The axle of the car is the drive shaft. When the car is turning, the left and right wheels have different trajectory radii, so the distance traveled during the turn is different. The outer wheel has to travel a long distance. If the power is transmitted to the same size wheel through a complete shaft, the two wheels The same speed, the same diameter and the difference between the two wheels when turning, it is necessary to make the wheels on the inside of the curve slip and idling (not walking), which makes the turning difficult; to overcome and improve the problem, the vehicle drive shaft is divided into The two halves are separated by left and right, and the middle is connected by "differential". When the vehicle is running straight, the two wheels can get the same driving force. When turning, the inner wheel rotates at a lower speed than the outer wheel due to the differential. In this way, it is achieved that the two wheels simultaneously drive the vehicle forward but the outer wheels move more than the inner side. The use of two half shafts on the drive shaft is designed to improve the cornering performance of the vehicle.