Komatsu PC88MR-10 Shop Manual page 130

10 Structure and function
Main pump
It is possible to change the discharged volume by changing the swash plate angle.
There are 2 pump discharge ports and each pump can supply pressurized oil separately.
Operation
(PC88MR-C200-044-K-00-A)
Cylinder block (7) rotates together with shaft (1) and shoe (5) slides on plane (A).
Rocker cam (4) pivots on ball (12), and accordingly angle (a) between center line (X) of rocker cam (4) and
the axis of cylinder block (7) changes.
Angle (a) is called the swash plate angle.
While angle (a) is made between center line (X) of rocker cam (4) and the axis of cylinder block (7), plane
(A) works as a cam for shoe (5).
Piston (6) slides inside cylinder block (7) and a difference is made between volumes (E) and (F) in cylinder
block (7).
Oil in amount of (F) minus (E) goes in and out of each cylinder.
Oil is discharged while cylinder block (7) rotates and the volume of chamber (E) decreases.
Oil is sucked in when the volume of chamber (F) increases.
When center line (X) of rocker cam (4) matches the axis of cylinder block (7) (the swash plate angle is
zero), the difference between volumes (E) and (F) inside cylinder block (7) is zero.
Suction and discharge of pressurized oil is not performed in this stage. Namely pumping action is not
performed. (Actually, however, a zero swash plate angle never occurs.)
The pump discharged volume is in proportion to swash plate angle (a).
Cylinder block (7) has even numbered holes (10 holes). Each hole fits in every second slot (2 places) of
valve plate (8). Pressurized oil which is worth of 5 pistons is discharged to each pump discharge ports
(P1) and (P2).
10-52 PC88MR-10