Geely Emgrand X7. Manual part — 234

2.13.1.5 Selection Table for Tappet Rod of Exhaust Valve

Installed tappet rod

thickness (mm/in) Clearance

measureme

n mm(in.)

935

2.13.2 Description and Operation

2.13.2.1 Description and operation

1. Cylinder

Hood

Cylinder hood is made from aluminum alloy casting process. Cylinder valve stem is a mechanical
system. Valve clearance can not be automatically adjusted, which is very important. The cylinder
valve is an integrated part. OEMs can offer 38 different sizes for choosing. During the
maintenance, required quite tube thickness can be calculated according to the formula. For details,
refer to 2.13.8.20 Valve Clearance Adjustments. The camshaft is arranged in a double-top mode; a
VVT actuator is further arranged on the inlet camshaft driving chain for regulating the air inlet
timing. The specific operation principles refer to 2.13.3.1 Operation Principle of System.

2. Timing

chain

Double overhead camshaft is driven through a timing chain. The timing chain must be replaced
every one hundred and twenty thousand kilometers. The timing chain system consists of a timing
chain, a timing chain guide rail, a timing chain tensioning rail and a timing chain tensioner acted
on the timing chain tensioning rail. Where, the tension pressure of the timing chain tensioner is
provided by the oil pump to ensure that the tension of the timing chain keeps balanced. The timing
chain is lubricated by an engine oil nozzle installed on the engine oil pump. The specific
information refers to 2.13.8.11 Check Timing Chain.

3. Intake

Manifold

Intake manifold has four independent long ports, using inertia to improve the engine torque at low
speed.

4. Camshaft

Dual overhead camshaft (DOHC) has two camshafts. A camshaft controls the intake valves, the
other camshaft controls the exhaust valves. The camshaft is located in the journal in the cylinder
hood on the top of the engine and fixed with camshaft cover. The cylinder hood camshaft journal
drilling is used for engine oil channel. Engine oil flows to the camshaft under pressure, lubricating
each camshaft journal. Engine oil flows through the cylinder hood to return to oil pan. Cam
convex corner is formed by machining, at the right time, according to the appropriate amount,
accurately open and close intake and exhaust valves. Cam convex is lubricated by high-pressure
oil escaped from the engine camshaft.

936

2.13.3 System Operating Principle

2.13.3.1 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 full write is Variable Valve Timing. 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.

937

(1) With VVT Valve Timing Diagram

排气门

进气门

持续开启角度：232度

持续开启角度：240度

调整最大提前角

调整最大滞后角

TDC

ATDC 4

度

ATDC20度

ABDC80

BBDC48度

ABDC30度

BTDC30度

BDC

TDC

BDC

TDC

BDC

FE02-2065b

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

When the engine is in normal operation, the oil pressure generated by an oil pump plays the role
on the VVT electromagnetic valve. ECM controls the VVT solenoid valve by means of pulse
width modulation signals. When needing VVT to regulate the intake valve in the maximum
position in advance, the ECM controls the VVT electromagnetic valve opening as 100%. At this
time, the engine oil pressure is applied to the advancement cavity and the VVT rotor blades
displace in the opposite direction to the crankshaft rotation angle to stop in the maximum position
finally.

A VVT actuator commonly stays at about 8? when idling without load. Because the
mechanical value of the opening angle of an intake valve is 5?, the actual opening

Air intakevalve

Air exhaust door

Continuous open

angle:232degree

ATDC4degree

BBDC48

degree

Continuous open angle:240 degree

Adjusting max.advance angle

Adjusting max.retard angle

BTDC30

degree

ABDC30

degree

ATDC20

degree

938