Hydraulic circuit gas or leak diagnosis method for a brake-by-wire system

Abstract

A kind of hydraulic circuit of brake-by-wire system gas or leakage diagnosis method, computer equipment and storage medium.The method utilizes the existing motor-driven electric cylinder, isolation valve group and pressure sensor of system, under the premise of not increasing additional hardware, different closed test volumes are formed by step-by-step progressive valve combination strategy, and electric cylinder circuit, master cylinder circuit, pedal simulator circuit are detected in turn.The present application realizes early, active and accurate distinction of two different fault modes of gas and leakage, and significantly improves the safety and reliability of brake-by-wire system.

Description

Technical Field

[0001] This invention belongs to the field of vehicle fault detection, and in particular relates to a method, equipment and medium for diagnosing air or leakage in the hydraulic circuit of a brake-by-wire system. Background Technology

[0002] With the rapid development of automotive electrification and intelligentization technologies, brake-by-wire systems have become key components for achieving high-level autonomous driving. Brake-by-wire systems eliminate the rigid mechanical connection between the traditional vacuum booster and the master cylinder, using an electric motor to drive an electric cylinder (or auxiliary master cylinder) to generate brake hydraulic pressure, which is then precisely controlled by a solenoid valve assembly to control the braking pressure of each wheel cylinder. Currently, mainstream brake-by-wire solutions mainly include the Two-box solution combining "eBooster + ESC" and the OneBox solution, which highly integrates brake assist and vehicle stability control functions. Among these, the OneBox solution is increasingly widely used in new energy and intelligent connected vehicles due to its high integration, small size, and fast response.

[0003] However, during long-term service, the hydraulic circuit of a brake-by-wire system inevitably faces two types of potential failures: first, brake fluid leakage, which may originate from aging seals, loose pipe joints, or fluid cross-contamination within the valve body; second, gas intrusion, which may result from low reservoir level, incomplete venting during filling, or air leakage due to system seal failure. Both types of failures can lead to serious consequences such as a decrease in the effective bulk modulus of hydraulic pressure, delayed pressure build-up response, and insufficient braking force, directly endangering driving safety.

[0004] In existing technologies, fault diagnosis methods for hydraulic circuits in brake-by-wire systems can be mainly classified into the following categories: One type of method is passive diagnosis based on brake pedal feel or wheel cylinder pressure response. This involves indirectly inferring a system malfunction by observing abnormally increased pedal travel or significantly insufficient braking force after the driver depresses the brake pedal. This type of method suffers from diagnostic lag, often only detecting the problem after it has progressed to the point of affecting normal braking function, thus failing to provide early warning.

[0005] Another approach utilizes existing pressure and motor position sensors within the system. By controlling the on / off state of solenoid valves to form a closed loop, a pressurization-holding test is performed on the system. Leakage is determined based on pressure decay or excessive piston stroke. For example, Korean Patent KR10-2015-0172058 discloses a self-test control method for vehicle braking systems. This method generates braking pressure by pushing brake fluid out of the secondary master cylinder piston and detects leaks by monitoring pressure changes during pressurization-holding or by detecting the correlation between piston stroke and pressure during pressurization. However, this type of method typically only determines the presence of a leak and cannot distinguish between "air-containing" and "leaking" fault modes. It also struggles to quantify the degree of air content and cannot pinpoint the internal fluid leakage fault within a specific valve body.

[0006] In addition, another method for leak detection in electric braking systems has been proposed. This method constructs a closed loop by adding a dedicated inspection valve and uses a binary search approach to determine whether pressure can be established to locate the leak source. However, this method requires additional hardware valves, increasing system cost and complexity. Furthermore, its diagnostic logic is a Boolean decision, which cannot identify the intermediate degradation state of gas content.

[0007] In recent years, some technologies have divided diagnostics into four parts: electric cylinder circuit diagnosis, master cylinder and simulator circuit diagnosis, PSV fault diagnosis, and CSV fault diagnosis, using displacement and pressure thresholds for fault judgment. While this method achieves relatively comprehensive fault location, its fault classification system does not model "gas-containing" as an independent fault mode, and its leakage diagnosis of the master cylinder isolation valve CSV relies on indirect inference from pressure crosstalk, lacking a means to directly compare the internal sealing interface of the CSV using differential methods.

[0008] In summary, existing technologies have the following shortcomings: First, there is a lack of a diagnostic method that can simultaneously distinguish between "gas content" and "leakage," two different physical mechanisms, particularly in the inability to quantify and identify the early stages of gas content. Second, for internal fluid leakage in the two-position three-way isolation valve (CSV), which is unique to brake-by-wire systems, there is a lack of direct and structured diagnostic methods. Third, existing diagnostic processes are mostly parallel enumeration-based detections, lacking progressive short-circuit logic based on fault severity grading, which may lead to unnecessary pressurization operations introducing secondary risks. Therefore, there is an urgent need in the field for a hydraulic circuit diagnostic method for brake-by-wire systems that can actively distinguish between gas content and leakage without adding extra hardware and can accurately locate internal fluid leakage faults within the valve body. Summary of the Invention

[0009] Therefore, it is necessary to provide a method for diagnosing air or leakage in the hydraulic circuit of a brake-by-wire system, a computer device, a computer-readable storage medium, and a computer program product to address the aforementioned technical problems.

