Dynamic simulation of electric vehicle driven by t

2022-08-07
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The dynamic simulation of electric vehicle driven by electric wheel

preface

the electric vehicle with independent electric wheel drive has broad development prospects. When adjusting the driving wheel torque according to the actual driving conditions, the traditional driving mode often has limitations. By using the four electric wheel independent drive mode, in theory, the output torque of each wheel can be directly controlled according to different conditions such as speed change and steering, which can not only avoid some wheels slipping to the ground due to excessive torque, but also provide sufficient driving force according to the demand. Therefore, the electric wheel independent driving mode has significant advantages over the traditional driving mode in terms of handling and driving efficiency

at present, there have been some active researches in this field. Yoichi ho2ri et al. Designed and manufactured the electric vehicle "uot electricmatch II" independently driven by four electric wheels, and tested the application of anti lock braking system (ABS) and traction control system (TCS) on this vehicle. In the literature, the sliding mode variable structure optimizer is applied to the optimal slip rate control of ABS and TCS of electric wheel drive electric vehicles, and ABS and TCS based on fixed slip rate control are designed. The paper designs and tests the electronic differential system of electric vehicle with four electric wheels. However, there are few studies on the torque demand of each wheel when the four electric wheels drive independently under the condition of variable speed or steering. The author uses the simple and effective method of modeling and simulation to investigate the detailed changes of output torque required by each wheel when the electric vehicle with four electric wheels drives independently changes speed or steering

1 establishment of simulation model

the dynamic model of electric vehicle is established in the natural coordinate system, and the speed function v (T) and radius function R (T) with time as variables can be used to describe the driving track and motion status of the vehicle in the xoy plane coordinate system. It is specified that R is positive when turning left and negative when turning right, and the absolute value of R represents the turning radius. R tends to infinity when driving in a straight line. In this way, the yaw rate, which is used to describe the vehicle motion in the absolute coordinate system, is eliminated, and the model is more concise

during the modeling process, the following assumptions are made for the environment and vehicle characteristics: the road surface is horizontal, the tire width is ignored and the tire body is rigid, and the torque of the four wheels can be controlled independently; The front and rear wheels can turn, and there is no slip to the ground during the travel, so that the turning radius passes through the mass center of the whole vehicle; The mass center of the whole vehicle is on the central axis; Without considering pitch and roll, there is no suspension effect; In addition to the air resistance in the forward direction, other aerodynamic factors are ignored

when the vehicle accelerates or decelerates, the load of each wheel will change according to the principle of moment balance. According to the above assumptions, in the direction parallel to the speed at the mass center of the whole vehicle, the following expression can be listed (I = 1 represents the front wheel, I = 2 represents the rear wheel, j = 1 represents the left wheel, j = 2 represents the right wheel) (1)

when there is steering in the direction perpendicular to the speed at the mass center of the whole vehicle, the formula

can be obtained Δ F → TIJ is the load change of each wheel caused by steering; L is the track width; R is the turning radius at the vehicle centroid

the force on each wheel in the forward direction and perpendicular to the forward direction can be expressed as

2 simulation test and result analysis

the main parameters of the vehicle model used in this paper are as follows: the windward area is 118m2; Wind resistance coefficient 013; The distance between the equivalent action point of air resistance and the ground 018m6) defects or damage caused by unauthorized maintenance, disassembly, etc;; Vehicle mass 113 T; The distance between the mass center of the whole vehicle and the ground is 016m; The horizontal distance between the mass center of the whole vehicle and the front axle is 112m; The horizontal distance between the mass center of the whole vehicle and the rear axle is 111m; The front and rear track widths are 1175m; The side deflection coefficient is 2 × 105。

the simulation test is divided into three items. First, set the vehicle to accelerate to 20m/S (72km/h) in a straight line from standstill within 15 s, and then decelerate. The speed of the whole vehicle, the power and torque curves of the front and rear wheels on one side during the test are shown in Figure 1 ~ Figure 3

Figure 1 rate curve

Figure 2 single side electric wheel power curve

Figure 3 single side electric wheel torque curve

analysis of the curves in Figure 2 and figure 3 shows that when the vehicle accelerates, the change law of power and torque is similar, but the time when the power peak appears is later than the time when the torque peak appears. When accelerating, the rear wheel bears a larger output torque, while when decelerating, the negative torque of the front wheel is slightly larger than that of the rear wheel. Although their torque reaches the maximum value almost at the same time, and the change trend is basically the same, the ratio of rear wheel torque to front wheel torque has been changing during the speed change process. The greater the torque value, the greater the proportion. When driving with linear speed change, the load change of each wheel caused by acceleration directly affects the power and torque difference between the front and rear wheels

in the second test, it is set that the vehicle turns right when the holding speed is 15m/S (54km/h, but there is still no inquiry; plus the steel plant is not active in purchasing), and the turning radius changes from 50m to 20m within 315 ~ 2115 s. The steering radius, power and torque curves of each wheel are shown in Figure 4 ~ Figure 6

Fig. 4 steering radius curve

Fig. 5 power curve of electric wheel

Fig. 6 torque curve of electric wheel

Fig. 5 and Fig. 6 show that when the steering radius is small, the power and torque of the right and left wheels differ by nearly 10 times, and the change law of power and torque is basically the same. The torque required by the left wheel increases significantly when the steering radius decreases, and the ratio of the torque of the left front wheel to the torque of the left rear wheel also increases. At the same time, the torque of the right wheel is reduced and tends to be equal. Among the left two wheels of the four electric wheels, the one with the larger load needs the largest torque, the one with the smaller load takes the second place, and the one with the smaller load on the right two wheels needs the smallest torque. When steering with constant speed and variable radius, the power and torque difference between the left and right wheels is mainly caused by the centripetal acceleration

finally, in combination with the changes of V in the first test and R in the second test, it is assumed that the vehicle turns to the left with variable speed and radius, and the power, torque curve and driving track of each wheel are shown in Figure 7 ~ Figure 9 in turn. In Figure 9, when the vehicle starts to drive from O, the positions reached by the vehicle every 5 s are marked as points a to E

Fig. 7 power curve of electric wheel

Fig. 8 torque curve of electric wheel

Fig. 9 vehicle running track

it can be seen from Fig. 7 to Fig. 9 that there is little difference in four wheel power and torque when starting to accelerate and turn. From the 5th s, when the steering radius starts to decrease and continues to accelerate, the torque of the right two wheels continues to increase, while the torque of the left two wheels has reached its maximum value, and then starts to decrease. Although the torque of the right two wheels increased to their respective maximum values after about 10 s, it was significantly greater than that of the left wheel from the 5th s to the 20th s. After 20 s, as the vehicle further puts the sample on the zigzag attachment to decelerate and the steering radius stabilizes at 20m, the torque of the four wheels becomes negative, and the torque change trend of the right wheel is more significant than that of the left wheel

obviously, it is not ideal to distribute the torque of four electric wheels according to a fixed proportion in a more complex steering process. Torque control needs to be carried out according to the actual demand of each wheel when acceleration, deceleration and steering are combined

3 conclusion

the torque required by each wheel of an electric vehicle driven by four electric wheels is often quite different during driving, keeping the loading rate constant, and the changing proportion is also different. Therefore, controlling and adjusting the output torque of each wheel according to the actual needs can not only avoid the sliding caused by the excessive output torque of the electric wheel, but also prevent the vehicle from failing to meet the driver's requirements during speed change or steering due to insufficient output torque, which is conducive to improving the handling performance. (end)

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