1. Engine Design and Operation

8/2/2019 1. Engine Design and Operation

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CHAPTER 1ENGINE SYSTEM


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OBJECTIVESExplain the principles of internal combustion

engine operation

Identify internal combustion engine parts

Describe the function of engine parts


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Engine characteristics


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ENGINE DESIGN AND OPERATION

Four Stroke Cycle

Intake

Compression

Power

Exhaust


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TWO-STROKE CYCLE

Common in some smallengine such as lawn moverengines, and some dieselengine

Valve train is eliminated

Each upward piston stroke is

a compression stroke, andeach downward piston strokeis a power stroke in a two-stroke cycle engine.


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OTTO CYCLE


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DIESEL CYCLE


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VALVE MECHANISM AND CAM SHAFT

DRIVES

Valve mechanisms vary depending on the

camshaft location


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CAMSHAFT AND VALVE OPERATION

Intake stroke: The crankshaft completed one-

half a revolution, while the camshaft rotated one-

quarter revolution.

Compression stroke: valves remain closed. the

crankshaft rotates for one half revolution while

the camshaft turns one-quarter revolution.


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..

Power stroke: Both valves remain closed the

crankshaft turns half revolution, and the

camshaft rotates one quarter revolution.

Exhaust stroke: The crankshaft completes

another half turn, and the camshaft rotates one-

quarter revolution.


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CAMSHAFT LOCATION

Flathead or Side Valve

Overhead Valve (OHV)

Overhead Cam (OHC


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ENGINE BLOCK TYPES

In-Line Blocks

V-Type Blocks

Opposed type Blocks:


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ENGINE SYSTEMS

Ignition System.

Fuel System

Emission Control Systems

Exhaust System.

Lubrication system:

Cooling system


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REVIEW OF ENGINE MEASUREMENTS

Bore and Stroke

The bore is thediameter of the

cylinder and ismeasured acrossthe cylinder.

Piston stroke:

It is the distance thatthe piston movesfrom TDC to BDC


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Continue.

Displacement:

The volume of the cylinder between TDC andBDC is referred to as displacement

valve overlap.The crankshaft rotation near TDC on the exhauststroke when both the intake and exhaust valvesare open is called valve overlap.

Compression ratioThe compression ratio is the ratio of the cylinder

volume with the piston at BDC to the cylindervolume with the piston at TDC


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COMPRESSION RATIO

CALCULATION:

If the cylinder volume with the piston at

BDC is 480 cubic centimeters [cc], and the

cylinder volume with the piston at TDC is

60 cc, the compression ratio is 8:1.


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EFFECTS OF COMPRESSION RATIO

Higher compression ratio produce more power thanengines with a lower compression ratio.

The cylinder heat on the compression stroke increasesproportionally.

The fuel may explode rather than burn smoothly in thecombustion chamber.

This exploding action causes detonation

Higher octane fuel reduces this detonation problem to

some extent.The type of fuel recommended by the vehicle

manufacturer is determined largely by thecompression ratio.


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Continue

Compression Ratio for BMW Engine Series

M 43 9.7:1

M54B22 10.8:1

M54B25 10.5:1

M54B30 10.2:1


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FIRING ORDER

The order in which various cylinders of

Multi cylinder engine fire is called the firing

order

4 Cylinder Engine 1 2 4 3 or 1 3 4 2

6 Cylinder Engine1 5 3 6 2 4 or 1 4 2 6 3 5


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ENERGY EFFICIENCY

Thermal Efficiency

Thermal energy is the relationship

between the engine power output and theheat energy available in the fuel. A

percentage is used to express this

relationship.


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Mechanical Efficiency

Mechanical efficiency is the relationship

between the engine power delivered and the

power that would be delivered if the engineoperated without any power loss. The

mechanical efficiency of an engine is expressed

as a percentage.


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Volumetric Efficiency.

Volumetric efficiency is the relationshipbetween the amounts of air actually taken into

the cylinder on the intake stroke compared to theamount of air required to fill the cylinder atatmospheric pressure. Volumetric pressure isalso expressed as a percentage.


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Torque and Horsepower

Torque is transferred from the engine

crankshaft through the drive train to the drive

wheels.

Torque = force x distance.

torque is measured in Newton-meters (Nm).


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BASIC ENGINE MECHANICAL

SYSTEM

Crank case

The crankcase is made of Aluminum alloy with

drawn cast iron bushes ( M54)Cast iron crankcase used in M 43 engine


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BLOCK ASSEMBLIES

Cast iron alloy

Aluminum block are becoming more common.

Aluminum block has steel cylinder liners

The aluminum in other block is mixed with silicon

so the silicon accumulates on the cylinder walls

to provide a hard surface that does not require a

sleeve.


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CYLINDER SLEEVES

The cylinder is cast integrally

with the block in most engines.

