DE102021207070A1 - Method for reducing brake pressure in a wheel brake cylinder of a brake system - Google Patents

Abstract

A method for reducing brake pressure in a wheel brake cylinder of a brake system to a predetermined target pressure includes reducing the brake pressure in the wheel brake cylinder by moving a piston in a master brake cylinder by means of a drive, detecting an overpressure situation in which a residual distance of the piston to a brake fluid reservoir connected Compensation bore is not sufficient to reduce residual pressure in the wheel brake cylinder by moving the piston to the target pressure, and if an overpressure situation is detected: closing a first isolating valve, through which the master brake cylinder is hydraulically connected to the wheel brake cylinder, positioning the piston in such a way that the compensation bore is open, and a reduction in the residual pressure by opening at least one valve which hydraulically connects the wheel brake cylinder to the master brake cylinder.

Description

technical field

The present invention relates to a method for reducing brake pressure in a wheel brake cylinder of a brake system.

State of the art

Electrohydraulic brake systems for vehicles, such as for passenger cars, usually have a master brake cylinder which is hydraulically coupled to a wheel brake cylinder in order to generate a brake pressure in the wheel brake cylinder by displacing a piston in the master brake cylinder. The movement of the piston can take place as a result of an actuation of a brake pedal or a brake lever, the actuation usually being supported by a drive, e.g. an electric drive, or being taken over by the drive. The brake master cylinder has a compensation bore connected to a brake fluid reservoir, via which brake fluid can be replenished into the brake master cylinder. As soon as the piston closes via the compensation bore, a closed volume is formed between the piston and the wheel brake cylinder, in which volume hydraulic pressure can be built up by moving the piston in a forward direction.

It is also common for electrohydraulic brake systems to have a brake pressure control system that has its own pressure generation device, such as a pump, and a valve arrangement in order to be able to vary the brake pressure in the wheel brake cylinder independently of the actuation of the master brake cylinder.

Furthermore, in brake systems with a hydraulic basic brake, a parking brake or parking brake can be provided, which has a parking brake actuator that actuates the wheel brake cylinder. For example, in the U.S. 8,776,958 B2 describes a wheel brake with a wheel brake cylinder which can be actuated by a parking brake actuator and by a hydraulic brake system.

If the wheel brake cylinder was actuated independently of an actuation of the master brake cylinder, e.g. by a parking brake actuator or by the pressure generating device of the brake pressure control system, it may be desirable to reduce brake pressure in the wheel brake cylinder in a defined manner. For example, a corresponding pressure can first be built up in the master brake cylinder by moving the master brake cylinder in the forward direction in order to at least partially maintain a braking force generated by the wheel brake cylinder for a specific time. Since the master brake cylinder is actuated in a situation in which the wheel brake cylinder is already actuated, the piston only has to cover a short distance in order to be able to generate high pressures. If the piston is moved in a reverse direction to reduce pressure after the parking brake actuator has been released, it may happen that the compensation bore is uncovered before a predetermined target pressure in the brake master cylinder is reached.

Disclosure of Invention

According to the invention, a method having the features of claim 1 is provided.

A method according to the invention for reducing brake pressure in a wheel brake cylinder of a brake system to a predetermined target pressure comprises reducing the brake pressure in the wheel brake cylinder by moving a piston in a master brake cylinder, in particular in a first direction or reverse direction, by means of a drive, e.g. an electric drive of a brake booster , detecting an overpressure situation in which a residual distance of the piston from a compensation bore connected to a brake fluid reservoir is not sufficient to reduce residual pressure in the wheel brake cylinder by moving the piston to the target pressure, and, if an overpressure situation is detected: closing a first isolation valve, through which the master brake cylinder is hydraulically connected to the wheel brake cylinder, positioning the piston such that the compensation bore is open, and reducing the residual pressure by at least partially opening n at least one valve which hydraulically connects the wheel brake cylinder to the master brake cylinder.

One of the ideas on which the invention is based is, in situations in which the pressure in the wheel brake cylinder cannot be reduced to a target pressure, which can be, for example, in a range between 2 bar and 15 bar, by moving the piston in the master brake cylinder without prior Reaching the target pressure, the compensation bore of the master brake cylinder would be released to reduce the residual pressure that cannot be reduced in the master brake cylinder via a valve that hydraulically connects the wheel brake cylinder to the master brake cylinder. For this purpose, the master brake cylinder is first hydraulically separated from the wheel brake cylinder, in which a separating valve is closed, and as far moves, eg in the reverse direction as far back that the compensation drilling is released. The corresponding valve is then opened in order to release the brake fluid from the wheel brake cylinder into the master brake cylinder or into the reservoir in a defined manner.

