Auxiliary drift control method considering torque vector control

Abstract

The invention is suitable for the technical field of auxiliary drifting control, and provides an auxiliary drifting control method considering torque vector control, which comprises the following steps: after the intention of a driver entering drifting is identified, an auxiliary drifting controller starts to work to maintain drifting, and the yaw velocity and the rear axle slip rate in a drifting equilibrium state are solved; the yaw velocity and the rear axle slip rate in the drifting equilibrium state are tracked through the additional yaw moment and the rear axle additional driving moment and distributed to the left wheel and the right wheel of the rear axle, and meanwhile the driving moment formed by stepping on an accelerator by a driver serves as feedforward to assist the driver to maintain drifting; and when the driver is identified to quit the drift intention, the driver is considered to quit the drift. On the premise that input of a driver is not changed, the driver is supported to complete some high-order drifting actions, and the driver can fully experience the pleasure of drifting and the control characteristics of the vehicle. And meanwhile, the vehicle can be more easily maintained in a drifting equilibrium state after starting drifting, and the time cost for a driver to learn drifting is further reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of assisted drift control, and particularly relates to an assisted drift control method considering torque vector control. Background Technique

[0002] With the rapid development of autonomous driving, automatic drift control technology has been widely applied in autonomous vehicles. This technology controls the vehicle state to the drift equilibrium point (i.e., the saddle point) by designing a feedback controller, and the control algorithms mostly adopt linear quadratic regulator (LQR), model predictive control (MPC), inverse method, etc. On the basis of autonomous driving, the assisted drift technology has emerged. However, the existing assisted drift technology still has the following defects: the driving experience is limited, that is, the existing assisted drift system will automatically correct the drift route and seize the driver's control of the vehicle at the critical moment of drifting, resulting in the driver feeling that the vehicle is out of their control, thus generating uneasiness and affecting the driving experience. In addition, this system is difficult to support the driver to achieve some high-order drift skills, restricting the driving pleasure. There are also defects such as a relatively high technical threshold. The driver needs to spend a lot of time learning drift skills, which increases the usage difficulty and restricts the popularization of the technology. Therefore, the present invention proposes an assisted drift control method considering torque vector control. Summary of the Invention

[0003] The purpose of the present invention is to provide an assisted drift control method considering torque vector control, aiming to solve the problems proposed in the above background technique.

[0004] The purpose of the present invention is achieved through the following technical solutions: An assisted drift control method considering torque vector control includes the following steps: Step 1: The driver enters the drift intention recognition. The driver's entry into the drift awareness recognition includes three conditions. When all three conditions are met simultaneously, it is considered that the driver has the intention to enter a drift. At this time, the assisted drift controller starts to work. The three conditions are as follows: Condition 1: The absolute value of the yaw rate of the vehicle is greater than the lowest threshold, that is, the vehicle enters a curve. Condition 2: It is recognized that the driver has the intention of counter-steering the steering wheel. Condition 3: The counter-steering lasts for a preset time length to improve the robustness of the driver intention recognition system. Step 2: Solve the state variables of the vehicle in the drift equilibrium state. When the vehicle is in the drift equilibrium state during the drift maintenance, according to the derivative of the vehicle three-degree-of-freedom model being zero and the rear-wheel tire saturation formula, the yaw rate, sideslip angle of the center of mass, longitudinal force of the rear wheels, and lateral force of the rear wheels in the drift equilibrium state are solved. Step 3: Solve the additional yaw moment and the additional driving torque of the rear axle; Form a closed-loop control structure based on the error relationship between the yaw rate in the drift equilibrium state and the actual state to obtain the additional yaw moment; then, according to the relationship between the force of the rear wheels and the slip speed during vehicle driving, use the rear-wheel thrust angle to relate the wheel speed, tire force of the vehicle to the state variables of the vehicle, inversely solve the desired wheel speed through the yaw rate, sideslip angle of the center of mass, longitudinal force of the rear wheels, and lateral force of the rear wheels, further solve the slip rate of the rear axle in the drift equilibrium state, and form a closed-loop control structure based on the error relationship between the slip rate of the rear axle in the drift equilibrium state and the actual state to obtain the additional driving torque of the rear axle; Step 4: Driving force distribution; The vehicle adopts rear-wheel drive, and the driving forces of the left and right rear wheels consist of the driving torque formed by the driver stepping on the accelerator and the additional driving torque solved by the auxiliary drift controller, where the driving torque formed by the driver stepping on the accelerator is the feedforward; the sum of the additional driving torques of the left and right rear wheels is equal to the additional driving torque of the rear axle, and at the same time, the torque formed by the differential of the left and right rear wheels is equal to the additional yaw moment. Solve the additional driving torques of the left and right rear wheels according to these two conditions; Step 5: Identify the driver's intention to exit the drift; When either of the following two conditions is met, it is considered that the driver exits the drift state: Condition 1: The absolute value of the yaw rate of the vehicle is less than the lowest threshold, that is, the vehicle exits the curve; Condition 2: The vehicle oscillates during the drift.

