GB1292537A - Improvements in or relating to hand power tools - Google Patents

Abstract

1292537 Power tools ROBERT BOSCH GmbH 11 Dec 1970 [13 Dee 1969] 58842/70 Heading B3N A power tool comprises a drive motor and a drive transmission for imparting rotary impacts to a workpiece holder 28 and wherein a flywheel 18 mounted on a drive shaft 5 is rotatable by the drive shaft and is longitudinally located on the shaft by resilient members 24, 25 so as to be capable of axial oscillation and has impact dogs 26 engageable with impact dogs 31 on the workpiece holder by an axial displacement of the workpiece holder towards the flywheel. The flywheel is rotatably mounted on bushes 14, 15 which are non-rotatably mounted ted on shaft 5. Members 24, 25 are in the form of cup springs and provide a friction drive to the flywheel and also allow axial movement thereof. The impact dogs 26, 31 are shown in Fig. 2 where it is clear that the flanks of a dog are of different slope with the steeper flank being for unfastening a nut. There may be 4 or 8 equally spaced dogs on each of the flywheel and holder 28. If there are 8 such dogs then alternate dogs on each part have a shortened length to allow suitable engaging of the dogs during impacting. In operation the motor, having permanent magnets 7, is activated to drive the flywheel to a maximum speed, about 6000 r.p.m. The tool is then forced toward a nut connection which is engaged by holder 28. Spring 34 is compressed and the impact dogs meet. Full engagement of the dogs is impossible and the flywheel is forced axially away from the holder 28. Thus the holder receives a series of impacts and the flywheel oscillates axially as well as rotating. In an alternative embodiment, Fig. 4, a holder 128 and flywheel 118 are biased apart by a cup spring 152 having a characteristic whereby the spring force in relation to its compression increases to a maximum and then falls. A yet further embodiment is shown in Fig. 6 where a flywheel 218 and a holder 228 are biased apart by a spring 234. In operation to tool is forced toward a nut and the motor started. At a predetermined speed balls 259 are forced outwardly against an annular spring 260. Balls 257 also move outwardly so that spring 234 is compressed abruptly and the dogs come into engagement. The motor is designed to be driven by the direct current from a car battery.