Patent GB-598381-A (GB)
Title: Change speed devices by means of a wheel of variable diameter
IPC: F16H9/00
Filed: 1945-06-22
Abstract: 598,381. Expanding wheel gearing. SOC. CIVILE D'ETUDES TECHNIQUES. June 22, 1945, No. 16007. Convention date, July 17, 1941. [Class 80(ii)] In an expanding wheel for a variablespeed gear, toothed elements move radially to lie on successive concentric circles and all elements but one move angularly to preserve pitch distances, by allowing a gap between the one element and its adjacent element, the gap being formed between elements not in connection with the chain at the time of change. The invention is also applicable to other forms of flexible transmission such as belt or cable. A shaft 5 has spaced flanges 3, 4 between which is a spool-shaped member 2 having flanges 6, 7 free to rotate about the shaft. The flanges 3, 4 and 6, 7 have slots 9, 10 respectively, formed of a series of straight lines and traced in such a manner that the common points of both sets of slots lie on common concentric circles. Toothed elements 11 have flanges 13 carrying the pins 14, 15 which engage with the slots 9, 10. The flange 7 has two diametrically opposed slots 18, 19 at its periphery, and the flange 4 has notches 20, the number of which corresponds to the number of speeds obtainable. A lug-carrier 21 is mounted with radial sliding movement on the shaft 5 adjacent to the flange 4 and has two lugs 22, 23 in engagement with the slots 18, 19 and capable of engagement with the notches 20. A cam 25 is rockably mounted on a stationary member 28 and can be tilted by a Bowden cable mechanism to engage with the lugs 22, 23 to cause radial movement of the lug carrier. When the wheel is working at its lowest effective diameter all toothed elements 11 are in contact to form a continuous sprocket, the pins 14, 15 are at the bases of the slots 9, 10 as in Fig. 1, and the lug 22 is at the bottom of slot 18 and engaged with one of the notches 20 to rigidly connect members 1, 2, which comprise flanges 3, 4 and 5, 6 respectively. When the cam 25 is rocked it engages with the lug 22 to lift the carrier 21 and disengage the lug from the notch 20, thus freeing members 1, 2, and allowing relative angular movement to cause the pins 14, 15 and therefore the toothed elements 11 to move radially and angularly due to the action of slots 9, 10. Continued rotation allows lug 23 to be depressed by the cam until it engages with another notch 20 to produce rigid connection between the members 1, 2. The toothed elements then lie on a circle whose circumference is greater by one or more multiples of the chain pitch, the differences in length of the circumferences of the smallest and subsequent circles being compensated by the spacing apart of two adjacent elements which were not in connection with the chain at the time of the change. Another movement of the cam produces another upward change in effective diameter and the spacing apart of two elements diametrically opposed to the already spaced elements, which preserves the balance of the wheel. Downward changes in diameter are effected by reversing the direction of rotation of the wheel and operating the cam in the reverse direction. Modifications are also described which allow changes to be made without reversing the wheel, when the wheel is used as a driven element, and which prevent straining of the mechanism should a downward or upward change be made when the toothed elements are already at their respective limits of travel.