ELECTRIC MOTOR ROTOR

Field of the Invention

The present invention relates to an electric motor rotor and, more particularly, an electric motor rotor of "squirrel cage" type induction.

According to the present invention, the electric motor rotor disclosed herein is primarily intended to increase the electric conductivity of the short-circuited buses existing between the short-circuited rings composing said electric motor rotor.

The present invention also relates to the manufacturing process of electric motor rotor and, more particularly, in the controlled solidification process which integrates the manufacturing process of the electric motor rotor.

The present invention also relates to the manufacturing system of electric motor rotor, system which allows the achievement of controlled solidification process which integrates the manufacturing process of the electric motor rotor.

Background of the Invention

As it is within the knowledge of technicians skilled in the subject, electric motors are fundamentally composed by a rotor and a stator.

In general, an electric motor stator is basically integrated by a metal frame in which there are inductors radially arranged. Said inductors are usually comprised by coils properly rolled in brackets existing in the metal frame.

Also in general, an electric motor rotor (squirrel cage type) is basically integrated by a metal core in which there are inductors radially arranged. Said inductors, which are short- circuited, are usually comprised by metal columns, which extend over the entire axial extent of the metal core. As the rotor inductors are in short circuit, then it is possible to observe that the metal columns have the ends thereof unified by short-circuited rings.

As previously mentioned, the basic constitution of electric motors and, specially, induction electric motors, is within the knowledge of the technicians skilled in the subject.

It is also within the knowledge of the technicians skilled in the subject that the electric conductivity of the motor rotor inductors comprises one of the aspects that determines the power efficiency of the motor as a whole. This is because there is a directly proportional ratio between the electromagnetic interaction established between stator and rotor and the electric conductivity of the stator and rotor inductors.

However, it is also known that there is a relationship between the cost-benefit of the manufacturing material of the rotor inductors and the electric conductivity of the same material. That is, it is known that it is economically impossible to manufacture electric motors rotors whose manufacturing material is a mainly noble material such as, for example, silver or copper. Therefore, and aiming to achieve an excellent relationship between the cost-benefit and the electric conductivity, it is known that electric motors rotors inductors are made of aluminum.

It is obvious to note that the choice of this material, besides being economically attractive, is extremely advantageous from the manufacturing point of view, after all, it is within the general knowledge that aluminum is an easy industrial handling material.

In this sense, the current state of the art provides several manufacturing processes of electric motors rotors. Among these several processes, it is evidenced the one described in the patent document PI 0106597-1.

Said document describes a manufacturing process of rotors wherein it is comprised the injection and centrifugation of aluminum, in the metallic core of a rotor, resulting in the shape of the short-circuited inductors (short-circuited columns and rings).

Furthermore, the manufacturing process of rotors described in the above mentioned patent document PI 0106597-1 further provides novel means of finalizing the process and, hence, novel means responsible for the finish optimization of the manufactured rotors.

Although the manufacturing process of electric motors rotors disclosed in the patent document PI 0106597-1 reaches all the aimed objectives, it is possible to check that it does not aim to optimize or improve any aspect related to the electric conductivity of the aluminum inductors (short-circuited columns and rings).

It is evident that the process disclosed in patent document PI 0106597-1 can use other materials whose electric conductivity is higher than that of aluminum, however, and as previously mentioned, the simple change of materials is not economically feasible.

It is then based on these premises that the present patent of invention arises.

Objectives of the Invention

Thus, it is an objective of the present invention to provide an electric motor rotor whose short-circuited inductors (short-circuited buses and rings) are made of aluminum or equivalent metal alloy, and yet possess high electric conductivity compared to the short- circuited inductors of electric motors rotors belonging to the current state of the art.

It is therefore one of the objectives of the subject invention to provide an electric motor rotor whose short-circuited inductors and, the buses especially, show improved microstructure.

It is therefore one of the objectives of the subject invention that the short-circuited buses of the electric motor rotor have linear crystals aligned with the direction of the electric current flow that circulates there. In this sense, it is also one of the objectives of the invention concerned that the linear crystals defined in the columns (or buses) of the short-circuited inductors of the electric motor rotor are of macrometric scale.

It is another objective of the present invention to disclose at least one manufacturing process of electric motor rotor able to achieve the specifications briefly mentioned above, that is, capable of manufacturing an electric motor rotor whose columns (or buses) of the short-circuited inductors of the electric motor rotor have linear crystals shaped in the direction of electric current flow that circulates there, said linear crystals being of constitution in macrometric scale.

