DE102022213325A1 - Brake system with improved leakage protection - Google Patents

Abstract

The invention relates to a hydraulic brake system for actuating a plurality of wheel brakes (5), having a linear actuator (2) for providing hydraulic pressure in the wheel brakes (5), which has a connection (80) to a pressure-free brake fluid reservoir (3). To improve availability in the event of leaks, an associated control unit (A, B) is designed to carry out leak detection and, if no leak is detected, to open the connection (80) to switch to sleep mode and/or standby mode by moving the linear actuator (3), and to close the connection (80) by moving the linear actuator (3) if a leak is detected.

Description

The invention relates to a hydraulic brake system for actuating a plurality of wheel brakes, comprising a linear actuator for providing hydraulic pressure in the wheel brakes, which has a connection to a pressure-free brake fluid reservoir.

The connection can be a suction or sniffer hole connection. A sniffer hole connection ensures the basic requirement of connecting the brake callipers to the atmosphere when the power is off or in a sleeping state. This is due to the need for pressure equalization, which is particularly necessary due to temperature fluctuations. If the brake is left hot, the brake fluid, which has expanded as a result of the heating, cools down again, which would lead to a negative pressure. This could result in the brake drawing in air. Air in the brake can seriously impair its functionality.

Subsequent heating, for example through heat conduction from the hot brake discs and pads, can also be problematic. The resulting expansion of the brake fluid leads to a build-up of pressure and thus to unwanted braking force.

To avoid this, with a classic sniffer hole connection through a tandem master brake cylinder, the brake system is always connected to the atmosphere when the pedal is released. This means that a wheel brake always has an atmosphere connection even when it is electrically switched off. With an e-pedal, i.e. a brake pedal that no longer has a hydraulic connection to the wheel brakes, this is not so easy. Instead, a connection must be actively established. This is possible, for example, via a sniffer hole in the linear actuator, which can be moved to a position in which the sniffer hole is open.

However, if a leak occurs in the brake system, particularly in one of the wheel brakes, this pressure equalization connection leads to a total loss of a large part of the brake fluid. A suction connection can also lead to a loss of brake fluid in the event of a leak, particularly if a check valve that may be present does not close tightly. The availability of the brake system is therefore greatly reduced.

It is therefore an object of the present invention to provide a braking system which has a high level of availability.

The object is achieved by a hydraulic brake system according to claim 1. According to the invention, an associated control unit is set up to carry out leak detection and, if no leak is detected, to open the connection to transition to a sleep mode and/or stand-by mode by moving the linear actuator and, if a leak is detected, to close the connection by moving the linear actuator.

In a preferred embodiment of the invention, the connection is a sniffer hole connection. The sniffer hole connection is a connection without a valve, which opens or closes a connection to the working space of the linear actuator depending on the position of a piston of the linear actuator. In particular, this can be designed simply as an opening that is passed over by the piston with its seal in order to open or close the opening.

According to the invention, the pressure equalization connection is thus established via the sniffer hole without any leakage, i.e. in the normal case. If, however, there is a leak, the required atmospheric connection to compensate for thermal expansion is already provided by the leak itself. An additional connection via the sniffer hole is therefore not necessary. The sniffer hole can therefore be closed to minimize the loss of brake fluid.

In a preferred embodiment of the invention, the linear actuator is connected to the wheel brakes via at least one normally open valve, so that when the valves are not energized, there is an open connection between the linear actuator and the wheel brakes. This means that the system can still build up braking force even in the event of a partial failure.

In a preferred embodiment of the invention, the control unit comprises a first electronic control and regulating unit and a second electronic control and regulating unit, and electrical and/or electronic means are provided which are configured such that, in the event of a failure of the first electronic control and regulating unit, the linear actuator is controlled by means of the second electronic control and regulating unit and builds up pressure to actuate the wheel brakes, and that, in the event of a failure of the second electronic control and regulating unit, the linear actuator is controlled by means of the first electronic control and regulating unit and builds up pressure to actuate the wheel brakes. The linear actuator can thus be controlled redundantly, which increases the reliability of the braking system. In particular Especially in combination with the inventive securing of the brake fluid, the braking system thus remains operational with a high degree of probability.

