The vehicles and
machineries with automatic transmission does not have a clutch, instead,
it has a torque converter. But, how a torque converter works or solves the
purpose of a clutch? To give you an idea, it works on the same principle as
the fluid coupling.
As the name
suggests, it converts the torque of the engine and transmits it to the
transmission system.
As soon as the
flywheel of engine starts rotating, the torque converter housing as well as the
pump also starts rotating in same speed and direction. Because of the profile
of the pump blades, the fluids inside the torque converter are pushed out
centrifugally. Because of the pressure developed by the pump, the fluids are
forced into the blades of the turbine and make it rotate in the same direction
as the pump. The fluids enter to the outer periphery of the turbine and leave
from the inner periphery and reaches to the stator blades there. The function
of the stator is to guide the incoming fluid from the turbine to reach at a
specific angle to the pump.
If the turbine is
rotating at a speed lower than that of the pump (i.e., when the vehicle is
accelerating) then the fluids from the turbine hits the front sides of the
stator blades and the one way clutch prevents it from rotating. In this
condition the fluids leave from the stator hits the pump at a “helping"
angle to increase the torque (or multiply the torque) and thus increase the
speed of the turbine.
When the vehicle
achieves its constant speed, then the angle at which the fluids leaving from
the stator change and no more torque multiplications happens.
While retarding, the
speed of the turbine increases than that of the pump and the fluid from the
turbine hits the back sides of the stator blades and make the stator rotate at
the same direction as the pump and turbine and the fluid from the stator hits
the pump in such angles that the torque reduces.
A torque converter
typically has three major components: impeller or pump, turbine and stator or
reactor.
Impeller or
Pump: The
pump is made up of blades and works very similar to a centrifugal pump. It
is mounted rigidly with the torque converter housing (shown in blue). The whole
torque converter housing in turns is mounted rigidly with the flywheel. So, it
rotates with the flywheel.
Turbine: Constructions of the
turbine is very much similar to that of the pump but the orientation of the
turbine blades are opposite to that of pump. The turbine is mounted on
transmission input shaft.
Stator or
Reactor: The
stator has very complex guiding blades arrangements. It is mounted by a one way
clutch with the transmission housing. The one way clutch allows the stator to
rotate in one direction and prevent it from rotating to another.
You will find the
use of the torque converter in almost all sort of automatic transmission
vehicles: from passenger cars to heavy off highway vehicles. The design of the
blades of the turbine, stator and the pump is the key of how effectively a
torque converter works.