ME 1015 PRODUCTION PLANNING AND CONTROL UNIT I INTRODUCTION

1ME2354 AUTOMOBILE ENGINEERINGNSK - APECN. SENTHIL KUMAR M.E, (Ph.D).,ASSISTANT PROFESSORDEPARTMENT OF MECHANICAL ENGINEERINGADHIPARASAKTHI ENGINEERING COLLEGE, MELMARUVATHUR.2UNIT I VEHICHLE STRUCTURE AND ENGINESTypes of automobiles , vehicle construction and different layouts, chassis, frame and body, resistances to vehicle motion and need for a gearbox, components of engine-their forms ,functions and materialsNSK - APEC3BOOKS REFERREDKirpal Singh, Automobile Engineering Vol 1 & 2 , Standard Publishers, 12th Edition 2009, New Delhi.Jain,K.K.,and Asthana .R.B, Automobile Engineering Tata McGraw Hill Publishers, New Delhi, 2002NSK - APEC4INTRODUCTIONAutomobile is a wheeled vehicle carrying its own motive power unit.An automobile is a self-propelled vehicle driven by an internal combustion engine and is used for transportation of goods and passengers.Automobiles are made up of a frame supporting the body and certain power developing and transmitting units, which are further supported by tyres and wheels through springs and axles.NSK - APEC5TYPES OF AUTOMOBILESBased on UsageMopeds.Motor cycles, scooters.Cars, jeeps.Buses and trucks.Based on CapacityHeavy transport vehicles (HTV) Trucks, buses.Light transport vehicles (LTV) Cars, jeeps.NSK - APEC6TYPES OF AUTOMOBILESBased on Make and ModelBajaj, Royal Enfield, Honda etc.Premier Padmini, Standard, Hindustan Ambassador, Maruti etc.Tata indica, Leyland, For Ikon, General motors Corsa etc. Based on Fuel usedPetrol Vehicles.Diesel Vehicles. NSK - APEC7TYPES OF AUTOMOBILESBase on Body StyleClose cars such as saloon, coupe etc.Open cars like sports car, convertible car etc.Special styles such as estate car, station wagon etc. Based on WheelsTwo wheelers scooters, motor cycles.Three wheelers autorickshaws, tempos.Four wheelers cars, jeeps.Six wheelers trucks, buses.NSK - APEC8TYPES OF AUTOMOBILESBased on DriveWhether the vehicle can be driven sitting towards right or left sideLeft hand drive American vehicles for use in U.S.ARight hand drive Indian vehicles.Whether the front axle, rear axle or both axles are driving axles. Front wheel drive Maruti car, Volkswagen car.Rear wheel drive Ambassador cars, Premier Padmini.All wheel drive Jeeps.NSK - APEC9TYPES OF AUTOMOBILESBased on TransmissionManual, in which ordinary crash type gear box is used (Indian cars).Semi-Automatic having a two pedal transmission using manual operation of the standard gear box, with automatic clutch control (Obsolete now).Fully-Automatic, which employs transmission that uses combinations of epicyclic gear trains and torque converters (Mercedes 7G-Tronic).Continuously variable with a transmission which can select any desired drive ratio within its range (Audi, Honda).Automated Manual, the cars with transmission that are basically manual, but operated hydraulically and electronically (Audi with DSG).10OFF-ROAD VEHICLESAn off-road vehicle is considered to be any type of vehicle which is capable of driving on and off paved or gravel surface.It is generally characterized by having large tires with deep, open treads, a flexible suspension, or even caterpillar tracks.Other vehicles that do not travel public streets or highways are generally termed off-highway vehicles, including tractors, forklifts, cranes, backhoes, bulldozers, and Golf carts11OFF-ROAD VEHICLES

