Control system and method to inhibit automatic transmission downshifting during trailer sway

[0001] 1. Field

[0002] The invention relates to systems and methods for improving the safety of a vehicle that is pulling a trailer. More particularly, the invention relates to a control system and method to inhibit automatic transmission downshifting during trailer sway.

[0003] 2. Background

[0004] Trailers, such as mobile homes, travel trailers, campers and the like, are conventionally equipped with electrically appliable brakes which may be operated by the driver in the towing vehicle. When pulling the trailer, a dangerous driving situation known as trailer sway may occur and can be inhibited by momentary application of the trailer brakes. Such momentary application results from briefly energizing the brake-actuating coils by means of manually or automatically operable devices.

[0005] Trailer sway may occur while applying braking of the towing vehicle without braking or balanced braking of the trailer. Trailer sway may also occur during a cross-wind from traffic or when traveling on a windy highway. A rapid turn of the steering wheel of the towing vehicle can also cause trailer sway.

[0006] Trailer sway can be mitigated by applying braking to the trailer without applying braking to the towing vehicle. Trailer sway can also be mitigated by accelerating the towing vehicle to pull the trailer to straighten out. These techniques, however, can still result in a dangerous driving situation.

[0007] Therefore, a need exists in the art for a control system and method that overcomes the drawbacks of the prior art.

[0008] A control system for a vehicle that is towing a trailer, the control system including a lateral acceleration sensor coupled to the vehicle for determining a lateral acceleration of the vehicle caused by the trailer swaying and generating a lateral acceleration signal based on the lateral acceleration of the vehicle and a transmission controller for receiving the lateral acceleration signal from the lateral acceleration sensor, comparing the lateral acceleration signal to a threshold, and prohibiting a gear switch signal from being transmitted to a transmission of the vehicle when the lateral acceleration signal exceeds the threshold.

[0009] A control system for a vehicle that is towing a trailer including a lateral acceleration sensor for generating a lateral acceleration signal based on a lateral acceleration of a vehicle caused by the trailer swaying and a yaw rate sensor for generating a yaw signal based on an angular velocity of the vehicle. The control system also includes a stability control system for receiving the lateral acceleration signal and the yaw signal, comparing the lateral acceleration signal to a first threshold value, comparing the yaw signal to a second threshold value, and generating a prohibit downshift signal when the lateral acceleration signal exceeds the first threshold value or when the yaw signal exceeds the second threshold value. The control system also includes a transmission controller for receiving the prohibit downshift signal from the stability control system and transmitting a prohibit downshift signal to a transmission of the vehicle to prevent a mechanical or electrical change of a gear of the transmission.

[0010] A method of controlling vehicle stability during trailer sway, the method including receiving from a lateral acceleration sensor a lateral acceleration signal measuring a lateral acceleration of a vehicle, receiving from a yaw sensor a yaw signal measuring an angular velocity of the vehicle, and generating a prohibit downshift signal when the lateral acceleration signal exceeds a first threshold value or when the yaw signal exceeds a second threshold value.

[0015] Apparatus, systems and methods that implement the embodiments of the various features of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate some embodiments of the invention and not to limit the scope of the invention. Throughout the drawings, reference numbers are re-used to indicate correspondence between referenced elements.

[0016] FIG. 1 is a schematic diagram of a vehicle 110 towing a trailer 115. Trailer sway often occurs to the trailer 115 while being towed by the vehicle 110 when the trailer's stability is disturbed. Trailer sway can be defined as a lateral movement of the trailer 115, which causes instability. When the trailer 115 sways, the vehicle 110 may accelerate in lateral directions, which can cause the vehicle 110 to become unstable.

[0017] FIG. 2 is a schematic block diagram of a control system 200 for the vehicle 110 that includes a vehicle stability control system 205 and a transmission control system 215. The vehicle stability control system 205 and the transmission control system 215 may be implemented using hardware, software, firmware, middleware, microcode, or any combination thereof. The vehicle stability control system 205 and the transmission control system 215 may be a processor, an Advanced RISC Machine (ARM), a controller, a digital signal processor (DSP), a microprocessor, a machine readable medium, any other device capable of processing data, and combinations thereof. The term “machine readable medium” includes, but is not limited to, random access memory (RAM), flash memory, read-only memory (ROM), EPROM, EEPROM, registers, hard disk, removable disk, CD-ROM, DVD, wireless channels, and various other mediums capable of storing, containing or carrying instruction(s) and/or data.

