Patent GB-693415-A (GB)
Title: Impact wrench torque control
IPC: B25B23/147
Filed: 1951-11-20
Abstract: 693,415. Screwing-up and unscrewing bolts &c. CHICAGO PNEUMATIC TOOL CO. Nov. 20, 1951 [Jan. 26, 1951], No. 27191/51. Class 83 (iii). [Also in Group XXIV] In an impact wrench, the energy of rebound of the impact means is stored by axial compression of a spring and then released to accelerate the movable members of the impact means so that a hammer blow is delivered, the rebound increasing with each blow by a predetermined amount, until the compression of the spring, corresponding to the required degree of tightness of the bolt or nut being driven, actuates means for stopping the operation of the impact means. The stopping means may control a switch or valve for the electric or pneumatic driving motor or may disengage a clutch in the drive to the impact means. As shown in Fig. 1, the impact means 87 comprises pivoted dogs 91 which deliver blows to projections 94 on the tool head 88 but are rotated into the inoperative position shown in Fig. 11 by surfaces on the driving cam 68, as described in Specification 551,071. Clutch teeth are provided on the rear of the driving cam, and when the tool is pressed on the work against the pressure of a spring 84, these teeth engage with teeth on a sleeve 67 fixed on a spindle 66. A flanged sleeve 75 is engaged with the spindle by balls 80 in V-shaped grooves 79, 81 in both members and is also in sliding engagement with a cage 58 carrying sun-wheels 60 which mesh with a gear 35 formed on the end of the motor shaft and with an internal gear 63. When the impact means begins to impart blows to the tool head the rebound is transmitted back to the spindle 66 and, through the balls 80 and grooves 79, 81, is translated into axial movement of the sleeve 75, which thus compresses a spring 77. The rebounds increase until the spring compression is sufficient to allow the flanged sleeve to contact an arm 55 on a push-rod 52, thus moving a hooked lever 43 out of contact with the corner 50 of a switch trigger 27 and allowing a spring 41 to move a switch lever 40 to cut off the current to the motor. The arm 55 is screwed on the push-rod and its position is adjustable by a screw-driver slot on the pushrod. A fan 36 cools the motor. The tool can be used in either direction of rotation. As shown in Fig. 23, a hammer 139 surrounding the energy-storing spring 142 engages helical grooves 138 on a spindle 115 and has clutch teeth 144 engaging clutch teeth 145 on the anvil 146. Clutch teeth 136 on the spindle are engageable with a clutch 118 which is slidably splined on the shaft 117 of the planetary gear-cage 111 and is floatingly-supported by springs 121, 151 in a position just forward of a latch 123. When the tool is pressed on the work, against the pressure of springs 137, 151, the clutch 118, 136 is engaged and when the work is almost tightened, the hammer 139 begins to rebound and, by reason of its helical engagement with the spindle, to compress the spring 142 at each rebound. As the driving resistance rises, the clutch teeth 144, 146 disengage and the inertia of the hammer causes it to lag behind the accelerating spindle 115 and further compress the spring 142, the energy stored then being released to accelerate the hammer beyond the speed of the spindle and deliver a blow as the teeth 144, 146 re-engage. The rebounds increase until the hammer moves back sufficiently to contact an adjustable arm 128 on a push-rod 127 and cause a fixed arm 126 to release the latch 123 so that the clutch 118 is moved rearwardly by the spring 151 to disengage the drive. On removing the tool from the work, the member 118 is returned to its position just forward of the latch 123. Specification 619,796 also is referred to.