Braking system for a vehicle and method for brake pressure control

Abstract

The invention relates to a braking system (1) for a vehicle, comprising an electro-hydraulic partial braking system (2) and an electromechanical brake pedal (3) for communicating a braking force request to the braking system (1). The electro-hydraulic partial braking system (2) comprises at least one hydraulic brake (4, 5), a pressure supply device (6), and a brake fluid reservoir (7). The design of the electro-hydraulic partial braking system is to be simplified. According to the invention, the electro-hydraulic partial braking system (2) therefore comprises a continuously adjustable pressure relief valve (8) arranged upstream of the brake fluid reservoir (7), which is configured to provide atmospheric pressure in the brake fluid reservoir (7) for brake pressure control of the hydraulic brake (4, 5).Furthermore, the electro-hydraulic partial brake system (2) comprises a continuously adjustable isolation valve (9) arranged between the at least one hydraulic brake (4, 5) on one side and the pressure supply device (6) and the brake fluid reservoir (7) on the other side, in order to maintain a built-up brake pressure at the at least one hydraulic brake (4, 5) when the pressure supply device (6) is in a priming phase. This allows the number of continuously adjustable valves to be reduced and the hydraulic layout to be simplified. The invention further relates to a method for brake pressure control in such a brake system (1).

Description

[0001] The invention relates to a braking system for a vehicle, comprising an electrohydraulic partial braking system and an electromechanical brake pedal for communicating a braking force request from a user to the braking system. The electrohydraulic partial braking system comprises at least one hydraulic brake, a pressure supply device, and a brake fluid reservoir. The invention further relates to a method for brake pressure control in such a braking system.

[0002] Such a by-wire braking system with an electromechanical brake pedal is known from WO 2023 138 720 A1. The braking system described therein proposes, among other things, to increase safety in a braking system without a hydraulic fallback function via an electro-hydraulic brake pedal by providing additional redundant control units with associated shut-off valves in series upstream of the brake fluid reservoir. Pressure control valves upstream of the pressure supply device can also be arranged redundantly in parallel. This significantly reduces the risk of an entire system failure due to a single component failure.

[0003] While such solutions increase the safety of a by-wire braking system with an electromechanical brake pedal, they also lead to increased complexity and costs due to the increased number of components. It should be noted that such braking systems often include at least one electromechanical partial braking system and frequently also a regenerative braking system (in which the electric motor can be operated as a generator). These non-hydraulic partial braking systems are often preferred over hydraulic brakes because they are more efficient and subject to less wear, which is why the electro-hydraulic partial braking system is only used for high braking force requirements. Thus, depending on the design of the rest of the braking system, it may be desirable to design the electro-hydraulic partial braking system to be less complex, while still providing sufficient redundancy in the overall system for a wide variety of individual faults.At the same time, however, full controllability of the hydraulic brakes must be ensured to provide the usual safety functions.

[0004] The object of the present invention is therefore to provide a braking system of the type mentioned above which meets as many of these requirements as possible.

[0005] This object is achieved according to the invention by a braking system according to claim 1. Due to the continuously adjustable pressure reduction valve and the continuously adjustable isolation valve, all essential safety functions can be provided together with an inlet valve and a discharge valve for each hydraulic brake, and at the same time the total number of valves and hydraulic lines and / or connections can be reduced, for example, compared to WO 2023 138 720 A1.

[0006] Preferably, the isolation valve and the pressure relief valve are normally open valves. This ensures that even if one of these valves fails, at least limited functionality of the electrohydraulic partial brake system can be maintained.

[0007] In one embodiment, the at least one hydraulic brake is supplied with hydraulic fluid via a normally open inlet valve and is connected to the brake fluid reservoir via a normally closed drain valve, wherein the inlet valve is continuously adjustable and the drain valve is a two-position valve. Together with the continuously adjustable pressure relief valve and the continuously adjustable isolation valve, such a hydraulic layout allows full controllability of the hydraulic brake(s), but significantly simpler two-position valves are used as drain valves for the hydraulic brake(s). In the prior art, the drain valves are typically continuously adjustable valves that are used in a variety of control functions.

[0008] The electrohydraulic partial braking system preferably comprises exactly two hydraulic brakes, in particular for the same vehicle axle. The solution according to the invention is particularly advantageous, for example, in a "semi-dry" braking system, since the other (in particular electromechanical and regenerative) partial braking systems of the braking system can then complement each other excellently, especially with regard to system safety, and enable a simplification of the electrohydraulic partial braking system.

[0009] The braking system is preferably configured to fully or partially open the pressure reduction valve to reduce brake pressure during brake pressure control. The inlet valve and the discharge valve can also be used for brake pressure control as usual. The continuously adjustable pressure reduction valve replaces part of the previous functionality of the discharge valve, which can no longer be partially opened but only has the open and closed positions.

