Vehicle braking system and braking method based on electronic hydraulic active boosting

Abstract

The present invention discloses a vehicle braking system and braking method based on electronic hydraulic active supercharging, belonging to the field of vehicle redundant braking. The system includes a main brake module and a redundant brake module, both of which are connected to the ECU. The redundant brake module includes an HCU and two low-pressure accumulators. The HCU includes a pump motor, a front axle pressure control assembly for regulating pressure on the two front wheels, and a rear axle pressure control assembly for regulating pressure on the two rear wheels. Using the above-mentioned vehicle braking system and braking method based on electronic hydraulic active supercharging, pressure control modules can be formed on the front and rear axles respectively using only four solenoid valves, thereby achieving a low-select ABS function when the main brake module fails. This simplifies the system structure, reduces hardware costs and the probability of failure, while still ensuring the vehicle's directional stability and anti-loss of control capabilities during braking, achieving a balance between efficiency and safety in redundant braking scenarios.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle redundant braking, and in particular to a vehicle braking system and braking method based on electronic hydraulic active boosting. Background Art

[0002] The braking system is a core component in ensuring safe driving. Its performance is directly related to vehicle handling stability and the safety of drivers and passengers. Currently, as the automotive industry accelerates toward intelligent and connected driving, the braking system is undergoing a technological evolution from traditional mechanical hydraulic control to electronic integrated control. High integration, fast response, miniaturization, and lightweighting have become core trends in the industry's development.

[0003] The reliability of the wire control brake system mainly depends on electronic components and hydraulic circuits. Under complex road conditions (such as pipeline vibration caused by bumpy roads), long-term high-frequency use (such as repeated braking in congested urban roads) or extreme environments (such as low temperature and high humidity), the main brake module may experience functional degradation or even complete failure due to problems such as hydraulic pipeline leakage, pressure sensor failure, and brake master cylinder failure.

[0004] To mitigate the risk of primary brake module failure, some vehicles are equipped with redundant brake modules. However, these redundant ABS modules still have limitations. To achieve precise pressure regulation and independent wheel control, most redundant brake modules require a large number of solenoid valves (e.g., at least two valves per wheel for fluid inlet and return control). This not only increases system complexity and manufacturing costs, but also complicates the layout of the hydraulic circuit and increases the probability of failure.

[0005] At the same time, in terms of control strategy, existing redundant ABS control methods often rely on complex multi-valve coordinated logic, requiring independent pressure buildup, pressure maintenance, and pressure release control for each wheel. This places high demands on the computing power of the electronic control unit (ECU). In emergency conditions after the main brake module fails, the complex control process may lead to response delays. In addition, some solutions fail to specifically optimize the ABS function in redundant mode, making it difficult to stably implement low-select control (i.e., pressure adjustment based on the side with lower slip on both coaxial wheels, prioritizing vehicle stability) while retaining only basic hydraulic components. After the main brake module fails, insufficient control accuracy or poor strategy adaptability may still lead to risks such as skidding and tailspin during emergency braking. Summary of the Invention

[0006] The purpose of the present invention is to provide a vehicle braking system and braking method based on electronic hydraulic active boosting to solve the above technical problems.

[0007] To achieve the above objectives, the present invention provides a vehicle braking system based on electronic hydraulic active boosting, comprising a primary brake module and a redundant brake module communicating with each other via a CAN bus, both of which are connected to an ECU, the redundant brake module comprising an HCU and two low-pressure accumulators, the HCU comprising a pump motor, a front axle pressure control assembly for regulating pressure on two front wheels, and a rear axle pressure control assembly for regulating pressure on two rear wheels;

[0008] The ECU is electrically connected to the pump motor, and the pump motor is connected to the front axle pressure control assembly and the rear axle pressure control assembly through two low-pressure accumulators respectively. The front axle pressure control assembly and the rear axle pressure control assembly are both connected to the brake master cylinder, and the brake master cylinder is connected to the brake caliper through a pipeline.

