Automobile composite braking torque optimal distribution method based on EMB multi-stage response characteristics

Abstract

The invention discloses an automobile composite braking torque optimal distribution method based on EMB multi-stage response characteristics. The method comprises the following steps that 1, all sensors collect data signals; step 2, calculating the required braking torque of the whole vehicle and distributing the front and rear braking torque; 3, judging whether the EMB intervenes or not: if the EMB needs to intervene, carrying out a step 4, and if the EMB does not need to intervene, directly carrying out a step 7; 4, primarily distributing a braking torque coefficient based on interval type-2 fuzzy control; step 5, discriminating an EMB working stage; step 6, carrying out secondary distribution on a braking torque coefficient based on EMB multi-stage response characteristics; 7, EMB / regenerative braking is implemented; and 8, whether braking is finished or not is judged. In the re-distribution process of the braking torque coefficient, the working characteristics that the braking torque of the EMB is vacant in the braking torque no-load stage and the braking torque is rapidly changed in the braking torque lifting stage are fully considered, and the braking recovery efficiency and the braking stability of the automobile are effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of torque optimization distribution of automotive composite braking systems, and particularly relates to a method for optimizing the distribution of automotive composite braking torque based on the multi-stage response characteristics of EMB. Background Art

[0002] With the acceleration of the electrification process of automobiles, the braking system is gradually transforming from traditional mechanical hydraulic braking to wire-controlled braking technology, mainly including electronic hydraulic braking (EHB) and electronic mechanical braking (EMB). Although EHB replaces the traditional vacuum booster with motor assistance, it still faces a series of problems such as response delay, complex assembly, and high maintenance costs. In contrast, EMB, without the design of hydraulic pipelines, transmits signals through communication harnesses and uses motors and force-increasing mechanisms for braking, showing the advantages of high efficiency, flexibility, and reliability. With the popularization of electric vehicles, researching the coordinated control strategy of EMB and the regenerative braking system has become one of the hotspots.

[0003] At present, in the field of torque optimization distribution of automotive composite braking systems, a variety of research methods have been proposed, mainly including methods based on genetic algorithms, model predictive control, and improved fuzzy control. For example, Patent No. 202410664420.3 proposes a method for determining braking torque coefficients based on genetic algorithms. This method optimizes the braking torque coefficients through gene coding, thereby achieving good braking performance and stability of the vehicle under different working conditions. Patent No. 202311384034.0 proposes a braking torque distribution method based on model predictive control, which uses the system dynamic model to predict future behavior and optimizes the braking force distribution based on the battery capacity loss during the vehicle braking process, reducing the loss of the battery while ensuring energy recovery. Patent No. 202310659609.9 proposes a method for solving braking torque coefficients based on type-2 fuzzy logic, which expands the membership function of traditional type-1 fuzzy control and enhances the system's ability to process uncertain information. Although the above methods effectively achieve the braking torque distribution of automotive composite braking systems, they usually adopt a one-time distribution strategy during the braking process, that is, directly calculate the braking torque coefficients through established distribution logic or control algorithms, which may result in the coordination between regenerative braking torque and frictional braking torque not reaching the optimal. Some scholars have proposed to perform secondary distribution of the braking torque coefficients on the basis of the initial distribution of braking torque coefficients, considering the lag in the response of frictional braking torque. Patent No. 202410616722.3 proposes a method for compensating electro-hydraulic composite braking torque based on fuzzy control. This method corrects the reserved available motor braking torque and adjusts the corrected braking torque coefficients by means of a fuzzy control algorithm, achieving braking torque compensation control. However, this method only considers the change relationship between the motor braking torque and the braking intensity during the secondary distribution process, without fully considering the mechanical response characteristics of the brake actuator, which may lead to problems such as insufficient accuracy of braking torque distribution and untimely response, thus affecting the control effect and braking recovery efficiency during the braking process.

[0004] Therefore, it is very important to comprehensively consider the influence of the response characteristics of EMB in different working stages on the torque optimization distribution of automotive composite braking systems. These working stages include stages such as the no-load, rising, holding, and releasing stages of braking torque, especially the influence of the fact that the EMB braking torque has not taken effect during the no-load stage of braking torque and the characteristics of the rapidly rising braking torque during the rising stage on the composite braking control effect. Therefore, it is of great theoretical and practical significance to propose an optimization distribution method for automotive composite braking torque based on the multi-stage response characteristics of EMB. Summary of the Invention

[0005] Aiming at the problem that the composite braking coordination control strategy based on EMB does not fully consider the response characteristics of EMB in different working stages during the implementation of composite braking torque distribution, which may lead to insufficient accuracy of vehicle braking torque distribution and untimely response, the present invention provides an optimized distribution method for vehicle composite braking torque based on the multi-stage response characteristics of EMB. During the re-distribution process of the braking torque coefficient, this method fully considers the working characteristics of EMB, such as the braking torque vacancy in the no-load stage of the braking torque and the rapid change of the braking torque in the braking torque increase stage, effectively improving the braking recovery efficiency and braking stability of the vehicle.

[0006] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0007] An optimized distribution method for vehicle composite braking torque based on the multi-stage response characteristics of EMB, comprising the following steps:

[0008] Step 1: Each sensor collects data signals;

[0009] Step 2: Calculate the vehicle's required braking torque and distribute the front and rear braking torques;

[0010] Step 3: Determine whether EMB intervenes: If it needs to intervene, proceed to Step 4; if it does not need to intervene, directly proceed to Step 7;

[0011] Step 4: Initial distribution of the braking torque coefficient based on interval type-2 fuzzy control;

[0012] Step 5: Discriminate the working stage of EMB:

[0013] Step 5.1: Initially discriminate the working stage of EMB;

[0014] Step 5.2: Select the iteration time according to the initial discrimination result;

[0015] Step 5.3: Accurately discriminate the working stage of EMB;

[0016] Step 6: Secondary distribution of the braking torque coefficient based on the multi-stage response characteristics of EMB;

[0017] Step 7: Implement EMB / regenerative braking;

[0018] Step 8: Determine whether the braking is over: If it does not need to end, loop to Step 1; if it needs to end, directly end.

