CN115723590A - Energy-saving torque vector control method for hub motor driven automobile - Google Patents
Energy-saving torque vector control method for hub motor driven automobile Download PDFInfo
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Abstract
The invention belongs to the technical field of electric vehicle control, and particularly relates to an energy-saving torque vector control method of a hub motor driven vehicle. A reference yaw rate is generated based on the vehicle steering characteristics, and a reference yaw moment is calculated using a feedforward controller and a feedback controller. And carrying out torque vector distribution on the obtained yaw moment and the expected total driving torque, determining the working states of the motors at different positions, reducing the driving redundancy in the driving process and improving the energy efficiency. The invention can reduce energy consumption to the utmost extent and improve the operation stability and the driving safety of the vehicle.
Description
Technical Field
The invention relates to the technical field of electric automobile control, in particular to an energy-saving torque vector control method for an automobile driven by a hub motor.
Background
Electric vehicles have been developed and produced in large scale in many countries around the world, the popularization targets of electric vehicles in developed countries and regions of automobiles are over one million in the coming years, and the proportion of the global electric vehicle output in the current year is rapidly increasing. Different from the traditional automobile which obtains power through a diesel engine or a gasoline engine, the pure electric automobile generally obtains power through one or more motors, so that the driving system of the pure electric automobile can be more flexibly arranged and distributed. With this advantage, a form of driving with the in-wheel motor as a power source is presented. The hub motor driven automobile omits all transmission systems of traditional automobiles such as a half shaft, a differential mechanism, a transmission shaft, a clutch, a gearbox and the like, directly drives wheels, greatly simplifies a chassis system of the automobile, and has very compact structure and high transmission efficiency. And because four wheels of the wheel hub motor driven automobile can be driven independently, the turning response and the active safety of the automobile can be obviously improved through independent wheel torque control, namely torque vector control.
The torque vector control technology is applied to the traditional vehicle for a long time, and generally adopts methods such as an inter-axle transfer case, an inter-wheel differential lock, differential braking and the like to enable the driving torque to achieve the effects of proportional distribution of front and rear axles and equal-difference driving of left and right wheels. However, the magnitude of differential torque that can be achieved by this type of torque vector distribution method is limited, and there are instances where longitudinal vehicle speed or acceleration is lost. However, the torque vector distribution of the independently driven wheels can realize the differential quantity of the maximum torque of the motor, and under the condition of meeting the requirement of a driver with unchanged longitudinal vehicle speed or acceleration, an additional yaw moment is applied to the vehicle to increase the stability of the vehicle and control the steering characteristic.
Based on the problems, an energy-saving torque vector control method for an in-wheel motor driven automobile is provided.
Disclosure of Invention
This section is for the purpose of summarizing some aspects of embodiments of the invention and to briefly introduce some preferred embodiments. In this section, as well as in the abstract and title of the application, simplifications or omissions may be made to avoid obscuring the purpose of the section, the abstract and the title, and such simplifications or omissions are not intended to limit the scope of the invention.
The present invention has been made in view of the problems occurring in the prior art.
Therefore, the invention aims to provide an energy-saving torque vector control method for an in-wheel motor driven automobile, which can realize a torque vector distribution strategy under different driving conditions, reduce driving redundancy during automobile driving, improve energy efficiency and improve the operation stability and driving safety of the automobile.
