A boost strategy and pressure precise control method of an electric power brake system

Abstract

The application provides a method for actively switching driving style and precisely controlling pressure of an electric power-assisted braking system, solves the problems that the current electric power-assisted braking system cannot realize continuous change of braking assistance ratio to realize free switching of driving style, and the performance parameter change caused by a brushless direct current motor leads to the problem that precise pressure control cannot be realized, and the like. The application comprises two braking modes of power-assisted braking and active braking. In the power-assisted braking mode, an electronic control unit judges the braking assistance required at the moment according to a preset braking assistance characteristic curve, and a switching device is used to autonomously select an assistance ratio to switch the driving style. In the active braking mode, a double-loop controller is designed for pressure control. An outer loop is used to adjust the pressure of a hydraulic system, an inner loop is used to track the motor current, and a tracking differentiator and an adaptive control algorithm are used to solve the parameter change problem in the motor.

Description

Technical Field

[0001] This invention belongs to the field of automotive control technology, and in particular relates to a method for actively switching driving styles and precisely controlling pressure in an electric power-assisted braking system. Background Technology

[0002] Braking by drive is key to achieving chassis controllability, integration, and intelligence. Based on different implementation methods, it can be divided into electromechanical braking systems (EMB) and electrohydraulic braking systems (EHB). EHB systems require less modification to traditional hydraulic braking systems and have certain advantages; however, they are more complex, pose safety hazards with high-voltage accumulators, and are costly in both cost and maintenance. EMB systems, on the other hand, are entirely electromechanical braking, eliminating the hydraulic braking system; however, at present, they are costly and lack fail-safe features, making them difficult to meet regulatory requirements. Currently, electric power-assisted braking systems with motor assistance are developing rapidly. Considering system complexity, cost, and efficiency, booster-based electric power-assisted systems have good feasibility and development potential.

[0003] Traditional vacuum boosters have an assist factor (the ratio of assist force to pedal force) determined by the initial structure, meaning that adjusting the assist factor to meet different assist needs is very difficult. In contrast, electric power-assisted braking systems use a combination of motor drive and mechanical transmission, resulting in faster response, more precise pressure control, and the ability to achieve drive-by-wire active braking. Current electro-hydraulic braking systems typically employ a uniform design, selecting a fixed assist ratio suitable for most drivers, lacking the ability to adjust the assist ratio to match different driving styles. Drivers cannot continuously change the braking assist ratio through manual operation.

[0004] Current electro-hydraulic braking systems use multiple solenoid valves to ensure brake fluid flow in conventional assisted braking and active braking modes. However, the addition of solenoid valves increases the difficulty of system control, and the consistency of these valves can significantly impact braking system performance. Furthermore, in traditional hydraulic brake assist systems, the driver's braking action corresponds one-to-one with the braking force. In cases of improper operation or delayed reaction, the system cannot quickly engage active safety functions to ensure safety. Active braking primarily involves controlling the pressure of the master cylinder, typically requiring only a closed-loop controller. Traditional pressure control loops often utilize PID controllers, which are prone to integral saturation and steady-state errors, affecting dynamic response speed. Additionally, motor parameters can drift due to excessive wear after prolonged operation and change with environmental conditions, making precise control difficult. Summary of the Invention

[0005] To address the shortcomings of the existing technology, the present invention aims to provide a method for actively switching driving styles and precisely controlling pressure in an electric power-assisted braking system. This method enables both power-assisted braking and active braking functions in the electric power-assisted braking system. Furthermore, it proposes solutions to problems such as performance parameter variations and uncertainties caused by brushless DC motors in pressure control, and has high application value.

[0006] The technical solution adopted in this invention is as follows:

[0007] An electric power-assisted braking system includes an active braking module, a power-assisted braking module, a mode switching command module, and an execution module. The active braking module uses an improved PID controller to obtain the desired current based on the input target pressure value and the actual pressure. The power-assisted braking module uses a displacement sensor to detect pedal travel information and inputs the power-assisted strategy to obtain the power-assisted braking current. The mode switching command module selects the driving mode based on different magnitudes of power-assisted braking current. The execution module controls the current input to the brushless DC motor based on the desired current / power-assisted braking current to control the motor output corresponding torque and speed, thereby controlling the hydraulic system to output corresponding hydraulic braking force to achieve vehicle braking. Simultaneously, the hydraulic system outputs the actual pressure value back to the active braking module.

