A hydraulic brake circuit fault diagnosis method based on OneBox brake-by-wire system

Abstract

This specification discloses a hydraulic brake circuit fault diagnosis method based on the OneBox wire control brake system, including four parts: electric cylinder circuit fault diagnosis, master cylinder and simulator brake circuit fault diagnosis, PSV fault diagnosis, and CSV fault diagnosis. The embodiment of this specification detects brake system circuit faults through four diagnostic processes, uses pressure sensors and electric cylinder units to achieve pressure detection and pressure increase and decrease control, realizes pressure building function diagnosis, valve, hydraulic cylinder, wheel cylinder leakage performance diagnosis; valve, electric power unit jam fault diagnosis, can quickly and comprehensively detect the boost isolation valve, master cylinder isolation valve, simulation valve, pedal simulator, isolation valve and wheel cylinder with high accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile braking, and in particular to a hydraulic brake circuit fault diagnosis method based on a OneBox brake-by-wire system. Background Art

[0002] In recent years, the intelligent driving technology of automobiles has developed rapidly, and the wire control brake system, which is indispensable in the intelligent driving solution, has become increasingly important. There are currently two main solutions for the wire control brake system, namely the Two-box solution of the "eBooster+ESC" combination and the OneBox solution that integrates the brake assist and ESC functions. Among them, OneBox integrates the functions of two control units into one control unit, and its integration and complexity will be higher. Once a failure occurs in the installation of such a brake system with high integration and complexity, it is more difficult to check and it is not easy to locate the source of the fault. Therefore, a method for fault diagnosis of the OneBox hydraulic brake circuit is needed. When a fault occurs in the brake system, the brake system is controlled by external commands without disassembling the OneBox components and related pipelines to quickly and accurately check whether the hydraulic brake circuit has a fault and the fault location.

[0003] Therefore, it is urgent to study a fault diagnosis method suitable for highly integrated brake systems to quickly and accurately troubleshoot faults. Summary of the invention

[0004] This specification provides a hydraulic brake circuit fault diagnosis method based on a OneBox brake-by-wire system to overcome at least one technical problem existing in the related art.

[0005] According to an embodiment of the present specification, a hydraulic brake circuit fault diagnosis method based on a OneBox brake-by-wire system is provided, comprising:

[0006] Obtain the actual vehicle calibration parameters of each device of the hydraulic brake circuit of the vehicle to be tested under normal conditions. The hydraulic brake circuit includes a hydraulic unit, a master cylinder unit, a circuit solenoid valve unit, a brake wheel cylinder, an isolation valve unit, a simulator and an electric cylinder unit.

[0007] A hydraulic unit, storing hydraulic pressure, used to connect the simulator, the master cylinder unit and the electric cylinder unit, including a fluid storage tank and hydraulic pipelines;

[0008] The master cylinder unit includes a master cylinder, a pedal rod, a displacement sensor, a test valve TSV and a first pressure sensor P1. The master cylinder is connected to the liquid storage tank through the hydraulic unit. The test valve TSV is arranged between the master cylinder unit and the liquid storage tank. The pedal rod is arranged on the master cylinder. The displacement sensor is arranged on the master cylinder to detect the braking displacement of the pedal rod. The first pressure sensor P1 is arranged on the master cylinder.

[0009] The circuit solenoid valve unit includes eight solenoid valves, including four boost solenoid valves ISO1, ISO2, ISO3, ISO4 and four pressure reducing solenoid valves Dump1, Dump2, Dump3, Dump4, ISO4 and Dump4 are arranged in series to form a first passage, ISO3 and Dump3 are arranged in series to form a second passage, ISO2 and Dump2 are arranged in series to form a third passage, ISO1 and Dump1 are arranged in series to form a fourth passage, the brake wheel cylinder includes four wheel cylinders, each wheel cylinder is connected to a passage, wherein the first passage is connected in parallel with the second passage, the third passage is connected in parallel with the fourth passage, and the four passages are connected to the hydraulic unit to form a circuit;

[0010] The isolation valve unit includes a first master cylinder isolation valve CSV1, a second master cylinder isolation valve CSV2, a first electric cylinder isolation valve PSV1 and a second electric cylinder isolation valve PSV2, wherein the first master cylinder isolation valve CSV1 is connected to the master cylinder and one end of the first passage and the second passage in parallel through a hydraulic pipeline, the second master cylinder isolation valve CSV2 is connected to the master cylinder and one end of the third passage and the fourth passage in parallel through a hydraulic pipeline, the first electric cylinder isolation valve PSV2 is connected to the electric cylinder and one end of the first passage and the second passage in parallel through a hydraulic pipeline, and the second electric cylinder isolation valve PSV2 is connected to the electric cylinder and one end of the third passage and the fourth passage in parallel through a hydraulic pipeline;

[0011] One end of the simulator is connected to the fluid storage tank through a hydraulic pipeline, and the other end is connected to the solenoid valve SSV through a hydraulic pipeline and connected to the master cylinder;

[0012] The electric cylinder unit includes an electric cylinder, a piston, a motor, a pressure relief valve PRV and a second pressure sensor P2. The motor drives the piston to move to change the pressure of the electric cylinder. The pressure relief valve is arranged between the electric cylinder unit and the hydraulic unit. The second pressure sensor is arranged on the pipeline between the electric cylinder and the electric cylinder isolation valve.

[0013] The electric cylinder, piston, first electric cylinder isolation valve PSV1, second electric cylinder isolation valve PSV2, second pressure sensor P2, pressure relief valve PRV and connected hydraulic pipelines constitute the electric cylinder circuit; the first master cylinder isolation valve CSV1, second master cylinder isolation valve CSV2, solenoid valve SSV, test valve TSV, simulator, master cylinder, first pressure sensor P1 constitute the master cylinder and simulator brake circuit;

[0014] The actual vehicle calibration parameters include the pressure value range of the first pressure sensor P1, the pressure value range of the second pressure sensor P2, the displacement range of the piston and the deviation value range of the brake circuit liquid volume;

[0015] Within the preset time, control the electric cylinder piston to move to the initial position, control PSV1, PSV2, SSV, PRV, and Dump1, Dump2, Dump3, Dump4 to close, control CSV1, CSV2, TSV, ISO1, ISO2, ISO3, ISO4 to open, control the electric cylinder unit to increase pressure, compare the actual parameters with the actual vehicle calibration parameters, and determine the fault of the hydraulic brake circuit based on the comparison results of the actual parameters and the actual vehicle calibration parameters. First, perform fault diagnosis on the electric cylinder circuit.

