CN110466602A - The timesharing four-wheel steering system and its control method of hub motor driven electric vehicle - Google Patents

Abstract

The invention discloses a control method for differential drive steering and stability of an electric vehicle driven by a wheel hub motor. By judging whether the phase track of the running vehicle exceeds the stable domain, the vehicle in the stable domain is regarded as a linear model, and the The differential drive steering control of the linear model; the vehicle that is outside the stability zone uses the direct yaw moment generated to actively intervene in the steering of the vehicle to return it from an unstable state to a stable state. The present invention adopts joint control, so that the non-linear vehicle that relies on differential drive steering can track the side slip angle and yaw angular velocity of the reference model well within the range of the steering wheel's allowable rotation angle and on roads with different adhesion coefficients, effectively Greatly improve the stability of the vehicle and ensure the safety of driving.

Description

Part-time four-wheel steering system and control method of in-wheel motor driven electric vehicle

technical field

The invention relates to a steering control system and method, in particular to a time-sharing four-wheel steering system and a control method for an electric vehicle driven by a hub motor, and belongs to the technical field of electric vehicles.

Background technique

Wheel independent drive steering is often realized by distributed drive, which can be divided into wheel motor drive and hub motor drive according to the motor drive form. The wheel motor drive is to install the motor system near the wheel and drive the wheel through the wheel reducer; the hub motor drive is to install the hub motor in the wheel hub to directly drive the wheel. The hub motor drive vehicle integrates the drive and transmission in the hub, which not only omits the mechanical components such as clutches, transmissions, drive shafts, and differentials required by traditional vehicles, greatly simplifies the mechanical structure of the vehicle, but also improves the performance of the vehicle. Space utilization. At the same time, the control of hub motor drive only needs motor and controller, which avoids the delay effect of mechanical structures such as solenoid valves and hydraulic pipelines. It has good real-time performance and precision, and various control schemes can also be fully utilized.

The active four-wheel steering (Active Four-Wheel-Steering, 4WS) system can effectively improve the maneuverability of the vehicle at low speeds, the handling stability at high speeds, and the path tracking of intelligent vehicles by actively controlling the front and rear wheel angles. However, since the rear wheels are involved in the steering, and the commonly used control idea is to make the center of mass slip angle of the vehicle zero, it will inevitably make the driver feel different from driving a traditional front-wheel steering vehicle. Therefore, how to give full play to the advantages of the active four-wheel steering system and at the same time, it is beneficial for the driver to have a good sense of road feedback when driving an electric wheel vehicle; Uncertainties such as mass, center of mass position, and tire cornering stiffness vary with working conditions, so designing a reasonable control strategy to improve the robustness of system response is also a problem that needs to be solved.

Contents of the invention

The main purpose of the present invention is to overcome the deficiencies in the prior art and provide a time-sharing four-wheel steering system and its control method for an in-wheel motor-driven electric vehicle, which can not only switch front-wheel steering and four-wheel steering according to the driver's needs , to provide the driver with a suitable road feeling, and has the advantages of simple structure, accurate steering, etc., and has good robustness.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A time-sharing four-wheel steering system for an electric vehicle driven by a hub motor, comprising:

The detection module is used to detect the driving parameters of the electric vehicle, and input the driving parameters to the vehicle controller; wherein, the driving parameters include the steering wheel angle signal, the pedal position signal of the accelerator pedal, the driving speed signal, the front wheel angle signal and the rear wheel corner signal;

The steering mode selection switch is used for the driver to artificially select the steering mode. The steering mode includes front-wheel steering and four-wheel steering, and the selected steering mode is input to the vehicle controller;

The vehicle speed tracking module is used to calculate the driving speed of the electric vehicle and the required front wheel drive torque according to the pedal position signal of the accelerator pedal, and control the hub motor to execute the driving speed signal of the driver, and input the driving speed to the vehicle control device;

The vehicle controller is used to receive the driving speed, and when the selected steering module is front-wheel steering, send the steering wheel angle signal to the front-wheel steer-by-wire control module, and output the rear-wheel lock signal to the rear-wheel steering lock module; and, when the selected steering mode is four-wheel steering, calculate the ideal front and rear wheel angles required for four-wheel steering and output the rear wheel unlocking signal to the rear wheel steering lock module, wherein the ideal front and rear wheel angles Including the ideal front wheel angle and the ideal rear wheel angle, and the ideal front wheel angle is sent to the front wheel steer-by-wire control module, and the ideal rear wheel angle is sent to the rear wheel differential steering control module;

The front wheel steer-by-wire control module is used to drive the front wheel steering executive motor to steer the front wheels according to the steering wheel angle signal and the front wheel angle signal or the ideal front wheel angle, and provide the driver with a corresponding sense of steering road, and direct the steering road sense feedback to the vehicle controller;

The rear wheel differential steering control module is used to calculate the rear wheel differential torque according to the ideal rear wheel angle, and drive the rear wheel hub motor to perform rear wheel steering according to the rear wheel differential torque;

The rear wheel steering lock module is used to drive the steering lock mechanism according to the rear wheel lock signal and the rear wheel angle signal to prevent the rear wheels from turning after the rear wheels are aligned, and to drive the steering lock mechanism to release according to the rear wheel unlock signal Steering lock.

The system of the present invention is further configured as follows: the steering lock mechanism includes a return motor and two sets of steering mechanisms that are symmetrically installed on the vehicle frame and have the same structure, the return motor is connected with the rear wheel steering lock module, and the two sets of steering mechanisms Both are connected with the return motor, and act on the left rear wheel and the right rear wheel respectively;

The steering mechanism includes an electromagnetic clutch, a return gear, a lock rod, a toe rod, a first steering knuckle arm and a second steering knuckle arm connected in sequence, which are lapped on the surface of the lock rod and connected with the Electromagnets, steering kingpins connected to one end of the first steering knuckle arm and one end of the second steering knuckle arm, both installed on the upper cross arm and lower cross arm on the frame, and used to detect the rear wheel angle and lock The lock rod displacement sensor on the pull rod; the electromagnetic clutch is connected with the return motor and the rear wheel steering lock module, the lock rod is connected with the return gear through the rod face rack, the lock rod and the toe-in rod, and between the toe-in rod and the first steering knuckle arm are all connected through a ball joint, and the two ends of the steering kingpin are respectively connected with the upper cross arm and the lower cross arm through a ball joint, and the electromagnet It is used to generate suction and engage with the locking rod after electrification, so that the locking rod is locked on the frame. The locking rod displacement sensor is used to detect the displacement parameters between the locking rod and the vehicle body in real time and measure the displacement. The parameters are fed back to the vehicle controller to determine the rear wheel angle.

The system of the present invention is further configured as follows: the front wheel steering executive motor drives the front wheel steering transmission part to make the front wheels turn, and the front wheel steering transmission part includes a left front wheel steering knuckle arm, a left front wheel steering transverse tie rod, rack, steering gear, right front wheel steering tie rod and right front wheel steering knuckle arm, the left front wheel steering knuckle arm acts on the left front wheel, the right front wheel steering knuckle arm acts on the right front wheel, The steering gear is connected with the front wheel steering executive motor.

