Komatsu PC20R-8 Shop Manual page 40

1. Operation
. This pump has the functions of load response con-
trol and constant horsepower control.
There are nine pistons (2) assembled inside cylin-
der block (1), and the face is in contact with valve
plate (3).
Suction port A and discharge port B are provided in
valve plate (3).
In this structure, swash plate (4) is secured to the
body at a certain angle, and pistons (2) rotate along
swash plate (4).
. By rotating shaft (5), cylinder block (1) rotates, and
pistons (2) assembled inside cylinder block (1)
move in a reciprocal motion following swash plate
(4). This movement performs the suction and dis-
charge action of the pump.
. Each of the nine pistons (2) performs one suction
and discharge stroke for each rotation of cylinder
block (1), so the rotation of shaft (5) provides contin-
uous suction and discharge.
The volume of the stroke of piston (2) depends on
the angle of swash plate (4), so by changing the an-
gle of swash plate (4) it is possible to change the
amount of the discharge flow.
2. Constant horsepower control
. Rocker pin (6) is assembled to swash plate (4), and
it is installed to the body to make it possible to
change the swash plate angle. In addition, swash
plate (4) is equipped with spring (7) and cylinder
block piston (2), which acts in the opposite way to
spring (7), and the discharge pressure of P1 acts
on piston (2).
. When the discharge pressure P1 is lower than the
set value of spring (7), the angle of swash plate (4)
is held at the maximum position by spring (7).
When the discharge pressure becomes greater
than the set value of spring (7), the angle of swash
plate (4) is made smaller by total piston force F1 x a
and is held at the position where the discharge
pressure is balanced with the force of the spring.
10-22
2
4
Suction
stroke
5 4 2
2
4
6
SPRING FORCE
a
1
A
B
Discharge
Suction
3
Discharge
stroke
RKP01061
1 3
RKP00080
7
P
1
F
1
RKP00082
PC20R-8 PC27R-8