078] ${\kappa }_2=\frac{1}{r_2}=\frac{\stackrel{.}{\beta }}{\stackrel{.}{\eta }}=\frac{\left(W+\frac{{\mathrm{KV}}^2}{g}\right)\sin \gamma +L\cos \gamma \tan \delta }{D\left(\left(W+\frac{{\mathrm{KV}}^2}{g}\right)\cos \gamma -L\sin \gamma \tan \delta \right)}$

[0079] Or, this relationship can be expressed to provide the steering angle δ as a function of trailer path curvature κ₂ and hitch angle γ.

[0080] $\delta ={\tan }^{-1}\left(\frac{\left(W+\frac{{\mathrm{KV}}^2}{g}\right)\left[{\kappa }_{2}D\cos \gamma -\sin \gamma \right]}{\mathrm{DL}{\kappa }_2\sin \gamma +L\cos \gamma }\right)=F\left(\gamma ,{\kappa }_2,K\right)$

[0081] Accordingly, for a particular vehicle and trailer combination, certain kinematic model parameters (e.g., D, W and L) are constant and assumed known. V is the vehicle longitudinal speed and g is the acceleration due to gravity. K is a speed dependent parameter which when set to zero makes the calculation of steering angle independent of vehicle speed. For example, vehicle-specific kinematic model parameters can be predefined in an electronic control system of a vehicle and trailer-specific kinematic model parameters can be inputted by a driver of the vehicle. Trailer path curvature κ₂ is determined from the driver input via a trailer backup steering input apparatus. Through the use of the equation for providing steering angle, a corresponding steering command can be generated for controlling a steering system (e.g., an actuator thereof) of the vehicle.

[0082] FIG. 6 shown an example of a trailer path curvature function plot 400 for a rotary-type trailer backup steering input apparatus (e.g., the trailer backup steering input apparatus 125 discussed above in reference to FIGS. 1 and 2). A value representing trailer path curvature (e.g., trailer path curvature κ2) is provided as an output signal from the rotary-type trailer backup steering input apparatus as a function of user input movement. In this example, a curve 402 specifying trailer path curvature relative to user input (e.g., amount of rotation) at a rotary input device (e.g., a knob) is defined by a cubic function. However, a skilled person will appreciate that embodiments of the disclosed subject matter are not limited to any particular function between a magnitude and/or rate of input at a trailer backup steering input apparatus (e.g., knob rotation) and a resulting trailer path curvature value.

[0083] Jackknife Detection

[0084] Referring to FIG. 5, in preferred embodiments of the disclosed subject matter, it is desirable to limit the potential for the vehicle 302 and the trailer 304 to attain a jackknife angle (i.e., the vehicle/trailer system achieving a jackknife condition). A jackknife angle γ(j) refers to a hitch angle γ that while backing cannot be overcome by the maximum steering input for a vehicle such as, for example, the steered front wheels 306 of the vehicle 302 being moved to a maximum steered angle δ at a maximum rate of steering angle change. The jackknife angle γ(j) is a function of a maximum wheel angle for the steered wheel 306 of the vehicle 302, the wheel base W of the vehicle 302, the distance L between hitch point 308 and the rear axle 310 of the vehicle 302, and the length D between the hitch point 308 and the effective axle 312 of the trailer 304 when the trailer has multiple axles. The effective axle 312 may be the actual axle for a single axle trailer or an effective axle location for a trailer with multiple axles. When the hitch angle γ for the vehicle 302 and the trailer 304 achieves or exceeds the jackknife angle γ(j), the vehicle 302 must be pulled forward to reduce the hitch angle γ. Thus, for limiting the potential for a vehicle/trailer system attaining a jackknife angle, it is preferable to control the yaw angle of the trailer while keeping the hitch angle of the vehicle/trailer system relatively small.

[0085] Referring to FIGS. 5 and 7, a steering angle limit for the steered front wheels 306 requires that the hitch angle γ cannot exceed the jackknife angle γ(j), which is also referred to as a critical hitch angle. Thus, under the limitation that the hitch angle γ cannot exceed the jackknife angle γ(j), the jackknife angle γ(j) is the hitch angle γ that maintains a circular motion for the vehicle/trailer system when the steered wheels 306 are at a maximum steering angle δ(max). The steering angle for circular motion with hitch angle is defined by the following equation.

[0086] $\tan {\delta }_{\max }=\frac{w\sin {\gamma }_{\max }}{D+L\cos {\gamma }_{\max }}$

[0087] Solving the above equation for hitch angle allows jackknife angle γ(j) to be determined. This solution, which is shown in the following equation, can be used in implementing trailer backup assist functionality in accordance with the inventive subject matter for monitoring hitch angle in relation to jackknife angle.

[0088] $\cos \stackrel{\_}{\gamma }=\frac{-b\pm \sqrt{b^2-4\mathrm{ac}}}{2a}$ $\mathrm{where},a=L^2{\tan }^2\delta \left(\max \right)+W^2;$ $b=2\mathrm{LD}{\tan }^2\delta \left(\max \right);\mathrm{and}$ $c=D^2{\tan }^2\delta \left(\max \right)-W^2.$

[0089] In certain instances of backing a trailer, a jackknife enabling condition can arise based on current operating parameters of a vehicle in combination with a corresponding hitch angle. This condition can be indicated when one or more specified vehicle operating thresholds are met while a particular hitch angle is present. For example, although the particular hitch angle is not currently at the jackknife angle for the vehicle and attached trailer, certain vehicle operating parameters can lead to a rapid (e.g., uncontrolled) transition of the hitch angle to the jackknife angle for a current commanded trailer path curvature and/or can reduce an ability to steer the trailer away from the jackknife angle. One reason for a jackknife enabling condition is that trailer curvature control mechanisms (e.g., those in accordance with the inventive subject matter) generally calculate steering commands at an instantaneous point in time during backing of a trailer. However, these calculations will typically not account for lag in the steering control system of the vehicle (e.g., lag in a steering EPAS controller). Another reason for the jackknife enabling condition is that trailer curvature control mechanisms generally exhibit reduced steering sensitivity and/or effectiveness when the vehicle is at relatively high speeds and/or when undergoing relatively high acceleration.

[0090] Jackknife Countermeasures

[0091] FIG. 8 shows a method 500 for implementing jackknife countermeasures functionality in accordance with an embodiment of the disclosed subject matter for a vehicle and attached trailer. Trailer backup assist functionality in accordance with the disclosed subject matter can include jackknife countermeasures functionality. Alternatively, jackknife countermeasures functionality in accordance with one embodiment can be implemented separately from other aspects of trailer backup assist functionality.

