Engine Lubrication Systems

Construction & Working of lubrication systems.

OBJECTIVES:-

·         To get knowledge about the lubricating system its additives, components.

INTRODUCTION:-

·         Lubrication system is used in the engine to run the engine by keeping wear proof, and working it without getting over heat, and keep the parts smooth and easily movable.

·         An Automatic Lubrication System, often referred to as a Centralized Lubrication System, generally comprises a controller or timer, a pump and reservoir, metering valves and fittings and supply and feed lines.

·         It typically delivers a controlled amount of lubricant (either grease or oil) to multiple, specific locations on a machine while the machine is operating, at specific times from a central location.

PROPERTIES OF LUBRICANTS:-

·         High oil film strength

·          Low friction

·          High wear resistance

·          High thermal stability

·          Non-corrosive

·          Highly anti-corrosive

·          Minimal dust/water content

·          Consistency of grease must not be altered to a significant extent even after it is repeatedly stirred.

TYPE OF LUBRICATING SYSTEMS:-

·         Splash Lubrication

·         Pressure Lubrication

PRESSURE LUBRICATING:-

·         Modern vehicle engines use a pressure or force-feed lubrication system where the oil is forced around the engine under pressure. A pump collects it through a pickup tube and a strainer and forces it through an oil filter, then into passageways in the engine block, called galleries.

·         The galleries allow oil to be fed to the camshaft bearings, the valve mechanism and the crankshaft main bearings. Holes drilled in the crankshaft webs allow the main bearings to supply oil to the big end bearings.

·         After circulating through the engine, the oil falls back to the sump to cool. This is called a wet-sump lubrication system because the oil is kept in the sump ready for the next time it’s used.

·         Some special engines use a dry sump lubrication system. It uses all of the parts that make up a wet sump system and it lubricates the engine in the same way.

SPLASH LUBRICATING:-

·         Most small 4-stroke petrol engines use what is called splash lubrication.

·         On horizontal-crankshaft engines, a dipper on the bottom of the connecting rod scoops up oil from the crankcase for the bearings.

·         In this engine it is also able to splash oil up to the valve mechanism. Alternatively, an oil slinger can be driven by the camshaft.

·         A similar system is used in most small vertical-crankshaft engines. Oil is also splashed up to the valve mechanism.

COMPONENTS OF LUBRICATION SYSTEM:-

OIL COOLER:-

·         Engines which operate under severe conditions may use an oil cooler to cool the oil in the engine.

·         In diesel engines, the oil cooler and oil filter are often on the same mounting, on the cylinder block.

·         The oil cooler is a heat exchanger. It transfers heat from the oil to coolant from the cooling system. Coolant circulates through tubes in the cooler and oil fed from the lubrication system surrounds the tubes. As the coolant circulates, heat is removed from the oil.

·         In another design, the oil cooler is mounted in the air stream at the front of the vehicle. This type of oil cooler uses the flow of air passing across its fins to cool the air circulating through it. It is called an oil-to air heat exchanger.

OIL INDICATORS:-

·         If a lubrication system fails it’s serious, so it’s crucial to know its working. If oil pressure falls too low, a pressure sensor in a gallery can light up a warning light, or register on a gauge.

·         Low oil pressure can mean a lack of oil. It may have leaked away, or it may have been burned. This can be caused by worn piston rings which let oil into the combustion chamber. Too little oil in the engine is a problem but so is too much. The simplest indicator of oil level is the dip stick.

OIL PRESSURE RELIEF VALVE:-

·         A normal pump is capable of delivering more oil than an engine needs. It’s a safety measure to ensure the engine is never starved for oil. As the pump rotates and engine speed increases, the volume of oil delivered also increases. The fixed clearances between the moving parts of the engine prevent oil escaping back to the sump and pressure builds up in the system.

·         An oil pressure relief valve stops excess pressure developing. It’s like a controlled leak, releasing just enough oil back to the sump to regulate the pressure of the whole system.

OIL PUMP:-

·         Oil pumps may be driven from the camshaft or the crankshaft. In a rotor-type oil pump, an inner rotor drives an outer one. This is generally driven by the camshaft. As they turn, the volume between them increases. This larger volume lowers the pressure at the pump inlet.

·         Outside atmospheric pressure is then higher. This forces oil into the pump and it fills the spaces between the rotor lobes. As the lobes of the inner rotor move into the spaces in the outer rotor, oil is squeezed out through the outlet. The crescent pumpuses a similar principle. It is mounted on the front of the cylinder block. This is generally driven by the crankshaft. The inner gear is on the end of the crankshaft which then drives the pump directly. An external toothed gear meshes with this inner one. Some gear teeth are meshed but others are separated by the crescent-shaped part of the pump housing.

·         The increasing volume between gear teeth causes pressure to fall. Oil is then taken through the intake port and carried around between the gears and crescent, then discharged to the outlet port. Similarly in a geared oilpump, the driving gear meshes with a second gear.

·         This is generally driven by the camshaft. As both gears turn, their teeth separate, creating a low pressure area. Higher atmospheric pressure outside forces oil up into the inlet. The spaces between the teeth fill with oil.

·         The gears rotate and carry oil around the chamber. The teeth mesh again and oil is forced from the outlet toward the oil filter.

PICKUP TUBE:-

·         Between the sump and oil pump is a pickup tube with a flat cup and a strainer immersed in the oil. The strainer stops large particles of dirt and carbon entering the pump and damaging it.

·         The pickup tube leads to the inlet of the oil pump on the low pressure side of the pump.

SPURT HOLES AND GALLERIES:-

·         Pistons, rings and pins are lubricated by oil thrown onto the cylinder walls from the connecting rod bearings. Some connecting rods have oil spurt holes. These holes are positioned to receive oil from similar holes in the crankshaft.

·         Oil can then spurt out at the point in the engine cycle when the largest area of cylinder wall is exposed. It lubricates the walls and gudgeon pin and also cools the underside of the piston.

SUMP:-

·         The sump is bolted to the engine under the crankcase. It is a reservoir or storage container for the engine lubricating oil and a collector for oil returning from the engine lubricating system.

·         The sump can be formed as a thin sheet metal pressing or aluminum and shaped to ensure that oil will return to its deepest section.

·         The oil pickup tube and strainer are located in this deep section to ensure they stay submerged in oil and to prevent air being drawn into the oil pump. Some high performance vehicles have a baffle tray fitted to prevent churning of the oil by the rotation of the crankshaft.

·         Baffles prevent oil from surging away from the pickup during cornering, braking and accelerating. The sump’s large external surface area helps heat transfer from the oil to the outside air. In some designs, the sump is aluminum alloy casting with fins and ribs to assist in this heat transfer.