An EMB-based vehicle braking torque calibration method

Abstract

The application provides a kind of EMB-based vehicle brake torque calibration method, it is related to vehicle engineering technical field, the motor rotation angle-brake torque curve under different constant experimental current is obtained in laboratory in the application and the basic torque lookup table is constructed, the deviation of slip rate is calculated in real time in the process of vehicle driving is combined to generate driving correction coefficient, the brake torque correction amount of wheel of VDC, ABS and TCS system is integrated simultaneously, and the internal correction coefficient of vehicle target brake torque is generated, finally, dynamic correction coefficient is formed by fusion, the basic current is corrected in real time, so as to realize the accurate, adaptive calibration of brake torque of each wheel, effectively improve the brake safety and stability of vehicle under complex working conditions.

Description

Technical Field

[0001] This invention relates to the field of vehicle engineering technology, specifically to a vehicle braking torque calibration method based on EMB. Background Technology

[0002] As automotive braking systems evolve towards electronic and intelligent control, EMB (Electrical Braking Brake) systems are gradually replacing traditional hydraulic brakes, becoming the core of next-generation vehicle braking technology. However, EMB systems face challenges in practical applications, including insufficient accuracy in braking torque calibration and poor adaptability to dynamic conditions. Existing calibration methods are mostly based on static laboratory data, failing to fully consider factors such as slip ratio changes and vehicle control system interventions during vehicle operation. This results in delayed response and decreased accuracy of braking torque control on high-traction surfaces or in emergency braking scenarios, impacting vehicle braking safety and stability. Furthermore, traditional methods rely on fixed torque mapping tables, lacking the ability to dynamically correct for multi-system collaborative interventions, thus limiting the performance optimization of EMB systems under complex conditions.

[0003] In the prior art, CN107499313B discloses a method and a torque calibration device for calibrating the required torque of a vehicle, comprising: determining the balance torque of the vehicle traveling at a target speed, wherein the balance torque is the torque required to overcome friction when traveling at the target speed; determining the critical acceleration of the vehicle at start-up; calibrating the acceleration curve required by the vehicle in a creeping state from start-up to reach the target speed based on the critical acceleration and the target speed; and calibrating the required torque curve of the vehicle in a creeping state from start-up to reach the target speed based on the calibrated acceleration, the mass of the vehicle, and the balance torque.

[0004] The main problem with the above solution is that it calibrates a preset, relatively ideal driving torque curve, which cannot cope with complex and diverse driving conditions such as braking, emergency acceleration, and high-speed cruising. The torque is calculated based on the vehicle's mass and a preset acceleration curve. Once calibrated, the system mechanically follows this preset torque curve during actual operation, failing to adjust in real time according to actual road conditions and vehicle status. It lacks self-adaptation and correction capabilities. When starting on low-traction surfaces, even if driven according to the calibrated torque, the drive wheels may slip severely, leading to vehicle instability or inability to start. It fails to balance safety and braking performance.

[0005] The information disclosed in the background section is only intended to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a vehicle braking torque calibration method based on EMB to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A vehicle braking torque calibration method based on EMB, comprising the following steps:

[0009] Step 1: Set up test conditions for various constant experimental currents, control the EMB motor to rotate under each test condition in the laboratory, record the clamping force of the brake pads on the brake disc, convert the clamping force into braking torque, record the corresponding motor rotation angle, obtain the motor rotation angle-braking torque curve under each constant experimental current, and build a basic torque lookup library.

[0010] Step 2: Obtain the optimal slip ratio for each wheel. During vehicle operation, read the real-time vehicle speed and wheel angular velocity, calculate the real-time slip ratio for each wheel, and generate a driving correction coefficient by combining the deviation between the real-time slip ratio and the optimal slip ratio of the same wheel.

[0011] Step 3: During vehicle operation, the braking torque correction amount issued by the VDC, ABS and TCS systems is acquired in real time, and then the real-time total requested torque increment of each wheel is calculated. The real-time total target braking torque of the whole vehicle is acquired through the pedal sensor, and the real-time target braking torque allocated to each wheel is calculated through the EBD system. An internal correction coefficient is generated based on the real-time total requested torque increment and the real-time target braking torque. The dynamic correction coefficient of each wheel is generated by combining the internal correction coefficient and the driving correction coefficient.

[0012] Step 4: Obtain the real-time target braking torque and motor angle for each wheel, find the corresponding base current based on the base torque lookup library, correct the base current using a dynamic correction coefficient, input the motor angle and the corrected current into the EMB motor, and the braking torque corresponding to the clamping force generated is the calibrated braking torque.

