Driving force distribution method and system for distributed drive vehicle, and vehicle

Abstract

A driving force distribution method and system for a distributed drive vehicle, and a vehicle. The driving force distribution method comprises: on the basis of the driving conditions of a vehicle, determining a driving force distribution mode of the vehicle, wherein the driving force distribution mode includes a first mode and a second mode; when the driving force distribution mode is the first mode, obtaining, on the basis of operating parameters of electric motors and a required torque of a driver, an optimal efficiency distribution coefficient of a drive system corresponding to rotation speeds of the electric motors and the required torque of the driver, and determining, on the basis of the optimal efficiency distribution coefficient of the drive system, a driving force of each in-wheel electric motor; and when the driving force distribution mode is the second mode, determining the current operating condition of the vehicle on the basis of a vehicle speed and a yaw rate deviation, and obtaining a driving force of each in-wheel electric motor on the basis of the current operating condition.

Description

Driving force distribution method, system and vehicle of distributed drive vehicle Cross-reference to related applications

[0001] This application claims priority to Chinese patent application No. 202410426445.X, filed on April 10, 2024, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0002] The present application belongs to the technical field of automobile torque distribution, and specifically relates to a driving force distribution method, system and vehicle of a distributed drive vehicle. BACKGROUND

[0003] Four-wheel motor-driven electric vehicles have become an important research direction for pure electric vehicles due to their four-wheel independent steering, high power transmission efficiency, and great potential for improving vehicle economy, stability and safety. Most of the existing torque distribution methods only consider economy without considering economy and stability comprehensively. SUMMARY

[0004] In order to improve the stability of torque distribution, the present application proposes a driving force distribution method, system and vehicle of a distributed drive vehicle.

[0005] A driving force distribution method of a distributed drive vehicle for achieving one of the purposes of the present application, comprising:

[0006] determining a vehicle driving force distribution mode according to a vehicle driving condition; the driving force distribution mode includes a first mode and a second mode;

[0007] When the driving force distribution mode is the first mode, the motor speed and the demand torque of the driver corresponding to the driving system optimal efficiency distribution coefficient are obtained according to the motor operating parameters and the demand torque of the driver; the driving force of each hub motor is determined according to the driving system optimal efficiency distribution coefficient.

[0008] When the driving force distribution mode is the second mode, the current condition of the vehicle is determined according to the speed and yaw rate deviation; the driving force of each hub motor is obtained according to the condition.

[0009] In the above method, the method for determining the vehicle driving force distribution mode according to the vehicle driving condition comprises:

[0010] When the angle value of the front wheel angle of the vehicle belongs to the first set range, the vehicle driving force distribution mode is the first mode, otherwise the vehicle driving force distribution mode is the second mode.

[0011] Further, when the driving force distribution mode is the first mode, the method for obtaining the driving system optimal efficiency distribution coefficient comprises:

[0012] constructing a target function of driving efficiency optimization according to motor operating parameters and required torque of the driver;

[0013] solving the target function to obtain a best efficiency distribution coefficient MAP table of the driving system, the MAP table being used to store the correspondence among motor speed , required torque of the driver , and the best efficiency distribution coefficient of the driving system;

[0014] querying the current best efficiency distribution coefficient of the driving system from the MAP table according to the current motor speed of the vehicle and the required torque of the driver.

[0015] In the above method, the best efficiency distribution coefficient of the driving system is further constrained, and the constraint method comprises:

[0016] obtaining total input power of all in-wheel motor driving systems under the best efficiency distribution coefficient of the driving system ;

[0017] performing weighted calculation on the total input power according to the set constraint coefficient to obtain weighted total input power ;

[0018] inputting the best efficiency distribution coefficient λ of the driving system into the vehicle, and if the total input power of all in-wheel motor driving systems of the vehicle is less than the weighted total input power , saving the best efficiency distribution coefficient λ of the driving system in the best efficiency distribution coefficient MAP table of the driving system.