The system of the present invention is further configured as follows: the detection module includes a torque sensor and a steering wheel angle sensor for detecting the steering wheel, a pedal position sensor for detecting the accelerator pedal, and a rack displacement on the rack for detecting the rotation angle of the front wheel sensor.

The present invention also provides a control method for a time-sharing four-wheel steering system of an in-wheel motor-driven electric vehicle, which operates in the aforementioned time-sharing four-wheel steering system for an in-wheel motor-driven electric vehicle, comprising the following steps:

1) The vehicle controller obtains the driving parameters collected by the detection module and the steering mode selected by the driver input by the steering mode selection switch, wherein the driving parameters include the steering wheel angle signal, the pedal position signal of the accelerator pedal, the driving speed signal, the front wheel Angle signal and rear wheel angle signal;

2) The vehicle speed tracking module calculates the driving speed of the electric vehicle and the required front wheel drive torque according to the pedal position signal of the accelerator pedal, and controls the in-wheel motor to execute the driving speed signal of the driver, and inputs the driving speed to the vehicle controller ;

3) When the vehicle is running, the vehicle controller judges that the steering mode selected by the driver is front-wheel steering or four-wheel steering;

If the steering mode is front-wheel steering, and the front-wheel steer-by-wire and rear-wheel steering locking methods are adopted, then perform step 4)-step 5), and then return to step 1);

If the steering mode is four-wheel steering, and the front wheel steering by wire and the rear wheel differential steering are adopted, then perform steps 6)-8), and then return to step 1);

4) When the selected steering module is front-wheel steering, the vehicle controller sends the steering wheel angle signal to the front-wheel steer-by-wire control module, and outputs the rear-wheel positive signal to the rear-wheel steering lock module to make the rear wheels turn to the rear And lock the rear wheel steering;

5) The front-wheel steer-by-wire control module drives the front-wheel steering executive motor to steer the front wheels according to the steering wheel angle signal and the front-wheel angle signal, and provides the corresponding steering sense to the driver, and feeds back the steering sense to the vehicle control At the same time, the rear wheel steering lock module drives the rotary lock mechanism according to the rear wheel lock signal and the rear wheel angle signal to return the rear wheel to the rear and prohibit the rear wheel from turning;

6) When the selected steering mode is four-wheel steering, the vehicle controller calculates the ideal front and rear wheel angles required by four-wheel steering and outputs the rear wheel unlocking signal to the rear wheel steering lock module. The wheel rotation angle includes an ideal front wheel rotation angle and an ideal rear wheel rotation angle, and the ideal front wheel rotation angle is sent to the front wheel steer-by-wire control module, and the ideal rear wheel rotation angle is sent to the rear wheel differential steering control module;

7) The front wheel steer-by-wire control module drives the front wheel steering executive motor to steer the front wheels according to the ideal front wheel angle, and provides the driver with the corresponding steering sense, and feeds back the steering sense to the vehicle controller; at the same time, The rear wheel steering lock module drives the rotary lock mechanism to release the steering lock according to the rear wheel unlock signal;

8) The rear wheel differential steering control module calculates the rear wheel differential torque according to the ideal rear wheel rotation angle, and drives the rear wheel hub motor to perform rear wheel steering according to the rear wheel differential torque.

The method of the present invention is further configured as follows: the vehicle speed tracking controller searches for the relationship curve between the predetermined longitudinal speed and the position of the accelerator pedal in the system according to the signal collected by the pedal position sensor of the accelerator pedal, so as to obtain the driving speed of the electric vehicle.

The method of the present invention is further set to: the vehicle controller calculates and obtains the ideal front and rear wheel angles required by the four-wheel steering, specifically,

The vehicle controller inputs the collected steering wheel angle to the reference model to obtain the ideal yaw rate and side slip angle, and uses an asymptotic tracking controller to control the yaw of the decoupled linear four-wheel steering model. The angular velocity and the center-of-mass sideslip angle track the ideal yaw rate and the sideslip angle of the center of mass, so as to obtain the ideal front and rear wheel steering angles of the four-wheel steering vehicle; where the reference model is the linear Two degrees of freedom vehicle model.

The method of the present invention is further set to: the state equation of the reference model is,

Let x _d = [γ _d β _d ] ^T , u _d = [δ _f ],

The reference model is expressed as

In the formula,

Among them, γ _d is the yaw rate of the reference model, β _d is the sideslip angle of the center of mass of the reference model, m is the mass of the car, u _x is the longitudinal velocity at the center of mass of the car, δ _f is the front wheel rotation angle, l _fd is the center of mass to The distance from the front axle, l _rd is the distance from the center of mass to the rear axle, k _f is the cornering stiffness of the front wheel, k _r is the cornering stiffness of the rear wheel, I _z is the moment of inertia of the vehicle about the Z axis;

A reduction filter is applied to the sideslip angle of the center of mass, and the transfer function of the reduction filter used is,

Among them, η is the gain coefficient, ξ is the damping coefficient, and ω _n is the circular frequency;

The magnitude of the center-of-mass sideslip angle is adjusted by adjusting the circular frequency ω _n .

The method of the present invention is further set to: the linear dynamic model adopted by the linear four-wheel steering model is

In the equation,

Among them, l _f is the distance from the front axle to the center of mass, and l _r is the distance from the rear axle to the center of mass;

Decoupling the input and output of the linear four-wheel steering model,

The transfer function used is

in,

_The parameters u ₁ and u ₂ are introduced to realize the decoupling _of the yaw rate γ and the sideslip angle β of the center of mass. The transfer functions are G ₁₁ (s) and G ₂₂ (s);

then there is

if and only if When , the yaw rate and the sideslip angle of the center of mass are controlled by the variables u ₁ and u ₂ respectively, thus,

Wherein, a ₀ =(a ₁₂ b ₂₁ -a ₂₂ b ₁₁ )(a ₂₁ b ₁₂ -a ₁₁ b ₂₂ +a ₁₁ b ₁₂ -a ₁₂ b ₂₂ ), a ₁ =a ₂₁ b ₁₂ b ₁₁ -a ₁₁ b ₂₂ b ₁₁ +a ₁₁ b ₁₂ b ₂₁ -a ₁₂ b ₂₁ b ₁₂ , a ₂ =b ₁₁ b ₂₂ -b ₂₁ b ₁₂ , b ₀ =(a ₂₁ b ₁₂ -a ₁₁ b ₂₂ )(a ₁₂ b ₂₁ -a ₂₂ b ₁₁ ), b ₁ =a ₂₁ b ₁₂ b ₁₁ -a ₁₁ b ₂₂ b ₁₁ +a ₁₂ b ₂₁ b ₂₂ -a ₂₂ b ₁₁ b ₂₂ , b ₂ =b ₂₂ b ₁₁ , b ₃ = (a ₁₁ b ₁₂ -a ₁₂ b ₂₂ )(a ₂₁ b ₁₂ -a ₁₁ b ₂₂ ), b ₄ =-a ₂₁ b ² ₁₂ +a ₁₁ b ₂₂ b ₁₂ +a ₁₁ b ₁₂ b ₂₂ -a ₁₂ b ² ₂₂ , b ₅ =-b ₁₂ b ₂₂ , b ₆ =(-a ₁₂ b ₂₁ +a ₂₂ b ₁₁ )(a ₂₁ b ₁₁ -a ₁₁ b ₂₁ ), b ₇ =-a ₁₂ b ² ₂₁ +a ₂₂ b ₁₁ b ₂₁ -a ₂₁ b ² ₁₁ +a ₁₁ b ₁₁ b ₂₁ , b ₈ =-b ₁₁ b ₂₁ , b ₉ =(a ₂₁ b ₁₂ -a ₁₁ b ₂₂ )(a ₁₂ b ₂₁ -a ₂₂ b ₁₁ ), b ₁₀ =a ₂₁ b ₁₂ b ₁₁ -a ₁₁ b ₂₂ b ₁₁ +a ₁₂ b ₂₁ b ₂₂ -a ₂₂ b ₁₁ b ₂₂ , b ₁₁ =b ₂₂ b ₁₁ ;

