Method for operating an electro-hydraulic brake control unit and electro-hydraulic brake control unit

Abstract

The invention discloses a method (100) for operating an electro-hydraulic brake control unit (1) of a motor vehicle with several hydraulic output connections (4a-4d) for hydraulically actuated wheel brakes (5a-5d) and an electrically controllable first pressure source (2) for hydraulically pressurizing the wheel brakes (5a-5d), which is formed by a cylinder-piston arrangement with a pressure chamber (30) and a piston (31) as well as an electromechanical actuator with an electric motor (32), wherein, to generate a predetermined hydraulic pressure by means of the first pressure source (2), a basic motor torque is generated by the electric motor (32) and an oscillating motor torque is superimposed on the basic motor torque. The invention further discloses an electro-hydraulic brake control unit (1) which is configured to carry out such a method (100).

Description

The invention relates to a method for operating an electrohydraulic brake control device of a motor vehicle. The invention further relates to an electrohydraulic brake control device which is designed to carry out such a method.In motor vehicles, brake systems having electrohydraulic brake control units have typically been used for many years to decelerate the motor vehicles in a controlled manner. In a brake application, hydraulic pressure is usually built up via the brake control unit and via a pressure medium, in particular via a brake fluid, which hydraulic pressure then results in a braking force at wheel brakes of the motor vehicle and thus ultimately in a deceleration of the motor vehicle. In this case, the brake system usually also has an actuating unit for a vehicle driver, which is connected to the brake control unit by a transmission of a driver's request signal. The brake system can be designed, for example, according to the brake-by-wire principle, wherein a braking force request initiated by the vehicle driver or by a safety or assistance function of the vehicle is sensed or received and is converted into an actual brake actuation by means of electrical or electrically actuated pressure sources such as a linear actuator, which usually has a cylinder-piston arrangement with a pressure chamber and a piston and an electric motor.Due to the high importance of such a brake system and particularly of the pressure source of the brake control device of the brake system, it is of particular importance for traffic safety to ensure a proper working state of the components of the brake system and particularly proper pressure generation or pressure build-up.However, a disadvantage of such a brake control device in a pressure source designed as a linear actuator is that certain frictional and sliding frictions can occur in the pressure source, in particular between the piston and the guide housing of the piston. It is precisely the static friction that occurs that leads to a discontinuity between an engine torque generated by the electric motor and a resulting system pressure generated by the pressure source, prevents a reliable, rapid and particularly uniform or continuous pressure build-up by the pressure source and can lead, for example, to pressure build-up inaccuracies or pressure errors of up to 30%, and can in particular result in a predefined engine torque requirement to the electric motor of the pressure source not always leading to an identical system pressure generated by means of the pressure source.This can result in an overall incorrect or non-required pressure build-up. In addition, a functional test of the brake control device, in particular a hydraulic self-test of the brake control device and in this case in particular a test of a valve of the brake control device for a leak, can thereby lead to inaccurate or incorrect results. It is precisely when, in addition, a current, actual system pressure cannot be directly detected, for example because no pressure sensor is arranged in the brake control unit at a position suitable for the corresponding system pressure detection, and the current, actual system pressure therefore cannot be directly measured and used within the scope of the function test, in particular in the case of a leakage test of a valve of the brake control unit, an accurate and robust function test is not possible.Against this background, it is now an object of the invention to specify an improved method for operating an electrohydraulic brake control unit for a motor vehicle and a corresponding brake control unit, which method enables a pressure build-up and accurate according to requirements and an accurate and reliable function test, in particular leakage check of a valve, of the brake control unit.The above object is achieved by the entire teaching of claim 1 and claim 13. Practical embodiments and developments of the invention are set forth in the dependent claims and the following description.In the method according to the invention for operating an electrohydraulic brake control device of a motor vehicle, the brake control device comprises a plurality of hydraulic output connections for hydraulically actuatable wheel brakes and an electrically actuatable first pressure source for hydraulically pressurizing the wheel brakes, wherein the first pressure source is formed by a cylinder-piston arrangement having a pressure chamber and a piston and an electromechanical actuator having an electric motor. In this case, within the scope of a generation of a predefined hydraulic pressure by means of the first pressure source, in particular for overcoming a static friction of the piston, a basic motor torque is generated by the electric motor and an oscillating motor torque is superimposed on the basic motor torque.An oscillating motor torque profile is therefore superimposed here on a current or currently existing basic motor torque. A total engine torque generated by the electric motor thus comprises the basic engine torque and the oscillating engine torque superimposed on the basic engine torque or the oscillating engine torque profile superimposed on the basic engine torque. The total engine torque is ultimately