The chassis of an automobile consists of following components suitably mounted.Engine and the radiator.Transmission system, consisting of the clutch, gear box, propeller shaft and the rear axle.Suspension system.Road wheels.Steering system.Brakes and fuel tank.CHASSISNSK - APEC12All the components are mounted either of two ways.Conventional Construction A separate frame is used. It is presently used only for heavy vehicles.Frameless or Unitary Construction No separate frame is used. For cars frameless type is used except of course for small manufacturers, who find it economical.CHASSISNSK - APEC13Conventional control chassis Engine is mounted in front of the drivers cabin, this arrangement avoids full utilization of the space.Semi-forward control chassis Engine is so mounted that half of it is in the drivers cabin whereas the other half is in front, outside the drivers cabin. Tata SE series is an example of it.Full-forward control chassis Engine is mounted completely inside the drivers cabin, going for maximum utilization of space. Tata E series of vehicle is an example of it.CHASSIS CLASSIFICATION14CONVENTIONAL CONSTRUCTION OF CHASSISIn this type of chassis construction the frame is the basic unit to which various components are attached and body is bolted onto the frame later on.FUNCTION OF THE FRAMETo support the chassis components and the body.To withstand static and dynamic loads without undue deflection or distortion.NSK - APEC15CONVENTIONAL CONSTRUCTION OF CHASSISLOADS ON THE FRAMEWeight of the vehicle and the passengers, which causes vertical bending of the side members.Vertical loads when the vehicle comes across a bump or hollow, which results in longitudinal torsion due to one wheel lifted (or lowered) with other wheels at the usual road level.Loads due to road camber, side wind, cornering force while taking a turn, which result in lateral bending of side members.NSK - APEC16CONVENTIONAL CONSTRUCTION OF CHASSISLOADS ON THE FRAMELoad due to wheel impact with road obstacles may cause that particular wheel to remain obstructed while the other wheel tends to move forward, distorting the frame to parallelogram shape.Engine torque and braking torque tending to bend the side members in the vertical plane.Sudden impact loads during a collision, which may result in a general collapse.NSK - APEC17FRAME CONSTRUCTIONThe frame structure shows the longitudinal members A and the cross members B.18

FRAME CONSTRUCTIONThe frame is upswept at the rear and front to accommodate the movement of the axles due to springing, which keeps the chassis height low.The frame is narrowed down at the front either as in figure to have a better steering lock, which gives a smaller turning circle.C are the brackets supporting the body.E1 are the dumb irons to act as bearing for spring shackles.Brackets E are meant for mounting the springs.NSK - APEC19FRAME CONSTRUCTIONThe extension of the chassis frame ahead of the front axle is called front overhang, whereas its extension beyond the rear axle is called rear overhang.NSK - APEC20

FRAME CONSTRUCTIONFramed construction is invariably used for commercial vehicles to carry large loads due to larger ground clearance and sufficient space.The engine clutch and the transmission are all bolted together to form one rigid assembly which is mounted usually on the front end of the frame, supported on the frame at three places by rubber blocks.The rubber blocks are used to isolate the engine from road shocks and the body from the engine vibrations.This method also accommodates any misalignment between the engine or the transmission relative to the frame or the bodyNSK - APEC21FRAME SECTIONSNSK - APEC22

FRAME MATERIALSNSK - APEC23Sl. NoMaterialAlloying %1Carbon0.25 0.35 %2Manganese0.35 0.75 %3Silicon0.30 % max4Nickel3 %5Phosphorous0.05 % max6Sulphur0.5 % maxAn Aluminium alloy called Alpax has also been used as frame materialSUB FRAMENormally the various components are bolted directly to the main frame.But many a time, these components are mounted on a separate frame called sub-frame.This sub-frame is further supported by the main frame at three points, isolating the effects of twisting and flexing of the main frames.NSK - APEC24SUB FRAME - AdvantagesThe mass of the sub-frame alone helps to damp vibrations.The provisions of sub-frame simplifies production on the assembly line and facilitates subsequent overhaul or repair.NSK - APEC25DEFECTS IN FRAMESThe only prominent defect that usually occurs in the frames due to accidents is the alignment fault, which is checked by means of plumb line.The vehicle is placed on a level surface and by suspending plumb line from four different points on each side of the frame, their position on the ground is marked.The vehicle is then taken away and the diagonals are measured between corresponding points.NSK - APEC26DEFECTS IN FRAMESThese should not differ more than 7 or 8 mm. If any of the corresponding diagonals do differ by more than this amount, the frame is out of alignment.The possible causes, them, may be due to,The dumb irons or side members may be bent.Cross members may be buckled.Some rivets may be loose or broken.NSK - APEC27DEFECTS IN FRAMESIf the damage to the frame members is small, they can be repaired by means of a hydraulic jack and wringing iron.If the damage is more, the bent frame member may be heated to straighten it.Another alternative may be to cut the damaged part and weld a new one instead.NSK - APEC28

FRAMELESS CONSTRUCTIONIn this type of construction, heavy side members used in conventional construction are eliminated.The floor is strengthened by cross-members and the body, all welded together.In some cases the sub-frames are used along with this type.NSK - APEC29VEHICLE DIMENSIONSTwo important dimensions used to describe the size of an automobile of the framed or the frameless type are,Wheel track This is the transverse distance between the tyre-to-ground centres on the near-side and the off-side.Wheel base This is the longitudinal distance between the centre lines of the front and the rear axles.

NSK - APEC30REQUIREMENTS OF AUTOMOBILE BODYThe body of an automobile, especially a car which is of frameless type, must satisfy the following requirements.In case of the heavier vehicles of the conventional frame type construction, the body and the frame should jointly meet these requirements.NSK - APEC31REQUIREMENTS OF AUTOMOBILE BODYStrength The body must be strong enough to withstand all types of forces to which the car is subjected, which include the weight of the car, passengers and the luggage, inertia, braking and side force. It should be able to cope with impact loads of reasonable magnitude.Stiffness The car body may be considered a beam supported on wheels at each end. It must posses sufficient stiffness to prevent excessive sagging in the middle. Stiffness is important for stability, handling and quietness.NSK - APEC32REQUIREMENTS OF AUTOMOBILE BODYTorsional Stiffness The body should be sufficiently rigid so as to resist twisting on bad roads.Space There must be adequate space in the body for the passengers and luggage both.Air drag The resistance of air during running depends upon the body shape and increases directly as the square of the vehicle speed. The shape of the body should be such that the air drag is minimum.NSK - APEC33REQUIREMENTS OF AUTOMOBILE BODYProtection against weather The design of the body must be such that the occupants and the luggage are protected from the bad weather.Lightness The body should be as light as possible in relation to the amount of space inside.Resistance to corrosion The body should be so designed that no moisture is accumulated which would produce rust. The materials used should be such that no corrosion takes place.NSK - APEC34REQUIREMENTS OF AUTOMOBILE BODYProtection in accident This is a very important consideration in the car body design. The body must be such that the driver is at maximum ease so that there are least chances of the accident taking place due to fatigue. However, in case the accident does take place, the body must protect the occupants.NSK - APEC35CONSTRUCTION DETAILS OF AUTOMOBILE BODYSince 1940s, most car bodies have been a unitary structure consisting of pressed steel panels spot-welded together, to which the engine, transmission, chassis components, seats and all other parts are attached.The modern car body, though still unitary in character, consists of a steel skeleton frame to which the body-sides, the bulkheads, the floor and the roof are attached.The frame members are often closed hollow beams formed by welding together two or more concave pressings.NSK - APEC36CONSTRUCTION DETAILS OF AUTOMOBILE BODYA modern car body can be seen as an upper body carried on a platform.The platform consists of following sections,Nose sub-assembly It includes the engine, front suspension mountings, front bulk-head, the inner wheel arches and the structural members for absorption of fontal impact energy. Rear sub-assembly It includes the rear suspension mountings, rear wheel arches and the structural members for absorption of rear impact energy.Centre floor It is required to be stiff as possible to help keep the cabin space intact while during impact the sub-assemblies collapse progressively.37CONSTRUCTION DETAILS OF AUTOMOBILE BODYBesides power train and suspension, the following components are also attached to the platform.The exhaust system.The fuel tank.The brake and the fuel line.To keep the design, development and production cost low, the same platform is usually used for different versions of the car model or even for several different car model.38CONSTRUCTION DETAILS OF AUTOMOBILE BODYThis can be done by changing the length of the centre floor section and thereby the wheel base.The nose sub-assembly is normally not changed, being most complex.The main components of a car body have been shown below, where the body sill and various pillars are the main load-taking members.39

CONSTRUCTION DETAILS OF AUTOMOBILE BODY40CONSTRUCTION DETAILS OF AUTOMOBILE BODYThe windscreen made out of safety glass should be large enough to provide a good vision to the driver.The door panels and the side panels should be strong enough to sustain some side impact.The shape of the body must be such that the air drag is minimum since at higher speeds, the streamlining of the bodywork becomes an important factor towards fuel consumption.The front and rear bumpers are expected to take resonable impact loads.41RESISTANCE TO VEHICLE MOTIONTo keep a vehicle moving, the engine has to develop sufficient power to overcome the opposing road resistance power, and to pull away from a standstill or to accelerate a reserve of power in addition to that absorbed by the road resistance must be available when required.Road resistance is expressed as tractive resistance (kN).The propelling thrust at the tyre to road interface needed to overcome this resistance is known as Tractive effect (kN). NSK - APEC42RESISTANCE TO VEHICLE MOTIONNSK - APEC43

