ELECTRICAL COMMUTATOR AND METHOD FOR MAKING SAME

Abstract: A commutator (10) for a motor is disclosed which includes a plurality of commutator segments (12) arranged in a cylindric array (14) such that the array has a cylindrical outer periphery (20) and two axial ends. An annular recess (26, 28) is formed adjacent each end (22, 24) of the array so that a portion of each commutator segment (12) forms a part of the radially inner wall of each recess. Two or more rings (34, 36) constructed of an insulating material are provided and one or more rings are press fit into each recess so that the rings (34, 36) exert a radially inward force on the commutator segment (12). The anchoring portions of the commutator segments (12) are then encapsulated with a settable and electrically insulating material (40), such as phenolic. Upon hardening and curing, the phenolic secures the commutator segments (12) together. At the same time, the radially inward force exerted by the rings (34, 36) on the commutator segments (12) serves to stabilize the commutator segments (12) against movement relative to each other during high speed rotation of the commutator (10). A method for manufacturing the commutator is also disclosed.

Description: ELECTRICAL COMMUTATOR AMD METHOD FOR MAKING SAME Background of the Invention I . Field of the Invention The present invention relates to a novel electrical commutator for electric motors as well as a method for manufacturing the same. II . Description of the Prior Art There are many types of previously known electrical commutators which are used in electric motors. These previously known electrical commutators typically comprise a plurality of commutator segments which are arranged in a cylindric array so that the outer perinhery of the cylindric array is cylindrical in shape. These segments are constructed of an electrically conductive material, such as copper, and are either separated from each other by an insulating material, such as mica, or subsequently machined to electrically insulate these segments from each other. Since the commutator segments are physically separated from each other, it is necessary to secure the commutator segments together during rotation of the commutator. In some instances, the cylindric array is molded with a settable material, such as a phenolic which, upon setting, rigidifies and holds these segments together. Such a previously known commutator construction, however, has not proven wholly satisfactory at high speed operation of the commutator. In order to maintain stability of the commutator segments during high speed rotation, many of the previously known commutators have included an annular recess in one or both ends of the commutator. A metal ring is placed into each annular recess and is simultaneously electrically isolated from the commutator segments. Thereafter, the commutator segments are molded with a settable material along with the metal reinforcing ring. The purpose of the reinforcing ring in this design is to strengthen the settable material so that it will have sufficient strength to resist fracture at the maximum rotational speed of the commutator. One disadvantage of this previously known commutator construction, however, is that, at high speed rotation of the commutator, the centrifugal force exerted on the commutator segments caused the commutator segments to incur small relative movement with respect to each other. This relative movement is caused in part to the shrinkage of the molding material away from the anchoring portion of the commutator segments during the setting process. Consequently, the outer cylindrical surface of the commutator is relatively unstable and the commutator segments move relative to each other. Relative movement of the commutator segments at high speed rotation of the commutator disadvantageously creates sparking between the brushes used with the commutator and the outer cylindrical surface of the commutator. Such sparking rapidly erodes the brushes due to the electrical discharge machining caused by this sparking. Summary of the Present Invention The present invention provides a commutator which stabilizes the commutator segments against movement with respect to each other at high rotational speeds thereby overcoming the above mentioned disadvantages of the previously known devices. In brief, the commutator of the present invention comprises a plurality of commutator segments which are arranged in a cylindric array. The segments are constructed of an electrically conductive material, such as copper. The commutator segments, however, are electrically insulated from each other either by an insulating material, such as mica, interposed between adjacent commutator segments or, alternatively, the commutator is subsequently machined following the manufacturing process to electrically insulate the segments from each other. Preferably, the commutator segments are pressed into a cylindrical die so that the outer periphery of the cylindric array is generally cylindrical in shape and has two axial ends. An annular recess is formed adjacent each axial end of the cylindric array so that a portion of each commutator segment also forms a part of a radially inner wall of each recess. The commutator further includes two or more rings wherein each ring or set of rings is associated with one of the annular recesses. Each ring is constructed of an electrical insulating material of substantial strength, such as glass fiber reinforced resin, and each ring has both an inner and outer diameter less than the corresponding inner and outer diameters of its associated recess. The rings are press fit into their associated recesses so that an interference fit is formed between the inside diameter of the ring and the inside wall of the recess. In doing so, the rings exert a radially inward force on the commutator segments. Thereafter, the anchoring portion of the commutator segments are encapsulated with a settable insulating material, such as phenolic. In operation, the radially inward force exerted by the rings offsets the centrifugal force of the commutator segment during high speed rotation. In doing so, the rings stabilize the commutator segments against relative movement or deflection with