supplied to the piston. In this way, static frictions of the first pressure source, more precisely static frictions of the piston, in particular static frictions between the piston and a piston guide housing of the first pressure source, are advantageously rapidly overcome or compensated and thus a rapid and accurate "adjustment" of a specific pressure value without or with only a slight stuffiness or discontinuity is made possible, as a result of which a wide variety of pressure and volume requirements can be implemented quickly, accurately and reproducibly. In this case, the oscillating motor torque or the motor torque oscillation explicitly does not represent a direct position or pressure oscillation of the first pressure source. An average value of a resulting total amplitude of the total engine torque advantageously corresponds to a specific engine torque specification.The configuration according to the invention thus has the overall advantage that an improved method is thereby provided, by means of which a pressure build-up according to requirements and accurate and reliable function testing, in particular leakage testing of a valve, of the brake control unit is ensured.The predetermined hydraulic pressure is in particular a predetermined hydraulic system pressure.Within the scope of this invention, static friction is understood to mean, in particular, the frictional force to be overcome for moving the piston, which frictional force prevails between the piston and a further component, in particular a piston guide housing, of the first pressure source.The first pressure source is in particular a hydrostatically operating pressure generator which operates discontinuously, i.e. which charges regularly and then discharges pressure. Advantageously, the first pressure source can hydraulically pressurize one wheel brake or a plurality of wheel brakes. The first pressure source serves in particular for the pressure build-up and pressure reduction in the wheel brakes as required. The piston of the first pressure source can be actuated by the electromechanical actuator, i.e. in particular for a pressure build-up in the pressure chamber and ultimately in the wheel brakes in a (brake) actuation direction and for a pressure reduction in the pressure chamber and ultimately in the wheel brakes in the direction opposite to the (brake) actuation direction, wherein the electromechanical actuator of the first pressure source advantageously further comprises a rotation-translation gear for this purpose. The first pressure source is preferably designed as a linear actuator.In an advantageous embodiment, the basic motor torque is generated during a limited first time period, wherein the oscillating motor torque is superimposed on the basic motor torque during the first time period. The oscillating motor torque can be superimposed on the basic motor torque during the entire first time period or during a second time period that is shorter than the first time period, wherein the total motor torque is composed of the basic motor torque and the oscillating motor torque superimposed on the basic motor torque in the first case during the entire first time period and the second case during the entire second time period or the oscillating motor torque profile superimposed on the basic motor torque.In a further advantageous embodiment, the oscillating motor torque is designed as a symmetrically oscillating motor torque, in particular as a sinusoidal motor torque. The current or currently existing basic motor torque is therefore superimposed by a symmetrically oscillating motor torque or a symmetrically oscillating motor torque profile. In this case, in principle any symmetrically oscillating motor torque or each symmetrically oscillating motor torque profile is conceivable, but advantageously this is a sinusoidal or pyramidal motor torque or a sinusoidal or pyramidal motor torque profile. The symmetrically oscillating motor torque or the symmetrically oscillating motor torque profile advantageously has an amplitude of + / - 0.1 Nm and / or a frequency in a range of 19 to 21 Hz, preferably a frequency of 20 Hz, or in a range of 1 to 3 Hz. This makes noise, vibration and roughness problems (especially narrow. Noise, vibration, Harshness [NVH]) and thus, for example, audible and / or perceptible oscillations in the corresponding motor vehicle are avoided or at least reduced.In a further advantageous embodiment, the predetermined hydraulic pressure is generated as part of a functional test of the brake control unit, preferably as part of a hydraulic self-test of the brake control unit. The function check is preferably carried out here for checking or detecting or determining a leak within the brake control unit, preferably for detecting or determining a leak of a valve, preferably of a circuit separating valve, of the brake control unit.In a further advantageous embodiment, the brake control device further comprises an inlet valve and an outlet valve per output connection and a pressure medium storage container under atmospheric pressure, wherein the first pressure source has a pressure connection which is connected to the inlet valves via a brake line section, wherein a shut-off valve is arranged in a hydraulic connection between the pressure connection of the first pressure source and the brake line section, wherein a pressure compensation valve is arranged in a hydraulic connection between a second connection of the pressure medium storage container and the shut-off valve, and wherein during a function test cycle which is limited over time the pressure compensation valve and at least part of the inlet valves, in particular all inlet valves, are closed. The brake control device has an inlet valve and an outlet valve per output connection, and therefore each output connection is assigned both an outlet valve and an inlet valve. The pressure compensation valve and at least a part of the inlet valves, in particular all inlet valves, are closed during the entire function test cycle.In a further advantageous embodiment, the brake control device further comprises an electrically controllable second pressure source for hydraulically pressurizing