[0010] In a first aspect, the present application provides a method for diagnosing air inclusion or leakage in a hydraulic circuit of a brake-by-wire system, wherein the brake-by-wire system comprises a motor-driven electric cylinder, electric cylinder isolation valves PSV1 and PSV2, master cylinder isolation valves CSV1 and CSV2, wheel cylinder isolation valves ISO1 to ISO4, a simulator isolation valve SIV, a test and diagnosis valve TSV, a pressure relief valve PRV, an electric cylinder pressure sensor BPS, a master cylinder pressure sensor MCPS, and a motor position sensor MPS, characterized in that the method comprises the following steps: Step S1: Electric cylinder circuit detection: set CSV1 and CSV2 in a conducting state, set all of ISO1 to ISO4 in a cut-off state, and set both PSV1 and PSV2 in a conducting state, so as to form a closed test volume V1 from the outlet of the electric cylinder to the inlets of the wheel cylinders via PSV1 / PSV2; drive the motor to discharge brake fluid at a constant rate, and record the actual motor displacement S_act when the electric cylinder pressure sensor BPS reaches the first target pressure P1; Perform three-state judgment according to the relationship between S_act and the preset first lower displacement limit S_Low and first upper displacement limit S_High: if S_act ≤ S_Low and BPS reaches P1, the electric cylinder circuit is determined to be healthy; if S_Low < S_act ≤ S_High and BPS reaches P1, it is determined that a small amount of air has intruded into the electric cylinder circuit, and said air causes the effective bulk modulus of the hydraulic pressure to decrease, and the pressure increase amplitude corresponding to the same discharged volume to decrease; if S_act > S_High or BPS cannot reach P1, it is determined that a large amount of air has intruded into the electric cylinder circuit or brake fluid leakage occurs in the electric cylinder circuit, and the subsequent steps of pressurizing the master cylinder side and the simulator side are terminated; Step S2: Master cylinder circuit detection: on the premise that the electric cylinder circuit is determined to be healthy in step S1, set PSV2, CSV1 and TSV in a conducting state, set ISO1 to ISO4 in a cut-off state, drive the motor to supply liquid to the first chamber of the master cylinder via PSV2 and CSV1, monitor the pressure build-up response by the master cylinder pressure sensor MCPS, and judge whether air intrusion or leakage exists in the master cylinder circuit according to the relationship between the motor displacement and the pressure of MCPS; Step S3: Pedal simulator circuit detection: after the master cylinder circuit is determined to be qualified in step S2, set the simulator isolation valve SIV in a conducting state, so that the additional volume discharged by the electric cylinder fills the simulator branch at the same time, and judge whether air intrusion or leakage exists in the pedal simulator circuit according to the relationship between the additional displacement of the motor and the pressure build-up rate of the simulator branch; Step S4, Three-way valve leakage detection: Control PSV2 to be energized and turned on, TSV to be energized and turned off, ISO1 to ISO4 to be energized and turned off, and SIV to be energized and turned on, and CSV1 to be energized and turned off; After the drive motor builds pressure to the electric cylinder to the first target pressure P1 or the first target displacement S_Req1, control CSV1 to be energized and turned off; Then control CSV1 and CSV2 to be energized and turned on simultaneously, and after a preset time, they are energized and turned off simultaneously; If the pressure detected by the main cylinder pressure sensor MCPS is less than the second target pressure P2 after CSV1 and CSV2 are energized simultaneously, it is determined that there is internal leakage at the sealing interface of CSV1 or CSV2. Step S5, Full-Circuit Detection: After passing the qualification test in Step S4, full-circuit leakage and gas content detection is performed. The system switches to the dedicated valve state for full-circuit detection. The electric cylinder outlet is connected to the wheel cylinder inlet via PSV1 / PSV2 / CSV1, and then connected to the main cylinder via PSV1 / PSV2 / CSV2. The drive motor builds pressure in the electric cylinder to the preset final test pressure P_final, and then enters the pressure holding window Δt_final. If the pressure decay rate dP / dt in the pressure holding window is greater than the decay threshold λ_leak, then a leakage fault is determined to exist in the full circuit. If dP / dt ≤ λ_leak, but the compensation displacement required by the motor to maintain P_final is greater than the gas compensation threshold S_gas, then residual gas content is determined to exist in the full circuit.

[0011] In one embodiment, the first lower displacement limit S_Low and the first upper displacement limit S_High in step S1 are motor displacement tolerance bands calculated based on the nominal hydraulic effective volume V_eff and brake fluid bulk modulus β_liq of the same batch of in-line brake hardware, according to the relationship P = β_liq · ΔV_actual / V_eff, where ΔV_actual is obtained by subtracting the temperature compensation term from the piston discharge volume converted from the motor rotor position.