Reducing the residual pressure via a valve when the compensation bores are open instead of moving the piston offers the advantage that a rapid, uncontrolled drop in pressure in the master brake cylinder and in the wheel brake cylinder can be avoided. A noise reduction is thus advantageously achieved. Furthermore, the safety of the braking system is improved.

Advantageous refinements and developments result from the further dependent claims and from the description with reference to the figures of the drawing.

According to some specific embodiments, it can be provided that the reduction of the residual pressure includes an opening of the first isolating valve. The brake fluid can thus be drained through the isolating valve in a controlled manner after the compensation bores have been opened. The isolating valve can be designed, for example, as a flow-controllable solenoid valve whose flow cross-section can be varied. This further facilitates controlled pressure reduction.

According to some embodiments, it can be provided that the reduction of the residual pressure includes opening an outlet valve of a brake pressure control system and a second isolating valve, the outlet valve being arranged in a suction path which connects the wheel brake cylinder to a pressure generating device of the brake pressure control system, and the second isolating valve closing the suction path connected to the master brake cylinder. As an alternative or in addition to the pressure reduction via the first isolating valve, the pressure reduction can be implemented via a valve arrangement of the brake pressure control system.

According to some embodiments, it can be provided that the at least one valve is opened in such a way that the residual pressure is reduced continuously, in particular linearly. For example, it can be provided that a flow cross section of the valve is set and/or regulated in such a way that a ramp-shaped pressure reduction takes place. A continuous reduction in pressure is particularly favorable with regard to noise development.

According to some embodiments, it can be provided that before the brake pressure in the wheel brake cylinder is reduced, the brake pressure in the master brake cylinder is built up by moving the piston, in particular in a second direction or a forward direction, by means of the drive, in order to maintain a frictional force generated by the wheel brake cylinder. According to these embodiments, the pressure in the master brake cylinder is built up in a state in which the wheel brake cylinder is already actuated. In such situations, there is a fundamental risk that, in the event of a subsequent pressure reduction, the distance between the piston and the compensation bore is not sufficient to reduce the brake pressure to the target pressure by moving the piston in the reverse direction.

According to some embodiments, the frictional force can be generated, for example, by operating a parking brake actuator to press a first friction piece, which is coupled to the wheel brake cylinder, against a second friction piece, which is provided for coupling to a wheel, the parking brake actuator being Building up the braking pressure is operated in order to reduce the force exerted on the first friction piece. Accordingly, it is provided that the master brake cylinder takes over the generation of the frictional force by the wheel brake cylinder, at least before the parking brake actuator is completely released. This means that the main brake cylinder first generates a braking pressure to generate a clamping force that is sufficient, for example, to hold the vehicle securely (e.g. depending on the incline). In particular, the master brake cylinder can have a braking pressure that is equivalent to the clamping force generated by the parking brake actuator, which can be in a range between 70 bar and 140 bar, for example, or a braking pressure that compensates for at least a predetermined proportion of the clamping force generated by the parking brake actuator, e.g. at least 50 % of the clamping force generated by the parking brake actuator, for example in a range from 35 bar to 50 bar. The braking pressure is then reduced in the manner described above by moving the master brake cylinder. Since high frictional forces are typically generated by the parking brake actuator, a high pressure difference at the wheel brake cylinder usually has to be reduced. In this case, the pressure reduction via one or more valves, as described above, is particularly advantageous since the valves facilitate a low-noise, controlled pressure reduction in a simple manner.

According to some embodiments, the frictional force can be generated, for example, by operating a pressure generating device of a brake pressure control system when the first separating valve is closed in order to generate the brake pressure in the wheel brake cylinder, with the first separating valve being opened after the brake pressure has built up in the master brake cylinder.

