Pump testing in redundant brake systems

Abstract

The invention relates to a method for controlling a hydraulic motor vehicle braking system comprising at least one hydraulic wheel brake (8) which can be connected via at least one hydraulic valve (6) to a first (5) and / or a second pressure supply device (2), wherein the first pressure supply device (5) is a linear actuator and the second pressure supply device (2) is a piston pump. To meet high safety standards, the pumping capacity of the piston pump (2) is verified by connecting the pressure side of the piston pump (2) to the linear actuator (5) as a volume sink, operating the piston pump (2) to pump brake fluid, which is received by the linear actuator (5), wherein the volume received by the linear actuator (5) is determined based on the piston position, piston movement and / or pV characteristics and is used as a measured variable for verification.

Description

[0001] The invention relates to a method for controlling a hydraulic motor vehicle brake system comprising at least one hydraulic wheel brake, which can be connected to a first and / or a second pressure supply device via at least one hydraulic valve, wherein the first pressure supply device is a linear actuator and the second pressure supply device is a piston pump. The invention also relates to such a motor vehicle brake system.

[0002] Such a motor vehicle brake system is known, for example, from the unpublished DE 10 2023 212 250. Here, a high level of redundancy is achieved by two separate pressure supply devices, a piston pump and a linear actuator, both of which can be connected to the wheel brakes.

[0003] Another such braking system is known from DE 10 2017 222 440 A1, in which a linear actuator and / or a piston pump can also be connected to the wheel brakes. A first and a second isolation valve can be switched for this purpose.

[0004] DE 10 2019 213 057 A1 shows another brake system with both a linear actuator and a pump. Here, the linear actuator is directly connected to a node to which the intake valves are also connected.

[0005] Modern automotive braking systems feature increased redundancy to avoid having to rely on the driver's muscle power as a last resort in the event of isolated failures. Two independent pressure supply devices are typically provided for this purpose. Combining different types, such as a piston pump and a linear actuator, can be particularly advantageous in improving a variety of functions.

[0006] For example, during extended ABS braking, a linear actuator must replenish brake fluid. To do this, its piston is operated in reverse while connected to a brake fluid reservoir. During this time, the linear actuator is unavailable to provide brake pressure. By combining the two pressure supply devices, this gap can be bridged by the piston pump as a pressure source. This significantly shortens the braking distance.

[0007] In other operating modes, the piston pump can also be responsible for building up pressure in at least some of the wheel brakes for extended periods. To ensure the most accurate pressure setting possible in all these cases, the piston pump, with its associated control unit, can be equipped with capacity for measuring the delivery volume.

[0008] However, this is generally not accurate enough to enable exact pressure setting and the implementation of important functions such as leakage monitoring.

[0009] It is therefore an object of the present invention to provide a method for controlling such a braking system which particularly advantageously combines two different pressure supply devices.

[0010] This object is achieved by a method according to the invention as claimed in claim 1. This method provides for checking the pumping capacity of the piston pump. For this purpose, the pressure side of the piston pump is connected to the linear actuator as a volume sink and the piston pump is operated to pump brake fluid. This is then pushed by the piston pump into the linear actuator and taken up by it. The volume taken up by the linear actuator is then determined with high accuracy based on the piston position and / or movement and used as a measurement variable for testing. For this purpose, for example, the pumped volume measured in this way can be compared with a corresponding target value. If the target value is reached within acceptable deviations, the piston pump can be classified as capable of pumping and / or fault-free.

[0011] In a preferred embodiment of the invention, the resulting pressure and / or the pressure curve can also be used for verification. The linear actuator can be controlled to maintain a predetermined counterpressure or countertorque. Alternatively, the linear actuator can be controlled to maintain its position, with the resulting pressure becoming the decisive measured variable.

