Theory of Operation
inclined thrust plate. To reverse rotation, oil flow is
The rotating group consists of cylinder block (H), nine
reversed. A small amount of supply oil flows through
pistons (I). The cylinder block is connected to the
the center of each piston to the ball joint and the face
output shaft (M). Each piston is connected to a slipper
of slippers for lubrication.
by a ball joint. Slippers slide on the inclined thrust
plate (K) forcing the cylinder block to turn. The retainer
The motor is internally lubricated from leakage inside
(J) holds the slippers on the thrust plate and the
the motor. Lubrication oil is routed up through the
retainer itself is held against the slippers by force pins
cover to the hydraulic oil tank.
(P) and springs (Q).
The swing motor park brake is spring applied and
Oil from swing control valve is routed through cover
hydraulically released. The plates in the brake pack
(A), valve plate (B), and port in the cylinder block to
are connected to the housing. The disks are connected
to and rotate with the cylinder block. When the pilot
controllers are in neutral, pilot oil is blocked from the
In operation, high pressure supply oil enters the
piston by the swing park brake release valve (R). The
cylinder bores through ports forcing pistons down
brake springs (E) squeeze the plates and disks
against the inclined thrust plate. The slippers slide
together to prevent the upperstructure from swinging.
down the inclined thrust plate causing the rotating
The swing park brake is release when the swing,
group to turn. The output shaft is turned by the
boom, arm, or bucket function is actuated. (See Swing
cylinder block. Swing speed varies depending on the
Motor Park Brake Release Valve Operation in this
amount of supply oil delivered by the pump through
the control valve.
During the second half of motor's revolution, low
pressure oil is discharged as pistons slide back up the