[0010] It is preferred if the braking system comprises precisely one hydraulic control unit, wherein the hydraulic control unit is configured to control the electrohydraulic partial braking system and to perform brake pressure regulation of the hydraulic brake. Thus, a single hydraulic control unit is provided for the entire electrohydraulic partial braking system (only the pressure supply device can then optionally comprise a separate engine control unit). In the past, separate control units were regularly used for by-wire braking systems, for example, for an actuator section (in particular, the pressure supply device and brake fluid reservoir) and a modulator section (in particular, hydraulic brakes and associated control valves) in order to ensure sufficient reliability.However, particularly when an electromechanical partial braking system and / or a regenerative partial braking system are present, this additional redundancy level is not always necessary and a simplification of the electronic components of the electrohydraulic partial braking system becomes possible.

[0011] In one embodiment, the braking system further comprises an electromechanical partial braking system, wherein the electromechanical partial braking system comprises at least one electromechanical brake assigned to a different axle of the vehicle than the hydraulic brake of the electrohydraulic partial braking system. For such a braking system, the inventive design of the electrohydraulic partial braking system is particularly advantageous because the electromechanical partial braking system provides an additional fallback level in the event of a partial failure of the electrohydraulic partial braking system.

[0012] Preferably, each electromechanical brake comprises its own brake control unit, which is configured to regulate the braking force or braking torque provided by the electromechanical brake. This embodiment is particularly advantageous because each electromechanical brake then provides an additional fallback level, e.g., in the event of a failure of one of the control units of the braking system, which no longer needs to be provided solely by the electrohydraulic partial braking system.

[0013] Preferably, the braking system further comprises a regenerative partial braking system, wherein an electric motor of the vehicle can be operated as a generator to provide braking force for the vehicle. In particular, when an electromechanical partial braking system and a regenerative partial braking system are present, the solution according to the invention for the electrohydraulic partial braking system is particularly advantageous. The multiple partial braking systems achieve a high level of reliability, which allows a reduction in the complexity of the electrohydraulic partial braking system.

[0014] The electro-hydraulic partial brake system preferably comprises an intake valve connected to the brake fluid reservoir via its own connection and parallel to the pressure relief valve. The intake valve is designed as a check valve that opens when the pressure supply device generates a negative pressure on the side of the intake valve facing away from the brake fluid reservoir during an intake process. The hydraulic lines from the intake valve and the pressure relief valve each meet at a first junction point away from the brake fluid reservoir, where a main line begins. This design eliminates the need for a hydraulic connection to the pressure supply device and simplifies its sealing.

[0015] Preferably, a hydraulic line from the isolation valve and a hydraulic line from the pressure supply device meet at a second junction point located along a main line from the brake fluid reservoir to the at least one hydraulic brake, with no valve located in the hydraulic line from the pressure supply device to the second junction point. This eliminates the need for a dedicated shut-off valve upstream of the pressure supply device, reducing the complexity of the braking system.

[0016] In one embodiment, only one hydraulic line leads from the pressure supply device into the hydraulic circuit to the at least one hydraulic brake and the brake fluid reservoir. This design eliminates the need for a hydraulic connection to the pressure supply device and simplifies its sealing.

[0017] The object of the invention is also achieved by a method according to claim 12. Accordingly, the brake pressure applied to the hydraulic brake is also controlled by partially opening and then closing the pressure relief valve. To provide the hydraulic brakes with a different brake pressure, the degree of opening of the associated inlet valves can also be varied, and the discharge valves can be opened in phases.

[0018] Preferably, the braking system comprises a pressure sensor configured to measure a brake pressure applied to the hydraulic brake, wherein the step of regulating the brake pressure includes the brake pressure measured by the pressure sensor. Preferably, the braking system comprises exactly one pressure sensor, which is sufficient for the relevant control functions, particularly due to the reduced number of valves.

[0019] Embodiments of the invention are explained in more detail below with reference to the accompanying figures. They show: Fig. 1 a hydraulic circuit diagram of a braking system according to the invention, and Fig. 2 a flowchart of a method according to the invention.

[0020] Fig. 1 shows an embodiment of a braking system 1 according to the invention, comprising an electrohydraulic partial braking system 2 and an electromechanical brake pedal 3 for communicating a braking force request by a user to the braking system 1. The electrohydraulic partial braking system 2 comprises at least one hydraulic brake 4, 5 (here two, e.g., for a front axle of a motor vehicle), a pressure supply device 6 and a brake fluid reservoir 7.

