Fallback level with soft pedal

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 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), wherein in a fault-free case the pressure at the at least one first wheel brake (8a, 8b) is built up by the first electrical pressure supply device (5).In order to provide both good pedal feel and high deceleration, in the event of a fault in the first subsystem (100), the system switches to a half-by-wire mode or a hydraulic fallback mode, whereby the pressure in the at least one first wheel brake (8a, 8b) is built up without electrical amplification by the muscle power of a driver via the hydraulically coupled brake pedal (12) as long as a switching condition is not met, and when the switching condition is met, the system switches to an amplification mode in which the hydraulically coupled brake pedal (12) is disconnected from the at least one first wheel brake (8a, 8b) and the pressure in the at least one first wheel brake (8a, 8b) is built up by the second electrical pressure supply device (2).

Description

[0001] The invention relates to a method for controlling a hydraulic motor vehicle brake system having a first hydraulic subsystem comprising a hydraulically coupled brake pedal for pressure build-up in at least one first wheel brake and 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, wherein in a fault-free case the pressure at the at least one wheel brake is built up by the first electrical pressure supply device.

[0002] DE 10 2022 202 019 A1 discloses a method for controlling a brake-by-wire braking system, which involves starting the braking system when the brake pedal is depressed. In order to switch the valves required to activate the brake-by-wire mode, the driver is encouraged to release the brake pedal by changing the pedal characteristic curve.

[0003] Modern automotive braking systems must be highly redundant so that there is a very high probability that braking force will always be available to decelerate the vehicle. For this purpose, two electrical pressure supply devices, such as pumps or linear actuators, are provided. If one of these pressure supply devices fails, another pressure source is still available, eliminating the need to immediately rely on the driver as the sole fallback. In the event of failure and / or errors in individual functions or components, redundant braking systems typically switch from a normal operating mode to corresponding failure modes or fallback modes. However, these are generally associated with minor or major restrictions depending on the fault.

[0004] Such a braking system is known from DE 10 2013 223 861 A1. It comprises a first subsystem with a hydraulically coupled brake pedal and an electric pressure supply device, and a second subsystem with a second pressure supply device. In this subsystem, if the first pressure supply device fails, the second pressure supply device is used directly to build up pressure.

[0005] It is therefore an object of the invention to provide a method which minimizes the restrictions to such an extent that the driver can drive the motor vehicle safely and comfortably even after an error has occurred.

[0006] The object is achieved according to the invention by a method according to claim 1, wherein in the event of a fault in the first subsystem, a switch is made to a half-by-wire mode or a hydraulic fallback mode, wherein the pressure in the at least one wheel brake is built up without electrical boost by the muscle power of a driver via the hydraulically coupled brake pedal as long as a switching condition is not met and when the switching condition is met, a switch is made to a boost mode in which the hydraulically coupled brake pedal is separated from the at least one wheel brake and the pressure in the at least one wheel brake is built up by the second electrical pressure supply device.

[0007] This combines the advantages of purely mechanical driver braking with electrically generated and thus amplified braking. Since the majority of all braking applications can be easily handled by purely mechanical pressure generation, booster braking is unnecessary in this case. The connection between the driver and the wheel brakes via the brake pedal results in good pedal feel, allowing the driver to precisely control the braking force. Only in special braking situations does the system switch to electrically generated braking force in booster mode, in order to support the driver beyond his or her capabilities.

[0008] In a preferred embodiment of the invention, in half-by-wire mode, the pressure in at least one second wheel brake is built up by the second electrical pressure supply device. This means that the wheel brakes are divided between the driver's muscle power and the second pressure supply device. Thus, the connection to the first wheel brakes provides the driver with a pedal feel that allows for precise metering of the braking force, while simultaneously providing increased braking force to the second wheel brakes.

[0009] In the hydraulic fallback mode, the pressure in the at least one second wheel brake is built up without electrical boost by the driver's muscle power via the hydraulically coupled brake pedal. Thus, the driver is connected to the first and second wheel brakes. The second pressure supply device is therefore not yet required in this mode.

