Adaptive friction compensation control method for electronic hydraulic brake system of new energy vehicle

Abstract

A new energy vehicle electronic hydraulic braking system adaptive friction compensation control method, comprising: collecting the running signal of the electronic hydraulic braking system; determining the low pressure area state variable; obtaining the mechanical side speed and the low pressure equivalent speed; constructing the low pressure area friction force estimation value, and writing the friction model on which the estimation value is based into a linear parameterized form about the to-be-identified friction parameter vector; constructing the equivalent friction observation quantity, and constructing the corresponding regression vector; judging whether the preset gating condition is met simultaneously: if met, the gating variable is in the active state, and the friction parameter vector is updated; if not met, the gating variable is in the frozen state; calculating the friction compensation authority, and obtaining the total control quantity, which is output to the hydraulic actuator after being limited in amplitude. The application can solve the problems of discontinuous friction estimation near zero speed in the low pressure area, online identification error update, and friction feed-forward over-compensation leading to pressure jitter or overshoot.

Description

Technical Field

[0001] This invention relates to the field of new energy vehicle technology, and more specifically to an adaptive friction compensation control method for an electronic hydraulic braking system of a new energy vehicle. Background Technology

[0002] Electro-hydraulic braking (EHB) systems, as a core technology of brake-by-wire in new energy vehicles, establish braking pressure through a hydraulic actuator driven by an electric motor. In the low-pressure range of 0–2 MPa in the wheel cylinders, the hydraulic actuator is often in a low-speed, micro-displacement, or alternating start-stop state, significantly increasing the proportion of combined friction among components such as the lead screw, seals, push rod, piston, and return spring in the total actuation force. Friction in this low-pressure range exhibits characteristics such as nonlinearity near zero speed, asymmetric pressure increase / decrease, drift with changes in oil temperature and braking frequency, and low signal-to-noise ratio of sensing signals. These characteristics can easily lead to wheel cylinder pressure tracking lag, decreased low-pressure resolution, inconsistent brake pedal feel, and pressure jitter.

[0003] Existing control methods typically employ fixed-parameter friction compensation, PID, or fuzzy PID pressure closed-loop control. While these methods can improve pressure tracking performance to some extent, they still have the following shortcomings in the low-pressure region: First, when using only a single velocity signal as the friction model input, near-zero velocity and encoder quantization errors can cause abrupt changes in friction estimation; second, if online identification is continuously updated under insufficient excitation or strong pressure pulsation, it is prone to erroneous updates due to parameter drift; third, if friction feedforward compensation does not consider the reliability of identification, it is prone to overcompensation and overshoot in the low-pressure region. Summary of the Invention

[0004] In view of this, the present invention provides an adaptive friction compensation control method for an electronic hydraulic braking system of new energy vehicles to solve the problems of discontinuous friction estimation near zero speed in the low-pressure zone, incorrect online identification updates, and pressure jitter or overshoot caused by friction feedforward overcompensation.

[0005] An adaptive friction compensation control method for an electro-hydraulic braking system of a new energy vehicle includes: Step S1: Real-time acquisition of the operating signals of the electro-hydraulic braking system and the desired deceleration output by the vehicle. The operating signals include actuator displacement, actuator speed, motor current, actual wheel cylinder pressure, hydraulic oil temperature, pedal displacement, and pedal speed. Step S2: Generate the target pressure of the wheel cylinder based on the pedal displacement, pedal speed and desired deceleration, and determine the low-pressure zone state variables based on the target pressure of the wheel cylinder, the actual pressure of the wheel cylinder, the preset entry pressure threshold and exit pressure threshold, wherein the entry pressure threshold is less than the exit pressure threshold. Step S3: When the system is determined to be in a low-pressure zone based on the low-pressure zone state variables, the mechanical side speed is obtained based on the rotational speed of the actuator, and the hydraulic equivalent speed is obtained based on the rate of change of the actual pressure of the wheel cylinder. The reliability of the mechanical side speed and the hydraulic equivalent speed are then fused to obtain the low-pressure equivalent speed. Step S4: Construct a friction force estimate for the low-pressure zone based on the low-pressure equivalent velocity and hydraulic oil temperature. The friction force estimate for the low-pressure zone is jointly determined by the low-speed continuous friction sub-model, the high-speed Stribeck friction sub-model, the velocity smoothing weight function, the low-pressure weight function, and the bounded working condition correction term. The friction model on which the friction force estimate for the low-pressure zone is based is written as a linear parameterized form about the friction parameter vector to be identified. Step S5: Construct equivalent friction observations based on motor current, motor angular acceleration, actual pressure load of wheel cylinder, actuator displacement, and hydraulic actuator return load, and construct a regression vector corresponding to the linear parameterized form. Step S6: Determine whether the preset gating conditions are met simultaneously. If they are met, the gating variable is set to the active state. Based on the constructed equivalent friction observation and regression vector, the friction parameter vector is updated using the recursive least squares method with an adaptive forgetting factor, and the covariance matrix is ​​updated simultaneously. If they are not met, the gating variable is set to the frozen state. The friction parameter vector at the current time is kept the same as that at the previous time, and the covariance matrix remains unchanged. Step S7: Calculate the friction compensation authority based on the covariance matrix and the identification residual generated during the recursive least squares calculation. Generate a friction compensation amount with amplitude and speed limits based on the estimated friction force in the low-pressure area and the friction compensation authority. At the same time, the pressure closed-loop controller generates a pressure closed-loop control amount. Then, the pressure closed-loop control amount is superimposed with the friction compensation amount to obtain the total control amount. After limiting the amplitude of the total control amount, it is output to the hydraulic actuator.