In a particularly preferred embodiment of the invention, the electrical and/or electronic means comprise that the linear actuator comprises a double-wound electric motor with a first motor winding and a second motor winding, wherein the first motor winding is controlled by the first electronic control and regulating unit and the second motor winding is controlled by the second electronic control and regulating unit. This means that the full power can be provided when both control units are functioning.

In a further preferred embodiment of the invention, the linear actuator has an additional refill connection to the brake fluid reservoir, which is routed via a check valve. The lines of this connection can be routed at least partially together with the sniffer hole connection. In the working space of the linear actuator, the sniffer hole connection is preferably arranged further back than the refill connection. The check valve can be designed in such a way that the spring force of the check valve is greater than the force of the liquid column, which acts in the event of a leak, so that the check valve is kept closed against gravity in the event of a leak.

In a further preferred embodiment of the invention, the leak detection is carried out by means of a level sensor in the brake fluid reservoir and/or by comparing a pressure built up in the wheel brakes and the brake fluid volume displaced into the wheel brakes with a pressure-volume characteristic curve of the wheel brakes. For example, a leak can be assumed from a brake fluid loss of 10mm ³ /s/bar.
In a further preferred embodiment of the invention, in the event of a leak, an inlet valve of the wheel brake with the leak is closed. To do this, the leak is preferably first localized so that it is known which wheel brake has the leak. This means that only one inlet valve needs to be closed. The localization can be carried out in such a way that a comparison of pressure and volume is carried out as described above for one wheel brake or a group of wheel brakes.

In a further preferred embodiment of the invention, the control unit is designed to carry out a pressure equalization in the wheel brake by briefly opening outlet valves. In this way, in particular, a pressure increase or decrease due to thermal expansion of the brake fluid can be counteracted.

In a further preferred embodiment of the invention, the control unit is designed to reduce a pressure applied to a wheel brake by opening the outlet valve of the wheel brake when a leak is detected in order to transition to sleep mode and/or stand-by mode.

In a further preferred embodiment of the invention, the control device is designed to wait for a waiting period before switching to a sleep mode and/or stand-by mode until the thermal expansion is at least partially completed and the resulting pressures are reduced. Preferably, the sniffer hole and/or the outlet valves can be opened briefly after predetermined times to equalize the pressure. The waiting period can be 30 minutes, for example. The brief opening can take place every two minutes, for example.

In a further preferred embodiment of the invention, the control unit is set up to move the linear actuator into a position in which the refill connection is also closed when switching to sleep mode and/or standby mode. This is thus blocked by the piston of the linear actuator in addition to the check valve. This ensures that the brake fluid volume is maintained even if the check valve is leaking. The refill connection is preferably only closed in sleep mode, since otherwise the working area of the linear actuator is required for pressure regulation. If the piston is positioned in a front area, this can be stored in a corresponding memory area. A position calibration after waking up can then in particular move to a closer front end point.

In a further preferred embodiment of the invention, the control unit is designed to calibrate the position measurement of the linear actuator after leaving the sleep mode and/or standby mode. For this purpose, a zero point detection or a detection at a front end stop can be carried out.

In a further preferred embodiment of the invention, the control unit is designed to maintain the closure of the sniffer hole in sleep mode and/or stand-by mode until a hydraulic self-test indicates that there are no leaks. For this purpose, for example, a corresponding flag can be set in the memory when a leak is detected. As long as this flag is set, the sniffer hole in the Stand-by and sleep mode closed. A hydraulic self-test, which guarantees that there are no leaks, can clear this flag again.

In a further preferred embodiment of the invention, the control unit is set up to carry out a hydraulic self-test to distinguish between a leak and air in the brake system when switching to sleep mode and/or stand-by mode. For this purpose, a pressure curve can be run, with the pressure volume curve being compared with target curves. From the curve, leaks and air can be distinguished.

The object is further achieved by a method for controlling a hydraulic brake system, wherein a leak detection is carried out and if no leak is detected, the sniffer hole connection is opened to transition to a sleep mode and/or stand-by mode by moving the linear actuator and if a leak is detected, the sniffer hole connection is closed by moving the linear actuator.

