A coordinated control method of a dual-motor steer-by-wire system based on dynamic programming

Abstract

The application discloses a kind of based on dynamic programming's coordinated control method of double-motor steer-by-wire system, it is related to automatic driving steering control technical field, solve the technical problem that double-motor steer-by-wire system energy consumption is higher, its technical scheme main point is by establishing double-motor coupling steering model, and deduces the coordinated control model with motor energy consumption minimum as target;Based on dynamic programming method, the coordinated control model is solved discretely, realizes the dynamic torque distribution of double-motor steer-by-wire system, under the premise of guaranteeing steering safety, makes automobile double-motor steer-by-wire system energy optimal, to match optimal steering mode under different working conditions, improve steering efficiency.

Description

Technical Field

[0001] This application relates to the field of autonomous driving steering control technology, and in particular to a coordinated control method for a dual-motor steer-by-wire system based on dynamic programming. Background Technology

[0002] As a key component of steer-by-wire chassis systems, steer-by-wire systems have consistently been a research hotspot for automakers and academia both domestically and internationally. According to China's "Intelligent Connected Vehicle Technology Roadmap," the industrialization and application of intelligent steer-by-wire chassis systems will be achieved by 2025. Through steer-by-wire and intelligent control, steer-by-wire systems can achieve goals such as personalized driving, assisted driving, and autonomous driving, making them a crucial technology for the practical application of intelligent connected vehicles.

[0003] The main structural feature of steer-by-wire systems, compared to traditional mechanical steering systems, is the elimination of mechanical connecting devices such as the steering column. Instead, commands are transmitted via wires or electrical signals to control the vehicle. Its flexible control method and rapid, precise response characteristics highly align with the development needs of modern electric and intelligent vehicles. By coordinating the control of the steer-by-wire components, the steering system can possess fault-tolerant capabilities. Using a dual-motor steer-by-wire system can significantly improve the system's fault tolerance; if one motor fails, the other can perform the steering operation, ensuring normal vehicle operation. However, increasing the number of motors leads to increased energy consumption. How to allocate the output power of multiple motors while balancing redundancy, safety, and energy efficiency in a dual-motor steering system remains a pressing issue. Summary of the Invention

[0004] This application provides a coordinated control method for a dual-motor steer-by-wire system based on dynamic programming. Its technical objective is to reduce the overall energy consumption of the steer-by-wire system while ensuring vehicle steering safety.

[0005] The above-mentioned technical objective of this application is achieved through the following technical solution:

[0006] A coordinated control method for a dual-motor steer-by-wire system based on dynamic programming is disclosed. The dual-motor steer-by-wire system includes an upper-level electronic control unit (ECU), a left steering motor controller, a right steering motor controller, a left steering motor, a right steering motor, a left clutch, a right clutch, a torque coupler, a steering gear, a rack, a left steering tie rod, a right steering tie rod, a left front wheel, and a right front wheel. The upper-level ECU controls the left and right steering motor controllers. The left steering motor controller controls the left steering motor via a torque signal and controls the engagement state of the left clutch. The right steering motor controller controls the right steering motor via a torque signal and controls the engagement state of the right clutch. The outputs of both the left and right clutches are connected to the input of the torque coupler. The output of the torque coupler is connected to the steering gear, which is connected to the rack. The rack is connected to the left and right front wheels via the left and right steering tie rods, respectively. The method includes:

[0007] S1: Construct a dynamic model of the dual-motor steer-by-wire system, and establish an efficiency model of the dual-motor steer-by-wire system based on the dynamic model;

[0008] S2: Obtain the objective function to be optimized for the coordinated control model of the dual-motor steer-by-wire system through the efficiency model;

[0009] S3: Construct failure models for the left and right steering motors, and obtain the constraints of the coordinated control model of the dual-motor steer-by-wire system based on the failure models and coupling characteristics.

[0010] S4: Construct a coordinated control model based on the objective function to be optimized and the constraints;

[0011] S5: Solve for the optimal solution of the coordinated control model, and perform coordinated control of the dual-motor steer-by-wire system based on the optimal solution.

