CN110962626B - Self-adaptive electronic differential control method for multi-shaft hub motor driven vehicle - Google Patents

Abstract

The invention proposes an adaptive electronic differential control method for a multi-axle in-wheel motor-driven vehicle, which aims to solve the problems that the electronic differential control of the existing electric wheel-driven vehicle cannot adapt to various driving conditions, and the motor performance requirements are relatively high. car control system. The control method includes the following steps: S1, establishing a motion equation of a vehicle body independently driven by an 8×8 in-wheel motor; S2, establishing a wheel vertical runout model; S3, establishing a wheel rotation dynamics equation; S4, formulating a control strategy, and selecting a driving Torque is the control parameter to control the motor. The advantage of the present invention is that it simulates the power distribution characteristics of traditional automobile power transmission by means of motor torque command control and rotational speed follow-up, so that the multi-axle in-wheel motor drives the vehicle under three working conditions of steering, uneven road and wheel rolling radius. It has better differential performance, which improves the accuracy of electronic differential control and the adaptive ability of the system under various working conditions.

Description

An adaptive electronic differential control method for a multi-axle in-wheel motor-driven vehicle

technical field

The invention belongs to an automobile control system, and in particular relates to an adaptive electronic differential speed control method for a multi-axle in-wheel motor-driven vehicle.

Background technique

The in-wheel motor drives the vehicle independently, because it saves the transmission system of the traditional vehicle, and at the same time, the driving torque of each wheel is independently controllable, and the information such as torque and speed can be accurately fed back in real time, which greatly improves the transmission efficiency of the whole vehicle, and the layout design is more flexible. The electronic differential is mainly used to replace the mechanical differential of the traditional vehicle. By coordinating the various drive motors, the steering stability of the vehicle is guaranteed. Due to the large self-weight and load of multi-axle heavy-duty vehicles, and the complex and changeable driving conditions, the differential problem is relatively more prominent and serious, so the adaptive ability of the in-wheel motor electronic differential controller is also proposed. Require. In this paper, a balance equation is established according to the actual force state of each wheel of a multi-axle in-wheel motor-driven vehicle, and at the same time, an adaptive electronic differential control of a multi-axle in-wheel motor-driven vehicle is proposed considering the differential performance requirements of the vehicle under various driving conditions. The method further improves the accuracy of the electronic differential control of the in-wheel motor and the adaptive ability of the system control, and ensures that the electronic differential control strategy can adapt to various differential conditions and has better differential performance.

Some car companies in Japan, Europe and the United States, such as Honda, Audi, and GM, have successively applied electronic differential systems to in-wheel motor-driven vehicles. In recent years, in order to make full use of the outstanding advantages of the electronic differential system to meet the actual driving needs, domestic scholars have also carried out related research on the electronic differential control system. For example, the Chinese patent publication number is CN110116635A, and the publication date is 2019-08-13, which discloses an electronic differential control method for a two-wheel independent drive vehicle. The control method is based on a two-wheel independent drive system. By adjusting the speed difference of the two motors, the driving wheels on both sides output basically the same driving torque, and a good cornering differential can be achieved, but the patent is mainly aimed at the low-speed driving conditions of the coal truck , the yaw stability and slip rate of the vehicle are not fully considered, and the applicability is poor. The Chinese patent publication number is CN108177693A, and the publication date is 2018-06-19, which discloses an electronic differential control system for a hub-driven electric vehicle. The system calculates the target speed of the inner and outer driving wheels through the measured wheel steering angle and the target driving speed, and completes the closed-loop control of the driving wheel speed by calculating the deviation from the actual speed, so that the actual speed of the driving wheel follows the target speed, Differential speed control is realized, but the single speed control of this control system has high requirements on the motor, and cannot coordinate the dynamic changes of the vehicle force during the driving process of the car. According to the requirements of the differential performance of the whole vehicle under various driving conditions, the invention realizes the motor torque control through the closed-loop feedback of the wheel motor speed signal, simulates the power distribution characteristics of the traditional vehicle from the power system to the differential, and makes the multi-axle wheel hub Motor-driven vehicles achieve better differential performance under various driving conditions, and have strong robustness and adaptability.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to overcome the problems that the existing multi-axle in-wheel motor-driven vehicle electronic differential control system cannot realize the differential speed coordination of each wheel under various working conditions, and cannot ensure that the system realizes self-adaptive control, etc. An adaptive electronic differential control method for a vehicle driven by a multi-axle in-wheel motor is provided.