ROLLING RESISTANCEPower has to be expended to overcome the restraining forces caused by the deformation of tyres and road surfaces and the interaction of frictional scrub when tractive effect is applied.Secondary causes of rolling resistance are wheel bearing, oil seal friction and the churning of the oil in the transmission system.It has been found that the flattening distortion of the tyre casing at the road surface interface consumes more energy as the wheel speed increases and therefore the rolling resistance will also rise slightly.NSK - APEC44ROLLING RESISTANCENSK - APEC45

ROLLING RESISTANCEFactors which influence the magnitude of the rolling resistance are the laden weight of the vehicle, type of road surface, and the design, construction and materials used in the manufacture of the tyre.NSK - APEC46

AIR RESISTANCEPower is needed to counteract the tractive resistance created by the vehicle moving through the air.This is caused by air being pushed aside and the formation of turbulence over the contour of the vehicles body.It has been found that the air resistance opposing force and air resistance power increase with the square and cube of the vehicles speed respectively.NSK - APEC47

AIR RESISTANCEThus at very low vehicle speeds air resistance is insignificant, but it becomes predominant in the upper speed range. Influencing factors which determine the amount of air resistance are frontal area of vehicle, vehicle speed, shape and streamlining of body and the wind speed and direction. NSK - APEC48GRADIENT RESISTANCEPower is required to propel a vehicle and its load not only along a level road but also up any gradient likely to be encountered.Therefore, a reserve of power must be available when climbing to overcome the potential energy produced by the weight of the vehicle as it is progressively lifted.The gradient resistance opposing motion, and therefore the tractive effect of power needed to drive the vehicle forward, is directly proportional to the laden weight of the vehicle and the magnitude of the gradient. NSK - APEC49GRADIENT RESISTANCEThus driving up a slope of 1 in 5 would require twice the reserve of power to that need to propel the same vehicle up a gradient of 1 in 10 at the same speed.NSK - APEC50

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NEED FOR A GEARBOXThe need of gear box in automobile is to increase / decrease the speed while driving the vehicle.Power from a petrol or diesel reciprocating engine transfers its power in the form of torque and angular speed to the propelling wheels of the vehicle to produce motion.The object of the gearbox is to enable the engines turning effect and its rotational speed output to be adjusted by choosing a range of under and overdrive gear ratios so that the vehicle responds to the drivers requirements within the limit of the various road conditions. 51NEED FOR A GEARBOXPower to weight ratio When choosing the lowest and highest gearbox gear ratios, the most important factor to consider is not just the available engine power but also the weight of the vehicle and any load it is expected to propel. Consequently, the power developed per unit weight of laden vehicle has to be known. This is usually expressed as the power to weight ratio,52

NEED FOR A GEARBOXRatio span Another major consideration when selecting gear ratios is deciding upon the steepest gradient, the vehicle is expected to climb (this may normally be taken as 20%, that is 1 in 5) and the maximum level road speed the vehicle is expected to reach in top gear with a small surplus of about 0.2% gradeability.The two extreme operating conditions just described set the highest and lowest gear ratios.53NEED FOR A GEARBOXTo fix these conditions, the ratio of road speed in highest gear to road speed in lowest gear at a given engine speed should be known (both road speeds being achieved at similar engine speed)..This quantity is referred to as the ratio span.54

NEED FOR A GEARBOXCar and light van gearboxes have ratio spans of about 3.5:1 if top gear is direct, but with overdrive this may be increased to about 4.5:1.Large commercial vehicles which have a low power to weight ratio, and therefore have very little surplus power when fully laden, require ratio spans of between 7.5 and 10:1, or even larger for special applications.55NEED FOR A GEARBOXEngine torque rise and speed operating range Commercial vehicle engines used to pull large loads are normally designed to have a positive torque rise curve, that is from maximum speed to peak torque with reducing engine speed the available torque increases. The amount of engine torque rise is normally expressed as a percentage of the peak torque from maximum speed (rated power) back to peak torque.56