[0010] In a further preferred embodiment of the invention, the brake pedal is isolated by closing an isolation valve of the second subsystem. This allows the isolation to occur, particularly in the event of a failure of the first subsystem, so that the second subsystem can build up pressure in the wheel brake without brake fluid flowing toward the brake pedal or a master cylinder connected to the brake pedal.

[0011] In a particularly preferred embodiment of the invention, in order to close the isolation valve, the inlet valves connected to it are closed so that no volume flow flows through the isolation valve. A volume flow can prevent the closing process, which means there is a risk that the valve has not been closed properly. The inlet valves are only closed briefly for the closing process and can then be opened again so that pressure can be built up in the wheel brakes. If the system is in half-by-wire mode, only the two connected inlet valves, in particular the inlet valves of the front axle, are closed. Starting from the hydraulic fallback level, all inlet valves are closed. The closing of the isolation valve can thus be ensured.

[0012] In a further preferred embodiment of the invention, the switching condition comprises a brake pedal pressure greater than a pressure threshold. The system therefore switches to boost mode as soon as the driver presses the brake pedal particularly hard and therefore requests high braking pressure. High braking pressures can only be achieved purely mechanically using muscle power by a few experienced drivers. The pressure threshold is selected so that it can still be set easily by all drivers. By switching, the higher braking pressures in boost mode are generated by the electrical pressure supply device. The pressure threshold can, for example, be between 10 and 30 bar, in particular 15 bar.

[0013] A further switching condition can be a brake pedal pressure gradient greater than a pressure gradient threshold. Not only are high brake pressures difficult to achieve purely mechanically, but so is a rapid brake pressure increase. Accordingly, in such a case, the system can also switch to booster mode. A value between 200 and 400 bar / s, particularly 300 bar / s, can be specified as the pressure gradient threshold.

[0014] Even when ABS and / or stability system intervention is present, it is possible to switch to booster mode. In ABS mode, the volume diverted to reduce pressure can be returned without the brake pedal slipping. In stability interventions, such as those by an ESP system, pressure can be built up independently of the driver. If the system is in half-by-wire mode, switching can be carried out on the first wheel brakes, for example on the front axle, during ABS / ESP interventions, i.e. for wheel-individual control. At the second wheel brakes, for example on the rear axle, no switching is necessary, since wheel-individual control is already possible there.

[0015] In a further preferred embodiment of the invention, the system switches back to the half-by-wire mode or the hydraulic fallback mode when the brake pedal is fully released, or when all wheel pressure requirements are equal, particularly for a predetermined period of time, and the driver's command is less than a threshold value. The threshold value can preferably be set to 10 bar. This provides the driver with better pedal feel.

[0016] In a further preferred embodiment of the invention, in the booster mode, the second pressure supply device builds up a pressure in the at least one first wheel brake that is greater than the brake pedal pressure. Thus, there is a boost factor between these two values, and the driver does not have to manually build up the entire required brake pressure.

[0017] In a further preferred embodiment of the invention, in booster mode, pressure is built up at at least two second wheel brakes and two first wheel brakes by means of the second pressure supply device. Thus, maximum deceleration is available.

[0018] In the half-by-wire mode, the pressure is built up at at least two second wheel brakes by means of the second pressure supply device and at two first wheel brakes without electrical amplification by the driver's muscle power via the hydraulically coupled brake pedal.

[0019] In the hydraulic fallback mode, the pressure is finally built up on at least two second wheel brakes and two first wheel brakes without electrical amplification by the driver's muscle power via the hydraulically coupled brake pedal.

[0020] In a further preferred embodiment of the invention, the first wheel brakes are assigned to a first vehicle axle, in particular a front axle, and the second wheel brakes are assigned to a second vehicle axle, in particular a rear axle. Such a black-and-white division is particularly advantageous in combination with regenerative brakes on a vehicle axle.