[0009] Preferably, the front axle pressure regulating assembly includes a front axle dual-channel hydraulic pipeline and a front axle fluid supply valve and a front axle pressure reducing valve respectively provided on the two channels of the front axle dual-channel hydraulic pipeline; the rear axle pressure regulating assembly includes a rear axle dual-channel hydraulic pipeline and a rear axle fluid supply valve and a rear axle pressure reducing valve respectively provided on the two channels of the rear axle dual-channel hydraulic pipeline;

[0010] One end of the front axle dual-channel hydraulic pipeline and one end of the rear axle dual-channel hydraulic pipeline are respectively connected to the two low-pressure accumulators, and the other end of the front axle dual-channel hydraulic pipeline and the other end of the rear axle dual-channel hydraulic pipeline are respectively connected to the two front wheel cylinders and the two rear wheel cylinders of the brake master cylinder;

[0011] The front axle fluid supply valve, the front axle pressure reducing valve, the rear axle fluid supply valve and the rear axle pressure reducing valve are all electrically connected to the ECU.

[0012] Preferably, the ECU is further connected to a pressure sensor for collecting the pressure value of the brake master cylinder, four wheel speed sensors respectively arranged on the four wheels, a pedal sensor and an ignition sensor.

[0013] A braking method for a vehicle braking system based on electronic hydraulic active boosting comprises the following steps:

[0014] S1, Fault diagnosis and redundancy triggering: When the main brake module fails, the ECU cuts off the main brake system and triggers the redundant brake module;

[0015] S2. collecting wheel speed signals of the four wheels, and calculating the slip rates of the four wheels based on the collected wheel speed signals;

[0016] S3. Based on the collected slip rates of the four wheels, use a Kalman filter to predict the dynamic slip rate at a future moment, and determine whether the predicted dynamic slip rate at the future moment is not less than a preset safety threshold. If so, execute step S4; otherwise, return to step S2;

[0017] S4. Generate low-select ABS strategy: Select the side with lower slip ratio between the front and rear wheels as the control reference, and generate pressure regulation command using PID closed-loop control algorithm;

[0018] S5. Execute ABS strategy: The pump motor operates according to the pressure regulation command generated in step S4. At the same time, the front axle pressure regulation component and the front axle pressure regulation component adjust the brake master cylinder pressure according to the duty cycle issued by the ECU to achieve a pressure build-up-maintain-release cycle.

[0019] Preferably, the slip rate calculation formula in step S2 is as follows:

[0020] (1);

[0021] Where, Indicates the The slip rate of each wheel; Indicates the vehicle's speed; Indicates the Angular velocity of each wheel; Indicates the The rolling radius of the wheels.

[0022] Preferably, step S3 specifically includes the following steps:

[0023] S31, state initialization: set the initial state estimate of the Kalman filter to , the initial covariance matrix is ,in, , They represent the initial vehicle speed, Estimated rolling radius and angular velocity of each wheel;

[0024] S32, prediction stage: using the state and covariance information corrected at the previous moment, combined with vehicle dynamics and control input, to estimate the current state and covariance;

[0025] Among them, the state prediction expression is as follows:

[0026] (2);

[0027] Where, express Moment, based on The predicted state of the moment state estimate; represents the state transition matrix; express The estimated value of the state after correction at each moment; represents the control input matrix; express The control input quantity at each moment;

[0028] The covariance matrix prediction expression is as follows:

[0029] (3);

[0030] Where, express Moment, based on The predicted covariance matrix of the moment covariance matrix; express The covariance matrix after correction at each moment; Represents a transpose operation; represents the process noise covariance matrix;

[0031] S33, update phase: use the actual measurement value at the current moment to correct the state and covariance obtained in the prediction phase:

[0032] (4);

[0033] (5);

[0034] Where, express The estimated value of the state after being corrected by the measured value at all times; represents the Kalman gain, and , represents the measurement moment, represents the measurement noise covariance matrix; express The covariance matrix after correction at each moment; represents the identity matrix;

[0035] S34, loop iterate step S32 and step S33 until convergence, output the vehicle speed at the future moment, The angular velocity and rolling radius of each wheel are calculated, and the prediction results are substituted into formula (1) to obtain the dynamic slip rate prediction results.

