Kubota M108S Workshop Manual page 109

M108S, WSM
SCV (Suction Control Valve)
The SCV (8) uses a linear solenoid type electromagnetic valve to control the time for which current is applied from
the ECU to the SCV (duty ratio control), and in this way controls the fuel flow quantity supplied to the high-pressure
plunger (4). When current flows through the SCV (8), the internal armature moves according to the duty ratio. The
fuel flow quantity changes in accordance with the armature operation, and is controlled in accordance with the size of
the cylinder fuel passage opening. As a result, the intake fuel quantity is controlled to achieve the target rail pressure
and the supply pump actuation load decreases.
1) Normally Open Type
When the solenoid is not energized, the return spring pushes the cylinder (7), completely opening the fuel passage
and supplying fuel to the plungers (4). (Full quantity intake and full quantity discharge.)
When the solenoid is energized, the armature presses the cylinder (7), which compresses the return spring and
closes the fuel passage.
The solenoid ON/OFF is actuated by duty ratio control. Fuel is supplied in an amount corresponding to the open
surface area of the passage, which depends on the duty ratio, and then is discharged by the plungers (4).
2) Duty Ratio Control
The engine ECU outputs sawtooth wave signals with a constant frequency. The value of the current (2) is the
effective (average) value of these signals (3). As the effective value increases, the valve opening decreases, and as
the effective value decreases, the valve opening increases.
3) When the SCV Energized Duration (Duty ON Time) is Short
When the SCV energized duration is short, the average current flowing through the solenoid becomes small, the
cylinder (7) is returned by the force of the spring, and the valve opening becomes large. As a result, the fuel suction
quantity increases.
4) When the SCV Energized Duration (Duty ON Time) is Long
When the SCV energized duration is long, the average current flowing through the solenoid becomes large, the
cylinder (7) is pressed out, and the valve opening becomes small. As a result, the fuel suction quantity decreases.
1-M14
ENGINE
(1) Actuating Voltage
(2) Current
(3) Average Current Difference
(4) Plunger
(5) Feed Pump
(6) Regulating Valve
(7) Cylinder
(8) SCV
A : Low Suction Quantity
B : High Suction Quantity
C : ON
D : OFF
W1022290
KiSC issued 06, 2007 A