11-58
140-3 SERIES
STRUCTURE AND FUNCTION, MAINTENANCE STANDARD OUTLINE OF CRI SYSTEM
STRUCTURE AND FUNCTION OF CRI SYSTEM
The CRI system consists of the fuel supply pump, common rail, and injectors, and the ECU and sensors that
control them.
The fuel supply pump generates fuel pressure inside the common rail. The fuel pressure is controlled by the
amount of fuel discharged from the supply pump. The amount of fuel discharged is controlled by sending an
electrical signal from the ECU to switch the PCV (discharge control valve) of the fuel supply pump ON-OFF.
The common rail accepts the fuel pressure generated by the fuel supply pump and distributes it to the cylinders.
The fuel pressure is detected by the common rail fuel pressure sensor installed in the common rail. It carries
out feed back control to ensure that the actual pressure value matches the command pressure value set in
accordance with the engine speed and engine load.
The fuel pressure of the common rail passes through the fuel injection pipes of each cylinder and is applied to
the control chamber and the nozzle of the injector.
The injector controls the amount of fuel injection and the fuel injection timing. It controls by switching the TWV
(Two-Way electromagnetic Valve) ON-OFF. When the TWV is turned ON (conducts electricity), the fuel circuit is
switched so that the high-pressure fuel in the control chamber passes through the orifice and flows out. The
needle valve goes up because of the nozzle cracking pressure actuated by the high-pressure fuel at the nozzle
end, and fuel injection is started. When the TWV is switched OFF (no current flows), the control chamber
becomes a fuel circuit with the high-pressure fuel applied through the orifice, so the needle valve goes down
and fuel injection is completed.
Therefore, the fuel injection timing is controlled electronically by the timing of the electricity passing through the
TWV, and the amount of fuel injected is controlled by the amount of time that electricity passes through the
TWV.
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