BRAKING SYSTEM WITH TWO PRESSURE SOURCES, AND METHOD FOR OPERATING A BRAKING SYSTEM WITH TWO PRESSURE SOURCES

Abstract

A braking system including four hydraulically actuatable wheel brakes. A normally closed outlet valve is assigned to each wheel brake and a normally open inlet valve is assigned to each wheel brake. Two pressure supply devices are provided for active pressure build-up in the wheel brakes. A first and a second brake circuit are hydraulically configured with two wheel brakes respectively, wherein in each brake circuit a respective pressure supply device is hydraulically connected to two wheel brakes. A first and a second control and regulating unit are provided, wherein the first control and regulating unit electrically controls the pressure supply device of the first brake circuit, and wherein the second control and regulating unit hydraulically controls the pressure supply device of the second brake circuit, and the two control and regulating units are connected together via a data interface.

Claims

1. A braking system comprising four hydraulically actuatable wheel brakes, wherein a normally closed outlet valve is assigned to each wheel brake and a normally open inlet valve is assigned to each wheel brake, wherein two pressure supply devices are provided for active pressure build-up in the wheel brakes, wherein a first and a second brake circuit are hydraulically configured with two wheel brakes respectively, wherein in each brake circuit a respective pressure supply device is hydraulically connected to two wheel brakes, wherein a first and a second control and regulating unit are provided, wherein the first control and regulating unit electrically controls the pressure supply device of the first brake circuit, and wherein the second control and regulating unit electrically controls the pressure supply device of the second brake circuit, and wherein the two control and regulating units are connected together via a data interface.

2. The braking system as claimed in claim 1, wherein the two brake circuits are connected in hydraulically isolatable fashion to two normally closed circuit switch-on valves, of which a first circuit switch-on valve can be controlled by the first control and regulating unit, and wherein a second circuit switch-on valve can be controlled by the second control and regulating unit.

3. The braking system as claimed in claim 2, wherein at least one outlet valve in the second brake circuit can be controlled by the first control and regulating unit, and wherein at least one outlet valve in the first brake circuit can be controlled by the second control and regulating unit.

4. The braking system as claimed in claim 3, wherein precisely one outlet valve in the second brake circuit can be controlled by the first control and regulating unit, and wherein precisely one outlet valve in the first brake circuit can be controlled by the second control and regulating unit.

5. The braking system as claimed in claim 1, wherein a pedal feel simulator is provided.

6. The braking system as claimed in claim 5, wherein the pedal feel simulator can be actuated by a brake pedal.

7. The braking system as claimed in claim 6, wherein the brake pedal is coupled by a coupling rod to an axially movable simulator piston, and wherein two redundantly designed travel sensors are provided which measure the piston travel and/or pedal travel respectively.

8. The braking system as claimed in claim 7, wherein a first of the two travel sensors is connected to the first control and regulating unit on the signal input side, and wherein a second of the two travel sensors is connected to the second control and regulating unit on the signal input side.

9. The braking system as claimed in claim 1, wherein the two pressure supply devices are configured as linear actuators.

10. The braking system as claimed in claim 1, wherein one pressure supply device is configured as a linear actuator, and wherein the other pressure supply device is formed as a pump.

11. The braking system as claimed in claim 1, wherein two separate on-board networks are provided, and wherein each pressure supply device is powered by a respective one of the two on-board networks.

12. The braking system as claimed in claim 1, wherein the wheel brakes are hydraulically divided between the two brake circuits by axle.

13. The braking system as claimed in claim 1, wherein a master brake cylinder is connected to the wheel brakes in hydraulically isolatable fashion.

14. A method for operating a braking system as claimed in claim 3, wherein on electrical failure of one brake circuit, in said failed brake circuit the pressure is controlled by actuation of a circuit connecting valve and an outlet valve by the control and regulating unit in the intact brake circuit, and wherein the pressure in the electrically intact brake circuit is controlled by two inlet valves and one outlet valve.

15. The method as claimed in claim 14, wherein to build up pressure in the failed brake circuit, a pre-pressure is built up by the intact pressure supply unit in the intact brake circuit, wherein a circuit connecting valve is opened so that brake fluid flows into the failed brake circuit.

