The role of the car engine is: the heat of gasoline, diesel fuel through the combustion in the sealed cylinder after the expansion of gas, push the piston to do work, transformed into mechanical energy. The engine is composed of: 1, gas distribution mechanism; 2, crank connecting rod mechanism; 3, ignition system; 4, cooling system; 5, lubrication system; 6, starting system; 7, supply system. The working principle of the engine is: 1, the air and gasoline in a certain ratio into a gas mixture; 2, the suction stroke will be mixed gas into the cylinder, mixed gas by compression and ignition combustion to generate heat; 3, high temperature and high pressure gas on the top of the piston, push the piston to do reciprocating linear motion, through the connecting rod crankshaft flywheel mechanism external output mechanical energy.

The engine works by converting other forms of energy into mechanical energy, two-stroke engines and four-stroke engines work differently, the vast majority of automobile engines are four-stroke. The work cycle of a four-stroke gasoline engine consists of four piston strokes, namely the intake stroke, compression stroke, work stroke and exhaust stroke.

The role of the car transmission is: 1, change the transmission ratio to meet the needs of different driving conditions for traction; 2, to achieve reverse driving, used to meet the needs of the car backward driving; 3, interrupt the power transmission; 4, to achieve neutral gear. Transmission, also known as gearbox, is a mechanism used to change the speed and torque from the engine, and can change the output shaft and input shaft ratio in fixed or split gear. Gearboxes are divided into: 1, stepped transmission: gear transmission, with a number of fixed transmission ratio; 2, stepless transmission: can continuously obtain a variable speed range of any ratio of the transmission system.

The transmission consists of the shell, transmission part and operation part. (1) Shell: The shell is the foundation for the installation and support of all parts of the transmission and storage of lubricants.