Torque distribution method for distributed driving system of new energy automobile

Abstract

The invention relates to the technical field of new energy motors, in particular to a torque distribution method of a new energy automobile distributed driving system, which is characterized in that a plurality of function modules (a maneuverability control module, a stability control module, a maneuverability stability coordination module and the like) are additionally arranged on the new energy automobile distributed driving system; torque distribution is conducted on the vehicle by combining the vehicle speed and the lateral acceleration in the vehicle steering process, yaw under a certain scale can be effectively controlled, the maneuverability stability of vehicle driving is improved, and extra burden on a braking system does not need to be caused; compared with a traditional ESP / ESC / VSC in the aspects of quick response, closed-loop tracking precision and the like, the method is suitable for intervening in vehicle driving for a long time, enables the vehicle to be easier to use under various adhesive force road conditions including steering, and can delay intervention of the ESP / ESC / VSC, improve snake-shaped passing speed and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy motor, in particular to a torque distribution method of a distributed drive system of a new energy vehicle. BACKGROUND

[0002] In the steering process of a traditional new energy vehicle, active safety systems such as ESP, ESC, VSC, etc. are mainly used to monitor the driving state of the vehicle and the operation intention of the driver in real time, so as to adjust the power output and brake distribution of the vehicle, so that the vehicle can respond to the operation of the driver. However, such active safety systems actually realize the power output and brake distribution in the steering process of the vehicle through the lateral force moment generated by the cooperation of the hydraulic brake system and the drive system of the new energy vehicle. The response speed of the hydraulic brake system is usually slower than that of the drive motor of the drive system. In the actual steering process of the new energy vehicle, there are many shortcomings.

[0003] ①Slow response speed: The hydraulic brake system of the new energy vehicle needs to establish pressure first, and then conduct the pressure to the mechanical brake device through hydraulic pressure to realize the braking effect. However, this process takes a long time, resulting in slow response speed of the hydraulic brake system, which is difficult to quickly play a role in the emergency situation that needs to be intervened briefly and quickly;

[0004] ②Low intervention accuracy: The hydraulic brake system of the new energy vehicle is a mechanical brake device, which has a large response scale and a long required time. In the scene that needs low-intensity intervention, it is difficult to accurately and timely adjust, and it is difficult to meet the demand for fine control;

[0005] ③High use cost: The mechanical brake device will be worn out in the process of frequent use, and the wear and tear cannot be checked in real time during vehicle driving. Only the maintenance and replacement of related parts can be carried out regularly, which greatly increases the maintenance cost of the vehicle, and is not conducive to the long-term maintenance of the system in the intervention state.

[0006] The above problems make it difficult for the traditional new energy vehicle to generate the required lateral force moment in the steering process. Once an emergency situation such as an obstacle in front of the vehicle, other vehicles suddenly changing lanes or pedestrians crossing the road occurs, the vehicle cannot quickly change the driving direction to avoid danger, which is easy to cause collision accidents and cause vehicle damage and casualties. SUMMARY

[0007] The purpose of the present application is to solve the problems of the prior art. A torque distribution method of a distributed drive system of a new energy vehicle is provided. A plurality of functional modules (maneuverability control module, stability control module, maneuvering stability coordination module, etc.) are added to the distributed drive system of the new energy vehicle, and the vehicle speed and lateral acceleration in the steering process of the vehicle are combined to distribute the torque of the vehicle.

[0008] The object of the present application is achieved with the following solution:

[0009] A torque distribution method of a distributed drive system of a new energy vehicle, comprising the following steps:

[0010] 1) A handling control module is arranged on the distributed drive system of the new energy vehicle, which is used to distribute torque when the vehicle is turning, so as to improve the handling of the vehicle; a stability control module is arranged, which is used to distribute torque when the vehicle is turning, so as to improve the stability of the vehicle; a handling stability coordination module is arranged, which is used to smoothly transition and switch the handling control module and the stability control module;

[0011] 2) A handling vehicle speed threshold, a stability vehicle speed threshold, a handling lateral acceleration threshold and a stability lateral acceleration threshold are set;

[0012] 3) The vehicle speed, lateral acceleration and steering wheel angle of the new energy vehicle are collected, and the following method is used to determine which control module is used to distribute torque:

[0013] If the steering wheel angle ≠ 0, the handling vehicle speed threshold ≤ the vehicle speed < the stability vehicle speed threshold, and the handling lateral acceleration threshold ≤ the lateral acceleration < the stability lateral acceleration threshold, the handling control module is used to distribute torque;

[0014] If the steering wheel angle ≠ 0, the vehicle speed ≥ the stability vehicle speed threshold, and the lateral acceleration ≥ the stability lateral acceleration threshold, the stability control module is used to distribute torque;

[0015] If the steering wheel angle = 0, or the vehicle speed < the handling vehicle speed threshold, the stability control module and the handling control module are not used to distribute torque.

[0016] Preferably, the handling control module comprises:

[0017] A driving intention analysis module: used to calculate the total motor driving demand torque according to the wheel speed, accelerator pedal opening degree, combined with the motor external characteristic curve and the vehicle architecture, and determine the front and rear axle motor demand driving torque through the front and rear axle torque distribution coefficient;

[0018] A handling algorithm enabling module: used to design a handling intervention and exit mechanism through vehicle state feedback and driver input, perform enabling condition judgment, and finally output a handling algorithm enabling signal;

[0019] A handling motion reference model module: used to set the handling control target as neutral steering according to the input signal of the driver and the current state feedback of the vehicle, so as to generate a handling reference motion state;

[0020] maneuvering direct yaw moment calculation module: for calculating direct yaw moment demand according to maneuvering reference motion state, vehicle state feedback, using feedforward control based on two-degree-of-freedom model combined with anti-windup integral sliding mode feedback control;

[0021] maneuvering motor torque control distribution module: for calculating driving torque output of each driving motor according to direct yaw moment demand and maneuvering control demand, obtaining different tire longitudinal force, realizing vehicle yaw torque control, and finally realizing control effect of improving vehicle maneuverability.

[0022] Preferably, the stability control module comprises:

[0023] drive intention analysis module: for calculating total motor driving demand torque according to wheel speed and accelerator pedal opening degree based on motor external characteristic curve and vehicle architecture, and determining front and rear axle motor demand driving torque through front and rear axle torque distribution coefficient;

[0024] stability algorithm enabling module: for designing stability intervention and exit mechanism based on vehicle state feedback, driver input, maneuvering intervention and exit, and enabling mechanism, and outputting stability algorithm enabling signal;

[0025] stability motion reference model module: for improving vehicle stability and safety, the control target is set to have certain understeering characteristics, and the stability reference motion state is generated;

[0026] stability direct yaw moment calculation module: for calculating stability direct yaw moment demand according to stability reference motion state and vehicle state feedback, using feedforward control based on two-degree-of-freedom model combined with anti-windup integral sliding mode feedback control;

[0027] stability motor torque control distribution module: for calculating driving torque output of each driving motor according to stability control demand, realizing vehicle yaw torque control, and realizing control effect of improving vehicle stability.

[0028] Preferably, the specific way of distributing torque by the maneuvering control module is as follows:

[0029] S1) Collecting left front wheel speed, right front wheel speed, left rear wheel speed, right rear wheel speed, and accelerator pedal opening degree of the vehicle;

[0030] S2) Using the maneuvering algorithm enabling module to determine whether to enable the maneuvering algorithm according to the following manner:

[0031] If the gear signal of the vehicle is D, and the accelerator pedal opening > 0, and the vehicle speed > the steering intervention vehicle speed threshold, and the steering wheel angle absolute value > the steering intervention steering wheel angle threshold, the control algorithm is enabled, and the steering enable signal is output;

[0032] If the gear signal of the vehicle is not D, or the accelerator pedal opening = 0, or the vehicle speed < the steering exit vehicle speed threshold, or the steering wheel angle absolute value < the steering exit steering wheel angle threshold in the continuous cumulative number of control periods, the control algorithm is not enabled;

[0033] S3) Using the driving intention analysis module, the front and rear axle motor demand driving torque is calculated:

[0034] S4) Using the steering motion reference model module, the steering reference yaw rate is calculated according to the following formula:

[0035]

[0036] In the formula, γ ref,h is the steering reference yaw rate, V is the vehicle speed of the vehicle mass center, δ f is the front wheel angle of the vehicle, γ is the yaw rate of the vehicle, i s is the calibration quantity, v x is the longitudinal vehicle speed;

[0037] S5) Using the steering direct yaw moment calculation module, the direct yaw moment demand is calculated according to the following formula:

[0038]

[0039] In the formula, M DB is the additional yaw moment, s is the control error;

[0040] S6) Using the steering motor torque control distribution module, the vehicle yaw torque control is performed according to the following manner:

[0041] ① When the rear axle motor demand driving torque < the driving torque generated by the rear axle motor, both the driving torque and the direct yaw moment demand can be met, and the torque of the left and right wheels is:

[0042]

[0043] In the formula, T rl is the torque of the left wheel, T rr is the torque of the right wheel, T req,r is the torque demand of the rear axle, r w is the wheel rolling radius, M D is the direct yaw torque demand, b is the rear track, η r is the rear wheel motor wheel side reduction ratio;

[0044] When the rear axle motor required driving torque > rear axle motor generated driving torque, the driving torque and the direct yaw moment demand cannot be satisfied at the same time, and the torque of the left and right wheels is:

[0045]

[0046] In the formula, T rl is the torque of the left wheel, T rr is the torque of the right wheel, T max,r is the maximum torque of the rear wheel motor under the constraint condition of meeting the external characteristic, T req,r is the torque demand of the rear axle, η r is the reduction ratio of the rear wheel motor, M D is the direct yaw torque demand.

