Method for controlling a braking system and motor vehicle braking system

Abstract

The present invention relates to a method for controlling a braking system (1) comprising a linear actuator (5) and a hydraulic pump (26). For fast pressure build-up, the linear actuator (5) and the hydraulic pump (26) are switched to synchronous operation when the rate of change of the braking demand signal is greater than a threshold. The present invention also relates to a braking system (1) for a motor vehicle.

Description

Technical Field

[0001] The present invention relates to a method for controlling a braking system having a linear actuator and a hydraulic pump.

Background Art

[0002] Today, the latest braking systems operate according to the brake-by-wire method. That is, the driver is no longer directly mechanically connected to the individual wheel brakes via the brake pedal in the normal driving mode. Instead, the driver's braking demand is detected by a sensor system, and generally an electric pressure application device is operated to increase the brake pressure in the wheel brakes in response to the driver's braking demand. The pressure application device used in this case has to meet many requirements in this case. In this case, hitherto, when the braking demand increases extremely rapidly, it has not been possible to provide, at an acceptable cost, a braking system that can increase the brake pressure as quickly as a conventional braking system having a direct mechanical connection between the driver and the wheel brakes. At high speeds, even a slight delay in pressure increase results in a significant extension of the braking distance, so a vehicle having such a braking system has a major drawback with respect to the braking distance compared to a vehicle having a conventional braking system.

Summary of the Invention

Problems to be Solved by the Invention

[0003] Accordingly, an object of the present invention is to provide a method for controlling a braking system that avoids these drawbacks.

Means for Solving the Problems

[0004] This object is achieved by the method according to claim 1, in which the braking demand signal is monitored and, if the rate of change of the braking demand signal is greater than a threshold value, the linear actuator and the hydraulic pump are switched to synchronous operation. In synchronous operation, the linear actuator and the hydraulic pump are operated simultaneously in order to increase the brake pressure in the wheel brakes and convey the hydraulic volume to at least one wheel brake. Thus, the linear actuator and the hydraulic pump deliver simultaneously to a common wheel brake. By means of the method according to the invention, the system directly determines from the braking demand signal whether both pressure sources are required to carry out the demand. Thus, the required brake pressure can be achieved particularly quickly, thereby making it possible to efficiently shorten the braking distance of the motor vehicle.

[0005] In a preferred embodiment of the invention, the braking demand signal is generated by a brake sensor or a driving assistance system. A brake pedal movement sensor and / or a pressure sensor are particularly suitable as the brake sensor. In this case, the master cylinder pressure or the system pressure can be measured and used directly. As an alternative, the brake pedal is of a dry design, i.e. there is no connection to hydraulic equipment. In this case, a corresponding brake pedal sensor can be used. Possible driving assistance systems are, in particular, an inter-vehicle control system and / or an emergency braking assistance system which generate the braking demand signal directly and independently from the driver.

[0006] In a further preferred embodiment of the invention, the hydraulic pump and the linear actuator are connected in series, in particular by opening a hydraulic valve between the suction side of the hydraulic pump and the outlet of the linear actuator. Here, the hydraulic pressure generated by the linear actuator is further enhanced by the hydraulic pump, thereby ensuring that a higher brake pressure is achieved more quickly in the wheel brakes.

[0007] In a further preferred embodiment of the present invention, the hydraulic pump and the linear actuator are connected in parallel, and the suction side of the hydraulic pump is connected to the hydraulic reservoir. Accordingly, the hydraulic pump and the linear actuator convey volume to the wheel brake substantially independently of each other. The volumes of the hydraulic pump and the linear actuator are hereby added to the total volume conveyed to the wheel brake. Accordingly, the volume required in the wheel brake is achieved particularly quickly. It is also possible to switch between two modes. Accordingly, the piston of the wheel brake still has to move a distance, and since the two pressure application devices can be connected in parallel therewith, a large volume is required at the start of braking. As soon as contact is made between the brake pad and the brake disc, the large hydraulic volume is no longer required. The two pressure application devices can then be connected in series.