[0036] Preferably, the PID closed-loop control algorithm described in step S4 is expressed as follows:

[0037] (6);

[0038] Where, Indicates the voltage regulation instruction calculated and output based on the current error and historical error; 、 and represent the proportional, integral and differential coefficients respectively; Indicates the difference between the actual slip rate and the target slip rate at the current moment.

[0039] Preferably, in the pressure building phase described in step S5, the front axle fluid supply valve and the rear axle fluid supply valve are both in the open state, and the front axle pressure regulating valve and the rear axle pressure regulating valve are both in the closed state. At this time, the high-pressure brake fluid pressurized by the pump motor enters the front wheel cylinder and the rear wheel cylinder respectively through the two low-pressure accumulators, and at the same time, the channel for the wheel cylinder brake fluid to flow back to the low-pressure accumulator is blocked, thereby achieving pressure building until the target pressure in the generated pressure regulation instruction is reached;

[0040] During the holding phase, the front axle fluid supply valve, rear axle fluid supply valve, front axle pressure regulating valve, and rear axle pressure regulating valve are all closed to maintain the current pressure.

[0041] During the release phase, the front axle fluid supply valve and the rear axle fluid supply valve are both in the closed state, and the front axle pressure regulating valve and the rear axle pressure regulating valve are both in the open state, cutting off the supply of high-pressure brake fluid and allowing the wheel cylinder brake fluid to flow back to the channel of the low-pressure accumulator.

[0042] Therefore, the present invention adopts the above-mentioned vehicle braking system and braking method based on electronic hydraulic active boosting, which has the following beneficial effects:

[0043] 1. Streamlined structure, reduced costs and failure risks: A streamlined valve group consisting of only four solenoid valves replaces the traditional multi-valve design, simplifying the hydraulic circuit layout, reducing the amount of hardware, and lowering manufacturing costs and the probability of failure caused by complex valve groups.

[0044] 2. Safeguarding ABS function in the event of main brake failure: In the event of main brake module failure, the streamlined valve group can achieve low-select ABS function, ensuring that the wheels do not lock during emergency braking, maintaining steering capability, reducing the risk of loss of control such as skidding and tailspin, and ensuring the safety of drivers and passengers;

[0045] 3. Efficient Pressure Regulation and Control: The front and rear axle pressure control components each control the corresponding wheels through a dual-channel hydraulic circuit. Combined with the pump motor's active pressure buildup and pressure sensor feedback, this achieves precise brake pressure "build-hold-release" cycle regulation with millisecond-level response speeds.

[0046] 4. Improved vehicle braking stability: The system adopts an axle control priority strategy and implements symmetrical joint control of the two coaxial wheels (front or rear). This effectively avoids yaw moment imbalance caused by excessive braking on one side, ensuring vehicle directional stability under degraded braking system conditions.

[0047] 5. Redundant design enhances system reliability: Through CAN bus communication with the main brake module and hard-wired signal input (brake pedal signal, ignition signal, wheel speed signal, etc.), combined with the ECU's dynamic control logic, a redundant braking mechanism is formed, significantly reducing the safety risks caused by failure of the main brake system, and providing braking safety redundancy support for advanced driver assistance and autonomous driving.

[0048] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a schematic diagram of a vehicle braking system based on electronic hydraulic active boosting according to the present invention. DETAILED DESCRIPTION

[0050] In order to make the purposes, technical solutions and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, where the same or similar numbers throughout represent the same or similar elements or elements with the same or similar functions.

[0051] It should be noted that the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or devices.

[0052] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0053] like Figure 1 As shown, a vehicle braking system based on electronic hydraulic active boosting includes a main braking module and a redundant braking module that communicate with each other via a CAN bus. The main braking module and the redundant braking module are both connected to the ECU. The redundant braking module includes an HCU and two low-pressure accumulators. The HCU includes a pump motor, a front axle pressure regulating assembly for regulating the pressure of the two front wheels, and a rear axle pressure regulating assembly for regulating the pressure of the two rear wheels. The ECU is electrically connected to the pump motor, and the pump motor is respectively connected to the front axle pressure regulating assembly and the rear axle pressure regulating assembly via two low-pressure accumulators. The front axle pressure regulating assembly and the rear axle pressure regulating assembly are both connected to the brake master cylinder, and the brake master cylinder is connected to the brake caliper via a pipeline.