[0047] Preferably, the specific way of distributing torque by the stability control module is as follows:

[0048] SS1) Collect the gear signal, accelerator pedal opening, vehicle speed, steering wheel angle, lateral acceleration of the vehicle;

[0049] SS2) Use the stability algorithm enable module to determine whether to output the stability algorithm enable signal in the following manner:

[0050] If the gear signal is D, the accelerator pedal opening is > 0, the vehicle speed is > the handling intervention vehicle speed threshold, the steering wheel angle absolute value is > the handling intervention steering angle threshold, and the lateral acceleration is > the stability intervention lateral acceleration or the vehicle speed is > the stability intervention vehicle speed, the enable signal is output;

[0051] If the gear signal is not D, or the accelerator pedal opening is 0, or the vehicle speed is < the exit vehicle speed threshold, or the steering wheel angle absolute value is continuously accumulated for a number of control periods < the exit steering angle threshold, or the lateral acceleration is < the stability intervention lateral acceleration and the vehicle speed is < the intervention vehicle speed, the enable signal is not output;

[0052] SS3) Use the driving intention analysis module to calculate the front and rear axle motor required driving torque:

[0053] SS4) Use the stability motion reference model module to calculate the stability reference yaw rate according to the following formula:

[0054]

[0055] In the formula, γ ref,s is the handling reference yaw rate, V is the vehicle speed of the vehicle mass center, K is the stability factor, δ f is the front wheel angle of the vehicle, γ is the yaw rate of the vehicle, i s is a calibration quantity;

[0056] SS5) using the stability direct yaw moment calculation module, the stability direct yaw moment is calculated according to the following formula:

[0057]

[0058] In the formula, M DB is the additional yaw moment, and s is the control error;

[0059] SS6) using the stability motor torque control distribution module, the vehicle yaw torque control is performed in the following manner:

[0060] ① If the rear axle required driving torque ≤ the maximum driving torque that the rear axle motor can generate, the left and right wheel torques are:

[0061]

[0062] In the formula, T rl is the left wheel torque, T rr is the right wheel torque, T req,r is the rear axle torque requirement, r w is the wheel rolling radius, M D is the direct yaw torque requirement, and b is the rear track width, η r is the rear wheel motor wheel edge reduction ratio;

[0063] ② If the rear axle required driving torque > the maximum driving torque that the rear axle motor can generate, the left and right wheel torques are:

[0064]

[0065]

[0066] In the formula, T rl is the left wheel torque, T rr is the right wheel torque, T max,r is the maximum torque of the rear wheel edge motor under the constraint condition of meeting the external characteristic, T req,r is the rear axle torque requirement, η r is the rear wheel motor wheel edge reduction ratio, and M D is the direct yaw torque requirement;

[0067] Preferably, the specific manner of calculating the generalized required driving force using the driving intention analysis module includes:

[0068] S3-1) According to the accelerator pedal opening degree, the motor torque load coefficient is calculated according to the following formula:

[0069] L D = 100%·Acc_Pedal

[0070] wherein L D is the motor torque load coefficient under driving condition, and Acc_Pedal is the accelerator pedal opening degree;

[0071] S3-2) According to the motor torque load coefficient, the required driving torque on the wheels is calculated according to the following formula:

[0072] T req = L D (η f ·T max,f + 2·η r ·T max,r )

[0073]

[0074] wherein f is the front axle centralized motor, r is the rear axle two wheel edge motors, T req is the required driving torque on the wheels, T max,i is the maximum driving torque provided by the front motor and the rear motor determined by the motor external characteristics, L D is the motor torque load coefficient, T peak,i is the motor peak torque, n i is the current motor speed, n b,i is the motor base speed, and η i is the reduction ratio of the front and rear motors;

[0075] S3-3) According to the required driving torque on the wheels, the front and rear axle motor required driving torque is calculated according to the following formula:

[0076]

[0077] wherein T req,f is the front axle motor required driving torque, T req,r is the rear axle motor required driving torque, K f is the front axle torque distribution coefficient, and T req is the required driving torque on the wheels.

[0078] Preferably, the handling control module and the stability control module are further involved in a transition phase, which specifically includes:

[0079] A) Establishing a vehicle speed-lateral acceleration-handling stability coordination coefficient MAP diagram;

[0080] B) Collecting three motor torques output by the handling module and three motor torques output by the stability module, and collecting the vehicle speed and lateral acceleration of the vehicle;

[0081] C) combining the vehicle speed-lateral acceleration-handling stability coordination coefficient MAP, determining the handling stability coordination coefficient according to the vehicle speed and the lateral acceleration of the vehicle;

[0082] D) calculating the front motor output torque, the left rear motor output torque, the right rear motor output torque according to the motor torque collected in step B) and the handling stability coordination coefficient determined in step C) according to the following formula:

[0083] T F = T F_Stab k Coop + T F_Hand (1-k Coop )

[0084] T RL = T RL_Stab k Coop + T RL_Hand (1-k Coop )

[0085] T RR = T RR_Stab k Coop + T RR_Hand (1-k Coop )

[0086] In the formula, T F is the front motor target output torque after the weighted connection processing, T RL is the left rear motor target output torque after the weighted connection processing, T RR is the right rear motor target output torque after the weighted connection processing, T F_Stab is the first motor torque output by the stability module, T RL_Stab is the second motor torque output by the stability module, T RR_Stab is the third motor torque output by the stability module, T F_Hand is the first motor torque output by the handling module, T RL_Hand is the second motor torque output by the handling module, T RR_Hand is the third motor torque output by the handling module, and k Coop is the handling stability coordination coefficient;

[0087] E) controlling the real-time output torque of the front motor of the vehicle to be equal to the front motor target output torque, the real-time output torque of the left rear motor to be equal to the left rear motor target output torque, and the real-time output torque of the right rear motor to be equal to the right rear motor target output torque.

[0088] The beneficial effects of the present application are as follows:

[0089] The application can keep the vehicle steering at low speed and keep the vehicle stable at high speed by setting a steering control module and a stability control module, and greatly improves the steering stability of the vehicle.

[0090] The application can make the steering control module and the stability control module smoothly transition and switch, so as to ensure that the control effect of the vehicle is always at a high level, and the vehicle does not lose stability.

[0091] The application has the following advantages:

[0092] The application adopts a distributed drive system and adds multiple function modules without increasing additional chassis components, so that the tracking performance of the vehicle on different adhesion road surfaces is improved to adapt to various road conditions, and the steering and stability of the vehicle are improved without increasing additional costs.

[0093] The distributed drive system has the characteristics of fast response speed, high precision and high efficiency, which can improve the steering response ability of the vehicle and improve the safety of the vehicle during driving.

[0094] The distributed drive system can effectively control the yaw within a certain scale, improve the steering stability of the vehicle, and does not need to cause additional burden to the brake system.

[0095] Nomenclature

[0096] Vehicle steering: refers to the ability of the vehicle to accurately and quickly respond to the actions and behaviors of the driver to realize the expected steering, acceleration and other operations of the driver.

[0097] Vehicle stability: refers to the ability of the vehicle to maintain stability and not to lose control during driving.

[0098] Enable Module: a functional unit in an electronic system used to control the working state of other circuits or modules. Only when the enable signal meets certain conditions, the controlled circuit or module can work according to the design requirements. English often expresses it as "Enable Module". Enable module is like a "switch controller" of the circuit. It receives an enable signal, which can be high, low, or a specific sequence of digital logic signals. When the enable signal is valid, the enable module will trigger or allow the circuit module connected to it to start working, change working mode or maintain a specific state; when the enable signal is invalid, the controlled circuit module may stop working, enter low-power mode or maintain the current state unchanged. For example, in a microprocessor, some functional units (such as multipliers, dividers) may be in standby state at ordinary times, and only when the enable signal arrives, the corresponding operation will be performed.

