WO2018091311A1

WO2018091311A1 - Brake system and method for operating a brake system

Info

Publication number: WO2018091311A1
Application number: PCT/EP2017/078445
Authority: WO
Inventors: Harald Biller; Stefan Drumm; Dominik DÜCHS; Roland Engelhardt; Boris Holzherr; Andreas Kohl; Ralf Schröder
Original assignee: Continental Teves Ag & Co. Ohg
Priority date: 2016-11-16
Filing date: 2017-11-07
Publication date: 2018-05-24
Also published as: DE102016222578A1

Abstract

Brake system (2) for motor vehicles, comprising hydraulically actuable wheel brakes (42, 44, 46, 48); at least one electrically actuable wheel valve (50, 52, 54, 56; 60, 62, 64, 66) per wheel brake (42, 44, 46, 48); an electrically controllable pressure provision device (20) which is formed by way of a cylinder/piston arrangement with a hydraulic pressure space (26); a brake master cylinder (10) with at least one pressure chamber (120, 122); a brake master cylinder piston displacement sensor (170); a brake master cylinder pressure sensor (188); a pressure medium storage vessel (18) which is under atmospheric pressure; a hydraulically configured simulator (14) with a simulator piston (198) and a simulator spring (196); at least one electrically actuable isolation valve (180, 182) which shuts off a hydraulic connection from the pressure chamber (120, 122) to the wheel brakes; at least one adding valve (240, 242) which, in the open state thereof, establishes a hydraulic connection from the pressure provision device (20) to the wheel brakes (42, 44, 46, 48) and the wheel valves (50, 52, 54, 56; 60, 62, 64, 66), and a simulator piston displacement sensor (206), the signal of which represents the displacement travel of the simulator piston (196).

Description

Brake system and method for operating a brake system

The invention relates to a brake system for motor vehicles, comprising hydraulically actuated wheel brakes, at least one electrically actuable wheel valve per wheel brake for setting wheel-individual brake pressures, an electrically controllable pressure supply device for the hydraulic actuation of the wheel brakes, which is formed by a cylinder-piston arrangement with a hydraulic pressure chamber, whose pressure piston is displaceable by an electromechanical actuator, an actuatable with a brake pedal actuation device, comprising a master cylinder with at least one pressure chamber into which a main ^¬ brake cylinder piston is displaced upon actuation of the brake pedal, a Hauptbremszylin- derkolbenwegsensor whose signal represents the travel of the master cylinder piston, a master cylinder pressure sensor whose signal represents a hydraulic pressure in the master cylinder caused by a brake pedal operating force under atmospheric pressure pressure fluid reservoir, which is hydraulically connected in the unactuated state of the master cylinder with the pressure chamber of the master cylinder, a hydraulically designed simulator with a simulator piston and a simulator spring, which is adapted to simulate the hydraulic volume intake pressurized wheel brakes, at least one electrically actuated isolation valve, that locks in its energized state, a hydraulic connection from the pressure chamber to the wheel brakes, at least one electrically and / or hydraulically actuated, closed in its inactive state to ^¬ switching valve that in its open state, a hydraulic connection from the pressure supply device to the wheel brakes or produces the wheel valves. It further relates to a method for operating a brake system.

In automotive engineering, electrohydraulic brake-by-wire brake systems are becoming increasingly widespread.

Such brake systems often include an electrically operable in addition to an operable by the driver master cylinder ("By-wire") controllable pressure supply device, by means of which in the "brake-by-wire" a

Pressurization of the wheel brakes takes place. In these electro-hydraulic brake systems, the driver is decoupled from the direct access to the brakes. This function is used in a "brake-by-wire" mode, in which a braking operation is carried out electronically, whereby a control unit controls the pressure supply device for active pressure build-up The hydraulic volume displaced from the master brake cylinder by the driver's pedal operation flows into the simulator, which serves to give the driver as familiar and comfortable a brake pedal feel as possible Determining a desired braking effect, from which then a desired brake pressure for the brakes is determined .The corresponding actual brake pressure in the wheel brakes is then actively provided by a pressure supply device.

The actual braking thus takes place by active pressure build-up in the brake circuits with the aid of a pressure-providing device, which is controlled by a control and regulation unit. The hydraulic decoupling of Bremspedalbetä ^¬ actuation of the pressure build-up can be in such brake systems, many functions such as ABS, ESC, TCS, etc. Hanganfahrhilfe in a technically efficient and the driver due to the pedal decoupling achieve particularly convenient manner.