To solve the above technical problem, according to an aspect of the present invention, the present invention provides the following technical solutions:
an energy-saving torque vector control method of an in-wheel motor driven automobile comprises the following steps:
step 1: designing a group of understeer characteristics, generating an offline look-up table through an offline optimization method, improving the steering dynamic response of the vehicle under different driving modes, and using the offline look-up table to generate a feedforward yaw moment M through a feedforward component query in an upper layer controller FF Z ；
Defining a set of relation curves of the dynamic steering angle delta dyn and the lateral acceleration ay under different longitudinal accelerations; the relationship among the dynamic steering angle, the Ackerman steering angle and the wheel turning angle is as follows:
δ dym ＝δ-δ kin
defining a set of equality and inequality constraints, wherein the equality constraints use an eight degree of freedom quasi-static vehicle model; the derivatives of the roll angle, the yaw angular velocity and the centroid slip angle of the model are all zero; the longitudinal and lateral constraint equations for this model are as follows:
in the formula, V dot Is the derivative of the velocity; γ is yaw rate; β is the centroid slip angle; f x,i And F y,i The longitudinal force and the lateral force of each wheel are respectively; delta. For the preparation of a coating i Is the angle of each wheel; f drag Is the total running resistance of the automobile;
the yaw and roll constraint equations for this model are as follows:
in the formula, M z Is a yaw moment; x i And y i Half of the wheel base and half of the wheel base respectively; m z,i Is the aligning moment of each wheel;
and
is the anti-roll moment of the front and rear suspensions, h CG Is the height of the center of mass; d f And d f Is the height of the front and rear suspension roll centers;
is the roll angle;
the inequality constraints for designing understeer characteristics are related to limitations imposed by the installed hardware, such as: 1) Motor torque limitation, M max (ii) a 2) Battery power limit as a function of battery state of charge, current and temperature; 3) The size of longitudinal slippage and lateral slippage;
taking the sum of the input power of the front motor transmission system and the input power of the rear motor transmission system as a target function, optimizing the target function aiming at the irregularity and the local minimum of a motor driving efficiency diagram to obtain a group of understeer characteristic curves which minimize the input power of the motor, wherein the group of curves form the response characteristic of the automobile in steering under different longitudinal accelerations;
step two: a reference yaw rate is generated from the vehicle steering characteristics, and the reference yaw rate is calculated as follows:
γ ref ＝(w c /s+w c )γ ref,s
in the formula, w c The tuning parameters of the dynamic response of different vehicles can be changed according to different driving modes; gamma ray ref,s Is the static reference yaw rate, gamma ref,s ＝a y /V；
Step three: calculating to obtain a feedforward reference yaw moment according to the reference yaw velocity in the step two, the vehicle speed and the lateral acceleration acquired by the sensor, the motor efficiency distribution and the slip ratio distribution; an off-line lookup table related to the yaw moment and the vehicle state parameters is generated by an off-line optimization method and used for quickly responding when the vehicle turns, and the tracking performance of the yaw angular velocity target is improved;
the off-line optimization process of the feedforward yaw moment is carried out on the basis of an interior point method, the understeer characteristic set designed in the step one is used as equality constraint, the maximum and minimum torques of the motor, the maximum and minimum power of a battery and the slip ratio range of tires are used as inequality constraint, and the sum of the input powers of the motor transmission system is selected as a target function to carry out optimization; the formula of the objective function is as follows:
step four: collecting the observed value of the yaw angular velocity through a sensor, comparing the observed value with a reference yaw angular velocity to obtain a yaw angular velocity error e (gamma), and calculating to obtain a feedback yaw moment M through a PID (proportion integration differentiation) feedback controller FB Z (ii) a Tracking target parameters through feedforward quick response in the steering process of the vehicle, and then further adjusting the tracking performance of the yaw velocity through a PID feedback controller to prevent oscillation in the steering process; the reference yaw moment consists of a feedforward yaw moment and a feedback yaw moment;
step five: distributing the reference yaw moment obtained in the step four and the expected total torque meeting the requirement of the driver to each specific wheel through a torque vector distribution control strategy so as to meet the longitudinal acceleration and the steering response expected by the driver; in the running process of the vehicle, judging whether the wheel rotation angle delta is equal to zero or not, and distributing driving torque according to two working conditions of straight running and steering running respectively;
when delta is equal to zero, the vehicle is in straight-line driving, the driving motor is enabled to work in a high-efficiency area as much as possible according to a motor efficiency MAP, the input power of the front and rear axle motors is taken as an objective function, an optimal front and rear axle driving torque distribution coefficient is searched, and the objective function minimization calculation formula is as follows:
in the formula of t Representing the ratio of front axle drive torque to total torque; eta f And η r Representing the efficiency of the front and rear axle motors; n represents a rotation speed; td represents the drive torque;
the constraints of the objective function are as follows:
0≤λ t ≤0.5
0≤0.5λ t T d ≤T max
0≤(1-λ t )T d ≤T max
when delta is not equal to zero, the vehicle is driven in a steering mode, and the total torque demand T is used tot Determining the number of output-driven motors, and determining the working state of each motor, thereby setting three logic gate limit values T switch,1 、T switch,2 、T switch,3 As a threshold for motor switching; when the number of the motors in the working state is different, the positions of the motors providing the driving force are also different; the energy consumption formula generated by the vehicle total motor transmission system at the moment is as follows:
and taking the total motor transmission system energy consumption as an objective function, respectively allocating the total torque demand to each motor torque, and minimizing the objective function according to the size and the position of the torque allocation.
