LUBRICATION SYSTEM

LUBRICATION SYSTEM

As you know that our body requires fluids like water and also oil in the form of fats like ghee, butter, cooking oil for maintenance of our system. Similarly lubrication is required for maintenance of engine. Lubrication circuit is one of the most important ones in the engine. The engine cannot run smoothly for more than a few minutes without the lubricating oil.

Whenever two metallic surfaces move over each other under direct contact, dry or solid friction is produced. This is due to the irregularities on the two surfaces interlocking each other. The dry friction thus created produces a lot of heat and results in wear of the metal surface.
Lubrication system delivers oil to the moving parts of the engine to reduce friction and to assist in keeping the parts cool.

Objective of Lubrication

• To reduce friction between moving parts to its minimum value so that power loss is minimized.
• To reduce wear of the moving parts as far as possible. Apart from these primary objectives, lubrication also serves other important purposes, which may be called secondary.

These are as follows:

1. To provide cooling effect – The lubricating oil takes heat from the hot moving parts during its circulation and delivers it to the surrounding air through the crankcase.
2. To provide cushioning effect – The lubricating oil serves also as a good cushion against the shocks experienced by the engine. For example, instant combustion of the fuel in the combustion chamber produces a sudden pressure rise in the cylinder and the shock goes to the bearings through the piston, gudgeon pin and the connecting rod. This shock is then absorbed by the layer of oil present in the main bearings.
3. To provide cleaning action – The lubricating oil serves another useful purpose in providing a cleaning action. During its circulation it carries away many impurities, e.g. carbon particles.
4. To provide a sealing action – The lubricating oil also helps the piston rings to maintain an effective seal against the high pressure gases in the cylinder from leaking out toward the crankcase side. Other than engine, lubricants are used for protecting following components also: Gearbox Differential Steering gear box In different joints grease is used as lubricant.

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

Properties of a good lubricant 

As we understand that the lubricant is a very important component of an engine. We must know some of the properties.

1. Viscosity: In simple language, Viscosity may be considered as the resistance of the lubricating oil to flow. It is this property alone, due to which, the bearing surfaces are kept apart, i.e. hydrodynamic lubrication is maintained. The viscosity of the lubricating oil should be just sufficient to ensure hydrodynamic lubrication. A higher value than this would be of no use since it will involve higher power losses due to the increased oil resistance.

 The viscosity of the lubricating oil, at the time of starting the engine, should be low otherwise the engine may not start. On the other hand with the engine running, the oil viscosity decreases due to increase of temperature, which is contrary to what is desirable, since at all operating temperatures, the viscosity should not fall below the minimum value required to maintain hydrodynamic lubrication. Therefore, the viscosity should ideally remain the same at all temperatures. Relative change of viscosity with temperature is called viscosity index.
        However, the viscosity of all the oils does vary with temperature and, therefore, the oil with minimum variation is preferred. Viscosity is the most important property of lubricants and they are mostly selected on the basis of their viscosity and temperature coefficient of viscosity (viscosity index). 

2. Physical Stability: The lubricating oil must be stable physically at the lowest and the highest temperatures encountered in practice. There should not be any separation of solids at the lower temperatures and at higher temperatures it should not vapourise beyond a certain limit.

3. Chemical Stability:At higher temperature the oil should remain chemically stable. There should not be any tendency for oxide formation, many of the oxidation products being sticky substances clog the lines and cause faulty piston rings and valve action. 

                                The oil should also not decompose at high temperatures to form carbon. Carbon thus formed, lowers rings efficiency, thus reducing engine compression. The spark plugs and the valves also do not function efficiently due to sticking of carbon particles.

4. Resistance against Corrosion: The oil should not have any tendency to corrode the pipe lines, crankcase and other engine parts with which it comes into contact.

5. Pour Point: The minimum temperature at which the oil will pour is called its pour point. Obviously, since the oil will not be able to flow below the pour point, it cannot be used below this temperature for lubrication. Thus, the pour point of the oil should be less than the lowest temperature encountered in the engine.
                     The pour point is the temperature at which a lubricant just ceases to flow when cooled under standard conditions. The lower the pour point, the better is the lubricant.

6. Flash Point: The flash point of the oil should be sufficiently high so as to avoid flashing of Automobile Technology Level-2 17 oil vapours at the temperatures occurring in common use. A flash point higher than the minimum desired value will not serve any useful purpose.
                                          Flash point of a lubricating oil is the minimum temperature at which it gives off sufficient vapour so as to form an explosive mixture with air. If the oil is heated further a stage will reach when it will begin to burn continuously on applying a flame to it. This temperature is called the fire point.

7. Cleanliness: The oil should be sufficiently clean and stable itself so that the crankcase and oil lines are kept clean. Further it must contain agents, called detergents, which remove the impurities from the engine parts during oil circulation. These impurities may either be filtered out or removed with the change of oil at periodic intervals.