[0019] Furthermore, the following steps are also included in the said Step 2:

[0020] Calculate the vehicle's required braking torque T according to the brake pedal displacement and brake pedal speed b , and distribute the front and rear axle braking forces according to the ideal brake braking force distribution curve.

[0021] Furthermore, the step 3 further includes the following steps:

[0022] If the required braking torque on a single wheel is less than the maximum regenerative braking torque, the EMB does not need to intervene, and the braking task is completed by regenerative braking, and directly enters the EMB / regenerative braking implementation stage of step 7; if the required braking torque on a single wheel is greater than the maximum regenerative braking torque, the EMB needs to intervene, enter step 4, and the braking task is completed by the in-wheel motor and the EMB together.

[0023] Furthermore, the step 4 further includes the following steps:

[0024] The initial distribution process includes four steps: converting the input quantity into a fuzzy set to obtain the fuzzy input variable, using the fuzzy input variable and the rule base for reasoning to obtain the fuzzy output variable, using the centroid method to convert the fuzzy output variable into a clear output value, and converting the output value into a specific control instruction.

[0025] Furthermore, the step 5 further includes the following steps:

[0026] The step 5.1 further includes the following steps:

[0027] Introduce variables t1 to represent the switching time point between the no-load stage of the braking torque and the torque increase stage, t2 to represent the switching time point between the torque increase stage and the torque holding stage, and t to represent the time from the start of braking to the present; the calculation formula for t1 is:

[0028]

[0029] In the formula, T gap is the time to eliminate the clearance; S gap is the braking clearance; i p is the reduction ratio of the planetary gear reducer; n0 is the maximum no-load speed of the EMB drive motor; L0 is the lead of the ball screw;

[0030] If 0 ≤ t < 0.8t1, the working stage of the EMB is the no-load stage of the braking torque; if 0.8t1 ≤ t ≤ 1.2t2, then enter step 5.3 to accurately determine the working stage of the EMB; if 1.2t2 < t, the working stage of the EMB is the torque holding stage; the initial discrimination result N satisfies the following formula:

[0031]

[0032] The step 5.2 further includes the following steps:

[0033] The iteration time refers to the time required to run a composite braking torque optimization distribution process once, and the value of the iteration time Δt satisfies the following formula:

[0034]

[0035] Step 5.3 further includes the following steps:

[0036] Judge the actual braking torque T e ' of the EMB and the target braking torque T e of the EMB to accurately distinguish the working stage of the EMB. For the case where the initial discrimination result N = 2, the working stage of the EMB needs to be further accurately judged. The result of accurately distinguishing the working stage of the EMB satisfies the following formula:

[0037]

[0038] In the formula, T ei ' is the current actual braking torque of the EMB for a single wheel, T ei is the target braking torque of the EMB for a single wheel. i = 1, 2, 3, 4 represent the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively; P1, P2, and P3 respectively represent the no-load stage of the braking torque, the rising stage of the braking torque, and the holding stage of the braking torque;

[0039] Combined with the above judgment process, if 0 < T ei ' < T ei and t > t2, it is the braking torque release stage, and no secondary distribution of the braking torque coefficient is required.

[0040] Furthermore, step 6 further includes the following steps:

[0041] Step 6.1: Secondary distribution of the regenerative braking torque

[0042] First, according to the discrimination result of the EMB working stage, if it is in the no-load stage of the braking torque, the single-wheel regenerative braking torque needs to fill the single-wheel EMB braking torque demand. At this time, T ri is equal to T rmax , the actual braking torque of the EMB is zero, and the values of T ri and T ei are as follows:

[0043]

[0044] In the formula, T ri is the single-wheel regenerative braking torque, i = 1, 2, 3, 4 represent the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively, T rmax is the maximum regenerative braking torque that the in-wheel motor can provide, T ei is the target braking torque of the EMB for a single wheel, i = 1, 2, 3, 4 represent the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively;

[0045] When the EMB working stage is in the braking torque increasing stage, judge KT i and T rmax The size relationship between them, K is the braking torque coefficient. If KT i ≥T rmax , it indicates that the regenerative braking has reached the maximum value, and the EMB system cannot obtain regenerative braking compensation;

[0046] Step 6.2: Judge whether there is a torque demand on the front wheels

[0047] For the no-load stage of the braking torque, there must be a braking torque demand on the front wheels, so no judgment is made;

[0048] For the braking torque increasing stage, judge T e1 -T e1 '+T r1 and T rmax The size relationship:

[0049] If T e1 -T e1 '+T r1 >T rmax , it indicates that there is a braking torque demand on the front wheels, and the values of T r1 and T r2 are as follows:

[0050]

[0051] In the formula, T e1 is the target braking torque of the left front wheel EMB, T e1 ’ is the actual braking torque of the left front wheel EMB, T r1 is the regenerative braking torque of the left front wheel, T r2 is the regenerative braking torque of the right front wheel, T rmax is the maximum regenerative braking torque that the in-wheel motor can provide;

[0052] If T e1 -T e1 '+T r1 <T rmax , it indicates that there is no braking torque demand on the front wheels, and the values of T r1 and T r2 are as follows:

[0053]

[0054] In the formula, T e1 ' is the actual braking torque of the left front wheel EMB, T e2 ' is the actual braking torque of the right front wheel EMB; Step 6.3: Judge whether there is a torque surplus on the rear wheels

