Section E - Hydraulics
Operation Description
Transmission Pump Operation
E - 13 E - 13
9803-9450-2
Transmission Pump Operation
The transmission pump consists of two pump units, one for
each drive motor, mounted in tandem on a common drive
shaft which is driven by the engine. The illustration below
shows one typical pump unit. Each unit consists of a series
of parallel axial pistons mounted in a barrel which is rotated
by the engine driven shaft. The pistons are operated by a
tiltable swashplate. The stroke of the pistons and therefore
the displacement of the pump is varied by increasing or
decreasing the angle of the swashplate. Also by reversing
the angle of the swashplate the flow of oil from the pump is
reversed which reverses the rotation of the appropriate
drive motor.
Slipper pads are fitted to the ball ends of the pistons and
these slide on the surface of the swashplate, adjusting to
the angle of the surface. The end face of the cylinder barrel
runs against a valve plate which directs the oil flow into and
out of the bores as the barrel rotates.
The angle of the swashplate is varied by means of a
hydraulic servo cylinder which is operated by the
machine’s control joystick. Thus the pumps’ displacement
is varied from full displacement in one direction to full
displacement in the opposite direction.
The components of the pump are contained within the
pump casing and are fully submerged in oil which is
supplied by the charge circuit. Charge flow is required to
make up internal leakage, maintain positive pressure in the
main circuit, provide flow for cooling and for operation of
the pump control system.
Charge Pressure
The charge pressure (and hence the drive system servo
pressure) is controlled by the charge pump which is set to
a predetermined limit. Oil is supplied by the machines gear
pump (P3).
High Pressure Relief Valves
There are four of these valves, one for each of the output
ports of the pump. They provide protection against high
transient pressures in the motor circuits.
Table 7. Key
A Piston Pa High Pressure Relief
Valve
B Swashplate Pb High Pressure Relief
Valve
C Servo Cylinder Pc High Pressure Relief
Valve
D Valve Plate Pd High Pressure Relief
Valve
M1 To Left Hand Motor T To Ta nk
M2 To Right Hand Motor x From Joystick
P From Charge Pump y From Joystick
P1 Pump Unit
P2 Pump Unit
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