Patent GB-619072-A (GB)
Title: A bracket change speed gear with a crank shifting mechanism in particular for a bicycle or like vehicle comprising a coaster hub
IPC: B62M11/06
Filed: 1946-09-12
Abstract: 619,072. Change-speed gearing. KLEFFENS, E. J. VAN. Sept. 12, 1946, No. 27462. Convention date, Sept. 12, 1945. Addition to 612,523. [Class 80 (ii)] The bicycle bottom bracket change-speed gear of the parent Specification is characterised by the braking pawl, provided for co-operation with a coaster hub, being controlled by an interrupter device comprising a pawl mounted on the gear casing and a disc, rotatable on the crank-shaft, having finely-toothed portions cooperating with the pawl, and being rotatable from a fixed abutment against a spring, so that the disc is held by back-pedalling in predetermined sectors, the interrupter disc being coupled by a cam to the braking pawls such that braking with the cranks in the shifting sectors is impossible. The crank-shaft 6 is rotatably supported in the bottom bracket casing and carries rotatably mounted thereon the gears 29, 23 and 28 for low, normal and high speeds respectively, the gear 23 carrying the driving chain sprocket 18. The gears are clutchable to the shaft 6 by driving pawls such as 31 and 33 respectively for the normal and high speeds and by a braking pawl 44 which can co-operate with the internal ratchet teeth of the gear 23. These pawls are mounted on a common shaft 37a and tend to be held in the operative position under the springs 40, 41 on the adjusting pawls 40b, 41b which, however, have to engage the shifting-in recesses 16<11> and 16<111> made in a shifting pin 16 rotatable in the shaft 6 and arranged that only one pawl can be in the operative position at any time. The shifting-pin 16 has a pinion 52 on its left-hand end engaging with a gear 53<1> rigid with the shifting disc 53 and rotatable about the shaft 6. The shifting disc 53 has four equi-spaced recesses in its circumference which are engageable by the shifting pawl 54, the shapes of these recesses, the pawl 54 and the locking disc 57 rigid with the shaft 6 are such that the action of a continuously rotatable shifting disc and a locking disc as described in the parent case is obtained. Behind the locking disc 57 is journalled an interrupter disc 50 having two finely-toothed portions co-operating with the interrupting pawl 48 rigidly connected with the shifting pawl 54 and arranged that when in engagement with the disc 50, the shifting disc 53 cannot be held by the pawl 54. The disc 50 has a laterally extending cam 64 which abuts a pin 62 and carries one end of a spring 65 whose remote end is hooked to the locking disc 57. The cam 64 also keeps the braking pawl 44 in the inoperative position by means of a cam 36b on the pawl shaft 36a. With back-pedalling with the cranks within the braking sectors R, the disc 50 is held by the pawl 48, the spring 65 is unstressed and the braking pawl spring 51 moves the pawl into the operative position. On forward pedalling, the spring 65 is stressed, the pawl locked in the inoperative position and the disc 50 again carried along in the direction of rotation by the pin 62. To ensure the mutual locking of the driving and braking pawls, a locking cam 37b is mounted on the common shaft 37a and is located in the plane of the disc 50 to cooperate with the recess 50<1> of the disc. Thus, relative rotation of the interrupter disc 50 and the driving shaft causes the pawls on the shaft 37a to be moved to the inoperative position and the braking pawl to the operative position, the adjusting pawls being coupled to the driving pawls with lost motion to allow this. In a modification, the driving pawls are uniformly spaced round the shaft 6 and their shafts are made to act as the shifting pins, in that each shaft carries a cam similar to 37b co-operable with shifting-in recesses in the bore of the interrupter disc 50. Constructions are described and illustrated in which the driving or braking pawls may be formed integral with their shafts and located in suitable slots milled in the shaft 6. A simplified embodiment of the invention is also shown in which the interrupting and shifting discs are combined to form one disc, and the braking pawl is controlled by a pin in this disc co-operating with a bellcrank lever. In order to produce an easy change of speed, the internal ratchet teeth may be arranged as specified in Specification 614,332.