EP1904353A1

EP1904353A1 - Braking system for a motor vehicle

Info

Publication number: EP1904353A1
Application number: EP06762244A
Authority: EP
Inventors: Benedikt Ohlig
Original assignee: Lucas Automotive GmbH
Current assignee: ZF Active Safety GmbH
Priority date: 2005-07-15
Filing date: 2006-06-28
Publication date: 2008-04-02
Also published as: US8047618B2; WO2007009561A1; DE102005033258B3; US20090108670A1; CN101223065A

Abstract

The invention relates to a braking system (10) for a motor vehicle having a hydraulic circuit (12) for generating a braking force, the hydraulic circuit (12) having a pressure source (50), for generating a hydraulic pressure, and a pressure accumulator (58), it being possible for the pressure accumulator (58) of the hydraulic circuit (12) to be supplied on demand with hydraulic fluid from a pressure side of the pressure source (50). In said braking system, it is provided that the pressure accumulator (58) can be fluidically coupled to, and decoupled from, a suction side of the pressure source (50) by means of a multiple-way valve (64), in particular a two-way valve, which is connected in between and can be actively actuated.

Description

Brake system for a motor vehicle

The invention relates to a brake system for a motor vehicle having a hydraulic circuit for generating a braking force, wherein the hydraulic circuit comprises a pressure source for generating a hydraulic pressure and a pressure accumulator, wherein the pressure accumulator of the hydraulic circuit can be supplied with hydraulic fluid from a pressure side of the pressure source as needed.

Such a brake system is already known from the prior art. Thus, document DE 103 18 850 A1 shows a brake system in which the pressure accumulator can be charged with hydraulic fluid as a function of the servo pressure prevailing in the servo pressure circuit. The accumulator serves to compensate for pressure fluctuations during a braking operation. This prior art provides that the pressure accumulator is essentially only supplied with hydraulic fluid when the hydraulic pressure provided by the pressure source is freely available and does not have to be used elsewhere, for example in the context of a braking operation. However, this arrangement has the disadvantage that the pump must be made relatively powerful, since the voltage applied to the pump pressure difference is relatively large. Namely, the pump has to pump hydraulic fluid from the pressureless fluid reservoir into the servo pressure circuit which is under relatively high pressure. Furthermore, the pump must be able to react very dynamically due to the relatively high pressure difference between the suction side and the pressure side just at the beginning of braking. The correspondingly powerful auszustegende pump leads to increased costs of the brake system. In addition, it comes also when driving the pump to relatively high loads on the electrical system.

A similar arrangement is further disclosed in document GB 2 132 294 A. Also in this document promotes the relatively powerful trainees pump hydraulic fluid from the unpressurized pressure accumulator in the under relatively high pressure fluid system. This results in the same disadvantages as described above for the brake system according to DE 103 18 850 Al.

For further prior art is generally referred to the documents DE 195 42 656 Al, DE 103 37 511 Al and DE 103 11 060 Al, all of which show braking systems in which a pressure accumulator is coupled or coupled only with the pressure side of the pressure source. Finally, document DE 38 14 045 A1 shows a brake system with a fluid intermediate store, wherein the hydraulic fluid which is temporarily stored in this largely pressure-free manner is permanently available on the suction side of the pump.

It is an object of the present invention to provide a brake system of the type described, which can provide a relatively high hydraulic fluid pressure at low power and thus cost-trained pressure source already at the beginning of braking.

This object is achieved by a brake system of the type described, in which it is provided that the pressure accumulator with a suction side of the pressure source via an intermediate actively controllable multi-way valve, in particular a two-way solenoid valve, fluidly coupled and decoupled from this.

Due to the possibility according to the invention, the pressure accumulator with the suction side of the

Pressure source, in particular a motor-driven pump to couple by an actively controllable multi-way valve or to decouple from this, the stored in the pressure accumulator fluid pressure can be utilized to reduce the voltage applied to the pump pressure difference. As a result, the suction side of the pressure source is acted upon by a pressure corresponding to the boost pressure of the pressure accumulator hydraulic pressure substantially without pressure loss, so that the pressure difference occurring in the context of braking at the pressure source is greatly reduced. Overall, this makes the pressure pump easier to activate, so that they also react faster and can achieve a relatively high pressure level in a shorter time. Furthermore, it is possible to use a pressure source or pump designed with a weaker motor drive, which is cheaper and less heavily loaded on the on-board power supply than in the embodiments according to the prior art.