[0016] If the electric cylinder circuit detects a non-PSV fault, determine the fault location and fault type;

[0017] If the electric cylinder circuit detects a PSV fault, perform PSV fault diagnosis to determine the faulty valve and fault type;

[0018] On the contrary, the master cylinder and simulator brake circuit are fault diagnosed.

[0019] If there is a fault in the master cylinder and simulator brake circuit, determine the specific faulty valve and fault type;

[0020] Conversely, CSV faults are diagnosed to determine the fault condition of the CSV valve;

[0021] Obtain the fault diagnosis result of the hydraulic brake circuit of the vehicle to be tested.

[0022] Furthermore, the step of diagnosing a fault in the electric cylinder circuit includes:

[0023] S101, control the electric cylinder unit to increase pressure steadily at a preset speed. If the pressure value collected by the second pressure sensor P2 reaches the target pressure value within a preset time, and the piston advance distance is within the displacement range, continue the test; otherwise, it is determined to be a serious leakage fault and the test is stopped;

[0024] S102, control the electric cylinder unit to continue to increase pressure for 1 second. In the first 500ms, calculate the piston advance distance and the liquid volume deviation of the electric cylinder circuit. After 500ms, perform the following fault diagnosis based on the calculation results:

[0025] If the piston advance distance is not greater than the first threshold value, and the liquid volume deviation of the electric cylinder circuit is not greater than the second threshold value, it is determined that there is no fault in the electric cylinder circuit, and the master cylinder and simulator brake circuit diagnosis is entered;

[0026] If the piston advance distance is greater than the first threshold and the liquid volume deviation of the electric cylinder circuit is not greater than the second threshold, it is determined to be a PSV or PRV leakage fault, and the process goes to step S103;

[0027] If the liquid volume deviation of the electric cylinder circuit is greater than the second threshold value and not greater than the third threshold value, it is determined to be a PSV fault;

[0028] If the liquid volume deviation of the electric cylinder circuit is greater than the third threshold, it is judged as a PRV failure;

[0029] S103, control the piston to return to the initial position, close the four ISO valves, CSV1, and CSV2. If the piston returns to the initial position within the preset time period, enter step S104. Otherwise, it is determined that the electric cylinder piston is stuck and the test is stopped;

[0030] S104, control the electric cylinder unit to increase pressure steadily at a preset speed. If the pressure value collected by the first pressure sensor P1 reaches the target pressure within a preset time, and the piston forward position is within the displacement range, enter step S105. Otherwise, it is determined to be a PRV leakage fault;

[0031] S105, continue to increase the pressure for 1 second. In the first 500ms, calculate the piston advance distance and the liquid volume deviation of the electric cylinder circuit. After 500ms, perform the following fault diagnosis based on the calculation results:

[0032] If the piston advance distance is between the fourth threshold and the sixth threshold and the liquid volume deviation is not greater than the fifth threshold, it is determined that the PRV is not faulty and the master cylinder and simulator brake circuit diagnosis is entered;

[0033] If the piston advance distance is not greater than the fourth threshold and the liquid volume deviation is not greater than the fifth threshold, it is determined to be a PSV opening failure;

[0034] If the piston advance distance is not greater than the sixth threshold and the liquid volume deviation is greater than the fifth threshold, it is determined to be a PRV failure;

[0035] If the piston advance distance is greater than the sixth threshold, it is determined to be a PRV failure.

[0036] Furthermore, the liquid volume deviation of the electric cylinder circuit is calculated according to the following steps:

[0037] The brake circuit fluid volume change value under normal conditions is obtained based on the brake circuit PV curve of the actual vehicle test, and compared with the hydraulic cylinder volume change value caused by the piston movement, the deviation value of the brake circuit fluid volume is obtained.

[0038] Furthermore, the step of performing fault diagnosis on the master cylinder and the simulator brake circuit and determining the specific fault valve and the fault type if there is a fault in the master cylinder and the simulator brake circuit comprises:

[0039] S201, when there is no fault in the electric cylinder circuit, control all hydraulic valves and pistons to return to their initial states;

[0040] S202, open PSV1, close TSV, close CSV2, control the electric cylinder unit to increase pressure with a preset fixed boost gradient, if the pressure value collected by the first pressure sensor reaches the target pressure within the preset time and the piston advance distance is within the displacement range, enter step S203; otherwise, it is determined that the master cylinder and the simulator brake circuit have serious leakage faults, and the test is stopped;

[0041] S203, control the electric cylinder unit to reduce pressure with a preset fixed pressure reduction gradient. If the pressure value collected by the first pressure sensor reaches the pressure reduction target value within a preset time, and the piston advance distance is within the displacement range, enter step S204; otherwise, it is determined that there is a serious leakage fault in this brake circuit, and the test is stopped;

[0042] S204, maintain the current pressure value for 1s, enter the pressure holding stage, if the pressure value of the first pressure sensor P1 is not greater than the seventh threshold value and the piston movement speed is not greater than the eighth threshold value, it is determined that the piston of the master cylinder sub-chamber in the circuit is stuck or the CSV1 is not opened, and the test is stopped; if the piston advance distance is greater than the seventh threshold value or the piston movement speed is greater than the eighth threshold value, it is determined that the circuit has a serious leakage fault, and the test is stopped; if the pressure value of the first pressure sensor P1 is greater than the seventh threshold value and there is no serious leakage fault, it is determined that the master cylinder and CSV are not faulty, and the process goes to step S205;

[0043] S205, testing the simulator circuit, controlling the electric cylinder to keep the current piston state unchanged, opening the SSV, and if the pressure value of the first pressure sensor P1 or the second pressure sensor P2 is greater than the ninth threshold, determining that the SSV is stuck; otherwise, entering step S206;

[0044] S206, close the SSV, control the electric cylinder unit to push the piston forward at a preset propulsion speed, open the SSV, and if the pressure value of the first pressure sensor P1 or the second pressure sensor P2 is greater than the ninth threshold value, determine that the TSV is stuck; otherwise, determine that the master cylinder and the simulator brake circuit are not faulty.