In order to solve the above-mentioned technical problems, the present invention adopts the following technical solutions to realize: comprise the following steps:

1. a self-adaptive electronic differential control method of a multi-axle in-wheel motor-driven vehicle, is characterized in that, comprises the following steps:

The first step is to establish the motion equation of the vehicle independently driven by the 8×8 in-wheel motor;

The coordinate system is established according to the 6 degrees of freedom of the longitudinal, lateral, vertical, yaw, pitch and roll motions of the vehicle body. The positive x-axis is along the longitudinal symmetry line of the vehicle body, and the forward is positive; the y-axis passes through the center of mass along the lateral position of the vehicle. , the right is positive; according to the right-hand rule, the z-axis is vertical and downward is positive; establish the body motion equation;

On the basis of the traditional vehicle wheel force, the interaction force between the suspension and the wheel is considered, and the wheel rotation dynamics equation is established as formula (1):

In the formula: I _w - the moment of inertia of the wheel

T _q - wheel driving torque

F _d - the longitudinal force between the tire and the ground

T _b ——braking torque

M _ω - wheel mass

ξ——action coefficient

In equation (1), the last term on the right side of the equation is the reaction force formed on the ground by the action of the axle on the center of the driven wheel. Through this supplementary term, equation (1) can express the power of the driving wheel and the driven wheel at the same time. To solve the problem of learning, use formula (2) to determine the value of ξ:

The second step is to calculate the actual speed of the wheel at the center of the wheel;

Use formula (3) to calculate the horizontal motion speed of the wheel center:

In the formula: v _{hi ——the} horizontal movement speed of the wheel center of each wheel

u is the longitudinal speed of the vehicle body

v - body lateral speed

r——body yaw rate

Li _——The distance from each axis in the plane to the center of mass

δ _i ——the deflection angle of each wheel

Use formula (4) to calculate the vertical motion speed w _ui of the wheel center:

In the formula: M _ui - unsprung mass at each wheel

w _ui - the vertical movement speed of the wheel center

K _ui - Tire vertical stiffness

Z _ri - the unevenness of the road surface on which the wheels are located

Z _ui - height of wheel center of mass

C _ui - Tire vertical damping

w _ri - rate of change of road surface roughness at the wheel

F _{vi ——The} force of each wheel acting on the suspension in the z-axis direction

B _i - suspension structure parameters

Use formula (5) to calculate the actual speed v _wi at the wheel center:

The third step is to calculate the comprehensive speed;

Obtain the driver's expected speed value VR according to the accelerator-vehicle speed look-up _{table; use the wheel speed to calculate the actual vehicle speed V Z ;} carry out weighted calculation according to the obtained driver's expected speed value and the actual vehicle speed value to obtain the comprehensive vehicle speed value, As shown in formula (6):

V _T =AV _R +BV _Z (6)

In the formula: V _T ——Comprehensive vehicle speed

A, B——weighting coefficient, calibrated by experiment;

The fourth step is to calculate the target torque of each drive motor;

Taking the accelerator pedal opening and the current steering wheel angle as the control input, according to the comprehensive vehicle speed value calculated by formula (6), the expected speed at the wheel center of each wheel is obtained by using the structural geometric relationship of the vehicle itself; and the desired speed at the wheel center of each wheel are input into the PID controller, and the target torque of each drive motor is calculated by formula (7):

