Study on electronic differential control of four wheel drive in-wheel motorelectric vehicle

Min DUAN, Ming-jiang SUN, Gang LI, Ji-kai YU, Peng-cheng LIU

(School of Automation and Traffic Engineering, Liaoning University of Technology, Jinzhou 121001, China)

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Study on electronic differential control of four wheel drive in-wheel motorelectric vehicle

Min DUAN, Ming-jiang SUN*, Gang LI, Ji-kai YU, Peng-cheng LIU

(SchoolofAutomationandTrafficEngineering,LiaoningUniversityofTechnology,Jinzhou121001,China)

For differential problem of four wheel drive in-wheel motor electric vehicle during steering process, the electronic differential control has been studied. The electronic differential control strategy was designed, and the differential reference kinematic model was established. According to the advantages that the four wheel drive torque of the four wheel in-wheel motor electric vehicle can be independently control, the four wheel drive torque was allocatedreasonably through the drive torque distributor, which could achieve the actual wheel speed tracking reference wheel speed. The electronic differential system model of the four wheel in-wheel motor electric vehicle was established in Matlab/Simulink. The model was verified through the co-simulation of CarSim and Matlab/Simulink. The results showed that the electronic differential control strategy could effectively realize four wheel differential during steering process and improve the handling stability of electric vehicle.

Four wheel in-wheel motor electric vehicle, Electronic differential, Drive torque distributor, CarSim

1 Introduction

The four wheel of the four-wheel drive in-wheel motor electric vehicleare independently driven, which isno rigid mechanical connection between four wheels. The motion state of wheels is mutually independent. In-wheel motor put the motor,transmission system and brake system integration. Its volume is small and it has the larger specific power, the traditional clutch, transmission, drive shaft, differential, constant velocity joints, axle shafts and other componentscould becanceled,whichsimplifies the structure of the vehicle,improves the transmission efficiency andreduces the entire vehicle equipment quality.It is beneficial to increase the electric vehicle mileage. As the scrambling for research object ofBritish Protean, France Michelin, Toyota, Mitsubishi and other companies [1-2], electronic differential control is one of the key technologies whenthe four wheel drive in-wheel motor electric vehicle steering, thereforemany domestic and foreign scholars have carried out the related research.

Based on sliding mode control theory reference [3], a set of electronic differential control system was developed through the control of drive torque, and the effectiveness of the electronic differential system was verified by using the Matlab/Simulink. Reference [4] studied the electronic differential systembased on four brushless DC in-wheel motor.According to thesteering wheel anglecommand, it realized four motor speed control system for the calculation and adjustment.Through the simulation on the motor and no-load experiment, the electronic differential control strategy that could satisfy the requirement of the electric vehicle drivingis verified. Based on the sliding mode control theory and take the wheel slip ratio as control target, reference [5] designed an electronic differential control strategy of rear wheel in-wheel drive electricvehicle, which was verified by using Matlab/Simulink. Through the steering kinematics analysis, reference [6] constructed the four in-wheel motor drive vehicle electronic differential control system, and put forward the electronic differential speed torque integrated control strategy. Reference [7] proposed an adaptive electronic differential control strategyforspeed difference but not for torquedifference, the feasibility of the design was verified by simulation. Through the control of left and right wheel speed and speed to achieve differential,reference [8] established the differential steering model,which verified the electric vehicle control system design are feasible and effective through the joint simulation of Matlab/Simulink and ADAMS. Numerous advantages of electronic differential system that the conventional electric vehicles use traditional mechanical differential system will be replaced by electronic differential system, but the choice of control variables and the design of differential control algorithm in the electronic differential systemis not mature enough, so it needsto be further study [9-11].

This paper established four wheel drive in-wheelmotor electric vehicle model by using the vehicle systematic software CarSim, and determined the electronic differential speed torque control strategy.Based onreference kinematic model, the four-wheel drive torque distributorhas beendesigned, through the control of four wheel drive torque to achieve the four actual wheel speed tracking reference wheel speed. Electric vehicles differential system model is built in Matlab / Simulink. The effectiveness of the control method was verifiedthrough the co-simulation of CarSim and Matlab/Simulink. The open-loop and closed-loop experiment conditions were select in CarSim.

2 Electronic differential control strategy

As shown in Fig.1, according to the driver’s steering wheel angle and electric vehicles in real-time state of motion, the electronic differential control system could provide a reference wheel speed and the actual wheel speedthrough the reference kinematic model. According to the difference between the reference wheel speed and actual wheel speed, although the drive torque distributor will redistributethe four-wheel drive torque, the actual wheel speed could better track the reference wheel speed.

