| 摘要 |
<p>711,751. Centrifugal switches; actuation of switches; control of A.C. motors. GENERAL ELECTRIC CO. July 7, 1952 [July 5, 1951], No. 17023/52. Classes 38(3) and 38(5) A switch for controlling an instantly reversible single-phase A.C. motor comprises a pair of independently movable contact arms, one on either side of the motor shaft, biased to the closed position by a centrifugal mechanism below a predetermined speed and being allowed to move to the " open" position when the predetermined speed is reached, one or other of the arms being held in the first position by a device responsive to the direction of rotation. The centrifugal mechanism, which may be that of Specification 504,678, acts on an axially-movable sleeve 12 which engages wear pads 22 on the free ends of the contact arms 20, 21 which are mounted on a plate 17. The sleeve 12 is moved to the left, Fig. 2, below the predetermined speed so that contact pairs. 23, 26 and 24, 27 are closed. Each contact arm 20, 21 has a hook 34 or 35 respectively lying in the path of hooks 32, 33 secured to the outer race 30 of an anti-friction bearing, the inner race 29 of which is secured to the shaft 3.' Assuming a selector switch 39 to be in the position shown in Fig. 6, the motor rotates in the direction of the arrow 36, Fig. 3, with the contact pairs closed until the predetermined speed is reached. At this speed, the sleeve 12 is moved to the right, Fig. 2, thereby permitting movement of arms 20, 21 to the right. However, due to movement of the outer race 30 in the direction of the arrow 37. due to the anti-friction elements 31, the hook 32 is engaged with hook 34 so that the arm 20 is retained in its closed position. Movement of arm 21 opens contacts 24, 27 and disconnects the motor starting winding 5. Although contacts 23, 26 are held closed, the circuit is broken at the contact 38 of the switch 39 and is only made when the switch 39 is changed over when it is desired to reverse the motor. When this happens, the winding 5 is energized in the reverse direction to slow down the motor which stops and then re-starts in the opposite direction. Contacts 24, 27 are re-closed as the motor slows down and are held closed by the engagement of hooks 33, 35, due to movement of race 30 in the direction opposite to that shown by arrow 37. Contacts 23, 26, however, open when the motor speeds up and the winding 5 is cut out again. The circuit is then ready for reversal of switch 39 again.</p> |
