Patent GB-474927-A (GB)
Title: Improvements in internally expanding clutches
IPC: F16D43/18
Filed: 1936-05-19
Abstract: 474,927. Friction clutches. BANKER, O. H. May 19, 1936, No. 14175. [Class 80 (ii)] A pair of clutch shoes 14 rotating with a spider 10 secured to a driving shaft 4 are forced outwardly into engagement with a drum 46 by the straightening of two pairs of toggle links 30, 31 under the action of spring-retracted speed-responsive means operating on the joint of each pair of links, the links 31 pivoting about the axis of the shaft while the links 30 act on the shoes through resilient means which yield at a predetermined pressure. Since, due to the straightening of the toggle links 30, 31, the resilient yielding means have no effect on the speed-responsive means when the clutch is engaged, the speed at which the clutch disengages is considerably smaller than that at which it engages. The links 31 are oppositely arranged and are formed as arms projecting from a sleeve 43 journalled on the hub 9 of the spider 10, so that the action of the two toggle linkages is equalized. Each speedresponsive means comprises a weight 50 on one arm of a lever 48 pivoted on the spider and retracted by a spring 55, the other arm being connected by a link 53 to a pin 45 which in the form shown in Fig. 1, forms the joint between the links 30, 31, or, in the form shown in Fig. 7, is carried by a longer arm projecting from the sleeve 43. A spring-pressed detent mounted in the weight 50 engages a depression 58 in the spider when the weight has swung outwards. The link 53 has a slot 54 engaging the pin 45, thereby providing a lost-motion connection, which ensures that the toggles operate with a snap action. A free-wheel roller clutch 63 is arranged between the hub 9 and the hub 47 of the drum 46, so that the latter cannot over-run the shaft 4. A manuallycontrolled claw clutch 59, 60 is provided between the drum 46 and the driven shaft 5, the claws having bevelled ends so as to preclude engagement thereof if the shaft 5 is over-running. As shown in Figs. 1 and 2, the shoes 14, which are normally retracted by springs 19 interconnecting their ends, are movable radially in centre guides 13 formed on the spider 10. Each link 30 acts on the joint of another pair of toggle links 28, 29, the link 29 being connected to the end of one shoe while the link 28, which is adjustable in length, has side pins 39 which carry rollers 40 bearing against the inner surface of the other shoe and which engage the forked ends of a bifurcated member 24 slidable on a pin 22 secured in a member 20 pivoted on the spider. The member 24 is urged away from the member 20 by a spring 25 which is adjustably preloaded by a nut 27. The shoes, which are somewhat flexible, have a slightly smaller radius of curvature than the drum 46, so that the central part of the shoe first engages the drum, the end portions thereafter being expanded. Alternatively, the adjustable link 28 may thrust against a block bearing against the inner surface of the shoe and backed by a preloaded spring. As shown in Fig. 7, the shoes are pivoted at one end 74 on the spider 10, and each link 30, adjustable in length, acts through a preloaded spring 79 to thrust a member 83 against a block 76 secured to the free end of the shoe. The shoes are normally retracted by springs 88.