[0055] For the braking torque increasing stage, compare T e3-T e3 '+T r1 Relationship with T rmax Magnitude relationship:

[0056] If T e3 -T e3 '+T r1 >T rmax , it indicates that there is no available regenerative braking torque for the rear-wheel hub motor; T r1 , T r2 , T r3 , T r4 Take the following values:

[0057]

[0058] In the formula, T e3 is the target braking torque of the left rear-wheel EMB, T e3 ’is the actual braking torque of the left rear-wheel EMB, T r3 is the regenerative braking torque of the left rear wheel, T r4 is the regenerative braking torque of the right rear wheel;

[0059] If T e3 -T e3 '+T r1 <T rmax , it indicates that there is available regenerative braking torque for the rear-wheel hub motor;

[0060] Step 6.4: Compensation of the rear-wheel hub motor to the front wheel

[0061] For the no-load stage of the braking torque, judge the magnitude relationship between T1 - T rmax and T rmax -T3:

[0062] If T1 - T rmax >T rmax -T3, T r3 , T r4 Take the following values:

[0063]

[0064] In the formula, T1 is the required braking torque of the left front wheel, T3 is the required braking torque of the left rear wheel, T r3 is the regenerative braking torque of the left rear wheel, T r4 is the regenerative braking torque of the right rear wheel;

[0065] If T1 - T rmax <T rmax -T3, T r3 , T r4 Take the following values:

[0066]

[0067] Wherein, T1 is the required braking torque of the left front wheel, and T2 is the required braking torque of the left rear wheel;

[0068] For the braking torque boosting stage, judge the magnitude relationship between T1 - T rmax and T rmax - T3:

[0069] If T1 - T rmax > T rmax - T3, T r3 and T r4 are taken as follows:

[0070]

[0071] If T1 - T rmax < T rmax - T3, T r3 and T r4 are taken as follows:

[0072]

[0073] Based on the above distribution strategy, introduce K' as the braking torque coefficient after secondary distribution compensation, which characterizes the participation degree of regenerative braking in the final braking process. The regenerative and EMB target braking torque distributions of each wheel satisfy the following formula:

[0074]

[0075] Wherein, T e1 is the EMB target braking torque of the left front wheel, T e2 is the EMB target braking torque of the right front wheel, T e3 is the EMB target braking torque of the left rear wheel, T e4 is the EMB target braking torque of the right rear wheel, T f is the front axle braking torque, and T r is the rear axle braking torque;

[0076] Step 6.5: Set the zeroing time t

[0077] The torque sensor outputs the current EMB actual braking torque T e ' to the composite braking torque coordination control system. When it is detected that the actual braking torque is equal to zero, let t be equal to zero.

[0078] Furthermore, the following steps are also included in the said step 7:

[0079] The vehicle control system will, according to the braking torque distribution results calculated in the previous steps, that is, according to T r1 and Tr2 、T r3 、T r4 、T e1 、T e2 、T e3 、T e4 The size controls the hub motors of each wheel and the EMB to generate corresponding braking torques, and implements the control of the EMB and the regenerative braking torque.

[0080] Furthermore, the step 8 further includes the following steps:

[0081] The vehicle speed sensor monitors the vehicle speed in real time and feeds the data back to the vehicle control system. The vehicle control system judges according to the current vehicle speed and the set braking conditions to determine whether the braking is over: when the vehicle speed drops below the preset threshold, the system will judge that the braking process has been completed and stop sending control signals to the braking system; if the vehicle speed is still higher than the threshold, the system will continue to maintain the braking state to ensure that the vehicle decelerates stably within a safe range.

[0082] The beneficial effects of the present invention are mainly manifested in:

[0083] (1) On the basis of the initial distribution of the braking torque coefficient of the composite braking system based on interval type-2 fuzzy control, fully consider the working characteristics of the EMB in stages such as the no-load stage of the braking torque, the rising stage of the braking torque, the holding stage of the braking torque, and the release stage of the braking torque. If the EMB is in the no-load stage of the braking torque, in order to fully compensate for the vacancy of the EMB braking torque in this stage, it is proposed that the electric motor braking torque dominate the braking; if the EMB is in the rising stage of the braking torque, considering the characteristic of the rapid change of the EMB braking torque in this stage, it is proposed that the motor and the EMB coordinate the braking and optimize the distribution. The above strategy aims to use the regenerative braking torque to compensate for the difference between the actual braking torque and the target braking torque of the EMB while maximizing the energy recovery, solves the problem of insufficient accuracy of the braking torque distribution, improves the influence caused by the untimely response of the braking torque, and effectively improves the braking recovery efficiency and braking stability of the vehicle.

[0084] (2) In the process of discriminating the working stage of the EMB, in order to avoid the problem of insufficient discrimination accuracy, a method for discriminating the working stage of the EMB based on the switching time point of the EMB working stage is proposed; a preliminary judgment is made by comparing the relative range of the current time and the switching time point of the EMB working stage, and a suitable iteration frequency is selected according to the preliminary discrimination result, and then combined with the actual braking torque of the EMB for accurate discrimination; effectively improves the discrimination accuracy and shortens the discrimination time. Description of the Drawings

[0085] Figure 1 is the flow chart of the optimized distribution of the composite braking torque of the vehicle based on the multi-stage response characteristics of the EMB.

[0086] Figure 2 It is the flowchart of the initial distribution of the braking torque coefficient based on interval type-2 fuzzy control.

[0087] Figure 3 It is the flowchart for discriminating the working stages of EMB.

[0088] Figure 4 It is the flowchart of the secondary distribution of the braking torque coefficient based on the multi-stage response characteristics of EMB.