It is therefore another object of the instant invention that the mentioned manufacturing process of electric motor rotor reaches said specifications through the heat control of the solidification of aluminum or equivalent metal alloy that comprises the short- circuited inductors of the electric motor rotor.

It is also an objective of the present invention that the mentioned manufacturing process of electric motor rotor, through the heat control of the solidification of aluminum or equivalent metal alloy that comprises the short-circuited inductors of the electric motor rotor, is able to expel the impurities of said aluminum or equivalent metal alloy to the grain boundaries zones that delimit and define the outline of the linear crystals present in the columns (or buses) of the short-circuited inductors of the electric motor rotor.

Finally, it is an objective of the present invention to disclose a manufacturing system of electric motor rotor able to execute the manufacturing process of electric motor rotor.

Summary of the Invention

These and other objects of the invention now disclosed are fully achieved by means of the electric motor rotor disclosed herein, which comprises at least one metal core and a plurality of short-circuited inductors, wherein said short-circuited inductors are mainly shaped by short-circuited buses and rings.

In accordance with the subject invention, the electric motor rotor provides at least one linear crystal analogously shaped to the functional direction of electric current flow, said linear crystal being disposed on at least one bus of at least one short-circuited inductor, and having a dimension aligned with the flow of electric current of at least two times greater than the other dimensions of the grains with respect to the axial extension of said buses wherein it is arranged.

Optionally, it may be provided linear crystals of extension similar to at least one third of the axial extension of said buses wherein they are arranged, or even, of extension equivalent to the axial extension of said buses wherein they are arranged.

In accordance with the subject invention, it is particularly interesting to be provided multiple linear crystals in a same bus. Furthermore, it is also particularly interesting that it is provided at least one linear crystal in each of the rotor buses.

Also optionally, it is possible to provide at least one linear crystal disposed in at least one short-circuited ring, in this case, the linear crystal being disposed in at least one short- circuited ring can be extended in at least one portion of at least one bus. In addition to the electric motor rotor itself, the subject invention also achieves the aimed objectives through the manufacturing process of electric motor rotor, which comprises at least one shaping step of the metal core and at least one shaping step of the short- circuited inductors by introducing molten metallic material in the metal core. As differential before the prior art, the subject method is distinguished by the fact that it promotes, along the shaping step of the short-circuited inductors, which solidification of the molten metal material introduced into the metal core, that this solidification is effected by guided cooling of the molten metal material.

In general, and in accordance with the concepts and objectives of the subject invention, said guided cooling of the molten metal material is accomplished in the axial direction of the metal core and, more particularly, from bottom to top.

In addition to the electric motor rotor and the manufacturing process of the electric motor rotor, the subject invention also achieves the aimed objectives through the manufacturing system of electric motor rotor, which comprises at least one retaining mold of the electric motor rotor. As differential before the state of the art, the manufacturing system of electric motor rotor further comprises at least one heating means linked to at least one axial extent portion of the mold and at least one cooling means linked to at least one of the axial ends of the mold.

In accordance with the subject invention, it is found that said heating means is able to maintain the temperature essentially constant of said molten metal material introduced into the mold through the introduction means of molten metal material. Further, it is also found that said cooling means is able to promote cooling guided in axial direction of said molten metal material introduced into the mold through the introduction means of molten metal material. In general, said manufacturing system of electric motor rotor provides an adjustable heat gradient between the heating means and the cooling mean.

Preferably, the heating means comprises an electrical resistance cooperating with the outer wall of the mold.

Additionally, the system of the present invention may comprise a means to reduce the heat loss gradually and, also, said means for reducing the heat loss can be a thermally insulating wall surrounding said mold. The cooling means comprises a refrigerated fluid circulation system and, more particularly, a refrigerated fluid circulation system defined inside the lower portion of the mold.

Brief Description of the Drawings

The present invention will be described in detail based on the figures listed below, which are:

Figure 1 illustrates a conventional electric motor rotor according to the current state of the art; Figure 2 illustrates the short-circuited inductors of a conventional electric motor rotor, as well as an enlarged detail of the granular composition thereof according to the current state of the art;

Figure 3 illustrates the short-circuited inductors of an electric motor rotor, as well as an enlarged detail of the granular composition thereof according to the present invention; and

Figure 4 illustrates, in schematic form, the manufacturing system of electric motor rotor according to the present invention.