[0006] The adaptive friction compensation control method for the electro-hydraulic braking system of new energy vehicles provided by the present invention has the following beneficial effects: 1. This invention reliably integrates the mechanical side speed with the hydraulic equivalent speed converted from the pressure change rate, so that the friction model can obtain continuous and smooth speed input near low speed and zero speed, thereby avoiding friction estimation jumps caused by single signal noise.

[0007] 2. This invention introduces gating conditions including velocity excitation, regression vector energy, pressure change rate, and noise level, and uses recursive least squares (RLS) with adaptive forgetting factor to update the friction parameter vector. The friction parameters are updated only when the observability and signal quality requirements are met; otherwise, the update is frozen, thereby effectively suppressing parameter drift and erroneous updates.

[0008] 3. This invention dynamically calculates the identification reliability based on the trace and identification residual of the covariance matrix, and generates friction compensation authority accordingly. When the identification is unreliable, the feedforward intensity is automatically reduced. Combined with amplitude and speed limiting measures, this suppresses overcompensation, overshoot and pressure jitter.

[0009] 4. This invention uses a hysteresis comparison logic composed of an entry pressure threshold and an exit pressure threshold to determine the low-pressure zone state, avoiding frequent switching of the control strategy when the cylinder pressure fluctuates near the boundary, ensuring the stability of low-pressure compensation, and significantly improving the pressure tracking accuracy and smoothness in the 0~2MPa low-pressure zone. Attached Figure Description

[0010] Figure 1 A flowchart illustrating the adaptive friction compensation control method for an electronic hydraulic braking system for new energy vehicles provided in this embodiment of the invention; Figure 2 This is a schematic diagram comparing the wheel cylinder pressure response of the present invention with frictionless compensation and fixed friction compensation methods during the low-pressure build-up process. Detailed Implementation

[0011] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain embodiments of the present invention, and should not be construed as limiting the present invention.

[0012] Please see Figure 1 The adaptive friction compensation control method for the electro-hydraulic braking system of new energy vehicles provided by the present invention includes steps S1 to S7: Step S1: Real-time acquisition of the operating signals of the electro-hydraulic braking system and the desired deceleration output by the vehicle. The operating signals include actuator displacement, actuator speed, motor current, actual wheel cylinder pressure, hydraulic oil temperature, pedal displacement, and pedal speed.

[0013] In specific implementation, the controller follows the sampling period. By collecting operating signals, the controller can perform low-pass filtering, amplitude limiting filtering, or extended Kalman filtering on the actual pressure of the wheel cylinder, pedal speed, and motor angular velocity to reduce the impact of high-frequency noise on low-pressure compensation.

[0014] Step S2: Generate the target pressure of the wheel cylinder based on the pedal displacement, pedal speed and desired deceleration, and determine the low-pressure zone state variables based on the target pressure of the wheel cylinder, the actual pressure of the wheel cylinder, the preset entry pressure threshold and exit pressure threshold, wherein the entry pressure threshold is less than the exit pressure threshold.

[0015] The target pressure of the wheel cylinder is calculated according to the following formula:

[0016] in, express The target pressure of the wheel cylinder at any given moment. For the amplitude limiting function, This represents the maximum allowable target pressure for the wheel cylinder. For pedal displacement gain, for The pedal displacement at any given moment For pedal speed gain, for The pedal speed at any given moment, For the equivalent mass of the whole vehicle, for Expected deceleration at time, This represents the equivalent working area of ​​the wheel cylinder.