[0008] Preferably, the control system includes an outer loop control and an inner loop control. The inner loop control is an execution module that performs braking based on the input current. The outer loop control is an active braking module that tracks the target pressure based on an improved PID controller and obtains the desired current input for the inner loop control. The inner loop control outputs the actual pressure value and returns it to the input of the outer loop control, thus realizing a closed-loop control.

[0009] This invention also discloses an assist strategy and pressure precision control method for an electric power-assisted braking system, comprising the following steps: Step 1, collecting driver intent and road environment information to calculate a target pressure value, and selecting an active braking mode or a brake assist mode; Step 2, when the active braking mode is selected, the target pressure value and the actual pressure value fed back by the hydraulic system are used as inputs to an improved PID controller to calculate the desired braking pressure r_p, and the desired current is obtained from the desired braking pressure r_p as the control command for active braking; when the assist braking mode is selected, the output value Δx of a linear displacement sensor that collects the reaction pedal travel information is used as the first input control variable to input a custom strategy to obtain a target assist current as the control command for assist braking; Step 3, motor control is achieved based on the target assist current / desired current, and the adaptive current controller controls the current input to the brushless DC motor based on the input target assist current / desired current, combined with the sliding mode control principle, and the hydraulic system establishes a corresponding hydraulic braking force to achieve vehicle braking; the hydraulic system feeds back the actual voltage value to the active braking mode to achieve closed-loop pressure control.

[0010] Preferably, in step 2, to shorten the response time in emergency situations, the derivative value of Δx is obtained by passing it through a tracking differentiator. As the second control input variable, it is used to describe the severity of the driver's braking and braking intention.

[0011] As a preferred option, the customized strategy for the power-assisted braking mode is as follows: the relative displacement between the pedal and the master cylinder piston measured by the displacement sensor and the relative displacement derivative calculated by the tracking differentiator are used as the first and second input variables. Different target currents are obtained as outputs according to the preset power-assisted curve, thereby controlling the hydraulic braking force.

[0012] As a preferred option The value is calculated by the tracking differentiator, which is expressed as follows:

[0013]

[0014] In the formula, Δx is the output value of the linear displacement sensor, which is the actual measured curve to be tracked. tr1 It is a tracking signal, Δx tr2 It is Δx tr1 The derivative of , r0, h0 are adjustable parameters, Δe tr F is the error between the actual and target output values. stp It is the tracking function of a second-order discrete system, and the superscript · indicates the derivative.

[0015] As a preferred method, the target current is obtained through a custom strategy as follows: based on the braking assist curve, different target currents are output according to the intervals where the sensor percentage values ​​are located. The braking assist curve intervals include the dead zone, the assist phase interval, and the hydraulic hysteresis compensation phase interval. The assist is 0 in the dead zone. The target assist current is obtained according to the relative displacement in the assist phase interval. A negative assist current is generated in the hydraulic hysteresis compensation phase interval to compensate for hydraulic hysteresis.

[0016] As a preferred embodiment, the method for implementing current control of the brushless DC motor using the adaptive current controller in step 3 is as follows: An approximate sliding mode control method without switching terms is adopted, and equivalent and switching terms are introduced to achieve stable control. The sliding mode surface is selected as S = ii. des , where i des The target current is the desired current / target assist current, and i is the actual current output by the motor. The actual current is returned to the input of the adaptive current controller as a feedback current signal to achieve current tracking control.

[0017] Preferably, the input of the adaptive current controller is Update the parameters according to the following formula.

[0018] In the formula, S is the sliding surface, parameters a1, b1, θ1, and x are all motor parameters, the superscript ^ indicates the estimated value, the superscript · indicates the derivative, γ is the tuning parameter, and λ is the attenuation ratio.

