Hitachi ZW180, Technical Manual

Page: 196 / 374

COMPONENT OPERATION / Pump Device
T3-1-8
Control by Pump Control Pressure
Decreasing Flow
1. When the control lever stroke is reduced,
pressure difference (difference between pressure
Pi1 and Pi2) arising at the flow control valve in the
control valve is larger.
2. Pump control pressure Pi1 pushes spool 1 (3)
and spool 1 (3) moves toward the arrow.
3. Therefore, primary pilot pressure Pg is led to
servo piston 1 (10).
4. As there are two servo pistons 1 (10), swash plate
(11) tilts toward the flow decreasing direction.
5. Movement of swash plate (11) is transmitted to
sleeve 1 (2) through feedback lever link (13).
Sleeve 1 (2) moves toward the movement of
spool 1 (3).
6. Pilot primary pressure Pg to servo piston 1 (10) is
blocked when sleeve 1 (2) has moved the same
distance as spool 1 (3). Therefore, servo piston 1
(10) stops and the flow decrease is completed.
T4GB-03-01-006
1 - Spring 10 - Servo Piston 1
2 - Sleeve 1 11 - Swash Plate
3 - Spool 1 12 - Servo Piston 2
4 - Piston 13 - Feedback Lever Link
Pd1 - Own Pump Pressure Pi1 - Pump Control
Pressure 1
ST - Torque Control
Pressure Pi2 - Pump Control
Pressure 2
T - Returning to Hydraulic
Oil Tank Pg - Primary Pilot Pressure
(From Pilot Pump)
Flow (Q)
Pump Control Pressure (Pi1-Pi2)
0
3 2 1
4
Pi1 T
Air
Vent
Pi2
Pg
T
ST
Pd1
T
Increase
Decrease
Displacement Angle
10 12
13