[0012] In one embodiment, in step S2, when the motor displacement has reached the first lower displacement limit S_Low but the pressure of the master cylinder pressure sensor MCPS has not yet reached the first target pressure P1, excluding the premise that the electric cylinder circuit has been confirmed to be healthy in step S1, the source of the fault is located to the presence of gas intrusion or leakage in the master cylinder chamber, master cylinder seal, or hydraulic connection section between the master cylinder and CSV1.

[0013] In one embodiment, in step S3, after confirming that there is no substantial leakage in the electric cylinder circuit and the main cylinder circuit, the simulator isolation valve SIV is opened so that the additional volume discharged by the electric cylinder simultaneously fills the simulator branch. When the theoretical pressure rise corresponding to the additional displacement of the motor does not match the rated volume of the simulator branch, and the pressure build-up rate of the simulator branch is lower than the calibrated value P2 / t_th, it is determined that the simulator branch contains gas.

[0014] In one embodiment, the preset curve deviation threshold κ(ΔV) in step S4 is a function of the discharge volume ΔV, and κ(ΔV) is obtained by calibrating the upper limit of the difference between the CSV bistate curves of qualified line control brake products in the same batch.

[0015] In one embodiment, steps S1 to S5 are executed sequentially. When step S1 or step S2 determines that there is a serious leak, the simulator isolation valve SIV is locked in the normally closed state to prevent contamination of the master cylinder sealing interface, and a diagnostic fault code corresponding to the fault level is output through the vehicle bus to stop the execution of subsequent steps.

[0016] In one embodiment, steps S1 to S5 are automatically triggered and executed before the vehicle is powered off and in a parking brake confirmation state.

[0017] In one embodiment, in step S1, the formation of the closed test volume V1 further includes a split-axis detection mode: first, only ISO1 and ISO2 corresponding to the front axle are placed in the on state, and ISO3 and ISO4 corresponding to the rear axle are placed in the off state. After the front axle electric cylinder circuit detection is completed, the axle states are exchanged to complete the rear axle electric cylinder circuit detection.

[0018] In one embodiment, in step S1, pressure changes are indirectly reflected by monitoring the waveforms of motor phase current or bus current: when the circuit contains gas, the current rises slowly during the initial pressure build-up phase; when the circuit leaks, the current continues to decrease during the steady-state pressure holding phase; and the actual current curve is compared with the calibrated healthy current curve to determine the degree of fault.

[0019] In one embodiment, in step S4, the closed test volume V_test is formed by controlling PSV2 to be on, selectively turning on either CSV1 or CSV2, turning on TSV, and turning off ISO1 to ISO4, so that the electric cylinder outlet forms a closed volume with the first chamber of the main cylinder through PSV2 and the turned-on CSV; when the on / off states of CSV1 and CSV2 are interchanged, the states of PSV2, TSV, and ISO1 to ISO4 remain unchanged.

[0020] In one embodiment, in step S5, the default valve state configuration for the full-loop detection dedicated valve state during vehicle braking is: controlling PSV2 to be energized to switch it from normally closed state to conducting state, while keeping PSV1 in an unenergized conducting state; Control CSV2 to be in a non-energized conducting state, and control CSV1 to be energized so that it switches from a normally open state to a cut-off state; Control ISO1 to ISO4 to be in a non-energized conducting state; Simultaneously, the TSV is powered on to switch it to the off state.

[0021] In one embodiment, in step S1, when it is determined that there is a large amount of gas intrusion or brake fluid leakage in the electric cylinder circuit, the gas intrusion and leakage are further distinguished in the following way: if the motor displacement exceeds S_High but BPS can still slowly climb to P1 within a preset time, it is determined to be a large amount of gas intrusion; if the motor displacement continues to increase but BPS can never reach 50% of P1, it is determined to be brake fluid leakage.

[0022] Secondly, this application also provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the method in any of the above embodiments.

[0023] Thirdly, this application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the methods in any of the above embodiments.

[0024] Fourthly, this application also provides a computer program product, including a computer program that, when executed by a processor, implements the steps of the methods in any of the above embodiments.

[0025] The aforementioned method, computer equipment, storage medium, and computer program product for diagnosing gas or leakage in the hydraulic circuit of a brake-by-wire system utilizes the existing motor-driven electric cylinder, isolation valve assembly, and pressure sensor. Without adding additional hardware, it employs a step-by-step valve combination strategy to create different closed test volumes, sequentially testing the electric cylinder circuit, master cylinder circuit, and pedal simulator circuit. Specifically, the electric cylinder circuit detection uses a three-state determination based on the relationship between the actual motor displacement and preset upper and lower displacement limits, distinguishing between healthy, small gas intrusion, and large gas intrusion or leakage states. By switching the on / off states of the master cylinder isolation valves CSV1 and CSV2 and comparing the deviation of the two displacement-pressure curves, internal leakage within the three-way valve is diagnosed. Finally, all valves are switched to a dedicated full-loop detection valve state for full-loop pressure holding detection, and the overall gas or leakage is determined by considering the pressure decay rate and compensated displacement. This invention achieves early, proactive, and accurate differentiation between two different fault modes: gas and leakage, significantly improving the safety and reliability of the brake-by-wire system. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the hydraulic circuit topology of a brake-by-wire system in one embodiment.

