construction and working of a torque convertor in an automobile | torque convertor a type of fluid coupling
Torque converter is a type of fluid coupling that uses a fluid to transmit turning effort from the one shaft to another. It is a device which performs a function similar to that of a gear box, namely, to increase the torque while reducing the speed. A gear box provides only a small number of fixed ratios, but the torque converter provides a continuous variation of ratio from the lowest to the highest.The torque convertor is somewhat similar to a fluid fly wheel, but differs from it in one aspect, namely it has three principal components instead of only two.
Torque converter consists of
(i) The driving element or impeller or pump which is connected to the engine.
(ii) The driven element or rotor or turbine which is connected to the propeller shaft and
(iii) The fixed element or reaction member or stator which is fixed to the frame. The fixed element is responsible to cause a change of torque between input and output shafts. The fluid flywheel does not have any fixed member, as such cannot produce any change of torque.
Working of a torque converter
The three element torque converter can be seen in the picture. In the torque converter, torque multiplication take place in the following way. The oil leaving vanes hits the stator vanes. This oil is redirected into the pump vanes in a direction which helps the pump operation. This oil is again thrown into the turbine by the pump. In fact, this is a continuous process. The fluid pushing repeatedly on the turbine vanes increases the torque on the turbine. In many designs of torque converters, the torque is almost doubled. However, as the speed of the turbine approaches the speed of the pump, the increase in torque falls of gradually till it becomes 1:1. At this stage, the oil starts striking the rear faces of the vanes in the stator, thus making the stator to turn. Now the stator does not take part in torque converter action. Under these conditions, the torque converter simply acts as a fluid fly-wheel.
The over running clutch or freewheeling device is used for mounting the stator. The spring loaded rollers in the freewheel allow the stator to freewheel when the oil starts striking the rear of the stator vanes. On the other hand, when the oil strikes the front of the stator vanes, it attempts to rotate the stator in the opposite direction. But this action locks up the freewheeling device and thus holds the stator stationary. Under such condition, the stator acts as a reaction member, and directs the oil leaving the turbine trailing edges in the proper direction before it enters the pump vanes.