EP1919729A1

EP1919729A1 - System for controlling a vehicle driving downhill

Info

Publication number: EP1919729A1
Application number: EP06791598A
Authority: EP
Inventors: Thomas Bach; Michael Bleser; Elmar Hoffmann; Harald Thelen
Original assignee: Lucas Automotive GmbH
Current assignee: ZF Active Safety GmbH
Priority date: 2005-08-30
Filing date: 2006-08-21
Publication date: 2008-05-14
Also published as: WO2007025660A1; CN101253066A; JP2009505893A; US20090287388A1; DE102005041070A1

Abstract

Disclosed is a hill descent control (HDC) in the braking equipment of a motor vehicle comprising an electrically controlled service brake assembly which is equipped for both an anti-blocking control function and a braking function that is actuated independently of the driver, and a brake positioning member which allows the brake pressures or braking moments generated for the individual wheels of a motor vehicle to be adjusted individually, said brake pressures or braking moments representing the manipulated variable influenced by the hill descent control. An electronic control unit is provided for electronic controlling or regulating purposes. Said control unit directly or indirectly detects variables related to modes of operation of the motor vehicle and adjusts additional braking moments when driving on steeply sloped roadways regardless of whether a brake pedal is actuated. A downhill momentum compensation circuit is also provided which superimposes a corrective signal (aN) that depends on the gradient (aNEIGUNG) of the hill traveled on onto the output signal of the brake regulator (aR).

Description

System for controlling the downhill of a motor vehicle

Description Background of the Invention

The invention relates to a system for a so-called "Hill Descent Control" (HDC) for a motor vehicle, that is to say a system for controlling the speed of downhill driving of a motor vehicle. Setting the hill descent control "and" Connecting the downhill drive as a disturbance variable ".

A down hill control system is known inter alia from EP 0 856 446 B1. It serves to ensure the traction and driving stability of the motor vehicle when driving on steeply inclined routes, especially in the field. This system is intended for a wheeled vehicle having a plurality of wheels, a plurality of brakes respectively for braking one of the wheels, an accelerator pedal, a brake pedal, and a wheel lock sensor to detect a lock on one of the wheels. A controller has an activated and a deactivated state. In its activated state, each brake is applied to decelerate the motor vehicle when a detected motor vehicle speed is above a predetermined desired speed and no wheel lock is detected. One of the brakes is released when a lock on the associated wheel is detected while the detected vehicle speed is above the desired speed. Upon entering the activated state, the controller controls the brake so that the rate of acceleration of the motor vehicle reaches the desired speed without actuating the pedals when the vehicle speed is substantially less than the desired speed.

When entering the activated state, the controller compares the vehicle speed with the target speed and controls the brake means so that the vehicle speed approaches the target speed. The deceleration rate of the motor vehicle is controlled to the desired speed when the vehicle speed is much higher than the target speed. The acceleration rate may be limited to a predetermined maximum value of about 0.2 to 0.3 g. The activated state can only be selected when the motor vehicle is in first gear or in reverse gear. In the activated The driver is overridden by the operation of a braking requesting means of the motor vehicle by a driver to increase the amount of braking beyond that provided by the controller. Thus, the motor vehicle is slowed down below the target speed if no wheel lock is detected. In its activated state, the control can at least partially release the brakes if the detected motor vehicle speed is below the setpoint speed. The control can be activated by a manually operated switch. The controller operates, if necessary, the brakes, provided that the detected vehicle speed is below the desired speed, to ensure that the rate of acceleration of the motor vehicle is less than a threshold.

To the invention zucrundelieαenes problem

Here is the particular problem that unfortified and slippery soil conditions make it difficult to drive on a motor vehicle considerably. As the driving of steeply inclined driving paths generally takes place at a low speed, a reduction or withdrawal of the drive torque applied by the motor vehicle engine, even if a lowermost gear step is engaged, is not sufficient on its own. Rather, additional braking torques must be provided on the wheels. 0

Modern motor vehicles are usually equipped with an electrically controllable service brake system, in addition to the anti-lock control function (ABS) also independent of a driver operation, so automatic braking functions, such as. Traction control (ASR) or vehicle dynamics control (ESP) to perform. For this purpose, the service brake system comprises a correspondingly configured electrohydraulic control unit, an electronically controllable brake booster or is designed as a so-called "brake-by-wire" (BBW) system electronic sensors with operating states of the motor vehicle are detected in relation to variables o Thus, for example, for the ABS control by means of wheel speed sensors, the slip of the motor vehicle wheels is detected in order to control the rotational behavior of the motor vehicle wheels in dependence on the slip in such a way that blocking is prevented.

