Hydraulic brake system for a motor vehicle and method for operating the brake system - Patents.com

Abstract

To provide a method for, in a braking system, controlling pressure generators depending on a brake request of a vehicle or a driver of the vehicle.SOLUTION: The braking system includes at least two brake circuits (3, 4). These brake circuits have at least one hydraulically operable wheel brake (5, 6, 7, 8) and at least one electrically operable pressure generator (9, 10), the pressure generator being controllable depending on a brake request of a vehicle or a driver of the vehicle. One electric actuator (11, 12) is provided in correspondence to each of the pressure generators for driving the pressure generators, and at least one controllable emergency valve (26) is interconnected between the brake circuits. The emergency valve disconnects the brake circuits from each other in a first switching position, and connects them to each other in a second switching position.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The invention relates to a hydraulic braking system for a motor vehicle having at least two brake circuits, each having at least one hydraulically actuable wheel brake and each having at least one electrically operable pressure generator, where the pressure generator is controllable depending on the braking request of the motor vehicle or of the driver of the motor vehicle.

[0002] The invention also relates to a method for operating such a braking system, in which the pressure generator is controlled in dependence on the braking request of the vehicle or of the vehicle driver. [Background technology]

[0003] Brake systems of the type mentioned at the beginning are known from the prior art. Conventional brake systems are configured as hydraulic brake systems in which a brake pedal that can be actuated by the driver is hydraulically connected, for example via a master brake cylinder and a brake booster, to one or more brake circuits, each of which has one or more wheel brakes. As motor vehicles are increasingly electrified, the electrical support of the brake systems is also increasing. In this case, it is known to provide one or more pressure generators, which, in addition to the application of force by the driver, generate hydraulic pressure in at least one of the brake circuits, if necessary, additionally or independently of the brake pedal actuation. For this purpose, a pressure generator is assigned to each brake circuit, which can be driven by an electric or electromagnetic actuator. This makes so-called wireless or radio braking possible (brake-by-wire). In this case, no hydraulic intervention by the driver takes place in the brake circuits. However, if the brake pedal is hydraulically disconnected from the respective brake circuit, the driver can no longer recognize a fault in the brake system himself, for example by a changed pedal feel. Therefore, in vehicles with a high degree of automation, particularly with regard to the brake system, safety-critical systems must be configured redundantly in order to further ensure safe operation of the vehicle in the event of a failure, and it is particularly important that the vehicle can be brought into a safer state in the event of an individual failure of the brake system. Summary of the Invention Effect of the Invention

[0004] The brake system according to the invention with the features of claim 1 has the advantage that in a simple manner and in a manner that allows the brake system to be always put into a safer state in the event of an individual failure, in particular without the need for a redundant hydraulic system. The proposed solution is space-saving and inexpensive to implement. The brake system according to the invention is characterized in that each pressure generator is assigned a respective individual electric actuator for operating the pressure generator, and at least one controllable emergency valve is interposed between the brake circuits, which in a first switching position separate the brake circuits from one another and in a second switching position connect the brake circuits to one another. In this way, the pressure generators can generate hydraulic pressure in the respective associated brake circuits independently of one another in the normal state. In the first switching position, the emergency valves are normally connected in such a way that the brake circuits are separated from one another. By controlling the emergency valve, the brake circuits are connected to one another, so that, for example, in the event of failure of one pressure generator, the remaining pressure generator can be used to generate hydraulic pressure in the two brake circuits. This allows the brake system to be brought into a safer operating state in a simple manner and manner.

[0005] In particular, the emergency valve is configured as a currentless closed valve which assumes a first switching position in the currentless state. If the emergency valve is not controlled, the brake circuits are separated from one another. Only when a fault in the brake system is detected, the emergency valve is electrically controlled, in particular in conjunction with a pressure generator or an electric actuator associated with this pressure generator, in order to connect the brake circuits to one another.

[0006] According to a preferred embodiment of the invention, the electric actuators are connected to mutually separated or separable on-board power grid parts of the electric on-board power grid of the motor vehicle, which ensures an individual energy supply for each electric actuator, so that in the event of a failure of an on-board power grid part, the remaining electric actuators can still be controlled, so that hydraulic pressure can be generated in the two brake circuits by controlling the emergency valves.

