VALVES AND VALVE GEAR DESIGN DEPENDS ON THE ARRANGEMENTS OF THE VALVES IN THE CYLINDER BLOCK OR IN THE HEAD. THE ARRANGEMENTS OF THE VALVES IN THE.

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

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

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

VALVE DIMENSIONSVALVE DIMENSIONS

VALVE DIMENSIONSVALVE DIMENSIONS

d

Dd d

i

vo i

0 42 0 46

1 06 1 16

. .

. .

TYPICAL INLET VALVETYPICAL INLET VALVE

VALVE DIMENSIONSVALVE DIMENSIONS

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

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. .

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'

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'

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

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

.

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

. . .

.

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

. . .

.

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

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

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

.

. .

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

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

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