Page 63 - Foton Workshop Manual - Auman EST-M

Diagnosis - Diagnosis-fault diagnosis of electronic and electrical parts DI - 9

2. Introduction of system function IN
a. Pressure control

The high pressure common rail system mainly consists of low pressure loop and high pressure loop The low DI
pressure return circuit includes the low pressure oil pipe, fuel filter, gear pump, etc. The high pressure return
circuit includes the high pressure oil pump, high pressure oil rail, high pressure oil pipe, injector, etc.
EG
The high pressure of high pressure common rail fuel injection technology is formed when the oil transfer

pump supplies the fuel through the filter into the high pressure oil pump which compresses the fuel into the
TR
high pressure rail When the engine works, the gear pump on the high pressure pump sucks the oil from the oil

tank through negative pressure and sends the filtered fuel into the high pressure pump at certain pressure
(0.5-0.7Mpa) Fuel is compressed after getting into the high pressure plunger chamber and goes into the AX
common rail tube through the high pressure oil pipe to form high pressure and maintain the common rail
pressure (about 160MPa) set up by ECM. Each injector is connected with the common rail tube via the high
FR
pressure oil pipe to realize the high pressure injection The redundant fuel flows back to the low pressure

circulation through the pressure control valve
ST
b. Fuel injection control

When operating normally, the engine ECM controls the injector working according to the order of 1-3-4-2 The
BR
fuel is supplied to the injector through a shorter high pressure oil pip connecting the oil rail. ECM controls the
injection solenoid valve according to the engine load. The injector injects proper amount of fuel into the
combustion chamber after the solenoid valve is actuated BW
Because the injection pressure is independent from the engine speed and load, actual injecting start time,
pressure and duration can be freely selected in a broad range. The pilot injection can be adopted as per the EL
demands of engine. It can reduce the noises of engine obviously and reduce the emission of NOx.

c. Control of injection quantity, pressure and timing

The important information of diesel engine electric control is to perform precise control of fuel injection
capacity, injection pressure and injection timing. The values of fuel injection capacity, injection pressure and

injection timing are mainly determined by diesel engine speed and throttle opening. The system will calculate

the fuel injection parameters under the corresponding operating conditions to realize precise control of fuel
injection parameters as per the received signals of diesel engine speed and accelerator pedal opening. Besides,
the system can modify the injection parameters according to intake temperature, pressure, water temperature,
atmospheric pressure, etc.
d. Control of injection times
In order to reduce NOx emission and diesel engine noises, Cummins diesel engine adopts pre-injection
technologies under some of operating conditions to reduce NOx emission and noises of diesel engine partly.

e. Idle control

The Cummins series diesel engine performs feedback control for idle injection quantity to ensure the diesel

engine idle speed is stable at the targeted speed. This avoids the problems such as diesel engine speed unstable,

starter acceleration slow and others which are produced by the external loads such as AC, etc. when the diesel

engine works at idle.

DI-009