An automatic transmission, unlike manual transmission, does not have a clutch. They use a torque converter to keep the engine running when the gears and wheels stop. It uses a torque converter to disconnect the engine from the transmissions. In essence, it is a fluid coupling that allows the engine to run independently of the transmission.
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When you stop at the traffic light, only a small amount of torque is transmitted to the torque converter. Braking to prevent the car from creeping.
Main functions of the torque converter are:
- Transmitting power from the engine to the input shaft
- Isolates the engine from the load when the automobile is stationary
- Multiplies engine torque and transmits it to the transmission
- Drives transmission front pump
How it works
The engine rotates the impeller hence directing the oil inside the torque converter towards the turbine. The turbine starts rotating as the oil hits the turbine blades. As a result, the transmission system rotates and the vehicle wheels moves. The turbine stops rotating when the engine stops. However, the impeller connected to vehicles engine continues to move. It, therefore, prevents the engine from dying.
Main parts of the Torque converter
A torque converter has three major parts:
The impeller is also known as the pump. It contains an automatic transmission fluid. It is connected to the engine shaft. The faster it spins, the more force it creates as fluids flow harder and faster. As it rotates the fluid moves toward the turbine due to centrifugal force. It sucks the transmission fluid from the automatic transmission delivering it to the turbine.
The stator is a collection of fins located between transmission shaft and the turbine. It reverses transmission fluid and sends it back to the impeller. It gives the transmission fluid direction as it returns from the turbine entering the impeller. The fluid enters the impeller in the direction of the impeller rotation multiplying torque.
Turbine is an assembly of angled and curved blades connected to the input shaft. The blades are designed to change the direction of fluid that land on it. This change of direction forces the blades to move in the same with the impeller. The input shaft rotates as the turbine rotates and hence moving the vehicle. Fluid coupling occurs as a result of the constant circulation of fluid from the impeller to the turbine and back.
Stages of Operation
Torque converter functions in three stages:
The engine supplies the compeller with power. However, the impeller can’t rotate because the driver exerts pressure on the brake pedal. Turbine speed is less than impeller speed. The vehicle does not move and neither does it stall.
Accelerations happen when the driver lifts his foot off the brake pedal and steps on the gas pedal. At this point, there is a big difference between turbine and impeller speed. As a result, the impeller rotates faster creating torque multiplication which is ideal for accelerations.
This is a situation where the turbine has achieved almost the same speed as the impeller hence stopping torque build up. This is a coupling point the torque converter just acts as a fluid coupling. The lock-up clutch locks the turbine to the propeller hence making them move at the same speed. During coupling, the stator, turbine and propeller move in the same direction.
Torque converter problems can a misinterpreted to be signs of a faulty transmission. Signs of failing torque include overheating, shaking, slipping, high stall speed and unusual sounds. If notice these symptoms have a qualified technician check your torque converter.
Learn more about your vehicle’s transmission: