CN108177692A - A kind of differential power-assisted steering of electric wheel drive vehicle and stability control method for coordinating - Google Patents

A kind of differential power-assisted steering of electric wheel drive vehicle and stability control method for coordinating Download PDF

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Publication number
CN108177692A
CN108177692A CN201711455263.1A CN201711455263A CN108177692A CN 108177692 A CN108177692 A CN 108177692A CN 201711455263 A CN201711455263 A CN 201711455263A CN 108177692 A CN108177692 A CN 108177692A
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wheel
torque
vehicle
differential
stability
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CN108177692B (en
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王军年
罗正
郭德东
刘培祥
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Jilin University
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Jilin University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D11/00—Steering non-deflectable wheels; Steering endless tracks or the like
    • B62D11/02—Steering non-deflectable wheels; Steering endless tracks or the like by differentially driving ground-engaging elements on opposite vehicle sides
    • B62D11/04—Steering non-deflectable wheels; Steering endless tracks or the like by differentially driving ground-engaging elements on opposite vehicle sides by means of separate power sources
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L15/00—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles
    • B60L15/20—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles for control of the vehicle or its driving motor to achieve a desired performance, e.g. speed, torque, programmed variation of speed
    • B60L15/2036—Electric differentials, e.g. for supporting steering vehicles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L15/00—Methods, circuits, or devices for controlling the traction-motor speed of electrically-propelled vehicles
    • B60L15/32—Control or regulation of multiple-unit electrically-propelled vehicles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60L—PROPULSION OF ELECTRICALLY-PROPELLED VEHICLES; SUPPLYING ELECTRIC POWER FOR AUXILIARY EQUIPMENT OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRODYNAMIC BRAKE SYSTEMS FOR VEHICLES IN GENERAL; MAGNETIC SUSPENSION OR LEVITATION FOR VEHICLES; MONITORING OPERATING VARIABLES OF ELECTRICALLY-PROPELLED VEHICLES; ELECTRIC SAFETY DEVICES FOR ELECTRICALLY-PROPELLED VEHICLES
    • B60L2240/00—Control parameters of input or output; Target parameters
    • B60L2240/40—Drive Train control parameters
    • B60L2240/42—Drive Train control parameters related to electric machines
    • B60L2240/423—Torque
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/72—Electric energy management in electromobility

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  • Engineering & Computer Science (AREA)
  • Transportation (AREA)
  • Mechanical Engineering (AREA)
  • Power Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Steering Control In Accordance With Driving Conditions (AREA)

Abstract

The invention discloses a kind of differential power-assisted steering of electric wheel drive vehicle and stability control method for coordinating, including：The yaw moment needed for the differential torque of front-wheel and maintenance stability after being travelled to vehicle calculates；Judge phase plane control area belonging in vehicle travel process, the work weight coefficient of differential steering is determined according to the phase plane control area, the differential torque of the front-wheel is adjusted by the work weight coefficient；Driving moment after being travelled to vehicle calculates；The differential torque of front-wheel after the driving moment, adjustment and the yaw moment are assigned to wheel and are modified, revised wheel demand torque data are exported by the phase plane control area according to belonging to vehicle.

Description

Coordinated control method for differential power-assisted steering and stability of electric wheel driven automobile
Technical Field
The invention relates to the technical field of automobiles, in particular to a coordinated control method for differential power-assisted steering and stability of an electric wheel driven automobile.
Background
The electric wheel independent driving automobile omits a transmission system of the traditional automobile, and power is directly provided by a hub motor or a wheel edge motor which is arranged in a wheel or at the wheel edge to drive the wheel. The electric wheel driven automobile has a simple structure, saves space and is easier to realize advanced chassis dynamics integrated control.
The Differential Drive Assistance Steering (DDAS) technology is a new Steering assistance technology proposed based on an electric wheel Drive automobile platform. The differential power-assisted steering fully utilizes the characteristic that the torque of each wheel of the electric wheel driven automobile can be independently controlled, and utilizes the torque difference generated by different torques of the left front wheel and the right front wheel to realize the power-assisted steering. The differential power-assisted steering system omits a power-assisted output part of the traditional power-assisted steering system, and meanwhile, the controller can be integrated into a whole vehicle controller, so that the structure is compact, the occupied space is small, and the cost is reduced.