[0092] The method 500 begins when operation 502 is performed for receiving jackknife determining information characterizing a jackknife enabling condition of the vehicle-trailer combination at a particular point in time (e.g., at the point in time when the jackknife determining information was sampled). Examples of the jackknife determining information includes, but are not limited to, information characterizing a hitch angle, information characterizing a vehicle accelerator pedal transient state, information characterizing a speed of the vehicle, information characterizing longitudinal acceleration of the vehicle, information characterizing a brake torque being applied by a brake system of the vehicle, information characterizing a powertrain torque being applied to driven wheels of the vehicle, and information characterizing the magnitude and rate of driver requested trailer curvature. The operation 502 for receiving jackknife determining information can be the first operation in a sampling process where jackknife determining information is sampled upon initiation of an instance of implementing jackknife countermeasures functionality. In this regard, jackknife determining information would be continually monitored such as, for example, by an electronic control unit (ECU) that carries out trailer backup assist (TBA) functionality. As discussed above in reference to FIG. 5, a kinematic model representation of the vehicle and the trailer can be used to determine a jackknife angle for the vehicle-trailer combination. However, the inventive subject matter is not unnecessarily limited to any specific approach for determining the jackknife angle.

[0093] After receiving the jackknife determining information, an operation 504 is performed for assessing the jackknife determining information for determining if the vehicle-trailer combination attained the jackknife enabling condition at the particular point in time. The objective of the operation 504 for assessing the jackknife determining information is determining if a jackknife enabling condition has been attained at the point in time defined by the jackknife determining information. If it is determined that a jackknife enabling condition is not present at the particular point in time, the method 500 returns to the operation 502 for receiving another instance of the jackknife determining information. If it is determined that a jackknife enabling condition is present at the particular point in time, an operation 506 is performed for determining an applicable countermeasure or countermeasures to implement. Accordingly, in some embodiments, an applicable countermeasure will be selected dependent upon a parameter identified as being a key influencer of the jackknife enabling condition. However, in other embodiments, an applicable countermeasure will be selected as being most able to readily alleviate the jackknife enabling condition. In still other embodiment, a predefined countermeasure or predefined set of countermeasures may be the applicable countermeasure(s).

[0094] The objective of a countermeasure in the context of the disclosed subject matter (i.e., a jackknife reduction countermeasure) is to alleviate a jackknife enabling condition. To this end, such a countermeasure can be configured to alleviate the jackknife enabling condition using a variety of different strategies. In a vehicle speed sensitive countermeasure strategy, actions taken for alleviating the jackknife enabling condition can include overriding and/or limiting driver requested trailer radius of curvature (e.g., being requested via a trailer backup steering input apparatus configured in accordance with the disclosed subject matter) as a function of vehicle speed (e.g., via a lookup table correlating radius of curvature limits to vehicle speed as shown in FIG. 6). In a countermeasure strategy where trailer curvature requests are limited as a function of speed and driver curvature command transient rates, actions taken for alleviating the jackknife enabling condition can include rate limiting trailer curvature command transients as requested by a driver above a predefined vehicle speed whereas, under the predefined vehicle speed, the as-requested trailer curvature are not rate limited. In a torque limiting countermeasure strategy, actions taken for alleviating the jackknife enabling condition can include application of full available powertrain torque being inhibited when the jackknife enabling condition is present while the vehicle is above a predefined speed and application of full available powertrain torque being allowed when the vehicle speed is reduced below the predefined speed while in the torque inhibiting mode. As opposed to a fixed predefined speed, the torque limiting countermeasure strategy can utilize a speed threshold that is a function of hitch angle (i.e., speed threshold inversely proportional to hitch angle acuteness). In a driver accelerator pedal transient detection countermeasure strategy, actions taken for alleviating the jackknife enabling condition can include overriding and/or limiting driver requested trailer radius of curvature as a function of transient accelerator pedal requests (e.g., requested trailer radius of curvature limited when a large accelerator pedal transient is detected). In a hitch angle rate sensitive countermeasure strategy, actions taken for alleviating the jackknife enabling condition can include using hitch angle rate in a predefined or calculated mapping with current hitch angle position to limit driver requested trailer radius of curvature. Accordingly, in view of the disclosures made herein, a skilled person will appreciate that embodiments of the disclosed subject matter are not unnecessarily limited to a countermeasure strategy of any particular configuration.

[0095] As disclosed above, implementation of trailer backup assist functionality in accordance with the disclosed subject matter can utilize a kinematic model for determining steering control information, jackknife enabling conditions, and jackknife angle. Such a kinematic model has many parameters than can influence trailer curvature control effectiveness. Examples of these parameters include, but are not limited to, the vehicle wheelbase, understeer gradient gain, vehicle track width, maximum steer angle at the vehicle front wheels, minimum turning radius of vehicle, maximum steering rate able to be commanded by the steering system, hitch ball to trailer axle length, and vehicle rear axle to hitch ball length. Sensitivity analysis for a given kinematic model can be used to provide an understanding (e.g., sensitivity) of the relationships between such parameters, thereby providing information necessary for improving curvature control performance and for reducing the potential for jackknife enabling conditions. For example, through an understanding of the sensitivity of the parameters of a kinematic model, scaling factors can be used with speed dependent jackknife countermeasures to reduce jackknife potential (e.g., for special applications such as short wheelbase conditions).