[0099] Closed-loop tracking accuracy: refers to the degree to which the actual output value of the system can accurately follow the target input value in a closed-loop system with feedback control. It is an important indicator to measure the performance of a closed-loop control system. BRIEF DESCRIPTION OF DRAWINGS

[0100] Figure 1 Flowchart of the present application;

[0101] Figure 2 Flowchart of the enable condition judgment of the manipulability algorithm enable module in the present embodiment;

[0102] Figure 3 Dynamics model of the vehicle in the present embodiment;

[0103] Figure 4 Schematic diagram of the feedforward control module in the present embodiment;

[0104] Figure 5 Schematic diagram of the feedforward control intervention coefficient in the present embodiment;

[0105] Figure 6 Flowchart of the stability control algorithm condition judgment in the present embodiment;

[0106] Figure 7 Schematic diagram of the manipulability stability coordination coefficient in the present embodiment. DETAILED DESCRIPTION

[0107] As Figures 1 to 7 shown, a torque distribution method of a distributed drive system of a new energy vehicle, comprising the following steps:

[0108] 1) In the distributed drive system of a new energy vehicle, a handling control module is arranged for torque distribution when the vehicle is turning, to improve the handling of the vehicle; a stability control module is arranged for torque distribution when the vehicle is turning, to improve the stability of the vehicle; a handling stability coordination module is arranged for smooth transition and switching of the handling control module and the stability control module;

[0109] 2) The handling vehicle speed threshold, the stability vehicle speed threshold, the handling lateral acceleration threshold and the stability lateral acceleration threshold are set;

[0110] 3) The vehicle speed, lateral acceleration and steering wheel angle of the new energy vehicle are collected, and the following method is used to determine which control module is used for torque distribution:

[0111] If the steering wheel angle ≠ 0, the handling vehicle speed threshold ≤ vehicle speed < stability vehicle speed threshold, and the handling lateral acceleration threshold ≤ lateral acceleration < stability lateral acceleration threshold, the handling control module is used for torque distribution;

[0112] If the steering wheel angle ≠ 0, the vehicle speed ≥ stability vehicle speed threshold, and the lateral acceleration ≥ lateral acceleration threshold, the stability control module is used for torque distribution;

[0113] If the steering wheel angle = 0, or the vehicle speed < handling vehicle speed threshold, the stability control module and the handling control module are not used for torque distribution.

[0114] According to the above method, the following implementation is made:

[0115] 1) In the distributed drive system of a new energy vehicle, a handling control module is arranged for torque distribution when the vehicle is turning, to improve the handling of the vehicle; a stability control module is arranged for torque distribution when the vehicle is turning, to improve the stability of the vehicle; a handling stability coordination module is arranged for smooth transition and switching of the handling control module and the stability control module;

[0116] In this embodiment, the handling control module comprises:

[0117] A driving intention analysis module is used to calculate the total motor driving demand torque according to the wheel speed, accelerator pedal opening degree and other information, and to determine the front and rear axle motor demand driving torque through the front and rear axle torque distribution coefficient, in combination with the motor external characteristic curve and the vehicle architecture;

[0118] A handling algorithm enabling module is used to design a handling intervention and exit mechanism through vehicle state feedback, driver input and other information, to determine the enabling condition, and finally output a handling algorithm enabling signal;

[0119] maneuverability reference model module: for setting the maneuverability control target as neutral steering according to the driver's input signal and the vehicle current state feedback, thereby generating the maneuverability reference motion state;

[0120] maneuverability direct yaw moment calculation module: for calculating the direct yaw moment demand according to the maneuverability reference motion state, vehicle state feedback and other information, using the method of combining feedforward control based on a two-degree-of-freedom model with anti-windup integral sliding mode feedback control;

[0121] maneuverability motor torque control distribution module: for calculating the driving torque output of each driving motor according to the direct yaw moment demand and maneuverability control demand, obtaining different tire longitudinal forces, realizing vehicle yaw torque control, and finally realizing the control effect of improving vehicle maneuverability.

[0122] In the embodiment, the stability control module comprises:

[0123] drive intention analysis module: for calculating the total motor driving demand torque according to the wheel speed, accelerator pedal opening degree and other information, combining the motor external characteristic curve and the overall vehicle architecture, and determining the front and rear axle motor demand driving torque through the front and rear axle torque distribution coefficients;

[0124] stability algorithm enabling module: for designing the stability intervention and exit mechanism based on the maneuverability intervention and exit and enabling mechanism through the vehicle state feedback and driver input and other information, and outputting the stability algorithm enabling signal;

[0125] stability motion reference model module: for setting the control target as having a certain understeering characteristic to improve vehicle stability and safety, thereby generating the stability reference motion state;

[0126] stability direct yaw moment calculation module: for calculating the stability direct yaw moment demand according to the stability reference motion state and vehicle state feedback, using the method of combining feedforward control based on a two-degree-of-freedom model with anti-windup integral sliding mode feedback control;

[0127] stability motor torque control distribution module: for calculating the driving torque output of each driving motor according to the stability control demand, realizing vehicle yaw torque control, and realizing the control effect of improving vehicle stability.

[0128] 2) Set the maneuverability vehicle speed threshold, stability vehicle speed threshold, maneuverability lateral acceleration threshold and stability lateral acceleration threshold;

[0129] Vehicle handling is the ability of the vehicle to accurately and quickly respond to the driver's actions and behaviors to achieve the driver's expected steering, acceleration and other operations. In the present embodiment, the main function of the handling control algorithm is to make the vehicle steering characteristics biased to neutral steering and improve the vehicle steering response ability in general steering conditions through torque distribution control, so as to improve the vehicle handling.

[0130] Vehicle stability is the ability of the vehicle to maintain stability and not to be out of control during driving. In the present embodiment, the main function of the stability control algorithm is to increase the understeering characteristics of the vehicle in the steering condition with potential instability risk through torque distribution control, thereby preventing the vehicle from sliding and losing stability, so as to improve the stability and safety of the vehicle.

[0131] According to the above analysis, it can be known that the stability control algorithm has a higher priority in the coordination control because it involves the guarantee of vehicle safety. In combination with the enabling condition of the stability control algorithm, the applicable working condition of the stability control algorithm can be obtained:

[0132] ①First, the basic conditions for enabling the stability control algorithm are met, including correct gear and zero brake pedal opening.

[0133] ②The steering condition is met, that is, there is a certain vehicle speed and a certain steering wheel angle.

[0134] ③The vehicle driving state has potential instability risk: it can be judged from two dimensions of vehicle speed and lateral acceleration. The lateral acceleration can directly reflect the severity of the vehicle steering, the higher the lateral acceleration, the more severe the steering and side slip, and the higher the risk of potential vehicle side slip instability; the higher the vehicle speed, the greater the yaw rate and lateral acceleration generated by the same steering wheel angle, and the response is often more rapid, which is more likely to cause instability. Due to the existence of the above potential risks, the three working conditions of high speed and low side slip, low speed and high side slip, and high speed and high side slip are all applicable working conditions of the stability control algorithm.

[0135] The applicable working condition of the handling control algorithm is the working condition without the above potential risks in the basic condition and the steering condition, that is, the low speed and low side slip steering condition. The working conditions of the handling control algorithm and the stability control algorithm are shown in Table 1:

[0136] Table 1 Applicable working condition analysis

[0137]

[0138] The switching condition from the maneuverability control algorithm to the stability control algorithm has two, namely the vehicle speed exceeds the stability vehicle speed threshold value with potential risk, or the lateral acceleration exceeds the stability lateral acceleration threshold value; and the condition from the stability control algorithm to the maneuverability control algorithm is that the vehicle speed and lateral acceleration do not reach the stability risk threshold value.

[0139] 3) Collect the vehicle speed, lateral acceleration, steering wheel angle of the new energy vehicle, and determine which control module to use for torque distribution in the following manner:

[0140] If the steering wheel angle ≠ 0, the maneuverability vehicle speed threshold value ≤ the vehicle speed < the stability vehicle speed threshold value, and the maneuverability lateral acceleration threshold value ≤ the lateral acceleration < the stability lateral acceleration threshold value, then the maneuverability control module is used for torque distribution;

[0141] If the steering wheel angle ≠ 0, the vehicle speed ≥ the stability vehicle speed threshold value, and the lateral acceleration ≥ the lateral acceleration threshold value, then the stability control module is used for torque distribution;

[0142] If the steering wheel angle = 0, or the vehicle speed < the maneuverability vehicle speed threshold value, then the stability control module and the maneuverability control module are not used for torque distribution.

[0143] In this embodiment, the specific manner of using the maneuverability control module to distribute torque is as follows:

[0144] S1) Collect the left front wheel speed, right front wheel speed, left rear wheel speed, right rear wheel speed, and accelerator pedal opening of the vehicle;

[0145] S2) Use the maneuverability algorithm enable module to determine whether to enable the maneuverability algorithm in the following manner:

[0146] The enable module block diagram of the maneuverability improvement control algorithm is shown in Figure 2 When the Handling_Enable signal is 1, the control algorithm is enabled, and when Handling_Enable = 0, the control algorithm is not enabled (the vehicle reference motion model module continues to calculate the reference yaw rate, but the yaw rate tracking module is disabled, i.e. the direct yaw moment output M D = 0).