[0008] In a further preferred embodiment of the present invention, the linear actuator is controlled by a first control unit and the hydraulic pump is controlled by a second control unit. In this case, the first control unit and the second control unit communicate with each other via a communication interface. This provides additional redundancy in that at least one of the pressure application devices still continues to function to brake the vehicle to a stop in the event of a failure of one of the control units.

[0009] In a particularly preferred embodiment of the present invention, the first control unit evaluates a braking demand signal and, if the detected rate of change of the braking demand signal is greater than a threshold value, transmits a command to the second control unit to operate the hydraulic pump. Accordingly, since the control logic remains with the second control unit, there is no need to provide an additional connection between the hydraulic pump and the first control unit.

[0010] In an even more particularly preferred embodiment of the present invention, the brake sensor is a hydraulic sensor read by a second control unit. This can be a system pressure sensor or a wheel brake pressure sensor. Thus, the second control unit responsible for controlling the hydraulic pump can automatically detect whether the hydraulic pump is required.

[0011] In a particularly preferred embodiment of the present invention, the second control unit evaluates the braking request signal in order to activate the hydraulic pump if the detected rate of change of the braking request signal is greater than a threshold value.

[0012] In a particularly preferred embodiment of the present invention, the second control unit evaluates a first braking request signal. This can in particular be the signal of a sensor directly monitored by the second control unit. If the detected rate of change of the first braking request signal is greater than a first threshold value, the second control unit activates the hydraulic pump with a first power. At the same time, the first control unit evaluates a second braking request signal and, if the detected rate of change of the second braking request signal is greater than a second threshold value, sends a command to the second control unit to activate the hydraulic pump. In particular, this can be the signal of a sensor directly connected to the first control unit. When the command is received, the second control unit then adjusts the hydraulic pump to a second power greater than the first power. Thus, the pump is started directly without delay but is set to the full required power only if the actual command is received from the first control unit.

[0013] In a particularly preferred embodiment of the present invention, the transition from synchronous operation to individual operation as described above for the hydraulic pump takes place when the linear actuator reaches its nip point, when the ABS control operation is triggered, or when a predetermined lock pressure is reached. The nip point of the linear actuator is reached when the piston of the linear actuator has moved completely forward and thus has to move backward again for further volume delivery and in doing so draws brake fluid from the brake fluid reservoir. As soon as a lock of a plurality of wheels or at least one wheel is detected, it is also possible to switch to the individual operation of the hydraulic pump, since the pressure at both ends of the hydraulic pump can be set particularly precisely by means of the associated overflow valve. In a particularly simple control device, a predetermined pressure value, i.e. the lock pressure, is stored in the vehicle's brake system. As soon as the system pressure reaches this pressure, the switch to the individual operation of the hydraulic pump takes place in the same way.

[0014] In a further preferred embodiment of the present invention, the hydraulic valve is arranged in parallel with the hydraulic pump and in series between the linear actuator and the wheel brake and is opened and closed in synchronous operation. When the valve is open, the linear actuator can convey volume to the wheel brake, on the one hand via this valve and on the other hand via the hydraulic pump.

[0015] In a further preferred embodiment of the present invention, the brake system comprises two sub-circuits, two wheel brakes and the hydraulic pump are assigned to each sub-circuit, and in synchronous operation both pumps operate and the linear actuator is connected to only one or both sub-circuits.

[0016] The object is further achieved by an automotive brake system having a linear actuator and a hydraulic pump, the brake system being designed to carry out the method described above.

