Operation Section
1
–
17
(4) Supply Pump Operation
Supply Pump Overall Fuel Flow
• The fuel is drawn by the feed pump from the fuel tank and sent to the pumping mechanism via the PCV. The PCV
adjusts the quantity of fuel pumped by the pumping mechanism to the necessary discharge quantity, and the fuel is
pumped to the rail via the delivery valve.
Fuel Discharge Quantity Control
• The fuel sent from the feed pump is pumped by the plunger. In order to adjust the rail pressure, the PCV controls the
discharge quantity. Actual operation is as follows.
PCV and Plunger Operation During Each Stroke
Intake Stroke (A) In the plunger's descent stroke, the PCV opens and low-pressure fuel is suctioned into the
plunger chamber via the PCV.
Pre-Stroke (B) Even when the plunger enters its ascent stroke, the PCV remains open while it is not energized.
During this time, fuel drawn in through the PCV is returned through the PCV without being pres-
surized (pre-stroke).
Pumping Stroke (C) At a timing suited to the required discharge quantity, power is supplied to close the PCV, the
return passage closes, and pressure in the plunger chamber rises. Therefore, the fuel passes
through the delivery valve (reverse cut-off valve) and is pumped to the rail. Specifically, the
plunger lift portion after the PCV closes becomes the discharge quantity, and by varying the tim-
ing for the PCV closing (the end point of the plunger pre-stroke), the discharge quantity is varied
to control the rail pressure.
Intake Stroke (A) When the cam exceeds the maximum lift, the plunger enters its descent stroke and pressure in
the plunger chamber decreases. At this time, the delivery valve closes and fuel pumping stops. In
addition, the PCV opens because it is de-energized, and low-pressure fuel is suctioned into the
plunger chamber. Specifically, the system goes into state A.
Q000775E
Cam Lift
PCV Operation Close Valve
Intake Stroke
Pumping Stroke
Pre-Stroke
Open Valve
PCV
Pump Operation
Plunger
Return
When Discharge
Quantity Increases
When Discharge
Quantity Decreases
To Rail
Pumping the Required
Discharge Quantity
H
Discharge Quantity
h
Q
=
4
2
d
(H-h)
(A) (B) (C) (A')
Delivery Valve
From Fuel Tank
Pumping
Mechanism
d
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