LUBRICATION SYSTEM OF I.C ENGINE

LUBRICATION SYSTEM OF I.C ENGINE

INTRODUCTION
When any two metal surfaces are in contact with each other and a relative motion takes place between them, then force of friction is developed however smooth the surfaces may appear to be.
The frictional force developed in an I.C.Engine which consists of no. of sliding & rotating components like bearings, pistons, valve gears etc may be so large that it may cause excessive wear & tear due to which replacement of components is very necessary. A large amount of the power developed by the engine may also be used to overcome this force of friction. Due to friction, heat is also generated. Due to generation of heat, the temp. of various components may rise to so high a value that a complete seizure of the engine components may take place.
Therefore, in order to overcome these difficulties, a thin film of a suitable lubricant is interposed where the metal-metal contact takes place. This thin film reduces the friction considerably by keeping the two metal surfaces apart from each other and thus wear, tear & temp. developed are also reduced greatly.

LUBRICATION
To supply lubricating oil between the moving parts is simply termed as “lubrication”.
Purpose of Lubrication
1. To reduce friction between the moving parts to a minimum value, thereby to reduce power loss due to friction.
2. To minimize wear of moving parts as far as possible.
3. To provide cooling effect by acting as a cooling medium & remove heat from various parts.
4. To form an effective seal between the piston rings & cylinder walls and thus prevent the escape of gases from the cylinder and avoid power loss.
5. To keep the engine parts clean by washing off and carrying away the impurities from the engine parts.
6. To provide cushion (protection) to the engine by absorbing the shocks developed by sudden application of load and instant combustion of fuel in the cylinder of the engine.
7. To reduce noise by absorbing shocks between the bearings and engine parts.
8. To prevent metallic components from corrosive attack by the acid formed during the combustion process.

Properties of Lubricant
1. Viscosity: Viscosity is a measure of the resistance to flow or the internal friction of the lubricant. It is used to grade lubricants. Viscosity is inversely proportional to temp. If temp. increases, the viscosity of the lubricant decreases and if temp. decreases, the viscosity of the lubricant increases. That is why low viscos oil is recommended for automobile engines in winter than summer. It also explains why engines are so hard to start in very cold weather. The viscosity of a lubricant should be just sufficient to ensure lubrication. If it is more than this value, power loss will be higher due to increased oil resistance.
2. Oiliness: It is the property of a lubricating oil to spread & attach itself firmly to the bearing surfaces. Generally, the oiliness of the lubricating oil should be high particularly when it is to be used for mating surfaces subjected to a high intensity of press. So that the metal is protected by a layer of the oil and the wear is considerably reduced.
3. Flash Point: Flash point of an oil is the min. temp. at which the lubricating oil will flash when a small flame is passed across its surface. The flash point of the lubricating oil must be higher than the temp. likely to be developed in the bearings in order to avoid the possibility of fire hazards.
4. Fire Point: If the lubricating oil is further heated after the flash point has been reached, the lowest temp. at which the oil will burn continuously is called fire point.
The fire point of a lubricant also must be high so that the oil does not burn in service.
5. Cloud Point: It is the temp. at which the lubricating oil changes its state from liquid to solid.
6. Pour Point: It is the lowest temp. at which the lubricating oil will pour. This property must be considered because of its effect on starting an engine in cold weather.
7. Corrosiveness: The present of acid (mineral acid, petroleum acid) is harmful to the metal surfaces. The lubrication oil should not attack chemically the materials used for the mating components.
The lubricant should not be corrosive, but it should give protection against corrosion.
8. Adhesives: It is the property of lubricating oil due to which the oil particles sticks with the metal surface.
9. Cleanliness: A lubricating oil must be clean. It should not contain dust and dirt particles

TYPES OF LUBRICANTS:
Lubricants are at following three types.
1. Solid: graphic, mica etc
2. Semi solid: grease
3. Liquid: mineral oil, vegetable oil, animal oil etc.
 Graphite is often mixed with oil to lubricate automobile spring. Graphite is also used as a cylinder lubricant.
 Grease is used for chassis lubrication.
 Mineral oils are almost used for engine lubrication.
Grade of lubricants: Generally lubricating oils are graded by their SAE ( society of automotive engineers) viscosity no.
5w,10w,20w SAE no. lubricating oil are for winter use.
20,30,40 SAE no. lubricating oil are for summer use.
Lubrication System: It is the system by means of which various engine parts are lubricated.

