Komatsu Galeo PC800-8 Shop Manual page 140

SEN00383-03
2. Servo piston
Outline
• Port (PA) pressure or port (PR) pressure, which-
ever is higher, is applied to port (PH) by the shut-
tle valve.
• Relation of pressure receiving area (A) of cham-
ber (a) and pressure receiving area (B) of cham-
ber (b) is expressed as (A) C [2 × (B)].
• Pressure of port (PH) is constantly applied to
chamber (b).
PA : Main pump discharge pressure
PR : Pilot basic pressure
PH : PA or PR pressure whichever is higher
Operation of VC valve
• The command current from the pump controller
is conducted to EPC solenoid (E1).
• This command current reduces the control basic
pressure applied to EPC valve (2).
• EPC valve (2) outputs pilot pressure according to
the command current.
• The pilot pressure goes to chamber (se1)
through port (SE1).
• Sleeve (4) of VC valve (1) is maintained at a po-
sition where the EPC valve (2) pilot pressure and
the spring (5) force are balanced.
• The pump controller controls magnitude of the
command current sent to EPC valve (2).
18
10 Structure, function and maintenance standard
Operation of servo piston
(Movement of swash plate to intermediate point
and mechanism of stopping servo piston)
• When sleeve (4) moves upward, port (PH) is dis-
connected from port (PS) and port (PS) and port
(TD) are connected.
• Since chamber (a) is connected to drain port
(TD), servo piston (3) is moved to the right by
(PH) pressure.
• When servo piston (3) moves to the right, cam
(6) which is coupled with servo piston (3) moves
to the right.
• Spool of VC valve (1) moves upward.
• If the spool of VC valve (1) moves up, port (PS)
is connected to port (PD) through the orifice part
and port (PS) is also connected to port (PH)
through the orifice part.
• Pressure (PS) in chamber (a) is reduced to a
middle pressure between pressure (PH) in
chamber (b) and drain pressure (TD), then servo
piston (3) is stopped by the orifice of (PS : PH =
1 : 2).
• The position of the servo piston is decided by the
EPC command current (excluding the effect of
hysteresis).
PC800, 850-8