COMPONENTS OF AN ENGINECooling System This prevents the engine from overheating. It may be of air cooling or water cooling types, the former being more commonly used in smaller engines of two-wheelers, while the later types of cooling systems are predominantly used in engines of the rest of the automobiles.Fuel System This includes storage tank for the fuel, piping work for supply to the engine and arrangement for mixing with air and spraying into the engine cylinder.NSK - APEC57COMPONENTS OF AN ENGINEExhaust System It function is to vent exhaust gases with least back pressure and also to reduce engine noise with the muffler. These days converters are also fitted in the exhaust pipe to reduce the harmful constituents in the exhaust system.Lubrication System This reduces friction to decrease wear of moving parts. Relatively less viscous lubricating oils are used in engines, whereas heavier oils and greases are used in the transmission and wheel bearings.NSK - APEC58COMPONENTS OF AN ENGINEIgnition System Its function is to supply high voltage surge at the desired instant and of adequate strength to produce a spark in the engine. Earlier electro-mechanical systems were used, which have given way to electronic systems in modern engine.Electrical System It consists of a storage battery, charging system and starting system. The battery supplies electricity for starting the engine, providing energy for spark and for all the electrical devices in the vehicle, e.g., lighting, heating, visiting, music system, etc. NSK - APEC59COMPONENTS OF AN ENGINEElectrical System The charging system consists mainly of an alternator and is used for continually charge the battery to keep it charged at all times. The starting system consists of a starting motor and a device to disconnect the same from the engine as soon as the engine is started.

NSK - APEC60COMPONENTS OF AN ENGINENSK - APEC61

COMPONENTS OF AN ENGINE Cylinder BlocksAll the major components, are installed on or in the engine block. These components including the cylinder bores, are machined very precisely. They must be thick enough to contain the pressure of the burning fuel mixture.A tight fit must be ensured between the cylinder base and the piston rings to enable piston rings to seal the combustible gas.If the cylinder becomes oval due to wear, some of the gas escapes through the piston rings. NSK - APEC62COMPONENTS OF AN ENGINE Cylinder BlocksThe gas which leaks through the piston rings is called blow-by, which reduces the efficiency of an engine.Most cylinder blocks were made of cast iron or grey iron as the material was easy to machine. The main disadvantage of iron being its weight, engine blocks are now being cast from lightweight aluminium, having less weight.

NSK - APEC63COMPONENTS OF AN ENGINE Cylinder BlocksNSK - APEC64

COMPONENTS OF AN ENGINE Cylinder LinerThe cylinder liner is a sleeve in which the piston of an engine reciprocates.The life of a cylinder between its re-bores depends on two main factors,Abrasion It depends on the atmospheric condition and the efficiency of the air filter and oil filter. Dusty atmospheric air is more harmful as it increases abrasion in the cylinder.Corrosion It is due to the corrosive products of combustion, which are formed after burning of fuel with air. Corrosion is accelerated at low cylinder temperature due to acid bearing moisture on the cylinder walls.65COMPONENTS OF AN ENGINE Cylinder LinerThe use of separate barrels or sleeves, which are known as cylinder liners, provides long life to the cylinder.These cylinder liners are made of superior material and are fitted in the cylinder block.The liners are removable and can be replaced when worn or damaged.The liners should have good wear resistance and the ability to retain oil to lubricate the surface between the walls and the piston rings.66COMPONENTS OF AN ENGINE Cylinder LinerFor cylinder liners, nickel-chromium iron has been popularly used, containing 3.5% carbon, 0.6% manganese, 1.5% phosphorous, 0.05% sulphur, 2% silicon, 2% nickel and 0.7% chromium.To increase the wear resistance, the liners are hardened by oil quenching.The cylinder liners are of two types.Dry liners They are not in direct contact with cooling water.Wet liners The cooling water comes in contact with the liner, hence the lower end of the liner is sealed using sealing rings or packing rings.67COMPONENTS OF AN ENGINE Cylinder Liner68