respect to each other during high speed rotation. This in turn minimizes electrical discharge machining (EDM) of the motor brushes . A method for constructing the commutator is also disclosed. Brief Description of the Drawing A better understanding of the present invention will be had upon reference to the following detailed description, when read in conjunction with the accompanying drawing, wherein like reference characters refer to like parts throughout the several views, and in which: FIG. 1 is an end view illustrating a first preferred embodiment of the present invention; FIG. 2 is an exploded view taken substantially along line 2-2 in FIG. 1; FIG. 3 is an end view similar to FIG. 1 but with additional parts; FIG. 4 is a sectional view similar to FIG. 2 but showing the preferred embodiment of the present invention at a further step of manufacturing; FIG. 5 is an exploded view illustrating a second preferred embodiment of the present invention; FIG. 6 is a longitudinal sectional view illustrating the embodiment of FIG. 5 and taken substantially along line 6-6 in FIG. 7; and FIG. 7 is an elevational view illustrating the second preferred embodiment of the present invention. Detailed Description of Preferred Embodiments of the Present Invention With reference first to FIGS. 1 and 2, a preferred embodiment of the commutator 10 of the present invention is thereshown and comprises a plurality of commutator segments 12 arranged in a cylindric array 14. Although any conventional means can be used to form the cylindric array 14 from the commutator segments 12, as best shown in FIGS. 1 and 2, preferably the commutator segments 12 are assembled within a die 16 having a cylindrical throughbore 18. The commutator segments 12 are constructed of an electrically conductive material, such as copper. However, as is well known, the commutator segments 12 must be electrically insulated from each other in the finished commutator. Any conventional means (not shown) can be used to accomplish this, such as insulating strips between the segments 12, machining the cylindric array 14 after completion of assembly to create air spaces between the segments 12, or other conventional means. As best shown in FIG. 2, the cylindric array 14 has a cylindrical outer periphery 20 and two axial ends 22 and 24. Annular recesses 26 and 28 are respectively formed in the axial ends 22 and 24 of the cylindric array 14. Furthermore, as best shown in FIG. 2, a portion 30 and 32 of each commutator segment 12 respectively forms a portion of the inner radial walls of the annular recesses 26 and 28. With reference now especially to FIG. 3, the commutator 10 of the present invention further includes a pair of rings 34 and 36 so that one ring 34 is associated with the annular recess 26 while, similarly, the second ring 36 is associated with the other annular recess 28. The rings 34 and 36 are constructed of an electrical insulating material, such as glass fiber reinforced resin. Other types of electrical insulating materials may, however, alternatively be used. The rings 34 and 36 are dimensioned so that both the inside and outside diameters of the rings 34 and 36 are smaller than the outside and inside diameters of their associated annular recesses 26 and 28. The rings 34 and 36 are then press fit into their associated recesses 26 and 28, as illustrated diagrammatically for the ring 36 in FIG. 2. Once the rings 34 and 36 are press fit into their associated recesses 26 and 28, an interference fit is created between the portions 30 and 32 of the commutator segments 12 and rings 34 and 36. Conversely, the outer periphery of the rings 34 and 36 are spaced radially inwardly from the outside radial wall of the recesses 26 and 28. Consequently, with the rings 34 and 36 press fit into their receiving recesses 26 and 28, the rings 34 and 36 exert a radially inward force on the commutator segments 12 in addition to any radial force exerted by the die 16 on the commutator segments 12. The amount of interference between the rings 34 and 36 and their associated recesses 26 and 28 will vary depending in large part upon the diameter of the commutator. For example, an interference of between .015 and .020 inches has proven sufficient for a one inch diameter commutator. Larger interferences would be used for a larger diameter commutator and vice versa. With reference now to FIG. 4, the cylindric array 14 as well as the rings 34 and 36 are molded with a flowable settable material 40 which is also an electrical insulator. Any conventional material 40 can be used, such as a phenolic, epoxy, melamine or polyester, which becomes rigid upon setting. In the well known fashion, the material 40, once it becomes rigid, secures the commutator segments 14 together and forms the commutator. After the material 40 has cooled or otherwise set, the commutator is then ejected from the die 16. Following construction of the commutator described above, the material 40 serves to hold the commutator segments 14 together against centrifugal force which occurs during high speed rotation of the commutator. Additionally, however, after formation of the commutator, the rings 34 and 36 continue to exert a radially inward force on the commutator segments 14. This radially inward force serves to stabilize the commutator segments against relative movement with respect to each other during high speed rotation of the commutator. Such stabiliation of the commutator segments 14 minimizes any electrical discharge machining of the brushes that would otherwise occur due to such relative movement between the commutator segments 14. With reference now to FIGS. 5-7, a modification to the present invention is thereshown in which the commutator segments 12', when arranged in the cylindric array 14', include an enlarged diameter bore 50 adjacent the end 24. The annular recess 28' is adjacent to but spaced radially inwardly from the end 24 of the cylindric array 14. In addition, a dovetail- shaped notch portion 52 is also formed within the cylindric array 14 * by the commutator segments 12' between the annular recess 28 ' and the axial end 24 of the cylindric array 14'. As best shown in FIG. 5, the commutator segments 12* are arranged as described before in the die 16 