Research on Steering Stability Control of Dual In- Wheel Motor-Driven EV Xiangrong Guo Changsha University of Science and Technology Yi Chen ( [email protected] ) Hong Li Changsha University of Science and Technology Original Article Keywords: in-wheel motor, steering stability, slip rate, yaw rate, sliding mode control, electronic differential Posted Date: June 17th, 2020 DOI: https://doi.org/10.21203/rs.3.rs-35691/v1 License: This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License Research on Steering Stability Control of Dual In-Wheel Motor-Driven EV Guo Xiangrong1, Chen Yi2 *, Li Hong1 (1. Changsha University of Science and Technology, Changsha 410004；2. Hunan Industry Polytechnic, Changsha 410208) Abstract：The dual in-wheel motor electric includes reducer, differential gear, drive shaft and vehicle has the advantages of fast response and other parts. A downside to hub motors being direct high flexibility, while its stability and safety are drive is that it wastes a certain amount of energy more difficult to control. To study the stability when drive wheels are rotated. Therefore, it can be control of the dual in-wheel electric vehicle when inferred that the energy waste will be very low turning, firstly, the paper establishes the Ackerman when we utilize hub motors drive without reducer model of the dual in-wheel electric vehicle, and and other parts.[1,2] controls the wheel speed and slip rate by the Aiming at the features of the independently method of logical threshold value; then establishes controllable and quick response of torque of the linear two degree of freedom model of the wheels in a hub motor-driven EV, the electronic double hub electric vehicle, obtains the vehicle differential control strategy is proposed with yaw moment and ideal yaw rate by using the driving wheel torque as control variable and slip mathematical formula, and controls the wheel rate equilibrium of two driving wheels as control speed and slip rate by the sliding mode control. objective. [3] In order to solve the problem of The moment is distributed so that the actual yaw traditional yaw moment control, for example, rate keeps tracking the ideal value. The electronic profound calculation and poor adaptability, several differential control strategy of wheel slip rate and solutions have been proposed, including an wheel yaw rate is established. Finally, the control adaptive lateral stability control system based on strategy is simulated by MATLAB. The simulation Fuzzy Neural Network(FNN)[4], a distributed results show that the proposed control strategy of estimation algorithm based on cooperation [5], and slip rate and yaw rate can make the vehicle drive an adaptive sliding mode control method based on stably when turning. feedback linearization[6]. Qu Shuai contended that Key words: in-wheel motor; steering the driving torque can be controlled by the sliding stability; slip rate; yaw rate; sliding mode mode, and he studied the rollover situation and put control; electronic differential forward the corresponding anti-rollover strategy in his master degree dissertation.[7] Wang Chen 1 Introduction argued in his master’s degree paper that, with the The continuous expansion of car ownership actual tyre-road friction and wheel slip ratio as the has not only brought tremendous convenience to input of fuzzy control, the torque output of each people’s production activities and daily life , but driving wheel is controlled by the sliding mode also caused the consumption of energy and variable structure control theory, so that the slip environmental pollution. Vigorously developing ratio is always kept near the desired slip ratio.[8] pure electric vehicles is an effective measure to The stability of all-wheel hub motor-driven EV is solve the environmental pollution caused by controlled by the direct-yaw-moment-control exhaust from fossil-fueled car, which is significant system(DYCS) based on Unscented Kalman Filter to alleviate the energy crisis, improve the energy Method.[9] The the total desired longitudinal force structure and construct a green transportation and yaw torque from the sliding mode vehicle system. controller are distributed to each wheel by the The traditional electric vehicle drive system corresponding advanced allocation mode. In this 1 *Corresponding Author This work was supported by National Key R&D Program of China (2018YFB1308200) way, the desired sliding ratio can be tracked.