5 WO 0114185A1 describes a service brake system with downhill control.

A device for supporting downhill control detects operating states of the vehicle and makes it independent when driving on steep slopes from an operation of a brake pedal additional braking torques. The vehicle behavior, which results from the setting of the manipulated variable, is continuously recorded on the basis of the vehicle speed and compared with a desired speed.

WO 9611826 describes a service brake system with downhill descent control which adjusts additional braking torques when driving on steeply inclined driving paths independently of an actuation of a brake pedal as soon as the vehicle speed exceeds a threshold value.

Inventive solution

By the invention, the "downhill hill" control (HDC) is provided as an automatic braking function in an electrically controllable service brake system to set regardless of an actuation of the brake pedal by the driver additional braking torque when driving on steeply inclined routes.

As a result, the driver is relieved of the operation of the brake system, so that he can concentrate in such an often critical situation on the steering of the motor vehicle. In this case, already existing modules (control computer, sensors, actuators, control electronics, etc.) can be used in an advantageous manner anyway. This not only keeps effort and costs low. Rather, existing functions (for example ABS or ASR) are available during the operation of the downhill control.

For explanation, FIG. 1 shows an electrically controllable service brake system according to the invention in a schematic control block diagram.

A component designated here as a brake actuator corresponds, for example, to an electrohydraulic control unit which makes it possible to individually set the brake pressures p_RAD, i or braking torques generated for the individual wheels i of a motor vehicle. In this case, the respective brake pressure p_RAD, i or the respective braking torque is the manipulated variable influenced by the downhill descent control (HDC). The influencing of the behavior of the motor vehicle, which results from the setting of the braking torques, is continuously recorded here on the basis of the actual or actual motor vehicle speed v_IST, which is the controlled variable. The controlled variable v_IST is generated at a desired vehicle speed v_SOLL, wel the leader is compared. The result of this comparison is fed to a brake controller which, depending on the result of the comparison via the brake actuator, influences the controlled variable v_IST in the sense of an adjustment to the reference variable v_SOLL. The brake controller can be designed in a known manner by combining proportional and / or integral and / or differential components, for example as a PI or PID controller.

In order to make a selection as to which function is to be performed by the electrically controllable service brake system, a decider can be connected upstream of the actual control circuit, giving priority to a particular function based on driver wishes, operating states of the motor vehicle, etc., in order to respectively control the control variable v_SOLL To make available.

Such a function may e.g. a cruise control referred to as "Adaptive Cruise Control" (ACC), which not only maintains a desired speed specified by the driver compared to the conventional speed control known as cruise control, but also, inter alia, by self-braking a dependent on the speed of one's own vehicle distance to one adheres to the preceding motor vehicle.

Furthermore, such a function may e.g. The braking request of the driver resulting from the actuation of the brake pedal, on the one hand in the case of a BBW announcement ge a brake request, on the other hand to decide whether, for example. a current, automatic HDC control in favor of a driver-controlled, conventional braking is aborted.

The invention also deals with the problem of uncomfortable motor vehicle behavior, which is particularly pronounced in particular the more the controlled variable vJST and the reference variable v_SOLL deviate from one another when entering the HDC control. In terms of control technology, this could be achieved with a suitable design of the brake controller. However, this would contradict the goal of using a common controller structure for various other brake functions (ABS, ASR, etc. - see above).

Therefore, as shown in FIG. 1, an HDC adjuster is proposed which makes an adjustment of the reference variable v_SOLL as a function of a target variable v_ZIEL, a signal ON / OFF and the controlled variable v_IST. The target size v_ZIEL is a desired speed, with which the downhill run is to take place in the context of HDC. This can either be a predefined constant variable in the system, eg v_ZIEL = 8 km / h, or one by means of a control element, eg potentiometer, by the driver within a range, eg 5 km / h <v_ZIEL <20 km / h h, selectable size act. If the motor vehicle is equipped with cruise control or with ACC, it can be provided to set the target variable v_ZIEL by means of the operating element provided therefor. Another way to vary the target size v_ZIEL by the driver is to increase the target size v_ZIEL by pressing the accelerator pedal and reduce the target size v_ZIEL by pressing the brake pedal. Finally, it is also possible to vary the target size v_ZIEL depending on the inclination of the currently traveled lane, and indeed the steeper the incline the lower the desired speed or vice versa.

