High-precision high-maneuvering steering control method for distributed electric drive vehicle

Abstract

The invention relates to the technical field of vehicle steering control, in particular to a high-precision high-maneuvering steering control method for a distributed electric drive vehicle. According to the method, on the basis of four wheels independently driven by a distributed electric drive vehicle, any wheel is controlled to be a circle center wheel, and on the basis of set parameters such as road gradient, adhesion coefficient, driving system / steering system / braking system state, steering direction, steering angle and steering speed, the driving system / steering system / braking system state is determined. The front wheel turning angle and the target rotating speed of the non-circle center wheel are solved, the optimization target is that the displacement error of the circle center wheel is minimum, and compass steering control is conducted through clockwise or anticlockwise rotation. According to the high-precision and high-maneuvering steering control method for the distributed electrically-driven vehicle, the rotating speed, the steering angle and the braking state of each driving wheel are controlled in a coordinated mode based on the four-wheel independent controllable characteristic of the distributed electrically-driven vehicle, the limitation of the fixed steering center and the steering radius of a traditional vehicle is broken through, and flexible maneuvering control with the higher degree of freedom is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of vehicle steering control, in particular to a high-precision high-maneuverability steering control method for a distributed electric drive vehicle. BACKGROUND

[0002] With the rapid development of urban traffic, especially in some old urban areas, due to the lagging of traffic network planning and the influence of non-standard traffic behaviors such as random parking, some roads are often narrow and congested, which seriously affects the efficiency of vehicle traffic, especially for emergency rescue vehicles. Due to the structural limitations of traditional vehicles, the steering radius is large and the steering center is fixed, so it is difficult to steer flexibly in narrow spaces, and frequent reversing adjustment is required, which leads to complex operation and low efficiency, and seriously restricts the maneuverability of the vehicle.

[0003] In recent years, with the development of distributed electric drive technology, some vehicle models have realized four-wheel independent drive control, which can adjust the torque of each wheel through differential, thereby breaking through the limitations of traditional steering radius and steering center. Typical methods include locking one wheel and driving the remaining wheels around the wheel through differential, forming so-called "compass steering" motion. This steering method not only significantly reduces the minimum turning radius of the vehicle, but also flexibly adjusts the position of the rotation center, effectively improving the passing and turning ability of the vehicle in narrow spaces.

[0004] However, vehicle control in narrow spaces requires higher accuracy of motion displacement. If the trajectory deviates during the compass steering process of the vehicle, it may cause scratching, collision and other safety problems, especially in environments with small parking space gaps and clear boundaries. Currently, there is still a lack of research and control strategies specifically for compass steering displacement accuracy. Improving the motion displacement control accuracy during compass steering can not only enhance the safety of this technology, but also further improve its practicality and promotional value in complex environments. SUMMARY

[0005] The present application provides a high-precision high-maneuverability steering control method for a distributed electric drive vehicle, which can be integrated into advanced control technologies such as vehicle assisted driving, improving the maneuverability of the vehicle and the efficiency of passing in narrow spaces.

[0006] The present application adopts the following technical solutions

[0007] The high-precision high-maneuverability steering control method for a distributed electric drive vehicle according to the present application is based on the four wheels of a distributed electric drive vehicle, and controls any wheel as a center wheel through compass steering motion. The clockwise or counterclockwise steering control method includes the following steps:

[0008] Step 1: Confirm that the current vehicle speed is 0, the vehicle is in P-gear parking state, and start the compass steering control system;

[0009] The second step, the compass turning control system obtains the road slope, the adhesion coefficient, the driving system / steering system / braking system state through the vehicle controller, and verifies whether the compass turning motion condition is met; if met, the next step is entered; if not met, the error information is cancelled and fed back;

[0010] The third step, the steering parameters of the vehicle, the center wheel, the steering direction, the steering angle and the steering speed are set;

[0011] The fourth step, based on the road slope, the adhesion coefficient, the driving system / steering system / braking system state, and the center wheel, the steering direction, the steering angle, the steering speed and other setting parameters, the front wheel turning angle and the target speed of the non-center wheel are solved, and the optimization target is the minimum displacement error of the center wheel;

[0012] The fifth step, according to the solving result of the fourth step combined with the parameters set in the third step, the center wheel is locked by the braking system, and the front wheel turning angle is turned to the target angle by the steering system.

