Patent GB-925030-A (GB)
Title: Clutches for transmitting rotary motion
IPC: F16D41/07
Filed: 1961-01-12
Abstract: 925,030. Ratchet clutches. H. A. CLEMENTS. Jan. 11, 1962 [Jan. 12, 1961], No. 1400/61. Class 80 (2). A ratchet clutch of the type comprising sprags biased by springs to engage with driving and driven clutch members but disengaged therefrom by centrifugal force when over-running occurs above a predetermined speed, includes a second set of sprags in parallel with the first, the second set of sprags being spring biased to disengage but centrifugally biased to engage the driving and driven members, so that the clutch can be re-engaged following over-running without bringing the parts to rest. When thus reengaged, torque is transmitted only through the second set of sprags. On starting from rest, torque is transmitted only through the first set of sprags. As shown, driving and driven shafts 1, 4 are connected by two sets of sprags 11, 18 in parallel. The sprags 11 are mounted in two concentric cages 12, 13 so biased to turn relatively to each other by springs 14 that the sprags are tilted into wedging engagement with inner and outer races 9, 10 on the driving-shaft 1 and a ring 8 fast with the driven shaft 4, respectively. The centre of gravity G of each sprag 11 is offset relatively to a radial plane T passing through the points of contact of the sprag with the races, whereby on over-running centrifugal force tilts the sprag against the spring bias out of engagement with the inner race 9, although it remains in light frictional engagement with the outer race 10. Accordingly, the sprags 11 cannot transmit torque from the driving shaft 1 to the driven shaft 4 following over-running until the driven shaft has slowed down sufficiently to allow the springs 14 to re-engage them with the races. The sprags 18 are of similar construction, but are mounted in cages 19, 20 spring biased to turn relatively in the opposite direction to disengage the sprags from a race 16 on the driving shaft, each of these sprags being so tilted relative to the plane through its points of contact with its races that centrifugal force tends to turn it against the spring bias to engage the race 16 and a race 17 on the driving shaft. Thus, following over-running and disengagement of the sprags 11, the sprags 18 engage when the driving shaft 1 again transmits power. If, following overrunning, the driving and driven shafts 1, 4 come to rest, the sprags 18 are spring biased to disengage and the sprags 11 are spring biased to re-engage. The speeds at which centrifugal engagement and disengagement of the sprags take place may be different. In one modification, Fig. 6 (not shown), the two sets of sprags are arranged in a single radial plane transverse to the driving and driven shafts, engaging with the outer and inner surfaces of a ring fast with the driving shaft and with the inner surfaces of a surrounding ring-shaped recess formed at the end of the driven shaft. In another modification, Fig. 7 (also not shown), the two sets of sprags are arranged side-by-side, engaging the outer surface of the driving shaft and the inner surface of a surrounding ring formed at the end of the driven shaft. In this modification, toroidal compression and tension springs engage directly with each set of sprags to bias them to the engaged and disengaged positions, respectively. According to the Provisional Specification, the sprags may be spring- biased by mounting them in a cage made from spring metal having openings through which the sprags project, the openings having resilient tongues, or alternatively when using coaxial inner and outer cages the spring bias may be provided by helical springs.