Let the transfer function of the asymptotic tracking controller be G _C1 (s), and the asymptotic tracking controller adopts P, PI, PD or PID controller;

Perform pull transformation on the governing equation e(t)=γd( _t )-γ(t)=γd( _t )-G _C1 (t)G ₁₁ (t)e(t),

have to

Assume

but

Simplify the characteristic polynomial d _g (s)d _c (s)+ _ng (s)n _c (s)=0 of its 2nd order system to d ₂ s ² +d ₁ s+d ₀ =0;

where, d ₂ =1+b ₁₁ k _d , d ₁ =b ₁₁ k _p +(-a ₂₂ b ₁₁ +a ₁₂ b ₂₁ )k _d -(a ₁₁ +a ₂₂ ),

d ₀ =a ₁₁ a ₂₂ -a ₂₁ a ₁₂ +k _p (-a ₂₂ b ₁₁ +a ₁₂ b ₂₁ );

According to the Routh judgment table and the Routh-Hurwitz stability criterion, the parameters of the asymptotic tracking controller controlling the yaw rate and the sideslip angle of the center of mass are determined;

Among them, the Routh decision table is In the formula

The Routh-Hurwitz stability criterion is that the coefficients of the characteristic polynomials of the second-order system are all positive or all negative.

The method of the present invention is further set to: the rear wheel differential steering control module calculates the rear wheel differential torque according to the ideal rear wheel angle, specifically,

The dynamic model is established, and the two-degree-of-freedom four-wheel steering vehicle with the ideal front and rear wheel angles as input is used as a reference model, and the sliding mode variable structure controller is designed to obtain the rear wheel differential torque driving the rear wheel steering;

Include the following steps:

a) Regardless of the follow-up rotation angle of the wheels, the state equations of front wheel steering by wire and rear wheel differential steering are:

Among them, β is the sideslip angle of the center of mass of the vehicle, γ is the yaw rate of the vehicle, is the yaw angular acceleration of the vehicle, is the side slip angular velocity of the center of mass of the vehicle, m is the mass of the vehicle, u _x is the longitudinal velocity at the center of mass of the vehicle, l _f is the distance from the front axle to the center of mass, l _r is the distance from the rear axle to the center of mass, δ _f is the rotation angle of the front wheel, k _f is the cornering stiffness of the front wheel, k _r is the cornering stiffness of the rear wheel, I _z is the moment of inertia of the vehicle about the Z axis, d _r is the track of the rear wheel, and R is the effective radius of the tire;

b) Let the state space variable x(t)=[β γ] ^T , the input is the front and rear wheel drive torque difference, i.e. u(t)=ΔT, the state equations of the front wheel steering by wire and the rear wheel differential steering are transformed into

in,

c) Define the sliding mode surface s=γ-γ _d +ξ(β-β _d ),

Among them, ξ is the weight coefficient, γ _d is the yaw rate of the reference model, and β _d is the sideslip angle of the center of mass of the reference model;

Guidance is available,

In the formula,

in, is the yaw angular acceleration of the reference model, is the side slip angular velocity of the center of mass of the reference model;

because Bounded, then one of them is a constant;

Using the reaching law with saturation function, the controller is obtained as

Compared with prior art, the beneficial effect that the present invention has is:

The time-sharing four-wheel steering system and control method of the in-wheel motor-driven electric vehicle provided by the present invention can not only switch the front-wheel steering and four-wheel steering according to the driver's demand, provide the driver with a suitable road feeling, but also have a simple structure. , Steering accuracy and other advantages, and has good robustness. When the selected steering mode is front-wheel steering, the front wheels are controlled by the front-wheel steer-by-wire control module to perform traditional front-wheel steering, and the rear wheels return to normal and lock. When the selected steering mode is four-wheel steering, the rear wheels are unlocked, and the front wheels use traditional steering and rear wheel differential steering to complete independent steering. The rear wheels are independently driven and combined with differential steering technology. It can effectively improve the maneuverability of the vehicle, and can effectively reduce the occurrence of tail flicking and sideslip when the vehicle is turning at high speed; it can also improve the active safety and handling stability of the vehicle.

The above content is only an overview of the technical solution of the present invention. In order to understand the technical means of the present invention more clearly, the present invention will be further described below in conjunction with the accompanying drawings.

Description of drawings

Fig. 1 is the structural representation of the time-sharing four-wheel steering system of the hub motor driven electric vehicle of the present invention;

Fig. 2 is the yaw rate at low speed obtained by the simulation of the method embodiment of the present invention;

Fig. 3 is the side slip angle of the center of mass at low speed obtained by the simulation of the method embodiment of the present invention;

Fig. 4 is the x and y positions at low speed obtained by the simulation of the method embodiment of the present invention;

Fig. 5 is the torque at low speed obtained by simulation of the method embodiment of the present invention;

Fig. 6 is the yaw rate at medium speed obtained by the simulation of the method embodiment of the present invention;

Fig. 7 is the yaw rate at medium speed obtained by the simulation of the method embodiment of the present invention;

Fig. 8 is the x and y position when the simulation of the method embodiment of the present invention obtains at medium speed;

Fig. 9 is the torque at medium speed obtained by the simulation of the method embodiment of the present invention;

Fig. 10 is the yaw rate at high speed obtained by the simulation of the method embodiment of the present invention;

Fig. 11 is the sideslip angle of the center of mass at high speed obtained by the simulation of the method embodiment of the present invention;

Fig. 12 is the x and y positions at high speed obtained by simulation of the method embodiment of the present invention;

Fig. 13 is the torque at high speed obtained by the simulation of the method embodiment of the present invention.