Detailed Description of the Invention

Preliminarily, and before going into deep details of the present invention, it is understood as interesting to point and describe some of the technical details pertaining to the framework of the technological field in question.

Thus, it is noted that the term "crystals", as is known to those skilled versed in metallurgy, refers to "grains" isolated in the matter in solid state.

Regarding the formation mechanism of "crystals", it is known that during solidification, the metals undergo a rearrangement of their atoms which determines the crystalline structure thereof. Depending on the manner in which the liquid becomes solid, it can occur faults in the stacking and / or in the organization of the atoms, resulting in structural imperfections. The atoms, of a solid metal, vibrate around geometrical positions defined depending on the crystalline arrangement, this feature being specific to each metal. In the liquid state, the atoms also have translational movements. During this movement, the atoms collide. In a collision, it is possible to have grouping of atoms in a balance state, in which a core will form, with a particular crystalline arrangement.

The core is a solid that can grow or dissolve, depending on the energy (thermal, electromagnetic, etc.) absorbed by the system. The solid growth occurs by migration of atoms from the liquid state to the solid state, arranging atoms in balance position of the reticulate, forming crystalline arrangements.

In the controlled solidification or controlled nucleation, the main feature is the quantity and size of the crystalline arrangement obtained. In this context, and according to the present invention, the "linear crystals" are those that can be conceived as those grains whose crystallographic orientations are fundamentally similar, with a low content of disagreement between the boundary zones thereof.

With the controlled cooling, the energy imposed to the system makes the transition from liquid to solid, providing sufficient time for the atoms, during their collisions, to make an arrangement and come into balance state, thus forming crystal cores. When the material, initially in liquid state, has impurity atoms (cooling under non balance conditions, atoms with different atomic radius, different crystalline structure or different valence of the metal desired to solidify) it can cause misalignment or rupture between the atoms, due the replacement of some atom or production of voids, imperfections or interruptions in the formation of the crystalline network. These types of defects often form the contours of the crystal (grain boundary), in which there are delimited two solid crystals of the same phase.

Therefore, and in general lines, the manufacturing process of electric motor rotor comprises a controlled unidirectional solidification process, aims to solidify a material initially in liquid state from one of the ends, performing a slow solidification rate in a single direction, allowing obtaining a solid with high crystalline perfection.

Accordingly, said manufacturing process of the electric motor rotor according to the present invention, besides providing the known conventional steps (shaping step of the metal core 2 of the rotor 1 and shaping step of the short-circuited inductors 3 through the introduction of molten metal material in the metal core 2), further comprises - along the shaping step of the short-circuited inductors 3 - the controlled solidification of molten metal material introduced into the metal core 2, said controlled solidification being effected controlled through the guided cooling of the molten metal material.

More particularly, and always according to the present invention, it is found that the guided cooling of the molten metal material is performed in the axial direction of the metal core 2, from bottom to top.

The above mentioned manufacturing process of electric motor rotor is preferably carried out in the manufacturing system of electric motor rotor, system which also integrates the scope of the subject invention.

According to a preferred embodiment of the manufacturing system of electric motor rotor, which is schematically illustrated in Figure 4, it can be seen that it comprises a retaining mold of the rotor 1 of electric motor formed by an upper portion 6 and a lower portion 7, at least one heating means 8 attached to at least one axial extension portion of the mold, and at least one cooling means 9 linked to at least one of the axial ends of the mold.

Preferably, the heating means 8 comprises an electric resistance cooperating with the outer wall of the mold, and the cooling means 9 comprises a refrigerated fluid circulating system preferably disposed in the lower portion 7 of said mold.

Still preferably, it is important to evidence that both the heating means 8 and the cooling means 9 can be integrated into sub-systems and / or equipment of control and adjust of temperature operating range. It means that, preferably, the manufacturing system of electric motor rotor may comprise an adjustable heat gradient between the heating means 8 and the cooling means 9.

The basic function of the said heating means 8 consists of maintaining the temperature essentially constant of said molten metal material introduced into the mold through an introducing means of molten metal material (not shown), while the basic function of said cooling means 9 consists of promoting guided cooling, in axial direction, of said molten metal material introduced into the mold through the introduction means of molten metal material.

Also, according to an alternative embodiment of the present invention, and in order to increase the efficiency of the system, it is possible to provide a means to minimize the heat loss in a gradual manner and, therefore, such a system may comprise a thermally insulating wall involving the mold (6, 7).

