Patent GB-840990-A (GB)
Title: Torque control for impact wrenches
IPC: B25B23/145
Filed: 1958-04-09
Abstract: 840,990. Screwing-up and unscrewing bolts. CHICAGO PNEUMATIC TOOL CO. April 9, 1958 [May 21, 1957], No. 11212/58. Addition to 772,382. Class 83 (3). [Also in Group XXIV] The impact-tool of the parent Specification is modified by the provision of a driver 57 for the flywheel 67, the driver being driven from the motor-shaft 53 by means including a lostmotion connection 59 which delays operation of the means 92, 49, 28 for automatically stopping the motor, making such means unresponsive to deceleration of short duration of shaft 53. The impact clutch (not shown), may be as in the parent Specification or in Specification 784,269, and is driven by a motor 15 to which compressed air is fed through a manually-operated controlvalve (not shown), automatic valve 28 and a reversing valve 33, controlled by a lever 39. Axial pockets 61, Fig. 8, in shaft 53 receive rollers 59 loaded by springs 65 to engage the bore of the driver 57, which is engaged by a friction-driving-plate 62 locked to the shaft by inner projections received in the pockets 61. The driver is retained against axial movement relatively to the flywheel 67 by balls 68 and a retaining-ring 72. Outward projections 73, Fig. 5, on the driver, drivingly engage inner projections 74 on the flywheel, and axial lugs 78 on a cam 75 extend between the projections 74. Co-operating inclined cam surfaces 83, 85 on the cam lugs and flywheel projections engage balls 84, through which adjustable pressure applied to the cam is transmitted to the flywheel and thence to the friction clutch 62. Axial movement of the cam to operate valve 28, as described below, is facilitated by balls 81 engaging axial races 79, 82 on the cam and driver respectively. A button 89 bearing in the cam is engaged by a lever 92 loaded by an adjustable spring-pressed pin 95. The valve 28 is held open by a trigger 49 biased, as by a spring 51, into the path of a shoulder 48 on the valve, as the valve is moved inwards by the pressure of air overcoming the resistance of its return-spring 41. Operation.-Valve 28 is closed automatically only when the motor is driving in a clockwise direction (i.e. the freewheeling direction of rollers 59), driver 57 being driven by the friction-plate 62. It is stated that for impacts of short duration, e.g. the first of a series in tightening a bolt, lost-motion in the freewheel clutch, before the rollers 59 are locked by slight over-running of the driver 57, prevents the full force of the impacts from being transmitted to the flywheel. When the force of impacts of longer duration is such as to cause over-running of the flywheel in relation to driver 57, the balls and cam-surfaces 83, 85 displace the cam rearwardly against the influence of pin 95. The lever 92 operates trigger 49, releasing valve 28 which is then closed by the compressed air. The valve remains closed until the compressedair supply is interrupted by closure of the manually-operated valve (not shown), which allows spring 41 to re-open valve 28. Air trapped between the valves escapes through a passage 101 in valve 28. Either of a pair of oppositely-located plungers 102 may be moved into the path of valve 28, preventing its automatic operation.