[0054] The front axle pressure control component includes a front axle dual-channel hydraulic pipeline and a front axle fluid supply valve and a front axle pressure reducing valve respectively arranged on the two channels of the front axle dual-channel hydraulic pipeline; the rear axle pressure control component includes a rear axle dual-channel hydraulic pipeline and a rear axle fluid supply valve and a rear axle pressure reducing valve respectively arranged on the two channels of the rear axle dual-channel hydraulic pipeline; one end of the front axle dual-channel hydraulic pipeline and one end of the rear axle dual-channel hydraulic pipeline are respectively connected to the two low-pressure accumulators, and the other end of the front axle dual-channel hydraulic pipeline and the other end of the rear axle dual-channel hydraulic pipeline are respectively connected to the two front wheel cylinders and the two rear wheel cylinders of the brake master cylinder; the front axle supply valve, the front axle pressure reducing valve, the rear axle supply valve and the rear axle pressure reducing valve are all electrically connected to the ECU.

[0055] The ECU is also connected to a pressure sensor for collecting the pressure value of the brake master cylinder, four wheel speed sensors arranged on the four wheels, a pedal sensor and an ignition sensor.

[0056] It should be noted that the above-mentioned electronic components are mature products on the market. This embodiment only needs to purchase them and connect them according to the instructions. No improvement is made to them, so their circuit connection structure and principles will not be described in detail here.

[0057] A braking method for a vehicle braking system based on electronic hydraulic active boosting comprises the following steps:

[0058] S1, Fault diagnosis and redundancy triggering: When the main brake module fails, the ECU cuts off the main brake system and triggers the redundant brake module;

[0059] S2. collecting wheel speed signals of the four wheels, and calculating the slip rates of the four wheels based on the collected wheel speed signals;

[0060] The slip ratio calculation formula in step S2 is as follows:

[0061] (1);

[0062] Where, Indicates the The slip rate of each wheel; Indicates the vehicle's speed; Indicates the Angular velocity of each wheel; Indicates the The rolling radius of the wheels.

[0063] S3. Based on the collected slip rates of the four wheels, use a Kalman filter to predict the dynamic slip rate at a future moment, and determine whether the predicted dynamic slip rate at the future moment is not less than a preset safety threshold. If so, execute step S4; otherwise, return to step S2;

[0064] Step S3 specifically includes the following steps:

[0065] S31, state initialization: set the initial state estimate of the Kalman filter to , the initial covariance matrix is ,in, , They represent the initial vehicle speed, Estimated rolling radius and angular velocity of each wheel;

[0066] S32, prediction stage: using the state and covariance information corrected at the previous moment, combined with vehicle dynamics and control input, to estimate the current state and covariance;

[0067] Among them, the state prediction expression is as follows:

[0068] (2);

[0069] Where, express Moment, based on The predicted state of the moment state estimate; represents the state transition matrix; express The estimated value of the state after correction at each moment; represents the control input matrix; express The control input quantity at each moment;

[0070] The covariance matrix prediction expression is as follows:

[0071] (3);

[0072] Where, express Moment, based on The predicted covariance matrix of the moment covariance matrix; express The covariance matrix after correction at each moment; Represents a transpose operation; represents the process noise covariance matrix;

[0073] S33, update phase: use the actual measurement value at the current moment to correct the state and covariance obtained in the prediction phase:

[0074] (4);

[0075] (5);

[0076] Where, express The estimated value of the state after being corrected by the measured value at all times; represents the Kalman gain, and , represents the measurement moment, represents the measurement noise covariance matrix; express The covariance matrix after correction at each moment; represents the identity matrix;

[0077] S34, loop iterate step S32 and step S33 until convergence, output the vehicle speed at the future moment, The angular velocity and rolling radius of each wheel are calculated, and the prediction results are substituted into formula (1) to obtain the dynamic slip rate prediction results.

