Post on 24-Dec-2015
NAMES 1-RAMY EBRAHEM ABDEL RAHMAN
2-MAHMOUD AHMED ABDEL RAOUF3-MOHAMED MAGD ALDEEN MOHAMED
4-MAHMOUD LOTFY ELHADY5-ADEL REFAT ABD ELQADER
6-AHMED MOHAMED ESAM
SUPERVISED BY/
PROF.DR./SAAD ABDELHAMEED
SIDE CAM
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Single Overhead Cam (OHC)/(SOHC)
Single cam mounted in head.
Opens both intake and exhaust
valves.One cam on an
inline engine and two cams on a vee
engine.
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Dual Overhead Cam (DOHC)
Camshafts mounted in cylinder head.
One cam opens intake valves and one opens exhaust valves.
Often used with 4 valves per cylinder.
Most high performance of all
types.Vee engines have 4
cams.
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DOHC
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Overhead Valve EnginesHas valves in cylinder
head increasing compression.
Camshaft still in block.
Uses lifters, pushrods and rocker arms.
Most common head design until 1990’s.
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CamshaftsOpens the valves at the
right time.Actually converts rotary
motion to reciprocating motion.
Uses a cam lobe for each valve.
Usually made of cast iron.
Has a great effect on engine performance.
Can be given auxiliary functions like running the
oil pump or distributor.
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CAMSHAFT CONSTRUCTIONCam lobesCamshaft thrust
plateCam bearingsCam housing and
cam cover
Patent Figures
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Cam Lobe TerminologyHeel as known as
the base circle.Nose is the tip of
the lobe which determines cam
lift.Opening and
closing flanks and ramps.
Timing points are where the cam
starts to open and close the valve.
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Cam Lobe LiftThe distance the
valve is pushed open.
It is determined by the height of
the lobe.
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Cam Duration
This chart is in degrees of
crankshaft rotation.Note when the
valves open and close and on which strokes. This is the
duration.It’s not what it may
seem to be!
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Camshaft DrivesGear on gearGear and chainBelt and notched
pulleyCam gear ALWAYS
is twice as large as the crank gear, this makes the
cam turn at ½ the speed of the
crank.
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Gear to Gear Drive
Simplest drive system.
Reliable and strong but noisy.
Reverses Direction of Power 2 times
CW>CCW>CW
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Gear and Chain Drive
Quieter the gear types.
Allows cam to be further away from
crankshaft.
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Timing Belt
Used primarily on overhead cam
engines.Uses a kevlar belt.
(police vests)Can snap or stretch
causing catastrophic damage to non-free
running engines.Chains remain more
popular with engine makers.
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PushrodsMetal rod which transfers force from the lifter
to the rocker arm.
Push Rod The push rod is used to control the
opening and closing of the valve. The push rod is controlled by the cam shaft. As the
rod is pushed up by the lob on the cam shaft, the push rod forces the rocker arm to
open the valve into the combustion chamber .
The push rod is used in engines where the camshaft is located in the block of the
engine .
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VALVE LIFTERS
Solid LiftersRoller LiftersHydraulic LiftersFollowers
Valve Lifter or Tappet
May be solid, roller, or hydraulicThe lifter follows the cam lobes and
pushes on the pushrodSolid and roller lifters require adjustable
rocker armsHydraulic type lifters fill with oil and
lengthen to compensate for any clearances in the valve system
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SOLID LIFTERS
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ROLLER LIFTERS
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HYDRAULIC LIFTERS
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FOLLOWERSohc
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Rocker Arms
Rocker arms are made of stamped steel, cast iron or
aluminum.They transmit the
force of the pushrod to the
valve.Some have
adjusters.
Reciprocating Engine Design and Construction
Rocker Arms
Transmits the lifting force from the cam to the valve.
