Method for Spacing Control for a Motor Vehicle

This invention relates to methods for controlling the spacing of a motor vehicle from an object in front of the vehicle, in which at least the present driving speed of the motor vehicle and the present spacing from an object in front of the motor vehicle are determined by sensor devices and a spacing-dependent required acceleration value is determined from the sensed variables, and to an arrangement for carrying out the method.

Improvements in the field of motor vehicle electronics have led to the situation in which electronic systems which relieve the vehicle driver of routine functions are gaining increasing importance. These electronic systems include, inter alia, a speed control system, which has been known for a long time, in which the driver can preselect a desired speed which is then maintained by the system.

Because of increasing volumes of traffic, it has become necessary to make such speed control additionally dependent on the current traffic situation since the driver would otherwise be compelled to intervene continually in the control of the vehicle speed.

In the publication "Abstandsregelung von Fahrzeugen mit Fuzzy Control" [spacing control of vehicles, using fuzzy control], Tagungsband der 3. Dortmunder Fuzzy Tage, Reihe Informatik Aktuell, Springer Verlag 1993, a fuzzy vehicle spacing controller is described which automatically maintains a predetermined required spacing of a vehicle from another motor vehicle travelling in front of the vehicle under various boundary conditions. The fuzzy spacing control described in the publication, which includes a three-stage fuzzy controller, uses simple min/max operators and the center of gravity method for defuzzification following each stage. Instead of a fixedly defined required spacing, a variable required spacing is determined in the first fuzzy controller which depends on the driver type and the weather, in addition to the current vehicle speed. The driver type and the weather are standardized parameters having a predetermined value range which is determined by an external sensing mechanism, but an arrangement for determination of a driver type is not described in the publication.

The three input data, i.e., driver type, weather, and vehicle speed, are fuzzified and projected onto the required spacing by two control matrices. In the second fuzzy controller, the current spacing supplied by the sensing mechanism is compared to a required spacing determined in the first fuzzy controller and the acceleration required to maintain the desired spacing, which is dependent on the driver type, is determined. The desired vehicle speed is entered directly by the driver and, in the third fuzzy controller, this leads to a threshold value determination as a function of the predetermined desired speed. Subsequently, as a function of the required acceleration and the actual acceleration, the pedal position of a combined accelerator and braking pedal is determined.

Accordingly, it is an object of the present invention to provide a method for spacing control for a motor vehicle which overcomes disadvantages of the prior art.

Another object of the invention is to provide a method for spacing control and an arrangement for carrying out the method by which a motor vehicle spacing can be controlled in a speed-varying traffic situation and, upon detection of a moving object in front of the motor vehicle, the speed of the vehicle is set equal to the speed of the object in front of the motor vehicle while maintaining a required spacing from the object.

These and other objects of the invention are attained by determining a speed-dependent required acceleration from at least a desired speed, which is manually predetermined by the vehicle driver, and which is compared to a spacing-dependent required acceleration. A manipulated variable for the driving engine and/or the braking system of the motor vehicle is generated as a function of the required acceleration value.

In order to determine the spacing-dependent required acceleration, a first controller is supplied with at least the present driving speed of the motor vehicle. In a preferred embodiment, the current road friction coefficient is additionally determined and likewise serves as an input variable to the controller. It is also possible to supply the controller with a parameter which is dependent upon the prevailing visibility conditions and/or the acceleration of the object from which a spacing must be maintained. From the input variables, the first controller determines a required spacing from the object in front of the motor vehicle. In addition, the present spacing from the object in front of the vehicle is determined by a sensor device and is compared with the current required spacing. The difference between the current spacing and the desired spacing, together with the speed difference between the motor vehicle and the object in front of it, is supplied to a second controller, which may additionally have as an input parameter the current vehicle speed. From these variables, the second controller determines the spacing-dependent required acceleration.

According to one embodiment of the invention, the determination of the driving speed-dependent required acceleration is carried out in a third controller which, in addition to the current vehicle speed, is supplied with a variable representing the difference between the manually predetermined desired speed and the current vehicle speed.

In order to take into account specific driving situations, for example getting-into-line maneuvers, a driving situation-dependent required spacing is determined and the normal required spacing formed by the first controller is modified as a function of this driving situation-dependent required spacing. In this case, the current spacing from the object in front of the motor vehicle is made to conform to the modified required spacing.

Furthermore, provision can be made to base the required spacing on the individual driving behavior of a driver. For this purpose it is possible to add to the required spacing, by a switch which can be operated by the driver, a further spacing component which is dependent upon the driver's mode of driving. According to another embodiment, the first controller, which generates the required spacing at least as a function of the current vehicle speed, can be adapted to a particular driver by a learning process.

