Differential turning control system and control method thereof for a distributed drive vehicle

Abstract

The present application relates to the technical field of vehicle chassis control, in particular to a kind of distributed drive vehicle in situ differential turning control system and control method thereof;Including wheel speed sensor, motor torque controller, current controller, actuator, reference speed acquisition module, road adhesion estimation module, MPC additional torque calculation module and torque distribution module, the adhesion coefficient of the road surface contacted by each tire is estimated by road adhesion estimation module, the active additional torque required by each wheel is calculated by MPC additional torque calculation module, and the actual torque is input to the motor torque controller of whole vehicle by torque distribution module;Current controller controls the current required by actuator in real time, and actuator applies the required active torque to each wheel in real time, so that the working speed of the wheel continuously approaches the reference speed, and the in situ turning control system and method utilize MPC control theory, and can realize the in situ turning function of distributed drive vehicle under different adhesion conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of vehicle chassis control, and particularly relates to a distributed drive vehicle original differential turning control system and a control method thereof. BACKGROUND

[0002] The original steering of an automobile mainly relies on two different mechanisms.

[0003] One is the way without a steering system. This method is commonly used in military vehicles such as tanks, which realize the original steering by reversing the rotation of the two sides of the track or wheel. BYD U8 also demonstrates a similar steering method, but when used on high adhesion road surface, there will be a certain degree of wear on the tires, transmission system and road surface.

[0004] The other way is to rely on the steering system of the automobile. JEEP's concept car Hurricane adopts a symmetrical structure design, realizes the function of zero turning radius original turning, and has no lateral friction of the tire in the steering process, so it can realize smooth original steering on asphalt road surface. This design needs to make complex adjustment and optimization to the transmission system, suspension structure and steering mechanism of the vehicle. At the same time, in order to realize the original steering, the coaxial wheels need to be reversed, which requires additional clutches and differentials to control the power transmission of the wheels.

[0005] In summary, the existing automobile original turning control method cannot realize the original turning function of the distributed drive automobile under different adhesion conditions, and has great limitations. SUMMARY

[0006] The present application aims to provide a distributed drive vehicle original differential turning control system and a control method thereof, which solves the problem that the existing automobile original turning control method cannot realize the original turning function of the distributed drive automobile under different adhesion conditions, and has great limitations.

[0007] To achieve the above object, the application provides a distributed drive vehicle differential turning control system and a control method thereof, which comprises a wheel speed sensor, a motor torque controller, a current controller, an actuator, a reference speed acquisition module, a road adhesion estimation module, an MPC additional torque calculation module and a torque distribution module, the wheel speed sensor is fixedly arranged on a vehicle body of the distributed drive vehicle and electrically connected with a vehicle system of the distributed drive vehicle, the wheel speed sensor and the road adhesion estimation module are connected with the reference speed acquisition module, an input end of the MPC additional torque calculation module is connected with an output end of the reference speed acquisition module, an output end of the MPC additional torque calculation module is connected with an input end of the torque distribution module, the current controller and the motor torque controller are connected with an output end of the torque distribution module, the current controller is bidirectionally connected with the actuator, and the current controller and the vehicle system of the distributed drive vehicle are connected with an output end of the motor torque controller.

[0008] The wheel speed sensor, the reference speed acquisition module, the road adhesion estimation module, the MPC additional torque calculation module, the torque distribution module, the motor torque controller and the vehicle system of the distributed drive vehicle constitute a main loop, the motor torque controller, the current controller, the actuator and the vehicle system of the distributed drive vehicle constitute an inner loop, the main loop uses Kalman filtering to estimate the road adhesion coefficient in real time, and the reference speed is calculated according to the throttle opening and the road adhesion coefficient, then the active torque is calculated by using the actual speed of the wheel and the reference speed, and the torque distribution is completed, and the inner loop controls the actuator to realize the expected active torque control.

[0009] The wheel speed sensor collects the speed signal of each wheel in real time and sends the speed signal to the MPC additional torque calculation module in real time.