As a preferable aspect of the energy-saving torque vector control method for an in-wheel motor driven vehicle according to the present invention, wherein: logic gate limit value T for judging working state of motor switch,1 、T switch,2 、T switch,3 As a switching threshold; comparing the relation between the total motor energy consumption loss and the total torque requirement under different motor quantities by using a motor efficiency MAP graph, wherein the intersection points of the four relation curves are the motor switch threshold T respectively switch,1 、T switch,2 、T switch ,. The specific motor energy loss function is as follows:
P EM，loss,tot ＝n*P EM，loss (T d，tot /n，V)。
as a preferable aspect of the energy-saving torque vector control method for an in-wheel motor driven vehicle according to the present invention, wherein: torque vectors are distributed to the motors, energy consumption generated by a transmission system of the total motor is minimized according to the size and the position of torque distribution, and torque distribution conditions under different torque requirements are obtained;
when the total torque requirement satisfies 0 ≦ T d，tot ≤T switch,1 When only the outer rear motor is driven, the driving torque of the wheel is:
T 21 ＝T d，tot
when the total torque demand satisfies T switch,1 ≤T d，tot ≤T switch,2 When the two motors work, the output torque of the two motors at the outer side is taken as a driving source, and the torque of the two motors at the time is as follows:
T 11 ＝T d，tot *σ L
T 21 ＝T d，tot *(1-σ L )
when the total torque demand satisfies T switch,2 ≤T d，tot ≤T switch,3 The two motors on the outer side and the rear motor on the inner side output driving torques under the condition (1), and the torque distribution of the motors is as follows:
T 11 ＝T 21 ＝T d，tot /2+ΔT LR
T 22 ＝T d，tot /2-ΔT LR
when the total torque demand satisfies T switch,3 ≤T d，tot When the condition is met, the four motors all work to output driving torque, and the torque distribution of the motors is as follows:
T 11 ＝(T d，tot /2+ΔT LR )σ L
T 21 ＝(T d，tot /2+ΔT LR )(1-σ L )
T 12 ＝(T d，tot /2-ΔT LR )σ R
T 12 ＝(T d，tot /2-ΔT LR )(1-σ R )
in the above formula, T ij As the wheel drive torques at different positions, i =1,2 indicates the front axle and the rear axle, respectively, and j =1,2 indicates the outside and the inside, respectivelyA side; sigma L And σ R The ratio of the left and right front axle drive torques to the total drive torque, respectively.
Compared with the prior art, the invention has the beneficial effects that:
the torque vector distribution strategy under different driving conditions can be realized, the driving redundancy of the automobile during driving is reduced, the energy efficiency is improved, and the operation stability and the driving safety of the automobile are improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and detailed embodiments, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without inventive labor. Wherein:
FIG. 1 is a flow chart of the understeer feature design proposed by the present invention;
FIG. 2 is a set of understeer characteristics set forth in the present invention;
FIG. 3 is a MAP of motor torque efficiency provided by the present invention;
FIG. 4 is a schematic diagram of the upper controller composed of feedforward and feedback parts according to the present invention;
fig. 5 is a schematic diagram of a torque vector control structure proposed by the present invention.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described herein, and it will be apparent to those of ordinary skill in the art that the present invention may be practiced without departing from the spirit and scope of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.
