Method for switching operating modes of a hydraulic motor vehicle braking system

Abstract

The invention relates to a method for controlling a hydraulic motor vehicle braking system comprising a first hydraulic subsystem (100) comprising a hydraulically coupled brake pedal (12) for pressure build-up in at least one first wheel brake (8a, 8b) and / or a first electrical pressure supply device (5) for driver-independent pressure build-up at the at least one first wheel brake (8a, 8b) and a second hydraulic subsystem (200) comprising a second electrical pressure supply device (2) for driver-independent pressure build-up at the at least one first wheel brake (8a, 8b), an isolating valve between the first hydraulic subsystem and the second hydraulic subsystem, wherein in a first operating mode the pressure at the at least one first wheel brake (8a, 8b) is built up by the first hydraulic subsystem.To guarantee safe operation, in a second operating mode the pressure in the at least one first wheel brake (8a, 8b) is built up by the second hydraulic subsystem, whereby the isolation valve is closed to switch from the first operating mode to the second operating mode, whereby the second electrical pressure supply device is activated to support the closing process, to provide a pressure greater than or equal to the pressure of the first hydraulic subsystem, or hydraulic valves in the second subsystem are closed so that no brake fluid flows from the first subsystem via the isolation valve into the second subsystem.

Description

[0001] The invention relates to a method for controlling a hydraulic motor vehicle braking system comprising a first hydraulic subsystem comprising a hydraulically coupled brake pedal for pressure build-up in at least one first wheel brake and / or a first electrical pressure supply device for driver-independent pressure build-up at the at least one first wheel brake, and a second hydraulic subsystem comprising a second electrical pressure supply device for driver-independent pressure build-up at the at least one first wheel brake, and an isolating valve between the first hydraulic subsystem and the second hydraulic subsystem, wherein in a first operating mode the pressure at the at least one first wheel brake is built up by the first hydraulic subsystem. The invention also relates to a corresponding computer program product and an associated braking system.

[0002] Modern vehicle braking systems must have a high degree of redundancy, ensuring that braking force is always available to decelerate the vehicle with a very high probability. Accordingly, two pressure supply devices are provided, so that if one of these pressure supply devices fails, a second pressure source is still available. In the event of a failure and / or fault of individual functions or components, redundant braking systems typically switch from a normal operating mode to corresponding fault modes or fallback modes. Such a braking system is known from DE 10 2023208177 A1, in which, under low braking demands, the driver is hydraulically connected to the wheel brakes to provide a soft pedal feel.

[0003] Another braking system is known from DE 10 2022 202 019 A1, in which the pedal characteristics are switched if a simulator valve does not open.

[0004] However, such redundancy can only increase safety if switching to such operating modes can be guaranteed.

[0005] The problem is solved by a method, particularly computer-implemented, for controlling a hydraulic motor vehicle braking system comprising - a first hydraulic subsystem comprising a hydraulically coupled brake pedal for pressure build-up in at least one first wheel brake and / or a first electrical pressure supply device for driver-independent pressure build-up at the at least one first wheel brake and - a second hydraulic subsystem comprising a second electrical pressure supply device for driver-independent pressure build-up at least one first wheel brake, - An isolation valve between the first hydraulic subsystem and the second hydraulic subsystem. When the isolation valve is closed, there is, in particular, no open-flow connection between the first subsystem and the second subsystem. - In a first operating mode, the pressure at the first wheel brake is built up by the first hydraulic subsystem, i.e., in particular by the first electrical pressure supply device or the hydraulically coupled brake pedal, for example by means of a master brake cylinder. In a second operating mode, the pressure in the first wheel brake is built up by the second hydraulic subsystem, i.e., in particular by the second electrical pressure supply device. - to switch from the first operating mode to the second operating mode, the isolation valve is closed, and to assist the closing process, the second electrical pressure supply device is activated to provide a pressure greater than or equal to the pressure of the first hydraulic subsystem, i.e., the pressure provided by the first electrical pressure supply device or by the hydraulically coupled brake pedal. This prevents brake fluid from flowing from the first subsystem through the isolation valve into the second subsystem. Alternatively, hydraulic valves in the second hydraulic subsystem can be closed, completely sealing the outlet side of the isolation valve, thus preventing any brake fluid from flowing through it.

