Braking system for a vehicle

Abstract

Braking system for a vehicle with a master brake cylinder (2), a fluid control unit (3) and at least one wheel brake (4.1, to 4.4), wherein the fluid control unit (3) for brake pressure modulation of the at least one wheel brake (4.1 to 4.4) in at least one brake circuit (10, 20) comprises a switching valve (12, 22), a control valve (50A, 50B) and a return pump (15, 25) for each brake circuit (10, 20), wherein the control valves (50A, 50B) are each connected in a suction line between the corresponding return pump (15, 25) and the master brake cylinder (2) and limit the effective pressure at a suction side of the respective return pump (15, 25) to a predefinable maximum pressure value, wherein a first fluid port (51A, 51B) of the respective control valve (50A, 50B) is connected to the The master brake cylinder (2) and a second fluid connection (52A, 52B) of the respective control valve (50A, 50B) are coupled to the respective return pump (15, 25), characterized in thatthat a pressure-relieved port (53A, 53B) of the respective control valve (50A, 50B) is coupled to a fluid accumulator (16, 26), wherein the respective control valve (50A, 50B) comprises a longitudinally movable control piston (54) which is acted upon on the pressure-relieved side by an actuating spring (55) with a spring force and in an initial position completely opens a fluid connection between the first fluid port (51A, 51B) and the second fluid port (52A, 52B) with a maximum flow cross-section, wherein a pressure building up at the first fluid port (52A, 52B) moves the control piston (54) against the spring force of the actuating spring (55) in the direction of the pressure-relieved port (53A, 53B), wherein the flow cross-section of the fluid connection between the first fluid port (51B) and the second fluid port (52B) 52B) can be reduced by the movement of the control piston (54), wherein the fluid connection between the first fluid port (51A,51B) and the second fluid port (52A, 52B) is completely interrupted by a stop position at the specified maximum pressure value at the second fluid port (52A, 52B), and wherein the spring force of the actuating spring (55) moves the control piston (54) from the stop position back towards the starting position when the current pressure at the second fluid port (52A, 52B) falls below the maximum pressure value.

Description

State of the art

[0001] The invention relates to a braking system for a vehicle according to the preamble of independent claim 1.

[0002] Vehicle braking systems are known from the prior art that include various safety systems, such as an anti-lock braking system (ABS), an electronic stability program (ESP), etc., and perform various safety functions, such as an anti-lock braking function, traction control (ASR), etc.

[0003] For example, German patent DE 10 2007 038 397 A1 describes a braking system for a vehicle with a master brake cylinder, a fluid control unit, and at least one wheel brake. For brake pressure modulation in at least one brake circuit, the fluid control unit comprises a changeover valve, a suction valve, and a return pump for each brake circuit. Furthermore, the fluid control unit has a spool valve for each brake circuit, which is integrated into a suction line between the return pump and the master brake cylinder and limits the effective pressure on one suction side of the return pump to a predefinable maximum pressure value. A first fluid port of each spool valve is connected to the master brake cylinder, and a second fluid port of each spool valve is connected to the respective return pump. A pressure-balanced port of each control valve is connected to the atmosphere.Thus, the control valve in the vehicle brake system protects the recirculation pump from increased pressure on the suction side.

[0004] For example, German patent DE 10 2008 002 539 A1 describes a control valve for a vehicle braking system and a corresponding vehicle braking system. The described vehicle braking system comprises a master brake cylinder, a fluid control unit, and at least one wheel brake. The fluid control unit, for modulating the brake pressure of the at least one wheel brake in at least one brake circuit, includes a changeover valve, a suction valve, and a return pump. The suction valve of the at least one brake circuit is designed as a control valve and is connected in series to a suction line between the corresponding return pump and the master brake cylinder. A first fluid port of each control valve is connected to the master brake cylinder, and a second fluid port of each control valve is connected to the respective return pump. A pressure-balanced port of each control valve is connected to atmospheric pressure.Thus, the control valve in the vehicle brake system takes over the function of the intake valve and additionally protects the return pump from increased pressure on the suction side. Disclosure of the invention

[0005] In contrast, the brake system according to the invention for a vehicle with the features of independent claim 1 has the advantage that the connection of the piston and the pressure-relieved connection is not to the atmosphere but to a storage chamber of a fluid accumulator in the brake system. By connecting to the fluid accumulator in the brake system, leakage to the outside in the event of a piston seal failure can be prevented, and failure of the corresponding brake circuit can be avoided. The storage chamber can be emptied without actuating the solenoid valves and the pump.

