GB612814A - Improvements in or relating to change speed gears for bicycles and the like - Google Patents

Abstract

612,814. Change speed chain gearing. DALLIMORE, C. J., and WILLIAMS, G. March 1, 1945, Nos. 5133 and 12909. [Class 80 (ii)] In a change-speed chain gear for bicycles and tricycles having low- and high-speed sprockets alternatively driven from a driving chain which is moved transversely by a fork member to engage either sprocket, the horizontal operating movement of the fork is effected by back-pedalling. As shown, a fork 19, Fig. 1, normally lying out of engagement with the driving chain 22, is movable under the action of a push-rod 28, first rotating to engage the chain 22 and then traversing horizontally to move it from one to the other of the low- and high-speed sprockets 3, 4 respectively. The push-rod 28 is operated by a pin 30 on the chain-wheel 29, which coacts with a gravity or spring-loaded lost-motion arm 31 pivoted as shown in Fig. 5 on a lever 32, itself pivoted on the bicycle frame. A pin 34 on the end of the lever 32 engages with spring-loaded frictional damping a slot in the push-rod 28 which on back-pedalling is thus moved rearwards from the position shown in Fig. 1 until it has moved sufficiently for the pin 30 to clear the arm 31. The rear end of the push-rod 28 carries a pin 11 guided in a slot 12 in a fixed frame plate 7. Pivoted on the pin 11 are an arm 20 and a pawl 13. The arm 20 is connected to the fork 19 pivoted in the frame plate 7 and controls its rotation, whilst the pawl 13 coacts with ratchet teeth 14 on a rotatable cam plate 15 also mounted on the frame plate 7 and controls the horizontal movement of the fork 19 through a cam track 16, Fig. 3, on the plate 15 against which track the outer end of the spindle 17 of the fork 19 is spring biassed. After a speed change has been effected, forward pedalling is resumed, the pin 30 then moving the push-rod 28 forwards so rotating the fork 19 out of engagement with the chain 22 and causing the pawl 13 to pick up the next tooth of the ratchet 14 ready for another change. The members 28, 32 may be of spring steel or other resilient material, and the levers 31, 32 may have spring-biassed slotted connections with their pivots. In a modification, the fork 19 is operated as before, but from a pin disc rigid with the sprockets 3 and 4 instead of from the chain wheel, the push-rod 28 being replaced by a direct lever system, and the action of the pin in picking up the lost-motion arm being rendered more positive by a friction weight device.