DE102011081463A1 - Brake assembly for motor cars, has closed valve arranged in hydraulic line connecting pressure supply device with wheel brakes, and open valve arranged in hydraulic line connecting master brake cylinder with wheel brakes - Google Patents

Abstract

The assembly has a master brake cylinder (4), a pressure supply device (2) and wheel brakes (6-9) hydraulically connected to a pressure control valve assembly (5) for regulating and/or controlling the wheel brakes. A closed valve (14) is arranged in a hydraulic line as a single valve connecting the pressure supply device with the wheel brakes. An open valve (15) is arranged in the hydraulic line connecting the master brake cylinder with the wheel brakes. A hydraulic actuatable simulation device (3) with an elastic element (33) is attached to the master brake cylinder.

Description

The invention relates to a brake system for motor vehicles with an actuatable by means of a brake pedal master cylinder, in particular tandem master cylinder, wheel brakes, an electrically controllable pressure supply device, and one to the master cylinder, the pressure supply device and the wheel brakes hydraulically connected pressure control valve arrangement for controlling and / or control of a wheel brake controlled Wheel brake pressure, each wheel brake is associated with a normally open and a normally closed valve of the pressure control valve assembly.

Such brake systems are usually operable in a so-called "brake-by-wire" mode in which, independently of the muscular strength of the vehicle driver (or possibly even with his assistance) brake pressure is built up by electronic control of a pressure supply device. While preferably operated in this "brake-by-wire" mode, at least one fall back mode is provided in which only operation by the vehicle operator is possible.

In automotive engineering, brake-by-wire brake systems are becoming increasingly widespread. Such brake systems often include a pedal decoupling unit, whereby brake pedal operation by the driver in the brake-by-wire mode causes disconnection of the direct hydraulic connection of the master cylinder to the wheel brakes as well as engagement of the hydraulic pressure delivered by the pressure supply to the wheel brakes. "By-wire", and therefore not hydraulically, is a section of the chain of effects of a driver request detection for establishing a corresponding brake system pressure in the pressure supply device.

In order to give the driver a pleasant pedal feel in the "brake-by-wire" mode of operation, the brake systems typically include a brake pedal feel simulation device. In these brake systems, the brake can be operated without active intervention of the driver due to electronic signals. These electronic signals can be output, for example, from an electronic stability program ESC or a distance control system ACC.

The object of the present invention is to provide a vehicle brake system which can be operated in the "brake-by-wire" mode with improved braking capability.

This object is achieved in that in each case in a pressure supply device with a wheel brake connecting hydraulic line, in particular as a single valve, the normally closed valve is arranged, and that in a master cylinder connecting to a wheel brake hydraulic line, the normally open valve is arranged ,

Further preferred embodiments and advantageous embodiments of the invention will become apparent from the dependent claims and the description of the invention with reference to a drawing.

The invention is based on the consideration that a brake system, in which preferably brake pressure is built up by an electronically controllable pressure supply device, should be optimized both with regard to the brake pressure build-up in by-wire operation and with regard to the operation in the fallback level, by as few, the pressure medium flow obstructing valves are to happen to the pressure medium exchange between the pressure supply device and the wheel brakes, and that the driver should be given in the fallback the opportunity to bring the vehicle quickly and safely to a standstill. In addition, switching to the fallback level should be as fast as possible and without loss of brake pressure.

As has now been recognized, these requirements can be realized by an interpretation of valves associated with the individual wheel brakes, wherein the valves, which are respectively connected to the hydraulic line connecting the pressure supply device with the brake as normally closed valves, and in the respective hydraulic line Valves connected between the master cylinder and the wheel brake are designed to be normally open.

Such a configuration is also suitable for connecting each of the wheel brakes in the fallback mode to one of the two chambers of a tandem master cylinder, so that in fallback mode a two-circuit system for braking the vehicle is available.

In a preferred embodiment, the valves associated with the wheel brakes are designed as analogue controllable seat valves, the valves being oriented such that the valve stem of the normally closed valve is pressurized by the pressure supply device in the direction of lifting from the valve seat and the wheel brake pressure in the direction of pressing the valve seat is loaded, and that the valve stem of the normally open valve from the wheel brake pressure in the direction of a lift is loaded from the valve seat. This valve orientation ensures, on the one hand, that in the fallback mode of operation the plungers of the non-energized closed valves are pressed into the valve seat. This avoids unwanted outflow of pressure medium to the pressure source which can not be controlled in the fallback level.

