Page 771 - Foton Workshop Manual - Auman EST-M

Engine section – Engine (Cummins ISF3.8) EG - 255

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. The high
EG
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 high pressure rail.
TR
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 common rail tube AX
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 pressure oil pipe
FR
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
fuel is supplied to the injector through a shorter high pressure oil pip connecting the oil rail. ECM controls the BR
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 NO x.

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 NO x emission and diesel engine noises, Cummins diesel engine adopts pre-injection

technologies under some of operating conditions to reduce NO x 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.
f. Control of each cylinder oil quantity
For a multi-cylinder diesel engine, the difference in the injection quantity of each cylinder will cause the
fluctuation of diesel engine speed. Cummins series diesel engine judge the difference of each cylinder
injection quantity through the change of diesel engine speed when each cylinder performs firing stroke and
modifies it so as to reduce the fluctuation of diesel engine speed.

EG-255