Method for controlling a redundant hydraulic motor vehicle braking system

Abstract

The invention relates to a method for controlling a redundant hydraulic motor vehicle braking system, comprising a first electrical pressure supply device (5), which is designed as a linear actuator, which can be connected to at least one hydraulic wheel brake (8) via an electrically switchable normally open isolation valve (26), and a second electrical pressure supply device (2), which is designed as a piston pump, which can be connected to the hydraulic wheel brake (8), wherein pressure is supplied by the piston pump (2) when the isolation valve (26) is closed and the pressure position is transferred to the linear actuator (5). To ensure that this transfer is carried out without errors, an opening routine for the isolation valve (26) is performed, comprising a pressure build-up using the linear actuator (5) to reduce the pressure difference across the isolation valve (26) and a de-energizing of the isolation valve (26), wherein the current switching state of the isolation valve (26) is subsequently determined by actuating the linear actuator (5) to perform a reverse movement, whereby a relationship between a motor torque quantity and a position quantity of the linear actuator (5) is determined and compared with an expected behavior for an open and / or a closed isolation valve (26).

Description

[0001] The invention relates to a method for controlling a redundant hydraulic vehicle braking system, comprising a first electrical pressure supply device, designed as a linear actuator, which can be connected to at least one hydraulic wheel brake via an electrically switchable, normally open isolation valve, and a second electrical pressure supply device, designed as a piston pump, which can be connected to the hydraulic wheel brake, wherein pressure is supplied by the piston pump when the isolation valve is closed and the pressure position is transferred to the linear actuator. The invention also relates to a corresponding redundant hydraulic vehicle braking system.

[0002] In redundant hydraulic vehicle braking systems with "brake-by-wire" operation, the driver is decoupled from direct access to the brakes. When the pedal is pressed, a pedal decoupling unit and a simulator are typically activated, with sensors detecting the driver's braking request. The pedal simulator serves to provide the driver with a familiar brake pedal feel. The detected braking request leads to the determination of a target braking torque, from which the target brake pressure is then calculated. The brake pressure is then actively generated by a pressure supply unit within the brakes.

[0003] Actual braking is achieved through active pressure build-up in the brake circuits using a pressure supply device controlled by a control unit. By hydraulically decoupling the brake pedal actuation from the pressure build-up, such braking systems allow for the convenient implementation of many functionalities for the driver, such as ABS, ESC, TCS, hill start assist, etc.

[0004] The pressure supply device in the braking systems described above is also referred to as an actuator or hydraulic actuator. Actuators are typically designed as linear actuators, in which a piston is axially displaced into a hydraulic pressure chamber, which is connected in series with a rotary-translation gearbox, to build up pressure. The motor shaft of an electric motor is converted into an axial displacement of the piston by the rotary-translation gearbox.

[0005] In such braking systems, a mechanical or hydraulic fallback system is usually provided, allowing the driver to decelerate or bring the vehicle to a stop using muscle power by pressing the brake pedal if the "by-wire" operating mode fails or malfunctions. Under normal operating conditions, in such an externally powered braking system, the driver operates a pedal simulator. This pedal actuation is detected by pedal sensors, which then determine the corresponding target pressure for the linear actuator to actuate the wheel brakes.

[0006] Moving the linear actuator forward from its rest position into the pressure chamber displaces brake fluid from the linear actuator, through the open valves, into the wheel brakes, thus increasing pressure. Conversely, moving the linear actuator back towards its rest position reduces the pressure in the wheel brakes. A suitable pressure regulator or pressure control system is used to set the required system pressure.

[0007] A hydraulic backup system is not required in a braking system with a dry pedal. In this case, a second pressure supply device must be provided for active pressure build-up in the wheel brakes to achieve redundancy in the backup system.

[0008] From DE 10 2017 219 598 A1, a braking system or braking assembly is known, comprising a master brake cylinder, a simulator, and a pressure supply device that can be hydraulically connected to the wheel brakes via a hydraulic valve. The system pressure, which corresponds to the pressure in the pressure chamber of the pressure supply device, is measured by a system pressure sensor located downstream of the hydraulic valve from the perspective of the pressure chamber of the pressure supply device.

[0009] In known braking systems, the system pressure sensor is used for an opening algorithm of the hydraulic valve(s) at the output of the pressure supply unit. The linear actuator can build up pressure in the wheel brakes by simply forcing the hydraulic valve open. The pressure increase can be detected by the sensor. When pressure equalizes between the pressure supply unit and the hydraulic system with the wheel brakes, the valve can be opened by applying current to the valve at that moment.