the wheel brakes, wherein a circuit isolation valve is arranged in a hydraulic connection between the shut-off valve and a pressure-side output of the second pressure source, and wherein, as part of the function test, the circuit isolation valve is tested for a leak during the function test cycle. The circuit isolation valve has in particular the function of making it possible to divide or isolate the brake circuit of the brake control device into two sub-circuits. Advantageously, the output connections or the wheel brakes of a rear axle of the motor vehicle are assigned to a first sub-circuit and the output connections or the wheel brakes of a front axle of the motor vehicle are assigned to a second sub-circuit.Advantageously, the second pressure source can hydraulically pressurize one wheel brake or a plurality of wheel brakes. The second pressure source serves in particular for the pressure build-up and pressure reduction in the wheel brakes as required. The second pressure source is advantageously designed as a pump arrangement with a hydraulic first pump and an electric drive device, in particular designed as an electric motor, for the first pump, preferably as a pump arrangement with a hydraulic first pump and a hydraulic second pump and an electric drive device, in particular designed as an electric motor, as a common drive device for the first pump and the second pump. The pump arrangement is understood in particular to mean a hydrodynamically operating device for generating pressure, which device can provide a continuous volume flow.Advantageously, the first pressure source and the second pressure source can each and independently hydraulically pressurize one wheel brake or a plurality of wheel brakes. However, hydraulic pressurization of a wheel brake or of a plurality of wheel brakes can also be effected together by the first pressure source and the second pressure source. The first pressure source and the second pressure source each serve in particular for the pressure build-up and pressure reduction in the wheel brakes as required.In a further advantageous embodiment, at the beginning of the function test cycle, with the circuit isolation valve open and the shut-off valve open, a system pressure is built up by means of the first pressure source by a calibration motor torque generated by the electric motor and the built-up system pressure is detected, wherein a relationship or ratio between the generated calibration motor torque and the detected system pressure is determined. At the beginning of the function test cycle, the circuit isolation valve and the shut-off valve are thus simultaneously opened, wherein the pressure compensation valve and at least a part of the inlet valves, in particular all inlet valves, are closed. The calibration motor torque generated by the electric motor is supplied to the piston of the first pressure source or applied to the piston of the first pressure source.In a further advantageous embodiment, after the correlation between the generated calibration motor torque and the detected system pressure is determined, the circuit separating valve is closed, wherein then, when the circuit separating valve is closed, the electric motor generates the basic motor torque by means of the first pressure source to generate the predefined hydraulic pressure, and the oscillating motor torque is superimposed on the basic motor torque. While the circuit isolation valve is closed, the pressure compensation valve and at least a part of the inlet valves, in particular all the inlet valves, are still closed.In a further advantageous embodiment, a system pressure currently or actually generated by the first pressure source is then determined based on the total engine torque generated by the electric motor, which comprises the basic engine torque and the oscillating engine torque superimposed on the basic engine torque, and the determined relationship between the generated calibration engine torque and the detected system pressure.In a further advantageous embodiment, a leakage, in particular a leakage conductance, of the circuit isolation valve is then determined on the basis of the ascertained current system pressure.In this case, in a further advantageous embodiment, the coating of the circuit separation valve is also determined on the basis of a travel path of the piston and / or a time duration, in particular for a path covered by the piston for the build-up of the current system pressure and / or for a readjustment path covered by the piston. The travel path represents in particular a path required or covered by the piston for the build-up of the current system pressure and / or a follow-up or follow-up control path required or covered by the piston, i.e. the path covered by the piston in the presence of a leak (due to the leak additionally) in order to generate or maintain the predefined (system) pressure. The time duration represents in particular a time required for the build-up of the current system pressure or for the distance travelled by the piston for the build-up of the current system pressure, advantageously 150 ms-250 ms, preferably 200 ms, and / or a time required for the travelling of the follow-up or follow-up travel of the piston, advantageously at least 500 ms.In a further advantageous embodiment, in which at the beginning of the function test cycle, with the circuit isolation valve opened and the shut-off valve opened, a system pressure is built up by means of the first pressure source by a calibration motor torque generated by the electric motor and the built-up system pressure is detected, wherein a relationship or ratio between the generated calibration motor torque and the detected system pressure is determined, the system pressure built up at the generated calibration torque is detected on the pressure side of the second pressure source, wherein preferably a pressure sensor is arranged in or on a hydraulic connection between the circuit isolation valve and an inlet valve, which senses the system pressure in the hydraulic connection between the circuit isolation valve and the inlet valve and provides it to an electronic control and regulating unit of the brake control