EMB system active calibration method and device for improving braking precision

Abstract

The invention relates to the technical field of automobile braking, in particular to an EMB system active calibration method and device.The method comprises the steps that the current and temperature of a brake motor winding in an automobile are collected in real time, the temperature of a brake disc in the automobile and the running speed of the automobile are collected in real time, and based on the current temperature change of the brake motor winding, the braking accuracy of the brake motor winding is improved; compensating the current current of the brake motor winding; determining a wear sensitive factor of the current brake; according to the difference between the clamping rotation angle and the back-off rotation angle of the current and previous multiple braking, the accumulated net rotation angle of the current braking is determined; acquiring a current temperature correction coefficient and a speed correction coefficient; the dynamic wear rate of current braking is determined in combination with the accumulated net rotation angle; and triggering active calibration of the EMB system through the wear sensitive factor and the dynamic wear rate, determining a brake pad wear coefficient based on the wear sensitive factor, and correcting the target rotation angles of the left caliper and the right caliper. Therefore, the braking precision of the EMB system is improved.

Description

Technical Field

[0001] The present application relates to the field of automobile braking technology, and in particular to an EMB system active calibration method and device for improving braking accuracy. Background Art

[0002] The Electromechanical Brake (EMB) system is a wire-controlled braking technology that directly drives the brake caliper through an electric motor, using electric energy instead of traditional hydraulic oil to transmit braking force. Its core architecture includes motors, transmission mechanisms, sensors and controllers, which accurately control the conversion of motor torque into friction plate clamping force by real-time analysis of brake pedal signals and vehicle status. Different from the mechanical lag of hydraulic brakes, the EMB system achieves millisecond-level response through electrical signal transmission, and has digital advantages such as brake energy recovery and intelligent distribution. It is one of the key technologies for automobiles and wire-controlled chassis.

[0003] During long-term operation of the vehicle, brake disc wear, friction pad thermal attenuation and transmission component deformation will cause the initial calibrated brake clearance parameters to fail, resulting in braking force deviation or response lag. Therefore, the EMB system needs to be calibrated. However, the existing EMB system calibration method has the problem of calibration lag, which cannot be automatically triggered to achieve active calibration. In addition, only the average brake clearance is calibrated during the calibration process, resulting in insufficient braking force on one side of the vehicle and low calibration accuracy. Summary of the invention

[0004] In order to solve the above technical problems, the purpose of this application is to provide an EMB system active calibration method and device for improving braking accuracy. The technical solutions adopted are as follows:

[0005] In a first aspect, an embodiment of the present application provides an EMB system active calibration method for improving braking accuracy, the method comprising the following steps:

[0006] respectively collecting the current and temperature of the brake motor winding in the car, and collecting the temperature of the brake disc in the car and the driving speed of the car in real time, wherein the brake motor includes a left front wheel motor and a right front wheel motor;

[0007] Based on the current temperature change of the brake motor winding, the current current of the brake motor winding is compensated; the compensated current is converted and filtered in the frequency domain to obtain the fifth harmonic current; the wear sensitivity factor of the current brake is determined by using the amplitude difference and phase difference of the fifth harmonic current of the left front wheel motor and the right front wheel motor;

[0008] Determine the cumulative net rotation angle of the current braking by the difference between the clamping rotation angle and the retraction rotation angle of the current and previous multiple brakings; utilize the difference between the temperature of the current brake disc and the preset reference temperature, and combine with the corresponding thermal expansion coefficient of the brake disc to obtain the current temperature correction coefficient;

[0009] Based on the difference between the current driving speed of the vehicle and the preset critical speed, and combine with the relationship between the driving speed and the wear amount of the brake pads to obtain the current speed correction coefficient; combine the cumulative net rotation angle, the temperature correction coefficient and the speed correction coefficient to determine the dynamic wear rate of the current braking;

[0010] Trigger the active calibration of the EMB system through the wear sensitivity factor and the dynamic wear rate, and determine the brake pad wear coefficient based on the wear sensitivity factor to correct the target rotation angles of the left and right calipers.

[0011] In one embodiment, the compensation for the current of the braking motor winding includes:

[0012] Calculate the difference between the current temperature of the braking motor winding and the preset reference temperature. The current of the braking motor winding after current compensation is negatively correlated with the difference and positively correlated with the physical quantity of the braking motor winding changing with temperature.

