ADAPTIVE CRUISE CONTROL SYSTEM FOR MOTOR VEHICLES

Abstract

An adaptive cruise control system for motor vehicles, including a sensor for measuring the distance to a preceding vehicle and an adaptive cruise controller for calculating control interventions into the drive system and/or braking system of the host vehicle for regulating the distance to a setpoint distance, a detuning parameter being adjustable in the adaptive cruise controller, which determines the intensity of the response of the adaptive cruise controller to control deviations, wherein a traffic jam detection module and a detuning controller which, with the detuning parameter as a manipulated variable, adjust the frequency of control interventions having an intensity above a certain minimum intensity to a setpoint frequency adapted to the traffic jam situation.

Claims

1-6. (canceled)

7. An adaptive cruise control system for a motor vehicle, comprising: a sensor for measuring a distance to a preceding vehicle; an adaptive cruise controller for calculating control interventions into at least one of a drive system and a braking system of the motor vehicle for regulating the distance to a setpoint distance, a detuning parameter being adjustable in the adaptive cruise controller, which determines an intensity of a response of the adaptive cruise controller to control deviations; a traffic jam detection module; and a detuning controller which, with the detuning parameter as a manipulated variable, adjusts a frequency of control interventions having an intensity above a certain minimum intensity to a setpoint frequency adapted to a traffic jam situation when the traffic jam detection module detects a traffic jam.

8. The adaptive cruise control system as recited in claim 7, wherein the traffic jam detection module in each case records a maximum value of the intrinsic velocity of the host vehicle achieved up to a point in time at which an acceleration of the motor vehicle drops below a specific negative threshold value, and decides that a traffic jam exists, if the maximum value reached is below a specific value.

9. The adaptive cruise control system as recited in claim 8, wherein the detuning controller establishes a minimum intensity of the control interventions as a function of a maximum value of the intrinsic velocity, on the basis of which the traffic jam detection module has detected the traffic jam.

10. The adaptive cruise control system as recited in claim 8, wherein the detuning controller counts control interventions, in which the acceleration of the vehicle drops below a negative threshold value, which indicates the minimum intensity of the control intervention.

11. The adaptive cruise control system as recited in claim 10, wherein the detuning controller reduces the detuning parameter at regular time intervals in each case by a specific decrement and increases by a specific increment the detuning parameter with each undercutting of the threshold value, which indicates the minimum intensity.

12. The adaptive cruise control as recited in claim 7, wherein the adaptive cruise controller carries out a control algorithm, which is characterized by a number of parameters, and at least one of these parameters is a function of the detuning parameter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. 1 shows a sketch of a vehicle following vehicle situation, in which the adaptive cruise control system according to the present invention is used.

[0018] FIG. 2 shows a block diagram of the adaptive cruise control system.

[0019] FIG. 3 shows a position/time diagram for explaining the mode of operation of the adaptive cruise control system according to the present invention.

[0020] FIG. 4 shows a flow chart for explaining the functioning of the adaptive cruise control system.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0021] FIG. 1 shows an outline of a motor vehicle 10, which is equipped with an adaptive cruise control system. This adaptive cruise control system also includes a radar sensor 12, which cyclically measures, in short intervals, distance d and relative velocity v.sub.r of a preceding vehicle 14. The intrinsic velocity of vehicle 10 equipped with the adaptive cruise control system is identified with v.sub.e, and the velocity of vehicle 14 (preceding vehicle) is identified with V.sub.t. The following applies: v.sub.r =v.sub.t −v.sub.e.

[0022] The adaptive cruise control system depicted in FIG. 2 as a block diagram includes an adaptive cruise controller 16, which evaluates the measured values d and v.sub.r in each measuring cycle of radar sensor 12 and computes therefrom a new setpoint value for acceleration a (or in the case of negative a, the deceleration) of vehicle 10. This setpoint value is then converted into an actual acceleration by the drive system or braking system of vehicle 10, with the result that distance d and relative velocity v.sub.r of vehicle 14 change, and thus other values are measured by radar sensor 12 in the next measuring cycle, with which the control loop is closed. A control algorithm of adaptive cruise controller 16 ensures that distance d to vehicle 14 is adjusted to a specific setpoint distance d.sub.setpoint.