[0006] Furthermore, the control valve in the vehicle's brake system advantageously protects the return pump from increased suction pressure. By limiting the effective pressure on the suction side of the return pump, wear, friction, and extrusion of the seals within the pump can be reduced. This also advantageously reduces external leakage, increases efficiency, and significantly extends the pump's service life. In a gear pump design, an expensive, complex, and high-pressure-resistant shaft seal is avoided, and a cost-effective shaft seal can be used.

[0007] Embodiments of the present invention provide a braking system for a vehicle comprising a master brake cylinder, a fluid control unit, and at least one wheel brake. For brake pressure modulation of the at least one wheel brake in at least one brake circuit, the fluid control unit includes a changeover valve, a control valve, and a return pump for each brake circuit. The control valves are each connected in series in a suction line between the corresponding return pump and the master brake cylinder and limit the effective pressure on one suction side of the respective return pump to a predefinable maximum pressure value. A first fluid port of each control valve is connected to the master brake cylinder, and a second fluid port of each control valve is connected to the respective return pump. Furthermore, a pressure-balanced port of each control valve is connected to a fluid accumulator.Each control valve comprises a longitudinally movable control piston, which is acted upon by a spring force on the pressure-relieved side and, in its initial position, completely opens a fluid connection between the first fluid port and the second fluid port with a maximum flow cross-section. In this process, pressure building up at the first fluid port moves the control piston against the spring force of the actuating spring towards the pressure-relieved port, thereby reducing the flow cross-section of the fluid connection between the first and second fluid ports.In this process, the fluid connection between the first fluid port and the second fluid port is completely interrupted by a stop position at the specified maximum pressure value at the second fluid port, whereby the spring force of the actuating spring moves the control piston from the stop position back towards the starting position when the current pressure at the second fluid port falls below the maximum pressure value.

[0008] The measures and further developments listed in the dependent claims enable advantageous improvements to the braking system for a vehicle specified in independent claim 1.

[0009] A particular advantage is that the pressure-relieved ports of the control valves can each be connected to a fluid accumulator via a fluid channel. These fluid channels can, for example, be integrated into a hydraulic block of the brake system.

[0010] In an advantageous embodiment of the brake system according to the invention, the respective control valve can be connected in parallel or in series with a suction valve in the suction line between the corresponding return pump and the master brake cylinder.

[0011] In an alternative advantageous embodiment of the brake system according to the invention, the respective control valve can additionally perform the function of an intake valve.

[0012] An embodiment of the invention is shown in the drawings and is explained in more detail in the following description. In the drawings, identical reference numerals denote components or elements that perform the same or analogous functions. Brief description of the drawings Fig. Figure 1 shows a schematic block diagram of an embodiment of a vehicle braking system according to the invention. Fig. Figure 2 shows a schematic sectional view of a control valve for the vehicle braking system according to the invention. Fig. 1. Embodiments of the invention

[0013] As from Fig. As can be seen in Figure 1, the illustrated embodiment of a brake system 1 according to the invention for a vehicle comprises a master brake cylinder 2, a fluid control unit 3 (shown in dashed lines), and four wheel brakes 4.1 to 4.4, each having an associated wheel brake cylinder (not shown). Two of the four wheel brakes 4.1 to 4.4 are assigned to each brake circuit 10, 20, with each brake circuit 10, 20 being connected to the master brake cylinder 2. Thus, a first wheel brake 4.1, which is arranged, for example, on the left side of a vehicle's rear axle, and a second wheel brake 4.2, which is arranged, for example, on the right side of a vehicle's front axle, are assigned to a first brake circuit 10, and a third wheel brake 4.3, which is arranged, for example, on the right side of the vehicle's front axle, and a fourth wheel brake 4.4 are assigned to a first brake circuit 10.The four brakes, which are located, for example, on the left side of a vehicle's rear axle, are assigned to a second brake circuit 20. Each wheel brake 4.1 to 4.4 is assigned an inlet valve 13.1, 13.2, 23.1, 23.2 and an outlet valve 14.1, 14.2, 24.1, 24.2, whereby pressure can be built up in the corresponding wheel brake 4.1 to 4.4 via the inlet valves 13.1, 13.2, 23.1, 23.2, and whereby pressure can be released in the corresponding wheel brake 4.1 to 4.4 via the outlet valves 14.1, 14.2, 24.1, 24.2.