[0017] The above-mentioned method of generating target pressure in the wheel cylinder can simultaneously reflect the driver's pedal input and the vehicle's target deceleration requirements.

[0018] To avoid frequent switching near the low-pressure boundary, the controller uses entry and exit pressure thresholds to construct the low-pressure zone state. The specific low-pressure zone state variables are determined as follows: When the low-pressure zone state variable of the previous moment is 0 and the actual pressure of the wheel cylinder at the current moment is less than or equal to the entry pressure threshold, the low-pressure zone state variable of the current moment is 1, indicating that the system is in the low-pressure zone. When the low-pressure zone state variable is 1 in the previous moment and the actual pressure of the wheel cylinder at the current moment is greater than or equal to the exit pressure threshold, the low-pressure zone state variable at the current moment is 0, indicating that the system is not in the low-pressure zone. When the low-pressure zone state variable of the previous moment is 0 and the actual pressure of the wheel cylinder at the current moment is greater than the entry pressure threshold, or when the low-pressure zone state variable of the previous moment is 1 and the actual pressure of the wheel cylinder at the current moment is less than the exit pressure threshold, the low-pressure zone state variable at the current moment is the same as that of the previous moment.

[0019] Preferably, the entry pressure threshold ranges from 1.5 to 2.0 MPa, and the exit pressure threshold ranges from 2.0 to 2.5 MPa. More preferably, the entry pressure threshold is 1.8 MPa, and the exit pressure threshold is 2.2 MPa.

[0020] Step S3: When the system is determined to be in a low-pressure zone based on the low-pressure zone state variables, the mechanical side speed is obtained based on the actuator rotation speed, and the hydraulic equivalent speed is obtained based on the change rate of the actual pressure of the wheel cylinder. Then, the reliability of the mechanical side speed and the hydraulic equivalent speed are fused to obtain the low-pressure equivalent speed.

[0021] Among them, when Low-pressure zone state variables at time 1 When the system is in a low-pressure zone, the mechanical speed is obtained based on the actuator rotation speed. The mechanical speed is calculated using the following formula:

[0022] The hydraulic equivalent velocity can be obtained by converting the hydraulic continuity equation in the low-pressure zone:

[0023] in, for The mechanical side velocity at any given moment, For the lead screw, for The angular velocity of the motor at any given moment. The transmission ratio is... for The hydraulic equivalent velocity at any given moment. The equivalent hydraulic volume in the low-pressure zone The equivalent bulk modulus, To calculate the equivalent piston area, for The actual pressure change rate of the engraved wheel cylinder; Since the mechanical speed in the low-pressure region may be affected by encoder quantization error, and the hydraulic equivalent speed may be affected by pressure sensor noise, this embodiment uses a reliability fusion method to obtain the low-pressure equivalent speed. Specifically, the low-pressure equivalent speed is obtained by fusion according to the following formula:

[0024]

[0025]

[0026]

[0027] in, for The low-pressure equivalent velocity at any given moment. for The velocity fusion weight at any given moment is determined in this embodiment based on the variance of the mechanical-side velocity residual and the hydraulic-side velocity residual within the sliding time window; and These are the lower and upper limits of the speed fusion weights, respectively. and They are respectively The reliability of the mechanical and hydraulic speeds at all times. and They are respectively The variance of the mechanical-side velocity residual and the hydraulic-side velocity residual within the sliding time window. To prevent positive numbers with a denominator of zero.

[0028] Through the above fusion, when the noise of the speed signal on one side increases, the controller automatically reduces the speed on that side. The impact.

[0029] It should be pointed out that when At that time, the low-pressure equivalent velocity is not used to participate in the friction compensation of the low-pressure zone, and the friction compensation amount of the low-pressure zone is reduced to zero according to the preset exit slope.

[0030] Step S4: Construct a friction force estimate for the low-pressure zone based on the low-pressure equivalent velocity and hydraulic oil temperature. The friction force estimate for the low-pressure zone is jointly determined by the low-speed continuous friction sub-model, the high-speed Stribeck friction sub-model, the velocity smoothing weight function, the low-pressure weight function, and the bounded working condition correction term. The friction model on which the friction force estimate for the low-pressure zone is based is written as a linear parameterized form about the friction parameter vector to be identified.

