Patent GB-858709-A (GB)
Title: Improvements in or relating to variable speed friction drive transmissions
Inventor: HAYWARD ALBERT JOHN
IPC: F16H15/28
Filed: 1957-11-12
Abstract: 858,709. Variable-speed gear. COHEN, 600 GROUP Ltd., G. Nov. 12, 1957, No. 35225/57. Class 80 (2). A continuously variable ratio gear for lathes &c. of the type comprising discs 1, 2, Fig. 1, engaged by non-planetating idlers 5 tilted to change the ratio, is controlled by operation of a ratio selector connected to the gear by resilient means of such strength that operation of the selector while the gear is stationary will not produce sufficient effect upon the idlers to tilt them against the forces of static friction. In the form shown, the idlers 5 are mounted upon axles 8 engaging at their ends in radial grooves 12, 13 in a surrounding casing 17, 18. A plate 16 has cam slots 15 engaging rollers on the ends of the idler axles 8, turning the plate 16 causing tilting of the idlers 5. The shape of cam slots 15 may be either as shown in Fig. 2, whereby variation in ratio is in geometrical progression relative to angular movement of the plate 16, or the cam slots 15 may be shaped to obtain variation in ratio in hyperbolic progression relative to angular movement of the plate, Fig. 3 (not shown). The plate 16 is fast with a selector rod 32 which is connected to the resilient means. The resilient means may comprise an hydraulic transmission embodying a spring-loaded accumulator or accumulators arranged to limit the pressure which can be transmitted and to provide for storing of energy sufficient to effect adjustment of the cam plate 16 when the drive unit is operated, or may embody an electrical transmission such as a stepped switch arrangement utilizing a solenoid &c. electric motor of suitably limited power for effecting movement of the ratio adjusting mechanism. Selection may be initiated manually, or by automatic means not further described. In one preferred embodiment, the ratio selecting shaft 32, Fig. 4, is connected to a torsion rod 58 fast upon the end of which is a selector lever 55 retained in any desired position by a spring-biased detent 60. To pre-select a desired ratio, a spring-biased detent 71 is released to engage it with the teeth of a gear 72 fast with the selector rod 32. The selector lever 55 is next turned to the position corresponding to the desired ratio, and a spring- biased detent 62 allowed to operate to retain the selector lever in this position with the torsion rod 58 stressed. The spring-biased detent 71 is then withdrawn from the teeth of the gear 72 so that the torsion rod 58 can turn the selector shaft 32. If the gear is transmitting drive, the selector rod 32 is accordingly turned and the new ratio is established. If, however, the gear is stationary, the torsion rod 58 is of insufficient strength to turn the selector shaft 32, and the gear ratio does not change. The spring-biased detent 71 can be retained in its disengaged position by a catch. In a modification, the selector shaft 32, Fig. 6, carries a disc 80 formed with sloped V- shaped cam faces 85, 86 engaged by diametrically opposite rollers 84 on a control member 82. The rollers 84 are biased to engage the cam faces 85, 86 by a spring 87. Fast with the control member 82 is a two-armed lever 81, Fig, 7, having its ends connected by links 91 to a lever 93 pivoted at 94 and turned by operation of a handle 95 retained in a desired position by a detent 97. On operation of the handle 95, the lever 81 is turned and, if the gear is not transmitting drive, the rollers 84 ride up the cam faces 85, 86 against the bias of the spring 87. When the gear begins to transmit drive, the energy stored in the spring 87 turns the cam disc 80 and the selector shaft 32 to establish the desired ratio. The discs 1, 2, Fig. 1, are connected to two concentric shafts 19, 21 having fast at their ends V-grooved pulleys 35, 36. The disc 1 is fast with a shaft 19, while in the disc 2 is connected to the inner shaft 21 by means responsive to the load transmitted to increase the frictional force engaging the discs and idlers, and comprising rollers 23 engaging inclined cam grooves 25 in the disc and in a collar 27 fast on the end of the shaft, respectively. A roller thrust bearing 29 opposes the reaction of the load responsive means 23 &c. upon the two shafts 19, 21. The shafts 19, 21 are journalled by bearings 20 in one part 17 only of the surrounding two-part casing 17, 18, the end-cover plate 18 not taking any of the load upon the two shafts. A roller bearing 30 centres the shaft 21 within the shaft 19. A ring 6 surrounds the idlers 5, and each idler axle 8 is formed at one end with a flat head to engage the radial groove 12 and at the other end carries a roller 11 engaging the radial groove 13. The main casing part 17 is provided with a drive tensioning lug 51, and with cooling passages 48 for air pumped in by a fan 37 fast with the pulley 36. As shown, the idlers 5 are spherical, but alternatively they may be formed as discs having part-spherically shaped friction surfaces. Specifications 618,774, 858,708 and 858,710 are referred to.