[0096] Still referring to FIG. 8, after determining the applicable countermeasure(s), an operation 508 is performed for implementing the chosen jackknife countermeasure(s) and an operation 510 is performed for initiating a jackknife warning. As discussed above in regard to countermeasure strategies, implementing the jackknife countermeasure(s) can include commanding a speed controlling system of the vehicle to transition to an altered state of operation in which a speed of the vehicle is reduced, commanding the steering control system of the vehicle to transition to an altered state of operation in which a radius of curvature of a path of the trailer is increased, command the steering control system of the vehicle to transition to an altered state of operation in which a decrease in the radius of the curvature of the path of the trailer is inhibited, commanding a brake control system of the vehicle to apply brake torque to reduce vehicle speed/inhibit vehicle acceleration, and/or commanding a powertrain control system of the vehicle to inhibit full available powertrain torque from being delivered to driven wheels of the vehicle until another jackknife enabling parameter (e.g., vehicle speed) is below a defined threshold. In certain embodiments of the inventive subject matter, the jackknife warning is provided to the driver using at least one vehicle control system through which the jackknife countermeasure is implemented. Speed reduction, in addition to applying the brakes, can be accomplished by any number of means such as, for example, limiting throttle inputs (e.g., via a terrain management feature) and/or transitioning a transmission to a reverse low gear if the vehicle is equipped with a multi-range reverse gear transmission. Examples of such system-specific warning approach include, but are not limited to, providing a warning through an accelerator pedal of the vehicle (e.g., via haptic feedback) if the countermeasure includes limiting speed of the vehicle and/or providing a warning through an input element (e.g., knob) of a trailer backup steering input apparatus of the vehicle (e.g., via haptic feedback if the countermeasure includes limiting driver requested trailer radius of curvature), through haptic seat vibration warning, through a visual warning (e.g., through a visual display apparatus of the towing vehicle) and/or through audible warnings (e.g., through an audio output apparatus of the towing vehicle), or the like. One embodiment of utilizing warnings relating to vehicle speed as it relates to onset or presence of a jackknife enabling condition includes implementation of a dual stage warning. For example, when a backing speed of the vehicle increases sufficiently for causing a speed of the vehicle to reach a lower (i.e., first) speed threshold during backing of the trailer, a driver of the vehicle would be provided with a first warning indication (e.g., via haptic, audible, and/or visual means as implemented by the trailer backup assist system) for informing the driver that there is the need to reduce the speed of the vehicle to alleviate or preclude the jackknife enabling condition. If the driver does not correspondingly respond by causing a speed of the vehicle to be reduced (or not to further increase) and the vehicle continues to gain speed such that it passes a higher (i.e., a second) speed threshold, the driver of the vehicle would be provided with a second warning indication (e.g., a more severe haptic, audible, and/or visual means as implemented by the trailer backup assist system) for informing the driver that there is an immediate need to reduce the speed of the vehicle to alleviate or preclude the jackknife enabling condition. The first and/or the second speed indication warnings can be implemented in conjunction with a respective speed limiting countermeasure measures (e.g., the trailer backup assist system causing activation of a brake system of the vehicle and/or reducing a throttle position of the vehicle).

[0097] Human Machine Interface

[0098] In order to implement the control features discussed above with respect to methods described in FIG. 5 and FIG. 8, a driver must interact with the trailer backup assist system 105 to configure the system 105. The vehicle 100 is also equipped, as shown in FIG. 9, with a human machine interface (HMI) device 102 to implement trailer backup assist functionality through driver interaction with the HMI device 102.

[0099] FIG. 9 shows an example of an HMI device 102 in the vehicle that a driver uses to interact with the trailer backup assist system 105. The driver is presented with multiple menus 104 (only one example menu is shown in FIG. 9) displayed by way of the HMI 102. The HMI menus 104 assist the driver through modules (shown in FIGS. 10 and 11) that setup 600, calibrate 700, and activate 800 the trailer backup assist system 105 so that control methods 200, 500 may be implemented to assist the driver with the backup of the trailer shown generally as a flow diagram in FIGS. 10 and 11, and to be discussed in greater detail later herein. Each module is directed to particular elements, or features, which are used to configure the trailer backup assist system to accurately implement control methods 200, 500. While each module is described with reference to particular features of the disclosed subject matter, it should be noted that each module is not necessarily limited to the particular features described in the examples herein. It is possible to rearrange the modules or to replace elements or features of a module without departing from the scope of the disclosed subject matter.

[0100] The trailer backup assist system 105 will guide a driver through the steps necessary to connect a trailer and attach a target. The driver may activate the setup by way of the backup steering input apparatus 125, for example by turning or pushing the rotary knob, or my merely making a selection for the trailer backup assist system from a menu on the HMI device 102. Referring to FIG. 10, a driver initiates the trailer backup assist system through the trailer backup assist steering input apparatus. In the case of a rotary knob, the driver presses or rotates the knob to initiate the trailer backup assist system. The system will guide the driver through the steps of connecting 580 a compatible trailer 110. A compatible trailer is one that pivots at a single point relative to the vehicle and behind the rear axle of the vehicle.

[0101] Once the system is selected by either the trailer backup steering input apparatus 125 or the HMI device 105, the system will guide the driver to prepare the vehicle and vehicle trailer combination as necessary. The vehicle 100 should be turned “on” and the vehicle 100 should be in “park” 590. In the event the vehicle 100 is on but is traveling at a speed that is greater than a predetermined limit, for example five miles per hour, the trailer backup assist system 105 will become inactive and inaccessible to the driver. The trailer backup assist system 105 setup module 600 will not begin or will be exited 585. If the type of trailer 110 selected by the driver is a trailer 110 that is not compatible with the trailer backup assist system 105, the setup module 600 will be exited 585 or will not begin. In the event, the trailer 110 is compatible with the trailer backup assist system 105, the setup module 600 verifies that the vehicle 100 gear shift mechanism is in “park.” Again, in the event the vehicle is not “on” and the gear shift mechanism is not on “park,” the setup module will not begin 585.

[0102] Upon connection 580 of a compatible trailer 110, the vehicle 100 being “on” 590 and the vehicle 100 being in “park” 590, the HMI 102 will present a menu 104 that has a “Towing” mode option to be selected by the driver. The driver selects “Towing” mode and a menu 104 is presented that provides a “Trailer Options” selection. The driver then selects a “Trailer Options” mode from the “Towing” menu. The driver is prompted to either “add a trailer” or “select a trailer” from a menu 104 presented on the HMI device and the “Setup” module 600 of the inventive subject matter has begun. For certain camera-based trailer angle detection systems, an operation 602 is performed wherein a warning menu may be presented to the driver, by way of the HMI, informing the driver that the trailer must be in a straight line, meaning there is no angle at the hitch between the vehicle and the trailer. The warning indicates that the driver may need to take corrective action, for example, pull the vehicle forward in order to align the trailer and the vehicle as required for the setup 600. A generic or static graphic may be presented by way of the HMI 102 to assist the driver in visually recognizing the alignment between the trailer 110 and the vehicle 100 that is necessary in order to properly setup and calibrate the trailer backup assist system 105. The driver applies any corrections 603 in that the driver makes any necessary adjustment he has been alerted to and indicates, by acknowledging that corrective actions have been applied 603 and that the trailer is in line with the vehicle. Other trailer angle detection systems may not need the driver to straighten the trailer during setup mode.