[0005] Furthermore, in the said Step 1, the calculation formulas for the three conditions to identify the driver's entry into the drift are respectively: Condition 1: ; In the formula, is the yaw rate; is the yaw rate threshold; Condition 2: ; In the formula, is the sign function; is the front-wheel steering angle; Condition 3: ; In the formula, is the average value of the front-wheel steering angle over a time length of 0.3 s; is the average value of the yaw rate over a time length of 0.3 s.

[0006] Furthermore, the said Step 2 includes the following specific steps: When the vehicle is in the drift equilibrium state, the derivatives of the vehicle's three-degree-of-freedom dynamic model are 0, that is , where is the derivative of the heading speed with respect to time, is the derivative of the sideslip angle of the center of mass with respect to time, is the derivative of the yaw rate with respect to time, and the equilibrium equations are shown as follows: ; ; ; wherein, and are respectively the sideslip angle of the center of mass, yaw rate, heading speed, front wheel steering angle, front wheel lateral force, rear wheel lateral force and rear wheel longitudinal force in the drift equilibrium state; and are respectively the distances from the vehicle center of mass to the front and rear axles; is the vehicle mass; is the moment of inertia of the vehicle; where and are known quantities, the front wheel steering angle is solved according to the driver's steering wheel angle and the steering system transmission ratio, and the front wheel lateral force is solved through the Fiala tire model; during the drift, the rear wheel tire forces are in the saturated state, and the rear wheel longitudinal force and rear wheel lateral force are coupled with each other and affected by the total force that the tire can generate, that is, the following formula is satisfied: ; wherein, is the road surface adhesion coefficient; is the rear axle load; Finally, the yaw rate , sideslip angle of the center of mass , rear wheel longitudinal force and rear wheel lateral force in the drift equilibrium state are solved.

[0007] Furthermore, the step 3 includes the following specific steps: Step 3.1: Use proportional control to achieve the control of the yaw rate and solve the additional yaw moment. The specific formula is as follows: ; wherein, is the additional yaw moment; is the adjustable yaw rate control parameter; Step 3.2: The rear wheel thrust angle satisfies the following formula: ; In the formula, is the lateral force of the rear wheels; is the longitudinal force of the rear wheels; is the distance from the vehicle's center of mass to the rear axle; is the yaw rate; is the vehicle speed; is the sideslip angle of the vehicle's center of mass; is the wheel speed; The desired wheel speed of the rear wheels is obtained by inverting the rear wheel thrust angle formula, as shown in the following formula: is the wheel radius; ; In the formula, is the desired wheel speed of the rear wheels; is the yaw rate in the drift equilibrium state; is the sideslip angle of the center of mass in the drift equilibrium state; Step 3.3: Solve the slip ratio of the rear axle in the drift equilibrium state. The calculation formula is as follows: ; In the formula, is the slip ratio of the rear axle in the drift equilibrium state; Step 3.4: Use proportional control to achieve control of the vehicle's rear axle slip ratio and solve the additional driving torque of the rear axle. The specific formula is as follows: ; In the formula, is the additional driving torque of the rear axle; is the slip ratio of the vehicle's rear axle; is an adjustable control parameter for the rear axle slip ratio; During the process of maintaining the drift, the drift equilibrium state of the vehicle changes according to the change of the steering wheel angle rotated by the driver and the depth of the accelerator pedal depression. The yaw rate, sideslip angle of the center of mass, longitudinal force of the rear wheels, and lateral force of the rear wheels in the drift equilibrium state are calculated in real time according to the driver's operation. Then, the additional yaw moment and the additional driving torque of the rear axle are used to track the yaw rate and the rear axle slip ratio in the drift equilibrium state, so as to change the drift attitude of the vehicle according to the driver's operation.