[0013] In one embodiment, the determination of the wear sensitivity factor includes:

[0014] Calculate the cosine value of the phase difference, and the wear sensitivity factor is the product of the cosine value and the amplitude difference.

[0015] In one embodiment, the calculation method of the cumulative net rotation angle is:

[0016] where, Δθ sum is the cumulative net rotation angle of the current braking, Δθ k is the difference between the clamping rotation angle and the retraction rotation angle of the k-th braking before the current one, μ is the preset time weighting factor, N is the preset number of brakings before the current one, and k is the serial number of the braking times.

[0017] In one embodiment, the determination of the temperature correction coefficient includes:

[0018] Record the difference between the temperature of the current brake disc and the preset reference temperature as the first difference, calculate the multiplication result of the first difference and the corresponding thermal expansion coefficient of the brake disc, and the temperature correction coefficient is positively correlated with the multiplication result.

[0019] In one embodiment, the determination of the speed correction coefficient includes:

[0020] Denote the difference between the preset critical speed and the current driving speed of the vehicle as the second difference. Using the relationship between the driving speed and the brake pad wear amount, preset a speed weight coefficient, and the speed correction coefficient is the product of the second difference and the speed weight coefficient.

[0021] In one embodiment, the calculation method of the dynamic wear rate is as follows:

[0022] In the formula, ω is the dynamic wear rate of the current braking, Δθ sum is the cumulative net rotation angle of the current braking, K T is the current temperature correction coefficient, K v is the current speed correction coefficient, η is the preset conversion coefficient between the rotation angle and the brake clearance, Δθ 0 is the initial net rotation angle when the vehicle has no wear.

[0023] In one embodiment, triggering the active calibration of the EMB system by the wear sensitivity factor and the dynamic wear rate includes:

[0024] If the absolute value of the wear sensitivity factor of the current braking is greater than the preset first threshold, or the dynamic wear rate of the current braking is greater than the preset second threshold, then trigger the EMB system to perform active calibration.

[0025] In one embodiment, correcting the target rotation angles of the left and right calipers includes:

[0026] The brake pad wear coefficient is the absolute value of the wear sensitivity factor. When the wear sensitivity factor is greater than 0, it is determined that the left caliper is worn. When the wear sensitivity factor is less than 0, it is determined that the right caliper is worn. When the left caliper or the right caliper is worn, increase the target rotation angle of the left caliper or the right caliper In the formula, Δθ b is the increase amount of the target rotation angle, Δg is the brake pad wear coefficient, P is the lead of the lead screw, and π is the pi.

[0027] In a second aspect, an active calibration device for an EMB system for improving braking accuracy provided by an embodiment of the present application includes a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, the steps of the method described in any one of the above are implemented.

[0028] The present application has at least the following beneficial effects:

[0029] This application respectively and real - time collects the current and temperature of the braking motor windings in the vehicle, and real - time collects the temperature of the brake disc in the vehicle and the driving speed of the vehicle. Among them, the braking motor includes a left front wheel motor and a right front wheel motor; based on the current temperature change of the braking motor windings, compensates the current of the braking motor windings; avoids the problem that the measured value of the current is falsely high due to the increase in the resistance of the motor windings with the increase in temperature, which affects the accuracy of determining the subsequent harmonic current; performs frequency - domain conversion and filtering on the compensated current to obtain the fifth - harmonic current; uses the amplitude difference and phase difference of the fifth - harmonic current of the left front wheel motor and the right front wheel motor to determine the wear - sensitive factor of the current braking; the wear - sensitive factor realizes high - precision detection, direction discrimination, and quantitative evaluation of unilateral wear during vehicle braking by fusing the amplitude difference and phase difference of the harmonic current, provides a key basis for the active calibration of the EMB system, and improves the braking accuracy and reliability of the EMB system; determines the cumulative net rotation angle of the current braking through the difference between the clamping rotation angle and the retraction rotation angle of the current and previous multiple brakings; uses the difference between the temperature of the current brake disc and the preset reference temperature, and combines the thermal expansion coefficient corresponding to the brake disc to obtain the current temperature correction coefficient; based on the difference between the current driving speed of the vehicle and the preset critical speed, and combines the relationship between the driving speed and the wear amount of the brake pads to obtain the current speed correction coefficient; combines the cumulative net rotation angle, the temperature correction coefficient, and the speed correction coefficient to determine the dynamic wear rate of the current braking; the dynamic wear rate takes into account the influence of different working conditions of temperature and vehicle speed on the wear of the brake pads, corrects the wear rate using the brake disc temperature and vehicle speed, improves the accuracy and reliability of determining the vehicle braking wear situation, triggers the active calibration of the EMB system through the wear - sensitive factor and the dynamic wear rate, overcomes the defect that the traditional calibration method of the EMB system cannot be actively calibrated, and determines the brake pad wear coefficient based on the wear - sensitive factor, corrects the target rotation angles of the left and right calipers, and improves the calibration accuracy of the EMB system by calibrating the left and right calipers respectively, thereby improving the braking accuracy of the vehicle. Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following - described drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0031] Figure 1 It is a flowchart of the steps of an active calibration method for an EMB system to improve braking accuracy provided by an embodiment of the present application;