In the figure: 1-left front wheel steering knuckle arm; 2-left front wheel steering tie rod; 3-rack; 4-steering gear; 5-steering executive motor and reducer; 6-rack displacement sensor; 7-rear Wheel hub motor; 8-steering wheel angle sensor; 9-road sense analog motor and reducer; 10-torque sensor; 11-steering wheel; 12-front wheel steering module; 13-vehicle controller; 14-rear wheel differential Dynamic steering control module; 15-left rear wheel; 16-toe rod; 17-upper cross arm; 18-steering kingpin; 19-ball joint; 20-lower cross arm; 23-electromagnetic clutch; 24-returning motor; 25-locking pull rod; 26-one end of the first steering knuckle arm, 27-electromagnet, 28-vehicle frame, 29-the second steering knuckle arm.

Detailed ways

Below in conjunction with accompanying drawing of description, the present invention will be further described.

The present invention provides a time-sharing four-wheel steering system for an in-wheel motor driven electric vehicle, as shown in Figure 1, comprising:

The detection module is used to detect the driving parameters of the electric vehicle, and input the driving parameters to the vehicle controller 13; wherein, the driving parameters include the steering wheel angle signal, the pedal position signal of the accelerator pedal, the driving speed signal, the front wheel angle signal and the rear wheel angle signal. wheel angle signal;

The steering mode selection switch is used for the driver to artificially select the steering mode, the steering mode includes front-wheel steering and four-wheel steering, and the selected steering mode is input to the vehicle controller 13;

The vehicle speed tracking module is used to calculate the driving speed of the electric vehicle and the required front wheel drive torque according to the pedal position signal of the accelerator pedal, and control the hub motor to execute the driving speed signal of the driver, and input the driving speed to the vehicle control Device 13;

The vehicle controller 13 is used to receive the driving speed, and when the selected steering module is front-wheel steering, transmit the steering wheel angle signal to the front-wheel steer-by-wire control module 12, and output the rear-wheel lock signal to the rear-wheel steering Locking module; and, when the selected steering mode is four-wheel steering, calculate and obtain the ideal front and rear wheel angles required by four-wheel steering and output the rear wheel unlocking signal to the rear wheel steering locking module, wherein the ideal front and rear The wheel rotation angle includes an ideal front wheel rotation angle and an ideal rear wheel rotation angle, and the ideal front wheel rotation angle is sent to the front wheel steer-by-wire control module, and the ideal rear wheel rotation angle is sent to the rear wheel differential steering control module;

The front wheel steer-by-wire control module 12 is used to drive the front wheel steering executive motor 5 to perform front wheel steering according to the steering wheel angle signal and the front wheel angle signal or the ideal front wheel angle, and provide the driver with the road feeling simulation motor and reducer 9 Provide corresponding steering sense, and feed back the steering sense to the vehicle controller 13;

The rear wheel differential steering control module 14 is used to calculate the rear wheel differential torque according to the ideal rear wheel angle, and drive the rear wheel hub motor 7 to perform rear wheel steering according to the rear wheel differential torque;

The rear wheel steering lock module is used to drive the steering lock mechanism according to the rear wheel lock signal and the rear wheel angle signal to prevent the rear wheels from turning after the rear wheels are aligned, and to drive the steering lock mechanism to release according to the rear wheel unlock signal Steering lock.

As shown in Figure 1, the steering lock mechanism includes a return motor 24 and two sets of steering mechanisms that are symmetrically installed on the vehicle frame 18 and have the same structure. The return motor 24 is connected with the rear wheel steering lock module, and the two groups Steering mechanisms are all linked to each other with the centering motor 24, and act on the left rear wheel 15 and the right rear wheel respectively.

The steering mechanism includes an electromagnetic clutch 23, a positive return gear 22, a locking rod 25, a toe-in rod 16, a first steering knuckle arm 26 and a second steering knuckle arm 29 connected in sequence, which are overlapped on the surface of the locking rod 25 and With the electromagnet 27 installed on the vehicle frame 28, the steering kingpin 18 that is all connected with one end of the first steering knuckle arm 26 and one end of the second steering knuckle arm 29, is all installed on the upper cross arm 17 and the lower cross arm 17 on the vehicle frame 28. The cross arm 20, and the locking rod displacement sensor 21 for detecting the rear wheel rotation angle and being located on the locking rod 25; the electromagnetic clutch 23 is connected with the return motor 24, and is connected with the rear wheel steering locking module. The locking rod 25 is connected to the spur gear 22 through the bar face rack, and the locking rod 25 and the toe-in rod 16, and between the toe-in rod 16 and the first steering knuckle arm 26 are all connected by a ball joint 19, The two ends of the steering kingpin 18 are respectively connected to the upper cross arm 17 and the lower cross arm 20 through a ball joint 19, and the electromagnet 27 is used to generate suction and engage with the locking pull rod 25 after being energized so that the locking pull rod 25 is locked on the vehicle frame 28, and the locking rod displacement sensor 21 is used to detect the displacement parameter between the locking rod 25 and the vehicle body in real time and feed back the displacement parameter to the vehicle controller 13 to determine the rear wheel angle.

As shown in Figure 1, the front wheel steering actuator 5 turns the front wheels by driving the front wheel steering transmission parts, and the front wheel steering transmission parts include the left front wheel steering knuckle arm 1, the left front wheel steering Tie rod 2, rack 3, steering gear 4, right front wheel steering tie rod and right front wheel steering knuckle arm, the left front wheel steering knuckle arm 1 acts on the left front wheel, and the right front wheel steering knuckle arm acts on For the right front wheel, the steering gear 4 is connected with the front wheel steering executive motor 5 .

As shown in Figure 1, the detection module includes a torque sensor 10 and a steering wheel angle sensor 8 for detecting the steering wheel 11, a pedal position sensor for detecting the accelerator pedal, and a sensor for detecting the front wheel rotation angle and located on the rack 3. Rack displacement sensor 6.

The present invention also provides a control method for a time-sharing four-wheel steering system of an in-wheel motor-driven electric vehicle, which operates in the time-sharing four-wheel steering system of an in-wheel motor-driven electric vehicle as shown in Figure 1, comprising the following steps:

1) The vehicle controller obtains the driving parameters collected by the detection module and the steering mode selected by the driver input by the steering mode selection switch, wherein the driving parameters include the steering wheel angle signal, the pedal position signal of the accelerator pedal, the driving speed signal, the front wheel Angle signal and rear wheel angle signal;

2) The vehicle speed tracking module calculates the driving speed of the electric vehicle and the required front wheel drive torque according to the pedal position signal of the accelerator pedal, and controls the in-wheel motor to execute the driving speed signal of the driver, and inputs the driving speed to the vehicle controller ;

3) When the vehicle is running, the vehicle controller judges that the steering mode selected by the driver is front-wheel steering or four-wheel steering;

If the steering mode is front-wheel steering, and the front-wheel steer-by-wire and rear-wheel steering locking methods are adopted, then perform step 4)-step 5), and then return to step 1);

If the steering mode is four-wheel steering, and the front wheel steering by wire and the rear wheel differential steering are adopted, then perform steps 6)-8), and then return to step 1);

4) When the selected steering module is front-wheel steering, the vehicle controller sends the steering wheel angle signal to the front-wheel steer-by-wire control module, and outputs the rear-wheel positive signal to the rear-wheel steering lock module to make the rear wheels turn to the rear And lock the rear wheel steering;

