GB1474611A - Power tool for driving threaded fasteners - Google Patents

Abstract

1474611 Power tools THOR POWER TOOL CO 3 May 1974 [14 May 1973] 19664/74 Headings B3N and B3C [Also in Division G1] In an output torque-controlled power tool T, such as a wrench or screwdriver, a reaction torque sensing transducer comprises an annular gear casing member 52 fixed at one end to the tool housing 65 while its other, free end 75 provides an internal ring gear 71 for the second stage of planetary gearing 54-82, the two ends being interconnected by an integrally-formed, thin-walled central portion 201. Torque reaction exerted by a fastener through the gears torsionally stresses the member 52 and the strain is sensed by means such as one or more strain gauges 211-218, the electrical output of which is passed along cable 14 to a readout and torque setting device A, which controls a shutoff valve assembly 120 to shut-off the air supply to pneumatic motor 35 when the predetermined torque value is reached. The illustrated tool is air operated but an electric motor may be used. Air is admitted to the motor by pressing manual lever 109 to open throttle valve 105, see Fig. 3. The air passes into chamber 114 around pilot valve 121, through ports 176 in bushing 157 for shut-off valve member 155 and through passage 156 to the motor 35. The noise of the air exhausted from the motor is attenuated by passing it in a tortuous path through the gearing and out through passages 53. When the desired torque value is reached and the signal is read by device A, a return signal is passed along cable 14 to solenoid 140, Fig. 2, which axially displaces pilot valve member 123 to vent chamber 177 at the top of shut-off valve member 155 which is normally maintained in its open position by equalization of pressure in upper chamber 177 and under cup 163 at the lower end of the valve through passages 178, 179. Valve 155 is thereby raised by the difference in pressure and ports 176 are blocked so cutting off the air supply to motor 35. The tool may be reset afterwards by releasing lever 109 which also releases a switch 255 connected to device A which in turn deenergizes solenoid 140. Other details of the tool include a two-part easily detachable gear housing 65, each part 247, 248 being semicylindrical and having end flanges 249, 250 which engage in grooves 251, 252 in gear case member 52 and motor housing 37 and are screwed thereto by screws 64. The routing of the cable 14 is provided internally through the tool alongside the air passages, Fig. 6 and Figs. 7-10 (not shown). Aligned bores 262, 263 in motor housing 37 and cylinder block 36 allow a rod to be inserted to lock the motor rotor against rotation so that a known load may be exerted on the torque output attachment 32 for calibrating the read-out device A. In the torque transducer construction, the central portion 201 may be externally octagonal while internally cylindrical, see Fig. 4, and the strain gauges 211-218 are alternately angled at 45 degrees to the axis of portion 201, see Fig. 5 and are connected via adjustable trimming resistors 236, 237 to contact strip 231-234.