[0028] Figure 2 This is a schematic diagram of the electric cylinder circuit detection topology of the hydraulic circuit of a brake-by-wire system in one embodiment.

[0029] Figure 3 This is a schematic diagram of the master cylinder circuit detection topology of the hydraulic circuit of a brake-by-wire system in one embodiment.

[0030] Figure 4 This is a schematic diagram of the pedal simulator detection topology for the hydraulic circuit of a brake-by-wire system in one embodiment.

[0031] Figure 5 This is a schematic diagram of the three-way valve leakage detection topology for the hydraulic circuit of a brake-by-wire system in one embodiment.

[0032] Figure 6 This is a schematic diagram of the full-loop detection topology of the hydraulic circuit of the brake-by-wire system in one embodiment. Detailed Implementation

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] This embodiment provides a method for diagnosing air contamination or leakage in the hydraulic circuit of a brake-by-wire system. The brake-by-wire system is preferably a OneBox brake-by-wire system, and its hydraulic circuit structure is as follows: Figure 1 As shown, the system includes: a motor-driven electric cylinder (or auxiliary master cylinder), electric cylinder isolation valves PSV1 and PSV2, master cylinder isolation valves CSV1 and CSV2, wheel cylinder isolation valves ISO1 to ISO4, simulator isolation valve SIV, test and diagnostic valve TSV, pressure relief valve PRV, electric cylinder pressure sensor BPS, master cylinder pressure sensor MCPS, and motor position sensor MPS. For ease of description, the four wheel cylinder isolation valves are designated ISO1, ISO2, ISO3, and ISO4, corresponding to the isolation valves of the front left wheel (FL), front right wheel (FR), rear left wheel (RL), and rear right wheel (RR), respectively. The pressure relief valve PRV in this system... Figure 1The corresponding valves are labeled Dump_FL, Dump_FR, Dump_RL, and Dump_RR, which are used for pressure relief of each wheel cylinder. PSV1 is a normally open solenoid valve (open when de-energized, closed when energized), PSV2 is a normally closed solenoid valve (closed when de-energized, open when energized), CSV1 and CSV2 are normally closed solenoid valves (open when de-energized, closed when energized), ISO1 to ISO4 are normally open solenoid valves, SIV is a normally closed solenoid valve, TSV is a normally open solenoid valve, and PRV is a normally closed solenoid valve. Note that the "conducting state" mentioned in this invention refers to the valve position that allows brake fluid flow: for normally closed valves (PSV2, CSVx, SIV, PRV), it is the energized open state; for normally open valves (PSV1, ISOx, TSV), it is the de-energized open state; the "cut-off state" is the opposite. The following describes the method of this invention in detail with reference to the overall diagnostic process.

[0035] Step S1: Electric cylinder circuit test First, once the vehicle is powered on and initialized, and the vehicle is in a parking brake confirmed state (or according to other triggering conditions), the system automatically enters diagnostic mode.

[0036] First, reset all hydraulic valves to their initial safe state: Normally closed valves: PSV2, SIV, DUMP1~DUMP4 are all de-energized; CSV1, CSV2 are all de-energized; TSV is de-energized. Normally open valves: PSV1, ISO1~ISO4 are all de-energized; subsequently, the drive motor moves the electric cylinder piston to the mechanical zero position at a preset speed (confirmed by feedback from the motor position sensor MPS), completing the initial position calibration.

[0037] refer to Figure 2 The system performs valve state switching for the electric cylinder circuit detection, forming a closed test volume V1: CSV1 and CSV2 are energized and conducting, while ISO1 to ISO4 are energized and de-energized; PSV1 is de-energized and conducting, while PSV2 is energized and conducting; SIV is kept energized and conducting, TSV is de-energized and conducting, and DUMP1 to DUMP4 are de-energized and de-energized. Next, the motor drives the electric cylinder piston forward at a preset constant speed, discharging brake fluid at a constant rate. During the process of the electric cylinder pressure sensor BPS reaching the first target pressure P1, the actual displacement S_act of the motor (obtained through the motor position sensor MPS) is recorded in real time. A three-state determination is performed based on the relationship between S_act and the preset first lower displacement limit S_Low and first upper displacement limit S_High: 1. If S_act ≤ S_Low and BPS reaches P1, then the electric cylinder circuit is considered healthy, with no gas intrusion or leakage. 2. If S_Low < S_act ≤ S_High and BPS reaches P1, it is determined that a small amount of gas has invaded the electric cylinder circuit. The physical mechanism is as follows: the invaded gas reduces the effective bulk modulus of the hydraulic pressure, which decreases the pressure increase corresponding to the same discharge volume, so a larger piston displacement is required to reach the same target pressure; 3. If S_act > S_High or BPS cannot reach P1, it is determined that a large amount of gas invasion or brake fluid leakage exists in the electric cylinder circuit. At this time, the subsequent steps of pressurizing the master cylinder side and the simulator side are terminated to avoid introducing gas or pollutants into the sealing interface of the master cylinder and the simulator circuit, and a corresponding diagnostic trouble code (DTC) is output via the vehicle bus.

