Avoiding hydraulic fallback levels

Abstract

The present invention relates to a method for controlling a hydraulic braking system of a motor vehicle, comprising a linear actuator (5) as a driver-independent pressure supply device and a hydraulic valve assembly (26) between the linear actuator (5) and wheel brakes (8) of the hydraulic braking system, in which in the event of reduced availability of the linear actuator (5), a pause mode is implemented, where hydraulic pressure is trapped in the wheel brakes (8) by the valve assembly (26), the output of the linear actuator (5) is reduced, a system pressure curve (70) is measured in the pause mode, and a transition from the pause mode to an alternative mode is implemented based on the system pressure curve (70).

Description

[Technical field]

[0001] The present invention relates to a method for regulating a hydraulic brake system of a motor vehicle having a linear actuator as a driver-independent pressure supply device and a hydraulic valve arrangement between the linear actuator and the wheel brakes of the hydraulic brake system. [Background technology]

[0002] The driver-independent pressure build-up by the linear actuator allows the realization of numerous complex modulating operations that improve the comfort and reliability of the brake system. However, the motor of the linear actuator has mechanical, and in particular thermal, limits that counteract the continuous load. In case of a specified overload and associated limited availability, the linear actuator must therefore be derated to a complete shutdown to prevent irreversible damage. To this end, the brake system is switched to a hydraulic fallback level where the driver must apply the brake force by muscle force alone. Summary of the Invention [Problem to be solved by the invention]

[0003] It is therefore an object of the present invention to avoid premature switchover to the hydraulic fallback level. [Means for solving the problem]

[0004] The object is to provide a method for regulating a hydraulic brake system of a motor vehicle having a linear actuator as a driver-independent pressure supply device and a hydraulic valve arrangement between the linear actuator and the wheel brakes of the hydraulic brake system, in which in the event of reduced availability of the linear actuator a hold mode is executed, in which case the hydraulic pressure in the wheel brakes is sealed off by the valve arrangement and the output of the linear actuator is reduced, in particular to zero, whereby the system pressure gradient, i.e. the hydraulic pressure in the areas connected to the wheel brakes and thus indicating information about the braking force, is measured in the hold mode and the transition from the hold mode to the alternative mode is executed on the basis of the system pressure gradient.

[0005] As entry conditions for the hold mode, for example, it may be provided that the linear actuator indicates reduced availability, e.g. a thermal overload, the vehicle is stopped, and the identified driver brake demand corresponds to a pressure demand greater than 5-10 bar. As exit conditions for the hold mode, it may be provided that the vehicle is rolling, i.e. has a speed greater than zero, the driver demand is reduced by a predefined absolute or percentage amount, or the driver actuates the brake pedal with a force greater than 500 N.

[0006] Transitioning to the alternate mode avoids a situation where the braking system must be reduced directly to the full hydraulic fallback level.

[0007] In a preferred embodiment of the invention, a determination is made as to how far the system pressure has dropped in the holding mode and a transition to the alternative mode is performed if the system pressure falls below a threshold value. The threshold value can in particular be selected as a percentage of the original value at the start of the holding mode. Alternatively, the system pressure gradient can be analyzed in some other way, for example checking how quickly the system pressure drops.

[0008] In a particularly preferred embodiment of the invention, the threshold value is set based on the roadway gradient, where only smaller deviations from the original value are permitted at steeper gradients compared to the horizontal. For example, two threshold values ​​can be provided. If the vehicle inclination is smaller than the inclination limit a and the system pressure measured during the holding mode drops by a first percentage threshold, the standstill protection is switched to the alternative mode. On the other hand, if the vehicle inclination is equal to or greater than the inclination limit a, the standstill protection is already switched to the alternative mode if the system pressure measured during the holding mode drops by a second percentage threshold, which is smaller than the first threshold.

[0009] In a further preferred embodiment of the invention, a reduced availability of the linear actuator is detected if a temperature assigned to the linear actuator exceeds a threshold value. The temperature can be determined by a temperature sensor in the linear actuator or can be calculated from variables such as the electrical resistance of the motor coils. Alternatively or additionally, the temperature can be determined by a temperature model.

