Leakage rehabilitation

Abstract

The invention relates to a method for controlling a hydraulic motor vehicle brake system, which has a circuit isolating valve (40) that can divide and connect the hydraulic system into a first sub-circuit comprising a first pressure supply device (5) and at least one first wheel brake (8), and a second sub-circuit comprising a second pressure supply device (2), a pressure sensor (19), and at least one second wheel brake (8), wherein the circuit isolating valve (40) is closed upon detection of a leak. In order to switch back to a fault-free mode, a leak-free check is performed in the first sub-circuit, comprising the following steps: - Opening the circuit separating valve (40) so that a flow-open connection exists between the first pressure supply device (5) and the pressure sensor (19), - Determining the volume delivered by the first pressure supply device (5) and the hydraulic pressure generated thereby by means of the pressure sensor (19) - Comparison of these values ​​with a stored pV characteristic curve.

Description

[0001] The invention relates to a method for controlling a hydraulic motor vehicle brake system, which has a circuit isolation valve which can divide and connect the hydraulics into a first partial circuit comprising a first pressure supply device and at least one first wheel brake and a second partial circuit comprising a second pressure supply device, a pressure sensor and at least one second wheel brake, wherein the circuit isolation valve is closed upon detection of a leak.

[0002] Modern automotive braking systems must be highly redundant so that there is a very high probability that sufficient braking force will always be available to decelerate the vehicle. In the event of failure and / or errors in individual functions or components, redundant braking systems typically switch to corresponding error modes or fallback modes. Since these generally do not offer the full range of functions, comfort, or safety, a return to normal operating mode should be possible. However, this is only possible if the corresponding errors or failures no longer exist. This is particularly the case if the original error detection was a so-called "false positive," meaning there was actually no real error. To determine this, appropriate hydraulic self-tests or service functions must be performed.However, this generally requires a large amount of measurement data, the corresponding sensor technology of which is associated with high costs.

[0003] It is therefore an object of the present invention to enable leakage rehabilitation without increasing the costs of the brake system.

[0004] This is achieved according to the invention by carrying out a leakage check in the first partial circle, with the following steps: - Opening the circuit isolation valve so that a flow-open connection is established between the first pressure supply device and the pressure sensor, - Determining the volume delivered by the first pressure supply device and the hydraulic pressure generated thereby by means of the pressure sensor - Comparison of these values ​​with a stored pV characteristic curve.

[0005] Preferably, before the circuit isolation valve is opened, the at least one second wheel brake is isolated by closing an associated inlet valve.

[0006] The first pressure-generating device can perform a specified movement, build up a specified pressure, or pump volume. The relationship between pressure and volume is always monitored. It is advisable to generate at least a pressure greater than a threshold value, so that a detectable leakage flow occurs in the event of a leak.

[0007] The delivered volume can be determined, for example, using a position sensor of the pressure supply device and corresponding conversion variables. With the inlet valves on the second wheel brakes closed, no brake fluid flows between the two partial circuits. This minimizes further brake fluid loss in the event of a real leak.

[0008] In a preferred embodiment of the invention, before opening the circuit isolation valve, a leak test is performed in the second partial circuit by measuring a pressure curve using the pressure sensor. The circuit isolation valve is only opened if the second partial circuit is shown to be leak-tight. For this purpose, a comparison can be made with an expected pressure curve. The simplest variant is to build up pressure and lock it in, with the pressure curve then being observed to determine how quickly the locked-in pressure drops. Volume measurements can also be used and compared with a pV curve.

[0009] In a particularly preferred embodiment of the invention, the leak test is performed with the intake valves of the second partial circuit closed. Thus, the leak test is performed on the exact area that will subsequently be connected to the first partial circuit.

[0010] In a further preferred embodiment of the invention, the second partial circle comprises two wheel brakes of the rear axle and / or the first partial circle comprises two wheel brakes of the front axle.