unit, and wherein preferably this pressure sensor is the only pressure sensor of the brake control unit.The present invention further comprises an electrohydraulic brake control device for a motor vehicle, wherein the brake control device has a plurality of hydraulic output connections for hydraulically actuatable wheel brakes and an electrically actuatable first pressure source for hydraulically pressurizing the wheel brakes, wherein the first pressure source is formed by a cylinder-piston arrangement having a pressure chamber and a piston and an electromechanical actuator having an electric motor, and wherein the brake control device is configured to carry out a method according to the invention.The advantages and preferred embodiments described for the method according to the invention also apply accordingly to the brake control device according to the invention.Exemplary embodiments of the invention are explained in more detail below with reference to a drawing. Shown therein are: FIG. 1 shows an exemplary embodiment of an electrohydraulic brake control device according to the invention in a schematic illustration, FIG. 2 shows a flow chart of a method according to the invention for checking the leakage of the circuit separating valve of the electrohydraulic brake control unit from FIG. 1, FIG. 3 a is a diagram illustrating a curve of a motor torque of the electric motor as a function of time in a method for operating the brake control device 1 from FIG. 1 ; and FIG. 3 bshows a diagram which represents a profile of a system pressure as a function of time, which profile results from the profile of the engine torque according to FIG. 3 a.FIG. 1 schematically shows an exemplary embodiment of an electrohydraulic brake control device 1 according to the invention for a motor vehicle having four hydraulically actuatable wheel brakes 5 a- 5 d.The electrohydraulic brake control unit 1 comprises a hydraulic block (hydraulic open-loop and closed-loop control unit HCU, valve block) with an output connection 4 a- 4 dfor each of the wheel brakes 5 a- 5 d. According to the example, the output connections 4 a, 4 bare assigned to the wheel brakes 5 a, 5 bof the rear axle (rear), e.g. the output connection 4 ato the left rear wheel RL (wheel brake 5 a) and the output connection 4 bto the right rear wheel RR (wheel brake 5 d), and the output connections 4 c, 4 dare assigned to the wheel brakes 5 c, 5 dof the front axle (front), e.g. the output connection 4 cto the left front wheel FL (wheel brake 5 c) and the output connection 4 dto the right front wheel FR (wheel brake 5 d). Other assignments are possible.On the hydraulic block, a pressure medium reservoir 3 is arranged which is at atmospheric pressure. The fill level of the pressure medium reservoir 3 is measured by means of a fill level sensor 44. The pressure medium storage container 3 comprises three container chambers 84 a, 84 b, 84 cwhich are at least partially separated from one another by a first partition wall 86 aand a second partition wall 86 b. Furthermore, the pressure medium reservoir 3 comprises a first connection 71, a second connection 72 and a third connection 73. the first connection 71 is connected to the first container chamber 84 a, the second connection 72 is connected to the second container chamber 84 band the third connection 73 is connected to the third container chamber 84 c. In this sense, the first connection 71 of the pressure medium storage container 3 is assigned to the first container chamber 84 a, the second connection 72 of the pressure medium storage container 3 is assigned to the second container chamber 84 b, and the third connection 73 of the pressure medium storage container 3 is assigned to the third container chamber 84 cEach output connection 4 a- 4 dis assigned an inlet valve 6 a- 6 dand an outlet valve 7 a- 7 d, wherein the inlet valves 6 a- 6 dare advantageously designed to be open when zero current is present and the outlet valves 7 a- 7 dare advantageously designed to be closed when zero current is present. According to the example, a nonreturn valve closing in the direction of the output connections 4 a- 4 dor wheel brakes 5 a- 5 dis connected in parallel with each inlet valve 6 a- 6 d.The respective output connection 4 a- 4 dis indirectly connected to the pressure medium storage container 3 via the outlet valve 7 a- 7 d. The outlet valves 7 a- 7 dare indirectly connected to the first connection 71 of the pressure medium storage container 3 via a (at least partially common) return line 62.An electrically controllable hydraulic first pressure source 2 is also provided, which is formed by a cylinder-piston arrangement with a pressure chamber 30, the piston 31 of which can be actuated by an electromechanical actuator with an electric motor 32, which is indicated schematically, and a rotation-translation gear 33, which is indicated schematically. According to the example, the pressure source 2 is designed as a single-circuit electrohydraulic linear actuator (LAC) with only one pressure chamber 30. The piston 31 can be advanced by means of the electromechanical actuator or the electric motor 32 to build up a pressure (brake actuation direction) and pushed back or pulled back to reduce a pressure. For controlling the first pressure source 2, the electrohydraulic brake control device 1 comprises a sensor element for detecting a rotational speed or a rotational angle of the electric motor 32.The pressure chamber 30 is hydraulically connected via a pressure port 83 to a brake line section 60 which is hydraulically connected to the inlet valves 6 a- 6 d(more precisely to the input ports of the inlet valves 6 a- 6 d). In the hydraulic connection between the pressure chamber 30 of the first pressure source 2 or the pressure connection 83 and the brake line section 60 or each of the inlet valves 6 a- 6 d, an electrically actuatable, in particular normally open, shut-off valve 10 is arranged. One function of the shut-off valve 10 is in particular to make it possible, after a volume-consuming pressure modulation (i.e. with discharge of pressure medium via the outlet valves 7 a- 7 d), for the first pressure source 2 to suck in pressure