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IDROCONVERT TRANSMISSION
347
Should oil flow Ie-enter the impeller vanes in
this unfavourable direction, an opposing torque
would counteract the engine torque thereby causing
a reduction in engine speed.
In such a situation the advantage gained by suit-
ably shaping the turbine vanes would be completely
lost.
To obviate this, a stator is inserted between im-
peller and turbine to reverse the direction
of oil
flow leaving the turbine in order to facilitate impeller
rotation thus increasing the torque.
The period
during which this torque increase occurs is known
as the conversion phase.
The torque multiplication obtained is proportional
to the speed differential existing between impeller
and turbine, reaching a maximum of 2 to 1 during
starting (turbine stationary).
During the conversion phase, the stator, under
the thrust exerted by the oil, tends to rotate in the
opposite direction to that of the impeller.
IT such
a tendency were not controlled the torque mul-
tiplication effect would be destroyed with ensuing
further loss of power.
In practice this does not
happen as stator rotation is prevented by a uni-
directional clutch.
As the speed differential between impeller and
turbine decreases, a variation occurs in the a...Tl.gle
at which the oil acts on stator vanes causing a re-
duction in torque multiplication.
Fig. 564 • Hydraulic torque converter unit.
When the speed differential between impeller and
turbine is down to a minimum the oil flow becomes
ahnost parallel to the torque converter centre line.
So the stator, no longer restrained by the uni-
directional clutch,
is
made to rotate in the same
direction as impeller and turbine. In this condition
there is no torque multiplication and the converter
acts as an ordinary fluid coupling.
IMPELLER
STATOR
TURBINE
Fig. 565 - Internal view of the hydraulic torque converter.
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