Patent Application
20060066168
The present technique relates generally to the field of electric motors and, particularly, to rotors for induction motors, such as a squirrel cage rotor, for example.
Electric motors of various types are commonly found in industrial, commercial, and consumer settings. In industry, such motors are employed to drive various kinds of machinery, such as pumps, conveyors, compressors, fans and so forth, to mention only a few. Conventional alternating current (ac) electric motors may be constructed for single- or multiple-phase power, and are typically designed to operate at predetermined speeds or revolutions per minute (rpm), such as 3600 rpm, 1800 rpm, 1200 rpm, and so on, or for the continuously changing speed within the certain speed range. The latter is called variable speed operation. Such motors generally include a stator comprising a multiplicity of windings surrounding a rotor, which is supported by bearings for rotation in the motor frame. Typically, the rotor comprises a core formed of a series of magnetically conductive laminations arranged to form a lamination stack capped at each end by electrically conductive end rings. Additionally, typical rotors include a series of conductors that are formed of a nonmagnetic, electrically conductive material and that extend through the rotor core. These conductors are electrically coupled to one another via the end rings, thereby forming one or more closed electrical pathways.
In the case of ac motors, applying ac power to the stator windings induces a current in the rotor, specifically in the conductors. The electromagnetic relationships between the rotor and the stator cause the rotor to rotate. The speed of this rotation is typically a function of the frequency of ac input power (i.e., frequency) and of the motor design (i.e., the number of poles defined by the stator windings). A rotor shaft extending through the motor housing takes advantage of this produced rotation and translates the rotor's movement into a driving force for a given piece of machinery. That is, rotation of the shaft drives the machine to which it is coupled.
Often, design parameters call for relatively high rotor rotation rates, i.e., high rpm's. By way of example, a rotor within an induction motor may operate at 14,000 rpm, and beyond. Based on the diameter of the rotor, operation at such rpm's translates into relatively high surface speeds on the rotor. Again, by way of example, rotor surface speeds may reach values of 200 meters per second (mps), and beyond. During operation, particularly during high-speed operation, it is desirable to mitigate the occurrence of resonance in the motor. Indeed, resonance in the motor can lessen performance of the motor and, in certain instances, lead to a malfunction of the motor. For example, if the stiffness of the rotor is not sufficient, the first natural frequency of variable speed motor may be below the maximal operational frequency, and, as such, difficulties in operating the motor at a speed corresponding to the first natural frequency often arise.
Typically the rotor laminations are not connected to each other in any way, so that the lamination stack is held together or by the shrink fit between the shaft and the laminations, or by the electrically conductive end rings and by the electrical conductors, or by additional plates located at the ends of the stack and connected to the rotor shaft, or by combination of the above. Accordingly, traditional rotors present inconsistencies with respect to stiffness of the rotor assembly, because of the uncertainty of the bending stiffness of the lamination stack. Unfortunately, the inconsistencies in the stiffness of the rotor hinder accurate modeling of the rotor assembly. That is to say, an inconsistency in the stiffness of the rotor impedes accurate prediction of the rotor's dynamic behavior.
Furthermore, traditional rotors present inconsistencies with respect to stiffness of the rotor assembly, because of the uncertainty of the bending stiffness of the lamination stack. Unfortunately, these inconsistencies in the stiffness of the rotor hinder accurate modeling of the rotor assembly. That is to say, inconsistencies in the stiffness of the rotor impeded accurate prediction of the rotor's dynamic behavior.
There is a need, therefore, for an improved rotor and rotor construction technique.
According to an exemplary embodiment, the present technique provides a rotor lamination for a motor rotor. The rotor lamination has an outer periphery that defines a generally circular lamination cross-section and an inner periphery that defines a central aperture configured to receive a rotor shaft therethrough. The exemplary lamination also has first and second end surfaces that extend from the outer periphery to the inner periphery and that are generally parallel to one another. Extending between the first and second end surfaces are a plurality of enclosed rotor-slots that are disposed concentrically about the central aperture. These rotor-slots extend generally transverse to the lamination cross-section. Additionally, the exemplary lamination has a bonding agent that is disposed on at least one of the first and second end surfaces. Advantageously, the bonding agent increases the stiffness of a rotor core formed of the exemplary lamination.