[0006] In a preferred embodiment of the invention, the first and second subsystems are formed in separate housing blocks. This increases the independence of the two subsystems, thereby improving the redundancy of the overall system by minimizing the probability of double failures. Furthermore, this allows for more flexible installation of the brake system within the vehicle. Additionally, a greater distance between the second subsystem and a firewall of the vehicle minimizes noise transmission into the passenger compartment.

[0007] In a further preferred embodiment of the invention, the isolation valve is designed as a normally open valve. This ensures that even in the event of a power supply failure, the first subsystem, in particular a master brake cylinder of a hydraulically coupled brake pedal, remains connected to the wheel brakes.

[0008] In a particularly preferred embodiment of the invention, the isolation valve is designed and oriented such that a hydraulic pressure on the side of the first hydraulic subsystem relative to the side of the second hydraulic subsystem and / or a volume flow from the side of the first hydraulic subsystem to the side of the second hydraulic subsystem exerts a force on a valve plunger of the isolation valve in an opening direction.

[0009] In a further preferred embodiment of the invention, if the first electrical pressure supply device fails, the braking system operates in the first operating mode up to a predetermined limit pressure and / or limit pressure gradient, wherein the pressure in the at least one wheel brake is supplied by the hydraulically coupled brake pedal, and when the limit pressure and / or limit pressure gradient is reached, i.e., when the pressure supplied by the driver via the brake pedal reaches the limit pressure, the system switches from the first operating mode to the second operating mode. In particular, the hydraulically coupled brake pedal operates without amplification, i.e., it does not include any electric or vacuum brake boosters. This combines the advantages of both operating modes. In low pressure ranges below the limit pressure, the driver thus has particularly good pedal feel.This is more important in this area than increasing the braking force, as the required forces can also be provided by the driver purely mechanically. In the pressure range above the limit pressure, the hydraulic pressure in the second operating mode is provided by the second pressure supply device, which is electrically amplified, thus achieving brake pressures that an average driver could not otherwise reach.

[0010] In a further preferred embodiment of the invention, the isolation valve is energized with a closing current simultaneously with the activation of the second electrical pressure supply device. This simultaneous activation minimizes the effects of the operation of the second pressure supply device on the first subsystem, in particular the hydraulically coupled brake pedal.

[0011] In a further preferred embodiment of the invention, the inlet valves of the wheel brakes, preferably all inlet valves of all wheel brakes, are closed simultaneously with the activation of the second electrical pressure supply device to close the isolation valve. This prevents the flow of brake fluid to the wheel brakes, which in turn stops the flow through the isolation valve more quickly. While this briefly disconnects the wheel brakes from the pressure sources, causing them to exhibit a pressure plateau, this disadvantage in pressure build-up is more than compensated for by the rapid and reliable switchover to the second operating mode, in which the pressure supply is amplified by the second pressure supply device.

[0012] In a particularly preferred embodiment of the invention, the valve flows of the inlet valves are set to a flow rate corresponding to a pressure between 30 bar above the main cylinder pressure and 150 bar. The inlet valves have a characteristic curve that specifies the valve flow required to keep them closed as a function of the differential pressure. Thus, if they are held closed with the flow rate corresponding to a specific differential pressure, they open automatically as soon as the pressure on their inlet side exceeds this pressure. This provides the pressure boost to the wheel brakes, since the valves are not opened by the control unit only after the isolation valve has closed, but rather the pressure effects are utilized directly.

[0013] In a further particularly preferred embodiment of the invention, the current value is gradually approached using a falling ramp starting from the switching current.

[0014] In a further preferred embodiment of the invention, normal pressure control is carried out in the second operating mode as soon as the isolation valve is assumed to be closed, wherein the isolation valve is assumed to be closed when a predetermined time, for example 100ms, has elapsed after the closing current has been applied or as soon as a pressure differential across the isolation valve is sensed which is higher on the side of the second hydraulic subsystem.

[0015] In a further preferred embodiment of the invention, in the second operating mode, a pressure is built up based on the main cylinder pressure, wherein the main cylinder pressure is smoothed and / or filtered and used as an input for a target pressure. Although the influence of the pressure of the second subsystem on the first subsystem is small, this can be further minimized by smoothing and / or filtering.

