Hydraulic Braking System for a Vehicle and Corresponding Operating Method

Abstract

A hydraulic braking system for a vehicle includes a master brake cylinder, a hydraulic unit and a plurality of wheel brakes, the hydraulic unit including at least one brake circuit for brake pressure modulation in the wheel brakes. A bistable solenoid valve is associated with at least one wheel brake, which valve is looped into the corresponding fluid channel, immediately upstream of the associated wheel brake, and in a de-energized open position enables brake pressure modulation in the associated wheel brake, and in a de-energized closed position seals a current brake pressure in the associated wheel brake, wherein a hydraulic force brought about by the sealed-in brake pressure acts in a seat-opening manner in the corresponding bistable solenoid valve.

Claims

1. A hydraulic brake system for a vehicle, comprising: a brake master cylinder; a plurality of wheel brakes; and a hydraulic unit comprising at least one brake circuit configured to modulate brake pressure in the wheel brakes, a bistable solenoid valve assigned to at least one wheel brake of the plurality of wheel brakes, the bistable solenoid valve looped into a corresponding fluid duct directly upstream of the associated wheel brake and, in a currentless open position, the bistable solenoid valve enables the brake pressure modulation in the associated wheel brake and, in a currentless closed position, the bistable solenoid valve encloses a current brake pressure in the associated wheel brake, a hydraulic force which is brought about by way of the enclosed brake pressure having a seat-opening effect in the bistable solenoid valve.

2. The hydraulic brake system as claimed in claim 1, wherein the bistable solenoid valve has a positive pressure function which opens the bistable solenoid valve in the currentless closed position and brings about a pressure equalization if the current brake pressure which is enclosed in the corresponding wheel brake exceeds a predefined first threshold value.

3. The hydraulic brake system as claimed in claim 2, wherein, in the currentless closed position of the bistable solenoid valve, a predefinable spring force acts in a seat-closing manner counter to the hydraulic force.

4. The hydraulic brake system as claimed in claim 3, wherein the first threshold value of the positive pressure function for the enclosed brake pressure can be set via the predefinable spring force.

5. The hydraulic brake system as claimed in claim 1, wherein the bistable solenoid valve has a negative pressure function which opens the bistable solenoid valve in the currentless closed position, and brings about a pressure build-up in the corresponding wheel brake via a fluid pump if the brake pressure which is enclosed in the corresponding wheel brake undershoots a predefined second threshold value.

6. An operating method for a hydraulic brake system that has a brake master cylinder, a plurality of wheel brakes, a hydraulic unit comprising at least one brake circuit configured to modulate brake pressure in the wheel brakes, and a bistable solenoid valve assigned to at least one wheel brake of the plurality of wheel brakes, the bistable solenoid valve looped into a corresponding fluid duct directly upstream of the associated wheel brake and, in a currentless open position, the bistable solenoid valve enables the brake pressure modulation in the associated wheel brake, the method comprising: conducting a pressure holding function in which the bistable solenoid valve is switched into a currentless closed position and a current brake pressure is enclosed in the associated wheel brake, a hydraulic force which is brought about by way of the enclosed brake pressure having a seat-opening effect in the corresponding bistable solenoid valve.

7. The operating method as claimed in claim 6, wherein, in the currentless closed position, the bistable solenoid valve is opened in order to implement a positive pressure function and a pressure equalization is brought about if the brake pressure which is enclosed in the corresponding wheel brake exceeds a predefined first threshold value.

8. The operating method as claimed in claim 7, wherein the first threshold value corresponds to a maximum permitted enclosed brake pressure in the corresponding wheel brake, the first threshold value being set via the predefined seat-closing spring force which acts counter to the hydraulic force and corresponds to a hydraulic force which acts in the case of the maximum permitted enclosed brake pressure and is calculated from the enclosed brake pressure and a sealing diameter of a corresponding valve seat of the bistable solenoid valve.

9. The operating method as claimed in claim 6, further comprising: measuring the brake pressure which is enclosed in the wheel brake.

10. The operating method as claimed in claim 9, further comprising: activating a fluid pump and opening the bistable solenoid valve to build up brake pressure in the corresponding wheel brake if the brake pressure which is enclosed in the wheel brake drops below a predefined second threshold value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 shows a diagrammatic hydraulic circuit diagram of a first exemplary embodiment of a hydraulic brake system according to the invention for a vehicle.

[0016] FIG. 2 shows a diagrammatic sectional illustration of a detail of a bistable solenoid valve of the hydraulic brake system according to the invention for a vehicle from FIG. 1.

EMBODIMENTS OF THE INVENTION

[0017] As can be seen from FIGS. 1 and 2, the exemplary embodiment shown of a hydraulic brake system 1 according to the invention for a vehicle comprises a brake master cylinder 5, a hydraulic unit 9 and a plurality of wheel brakes RR, FL, FR, RL. For the brake pressure modulation in the wheel brakes RR, FL, FR, RL, the hydraulic unit 9 comprises at least one brake circuit BC1, BC2. Here, at least one wheel brake RR, FL, FR, RL is assigned a bistable solenoid valve BM which is looped into the corresponding fluid duct directly upstream of the associated wheel brake RR, FL, FR, RL, and enables the brake pressure modulation in the associated wheel brake RR, FL, FR, RL in a currentless open position and encloses a current brake pressure in the associated wheel brake RR, FL, FR, RL in a currentless closed position, a hydraulic force FH which is brought about by way of the enclosed brake pressure having a seat-opening effect in the corresponding bistable solenoid valve 10.