In accordance with another embodiment, the present technique provides a rotor for use in an electric motor. The rotor comprises a rotor core formed of a plurality of rotor laminations stacked with respect to one another. The rotor laminations cooperate to form enclosed rotor-slots and a central aperture that extend through the rotor core generally transverse to the rotor core's cross-section. The exemplary rotor also includes a rotor shaft disposed in the shaft chamber and a plurality of electrically conductive members disposed in the rotor channels. To increase the stiffness of the rotor assembly, a bonding agent located between at least one pair of adjacent rotor laminations is configured to bond the at least one pair of adjacent rotor laminations to one another. Advantageously, bonding of the rotor laminations facilitates operation of the rotor at higher speeds, i.e., high-speed operation.
In accordance with yet another embodiment, the present technique provides a method of manufacturing a rotor lamination. The exemplary method includes the act of providing a rotor lamination that has a generally circular cross-section and first and second end surfaces that extend from the outer periphery to an inner periphery of the rotor lamination, wherein the first and second end surfaces are generally parallel to one another. By way of example, the rotor lamination may be provided via a fabrication process, such as stamping or laser cutting. The exemplary process also includes the act of applying a bonding agent to at least one of the first and second end surfaces. By way of example, the bonding agent may be applied to the lamination by dipping the rotor lamination into a container of the bonding agent. Alternatively, the bonding agent may be applied via a spray coating process.
In accordance with yet another embodiment, the present technique provides a method for fabricating a rotor core. The exemplary method includes the act of aligning a plurality of rotor laminations with respect to one another to form a rotor core that has a central shaft chamber and a plurality of rotor channels that both extend through the rotor core generally transverse to the core's cross-section. Additionally, the exemplary method includes placing a plurality of conducting members into the plurality of rotor channels. Furthermore, the exemplary method includes the act of bonding at least one pair of adjacent laminations with respect to one another. Advantageously, bonding a pair of adjacent laminations with respect to one another increases the stiffness of the rotor core.
These and other features, aspects, and advantages of the present technique will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
As discussed in detail below, embodiments of the present technique provide apparatus and methods for rotors and rotor construction. Although the following discussion focuses on induction motors, the present technique also affords benefits to a number of applications in which the rotor integrity is a concern. Indeed, the present technique is applicable to any number of induction motor and generators as well as non-induction based motors and generators. Accordingly, the following discussion provides exemplary embodiments of the present technique and, as such, should not be viewed as limiting the appended claims to the embodiments described.
Additionally, as a preliminary matter, the definition of the term “or” for the purposes of the following discussion and the appended claims is intended to be an inclusive “or.” That is, the term “or” is not intended to differentiate between two mutually exclusive alternatives. Rather, the term “or” when employed as a conjunction between two elements is defined as including one element by itself, the other element itself, and combinations and permutations of the elements. For example, a discussion or recitation employing the terminology “‘A’ or ‘B’” includes: “A” by itself, “B” by itself, and any combination thereof, such as “AB” and/or “BA.”
Turning to the drawings,
To induce rotation of the rotor, current is routed through stator windings disposed in the stator. (See
During operation, centripetal and centrifugal forces are produced in the rotor. If not accounted for, these forces may strain various components of the rotor, thereby leading to losses in performance and, in certain instances, failure of the rotor. Accordingly, as discussed further below, the exemplary rotor includes features that improve the mechanical integrity of the rotor and that facilitate operation of the rotor at higher speeds.
