as been described before the principles of fluid coupling and torque converters, the converter is a closed unit. so the flow of oil is repeated continuously. many streams of fluid act against the vanes at once giving power to drive heavy machinery. in a torque converter, the vanes of the locked up reactor (STATOR) gives more thrust to drive the turbine blades this give torque multiplication, the torque is increased at the beginning and as the vehicle picks up speed torque is reduced. the torque converter of fluid coupling can’t be declutched by the driver. so they are used in may epicyclic transmission allowing gear change without engine disengaging. some torque converters may be fitted with a frictional clutch allowing to use a synchro mesh gearbox where the clutch disconnects the engine when gears are being changed.
the free wheeling is one way clutch that allows the stator to rotate in one direction only. the clutch locks the stator if the stator tries to move in other direction. the mechanism uses an overrunning clutch.
when their is a push from the fluid leaving the turbine, the stator attempt to roll backwards. but this can’t be done because of the overrunning clutch, instead it change the direction of the fluid into helping direction.
however, when the impeller speed approaches the pump speed. the direction of oil has no longer to be changed as it leaves the turbine. the oil begins to hit the other side of the vanes allowing it to move forward to get out the way of the fluid.
what is Fluid coupling ???
considering two fans at a few centimeters away from each other. If fan (A) is turned on, air will flow and strike the blades of fan (B) which is originally at rest this will cause the blades of fan (B) to rotate in the same direction of fan (A). this is basic fluid drive which is known as fluid coupling.
it mainly consists of an impeller and turbine with oil continuously flowing between them. the impeller is driven by the engine while the turbine drives the input shaft of the gearbox.
when the engine is idling, oil flows from the impeller by means of centrifugal force to the turbine which remains stationary as the force of oil is not sufficient yet for turning the turbine. but when the speed of the impeller increases it will increase the turning effort of the fast moving oil. so the oil force will be great enough to rotate the turbine which begins to rotate and sets the car in motion. after giving up energy to the turbine, the oil re-enters the impeller and is circulated back to the turbine again. if the speed of the engine continues to increase, the difference between the rotational speed of turbine and impeller gradually decreases until the slip between them is reduced.
the above figure shows the oil circulation between the impeller and turbine, when the engine is driving, the oil circulates fast between the members when the driven member is stationary (turbine) but it slows down when they both approaches the same speed. under over running conditions the direction of oil flow is reversed, and a drive from the output shaft tends to brake the engine, so. a stator is placed between the impeller and turbine to overcome this process and to multiply the torque.
principle of torque multiplication
as described before, oil flows from impeller to turbine and from turbine back to impeller by means of a stator. this will lead in torque multiplication. thus the torque converter converts the torque of engine into higher one. the stator vanes enable the pump to increase the twisting force or multiply the torque as shown in the above figure.