DE102011079454A1 - Brake-by-wire type electro-hydraulic brake system for vehicles, comprises brake actuating element, and brake master cylinder, where simulator is hydraulically connected with displaceable simulator piston - Google Patents

Abstract

The brake-by-wire type electro-hydraulic brake system (2) comprises a brake actuating element (8), and a brake master cylinder (14). A simulator (20) is hydraulically connected with a displaceable simulator piston (26), in an actuation direction (34) against a spring element (32). An actuator position sensor and a pressure sensor detect an operation by the brake actuation element for expressed desire to brake. A pressure source (40) is controlled for setting up of brake pressure, where a blocking actuator (120) is provided with a movable drive device locking element. An independent claim is included for a method for operating a brake-by-wire type electro-hydraulic brake system.

Description

The invention relates to an electro-hydraulic brake system of the type brake-by-wire with a brake actuator, a master cylinder, a hydraulically connected simulator with a movable in the direction of actuation against a spring element simulator piston, at least one Betätigungswegsensor and at least one pressure sensor for detecting a by actuation of the brake actuator for Expressed braking request, with the help of the simulator, a reproducible pedal feeling in the sense of a constant relation between pedal travel and pedal force is generated and in accordance with the determined braking request, a pressure source is controlled to build up brake pressure, and wherein a hydraulic fallback level is provided. It also relates to an associated operating method.

In electronic brake-by-wire braking systems, in a normal mode, the brake pedal operation by the driver and the pressure build-up in the brakes are not directly hydraulically coupled. This means that when the driver accesses the brakes via the brake pedal, part of the chain of effects for this access is electrically or electronically and thus completely controllable by software. For example, while in conventional hydraulic brake systems by the operation of the brake pedal directly from a tandem master cylinder brake fluid is displaced into the wheel brakes, in electro-hydraulic brake-by-wire systems, a simulator is used to determine the braking request of the driver. In this case, a simulator piston is usually displaced against a spring to obtain a pedal force associated with the pedal travel. The braking request of the driver can be generated with the aid of a displacement sensor for the pedal travel and / or a pressure sensor for the pedal force. From this braking request then a brake setpoint is generated, which is then decisive for the pressure build-up in the brakes. For this purpose, a pressure source is electronically controlled, which actively shifts brake fluid into the brakes as a function of the braking torque setpoint.

Since in such systems, the brake pressure is actively generated in the brakes by electronic control of a pressure source, a fallback level must necessarily be provided in their construction, which corresponds to the state of the brake system with failed electronics and / or power supply and in the vehicle by the driver with a can be slowed down by the legally prescribed minimum delay.

In electro-hydraulic brake-by-wire braking systems, this fallback level is usually realized so that in case of failure of the power supply, the driver can shift brake fluid into the wheel brakes directly by muscle power by the operation of the brake pedal. In such a case, a sufficiently large volume of brake fluid must be available. For this reason, in known electro-hydraulic brake-by-wire systems - depending on the specific design - either provided a valve that shuts off a hydraulic flow to the simulator in the fallback level or provided a hydraulic valve which blocks outflow of pressure medium from the simulator , This prevents brake fluid from flowing out of the simulator in the fallback mode in or in other cases and is not directly available for building up pressure in the wheel brakes.

A disadvantage of such solutions is that there is no assurance that in such a case, the valve actually blocks the influx or outflow of brake fluid. For example, such a shut-off valve may lose its function due to a leak. Such malfunctions are classified as safety-critical, since in such a malfunction can not be ensured that the vehicle can be stopped in a sufficiently short time and with a sufficiently large deceleration torque from the driver by muscle power.

The invention is therefore based on the object to ensure the provision of a sufficient amount of brake fluid in the fallback level in a reliable manner.

With regard to the electrohydraulic brake system, this object is achieved in that a blocking actuator is provided with a movable by a drive device blocking element, which has a distance to the simulator piston in a normal operating position or release position and to block the simulator in a blocking position in the fallback level the simulator piston is moved counter to the direction of actuation and blocks its movement in the direction of actuation.

Advantageous embodiments of the invention are the subject of the dependent claims.

The invention is based on the consideration that particularly high safety requirements should be set for the brake fluid supply in fallback mode in case of failure of the operability of the electronically controlled pressure source. A vehicle that can not be decelerated with a sufficiently long delay in a critical situation poses a threat to the driver's health and life If necessary, other people. Blocking the inflow or outflow of brake fluid in or out of the simulator on purely hydraulic means is classified as insufficient, since such shut-off must be done by valves in which on the one hand due to malfunction or material error leakage may occur and on the other hand, such a malfunction is not or hardly detectable.