[0038] Further, when it is determined that there is a large amount of gas invasion or brake fluid leakage, the two can be distinguished by the following method: if the motor displacement exceeds S_High but BPS can still slowly climb to P1 within a preset time, it is determined to be a large amount of gas invasion; if the motor displacement continues to increase while BPS can never reach 50% of P1, it is determined to be brake fluid leakage.

[0039] The first lower displacement limit S_Low and the first upper displacement limit S_High are motor displacement tolerance bands obtained by conversion according to the relational expression P = β_liq · ΔV_actual / V_eff, based on the nominal effective hydraulic volume V_eff and brake fluid bulk modulus β_liq of the same batch of brake-by-wire hardware. Wherein, ΔV_actual is obtained by deducting the temperature compensation term from the piston discharge volume converted from the motor rotor position. The specific calibration method is: perform a PV curve test on products of the same batch on a test bench, obtain the displacement-pressure relationship in a healthy state, and set the tolerance band taking into account factors such as sensor error and batch tolerance.

[0040] As an expansion of this embodiment, the formation method of the closed test volume V1 described in step S1 can also adopt a shaft-separated detection mode: first, only set ISO1 and ISO2 corresponding to the front axle to the conducting state, and set ISO3 and ISO4 corresponding to the rear axle to the cut-off state. After completing the detection of the front axle electric cylinder circuit, exchange the axle states to complete the detection of the rear axle electric cylinder circuit. This method can accurately locate the axle (front axle or rear axle) where gas inclusion or leakage occurs, which is convenient for subsequent maintenance.

[0041] Step S2: Master cylinder circuit detection On the premise that step S1 determines a healthy state, the master cylinder circuit detection is performed. Reference Figure 3Firstly, retract the electric cylinder piston to the initial position and switch the valve states: control PSV2 to be energized and conducted, CSV1 to be energized and conducted, TSV to be energized and cut off, and all ISO1 to ISO4 to be energized and cut off, while keeping PSV1 de-energized and conducted, CSV2 de-energized and cut off, and SIV de-energized and cut off. At this time, the outlet of the electric cylinder communicates with the first chamber of the master cylinder via PSV2 and CSV1, forming a closed test volume V2 from the electric cylinder to the first chamber of the master cylinder.

[0042] The driving motor discharges brake fluid at a constant rate, and the pressure build-up response is monitored by the master cylinder pressure sensor MCPS. When the motor displacement has reached the first displacement lower limit S_Low but the pressure of MCPS still has not reached the first target pressure P1, on the premise that the health of the electric cylinder circuit has been confirmed in step S1, the fault source is positioned as gas intrusion or leakage existing in the master cylinder chamber, the master cylinder seal or the hydraulic connection section between the master cylinder and CSV1, and the corresponding diagnostic trouble code is output.

[0043] If MCPS can reach P1 before the motor displacement reaches S_Low, it is determined that the master cylinder circuit is healthy, and the next step is continued.

[0044] Step S3: Pedal Simulator Circuit Detection After the qualified determination in step S2, the pedal simulator circuit detection is performed. With reference to Figure 4 , keep the current position of the electric cylinder piston unchanged, energize and conduct the simulator isolation valve SIV, so that the additional volume discharged by the electric cylinder fills the simulator branch (including the pipeline downstream of SIV and the pedal simulator cavity) at the same time. The driving motor continues to push forward at a constant rate, and the additional displacement of the motor and the pressure build-up rate of the simulator branch (monitored by MCPS or BPS) are recorded.

[0045] When the theoretical pressure increase corresponding to the additional displacement of the motor does not match the rated volume of the simulator branch, and the pressure build-up rate of the simulator branch is lower than the calibrated value P2 / t_th, it is determined that the simulator branch contains gas. If the pressure build-up is normal and the displacement is within the expected range, it is determined that the pedal simulator circuit is healthy.

[0046] Step S4: Three-way Valve Leakage Detection After the qualified determination in step S3, the three-way valve leakage detection is performed. With reference to Figure 5 , firstly restore all hydraulic valves to the initial state, and retract the electric cylinder piston to the initial position. Then, a closed test volume V_test is formed between the electric cylinder, PSV2 and the first hydraulic section divided by CSV1 and CSV2. Specifically, control PSV2 to be energized and conducted, TSV to be energized and cut off, all ISO1 to ISO4 to be energized and cut off, SIV to be de-energized and cut off, CSV1 to be energized and conducted, and CSV2 to be de-energized and cut off.