[0011] In a further preferred embodiment of the invention, the system switches to a normal mode with the circuit isolation valve open to provide pressure when a rehabilitation check indicates that both sub-circuits are free of leaks. Thus, if there are no faults, the full functionality of the braking system can be utilized again.

[0012] In a further preferred embodiment of the invention, the stored pV characteristic curve is a pV characteristic curve of the first partial circuit, which is adapted to the additional hydraulic coupling of the pressure sensor and the connecting lines. Since a pV characteristic curve is already provided for the first partial circuit for circuit separation operation, this can be modified particularly easily.

[0013] In a further preferred embodiment of the invention, the first partial circuit does not have a pressure sensor. The method according to the invention eliminates the need for this sensor and can thus be eliminated, reducing costs.

[0014] In a further preferred embodiment of the invention, the determination of the volume delivered by the first pressure supply device and the hydraulic pressure generated thereby is carried out during a deceleration request, with the inlet valves in the second partial circuit being open. For the check, a pV characteristic curve is then used accordingly, which includes the second wheel brakes. Thus, no separate pressure build-up is required, and the check and thus, if possible, the rehabilitation can simply take place during normal operation. Provision can be made to specify minimum requirements for pressure and / or volume delivery that must be met in order to implement the leakage-free check during the deceleration request.

[0015] In a further preferred embodiment of the invention, the second pressure supply device is a piston pump. Such pumps can generate particularly high pressures at relatively low cost. Continuous volume delivery without interruptions in the suction process is also possible.

[0016] In a further preferred embodiment of the invention, the first pressure supply device is a linear actuator. This allows for particularly precise pressure positioning and, in particular, pressure reductions to be implemented very precisely. Due to a direct physical relationship between the piston position or its speed and the pumped volume, the pumped volume flow can be determined very precisely.

[0017] In a further preferred embodiment of the invention, when the circuit isolation valve is closed, a delay request in the second partial circuit is implemented by a pressure build-up by means of the second pressure supply device and / or in the first partial circuit by means of the first pressure supply device.

[0018] The object is also achieved by a hydraulic motor vehicle brake system having a circuit separation valve which can divide and connect the hydraulics into a first partial circuit having a first pressure supply device and at least one first wheel brake and a second partial circuit having a second pressure supply device, a pressure sensor and at least one second wheel brake, wherein a control device of the motor vehicle brake system is configured to carry out the above method.

[0019] 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;

[0020] 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.

[0021] 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 ECU1, 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 ECU2.

[0022] 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.

[0023] A first electrically actuated pressure source 5 is arranged in the first structural unit.

[0024] 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.

[0025] 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.

[0026] 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, or a first partial circuit and a second partial circuit.In the first brake circuit I, pressure source 2 is connected (via the first line section) only to the wheel brakes 8 of the rear axle, and in the second brake circuit II, the first pressure source 5 is connected (via the second line section) only to the wheel brakes 8 of the front axle. The circuit separation valve 40 is advantageously designed to be open when de-energized. Such an operating mode can be called circuit separation mode or ACS for "Active Circuit Separation."

[0027] 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.

[0028] 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, 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. To control the electric motor, a rotor position sensor (only schematically indicated) is provided that detects the rotor position of the electric motor. By means of this sensor, the piston position and speed, and thus the released or absorbed brake fluid volume, can be determined.

[0029] A system pressure line section is connected to the pressure chamber of the first electrically controllable pressure source 5. By means of the 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, in particular the only hydraulic connection, between the first and second structural units. It is a hydraulic connection for transmitting brake pressure for actuating the wheel brakes 8.

[0030] The pressure chamber is connected to the pressure fluid reservoir 4 via a (suction) line, regardless of the actuation state of the piston. A check valve 53, closing in the direction of the pressure fluid reservoir 4, is arranged in the line in connection with 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. This isolating valve 23 is designed to be open when de-energized, so that when de-energized, the wheel brakes 8 are connected to the brake fluid reservoir 4. The cylinder-piston arrangement 5, for example, has no sniffing holes.

