Geely JL481Q, Руководство пользователя

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II. Characteristics of Valve Train
Each cylinder has 4 valves, laid in two columns. The intake path takes up a relatively large area and as a result, this
increases the rotation speed at maximum power, rotation speed atmaximum torque and its litre power, and decreases the
thermal load of the exhaust gas.
The DOHC (Double Overhead Camshaft Valve train) construction reduces the height of the cylinder head, and facilitates
the installation of the intake pipes. It also features low motion mass, high rigidity, high natural frequency and good high-
speed property.
The transmit mechanism adopts serrated belt transmit and helical gear with the auxiliary gears, featuring longer transmis-
sion distance, smooth movement, low noise level and cost.
Its excellent cam shape and motion pattern elevate inflation efficiency, and assures a reliable and low-noise level opera-
tion at high speed.
1. General
Valve timing refers to the rotated angle of crankshaft corresponding to the top and bottom dead centers at the moment of
opening and closing the valves of intake and exhaust in each engine cylinder. Generally, it is illustrated with a loop diagram.
In theory, the intake valve should be opened at the moment that the piston reaches the top dead center and closed at the
moment that the crank reaches the bottom dead center, and the exhaust valve follows a reverse pattern. However, due to
the high rotation speed of engine, each stroke of piston is completed in such a short time that makes it impossible to get
adequate air intake, clean exhaust, and hence leads to lower power. Therefore, the actual moments of opening and closing
of valves do not correspond to the top and bottom dead centers, but in an earlier time for opening and a later time for
closing.
In general, different engines have different timing. The best one is chosen according to the experiment results. Once the
timing is chosen, the angle between the intake cam and the exhaust cam of the same cylinder and the marks of meshing
engagement for each timing gear can be determined. Then, assemble the timing gears according to the marks to achieve
the selected timing.
For the transmit gear and the sub gear of the engine, there are two marks respectively on their front sides. One is the timing
mark. When two timing marks overlap, it indicates that the piston is in the top dead center of its compression stroke.
Another is installation mark, vertical to the timing mark. For the transmit gear, the installation mark comes first clockwise
and is nearly right above the camshaft fixing pin. For the sub gear, the installation mark comes first counterclockwise.
II.Valve Timing Diagram
The valve timing diagram for engine is shown as Fig. 199. The intake valve is opened before reaching top dead center to
assure that the intake valve has been opened fully in the beginning of the intake stroke, thus the combustible gas mixture
can enter into cylinder smoothly. The intake valve is closed sometime after reaching BDC so that the combustible gas
mixture may continue to enter into the cylinder in the early compression stroke by making use of inertia and pressure differ-
ence. The exhaust valve is opened before reaching the BDC (late power stroke). High pressure in the cylinder forces out
the exhaust gas and thus prevents engine from overheating. After reaching TDC, the exhaust gas can still be drained by
making use of inertia of exhaust gas.
Section 2 Valve Timing
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