[0023] Indicated below merely as an example is a formula (1), on which the control algorithm of adaptive cruise controller 16 may be based.

a.sub.i =MIN (a.sub.v, a.sub.e, (MIN(a.sub.i−1+a.sub.+, a.sub.max, MAX (a.sub.i−1−a.sub.−, α(d−d.sub.setpoint)+βv.sub.r)))   (1)

[0024] In this formula, a.sub.i is the setpoint acceleration, which is calculated in the instantaneous measuring cycle.

[0025] (Positive) parameter a indicates the (in this example, linear) dependency of the setpoint acceleration on the control deviation d−d.sub.setpoint. If actual distance d becomes smaller than setpoint distance d.sub.setpoint, term α (d−d.sub.setpoint) becomes negative, and the controller accordingly outputs a negative setpoint acceleration in order to decelerate vehicle 10.

[0026] (Positive) parameter β indicates the dependency of the setpoint acceleration on relative velocity v.sub.r. If, for example, the control deviation (d−d.sub.setpoint) equals zero and v.sub.r is negative, i.e., the distance between vehicles 10 and 14 becomes smaller, then factor β v.sub.r is also negative, corresponding to a deceleration of the host vehicle, as a result of which v.sub.r is again reset to zero.

[0027] Variable a.sub.i−1 indicates the setpoint acceleration, which was calculated in the previous measuring cycle and which now, since the setpoint acceleration is converted by the drive system or braking system into an actual acceleration, corresponds to the instantaneous acceleration of vehicle 10. Variables a.sub.+and a.sub.−define a corridor, within which the new setpoint acceleration a.sub.i may change relative to the previous setpoint acceleration a.sub.i−1. Variable a.sub.max indicates an absolute upper limit for the setpoint variable.

[0028] Variable a.sub.v is provided by a cruise control system not shown and normally has the value a.sub.max, so that it is ineffective. It assumes a lower value only if velocity V.sub.e of the host vehicle increases beyond the setpoint velocity selected by the driver.

[0029] Variable a.sub.e is provided by a collision avoidance system not shown and also normally has the value a.sub.max, i.e., it is ineffective. The collision avoidance system calculates a negative value a.sub.e, which is necessary in order to avert a collision, only if the collision avoidance system determines that an acute risk of a collision with preceding vehicle 14 is imminent.

[0030] FIG. 2 also shows a traffic jam detection module 18, which tracks chronological acceleration curve a of vehicle 10 as well as the chronological curve of intrinsic velocity v.sub.e. As long as acceleration a is above a specific negative threshold value of, for example, −1 m/s.sup.2, traffic jam detection module 18 stores in each case the previously achieved maximum of intrinsic velocity v.sub.e. Once acceleration a drops below the threshold value, traffic jam detection module 18 decides on the basis of this maximum velocity reached whether a traffic jam exists and, if necessary, to which class this traffic jam belongs.

[0031] If the stored maximum velocity is greater than, for example, 60 km/h, traffic jam detection module 18 then decides that no traffic jam exists. If the maximum velocity is below 60 km/h but above a second threshold value of, for example, 25 km/h, traffic jam detection module 18 then decides that slow-moving traffic or else a light traffic jam exists, as typically occurs in the case of lane constrictions. In this case, a threshold value a.sub.lim for the acceleration is set at, for example, −1.5 m/s.sup.2 and conveyed to a detuning controller 20.

[0032] If the stored maximum velocity is below 25 km/h, traffic jam detection module 18 decides that a slow traffic jam (stop and go) exists, and threshold value a.sub.lim is set at −1.0 m/s.sup.2.

[0033] Following this decision, the stored maximum velocity is deleted and the velocity recording starts over again.

[0034] As is symbolically depicted in FIG. 2, detuning controller 20 responds to a frequency n of events, in which the setpoint acceleration calculated by adaptive cruise controller 16 drops below a.sub.lim. As a function of this frequency n, detuning controller 20 outputs an detuning parameter m to adaptive cruise controller 16, which influences the behavior of the adaptive cruise controller by modifying one or multiple of parameters α, β, a.sub.max, a.sub.+, a.sub.−.