[0017] Further features, advantages, and possible applications of the present invention can also be obtained from the following description of exemplary embodiments and the drawings. All features described and / or illustrated, individually or in any combination, belong to the subject matter of the present invention, independent of the claims or their summary in the citation thereof.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0019] Figure 1 shows a hydraulic brake system 1 that can execute the method according to the present invention. The brake system 1 has the type of extended redundancy required for autonomous driving, which is achieved in particular by two independent pressure application devices. In the normal operation mode, the brake system 1 operates according to the by-wire braking method. In this case, the braking force is applied by the driver to a brake master cylinder 3 designed as a tandem-type brake master cylinder 3 having two chambers. As a result, the hydraulic volume is displaced into the simulator 4 via the opened simulator valve 10, thereby generating a pedal feeling. In the illustrated embodiment, only one chamber of the tandem-type brake master cylinder 3 is connected to the simulator 4, while the second chamber only applies pressure to the closed first shut-off valve 21. The first shut-off valve 21 separates the tandem-type brake master cylinder 3 from and connects it to the first sub-circuit of the brake system 1 comprising wheel brakes 7, 8 of the left rear wheel and the right front wheel each having an inlet valve 14 and an outlet valve 15. The second shut-off valve 22 connects the tandem-type brake master cylinder 3 to the second sub-circuit of the brake system 1. The second sub-circuit of the brake system 1 comprises wheel brakes 6, 9 of the right rear wheel and the left front wheel each having an inlet valve 14 and an outlet valve 15. The second shut-off valve 22 is also closed in the normal operation mode. In the illustrated embodiment, the first and second sub-circuits have a substantially symmetrical structure. It is also possible to divide the wheel brakes 6, 7, 8, 9 differently between the first sub-circuit and the second sub-circuit, for example, to place both front wheel brakes in the first sub-circuit and the rear wheel brakes in the second sub-circuit.

[0020] Furthermore, the braking system 1 is provided with a linear actuator 5, which is connected to the first sub-circuit via the first supply valve 19 and to the second sub-circuit via the second supply valve 20. The first supply valve 19 connects and then separates the first sub-circuit from the linear actuator 5, and the second supply valve 20 connects and then separates the second sub-circuit from the linear actuator 5. Due to the symmetrical structure, for the purposes of the present invention, the second sub-circuit can also be regarded as the first sub-circuit, and the first sub-circuit can also be regarded as the second sub-circuit. In the normal operating mode, the first supply valve 19 and the second supply valve 20 are open, and thus the linear actuator 5 can convey the brake fluid to all the wheel brakes 6, 7, 8, 9. The brake fluid here flows from the linear actuator 5 through the open switching valves 25 of the respective sub-circuits and the inlet valves 14 of the respective wheel brakes 6, 7, 8, 9 into the wheel brakes 6, 7, 8, 9. The pump isolation valves 24 of the two sub-circuits are closed in the normal operating mode. Thus, the braking force is generated by the linear actuator 5.

[0021] To reduce the pressure in the wheel brakes 6, 7, 8, 9, for example in the case of ABS control, the outlet valves 15 of the individual wheel brakes 6, 7, 8, 9 can be opened. The brake fluid then flows through the respective outlet valves 15 into the low-pressure accumulators 27 of the respective sub-circuits.

[0022] Each of the two sub-circuits has a hydraulic pump 26 which is connected to the switching valve 25, the pump isolation valve 24 and the low-pressure accumulator 27 in each case. At the fallback level, for example in the event of a failure of the linear actuator, the shut-off valves 21, 22 are open, the switching valve 25 is closed and the pump isolation valve 24 is open. When the brake pedal is operated, the hydraulic pump 26 is activated, and as a result the pump pumps the brake fluid to the wheel brakes 6, 7, 8, 9. The hydraulic pump 26 thus increases the braking pressure exerted by the driver via the tandem brake master cylinder 3.

[0023] The first sub-circuit and the second sub-circuit are thus configured substantially in parallel. The system pressure within the first sub-circuit can be identified by a pressure measuring device 16 designated as system pressure sensor 16. Further, in order to identify the brake pressure exerted by the driver, a further pressure measuring device 17 is arranged in the tandem type brake master cylinder 3, and this sensor is designated as master cylinder pressure sensor 17. The connection of the second sub-circuit to the reservoir 2 can be established by a feeder valve 23. This valve can be opened especially when reducing or increasing the brake fluid volume within the brake circuit.