[0045] Furthermore, if the electric cylinder circuit detects a PSV fault, the steps of performing PSV fault diagnosis and determining the faulty valve and the fault type include:

[0046] S301, when the electric cylinder circuit fault diagnosis determines that it is a PSV fault, control all hydraulic valves to return to the initial state and the electric cylinder piston to return to the initial position;

[0047] S302, open PSV1, close CSV1, close 4 ISOs, control the electric cylinder unit to increase pressure steadily at the preset speed,

[0048] If the pressure value collected by the second pressure sensor P2 reaches the target pressure within the preset time period, and the piston forward position is within the displacement range, step S303 is executed;

[0049] Otherwise, it is judged as a serious leakage fault and the test is stopped;

[0050] S303, control the electric cylinder unit to continue pressurizing, the fault diagnosis is as follows:

[0051] If the piston advance distance is not greater than the tenth threshold, it is determined that PSV1 is stuck;

[0052] If the piston advance distance is between the sixth threshold and the tenth threshold and the P1 pressure value is not greater than the ninth threshold, it is determined that PSV1 has no fault and the process goes to step S304;

[0053] If the piston advance distance is between the sixth threshold and the tenth threshold and the P1 pressure value is greater than the ninth threshold, it is determined that PSV2 has a leakage fault;

[0054] S304, open PSV2 and CSV1, close PSV1 and CSV2, control the electric cylinder unit to increase pressure steadily at a preset speed, if within a preset time, the pressure value collected by the second pressure sensor P2 reaches the target pressure and the piston forward position is within the displacement range, enter step S305, otherwise, it is determined to be a serious leakage fault and the test is stopped;

[0055] S305, continue to boost pressure and perform the following fault diagnosis:

[0056] If the piston advance distance is not greater than the tenth threshold, it is determined that the PSV2 valve is stuck;

[0057] If the piston advance distance is between the sixth threshold and the tenth threshold and the first P1 pressure is not greater than the ninth threshold, it is determined that PSV2 has no fault;

[0058] If the piston advancement distance is between the sixth threshold and the tenth threshold and the first P1 pressure is greater than the ninth threshold, it is determined that PSV1 has a leakage fault.

[0059] Furthermore, the step of diagnosing the CSV fault and determining the fault condition of the CSV valve includes:

[0060] S401, when the electric cylinder circuit fault diagnosis is normal, control all hydraulic valves and electric cylinder pistons to return to their initial states;

[0061] S402, open PSV1, close CSV1, close the four ISO valves, control the electric cylinder unit to increase pressure steadily at a preset speed, if within the preset time, the pressure value collected by the second pressure sensor P2 reaches the target pressure, and the piston forward position is within the displacement range, enter step S403, otherwise, it is judged as a serious leakage fault and the test is stopped;

[0062] S403, continue to pressurize, the fault diagnosis is as follows:

[0063] If the piston advance distance is not greater than the sixth threshold and the P1 pressure value is greater than the ninth threshold, it is determined that CSV1 is leaking;

[0064] If the piston advance distance is not greater than the eleventh threshold and the pressure value collected by the first sensor P1 is not greater than the ninth threshold, then CSV1 and ISO3 and ISO4 valves are all fault-free, and the process goes to step S404;

[0065] If the piston advance distance is between the sixth threshold and the eleventh threshold and the pressure collected by the first pressure sensor P1 is not greater than the ninth threshold, the ISO valve has a leakage fault;

[0066] S404, open PSV2 and CSV1, close PSV1 and CSV2, control the electric cylinder unit to increase pressure steadily at a preset speed, within a preset time, the pressure value collected by the second pressure sensor P2 reaches the target pressure, and the piston forward position is within the displacement range, enter step S405, otherwise, it is judged as a serious leakage fault and the test is stopped;

[0067] S405, continue to pressurize, the fault diagnosis is as follows:

[0068] If the piston advance distance is not greater than the sixth threshold and the pressure value of the first pressure sensor P1 is greater than the ninth threshold, it is determined that CSV2 is leaking;

[0069] If the piston advance distance is not greater than the eleventh threshold and the pressure value of the first pressure sensor P1 is not greater than the ninth threshold, then there is no fault in CSV2 and ISO1 and ISO2 valves;

[0070] If the piston advance distance is between the sixth threshold value and the eleventh threshold value and the pressure value of the first sensor P1 is not greater than the ninth threshold value, the ISO valve has a leakage fault.

[0071] The beneficial effects of the embodiments of this specification are as follows:

[0072] The embodiments of this specification provide a hydraulic brake circuit fault diagnosis method based on the OneBox brake-by-wire system. Aiming at the highly integrated system design of the brake-by-wire system, four diagnostic processes are reasonably designed by utilizing the existing pressure sensors and electric cylinder units of the brake system. The system automatically selects the steps to be executed according to the current state, and can realize comprehensive fault diagnosis and pressure building function diagnosis of the brake circuit, including various valves, hydraulic cylinders, wheel cylinders, leakage performance diagnosis, and various valves and electric cylinder unit jamming fault diagnosis. The method of the embodiments of this specification can realize rapid and comprehensive detection of boost isolation valves, master cylinder isolation valves, simulation valves, pedal simulators, isolation valves and wheel cylinders, with high accuracy and strong practicality.

[0073] The innovative features of the embodiments of this specification include:

[0074] 1. In this manual, the fault diagnosis of the hydraulic brake system is divided into four parts: electric cylinder fault diagnosis, master cylinder and simulator brake circuit fault diagnosis, PSV fault diagnosis, and CSV fault diagnosis. One of the innovative points of the embodiments of this manual is to complete fault detection by utilizing the status of the existing equipment in the system.

[0075] 2. In this specification, the boost isolation valve, master cylinder isolation valve, simulation valve, pedal simulator, isolation valve and wheel cylinder are quickly and comprehensively tested with high accuracy, which is one of the innovative points of the embodiments of this specification.

[0076] 3. In this specification, the four diagnostic processes do not need to be executed in full. The system can automatically select the steps to be executed according to the current status. The high efficiency of fault detection is one of the innovative points of the embodiments of this specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] In order to more clearly illustrate the technical solutions in the embodiments of this specification or related technologies, the drawings required for use in the embodiments or related technical descriptions will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0078] Figure 1 A schematic diagram of the structure of the hydraulic brake circuit of the OneBox brake-by-wire system provided in an embodiment of this specification;

[0079] Figure 2 A flow chart of a OneBox brake-by-wire system hydraulic brake circuit diagnostic method provided in an embodiment of this specification;

[0080] Figure 3 A schematic diagram of a flow chart of the electric cylinder circuit diagnostic steps provided in an embodiment of this specification;

[0081] Figure 4 A schematic flow chart of the master cylinder and simulator brake circuit diagnostic steps provided in an embodiment of this specification;

[0082] Figure 5 A flowchart of PSV fault diagnosis steps provided in an embodiment of this specification;

[0083] Figure 6 A flowchart of CSV fault diagnosis steps provided in an embodiment of this specification. DETAILED DESCRIPTION

[0084] The following will be combined with the drawings in the embodiments of this specification to clearly and completely describe the technical solutions in the embodiments of this specification. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0085] It should be noted that the terms "including" and "having" and any variations thereof in the embodiments of this specification and the accompanying drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device including a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units that are not listed, or may optionally include other steps or units that are inherent to these processes, methods, products or devices.