[0019] In the above method, the working condition comprises a first working condition, and the method of obtaining and adjusting the driving force of each in-wheel motor according to the working condition comprises:

[0020] obtaining wheel speed difference of each wheel according to target wheel speed and actual wheel speed of each wheel;

[0021] obtaining driving force of each wheel according to the wheel speed difference of each wheel;

[0022] outputting the driving force of each wheel and the total required driving force distributed averagely to a motor controller to adjust the driving force of each in-wheel motor.

[0023] Further, the working condition further comprises a second working condition, and the method of obtaining the driving force of each in-wheel motor according to the working condition comprises:

[0024] calculating additional yaw moment according to yaw motion deviation of the vehicle;

[0025] The driving force of each hub motor is calculated when the objective function is optimal according to the additional yaw moment, the front wheelbase, and the front wheel steering angle.

[0026] The calculation method of the additional yaw moment comprises:

[0027]

[0028] In the formula:

[0029] is the additional yaw moment;

[0030] is the front wheelbase, is the rear wheelbase;

[0031] F yij is the lateral force of each wheel, wherein (ij = 11, 12, 21, 22) respectively represents the left and right front wheels and the left and right rear wheels;

[0032] is the front wheel steering angle;

[0033] I z is the yaw moment of inertia;

[0034] represents the derivative of the yaw angle reference value;

[0035] and respectively represent the mass center side slip angle and the reference value of the mass center side slip angle;

[0036] is the weight coefficient of the mass center side slip angle β;

[0037] represents the rate at which the state point approaches the sliding surface;

[0038] s represents the tracking error function in the exponential approach law;

[0039] k r represents a set coefficient.

[0040] The calculation method of the objective function comprises:

[0041]

[0042] In the formula:

[0043] is the road adhesion consumption rate of each wheel; ij = 11, 12, 21, 22, respectively representing the left and right front wheels and the left and right rear wheels;

[0044] ;

[0045] is a set weight coefficient.

[0046] In the method, the working condition includes a first working condition and a second working condition, and the method for obtaining the driving force of each wheel hub motor according to the working condition includes:

[0047] When the yaw angle velocity deviation is less than a first deviation value and the vehicle speed is lower than a first vehicle speed, the working condition is the first working condition, and the method for obtaining the driving force of each wheel hub motor according to the first working condition includes:

[0048] The wheel speed difference of each wheel is obtained according to the target wheel speed and the actual wheel speed of each wheel.

[0049] The driving force of each wheel is obtained according to the wheel speed difference of each wheel.

[0050] The driving force of each wheel and the total required driving force distributed averagely are output to the motor controller to adjust the driving force of each wheel hub motor.

[0051] When the vehicle speed is higher than a second vehicle speed, the working condition is the second working condition, and the method for obtaining the driving force of each wheel hub motor according to the second working condition includes:

[0052] The additional yaw moment is calculated according to the vehicle yaw motion deviation.

[0053] The driving force of each wheel hub motor when the target function is optimal is calculated according to the additional yaw moment, the front axle track and the front wheel rotation angle.

[0054] When the yaw angle velocity deviation is greater than the first deviation value and the vehicle speed is lower than the second vehicle speed, the driving force F of each wheel hub motor is determined according to the following formula: ij :

[0055]

[0056] In the formula, F

[0057] F lij represents the four-wheel driving force obtained according to the first working condition.

[0058] F hij represents the four-wheel driving force obtained according to the second working condition.

[0059] ij = 11, 12, 21, 22, which represent the left and right front wheels and the left and right rear wheels in turn, respectively.

[0060] is a weight coefficient of the speed tracking distribution strategy.

[0061] A driving force distribution system of a distributed drive vehicle for achieving the second purpose of the application, comprising:

[0062] The driving force distribution mode determination module is configured to determine a driving force distribution mode of the vehicle according to a driving condition of the vehicle, wherein the driving force distribution mode comprises a first mode and a second mode.