[0021] In a further preferred embodiment of the invention, pressure reduction is implemented in booster mode by means of outlet valves of the wheel brakes. These can discharge a volume flow into a brake fluid reservoir by selectively opening them briefly, so that the brake pressure in the respective wheel brake drops to a desired value.

[0022] In a further preferred embodiment of the invention, the first subsystem and the second subsystem each comprise their own electrical control unit. This control unit is, in particular, exclusively responsible for controlling the respective electrohydraulic components of the respective subsystem.

[0023] In a further preferred embodiment of the invention, in half-by-wire mode, the first and second wheel brakes are fluidly separated from each other by closing a circuit isolation valve. This transforms the braking system into a dual-circuit system.

[0024] In a further preferred embodiment of the invention, in the half-by-wire mode, the pressure in the second wheel brakes is limited to a threshold value, in particular between 2 and 50 bar, preferably 30 bar, wherein the threshold value is selected such that the circuit isolation valve can reliably open at pressures less than or equal to the threshold value.

[0025] The object is further achieved by a hydraulic motor vehicle brake system according to claim 14, comprising a first hydraulic subsystem comprising a hydraulically coupled brake pedal for pressure build-up in at least one first wheel brake and 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, wherein a control unit is configured to build up pressure at the at least one wheel brake by means of the first electrical pressure supply device in a fault-free case, wherein the control unit switches to a half-by-wire mode or a hydraulic fallback mode when a fault occurs in the first subsystem,in which the pressure in the at least one wheel brake is built up without electrical amplification by the muscle power of a driver via the hydraulically coupled brake pedal as long as a switching condition is not met and, when the switching condition is met, a boost mode is activated in which the hydraulically coupled brake pedal is separated from the at least one wheel brake and the pressure in the at least one wheel brake is built up by the second electrical pressure supply device.

[0026] According to a further aspect of the invention, a hydraulic brake system is provided with a first structural unit comprising a master brake cylinder coupled to a brake pedal with a pedal travel simulator and a pressure source designed as a linear actuator, wherein a brake fluid reservoir has three chambers and the master brake cylinder is connected to a first chamber via a sniffer hole, the linear actuator is connected to a second chamber with a suction opening and a second pressure source of a second structural unit is connected with its suction side to a third chamber.

[0027] Further features, advantages, and possible applications of the invention will become apparent from the following description of exemplary embodiments and the drawings. All described and / or illustrated features, both individually and in any combination, are part of the subject matter of the invention, regardless of their summary in the claims or their references. Fig. 1 shows schematically a braking system according to the invention;

[0028] In Fig. Figure 1 schematically shows an embodiment of a braking system according to the invention for a motor vehicle. The braking system is designed to actuate four hydraulically actuated wheel brakes 8a-8d. The wheel brakes 8a, 8b are assigned to the rear axle and the wheel brakes 8c, 8d to the front axle of the vehicle.

[0029] The brake system comprises a first structural unit 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 structural unit 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).

[0030] A pressure medium reservoir 4 with, for example, two chambers is arranged on the first structural unit 100, with a first reservoir connection being assigned to the first chamber 401 and a second reservoir connection being assigned to the second chamber 402. Other embodiments have three or more chambers.

[0031] 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.

[0032] Master brake cylinder 1 is, for example, single-circuit and has a piston 11 that defines a hydraulic pressure chamber 10. The pressure chamber 10 is connected to the pressure fluid reservoir 4 via radial bores (sniffing holes) formed in the piston 11 and a corresponding pressure equalization line 43, whereby this hydraulic connection can be shut off by a relative movement of the piston 11. The pressure chamber 10 accommodates a return spring that positions the piston 11 in an initial 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 pressure fluid reservoir 4 via the sniffing holes and the pressure equalization line 43. For example, the pressure chamber 10 is connected to a hydraulic equalization connection 63 of the assembly 100, which is connected to a first chamber 401 of the pressure fluid reservoir 4.

