| 摘要 |
609,264. Electromagnetic clutches. WINTHER, A. March 9, 1946, No. 7428. Convention date, Jan. 27, 1945. [Class 80 (ii)] [Also in Group XXXIV] To provide a current of short duration sufficient to move the armature and magnet of an electromagnetic brake or clutch into initial frictional engagement, a condenser is arranged in parallel with the regulating resistance and is connected in the magnet circuit prior to reducing the resistance for increasing the pressure between the armature and magnet. Fig. 2 shows a brake comprising a magnet ring 3 of channel-section to contain the coil 1 and secured to a disc 5 bolted to a stationary frame 7. The ring 3 is closed by a friction ring 25. The armature disc 19 is slidable on pins 17 on a spider 15 keyed to the shaft 11 to be braked and is normally held spaced from the magnet by weak springs 23. A clutch of similar construction is also shown the armature disc and the magnet being mounted on coaxial shafts and the current being conducted to the coil by slip rings. A cooling fan is carried by the armature shaft. The circuit of the coil 1 includes a rheostat 39 comprising a series of leaf-springs 35 carrying contacts 37 that are normally spaced from each other and are controlled by a swinging arm 41. A condenser 43 is connected in parallel with the rheostat. To apply the brake, the master switch 31 is closed and the arm 41 is moved to engage the first two contacts with each other to apply the voltage of the battery 29 across the total resistance. The condenser is thus charged and causes an instantaneous rush of current through the coil 1 moving the armature 19 into contact with the magnet. When the condenser current has died out, the current that flows through the coil and the total resistance is sufficient to hold the armature in light contact. The resistance may then be progressively reduced to increase the pressure between the armature and the magnet by further movement of the arm 41 to close the contacts 37 successively. The condenser also acts to reduce arcing at the several contacts when these are disengaged. |