[0089] Figure 5 It is the curve graph of the change in the braking torque response of EMB. Specific implementation manners

[0090] The present invention will be further described below with reference to the accompanying drawings.

[0091] As Figure 1 shown, the optimization distribution process of the composite braking torque of the vehicle based on the multi-stage response characteristics of EMB mainly includes eight steps: the data signals are collected by each sensor, the braking torque required for the whole vehicle is calculated and the front and rear braking torques are distributed, it is judged whether EMB intervenes, the initial distribution of the braking torque coefficient based on interval type-2 fuzzy control, the working stages of EMB are discriminated, the secondary distribution of the braking torque coefficient based on the multi-stage response characteristics of EMB, the implementation of EMB / regenerative braking, and it is judged whether the braking is ended. The specific implementation of each step is as follows:

[0092] Step 1: Each sensor collects data signals

[0093] Multiple sensors of the vehicle will collect key data signals in real time to support the decision-making of the coordinated control of the composite braking torque. The sensor of the battery management system is responsible for monitoring the state of charge SOC of the battery; the vehicle speed sensor measures the vehicle speed v; the brake pedal displacement sensor detects the displacement of the brake pedal; the brake pedal speed sensor detects the speed of the brake pedal; and the torque sensor is used to detect the actual braking torque of EMB.

[0094] Step 2: Calculate the braking torque required for the whole vehicle and distribute the front and rear braking torques

[0095] The braking torque T required for the whole vehicle is calculated according to the brake pedal displacement and the brake pedal speed b 、the front axle braking torque T f 、and the rear axle braking torque T r satisfy the following formula:

[0096] T b =T f +T r (1)

[0097] The front and rear axle braking forces are distributed according to the ideal brake force distribution curve, and the front and rear axle braking forces satisfy the following relationship:

[0098]

[0099] Among them, F f is the required braking force of the front wheel, F r is the required braking force of the rear wheel, a is the distance from the center of mass to the center line of the front axle, b is the distance from the center of mass to the center line of the rear axle, is the road surface adhesion coefficient, g is the acceleration due to gravity, m is the mass of the vehicle, h g is the height of the vehicle's center of mass.

[0100] Step 3: Determine whether the EMB intervenes

[0101] By judging the magnitude relationship between the required braking torque on a single wheel and the maximum regenerative braking torque, it is clear whether the EMB needs to intervene and adjust the magnitude of the braking torque. If the required braking torque on a single wheel is less than the maximum regenerative braking torque, the EMB does not need to intervene, and the braking task can be completed by regenerative braking, and it can directly enter the EMB / regenerative braking implementation stage in Step 7. The value satisfies the following formula:

[0102] T ri = T i (3)

[0103] In the formula, T i is the required braking torque of a single wheel, i = 1, 2, 3, 4, which are the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively; T ri is the regenerative braking torque of a single wheel, i = 1, 2, 3, 4, which are the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively.

[0104] If the required braking torque on a single wheel is greater than the maximum regenerative braking torque, the EMB needs to intervene and enter Step 4. The braking task is completed by the in-wheel motor and the EMB together.

[0105] Step 4: Initial distribution of braking torque coefficients based on interval type-2 fuzzy control

[0106] Introduce the braking torque coefficient K to characterize the degree of participation of regenerative braking. The regenerative and EMB braking torque distributions of each wheel satisfy the following formula:

[0107]

[0108] In the formula, T r1 、T r2 、T r3 、T r4 are the regenerative braking torques of the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively, T e1 、T e2, T e3 , T e4 are the EMB target braking torques of the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively;

[0109] As Figure 2 shown, the initial distribution process of the braking torque coefficient based on interval type-2 fuzzy control mainly includes four steps: converting the input quantity into a fuzzy set to obtain the fuzzy input variable, using the fuzzy input variable and the rule base for reasoning to obtain the fuzzy output variable, using the centroid method to convert the fuzzy output variable into a clear output value, and converting the output value into specific control instructions. The specific implementation of each step is as follows:

[0110] Step 4.1: Convert the input quantity into a fuzzy set to obtain the fuzzy input variable

[0111] The initial distribution of the braking torque coefficient adopts the Takagi-Sugeno interval type-2 fuzzy logic algorithm. Set the braking intensity z , the state of charge (SOC) of the battery, and the vehicle speed v as the fuzzy logic input variables, and the braking torque coefficient K as the fuzzy logic output variable. The calculation formula for the braking intensity z is:

[0112]

[0113] where is the derivative of the vehicle speed, that is, the vehicle acceleration.

[0114] The braking intensity z has a fuzzy domain range of (0, 1), and its interval type-2 fuzzy set is:

[0115]

[0116] where x1 represents the main variable of the braking intensity z mapped to the domain after fuzzification; X1 is the domain of x1; represents the main membership degree of x1; u is the secondary variable; N, Z, and P represent low, medium, and high in sequence.

[0117] Both the upper membership function (UMF) and the lower membership function (LMF) of the braking intensity z fuzzy subset are selected as Gaussian membership functions, and the expressions are as follows:

[0118]

[0119] where crespectively represent the upper bound and lower bound of the mean value of the membership function of the fuzzy set; σ represents the standard deviation of the membership function of the fuzzy set.

[0120] The fuzzy domain range of the state of charge (SOC) of the battery is (0, 1), and its interval type-2 fuzzy set is:

[0121]

[0122] In the formula, x2 represents the main variable mapped to the domain after the state of charge (SOC) of the battery is fuzzified; X2 is the domain of x2; represents the main membership degree of x2; u is the secondary variable; N, Z, and P represent low, medium, and high in sequence.