[0033] Furthermore, assembly 100 comprises a simulator 3 (also called a brake pedal feel simulator or travel simulator) for generating a 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 has, for example, a simulator chamber 301, a simulator rear chamber 302, and a simulator piston 303 separating the two chambers 301, 302. 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 rear chamber 302. The simulator chamber 301 can be connected to the pressure chamber 10 of the master brake cylinder 1, for example, by means of an electrically actuated simulator valve 28, which is advantageously designed to be closed when de-energized. Simulator valve 28 serves to switch the simulator 3 on and off.

[0034] The electrically controllable pressure source 5 of the assembly 100 is designed as a hydraulic cylinder-piston arrangement (or a single-circuit electro-hydraulic actuator (linear actuator)), the piston 36 of which can be actuated by a schematically indicated electric motor 35 with the interposition of a rotation-translation gear 39, also shown schematically, in particular can be moved forwards and backwards in order to build up and reduce pressure in a pressure chamber 37. The piston 36 delimits the pressure chamber 37 of the pressure source 5. To control the electric motor, a rotor position sensor 44, which detects the rotor position of the electric motor 35 and is only indicated schematically, is provided.

[0035] Pressure chamber 37 is connected, regardless of the actuation state of piston 36, via a (suction) line 42 to the hydraulic equalization connection 63 of assembly 100, which is connected to the pressure fluid reservoir 4 or its first chamber 401. A check valve 53 closing in the direction of the pressure fluid reservoir 4 is arranged in the line 42. Alternatively, the pressure chamber 37 can be connected to a third chamber of the pressure fluid reservoir 4.

[0036] Apart from the compensation connection 63 and the pressure connection 60, the assembly 100 does not include any further hydraulic connections.

[0037] 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 connection 60 of the assembly 100. The assembly 100 comprises only one pressure connection for transmitting brake pressure to the wheel brakes or for actuating the wheel brakes, namely the pressure connection 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 connection 60 of the assembly 100 via the system pressure line 38.

[0038] Master brake cylinder 1 or 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. In the hydraulic connection between master brake cylinder 1 and pressure port 60, no further electrically actuated valve is arranged besides the isolating valve 23.

[0039] For example, master brake cylinder 1 is connected to the isolation valve 23 and the simulator valve 28 via a hydraulic line 48.

[0040] Pressure source 5 or its pressure chamber 37 is connected to the system pressure line 38, and thus to the single pressure connection 60 of the assembly 100, via an electrically actuated, normally closed connection valve 27. Thus, pressure source 5 is connected to the pressure connection 60 in such a way that no pressure medium can flow into this connection in the event of a failure of the pressure source 5. In the hydraulic connection between the pressure source 5 and the pressure connection 60, for example, no further electrically actuated valve is arranged besides the connection valve 27.

[0041] The second structural unit 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.

[0042] To transmit brake pressure to actuate the wheel brakes 8a-8d, the single pressure connection 60 of the first structural unit 100 is hydraulically connected to a pressure connection 61 of the second structural unit 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 structural unit 100 and the second structural unit 200. This is a hydraulic connection for transmitting brake pressure to actuate the wheel brakes 8a-8d. Connecting element 80 must therefore be pressure-resistant.

[0043] The pressure connection 60, and thus the first pressure source 5 as well as 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. Thus, all four wheel brakes 8a-8d can be actuated selectively, 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.

[0044] An electrically actuated circuit isolation valve 40 is arranged in the brake supply line 13, so that when the circuit isolation valve 40 is closed, the brake supply line 13 is separated 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 connection 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 isolation valve 40 is closed, the brake system is thus separated or divided into two hydraulic brake circuits I and II.In the first brake circuit I, pressure source 2 is connected (via the first line section 13a) only to the wheel brakes 8a and 8b, and in the second brake circuit II, pressure connection 60 or 61 is connected (via the second line section 13b) only to the wheel brakes 8c and 8d. The circuit isolation valve 40 is advantageously designed to be open when de-energized.