[0032] Figure 2 It is a flowchart of the relationship between the correction indexes of the caliper target rotation angle. Detailed implementation manners

[0033] In order to further elaborate on the technical means and effects adopted by this application to achieve the intended invention purpose, the following, in combination with the accompanying drawings and preferred embodiments, details the specific implementation manners, structures, features, and effects of an active calibration method and device for an EMB system for improving braking accuracy proposed according to this application. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. In addition, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs.

[0035] The following specifically describes the specific solutions of an active calibration method and device for an EMB system for improving braking accuracy provided by this application in combination with the accompanying drawings.

[0036] Please refer to Figure 1 , which shows a flowchart of the steps of an active calibration method for an EMB system for improving braking accuracy provided by an embodiment of this application. The method includes the following steps:

[0037] S1. Respectively and in real time collect the current and temperature of the braking motor windings in the vehicle, and in real time collect the temperature of the brake disc in the vehicle and the driving speed of the vehicle. Among them, the braking motor includes a left front wheel motor and a right front wheel motor.

[0038] The EMB system realizes braking control through electrical signals. When the brake pedal is depressed, the stroke sensor collects the pedal stroke signal in real time. After being parsed by the controller, it drives the motor to rotate, and converts the rotational motion into a linear motion of the caliper through a lead screw-nut transmission mechanism, so that the brake pads, that is, the brake linings, clamp the brake disc to generate braking force.

[0039] In this embodiment, current sensors are installed on the conductive lines of the braking motor windings to respectively and in real time collect the line currents of the left front wheel motor and the right front wheel motor. At the same time, temperature sensors are used to respectively and in real time collect the temperatures of the left and right motor windings, and in real time collect the temperature of the brake disc, and a vehicle speed sensor is used to in real time collect the driving speed of the vehicle.

[0040] It should be noted that all the data collected in real time in this embodiment are collected synchronously, and the collection frequency is 10 kHz. The implementer can set it according to the actual situation, and this embodiment does not limit it here.

[0041] S2, compensate the current of the braking motor winding based on the current temperature change of the braking motor winding; perform frequency domain conversion and filtering on the compensated current to obtain the fifth harmonic current; use the amplitude difference and phase difference of the fifth harmonic currents of the left front wheel motor and the right front wheel motor to determine the wear sensitivity factor of the current braking.

[0042] When the EMB system brakes, the resistance of the motor-driven caliper to clamp can directly reflect the contact state between the brake pad and the brake disc. When the brake pad wears and becomes thinner, the motor needs to rotate more angles to compensate for the braking gap. At the same time, due to the changes in the contact area and pressure distribution, the load torque increases, resulting in an increase in the effective value of the line current. Unilateral wear will cause an imbalance in the resistance of the left and right calipers. For example, if the left caliper wears more severely, the left caliper needs additional torque to overcome a larger braking gap, and the peak value of the line current of the left front wheel motor will be higher than that of the right front wheel motor, and there will be a phase difference in the current waveform during the clamping stage. Therefore, in this embodiment, the wear characteristics are extracted through the line current signal of the braking motor.