medium by the shut-off valve 10 being closed and the electric motor 32 retracting the piston 31.A re-suction of pressure medium from the pressure medium storage container 3 into the first pressure source 2 can also take place via the pressure connection 83. For this purpose, the pressure connection 83 is connected to the third connection 73 of the pressure medium reservoir 3 and thus to the third reservoir chamber 84 cof the pressure medium reservoir 3 via a suction line section 61 aand a suction valve 14 arranged in the suction line section 61 a, which is designed as a check valve opening in the direction of the pressure connection 83, for example.In a hydraulic connection between the second connection 72 of the pressure medium storage container 3 and the shut-off valve 10, an electrically actuatable pressure compensation valve 20 is arranged in a follow-on line section 61 b. One function of the pressure compensation valve 20 is in particular to make it possible to depressuris the wheel brakes 5 a- 5 d, i.e. to connect the wheel brakes 5 a- 5 dto the pressure medium storage container 3 which is at atmospheric pressure.The suck back pipe portion 61 aand the suck back pipe portion 61 bare not directly connected to the return pipe 62. There is only a certain indirect hydraulic connection, among other things, via the pressure medium reservoir container 3, if the fill level of the pressure medium reservoir container 3 lies above the first bulkhead 86 aand the second bulkhead 86 b.In addition, the brake control device 1 has a pump arrangement 4 likewise for the hydraulic pressurization of the wheel brakes 5 a- 5 d, as required. The pump arrangement 4 comprises a hydraulic first pump 51 aand a hydraulic second pump 51 band also a (common) electric drive device 53 designed as an electric motor for the first pump 51 aand the second pump 51 b, wherein the wheel brakes 5 a- 5 dmay be supplied with pressure from the pump arrangement 4 as required via a first pressure supply line 63 and a second pressure supply line 64. The pump arrangement 4 can be operated at a plurality of different pump speeds, wherein a current pump speed can be detected with a speed sensor (not shown) coupled to the pump arrangement.The pump arrangement 4 is hydraulically connected on the suction side via a suction line 65 indirectly to the first connection 71 of the pressure medium storage container 3. A check valve 54 a, 54 bthat closes in the direction of the outlet side of the corresponding pump 51 a, 51 bis arranged on the pressure side in each case, and a check valve 55 a, 55 bthat closes in the direction of the suction line 65 or of the first connection 71 of the pressure medium storage container 3 or opens in the direction of the suction side of the respective pump 51 a, 51 bis arranged on the suction side in each case.A circuit-separating valve 70 is arranged in a hydraulic connection between a pressure-side outlet of the pump arrangement 4 or the second pressure supply line 64 and the shut-off valve 10. One function of the circuit isolation valve 70 which is open in a normal operation according to the example is in particular to enable the brake circuit of the brake control unit 1 or of a corresponding brake system to be divided or isolated into two sub-circuits. In this case, the output connections 4 a, 4 bor the wheel brakes 5 a, 5 bof the rear axle are assigned to a first sub-circuit, and the output connections 4 c, 4 dor the wheel brakes 5 c, 5 dare assigned to a second sub-circuit.Furthermore, a pressure sensor 40 is arranged between the pressure-side output of the pump arrangement 4 and the inlet valves 6 a, 6 bwhich are assigned to the output connections 4 a, 4 bof the wheel brakes 5 a, 5 bof the rear axle, said pressure sensor sensing a system pressure in the hydraulic connection between the pressure-side output of the pump arrangement 4 and the corresponding inlet valves 6 a, 6 b. This pressure sensor 40 represents the only pressure sensor of the brake control device 1, i.e., the brake control device 1 does not have a further pressure sensor. Thus, the brake control device does not have a pressure sensor even precisely in a hydraulic connection between the pressure connection 83 of the first pressure source 2 and the circuit isolation valve 70, so that a current, actual system pressure cannot be directly detected, in particular when the circuit isolation valve 70 is closed.The electrohydraulic brake control unit 1 further comprises a first electronic control and regulating unit (ECU) A and a second electronic control and regulating unit (ECU) B, in particular for controlling the electrically actuatable components of the electrohydraulic brake control unit 1. the first electronic control and regulating unit A and the second electronic control and regulating unit B are advantageously electrically independent of one another in the sense that a failure of the first electronic control and regulating unit A does not cause a failure of the second electronic control and regulating unit B, and vice versa. For this purpose, the electronic control and regulating units A and B can be embodied as separate units, but they can also be embodied as independent subunits in the same electronic control and regulating unit. The open-loop and closed-loop control units A and B are connected to one another by way of redundant signal lines 80 as an example.The electric motor 32 of the pressure source 2 and the drive device 53 of the pump arrangement 4 can be controlled in each case by the first and the second electronic open-loop and closed-loop control units A, B, i.e. each of the electronic open-loop and closed-loop control units A, B is suitable on its own for building up a pressure by means of the first pressure source 2 and / or the pump arrangement 4, in particular for carrying out a service braking operation. This means that the first pressure source 2 and the pump arrangement 4 and the electronic open-loop and closed-loop control units A, B are designed in such a way that, in the event of a failure of the first electronic open-loop and closed-loop control unit A, the first pressure source 2 and the pump arrangement 4 can be actuated by means of the