CRUISE CONTROL SYSTEM FOR MOTOR VEHICLES

Abstract

A cruise control system for a motor vehicle. The system includes a setpoint value generator for generating a setpoint value determining the vehicle speed, and an actuating device that controls the speed of the vehicle to a setpoint speed through intervention into the drive and/or braking system. The system automatically adapts the setpoint speed to a predicted roadway curvature. The setpoint value generator includes at least two modules working independently from one another, including a base module for generating a base setpoint value and a curve module for generating a curve setpoint value that represents a maximum speed at which a curve having a given curvature may be negotiated without exceeding a predefined limiting value for the lateral acceleration of the vehicle, and includes a fusion module that forms a final setpoint value for the actuating device from the base setpoint value and the curve setpoint value through minimum selection.

Claims

1. A cruise control system for a motor vehicle, comprising: a setpoint value generator configured to generate a setpoint value determining a speed of the vehicle; an actuating device configured to control the speed of the vehicle to the setpoint speed through intervention into a drive and/or braking system of the vehicle; wherein the cruise control system is configured to automatically adapt the setpoint speed to a predicted roadway curvature, the setpoint value generator including at least two modules working independently of one another, the at least two modules including a base module configured to generate a base setpoint value, and a curve module configured to generate a curve setpoint value that represents a maximum speed at which a curve having a given curvature may be negotiated without exceeding a predefined limiting value for a lateral acceleration of the vehicle, and wherein the setpoint value generator further includes a fusion module that is configured to form a final setpoint value for the actuating device from the base setpoint value and the curve setpoint value through minimum selection.

2. The system as recited in claim 1, wherein the base module includes several submodules for generating several setpoint values, and the fusion module is configured to fuse the setpoint values with the curve setpoint value through minimum selection.

3. The system as recited in claim 1, further comprising a curve module that is configured to detect, based on data of a surroundings sensor system, a course of a roadway ahead of the vehicle, and to compute a curvature of the roadway for a focal point on the roadway that is at a specific distance ahead of the instantaneous position of the vehicle.

4. The system as recited in claim 3, further comprising a video system as part of the surroundings sensor system.

5. The system as recited in claim 3, further comprising a radar sensor as part of the surroundings sensor system.

6. The system as recited in claim 3, further comprising a navigation system as part of the surroundings sensor system.

7. The system as recited in claim 3, wherein the base module includes a curve speed module that is configured to determine, based on dynamic data of the vehicle, a curvature of the roadway at a location of the vehicle and to generate a setpoint value that corresponds to a maximum speed, up to which the lateral acceleration of the vehicle remains below a predefined limiting value.

8. The system as recited in claim 7, wherein the curve module is configured to transfer curvature data to the curve speed module.

9. The system as recited in claim 7, wherein the curve module is configured to receive curvature data from the curve speed module and to compare the curvature data to its own curvature data.

10. The system as recited in claim 7, wherein the curve module is configured to form, during the computation of the roadway curvature at a given location, a mean value from local roadway curvatures that are recorded during a time period, in which the focal point moves over the given location.

11. The system as recited in claim 7, wherein the curve speed module is configured to determine a limiting value for the lateral acceleration of the vehicle based on driving state variables, and to compute the setpoint value based on the limiting value.

12. The system as recited in claim 11, wherein the driving state variables include driving speed or a road condition.

13. The system as recited in claim 3, wherein the fusion module has a holding function that delays an increase in the curve setpoint value by a predefined time period, when the curve setpoint value reaches a minimum.

14. The system as recited in claim 13, wherein a distance between the vehicle and the focal point is variable and the time period varies as a function of the distance.