[0147] The maneuverability algorithm is mainly aimed at the turning working condition at medium and high vehicle speeds (not exceeding the stability intervention vehicle speed), and needs to consider the fluctuation of actual sensor signals to prevent false intervention in straight running working conditions. The above principles are used to design the following enable conditions. The implementation of the enable module uses one-time logical judgment. When all the following conditions are met at the same time, Handling_Enable is set to 1, and the maneuverability algorithm is enabled:

[0148] The gear signal of the vehicle is D, the accelerator pedal opening is > 0 (i.e. the driver steps on the accelerator pedal), the vehicle speed is > the steering intervention vehicle speed threshold, and the steering wheel angle absolute value is > the steering intervention angle threshold, then the control algorithm is enabled, and the steering enable signal is output;

[0149] When any one of the following conditions is met, Handling_Enable is set to 0, and the steering algorithm is not available:

[0150] The gear signal of the vehicle is not D, or the accelerator pedal opening is = 0 (i.e. the driver does not step on the accelerator pedal), or the vehicle speed is < the steering exit vehicle speed threshold, or the steering wheel angle absolute value is < the steering exit angle threshold for a number of consecutive control periods, then the control algorithm is not enabled;

[0151] Table 1 Input signals of the steering algorithm enable module

[0152]

[0153] Table 2 Output signals of the steering algorithm enable module

[0154]

[0155] S3) The specific way of calculating the front and rear axle motor demand driving torque using the driving intention analysis module includes:

[0156] Generally speaking, the requirement of accelerator pedal analysis is close to linear, and overall, the throttle is biased "hard" when the vehicle speed is low, and conversely, the throttle is biased "soft" when the vehicle speed is high, so as to achieve good throttle pedal feeling. Since the accelerator pedal analysis curve can be fine-tuned, in order to meet general or typical conditions, the driving intention analysis module here temporarily adopts linear accelerator pedal analysis, and according to the four wheel speeds, accelerator pedal opening and other information, the front axle motor demand torque and rear axle motor are obtained, then the accelerator pedal opening is analyzed in a linear manner, i.e. the motor torque load coefficient and the accelerator pedal opening have a linear corresponding relationship, as shown in equation (3.1.1).

[0157] S3-1) According to the accelerator pedal opening, the motor torque load coefficient is calculated according to the following formula:

[0158] L D = 100% Acc_Pedal (3.1.1)

[0159] In the formula, L D is the motor torque load coefficient under driving conditions, and Acc_Pedal is the accelerator pedal opening;

[0160] S3-2) According to the motor torque load coefficient, the demand wheel driving torque is calculated according to the following formula:

[0161] T req = L D (η f · T max,f + 2 · η r · T max,r )

[0162]

[0163] where f is the front axle concentrated motor, r is the rear axle two wheel edge motors, T req is the required wheel driving torque, T max,i is the maximum driving torque provided by the front motor and rear motor determined by the motor external characteristics, L D is the motor torque load coefficient, T peak,i is the motor peak torque, n i is the current motor speed, n b,i is the motor base speed, η i is the front and rear motor reduction ratio;

[0164] S3-3) According to the required wheel driving torque, the front and rear axle motor required driving torque is calculated in the following manner:

[0165] The motor driving torque allocated to the front and rear axle is T req,f , T req,r . Define the front axle torque allocation coefficient K f , that is, the ratio of the torque allocated to the front axle wheel to the total required torque:

[0166]

[0167] where the total required torque satisfies the following formula:

[0168] T req = T req,f · η f + T req,r · η r (3.1.4)

[0169] Therefore, according to the front axle torque allocation coefficient and the total required torque, the front and rear axle driving motor torque is allocated as follows:

[0170]

[0171] where T req,f is the front axle motor required driving torque, T req,r is the rear axle motor required driving torque, K f is the front axle torque allocation coefficient, T req is the required wheel driving torque.

[0172] Specifically, after front-to-rear axle distribution, if the torque demanded on either the front or rear axle exceeds the external characteristics of the motor on that axle, the excess torque will be shifted to the other axle to prioritize the driver's driving intent. In this case, the ratio of the front axle torque demand to the total torque demand may not necessarily satisfy the input value for the front axle distribution coefficient.

[0173] Table 3 Input signals of driving intention analysis module

[0174]

[0175] Table 4 Output signals of driving intention analysis module

[0176]

[0177] S4) Calculate the maneuverability reference yaw rate using the maneuverability motion reference model module in the following manner:

[0178] The vehicle maneuverability is studied using a linear two-degree-of-freedom vehicle model, such as Figure 3 In order to study the maneuverability of the vehicle, in the linear two-degree-of-freedom vehicle model, it is assumed that the vehicle only moves in a plane parallel to the ground, and the longitudinal speed of the vehicle is a constant. At this time, the vehicle has two degrees of freedom: yaw rate and sideslip angle of the center of mass.

[0179] By designing a control method, the actual vehicle is made to track the reference model as closely as possible. To design the control law, the above model is further simplified, assuming that the inner and outer wheels have the same tire model, that is, the tire sideways characteristics are consistent, thus obtaining the state space form of the vehicle model:

[0180] C =

[01] , D = 0, x = [βγ] T , u=δ f , y = γ

[0181] Where m is the vehicle mass, J z is the vehicle's yaw moment of inertia, C f is the cornering stiffness of the front axle, C r is the cornering stiffness of the rear axle, l f is the distance from the vehicle's center of mass to the front axle, l r is the distance from the vehicle's center of mass to the rear axle, V is the speed of the vehicle's center of mass, β is the sideslip angle at the vehicle's center of mass, γ is the vehicle's yaw rate, and δ f is the front wheel turning angle of the vehicle.

[0182] Thus, the second-order system transfer function from the front wheel angle input to the yaw rate response can be obtained:

[0183]

[0184] The steady-state gain of the system to the front wheel steering angle can be designed according to formula (3.3.2) as follows:

[0185]

[0186] In the formula, K is a stability factor;

[0187] In the stability control, the control target is quite different from that in the handling control. In the handling control, the control target is to make the vehicle steering characteristic deviate to neutral steering in order to improve the handling of the vehicle and the driving experience of the driver, so the stability factor K is set to 0, and the handling reference motion state can be obtained.

[0188] In the handling reference motion state, it is set to 0, i.e. the reference vehicle steering characteristic of the handling control is neutral steering, and the handling reference yaw rate when K = 0 can be obtained from formula (3.3.3) as follows:

[0189]

[0190] That is, the handling reference yaw rate is determined by the vehicle parameters, the current vehicle speed and the stability factor.

[0191] At the same time, considering the limitation of the road condition (a y ≤ μg) and the small vehicle mass side slip angle, the handling yaw rate limited by the road condition can be obtained according to the two-degree-of-freedom single-track model of the vehicle as follows:

[0192]

[0193] In the formula, i s is a calibration quantity, which is temporarily set to 0.85 according to experience, and can be adjusted according to the actual situation.

[0194] In summary, the handling reference yaw rate is as follows:

[0195]

[0196] In the formula, γ ref,h is the handling reference yaw rate, V is the vehicle speed of the vehicle mass center, δ f is the front wheel steering angle of the vehicle, γ is the yaw rate of the vehicle, i s is a calibration quantity, v x is the longitudinal vehicle speed.

[0197] Table 5 Input signals of the handling motion reference model module

[0198]

[0199] Table 6 Output signals of the handling motion reference model module

[0200]

[0201] S5) Calculate the direct yaw moment demand by the handling direct yaw moment calculation module in the following way:

[0202] The handling direct yaw moment calculation module calculates the direct yaw moment demand to improve the current vehicle motion state according to the ideal state of the reference vehicle model, vehicle state feedback, etc., and outputs it to the motor torque control distribution module for further distribution. This module includes a feedforward control module based on a two-degree-of-freedom vehicle model and an anti-saturation integral sliding mode feedback control module, and to prevent the front-wheel feedforward yaw moment from being too large to cause vehicle instability at a large side slip, a feedforward exit mechanism is included.

[0203] S5-1) Feedforward control algorithm design

[0204] Let the feedforward control yaw moment be M DF , and the feedforward coefficient be K f , then M DF = K f δ f . Substituting equation (3.3.1), the yaw motion dynamics equation of the vehicle can be expressed as:

[0205]

[0206] The corresponding B in equation (3.3.1) is changed to:

[0207]

[0208] Thus, the second-order system transfer function of the front wheel steering angle input to the yaw rate response can be obtained:

[0209]

[0210] According to equation (3.4.2), the steady-state gain of the system to the front wheel steering angle can be designed as:

[0211]

[0212] K is a stability factor, which can be adjusted according to the actual situation. When K = 0, the steady-state gain of the reference is the steady-state gain when the vehicle is neutrally steered, and the corresponding handling feedforward coefficient K f_H can be solved as:

[0213]

[0214] The feedforward control module is constructed in the above way (such as Figure 4As shown), the main function corresponds to formula (3.4.4), which is used to calculate the maneuverability feedforward coefficient K in real time f_H The maneuverability feedforward coefficient is multiplied by the front wheel angle and the feedforward control intervention coefficient k DF , the corresponding feedforward control torque can be obtained.

[0215] The feedforward control intervention coefficient k DF like Figure 5 This is because under large cornering conditions, the feedforward control based on the linear two-degree-of-freedom model is no longer accurate due to the changes in the cornering stiffness of the front and rear axles. The main function of the maneuvering feedforward yaw moment is to shift the vehicle's steering characteristics toward neutral steering or even oversteering. Excessive feedforward control may actually exacerbate vehicle instability. To prevent system chatter, a transition period should be included when exiting feedforward control.