[0086] The embodiments of this specification disclose a hydraulic brake circuit fault diagnosis method based on the OneBox wire control brake system, including four parts: electric cylinder fault diagnosis, master cylinder and simulator brake circuit diagnosis, PSV fault diagnosis, and CSV fault diagnosis.

[0087] First, the actual vehicle calibration parameters of each device of the hydraulic brake circuit of the vehicle to be tested under normal conditions are obtained.

[0088] Figure 1 This is a schematic diagram of the structure of the hydraulic brake circuit of the OneBox wire control brake system provided in an embodiment of this specification. Figure 1 As shown, the hydraulic brake circuit includes a hydraulic unit 1 , a master cylinder unit 2 , a circuit solenoid valve unit 3 , a wheel brake cylinder 4 , an isolation valve unit 5 , a simulator 6 and an electric cylinder unit 7 .

[0089] The hydraulic unit 1 stores hydraulic pressure and is used to connect the simulator, the master cylinder unit and the electric cylinder unit, and includes a fluid storage tank and hydraulic pipelines.

[0090] The master cylinder unit 2 includes a master cylinder, a pedal rod, a displacement sensor, a test valve TSV and a first pressure sensor P1. The master cylinder is connected to the fluid storage tank through a hydraulic unit. The test valve TSV is arranged between the master cylinder unit and the fluid storage tank. The pedal rod is arranged on the master cylinder. The displacement sensor is arranged on the master cylinder to detect the braking displacement of the pedal rod. The first pressure sensor P1 is arranged on the master cylinder.

[0091] The circuit solenoid valve unit 3 includes eight solenoid valves, including four boost solenoid valves ISO1, ISO2, ISO3, ISO4 and four pressure reducing solenoid valves Dump1, Dump2, Dump3, Dump4, ISO4 and Dump4 are arranged in series to form a first passage, ISO3 and Dump3 are arranged in series to form a second passage, ISO2 and Dump2 are arranged in series to form a third passage, and ISO1 and Dump1 are arranged in series to form a fourth passage. The brake wheel cylinder 4 includes four wheel cylinders, each wheel cylinder is connected to a passage, wherein the first passage is connected in parallel with the second passage, the third passage is connected in parallel with the fourth passage, and the four passages are connected to the hydraulic unit to form a circuit.

[0092] The isolation valve unit 5 includes a first master cylinder isolation valve CSV1, a second master cylinder isolation valve CSV2, a first electric cylinder isolation valve PSV1 and a second electric cylinder isolation valve PSV2, wherein the first master cylinder isolation valve CSV1 is connected to the master cylinder and one end of the first passage and the second passage in parallel through a hydraulic pipeline, the second master cylinder isolation valve CSV2 is connected to the master cylinder and one end of the third passage and the fourth passage in parallel through a hydraulic pipeline, the first electric cylinder isolation valve PSV2 is connected to the electric cylinder and one end of the first passage and the second passage in parallel through a hydraulic pipeline, and the second electric cylinder isolation valve PSV2 is connected to the electric cylinder and one end of the third passage and the fourth passage in parallel through a hydraulic pipeline.

[0093] One end of the simulator 6 is connected to the fluid storage tank through a hydraulic pipeline, and the other end is connected to the solenoid valve SSV through a hydraulic pipeline and connected to the master cylinder.

[0094] The electric cylinder unit 7 includes an electric cylinder, a piston, an electric motor, a pressure relief valve PRV and a second pressure sensor P2. The electric motor drives the piston to move to change the pressure of the electric cylinder. The pressure relief valve is arranged between the electric cylinder unit and the hydraulic unit. The second pressure sensor is arranged on the pipeline between the electric cylinder and the electric cylinder isolation valve.

[0095] The electric cylinder, piston, first electric cylinder isolation valve PSV1, second electric cylinder isolation valve PSV2, second pressure sensor P2, pressure relief valve PRV and interconnected hydraulic pipelines constitute the electric cylinder circuit; the first master cylinder isolation valve CSV1, second master cylinder isolation valve CSV2, solenoid valve SSV, test valve TSV, simulator, master cylinder, first pressure sensor P1 constitute the master cylinder and simulator braking circuit.

[0096] The actual vehicle calibration parameters include the pressure value range of the first pressure sensor P1, the pressure value range P2 of the second pressure sensor, the displacement range of the piston, and the deviation value range of the brake circuit fluid volume.

[0097] Within the preset time, control the electric cylinder piston to move to the initial position, control PSV1, PSV2, SSV, PRV, and Dump1, Dump2, Dump3, and Dump4 to be closed, control CSV1, CSV2, TSV, ISO1, ISO2, ISO3, and ISO4 to be opened, control the electric cylinder unit to increase pressure, compare the actual parameters with the actual vehicle calibration parameters, and determine the fault of the hydraulic brake circuit based on the comparison results of the actual parameters and the actual vehicle calibration parameters.

[0098] Figure 2 This is a flow chart of a OneBox brake-by-wire system hydraulic brake circuit diagnostic method provided in an embodiment of this specification. Figure 2 As shown, firstly, the electric cylinder circuit is diagnosed for fault. If the electric cylinder circuit detects a non-PSV fault, the fault location and fault type are determined. If the electric cylinder circuit detects a PSV fault, PSV fault diagnosis is performed to determine the faulty valve and fault type. Otherwise, the master cylinder and simulator brake circuits are diagnosed for fault. If the master cylinder and simulator brake circuits have faults, the specific faulty valve and fault type are determined. Otherwise, the CSV fault is diagnosed to determine the fault condition of the CSV valve. The fault diagnosis result of the hydraulic brake circuit of the vehicle to be tested is obtained.