[0013] The fourth step in the high-precision high-maneuvering steering control method of the distributed electric drive vehicle, when the left front wheel is set as the center wheel, the wheel speed And the optimization model of the front wheel turning angle δ is as follows:

[0014]

[0015]

[0016] Wherein, is the longitudinal component of the tire force of each wheel in the vehicle body coordinate system, is the transverse component, LF, RF, LR and RR represent the left front wheel, the right front wheel, the left rear wheel and the right rear wheel respectively; are the longitudinal force and the lateral force of the tire respectively; are the speed components of the non-center wheel in the X-axis and Y-axis of the vehicle body coordinate system respectively; are the longitudinal and lateral slip speeds respectively;

[0017] are the maximum slip tire force of the left front wheel, the right front wheel, the left rear wheel and the right rear wheel respectively, B is the wheel track, r is the wheel rolling radius, L is the wheelbase, m is the mass of the vehicle, g is the gravitational acceleration, μ is the road adhesion coefficient, L f is the distance from the mass center to the front axle, L r is the distance from the mass center to the rear axle, because ω v is a preset target value, and the to-be-optimized parameters are: δ,

[0018] Furthermore, y (mu, F z , x) = d*sin(c*arctan(b*x*(1-e)+e*arctan(b*x)));

[0019] d = mu (a1*F z 2 +a2*F z ) as a peak factor, a1 and a2 are related parameters, c is a shape factor, b is a stiffness factor, and e is a curvature factor.

[0020] The fourth step of the high-precision high-maneuverability steering control method for the distributed electric drive vehicle is to solve the target rotating speed of the non-circular center wheel and the front wheel rotating angle, when the right front wheel is set as the circular center wheel, the wheel speed and the front wheel rotating angle δ are optimized as follows:

[0021]

[0022] wherein,

[0023]

[0024] The to-be-optimized parameters are δ,

[0025] is the longitudinal force of each wheel tire in the body coordinate system, is the transverse force, and LF, RF, LR and RR represent the left front wheel, the right front wheel, the left rear wheel and the right rear wheel respectively; are the longitudinal force and the lateral force of the tire respectively; are the speed components of the non-circular center wheel in the X-axis and Y-axis of the body coordinate system respectively; are the longitudinal and lateral slip speeds respectively;

[0026] are the maximum slip tire forces of the left front wheel, the right front wheel, the left rear wheel and the right rear wheel respectively, B is the wheel track, r is the wheel rolling radius, L is the wheelbase, m is the vehicle mass, g is the gravity acceleration, mu is the road adhesion coefficient, L f is the distance from the mass center to the front axle, L r is the distance from the mass center to the rear axle, because omega v is a preset target value, and the to-be-optimized parameters are δ,

[0027] The fourth step of the high-precision high-maneuverability steering control method for the distributed electric drive vehicle is to solve the target rotating speed of the non-circular center wheel and the front wheel rotating angle, when the left rear wheel is set as the circular center wheel, the wheel speed and the front wheel rotating angle δ are optimized as follows:

[0028]

[0029] wherein:

[0030]

[0031] is the longitudinal component of the tire force of each wheel in the body coordinate system, is the lateral component, and LF, RF, LR and RR represent the left front wheel, the right front wheel, the left rear wheel and the right rear wheel, respectively; are the longitudinal and lateral forces of the tire, respectively; are the component velocities of the non-circular center wheel in the X and Y axes of the body coordinate system, respectively; are the longitudinal and lateral slip velocities, respectively;

[0032] are the maximum slip tire force magnitudes of the left front wheel, the right front wheel, the left rear wheel and the right rear wheel, respectively, B is the wheel track, r is the rolling radius of the wheel, L is the wheelbase, m is the mass of the vehicle, g is the gravitational acceleration, and μ is the road adhesion coefficient, L f is the distance from the center of mass to the front axle, L r is the distance from the center of mass to the rear axle, and ω v is a preset target value, and the to-be-optimized parameters are: δ,

[0033] The high-precision high-maneuverability steering control method for the distributed electric drive vehicle, the fourth step is to solve the target rotating speed of the front wheel and the non-circular center wheel, when the right rear wheel is set as the circular center wheel, the wheel speed and the optimization model of the front wheel rotating angle δ is established as follows:

[0034]

[0035] wherein:

[0036]

[0037] is the longitudinal component of the tire force of each wheel in the body coordinate system, is the lateral component, and LF, RF, LR and RR represent the left front wheel, the right front wheel, the left rear wheel and the right rear wheel, respectively; are the longitudinal and lateral forces of the tire, respectively; are the component velocities of the non-circular center wheel in the X and Y axes of the body coordinate system, respectively; are the longitudinal and lateral slip velocities, respectively;

[0038] respectively, are the maximum slip tire force of the left front wheel, the right front wheel, the left rear wheel and the right rear wheel, B is the wheel track, r is the wheel rolling radius, L is the wheel base, m is the vehicle mass, g is the gravity acceleration, μ is the road adhesion coefficient, L f is the distance from the mass center to the front axle, L r is the distance from the mass center to the rear axle, because ω v is the preset target value, and the to-be-optimized parameters are δ,

[0039] The high-precision high-maneuverability steering control method of the distributed electric drive vehicle disclosed by the application solves the optimization model by using a particle swarm optimization algorithm respectively according to the optimization models of the left front wheel, the right front wheel, the left rear wheel and the right rear wheel, and obtains a target front wheel steering angle and a non-circular center wheel target rotating speed.

