manufacturing. By the use of the phase changing system INDUCTION MOTOR SWITCHABLE BETWEEN of the invention, there occurs no interruption of the SERIES DELTA AND PARALLEL WYE load current at the time of operation of the switches
concerned and there occurs only a small torque change BACKGROUND OF THE INVENTION 5 and an increase in the load current.
The present invention relates to an induction motor According to the present invention, there is provided having a single one-piece rotor and a plurality of stators an induction motor comprising: which can start smoothly and output a high driving a single rotor formed in one-piece having a first and a torque in a wide range from a low speed range to a high second rotor core axially mounted on a common axis speed range and, more particularly, to a phase changing 10 with an airspace or a non-magnetic portion being prosystem for the motor which effects a phase shifting vided between the two rotor cores and having on the operation in the rotating magnetic fields around the two rotor cores a plurality of rotor conductive members rotor conductive members of the rotor, generated by extending therethrough;
the stators surrounding the rotor. a first and a second stator disposed side by side and
As for the methods for controlling the torque and 15 surroundingly facing the respective rotor cores, the first speed in an induction motor of the type having a plural- second stators having a first and a second stator
ity of stators, a conventional method available is to core on which a piuraiity of windings of polyphase are cause phase differences between the stators. A mechani- Wound, the plurality of polyphase windings of the first cal system for effecting such phase differences may and second stators being interconnected so as to form a have an arrangement wherein the relative rotation of 20 ^ ^
stators is relied upon to produce a phase difference and, fl hase ch ; means havi shon^TCuiting an electrical system therefor may have an arrangement ^ disposed respectively between series-junction wherein the connections of stator windings are changed . - ,,r r. , / . .. _ J,.cc
to produce several kinds of phase differences. Other off the ««or windings of different
available systems include one wherein Y-A-connection 25 phases of the first and second stators for varying the changing system is combined. Phase f ^rence between the rotational magnetic fields
Any appropriate method is selected in a number of around the flrst rotor core generated by the first stator different ways from among the above methods or sys- and the rotational magnetic fields around the second terns according to the load characteristics of load con- rotor core generated by the second stator by the operanected to the motor or the use of the motor, such as the 30 tion of the short-circuiting switches, need to meet the load by changing the torque or the The connection ofthe stator windings, at the starting, speed of the motor and the need to make a smooth of the motor according to the present invention is arincrease in the speed at the starting of the motor. ranged to be a series A-connection or a parallel Y-con
The present invention provides an arrangement in nection each of which provides a predetermined electriwhich certain stepwise phase differences are provided 35 cal phase difference by way of wiring connections of to meet the load connected and which may be regarded the stator windings. The phase differences thus obtained as falling within the electrical systems for effecting may be either one of 180°, 120° and 60". In the stator phase changes as referred to above in the explanation of windings having such wiring connections, there are the conventional methods. provided short-circuiting switches for effecting short
In the conventional electrical systems explained 40 circuiting between the respective connection nodes at above, the phase changing is effected by the connec- wnich the stator windings are serially connected. For tion-changing of the stator windings, so that, while the example, such switches may consist of a first short-cirphase differences available can be of 0% 60% 120% 180° cuiting swjtch for snort-circuiting certain series connecm the electrical angles, the number of the switches tion nodes ^ a xcond short-circuiting switch for required will exceed a dozen or more. This is one of the 45 short-circuiting certain other connection nodes. Since reasons for the high manufacturing cost of such system. the flrst short-circuiting switch is ^ arranged as to There is also an ordinary induction motor in which a shortK:ircuit onl part of the xries connection nodes Y-A-connection changing system is provided for the the d . of ^ sM> the
stator windings are
purpose of improving the starting characteristics of the ^ tQ ^ m%amced once. when the fhort.
motor. In such a motor, despite the provision of only 50 . ... .4 . . . . , ,. r
r . j A i circuiting switch is also closed, the connection of the
one stator, its wirings are quite complicated. Also, there ... . , ' .
_ . , Ju._ ■ . stator windings again changes to a balanced connection.
occurs a torque change caused by a temporary lnterrup- „ f * . * . it_ . r .
tion ofthe load current at the time when Y to A connec- Thus, in the state m which the connection of the tion changing takes place, and further, there occurs an stator wmd,n*s a! startulS °f the mot°r » ■ «=nesA-conunavoidable shock caused by a sudden increase in the 55 nec'lon for causing a predetermined phase difference load current and by a sudden change in the generated <e,ther one of 180' 120 60 >• the connection torque immediately after the above connection chang- changes to an unbalanced connection as the first switch big. The torque-speed and current-speed characteristic * dosed and changes to a parallel Y-connection, the curves obtained according to the conventional Y-A Phase difference of which is different from that of the connection changing are shown in FIG. 14. 60 XTies A-connection, as the second switch is also closed.
In this instance, when the series A-connection having an SUMMARY OF THE INVENTION electrical phase difference (of 180% 120' or 60°) is di
The present invention, therefore, aims at providing a rectly changed as it is to the parallel Y-connection, the phase changing system in which, while the torque char- phase difference is also simultaneously changed. Specifacteristics based on the phase differences as obtained by 65 ically, when the series A-connection is changed directly the conventional methods are retained, only a minimum to the parallel Y-connection, the respective phase difnumber of switches is required for the switching opera- ferences are changed to 180°—»120% 120°—►60°, and tion, resulting in a considerable reduction of the cost of 60°—>0°.