[0099] Figure 3 This is a flow chart of the electric cylinder circuit diagnosis steps provided in one embodiment of this specification. Figure 3 As shown in the figure, the steps for fault diagnosis of the electric cylinder circuit include:

[0100] S101, control the electric cylinder unit to increase pressure steadily at a preset speed. If the pressure value collected by the second pressure sensor P2 reaches the target pressure value within a preset time and the piston advance distance is within the displacement range, continue testing; otherwise, it is determined to be a serious leakage fault and the test is stopped.

[0101] S102, control the electric cylinder unit to continue to increase pressure for 1 second. In the first 500ms, calculate the piston advance distance and the liquid volume deviation of the electric cylinder circuit. After 500ms, perform the following fault diagnosis based on the calculation results:

[0102] If the piston advance distance is not greater than the first threshold value, and the liquid volume deviation of the electric cylinder circuit is not greater than the second threshold value, it is determined that there is no fault in the electric cylinder circuit, and the master cylinder and simulator brake circuit diagnosis is entered;

[0103] If the piston advance distance is greater than the first threshold and the liquid volume deviation of the electric cylinder circuit is not greater than the second threshold, it is determined to be a PSV or PRV leakage fault, and the process goes to step S103;

[0104] If the liquid volume deviation of the electric cylinder circuit is greater than the second threshold value and not greater than the third threshold value, it is determined to be a PSV fault;

[0105] If the liquid volume deviation of the electric cylinder circuit is greater than the third threshold, it is determined to be a PRV failure.

[0106] S103, control the piston to return to the initial position, close the four ISO valves, CSV1, and CSV2. If the piston returns to the initial position within a preset time period, enter step S104. Otherwise, it is determined that the electric cylinder piston is stuck and the test is stopped.

[0107] S104, control the electric cylinder unit to increase pressure steadily at a preset speed. If the pressure value collected by the first pressure sensor P1 reaches the target pressure within a preset time and the piston forward position is within the displacement range, enter step S105. Otherwise, it is determined to be a PRV leakage fault.

[0108] S105, continue to increase the pressure for 1 second. In the first 500ms, calculate the piston advance distance and the liquid volume deviation of the electric cylinder circuit. After 500ms, perform the following fault diagnosis based on the calculation results:

[0109] If the piston advance distance is between the fourth threshold and the sixth threshold and the liquid volume deviation is not greater than the fifth threshold, it is determined that the PRV is not faulty and the master cylinder and simulator brake circuit diagnosis is entered;

[0110] If the piston advance distance is not greater than the fourth threshold and the liquid volume deviation is not greater than the fifth threshold, it is determined to be a PSV opening failure;

[0111] If the piston advance distance is not greater than the sixth threshold and the liquid volume deviation is greater than the fifth threshold, it is determined to be a PRV failure;

[0112] If the piston advance distance is greater than the sixth threshold, it is determined to be a PRV failure.

[0113] In a specific implementation, the liquid volume deviation of the electric cylinder circuit is calculated according to the following steps:

[0114] The brake circuit fluid volume change value under normal conditions is obtained based on the brake circuit PV curve of the actual vehicle test, and compared with the hydraulic cylinder volume change value caused by the piston movement, the deviation value of the brake circuit fluid volume is obtained.

[0115] The first threshold, the second threshold, the third threshold, the fourth threshold, the fifth threshold and the sixth threshold in the test steps are all data obtained by calibrating parameters of the actual vehicle.

[0116] Figure 4 This is a flow chart of the master cylinder and simulator brake circuit diagnostic steps provided in one embodiment of this specification. Figure 4 As shown, the master cylinder and simulator brake circuit are fault diagnosed. If the master cylinder and simulator brake circuit are faulty, the steps to determine the specific faulty valve and fault type include:

[0117] S201. When there is no fault in the electric cylinder circuit, control all hydraulic valves and pistons to return to their initial states.

[0118] S202, open PSV1, close TSV, close CSV2, control the electric cylinder unit to increase the pressure with a preset fixed boost gradient. If the pressure value collected by the first pressure sensor reaches the target pressure within the preset time and the piston forward distance is within the displacement range, enter step S203; otherwise, it is determined that the master cylinder and simulator brake circuit have serious leakage faults and the test is stopped.

[0119] S203, control the electric cylinder unit to reduce the pressure with a preset fixed pressure reduction gradient. If the pressure value collected by the first pressure sensor reaches the pressure reduction target value within a preset time, and the piston forward distance is within the displacement range, enter step S204; otherwise, it is determined that this brake circuit has a serious leakage fault and the test is stopped.

[0120] S204, maintain the current pressure value for 1s and enter the pressure holding stage. If the pressure value of the first pressure sensor P1 is not greater than the seventh threshold value and the piston movement speed is not greater than the eighth threshold value, it is determined that the piston of the master cylinder sub-chamber in the circuit is stuck or the CSV1 is not opened, and the test is stopped; if the piston forward distance is greater than the seventh threshold value or the piston movement speed is greater than the eighth threshold value, it is determined that the circuit has a serious leakage fault and the test is stopped; if the pressure value of the first pressure sensor P1 is greater than the seventh threshold value and there is no serious leakage fault, it is determined that the master cylinder and CSV are not faulty, and the test goes to step S205.

[0121] S205, test the simulator circuit, control the electric cylinder to keep the current piston state unchanged, open the SSV, if the pressure value of the first pressure sensor P1 or the second pressure sensor P2 is greater than the ninth threshold value, determine that the SSV is stuck; otherwise, enter step S206.

[0122] S206, close the SSV, control the electric cylinder unit to push the piston forward at a preset propulsion speed, open the SSV, and if the pressure value of the first pressure sensor P1 or the second pressure sensor P2 is greater than the ninth threshold value, determine that the TSV is stuck; otherwise, determine that the master cylinder and the simulator brake circuit are not faulty.

[0123] The seventh threshold, the eighth threshold, and the ninth threshold in the test steps are data obtained by calibrating parameters of the actual vehicle.

[0124] Figure 5 The following is a flow chart of the PSV fault diagnosis steps provided in an embodiment of this specification. Figure 5 As shown in the figure, the steps of PSV fault diagnosis include:

[0125] S301, when the electric cylinder circuit fault diagnosis determines that it is a PSV fault, control all hydraulic valves to return to the initial state and the electric cylinder piston to return to the initial position;

[0126] S302, open PSV1, close CSV1, close 4 ISOs, control the electric cylinder unit to increase pressure steadily at the preset speed,

[0127] If the pressure value collected by the second pressure sensor P2 reaches the target pressure within the preset time period, and the piston forward position is within the displacement range, step S303 is executed;

[0128] Otherwise, it is judged as a serious leakage fault and the test is stopped.