In such brake systems, a hydraulic fallback level is usually provided, in which the driver decelerates the vehicle by muscular force when the brake pedal is actuated or decelerates the vehicle. can come to a halt when the "by-wire" mode fails or is disturbed During normal operation by a Pedalent ^¬ coupling unit, the above-described hydraulic decoupling between brake pedal operation and brake pressure build-up, this decoupling is canceled in the fallback so that the driver can move pressure medium directly into the brake circuits. In the fallback level is switched when with the help of the pressure supply device no pressure build-up is possible. This is the case, inter alia, when the check valve, which connects the pressure supply device to the reservoir, no longer reliably locks, so that a pressure build-up is no longer reliably possible.

The pressure supply device in brake systems described above is also referred to as an actuator or electro-hydraulic actuator. For example, an electrohydraulic actuator ^¬ Lischer by an electromechanical linear actuator is formed, which shifts to the pressure build a piston axially in a hydraulic pressure chamber. The electromechanical linear actuator is usually formed by the combination of an electric motor with a rotational-translation gear.

The master cylinder is usually designed as a tandem master cylinder (THZ) with a primary pressure chamber or primary chamber and a secondary pressure chamber or secondary chamber. In the primary chamber, a primary piston is displaceable, in the secondary chamber is a secondary piston, preferably floating, displaced.

From DE 10 2013 204 778 AI a "brake-by-wire" -Bremsanlage for motor vehicles is known which a brake pedal operable tandem master cylinder whose pressure chambers are connected via an electrically actuated release valve separable with a brake circuit with two wheel brakes, a hydraulically connected to the master cylinder, on and off switchable simulation device, and an electrically controllable pressure supply device, which is formed by a cylinder-piston arrangement with a hydraulic pressure chamber whose piston is displaceable by an electromechanical linear actuator includes, wherein the Druckbe ^¬ provisioning device via two electrically operated Connecting valves can be connected to brake circuit supply lines.

During the by-wire braking system operation reliably the driver's braking request has to be detected, so that it can be implemented through the pressure supply ^¬ provision means into a corresponding pressurization of the wheel brakes by means of the active pressure build-up. One known concept for detecting a brake pedal operation uses one

THZ primary piston travel signal and a secondary chamber pressure signal. This is to ensure that in case of failure of the displacement sensor signal, the pedal operation can be detected by means of the pressure ^¬ sensor signal that in case of failure of the pressure sensor signal, the pedal operation can be detected by means of the Wegs- sensor signal that a falsely closed simulator valve can be detected in that the path signal is too small in comparison with the pressure signal, and that a hydraulic leak can be detected by the pressure signal being too small compared to the path signal.

In this case, a piston travel sensor is used, which supplies a precise absolute signal immediately after the application of a supply voltage. In contrast, the pressure sensor delivers a signal which is shifted by an initially unknown offset. This offset must first be determined before the offset-adjusted pressure signal can be used. The offset is determined by averaging the pressure sensor signal over a period during which it is ensured that the Se ^¬ kundärkammer is connected to the pressure fluid reservoir and therefore has the atmospheric pressure. Thus, it may happen that in a pedal operation with a low pedal travel of the THZ primary piston is already well detected, while the secondary chamber pressure signal is so little different from the atmosphere ^¬ pressure that due to a not yet reliably determined offset value no pedal actuation information can be derived therefrom. The characteristic of the simulator spring is also usually non-linear. In the area of small paths, path changes only result in very small pressure changes. In addition, the detected pressures depend not only on the Pedaltbetätigungsweg, but also on the pedal speed. This is primarily an effect of the hydraulic flow resistance of the open Simula ^¬ gate valve. It has been found that a detection of hydraulic-mechanical errors by means of an adjustment of path and pressure signal can lead to false triggering.

It is furthermore known to check the function of the sealing rings in the THZ and in the simulator by closing a diagnosis valve in the hydraulic connection between the THZ primary chamber compensation connection and the pressure medium reservoir when the brake pedal is unactuated, in order then to build up pressure with the aid of the actuator, which must be possible with an intact system without a drainage of pressure medium to the container. During such checking operations, the braking system is not available for a short time, which creates potential danger in the event of suddenly necessary emergency braking.

The invention is therefore based on the object to improve the above brake system to the effect that it allows reliable and accurate detection of the pedal operation and the simulator state during operation. Furthermore, a particularly reliable method for operating a brake system should be specified.