According to some specific embodiments, it can be provided that the method includes determining a residual distance of the piston from the compensation bore of the master brake cylinder and determining the residual pressure to be reduced. the remaining distance can be determined, for example, based on the distance from the compensation bore to a reference point and a travel of the piston, which is detected by means of a travel sensor, in relation to the reference point. To determine the residual pressure to be reduced, it is conceivable to detect an actual pressure in the master brake cylinder using a pressure sensor and to determine a difference between the actual pressure in the master brake cylinder and the target pressure. An overpressure situation can be detected in a simple manner, for example, if the residual pressure is above a threshold value at a certain residual distance of the piston.

According to some specific embodiments, it can be provided that the detection of the overpressure situation includes detecting an actuation of the wheel brake cylinder independently of a movement of the piston of the master brake cylinder. Accordingly, the existence of an overpressure situation can be generally concluded if the wheel brake cylinder generates or is actuated a frictional force without the piston having performed a movement equivalent thereto. This type of detection offers the advantage that it is extremely easy to implement in terms of control technology.

According to some specific embodiments, it can be provided that the detection of the actuation of the wheel brake cylinder includes retrieving at least one of the following information from a memory: an actuation state of a parking brake actuator, an actual pressure in the wheel brake cylinder. Such values can, for example, be stored in a memory, for example it can be stored that and for how long the pressure generating device of the brake pressure control system is operated when the first isolating valve is closed. Likewise, an actuation state can optionally be stored together with a generated clamping force. It is thus easy to recognize situations in which pressure may have to be built up in the master brake cylinder in a state in which the wheel brake cylinder is already actuated.

• 1 eine schematische Ansicht eines hydraulischen Schaltplans eines Bremssystems zur Ausführung eines Verfahrens gemäß einem Ausführungsbeispiel der Erfindung;
• 2 eine vereinfachte Schnittansicht von Komponenten eines Bremssystems während eines Verfahrens gemäß einem Ausführungsbeispiel der Erfindung, wobei ein Zustand dargestellt ist, in welchem ein Druckabbau durch Bewegen eines Kolbens eines Hauptbremszylinders erfolgt;
• 3 das in 2 gezeigte Bremssystem, während des Druckabbaus zu einem späteren Zeitpunkt;
• 4 das in den 2 und 3 gezeigte Bremssystem, in einem Zustand, in dem ein Trennventil geschlossen und der Kolben in eine Stellung bewegt ist, um eine Kompensationsbohrung freizugeben;
• 5 das in den 2 bis 4 gezeigte Bremssystem, in einem Zustand, in dem ein Druckabbau über das Trennventil erfolgt; und
• 6 ein Ablaufdiagramm eines Verfahrens gemäß einem Ausführungsbeispiel der Erfindung.

The invention is explained below with reference to the figures of the drawings. From the figures show:

• 1 a schematic view of a hydraulic circuit diagram of a brake system for carrying out a method according to an embodiment of the invention;
• 2 a simplified sectional view of components of a brake system during a method according to an embodiment of the invention, wherein a state is shown in which a pressure reduction takes place by moving a piston of a master brake cylinder;
• 3 this in 2 brake system shown, during the pressure reduction at a later point in time;
• 4 that in the 2 and 3 brake system shown, in a condition in which an isolation valve is closed and the piston is moved to a position to uncover a compensation bore;
• 5 that in the 2 until 4 Brake system shown, in a state in which a pressure reduction takes place via the isolation valve; and
• 6 a flowchart of a method according to an embodiment of the invention.

In the figures, the same reference symbols designate identical or functionally identical components, unless otherwise stated.

1 shows schematically and purely by way of example a brake system 100, in particular for a vehicle such as a passenger car. As in 1 shown as an example, brake system 100 includes wheel brakes, each with a wheel brake cylinder 1, a master brake cylinder 2, a brake booster or drive 22, a brake fluid reservoir 3, a brake pressure control system 5, and a control system with at least one control unit 120. 2 shows a highly simplified brake system 100 with master brake cylinder 2, drive 22, reservoir 3, and wheel brake cylinder 1.

The wheel brake cylinders 1 are designed as hydraulically actuated cylinders to which a first friction piece 111, for example in the form of brake pads, can be coupled, as is shown in 2 is shown schematically. By generating a hydraulic brake pressure in the wheel brake cylinder 1, the first friction piece 111 can be pressed against a second friction piece 112, for example a brake disc, it being possible for the second friction piece 112 to be coupled to a wheel of the vehicle. As in 2 is also shown, a parking brake actuator 110 can optionally be coupled to the wheel brake cylinder 1, which is designed to actuate the wheel brake cylinder 1 or to apply a force to the first friction piece 111 in order to press it against the second friction piece 112 and generate a friction force or to generate clamping force.