[0129] S303, control the electric cylinder unit to continue pressurizing, the fault diagnosis is as follows:

[0130] If the piston advance distance is not greater than the tenth threshold, it is determined that PSV1 is stuck;

[0131] If the piston advance distance is between the sixth threshold and the tenth threshold and the P1 pressure value is not greater than the ninth threshold, it is determined that PSV1 has no fault and the process goes to step S304;

[0132] If the piston advance distance is between the sixth threshold and the tenth threshold and the P1 pressure value is greater than the ninth threshold, it is determined that PSV2 has a leakage fault.

[0133] S304, open PSV2 and CSV1, close PSV1 and CSV2, control the electric cylinder unit to increase pressure steadily at a preset speed, if within the preset time, the pressure value collected by the second pressure sensor P2 reaches the target pressure and the piston forward position is within the displacement range, enter step S305, otherwise, it is determined to be a serious leakage fault and the test is stopped.

[0134] S305, continue to boost pressure and perform the following fault diagnosis:

[0135] If the piston advance distance is not greater than the tenth threshold, it is determined that the PSV2 valve is stuck;

[0136] If the piston advance distance is between the sixth threshold and the tenth threshold and the first P1 pressure is not greater than the ninth threshold, it is determined that PSV2 has no fault;

[0137] If the piston advancement distance is between the sixth threshold and the tenth threshold and the first P1 pressure is greater than the ninth threshold, it is determined that PSV1 has a leakage fault.

[0138] The tenth threshold in the test step is the actual vehicle calibration data.

[0139] Figure 6 The following is a flow chart of the CSV fault diagnosis steps provided in an embodiment of this specification. Figure 6 As shown in the figure, the steps to diagnose CSV faults include:

[0140] S401. When the fault diagnosis of the electric cylinder circuit is normal, control all hydraulic valves and the electric cylinder piston to return to the initial state.

[0141] S402, open PSV1, close CSV1, close the four ISO valves, control the electric cylinder unit to increase pressure steadily at a preset speed, if within the preset time, the pressure value collected by the second pressure sensor P2 reaches the target pressure, and the piston forward position is within the displacement range, enter step S403, otherwise, it is judged as a serious leakage fault and the test is stopped;

[0142] S403, continue to pressurize, the fault diagnosis is as follows:

[0143] If the piston advance distance is not greater than the sixth threshold and the P1 pressure value is greater than the ninth threshold, it is determined that CSV1 is leaking;

[0144] If the piston advance distance is not greater than the eleventh threshold and the pressure value collected by the first sensor P1 is not greater than the ninth threshold, then CSV1 and ISO3 and ISO4 valves are all fault-free, and the process goes to step S404;

[0145] If the piston advance distance is between the sixth threshold and the eleventh threshold and the pressure collected by the first pressure sensor P1 is not greater than the ninth threshold, the ISO valve has a leakage fault;

[0146] S404, open PSV2 and CSV1, close PSV1 and CSV2, control the electric cylinder unit to increase pressure steadily at a preset speed, within a preset time, the pressure value collected by the second pressure sensor P2 reaches the target pressure, and the piston forward position is within the displacement range, enter step S405, otherwise, it is judged as a serious leakage fault and the test is stopped;

[0147] S405, continue to pressurize, the fault diagnosis is as follows:

[0148] If the piston advance distance is not greater than the sixth threshold and the pressure value of the first pressure sensor P1 is greater than the ninth threshold, it is determined that CSV2 is leaking;

[0149] If the piston advance distance is not greater than the eleventh threshold and the pressure value of the first pressure sensor P1 is not greater than the ninth threshold, then there is no fault in CSV2 and ISO1 and ISO2 valves;

[0150] If the piston advance distance is between the sixth threshold value and the eleventh threshold value and the pressure value of the first sensor P1 is not greater than the ninth threshold value, the ISO valve has a leakage fault.

[0151] The eleventh threshold in the test step is the actual vehicle calibration data.

[0152] The above processes are all carried out under the condition that the P1, P2 pressure sensors and piston position sensors can be used normally.

[0153] In summary, the embodiments of this specification provide a hydraulic brake circuit fault diagnosis method based on the OneBox wire-controlled brake system, and provide a fault diagnosis method suitable for an integrated brake circuit. It has a complete judgment and execution logic, and uses the existing pressure sensors and electric cylinder units of the brake system to achieve comprehensive fault diagnosis of the brake circuit.

[0154] Those skilled in the art can understand that the accompanying drawings are only schematic diagrams of an embodiment, and the modules or processes in the accompanying drawings are not necessarily required to implement the present invention.

[0155] Those skilled in the art can understand that the modules in the device in the embodiment can be distributed in the device in the embodiment according to the description of the embodiment, or can be changed accordingly and located in one or more devices different from the embodiment. The modules in the above embodiment can be combined into one module, or can be further divided into multiple sub-modules.

