GB1180771A - Improved power-operated impact wrench or screwdriver. - Google Patents

Abstract

1,180,771. Screwing-up and unscrewing nuts, &C. DESOUTTER BROS. Ltd. 28 June, 1968 [21 July, 1967], No. 33648/67. Heading B3N. In a power-operated impact wrench or screwdriver including automatic means for causing cyclic engagement and disengagement of a rotary hammer 67 and anvil 65 an inertia cylinder 66 is coupled to the hammer 67 by a torsionally resilient cylinder 75 which constrains the inertia cylinder from moving relative to the hammer 67 until the impact torque delivered to the anvil 65 reaches a predetermined value whereupon the inertia cylinder 66 moves in relation to the hammer and so acts on the automatic means as to increase the amount of disengagement of the hammer from the anvil and thereby operate control means for interrupting the supply of power to the tool. The hammer 67 comprises inner and outer parts 68, 69 rigidly connected by balls 70 and splines 71. A spring 73 and balls 72 which are disposed in inclined grooves in the inner hammer part 69 and in a drive spindle 11 engage and disengage the hammer 67 and anvil 65 as the spindle 11 is driven by a vane type air motor 6 through planetary gearing 10. The inertia cylinder 66 is connected with provision for limited relative rotation to the outer hammer part 68 by loose splines 74, and has splines 78 engaging helical splines 77 on the resilient cylinder 75. The resilient cylinder 75 is integral with the inner hammer part 69 and has longitudinal slits cut therein. An adjusting worm 80 accessible through an opening in the tool casing engages the helical splines 77 and rotates a sleeve 79 in threaded engagement with the inertia cylinder 66 to displace the splines 78 along the helical splines 77 and thereby twist the cylinder 75 to variably preload the splines 74. In operation the splines 74 remain in engagement so that the inertia cylinder 66 and hammer 67 move in unison until the resistance to movement of the anvil 65 under the impact of the hammer reaches a predetermined value whereupon the cylinder 66 continues to move when the hammer strikes the anvil and further twists the resilient cylinder 75. Rebound of the inertia cylinder 66 transmits the energy stored in the resilient cylinder 75 to the hammer 67 through the splines 74 to increase the disengagement of the hammer from the anvil 65 so that the end of the resilient cylinder 75 displaces a ring 18 connected by a transverse rod 16 and spring-loaded head member 15 to a rod 13 which unseats a ball-valve 20 to pressurize a piston valve 25 for cutting off the air supply to the motor 6. The piston valve 25 is retained in the closed position by air supplied through a bore 31 until the air supply to the tool is cut-off by release of a press-button control valve 34. A reversing valve 44 provides for operation of the motor 6 in either direction but automatic torque control is effective only when the tool is used for screwing-up.