[0010] For the temperature model, the starting point is the starting temperature of the component. This starting temperature can be determined, for example, by the sensed ambient temperature. The motor's electrical energy input, i.e. the magnitude of energization and duration of energization, is then added to the calculation. This energy input is added to the calculation of the starting temperature of the component and a new actual temperature is thus determined.

[0011] In a further preferred embodiment of the invention, a refill mode is performed based on the system pressure gradient and the availability of the linear actuator, in which case the sealing pressure is increased by the linear actuator and then a switch to the holding mode is performed again. The refill mode can in particular be performed as soon as the system pressure falls below a second threshold value which is above the first threshold value. At the same time, the linear actuator must allow refilling for at least a short time. To this end, for example, a second temperature threshold can be provided. As a result of the refill, the linear actuator is in each case electrically actuated only for a short time for the pressure increase and in each case can cool down again during pressure holding, so that the total time during which the brake pressure can be maintained can be significantly increased.

[0012] In a further preferred embodiment of the invention, the hold mode is implemented when the vehicle is stationary, in which state the safety requirements are low so that maintaining pressure is sufficient for the operation of the brake system.

[0013] In a further preferred embodiment of the present invention, the alternate mode is specifically not a hydraulic fallback level where only the driver can apply braking force.

[0014] In a further preferred embodiment of the invention, the alternative mode is a parking brake mode, in which the electromechanical parking brake of the motor vehicle is activated and the hydraulic brake system is deactivated, so that the vehicle is held by the parking brake. Thus, in addition to the linear actuators, the electrohydraulic valves can also be set to a currentless state, allowing cooling. The hydraulic brake system can also be switched off only partially, if necessary.

[0015] In a further preferred embodiment of the invention, the alternative mode is a cooperation mode, in which an additional hydraulic supply device is activated to increase the sealing pressure, after which a switch to the hold mode is made again, in this way the linear actuator can be released by the use of a further pressure supply device.

[0016] In a further preferred embodiment of the invention, the alternative mode is a half mode, in which the valve arrangement is operated to connect the wheel brakes of the first axle in an open-flow manner to a brake master cylinder that can be activated by the driver, and to seal off the hydraulic pressure of the wheel brakes of the second axle, thus providing separation of the two circuits by the circuit isolation valve.

[0017] In a particularly preferred embodiment of the invention, when switching to half mode, the pressure of the wheel brakes is matched to the pressure of the brake master cylinder before the valve arrangement establishes an open flow connection. To this end, for example, the outlet valve can be opened for a short time. In this way, it is avoided that pressure pulses are transmitted to the brake pedal and thus to the driver.

[0018] In a further preferred embodiment of the invention, at the start of the holding mode, a pressure higher than the requested pressure is increased by the linear actuator and the higher pressure is sealed off. Thus, a certain pressure drop is already calculated over a period of time, which can be determined, for example, via known leakage values ​​of the individual valves. As a result of the original value being higher at the start of the holding mode, the threshold value can be selected to be lower in percentage, so that the minimum pressure for holding the vehicle stationary can be maintained for a longer time.

[0019] Moreover, the object is achieved by a hydraulic braking system for a motor vehicle having a linear actuator as a driver-independent pressure supply device, a hydraulic valve arrangement between the linear actuator and the wheel brakes of the hydraulic braking system, and a control device configured to perform the above method.

[0020] Further features, advantages and possible applications of the invention emerge from the following description of exemplary embodiments and from the drawings, in which: All the features described and / or shown, individually and in any combination, belong to the subject matter of the invention, independently of their abstraction in the claims or their references. [Brief description of the drawings]

[0021] [Figure 1] 1 shows a schematic diagram of a braking system according to a first embodiment of the invention; [Diagram 2] 2 shows a schematic diagram of a braking system according to a second embodiment of the invention; [Diagram 3] The timeline for transition to retention mode is shown below. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The braking system for a motor vehicle shown in Fig. 1 comprises four hydraulically actuated wheel brakes 8a-8d. The braking system comprises a brake master cylinder 2 actuable by an actuation or brake pedal 1, a movement simulator or simulation device 3 interacting with the brake master cylinder 2, a pressure medium reservoir 4 under atmospheric pressure, an electrically controllable pressure supply device 5 and a valve arrangement with wheel-individual brake pressure regulating valves which according to the embodiment are configured as inlet valves 6a-6d and outlet valves 7a-7d. Furthermore, the braking system comprises at least one electronic control and regulating unit 12 for actuating the electrically actuable components of the braking system.