[0021] The electrohydraulic partial brake system 2 further comprises a continuously adjustable pressure relief valve 8 (solenoid valve) arranged upstream of the brake fluid reservoir 7. The pressure relief valve 8 is configured to provide an atmospheric pressure of the brake fluid reservoir 7 for brake pressure control of the hydraulic brakes 4, 5.

[0022] In addition, the electrohydraulic partial brake system 2 comprises a continuously adjustable isolation valve 9 (solenoid valve) arranged between the hydraulic brakes 4, 5 on one side and the pressure supply device 6 and the brake fluid reservoir 7 on the other side. The isolation valve 9 is configured to maintain a built-up brake pressure at the at least one hydraulic brake 4, 5 when the pressure supply device 6 is in a suction process for sucking brake fluid from the brake fluid reservoir 7.

[0023] Each hydraulic brake 4, 5 is supplied with hydraulic fluid via a normally open inlet valve 10, 11 (solenoid valves) and is connected to the brake fluid reservoir 7 via a normally closed drain valve 12, 13. The inlet valves 10, 11 are continuously adjustable, while the drain valves 12, 13 are simple two-position valves. Together with the continuously adjustable pressure relief valve 8 and the continuously adjustable isolation valve 9, such a hydraulic layout allows full control of the hydraulic brakes 4, 5, although significantly simpler two-position valves can be used as drain valves 12, 13 for the hydraulic brakes 4, 5 than is usually the case in the prior art.

[0024] The braking system 1 comprises a hydraulic control unit 14 which is designed to control the electro-hydraulic partial braking system 2 and to carry out a brake pressure control of the hydraulic brakes 4, 5.

[0025] The braking system 1 further comprises an electromechanical partial braking system 15, wherein the electromechanical partial braking system 15 comprises at least one (here two) electromechanical brake(s) 16, 17. The electromechanical brakes 16, 17 are assigned to a different axle of the vehicle (e.g., the rear axle) than the hydraulic brakes 4, 5 of the electrohydraulic partial braking system 2 (which are assigned, e.g., to the front axle). The electromechanical brakes 16, 17 are preferably electromechanical drum brakes. Each electromechanical brake 16, 17 comprises its own brake control unit 18, 19, each of which is configured to regulate the braking force or braking torque provided by the associated electromechanical brake 16, 17.

[0026] The braking system 1 also has a regenerative partial braking system 20, for which an electric motor of the vehicle can be operated as a generator in order to provide braking force for the vehicle.

[0027] The electro-hydraulic partial brake system 2 additionally comprises an intake valve 21, which is connected to the brake fluid reservoir 7 via its own connection 22 and parallel to the pressure relief valve 8. The pressure relief valve 8 is thus connected to the brake fluid reservoir 7 via another connection 23. The intake valve 21 is designed as a check valve that opens when the pressure supply device 6 generates a negative pressure on the side of the intake valve 21 facing away from the brake fluid reservoir 7 during an intake process. The hydraulic lines from the intake valve 21 and the pressure relief valve 8 each meet away from the brake fluid reservoir 7 at a first junction 24, where a main line begins.

[0028] A hydraulic line from the isolation valve 9 and a hydraulic line from the pressure supply device 6 meet at a second junction 25, which lies along a main line from the brake fluid reservoir 7 to the hydraulic brakes 4, 5. There is no valve in the hydraulic line from the pressure supply device 6 to the second junction 25. Therefore, exactly one hydraulic line leads from the pressure supply device 6 into the hydraulic circuit to the hydraulic brakes 4, 5 and to the brake fluid reservoir 7.

[0029] The braking system 1 also comprises a pressure sensor 26 which is configured to measure a braking pressure applied to the hydraulic brakes 4, 5.

[0030] Fig.Figure 2 shows a flowchart of a method according to the invention. The method for brake pressure control initially comprises the step of closing 100 the pressure reduction valve 8 and the discharge valves 12, 13 upon detection of a brake pressure request to the electrohydraulic partial brake system 2. Then, in a further step, the isolation valve 9 and the inlet valves 10, 11 are opened 110, if this is not already the case. Then, a build-up 120 of brake pressure at the hydraulic brakes 4, 5 takes place via the pressure supply device 6. A regulation 130 of the brake pressures applied to the hydraulic brakes 4, 5 (which may differ) also takes place via a partial opening and closing of the pressure reduction valve 8. The regulation 130 of the brake pressures can comprise a phased opening of the two-position relief valves 12, 13, and optionally a partial opening and closing of the inlet valves 10, 11.At the end of the brake pressure request, pressure is reduced 140 at the hydraulic brakes 4, 5 by opening the release valves 12, 13. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 2023 138 720 A1 [0002, 0005]