[0031] The estimated friction force in the low-pressure zone satisfies the following formula:

[0032] in, express Estimated value of frictional force in the low-pressure area at time [time]. for The value of the low-pressure weighting function at any given time. for The value of the time-bounded operating condition correction term, for The value of the velocity smoothing weight function at each time step. for The value of the low-speed continuous friction sub-model at time t. for The value of the high-speed Stribeck friction model at any given time.

[0033] Specifically, the speed smoothing weight function Low-pressure weighting function Low-speed continuous friction sub-model and high-speed Stribeck friction model They respectively satisfy:

[0034]

[0035]

[0036]

[0037] in, For low-pressure equivalent velocity, The transition speed threshold from low speed to high speed, when hour, Approaching 1, the low-speed continuous friction sub-model dominates; when hour, Approaching 0, the high-speed Stribeck tribometer model becomes dominant; The transition width is within the transition area. Continuous changes are made to avoid abrupt changes during model switching; This is the lower limit of the pressure weight. This refers to the actual pressure of the wheel cylinder. This is the reference pressure for the low-pressure zone; when the wheel cylinder pressure is low, The larger the friction compensation, the stronger its impact on the total control quantity; when the wheel cylinder pressure approaches the upper boundary of the low-pressure zone, This reduces the pressure, allowing the low-voltage compensation strategy to exit smoothly. The coefficient of friction is the continuous coefficient of friction near zero velocity. For smoothing parameters of low-speed continuous sign functions, The low-speed viscous damping coefficient, Here are the Coulomb friction parameters. These are static friction parameters. Stribeck characteristic velocity, Stribeck index, For smoothing parameters of high-speed continuous sign functions, The high-speed viscous damping coefficient is used; The form of continuous sign function can avoid compensatory jumps caused by abrupt changes in sign function near zero velocity.

[0038] The bounded operating condition correction term describes the effects of oil temperature, braking frequency, pedal displacement, and braking duration on friction characteristics, specifically satisfying:

[0039] in, and These are the lower and upper limits of the operating condition correction item, respectively. for The hydraulic oil temperature at any given time, The reference hydraulic oil temperature, The braking frequency per unit time. As the reference braking frequency, To meet braking requirements, For braking duration, , , and These are the correction factors corresponding to oil temperature, braking frequency, braking intensity, and braking duration, respectively.

[0040] Through the Limiting the amplitude can prevent excessively large operating condition correction items from compromising the control stability of the low-pressure area.

[0041] In this embodiment, the friction parameter vector to be identified is stored as a first parameter group and a second parameter group according to the pressure increase direction and the pressure decrease direction, respectively; when the low-pressure equivalent velocity obtained in step S3... The first parameter group is called when... The second parameter group is invoked at the same time to compensate for asymmetric friction during the pressurization and depressurization processes; The pressure closed-loop control quantity and friction compensation quantity are calculated according to the sampling period. Updated, the friction parameter vector to be identified is according to Update, in which The update cycle is set as a multiple; when the absolute value of the pressure deviation is greater than the rapid update threshold and the preset gating conditions in step S6 are met simultaneously, the update cycle of the friction parameter vector to be identified is shortened; when the speed excitation is insufficient or the quality of the sensing signal does not meet the preset requirements, the friction parameter vector to be identified remains unchanged.

[0042] Step S5: Construct equivalent friction observations based on motor current, motor angular acceleration, actual pressure load of wheel cylinder, actuator displacement, and hydraulic actuator return load, and construct a regression vector corresponding to the linear parameterized form.

[0043] The equivalent friction observation is constructed according to the following formula:

[0044] in, for Equivalent friction observations at time points, The torque constant of the motor. for Motor current at any given moment For transmission efficiency, The equivalent transmission gain from the motor side to the hydraulic actuator side. For equivalent rotational inertia, for The motor's angular acceleration at time t. For equivalent damping, Let k be the angular velocity of the motor at time k. To calculate the equivalent piston area, Let k be the actual pressure of the wheel cylinder at time k. The return elasticity coefficient, Let k be the displacement of the actuator at time k. This is for preload.

[0045] This equivalent friction observation balances the motor driving force, inertial term, viscous damping term, hydraulic load, and return elastic load, and is used to identify the friction model parameters in the low-pressure zone online.

[0046] Simultaneously, construct the regression vector corresponding to the linear parameterized friction model. This ensures that the equivalent friction observations satisfy:

[0047] in, for Friction parameter vector at time t, for The regression vector at time step, To model the error and noise terms. Regression vector. It consists of low-pressure equivalent velocity, continuous sign function, Stribeck attenuation term, low-pressure weight, and operating condition variables.

