Isuzu N-Series. Manual - part 801

 Engine Control System (4JH1)    6E-255

The timing device changes the optimum injection timing
against various engine conditions.  The pressure of the
fuel fed from the feed pump is adjusted and it acts to
the timing plunger by TCV controlled fuel pressure.
(The TCV is installed to the fuel injection pump rear
side and it is controlled by duty ratio cycle from the
PCU.) The timing plunger is connected to the cam ring
by a ball pin.  Axial movement of the timing plunger is
transferred to the cam ring in the form of rotational
movement.

Legend

1. Drive Shaft
2. Feed Pump
3. Pump Camshaft Position (CMP) Sensor
4. Fuel Injection Pump Control Unit (PCU)
5. Distributor Head
6. Constant Pressure Valve (CPV) Holder
7. Fuel Injection Solenoid Valve
8. Constant Pressure Valve (CPV)
9. Timing Control Valve (TCV)

10. Timer

11. Radial Plunger

 

Legend

1. Rotor Shaft
2. Radial Plunger
3. High Pressure Passage
4. Low Pressure Inlet
5. Distribution Slit
6. Valve Needle
7. Barrel
8. Annular Passage
9. Fuel Return

10. Fuel Injection Solenoid Valve

11. High Pressure Outlet

12. Diaphragm Chamber
13. Accumulator Diaphragm

 

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6E-256    Engine Control System (4JH1) 

Low Pressure Fuel Circuit Description

Legend

1. Fuel Suction
2. Regulating Valve
3. Overflow Valve
4. Feed Pump
5. To Fuel Tank

 

The low pressure fuel circuit must supply sufficient fuel
to the high pressure fuel circuit.  The main components
are the feed pump, the regulating valve and the
overflow valve.

Feed Pump

Legend

1. Rotor
2. Casing Ring
3. Fuel Supply
4. Outlet
5. Chamber
6. Vane
7. Driveshaft
8. Inlet
9. Fuel Suction

 

The feed pump is driven by the drive shaft, performs
suction and supply of fuel.  The vanes assembled in the
rotor are pressed against the inside of the casing ring
by spring forces and centrifugal force during rotation to
form chambers.  When the vanes rotate, the volume of
these chambers increase when they reach recesses
the casing ring connected to the inlet port.  Pressure
then decreases and fuel is drawn in.  When the
chambers have passed the inlets and recesses, the
volume decreases and the fuel is compressed.  Fuel
pressure increases until the chamber reaches the
outlet, where the fuel passes through the regulating
valve to the high pressure fuel circuit.

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 Engine Control System (4JH1)    6E-257

Regulating Valve

Legend

1. To Inlet
2. Spring
3. Valve Piston
4. Port
5. From Outlet

 

When feed pump speed increases so that the delivery
pressure of the fuel delivered from the outlet exceeds
the regulating valve spring force, the plunger is pushed
upwards.  Excess fuel passes through the ports and
returns to the inlet side, and the delivery pressure is
maintained within a specified range.  When feed pump
speed decreases so that the delivery pressure
decreases, the plunger is pushed downwards by spring
force to close the port.

Overflow Valve

Legend

1. Valve Holder
2. Port
3. To Fuel Tank
4. Orifice Port
5. From Fuel Tank
6. Ball Valve
7. Spring

 

When the pressure of the fuel, returned from the
distributor head, exceeds the spring force, the overflow
valve’s ball valve is pushed up.  Excess fuel presses
through the port and returns to the tank, and fuel
pressure inside the pump chamber does not exceed a
specified pressure.  The flow of excess fuel serves
cooling and automatic bleeding of the fuel pump during
operation.  Also the orifice port is installed to assist in
automatic air bleeding.

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6E-258    Engine Control System (4JH1) 

High Pressure Fuel Circuit Description

Legend

1. Fuel Injection Pump Control Unit (PCU)
2. Distributor Head
3. Fuel Injection Solenoid Valve
4. Constant Pressure Valve (CPV)
5. Radial Plunger

 

In addition high pressure generating device, the high
pressure circuit also consists of fuel piping, and devices
to set the beginning of injection and fuel injection
quantity.  The main components are as follows:

• High pressure generation: Radial Plunger
• Fuel distribution: Distributor Head
• Beginning of injection timing: Timing Device
• Prevention of secondary injection: Constant

Pressure Valve (CPV)

Radial Plunger

Legend

1. Radial Plunger
2. Internal Cam
3. Cam Ring
4. Rotor Shaft
5. Plunger Chamber
6. Roller Shoe
7. Roller

 

While the radial plungers assembled to the rotor shaft
rotate, they are held against the inside of the cam ring
(via the roller shoes and rollers) by fuel delivery
pressure from the feed pump and centrifugal force.
The radial plungers perform rotational movement as
well as internal cam induced reciprocating movement
to suck in and compress the fuel in the plunger
chamber.

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