[0078] S4. Generate low-select ABS strategy: Select the side with lower slip ratio between the front and rear wheels as the control reference, and use the PID closed-loop control algorithm to generate a pressure regulation command;

[0079] The PID closed-loop control algorithm expression described in step S4 is as follows:

[0080] (6);

[0081] Where, Indicates the voltage regulation instruction calculated and output based on the current error and historical error; 、 and represent the proportional, integral and differential coefficients respectively; Indicates the difference between the actual slip rate and the target slip rate at the current moment.

[0082] S5. Execute ABS strategy: The pump motor operates according to the pressure regulation command generated in step S4. At the same time, the front axle pressure regulation component and the front axle pressure regulation component adjust the brake master cylinder pressure according to the duty cycle issued by the ECU to achieve a pressure build-up-maintain-release cycle.

[0083] In the pressure building phase described in step S5, the front axle fluid supply valve and the rear axle fluid supply valve are both in the open state, and the front axle pressure regulating valve and the rear axle pressure regulating valve are both in the closed state. At this time, the high-pressure brake fluid pressurized by the pump motor enters the front wheel cylinder and the rear wheel cylinder respectively through the two low-pressure accumulators, while the channel for the wheel cylinder brake fluid to flow back to the low-pressure accumulator is blocked, thereby achieving pressure building until the target pressure in the generated pressure regulation command is reached;

[0084] During the holding phase, the front axle fluid supply valve, rear axle fluid supply valve, front axle pressure regulating valve, and rear axle pressure regulating valve are all in the closed state to maintain the current pressure;

[0085] During the release phase, the front axle fluid supply valve and the rear axle fluid supply valve are both in the closed state, and the front axle pressure regulating valve and the rear axle pressure regulating valve are both in the open state, cutting off the supply of high-pressure brake fluid and allowing the wheel cylinder brake fluid to flow back to the channel of the low-pressure accumulator.

