Maeda MK0003, Service Manual, Page: 82 / 348

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5.4 OPERATING PRINCIPLES
1. Overview
This hydraulic pump consists of such a mechanism that allows this
compact and light-weight pump to perform pumping actions equivalent to
two pumps while occupying a space required for a single pump only.
To utilize the engine power effectively, this pump has been designed to
have a fixed horsepower control characteristic for suppressing the
discharge rate in commensurate with the increase of pump load.
Accordingly, this pump is equipped with a mechanism to decrease its
discharge rate in such a way that when pump discharge pressures P1 and
P2 increase to raise the resultant force in combination with the piston
force to allow the swash plate to overcome the spring tension so that it tilts
around the rocking center of the rocking pin.
2. Structure and actions
In a swash plate type variable piston pump, in order for the pump to be
equipped with the pumping function of two pumps each having an equal
capacity that are accommodated in the pump case for a single pump, an
even number of pistons are incorporated.
While a conventional valve plate has, as shown in the bottom right figure,
a single port each for the intake and discharge is provided, this system
comprises a pair of intake port and discharge port each on the outside
(P1) and the inside (P2).
Every other pump box in row of the cylinder barrel opens either toward the
outside (P1) or inside (P2).
While the intake occurs in similar way for both inside and outside, the
discharge of inside and outside performs different delivery actions.
Since this system has an even number of pistons, each having the same
diameter, being mounted on the common pitch circle with others, and
slides on the common swash plate, the discharge rates from outside (P1)
and inside (P2) are equal.
Further, since the sole swash plate allows the discharge rate of both P1
and P2 plates to vary equally with the variation of tilt angle of swash plate
in its variable control action, no difference in discharge rate is brought
about.
Conventional swash plate type
piston pump
Operating principle
Intake port
Discharge port P
1
Discharge port P
2
(a) Valve plate
Discharge port P
1
and opening
Discharge port P
2
and opening
Intake port
Discharge port
(a) Valve plate
(b) Cylinder barrel
Engine pump
Item number: 353S57600000
Electric pump
Item number: 329S33800001
Discharge pressure P1 = P2 (MPa)
Discharge pressure P1 = P2 (MPa)
Di
sc
harge ra
te
q1 =
q2 (
cc/
rev
)
Di
sc
harge ra
te
q1 =
q2 (
cc/
rev
)
(b) Cylinder barrel