• 1 zeigt schematisch eine erfindungsgemäße Bremsanlage;

Further features, advantages and possible applications of the invention will become apparent from the following description of embodiments and the drawings. All described and/or illustrated features, both individually and in any combination, are part of the subject matter of the invention, regardless of their summary in the claims or their references.

• 1 shows schematically a braking system according to the invention;

In 1 A first embodiment of a braking system 1 according to the invention for a motor vehicle with four hydraulically actuated wheel brakes 5a-5d is shown schematically.

Braking system 1 advantageously comprises a brake control unit (HECU) with a hydraulic block 20 (hydraulic control and regulating unit HCU, valve block) with an output connection 4a-4d for each of the wheel brakes 5a-5d. A pressure medium reservoir 3 under atmospheric pressure is arranged on the valve block 20. For example, the output connections 4a, 4b are assigned to the wheel brakes 5a, 5b of the front axle (front), e.g. the output connection 4a to the left front wheel FL (wheel brake 5a) and the output connection 4b to the right front wheel FR (wheel brake 5b), and the output connections 4c, 4d are assigned to the wheel brakes 5c, 5d of the rear axle (rear), e.g. the output connection 4c to the left rear wheel RL (wheel brake 5c) and the output connection 4d to the right rear wheel RR (wheel brake 5d).

The fill level of the pressure medium reservoir 3 is measured by means of a fill level sensor 44. If a leak occurs in the brake system, the fill level drops, which can be detected by the sensor.

The pressure medium reservoir 3 comprises at least two container chambers 84, 85, which are at least partially separated from one another by a bulkhead 86. The pressure medium reservoir 3 also comprises a first connection 71 and a second connection 72. The first connection 71 is connected to the first container chamber 84, the second connection 72 is connected to the second container chamber 85. In this sense, a first connection 71 of the pressure medium reservoir 3 is assigned to the first container chamber 84 and the second connection 72 of the pressure medium reservoir 3 is assigned to the second container chamber 85.

Each output connection 4a-4d is assigned an inlet valve 6a-6d and an outlet valve 7a-7d, wherein the inlet valves 6a-6d are advantageously designed to be open when de-energized and the outlet valves 7a-7d are advantageously designed to be closed when de-energized. For example, no check valve is connected in parallel to each inlet valve 6a-6d.

The respective output connection 4a-4d is connected to the pressure medium reservoir 3 via the outlet valve 7a-7d. The outlet valves 7a-7d are connected to the first connection 71 of the pressure medium reservoir 3 via a return line 61b, 61 (which is at least partially common).

An electrically controllable hydraulic pressure source 2 is provided, which is formed by a cylinder-piston arrangement with a pressure chamber 30, the piston 31 of which can be actuated by an electromechanical actuator with a schematically indicated electric motor 32 and a schematically shown rotation-translation gear 33. Pressure source 2 is designed, for example, as a single-circuit electrohydraulic linear actuator (LAC) with only one pressure chamber 30. Piston 31 can be pushed forward by means of the electromechanical actuator to build up pressure (brake actuation direction) and pushed or retracted to reduce pressure.

For example, the electric motor is designed as a double-wound electric motor 32 with a first motor winding 34a and a second motor winding 34b. If both motor windings 34a, 34b are controlled, the electric motor 32 delivers full power. If only one of the two motor windings 34a, 34b is controlled, the power of the electric motor 32 is reduced, but However, pressure can still be built up by means of pressure source 2, albeit at a reduced level and with reduced dynamics.

Pressure chamber 30 is hydraulically connected via a pressure connection 83 to a brake line section 60, which is hydraulically connected to the inlet valves 6a-6d (more precisely the input connections of the inlet valves 6a-6d). In the hydraulic connection between the pressure chamber 30 of the pressure source 2 and the brake line section 60 or each of the inlet valves 6a-6d, for example, no isolating valve is arranged.