[0048] Step S6: Determine whether the preset gating conditions are met simultaneously. If they are met, the gating variable is set to the active state. Based on the constructed equivalent friction observation and regression vector, the friction parameter vector is updated using the recursive least squares method with an adaptive forgetting factor, and the covariance matrix is ​​updated simultaneously. If they are not met, the gating variable is set to the frozen state, keeping the friction parameter vector at the current time the same as the previous time, and keeping the covariance matrix unchanged.

[0049] The controller does not update the friction model parameters at every sampling time. Instead, it first determines whether preset gating conditions are met simultaneously. These preset gating conditions include at least the following:

[0050]

[0051]

[0052]

[0053]

[0054] in, The speed excitation threshold, for The regression vector at time step, Indicates transpose. The threshold for the energy of the regression vector. This represents the upper limit of the rate of change of pressure. for The state variables of the low-pressure zone at time t. for Pressure noise index at any given time. This represents the upper limit of noise.

[0055] When speed excitation is insufficient ( Insufficient energy of regression vectors ), excessively strong transient pressure ( ) or excessive noise ( (or when not in a low-pressure area) Gating variables at time (Frozen state); when all the above conditions are met, Gating variables at time (Active state).

[0056] when At that time, the controller uses recursive least squares (RLS) with an adaptive forgetting factor to update the friction model parameter vector. The details are as follows: First, calculate the identification residuals:

[0057] Then calculate the adaptive forgetting factor:

[0058] Then calculate the gain vector:

[0059] in, To identify the residuals, for Friction parameter vector at time t, An adaptive forgetting factor. and These are the lower and upper limits of the forgetting factor, respectively. The threshold for residual normalization. For the gain vector, for The covariance matrix at time t; when Gating variables at time step When the gated variable is active, a projection limit is applied, and the parameters and covariance matrix are updated as follows:

[0060]

[0061] in, for Friction parameter vector at time t, For parametric projection limiting operators, and These are the lower and upper limits of the friction parameter vector, respectively, to ensure that the parameters are within a reasonable range. for The covariance matrix at time t.

[0062] when Gating variables at time step When the gated variable is in a frozen state, the parameters and covariance matrix remain unchanged, as expressed by:

[0063] .

[0064] Step S7: Calculate the friction compensation authority based on the covariance matrix and the identification residual generated during the recursive least squares calculation. Generate a friction compensation amount with amplitude and speed limits based on the estimated friction force in the low-pressure area and the friction compensation authority. At the same time, the pressure closed-loop controller generates a pressure closed-loop control amount. Then, the pressure closed-loop control amount is superimposed with the friction compensation amount to obtain the total control amount. After limiting the amplitude of the total control amount, it is output to the hydraulic actuator.

[0065] The friction compensation limit is calculated according to the following formula:

[0066]

[0067] in, To determine credibility, The trace of the matrix, Let be the calibration scale constant of the trace of the covariance matrix. The residual calibration scale constant, for Real-time friction compensation permissions and These are the lower and upper limits of the friction compensation authority, respectively. To compensate for the baseline coefficient of authority, for The gating hold factor at any given time.

[0068] When the covariance is large (high parameter uncertainty) or the residual is large (large model error), reduce.

[0069] when hour, One can be chosen; when However, the number of freezes did not exceed the preset retention limit. hour, Maintain or slowly decay; when the number of consecutive freezes exceeds hour, The threshold is gradually lowered. Therefore, when unreliable or low-voltage compensation is identified as not warranting strong intervention, the authority of friction feedforward compensation is automatically reduced.

[0070] Friction compensation amount and total control quantity Satisfy the following formula:

[0071]

[0072] in, for Friction compensation amount at any given time. For rate-of-change constraint operators, This is the upper limit of friction compensation. This is the conversion factor from the friction force estimate to the actuator control quantity. for Total control quantity at any given moment. and These represent the lower and upper limits of the total control allowed by the implementing agency, respectively. for Pressure closed-loop control quantity at any given time.

[0073] When the total control quantity reaches the upper or lower limit of the actuator output, the controller stops accumulating the integral term or recalculates the integral term based on the saturation difference to suppress overcompensation and integral saturation in the low-voltage region. Total control quantity The output is sent to the motor driver or hydraulic actuator to achieve low-pressure zone wheel cylinder pressure tracking.

