METHOD AND ELECTRONIC CONTROL UNIT FOR CONTROLLING A BRAKE SYSTEM OF A MOTOR VEHICLE

Abstract

A method is provided for controlling a brake system (12) of a motor vehicle (2), having wheel brakes controllable for carrying out an anti-lock function (ABS) and for carrying out a roll stability control function (RSC). During cornering or in the event of a sudden evasive movement, the motor vehicle (2) is braked by actuation of the wheel brakes (26a, 26b, 28a, 28b) on account of a determined risk of tilting. With the start (t1) of an ABS control operation on the braking force (p.sub.B_KA) of a wheel brake (26b; 28b) on the inside of the bend on at least one motor vehicle axle (4; 8), the braking force (p.sub.B_KA) of at least one wheel brake (26a; 28a) on the outside of the bend is increased, and is lowered again with the end of the ABS control operation (t3).

Claims

1. A method for controlling a brake system (12) of a motor vehicle (2), which system has wheel brakes (26a, 26b, 28a, 28b), which can be controlled by an electronic control unit (14) in respect of their actuation, and control devices for carrying out an anti-lock function (ABS) and for carrying out a roll stability control function (RSC), the method comprising: determining, by the electronic control unit (14) during cornering or in the event of a sudden evasive movement defining a bend, a determined risk of tilting of the motor vehicle (2) about a longitudinal axis (84) thereof; executing a roll stability control function by the electronic control unit and braking the vehicle by actuation of the wheel brakes (26a, 26b, 28a, 28b) on account of the determined risk of tilting; starting (t1) an ABS control operation on a braking force (p.sub.B_KA) of a wheel brake (26b; 28b) on an inside of the bend on at least one motor vehicle axle (4; 8), with the starting of the ABS control operation, increasing a braking force (p.sub.B_KA) of at least one wheel brake (26a; 28a) on an outside of the bend, and lowering the braking force (p.sub.B_KA) of the at least one wheel brake (26a; 28a) on the outside of the bend with the end of the ABS control operation (t3).

2. The method as claimed in claim 1, wherein the increase in the braking force (?p.sub.B_KA) of the at least one wheel brake (26a; 28a) on the outside of the bend is dimensioned in such a way that a loss of braking force of the wheel brake (26b; 28b) on the inside of the bend due to the ABS control operation is thereby compensated.

3. The method as claimed in claim 2, wherein a mean braking force (p.sub.B_R-m) of the wheel brake (26b; 28b) on the inside of the bend is determined during the ABS control operation, and a value of the increase in the braking force (?p.sub.B_KA) of the wheel brake (26a; 28a) on the outside of the bend corresponds to a force difference (?p.sub.B_KI) between a standard braking force (p.sub.B_KS_Std) provided from the start of the execution of the roll stability control function and the mean braking force (p.sub.B_R-m) of the wheel brake (26b) on the inside of the bend (?p.sub.B_KA=?p.sub.B_KI=p.sub.B_KS_Std?p.sub.B_R-m).

4. The method as claimed in claim 3, wherein, during the ABS control operation, the braking force (p.sub.B_KI) at the wheel brake (26b; 28b) on the inside of the bend is determined as an upper braking force (p.sub.B_R-o) and a lower braking force (p.sub.B_R-u), and the mean braking force (p.sub.B_R-m) at the wheel brake (26b; 28b) on the inside of the bend is determined as the arithmetic mean value of the upper braking force (p.sub.B_R-o) and the lower braking force (p.sub.B_R-u) during the ABS control operation (p.sub.B_R-m=(p.sub.B_R-o+p.sub.B_R-u)/2).