[0086] 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 the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A braking method for a vehicle braking system based on electronic hydraulic active boosting, characterized in that: a vehicle braking system, comprising a primary brake module and a redundant brake module communicating with each other via a CAN bus, the primary brake module and the redundant brake module being connected to an ECU, the redundant brake module comprising an HCU and two low-pressure accumulators, the HCU comprising a pump motor, a front axle pressure control assembly for regulating pressure on two front wheels, and a rear axle pressure control assembly for regulating pressure on two rear wheels; The ECU is electrically connected to the pump motor, which is connected to the front axle pressure control assembly and the rear axle pressure control assembly via two low-pressure accumulators. The front axle pressure control assembly and the rear axle pressure control assembly are both connected to the brake master cylinder, which is connected to the brake caliper via a pipeline. The front axle pressure control assembly includes a front axle dual-channel hydraulic pipeline and a front axle fluid supply valve and a front axle pressure reducing valve respectively provided on the two channels of the front axle dual-channel hydraulic pipeline; the rear axle pressure control assembly includes a rear axle dual-channel hydraulic pipeline and a rear axle fluid supply valve and a rear axle pressure reducing valve respectively provided on the two channels of the rear axle dual-channel hydraulic pipeline; One end of the front axle dual-channel hydraulic pipeline and one end of the rear axle dual-channel hydraulic pipeline are respectively connected to the two low-pressure accumulators, and the other end of the front axle dual-channel hydraulic pipeline and the other end of the rear axle dual-channel hydraulic pipeline are respectively connected to the two front wheel cylinders and the two rear wheel cylinders of the brake master cylinder; The front axle fluid supply valve, front axle pressure reducing valve, rear axle fluid supply valve and rear axle pressure reducing valve are all electrically connected to the ECU; The braking method includes the following steps: S1, Fault diagnosis and redundancy triggering: When the main brake module fails, the ECU cuts off the main brake system and triggers the redundant brake module; S2. collecting wheel speed signals of the four wheels, and calculating the slip rates of the four wheels based on the collected wheel speed signals; The slip ratio calculation formula in step S2 is as follows: （1）； Where, Indicates the The slip rate of each wheel; Indicates the vehicle's speed; Indicates the Angular velocity of each wheel; Indicates the The rolling radius of each wheel; S3. Based on the collected slip rates of the four wheels, use a Kalman filter to predict the dynamic slip rate at a future moment, and determine whether the predicted dynamic slip rate at the future moment is not less than a preset safety threshold. If so, execute step S4; otherwise, return to step S2; Step S3 specifically includes the following steps: S31, state initialization: set the initial state estimate of the Kalman filter to , the initial covariance matrix is ,in, , They represent the initial vehicle speed, Estimated rolling radius and angular velocity of each wheel; S32, prediction stage: using the state and covariance information corrected at the previous moment, combined with vehicle dynamics and control input, to estimate the current state and covariance; Among them, the state prediction expression is as follows: （2）； Where, express Moment, based on The predicted state of the moment state estimate; represents the state transition matrix; express The estimated value of the state after correction at each moment; represents the control input matrix; express The control input quantity at each moment; The covariance matrix prediction expression is as follows: （3）； Where, express Moment, based on The predicted covariance matrix of the moment covariance matrix; express The covariance matrix after correction at each moment; Represents a transpose operation; represents the process noise covariance matrix; S33, update phase: use the actual measurement value at the current moment to correct the state and covariance obtained in the prediction phase: （4）； （5）； Where, express The estimated value of the state after being corrected by the measured value at all times; represents the Kalman gain, and , represents the measurement matrix, represents the measurement noise covariance matrix; express The covariance matrix after correction at each moment; represents the identity matrix; S34, loop iterate step S32 and step S33 until convergence, output the vehicle speed at the future moment, The angular velocity and rolling radius of each wheel are calculated, and the prediction results are substituted into formula (1) to obtain the dynamic slip rate prediction result l; S4. Generate low-select ABS strategy: Select the side with lower slip ratio between the front and rear wheels as the control reference, and generate pressure regulation command using PID closed-loop control algorithm; S5. Execute ABS strategy: The pump motor operates according to the pressure regulation command generated in step S4. At the same time, the front axle pressure regulation component and the rear axle pressure regulation component adjust the brake master cylinder pressure according to the duty cycle issued by the ECU, realizing a pressure build-up-maintain-release cycle.

2. The braking method of a vehicle braking system based on electronic hydraulic active boosting according to claim 1, characterized in that: The ECU is also connected to a pressure sensor for collecting the pressure value of the brake master cylinder, four wheel speed sensors arranged on the four wheels, a pedal sensor and an ignition sensor.

3. The braking method of a vehicle braking system based on electronic hydraulic active boosting according to claim 1, characterized in that: The PID closed-loop control algorithm expression described in step S4 is as follows: （6）； Where, Indicates the voltage regulation instruction calculated and output based on the current error and historical error; 、 and represent the proportional, integral and differential coefficients respectively; Indicates the difference between the actual slip rate and the target slip rate at the current moment.

4. The braking method of a vehicle braking system based on electronic hydraulic active boosting according to claim 3, characterized in that: In the pressure building phase described in step S5, the front axle fluid supply valve and the rear axle fluid supply valve are both in the open state, and the front axle pressure regulating valve and the rear axle pressure regulating valve are both in the closed state. At this time, the high-pressure brake fluid pressurized by the pump motor enters the front wheel cylinder and the rear wheel cylinder respectively through the two low-pressure accumulators, while the channel for the wheel cylinder brake fluid to flow back to the low-pressure accumulator is blocked, thereby achieving pressure building until the target pressure in the generated pressure regulation command is reached; During the holding phase, the front axle fluid supply valve, rear axle fluid supply valve, front axle pressure regulating valve, and rear axle pressure regulating valve are all closed to maintain the current pressure. During the release phase, the front axle fluid supply valve and the rear axle fluid supply valve are both in the closed state, and the front axle pressure regulating valve and the rear axle pressure regulating valve are both in the open state, cutting off the supply of high-pressure brake fluid and allowing the wheel cylinder brake fluid to flow back to the channel of the low-pressure accumulator.

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