[0023] According to the embodiment, wheel brake 8a is assigned to the front left wheel (FL), wheel brake 8b is assigned to the front right wheel (FR), wheel brake 8c is assigned to the rear left wheel (RL) and wheel brake 8d is assigned to the rear right wheel (RR).

[0024] In the housing 16, the brake master cylinder 2 defines a hydraulic pressure chamber 17 and has a brake master cylinder piston 15, which is a single-circuit brake master cylinder 2. The pressure chamber 17 accommodates a restoring spring 9, which positions the piston 15 in a starting position when the master brake cylinder 2 is not activated. The pressure chamber 17 is firstly connected to the pressure medium reservoir 4 via radial bores configured in the piston 15 and corresponding pressure equalization lines 41, which bores and lines can be blocked by the relative movement of the piston 15 in the housing 16. Secondly, the pressure chamber 17 is connected by a hydraulic line section (also called the first feed line) 22 to the brake supply line 13, to which the inlet ports of the inlet valves 6a-6d are connected. The pressure chamber 17 of the brake master cylinder 2 is therefore connected to all the inlet valves 6a-6d.

[0025] According to the embodiment, no hydraulic valves, in particular electrically or hydraulically operable valves and no check valves are arranged in the pressure equalization line 41 or in the connection between the pressure chamber 17 and the pressure medium reservoir 4.

[0026] Alternatively, in particular a normally open diagnostic valve, preferably a parallel connection of a normally open diagnostic valve with a check valve closing in the direction of the pressure medium reservoir 4, can be included in the equalization line 41 or between the brake master cylinder 2 and the pressure medium reservoir 4.

[0027] Moreover, the valve arrangement can also comprise further hydraulic valves. An isolation valve 23 is arranged between the feed line 22 connected to the pressure chamber 17 and the brake supply line 13, or the pressure chamber 17 is connected to the brake supply line 13 via a first feed line 22 which has the isolation valve 23. The isolation valve 23 is configured as an electrically actuatable, preferably normally open (NO) 2 / 2-way valve. The isolation valve 23 makes it possible to cut off the hydraulic connection between the pressure chamber 17 and the brake supply line 13.

[0028] A piston rod 24 couples the pivotal movement of the brake pedal 1 as a result of pedal actuation to a translational movement of the brake master cylinder piston 15, the actuation movement of which is detected by a preferably redundant displacement sensor 25. In this way, the corresponding piston movement signal is an indication of the brake pedal actuation angle, which represents the vehicle driver's braking demand.

[0029] A pressure sensor 20 connected to the first feed line 22 detects the pressure built up in the pressure chamber 17 as a result of the displacement of the piston 15. This pressure value can likewise be evaluated to characterize or determine the braking request of the vehicle driver. As an alternative to the pressure sensor 20, a force sensor 20 can also be used to determine the braking request of the vehicle driver.

[0030] According to an embodiment, the simulation device 3 is of hydraulic construction and is hydraulically coupled to the brake master cylinder 2. The simulation device 3, for example, substantially comprises a simulator chamber 29, a simulator rear chamber 30 and a simulator piston 31 separating the two chambers 29, 30 from each other. The simulator piston 31 is supported on the housing via an elastic element 33 (e.g. a simulator spring) which is arranged in the simulator rear chamber 30 (dry according to the embodiment). According to the embodiment, the hydraulic simulator chamber 29 is connected to the pressure chamber 17 of the brake master cylinder 2 by a preferably electrically actuable, preferably normally closed, simulator enable valve 32.

[0031] For each hydraulically actuable wheel brake 8a-8d the brake assembly or brake system comprises an inlet valve 6a-6d and an outlet valve 7a-7d which are hydraulically connected together in pairs via a central port and connected to the wheel brake 8a-8d. A non-return valve, not shown in detail, opening into a brake supply line 13 is in each case connected in parallel to the inlet valve 6a-6d. The outlet ports of the outlet valves 7a-7d are connected to the pressure medium reservoir 4 via a common return line 14.