5) The front-wheel steer-by-wire control module drives the front-wheel steering executive motor to steer the front wheels according to the steering wheel angle signal and the front-wheel angle signal, and provides the corresponding steering sense to the driver, and feeds back the steering sense to the vehicle control At the same time, the rear wheel steering lock module drives the rotary lock mechanism according to the rear wheel lock signal and the rear wheel angle signal to return the rear wheel to the rear and prohibit the rear wheel from turning;

6) When the selected steering mode is four-wheel steering, the vehicle controller calculates the ideal front and rear wheel angles required by four-wheel steering and outputs the rear wheel unlocking signal to the rear wheel steering lock module. The wheel rotation angle includes an ideal front wheel rotation angle and an ideal rear wheel rotation angle, and the ideal front wheel rotation angle is sent to the front wheel steer-by-wire control module, and the ideal rear wheel rotation angle is sent to the rear wheel differential steering control module;

7) The front wheel steer-by-wire control module drives the front wheel steering executive motor to steer the front wheels according to the ideal front wheel angle, and provides the driver with the corresponding steering sense, and feeds back the steering sense to the vehicle controller; at the same time, The rear wheel steering lock module drives the rotary lock mechanism to release the steering lock according to the rear wheel unlock signal;

8) The rear wheel differential steering control module calculates the rear wheel differential torque according to the ideal rear wheel rotation angle, and drives the rear wheel hub motor to perform rear wheel steering according to the rear wheel differential torque.

In the method of the present invention, the vehicle speed tracking controller searches for the relationship curve between the predetermined longitudinal speed and the position of the accelerator pedal in the system according to the signal collected by the pedal position sensor of the accelerator pedal, so as to obtain the driving speed of the electric vehicle.

In the method of the present invention, the vehicle controller calculates and obtains the ideal front and rear wheel angles required for four-wheel steering, specifically, the vehicle controller inputs the collected steering wheel angles into the reference model to obtain the ideal yaw rate and center-of-mass sideslip angle, and the yaw rate and side-slip angle of the decoupled linear four-wheel steering model track the ideal yaw rate and side-slip angle by using an asymptotic tracking controller to obtain four-wheel steering The ideal front and rear wheel rotation angles of the vehicle; where the reference model is a linear two-degree-of-freedom vehicle model with neutral steering characteristics after filtering for center-of-mass sideslip angle reduction.

In the method of the present invention, the state equation of the reference model is,

Let x _d = [γ _d β _d ] ^T , u _d = [δ _f ],

The reference model is expressed as

In the formula,

Among them, γ _d is the yaw rate of the reference model, β _d is the sideslip angle of the center of mass of the reference model, m is the mass of the car, u _x is the longitudinal velocity at the center of mass of the car, δ _f is the front wheel rotation angle, l _fd is the center of mass to The distance from the front axle, l _rd is the distance from the center of mass to the rear axle, k _f is the cornering stiffness of the front wheel, k _r is the cornering stiffness of the rear wheel, I _z is the moment of inertia of the vehicle about the Z axis;

A reduction filter is applied to the sideslip angle of the center of mass, and the transfer function of the reduction filter used is,

Among them, η is the gain coefficient, ξ is the damping coefficient, and ω _n is the circular frequency;

The magnitude of the center-of-mass sideslip angle is adjusted by adjusting the circular frequency ω _n .

In the method of the present invention, the linear dynamics model that described linear four-wheel steering model adopts is

In the equation,

Among them, l _f is the distance from the front axle to the center of mass, and l _r is the distance from the rear axle to the center of mass;

Decoupling the input and output of the linear four-wheel steering model,

The transfer function used is

in,

_The parameters u ₁ and u ₂ are introduced to realize the decoupling _of the yaw rate γ and the sideslip angle β of the center of mass. The transfer functions are G ₁₁ (s) and G ₂₂ (s);

then there is

if and only if When , the yaw rate and the sideslip angle of the center of mass are controlled by the variables u ₁ and u ₂ respectively, thus,

Wherein, a ₀ =(a ₁₂ b ₂₁ -a ₂₂ b ₁₁ )(a ₂₁ b ₁₂ -a ₁₁ b ₂₂ +a ₁₁ b ₁₂ -a ₁₂ b ₂₂ ), a ₁ =a ₂₁ b ₁₂ b ₁₁ -a ₁₁ b ₂₂ b ₁₁ +a ₁₁ b ₁₂ b ₂₁ -a ₁₂ b ₂₁ b ₁₂ , a ₂ =b ₁₁ b ₂₂ -b ₂₁ b ₁₂ , b ₀ =(a ₂₁ b ₁₂ -a ₁₁ b ₂₂ )(a ₁₂ b ₂₁ -a ₂₂ b ₁₁ ), b ₁ =a ₂₁ b ₁₂ b ₁₁ -a ₁₁ b ₂₂ b ₁₁ +a ₁₂ b ₂₁ b ₂₂ -a ₂₂ b ₁₁ b ₂₂ , b ₂ =b ₂₂ b ₁₁ , b ₃ = (a ₁₁ b ₁₂ -a ₁₂ b ₂₂ )(a ₂₁ b ₁₂ -a ₁₁ b ₂₂ ), b ₄ =-a ₂₁ b ² ₁₂ +a ₁₁ b ₂₂ b ₁₂ +a ₁₁ b ₁₂ b ₂₂ -a ₁₂ b ² ₂₂ , b ₅ =-b ₁₂ b ₂₂ , b ₆ =(-a ₁₂ b ₂₁ +a ₂₂ b ₁₁ )(a ₂₁ b ₁₁ -a ₁₁ b ₂₁ ), b ₇ =-a ₁₂ b ² ₂₁ +a ₂₂ b ₁₁ b ₂₁ -a ₂₁ b ² ₁₁ +a ₁₁ b ₁₁ b ₂₁ , b ₈ =-b ₁₁ b ₂₁ , b ₉ =(a ₂₁ b ₁₂ -a ₁₁ b ₂₂ )(a ₁₂ b ₂₁ -a ₂₂ b ₁₁ ), b ₁₀ =a ₂₁ b ₁₂ b ₁₁ -a ₁₁ b ₂₂ b ₁₁ +a ₁₂ b ₂₁ b ₂₂ -a ₂₂ b ₁₁ b ₂₂ , b ₁₁ =b ₂₂ b ₁₁ ;

Let the transfer function of the asymptotic tracking controller be G _C1 (s), and the asymptotic tracking controller adopts P, PI, PD or PID controller;

Perform pull transformation on the governing equation e(t)=γd( _t )-γ(t)=γd( _t )-G _C1 (t)G ₁₁ (t)e(t),

have to

Assume

but

Simplify the characteristic polynomial d _g (s)d _c (s)+ _ng (s)n _c (s)=0 of its 2nd order system to d ₂ s ² +d ₁ s+d ₀ =0;

where, d ₂ =1+b ₁₁ k _d , d ₁ =b ₁₁ k _p +(-a ₂₂ b ₁₁ +a ₁₂ b ₂₁ )k _d -(a ₁₁ +a ₂₂ ),

d ₀ =a ₁₁ a ₂₂ -a ₂₁ a ₁₂ +k _p (-a ₂₂ b ₁₁ +a ₁₂ b ₂₁ );

According to the Routh judgment table and the Routh-Hurwitz stability criterion, the parameters of the asymptotic tracking controller controlling the yaw rate and the sideslip angle of the center of mass are determined;

Among them, the Routh decision table is In the formula

The Routh-Hurwitz stability criterion is that the coefficients of the characteristic polynomials of the second-order system are all positive or all negative.

