Patent GB-612523-A (GB)
Title: Improvements in or relating to change speed gears for bicycles and like vehicles
IPC: B62M11/06
Filed: 1946-01-30
Abstract: 612,523. Change-speed gearing. KIEFFENS, E. J. VAN. Jan. 30, 1946, No. 3028. Convention date, July 18, 1941. [Class 80 (ii)] A countershaft change - speed gear for bicycles, in which the gears or sprockets are connected to the driving shaft through internal ratchet mechanism, has the change of ratio produced by motion of the cranks, and has a rotatably mounted shifting disc retained at predetermined positions of the cranks by a pawl- and-ratchet disc rigid, or limitedly movable, with the driving shaft and having re-entrant portions, the pawl bearing on the ratchet disc so that retention of the shifting disc is only possible within predetermined crank positions. A pedal crank-shaft 6 has an enlarged central portion on which are journalled three gears 23, 28, 29 meshing with corresponding gears on a countershaft (not shown) to provide normal, high and low speeds respectively when they are connected to the shaft 6 by the respective pawls 30, 31, 32, 33 and 34, 35. The gear 23 extends to the right and is rigid with a normal chain sprocket for transmitting the drive to a rear coaster hub, The pawls of the gears 23, 28 are pivoted on spindles 36a, 37a and are arranged to be pressed into engagement with the internal ratchet teeth of the gears by springs 40a, 41a passing over shifting pins 16a, 16b. The shifting pins extend through the thickened portion of the shaft 6 and have semicircular recesses cut in them at 90 degrees such that when one spring, say, 40a is in a recess, thereby allowing the pawls 30, 31 to be engaged, the spring 41a is on the circular part of the pin and the pawls 32, 33 are held out of engagement. The shifting pins 36a, 37a are rotated through two 90 degrees sectors, against the action of left-hand coil springs 52c, by cranks 52 engaging the slots 52b in the shifting disc 53 rotatably mounted on the shaft 6. The low-speed gear 29 is engageable with the shaft 6 through the pawls 34, 35 which engage under the action of the springs 51 when the two other gears are disengaged and the gear 29 no longer overruns the shaft 6. A braking pawl 44 is also contained within the gear 29 and is rigid with the spindle 36a, which spindle has flats formed thereon which co-operate with projections in the bores of the pawls 30, 31, 32, 33 to prevent simultaneous engagement of the braking pawl and the normal and high-speed pawls with the consequent locking of the mechanism. The change of gear is effected by pedalling forward from one of the dead-centre positions of the cranks, after the particular change has been selected by back-pedalling with the cranks within a sector embracing the dead-centre positions, upward changes taking place when the left-hand crank is near the upper deadcentre and conversely. When the cranks are out of the dead-centre sectors, back pedalling produces braking through the coaster hub. To these ends a ratchet disc 57 is mounted for rotation, limited by a pin 62 abutting a driving ring 63, about the shaft 6 and is restrained to a normal position by the tension spring 61. During normal rotation, the ratchet disc is driven in a forward direction by the pin 62 bearing against the stop c1 of the ring 63 clamped to the shaft 6. The shifting disc 53 is provided with ratchet teeth 55, 56 engageable by a spring-loaded shifting pawl 54 pivoted on an arcuate segment 50a rigid with the gear casing. Rollers 54a at the ends of the pawls bear against the periphery of the ratchet disc 57 and during forward rotation of the disc drop into recesses 55a down the steep side d and up the sloping side d1. On reverse pedalling the roller 54a drops into a recess 55a and abuts face d, whereby the disc 57 is arrested and spring 61 is stressed until the pin 62 abuts the stop c of the ring 63. Further pedalling rotates the disc 57 backwards and presses the roller out of the recess, whereupon the disc returns to its normal position under the action of the spring 61. If forward pedalling takes place from one of the dead-centre positions after the roller has entered the recess, the pawl 54 engages one of the ratchet teeth 55, 56 to arrest the shifting disc and so cause rotation of the cranks 52 to change the gear. The shifting disc is prevented from moving back under the action of the springs 52c by a pawl catch 58 mounted on the shaft 6 and engaging pins 59 or 60 on the disc. Release of this pawl catch for downward changes is occasioned by one of the pawls 54 engaging the tail of pawl 58. Prevention of braking by back pedalling at the shifting sectors is caused by the segments 50a engaging an arm 48 resiliently connected to the spindle 36a of the braking pawl and thus holding the pawl out of engagement over these sectors. In a second embodiment, the ratchet and shifting discs are modified and the pawl catch is reversed so that the actual change of gear occurs during the back-pedalling period as opposed to forward pedalling in the first embodiment. Further, the low speed may be engaged from the high speed directly after back-pedal braking. A further modification is also described in which the cranks 52 may be replaced by gears having eight teeth and engaging with a thirty-two toothed gear on the shifting disc. Specification 502,818 is referred to.