2.1 Reference kinematic model

The design of the vehicle electronic differential control reference kinematic model is shown in Fig.2. The assumed condition of this model is as follows: four wheels axis intersected in the same the rotation center during the steering process [12].

Fig.1 Electronic differential control principle diagram

Fig.2 Reference kinematic model

L1,R1,L2 andR2 are the left front wheel, right front wheel, rear left wheel and right rear wheel of electric vehicle, respectively. In Fig.2,VL1,VR1,VL2andVR2are the four wheel speeds, respectively,δfandδrare the front wheel steering angles, respectively,ais the distance from the center of mass to the front axle,bis the distance from the center of mass to the rear axle,Bis the tread,Ois the instantaneous center of rotation. The four wheel speeds could be repre-sented as:

(1)

(2)

(3)

(4)

In the above formula,Vx,Vyandrare the vehicle longitudinal velocity, lateral velocity and yaw rate, respectively.

2.2 Drive torque distributor

When electric vehicle steering, if the two sides of the driving torque are equally distributed, it will lead toboth sides of wheel slip rate are not equal, the stability and security of the vehicle will be seriously affected [13]. Therefore, when the electric vehicle steering, according to the driver’s expectation,the four wheelsare assignedwith different drive torque to realize the four wheel differential. The below figure is the drive torque distributor designed in this paper.

Fig.3 Drive torque distributor

In Fig.3,Vis the vehicle speed,Tis the total drive torque,TL1,TR1,TL2andTR2are the four wheel drive torque, respectively. When the electric vehicle is driving straight, additional drive torque becomes zero, four wheels are provided with the same drive torque.When the electric vehicle is steering, the wheel speed of the insideis fasterthan that of the outer side. Depending on the speed of each wheel, electronic differential control derived additional drive torque (additional driving torque could be positive or negative). The outside wheel drive torque gets increased by ΔT1and the inside wheel drive torque will be reduced by ΔT2to satisfy the total drive torque. The electronic differential control system redistributed four wheels drive torque to realize the control thought of wheel speed differenceand drive torque difference.

3 Co-simulation model is built based on CarSim and Matlab/Simulink

CarSim is the simulation software designed for vehicle dynamics. CarSim run faster on the computer,which can achieve the vehicle on the driver, road and aerodynamic input response simulation,and mainly used to simulate and predict vehicle handling stability, braking performance, comfort, power and economy, but also has been widely applied to the development of modern automotive control systems [14]. In this paper, CarSim software is chose and the traditional engine, transmission are all removed to the motor drive,a fourwheel in-wheel motor electric vehicle modelcould be established, some parameters of the vehicleare shown in Table 3.1

Table 1 Part parameters of vehicle

DParameternameSymbolNumericalVehiclemass/kgm1171Sprungmass/kgms1111Thedistancefromthecenterofmasstothefrontaxle/ma1.040Thedistancefromthecenterofmasstotherearaxle/mb1.560Vehiclefrontwheeltread/md11.481Vehiclerearwheeltread/md21.486Thedistancefromthecenterofmasstoground/mh0.54InertiaofZaxisinvehicleco-ordinatesystem/(kg·m2)Iz2031.4

Based on CarSim and Simulink, this paper introduced the co-simulation model, as shown in Fig.4.

Fig.4 Four-wheel drive electronic differential system diagram

Through the PID control of the difference between the actual vehicle speed and the target vehicle speed, the speed controller could achieve total vehicle drive torque to meet the needs of the target vehicle speed. The reference wheel speed offour wheels could beevaluated by the formula (1)-(4), the four wheel speed could be output from CarSim in real-time. Through the PID control of the difference between actual wheel speed and the target wheel speed, the wheel speed controller could provide additional drive torqueto electric vehicle wheel. According to the demand of total drive torque and the additional driving torqueobtained from the each wheel’s actual and the target motion state control,thetorque distributorwill output the end ofdrivetorque of each wheel, and the actual wheel speedof four wheels couldbetter track the reference wheel speed.

4 Simulation verification

Based on the co-simulation of CarSim and Matlab/Simulink, this paper selected the open-loop and closed-loop control of experiment conditions toverify the differential control method.

1) The experiment conditions of open-loop steering step are as follows: speed is 60 km/h and the road surface friction coefficient is 0.85.

The steering angle of manual inputangle linear gets increased to 70 degrees in 5 seconds, as shown in Fig.5. As shown in Fig.6, although the four wheel speedsare different beforethe control, but the distribution ofeach wheel drive torque is the same. Each wheel drive torque is different after the control. The control thought of speed difference and drive torque difference could be realized, and the results are consistent with the facts. Through figures 7-8, it could be seen that the side slip angle and yaw rate of the vehicle have been improved, and this shows that the control could improve the handling and stability of electric vehicles.

