MXPA96006097A

MXPA96006097A - Iman motor permanent start in li

Info

Publication number: MXPA96006097A
Application number: MXPA/A/1996/006097A
Authority: MX
Inventors: Henry Boyd John Jr
Original assignee: General Electric Company
Priority date: 1995-12-04
Filing date: 1996-12-04
Publication date: 1997-08-01

Abstract

The present invention relates to an electric motor that includes a stator having a stator core, a start winding and first and second main windings. The first main winding and the start winding are configured to form a lower number of poles than the second main winding. The stator core forms a stator hole. The motor also includes a rotor having a rotor shaft concentrically disposed axially of the stator core and a rotor core positioned concentrically with the rotor shaft. The secondary conductors are axially disposed of the rotor shaft and extend through the rotor core. A plurality of permanent magnets are located on an outer periphery of the rotor core and are magnetized to form a number of poles equal to the number of poles formed by the second main winding.

Description

PERMANENT MAGNET MOTOR OF HOME ON LINE FIELD OF THE INVENTION This invention relates generally to electric motors and, more particularly, to an AC motor of magnetically outgoing start-up rotor, which, in at least one embodiment, is operable as a two-speed motor.

BACKGROUND OF THE INVENTION The two-speed induction motors are well known. Such engines are typically used for applications such as furnace blower motors where, under certain predetermined conditions, a high or low speed motor is required. For example, in some furnace systems, the furnace includes an impeller fan, which selectively operates in low and high draft modes. The impeller blows at a slower speed in the low shooting mode and rotates at a higher speed in the high shooting mode. An engine, which drives the blower, therefore operates at a low speed for the low shooting mode, and at a high speed for the high shooting mode. The two-speed induction motors can be used in applications such as furnace blower motors that typically include stators that have two main windings and a start winding. A first main winding forms a first, lower number of poles and a second main winding forms a second, higher number of poles. The start winding forms the first number of poles. The rotor can be a "short circuit" type rotor.