[0043] In actual working conditions, the line current of the braking motor is easily affected by temperature drift, that is, the winding resistance changes with temperature, electromagnetic noise, and mechanical vibration, that is, the caliper friction fluctuation, resulting in the distortion of the current signal. These interferences will obscure the unilateral wear characteristics contained in the current harmonics and directly affect the discrimination accuracy of the wear of the EMB system. Therefore, in this embodiment, the current signal is first preprocessed.

[0044] The resistance of the motor winding increases with the increase in temperature, resulting in a falsely high current measurement value, which directly affects the calculation of the harmonic amplitude. Therefore, in this embodiment, the measured current higher than the reference temperature is temperature-compensated. Taking the line current collected by the left front wheel motor as an example, the current collected on this side is compensated according to the corresponding motor winding temperature. The specific calculation method is as follows:

[0045] In the formula, I n is the current value after temperature compensation of the left front wheel motor at the current moment, I is the current value collected by the left front wheel motor at the current moment, α is the conductor temperature coefficient, that is, the physical quantity of the braking motor winding that changes with temperature, which measures the percentage of the change in conductor resistance when the temperature changes by 1°C. In this embodiment, the motor winding is made of copper wire, and α is set to 0.00393 / °C. The implementer can set it according to the actual situation. T is the current temperature of the left front wheel motor winding, and T ref represents the reference temperature of the braking motor winding. In this embodiment, the reference temperature is set to 25°C. The implementer can set it according to the actual situation, and this embodiment does not limit it here.

[0046] Use the same calculation method as the current value after temperature compensation of the left front wheel motor at the current moment to obtain the current value after temperature compensation of the right front wheel motor at the current moment.

[0047] Taking the current time and the current value of the current compensated by the left front wheel motor temperature at all times before it as an example, in this embodiment, the fast Fourier transform is used to convert the compensated current data into the frequency domain, and then a Butterworth band-pass filter is used for filtering. The lower cut-off frequency is 250 Hz, the upper cut-off frequency is 400 Hz, and the quality factor Q = 1.5. Then, the 5th to 7th harmonics are retained. Since the fundamental frequency contains the main component of the motor torque and is independent of the braking gap, the high-frequency noise is suppressed at the same time. The purpose of retaining the 5th to 7th harmonics is to isolate the harmonic characteristics strongly related to unilateral wear and exclude the interference of irrelevant signals.

[0048] Then, the Hilbert transform is used to perform orthogonal decomposition on the filtered current data to calculate the amplitude A5 and phase of the 5th harmonic. Because when the brake pads are worn unilaterally, the imbalance of the gap between the brake disc and the caliper will cause the motor load to exhibit spatial asymmetry, and this asymmetry is coupled to the stator current through the change of the air-gap permeance. According to the principles of electrical machinery, the unilateral stiffness defect of a rotating machine will excite characteristic harmonics related to the number of pole pairs in the current.

[0049] It should be understood that the unilateral gap expansion caused by the wear of the EMB system will increase the local magnetic resistance, resulting in a positive correlation between the amplitude of the 5th harmonic in the stator current and the braking gap. The wear on the left and right sides will cause a characteristic phase difference in the 5th harmonic of the line current, which stems from the orthogonal response of the asymmetric load on the dq axis. In addition, compared with the 3rd harmonic that is easily contaminated by zero-sequence noise and the 7th harmonic that is easily interfered by bearing vibration, the 5th harmonic has a higher separation degree from the multiple frequency of the mechanical main frequency under braking conditions and is not directly interfered by the PWM carrier frequency. Therefore, in this embodiment, the 5th harmonic of the current data is analyzed.