[0032] The electrically controllable pressure supply device 5 is configured as a hydraulic cylinder / piston arrangement (or single-circuit electrohydraulic actuator) or as a linear actuator, whose piston 36 can be actuated by a diagrammatically illustrated electric motor 35, with a similarly diagrammatically illustrated rotary / translational gear mechanism 39 connected between the piston 36 and the electric motor 35. The piston 36 defines a single pressure space 37 of the pressure supply device 5. A rotor position sensor, shown only diagrammatically, serving to detect the rotor position of the electric motor 35 is indicated by the reference number 44.

[0033] A line section (also referred to as second feed line) 38 is connected to a pressure space 37 of the electrically controllable pressure supply device 5. The feed line 38 is connected to the brake supply line 13 via an electrically actuatable, preferably normally closed, additive valve 26 as part of the valve arrangement. The additive valve 26 makes it possible to open and close in a controlled manner the hydraulic connection between the pressure space 37 of the electrically controllable pressure supply device 5 and the brake supply line 13 (and thus the inlet ports of the inlet valves 6a-6d).

[0034] The actuator pressure generated by the action of the force of the piston 36 on the pressure medium contained in the pressure space 37 is fed to a second feed line 38. In a "brake-by-wire" type of actuation, in particular in an undisturbed condition of the brake system, the feed line 38 is connected to the brake supply line 13 via the dosing valve 26. In this way, during normal braking, the forward and rearward movements of the piston 36 result in an increase and a decrease in wheel brake pressure of all wheel brakes 8a-8d.

[0035] In the event of a pressure drop due to a rearward movement of the piston 36, the pressure medium displaced forward from the pressure space 37 of the pressure supply device 5 into the wheel brakes 8a-8d likewise flows back into the pressure space 37.

[0036] Alternatively, different wheel brake pressures for the different wheels can simply be set by the inlet valves 6a-6d and the outlet valves 7a-7d. In the event of a corresponding pressure drop, the part of the pressure medium discharged via the outlet valves 7a-7d flows via the return line 14 into the pressure medium reservoir 4.

[0037] Refilling of the pressure space 37 with pressure medium is possible by the piston 36 retracting in the case of a closed addition valve 26, whereby pressure medium can flow out of the container 4 via the line 42 into the actuator pressure space or into the pressure space 37, with the check valve 53 open in the direction of flow towards the actuator 5. According to an embodiment, the pressure space 37 is additionally connected to the pressure medium reservoir 4 via one or more leak holes in the non-actuated state of the piston 36. This connection between the pressure space 37 and the pressure medium reservoir 4 is disconnected when the piston 36 is (fully) actuated in the actuation direction 27.

[0038] An electrically actuable normally open circuit isolation valve 40 is arranged in the brake supply line 13 by which the brake system is divided into two hydraulic subcircuits. The brake supply line 13 is divided into a first line section 13a connected (via an isolation valve 23) to the brake master cylinder 2 and a second line section 13b in the second hydraulic subcircuit connected (via an additive valve 26) to the pressure supply device 5. The first line section 13a is connected to the inlet valves 6a, 6b of the wheel brakes 8a, 8b and the second line section 13b is connected to the inlet valves 6c, 6d of the wheel brakes 8c, 8d.

[0039] With the circuit isolation valve 40 open, the brake system is of single-circuit design. By closing the circuit isolation valve 40, the brake system can be distributed or split into two hydraulic partial circuits, brake circuits I and II, in a manner that is controlled in particular according to the situation. Here, in the first brake circuit I, the brake master cylinder 2 is connected (via the isolation valve 23) only to the inlet valves 6a, 6b of the wheel brakes 8a, 8b of the front axle VA, and in the second brake circuit II, the pressure supply device 5 is connected (with the addition valve 26 open) only to the wheel brakes 8c and 8d of the rear axle HA.

[0040] In the case of the open circuit isolation valve 40, the inlet ports of all inlet valves 6a-6d can be supplied by the brake supply line 13 with a pressure corresponding to the brake pressure supplied by the pressure supply device 5 in a first operating mode (e.g., a "brake-by-wire" operating mode). In a second operating mode (e.g., a no-current fallback operating mode), the brake supply line 13 can be subjected to the pressure of the pressure chamber 17 of the brake master cylinder 2.

[0041] The braking system advantageously comprises a level measuring device 50 for determining the pressure medium level in the pressure medium reservoir 4 .