A further development of the invention provides, with regard to the design of the brake system, that it has a master brake cylinder in which a primary piston for generating a brake pressure in a hydraulic brake circuit can be displaced in accordance with actuation of a brake pedal under the effect of the hydraulic circuit. For example, it may be provided that the primary piston is displaced purely hydraulically by interaction with the hydraulic circuit without direct coupling with a force input member, wherein the hydraulic circuit serves as a servo pressure circuit. However, there are also alternative embodiments conceivable in which the hydraulic circuit is otherwise used for braking force generation or at least for brake booster. A development of the invention provides that the pressure accumulator is fluidly connected or connected via a feed line to the pressure side of the pressure source and via a discharge line to the master cylinder. About the feed line, the pressure accumulator can be charged optionally, whereas on the separate discharge line discharging the pressure accumulator to provide its charge pressure for braking force generation on the master cylinder is possible. This means that the charge pressure of the pressure accumulator can be used both on the suction side of the pump and for generating the braking force on the master cylinder.

Furthermore, it can be provided according to the invention that the feed line has a fluid supply control device, in particular an actively activatable multiway valve, for controlling the supply of hydraulic fluid to the pressure accumulator. This measure makes it possible to always supply the pressure accumulator with hydraulic fluid from the pressure source only if the fluid pressure emanating from the pressure source does not have to be otherwise used for a braking operation. Otherwise, the Fluidzufuhrsteuereinrich- device fluidly separates the pressure accumulator from the pressure source. It is also conceivable to briefly open the fluid supply control device during a braking operation in order to temporarily recharge the pressure accumulator.

The brake system can be controlled by various parameters. Preferably, at least one pressure sensor arranged in the hydraulic circuit is provided which detects the hydraulic pressure applied in the hydraulic circuit. In a further development of the invention, a plurality of pressure sensors may be provided, for example, additional pressure sensors on the pressure accumulator, on the suction side, as well as on the Hydraulikfluidzuführleitung to the master cylinder. In this context, it can further be provided that the fluid supply control device can be controlled in accordance with the hydraulic pressure detected by the at least one pressure sensor.

A development of the invention provides that the discharge line is formed with a check valve opening in the discharge direction. This ensures that whenever the hydraulic pressure from the accumulator is required for a braking operation, this can also be provided without delay.

Furthermore, it can be provided according to the invention that a hydraulic fluid supply line leading away from the pressure side of the pressure source is formed with a non-return valve which blocks a backflow of hydraulic fluid to the pressure side of the pressure source. These measures prevents the hydraulic pressure from the pressure accumulator acting as a back pressure from affecting the function of the pressure source, in particular the motor-driven pump.

Furthermore, according to the invention, it can be provided that the hydraulic circuit has a further actively activatable multi-way valve, in particular a two-way solenoid valve, interposed between the master brake cylinder and a hydraulic fluid reservoir. With such an actively controllable multi-way valve, which is arranged in a corresponding bypass channel, can be selectively dissipate hydraulic fluid from the master cylinder to the hydraulic fluid reservoir.

In addition, the hydraulic circuit and a between the master cylinder and the pressure accumulator leading to the feed line interposed further actively controllable multi-way valve, in particular a two-way solenoid valve having. This allows a control of the hydraulic fluid supply from the pressure source or the accumulator to the master cylinder.

The two above-mentioned further actively controllable multi-way valves thus allow a targeted control of the pressure build-up and pressure reduction in the Hauptbremszy- by active control and optional switching between their respective open and closed position.

A development of the invention provides that the primary piston is mechanically decoupled from the brake pedal.

The invention is explained below by way of example with reference to the accompanying figure, which represents a schematic overview of an inventive brake system.

In the figure, a brake system according to the invention is shown and generally designated 10. This includes a servo pressure providing hydraulic circuit 12 and a brake cylinder assembly 14.