The signal ON / OFF comes from a control element, e.g. A switch that allows the driver to tell the system about their desire to enable HDC. If, in a first step, there is a desire to activate HDC, in a second step an activation of HDC for plausibility is checked. For this verification certain criteria based on operating conditions of the motor vehicle are used, including:

Is the current vehicle speed below a low speed (e.g., v_IST <30 Km / h)? Is a low gear (first gear, for example) engaged? Is the vehicle not in an uphill drive?

If the check concludes positively, then in a third step, the reference variable v_SOLL is adapted to the target variable v_ZIEL.

A preferred exemplary embodiment, such as the adaptation or prefetching of the reference variable v_SOLL to the target variable v_ZIEL, can be carried out, is illustrated in the velocity-time diagram according to FIG. 2.

In this case, the adaptation takes place as a function of the control variable v_IST, which is acted upon in the negative and positive direction by an offset Δv. The resulting curves v_IST-Δv and v_IST + Δv as a function of time intersect in the Points A and B show the course of the constant target size v_ZIEL This causes sectors L, II. And III. for which the reference variable v_SOLL is set in each case as follows:

Sector I is determined by the condition:

v_IST-Δv> v_ZIEL

If this is fulfilled, the following applies: v_SOLL: = v_IST-Δv

As a result, the reference variable v_SOLL is uniformly approximated as a function of the control variable v_IST to the target variable v_ZIEL, so that a very comfortable motor vehicle behavior is established, especially when entering the HDC control.

Sector II. Is determined by the condition:

v_IST-Δv <= v_ZIEL

If this is fulfilled, the following applies: v_SOLL: = v_ZIEL

This means that as soon as the control variable v_IST less the offset Δv reaches the target variable v_ZIEL or drops below the target variable v_ZIEL, the target variable v_ZIEL is taken over directly as the reference variable v_SOLL in order to achieve a dynamic adjustment behavior.

The sector III. is determined by the condition:

v_IST + Δv> = v_ZIEL

If this is fulfilled, then either: v_SOLL: = v_ZIEL

or: v_SOLL: = v_IST + Δv

In this case either the target variable v_ZIEL is taken over directly as leading variable v_SOLL, or, if a less dynamic adjustment behavior is desired, the leading variable v_SOLL is uniformly approximated to the target variable v_ZIEL as a function of the control variable v_IST. A less dynamic one For example, control behavior may be desired when the influence of the downhill force decreases towards the end of a downhill descent with decreasing inclination of the driveway, as a result of which the actual motor vehicle speed v_IST can break in the short term.

Alternatively, the offset .DELTA.v can be varied dynamically as a function of the control variable v_IST instead of as a constant, in the sense that it increases with increasing control variable v_IST, so that no straight lines, as shown in FIG 2, but would produce envelopes. This would ensure that the reference variable v_SOLL in sector I would approximate more quickly to the target variable v_ZIEL. This is particularly advantageous if, when entering the HDC control, the controlled variable v_IST is significantly above (that is, more than a predetermined value above) the target variable v_ZIEL.

Furthermore, the invention is concerned with the influence of the slope force on the HDC control, which can be very strong when driving on steep slopes.

In principle, the influence of the slope force is regulated by the brake controller, since the controlled variable is the current or actual vehicle speed v_IST, with which the motor vehicle is moving. However, variations or jump-like changes in the angle of inclination, e.g. When entering and exiting into the slope can occur in the time response of the control variable v_IST to overshoot or undershoot, which the driver feels very uncomfortable due to the acceleration or deceleration phases occurring thereby. This problem could be controlled by means of a suitable interpretation of the

Brake control, e.g. as an adaptive controller, solve. However, then, as already explained above, there would be a contradiction to the goal of using a common controller structure for various braking functions.

To solve this problem serves a slope output, as shown in Fig. 1. The Hangabtriebsaufschaltung superimposed on the output of the brake controller a_R a correction signal a_N, which is determined in dependence on the current or actual inclination of the busy slope α_NEIGUNG of the Hangabtriebsaufschaltung. By returning the inclination α_NEIGUNG to the output of the brake controller, its action on the control loop is almost completely compensated, so that the dynamic behavior of the brake controller is not appreciably adversely affected. The brake controller responsible for the quality of the control Therefore regulator needs to be designed only for the simple case that the motor vehicle is moved in the plane. As a result, in addition to the control technical advantages and expenses and costs for the necessary equipment (computer / storage capacity, etc.) can be kept low. Another advantage is that the invention Hangabtriebsschaltung can also be used by other functions such as ACC.