On the other hand, the valve orientation allows the use of analog controllability of both valve types in the by-wire mode. For this it is necessary that the valve seats are flowed through by the pressure medium in the direction of the valve tappets. This is given for a Radbremsdruckaufbau, in which the normally closed valve is flowed through by the controllable pressure source to the wheel and for a Radbremsdruckabbau in which the normally open valve is flowed through by the wheel brake in the direction of the pressure medium reservoir.

It should be expressly mentioned at this point that a controlled by the analog function of the valve pressure reduction by a fully open (normally closed) valve from the wheel brake to the controllable pressure source is also possible. The above-mentioned wheel individually analog controlled pressure reduction via the normally open valves is therefore preferably used when the wheel brake pressures must be different.

Advantageously, the remote from the wheel brake connection of a normally open valve, in particular via a further normally closed valve with a pressure medium reservoir under atmospheric pressure is connectable. In this way, if necessary, a pressure equalization of the flowing back through the normally open valve from the brake pressure medium with atmospheric pressure or with the pressure fluid reservoir can be made.

The use of a normally closed valve ensures that this pressure compensation takes place only when the valve is actively activated. In case of failure of the electrical system, if the pressure supply device can actively build up no brake pressure and the brake system is operated in the fallback level, such a compensation is not desirable, since in this case to maintain brake pressure, the normally closed valves are closed and the normally open valves with the master cylinder are hydraulically connected, whereby a pressure build-up in the wheel brakes is made possible by muscular strength of the driver.

In a normal operating mode "brake-by-wire", the wheel brake pressure in the respective wheel brake is preferably provided by the pressure supply device. In this case, a Radbremsdruckaufbau is advantageously carried out on a wheel brake on the normally closed valve and a Radbremsdruckabbau over the normally open valve. This means that the normally closed valves are opened actively (by electronic control) in this operating mode. In the fallback level, these valves then close, so that the connection to the pressure supply device is disconnected and no pressure fluid flows back into the pressure supply device and is therefore not available for pressure buildup.

The pressure supply device is advantageously formed by a cylinder-piston arrangement, the piston is actuated by an electromechanical actuator.

In the brake system according to the invention, it is advantageous if the driver, especially in the "brake-by-wire" mode, experiences a pleasant pedal feel. For this purpose, a hydraulically actuated simulation device with at least one elastic element is advantageously connected to the master brake cylinder. Upon actuation of a brake actuation device, for example a brake pedal, pressure medium is pressed out of the master brake cylinder into the simulation device in this way, as a result of which the elastic element is compressed, preferably by a piston. The resistance felt by the driver as he squeezes the elastic element provides him with a pedal feel familiar from simple hydraulic brake systems. In this way, in particular a reproducible relationship between pedal travel and pedal force can be realized.

The simulation device preferably comprises two hydraulic active surfaces whose movement, in particular rigidly, is coupled to one another, wherein each of the active surfaces is connected to one of the brake circuits of the master brake cylinder or to the pressure of an associated chamber of the master brake cylinder. In other words, these two active surfaces, which may be surfaces of a piston, for example, can each be subjected to the pressure of one of the brake circuits. For this purpose, chambers are preferably provided in the simulation device, which are in hydraulic communication with the chambers of the master cylinder in the normal operating state.

The simulation device is advantageously designed to be switched on and off, wherein, in particular, a hydraulic space of the simulation device can be connected to and shut off by means of an electrically controllable simulator release valve with atmospheric pressure. This is particularly advantageous Way provided a separable connection to a pressure medium reservoir.

In the hydraulic connection between the master cylinder and normally open valve advantageously at least one electrically controllable isolation valve is arranged, which allows a shut-off of this connection. As a result, in the normal operating state "brake-by-wire", the hydraulic connection can be separated from the master brake cylinder to the wheel brakes, so that the pressure buildup in the wheel brakes takes place exclusively by the electronically controllable pressure supply device.

