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DI08-12
FUEL PRESSURE CONTROL
Fuel Pressure Control Elements
Pressure control consists of 2 principle modules.
• Determines rail pressure according to engine operating conditions.
• Controls IMV to make the rail pressure to reach to the required value.
Pressure in the fuel rail is determined according to engine speed and load on the engine. The aim is to adapt the
injection pressure to the engine's requirements.
• When engine speed and load are high
: The degree of turbulence is very great and the fuel can be injected at very high pressure in order to optimize
combustion.
• When engine speed and load are low
: The degree of turbulence is low. If injection pressure is too high, the nozzle's penetration will be excessive and part
of the fuel will be sprayed directly onto the sides of the cylinder, causing incomplete combustion. So there occurs
smoke and damages engine durability.
Fuel pressure is corrected according to air temperature, coolant temperature and atmospheric pressure and to take
account of the added ignition time caused by cold running or by high altitude driving. A special pressure demand is
necessary in order to obtain the additional flow required during starts. This demand is determined according to injected
fuel and coolant temperature.
Fuel Pressure Control
Rail pressure is controlled by closed loop regulation of IMV. A mapping system – open loop – determines the current
which needs to be sent to the actuator in order to obtain the flow demanded by the ECU. The closed loop will correct the
current value depending on the difference between the pressure demand and the pressure measured.
• If the pressure is lower than the demand, current is reduced so that the fuel sent to the high pressure pump is
increased.
• If the pressure is higher than the demand, current is increased so that the fuel sent to the high pressure pump is
reduced.
CHANGED BY
EFFECTIVE DATE
AFFECTED VIN
Flow demand
Open
Engine speed
Rail pressure
demand
Error
Measured rail
pressure
IMV current
IMV
Current
PIG
Correction
governor
Y220_08008
ENGINE CONTROL SYSTEM
DI ENG SM - 2004.4
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