In the exemplary motor 10, a rotor assembly 40 resides within the rotor chamber 34. Similar to the stator core 32, the rotor assembly 40 comprises a plurality of rotor laminations 42 aligned and adjacently placed with respect to one another. Thus, the rotor laminations 42 cooperate to form a contiguous rotor core 44. The exemplary rotor assembly 40 also includes rotor end members 46, disposed on each end of the rotor core 44, that cooperate to secure the rotor laminations 42 with respect to one another. When assembled, the rotor laminations 42 cooperate to form shaft chamber that extends through the center of the rotor core 44 and that is configured to receive the rotor shaft 26 therethrough. The rotor shaft 26 is secured with respect to the rotor core 44 such that the rotor core 44 and the rotor shaft 26 rotate as a single entity, the rotor assembly 40. Moreover, a bonding agent (see
To support the rotor assembly 40, the exemplary motor 10 includes front and rear bearing sets 50 and 52, respectively, that are secured to the rotor shaft 26 and that facilitate rotation of the rotor assembly 40 within the stationary stator core 32. During operation of the motor 10, the bearing sets 50 and 52 transfer the radial and thrust loads produced by the rotor assembly 40 to the motor housing. Each bearing set 50 and 52 includes an inner race 54 disposed circumferentially about the rotor shaft 26. The tight fit between the inner race 54 and the rotor shaft 26 causes the inner race 54 to rotate in conjunction with the rotor shaft 26. Each bearing set 50 and 52 also includes an outer race 56 and ball bearings 58, which are disposed between the inner and outer races 54 and 56. The ball bearings 58 facilitate rotation of the inner races 54 while the outer races 56 remain stationary and mounted with respect to the endcaps 14 and 16. Thus, the bearing sets 50 and 52 facilitate rotation of the rotor assembly 40 while supporting the rotor assembly 40 within the motor housing, i.e., the frame 12 and the endcaps 14 and 16. To reduce the coefficient of friction between the races 54 and 56 and the ball bearings 58, the ball bearings 58 are coated with a lubricant.
The exemplary rotor laminations 42 are formed of a magnetically conductive material, such as steel. Advantageously, to prevent electrical interference with the conductor bars 48 (see
Because the rotor laminations 42 are substantially identical to one another, each rotor lamination 42 includes features that, when aligned with corresponding features of adjacent laminations 42, form cumulative features that extend axially through the rotor core 44. For example, the central apertures 66 of adjacent laminations 42 cooperate to form a shaft chamber that extends through the rotor core and that is configured to receive a rotor shaft (see
Turning to
In any case, the bonding agent 80 bonds (cohesively, adhesively, etc.) adjacent laminations 42 with respect to one another. Advantageously, this bonding between adjacent laminations increases the overall stiffness of the laminated rotor core 44. For example, the bonding agent 80 disposed between each of the adjacent rotor laminations 42 may increase the bending stiffness of the rotor core 44 and rotor assembly 42 by two hundred to three hundred percent, and beyond. Moreover, the bonded relationship between adjacent laminations 42 improves the consistency of the stiffness of the rotor core 44. Advantageously, increasing such consistency facilitates modeling of the performance of the rotor assembly 40 during operation. That is to say, improving stiffness consistency within the rotor core 44 and the rotor assembly 42 improves the accuracy of models that are designed to predict the rotor assembly's dynamic performance.
Keeping
An axial compression force may be applied to the rotor core 44. (Block 108.) Advantageously, the axial compression force forces the rotor laminations 42 closer with respect to one another and, as such, expels excess bonding agent 80. If the bonding agent is a heat-activated compound, the rotor core 44 may be heat treated. (Block 110.) In any event, a sufficient curing time is provided to bond the laminations to one another. (Block 112). After the curing is completed, the external compression force is removed. The exemplary process also includes placing conductor bars 48 into the rotor core 44. (Block 114.) As one example, prefabricated bars, which are typically shaped to match the shape of the rotor-slots 64, are inserted into the rotor channels 49. (Block 118.) Rotor assemblies 40 assembled via this process are typically identified as fabricated rotors. Alternatively, the conductor bars 48 may be formed by placing molten conductive material into the rotor channels 49 and subsequently cooled. (Block 120.) Rotors fabricated via this process are typically identified as cast rotors. In any event, after the rotor manufacturing is completed, the rotor 40 may be inserted into the motor 10.
While only certain features of the technique have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the technique.
