Hitachi ZW180, Technical Manual

Page: 344 / 374

COMPONENT OPERATION / Drive Unit
T3-9-38
PROPORTIONAL SOLENOID VALVE
The proportional solenoid valve is used as a pilot valve
for the clutch oil pressure, and supplies pressure oil to
the modulation spool by receiving the electric signal
from the controller and by increasing or decreasing oil
pressure.
Operation
•
In Neutral: Spool (1) is pushed rightward by spring
(2). Output port S is connected to tank port T.
•
When Excited: Solenoid (3) pushes spool (1)
leftward with a force in proportion to the electric
current flowing through solenoid (3). Pilot
pressure oil flows to output port S from port P, and
the pressure at output port S increases.
This pressure at output port S acts on step part a
of spool (1). A force to push spool (1) rightward
occurs due to the difference of pressure-receiving
area at step part a. When the pressure at output
port S increases, and the force to push spool (1)
rightward becomes larger than the force to push
spool (1) leftward by solenoid (3), spool (1) is
returned to the right, the passage between output
port S and port P is closed, and the pressure at
output port S stops increasing.