[0047] Then, after the drive motor builds up pressure to the electric cylinder to the first target pressure P1 or the first target displacement S_Req1, it controls CSV1 to be de-energized and cut off. Subsequently, it controls CSV1 and CSV2 to be energized and conducted simultaneously, and after a preset time, they are de-energized and cut off simultaneously. If, after CSV1 and CSV2 are de-energized simultaneously, the pressure detected by the main cylinder pressure sensor MCPS is less than the second target pressure P2, it is determined that there is internal leakage at the sealing interface of CSV1 or CSV2.

[0048] Step S5: Full-loop detection After passing the test in step S4, a full-loop test is performed. (Reference) Figure 6 Switch all hydraulic valves to the dedicated valve configuration for full-loop detection: energize PSV2 to switch it from normally closed to open, while keeping PSV1 in an unenergized open state; keep CSV2 in an unenergized open state, and energize CSV1 to switch it from normally open to closed; keep ISO1 to ISO4 in an unenergized open state; and simultaneously energize TSV to switch it to closed.

[0049] The drive motor builds pressure in the electric cylinder to the preset final test pressure P_final, and then enters the pressure holding window Δt_final. During the pressure holding period, the pressure change of the BPS and the displacement change of the motor position sensor MPS are continuously monitored. If the pressure decay rate dP / dt within the pressure holding window is greater than the decay threshold λ_leak, a leakage fault is determined in the entire circuit; if dP / dt ≤ λ_leak but the compensation displacement required by the motor to maintain P_final is greater than the gas compensation threshold S_gas, residual gas is determined in the entire circuit. If both indicators are within the normal range, the entire circuit is determined to be healthy, and the diagnosis is complete.

[0050] Steps S1 to S5 are executed sequentially. If a serious leak is detected in step S1 or S2, the simulator isolation valve SIV is immediately locked in the de-energized normally closed state to prevent contaminants from entering the master cylinder sealing interface. A diagnostic fault code corresponding to the fault level is output via the vehicle bus, halting the execution of subsequent steps. This short-circuit logic avoids unnecessary pressurization operations in the event of a serious fault, reducing secondary risks.

[0051] The diagnostic method of the present invention can be automatically triggered at the following times: Automatically triggered before the vehicle is powered off and in a parking brake confirmation state; The vehicle has been powered on and initialized, and the vehicle is in the parking brake confirmed state. When a continuous cruise window in a non-braking condition is detected while the vehicle is in motion, it is initiated periodically or by an event triggered by the upper-level controller. When triggered while in motion, the pressure build-up amplitude and time window are limited to a range that will not affect the driver's normal braking feel (e.g., pressure build-up to 5 bar within 0.3 seconds and immediate release).

[0052] Another embodiment is essentially the same as Embodiment 1, except that in step S1, pressure changes are indirectly reflected by monitoring the waveforms of motor phase current or bus current, thus reducing reliance on pressure sensors. Specifically, with the same valve combination, the drive motor operates at a constant speed, and the motor current I(t) is monitored. Since motor torque is proportional to hydraulic pressure (ignoring friction), the current waveform can indirectly reflect pressure changes. When the circuit contains gas, the current rises slowly during the initial pressure build-up phase due to the compressibility of gas; when the circuit leaks, the current continuously decreases during the steady-state pressure holding phase. The actual current curve is compared with the calibrated healthy current curve, and the area difference or peak delay is calculated to determine the degree of fault. This embodiment is suitable for low-cost configurations or backup diagnostics when sensors fail.

[0053] Another embodiment is essentially the same as Embodiment 1, except that the closed test volume V_test is formed in step S4 as follows: PSV2 is turned on, either CSV1 or CSV2 is turned on, TSV is turned on, and ISO1 to ISO4 are all turned off, so that the electric cylinder outlet, through PSV2, the turned-on CSV, and the first chamber of the main cylinder form a closed volume. When the on / off states of CSV1 and CSV2 are interchanged, the states of PSV2, TSV, and ISO1 to ISO4 remain unchanged. This method utilizes the first chamber of the main cylinder as part of the closed volume, enabling more sensitive detection of sealing leaks from the CSV to the main cylinder side.