[0012] The beneficial effects of this application are as follows: The coordinated control method for a dual-motor steer-by-wire system based on dynamic programming described in this application establishes a dual-motor coupled steering model and derives a coordinated control model with the goal of minimizing motor energy consumption; the coordinated control model is solved discretely based on dynamic programming to achieve dynamic torque distribution of the dual-motor steer-by-wire system, thereby optimizing the energy of the dual-motor steer-by-wire system under the premise of ensuring steering safety, and thus matching the optimal steering mode under different operating conditions, thereby improving steering efficiency. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the dual-motor steer-by-wire system in an embodiment of this application;

[0014] Figure 2 This is a flowchart of the coordinated control method for a dual-motor steer-by-wire system based on dynamic programming, as described in this application.

[0015] In the diagram: 1-Upper-level electronic control unit, 2-Left steering motor controller, 3-Left steering motor, 4-Left clutch, 5-Right clutch, 6-Right steering motor, 7-Right steering motor controller, 8-Torque coupler, 9-Steering gear, 10-Rack, 11-Left front wheel, 12-Left steering tie rod, 13-Right steering tie rod, 14-Right front wheel. Detailed Implementation

[0016] The technical solution of this application will be described in detail below with reference to the accompanying drawings.

[0017] Figure 1 This is a schematic diagram of the dual-motor steer-by-wire system in an embodiment of this application, as shown below. Figure 1 As shown, the dual-motor steer-by-wire system includes an upper-level electronic control unit 1, which receives the vehicle's desired front wheel steering angle command δ. f After calculations by the dual-motor steer-by-wire coordinated control strategy, the output torque command of the motors is sent to the left steering motor controller 2 and the right steering motor controller 7. The left steering motor controller 2 controls the left steering motor 3, and through the left clutch 4, outputs torque to the input of the torque coupler 8. The right steering motor controller 7 controls the right steering motor 6, and through the right clutch 5, outputs torque to the input of the torque coupler 8. The torque coupler 8 outputs the coupled torque to the connected steering gear 9. The steering gear 9 in the rack and pinion rotates to a specific angle θ, causing the rack 10 to produce lateral displacement. The rack 10 drives the left steering tie rod 12 and the right steering tie rod 13 to produce displacement, ultimately pulling the left front wheel 11 and the right front wheel 14, completing the steering command.

[0018] Figure 2 This is a flowchart of a coordinated control method for a dual-motor steer-by-wire system based on dynamic programming, as described in this application. The specific steps of this method include:

[0019] S1: Construct a dynamic model of the dual-motor steer-by-wire system, and establish an efficiency model of the dual-motor steer-by-wire system based on the dynamic model.

[0020] Specifically, the dynamic model of the dual-motor steer-by-wire system is expressed as follows:

[0021]

[0022] Where θ represents the gear rotation angle, B R J represents the equivalent damping coefficient. R Let G represent the equivalent moment of inertia, G represent the gear rotation angle to wheel deceleration, T represent the output torque of the torque coupler, and τ represent the torque of the torque coupler. R The t represents the tire's self-aligning torque. L and tR Let β represent the trail of the left and right front wheels respectively, β represent the sideslip angle of the vehicle's center of gravity, a represent the distance from the vehicle's center of gravity to the front axle, u represent the vehicle's longitudinal speed, and ω represent the following values: r δ represents the yaw rate. f The front wheel steering angle is represented by k1, and the front wheel lateral stiffness is represented by k1.

[0023] An efficiency model for the dual-motor steer-by-wire system is established using a dynamic model, including:

[0024] Based on the dynamic model, the desired gear angle θ of the vehicle is obtained through the upper-level electronic control unit. req And the steering torque T required by the vehicle req Calculate the required steering torque T req The ratio α is allocated between the left steering motor and the right steering motor, expressed as follows:

[0025]

[0026] Among them, T m1 T represents the steering torque provided by the left steering motor. m2 This indicates the steering torque provided by the right steering motor;

[0027] According to T m1 and T m2 The efficiency model of the dual-motor steer-by-wire system is established as follows:

[0028]

[0029] Among them, P m1 and P m2 ω represents the power of the left steering motor and the right steering motor, respectively. m1 and ω m2 η represents the rotational speeds of the left and right steering motors, respectively. m1 and η m2 These represent the output efficiencies of the left steering motor and the right steering motor, respectively.