[0123] The expressions of the fuzzy subsets UMF and LMF of the state of charge (SOC) of the battery are as follows:

[0124]

[0125] In the formula, c respectively represent the upper bound and lower bound of the mean value of the membership function of the fuzzy set; σ represents the standard deviation of the membership function of the fuzzy set.

[0126] The fuzzy domain range of the vehicle speed v is (0, 1), and the actual range is 0 - 120 km / h. Its interval type-2 fuzzy set is:

[0127]

[0128] In the formula, x3 represents the main variable mapped to the domain after the braking vehicle speed v is fuzzified; X3 is the domain of x3; represents the main membership degree of x3; u is the secondary variable; N, Z, and P represent low, medium, and high in sequence.

[0129] The expressions of the fuzzy subsets UMF and LMF of the vehicle speed v are as follows:

[0130]

[0131] In the formula, c respectively represent the upper bound and lower bound of the mean value of the membership function of the fuzzy set; σ represents the standard deviation of the membership function of the fuzzy set.

[0132] The fuzzy domain range of the braking torque coefficient K is (0, 1), and its interval type-2 fuzzy set is:

[0133]

[0134] wherein, y represents the main variable mapped to the universe of discourse after the braking torque coefficient K is fuzzified, Y is the universe of discourse of y, and J y represents the main membership degree of y; NB represents small; NM represents relatively small; Z represents medium; PM represents relatively large; PB represents large.

[0135] The fuzzy subset expression of the braking torque coefficient K is as follows:

[0136]

[0137] Step 4.2: Use the fuzzy input variables and the rule base to perform reasoning to obtain the fuzzy output variables

[0138] Braking intensity z When it is relatively small, the hub motor is preferably used to provide the braking force, and the degree of participation of regenerative braking is large; when the braking intensity z is relatively large, it belongs to the emergency braking condition, and it is necessary to achieve braking in a shorter time. The braking force is mainly provided by the EMB, and the degree of participation of regenerative braking is small. When the state of charge SOC of the battery is relatively high, the battery charging ability is weak, and the degree of participation of regenerative braking is small; when the state of charge SOC of the battery is relatively low, the battery charging ability is strong, and the degree of participation of regenerative braking is large. When the vehicle speed v is relatively low, the recoverable braking energy is small, and the degree of participation of regenerative braking is small; when the vehicle speed v is relatively high, the recoverable braking energy is large, and the degree of participation of regenerative braking is large. Then the interval type-2 fuzzy logic rule is:

[0139] If z is and SOC is and v is then K is

[0140] Specifically, the interval type-2 fuzzy logic rules are shown in Table 1.

[0141] Table 1 Interval type-2 fuzzy logic rules

[0142]

[0143]

[0144] Step 4.3: Use the centroid method to convert the fuzzy output variable into a clear output value

[0145] Fuse the activation degree interval of each rule with the membership function of the output variable, output the fused type-2 fuzzy set, and use the EKM algorithm for type reduction. The expression of the fuzzy reasoning result is:

[0146] Y cos (X) = [K l , K r (17)

[0147]

[0148] Wherein, respectively represent the lower bound and upper bound of the membership degree of K belonging to the fuzzy set ; K l , K r respectively represent the left and right endpoints of the output of the interval type-2 fuzzy set; Y' is the upper bound of the interval type-2 fuzzy output in the fuzzy set universe of discourse; L and R are the left and right conversion points in the fuzzy defuzzification process respectively;

[0149] Step 4.4: Convert the output value into a specific control instruction

[0150] The result of the braking torque coefficient K satisfies:

[0151]

[0152] Step 5: Discriminate the working stage of the EMB

[0153] As Figure 5 shown, based on the change of the braking torque, the braking torque response curve of the EMB divides the working process of the EMB into four main stages: the no-load stage of the braking torque, the rising stage of the braking torque, the holding stage of the braking torque, and the releasing stage of the braking torque.

[0154] As Figure 3 shown, the discrimination process of the EMB working stage mainly includes three steps: initially discriminating the EMB working stage, selecting the iteration time according to the initial discrimination result, and accurately discriminating the EMB working stage. The specific implementation of each step is as follows:

[0155] Step 5.1: Initially discriminate the EMB working stage

[0156] Introduce the variable t1 to represent the switching time point between the no-load stage and the rising stage of the braking torque, t2 to represent the switching time point between the rising stage and the holding stage of the braking torque, and t to represent the time from the start of braking to the present. The calculation formula of t1 is:

[0157]

[0158] Wherein, T gap is the time to eliminate the clearance; S gap is the braking clearance; i p is the reduction ratio of the planetary gear reducer; n0 is the maximum no-load speed of the EMB drive motor; L0 is the lead of the ball screw.

[0159] If \(0\leq t < 0.8t_1\), the working stage of the EMB is the no-load stage of the braking torque; if \(0.8t_1\leq t\leq1.2t_2\), then proceed to Step 5.3 for accurate discrimination of the EMB working stage; if \(1.2t_2 < t\), the working stage of the EMB is the braking torque holding stage. The initial discrimination result \(N\) satisfies the following formula:

[0160]

[0161] Step 5.2: Select the iteration time according to the initial discrimination result

[0162] The iteration time refers to the time required to run a composite braking torque optimization and distribution process once, that is, the time spent from the start to the end of the iteration. The value of the iteration time \(\Delta t\) satisfies the following formula:

[0163]

[0164] Step 5.3: Accurately discriminate the EMB working stage

[0165] Judge the actual braking torque \(T\) of the EMB e ' of the EMB and the target braking torque \(T\) of the EMB e for accurate discrimination of the EMB working stage. For the case where the initial discrimination result \(N = 2\), the EMB working stage needs to be further accurately judged. The result of accurately discriminating the EMB working stage satisfies the following formula:

[0166]

[0167] In the formula, \(T\) ei ' is the current actual braking torque of the EMB for a single wheel, \(T\) ei is the target braking torque of the EMB for a single wheel, \(i = 1, 2, 3, 4\), representing the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively; \(P1\), \(P2\), and \(P3\) respectively represent the no-load stage of the braking torque, the braking torque increasing stage, and the braking torque holding stage.