_{T Ti} =K _P (v _Ti -v _wi )+KI (v _Ti -v _wi )+K _D (v _Ti -v _wi ) (7)

In the formula: T _Ti ——the target torque of each drive motor

v _Ti —— Expected speed at the center of each wheel

K _P , K _I , K _D ——PID controller parameters, calibrated through experiments;

The actual wheel speed is determined by the balance point between the motor drive torque and the actual wheel force, and is fed back to the vehicle controller to achieve closed-loop control. The control system outputs the drive motor torque command signal according to the motion state of the vehicle, so that the accelerator pedal controls the vehicle speed and the motor torque at the same time; among them, the motor torque can be controlled by open-loop control or closed-loop feedback control.

The wheel differential conditions include: A. When steering, the vehicle yaws, resulting in different accelerations at the wheel centers of each wheel, resulting in different wheel speeds; B. When driving on uneven roads, each wheel There are differences in the length of the track passed by the wheel center, resulting in different speeds of each wheel; C. When the rolling radius of each wheel is different, the speed of each wheel is different due to the same track length passed by the wheel center.

2. The electronic differential speed control system includes: a main controller, each in-wheel motor and a controller system, and a CAN bus communication network.

Compared with the prior art, the beneficial effects of the present invention are:

1. The self-adaptive electronic differential control method for a multi-axle in-wheel motor-driven vehicle according to the present invention can adapt to various driving conditions by adopting the torque command control of the in-wheel motor and the follow-up mode of the rotational speed, so that the wheels can be It rotates freely under its own force, with better differential performance and strong robustness;

2. The self-adaptive electronic differential control method for a multi-axle in-wheel motor-driven vehicle according to the present invention realizes motor torque control through closed-loop feedback of the in-wheel motor speed signal, and can simulate the power of a traditional vehicle from the power system to the differential. The distribution characteristics make the control method of the electronic differential system more reasonable, and give full play to the independent drive characteristics of the in-wheel motor;

3. The self-adaptive electronic differential control method of a multi-axle in-wheel motor-driven vehicle described in the present invention is established by considering the interaction force between the suspension and the wheel and the problem of the active and driven wheels on the basis of the force on the wheel of the traditional vehicle. The wheel rotation dynamics equation, which can simultaneously reflect the effect of the driving wheel by driving, braking and road surface, and the influence of the interaction between the vehicle body and the wheel on the motion of the driven wheel, fully meets the requirements of the rotational dynamics analysis of the wheel driven independently by the in-wheel motor.

Description of drawings

Below in conjunction with accompanying drawing, the present invention is further described:

1 is a flowchart of an adaptive electronic differential control method for a multi-axle in-wheel motor-driven vehicle according to the present invention;

2 is a schematic diagram of a complete rotational dynamics model of a wheel of a multi-axis in-wheel motor-driven vehicle according to the present invention;

FIG. 3 is a schematic diagram of the suspension model of the multi-axle in-wheel motor-driven vehicle according to the present invention.

Detailed ways

Below in conjunction with accompanying drawing, the present invention is described in detail:

The invention discloses an adaptive electronic differential control method for driving a vehicle with a multi-axle in-wheel motor. The deviation value between the driver's expected vehicle speed and the wheel speed signal is used to obtain the target torque of the driving motor, and the torque control of each wheel is carried out. , and feedback the actual speed of the wheel to the vehicle controller to form a closed-loop control, realize the torque command control of the in-wheel motor, and the control mode of the speed follow-up, simulate the power distribution characteristics of the traditional vehicle from the power system to the differential, and effectively avoid the various The slip phenomenon of the wheels due to the differential problem ensures that the multi-axle in-wheel motor-driven vehicle has good differential performance under three driving conditions: steering, uneven road surface and wheel rolling radius.