[0010] From DE 10 2020 202 368 A1, it is known to use the motor torque of the linear actuator instead of the system pressure sensor. If a kink is detected there during pressure build-up, pressure equality is assumed and the hydraulic valve is acted upon with an opening flow. Due to the design and orientation of the hydraulic valve, the valve is always secured in the open state, thus ensuring pressure build-up.

[0011] In redundant braking systems, a normally open valve is often used to ensure an open connection in the event of a power supply or control failure. However, the opening force of normally open valves is limited to the valve's spring force, meaning that opening by applying an electromagnetic force cannot be guaranteed. Such a valve can close unintentionally, especially during pressure drop caused by a flow of fluid from a wheel brake towards the linear actuator. Furthermore, depending on pressure differentials and flow rates, the valve may not respond to an intended opening.

[0012] The invention is therefore based on the objective of providing a method for controlling a redundant hydraulic motor vehicle braking system which has an electrically switchable normally open isolation valve, wherein a switching state of the isolation valve can be reliably detected.

[0013] The problem is solved by a method for controlling a redundant hydraulic motor vehicle braking system, comprising a first electrical pressure supply device, which is designed as a linear actuator and can be connected to at least one hydraulic wheel brake via an electrically switchable normally open isolation valve, and a second electrical pressure supply device, which is designed as a piston pump and can be connected to the hydraulic wheel brake, wherein pressure is supplied by the piston pump when the isolation valve is closed and the pressure position is transferred to the linear actuator, wherein an opening routine for the isolation valve is performed for the transfer, comprising a pressure build-up by means of the linear actuator to reduce the pressure difference across the isolation valve and a de-energizing of the isolation valve.where the current switching state of the isolation valve is subsequently determined by controlling the linear actuator to perform a reverse movement, whereby a relationship between a motor torque quantity and a position quantity of the linear actuator is determined and compared with an expected behavior for an open and / or a closed isolation valve.

[0014] Providing pressure via the piston pump may be particularly useful if the piston pump is designed to deliver a maximum pressure greater than that of the linear actuator. The latter might, for example, be rated for only 190 bar. For higher pressures, such as those that can occur during brake fade, the piston pump takes over pressure regulation. For this, the isolation valve closes, the linear actuator relaxes, and the pump maintains the pressure. When switching from this operating mode to normal linear actuator operation, for example, due to a decrease in pressure demand, the opening routine with monitoring is performed as described above. This ensures that pressure reduction is always possible to prevent overbraking. The connection between the pressure side of the piston pump and the wheel brakes does not pass through the isolation valve.

[0015] The relationship between motor torque and position essentially reflects the stiffness of the respective hydraulic chamber or the pressure-volume characteristic. Since this characteristic varies significantly in the different switching states of the isolation valve, the switching state can be reliably determined. In particular, the switching state can be determined absolutely, unlike known methods that can only detect a change in the switching state.

[0016] In a preferred embodiment of the invention, the linear actuator is controlled to perform a reverse movement by receiving a specific reverse speed as a control variable, moving to a target position that requires reverse movement, and / or generating a specific motor torque. The torque required for reverse speed depends on the switching state of the isolation valve. If the valve is open, thus providing a flow-open connection to the wheel brakes, which are under the pressure previously supplied by the piston pump, the piston of the linear actuator is pushed back by this pressure. For reverse movement at a controlled speed, the piston must be braked, i.e., driven with a positive motor torque. If, on the other hand, the valve is closed, a negative motor torque is required.If, however, the motor is driven with a specific torque, the speed can be observed. For example, if the motor is simply driven with zero torque, it should not move with the isolation valve closed. However, if the wheel brake pressure is applied to the linear actuator piston through an open isolation valve, it will execute the reverse movement even without applied motor torque.

[0017] In a preferred embodiment, the transfer occurs when the second pressure supply device is detected to be faulty. In particular, the first pressure supply device can be part of a first subsystem which includes a first control unit. The second pressure supply device, in turn, is then part of a second subsystem which includes a second control unit. The transfer occurs when the first subsystem detects the unavailability of the second subsystem. Specifically, the first subsystem can determine the switching state of the isolation valve without access to a pressure sensor on the wheel brake side of the isolation valve.

[0018] In a further preferred embodiment of the invention, the isolation valve is designed and aligned in such a way that it remains closed even when de-energized at a pressure greater than a first threshold value on the side facing the wheel brake.

[0019] In a further preferred embodiment of the invention, the isolation valve has a pilot stage and a main stage, wherein the pilot stage opens at a pressure differential corresponding to the first threshold value, and the main stage opens only at a lower pressure differential, a second threshold value. Preferably, the pilot stage opens at 30 to 70 bar, particularly preferably at 50 bar. The main stage opens at a pressure of less than 20 bar, preferably at the same pressure or a pressure differential of less than approximately 6 bar. With the pilot stage open, only very small volume flows, up to 0.5 cm³, are possible compared to an open main stage. 3 / (s bar) possible. At a pressure difference of 25 bar, approximately 10 cm can be achieved. 3 / s flow through the opened pilot stage.

[0020] In a particularly preferred embodiment of the invention, the specific relationship is compared with the expected behavior for an open and / or closed pilot stage and / or main stage. This allows it to be determined whether the isolation valve is completely closed, or whether only the pilot stage or also the main stage is open. For example, if the linear actuator is driven with a motor torque of zero, no movement can be observed. With an open pilot stage and a closed main stage, a slow movement greater than zero but less than a limiting velocity is observed, since the flow rate of brake fluid through the pilot stage is limited. The exact velocity is determined by the flow opening of the pilot stage, the pressure differential, and the geometry of the linear actuator. If the main stage is also open, the reverse movement is correspondingly faster than the limiting velocity.At a fixed speed, the engine torque also varies accordingly. This highly detailed knowledge of the shift state allows the braking system to react specifically.

[0021] In a further preferred embodiment of the invention, the pressure build-up of the linear actuator during the opening routine is regulated to a pressure on the wheel brake side of the isolation valve. This pressure can be measured, estimated, or otherwise determined. In particular, the linear actuator is controlled to adjust this pressure to the extent possible, or at least to a predetermined maximum pressure differential that enables opening. If the pressure to be adjusted exceeds the pressure-setting capabilities of the linear actuator, it can be operated at high speed so that a dynamic pressure is generated via its inertia, which at least briefly reaches the required pressure.

[0022] In a particularly preferred embodiment of the invention, the pressure is determined by adjusting a last known pressure by taking into account pressure equalization processes that occur when hydraulic units on the wheel brake side of the isolation valve are de-energized. This is particularly important if a second subsystem comprising the second pressure supply device fails and, consequently, no pressure sensor is available on the wheel brake side of the isolation valve. This allows the pressure to be determined with high accuracy nonetheless, enabling precise adjustment of the pressure to be controlled by the linear actuator during the opening routine.

[0023] In a particularly preferred embodiment of the invention, the pressure equalization processes include the run-down behavior of the piston pump and / or the opening of at least one inlet valve of a wheel brake and the associated volume flow of brake fluid. In particular, current valve states, wheel pressures, the applied pump speed, a residual pump flow volume, inlet valve states, the system pressure (model or sensor value), pressure-volume characteristics, the state of a circuit separator valve, a switching valve, and / or the position of the linear actuator piston can be taken into account.

[0024] In a further preferred embodiment of the invention, the opening routine is repeated when a closed isolation valve is detected. This allows for a quick response to a valve that does not open, enabling it to be opened and thus implementing a required pressure reduction.

[0025] In a particularly preferred embodiment of the invention, the opening routine is repeated with modified parameters. In particular, the linear actuator is controlled to approach a higher pressure and / or a higher speed. This can also be done multiple times, resulting in an oscillation of the linear actuator. This ensures that the isolation valve can be opened.

[0026] In a preferred embodiment of the invention, pressure control is initiated upon detection of an open isolation valve. This means that a setpoint for at least one wheel pressure is adjusted using the linear actuator. The transition is then considered complete.

[0027] In a preferred embodiment of the invention, if only one pilot stage is detected to be open, the linear actuator is controlled to at least hold the position until the main stage also opens. This allows brake fluid to flow through the open pilot stage, gradually reducing the pressure differential across the isolation valve. Once this differential has dropped sufficiently, the main stage also opens, allowing pressure regulation to commence.

[0028] The problem is further solved by a redundant hydraulic motor vehicle braking system comprising a first electrical pressure supply device, which is designed as a linear actuator, which can be connected to at least one hydraulic wheel brake via an electrically switchable normally open isolation valve, and a second electrical pressure supply device, which is designed as a piston pump, which can be connected to the hydraulic wheel brake, wherein a control device is provided which is configured to carry out a method described above.

[0029] Further features, advantages, and applications of the invention will also become apparent from the following description of exemplary embodiments and the drawings. All features described and / or illustrated, both individually and in any combination, are part of the subject matter of the invention, even independently of their compilation in the claims or their cross-references. Fig. Figure 1 shows a brake system according to the invention, Fig. Figure 2 shows the linear actuator position during the execution of the method according to the invention. Fig. Figure 3 shows the motor torque during the execution of the method according to the invention.

[0030] In Fig. Figure 1 shows a redundant hydraulic braking system for motor vehicles. By way of example, the braking system is designed to actuate four hydraulically actuated wheel brakes 8; expansion to more wheel brakes is easily possible. By way of example, the two upper wheel brakes (HL, HR) in the figure are assigned to the rear axle and the wheel brakes (VL, VR) to the front axle of the vehicle.

[0031] The braking system comprises a first component or subsystem, which is, for example, designed as a first electro-hydraulic brake control unit with a valve block and a first electronic control unit ECU1, and a second component or subsystem, which is, for example, designed as a second electro-hydraulic brake control unit with a valve block and a second electronic control unit ECU2. Each valve block forms its own housing.

[0032] The first assembly unit has a pressure medium reservoir 4 with three chambers, wherein the first chamber is assigned a first reservoir connection, the second chamber a second reservoir connection, and the third chamber a third reservoir connection. Reservoirs with two or more chambers are also possible.

[0033] In the first assembly unit, a first electrically actuated pressure source 5 or pressure supply device is arranged.

[0034] In the second assembly unit, a second electrically actuated pressure source 2 and wheel-specific brake pressure modulation valves are arranged, which are designed as an electrically actuated inlet valve 6 and an electrically actuated outlet valve 7 for each wheel brake 8.

[0035] The first pressure source 5 and the second pressure source 2 are connected on the pressure side to a brake supply line, to which the four inlet valves 6 are connected. This allows all four wheel brakes 8 to be actuated by means of the first pressure source 5 and / or by means of the second pressure source 2.

[0036] An electrically actuated circuit isolator valve 40 is arranged in the brake supply line, and thus in the second component unit. When the circuit isolator valve 40 is closed, the brake supply line is divided into a first line section, to which the inlet valves 6 and the wheel brakes 8 of the rear axle are connected, and a second line section, to which the inlet valves 6 and the wheel brakes 8 of the front axle are connected. The second pressure source 2 is hydraulically connected to the first line section, and the first pressure source 5 is hydraulically connected to the second line section. With the circuit isolator valve 40 closed, the brake system is thus divided into two hydraulic brake circuits, I and II, or a first sub-circuit and a second sub-circuit.In the first brake circuit I, pressure source 2 (via the first line section) is connected only to the rear axle wheel brakes 8, and in the second brake circuit II, pressure source 5 (via the second line section) is connected only to the front axle wheel brakes 8. The circuit isolating valve 40 is advantageously designed to be normally open (de-energized). Such an operating mode can be called circuit isolating mode or ACS for "Active Circuit Separation".

[0037] As already mentioned, the brake system comprises, for each hydraulically actuated wheel brake 8, an inlet valve 6 and an outlet valve 7, which are hydraulically connected in pairs via center connections and each pair is connected to a hydraulic wheel connection of the second assembly, to which the corresponding wheel brake 8 is connected. A check valve opening towards the brake supply line is connected in parallel to each inlet valve 6. The outlet connections of the outlet valves 7 are connected to the pressure medium reservoir 4 or its third chamber via a common return line. The inlet connections of all inlet valves 6 can be supplied with pressure via the brake supply line (i.e., with the circuit separator valve 40 open), which is provided by the first pressure source 5 or, for example, in the event of a failure of the first pressure source 5, by the second pressure source 2.

[0038] The first electrically controlled pressure source 5 of the valve block is designed as a hydraulic cylinder-piston arrangement (or a single-circuit electrohydraulic actuator (linear actuator)), whose piston can be actuated by a schematically indicated electric motor via a similarly schematically depicted rotary-translational transmission, in particular by moving it back and forth to build up and release pressure in a pressure chamber. The piston defines the pressure chamber of pressure source 5. A rotor position sensor, also only schematically indicated, is provided to control the electric motor. This sensor allows the piston position and speed, and thus the volume of brake fluid delivered or received, to be determined.