[0031] 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.

[0032] 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.

[0033] For example, the braking system includes 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 located in brake circuit II.

[0034] 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.

[0035] Each valve block is assigned an electronic control unit (ECU1 and ECU2). Each electronic control unit 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, as is known in the art.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] The brake system 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. For example, 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] During normal operation, the pressure in the wheel brakes is built up by primary pressure source 5. The pressure in primary pressure source 5 is released by retracting its piston. 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.

[0044] 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.

[0045] Isolation valve 26 is preferably controlled by the secondary ECU. The following description of operation in the event of a fault refers to this valve assignment.

[0046] If the primary system fails electrically, particularly the primary or its power supply, the secondary ECU closes the isolation valve 26 to build up pressure via the secondary pressure source 2. Pressure is released via the exhaust valves 7. Preferably, the intake and exhaust valves are controlled by the secondary ECU so that the pressure can be modulated for each individual wheel.

[0047] 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.

[0048] The control units ECU1 and ECU2 are configured to implement a pressure buildup using the linear actuator 5 and / or the piston pump 2 based on pressure requests. These requests can originate from automatic functions of the assistance program and, in particular, from the driver, who transmits the driver's request via the brake pedal. This is transmitted to the control units as a brake pedal actuation variable. The brake pedal actuation variable can be a brake pedal travel, a brake pedal force, and / or similar variables.

[0049] If a leak occurs in the brake system, the circuit separation valve 40 is closed, dividing the system into two independent brake circuits, I and II. The leak can be monitored using various monitors. A Volume Deviation Monitor (VDM) is a leak monitoring device that can detect a hydraulic leak based on the pressure-to-volume ratio (PV ratio). The volume is determined by sensing the linear actuator or pedal position. The expected PV behavior can be stored using functions or stored characteristic curves. A low brake fluid sensor level (BFLS) in the reservoir or excessively low pressure can also lead to leak detection.

[0050] To restore the brake system to full functionality, a so-called rehabilitation process must be performed. This involves verifying that no leaks have been detected on either side of the circuit isolation valve 40, i.e., in both partial circuits. However, this is necessary all the way to the wheel brakes, since the leak may be located not only in the valve block, but also directly in the wheel brakes or the supply lines to the wheel brakes.

[0051] According to the invention, self-tests are therefore provided to determine the absence of leaks. In the second brake circuit, when implementing a pressure request for the rear wheel brakes, the volume delivered by hydraulic pump 2 and the resulting pressure, which is measured by the pressure sensor, can be compared with a pV characteristic curve of the second partial circuit. Alternatively, a pressure build-up can be implemented explicitly for the self-test, independent of a pressure request, particularly when stationary.

[0052] In the first brake circuit, no pressure sensor is available for such a self-test. Using variables from the linear actuator 5, such as its current, power, and / or torque, is too imprecise to meet high safety standards. The invention therefore provides for the pressure sensor of the second partial circuit to be used. In order to avoid the risk of unnecessary loss of further brake fluid, a preliminary test is carried out in the second partial circuit to determine whether there are any leaks at least up to the inlet valves. For this purpose, the inlet valves 6 of the wheel brakes 8 of the second partial circuit are closed, creating a hydraulically separated area between the outlet side of the pump 2, the inlet valves 6, and the circuit isolation valve 40, in which the pressure sensor is located. For this leak test, pressure can be built up using the pump 2.After pump 2 is shut down, this pressure remains trapped by the closed valves 6, 40 and the check valve at the pump 2 outlet. Pressure reduction therefore only occurs through leakage flows, which can never be completely avoided. The pressure sensor can thus measure a slow pressure reduction, from which the total leakage flow can be calculated. If the leakage flow and thus the pressure reduction are within an acceptable range and less than a specified threshold, this area is assumed to be sealed.