[0014] As from Fig. As can be seen further in Figure 1, the first brake circuit 10 has a first intake valve 11, a first switching valve 12, a first fluid accumulator 16, and a first return pump 15. The second brake circuit 20 has a second intake valve 21, a second switching valve 22, a second fluid accumulator 26, and a second return pump 25, wherein the first and second return pumps 15, 25 are driven by a common electric motor 35 in the illustrated example. Furthermore, the fluid control unit 3 includes a sensor unit 30 for determining the current brake pressure. The fluid control unit 3 uses the first switching valve 12, the first intake valve 11, and the first return pump 15 for brake pressure modulation in the first brake circuit 10, and the second switching valve 22, the second intake valve 21, and the second return pump 25 for brake pressure modulation in the second brake circuit 20.

[0015] The return pumps 15, 25 of the two brake circuits 10, 20 can be designed, for example, as piston pumps or gear pumps. During ESP control, a brake pressure of up to 140 bar can be established through the open intake valves 11 and 21, respectively. This pressure is applied to the suction side of the corresponding return pump 15, 25 when the system needs to be braked in. Even in a partially active system state, the return pump 15, 25 can be subjected to a suction pressure of up to 140 bar. Furthermore, a pre-pressure can occur on the suction side of the return pump 15, 25 when the pressure from the master brake cylinder 2 is routed to the return pumps 15, 25 via the open changeover valves 12 and 22, respectively, and then increased by the corresponding return pump 15 or 25 to the wheel pressure required for control.In the case of return pumps 15, 25 being designed as piston pumps, this high pressure acting on an eccentric-side seal of the return pump 15, 25 can lead to very high wear, extrusion, and consequently, increased leakage. If a gear pump is used as the return pump 15, 25, this high pressure stresses the shaft seals of the return pumps 15, 25, which can lead to increased friction and, as with the piston pump, to increased wear of the seals. High-pressure-resistant shaft seals are very expensive.

[0016] As from Fig. As can be seen further in Figure 1, to limit the effective pressure on the suction side of the corresponding return pump 15, 25, a control valve 50A, 50B is connected in series in a suction line between the respective return pump 15, 25 and the master brake cylinder 2, so that the respective return pump 15, 25 is connected to the master brake cylinder 2 on the suction side via the control valve 50A, 50B, which in the illustrated embodiment takes over the function of the intake valve 11, 21. In alternative embodiments of the brake system according to the invention for a vehicle, not shown, the control valves 50A, 50B can be connected in parallel or in series with the respective intake valve 11, 21 in the suction line and limit the effective pressure on the suction side of the return pump 15, 25 to the predefinable maximum pressure value.

[0017] In the illustrated embodiment, the first control valve 50A is in Fig. 1 and Fig. 2 is shown in the open initial state during a suction operation of the first return pump 15, and the second control valve 50B is in Fig. 1 in the closed stop position and in Fig. 2 shown in the open initial state.

[0018] As from Fig. 1 and Fig. As can be seen in Figure 2, the control valves 50A, 50B each have a first fluid connection 51A, 51B coupled to the master brake cylinder 2 and a second fluid connection 52A, 52B coupled to the respective pump 15, 25. A pressure-balanced connection 53A, 53B of each control valve 50A, 50B is coupled to a fluid accumulator 16, 26. This connection to the fluid accumulator 16, 26 in the brake system 1 advantageously prevents external leakage in the event of a piston seal failure in the control valve 50A, 50B and avoids failure of the corresponding brake circuit. In the illustrated embodiment, the pressure-balanced connections 53A, 53B of the control valves 50A, 50B are each connected to a fluid accumulator 16, 26 via a fluid channel 5A, 5B.