[0050] Since the air-gap permeance asymmetry caused by unilateral wear on the left and right sides of the vehicle results in the formation of the 5th harmonic in the current data, and the amplitude of the 5th harmonic is sensitive to the change of the braking gap and is not affected by the motor speed. Therefore, in this embodiment, in the same way as using the current value of the current compensated by the left front wheel motor temperature at the current time and all times before it to obtain the 5th harmonic, the current value of the current compensated by the right front wheel motor temperature at the current time and all times before it is used to obtain the 5th harmonic corresponding to the current value of the current compensated by the right front wheel motor temperature. Then, the amplitude difference ΔA5 between the 5th harmonic corresponding to the current value of the current compensated by the left front wheel motor temperature and the 5th harmonic corresponding to the current value of the current compensated by the right front wheel motor temperature is calculated. The specific calculation method is as follows:

[0051] ΔA5 = |A5 left - A5 right |; where A5 left is the amplitude of the 5th harmonic corresponding to the current value of the current compensated by the left front wheel motor temperature, and A5 rightis the amplitude of the 5th harmonic corresponding to the current value after the temperature compensation of the right front wheel motor. ΔA5 reflects the wear degree of the EMB system. When the braking gap is larger, the local magnetic resistance is higher, and the difference in the amplitude of the 5th harmonic is larger.

[0052] In addition, obtain the phase difference between the 5th harmonic corresponding to the current value after the temperature compensation of the left front wheel motor and the 5th harmonic corresponding to the current value after the temperature compensation of the right front wheel motor The specific calculation method is:

[0053] In the formula, is the phase of the 5th harmonic corresponding to the current value after the temperature compensation of the left front wheel motor, is the phase of the 5th harmonic corresponding to the current value after the temperature compensation of the right front wheel motor.

[0054] It should be understood that when the left side of the vehicle is worn, the stiffness of the left caliper decreases, and the inductance of the left-phase winding of the motor decreases, resulting in the phase of the 5th harmonic advancing, that is, the phase difference increases. The opposite is true for the right side wear, that is, when the left side is worn, the phase difference is greater than 0, and when the right side is worn, the phase difference is less than 0. Therefore, the phase difference can represent the wear direction.

[0055] However, a single ΔA5 or is vulnerable to noise interference. Therefore, in this embodiment, the amplitude difference is projected onto the phase difference direction to eliminate the influence of phase angle fluctuations, avoid the ambiguity of a single feature, and determine the wear sensitive factor of the current braking. The specific calculation method is:

[0056] In the formula, S is the wear sensitive factor of the current braking, and cos() is the cosine function of the triangle.

[0057] It should be understood that due to the mechanical wear of the EMB system, the amplitude and phase of the 5th harmonic corresponding to the left front wheel motor and the right front wheel motor will increase synergistically, while short-term noise will cause random phase jitter; by multiplying the amplitude difference by the cosine value of the phase difference, only the co-frequency and co-phase changes related to mechanical wear are retained, and at the same time, the asynchronous fluctuations caused by noise are attenuated, so as to highlight the wear characteristics and suppress interference. The wear sensitive factor realizes high-precision detection, direction discrimination and quantitative evaluation of unilateral wear by fusing the amplitude difference and phase difference of the current signal, provides a key basis for active calibration, and finally improves the braking accuracy and reliability of the EMB system.

[0058] S3. Determine the cumulative net rotation angle of the current braking based on the differences between the clamping rotation angles and the retraction rotation angles of the current and multiple previous brakings; and obtain the current temperature correction factor by using the difference between the temperature of the current brake disc and the preset reference temperature in combination with the corresponding coefficient of thermal expansion of the brake disc.

[0059] Currently, existing EMB system calibration methods often perform off-line calibration or fixed mileage calibration, and cannot achieve active calibration. Since the wear of brake pads is affected by different working conditions such as braking frequency, temperature, and vehicle speed, the existing EMB system calibration methods cannot reflect the real loss in real time. In this embodiment, the difference in clamping and retraction rotation angles is obtained through the motor encoder, and corrections are made in combination with the temperature and vehicle speed of the brake disc, converting the physical gap into a real-time wear rate, thereby achieving active calibration.

[0060] When the vehicle brakes, the motor drives the caliper to clamp and generate friction, and wear will cause the brake pads to become thinner and the braking gap to increase; when retracting, the spring resets. When there is no wear, the difference between the clamping rotation angle and the retraction rotation angle is close to the theoretical gap. Therefore, the net rotation angle Δθ of a single braking i = θ clamp - θ release , which can reflect the effective wear consumption of a single braking. The greater the wear, the more the clamping needs to rotate, that is, the greater the net rotation angle. Where θ clamp , θ release represent the clamping rotation angle and the retraction rotation angle respectively. It should be noted that the clamping rotation angle and the retraction rotation angle are obtained through the motor encoder.

