Geely EC718, EC718RV, EC715, EC715RV. Manual part — 98

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

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

Engine

Engine Mechanical System JL4G18-D

2-307

(2). VVT Control Strategy

Driving

Conditions

Intake Valve

Timing

Cause

Low-Load

Lag

Steady
Combustion

High Load, High
Speed

Lag

Increased Output
Characteristics

High Load, Low
Speed

Advance

Increased Torque

Medium-Speed
Condition

Advance

Improved

Fuel

Consumption

(3). Advance Process

3
4

2

1

5

FE02-2066b

Legend

1. Lag Chamber
2. Locking Pin
3. Advance Chamber
4. Rotor Blade
5. Bracket
In normal operation condition, the oil pump generated engine
oil pressure applies on the VVT solenoid valves. ECM controls
the VVT solenoid valve by pulse-width modulation. When ECM
needs VVT to adjust the intake valve to the maximum advance
position, ECM controlled the VVT solenoid valve opening is
100%. At this point the engine oil pressure applies to the
advance chamber, VVT rotor blades move in the opposite
direction relative to the crank angle and eventually stay at the
maximum position.
idling without load VVT actuator position will generally remain
at the 8 ° or so, due to intake valve mechanical opening angle

is 5 °, so the intake valve opens at idle with actual angle of 13
°.

(4). Lag Process

1

FE02-2067b

Legend

1. Lag Chamber
In normal operation condition, the oil pump generated engine
oil pressure applies on the VVT solenoid valves. ECM controls
the VVT solenoid valve by pulse-width modulation. When ECM
needs VVT to adjust the intake valve to the maximum lag
position, ECM controlled the VVT solenoid valve opening is
0%. At this point the engine oil pressure applies to the lag
chamber, VVT rotor blades move in the same direction relative
to the crank angle and eventually stay at the maximum position.

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Engine Mechanical System JL4G18-D

Engine

2.6.4 Component Locator
2.6.4.1 Component Locator

VVT System Component Locator

3

2

1

FE02-2068b

Legend

1. VVT Actuator
2. VVT Solenoid Valve

3. VVT Solenoid Valve Filter

Engine

Engine Mechanical System JL4G18-D

2-309

2.6.5 Disassemble View
2.6.5.1 Cylinder Head Covers

6

1

7

4

3

4

5

2

6

8

8

4

4

4

FE02-2069b

Legend

1. Cylinder Head Covers
2. Cylinder Head Cover Gasket
3. Engine Oil Cap
4. Cylinder Head Cover Bolts
5. Cylinder Head Cover Bolts Washer

6. Cylinder Head Covers Retaining Nut
7. Purged Crankcase Ventilation Valve
8. Hood Retaining Bolts

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Engine Mechanical System JL4G18-D

Engine