[0156] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A hydraulic brake circuit fault diagnosis method based on a OneBox wire control brake system, characterized in that: include Obtain the actual vehicle calibration parameters of each device of the hydraulic brake circuit of the vehicle to be tested under normal conditions. The hydraulic brake circuit includes a hydraulic unit, a master cylinder unit, a circuit solenoid valve unit, a brake wheel cylinder, an isolation valve unit, a simulator and an electric cylinder unit. A hydraulic unit, storing hydraulic pressure, used to connect the simulator, the master cylinder unit and the electric cylinder unit, including a fluid storage tank and hydraulic pipelines; The master cylinder unit includes a master cylinder, a pedal rod, a displacement sensor, a test valve TSV and a first pressure sensor P1. The master cylinder is connected to the liquid storage tank through the hydraulic unit. The test valve TSV is arranged between the master cylinder unit and the liquid storage tank. The pedal rod is arranged on the master cylinder. The displacement sensor is arranged on the master cylinder to detect the braking displacement of the pedal rod. The first pressure sensor P1 is arranged on the master cylinder. The circuit solenoid valve unit includes eight solenoid valves, including four boost solenoid valves ISO1, ISO2, ISO3, ISO4 and four pressure reducing solenoid valves Dump1, Dump2, Dump3, Dump4, ISO4 and Dump4 are arranged in series to form a first passage, ISO3 and Dump3 are arranged in series to form a second passage, ISO2 and Dump2 are arranged in series to form a third passage, ISO1 and Dump1 are arranged in series to form a fourth passage, the brake wheel cylinder includes four wheel cylinders, each wheel cylinder is connected to a passage, wherein the first passage is connected in parallel with the second passage, the third passage is connected in parallel with the fourth passage, and the four passages are connected to the hydraulic unit to form a circuit; The isolation valve unit includes a first master cylinder isolation valve CSV1, a second master cylinder isolation valve CSV2, a first electric cylinder isolation valve PSV1 and a second electric cylinder isolation valve PSV2, wherein the first master cylinder isolation valve CSV1 is connected to the master cylinder and one end of the first passage and the second passage in parallel through a hydraulic pipeline, the second master cylinder isolation valve CSV2 is connected to the master cylinder and one end of the third passage and the fourth passage in parallel through a hydraulic pipeline, the first electric cylinder isolation valve PSV2 is connected to the electric cylinder and one end of the first passage and the second passage in parallel through a hydraulic pipeline, and the second electric cylinder isolation valve PSV2 is connected to the electric cylinder and one end of the third passage and the fourth passage in parallel through a hydraulic pipeline; One end of the simulator is connected to the fluid storage tank through a hydraulic pipeline, and the other end is connected to the solenoid valve SSV through a hydraulic pipeline and connected to the master cylinder; The electric cylinder unit includes an electric cylinder, a piston, a motor, a pressure relief valve PRV and a second pressure sensor P2. The motor drives the piston to move to change the pressure of the electric cylinder. The pressure relief valve is arranged between the electric cylinder unit and the hydraulic unit. The second pressure sensor is arranged on the pipeline between the electric cylinder and the electric cylinder isolation valve. The electric cylinder, piston, first electric cylinder isolation valve PSV1, second electric cylinder isolation valve PSV2, second pressure sensor P2, pressure relief valve PRV and connected hydraulic pipelines constitute the electric cylinder circuit; the first master cylinder isolation valve CSV1, second master cylinder isolation valve CSV2, solenoid valve SSV, test valve TSV, simulator, master cylinder, first pressure sensor P1 constitute the master cylinder and simulator brake circuit; The actual vehicle calibration parameters include the pressure value range of the first pressure sensor P1, the pressure value range of the second pressure sensor P2, the displacement range of the piston and the deviation value range of the brake circuit liquid volume; Within the preset time, control the electric cylinder piston to move to the initial position, control PSV1, PSV2, SSV, PRV, and Dump1, Dump2, Dump3, Dump4 to close, control CSV1, CSV2, TSV, ISO1, ISO2, ISO3, ISO4 to open, control the electric cylinder unit to increase pressure, compare the actual parameters with the actual vehicle calibration parameters, and determine the fault of the hydraulic brake circuit based on the comparison results of the actual parameters and the actual vehicle calibration parameters. First, perform fault diagnosis on the electric cylinder circuit. If the electric cylinder circuit detects a non-PSV fault, determine the fault location and fault type; If the electric cylinder circuit detects a PSV fault, perform PSV fault diagnosis to determine the faulty valve and fault type; On the contrary, the master cylinder and simulator brake circuit are fault diagnosed. If there is a fault in the master cylinder and simulator brake circuit, determine the specific faulty valve and fault type; Conversely, CSV faults are diagnosed to determine the fault condition of the CSV valve; Obtain the fault diagnosis result of the hydraulic brake circuit of the vehicle to be tested.

2. The method according to claim 1, characterized in that The steps of diagnosing the fault of the electric cylinder circuit include: S101, control the electric cylinder unit to increase pressure steadily at a preset speed. If the pressure value collected by the second pressure sensor P2 reaches the target pressure value within a preset time, and the piston advance distance is within the displacement range, continue the test; otherwise, it is determined to be a serious leakage fault and the test is stopped; S102, control the electric cylinder unit to continue pressurizing for 1 second. In the first 500ms, calculate the piston advance distance and the liquid volume deviation of the electric cylinder circuit. After 500ms, perform the following fault diagnosis based on the calculation results: If the piston advance distance is not greater than the first threshold value, and the liquid volume deviation of the electric cylinder circuit is not greater than the second threshold value, it is determined that there is no fault in the electric cylinder circuit, and the master cylinder and simulator brake circuit diagnosis is entered; If the piston advance distance is greater than the first threshold and the liquid volume deviation of the electric cylinder circuit is not greater than the second threshold, it is determined to be a PSV or PRV leakage fault, and the process goes to step S103; If the liquid volume deviation of the electric cylinder circuit is greater than the second threshold value and not greater than the third threshold value, it is determined to be a PSV fault; If the liquid volume deviation of the electric cylinder circuit is greater than the third threshold, it is judged as a PRV failure; S103, control the piston to return to the initial position, close the four ISO valves, CSV1, and CSV2. If the piston returns to the initial position within the preset time period, enter step S104. Otherwise, it is determined that the electric cylinder piston is stuck and the test is stopped; S104, control the electric cylinder unit to increase pressure steadily at a preset speed. If the pressure value collected by the first pressure sensor P1 reaches the target pressure within a preset time, and the piston forward position is within the displacement range, enter step S105. Otherwise, it is determined to be a PRV leakage fault. S105, continue to increase the pressure for 1 second. In the first 500ms, calculate the piston advance distance and the liquid volume deviation of the electric cylinder circuit. After 500ms, perform the following fault diagnosis based on the calculation results: If the piston advance distance is between the fourth threshold and the sixth threshold and the liquid volume deviation is not greater than the fifth threshold, it is determined that the PRV is not faulty and the master cylinder and simulator brake circuit diagnosis is entered; If the piston advance distance is not greater than the fourth threshold and the liquid volume deviation is not greater than the fifth threshold, it is determined to be a PSV opening failure; If the piston advance distance is not greater than the sixth threshold and the liquid volume deviation is greater than the fifth threshold, it is determined to be a PRV failure; If the piston advance distance is greater than the sixth threshold, it is determined to be a PRV failure.

3. The method according to claim 2, characterized in that The liquid volume deviation of the electric cylinder circuit is calculated according to the following steps: The brake circuit fluid volume change value under normal conditions is obtained based on the brake circuit PV curve of the actual vehicle test, and compared with the hydraulic cylinder volume change value caused by the piston movement, the deviation value of the brake circuit fluid volume is obtained.

