Chapter:Nine

Engine lubrication system

Prepared By: Helen G
Lubrication system of IC engine
üLubrication is an art of admitting a lubricant (oil,grease,etc)
between two surfaces that are in contact and in relative
motion.
üThe purpose of lubrication in engine is to perform one or
several of the following function:-
1.To reduce friction and wear between the moving parts and
there by the energy loss and to increase the life of the engine.
2.To provide selling action e.g. the lubrication oil helps the
piston rings to maintain an effective seal against the high
pressure gasses in the cylinder from leaking out in to the
crankcase.
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3.To cool the surface by carrying away the heat generated in
engine components.
4.To clean the surface by washing away carbon and the metal
particles caused by wear.
üOf all this function, the first function is considered to be the
most important one.
üThe energy losses from the friction between components of
the engine can be minimized by providing proper lubrication.
Lubricating System Components
üYou must remember that the lubricating system is actually an
integral part of the engine and the operation of one depends
upon the operation of the other.
üThus the lubricating system, in actual practice, cannot be
considered as a separate and independent system; it is part of
the engine.
üThe lubricating system basically consists of the following:
ØOil pump—forces oil throughout the system.
ØOil pickup and strainers—carries oil to the pump and
removes large particles.
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ØPressure relief valve—limits maximum oil pressure.
ØOil filter—strains out impurities in the oil.
ØOil cooler—provides cooling for the oil system.
ØOil pan—reservoir or storage area for engine oil.
ØOil level gauge—checks the amount of oil in the oil pan.
ØOil galleries—oil passages through the engine.
Oil Pump
üThe oil pump is the heart of the lubricating system; it forces
oil out of the oil pan, through the oil filter and galleries, and
to the engine bearings. Normally, a gear on the engine
camshaft drives the oil pump; however, a belt or a direct
connection with the end of the camshaft or crankshaft drives
the pump in some cases.
üThere are two basic types of oil pumps:
1.Rotary type oil pump
2.Gear type oil pump
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1.Rotary type oil pump
üThe rotary pump has an inner rotor with lobes that match similar
shaped depressions in the outer rotor.
üThe inner rotor is off center from the outer rotor.As the oil pump
shaft turns, the inner rotor causes the outer rotor to spin.
üThe eccentric action of the two rotors forms pockets that change size.
A large pocket is formed on the inlet side of the pump.
üAs the rotors turn, the oil-filled pocket becomes smaller as it nears
the outlet of the pump.
üThis action squeezes the oil and makes it spurt out under pressure.
As the pump spins, this action is repeated over and over to produce a
relatively smooth flow of oil.
Rotary type oil pump
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2.Gear type oil pump
üThe gear pump consists of two pump gears mounted within a close-
fitting housing. A shaft, usually turned by the distributor, crankshaft,
or accessory shaft, rotates one of the pump gears.
üThe gear turns the other pump gear that is supported on a short shaft
inside the pump housing.Oil on the inlet side of the pump is caught in
the gear teeth and carried around the outer wall inside the pump
housing.
üWhen oil reaches the outlet side of the pump, the gear teeth mesh and
seal. Oil caught in each gear tooth is forced into the pocket at the
pump outlet and pressure is formed. Oil squirts out of the pump and
to the engine bearings.
Gear type oil pump
Oil Pickup and Strainer
üThe oil pickup is a tube that extends from the oil pump to the
bottom of the oil pan.
üOne end of the pickup tube bolts or screws into the oil pump
or to the engine block. The other end holds the strainer.
üThe strainer has a mesh screen suitable for straining large
particles from the oil and yet passes a sufficient quantity of
oil to the inlet side of the oil pump.
üThe strainer is located so all oil entering the pump from the
oil pan must flow through it.
Oil Pickup and Strainer
Pressure relief valve
üA "pressure relief valve" in an engine lubrication system is a
safety mechanism that limits the maximum oil pressure by
allowing excess oil to flow back to the oil pan when the
pressure exceeds a preset level, essentially acting as a safety
valve to protect the engine components from damage caused
by excessive oil pressure.