With respect to the brake system, this object is achieved by a simulator piston stroke sensor, whose signal represents the displacement of the simulator piston.

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

The invention is based on the consideration that for a reliable and safe operation of a by-wire braking system the exact knowledge of the driver's brake request is of the utmost importance.

As has now been recognized, incorrect determinations of the driver braking request can be avoided by using an additional signal which essentially represents the operating state of the simulator. In the present case, this is the distance traveled by the simulator piston. As has also been recognized, the detection of the simulator piston displacement signal also enables diagnostic measures to determine the operability of hydraulic components of the brake system, thereby further increasing the safety of the driver.

The term "electro-mechanical actuator referred to in the context of the application of an electric motor whose rotor or motor shaft is coupled to a rotation-translation gear which converts the rotation of the rotor or of the motor shaft into a translatory ^¬ toric movement of the pressure piston of the pressure provisioning ^¬ device.

The brake system has an electronic control and Re ^¬ geleinheit or electronic unit, which in an electronically performed / controlled or

By-wire braking, if necessary, controls the pressure supply device and activates the valves.

In a first preferred embodiment, the brake system on a simulator valve, which in its inactive, d. H. de-energized state locks a hydraulic connection from the pressure chamber to the simulator and in its activated, i. energized, state this connection establishes.

In a second preferred embodiment, the

Master cylinder of the brake system on a donor chamber, wherein a simulator valve is provided, which in its de-energized state, a hydraulic connection from the master chamber or hydraulically connected to the master chamber

Simulator chamber to container and in its activated State locks.

Advantageously, the Simulatorkolbenwegsensor is redundant. In this way, a monitoring of this sensor by the electronic unit is enabled, which evaluates the two signals and compared with each other.

With regard to the method, the above-mentioned object is achieved according to the invention in that the path of the

Simulator piston is detected by means of a Simulatorkolbenwegsensors.

In a first preferred embodiment of the method, the brake system has a simulator valve that blocks a hydraulic connection from the pressure chamber to the simulator in its inactive or de-energized state and establishes this connection in its activated or energized state, wherein for performing an electronically controlled braking the simulator valve is opened to hydraulically couple the Hauptzylin ^¬ the primary piston movement with the Simulatorkolbenbewegung, and wherein the at least one isolating valve is closed to prevent pressure medium exchange between the master cylinder and the wheel brakes, wherein a driver brake request from the signals of Hauptbremszylinder- piston stroke sensor and Master cylinder pressure sensor is formed, and is monitored by means of the Simulatorkolbenwegsensorsignals whether a hydraulic coupling of master cylinder and simulator with simultaneous decoupling of master cylinder and wheel brakes vorl ying.

In this way, it is particularly monitored or checked whether the hydraulic Umschaltmaßnahmen performed at the beginning of the braking show the intended effect of a hydraulic coupling of master cylinder and simulator with simultaneous decoupling of the master cylinder and wheel brakes.

In a second preferred embodiment of the method, the master cylinder has a donor chamber, wherein a Simulator valve is provided which produces a hydraulic connection from the master chamber or a hydraulically connected to the transmitter chamber simulator chamber to the container in its de-energized state and locks in its activated state, wherein for carrying out an electronically controlled braking the simulator valve is closed to the main ^¬ cylinder Primary piston movement hydraulically coupled to the Simulatorkolbenbewegung and a primary piston relief valve is opened to produce a hydraulic connection of Hauptzy- primary cylinder with the container, and wherein the at least one isolation valve is closed to prevent a pressure ^¬ medium exchange between the master cylinder and the wheel brakes, and wherein a driver's brake request from the signals of the master brake cylinder piston stroke sensor and master cylinder pressure sensor is formed, and is monitored by means of the Simulatorkolbenwegsensorsignals whether a hyd ^¬ rauli Coupling of master cylinder and simulator with simultaneous decoupling of master cylinder and wheel brakes is present.

In this way, it is particularly monitored or checked whether the hydraulic Umschaltmaßnahmen performed at the beginning of the braking show the intended effect of a hydraulic coupling of master cylinder and simulator with simultaneous decoupling of the master cylinder and wheel brakes. If this is not the case, leakage, i. H. closed an unwanted drainage of pressurized brake fluid.

Advantageously, it is determined on the basis of the signals of the master brake cylinder piston stroke sensor and simulator piston stroke sensor, whether this is due to a pedal operation from the

Master cylinder displaced pressure fluid volume completely flows to the simulator.