5. A method for controlling a brake system (12) of a motor vehicle (2), which system can be controlled by an electronic control unit (14) and which has wheel brakes (26a, 26b, 28a, 28b), which can be actuated by a pressure medium, and control devices for carrying out an anti-lock function (ABS) and for carrying out a roll stability control function (RSC), the method comprising: executing, during cornering or in the event of a sudden evasive movement defining a bend, a roll stability control function by the electronic control unit, and braking the motor vehicle (2) by introducing a brake pressure into the wheel brakes (26a, 26b, 28a, 28b) on account of a determined risk of tilting about the longitudinal axis (84) of the motor vehicle, wherein the determined risk is determined by the electronic control unit and the braking is controlled by the electronic control unit; starting an ABS control operation by the electronic control unit, wherein, with the start (t1) of the ABS control operation on a brake pressure (p.sub.B_KI) of the wheel brake (26b; 28b) on the inside of the bend on at least one motor vehicle axle (4; 8), increasing the brake pressure (p.sub.B_KA) of a wheel brake (26a; 28a) on the outside of the bend, and lowering the brake pressure (p.sub.B_KA) of the at least one wheel brake (26a; 28a) on the outside of the bend with an end of the ABS control operation (t3).

6. The method as claimed in claim 5, wherein the increase in the brake pressure (?p.sub.B_KA) of the wheel brake (26a; 28a) on the outside of the bend is dimensioned in such a way that a loss of braking force of the wheel brake (26b; 28b) on the inside of the bend due to the ABS control operation is thereby compensated.

7. The method as claimed in claim 6, wherein a mean brake pressure (p.sub.B_R-m) of the wheel brake (26b; 28b) on the inside of the bend is determined during the ABS control operation, and the value of the increase in the brake pressure (?p.sub.B_KA) of the wheel brake (26a; 28a) on the outside of the bend corresponds to a pressure difference (?p.sub.B_KI) between a standard brake pressure (p.sub.B_KS_Std) provided from the start of the execution of the roll stability control function and the mean brake pressure (p.sub.B_R-m) of the wheel brake (26b) on the inside of the bend (?p.sub.B_KA=?p.sub.B_KI=p.sub.B_KS_Std?p.sub.B_R-m).

8. The method as claimed in claim 7, wherein, during the ABS control operation on the brake pressure (p.sub.B_KI) at the wheel brake (26b; 28b) on the inside of the bend, an upper brake pressure (p.sub.B_R-o) and a lower brake pressure (p.sub.B_R-u) are determined, and in that the mean brake pressure (p.sub.B_R-m) at the wheel brake (26b; 28b) on the inside of the bend is determined as an arithmetic mean value of the upper brake pressure (p.sub.B_R-o) and the lower brake pressure (p.sub.B_R-u) during the ABS control operation (p.sub.B_R-m=(p.sub.B_R-o+p.sub.B_R-u)/2).

9. The method as claimed in claim 5, wherein characterized in that the increase in the brake pressure (p.sub.B_KA) of the wheel brake (26a; 28a) on the outside of the bend is accomplished by setting a correspondingly increased brake pressure (p.sub.B_KA_max) in a relay valve (70c; 54c) assigned to the relevant motor vehicle axle (4; 8).

10. The method as claimed in claim 5, wherein characterized in that, at the end of the ABS control operation, the brake pressure (p.sub.B_KA) set in the relay valve (70c; 54c) of the motor vehicle axle (4; 8) is lowered again to the standard brake pressure (p.sub.B_KS_Std) provided by the roll stability control function.

11. An electronic control unit (14) for a motor vehicle (2), which control unit carries out the method steps as claimed in claim 1.

12. An electronic control unit (14) for a motor vehicle (2), which control carries out the method steps as claimed in claim 5.

13. The method as claimed in claim 5, wherein the increase in the brake pressure on the wheel brake on the outside of the bend progresses at first rate for a first period of time and, following a determination of a loss of pressure on the wheel brake on the inside of the bend due to the ABS control operation, the increase in the brake pressure progresses at a greater rate relative to the first rate.

14. The method as claimed in claim 1, wherein the increase in the brake pressure on the wheel brake on the outside of the bend progresses at first rate for a first period of time and, following a determination of a loss of pressure on the wheel brake on the inside of the bend due to the ABS control operation, the increase in the brake pressure progresses at a second rate that is a greater rate relative to the first rate.

15. The method as claimed in claim 13, wherein the increase in brake pressure progresses at the second rate until the pressure reaches a level that exceeds a target pressure, determined by the RSC operation, by the same amount as an average loss of pressure, relative to the target pressure, due to the ABS control operation.

