Hydraulic Pump - Variable Flow
Operation
The pump is a variable displacement axial piston type.
Displacement of oil is achieved by the continuous operation
of nine pistons. Pump fluid output is controlled by a tilting
cam (swashplate), the angle of which is regulated to ensure
that only the amount of fluid necessary to satisfy load
conditions is delivered. If a load condition is such that no
flow is required, only sufficient fluid for cooling and
lubrication is provided.
Main components of pump P are a cylinder barrel 1 splined
to a drive shaft 2 which is held against a kidney plate 3.
Contained in the cylinder barrel are the axial pistons 4, each
having an articulated shoe that is in held contact with the
swashplate 5 by an attachment plate 6. The tilting action of
the swashplate is exercised by a stroking piston 7 and a
control piston 8, the latter fed by servo pressure. Fitted to
the pump exterior is the valve block 9 housing the
pressure/flow regulators that provide servo control.
Rotation of the cylinder barrel causes linear movement of the
axial pistons and fluid from the suction port is drawn into the
pump through the kidney plate to fill a developing vacuum
behind the piston. As the cylinder barrel rotates the fluid is
carried from an elongated suction kidney to an elongated
pressure kidney where linear movement starts to return the
piston into the cylinder barrel. Fluid is forced from the pump
through the pressure port.
The stroke length of the pistons and consequently the output
of fluid is directly related to the swashplate angle. The
swashplate is normally held in its maximum displacement
angle by the stroking piston spring and system pressure
inside the stroking piston.
Component Key:
P Pump
1 Cylinder Barrel
2 Drive Shaft
3 Kidney Plate
4 Axial Piston
5 Swashplate
6 Shoe Plate
7 Stroking Piston
8 Control Piston
9 Pressure/Flow Compensator Valve
5 - 3
Section E
Hydraulics
9803/3280
Section E
5 - 3
Issue 1
Circuit Descriptions
1
S271440
7 3
5
2
4
6
8
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