[0061] Under different working conditions, for example, when the vehicle is driving in the city, the braking frequency is high and the wear is fast. Therefore, the net rotation angle of the single braking closer to the current is more critical. When the vehicle is driving on the highway, the braking frequency is low and the wear is slow. Therefore, the wear within a certain period of time can better reflect the real situation. Therefore, in this embodiment, the net rotation angles of single brakings for a certain number of brakings are weighted to obtain the cumulative net rotation angle. In this embodiment, 100 brakings before the current braking are selected for analysis to balance real-time performance and noise. The implementer can determine the number of selected brakings by himself / herself, and this embodiment does not make any restrictions here.

[0062] In this embodiment, the calculation method of the cumulative net rotation angle of the current braking is as follows: In the formula, Δθ sum is the cumulative net rotation angle of the current braking, Δθ k is the difference between the clamping rotation angle and the retraction rotation angle of the kth braking before the current one, μ is the preset time weighting factor, in this embodiment μ = 0.95, giving a higher weight to the net rotation angle of the single braking closer to the current to reflect the change of the vehicle driving conditions, N is the preset number of brakings before the current one, in this embodiment N = 100, and k is the serial number of the braking times.

[0063] In addition, based on the real-time temperature of the brake disc, the present embodiment obtains the current temperature correction coefficient, and the specific calculation method is: K T = 1 + β T × (T - T 0 ); In the formula, K T is the current temperature correction coefficient, T is the current temperature of the brake disc, and T 0 is the preset reference temperature. In the present embodiment, T 0 = 25 °C, and the implementer can set it according to the actual situation. β T is the thermal expansion coefficient corresponding to the brake disc, denoted as the temperature sensitivity coefficient. In the present embodiment, β T = 0.003 / °C, indicating that for every 1 °C increase in the temperature of the brake disc above the reference temperature, the wear rate of the EMB system increases by 0.3%. The greater the difference between the temperature of the brake disc and the reference temperature, the more serious the wear of the EMB system, and the greater the temperature correction coefficient. Denote (T - T 0 ) as the first difference.

[0064] It should be noted that the difference represents the degree of difference between two variables, and specifically, it can be calculated by means such as difference value, absolute value of difference, ratio, etc.

[0065] S4. Based on the difference between the current driving speed of the vehicle and the preset critical speed, combined with the relationship between the driving speed and the wear amount of the brake pads, obtain the current speed correction coefficient; combine the cumulative net rotation angle, the temperature correction coefficient, and the speed correction coefficient to determine the dynamic wear rate of the current braking.

[0066] Comparing the cumulative net rotation angle of the current braking with the initial net rotation angle when the vehicle has no wear can obtain the real-time dynamic wear rate. However, the brake pads expand at high temperatures, resulting in the net rotation angle measured by the encoder including thermal deformation rather than real wear. In addition, during low-speed emergency braking, the contact time between the brake pads and the brake disc is extended, and the contact pressure is concentrated, mainly adhesive wear; during high-speed light braking, the slip speed of the friction pair is high, and the proportion of abrasive wear increases. Under the same net rotation angle, the wear amount at low speed is more than that at high speed. Therefore, the present embodiment corrects the wear rate for temperature and speed.

[0067] In the present embodiment, the calculation method of the dynamic wear rate ω of the current braking is: In the formula, Δθ sum is the cumulative net rotation angle of the current braking, Δθ 0 is the initial net rotation angle when the vehicle has no wear. In the present embodiment, Δθ 0 = 2 °, η is the conversion coefficient between the preset rotation angle and the braking gap. In the present embodiment, η = 0.02, converting the angle change into a braking gap change, that is, 1 ° rotation angle = 0.02 mm braking gap change. K vThe current speed correction coefficient, and the specific calculation method is where v is the driving speed of the current vehicle, and v c is the preset critical speed, and the critical speed takes a value of 50 km / h in this embodiment, which is used to distinguish between low-speed conditions and high-speed conditions. When the vehicle speed is higher, compared with low speed, the wear of the EMB system is lighter. β v is the preset speed weight coefficient, which is mapped based on the relationship between different vehicle speeds and the wear amount of the brake pads. In this embodiment, when the vehicle speed is between 0 and 50 km / h, β v = 1.5, indicating that the wear rate during low-speed braking is magnified by 1.5 times. When the vehicle speed is between 50 and 90 km / h, β v = 1. When the vehicle speed is greater than 90 km / h, β v = 0.5. When the vehicle speed is less than the critical speed, the wear contribution of the net rotation angle is amplified by the speed weight coefficient, that is, in the urban condition, low-speed driving and high braking frequency lead to more wear of the brake pads. K T is the current temperature correction coefficient, N is the preset number of braking times before the current time, and N = 100 in this embodiment. Denote as the second difference.