[0010] The road adhesion estimation module is used for estimating the road adhesion coefficient of each tire in real time based on the vehicle dynamics model according to the wheel end torque, the wheel speed and the yaw angular velocity.

[0011] The reference speed acquisition module is used for acquiring the reference speed of the vehicle by the opening of the accelerator pedal and the adhesion coefficient of the road where the wheel is currently located.

[0012] The current controller controls the current required by the actuator in real time according to the control instruction of the motor torque controller, and the actuator applies the required active torque on the wheel under the action of the current control, so that the wheel speed continuously approaches the reference value.

[0013] The application also provides a method for controlling the turning around of a distributed drive vehicle, which is applied to the turning around control system of a distributed drive vehicle and comprises the following steps:

[0014] S1, obtaining the calculation parameters of the turning around control system of the distributed drive vehicle;

[0015] S2, obtaining the wheel speed signal;

[0016] S3, estimating the road adhesion coefficient;

[0017] S4, considering the reference speed calculation of the road adhesion;

[0018] S5, designing the MPC controller;

[0019] S6, calculating the active torque of the wheel;

[0020] S7, the current controller controls the actuator;

[0021] S8, the wheel speed constantly approaches the reference value.

[0022] In the step S1, the calculation parameters include the wheel speed and torque of the left front wheel, the wheel speed and torque of the left rear wheel, the wheel speed and torque of the right front wheel, the wheel speed and torque of the right rear wheel and the reference wheel speed.

[0023] The turning around control system of a distributed drive vehicle and the control method thereof, which comprises a wheel speed sensor, a motor torque controller, a current controller, an actuator, a reference speed acquisition module, a road adhesion estimation module, an MPC additional torque calculation module and a torque distribution module. The road adhesion estimation module estimates the adhesion coefficient of the road surface contacted by each tire in real time by using Kalman filtering. The MPC additional torque calculation module calculates the reference speed according to the throttle opening and the estimated road adhesion coefficient, and calculates the active additional torque required by each wheel by processing the reference speed and the actual wheel speed through the model predictive controller (MPC). The torque distribution module inputs the actual torque required by each wheel into the motor torque controller of the whole vehicle. The current controller controls the current required by the actuator in real time according to the control instruction of the motor torque controller. The actuator applies the required active torque to each wheel in real time under the action of current control, so that the working speed of the wheel constantly approaches the reference speed. The turning around control system and method utilize the MPC control theory and can realize the turning around function of the distributed drive vehicle under different adhesion conditions. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative effort.

[0025] Figure 1 is the principle diagram of the distributed drive vehicle original differential U-turn control system provided by the present application.

[0026] Figure 2 is the step flow chart of the distributed drive vehicle original differential U-turn control method provided by the present application.

[0027] Figure 3 is the whole vehicle single degree of freedom equivalent model diagram of the distributed drive vehicle provided by the present application. DETAILED DESCRIPTION

[0028] The embodiments of the present application will be described in detail below, and examples of the embodiments are shown in the drawings, wherein the same or similar notations represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0029] Please refer to Figure 1 The present application provides a distributed drive vehicle original differential U-turn control system, which comprises a wheel speed sensor, a motor torque controller, a current controller, an actuator, a reference speed acquisition module, a road adhesion estimation module, an MPC additional torque calculation module and a torque distribution module. The wheel speed sensor is fixedly arranged on the vehicle body of the distributed drive vehicle and electrically connected with the vehicle system of the distributed drive vehicle. The wheel speed sensor and the road adhesion estimation module are connected with the reference speed acquisition module. The input end of the MPC additional torque calculation module is connected with the output end of the reference speed acquisition module. The output end of the MPC additional torque calculation module is connected with the input end of the torque distribution module. The current controller and the motor torque controller are connected with the output end of the torque distribution module. The current controller is bidirectionally connected with the actuator. The current controller and the vehicle system of the distributed drive vehicle are connected with the output end of the motor torque controller.