[0012] In a preferred embodiment of the invention, a displacement measurement of the piston pump can also be calibrated during operation. The volume recorded by the linear actuator and thus actually delivered by the pump is then used as a reference value for calibration. Thus, the high accuracy of the linear actuator's volume measurement can be transferred to the piston pump. This makes it possible to know the exact volume delivered even during pump operation. This allows, in particular, volume monitoring to be active even when the pump is in use, comparing the delivered volume with the achieved pressure and thus quickly detecting errors such as leaks.

[0013] In a preferred embodiment of the invention, before operating the piston pump, the linear actuator is connected to a brake fluid reservoir in a flow-open manner and advanced to a position that allows it to absorb a specified volume. In this process, brake fluid is displaced from the piston of the linear actuator into the brake fluid reservoir, increasing its capacity to absorb brake fluid. This ensures that the linear actuator does not reach its rear stop when absorbing the volume delivered by the piston pump and cannot absorb any further volume.

[0014] In a further preferred embodiment of the invention, the displacement measurement, in particular by means of a current ripple meter, uses sensed pump rotations and / or a model of the electrical control voltage. Such volume measurements are particularly advantageous and can be easily implemented. Such a displacement measurement comprises a parameter that converts the sensed pump rotations and / or a model of the electrical control voltage into a displacement volume. This parameter can be redefined by comparing it with the measured variable of the displacement volume measured by the linear actuator, thus calibrating the displacement measurement. The calibration according to the invention can thus significantly improve the accuracy of the displacement measurement.

[0015] In a further preferred embodiment of the invention, during testing and / or calibration, an inlet valve of at least one wheel brake, in particular all inlet valves of the wheel brakes, is closed, so that the piston pump is connected to the linear actuator as the sole volume sink. This makes determining the pumped volume particularly simple and accurate, as sources of inaccuracy, such as the pV characteristic curve of the wheel brakes, are eliminated. Furthermore, no unwanted braking forces are generated, and finger crushing during standstill is prevented.

[0016] In a further preferred embodiment of the invention, the linear actuator is controlled to maintain a predetermined counter-torque and / or is regulated to a predetermined pressure when receiving the pumped volume. This allows the piston pump to be calibrated not only with respect to the pumped volume, but also with respect to a predetermined counter-pressure. The linear actuator can be controlled with a constant counter-torque / counter-pressure or with a time-varying profile.

[0017] In a further preferred embodiment of the invention, when the pressure is adjusted by means of the pump, no overflow valve is used and / or no pressure sensor is available on the pressure side of the pump. Calibration according to the invention eliminates these components while still enabling precise pressure adjustment.

[0018] In a further preferred embodiment of the invention, the calibration is carried out during a braking operation with the intake valves open. This has the great advantage that the test cannot be determined with regard to possible external noise. Advantageously, the linear actuator can be pre-parked in a depressurized state before braking in order to be able to absorb the pump volume. This pump test can be considered successful if the pressure-volume ratio indicates that volume was fed through the pump when pressure was applied. The pump then delivers more volume during braking than required for pressure regulation, and the linear actuator compensates for this by moving back. Alternatively, the test can be carried out outside of braking while driving with the intake valves closed.

[0019] In a further preferred embodiment of the invention, the linear actuator is controlled to draw brake fluid from the brake fluid reservoir while a valve between the linear actuator and the wheel brakes is closed. During the draw-in process, the pump delivers brake fluid to provide the required pressure in the wheel brakes. This bypassing by the piston pump is sufficiently accurate due to calibration to meet the requirements.

[0020] The object is further achieved by a hydraulic motor vehicle brake system according to claim 11, comprising at least one hydraulic wheel brake which can be connected to a first and / or a second pressure supply device via at least one hydraulic valve, wherein the first pressure supply device is a linear actuator and the second pressure supply device is a piston pump, wherein at least one control unit is configured to check the delivery capacity of the piston pump. For this purpose, the pressure side of the piston pump is connected to the linear actuator as a volume sink and the piston pump is operated to deliver brake fluid. This is thus displaced by the piston pump into the linear actuator and absorbed by it. The volume absorbed by the linear actuator is then determined with high accuracy based on the piston position and / or movement and used as a measured variable for testing.

