Yanmar 4LHA-HTP Operation Manual page 397

Chapter 3 Fuel Injection Equipment
7. Timer Construction and Operation
Timer spring Servo valve
J
High pressure chamber'
Low pressure chamber
ig. 46 Servo valve timer operation: when
advance angle is " 0 "
Timer spring Servo valve
High pressure chamber
Low pressure chamber
Fig. 47 Servo valve timer operation: when
pump chamber pressure has increased
Timer spring Servo valve
High pressure chamber'
Low pressure chamber
i g . 48 Servo valve timer operation: stable
:
condition (balanced)
r
' L
1
Bushing
n
Bushing
When advance angle is "0"
(Low pump chamber pressure)
The pump chamber pressure, compared to the
timer spring force, is still low, and the servo
valve and the timer piston are pushed fully in
the retard direction by the timer spring. The
passage between the pump chamber (high
pressure side) and the timer's high pressure
chamber is closed, and the timer's high press-
ure chamber is connected to the timer's low
pressure chamber (fuel inlet side) by the servo
valve.
When pump chamber pressure has
increased
The pump chamber pressure has increased,
the pump chamber pressure exceeds the timer
spring set force, and the servo valve has been
moved to the left (Fig. 47).
The passage between the pump chamber and
the timer's high pressure chamber is open and
the pump chamber pressure acts on the tim-
er's high pressure chamber. Due to this the
timer piston is moved in the advance direction
(to the right in Fig. 47)
Stable condition (balanced)
The pump chamber pressure and the timer
spring force are balanced, and the servo valve
is stationary in a suitable position. The timer
piston moves until the bushing hole is closed
by the servo valve.
When the bushing hole is completely closed,
there will be no change in the timer's high
pressure chamber pressure and the timer pis-
ton will be stationary.
3-1-40
i 4LHA Series