Engine Lubrication System: Engine lubrication system is mainly of following types.
1. Splash system
2. Pressure system
3. Petroil system
Splash System: In this system of lubrication the lubricating oil is stored in an oil sump. A scoop or dipper is made in the lower part of the connecting rod. When the engine runs, the dipper dips in the oil once in every revolution of the crank shaft, the oil is splashed on the cylinder wall. Due to this action engine walls, piston ring, crank shaft bearings are lubricated.
Pressure System: In this system of lubrication, the engine parts are lubricated under pressure feed. The lubricating oil is stored in a separate tank (in case of dry sump system) or in the sump (in case of wet sump system), from where an oil pump (gear pump) delivers the oil to the main oil gallery at a pressure of 2-4 kg/cm2 through an oil filter.
The oil from the main gallery goes to main bearing, from where some of it falls back to the sump after lubricating the main bearing and some is splashed to lubricate the cylinder walls and remaining goes through a hole to the crank pin. From the crank pin the lubricating oil goes to the piston pin through a hole in the connecting rod, where it lubricates the piston rings.
For lubricating cam shaft and liming gears the oil is led trough a separate oil line from the oil gallery.
The oil pressure gauge used in the system indicates the oil pressure in the system. Oil filter & strainer in the system clear off the oil from dust, metal particles and other harmful particles.
Petroil System: This system of lubrication is generally adopted in two stroke petrol engine line scooter and motor cycle. It is the simplest form of lubricating system. It does not consist of any separate part like oil pump for the purpose of lubrication.
In this system the lubricating oil is mixed into the fuel (petrol) while filling in the petrol tank of the vehicle in a specified ratio (ratio of fuel and lubricating oil is from 12:1 to 50:10 as per manufacturers specifications or recommendations.
When the fuel goes into the crank chamber during the engine operation, the oil particles go deep into the bearing surfaces due to gravity and lubricate then. The piston rings, cylinder walls, piston pin etc are lubricated in the same way.
If the engine is allowed to remain unused for a considerable time, the lubricating oil separates oil from petrol & leads to clogging (blocking) of passages in the carburetor, resulting the engine starting trouble. This is the main disadvantage of this system.

Parts of lubricating system
1. Oil sump: It is the lowest part of the crank chamber. It provides a covering for the crank shaft and contains oil. It is usually made of steel pressings. Sometimes it is made of aluminium or cast iron. It contains a drain plug at its bottom to drain out the oil.
2. Oil pump: Generally gear pump is used for pressure lubrication of I.C Engine. The function of the oil pump is to supply oil under pressure to various engine parts to be lubricated.
Gear pump: It consists of two messed spur gears enclosed in a housing. There is a very little clearance between the gear teeth and housing. One gear is attached to a shaft which is driven through suitable gear from the cam shaft or crank shaft of the engine. The other gear is free to rotates on its own bearing. When the pump is in operation, the oil is driven between the gear teeth from the inlet side to the outlet side. The pressure & quantity of the oil supplied by the pump can be varied by varying the speed of the gears at which they rotate. It delivers oil at a pressure of about 2-4 kg/cm2. A pressure relief valve is also provided in many oil pump to relieve the excessive pressure due to high engine speed.
3. Oil filter: as its name indicates, lubricating oil is filtered through it. The function of filter is to remove the impurities from the lubricating oil which may damage the engine bearings.
It consists of a filtering element placed in metallic casing. At the centre of the filtering element a perforated metal tube is fitted which collect the filtered oil and supply it to oil gallery.
4. Oil strainer: it is simply a wire mesh screen. It is attached to the inlet of the pump so that the oil going into the oil pump is free from impurities.

CONCLUSION:
We often think that the function of lubricating oil is only to lubricate the engine parts so that the power loss due to friction is minimum. But a lubricating oil has many other functions which are explained before.
Lubrication must be done properly and right type of lubricant should be used. Improper or inadequate lubrication of engine will cause serious trouble such as scored cylinders, worn or burnt out bearing, misfiring cylinders, dirty spark plug, stuck piston rings, engine deposits and sludge and excessive fuel consumption.

Reference Books
 The Automobile By Harbans Singh Reyat
 Thermal Engg. By A.S.Sarao
 Automobile Engineering By R.B.Gupta