The brake cylinder assembly 14 is composed of a master cylinder 16, in which a primary piston 18 is guided displaceably. In the master cylinder 16, a secondary piston 20 is also guided displaceably and mechanically coupled to the primary piston 18 via a spring arrangement. The primary piston 18 closes with the master cylinder 16 and the secondary piston 20, a primary pressure chamber 22 a. The secondary piston 20 includes a secondary pressure chamber 24 with the master cylinder 16. The primary pressure chamber 22 and the secondary pressure chamber 24 are fluidly coupled via respective feed channels to a hydraulic fluid reservoir 26 for supplying hydraulic fluid in the idle state shown in FIG. Furthermore, the primary pressure chamber 22 and the secondary pressure chamber 24 are fluidically coupled to a brake system 28, which can bring about a deceleration of the wheels of a motor vehicle in a manner known per se.

The brake cylinder assembly 14 further includes a pedal simulation device 30. Specifically, the pedal simulation device 30 includes a force input member 32 mechanically coupled to a brake pedal and force transmittingly connected to a power piston 34. The working piston 34 is displaceable in a piston chamber 36, wherein it limits working chambers within the piston chamber 36 on both sides. By a displacement of the working piston 34 within the piston chamber 36, a fluid contained in the Arbeitskammem on both sides of the working piston 34, in particular gas, displaced via a throttle device 38 from one to the other working chamber and thereby generates a resistance to movement of the force input member 32. In addition to the pneumatically generated resistance acts on the force input element 32, a resistor resulting from a simulation spring assembly 40. This simulation spring assembly 40 is constructed in multiple stages, d. H. it has a spring of lesser spring rate and a spring of increased spring rate which is stepped, i. can be compressed with progressive spring characteristic.

Each pedal operation, d. H. Each displacement of the force input member 32 is detected via a position sensor 42, the position sensor 42 outputs a position signal to an electronic control unit 44, by means of which the presence of a pedal operation can be determined.

The brake system 10 according to Figure 1 is designed such that a pedal operation, and a resulting displacement of the force input element 32 is not mechanically on the

Primary piston 18 is transmitted, but rather dissipates the energy applied in the pedal operation in the brake system 10. In order to carry out the braking operation, an hydraulic pressure is generated in an actuating pressure chamber 46 by means of the hydraulic circuit 12 in accordance with a detected brake pedal actuation which displaces the primary piston 18 and, as a consequence, the secondary piston 20 and thereby for a pressure build-up in the

Primary pressure chamber 22 and in the secondary pressure chamber 24 provides. The primary piston 18 is in normal operation of the brake system 10 thus completely decoupled from the force input element 32 mechanically.

In the following, the structure of the hydraulic circuit 12 will be explained. The hydraulic circuit 12 is supplied with hydraulic fluid from the hydraulic fluid reservoir 26. This is conveyed via a supply line 48 from a pump 50, which is driven by a motor 52, from the hydraulic fluid reservoir 26. The pump 50 is fluidically coupled to the actuating pressure chamber 46 via a hydraulic fluid supply line 54. From the hydraulic fluid supply line 54, starting from the pump 50, a few branches start. A first branch 56 is a discharge line coupled to a pressure accumulator 58. In the discharge line 56, a check valve 60 is provided, which allows a flow from the pressure accumulator 58 via the discharge line 56 into the Hydraulikfluidzuführ- line 54. Furthermore, the discharge line 56 has a return branch 62, which connects the pressure accumulator 58 with the suction side of the pump 50.

In the return branch 62, an electromagnetically controllable two-way valve 64 is arranged, which is actuated via the electronic control unit 44. The pressure accumulator 58 is also connectable via a further two-way electromagnetic valve 66 via a feed line 68 with the Hydraulikfluidzuführleitung 54. Between the discharge line 56 and the pump 50, a further check valve 70 is arranged in the Hydraulikfluidzuführleitung 54 which blocks a return flow of hydraulic fluid to the pressure side of the pump 50.

Subsequent to the feed line 68, a further electromagnetically controllable two-way valve 72 is furthermore provided in the hydraulic fluid supply line 54, which completely blocks the hydraulic fluid supply line 54 in its rest position. Between the actuating pressure chamber 46 and the two-way valve 72, a bypass passage 74 is also provided, which connects the Hydraulikfluidzuführleitung 54 with the supply line 48. Also in the bypass channel 74, a two-way valve 76 is provided, which is opened in its rest position and electromagnetically controlled via the electronic control unit 44.

For the sake of completeness, it should be pointed out that a check valve 78 is also provided in the supply line 48, which prevents a return flow of hydraulic fluid from the pressure accumulator 58 and from the suction side of the pump 50 to the hydraulic fluid accumulator 26. In addition, in the hydraulic fluid supply line 54, a pressure sensor 80 is provided, which is also coupled to the electronic control unit 44, so that a control of the individual actively controllable two-way valves and the pump 52 based on the detected pressure is possible.

The hydraulic circuit 12 operates as follows: First, the pressure accumulator 58 is filled by activating the pump 50 and opening the control valve 66 so that it is put in a "standby state". For example, the pressure accumulator 58 provides a pressure of 60 bar in the charged state. If braking is now initiated in this standby state as a result of an actuation of the brake pedal by the driver, the motor 52 is controlled in accordance with the control of the electronic control unit 44, which motor drives the pump 50. This promotes from the hydraulic fluid reservoir 26 hydraulic fluid in the Hydraulikfluidzuführleitung 54. About the Hydraulikfluidzuführleitung 54, the actuating pressure chamber 46 is charged with hydraulic fluid, so that builds up in this pressure, which causes the primary piston 18 without mechanical coupling of force input element 32 and primary piston 18 displaced to the left in the figure under the action of the built-up in the actuating chamber 56 hydraulic pressure. As a result, a hydraulic pressure builds up in the primary pressure chamber 22 and under displacement of the secondary piston 20 in the secondary pressure chamber 24.

The arrangement of the pressure accumulator 58 in combination with the two-way valve 64 disposed in the return branch 62, the two-way valve 64 and the check valve 78 has the purpose that when a brake pedal operation, the two-way valve 64 can be opened from its closed rest position, so that the stored in the pressure accumulator 58 Hydraulic pressure on the one hand via the open two-way valve 64 and the return branch 62 on the suction side of the pump 50 is present and on the other hand via the discharge line 56 and the check valve 60 in the Hydraulikfluidzuführleitung 54 is available. This has the consequence that the suction side of the pump 50 is acted upon by a pre-pressure and that the hydraulic pressure from the pressure accumulator 58 also rests equally in the Hydraulikfluidzuführleitung 54. Thus, in the case of a brake operation in which the two-way valve 72 is switched to its flow position shown in the figure, the pump 50 merely has to build up the differential pressure resulting from the difference between the desired effective pressure required to achieve the requested braking effect in the actuating pressure chamber 46 and the charge pressure stored in the accumulator 58 results. The charge pressure stored in the pressure accumulator 58 can therefore be used without delay to act on the actuating pressure chamber 46. However, it is also used as a pre-pressure on the suction side of the pump 50, so that these with relatively little additional

Drive power can build up a relatively high total effective pressure in the actuating pressure chamber 46. In other words, by using the boost pressure in the Pressure accumulator 58 can be achieved on the suction side of the pump 50, that the motor 52 of the pump can be designed relatively low performance and beyond relatively low electrical power is required to build the required target differential pressure in the actuating pressure chamber 46.

After completion of the braking, the two-way valve 72 is switched to its closed position (rest position) and the two-way valve 76 in its open position (rest position). The pressure built up in the actuating pressure chamber 46 can then dissipate via the Hydraulikfluidzuführleitung 54 and the bypass channel 74, wherein hydraulic fluid finally flows through the supply line 48 into the fluid reservoir 26.

In the passive state of the brake system 10, the two-way valves 64 and 72 remain in their rest position and thus remain closed. The valve 66, which is closed in its rest position, may be temporarily opened to recharge the accumulator 58 via the then or temporarily activated pump 50. The charging process can be monitored via the pressure sensor 80 and ended in time.