To suck pressure medium from the pressure medium reservoir 3 into the pressure source 2, the pressure source 2 has a suction connection 81. The pressure chamber 30 is connected to the first connection 71 of the pressure medium reservoir 3 and thus to the first container chamber 84 of the pressure medium reservoir 3 via the suction connection 81 and a suction valve 14, which is designed, for example, as a check valve opening in the direction of the pressure chamber 30. Alternatively, the suction connection 81 can also be connected to a second chamber 85 of the pressure medium reservoir 3.

Furthermore, pressure source 2 has a compensation connection 82 for hydraulically connecting the pressure chamber 30 to the pressure medium reservoir 3 in a predetermined position of the piston 31. This makes it possible to depressurize the wheel brakes 5a-5d, i.e. to connect the wheel brakes 5a-5d to the pressure medium reservoir 3 under atmospheric pressure, in the predetermined position of the piston 31. The predetermined position of the piston 31 is advantageously the unactuated state of the piston 31. Compensation connection 82 is connected to the other (second) reservoir chamber 85, i.e. the second connection 72, of the pressure medium reservoir 3.

According to the example, pressure source 2 has a sniffer hole 80 as a compensation connection 82. Sniffer hole 80 is connected to the second connection 72 of the pressure medium reservoir 3 via a follow-up line section 62. When the piston 31 is not actuated, the pressure chamber 30 is connected to the second container chamber 85 of the pressure medium reservoir 3 via the sniffer hole 80 and the follow-up line section 62, wherein the sniffer hole 80 is overrun/closed when the piston 31 is actuated, thus breaking the connection to the pressure medium reservoir 3. According to the example, the piston 31 is provided with at least one bore via which the hydraulic connection between the pressure chamber 30 and the follow-up line section 62 is established when the piston 31 is not actuated, and which overruns a seal when the piston 31 is actuated, so that the hydraulic connection between the pressure chamber 30 and the follow-up line section 62 is broken. Other mechanical designs are possible.

For example, the return line 61 b, 61 for the outlet valves 7a-7d and an intake line 61a, 61 of the pressure source 2 are designed together in pieces. For this purpose, the suction connection 81 is connected to the return line 61b, 61 via the suction valve 14 and an intake line section 61a. The outlet valves 7a-7d and the suction valve 14 are therefore connected to the first connection 71 of the pressure medium reservoir 3 via a common line section 61. In other words, the intake line section 61a and a return line section 61b open into the line section 61 to the first connection 71. In this sense, the pressure chamber 30 is connected to the return line 61 b, 61 (from the return line section 61 b and line section 61) via the suction valve 14 and the intake line section 61a.

The afterflow line section 62 and the suction line section 61a (or the return line 61b, 61 or the return line section 61b or the line section 61) are not directly connected to one another. There is only a certain indirect hydraulic connection via the pressure medium reservoir 3 if the filling level of the pressure medium reservoir 3 is above the bulkhead 86. In the above-mentioned alternative connection of the after-suction connection 81 to the second chamber, however, a connection of the after-suction connection 81 to the line 62 can be made.

A (system) pressure sensor 40 is connected to the brake line section 60, by means of which the pressure generated by the pressure source 2 can be determined. The pressure sensor 40 is preferably the only pressure sensor of the brake system 1 or the brake control unit.

To control the pressure source 2, the braking system 1 comprises redundant sensor elements for detecting a rotational speed or a rotation angle of the electric motor 32. For example, a first motor angle sensor 43 and a second motor angle sensor 42 are provided.

Braking system 1 advantageously comprises only one hydraulic pressure source 2. Braking system 1 comprises neither a second electrically controllable hydraulic pressure source nor a pressure source that can be actuated by the driver, e.g. a brake pedal-actuated master brake cylinder, for realizing a hydraulic, driver-actuated fallback level.

Braking system 1 further comprises a first electronic control and regulating unit (ECU) A and a second electronic control and regulating unit (ECU) B for controlling the electrically actuable components of braking system 1. The first electronic control and regulating unit A and the second electronic control and regulating unit B are advantageously electrically independent of one another in the sense that a failure of the first electronic control and regulating unit does not cause a failure of the second electronic control and regulating unit and vice versa. For this purpose, electronic control and regulating units A and B can be designed as separate units, but they can also be designed as independent subunits in the same electronic control and regulating unit.