[0016] The problem is also solved by a hydraulic brake system for motor vehicles comprising a control device which is designed to carry out the aforementioned procedure.

[0017] The task is also solved by a computer program product which, when executed on a suitable computing unit, performs the aforementioned procedure.

[0018] 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 schematically shows a brake system according to the invention; Fig. 2 shows the braking system of the Fig. 1 with an illustration of a switching problem, Fig. 3 shows the braking system of the Fig. 1 with illustration of the method according to the invention;

[0019] In Fig. Figure 1 schematically illustrates an embodiment of a braking system according to the invention for a motor vehicle. By way of example, the braking system is designed to actuate four hydraulically actuated wheel brakes 8a-8d. By way of example, the wheel brakes 8a, 8b are assigned to the rear axle (rear) and the wheel brakes 8c, 8d to the front axle (front) of the vehicle.

[0020] The brake system comprises a first assembly or first subsystem 100, which is designed, for example, as a first electro-hydraulic brake control unit (HECU1) with a valve block HCU1 and a first electronic control device 101 (ECU1), and a second assembly or second subsystem 200, which is designed, for example, as a second electro-hydraulic brake control unit (HECU2) with a valve block HCU2 and a second electronic control device 201 (ECU2).

[0021] A pressure medium reservoir 4 with, for example, two chambers is arranged on the first assembly unit 100, wherein the first chamber 401 is assigned a first reservoir connection and the second chamber 402 is assigned a second reservoir connection. Other embodiments have three or more chambers.

[0022] The assembly unit 100 comprises a (first) electrically actuated pressure source 5 or pressure supply device 5 and a master brake cylinder 1, which can be actuated by means of a brake pedal 12.

[0023] The master brake cylinder 1 is, for example, a single-circuit design and has a piston 11 that defines a hydraulic pressure chamber 10. The pressure chamber 10 is connected to the hydraulic fluid reservoir 4 via radial bores (vent holes) formed in the piston 11 and a corresponding pressure equalization line 43. This hydraulic connection can be closed by a relative movement of the piston 11. The pressure chamber 10 accommodates a return spring that positions the piston 11 in a neutral position when the master brake cylinder 1 is not actuated. Thus, when the brake pedal 12 is not actuated, the pressure chamber 10 of the master brake cylinder 1 is connected to the hydraulic fluid reservoir 4 via the vent holes and the pressure equalization line 43. For example, the pressure chamber 10 is connected to a hydraulic equalization port 63 of the assembly 100, which is connected to a first chamber 401 of the hydraulic fluid reservoir 4. Furthermore, construction unit 100 includes a simulator 3 (also

[0024] (Called brake pedal feel simulator or travel simulator) for generating brake pedal feel for the driver, particularly in a by-wire operating mode. Simulator 3 is hydraulically coupled to the master brake cylinder 1 and essentially comprises, for example, a simulator chamber 301, a simulator return chamber 302, and a simulator piston 303 separating the two chambers 301 and 302. The simulator piston 303 is supported on the valve block of the assembly by an elastic element 304 (e.g., a simulator spring) arranged in the simulator return chamber 302. The simulator chamber 301 can be connected, for example, to the pressure chamber 10 of the master brake cylinder 1 by means of an electrically actuated simulator valve 28, which is advantageously normally closed. The simulator valve 28 serves to switch the simulator 3 on and off.

[0025] The electrically controlled pressure source 5 of the assembly 100 is designed as a hydraulic cylinder-piston arrangement (or a single-circuit electrohydraulic actuator (linear actuator)), whose piston 36 can be actuated by a schematically indicated electric motor 35 via an interposed rotary-translational transmission 39, in particular by moving it back and forth to build up and release pressure in a pressure chamber 37. The piston 36 defines the pressure chamber 37 of the pressure source 5. A rotor position sensor 44, also only schematically indicated, is provided for controlling the electric motor.