[0030] The wheel speed sensor, the reference speed acquisition module, the road adhesion estimation module, the MPC additional torque calculation module, the torque distribution module, the motor torque controller and the vehicle system of the distributed drive vehicle constitute a main loop, the motor torque controller, the current controller, the actuator and the vehicle system of the distributed drive vehicle constitute an inner loop, the main loop uses Kalman filtering to estimate the road adhesion coefficient in real time, and the reference speed calculated according to the accelerator opening degree and the road adhesion coefficient, then the active torque is calculated by using the actual speed of the wheel and the reference speed, and the torque distribution is completed, and the inner loop controls the actuator to realize the desired active torque control.

[0031] In the embodiment, the road adhesion estimation module estimates the adhesion coefficient of the road contacted by each tire in real time by using Kalman filtering, the MPC additional torque calculation module first calculates the reference speed according to the accelerator opening degree and the estimated road adhesion coefficient, and the active additional torque required by each wheel is calculated by using the model predictive controller (MPC) to process the reference speed and the actual speed of the wheel, and the torque distribution module inputs the actual torque required by each wheel to the motor torque controller of the whole vehicle; the current controller controls the current required by the actuator in real time according to the control instruction of the motor torque controller, and the actuator applies the required active torque to each wheel in real time under the action of current control, so that the working speed of the wheel continuously approaches the reference speed. The in-place turning control system and method can realize the in-place turning function of the distributed drive vehicle under different adhesion conditions by using the MPC control theory.

[0032] Further, the wheel speed sensor collects the speed signal of each wheel in real time and sends it to the MPC additional torque calculation module in real time.

[0033] Further, the road adhesion estimation module is used to estimate the road adhesion coefficient of each tire in real time based on the vehicle dynamics model according to the wheel end torque, the wheel speed and the yaw angular velocity.

[0034] Further, the reference speed acquisition module is used to acquire the reference speed of the vehicle by the opening degree of the accelerator pedal and the adhesion coefficient of the road currently occupied by the wheel.

[0035] Further, the current controller controls the current required by the actuator in real time according to the control instruction of the motor torque controller, and the actuator applies the required active torque to the wheel under the action of current control, so that the wheel speed continuously approaches the reference value.

[0036] Please refer to Figure 2 and Figure 3The application also provides a method for controlling differential turning of a distributed drive vehicle, which is applied to the system for controlling differential turning of a distributed drive vehicle and comprises the following steps.

[0037] S1, obtaining system calculation parameters

[0038] The equivalent model diagram of the controlled object of the system for controlling differential turning of a distributed drive vehicle is shown in the figure. Figure 3 The equivalent model diagram of the controlled object of the system for controlling differential turning of a distributed drive vehicle is shown in the figure. Figure 3 The equivalent model diagram of the controlled object of the system for controlling differential turning of a distributed drive vehicle is shown in the figure. fl The equivalent model diagram of the controlled object of the system for controlling differential turning of a distributed drive vehicle is shown in the figure. dfl The equivalent model diagram of the controlled object of the system for controlling differential turning of a distributed drive vehicle is shown in the figure. rl The equivalent model diagram of the controlled object of the system for controlling differential turning of a distributed drive vehicle is shown in the figure. drl The equivalent model diagram of the controlled object of the system for controlling differential turning of a distributed drive vehicle is shown in the figure. fr The equivalent model diagram of the controlled object of the system for controlling differential turning of a distributed drive vehicle is shown in the figure. dfr The equivalent model diagram of the controlled object of the system for controlling differential turning of a distributed drive vehicle is shown in the figure. rr The equivalent model diagram of the controlled object of the system for controlling differential turning of a distributed drive vehicle is shown in the figure. drr The equivalent model diagram of the controlled object of the system for controlling differential turning of a distributed drive vehicle is shown in the figure.

[0039] The equivalent model diagram of the controlled object of the system for controlling differential turning of a distributed drive vehicle is shown in the figure.

[0040] S2, obtaining wheel speed signals:

[0041] The wheel speed sensor collects the speed signals V ij of each wheel in real time and sends them to the additional torque calculation module in real time.

