Author Description

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1912 edition. Excerpt: ...diameter to total lift appears much steeper than the other one, and it is therefore interesting to determine the values of angle 0. In Fig. i42 is plotted a curve for each of these cams, showing the angularity 6 of the thrust for any angle of cam motion from the point of valve opening. It will be seen that the angularity at the beginning of valve opening is least with the smaller base circle, but as the lifting progresses the angularity with the small base circle becomes the greater. The maximum values are 0 = 32 3o' for r = 4, and 9 = 34 for r = 3. These maximum angularities would, of course, be less if the corners of the cam were rounded off, as they always are in practice, but this rounding would reduce them in the same proportion. Another effect of the rounding would be that the angularity would vanish more fcradually than shown in the diagram. The cam with the larger base circle will open and close the valve more quickly, will strike the cam follower a slightly sharper blow, and require a somewhat stronger spring. Offset Cams--Cams with their centre lines offset from the axis of the cam follower in the direction of the cam travel--that is, toward the right if the cam turns right handedly, and Cam Motion from Beginning of Valve Opening. Fig. i42.--Angularity Of Cam Thrust. vice versa--have been used to a certain extent in order to decrease the side thrust on the push rod guide. The dropping slope of such cams must be very much convexed in order to allow the valve to close quietly. The advantage gained by using offset cams is due to the fact that the valve spring exerts a stronger pressure when the valve is fully lifted than when it is closed. The vertical reactions between the cam and push rod during the various phases of valve travel are as...