[0021] 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 a braking system according to the invention, Fig. 2 shows the volume flow of the brake system according to the invention during calibration;

[0022] In Fig. Figure 1 shows a redundant hydraulic braking system for motor vehicles. For example, the braking system is designed to actuate four hydraulically actuated wheel brakes 8; expansion to more wheel brakes is easily possible. For example, the wheel brakes (HL, HR) are assigned to the rear axle, and the wheel brakes (VL, VR) to the front axle of the vehicle.

[0023] The brake system comprises a first structural unit, which is designed, for example, as a first electro-hydraulic brake control unit with a valve block and a first electronic control device, and a second structural unit, which is designed, for example, as a second electro-hydraulic brake control unit with a valve block and a second electronic control device.

[0024] A pressure fluid reservoir 4 with two chambers is arranged on the first structural unit, with a first reservoir connection being assigned to the first chamber and a second reservoir connection being assigned to the second chamber. Reservoirs with three or more chambers are also possible.

[0025] A first electrically actuated pressure source 5 is arranged in the first structural unit.

[0026] In the second structural unit, a second electrically actuated pressure source 2 and wheel-individual brake pressure modulation valves are arranged, which are designed as an electrically actuated inlet valve 6 and an electrically actuated outlet valve 7 for each wheel brake 8.

[0027] The first pressure source 5 and the second pressure source 2 are connected on the pressure side to a brake supply line to which the four inlet valves 6 are connected. Thus, all four wheel brakes 8 can be actuated by means of the first pressure source 5 and / or the second pressure source 2.

[0028] An electrically actuated circuit isolation valve 40 is arranged in the brake supply line, so that when the circuit isolation valve 40 is closed, the brake supply line is separated into a first line section, to which the inlet valves 6 or the wheel brakes 8 of the rear axle are connected, and a second line section, to which the inlet valves 6 or the wheel brakes 8 of the front axle are connected. The second pressure source 2 is hydraulically connected to the first line section, and the first pressure source 5 is hydraulically connected to the second line section. 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 (via the first line section) is connected only to the wheel brakes 8 of the rear axle, and in the second brake circuit II, the first pressure source 5 (via the second line section) is connected only to the wheel brakes 8 of the front axle. The circuit isolation valve 40 is advantageously designed to be open when de-energized.

[0029] As already mentioned, the braking system comprises an inlet valve 6 and an outlet valve 7 for each hydraulically actuated wheel brake 8, which are hydraulically interconnected in pairs via central connections and each connected to a hydraulic wheel connection of the second structural unit to which the corresponding wheel brake 8 is connected. A check valve opening towards the brake supply line is connected in parallel to each of the inlet valves 6. The output connections of the outlet valves 7 are connected to the pressure fluid reservoir 4 or its second chamber via a common return line. The input connections of all inlet valves 6 can be supplied with a pressure provided by the first pressure source 5 or, for example, if the first pressure source 5 fails, by the second pressure source 2.

[0030] The first electrically controllable pressure source 5 of the valve block is designed as a hydraulic cylinder-piston arrangement (or a single-circuit electro-hydraulic actuator (linear actuator)), the piston of which can be actuated by a schematically indicated electric motor with the interposition of a rotation-translation gear, also shown schematically, and in particular can be moved forwards and backwards in order to build up and reduce pressure in a pressure chamber. The piston delimits the pressure chamber of the pressure source 5. A rotor position sensor, only shown schematically, is provided to control the electric motor. This sensor detects the rotor position of the electric motor. This sensor can be used to determine the piston position and speed, and thus the volume of brake fluid delivered or absorbed.