[0026] Pressure chamber 37 is connected, regardless of the actuation state of the piston 36, via a (suction) line 42 to the hydraulic compensating port 63 of the assembly 100, which is connected to the pressure medium reservoir 4 or its first chamber 401. A check valve 53, closing towards the pressure medium reservoir 4, is arranged in the line 42. Alternatively, pressure chamber 37 can be connected to a third chamber of the pressure medium reservoir 4.

[0027] In addition to the compensating port 63 and the pressure port 60, the assembly unit 100 does not include any other hydraulic ports.

[0028] The pressure source 5 and the master brake cylinder 1 are both connected to a system pressure line 38, which is connected to a pressure port 60 of the assembly 100. The assembly 100 comprises only one pressure port for transmitting brake pressure to the wheel brakes or for actuating the wheel brakes, namely the pressure port 60. The two pressure generators, master brake cylinder 1 and electrical pressure source 5, which are designed to generate brake pressure for actuating the wheel brakes, are connected to this single pressure port 60 of the assembly 100 via the system pressure line 38.

[0029] The master brake cylinder 1, or rather its pressure chamber 10, is connected to the system pressure line 38, and thus to the single pressure port 60 of the assembly 100, via an electrically actuated, preferably normally open, isolating valve 23. No other electrically actuated valve is arranged in the hydraulic connection between the master brake cylinder 1 and the pressure port 60 besides the isolating valve 23.

[0030] For example, the master brake cylinder 1 is connected to the isolating valve 23 and the simulator valve 28 by means of a hydraulic line 48.

[0031] Pressure source 5, or rather its pressure chamber 37, is connected to the system pressure line 38, and thus to the single pressure port 60 of the assembly 100, via an electrically actuated, normally closed (NC) switching valve 27. Pressure source 5 is therefore connected to the pressure port 60 in such a way that no hydraulic fluid can flow into this connection in the event of a failure of pressure source 5. For example, no other electrically actuated valve is arranged in the hydraulic connection between pressure source 5 and pressure port 60 besides the switching valve 27.

[0032] The second assembly 200 comprises a second electrically actuated pressure source 2 and at least one electrically actuated inlet valve 6a-6d per wheel brake, wherein the second electrically actuated pressure source 2 is hydraulically connected to the four inlet valves 6a-6d.

[0033] To transmit brake pressure for actuating the wheel brakes 8a-8d, the single pressure port 60 of the first assembly 100 is hydraulically connected to a pressure port 61 of the second assembly 200 via a hydraulic, pressure-resistant connecting element 80. Connection 80 represents the only hydraulic pressure connection, for example, the only hydraulic connection, between the first assembly 100 and the second assembly 200. This hydraulic connection is for transmitting brake pressure to actuate the wheel brakes 8a-8d. Connecting element 80 must therefore be pressure-resistant.

[0034] The pressure port 60, and thus the first pressure source 5 and the master brake cylinder 1, and the second pressure source 2 are connected on the pressure side to a brake supply line 13, to which the four inlet valves 6a-6d are connected. This allows all four wheel brakes 8a-8d to be selectively actuated, depending on the operating mode, by means of the first pressure source 5 and / or the second pressure source 2 and / or the master brake cylinder 1.

[0035] An electrically actuated circuit isolating valve 40 is arranged in the brake supply line 13, so that when the circuit isolating valve 40 is closed, the brake supply line 13 is divided into a first line section 13a, to which the inlet valves 6a, 6b and the wheel brakes 8a, 8b are connected, and a second line section 13b, to which the inlet valves 6c, 6d and the wheel brakes 8c, 8d are connected. The second pressure source 2 is hydraulically connected to the first line section 13a, and the pressure port 60, and thus the first pressure source 5 and the master brake cylinder 1, is hydraulically connected to the second line section 13b. When the circuit isolating valve 40 is closed, the brake system is therefore separated or divided into two hydraulic brake circuits I and II.In the first brake circuit I, the pressure source 2 (via the first line section 13a) is connected only to the wheel brakes 8a and 8b, and in the second brake circuit II, the pressure connection 60 or 61 (via the second line section 13b) is connected only to the wheel brakes 8c and 8d. The circuit isolating valve 40 is advantageously designed to be normally open.