16. The method as claimed in claim 14, wherein to dissipate pressure in the failed brake circuit, an outlet valve in the failed brake circuit is opened by the intact control and regulating unit.

17. The method as claimed in claim 14, wherein to build up pressure in the intact brake circuit, brake fluid from the pressure chamber of the pressure supply device is conducted through at least one inlet valve into a wheel brake.

18. The method as claimed in claim 14, wherein to dissipate pressure in the intact brake circuit, an outlet valve is actuated by the control and regulating unit of the intact brake circuit, and wherein the inlet valve is opened of the wheel brake, to which the intact outlet valve is assigned.

19. The method as claimed in claim 18, wherein in addition, the inlet valve of the wheel brake is opened which is assigned to the wheel brake with the failed outlet valve.

20. The method as claimed in claim 18, wherein the pressure supply device is configured as a linear actuator and wherein the actuator piston position is maintained during pressure dissipation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] One exemplary embodiment of the invention will be described in greater detail with reference to a drawing, in which, in a highly schematic view:

[0045] FIG. 1 shows a braking system with two pressure sources in a first preferred embodiment;

[0046] FIG. 2 shows a braking system with two pressure sources in a second preferred embodiment;

[0047] FIG. 3 shows a braking system with two pressure sources in a third preferred embodiment; and

[0048] FIG. 4 shows a braking system with two pressure sources in a fourth preferred embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0049] In all of the figures, identical parts are denoted by the same reference designations.

[0050] A braking system 2 shown in FIG. 1 comprises four hydraulically actuatable wheel brakes 4, 6, 8, 10, a pedal feel simulator or simulator 12, two pressure supply devices 14, 16, two electronic control and regulating units 18, 20, a pressure medium reservoir 22 (not shown) under atmospheric pressure.

[0051] The simulator 12 comprises a cylinder 22 in which an elastic simulator element 24 is arranged. A brake pedal 26 is connected to a simulator piston 32 via a piston rod 28, such that actuation of the brake pedal 26 from the rest position presses the simulator piston 32 against a simulator element 24, whereby the driver feels a counter-force. A pedal feel is advantageously simulated in this way. The simulator 12 is of dry design, i.e. it comprises no pressure chamber filled with pressure medium.

[0052] Two preferably redundantly designed travel sensors 40, 42 measure the piston travel of the piston 32 or the actuation travel of the brake pedal 26 respectively. One of the two travel sensors 40 is connected to a control and regulating unit 18 on the signal input side. The other travel sensor 42 is connected to the other control and regulating unit 20 on the signal input side. This ensures that on failure of one of the two sensors 40, 42, or one of the two control and regulating units 18, 20, the driver's braking intention can still be determined.

[0053] Both pressure supply devices 14, 16 are electrically actuatable and configured as linear actuators. For this purpose, the two pressure supply devices 14, 16 each have an electric motor 60, the rotational movement of which is converted by means of a schematically indicated rotation-translation mechanism 62 into a translational movement of a pressure piston 64, which, for the active build-up of pressure in the wheel brakes 4-10, is displaced into a hydraulic pressure chamber 68. The pressure chambers 68 are connected via a respective intake line 72 via a reservoir port 74 to the pressure medium reservoir 22, wherein, in each case between the pressure chamber 68 and the intake line 72, a check valve 76 is arranged which permits a flow of pressure medium from the pressure medium reservoir 22 into the pressure chamber 68 and which blocks in the opposite direction. A preferably redundantly designed pressure sensor 244 measures the pressure in the pressure chamber 68.

[0054] The braking system 2 comprises two brake circuits I, II. A first brake circuit I comprises the wheel brakes 4, 6; a second brake circuit II comprises the wheel brakes 8, 10. In the preferred embodiment shown, the wheel brake 4 is the left front wheel brake, wheel brake 6 is the right front wheel brake, wheel brake 8 is the right rear wheel brake, and wheel brake 10 is the left rear wheel brake. The division of the brake circuits 4-10 is accordingly black-white, or by axle.