[0019] Preferably, the improved PID controller suppresses steady-state error through finite integrals and avoids integral saturation. Simultaneously, it employs a rolling optimization method for the integral term, resulting in a higher output u of the improved PID controller. c As shown in the following formula:

[0020]

[0021] In the formula, K p K i K d These are the coefficients of the proportional term, integral term, and differential term, respectively, e p For pressure error, For e p The derivative value, e L It is a threshold value, indicating that the integral action is effective when the pressure error is within a certain range.

[0022] Beneficial effects

[0023] (1) In a control architecture, active braking function and power-assisted braking function are realized at the same time, and the mode can be switched through the mode switching command. It can accurately track the driver's braking intention. The intelligent switching between different modes is highly efficient, which improves the speed and accuracy of braking response.

[0024] (2) The power-assisted braking function enables the power assist ratio to be continuously adjusted. The driver can change the braking power assist ratio arbitrarily and continuously through autonomous operation, and realize the autonomous switching of driving style from aggressive to conservative.

[0025] (3) The outer control loop of the dual-loop controller is PID control. The steady-state error is suppressed by integral and integral saturation is avoided. The integral term uses the rolling optimization method to calculate only the error in the most recent period. When the pressure error decreases within the given range, the integral term will take effect. The noise interference problem of the differential term can be solved by the above tracking differentiator.

[0026] (4) The improved PID controller in the pressure loop of the dual-loop controller exhibits excellent dynamic response speed and effectively overcomes integral saturation and steady-state errors. This results in more precise control of the master cylinder hydraulic pressure. The use of adaptive control methods in the controller addresses parameter variations and uncertainties, enabling the system to achieve a higher level of accuracy. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0028] Figure 1 This is a comprehensive control architecture for implementing the power-assisted braking mode and the active mode according to one embodiment of the present invention;

[0029] Figure 2 This is a diagram showing the assist current curve of one embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of an improved PID controller according to an embodiment of the present invention.

[0031] Figure 4 This is a schematic diagram of a control method according to an embodiment of the present invention. Detailed Implementation

[0032] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0033] like Figure 1 As shown, this invention discloses a power assist strategy and pressure precision control system for an electric power-assisted braking system, including an active braking module, a power assist braking module, a mode switching command module, and an execution module.

[0034] The active braking module, based on an improved PID controller, obtains the desired current according to the input target pressure value and the actual pressure. The power-assisted braking module, based on the displacement sensor, detects pedal travel information and inputs a power-assisted strategy to obtain the power-assisted braking current.

[0035] The mode switching command module selects the driving mode based on the different levels of power-assisted braking current.

[0036] The execution module is a brake-by-wire system that controls the current of the input brushless DC motor through an adaptive current controller. Simultaneously, it incorporates motor current and speed as feedback information to further control the motor, resolving the difficulty in accurately measuring precise motor parameters and various nonlinear issues. Specifically, it controls the input current of the brushless DC motor based on the desired current / assisted braking current to control the motor's output torque and speed, thereby controlling the hydraulic system to output corresponding hydraulic braking force to achieve vehicle braking; at the same time, the actual pressure value output by the hydraulic system is returned to the active braking module.

[0037] The control system is divided into outer loop control and inner loop control. The outer loop regulates the pressure of the hydraulic system, while the inner loop tracks the motor current and uses a tracking differentiator and adaptive control algorithms to address parameter variations in the motor. The inner loop control module implements braking based on the input current, while the outer loop control module, an active braking module, tracks the target pressure using an improved PID controller to obtain the desired current input to the inner loop control. The actual pressure value output from the inner loop control is returned to the input of the outer loop control, thus achieving a closed-loop control.

[0038] This invention also discloses an assist strategy and a method for precise pressure control in an electric power-assisted braking system, comprising the following steps:

[0039] Step 1: Collect driver intent and road environment information to calculate target pressure value, and select active braking mode or brake assist mode.

[0040] Step 2: When the active braking function is selected, the target pressure value and the actual pressure value fed back by the hydraulic system are input to the improved PID controller to calculate the desired braking pressure r. p And by the desired braking pressure r p The desired current is obtained as the control command for active braking.