Next, the present invention is described in detail with reference to the drawings, and in the detailed description of the embodiments of the present invention, the cross-sectional view illustrating the structure of the device is not enlarged partially in general scale for the convenience of illustration, and the drawings are only exemplary, which should not limit the scope of the present invention. In addition, the three-dimensional dimensions of length, width and depth should be included in the actual fabrication.
To make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
The invention provides the following technical scheme: an energy-saving torque vector control method of a hub motor driven automobile can realize torque vector distribution strategies under different driving working conditions in the using process, reduce the driving redundancy of the automobile in driving, improve the energy efficiency and improve the operation stability and the driving safety of the automobile;
example 1
An energy-saving torque vector control method of an in-wheel motor driven automobile comprises the following steps:
step 1: designing a group of understeer characteristics, generating an offline look-up table through an offline optimization method, improving the steering dynamic response of the vehicle under different driving modes, and using the offline look-up table to generate a feedforward yaw moment M through a feedforward component query in an upper layer controller FF Z ；
Defining a relation curve of the dynamic steering angle delta dyn and the lateral acceleration ay under different longitudinal accelerations; the relationship among the dynamic steering angle, the Ackerman steering angle and the wheel turning angle is as follows:
δ dyn ＝δ-δ kin
defining a set of equality and inequality constraints, wherein the equality constraints use an eight degree of freedom quasi-static vehicle model; the derivatives of the roll angle, yaw rate and centroid slip angle of the model are all zero; the longitudinal and lateral constraint equations for this model are as follows:
in the formula, V dot Is the derivative of the velocity; γ is yaw rate; β is the centroid slip angle; f x,i And F y,i The longitudinal force and the lateral force of each wheel are respectively; delta i Is the angle of each wheel; f drag Is the total running resistance of the automobile;
the yaw and roll constraint equations for this model are as follows:
in the formula, M z Is a yaw moment; x i And y i Half of the wheel base and half of the wheel base respectively; m is a group of z,i Is the aligning moment of each wheel;
and
is the anti-roll moment of the front and rear suspensions, h CG Is the height of the center of mass; d is a radical of f And d f Is the height of the front and rear suspension roll centers;
is the roll angle;
the inequality constraints for designing understeer characteristics are related to limitations imposed by the installed hardware, such as: 1) Motor torque limitation, M max (ii) a 2) Battery power limits as a function of battery state of charge, current, and temperature; 3) The size of longitudinal slippage and lateral slippage;
taking the sum of the input power of the front motor transmission system and the input power of the rear motor transmission system as a target function, optimizing the target function aiming at the irregularity and local minimum of a motor driving efficiency diagram to obtain a group of understeer characteristic curves minimizing the input power of the motor, wherein the group of curves form the response characteristic of the automobile during steering under different longitudinal accelerations;
step two: generating a reference yaw rate according to the vehicle steering characteristics, the reference yaw rate being calculated as follows:
γ ref ＝(w c /s+w c )γ ref,s
in the formula, w c The tuning parameters of the dynamic response of different vehicles can be changed according to different driving modes; gamma ray ref,s Is a static reference yaw rate, gamma ref,s ＝a y /V；
Step three: calculating to obtain a feedforward reference yaw moment according to the nonlinear quasi-static model through the reference yaw velocity in the step two and the states of the vehicle speed and the lateral acceleration, the motor efficiency distribution and the slip rate distribution which are acquired by the sensor; an off-line lookup table related to the yaw moment and the vehicle state parameters is generated through an off-line optimization method and used for quickly responding when a vehicle turns, and the tracking performance of the yaw velocity target is improved;
the off-line optimization process of the feedforward yaw moment is carried out on the basis of an interior point method, the understeer characteristic set designed in the step one is used as equality constraint, the maximum and minimum torques of the motor, the maximum and minimum power of a battery and the slip ratio range of tires are used as inequality constraint, and the sum of the input powers of the motor transmission system is selected as a target function to carry out optimization; the formula of the objective function is as follows:
step four: collecting the observed value of the yaw angular velocity through a sensor, comparing the observed value with a reference yaw angular velocity to obtain a yaw angular velocity error e (gamma), and calculating to obtain a feedback yaw moment M through a PID (proportion integration differentiation) feedback controller FB Z (ii) a Tracking target parameters by feed-forward fast response during vehicle steering, followed byThe tracking performance of the yaw angular velocity is further adjusted through a PID feedback controller, so that oscillation in the steering process is prevented; the reference yaw moment consists of a feedforward yaw moment and a feedback yaw moment;
step five: distributing the reference yaw moment obtained in the step four and the expected total torque meeting the requirement of the driver to specific wheels through a torque vector distribution control strategy so as to meet the longitudinal acceleration and steering response expected by the driver; in the running process of the vehicle, judging whether the wheel rotation angle delta is equal to zero or not, and distributing driving torque according to two working conditions of straight running and steering running respectively;
when delta is equal to zero, the vehicle runs in a straight line, the driving motor works in a high-efficiency area as far as possible according to a motor efficiency MAP, the input power of the front and rear axle motors is used as an objective function, an optimal front and rear axle driving torque distribution coefficient is searched, and the objective function minimization calculation formula is as follows:
in the formula of lambda t Representing the proportion of front axle drive torque to total torque; eta f And η r Representing the efficiency of the front and rear axle motors; n represents a rotation speed; t is d Represents the driving torque;
the constraints of the objective function are as follows:
0≤λ t ≤0.5
0≤0.5λ t T d ≤T max
0≤(1-λ t )T d ≤T max
when delta is not equal to zero, the vehicle is driven in a steering mode, and the total torque demand T is used tot Determining the number of motors driven by the output, judging the working state of each motor, and setting three logic gate limit values T switch,1 、T switch,2 、T switch,3 As a threshold for motor switching; when the number of the motors in the working state is different, the positions of the motors providing the driving force are also different; the energy consumption formula generated by the vehicle total motor transmission system at the moment is as follows:
and taking the total motor transmission system energy consumption as an objective function, respectively allocating the total torque demand to each motor torque, and minimizing the objective function according to the size and the position of the torque allocation.
Wherein: logic gate limit value T for judging working state of motor switch,1 、T switch,2 、T switch,3 As a switching threshold; comparing the relation between the total motor energy consumption loss and the total torque requirement under different motor quantities by using a motor efficiency MAP (MAP), wherein the intersection points of the four relation curves are the motor switch threshold T respectively switch,1 、T switch,2 、T switch ,. The specific motor energy loss function is as follows:
P EM,loss,tot ＝n*P EM，loss (T d，tot /n，V)
wherein: torque vectors are distributed to the motors, energy consumption generated by a transmission system of the total motor is minimized according to the size and the position of torque distribution, and torque distribution conditions under different torque requirements are obtained;
when the total torque requirement satisfies 0 ≦ T d，tot ≤T switch,1 When only the outer rear motor is driven, the driving torque of the wheel is as follows:
T 21 ＝T d，tot
when the total torque demand satisfies T switch,1 ≤T d，tot ≤T switch,2 When the two motors on the outer side work and output torque is used as a driving source, the torque of the two motors is as follows:
T 11 ＝T d，tot *σ L
T 21 ＝T d，tot *(1-σ L )
when the total torque demand satisfies T switch,2 ≤T d，tot ≤T switch,3 The two motors on the outer side and the rear motor on the inner side output driving torques under the condition (1), and the torque distribution of the motors is as follows:
T 11 ＝T 21 ＝T d，tot /2+ΔT LR
T 22 ＝T d，tot /2-ΔT LR
when the total torque demand satisfies T switch,3 ≤T d，tot When the condition is met, the four motors all work to output driving torque, and the torque distribution of the motors is as follows:
T 11 ＝(T d，tot /2+ΔT LR )σ L
T 21 ＝(T d，tot /2+ΔT LR )(1-σ L )
T 12 ＝(T d，tot /2-ΔT LR )σ R
T 12 ＝(T d，tot /2-ΔT LR )(1-σ R )
in the above formula, T ij As wheel drive torques at different positions, i =1,2 denotes a front axle and a rear axle, respectively, and j =1,2 denotes an outer side and an inner side, respectively; sigma L And σ R The ratio of the left and right front axle drive torques to the total drive torque, respectively.