[0036] The brake system comprises, for example, an inlet valve 6a-6d and an outlet valve 7a-7d for each hydraulically actuated wheel brake 8a-8d. These valves are hydraulically connected in pairs via center connections and each pair is connected to a hydraulic wheel connection 9a-9d of the second assembly 200, to which the corresponding wheel brake 8a-8d is connected. A check valve 70a-70d, opening towards the brake supply line 13, is connected in parallel to each inlet valve 6a-6d. The outlet connections of the outlet valves 7a-7d are connected via a common return line 14 to a hydraulic compensating connection 62, which is connected to the pressure medium reservoir 4 or its second chamber 402. The inlet ports of all inlet valves 6a-6d can be supplied with pressure via the brake supply line 13 (i.e., with the circuit separator valve 40 open), which is supplied by the first pressure source 5 or, e.g.In the event of failure of the first pressure source 5, pressure is provided by the second pressure source 2, or, for example, in the event of failure of both the first and second pressure sources 5, 2, by the master brake cylinder 1 (hydraulic fallback level).

[0037] The second electrically controlled pressure source 2 of the second assembly 200 is, for example, designed as a two-piston pump whose two pressure outlets are connected together (to pressure side 220 of pressure source 2) and whose two suction inlets are connected together (to suction side 221 of pressure source 2). The suction side 221 is connected to the return line 14 and thus to the compensating connection 62 or the pressure medium reservoir 4. The pressure side 220 is connected to the first line section 13a of the brake supply line 13.

[0038] The compensating port 62, and thus the suction side 221 of the second pressure source 2, is directly connected to the pressure medium reservoir 4 via a line or hose 90. This connection 90 does not carry pressure and can therefore have a large diameter. For example, line 90 is connected to the second chamber 402 of the pressure medium reservoir 4.

[0039] In addition to the pressure source 2 and the brake pressure modulation valves 6a-6d, 7a-7d, an electrically actuated, preferably normally open, isolating valve or isolation valve 26 is arranged in the second assembly 200. The isolation valve 26 is hydraulically arranged between the pressure port 61 of the second assembly 200 and the second line section 13b of the brake supply line 13. Thus, the pressure port 60 of the first assembly 100, or the system pressure line 38 of the first assembly 100, is separably connected to the second line section 13b, or the brake supply line 13, via the isolation valve 26.

[0040] The brake system includes, for example, a pressure sensor 19 in brake circuit II (line section 13b), which is thus assigned to the second pressure source 2. However, pressure sensor 19 can also be located in brake circuit I, or a second pressure sensor can be provided so that each of the two brake circuits I and II can be directly monitored by means of a pressure sensor.

[0041] For example, the brake system for leakage monitoring includes a level measuring device 50 for determining a pressure medium level in the pressure medium reservoir 4.

[0042] For example, components 5, 53, 27, 1, 23, 3, 28 and line sections 38, 42, 43, 48 are arranged in the first valve block HCU1 and components 2, 6a-6d, 70a-70d, 7a-7d, 40, 26, 19 and line sections 13a, 13b, 14 (and the line sections between the inlet and outlet valves on the one hand and the wheel connections on the other) are arranged in the second valve block HCU2.

[0043] Each valve block HCU1, HCU2 is associated with an electronic control unit 101, 201 (ECU1, ECU2). Each electronic control unit 101, 201 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. Advantageously, the valve block and electronic control unit are designed as an electrohydraulic unit (HECU) in a known manner.

[0044] For the electrical connection, linking and supply of the individual electrical or electrically actuated, controllable, evaluable or similar components of the brake system, a first electrical partition A and a second electrical partition B are provided, which are electrically independent of each other.

[0045] In the figures, those electrical components which are assigned to or belong to the first electrical partition A are marked by an arrow with A, while those electrical components which are assigned to or belong to the second electrical partition B are marked by an arrow with B.

[0046] The electronic control device 101 is assigned to, or belongs to, the first electrical partition A, while the second electronic control device 201 is assigned to, or belongs to, the second electrical partition B. Accordingly, the electronic control device 101 and the second electronic control device 201 are electrically independent.

[0047] To supply the braking system with electrical energy, a first electrical energy source 103, e.g., a vehicle electrical system, and a second electrical energy source 203, e.g., a vehicle electrical system, independent of the first energy source, are provided. The first electrical energy source 103 supplies the first electrical partition A with energy, and the second electrical energy source 203 supplies the second electrical partition B.