[0054] Another embodiment is essentially the same as Embodiment 1, except that steps S1 and S2 are combined into a continuous pressure-building process to reduce the number of valve switching operations and the total diagnostic time. Specifically, in the initial state, PSV2, CSV1, CSV2, TSV, and all ISO valves are controlled to form a closed large loop including both the electric cylinder and the main cylinder. In the first stage, the drive motor slowly builds pressure to the first intermediate pressure P_mid, and the motor displacement S_mid is recorded. If S_mid is less than the first threshold, it indicates that the total volume of the electric cylinder to main cylinder loop is small (healthy); if S_mid is too large, there may be gas. In the second stage, the valve state remains unchanged, and pressure is continued to be built up to the first target pressure P1 or the first target displacement S_Req1. By analyzing the change in the slope of the displacement-pressure curve throughout the entire pressure-building process, it is distinguished whether the gas is present on the electric cylinder side or the main cylinder side (for example, if the initial slope is low and the slope returns to normal later, the gas may be concentrated in the electric cylinder loop).

[0055] The present invention also provides a computer device, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of any of the methods described above. The computer device may be an electronic control unit (ECU) of a vehicle or a dedicated diagnostic controller.

[0056] The present invention also provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of the method described in any of the preceding claims. The storage medium may be a non-volatile storage medium such as flash memory, hard disk, or optical disk.

[0057] The present invention also provides a computer program product, including a computer program that, when executed by a processor, implements the steps of the method described in any of the preceding claims.

[0058] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0059] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium. When executed, the computer program can include the processes of the embodiments described above. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0060] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0061] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this application. It is understood that this invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of this invention. Furthermore, under the teachings of this invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of this invention. Therefore, this invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are protected by this invention.

Claims

1. A method for diagnosing air or leakage in the hydraulic circuit of a brake-by-wire system, the brake-by-wire system comprising a motor-driven electric cylinder, electric cylinder isolation valves PSV1 and PSV2, master cylinder isolation valves CSV1 and CSV2, wheel cylinder isolation valves ISO1 to ISO4, simulator isolation valve SIV, test and diagnostic valve TSV, pressure relief valve PRV, electric cylinder pressure sensor BPS, master cylinder pressure sensor MCPS, and motor position sensor MPS, characterized in that, The method comprises the following steps: Step S1, electric cylinder circuit detection: placing CSV1 and CSV2 in a conducting state, placing ISO1 to ISO4 all in a cut-off state, placing both PSV1 and PSV2 in a conducting state, and forming a closed test volume V1 from an outlet of the electric cylinder to an inlet of a wheel cylinder via PSV1 / PSV2; driving a motor to discharge brake fluid at a constant rate, and recording an actual displacement S_act of the motor when an electric cylinder pressure sensor BPS reaches a first target pressure P1; performing three-state determination according to a relationship between S_act and a preset first lower displacement limit value S_Low and a preset first upper displacement limit value S_High: if S_act ≤ S_Low and BPS reaches P1, determining that the electric cylinder circuit is healthy; if S_Low < S_act ≤ S_High and BPS reaches P1, determining that a small amount of gas invades the electric cylinder circuit, wherein the gas causes reduction of an effective bulk modulus of hydraulic pressure and reduction of a pressure increase amplitude corresponding to the same discharge volume; if S_act > S_High or BPS cannot reach P1, determining that a large amount of gas invades the electric cylinder circuit or brake fluid leakage occurs in the electric cylinder circuit, and terminating the subsequent steps of pressurizing a master cylinder side and a simulator side; Step S2, master cylinder circuit detection: on the premise that the electric cylinder circuit is determined to be healthy in step S1, placing PSV2, CSV1 and TSV in a conducting state, placing ISO1 to ISO4 in a cut-off state, driving the motor to supply liquid to a first chamber of the master cylinder via PSV2 and CSV1, monitoring a pressure building response by a master cylinder pressure sensor MCPS, and determining whether gas invasion or leakage exists in the master cylinder circuit according to a relationship between motor displacement and MCPS pressure; Step S3, pedal simulator circuit detection: after the master cylinder circuit is determined to be qualified in step S2, placing a simulator isolation valve SIV in a conducting state, so that an additional volume discharged by the electric cylinder fills a simulator branch at the same time, and determining whether gas invasion or leakage exists in the pedal simulator circuit according to a relationship between additional displacement of the motor and a pressure building rate of the simulator branch; Step S4, three-way valve leakage detection: controlling PSV2 to be powered on and conducted, TSV to be powered on and cut off, ISO1 to ISO4 to be powered on and cut off, SIV to be powered off and cut off, and controlling CSV1 to be powered on and conducted, and CSV2 to be powered off and cut off; after driving the motor to build pressure in the electric cylinder to the first target pressure P1 or a first target displacement S_Req1, controlling CSV1 to be powered off and cut off; then controlling CSV1 and CSV2 to be powered on and conducted at the same time, and after a preset duration, controlling CSV1 and CSV2 to be powered off and cut off at the same time; if pressure detected by the master cylinder pressure sensor MCPS is less than a second target pressure P2 after CSV1 and CSV2 are powered off at the same time, determining that internal liquid cross leakage exists at an internal sealing interface in CSV1 or CSV2; Step S5, Full-Circuit Detection: After passing the qualification test in Step S4, full-circuit leakage and gas content detection is performed, and the system switches to the dedicated valve state for full-circuit detection; the drive motor builds pressure to the electric cylinder to the preset final test pressure P_final and then enters the pressure holding window Δt_final. If the pressure decay rate dP / dt in the pressure holding window is greater than the decay threshold λ_leak, then a leakage fault is determined to exist in the full circuit; if dP / dt ≤ λ_leak but the compensation displacement required by the motor to maintain P_final is greater than the gas compensation threshold S_gas, then residual gas content is determined to exist in the full circuit.

