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IDROCONVERT TRANSMISSION
349
OPERATION
OF THE HYDRAULIC SYSTEM
Clutch Engaged
(see fig. 566).
Oil is drawn by gear pump (6) from oil reservoir
(9) via an interconnecting suction duct.
Oil under
pressure is then fed from the pump to pressure
regulating valve (6) where a maximwn pressure of
71-85 psi
(5~6 kg/cm~)
is constantly maintained, ex-
cess oil being exhausted to reservoir (9).
A second oil feed from the pump reaches plunger
valve (8) which, when clutch is engaged directs oil
pressure into the hollow converter output shaft.
From the hollow shaft oil is fed to the pressure
plate, so as to exert pressure in the same direction
as that of the disc spring
I
and to the torque converter
where a build-up in pressure occurs.
From the
converter, oil passes through the bell housing and
returns to reservoir via the annular chamber formed
around the output shaft.
This interconnection between torque converter
and bell housing is designed to permit oil circulation
but must at all times prevent the formation of a
back pressure on the pressure plate - against the
disc spring - to avoid any risk of clutch disen-
gagement. To avoid any such risk, interconnection
is achieved by a small orifice allowing a limited
amount of oil to pass through.
Clutch Disengaged
(see fig. 568).
In
this position oil reaches pump (5), pressure
regulating valve (6) and plunger valve (8) in the
same manner as that shown for clutch engaged.
However, the solenoid (7) operated plunger valve
is moved to the rear causing the oil flow to be
reversed, i.e., from plunger valve through the
annular chamber over output shaft to the bell hous-
ing where, by acting on the pressure plate, causes
the clutch to disengage thus discontinuing torque
transfer.
Torque converter pressure will subside as the
return line is connected to reservoir via output
shaft and plunger valve.
Although oil will pass from bell housing to torque
converter through the orifice, the oil pump suc-
ceeds in compensating this loss to prevent any
pressure drop within the bell housing.
OPERATION OF RELEASE
MECHANISM (CLUTCH)
The release mechanism, situated between torque
converter and engine flywheel, is a wet clutch (oil
bath) of the bell housing type.
The bell housing is fixed to the turbine; the
driven plate, designed to ensure a positive trans-
mission, is pressed between bell housing and pres-
sure plate, though free to slide within the bell
housing itseU.
Oil pressure may be applied from B or A (see
fig. 569).
Oil pressure from B causes the pres-
sure plate to exert a thrust on the driven plate,
thereby coupling torque converter to gearbox,
whereas oil pressure from A will cause the pres-
sure plate to move away from the driven plate,
thus discontinuing torque transfer.
Also acting in the direction of arrow B is a disc
type spring which is pre-loaded to 14.5-21.7 ft.llis
(2 to 3 kgm), this value being sufficient to push
(or tow) start the vehicle as in this condition there
is no oil pressure.
Oil pressure acts from A or B according to the
position of the solenoid operated plunger valve;
moreover, oil pressure is not modulated, Le., it is
either absent or acting to the maximum value per-
mitted by the pressure regulating valve (71 to
85 psi = 5 to 6 kg/em').
During disengagement, oil pressure acting in A
flows from 0 to chamber C through a passage in
the driven plate.
Oil flow through this passage is
controlled by an orifice and a valve which may
take two positions according to whether the car is
pulling or coasting.
This double positioning is
automatic and governed by the amount of backlash
existing between the driven plate and hub splines.
The orifice is uncovered by the valve during
normal driving and closed when coasting.
With an uncovered orifice, Le. under pull, a
considerable amount of oil passes between cham-
bers C and 0 to obtain rapid clutch engagement
and disengagement.
When the orifice is closed, i.e. during coasting,
oil pressure will overcome the resistance of the
Fig. 567 - Clutch driven plate.
1. Driven plate.• 2. Partialising valve. - 3. Friction lining.
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