[0013] Furthermore, the principle underlying the acquisition of the motor rotation angle-braking torque curves under various constant experimental currents is as follows:

[0014] The EMB motor converts rotational motion into clamping force between the brake caliper and the brake disc through a transmission mechanism. The motor output torque is calculated based on the motor current using the following formula:

[0015]

[0016] in, This indicates the motor's output torque. This represents the motor torque constant. This indicates the current flowing through the motor;

[0017] The motor output torque is converted into the clamping force of the brake caliper through the transmission mechanism, based on the following formula:

[0018]

[0019] in, Indicates clamping force. This indicates the motor's transmission efficiency. Indicates the total transmission ratio. Indicates the equivalent radius of action;

[0020] The formula for converting clamping force into braking torque is as follows:

[0021]

[0022] in, Indicates braking torque. This indicates the coefficient of friction between the brake pads and the brake disc during laboratory testing. Indicates the effective friction radius of the brake disc;

[0023] The motor rotation angles and calculated braking torques collected under various constant experimental currents of the EMB motor are fitted to form the motor rotation angle-braking torque curve under the constant experimental current. The motor rotation angle-braking torque curves under all constant experimental currents are integrated to build a basic torque lookup library.

[0024] Furthermore, the principle underlying the generation of driving correction factors is as follows:

[0025] The formula used to calculate the real-time slip ratio of each wheel is as follows:

[0026]

[0027] in, Indicates the first Real-time slip ratio of each wheel Indicates real-time vehicle speed. Indicates the first Real-time angular velocity of each wheel Indicates the first The rolling radius of each wheel;

[0028] The formula used to generate the driving correction factor is:

[0029]

[0030]

[0031] in, Indicates the first The driving correction factor for each wheel This represents the proportionality coefficient. Indicates the first The deviation between the real-time slip ratio and the optimal slip ratio of each wheel. This indicates the optimal slip ratio.

[0032] Furthermore, the principle underlying the generation of internal correction coefficients is as follows:

[0033] For each wheel, the braking torque correction is obtained in real time from the VDC, ABS, and TCS systems, and the total requested torque increment is generated based on the following formula:

[0034]

[0035] in, Indicates the first The total requested torque increment for each wheel Indicates the VDC system for the first Braking torque correction for each wheel Indicates the ABS system for the first Braking torque correction for each wheel This indicates that the TCS system is for the first Braking torque correction for each wheel;

[0036] The EMB controller reads the signal generated by the pedal sensor to obtain the pedal travel and the rate of change of pedal travel. Combined with the pedal feel curve inside the vehicle, the total target braking torque corresponding to the pedal travel and the rate of change of pedal travel is obtained. After the EBD system calculates the target braking torque allocated to each wheel, the internal correction coefficient for each wheel is calculated using the following formula:

[0037]

[0038]

[0039] in, Indicates the first The original correction factor for each wheel, Indicates the first The target braking torque for each wheel Indicates the first Internal correction coefficient for each wheel This represents the upper limit of the correction factor, taken as... .

[0040] The principle underlying the generation of the dynamic correction coefficient for each wheel is as follows:

[0041]

[0042] in, Indicates the first Dynamic correction coefficient for each wheel Indicates the system interference threshold, take .

[0043] Furthermore, the principle underlying the retrieval of the corresponding base current based on the base torque lookup library is as follows:

[0044] After obtaining the real-time target braking torque and motor rotation angle for each wheel, the first wheel will be... Motor rotation angle of each wheel Substitute the values ​​into the expressions for motor rotation angle-braking torque curves with different constant experimental currents in the basic torque lookup library to obtain the calculated braking torque value. ,in, Indicates will Substitute the first The calculated braking torque value is obtained from the expression of the motor rotation angle-braking torque curve. This indicates the index of the motor rotation angle-braking torque curve in the basic torque lookup library; the principle underlying the calculation of the fluctuation range of the target braking torque is: The target braking torque for each wheel is Its fluctuation range is ,in, Indicates the first The tolerance for brake torque fluctuations in each wheel, and , This represents the tolerance adjustment factor, and ;

[0045] When the calculated braking torque value is within the fluctuation range of the target braking torque, retain the curves of the calculated braking torque value and the corresponding constant experimental current, and combine all the retained constant experimental current curves to generate an effective current set; plot the curves of the effective current set on the same plane coordinate system with the motor rotation angle on the horizontal axis and the braking torque on the vertical axis. In the curves of the effective current set, each current corresponds to a... The calculated braking torque value is generated under the following conditions. Down With Discrete mapping relationship, where, Represents the first in the effective current set One current, The index representing the effective current lumped current. Indicates in Below, current The corresponding calculated braking torque value is fitted to the above discrete mapping relationship to generate the value in... The principle underlying the torque-current function relationship is as follows:

[0046] based on With Discrete mapping relationships construct a set of discrete data points , ,in, This represents the quantity of the effective condensed current; a fitting function between the effective condensed current and the braking torque is established using a polynomial function, the specific formula of which is:

[0047]

[0048] in, Indicates braking torque. Represents current. Denotes the order of a polynomial. The coefficients are to be fitted.