[0103] To aid the driver in the setup process, the reverse back lights, or any other supplemental lighting that may be available on the vehicle, are illuminated 604. In the event the trailer is a new trailer, one that has not been attached to the vehicle before or has not been previously stored in the trailer backup assist system, the driver is presented 606 with an option to either name the trailer or select a previously stored trailer configuration. Naming the trailer 608 allows the trailer to be easily identified the next time it is attached to the vehicle so that the driver does not have to repeat the setup process. The driver either enters a unique name to identify the trailer that is to be stored in the trailer backup assist system or selects a previously stored trailer configuration associated with the attached trailer. The trailer backup assist system will not allow more than one trailer to have the same name. Therefore, if a driver attempts to name a trailer using a name that has already been applied to a previously stored trailer configuration, the HMI will display a message to the driver indicating so and requesting the driver enter a different name for the trailer configuration. In the case where a previously stored trailer configuration is available and selected 610 by the driver, certain steps in the setup process may be skipped.

[0104] The following discussion is directed to a first time trailer configuration for a camera-based trailer angle detection system. The driver is instructed 612 to place a hitch angle target on the trailer that is used for calibration purposes. A generic static image may be displayed on the HMI that provides direction to the driver as to placement of a target on the trailer that is used for hitch angle detection. The target placement is dependent upon the type of trailer being towed and therefore, options may be presented to the driver to aid the driver in selecting an appropriate trailer type. The static image may indicate areas that are acceptable for target placement as well as areas that are unacceptable for target placement. The static image indicating the appropriate areas for attaching the target may be an overlay of the rear view of the trailer hitch. Once the driver attaches the target to the trailer and indicates by way of the HMI that the target has been attached to the trailer the setup mode provides 614 visual feedback to the driver identifying that the target has been located, or acquired. The driver acknowledges 616, by way of the HMI, that the target has been properly identified by the trailer backup assist system. Similarly, for a previously stored trailer configuration, the trailer will already have a target placed thereon. The trailer backup assist system will acquire the target and provide 614 visual feedback to the driver confirming acquisition of the target.

[0105] In the event the target is not acquired 614 after a predetermined amount of time lapses, the driver is notified 618 of the need to reposition the target and presented with possible corrective measures that may be taken. Possible corrective measures may be presented to the driver such as cleaning the camera lens, cleaning the target, replacing the target if it has been damaged or faded, pulling the vehicle-trailer combination forward to improve lighting conditions around the camera and/or target, and moving the target to an acceptable location. The driver applies the necessary corrections 603. As mentioned above, some trailer angle detection systems may not require the driver to attach a target to the trailer during set up mode. The target and acquisition of the target are directed to camera-based trailer angle detection systems.

[0106] When the target is acquired 614 by the trailer backup assist system and the driver has acknowledged 616 the acquisition, the driver is then prompted through a series of menus to input 620 trailer measurement information that may be stored in the trailer backup assist system for a trailer configuration that is to be associated with the named trailer. The next time the same trailer is attached to the vehicle, its unique trailer configuration will already be stored and progress through the setup module will be faster or, in some cases, may be skipped entirely. Generic static images may be displayed at the HMI screen in order to assist the driver with the measurement information. Visual examples, see FIG. 12, may be provided to aid the driver in identifying the location on the vehicle, the trailer or between the vehicle and trailer that the driver is being prompted to enter. In addition, numerical limits for the driver entered measurements are set within the trailer backup assist system and may be displayed to the driver. The driver may be warned about entered measurements that exceed the numerical limits. Additionally, the measurement information requests that the driver is prompted to enter may be presented to the driver in the order that the measurements should be entered into the trailer backup assist system.

[0107] It should be noted that while measurement information is discussed above as being entered by the driver, various methods of entering measurement information may also be employed without departing from the scope of the inventive subject matter. For example, a system to automatically detect measurements using existing vehicle and trailer data including, but not limited to, vehicle speed, wheel rotation, steering wheel angle, vehicle to trailer relative angle, and a rate of change of the vehicle to trailer angle.

[0108] Examples of the measurement information may include a horizontal distance from the rear of the vehicle to the center of a hitch ball, a horizontal distance from the rear of the vehicle to a center of the target, a vertical distance from the target to the ground, and a horizontal offset of the target from a centerline of the hitch ball. In the event the target is attached at other than the centerline of the hitch ball, then the trailer backup assist system must know which side of the vehicle the target is attached to, the passenger side or the driver side. A menu on the HMI may be presented for the driver to indicate passenger side or driver side for the placement of the target. The trailer backup assist system also needs to know the horizontal distance from the rear of the vehicle to a center of the axle or axles of the trailer. The measurements may be entered in either English or metric units.

[0109] The driver is presented 622 with the option to revise any of the measurements before proceeding with the setup process. Otherwise, the setup module 600 is complete 624 and the calibration module 700 begins.

[0110] The calibration module 700 is designed to calibrate the curvature control algorithm with the proper trailer measurements and calibrate the trailer backup assist system for any hitch angle offset that may be present. After completing the setup module 600, the calibration module begins 700 and the driver is instructed 702 to pull the vehicle-trailer combination straight forward until a hitch angle sensor calibration is complete. The HMI may notify 704 the driver, by way of a pop up or screen display that the vehicle-trailer combination needs to be pulled forward until calibration is complete. When calibration is complete, the HMI may notify 704 the driver. Any hitch angle offset value is stored 706 in memory, accessed as necessary by the curvature control algorithm, and the calibration module 700 ends 704.

[0111] It should be noted that while hitch angle calibration is described above as may be requesting the driver pull forward information, various other methods of hitch angle calibration may also be employed without departing from the scope of the embodiment.

[0112] Upon completion of the setup module 600 and the calibration module 700, the activation module 800 may begin. The activation module 800 is described with reference to FIG. 11. The activation module 800 is designed to activate automatic steering of the vehicle during trailer backup assist operations. The driver is instructed 802 to place the vehicle in reverse. Upon activation of the trailer backup assist system, the steering system will not accept any steering angle commands from any source other than the trailer backup assist system 804. The trailer setup 600 and calibration 700 modules must be completed and a current hitch angle must be within a predetermined operating range for the trailer backup assist system 806. The vehicle speed must also be less than a predetermined activation speed 808. In the event any one, or all, of these conditions 804, 806, 808 are not met, the driver is prompted to apply a corrective measure 810. The driver must confirm 814 that the corrective action has been taken in order for the control module to begin. If a corrective action is taken, but the activation module deems it unacceptable, the driver will be instructed 810 to try another corrective action.