4. The method according to claim 1, characterized in that: The step of diagnosing the fault of the master cylinder and the simulator brake circuit and determining the specific fault valve and the fault type if the master cylinder and the simulator brake circuit have a fault comprises: S201, when there is no fault in the electric cylinder circuit, control all hydraulic valves and pistons to return to their initial states; S202, open PSV1, close TSV, close CSV2, control the electric cylinder unit to increase pressure with a preset fixed boost gradient, if the pressure value collected by the first pressure sensor reaches the target pressure within the preset time and the piston advance distance is within the displacement range, enter step S203; otherwise, it is determined that the master cylinder and the simulator brake circuit have serious leakage faults, and the test is stopped; S203, control the electric cylinder unit to reduce pressure with a preset fixed pressure reduction gradient. If the pressure value collected by the first pressure sensor reaches the pressure reduction target value within a preset time, and the piston advance distance is within the displacement range, enter step S204; otherwise, it is determined that there is a serious leakage fault in this brake circuit, and the test is stopped; S204, maintain the current pressure value for 1s, enter the pressure holding stage, if the pressure value of the first pressure sensor P1 is not greater than the seventh threshold value and the piston movement speed is not greater than the eighth threshold value, it is determined that the piston of the master cylinder sub-chamber in the circuit is stuck or the CSV1 is not opened, and the test is stopped; if the piston advance distance is greater than the seventh threshold value or the piston movement speed is greater than the eighth threshold value, it is determined that the circuit has a serious leakage fault, and the test is stopped; if the pressure value of the first pressure sensor P1 is greater than the seventh threshold value and there is no serious leakage fault, it is determined that the master cylinder and CSV are not faulty, and the process goes to step S205; S205, testing the simulator circuit, controlling the electric cylinder to keep the current piston state unchanged, opening the SSV, and if the pressure value of the first pressure sensor P1 or the second pressure sensor P2 is greater than the ninth threshold, determining that the SSV is stuck; otherwise, entering step S206; S206, close the SSV, control the electric cylinder unit to push the piston forward at a preset propulsion speed, open the SSV, and if the pressure value of the first pressure sensor P1 or the second pressure sensor P2 is greater than the ninth threshold value, determine that the TSV is stuck; otherwise, determine that the master cylinder and the simulator brake circuit are not faulty.

5. The method according to claim 1, characterized in that If the electric cylinder circuit detects a PSV fault, the steps of performing PSV fault diagnosis and determining the faulty valve and the fault type include: S301, when the electric cylinder circuit fault diagnosis determines that it is a PSV fault, control all hydraulic valves to return to the initial state and the electric cylinder piston to return to the initial position; S302, open PSV1, close CSV1, close 4 ISOs, control the electric cylinder unit to increase pressure steadily at the preset speed, If the pressure value collected by the second pressure sensor P2 reaches the target pressure within the preset time period, and the piston forward position is within the displacement range, step S303 is executed; Otherwise, it is judged as a serious leakage fault and the test is stopped; S303, control the electric cylinder unit to continue pressurizing, the fault diagnosis is as follows: If the piston advance distance is not greater than the tenth threshold, it is determined that PSV1 is stuck; If the piston advance distance is between the sixth threshold and the tenth threshold and the P1 pressure value is not greater than the ninth threshold, it is determined that PSV1 has no fault and the process goes to step S304; If the piston advance distance is between the sixth threshold and the tenth threshold and the P1 pressure value is greater than the ninth threshold, it is determined that PSV2 has a leakage fault; S304, open PSV2 and CSV1, close PSV1 and CSV2, control the electric cylinder unit to increase pressure steadily at a preset speed, if within a preset time, the pressure value collected by the second pressure sensor P2 reaches the target pressure and the piston forward position is within the displacement range, enter step S305, otherwise, it is determined to be a serious leakage fault and the test is stopped; S305, continue to boost pressure and perform the following fault diagnosis: If the piston advance distance is not greater than the tenth threshold, it is determined that the PSV2 valve is stuck; If the piston advance distance is between the sixth threshold and the tenth threshold and the first P1 pressure is not greater than the ninth threshold, it is determined that PSV2 has no fault; If the piston advancement distance is between the sixth threshold and the tenth threshold and the first P1 pressure is greater than the ninth threshold, it is determined that PSV1 has a leakage fault.

6. The method according to claim 1, characterized in that The step of diagnosing the CSV fault and determining the fault condition of the CSV valve comprises: S401, when the electric cylinder circuit fault diagnosis is normal, control all hydraulic valves and electric cylinder pistons to return to their initial states; S402, open PSV1, close CSV1, close the four ISO valves, control the electric cylinder unit to increase pressure steadily at a preset speed, if within the preset time, the pressure value collected by the second pressure sensor P2 reaches the target pressure, and the piston forward position is within the displacement range, enter step S403, otherwise, it is judged as a serious leakage fault and the test is stopped; S403, continue to pressurize, the fault diagnosis is as follows: If the piston advance distance is not greater than the sixth threshold and the P1 pressure value is greater than the ninth threshold, it is determined that CSV1 is leaking; If the piston advance distance is not greater than the eleventh threshold and the pressure value collected by the first sensor P1 is not greater than the ninth threshold, then CSV1 and ISO3 and ISO4 valves are all fault-free, and the process goes to step S404; If the piston advance distance is between the sixth threshold and the eleventh threshold and the pressure collected by the first pressure sensor P1 is not greater than the ninth threshold, the ISO valve has a leakage fault; S404, open PSV2 and CSV1, close PSV1 and CSV2, control the electric cylinder unit to increase pressure steadily at a preset speed, within a preset time, the pressure value collected by the second pressure sensor P2 reaches the target pressure, and the piston forward position is within the displacement range, enter step S405, otherwise, it is judged as a serious leakage fault and the test is stopped; S405, continue to pressurize, the fault diagnosis is as follows: If the piston advance distance is not greater than the sixth threshold and the pressure value of the first pressure sensor P1 is greater than the ninth threshold, it is determined that CSV2 is leaking; If the piston advance distance is not greater than the eleventh threshold and the pressure value of the first pressure sensor P1 is not greater than the ninth threshold, then there is no fault in CSV2 and ISO1 and ISO2 valves; If the piston advance distance is between the sixth threshold value and the eleventh threshold value and the pressure value of the first sensor P1 is not greater than the ninth threshold value, the ISO valve has a leakage fault.

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