[0063] The first driving force adjustment module is configured to, when the driving force distribution mode is the first mode, obtain a driving system optimal efficiency distribution coefficient corresponding to a motor speed and a required torque of the driver according to a motor operation parameter and the required torque of the driver, and determine a driving force of each hub motor according to the driving system optimal efficiency distribution coefficient.

[0064] The second driving force adjustment module is configured to, when the driving force distribution mode is the second mode, determine a current condition of the vehicle according to a vehicle speed and a yaw rate deviation, and determine a driving force of each hub motor according to the condition.

[0065] The application also comprises a vehicle comprising a controller configured to perform any step of the driving force distribution method of the distributed drive vehicle.

[0066] The application has the following advantages:

[0067] The application comprehensively considers the economy and stability of the four-wheel drive vehicle, improves the economy of the four-wheel drive vehicle when driving straight, and has good control effect in both low-speed and high-speed conditions when the vehicle is turning, and smoothly switches between the two conditions. BRIEF DESCRIPTION OF DRAWINGS

[0068] FIG. 1 is a flowchart of the technical solution of the method of the application;

[0069] FIG. 2 is a schematic diagram of a geometric model of a vehicle steering system;

[0070] FIG. 3 is a flowchart of a high-speed turning condition of the vehicle. DETAILED DESCRIPTION

[0071] The following detailed description is used to explain the technical solution of the claims of the application, so that those skilled in the art can understand the claims of the application. The protection scope of the application is not limited to the following specific implementation structure. The technical solution of the claims of the application which is different from the following specific embodiment and contains the technical solution of the claims of the application is also within the protection scope of the application.

[0072] FIG. 1 is a driving force distribution method of a distributed drive vehicle according to the technical solution of the application, comprising the following steps:

[0073] Step 1, form a switching logic of the longitudinal driving force distribution algorithm;

[0074] The economic mode is adopted by default to prolong the vehicle's cruising range;

[0075] When the driver has a steering demand or the vehicle is in a critical instability state, the longitudinal driving force distribution algorithm is switched to the stability mode;

[0076] In the sliding and braking conditions, in order to reduce the influence of the longitudinal driving force distribution on the stability of the braking system, a fixed proportional distribution is adopted.

[0077] Finally, the longitudinal driving force distribution control function of economic optimization in the stable driving condition and stability optimization in the dynamic driving or critical instability condition is realized.

[0078] In another technical scheme, the vehicle determines whether the control strategy of the longitudinal driving force distribution algorithm is in the economic mode or the stability mode according to the range of the front wheel steering angle Specifically, when the front wheel steering angle ranges from -3° to 3°, the economic mode is switched to; when the front wheel steering angle or ranges from -3° to 3°, the stability mode is switched to.

[0079] Step 2, formulating an economic-based longitudinal driving force distribution method;

[0080] First, a target function of driving system efficiency optimization is established, all necessary torque and speed combinations are input, the driving system efficiency distribution coefficient is calculated, in order to avoid the back-and-forth fluctuation of the distribution coefficient, an automatic script tolerance constraint is constructed, thereby generating a MAP diagram of the optimal distribution coefficient of the driving system efficiency .

[0081] Specifically, the target function of the driving efficiency optimization is as follows:

[0082] Formula (1)

[0083] In the formula, P is the input power of the driving system for solving λ;

[0084] is the upper limit of the single-shaft motor torque;

[0085] is the required torque of the driver;

[0086] is the driving system efficiency distribution coefficient; in the technical scheme, the driving force distribution coefficient corresponding to the rear axle motor;

[0087] is the efficiency of the front axle motor and the rear axle motor, respectively.

[0088] and are the efficiencies of the front axle motor and the rear axle motor, respectively.

[0089] is the motor speed.

[0090] Solve by matlab built-in quadprog function and build automatic script, offline solve different motor speed and the demand torque of the driver the ideal efficiency of the drive system (min) the drive system efficiency distribution coefficient .