[0031] A system pressure line section is connected to the pressure chamber of the first electrically controllable pressure source 5. By means of this line section, the pressure source 5 or its pressure chamber is connected to a hydraulic connection of the first structural unit, which is connected to a hydraulic connection of the second structural unit via a hydraulic connecting element. This connection represents the only hydraulic pressure connection between the first and second structural units. It is a hydraulic connection for transmitting brake pressure for actuating the wheel brakes 8.

[0032] The pressure chamber is connected to the pressure fluid reservoir 4 via a (suction) line, regardless of the piston's actuation state. A check valve 53, closing toward the pressure fluid reservoir 4, is arranged in the line and connected to the second chamber. An electrically switchable valve 23 forms a further connection to this line, which is connected to the output port of the linear actuator 5. The cylinder-piston assembly 5, for example, has no sniffing holes.

[0033] The second electrically controllable pressure source 2 of the second assembly is designed, for example, as a two-piston pump whose two pressure sides are interconnected. The suction sides are connected to the return line and thus to the pressure fluid reservoir 4. The pressure sides are connected to the first line section of the brake supply line.

[0034] In addition to the pressure source 2 and the brake pressure modulation valves 6, 7, an electrically actuated, preferably normally open, isolation valve 26 is arranged in the second structural unit, for example. Isolation valve 26 is hydraulically arranged between the connection and the second line section of the brake supply line. Thus, the first pressure source 5 is detachably connected to the second line section or the brake supply line via the isolation valve 26.

[0035] The brake system includes, for example, a pressure sensor in brake circuit I, which is thus assigned to the second pressure source 2. This is advantageous for burst protection during active circuit separation, i.e., when the circuit separation valve 40 is closed. However, the pressure sensor can also be arranged in brake circuit II, as in Fig. 2 is shown.

[0036] For example, the brake system for leakage monitoring comprises a level measuring device for determining a pressure medium level in the pressure medium reservoir 4.

[0037] Each valve block is assigned an electronic control device. Each electronic control device 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.

[0038] The valve block and electronic control device are advantageously designed as an electro-hydraulic unit.

[0039] The first electronic control device controls the first pressure source 5. For example, the first pressure source 5 is supplied with energy (from a first electrical energy source) via the first electronic control device.

[0040] The second electronic control device controls the second pressure source 2. For example, the second pressure source 2 is supplied with energy (from a second electrical energy source) via the second electronic control device.

[0041] For example, the first pressure source 5 can be or is controlled exclusively by the first electronic control device and the second pressure source 2 can be or is controlled exclusively by the second electronic control device.

[0042] The brake system thus has a primary pressure source 5 and a secondary pressure source 2, each electrically operated by an ECU and having a suction port and a pressure port. No brake fluid can flow into the pressure port of the secondary pressure source 2, even when de-energized. Preferably, the primary pressure source 5 is a linear actuator with a suction check valve 53, and the secondary pressure source 2 is a piston pump. Preferably, the secondary pressure source 2 can generate a higher pressure than the primary pressure source 5.

[0043] The suction sides of the two pressure sources 2, 5 are connected to a pressure medium reservoir 4, preferably each to at least one of two separate chambers. The suction side of a linear actuator can be identical to the pressure side and can be switched between suction and discharge via appropriate valves.

[0044] The pressure side of the primary pressure source 5 is connected to a primary circuit node via an electromagnetic valve 26, also called a pressure connection valve or isolation valve.

[0045] The pressure side of secondary pressure source 2 is connected directly (without the interposition of a valve) to a secondary circuit node. The two circuit nodes are connected via an electromagnetic valve 40, also called a circuit dividing valve.

[0046] During normal operation, the pressure in the wheel brakes is built up by primary pressure source 5. The pressure is released into primary pressure source 5. The pressure is modulated for each wheel as needed by the inlet and outlet valves. If necessary, isolation valve 26 is closed so that primary pressure source 5 can draw in additional volume.

[0047] If a particularly high flow rate is required, both pressure sources 5 and 2 operate in parallel. If a particularly high pressure is required, the isolation valve 26 is closed, and the secondary pressure source 2 increases the pressure above the pressure of the primary pressure source 5. Outside of braking situations, atmospheric pressure equalization can be permanently ensured via the isolation valve 23 and the isolation valve 26.