second electronic open-loop and closed-loop control unit B in order to build up a brake pressure for actuating the wheel brakes 5 a- 5 dduring an operating or closed-loop braking operation, and that, in the event of a failure of the second electronic open-loop and closed-loop control unit B, the first pressure source 2 and the pump arrangement 4 can be actuated by means of the first electronic open-loop and closed-loop control unit A in order to build up a pressure for actuating the wheel brakes 5 a- 5 dduring an operating or closed-loop braking operation.The electrically actuatable inlet and outlet valves 6 a- 6 d, 7 a- 7 d, the shut-off valve 10, the pressure compensation valve 20 and the circuit separation valve 70 of the electrohydraulic brake control unit 1 can be assigned, in particular in each case, to both electronic open-loop and closed-loop control units A, B, but are advantageously assigned in each case only to one of the electronic open-loop and closed-loop control units A, B. That is, each electrically actuatable valve 6 a- 6 d, 7 a- 7 d, 10, 20, 70 is actuated exclusively by the electronic open-loop and closed-loop control unit A or exclusively by the electronic open-loop and closed-loop control unit B.This avoids complicated, double-controllable valves / valve coils. All electrically actuatable valves 6 a- 6 d, 7 a- 7 d, 10, 20, 70 are advantageously assigned to the same electronic control and regulating unit A, B, for example the electronic control and regulating unit A, and are exclusively actuated by the electronic control and regulating unit A. In addition, the signals of the motor angle sensor 43, the pressure sensor 40 and the speed sensor can be fed to both electronic open-loop and closed-loop control units A, B in each case and evaluated by these. Advantageously, however, the signals of the motor angle sensor 43, the pressure sensor 40 and the speed sensor are each fed to only one of the two electronic control and regulating units A, B, for example the first electronic control and regulating unit A, and evaluated by the latter.According to the example, the electrohydraulic brake control unit 1 is supplied from a redundant on-board power supply system with two independent voltage sources (a first electrical energy supply and a second electrical energy supply), so that not both open-loop and closed-loop control units A and B are supplied from the same electrical energy supply. For example, control and regulating units A are supplied by the first electrical energy supply and control and regulating units B are supplied by the second electrical energy supply.Preferably, an actuating unit for a vehicle driver (not shown in FIG. 1 ) is also connected on the signal side to the electrohydraulic brake control device 1 for transmitting a driver's request signal.The brake control device 1 is further designed to generate a basic motor torque by the electric motor 32 to generate a predefined hydraulic pressure by means of the first pressure source 2 and to superimpose a symmetrically oscillating motor torque or a symmetrically oscillating motor torque profile on the basic motor torque. A total engine torque generated by the electric motor 32 then comprises the basic engine torque and the symmetrically oscillating engine torque superimposed on the basic engine torque or the symmetrically oscillating engine torque profile superimposed on the basic engine torque. The total engine torque is ultimately supplied to the piston 31.The brake control device 1 is further configured to generate the basic motor torque during a limited first time period, wherein the oscillating motor torque is superimposed on the basic motor torque during the first time period.In this way, in particular static frictions of the first pressure source 2 or of the piston 31 can be quickly overcome or compensated and thus a fast and accurate "adjustment" of a specific (system) pressure difference can be made possible without or with only a slight stuffiness or discontinuity, as a result of which a wide variety of pressure and volume requirements can be implemented quickly and accurately, and as a result of which ultimately a pressure build-up according to requirements and accurate by the first pressure source 2 can be ensured.According to the example, the brake control unit 1 is further configured to perform the corresponding generation of the predefined hydraulic pressure within the scope of a hydraulic self-test of the brake control unit 1 and here for checking or detecting or determining a leak of the circuit isolation valve 70. For this purpose, at the beginning of a function test cycle of the corresponding hydraulic self-test, both the pressure compensation valve 20 and all the input valves 6 a- 6 dare closed and both the circuit isolation valve 70 and the shut-off valve 10 are or are opened, wherein then in this (valve) state a system pressure is built up by means of a calibration motor torque generated by the electric motor 32, the built-up system pressure is detected by the pressure sensor 40 and a relationship or ratio between the generated calibration motor torque and the detected system pressure is determined. Furthermore, the circuit separating valve 70 is then closed and, when the circuit separating valve 70 is closed and the pressure compensating valve 20 is also closed and the inlet valves 6 a- 6 dis also closed, the electric motor 32 generates the basic engine torque for generating the predefined hydraulic pressure by means of the first pressure source 2, and the oscillating engine torque is superimposed on the basic engine torque.Furthermore, a system pressure currently or actually generated by the first pressure source 2 is subsequently determined based on the total engine torque generated by the electric motor 32, which comprises the basic engine torque and the oscillating engine torque superimposed on the basic engine torque, and the determined relationship between the generated calibration engine torque and the detected system pressure. Furthermore, based on the determined current or actual system pressure and a travel path of the piston and a time duration, for example for a path covered by the piston 31 for the