[0055] A normally open inlet valve 100 and a normally closed outlet valve 106 are arranged in a hydraulic connection between the pressure chamber 68 of the pressure supply device 14 and the wheel brake 4. A check valve 108, which blocks a flow of pressure medium from the pressure chamber 68 in the direction of the wheel brake 4 and permits this in the opposite direction, is connected in parallel with the inlet valve 100. The outlet valve is connected to the pressure medium reservoir via a reservoir port 110. In the same way, an inlet valve 120 with parallel-connected check valve 122, and an outlet valve 124 with reservoir port 126, are arranged in a hydraulic connection between the pressure chamber 69 of the pressure supply device 14.

[0056] In the same way, in brake circuit II, a respective inlet valve 130, 134 with parallel-connected check valve 132, 136, and a respective outlet valve 140, 144 with reservoir port 148, 150, are arranged in a connecting line between the pressure chamber 68 of the pressure supply device 16 and the respective wheel brake. In this way, the braking system 2 allows brake pressure to be built up and dissipated per individual wheel.

[0057] The pressure chamber 68 of the pressure supply device 14 can be hydraulically connected to the wheel brakes 4, 6 of the brake circuit I via a normally closed pressure switch-on valve 162. The pressure chamber 68 of the pressure supply device 16 can be hydraulically connected to the wheel brakes 8, 10 of the brake circuit via a normally closed pressure switch-on valve 164.

[0058] In unactivated state, or in the starting position of the piston 64, the pressure chamber 68 of the pressure supply device 14 is connected to the brake fluid reservoir via a reservoir port 70. Also in this state, the pressure chamber 68 of the pressure supply device 16 is connected to the brake fluid reservoir via a reservoir port 78. Accordingly, the linear actuators comprise snifter holes with reservoir connection which, in the actuator neutral position, allow balancing of the pressure and volume to the reservoir for both brake circuits I, II. This is also the case for the wheel brakes 4, 6, 8, 10, since during operation or during a brake pressure setting, the actuator switch-on valves 162, 164 are opened.

[0059] In the pressure supply device 14, the rotor position of the motor 60 is measured by means of a preferably redundantly designed rotor position sensor 170. An optional, preferably redundantly designed sensor 172 measures the temperature of the motor winding. In the pressure supply device 16, the rotor position of the motor 60 is measured by means of a preferably redundantly designed rotor position sensor 170. An optional, preferably redundantly designed sensor 172 measures the temperature of the motor winding.

[0060] The brake circuits I and II are connected together in hydraulically isolatable fashion. For this, a normally closed circuit connecting valve 152, to which a further normally closed circuit connecting valve 154 is connected in parallel, is arranged in a hydraulic connecting line 150.

[0061] In the braking system 2 shown, the two separate control and regulating units 18, 20 or electronic units are assigned to the two hydraulic circuits or brake circuits I, II. The two control and regulating units 18, 20 can communicate with each other via a data interface 160. If one electronic unit has failed, the still intact electronic unit eliminates the dual-circuit structure and also operates the wheel brakes of the electrically failed brake circuit I, II. For this, it opens a circuit connecting valve 150, 152 and also operates the wheel brakes 4, 6; 8, 10 of the electronically failed brake circuit I, II.

[0062] In each of the two brake circuits I, II, one of the two outlet valves 106, 124, 140, 144 can be actuated by the control and regulating unit 18, 20 of the respective other brake circuit I, II. For example, the outlet valve 106 is actuated by the control and regulating unit 20, and the outlet valve 140 is actuated by the control and regulating unit 18. Thus after failure of one of the two electronic units, all wheel brakes 4-10 can be loaded with an electronically adjustable brake pressure.

