GB1232994A - - Google Patents

Abstract

1,232,994. Power-operated screwdrivers. DESOUTTER BROS. Ltd. 2 July 1968 [31 July, 1967], No. 35088/67], Heading B3N In a power-operated screw-driver in which power is transmitted from a pneumatic motor 2 by way of driving and driven dog clutch members 32, 33 which are relatively rotatable under the action of the driving torque and the dog clutch members have interengaging ramps (33a) (Fig. 4, not shown) which slide over one another under a predetermined driving torque, a motor control valve is provided which is actuated by a rod 8 extending axially of the tool to stop the motor on axial movement of the rod caused by relative movement of the dog clutch members. Preferably the control valve 1 is biased by air pressure to remain closed, when once closed by the rods, until the rod is withdrawn and the air supply to the valve interrupted. In operation the rod 8 and a valve operating rod 20 are moved an initial distance (Fig. 4) by pressure of the screw-driver on a screw, to open the air valve 11 when air passes through bores 12, 13, annulus 14, chamber 15 and passage 16 to drive the motor. The motor drives a cup-shaped member 28 with slots 30 in which are slidable ears (31) (Fig. 3, not shown) of the clutch driving member 32. On reaching a predetermined torque, the clutch member 32 moves, in opposition to a central spring 35, together with a block 42, which actuates the rod 8 and is mounted on a rod 40 passing through a transverse bore of the clutch member 32. The clutch operating torque can be adjusted by screwing an internally threaded bevel gear 50, by means of a removable key 51, along a sleeve 36 to adjust the pressure of the control spring 35. The further movement of the rod 8 lifts a piston valve 18 until its maximum diameter portion closes the passage from the annulus 14 to the chamber 15 and hence the air supply to the motor, the unbalanced air pressure below the piston valve lifting it smartly and holding it in place until the air supply to the inlet 10 is interrupted. In an alternative screw-driver (Figs. 5-8, not shown) provided with finger-button controlled starting and reversing valves (92) and (66) in a pistol grip handle the rod (8), when the desired torque is reached, lifts a ball (57) to permit pressure air to pass through a passage (55) to the lower end of and to lift a piston valve (59) thereby closing off the passage (58) and annulus (61) from the annulus (60) and passage (63) between the reversing valve and motor.