[0042] According to an embodiment, the hydraulic components, i.e. the brake master cylinder 2, the simulation device 3, the pressure supply device 5, the valve arrangement with hydraulic valves 6a-6d, 7a-7d, 23, 26, 40 and 32 as well as the hydraulic connections including the brake supply line 13 are arranged together in a hydraulic control and regulating unit 60 (HCU). Assigned to the hydraulic control and regulating unit 60 is an electronic control and regulating unit (ECU) 12. The hydraulic and electronic control and regulating units 60, 12 are preferably configured as one unit (HECU).

[0043] The braking system comprises a pressure sensor 19 or a system pressure sensor for detecting the pressure supplied by the pressure supply device 5. Here, the pressure sensor 19 is arranged downstream of the dosing valve 26 when viewed from the pressure chamber 37 of the pressure supply device 5.

[0044] In addition to hydraulic actuation, the two rear wheel brakes 8c, 8d are each equipped with an integrated parking brake 48c, 48d which is configured as an electromechanical parking brake.

[0045] In normal operating mode, the isolation valve 23 is closed, the addition valve 26 and the circuit isolation valve 40 are opened, so that the hydraulic pressure in all wheel brakes 8a-8d is set by the linear actuator 5. If, when the vehicle is stopped, the brake pressure is then maintained for a relatively long time, the linear actuators, at the end of which they operate with a power input different from zero, must continuously hold a reaction force against the hydraulic pressure. This can lead to an overheating of the linear actuator 5. If an exceedance of the temperature threshold is identified, a switchover to the holding mode is performed according to the invention.

[0046] FIG. 2 then shows a further embodiment of the brake system. The connection to the front wheel brakes 8a, 8b is via a further brake unit 54 with in each case one switching valve 59a, 59b, which is open during normal operation. For redundancy reasons, the further brake unit comprises a further pressure loading device 57 configured as two hydraulic pumps 57a, 57b with a common motor. The hydraulic pumps 57a, 57b are connected on the suction side to associated low-pressure accumulators 55a, 55b, which in each case have normally closed pump isolation valves 58a, 58b and thus have a connection to the brake fluid reservoir 4. Moreover, the low-pressure accumulators 55a, 55b are connected to the associated wheel brakes 8a, 8b by further valves 56a, 56b in each case.

[0047] The actuation of the hydraulic pump 57 and the linear actuator 5 can be performed by two separate control units.

[0048] 3 shows the corresponding sequence of system pressure 70 and valve flow 60 of the additive valve 26. The valve flow 60 of the additive valve 26 momentarily increases to an open flow 61, which causes the additive valve 26 to open. The valve flow 60 is then decreased to a hold flow 62, which holds the additive valve 26 open. While the additive valve 26 is open, hydraulic pressure is built up by the linear actuator 5, and the system pressure 70 rises accordingly.

[0049] To switch to the holding mode, the additive valve 26 is then closed, so that the hydraulic pressure is trapped in the wheel brakes 8a-8d. To this end, the valve flow 60 of the additive valve 26 is reduced from the holding flow 62 to the closing flow 63. The current in the linear actuator 5 can be interrupted accordingly, so that the linear actuator can be cooled. However, as shown in FIG. 3, all hydraulic units, and in particular the hydraulic valves of the valve arrangement, have a certain leakage flow, so that the closing hydraulic pressure does not remain unchanged at the initial level.

[0050] According to the invention, the system pressure 70 is therefore monitored. At a point in time 71, the system pressure 70 falls below a threshold 73 which is set at 90% of the original value 74 upon transition to the hold mode. A switch to the alternative mode is therefore performed according to the invention.

[0051] In a first embodiment, a switchover to the parking brake mode is performed as an alternative mode. To this end, the electromechanical parking brakes 48c, 48d are activated, so that the vehicle is held stationary. The hydraulic brake system can therefore be switched off at a later point in time in order to be fully operational again, or at least switched off so that all components can be cooled down.

[0052] In a second embodiment, a switchover to the cooperation mode is performed as an alternative mode. This is possible in the case of the brake system of FIG. 2, which in addition to the linear actuator 5 also has a further pressure supply device 57. The electric pumps 57a and 57b are now activated to boost the brake pressure of the wheel brakes 8a and 8b. As soon as the target pressure is reached, the pressure can be sealed again. The cooperation mode can also be combined with the parking brake mode by simultaneously activating the electromechanical parking brakes 48c, 48d on the rear axle.

