Yanmar 4LHA-HTP Operation Manual page 395

Chapter 3 Fuel Injection Equipment
7. Timer Construction and Operation
7, Timer Construction and Operation
It is well-known that the relationship between
fuel injection timing and engine performance
(power, exhaust gas, engine vibration) is very
important.
If actual fuel injection timing differs only slight-
ly from the standard specified timing, then
diesel engine performance will be adversely
Standard Type Timer (Speed Timer)
Timer spring \
ig. 44 Speed timer construction and operation
:
As shown in Fig. 44, a timer spring is installed
in the low pressure chamber of the timer.
Pump chamber pressure, passing through the
timer piston orifice, acts on the high pressure
side of the timer piston.
This timer piston orifice acts to prevent timer
piston pulsation generated by fuel pressure
fluctuations.
Timer piston movement results in the pin mov-
ing the roller holder assembly in the direction
Drive shaft
Roller holder assembly
Roller
Timer piston
\ Pin_ pressure c h a m b e r /
L o w
3-1-38
effected.
Because the ignition lag arising during diesel
engine combustion increases as engine speed
increases, it is necessary to compensate for
this ignition lag by advancing injection timing.
To do this, a timer is installed at the bottom of
the injection pump.
Orifice
High pressure chamber
opposite to injection pump rotation.
When pump chamber pressure exceeds the
set force of the timer spring due to an increase
in pump speed, the timer piston compresses
the timer spring and turns the roller holder
assembly in the direction opposite to that of
injection pump rotation. With this movement
the cam disk's face cams contactthe roller hold-
er's rollers more quickly and injection timing is
advanced.
, 4LHA Series