- Typical structure of pure electric vehicle
The main components of pure electric vehicle are composed of power battery pack and its controller, body and chassis, driving motor and its controller, and transmission system. In the early electric vehicles, compared with the traditional vehicles, the engine was replaced by the driving motor and the throttle was replaced by the electronic input device; The fuel tank is composed of power battery pack, and other mechanical and body structures are not much different from traditional cars.
Due to the diversity of electric drive characteristics and energy sources, there can be various possible EV structures, as shown in the figure below.
(1) Traditional drive system (Figure (a)).
The main features of the traditional drive system are as follows:
① The motor replaces the engine.
② The transmission system of internal combustion engine vehicles is still used, including clutch, transmission, transmission shaft, drive axle and other assemblies.
③ There are various driving modes, such as motor front, drive axle front (f-f), motor front, drive axle rear (F-R), etc.
④ Complex structure, low efficiency, can not give full play to the performance of the motor.
(2) Simplified conventional drive system (Figure (b)).
Using a fixed speed ratio reducer and removing the clutch can reduce the mass and volume of the mechanical transmission device.
(3) Motor drive axle integrated drive system (Figure (c)).
① It is similar to the arrangement of internal combustion engine vehicles with transverse front engine and front wheel drive.
② The motor, fixed ratio reducer and differential are integrated into a whole, and the two half shafts are connected to drive the wheels.
③ With compact transmission mechanism, high transmission efficiency and convenient installation, it is most widely used in small electric vehicles.
(4) Dual motor drive system (Figure (d)).
① Two motors are used to drive two wheels respectively through fixed speed ratio reducer.
② It is not necessary to use electronic differential to realize independent speed control of each motor.
③ The electronic differential has the advantages of small volume and light weight. It can realize accurate electronic control when turning and improve the performance of electric vehicles; The disadvantage is that due to the increase of motor and power converter, the initial cost is increased, and the reliability of accurate control of two motors under different conditions needs to be further developed.
(5) Inner rotor electric wheel drive system (Figure (E)).
① The motor is installed in the wheel to form a hub motor, which can further shorten the transmission path from the motor to the driving wheel.
② Adopt high-speed inner rotor motor (about 10000r / min), and install fixed speed ratio reducer to reduce the speed. Generally, high reduction ratio planetary gear reduction device is adopted, which is installed between the motor output shaft and the wheel rim, and the input and output shafts can be arranged on the same axis.
③ High speed inner rotor motor has the advantages of small volume, light weight and low cost, but it needs to add planetary gear speed change mechanism.
(6) Outer rotor electric wheel drive system (Figure (f)).
① The low-speed external rotor motor can completely remove the speed change device.
② The outer rotor of the motor is directly installed on the wheel rim. The motor speed is equal to the wheel speed. The wheel speed and speed control completely depend on the speed control of the motor.
③ Low speed external rotor motor has simple structure and does not need gear speed change transmission mechanism, but it has large volume, large mass and high cost.
- Main structure of motor and its controller
Motor is the only power source of pure electric vehicle, and its performance is closely related to the performance of the whole electric vehicle. Therefore, the selection and parameter matching of motor is one of the keys to the research and design of pure electric vehicle power system.
In order to drive electric vehicles with high performance, the driving motor must meet certain requirements in performance. Generally, the driving motor is required to start / stop, accelerate / decelerate frequently, and the dynamic performance of torque control is required to be high; At low speed or climbing, the torque should be high, while at high speed, the torque should be low; Secondly, the speed regulation range of the drive motor should be wide. It should not only work in the constant torque area, but also operate in the constant power area. At the same time, it must maintain high operation efficiency in the whole speed regulation range.
The motor structure includes two parts: the rotor and stator of the motor and the motor controller. The function of the rotor and stator of the motor is to realize the conversion between electric energy and mechanical energy, and the function of the motor controller is to control the speed and torque of the motor efficiently and controllably, so as to meet the requirements of various working conditions of the automobile. Motors suitable for electric vehicles can be divided into two categories: commutator motors and non commutator motors. The former indicates that they usually have commutator components, while the latter has no commutator components.
There are mainly the following types of motors: DC motor with commutator; Induction motor, permanent magnet motor and switched reluctance motor in DC motor without commutator.
Because the operating conditions of the vehicle are relatively complex, the requirements of electric vehicles for motors are relatively high. The main basic requirements are as follows.
(1) Wide range of speed regulation performance.
(2) High efficiency and low loss.
(3) When the vehicle decelerates, the braking energy is recovered and fed back to the battery.
(4) The quality of the motor, the quality of various control devices and the quality of the cooling system shall be as small as possible.
(5) The safety of electrical system and control system must comply with national (or international) standards and regulations on the safety performance of vehicle electrical control, and high-voltage protection equipment must be installed.
(6) It has good reliability, strong temperature and humidity resistance, and can work for a long time in a harsh environment.
(7) Simple structure, suitable for mass production, low operation noise, convenient use and maintenance, low price, etc.
- Main structure of battery and management system
The battery of electric vehicles is generally called power battery, because electric vehicles have high requirements for battery power density and energy density. Power battery has always been the key reason restricting the development of electric vehicles. At present, lithium-ion battery and traditional lead-acid battery have entered the practical stage. Due to the poor volume, specific energy and other parameters of lead-acid battery, it has not become the mainstream power source of electric vehicles. Therefore, lithium-ion battery technology is developing rapidly at present. In recent years, lithium-ion battery technology has made great progress in a series of key technologies, but due to its physical characteristics and manufacturing process, the performance of lithium-ion battery has not fully reached the level of economic applicability. The correct use and management of battery system can greatly improve the service performance, battery life and driving mileage of electric vehicles, and the service cost will also be greatly reduced, It is of great significance for the development of electric vehicle industry. Therefore, in actual use, the working state of the battery must be monitored and managed in real time. Therefore, the power battery system on the electric vehicle includes the battery itself and its management system (BMS).
- Main structure of auxiliary system
The auxiliary system of electric vehicle is similar to that of traditional vehicle. Its main function is to provide a safe, comfortable and convenient vehicle use environment. The auxiliary system mainly includes entertainment, communication, air conditioning, lighting, human-computer interaction and other systems.