15. A non-transitory computer-readable storage medium on which is stored program code for a control computer of a cruise control system of a motor vehicle, the control computer, when executing the program code, causing the control computer to perform: generating, by a setpoint generator, a setpoint value determining a speed of the vehicle; controlling, by an actuating device, the speed of the vehicle to the setpoint speed through intervention into a drive and/or braking system of the vehicle; automatically adapting the setpoint speed to a predicted roadway curvature; wherein the setpoint value generator includes at least two modules working independently of one another, the at least two modules including a base module configured to generate a base setpoint value, and a curve module configured to generate a curve setpoint value that represents a maximum speed at which a curve having a given curvature may be negotiated without exceeding a predefined limiting value for a lateral acceleration of the vehicle, and wherein the setpoint value generator further includes a fusion module that is configured to form a final setpoint value for the actuating device from the base setpoint value and the curve setpoint value through minimum selection.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 shows a block diagram of a cruise control system according to an example embodiment of the present invention.

[0021] FIG. 2 shows a draft of three consecutive phases when negotiating a hairpin turn.

[0022] FIGS. 3 through 5 show setpoint value curves for the three phases illustrated in FIG. 2.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0023] In FIG. 1, a cruise control system for a motor vehicle is illustrated as a block diagram. The system includes a setpoint value generator 10 that continuously provides updated acceleration setpoint values a to a actuating device 12. Actuating device 12 implements these setpoint values into control commands for a drive system 14 and a braking system 16 of the vehicle.

[0024] A sensor system 18 of the host vehicle includes a speedometer 20 for measuring actual speed v of the vehicle and a yaw motion sensor 22 for measuring the data that refer to the yaw motion of the vehicle, for example yaw speed ω, the yaw angle acceleration, the lateral acceleration and/or the steering angle.

[0025] In the example shown, setpoint value generator 10 has four setpoint value modules, namely a desired speed module SSC (set speed controller), a distance module FOC (forward object controller), a curve speed controller CSC and a predictive curve module PCC (predictive curve controller). First three modules SSC, FOC, and CSC are also referred to in summary as base module BM.

[0026] Desired speed module SSC stores a desired speed input by the driver via a driver interface F and continuously compares same to actual speed v reported by speedometer 20. The difference between these two speeds is divided by a time constant and the result forms an acceleration setpoint value a.sub.s that is transferred to a fusion module 24.

[0027] Distance module FOC fulfils the function of a conventional radar-based distance controller. If a radar sensor R that belongs to the surroundings sensor system of the vehicle locates a preceding vehicle in the driving lane traveled by the host vehicle, it reports the distance and relative speed data of the preceding vehicle to the distance module. Moreover, a setpoint time gap that determines the time distance, at which the host vehicle is to follow the preceding vehicle (the target object), may be set in the distance module via driver interface F. In the distance module, a speed profile that results in that the speed of the host vehicle is adapted to that of the preceding vehicle and the time gap between the two vehicles is controlled to the setpoint time gap, is then computed according to known algorithms. The setpoint speed determined by this speed profile is compared to actual speed v and an acceleration setpoint value of is computed through division of the difference by a time constant (that does not need to be congruent with the time constant in the desired speed module) and transferred to fusion module 24.

[0028] Radar sensor R also provides locating angle data on the target object. Moreover, distance module FOC receives information on the anticipated course of the roadway from a roadway module 26. Based on these data, the distance module is able to decide whether the located preceding vehicle is still in the lane traveled by the host vehicle or in an adjacent lane. If the preceding vehicle has left one's own lane, the distance control is terminated in that the setpoint speed computed in the distance module is set to a very high value that is unreachable in practice. Since fusion module 24 selects the minimum from the setpoint values that it receives from the different setpoint value modules in each case, setpoint value of no longer serves a function as a result.

[0029] Curve speed module CSC receives from speedometer 20 actual speed v of the vehicle and from yaw motion sensor 22 the data (yaw speed and/or lateral acceleration) that make possible a computation of the curvature of the roadway section that is instantaneously traveled by the host vehicle. In the example shown, these data include yaw speed ω. This yaw speed ω is at the same time the angular speed of the host vehicle in the case of an orbital motion on a circle having radius (curvature radius) r. Consequently, for actual speed v of the vehicle the following applies: v=ωr. Curvature radius r is consequently quotient v/ω and the reciprocal value of this curvature radius is the instantaneous roadway curvature at the location of the vehicle.