[0008] Furthermore, the said step 4 includes the following specific steps: Step 4.1: The vehicle is rear-wheel drive. The sum of the additional driving torques of the left and right rear wheels is equal to the additional driving torque of the rear axle, and the torque formed by the differential of the left and right rear wheels is equal to the additional yaw moment, as shown in the following formula: ; ; In the formula, is the additional driving torque of the left rear wheel; is the additional driving torque of the right rear wheel; is the additional driving torque of the rear axle; is the wheel radius; is the wheelbase of the rear axle of the vehicle; is the additional yaw moment; The calculation formulas for the additional driving torques of the left and right rear wheels are as follows: ; ; Step 4.2: The driving forces of the left and right rear wheels are composed of the driving torque formed by the driver stepping on the accelerator and the additional driving torque solved by the auxiliary drift controller. The formula is as follows: ; ; In the formula, and are the total driving torques of the left and right rear wheels respectively; and are the driving torques of the left and right rear wheels formed by the driver stepping on the accelerator respectively.

[0009] Furthermore, in the said Step 5, the calculation formulas for identifying the two conditions for the driver to exit the drift are as follows. When either condition is met, it is considered that the driver has exited the drift state; Condition 1: ; In the formula, is the yaw rate; is the yaw rate threshold; Condition 2: ; In the formula, and are the yaw rates at the current moment and the previous moment respectively.

[0010] Compared with the prior art, the beneficial effects of the present invention are: The present invention identifies the driver's intention to enter a drift based on three conditions, which can accurately identify the driver's intention to enter a drift and has strong robustness. The present invention solves the additional driving torque of the left and right rear wheels in real time according to the driver's operation, uses the driving torque formed by the driver stepping on the accelerator pedal as a feedforward to maintain the drift, and allows the driver to directly control the accelerator, brake and steering wheel without changing the driver's input, and drift according to the driver's intention. It not only supports the driver to complete some high-order drift actions, but also allows the driver to fully experience the fun of drifting and the handling characteristics of the vehicle. At the same time, the present invention controls the rear axle slip ratio while controlling the yaw angular velocity of the vehicle, making it easier for the vehicle to maintain the drift equilibrium state after starting to drift, and further reducing the time cost for the driver to learn drifting. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a flowchart of the method of the present invention.

[0012] Figure 2 It is a framework diagram of the method of the present invention.

[0013] Figure 3 It is a residual image diagram of the driver's operation using the auxiliary drift controller in Embodiment 1 of the present invention.

[0014] Figure 4 It is a residual image diagram of the driver's operation without the auxiliary drift controller in Embodiment 1 of the present invention.

[0015] Figure 5 It is the opening degree of the accelerator pedal stepped on by the driver in Embodiment 1 of the present invention.

[0016] Figure 6 It is the steering angle of the steering wheel turned by the driver in Embodiment 1 of the present invention.

[0017] Figure 7 It is the sideslip angle of the center of mass in Embodiment 1 of the present invention.

[0018] Figure 8 It is a comparison diagram of the slip ratio in Embodiment 1 of the present invention.

[0019] Figure 9 It is a comparison diagram of the yaw angular velocity in Embodiment 1 of the present invention.

[0020] Figure 10 It is the driving torque of the rear wheels in Embodiment 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will be described in detail below, but it should not be construed as a limitation on the scope of implementation of the present invention.

[0022] The specific implementation of the present invention will be described in detail below in conjunction with specific embodiments.