[0049] Based on the least squares method, discrete data points are substituted into the fitting function to calculate the coefficients to be fitted. Substituting the coefficients to be fitted into the fitting function yields the torque-current function;

[0050] Will Substituting into the torque-current function, we obtain the corresponding first... The base current of each wheel .

[0051] Furthermore, the principle underlying the correction of the base current using a dynamic correction factor is as follows:

[0052]

[0053] in, Indicates the first Current correction value for each wheel Indicates the first The base current of each wheel;

[0054] The first The current correction value for each wheel is input to the corresponding EMB motor. The EMB motor controls the brake pads of the brake caliper to generate a clamping force on the brake disc, converting the clamping force into braking torque, which is the first wheel's current correction value. The standard driving torque of each wheel is adjusted.

[0055] Compared with the prior art, the beneficial effects of the present invention are:

[0056] This invention constructs a basic torque lookup table to obtain the true physical relationship between current, angle, and torque, clarifying how much torque a given current and angle can generate, providing an accurate basis for subsequent dynamic correction. Compared to existing technologies where calibration is impossible to adjust based on actual vehicle driving conditions, this solution considers both wheel states during driving and feedback signals from other vehicle control systems regarding torque. It introduces real-time slip ratio as a key feedback signal, enabling dynamic torque adjustment based on the real-time wheel states during vehicle operation. Furthermore, it obtains the braking torque correction amounts for each wheel from other vehicle control systems during driving, specifically VDC, ABS, and TCS, considering both driving correction and system intervention correction. Different fusion strategies are adopted based on the urgency of the intervention, prioritizing vehicle stability. When VDC, ABS, and TCS interventions are strong, they take the lead to ensure rapid response to sudden dangers. In other situations, slip ratio-based correction takes precedence, improving system safety and adaptability under complex conditions. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the method flow of an embodiment of the present invention;

[0058] Figure 2 This is a schematic diagram of the braking torque fitting curve under the same turning angle in an embodiment of the present invention;

[0059] Figure 3 This is a schematic diagram of the braking torque fitting curve under the same current in an embodiment of the present invention. Detailed Implementation

[0060] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0061] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0062] Example:

[0063] Please see Figures 1 to 3 The present invention provides a technical solution:

[0064] A vehicle braking torque calibration method based on EMB, comprising the following steps:

[0065] Step 1: Set up test conditions for various constant experimental currents, control the EMB motor to rotate under each test condition in the laboratory, record the clamping force of the brake pads on the brake disc, convert the clamping force into braking torque, record the corresponding motor rotation angle, obtain the motor rotation angle-braking torque curve under each constant experimental current, and build a basic torque lookup library.

[0066] In this embodiment, the principle underlying the acquisition of the motor rotation angle-braking torque curves under various constant experimental currents is as follows:

[0067] The EMB motor converts rotational motion into clamping force between the brake caliper and the brake disc through a transmission mechanism. The motor output torque is calculated based on the motor current using the following formula:

[0068]

[0069] in, This indicates the motor's output torque. This represents the motor torque constant. This indicates the current flowing through the motor;

[0070] The motor output torque T is the actual physical quantity output from the motor shaft that can perform mechanical work. By controlling the magnitude of the current I, the motor's output force is indirectly controlled. A higher motor output torque means the motor can drive the transmission mechanism more quickly, thereby rapidly generating clamping force and resulting in a shorter braking response time. The motor torque constant... This reflects the efficiency of an electric motor in converting electrical energy into mechanical energy. It is an inherent physical parameter of the motor, indicating how many Newton-meters of torque can be generated per ampere of current. The larger the value, the greater the torque the motor can output under the same current. The output torque of the motor is proportional to the current I and the motor torque constant.

[0071] The motor output torque is converted into the clamping force of the brake caliper through the transmission mechanism, based on the following formula:

[0072]

[0073] in, Indicates clamping force. This indicates the motor's transmission efficiency. Indicates the total transmission ratio. Indicates the equivalent radius of action;

[0074] Clamping force This reflects the positive pressure acting on both sides of the brake disc. The larger the clamping force, the more tightly the brake pads press against the brake disc, resulting in a greater braking torque. However, excessive clamping force can accelerate the wear of the brake pads and disc, and may cause vibration and noise. The torque T generated by the motor must be converted into the linear clamping force F required by the brake caliper to press the brake pads firmly. The force-multiplying effect of speed reduction and torque-increasing transmission mechanisms (such as gear sets and worm gears) was quantified. The larger the value, the greater the amplification of the motor's output torque and the greater the reduction in speed. According to the law of conservation of energy, output power ≈ input power, and power = torque × angular velocity. Therefore, during deceleration, the angular velocity decreases, and the corresponding torque increases, thus increasing the overall transmission ratio. This is the increase; motor transmission efficiency It reflects the energy loss caused by friction and vibration in the transmission mechanism and is a coefficient less than 1; the clamping force F is the result of the motor output torque T being amplified and converted by the transmission system; the equivalent radius of action... It is a lever used to ultimately convert rotational torque into linear force. In an EMB system, the motor output torque T is converted into the clamping force of the brake caliper on the brake disc via a transmission mechanism (ball screw). In this process, This indicates the equivalent lever arm radius that converts the selected torque into linear clamping force, corresponding to the lead radius of the ball screw; A smaller torque indicates that this is a labor-saving but distance-saving mechanism, meaning that a smaller torque can generate a larger clamping force. A larger value indicates that this is a labor-intensive and distance-saving mechanism, requiring a larger motor torque to generate the same clamping force.

