Design of a 200 horsepower aeronautical engine . iven above. Layoff the clearance circle C outside the base off from the center line connecting the twocenters, an angle equal to ^ the valve period. Letthis line intersect the clearance circle at thepoint P. Prom P draw a tangent T to the clearancecircle. Now draw an arc A which is tangent to thebase circle, the top circle and the tangent T tothe clearance circle. If the arc A becomes straightthe radii R and r must be changed. Drawing #17 shows the valve lift diagrams forboth the inlet and exhaust cams. The curves wereplotted directly
Design of a 200 horsepower aeronautical engine . iven above. Layoff the clearance circle C outside the base off from the center line connecting the twocenters, an angle equal to ^ the valve period. Letthis line intersect the clearance circle at thepoint P. Prom P draw a tangent T to the clearancecircle. Now draw an arc A which is tangent to thebase circle, the top circle and the tangent T tothe clearance circle. If the arc A becomes straightthe radii R and r must be changed. Drawing #17 shows the valve lift diagrams forboth the inlet and exhaust cams. The curves wereplotted directly from the cam layout given on draw-ing number 9. The advantage in using the mushroom type camis that the valve accelerates very quickly at the ? n ? • *?.^ ? ?. • -;: J ?.., a i. c :> an 00 r-;; 11 - c >^ J^ie 0 if J ?\c ?? »..;? ,., .: .; ?. *>-\ i,; ??••? ! avoxift VX7 oni ? . : !:•• ; ? fi i Page # Page # of the lift. As compared with the tan-gential and constant acceleration ceuiis it ranicsfirst in quick opening; but the steepness at thebeginning of the lift curve is a measure of theblow dealt the cam follower by the cam when firstcoming in contact with it. On comparing the liftdiagrams of the mushroom, tajigential aind constantacceleration cams it can be seen that the mushroomtype cam crosses the clearance line by far thegreatest angle, consequently this cam would be ex-pected to be the most noisy. However, in the mush-room cam the speed of lift at the beginning exceedsthat of the other two cams, hence the volumetricefficiency would be expected to be greatest withthat type of cam. From a standpoint of strength ofvalve spring required the mushroom cam ranks firstin merit. From drawing #17, it can be seen that the valveaccelerates to the point A and from there to fulllift it is retarded. It is also evident that the s . .. b*^•?.:/? _^.oo ik . ,1!. ?i
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