[0019] As from Fig. 1 and Fig. As can be seen further in Figure 2, the control valves 50A, 50B in the illustrated embodiment each comprise a valve body 60 with a sealing seat 61 and a sealing element 59 coupled to a control piston 54. A sealing area 59.2 of the sealing element 59 interacts with the sealing seat 61 of the valve body 60 to limit the effective pressure at the pump connection 52A, 52B to a predefinable maximum pressure value. In the illustrated embodiment, the valve body 60 is tightly riveted to a valve wall at a riveting area 62, and an effective diameter 58.1 of the control piston 54 is larger than an effective diameter 58.2 of the sealing element 59. This advantageously allows for an improvement in control accuracy and / or a reduction in the control pressure required to actuate the control valve. The longitudinally movable control piston 54 is subjected to a spring force on the pressure-relieved side by an adjusting spring 55 and outputs in the Fig. In the initial position shown in Figure 2, a fluid connection between the master brake cylinder connection 51A, 51B and the pump connection 52A, 52B is completely free.

[0020] As from Fig. 1 and Fig. As can be seen further in Figure 2, the control piston 54 is coupled to the sealing element 59 by a pin 57. The control piston 54 and the sealing element 59 are arranged on opposite sides of the valve body 60; that is, in the illustrated embodiment, the control piston 54 is located to the left of the valve body 60, and the sealing element 59 is located to the right of the valve body 60. The pin 57 is guided through a flow opening in the valve body 60 to couple the control piston 54 to the sealing element 59. The sealing element 59 is placed onto the pin 57 and is sealed at the rear by a sealing lip 59.1, for example, made of plastic. At the front, the sealing element 59 has a radial clearance 59.3 relative to the pin 57 to compensate for manufacturing tolerances and to ensure reliable closure of the control valve.In the illustrated embodiment, the pin 57 is engaged at one end by means of detent lugs in a blind bore in the control piston 54 and is thus firmly connected to the control piston 54, which is sealed against a first valve wall 50.1 by means of a first sealing ring 56.1. Alternatively, the pin 57 can be pressed into the blind bore in the control piston 54 at one end and thus firmly connected to the control piston 54. At the other end, the pin 57 has a collar 57.1 against which a second sealing ring 56.2 rests. This second sealing ring is axially pre-tensioned by a spring element 59.4, which is supported on the sealing element 59, and seals the pin 57 against a second valve wall 50.2.

[0021] During an ABS intervention, the first diameter 58.1 of the control piston 54 is subjected to a pressure of approximately 2 bar from the side of the master brake cylinder connection 51A, 51B, which moves the control piston 54 against the spring force of the actuating spring 55 towards the pressure-relieved connection 53A, 53B and thereby pulls the sealing element 59 with the second diameter 58.2 via the pin 57, until the sealing area 59.2 of the sealing element 59, designed as a sealing cone, rests in a stop position against the sealing seat 61 of the valve body 60. When the maximum pressure value of approximately 2 bar and the corresponding stop position are reached, the sealing area 59.2 of the sealing element 59, designed as a sealing cone, seals in the sealing seat 61 of the valve body 60, and the fluid connection between the master brake cylinder connection 51A, 51B and the pump connection 52A, 52B is completely interrupted, with the fluid control unit 3 performing ABS control in this state.Since the diameter of the sealing area 59.2 and the diameter of the sealing seat 61 can be designed to be the same size, a higher pressure of the master brake cylinder 2 can be maintained after closing the control valve 50A, 50B, without the high pressure reaching the inlet of the return pump 25.

