TM 5-3805-258-24-1
POWER TRAIN
TRANSMISSION HYDRAULIC CONTROLS
S Y S T E M S O P E R A T I O N
When the No. 6 clutch is full of oil, the pressure in
the speed clutch circuit starts to increase. The in-
crease is felt in the slug chamber of modulation relief
valve (13) and the chamber at the left end of pressure
differential valve (14).
The oil to pressure differential valve (14) starts to
fill the chamber at the left end of the valve spool,
through the small orifice.
When the pressure in the No. 6 clutch is approxi-
mately 380 kPa (55 psi), pressure differential valve
(14) starts to move to the right. The movement of the
valve spool opens No. 2 clutch (2) to pump oil. It also
closes a passage from the chamber behind load piston
(11) to the reservoir.
When the No. 2 clutch is full of oil, the pressure in
the direction clutch circuit increases. The increase is
felt in the spring chamber of pressure differential
valve (14). The pressure in the spring chamber and
the force of the springs moves the valve to the left
against the speed clutch pressure at the left end of the
valve spool.
As the pressure in the speed clutch circuit in-
creases, the pressure in the chamber at the left end of
pressure differential valve (14) increases.
The increase in pressure moves the valve spool to
the right against the force of the springs. This opens
No. 2 clutch (20) to pump oil.
As the pressure in the No. 2 clutch increases, the
pressure in the spring chamber of valve (14) in-
creases. The increased pressure in the spring
chamber and the force of the springs, moves the valve
spool to the left.
This stops the flow of pump oil to the No. 2 clutch.
This function continues until the pressure in the No.
2 clutch is at its maximum. At this time, the pressure
in the spring chamber and the force of the springs
moves the valve spool to the left, until the flow of oil
to the clutch is stopped. Now the valve moves to the
right and left (meters) to keep a constant pressure in
the No. 2 clutch. This pressure is approximately 380
kPa (55 psi) less than the pressure in the speed
clutch. This difference is determined by the force of
the springs of the pressure differential valve.
Pump oil also goes through flow control orifice
(22) to ratio valve (16) for the torque converter. It
goes through an orifice in the valve spool and fills the
slug chamber.
Oil, from the pump, also goes to modulation relief
valve (13). It fills the chamber around the valve
spool. The oil goes through an orifice in the valve
spool and opens the poppet valve at the left end of the
valve spool. This lets oil fill the slug chamber at the
left end of the valve spool.
The function of modulation relief valve (13) and
load piston (11), is to control the rate of the pressure
increase in the speed clutch circuit as follows:
As the pressure in the No. 6 clutch increases,
modulation relief valve (13) moves to the right and
load piston (11) moves to the left. The orifice in the
supply passage to the load piston, causes the oil to go
to the area behind the load piston at a specific rate.
As the modulation relief valve moves to the right and
the load piston moves to the left, the pressure in No. 6
clutch (8) increases gradually. This gradual increase
in pressure is known as modulation.
The load piston moves more to the left against the
force of its springs, until the area behind the load
piston is open to a drain passage. At this time, modu-
lation stops. As the oil goes out the drain passage, oil
continues to fill the area behind the load piston. This
keeps the load piston in this position. After the pres-
sures in the clutches are at their maximum, modula-
tion relief valve (13) lets the extra oil go to the torque
converter.
The operation of the load piston and the modula-
tion relief valve keeps the system pressure at a con-
stant rate.
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