Patent GB-490596-A (GB)
Title: Improvements in variable ratio gearing
IPC: G07F15/08
Filed: 1937-02-12
Abstract: 490,596. Variable-ratio gear mechanism for prepayment meters. ENGLISH ELECTRIC CO., Ltd., TILSTONE, G., and DONELLY, J. F. Feb. 12, 1937, Nos. 4260, 8790, and 24878. [Class 27] [Also in Groups XXIV and XIX] Variable-ratio gearing, particularly for use in the price-changing mechanism of prepayment meters, comprises a driving wheel 1, Fig. 1, provided with a set of pin teeth 4, arranged concyclically around, and parallel to the axis of the wheel, which are urged into a retracted position by springs 6 but are adapted to be pushed out into an engaging position with a star wheel 5 by relative rotation of a cam-plate 2 to the wheel 1. By varying the number of effective teeth the motion transmitted to the star wheel 5 each revolution of the driving wheel is varied. The adjustment of the cam-plate 2 is effected by means of a knob 7 which also carries an apertured plate 8 which may uncover indicating numerals on the face of the wheel 1 and may also have a spring catch 9 for engaging locating recesses on the face of the wheel 1. Two of these devices may be combined as shown in Fig. 5, to provide for a fine and a coarse adjustment of the gear ratio between a clock motor 13 and a spindle 17 of a prepayment type electric supply meter for price-changing purposes. The two pin wheels 1, 1a are geared together and drive star wheels 5, 5a respectively. One star wheel 5a drives the spindle 17 through a differential and step-up gearing 15 whilst the other 5 drives directly through the differential so that the star wheel 5 imparts a much smaller movement to the spindle 17 which is added to, or subtracted from, that derived from the star wheel 5a. This enables a fine and a coarse adjustment of the gear ratio by adjustment of the number of effective driving pins on the wheels 5 and 5a respectively. In another modification, Figs. 6 and 7, the star wheel 5 forms part of a planetary system the carrier 25 of which is driven by the shaft 24, a loose sun wheel 26 constituting the driven member, and the pin wheel 20 being stationary. In this arrangement with no pin teeth 4 projecting the carrier 25 and driven wheel 26 rotate with the driving shaft, the star wheel 5 being held by a light detent (not shown), but when the pin teeth 4 are moved into the path of the star wheel a backward movement is superimposed on the sun wheel 26 depending upon the number of teeth brought into action. In this construction the pins 4 are forced into engaging position by a flexible metal strip 21 which is withdrawn from an outer idle groove 19a into an inner groove 19b to move the required number of pins 4 into effective engaging position by rotation of an arm 23 to which the strip 21 is attached. This arrangement allows a complete or practically complete circle of pin teeth to be utilized on the wheel 20 whereas in the other arrangements only half the full circle can be utilized for variation of the ratio. Two of the planetary devices according to Figs. 6 and 7 may be combined in a single unit to provide a coarse and fine adjustment of gear ratio and a single pin wheel may carry both sets of pins, each set comprising a half-circle of pins and co-operating with its own star wheel the two star wheels driving a single driven wheel through ratchet devices. The adjustment may be effected through a common member and a cyclometer type indicator may be employed to indicate the combined setting. In a further modification a single star wheel may be employed to co-operate with both sets of teeth, the gear ratio from the star wheel to the driven wheel being changed by a cam device each half revolution. In another form of the invention, instead of the pins 4 being moved axially on their wheel, two discs are provided each with a half-circle of pins which are moved circumferentially relatively to each other to vary the number of effective pins driving onto a wide-faced or double star wheel from a half-circle to a complete circle. One of the wheels may further be provided with axially movable pins to enable any number of pins from none at all up to the full circle to be obtained. Specification 490,657 is referred to.