[0074] Figure 2 The paper presents a comparison of wheel cylinder pressure responses using different methods during the low-pressure build-up process of an electro-hydraulic braking system. Figure 2 In the diagram, the curve of the target pressure represents the target pressure of the wheel cylinder generated by the controller; the curve of the actual pressure without friction compensation represents the actual pressure response of the wheel cylinder without the introduction of friction feedforward compensation; the curve of the actual pressure with fixed friction compensation represents the actual pressure response of the wheel cylinder with fixed parameter friction compensation; and the curve of the actual pressure of the method of this invention represents the actual pressure response of the wheel cylinder after adopting the low-pressure zone gated adaptive friction compensation control method.

[0075] from Figure 2It can be seen that in the initial stage of low-pressure build-up, due to the combined friction of components such as the lead screw, seals, push rod, piston, and return spring, the frictionless compensation scheme is prone to pressure build-up lag and following errors. Although the fixed friction compensation scheme can improve the pressure build-up speed to a certain extent, it may cause overshoot or pressure fluctuations when the low pressure approaches the target pressure due to the fixed compensation parameters. The method of this invention, through low-pressure zone state hysteresis judgment, fusion of mechanical side speed and hydraulic equivalent speed, smooth switching between low-speed continuous friction model and high-speed Stribeck friction model, gated RLS parameter update, and compensation authority adjustment based on identification credibility, enables the actual pressure to follow the target pressure more smoothly in the low-pressure zone and reduces the risk of overshoot and jitter in the low-pressure zone.

[0076] In summary, the adaptive friction compensation control method for the electro-hydraulic braking system of new energy vehicles according to the above embodiments has the following beneficial effects: 1. This invention reliably integrates the mechanical side speed with the hydraulic equivalent speed converted from the pressure change rate, so that the friction model can obtain continuous and smooth speed input near low speed and zero speed, thereby avoiding friction estimation jumps caused by single signal noise.

[0077] 2. This invention introduces gating conditions including velocity excitation, regression vector energy, pressure change rate, and noise level, and uses recursive least squares (RLS) with adaptive forgetting factor to update the friction parameter vector. The friction parameters are updated only when the observability and signal quality requirements are met; otherwise, the update is frozen, thereby effectively suppressing parameter drift and erroneous updates.

[0078] 3. This invention dynamically calculates the identification reliability based on the trace and identification residual of the covariance matrix, and generates friction compensation authority accordingly. When the identification is unreliable, the feedforward intensity is automatically reduced. Combined with amplitude and speed limiting measures, this suppresses overcompensation, overshoot and pressure jitter.

[0079] 4. This invention uses a hysteresis comparison logic composed of an entry pressure threshold and an exit pressure threshold to determine the low-pressure zone state, avoiding frequent switching of the control strategy when the cylinder pressure fluctuates near the boundary, ensuring the stability of low-pressure compensation, and significantly improving the pressure tracking accuracy and smoothness in the 0~2MPa low-pressure zone.