[0216] S5-2) Feedback control algorithm design

[0217] In order to improve the robustness of yaw rate error feedback control to modeling errors and external disturbances, sliding mode control is used to achieve the tracking of vehicle yaw rate to reference yaw rate.

[0218] Motion tracking error (yaw angular velocity error γ e )for:

[0219] γ e =γ-γ ref (3.4.6)

[0220] In order to quickly reach the reference state, the constant speed approach law is selected:

[0221]

[0222] Here, k>0 and is a constant, indicating the rate of approaching the sliding surface; the larger k is, the faster the approach speed.

[0223] Therefore, the additional yaw moment applied is:

[0224] M DB =-J z ksgn(γ e )=-k p sgn(γ e ) (3.4.8)

[0225] k p It is generally designed to be large enough within the allowable control capability to allow the error to converge quickly.

[0226] The disadvantage of sliding mode control is that the discontinuous characteristics of the sliding surface near the sliding surface cause the control signal to jitter, affecting the control effect. To eliminate the jitter problem of the sliding mode controller, a saturation function is generally used instead of a sign function to design the control law, obtaining a continuous sliding mode control law. Therefore, the additional yaw moment is changed to:

[0227]

[0228] where θ>0 is the thickness of the saturation function boundary layer. If θ is too large, the control signal will be unstable, and if it is too small, the control signal will jitter.

[0229] Using a saturation function can improve chattering, but at the same time it will produce tracking errors. Sliding mode integral control can improve the response in the boundary layer and reduce errors. In addition, considering integral saturation, an anti-integral saturation sliding mode controller is designed.

[0230] The error variable is selected as:

[0231] s = γ e + k i σ (3.4.10)

[0232] where k i is the control coefficient of error integration, and σ is dynamic:

[0233]

[0234] Therefore, the motion tracking additional yaw moment after adding anti-integral saturation is:

[0235]

[0236] where M DB is the additional yaw moment, and s is the control error.

[0237] When the control error |s|≥θ, M DB =-k p sgn(s), which makes the error quickly approach the sliding surface. When |s|<θ, there is:

[0238]

[0239] The integral term k i can help the control to reduce the error and improve the control effect in the sliding surface. Generally, the larger k i is, the smaller the steady-state error is, but the adjustment time will be increased.

[0240] Table 7 Input signals of the direct yaw moment calculation module for maneuverability

[0241]

[0242]

[0243] Table 8 Output signal of steering direct yaw moment calculation module

[0244]

[0245] S6) Using the steering motor torque control distribution module, the vehicle yaw torque control is performed in the following manner:

[0246] The module calculates the driving torque of each driving motor by considering the motor power, torque limit, and battery charge and discharge limit conditions, and finally controls the output of each driving motor to obtain different tire longitudinal forces, thereby realizing vehicle yaw torque control.

[0247] S6-1) Constraints of motor external characteristics, road adhesion conditions, peak power, and fault diagnosis torque limit on output torque

[0248] The constraints of motor output torque mainly include motor external characteristics, road adhesion conditions, peak power, and fault diagnosis torque limit.

[0249] When determining the motor external characteristics, the power supply voltage of the motor and the power supply power of the battery should be considered. The peak power of the front axle concentrated motor is 255 kW, and the rated power is 80 kW. The peak power of the rear axle wheel motor is 135 kW, and the rated power is 80 kW. The total peak power requirement is 390 kW. Since Qingshan has not yet provided the 10s maximum discharge power of the battery, it is temporarily considered that the battery power can fully exert the ability of the motor external characteristics, i.e., the motor external characteristics in the simulation test use the data under the peak power of the motor.

[0250] The road adhesion constraint condition is as follows:

[0251]

[0252] In the formula, k = fl, fr, rl, and rr represent the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel, respectively. In the road adhesion constraint, the longitudinal-lateral combined adhesion coefficient θ xy,k can be obtained through online parameter identification, while the tire vertical force F z,k and the tire lateral force F y,k can be estimated by longitudinal and lateral acceleration.

[0253] In particular, when the motor occurs a level 3 fault, the motor can still operate, but the fault diagnosis module will send the output torque limit value at level 3 fault, which needs to be compared with other output torque constraint conditions to finally generate the maximum and minimum values of the motor output torque.

[0254] S6-2) Strategy of torque distribution for rear axle left and right motor

[0255] In the handling module and the stability module, the principle of torque distribution strategy will be different due to different control objectives. In the case of small direct yaw moment demand and small driving torque demand, both demands can be met at the same time. However, when the direct yaw moment and the driving torque demand are both large, they may conflict. When handling is the main control objective, the driver's intention to accelerate during steering should be guaranteed, otherwise the driver will feel the loss of power, so the driving torque should be guaranteed first, and the remaining capacity of the motor after longitudinal acceleration is used to generate direct yaw moment to minimize the weakening of acceleration on the improvement effect of handling under the principle of guaranteeing power.

[0256] The relationship between direct yaw moment and rear wheel driving torque is as follows:

[0257]

[0258] In the formula, b is the rear track; r w is the wheel rolling radius, T rr and T rl are the right rear wheel and left rear wheel motor driving torque respectively, η r is the rear wheel motor wheel edge reduction ratio.

[0259] Suppose that the driving torque (not multiplied by the reduction ratio) generated by the rear axle motor is T r_axle,max when it can just meet the driving torque demand and the direct yaw moment at the same time. This value can be used as a critical value to determine whether the direct yaw moment demand and the driving torque demand can be met at the same time. When the actual rear axle driving torque demand is less than T r_axle,max , both demands can be met at the same time; when the actual rear axle driving torque demand is equal to T r_axle,max , one side motor reaches the maximum output limit value and the other side motor output is the limit value minus the differential torque, at this time, the driving and direct yaw moment demands are met at the same time; when the actual rear axle driving torque demand is greater than T r_axle,max , only one of them can be met. The formula of T r_axle,max is as follows:

[0260]

[0261] In the formula, T max,r is the maximum torque of the rear wheel edge motor under the constraint condition of meeting the external characteristic.

[0262] It is known that the torque demand of the rear axle is T req,r , the direct yaw torque demand is M D , and the maximum torque of the rear wheel edge motor under the constraint condition of meeting the external characteristic is T max,rAccording to the above distribution principle, the left and right wheel torque distribution in the maneuverability module is divided into the following two cases:

[0263] When the rear axle motor required driving torque T req,r is greater than the rear axle motor generated driving torque T r_axle,max , the driving torque and the direct yaw moment demand can be met, and the left and right wheel torques are:

[0264]

[0265] wherein T rl is the torque of the left wheel, T rr is the torque of the right wheel, T req,r is the torque demand of the rear axle, r w is the wheel rolling radius, M D is the direct yaw torque demand, b is the rear wheel track, and η r is the rear wheel motor wheel edge reduction ratio.

[0266] When T req,r is greater than T r_axle,max , the driving torque and the direct yaw moment demand cannot be met at the same time, in the maneuverability module, in order to improve the comprehensive driving experience of the driver, it is necessary to give priority to guarantee the driving torque demand, and prevent the driver from feeling that the vehicle power is lost. It should be noted that since one of the rear motors reaches the maximum output torque at this time, the driving torque demand minus the output torque of the rear motor is the output torque of the other rear motor. In this case, the left and right wheel torques are:

[0267] When the rear axle motor required driving torque T req,r is greater than the rear axle motor generated driving torque T r_axle,max , the driving torque and the direct yaw moment demand cannot be met at the same time, and the left and right wheel torques are:

[0268]

[0269] wherein T rl is the torque of the left wheel, T rr is the torque of the right wheel, T max,r is the maximum torque of the rear wheel edge motor under the constraint condition of meeting the external characteristic, T req,r is the torque demand of the rear axle, η r is the rear wheel motor wheel edge reduction ratio, and M D is the direct yaw torque demand.

[0270] Table 9 Input signals of the maneuverability motor torque control distribution module

[0271]

[0272] Table 10 Output signal of the maneuverability motor torque control distribution module

[0273]

[0274] In this embodiment, the specific way of distributing torque by the stability control module is as follows:

[0275] SS1) Collect the gear signal, accelerator pedal opening, vehicle speed, steering wheel angle, lateral acceleration of the vehicle;

[0276] SS2) Use the stability algorithm enable module to determine whether to output the stability algorithm enable signal in the following manner:

[0277] The block diagram of the stability improvement control algorithm enable module is shown in Figure 6 When the Stability_Enable signal is 1, the control algorithm is enabled, and when Stability_Enable = 0, the control algorithm is not enabled. The stability algorithm is mainly aimed at the turning conditions that reach the stability intervention vehicle speed and the stability intervention lateral acceleration, so the prerequisite for enabling the stability algorithm is to first meet the maneuverability algorithm enable condition, and the stability vehicle speed and lateral acceleration criterion is added. The following enable condition is designed according to the above principle. The specific implementation of the stability algorithm uses one-time logical judgment. When all the following conditions are met at the same time, Stability_Enable is set to 1, and the stability algorithm is enabled:

[0278] The gear signal is D, the accelerator pedal opening is > 0, i.e. the driver is stepping on the accelerator pedal, the vehicle speed is > the maneuverability intervention vehicle speed threshold, the steering wheel angle absolute value is > the maneuverability intervention angle threshold, the lateral acceleration reaches the stability intervention lateral acceleration, or the vehicle speed reaches the stability intervention vehicle speed, then the enable signal is output;

[0279] When any of the following conditions is met, Stability_Enable is set to 0, and the stability algorithm is not enabled:

[0280] The gear signal is not D, or the accelerator pedal opening is 0, i.e. the driver is not stepping on the accelerator pedal, or the vehicle speed is < the exit vehicle speed threshold, or the steering wheel angle absolute value is continuously accumulated < the exit angle threshold for a number of control periods to consider sensor signal fluctuations and prevent straight-line working conditions from being misintervened, or the lateral acceleration is < the stability intervention lateral acceleration and the vehicle speed is < the intervention vehicle speed, then the enable signal is not output;

[0281] It can be seen that the gear signal is D, the accelerator pedal opening is greater than 0, that is, the driver steps on the accelerator pedal, the vehicle speed is greater than the steering intervention vehicle speed threshold, and the steering wheel angle absolute value is greater than the steering intervention steering wheel angle threshold, which is the basic condition shared by the steering and stability algorithm; the lateral acceleration reaches the stability intervention lateral acceleration, or the vehicle speed reaches the stability intervention vehicle speed, which is the unique judgment condition of the stability algorithm, by setting the lateral acceleration and vehicle speed conditions, the stability control algorithm is enabled under the three potential dangerous steering scenarios of low vehicle speed and large side slip, high vehicle speed and small side slip, and high vehicle speed and high side slip.

[0282] Table 11 Stability algorithm enable module input signal

[0283]

[0284] Table 12 Stability algorithm enable module output signal

[0285]

[0286] SS3) The specific way of calculating the front and rear axle motor demand driving torque by using the driving intention analysis module includes:

[0287] The stability algorithm driving intention analysis is the same as the steering algorithm driving intention analysis, as follows:

[0288] SS3-1) According to the accelerator pedal opening, the motor torque load coefficient is calculated according to the following formula:

[0289] L D =100%·Acc_Pedal

[0290] In the formula, L D is the motor torque load coefficient under driving conditions, and Acc_Pedal is the accelerator pedal opening;

[0291] SS3-2) According to the motor torque load coefficient, the demand wheel driving torque is calculated according to the following formula:

[0292] T req =L D (η f ·T max,f +2·η r ·T max,r )

[0293]

[0294] In the formula, f is the front axle concentrated motor, r is the rear axle two wheel edge motors, T req is the demand wheel driving torque, T max,i is the maximum driving torque that the front motor and rear motor can provide determined by the motor external characteristic, and LD is the motor torque load factor, T peak,i is the peak torque of the motor, n i is the current speed of the motor, n b,i is the motor base speed, η i is the reduction ratio of the front and rear motors;

[0295] SS3-3) Based on the required wheel drive torque, calculate the required drive torque of the front and rear axle motors according to the following formula:

[0296]

[0297] Where, T req,f is the required driving torque of the front axle motor, T req,r is the required driving torque of the rear axle motor, K f is the front axle torque distribution coefficient, T req is the required wheel drive torque.

[0298] Specifically, after front-to-rear axle distribution, if the torque demanded on either the front or rear axle exceeds the external characteristics of the motor on that axle, the excess torque will be shifted to the other axle to prioritize the driver's driving intent. In this case, the ratio of the front axle torque demand to the total torque demand may not necessarily satisfy the input value for the front axle distribution coefficient.

[0299] Table 13 Input signals of driving intention analysis module

[0300]

[0301] Table 14 Output signals of the driving intention analysis module

[0302]

[0303] SS4) Using the stability motion reference model module, calculate the stability reference yaw rate as follows:

[0304] Similar to the Maneuverability module, a linear two-degree-of-freedom vehicle model is used to study vehicle stability. To investigate vehicle stability, the linear two-degree-of-freedom vehicle model assumes that the vehicle moves only in a plane parallel to the ground, with a constant longitudinal velocity. The vehicle then has two degrees of freedom: yaw rate and sideslip angle.

[0305] However, in stability control, the control goal is to improve vehicle stability, so the stability factor K must be set to a positive number so that the vehicle's reference motion state has a certain understeer characteristic, thereby improving the vehicle's stability and safety under high-speed or large side deviation conditions.

[0306] From formula (3.3.3), we can get the stability reference yaw rate when K is a positive number:

[0307]

[0308] i.e. stability reference yaw rate γ ref,s determined by vehicle parameters, current vehicle speed, stability factor.

[0309] Meanwhile, considering the limitation of road condition (a y ≤ μg) and small vehicle sideslip angle, the stability yaw rate limited by road condition can be obtained according to two-degree-of-freedom single-track model of vehicle:

[0310]

[0311] In summary, the stability reference yaw rate γ ref,s is:

[0312]

[0313] where γ ref,s is the handling reference yaw rate, V is the vehicle speed of vehicle mass center, K is the stability factor, δ f is the front wheel steering angle of vehicle, γ is the yaw rate of vehicle, i s is the calibration value.

[0314] Table 15 Input signals of stability motion reference model module

[0315]

[0316] Table 16 Output signals of stability motion reference model module

[0317]

[0318] SS5) Calculate the stability direct yaw moment by using stability direct yaw moment calculation module in the following way:

[0319] The function and internal structure of stability direct yaw moment calculation module are similar to those of handling direct yaw moment calculation module. Its main function is to calculate the stability direct yaw moment and hand it over to the lower controller for distribution. Its structure contains a feedforward control module based on two-degree-of-freedom vehicle model and an anti-windup integral sliding mode feedback control module, in which the anti-windup integral sliding mode feedback control module is consistent with that in the handling module, while the stability feedforward control part is quite different.

[0320] SS5-1) Stability feedforward control algorithm design

[0321] According to the design of handling stability feedforward control algorithm, the yaw motion dynamics equation of vehicle can be expressed as:

[0322]

[0323] where M DF is the feedforward control yaw moment, K f is the feedforward coefficient, M DF = K f δ f .

[0324] The B in the corresponding state equation formula (3.3.1) is changed to:

[0325]

[0326] Thus, the second-order system transfer function of the front wheel steering angle input to the yaw rate response is obtained:

[0327]

[0328] According to formula (4.3.2), the steady-state gain of the system to the front wheel steering angle can be designed as:

[0329]

[0330] K is a stability factor. In stability control, in order to make the vehicle have a certain understeer characteristic, K cannot be equal to 0, but the stability factor K needs to be set to a normal number, from which the corresponding stability feedforward coefficient K f_S is:

[0331]

[0332] The main function of the feedforward control module corresponds to formula (4.3.4), which calculates the stability feedforward coefficient K f_S in real time. The stability feedforward coefficient is multiplied by the front wheel steering angle, the stability feedforward control gain, and the change rate and absolute value of the feedforward yaw moment are limited, and the corresponding stability feedforward control moment is obtained.

[0333] Considering that a sudden or too large direct feedforward yaw moment under large sideslip may cause the vehicle to slide or lose stability, leading to potential danger, the Rate Limiter and Saturation modules are used to limit the change rate and maximum value of the stability feedforward direct yaw moment.

[0334] SS5-2) Feedback control algorithm design

[0335] In this step, the feedback control algorithm design is exactly the same as in step S5-2):

[0336] Then, the motion tracking additional yaw moment after adding anti-integral saturation is:

[0337]

[0338] In the formula, M DB is the additional yaw moment, s is the control error;

[0339] When the control error |s|≥θ, M DB =-k p sgn(s), so that the error rapidly approaches the sliding mode surface. When |s|<θ, has:

[0340]

[0341] The integral term k i can help control to reduce the error and improve the control effect in the sliding mode surface. Generally, the larger k i is, the smaller the steady-state error is, but the regulation time will be increased.

[0342] Table 17 Input signals of the stability direct yaw moment calculation module

[0343]

[0344] Table 18 Output signals of the stability direct yaw moment calculation module

[0345]

[0346] SS6) The stability motor torque control distribution module is used to control the vehicle yaw moment in the following manner:

[0347] The module calculates the driving torque of each driving motor by considering the direct yaw moment demand obtained through the stability reference motion model module and the stability direct yaw moment calculation module, the motor power, the road adhesion, the torque limit, and the battery charge and discharge limit (the constraint condition part is the same as the stability and maneuverability, see step S5-2) feedback control algorithm design), and finally controls the output of each driving motor to obtain different tire longitudinal forces, thereby realizing vehicle yaw moment control.

[0348] Unlike in the maneuverability module, in order to improve the stability in the steering working condition, when the direct yaw moment and the driving torque demand conflict, the motor torque distribution in the stability module will sacrifice part of the power, thereby giving priority to the direct yaw moment demand to ensure the safety of the vehicle.

[0349] The principle of the stability distribution strategy of the left and right motor torques of the rear axle is opposite to the steering distribution strategy. When the stability of the vehicle is the main control target, if the driving torque demand and the direct yaw moment demand conflict, the latter should be given priority, that is, the driving performance and the experience of the driver are sacrificed to ensure that sufficient direct yaw moment is provided to maintain the stability of the vehicle. Therefore, the direct yaw moment should be generated by the motor first, and then the remaining capacity is used to generate acceleration to minimize the weakening of the direct yaw moment on the driving performance.

