Page 156 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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140 Automobile mechanical and electrical systems

2.2.2 Methods of lubrication

Bath lubrication or splash lubrication (used in gearboxes and rear axles) may
be used for gears, chains, bearings and other moving parts that can be partly
submerged in an oil reservoir. In the bath system the gear simply picks up oil
as it dips into the reservoir and sprays or carries it to other parts along its path.
The splash system increases the effi ciency by attaching a special splash ring
to a moving part so that the oil is splashed against other parts that need to be
lubricated. This is similar to oil-mist lubrication, created by the oil escaping from
the engine’s rotating crankshaft, in which the oil is atomized in a stream of air.
Force-feed lubrication uses an oil pump to force the oil under pressure to the
parts to be lubricated, normally the engine crankshaft and camshaft. On some
Key fact high-performance vehicles the mainshaft in the gearbox is pressure fed. Some

Force-feed lubrication uses an oil parts are self-lubricating and require no external lubrication; the lubricant may
pump to force the oil under pressure be sealed in against loss as in sealed ball bearings, or a porous material such as
to the parts to be lubricated, normally porous bronze can be used so that oil impregnated in the material can penetrate
the engine crankshaft and camshaft. to the point of contact of the moving parts through pores in the material. In small
two-stroke gasoline engines the oil is mixed in with the fuel to bring it to the
moving parts inside the engine.
Although lubricating oil is used elsewhere in a car, the lubrication of the engine is
of greatest importance because it reduces the friction and wear between moving
metal parts and also removes heat from the engine. A supply of oil is kept in the
engine crankcase. An oil pump, which is powered by the engine, forces oil from
the crankcase under pressure to the cylinder block main oil gallery. Passages in
the engine block channel the oil to various moving parts, such as the crankshaft
and camshaft, and the oil eventually drains back down in the crankcase. An oil
fi lter is fi tted in the oil circuit to fi lter out metal shavings, carbon deposits and
dirt. Because the fi lter is not completely effective, and because of prolonged
exposure to high temperatures, the oil eventually becomes contaminated,
decomposes and loses its lubricating qualities. This is why routine maintenance

calls for changing the oil and oil fi lter at regular intervals.

2.2.3 Lubrication system

From the sump reservoir under the crankshaft oil is drawn through a strainer into
the pump ( Fig. 2.118 ).

Oil pumps have an output of tens of litres per minute and operating pressures
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of over 5 kg/cm at high speeds. A pressure relief valve limits the pressure of
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the lubrication system to between 2.5 and 4 kg/cm . The pressure relief valve is
a spring-loaded conical, or ball, valve that opens when the pressure in the oil
exceeds the spring force acting on the valve seat ( Fig. 2.119 ). When the valve
opens, a return drilling is uncovered and the excess oil fl ows through this to
return to the sump. This control is needed because the pump would produce
excessive pressure at high speeds. After leaving the pump, oil passes into a fi lter
and then into a main oil gallery in the engine block or crankcase ( Fig. 2.120 ).
Drillings connect the gallery to the crankshaft bearing housings and when the
engine is running, oil is forced under pressure between the rotating crank journals
and the main bearings. The crankshaft is drilled so that the oil supply from the
main bearings is also to the big-end bearing bases of the connecting rods.
The connecting rods are often drilled near the base so that a jet of oil sprays the
cylinder walls and the underside of the pistons ( Fig. 2.121 ). In some cases the