Referring to FIG. 1 , an adaptive electronic differential control method for a vehicle driven by a multi-axle in-wheel motor according to the present invention mainly includes: establishing a motion equation of the vehicle body independently driven by an 8×8 in-wheel motor; calculating the actual motion speed at the wheel center; Calculate the comprehensive vehicle speed; calculate the target torque of each drive motor in four steps. The following is a step-by-step description of an adaptive electronic differential control method for a vehicle driven by a multi-axle in-wheel motor.

Include the following steps:

The first step is to establish the motion equation of the vehicle body independently driven by the 8×8 in-wheel motor;

The coordinate system is established according to the 6 degrees of freedom of the longitudinal, lateral, vertical, yaw, pitch and roll motions of the vehicle body. The x-axis is along the longitudinal symmetry line of the vehicle body, and forward is positive; The right is positive; the z-axis is positive vertically downwards according to the right-hand rule. According to the force of the vehicle, and considering the influence between the movements in all directions, the body motion equation is calculated by equations (1), (2), (3), (4), (5), (6):

longitudinal movement

lateral movement

vertical movement

In the formula: M _t - the total mass of the vehicle

u is the longitudinal speed of the vehicle body

v - body lateral speed

w - the vertical speed of the body

r——body yaw rate

p - body roll angular velocity

q——body pitch angular velocity

M _s — sprung mass

h'——the distance from the center of mass of the sprung mass to the roll axis

F _f ——Total running resistance

F _xi - the force acting on the suspension by each wheel along the x-axis

F _{yi ——The} force of each wheel acting on the suspension along the y-axis direction

F _{vi ——The} force of each wheel acting on the suspension in the z-axis direction

B _i - suspension structure parameters

pitching motion

yaw motion

roll movement

In the formula: I _{xxs ——the} moment of inertia of the sprung mass around the x-axis

I _{yys ——The} moment of inertia of the sprung mass around the y-axis

I _zzs - the moment of inertia of the sprung mass around the z-axis

I _xx ——The moment of inertia of the whole vehicle around the x-axis

I _{yy ——The} moment of inertia of the whole vehicle around the y-axis

I _{zz ——The} moment of inertia of the whole vehicle around the z-axis

A _i - suspension structure parameters

T - wheelbase

Li _——The distance from each axis in the plane to the center of mass

φ——body roll angle

Referring to FIG. 2 , a schematic diagram of a complete rotational dynamics model of a vehicle wheel driven by a multi-axis in-wheel motor according to the present invention. Using formula (7), calculate the angular acceleration of the driven wheel around the ground point p when the driven wheel is not braking:

In the formula: ω _p ——the angular velocity of the wheel center around the ground point p

r _ω — wheel rolling radius

v _ω - speed at the wheel center

The rotational angular acceleration of the wheel is equal to the angular acceleration of the wheel center around the ground point. Equation (7) can be expressed as Equation (8):

In the formula: ω _o - angular velocity of wheel rotation

On the basis of the traditional vehicle wheel force, the interaction force between the suspension and the wheel is considered, and the wheel rotation dynamics equation is established as formula (9):

In the formula: I _w - the moment of inertia of the wheel

T _q - wheel driving torque

F _d - the longitudinal force between the tire and the ground

T _b ——braking torque

M _ω - wheel mass

ξ——action coefficient

In equation (9), the last term on the right side of the equation is the reaction force formed on the ground by the action of the axle on the center of the driven wheel. Through this supplementary term, equation (9) can express the power of the driving wheel and the driven wheel at the same time. problem, use formula (10) to determine the value of ξ

The second step is to calculate the actual speed of the wheel at the center of the wheel;

Use formula (11) to calculate the horizontal motion speed of the wheel center:

In the formula: v _{hi ——the} horizontal movement speed of the wheel center of each wheel