[0018] Referring to FIGS. 1 and 2, the vehicle stability control system 205 may have a lateral acceleration sensor 206, a yaw rate sensor 207, a steering wheel angle sensor 208, a wheel speed sensor 209, a brake switch sensor 210, and a brake pressure sensor 211. The sensors may be wirelessly connected or wire connected to the vehicle stability control system 205.

[0019] The lateral acceleration sensor 206 detects or senses any lateral acceleration of the vehicle 110. The lateral acceleration sensor 206 can detect lateral accelerations of the vehicle 110 without the vehicle 110 moving in a lateral direction. The lateral acceleration refers to the lateral force applied to the vehicle 110 rather than the movement of the vehicle 110. Trailer sway refers to the trailer 115 moving back and forth, which causes a lateral force to be applied to or placed on the vehicle 110. The lateral force placed on the vehicle 110 in lateral directions is detected or measured by the lateral acceleration sensor 206 (Force=Mass*Acceleration). The lateral force caused by the trailer sway eventually causes the vehicle 110 to move laterally but at this point in time, the driver may have already lost control of the vehicle 110 and the vehicle 110 may have been forced off the road. The lateral acceleration sensor 206 may detect alternating back and forth forces on the vehicle 110 indicating that the trailer 115 is swaying and may generate a lateral acceleration or force signal indicating a back (e.g., negative) and forth (e.g., positive) acceleration or force on the vehicle 110 for analysis by the vehicle stability control system 205. The lateral acceleration signal is a signal representing lateral acceleration of the vehicle 110 in both opposite directions, which determines sway and intensity of the sway.

[0020] The yaw rate sensor 207 determines or measures the vehicle's angular velocity about its vertical axis and generates a yaw signal for analysis by the vehicle stability control system 205. The angular velocity indicates how much the vehicle is rotating or spinning about its vertical axis. When the angular velocity is 0, the vehicle is not rotating or spinning about its vertical axis.

[0021] The steering wheel angle sensor 208 determines an angle in which the steering wheel has rotated from a center position. That is, the steering wheel angle sensor 208 determines how much the steering wheel has moved in the left direction or the right direction. When the steering wheel is centered (i.e., the vehicle 110 is moving in a straight forward direction), the steering wheel angle sensor 208 generates a steering wheel angle signal of 0 for analysis by the vehicle stability control system 205.

[0022] The wheel speed sensor 209 determines or measures the speed of each wheel and transmits a wheel speed signal for each wheel to the vehicle stability control system 205 for analysis. If the speed of one or more wheels is different from the speed of the other wheels, the vehicle 110 or one or more wheels may be experiencing a skid or a spin.

[0023] The brake sensor 210 determines whether the brakes of the vehicle 110 are being applied by the driver. If the brakes are being applied, the brake sensor 210 generates an on signal and if the brakes are not being applied, the brake sensor 210 generates an off signal. The brake signal is sent to the vehicle stability control system 205.

[0024] The brake pressure sensor 211 determines or measures the amount of force or pressure being applied to the brakes and generates a brake pressure signal for analysis by the vehicle stability control system 205.

[0025] The vehicle stability control system 205 receives the lateral acceleration signal, the yaw signal, the steering wheel angle signal, the wheel speed signals, the brake signal, and the brake pressure signal. The vehicle stability control system 205 compares each of the signals to a normal threshold. If one or more of the signals exceeds its normal threshold, the vehicle 110 may be in an unstable situation. For example, if the lateral acceleration signal exceeds a normal threshold, the vehicle stability control system 205 may determine that trailer sway is occurring. The vehicle stability control system 205 may receive alternating lateral acceleration signals from the lateral acceleration sensor 206 indicating that the vehicle 110 is experiencing a back and forth lateral force caused by trailer sway. In this situation, the vehicle stability control system 205 sends a prohibit downshift signal to the transmission control system 215 of the vehicle 110. Also, if the yaw signal exceeds a normal threshold, the vehicle stability control system 205 sends a prohibit downshift signal to the transmission control signal 215. In one embodiment, trailer sway can be detected if the lateral acceleration signal and the yaw signal exceed respective normal thresholds. If the signals are within their respective normal thresholds, the vehicle stability control system 205 sends an allow downshift signal to the transmission control system 215.

[0026] The transmission control system 215 has a transmission controller 220 (e.g., an Electronic Control Unit (ECU)) that is wirelessly connected or wire connected to the vehicle stability control system 205, a transmission 225 of the vehicle 110 and a transmission speed sensor 230. The transmission 225 is an electronically controlled transmission that is configured to send a gear change request 242 to the transmission controller 220. The transmission controller 220 does not send a gear shift signal 240 to the transmission 225 until the transmission controller 220 receives an allow downshift signal from the vehicle stability control system 205. In one embodiment, the transmission controller 220 sends a prohibit downshift signal to the transmission 225 to prevent a mechanical or electrical change of a gear of the transmission 225.

