Patent GB-191023907-A (GB)
Title: Improvements in Change-speed Worm Gearing.
Inventor: DAWSON THOMAS
IPC: F16H3/06
Filed: 1910-10-15
Granted: 1912-01-15
Abstract: 23,907. Dawson, T. Oct. 15. [Cognate Application, 4013/11.] Variable - speed and reversing g e a r i n g. - R elates to a variablespeed or simple reversing worm driving-gear, applicable to motorvehicles &c.', and of the kind in which a slidable series of worms upon the driving-shaft are adapted to gear with a single worm-wheel or with a corresponding slidable series of worm-wheels upon a driven shaft at right-angles thereto. The invention is characterized by the provision of a tensile appliance connected to the end of the worm shaft and operated by a suitable lever to raise the end of this shaft to lift the worm in action out of engagement with its worm-wheel prior to axial adjustment of the worms to obtain variation of speed ratio or reversal. In the arrangement shown in Fig. 1, the pedal i serves to lift the worm shaft b out of action by means of a wire or other tensile member k connected to an intermediate rock-shaft j<1>. When so disengaged, a rocking lever h operates through bevel-gearing a longitudinal shaft carrying a worm engaging a rack formed on the side of the worm frame or box f, serving to adjust this longitudinally to bring any of the worms a<1>, a<2>, a<3> into position for engagement with a worm-wheel c upon a differential-driven axle d. The worms a<1>, a<2>, a<3> are of similar pitch and helical angle to permit engagement with the single worm - wheel. Toothed edges on the frame f engage teeth f<2>, f<3>, f<4> formed at different levels in the main casing to support the driving-shaft and to withstand end-thrust in the different positions of engagement. The teeth may be flat-topped to support the driving-shaft in a position of disengagement. The gears are retained in mesh by means of cams j adapted to be operated by the pedal i in conjunction with the tensile members k, and to engage surfaces j<2>, j<3>, j<4> at different levels, or grooves or recesses j<5>, j<6> in the disengaged position. Reversal is effected by means of a pivotally supported countershaft b<1>, normally held out of engagement by a spring n, but moved into engagement and also driven by bevel-gearing l<1>, l<2> when the worm frame f is moved into the extreme position shown in Fig. 1. In the modification shown in Fig. 3, the worm-shaft b is arranged and operated as previously indicated, but the respective driving- worms are adapted to co-operate with a suitable corresponding series of worm-wheels c<1>, c<2>, c<3> arranged to slide together on the differential casing of the axle d, and provided with adjusting-means acting synchronously with the worm-adjusting means, so as to bring the proper worm-wheel into position for engagement with the worm selected to transmit the drive. This adjustment is effected by means of cams p of the form shown in Fig. 5, acting against springs q, and mounted upon spindles p' geared by pinions s to racks r<2> connected to the operating-lever h shown in Fig. 1, so that such lever simultaneously controls the series of driving- worms and the series of driven worm-wheels shown in Fig. 3. The springs q may be dispensed with, and a duplicate set of cams p with similar operating - gear arranged in place thereof. Reversal in this arrangement is effected by means of a reversely threaded worm and worm-wheel pair in the series shown. The arrangement described with reference to Fig. 3 may be applied to give simply a single forward speed and a reverse drive.