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WSM U15-3
8. Function
1) Outline
This compact, lightweight hydraulic pump has a
mechanism that provides for the performance of
two variable pumps. Yet it needs as small a space
as for just one conventional pump. This pump is
also equipped with a pilot gear pump.
The pump features a constant horsepower control
function for making most of the engine power. The
greater the pump load becomes, the lesser the
discharge rate becomes. As a result, when the
pump discharge pressures P
and the resultant force of the piston higher, the
swash plate exceeds the spring force and tilts
from the oscillating center of the oscillating pin. In
this way, the discharge rate can be kept low.
2) Function
An even number of pistons are used in this swash
plate variable piston pump. This is to produce the
performance of two same-capacity pumps in one
pump casing.
Conventional valve plates have one suction
groove and one discharge groove, as shown in
Fig. 4. The new system, on the other hand, is pro-
vided with two suction grooves and two discharge
grooves, as shown in Fig. 3. The discharge
grooves P
and P
1
2
inner sides, respectively. Every other piston cham-
ber of cylinder barrel gets open to either of these
discharge grooves in the valve plate. In other
words, both the inner and outer suction grooves
behave just the same way, whereas the inner and
outer discharge grooves work independently from
each other.
In this design with an even number of pistons, the
same number of pistons gets open outward and
inward of the valve plate. Because all the pistons
are of the same diameter, located in a same-pitch
circle and slide over the same swash plate, the
discharge rates of the discharge grooves P
P
are the same.
2
There is another advantage in employing just a
single swash plate. Even though the swash plates
tilting angle varies according to the variable con-
trol, the discharge rates of P
accordingly and equally.
and P
have risen
1
2
are located in the outer and
and P
ports change
1
2
Suction groove (1)
Suction groove (2)
Discharge groove
P
and opening
1
(b) Cylinder barrel
Fig. 3 Operating principle
Suction groove
and
1
(b) Cylinder barrel
Fig. 4 Conventional swash plate piston pump
II-60
Discharge groove P
2
Discharge groove P
(a) Valve plate
Discharge groove
P
and opening
2
Discharge groove
(a) Valve plate
1
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