δ _i ——the deflection angle of each wheel

Referring to Fig. 3, the multi-axle in-wheel motor-driven vehicle of the present invention adopts the McPherson independent suspension, and C' in the figure is the sprung mass center; K _ui and K _si are the vertical stiffness of each tire and suspension, respectively; C _ui and C _si are the corresponding damping respectively; Z _ri is the roughness of the road surface where the wheels are located; Z _ui is the height of the center of mass of each wheel; Z _s is the height of the mass center of the sprung mass; a _i , b _i , d _i are the geometric parameters of the suspension . Its wheel vertical runout is calculated as formula (12):

In the formula: M _ui - unsprung mass at each wheel

w _ui - the vertical speed of the wheel

w _ri - rate of change of road surface roughness at the wheel

The suspension structure parameters A _i , B _i in equations (3), (4), (6), (12) are calculated by the following equations (13), (14), respectively:

Use formula (15) to calculate the actual speed v _wi at the wheel center:

The third step is to calculate the comprehensive speed;

Obtain the driver's expected speed value VR according to the accelerator-vehicle speed look-up _{table; use the wheel speed to calculate the actual vehicle speed V Z ;} carry out weighted calculation according to the obtained driver's expected speed value and the actual vehicle speed value to obtain the comprehensive vehicle speed value, As shown in formula (16):

V _T =AV _R +BV _Z (16)

In the formula: V _T ——Comprehensive vehicle speed

A, B——weighting coefficient, calibrated by experiment;

The fourth step is to calculate the target torque of each drive motor;

Taking the accelerator pedal opening and the current steering wheel angle as the control input, according to the comprehensive vehicle speed value calculated by formula (16), the expected speed at the wheel center of each wheel is obtained by using the structural geometric relationship of the vehicle itself; the calculated actual speed at the wheel center is used to calculate and the desired speed at the center of each wheel are input into the PID controller, and the target torque of each drive motor is calculated by formula (17):

_{T Ti} =K _P (v _Ti -v _wi )+KI (v _Ti -v _wi )+K _D (v _Ti -v _wi ) (17)

In the formula: T _Ti ——the target torque of each drive motor

v _Ti —— Expected speed at the center of each wheel

K _P , K _I , K _D ——PID controller parameters, calibrated through experiments;

The actual wheel speed is determined by the balance point between the motor drive torque and the actual wheel force, and is fed back to the vehicle controller to achieve closed-loop control. The control system outputs the drive motor torque command signal according to the motion state of the vehicle, so that the accelerator pedal controls the vehicle speed and the motor torque at the same time; among them, the motor torque can be controlled by open-loop control or closed-loop feedback control.

An adaptive electronic differential control method for a vehicle driven by a multi-axle in-wheel motor according to the present invention is characterized in that the wheel differential conditions include: A. When steering, the vehicle yaws, causing The accelerations at the wheel centers of each wheel are different, resulting in different wheel speeds; B. When driving on uneven roads, the lengths of the tracks passed by the wheel centers are different, resulting in different wheel speeds; C. When the rolling radius of each wheel is different At the same time, the rotational speed of each wheel is different because each wheel center passes through the same track length.

The self-adaptive electronic differential control method for a vehicle driven by a multi-axle in-wheel motor according to the present invention is characterized in that the electronic differential control system includes: a main controller, each in-wheel motor and a controller system, a CAN bus communication network.

Claims (3)

1. a self-adaptive electronic differential control method of a multi-axle in-wheel motor-driven vehicle, is characterized in that, comprises the following steps: The first step is to establish the motion equation of the vehicle independently driven by the 8×8 in-wheel motor; The coordinate system is established according to the 6 degrees of freedom of the longitudinal, lateral, vertical, yaw, pitch and roll motions of the vehicle body. The positive x-axis is along the longitudinal symmetry line of the vehicle body, and the forward is positive; the y-axis passes through the center of mass along the lateral position of the vehicle. , the right is positive; according to the right-hand rule, the z-axis is vertical and downward is positive; establish the body motion equation; On the basis of the traditional vehicle wheel force, the interaction force between the suspension and the wheel is considered, and the wheel rotation dynamics equation is established as formula (1):