2. The method according to claim 1, characterized in that, In step S1, the first lower displacement limit S_Low and the first upper displacement limit S_High are motor displacement tolerance bands calculated based on the nominal hydraulic effective volume V_eff and brake fluid bulk modulus β_liq of the same line-controlled braking hardware batch, according to the relationship P = β_liq · ΔV_actual / V_eff, where ΔV_actual is obtained by subtracting the temperature compensation term from the piston discharge volume converted from the motor rotor position.

3. The method according to claim 1, characterized in that, In step S2, when the motor displacement has reached the first lower displacement limit S_Low but the pressure of the master cylinder pressure sensor MCPS has not yet reached the first target pressure P1, excluding the premise that the electric cylinder circuit has been confirmed to be healthy in step S1, the source of the fault is located in the master cylinder chamber, master cylinder seal, or hydraulic connection section between the master cylinder and CSV1 where gas intrusion or leakage exists.

4. The method according to claim 1, characterized in that, In step S3, after confirming that there is no substantial leakage in the electric cylinder circuit and the main cylinder circuit, the simulator isolation valve SIV is opened so that the additional volume discharged by the electric cylinder simultaneously fills the simulator branch. When the theoretical pressure rise corresponding to the additional displacement of the motor does not match the rated volume of the simulator branch, and the pressure build-up rate of the simulator branch is lower than the calibrated value P2 / t_th, it is determined that the simulator branch contains gas.

5. The method according to claim 1, characterized in that, The preset curve deviation threshold κ(ΔV) mentioned in step S4 is a function of the discharge volume ΔV. κ(ΔV) is obtained by calibrating the upper limit of the difference between the CSV bistate curves of qualified line control brake products in the same batch.

6. The method according to claim 1, characterized in that, Steps S1 to S5 are executed sequentially. When step S1 or step S2 determines that there is a serious leak, the simulator isolation valve SIV is locked in the normally closed state to prevent contamination of the master cylinder sealing interface, and a diagnostic fault code corresponding to the fault level is output through the vehicle bus, thus suspending the execution of subsequent steps.

7. The method according to claim 1, characterized in that, Steps S1 to S5 are automatically triggered and executed before the vehicle is powered off and in a parking brake confirmation state.

8. The method according to claim 1, characterized in that, In step S1, the formation of the closed test volume V1 also includes a split-axis detection mode: first, only ISO1 and ISO2 corresponding to the front axle are placed in the on state, and ISO3 and ISO4 corresponding to the rear axle are placed in the off state. After the front axle electric cylinder circuit detection is completed, the axle states are exchanged to complete the rear axle electric cylinder circuit detection.

9. The method according to claim 1, characterized in that, In step S1, pressure changes are indirectly reflected by monitoring the waveforms of motor phase current or bus current: when the circuit contains gas, the current rises slowly in the initial stage of pressure building; when the circuit leaks, the current continues to decrease in the steady-state pressure holding stage. The actual current curve is compared with the calibrated healthy current curve to determine the degree of fault.

10. The method according to claim 1, characterized in that, In step S4, the closed test volume V_test is formed by controlling PSV2 to be on, selectively turning on either CSV1 or CSV2, turning on TSV, and turning off ISO1 to ISO4, so that the electric cylinder outlet forms a closed volume with the first chamber of the main cylinder through PSV2 and the turned-on CSV; when the on / off states of CSV1 and CSV2 are interchanged, the states of PSV2, TSV, and ISO1 to ISO4 remain unchanged.

11. The method according to claim 1, characterized in that, In step S5, the dedicated valve state configuration for full-loop detection is as follows: control PSV2 to be energized so that it switches from normally closed state to conducting state, while keeping PSV1 in an unenergized conducting state; Control CSV2 to be in a non-energized conducting state, and control CSV1 to be energized so that it switches from a normally open state to a cut-off state; Control ISO1 to ISO4 to be in a non-energized conducting state; Simultaneously, the TSV is powered on to switch it to the off state.

12. The method according to claim 1, characterized in that, In step S1, when it is determined that there is a large amount of gas intrusion or brake fluid leakage in the electric cylinder circuit, the gas intrusion and leakage are further distinguished in the following ways: if the motor displacement exceeds S_High but BPS can still slowly climb to P1 within a preset time, it is determined to be a large amount of gas intrusion; if the motor displacement continues to increase but BPS can never reach 50% of P1, it is determined to be brake fluid leakage.

13. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 12.

14. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 12.

15. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 12.

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