It is preferably determined on the basis of the signals from Hauptbremszylinderkolben- wegfühler and Simulatorkolbenwegsensor whether the inflow as a result of a Pedalwegzurücknahme in the master cylinder pressure medium volume of Simulator-pressure medium volume delivery corresponds.

From the master brake cylinder piston travel signal, a master brake cylinder volume value is preferably calculated by multiplication with the master brake cylinder piston cross-sectional area and from the simulator piston travel signal by multiplication with the simulator piston cross-sectional area

Simulator volume value.

It is advantageously checked on the basis of the master brake cylinder volume value and the simulator volume value whether the sum of the pressure medium volumes of master brake cylinder and simulator remains constant during pedal-controlled braking.

Preferably is closed at a decreasing over time the main brake cylinder actuating ^¬ total volume of leakage.

Preferably, in the case of an increasing sum volume, a leaking separating valve is closed, via which pressure is wrongly set by the pressure supply device

Pressure fluid flows to the brake master cylinder and simulator.

Preferably, the signals of the simulator piston path and the master brake cylinder piston travel are related to the

Secondary chamber pressure signal. In this case, a limit value of the pressure signal is preferably assigned to each of the two path signals. If the value of the pressure signal is less than the respective limit, an incorrectly closed

Simulator valve closed or recognized the closed state of the simulator valve.

In the event of a detected failure of the master brake cylinder piston travel signal to determine the driver's brake request, a replacement master brake cylinder piston travel signal, which is formed from the simulator piston travel signal, is advantageously used. A failure of the Hauptbremszylinderkolbenwegsignals is advantageously recognized as follows: First, the electronic unit checks whether the sensor correctly supplies the two signals of its redundant sub-sensors. On the other hand, the electronic unit compares the two signals of the redundant units with each other and closes at a match of the two signals with very high

Probability of a fully functional sensor. Advantageously, in the case of a detected failure of the

Master brake cylinder piston stroke signal as a replacement master brake cylinder piston stroke signal the simulator piston stroke signal

multiplied by the quotient of the cross-sectional area of the simulator piston and the cross-sectional area of the simulator piston

Master brake cylinder piston used. In this way, the missing Hauptbremszylinderkolbenwegsignal can be replaced by an adequate replacement signal, so that the brake system continue to operate reliably in the by-wire mode. The advantages of the invention are, in particular, that the detection of the simulatormolbenweges the brake system even in case of failure of Hauptbremszylinderkolbenwegsignals the

Driver brake request can be detected reliably and precisely by forming a suitable substitute signal. Even in normal operation, ^false signals or leaks in the brake system can be detected with the aid of this additional signal.

A check of the oil seals in the master cylinder and in the simulator is not required with the pedal de-energized as this check is possible with each pedal operation without disturbing the regular operation of the brake system. All pressure bearing gaskets are checked by the fact that, when pedaling, the THZ primary piston travel sensor signal and the simulator piston travel signal must be proportional as soon as the pressure equalization connections of the THZ are closed. Such a review is simple and robust representable. It is not subject to any parameter fluctuations because it depends only on design dimensions, which in contrast to eg Simulator spring characteristic does not depend on temperature, material aging and the like. That the non-pressure bearing primary piston secondary sleeve is not tested is unprob ^¬ lematic. If this leaks, the tank level warning device responds as it is prior art for conventional brake systems. A diagnostic valve to check the functionality of the simulator is not needed. An embodiment of the invention will be described with reference to a

Drawing explained in more detail. In it show in a highly schematic representation:

FIG. 1 shows a brake system in a first preferred embodiment; and

FIG. 2 shows a brake system in a second preferred embodiment. Identical parts are provided in both figures with the same reference numerals.

In FIG. 1 shows an exemplary embodiment of a brake system 2 according to the invention. The brake system 2 or the brake system comprises an actuatable by means of an actuating or brake pedal 6 master cylinder 10, cooperating with the master cylinder 10 simulation device 14, the master cylinder 10 associated, under atmospheric pressure pressure medium reservoir 18, an electrically controllable pressure supply device 20, which by a cylinder-piston arrangement with a hydraulic

Pressure chamber 26 is formed, the piston 32 is displaceable by an electromechanical actuator, an electrically controllable pressure modulation device for adjusting wheel-individual brake pressures and an electronic control and regulating unit 40th The unspecified pressure modulation device comprises, for example, hydraulically actuated wheel brakes 42, 44, 46, 48 and each operable wheel brake 42 to 48, an inlet valve 50, 52, 54, 56 and an outlet valve 60, 62, 64, 66, which are hydraulically interconnected in pairs via center ports and to the

