Maintenance manual for sunray hfc4da1-2c china-IV diesel engines
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Section III Working Theory of High Pressure Fuel Line
I. High pressure fuel line parts
The high pressure fuel line generates and accumulates
sufficient fuel pressure required for the fuel injectors.
The parts include: High pressure pump, fuel rail, high
pressure fuel pipe, and fuel injector.
II. High pressure pump
The high pressure pump compresses the fuel to a system
pressure of up to 1,450bar and then the fuel is
transmitted to the tubular high pressure fuel accumulator
(rail) via the high pressure pipe.
The high pressure pump is the interface between low pressure stage and high pressure stage. Under all working
conditions, it can reliably supply sufficient high pressure fuel throughout the entire service life of the vehicle,
including supplying addition fuel required for rapid start and the
rapid establishment of pressure in the common rail. The high
pressure pump continually generates the system pressure required
for the high pressure accumulator (rail). Therefore, it means that,
compared with traditional system, it’s unnecessary to compress the
fuel for each individual injection cycle.
The fuel is compressed by three plunger pumps arranged radially at
spacing of 120º from each other. As each rotation turn can generate
three compression strokes and only generate low peak drive torque,
the drive unit of the pump maintains uniform force application. As
far as 16Nm torque is concerned, this torque is only 1/9 of the
torque required for driving similar distribution pump. This means
that, compared with traditional fuel injection systems, the common rail generates lower load onto the drive unit of the
pump. The raising power of the drive pump is in proportion to the preset pressure of common rail and the speed of the
fuel pump (fuel delivery amount).
Working mode:
Through one water separator, the fuel delivery pump pumps out the fuel from the fuel tank and the fuel enters into the
lubricating and cooling lines of high pressure pump via the fuel inlet. The drive shaft with eccentric wheel drives three
pump plungers for upward and downward movements along with the profile of the cam. The pump plungers move
downward under the application of the fuel delivery pressure (fuel suction stroke). When the plungers overpass the
bottom dead center, the fuel inlet valve is closed so that the fuel in the pump chamber will not leak out. In such case,
the fuel is compressed so that the fuel pressure exceeds the fuel delivery pressure of the fuel delivery pump. In such
case, once the pressure established exceeds the pressure in the common rail, the fuel outlet valve opens so that the fuel
enters into the high pressure line. The pump plungers will continue the fuel supply, till the top dead center is reached
(fuel delivery stroke). Then the pressure drops and the fuel outlet valve closes. The residual fuel is pressure relieved:
The pump plungers move downward. When the pressure in the pump chamber is less than the fuel delivery pressure,
the fuel inlet valve re-opens and the pumping process is started again.
III. Fuel rail (Common rail)
The high pressure accumulator (rail) stores the high pressure fuel and at the same time restrains the pressure variation
generated during the fuel supply and fuel injection of the high pressure pump. The high pressure accumulator is
shared by all cylinders and therefore is referred to as “common rail”. Even when a great amount of fuel is drained, the
common rail can maintain its internal pressure basically unchanged. Therefore it maintains the constant fuel injection
pressure of the fuel injector.
1. Drive shaft
2. Eccentric cam
3. Plunger pump
4. Fuel suction valve
5. Fuel outlet valve
6. Fuel inlet
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