The at least one electrically controllable isolation valve preferably maintains pressure in the closed state in both directions of the connection between the master cylinder and normally open valve. In other words, in the energized, closed state, pressure fluid can flow through the valve neither in the direction of the master cylinder nor in the direction of the normally open valve. In the event that no different wheel brake pressures are required in "brake-by-wire" operation, in this way the Radbremsdruckabbauventile remain energized and thus open.

The advantages of the invention are, in particular, that an effective and responsive valve arrangement is provided by a connection of the pressure supply device with a wheel brake in each case via a normally closed valve and a connection of the master cylinder with a wheel brake via a normally open valve, on the one hand fast pressure regulation in allows the individual wheel brakes and on the other hand allows a quick and immediate switching between a "brake-by-wire" mode and a fallback level. The hydraulic connection of a simulation device with the master brake cylinder gives the driver a pleasant and reproducible pedal feel in the "brake-by-wire" mode.

Two embodiments of the invention will be explained in more detail with reference to a drawing. Therein show in a schematic representation:

1 a first embodiment of a brake system according to the invention, and

2 A second embodiment of a brake system according to the invention.

Identical parts are provided with the same reference numerals in all figures.

In the 1 illustrated exemplary electro-hydraulic brake system consists essentially of an actuator 1 with a tandem master cylinder 4 and a simulation device 3 , an electrically controllable pressure supply device 2 a wheel brake pressure modulation device 5 and an electronic control unit (ECU) 10 , To the wheel brake pressure modulation device 5 are wheel brakes 6 . 7 . 8th . 9 connected. The pressure chambers of the tandem master cylinder 4 are with a pressure medium reservoir under atmospheric pressure 11 (Preferably with completely dissolved brake actuator 1 ) connectable.

The assignment of the wheel brakes 6 . 7 . 8th . 9 to the brake circuits I, II is for example made such that the connected to the first brake circuit I wheel brakes 8th . 9 are associated with a vehicle axle, while the wheel brakes connected to the second brake circuit II 6 . 7 serve the deceleration of the other vehicle axle. Indirect detection of in the wheel brakes 6 to 9 For example, when a pressure is applied during a braking operation, wheel speed sensors (not shown) can serve as an example.

The master cylinder or tandem master cylinder 4 is about a brake pedal 19 actuated. The actuating travel of the brake pedal 19 is by means of a preferably redundant displacement sensor 30 recorded, the z. B. senses the path of a piston and thus the driver request detection or a setpoint generation in the electronic control unit 10 serves.

The electrohydraulic pressure supply device 2 For example, essentially consists of a hydraulic cylinder-piston assembly 43 and an electromechanical actuator 44 For example, which is formed by an electric motor with a reduction gear, the rotational movement of the electric motor in a translational movement of a hydraulic piston 45 so that in a pressure room 46 the hydraulic cylinder-piston arrangement 43 a hydraulic pressure is built up. The electromechanical actuator 44 is powered from the electrical system (not shown) of the vehicle, optionally buffered by an electrical energy storage (not shown) with energy. The movement of the piston 45 is indirectly by means of at least one rotation angle sensor 48 detects the rotor position of the electromechanical actuator 44 sensed.

The pressure room 46 the cylinder-piston arrangement 43 is via wheel-individual, normally closed valves 14 , In particular without the interposition of another valve, connectable to the wheel brakes.

In normal operation of the brake system ("brake-by-wire" mode) builds the electromechanical-hydraulic actuator 43 . 44 the system brake pressure from which the Radbremsdruckmodulationseinrichtung 5 generates wheel-specific brake pressures. A Radbremsdruckaufbau takes place in normal operation via an open, normally closed analog seat valve 14 and a Radbremsdruckabbau done either via a backflow through the normally closed analog seat valve 14 , in principle, in this flow direction no analog valve control, but only a complete opening is possible, so that such a pressure reduction at all open normally closed valves 14 at the same time, or - if a wheel-individual pressure reduction is required - via a normally open analog seat valve 15 (The output example, via a normally closed valve 17 each brake circuit with the container 11 is connectable).

The (seat) valves 14 . 15 are oriented such that the valve stem of the valve acting as a pressure build-up valve 14 is loaded by the actuator pressure in the direction of lifting the valve seat and the wheel brake pressure in the direction of pressing against the valve seat, and that acting as a pressure relief valve valve 15 is loaded by the wheel brake pressure in the direction of lifting from the valve seat.