As in the 1 and 2 shown schematically, the master cylinder 2 is hydraulic connected to each of the wheel brake cylinders 1. As in 2 shown schematically, the master brake cylinder (HBZ) 2 forms a volume in which a piston 20 can be moved back and forth linearly in a forward direction D1 and in a reverse direction D2. As in 2 shown purely as an example, the master brake cylinder 2 can be designed as a tandem master brake cylinder with a double piston or two pistons 20 kinematically coupled to one another. For the sake of simplicity, the term piston 20 is used below without restricting generality. As in 2 Also shown is that the master brake cylinder 2 has a compensation bore 21 , one compensation bore 21 being provided for each piston 20 . Furthermore, the HBZ 2 has a connection bore 24 which is spaced apart from the compensation bore 21 in the forward direction D1 and via which one or more wheel brake cylinders 1 are connected to the HBZ 2 . The reservoir 3, in which brake fluid is accommodated, is fluidically connected to the compensation bore 21. When the piston 20 is moved in the forward direction D1, a closed volume is formed between the wheel brake cylinder 1 and the piston 20 as soon as the piston 20 moves as shown in FIG 2 shown schematically, the compensation bore 21 has passed in the forward direction D1 and is arranged between the connection bore 24 and the compensation bore 21 . Pressure can thus be built up in the wheel brake cylinder 1 by moving the piston 20 in the forward direction D1 and reduced again by moving the piston 20 in the backward direction D2. As in 1 is shown purely by way of example, two wheel brake cylinders 1, for example, can be hydraulically connected to each connection bore 24.

The piston 20 can be actuated or movable, for example, by a pedal 4 kinematically coupled to the piston 20 or by another actuating device, such as a lever. As in the 1 and 2 shown schematically, a drive 22 can be provided to increase the force applied by the pedal 4 to the piston 20 and/or to move the piston 20 independently of an actuation of the pedal 4 . The drive 22 can be designed as an electric drive, for example.

As in the 1 and 2 is also shown, the brake system 100 on first isolation valves 41, which is arranged in a hydraulic path between the HBZ 2 and the wheel brake cylinders 1. For example, a first isolation valve 41 can be provided for each connection bore 24, as in FIGS 1 and 2 shown as an example. The first isolating valves 41 can be designed as solenoid valves, in particular as flow-controllable solenoid valves. In general, the first isolating valves 41 are set up to interrupt a hydraulic connection between the wheel brake cylinder 1 and the HBZ 2 in a closed state and to allow a fluid flow between the HBZ 2 and the wheel brake cylinder 1 in an open state.

The brake pressure control system 5 is in 1 shown only schematically and is used for wheel-specific variation of the brake pressure in the wheel brake cylinder 1 or for actuating the wheel brake cylinder 1 independently of the actuation of the HBZ 2. As in 1 shown schematically, the brake pressure control system 5 has a pressure generating device 50, for example in the form of a pump driven by a motor 55, a second isolating valve 53 and each wheel brake cylinder 1 has an inlet valve 51 and an outlet valve 52. As in 1 shown by way of example, a common pressure generating device 50 and a common second isolating valve 53 can be provided for the wheel brake cylinders 1 that are connected to the same connection bore 24 of the HBZ 2 . Provision can also be made for all pressure generating devices 50 to be driven by the same drive 55 .

As in 1 shown as an example and schematically, the inlet valve 51 of the respective wheel brake cylinder 1 is arranged in a hydraulic path between the first isolation valve 41 and the wheel brake cylinder 1 . The outlet valve 52 of the respective wheel brake cylinder 1 is arranged in a suction path which connects a region of the hydraulic path between the inlet valve 51 and the wheel brake cylinder 1 to a suction inlet of the pressure generating device 50 . A pressure outlet of the pressure generating device 50 is correspondingly connected to a region of the hydraulic path between the first separating valve 41 and the wheel brake cylinder 1 located between the first separating valve 41 and the inlet valve 51 . As in 1 As further shown, the second isolating valve 53 is arranged in a return line path which connects the suction path to the HBZ 2 .