[0053] In a third embodiment, a switch to half mode is performed as an alternative mode. Here, the circuit isolation valve 40 is closed in order to divide the brake system into two partial circuits. The wheel brakes 8c and 8d of the rear axle then remain in a hydraulically trapped state. At the front axle, the wheel pressure of the wheel brakes 8a and 8b is matched to the hydraulic pressure in the brake master cylinder 2 by a brief opening of the outlet valve. As soon as the pressure equalization has substantially taken place, the isolation valve 23 is opened, so that the brake master cylinder 2 is connected in an open-flow manner to the wheel brakes 8a, 8b. In this way, the driver can directly control the front wheel brakes. If the braking force is not sufficient to hold the vehicle stationary, the driver can depress the brake pedal further in order to increase the braking force.

[0054] The use of the alternative mode according to the invention therefore avoids the need to switch the brake system directly to the hydraulic fallback level, without the driver having to increase the required brake pressure solely via the brake master cylinder. The present invention may also include the following aspects: 1. A method for regulating a hydraulic braking system of a motor vehicle having a linear actuator (5) as a driver-independent pressure supply device and a hydraulic valve arrangement (26) between the linear actuator (5) and wheel brakes (8) of the hydraulic braking system, characterized in that in case of reduced availability of the linear actuator (5), a hold mode is executed, in which case the hydraulic pressure in the wheel brakes (8) is sealed off by the valve arrangement (26) and the output of the linear actuator (5) is reduced, a system pressure gradient (70) in the hold mode is measured, and a transition from the hold mode to an alternative mode is executed based on the system pressure gradient (70). 2. The method according to claim 1, characterized in that a determination is made as to how far the system pressure (70) has dropped in the holding mode, and a transition to the alternative mode is made if the system pressure falls below a threshold value (72). 3. The method according to claim 2, wherein the threshold value (72) is set based on the roadway gradient. 4. A method according to any one of 1. to 3. above, characterized in that a decrease in the availability of the linear actuator (5) is detected when the temperature assigned to the linear actuator (5) exceeds a threshold value. 5. A method according to any one of 1. to 4. above, characterized in that a refill mode is executed based on the system pressure gradient (70) and the availability of the linear actuator (5), and in the refill mode, the sealing pressure is increased by the linear actuator (5), after which switching to the holding mode is executed again. 6. A method according to any one of 1 to 5 above, characterized in that the holding mode is executed when the vehicle is stopped. 7. A method according to any one of claims 1 to 6, wherein the alternative mode is not a hydraulic fallback level. 8. A method according to any one of 1. to 7. above, characterized in that the alternative mode is a parking brake mode, in which the electromechanical parking brake (48) of the vehicle is activated and the hydraulic braking system is deactivated, so that the vehicle is held by the parking brake (48). 9. A method according to any one of claims 1 to 8, characterized in that the alternative mode is a cooperative mode, in which an additional hydraulic supply device (57) is activated to increase the sealing pressure, after which switching back to the holding mode is performed again. 10. A method according to any one of claims 1 to 9 above, characterized in that the alternative mode is a half mode, in which case the valve arrangement (23, 26) is operated to connect the wheel brakes (8a, 8b) of a first axle in an open-flow manner to a brake master cylinder (2) that can be activated by the driver, and to seal off the hydraulic pressure of the wheel brakes (8c, 8d) of a second axle. 11. The method according to claim 10, characterized in that in the event of switching to half mode, the pressure in the wheel brakes (8a, 8b) is matched to the pressure in the brake master cylinder (2) before the valve arrangement (23) establishes an open flow connection. 12. A method according to any one of claims 1 to 11, characterized in that at the start of the holding mode, a pressure higher than the required pressure is increased by the linear actuator (5) and the higher pressure is sealed off. 13. A hydraulic braking system for a motor vehicle having a linear actuator (5) as a driver-independent pressure supply device, a hydraulic valve arrangement (26) between the linear actuator (5) and a wheel brake (8) of the hydraulic braking system, and a control device (12), characterized in that the control device (12) is configured to perform the method according to any one of 1. to 12. above. [Explanation of symbols]