[0041] When the power-assisted braking function is selected, the output value Δx of the linear displacement sensor is collected. This value is divided by the maximum output value during the process to obtain the sensor opening value, which is then input into the custom strategy to obtain the target assist current. Considering the short response time in emergency situations, the derivative value of the output value calculated by the tracking differentiator is also added. The second control input variable is used to describe the severity of the driver's braking and braking intention; the target assist current is obtained based on the assist curve, thereby controlling the hydraulic braking force.

[0042] The preset braking assist curve is as follows:

[0043] During normal braking, the sensor value is defined by dividing the output Δx of the linear displacement sensor by its maximum value, and then converted to a percentage as the abscissa to obtain the assist characteristic curve, which is used to describe the braking intensity and the driver's driving intention. For example... Figure 2As shown, the power assist characteristic curves include the dead zone, the power assist phase, and the hydraulic hysteresis compensation phase. The corresponding characteristics are: between the dead zone (OA, OB), power assist oscillations are avoided due to the driver accidentally touching the brake pedal; within the power assist phase, the curve curvature obtained based on the relative displacement reflects the power assist performance; within the hydraulic hysteresis compensation phase, the curves for pressing and releasing the brake pedal do not coincide. In order to compensate for the hysteresis caused by factors such as the EHB system valve group, a hydraulic compensation algorithm is used, which is represented as a closed figure in the power assist curve.

[0044] The control based on the power assist curve enables active switching of driving styles. The principle of the power assist curve is as follows:

[0045] (1) O→A: When the driver presses the brake pedal, the upper controller identifies the driver's intention based on the sensor information. The obtained sensor information will be used to identify the driver's braking intensity in order to slow down the vehicle. However, due to the existence of mechanical clearance in the booster, i.e. dead zone, the current boosting effect is zero. This can also prevent the driver from accidentally touching the brake pedal and causing boosting oscillation.

[0046] (2) A→E: As the driver further depresses the brake pedal, the sensor position moves beyond point a, generating an assist current. The assist system enters the assist phase. During this phase, the rate of increase of the assist current is determined by the pressure applied to the brake pedal by the driver until the maximum assist current is reached to achieve the intended braking effect. The maximum assist current during this phase is I. ft .

[0047] (3) E→D: As the driver continues to depress the brake pedal, the power assist increases. Generally, the curvature in this phase increases with increasing braking pressure until it reaches the maximum assist current I. p This achieves the desired braking effect.

[0048] (4) D→C: When the driver releases the brake pedal, due to the influence of the valve group and inherent characteristics of the hydraulic braking system, there is an unavoidable hysteresis phenomenon. At this time, the hydraulic hysteresis compensation stage is entered. In order to compensate for the hydraulic hysteresis, the generated negative assist current causes the assist current to decrease at a relatively fast rate (from I). p Reduce to I bt And generally I bt ≠I ft ).

[0049] (5) C→A: As the pedal is released, the assist current begins to decrease at a relatively low rate. This shifting can stabilize the pedal and prevent unexpected pedal wobble.

[0050] (6) A→O: Finally, the sensor will enter the dead zone again, and an operation process is completed.

[0051] The working principle of actively switching driving styles is as follows:

[0052] Driving styles can be broadly categorized into aggressive and conservative. Aggressive driving involves generating significant braking force with minimal pedal effort for rapid braking, while conservative driving involves slow and smooth braking with minimal force. In reality, driving styles can fall somewhere in between. The driving style matched by the algorithm may not align with the driver's expectations and cannot accurately reflect different driving styles under varying conditions.

[0053] When the driver provides the same pedal travel, the ECU controls the output torque and speed of the power assist motor according to the preset power assist characteristic curve, ensuring the same output. To switch driving styles, a different belt drive ratio is selected via a switching device. With a smaller gear ratio, the master cylinder pushrod moves faster, allowing for greater braking pressure to be built up in the master cylinder for the same pushrod travel. This results in a greater braking assist ratio, enabling the vehicle to brake more quickly and achieve a more aggressive driving style. Conversely, as the gear ratio increases, the master cylinder pushrod moves slower, resulting in less pressure in the master cylinder and a smaller braking assist ratio, allowing for a slower and smoother braking process.