[0168] Combined with the above judgment process, if \(0 < T\) ei ' < \(T\) ei and \(t > t_2\), then it is the braking torque release stage, and no secondary distribution of the braking torque coefficient is required.

[0169] Step 6: Secondary distribution of the braking torque coefficient based on the multi-stage response characteristics of the EMB

[0170] As Figure 4 shown, the secondary distribution process of the braking torque coefficient based on the multi-stage response characteristics of the EMB mainly includes 5 steps: secondary distribution of the regenerative braking torque, judgment of whether there is a torque demand on the front wheels, judgment of whether there is a torque surplus on the rear wheels, compensation of the rear wheel hub motor to the front wheels, and setting the zero time \(t\) according to the conditions. The specific implementation of each step is as follows:

[0171] Step 6.1: Secondary distribution of regenerative braking torque

[0172] First, according to the discrimination result of the EMB working stage, if it is in the no-load stage of braking torque, the single-wheel regenerative braking torque is required to fill the single-wheel EMB braking torque demand. At this time, T ri is equal to T rmax , the actual braking torque of EMB is zero, and the values of T ri and T ei are as follows:

[0173]

[0174] In the formula, T ri is the single-wheel regenerative braking torque, i = 1, 2, 3, 4, which are the left front wheel, right front wheel, left rear wheel and right rear wheel respectively. T rmax is the maximum regenerative braking torque that the in-wheel motor can provide, and T ei is the single-wheel EMB target braking torque, i = 1, 2, 3, 4, which are the left front wheel, right front wheel, left rear wheel and right rear wheel respectively.

[0175] When the EMB working stage is in the braking torque increasing stage, judge the magnitude relationship between KT i and T rmax . If KT i ≥T rmax , it indicates that the regenerative braking has reached the maximum value, and the EMB system cannot obtain regenerative braking compensation.

[0176] Step 6.2: Judge whether there is a torque demand for the front wheels

[0177] For the no-load stage of braking torque, there must be a braking torque demand for the front wheels, so no judgment is required.

[0178] For the braking torque increasing stage, judge the magnitude relationship between T e1 -T e1 '+T r1 and T rmax .

[0179] If T e1 -T e1 '+T r1 >T rmax , it indicates that there is a braking torque demand for the front wheels, and the values of T r1 and T r2 are as follows:

[0180]

[0181] In the formula, T e1 is the left front wheel EMB target braking torque, and T e1’ is the actual braking torque of the left front wheel EMB, T r1 is the regenerative braking torque of the left front wheel, T r2 is the regenerative braking torque of the right front wheel, T rmax is the maximum regenerative braking torque that the in-wheel motor can provide.

[0182] If T e1 -T e1 '+T r1 <T rmax , it indicates that there is no braking torque demand for the front wheels. T r1 、T r2 take the following values:

[0183]

[0184] In the formula, T e1 ’ is the actual braking torque of the left front wheel EMB, T e2 ’ is the actual braking torque of the right front wheel EMB.

[0185] Step 6.3: Determine whether there is torque surplus for the rear wheels

[0186] For the braking torque boost stage, compare T e3 -T e3 '+T r1 with T rmax in terms of magnitude relationship.

[0187] If T e3 -T e3 '+T r1 >T rmax , it indicates that there is no available regenerative braking torque for the rear wheel in-wheel motor. T r1 、T r2 、T r3 、T r4 take the following values:

[0188]

[0189] In the formula, T e3 is the target braking torque of the left rear wheel EMB, T e3 ’ is the actual braking torque of the left rear wheel EMB, T r3 is the regenerative braking torque of the left rear wheel, T r4 is the regenerative braking torque of the right rear wheel;

[0190] If T e3 -T e3 '+T r1 <T rmax , it indicates that there is available regenerative braking torque for the rear wheel in-wheel motor.

[0191] Step 6.4: The rear-wheel hub motor compensates for the front wheels

[0192] For the no-load stage of the braking torque, judge the magnitude relationship between T1 - T rmax and T rmax - T3.

[0193] If T1 - T rmax > T rmax - T3, T r3 、T r4 are taken as follows:

[0194]

[0195] In the formula, T1 is the required braking torque of the left front wheel, T3 is the required braking torque of the left rear wheel, T r3 is the regenerative braking torque of the left rear wheel, T r4 is the regenerative braking torque of the right rear wheel, and T rmax is the maximum regenerative braking torque that the hub motor can provide.

[0196] If T1 - T rmax < T rmax - T3, T r3 、T r4 are taken as follows:

[0197]

[0198] In the formula, T1 is the required braking torque of the left front wheel, T2 is the required braking torque of the left rear wheel, and T rmax is the maximum regenerative braking torque that the hub motor can provide.

[0199] For the braking torque increase stage, judge the magnitude relationship between T1 - T rmax and T rmax - T3.

[0200] If T1 - T rmax > T rmax - T3, T r3 、T r4 are taken as follows:

[0201]

[0202] If T1 - T rmax < T rmax - T3, T r3 、T r4 are taken as follows:

[0203]

[0204] Based on the above distribution strategy, introduce K' as the braking torque coefficient after secondary distribution compensation, which characterizes the participation degree of regenerative braking in the final braking process. The regenerative and EMB target braking torque distributions of each wheel satisfy the following formula:

[0205]

[0206] In the formula, T e1 is the EMB target braking torque of the left front wheel, T e2 is the EMB target braking torque of the right front wheel, T e3 is the EMB target braking torque of the left rear wheel, T e4 is the EMB target braking torque of the right rear wheel, T f is the front axle braking torque, T r is the rear axle braking torque;

[0207] Step 6.5: Set the zeroing time t

[0208] The torque sensor outputs the current actual braking torque T e ' of the EMB to the composite braking torque coordination control system. When it is detected that the actual braking torque is equal to zero, let t be equal to zero.