[0023] Figure 1 The following is a flowchart of an auxiliary drift control method considering torque vector control provided by an embodiment of the present invention. As Figure 1 shown, the method includes the following specific steps: Step 1: The driver enters the drift intention recognition. The driver's entry into the drift intention recognition includes three conditions: the absolute value of the yaw rate of the vehicle is greater than the lowest threshold, the steering wheel is counter-rotated, and the counter-rotation of the steering wheel lasts for a preset time length. When all three conditions are met simultaneously, it is considered that the driver has the intention to enter a drift. At this time, the auxiliary drift controller starts to work.

[0024] Step 2: Solve the state variables of the vehicle in the drift equilibrium state. When the vehicle maintains a drift, it is in a drift equilibrium state. According to the derivative of the vehicle three-degree-of-freedom model being zero and the rear-wheel tire saturation formula, the yaw rate , the sideslip angle of the center of mass , the longitudinal force of the rear wheels and the lateral force of the rear wheels in the drift equilibrium state are solved.

[0025] Step 3: Solve the additional yaw moment and the additional driving torque of the rear axle. The error relationship between the yaw rate in the drift equilibrium state and the actual state forms a closed-loop control structure to obtain the additional yaw moment. Then, according to the relationship between the force of the rear wheels and the slip speed during vehicle driving, the wheel speed, tire force of the vehicle and the state variables of the vehicle are related by using the rear-wheel thrust angle. Through the yaw rate , the sideslip angle of the center of mass , the longitudinal force of the rear wheels and the lateral force of the rear wheels , the expected wheel speed is inversely solved. Further, the slip ratio of the rear axle in the drift equilibrium state is solved. The error relationship between the slip ratio of the rear axle in the drift equilibrium state and the actual state forms a closed-loop control structure to obtain the additional driving torque of the rear axle. During the process of maintaining a drift, the drift equilibrium state of the vehicle changes according to the change of the steering wheel angle rotated by the driver and the depth of the accelerator pedal depressed. According to the driver's operation, the yaw rate, sideslip angle of the center of mass, longitudinal force of the rear wheels and lateral force of the rear wheels in the drift equilibrium state are obtained in real time. Furthermore, the additional yaw moment and the additional driving torque of the rear axle are used to track the yaw rate and the slip ratio of the rear axle in the drift equilibrium state, so as to change the drift attitude of the vehicle according to the driver's operation.

[0026] Step 4: Driving force distribution. The driving mode of the vehicle adopts rear-wheel drive, and the driving forces of the left and right rear wheels are composed of the driving torque formed by the driver stepping on the accelerator and the additional driving torque of the rear axle solved by the auxiliary drift controller , wherein the driving torque formed by the driver stepping on the accelerator is the feedforward; the sum of the additional driving torques of the left and right rear wheels is equal to the additional driving torque of the rear axle solved in step 3, and at the same time, the torque formed by the differential of the left and right rear wheels is equal to the additional yaw torque solved in step 2. According to these two conditions, the additional driving torques of the left and right rear wheels are solved.

[0027] Step 5: The driver exits the drift intention recognition; When the absolute value of the yaw rate is less than the lowest threshold or the vehicle oscillates during the drift, it is considered that the driver exits the drift state, and the auxiliary drift controller stops working.

[0028] On the basis of the above implementation, it is further refined Figure 2 which is a framework diagram of an auxiliary drift control method considering torque vector control provided by an embodiment of the present invention. As Figure 2 shown, the method specifically includes: 1. The driver enters the drift intention recognition; The driver's entry into the drift intention recognition includes three conditions. Only when all three conditions are met at the same time, it is considered that the driver has the intention to enter the drift. At this time, the auxiliary drift controller starts to work. The specific conditions are as follows: Condition 1: The absolute value of the yaw rate of the vehicle is greater than the lowest threshold, and it is recognized that the vehicle is turning; the formula is as follows: ; In the formula, is the yaw rate; is the yaw rate threshold; Condition 2: It is recognized that the driver has the intention to counter-steer the steering wheel; the formula is as follows: ; In the formula, is the sign function; is the front wheel angle; Condition 3: The driver's counter-steering of the steering wheel needs to last for a preset time length (0.3 s) to improve the robustness of the system; the formula is as follows: ; In the formula, is the average value of the front wheel angle in a time length of 0.3 s; is the average value of the yaw rate in a time length of 0.3 s.