[10] tread and A wheelbase centroid distance. And r is Admittedly, the hub motor-driven EVs build the radius of the vehicle mass center around the compact electric motor into each wheel. Compared steering center O while R is the radius of front with traditional vehicles’ stability controlled by axle center around the steering center O; R1 is the mechanical differential braking, the hub motor radius of the steering circle of the left rear wheel; works independently and responds quickly. With R2 is the radius of the steering circle of the right the increase of vehicle flexibility and freedom, it’s rear wheel; Vl the speed of the left rear wheel, and also harder to control vehicle, which means a Vr the speed of the right rear wheel, see Fig.1. higher requirement for the stability and safety of L tan R the vehicle, as a result, a new control strategy 1 (1) L tan should be put forward.[11-12] Generally, the 1 C R 1 stability is well during straight line driving. 2 L tan 2 R However, it is a big difference when hub 2 C 2 motor-driven EV turns, which thereby is worth r B2 R 1 2 studying the vehicle steering stability. Currently, most hub motor-driven EVs adopt From Instantaneous Center Theorem, we can direct-yaw-moment control(DYC) to accomplish get: V V V vehicle stability manipulation. This paper aims to l r (2) r R R put forward a new strategy of vehicle stability 1 2 during turning with slipping ratio and yaw ratio as Substituting (1) into (2) yields control variable. L C V 2 Dynamic Model of Dual In-Wheel Hub tan 2 Vl (3) L 2 - 2 Motor Driven EV B tan - - 2.1 Model of Dual In Wheel Hub Motor Driven L C V EV Based on Ackermann Steering Model V tan 2 r L 2 B2 Assumption: 1) A vehicle is a rigid body; 2) The tan yawing force in driving is zero; 3) Drive wheel is for pure rolling motion. And the slip rate S can be given by W * R 1V W ,* VR 0 V (4) s V 1 V W ,* WR 0 W * R The equation (3) and (4) can be solved to yield the desired V1(left rear wheel), Vr(right rear wheel) and slip rate. Then, the actual speed of the vehicle is compared with the desired speed. The Fig.1 Ackermann Steering Model wheel speed is appropriately increased or Supposing that the vehicle turn left, V is the decreased to ensure that the slip rate of the vehicle actual vehicle speed when turning, δ Ackermann remains at a stable level. steering Angle (vehicle steering Angle), 1 the left front wheel steering Angle, 2 the right front 2.2 Model for Hub Motor-Driven Electric Car δ wheel steering Angle, and 1> 2. O is vehicle Based on 2 DOFs Linear Model δ steering center where the centerline of the four In order to achieve 2 DOFs Linear Model as δ δ wheels meet, with L for wheelbase, C for wheel shown in Fig.2, only lateral and yaw motion are 2 considered with front wheel angle and vehicle The motion differential equations of 2 DOFs speed forward unchanged. The model ignores the linear model is AW BW role of steering and suspension system. The K r K r VM VW 1 2 r V V vehicle is fixed in the plane of parallel ground. AWr BWr AK BK WI 1 V 2 V rZ Tire sideslip property is always within the linear range with a small side-slip Angle. （5） The ideal yaw rate Wrd is generated with , in (5), V 푟 W （ ） ̇ = 0, 푊̇ =rd 0 6 A B 1 KV 2 where K is stability coefficient determined by the parameters of vehicle itself. The equation of K is Fig.2. 2 DOFs linear model M A B K （7） A B 2 K K 1 2 The calculation of slipping rate and yaw rate in doing so, the stability control strategy for is achieved on the basis of the Ackermann vehicle differential steering is achieved. Steering Model and 2 DOFs linear model. Procedure: 3 Stability Strategy for Vehicle Steering Electrical differential control system is In this section, stability control strategy for activated when vehicle turns. The ideal speed of vehicle differential steering is presented based on left rear wheel and right rear wheel are worked out sliding mode control. based on the Ackermann steering model with δ and When the vehicle is on the road, the braking V put into controller. The motor is controlled to effect is best when the slip rate is around 20%, track the reference speed, with the speed of the while the slip rate turns 0%, the vehicle has the inner wheel down and the speed of the outer wheel strongest resistance to sideslip and the best up, which may lead to wheel slip. Therefore, the stability. So the optimal range of slip rate is from 0% controller should calculate the slip rate in real time. to 20%, where the stability of vehicle can be When the wheel speed is detected, the outer speed guaranteed.[13]Because the yaw rate is affected by decelerates and the inner speed accelerates with vehicle parameters, speed and steering angle, the the slip rate within 0 ~ 20%.