Heavy-duty engines have

removable dry-type or wet-typereplaceable cylinder sleeves.

A wet-type cylinder sleeve is in

contact with the coolant. This

type of sleeve must be sealedin the block at the top and

bottom


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MAIN BEARING BORES.

The main bearing bores

support the crankshaft in the

block.

The main bearing boresmust be strong enough to

withstand combustion

forces without distorting or

stretching.


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CAMSHAFT BEARING

Camshaft bearing and bearing bores must

support the load of the camshaft and valve train.


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VALVE LIFTER BORES

The valve lifter bores are machined in the block

directly above the camshaft lobes.

Oil is supplied from the main oil gallery in the

block to each valve lifter bore.


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COOLANT JACKETS.

Coolant jackets surround the outside ofeach cylinder wall in the block.

Coolant is circulated through each of thesecoolant jackets to cool the cylinder walls.

A threaded coolant drain plug is positionednear the bottom of the coolant jackets inthe block


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CRANKSHAFTS


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3

1

2 4

5

6

7


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INDEX EXPLANATION

1 Crankshaft

2 Upper bearing shells

3 Lower bearing shells

4 Upper thrust bearing shell

5 Lower bearing shell

6 Incremental gearwheel

7 Ball bearing for gear shaft


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.

The crankshaft changes the vertical piston

movement to rotary motion

Crankshafts may contain cast iron alloy or

forged steel.

All the main bearing and connecting rod bearingjournals are machined to a highly polished finish.


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.

Bearing inserts are located between the main

bearing bores and the main bearing journals on

the crankshaft

Connecting rod bearing inserts are mountedbetween the connecting rod bores and the

crankshaft journals.

Oil passages are drilled from each main bearing

journal to the connecting rod journals to assure

adequate oil supply at the connecting rod

bearings.


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A flex plate, or

flywheel, is bolted to

the transmission end

of the crankshaft and

a vibration damper

and pulley is pressed

onto the front of the

crankshaft


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CONNECTING RODS, PISTONS,

PISTON PINS, AND PISTON RINGS.

Connecting Rod


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Connecting Rod.

Steel-forged, tapered I

beam design.

The connecting rod bore fits

over the crankshaft journal,and the eye in the upper end

of the connecting rod fits

over the piston pin

The connecting rod cap is

bolted to the upper part of

the rod.


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PistonPISTON


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Piston.


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Piston..


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Piston..

Aluminum alloy pistons

The top of the piston is called the head, or

domePiston ring grooves are cut into the sides

of the piston just below the piston head

The ridges between the ring grooves are

referred to as lands


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Piston

Piston must be assembled on the

connecting rods correctly, and the

complete piston and rod

assembly must be installed

properly in the cylinder to

maintain the pin offset in the

correct position

The piston must have sufficientclearance to allow a film of oil

between the piston and the

cylinder wall.


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PISTON PIN.

Piston pins are manufactured from hard steel

Polished exterior surface

One of the most common methods of a mountingthe pin the piston and connecting rod is to pressthe pin into the rod and allow it to rotate in thepiston with a precision clearance

There must be enough clearance between the pinand the piston pin bore or rod bushing to allow afilm of oil between these components.


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PISTON RINGS

The piston rings fit into the piston ringgrooves and provide sealing betweenthe piston and the cylinder walls

Control the amount of oil on the cylinder

walls to prevent excessive amounts ofoil from moving past the rings into thecombustion chamber.

Made from cast iron or nodular iron.

Piston rings may be classified ascompression rings or oil rings. Manypistons have two compression rings inthe upper ring grooves and an oil ring inthe lower groove.


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CAMSHAFT

camshafts are made from a hardened cast ironalloy

A lobe is positioned on the camshaft for each

valve in the engine.The camshaft changes the rotary motion of this

shaft to reciprocating motion of the valves

Marks on the camshaft and crankshaft sprockets

must be properly aligned before the timing chainis installed to time the camshaft in relation to thecrankshaft.


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PARTS OF A CAM LOBE AND A VALVE

TIMING CHART

Parts of a cam lobeA Valve timing chart


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VALVE LIFTERS,PUSH ROD,ROCKER

ARMS AND VALVES


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CYLINDER HEAD

Cylinder heads were made from cast iron

modern engines are usually equipped with

aluminum cylinder heads.

The lower side of the cylinder head contains thecombustion chamber recesses

Threaded openings in the combustion chamber

accept the spark plugs

Coolant passages surround the combustion

chamber and spark plug to provide adequate

cooling.


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CYLINDER HEADS AND INTAKE

MANIFOLD

Warning: The torque on engine bolts is

extremely important, especially on aluminum

components. Improper torque results in warpedcomponents. When servicing an engine, always

follow the torque instructions in the vehicle

manufacturers service manual.

1. Engine Design and Operation

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