Wheel brakes 42 to 48 are connected. The input terminals of the intake valves 50 to 56 are supplied by means of Bremskreisver ^¬ supply lines 70 72 at pressures, which are derived in a 'brake-by-wire' mode of a system pressure in a line connected to the pressure chamber 26 of the pressure supply device 20 system pressure line 80 The brakes 42, 44 are connected to a first brake circuit 84, the brakes 46, 48 to a second brake circuit 88 hydraulically connected.

The inlet valves 50 to 56 is in each case an opening to the brake ^¬ circular supply lines 70, 72 through check valve 90, 92, 94, 96 connected in parallel. In a fallback mode of operation, the brake circuit supply lines 70, 72 are acted upon by hydraulic lines 100, 102 with the pressures of the brake means from pressure chambers 120, 122 of the master cylinder 10. The output ports of the exhaust valves 60 to 66 are connected via a return line 130 to the pressure fluid reservoir 18.

The master cylinder 10 includes a housing 136 in two successively arranged pistons 140, 142 which limit the hyd ^¬ raulischen pressure chambers 120, 122nd The pressure chambers 120, 122 are on the one hand via formed in the piston 140, 142 radial bores and corresponding pressure equalization lines 150, 152 with the pressure medium reservoir 18 in connection, the compounds by a relative movement of the pistons 140, 42 in the housing 136 can be shut off. On the other hand, the pressure chambers 120, 122 communicate with the already mentioned brake circuit supply lines 70, 72 by means of the hydraulic lines 100, 102. In the pressure equalization line 150, a normally open valve 160 is included. The pressure chambers 120, 122 receive unspecified return springs which position the pistons 140, 142 in an initial position when the master brake cylinder 10 is not actuated. A piston rod 166 couples the pivoting movement of the brake pedal 6 due to a pedal operation with the

Translational movement of the first master cylinder piston 140 and primary piston, whose actuation path is detected by a, before ^¬ preferably redundantly executed, displacement sensor 170. As a result, the corresponding piston travel signal is a measure of the brake pedal actuation angle. It represents a braking request of the driver.

In the line sections 100, 102 connected to the pressure chambers 120, 122, an isolation valve 180, 182 is arranged, which is designed as an electrically actuated, preferably normally open, 2/2-way valve. By separating valves 180, 182, the hydraulic connection between the

Pressure chambers 120, 122 of the master cylinder 10 and the

Brake circuit supply lines 70, 72 are shut off. A pressure sensor 188 connected to the line section 102 detects the pressure built up in the pressure chamber 122 by displacing the second piston 142. The simulation device 14 can be coupled hydraulically to the master brake cylinder 10 and, according to the example, essentially comprises a simulator chamber 190, a simulator spring chamber 194 and a simulator piston 198 separating the two chambers 190, 194. The simulator piston 198 is supported by an elastic element (shown in the simulator spring chamber 194) (FIG. For example, a spring), which is vorteilhaf ^¬ terweise biased on the housing 136 from. The simulator chamber 190 can be connected by means of an electrically operable simulator valve 200 to the first pressure chamber 120 of the master cylinder 10. Upon presetting a pedal force and open Si ^¬ mulatorventil 200 pressure fluid flows from Hauptbremszylin ^¬ the pressure chamber 120 in the simulator chamber 190. A hydraulically antiparallel to the simulator valve 200 arranged return Impact valve 210 allows independent of the switching state of the simulator valve 200 largely unhindered backflow of the pressure medium from the simulator chamber 190 for Hauptbrems ^¬ cylinder pressure chamber 120. Other designs and connections of the simulation device to the master cylinder 10 are conceivable.

The electrically controllable pressure supply device 20 is designed as a hydraulic cylinder-piston arrangement or a single-circuit electrohydraulic actuator whose / which pressure piston 32, which limits the pressure chamber 26, by a schematically indicated electric motor 220 with the interposition of a likewise schematically shown Rota- Translationsgetriebes, which is preferably designed as a ball screw (KGT), can be actuated. One of the detection of the rotor position of the electric motor 220 serving, le ^¬ diglich schematically indicated rotor position sensor is designated by the reference numeral 226. In addition, a temperature sensor 228 may be used to sense the temperature of the motor winding.