Particularly, said rotor includes a rotor core formed by a plurality of laminations. The shaft of the rotor shaft, of course, is coaxial with the axis of rotation of the rotor core. Short-circuited secondary conductors extend through the rotor core and are arranged axially with respect to the rotor shaft on the outer periphery of the rotor. During the initial operation, the start winding and the first main winding are activated. The magnetic fields generated by said windings induce currents in the secondary, moving conductors of the rotor. As is well known, the magnetic fields generated by said windings and the current carried by the secondary conductors, couple and create a torque, which causes the rotation of the rotor. Once a sufficient speed of the rotor is obtained, for example, the rotor speed exceeds the synchronous speed of the second main winding, the start winding and the first main winding are deactivated and the second main winding is activated, i.e. , for a low shooting mode. Typically, the motor will continue to operate only with the second main winding activated, that is, the low firing mode. However, under certain circumstances, the first main winding is activated and the second main winding is deactivated. For example, if the furnace is required to operate in high firing mode, on a particularly cold day, the furnace blower motor will operate with the first main winding activated and the second main winding is deactivated. With the first main winding activated, the motor speed is increased, compared to the motor speed when the second main winding is activated. When a hotter climate returns, the furnace operates in low draft mode, only with the second main motor winding activated. Although conventional induction motors, known to be relatively calm compared to other known types of motors, the rotor, in an induction motor, rotates at a speed less than the speed of synchrony. For example, in the case of a six-pole induction motor, the synchronous speed (for an operation of 60 hertz) is 1200 rpm. However, the rotor can have a real speed of 1 100 rpm. Said condition is known as "slippage" and results in losses associated with induction type motors, since these losses occur without considering the operational speed of the motor., said losses are particularly undesired, if the engine operates for extended periods, such as a furnace blower motor. Compared to two-speed induction motors, two-speed synchronous motors (for example, permanent magnet motors) are typically more efficient because the slippage is eliminated. For example, with C.A engines. synchronous permanent magnet, known, the stator includes a winding start and a main winding. The permanent magnets are secured in the outer circumference of the rotor. The permanent magnets are magnetized to form a number of poles equal to the number of poles formed by the primary winding. During the initial operation, the magnetic fields generated by the start and main windings and the magnetic fields of the permanent magnets of the rotor are coupled and produce the necessary torque to cause rotation of the rotor. Once a sufficient speed of the rotor is obtained, the start winding is deactivated. The rotor continues to rotate due to the coupling between the magnetic fields of the main winding and the permanent magnets. No energy is lost as a result of driving currents in secondary conductors. With permanent magnet motors, and in order to operate said motors at two speeds, a frequency controller is required. Specifically, the permanent magnets of the rotor form a fixed number of poles. Therefore, since the number of poles is fixed, in order to change the rotor speed, the frequency of the supply voltage must be changed. The circuit control system for controlling the frequency of the supply voltage can be complex and expensive. In addition, with synchronous AC motors, permanent magnet, in the ignition of the engine, a torque is generated, parasitic, significant. Specifically, in the ignition of the engine, the fields of the stator windings and of the permanent magnets try to cause the rotor to move instantaneously from a condition at rest to a condition, in which the rotor is rotating at a synchronous speed. Of course, the rotor can not perform this instantaneous movement. Significant forces acting on the permanent magnet rotor, in the ignition of the motor, result in the generation of unwanted noise and vibration. Such noise and vibration are highly undesirable, particularly in applications such as a furnace blower motor or other air movement applications, wherein said noise can be destructive and annoying. Vibration can also reduce the life of the motor operation. Therefore, although the synchronous, permanent magnet AC motors have improved their operating efficiency, compared to the induction motors, said permanent magnet motors have undesirable ignition characteristics. Accordingly, it is desirable and advantageous to provide a two-speed electric motor, which is more efficient than known two-speed induction motors. Also, it is desirable and advantageous to provide said motor, which does not require a supply voltage frequency controller to change the motor speed. Furthermore, it is desirable and advantageous to provide an electric motor, which can exhibit the operating efficiency of a permanent magnet motor and the ignition characteristics of an induction motor. Said electric motor, of course, must also have an effective cost of manufacture and use, so that the increases in the manufacturing cost associated with the manufacture of said motor can be significantly deviated by the savings resulting from the use of said motor. An object of the present invention is to provide a two-speed electric motor, which has a short-circuited rotor and which is more efficient than two-speed induction motors., known. Another object of the present invention is to provide said motor, which includes permanent rotor magnets, but does not require a supply voltage frequency controller. A further object of the present invention is to provide an electric motor, which has the advantages of operating efficiency of a synchronous AC motor, of permanent magnet, but which does not have the adverse ignition characteristics of a permanent magnet AC motor. . Another object of the present invention is to provide said electric motor, which, during at least one mode of operating condition, does not exhibit slippage, or losses, associated with typical induction operation motors. A further object of the present invention is to provide said electric motor, which has an effective cost of manufacture and use.

COMPENDIUM OF THE INVENTION These and other objects of the invention are obtained by the various forms of the apparatus, which, in one embodiment, is in the form of a two-speed electric motor, including a motor stator, having a start winding and first and second main windings. The first main winding forms a first number of poles, lower, and the second main winding forms a second number of poles, higher, when activated. For example, the first main winding forms two poles and the second main winding forms four poles. Four poles / six poles, six poles / eight poles, and many other combinations of pole configuration are possible. The motor also includes a motor rotor, which has a rotor core, a rotor shaft, permanently magnetized sites and secondary conductors. The rotor core preferably comprises a plurality of laminations. The rotor shaft extends through the rotor core and is coaxial with the axis of rotation of the rotor core. The secondary conductors also extend through the rotor core and are axially disposed with respect to the rotor shaft. Said secondary conductors are deviated from the circumference or outer periphery of the rotor core and are connected at opposite ends of the core by end rings, as will be understood by those skilled in the art.

