How Does a Torque Converter Work?

Have you ever wondered what a torque converter is, or what it does? A torque converter is a mechanical device that transfers engine power to the transmission. It is analogous to the clutch in manual transmission. However, the torque converter automatically matches engine power to the appropriate gear without the driver’s intervention. It also allows the engine to run while the transmission and wheels are at rest though a coupling system that utilizes hydrodynamic fluid.

During idling of the engine, e.g. while at a stoplight, a small of torque is transmitted via the torque converter, but still adequate to necessitate a slight depression of the brake pedal to prevent the vehicle from creeping. Upon releasing the brake and depressing the accelerator, the engine gains speed and pumps extra fluid into the torque converter. This causes more power to be transmitted to the wheels. There are three main components of a torque converter.

  • The impeller

Also known as a pump, the impeller is the initial part of the device’s assembly. It contains transmission fluid and spins in tandem with the crankshaft. As it spins faster, more force is generated since the fluid goes through it faster and more forcefully.

  • The turbine

The impeller pushes the transmission fluid into a blade assembly known as the turbine. This turbine is usually located opposite the impeller. The fluid hits the turbine blades causing it to rotate. As the transmission fluid flows through the turbine, it is once again directed to the inner side of the turbine, then back to the impeller. Such a continuous circulation of transmission fluid from the impeller into the turbine, then back again to the impeller, forms the fluid coupling.

  • The stator

The function of the stator is to redirect the transmission fluid back towards the impeller. This process slows the velocity of the fluid. It is at this point that torque is generated as the fluid makes its way back to the impeller in order to maintain the cycle. The stator comprises a series of fins situated between the 2 turbines on the gear shaft. The blades are appropriately angled to reverse the direction of the fluid as it flows into them. When the car comes to a halt, the one-way clutch within the stator stops its spinning, thereby breaking the hydrodynamic circuit.

The stages of a torque converter’s operation

Torque converters typically operate in three stages involving the separate components. The stages are as follows:

  • Stall

At this stage, the engine transmits power to the impeller. However, the impeller remains stationary since the driver has kept the foot on the brake, for instance, when on a temporary stop. The vehicle is motionless, yet it doesn’t stall.

  • Acceleration

This process takes place when the driver lifts the foot off the brake pedal and depresses the acceleration pedal. The impeller begins to rotate at a higher speed resulting in a big difference between the turbine and impeller speed. This results in torque, which is then multiplied by the torque converter- a process necessary for vehicle acceleration.

  • Coupling

As the car approaches top speed, the turbine rotates almost at the same speed as the impeller. This causes the buildup of torque to cease. During this process, torque converters simply exist as a coupling of fluid. In an automatic transmission, the lockup clutch is what locks the turbines to the impeller to eradicate any loss of power as well as maintain the vehicle’s smooth motion. Since the impeller is attached to the housing of the torque converter, and the converter connects to the engine, the impeller’s power is derived from the engine. Furthermore, the turbine connects to the drive shaft, which transmits power to the transmission.

In conclusion, the above description is adequate to offer you a basic understanding of how the automatic transmission system functions.

Justin Author