The pressure chambers of the tandem master cylinder 4 are each a normally open isolation valve 13 , which, for example, in the energized state, the effect of a check valve, with the normally open (pressure reducing) valves 15 the wheel brakes 6 to 9 connected or connectable.

In a fallback mode, the two circles of the pedal tandem master cylinder 4 (via the open isolation valves 13 ) with the normally open analog brake pressure reduction seat valves 15 connected. To avoid a compression of these valves in pedal-controlled pressure build-up check valves are connected in parallel. To claim the fallback mode of operation any energization of the valves and the actuator are turned off in the exemplary brake system. Due to the connection of each wheel brake with one of the two chambers of the tandem master cylinder 4 In this operating mode, two brake circuits I and II, which are hydraulically separated from one another, are produced, which ensures that the vehicle is in the fallback mode or in the fallback mode by all the wheel brakes 6 . 7 . 8th . 9 can be braked and sufficient braking torque can be built even if one of the two brake circuits fails.

A switching of the modulator or the Radbremsdruckmodulationseinrichtung 5 from the fallback mode into normal operation is carried out by energizing four valves acting as switching valves 13 . 17 , This is the connection of the normally open valves 15 with the tandem master cylinder 4 interrupted and acting as brake pressure reduction valves 15 are the output side with the container 11 connected.

In a normal operation mode of the brake system ("brake-by-wire" mode) is the tandem master cylinder 4 by means of the valves 13 decoupled from the wheel brakes and pressure medium is by the driver from the two pressure chambers of the tandem master cylinder 4 into the simulation device 3 shifted, which gives the driver a pleasant pedal feel. The brake pressure at the wheel brakes is through the pressure supply device 2 provided. The realization of the brake system with a pedal-operated (plunger) tandem master cylinder 4 and a hydraulically coupled pedal feel simulator or simulation device 3 makes it possible to give the driver in this mode a familiar and pleasant pedal feel.

In an emergency mode of operation, which is also referred to as a fallback level (all valves are in a de-energized state), which occurs, for example, in case of failure of the electrical system, the wheel brakes on the valves 15 . 13 with the skin brake cylinder 4 connected and the brake pressure is provided by the driver.

As mentioned above, the simulation device provides 3 a hydraulically operated pedal feel simulator. It includes, for example, an elastic element 33 (eg a simulator spring) and a piston 28 which is a boundary of a hydraulic room 26 represents. The hydraulic room 26 is via a normally open valve 50 with the pressure medium reservoir 11 connected. The piston 28 owns on the elastic element 33 opposite side preferably two hydraulic active surfaces 51 . 52 , which in each case with the pressure of a hydraulic circuit I, II of the tandem master cylinder 4 can be acted upon.

Alternatively, two simulators with simple, non-stepped piston to the two pressure chambers of the tandem master cylinder 4 or a single such simulator is simply connected to a pressure chamber of the tandem master cylinder 4 connected. The proposed simulator device or simulation device 3 However, with a stepped piston has the advantage that in this variant at a possible leakage of a Simulatorkreises the resulting idle travel of the pedal is the smallest.

In a normal operation of the brake system are hydraulic connections from the tandem master cylinder 4 locked to the wheel brakes while the simulator is released. In a fallback mode, the tandem master cylinder is 4 connected to the wheel brakes and the simulator is locked. The brake system according to the invention can be used both for axle as well as for diagonal brake circuit distribution.

The first ( 1 ) and the second embodiment ( 2 ) differ in the design of the isolation valves 13 . 113 , For hydraulic separation of the actuation unit 1 from the wheel brakes 6 to 9 is according to the second embodiment, the use of two isolation valves 113 proposed that hold in the energized state in both directions pressure. As a result, as long as no different wheel brake pressures are required in normal operation, the normally open Radbremsdruckabbauventile 15 de-energized and thus remain open, which on the one hand less power is needed and on the other hand, the normally closed container connection valves 17 be tested.

LIST OF REFERENCE NUMBERS

1

actuator

2

Pressure supply device

3

simulation device

4

Tandem master cylinder

5

Radbremsdruckmodulationseinrichtung

6, 7, 8, 9

wheel brakes

10

Control unit

11

Pressure fluid reservoir

13

isolation valve

14

normally closed valve

15

normally open valve

17

normally closed valve

19

brake pedal

26

hydraulic room

28

piston

30

displacement sensor

33

elastic element

43

Cylinder-piston arrangement

44

actuator

45

piston

46

pressure chamber

48

Rotation angle sensor

50

Valve

51, 52

active surfaces

113

isolation valve

I, II

brake circuits

Claims (10)

Brake system for motor vehicles with a brake pedal ( 19 ) operable master cylinder ( 4 ), in particular tandem master cylinder, wheel brakes ( 6 . 7 . 8th . 9 ), an electrically controllable pressure supply device ( 2 ), and one to the master cylinder ( 4 ), the pressure delivery device ( 2 ) and the wheel brakes ( 6 . 7 . 8th . 9 ) hydraulically connected pressure control valve arrangement ( 5 ) for controlling and / or controlling a wheel brake ( 6 . 7 . 8th . 9 ) wheel brake pressure input, each wheel brake a normally closed valve ( 14 ) and a normally open valve ( 15 ) of the pressure regulating valve arrangement ( 5 ), characterized in that in each case the pressure supply device ( 2 ) with a wheel brake ( 6 . 7 . 8th . 9 ) connecting hydraulic line, in particular as a single valve, the normally closed valve ( 14 ) is arranged, and that in a master cylinder ( 4 ) with a wheel brake ( 6 . 7 . 8th . 9 ) connecting hydraulic line the normally open valve ( 15 ) is arranged. Brake system according to claim 1, characterized in that the wheel-individual valves ( 14 . 15 ) are designed as analog seat valves, wherein the valves are oriented such that the valve stem of the normally closed valve ( 14 ) from the pressure of the pressure delivery device ( 2 ) is loaded in the direction of lifting from the valve seat and the wheel brake pressure in the direction of pressing against the valve seat, and that the valve stem of the normally open valve ( 15 ) is loaded by the wheel brake pressure in the direction of lifting from the valve seat. Brake system according to claim 1 or 2, characterized in that the wheel brake ( 6 . 7 . 8th . 9 ) facing away from a normally open valve ( 15 ), in particular via another normally closed valve ( 17 ), with atmospheric pressure, in particular a pressure fluid reservoir, connectable. Brake system according to one of claims 1 to 3, characterized in that in a normal mode "brake-by-wire" a wheel brake pressure from the pressure supply device ( 2 ) and that a Radbremsdruckaufbau at a wheel brake via the normally closed valve ( 14 ) and a Radbremsdruckabbau over the normally open valve ( 15 ) is carried out. Brake system according to one of claims 1 to 4, characterized in that the pressure supply device ( 2 ) by a cylinder-piston arrangement ( 43 ) is formed whose piston ( 45 ) by an electromechanical actuator ( 44 ) is operable. Brake system according to one of claims 1 to 5, characterized in that the Master brake cylinder ( 4 ) a hydraulically actuable simulation device ( 3 ) with at least one elastic element ( 33 ) is connected, which, in particular in a mode "brake-by-wire", gives the driver a pleasant pedal feel. Brake system according to claim 6, characterized in that the simulation device ( 3 ) two hydraulic active surfaces ( 51 . 52 ) whose movement, in particular rigidly, is coupled to one another, wherein each of the active surfaces ( 51 . 52 ) with the pressure of an associated chamber of the master cylinder ( 4 ) connected is. Brake system according to claim 6 or 7, characterized in that the simulation device ( 3 ) is switched on and off, in particular a hydraulic space ( 26 ) of the simulation facility ( 3 ) by means of an electrically controllable simulator release valve ( 50 ) Is connectable / separable with atmospheric pressure. Brake system according to one of claims 1 to 8, characterized in that in the hydraulic connection between the master cylinder ( 4 ) and normally open valve ( 15 ) at least one electrically controllable isolation valve ( 13 . 113 ), which makes it possible to shut off the connection. Brake system according to claim 9, characterized in that the at least one electrically controllable isolation valve ( 113 ) in the closed state in both directions of the connection between the master cylinder ( 4 ) and normally open valve ( 15 ) Holds pressure.

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