The actuator pressure generated by the force action of the piston 32 on the pressure medium enclosed in the pressure chamber 26 pressure actuator is fed into the system pressure line 80 and detected with a preferably redundant pressure sensor 230. With open pressure switching valves 240, 242, the pressure medium enters the wheel brakes 42 to 48 for their actuation. By pushing back and forth of the piston 32 takes place with open pressure switching valves 240, 242 in a normal braking in the "brake-by-wire" mode a Radbremsdruckaufbau and degradation for all wheel brakes 42 to 48.

When pressure is reduced, the pressure medium previously displaced from the pressure chamber 26 into the wheel brakes 42 to 48 flows back into the pressure chamber 26 in the same way. On the other hand, during braking, wheel brake pressures that are different for each individual wheel, controlled by means of the intake and exhaust valves 50 to 56, 60 to 66 (eg in the case of anti-skid control (ABS control)) of the discharged via the outlet valves 60 to 66 pressure medium component in the pressure fluid reservoir 18 and thus is initially the pressure supply device 20 for actuating the wheel brakes 42 to 48 are no longer available.

The path of the simulator piston is measured by means of a simulator ^¬ piston displacement sensor 206th The signal of the Simulatorkol ^¬ benwegsensors 206 may be used to ensure safe operation of the braking system 2 and reliably detect various malfunctions.

When braking in brake-by-wire mode of the brake system 2, the simulator valve 200 is opened, whereby the movement of the master cylinder primary piston 140 is hydraulically coupled with the movement of the simulator piston, and the isolation valves 180, 182 are closed to a pressure medium exchange between the master cylinder 10 and the wheel brakes 42, 44, 46, 48 to prevent. A driver brake request is formed from the signals of master brake cylinder piston travel sensor 170 and master brake cylinder pressure sensor 188, during the electronically controlled braking using the Simulatorkolbenwegsensor- signal monitors whether a hydraulic coupling of master cylinder 10 and simulator 14 with simultaneous decoupling of master cylinder 10 and wheel brakes 43, 44, 46, 48 is present. By the simultaneous monitoring of the skin ^¬ brake cylinder travel and pressure signals, the described hydraulic switching can be verified.

The in FIG. 2 brake system 2 differs from that shown in FIG. 1 illustrated brake system by the hydraulic connection of the simulator 14. The master cylinder 10 has a donor chamber 202, in which upon actuation of the brake pedal 6, an annular region of the primary piston 140 is moved. As a result, brake fluid is displaced from the master chamber 202. In the fallback plane mode the displaced pressure medium ^¬ volume via the hydraulically open simulator valve 160 into the container 18 and when releasing the pedal the same route flows back. In the by-wire mode, the simulator valve 160 is ak ^¬ tivated, thus hydraulically closed, whereby the from the ring portion of the primary piston 140, ie, the timer chamber thereby the simulator piston is displaced 198 is passed 202 displaced pressure medium in the simulator chamber 190, whose path is measured by the simulator piston stroke sensor 206.

Simultaneously with the simulator valve 160, the normally closed valve 204 is activated, whereby the valve 204 opens and establishes a hydraulic connection from the skin brake cylinder chamber 120 to the container 18. This allows the movement of the master cylinder piston 140 in the closed separation ^¬ valves 180., 182

To perform a brake-by-wire braking is in the brake system of FIG. 2 - deviating from the braking system of FIG. 1 - a normally open open simulator activated and thus hydraulically closed, whereby the pressure medium volume displaced from the master chamber 202 is passed into the simulatory chamber 190 hydraulically connected to the master chamber 202. This hydraulically couples the master cylinder primary piston movement to the simulator piston movement. At the same time, a primary piston relief valve 204 is opened to establish a hydraulic connection of the master cylinder primary chamber 120 to the pressure medium reservoir 18. The isolation valves 180, 182 are closed to inhibit fluid exchange between the master cylinder 10 and the wheel brakes 42, 44, 46, 48. During the electronically controlled braking or by-wire braking, a driver's braking request from the signals of master brake cylinder piston stroke sensor 170 and

Master cylinder pressure sensor 188 formed.

Based on the Simulatorkolbenwegsensorsignals is monitored whether a hydraulic coupling of master cylinder 10 and simulator 14 with simultaneous decoupling of master cylinder 10 and wheel brakes 42, 44, 46, 48 is present. As with the in FIG. 1 illustrated variant of the brake system 2 can by the simultaneous monitoring of Hautbremszylinderweg- and -pressure signals the described hydraulic switching ve ^{¬ be} verified.

