| 摘要 |
693,764. Change-speed friction gearing. GUEST, L. V.. SHEPHARD, P., and BIRMINGHAM SOUND REPRODUCERS, Ltd. June 8, 1951 [June 28, 1950], No. 16215/50. Class 80 (ii). Change-speed friction gearing for gramophones, of the kind including a stepped friction wheel 9 adapted to be driven by the motor 3 of the machine and a rubber-tyred friction idler disc 13 adapted to engage between the stepped friction wheel and a circumferential surface 6 on the turntable, the stepped friction wheel and the friction idler disc being disposed for relative axial movement, is characterized by cams or projections 33, 34 being provided between adjacent portions 10, 11, 12 of the stepped wheel, to facilitate the passage of the idler from its smaller to its larger diameter portions, and by either the stepped friction wheel or the friction idler disc being biased in the axial direction to engage the idler disc with the larger diameter portion of the stepped friction wheel. As shown, the friction idler disc 13 is mounted for rotation on a pin 18 movable in a slot along an arm 16, and is urged to engage the stepped friction wheel &c. by a spring 21. The arm 16 is attached to a spindle 14, rotatable and axially movable in a sleeve 15, which is biased downwardly both by gravity and by a spring 30, so that the idler tends to engage with the portion 12 of the stepped wheel. The velocity ratio is changed by moving the spindle 14 vertically, this being effected by a lever 25, pivoted in a support 24, engaging the spindle 14 at one end and being engaged at its other end by a cam 26 on a rotatable spindle 27 turned by means of a knob 28. The cam 26 has three flat portions corresponding to the three ratios of the change speed gear, and is retained in one of the positions corresponding to a particular velocity ratio by a leaf spring 29. In a modification, Figs. 13, 14 (not shown), the stepped friction wheel 9, instead of being mounted directly on the motor spindle, is freely rotatable on a separate pin and has a rubber-tyred portion constantly engaging a cylindrical friction wheel on the motor spindle. In another modification, the idler is held against vertical motion, the stepped friction wheel 9 being splined to the motor shaft and itself moved vertically to produce a change of speed.
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