GB468969A - Improvements in or relating to variable-speed gearing - Google Patents

Abstract

468,969. Variable-speed gearing. FROST, S. J. Jan. 17, 1936, Nos. 1610 and 23652. [Class 80 (ii)] A two-speed gear particularly for cycles comprises two chain sprockets 12, 17 driven at different speeds from a pedal crank having two co-operating sprockets and connecting chains. The high-speed sprocket 17 drives, through dogs 19 and 20 allowing a certain amount of lost motion, a ratchet wheel 18, with teeth 21, which drives the wheel hub 8 of the bicycle by means of a spring-loaded pawl 34. The low-speed sprocket 12 drives through. a freewheel device 14, a sleeve 10 carrying a cam member 16 with cam slopes 28 and 37. For the low-speed drive a pocket 41 in the cam slope 28 engages a roller 27 on a lever 26 pivotally mounted on the hub 8, the high-speed pawl being lifted from engagement by the cam 37 when this occurs. The lever 26 is biassed against a stop 31 by a tension spring 30 and a considerable force is required to force the roller 27 up the cam slope 28, against the spring 30 for the positive engagement of the low speed drive. Thus, on backpedalling or momentarily free-wheeling in high or low gear, the driving force is relieved and the pawl 34 overruns or due to the lostmotion connection of the dogs 19, 20 the roller 27 moves down the cam slope 28, until the lever 26 comes against the stop 31. On resuming the drive, if high gear is desired a comparatively gentle pedalling effort is made which is insufficient to lift the lever 26 and therefore the pawl 34 so that the high-speed pawl 34 drives, the cam 16 being carried around by a shoulder 40 on the lever 26 at a greater speed than the sprocket 12, which is allowed by the freewheel 14. The drive is then positive and any effort can be exerted on the pedals without effecting a change of speed. If however, on resuming the drive, a considerable pedalling effort is made, the roller 27 is forced up the cam slope 28 into its low-speed driving position and the pawl 34 is lifted out of engagement by the cam 37, the sprocket 12 thus taking up the low-speed drive, which is maintained until another freewheeling or back-pedalling movement is made. The freewheel device 14 and the pawl 34 provide freewheeling from either gear and to enable a fixed wheel action to be obtained when desired a set of dogs 22 is provided on the ratchet wheel 18 which are adapted to be engaged by a tongue 29 on the lever 26 when the stop 31 is removed. High or low gear can still be engaged in the normal manner, but on attempting to freewheel the tongue 29 positively engages the dogs 22.