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VALVES AND VALVE GEARVALVES AND VALVE GEAR
DESIGN DEPENDS ONDESIGN DEPENDS ON
• THE ARRANGEMENTS OF THE VALVES IN THE ARRANGEMENTS OF THE VALVES IN THE CYLINDER BLOCK OR IN THE HEAD.THE CYLINDER BLOCK OR IN THE HEAD.
• THE SHAPE OF THE COMBUSTION THE SHAPE OF THE COMBUSTION CHAMBERCHAMBER
• THE ARRANGEMENT OF THE VALVES THE ARRANGEMENT OF THE VALVES –UNILATERALLY ALONG THE ENGINES UNILATERALLY ALONG THE ENGINES LONGITUDINAL AXI SLONGITUDINAL AXI S
–BILATERAL CROSS-WISEBILATERAL CROSS-WISE
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DESIGN DEPENDS ONDESIGN DEPENDS ON
•ARRANGEMENT OF THE ARRANGEMENT OF THE CAMSHAFTCAMSHAFT
•THE TYPE OF TAPPETSTHE TYPE OF TAPPETS–FLAT FACEFLAT FACE–ROLLERROLLER–BARREL BARREL –LEVERLEVER
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DESIGN DEPENDS ONDESIGN DEPENDS ON
•THE DESIGN OF THE ROKKERS THE DESIGN OF THE ROKKERS –ONE OR TWO ARM ROKKERSONE OR TWO ARM ROKKERS
•THE NUMBER AND TYPE OF THE NUMBER AND TYPE OF SPRINGSSPRINGS–CYLINDRICALCYLINDRICAL–TAPEREDTAPERED
•THE TYPE OF DRIVE FROM THE TYPE OF DRIVE FROM CRANKSHAFT TO CAMSHAFTCRANKSHAFT TO CAMSHAFT
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VALVE DIMENSIONSVALVE DIMENSIONS
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VALVE DIMENSIONSVALVE DIMENSIONS
d
Dd d
i
vo i
0 42 0 46
1 06 1 16
. .
. .
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TYPICAL INLET VALVETYPICAL INLET VALVE
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VALVE DIMENSIONSVALVE DIMENSIONS
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INLET VALVE DIMENSIONSINLET VALVE DIMENSIONS
d
Dd d
i
vo i
0 42 0 46
1 06 1 16
. .
. .
vi
vis
d
mmdd
)25.017.0(
2.58
1
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VALVE FLOW AREAVALVE FLOW AREA
FOR FOR = 45 = 45 oo THE MINIMUM FLOW AREA CAN BE THE MINIMUM FLOW AREA CAN BE
REDUCED TO THE FOLLOWING RELATION :REDUCED TO THE FOLLOWING RELATION :
WHERE WHERE
ah
dh
v vi
2 2
h d or h Dvo 0 25 0 12. .
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STRENGTH CONTROLSTRENGTH CONTROLfor valve head thicknessfor valve head thickness
THE HEAD OF THE VALVE IS SUBJECTED TO THE HEAD OF THE VALVE IS SUBJECTED TO – UNIFORM MAXIMUM GAS PRESSUREUNIFORM MAXIMUM GAS PRESSURE– VALVE SPRING FORCE WHEN VALVE IS SEATEDVALVE SPRING FORCE WHEN VALVE IS SEATED
CONCENTRATED LOAD DUE TO VALVE SPRING : CONCENTRATED LOAD DUE TO VALVE SPRING :
F P P d ds vi s 4 1
2 2'
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STRENGTH CONTROLSTRENGTH CONTROLfor valve head thicknessfor valve head thickness
CONCENTRATED LOAD DUE TO VALVE SPRING : CONCENTRATED LOAD DUE TO VALVE SPRING :
WHEREWHERE
PP’’ = = PRESSURE DIFFERENCE BETWEEN THE EXHAUST PRESSURE DIFFERENCE BETWEEN THE EXHAUST GAS AT THE EXHAUST MANIFOLD AND THE IN-GAS AT THE EXHAUST MANIFOLD AND THE IN-CYLINDER GAS PRESSURE DURING INTAKECYLINDER GAS PRESSURE DURING INTAKE
PP1 1 == MINIMUM PRESSURE REQUIRED BETWEEN MINIMUM PRESSURE REQUIRED BETWEEN VALVE VALVE AND SEAT IN ORDER TO AVOID LEAKGAGEAND SEAT IN ORDER TO AVOID LEAKGAGE
PP’’ = 0.2 BAR AND P = 0.2 BAR AND P11 = 0.7 BAR= 0.7 BAR
F P P d ds vi s 4 1
2 2'
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STRENGTH CONTROLSTRENGTH CONTROLfor valve head thicknessfor valve head thickness
• BENDING STRESS AT VALVE HEAD DUE BENDING STRESS AT VALVE HEAD DUE TO CONCENTRATED LOAD AT CENTER :TO CONCENTRATED LOAD AT CENTER :
• STRESS DUE TO UNFORM LOADING :STRESS DUE TO UNFORM LOADING :
TOTAL STRESS :TOTAL STRESS :
2s
vi
sb
F
d3
d214.1
2
vimax
'b
dP.