As has now been recognized, this blocking function can be realized in the fallback mode by other means, namely by electromechanical blocking of the simulator piston. By blocking the movement of the simulator piston in the direction of actuation, i. in the direction in which the piston moves when the brake pedal is actuated, it is achieved that in a further actuation of the brake pedal in the fallback mode, the space in the corresponding simulator chamber, in which brake fluid is located, is not increased. That means, the simulator does not pick up any more brake fluid. In this way, it is ensured that upon actuation of the brake pedal by the driver brake fluid is now no longer moved into the simulator or its chambers, but in the wheel brakes.

For blocking the piston, a blocking element may be provided for this purpose, which is movable by a drive device, this blocking element has a predetermined distance to the piston in normal electro-hydraulic operation in a normal operating position or release position, so that the piston in the actuating direction for receiving brake fluid in Simulator can move. If, on the other hand, a malfunction of the pressure source is detected, the blocking element can be moved up to the piston so that its further movement in the actuating direction is blocked.

In the context of this application, an actuation path sensor designates a sensor which quantitatively determines or senses the actuation of the actuation element (or of a brake pedal) and thus the braking request. This can be done, for example, directly via the pedal travel or via the pedal angle.

In a preferred embodiment of the brake system this is designed with respect to the dimensioning of the blocking element such that the blocking element can be moved opposite to the actuating direction against the simulator piston to amplify the brake pressure in fallback mode or in the fallback. That is, in fallback mode, the simulator piston is moved counter to the actuator by the blocking member so that the volume of brake fluid in the simulator or simulator chamber is displaced therefrom and is available in the brakes in addition to pressure build-up. For this purpose, the blocking element must be sufficiently far opposite to the direction of actuation movable.

If, for example, a pressure medium volume is supplied to a pedal actuation which corresponds to the volume displaced from the master brake cylinder or tandem master cylinder with unamplified braking, the brake actuation energy is applied to the driver and to the other half by the additional functionality or additional reinforcement just described. Such additional reinforcement could not be realized at the hydraulic level by means of valves.

The drive device is advantageously designed as an electric motor with a self-locking spindle drive. The blocking element is advantageously designed as a spindle, which is rotated by the electric motor. In other words, upon rotation of the spindle, it shifts counter to the actuating direction for blocking the simulator or for the amplification function or in the actuating direction, in order to be brought into the normal operating position. As possible embodiments, a rotatably driven spindle, which cooperates with a non-rotating nut and a rotationally driven nut, which cooperates with a non-rotating spindle called.

In an alternative embodiment, the drive device can also be designed as a linear drive, which shifts a designed as a piston or other designed element blocking element.

In the event that there is a malfunction of the pressure source, but the power supply (electrical system) is still present, the drive device can move through this power supply, the blocking element. But it may also be the case that the entire electrical system fails and thus an energy supply is no longer guaranteed. In order to allow even in such a case, a blocking of the simulator piston, an electrical energy storage device is advantageously provided, which is dimensioned such that it can provide such a large amount of energy available in case of failure of the central power supply that thus moves the blocking element to the simulator zoom can be blocked and blocked this way. In an advantageous embodiment of the drive device described above as a self-locking spindle drive then no further energy is required to maintain this state. By such a measure can Thus, it is ensured that even with complete collapse of the power supply of the simulator piston is blocked and thus there is enough brake fluid volume or pressure fluid volume for a initiated by muscle power of the driver braking available.

To determine the position of the current or current position of the blocking element, a blocking element travel sensor can be provided which measures the distance traveled by the blocking element. Alternatively or in combination with this, a monitoring unit for the motor current of the drive device can be provided, which can be provided as a drive device with a motor, which detects the contact of the blocking element with the simulator piston on the basis of the current profile.

With regard to the method, the above-mentioned object is achieved in that in case of failure of the pressure source from a motor, a blocking element is moved to the simulator piston such that it is blocked in its movement in the direction of actuation and upon actuation of the brake actuator or brake pedal by the Driver completely displaced from the master cylinder brake fluid volume is used to apply the brakes. To increase the brake pressure, the blocking element is advantageously moved further opposite to the actuating direction, so that in addition to the master brake cylinder volume, a further brake fluid volume is provided from the at least one simulator chamber to build up pressure in the brakes.

The advantages of the invention are, in particular, that a robust and reliable technical measure is made available by an electromechanical locking or blocking the movement of the simulator piston, which allows a displacement of brake fluid from the master cylinder into the wheel brakes in a fallback. An embodiment of the drive device as a self-locking spindle drive also ensures that no further energy is needed to maintain this blockage.

An electrical energy storage that can provide enough energy to achieve this blocking, the blocking of the simulator piston can be guaranteed even in complete failure of the power supply.

Another advantage of this electromechanical blocking consists in the realization of an additional function as a brake booster, which can be pushed out of the simulator or from the simulator chamber by moving the simulator piston counter to the actuation direction brake fluid volume and is thus additionally available to the pressure buildup on the brakes available.