[0040] In the fifth step, the driving system tracks the non-circular center wheel target rotating speed through a PI controller, and the expression is as follows:

[0041]

[0042] wherein T i is the output torque of each wheel, K P and K I are controller parameters, is the target rotating speed of each wheel, is the real-time rotating speed of each wheel.

[0043] In the high-precision high-maneuverability steering control method of the distributed electric drive vehicle, when it is detected that there is an obstacle in the motion trajectory, or the function self-checking condition is not met, or the steering angle is about to reach, the driving system and the braking system control the non-circular center wheel rotating speed to be 0.

[0044] Advantages

[0045] The high-precision high-maneuverability steering control method of the distributed electric drive vehicle provided by the application breaks through the limitation of the fixed steering center and the steering radius of the traditional vehicle, realizes higher degree of freedom flexible maneuvering control, and is based on the four-wheel independent control characteristics, coordinates the rotating speed, the steering angle and the braking state of each driving wheel.

[0046] The high-precision high-maneuverability steering control method of the distributed electric drive vehicle provided by the application effectively reduces the displacement error of the circular center wheel and improves the control precision of the whole vehicle by modeling the compass steering control as a nonlinear optimization problem and a rotating speed tracking problem, and globally optimizing the control variables by using a particle swarm algorithm. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1is a flow chart of the high-precision high-maneuverability steering control method of the distributed electric drive vehicle of the present application;

[0048] Figure 2 is an 8-way steering schematic diagram of the high-precision high-maneuverability steering control method of the distributed electric drive vehicle of the present application. DETAILED DESCRIPTION

[0049] To make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the embodiments of the present application will be described below in connection with the drawings of the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the described embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without any creative effort belong to the scope of the present application.

[0050] As shown in Figure 1 , Figure 2 , the high-precision high-maneuverability steering control method of the distributed electric drive vehicle of the present application is described. For the distributed electric drive vehicle, the four wheels can be independently driven, the compass steering motion can select any one of the four wheels as the center wheel, the motion direction can select clockwise rotation or counterclockwise rotation, and the front wheel steering angle can assist the compass steering motion. Specifically, the following steps are included:

[0051] Step 1: Function start: the vehicle speed is 0, the vehicle is in P gear, and the driver selects to start the compass steering motion function through the central control screen.

[0052] Step 2: Function self-check: the compass steering control system obtains the road slope, adhesion coefficient, driving system / steering system / braking system state through the vehicle controller, and verifies whether the compass steering motion condition is met. If the verification fails, the failure reason is directly fed back through the central control screen, and if the verification passes, the next step is entered.

[0053] Step 3: Function setting: the driver sets the center wheel, steering direction, steering angle, and steering speed through the central control screen.

[0054] Step 4: Target wheel speed-front wheel steering angle optimization: the compass steering control system solves the target speed of the non-center wheel and the front wheel steering angle according to the environmental parameters and the set parameters in steps 1 and 3, and the optimization target is the minimum displacement error of the center wheel.

[0055] When the left front wheel is set as the center wheel, the wheel speed and the front wheel steering angle δ optimization model is as follows:

[0056]

[0057] wherein, are the maximum slip tire forces of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively. B is the wheel base, L is the wheel track, m is the mass of the vehicle, g is the acceleration of gravity, μ is the road adhesion coefficient, L f is the distance from the mass center to the front axle, L r is the distance from the mass center to the rear axle. Because ω v is a preset target value, the parameters to be optimized are: δ,

[0058] In addition, y(μ, F z , x) = d sin(c arctan(bx(1-e)+e arctan(bx))), d = μ(a1F z 2 +a2F z ) is a peak factor, a1 and a2 are related parameters, c is a shape factor, b is a stiffness factor, and e is a curvature factor.