16. The method as claimed in claim 14, wherein the increase in brake pressure progresses at the second rate until the pressure reaches an upper level that exceeds a target pressure, determined by the RSC operation, by the same amount as an average loss of pressure, relative to the target pressure, due to the ABS control operation.

17. The method as claimed in claim 15, wherein the brake pressure on the wheel brake on the outside of the bend is held constant at the upper level until the ABS control operation ends, at which time the brake pressure on the wheel brake on the outside of the bend decreases to the target pressure and is then held at the target pressure.

18. The method as claimed in claim 16, wherein the brake pressure on the wheel brake on the outside of the bend is held constant at the upper level until the ABS control operation ends, at which time the brake pressure on the wheel brake on the outside of the bend decreases to the target pressure and the brake pressure on the wheel brake on the inside of the bend increases to the target pressure, each of which are then held at the target pressure.

19. The method as claimed in claim 17, wherein the brake pressure on the wheel brakes on both the inside of the bend and the outside of the bend remain at the target pressure until the RSC operation ends, at which time the brake pressure on the wheel brakes on both the inside and outside of the bend decreases to zero.

20. The method as claimed in claim 18, wherein the brake pressure on the wheel brakes on both the inside of the bend and the outside of the bend remain at the target pressure until the RSC operation ends, at which time the brake pressure on the wheel brakes on both the inside and outside of the bend decreases to zero.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The method according to the present disclosure is explained in greater detail below by way of an exemplary embodiment illustrated in the appended drawings. In the drawings:

[0028] FIG. 1 shows a braking process with an application of the control method according to the present disclosure in a brake pressure-time diagram, and

[0029] FIG. 2 shows a pneumatic brake system of a motor vehicle in a schematic view to illustrate the method according to the present disclosure.

DETAILED DESCRIPTION

[0030] The motor vehicle 2 depicted in FIG. 2, which is shown to be a commercial vehicle, has a single-tire front axle 4 with two wheels 6a, 6b and a double-tire rear axle 8 with a total of four wheels 10a, 10a, 10b, 10b.

[0031] A brake system 12 of the motor vehicle 2 is designed as an electronically controllable compressed air brake system. In addition to an electronic control unit 14, the brake system 12 includes a compressed air supply device 16, a foot brake valve 20 that can be actuated via a brake pedal 18 and has a brake value transmitter 22 embodied as a travel sensor, as well as pressure-medium-actuatable wheel brakes 26a, 26b, 28a, 28b designed as friction brakes. The brake value transmitter 22 of the foot brake valve 20 is connected to the control unit 14 via an electrical sensor line 24. A wheel speed sensor 30a, 30b, 34a, 34b is arranged at each of the wheels 6a, 6b of the front axle 4 and the wheel pairs 10a, 10a; 10b, 10b of the rear axle 8, and each wheel speed sensor is connected to the control unit 14 via an electrical sensor line 32a, 32b, 36a, 36b.

[0032] The compressed air supply device 16 has a compressor 38, a pressure regulator 40, and a multi-circuit protection valve 42. Compressed air is delivered by the compressor 38, which can be driven by a drive motor (not shown), via the pressure regulator 40 and the multi-circuit protection valve 42, into two brake circuits 44, 46 of the brake system 12.

[0033] The first brake circuit 44 has a first pressure accumulator 50 and a first supply line 48, which is routed from the multi-circuit protection valve 42 to the foot brake valve 20 and to a first axle valve module 54 on the rear axle 8. A first axle brake line 52, into which a brake pressure is introduced as a function of the actuation of the brake pedal 18, extends from the foot brake valve 20 to the first axle valve module 54. The first axle valve module 54 includes a first relay valve 54c and in each case one ABS valve assembly 54a, 54b per wheel pair 10a, 10a; 10b, 10b of the rear axle 8. From each of the two ABS valve assemblies 54a, 54b of the first axle valve module 54, a wheel brake line 56a, 56b is routed to the associated wheel brake 28a, 28b of the rear axle 8. The two rear ABS valve assemblies 54a, 54b each comprise an ABS inlet valve and an ABS outlet valve, as well as a pressure sensor (not illustrated). The ABS inlet valves and the ABS outlet valves are each connected to the control unit 14 via an electrical control line 58a, 58b. The pressure sensors are connected pneumatically to the respective wheel brake line 56a, 56b and are each connected to the control unit 14 via an electrical sensor line 60a, 60b.

