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What is lubrication system?
Lubrication is required for the maintenance of automobile engine. The engine cannot run smoothly, for more than a few minutes, without any lubrication.
Whenever two dry metallic surfaces glide over each other, under direct contact friction is produced, that results in abrasion of the metal parts.
The Lubrication system delivers oil, to the moving parts of the engine, to reduce friction.
So the ‘Lubrication Circuit’ is one of the most important things in the engine, to assist keeping the parts cool.
Automobile Engine Lubrication
The main parts of an automotive engine which require lubrication are:
1.Main crankshaft bearings
2.Big end bearings
3.Gudgeon pin bearings
4.Piston rings and cylinder walls
5.Timing Gears
6.Camshaft and camshaft bearings
crankshaft
connecting rod
Gudgeon pin bearings
Piston rings
Timing Gears
Camshaft assembly
Properties of a good lubricant
1. Viscosity: Viscosity can be defined as the resistance of any fluid to flow.
Due to the viscosity of Lubricant, the bearing surfaces are kept apart, meaning that the Hydrodynamic Lubrication is maintained.
The viscosity of the lubricating oil should be, just sufficient to ensure the hydrodynamic lubrication. A higher viscosity will cause power losses due to the increased oil resistance. It will also cause difficulty in starting the engine.
While the engine running the oil viscosity decreases, due to high temperature, which is not desirable. Therefore, the viscosity of oil should preferably have minimum variation at all temperatures.
The viscosity index is a fluid's change in viscosity, relative to temperature change.
2. Physical stability
The lubricating oil must be stable physically at the lowest and the highest temperatures exposed.
There should not be any separation of solids at the lower temperatures, and it should not vapourise beyond a certain limit at higher temperatures.
3. Chemical Stability
A lubricating oil should also be stable chemically. There should not be any tendancy for oxidation, that may create sticky substances. It will clog the working partssuch as piston rings and valves.
Oil should not decompose even at high temperatures to form carbon particles which will make the spark plugs and valves defective.
4. Resistance Against Corrosion
Corrosion is defined as the unintentional destruction of surface of a solid body by chemical action. The oil should have resistance to corrode any engine parts, with which it comes into contact.
5. Pour Point
Pour Point is the lowest temperature at which lubricating oil will be poured.
This property is important because of its effect, on starting an engine in cold weather and, on the free circulation of oil through feed pipes.
Therefore, the pour point of the oil should be less than the lowest temperature found in the engine.
6. Flash Point
The flashpoint is defined as the lowest temperature, at which the lubricating oil will flash, when a small flame crosses its surface.
It happens due to the evaporation of the light particles in the heated oil. The flashpoint of the oil should be sufficiently high, to avoid flashing of oil vapours at common temperatures.
7. Cleanliness
Lubricating oil must be clean. It should not contain dust and dirt particles. These impurities may either be filtered out, or removed with the change of oil at periodic intervals.
Further, the oil must contain additives called detergents, which will washout the impurities, from the engine parts during circulation.
Types of Lubricant
Depending on requirements of different parts, the automotive lubricants can be classified as below:
1. Based on state
Solid lubricant such as graphite, soapstone, talc, mica, molybdenum disulphide.
graphite
soapstone
talc
mica
Semi-solid lubricants such as grease, vaseline.
Liquid lubricants such as mineral oil, vegetable oils and animal oils.
grease
2. Origin Based
Natural lubricants such as mineral oils, vegetable oils, animals oils, graphite.
Synthetic Lubricants derived from Petroleum, and oils produced using synthetic hydrocarbons such as, Polyalpha-olefin, Perfluoro-polyether etc.
3.Variation in Viscosity
Mono-grade oils such as SAE 20, SAE 30, SAE 50 etc.
Multi-grade oils such as SAE 20W 40, SAE 15W 40 etc.
The number denotes the viscosity level of the lubrication oil
Lower the number, lower the viscosity and more readily the oil flows.
20W-40 is a code where 'W' is for winter.
In this case oil has viscosity of 20 (SAE) during winter , when Engine becomes hotter the oil now will have viscosity of 40(SAE).
4. On the basis of manufacturing
Blended lubricants such as blended by castor oil, palmitic acid, oleic acid.
Compounded lubricants such as compounded with polyglycols, fluorocarbons,silicones.
***End of session -4 of unit 1***
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