In the method of the present invention, the rear wheel differential steering control module calculates the rear wheel differential torque according to the ideal rear wheel angle, specifically,

The dynamic model is established, and the two-degree-of-freedom four-wheel steering vehicle with the ideal front and rear wheel angles as input is used as a reference model, and the sliding mode variable structure controller is designed to obtain the rear wheel differential torque driving the rear wheel steering;

Include the following steps:

a) Regardless of the follow-up rotation angle of the wheels, the state equations of front wheel steering by wire and rear wheel differential steering are:

Among them, β is the sideslip angle of the center of mass of the vehicle, γ is the yaw rate of the vehicle, is the yaw angular acceleration of the vehicle, is the side slip angular velocity of the center of mass of the vehicle, m is the mass of the vehicle, u _x is the longitudinal velocity at the center of mass of the vehicle, l _f is the distance from the front axle to the center of mass, l _r is the distance from the rear axle to the center of mass, δ _f is the rotation angle of the front wheel, k _f is the cornering stiffness of the front wheel, k _r is the cornering stiffness of the rear wheel, I _z is the moment of inertia of the vehicle about the Z axis, d _r is the track of the rear wheel, and R is the effective radius of the tire;

b) Let the state space variable x(t)=[βγ] ^T , the input is the front and rear wheel drive torque difference, i.e. u(t)=ΔT, the state equations of the front wheel steering by wire and the rear wheel differential steering are transformed into

in,

c) Define the sliding mode surface s=γ-γ _d +ξ(β-β _d ),

Among them, ξ is the weight coefficient, γ _d is the yaw rate of the reference model, and β _d is the sideslip angle of the center of mass of the reference model;

Guidance is available,

In the formula,

in, is the yaw angular acceleration of the reference model, is the side slip angular velocity of the center of mass of the reference model;

because Bounded, then one of them is a constant;

Using the reaching law with saturation function, the controller is obtained as

Simulation analysis:

In the following, when the steering mode is four-wheel steering, the four-wheel steering is used as a reference model, and the front wheels adopt the traditional steering and the rear wheel differential steering to complete independent steering, and carry out simulation analysis.

Different vehicle speeds and front wheel angles are used as input, and front and rear wheel angles are used as output. After decoupling calculations, parameter curves such as yaw rate and side slip angle are simulated.

At low speed, select u=5m/s, v=5m/s, front wheel angle δ _f =0.2094rad,

After decoupling, δ _f1 =0.2092rad, δ _r1 =-0.0005454rad.

At medium speed, select u=15m/s, v=15m/s, front wheel angle δ _f =0.0721rad,

After decoupling, δ _f1 =0.07194rad, δ _r1 =-2.505e-06rad.

At high speed, select u=25m/s, v=25m/s, front wheel angle δ _f =0.0454rad,

After decoupling, δ _f1 =0.04512rad, δ _r1 =-0.0001544rad.

Taking the corresponding vehicle speed and the decoupled front and rear wheel angles as input, the curves of yaw rate and side slip angle of the center of mass are obtained through simulation, as shown in Figures 1 to 12.

From Figure 1 to Figure 12, it can be seen that the curves of the traditional front wheel steering and rear wheel differential steering model are basically consistent with the four-wheel steering model curves, indicating that this method can well realize four-wheel steering.

It can be seen from Fig. 1, Fig. 5 and Fig. 9 that the stable value of yaw rate increases with the increase of vehicle speed, and is stable between 3.3rad/s-3.8rad/s. At the same time, it can be seen from Figure 1 that at low speeds, the yaw rate stability of the traditional front wheel steering and rear wheel differential steering is more stable than that of the four-wheel steering model.

From Fig. 2, Fig. 6 and Fig. 10, it can be seen that the stable value of the side slip angle of the center of mass decreases with the increase of the vehicle speed. The stable value of the center of mass slip angle is 0.058rad at low speeds; -0.03rad at medium speeds; and -0.078rad at high speeds. At the same time, it can be seen from Figure 2 that at low speeds, the traditional steering of the front wheels and the differential steering of the rear wheels are more stable than the stable value of the side slip angle of the four-wheel steering model.

It can be seen from Fig. 3, Fig. 7 and Fig. 11 that the x and y position curves of the front wheel traditional steering and rear wheel differential steering models are consistent with the x and y position curves of the four-wheel steering model, and the maximum values of the x position and y position vary with the speed of the vehicle. increase and increase.

It can be seen from Figure 4, Figure 8 and Figure 12 that with the increase of vehicle speed, the torque value becomes smaller and stabilizes within a certain range.

The simulation results show that the steering characteristics presented by the traditional steering of the front wheels and the differential steering of the rear wheels are ideal. Therefore, the independent drive of the rear wheels and the combination of differential steering technology can not only effectively improve the maneuverability of the vehicle under low-speed conditions , and at high speeds, it can effectively reduce the occurrence of tail flick and sideslip when the vehicle is turning; at the same time, it can also improve the active safety and handling stability of the car.

The basic principles, main features and advantages of the present invention have been shown and described above. Those skilled in the industry should understand that the present invention is not limited by the above-mentioned embodiments. What are described in the above-mentioned embodiments and the description only illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have Variations and improvements are possible, which fall within the scope of the claimed invention. The protection scope of the present invention is defined by the appended claims and their equivalents.

Claims (10)

1. The utility model provides an in-wheel motor drive electric automobile's timesharing four-wheel steering system which characterized in that includes:

the detection module is used for detecting the driving parameters of the electric automobile and inputting the driving parameters to the whole automobile controller; the driving parameters comprise a steering wheel angle signal, a pedal position signal of an accelerator pedal, a driving vehicle speed signal, a front wheel steering angle signal and a rear wheel steering angle signal;

the steering mode selection switch is used for manually selecting a steering mode by a driver, wherein the steering mode comprises front wheel steering and four-wheel steering, and the selected steering mode is input to the whole vehicle controller;

the vehicle speed tracking module is used for calculating the running speed of the electric vehicle and the required front wheel driving torque according to the pedal position signal of the accelerator pedal, controlling the in-wheel motor to execute a running vehicle speed signal of a driver and inputting the running speed to the vehicle control unit;

the vehicle control unit is used for receiving the driving speed, transmitting a steering wheel turning angle signal to the front wheel linear control steering control module when the selected steering module is front wheel steering, and outputting a rear wheel locking signal to the rear wheel steering locking module; when the selected steering mode is four-wheel steering, calculating to obtain an ideal front and rear wheel steering angle required by the four-wheel steering and outputting a rear wheel unlocking signal to a rear wheel steering locking module, wherein the ideal front and rear wheel steering angle comprises an ideal front wheel steering angle and an ideal rear wheel steering angle, and transmitting the ideal front wheel steering angle to a front wheel linear control steering control module and the ideal rear wheel steering angle to a rear wheel differential steering control module;