The arrows A or B on the electrical or electrically actuated components, such as the valves 6a-6d, 7a-7d and the sensors 40, 42, 43, 44, indicate the assignment to the electronic control and regulation unit A or B.

The electric motor 32 of the pressure source 2 can be controlled by the first and the second electronic control and regulating unit A, B, i.e. each of the electronic control and regulating units A, B is suitable on its own for building up a brake pressure by means of the pressure source 2 in order to carry out a service braking. This means that the pressure source 2 and the electronic control and regulating units A, B are designed in such a way that if the first electronic control and regulating unit A fails, the pressure source 2 can be controlled by means of the second electronic control and regulating unit B in order to build up a brake pressure for actuating the wheel brakes 5a-5d during a service or control braking, and that if the second electronic control and regulating unit B fails, the pressure source 2 can be controlled by means of the first electronic control and regulating unit A in order to build up a pressure for actuating the wheel brakes 5a-5d during a service or control braking.

According to the example, the electric motor is designed as a double-wound electric motor 32 with the first motor winding 34a and the second motor winding 34b. The electric motor 32 of the pressure source 2 is controlled by the first and the second electronic control and regulating unit in the sense that the first motor winding 34a is (preferably only) controlled by the first electronic control and regulating unit A (marked with an arrow with A) and the second motor winding 34b is (preferably only) controlled by the second electronic control and regulating unit B (marked with an arrow with B), in particular is supplied with electrical energy by the electronic control and regulating unit. For this purpose, motor winding 34a is connected to the first control and regulating unit A and the other motor winding 34b to the second control and regulating unit B. To control the pressure source 2, each of the two control and regulating units A, B comprises a motor processor for processing the motor control functions, an output stage with transistors for providing the phase voltages at the electric motor 32 (e.g. B6 bridge) and a driver stage (gate drive unit) for controlling the transistors of the output stage.

If one of the electronic control and regulating units A or B fails, the pressure source 2 is controlled by means of the other electronic control and regulating unit B or A and a pressure is built up to actuate the wheel brakes 5a-5d in the brake-by-wire operating mode for service braking. The one functional electronic control and regulating unit B of A operates the pressure source 2 or the electric motor 34 with at least part of its power to build up a pressure to actuate the wheel brakes.

The electrically actuated inlet and outlet valves 6a-6d, 7a-7d, and the sensors 40, 42, 43, 44 of the braking system 1 are each assigned to only one of the electronic control and regulating units. This means that each electrically actuated valve 6a-6d, 7a-7d is controlled exclusively by the electronic control and regulating unit A or exclusively by the electronic control and regulating unit B. This avoids complex, doubly controllable valves/valve coils. The signals of each sensor 40, 42, 43 or 44 are fed exclusively to the electronic control and regulating unit A or exclusively to the electronic control and regulating unit B.

All electrically actuated valves, i.e., for example, the electrically actuated inlet and outlet valves 6a-6d, 7a-7d, are advantageously assigned to the same electronic control and regulating unit, for example, the electronic control and regulating unit A, and are controlled exclusively by the electronic control and regulating unit A.

The signals of the (first) engine angle sensor 43 are fed to the second electronic control and regulating unit B and evaluated by it, whereas the signals of the (second) engine angle sensor 42 are fed to the first electronic control and regulating unit A and evaluated by it.

The signals of the pressure sensor 40 are advantageously fed to the same electronic control and regulation unit A, which also controls the inlet and outlet valves 6a-6d, 7a-7d, ie the signals of the pressure sensor 40 are fed to the first electronic control and regulating unit A and evaluated by it.

If one of the electronic control and regulation units A or B fails, the pressure source 2 can still be controlled by means of one of the motor windings 34a or 34b and one of the motor angle sensors 42 or 43 (or if necessary the pressure sensor 40) and thus a suitable pressure can be built up, albeit possibly at a reduced level and/or with reduced dynamics. All wheel brakes 5a-5d can be subjected to this (central) pressure. The (central) pressure can also be modulated by pushing the piston 31 back and forth.

