When mechanical power is created by an engine, it moves from the transmission to the differential to the wheels of the car themselves. Although many aspects of these processes are understood decently well by car owners, sometimes people blank a little when it comes to the precise role of the differentials. Here’s an article to explain exactly what your car’s differentials are and what role they play in moving you from point A to point B.
The differentials perform three important tasks; they aim the engine power at the wheels, act as the final gear reduction in the vehicle (they help to slow the rotational speed of the transmission one final time before that energy hits the wheels), and they transmit the engine and transmission’s power to the wheels while allowing them to rotate at different speeds (hence the name, “differential”.
You ned your wheels to spin at different speeds in order to turn your car. Any rotation of your car’s direction will involve each wheel traveling a different distance over a set period of time, yet the car must maintain a consistent speed as a whole, so that means that the wheels have to turn at different speeds.
The non-driven wheels of your car (the opposite wheels to whatever-wheel drive your car is said to be) don’t really have an issue with this. They’re not connected to each other anyway, so spinning independently is the norm. The driven wheels, however, are linked together so that a single engine and transmission can cause both of the two wheels to turn. Without a differential, every turn would require that one wheel slip while the other turned, which would put a whole lot of pressure on your car’s axle and be much more difficult for drivers to execute consistently.
So that’s why we need a differential, but how does it work? It splits the engine torque into two different channels, allowing each output to spin a different speed if need be. By the way, all wheel drives require a differential between each set of wheel sand between the front and back wheels.
Anyway, there are many different kinds of differentials, the simplest of which is called an open differential. The open differential involves a few different components: the ring gear, the side gear, the axle shaft, the pinion gears, the input pinion and the pinion shaft. When a car is moving straight, both drive wheels are spinning at the same speed and the input pinion turns the ring gear and cage, while none of the pinions within the cage are rotating.
When the car turns and wheels must turn at different speeds, the pinions in the cage start to spin, allowing the wheels to move along at different rates. The inside wheel might spin slower than the cage, while the outside wheel might spin faster, for example.
One final pro tip: when you hear terms like the rear axle ration or final drive ratio, they refer to the gear ration within the differential. Say the ratio is 4.40; that would mean that the ring eat has 4.40 times as many teeth as the input pinion gear.