[0007] In a preferred manner, each electric actuator is connected to a respective control unit, as a result of which individual control of the electric actuators is ensured, in particular the control units are each associated with a respective on-board power supply network part of the electric on-board power supply network, so that the control units are supplied with energy and operated independently of one another.

[0008] In a preferred form, the brake system has an operable brake element, in particular a brake pedal, for detecting the driver's braking request, in which the brake circuit is permanently hydraulically disconnected from the brake element. The brake system provided is therefore a mechanically / hydraulically separated (brake-by-wire) brake system, in which hydraulic intervention by the driver in the brake circuit is not possible, nor as a fallback position in case of failure of one of the electric actuators and / or the pressure generator. This makes it possible to dispense with hydraulic or emergency connections, which saves costs and installation space during the manufacture of the brake system.

[0009] In a preferred embodiment, the brake system has at least one further controllable pressure generator connected to one or both brake circuits. The further pressure generator in particular has a controllable electric actuator which is connected to one or preferably both further pressure generators in order to simultaneously control one or both pressure generators during operation, with one pressure generator being assigned to one of the brake circuits in each case when both pressure generators are controlled simultaneously. The further pressure generator or generators increase the operating versatility of the brake system, for example ensuring that higher hydraulic pressures can be provided in a shorter time.

[0010] In a preferred embodiment, the pressure generators are each connected on their suction side to a tank, in particular a common tank, which is designed to receive, store and provide the hydraulic medium, so that the pressure generators are preferably supplied with hydraulic medium from a common tank.

[0011] In a preferred embodiment, each wheel brake is assigned an individually operable intake valve and an individually operable discharge valve, the intake valve being configured as a currentless opening valve, the intake valve being configured as a passive valve, so that the braking force at the respective wheel brake can only be adjusted by actuating the pressure generator or generators, and in order to concentrate the hydraulic pressure, for example, at an individual wheel brake, a high hydraulic pressure is generated for a short time at the individual wheel brake, so that, for example, a number of further intake valves are closed.

[0012] In a preferred embodiment, the outlet valve is connected on the suction side to a further pressure generator. If a further pressure generator is provided, the return hydraulic medium permitted when the outlet valve opens and thus when the braking force of the respective wheel brake is reduced is fed to the suction side of the further pressure generator, so that when the further pressure generator is actuated, hydraulic medium is further provided to the further pressure generator. In this respect, the brake system corresponds to a closed brake system, since in this case the hydraulic medium is not guided past the pressure generator to the tank.

[0013] In a preferred embodiment, the brake circuits have changeover valves by means of which the brake circuits can be connected to or separated from the respective pressure generators. The changeover valves ensure that the brake circuits can be hydraulically loaded separately even in the event of failure of the pressure generators and / or the electric actuators. An emergency valve distributes the provided pressure to the two brake circuits and, if necessary, can be limited to one of the brake circuits by controlling one of the changeover valves.

[0014] Therefore, in a preferred manner, a switching valve is connected downstream of the emergency valve.

[0015] The method according to the invention having the features of claim 13 is characterized in that each pressure generator is operated by a dedicated electric actuator and that during emergency operation the brake circuits are connected to one another by controlling emergency valves interposed between the brake circuits and which during normal operation separate the brake circuits from one another. Emergency operation is carried out in particular when the presence of a functional fault in the brake system associated with one of the electric actuators and / or the pressure generator is detected. For this purpose, the electric actuators and the pressure generators of the brake system are in particular continuously monitored for their functional correctness.

[0016] In a preferred embodiment, the braking force at at least one wheel brake is adjusted solely by controlling one electric actuator, whereby the braking force is increased or decreased by controlling the electric actuator, and since valve control is omitted, an inexpensive and energy-efficient operation of the brake system is ensured.