[0068] S5. Trigger the active calibration of the EMB system through the wear sensitivity factor and the dynamic wear rate, and determine the brake pad wear coefficient based on the wear sensitivity factor to correct the target rotation angles of the left and right calipers.

[0069] Trigger the active calibration of the EMB system according to the wear sensitivity factor and the dynamic wear rate of the current braking. Trigger condition 1: |S| > 0.15A. The wear sensitivity factor S combines the amplitude difference and the phase difference. When |S| exceeds the preset first threshold, that is, 0.15A, it is determined that there is unilateral wear during vehicle braking. In this embodiment, the first threshold is determined to be 0.15A according to the allowable maximum braking clearance difference of 0.1 mm. Trigger condition 2: ω > 0.015 mm / 100 times, and 0.015 mm / 100 times is the preset second threshold. The dynamic wear rate ω reflects the true wear rate through the cumulative net rotation angle, temperature correction, and speed correction. For example, frequent low-speed braking in the urban condition will accelerate wear and requires high-frequency calibration. In this embodiment, the value range of the second threshold is 0.01 - 0.02 mm / 100 times. If the second threshold is too low, it will lead to too frequent calibration. If the second threshold is too high, it may miss early wear and increase safety risks. If the wear sensitivity factor and the dynamic wear rate of the current braking meet trigger condition 1 or trigger condition 2, both can trigger the active calibration of the EMB system.

[0070] During the active calibration process of the EMB system, the wear direction and wear degree are determined according to the wear sensitivity factor. If the wear sensitivity factor S > 0, it indicates that the left caliper is worn. If the wear sensitivity factor S < 0, it indicates that the right caliper is worn. Calculate the brake pad wear coefficient Δg, where Δg = |S|.

[0071] Calibration is performed according to the brake pad wear coefficient. In this embodiment, compensation is driven by a motor. When the left caliper is worn, the target rotation angle of the left caliper is increased by the motor In the formula, Δθ b is the increase in the target rotation angle, Δg is the brake pad wear coefficient, P is the lead of the lead screw, and π is the pi. The rotation angle of the motor is converted into the actual displacement of the caliper. Similarly, when the right caliper is worn, the target rotation angle of the right caliper is increased by the motor The flow chart of the relationship between the caliper target rotation angle correction indicators is as Figure 2 shown.

[0072] Based on the same inventive concept as the above method, the embodiment of the present application also provides an active calibration device for an EMB system to improve braking accuracy, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, it implements the steps of any one of the above methods for actively calibrating an EMB system to improve braking accuracy.

[0073] It should be noted that: the above sequence of the embodiments of the present application is only for description and does not represent the superiority or inferiority of the embodiments. And the above describes specific embodiments of this specification. In addition, the processes depicted in the drawings do not necessarily require the specific order or continuous order shown to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0074] Each embodiment in this specification is described in a progressive manner. The same or similar parts between each embodiment can be referred to each other, and each embodiment focuses on the differences from other embodiments.

[0075] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the principle of the present application shall be included in the protection scope of the present application.