In the first embodiment, notches are formed on the outer periphery of the rotor core. Each notch is radially aligned with at least one of the secondary conductors. The permanent magnets are located in the notches. The permanent magnets are magnetized to form a number of poles equal to the upper number of poles for the particular two-speed configuration that has been selected. A switch unit, which responds to the requirements of the system, in which the motor is used, can be advantageously used to control the selection of the activation mode of the stator winding. For example, in a furnace blower motor application, the breaker unit causes the second main winding to be activated, when the furnace is required to operate in the low firing mode. When the furnace is required to operate in high firing mode, the breaker unit causes the first main winding to be activated. In a specific embodiment for a furnace blower motor application, the first and second main stator windings are configured to form four poles and six poles, respectively. The permanent magnet sites of the motor rotor are magnetized to form six magnetic poles. In this mode, the interrupter unit causes the first main winding to be activated for the high wire mode and the main winding of the main stator is activated for the low draft mode. During operation, and under all conditions of the motor start, the stator start winding and the first main winding are activated. The magnetic fields generated by said windings induce currents in the short-circuit conductors of the rotor, and the magnetic fields of said windings and rotor conductors are coupled and the rotor begins to rotate. Since the first winding of. Starting and the first main winding form four poles, the magnetic fields of said windings do not effectively match the magnetic fields of the permanent magnets of the rotor, configured to form six poles. Once the rotor has a sufficient speed, the start winding is deactivated. If the furnace is going to operate in high firing mode, the breaker unit makes the first main winding remain activated. As a result, the motor continues to operate, in a four-pole operation mode, at a relatively higher speed. If the oven will operate in low draft mode, and once the rotor speed exceeds the six pole synchronous speed, the switch unit activates the second main winding and the first main winding is deactivated. As a result, the rotor speed is reduced. When the rotor speed is equal to the synchronous speed of six poles, ie 1200 rpm, the magnetic fields of the permanent magnets of the rotor are coupled with, and "locked" in, the magnetic fields generated by the stator windings. The rotor then rotates substantially at the synchronous speed for the six pole configuration, i.e. 1200 rpm. If the oven is required to finally operate in the high firing mode, the switch unit will activate the first main winding and deactivate the second main winding. The motor then operates as an induction motor and the rotor speed increases. In applications, such as furnace blower motors, low firing mode is used for significantly longer periods than for high firing mode. For example, a normal heat station, in some parts of the world, lasts approximately 200 days over a period of one year. During the hot season, the cold weather required by the furnace to operate in high draft mode may persist for approximately 10 days. During the other, and more moderate, 190 days, the weather conditions require the furnace to operate in low draft mode. Since the motors, described above, operate as a permanent magnet motor in the low draft mode, efficiencies of said permanent magnet motor are provided at approximately 95% in time during a heat station. Operating as a permanent magnet motor, during that significant period, significant savings in reduced power consumption will be obtained, compared to the power consumption of a two-speed induction motor. In addition, such efficiencies are obtained without requiring any complex control of voltage source frequency. Also, these efficiencies are obtained without the adverse ignition characteristics of a permanent magnet motor. As explained above, the motor of the present is turned on as an induction motor. Therefore, noise and harmful vibrations, usually associated with the ignition of a permanent magnet motor, are eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an end plan view of a motor rotor with the end ring separated. Figure 2 is a perspective view of the motor rotor shown in Figure 1. Figure 3 is a cross-sectional view of an electric motor, including the motor rotor shown in Figures 1 and 2.