[0045] The braking system comprises, for example, an inlet valve 6a-6d and an outlet valve 7a-7d for each hydraulically actuated wheel brake 8a-8d, which are hydraulically interconnected in pairs via central connections and each connected to a hydraulic wheel connection 9a-9d of the second structural unit 200, to which the corresponding wheel brake 8a-8d is connected. A check valve 70a-70d opening toward the brake supply line 13 is connected in parallel to each of the inlet valves 6a-6d. The output connections of the outlet valves 7a-7d are connected via a common return line 14 to a hydraulic equalization connection 62, which is connected to the pressure fluid reservoir 4 or its second chamber 402. The input connections of all inlet valves 6a-6d can be supplied with a pressure by means of the brake supply line 13 (i.e. with the circuit isolation valve 40 open) which is supplied by the first pressure source 5 or, for example,in case of failure of the first pressure source 5, from the second pressure source 2, or, e.g. in case of failure of the first and second pressure sources 5, 2, from the master brake cylinder 1 (hydraulic fallback level).

[0046] The second electrically controllable pressure source 2 of the second structural unit 200 is designed, for example, as a two-piston pump whose two pressure outputs are interconnected (to the pressure side 220 of the pressure source 2) and whose two suction inlets are interconnected (to the suction side 221 of the pressure source 2). The suction side 221 is connected to the return line 14 and thus to the equalization connection 62 or the pressure fluid reservoir 4. The pressure side 220 is connected to the first line section 13a of the brake supply line 13.

[0047] The equalization connection 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 carries no pressure and can therefore have a large diameter. Line 90 is connected, for example, to the second chamber 402 of the pressure medium reservoir 4.

[0048] In addition to the pressure source 2 and the brake pressure modulation valves 6a-6d, 7a-7d, an electrically actuated, advantageously normally open, isolating valve or isolation valve 26 is arranged in the second structural unit 200, for example. The isolating valve 26 is hydraulically arranged between the pressure connection 61 of the second structural unit 200 and the second line section 13b of the brake supply line 13. Thus, the pressure connection 60 of the first structural unit 100 or the system pressure line 38 of the first structural unit 100 is detachably connected to the second line section 13b or the brake supply line 13 via the isolating valve 26.

[0049] The braking system comprises, 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 arranged 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.

[0050] For example, the brake system for leakage monitoring comprises a level measuring device 50 for determining a pressure medium level in the pressure medium reservoir 4.

[0051] For example, the components 5, 53, 27, 1, 23, 3, 28 and the line sections 38, 42, 43, 48 are arranged in the first valve block HCU1 and the components 2, 6a-6d, 70a-70d, 7a-7d, 40, 26, 19 and the 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 hand) are arranged in the second valve block HCU2.

[0052] Each valve block HCU1, HCU2 is assigned an electronic control unit 101, 201 (ECU1, ECU2). Each electronic control unit 101, 201 comprises electrical and / or electronic elements (e.g., microcontrollers, power units, valve drivers, other electronic components, etc.) for controlling the electrically actuated components of the associated valve block and, if applicable, the associated sensors. The valve block and electronic control unit are advantageously designed as an electrohydraulic unit (HECU).

[0053] For the electrical connection, connection and supply of the individual electrical or electrically actuated, controllable, evaluable or similar components of the braking system, a first electrical partition A and a second electrical partition B are provided, which are electrically independent of each other.

[0054] In the figures, those electrical components which are assigned to or belong to the first electrical partition A are marked with an arrow A, while those electrical components which are assigned to or belong to the second electrical partition B are marked with an arrow B.

[0055] 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.

[0056] To supply the braking system with electrical energy, a first electrical energy source 103, e.g., an on-board electrical system, and a second electrical energy source 203, e.g., an on-board 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.