An embodiment of the invention will be explained in more detail with reference to a drawing. In it show in a highly schematic representation:

1 an electrohydraulic brake system having a brake operating element configured as a brake pedal, a master cylinder configured as a tandem master cylinder, the chambers of which are supplied with brake fluid by a reservoir, a pressure source, a simulator, and a blocking actuator in a blocking position,

2 the brake system off 1 , wherein the blocking actuator is in a release position, and

3 the brake system off 1 and 2 with the blocking actuator in an amplified position.

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

This in 1 illustrated electro-hydraulic brake system 2 comprises a designed as a brake pedal brake actuator 8th , When actuated piston in a designed as a tandem master cylinder master cylinder 14 be moved, causing brake fluid from the chambers 18 . 24 of the master cylinder is pushed out. The chambers 18 . 24 are at completely dissolved brake actuators with a reservoir 16 connected for brake fluid.

For a pedal feel simulation is a simulator 20 intended. The simulator 20 includes a simulator piston 26 , a first simulator chamber 28 and a second simulator chamber 30 , Upon actuation of the brake actuation element 8th to initiate a braking process is the simulator piston 26 because of in the simulator chambers 28 . 30 self-building pressure against a spring element 32 in the direction of actuation 34 pressed. By moving brake fluid out of the chambers 18 . 24 of the master cylinder 14 into the simulator chambers 28 . 30 during actuation of the brake actuator 8th or brake pedal the brake pedal feeling is generated at the driver. In addition, with the aid of a displacement sensor, the displacement of a coupled to the brake actuator master cylinder piston, and / or one or more pressure sensors, the braking request of the driver determined from which the brake system pressure is determined, with which the pressure source acts on the wheel brakes. Optionally, the determined driver brake request can also be used as a default of a desired Vehicle deceleration are interpreted and the brake system pressure results when adjusting this desired delay.

Upon actuation of the brake actuator 8th accordingly, the driver shifts 8th with his muscle power brake fluid volume not in the brakes but in the simulator. In the normal operating mode, a pressure source is built up in the brakes as a function of the determined braking request 40 electronically controlled, which is an electric motor 46 , a piston 52 and a pressure chamber 58 having. During a braking process then shifts the pressure source 40 Brake fluid in the brakes 64 . 70 . 76 . 82 of the brake system 2 , Furthermore, isolation valves 100 . 106 provided which are closed during braking in normal operation mode.

In the brake system 2 For example, a hydraulic fallback mode is implemented which becomes active when the pressure source 40 is impaired in functionality or completely fails. The fallback level allows, in this case, by the driver's muscular strength via the actuation of the brake actuation element 8th Brake fluid to build up pressure in the brakes 64 . 70 . 76 . 82 can be moved.

If such a case occurs, as much brake fluid or pressure medium volume as possible should be available to build up pressure right from the start. This is achieved by moving the simulator piston 26 in the direction of actuation 34 blocked in this case. For this purpose, according to the invention is a blocking actuator 120 provided, in the present preferred embodiment, an electric motor 126 and a spindle displaceable by the rotation of the electric motor 132 having. In fallback mode, the spindle becomes 132 so on the simulator piston 26 moved on that further movement of the simulator piston 26 in the direction of actuation 34 is no longer possible. This ensures that upon actuation of the brake actuator 8th the simulator piston 26 not further in the direction of actuation 34 is moved, causing the simulator chambers 28 . 30 would continue to fill with brake fluid volume. Instead, this volume directly stands for pressure build-up in the brakes 64 . 70 . 76 . 82 to disposal. The 1 shows the blocking actuator in a blocking position in which further movement of the simulator piston 26 in the direction of actuation 34 is inhibited.

In the present embodiment, the blocking actuator comprises 120 a self-locking spindle drive, so that after approaching the spindle 132 to the simulator piston 26 even with a complete failure of the power supply is ensured that the inhibitory or blocking effect of the blocking actuator 120 is maintained.

To block the simulator piston 26 Also in case make sure not only the pressure source 40 loses its function, but also a total collapses the electrical system or no longer provides the power supply, an electrical energy storage device may be provided, such as a battery or a capacitor, in such a case the blocking actuator 120 provides enough energy to the spindle 132 to the simulator piston 26 : approaching. With such a blocking actuator 120 is a robust and reliable blocking of the simulator piston 26 realized in hydraulic fallback mode.

The release position or normal operating position of the simulator lock is in 2 shown. In this state, the spring element 32 or the simulator spring by hydraulic loading of the simulator 20 compressible.

A particularly advantageous development of the invention is in 3 shown. With the components proposed for the electromechanical simulator lock (blocking actuator 120 with electric motor 126 and spindle 132 ) can be an additional gain realized by the spindle drive the simulator piston 26 about the in 1 illustrated locking position out against the operating direction 34 or pedal feel simulation operation direction shifts. This additional gain is then activated when provided in normal operation brake system pressure build-up of the brake system 2 with the help of the pressure source 40 not available.

