Geely JL481Q, Руководство пользователя

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When the engine is running normally, partial combustion gas
within the cylinder will inevitably flee through the gap between the
piston and the cylinder into the crankcase, thereby increasing its
internal gas amount and pressure. As the engine’s load and
pressure increase, the gas leakage will increase. If the cylinder is
abraded or has poor sealing, the gas leakage will also increase.
Generally, the gas mixture entering into the crankcase includes
the following products of imperfect combustion: NOx, CHx, H2O,
etc. If the waste gas within the crankcase cannot be discharged
timely, its internal pressure will become higher and higher,
leading to continuous waste gas leakage at tiny gaps, such as the
one between the crankshaft’s protruding end and the cylinder
block and the one between the oil sump and the cylinder block,
accompanied with increased noise and deteriorated engine oil.
So, engine adopts closed positive crankcase ventilation (PCV)
system, whose schematic diagram is shown in Fig. 298. On the
internal sidewall of the cylinder head, there are vertical ventilation
holes enabling interconnection between the crankcase and the
valve chamber on the cylinder head, and furthermore on the
cylinder head hood there are two forced interfaces placed, one of
which is connected to the air filter and the other is connected to
the resonant chamber of the intake manifold. Such design can
produce a vacuum difference between the air filter’s rear end and
the resonant chamber of the intake manifold, which will bring a
negative pressure for the crankcase. Thus, the fresh air can flow
into the crankcase, mix with its internal waste gas, and flow
through the ventilation holes into the intake manifold and then the
cylinder for combustion, consequently realizing a simply exhaust
gas recycle (EGR). However, this practice will certainly lead to a
very unstable idling speed and a large amount of fleeing engine
oil. For this reason, engine uses a check valve, which ensures low
flow rate at large opening, and prevents engine oil from leaking
out. In short, if the check valve cannot work normally, more and
more waste gas and engine oil vapor in the cylinder head hood
will not only cause a large amount of gas to flee out through the
joints of the cylinder head hood and sealing gaps, but also
increase the noise of valve springs and deteriorate the engine’s
working condition.
Fig. 297 Structural diagram for the engine oil filter
IV. Influence of Positive Crankcase Ventila-
tion (PCV) on Engine Oil Lubrication Effect
Bypass valve
open at 0.1MPa
PCV
Fig. 298 Schematic diagram for positive
crankcase ventilation system
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