[0209] Step 7: Implement EMB / regenerative braking

[0210] The vehicle control system will, according to the braking torque distribution results calculated in the previous steps, that is, according to T r1 , T r2 , T r3 , T r4 , T e1 , T e2 , T e3 , T e4 control the hub motors and EMB of each wheel to generate corresponding braking torques according to their magnitudes. Implement the control of EMB and regenerative braking torques. Specifically, the control system will send current signals to the brake electronic control unit to adjust the hub motors and EMB of each wheel, so as to achieve the required braking torque

[0211] Step 8: Judge whether the braking is over

[0212] The vehicle speed sensor monitors the vehicle speed in real time and feeds the data back to the vehicle control system. The vehicle control system makes a judgment based on the current vehicle speed and the set braking conditions to determine whether the braking is over. When the vehicle speed drops below the preset threshold, the system will judge that the braking process has been completed and stop sending control signals to the braking system. If the vehicle speed is still higher than this threshold, the system will continue to maintain the braking state to ensure that the vehicle decelerates stably within a safe range.

Claims

1. An optimized distribution method for the composite braking torque of an automobile based on the multi-stage response characteristics of EMB, characterized in that: The torque coordination distribution method includes the following steps: Step 1: Each sensor collects data signals; Step 2: Calculate the vehicle's required braking torque and distribute the front and rear braking torques; Step 3: Determine whether the EMB intervenes: If intervention is required, proceed to Step 4; if no intervention is required, directly proceed to Step 7; Step 4: Initial distribution of the braking torque coefficient based on interval type-2 fuzzy control; Step 5: Discriminate the EMB working stage: Step 5.1: Initially discriminate the EMB working stage; Step 5.2: Select the iteration time according to the initial discrimination result; Step 5.3: Accurately discriminate the EMB working stage; Step 6: Secondary distribution of the braking torque coefficient based on the multi-stage response characteristics of the EMB; Step 7: Implement EMB / regenerative braking; Step 8: Determine whether braking is completed: If not, loop back to Step 1; if so, directly end.

2. The optimized distribution method of the automotive composite braking torque based on the EMB multi-stage response characteristics as claimed in claim 1, wherein: The following steps are also included in Step 2: The total vehicle required braking torque T is calculated based on the brake pedal displacement and brake pedal speed. b The front and rear axle braking forces are distributed according to the ideal brake force distribution curve.

3. The method for optimizing the distribution of the composite braking torque of an automobile based on the multi-stage response characteristics of EMB according to claim 2, wherein: The following steps are also included in Step 3: If the required braking torque on a single wheel is less than the maximum regenerative braking torque, the EMB does not need to intervene, and the braking task is completed by regenerative braking, and directly enter the EMB / regenerative braking implementation stage of Step 7; if the required braking torque on a single wheel is greater than the maximum regenerative braking torque, the EMB needs to intervene, enter Step 4, and the braking task is completed by the in-wheel motor and the EMB together.

4. The optimized distribution method of the automotive composite braking torque based on the EMB multi-stage response characteristics according to claim 3, characterized in that: The following steps are also included in Step 4: The initial distribution process includes 4 steps: converting the input quantity into a fuzzy set to obtain the fuzzy input variable, using the fuzzy input variable and the rule base for reasoning to obtain the fuzzy output variable, using the centroid method to convert the fuzzy output variable into a clear output value, and converting the output value into a specific control instruction.

5. The optimized distribution method of the automotive composite braking torque based on the EMB multi-stage response characteristics as described in claim 4, wherein: The following steps are also included in Step 5: The following steps are also included in Step 5.1: Introduce variables t1 to represent the switching time point between the no-load stage of the braking torque and the torque boost stage, t2 to represent the switching time point between the torque boost stage and the torque holding stage, and t to represent the time from the start of braking to the present; the calculation formula for t1 is: Where, T gap is the time for eliminating clearance; S gap is the braking clearance; i p is the reduction ratio of the planetary gear reducer; n0 is the maximum no-load speed of the EMB drive motor; L0 is the lead of the ball screw. If 0 ≤ t < 0.8t1, the working stage of the EMB is the no-load stage of the braking torque; if 0.8t1 ≤ t ≤ 1.2t2, then enter Step 5.3 to accurately discriminate the EMB working stage; if 1.2t2 < t, the working stage of the EMB is the torque holding stage; the initial discrimination result N satisfies the following formula: The following steps are also included in Step 5.2: The iteration time refers to the time required to run a composite braking torque optimization distribution process once, and the value of the iteration time Δt satisfies the following formula: The following steps are also included in Step 5.3: Judge the actual braking torque T of the EMB e ' and the target braking torque T of the EMB e Precisely discriminate the working stage of the EMB based on the magnitude relationship. For the case where the initial discrimination result N = 2, the working stage of the EMB needs to be further precisely judged. The result of precisely discriminating the working stage of the EMB satisfies the following formula: where, T ei ' is the actual braking torque of the EMB of the single wheel at present, and T ei is the target braking torque of the EMB of the single wheel. i = 1, 2, 3, 4 represent the left front wheel, the right front wheel, the left rear wheel and the right rear wheel respectively; P1, P2, and P3 represent the no-load stage of the braking torque, the rising stage of the braking torque, and the holding stage of the braking torque respectively; Combined with the above judgment process, if 0 < T ei '< T ei and t > t2, it is the braking torque release stage, and no secondary distribution of the braking torque coefficient is required.