ü It is usually located near the oil pump outlet and operates
with a spring-loaded mechanism that opens when pressure
becomes too high.
Pressure relief valve
 Oil cooler
üThe oil which returns from various engine parts and then falls in to
the sump is hot.this hot oil should be cooled by the wind flowing
from the front side of the engine.
üOil coolers are provided for effective cooling. These coolers consist
of a small sized tubing.the oil passes through these tubes. These
tubes are placed in the air stream of the blower in the air cooled
engines. The heat of the oil is transferred to the air.the oil is thus
cooled.
üThere are heat ex-changers in water cooled engines. The water
passes through these heat ex-changers.when the oil also passes
through the heat ex-changers, the heat of the oil is transferred to the
water. The oil is thus cooled.
Oil filter
üDuring the period between when the lubricating oil reaches
the various engine parts and returns to the oil pump,it picks
up burnt carbon particles, water and road dust.
üIn order to remove these foreign materials, the oil should be
filtered.
üThe filtered oil is to be then again supplied to the engine
parts. Therefor,an oil filter is quite necessary.
Oil Pan
üThe oil pan is normally made of thin sheet metal or
aluminum, and bolts to the bottom of the engine block.
üIt holds a supply of oil for the lubrication system.
üThe oil pan is fitted with a screw-in drain plug for oil
changes. Baffles may be used to keep the oil from splashing
around in the pan.
üThe sump is the lowest area in the oil pan where oil collects.
As oil drains from the engine, it fills the sump. Then the oil
pump can pull oil out of the pan for re-circulation.
Oil Level Gauge
üThe oil level gauge, also known as a dipstick. It consists of a
long rod or blade that extends into the oil pan.
üIt is marked to show the level of oil within the oil pan.
Readings are taken by pulling the rod out from its normal
place in the crankcase, wiping it clean, replacing it, and again
removing and noting the height of the oil on the lower or
marked end.
üIt is important that the oil level not drop below the low mark
or rise above the full mark.
Oil Galleries
üOil galleries are small passages through the cylinder block
and head for lubricating oil.
üThey are cast or machined passages that allow oil to flow to
the engine bearings and other moving parts.
üThe main oil galleries are large passages through the center
of the block. They feed oil to the crankshaft bearings,
camshaft bearings, and lifters.
üThe main oil galleries also feed oil to smaller passages
running up to the cylinder heads.
TYPES OF LUBRICATION SYSTEM
üThe function of lubrication system is to provide sufficient
quantity of cool, filtered oil to give positive and adequate
lubrication to all moving parts of an engine.
üThe various systems used for internal combustion engine
classified as:-
➢MIST LUBRICATION SYSTEM
➢WET SUMP LUBRICATION SYSTEM
➢DRY LUBRICATION SYSTEM
1.MIST LUBRICATION SYSTEM
üThis system is used where crankcase lubrication is not
suitable. In two stroke engine, as the charge is compressed in
the crankcase, it is not possible to have the lubrication oil in
the sump. Hence mist lubrication is used in practice.
üThe lubrication oil is mixed with the fuel, the usual ratio
being 2% to 5%. Oil and fuel mixture is inducted through the
carburetor. Fuel is vaporized and the oil in the form of mist
goes via the crankcase into the cylinder.
üThe oil which strikes the crankcase walls lubricates the main
and connecting rod bearings and the rest of oil lubricate the
piston, piston rings and the cylinder.
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Advantage:
ØSimplicity and
ØLow cost as it does not require an oil pump, filter, etc.
Disadvantages:
ØCause heavy exhaust smoke due to burning of lubricating oil
ØForms deposit on piston crown and exhaust port which affect engine
efficiency.
ØRequires a thorough mixing for effective lubrication. This requires
either separate mixing prior to use or use of some additive to give the
oil good mixing characteristics.
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ØDuring closed throttle operation as in the case of vehicle
moving down the hill, the engine will suffer from insufficient
lubrication as the supply of fuel is less. This is an important
limitation of system.
2. WET SUMP LUBRICATION SYSTEM
üIn the wet sump system, the bottom of the crankcase contains
an oil pan or sump from which the lubricating oi1 is pumped
to various engine components by a pump .