while the insulating stabilizing rings 34 and 36 are press fit into their associated recesses 26 and 28'. An insulating material 54 is then injected so that it covers the segments 12' and, upon hardening, secures the commutator segments 12' together. As best shown in FIG. 6, the insulating material 54 completely fills the notch portion 52 of the cylindric array 14' thereby strengthening the commutator. Simultaneously, the insulating material 54 forms a cylindrical recess 56 in the end fit 24 of the commutator. This recess 56 is dimensioned to receive a portion of the motor assembly, such as a bearing assembly, thereby shortening the effective axial length of the commutator. This construction is thus particularly desirable for applications in which the axial length of the commutator is critical. Although the commutator has been described as having one ring 34 or 36 in their respective recesses 26 and 28, in practice one or more rings are posiionted in each recess. For example, in some applications two or even more rings are positioned in a single recess so that the rings are axially aligned with each other. Similarly, although the commutator segments have been described as separate elements prior to the molding operation, in some applications the segments are of a one piece construction prior to the molding process. In this case, the commutator is machined after molding in order to electrically isolate the segments from each other. In any event, as used in this patent, the term "segments" shall include commutator segments which are both discreet from each other prior to molding and which are integral with each other prior to molding and subsequently machined to electrically isolate them from each other. From the foregoing, it can be seen that the present invention provides a simple and yet effective means for stabilizing the commutator segments against relative movement during high speed rotation. Having described my invention, however, many modifications thereto will become apparent to those skilled in the art to which is pertains without deviation from the spirit of the invention as defined by the scope of the appended claims. I claim:

Claims: C AI MS 1. A commutator for a motor comprising: a plurality of commutator segments arranged in a cylindric array, said segments being constructed of an electrically conductive material, said cylindric array having a cylindrical outer periphery, two axial ends, and an annular recess formed adjacent each end so that a portion of each segment forms a part of a radially inner wall of each recess, means for stabilizing said segments against relative movement during rotation of said commutator comprising: at least two rings, at least one ring being associated with one recess and being constructed of an electrical insulating material, each at least one ring having an inner diameter less than the inner diameter of its associated recess and an outer diameter less than the outer diameter of its associated recess, said rings being positioned into their associated recesses so that said rings exert a radially inward force on said commutator segments, and means for securing said commutator segments together. 2. The invention as defined in claim 1 wherein said rings are constructed of glass fibers. 3. The invention as defined in claim 2 wherein said rings each include a resin binder. 4. The invention as defined in claim 1 wherein said securing means comprises a settable material in a liquid form which encapsulates a portion of each segment and which becomes rigid upon setting. 5. The invention as defined in claim 4 wherein said settable material is a phenolic resin. 6. The invention as defined in claim 4 wherein said settable material is an epoxy. 7. The invention as defined in claim 4 wherein said settable material is a polyester. 8. The invention as defined in claim 4 wherein said settable material is a elamine. 9. The invention as defined in claim 1 wherein said rings are press fit into their associated recesses. 10. The invention as defined in claim 1 wherein at least one annular recess is spaced inwardly from its adjacent axial end, and wherein said cylindric array includes an annular notch portion between said last mentioned recess and axial end, said notch portion being filled with said settable material which rigidifies said commutator. 11. A method for manufacturing a commutator for a motor comprising the steps of: arranging a plurality of commutator segments in a cylindric array, said segments being constructed of an electrically conductive material, said cylindric array having a circular outer periphery, two axial ends, and an annular recess formed adjacent each end so that a portion of each segment forms a part of a radially inner wall of each recess. press fitting a pair of rings into said recesses, each ring being associated with one recess and being constructed of an electrical insulating material, each ring having an inner diameter less than the inner diameter of its associated recess and an outer diameter less than the outer diameter of its associated recess, said rings being positioned into their associated recesses so that said rings exert a radially inward force on said commutator segments, and securing said commutator segments together. 12. The invention as defined in claim 11 wherein said rings are constructed of glass fibers. 13. The invention as defined in claim 12 wherein said rings each include a resin binder. 14. The invention as defined in claim 12 wherein said rings each include an epoxy binder. 15. The invention as defined in claim 12 wherein said rings each include a polyester binder. 16. The invention as defined in claim 12 wherein said rings each include a melamine binder. 17. The invention as defined in claim 11 wherein said securing step comprises flowing a settable material in a liquid form so that said material encapsulates a portion of each segment allowing said material to set and rigidify. 18. The invention as defined in claim 17 wherein said material is a ohenolic resin.

Inventors: ELOW DAVID I, LANGDON DALE, ELOW, DAVID, I., LANGDON, DALE
Applicants: ELOW DAVID I, LANGDON DALE, ELOW, DAVID, I., LANGDON, DALE
Application year: 1990
Main classification: H02K13
IPC codes: H01R39, H01R43, H02K13