[0091] In the optimization process, in order to avoid the ideal drive system efficiency distribution coefficient back and forth fluctuation, the introduction of tolerance constraint condition, as follows:

[0092] Equation (2)

[0093] In the formula:

[0094] is the total input power of the four wheel hub motor drive system corresponding to a drive system efficiency distribution coefficient .

[0095] Tolerance represents the tolerance constraint coefficient, usually the value range is [5,10].

[0096] is the total input power under the constraint of tolerance constraint coefficient tolerance;

[0097] When the objective function is solved λ is substituted into the vehicle drive system efficiency distribution coefficient, if the sum of the actual input power of the vehicle drive system is less than , then the drive system efficiency distribution coefficient is the best distribution coefficient of longitudinal driving force . The best distribution coefficient and the corresponding motor speed , the demand torque of the driver embedded in the optimal distribution coefficient MAP of the vehicle control software.

[0098] In the driving process, according to the demand torque of the driver and the motor speed , the optimal efficiency distribution coefficient of the drive system is obtained by looking up the MAP in real time under the current working condition. Thus the longitudinal driving force distribution of the four wheel hub motors is adjusted, and the economy is improved.

[0099] In another technical solution, according to the optimal efficiency distribution coefficient of the driving force The method for adjusting the longitudinal driving force distribution of the four hub motors comprises:

[0100] The driving force of the two rear wheels is:

[0101] The driving force of the two front wheels is:

[0102] Wherein, Fall represents the total driving force required by the vehicle.

[0103] Step 3, formulating a longitudinal driving force distribution algorithm based on stability;

[0104] The vehicle stability requirement is high when turning, which is divided into low-speed turning and high-speed turning working conditions.

[0105] Step 3.1, when the vehicle is in low-speed turning working condition, the speed difference of the inner and outer wheels is calculated through geometric relationship, and electronic differential is realized by controlling the wheel speed, the specific steps comprising:

[0106] A geometric model of the vehicle steering system is established, and the target wheel speed of each wheel can be calculated from the vehicle speed and the steering angle. After the actual wheel speed deviation is obtained according to the feedback of the underlying motor, the wheel speed error of each wheel is converted into the driving force of each wheel through the control algorithm, and the total demand driving force is output to the motor controller together with the average distribution, and the motor controller adjusts the calculated torque value of the hub motor. The hub motor can feedback the motor speed in real time to complete the feedback control process. As shown in FIG. 2, to make the front wheels of the vehicle keep the same steering center, the front wheel steering angle has the following relationship:

[0107] Formula (3)

[0108] In the formula:

[0109] And are the left front wheel and right front wheel steering angles respectively;

[0110] B is the wheel track;

[0111] L is the wheelbase.

[0112] Let the steering radius of the vehicle center of mass be R v From the geometric relationship, we can get:

[0113] Formula (4)

[0114] The ideal steering radius of the four wheels R ij (ij = 11, 12, 21, 22), as follows:

[0115] Formula (5)

[0116] wherein R 11 , R 12 , R 21 , R 22 represent the steering radius of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel, respectively.

[0117] Let the effective radius of the wheel be r e , and the desired vehicle speed be v d , then the desired speed of the four wheels can be obtained:

[0118] Equation (6)

[0119] wherein:

[0120] r d11 , r d12 , r d21 , r d22 represent the desired speed of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel, respectively.

[0121] The calculated desired wheel speed r dij may not match the actual wheel speed r aij of the current vehicle, and the motor usually adopts double closed-loop control of speed loop and torque loop, and a feedback controller needs to be designed to solve the wheel hub motor torque for tracking the desired speed. The motor driver controls the wheel to reach the specified speed by receiving the wheel edge torque signal sent by the controller, and realizes the driving force distribution of each wheel under low speed.