the front wheel linear control steering control module is used for driving a front wheel steering execution motor to steer the front wheels according to the steering wheel angle signal and the front wheel steering angle signal or the ideal front wheel steering angle, providing corresponding steering road feel for a driver and feeding the steering road feel back to the whole vehicle controller;

the rear wheel differential steering control module is used for calculating to obtain a rear wheel differential torque according to an ideal rear wheel steering angle and driving a rear wheel hub motor to steer the rear wheel according to the rear wheel differential torque;

and the rear wheel steering locking module is used for driving the steering locking mechanism to rotate the rear wheels in a right direction according to the rear wheel locking signal and the rear wheel steering angle signal, forbidding the rear wheels to steer, and driving the steering locking mechanism to release the steering locking according to the rear wheel unlocking signal.

2. The time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle according to claim 1, characterized in that: the steering locking mechanism comprises a return motor and two groups of steering mechanisms which are symmetrically arranged on the frame and have the same structure, the return motor is connected with the rear wheel steering locking module, and the two groups of steering mechanisms are connected with the return motor and respectively act on the left rear wheel and the right rear wheel;

the steering mechanism comprises an electromagnetic clutch, a return spur gear, a locking pull rod, a front binding rod, a first steering knuckle arm and a second steering knuckle arm which are sequentially connected, an electromagnet which is lapped on the surface of the locking pull rod and is arranged on the frame, steering main pins which are connected with one end of the first steering knuckle arm and one end of the second steering knuckle arm, an upper cross arm and a lower cross arm which are arranged on the frame, and a locking pull rod displacement sensor which is used for detecting the angle of a rear wheel and is arranged on the locking pull rod; the electromagnetic clutch is connected with the positive electricity return machine and connected with the rear wheel steering locking module, the locking pull rod is connected with the positive electricity return machine through a rod face rack, the locking pull rod and the toe rod as well as the toe rod and the first steering knuckle arm are connected through spherical hinges, two ends of the steering main pin are respectively connected with the upper cross arm and the lower cross arm through the spherical hinges, the electromagnet is used for generating suction after being electrified and attracting the locking pull rod to enable the locking pull rod to be locked on the frame, and the locking pull rod displacement sensor is used for detecting displacement parameters between the locking pull rod and the vehicle body in real time and feeding the displacement parameters back to the vehicle controller to determine the rear wheel steering angle.

3. The time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle according to claim 1, characterized in that: the front wheel steering actuating motor makes the front wheel turn to through drive front wheel steering driving medium, drive front wheel steering driving medium is including consecutive left front wheel knuckle arm, left front wheel steering tie rod, rack, steering gear, right front wheel steering tie rod and right front wheel knuckle arm, left front wheel steering knuckle arm acts on left front wheel, right front wheel steering knuckle arm acts on right front wheel, steering gear links to each other with front wheel steering actuating motor.

4. The time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle according to claim 3, characterized in that: the detection module comprises a torque sensor and a steering wheel angle sensor for detecting a steering wheel, a pedal position sensor for detecting an accelerator pedal, and a rack displacement sensor for detecting the angle of rotation of a front wheel and located on a rack.

5. A control method of a time-sharing four-wheel steering system of an in-wheel motor driven electric vehicle, which is operated in the time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle of any one of claims 1 to 4, comprising the steps of:

1) the vehicle control unit acquires driving parameters acquired by the detection module and a steering mode selected by a driver and input by a steering mode selection switch, wherein the driving parameters comprise a steering wheel angle signal, a pedal position signal of an accelerator pedal, a driving vehicle speed signal, a front wheel steering angle signal and a rear wheel steering angle signal;

2) the vehicle speed tracking module calculates the running speed of the electric vehicle and the required front wheel driving torque according to the pedal position signal of an accelerator pedal, controls the hub motor to execute a running vehicle speed signal of a driver and inputs the running speed to the vehicle control unit;

3) when the vehicle runs, the vehicle control unit judges whether the steering mode selected by the driver is front wheel steering or four-wheel steering;

if the steering mode is front wheel steering, adopting a front wheel linear control steering and rear wheel steering locking mode, executing the steps 4) to 5), and then returning to the step 1);

if the steering mode is four-wheel steering, adopting a front wheel linear control steering mode and a rear wheel differential steering mode, executing the steps 6) -8), and then returning to the step 1);

4) when the selected steering module is used for steering the front wheel, the vehicle control unit transmits a steering wheel turning angle signal to the front wheel linear control steering control module and outputs a rear wheel aligning signal to the rear wheel steering locking module so that the rear wheel is aligned and then the rear wheel steering is locked;

5) the front wheel linear control steering control module drives a front wheel steering execution motor to perform front wheel steering according to the steering wheel angle signal and the front wheel steering angle signal, provides corresponding steering road feel for a driver and feeds the steering road feel back to the whole vehicle controller; meanwhile, the rear wheel steering locking module drives the rotary locking mechanism to correct the rear wheel and forbid the rear wheel to steer according to the rear wheel locking signal and the rear wheel steering signal;

6) when the selected steering mode is four-wheel steering, the vehicle control unit calculates to obtain ideal front and rear wheel turning angles required by the four-wheel steering and outputs a rear wheel unlocking signal to the rear wheel steering locking module, wherein the ideal front and rear wheel turning angles comprise the ideal front wheel turning angle and the ideal rear wheel turning angle, the ideal front wheel turning angle is transmitted to the front wheel linear control steering control module, and the ideal rear wheel turning angle is transmitted to the rear wheel differential steering control module;

7) the front wheel linear control steering control module drives a front wheel steering execution motor to steer the front wheel according to an ideal front wheel steering angle, provides corresponding steering road feel for a driver and feeds the steering road feel back to the whole vehicle controller; meanwhile, the rear wheel steering locking module drives the rotary locking mechanism to release steering locking according to the rear wheel unlocking signal;

8) and the rear wheel differential steering control module calculates to obtain a rear wheel differential torque according to the ideal rear wheel steering angle, and drives a rear wheel hub motor to steer the rear wheel according to the rear wheel differential torque.

6. The control method of the time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle according to claim 5, characterized in that: the vehicle speed tracking controller searches a relationship curve of the longitudinal speed and the position of the accelerator pedal which is predetermined in the system according to a signal acquired by a pedal position sensor of the accelerator pedal, so that the running speed of the electric vehicle is obtained.

7. The control method of the time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle according to claim 5, characterized in that: the vehicle control unit calculates and obtains ideal front and rear wheel rotation angles required by four-wheel steering, specifically,

the vehicle control unit inputs the collected steering wheel angles to a reference model to obtain ideal yaw rate and centroid yaw angle, and the ideal yaw rate and centroid yaw angle of the decoupled linear four-wheel steering model are controlled by an asymptotic tracking controller to track the ideal yaw rate and centroid yaw angle, so that ideal front and rear wheel angles of the four-wheel steering vehicle are obtained; the reference model is a linear two-degree-of-freedom vehicle model with neutral steering characteristics after the centroid slip angle amplitude reduction filtering.