[0059] When the right front wheel is set as a center pivot wheel, the optimization model of wheel speed and front wheel steering angle is established as follows:

[0060]

[0061] wherein, The parameters to be optimized are: δ,

[0062] When the left rear wheel is set as a center pivot wheel, the optimization model of wheel speed and front wheel steering angle is established as follows:

[0063]

[0064] wherein,

[0065]

[0066] The parameters to be optimized are: δ,

[0067] When the right rear wheel is set as a center pivot wheel, the optimization model of wheel speed and front wheel steering angle is established as follows:

[0068]

[0069] wherein,

[0070]

[0071] The parameters to be optimized are: δ,

[0072] For the above four optimization problems, the particle swarm optimization algorithm is used to solve them, and the target front wheel steering angle and the target speed of the non-circular center wheel are obtained.

[0073] The particle swarm algorithm solving process is as follows:

[0074] 1) Initialize the particle swarm: set the particle swarm size N, each particle corresponds to a control parameter combination X i , and initialize the velocity vector V i ;

[0075] 2) Evaluate fitness: each particle calculates the corresponding displacement error objective function J(X i ) according to the vehicle simulation model;

[0076] 3) Update individual optimal and global optimal solutions;

[0077] 4) According to the particle swarm update formula:

[0078] V i (t+1)=ωV i (t)+c1r1(p i -X i )+c2r2(g-X i )

[0079] X i (t+1)=X i (t)+V i (t+1)

[0080] Where ω is the inertia weight, c1 and c2 are learning factors, and r1 and r2 are random numbers in the interval [0, 1];

[0081] 5) Repeat iteration until the maximum iteration number or error convergence condition is met.

[0082] Step 5, function execution: according to the parameters set in step three and the solution results in step four, the brake system locks the circular center wheel, the steering system turns the front wheel steering angle to the target angle, and the drive system tracks the target speed of the non-circular center wheel through the PI controller.

[0083] First, the steering system turns the front wheel steering angle to the target angle to ensure that it does not rotate. Then, the brake system applies sufficient brake pressure to the circular center wheel brake. Finally, the drive system controls the torque output through the PI controller to track the target speed of the non-circular center wheel, as follows.

[0084]

[0085] Where T i is the output torque of each wheel, K P and KI for the controller parameters, for each wheel target speed, for each wheel real-time speed.

[0086] Sixth step, function stop: when detecting that there is an obstacle in the movement track, or the function self-check condition is not met, or the steering angle is about to reach, the driving system and the braking system control the non-circular center wheel speed to be 0 during the movement.

[0087] Those skilled in the art can understand that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless otherwise defined.

[0088] With the above ideal embodiments according to the present application as the inspiration, through the above description, relevant personnel can certainly make various changes and modifications within the scope of not deviating from the technical idea of the present application. The technical scope of the present application is not limited to the content in the specification, and must be determined according to the scope of claims.

Claims

1. A high-precision and high-maneuverability steering control method for a distributed electric drive vehicle, characterized in that: A method for controlling the four independently driven wheels of a distributed electric drive vehicle to rotate clockwise or counterclockwise by controlling any one of the four wheels as the center wheel through compass steering motion includes the following steps: Step 1: Confirm that the current vehicle speed is 0, the vehicle is in the P gear parking state, and start the compass steering control system; In the second step, the compass steering control system obtains the road slope, adhesion coefficient, and the status of the drive system / steering system / brake system through the vehicle controller, and verifies whether the compass steering motion conditions are met; if so, it proceeds to the next step; if not, it cancels and returns an error message; Step 3: Set the vehicle's steering parameters, center wheel, steering direction, steering angle, and steering speed; Step 4: Based on the road slope, adhesion coefficient, drive system / steering system / brake system status, as well as the center wheel, steering direction, steering angle, and steering speed as set parameters, the front wheel angle and the target speed of the non-center wheel are solved. The optimization goal is to minimize the displacement error of the center wheel. Step 5. Based on the solution of step 4 and the parameters set in step 3, the braking system locks the center wheel and the steering system turns the front wheel angle to the target angle.