The signal of the simulator path sensor can be seen in both in FIG. 1 and FIG. 2 shown embodiments of the brake system 2 are used to form a substitute signal, which in case of failure of the signals of Hauptbremszylinderkolbenweges and / or the

Master cylinder pressure signal for detecting the

Driver brake request can be used. In this way, the brake system 2 can still be operated even if one of the two signals associated with the master cylinder is no longer reliable or no longer available.

The substitute signal is preferably formed by the

Hauptbremszylinderkolbenwegsignal by multiplying the Hauptbremszylinderkolbenquerschnittsflache a Hauptbremszy- lindervolumenwert is calculated and from the Simulatorkol ^¬ benwegsignal by multiplication with the Simulatorkolben- cross-sectional area a simulator volume value. In the embodiment shown in FIG.l preferred embodiment of the brake system master cylinder 2, the piston cross-sectional area is the Primärkol ^¬ benstirnfläche. In the in FIG. From ^¬ preferred execution of the brake system 2 shown in Figure 2 is the cross-sectional area Hauptbremszylinderkolben- the donor chamber annular surface.

Claims

Brake system (2) for motor vehicles, comprising

Hydraulically actuated wheel brakes (42, 44, 46, 48);

• at least one electrically actuatable wheel valve (50, 52, 54, 56, 60, 62, 64, 66) per wheel brake (42, 44, 46, 48) for setting wheel-specific brake pressures;

• An electrically controllable pressure supply device (20) for the hydraulic actuation of the wheel brakes (42, 44, 46, 48), which by a

Cylinder-piston arrangement with a hydraulic

Pressure chamber (26) is formed, the pressure piston (32) by an electromechanical actuator (220) is displaceable;

• one with a brake pedal (6) operable actuating ^¬ device comprising a master cylinder (10) with at least one pressure chamber (120, 122), in which upon actuation of the brake pedal (6), a master brake cylinder piston (140, 142) is moved;

A master brake cylinder piston stroke sensor (170) whose signal represents the travel of the master brake cylinder piston (140);

A master brake cylinder pressure sensor (188) whose signal has a hydraulic pressure in the master brake cylinder (10) caused by a brake pedal actuation force

represents;

• a pressurized medium reservoir (18) under atmospheric pressure, which is hydraulically connected to the pressure chamber (120, 122) of the master brake cylinder (10) in the non-actuated state of the master brake cylinder (10);

A hydraulically designed simulator (14) with a simulator piston (198) and a simulator spring (196), which is adapted to the hydraulic volume intake to simulate pressurized wheel brakes;

• at least one electrically actuatable separating valve (180, 182) which, in its energized state, blocks a hydraulic connection from the pressure chamber (120, 122) to the wheel brakes;

At least one electrically and / or hydraulically actuatable, in its inactive state closed Zuschalt ^¬ valve (240, 242), in its open state, a hydraulic connection from the Druckbereit ^¬ positioning device (20) to the wheel brakes (42, 44, 46, 48) and the wheel valves (50, 52, 54, 56; 60, 62, 64, 66),

marked by

a simulator piston stroke sensor (206) whose signal represents the displacement travel of the simulator piston (196).

Brake system (2) according to claim 1 with a simulator valve (200) which in its inactive state blocks a hydraulic connection from the pressure chamber (120) to the simulator (14) and establishes this connection in its activated state.

Brake system (2) according to claim 1, wherein the Hauptbrems ^¬ cylinder (10) has a donor chamber (202), and wherein a simulator valve (160) is provided which in its de-energized state, a hydraulic connection from the donor chamber (202) or with a the encoder chamber (202) hydraulically connected simulator chamber (190) for

Pressure medium reservoir (18) produces and locks in its activated state.

Brake system (2) according to one of claims 1 to 3, wherein the Simulatorkolbenwegsensor (206) is designed redundant. Method for operating a brake system (2), which comprises

Hydraulically actuated wheel brakes (42, 44, 46, 48);

Cylinder-piston arrangement with a hydraulic

represents;

A hydraulically-trained simulator (14) having a simulator piston (198) and a simulator spring (196) adapted to simulate the hydraulic volume intake of pressurized wheel brakes; • at least one electrically actuatable separating valve (180, 182) which, in its energized state, blocks a hydraulic connection from the pressure chamber (120, 122) to the wheel brakes;

At least one electrically and / or hydraulically operable, in its inactive state closed Zuschalt ^¬ valve (240, 242), in its open state, a hydraulic connection from the pressure supply means (20) to the wheel brakes (42, 44, 46, 48) and the wheel valves (50, 52, 54, 56, 60, 62, 64, 66),

characterized in that

the travel of the simulator piston (198) by means of a simulator ^¬ piston displacement sensor (206) is detected.