[0022] During a partially active state of the vehicle brake system 1, the piston 54 of the first control valve 50A, 50B is pressurized from the master cylinder port 51A, 51B. This pressure moves the piston 54 against the spring force of the actuating spring 55 towards the pressure-relieved port 53A, 53B, thereby reducing the fluid connection between the master cylinder port 51A, 51B and the pump port 52A, 52B by the corresponding movement of the sealing element 59. Upon reaching the maximum pressure, the piston 54 is in the corresponding stop position, in which the connection between the master cylinder port 51A, 51B and the pump port 52A, 52B is completely interrupted by the sealing element 59. This ensures that the pressure in the line to the master brake cylinder 2 can build up without allowing the pressure in the suction side of the return pump 15, 25 to rise above the specified maximum pressure value.If the current pressure at pump connection 52A, 52B' is reduced, for example by the return pump 15, 25 drawing in fluid, the spring force of the actuating spring 55 moves the piston 54 from its stop position towards its initial position, thereby re-opening the connection between the master cylinder connection 51A, 51B and the pump connection 52A, 52B until the pressure of approximately 2 bar is reached by actuation of the master cylinder 2. The return pump 15, 25 thus always maintains a pre-pressure but remains protected against the high pressure of the master cylinder 2. In the ESP (Electronic Stability Program) case, the control valve 50A, 50B remains open, and the brake fluid can be drawn in unhindered by the return pump 15, 25. Fig. Reference numeral 57.2 denotes the maximum stroke of the sealing element 59.

[0023] Of course, instead of the described embodiment of the control valve 50A, 50B, other suitable control valves can also be used in the brake system according to the invention, as long as their pressure-relieved connections are coupled to a fluid accumulator in order to prevent leakage to the outside in the event of failure of the piston seal of the control valve.

Claims

[1] Braking system for a vehicle with a master brake cylinder (2), a fluid control unit (3) and at least one wheel brake (4.1, to 4.4), wherein the fluid control unit (3) for brake pressure modulation of the at least one wheel brake (4.1 to 4.4) in at least one brake circuit (10, 20) comprises a changeover valve (12, 22), a control valve (50A, 50B) and a return pump (15, 25) for each brake circuit (10, 20), wherein the control valves (50A, 50B) are each connected in a suction line between the corresponding return pump (15, 25) and the master brake cylinder (2) and limit the effective pressure at a suction side of the respective return pump (15, 25) to a predefinable maximum pressure value, wherein a first fluid port (51A, 51B) of the respective control valve (50A, 50B) with the master brake cylinder (2) and a second fluid connection (52A, 52B) of the respective control valve (50A, 50B) is coupled to the respective return pump (15, 25), characterized by, that a pressure-relieved port (53A, 53B) of the respective control valve (50A, 50B) is coupled to a fluid accumulator (16, 26), wherein the respective control valve (50A, 50B) comprises a longitudinally movable control piston (54) which is acted upon on the pressure-relieved side by an actuating spring (55) and in an initial position completely opens a fluid connection between the first fluid port (51A, 51B) and the second fluid port (52A, 52B) with a maximum flow cross-section, wherein a pressure building up at the first fluid port (52A, 52B) moves the control piston (54) against the spring force of the actuating spring (55) in the direction of the pressure-relieved port (53A, 53B), wherein the flow cross-section of the fluid connection between the first fluid port (51A, 51B) and the second fluid port (52B, 52B) can be reduced by the movement of the control piston (54), wherein the fluid connection between the first fluid port (51A,51B) and the second fluid port (52A, 52B) is completely interrupted by a stop position at the specified maximum pressure value at the second fluid port (52A, 52B), and wherein the spring force of the actuating spring (55) moves the control piston (54) from the stop position back towards the starting position when the current pressure at the second fluid port (52A, 52B) falls below the maximum pressure value. [2] Braking system according to claim 1, characterized by , that the pressure-relieved ports (53A, 53B) of the control valves (50A, 50B) are each connected to a fluid accumulator (16, 26) via a fluid channel (5A, 5B). [3] Braking system according to claim 1 or 2, characterized by , that the respective control valve (50A, 50B) is connected in parallel or in series to a suction valve in the suction line between the corresponding return pump (15, 25) and the master brake cylinder (2). [4] Braking system according to claim 1 or 2, characterized by, that the respective control valve (50A, 50B) performs the function of an intake valve.

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