[0042] S3, estimating the road adhesion coefficient:

[0043] The road adhesion coefficient of each tire is estimated in real time based on the vehicle dynamics model according to the feedback wheel end torque, wheel speed and yaw rate.

[0044] The tire longitudinal force is estimated according to the vehicle dynamics model:

[0045]

[0046] Where B is the wheel track, R is the wheel radius, Iz is the vehicle moment of inertia, and the tire force is

[0047]

[0048] Where m is the vehicle weight, g is the acceleration of gravity, L is the wheelbase, a and b are the distances from the mass center to the front and rear axles, T fij represents the resistance torque of the ground, and the state is defined as The output is The system model is:

[0049]

[0050] where the system matrix is

[0051]

[0052] The road adhesion coefficient of each wheel can be estimated according to the following five equations of Kalman filter:

[0053]

[0054] S4, the reference speed calculation considering road adhesion:

[0055] The reference speed V of the vehicle ij,ref (ij = fl, fr, rl, rr) is determined by the opening degree of the accelerator pedal and the adhesion of the road where the wheel is currently located, wherein the part determined by the accelerator opening degree τ (range from 0-1) is expressed as:

[0056]

[0057] where V max represents the maximum speed limit.

[0058] The compensation part fed back by the road adhesion coefficient is expressed as:

[0059]

[0060] where f PID (error) represents the PID control calculation, represents the average of the road adhesion coefficients of the four wheels.

[0061] The final calculation expression of the reference speed of each wheel is:

[0062]

[0063] S5, design the MPC controller:

[0064] Establish the dynamic model of the four wheels:

[0065]

[0066] Write the state space equation:

[0067]

[0068] where the state quantity The control quantity u = [T dfl ,T dfr ,T drl ,T drr ] Tfeedforward output vector

[0069]

[0070] state matrix

[0071] control matrix

[0072] output matrix

[0073] The continuous system is discretized by using forward Euler method, where t s is the sampling time, and the discrete state space equation is obtained, that is:

[0074]

[0075] Wherein: A d =A c t s +I; B d =B c t s ; C d =C c ; I is the unit matrix of equal dimension.

[0076] A model predictive control model based on quadratic programming is constructed:

[0077]

[0078] In the formula: the expected output state vector X r =[V flref ,V frref ,V rlref ,V rrref ] T ; Control amount U=[T dfl ,T dfr ,T drl ,T drr ] T ; In the objective function, the first term represents the following ability of the system to the target speed; The second term represents the requirement of the system to the control increment size; Q and R are the corresponding weight matrices, and the control purpose is to make the system consume the minimum energy as the cost, and can follow the expected trajectory as much as possible; In the third term, ε is the relaxation factor of the constraint boundary, which ensures that the optimization problem has a feasible solution; ρ is the weight coefficient of the relaxation factor. N p and N c are the prediction time domain and control time domain of the model predictive controller respectively; u min and u max are the minimum and maximum constraints of the control amount respectively; Δu min and Δumax respectively, are minimum and maximum constraints of the control increment.

[0079] S6, calculate the active additional torque of the wheel:

[0080] Each calculation cycle estimates the road adhesion according to Kalman filtering and calculates the reference speed in combination with the accelerator pedal, and then the MPC controller calculates a torque according to the wheel speed signal collected by the sensor and the reference speed until the cost function reaches the minimum value, and the active torque required for the differential turning control at the spot can be calculated by using the MPC optimization solution, and a control command is issued.

[0081] S7, the current controller controls the actuator:

[0082] The current controller controls the current required by the actuator in real time according to the control command of the differential turning controller at the spot of the distributed drive vehicle, and the actuator applies the required active torque to the wheel under the action of current control, so that the wheel speed continuously approaches the reference value.

[0083] S8, the wheel speed continuously approaches the expected value.

[0084] The active differential turning control method at the spot estimates the road adhesion according to Kalman filtering and calculates the reference speed in combination with the accelerator pedal, and then uses the speed sensor to collect the wheel speed in real time, calculates the additional torque required by each wheel in the current period through the MPC controller, and then distributes the torque to each wheel through the torque distribution layer, until the wheel speed reaches the corresponding reference speed and the vehicle system reaches dynamic balance, so as to realize the effect of differential turning at the spot of the distributed drive vehicle.