[0080] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An adaptive friction compensation control method for an electro-hydraulic braking system of a new energy vehicle, characterized in that, include: Step S1: Real-time acquisition of the operating signals of the electro-hydraulic braking system and the desired deceleration output by the vehicle. The operating signals include actuator displacement, actuator speed, motor current, actual wheel cylinder pressure, hydraulic oil temperature, pedal displacement, and pedal speed. Step S2: Generate the target pressure of the wheel cylinder based on the pedal displacement, pedal speed and desired deceleration, and determine the low-pressure zone state variables based on the target pressure of the wheel cylinder, the actual pressure of the wheel cylinder, the preset entry pressure threshold and exit pressure threshold, wherein the entry pressure threshold is less than the exit pressure threshold. Step S3: When the system is determined to be in a low-pressure zone based on the low-pressure zone state variables, the mechanical side speed is obtained based on the rotational speed of the actuator, and the hydraulic equivalent speed is obtained based on the rate of change of the actual pressure of the wheel cylinder. The reliability of the mechanical side speed and the hydraulic equivalent speed are then fused to obtain the low-pressure equivalent speed. Step S4: Construct a friction force estimate for the low-pressure zone based on the low-pressure equivalent velocity and hydraulic oil temperature. The friction force estimate for the low-pressure zone is jointly determined by the low-speed continuous friction sub-model, the high-speed Stribeck friction sub-model, the velocity smoothing weight function, the low-pressure weight function, and the bounded working condition correction term. The friction model on which the friction force estimate for the low-pressure zone is based is written as a linear parameterized form about the friction parameter vector to be identified. Step S5: Construct equivalent friction observations based on motor current, motor angular acceleration, actual pressure load of wheel cylinder, actuator displacement, and hydraulic actuator return load, and construct a regression vector corresponding to the linear parameterized form. Step S6: Determine whether the preset gating conditions are met simultaneously. If they are met, the gating variable is set to the active state. Based on the constructed equivalent friction observation and regression vector, the friction parameter vector is updated using the recursive least squares method with an adaptive forgetting factor, and the covariance matrix is ​​updated simultaneously. If they are not met, the gating variable is set to the frozen state. The friction parameter vector at the current time is kept the same as that at the previous time, and the covariance matrix remains unchanged. Step S7: Calculate the friction compensation authority based on the covariance matrix and the identification residual generated during the recursive least squares calculation. Generate a friction compensation amount with amplitude and speed limits based on the estimated friction force in the low-pressure area and the friction compensation authority. At the same time, the pressure closed-loop controller generates a pressure closed-loop control amount. Then, the pressure closed-loop control amount is superimposed with the friction compensation amount to obtain the total control amount. The total control amount is then limited and output to the hydraulic actuator. In step S3, the mechanical side velocity and the hydraulic equivalent velocity are calculated according to the following formulas: in, for The mechanical side velocity at any given moment, For the lead screw, for The angular velocity of the motor at any given moment. The transmission ratio is... for The hydraulic equivalent velocity at any given moment. The equivalent hydraulic volume in the low-pressure zone The equivalent bulk modulus, To calculate the equivalent piston area, for The actual pressure change rate of the engraved wheel cylinder; The low-pressure equivalent velocity is obtained by fusing the following formula: in, for The low-pressure equivalent velocity at any given moment. for Moment-time velocity fusion weights For the amplitude limiting function, and These are the lower and upper limits of the speed fusion weights, respectively. and They are respectively The reliability of the mechanical and hydraulic speeds at all times. and They are respectively The variance of the mechanical-side velocity residual and the hydraulic-side velocity residual within the sliding time window. To prevent positive numbers with a denominator of zero.

2. The adaptive friction compensation control method for the electro-hydraulic braking system of new energy vehicles according to claim 1, characterized in that, In step S2, the target pressure of the wheel cylinder is calculated according to the following formula: in, express The target pressure of the wheel cylinder at any given moment. This represents the maximum allowable target pressure for the wheel cylinder. For pedal displacement gain, for The pedal displacement at any given moment For pedal speed gain, for The pedal speed at any given moment, For the equivalent mass of the whole vehicle, for Expected deceleration at time, This represents the equivalent working area of ​​the wheel cylinder.

3. The adaptive friction compensation control method for the electro-hydraulic braking system of new energy vehicles according to claim 2, characterized in that, In step S2, the state variables of the low-pressure area are determined as follows: When the low-pressure zone state variable of the previous moment is 0 and the actual pressure of the wheel cylinder at the current moment is less than or equal to the entry pressure threshold, the low-pressure zone state variable of the current moment is 1, indicating that the system is in the low-pressure zone. When the low-pressure zone state variable is 1 in the previous moment and the actual pressure of the wheel cylinder at the current moment is greater than or equal to the exit pressure threshold, the low-pressure zone state variable at the current moment is 0, indicating that the system is not in the low-pressure zone. When the low-pressure zone state variable of the previous moment is 0 and the actual pressure of the wheel cylinder at the current moment is greater than the entry pressure threshold, or when the low-pressure zone state variable of the previous moment is 1 and the actual pressure of the wheel cylinder at the current moment is less than the exit pressure threshold, the low-pressure zone state variable at the current moment is the same as that of the previous moment. The entry pressure threshold ranges from 1.5 to 2.0 MPa, and the exit pressure threshold ranges from 2.0 to 2.5 MPa.

4. The adaptive friction compensation control method for the electro-hydraulic braking system of new energy vehicles according to claim 3, characterized in that, In step S4, the estimated frictional force in the low-pressure zone satisfies the following formula: in, express Estimated value of frictional force in the low-pressure area at time [time]. for The value of the low-pressure weighting function at any given time. for The value of the time-bounded operating condition correction term, for The value of the velocity smoothing weight function at each time step. for The value of the low-speed continuous friction sub-model at time t. for The value of the high-speed Stribeck friction model at any given time.