[0030] S2: The objective function to be optimized for the coordinated control model of the dual-motor steer-by-wire system is obtained through the efficiency model. This objective function is expressed as:

[0031]

[0032] S3: Construct failure models for the left and right steering motors, and obtain the constraints of the coordinated control model of the dual-motor steer-by-wire system based on the failure models and coupling characteristics.

[0033] The fault condition of dual motors can be represented by the motor failure model, namely:

[0034]

[0035] Where λ1 and λ2 represent the failure coefficients of the left steering motor and the right steering motor, respectively, and T dmin1 and T dmax1 T represents the ideal minimum output torque and ideal maximum output torque of the left steering motor, respectively. dmin2 and T dmax2 These represent the ideal minimum output torque and the ideal maximum output torque of the right steering motor, respectively.

[0036] Based on the failure model and coupling characteristics, the constraints of the coordinated control model of the dual-motor steer-by-wire system are obtained, and are expressed as follows:

[0037]

[0038] S4: Construct a coordinated control model based on the objective function to be optimized and the constraints. This coordinated control model is then expressed as:

[0039]

[0040] S5: Solve for the optimal solution of the coordinated control model, and perform coordinated control of the dual-motor steer-by-wire system based on the optimal solution.

[0041] Specifically, the optimal solution of the coordinated control model is obtained, including:

[0042] S51: Connect the coordinated control model in the control time domain to obtain the discrete objective function, expressed as:

[0043]

[0044] Where Δt represents the time step, N represents the number of steps, and P m1 (k) and P m2 (k) represents the output torque of the left steering motor and the right steering motor at step k, respectively, and θ(k) represents the gear rotation angle at step k. req (k) represents the ideal gear rotation angle at step k;

[0045] S52: Discretize the dynamic model described in equation (1) to obtain:

[0046]

[0047] S53: Discretizing the constraint conditions described in equation (6), we obtain:

[0048]

[0049] S54: The discretized coordinated control model is obtained from equations (8) to (10). The discretized coordinated control model is solved in reverse and optimized in forward to obtain the optimal output torque sequence of the left steering motor and the right steering motor. The solution process is expressed as follows:

[0050]

[0051] Where L(θ(k),u(k)) both represent state transition costs; J * (θ * (k) represents the optimal objective function value at step k; u * (k) represents the optimal control law, i.e., the optimal motor output torque; θ * (k) is the optimal state variable, i.e., the optimal gear rotation angle.

[0052] The above are exemplary embodiments of this application, and the scope of protection of this application is defined by the claims and their equivalents.

Claims

1. A coordinated control method for a dual-motor steer-by-wire system based on dynamic programming, the dual-motor steer-by-wire system comprising an upper-level electronic control unit, a left steering motor controller, a right steering motor controller, a left steering motor, a right steering motor, a left clutch, a right clutch, a torque coupler, a steering gear, a rack, a left steering tie rod, a right steering tie rod, a left front wheel, and a right front wheel; the upper-level electronic control unit controls the left steering motor controller and the right steering motor controller; the left steering motor controller controls the left steering motor via a torque signal and controls the engagement state of the left clutch; the right steering motor controller controls the right steering motor via a torque signal and controls the engagement state of the right clutch; the output ends of both the left and right clutches are connected to the input end of the torque coupler, the output end of the torque coupler is connected to the steering gear, the steering gear is connected to the rack, and the rack is connected to the left front wheel and the right front wheel via the left and right steering tie rods, respectively; characterized in that... The method includes: S1: Construct a dynamic model of the dual-motor steer-by-wire system, and establish an efficiency model of the dual-motor steer-by-wire system based on the dynamic model; S2: Obtain the objective function to be optimized for the coordinated control model of the dual-motor steer-by-wire system through the efficiency model; S3: Construct failure models for the left and right steering motors, and obtain the constraints of the coordinated control model of the dual-motor steer-by-wire system based on the failure models and coupling characteristics. S4: Construct a coordinated control model based on the objective function to be optimized and the constraints; S5: Solve for the optimal solution of the coordinated control model, and perform coordinated control of the dual-motor steer-by-wire system based on the optimal solution; In step S2, the objective function to be optimized is expressed as: Among them, P m1 and P m2 These represent the power of the left steering motor and the right steering motor, respectively, and θ represents the gear rotation angle. req This indicates the desired gear rotation angle of the vehicle.

