COMBINED PORTABLE ELECTRIC IMPACT WRENCH AND CHIPPING HAMMER

1447867 Percussive drills ROBERT BOSCH GmbH 30 Aug 1973 [31 Aug 1972] 40856/73 Heading B3C [Also in Divisions B4 and F2] An electrically operated hammer drill comprises a two-speed transmission unit having a clutch movable into a central position for disengaging the rotary drive, and a percussive mechanism which is disengageable independently of the rotary drive. As shown in Figs. 1 and 3 in which the drill is set for percussive action only, the output shaft 6 of the motor 4 continuously rotates an intermediate shaft 10 through gears 9, 11, the gears 12, 13 on the intermediate shaft meshing continuously with axially-shiftable gears 15, 16 which are freely rotatable about a hollow output shaft 14 unless selected to be drivingly connected thereto. In the position shown, the gears 15, 16 are in the neutral position where an annular recess 19 is opposite four equi-angularly spaced projections 18 on the shaft 14. When the gears 15, 16 are shifted axially one way or the other by means of a shift fork 17 having spring arms 23 movable from outside the housing by an eccentric shift 24 the appropriate axial grooves 20, 21 in the gears drivingly engage the projections 18. The tool head 37 is connected for axial movement in a sleeve 36 by means of balls 38 and the sleeve is connected to the shaft 14 through a safety clutch having balls 30 which yield against a spring-urged ring 31 when a drill bit carried by the tool head jams; the sleeve 36 is secured against rotation by a dog 45. The tool head is hammered by a striker 62 which is driven through an air cushion created by a crank driven cylinder 61. When the motor is to be connected to drive the percussive mechanism through bevel gears 46, 48, a clutch shaft 47 is shifted to the position shown by an eccentric shift 55 where balls 51 drivingly connect the gear 48 to the shaft 47; when the shaft 47 is raised to disengage the clutch, the balls 51 move into an annular groove 57 from the radial bores 51' in the shaft and recesses 52 in the gear. In a second embodiment, Fig. 4 (not shown) the clutch for the crank mechanism consists of an axially-displaceable gear (66) on the inter- . mediate shaft (65) which can be axially moved to drivingly engage one of the two bevel gears of the crank mechanism. In a third embodiment, Fig. 5, the two-speed transmission unit includes a shift sleeve 74 which rotates with the output shaft 14 and is axially movable from the neutral position shown where drivers 75 are opposite an annular rece