[0054] Step 3: Implement motor control. In power-assisted braking mode, the electronic control unit provides braking assistance based on the target assist current and switches driving styles by autonomously selecting the assist ratio through a switching device. In active braking mode, a dual-loop controller is designed. The outer loop is used to adjust the pressure of the hydraulic system, and the inner loop tracks the motor current. The tracking differentiator and adaptive control algorithm are used to solve the problem of parameter changes in the motor.

[0055] Specifically, such as Figures 3 to 4 As shown,

[0056] (1) Normally, the system enters the power-assisted braking mode (inner loop control):

[0057] After the motor-controlled push rod moves forward and cancels out the mechanical backlash, the motor's assist effect becomes linearly related to the assist current. In the customized assist strategy, the driver depresses the brake pedal, pushing the pedal push rod forward. The pedal displacement sensor measures the pedal travel information as input, including the relative displacement Δx between the pedal and the master cylinder piston and the relative displacement derivative calculated by the tracking differentiator. Δx, As input, the electronic control unit (ECU) adjusts the amount of braking assistance according to the preset braking assistance curve.

[0058] The value is calculated by the tracking differentiator, which has nonlinear filtering characteristics and obtains an ideal differential curve when the feedback signal noise is small. Its expression is as follows:

[0059]

[0060] Where Δx is the actual measured curve that needs to be tracked, Δx tr1 It is a tracking signal, Δx tr2 It is Δx tr1 The derivative of is also The approximate value, Δe tr This represents the error between the actual and target output values. r0 and h0 are adjustable parameters used to obtain the ideal tracking curve. F stp It is the fastest tracking function for a second-order discrete system, derived from continuous function.

[0061] The electronic control unit (ECU) outputs different target currents according to the preset brake assist curve to control the assist motor to output corresponding torque and speed, thereby pushing the master cylinder push rod to establish corresponding hydraulic braking force in the master cylinder. The ECU controls the normally open solenoid valve to open when de-energized, and the brake fluid in the master cylinder can enter each wheel cylinder through the hydraulic control unit (HCU) to achieve vehicle braking.

[0062] (2) In an emergency, enter active braking mode (including outer loop control and inner loop control):

[0063] The controller switches to active braking mode, using a closed loop to rapidly control the master cylinder pressure. Precise pressure control is a prerequisite for active braking. Pressure sensors provide real-time feedback on the brake assist system pressure to achieve closed-loop control. The speed and current of the brushless DC motor are obtained from embedded sensors. Based on this, a dual-loop controller is established using state feedback technology. The outer loop control circuit mainly regulates the hydraulic system pressure, while the inner loop control circuit mainly tracks the motor current, achieving rapid dynamic response and precise pressure control.

[0064] The drive motor quickly generates the corresponding torque and speed, pushing the master cylinder push rod to establish hydraulic braking force in the master cylinder. At this time, the normally open solenoid valve opens, and the brake fluid in the master cylinder enters the wheel cylinder through the hydraulic control unit (HCU) to generate the target active braking force, thus completing the active braking process.

[0065] Because the current control in electric boost mode and the pressure control in active braking mode frequently change in daily life, the two control loops are merged into a single control system architecture. The inner loop controls the brushless DC motor, while the outer loop is responsible for obtaining the required current.

[0066] In the active braking mode of the outer loop, the improved PID controller tracks the target pressure and outputs the target current to the inner loop for control.

[0067] In this embodiment, the improved PID controller is an outer-loop pressure controller. Traditional PID controllers improve the accuracy of the control system by eliminating steady-state errors through the integral term. However, when trying to further improve its dynamic response performance, integral saturation can easily occur, even leading to a deterioration of the dynamic response. To address this issue, a tracking differentiator is used as the differentiating term of the PID controller to reduce noise interference. The integral term employs a rolling optimization method to calculate only the error over the most recent period.