[0075] The formula for converting clamping force into braking torque is as follows:

[0076]

[0077] in, Indicates braking torque. This indicates the coefficient of friction between the brake pads and the brake disc during laboratory testing. Indicates the effective friction radius of the brake disc;

[0078] Braking torque reflects the torque that ultimately acts on the wheels to overcome the vehicle's kinetic energy and decelerate it; clamping force is the normal force that generates friction and is the fundamental source of braking torque, with the coefficient of friction being the primary factor. It describes how much normal force can generate how much frictional force. Friction acts on the brake disc, but what is needed is the torque that this frictional force produces about the wheel axle. This represents the frictional force exerted by the clamping force on the brake disc. Based on the lever principle, friction can be considered as a concentrated force on the friction surface of the brake disc. This is the equivalent force arm of the force. The larger the value, the better the braking effect; under the same clamping force and coefficient of friction, it can generate greater braking torque. The smaller the value, the shorter the brake lever. In order to achieve the same braking torque, the clamping force and the coefficient of friction required are greater.

[0079] The EMB motor is a braking system actuator that directly drives the braking mechanism. It controls the motor's rotation via electronic signals, thereby clamping and releasing the brake disc. The EMB motor converts the motor's rotational motion into a linear clamping force of the brake caliper on the brake disc. First, the motor receives a current signal from the controller—a constant experimental current—and then outputs rotational torque. Then the rotational torque output by the motor A speed reduction and torque amplification transmission mechanism converts the high-speed rotation of the motor into a slower rotation. As the speed decreases, the output torque is amplified. At the end of the transmission mechanism, a ball screw converts the rotational motion into linear motion. The thrust of this linear motion is the clamping force, which acts directly on the brake caliper, pushing the brake pads to clamp the brake disc fixed to the wheel. When the brake pads clamp the rotating brake disc, a huge frictional force is generated between them. This frictional force acts on the brake disc to form a braking torque that is opposite to the direction of wheel rotation. This braking torque is the reason why the wheel slows down and the vehicle stops.

[0080] Multiple motor rotation angles collected under various constant experimental currents and the calculated braking torques of the EMB motor were fitted to form a motor rotation angle-braking torque curve under that constant experimental current. A basic torque lookup library was constructed by integrating all motor rotation angle-braking torque curves under all constant experimental currents, as shown in Table 1, which reflects the change in braking torque with current when the motor rotation angle is 180°. , , , , , It can be seen that under a fixed motor rotation angle, the braking torque is directly proportional to the current.

[0081] Table 1. Braking torque variation with current

[0082]

[0083] Table 2 shows the variation of braking torque with motor rotation angle under the same constant experimental current (5A in this case). Under the constant experimental current, as the motor rotation angle increases, the braking torque rises rapidly at the initial contact point, and then gradually levels off as the brake pads clamp closer. Specifically, in the 90° to 120° range, the torque rises rapidly as the brake pads approach the brake disc, reaching its maximum value at approximately 135°, near the center point. In the 150° to 180° range, the clamping force tends to saturate, and the torque increases slowly.

[0084] Table 2. Variation of Braking Torque with Motor Rotation Angle

[0085]

[0086] The basic torque lookup library contains several curves, each of which is a fitting curve of motor rotation angle and braking torque under constant experimental current. An nth-order polynomial function with braking torque as the dependent variable and motor rotation angle as the independent variable is found, and the least squares method is used to fit it to obtain the functional expression of different motor rotation angle-braking torque curves.

[0087] Step 2: Obtain the optimal slip ratio for each wheel. During vehicle operation, read the real-time vehicle speed and wheel angular velocity, calculate the real-time slip ratio for each wheel, and generate a driving correction coefficient by combining the deviation between the real-time slip ratio and the optimal slip ratio of the same wheel.

[0088] In this embodiment, the principle underlying the generation of the driving correction coefficient is as follows:

[0089] The formula used to calculate the real-time slip ratio of each wheel is as follows:

[0090]

[0091] in, Indicates the first Real-time slip ratio of each wheel Indicates real-time vehicle speed. Indicates the first Real-time angular velocity of each wheel Indicates the first The rolling radius of each wheel;

[0092] The real-time slip ratio of a wheel reflects the degree of relative slippage between the wheel and the road surface during braking, and is used to assess the braking state of a vehicle. When the wheel speed is lower than the vehicle speed, it indicates slippage. The optimal slip ratio is usually set between 10% and 30%. When the real-time slip ratio is close to the optimal slip ratio, it indicates higher braking efficiency and greater adhesion between the tire and the road surface. When the value approaches 1, it indicates that the vehicle is close to locking up, which can easily lead to excessive braking distance, loss of steering control, and other situations.