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 is an end plan view of a motor rotor 10 with the end ring cut off. The rotor 10 includes a rotor shaft 12 mounted so that the axis of the arrow 12 is coaxial with the axis of rotation of the rotor. In Figure 1 an outermost lamination 14 is shown, which forms a part of the core of the rotor 10. The lamination 14 includes a rotor arrow opening 16, through which the rotor shaft 12 extends and a plurality of openings 18 of the secondary conductor. A plurality of T-shaped notches 20 are formed in an outer periphery 22 of the lamination 14. Portions of teeth 24, of the lamination 14, define the edges of the notches 20. The external laminations 20, which form the rotor core 10, are identical to the outermost lamination 14. The rotor 10 includes shorted or secondary conductors 26 arranged axially with respect to the rotor shaft 12. The conductors 26 are radially deflected from the outer periphery 22 of the lamination 14 and extend through the openings 18. In the notches 20 are radially placed permanent magnets 28. Each permanent magnet 28 is radially aligned with at least one of the conductors 26 shorted. The permanent magnets 28, as shown in Figure 1, have a substantially T-shaped cross-sectional shape, and are located within similarly shaped notches 20 formed in the outer periphery 22 of the lamination 14. The shape of the magnets 28 and notches 20 facilitate the securing of magnets 28 on the outer periphery 22 of laminations 14 without requiring adhesives or other securing apparatus. Of course, the specific configuration of the permanent magnets 28 is not limited to the T-shaped configuration, shown in Figure 1. For example, the magnets 28 and the notches 20 may be wedge-shaped, with the narrow portion of said wedge-shaped magnets, placed on the outer periphery 22 of the laminations 14. When using said configurations for the magnets 28, it eliminates the need to use adhesives to secure said magnets 28 to the outer periphery 22 of the laminations 14. Of course, magnets can be used that are attached to the outer periphery 22 of the laminations 12 using adhesive or other bonding methods. The secondary conductors 26 and the permanent magnets 28 are separated by approximately 0.0381 cm. , in a narrower portion of the lamination 14 between the secondary conductors 26 and the permanent magnets 28. Of course, the secondary conductors 26 and the magnets 28 can be separated by more or less than 0.381 cm. However, as said space increases, the losses of the magnet flow of secondary conductors 26 may increase. More particularly, there is a flow leakage path between the secondary conductors 26 and the permanent magnets 28. During operation, until the rolling material, between the conductors 26 and the magnets 28, becomes saturated, the magnetic fluxes are conducted along said flow leakage paths. The amount of flow leakage can be reduced by decreasing the rolling material between the conductors 26 and the magnets 28. The conductors 26 and the magnets 28 can still be in contact. However, the laminations 14 must be configured to provide sufficient support for the magnets 28. Although twenty short-circuited conductors 26 are illustrated together with the rotor 10, it is contemplated that more or fewer conductors may be used 26. The exact number of drivers 26, typically used, is a function of noise reduction, the number of stator slots, pole structure, and other desired motor characteristics. In Figure 2 a perspective view of the rotor 10 is shown. As shown in Figure 2, the laminations 14 and the magnets 28 are inclined, as will be described hereinafter. Said inclination can reduce the noise and improve the ignition characteristics, as is well known in the art. Also shown in Figure 2 are first and second end rings 32A-B, formed at opposite ends of rotor 10. End rings 32A-B turn secondary conductors 26 out of circuit. With respect to the manufacture and assembly of the 10, the laminations 14 are stamped from the steel. As is well known, each lamination 14 can be annealed or otherwise treated, so that a coating of insulation material is formed thereon. The laminations 14 are then stacked at a desired height to form the rotor core. The laminations 14 of the rotor are stacked, so that the openings 16, for the rotor shaft 12, are aligned and the openings 18, for the shorted conductors 26 and the grooves 20, for the permanent magnets 28, are inclined. Once the laminations 14 are stacked at the selected height and aligned, the permanent magnets 28 are formed in the notches 20 at the outer periphery 22 of the laminations 14 using an injection molding process.