However, the actuator of the differential power-assisted steering system is a left front wheel motor and a right front wheel motor, and is the same as a part of an actuating mechanism of a vehicle stability control system (VSC), the left front wheel motor and the right front wheel motor can interfere with each other certainly, and meanwhile, the differential power-assisted steering can introduce an extra yaw moment for the whole vehicle while assisting power, which can affect the stability of the whole vehicle undoubtedly, and can cause vehicle instability under certain working conditions. Therefore, reliable coordination control must be performed on the differential power steering and the driving stability, so that the differential power steering system provides stable and reliable power assistance without affecting the stability control system of the whole vehicle.
The existing coordinated control method for the differential power-assisted steering and the stability mainly adopts a method for compensating the yaw velocity of the rear wheels in a real-time differential mode, but the method does not consider the influence of the real-time differential motion of the rear wheels on the road feel of the front wheels and also limits the exertion of the efficacy of the differential power-assisted steering, and does not consider the limit working condition.
Disclosure of Invention
The invention designs and develops a method for coordinately controlling differential power-assisted steering and stability of an electric wheel driven automobile, and aims to enable a differential power-assisted steering system to provide stable and reliable power assistance under the condition of not influencing a finished automobile stability control system so as to distribute wheel torque.
The technical scheme provided by the invention is as follows:
a method for coordinately controlling differential power-assisted steering and stability of an electric wheel driven automobile comprises the following steps:
calculating a front wheel differential torque after the vehicle is driven, a yaw torque and a driving torque required for maintaining stability;
judging a phase plane control area to which the vehicle belongs in the running process, determining a working weight coefficient of differential steering according to the phase plane control area, and adjusting the differential torque of the front wheels through the working weight coefficient;
distributing the driving torque, the adjusted front wheel differential torque and the adjusted yaw torque to wheels according to a phase plane control area of the vehicle, correcting the driving torque, the adjusted front wheel differential torque and the adjusted yaw torque, and outputting corrected wheel demand torque data;
the method for judging the phase plane control area of the vehicle in the driving process comprises the following steps:
step one, collecting the yaw angular velocity omega of the whole vehiclerspeed v, centroid slip angle β, centroid slip angular velocityAnd road surface adhesion coefficient mu;
step two, calculatingAnd the following judgment is made:
if it is notThe vehicle state belongs to the stable region;
if it is notThe vehicle state belongs to the coordinated control zone;
if it is notThe vehicle state belongs to the unstable region;
in the formula, Bx、BsRespectively are the intercept of the upper and lower boundaries of the coordination area on the horizontal axis; wherein, Bx＝q1×B2， Bs＝q2×B2，B1、B2To stabilize the domain boundary parameter values, q1、q2Respectively, upper and lower boundary coordination factors.