[0093] The formula used to generate the driving correction factor is:

[0094]

[0095]

[0096] in, Indicates the first The driving correction factor for each wheel This represents the proportionality coefficient. Indicates the first The deviation between the real-time slip ratio and the optimal slip ratio of each wheel. This indicates the optimal slip ratio.

[0097] The driving correction coefficient dynamically adjusts the braking torque by monitoring the deviation between the real-time slip ratio and the ideal optimal slip ratio to prevent wheel lock-up or insufficient braking force, thereby always keeping the braking process near the optimal adhesion zone. (Proportional coefficient) Used to determine the system's sensitivity to slip ratio deviations. The value range is generally 1.0 to 5.0. The larger the value, the stronger the correction and the faster the response for the same deviation, but it may cause system overshoot or oscillation. The smaller the value, the smoother the correction process, but the response may be slower. On dry roads, take... To balance braking response speed and stability, in low-traction road conditions such as rain and snow, take To avoid excessive braking that could lead to loss of vehicle control, under track conditions, take... To achieve maximum braking efficiency; the driving correction coefficient reflects the magnitude of the correction force that the system needs to apply based on the base current to correct the current slip ratio deviation. Time means This indicates that the real-time slip ratio equals the optimal slip ratio, the braking state is ideal, and no correction to the base current is needed; when When, explain This means that the real-time slip ratio is less than the optimal slip ratio, indicating insufficient wheel slip. This suggests that the tire's adhesion potential with the road surface has not been fully utilized, and there is room to increase braking force. When, explain This means that if the real-time slip ratio is greater than the optimal slip ratio, the wheel area will lock up, posing a risk of slippage, and the vehicle needs to reduce its braking force.

[0098] Step 3: During vehicle operation, the braking torque correction amount issued by the VDC, ABS and TCS systems is acquired in real time, and then the real-time total requested torque increment of each wheel is calculated. The real-time total target braking torque of the whole vehicle is acquired through the pedal sensor, and the real-time target braking torque allocated to each wheel is calculated through the EBD system. An internal correction coefficient is generated based on the real-time total requested torque increment and the real-time target braking torque. The dynamic correction coefficient of each wheel is generated by combining the internal correction coefficient and the driving correction coefficient.

[0099] In this embodiment, the principle underlying the generation of the internal correction coefficient is as follows:

[0100] VDC stands for Vehicle Stability Control. It monitors signals such as yaw rate, lateral acceleration, and steering wheel angle to determine if the vehicle is experiencing instability, such as understeer or oversteer. When the system detects that the vehicle's actual trajectory is inconsistent with the driver's expected trajectory, VDC applies braking force to one or more wheels, generating a corrective torque to help the vehicle regain stability. The specific correction logic is as follows: In case of understeer, the front wheels slip out, and VDC applies braking force to the inner rear wheel; in case of oversteer, the rear wheels fishtail, and VDC applies braking force to the outer front wheel. ABS is a system that prevents wheels from locking up during braking. It monitors the angular velocity of the wheels to determine if there is a tendency to lock up, and adjusts the braking torque to prevent the wheels from locking up completely. When the ABS detects a sharp drop in the angular velocity of a wheel, i.e., the slip ratio is close to 1 and the wheel is about to lock up, the ABS sends a braking torque correction amount to reduce the wheel slip ratio by adjusting the braking force. TCS stands for Traction Control System, which prevents the drive wheels from excessively slipping during acceleration, especially on low-traction surfaces. When it detects that the speed of the drive wheels is significantly higher than that of the non-drive wheels, it determines that the drive wheels are slipping and the tire adhesion is insufficient. TCS intervenes in two ways: requesting the engine management system to reduce torque output and applying appropriate braking force to the slipping drive wheels. Therefore, when the vehicle's driving is abnormal, the VDC, ABS and TCS systems will simultaneously correct the vehicle's torque. The main goal of TCS is to control the vehicle's longitudinal traction and prevent slippage. The EMB controller adds the correction amounts from VDC, ABS and TCS to obtain the torque correction amount of the vehicle's internal systems for the tires.

[0101] For each wheel, the braking torque correction is obtained in real time from the VDC, ABS, and TCS systems, and the total requested torque increment is generated based on the following formula:

[0102]

[0103] in, Indicates the first The total requested torque increment for each wheel Indicates the VDC system for the first Braking torque correction for each wheel Indicates the ABS system for the first Braking torque correction for each wheel This indicates that the TCS system is for the first Braking torque correction for each wheel;

[0104] The EMB controller reads the signal generated by the pedal sensor to obtain the pedal travel and the rate of change of pedal travel. Combined with the pedal feel curve inside the vehicle, the total target braking torque corresponding to the pedal travel and the rate of change of pedal travel is obtained. After the EBD system calculates the target braking torque allocated to each wheel, the internal correction coefficient for each wheel is calculated using the following formula:

[0105]

[0106]

[0107] in, Indicates the first The original correction factor for each wheel, Indicates the first The target braking torque for each wheel Indicates the first Internal correction coefficient for each wheel This represents the upper limit of the correction factor, taken as... .