[0029] 2. Auxiliary drift control algorithm; 2.1. Solving the state variables of the vehicle in the drifting equilibrium state; When the vehicle is in the drifting equilibrium state, that is, maintaining a relatively stable vehicle state and input during the drifting process. Therefore, when the vehicle is in the equilibrium state, the derivative of the vehicle's three-degree-of-freedom dynamic model is 0, that is , where is the derivative of the heading speed with respect to time, is the derivative of the sideslip angle of the center of mass with respect to time, is the derivative of the yaw rate with respect to time, and the equilibrium equation is shown as follows: ; ; ; In the formula, and are respectively the sideslip angle of the center of mass, yaw rate, heading speed, front wheel steering angle, front wheel lateral force, rear wheel lateral force and rear wheel longitudinal force in the drifting equilibrium state; and are respectively the distances from the vehicle's center of mass to the front and rear axles; is the vehicle mass; is the moment of inertia of the vehicle; and are known quantities. The front wheel steering angle is solved according to the driver's steering wheel angle and the steering system transmission ratio. The front wheel lateral force is solved through the Fiala tire model. The Fiala tire model is shown as follows: ; In the formula, is the front wheel lateral force; is the cornering stiffness of the front wheel tire; is the front wheel tire sideslip angle; is the tangent value of the front wheel tire sideslip angle; is the critical value of the front wheel tire sideslip angle; is the road surface adhesion coefficient; is the front axle load; is the coupling factor of the tire longitudinal force and lateral force. The formula is as follows: ; In the formula, is the front wheel longitudinal force. For a rear-wheel drive vehicle, the front wheel longitudinal force , that is ; During the drifting process, the rear wheel tire forces are in a saturated state, and the longitudinal force and lateral force of the tire are coupled with each other and affected by the total force that the tire can generate, that is, the following formula is satisfied: ; In the formula, is the road surface adhesion coefficient; is the rear axle load; The vehicle three-degree-of-freedom model and the saturation of the rear wheel tire force have four equations and four unknowns , so and can be solved.

[0030] 2.2. Solving the additional yaw moment and the additional driving torque of the rear axle; 2.2.1. Solving the additional yaw moment; The additional yaw moment is solved by using proportional control to control the yaw rate, and the specific formula is as follows: ; In the formula, is the additional yaw moment; is the adjustable yaw rate control parameter.

[0031] 2.2.2. Solving the additional driving torque of the rear axle; 1) Solving the desired wheel speed; The rear wheel thrust angle satisfies the following formula: ; In the formula, is the rear wheel lateral force; is the rear wheel longitudinal force; is the distance from the vehicle center of mass to the rear axle; is the yaw rate; is the heading speed; is the center of mass side slip angle; is the wheel speed; is the wheel radius. The inverse of the rear wheel thrust angle formula can obtain the desired wheel speed of the rear wheel, as shown in the following formula: ; In the formula, is the desired wheel speed of the rear wheel; is the yaw rate in the drift equilibrium state; is the center of mass side slip angle in the drift equilibrium state; 2) Solving the rear axle slip ratio in the drift equilibrium state; The rear axle slip ratio in the drift equilibrium state is solved according to the desired wheel speed of the rear wheel and the heading speed, and the calculation formula is as follows: ; In the formula, is the rear axle slip ratio in the drift equilibrium state; 3) Solve the additional torque of the rear axle; Use proportional control to control the slip ratio of the vehicle's rear axle and solve the additional driving torque of the rear axle. The specific formula is as follows: ; In the formula, is the additional driving torque of the rear axle; is the slip ratio of the vehicle's rear axle; is the adjustable control parameter of the rear axle slip ratio.