The second isolating valves 53 can be designed as solenoid valves, in particular as flow-controllable solenoid valves. The inlet and outlet valves 51, 52 can also be designed as solenoid valves, it also being conceivable that at least the outlet valves 52 are implemented as flow-controllable valves.

The control system may include one or more controllers 120 . In 1 a control unit 120 is shown only symbolically, which can be embodied, for example, as an electronic control unit with a processor and a data memory. General is the control system set up to generate output signals based on input signals, eg sensor signals. The control system is connected to the drive 22, the motor 55 of the brake pressure control system 5 and the valves 41, 51, 52, 53. The control system can also be connected to a pressure sensor 42, which detects a pressure in HBZ 2, and/or to a travel sensor 43, which detects a travel distance covered by piston 20 in relation to a reference point. The control system can generally be designed to output output signals to the drive 22, the motor 55 and the valves 41, 51, 52, 53 in order to actuate or control them in each case.

At the in the 1 and 2 Braking systems 100 shown can occur during operation in which wheel brake cylinder 1 is actuated independently of HBZ 2. For example, the wheel brake cylinder 1 can be actuated by the parking brake actuator 110 or the pressure generating device 50 builds up a brake pressure in the wheel brake cylinder 1 when the first isolating valve 41 is fully or partially closed and the second isolating valve 53 is open. In such situations, it may be necessary to reduce the braking pressure in wheel brake cylinder 1 in a defined manner or, if wheel brake cylinder 1 is actuated by parking brake actuator 110, before releasing parking brake actuator 110, first of all to increase a braking pressure or build up a brake pressure in the wheel brake cylinder 1 that at least partially compensates for the force generated and then reduce it in a defined manner.

In 6 a method M for reducing a brake pressure in a wheel brake cylinder 1 to a predetermined target pressure is shown schematically, which in the above situations using the in the 1 and 2 Brake systems 100 shown can be carried out. the 2 until 5 show various states of braking system 100 during method M.

As in 6 shown schematically, method M can start from a state M01 or M01', in which wheel brake cylinder 1 is actuated independently of HBZ 2 to generate a frictional force. For example, as shown in 2 As shown schematically, the parking brake actuator 110 is operated (step M01) to press the first friction piece 111 to the second friction piece 112. Alternatively, in step M01′ the frictional force can be generated by operating the pressure generating device 50 of the brake pressure control system 5 to generate the brake pressure in the wheel brake cylinder 1 when the first isolating valve 41 is closed and the second isolating valve 53 is open. In step MO1', the exhaust valves 52 are closed while the intake valves 51 are opened. After the pressure has built up in step M01', the second isolating valves 53 are closed again. If the piston 20 is arranged during step MO1 or MO1' in such a way that it releases the compensation bore 21, the pressure in the HBZ 2 is the same as that in the reservoir 3, ie ambient pressure.

In a further step M02 of method M, a brake pressure is built up in master brake cylinder 2 that is sufficiently high to maintain the frictional force generated by wheel brake cylinder 3 . For this purpose, the piston 20 is moved in the forward direction D1 by means of the drive 22 in the HBZ 2 . 2 shows an example of the state of the brake system 100 after the execution of step M02. If the method M starts from step M01, the first isolation valve 41 is opened in step M02, and in a further step M03 the parking brake actuator 110 is operated in such a way as to reduce the force exerted on the first friction piece 111. That is, the parking brake actuator 110 is fully or partially released, the first friction piece 111 is held or only partially released as a result of the hydraulic brake pressure in the wheel brake cylinder 1, which was built up in step M02 in HBZ 2, in order to continue to hold the vehicle. If method M starts from step MO1`, first separating valve 41 is closed in step MO2, and in a further step MO3`, after the brake pressure has built up in master brake cylinder 2, first separating valve 41 is opened.

Since the brake pressure is built up in step M02 in HBZ 2 in a state in which wheel brake cylinder 1 is already being actuated and there is therefore already a correspondingly large volume of brake fluid between piston 20 and wheel brake cylinder 1, a relatively short displacement path of the piston 20 in the forward direction D1, a large hydraulic pressure can be built up. In 2 a distance s21 between the piston and the compensation bore 21 is drawn in at the end of step M02.

in the in 6 Step M1 shown is a reduction M1 of the brake pressure in the wheel brake cylinder 1 by moving the piston 20 in the master brake cylinder 2. For this purpose, the piston 20 is moved in the reverse direction by means of the drive 22.

