Torque Converter: Notes

The converter consists of the impeller, the turbine wheel, the reactive element (stator) and the fluid used to transmit the torque. The impeller is driven by the engine and imparts a circular flow to the fluid in the converter. The angle of the fluid flow is deflected when it strikes the turbine wheel. The fluid leaves the turbine wheel close to the hub, and passes through the stator, where it is again deflected and enters the impeller at an angle. The change in the direction of fluid flow at the stator generates a reaction torque that increases the torque at the turbine. The ratio between turbine torque and impeller torque is the torque conversion ratio. The greater the speed difference between the impeller and the turbine, the greater the increase in torque; this increase reaches a maximum when the turbine is stationary. As turbine speed rises, the increase in torque lessens. When the turbine is running at about 85 percent of the impeller speed, the increase in torque drops to one, that is to say turbine and impeller torques are identical. The stator, which bears against the gearbox housing via a one-way clutch and the stator shaft, can then revolve freely in the fluid flow, and the freewheel is overrun. From this moment, the converter operates purely as a fluid coupling. During the torque conversion phase, the stator is stationary and bears against the housing through the freewheel.