[0039] A section of system pressure line is connected to the pressure chamber of the first electrically controlled pressure source 5. This line section connects the pressure source 5, or rather its pressure chamber, to a hydraulic connection of the first component, which in turn is connected via a hydraulic connecting element to a hydraulic connection of the second component. This connection constitutes the only hydraulic pressure connection between the first and second components. It is a hydraulic connection for transmitting brake pressure to actuate the wheel brakes 8.

[0040] The system pressure line section, and thus the pressure chamber, is connected to the pressure medium reservoir 4 via a (suction) line, regardless of the piston's actuation state. A check valve 53, closing towards the pressure medium reservoir 4, is arranged in the line in connection with the second chamber. An electrically switchable valve 23 forms a further connection to a first chamber of the pressure medium reservoir 4, which is connected to the output port of the linear actuator 5. This isolation valve 23 is normally open, so that in the de-energized state, the wheel brakes 8 are connected to the brake fluid reservoir 4. The cylinder-piston assembly 5, for example, has no vent holes.

[0041] The second electrically controlled pressure source 2 of the second assembly is, for example, designed as a two-piston pump whose two pressure sides are connected together. The suction sides are connected to the return line and thus to the pressure medium reservoir 4. The pressure sides are connected to the first section of the brake supply line.

[0042] In addition to the pressure source 2 and the brake pressure modulation valves 6, 7, the second assembly includes, for example, an electrically actuated, normally open, isolation valve 26. The isolation valve 26 is hydraulically positioned between the connection and the second section of the brake supply line. Thus, the first pressure source 5, and therefore the entire first assembly, is disconnected via the isolation valve 26 from the second section of the brake supply line and thus from the wheel brakes 8.

[0043] The brake system includes, for example, a pressure sensor 19 in brake circuit I, which is thus assigned to the second pressure source 2. This is advantageous for burst protection when the circuit isolating valve 40 is closed. However, the pressure sensor can also be located in brake circuit II.

[0044] Each valve block is assigned an electronic control unit (ECU1) and an electronic control unit (ECU2). Each electronic control unit comprises electrical and / or electronic elements (e.g., microcontrollers, power components, valve drivers, other electronic components, etc.) for controlling the electrically actuated components of the associated valve block and, if applicable, the associated sensors—that is, the entire respective assembly. Advantageously, the valve block and the electronic control unit are designed as a single electrohydraulic unit, as is known.

[0045] The first electronic control device controls the first pressure source 5. For example, the first pressure source 5 is supplied with energy (from a first electrical energy source) via the first electronic control device.

[0046] The second electronic control device controls the second pressure source 2. For example, the second pressure source 2 is supplied with energy (from a second electrical energy source) via the second electronic control device.

[0047] For example, the first pressure source or primary pressure source 5 can be controlled exclusively by the first electronic control device, and the second pressure source or secondary pressure source 2 can be controlled exclusively by the second electronic control device.

[0048] Under normal operating conditions, the pressure in the wheel brakes is built up by the primary pressure source 5. The pressure in the primary pressure source 5 is reduced by retracting its piston. The pressure is modulated individually for each wheel as needed by the inlet and outlet valves. If necessary, the isolation valve 26 is closed to allow the primary pressure source 5 to draw in additional volume.

[0049] Outside of braking situations, atmospheric pressure equalization can be permanently ensured via separating valve 23 and isolation valve 26.

[0050] The control units ECU1 and ECU2 are configured to implement pressure build-up using the linear actuator 5 and / or the piston pump 2 based on pressure requirements. These requirements can originate from automatic functions, assistance programs, and, in particular, from the driver, who transmits their request via the brake pedal. This request is then transmitted to the control units as a brake pedal actuation signal. The brake pedal actuation signal can be brake pedal travel, brake pedal force, and / or similar parameters.

[0051] Preferably, the isolation valve 26 is controlled by the secondary ECU. The following description of operation in the event of a fault refers to this valve assignment.

[0052] If the secondary system fails electrically, particularly the secondary ECU or its power supply, the pressure is built up and released via the primary pressure source 5 as in normal operation. Individual wheel pressure control is not possible, but collective modulation of the wheel pressures remains possible to prevent the vehicle from being destabilized by wheel lock-up.