[0032] 2.3. Driving force distribution; The vehicle is rear-wheel drive. The sum of the additional driving torques of the left and right rear wheels is equal to the additional driving torque of the rear axle, and the torque formed by the differential of the left and right rear wheels is equal to the additional yaw torque, as shown in the following formula: ; ; In the formula, is the additional driving torque of the left rear wheel; is the additional driving torque of the right rear wheel; is the additional driving torque of the rear axle; is the wheel radius; is the wheelbase of the vehicle's rear axle; is the additional yaw torque; The calculation formulas for the additional driving torques of the left and right rear wheels are as follows: ; ; The driving forces of the left and right rear wheels are composed of the driving torque formed by the driver stepping on the accelerator and the additional driving torque of the rear axle solved by the assisted drift control algorithm. Among them, the driving torque formed by the driver stepping on the accelerator is the feedforward, and the formula is as follows: ; ; In the formula, and are the total driving torques of the left and right rear wheels respectively; and are the driving torques of the left and right rear wheels formed by the driver stepping on the accelerator respectively.

[0033] 3. Recognition of the driver's intention to exit the drift; When either of the following two conditions is met, it is considered that the driver has exited the drift state: Condition 1: The absolute value of the vehicle's yaw rate is less than the lowest threshold, that is, the vehicle has exited the curve; The formula is as follows: ; In the formula, is the yaw rate; is the yaw rate threshold; Condition 2: During the drifting process, the vehicle oscillates. To ensure the safety of vehicle driving, the drifting also exits. The formula is as follows: ; In the formula, and are the yaw rates at the current moment and the previous moment respectively. When the product of the two is less than 0, it indicates that the vehicle oscillates, and in this case, the assisted drifting also exits.

[0034] Embodiment 1: Performance verification; In this embodiment, a U-shaped curve is used to verify the effectiveness of the method. For this purpose, a hardware-in-the-loop simulation experimental platform is built. The main components include a Senso Wheel steering wheel, an accelerator pedal, a brake pedal (the three can respectively simulate the actions of steering, stepping on the accelerator, and stepping on the brake of a real vehicle), as well as an NI PXI working condition machine and a Speedgoat real-time simulation and control system. In the structure of the simulation experimental platform, the host PC-1 is connected to the NI PXI working condition machine, which is mainly used to run the Carsim vehicle model; the host PC-2 is connected to the Speedgoat real-time simulation and control system, and runs an assisted drifting algorithm considering torque vector control based on the Simulink environment. The driver interacts with the Speedgoat real-time simulation and control system through operating input devices (Senso Wheel steering wheel, accelerator pedal, brake pedal) to achieve assisted drifting control during the vehicle drifting process according to the driver's operations.

[0035] Figure 3 shows the afterimage of the driver's operation using the assisted drifting controller, Figure 4 shows the afterimage of the driver's operation without the assisted drifting controller. By comparing the two, it can be clearly seen that the assisted drifting controller can assist the driver to maintain drifting, and the driver can easily complete the drifting. Without the assisted drifting controller, after the vehicle starts to drift, it immediately becomes unstable and turns around, and the vehicle is out of the driver's control. Therefore, the assisted drifting controller considering torque vector control can better assist the driver to complete the drifting.

[0036] Figure 5 and Figure 6 respectively show the changes in the accelerator pedal opening and the steering wheel angle. From Figure 5 it can be seen that after starting to drift, the throttle opening reaches 100%, and the driver fully depresses the accelerator pedal; from Figure 6 it can be seen that the driver first turns the steering wheel sharply to the left. At this time, the yaw rate of the vehicle increases rapidly, and then immediately turns the steering wheel back and maintains the reverse turn.

[0037] Figure 7 The centroidal side slip angle is shown. It can be seen that during the vehicle drifting process, the centroidal side slip angle is stable at about -28 degrees.

[0038] Figure 8 and Figure 9 are respectively the comparison diagrams of the rear axle slip ratio and the yaw rate of the vehicle. Since the auxiliary drift controller only starts to calculate the rear axle slip ratio and the yaw rate in the drift equilibrium state in real time after the vehicle drifts, therefore Figure 8 and Figure 9 are the data during the vehicle maintaining the drift process. It can be seen from Figure 8 that the rear axle slip ratio of the vehicle can better track the rear axle slip ratio in the drift equilibrium state and maintain at about 0.5, indicating that the additional driving torque of the rear axle plays a role; it can be seen from Figure 9 that at the beginning, the yaw rate is relatively large. At this time, the additional yaw torque formed by the differential of the rear wheels plays a role and stabilizes the yaw rate at about 0.3; Figure 10 The driving torque of the rear wheels is shown. It can be seen that during normal driving, the auxiliary drift controller does not work. At this time, the driving force is the driving torque formed by the driver stepping on the accelerator pedal. When the vehicle starts to drift, the auxiliary drift controller starts to work, and the differential of the two rear wheels forms an additional yaw torque to stabilize the yaw rate.

