Patent GB-705948-A (GB)
Title: Releasable torque transmitting apparatus
IPC: F16D43/206
Filed: 1951-09-17
Abstract: 705,948. Overload-release clutches. STEVENS, D. Sept. 17, 1951 [Oct. 16, 1950], No. 21824/51. Class 80 (2) In an overload-release positive clutch, the means normally holding the clutch parts in engagement loses a large proportion of its holding force immediately upon an initial minor separation of the parts, thereby enabling the subsequent main portion of the separating movement to take place under practically no load. As applied to a portable power-operated tool, a driving clutch sleeve 21, Fig. 1, rigid with a member 20 driven from the motor 14, has bevelled clutch teeth 28, Fig. 3, co-acting through rollers 29 with bevelled recesses 57 in a driven clutch sleeve 31, the clutch being normally maintained engaged by the attraction of a permanent magnet 35, housed in member 20, on an armature 37 carried through a spindle 40 by a member 45 rigid with sleeve 31. The armature has a central section 38 into which is threaded the screwed end of the spindle 40 and which seats in the outer portion 39 of the armature through a rubber ring 47 while being prevented from turning in the portion 39 by a pin 42, so that by turning the spindle 40 the central section 38 can be adjusted axially to vary the holding force of the magnet on the armature. The rollers 29 are mounted in a cage 51 urged downwardly by a spring 52 and capable of limited resilient angular movement relative to member 31 by pins 53 on member 45 extending upwardly into arcuate channels 54 in the cage 51 containing rubber blocks. Rotation of member 31 is transmitted, through axial projections 68 and recesses 73, with interposed caged rollers 69, to a member 58 rigid with a member 59 which is located axially in the casing 12 and which co-acts through clutch teeth 76, 77 with a member 78 secured to the tool spindle 10, which latter is normally pressed downwards by a spring 102 so as to disengage the clutch 76, 77. A sleeve 88 extending upwardly from member 59 has radical holes receiving latch balls 90 adapted to co-operate with an inclined shoulder 86 on a sleeve 72 depending from member 45 and with an inclined shoulder 92 on a sleeve 91 urged upwardly in sleeve 88 by a spring 93 bearing against a recess in the spindle 10. As shown in Fig. 1, all the parts are in driving position, the spindle 10 being pressed upwards by applying it to the work so that the clutch 76, 77 is,engaged, and the clutch 28, 29, 57 being held engaged by the magnetic holding force. At a predetermined torque, the armature 37 is pulled away from the magnet by the camming action of the rollers 29 and the clutch 28, 29, 57 disengages, the holding force of the magnet being reduced almost to zero immediately the disengaging movement commences. During this disengaging action, the cage 51 turns relative to member 31, but as soon as disengagement is complete it returns and the rollers 29 engage in the recesses 57. The clutch is then locked in disengaged position by the balls 90 engaging the shoulder 86. To release the balls, the spindle 10 is removed from the work so that it moves downwards, disengaging the clutch 76, 77 and, by means of a head 101 on a spindle 96 secured in spindle 10, pulling down the sleeve 91. The spindle 96 is hollow and slidably receives the lower end of the spindle 40. As the latch is released, the magnetic holding force, augmented by a spring 100, is sufficient to reengage the clutch 28, 29, 57. In the modified form shown in Fig. 15, magnetic holding force is replaced by fluid pressure. The spindle 40 is threaded into member 116 co-acting with the lower end of member 20 to control a restricted exhaust passage 117 in the latter. Pressure fluid supplied to the casing 12 through an inlet 125 normally acts, together with spring 100, to 'hold member 116 upwards-'against member 20. At the predetermined torque, member 116 begins to move downwardly, opening the exhaust passage 117, and the fluid holding force at once falls substantially to zero.