[0030] This curvature may be reported back to roadway module 26 for control purposes.

[0031] Actual speed v of the vehicle multiplied by yaw speed ω is the lateral acceleration of the vehicle. To maintain driving stability, this lateral acceleration should not exceed a specific limiting value, for example 3 m/s.sup.2. If, however, a specific lateral acceleration q is predefined, a speed, at which the vehicle would have exactly the predefined lateral acceleration, may be computed from relation q=ωv=v.sup.2/r. If instantaneous actual speed v is above this value, an acceleration setpoint value a.sub.c, which results in the vehicle speed being reduced to the maximum value admissible in the case of this roadway curvature, may be formed from the difference, again through division by a time constant.

[0032] In addition to radar sensor R, a video system V, with the aid of which images of the roadway lying ahead of the vehicle are recorded, in particular continuously, is also part of the surroundings sensor system of the vehicle. With the aid of known image processing algorithms, the roadway boundaries (for example markings) may be identified and, following the compensation for the perspective distortion curvature k of the roadway, may be determined from the curved course of these roadway boundaries on the entire section that the video system is able to see. Roadway module 26 may thus compute a curvature value k for each point on this roadway section.

[0033] The curvature values for the section lying directly ahead of the host vehicle may be reported to curve speed module CSC and used there for a proactive adaptation of the speed. Curvature value k for a point (referred to as a “focal point” in the following) lying somewhat further ahead of the host vehicle is reported to predictive curve module PCC and used there in the same manner as in curve speed module CSC for the purpose of computing a speed that the vehicle should not exceed when it reaches this point on the roadway, so that the predefined value is maintained for the lateral acceleration. Through comparison of this speed to actual speed v and through division by a time constant, a further acceleration setpoint value a.sub.p is computed and transferred to fusion module 24.

[0034] Overall, fusion module 24 thus receives four acceleration setpoint values a.sub.s, a.sub.f, a.sub.c and a.sub.p, and fusion module 24 selects at any given point in time the smallest of these setpoint values and provides it as final acceleration setpoint value a to actuating device 12.

[0035] During undisturbed driving on a straight roadway, i.e., when no preceding vehicle is located, setpoint value a is equal to setpoint value a.sub.s, which corresponds to the desired speed selected by the driver. When a preceding vehicle is located that is slower than this desired speed, the roadway is still straight, however, setpoint value a is formed by setpoint value of provided by the distance module.

[0036] When the vehicle approaches a curve, curvature k, which roadway module 26 provides to predictive curve module PCC and which refers to a focal point that is relatively far ahead of the host vehicle, will initially increase. When the lateral acceleration, which results from this curvature and instantaneous actual speed v of the vehicle, is too high, the module outputs a very small acceleration setpoint value a.sub.p and it is this value that determines final setpoint value a.

[0037] When the vehicle further approaches the curve, the curvature that is reported to predictive curve module PCC will slowly decrease again, since the focal point is moved further ahead. At the same time, the curvature reported to curve speed module CSC will increase, since the host vehicle is now entering the curve. In this case, final acceleration setpoint value a is equal to setpoint value a.sub.c provided by curve speed module CSC.

[0038] In the example shown, roadway module 26 also receives information on the roadway from two further sources of information, namely from radar sensor R and from a navigation system N or the digital map of the road network stored therein. The information provided by radar sensor R may be distance and angle data from guardrail posts and the like, for example, which also make possible a determination of the roadway course. By comparing the data of the radar sensor to the data of the video system, the error susceptibility may thus be reduced and the accuracy improved. The same is true for the comparison of the data to the data from navigation system N. Optionally or in addition, the surroundings sensor system may also include a LIDAR sensor.