[0024] In normal operation, the pedal movement sensor and the master cylinder pressure sensor 17 are monitored by the control unit, and a braking demand signal is generated based on the sensor signals. The control unit then controls the linear actuator 5 based on the braking demand signal to generate a braking pressure.

[0025] Here, when it is identified that the rate of change of the braking demand signal, i.e., the time derivative, exceeds a threshold value, a synchronous operation is started in which both the linear actuator 5 and the hydraulic pump 26 are operated to jointly convey the brake fluid to at least one of the wheel brakes 6, 7, 8, 9. The brake system is here continued to be operated in the brake-by-wire mode, i.e., the shut-off valves 21, 22 remain closed, and the brake fluid continues to be displaced only into the simulator 4 by the brake master cylinder 3. The switching valve 25 is closed and the pump isolation valve 24 is opened, so that the hydraulic pump 26 is connected in series downstream of the linear actuator. The hydraulic pressure increased by the linear actuator is thus further increased by the hydraulic pump 26. A large braking pressure is thus rapidly applied to the wheel brakes 6, 7, 8, 9. Thus, when the pedal is depressed quickly, the required braking force can be rapidly increased, and thus the braking distance can be significantly shortened.

[0026] Alternatively, the hydraulic pump can be connected in parallel with the linear actuator. For this purpose, the switching valve 25 is opened and the pump isolation valve 24 is closed. The hydraulic pump 26 then sucks fluid from the low-pressure accumulator 27 and pumps this volume to the respective wheel brakes 6, 7, 8, 9, while the linear actuator conveys the volume to the wheel brakes 6, 7, 8, 9 simultaneously through the open switching valve.

[0027] The linear actuator 5 is here controlled by the control unit ECU2, and the hydraulic pump 26 is controlled by the control unit ECU 1. The control unit ECU 1 also receives data from a system pressure sensor 16 directly connected to this control unit ECU 1. In this case, the control unit ECU 1 monitors the system pressure by means of the system pressure sensor 16 and, if the rate of change is greater than the relevant system pressure change threshold, opens the pump isolation valve and actuates the hydraulic pump 26 with a first power or duty cycle. At the same time, the control unit ECU2 monitors the master cylinder pressure by means of the master cylinder pressure sensor 17 and, if a rate of change greater than the relevant master cylinder pressure change threshold is detected, transmits a pump actuation signal to the control unit ECU 1 via the CAN interface. As soon as the control unit ECU 1 receives the pump actuation signal, it switches the hydraulic pump 26 to a second, higher pump power or duty cycle. Thus, although the actual control of the synchronous operation is adjusted in the control unit ECU 2, it is possible to bridge the signal transit time by the anticipatory control of the hydraulic pump 26 by the control unit ECU 1.

[0028] Here, a second embodiment of the braking system is shown in FIG. 2. The braking system of FIG. 2 has a brake master cylinder 3 embodied in only a single chamber. In normal operation, this is connected to the simulator 4 via an open simulator valve 10. The shut-off valve 21 is closed during normal operation, and thus the brake master cylinder does not have an open flow connection to the wheel brakes 6, 7, 8, 9. The linear actuator 5 is connected to the wheel brakes 8, 9 via a supply valve 19 that is opened during normal operation and an inlet valve 14 that is likewise opened. Furthermore, the linear actuator 5 has a connection to the wheel brakes 6, 7 of the front axle via a circuit breaker valve 28 and the corresponding inlet valve 14. The connection is made via a further brake unit having a switching valve 25 that is opened during normal operation. For reasons of redundancy, the further brake unit comprises a further pressure application device embodied as a hydraulic pump 26. The hydraulic pump 26 is connected on the suction side to a low-pressure accumulator 27 that in turn has a connection to the brake fluid reservoir 2 via a normally closed pump isolation valve 24. The low-pressure accumulator 27 is further connected to the wheel brakes 6, 7 by a further valve.