[0122] According to the PID feedback control theory, let e rij = r aij - r dij be the speed difference of each wheel, then:

[0123] Equation (7)

[0124] wherein:

[0125] F sij represents the four-wheel speed tracking driving force, i=1, 2; j=1, 2;

[0126] K p represents the proportional adjustment coefficient;

[0127] e rij represents the four-wheel speed difference;

[0128] K i represents the integral adjustment coefficient;

[0129] represents time, which is the integral of time here;

[0130] denotes the differential of the four-wheel rotational speed difference, i.e., the derivative;

[0131] K d denotes the differential adjustment coefficient;

[0132] The longitudinal speed control module first performs average distribution after inputting the total demand driving force into the rotational speed tracking module, and respectively superimposes the wheel rotational speed tracking driving force F sij on the input motor model for rotational speed tracking.

[0133] Equation (8)

[0134] In the equation:

[0135] F lij denotes the four-wheel driving force of the input motor model in the low-speed working condition; F l11 , F l12 , F l21 , and F l22 respectively correspond to the driving force of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel.

[0136] Fall denotes the total demand driving force.

[0137] Step 3.2, when the vehicle is in the high-speed steering working condition, the sliding mode control is used to track the vehicle yaw motion deviation, to calculate the additional yaw moment and to optimize the distribution to each wheel to realize stability control, and the specific steps include:

[0138] The high-speed steering working condition stability control process is as shown in FIG. 3, and a hierarchical control strategy is adopted, in which an upper-layer SMC (sliding mode control) controller obtains the vehicle running state quantity and calculates the additional yaw moment ; a lower-layer QP (optimal control) controller designs a driving force distribution strategy to optimize the distribution of the driving force of each wheel to meet the demand of the vehicle longitudinal speed and the additional yaw moment.

[0139] Firstly, the upper-layer SMC (sliding mode control) controller calculates the lateral additional yaw moment based on the sliding mode control, to ensure the vehicle yaw stability, the vehicle center side slip angle and the yaw angular velocity should be as close as possible to the reference value or slightly less than the reference value. In order to achieve the above-mentioned goal, a linear two-degree-of-freedom vehicle model is established to obtain the reference value of the ideal steady-state yaw angular velocity r:

[0140] Equation (9)

[0141] The reference value of the vehicle center side slip angle : ​​

[0142] Equation (10)

[0143] Considering the influence of road conditions during driving, the lateral angular velocity and the mass side slip angle limit constraint are added, and the lateral angular velocity reference value is updated and the mass side slip angle reference value is as shown in the following equation (11):

[0144] Equation (11)

[0145] The vehicle yaw motion equation is established, and the yaw formula is:

[0146] Equation (12)

[0147] In the formula:

[0148] denotes the longitudinal vehicle speed;

[0149] denotes the stability factor;

[0150] is the rear roll stiffness;

[0151] is the front wheelbase, is the rear wheelbase;

[0152] denotes the use of the adhesion coefficient;

[0153] denotes the acceleration of gravity;

[0154] is the total vehicle mass;

[0155] denotes the yaw angular acceleration;

[0156] F yij is the lateral force of each wheel, where (ij =11, 12, 21, 22) represents the left and right front wheels and the left and right rear wheels respectively;

[0157] is the front wheel steering angle;

[0158] is the additional yaw moment;

[0159] is the yaw moment of inertia.

[0160] The tracking error function is designed as: , in the formula, > 0, which is the weight coefficient of the centroid side-slip angle, generally taken as 0.3. The derivative of the sliding surface is: Equation (13)

[0161] The appropriate reaching law is selected. The exponential reaching law can reach the switching surface in a shorter time than other reaching laws, and has a simple structure. Therefore, the exponential reaching law is selected:

[0162] Equation (14)

[0163] To make the state point quickly approach the switching surface and reduce chattering, k r should be increased and k should be decreased. The sign function sgn(s) is changed to the saturation function sat(s) to weaken the chattering phenomenon.

[0164] Equation (15)

[0165] The additional yaw moment M is obtained by solving Equations (12)-(15) simultaneously:

[0166] Equation (16)

[0167] represents the rate at which the state point approaches the sliding surface;

[0168] k r represents the coefficient of the tracking error function s in the exponential reaching law;

[0169] Next, the lower-layer QP (optimal control) controller is added with the following dynamic constraints:

[0170] The optimized distribution of the driving force should meet the requirement of the total demand driving force Fall.