[0057] The first electronic control device 101 controls the first pressure source 5. Accordingly, the first pressure source 5 is assigned or associated with 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.

[0058] The second electronic control device 201 controls the second pressure source 2. Accordingly, the second pressure source 2 is assigned or associated with 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.

[0059] For example, the first pressure source 5 can be or is controlled exclusively by the first electronic control device 101 and the second pressure source 2 can be or is controlled exclusively by the second electronic control device 201.

[0060] The remaining components of the braking system are advantageously assigned either to the first electronic control device 101 (partition A) or to the second electronic control device 201 (partition B). This means that they are controlled or actuated by this control device and / or supplied with electrical energy and / or are connected to this control device on the signal side and / or are evaluated by this control device. To avoid further redundancies, a component can advantageously be controlled or actuated or supplied with electrical energy or connected or evaluated on the signal side only by one of the two electronic control devices 101, 201, but not by the other electronic control device.

[0061] 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.

[0062] Accordingly, the intake and exhaust 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 isolation valve 40 is assigned to the second electrical partition B and is controlled by the second electronic control device 201.

[0063] The isolation valve 26 for the hydraulic separation of the first structural unit 100 (pressure connection 60) and the brake supply line 13 is also assigned to the second electrical partition B and is controlled by the second electronic control device 201.

[0064] Pressure sensor 19 is also assigned to the second electrical partition B. Its signals are fed to the second electronic control device 201 and evaluated and processed by it.

[0065] The connection valve 27, the isolation valve 23 and the simulator valve 28, however, are assigned to the first electrical partition A and are controlled by the first electronic control device 101.

[0066] Furthermore, the signals of the level measuring device 50 are fed to the first electronic control device 101 and evaluated and processed by it.

[0067] The braking system preferably comprises electrically actuated parking brakes on the rear wheels. These are advantageously controlled and actuated by the first electronic control device 101 (identified by A on the wheel brakes 8a, 8b in Fig. 1). It is also possible to divide the control between both control devices.

[0068] The exemplary braking system with a first structural unit 100 enables highly automated driving by containing two electrically controllable pressure sources 5, 2, and also provides a mechanical-hydraulic fallback level (via master brake cylinder 1) in the event of a total electrical failure. The first structural unit 100 advantageously comprises the primary of the two electrically controllable pressure sources 5, a master brake cylinder 1, which the driver can actuate via the brake pedal 12, and a pedal feel simulator 3.

[0069] The first assembly 100 comprises only a single pressure connection 60. This pressure connection 60 can be connected to the atmosphere at the same time, and it is always connected to the atmosphere when the first assembly 100 has failed electrically and the brake pedal 12 is not actuated.

[0070] For this purpose, the master brake cylinder 1 is preferably provided with a sniffer hole and connected to the pressure port 60 via an electrically operated isolating valve 23, particularly preferably open when de-energized. Furthermore, the master brake cylinder 1 is connected to the pedal feel simulator 3 via an electrically operated simulator valve 28, particularly preferably closed when de-energized. The primary pressure source 5 is connected to the pressure port 60, preferably in such a way that no pressure medium flows into this connection after the failure of the primary pressure source 5. An electrically operated connection valve 27, particularly preferably closed when de-energized, is preferably arranged in this connection.

[0071] During normal operation, when the brake pedal 12 is actuated or when an autopilot requests braking, the isolation valve 23 is closed, the simulator valve 28 is opened, and the activation valve 27 is opened. The pedal feel is generated by the pedal feel simulator 3. The pressure buildup for actuating the wheel brakes 8a-8d occurs individually or jointly through the two pressure sources 5 and 2. Any wheel-specific pressure modulation is handled by the second unit 200.

[0072] If the second assembly 200 fails, the first assembly 100 builds up the wheel brake pressure in the same way and can centrally modulate the wheel brake pressure for all wheel brakes 8a-8d together.

[0073] After failure of the first unit 100, braking is carried out 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.