Preferably, the differential torque T is applied to the front wheelszThe calculation is carried out by adopting a fuzzy PID controller, and the input of the fuzzy PID controller is the actual steering wheel torque TswAnd ideal steering wheel torque TswdThe difference value of (a) is output as the differential torque T of the front wheel required by the boostingz。
Preferably, the calculation of the yaw moment Δ M required to maintain stability by the stability controller includes:
step one, establishing a linear two-degree-of-freedom model:
in the formula, kfAnd k isrThe stiffness of the front and rear axes, respectively; l isfAnd LrDistances from the center of mass to the front axis and to the rear axis, respectively; deltafIs a front wheel corner; i iszThe moment of inertia of the whole vehicle mass around the Z axis; m is the mass of the whole vehicle;
calculating to obtain an ideal yaw velocity through the linear two-degree-of-freedom model:
in the formula,
step three, the stability controller is a sliding mode controller, and the yaw moment required by tracking the ideal yaw rate is calculated through the following calculation formula:
calculating the yaw moment required for tracking the ideal centroid yaw angle through the following calculation formula:
wherein e is1＝ωr-ωrd，e2＝β-βd，a1、a2、b1And b2Controlling parameters for the sliding mode controller;
step four, when the road surface adhesion coefficient mu is larger than or equal to 0.4 and the centroid slip angle β is larger than or equal to 5 degrees, changing delta M to M2when the road adhesion coefficient mu is less than 0.4 and the centroid slip angle β is greater than or equal to 12 degrees, the value of delta M is equal to M2(ii) a When in other cases, Δ M ═ M1-M2。
Preferably, the determining the working weight coefficient k includes the following steps:
when the vehicle belongs to a stable region, the work weight coefficient k of the differential power-assisted steering is 1;
when the vehicle state belongs to an unstable region, the working weight coefficient k of the differential power-assisted steering is 0; and
when the vehicle state belongs to the coordination control area, the work weight coefficient k of the differential power-assisted steering needs to be dynamically adjusted, and the method comprises the following steps: firstly, judging the directions of differential torque required by the output of a differential power steering controller and differential torque required by the output of a stability controller, if the directions are the same, the working weight coefficient k of the differential power steering is 1, if the directions are different, calculating the weight coefficient k by adopting a continuous symmetrical Sigmoid function, and calculating the working weight coefficient k of the differential power steering according to the following formula:
preferably, the adjusted front wheel differential torque is Δ Tz＝kTz。
Preferably, the distributing the driving torque, the adjusted front wheel differential torque, and the yaw torque to the wheels according to a phase plane control region to which the vehicle belongs includes:
when the vehicle state belongs to the stable region, the following distribution mode is adopted:
when the vehicle state belongs to the coordination control area, the following distribution mode is adopted:
when the vehicle state belongs to the unstable region, the following distribution mode is adopted:
first, an objective function for optimal allocation is determined:
then, a constraint equation for the objective function is determined:
|Ti|≤min(μrFzi,Tmax)，
(T1+T2)cosδf+T3+T4＝Tg，
wherein, Fyi(i ═ 1,2,3,4) are the left front wheel, right front wheel, left rear wheel, and right rear wheel longitudinal forces, respectively, Fyi＝Ti/r(i＝1,2,3,4)；Ti(i ═ 1,2,3,4) are the left front wheel, right front wheel, left rear wheel, and right rear wheel output torques, TgFor total drive demand torque, Fzi(i ═ 1,2,3,4) are the left front wheel, right front wheel, left rear wheel, and right rear wheel vertical loads, respectively; fzfAnd FzrThe vertical loads of the front axle and the rear axle are respectively measured, wherein delta M is a yaw moment value required by stability maintenance, r is the rolling radius of the wheels, and l is the wheel track.
Preferably, the calculating the corrected wheel demand torque includes:
calculating the slip rate of the wheel in real time, calculating the optimal slip rate of the wheel at each moment in real time, inputting the difference between the slip rate and the optimal slip rate into a controller, and outputting a slip rate control correction torque T by the controller when the actual slip rate of the wheel is greater than the optimal slip rate of the wheel at the momentxiCorrected wheel demand torque TsiThe calculation formula is as follows: t issi＝Ti+Txi(ii) a Wherein i is 1,2,3, 4.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention has better road feel when the vehicle is in stable working condition, and in fact, the vehicle is in stable working condition for most of time;
2. the control logic is clear and reliable, the stability of the whole vehicle is ensured, meanwhile, reliable power assistance is provided, and the application range of differential power-assisted steering is expanded;
3. the invention has simple real vehicle calibration, can calibrate the stability control system at the same time, greatly shortens the development process, reduces the cost and has wide practical value.
Drawings
FIG. 1 is a flow chart of a method for coordination control of differential power steering and stability according to the present invention.
Fig. 2 is a control area division flowchart of the differential power steering and stability coordination control method according to the present invention.
Fig. 3 is a schematic diagram of dividing a phase plane control region according to the method for coordinately controlling differential power steering and stability.
FIG. 4 is a diagram of an ideal directional torque MAP for a method of coordinated control of differential power steering and stability according to the present invention.