[0108] The pedal travel reflects the depth to which the driver depresses the brake pedal, representing the intensity of their braking intention. The rate of change of pedal travel reflects the speed at which the driver depresses the pedal, used to judge the urgency of braking. The pedal feel curve is essentially a pre-set lookup table in the vehicle, used to reflect the mapping relationship between the measured values ​​of the pedal sensor and the target braking torque of the whole vehicle. The pedal feel curve is a multi-dimensional mapping relationship, with the main input being the pedal travel, the auxiliary input being the rate of change of pedal travel, and the output being the total braking torque of the whole vehicle, that is, the total braking torque expected to be generated by the vehicle. The EBD system is the vehicle's electronic brake force distribution system, which contains an I-curve. This curve ensures that under any braking intensity, the braking distance is minimized and the rear wheels do not lock up before the front wheels. After obtaining the total target braking torque of the whole vehicle, the target braking torque is distributed to different wheels through the EBD system.

[0109] The internal correction factor reflects the intensity of the vehicle's internal stability control system's intervention in braking torque, embodies the system's ability to identify and respond to vehicle instability risks, and quantifies the torque correction magnitude under the principle of safety priority. This indicates the total requested torque increment for the wheel. This represents the target braking torque. The ratio of the two values ​​reflects the urgency and intensity of vehicle stability intervention. A larger ratio indicates a stronger system intervention relative to the driver's braking intention, typically occurring in scenarios such as loss of steering control on low-traction surfaces or skidding due to sudden acceleration. In these situations, stability control has extremely high priority. A smaller ratio indicates safer vehicle operation, with the driver taking the lead and less intervention from the vehicle's internal systems. At this time, there is no intervention from the vehicle's internal systems, and no corrections are made due to the vehicle's internal systems; the upper limit of the correction coefficient is set to 3, which indicates that... The system's intervention intensity has reached twice the driver's intention, and the braking torque has been greatly enhanced. If it is increased further, it may cause a sharp increase in current or a sudden change in braking torque, leading to more dangerous situations.

[0110] The principle underlying the generation of the dynamic correction coefficient for each wheel is as follows:

[0111]

[0112] in, Indicates the first Dynamic correction coefficient for each wheel Indicates the system interference threshold, take .

[0113] Dynamic correction coefficient By combining the slip ratio-based driving correction coefficient and the internal correction coefficient based on stability control, when stability is not strongly intervened, Within a small neighborhood of 1, it indicates that the vehicle's internal systems have not issued strong braking intervention commands. At this point, the vehicle is in a relatively stable driving state, possibly only undergoing normal braking or slight slippage. The primary tasks are optimizing braking efficiency and preventing lock-up. Therefore, slip ratio feedback is dominant. When the stability system is strongly interfered with, at this time A value significantly greater than 1 indicates that the VDC, ABS, or TCS system is actively and strongly intervening in the braking force of one or more wheels. The system's primary task is to restore vehicle stability. As the primary indicator, it directly reflects the braking force adjusted by the vehicle's internal systems to restore stability, and also... To impose restrictions, if This indicates insufficient slip, meaning the vehicle wants to increase braking force. However, this is limited to 1, and further increases in braking force to improve braking efficiency are not permitted, as this could interfere with the stability control of the vehicle's internal systems. Then keep The value of represents the slip ratio used to help prevent vehicle lock-up, in addition to the braking system within the vehicle.

[0114] Step 4: Obtain the real-time target braking torque and motor angle for each wheel, find the corresponding base current based on the base torque lookup library, correct the base current using a dynamic correction coefficient, input the motor angle and the corrected current into the EMB motor, and the braking torque corresponding to the clamping force generated is the calibrated braking torque.

[0115] In this embodiment, the principle underlying the acquisition of the corresponding base current based on the base torque lookup library is as follows:

[0116] After obtaining the real-time target braking torque and motor rotation angle for each wheel, the first wheel will be... Motor rotation angle of each wheel Substitute the values ​​into the expressions for motor rotation angle-braking torque curves with different constant experimental currents in the basic torque lookup library to obtain the calculated braking torque value. ,in, Indicates will Substitute the first The calculated braking torque value is obtained from the expression of the motor rotation angle-braking torque curve. This indicates the index of the motor rotation angle-braking torque curve in the basic torque lookup library; the principle underlying the calculation of the fluctuation range of the target braking torque is: The target braking torque for each wheel is Its fluctuation range is ,in, Indicates the first The tolerance for brake torque fluctuations in each wheel, and , This represents the tolerance adjustment factor, and ;Pick This indicates that the braking torque fluctuation range is... .