[0113] For steering systems where the steering wheel is directly coupled to the steered wheels of the vehicle, the driver cannot engage with the steering wheel during trailer backup assist. If any steering wheel motion is obstructed, by the driver or otherwise, the trailer backup assist system will present instructions 810 to the driver to remove their hands from the steering wheel. Activation 800 will be suspended or discontinued until the obstruction is removed. If the vehicle speed exceeds a threshold speed or if the vehicle hitch angle is not acceptable, the driver will be prompted 810 to take corrective action. Until corrective action is taken, accepted and acknowledged, the activation 800 and control 200, 500 modules will be interrupted.

[0114] When the driver moves the gear shift from “park” to “reverse” 802 and presses or turns a trailer backup steering input apparatus 125 a rear view camera image may appear in a display of the HMI. If at any time during the reversing process the hitch angle becomes too large for the system to control the curvature of the trailer, the TBA will provide a warning to the driver to pull forward to reduce the hitch angle. If at any time during the reversing process the system is unable to track the hitch angle target, the driver is presented with instructions to correct the problem. If at any time the vehicle speed exceeds that predetermined activation speed, the driver is visually and audibly warned to stop or slow down.

[0115] When all of the conditions of the activation module are met and maintained, the control module may begin. The control module executes the directives described above with reference to FIGS. 5 and 7. However, the activation module 800 includes a monitoring function 816 so that, if at any time during execution of the control module 200, 500 the control is interrupted, the driver is instructed to make necessary corrections. In the event any one of the necessary corrections is not made, the control of the vehicle by way of the trailer backup assist system will end. The driver may also intentionally end the control by exiting the system through a menu selection on the HMI or placing the vehicle in a gear setting that is other than park or reverse.

[0116] Referring now to instructions processable by a data processing device, it will be understood from the disclosures made herein that methods, processes and/or operations adapted for carrying out trailer backup assist functionality as disclosed herein are tangibly embodied by non-transitory computer readable medium having instructions thereon that are configured for carrying out such functionality. The instructions are tangibly embodied for carrying out the method 200, 500, 600, 700 and 800 disclosed and discussed above and can be further configured for limiting the potential for a jackknife condition such as, for example, by monitoring jackknife angle through use of the equations discussed in reference to FIGS. 5 and 7 and/or by implementing jackknife countermeasures functionality discussed above in reference to FIG. 8. The instructions may be accessible by one or more data processing devices from a memory apparatus (e.g. RAM, ROM, virtual memory, hard drive memory, etc.), from an apparatus readable by a drive unit of a data processing system (e.g., a diskette, a compact disk, a tape cartridge, etc.) or both. Accordingly, embodiments of computer readable medium in accordance with the inventive subject matter include a compact disk, a hard drive, RAM or other type of storage apparatus that has imaged thereon a computer program (i.e., instructions) configured for carrying out trailer backup assist functionality in accordance with the inventive subject matter.

[0117] In a preferred embodiment of the disclosed subject matter, a trailer backup assist control module (e.g., the trailer backup assist control module 120 discussed above in reference to FIG. 1) comprises such a data processing device, such a non-transitory computer readable medium, and such instructions on the computer readable medium for carrying out trailer backup assist functionality (e.g., in accordance with the method 200 discussed above in reference to FIG. 2) and/or the method 500 discussed above in reference to FIG. 8 and/or the methods 600, 700 and 800 discussed above in reference to FIGS. 10 and 11. To this end, the trailer backup assist control module can comprise various signal interfaces for receiving and outputting signals. For example, a jackknife enabling condition detector can include a device providing hitch angle information and hitch angle calculating logic of the trailer backup assist control module. A trailer backup assist control module in the context of the inventive subject matter can be any control module of an electronic control system that provides for trailer backup assist control functionality in accordance with the disclosed subject matter. Furthermore, it is disclosed herein that such a control functionality can be implemented within a standalone control module (physically and logically) or can be implemented logically within two or more separate but interconnected control modules (e.g., of an electronic control system of a vehicle) In one example, trailer backup assist control module in accordance with the disclosed subject matter is implemented within a standalone controller unit that provides only trailer backup assist functionality. In another example, trailer backup assist functionality in accordance with the disclosed subject matter is implemented within a standalone controller unit of an electronic control system of a vehicle that provides trailer backup assist functionality as well as one or more other types of system control functionality of a vehicle (e.g., anti-lock brake system functionality, steering power assist functionality, etc.). In still another example, trailer backup assist functionality in accordance with the disclosed subject matter is implemented logically in a distributed manner whereby a plurality of control units, control modules, computers, or the like (e.g., an electronic control system) jointly carry out operations for providing such trailer backup assist functionality.

[0118] Trailer Target Placement and Monitoring

[0119] The vehicle trailer backup assist system may utilize a target placed on the trailer to serve as the hitch angle detection component 155. In doing so, the trailer backup assist system may employ information acquired via image acquisition and processing of the target for use in the hitch angle detection apparatus 130, according to one embodiment. According to other embodiments, the target may be used to identify if a connected trailer has changed, trailer connection or disconnection, and other trailer related information. The target is an identifiable visual target that can be captured in an image by the video imaging camera and detected and processed via image processing. According to one embodiment, the target may include an adhesive target, also referred to as a sticker, that may be adhered via adhesive on one side onto the trailer, preferably within a target placement zone, such that the camera and image processing may detect the target and its location on the trailer to determine trailer related information, such as the hitch angle between the trailer and the towing vehicle. The trailer backup assist system may provide to the user one or more image(s) of the trailer target zone for proper placement of the target to assist with placement of the target on the trailer. Additionally, the vehicle trailer backup assist system may monitor the target to determine if the target has been correctly placed within a desired target placement zone and provide feedback alert(s) to the user. Further, the trailer backup assist system may monitor the trailer connection by monitoring the target to determine if the target has moved to determine whether the same trailer remains connected to the tow vehicle, and may initiate action in response thereto. Further, the trailer backup assist system may monitor the hitch angle or the target to determine if the trailer may have been changed out (i.e., disconnected and replaced with another trailer), and may initiate action in response thereto.

[0120] Referring to FIG. 13, the vehicle trailer backup assist system 105 is shown including the hitch angle detection apparatus 130 and a target monitor controller 10 for monitoring the target, assisting with placement of the target, monitoring connection of the trailer, determining if the trailer has moved, and initiating certain actions. The target monitor controller 10 may include a microprocessor 12 and/or other analog and/or digital circuitry for processing one or more routines. Additionally, the target monitor controller 10 may include memory 14 for storing one or more routines including image processing routine(s) 16, a target placement assist routine 900, a target monitoring routine 920, an initial setup for target moved detection routine 940, a target moved detection routine 960, and a trailer connection monitoring routine 990. It should be appreciated that the target monitor controller 10 may be a standalone dedicated controller or may be a shared controller integrated with other control functions, such as integrated with the hitch angle detection apparatus 130, to process the images of the trailer and target and perform related functionality. In one embodiment, the hitch angle detection apparatus 130 processes the acquired images of the target from the target monitor controller 10 and other information such as trailer length for use in determining the hitch angle between the trailer and the towing vehicle.