FIG. 5 is a flow chart of determining the work weight coefficient of differential power steering in the coordination control area of the method for coordinating and controlling differential power steering and stability according to the present invention.
Detailed Description
The present invention is further described in detail below with reference to the attached drawings so that those skilled in the art can implement the invention by referring to the description.
As shown in fig. 1, the present invention provides a flow chart for implementing a coordinated control method of differential power steering and stability, which comprises the following steps:
step one, obtaining the yaw velocity omega of the whole vehicle by a yaw velocity sensorrThe signal is obtained by a vehicle speed sensor or a vehicle speed observer, and the signal is obtained by the mass center sidethe deflection angle observer obtains a centroid side deflection angle β and a centroid side deflection angular velocityAnd the signal is observed by a road adhesion coefficient observer in real time to obtain a road adhesion coefficient mu.
Step two, obtaining a stable region boundary parameter value B by looking up a table according to the road adhesion coefficient mu1、B2Upper and lower boundary coordination factor q1、q2. CalculatedAnd determining the control region to which the vehicle state belongs by: if it isThe vehicle now belongs to the stable zone; if it isThe vehicle state now belongs to the coordinated control zone; if it isThe vehicle state belongs to an unstable region at this time, the specific control region division process is shown in fig. 2, and the specific phase plane division region is shown in fig. 3;
the value of the boundary parameter B of the stable region1、B2Derived fromAnd (3) dividing a phase plane stable domain, wherein the boundary is divided by a bilinear method, namely two parallel straight lines are adopted to divide the stable domain boundary. As described inThe phase plane stability region can be represented by the following equation:
wherein, B1And B2The method is characterized in that the method is a stable domain boundary parameter, the stable domain boundary parameter is mainly related to road adhesion coefficients, different road adhesion coefficients are given, and boundary coefficient values under all the adhesion coefficients are obtained through a computer simulation or real vehicle calibration method. In actual use, B is1、B2Making a data table and storing the data table in the ECU in advance, and directly looking up the table when in use, such as the embodiment shown in the table 1;
TABLE 1 Steady Domain boundary parameters
Coefficient of road surface adhesion B1 B2
0.8≤μ≤1 0.283 0.175
0.6≤μ＜0.8 0.343 0.167
0.4≤μ＜0.6 0.378 0.152
0.3≤μ＜0.4 0.454 0.150
0.2≤μ＜0.3 0.624 0.138
μ＜0.2 0.938 0.03
BxAnd BsRespectively, the intercept of the upper and lower boundaries of the coordination area on the horizontal axis, Bx＝q1×B2；Bs＝q2×B2； q1、q2Respectively an upper boundary coordination factor and a lower boundary coordination factor; is easy to obtain, q1And q is2Q is directly related to the stability of the vehicle, in order to further ensure the stable state of the vehicle1And q is2And carrying out offline optimization solution on the values by using an optimization algorithm.
In another embodiment, the invention selects a simulated annealing algorithm to solve the boundary coordination factor under each working condition. In order to improve the optimization speed and accuracy of the algorithm, firstly, obtaining an initial value by a large number of simulation methods, and then, carrying out multi-objective optimization on the initial value by using a simulated annealing algorithm; the optimization objective function is as follows:
wherein, a1、a2、a3And a4Respectively are the weight coefficients of the corresponding variables; t isswIs the actual torque of the steering wheel; t isswdIdeal steering wheel torque, t is time; the smaller J is, the better the performance of the coordinated control system is, the offline optimization solution is respectively carried out under different road adhesion coefficients and different vehicle speeds, and each coefficient and q under each vehicle speed are obtained1And q is2The value-taking table is actually used for looking up the table, the obtained boundary coordination factors under each attachment coefficient are made into a MAP and stored in the ECU in advance,the table look-up is directly carried out when in use.
The coordination factor optimization method selects a simulated annealing algorithm, but the coordination control method is not limited to the application of the optimization method and the optimization objective function, and other optimization methods and optimization objective functions can be selected according to requirements.