[0029] In this embodiment, the linear actuator 5 and the hydraulic pump 26 are connected in parallel and operate simultaneously in a synchronous operation according to the invention. For this purpose, the switching valve 25 remains open, with the result that the linear actuator 5 has an open flow connection to the wheel brakes 6, 7. Furthermore, the pump isolation valve 24 is opened, with the result that the hydraulic pump 26 can suck in brake fluid from the low-pressure accumulator 27 and, via it, from the brake fluid reservoir 2. Thus, the linear actuator 5 and the hydraulic pump each convey their own volume, which together is the total volume conveyed to the wheel brakes 6, 7.

[0030] The control of the hydraulic pump 26 and the linear actuator 5 can be effected by two separate control units, as explained above with respect to the first embodiment. The present invention may also include the following aspects: 1. A method for controlling a braking system (1) having a linear actuator (5) and a hydraulic pump (26), wherein a braking demand signal is monitored, and when a rate of change of the braking demand signal is greater than a threshold value, the linear actuator (5) and the hydraulic pump (26) are switched to a synchronous operation, and in the synchronous operation, the linear actuator (5) and the hydraulic pump (26) are simultaneously operated to increase a braking pressure in wheel brakes (6, 7, 8, 9) and convey a hydraulic volume to at least one of the wheel brakes (6, 7, 8, 9). 2. The method according to 1. above, characterized in that the braking demand signal is generated by a brake sensor (17) or a driving assistance system. 3. The method according to 1. or 2. above, characterized in that the hydraulic pump (26) and the linear actuator (5) are connected in series, in particular by opening a hydraulic valve (24) between a suction side of the hydraulic pump (26) and an outlet of the linear actuator (5). 4. The method according to any one of 1. to 3. above, characterized in that the hydraulic pump (26) and the linear actuator (5) are connected in parallel, and the suction side of the hydraulic pump (26) is connected to a hydraulic reservoir (2, 27). 5. The method according to any one of 1. to 4. above, characterized in that the linear actuator (5) is controlled by a first control unit, the hydraulic pump (26) is controlled by a second control unit, and the first control unit and the second control unit communicate with each other via a communication interface. 6. The method according to any one of 1. to 5. above, characterized in that the first control unit evaluates the braking demand signal, and when a detected rate of change of the braking demand signal is greater than the threshold value, transmits a command for operating the hydraulic pump (26) to the second control unit. 7. The method according to 2. above, characterized in that the brake sensor is a hydraulic sensor (16) read by the second control unit. 8. The method according to any one of 1. to 7. above, characterized in that the second control unit evaluates the braking request signal and activates the hydraulic pump (26) when the detected rate of change of the braking request signal is greater than the threshold value. 9. The second control unit evaluates a first braking request signal and, when the detected rate of change of the first braking request signal is greater than a first threshold value, activates the hydraulic pump (26) with a first power. The first control unit evaluates a second braking request signal and, when the detected rate of change of the second braking request signal is greater than a second threshold value, transmits a command to the second control unit to activate the hydraulic pump (26). The second control unit, when the command is received, activates the hydraulic pump (26) with a second power greater than the first power. The method according to any one of 1. to 8. above. 10. The method according to any one of 1. to 9. above, characterized in that the transition from the synchronous operation to the individual operation of the hydraulic pump (26) is executed when the linear actuator (5) reaches its near point, when the ABS control operation is triggered, or when a predetermined lock pressure is reached. 11. The hydraulic valve (25) is arranged in parallel with the hydraulic pump (26) and in series between the linear actuator (5) and the wheel brakes (6, 7, 8, 9). The hydraulic valve (25) is opened and closed in the synchronous operation. The method according to any one of 1. to 10. above. 12. The braking system (1) comprises two sub-circuits. Two wheel brakes (6, 7, 8, 9) and the hydraulic pump (26) are assigned to each sub-circuit. In the synchronous operation, both pumps (26) are activated, and the linear actuator (5) is connected to only one of the sub-circuits or both sub-circuits. The method according to any one of 1. to 11. above. 13. A braking system for an automobile having a linear actuator (5) and a hydraulic pump (26), characterized in that it is designed to execute the method according to any one of 1. to 12. above.