[0121] A camera 20 is shown as an input for providing video images to the target monitor controller 10 of the vehicle trailer backup assist system 105. The camera 20 may be a rearview camera mounted on the tow vehicle in a position and orientation to acquire images of the trailer towed by the vehicle rearward of the vehicle. The camera 20 may include an imaging camera that generates one or more camera images of the trailer including the region where a target placement zone is expected to be located on the trailer. The camera 20 may include a video imaging camera that repeatedly captures successive images of the trailer for processing by the target monitor controller 10. The target monitor controller 10 processes the one or more images from the camera 20 with one or more image processing routine(s) 16 to identify the target and its location on the trailer. The target monitor controller 14 further processes the processed images in connection with one or more of routines 900, 920, 940, 960 and 990.

[0122] The trailer monitor controller 10 may communicate with one or more devices including vehicle exterior alerts 24 which may include vehicle brake lights and vehicle emergency flashers for providing a visual alert and a vehicle horn for providing an audible alert. Additionally, the trailer monitor controller may communicate with one or more vehicle human machine interfaces (HMIs) 25 including a vehicle display such as a center stack mounted navigation/entertainment display. Further, the trailer monitor controller 10 may communicate via wireless communication 22 with one or more handheld or portable devices 26, such as one or more smartphones. The portable device 26 may include a display 28 for displaying one or more images and other information to a user. The portable device 26 may display one or more images of the trailer and the target location within a desired target placement zone on display 28. In addition, the portable device 26 may provide feedback information about the vehicle target connection including visual and audible alerts.

[0123] Referring to FIGS. 14-17, the placement of the target 30 onto trailer 110 using the target monitor controller 10 processing the target placement assist routine 900 is illustrated according to one exemplary embodiment. In FIGS. 14 and 15, a tow vehicle 100 is shown towing a trailer 110. The trailer 110 has a trailer hitch connector in the form of a coupler assembly 114 connected to a vehicle hitch connector in the form of a receiver hitch and ball 15. The coupler assembly 114 latches onto the hitch ball 15 to provide a pivoting ball joint. The trailer 110 is shown having a frame including a longitudinally extending bar or trailer tongue 112. A top horizontal surface of trailer tongue 112 is shown providing a desired target placement zone 32 for receiving the target 30. It should be appreciated that the trailer 110 may be configured in various shapes and sizes and may offer one or more other suitable target placement zones 32 for receiving the target 30. The target placement zone 32 defines the desired location for placement of the target 30.

[0124] The vehicle 100 is equipped with a video imaging camera 20 shown located in an upper region of the vehicle tailgate at the rear of the vehicle 100. The video imaging camera 20 is elevated relative to the target placement zone(s) and has an imaging field of view and is located and oriented to capture one or more images of the trailer 110 including a region containing one or more desired target placement zone(s). It should be appreciated that one or more cameras may be located at other locations on the vehicle 100 to acquire images of the trailer 110 and the target placement zone(s) 32.

[0125] In order to utilize a target on a trailer that is not currently equipped with a suitable pre-existing target, a user 2 may be instructed or directed to place the target 30 onto the trailer 110 within a desired target placement zone 32 so that the camera 20 may capture one or more images of the target 30 to determine trailer related information for the trailer backup assist system, such as hitch angle information for the hitch angle detection apparatus 130. In doing so, a user 2 may be prompted by an audible or visual message on an HMI such as the vehicle HMI 25 or portable device 26 to place the target 30 on the trailer 110. The vehicle HMI 25 may include visual and/or audible outputs generating instructions for proper target placement.

[0126] To allow for efficient and proper placement of the target 30 onto the trailer 110, the trailer backup assist system employs a target placement assist method or routine 900 shown in FIG. 17 that is processed by the target monitor controller 10. The target placement assist method 900 includes step 902 in which a user may connect a portable device having an image display to communicate with the vehicle. The user may connect the device electronically to the vehicle which can be achieved by way of a wireless protocol, according to one embodiment. The device may be a wireless device that may communicate via Wi-Fi, BLUETOOTH® or other wireless protocol. Alternatively, the device could be connected via a wired connection. Next, at step 904, the user initiates the hitch angle detection system setup which requires initiating the setup procedure for the hitch angle detection system. As part of this procedure, the user will be required to place a target onto the trailer of the vehicle within a target placement zone. At step 906, the system generates with the camera one or more images of the towed trailer which include a region where the desired target placement zone(s) is expected to be located. There may be more than one target placement zone and one zone may be preferred over another zone. At step 908, the system processes the generated images and determines the desired target placement zone on the trailer. The desired target placement zone may be determined based on camera location and orientation, desired distance of the target from the hitch connection and the physical structure of the trailer. At step 910, the system generates a target overlay on the one or more generated images. The target overlay is a visual indication of the desired location of the target within the target placement zone upon which the user is instructed to place the target. The target overlay may include border lines marking the target placement zone or other identifier. The target overlay may be shown by flashing colored (e.g., red) lines on a displayed image. Target overlays of a plurality target placement zones may be generated and shown. At step 912, the system communicates the one or more images and the target overlay to the vehicle's display and if connected in step 902, the user's display on the portable device by utilizing the wireless or wired connection. Next, at step 914, the user's display on the portable device displays an image of the target placement zone indicated by the target overlay. At step 916, the user is then prompted by an HMI to place the target on the trailer within the target placement zone with assistance from the displayed image and target overlay on the vehicle's display and/or the portable display.

[0127] One example of a displayed image on the display 28 of a portable device 26 showing an overlay of the target location for the target to be placed on the trailer is illustrated in FIG. 16. The image displayed on the display 28 includes an image of the trailer 110 as captured by the camera and further includes an overlay of the desired target placement zone 32. The user 2 may view the image on the display 28 of the portable device 28 to determine where to place the target relative to the trailer 110. In this example, the user may place the target 30 onto the target placement zone 32 as indicated by the target overlay. Placement of the target may be achieved by adhering a target sticker onto a surface of the trailer. As a result, the user may employ a portable device with a display, such as a phone, a tablet, or a computer to view the proper location for placement of the target on the trailer prior to and during application of the target onto the trailer.

