Distributed driving vehicle in-situ differential U-turn control system and control method thereof

Abstract

The invention relates to the technical field of vehicle chassis control, in particular to a distributed driving vehicle in-situ differential turning control system and a control method thereof. The distributed driving vehicle in-situ differential turning control system 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 in contact with each tire, the MPC additional torque calculation module calculates the active additional torque required by each wheel, and the torque distribution module inputs the actual torque to the whole vehicle motor torque controller; the current controller controls the current needed by the actuator in real time, the actuator applies the needed active torque to each wheel in real time, the working speed of the wheels is made to continuously approach the reference speed, and the in-situ turning control system and method can achieve the in-situ turning function of the distributed driving automobile under different attachment working conditions by means of the MPC control theory.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle chassis control, and in particular to a distributed drive vehicle on-site differential U-turn control system and a control method thereof. Background Art

[0002] The technology of turning a car on the spot mainly relies on two different mechanisms to achieve it.

[0003] One is the method without a steering system. This method is common in tanks, etc., which achieve on-the-spot steering by making the tracks or wheels on both sides rotate in opposite directions. Some cars also show similar steering methods, but when used on high-adhesion roads, there will be a certain degree of wear on the tires, transmission system and road surface.

[0004] Another way is to rely on the car's steering system. Hurricane, a concept car from JEEP, adopts a front-to-rear symmetrical structural design to achieve a zero-turn radius U-turn function. In this way, there is no lateral friction during the steering process of the tire, so smooth in-situ turning can be achieved on asphalt roads. This design requires complex adjustments and optimizations to the vehicle's transmission system, suspension structure, and steering mechanism. At the same time, in order to achieve in-situ turning, the coaxial wheels need to rotate in the opposite direction, which requires the addition of additional clutches and differentials to control the power transmission of the wheels.

[0005] In summary, the existing vehicle U-turn control method cannot realize the U-turn function of the distributed drive vehicle under different adhesion conditions, and has great limitations. Summary of the invention

[0006] The purpose of the present invention is to provide a distributed drive vehicle differential U-turn control system and a control method thereof, so as to solve the problem that the existing vehicle U-turn control method cannot realize the distributed drive vehicle U-turn function under different adhesion conditions and has great limitations.

[0007] To achieve the above-mentioned object, the present invention provides a distributed drive vehicle on-site differential U-turn control system and a control method thereof, wherein the distributed drive vehicle on-site differential U-turn control system and the control method thereof include 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, wherein the wheel speed sensors are fixedly arranged on the body of the distributed drive vehicle and are electrically connected to the vehicle system of the distributed drive vehicle, the wheel speed sensors and the road adhesion estimation module are both connected to the reference speed acquisition module, the input end of the MPC additional torque calculation module is connected to the output end of the reference speed acquisition module, the output end of the MPC additional torque calculation module is connected to the input end of the torque distribution module, the current controller and the motor torque controller are both connected to the output end 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 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, and 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 calculates the reference speed based on the throttle opening and the road adhesion coefficient, and then uses the actual wheel speed and the reference speed to calculate the active torque and complete the torque distribution. The inner loop controls the actuator to achieve the desired active torque control.

[0009] 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.

[0010] 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, wheel speed and yaw angular velocity.

[0011] The reference speed acquisition module is used to acquire the reference speed of the vehicle through the opening of the accelerator pedal and the adhesion coefficient of the road surface on which the wheels are currently located.

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

[0013] The present invention also provides a distributed drive vehicle on-site differential U-turn control method, which is applied to the distributed drive vehicle on-site differential U-turn control system as described above, and comprises the following steps:

[0014] S1. Obtaining calculation parameters of the distributed drive vehicle in-situ differential U-turn control system;

[0015] S2, obtaining wheel speed signal;

[0016] S3, estimate the road adhesion coefficient;

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

[0018] S5. Design MPC controller;

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

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

[0021] S8. The wheel speed continues to approach the reference value.

[0022] Among them, in step "S1", the calculation parameters include the wheel speed and torque of the left front wheel of the vehicle, the wheel speed and torque of the left rear wheel of the vehicle, the wheel speed and torque of the right front wheel of the vehicle, the wheel speed and torque of the right rear wheel of the vehicle and the reference wheel speed.

