GB1303571A - - Google Patents

Abstract

1303571 Impact wrench DESOUTTER BROS Ltd 30 April 1971 12319/71 Addition to 1180771 Heading B3N In a power-operated impact wrench or screwdriver as claimed in claim 1 of the parent Specification, the inertia means is supported on and moves axially of the hammer member to act upon, and be acted upon by, axially resilient means. As shown, the hammer member comprises outer and inner rings 29, 30 circumferentially located by balls 40. Keyed to the inner ring for axial movement thereon is an inertia cylinder 33 which is urged by dished annular springs 36 into abutment with balls 38 which act between similar depressions on facing surfaces of the outer ring 29 and inertia cylinder 33. The stressing of springs 36 is adjustable by moving a rear abutment member 39. In operation, when anvils 27 exert a predetermined back torque, on hammers 28, slight relative rotation between the outer and inner rings 29, 30 causes balls 38 to move slightly from their depressions, thus moving inertia cylinder 33 axially to compress springs 36. The subsequent expansion of these springs against the inertia cylinder 33 results in a kick being applied to the hammer member. The latter thus moves rearwardly to cause a flange 51 thereof to actuate a plunger 21 to close a valve 19 and thereby cease actuation of the pneumatic vane motor 6. At back torque values below the predetermined maximum the springs 36 exert such a force as to prevent the relative rotation between the rings 29, 30; thus the motor continues to be driven, and the hammers and anvils engage and disengage cylindrically.