How Torque Convertors Work

If you have read about manual transmissions, you know that an engine is connected to a transmission by way of a clutch. Without this connection, a car would not be able to come to a complete stop without killing the engine. But cars with an automatic transmission have no clutch that disconnects the transmission from the engine. Instead, they use an amazing device called a torque convertor.

The torque convertor is situated between the engine and the transmission.

A torque convertor is a type of fluid coupling, which allows the engine to spin somewhat independently of the transmission. If the engine is turning slowly, such as when a car is idling at a stop light, the amount of torque passed through the torque convertor is very small, so keeping the car still requires only a light pressure on the brake pedal.

How the parts of the torque convertor connect to the tranmission and engine.

The pump inside a torque convertor is a type of centrifugal pump. As it spins, fluid is flung to the outside, much as the spin cycle of a washing machine flings water and clothese to the outside of the wash tub. As fluid is flung to the outside, a vacuum is created that draws more fluid in at the centre.

Benefits and Weak Points

In addition to the very important job of allowing your car to a complete stop without stalling the engine, the torque convertor actually gives your car more torque when you accelerate out of a stop. Modern torque convertors can multiply the torque of the engine by 2 or 3 times. This effect only happens when the engine is turning much faster than the transmission.

At higher speeds, the transmission catches up to the engine, eventually moving at almost the same speed. Ideally though, the transmission would move at exactly the same speed as the engine because this difference in speed wastes power. This is part of the reason why cars with automatic transmissions get worse gas mileage than cars with manual transmissions.

To counter this effect, some cars have a torque converter with a lockup clutch. When the two halves of the torque converter get up to speed, this clutch locks them together, eliminating the slippage and improving efficiency.