[0171] Equation (17)

[0172] F xij is the driving force of each wheel, where (ij = 11, 12, 21, 22) respectively represent the left and right front wheels and the left and right rear wheels;

[0173] The four-wheel driving force should meet the additional yaw moment .

[0174] Equation (18)

[0175] In the equation, B represents the front axle track;

[0176] The objective function of the QP controller is designed, and the following formula is introduced based on the tire adhesion ellipse principle: ​

[0177] Equation (19)

[0178] F zij is the vertical force of each wheel; μ ij represents the utilization coefficient of four wheels; e ij is the road adhesion consumption rate of each wheel; wherein (ij = 11, 12, 21, 22) respectively represent the left and right front wheels and the left and right rear wheels; The smaller the value is, the larger the driving force adjustment space left for the wheels is, the smaller the possibility of slipping is, and the higher the operation stability of the vehicle turning is.

[0179] For a distributed drive vehicle, the four-wheel The sum of the values is the smallest, and more utilization space is provided for the lateral force.

[0180] Neglecting the lateral force, a target function to be optimized is designed , wherein C ij represents a proportionality coefficient of four wheels;

[0181] For the optimal planning problem of a nonlinear system, a quadratic programming algorithm is used for solving, the target function is improved accordingly, and the optimization of the mean value and the variance of the road adhesion consumption rate e is considered. A target function is designed The mean value is: .

[0182] The target function is modified as:

[0183] Equation (20)

[0184] In the equation,

[0185] represents the weight coefficient of the mean value of the road adhesion consumption rate in the target function;

[0186] The four-wheel driving force F xij is taken as an output unknown quantity for solving, and finally the quadratic programming formula is expressed in a matrix form. The optimal solution of the four-wheel driving force of the vehicle can be obtained by substituting the quadratic programming solving function in matlab, that is, This optimal solution is also the four-wheel driving force of the input motor model in the high-speed working condition. The driving force is converted into an output torque by the hub motor model to drive the vehicle to travel.

[0187] In another technical solution, different weights can be designed for the high-speed turning working condition and the low-speed turning working condition according to the change of the working condition, the low-speed and high-speed modes are coordinated and switched, the vehicle driving force changes gently, and specifically includes:

[0188] Fuzzy control is used to adjust its weight. When the yaw rate deviation is small (the absolute value is less than 10 in this technical solution) and the vehicle speed is lower than 40 km / h, the vehicle is considered to be driving stably. At this time, the speed tracking strategy (i.e., the longitudinal driving force distribution algorithm under low-speed steering driving conditions) should be fully adopted. =1; when the vehicle speed gradually increases or the yaw rate deviation gradually increases, the fuzzy control output should gradually reduce the weight coefficient of the speed tracking distribution strategy When the vehicle speed is greater than 60km / h, it is considered that the vehicle is in a dangerous state. =0, the SMC-QP drive distribution strategy is fully adopted (i.e., the longitudinal drive force distribution algorithm under high-speed steering conditions).

[0189] Formula (21)

[0190] Where:

[0191] F hij Indicates the four-wheel drive force input to the motor model under high-speed working conditions;

[0192] F lij Indicates the four-wheel drive force input to the motor model under low-speed conditions;

[0193] It indicates the comprehensive consideration of the four-wheel drive force under low-speed and high-speed conditions;

[0194] The above ij = 11, 12, 21, 22 represent the left and right front wheels and the left and right rear wheels respectively.

[0195] In another technical solution, a fuzzy control system is used to obtain the weight coefficient of the speed tracking strategy. The input of the fuzzy control system is: vehicle speed v, whose domain is [30,50]; yaw rate deviation r, whose domain is [-10,10]; the output is the weight coefficient of the speed tracking strategy , The domain of is [0,1].