build-up of the current system pressure and / or for a readjustment path covered by the piston 31, a leakage, for example a leakage conductance, of the circuit separating valve 70 is then determined.In this way, a precise, robust and reliable hydraulic self-test, in particular a leak check of the circuit isolation valve 70, of the brake control unit 1 is made possible, although no pressure sensor is present in a hydraulic connection between the pressure connection 83 of the first pressure source 2 and the circuit isolation valve 70, so that a current, actual system pressure cannot be directly detected, in particular in the case of a closed circuit isolation valve 70.FIG. 2 shows a flow chart of a method 100 for checking the leakage or determining the circuit separating valve 70 of the brake control unit 1 from FIG. 1.At the beginning of a function test cycle, in a step 101, if these valves are not already in a closed state in any case, both the pressure compensation valve 20 and all the inlet valves 6 a- 6 dare closed. In addition, if these valves are not already in an open state, both the circuit-separating valve 70 and the shut-off valve 10 are opened.In a next step 102, a system pressure is built up by means of the first pressure source 2 by means of a calibration motor torque generated by the electric motor 32, and the built-up system pressure is detected by the pressure sensor 40. A relationship or ratio between the generated calibration motor torque and the detected system pressure is then determined.In a next step 103, the circuit separating valve 70 is closed and the electric motor 32 generates the basic engine torque when the circuit separating valve 70 is closed and the pressure compensation valve 20 is also closed and the inlet valves 6 a- 6 dis also closed in order to generate the predefined hydraulic pressure by means of the first pressure source 2, and the oscillating engine torque is superimposed on the basic engine torque.In a next step 104, a system pressure currently or actually generated by the first pressure source 2 is determined based on the total engine torque generated by the electric motor 32, which comprises the basic engine torque and the oscillating engine torque superimposed on the basic engine torque, and the determined relationship between the generated calibration engine torque and the detected system pressure.Furthermore, in a next step 105, a leak, for example a leak conductance, of the circuit separating valve 70 is determined on the basis of the ascertained current or actual system pressure and a travel path of the piston 31 and a time duration, for example for a path covered by the piston 31 for the build-up of the current system pressure and / or for a readjustment path covered by the piston 31.In this case, in a further advantageous embodiment, the coating of the circuit separation valve is also determined on the basis of a travel path of the piston and / or a time duration, in particular for a path covered by the piston for the build-up of the current system pressure and / or for a readjustment path covered by the piston. The travel path represents in particular a path required or covered by the piston for the build-up of the current system pressure and / or a follow-up or follow-up control path required or covered by the piston, i.e. the path covered by the piston in the presence of a leak (due to the leak additionally) in order to generate or maintain the predefined (system) pressure. The time duration represents, in particular, a time required for the build-up of the current system pressure or for the distance covered by the piston for the build-up of the current system pressure and / or a time required for the moving of the follow-up or follow-up path of the piston.FIG. 3 ashows a diagram which shows a profile of an engine torque of the electric motor 32 as a function of time in a method for operating the brake control device 1 from FIG. 1. The engine torque represents the total engine torque generated by the electric motor 32. The method corresponds substantially to the method or method step 103 described in FIG. 2 for generating a predefined hydraulic pressure, wherein, according to the example and in particular purely for illustration, the electric motor 32 is operated over time with four different (total) engine torques, namely 0.25 Nm, 0.5 Nm, 0.75 Nm and 1 Nm, and wherein, according to the example and in particular purely for illustration of the effect of the superposition of the basic engine torque with the oscillating engine torque, only a substantially static basic engine torque is generated here in each case during a first time interval of a first time duration and then in each case during a second time interval of the first time duration immediately following the first time interval, a symmetrically oscillating engine torque of + / - 0.1 Nm is superposed on the basic engine torque for a second time duration. The respective time of the start of the second time interval, i.e. of the start of the respective symmetrically oscillating engine torque superposition, is in each case marked with a dashed vertical line.FIG. 3 bshows a diagram which represents a profile of a system pressure as a function of time, which profile results from the profile of the engine torque according to FIG. 3 a, wherein here too the respective time of the start of the second time segment, that is to say of the start of the respective symmetrically oscillating engine torque superposition, according to FIG. 3 ais again marked in each case with a dashed vertical line. Here, in each case from or already at the beginning of the second time interval, i.e. the beginning of the respective symmetrically oscillating engine torque superposition, fast setting effects in the system pressure can be detected. These are to be interpreted as overcoming the static friction effects of the first pressure source 2, in particular of the piston 31. As can be further seen from FIG. 3 b, after the start of the engine torque oscillation, the static friction is rapidly overcome and thus a (pre-)determined pressure value is quickly and accurately "adjusted" without or with only a slight stuffiness or discontinuity.

Claims

Method (100) for operating an electrohydraulic brake control device (1) of a motor vehicle having a plurality of hydraulic output connections (4a-4d) for hydraulically actuatable wheel brakes (5a-5d) and an electrically actuatable first pressure source (2) for hydraulically pressurizing the wheel brakes (5a-5d), which is formed by a cylinder-piston arrangement having a pressure chamber (30) and a piston (31) and an electromechanical actuator having an electric motor (32), wherein, as part of a generation of a predefined hydraulic pressure by means of the first pressure source (2), in particular for overcoming a static friction of the piston (31), a basic motor torque is generated by the electric motor (32) and an oscillating motor torque is superimposed on the basic motor torque.The method (100) of claim 1, wherein the base engine torque is generated during a limited first time period, and wherein during the first time period, the oscillating engine torque is superimposed on the base engine torque.Method (100) according to one of the preceding claims, wherein the oscillating motor torque is designed as a symmetrically oscillating, in particular as a sinusoidal, motor torque.Method (100) according to one of the preceding claims, wherein the predetermined hydraulic pressure is generated as part of a function test of the brake control unit (1), preferably as part of a hydraulic self-test of the brake control unit (1), preferably for checking for a leakage within the brake control unit (1).Method (100) according to Claim 4, wherein the brake control device (1) further comprises an inlet valve (6a-6d) and an outlet valve (7a-7d) per output connection (4a-4d) and a pressure medium storage container (3) which is at atmospheric pressure, wherein the first pressure source (2) has a pressure connection (83) which is connected to the inlet valves (6a-6d) via a brake line section (60), wherein a shut-off valve (10) is arranged in a hydraulic connection between the pressure connection (83) of the first pressure source (2) and the brake line section (60), wherein a pressure compensation valve (20) is arranged in a hydraulic connection between a second connection (72) of the pressure medium storage container (3) and the shut-off valve (10), and wherein during a function test cycle that is limited over time, the pressure compensation valve (20) and at least a part of the inlet valves (6a-6d), in particular all the inlet valves (6a-6d), are closed.Method (100) according to Claim 5, wherein the brake control unit (1) further comprises an electrically controllable second pressure source (4) for hydraulically pressurizing the wheel brakes (5a-5d), wherein a circuit isolation valve (70) is arranged in a hydraulic connection between the shut-off valve (10) and a pressure-side output of the second pressure source (4), and wherein, during the function test, the circuit isolation valve (70) is checked for a leak during the function test cycle.Method (100) according to Claim 6, wherein at the beginning of the function test cycle, with the circuit isolation valve (70) open and the shut-off valve (10) open, a system pressure is built up by means of the first pressure source (2) by means of a calibration motor torque generated by the electric motor (32) and the built-up system pressure is detected, and wherein a relationship between the generated calibration motor torque and the detected system pressure is determined.Method (100) according to Claim 7, wherein, after the relationship between the generated calibration motor torque and the detected system pressure has been determined, the circuit separating valve (70) is closed, and wherein, when the circuit separating valve (70) is closed, the electric motor (32) generates the basic motor torque by means of the first pressure source (2) in order to generate the predefined hydraulic pressure, and the oscillating motor torque is superimposed on the basic motor torque.Method (100) according to Claim 8, wherein a system pressure currently generated by the first pressure source (2) is determined on the basis of the total engine torque generated by the electric motor (32), which comprises the basic engine torque and the oscillating engine torque superimposed on the basic engine torque, and the determined relationship between the generated calibration engine torque and the detected system pressure.Method (100) according to Claim 9, wherein a leakage of the circuit separation valve (70) is determined on the basis of the ascertained current system pressure.Method according to Claim 10, wherein the leakage of the circuit-separating valve (70) is also determined on the basis of a travel path of the piston (31) and / or a time duration, in particular for a path covered by the piston for the build-up of the current system pressure and / or for a readjustment path covered by the piston.Method (100) according to one of Claims 7 to 11, wherein the system pressure which is built up at the generated calibration torque is detected on the pressure side of the second pressure source (4), wherein preferably a pressure sensor (40) is arranged in or on a hydraulic connection between the circuit isolating valve (70) and an inlet valve (6a-6d), which sensor senses the system pressure in the hydraulic connection between the circuit isolating valve (70) and the inlet valve (6a-6d) and provides it to an electronic open-loop and closed-loop control unit (A, B) of the brake control unit (1), and wherein preferably the pressure sensor (40) is the only pressure sensor of the brake control unit (1).Electrohydraulic brake control device (1) for a motor vehicle having a plurality of hydraulic output connections (4a-4d) for hydraulically actuatable wheel brakes (5a-5d) and an electrically actuatable first pressure source (2) for hydraulically pressurizing the wheel brakes (5a-5d), which pressure source is formed by a cylinder-piston arrangement having a pressure chamber (30) and a piston (31) and an electromechanical actuator having an electric motor (32), wherein the brake control device (1) is configured to carry out a method (100) according to one of the preceding claims.

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