DRY LINER Vs. WET LINERNSK - APEC69Sl. NoWet LinerDry Liner1Can be easily replacedNeeds special tools because it is tight fitted in the cylinder block2It is properly cooled as it comes in direct contact with the cooling waterIt does not comes in direct contact with the cooling water. Hence the working temperature is more than wet liner3It needs leak proof joints, so that the cooling water does not leak into the crankcase.No such requirement is needed4It does not require accurate finishing on the outsideIt requires accurate finishing5Finishing may be completed before assemblyIt needs finishing after assemblyCOMPONENTS OF AN ENGINE - CrankcaseThe crankcase supports the cylinders and the crankshaft and is an important structure in the internal combustion engine.It also functions like a housing and protects the engine parts against dust, water and splashing mud.The crankcase stores lubricating oil required for lubricating the engine parts.The crankcase not only gives support to the engine parts and engine mountings, but also withstands the loads caused by piston thrust, gas pressure, primary and secondary forces and couples etc.70COMPONENTS OF AN ENGINE - CrankcaseThe cylinder block and the upper part of the crankcase form an integral cast.Thus a crankcase is usually divided into an upper and a lower section.The lower section is known as oil pan and acts as a reservoir for the storage of lubricating oil, which splashes due to the rotation of crank and also pumped to the engine bearings, thus lubricating the various engine parts.71COMPONENTS OF AN ENGINE - CrankcaseThe main forces acting on a cylinder block are due to,Gas pressure including force of explosion.Inertia forces due to reciprocating masses.Both these forces act along the connecting rod, i.e., line of stroke, which tends to lift the cylinder blocks from the crankcase.When the cylinder block and the crankcase are cast together in one unit, grey cast iron is used because it has rigidity, low cost and high wear resistance.72COMPONENTS OF AN ENGINE - Crankcase73

COMPONENTS OF AN ENGINE Cylinder HeadThe volume enclosed by the piston at TDC, the cylinder block and the cylinder head is known as the clearance volume.This is the combustion chamber.The various types of cylinder heads and the valve arrangements are,

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COMPONENTS OF AN ENGINE GasketsThe gasket is a piece of soft sheet or spongy sheet having similar holes and cuts as in the cylinder head and cylinder block so that the packing (gasket) placed between the cylinder block and cylinder head does not interfere with the flow of gases or water or bolts passed.The gasket prevents leakage and ensures tight fit joints.Sealing action is provided by the elastic deformation of the gasket material.The material of the gasket must be able to withstand high pressure and temperature.75COMPONENTS OF AN ENGINE GasketsThe types of gaskets which are frequently used are,Copper-asbestos gasket.Steel-asbestos gasket.Single sheet rigid or corrugated gasket.Stainless steel gasket.Cork gasket Used for the oil pan in crankcase.Rubber gasket.

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COMPONENTS OF AN ENGINE PistonA piston of an internal combustion engine is in the form of an inverted bucket shape and it is free to slide in the cylinder barrel.The gas tightness is secured by means of flexible piston rings, which are in the grooves of the piston, cut in the upper part of piston.A piston of an internal combustion engine serves three functions,It forms a moveable wall of the combustion chamber.It transmits turning force to the crankshaft via the connecting rod.It functions like a crosshead and transmits side thrust.77COMPONENTS OF AN ENGINE PistonThe piston must posses the following qualities,It must be strong enough to withstand high pressure caused due to the combustion of fuel.It must be very light in weight to have minimum primary and secondary forces.The piston material should be a good conductor of heat so that detonation is suppressed and higher compression ratio is possible.The piston operation must not be noisy.The piston must be of less coefficient of expansion.78COMPONENTS OF AN ENGINE PistonAn engine having a piston and cylinder head of aluminium alloy can be used at a compression ratio of 6.3 and it gives more power and fuel economy than a similar engine having a cast iron piton and cylinder head at a compression ratio of 5.3.79

COMPONENTS OF AN ENGINE Piston RingsPiston rings are those rings which are fitted in the grooves provided in pistons. Their functions are,To seal the passage inside the cylinder so that gases cannot leak from one side of the piston to the other side, which affects power and fuel consumption.They provide a path for conducting heat from the piston head to the cylinder walls, thus helping in reducing the piston temperature.The crankcase oil, used for engine lubrication is splashed by the crank, is prevented from passing into the combustion chamber. Piston rings scrap the excess oil from the cylinder walls and only a thin film of oil is left to lubricate the piston rings.80COMPONENTS OF AN ENGINE Piston RingsPiston rings are not completely closed and are provided with a gap at the ends.The gap allows the rings to fit over the piston and lets the rings expand without breaking.Generally two forms of gaps are provided.Straight or normal gapDiagonal or scarf gap81