[0196] The fuzzy subsets of the input of the fuzzy control system are divided into {NB, NS, ZO, PS, PB}, and the fuzzy subsets of the output are divided into {NB, NM, NS, ZO, PS, PM, PB}. The Gaussian function is selected as the membership function. The fuzzy rules are formulated as shown in the following table:

[0197] Table 1 Fuzzy rule table

[0198]

[0199] This enables smooth switching between low-speed and high-speed operating conditions.

[0200] It should be understood that the size of the serial number of each step in the above technical solutions does not mean the order of execution, and the execution order of each process should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the technical solutions of the present application.

[0201] The technical solutions of the present application also provide a driving force distribution system of a distributed drive vehicle, comprising:

[0202] The driving force distribution mode determination module is configured to determine the driving force distribution mode of the vehicle according to the driving condition of the vehicle; the driving force distribution mode comprises a first mode and a second mode;

[0203] The first driving force adjustment module is configured to, when the driving force distribution mode is the first mode, obtain the driving system optimal efficiency distribution coefficient corresponding to the motor speed and the required torque of the driver according to the motor operating parameters and the required torque of the driver; and determine the driving force of each hub motor according to the driving system optimal efficiency distribution coefficient.

[0204] The second driving force adjustment module is configured to, when the driving force distribution mode is the second mode, determine the current working condition of the vehicle according to the speed and yaw rate deviation; and obtain the driving force of each hub motor according to the working condition.

[0205] The contents not described in detail in the specification belong to the prior art known to those skilled in the art.

Claims

1. A driving force distribution method for a distributed drive vehicle, characterized in that: include: Determining a vehicle driving force distribution mode according to a vehicle driving condition; the driving force distribution mode includes a first mode and a second mode; When the driving force distribution mode is the first mode, the optimal efficiency distribution coefficient of the driving system corresponding to the motor speed and the required torque of the driver is obtained according to the motor operating parameters and the required torque of the driver; and the driving force of each wheel hub motor is determined according to the optimal efficiency distribution coefficient of the driving system; When the driving force distribution mode is the second mode, the current operating condition of the vehicle is determined according to the vehicle speed and the yaw rate deviation; and the driving force of each wheel hub motor is obtained according to the operating condition.

2. The driving force distribution method of a distributed drive vehicle according to claim 1, characterized in that: The method for determining a vehicle driving force distribution mode according to a vehicle driving condition includes: When the angle value of the front wheel steering angle of the vehicle falls within the first set range, the driving force distribution mode is the first mode; otherwise, the driving force distribution mode is the second mode.

3. The driving force distribution method of a distributed drive vehicle according to claim 1, characterized in that: When the driving force distribution mode is the first mode, the method for obtaining the optimal efficiency distribution coefficient of the driving system includes: Construct the objective function of drive efficiency optimization based on the motor operating parameters and the required torque of the drive; Solve the objective function to obtain the optimal efficiency distribution coefficient MAP table of the drive system, which is used to store the motor speed and the required torque of the drive and the corresponding relationship of the optimal efficiency distribution coefficient of the drive system; The current drive system's optimal efficiency distribution coefficient is retrieved from the MAP table based on the vehicle's current motor speed and the driver's required torque.

4. The driving force distribution method of a distributed drive vehicle according to claim 3, characterized in that: The method also includes constraining the optimal efficiency distribution coefficient of the drive system, wherein the constraint method includes: According to the optimal efficiency distribution coefficient of the drive system, the total input power of all wheel hub motor drive systems under the distribution coefficient is obtained ； According to the set constraint coefficient, the total input power Perform weighted calculation to obtain the weighted total input power ； The optimal efficiency distribution coefficient of the drive system is input into the vehicle. If the total input power of all wheel hub motor drive systems of the vehicle is greater than the weighted total input power If the optimal efficiency distribution coefficient λ of the driving system is small, the optimal efficiency distribution coefficient λ of the driving system is saved in the optimal efficiency distribution coefficient MAP table of the driving system.

