Engine Design -Block

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Vehicle Design II

ENGINE BLOCK

Dr. Nouby M. Ghazaly

Automotive and Tractor Engineering Dept.

College of Engineering,Minia University-61111

[email protected]


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Engine block

The engine block is the main body

of the engine; all parts of the

engine are either inside the engine

block or attached to the outside of

it.

The engine block is casting of cast

iron, it is considered in two parts,

the crankcase and the cylinder

block.

The crankcase, which supports the

crankshaft, is hollow inside with one

or more rib-like castings that form

the main frame


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Cylinder block

The upper portion of the engine block is the cylinder block. This

portion contains the cylinders, the water passages (commonly

known as the "water jacket") (fig. 1), and oil passages (fig. 2).


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Cylinder block

Core plugs

Core (frost or expansion) plugs are used to seal core

holes in all cast cylinder blocks.

The purpose of the core holes is to allow the sand fromthe sand core moulds to exit the block after the blocks

are cast.


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Cylinder Block Material

The cylinder blocks are casting from:

Gray cast iron

Cast iron alloy containing nickel and chromium for high

strength and wear resistance. Some cylinder blocks are cast from a silicon aluminium

alloy.


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Cylinder-block material

The cylinder-block material should

(a) be relatively cheap,

(b) readily produce castings with good impressions,

(c) be easily machined,

d) be rigid and strong enough in both bending and torsion,

(e) have good abrasion resistance,(f) have good corrosion resistance,

g) have high thermal expansion,

(h) have a high thermal conductivity,

(i) hold its strength at high operating temperatures, and

(J) have a relatively low density.

Note: Although cast iron meets most of these requirements, it has a low thermal

conductivity and is comparatively heavier. Due to these limitations, light

aluminium alloys have been used as alternative cylinder-block materials for

petrol engines.


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Advantages of aluminium

cylinder blocks Advantages of aluminium cylinder blocks are ;

(i) Lighter in weight.

(ii) Attractive appearance.

(Hi) Easier machining during production.

(iv) Better heat dissipation.

A common aluminium alloy composition is 11.5% silicon, 0.5% manganese,

and 0.4% magnesium, with the balance (87.6%) aluminium. The high silicon

content in this alloy reduces expansion but improves cast-ability, strength,and abrasion resistance, while the other two elements strengthen the

aluminium structure. While this alloy provides a good corrosion resistance, it

can absorb only moderate shock loads.


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Cylinder Liners

(Sleeves)

The cylinder liners are :

the most loaded parts of an engine.,

They resist to the stresses due to the

action of gas pressures, side pressureof the piston, and heat stresses.

There are two types:

Dry liner

Wet liner

L


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y n er L ners

(Sleeves)

(i) dry liners are in direct contact

with the cylinder bore walls of

the cylinder block.

(ii) Wet Liners are supported only at

each end in the cylinder block and are

elsewhere in direct contact with the

engine coolant.


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Dry Liners.

Normally dry cylinder liners are provided under the following considerations:

(a) When the cylinder block is made from aluminium alloy, the cylinder bore

wall should be stronger and of much harder wear resistant material.

(b) For heavy duty operating conditions, the normal wear resistance of a cast-iron cylinder block can be improved through sleeves with superior properties.

(c) When the cylinder block is designed with siamesed adjacent cylinder bores in

order to reduce the over all length, then only dry liners are suitable.

(d) When a cylinder block has been rebored two or three times, then dry liners

are used to restore to the original size of the cylinder bore.


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Wet Liners.

Wet cylinder liners provide the following advantages if used in petrol engines

with aluminium alloy cylinder block having a high coefficient of expansion.

(a) Due to isolation of the bulk of the sleeve from the block, difficult expansion

problems can be resolved at one or two locations only.

(b) The use of wet liners simplifies the casting of the cylinder block. Also,

castings of suitable material can be used with an appropriate heat treatment for

structural requirements, rather than the cylinder-bore wear-resistance

treatments.

(c) With better outside surface finish and constant wall thickness the liner

improves the thermal conductance and uniformity of cylinder cooling.


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Wet liners fit

Wet liners fit into the cylinder block at the top and near the bottom, and the

remaining portion of the sleeve is unsupported.

O-rings are used to prevent leakage of the coolant. Some wet liner sleeves

have a flange at the top, which sits into a recess machined in the upper deck

of the block.

The liner is sealed at the bottom by one or more rubber O-rings, usually fitted

in grooves.

A flat gasket is used between these two joint faces . Since the top of the liner

sleeve has no side support, it depends totally on vertical compression of the

liner caused by the cylinder head and gasket during tightening down.


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Liner Materials

Some commonly used liner materials are

Steel alloy,

Nickel cast iron

alloy cast irons,

and heat treated chromium and other alloy cast irons.

The wear resistance of these metals is at least 50% more than the

cylinder block material. The typical specification of liner material is :

Iron 93.92 to 92.22%

Carbon 3 to 3.5%Silicon 1.8 to 2.4%

Manganese 0.5 to 0.8%

Phosphorous 0.4 to 0.7%

Sulphur 0.08%)

Chromium 0.3%


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Gaskets

Gaskets or static seals are used between attaching engine parts to seal thejoints for preventing either internal or external leakage. A gasket must

withstand the high pressure and temperature of the engine. Therefore, the

gasket

(i) must be prevent to the fluids in contact,

(ii) must fit to any existing surface imperfections,(iii) must be resilient to maintain sealing pressure, even when the joints are

slightly loosened as a result of temperature changes or vibration,

(iv) must be resistant to all expected changes in its environment due to

temperature, pressure variations, and age

(v) must be stable under compression conditions, avoiding excessive setting.


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Gasket

The following gaskets are commonly used in automobile engines.

(a) Copper-asbestos gasket.

(b) Steel-asbestos gasket.

(c) Steel-asbestos-copper gasket.

(d) Single steel ridged or corrugated gasket.

(e) Stainless steel gasket.

(f) Asbestos-coated steel sheet with separate steel beading around bore.

(g) Laminated steel and graphitized asbestos sheet with formed steel bore

bead.

(h) Asbestos impregnated rubber bonded with reinforced ferrule bead.(i) Asbestos/steel wire-reinforced tissue.


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Gaskets

Copper-Asbestos Gaskets.

This consists of an asbestos sheet cut to the required form, which is protected

with thin sheet copper. There is a copper sheet on each side of the asbestos

sheet, and the two copper sheets lap along the outer edges of the asbestos

sheet, so that the latter is completely covered.

Steel-Encased Gaskets.

Cylinder-head gaskets are made also of asbestos sheet covered in steel instead

of copper. Steel being harder does not have as good sealing properties as

copper, and a sealing coat of some heat-resistant, non-hardening material isgenerally applied to the gasket, either in the manufacturing process or during

installation. The edges of the steel sheet, of course, are not rust-proofed, and

some steel-encased gaskets are fitted with copper grommets at the waterways.

The principal advantage of steel- over copper-encased gaskets is that the

production cost of the former is about 20 per cent less.


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Cylinder Wear

The characteristic which is most important in judging cylinder irons is their

resistance to wear under engine- operating conditions.

Abrasion, which is due to foreign particles in the oil film;

Erosion, which is due to metal-to-metal contact between the cylinder wallon the one hand and the piston and rings on the other; and

Corrosion, which results from chemical action on the cylinder walls by the

products of combustion.


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LINER DIMENSIONS

Wet liner dim.

Dry liner dim.


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Questions?

Engine Design -Block

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