Step three, the differential power-assisted steering controller outputs the power-assisted front wheel differential torque Tz(ii) a The stability controller outputs a yaw moment delta M required by stability maintenance;
the differential power-assisted steering controller adopts a steering wheel torque direct control strategy, and the control strategy is characterized in that the actual steering wheel torque T is measured by a steering wheel torque sensorswMeanwhile, the vehicle speed v and the steering wheel angle signal on the CAN bus are obtained, and the ideal steering wheel torque T at the moment is obtained by reading the ideal steering wheel torque MAPswdThe controller outputs the torque difference of the left wheel and the right wheel so that the actual steering wheel torque tracks the ideal steering wheel torque, and the purpose of reducing the steering hand force is achieved;
the ideal steering wheel torque MAP is formulated according to the steering wheel torque preferred by a driver, which is obtained by a plurality of companies and research institutions through a large number of experiments in the past, and the vehicle speed and the steering wheel rotation angle are combined, as shown in the embodiment shown in FIG. 4, the ideal steering wheel torque MAP data is stored in the ECU in advance, and the ideal steering wheel torque MAP can be directly looked up when the ideal steering wheel torque MAP is used;
in another embodiment, the differential power steering controller is chosen as a fuzzy PID controller, the controller input being the actual steering wheel torque TswAnd ideal steering wheel torque TswdThe difference value of (a) is output as the differential torque T of the front wheel required by the boostingz(ii) a The fuzzy PID controller is divided into two parts, namely a traditional PID controller and a fuzzy controller, and the fuzzy controller corrects three parameters Kp, Ki and Kd of the PID controller in real time. The input to the fuzzy controller is the actual steering wheel torque TswAnd ideal steering wheel torque TswdThe difference e and the difference change rate de/dt are output as correction values Kp, Ki and KdThe values are input to a PID controller. The argument of the difference e is { -5, 5}, the fuzzy set is { big Negative (NB), medium Negative (NM), small Negative (NS), Zero (ZO), small Positive (PS), medium Positive (PM), big Positive (PB) }, the argument of the difference change rate de/dt is { -10, 10}, the fuzzy set is { big Negative (NB), medium Negative (NM), small Negative (NS), Zero (ZO), small Positive (PS), medium Positive (PM), big Positive (PB) }, the argument of the output control parameters Kp, Ki and Kd are {0, 3}, and the fuzzy set is { Zero (ZO), small Positive (PS), medium Positive (PM) and big Positive (PB) }. The fuzzy control rules are shown in table 2;
TABLE 2 fuzzy PID controller fuzzy control rule table
In another embodiment, the stability controller adopts a model tracking method, selects a linear two-degree-of-freedom model as a tracking model, and the differential equation of the linear two-degree-of-freedom model is as follows:
wherein k isfAnd k isrThe stiffness of the front and rear axes, respectively; l isfAnd LrDistances from the center of mass to the front axis and to the rear axis, respectively; deltafIs a front wheel corner; i iszThe moment of inertia of the whole vehicle mass around the Z axis; m is the mass of the whole vehicle;
through the linear two-degree-of-freedom model, the ideal yaw angular velocity can be obtained in real time, and the ideal yaw angular velocity omegardThe calculation formula is as follows:
wherein,
in another embodiment, where control is convenient, the desired centroid slip angle β is setdSet to 0 degrees.
In another embodiment, the stability controller selects a sliding mode controller; according to the principle of sliding mode control, the required yaw moment for tracking the ideal yaw rate is calculated as follows:
wherein e is1＝ωr-ωrd；
The yaw moment required to track the ideal centroid slip angle is calculated as follows:
wherein e is2＝β-βd，a1、a2、b1And b2For the control parameters of the sliding mode controller, offline optimization can be performed through an optimization algorithm.
The final control yaw moment delta M output by the stability controller is equal to M1-M2meanwhile, the following judgment is set, the mass center slip angle β and the road surface adhesion coefficient mu of the whole vehicle are monitored in real time, and when the road surface adhesion coefficient mu is larger than or equal to 0.4 and the mass center slip angle β is larger than or equal to 5 degrees, the delta M is equal to M2when the road surface adhesion coefficient mu is less than 0.4, if the centroid slip angle β is greater than or equal to 12 degrees, the value of delta M is equal to M2(ii) a Otherwise, Δ M ═ M1-M2。
Preferably, the method for coordinately controlling the differential power steering and the stability is not limited to the sliding mode stability controller and the differential power steering fuzzy PID controller, and other types of stability and differential power steering controllers can be optionally designed according to needs.