6. The optimized allocation method for the combined braking torque of an automobile based on the multi-stage response characteristics of EMB as claimed in claim 5, characterized in that: The following steps are also included in Step 6: Step 6.1: Secondary distribution of the regenerative braking torque First, according to the discrimination result of the EMB working stage, if it is in the no-load stage of the braking torque, the single-wheel regenerative braking torque is required to fill the single-wheel EMB braking torque demand. At this time, T ri is equal to T rmax . The actual braking torque of the EMB is zero. The values of T ri and T ei are as follows: Where, T ri is the single-wheel regenerative braking torque, i = 1, 2, 3, 4, representing the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively, T rmax is the maximum regenerative braking torque that the in-wheel motor can provide, T ei is the single-wheel EMB target braking torque, i = 1, 2, 3, 4, representing the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively; When the EMB working stage is in the braking torque increasing stage, judge the magnitude relationship between KT i and T rmax . K is the braking torque coefficient. If KT i ≥T rmax , it indicates that the regenerative braking has reached the maximum value and the EMB system cannot obtain regenerative braking compensation; Step 6.2: Determine whether there is a torque requirement for the front wheels For the no-load stage of the braking torque, there must be a braking torque requirement for the front wheels, and no judgment is made; For the braking torque increasing stage, judge T e1 -T e1 '+T r1 and T rmax magnitude relationship: If T e1 -T e1 '+T r1 >T rmax , it indicates that there is a braking torque requirement for the front wheel, and T r1 、T r2 are valued as follows: Where, T e1 is the target braking torque of the left front wheel EMB, T e1 ’ is the actual braking torque of the left front wheel EMB, T r1 is the regenerative braking torque of the left front wheel, T r2 is the regenerative braking torque of the right front wheel, T rmax is the maximum regenerative braking torque that the in-wheel motor can provide; If T e1 -T e1 '+T r1 <T rmax , it indicates that there is no braking torque requirement for the front wheel, and T r1 、T r2 take the following values: where T e1 ' is the actual braking torque of the left front wheel EMB, and T e2 ' is the actual braking torque of the right front wheel EMB; Step 6.3: Determine whether there is torque surplus in the rear wheels For the braking torque increasing stage, compare T e3 -T e3 '+T r1 with T rmax in terms of magnitude relationship: If T e3 -T e3 '+T r1 >T rmax , it indicates that there is no available regenerative braking torque for the rear wheel hub motor; T r1 、T r2 、T r3 、T r4 The values are as follows: Where, T e3 is the target braking torque of the left rear wheel EMB, T e3 ' is the actual braking torque of the left rear wheel EMB, T r3 is the regenerative braking torque of the left rear wheel, T r4 is the regenerative braking torque of the right rear wheel; If T e3 -T e3 '+T r1 <T rmax , it indicates that there is available regenerative braking torque for the rear wheel hub motor; Step 6.4: The in-wheel motor of the rear wheels compensates for the front wheels For the no-load stage of the braking torque, judge the magnitude relationship between T1 - T rmax and T rmax - T3: If T1 - T rmax > T rmax - T3, T r3 、T r4 takes the following values: Wherein, T1 is the required braking torque of the left front wheel, T3 is the required braking torque of the left rear wheel, T r3 is the regenerative braking torque of the left rear wheel, T r4 is the regenerative braking torque of the right rear wheel; If T1 - T rmax <T rmax - T3, T r3 、T r4 takes the following values: In the formula, T1 is the required braking torque of the left front wheel, and T2 is the required braking torque of the left rear wheel; For the braking torque increasing stage, judge the magnitude relationship between T1 - T rmax and T rmax - T3: If T1 - T rmax > T rmax - T3, T r3 、T r4 takes the following values: If T1 - T rmax <T rmax - T3, T r3 、T r4 takes values as follows: Based on the above distribution strategy, introduce K' as the braking torque coefficient after secondary distribution compensation, which characterizes the participation degree of regenerative braking in the final braking process. The regenerative and EMB target braking torque distributions of each wheel satisfy the following formula: where, T e1 is the target braking torque of the left front wheel EMB, T e2 is the target braking torque of the right front wheel EMB, T e3 is the target braking torque of the left rear wheel EMB, T e4 is the target braking torque of the right rear wheel EMB, T f is the braking torque of the front axle, T r is the braking torque of the rear axle; Step 6.5: Set the zero time t according to the conditions The torque sensor outputs the current actual braking torque T of the EMB e 'To the composite braking torque coordination control system, when it is detected that the actual braking torque is equal to zero, let t be equal to zero.

7. The optimized allocation method of the automotive composite braking torque based on the EMB multi-stage response characteristic according to claim 6, wherein: The steps in step 7 further include the following steps: The vehicle control system will control the hub motors and EMB of each wheel to generate corresponding braking torques according to the braking torque distribution results calculated in the previous steps, that is, according to T r1 , T r2 , T r3 , T r4 , T e1 , T e2 , T e3 , T e4 to implement the control of EMB and regenerative braking torques.

8. The optimized distribution method of the composite braking torque of the vehicle based on the EMB multi-stage response characteristics as claimed in claim 7, characterized in that: The steps in step 8 further include the following steps: The vehicle speed sensor monitors the vehicle speed in real time and feeds the data back to the vehicle control system. The vehicle control system judges according to the current vehicle speed and the set braking conditions to determine whether the braking is over: when the vehicle speed drops below the preset threshold, the system will judge that the braking process has been completed and stop sending control signals to the braking system; if the vehicle speed is still higher than the threshold, the system will continue to maintain the braking state to ensure that the vehicle decelerates stably within a safe range.

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