[0048] The first electronic control device 101 controls the first pressure source 5.

[0049] Accordingly, the first pressure source 5 is assigned to or belongs to the first electrical partition A. For example, the first pressure source 5 is supplied with energy (from the first electrical energy source 103) via the first electronic control device 101.

[0050] The second electronic control device 201 controls the second pressure source 2. Accordingly, the second pressure source 2 is assigned to or belongs to the second electrical partition B. For example, the second pressure source 2 is supplied with energy (from the second electrical energy source 203) via the second electronic control device 201.

[0051] For example, the first pressure source 5 can be controlled exclusively by the first electronic control device 101 and the second pressure source 2 can be controlled exclusively by the second electronic control device 201.

[0052] The remaining components of the brake system are advantageously assigned to either the first electronic control unit 101 (partition A) or the second electronic control unit 201 (partition B). That is, they are controlled or actuated by this control unit and / or supplied with electrical energy and / or are connected to this control unit via signals and / or are evaluated by this control unit. To avoid further redundancies, a component is advantageously controllable or actuated, supplied with electrical energy, connected to, or evaluated by only or exclusively by one of the two electronic control units 101, 201, but not by the other electronic control unit.

[0053] The first electronic control device 101 controls the electrically actuated components of the first assembly 100 and the second electronic control device 201 controls the electrically actuated components of the second assembly 200.

[0054] Accordingly, the inlet and outlet valves 6a-6d, 7a-7d are assigned to the second electrical partition B and are controlled by the second electronic control device 201. Likewise, the circuit separator valve 40 is assigned to the second electrical partition B and is controlled by the second electronic control device 201.

[0055] The isolation valve 26 for hydraulic separation of the first assembly unit 100 (pressure connection 60) and brake supply line 13 is also assigned to the second electrical partition B and is controlled by the second electronic control device 201.

[0056] Pressure sensor 19 is also assigned to the second electrical partition B. Its signals are fed to the second electronic control device 201, which evaluates and processes them.

[0057] The switching valve 27, the separating valve 23 and the simulator valve 28, on the other hand, are assigned to the first electrical partition A and are controlled by the first electronic control device 101.

[0058] Furthermore, the signals from the level measuring device 50 are fed to the first electronic control device 101 and evaluated and processed by it.

[0059] Preferably, the braking system includes electrically operated parking brakes on the rear wheels. These are advantageously controlled and actuated by the first electronic control device 101 (identified by A at the wheel brakes 8a, 8b in the Fig. 1) It is also possible to split the control between both control devices.

[0060] The exemplary braking system with a first assembly 100 enables highly automated driving by including two electrically controlled pressure sources 5, 2, and also provides a mechanical-hydraulic fallback level (by means of a master brake cylinder 1) in the event of a total electrical failure. The first assembly 100 advantageously comprises the primary of the two electrically controlled pressure sources 5, a master brake cylinder 1 which the driver can actuate via the brake pedal 12, and a pedal feel simulator 3.

[0061] The first assembly 100 comprises only a single pressure port 60. This pressure port 60 can also be atmospherically connected, and it is always atmospherically connected when the first assembly 100 has electrically failed and the brake pedal 12 is not actuated.

[0062] For this purpose, the master brake cylinder 1 is preferably provided with a vent hole and connected to the pressure port 60 via an electrically actuated isolating valve 23, particularly preferably normally open. Furthermore, the master brake cylinder 1 is connected to the pedal feel simulator 3 via an electrically actuated simulator valve 28, particularly preferably normally closed. The primary pressure source 5 is connected to the pressure port 60, preferably such that no pressure medium flows into this connection after a failure of the primary pressure source 5. Preferably, an electrically actuated switching valve 27, particularly preferably normally closed, is arranged in this connection.

[0063] In normal operation, when the brake pedal 12 is pressed or when the autopilot requests braking, the isolating valve 23 closes, the simulator valve 28 opens, and the switching valve 27 opens. The isolation valve 26 is also open. The pedal feel is generated by the pedal feel simulator 3. The pressure build-up for actuating the wheel brakes 8a-8d is achieved by the two pressure sources 5 and 2, either individually or together. Any wheel-specific pressure modulation is handled by the second unit 200.