Fig.5 Steering wheel angle curve

Fig.6 Four-wheel drive torque curve

Fig.7 Yaw rate curve

Fig.8 Sideslip angle curve

Through Fig.9-10, it can be seen thatit is achieved four wheels differential of the electric vehicleafter control under the condition of steering, and the four wheel speeds could well trackthe reference wheel speed.

Fig.9 Left wheel speed curve

Fig.10 Right wheel speed curve

2) The closed-loop serpentine experiment conditions: speed is 60 km/h and the road surface friction coefficient is 0.5.

The curve of electric vehicle steering wheel angle under the serpentine experimental condition is shown in Fig.11. As can be seen in Fig.12, although the four wheel speeds are different before the control, the distribution ofeach wheel drive torque is the same. Each wheel drive torque is different after the control. The control thought of wheel speed difference and drive torque difference could be realized, and the results are consistent with the facts. Through figures 13-15, it can be seen that electric vehicles can follow the target trajectory, the sideslip angle and yaw rate of the vehicle havebeen decreased, and this shows that the handling and stability of electric vehicles have been increased after the control.

Fig.11 Steering wheel angle curve

Fig.12 Four-wheel drive torque curve

Through figures 16-19, it can be seen that the four wheels differential of electric vehicle has been achieved under steering state, and the four wheel speeds could better track the reference wheel speed after the control.

Comprehensive analysis of serpentine experiment conditions and steering step input experiment conditions can be seen, although the road surface friction coefficient is different, it will not affect the control effect. Therefore, it indicates that the control method has versatility.

Fig.13 Movement track

Fig.14 Yaw rate curve

Fig.15 Sideslip angle curve

Fig.16 Left front wheel speed curve

Fig.17 Left rear wheel speed curve

Fig.18 Right front wheel speed curve

Fig.19 Right rear wheel speed curve

5 Conclusions

1) It has been designed that the electronic differential control strategy of four wheel in-wheel motor electric vehicle during steering process, and the reference kinematic model is established, through drive torque distributor, a reasonable distribution of torque could be achieved and the control thought of wheel speed difference and drive torque difference could be realized.

2) Based on CarSim and Matlab/Simulink the co-simulation model has been established, the electronic differential control strategy was verified by selecting a typical experiment conditions. Verification results show that the four wheel speeds are better able to track the reference wheel speed after the control, and the handling and stability of four wheel in-wheel motor electric vehicle could be improved.

Acknowledgements

This paper is supported by National Youth Natural Science Foundation of China (No.51305190) and the Education Department of Liaoning Province (No.L2012217).

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摘要：為充分挖掘QAR數據中所包含的大量原始監控數據，檢驗ACARS報文的可靠性，更好地協助航空公司進行飛機和發動機的狀態監控及故障診斷，對發動機穩態報文DFD的報文結構進行了解析研究，提出了一種從QAR數據中提取滿足觸發條件的DFD報文的研究思路和方法，以豐富發動機性能監控的信息量。通過對B747-400飛機實際ACARS報文數據和所提取的報文數據進行計算分析，驗證了該方法的可靠性，具有良好的工程應用前景。

關鍵詞：QAR 數據挖掘；ACARS報文解析；發動機穩態巡航報文；DFD 報文結構；波音747-400

10.3969/j.issn.1001-3881.2015.24.012 Document code: A

U463.218+.4

四輪輪轂電機電動汽車電子差速控制研究

段敏，孫明江*，李剛，于繼開，劉鵬程

遼寧工業大學 汽車與交通工程學院， 遼寧 錦州121001

針對四輪輪轂電機電動汽車轉向時四輪差速問題，進行了電子差速控制研究。設計了電子差速控制策略，建立差速運動參考模型，根據四輪輪轂電機電動汽車四輪驅動力矩獨立可控的優勢，通過驅動力矩分配器對四輪驅動力矩進行合理分配，實現了實際輪速跟蹤參考輪速，并在Matlab/Simulink里搭建了四輪輪轂電機電動汽車電子差速系統模型，通過CarSim與Matlab/Simulink聯合仿真進行了驗證。結果表明：電子差速差速控制策略能夠有效實現轉向時四輪差速控制，提高電動汽車的操縱穩定性。

四輪輪轂電機電動汽車；電子差速；驅動力矩分配器；CarSim

基于QAR數據的波音747-400飛機巡航報文解析研究

瞿紅春*，黃遠強，張興川

中國民航大學 航空工程學院， 天津300300

12 March 2015; revised 15 June 2015;

Ming-jiang SUN, Master graduate

student. E-mail:786359405@qq.com

accepted 2 September 2015

Hydromechatronics Engineering

http://jdy.qks.cqut.edu.cn

E-mail: jdygcyw@126.com