Shibaura ST318, Руководство по ремонту

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4) Operation
(1) Variable type pump
T510
1. Shaft (input)
2. Swash plate
3. Cylinder block
4. Piston
5. Valve port plate
T511
Above figure shows the rotary parts of a swash plate type axial piston pump. Nine pistons are incorporated in the
cylinder block. The shaft is interconnected with the engine and when the shaft rotates, the cylinder block rotates at the
same time (the swash plate does not rotate). When the HST pedal is at the neutral position, the shaft axis and the swash
plate are perpendicularly positioned. At this time, nothing is sucked or discharged because the blank A and B of the
cylinder of the cylinder block have the same volume and therefore pumping action is not taken place.
T512
1. Swash plate inclination angle
2. Valve port plate
T513
When the HST pedal is depressed in the forward direction, the swash plate is inclined and proportion of the volume of A
and B is changed to A > B. When the shaft is rotated at this condition in the arrow mark direction, the piston moves
from A to B for discharge action in the angle 180°. When the piston moves from B to A, suction step takes place
through the angle of 180°. Therefore, the crescent-shaped port Ps of the valve port plate is the suction port and another
crescent-shaped port Pd is the discharge port.
With the increase of the depressing distance of the HST pedal (swash plate inclination angle), discharge volume and
speed increase. By stepping the pedal in the opposing direction, the port Ps becomes the discharge port and Pd the
suction port.