Principle Of Operation; Full Pump Volume; Half Pump Volume; Neutral Position - Komatsu 930E-2 Shop Manual

PRINCIPLE OF OPERATION

Full Pump Volume:

Control piston (1, Figure 4-11) controls the angle of the
swashblock (4). When control piston moves to the full
right position, the pump is at maximum pumping ca-
pacity.
The driveshaft turns the splined housing (2) which
contains the pumping pistons (3). When the housing is
rotated, the pistons move in and out of their bores and
the piston shoes "ride" against the angled swashblock
(4).
As the cylinder rotates, the individual piston bores are
connected, alternately to the left (port "A") and right
(port "B") crescent shaped ports in the valve plate.
While connected to left side (suction) port "A", each
piston moves outward, drawing fluid from port "A" into
the piston bore until its outermost stoke is reached. At
that point the piston bore passes from the left crescent
port to the right crescent port.
While rotating across the right side crescent, each
piston moves downward on the angled swashblock
face. Thus, each piston is forced inward. Each piston
displaces fluid through the right side crescent to port
"B" until it's innermost stroke is reached. At that point,
the piston bore again passes from the right to the left
side crescent and the operating cycle is repeated.

Half Pump Volume:

Figure 4-12 shows that the position of the control piston
(1) is near the center of its travel. The swashblock is not
angled as steep as before, and therefore the pistons
have a shorter stroke. As the piston stroke gets shorter,
the pump output also decreases.

Neutral Position:

Neutral position (Figure 4-13) results when the control
piston (1) centers the swashblock (4). The swashblock
angle is now zero and swashblock face is now parallel
to cylinder face. Therefore, no inward or outward mo-
tion of the pump pistons exists as piston shoes rotate
around the swashblock face. The lack of inward and
outward motion results in no fluid being displaced from
the piston bores to the crescents in the valve plate and
subsequently no delivery from pump ports.
L4-18
FIGURE 4-11. PUMP AT FULL VOLUME
1. Control Piston
2. Housing
FIGURE 4-12. PUMP AT HALF VOLUME
1. Control Piston
2. Housing
FIGURE 4-13. PUMP IN NEUTRAL POSITION
1. Control Piston
2. Housing
Steering Circuit
3. Piston
4. Swashblock
3. Piston
4. Swashblock
3. Piston
4. Swashblock
L04031