2. The high-precision and high-maneuverability steering control method for a distributed electric drive vehicle according to claim 1, characterized in that: In the fourth step, the target speed of the front wheel angle and the non-center wheel is solved. When the left front wheel is set as the center wheel, the wheel speed is established. The optimization model of the front wheel steering angle δ is as follows: in, is the longitudinal component of each wheel tire force in the vehicle body coordinate system, is the lateral force component, LF, RF, LR, and RR represent the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively; are the tire longitudinal force and lateral force respectively; are the component velocities of the non-center wheel in the X-axis and Y-axis of the vehicle body coordinate system respectively; are the longitudinal and lateral slip velocities, respectively; They are the maximum slip tire forces of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively, B is the wheelbase, r is the wheel rolling radius, L is the wheelbase, m is the vehicle mass, g is the acceleration of gravity, μ is the road adhesion coefficient, and L f is the distance from the center of mass to the front axle, L r is the distance from the center of mass to the rear axle, because ω v is the preset target value, and the parameters to be optimized are: δ, 3. The high-precision and high-maneuverability steering control method for a distributed electric drive vehicle according to claim 1, characterized in that: In the fourth step, the target speed of the front wheel angle and the non-center wheel is solved. When the right front wheel is set as the center wheel, the wheel speed is established. The optimization model of the front wheel steering angle δ is as follows: in, The parameters to be optimized are: δ, is the longitudinal component of each wheel tire force in the vehicle body coordinate system, is the lateral force component, LF, RF, LR, and RR represent the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively; are the tire longitudinal force and lateral force respectively; are the component velocities of the non-center wheel in the X-axis and Y-axis of the vehicle body coordinate system respectively; are the longitudinal and lateral slip velocities, respectively; They are the maximum slip tire forces of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively, B is the wheelbase, r is the wheel rolling radius, L is the wheelbase, m is the vehicle mass, g is the acceleration of gravity, μ is the road adhesion coefficient, and L f is the distance from the center of mass to the front axle, L r is the distance from the center of mass to the rear axle, because ω v is the preset target value, and the parameters to be optimized are: δ, 4. The high-precision and high-maneuverability steering control method for a distributed electric drive vehicle according to claim 1, characterized in that: In the fourth step, the target speed of the front wheel angle and the non-center wheel is solved. When the left rear wheel is set as the center wheel, the wheel speed is established. The optimization model of the front wheel steering angle δ is as follows: in: is the longitudinal component of each wheel tire force in the vehicle body coordinate system, is the lateral force component, LF, RF, LR, and RR represent the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively; are the tire longitudinal force and lateral force respectively; are the component velocities of the non-center wheel in the X-axis and Y-axis of the vehicle body coordinate system respectively; are the longitudinal and lateral slip velocities, respectively; They are the maximum slip tire forces of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively, B is the wheelbase, r is the wheel rolling radius, L is the wheelbase, m is the vehicle mass, g is the acceleration of gravity, μ is the road adhesion coefficient, and L f is the distance from the center of mass to the front axle, L r is the distance from the center of mass to the rear axle, because ω v is the preset target value, and the parameters to be optimized are: δ, 5. The high-precision and high-maneuverability steering control method for a distributed electric drive vehicle according to claim 1, characterized in that: In the fourth step, the target speed of the front wheel angle and the non-center wheel is solved. When the right rear wheel is set as the center wheel, the wheel speed is established. The optimization model of the front wheel steering angle δ is as follows: in: is the longitudinal component of each wheel tire force in the vehicle body coordinate system, is the lateral force component, LF, RF, LR, and RR represent the left front wheel, right front wheel, left rear wheel, and right rear wheel respectively; are the tire longitudinal force and lateral force respectively; are the component velocities of the non-center wheel in the X-axis and Y-axis of the vehicle body coordinate system respectively; are the longitudinal and lateral slip velocities, respectively; They are the maximum slip tire forces of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively, B is the wheelbase, r is the wheel rolling radius, L is the wheelbase, m is the vehicle mass, g is the acceleration of gravity, μ is the road adhesion coefficient, and L f is the distance from the center of mass to the front axle, L r is the distance from the center of mass to the rear axle, because ω v is the preset target value, and the parameters to be optimized are: δ, 6. The high-precision and high-maneuverability steering control method for a distributed electric drive vehicle according to claim 2, 3, 4, or 5, characterized in that: The particle swarm optimization algorithm is used to solve the optimization models of the left front wheel, right front wheel, left rear wheel and right rear wheel respectively, and the target front wheel angle and the target speed of the non-center wheel are obtained.

7. The high-precision and high-maneuverability steering control method for a distributed electric drive vehicle according to claim 1, characterized in that: In the fifth step, the drive system tracks the target speed of the non-center wheel through the PI controller, which is expressed as follows: Among them, T i is the output torque of each wheel, K P and K I is the controller parameter, is the target speed of each wheel, The real-time rotation speed of each wheel.

8. The high-precision and high-maneuverability steering control method for a distributed electric drive vehicle according to claim 1, characterized in that: During vehicle movement, when an obstacle is detected in the motion trajectory, or the function self-test conditions are not met, or the steering angle is about to be reached, the drive system and braking system control the non-center wheel speed to 0.

Images