Geely EC718 2009 Workshop Manual page 389

Engine
2.6.3 System Working Principle
2.6.3.1 System Working Principle
1. Reciprocating Piston Engine Working
Principle:
–
Intake Stroke:the crankshaft driven piston moves from TDC
to BDC. At this point exhaust valve closes, intake valve
opens. In the piston moving process, the cylinder volume
gradually increased and the vacuum is formed within the
cylinder. ECM controlled fuel injectors spray fuel into the
intake pipe. At this time the intake valves open, air and fuel
mixture sucked through the intake valve into cylinder and
forms a combustible mixture.
–
Compression Stroke:At the end of the intake stroke,
crankshaft continues to drive the piston from the BDC to the
TDC. intake and exhaust valves are closed. With the piston
moving up, the cylinder volume became smaller and
smaller. Because gas is compressed, the temperature of
the compressed gas rose rapidly.
– Power Stroke:At the end of compression stroke, ECM
controlled ignition coil primary coil circuit is disconnected
and the secondary sensor produces a high voltage, which
passes rapid through the cylinder head to the top of the
spark plug, and finally the high-voltage breaks through the
spark plug gap to generate electric spark, igniting the
combustible mixture within the cylinder. Fire spreads
rapidly inside the combustion chamber, while releasing a
large number of heat. Combustion gases rapid expands,
the pressure and temperature is also increased, swelling
force acting on the piston top, prompting the piston from the
TDC moving to the BDC, and through the connecting rod
to change piston reciprocating motion into rotary
movement. At this point, intake and exhaust valves are still
closed.
– Exhaust Stroke:At the beginning of the exhaust stroke,
exhaust valve opens, intake valve is still closed. the
crankshaft connecting rod drives the piston from the BDC
to the TDC. After burning the expanded gas residue will be
discharged through the exhaust valve to outside the
cylinder by its own pressure and the piston movement.
When the piston reaches the TDC, the exhaust stroke ends
and exhaust valve closes.
But in the actual process, the intake valve opens before the
TDC and closes after BDC. This design is intended to draw
more air into cylinder and reduce the power consumed in the
intake process. In the exhaust process, the exhaust valve
opens before BDC and closes after TDC. The aim is to reduce
Engine Mechanical System JL4G18-D
the mixture within the cylinder and reduce the power consumed
in the intake process. Because intake and exhaust valves have
a certain overlap angles, namely, at a certain crank angle
intake and exhaust valves open at the same time. At this time
the gas discharged through the exhaust valve forms a certain
amount of inertia and draws the mixture into the cylinder. This
will draw more air into the cylinder. But the valve overlap angle
is not the bigger the better. In different operating conditions, the
valve overlap angle requirements vary, therefore, in this engine
there is intake valve variable valve timing, which aims to meet
the engine intake valve opening angle requirements at different
operating conditions. this function is achieved through the VVT
system.
2. VVT System Working Principle
VVT stands for Variable Valve Timing, referring to the variable
valve timing system. Where there is mass, there is inertia. The
air drawn into the engine cylinders also has inertia, after the
intake process the air tends to heep entering into the cylinder.
At this time if the valve closing time is delayed, more air will be
drawn into the cylinder, so that volumetric efficiency will be
improved. As a result, the longer the delay in valve closing time,
the better the High-Speed performance; On the contrary the
more advanced valve closing, the better performance and the
more torque at the Low-Speed.
(1). With A Body-Valve VVT Valve Timing Diagram
Legend
1. TDC: Top Dead Center
2. BDC: Bottom Dead Center
3. ATDC: After TDC
4. BTDC: Before TDC
5. ABDC: After BDC
6. BBDC: Before BDC
EC718/EC718RV EC715/EC715RV 10/2009
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