4
1
kPa10x5.0 5'bbb
'bbb
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STRENGTH CONTROLSTRENGTH CONTROLfor valve seatfor valve seat
VALVE SEAT IS CHECKED FOR COMPRESSION :VALVE SEAT IS CHECKED FOR COMPRESSION :
sc
vo
vo vi
d P
d dx kPa
4
4 4
2 8 10
2
2 2
5max
.
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VALVE SPRINGVALVE SPRING
DEFLECTION OF VALVE DEFLECTION OF VALVE WHEN SEATEDWHEN SEATED
ffdd= = Pretension (m)Pretension (m)
i =i = number of number of effective effective turnsturns
G =G = 8.5 x 108.5 x 1077 kPa kPa (Modulus (Modulus of rigidity )of rigidity )
r =r = coil radiuscoil radius
ddww = = spring wire spring wire diameterdiameter
fi r F
d Gds
w
64 3
4
. . .
.
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VALVE SPRINGVALVE SPRING
ffdd= h= hmaxmax
ddww = (4 - 5) mm = (4 - 5) mm
2r = (0.63 - 0.88) . d2r = (0.63 - 0.88) . dvivi
(choose a rounded (choose a rounded figure)figure)
THEREFORE THEREFORE
• ROUND OFF TO THE ROUND OFF TO THE NEXT HIGHER INTEGER NEXT HIGHER INTEGER VALUEVALUE
DEFLECTION OF VALVE DEFLECTION OF VALVE WHEN SEATEDWHEN SEATED
ffdd= = Pretension (m)Pretension (m)
i =i = number of number of effective effective turnsturns
G =G = 8.5 x 108.5 x 1077 kPa kPa (Modulus (Modulus of rigidity )of rigidity )
r =r = coil radiuscoil radius
ddww = = spring wire spring wire diameterdiameter
if d G
r Fd w
s
. .
. .
4
364
fi r F
d Gds
w
64 3
4
. . .
.
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VALVE SPRINGVALVE SPRING
• MINIMUM LENGTH OF COMPRESSED COIL :MINIMUM LENGTH OF COMPRESSED COIL :
• FREE LENGTH OF THE SPRING :FREE LENGTH OF THE SPRING :
• CHECKING AGAINST RESONANCE :CHECKING AGAINST RESONANCE :
lmin . . d i i mmw coil coil 2 0 3
l lfree df h min
361 62
122. .d
i rw
cam
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STRENGTH CHECK FORSTRENGTH CHECK FORVALVE SPRINGVALVE SPRING
• FORCE APPLIED TO THE SPRING AT MAXIMUM FORCE APPLIED TO THE SPRING AT MAXIMUM VALVE OPENNING:VALVE OPENNING:
• MAXIMUM SHEAR STRESS :MAXIMUM SHEAR STRESS :
F Fh f
fsd
dmax
max
max. .
..
162 8 103
5F r
dx kPa
w
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CAMSHAFTCAMSHAFT
• THE CAMSHAFTS OF IN-LINE ENGINES ARE THE CAMSHAFTS OF IN-LINE ENGINES ARE USUALLY PROVIDED WITH SUPPORTS AFTER USUALLY PROVIDED WITH SUPPORTS AFTER EVERY OTHER CYLINDEREVERY OTHER CYLINDER
• TAPPETS :TAPPETS :– LENGTH TO DIAMETER RATIOLENGTH TO DIAMETER RATIO
Diameter d Dc sh: . . .. . 0 28 0 35
l
l
t
t
t
t
doverhead
dnormal
0 6
2 0 2 2
.
. .
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KINEMATICS OF VALVESKINEMATICS OF VALVES
CONVEX CAMSCONVEX CAMS
THEY CONSIST OF TWO ARCS WITH RAD I I :THEY CONSIST OF TWO ARCS WITH RAD I I :
1 AND n
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KINEMATICS OF VALVESKINEMATICS OF VALVES
TANGENTIAL CAMSTANGENTIAL CAMS
THEY CONSIST OF TWO STARIGHT LINES THEY CONSIST OF TWO STARIGHT LINES TANGENTIAL TO THE BASE CIRCLE AND AN ARC TANGENTIAL TO THE BASE CIRCLE AND AN ARC
WITH A RADIUS WITH A RADIUS
nn
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TAPPET AND ROKKER ARMTAPPET AND ROKKER ARM
• MAXIMUM LIFT OF MAXIMUM LIFT OF TAPPETTAPPET
• ROLLER TAPPETS ARE USED FOR TANGENTIAL CAMS
hd
i
i y
tvi
r
r
max. .
. .
0 25 0 28
1 4 1 75