[0064] If the second unit 200 fails, the first unit 100 builds up the wheel brake pressure in the same way, and it can centrally modulate the wheel brake pressure for all wheel brakes 8a-8d together.

[0065] After the failure of the first unit 100, braking is performed differently by the autopilot and by the driver: If the first unit 100 fails and the autopilot transmits a braking request, the second unit 200 takes over the build-up and modulation of the wheel brake pressure, as would be the case in a braking system without a mechanical-hydraulic fallback level.

[0066] Now consider the case where the first unit 100 fails and the pedal 12 is depressed. After the failure of the first unit 100, the master brake cylinder 1 is connected to the pressure port 60 of the first unit 100 via the normally open isolating valve 23. When the pedal is depressed, the second unit 200 can remain passive and transmit the pressure generated by the driver to the wheel brakes 8a-8d. This operating mode is referred to as a hydraulic fallback system, since the braking force is generated purely mechanically by the driver's muscle power via the brake pressure. Alternatively, the driver can also be assisted by the second pressure source 2. For this purpose, a half-by-wire mode can be activated by closing the circuit isolating valve 40.The master brake cylinder is then only connected to the wheel brakes 8c, 8d of the front axle, while the brake pressure in the wheel brakes 8a, 8b of the rear axle is provided by the second pressure supply device 2.

[0067] To enable even greater functionality in the event of a failure of the first unit 100, a second unit 200 is optionally added. For example, a (third) pressure sensor can be installed in the pressure connection between the two units 100 and 200 to detect the driver's request (preferably upstream of the isolation valve 26 in the second unit 200). Then, when pressure builds up in the master brake cylinder 1, the switching valve 26 can be closed, and the second pressure source 2 builds up pressure in all wheel brakes 8a-8d. In such a booster mode, the maximum possible brake pressure, and thus the full braking force, is available at all wheel brakes.

[0068] However, if the first assembly unit or part of it fails, it is often not possible to open the simulator valve 28. The main cylinder 1 then operates against the closed isolation valve 26 and thus in a hydraulically rigid space.

[0069] The brake pedal is therefore essentially immobile, making it very difficult for the driver to modulate the braking force.

[0070] It may therefore be provided that in the event of failure of the first assembly 100, a part thereof or other faults, such as a failure of the communication link between the assemblies, a switch to a half-by-wire mode is made as soon as braking occurs via the brake pedal 12.

[0071] Since most braking operations are performed with a moderate pressure level and pressure gradient, such an operating mode with only two electrically enhanced wheel brakes is usually sufficient, but which has an improved pedal feel due to the direct connection of the brake pedal 12 via its master brake cylinder 1 with at least one wheel brake 8.

[0072] When a pressure demand or pedal activation exceeds a certain gradient (e.g., 200 bar / s) or a certain threshold (e.g., 15 bar), the system switches from half-by-wire to boost mode. Individual wheel control at the front axle also triggers this switch. The system can then revert to half-by-wire when the pressure demand falls below the starting threshold and no individual wheel control is active at the front axle. Optionally, the system can also revert to half-by-wire when the pedal is fully released.

[0073] In the half-by-wire system, the maximum pressure at the rear axle is limited to 30 bar. This ensures that the circuit isolation valve 40 can always be opened to switch to boost mode.

[0074] When transitioning from half-by-wire to amplifier mode, the isolation valve 26 must be securely closed.

[0075] As in Fig. As shown in Figure 2, a volume flow through the isolation valve 26 from the first subsystem to the second subsystem could prevent the isolation valve 26 from closing.

[0076] Therefore, the inlet valves 6 of the front axle are temporarily closed and the isolation valve 26 is energized. Simultaneously, according to the invention, the second hydraulic pressure supply device is activated to pump brake fluid in order to provide a pressure that at least corresponds to the pressure of the first subsystem. In this Fig.In the situation shown in Figure 3, the isolation valve 26 is not overflowed with brake fluid, or at least slightly overflowed in the direction of the first subsystem, and can therefore close. Subsequently, the inlet valves of the front axle are reopened and the circuit isolation valve 40 is opened. The valve state of the booster mode is now present.