[0018] Furthermore, as can be seen from FIG. 1, the exemplary embodiment which is shown of the hydraulic brake system 1 according to the invention for a vehicle comprises two brake circuits BC1, BC2 which are assigned in each case two of four wheel brakes RR, FL, FR, RL. Thus, a first wheel brake FR which is arranged, for example, on a vehicle front axle on the right hand side and a second wheel brake RL which is arranged, for example, on a vehicle rear axle on the left hand side are assigned to a first brake circuit BC1. A third wheel brake RR which is arranged, for example, on a vehicle rear axle on the right hand side and a fourth wheel brake FL which is arranged, for example, on the vehicle front axle on the left hand side are assigned to a second brake circuit BC2. Each wheel brake RR, FL, FR, RL is assigned an inlet valve EV11, EV21, EV12, EV22 and an outlet valve AV11, AV21, AV12, AV22, it being possible in each case for pressure to be built up in the corresponding wheel brake RR, FL, FR, RL via the inlet valves EV11, EV21, EV12, EV22, and it being possible in each case for pressure to be dissipated in the corresponding wheel brake RR, FL, FR, RL via the outlet valves AV11, AV21, AV12, AV22. For the build-up of pressure in the respective wheel brake RR, FL, FR, RL, the corresponding inlet valve EV11, EV12, EV21, EV22 is opened and the corresponding outlet valve AV11, AV12, AV21, AV22 is closed. For the dissipation of pressure in the respective wheel brake RR, FL, FR, RL, the corresponding inlet valve EV11, EV21, EV12, EV22 is closed and the corresponding outlet valve AV11, AV21, AV12, AV22 is opened.

[0019] Furthermore, as can be seen from FIG. 1, the first wheel brake FR is assigned a first inlet valve EV11 and a first outlet valve AV11, the second wheel brake RL is assigned a second inlet valve EV2l and a second outlet valve AV21, the third wheel brake RR is assigned a third inlet valve EV12 and a third outlet valve AV12, and the fourth wheel brake FL is assigned a fourth inlet valve EV22 and a fourth outlet valve AV22. Control and/or regulation operations for implementing an ABS function can be carried out via the inlet valves EV11, EV21, EV12, EV22 and the outlet valves AV11, AV21, AV12, AV22.

[0020] In addition, the first brake circuit BC1 has a first intake valve HSV1, a first system pressure control valve USV1, a first equalization container A1 with a first check valve RSV1, and a first fluid pump PE1. The second brake circuit BC2 has a second intake valve HSV2, a second system pressure control valve USV2, a second equalization container A2 with a second check valve RSV2, and a second fluid pump PE2, the first and second fluid pump PE1, PE2 being driven by a common electric motor M. Furthermore, the hydraulic unit 9 comprises a sensor unit 9.1 for the determination of the current system pressure or brake pressure. For the brake pressure modulation and for the implementation of an ASR function and/or an ESP function, the hydraulic unit 9 uses, in the first brake circuit BC1, the first system pressure control valve USV1, the first intake valve HSV1 and the first recirculating pump PE1 and, in the second brake circuit BC2, the second system pressure control valve USV2, the second intake valve HSV2 and the second recirculating pump PE2. Furthermore, as can be seen from FIG. 1, each brake circuit BC1, BC2 is connected to the brake master cylinder 5 which can be actuated via a brake pedal 3. In addition, a fluid container 7 is connected to the brake master cylinder 5. The intake valves HSV1, HSV2 make an intervention in the brake system possible, without there being a driver's request. To this end, the respective suction path for the corresponding fluid pump PE1, PE2 to the brake master cylinder 5 is opened via the intake valves HSV1, HSV2, with the result that said corresponding fluid pump PE1, PE2 can provide the required pressure for the regulation instead of the driver. The system pressure control valves USV1, USV2 are arranged between the brake master cylinder 5 and at least one associated wheel brake RR, FL, FR, RL, and set the system pressure or brake pressure in the associated brake circuit BC1, BC2. Furthermore, as can be seen from FIG. 1, a first system pressure control valve USV1 sets the system pressure or brake pressure in the first brake circuit BC1, and a second system pressure control valve USV2 sets the system pressure or brake pressure in the second brake circuit BC2.