Explanation of Symbols

[0031] 1 Brake system 2 Brake fluid reservoir 3 Brake master cylinder 4 Simulator 5 Linear actuator 6 Wheel brake 7 Wheel brake 8 Wheel brake 9 Wheel brake 10 Simulator valve 14 Inlet valve 15 Outlet valve 16 System pressure sensor 17 Brake master cylinder pressure sensor 19 First supply valve 20 Second supply valve 21 First shut-off valve 22 Second shut-off valve 23 Feeder valve 24 Pump isolation valve 25 Changeover valve 26 Hydraulic pump 27 Low-pressure accumulator 28 Circuit isolation valve

Claims

1. A method for controlling a braking system (1) having a linear actuator (5) and a hydraulic pump (26), comprising: monitoring a braking demand signal; and when a rate of change of the braking demand signal is greater than a threshold value, switching the linear actuator (5) and the hydraulic pump (26) to synchronous operation, wherein in the synchronous operation, the linear actuator (5) and the hydraulic pump (26) are operated simultaneously to increase a braking pressure in wheel brakes (6, 7, 8, 9) and to convey a hydraulic volume to at least one of the wheel brakes (6, 7, 8, 9); the hydraulic pump (26) and the linear actuator (5) are connected in parallel; a suction side of the hydraulic pump (26) is connected to a hydraulic reservoir (2, 27); and a hydraulic valve (25) is arranged in parallel with the hydraulic pump (26) and in series between the linear actuator (5) and the wheel brakes (6, 7, 8, 9), and the hydraulic valve (25) is opened and closed in the synchronous operation.

2. The method according to claim 1, wherein the braking demand signal is generated by a brake sensor (17) or a driving assistance system.

3. The method according to claim 1 or 2, wherein the linear actuator (5) is controlled by a first control unit, the hydraulic pump (26) is controlled by a second control unit, and the first control unit and the second control unit communicate with each other via a communication interface.

4. The method according to claim 3, wherein the first control unit evaluates the braking demand signal and, when a detected rate of change of the braking demand signal is greater than the threshold value, transmits a command for operating the hydraulic pump (26) to the second control unit.

5. The method according to claim 2, wherein the brake sensor is a hydraulic sensor (17) read by a first control unit that controls the linear actuator (5).

6. The method according to claim 3 or 4, wherein the first control unit evaluates the braking demand signal and, when a detected rate of change of the braking demand signal is greater than the threshold value, the second control unit operates the hydraulic pump (26).

7. The second control unit evaluates a first braking request signal, and if a detected rate of change of the first braking request signal is greater than a first threshold value, operates the hydraulic pump (26) with a first power. The first control unit evaluates a second braking request signal, and if a detected rate of change of the second braking request signal is greater than a second threshold value, transmits a command for operating the hydraulic pump (26) to the second control unit. The second control unit, when the command is received, operates the hydraulic pump (26) with a second power greater than the first power. The method according to claim 3, 4 or 6, characterized in that.

8. The transition from the synchronous operation to the individual operation of the hydraulic pump (26) is carried out when the linear actuator (5) reaches its nip point, when the ABS control operation is triggered, or when a predetermined lock pressure is reached. The method according to any one of claims 1 to 7, characterized in that.

9. The brake system (1) comprises two sub-circuits, and two wheel brakes (6, 7, 8, 9) and a hydraulic pump (26) are assigned to each sub-circuit. In the synchronous operation, both pumps (26) operate, and the linear actuator (5) is connected to only one sub-circuit or both sub-circuits. The method according to any one of claims 1 to 8, characterized in that.

10. A brake system for an automobile having a linear actuator (5) and a hydraulic pump (26), characterized in that it is designed to execute the method according to any one of claims 1 to 9.

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