Claims

1. An active calibration method for an EMB system for improving braking accuracy, characterized in that: The method comprises the following steps: respectively collecting the current and temperature of the brake motor winding in the car, and collecting the temperature of the brake disc in the car and the driving speed of the car in real time, wherein the brake motor includes a left front wheel motor and a right front wheel motor; Based on the current temperature change of the brake motor winding, the current current of the brake motor winding is compensated; the compensated current is converted and filtered in the frequency domain to obtain the fifth harmonic current; the wear sensitivity factor of the current brake is determined by using the amplitude difference and phase difference of the fifth harmonic current of the left front wheel motor and the right front wheel motor; The accumulated net angle of the current brake is determined by the difference between the clamping angle and the retraction angle of the current and previous multiple brakes; the current temperature correction coefficient is obtained by using the difference between the current brake disc temperature and the preset reference temperature, combined with the thermal expansion coefficient corresponding to the brake disc; Based on the difference between the current driving speed of the vehicle and the preset critical speed, combined with the relationship between the driving speed and the amount of brake pad wear, the current speed correction coefficient is obtained; combined with the cumulative net turning angle, the temperature correction coefficient and the speed correction coefficient, the current dynamic wear rate of the brake is determined; The active calibration of the EMB system is triggered by the wear sensitivity factor and the dynamic wear rate, and the brake pad wear coefficient is determined based on the wear sensitivity factor to correct the left and right caliper target angles.

2. The active calibration method for an EMB system for improving braking accuracy as claimed in claim 1, characterized in that: The present current of the brake motor winding is compensated, including: The difference between the current temperature of the brake motor winding and the preset reference temperature is calculated. The current compensated current of the brake motor winding is negatively correlated with the difference and the physical quantity of the brake motor winding that changes with temperature, and is positively correlated with the current current of the brake motor winding.

3. The active calibration method for an EMB system for improving braking accuracy as claimed in claim 1, characterized in that: The determination of the wear sensitivity factor includes: The cosine value of the phase difference is calculated, and the wear sensitivity factor is the product of the cosine value and the amplitude difference.

4. The active calibration method for an EMB system for improving braking accuracy as claimed in claim 3, characterized in that: The cumulative net turning angle is calculated as follows: In the formula, Δθ sum is the cumulative net turning angle of the current braking, Δθ k is the difference between the clamping angle and the retracting angle of the kth braking before the current time, μ is the preset time weighting factor, N is the preset number of braking times before the current time, and k is the sequence number of braking times.

5. The active calibration method for an EMB system for improving braking accuracy as claimed in claim 1, characterized in that: The determination of the temperature correction coefficient includes: The difference between the current temperature of the brake disc and the preset reference temperature is recorded as a first difference, and a multiplication result of the first difference and the thermal expansion coefficient corresponding to the brake disc is calculated, and the temperature correction coefficient is positively correlated with the multiplication result.

6. The active calibration method for an EMB system for improving braking accuracy as claimed in claim 1, characterized in that: The determination of the speed correction coefficient includes: The difference between the preset critical speed and the current driving speed of the vehicle is recorded as the second difference. The speed weight coefficient is preset using the relationship between the driving speed and the amount of brake pad wear. The speed correction coefficient is the product of the second difference and the speed weight coefficient.

7. The active calibration method for an EMB system for improving braking accuracy as claimed in claim 4, characterized in that: The dynamic wear rate is calculated as follows: Where ω is the dynamic wear rate of the current brake, Δθ sum is the cumulative net turning angle of the current braking, K T is the current temperature correction coefficient, K v is the current speed correction coefficient, η is the conversion coefficient between the preset turning angle and the braking clearance, and Δθ0 is the initial net turning angle when the vehicle has no wear.

8. The active calibration method for an EMB system for improving braking accuracy as claimed in claim 1, characterized in that: The triggering of active calibration of the EMB system by the wear sensitivity factor and the dynamic wear rate includes: If the absolute value of the wear sensitivity factor of the current braking is greater than the preset first threshold, or the dynamic wear rate of the current braking is greater than the preset second threshold, the EMB system is triggered to perform active calibration.

9. The active calibration method for an EMB system for improving braking accuracy as claimed in claim 1, characterized in that: The correcting of the target turning angles of the left and right calipers includes: The brake pad wear coefficient is the absolute value of the wear sensitivity factor. When the wear sensitivity factor is greater than 0, the left caliper is judged to be worn. When the wear sensitivity factor is less than 0, the right caliper is judged to be worn. When the left caliper or the right caliper is worn, the target turning angle of the left caliper or the right caliper is increased. In the formula, Δθ b is the increase in the target rotation angle, Δg is the wear coefficient of the brake pad, P is the lead of the screw, and π is the pi.

10. An active calibration device for an EMB system for improving braking accuracy, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 9 are implemented.

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