Thus, and during the manufacturing process of electric motor rotor according to the present invention, a certain amount of aluminum, in liquid state, is poured into the mold 7 (which holds and maintains the position of the metal core 2 of the rotor 1 ).

Throughout the period of filling the mold, said aluminum tends to maintain the liquid state thereof depending on the heating means 8.

During or after the filling of the mold, the cooling means 9 is activated and creates a "low temperature" zone (always in relation to the mold and liquid aluminum temperature, which is only maintained due to the existence of the heating means 8) at the lower end of said mold.

This "low temperature" zone then promotes the controlled solidification of molten metal material introduced into the metal core 2, and this controlled solidification, as previously described, ultimately defines "linear crystals" 4 and, more particularly, ultimately defines "linear crystals" 4 arranged on the bus 31 of the short-circuited inductors 3 of the rotor 1.

In this context, and already with reference to Figure 3, it can be seen that the manufacturing process of electric motor, this system being executed in the manufacturing system of motor rotor, results in the manufacturing of an electric motor rotor, which figures as the main object of the present patent application.

Therefore, and as schematically illustrated in Figure 3, the rotor 1 now devised comprises a metal core 2 and a plurality of short-circuited inductors 3 manufactured from the solidification of aluminum. The above short-circuited inductors 3 are, on the other hand, mainly shaped by short-circuited buses 31 and rings 32.

As previously mentioned, said rotor 1 has its great differential with respect to the microstructure thereof and, more particularly, to the microstructure of the short-circuited inductors 3 thereof.

Such a microstructure provides at least one linear crystal 4 shaped in analogous direction to the functional direction of electric current flow 5, being said linear crystal 4 disposed in at least one bus 31 of at least one short-circuited inductor 3, and having a dimension aligned to electric current flow of at least twice the other dimensions of the grain of said bus 31 in which it is arranged.

Optionally, one or more linear crystals 4 may also comprise an extension analogous to the at least one third of the axial extension of said bus 31 wherein it is arranged, or even, equivalent to the axial extension of said buses 31 wherein it is arranged.

It is worth highlighting that the manufacturing system of electric motor rotor detailed above allows that a single rotor 1 has multiple linear crystals 4 in a same bus 31 , while it ensures the existence of at least one linear crystal 4 on each bus 31 of the rotor 1.

Eventually, linear crystals 4 are also defined in the short-circuited rings 32, in these instances, it is usual to note that the linear crystal 4 arranged on a short-circuited ring is also extended in at least one portion of at least one bus 31.

The rotor 1 now disclosed, due to the microstructural improvement thereof where there are defined linear crystals 4 in direction analogous to the functional direction of electric current flow 5, presents very low degradation of electric current, and this is one of the biggest advantages of the present invention.

This is because it is known that grain boundary regions form a degradation mechanism of the electric current (movement of electrons per volume unit).

The total electric current, given by the movement of electrons and gaps (positive charges) accelerated by an electric field, produces an electric field through vibrations, in this case, electromagnetic vibrations, this field accelerates the charge carriers (electrons and gaps) to a maximum speed which remains constant after a certain time range. The charge carriers suffer collisions along the trajectory thereof, and such collisions occur in the so called scattering centers, thus the carriers transfer energy to the crystalline network.

The scattering mechanism can then be described as a resistive force that opposes to the movement of the charge carriers. The efficiency of the carriers movement (total current) is measured by the sensitivity with which they respond to the electric field, this quantity is known as electron mobility. The electron mobility is the "ease" with which the carriers respond to an electric field, and it will be greater the lower the mass of the particles and the lower the density and effectiveness of the scattering centers.

The grain boundary, or grain surface, is one of the properties that cause the scattering of the charge carriers and it is the subject of this invention. The lower density of the grain boundaries, the smaller the influence of the scattering centers.

It is worth evidencing that, although it has been shown only one constructive way of the manufacturing system of electric motor rotor, as well as a sole preferred embodiment of the electric motor rotor itself, it is understood that any constructive omissions, substitutions and alterations can be made by a technician skilled in the subject, without departing from the spirit and scope of protection required. It is also expressly stated that all combinations of the elements that perform the same function, in substantially the same way, to achieve the same results, are within the scope of the invention. Substitutions of elements of a described embodiment by others are also fully intended and contemplated.