[0021] Furthermore, as can be seen from FIG. 1, in the case of the exemplary embodiments which are shown, four bistable solenoid valves 10 are looped into the respective fluid duct in each case directly upstream of an associated wheel brake RR, FL, FR, RL. Furthermore, as can be seen from FIG. 2, the individual bistable solenoid valves 10 in each case comprise an axially movable plunger 12 with a sealing element 14 which is configured as a ball in the exemplary embodiment which is shown and, in the closed state, interacts with a sealing seat 18 which is configured at the edge of a through bore of a valve body 14. In the exemplary embodiment which is shown, the valve body 14 is configured as a hat-shaped sleeve. In order to implement the seat-closing effect of the hydraulic force FH, a seat-side connector of the bistable solenoid valve 10 is configured as a wheel connector and is connected to the corresponding wheel brake RR, FL, FR, RL. A sealing element-side connector of the bistable solenoid valve 10 is configured as a pump connector and is connected to a corresponding fluid pump PE1, PE2.

[0022] Furthermore, as can be seen from FIG. 2, a predefinable spring force FF has a seat-closing effect counter to the hydraulic force FH in the currentless closed position of the bistable solenoid valve 10 which is shown. As a result, a positive pressure function for the bistable solenoid valve 10 can be provided simply, which positive pressure function opens the bistable solenoid valve 10 in the currentless closed position and brings about a pressure equalization if the brake pressure which is enclosed in the corresponding wheel brake RR, FL, FR, RL exceeds a predefined first threshold value. The first threshold value of the positive pressure function for the enclosed brake pressure can be set via the predefined spring force FF. To this end, the bistable solenoid valve 10 is configured in such a way that the spring force FF holds the bistable solenoid valve 10 closed up to a desired brake pressure, of 90 bar, for example. If the brake pressure rises, for example, as a result of a temperature increase, the positive pressure escapes and flows through the corresponding inlet valve EV11, EV21, EV12, EV22 and the corresponding system pressure control valve USV1, USB2 into the fluid container 7 until the first threshold value of 90 bar which is defined by way of the spring force FF is undershot again. In this way, the system is protected against destruction as a result of positive pressure without expensive additional measures.

[0023] In the exemplary embodiment which is shown, the bistable solenoid valve 10 has a negative pressure function which opens the bistable solenoid valve 10 in the currentless closed position and brings about a pressure build-up in the corresponding wheel brake RR, FL, FR, RL via a corresponding fluid pump PE1, PE2 if the brake pressure which is enclosed in the corresponding wheel brake RR, FL, FR, RL undershoots a predefined second threshold value. If the brake pressure which is enclosed in the wheel brake RR, FL, FR, RL drops, for example on account of a leak at the sealing seat 18, the hydraulic force FH which acts also drops, with the result that the excess of the spring force FF which has a closing action and reduces leakage rises. If the brake pressure which is enclosed in the wheel brake RR, FL, FR, RL drops below the second threshold value of, for example, 30 bar, the brake pressure in the corresponding wheel brake RR, FL, FR, RL can be increased via the corresponding fluid pump PE1, PE2, and the bistable solenoid valve 10 can be closed again subsequently, in order to enclose or shut in the brake pressure which has built up again in the corresponding wheel brake RR, FL, FR, RL.

[0024] By way of the measures which are described, the brake pressure which is required for a pressure holding function can be set in the corresponding wheel brake RR, FL, FR, RL between 30 bar and 90 bar.

[0025] In accordance with embodiments of the operating method according to the invention, in the case of the pressure holding function, the bistable solenoid valve 10 which is assigned to the at least one wheel brake RR, FL, FR, RL can be switched into the currentless closed position, and a current brake pressure can be enclosed in the associated wheel brake RR, FL, FR, RL, a hydraulic force FH which is brought about by way of the enclosed brake pressure having a seat-opening effect in the corresponding bistable solenoid valve 10. In order to implement the positive pressure function, the bistable solenoid valve 10 is opened in the currentless closed position and brings about a pressure equalization if the brake pressure which is enclosed in the corresponding wheel brake RR, FL, FR, RL exceeds the predefined first threshold value. Here, the first threshold value corresponds to a maximum permitted enclosed brake pressure in the corresponding wheel brake RR, FL, FR, RL. The first threshold value is set via the predefined seat-closing spring force FF which acts counter to the hydraulic force FH and corresponds to a hydraulic force FH which acts in the case of the maximum permitted enclosed brake pressure. The hydraulic force which acts is calculated from the enclosed brake pressure and a sealing diameter DD of the corresponding valve seat 18 of the bistable solenoid valve 10.

[0026] In order to improve the operating method, the brake pressure which is enclosed in the wheel brake RR, FL, FR, RL is measured. As a result, the negative pressure function can also be implemented which activates a fluid pump PE1, PE2 and opens the bistable solenoid valve 10, in order to build up brake pressure in the corresponding wheel brake RR, FL, FR, RL if the brake pressure which is enclosed in the wheel brake RR, FL, FR, RL drops below the predefined second threshold value.

[0027] Embodiments of the present invention provide a hydraulic brake system for a vehicle, which hydraulic brake system comprises the additional function of electrohydraulic pressure holding in the wheel brakes with low additional complexity of the hydraulic unit. Here, embodiments of the hydraulic brake system are protected against destruction as a result of positive pressure in an advantageous way without expensive additional measures.