Claims

[1] Braking system (1) for a vehicle, comprising an electro-hydraulic partial braking system (2) and an electromechanical brake pedal (3) for communicating a braking force request by a user to the braking system (1), wherein the electro-hydraulic partial brake system (2) comprises at least one hydraulic brake (4, 5), a pressure supply device (6) and a brake fluid reservoir (7), characterized by , that the electro-hydraulic partial brake system (2) comprises a continuously adjustable pressure reduction valve (8) arranged in front of the brake fluid reservoir (7), which is designed to provide an atmospheric pressure of the brake fluid reservoir (7) for brake pressure control of the hydraulic brake (4, 5), wherein the electro-hydraulic partial brake system (2) comprises a continuously adjustable isolation valve (9) arranged between the at least one hydraulic brake (4, 5) on the one side and the pressure supply device (6) and the brake fluid reservoir (7) on the other side, which is designed to maintain a built-up brake pressure at the at least one hydraulic brake (4, 5) when the pressure supply device (6) is in a suction process for sucking brake fluid from the brake fluid reservoir (7). [2] Brake system (1) according to claim 1, wherein the isolation valve (9) and the pressure reduction valve (8) are normally open valves. [3] Brake system (1) according to one of the preceding claims, wherein the at least one hydraulic brake (4, 5) is supplied with hydraulic fluid via a normally open inlet valve (10, 11) and is connected to the brake fluid reservoir (7) via a normally closed drain valve (12, 13), wherein the inlet valve (10, 11) is continuously adjustable and the drain valve (12, 13) is a two-position valve. [4] Brake system (1) according to one of the preceding claims, wherein the brake system (1) is designed to open the pressure reduction valve (8) completely or partially in order to reduce the brake pressure during a brake pressure control. [5] Brake system (1) according to one of the preceding claims, wherein the electro-hydraulic partial brake system (2) comprises exactly one hydraulic control unit (14), wherein the hydraulic control unit (14) is designed to control the electro-hydraulic partial brake system (2) and to carry out a brake pressure control of the hydraulic brake (4, 5). [6] Braking system (1) according to one of the preceding claims, wherein the braking system (1) further comprises an electromechanical partial braking system (15), wherein the electromechanical partial braking system (15) comprises at least one electromechanical brake (16, 17) which is assigned to a different axle of the vehicle than the hydraulic brake (4, 5) of the electrohydraulic partial braking system (2). [7] Braking system (1) according to claim 6, wherein each electromechanical brake (16, 17) comprises its own brake control unit (18, 19) which is adapted to regulate the braking force or the braking torque provided by the electromechanical brake (16, 17). [8] Braking system (1) according to any one of the preceding claims, wherein the braking system (1) further comprises a regenerative partial braking system (20), wherein an electric motor of the vehicle is operable as a generator to provide a braking force for the vehicle. [9] Brake system (1) according to one of the preceding claims, wherein the electro-hydraulic partial brake system (2) comprises a suction valve (21) which is connected to the brake fluid reservoir (7) via its own connection (22) and parallel to the pressure reduction valve (8), wherein the suction valve (21) is designed as a check valve which opens when the pressure supply device (6) generates a negative pressure on the side of the suction valve (21) facing away from the brake fluid reservoir (7) during a suction process, wherein the hydraulic lines from the intake valve (21) and from the pressure reduction valve (8) each meet away from the brake fluid reservoir (7) at a first junction point (24) at which a main line begins. [10] Brake system (1) according to one of the preceding claims, wherein a hydraulic line from the isolation valve (9) and a hydraulic line from the pressure supply device (6) meet at a second node (25) which lies along a main line from the brake fluid reservoir (7) to the at least one hydraulic brake (4, 5), wherein there is no valve in the hydraulic line from the pressure supply device (6) to the second node (25). [11] Brake system (1) according to one of the preceding claims, wherein exactly one hydraulic line leads from the pressure supply device (6) into the hydraulic circuit to the at least one hydraulic brake (4, 5) and to the brake fluid reservoir (7). [12] Method for brake pressure control in a brake system (1) according to one of claims 3 to 11, comprising the steps: - Closing (100) the pressure reduction valve (8) and the drain valve (12, 13), - Opening (110) of the isolation valve (9) and the inlet valve (10, 11), - building up (120) a brake pressure at the hydraulic brake (4, 5) via the pressure supply device (6), - regulating (130) the brake pressure applied to the hydraulic brake (4, 5), wherein the regulating (130) of the brake pressure comprises partially opening and closing the pressure reduction valve (8). [13] Method according to claim 12, wherein the braking system (1) comprises a pressure sensor (26) which is arranged to measure a braking pressure applied to the hydraulic brake (4, 5), wherein the step of regulating (130) the brake pressure includes the brake pressure measured by the pressure sensor (26).

Images