What is the function of a car differential?

[DeLaila]

The function of a differential is: To distribute torque between two output shafts; ensure that the two output shafts rotate at different angular speeds; guarantee power transmission to each driving wheel under various motion conditions; and prevent tire slippage on the ground. A car differential is a mechanism that enables the left and right (or upper and lower) driving wheels to rotate at different speeds. It consists of left and right axle gears, planetary gears, and a gear carrier. When a car turns, the wheel tracks form arcs. If the car turns left, the center of the arc is on the left side. During the same time, the outer wheel travels a longer path than the inner wheel. If the left and right wheels were rigidly connected directly, the outer wheel would experience drag while rolling, and the inner wheel would experience slip while rolling. Even when driving straight, wheel slippage can occur due to uneven road surfaces or differences in tire rolling radii, even on flat roads. Wheel slippage not only accelerates tire wear and increases power and fuel consumption but also makes steering more difficult and reduces braking performance, among other adverse driving factors. The differential balances the speed difference between the wheels, enabling the necessary speed difference between the left and right wheels during turns.

[VanWillow]

As a veteran truck driver with twenty years of experience, I have personally witnessed the importance of differentials. The phenomenon where the inner wheels rotate slower and the outer wheels faster during a turn is precisely what it coordinates. Once, while making a sharp turn on a mountain road with a heavy load, I distinctly felt the four wheels' rotation speeds being automatically adjusted, keeping the vehicle firmly planted on the road. In fact, a truck's differential houses a sophisticated planetary gear set that intelligently distributes the engine's power to the wheels that need it most. Especially on slippery rainy days, if a wheel starts to spin, the differential prevents all the power from being wasted on the spinning wheel. However, open differentials can still falter in extreme conditions, which is why off-road vehicles often come equipped with differential locks.

[LaLeah]

When repairing cars, I always like to use analogies for customers: the differential is like a smart distributor. When the car is moving straight, the left and right axle gears rotate at the same speed, but the moment you turn, the resistance on the inner wheel increases, and the planetary gears automatically adjust the torque distribution on both sides. The most typical example is the open differential structure, which uses a cross shaft to drive two sets of bevel gears. Once, when disassembling a rusty differential, I found that it was precisely the lack of gear oil that caused the planetary gears to seize up, resulting in the rear wheels grinding dry when the owner turned. Therefore, it's crucial to regularly check the rear axle oil, especially for vehicles that frequently drive on rough roads—it's best to change it every 50,000 kilometers.

[Tammy]

When it comes to modifying off-road vehicles, differential upgrades are among the most common modifications. The factory open differential is at a significant disadvantage in cross-axle terrain, as power is entirely lost to the spinning wheel when one wheel is lifted. I usually recommend upgrading to a limited-slip differential (LSD), which uses friction plates to create resistance and forcibly distribute power. More advanced options like the Torsen differential are even smarter, utilizing a worm gear mechanism to automatically adjust torque. Once, I helped a fellow off-roader install a differential lock, and he later sent a video thanking me after crossing a desert—when three wheels were slipping, locking the differential allowed the single grounded wheel to pull the entire vehicle out.