[0350] Similar to the feedback control algorithm design of step 5-2), the relationship between the direct yaw moment and the driving torque of the rear wheel is written as:

[0351]

[0352] b is the rear wheel track; r w is the wheel rolling radius, T rr , T rl are the right rear wheel motor driving torque and the left rear wheel motor driving torque respectively, η r is the rear wheel motor wheel edge reduction ratio.

[0353] Assuming that the direct yaw moment condition is given priority, the maximum driving torque T r_axle,max that can be generated by the rear axle motor is:

[0354]

[0355] T max,r is the maximum torque of the rear wheel edge motor under the condition of meeting the external characteristic constraint.

[0356] It is known that the torque demand of the rear axle is T req,r , the direct yaw torque demand is M D , and the maximum torque of the rear wheel edge motor under the condition of meeting the external characteristic constraint is T max,r . According to the above stability distribution principle, the left and right wheel torque distribution is divided into the following two cases.

[0357] ① If the driving torque demand of the rear axle T req,r ≤ the maximum driving torque T r_axle,max that can be generated by the rear axle motor, the torques of the left and right wheels are:

[0358]

[0359] In the formula, T rl is the torque of the left wheel, T rr is the torque of the right wheel, T req,r is the torque demand of the rear axle, r w is the wheel rolling radius, M D is the direct yaw torque demand, and b is the rear wheel track.r For rear wheel motor wheel edge reduction ratio;

[0360] When T req,r > T r_axle,max , the driving torque and the direct yaw moment demand cannot be satisfied at the same time, when the stability is considered, it is necessary to ensure sufficient direct yaw moment demand, and sacrifice a certain vehicle power, that is, sacrifice the driving torque demand. It should be noted that at this time, one of the rear motors reaches the maximum output torque, and the output torque of the other rear motor is the maximum output torque minus the differential torque to meet the direct yaw moment demand. At this time, the torque of the left and right wheels is:

[0361] ② If the rear axle demand driving torque T req,r > The maximum driving torque T r_axle,max that the rear motor can generate, the torque of the left and right wheels is:

[0362]

[0363] In the formula, T rl is the torque of the left wheel, T rr is the torque of the right wheel, T max,r is the maximum torque of the rear wheel edge motor under the constraint condition of meeting the external characteristic, T req,r is the torque demand of the rear axle, η r is the rear wheel motor wheel edge reduction ratio, M D is the direct yaw torque demand;

[0364] Table 19 Input signals of the stability motor torque control distribution module

[0365]

[0366]

[0367] Table 20 Output signals of the stability motor torque control distribution module

[0368]

[0369] In this embodiment, the maneuverability control module and the stability control module also involve a transition stage, and the transition stage specifically includes:

[0370] However, in actual engineering practice, if a transition link is not added in the module switching process, the direct yaw moment and the output torque will all change suddenly due to the sudden change of the reference motion state, which may easily lead to the decline of the vehicle control effect, and even the instability of the vehicle. In order to solve the transition problem of the maneuverability module and the stability module, it is necessary to design a coordination coefficient according to the switching condition:

[0371] A) For the switching transition process between the handling and stability modules, a vehicle speed-lateral acceleration-handling stability coordination coefficient MAP chart is established, as shown in Figure 7

[0372] wherein the value range of the handling stability coordination coefficient k Coop is [0, 1], k Coop = 0 represents that the stability module weight is 0 and the handling module weight is 1, i.e. the motor torque is completely output by the handling module; k Coop = 1 represents that the stability module weight is 1 and the handling module weight is 0, i.e. the motor torque is completely output by the stability module. When the handling stability coordination coefficient k Coop takes a value in (0, 1), the final coordinated output torque is obtained by weighting the torques output by the two modules.

[0373] Based on prior knowledge and joint simulation test debugging results, four transition condition values are preliminarily determined: stability intervention initial vehicle speed, stability intervention completion vehicle speed, stability intervention initial lateral acceleration, and stability intervention completion lateral acceleration. When the vehicle gradually reaches the stability intervention initial vehicle speed or the stability intervention initial lateral acceleration from a low speed or a low lateral acceleration, the transition switching process from the handling module to the stability module is started; when the vehicle reaches the stability intervention completion vehicle speed or the stability intervention completion lateral acceleration, the transition switching process is completed; the transition switching process from the stability module to the handling module is the same.

[0374] B) Collect the three motor torques output by the handling module and the three motor torques output by the stability module, and collect the vehicle speed and lateral acceleration of the vehicle;

[0375] C) According to the vehicle speed and lateral acceleration of the vehicle, determine the handling stability coordination coefficient by combining the vehicle speed-lateral acceleration-handling stability coordination coefficient MAP chart;

[0376] D) According to the motor torques collected in step B) and the handling stability coordination coefficient determined in step C), perform weighted connection processing on the three motor torques T F_Hand , T RL_Hand , T RR_Hand output by the handling module and the three motor torques T F_Stab , T RL_Stab , T RR_Stab output by the stability module according to the following formula, to calculate the front motor output torque, the left rear motor output torque, and the right rear motor output torque:

[0377] T F = T F_Stab k Coop + T F_Hand (1-k Coop )​

[0378] T RL = T RL_Stab k Coop + T RL_Hand (1-k Coop )

[0379] T RR = T RR_Stab k Coop + T RR_Hand (1-k Coop )

[0380] In the formula, T F is the front motor target output torque after weighted connection processing, T RL is the left rear motor target output torque after weighted connection processing, T RR is the right rear motor target output torque after weighted connection processing, T F_Stab is the first motor torque output by the stability module, T RL_Stab is the second motor torque output by the stability module, T RR_Stab is the third motor torque output by the stability module, T F_Hand is the first motor torque output by the maneuverability module, T RL_Hand is the second motor torque output by the maneuverability module, T RR_Hand is the third motor torque output by the maneuverability module, k Coop is the maneuverability-stability coordination coefficient.

[0381] E) controlling the real-time output torque of the front motor of the vehicle to be equal to the front motor target output torque, the real-time output torque of the left rear motor to be equal to the left rear motor target output torque, and the real-time output torque of the right rear motor to be equal to the right rear motor target output torque.

[0382] Table 21 Input signals of the maneuverability-stability coordination module

[0383]

[0384] Table 22 Output signals of the maneuverability-stability coordination module

[0385]

[0386] The above description is merely preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made by those skilled in the art without departing from the spirit of the present application shall fall within the scope of the present application.

Claims

1. A torque distribution method for a distributed drive system of a new energy vehicle, characterized in that: The following steps are involved: 1) A maneuverability control module is provided on the distributed drive system of a new energy vehicle to distribute torque when the vehicle is turning and improve the maneuverability of the vehicle; A stability control module is provided to distribute torque when the vehicle is turning to improve vehicle stability; A handling stability coordination module is provided to allow smooth transition and switching between the handling control module and the stability control module; 2) Setting the maneuverability speed threshold, stability speed threshold, maneuverability lateral acceleration threshold, and stability lateral acceleration threshold; 3) Collect the vehicle speed, lateral acceleration, and steering wheel angle of the new energy vehicle and determine which control module to use for torque distribution according to the following method: If the steering wheel angle ≠ 0, and the maneuverability speed threshold ≤ vehicle speed < stability speed threshold, and the maneuverability lateral acceleration threshold ≤ lateral acceleration < stability lateral acceleration threshold, the maneuverability control module is used to distribute torque; If the steering wheel angle ≠ 0, and the vehicle speed ≥ the stability speed threshold, and the lateral acceleration ≥ the stability lateral acceleration threshold, the stability control module is used for torque distribution; If the steering wheel angle = 0, or the vehicle speed is less than the maneuverability speed threshold, the stability control module and the maneuverability control module are not used for torque distribution.

2. The torque distribution method according to claim 1, characterized in that: The maneuverability control module includes: Driving Intention Analysis Module: This module calculates the total motor drive torque requirement based on wheel speed, accelerator pedal opening, motor external characteristic curve, and vehicle architecture. It also determines the front and rear axle motor drive torque requirements using the front and rear axle torque distribution coefficients. Maneuverability Algorithm Enable Module: This module is used to design a maneuverability intervention and exit mechanism based on vehicle status feedback and driver input, determine enabling conditions, and ultimately output a maneuverability algorithm enable signal. Maneuverability motion reference model module: used to set the maneuverability control target to neutral steering based on the driver's input signal and the vehicle's current state feedback, thereby generating a maneuverability reference motion state; Maneuverability direct yaw moment calculation module: This module calculates the direct yaw moment demand based on the maneuverability reference motion state and vehicle state feedback, using a method that combines feedforward control based on a two-degree-of-freedom model with anti-saturation integral sliding mode feedback control. Maneuverability motor torque control distribution module: It is used to calculate the drive torque output of each drive motor based on the direct yaw moment demand and maneuverability control demand, with the principle of prioritizing dynamics, to obtain different tire longitudinal forces, realize vehicle yaw torque control, and ultimately achieve a control effect that improves vehicle maneuverability.

