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 TM 9-8000
(2) The majority of the heat generated
considerations are the most common in the modulation
within the transmission originates in the torque converter.
of line pressure:
It is therefore logical that the oil, after it circulates
through the torque converter, should pass directly to the
(1) Under normal conditions the regulator
cooler. This arrangement effectively isolates the
valve functions in an unmodulated mode as described in
transmission from this major heat source.
paragraph 23-12d. The normal line pressure is sufficient
to operate the transmission and still maintain a smooth
(3) One of the major reasons for lubrication
shifting quality.
within the transmission is to cool the localized areas
(2) During periods of heavy acceleration,
where heat is generated between moving parts. For this
additional line pressure is required to hold the clutches
reason, the lubrication of the transmission is handled by
and brake bands tight enough to transmit the increased
the oil after it is passed through the cooler.
engine torque. This is particularly important during the
initial application of the elements during shift changes to
b. Oil Supply. The supply of oil for the converter
minimize slip- page during engagement, which would
cause burning and premature wear of friction facings.
feed circuit passes through the regulator valve (para 23-
(3) Operation in reverse places additional
12c). The regulator valve will cut off this oil supply if line
torque requirements on the clutch or brake band that
pressure drops below an operating minimum. Under
holds the element of the planetary gearset. For this
normal circumstances, however, the oil pressure cutoff
reason, the line pressure is increased at least twofold
will last no more than a few seconds and will not affect
during operation in reverse.
transmission operation. During periods of engine
shutdown, the regulator valve also prevents the torque
(4) Any condition that causes a drop below
converter from draining back to the oil sump. This
line pressure will cause the regulator valve to temporarily
condition otherwise would require the pump to refill the
cut off the oil supply to the torque converter. A common
converter at each engine restart, creating an
occurrence of this condition is the shifting to reverse,
unacceptable delay in operation.
which temporarily increases the requirements placed on
c. Regulation of Circuit Oil Pressure. The
the pump while the engine is idling and the pump is
turning slowly.
regulator valve supplies the converter feed circuit at
regulated line pressure. The converter feed circuit,
Modulation of the line pressure is a fairly simple matter.
however, requires a constant pressure that is
Pressure signals are fed back into the regulator valve to
independent of transmission operating modes and
assist the spring. The result is that the line pressure
generally lower than line pressure. The converter control
must increase to overcome the higher pressure before
valve controls the pressure for the converter feed circuit.
the suction feedback port is uncovered. The feedback
The converter control valve is a balance-type spool valve
signals come from the manual valve and the throttle
whose operating principles are much like that of the
modulation system.
regulator valve (para 23-12c). When operating pressure
is low, the calibrated spring pushes the spool to the left,
23-13. Converter Feed Circuit (Fig. 23-12).
opening the delivery port. As pressure reaches the
desired level, the spool is forced to the right, blocking the
a. General The torque converter supply, cooling,
delivery port. A metered orifice is usually provided
between the torque converter and the cooler to control
and lubrication tasks are all handled by the converter
the volume of oil flow through the system.
feed circuit of the hydraulic system. This integration is a
logical one for the following reasons:
d. Oil Flow Through the Torque Converter. Oil
(1) All phases of this circuit will function
flow through the converter, in most cases, is as follows:
within approximately the same operating pressure range.
23-14
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