[0048] In the event of a leak in the brake system, the circuit isolation valve 40 is closed and the system is divided into two independent brake circuits I and II.

[0049] The isolation valve 26 is preferably controlled by the secondary control unit (ECU). The following description of operation in the event of a fault refers to this valve assignment.

[0050] If the primary system fails electrically, specifically the primary control unit or its power supply, the secondary control unit closes the isolation valve 26 to build up pressure via the secondary pressure source 2. Pressure is released via the isolation valve 26 or via the outlet valves 7.

[0051] Preferably, the intake and exhaust valves are controlled by the secondary ECU so that the pressure can be modulated individually for each wheel.

[0052] If the secondary system fails electrically, specifically the secondary ECU or its voltage source, the pressure is increased and decreased via the primary pressure source 5, as in normal operation. Individual wheel pressure control is not required, but joint modulation of the wheel pressures remains possible to prevent the vehicle from being destabilized by locking wheels.

[0053] In the above operating modes, piston pump 2 is therefore the pressure source for at least two wheel brakes. To check their functionality, a check according to the invention can be performed during operation at specified times or as needed.

[0054] This is in Fig.2. The inlet valves 6 of the wheel brakes 8 are closed so that the check can be carried out while driving without brake pressure building up at the wheel brakes 8. The circuit isolation valve 40 and the isolation valve 26 are open. The isolation valve 23 remains closed. Thus, there is an open flow connection between the pressure side of the piston pump 2 and the linear actuator 5. The linear actuator 5 is now controlled to provide a constant counter torque or to maintain a constant pressure. For example, the linear actuator 5 can be controlled to a pressure of 20 bar. At the same time, the piston pump 2 is controlled to pump brake fluid. This causes the linear actuator 5 to be pushed back, whereby it absorbs the pumped volume.The absorbed volume can be determined very precisely using a motor position sensor, its relationship to the piston position and the geometry of the linear actuator 5.

[0055] In the simplest embodiment of the invention, the pump can be operated for a predetermined period of time, and the linear actuator can simply be used to check whether at least a predetermined minimum amount has been pumped. This makes it very easy to determine whether the pump is actually pumping.

[0056] For a more precise check, a second value for the pumped volume can be determined by measuring the pump's displacement. The piston pump 2 includes a current ripple counter that measures the pump rotations, which can be converted into a pumped volume using a parameter stored in the control unit. This second value can be compared with the first value from the linear actuator's volume measurement. If the deviations are within an acceptable range, it can be assumed that the pump is pumping as intended.

[0057] However, if the deviations exceed a certain tolerance, a corresponding warning signal can be issued to the driver. Alternatively, or additionally, the flow measurement of pump 2 can be recalibrated so that it delivers correct values ​​again.

[0058] The displacement measurement parameter is factory-set to a theoretical standard value. However, normal production deviations, as well as other temporal deviations due to wear and other influences, can lead to significant inaccuracies. To define the parameter more precisely and thus improve the accuracy of the displacement measurement of piston pump 2, a calibration is now performed. For this purpose, the parameter is adjusted so that the displacement determination of pump 2 corresponds to the value measured by linear actuator 5.

[0059] For example, the measurement might show that the linear actuator had to retract 3 mm to maintain a pressure of 20 bar. With a piston area of ​​363 mm, the 3 mm corresponds to 2 a volume of about 1cm 3 . With a pump piston volume of 130mm 3 and 2 piston strokes per pump revolution, this corresponds to approximately 3.8 pump revolutions.

[0060] This measurement result can then be compared with the actual detected pump strokes, and appropriate adjustments can be made. For example, the flow measurement can be adjusted by adding a factor to compensate for any discrepancies.

