| Control system (The traction control of Electric Vehicle) |
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Figure 2 shows an example of the torque characteristic of the motor for electric vehicles. The torque is proportional to the rate of operation of the accelerator pedal, but at higher speeds and lower pedal operation rates negative torque, or deceleration like an engine brake, is applied.
Because the motor can easily change its direction of rotation by changing the magnetic field or the current, the electric vehicle does not need a mechanical reverse gear. However, the maximum reverse vehicle speed should be restricted by the control logic.
In addition, if the vehicle is going in the opposite direction of the driver's operation, such rolling backward on an incline, the torque direction should be kept forward.
Therefore, the requirement of the motor characteristic of the electric vehicle should be the four quadrants drive characteristic that is shown in fig. 2. This characteristic should be separately designed according to the direction of speed and torque, and the accelerator pedal should control the amount of the torque as the figure shows.
Figure 3 shows an example of the torque characteristic of the electric vehicle.
Here are the summarized characteristics of the motor for the electric vehicle.
- Torque demand control
- Constant torque at low speeds
- Constant power at high speeds
- Torque-on-demand at a dead stop
- Negative torque when decelerating
- Regenerating control
- Positive torque when rolling backward
In addition to the motor control, here are the requirements for controlling the vehicle using the accelerator pedal and the forward and reverse shift
- Torque control according to the accelerator pedal operation rate
- Engine brake characteristic, especially at high speeds
- Creeping torque if necessary
- Forward and reverse shift, and ability to select the torque characteristics.
Reference
Book title: EV Handbook
Written by: EV Handbook Publisher's Group
Published by: Maruzen Co., Ltd. (URL http://www.maruzen.co.jp)
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