[0017] In a preferred embodiment, the braking force at at least one of the wheel brakes is selectively adjusted by controlling at least one intake valve associated with one of the wheel brakes. If, for example, an increased braking force is required for one wheel brake, the intake valve of the other wheel brake is preferably closed, so that the applied hydraulic pressure acts only on this one wheel brake. In order to ensure high driving stability of the vehicle with maximum braking performance, in particular the intake valve is controlled in such a way that all wheel brakes of the brake system are loaded with the desired hydraulic pressure, the hydraulic pressure being adjusted to the wheel brakes individually. [Brief description of the drawings]

[0018] [Figure 1] 1 is a simplified schematic diagram of a first embodiment of a preferred braking system for a motor vehicle. [Diagram 2] 4 is a simplified schematic diagram of a second embodiment of a braking system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present invention will now be described in detail with reference to the accompanying drawings.

[0020] 1 shows a simplified diagram of a first embodiment of a suitable brake system 1 for a motor vehicle, not shown in detail here. The brake system 1 has, in particular, a fillable tank 2, which stores and provides a hydraulic medium, in particular brake fluid, for the brake system 1. The tank is fluidly connected to two brake circuits 3 and 4. As shown by dashed lines in the tank 2, a respective separate tank 2 is optionally provided for each brake circuit 3, 4.

[0021] Each brake circuit 3, 4 has, in the exemplary embodiment shown, two wheel brakes 5, 6 or 7, 8, which are each designed as hydraulically actuated wheel brakes. In the exemplary embodiment shown, in a vehicle having four wheels and two axles, the wheel brake 5 is arranged on the right wheel of the front axle, the wheel brake 6 is arranged on the left wheel of the rear axle, the wheel brake 7 is arranged on the left wheel of the front axle and the wheel brake 8 is arranged on the right wheel of the rear axle.

[0022] Each brake circuit has a respective pressure generator 9, 10, which generates hydraulic pressure in the respective brake circuit 3, 4. For this purpose, the pressure generators 9, 10 are connected on the discharge side to the respective brake circuit 3, 4 and on the suction side to the tank 2. An electric actuator 11 or 12 is assigned to each pressure generator 9, 10. In the exemplary embodiment shown, the electric actuators 11, 12 are designed as electric motors and the pressure generators 9, 10 are designed as piston pumps. Optionally, the pressure generators 9, 10 can also be designed as rotary pumps, etc. Electromagnetic actuators are also considered as electric actuators 11, 12.

[0023] Each pressure generator 9, 10 is fluidly connected on its discharge side to a wheel brake 5, 6 or 7, 8 of the associated brake circuit 3, 4. A respective intake valve 13, 14, 15, 16, designed as a currentless open valve, is associated with each wheel brake 5, 6, 7, 8, through which the respective pressure generator 9, 10 is directly connected in the currentless state to the inlet side of the associated wheel brake 5, 6, 7, 8. Furthermore, each wheel brake 5 to 8 is associated with a controllable discharge valve 17, 18, 19, 20, designed as a currentless closed valve. According to the exemplary embodiment shown, the discharge valves 17 to 20 are connected on their discharge side to a pressure accumulator 21 or 22 of the respective brake circuit 3, 4 and, optionally, to the intake side of a further pressure generator 23, 24 of the respective brake circuit 3, 4. The pressure generator 23, 24, on the other hand, is connected on its discharge side to the intake valve 13, 14 or 15, 16. The further pressure generators 23, 24 are associated with a common electric actuator 25, here as an electric motor, which drives the two pressure generators 23, 24, in particular the hydraulic pumps, if necessary. Since hydraulic medium can be stored intermediately in each pressure accumulator 21, 22, pressure fluctuations are avoided and hydraulic medium can always be provided for the pressure generators 23, 24.

[0024] The two brake circuits 3, 4 are hydraulically connectable to one another downstream of the pressure generators 9, 10 and upstream of the intake valves 13-16, as well as upstream of the optional pressure generators 23, 24, via an emergency valve 26. The emergency valve 26 is electrically controllable and is configured to be closed in a current-free or uncontrolled switching position, so that the brake circuits 3, 4 are separated from one another. By electrically controlling the emergency valve 26, the emergency valve 26 is moved from a first switching position to a second switching position, in which the brake circuits 3, 4 are hydraulically connected to one another via the emergency valve 26.

