Chapter 3 Fuel Injection Equipment
5. Injection Pump Construction and Operation
i
4LHA Series
i
This
effective stroke is the plunger stroke from
the plunger's
cut-off
port
to the control
sleeve's
end-face during the delivery stroke, af-
ter the plunger barrel's inlet
port
and the plung-
er's
inlet slit are
closed.
It is proportional to the fuel injection quantity.
As
can be seen in Fig. 15, control sleeve travel
to the
left
decreases the effective stroke, and
conversely
control sleeve travel to the
right
in-
creases
the effective stroke and the fuel injec-
tion
quantity.
Although the beginning-of-injection position is
constant, end-of-injection varies according to
the control sleeve position. The control sleeve
position is determined by the governor.
Delivery
Valve
and
Damping
Valve
When
the increased fuel oil pressure resulting
from the plunger's compression stroke has
overcome
the delivery valve spring's set force
and
the injection pipe's in-line residual pres-
sure,
the delivery valve opens and fuel oil is
delivered to the nozzle holder and the
nozzle.
(Fig.
16-A)
Then,
when nozzle opening pressure is
reached,
initial injection
into
the engine cylinder
occurs.
When
the plunger has
lifted
and injection has
ended,
the pressure in the pressure chamber
suddenly
decreases and the delivery valve
spring
closes
the delivery valve. In order to pre-
vent delayed injection it is necessary to main-
tain the residual pressure of the fuel oil in the
injection pipe for the next injection. The deliv-
ery valve functions to prevent reverse fuel oil
flow during the plunger's suction stroke.
Delivery
valve spring
Delivery
valve
Delivery
valve seat
.ri—IR, Seating portion
Piston
J
- Retraction
. stroke
Fig.
16 Delivery valve operation
In the centre of the delivery valve is a piston.
After injection has ended and the piston edge
is
contacting the top of the valve seat (Fig. 16-
B).
the amount by which the injection pipe's in-
line pressure is reduced is proportional to the
volume of fuel retracted up to the time
that
the
delivery valve is completely
closed.
jt:(piston
diameter)
2
x retraction stroke
Because
of this,
cut-off
of injection occurs im-
mediately after the end-of-injection and
subse-
quent dripping is prevented. (Fig. 16-C)
3-1-14
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