2.12 Lubrication System in I.C. Engines 2.12.1 Need for Lubrication
In an I.C. engine, moving parts rub against each other causing frictional force. Due to the frictional force, heat is generated and the engine parts wear easily. Power is also lost due to friction, since more power is required to drive an engine having more friction between rubbing surfaces. To reduce the power lost and also wear and tear of the moving part substance called lubricant is introduced between, the rubbing surfaces. 2.12.2 Function of Lubrication
(a)
Lubricant reduces friction between moving part
(b)
It reduces wear and tear of the moving parts.
(c)
It minimizes power loss due to friction.
(d) It provides cooling effect. While lubricating it also carries some heat from the moving parts and delivers it to the surroundings through the bottom of the engine (crank case). (e)
It helps reduce noise created by the moving parts.
2.12.3 Engine parts which are lubricated
The following are some engine parts that require adequate lubrication. 1. Crank shaft
2. Crank pin
3. Big and small end of the connecting rode
4. Piston pin
5. Internal surfaces of cylinder walls
6. Piston rings
7. Valve mechanisms 8. Cam shaft etc.
2.12.4 Lubrication Systems
The main lubrication systems are: 1. Petrol lubrication system or Mist lubrication system. system. 2. Wet sump lubrication system. 2.12.5 Petrol Lubrication System or Mist Lubrication System.
This system of lubrication is used in scooters and motor cycles. About 3% to 6% of lubricating oil is added with petrol in the petrol tank. The petrol evaporates when the engine is working. The lubricating oil is left behind in the form of mist. The parts of the engine such as piston cylinder walls, connecting rod are lubricated by being wetted with the oil mist Disadvantage
(i) If the added oil is less, there will not be sufficient lubrication and even result in seizure of the engine, (ii) If the added oil is more, it will lead to excess exhaust smoke and carbon deposits in the cylinder, exhaust parts and spark plugs. 2.12.6 Wet sump Lubrication System Engine Lubrication
Two types of engine lubrication systems are used in internal-combustion engines: the splash system and the pressure-feed system. The pressure-feed system, with small modifications, is the more popular for more popular for modern automobile engines. The splash system is used on most lawn mower and outboard engines. 2.12.7 Pressure-Feed System.
In the pressure-feed system, oil is forced by the oil pump through oil lines and drilled passageways. The oil, passing through the drilled passageways under pressure, supplies the necessary lubrication for the crankshaft main bearings, the connecting-rod bearings piston-pin bushings, camshaft bearings, valve lifters, valve push rods, and rocker studs. Oil passing through the oil lines is directed to the timing gears and the valve rocker shafts in order to lubricate these parts. The cylinder walls are lubricated by oil thrown off the connecting-rod and piston-pin bearings. Some engines have oil spit holes in the connecting rods that line up with drilled holes in the crankshaft journal during each revolution, and through or spit a steam of oil onto the cylinder walls.
Pressure-Feed System
To enable the oil to pass from the drilled passageways in the engine block to the rotating crankshaft, the main bearings must have oil feed holes or grooves that line up with the drilled holes in the crankshaft each time the crankshaft rotates. The same is true in the case of the connecting-rod bearings and the drilled passageways in the connecting rods. Since the oil in the passageways is under pressure, each time the drilled holes in the crankshaft and connecting rod line up with the holes in the bearings, the pressure forces the oil through these drilled passages into the crankshaftand connecting rod, lubricating their respective bearings. After the oil has been forced to the area requiring lubrication, it falls back down into the oil pan ready to be picked up again and returned through the system. As the oil falls, it is frequently splashed by the moving parts onto some other part requiring lubrication. 2.12.8 The Splash system
The splash system is used only on small four-stroke-cycle engines such as lawn mower engines. As the engine is operating, dippers on the ends of the connecting rods enter the oil supply, pick up sufficient oil to lubricate the connecting-rod bearing, and splash oil to the upper parts of the engine. The oil is thrown up as droplets, or fine spray, which lubricates the cylinder walls, piston pins and valve mechanism.
The Splash system
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