Advantageously, the braking system 1 is supplied by a redundant on-board network with two independent voltage sources (a first electrical energy supply and a second electrical energy supply), so that both control and regulating units A and B are not supplied by the same electrical energy supply. For example, control and regulating units A are supplied by the first electrical energy supply and control and regulating units B are supplied by the second electrical energy supply.

Braking system 1 comprises, for example, electric parking brakes 50a, 50b on the wheels of one of the axles, for example on the rear wheels RL, RR. The electric parking brakes 50a, 50b are controlled or actuated by the electrohydraulic brake control unit.

Advantageously, the wheel brakes on the rear axle are designed as combination brake calipers with a hydraulic wheel brake 5c, 5d and an integrated, electrically operated parking brake (IPB).

For example, one of the electric parking brakes, e.g. parking brake 50a, is actuated/controlled by the first electronic control and regulating unit A (this is indicated by the arrow with A), while the other of the electric parking brakes, e.g. parking brake 50b, is actuated/controlled by the second electronic control and regulating unit B (this is indicated by the arrow with B). After a failure of one of the control and regulating units A or B, the vehicle can still be secured with at least one of the parking brakes, which is actuated by the functional control and regulating unit B or A. This means that a transmission parking lock can be omitted.

Preferably, the braking system also comprises an actuating unit, such as in particular a brake pedal, for a vehicle driver (not shown in 1 ). The actuating unit is connected to the brake control unit (HECU) on the signal side for transmitting a driver request signal, but there is no mechanical-hydraulic connection from the actuating unit to the brake control unit or the wheel brakes 55a-5d.

In the event of a failure of the second electronic control and regulating unit B, the hydraulic braking function of the braking system by means of the pressure source 2, including the wheel pressure control by means of the inlet and outlet valves 6a-6d, 7a-7d, can be carried out by means of the first electronic control and regulating unit A, the only limitation being, if applicable, that the performance of the pressure source 2 is reduced.

Since the outlet valves 7a-7d are closed when de-energized and the inlet valves 6a-6d are open when de-energized, all wheels can be braked hydraulically in the event of a failure of the first electronic control and regulation unit A. To do this, the second electronic control and regulation unit B regulates the pressure medium volume delivered if no pressure signal is available. A common pressure modulation on all wheel brakes 5a-5d remains possible.

When using the outlet valves 7a-7d for wheel-individual pressure control, pressure medium volume is consumed in the sense that pressure medium is drained from the pressure chamber 30 via the wheel brakes 5a-5d into the pressure medium reservoir 3. Accordingly, pressure medium volume must be sucked into the pressure chamber 30 of the pressure source 2 via the suction valve 14 at the latest when the pressure medium volume in the pressure chamber 30 reaches a lower limit value.

Advantageously, the exemplary braking system 1 of the 1 In addition to the electrically operated inlet and exhaust valves 6a-6d, 7a-7d, there are no other electrically operated valves.

When no braking is taking place, i.e. when the brake is in standby mode, the wheel brakes 5a-5d should be under atmospheric pressure. To do this, the pressure source 2 is controlled and returned to its non-actuated state in such a way that a hydraulic connection to the pressure medium reservoir 3, which is under atmospheric pressure, is created via the sniffer hole 80. This connection is also established in sleep mode, i.e. when the brake is essentially de-energized in order to turn off the vehicle.

To avoid the loss of brake fluid due to a leak in this stand-by mode and/or sleep mode, it is intended that the control unit carries out leak detection. To do this, the fluid level in the brake fluid reservoir is monitored. In addition, the relationship between the volume displaced by the linear actuator and the pressure that builds up is monitored. If deviations from standard behavior occur, a leak is assumed to have been detected.

In this case, for example, the sniffer hole is not opened when switching to standby mode or sleep mode. In these modes, the sniffer hole is therefore closed so that there is no connection between the brake fluid reservoir and a leaking wheel brake. The loss of brake fluid is thus minimized. In this case, the connection to the atmosphere for pressure equalization is already provided by the leak itself.

