MAINTENANCE MANUAL OF ENGINE
115
Chapter 2 Operating principle
1. Valve mechanism
1.1 Function of valve mechanism
The cylinder head is used to enclose the top of
the cylinder, and works with the cylinder and piston
to jointly form the combustion chamber and work-
ing chamber. The cylinder head is directly in con-
tact with high temperature gas mixture, withstands
pre-tightening force of the bolts, gas pressure and
alternating stress, so it is required that the cylinder
head should have a certain strength and rigidness,
and be cooled reliably, and have a flat mating sur-
face to ensure reliable sealing.
Function:
When working cycle of the cylinder requires
opening the valve for air change, the camshaft ro-
tates with help of the drive mechanism under driv-
ing of the crankshaft, so as to enable the raised part
of the cam on the camshaft to push the rocker arm
through the tappet, pushrod and adjusting screw;
thus, the other end of the rocker arm pushes the
valve downward, enabling the valve to be open and
the spring to be further compressed. After the apex
of raised part of the cam rotates by the tappet, the
thrust force is gradually decreased, and the opening
of the valve decreases gradually under action of the
spring tension until it is closed eventually. In the
compression and power stroke, the valve is always
left closed under action of the spring.
According to the requirements for working cy-
cle completed in each cylinder of the engine and
ignition sequence, open and close the air intake and
exhaust valves regularly, so that sufficient fresh air
enters the cylinder, and the exhaust gas is dis-
charged from the cylinder in time.
A-Valve rocker arm
B-Valve
C-Tappet
D-Pushrod
E-Camshaft
E
C
D
B
A
Summary of Contents for KM/4L22
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