[0039] The above is only the preferred embodiment of the present invention. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicability of the patent.

Claims

1. An auxiliary drift control method considering torque vector control, characterized in that: The following steps are involved: Step 1: Driver enters drift intention recognition; The driver's drift awareness recognition includes three conditions. When all three conditions are met at the same time, it is considered that the driver has the intention to drift. At this time, the auxiliary drift controller starts to work. The three conditions are as follows: Condition 1: The absolute value of the vehicle's yaw rate is greater than the minimum threshold, that is, the vehicle enters a curve; Condition 2: Steering wheel reverses; Condition 3: The steering wheel is reversed continuously for a preset time period; Step 2: Solve the state quantity of the vehicle in drift equilibrium state; The vehicle is in a drift equilibrium state during the drifting process. According to the derivative of the three-degree-of-freedom model of the vehicle being zero, the rear tire saturation formula is used to solve the yaw rate, center of mass sideslip angle, rear wheel longitudinal force, and rear wheel lateral force in the drift equilibrium state. Step 3: Solve the additional yaw moment and the additional driving moment of the rear axle; The error relationship between the yaw rate in the drift equilibrium state and the actual state forms a closed-loop control structure to obtain an additional yaw moment; then, according to the relationship between the force and slip speed of the rear wheels when the vehicle is traveling, the rear wheel thrust angle is used to link the wheel speed, tire force and the state quantity of the vehicle, and the desired wheel speed is solved by inversion of the yaw rate, the sideslip angle of the center of mass, the longitudinal force of the rear wheels and the lateral force of the rear wheels, and the rear axle slip rate in the drift equilibrium state is further solved, and the error relationship between the rear axle slip rate in the drift equilibrium state and the actual state forms a closed-loop control structure to obtain the additional driving torque of the rear axle; Step 4: driving force distribution; The vehicle is driven by rear wheels. The driving force of the left and right rear wheels is composed of the driving torque formed by the driver stepping on the accelerator and the additional driving torque solved by the auxiliary drift controller. The driving torque formed by the driver stepping on the accelerator is the feedforward; the sum of the additional driving torques of the left and right rear wheels is equal to the additional driving torque of the rear axle. At the same time, the torque formed by the differential of the left and right rear wheels is equal to the additional yaw torque. The additional driving torque of the left and right rear wheels is solved according to these two conditions; Step 5: The driver exits the drift intention recognition; The driver is considered to have exited the drift state when any of the following two conditions are met: Condition 1: The absolute value of the yaw rate is less than the yaw rate threshold, that is, the vehicle exits the curve; Condition 2: The vehicle vibrates.

2. The auxiliary drift control method considering torque vector control according to claim 1, characterized in that: In step 1, the calculation formulas for identifying the three conditions for the driver to enter drift are: Condition 1: ； In the formula, is the yaw angular velocity; is the yaw angular velocity threshold; Condition 2: ； In the formula, is a symbolic function; is the front wheel turning angle; Condition 3: ； In the formula, The average value of the front wheel turning angle over a period of 0.3s; is the average value of the yaw rate over a period of 0.3 s.

