POWER TRANSMISSION ELEMENTS AND MECHANISMS 199 



VARIABLE-SPEED DEVICES 



Fig. 415. — Device for transmitting power between fixed parallel 

 shafts. Convex disks mounted freely on a rocker arm and pressing 

 firmly against the flanges of the shaft wlieels by a coiled spring 

 form the intermediate sheave. Speed ratio changed bj^ moving 

 rocker lever. No reverse possible, but driven shaft may rotate 

 above or below driver speed. Convex disk must be mounted on 

 self-aligning bearings to ensure good contact at all positions. 



Driven cone^ 



^-Driving cone 

 Fig. 416. — These speed cones are moimted 

 at any convenient distance apart and con- 

 nected bj' a belt, whose outside edges consist 

 of an envelope of tough, flexible, wear- 

 resisting rubberized fabric built to withstand 

 the wear caused by the belt edge traveling 

 at a slightly different velocity from the part 

 of the cone in actual contact. Speed ratio 

 changed by sliding the belt longitudinally. 



Shaft 



Driven cone 



^Squeezed 

 belt 



Fig. 417. — Two cones mounted close 

 together and making actual contact through 

 a squeezed belt. Speed ratio is changed by 

 shifting the belt longitudinally. Taper on 

 cones must be moderate in order to avoid 

 excessive wear on the sides of the belt. 



-Drivinq 

 belt 



Fig. 418. — Another device to avoid belt 

 "creep" and wear in speed-cone transmis- 

 sions. The inner bands are tapered on the 

 mside and present a flat or crowned surface 

 to the belts in all positions. Speed ratio is 

 changed bj' moving the inner bands rather 

 than the main belts. 