[0128] Accordingly, the target placement assist method 900 advantageously assists the user with placement of the target 30 onto the trailer 110 in a manner that is simple to use, accurate and efficient. The user 2 may easily transport a portable device having a display to communicate with the vehicle and view the correct placement location for the target prior to and during the target placement procedure without having to return to the vehicle or otherwise be prompted for target placement.

[0129] The trailer backup assist system 105 further includes a target monitoring method or routine for monitoring placement of the target on the trailer and providing feedback to the user as to whether the target has been placed within a proper target placement zone. A user may place a target on the trailer in various ways. In some situations, the user may be prompted by the TBA system via a vehicle HMI to place a target on the trailer and may be given instructions as to the location. The user may employ the target placement assist method 900 to assist with placement of the target on the trailer. In other situations, the user may place the target on the trailer using their best judgment or following instructions printed on the target or packaging provided therewith. In any event, once the target is placed on the trailer, the target monitoring method 920 will monitor the location of the target relative to the trailer and provide feedback to the user as to correct or incorrect placement of the target on the trailer.

[0130] The target monitoring method 920 is illustrated in FIG. 18, according to one embodiment. At step 922, method 920 requires attaching the trailer to the vehicle onto the ball and hitch if it is not already attached. Next, at step 924, setup for the hitch angle detection is initiated. At step 926, the user is prompted via an interface to place the target on the trailer. The user may place a target on the trailer based on predefined criteria or the user's best judgment or knowledge, according to one embodiment. The user may be instructed on where to place the target on the trailer by use of a user's manual, an instruction sheet, or other visual or audible communication of instructions, according to other embodiments. Generally, the target should be placed in a region that is unobstructed from view by the camera and that allows for the acquisition of an image and determination of desired trailer related information, such as the hitch angle. Depending on the trailer configuration and camera orientation and height, the target may be required to be placed within a certain region of the trailer, within a distance range from the trailer hitch connection having a minimum distance from the hitch connection, such as 7 inches (17.78 cm), within a range from the tow vehicle bumper, and within a range of height from the ground. The target placement may require a location within a certain distance from a centerline of the longitudinal axis of the trailer, and may require a vertical or horizontal angle or some angle in between the vertical and horizontal positions. According to another embodiment, the user may utilize the target placement assist method 900 to place the target on the trailer.

[0131] At step 928, the system generates one or more images of the target placement zone on the towed trailer. The system then processes the one or more images to determine the presence of a target within a desired target placement zone at step 930. The desired target placement zone may be determined by criteria, such as distance from the trailer hitch connection 114, distance from a centerline of the longitudinal axis of the trailer, height of the camera relative to the trailer, and distance of the camera from the trailer. At decision step 932, method 900 determines if the target has been detected by the processed image(s) and, if not, returns to step 926 to prompt the user via an HMI to place the target on the trailer.

[0132] If the target has been detected by the processed images, the vehicle trailer backup assist system provides a feedback alert to the user at step 934. The feedback alert may include one or more of vehicle exterior alerts including visual alerts, such as flashing the vehicle brake lights and/or flashing the vehicle emergency flashers, and/or audible alerts, such as sounding the vehicle horn. Additionally, the feedback alerts may include providing a message via the portable device 26, providing an audible tone via the portable device 26 or a visual lighted indication via the portable device 26. Further, feedback alerts may include sending a text message or audible instructions to a user via a portable device, such as a phone or computer. It should be appreciated that other vehicle exterior and alternative feedback alerts may be communicated to the user to indicate that proper placement of the target has been detected on the trailer. Alternatively, the feedback alerts could be used to indicate improper placement of the target on the trailer. Once the trailer is properly equipped with the target in the proper location, the trailer backup assist system may process information by monitoring the target to determine the hitch angle and other trailer towing related functionality.

[0133] The target 30 may include a sticker having adhesive on the bottom surface and a predetermined image pattern of a certain size and shape provided on the top surface for capture by the video camera and recognition by the image processing. The target 30 may have a rectangular shape, according to one embodiment, and may have a camera image recognizable pattern such as the checker pattern shown. The image processing may include known image pattern recognition routines for identifying a target pattern and its location on a trailer. However, it should be appreciated that other target shapes, sizes and patterns may be employed. It should further be appreciated that the target may otherwise be connected to the trailer using connectors, such as fasteners, which may connect to the trailer or to an attachment to the trailer. It should further be appreciated that the target can be attached via magnet, glued on, painted on, or any number of other suitable means.

[0134] It should be appreciated that not all trailers are necessarily configured to provide a well-suited location for placement of a target sticker on the trailer. Accordingly, a target location may be added to a given trailer by use of a target mounting system 40 as shown in FIGS. 19 and 20, according to one embodiment. The target mounting system 40 is shown installed onto trailer 110 to present a target 30 that is viewable by the camera within a desired target placement zone. The target mounting system 40 includes a vertical mounting post or bracket 44 having a plurality of bolt receiver holes 46 extending vertically to allow for a desired vertical height adjustment. The bracket 44 may be assembled onto the trailer via holes 54 using bolts 48, washers 52 and nuts 50. The height of the bracket 44 may be adjusted depending on which holes 46 are aligned with the trailer holes 54. Mounted to the top of the bracket 44 is a target plate 42 having a top target placement zone 32 onto which the target 30 is located. The plate 42 likewise has a plurality of holes 46 that align horizontally with the holes in the bracket 44 and may be assembled thereto via bolts 48, washers 52 and nuts 50. Accordingly, the plate 42 may be adjusted both vertically and horizontally to a desired position so as place the target 30 adjustably within a desired location so that the target is easily acquired by the camera and processed by the image processing. It should be appreciated that assistance in mounting the target mounting system 40 along with the target 30 and verification of proper location of the target mounting system 40 and target 30 may be achieved by utilizing the target placement assist method 900 and target monitoring method 920 discussed above.

[0135] The target moved detection method includes an initial setup routine 940 and subsequent processing routine 960 for target moved detection used for prompting the entry of trailer information. The target moved detection method determines if the location of a hitch angle target on a trailer, such as a trailer tongue, has moved and may also determine if the distance has changed. Images of the target in a previously stored image and a newly acquired image are compared to determine if the location and/or distance to the target has changed. The comparison may include comparing camera image pixel sizes of the images. If either the location or the distance changes, the user is then prompted by an HMI to reenter new trailer information for subsequent processing of the trailer backup assist system.