Particularly, the magnets 28 formed of neodymium steel using injection molding. Neodymium steel, in a form suitable for injection molding, is commercially available from Magnaquench Division of General Motors, located in Anderson, Indiana. Alternatively, the magnets 28 can be manufactured using alternative techniques such as extrusion, casting and concreting processes, and then secured to the outer periphery 22 of the laminations 14. The shorted conductors 26 and the end rings 32A-B of the rotor are formed after using an aluminum die casting method. The rotor shaft 12 is then inserted through the aligned openings 16 in each lamination 14 and the end rings 32A-B. The rotor shaft 12 is secured to the end rings 32A-B by, for example, welding. The magnets 28 can then be magnetized. Further details, with respect to the assembly of a rotor and a motor, are set forth, for example, in the U.S. Patent. No. 4,726,112, which is assigned to the assignee hereof. Figure 3 illustrates a motor 50 including the rotor 10. The motor 50 includes a housing 52 having motor spiders 54A-B secured to it. The motor spiders 54A-B include supports 56A-B for bearing assemblies 58A-B. The rotor shaft 12 is coaxially aligned with the bearing assemblies 58A-B and extends through openings 60A-B formed in the spiders 54A-B.

The motor 50 also includes a stator 62 having a stator core 64 and stator windings 66. The stator windings 66 include a start winding and a first and second main winding. The first winding is wound to form a first, lower number of poles, and the second main winding is wound to form a second, higher number of poles. The start winding is wound to form a number of poles equal to the number of poles of the first main winding. The stator core 64 forms a rotor hole 68. The stator shaft 12 is concentrically disposed, axially, of the stator core 64, and the rotor core 14 is concentrically positioned with the rotor shaft 12. A switch unit 70, shown dotted line, is mounted to spider 54A. The switch unit 70 includes, in one form, a movable mechanical arm 72. An assembly 74, which responds to a centrifugal force, also shown in dotted lines, is mounted to the rotor shaft 12 and includes a thrust collar 76, the which engages the mechanical arm 72. The thrust collar 76 is slidably mounted on the rotor shaft 12. The assembly 74 also includes a weighted arm and a spring (not shown in detail) secured to the rotor shaft 12. The weighted arm it is calibrated to move from a first position to a second position, when the rotor speed exceeds a predetermined speed. When the weighted arm moves to the second position, the thrust collar 76 also moves from a first position to a second position. As a result, the mechanical arm 72 of the switch unit 70 moves from a first position to a second position, which causes the switch unit 70 to switch from a first position to circuit to a second circuit position. The switch unit 70 is used, separately, in some applications (without the arm 72) and the switch unit 70 and the assembly 74 are used in combination in other applications. The switches used to control the activation of the start and main windings are well known. In a specific embodiment, the first main stator winding is wound to form four poles and the second main stator winding is wound to form six poles. The permanent magnets 28 of the motor rotor are magnetized to form six poles. The switch unit 70 is coupled to an external control, such as an oven control. The assembly 74, which responds to a centrifugal force, is not used in this particular application. The interrupter unit 70 causes the first winding to be activated for the high draft mode, and the second main stator winding to be activated for the low draft mode. During operation, and when the motor is switched on, the main stator winding and the first main winding are activated. The magnetic fields generated by said windings induce currents in the short-circuited conductors 26 of the motor rotor 10, and the magnetic fields of said windings and conductors 26 are coupled and the rotor 10 starts to rotate. Since the start winding and the first main winding form four poles, the magnetic fields of said windings are not effectively coupled to the magnetic fields of the permanent magnets 28 of the rotor, configured to form six poles. Once the rotor 10 has sufficient speed, the start winding is deactivated. If the furnace is to operate in the high draft mode, the switch unit 70 causes the first main winding to remain activated. As a result, the motor 50 operates as an induction motor in a four-pole operating mode, at a relatively higher speed. If the furnace is to operate in the low firing mode, however, the switch unit 70 activates the second main winding and the first main winding is deactivated. As a result, the rotor speed is reduced. When the rotor speed is equal to the synchronous speed of six poles, ie 1200 rpm, the magnetic fields of the permanent magnets 28 of the rotor are coupled with, and "locked" in, the magnetic fields generated by the second winding principal. The rotor 10 then rotates substantially at the synchronous speed for the six pole configuration, i.e., 1200 rpm. If the furnace is then required to operate in the high firing mode, the switch unit 70 activates the first main winding and deactivates the second main winding. The motor 50 then operates as an induction motor and the rotor speed is reduced.