[0034] The relay valve 54c of the first axle valve module 54 is electronically controlled primarily in accordance with the brake value detected by the brake value transmitter 22 of the foot brake valve 20. For this purpose, the first relay valve 54c is connected via an electrical control line 62 to the electronic control unit 14. In the event of redundancy, i.e. in the event of a failed electronic control system, the relay valve 54c of the first axle valve module 54 is controlled pneumatically in accordance with the brake pressure prevailing in the first axle brake line 52.

[0035] The second brake circuit 46 has a second pressure accumulator 66 and a second supply line 64, which is routed from the multi-circuit protection valve 42 to the foot brake valve 20 and to a second axle valve module 70 on the rear axle 4. A second axle brake line 68, into which a brake pressure is introduced as a function of the actuation of the brake pedal 18, extends from the foot brake valve 20 to the second axle valve module 70. The second axle valve module 70 includes a second relay valve 70c and in each case one ABS valve assembly 70a, 70b per wheel 6a, 6b of the rear axle 4. From each of the two front ABS valve assemblies 70a, 70b of the second axle valve module 70, a wheel brake line 72a, 72b is routed to the associated wheel brake 26a, 26b of the front axle 4. The two front ABS valve assemblies 70a, 70b each comprise an ABS inlet valve and an ABS outlet valve, as well as a pressure sensor (not illustrated). The two front ABS inlet valves and ABS outlet valves are each connected to the control unit 14 via an electrical control line 74a, 74b. The pressure sensors are connected to the respective front wheel brake line 72a, 72b and are each connected to the control unit 14 via an electrical sensor line 76a, 76b.

[0036] The relay valve 70c of the second axle valve module 70 is likewise electronically controlled primarily in accordance with the braking value detected by the braking value transmitter 22 of the foot brake valve 20, and for this purpose is connected via an electrical control line 78 to the electronic control unit 14. In the event of redundancy, the relay valve 70c of the second axle valve module 70 is controlled pneumatically in accordance with the brake pressure prevailing in the second axle brake line 68.

[0037] In an anti-lock function, which is stored as a control program in a program memory of the control unit 14, the travel signal of the brake value transmitter 22, the rotational speed signals of the wheel speed sensors 30a, 30b, 34a, 34b and the pressure signals of the pressure sensors of the ABS valve devices 54a, 54b, 70a, 70b and other information, such as the current driving speed, the current steering angle and the current loading state, are evaluated during a braking process. When an approach of a wheel 6a, 6b or a wheel pair 10a, 10a; 10b, 10b to its slip limit is detected, the brake pressure in the associated wheel brake 26a, 26b, 28a, 28b is regulated in a kind of intermittent braking process by control of the ABS inlet valve and the ABS outlet valve of the respective ABS valve assembly 54a, 54b, 70a, 70b. This prevents wheel slip on the roadway.

[0038] In a roll stability control function, which is likewise stored as a control program in the program memory of the control unit 14, the sensor signal of a tilt sensor 80 and other information, such as the current driving speed, the current steering angle, and the current loading state, are evaluated during cornering. If an approach to a tilt limit is detected, the exceeding of which could lead to the motor vehicle 2 tipping over about the longitudinal axis 84 of the motor vehicle, the motor vehicle 2 is braked by introducing a brake pressure into the wheel brakes 26a, 26b, 28a, 28b by control of the two relay valves 54c, 70c. The tilt sensor 80, which is connected to the control unit 14 via a sensor line 82, can be a transverse acceleration sensor or a roll angle sensor.

[0039] In the following, the brake pressure curves in the diagram of FIG. 1 will be used to explain how the motor vehicle 2 is braked during cornering according to the method according to the present disclosure in the roll stability control function when an ABS control operation is performed on the brake pressure by the anti-lock function on account of the dynamic shift in the wheel loads at the wheel brake on the inside of the bend on a motor vehicle axle.