Claims (15)

Hydraulic brake system for actuating a plurality of wheel brakes (5), comprising a linear actuator (2) for providing a hydraulic pressure in the wheel brakes (5), which has a connection (80) to a pressure-free brake fluid reservoir (3), characterized in that an associated control unit (A, B) is set up to carry out leak detection and, if no leak is detected, to open the connection (80) to transition to a sleep mode and/or stand-by mode by moving the linear actuator (3), and, if a leak is detected, to close the connection (80) by moving the linear actuator (3). Hydraulic brake system according to Claim 1 , characterized in that the connection is a sniffer hole connection. Hydraulic brake system according to Claim 1 or 2 , characterized in that the linear actuator is connected to the wheel brakes via at least one normally open valve, so that when the valves are in a de-energized state there is a flow-open connection between the linear actuator and the wheel brakes. Hydraulic brake unit according to one of the preceding claims, characterized in that the control device (A, B) comprises a first electronic control and regulating unit (A) and a second electronic control and regulating unit (B), and electrical and/or electronic means are provided which are configured such that, in the event of a failure of the first electronic control and regulating unit (A), the linear actuator is controlled by means of the second electronic control and regulating unit (B) and builds up a pressure for actuating the wheel brakes (5a-5d), and that, in the event of a failure of the second electronic control and regulating unit (B), the linear actuator is controlled by means of the first electronic control and regulating unit (A) and builds up a pressure for actuating the wheel brakes (5a-5d). Hydraulic brake unit according to Claim 4 , characterized in that the electrical and/or electronic means comprise that the linear actuator (2) comprises a double-wound electric motor (32) with a first motor winding (34a) and a second motor winding (34b), wherein the first motor winding (34a) is controlled by the first electronic control and regulating unit (A) and the second motor winding (34b) is controlled by the second electronic control and regulating unit (B). Hydraulic brake unit according to one of the preceding claims, characterized in that the linear actuator (2) has an additional refill connection (81) to the brake fluid container (3), which is guided via a check valve (14). Hydraulic brake unit according to one of the preceding claims, characterized in that the leak detection is carried out by means of a level sensor in the brake fluid container (3) and/or by comparing a pressure built up in the wheel brakes (5) and the brake fluid volume displaced into the wheel brakes (5) with a pressure-volume characteristic curve of the wheel brakes (5). Hydraulic brake unit according to one of the preceding claims, characterized in that in the event of a leak, an inlet valve (6) of the wheel brake (5) with leakage is closed. Hydraulic brake unit according to one of the preceding claims, characterized in that the control unit is designed to reduce a pressure applied to a wheel brake (5) by opening the outlet valve of the wheel brake (5) upon detection of a leak in order to transition to sleep mode and/or stand-by mode. Hydraulic brake unit according to one of the preceding claims, characterized in that the control unit is designed to wait for a waiting time to transition to a sleep mode and/or stand-by mode until the thermal expansion is at least partially completed and to reduce the resulting pressures. Hydraulic brake unit after a Claim 6 until 10 , characterized in that the control device is designed to move the linear actuator into a position in which the refill connection is also closed for the transition to sleep mode and/or stand-by mode. Hydraulic brake unit according to one of the preceding claims, characterized in that the control unit is set up to calibrate the position measurement of the linear actuator (2) after leaving the sleep mode and/or stand-by mode. Hydraulic brake unit according to one of the preceding claims, characterized in that the control unit is designed to maintain the closure of the sniffer hole (80) for sleep mode and/or stand-by mode until a hydraulic self-test indicates that there are no leaks. Hydraulic brake unit according to one of the preceding claims, characterized in that the control unit is designed to carry out a hydraulic self-test to distinguish a leakage of air in the brake system when switching to sleep mode and/or stand-by mode. Method for controlling a hydraulic brake system, characterized in that a leak detection is carried out and if no leak is detected, the sniffer hole connection (80) is opened to transition to a sleep mode and/or stand-by mode by moving the linear actuator (2) and if a leak is detected, the sniffer hole connection (80) is closed by moving the linear actuator (2).

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