Design principles of electric drive system:
①Satisfy vehicle dynamic requirements, such as gradeability, acceleration performance, etc.
②Meet the economic requirements of the whole vehicle, maintain high system working efficiency under most working conditions, to improve pure electric
③High power density, wide speed range, good stability and control accuracy.
④Small size, light weight and low cost.
⑤High reliability, high safety, long life and low noise.
The design of the electric drive assembly is to determine the selected system configuration and assembly parameters according to the vehicle working conditions and target requirements.
The main points of assembly and component design are verified by post-design tests.
1.Centralized drive system
Centralized drive system is currently the main power system form of pure electric vehicles on the domestic and foreign markets. Cars mostly use a three-in-one electric drive system configuration of motor, reducer and motor controller; commercial vehicle centralized drive systems mainly include motor direct drive, motor + transmission type; commercial trucks mostly use motor + axle integration Electric drive bridge configuration. At present, centralized drives are mainly divided into four categories: motor direct drive, motor + reducer/AMT system, three-in-one system and electric drive axle system.
Motor Direct Drive
1. Parameter selection and verification
In the direct-drive configuration of the electric motor, the power transmission components such as the engine, clutch and transmission of the traditional fuel vehicle are eliminated, so that the structure of the power system is simplified and the maintenance is convenient.
At the output shaft of the end cover of the drive motor, the drive shaft is connected to the final drive and differential of the rear axle to form the drive part, and the drive motor outputs power deceleration and torque increase through the rear axle final drive. This arrangement has the advantages of simple structure, compact layout of the transmission part, high reliability, continuously variable transmission, high driving efficiency, etc., and the components are basically mature, and the failure rate of the whole vehicle is low. However, the system has relatively high cost, heavier weight, and redundant power.
The main reducer speed ratio is the gear ratio of the main reducer in the rear axle of the direct drive system. It is equal to the ratio of the rotational angular velocity of the drive shaft to the rotational angular velocity of the axle shaft, and it is also equal to the ratio of the rotational speed. The main reduction ratio of the rear axle is selected according to the vehicle layout and the torque range of the rear axle. The speed ratio of the passenger car sergeant reducer is 3.0-6.33. Under the premise that the final reduction ratio i is known, the motor is selected according to the power demand of the whole vehicle obtained in Chapter 2, and then the power performance indicators are checked, and finally according to the calibration Optimize the nuclear results.