2. The method as described in claim 1, characterized in that, In step S1, the dynamic model is expressed as: Where θ represents the gear rotation angle, B R J represents the equivalent damping coefficient. R Let G represent the equivalent moment of inertia, G represent the gear rotation angle to wheel deceleration, T represent the output torque of the torque coupler, and τ represent the torque of the torque coupler. R The t represents the tire's self-aligning torque. L and t R Let β represent the trail of the left and right front wheels respectively, β represent the sideslip angle of the vehicle's center of gravity, a represent the distance from the vehicle's center of gravity to the front axle, u represent the vehicle's longitudinal speed, and ω represent the following values: r δ represents the yaw rate. f k1 represents the front wheel steering angle, and k1 represents the front wheel lateral stiffness. An efficiency model for the dual-motor steer-by-wire system is established using a dynamic model, including: Based on the dynamic model, the desired gear angle θ of the vehicle is obtained through the upper-level electronic control unit. req And the steering torque T required by the vehicle req Calculate the required steering torque T req The ratio α is allocated between the left steering motor and the right steering motor, expressed as follows: Among them, T m1 T represents the steering torque provided by the left steering motor. m2 This indicates the steering torque provided by the right steering motor; According to T m1 and T m2 The efficiency model of the dual-motor steer-by-wire system is established as follows: Among them, P m1 and P m2 ω represents the power of the left steering motor and the right steering motor, respectively. m1 and ω m2 η represents the rotational speeds of the left and right steering motors, respectively. m1 and η m2 These represent the output efficiencies of the left steering motor and the right steering motor, respectively.

3. The method as described in claim 2, characterized in that, In step S3, the failure model is represented as: Where λ1 and λ2 represent the failure coefficients of the left steering motor and the right steering motor, respectively, and T dmin1 and T dmax1 T represents the ideal minimum output torque and ideal maximum output torque of the left steering motor, respectively. dmin2 and T dmax2 These represent the ideal minimum output torque and the ideal maximum output torque of the right steering motor, respectively. Based on the failure model and coupling characteristics, the constraints of the coordinated control model of the dual-motor steer-by-wire system are obtained, and are expressed as follows:

4. The method as described in claim 3, characterized in that, In step S4, the coordination control model is represented as follows:

5. The method as described in claim 4, characterized in that, In step S5, the optimal solution of the coordinated control model is obtained, including: S51: Connect the coordinated control model in the control time domain to obtain the discrete objective function, expressed as: Where Δt represents the time step, N represents the number of steps, and P m1 (k) and P m2 (k) represents the output torque of the left steering motor and the right steering motor at step k, respectively, and θ(k) represents the gear rotation angle at step k. req (k) represents the ideal gear rotation angle at step k; S52: Discretize the dynamic model described in equation (1) to obtain: S53: Discretizing the constraint conditions described in equation (6), we obtain: S54: The discretized coordinated control model is obtained from equations (8) to (10). The discretized coordinated control model is solved in reverse and optimized in forward to obtain the optimal output torque sequence of the left steering motor and the right steering motor. The solution process is expressed as follows: Where L(θ(k),u(k)) both represent state transition costs; J * (θ * (k) represents the optimal objective function value at step k; u * (k) represents the optimal control law, i.e., the optimal motor output torque; θ * (k) is the optimal state variable, i.e., the optimal gear rotation angle.

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