[0053] If the primary system fails electrically, particularly the primary unit or its power supply, the secondary ECU switches to a fallback mode in which the second unit becomes the sole pressure source for the vehicle's wheel brakes 8. To achieve this, it closes the isolation valve 26 to allow pressure to build up via the secondary pressure source 2. Without the isolation valve 26 closed, the brake fluid would continue to flow into the reservoir via the normally open shut-off valve 23, thus preventing pressure build-up. Pressure is released via the outlet valves 7. Preferably, the inlet and outlet valves are controlled by the secondary ECU so that the pressure can be modulated individually for each wheel.

[0054] For example, the brake system for leakage monitoring includes a level measuring device for determining a pressure medium level in the pressure medium reservoir 4. If the pressure medium level falls below a predetermined value, a leak is considered to have been detected.

[0055] Leakage monitoring can also be implemented using other monitors. A Volume Deviation Monitor (VDM) is a leakage monitoring system that can detect hydraulic leaks based on the pressure-volume ratio (PV ratio). The volume required to build up a specific pressure is determined by sensing the linear actuator or pedal position. The expected PV behavior can be defined using functions or predefined characteristic curves. In other words, the building pressure is compared to the delivered volume using a characteristic curve. A low brake fluid level (BFLS) in the reservoir or excessively low pressure will also trigger leakage detection.

[0056] In the event of a leak in the brake system, the circuit separating valve 40 is typically closed, thereby dividing the system into two independent brake circuits I and II.

[0057] When a particularly high flow rate is required, both pressure sources 5 and 2 operate simultaneously in parallel. When a particularly high pressure is required, the pressure supply devices reach their respective pressure limits. Designing for such high pressures requires extensive modifications to these pressure sources, which is very costly. Therefore, it may be possible to design only one of the two pressure sources for the rarely required pressures in the range of 200 bar. The piston pump 2 is generally suitable for this purpose. The piston pump 2 is therefore designed to generate a higher maximum pressure than the linear actuator 5. The linear actuator can accordingly be designed to offer advantages in pressure setting at lower pressure levels.If a very high pressure is requested, exceeding the limit pressure of the linear actuator, the isolation valve 26 is closed, and the secondary pressure source 2 increases the pressure above the pressure of the primary pressure source 5. The linear actuator 5 can then be controlled accordingly to minimize the pressure within its pressure range by producing no or at least a reduced motor torque. This allows it to be relieved of stress and cool down.

[0058] If the pressure demand drops again, the pressure is transferred back to the linear actuator 5 as the pressure source. Crucially, this requires the isolation valve 26 to reopen. However, because there is a very high pressure differential across this valve between the currently set high wheel pressure, which is higher than the limit pressure of the linear actuator 5, and the minimized pressure in the linear actuator 5, the hydraulic forces hold this valve closed. Simply de-energizing this normally open valve would therefore not open it.

[0059] Therefore, an opening routine is performed in which the linear actuator 5 moves forward to build up pressure on the linear actuator side of the isolation valve 26 in order to minimize the pressure difference. If this allows the isolation valve 26 to open, this can be detected in the pressure curve, which is recorded by the pressure sensor 19. If this is the case, the linear actuator can then reverse its movement to implement the requested pressure reduction.

[0060] A transfer back to the linear actuator 5 as the pressure source must be performed not only when the pressure demand decreases, but also in the event of a failure of the second unit with the piston pump 2. However, no pressure sensor 19 is available in this case. The linear actuator 5 is therefore controlled to provide the pressure that prevails on the wheel pressure side of the isolation valve 26. If this pressure is present, the de-energized isolation valve 26 should open. To verify this, according to the invention, the linear actuator 5 is controlled to execute a predetermined reverse speed, for example, 20 revolutions per minute. This is shown in the diagram of the linear actuator position versus time. Fig. 2 is represented by the two falling ramps, each with durations of 4.6s and 7.8s. The motor torque required for this, which is shown in Fig.The process shown in Figure 3 is analyzed. For the example process at 4.6 seconds, a motor torque of -0.15 Nm is observed. The linear actuator must therefore apply torque in the reverse direction, indicated by a closed isolation valve 26. The linear actuator 5 draws brake fluid via the check valve 53. In the second example process at 7.8 seconds, the linear actuator must provide a positive motor torque of 1.27 Nm, which decreases slowly. This is indicated by an open isolation valve 26. Since the high pressure in the wheel brakes acts directly on the piston of the linear actuator through the open isolation valve 26 and pushes it back, the linear actuator must provide a positive motor torque to counteract this force, thus maintaining the piston at a slow reverse speed. As the wheel pressure decreases slowly due to the reverse movement, the required counter-torque also decreases slowly.Thus, by determining the relationship between the reverse speed and the motor torque, the switching state of the isolation valve can be determined.