[0023] A distributed drive vehicle on-site differential U-turn control system and control method thereof of the present invention 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, wherein the road adhesion estimation module estimates the adhesion coefficient of the road surface contacted by each tire in real time by using a Kalman filter, the MPC additional torque calculation module first calculates the reference speed according to the throttle opening and the estimated road adhesion coefficient, and processes the reference speed and the actual wheel speed through a model predictive controller (MPC) to calculate the active additional torque required by each 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 the current control, so that the working speed of the wheel continuously approaches the reference speed. The on-site U-turn control system and method utilize the MPC control theory, and can realize the on-site U-turn function of the distributed drive vehicle under different adhesion conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 The invention provides a principle block diagram of a distributed drive vehicle on-site differential U-turn control system.

[0026] Figure 2 It is a flow chart of the steps of the distributed drive vehicle on-site differential U-turn control method provided by the present invention.

[0027] Figure 3 It is a schematic diagram of a single degree of freedom equivalent model of a distributed drive vehicle provided by the present invention. DETAILED DESCRIPTION

[0028] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0029] See also Figure 1 The present invention provides a distributed drive vehicle on-site differential U-turn control system, the distributed drive vehicle on-site differential U-turn control system includes 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 sensors are fixedly arranged on the body of the distributed drive vehicle and are electrically connected to the vehicle system of the distributed drive vehicle, the wheel speed sensor and the road adhesion estimation module are both connected to the reference speed acquisition module, the input end of the MPC additional torque calculation module is connected to the output end of the reference speed acquisition module, the output end of the MPC additional torque calculation module is connected to the input end of the torque distribution module, the current controller and the motor torque controller are both connected to the output end 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 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, and 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 calculates the reference speed based on the throttle opening and the road adhesion coefficient, and then uses the actual wheel speed and the reference speed to calculate the active torque and complete the torque distribution. The inner loop controls the actuator to achieve the desired active torque control.

[0031] In this embodiment, 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 first calculates the reference speed according to the throttle opening and the estimated road adhesion coefficient, and processes the reference speed and the actual wheel speed through the model predictive controller (MPC) to calculate the active additional torque required by each wheel, and the torque distribution module inputs the actual torque required by each wheel into the motor torque controller of the 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 constantly approaches the reference speed. The on-site U-turn control system and method utilize MPC control theory to realize the on-site U-turn function of the distributed drive vehicle under different adhesion conditions.

[0032] Furthermore, 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] Furthermore, 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, wheel speed and yaw angular velocity.

[0034] Furthermore, the reference speed acquisition module is used to acquire a reference speed of the vehicle through the opening of the accelerator pedal and the adhesion coefficient of the road surface on which the wheels are currently located.

[0035] Furthermore, the current controller controls the current required by the actuator in real time according to the control instructions 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.

[0036] See also Figure 2 and Figure 3The present invention also provides a distributed drive vehicle on-site differential U-turn control method, which is applied to the distributed drive vehicle on-site differential U-turn control system as described above, and comprises the following steps:

[0037] S1. Obtain system calculation parameters

[0038] The equivalent model diagram of the controlled object of a distributed drive vehicle on-site differential U-turn control system provided by this technical solution is as follows: Figure 3 As shown, Figure 3 Represents a schematic diagram of the equivalent model of a single degree of freedom of the whole vehicle. The calculation parameters here include the left front wheel speed V in the figure fl With torque T dfl , left rear wheel speed V rl With torque T drl , right front wheel speed V fr With torque T dfr , right rear wheel speed V rr With torque T drr , and the vehicle yaw rate γ.

[0039] The system refers to a distributed drive vehicle on-site differential turn control system provided by the technical solution.

[0040] S2. Obtain wheel speed signal:

[0041] The wheel speed sensor collects the speed signal V of each wheel in real time ij , and sent to the additional torque calculation module in real time.

[0042] S3. Estimation of road adhesion coefficient:

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

[0044] Estimate tire longitudinal forces based on the vehicle dynamics model:

[0045]

[0046] Where B is the wheelbase, R is the wheel radius, and Iz is the vehicle's moment of inertia. The tire force is

[0047]

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

[0049]

[0050] The system matrix is

[0051]

[0052] The road adhesion coefficient of each wheel can be estimated according to the five formulas of Kalman filtering as shown below:

[0053]

[0054] S4. Calculation of reference speed considering road adhesion:

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

[0056]

[0057] Among them, V max Indicates the maximum speed limit.

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

[0059]

[0060] Among them, f PID (error) indicates 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 MPC controller:

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

[0065]

[0066] Written as state space equation:

[0067]

[0068] Among them, the state quantity Control quantity u=[T dfl ,T dfr ,T drl ,T drr ] T, feedforward Output vector:

[0069]

[0070] State Matrix

[0071] Control Matrix

[0072] Output Matrix

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

[0074]

[0075] Among them: A d =A c t s +I;B d =B c t s ; C d =C c ; I is an equal-dimensional identity matrix.