Optionally, a remaining distance s21 of the piston 20 from the compensation bore 21 of the brake master cylinder 2 can be determined in step M2. For example, the travel sensor 43 can detect the travel traveled by the piston 20 in relation to a reference point, wherein the control system can be set up to do this based on a position of the compensation bore 21 in relation to the reference point and to determine the remaining distance s21 based on the detected travel.

In a further optional step M3, a residual pressure still to be reduced is determined, i.e. a difference between the target pressure and a current pressure or actual pressure in HBZ 2. For example, the actual pressure in HBZ 2 can be detected by pressure sensor 42 and that Control system can calculate the difference between the actual pressure and the target pressure.

In step M4, the presence of an overpressure situation is detected, in which the remaining distance s21 of the piston 20 from the compensation bore 21 is not sufficient to generate a residual pressure in the wheel brake cylinder 1, i.e. the difference between the actual pressure and the target pressure, by moving the piston 20 reduce the pressure to aim. In other words, an overpressure situation occurs when the piston 20 would be moved further in the reverse direction D2 and at the point in time at which the piston 20 would release the compensation bore 21, the presence of pressure in the master brake cylinder 2 or in the wheel brake cylinder 1 is to be expected , which is greater than the target pressure. In this case, the brake fluid would escape from the HBZ 2 through the compensation bore 21, which would lead to a collapse of the brake pressure. This could lead to an unwanted drop in the frictional force between the friction pieces 111, 112. In addition, the high flow velocities and the throttling effect of the compensation bore can lead to unwanted noise. This also applies if an attempt were made to compensate for the drop in pressure by moving the piston 20 quickly and briefly in the forward direction D1.

The presence of an overpressure situation can be determined, for example, by evaluating the determined residual pressure and the determined remaining distance s21, for example by the control system comparing the determined residual pressure with a predetermined threshold value when a predetermined remaining distance s21 is reached. If the residual pressure is greater than the threshold, an overpressure situation is detected. Alternatively or additionally, an actuation of the wheel brake cylinder 1 can be detected independently of a movement of the piston 20 of the master brake cylinder 2 in order to detect M4 an overpressure situation. For example, typical situations or states of brake system 100 in which an overpressure situation can occur can be recorded and stored in the data memory of the control system. For example, the actuation state of parking brake actuator 110 and/or an actual pressure in wheel brake cylinder 1 can be recorded or approximated as a model pressure and stored in the data memory. If the piston 20 is actuated in the HBZ 1, e.g. in step M02 and/or in step M1, the information stored in the data memory can be retrieved and a state can be concluded therefrom which corresponds to an overpressure situation.

If an overpressure situation is detected in step M4, as is the case in 6 is represented by the symbol "+", the process proceeds to step M5. If no overpressure situation is detected in step M4, the pressure can be released further by moving the piston 20 in the reverse direction D2. Accordingly, the procedure as in 6 shown, return to step M1 again.

In step M5, the first isolation valve 41 is closed. This is an example in 3 shown. The HBZ 2 is hydraulically decoupled from the wheel brake cylinder 1 by the closing of the first isolating valve 41 . In a further step M6, the piston 20 is moved further in the reverse direction D2 by the drive 22 in order to position the piston 20 in such a way that the compensation bore 21 is open. This state is shown schematically in 4 shown.

In order to reduce the residual pressure still present in the wheel brake cylinder 1 in this state to the target pressure, in step M7, for example, the first isolating valve 41 can be fully or partially opened. Alternatively or in addition to this, in step M7 at the in 1 Brake system 100 shown as an example, the outlet valve 52 and the second isolation valve 53 are opened. In general, the residual pressure is thus reduced in step M7 by at least partially opening at least one valve 41, 52, 53, which hydraulically connects the wheel brake cylinder 1 to the master brake cylinder 2. By opening the respective valves 41, 52, 53, the residual pressure can be reduced in a controlled manner by releasing the brake fluid from the wheel brake cylinder 1 into the HBZ 2, in which the compensation bore 21 is open. In particular, a continuous pressure reduction can take place in a simple manner, for example by adjusting the flow cross section of the respective valve when using flow-controlled valves in such a way that a continuous, for example linear, pressure reduction takes place. It should be noted that the execution of step M7 can already be started during the execution of step M6.