[0063] The braking system 2 shown in FIG. 1 is particularly suitable for vehicles with full automation of the driving function (level 4 or 5). For vehicles without brake pedal, the brake pedal 26 shown and/or the simulator 12 may be omitted. Known simulator braking systems have the disadvantage that during a refill process for refilling a linear actuator pressure chamber, no system pressure can be provided. It is therefore not possible to increase the wheel brake pressures in this phase. In the braking system shown in FIGS. 1 and 2, the system pressure is provided uninterruptedly. If refilling is required for a linear actuator, its pressure switch-on valve 162, 164 is closed and the circuit connection is created by opening at least one circuit connecting valve 152, 154. Thus in this time, the respective other linear actuator can provide the system pressure for all wheel brakes 4, 6, 8, 10. The states of the two ECU's and their connected actuators are exchanged via the data interface 160. Also, information on brake regulating functions and required braking instructions from the brake pedal, autopilot or other vehicle systems, is exchanged and adapted.

[0064] FIG. 2 shows a preferred variant of a braking system with a hydraulically connected tandem master brake cylinder (THZ) 180 which can be actuated by the brake pedal 26. The tandem master brake cylinder 180 comprises two pressure chambers 184, 186 arranged in a housing 182, namely the primary pressure chamber 184 and the secondary pressure chamber 186. The primary pressure chamber 184 is delimited by a primary piston 190 that can be actuated by means of the brake pedal 26, and the secondary pressure chamber 186 is delimited by a secondary piston 194 of floating design. In the unactivated state of the primary piston 190, the primary pressure chamber 184 is connected to a brake fluid reservoir 200. In the unactivated state of the secondary piston 194, the secondary pressure chamber 18 is connected to the brake fluid reservoir 200.

[0065] In the present exemplary embodiment, the simulator 12 is hydraulic. It can be connected hydraulically to the primary pressure chamber 184 via a simulator valve 202. In by-wire operating mode, the hydraulic connection of the tandem master brake cylinder 180 to the wheel brakes 4, 6, 8, 10 is blocked and a hydraulic connection to the simulator 12 is created. If both electronic units or control and regulating units are inactive, the driver can actuate the wheel brakes 4, 6, 8, 10 directly hydraulically.

[0066] The primary pressure chamber 184 can be connected to the brake circuit I via a primary line 210, and in by-wire mode can be blocked by a normally open isolating valve 212. A preferably redundantly designed pressure sensor 216 measures the pressure in the primary pressure chamber 184. The secondary pressure chamber 186 can be connected to the brake circuit I via a secondary line 220, and in by-wire mode can be blocked by a normally open isolating valve 224. A preferably redundantly designed pressure sensor 226 measures the pressure in the secondary pressure chamber 186.

[0067] To detect the driver's braking intention, preferably redundantly designed travel sensors 230, 232 are provided for measuring the pedal travel and/or travel of the primary piston 190. Each of the two sensors 230, 232 is connected to another control and regulating unit 18, 20 on the signal input side. This embodiment of the braking system 2 is necessary in particular also for vehicles which offer no redundant energy supply for the two ECU's and pressure setting devices, since here on occurrence of a fault, namely the failure of the energy supply, only hydraulic actuation by the driver is still possible.

[0068] FIG. 3 shows a preferred embodiment of the braking system 2 with asymmetric configuration of the pressure setting device. Here, a pressure setting device or pressure supply device 14 is configured as a linear actuator, and a pressure supply device 240 as a combination of a pump 244 driven by electric motor and of a pressure control valve 250. The pressure provided on the pump pressure side is measured by means of a preferably redundantly designed pressure sensor 270. Furthermore, a switch-on valve 242 is provided.

[0069] In this variant, the circuit separation of the brake circuits I, II takes place via series-connected, normally open solenoid valves or circuit separating valves 262, 264. In normal operation, these remain open and the linear actuator provides the system pressure for all wheel brakes 4, 6, 8, 10. Whereas in the variants shown in FIGS. 1 and 2, the circuit separation is present in normal operating mode, here it may be provided by closing one of the two circuit separating valves 262, 264 in order to obtain the advantageous functionalities described above.

[0070] FIG. 4 shows a preferred embodiment of the braking system 2, similar to FIG. 1 but with pressure supplied by means of two pumps 240, 280. In this variant, both pressure supply devices are configured as pumps 240, 280. The circuit separation takes place, as shown in FIG. 1, by means of two parallel-connected, normally closed circuits switch-on valves 152, 154.