8. The control method of the time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle according to claim 7, characterized in that: the equation of state of the reference model is,

let x_d＝[γ_d β_d]^T，u_d＝[δ_f]，

The reference model is expressed as

in the formula,

wherein ,γ_dIs the yaw rate, beta, of the reference model_dIs the centroid slip angle of the reference model, m is the vehicle mass, u_xIs the longitudinal speed, delta, at the centre of mass of the vehicle_fFor the angle of rotation of the front wheel, /)_fdIs the distance of the center of mass to the front axis,/_rdIs the distance of the center of mass to the rear axis, k_fYaw stiffness, k, of the front wheel_rFor the side-bias of the rear wheelsRigidity, I_zThe moment of inertia of the vehicle to the Z axis;

the centroid side drift angle is processed by an amplitude reduction filter, the transfer function of the amplitude reduction filter is adopted as,

wherein eta is a gain coefficient, xi is a damping coefficient, and omega_nIs the circular frequency;

by adjusting the frequency omega of the circle_nThe magnitude of the centroid slip angle is adjusted.

9. The control method of the time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle according to claim 8, characterized in that: the linear dynamic model adopted by the linear four-wheel steering model is

In the equation, the ratio of the total of the components,

wherein ,l_fDistance of front axle to center of mass,/_rIs the distance from the rear axle to the center of mass;

the input and output of the linear four-wheel steering model are decoupled,

the transfer function adopted is

wherein ,

introduction of parameter u₁、u₂To realize transverselyDecoupling the yaw angular velocity gamma and the centroid slip angle beta, and obtaining the yaw angular velocity gamma relative to u after decoupling₁And centroid slip angle β with respect to u₂Respectively is G₁₁(s) and G₂₂(s)；

Then there is

If and only ifWhile the yaw rate and the centroid slip angle are controlled by variables u₁ and u₂And thus, the method can obtain the product,

wherein ,a₀＝(a₁₂b₂₁-a₂₂b₁₁)(a₂₁b₁₂-a₁₁b₂₂+a₁₁b₁₂-a₁₂b₂₂)，a₁＝a₂₁b₁₂b₁₁-a₁₁b₂₂b₁₁+a₁₁b₁₂b₂₁-a₁₂b₂₁b₁₂，a₂＝b₁₁b₂₂-b₂₁b₁₂，b₀＝(a₂₁b₁₂-a₁₁b₂₂)(a₁₂b₂₁-a₂₂b₁₁)，b₁＝a₂₁b₁₂b₁₁-a₁₁b₂₂b₁₁+a₁₂b₂₁b₂₂-a₂₂b₁₁b₂₂，b₂＝b₂₂b₁₁，b₃＝(a₁₁b₁₂-a₁₂b₂₂)(a₂₁b₁₂-a₁₁b₂₂)，b₄＝-a₂₁b² ₁₂+a₁₁b₂₂b₁₂+a₁₁b₁₂b₂₂-a₁₂b² ₂₂，b₅＝-b₁₂b₂₂，b₆＝(-a₁₂b₂₁+a₂₂b₁₁)(a₂₁b₁₁-a₁₁b₂₁)，b₇＝-a₁₂b² ₂₁+a₂₂b₁₁b₂₁-a₂₁b² ₁₁+a₁₁b₁₁b₂₁，b₈＝-b₁₁b₂₁，b₉＝(a₂₁b₁₂-a₁₁b₂₂)(a₁₂b₂₁-a₂₂b₁₁)，b₁₀＝a₂₁b₁₂b₁₁-a₁₁b₂₂b₁₁+a₁₂b₂₁b₂₂-a₂₂b₁₁b₂₂，b₁₁＝b₂₂b₁₁；

Let the transfer function of the asymptotic tracking controller be G_C1(s) the asymptotic tracking controller is a P, PI, PD or PID controller;

for control equation e (t) ═ γ_d(t)-γ(t)＝γ_d(t)-G_C1(t)G₁₁(t) e (t) pull transform,

to obtain

Is provided with

Then

Characteristic polynomial d of 2-order system_g(s)d_c(s)+n_g(s)n_cReduction of(s) to (0) to (d)₂s²+d₁s+d₀＝0；

wherein ,d₂＝1+b₁₁k_d，d₁＝b₁₁k_p+(-a₂₂b₁₁+a₁₂b₂₁)k_d-(a₁₁+a₂₂)，

d₀＝a₁₁a₂₂-a₂₁a₁₂+k_p(-a₂₂b₁₁+a₁₂b₂₁)；

Determining parameters of an asymptotic tracking controller for controlling yaw velocity and centroid yaw angle according to a Route decision table and a Route-Hurwitz stability criterion;

wherein the route judgment table is in the formula

The Router-Hurwitz stability criterion is that the coefficients of the characteristic polynomials of the 2-order system are all positive or all negative.

10. The control method of the time-sharing four-wheel steering system of the in-wheel motor driven electric vehicle according to claim 5, characterized in that: the rear wheel differential steering control module calculates to obtain the rear wheel differential torque according to the ideal rear wheel steering angle, specifically,

establishing a dynamic model, taking a two-degree-of-freedom four-wheel steering vehicle with ideal front and rear wheel corners as input as a reference model, and designing a sliding mode variable structure controller to obtain a rear wheel differential torque for driving the rear wheel to steer;

the method comprises the following steps:

a) the equation of state of the front wheel linear control steering and the rear wheel differential steering is as follows, except the following turning angle of the wheels,

whereinBeta is the vehicle mass center slip angle, gamma is the vehicle yaw rate,as the yaw angular acceleration of the vehicle,is the vehicle mass center slip angle velocity, m is the vehicle mass, u_xIs the longitudinal speed at the centre of mass of the car,/_fDistance of front axle to center of mass,/_rIs the distance of the rear axle to the center of mass, δ_fIs the angle of rotation of the front wheel, k_fYaw stiffness, k, of the front wheel_rFor cornering stiffness of the rear wheels, I_zIs the moment of inertia of the vehicle about the Z axis, d_rIs the rear wheel track, R is the effective radius of the tire;

b) let state space variable x (t) be [ β γ [ ]]^TThe driving torque difference u (T) of the front and rear wheels is input as Δ T, and the state equations of the front wheel linear steering and the rear wheel differential steering are converted into

wherein ,

c) definition of slip form surface s ═ gamma-gamma_d+ξ(β-β_d)，

Where ξ is the weight coefficient, γ_dYaw rate, beta, for reference model_dIs the centroid slip angle of the reference model;

the derivation is carried out to obtain the result,

in the formula,

wherein ,in order to refer to the yaw angular acceleration of the model,is the centroid yaw angular velocity of the reference model;

due to the fact thatIs bounded, thenThereinIs a constant;

using an approach law with a saturation function, the controller is