[0053] In this case, the circuit isolation valve can then be opened. Since the section now connected to the first partial circuit is a hydraulically rigid space and can be considered sealed, essentially no brake fluid flows through the circuit isolation valve 40.

[0054] The first pressure supply device is now connected to the pressure sensor, allowing it to be used for the hydraulic self-test of the first partial circuit. For this purpose, a volume can be pumped as part of an external pressure request or explicitly for the hydraulic self-test, thus building up pressure to the front axle wheel brakes. The volume and pressure are again compared with an expected behavior according to a pV characteristic curve. If the deviation is smaller than a threshold value, the first partial circuit can be assumed to be leak-tight.

[0055] If both partial circuits are tested as tight, the braking system switches back to a normal operating mode in which the circuit isolation valve is open.

[0056] The method according to the invention thus minimizes the time the braking system must operate in a fault mode. Therefore, the driver only needs to be shown a warning light for a short time, thus avoiding the need to visit a workshop.

Claims

[1] Method for controlling a hydraulic motor vehicle brake system, which has a circuit separation valve (40) which can divide and connect the hydraulics into a first partial circuit comprising a first pressure supply device (5) and at least one first wheel brake (8) and a second partial circuit comprising a second pressure supply device (2), a pressure sensor (19) and at least one second wheel brake (8), wherein the circuit separation valve (40) is closed upon detection of a leak, characterized by that a leakage check is carried out in the first partial circle, with the following steps: - opening the circuit isolation valve (40) so that a flow-open connection is provided between the first pressure supply device (5) and the pressure sensor (19), - Determining the volume delivered by the first pressure supply device (5) and the hydraulic pressure generated thereby by means of the pressure sensor (19) - Comparison of these values ​​with a stored pV characteristic curve. [2] Method according to claim 1 characterized by that before opening the circuit isolation valve (40) a leak test is carried out in the second partial circuit by measuring a pressure curve by means of the pressure sensor (19), wherein the circuit isolation valve (40) is only opened when the leaktightness of the second partial circuit is demonstrated. [3] Method according to claim 2 characterized by that the leak test is carried out with the inlet valves (6) of the second partial circuit closed. [4] Method according to one of the preceding claims, characterized by that the second partial circle comprises two wheel brakes (8) of the rear axle and / or the first partial circle comprises two wheel brakes (8) of the front axle. [5] Method according to one of the preceding claims, characterized bythat a switch is made to a normal mode with the circuit isolation valve (40) open to provide pressure when a rehabilitation check indicates that there are no leaks in both sub-circuits. [6] Method according to one of the preceding claims, characterized by that the stored pV characteristic curve is a pV characteristic curve of the first partial circuit, which is adapted to the additional hydraulic coupling of the pressure sensor (19) and the connecting lines. [7] Method according to one of the preceding claims, characterized by that the first partial circuit does not have a pressure sensor. [8] Method according to one of the preceding claims, characterized by that the determination of the volume delivered by the first pressure supply device (5) and the hydraulic pressure generated thereby is carried out during a deceleration request, wherein the inlet valves are open in the first partial circuit. [9] Method according to one of the preceding claims, characterized by that the second pressure supply device (2) is a piston pump. [10] Method according to one of the preceding claims, characterized by that the first pressure supply device (5) is a linear actuator. [11] Method according to one of the preceding claims, characterized by that when the circuit isolation valve (40) is closed, a delay request in the second partial circuit is implemented by a pressure build-up by means of the second pressure supply device (2) and / or in the first partial circuit by means of the first pressure supply device (5). [12] Hydraulic motor vehicle brake system comprising a circuit separation valve (40) which can divide and connect the hydraulics into a first partial circuit comprising a first pressure supply device (5) and at least one first wheel brake (8) and a second partial circuit comprising a second pressure supply device (2), a pressure sensor (19) and at least one second wheel brake (8), characterized by that a control device of the motor vehicle brake system is designed to carry out a method according to one of claims 1 to 11.

Images