[0117] When the calculated braking torque value is within the fluctuation range of the target braking torque, retain the curves of the calculated braking torque value and the corresponding constant experimental current, and combine all the retained constant experimental current curves to generate an effective current set; plot the curves of the effective current set on the same plane coordinate system with the motor rotation angle on the horizontal axis and the braking torque on the vertical axis. In the curves of the effective current set, each current corresponds to a... The calculated braking torque value is generated under the following conditions. Down With Discrete mapping relationship, where, Represents the first in the effective current set One current, The index representing the effective current lumped current. Indicates in Below, current The corresponding calculated braking torque value is fitted to the above discrete mapping relationship to generate the value in... The principle underlying the torque-current function relationship is as follows:

[0118] based on With Discrete mapping relationships construct a set of discrete data points , ,in, This represents the quantity of the effective condensed current; a fitting function between the effective condensed current and the braking torque is established using a polynomial function, the specific formula of which is:

[0119]

[0120] in, Indicates braking torque. Represents current. Denotes the order of a polynomial. The coefficients are to be fitted.

[0121] Based on the least squares method, discrete data points are substituted into the fitting function to calculate the coefficients to be fitted. Substituting the coefficients to be fitted into the fitting function yields the torque-current function;

[0122] Will Substituting into the torque-current function, we obtain the corresponding first... The base current of each wheel .

[0123] The principle underlying the correction of base current using dynamic correction factors is as follows:

[0124]

[0125] in, Indicates the first Current correction value for each wheel Indicates the first The base current of each wheel;

[0126] The base current is obtained from the base torque lookup library based on the real-time target braking torque and motor rotation angle. It reflects the current value required to achieve the target braking torque under ideal laboratory conditions. During vehicle operation, it is affected by real-time driving parameters and the internal control system. To reflect this impact, When this time is reached, it indicates that the ideal state has been achieved. At this point, the slip ratio is optimal, and there is no intervention from the vehicle's internal systems, so no correction to the base current is required. When this occurs, it indicates that the current braking force is insufficient, which may result in insufficient slip or insufficient system stability, and it is necessary to increase the current to improve the braking torque. If the braking force is too high, it indicates that the current needs to be reduced to decrease the braking torque.

[0127] The first The current correction value for each wheel is input to the corresponding EMB motor. The EMB motor controls the brake pads of the brake caliper to generate a clamping force on the brake disc, converting the clamping force into braking torque, which is the first wheel's current correction value. The standard driving torque of each wheel is adjusted.

[0128] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0129] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented in software, the above embodiments can be implemented, in whole or in part, as a computer program product. Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution.

[0130] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment, depending on actual needs.

[0131] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. An EMB-based vehicle brake torque calibration method, characterized in that, The specific steps include: Step 1: Set a plurality of different constant test current test conditions, control the EMB motor to rotate under each test condition in the laboratory, and record the clamping force of the brake pad of the brake caliper on the brake disc, convert the clamping force into brake torque, and record the corresponding motor rotation angle, obtain the motor rotation angle-brake torque curve under each constant test current, and construct a basic torque lookup library; Step 2: Obtain the optimal slip rate corresponding to each wheel, read the real-time vehicle speed and wheel angular velocity of the vehicle during vehicle driving, calculate the real-time slip rate of each wheel, and generate a driving correction coefficient according to the deviation between the real-time slip rate and the optimal slip rate of the same wheel; Step 3: In the process of vehicle driving, the brake torque correction amount issued by the VDC, ABS and TCS systems is obtained in real time, and then the real-time total requested torque increment of each wheel is calculated, the real-time total target brake torque of the vehicle is obtained through the pedal sensor, the real-time target brake torque distributed to each wheel is calculated through the EBD system, the internal correction coefficient is generated based on the real-time total requested torque increment and the real-time target brake torque, and the dynamic correction coefficient of each wheel is generated by combining the internal correction coefficient and the driving correction coefficient; Step 4: Obtain the real-time target brake torque of each wheel and the motor rotation angle, obtain the corresponding basic current based on the basic torque lookup library, correct the basic current through the dynamic correction coefficient, input the motor rotation angle and the corrected current into the EMB motor, and the clamping force corresponding to the brake torque generated by the EMB motor is the calibrated brake torque.