[0025] Due to the preferred configuration of the brake system 1, if one of the pressure generators 9, 10 or the associated electric actuators 11, 12 fails due to a malfunction, hydraulic pressure can nevertheless be generated by the remaining pressure generators 10, 9 and provided to the two brake circuits 3, 4 by controlling the emergency valve 26, so that a braking force can be adjusted to all wheel brakes 5 to 8 of the brake system 1. In this way, a safe driving state of the vehicle is always guaranteed, even in the event of a failure of one of the pressure generators 9, 10 or the associated electric actuators 11, 12. In the event of a failure of the pressure generator 9, for example, the emergency valve 26 is opened or switched to the second switching state, so that the pressure provided by the pressure generator 10 is distributed to the two brake circuits 3, 4.

[0026] To further increase the fail-safety, the electric actuators 11, 12 are each connected to a dedicated control unit 27 or 28, so that they can be driven independently of one another. In particular, the control units 27, 28 are connected or can be connected to a respective on-board power supply network part 29 or 30 of the on-board power supply network of the motor vehicle, not shown here, so that they are also connected or can be connected independently of one another in the energy supply of the electric actuators 11, 12. In the event of a failure of the on-board power supply network part 29, 30 or of one of the control units 27, 28, the further operation of the wheel brakes 5 to 8 is additionally ensured by suitable emergency valves 26.

[0027] The above described embodiment relates to a closed brake system, in which high variability is ensured in the regulation of the required hydraulic pressure by controlling the further pressure generators 23, 24. The configuration of the intake valves 13-16 as currentless opening intake valves ensures that the hydraulic pressure in the wheel brakes and thus the braking force in the wheel brakes 5-8 can be adjusted solely by controlling the pressure generators 9, 10. Furthermore, by closing one or more intake valves, the hydraulic pressure provided by the pressure generators 9, 10 can be concentrated in selected wheel brakes whose intake valves are kept open.

[0028] Figure 2 shows a further embodiment of the brake system 1, in which components known from figure 1 are given the same reference numerals and in the following mainly only the differences will be explained in more detail.

[0029] In contrast to the previous exemplary embodiment, here the brake system 1 is configured as an open brake system in which the outlet valves 17 to 20 are each connected directly to the tank 2 on the outlet side, so that the outflowing hydraulic medium is guided directly back into the tank 2. Furthermore, according to this exemplary embodiment, the additional pressure generators 23, 24 as well as the electric actuator 25 can optionally be omitted.

[0030] Furthermore, according to this exemplary embodiment, an electrically controllable switching valve 31 or 32 is connected downstream of the emergency valve 26 in each brake circuit 3, 4, which switching valve 31, 32 is open in the current-free state. By controlling the switching valve 31, 32, the connection between the pressure generator 9, 10 and the brake circuit 3, 4 is interrupted. This makes it possible, during emergency driving, after the emergency valve 26 is opened, to concentrate the pressure provided by the remaining pressure generator in one of the brake circuits 3, 4 by controlling one of the switching valves 31, 32, for example, if an increased braking force is required on the front or rear axle. Although the brake circuits 3, 4 are here provided in an X-division, a parallel or II-division of the brake circuits 3, 4 is also conceivable, in which one brake circuit 3 has the wheel brakes 5, 7 of the front axle and the other brake circuit 4 has the wheel brakes 6, 8 of the rear axle. In this case, an axle-specific pressure loading of the wheel brakes in particular is possible, as already mentioned above.

[0031] During emergency operation, the pressure generators 9, 10 therefore only act on one brake circuit 3, 4, respectively, but can also act on all four wheel brakes 5-8 by controlling the emergency valve 26. In the event of a failure of one of the pressure generators 9, 10, it is therefore also possible to brake all four wheels of the vehicle. In particular, the brake system 1 is configured in such a way that an electrically redundant control of the emergency valve 26 is ensured here, since the emergency valve 26 can be controlled independently of one another by the two control units 27, 28. Thus, in the event of a failure of one of the control units 27, 28 or the on-board power grid parts 29, 30, the operation of the emergency valve 26 is also ensured.