[0055] 1 Brake pedal 2 Brake master cylinder 3. Simulation Device 4 Pressure medium reservoir 5. Pressure Supply Device 6a~d Inlet valve 7a~d Outlet valve 8a~d Wheel brakes 9. Return spring 12 Control System 13 Brake supply line 14 Return line 16 Housing 17 Pressure Chamber 19 System Pressure Sensor 20 Master cylinder pressure sensor 22 First Feed Line 23 Isolation valve 24 Piston rod 25 Displacement Sensor 26 Additive valve 29 Simulator Chamber 30 Simulator rear chamber 31 Simulator piston 32 Simulator enable valve 33 Elastic Elements 35 Piston 36 Electric motor 37 Pressure Space 38 Feed Line 39 Rotational / translational gear mechanism 40 Circuit isolation valve 41 Pressure Equalization Line 42 Line 44 Rotor Position Sensor 50 Filling Level Sensor 53 Check valve 54 Switching valve 55 Low Pressure Accumulator 56 Refill valve 57 Hydraulic Pump 58 Pump isolation valve 60 Valve Flow 61 Open flow rate 62 Holding flow rate 63 Closing flow rate 70 System Pressure 71 Switching point 72 Threshold 73 Original value

Claims

1. 1. A method for regulating a hydraulic brake system of a motor vehicle having a linear actuator (5) as a driver-independent pressure supply device and a hydraulic valve arrangement (26) between the linear actuator (5) and wheel brakes (8) of a hydraulic brake system, characterized in that in case of reduced availability of the linear actuator (5), a hold mode is executed, in which the pressure in the wheel brakes (8) is sealed off by the valve arrangement (26) and the output of the linear actuator (5) is reduced, in the hold mode a sealed pressure (70) in the wheel brakes (8) is measured by a pressure sensor (19) arranged between the hydraulic valve arrangement (26) and the wheel brakes (8) and a transition from the hold mode to an alternative mode is executed based on said pressure (70).

2. 2. The method of claim 1, further comprising: determining how much the pressure (70) has dropped in the holding mode; and transitioning to the alternative mode is performed if the pressure falls below a threshold (72).

3. 3. The method of claim 2, wherein the threshold (72) is set based on roadway slope.

4. The method according to any one of claims 1 to 3, characterized in that a reduced availability of the linear actuator (5) is detected if the temperature assigned to the linear actuator (5) exceeds a threshold value.

5. 4. The method according to claim 1, characterized in that a refill mode is performed depending on the pressure (70) and the availability of the linear actuator (5), in which in the refill mode the sealing pressure is increased by the linear actuator (5) and then a switch to the holding mode is performed again.

6. Method according to any one of claims 1 to 3, characterized in that the holding mode is executed when the vehicle is stationary.

7. The method according to any one of claims 1 to 3, characterized in that the alternative mode is not a hydraulic fallback level.

8. The method according to any one of claims 1 to 3, characterized in that the alternative mode is a parking brake mode, in which an electromechanical parking brake (48) of the vehicle is activated and the hydraulic braking system is deactivated, so that the vehicle is held by the parking brake (48).

9. The method according to any one of claims 1 to 3, characterized in that the alternative mode is a cooperation mode, in which an additional hydraulic supply device (57) is actuated to increase the pressure, after which a switchover to the holding mode is made again.

10. 4. The method according to claim 1, wherein the alternative mode is a half mode, in which the valve arrangement (23, 26) is operated to connect the wheel brakes (8a, 8b) of a first axle in an open-flow manner to a brake master cylinder (2) that can be actuated by the driver, and to seal off the hydraulic pressure of the wheel brakes (8c, 8d) of a second axle.

11. 11. The method according to claim 10, characterized in that in the case of switching to the half mode, the pressure in the wheel brakes (8a, 8b) is matched to the pressure in the brake master cylinder (2) before the valve arrangement (23) establishes an open flow connection.

12. The method according to any one of claims 1 to 3, characterized in that at the start of the holding mode a pressure higher than the required pressure is increased by a linear actuator (5) and said higher pressure is sealed off.

13. A hydraulic braking system for a motor vehicle having a linear actuator (5) as a driver-independent pressure supply device, a hydraulic valve arrangement (26) between said linear actuator (5) and wheel brakes (8) of a hydraulic braking system, and a control device (12), characterized in that said control device (12) is configured to perform the method according to any one of claims 1 to 3.

Images