[0074] Now consider the case where the first structural unit 100 fails and the pedal 12 is actuated. After the failure of the first structural unit 100, the master brake cylinder 1 is connected to the pressure connection 60 of the first structural unit 100 via the normally open isolating valve 23. When the pedal is actuated, the second structural unit 200 can remain passive and transmit the pressure generated by the driver to the wheel brakes 8a-8d. Such an operating mode is referred to as a hydraulic fallback level, since the braking force is built up purely mechanically via the brake pressure through the driver's muscle power. Alternatively, the driver can also be assisted by the second pressure source 2. For this purpose, a half-by-wire mode can be switched on 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.

[0075] To enable even greater functionality in the event of failure of the first assembly 100, the second assembly 200 is optionally added. For example, a (third) pressure sensor can be installed in the pressure connection between the two assemblies 100, 200 to detect the driver's input (preferably upstream of the isolation valve 26 in the second assembly 200). Then, when pressure builds up in the master brake cylinder 1, the activation 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 are available at all wheel brakes.

[0076] However, if the first component or part of it fails, it is often not possible to open the simulator valve 28. Master cylinder 1 then operates against the closed ISV 26 and thus in a hydraulically rigid space. The brake pedal is thus essentially immobile, making it very difficult for the driver to control the braking force.

[0077] According to the invention, it is therefore provided in a first variant that in the event of failure of the first structural unit 100, a part thereof or in the event of other errors, such as failure of the communication connection between the structural units, a switch is made to a half-by-wire mode as soon as braking occurs via the brake pedal 12.

[0078] Since most braking operations are carried out with a moderate pressure level and pressure gradient, this mode is usually sufficient and there is 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.

[0079] If a pressure request 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 booster mode. Individual wheel control on the front axle also leads to a switch from half-by-wire to booster mode. The system can then switch back to half-by-wire if the pressure request is below the starting condition and no individual wheel control is present on the front axle. Optionally, the system can switch back to half-by-wire when the pedal is completely released.

[0080] In half-by-wire mode, the maximum pressure of 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.

[0081] When transitioning from half-by-wire to booster mode, isolation valve 26 must be securely closed. To do this, the front axle intake valves 6 are temporarily closed and the isolation valve 26 is energized. In this situation, the isolation valve 26 is not overflowed by brake fluid and can close. Subsequently, the front axle intake valves are reopened, and the circuit isolation valve 40 is opened. The valve is now in booster mode.

[0082] According to the invention, a further variant therefore provides that in the event of failure of the first structural unit 100, a part thereof, or other errors, such as failure of the communication link between the structural units, the system switches to a hydraulic fallback mode as soon as braking occurs via the brake pedal 12. In this case, too, the system switches to booster mode under the above conditions.

[0083] If the goal is to reconnect the pedal as a wheel pressure source during pedal actuation, pressure equality should be created via the isolation valve to ensure a smooth transition. Pressure equality can be monitored by both pressure sensors of the second unit.

