4
-1500/-1700 IHT
HYDRAULIC SCHEMATIC
Figures 4 and 5 provide illustrations of the hy-
drau lic oil circuit. The oil supply for the hy drau lic
sys tem of the IHT is also utilized for the lu bri -
ca tion of the planetary differential drive gears.
The input shaft and pump cylinder block are
turned in one direction only by the engine/drive
belt/pul ley com bi na tion. Output of the oil
fl
ow
is con trolled by the direction and amount that
the swashplate is angled. As the pump pistons
com press they force the oil to
fl
ow through one
of two pas sage ways (forward or reverse) in
the center section (or valve body) to the motor
cyl in der block and motor shaft. Since the mo-
tor has a
fi
xed dis place ment angle it is forced
to turn with the
fl
ow of oil. As the angle of the
swashplate is in creased the amount of oil being
pumped will increase and cause a higher RPM
output of the motor. Re vers ing the angle of the
pump swashplate will re verse the direction of
oil
fl
ow.
During the operation of the transaxle,
fl
uid
is “lost” from the hydraulic loop through leak
paths de signed into the product for lubrication
pur pos es (around pistons, under the rotating
cylinder blocks, etc.). This “lost”
fl
uid returns
Figure 4. -1500 Hydraulic Flow Illustration
to the trans mis sion housing and must be made
up in the loop. A charge pump is included on
the IHT to supply this makeup
fl
ow. The make
up
fl
ow is con trolled (or directed) by the check
valves. Each check valve will either be held
opened or closed (de pend ing upon the direction
of vehicle op er a tion) by the system operating
pressure (closed) or by charge pressure (open)
from the charge pump.
The charge pump maintains a continuous
fl
ow
of oil as long as the input shaft is turning. All of
the oil being pulled into the charge pump
fi
rst
must pass through an internal
fi
lter. Any oil not
needed by the transmission for make up
fl
ow
is dis charged through the charge relief valve.
The charge relief valve maintains the charge
pres sure.
The motor cylinder block mounts onto the
splined motor shaft which drives the planetary
dif fer en tial gear/dif fer en tial as sem bly.
The bypass feature in the IHT has a me chan i cal
le ver which lifts the motor block off of the center
section running surface, allowing any oil
fl
owing
from the pump block to be dis charged into the
housing without turning the mo tor.
