The function of a drive motor is to convert electrical energy from a power source into mechanical energy, which then drives the wheels and working devices through a transmission device or directly. Currently, DC series motors are widely used in electric vehicles. These motors have "soft" mechanical characteristics, which are very compatible with the driving characteristics of automobiles. However, they have low power, low efficiency, and require a large amount of maintenance. With the development of motor control technology, they will inevitably be gradually replaced by brushless DC motors (BLDCM), switched reluctance motors (SRM), and AC asynchronous motors.
1. Speed control device
The motor speed control device is designed for the speed change and direction change of electric vehicles. Its function is to control the voltage or current of the motor to control the driving torque and rotation direction of the motor.
In early electric vehicles, DC motor speed control was achieved by connecting series resistors or changing the number of turns in the motor's magnetic field coil. Because this speed control was stepped and resulted in additional energy consumption or complex motor structure, it is rarely used now. Currently, thyristor chopper speed control is more widely used, which controls the motor current by uniformly changing the motor's terminal voltage to achieve stepless speed regulation. With the continuous development of electronic power technology, it has gradually been replaced by chopper speed control devices using other power transistors (such as GTOs, MOSFETs, BTRs, and IGBTs). From a technological development perspective, with the application of new drive motors, the shift of electric vehicle speed control to DC inverter technology will inevitably become a trend.
In the rotation direction control of drive motors, DC motors rely on contactors to change the direction of the armature or magnetic field current to achieve rotation direction change, which makes the circuit complex and reduces reliability. When using an AC asynchronous motor, changing the motor's direction only requires changing the phase sequence of the three-phase current in the magnetic field, simplifying the control circuit. Furthermore, using AC motors and their variable frequency speed control technology makes the regenerative braking control of electric vehicles more convenient and the control circuit simpler.
2. Transmission device
The function of the electric vehicle's transmission is to transmit the driving torque of the electric motor to the vehicle's drive shaft. When using electric wheel drive, most components of the transmission can often be ignored. Because the electric motor can start under load, electric vehicles do not require the clutch found in traditional internal combustion engine vehicles. Since the direction of rotation of the drive motor can be changed through circuit control, electric vehicles do not require the reverse gear found in the transmissions of internal combustion engine vehicles. When using continuously variable speed control (CVT) for the electric motor, electric vehicles can eliminate the need for a traditional transmission. Furthermore, when using electric wheel drive, electric vehicles can also omit the differential found in the traditional internal combustion engine vehicle's transmission system.
3. Driving device
The function of the running gear is to convert the driving torque of the electric motor into a force exerted on the ground through the wheels, thus driving the wheels to move. Its structure is the same as other automobiles, consisting of wheels, tires, and suspension.
4. Steering device
The steering system is designed to enable a car to turn, and consists of a steering gear, steering wheel, steering mechanism, and steering wheels. The control force applied to the steering wheel, through the steering gear and steering mechanism, causes the steering wheels to deflect at a certain angle, thus turning the car. Most electric vehicles are front-wheel steering, while electric forklifts used in industry often use rear-wheel steering. Electric vehicle steering systems include mechanical steering, hydraulic steering, and hydraulic power steering.
5. Braking device
Like other vehicles, electric vehicles have braking systems designed for deceleration or stopping, typically consisting of brakes and their control mechanisms. Electric vehicles generally also include electromagnetic braking systems, which utilize the control circuitry of the drive motor to generate electricity, converting the energy generated during deceleration and braking into current that charges the battery, thus achieving regeneration.