[0068] The outer loop uses an improved PID controller for target pressure tracking, suppressing steady-state error through finite integration to avoid integral saturation; the integral term employs a rolling optimization method, calculating only the error over the most recent period. Figure 3 As shown. The output is as follows:

[0069]

[0070] K p K i K d These are the coefficients of the proportional term, integral term, and differential term, respectively. p For pressure error, For e p The derivative value, e L The threshold value indicates that the integral action is effective when the pressure error is within a certain range. The inner loop uses an adaptive current controller based on sliding mode control to control the current of the input brushless DC motor. Feedback information such as motor current and speed is incorporated to further control the motor, solving the problems of accurately measuring precise motor parameters and various nonlinearities. Simultaneously, the actual voltage value of the hydraulic system output from the inner loop is fed back to the outer loop for pressure control.

[0071] In the inner-loop control (active braking mode or brake assist mode), the current tracking controller draws on sliding mode control theory, employing an approximate sliding mode control method without switching terms, and introducing equivalent and switching terms to achieve stable control. The sliding surface is chosen as S = ii. des Where i des The target current is , and 'i' is the feedback current signal. Based on the motor formula, the input and output variables of this controller are:

[0072] The precise values ​​of parameters a1, b1, and θ1 are calculated by the adaptive control algorithm, and the input variables are defined as follows: in, It is an estimated value of the variable a1. This is an estimate of the variable b1. It is the estimated value of the variable θ1.

[0073] Update the parameters according to the update rules:

[0074]

[0075] S is the sliding surface, the superscript indicates the estimated value, the superscript · indicates the derivative, γ is the tuning parameter, λ is the attenuation ratio, and the parameters a1, b1, θ1, and x are all motor parameters, obtained from the following motor formula:

[0076] Motor formula It can be represented as Where x = [i, ω] m ], x1 = i, x2 = ω m .

[0077] i is the motor current, ω m R is the motor speed. e For the equivalent resistance, L e K is the armature inductance coefficient. e V is the equivalent back electromotive force coefficient, and V is the motor voltage.

[0078] In summary, accurate current tracking is achieved based on the adaptive control algorithm, thus ensuring the stability of the controller.

[0079] The current tracking controller controls the motor to output the corresponding torque and speed, which in turn pushes the master cylinder push rod to establish the corresponding hydraulic braking force in the master cylinder. The electronic control unit controls the normally open solenoid valve to open when de-energized, and the brake fluid in the master cylinder can enter each wheel cylinder through the hydraulic control unit (HCU) to achieve vehicle braking.

[0080] The hydraulic control unit (HCU) is the actuator of the electric power-assisted braking system. It typically consists of a pressure-boosting valve (normally open), a pressure-reducing valve (normally closed), a return pump, and an accumulator. The valve body is controlled by signals from the electronic control unit (ECU) to open and close the hydraulic circuits, achieving pressure holding, boosting, and depressurization processes. The electric pump includes a plunger-type oil pump and a drive motor.

[0081] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A power assist strategy and precise pressure control method for an electric power-assisted braking system, characterized in that, Includes the following steps: Step 1: Collect driver intent and road environment information to calculate target pressure value, and select active braking mode or brake assist mode; Step 2: When the active braking mode is selected, the target pressure value and the actual pressure value fed back by the hydraulic system are used as inputs to the improved PID controller to calculate the desired braking pressure r. p And by the desired braking pressure r p The desired current is obtained as the control command for active braking. When the power-assisted braking mode is selected, a custom strategy is adopted, which includes: taking the relative displacement Δx between the pedal and the master cylinder piston measured by the displacement sensor as the first input variable, and taking the relative displacement derivative calculated by the tracking differentiator as the second input variable, and taking different target power-assisted currents as control commands for power-assisted braking according to the preset power-assisted curve. Step 3: Motor control is achieved based on the target assist current / desired current. The adaptive current controller controls the current of the input brushless DC motor based on the input target assist current / desired current and the sliding mode control principle. The hydraulic system establishes the corresponding hydraulic braking force to achieve vehicle braking. The hydraulic system feeds back the actual voltage value to the active braking mode to achieve closed-loop pressure control.