[0061] Additionally, a measurement can also be performed with the linear actuator 5 holding its position. The relationship between pressure and the volume pumped by the pump 2 then results solely from the elasticities in the hydraulic space, which are primarily determined by the linear actuator 5. These can be described as a pressure-volume relationship.

[0062] In order to simplify the pressure-volume behavior, only the linear actuator 5 is taken into account for the calculation and the remaining elastic components of the hydraulic components and the intermediate lines are assumed to be negligible. ΔV=ΔPSys∗pv_factor

[0063] The pv_factor can be 3bar / mm, for example ΔV=ΔPSys∗3mm3bar

[0064] If the pressure increases by 50 bar when the pump is running, for example, the pump would have to pump a volume of 150 mm 3 This corresponds to a pump piston size of 130mm 3 just over half a pump revolution. Even in this case, adjustments can be made to calibrate the flow measurement.

Claims

[1] Method for controlling a hydraulic motor vehicle brake system comprising at least one hydraulic wheel brake (8) which can be connected via at least one hydraulic valve (6) to a first (5) and / or a second pressure supply device (2), wherein the first pressure supply device (5) is a linear actuator and the second pressure supply device (2) is a piston pump, characterized by that the delivery capacity of the piston pump (2) is checked by connecting the pressure side of the piston pump (2) to the linear actuator (5) as a volume sink, the piston pump (2) is operated to deliver brake fluid which is taken up by the linear actuator (5), wherein the volume taken up by the linear actuator (5) is determined based on the piston position, piston movement and / or pV properties and is used as a measured variable for a check. [2] Method according to claim 1, characterized bythat the resulting pressure and / or the pressure curve is also used for checking [3] Method according to claim 1 or 2, characterized by that a displacement measurement of the piston pump (2) is calibrated by using the volume absorbed by the linear actuator (5) as a reference value for the calibration. [4] Method according to one of the preceding claims, characterized by that before operating the piston pump (2) the linear actuator (5) is connected to a brake fluid reservoir (4) in a flow-open manner and is moved into a position which enables a predetermined volume to be absorbed. [5] Method according to one of the preceding claims, characterized by that the displacement measurement uses sensed pump rotations and / or a model of the electrical control voltage. [6] Method according to one of the preceding claims, characterized bythat during the checking and / or calibration, an inlet valve (6) of the at least one wheel brake (8), in particular all inlet valves (6) of the wheel brakes (8) are closed, so that the piston pump (2) is connected to the linear actuator (5) as the only volume sink. [7] Method according to one of the preceding claims, characterized by that the linear actuator (5) maintains a predetermined counter-torque and / or regulates it to a predetermined pressure when receiving the pumped volume. [8] Method according to one of the preceding claims, characterized by that when the pressure is applied by means of the pump (2), no overflow valve is used and / or no pressure sensor is available on the pressure side of the pump. [9] Method according to one of the preceding claims, characterized by that the check and / or calibration is carried out during a braking operation with the inlet valves (6) open. [10] Method according to one of the preceding claims, characterized by that the linear actuator (5) is controlled to suck brake fluid from the brake fluid reservoir while a valve (26) between the linear actuator (5) and the wheel brakes (8) is closed, wherein during the sucking the pump (2) delivers brake fluid in order to provide a requested pressure in the wheel brakes (8). [11] Hydraulic motor vehicle brake system comprising at least one hydraulic wheel brake (8) which can be connected to a first and / or a second pressure supply device (2, 5) via at least one hydraulic valve (6, 26, 40), wherein the first pressure supply device (5) is a linear actuator and the second pressure supply device (2) is a piston pump, characterized bythat a control device is set up to check the delivery capacity of the piston pump (2) by connecting the pressure side of the piston pump (2) to the linear actuator (5) as a volume sink, the piston pump (2) is operated to deliver brake fluid which is taken up by the linear actuator (5), wherein the volume taken up by the linear actuator (5) is determined on the basis of the piston position and / or movement and is used as a measured variable for a check.

Images