PROPEL TRANSMISSION
SUBSECTION 9B
Since either of the main hydraulic lines can be high pres-
direction, from the pump to the motor, then back to the
sure, two charge check valves are used to direct the charge
pump in the closed circuit (see Figure 9B-10). The position
supply into the low pressure line. The check valves are con-
of the pump swash plate determines which Iine is high
pressure as well as the direction of flow.
tained in the pump end cap beneath the charge pump
PUMPS
The charge pump draws the fluid from the reservoir An in-
let filter insures that only clean fluid enters the system
The variable displacement pumps use a tiltable swash plate
This filter has a 10 micron rating and does not have a by-
to vary displacement (output flow). The swash plate is
pass.
mounted on trunnion bearings and IS connected to hydrau-
RELIEF VALVES
lic control (servo) cylinders. The control directs fluid to and
from the servo cylinders causing the swash plate to tilt and
Two system relief valves are provided for overload protec-
change displacement of the pump. The swash plate can be
tion on each pump and motor and are located in the mani-
tilted in either direction from 0 angle to provide pump flow
fold assembly mounted on the motor (see Figure 9B-3).
in either direction.
These relief valves are factory set and are of the pilot oper-
ated, cartridge type The first two digits of the pressure
Since the angle of the swash plate causes the pistons to
setting are stamped on the end of the relief valve cartridge.
stroke in and out of the cylinder block bores as it is rotated,
changing this angle varies the piston stroke, and therefore,
the amount of fluid being displaced (pumped) to the motor.
SYSTEM PRESSURE GAUGE PORT
This results in a change in the output speed of the motor
IS LOCATED ON SIDE OPPOSITE THE
Tilting the swash plate in the opposite direction reverses
CORRESPONDING HIGH PRESSURE
RELIEF VALVE CARTRIDGE
fluid flow to the motor and its direction of rotation. Since
each servo control cylinder is spring loaded, loss of control
pressure or charge pressure will cause the swash plate to
return to the neutral position.
CHARGE SYSTEM
A fixed displacement (gear type) charge pump is mounted
on each variable displacement pump and driven off the
main pump shaft (see Figure 9B-2). The charge pump sup-
plies cool fluid to the system, keeps the systern charged and
supplies fluid to operate the control system. Charge pres-
sure, with the purnp in neutral (0 flow), is Iimited by a relief
valve which is normally factory set for 190-210 psi (above
case pressure).
Figure 9B-3 Propel Motor
The relief valves are factory set and should not
be tampered with except to replace the entire
cartridge.
COOLING CIRCUIT
A shuttle valve and second charge relief valve are included
in the motor manifold assembly The shuttle valve provides
a circuit between the low pressure hydraulic line of the
Figure 9B-2. Propel Pump
9B-2