By reducing the residual pressure via at least one of the valves 41 or 52 and 53, an uncontrolled pressure drop in overpressure situations is advantageously avoided.

The control system of brake system 100 can be designed in particular to cause brake system 100 to carry out the steps of method M described above. For example, the control unit 120 can output corresponding actuation signals in order to actuate the drive 22 and the valves 41, 51, 52, 53.

Although the present invention has been explained above by way of example using exemplary embodiments, it is not limited thereto but can be modified in many different ways. In particular, combinations of the above exemplary embodiments are also conceivable.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US8776958B2 [0004]

Claims (10)

Method (M) for reducing a brake pressure in a wheel brake cylinder (1) of a brake system (100) to a predetermined target pressure, comprising: Reducing (M1) the braking pressure in the wheel brake cylinder (1) by moving a piston (20) in a master brake cylinder (2) by means of a drive (22); Detecting (M4) an overpressure situation in which a residual distance (s21) of the piston (20) from a compensation bore (21) connected to a brake fluid reservoir (3) is not sufficient to release a residual pressure in the wheel brake cylinder (1) by moving the piston (20) to reduce to target pressure; and, if an overpressure situation is detected: Closing (M5) a first isolating valve (41) through which the master brake cylinder (2) is hydraulically connected to the wheel brake cylinder (1); Positioning (M6) of the piston (20) such that the compensation bore (21) is open; and Reducing (M7) the residual pressure by at least partially opening at least one valve (41; 52; 53) which hydraulically connects the wheel brake cylinder (1) to the master brake cylinder (2). Procedure (M) according to claim 1 , wherein the reduction (M7) of the residual pressure comprises an opening of the first isolating valve (41). Procedure (M) according to claim 1 or 2 , wherein the reduction (M7) of the residual pressure comprises opening an outlet valve (52) of a brake pressure control system (5) and a second isolating valve (53), the outlet valve (52) being arranged in a suction path which connects the wheel brake cylinder (1) with a Pressure generating device (50) of the brake pressure control system (5) connects, and wherein the second isolation valve (53) connects the suction path to the master cylinder (2). Method (M) according to one of the preceding claims, wherein the at least one valve (41; 52; 53) is opened in such a way that the residual pressure is reduced continuously, in particular linearly. Method (M) according to one of the preceding claims, wherein before the reduction (M1) of the brake pressure in the wheel brake cylinder (1) the brake pressure in the master brake cylinder (2) is built up (M02) by moving the piston (2) by means of the drive (22). , in order to maintain a frictional force generated by the wheel brake cylinder (1). Procedure (M) according to claim 5 , wherein the frictional force is generated by a parking brake actuator (110) being operated (M01) to press a first friction piece (111), which is coupled to the wheel brake cylinder (1), to a second friction piece (112), which is used for Coupling is provided with a wheel, and wherein the parking brake actuator (110) is operated (M03`) after the build-up (M02) of the braking pressure in order to reduce the force exerted on the first friction piece (111). Procedure (M) according to claim 5 , wherein the frictional force is generated in that, when the first separating valve (41) is closed, a pressure generation device (50) of a brake pressure control system (5) is operated (M01') in order to generate the brake pressure in the wheel brake cylinder (1), wherein after the build-up (M02 ) of the brake pressure in the master brake cylinder (2), the first isolating valve (41) is opened. Method (M) according to any one of the preceding claims, additionally comprising: Determination (M2) of the remaining distance (s21) of the piston (20) to the compensation bore (21) of the master brake cylinder (2); and Determining (M3) the residual pressure to be reduced, in particular by detecting an actual pressure in the master brake cylinder (2) and determining a difference between the actual pressure in the master brake cylinder (2) and the target pressure. Method (M) according to one of the preceding claims, wherein the detection (M4) of the overpressure situation includes detecting an actuation of the wheel brake cylinder (1) independently of a movement of the piston (20) of the master brake cylinder (2). Procedure (M) according to claim 9 , wherein the detection of the actuation of the wheel brake cylinder (1) comprises retrieving at least one of the following information from a memory: an actuation state of a parking brake actuator (110); an actual pressure in the wheel brake cylinder (1).

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