[0136] The initial setup routine 940 is illustrated in FIG. 21. Initially, the trailer must be attached to the vehicle at step 942. At step 944, the attached trailer is setup for hitch angle tracking. For a vision-based system, this may include applying a target sticker to the trailer, such as in the vicinity of the tongue of the trailer, so that the vehicle-based camera can detect motion of the target as the trailer maneuvers and swings around curves. In addition, a number of parameters associated with the location of the target that are used to properly calculate the hitch angle based on the vision processing may be entered. These parameters may include the distance of the target to the ground and the distance from the target to the bumper of the vehicle. At step 946, the vehicle and the trailer are directed to be driven straight, which may be achieved by driving the vehicle and towed trailer in the forward direction. This is to ensure that there is about zero hitch angle between the vehicle and trailer with the trailer in-line with the vehicle and that the image generated in subsequent steps will be taken in the same orientation and will be valid for image comparisons. At step 948, a picture (image) of the target and trailer are acquired with the use of the camera while the vehicle and the trailer are in a straight line at a hitch angle of about zero degrees. At step 950, the image processing performs vision processing on the image. The vision processing may first detect a target and then compute the size and location of the target based on processing the pixels of the image. At step 952, the image acquired in step 948 is stored in memory and the information calculated in step 950 is stored in memory. The image and calculated information are then subsequently used to determine if the target has moved. If the target has moved, the system may assume that the trailer may have been changed or replaced with a different trailer, and hence prompts the user via an HMI to enter trailer information.

[0137] Referring to FIG. 22, the target moved detection routine 960 is shown beginning at step 962 in which the driver is instructed to reattach to the vehicle a trailer that was previously set up and used in the initial setup routine 940. At step 964, the user is prompted by the hitch angle detection system to select the trailer that was previously setup and stored, rather than selecting a new trailer. At step 966, the user is prompted to drive the trailer and vehicle combination forward in a straight line to achieve a hitch angle of about zero degrees. Next, at step 968, a new image of the target and the trailer are acquired by the camera. At step 970, vision processing is performed on the image to detect the target and compute the size and location of the target by processing the pixels of the image. At step 972, the target location and size as calculated above are compared to the location and size of the target taken in the prior image from the initial setup. At step 974, a determination is made to determine if the new target information is a match or within tolerance of the original target information. If the newly acquired target is still a similar size and in the similar location on the image as compared to the prior image from the initial setup, then the target is likely to be in the same location and will allow for a proper hitch angle detection if determination of such is made in step 980. If the target has a different location or has a different size, then the target is presumed to have moved and routine 960 proceeds to step 976. Detected movement of the target may occur when the trailer is a different trailer as compared to the trailer last selected by the user. The use of the prior selected trailer configuration may provide erroneous results for hitch angle target tracking. As such, method 960 proceeds to step 978 to prompt the user (e.g., driver) to reselect or re-setup the trailer configuration with new target and trailer information. Accordingly, the target moved detection routine 960 advantageously detects movement of the target which may indicate potential connection of a new trailer to the vehicle, such that the user is prompted via an HMI to select new trailer configuration information. Additionally, the target moved routine could also detect that a target has moved due to a different sized drawbar being installed than what was installed when the trailer was initially setup.

[0138] Examples of images of the trailer and the target moved to a different position are illustrated in FIGS. 23A and 23B. As shown in FIG. 23A, an image of the trailer and the target 30 is shown aligned on the trailer in a first position as compared to the subsequent image in FIG. 23B showing the target 30 moved to a new second closer position. The change in location of the target may be an indication that the trailer has been changed out with a new trailer or that the target has otherwise been moved on the trailer. When this occurs, the target move detection routine 960 requires the user to re-enter trailer configuration information so that the wrong information is not used to provide incorrect hitch angle data. Furthermore, it is possible that the right (correct) trailer has been selected and the target is still in the same location on the trailer, but the system still indicates that the target has moved. This could occur if the drawbar length on the vehicle has changed.

[0139] Target monitor controller 10 further processes a trailer connection monitoring routine 990 to determine whether a trailer is connected to the vehicle and whether a new trailer may have been connected. When the trailer is disconnected from the vehicle, the target information and the hitch angle information may be unavailable for a period of time. Accordingly, the trailer connection monitoring method 990 monitors the availability of the hitch angle data and/or the detection of the target to determine if the hitch angle data or target data is lost for a substantial period of time. If this occurs, the driver is then prompted via an HMI to reselect the attached trailer or to re-enter trailer configuration data to ensure that the wrong trailer information is not employed.

[0140] The trailer connection monitoring routine 990 is illustrated in FIG. 24. At step 992, a trailer is connected to the vehicle. At step 994, the trailer is setup for hitch angle detection and monitoring. If a vision based system is employed, this may include placing a target on the trailer for the vision-based system to detect as well as entering pertinent parameters. Alternatively, if the trailer has been previously setup for hitch angle monitoring, it may be possible to select the previously stored setup configuration for that trailer. At step 996, once the trailer has been setup for hitch angle detection, the hitch angle detection system will continuously monitor the hitch angle or target. At decision step 998, routine 990 determines if the hitch angle or the target has been dropped for a time period greater than X seconds.

[0141] Depending on the type of hitch angle system, the hitch angle signal may drop or become unavailable for different reason, but one potential reason is that the trailer has been disconnected from the vehicle. A disconnected trailer may also result in the target detection being unavailable. As such, a check is made to see how much time has expired since the hitch angle signal or target detected has been dropped. If the hitch angle or target detection has been dropped for a time period of less than X seconds, then routine 990 returns to track the hitch angle or target at step 996. If the hitch angle or target detection has been dropped for a time period greater than X seconds, then the user is prompted via an HMI to reselect or re-setup the trailer configuration in step 1000. The time period X is set to represent a reasonable amount of time needed to swap or change-out trailers. For example, for extremely small, lightweight trailers, it may be possible to swap trailers out in less than sixty (60) seconds, so this could be a reasonable time period. According to one embodiment, the time period X is set for thirty (30) seconds.

[0142] While the hitch angle is monitored to determine disconnection of a trailer from the vehicle, it should be appreciated that the trailer connection monitoring routine 990 may monitor detection of the target as an alternative, such that if the target is no longer detected for X seconds, then the vehicle driver may be prompted to reselect or reconfigure the trailer.

[0143] It is to be understood that variations and modifications can be made on the aforementioned structure without departing from the concepts of the present invention, and further it is to be understood that such concepts are intended to be covered by the following claims unless these claims by their language expressly state otherwise.