The inclination α_NEIGUNG is ideally detected by means of suitable sensor means (for example inclination angle meter) by measurement and fed to the downgrade drive as an input variable. If the motor vehicle has sensor means for detecting the total longitudinal acceleration of the motor vehicle, the inclination can also be determined by subtracting the longitudinal acceleration of the motor vehicle determined from the signals of the wheel speed sensors from the total longitudinal acceleration of the motor vehicle.

The downslope override determines the correction signal a_N based on the inclination α_NEIGUNG, using motor vehicle parameters (e.g., weight) and operating conditions of the motor vehicle (e.g., load state).

If the output signal of the brake controller a_R is dimensioned as a delay, the correction signal a_N is also dimensioned as a delay, as a result of which the deceleration requested with the brake actuator is increased with increasing inclination α_NEIGUNG.

The value of the inclination α_NEIGUNG can vary between about + 45 ° and about -45 °.

In summary, the following principles and advantages of the system according to the invention can be mentioned: The setpoint for the speed control in the HDC according to the invention

Operation is a function of the current vehicle speed, the (target) variable speed, and a dynamically changing maximum difference between the desired speed and the current vehicle speed. • A hard control use in HDC operation according to the invention is avoided; this results in a more comfortable vehicle behavior. In the inventive determination of the setpoint, the current vehicle speed is included; This leads to a perceived as natural driving behavior.

The determination according to the invention of the desired speed is effected as a function of the motor vehicle speed as long as the target speed is not within a limit range.

The system according to the invention also works with changing target speed.

The downgrade engagement according to the invention allows the use of conventional control structures and algorithms, which assume that the motor vehicle is moving on a substantially level ground. The downgrade force or acceleration is determined and fed as disturbance to the control loop. This leads to a simple control algorithm and to a shorter reaction time of the controller in slope / slope changes.

Finally, it should be noted that the invention is to be implemented as software on the computer unit of the already existing electronic control unit of the brake equipment, so that additional costs for hardware does not arise.

Claims

claims

1. Downhill control system (HDC) in the braking equipment of a motor vehicle with an electrically controllable service brake system, a brake actuator that allows individual adjustment of the brake pressures (p_RAD, i) or braking torques generated for the individual wheels (i) of a motor vehicle which are respective manipulated variables influenced by the down hill control (HDC), wherein an electronic control unit is provided which directly or indirectly detects quantities related to operating states of the motor vehicle,

i5 wherein a downgrade engagement circuit is provided which superimposes on the output signal of the brake controller a_R a correction signal a_N which is determined by the downgrade engagement in dependence on the current or the actual inclination of the traveled slope α_NEIGUNG and is fed back to the output of the brake controller; 0, characterized in that by the return of the correction signal a_N to the output of the brake controller, an effect of short-term fluctuations or sudden changes in inclination is almost completely compensated for the vehicle speed. 5

The system of claim 1, wherein the correction signal a_N is a signal indicative of a delay.

3. System according to claim 1 or 2, wherein the inclination α_NEIGUNG detected by o of a tilt angle sensor and the Hangabtriebsaufschaltung as

Input is supplied.

4. System according to claim 3, wherein the inclination α_NEIGUNG is determined by means of a sensor provided in the motor vehicle for detecting the total longitudinal acceleration of the motor vehicle 5 determines this and the

Signals detected by existing in the motor vehicle wheel speed sensors Longitudinal acceleration of the motor vehicle is subtracted from the total longitudinal acceleration of the motor vehicle.

5. System according to one of the preceding claims, in which the slope

5 drive input based on the inclination α_NEIGUNG, other vehicle parameters and operating conditions of the motor vehicle, the correction signal a_N determined.

6. System according to any one of the preceding claims, in which the output lo signal of the brake controller a_R and the correction signal a_N are dimensioned as a delay, and the delay requested at the brake actuator with increasing inclination α_NEIGUNG is increased.

7. System according to any one of the preceding claims, wherein as Bremsstell- i5 member an electro-hydraulic control unit, an electronically controllable

Brake booster or a brake-by-wire equipment is provided.

8. System according to any one of the preceding claims, wherein the electronic control unit adjusts the additional braking torques independently of an actuation of a brake pedal.

9. System according to one of the preceding claims, wherein the electrically controllable service brake system for both an anti-lock control function (ABS), as well as for a driver operation independent brake function 5 (ASR, ESP) is set up.

10. System according to any one of the preceding claims, wherein the influencing of the motor vehicle behavior, which results from the Einsteilens the manipulated variable, on the basis of the current motor vehicle speed v_IST, 0 which is the controlled variable, is continuously recorded.