[0040] In the diagram of FIG. 1, the theoretical curve of the pneumatic brake pressure p.sub.B_KS of both wheel brakes on a motor vehicle axle in the absence of ABS control is shown in dashed lines. The partially deviating curve of the pneumatic brake pressure p.sub.B_KI of the wheel brake on the inside of the bend is represented by a dash-dot line, and the likewise partially deviating curve of the pneumatic brake pressure p.sub.B_KA of the wheel brake on the outside of the bend is represented by a double-dot-dash line.

[0041] Assuming a left-hand bend currently being traversed and considering the brake pressures in the wheel brakes 26a, 26b at the front axle of the motor vehicle 2, an approach to the tilt limit of the vehicle 2 is observed when the roll stability control function is applied at time to. This leads to the introduction of a brake pressure p.sub.B_KS into the wheel brakes 26a, 26b on the front axle 4 via the second relay valve 70c. In order for the motor vehicle 2 to be braked sufficiently to prevent it from tipping over sideways, the brake pressure p.sub.B_KS should be set to a standard brake pressure p.sub.B_KS_Std provided and then initially remain constant.

[0042] However, before the standard brake pressure p.sub.B_KS_Std is reached, the anti-lock function detects an approach to or exceeding of the wheel slip limit at the front wheel 6b on the inside of the bend at time t1, leading to the start of ABS control of the brake pressure p.sub.B_KI of the wheel brake 26b on the inside of the bend between the upper control pressure p.sub.B_R-o and the lower control pressure p.sub.B_R-u. At time t1, the brake pressure p.sub.B_KA of the wheel brake 26a on the outside of the bend reaches the standard brake pressure p.sub.B_KS_Std provided per se and is then increased further, initially with a relatively low pressure gradient, by corresponding control of the second relay valve 70c. At time t2, the mean brake pressure p.sub.B_R-m of the ABS control operation and its pressure difference ?p.sub.B_KI from the standard brake pressure p.sub.B_KS_Std provided per se have been determined from the first control cycles of the ABS control of the brake pressure p.sub.B_KI of the wheel brake 26b on the inside of the bend. The mean brake pressure p.sub.B_R-m is preferably determined as the arithmetic mean of the upper brake pressure p.sub.B_R-o and the lower brake pressure p.sub.B_R-u during the ABS control operation (p.sub.B_R-m=(p.sub.B_R-o+p.sub.B_R-u)/2).

[0043] In order to compensate for the loss of braking force of the wheel brake 26b on the inside of the bend caused by the current ABS control operation in comparison with the wheel brake 26a on the outside of the bend, it is provided that the brake pressure p.sub.B_KA of the wheel brake 26a on the outside of the bend is increased to a maximum brake pressure p.sub.B_KA_max, which is above the standard brake pressure p.sub.B_KS_Std provided per se by the same pressure difference ?p.sub.B_KA=?p.sub.B_KI (p.sub.B_KA_max=p.sub.B_KS_Std+?p.sub.B_KA). Therefore, the brake pressure p.sub.B_KA of the wheel brake 26a on the outside of the bend is increased further with a high pressure gradient from time t2 and reaches the intended target pressure p.sub.B_KA_max at time t2.

[0044] Owing to the driving speed at time t3, which has been reduced in the meantime, the certain undershooting of the slip limit of the wheel 6b on the inside of the bend is detected by the anti-lock function, and therefore the ABS control of the brake pressure p.sub.B_KI of the wheel brake 26b on the inside of the bend is then terminated. At the same time, the roll stability control function lowers the brake pressure p.sub.B_KA_max introduced via the second relay valve 70c to the standard brake pressure p.sub.B_KS_Std provided in the absence of ABS control, which is reached approximately at time t3 in both wheel brakes 26a, 26b on the front axle 4. After this, there is no longer any danger of tipping over at time t4 thanks to the further fall in the driving speed of the motor vehicle 2, and therefore the brake pressure p.sub.B_KS is then reduced to the value zero via the second relay valve 70c by time t4, and thus the braking process for preventing the vehicle from tipping over sideways is terminated.