5. The driving force distribution method of a distributed drive vehicle according to claim 1, characterized in that: The operating condition includes a first operating condition, and a method for obtaining and adjusting the driving force of each hub motor according to the operating condition includes: Obtain the wheel speed difference of each wheel according to the target wheel speed and the actual wheel speed of each wheel; Obtaining the driving force of each wheel according to the wheel speed difference of each wheel; The driving force of each wheel and the evenly distributed total required driving force are output to a motor controller to adjust the driving force of each hub motor.

6. The driving force distribution method of a distributed drive vehicle according to claim 1, characterized in that: The operating condition includes a second operating condition, and a method for obtaining the driving force of each hub motor according to the operating condition includes: Calculate additional yaw moment based on vehicle yaw motion deviation; The driving force of each wheel hub motor is calculated based on the additional yaw moment, front axle track, and front wheel angle when the objective function is optimal.

7. The driving force distribution method of a distributed drive vehicle according to claim 6, characterized in that: The calculation method of the additional yaw moment includes: ， Where: is the additional yaw moment; is the front wheelbase, is the rear wheelbase; F yij is the lateral force of each wheel, where (ij = 11, 12, 21, 22) represent the left and right front wheels and the left and right rear wheels respectively; is the front wheel turning angle; I z is the yaw moment of inertia; represents the derivative of the yaw angle reference value; and denote the reference values ​​of the center of mass slip angle and the center of mass slip angle, respectively; is the weight coefficient of the center of mass sideslip angle β; Indicates the rate at which the state point approaches the sliding surface; s represents the tracking error function in the exponential reaching law; k r Indicates the setting coefficient.

8. The driving force distribution method of a distributed drive vehicle according to claim 1, characterized in that: The operating conditions include a first operating condition and a second operating condition, and a method for obtaining the driving force of each hub motor according to the operating conditions includes: When the yaw rate deviation is less than the first deviation value and the vehicle speed is lower than the first vehicle speed, the operating condition is the first operating condition, and the method for obtaining the driving force of each wheel hub motor according to the first operating condition includes: Obtain the wheel speed difference of each wheel according to the target wheel speed and the actual wheel speed of each wheel; Obtaining the driving force of each wheel according to the wheel speed difference of each wheel; Outputting the driving force of each wheel and the evenly distributed total required driving force to a motor controller to adjust the driving force of each wheel hub motor; When the vehicle speed is higher than the second vehicle speed, the operating condition is the second operating condition, and the method for obtaining the driving force of each wheel hub motor according to the second operating condition includes: Calculate additional yaw moment based on vehicle yaw motion deviation; Calculate the driving force of each wheel hub motor when the objective function is optimal based on the additional yaw moment, front axle track, and front wheel angle; When the yaw rate deviation is greater than the first deviation value and the vehicle speed is lower than the second vehicle speed, the driving force F of each wheel hub motor is determined according to the following formula: ij : ， Where: F lij represents the four-wheel drive force obtained according to the first working condition; F hij represents the four-wheel drive force obtained according to the second working condition; ij = 11, 12, 21, 22, representing the left and right front wheels and the left and right rear wheels respectively; is the set weight coefficient.

9. A driving force distribution system for a distributed drive vehicle using the method of claim 1, characterized in that: include: A driving force distribution mode determination module is used to determine the vehicle driving force distribution mode according to the vehicle driving conditions; The driving force distribution mode includes a first mode and a second mode; A first driving force adjustment module: when the driving force distribution mode is the first mode, obtains a driving system optimal efficiency distribution coefficient corresponding to the motor speed and the required torque of the driver based on the motor operating parameters and the required torque of the driver; and determines the driving force of each wheel hub motor based on the driving system optimal efficiency distribution coefficient; The second driving force adjustment module: when the driving force distribution mode is the second mode, the current working condition of the vehicle is determined according to the vehicle speed and the yaw rate deviation; and the driving force of each wheel hub motor is obtained according to the working condition.

10. A vehicle, characterized in that: The invention comprises a controller configured to execute the driving force distribution method of a distributed drive vehicle according to any one of claims 1 to 8.

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