3. The auxiliary drift control method considering torque vector control according to claim 1, characterized in that: The step 2 comprises the following specific steps: When the vehicle is in a drift equilibrium state, the derivative of the vehicle's three-degree-of-freedom dynamic model is 0, that is, , where is the time derivative of the heading velocity, is the time derivative of the center of mass slip angle, is the derivative of the yaw rate with respect to time, and the equilibrium equation is as follows: ； ； ； In the formula, and They are the sideslip angle of the center of mass, yaw rate, heading rate, front wheel turning angle, front wheel lateral force, rear wheel lateral force and rear wheel longitudinal force in the drift equilibrium state; and are the distances from the vehicle's center of mass to the front and rear axles, respectively; is the vehicle mass; is the moment of inertia of the vehicle; and is a known quantity, the front wheel angle According to the driver's steering wheel angle and the steering system transmission ratio, the lateral force of the front wheel Solved by Fiala tire model; during drifting, the rear tire force is in saturation state, the rear wheel longitudinal force and the rear wheel lateral force are coupled with each other, and are affected by the total force that the tire can generate, that is, they satisfy the following formula: ； In the formula, is the road adhesion coefficient; is the rear axle load; Finally, the yaw angular velocity in the drift equilibrium state is solved , Center of mass slip angle , rear wheel longitudinal force and rear wheel lateral force .

4. The auxiliary drift control method considering torque vector control according to claim 3, characterized in that: The step 3 comprises the following specific steps: Step 3.1: Use proportional control to control the yaw rate and solve the additional yaw moment. The specific formula is as follows: ； In the formula, is the additional yaw moment; is an adjustable yaw rate control parameter; Step 3.2: Rear wheel thrust angle Satisfies the following formula: ； In the formula, is the rear wheel lateral force; is the rear wheel longitudinal force; is the distance from the vehicle's center of mass to the rear axle; is the yaw angular velocity; is the vehicle speed; is the vehicle's center of mass sideslip angle; is the wheel speed; is the wheel radius; the rear wheel thrust angle formula is inverted to obtain the expected wheel speed of the rear wheel, as shown in the following formula: ； In the formula, is the expected wheel speed of the rear wheel; is the yaw angular velocity in drift equilibrium state; is the sideslip angle of the center of mass in drift equilibrium state; Step 3.3: Solve the rear axle slip rate in drift equilibrium state. The calculation formula is as follows: ； In the formula, is the rear axle slip rate in drift equilibrium state; Step 3.4: Use proportional control to control the rear axle slip rate of the vehicle and solve the additional driving torque of the rear axle. The specific formula is as follows: ； In the formula, Adding drive torque to the rear axle; is the rear axle slip rate of the vehicle; It is an adjustable rear axle slip rate control parameter; In the process of maintaining drift, the vehicle's drift equilibrium state changes according to the steering wheel angle turned by the driver and the change of accelerator pedal depth. The yaw rate, center of mass sideslip angle, rear wheel longitudinal force and rear wheel lateral force in the drift equilibrium state are calculated in real time according to the driver's operation, and then the yaw rate and rear axle slip rate in the drift equilibrium state are tracked through additional yaw torque and additional rear axle drive torque, thereby changing the vehicle's drift posture according to the driver's operation.

5. The auxiliary drift control method considering torque vector control according to claim 4, characterized in that: The step 4 comprises the following specific steps: Step 4.1: The vehicle is driven by rear wheels. The sum of the additional driving torques of the left and right rear wheels is equal to the additional driving torque of the rear axle. The torque formed by the differential of the left and right rear wheels is equal to the additional yaw torque, as shown in the following formula: ； ； In the formula, Adding driving torque to the left rear wheel; Adding driving torque to the right rear wheel; Adding drive torque to the rear axle; is the wheel radius; is the rear axle track of the vehicle; is the additional yaw moment; The calculation formula for the additional driving torque of the left and right rear wheels is as follows: ； ； Step 4.2: The driving force of the left and right rear wheels is composed of the driving torque generated by the driver stepping on the accelerator and the additional driving torque solved by the auxiliary drift controller. The formula is as follows: ； ； In the formula, and are the total driving torque of the left and right rear wheels respectively; and They are the driving torques of the left and right rear wheels formed by the driver stepping on the accelerator.

6. The auxiliary drift control method considering torque vector control according to claim 1, characterized in that: In step 5, the calculation formula for identifying the two conditions for the driver to exit the drift is as follows. When any one of the conditions is met, it is considered that the driver exits the drift state; Condition 1: ； In the formula, is the yaw angular velocity; is the yaw angular velocity threshold; Condition 2: ； In the formula, and are the yaw angular velocity at the current moment and the previous moment respectively.

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