3. The torque distribution method according to claim 1, characterized in that: The stability control module includes: Drive Intent Analysis Module: This module calculates the total motor drive torque requirement based on the motor's external characteristic curve and vehicle architecture, along with the wheel speed and accelerator pedal position. It also determines the front and rear axle motor drive torque requirements using the front and rear axle torque distribution coefficients. Stability algorithm enable module: This module is used to design a stability intervention and exit mechanism based on vehicle status feedback and driver input, and output a stability algorithm enable signal based on the maneuverability intervention and exit and enable mechanism. Stability motion reference model module: used to improve vehicle stability and safety, with the control target set to have a certain understeering characteristic, and generate a stability reference motion state; Stability direct yaw moment calculation module: This module calculates the stability direct yaw moment demand based on the stability reference motion state and vehicle state feedback, using a method that combines feedforward control based on a two-degree-of-freedom model with anti-saturation integral sliding mode feedback control. Stability motor torque control distribution module: Based on the stability control requirements, with the principle of prioritizing stability, the drive torque output of each drive motor is calculated to achieve vehicle yaw torque control and achieve a control effect that improves vehicle stability.

4. The torque distribution method according to claim 1, characterized in that: The specific method of distributing torque using the maneuverability control module is as follows: S1) collecting the vehicle's left front wheel speed, right front wheel speed, left rear wheel speed, right rear wheel speed, and accelerator pedal opening; S2) Using the manipulability algorithm enabling module, determine whether to enable the manipulability algorithm in the following manner: If the vehicle's gear signal is D gear, the accelerator pedal opening is greater than 0, the vehicle speed is greater than the maneuverability intervention speed threshold, and the steering wheel angle absolute value is greater than the maneuverability intervention angle threshold, the control algorithm is enabled and a maneuverability enable signal is output; If the vehicle's gear signal is not D, or the accelerator pedal opening is 0, or the vehicle speed is less than the maneuverability exit speed threshold, or the steering wheel angle absolute value within several consecutive control cycles is less than the maneuverability exit angle threshold, the control algorithm is not enabled; S3) using the driving intention analysis module to calculate the required driving torque of the front and rear axle motors; S4) Calculate the maneuverability reference yaw rate using the maneuverability motion reference model module according to the following formula: Where, γ ref,h is the maneuverability reference yaw rate, V is the speed of the vehicle center of mass, δ f is the front wheel turning angle of the vehicle, γ is the yaw rate of the vehicle, i s is the calibration quantity, v x is the longitudinal speed; S5) using the maneuverability direct yaw moment calculation module to calculate the direct yaw moment demand according to the following formula; Where M DB is the additional yaw moment, s is the control error; S6) Using the maneuverability motor torque control distribution module, the vehicle yaw torque is controlled in the following manner: ① When the rear axle motor's required driving torque is less than the rear axle motor's generated driving torque, both the driving torque and the direct yaw moment requirements can be met, and the torques of the left and right wheels are: Where, T rl is the torque of the left wheel, T rr is the torque of the right wheel, T req,r is the torque requirement of the rear axle, r w is the wheel rolling radius, M D is the direct yaw torque demand, b is the rear wheelbase, η r is the wheel-side reduction ratio of the rear wheel motor; ② When the rear axle motor's required driving torque is greater than the rear axle motor's generated driving torque, the driving torque and direct yaw moment requirements cannot be met simultaneously. The torques of the left and right wheels are: Where, T rl is the torque of the left wheel, T rr is the torque of the right wheel, T max,r is the maximum torque of the rear wheel motor under the constraints of external characteristics, T req,r is the torque demand of the rear axle, η r is the rear wheel motor reduction ratio, M D is the direct yaw torque demand.

5. The torque distribution method according to claim 1, characterized in that: The specific method of distributing torque using the stability control module is as follows: SS1) collects vehicle gear signals, accelerator pedal opening, vehicle speed, steering wheel angle, and lateral acceleration; SS2) Using the stability algorithm enable module, determine whether to output a stability algorithm enable signal in the following manner: If the gear signal is D gear, the accelerator pedal opening is greater than 0, the vehicle speed is greater than the maneuverability intervention speed threshold, the steering wheel angle absolute value is greater than the maneuverability intervention angle threshold, and the lateral acceleration is greater than the stability intervention lateral acceleration or the vehicle speed is greater than the stability intervention speed, then an enable signal is output; If the gear signal is not D, or the accelerator pedal opening is 0, or the vehicle speed is less than the exit speed threshold, or the absolute value of the steering wheel angle is less than the exit angle threshold for several consecutive control cycles, or the lateral acceleration is less than the stability intervention lateral acceleration and the vehicle speed is less than the intervention speed, then the enable signal is not output; SS3) Calculate the required driving torque of the front and rear axle motors using the driving intention analysis module; SS4) Use the stability motion reference model module to calculate the stability reference yaw rate according to the following formula: Where, γ ref,s is the maneuverability reference yaw rate, V is the speed of the vehicle center of mass, K is the stability factor, δ f is the front wheel turning angle of the vehicle, γ is the yaw rate of the vehicle, i s is the calibration quantity; SS5) Use the stability direct yaw moment calculation module to calculate the stability direct yaw moment according to the following formula: Where M DB is the additional yaw moment, s is the control error; SS6) Using the stability motor torque control distribution module, the vehicle yaw torque is controlled in the following manner; ① If the rear axle required driving torque is less than or equal to the maximum driving torque that the rear axle motor can generate, the torque of the left and right wheels is: Where, T rl is the torque of the left wheel, T rr is the torque of the right wheel, T req,r is the torque requirement of the rear axle, r w is the wheel rolling radius, M D is the direct yaw torque demand, b is the rear wheelbase, η r is the wheel-side reduction ratio of the rear wheel motor; ② If the rear axle required driving torque is greater than the maximum driving torque that the rear axle motor can generate, the torque of the left and right wheels is: Where, T rl is the torque of the left wheel, T rr is the torque of the right wheel, T max,r is the maximum torque of the rear wheel motor under the constraints of external characteristics, T req,r is the torque demand of the rear axle, η r is the rear wheel motor reduction ratio, M D is the direct yaw torque demand.

6. The torque distribution method according to claim 4 or 5, characterized in that: The specific method of calculating the generalized demand driving force by using the driving intention analysis module includes: S3-1) Calculate the motor torque load factor based on the accelerator pedal opening according to the following formula: L D =100%·Acc_Pedal Where, L D is the motor torque load coefficient under driving conditions, Acc_Pedal is the accelerator pedal opening; S3-2) Calculate the required wheel drive torque based on the motor torque load factor using the following formula: T req =L D (or f ·T max,f +2·h r ·T max,r ) Where, f is the front axle centralized motor, r is the two wheel-side motors on the rear axle, T req is the required wheel drive torque, T max,i is the maximum driving torque that the front motor and the rear motor can provide, determined by the external characteristics of the motor, L D is the motor torque load factor, T peak,i is the peak torque of the motor, n i is the current speed of the motor, n b,i is the motor base speed, η i is the reduction ratio of the front and rear motors; S3-3) Calculate the required driving torque of the front and rear axle motors according to the following formula based on the required wheel driving torque: Where, T req,f is the driving torque required by the front axle motor, T req,r is the required driving torque of the rear axle motor, K f is the front axle torque distribution coefficient, T req is the required wheel drive torque.

7. The torque distribution method according to claim 1, characterized in that: There is also a transition phase between the maneuverability control module and the stability control module, and the transition phase specifically includes: A) Create a vehicle speed-lateral acceleration-handling stability coordination coefficient MAP diagram; B) collecting the three motor torques output by the maneuverability module and the three motor torques output by the stability module, and collecting the vehicle speed and lateral acceleration; C) Determine the handling stability coordination coefficient based on the vehicle speed and lateral acceleration using the vehicle speed-lateral acceleration-handling stability coordination coefficient MAP diagram; D) Based on the motor torques acquired in step B) and the handling stability coordination coefficient determined in step C), the front motor output torque, the left rear motor output torque, and the right rear motor output torque are calculated according to the following formula: T F =T F_Stab k Coop +T F_Hand (1-k Coop ) T RL =T RL_Stab k Coop +T RL_Hand (1-k Coop ) T RR =T RR_Stab k Coop +T RR_Hand (1-k Coop ) Where, T F is the target output torque of the front motor obtained after weighted connection processing, T RL is the target output torque of the left rear motor obtained after weighted connection processing, T RR is the target output torque of the right rear motor obtained after weighted connection processing, T F_Stab The first motor torque output by the stability module, T RL_Stab The second motor torque output by the stability module, T RR_Stab The third motor torque output by the stability module, T F_Hand The first motor torque output by the maneuverability module, T RL_Hand The second motor torque output by the maneuverability module, T RR_Hand The third motor torque output by the maneuverability module, k Coop is the handling stability coordination coefficient; E) Control the vehicle's front motor's real-time output torque to be equal to the front motor's target output torque, the left rear motor's real-time output torque to be equal to the left rear motor's target output torque, and the right rear motor's real-time output torque to be equal to the right rear motor's target output torque.

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