Geely Emgrand X7. Manual part — 106

2.6.3 System operating principle

2.6.3.1 System operating Principle

1. Reciprocating Piston Engine Operating Principle:

z 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.

z 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.

z Power Stroke: At the end of compression stroke, the primary coil circuit of ignition coil

controlled by ECM is disconnected and the secondary sensor produces a high voltage, which
passes rapidly through the cylinder hood 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 amount of heat. Combustion gas expands rapidly .The pressure and
temperature also increases. Swelling force acts on the piston top, prompting the piston to
move from the TDC to the BDC and changing piston reciprocating motion into rotary
movement through the connecting rod. At this point, intake and exhaust valves are still
closed.

z 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 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 help enter 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 VVT Valve Timing Diagram

Air intakevalve

Air exhaust door

423

进气门

持续角度：273.5°

最大提前

BTDC

68.5°

BTDC
18.5°

ATDC

26.5°

25°

ABDC

75°

ABDC

58°

BBDC

初始相位

排气门

持续角度：264.5°

GC02-0004c

TDC: Top dead center

BDC: Below dead center

ATDC: After Top dead center

BTDC: Before Top dead center

ABDC: After Below dead center

BBDC: Before Below dead center

(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
Performance

(3) Advance

Process

In normal operation condition, the engine oil pressure that the engine oil pump generated applies
on the OCV valves. ECM controls the OCV valve by pulse-width modulation. When ECU needs
VVT to adjust the intake valve to the maximum advance position, ECU controlled the VVT
solenoid valve opening is 100%. At this point, the engine oil pressure applies to the advance
chamber, and the VVT rotor blades generate clockwise movement and eventually stay at the
maximum advance position.

During idling without loading, VVT actuator generally doesn’t deflect.

424

3
4

2

1

5

CE02-0147b

1. Lag chamber 2. Locking pin 3. Advance chamber

4. Rotor blade 5. Stator

(4) Lag

Process

JL4G24 Engine intake VVT actuator can only advance the timing, the lag status is the initial
timing status.

425

2.6.4 Component position

2 . 6 . 4 . 1 Part position of VVT system

1

2

NL02-1001e

1. VVT Solenoid valve

2. VVT

Actuator

426