[0039] The operating mode of the system is to be elucidated with reference to FIGS. 2 through 5 based on one exemplary situation.

[0040] In FIG. 2, a roadway 28 is schematically shown that runs in the shape of a hairpin turn. P3 identifies the position on this roadway 28 of a vehicle, which is equipped with the above-described cruise control system. F3 identifies the focal point on the roadway, for which roadway module 26 computes the predicted roadway curvature, when the vehicle is in position P3. In this situation, roadway module 26 only reports a relatively small curvature k, so that proactive curvature module PCC is not yet active.

[0041] In order to compensate for statistical variations, curvature k is computed for focal point F3 in that a varying mean value of a sequence of local curvatures, which are computed and recorded, is formed over a certain time period of several milliseconds, for example, while the focal point is moving along the roadway.

[0042] At a slightly later point in time, the vehicle has reached a position P4 and the associated focus of the curvature prediction is at F4, at the most narrow point of the curve. At an even later point in time, the vehicle has reached a position P5 and is about to enter the most narrow part of the curve. The associated focus of the curvature position is then at F5, already behind the curve, so that a smaller curvature is measured once again. Without additional measures, this would result in the control being transferred from predictive curve module PCC to curve speed module CSC. This module could then allow under certain circumstances a speed that is too high, since the instantaneous lateral acceleration at location P5 is still relatively small.

[0043] In FIGS. 3 through 5, the relevant setpoint speeds are illustrated in a time diagram for positions P3, P4, and P5 shown in FIG. 2 in each case. It is not the setpoint accelerations according to FIG. 1 that are represented here, but the associated setpoint speeds, since these setpoint speeds are independent from the particular actual speed of the vehicle and the diagrams may thus be better compared to one another.

[0044] In FIG. 3, the situation around the point in time at which the vehicle drives through position P3 is illustrated. Setpoint speed V.sub.p, which is computed by predictive curvature module PCC and which determines setpoint acceleration a.sub.p, is relatively high due to the minor roadway curvature and greater than setpoint speed V.sub.s that corresponds to the desired speed selected by the driver. For this reason, the setpoint acceleration is determined by desired speed V.sub.s in this case.

[0045] In FIG. 4, setpoint speed V.sub.p significantly decreases, since the focus of the curvature measurement (at F4) enters the narrow part of the curve and the roadway curvature thus increases. Setpoint speed V.sub.p decreases below desired speed V.sub.s and then predictive curvature module PCC assumes control.

[0046] In FIG. 5, setpoint speed V.sub.p increases again, since the focus of the curvature determination has again left the curve behind. Curve speed module CSC computes a setpoint speed V.sub.c that decreases with increasing roadway curvature, but is initially still greater than V.sub.p, so that the predictive curvature module maintains control. If a pure minimum selection took place in fusion module 24, final setpoint speed a would increase correspondingly to the curve for setpoint speed V.sub.p until desired speed V.sub.s is reached again. Only then would the vehicle enter the curve and decreasing setpoint speed V.sub.c would force a deceleration of the vehicle once again. This would result in a very choppy way of driving, during which the vehicle is initially accelerated and decelerated again immediately after that.

[0047] To prevent this from happening, a holding function is implemented in fusion module 24 that ensures that setpoint speed V.sub.p cannot increase again, after reaching a minimum, until a certain delay time td has elapsed. This delay time approximately corresponds to the time required by the vehicle to travel the road from its instantaneous position to the position of focus of the curvature determination. In the example shown, delay time td has not elapsed until setpoint speed V.sub.c has already decreased to the extent that it prevents an undesired increase in speed. The fact that the final setpoint speed changes abruptly in FIG. 5 does not have a significant effect on the driving behavior, since the corresponding change in acceleration setpoint value a takes effect only slowly due to the time constant.