COMPONENTS OF AN ENGINE Piston RingsPiston ring materials have changed from plain cast iron to materials such as pearlitic and modular iron as well as steel. Piston rings may be coated with chromium or molybdenum materials.Two types of piston rings widely used are,Compression ring Used to seal the combustion chamber and to provide a path for heat transfer from the piston to the cylinder wall, providing effective cooling.Oil control ring It is similar to a compression ring, but has a circumferential groove on its outer circumference. The function of the oil rings is to strip some of the lubricating oil from the cylinder walls and return the oil to the crankcase through the radial passage in the oil ring.82COMPONENTS OF AN ENGINE Piston Rings83

COMPONENTS OF AN ENGINE Piston PinA piston pin is also known as wrist pin or gudgeon pin because of its similarity in construction with human hand and arm joint.A piston pin is a link for connecting the piston and the connecting rods.Since the piston pin reciprocates with the piston, its weight is minimized by making it hollow, so that inertia forces at piston TDC are decreased.The piston pin is fitted in the bosses which are in the piston.84COMPONENTS OF AN ENGINE Piston PinPiston pins are made of case hardening steel, either plain carbon steel, nickel steel or chrome-nickel steel.85

COMPONENTS OF AN ENGINE Connecting RodThe connecting rod is a link, which connects the reciprocating piston and the rotating crank.Most connecting rods are made of medium carbon steel which has 0.35 to 0.45% carbon.However, the connecting rods of heavy duty engines are made of chrome-nickel and chrome-molybdenum steel.The connecting rods are drop forged.Connecting rods are made of I-section.86COMPONENTS OF AN ENGINE Connecting RodThe end of the connecting rod connected to the piston pin is called the small end because its size is smaller.The other end of the connecting rod attached to the crank pin is called the big end.

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COMPONENTS OF AN ENGINE Crank shaftThe crankshaft is an important part of the engine, which converts the reciprocating motion of the piston into rotary motion.This rotary motion of the crankshaft is used to rotate the shaft of a machine to get work.The motion of the piston is transmitted to the crank by the connecting rod.The crankshaft is subjected to torsional and bending stresses and is supported on the crankcase structure on large bearings.88COMPONENTS OF AN ENGINE Crank shaftA crankshaft is composed of crankpins, crank arms, crank journals and driving ends.Generally cranks are made of medium carbon steel and forged in a single piece.The physical properties of the material are restored by suitable heat treatment, consisting of normalizing, reheating and quenching.89COMPONENTS OF AN ENGINE Crank shaft90

COMPONENTS OF AN ENGINE Cam shaftThe camshaft receives the drive from the crankshaft.A camshaft consists of cams.Components like fuel pump, lubricating oil pump, generator, ignition unit and fan are driven by the camshaft.Either gear drive or chain drive may be used between the crankshaft and the camshaft.Non-metallic gear on a camshaft give noiseless drive.Usually Bakelite is used to mould gear with helical teeth.91

COMPONENTS OF AN ENGINE Cam shaftBakelite has a considerable degree of elasticity and it can also withstand greater loads than a cast iron gear at high speed.

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COMPONENTS OF AN ENGINE Cam shaft93

COMPONENTS OF AN ENGINE ValvesThe valves used in an engine following four-stroke cycle are mushroom-shaped with a conical seating surface.The valve head rests in the cylinder head on conical seating, the angle of the cone being 45.The valve stem passes through a guide, which has a plain hole.The valve guide is fitted in the cylinder head casting.The valve is closed and pressed on its seat by a spring or springs coiled in opposite directions.94COMPONENTS OF AN ENGINE ValvesThe valves in the modern engines are made of special alloy steels which are capable of retaining their mechanical strength at high temperaturesThey are able to resist the corrosive and erosive effects of the high temperature and high velocity of cylinder gases.The inlet valve is made up of chromium-nickel-molybdenum steel containing 0.35-0.65% chromium, 0.35-0.75% nickel and 0.12-0.25% molybdenum along with carbon and manganese.95COMPONENTS OF AN ENGINE ValvesThe exhaust valves, which run at high temperatures are made of silicon-chromium alloy steel.But nowadays, the exhaust valve is made of austenitic steel, which is better in impact value, hot hardness and resistance to oxidation and corrosion.Austenitic steel contains high percentage of chromium and nickel.96

COMPONENTS OF AN ENGINE Valves97

COMPONENTS OF AN ENGINE ManifoldsThe passages in the cylinder head leading to or from the valves are called ports.The system of pipes, which connect the intake ports of various engines, is called the inlet manifold.If the exhaust ports are similarly connected to a common exhaust system, then this system of piping is called the exhaust manifold.98COMPONENTS OF AN ENGINE Manifolds99

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