It should also be noted that in the braking operation by selectively opening and closing the two-way valves 72 and 76, the pressure in the actuating pressure chamber 46 can be selectively increased and reduced. The entire control of all two-way valves is based on the pressure monitored by the pressure sensor 80 pressure via the electronic control unit 44th

The inventive arrangement of the pressure accumulator 58 can thus achieve that a relatively weak motor 52 can be used for the pump 50. Since the pump power according to the relationship

Pump = V * Δp,

where P pump is the pump power, V is the delivered fluid volume and Δp is the differential pressure between suction side and pressure side,

directly dependent on the pressure difference applied to the pump, the utilization of the charge pressure in the pressure accumulator on the suction side of the pump results in a significantly reduced required pump capacity. The accumulator can temporarily be recharged during braking by switching the valve 72 in its blocking position and opening the valve 66 when the pump 50 continues to run. Furthermore, the pressure gradient dynamics at the beginning of the braking can be improved by the arrangement of the pressure accumulator 58, since the pressure stored in the pressure accumulator 58 pressure can be applied via the return line 62 with open two-way valve 64 to the suction side of the pump and thus the brake system - Low required pressure difference between the suction side and the pressure side of the pump - can react faster. This is especially noticeable at the beginning of braking when pressure peaks have to be reached.

If it is not necessary to increase the effective pressure or the pressure gradient dynamics, then the invention has the advantage in each case that a smaller, less powerful and thus more cost-effective drive motor can be used. In addition, the electrical system load is also lower due to the low required electrical power of the engine.

It should be noted that the above-mentioned check valves can be replaced in individual cases by actively controllable multi-way valves.

Claims

claims

1. brake system (10) for a motor vehicle with a hydraulic circuit (12) for

5 generating a braking force, wherein the hydraulic circuit (12) has a pressure source (50) for generating a hydraulic pressure and a pressure accumulator (58), wherein the pressure accumulator (58) of the hydraulic circuit (12) as required with hydraulic fluid from a pressure side of the pressure source (50) is chargeable, characterized in that the pressure accumulator (58) with a suction side of the pressure source (50) via an intermediate actively controllable multi-way valve (64), in particular a two-way solenoid valve, fluidly coupled and decoupled from this.

2. Brake system (10) according to claim 1, characterized i5 by a master cylinder (16) in which in accordance with an operation of a brake pedal under the action of the hydraulic circuit (12) a primary piston (18) for generating a brake pressure in a hydraulic brake circuit is displaceable ,

20 3. brake system (10) according to claim 2, characterized in that the pressure accumulator (58) via a feed line (68) to the pressure side of the pressure source (50) and via a discharge line (56) to the master cylinder (16) fluidly connectable or connected is.

25. The brake system (10) according to claim 3, characterized in that the feed line (68) has a Fluidzufuhrsteue- reinrichtung (66), in particular an actively controllable multi-way valve (66) for controlling the supply of hydraulic fluid to the pressure accumulator (58) ,

30 5. brake system (10) according to any one of the preceding claims, characterized by at least one in the hydraulic circuit (12) arranged pressure sensor (80) for detecting the hydraulic pressure.

6. Brake system (10) according to claim 4 and 5,

35, characterized in that the fluid supply control device (66) in accordance with the of the at least one pressure sensor (80) detected hydraulic pressure can be controlled.

7. Brake system (10) according to any one of claims 3 to 6, characterized in that the discharge line (56) is formed with an opening in the discharge direction check valve (60).

5

8. Brake system (10) according to any one of the preceding claims, characterized in that from the pressure side of the pressure source (50) leading away Hydraulikfluidzuführleitung (54) with a check valve (70) is formed, the backflow of hydraulic fluid to the pressure side of the pressure source ( 50) lo blocked.

9. brake system (10) according to any one of claims 2 to 8, characterized in that the hydraulic circuit (12) between the master cylinder (16) and a hydraulic fluid reservoir (26) interposed i5 further actively controllable multi-way valve (76), in particular a two-way Way solenoid valve, comprising.

10. Brake system (10) according to claim 3 and a further of the preceding claims,

20, characterized in that the hydraulic circuit (12) between the master brake cylinder (16) and the feed line (68) interposed further actively controllable multi-way valve (72), in particular a two-way solenoid valve.

25 11. brake system (10) according to one of the preceding claims, characterized in that the pressure source has a motor (52) driven pump (50).

12. Brake system (10) according to one of the preceding claims,

3o characterized by a control device (44) for evaluating detected hydraulic pressures and for driving actively controllable components.

13. Brake system (10) according to any one of claims 2 to 12, characterized in that the primary piston (18) is mechanically decoupled from the brake pedal 35 nisch.