An automotive differential is a mechanism that rotates the left and right (or front and rear) driving wheels at different speeds. It is mainly composed of left and right side gears, two planetary gears, and a gear carrier. Its function is to rotate the left and right wheels at different speeds when the car turns or runs on a bumpy road, that is, to ensure the pure rotational motion of the driving wheels on both sides. The differential is installed to adjust the speed difference between the left and right wheels. In four-wheel drive, all wheels must be connected to drive the four wheels. If the four wheels are mechanically connected, the car cannot rotate at the same speed when running on a curve. When running on a curve, the rotation speed is basically constant. At this time, a middle differential must be added to adjust the speed difference between the front and rear wheels.
Consists of
A typical differential consists of parts such as a planetary gear, a planetary carrier (differential case), and a side gear. The engine power enters the differential through the transmission shaft, directly drives the planetary gear carrier, and the planetary gear drives the left and right half shafts to drive the left and right wheels respectively. The design requirements of the differential meet (left half shaft speed) + (right half shaft speed) = 2 (planet carrier speed). When the car is going straight, the rotation speeds of the left and right wheels and the planet carrier are equal and in a balanced state, but when the car turns, these three equilibrium states are broken and the rotation speed decreases. The rotation speed of the inner wheel increases, and the rotation speed of the outer wheel increases.
Principle
When turning, the outer wheel slips and the inner wheel slips, so that the wheels on both sides will inevitably generate additional forces in the opposite direction according to the rotation speed of the planet gear, according to the "minimum energy consumption principle". , the three balance relationships are broken, which is reflected in the side shaft gear through the half shaft, forcing the planet gear to rotate, slowing down the speed of the inner half shaft and speeding up the speed of the outer half shaft. The rotation speeds of the wheels on both sides are different.
Differential circuit diagram
If the driving wheels on both sides of the drive shaft are tightly connected throughout the shaft, the two wheels can only rotate at the same angle. Thus, when the car turns, the outside wheel has moved more than the inside wheel, so the outside wheel slips while rolling, and the inside wheel slips while rolling. Even if the car is going straight and the road surface is flat, the wheels will slip due to unevenness of the road surface and unevenness of the tire rolling radius (tire manufacturing error, difference in wear, uneven load, difference in air pressure). .
When the wheels slip, not only does it increase tire wear, but it also increases power.
When the wheels slip, not only does it increase tire wear and increase power and fuel consumption, but it also makes the car difficult to turn and reduces braking performance. In order to prevent wheel slip as much as possible, it is necessary to have a structure that allows each wheel to rotate at a different angle.
Inter-axle: Usually, the driven wheels are supported on the main shaft by bearings so that they can rotate at any angle, while the driving wheels are firmly connected to two half shafts, and a differential is installed between the two half shafts. This type of differential is also called an inter-axle differential.
For multi-axle drive off-road vehicles, some are equipped with an inter-axle differential between the two drive axles so that each drive axle rotates at a different angular speed to eliminate slippage of the drive wheels on each axle.
Effect
When a car turns, the turning radius of the inner and outer wheels is different. The turning radius of the outer wheel is larger than that of the inner wheel, so the turning speed of the outer wheel must be faster. The speed of the inner wheel when turning. The function of the differential is to meet the requirements of different wheel speeds on the left and right sides when the car turns. This function is the most basic function of differentials such as center differentials, anti-slip differentials, and LSD differentials. Later developed Torsen differentials, etc., are intended to improve the driving and handling performance of the car.
Designed with an emphasis on performance and controllability.
Function
When a car turns a corner, the wheel trajectory is an arc. If the car turns left, the center point of the arc is on the right side. To balance this difference, the left wheel needs to be slower and the right wheel faster, using different rotational speeds to make up for the difference in distance.
If the rear axle was made as a whole, the difference in rotational speed between the left and right wheels would not be compensated for, and automatic adjustment would not be possible. To solve this problem, Louis Renault, founder of the French Renault automobile company, designed the differential 100 years ago.