The method of claim 5, wherein the brake system (2) comprises a simulator valve (200), which in its inactive state, a hydraulic connection from the pressure chamber

(120) to the simulator (14) blocks and in its activated state makes this connection, wherein for performing an electronically controlled braking the

Simulator valve (200) is opened by a movement of a primary piston (140) of the master cylinder (10)

hydraulically coupled to the simulator piston movement, and wherein the at least one isolation valve (180, 182) is closed to a pressure medium exchange between the

Master cylinder (10) and the wheel brakes (42, 44, 46, 48) to prevent, with a driver's brake request from the signals of master brake cylinder piston stroke sensor (170) and

Master cylinder pressure sensor (188) is formed, and is monitored by the simulator piston stroke sensor signal, whether a hydraulic coupling of master cylinder

(10) and simulator (14) with simultaneous decoupling of master cylinder (10) and wheel brakes (42, 44, 46, 48) present.

7. The method of claim 5, wherein the master cylinder (10) has a donor chamber (202), and wherein a

Simulator valve 160 is provided which in its non-energized state, a hydraulic connection from the master chamber (202) or with the transmitter chamber (202) hydraulically connected simulator chamber (190) to the pressure medium reservoir (18) produces and blocks in its activated state, wherein the Performing electronically controlled braking, the simulator valve (160) is closed to hydraulically couple the master cylinder primary piston motion to the simulator piston movement, and a primary piston relief valve 204 is opened to provide hydraulic communication to the primary piston

Master cylinder primary chamber (120) with the

Pressure medium reservoir (18) to produce or maintain, and wherein the at least one isolation valve (180, 182) is closed to prevent pressure fluid exchange between the master cylinder (10) and the wheel brakes (42, 44, 46, 48), and wherein a driver brake request is formed from the signals of master brake cylinder piston stroke sensor (170) and master cylinder pressure sensor (188), and wherein monitored during the electronically controlled braking using the Simulatorkolbenwegsensorsignals whether a hydraulic coupling of master cylinder (10) and simulator (14) with simultaneous decoupling of master cylinder (10 ) and wheel brakes (42, 44, 46, 48).

8. The method of claim 6 or 7, wherein based on the signals of master brake cylinder piston stroke sensor (170) and

Simulatorkolbenwegsensor (206) is determined whether that due to a pedal operation of the master cylinder (10) completely displaces the pressure medium volume

Simulator (14) flows.

The method of claim 8, wherein it is determined from the signals of master brake cylinder piston stroke sensor (170) and simulator piston stroke sensor (206), whether the pressure medium volume flowing into the master cylinder (10) due to a pedal travel cancellation corresponds to the simulator pressure medium volume delivery.

The method of claim 8 or 9, wherein from the

Master brake cylinder piston travel signal by multiplying by the master brake cylinder piston cross sectional area

Master cylinder cylinder volume value is calculated and from the Simulatorkolbenwegsignal by multiplication with the Simulatorkolbenquerschnittsfläche a simulator volume value is calculated.

The method of claim 10, wherein it is checked on the basis of the master brake cylinder volume value and the simulator volume value, whether during the pedal-controlled braking, the sum of the pressure fluid volumes of the master cylinder (10) and simulator (14) remains constant.

The method of claim 11, wherein is closed at a decreasing in the time course of the master cylinder actuation sum volume on a leak.

A method according to claim 10, wherein, in the case of an increasing sum volume, a leaking separating valve (180, 182) is closed.

The method of any of claims 5 to 13, wherein upon a detected failure of the master cylinder piston stroke signal For determining the driver's brake request, a substitute master brake cylinder piston travel signal is used which is formed from the simulator piston displacement signal. 15. The method of claim 14, wherein upon a detected failure of the Hauptbremszylinderkolbenwegsignals as

Replacement master brake cylinder piston stroke signal the Simulator ^¬ piston travel signal multiplied by the quotient of the cross-sectional area of the simulator piston (198) and the cross-sectional area of the master brake cylinder piston (140) is used.