Yanmar 4JH2E Service Manual page 116

Chapter 3 Fuel Injection Equipment
15. Injection Pump Construction and Operation
"""'----------------------------------------------------------4JH2-UTE
Plunger
Magnet
valve
Inlet port
Inlet slit
fL:Jle~~~~~~
Pressure
chamber
Plunger spring
Delivery valve
spring
Delivery valve
Cross-sectional view
Cutaway view
Fig.
10
Plunger operation: suction stroke
Cross-sectional view
Cutaway view
Fig.
11
Plunger operation: delivery stroke
Printed in Japan
AOA1029-9109SP
3-51
Suction stroke
During the plunger's return stroke. when the
plunger barrel's inlet port and the plunger's in-
let slit are aligned, pressurized fuel oil in the
pump chamber is sucked into the pressure
chamber. (Fig. 10)
Delivery stroke
As the plunger is rotated and lifted by the cam
disk, the plunger's outside face blocks the
plunger barrel's inlet port and compression of
fuel oil begins. At almost the same time the
plunger's outlet slit meets the plunger barrel's
outlet port. As a result of this. the fuel oil pres-
surized by the plunger lift overcomes the set
force of the delivery valve spring and the injec-
tion pipe's in-line residual pressure, and opens
the delivery valve. The fuel oil is then injected
through the nozzle and nozzle holder into the
engine's combustion chamber. (Fig. 11)