Patent GB-326582-A (GB)
Title: Improvements in or relating to dynamo electric machines
IPC: H02K7/118
Filed: 1928-12-28
Abstract: 326,582. Jackson, L. Mellersh-, (Sunlight Electrical Manufacturing Co.). Dec. 28, 1928. Motors, controlling; alternating-current motors; driving arrangements.-An induction motor with a split-phase starting circuit is provided with a device which allows the rotor to run up to speed freely on the shaft under the action of a starting winding and which at full speed cuts out the starting winding and causes an electrically-withdrawn spring-pressed friction clutch to engage the rotor with the shaft, the operations being effected by a centrifugal switch device with a 3- part split cup one segment of which is connected to the electromagnet which controls the clutch. The arrangements are such as to disengage the clutch before energizing the starting winding in order to protect this winding from burn-outs or, alternatively, to group the starting windings so as to take a minimum current during the first stages of starting. The clutch cone 15, Fig. 1, which is splined on the shaft and normally engages the cup 16 on the armature, is attached to a magnetic ring 12 surrounding an annular extension 8 of the casing and forming the armature of a fixed coil 10, the energization of which disengages the clutch and frees the armature from the shaft. To eliminate magnetic vibrations due to the alternating field, the armature 8 is arranged to float freely in the annular channel 9 and the natural frequency of the armature and spring is made different from that of the supply. The switch device consists of three centrifugal members 24, Fig. 3, carried on a ring 25 and normally spring-pressed on to three cup-shaped segments 27, 28, 29 connected respectively to the starting winding 22, Fig. 4, the clutch coil 10 and one main 33. The running winding 21 is joined to the other main and the starting winding, the starting current flows through both windings 21, 22 and the clutch coil and when the rotor is up to speed the members 24 leave the switch, cutting out the starting winding and de-energizing the clutch coil. The spring 18, Fig. 1, thereupon engages the clutch. In an alternative arrangement, the cup segments are mounted eccentrically to the shaft so that the clutch coil is energized shortly after the starting winding is cut out. Should the rotor speed fall due to overload, the clutch coil is first switched in to disconnect the. rotor which then picks up speed and this action may be repeated until the motor is no longer overloaded or is stopped. Fig 6 shows an arrangement for giving a reduced starting current. The running winding is in two parts 21, 21<1> one of which is controlled by a relay the coil 35 of which is in series with the clutch coil. On starting, the switch instantly disconnects the clutch and de-energizes the coil 21<1>, leaving the starting and running windings 22, 21 only in circuit. At a limiting speed, the coils are deenergized by the centrifugal switch and the motor runs with both running coils excited. In an alternative arrangement for obtaining a low starting current, the running windings are in two parts which are connected first in series and then in parallel when the motor has attained speed, the change-over being effected by means of a switch of which the magnet coil is in series with the clutch coil.