According to further embodiment of the invention, the manually predetermined desired speed is changed as a function of a curve-dependent required speed, in order to adapt part of the speed control to driving through curves. Preferably, for this purpose at least, a detected transverse slip or transverse acceleration and the prevailing road friction coefficient are supplied to a sixth controller, which forms the curve-dependent required speed from its input variables. In one arrangement, the controller additionally receives the current vehicle speed as an input variable.

The manually predetermined desired speed can also be changed as a function of a virtual desired speed, which is formed on the basis of detected driving states.

Furthermore, in another embodiment of the invention, a seventh controller is supplied with the current vehicle speed and with a registered actuating time of a device such as a turn indicator identifying an overtaking maneuver, and the controller generates from the two variables an acceleration factor which modifies the required acceleration to produce the manipulated variables for the driving engine.

In order to form one of manipulated variables for the driving engine, a fourth controller is preferably supplied with the current vehicle speed and, in addition to the required acceleration, the difference between the required acceleration and the current acceleration of the motor vehicle over time. In addition, the prevailing road friction coefficient is supplied to the fourth controller for adaptation of the manipulated variable to the road conditions.

According to a further embodiment of the invention, these variables are also made available to a fifth controller for forming the manipulated variable for the braking system.

One advantage of the method according to the invention is that no size requirements of the driving engine or of the braking system are needed.

According to a further aspect of the invention, an arrangement for carrying out the method includes a plurality of mutually interlinked fuzzy controllers which are adaptable in their membership functions and in their rules in order to simulate the driving behavior of each individual driver.

Further objects and advantages of the invention will be apparent from a reading of the following description in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic block diagram showing a representative arrangement for spacing control; and

FIGS. 2a and 2b are sections of a schematic diagram illustrating a representative embodiment of a spacing control arrangement having a system of mutually interlinked fuzzy controllers.

In the typical embodiment of the invention shown in FIG. 1, a unit AFDR is provided for controlling the spacing from an object in front of a motor vehicle containing the unit, in particular another vehicle travelling in front, and another unit FGRA is provided for controlling the current speed of the motor vehicle to a desired speed v.sub.wu which may be predetermined at least manually by the vehicle driver. The unit AFDR for controlling the spacing from the other vehicle generates a spacing-dependent required acceleration a.sub.wul as a function of five input variables, i.e., the current driving speed v.sub.e, the road friction coefficient r, the current spacing from the other vehicle d.sub.o, the speed difference between the vehicle and the vehicle in front of it v.sub.r, and the spacing appropriate to the particular driver of the vehicle .DELTA.d.sub.0. The unit FGRA for controlling the vehicle speed generates a speed-dependent required acceleration a.sub.wu2 based on four input variables i.e.: v.sub.e ; the transverse slip q; r; and the required speed v.sub.wu. The meaning of the input variables will be explained in more detail later with reference to FIG. 2.

The two required accelerations a.sub.wu1 and a.sub.wu2 are evaluated by an operator 11 as a function of the driving situation and, dependent on that evaluation, one of the two required accelerations a.sub.wu, together with at least the current acceleration a.sub.e and the current vehicle speed v.sub.e, are supplied to a unit STB for calculating two manipulated variables, i.e., a variable D.sub.ks, for controlling the driving engine and a variable B.sub.rs for controlling the braking system of the motor vehicle.

FIGS. 2a and 2b, taken together, constitute a detailed schematic diagram of an arrangement for spacing control having a plurality of interlinked multidimensional fuzzy controllers 1, 2, 4, 5, 8 and 10. These fuzzy controllers may, for example, be of the type described in detail in the copending application of the same inventors Ser. No. 08/859,636, filed May 20, 1997. The spacing control arrangement is provided as an aid to a driver of a vehicle which is capable of simulating the individual driving behavior of the driver.

As shown in FIG. 2a, the unit AFDR, which determines the spacing-dependent required acceleration a.sub.wu1, comprises a two-dimensional fuzzy controller to which the current driving speed v.sub.e of the motor vehicle and the current road friction coefficient r are supplied as input variables. From those two input variables, the fuzzy controller 5 determines a required spacing d.sub.soll from another vehicle travelling in front of the vehicle containing the spacing control arrangement. In order to increase the utility of the spacing control arrangement, this controller may be adaptable by a learning phase to the driving characteristics of a particular vehicle driver.