üAfter lubricating these parts, the oil flows back to the sump
by gravity. Again it is picked up by a pump and recirculated
through the engine lubricating system.
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üThere are three varieties in the wet sump lubrication system.
They are:
ØThe splash system
ØThe splash and pressure system
ØThe pressure system
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ØThe splash system
üThis types of lubricating system is used in light duty engines ,
slow speed engines.
üLubricating oil is stored at the bottom of engine crankcase
and maintained at a predetermined level.The oil is drawn by
the pump and delivered through a distributing pipe into the
splash trough located under the big end of all the connecting
rods.These troughs are provided with overflows and oil in the
trough is therefore kept at a constant level.
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üA splasher or dipper is provided under each connecting rod
cap which dips into oil in the trough at every revolution of the
crankshaft and the oil is splashed all over the interior of
crankcase, into the pistons and onto the exposed portion of
cylinder walls.The oil dripping from the cylinder is collected
in the sump where it is cooled by the air flowing around. The
cooled oil is then recirculated.
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ØThe splash and pressure system
üIn this system, the lubricating oil is supplied under pressure
to main and camshaft bearings. Oil is also supplied under
pressure to pipes which direct a stream of oil against the
dippers on the big end connecting rod bearing cup and thus
the crankpin bearings are lubricated by the splash or spray of
oil thrown up by the dipper.
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ØThe pressure system
In this system , lubrication is done with the help of pressure
pump which is submerged in the Sump. With the help of
pressure pump after filtration,oil is forced under pressure to
different parts of the engine through oil tubes. From the
bearing oil floats to connecting rod through oil holes between
connecting rod and cam shaft. Then this oil flows to piston pin
through oil holes and sprayed over piston ,piston
rings ,cylinder valves and other parts.
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ØDRY LUBRICATION SYSTEM
üThe dry sump lubrication system uses two oil pumps and a
separate oil reservoir.
üNo oil is stored in the oil pan itself. The main pump pulls oil
from the reservoir and pushes it into the engine bearings and
other high-friction points.
üThe second pump, called the scavenge pump, pulls oil out of
the pan and sends it to the oil reservoir.
üT h e s e t y p e s o f s y s t e m s a r e f o u n d o n e x o t i c h i g h -
performance cars. Because there is no oil in the oil pan,
engine horsepower and dependability are increased.
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PROPERTIES OF LUBRICATING OIL
Given below are the properties that an oil should have to be
suitable for lubrication.
1.Proper viscosity
2.Resistance to corrosion
3.Good cleaning power
4.Resistance to oxidation and carbon formation
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üIn order to make the oil suitable for lubrication, the mineral
oil is mixed with many chemical additives.
üThe various ways in which these additives help to make the
oil suitable for lubrication is given below.
Viscosity: Oil must have the correct viscosity. If the oil is too
thick, the moving parts cannot slide easily. If the oil is too
thin,the moving parts will have contact and wear. The additives
help ensure that the oil has proper viscosity.
Pour point: The oil becomes very thick at low temperatures
and does not flow. The addition of an additive enables the oil
to flow at even low temperature.
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Carbon formation:The oil is heated due to the high
temperature of the cylinder, valve and piston. With only high
temperature it would begin to break down and form carbon.
The additives do not allow the carbon to form.
Oil oxidation: when the oil is heated and churned, it combines
with oxygen. Oxidized oil forms tar and varnish. The
formation of this is prevented by adding additives to the oil.
The additives also make the oil slightly alkaline. This
neutralizes the acidity in the oil. Thus corrosion is reduced.
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Detergents: burnt materials flow past the piston rings in to the
sump. This product is acidic and contains carbon. The oil
should absorb the acid and carbon material. Other wise they
would get converted in to the form of deposits. Additives are
added to the oil to prevent the formation of sludge and other
deposits.
Foaming resistance: the oil should not develop foam because
of churning in the crankcase. To prevent foaming, anti-foaming
additives are mixed with the oil.
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OIL CHANGES
The manufacturers specify the time interval for changing the
oil. The oil should be changed accordingly. The smooth
running of the engine is then ensured.