Isuzu N-Series. Manual - part 735

6E-362    Engine Control System (4HK1) 

Fuel System Description

The common rail system uses a type of accumulator
chamber called the fuel rail to store pressurized fuel,
and injectors that contain electronically controlled
solenoid valves to spray the pressurized fuel in the
combustion chambers. The injection system (injection
pressure, injection rate, and injection timing) is
controlled by the engine control module (ECM), and
therefore the common rail system can be controlled
independently, free from the influence of engine speed
and load. This ensures a stable injection pressure at all
time, particularly in the low engine speed range, so that
black smoke specific to diesel engines generated
during vehicle starting or acceleration can be reduced
dramatically. As a result, exhaust gas emissions are
clear and reduced, and higher output is achieved.

1. High Pressure Control

• Enables high pressure injection from low engine

speed range.

• Optimizes control to minimize particulate matter

and NOx emissions.

2. Injection Timing Control

• Enables finely tuned optimized control in

accordance with running conditions.

3. Injection Rate Control

• Pilot injection control that performs a small amount

of injection before main injection.

The fuel rail system consists primarily of a fuel supply
pump, fuel rail, injectors, and ECM.

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Fuel System Component Description

Injector

Legend

1. Terminal Stud
2. Fuel Leak Off Port
3. O-ring
4. Fuel Inlet Port
5. Injector Parts Number Marking
6. Fuel Injector ID Plate

 

Electronic control type injectors controlled by the
engine control module (ECM) are used. Compared with
conventional injection nozzles, a command piston,
solenoid valve, etc. are added.
ID codes displaying various injector characteristic are
laser marked in the plate, and ID codes showing these
in numeric form (30 alphanumeric figures are displayed
and only 24 are used) are laser marked in the plate.
This system uses fuel injector flow rate information (ID
codes) to optimize injection quantity control. When an
injector is newly installed in a vehicle, it is necessary to
input the ID codes in the ECM.
QR (Quick Response) codes or fuel injector flow rate
(ID codes) have been adopted to enhance the injection
quantity precision of the injectors. The adoption of
codes enables injection quantity dispersion control
throughout all pressure ranges, contributing to
improvement in combustion efficiency, reduction in
exhaust gas emissions and consistent horsepower
throughout the vehicle built.

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6E-364    Engine Control System (4HK1) 

1) Non-injection state
The two way valve (TWV) closes the outlet orifice by
means of a spring force, when no current is supplied
from the engine control module (ECM) to the solenoid.
At this time, the fuel pressure applied to the nozzle
leading end is equal to the fuel pressure applied to the
control chamber through the inlet orifice. As for the
force competition in this state, the pressure on the
command piston upper surface + nozzle spring force
defeat the pressure on the nozzle leading end, and
consequently the nozzle is pushed downward to close
the injection holes.

2) Injection start
The TWV is pulled up to open the outlet orifice, and
thus the fuel leaks toward the return port, when the
current is supplied from the ECM to the solenoid. As a
result, the nozzle is pushed up together with the
command piston by the fuel pressure applied to the
nozzle leading end, and then the nozzle injection holes
open to inject the fuel.

3) Injection end
The TWV lowers to close the outlet orifice, when the
ECM shuts off a current supply to the solenoid. As a
result, the fuel cannot leak from the control chamber,
and thus the fuel pressure in the control chamber rises
abruptly and then the nozzle is pushed down by the
command piston to close the nozzle injection holes,
resulting in the end of fuel injection.

No injection

Injection

Injection end

Injection rate

Injection rate

Pressure in

control chamber

Pressure in

control chamber

Pressure in

control chamber

Driving current

Driving current

Driving current

From common rail

Return port

Solenoid

TWV

Outlet orifice

Inlet orifice

Control chamber

Command piston

Nozzle

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Fuel Supply Pump

The fuel supply pump is the heart of the common rail
type electronic fuel injection system. The fuel supply
pump is installed at the same location as the
conventional injection type pump, which spins at a 1 to
1 ratio of fuel supply pump to crankshaft speed. A fuel
rail pressure (FRP) regulator and fuel temperature
sensor are part of the fuel supply pump assembly.
Fuel is drawn from the fuel tank via the fuel supply
pump by the use of an internal feed pump (trochoid
type). This feed pump pumps fuel into a 2-plunger
chamber also internal to the fuel supply pump. Fuel into
this chamber is regulated by the FRP regulator solely
controlled by current supplied from the engine control
module (ECM). No current to the solenoid results in
maximum fuel flow whereas full current to the solenoid
produces no fuel flow. As the engine spins, these two
plungers produce high pressure in the fuel rail. Since
the ECM controls the flow of fuel into this 2-plunger
chamber, it therefore controls the quantity and pressure
of the fuel supply to the fuel rail. This optimizes
performance, improves economy and reduces NOx
emissions.

Fuel Rail (Common Rail)

Legend

1. Flow Damper
2. Pressure Limiter
3. Fuel Rail Pressure (FRP) Sensor

 

Fuel tank

Camshaft

Fuel overflow

Fuel filter
(with priming pump)

Fuel inlet

Feed pump

Regulation valve

Suction

Return

Injector

Fuel rail

Delivery valve

Plunger

Return spring

FRP regulator

Suction valve

Suction pressure
Feed pressure
High pressure
Return pressure

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