[0061] As described above, the linear actuator 5 must provide the pressure present on the wheel pressure side of the isolation valve 26 to open it. However, the pressure sensor 19 is not available at this stage, so the pressure is initially unknown. To determine this pressure, an adjustment is made based on the last known measurement before the failure of the second component. In particular, the volume still being pumped by the piston pump is determined based on the last known pump speed. Furthermore, the compensating flows resulting from the change in valve states due to the de-energization position when the second component fails, especially to and from the wheel brakes, are taken into account. The pressure-volume curves of the individual hydraulic units or areas are used for this purpose. Thus, the resulting pressure can be calculated and used for control purposes. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2017 219 598 A1

[0008] DE 10 2020 202 368 A1

[0010]

Claims

[1] Method for controlling a redundant hydraulic motor vehicle braking system, comprising a first electrical pressure supply device (5) designed as a linear actuator which can be connected to at least one hydraulic wheel brake (8) via an electrically switchable normally open isolation valve (26), and a second electrical pressure supply device (2) designed as a piston pump which can be connected to the hydraulic wheel brake (8), - wherein pressure is provided by the piston pump (2) when the isolation valve (26) is closed and the pressure position is transferred to the linear actuator (5), characterized by , that for the transfer an opening routine for the isolation valve (26) is carried out, comprising a pressure build-up by means of the linear actuator (5) to reduce the pressure difference across the isolation valve (26) and a de-energizing of the isolation valve (26), - wherein the current switching state of the isolation valve (26) is subsequently determined by controlling the linear actuator (5) to perform a reverse movement, wherein - a relationship between a motor torque quantity and a position quantity of the linear actuator (5) is determined and compared with an expected behavior for an open and / or a closed isolation valve (26). [2] Method according to claim 1, characterized by , that the linear actuator (5) is controlled to perform a reverse movement by being given a specific reverse speed as a control variable, to move to a target position that requires a reverse movement and / or to generate a specific motor torque. [3] Method according to any one of the preceding claims, characterized by , that the transfer takes place when it is determined that the second pressure supply device (2) is faulty. [4] Method according to any one of the preceding claims, characterized by , that the isolation valve (26) is designed and aligned in such a way that it is kept closed even when de-energized at a pressure greater than a first threshold value on the side facing the wheel brake (8). [5] Method according to any one of the preceding claims, characterized by , that the isolation valve (26) has a pilot stage and a main stage, wherein the pilot stage opens at the first threshold and the main stage opens only at a lower pressure difference. [6] Method according to claim 5, characterized by , that the specific relationship is compared with an expected behavior for an open and / or closed pilot stage and / or main stage. [7] Method according to any one of the preceding claims, characterized by, that the pressure build-up of the linear actuator (5) during the opening routine is regulated to an expected pressure on the wheel brake side of the isolation valve (26). [8] Method according to claim 5, characterized by , that the expected pressure is determined by adjusting a last known pressure by taking into account pressure equalization processes that occur due to de-energizing hydraulic units on the wheel brake side of the isolation valve (26). [9] Method according to claim 6, characterized by , that the pressure equalization processes include a discharge behavior of the piston pump (2) and / or an opening of at least one inlet valve (6) of a wheel brake (8) and the associated volume flow of brake fluid. [10] Method according to any one of the preceding claims, characterized by , that if a closed isolation valve (26) is detected, the opening routine is repeated. [11] Method according to claim 9, characterized by, that the opening routine is repeated with changed parameters. [12] Method according to any one of the preceding claims, characterized by , that when an open isolation valve (26) is detected, the system switches to pressure control. [13] Method according to any one of the preceding claims, characterized by , that if only one pilot stage is detected to be open, the linear actuator (5) is controlled to at least hold the position until the main stage also opens. [14] Redundant hydraulic motor vehicle braking system comprising a first electrical pressure supply device (5) designed as a linear actuator which can be connected to at least one hydraulic wheel brake (8) via an electrically switchable normally open isolation valve (26), and a second electrical pressure supply device (2) designed as a piston pump which can be connected to the hydraulic wheel brake (8), characterized bythat a control device is provided which is configured to carry out a method according to one of claims 1 to 13.

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