2. The assist strategy and pressure precision control method of the electric power-assisted braking system according to claim 1, characterized in that, In step 2, to shorten the response time in emergency situations, the derivative value of Δx is obtained by passing it through a tracking differentiator. As the second control input variable, it is used to describe the severity of the driver's braking and braking intention.

3. The assist strategy and pressure precision control method of the electric power-assisted braking system according to claim 2, characterized in that, The value is calculated by the tracking differentiator, which is expressed as follows: In the formula, Δx is the output value of the linear displacement sensor, which is the actual measured curve to be tracked. tr1 It is a tracking signal, Δx tr2 It is Δx tr1 The derivative of , r0, h0 are adjustable parameters, Δe tr F is the error between the actual and target output values. stp It is the tracking function of a second-order discrete system, and the superscript · indicates the derivative.

4. The assist strategy and pressure precision control method of the electric power-assisted braking system according to any one of claims 1 to 3, characterized in that, The method for obtaining the target current through a custom strategy is as follows: based on the braking assist curve, different target currents are output according to the intervals where the sensor percentage values ​​are located. The braking assist curve intervals include the dead zone, the assist phase interval, and the hydraulic hysteresis compensation phase interval. The assist is 0 in the dead zone. The target assist current is obtained according to the relative displacement in the assist phase interval. A negative assist current is generated in the hydraulic hysteresis compensation phase interval to compensate for hydraulic hysteresis.

5. The assist strategy and pressure precision control method of the electric power-assisted braking system according to claim 4, characterized in that, The method for implementing current control of the brushless DC motor using the adaptive current controller in step 3 is as follows: An approximate sliding mode control method without switching terms is adopted, and equivalent and switching terms are introduced to achieve stable control. The sliding mode surface is selected as S = ii. des , where i des The target current is the desired current / target assist current, and i is the actual current output by the motor. The actual current is returned to the input of the adaptive current controller as a feedback current signal to achieve current tracking control.

6. The assist strategy and pressure precision control method of the electric power-assisted braking system according to claim 5, characterized in that, The input to the adaptive current controller is Update the parameters according to the following formula. S is the sliding surface, and the parameters a1, b1, θ1, and x are all motor parameters. The superscript ^ indicates the estimated value, the superscript · indicates the derivative, γ is the tuning parameter, and λ is the attenuation ratio.

7. The assist strategy and pressure precision control method of the electric power-assisted braking system according to claim 6, characterized in that, The improved PID controller suppresses steady-state error and avoids integral saturation through finite integrals. Furthermore, it employs a rolling optimization method for the integral term. The improved PID controller output u... c As shown in the following formula: In the formula, K p K i K d These are the coefficients of the proportional term, integral term, and differential term, respectively, e p For pressure error, For e p The derivative value, e L It is a threshold value, indicating that the integral action is effective when the pressure error is within a certain range.

8. A power assist strategy and pressure precision control system for an electric power-assisted braking system, implementing the power assist strategy and pressure precision control method for the electric power-assisted braking system according to any one of claims 1-7, characterized in that, It includes an active braking module, a power-assisted braking module, a mode switching command module, and an execution module. The active braking module obtains the desired current based on the input target pressure value and the actual pressure using an improved PID controller. The power-assisted braking module obtains the power-assisted braking current by inputting a power-assisted strategy based on the pedal travel information detected by the displacement sensor. The mode switching command module selects the driving mode based on the different levels of power-assisted braking current; The execution module controls the input current of the brushless DC motor based on the desired current / assisted braking current, so as to control the motor to output the corresponding torque and speed, and then control the hydraulic system to output the corresponding hydraulic braking force to achieve vehicle braking; at the same time, the hydraulic system outputs the actual pressure value back to the active braking module.

9. The assist strategy and pressure precision control system of the electric power-assisted braking system according to claim 8, characterized in that, The control system includes an outer loop control and an inner loop control. The inner loop control is implemented by the execution module based on the input current to achieve braking. The outer loop control is implemented by the active braking module based on an improved PID controller to track the target pressure and obtain the desired current input for the inner loop control. The inner loop control outputs the actual pressure value and returns it to the input of the outer loop control to achieve a closed-loop control.

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