In the formula: I _w - the moment of inertia of the wheel T _q - wheel driving torque F _d - the longitudinal force between the tire and the ground T _b ——braking torque M _ω - wheel mass ξ——action coefficient r _ω — wheel rolling radius v _ω - speed at the wheel center ω _o - angular velocity of wheel rotation In equation (1), the last term on the right side of the equation is the reaction force formed on the ground by the action of the axle on the center of the driven wheel. Through the last term on the right side, equation (1) can simultaneously represent the driving wheel and the For the driven wheel dynamics problem, use formula (2) to determine the value of ξ:

The second step is to calculate the actual speed of the wheel at the center of the wheel; Use formula (3) to calculate the horizontal motion speed of the wheel center:

In the formula: v _{hi ——the} horizontal movement speed of the wheel center of each wheel u is the longitudinal speed of the vehicle body v - body lateral speed r——body yaw rate Li _——The distance from each axis in the plane to the center of mass δ _i ——the deflection angle of each wheel Use formula (4) to calculate the vertical motion speed w _ui of the wheel center:

In the formula: M _ui - unsprung mass at each wheel w _ui - the vertical movement speed of the wheel center K _ui - Tire vertical stiffness Z _ri - the unevenness of the road surface on which the wheels are located Z _ui - height of wheel center of mass C _ui - Tire vertical damping w _ri - rate of change of road surface roughness at the wheel F _{vi ——The} force of each wheel acting on the suspension in the z-axis direction B _i - suspension structure parameters Use formula (5) to calculate the actual speed v _wi at the wheel center:

The third step is to calculate the comprehensive speed; Obtain the driver's expected speed value VR according to the accelerator-vehicle speed look-up _{table; use the wheel speed to calculate the actual vehicle speed V Z ;} carry out weighted calculation according to the obtained driver's expected speed value and the actual vehicle speed value to obtain the comprehensive vehicle speed value, As shown in formula (6): V _T =AV _R +BV _Z (6) In the formula: V _T ——Comprehensive vehicle speed A, B——weighting coefficient, calibrated by experiment; The fourth step is to calculate the target torque of each drive motor; Taking the accelerator pedal opening and the current steering wheel angle as the control input, according to the comprehensive vehicle speed value calculated by formula (6), the expected speed at the wheel center of each wheel is obtained by using the structural geometric relationship of the vehicle itself; and the desired speed at the wheel center of each wheel are input into the PID controller, and the target torque of each drive motor is calculated by formula (7): _{T Ti} =K _P (v _Ti -v _wi )+KI (v _Ti -v _wi )+K _D (v _Ti -v _wi ) (7) In the formula: T _Ti ——the target torque of each drive motor v _Ti —— Expected speed at the center of each wheel K _P , K _I , K _D ——PID controller parameters, calibrated through experiments; The actual wheel speed is determined by the balance point between the motor drive torque and the actual wheel force, and is fed back to the vehicle controller to achieve closed-loop control. The control system outputs the drive motor torque command signal according to the motion state of the vehicle, so that the accelerator pedal controls the vehicle speed and the motor torque at the same time; among them, the motor torque can be controlled by open-loop control or closed-loop feedback control. 2. The self-adaptive electronic differential control method of a multi-axle in-wheel motor-driven vehicle according to claim 1, wherein the wheel differential conditions include: A. When steering and driving, the vehicle yaw motion , resulting in different accelerations at the wheel centers of each wheel, resulting in different wheel speeds of each wheel; B. When driving on uneven roads, the length of the track passed by each wheel center is different, resulting in different speeds of each wheel; C. When each wheel rolls When the radius is different, the rotation speed of each wheel is different due to the same track length of each wheel center. 3. The self-adaptive electronic differential control method of a multi-axle in-wheel motor-driven vehicle according to claim 1, wherein the electronic differential control system comprises: a main controller, each in-wheel motor and a controller system, a CAN bus communication network.

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