[0045] If a motor vehicle 2 is braked by a roll stability control function during cornering, and, at the same time, during ABS control of the brake pressure p.sub.B_KI of a wheel brake 26b on the inside of the bend on at least one motor vehicle axle 4, the brake pressure p.sub.B_KA of the wheel brake 26a on the outside of the bend on the same or a different motor vehicle axle 4 is increased by a pressure difference ?p.sub.B_KA, which largely corresponds to the pressure loss ?p.sub.B_KI of the wheel brake 26b on the inside of the bend due to the ABS control operation, the braking of the motor vehicle 2 takes place with approximately the same braking force as in the absence of active ABS control, thus making it possible to reliably prevent the motor vehicle 2 from tipping over sideways.

[0046] It will be appreciated that the above description describes an embodiment of the novel aspects of the present disclosure, and that various modifications to the illustrated embodiment are similarly envisaged, including different combinations of various features described above.

LIST OF REFERENCE SIGNS (PART OF THE DESCRIPTION)

[0047] 2 motor vehicle, commercial vehicle [0048] 4 motor vehicle axle, front axle [0049] 6a, 6b wheels on the front axle [0050] 8 motor vehicle axle, rear axle [0051] 10a, 10a wheels on the rear axle [0052] 10b, 10b wheels on the rear axle [0053] 12 brake system, compressed air brake system [0054] 14 electronic control unit [0055] 16 compressed air supply device [0056] 18 brake pedal [0057] 20 foot brake valve [0058] 22 brake value transmitter, travel sensor [0059] 24 sensor line [0060] 26a, 26b wheel brakes, friction brakes on the front axle [0061] 28a, 28b wheel brakes, friction brakes on the rear axle [0062] 30a, 30b wheel speed sensors on the front axle [0063] 32a, 32b sensor lines [0064] 34a, 34b wheel speed sensors on the rear axle [0065] 36a, 36b sensor lines [0066] 38 compressor [0067] 40 pressure regulator [0068] 42 multi-circuit protection valve [0069] 44 first brake circuit [0070] 46 second brake circuit [0071] 48 first supply line [0072] 50 first pressure accumulator [0073] 52 first axle brake line [0074] 54 first axle valve module [0075] 54a, 54b ABS valve assemblies [0076] 54c first relay valve [0077] 56a, 56b wheel brake lines on the rear axle [0078] 58a, 58b control lines [0079] 60a, 60b sensor lines [0080] 62 control line [0081] 64 second supply line [0082] 66 second pressure accumulator [0083] 68 second axle brake line [0084] 70 second axle valve module [0085] 70a, 70b ABS valve assemblies [0086] 70c second relay valve [0087] 72a, 72b wheel brake lines on the front axle [0088] 74a, 74b control lines [0089] 76a, 76b sensor lines [0090] 78 control line [0091] 80 tilt sensor, transverse acceleration sensor, roll angle sensor [0092] 82 sensor line [0093] 84 motor vehicle longitudinal axis [0094] ABS anti-lock brake system [0095] p.sub.B brake pressure; braking force [0096] p.sub.B_KA brake pressure (braking force) at the wheel brake on the outside of the bend [0097] p.sub.B_KA_max maximum brake pressure (braking force) at the wheel brake on the outside of the bend [0098] p.sub.B_KI brake pressure (braking force) at the wheel brake on the inside of the bend [0099] p.sub.B_KS brake pressure (braking force) of the roll stability control function [0100] p.sub.B_KS_Std standard brake pressure (standard braking force) of the roll stability control function [0101] p.sub.B_R-m mean brake pressure (braking force) of the ABS control operation [0102] p.sub.B_R-o upper brake pressure (braking force) of the ABS control operation [0103] p.sub.B_R-u lower brake pressure (braking force) of the ABS control operation [0104] RSC Roll Stability Control [0105] t time [0106] t0 time [0107] t1, t1 times [0108] t2, t2 times [0109] t3, t3 times [0110] t4, t4 times