5. The adaptive friction compensation control method for the electro-hydraulic braking system of new energy vehicles according to claim 4, characterized in that, Velocity smoothing weight function Low-pressure weighting function Low-speed continuous friction sub-model and high-speed Stribeck friction model They respectively satisfy: in, For low-pressure equivalent velocity, This is the transition speed threshold from low speed to high speed. For the transition width, This is the lower limit of the pressure weight. This refers to the actual pressure of the wheel cylinder. This is the reference pressure for the low-pressure area. The coefficient of friction is the continuous coefficient of friction near zero velocity. For smoothing parameters of low-speed continuous sign functions, The low-speed viscous damping coefficient, Here are the Coulomb friction parameters. These are static friction parameters. Stribeck characteristic velocity, Stribeck index, For smoothing parameters of high-speed continuous sign functions, This is the high-speed viscous damping coefficient; The bounded condition correction term satisfies: in, and These are the lower and upper limits of the operating condition correction item, respectively. for The hydraulic oil temperature at any given time, The reference hydraulic oil temperature, The braking frequency per unit time. As the reference braking frequency, To meet braking requirements, For braking duration, , , and These are the correction factors corresponding to oil temperature, braking frequency, braking intensity, and braking duration, respectively.

6. The adaptive friction compensation control method for the electro-hydraulic braking system of new energy vehicles according to claim 5, characterized in that, In step S5, the equivalent friction observation is constructed according to the following formula: in, for Equivalent friction observations at time points, The torque constant of the motor. for Motor current at any given moment For transmission efficiency, The equivalent transmission gain from the motor side to the hydraulic actuator side. For equivalent rotational inertia, for The motor's angular acceleration at time t. For equivalent damping, Let k be the angular velocity of the motor at time k. To calculate the equivalent piston area, Let k be the actual pressure of the wheel cylinder at time k. The return elasticity coefficient, Let k be the displacement of the actuator at time k. This is for preload.

7. The adaptive friction compensation control method for the electro-hydraulic braking system of new energy vehicles according to claim 6, characterized in that, In step S6, the preset gating conditions include at least: in, The speed excitation threshold, for The regression vector at time step, Indicates transpose. The threshold for the energy of the regression vector. This represents the upper limit of the rate of change of pressure. for The state variables of the low-pressure zone at time t. for Pressure noise index at any given time. This is the upper limit of noise; The recursive least squares method with adaptive forgetting factor satisfies the following equation: in, To identify the residuals, for Friction parameter vector at time t, An adaptive forgetting factor. and These are the lower and upper limits of the forgetting factor, respectively. The threshold for residual normalization. For the gain vector, for The covariance matrix at time t; when Gating variables at time step At that time, the parameters and covariance matrix are updated as follows: in, for Friction parameter vector at time t, For parametric projection limiting operators, and These are the lower and upper physical limits of the friction parameter vector, respectively. for The covariance matrix at time t; when Gating variables at time step When the parameters and covariance matrix remain unchanged, the expression is: 。 8. The adaptive friction compensation control method for the electro-hydraulic braking system of new energy vehicles according to claim 7, characterized in that, In step S7, the friction compensation authority is calculated according to the following formula: in, To determine credibility, The trace of the matrix, Let be the calibration scale constant of the trace of the covariance matrix. The residual calibration scale constant, for Real-time friction compensation permissions and These are the lower and upper limits of the friction compensation authority, respectively. To compensate for the baseline coefficient of authority, for The gating hold factor at any given time; Friction compensation amount and total control quantity Satisfy the following formula: in, for Friction compensation amount at any given time. For rate-of-change constraint operators, This is the upper limit of friction compensation. This is the conversion factor from the friction force estimate to the actuator control quantity. for Total control quantity at any given moment. and These represent the lower and upper limits of the total control allowed by the implementing agency, respectively. for Pressure closed-loop control quantity at any given time.

9. The adaptive friction compensation control method for the electro-hydraulic braking system of new energy vehicles according to claim 8, characterized in that, The friction parameter vector to be identified in step S4 is stored as the first parameter group and the second parameter group according to the pressure increase direction and the pressure decrease direction, respectively; when the low-pressure equivalent velocity obtained in step S3... The first parameter group is called when... The second parameter group is invoked at the same time to compensate for asymmetric friction during the pressurization and depressurization processes; The pressure closed-loop control quantity and friction compensation quantity are calculated according to the sampling period. Updated, the friction parameter vector to be identified is according to Update, in which The update cycle is set as a multiple; when the absolute value of the pressure deviation is greater than the rapid update threshold and the preset gating conditions in step S6 are met simultaneously, the update cycle of the friction parameter vector to be identified is shortened; when the speed excitation is insufficient or the quality of the sensing signal does not meet the preset requirements, the friction parameter vector to be identified remains unchanged.

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