[0076] Construct a quadratic programming-based model predictive control model:

[0077]

[0078] Where: The expected output state vector X r =[V flref ,V frref ,V rlref ,V rrref ] T ; Control quantity U = [T dfl ,T dfr ,T drl ,T drr ] T ; In the objective function, the first term represents the system's ability to follow the target vehicle speed; the second term represents the system's requirement for the size of the control increment; Q and R are the corresponding weight matrices, and the control objective is to make the system follow the desired trajectory as much as possible at the cost of minimum energy consumption; in the third term, ε is the relaxation factor of the constraint boundary to ensure that there is a feasible solution to the optimization problem; 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 quantity respectively; Δu min and Δumax They are the minimum and maximum constraints that control the increment respectively.

[0079] S6. Calculate the active additional torque of the wheel:

[0080] In each calculation cycle, the road adhesion is estimated based on the Kalman filter and the reference speed is calculated in combination with the accelerator pedal. Then the MPC controller calculates a torque based on the wheel speed signal collected by the sensor and the reference speed until the cost function reaches the minimum value. The MPC is used for optimization solution to calculate the active torque required for the on-the-spot differential U-turn control and issue a control command.

[0081] S7, current controller controls the actuator:

[0082] The current controller controls the current required by the actuator in real time according to the control instructions of the distributed drive vehicle's on-site differential U-turn 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.

[0083] S8. The wheel speed continues to approach the expected value.

[0084] The active differential U-turn control method estimates the road adhesion based on the Kalman filter and calculates the reference speed in combination with the accelerator pedal, then uses the speed sensor to collect the wheel speed in real time, and uses the MPC controller to calculate the additional torque required for each wheel in the current cycle in real time, 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, thereby achieving the effect of differential U-turn in place of distributed drive vehicles.

[0085] What is disclosed above is only a preferred embodiment of the present invention, and it certainly cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A distributed drive vehicle on-site differential U-turn control system, characterized in that: The invention 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, wherein the wheel speed sensors are fixedly arranged on the body of the distributed drive vehicle and are electrically connected to the vehicle system of the distributed drive vehicle, the wheel speed sensor and the road adhesion estimation module are connected to the reference speed acquisition module, the input end of the MPC additional torque calculation module is connected to the output end of the reference speed acquisition module, the output end of the MPC additional torque calculation module is connected to the input end of the torque distribution module, the current controller and the motor torque controller are connected to the output end 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 connected to the output end of the motor torque controller; 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, and 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 calculates the reference speed based on the throttle opening and the road adhesion coefficient, and then uses the actual wheel speed and the reference speed to calculate the active torque and complete the torque distribution. The inner loop controls the actuator to achieve the desired active torque control.

2. The distributed drive vehicle in-situ differential U-turn control system according to 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 on-site differential U-turn control system and control method thereof as claimed in claim 2, characterized in that: 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, wheel speed and yaw angular velocity.

4. The distributed drive vehicle in-situ differential U-turn control system according to claim 3, characterized in that: The reference speed acquisition module is used to acquire the reference speed of the vehicle according to the opening of the accelerator pedal and the adhesion coefficient of the road surface on which the wheels are currently located.

5. The distributed drive vehicle in-situ differential U-turn control system according to claim 4, characterized in that: The current controller controls the current required by the actuator in real time according to the control instruction 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 distributed drive vehicle to make a differential U-turn in situ, applied to the distributed drive vehicle to make a differential U-turn in situ control system as claimed in claim 1, characterized in that: The steps include: S1. Obtaining calculation parameters of the distributed drive vehicle in-situ differential U-turn control system; S2, obtaining wheel speed signal; S3, estimate the road adhesion coefficient; S4, calculation of reference speed considering road adhesion; S5. Design MPC controller; S6, calculating the active torque of the wheel; S7, the current controller controls the actuator; S8. The wheel speed continues to approach the reference value.

7. The distributed drive vehicle on-site differential U-turn control system and control method thereof as claimed in claim 6, characterized in that: In step "S1", the calculation parameters include the wheel speed and torque of the left front wheel of the vehicle, the wheel speed and torque of the left rear wheel of the vehicle, the wheel speed and torque of the right front wheel of the vehicle, the wheel speed and torque of the right rear wheel of the vehicle and the reference wheel speed.

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