In another application, and as in the embodiment discussed above, the first stator main winding is wound to form four poles and the second stator main winding is wound to form six poles. The permanent magnets 28 of the motor rotor are magnetized to form six poles. In this particular application, the motor 50 operates as an individual speed motor. The assembly 74, which responds to a centrifugal force, is used and is calibrated to move from a first position to a second position, when the rotor speed exceeds 1200 rpm, that is, the synchronous speed of six poles. When the switch unit 70 is in the first position to make circuit, the first main winding is activated, that is, the low firing mode. When the unit 70 is in the second position to make circuit, the second main winding is activated, that is, the high shooting mode. The assemblies which respond to a centrifugal force and the switches are well known and are described in more detail, for example in the U.S. Patent. No.4, 726, 1 12 and 4, 856, 182, both assigned to the assignee hereof. During operation, and when the motor is switched on, the switch unit 70 is in the first position to make circuit and the first main winding and the start winding are activated. The magnetic fields generated by said windings induce currents in the short-circuited conductors 26 of the rotor 10 of the motor. The magnetic fields of said windings and the secondary conductors 26 of the rotor are coupled, and the rotor 10 begins to rotate. Since the first main winding and the start winding are activated to form four poles, the magnetic fields of said windings are not effectively coupled to the magnetic fields of the permanent magnets 28, which are magnetized to form six poles. Once the speed of the rotor 10 exceeds 1200 rpm, the arm weighted the assembly 74 causes the thrust collar 76 to move to a second position. The thrust collar 76 causes the mechanical arm 72 to move to the second position, and the switch unit 70 is switched to the second position to make circuit. The second main winding is then activated. As a result, the speed of the rotor 10 increases. When the rotor speed is equal to the synchronous speed of six poles, ie 1200 rpm, the magnetic fields of the permanent magnets 28 of the rotor are coupled with, and "locked" in, the magnetic fields generated by the second main winding . The rotor 10 then rotates substantially at the synchronous speed for the six pole configuration, i.e., 1200 rpm. As described above, the rotor 10 is "driven" or "lowered" at the synchronous speed, instead of being "pushed" toward the synchronous speed. Allowing the rotor 10 to descend at the synchronous speed is much easier than trying to "push" the rotor 10 toward the synchronous speed with a lower pole induction winding, which is typical in synchronous AC motors, starting at line.

In the configurations, both of one and two speeds described herein, the onset of noise and vibration is substantially eliminated. Specifically, since the motor is turned on as an induction motor, noise and vibration, usually associated with permanent magnet motors, are eliminated. In addition, since there is no mutual coupling between the stator winding and the magnetic fields of the permanent magnet during the ignition of the engine, the parasitic torque is substantially eliminated. Also, by operating the motor as a permanent magnet motor for a significant percentage of the motor's operating time, the motor improves its operating efficiency, compared to the induction operation motors. In addition, in the two-speed configuration, no supply voltage frequency controller is required. ThusIn addition to the improved operation efficiency, a lower cost two speed motor is provided. Also, in the configurations of both two speeds and one speed, the rotor "descends" or "drags" at the synchronous speed, as described above. The problems associated with known synchronous AC motors, which attempt to push a rotor toward a synchronous speed, are substantially eliminated by allowing the rotor to descend at the synchronous speed. Many modifications and variations of the engine 50, illustrated in Figure 3, are possible and contemplated. For example, the engine 50 can be configured to operate as a two-pole / four-pole, six-pole / eight-pole motor, or any another motor in two modes. The specific structure of the motor 50, such as the type of bearing assemblies 58A-B and a motor frame, of course, can also vary. For the speed unit, switches other than switches that respond to a centrifugal force may also be used. For example, a sensor and a rotor speed switch mounted to the stator 62 or optical controls may be used. In addition, the laminations 14, the permanent magnets 28 and the secondary conductors 26 of the rotor 10 can be formed from many different materials and are not limited to the specific materials and assembly methods described herein. From the above description, it is clear that the objects of the invention are obtained. Although specific modalities have been described and illustrated in detail, it is clearly understood that it is intended to be only a form of illustration and example, and is not intended as a limitation. As a result, the spirit and scope of the invention will be limited only by the terms of the appended claims.