[0085] The above only discloses one preferred embodiment of the present application, and of course cannot limit the scope of the present application, and those skilled in the art can understand that all or part of the above-mentioned embodiments can be implemented, and equivalent changes made according to the claims of the present application still belong to the scope covered by the present application.

Claims

1. A distributed drive vehicle differential turn-around control system, characterized in that, The system includes wheel speed sensors, a motor torque controller, a current controller, an actuator, a reference speed acquisition module, a road surface adhesion estimation module, an MPC additional torque calculation module, and a torque distribution module. The wheel speed sensors are all fixedly mounted on the vehicle body of the distributed drive vehicle and electrically connected to the vehicle system. The wheel speed sensors and the road surface adhesion estimation module are both connected to the reference speed acquisition module. The input terminal of the MPC additional torque calculation module is connected to the output terminal of the reference speed acquisition module, and the output terminal of the MPC additional torque calculation module is connected to the input terminal of the torque distribution module. The current controller and the motor torque controller are both connected to the output terminal of the torque distribution module. The current controller is bidirectionally connected to the actuator, and the current controller and the vehicle system of the distributed drive vehicle are both connected to the output terminal of the motor torque controller. The wheel speed sensor, the reference speed acquisition module, the road surface adhesion estimation module, the MPC additional torque calculation module, the torque distribution module, the motor torque controller, and the vehicle system of the distributed drive vehicle constitute the main loop. The motor torque controller, the current controller, the actuator, and the vehicle system of the distributed drive vehicle constitute the inner loop. The main loop uses Kalman filtering to estimate the road surface adhesion coefficient in real time and calculates the reference speed based on the throttle opening and the road surface adhesion coefficient. Then, it calculates the active torque using the actual wheel speed and the reference speed and completes the torque distribution. The inner loop controls the actuator to achieve the desired active torque control.

2. The distributed drive vehicle differential turn-around control system as described in claim 1, characterized in that, The wheel speed sensor collects the speed signal of each wheel in real time and sends it to the MPC additional torque calculation module in real time.

3. The distributed drive vehicle in-situ differential turn control system and its control method as described in claim 2, characterized in that, The road surface adhesion estimation module is used to estimate the road surface adhesion coefficient of each tire in real time based on the vehicle dynamics model, according to the wheel end torque, wheel speed and yaw rate.

4. The distributed drive vehicle differential turn-around control system as described in claim 3, characterized in that, The reference speed acquisition module is used to obtain the vehicle's reference speed by the opening of the accelerator pedal and the coefficient of adhesion of the road surface where the wheels are currently located.

5. The distributed drive vehicle differential turn-around control system as described in claim 4, characterized in that, The current controller controls the current required by the actuator in real time according to the control command of the motor torque controller. Under the action of current control, the actuator applies the required active torque to the wheel in real time, so that the wheel speed continuously approaches the reference value.

6. A method for controlling a differential U-turn in place using a distributed drive vehicle, applied to the distributed drive vehicle differential U-turn control system as described in claim 1, characterized in that... Includes the following steps: S1. Obtain the calculation parameters of the distributed drive vehicle in-situ differential turn control system; S2. Obtain wheel speed signal; S3. Estimate the road surface adhesion coefficient; S4. Calculation of reference speed considering road surface adhesion; S5. Design the MPC controller; S6. Calculate the active torque of the wheel; S7. The current controller controls the actuator; S8, the wheel speed is constantly approaching the reference value.

7. The distributed drive vehicle in-situ differential turn control method as described in claim 6, characterized in that, In step "S1", the calculated parameters include the wheel speed and torque of the left front wheel of the car, the wheel speed and torque of the left rear wheel of the car, the wheel speed and torque of the right front wheel of the car, the wheel speed and torque of the right rear wheel of the car, and the reference wheel speed.

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