Tractor is a self-propelled power machine used to pull and drive operating machinery to complete various mobile operations.Also can do the fixed work motivation.By the engine, transmission, walking, steering, hydraulic suspension, power output, electrical instrumentation, driving control and traction system or device composition.The power of the engine is passed from the transmission system to the driving wheel to make the tractor run.It is divided into agricultural, industrial and special purpose tractors according to their functions and USES.According to the structure type of wheel, crawler, boat - shaped tractor and self - walking chassis

Although tractor is a kind of more complex machine, its type and size also different from each other, but they are composed of engine, chassis and electrical equipment three major parts, each is indispensable.

It is a tractor power generation device, its role is to change the heat of the fuel into mechanical energy to output power.Most agricultural tractors produced in China use diesel engines.It is a device for the tractor to transmit power.Its function is to transfer the power of the engine to the driving wheel and working device to enable the tractor to move and complete the operation of moving or fixing.This function is through the transmission system, the walking system, the steering system, the braking system and the working device to cooperate with each other, the coordination work to achieve, at the same time they constitute the frame and the body of the tractor.Therefore, we refer to the above four systems and a large device collectively as the chassis.That is, in the tractor as a whole, all other systems and devices except the engine and electrical equipment, collectively referred to as the tractor chassis.

Electrical equipment it is a device that keeps the tractor running on electricity.Its role is to solve lighting, safety signals and engine starting.

Tractor can is to rely on internal combustion engine power through the transmission system, make driving wheel drive torque Mk, get the driving torque of driving wheel through the tire pattern and tire surface to the ground again small, or the level of backward reaction (tangential force), and a driving force to the level of the equal and opposite rice force Pk, the Pk rice force is driving the tractor driving forward the driving force (also known as feed for propulsion).When the driving force Pk is enough to overcome the forward rolling resistance of the front and rear wheels and the traction resistance of the farm tools, the tractor will move forward.If the drive wheel to the ground, that is, the driving force Pk equal to zero, then the drive wheel can only idling, the tractor can not run;If the sum of rolling resistance and traction resistance is greater than the driving force Pk, the tractor can not run.Thus it can be seen that wheeled tractor driving is realized by the interaction between driving torque driving wheel and the ground, and the driving force is greater than the sum of rolling resistance and traction resistance.