Claims

CLAIMS 1.- A rotor for an electric motor, said rotor comprising: a rotor core including a plurality of laminations, each of said laminations having an outer periphery, a central rotor arrow opening, a plurality of conductor openings secondary radially deviated from the outer periphery, and a plurality of notches having an open end at said outer periphery; a rotor arrow having an axis, which is coaxial with an axis of rotation of the rotor core and extending through said central rotor arrow aperture; a plurality of secondary conductors extending through said secondary conductor openings; and a plurality of permanent magnets located in said grooves of the lamination. 2 - A rotor according to claim 1, wherein said laminations are inclined. 3 - A rotor according to claim 1, wherein said permanent magnets have a transverse T-shaped configuration. 4. A rotor according to claim 1, wherein said permanent magnets have a wedge-shaped transverse configuration. . 5. A rotor according to claim 1, wherein each of said permanent magnets is radially aligned with at least one of the secondary conductors. 6 - A rotor according to claim 5, wherein each of said permanent magnets is positioned between one of the secondary conductors and the outer periphery of said laminations. 7. A rotor according to claim 1, wherein said permanent magnets are formed of neodymium steel. 8. A rotor according to claim 1, further comprising first and second end rings, said first end rings electrically connected to one end of each of the secondary conductors and said second end rings electrically connected to the other end of each one of the secondary drivers. 9. An electric motor, comprising: a stator comprising a stator core, first and second main windings, said first main winding configured to form a number of poles lower than said second main winding, said stator core forming a stator hole; and a rotor comprising a rotor arrow concentrically axially disposed to the stator core, a stator core positioned concentrically with said rotor shaft and attached thereto, secondary conductors axially disposed to said rotor shaft and extending through of said rotor core, a plurality of permanent magnets located on an outer periphery of said stator core and magnetized to form a number of poles equal to the number of poles formed by said second main winding. 10. An electric motor according to claim 9, wherein said secondary rotor conductors are radially offset from the outer periphery of the rotor, and wherein each of said permanent magnets is radially aligned with at least one of the conductors. secondary 1 - An electric motor according to claim 10, wherein a plurality of notches are formed in said rotor core, said notches having an open end on said outer periphery of the rotor, at least one of the permanent magnets located inside one of said notches. 12 - An electric motor according to claim 1, wherein said permanent magnets have a transverse T-shaped configuration. 13. An electric motor according to claim 1, wherein said permanent magnets have a transverse configuration. with wedge shape. 14. An electric motor according to claim 9, wherein said rotor further comprises first and second end rings, said first end ring electrically connected to one end of each of the secondary conductors and said second end ring electrically connected to the other end of each of the secondary drivers. 15. An electric motor, comprising: a stator comprising a stator core, first and second main windings, said first main winding configured to form a number of poles lower than said second main winding, said stator core forming a stator hole; and a rotor comprising a rotor arrow concentrically axially disposed to the stator core, a stator core positioned concentrically with said rotor shaft and attached thereto, the secondary conductors axially disposed to said rotor shaft and extending through from said rotor core, a plurality of permanent magnets located on an outer periphery of said stator core and magnetized to form a number of poles equal to the number of poles formed by said second main winding; and a switch unit having a first position and a second position, said switch unit being responsible for the rotational speed of said rotor and coupled to said stator windings to control the activation mode of said stator windings. 16 - An electric motor according to claim 15, wherein said secondary rotor conductors are radially offset from the outer periphery of the rotor, and wherein each of said permanent magnets is radially aligned with at least one of the secondary conductors . 17. An electric motor according to claim 16, wherein a plurality of notches are formed in said rotor core, said notches having an open end on said outer periphery of the rotor, at least one of the permanent magnets located therein. of one of said notches. 18. An electric motor according to claim 17, wherein said permanent magnets have a transverse T-shaped configuration. 19. An electric motor according to claim 17, wherein said permanent magnets have a transverse configuration. with wedge shape. 