Specific driving situations, for example, closely grouped vehicles getting into line, are detected by a detecting device 12, and a driving situation-dependent required spacing d'.sub.soll, is determined which, together with the desired spacing d.sub.soll is supplied to a MIN operator 13 which selects the smaller value d*.sub.s of the two required spacings d.sub.soll and d'.sub.soll for the spacing control. If the controller 5 is not arranged to be adaptable to the driver by learning, a spacing difference value .DELTA.d.sub.0 that is appropriate to the specific driver and takes into account the driving mode of that driver can optionally be set by the driver by a switch in the motor vehicle.

The difference value .DELTA.d.sub.0 is added to the value d.sub.soll to produce a modified required spacing d*.sub.soll which is compared with the driving situation-dependent required spacing d'.sub.soll. In the case of a vehicle driver driving in a very sporty manner, .DELTA.d.sub.0 may be very small or zero. The modified required spacing d*.sub.s is transmitted to a further operator 15 to which the current spacing d.sub.0 to the motor vehicle travelling in front is also supplied. In the operator 15, the current spacing d.sub.0 is compared with the modified required spacing d*.sub.s and the ratio d.sub.0 /d*.sub.s is determined. This ratio is supplied, together with the current vehicle speed v.sub.e and the speed difference v.sub.r from the vehicle travelling in front, to the fuzzy controller 4, which determines the spacing dependent required acceleration awl from these variables.

The unit FGRA of the spacing control arrangement, which determines the speed-dependent required acceleration a.sub.wu2, includes the fuzzy controller 1 to which the current vehicle speed v.sub.e, and the difference between a desired speed v*.sub.wu and the current vehicle speed v.sub.e which is provided by an operator 16, are supplied in order to generate the required acceleration a.sub.wu2. In the illustrated embodiment, the desired speed v*.sub.wu takes into account a plurality of speed-related variables. First, it can represent either the desired speed v.sub.wu which is predetermined by the vehicle driver, or a curve-dependent required speed v.sub.kur, or a virtual required speed v.sub.virt. These speed values are compared with one another via a MIN operator 17, and the lowest speed value is transmitted to the operator 16 as the desired speed v*.sub.wu. The virtual required speed v.sub.virt is determined in a device 19 as a function of predetermined driving states. In order to form the curve-dependent required speed v.sub.kur according to the illustrated embodiment, the fuzzy controller 8 receives the transverse slip q or else the transverse acceleration and the current road friction coefficient r, which may be determined in any conventional manner, as input variables, and generates a curve-dependent speed value v.sub.kur1. Furthermore, the fuzzy controller 10 forms a differential speed value .DELTA.v.sub.kur from the current vehicle speed v.sub.e and the transverse slip q and this value is added to the speed value v.sub.kur1 in an operator 18.

In order to produce the differential speed value .DELTA.v.sub.kur, provision can alternatively be made to calculate a maximum permissible transverse slip q.sub.max from the transverse slip q and the friction coefficient r, and to transmit the magnitude of the difference between the maximum permissible transverse slip q.sub.max and the instantaneous transverse slip q to the fuzzy controller 10.

As shown in FIG. 2b, the spacing-dependent required acceleration a.sub.wu1 and the speed-dependent required acceleration a.sub.wu2 are compared with each other by an operator 11 and the smaller of the two required accelerations a.sub.wu is supplied to the unit STB for calculating the manipulated variables D.sub.ks and B.sub.rs. It is also possible to evaluate the spacing-dependent required acceleration a.sub.wu1 and the speed-dependent required acceleration a.sub.wu2 as a function of the driving situation and, depending on that evaluation, transfer one of the two required accelerations a.sub.wu to the unit STB.

The fuzzy controller 9 in the STB unit detects and interprets from its input variables, the vehicle speed v.sub.e and the actuating time t.sub.b1 of the left-hand turn indicating flasher device of the motor vehicle, and then generates an acceleration factor F.sub.a, by which the required acceleration a.sub.wu is multiplied in an operator 21. The required acceleration a*.sub.wu formed in this way is supplied to the fuzzy controllers 2 and 6 for forming the manipulated variables D.sub.ks and B.sub.rs and to an operator 22. The operator 22 forms the difference between the required acceleration a*.sub.wu and the current acceleration a.sub.e of the motor vehicle as an input variable for the two fuzzy controllers 2 and 6. The present driving speed v.sub.e and the prevailing road friction coefficient r form further input variables of the fuzzy controllers 2 and 6.

Although the invention has been described herein with reference to specific embodiments, many modifications and variations therein will readily occur to those skilled in the art. Accordingly, all such variations and modifications are included within the intended scope of the invention.