2. The EMB-based vehicle brake torque calibration method of claim 1, wherein: The principle for obtaining the motor rotation angle-brake torque curve under each constant test current in step 1 is: The EMB motor converts rotary motion into the clamping force of the brake caliper on the brake disc through a transmission mechanism, the motor output torque is calculated based on the motor current, and the formula is: wherein, represents the motor output torque, represents the motor torque constant, represents the current through the motor; The motor output torque is converted into the clamping force of the brake caliper through the transmission mechanism, and the formula is: wherein, represents the clamping force, represents the motor transmission efficiency, represents the total transmission ratio, represents the equivalent action radius; The clamping force is converted into the brake torque, and the formula is: wherein represents the braking torque, represents the friction coefficient between the brake pad and the brake disc at the time of the laboratory test, represents the effective friction radius of the brake disc; The motor rotation angles and the calculated brake torques of the EMB motor under each constant test current are fitted to form the motor rotation angle-brake torque curve under the constant test current, and the basic torque lookup library is constructed by integrating the motor rotation angle-brake torque curves under all constant test currents.

3. The EMB-based vehicle brake torque calibration method of claim 1, wherein: The principle for generating the driving correction coefficient in step 2 is: The formula for calculating the real-time slip rate of each wheel is: wherein, represents the real-time slip ratio of the th wheel, represents the real-time vehicle speed, represents the real-time angular velocity of the th wheel, represents the rolling radius of the th wheel; The formula for generating the driving correction coefficient is: wherein, represents a travel correction coefficient of the th wheel, represents a proportional coefficient, represents a deviation of a real-time slip ratio of the th wheel from an optimal slip ratio, represents an optimal slip ratio.

4. The EMB-based vehicle brake torque calibration method of claim 3, wherein: The principle for generating the internal correction coefficient in step 3 is: For each wheel, the brake torque correction amount is obtained from the VDC, ABS and TCS systems in real time, and the total requested torque increment is generated, and the formula is: in, Indicates the first The total requested torque increment for each wheel Indicates the VDC system for the first Braking torque correction for each wheel Indicates the ABS system for the first Braking torque correction for each wheel This indicates that the TCS system is for the first Braking torque correction for each wheel; The signals generated by the pedal sensor are read through the EMB controller to obtain the pedal stroke and the pedal stroke change rate, the vehicle internal pedal feel curve is combined to obtain the total target brake torque corresponding to the pedal stroke and the pedal stroke change rate; after calculating the target brake torque distributed to each wheel through the EBD system, the internal correction coefficient of each wheel is calculated, and the formula is: wherein, represents an original correction coefficient of the wheel, represents a target brake torque of the wheel, represents an internal correction coefficient of the wheel, represents a correction coefficient upper limit, taken .

5. The EMB-based vehicle brake torque calibration method of claim 4, wherein: The principle for generating the dynamic correction coefficient of each wheel in the step 3 is as follows: wherein, represents a dynamic correction factor for the .​​ 6. The EMB-based vehicle brake torque calibration method of claim 5, wherein: The principle for obtaining the corresponding basic current based on the basic torque lookup library in the step 4 is as follows: After obtaining the real-time target braking torque and motor angle of each wheel, the motor angle of the first wheel is substituted into the expression of the motor angle-braking torque curve of the first wheel to obtain the braking torque calculation value , The braking torque calculation value is substituted into the expression of the motor angle-braking torque curve of the first wheel to obtain the braking torque calculation value , , , , , The target braking torque of the first wheel is , and the fluctuation range of the target braking torque of the first wheel is , , , , , ; When the calculated braking torque value is within the fluctuation range of the target braking torque, retain the curves of the calculated braking torque value and the corresponding constant experimental current, and combine all the retained constant experimental current curves to generate an effective current set; plot the curves of the effective current set on the same plane coordinate system with the motor rotation angle on the horizontal axis and the braking torque on the vertical axis. In the curves of the effective current set, each current corresponds to a... The calculated braking torque value is generated under the following conditions. Down and The discrete mapping relationship, where, Represents the first in the effective current set One current, The index representing the effective current lumped current. Indicates in Below, current The corresponding calculated braking torque value is fitted to the above discrete mapping relationship to generate the value in... The torque-current function relationship is based on the principle that: and Construct a set of discrete data points from discrete mapping relationships , ,in, This represents the quantity of the effective condensed current; a fitting function between the effective condensed current and the braking torque is established using a polynomial function, the specific formula of which is: wherein, denotes the braking torque, denotes the current, denotes the polynomial order, is a coefficient to be fitted; Based on the least square method, the discrete data points are substituted into the fitting function to calculate the coefficients to be fitted The coefficients to be fitted are substituted into the fitting function to obtain the torque-current function; Substituting into the torque-current function, the corresponding base current for the i-th wheel is obtained .​ 7. The EMB-based vehicle brake torque calibration method of claim 6, wherein: The principle for correcting the basic current by the dynamic correction coefficient in the step 4 is as follows: The principle for correcting the basic current by the dynamic correction coefficient in the step 4 is as follows: wherein, represents a current correction value of the nth wheel, represents a basic current of the nth wheel, the nth wheel,​ The first The current correction value for each wheel is input to the corresponding EMB motor. The EMB motor controls the brake pads of the brake caliper to generate a clamping force on the brake disc, converting the clamping force into braking torque, which is the first wheel's current correction value. The standard driving torque of each wheel is adjusted.

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