Step four, determining the working modes of the differential power-assisted steering and stability control system and the working weight coefficient k of the differential power-assisted steering according to the control area and the differential power-assisted steering controller, namely determining and outputting the final output front wheel power-assisted demand differential torque delta TzAnd maintaining a stability demand yaw moment Δ M;
as shown in fig. 2, when the vehicle state belongs to the stable regionThe differential power-assisted steering works on the front wheels independently, namely the working weight coefficient k of the differential power-assisted steering is 1, and the stability control system is closed; when the vehicle state belongs to the unstable regionThe differential power-assisted steering does not work, namely the weight coefficient k of the differential power-assisted steering is 0, and the stability control system works on four wheels; when the vehicle state belongs to the coordination control areaThe differential power-assisted steering and the stability control system work together, the differential power-assisted steering works on the front wheels, the stability control works on the rear wheels, and the working weight coefficient k of the differential power-assisted steering needs to be dynamically adjusted because the state of the vehicle is unstable when the vehicle is in a coordinated control region; as shown in fig. 5, after entering the cooperative control area, the method for dynamically adjusting the differential power steering weight coefficient k in the cooperative control area needs to first determine the direction of the differential torque required by the output of the differential power steering controller and the differential torque required by the output of the stability control system, if the directions of the two are the same, the working weight coefficient k of the differential power steering is 1, if the directions of the two are different, in order to prevent the intervention and the exit of the differential power steering from generating an excessive steering torque impact, the weight coefficient k is calculated by using a continuous symmetric Sigmoid function, and the working weight coefficient k of the differential power steering is calculated according to the following formula:
the boosted front wheel differential torque DeltaT actually output to the torque distribution controllerzThe obtained work weight coefficient k, i.e. Δ T, of the differential power steering needs to be combinedzCalculated by the following formula:
ΔTz＝kTz。
step five, according to the obtained actual vehicle speed v of the vehicle and the target vehicle speed vdDifferencing by a PID controller to obtain the desired total drive torque Tg。
Step six, outputting the total driving torque, the required yaw moment output by the stability control and the required front wheel differential torque delta T output by the differential power steering controllerzSelecting different distribution methods to distribute the four wheels according to different control areas;
as a preference, the following is used for allocation:
when the vehicle state belongs to a stable region, an average distribution mode is adopted, and the following formula is shown:
wherein，Ti(i ═ 1,2,3,4) are the left front wheel, right front wheel, left rear wheel, and right rear wheel output torques, TgTotal drive demand torque;
when the vehicle belongs to the coordination control area, a dynamic load-based distribution method is adopted, and the following formula is shown:
wherein,Fzf＝Fz1+Fz2，Fzr＝Fz3+Fz4；Fzi(i ═ 1,2,3,4) for four wheel vertical loads, respectively; fzfAnd FzrRespectively inquiring the vertical load of the front shaft and the rear shaft;
when the vehicle belongs to an unstable area, in order to enable the vehicle to be in a stable working condition, the tire utilization rate should be controlled as much as possible to be at a lower level. Therefore, in order to make the VSC system control more effective, an online optimal allocation method is adopted, and the allocation target is even if the sum of all the tire utilization rates is minimum, that is, the vehicle stability margin is optimal at this time. The objective function is as follows:
wherein, Fyi(i ═ 1,2,3,4) are the left front wheel, right front wheel, left rear wheel, and right rear wheel longitudinal forces, respectively, Fyi＝Ti/r(i＝1,2,3,4)；
Preferably, the moments are distributed online by a sequential quadratic programming method, and the target function constraint conditions are as follows:
|Ti|≤min(μrFzi,Tmax)，
(T1+T2)cosδf+T3+T4＝Tg，
wherein, Δ M is a yaw moment value required by stability maintenance, r is a rolling radius of the wheels, and l is a wheel track;
preferably, the torque optimal allocation method selected by the invention is a sequential quadratic programming method, but the torque optimal allocation method is not limited to this method, and other optimal solution methods can be selected as required.