11. System according to one of the preceding claims, in which the controlled variable v_IST is compared with a desired motor vehicle speed v_SOLL, which is the reference variable. 5

12. System according to any one of the preceding claims, wherein the result of the comparison is supplied to a brake controller, which depends on the result of Comparison via the brake actuator the controlled variable v_IST in the sense of an adjustment to the reference variable v_SOLL influenced.

13. System according to any one of the preceding claims, wherein the result of the comparison 5 is fed to a brake controller, which depends on the result of

Comparison via the brake actuator the controlled variable v_IST in the sense of an adjustment to the reference variable v_SOLL influenced.

14. System according to any one of the preceding claims, wherein the brake controller lo is designed by combining proportional and / or integral and / or differential proportions as P, PI or PID controller.

15. System according to any one of the preceding claims, in which the control circuit is preceded by a decision maker, who gives priority to a particular function based on external or internal variables such as driver's wishes, operating states of the motor vehicle, etc., by their control variable v_SOLL the control loop to provide.

16. System according to the preceding claim, wherein the function is a GE speed control (ACC), which maintains a predetermined by the driver desired speed and complies by self-braking a dependent on the speed of the own motor vehicle distance to a preceding motor vehicle.

17. The system of claim 15, wherein the function is the driver's braking request resulting from the operation of the brake pedal to notify a brake request in the case of a BBW system, and to decide whether an ongoing automatic HDC control is in favor a controlled by the driver, conventional braking is aborted. 0

18. System according to one of the preceding claims, in which an HDC

Adjuster is provided, which makes an adjustment of the reference variable v_SOLL depending on a target size v_ZIEL, a signal ON / OFF and the controlled variable v_IST. 5

19. System according to the preceding claim, wherein the target size v_ZIEL is a desired speed with which the downhill in HDC operation is to take place.

20. System according to the preceding claim, wherein the desired speed is either a predefined constant size, or a selectable by means of a control by the driver within a range, size.

21. System according to the preceding claim, in which the desired speed is achieved by means of a cruise control system present in the motor vehicle.

Control element is set.

22. The system of claim 20 or 21, wherein the desired speed by the driver by means of an accelerator pedal to increase and reduce by means of an i5 ner actuation of the brake pedal.

23. System according to claim 20 or 21, wherein the desired speed is to be varied in dependence on the inclination of the currently traveled lane, with a steeper slope leads to a lower desired speed and 0 vice versa.

24. System according to any one of the preceding claims, wherein the signal ON / OFF in a first step to the system by means of a control element informs the driver to activate the HDC operation. 5

25. System according to any one of the preceding claims, wherein the signal ON / OFF is checked for plausibility in a second step before activation of the HDC operation such activation.

26. The system according to any one of the preceding claims, in which for the Plausibili- tätsüberprüfung certain criteria derived from operating conditions of the motor vehicle are checked.

27. System according to one of the preceding claims, in which the following operating states of the motor vehicle are checked:

(i) If the current vehicle speed is below a low speed, and / or (ii) a lower gear is engaged, and / or

(iii) is the motor vehicle not in an uphill drive?

28. System according to claim 27, wherein in the case of a positive check in a third step, the control variable v_SOLL is adapted to the target variable v_ZIEL.

29. System according to one of the preceding claims, in which the adaptation of the reference variable v_SOLL to the target variable v_ZIEL takes place as a function of the control variable v_IST, which is applied in the negative and / or positive direction with a substantially constant offset Δv, whereby v_IST - Δv and v_IST + Δv are determined as a function of time.

30. System according to any one of the preceding claims, wherein for

a first range (v_IST-Δv> v_ZIEL) applies: v_SOLL: = v_IST-Δv, whereby the reference variable v_SOLL is uniformly approximated as a function of the control variable v_IST to the target variable v_ZIEL, and / or

a second range (v_IST-Δv <= v_ZIEL) applies: v_SOLL: = v_ZIEL, whereby, as soon as the control variable v_IST minus the offset Δv reaches the target variable v_ZIEL or falls below the target variable v_ZIEL, the target variable v_ZIEL is taken over directly as the leading variable v_SOLL, and /or

a third range (v_IST + Δv> = v_ZIEL) applies: v_SOLL: = v_ZIEL or v_SOLL: = v_IST + Δv, whereby either the target quantity v_ZIEL is taken over directly as reference variable v_SOLL, or the reference variable v_SOLL evenly as a function of the control variable v_IST to the target variable v_ZIEL is approximated.

31. System according to any one of the preceding claims, wherein the offset .DELTA.v is dynamically varied as a function of the control variable v_IST so that it becomes larger with increasing control variable v_IST.

92