[0027] The transmission speed sensor 230 may be wirelessly connected or wire connected to the transmission 225. The transmission speed sensor 230 periodically (e.g., every 1/1000 of a second) determines or senses a speed 250 of the transmission 225, generates a transmission speed signal 245 representing the speed 250 of the transmission 225 and sends the transmission speed signal 245 to the transmission controller 220.

[0028] The transmission controller 220 receives the gear change request 242 from the transmission 225, the transmission speed signal 245 from the transmission speed sensor 230, and the downshift signal (i.e., allow or prohibit) from the vehicle stability control system 205. The transmission controller 220 uses the gear change request 242, the transmission speed signal 245, and the downshift signal to determine whether or not to send an upshift signal 240 or a downshift signal 240 to the transmission 225. For example, if the prohibit downshift signal is received from the vehicle stability control system 205, the transmission controller 220 will not send a gear shift signal 240 to the transmission 225. The transmission controller 220 prevents downshifting of the transmission 225 during trailer sway to eliminate any other vehicle factors that can intensify the sway and make the situation more dangerous.

[0029] If the transmission controller 220 receives the allow downshift signal from the vehicle stability control system 205 and receives the gear change request 242, the transmission controller 220 will determine whether or not to send a gear shift signal 240 to the transmission 225 based on the transmission speed signal 245. The transmission controller 220 may also determine to send a gear shift signal 240 to the transmission 225 based on the transmission speed signal 245 regardless of whether the transmission controller 220 received the gear change request 242 from the transmission 225 as long as the prohibit downshift signal is not received from the vehicle stability control system 205. Upon receipt of the upshift signal 240 or the downshift signal 240, the transmission 225 will force a mechanical change of a gear to the transmission 225.

[0030] FIG. 3 is a flow chart of a method 300 of controlling vehicle stability during trailer sway. The method begins at step 305. At step 310, the transmission controller 220 is waiting for a gear change request 242 (e.g., a downshift request) from the transmission 225. Upon receiving the gear change request 242, the transmission controller 220 determines whether the transmission speed signal 245 is above a minimum speed threshold for the current gear (step 315). If no, the method returns to step 305. If yes, the transmission controller 220 determines whether the transmission speed signal 245 is below a maximum speed threshold for the current gear (step 320). If no, the method returns to step 305.

[0031] At step 325, the transmission controller 220 determines whether the vehicle 110 is stable based on the allow downshift signal or the prohibit downshift signal. The allow downshift signal indicates that the vehicle 110 is stable and the prohibit downshift signal indicates that the vehicle 110 is not stable. The vehicle stability control system 205 analyzes the vehicle's stability through one or more sensors 206-211 by comparing the signals generated from these sensors to predetermined normal thresholds, which indicate stability of the vehicle 110. In one embodiment, the vehicle stability control system 205 analyzes the vehicle's stability by analyzing only the lateral acceleration signal and/or the yaw rate signal and determining whether the vehicle is stable based on only one or two signals.

[0032] At step 330, the transmission controller 220 determines whether wheel slip is occurring based on monitoring the individual wheel speed sensors 209. The wheel speed sensors 209 determine or measure how fast each wheel is spinning. If the transmission controller 220 determines that one or more wheels have stopped and one or more wheels have not stopped, the vehicle 110 is skidding. If the transmission controller 220 determines that one or more wheels are spinning faster than the other wheels, the wheels are spinning out.

[0033] At step 335, the transmission controller 220 determines whether trailer sway is occurring by analyzing one or more signals from the sensors 206-211 that have not been previously analyzed. For example, the transmission controller 220 may analyze the steering wheel angle signal, the brake signal, and the brake pressure signal, and compare these signals to their respective normal thresholds to determine whether trailer sway is occurring.

[0034] If trailer sway is not occurring, the transmission controller 220 sends a gear change request 242 (i.e., a downshift request) to the transmission 225 (step 340).

[0035] Those of ordinary skill would appreciate that the various illustrative logical blocks, modules, and algorithm steps described in connection with the examples disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the disclosed apparatus and methods.

[0036] The previous description of the disclosed examples is provided to enable any person of ordinary skill in the art to make or use the disclosed methods and apparatus. Various modifications to these examples will be readily apparent to those skilled in the art, and the principles defined herein may be applied to other examples without departing from the spirit or scope of the disclosed method and apparatus. The described embodiments are to be considered in all respects only as illustrative and not restrictive and the scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.