20. An electric motor according to claim 15, wherein said rotor further comprises first and second end rings, said first end ring electrically connected to one end of each of the secondary conductors and said second end ring electrically connected to the other end of each of the secondary drivers. 21 - An electric motor according to claim 15, wherein said motor further comprises an assembly responding to a centrifugal force mounted on said rotor, said assembly responding to a centrifugal force comprising a thrust collar slidably mounted to said arrow of rotor, and said switch unit comprises a mechanical arm, said thrust collar configured to couple said mechanical arm. 22. - A method for assembling a rotor for an electric motor, said method comprising the steps of: forming a rotor core, the core having an outer periphery, a central rotor arrow opening, a plurality of radially deflected secondary conductor openings the outer periphery, and a plurality of notches having an open end at the outer periphery; secure the permanent magnet material in each of the notches; and securing the secondary conductors within each of the openings of the secondary conductors. 23. A method according to claim 22, wherein the secondary conductors are formed in the openings of the secondary conductors using an aluminum compression casting process. 24. A method according to claim 23, further comprising the step of forming first and second end rings attached to the respective ends of said secondary conductors. 25. A method according to claim 22, wherein the permanent magnet material is secured in the notches using an injection molding process. 26. A method according to claim 25, wherein the permanent magnet material is neodymium steel. 27. A method according to claim 22, wherein the formation of the rotor core comprises the step of stamping laminations from steel. 28.- A method for operating an electric motor, the motor including a rotor having a rotor core, a rotor arrow, permanent magnets located on an outer periphery of the rotor core and secondary conductors extending through the rotor core , the motor further including a stator having a stator core and first and second main windings, the first main winding configured to form a number of poles lower than that of the second main winding, the stator core forming a stator hole, the rotor shaft concentrically disposed axially to the stator core, the stator core positioned concentrically with the rotor shaft attached thereto, said method comprising the steps of: upon starting the motor, activating the first main winding; and when at least one first predetermined condition occurs, activate the second main winding and deactivate the first main winding. 29. A method according to claim 28, wherein the predetermined condition is that of the rotor speed that is at least equal to the synchronous speed of the second main winding. 30. A method according to claim 28, wherein the stator further includes a first winding configured to form the same number of poles as in the first main winding, and said method further comprises the steps of: in the ignition of the engine , activate the start winding; and after sufficient rotor speed has been obtained, deactivate the start winding. 31. A method according to claim 28, further comprising the steps of: upon the occurrence of a second predetermined condition subsequent to the activation of the second main winding, activating the first main winding and deactivating the second main winding. 32 - A lamination of a rotor for an electric motor, said lamination having a generally circular shape and an outer periphery, said lamination comprising a central opening sized to have a rotor arrow inserted therethrough, a plurality of conductor openings secondary axially disposed of said central opening and deviated from the outer periphery, and a plurality of portions of teeth in said outer periphery. 33.- A lamination according to claim 32, wherein the portions of adjacent teeth define notches having open ends at said outer periphery, each of said notches radially aligned with at least one of the openings of the secondary conductor. 34 - A lamination according to claim 32, wherein said lamination is formed of steel. SUMMARY An electric motor is described which includes a stator having a stator core, a start winding and first and second main windings. The first main winding and the start winding are configured to form a lower number of poles than the second main winding. The stator core forms a stator hole. The motor also includes a rotor having a rotor shaft concentrically disposed axially of the stator core and a rotor core positioned concentrically with the rotor shaft. The secondary conductors are axially disposed of the rotor shaft and extend through the rotor core. A plurality of permanent magnets is located on an outer periphery of the rotor core and are magnetized to form a number of poles equal to the number of poles formed by the second main winding.