Claims

[1] Method for controlling a hydraulic motor vehicle brake 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 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), wherein in a fault-free case, the pressure at the at least one first wheel brake (8a, 8b) is built up by the first electrical pressure supply device (5) characterized byin that in the event of a fault in the first subsystem (100) a switch is made to a half-by-wire mode or a hydraulic fallback mode, wherein the pressure in the at least one first wheel brake (8a, 8b) is built up without electrical amplification by the muscle power of a driver via the hydraulically coupled brake pedal (12) as long as a switchover condition which indicates whether braking can still be carried out without problems by the purely mechanical pressure generation is not met, and when the switchover condition is met a switch is made to a boost mode in which the hydraulically coupled brake pedal (12) is separated from the at least one first wheel brake (8a, 8b) and the pressure in the at least one first wheel brake (8a, 8b) is built up by the second electrical pressure supply device (2). [2] Method according to claim 1, characterized byin that in the half-by-wire mode the pressure in at least one second wheel brake (8c, 8d) is built up by the second electrical pressure supply device (2), wherein in the hydraulic fallback mode the pressure in the at least one second wheel brake (8c, 8d) is built up without electrical amplification by the muscle power of the driver via the hydraulically coupled brake pedal (12). [3] Method according to one of the preceding claims, characterized by that the separation of the brake pedal (12) takes place by closing an isolation valve (26) of the second subsystem (200). [4] Method according to claim 3, characterized by that to close the isolation valve (26), the connected inlet valves (6a, 6b, 6c, 6d) are closed so that no volume flow flows through the isolation valve (26). [5] Method according to one of the preceding claims, characterized by that the switching condition includes: - Brake pedal pressure greater than a pressure threshold, - Brake pedal pressure gradient greater than a pressure gradient threshold, - Presence of ABS intervention - Presence of a stability system intervention [6] Method according to one of the preceding claims, characterized by that the system switches back to half by wire mode or hydraulic fallback mode when - the brake pedal is completely released, - or if all wheel pressure requirements are the same, especially for a given period of time, and the driver's request is less than a threshold value. [7] Method according to one of the preceding claims, characterized by that in the booster mode, the second pressure supply device (2) builds up a pressure in the at least one first wheel brake (8a, 8b) which is greater than the brake pedal pressure. [8] Method according to one of the preceding claims, characterized byin that in the booster mode the pressure is built up at at least two second wheel brakes (8c, 8d) and two first wheel brakes (8a, 8b) by means of the second pressure supply device (2), in the half-by-wire mode the pressure is built up at at least two second wheel brakes (8c, 8d) by means of the second pressure supply device (2) and is built up at two first wheel brakes (8a, 8b) without electrical boost by the driver's muscle power via the hydraulically coupled brake pedal (12), and in the hydraulic fallback mode the pressure is built up at at least two second wheel brakes (8c, 8d) and two first wheel brakes (8a, 8b) without electrical boost by the driver's muscle power via the hydraulically coupled brake pedal (12). [9] Method according to one of the preceding claims, characterized bythat the first wheel brakes (8a, 8b) are assigned to a first vehicle axle, in particular a front axle, and the second wheel brakes (8c, 8d) are assigned to a second vehicle axle, in particular a rear axle. [10] Method according to one of the preceding claims, characterized by that in the booster mode a pressure reduction is implemented by outlet valves (7a, 7b, 7c, 7d) of the wheel brakes. [11] Method according to one of the preceding claims, characterized by that the first subsystem (100) and the second subsystem (200) each comprise their own electrical control unit (101, 201). [12] Method according to one of the preceding claims, characterized by that in the half-by-wire mode, the first and second wheel brakes are fluidically separated from one another by closing a circuit separation valve (40). [13] Method according to one of the preceding claims, characterized bythat in the half-by-wire mode the pressure in the second wheel brakes (8c, 8d) is limited to a threshold value, wherein the threshold value is selected such that the circuit isolation valve (40) can reliably open at pressures less than or equal to the threshold value. [14] Hydraulic motor vehicle brake 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 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), wherein a control unit (101, 201) is configured to build up a pressure at the at least one first wheel brake (8a, 8b) by means of the first electrical pressure supply device (5) in a fault-free case characterized bythat the control unit (101, 201) switches to a half-by-wire mode or a hydraulic fallback mode when a fault occurs in the first subsystem (100), in which the pressure in the at least one first wheel brake is built up without electrical amplification by the muscle power of a driver via the hydraulically coupled brake pedal (12) as long as a switching condition which indicates whether braking can still be easily implemented by purely mechanical pressure generation is not met, and when the switching condition is met, it switches to a boost mode in which the hydraulically coupled brake pedal (12) is separated from the at least one first wheel brake (8a, 8b) and the pressure in the at least one first wheel brake (8a, 8b) is built up by the second electrical pressure supply device (2).

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