[0035] Parameter α=α(m), for example, may be a monotonically decreasing function of m. If m becomes greater, the adaptive cruise controller consequently responds more tolerantly to control deviations (d−d.sub.setpoint).

[0036] β=βm) may likewise also be a monotonically decreasing function of m, so that the adaptive cruise controller tolerates greater fluctuations of relative velocity v.sub.r.

[0037] a.sub.max =a.sub.max(m) may also be a monotonically decreasing function of m, with the result that as m increases, the maximum velocity of vehicle 10 decreases.

[0038] In one modified specific embodiment, d.sub.setpoint could also be modified as a function of m or be replaced by a tolerance interval as a function of m.

[0039] The effect of detuning parameter m is graphically illustrated in FIG. 3. Curve K14 in FIG. 3 shows position x of vehicle 14 as a function of time t for a typical traffic jam situation with alternating acceleration phases and deceleration phases. Curve K10 in FIG. 3 shows the corresponding position/time curve of vehicle 10 in the event adaptive cruise controller 16 is not detuned (m=0). In this case, the controller maintains distance d virtually constant at setpoint value d.sub.setpoint, so that curve K10 is practically a copy of curve K14 displaced along the x-axis. Host vehicle 10 therefore also experiences all accelerations and decelerations of preceding vehicle 14, which in general results in an increased fuel consumption. In practice, distance d will fluctuate by d.sub.setpoint within a certain bandwidth, which is a function of the attunement of the adaptive cruise controller, which, however is not depicted in FIG. 3.

[0040] Curve K10m in FIG. 3 illustrates the case in which adaptive cruise controller 16 is detuned (m>0). The result is that greater control deviations (d−d.sub.setpoint) are permitted, so that in the acceleration phases, vehicle 10 accelerates less vigorously and accordingly needs to be braked less vigorously in the deceleration phases. Frequency n decreases accordingly and a significantly more fuel-saving driving style is achieved.

[0041] FIG. 4 depicts the functioning of the above described adaptive cruise control system in a flow chart. The sequence of steps according to this flow chart is carried out cyclically, for example, in intervals of one second, of one tenth of a second or the like. In step S1, the traffic jam class is determined based on the maximum velocity of the host vehicle last stored in traffic jam detection module 18. In step S2, a threshold value a.sub.lim corresponding to the traffic jam class is set. In step S3, it is then checked whether instantaneous setpoint acceleration a instantaneously output by adaptive cruise controller 16 is less than a.sub.lim. If that is the case, detuning parameter m is increased in step S4 by a specific increment Δm by detuning controller 20. If in the process the detuning parameter exceeds a specific maximum value, it is limited in step S5 to this maximum value. A jump is subsequently made back to step S1, and the sequence of steps is run through again in the next cycle.

[0042] If the query in step S3 indicates that the vehicle has not been so vigorously braked and thus, the threshold value a.sub.lim has not been undercut, the detuning parameter is reduced in step S7 by a decrement δm. If in the process the detuning parameter drops below a certain minimum value, for example, the value zero, it is limited in step S8 to the minimum value, and a jump is subsequently again made back to step S1.

[0043] Decrement δm is smaller in terms of absolute value than increment Δm and amounts, for example to 1/20 Δm. When the sequence of steps according to FIG. 4 is run through in one second intervals, for example, this means that detuning parameter m persists practically at the standard value zero, if within a period of twenty seconds the acceleration of vehicle 10 is below a.sub.lim for no more than one second. The increase of m in step S4 predominates only if braking operations accumulate, in which a.sub.lim is undercut, so that the adaptive cruise controller is gradually detuned in the direction of a more balanced driving style. If the frequency of these more vigorous brake applications decreases again, the detuning declines again in step S7 in accordance with decrements δm.

[0044] In the example described above, the duration of the individual braking operations, i.e. the duration of the times, in which a.sub.lim is undercut, also has an influence on the detuning. A specific embodiment is also conceivable, however, in which step S4 is carried out only once, as soon as the acceleration drops below threshold value a.sub.lim, and the jump back to S1 is carried out only after a.sub.lim has at least briefly been exceeded again.

[0045] Specific embodiments are also conceivable, in which detuning controller 20 responds not only to the frequency of vigorous braking operations (undercuttings of a.sub.lim) but additionally also to vigorous acceleration operations.