Step seven, the distributed required torque of the four wheels is corrected through the slip ratio controllers of the wheels respectively:
the specific modification method is described in the following embodiment: based on the measured or estimated relevant state parameters of the vehicle, the slip rate of each wheel is calculated in real time, the optimal slip rate of the wheel at each moment is estimated in real time, the difference between the two slip rates is input into a PID controller, when the actual slip rate of the wheel is larger than the optimal slip rate of the wheel at the moment, the slip rate controller starts to work, and the PID controller outputs the slip rate to control a correction torque Txi(i ═ 1,2,3,4), the correction torque is directly related to the initial wheel demand torque TiBy algebraic summing, i.e. corrected, wheel-demanded torque Tsi(i-1, 2,3,4) the formula is as follows：
Tsi＝Ti+Txi；
Preferably, the slip rate control method of the present invention selects the optimal slip rate control, but the coordination control method of the present invention is not limited to the application of such slip rate control method and controller, and other slip rate control methods and controllers, such as wheel slip control based on logic threshold values, may be selected as desired.
Step eight, correcting the required wheel torque T of each wheelsi(i ═ 1,2,3,4) control commands are sent to the controllers of the in-wheel motors in the respective wheels.
While embodiments of the invention have been described above, it is not limited to the applications set forth in the description and the embodiments, which are fully applicable to various fields of endeavor with which the invention may be practiced, and further modifications may readily be effected therein by those skilled in the art, without departing from the general concept as defined by the claims and their equivalents, which are not limited to the details given herein and the examples shown and described herein.

Claims (7)

1. A method for coordinately controlling differential power-assisted steering and stability of an electric wheel driven automobile is characterized by comprising the following steps:
calculating a front wheel differential torque after the vehicle is driven, a yaw torque and a driving torque required for maintaining stability;
judging a phase plane control area to which the vehicle belongs in the running process, determining a working weight coefficient of differential steering according to the phase plane control area, and adjusting the differential torque of the front wheels through the working weight coefficient;
distributing the driving torque, the adjusted front wheel differential torque and the yaw torque to wheels according to a phase plane control area of the vehicle, correcting the driving torque, the adjusted front wheel differential torque and the adjusted yaw torque, and outputting corrected wheel demand torque data;
the method for judging the phase plane control area of the vehicle in the driving process comprises the following steps:
step one, collecting the yaw angular velocity omega of the whole vehiclerspeed v, centroid slip angle β, centroid slip angular velocityAnd road surface adhesion coefficient mu;
step two, calculatingAnd the following judgment is made:
if it is notThe vehicle state belongs to the stable region;
if it is notThe vehicle state belongs to the coordinated control zone;
if it is notThe vehicle state belongs to the unstable region;
in the formula, Bx、BsRespectively are the intercept of the upper and lower boundaries of the coordination area on the horizontal axis; wherein, Bx＝q1×B2，Bs＝q2×B2，B1、B2To stabilize the domain boundary parameter values, q1、q2Respectively, upper and lower boundary coordination factors.