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Rocker ArmsRoller- Stamped
Stamped
CastAdjuster
Pivot
Rocker arms•Wear on faces & push rod
sockets•Wear in adjusting screws
•Stamped rockers cannot be refaced •Forged, cast, & fabricated rockers can be
refaced
ComponentMaterialYield Strength (GPa)
Base Plate, Cylinder Head
Aluminum Alloy 29669
Camshaft, Fulcrums, Rocker Arms,
Tappets, Tappet Guides
Cast Iron (ASTM 60)150
Rocker Arm Supports, Rocker Arm Pins
1020 Steel200
Reciprocating Engine Design and Construction
Valves
Reciprocating Engine Design and Construction
Valves
Fuel/air mixture enters the cylinders through the intake valve.
Burned gases are expelled through the exhaust valve.
Mushroom or tulip type depending on shape.
Reciprocating Engine Design and Construction
Reciprocating Engine Design and Construction
Valve Construction
Intake valves, because of lower operating temperatures, can be made of chrome-nickel
steel.
Exhaust valves are made of exotic metals such as inconel, silicon-chromium or cobalt-
chromium alloys.
Reciprocating Engine Design and Construction
Valve Construction
Head
Face
Neck
Tip
Stem
Reciprocating Engine Design and Construction
Valve Construction
Valve head has ground face which forms a seal against the ground valve seat in the cylinder
head.
Valve face ground to an angle of either 30° or 45°.
Valve face made more durable by the application of stellite (an alloy of cobalt and
chromium).
Reciprocating Engine Design and Construction
Valve Construction
Valve stem acts as a pilot for the valve head and rides in the valve guide.
Surface-hardened to resist wear.
Some stems are hollow and partially filled with metallic sodium.
Reciprocating Engine Design and Construction
Valve Construction
The neck is the part that forms the junction between the head and the stem.
The tip is hardened to with stand the hammering of the valve rocker arm.
Reciprocating Engine Design and Construction
Valve Construction
Machined groove near tip receives the split-ring keys which form a lock ring to hold the
valve spring retaining washer.
Reciprocating Engine Design and Construction
Valve-Operating Mechanism
Each valve must open at the proper time, stay open for the required length of time, and close
at the proper time.
Timing of the valves is controlled by the valve-operating mechanism.
Reciprocating Engine Design and Construction
Valve-Operating Mechanism
Intake valves open just before the piston reaches top dead center, and exhaust valves
remain open after top dead center.
At this particular instant both valves are open at the same time (end of the exhaust stroke
and beginning of the intake stroke).
This valve overlap results in better volumetric efficiency and lower operating temperatures.
Reciprocating Engine Design and Construction
Valve-Operating Mechanism (Opposed engine)
Reciprocating Engine Design and Construction
Valve-Operating Mechanism
(Radial engine)
Reciprocating Engine Design and Construction
Valve Springs
Function is to
close the valveand to hold thevalve securely
on the valveseat.
Reciprocating Engine Design and Construction
Valve Springs
Two or more springs used to eliminate spring vibration or surging during different engine
speeds.
Held in place by split locks installed in the recess of the valve spring upper retainer
washer.
Reciprocating Engine Design and Construction
Bearings
Reciprocating Engine Design and Construction
Bearings
Any surface which supports, or is supported by, another surface.
Composed of material that is strong enough to withstand the pressure imposed on it.
Permit the other surface to move with a minimum of friction and wear.
Lubricated bearings.
Reciprocating Engine Design and Construction
Bearings
Three types of lubricated bearings used:
Plain BearingsBall BearingsRoller Bearings
Bearings are required to take radial loads, thrust loads, and a combination of the two.
Reciprocating Engine Design and Construction
Plain BearingsUsed for crankshaft, cam ring, camshaft,
connecting rods, and accessory drive shaft.
Subjected to radialloads.
Made of nonferrousmetals.
Reciprocating Engine Design and Construction
Ball BearingsUsed in supercharger impeller shaft bearings
and rocker arm bearings.
Special deep groove ball bearings are used in some aircraft engines to transmit propeller
thrust to the engines nose section.
Reciprocating Engine Design and Construction
Roller BearingsStraight roller bearings used where the
bearing is subjected to radial loads only.
Tapered roller bearings used where bearing is subjected to both radial and thrust loads.