Claims

[1] comprising a method for controlling a hydraulic motor vehicle braking system - a first hydraulic subsystem (100) comprising a hydraulically coupled brake pedal (12) for pressure build-up in at least one first wheel brake (8a, 8b) and / or a first electrical pressure supply device (5) for driver-independent pressure build-up at the at least one first wheel brake (8a, 8b) and - a second hydraulic subsystem (200) comprising a second electrical pressure supply device (2) for driver-independent pressure build-up at the at least one first wheel brake (8a, 8b), - an isolation valve (26) between the first hydraulic subsystem (100) and the second hydraulic subsystem (200), - wherein in a first operating mode the pressure at the at least one first wheel brake (8a, 8b) is built up by the first hydraulic subsystem (100). characterized by, that in a second operating mode the pressure in at least one first wheel brake (8a, 8b) is built up by the second hydraulic subsystem (200), - wherein to switch from the first operating mode to the second operating mode the isolation valve (26) is closed, wherein to assist the closing process the second electrical pressure supply device (2) is activated to provide a pressure greater than or equal to the pressure of the first hydraulic subsystem (100), and / or hydraulic valves (6a, 6b, 6c, 6d, 40) in the second subsystem (200) are closed so that no brake fluid flows from the first subsystem (100) via the isolation valve (26) into the second subsystem (200). [2] Method according to claim 1, characterized by , that the first hydraulic subsystem (100) and the second hydraulic subsystem (200) are formed in separate housing blocks. [3] Method according to claim 1 or 2, characterized by , that the isolation valve (26) is designed as a normally open valve. [4] Method according to claim 3, characterized by , that the isolation valve (26) is designed such that a hydraulic pressure on the side of the first hydraulic subsystem (100) relative to the side of the second hydraulic subsystem (200) and / or a volume flow from the side of the first hydraulic subsystem (100) to the side of the second hydraulic subsystem (200) exerts a force on a valve plunger of the isolation valve (26) in an opening direction. [5] Method according to any one of the preceding claims, characterized by, that in the event of a failure of the first electrical pressure supply device (5) the braking system operates in the first operating mode up to a predetermined limit pressure and / or limit pressure gradient, wherein the pressure in the at least one wheel brake (8a, 8b) is supplied by the hydraulically coupled brake pedal (12), and upon reaching the limit pressure and / or limit pressure gradient, the system switches from the first operating mode to the second operating mode. [6] Method according to any one of the preceding claims, characterized by , that to close the isolation valve (26) simultaneously with the activation of the second electrical pressure supply device (2) the isolation valve (26) is energized with a closing current. [7] Method according to any one of the preceding claims, characterized by, that in order to close the isolation valve (26) simultaneously with the activation of the second electrical pressure supply device (2) the inlet valves (6a, 6b, 6c, 6d) are or become closed. [8] Method according to claim 7, characterized by , that the valve flows of the inlet valves (6a, 6b, 6c, 6d) are set to a flow value corresponding to a pressure value between 30 bar above a main cylinder pressure and 150 bar. [9] Method according to claim 8, characterized by , that the current value is gradually approached with a falling ramp starting from the switching current. [10] Method according to any one of the preceding claims, characterized by, that in the second operating mode normal pressure control is carried out as soon as the isolation valve (26) is assumed to be closed, wherein the isolation valve (26) is assumed to be closed when a predetermined time has elapsed after the closing current has been applied or as soon as a pressure differential across the isolation valve (26) is sensed which is higher on the side of the second hydraulic subsystem (200). [11] Method according to any one of the preceding claims, characterized by , that in the second operating mode a pressure is built up which is based on the main cylinder pressure, whereby the main cylinder pressure is smoothed and / or filtered and used as an input variable for a target pressure. [12] Method according to any one of the preceding claims, characterized by , that in the first operating mode the pressure on at least one second wheel brake (8a, 8b) is built up by the second hydraulic subsystem. [13] Hydraulic brake system for motor vehicles comprising a control device which is configured to perform a method according to any one of claims 1 to 12. [14] Computer program product which, when executed on a corresponding computing unit, performs a method according to any one of claims 1 to 11.

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