While the invention has been described with reference to an embodiment, various modifications may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In particular, the various features of the disclosed embodiments of the invention may be used in any combination, provided that no structural conflict exists, and the combinations are not exhaustively described in this specification merely for the sake of brevity and resource conservation. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
Claims (3)
1. An energy-saving torque vector control method of an in-wheel motor driven automobile is characterized by comprising the following steps:
step 1: designing a group of understeer characteristics, generating an offline look-up table through an offline optimization method, improving the steering dynamic response of the vehicle under different driving modes, and using the offline look-up table to generate a feedforward yaw moment M through a feedforward component query in an upper layer controller FF Z ；
Defining a relation curve of the dynamic steering angle delta dyn and the lateral acceleration ay under different longitudinal accelerations; the relationship among the dynamic steering angle, the Ackerman steering angle and the wheel turning angle is as follows:
δ dyn ＝δ-δ kin
defining a set of equality and inequality constraints, wherein the equality constraints use an eight degree of freedom quasi-static vehicle model; the derivatives of the roll angle, the yaw angular velocity and the centroid slip angle of the model are all zero; the longitudinal and lateral constraint equations for this model are as follows:
in the formula, V dot Is the derivative of the velocity; γ is yaw angular velocity; β is the centroid slip angle; f x,i And F y,i The longitudinal force and the lateral force of each wheel are respectively; delta i Is the angle of each wheel; f drag Is the total running resistance of the automobile;
the yaw and roll constraint equations for this model are as follows:
in the formula, M z Is a yaw moment; x i And y i Half of the wheel base and half of the wheel base respectively; m is a group of z,i Is the aligning moment of each wheel;
and
is the anti-roll moment of the front and rear suspensions, h CG Is the height of the center of mass; d f And d f Is the height of the front and rear suspension roll centers;
is the roll angle;
the inequality constraints for designing understeer characteristics are related to limitations imposed by the installed hardware, such as: 1) Motor torque limitation, M max (ii) a 2) Battery power limit as a function of battery state of charge, current and temperature; 3) The size of longitudinal slippage and lateral slippage;
taking the sum of the input power of the front motor transmission system and the input power of the rear motor transmission system as a target function, optimizing the target function aiming at the irregularity and local minimum of a motor driving efficiency diagram to obtain a group of understeer characteristic curves minimizing the input power of the motor, wherein the group of curves form the response characteristic of the automobile during steering under different longitudinal accelerations;
step two: generating a reference yaw rate according to the vehicle steering characteristics, the reference yaw rate being calculated as follows:
γ ref ＝(w c /s+w c )γ ref,s
in the formula, w c The tuning parameters of the dynamic response of different vehicles can be changed according to different driving modes; gamma ray ref,s Is the static reference yaw rate, gamma ref,s ＝a y /V；
Step three: calculating to obtain a feedforward reference yaw moment according to the reference yaw velocity in the step two, the vehicle speed and the lateral acceleration acquired by the sensor, the motor efficiency distribution and the slip ratio distribution; an off-line lookup table related to the yaw moment and the vehicle state parameters is generated by an off-line optimization method and used for quickly responding when the vehicle turns, and the tracking performance of the yaw angular velocity target is improved;
performing an off-line optimization process of the feedforward yaw moment on the basis of an interior point method, taking the understeer characteristic set designed in the step one as equality constraint, taking the maximum and minimum torque of the motor, the maximum and minimum power of a battery and the slip ratio range of tires as inequality constraint, and selecting the sum of the input power of a motor transmission system as a target function to optimize the sum; the formula of the objective function is as follows:
step four: collecting the observed value of the yaw angular velocity through a sensor, comparing the observed value with a reference yaw angular velocity to obtain a yaw angular velocity error e (gamma), and calculating to obtain a feedback yaw moment M through a PID (proportion integration differentiation) feedback controller FB Z (ii) a Tracking target parameters through feedforward quick response in the steering process of the vehicle, and then further adjusting the tracking performance of the yaw rate through a PID feedback controller to prevent oscillation in the steering process; the reference yaw moment consists of a feedforward yaw moment and a feedback yaw moment;
step five: distributing the reference yaw moment obtained in the step four and the expected total torque meeting the requirement of the driver to each specific wheel through a torque vector distribution control strategy so as to meet the longitudinal acceleration and the steering response expected by the driver; in the running process of the vehicle, judging whether the wheel rotation angle delta is equal to zero or not, and distributing driving torque under two working conditions of straight running and steering running respectively;
when delta is equal to zero, the vehicle runs in a straight line, the driving motor works in a high-efficiency area as far as possible according to a motor efficiency MAP, the input power of the front and rear axle motors is used as an objective function, an optimal front and rear axle driving torque distribution coefficient is searched, and the objective function minimization calculation formula is as follows:
in the formula of t Representing the ratio of front axle drive torque to total torque; eta f And η r Representing the efficiency of the front and rear axle motors; n represents a rotation speed; t is d Represents a driving torque;
the constraints of the objective function are as follows:
0≤λ t ≤0.5
0≤0.5λ t T d ≤T max
0≤(1-λ t )T d ≤T max
when delta is not equal to zero, the vehicle is driven in a steering mode, and the total torque demand T is used tot Determining the number of motors driven by the output, judging the working state of each motor, and setting three logic gate limit values T switch,1 、T switch,2 、T switch,3 As a threshold for motor switching; when the number of the motors in the working state is different, the positions of the motors providing the driving force are also different; the energy consumption formula generated by the vehicle total motor transmission system at the moment is as follows:
and taking the total motor transmission system energy consumption as an objective function, respectively allocating the total torque demand to each motor torque, and minimizing the objective function according to the size and the position of the torque allocation.
2. The energy-saving torque vector control method of an in-wheel motor driven vehicle according to claim 1, characterized in that: logic gate limit value T for judging working state of motor switch,1 、T switch,2 、T switch,3 As a switching threshold; comparing the relation between the total motor energy consumption loss and the total torque requirement under different motor quantities by using a motor efficiency MAP graph, wherein the intersection points of the four relation curves are the motor switch threshold T respectively switch,1 、T switch,2 、T switch, . The specific motor energy loss function is as follows:
P EM,loss,tot ＝n*P EM,loss (T d,tot /n,V)
3. the energy-saving torque vector control method of an in-wheel motor driven vehicle according to claim 2, characterized in that: torque vectors are distributed to the motors, energy consumption generated by a transmission system of the total motor is minimized according to the size and the position of torque distribution, and torque distribution conditions under different torque requirements are obtained;
when the total torque requirement meets 0 and is less than or equal to T d,tot ≤T switch,1 When only the outer rear motor is driven, the driving torque of the wheel is:
T 21 ＝T d,tot
when the total torque demand satisfies T switch,1 ≤T d,tot ≤T switch,2 When the two motors on the outer side work and output torque is used as a driving source, the torque of the two motors is as follows:
T 11 ＝T d,tot *σ L
T 21 ＝T d,tot *(1-σ L )
when the total torque demand satisfies T switch,2 ≤T d,tot ≤T switch,3 The two motors on the outer side and the rear motor on the inner side output driving torques under the condition (1), and the torque distribution of the motors is as follows:
T 11 ＝T 21 ＝T d,tot /2+ΔT LR
T 22 ＝T d,tot /2-ΔT LR
when the total torque demand satisfies T switch,3 ≤T d,tot When the four motors work to output driving torque, the torque distribution of the motors is as follows:
T 11 ＝(T d,tot /2+ΔT LR )σ L
T 21 ＝(T d,tot /2+ΔT LR )(1-σ L )
T 12 ＝(T d,tot /2-ΔT LR )σ R
T 12 ＝(T d,tot /2-ΔT LR )(1-σ R )
in the above formula, T ij As wheel drive torques at different positions, i =1,2 represents a front axle and a rear axle, respectively, and j =1,2 represents an outer side and an inner side, respectively; sigma L And σ R The front axle drive torque on the left and right sides, respectively, is a proportion of the total drive torque.
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