[0032] In the exemplary embodiment shown, the brake system 1 is in each case configured as a brake-by-wire system in which the pressure generators 9, 10 as well as the brake circuits 3, 4 are hydraulically isolated from a brake pedal 33 which can be actuated by the driver. The control units 27, 28 are connected to the brake pedal 33, preferably in such a way as to constantly monitor the brake pedal position, in order to control the pressure generators 9, 10 to set the desired braking torque at the wheel brakes 5 to 8 as a function of the detected brake pedal position. [Explanation of symbols]

[0033] 1 Brake system 2 Tank 3,4 Brake circuit 5,6,7,8 Wheel brakes 9,10 Pressure generator 11,12 Electric actuator 13,14,15,16 Intake valve 17,18,19,20 Discharge valve 21,22 Accumulator 23,24 Pressure Generator 25 Electric Actuator 26 Emergency valve 27,28 Control unit 29,30 In-vehicle power network part 31,32 Switching valve 33 Brake pedal, brake element

Claims

1. A hydraulic braking system (1) for a motor vehicle, comprising at least two brake circuits (3, 4), each of which has at least one hydraulically actuable wheel brake (5, 6, 7, 8) and each of which has at least one electrically operable pressure generator (9, 10), the pressure generators (9, 10) being controllable as a function of the braking request of the motor vehicle or of a driver of the motor vehicle, Each pressure generator (9, 10) is respectively assigned an electric actuator (11, 12) for operating said pressure generators, at least one controllable emergency valve (26) is interposed between said brake circuits (3, 4), said emergency valve (26) isolating said brake circuits (3, 4) from one another in a first switching position and connecting them to one another in a second switching position, each brake circuit (3, 4) has a respective change-over valve (31, 32) by means of which the brake circuit (3, 4) can be connected to or separated from the respective associated pressure generator (9, 10), A hydraulic brake system for a motor vehicle, characterized in that the switching valves (31, 32) are connected downstream of the emergency valve (26).

2. 2. The brake system according to claim 1, wherein the emergency valve (26) is configured as a currentless closed emergency valve which occupies a first switching position in a currentless state.

3. 3. A brake system according to claim 1, wherein the electric actuators (11, 12) are connected to separate or separable on-board power supply network parts (29, 30) of an electrical on-board power supply network of a motor vehicle.

4. 4. A brake system according to claim 1, wherein each electric actuator (11, 12) is connected to a respective control unit (27, 28).

5. 5. The brake system according to claim 1, further comprising an actuable brake element, in particular a brake pedal, for detecting a driver's braking request, and the brake circuit is hydraulically disconnected from the brake element.

6. 6. The braking system according to claim 1, further comprising at least one further controllable pressure generator (23, 24) connected to one or both of the brake circuits (3, 4).

7. 7. A brake system according to claim 1, characterized in that the pressure generator (9, 10) is connected on the suction side to a tank (2), the tank (2) being designed for receiving, storing and providing hydraulic medium.

8. 8. A brake system according to claim 1, characterized in that each wheel brake (5, 6, 7, 8) is assigned an individually operable intake valve (13, 14, 15, 16) and an individually operable discharge valve (17, 18, 19, 20), the intake valves (13, 14, 15, 16) being designed as currentless opening valves.

9. 7. Brake system according to claim 6, characterized in that the outlet valves (17, 18, 19, 20) are connected on the suction side to at least one further pressure generator (23, 24).

10. 10. Brake system according to claim 1, characterized in that the discharge valve (17, 18, 19, 20) is connected to the tank (2).

11. A method for operating a brake system (1) according to any one of claims 1 to 10, comprising at least two brake circuits (3, 4), each of which has at least one hydraulically operable wheel brake (5, 6, 7, 8) and at least one electrically operable pressure generator (9, 10), wherein the pressure generators (9, 10) are controllable depending on a braking request of the motor vehicle or of a driver of the motor vehicle, 1. A method for operating a brake system, characterized in that each pressure generator (9, 10) is operated by one electric actuator (11, 12) and the brake circuits (3, 4) are connected to each other for emergency operation by control of emergency valves (26) interposed between the brake circuits (3, 4) and isolating the brake circuits (3, 4) from each other during normal operation.

12. The method as described in claim 11, characterized in that the braking force in at least one of the wheel brakes (5, 6, 7, 8) is adjusted by controlling only one of the electric actuators (11, 12).

13. A method as described in claim 11 or 12, characterized in that the braking force in at least one of the wheel brakes (5, 6, 7, 8) is adjusted by controlling at least one intake valve (13, 14, 15, 16) arranged corresponding to one of the wheel brakes (5, 6, 7, 8).

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