In such operation of the blocking actuator 120 So is in addition to that of the driver by pressing the actuator 8th shifted pressure medium volume still active by the displacement of the simulator piston opposite to the actuation direction 34 further pressure medium volume from the simulator chambers 28 . 30 to build up pressure in the brakes 64 . 70 . 76 . 82 made available. In this way, so to speak, in the malfunction of the pressure source 40 by the additional functionality of the blocking actuator 120 provided an alternative pressure source that assists the driver during the braking process. The blocking actuator 120 is located in 3 in the reinforcement position. In order to realize a hydraulic fallback with brake booster no hydraulic components are necessary. It is just an extended travel of the simulator 20 provide against the direction of actuation.

LIST OF REFERENCE NUMBERS

2

 braking system

8th

 Brake actuator

14

 Master Cylinder

16

 reservoir

18

 chamber

20

 simulator

24

 chamber

26

 simulator piston

28

 First simulator chamber

30

 Second simulator chamber

32

 spring element

34

 operating direction

40

 pressure source

46

 electric motor

52

 piston

58

 pressure chamber

64, 70, 76, 82

 brake

100, 106

 isolation valve

120

 Blockierungsaktuator

126

 electric motor

132

 spindle

Claims (9)

Electrohydraulic braking system ( 2 ) of the type brake-by-wire, with a brake actuator ( 8th ), a master cylinder ( 14 ), a hydraulically connected simulator ( 20 ) with one in an actuating direction ( 34 ) against a spring element ( 32 ) displaceable simulator pistons ( 26 ), at least one actuation path sensor and at least one pressure sensor for detecting an actuation of the brake actuation element (US Pat. 8th ) expressed desired braking, using the simulator ( 20 ) a reproducible pedal feeling in the sense of a constant relation between pedal travel and pedal force is generated and in accordance with the determined braking request a pressure source ( 40 ) is actuated to build up brake pressure, and wherein a hydraulic fallback level is provided, characterized in that a blocking actuator ( 120 ) is provided with a movable by a drive device blocking element, which in a normal operating position a distance from the simulator piston ( 26 ) and to block the simulator ( 20 ) in a blocking position in the fallback level to the simulator piston ( 26 ) opposite to the direction of actuation ( 34 ) is moved and its movement in the direction of actuation ( 34 ) blocked. Brake system ( 2 ) according to claim 1, which is designed in terms of the dimensioning of the blocking element such that for increasing the brake pressure in the fallback mode, the blocking element opposite to the actuation direction ( 34 ) against the simulator piston ( 26 ) can be moved. Brake system ( 2 ) according to claim 1 or 2, wherein the drive device as an electric motor ( 46 ) is designed with a self-locking spindle drive and wherein the blocking element is a spindle ( 132 ), which of the electric motor ( 46 ) is rotated. Brake system ( 2 ) according to claim 1 or 2, wherein the drive device is designed as a linear drive and the blocking element is a piston ( 52 ). Brake system ( 2 ) according to one of claims 1 to 4, wherein an electrical energy store is provided, which is dimensioned such that it provides in case of failure of the central power supply an amount of energy that is sufficient, the blocking element to the simulator ( 20 ) to move up. Brake system ( 2 ) according to one of claims 1 to 5, wherein a blocking element displacement sensor is provided which measures the distance traveled by the blocking element. Brake system ( 2 ) according to one of claims 1 to 6, wherein a monitoring unit for the motor current is provided which the contact of the blocking element with the simulator piston ( 26 ) detected on the basis of the current profile. Method for operating an electrohydraulic brake system ( 2 ) of the type brake-by-wire, with a brake actuator ( 8th ), a master cylinder ( 14 ), an associated simulator ( 20 ) with a against a spring element ( 32 ) in the direction of actuation ( 34 ) displaceable simulator pistons ( 26 ) and at least one simulator chamber ( 28 . 30 ), depending on the with the help of the simulator ( 20 ) determined braking request a pressure source ( 40 ) is controlled to build up brake pressure, and wherein a hydraulic fallback level is provided, characterized in that in case of failure of the pressure source ( 40 ) from a motor ( 126 ) a blocking element in such a way to the simulator piston ( 26 ) is moved, that this in its movement in the direction of actuation ( 34 ) is blocked and upon actuation of the brake actuator ( 8th ) by the driver from the master cylinder ( 14 ) displaced brake fluid volume is completely used to apply the brakes. A method according to claim 8, wherein to increase the brake pressure, the blocking element still further opposite to the actuating direction ( 34 ) is moved, so that brake fluid from the at least one simulator chamber ( 28 . 30 ) is provided to build up pressure in the brakes.

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