2. The electric wheel drive vehicle differential power steering and stability coordination control method of claim 1,characterized in that the differential torque T of the front wheelszThe calculation is carried out by adopting a fuzzy PID controller, and the input of the fuzzy PID controller is the actual steering wheel torque TswAnd ideal steering wheel torque TswdThe difference value of (a) is output as the differential torque T of the front wheel required by the boostingz。
3. The electric wheel drive vehicle differential power steering and stability cooperative control method according to claim 1 or 2, wherein the calculation of the yaw moment Δ M required to maintain the stability by the stability controller comprises:
step one, establishing a linear two-degree-of-freedom model:
in the formula, kfAnd k isrThe stiffness of the front and rear axes, respectively; l isfAnd LrDistances from the center of mass to the front axis and to the rear axis, respectively; deltafIs a front wheel corner; i iszThe moment of inertia of the whole vehicle mass around the Z axis; m is the mass of the whole vehicle;
calculating to obtain an ideal yaw velocity through the linear two-degree-of-freedom model:
in the formula,
step three, the stability controller is a sliding mode controller, and the yaw moment required by tracking the ideal yaw rate is calculated through the following calculation formula:
calculating the yaw moment required for tracking the ideal centroid yaw angle through the following calculation formula:
wherein e is1＝ωr-ωrd，e2＝β-βd，a1、a2、b1And b2Controlling parameters for the sliding mode controller;
step four, when the road surface adhesion coefficient mu is larger than or equal to 0.4 and the centroid slip angle β is larger than or equal to 5 degrees, changing delta M to M2when the road adhesion coefficient mu is less than 0.4 and the centroid slip angle β is greater than or equal to 12 degrees, the value of delta M is equal to M2(ii) a When in other cases, Δ M ═ M1-M2。
4. The method for coordinately controlling differential power steering and stability of an electric wheel drive vehicle according to claim 3, wherein the determining of the operation weight coefficient k comprises the steps of:
when the vehicle belongs to a stable region, the work weight coefficient k of the differential power-assisted steering is 1;
when the vehicle state belongs to an unstable region, the working weight coefficient k of the differential power-assisted steering is 0; and
when the vehicle state belongs to the coordination control area, the work weight coefficient k of the differential power-assisted steering needs to be dynamically adjusted, and the work weight coefficient k comprises the following steps: firstly, judging the directions of differential torque required by the output of a differential power steering controller and differential torque required by the output of a stability controller, if the directions are the same, the working weight coefficient k of the differential power steering is 1, if the directions are different, calculating the weight coefficient k by adopting a continuous symmetrical Sigmoid function, and calculating the working weight coefficient k of the differential power steering according to the following formula:
5. the electric wheel driven vehicle differential power steering and stability coordination control method of claim 4Characterized in that the adjusted differential torque of the front wheels is DeltaTz＝kTz。
6. The electric wheel drive vehicle differential power steering and stability cooperative control method according to claim 5, wherein distributing the driving torque, the adjusted front wheel differential torque, and the yaw torque to wheels according to a phase plane control region to which a vehicle belongs comprises:
when the vehicle state belongs to the stable region, the following distribution mode is adopted:
when the vehicle state belongs to the coordination control area, the following distribution mode is adopted:
when the vehicle state belongs to the unstable region, the following distribution mode is adopted:
first, an objective function for optimal allocation is determined:
then, a constraint equation for the objective function is determined:
|Ti|≤min(μrFzi,Tmax)，
(T1+T2)cosδf+T3+T4＝Tg，
wherein, Fyi(i ═ 1,2,3,4) are the left front wheel, right front wheel, left rear wheel, and right rear wheel longitudinal forces, respectively, Fyi＝Ti/r(i＝1,2,3,4)；Ti(i ═ 1,2,3,4) for the front left wheel, front right wheel, and rear left wheel, respectivelyAnd right rear wheel output torque, TgFor total drive demand torque, Fzi(i ═ 1,2,3,4) are the left front wheel, right front wheel, left rear wheel, and right rear wheel vertical loads, respectively; fzfAnd FzrThe vertical loads of the front axle and the rear axle are respectively measured, wherein delta M is a yaw moment value required by stability maintenance, r is the rolling radius of the wheels, and l is the wheel track.
7. The electric wheel drive vehicle differential power steering and stability coordination control method according to any one of claims 1,2, and 4-6, characterized in that calculating the corrected wheel demand torque comprises:
calculating the slip rate of the wheel in real time, calculating the optimal slip rate of the wheel at each moment in real time, inputting the slip rate and the optimal slip rate into a controller as a difference, and outputting a slip rate control correction torque T by the controller when the actual slip rate of the wheel is greater than the optimal slip rate of the wheel at the momentxiCorrected wheel demand torque TsiThe calculation formula is as follows: t issi＝Ti+Txi(ii) a Wherein i is 1,2,3, 4.
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