US3279041A

US3279041A - Undercut commutator

Info

Publication number: US3279041A
Application number: US364743A
Authority: US
Inventors: Thomas J Boyer
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1962-12-20
Filing date: 1964-05-04
Publication date: 1966-10-18
Anticipated expiration: 1983-10-18

Description

Oct. 18, 1966 T. J. BOYER 3,279,041

UNDERCUT COMMUTATOR Original Filed Dec. 20. 1962 2 Sheets-Sheet 2,

f1 zzgmf "\7-*2/ l l INVENTOR ffm/w45 ATTORNEYS if YER BY Mw?" the cut toward the center of lthe commuator.

United States Patent O 3,279,041 UNDERCUT COMMUTATOR Thomas I. Boyer, Livonia, Mich., assignor to Ford Motor Company, Dearborn, Mich., a corporation of Delaware Original application Dec. 20, 1962, Ser. No. 246,099, now

Patent No. 3,205,387, dated Sept. 7, 1965. Divided and this application May 4, 1964, Ser. No. 364,743

5 Claims. (Cl. 29-155.54)

This application is a division of my copending application Ser. No. 246,099, led December 20, 1962, now Patent 3,205,387, issued September 7, 1965.

This invention relates to a method of undercutting the insulators of a commutator employed on dynamoelectric machines and to the commutator produced thereby.

In a dynamoelectric machine, it is desirable to use a narrow undercut at the commutator insulator segments to preserve the maximum amount of commutator bar surface in contact with the brushes of the machine. A narrow undercut is also effective in reducing the magnitude of -brush noise. It is very difficult, however, to utilize a narrow undercut and still remove all of the insulator segment `at the undercut. The reason for this difficulty is that commutator bars are usually not perfectly formed, and as a result the commutator segments may `not Vbe properly positioned angularly with the commutator. Also, the commutator bars and insulator segments are often poorly indexed relative to one another, even in premium commutators. This means that the circumferential dimension between 'the insulator segments may not be uniform. In mass production techniques, therefore, it is diicult to employ machines that utilize `a narrow undercut and will at the same time remove all of the insulator segments at the undercuts. This results in poor commutation, poor performance, poor durability and poor brush life, and it also results in brush noise.

The present invention is directed to a method of obviating the above-mentioned difliculties and to the commutator formed thereby. The method of the invention entails undercutting the insulator `segment in such as manner as to produce a dovetail slot. The slot is narrow at the commutator surface and widens at the deepest portion of This provides the benefit of a narrow slot at the surface of the commutator so that the commutator has low brush noise characteristics and has maximum commutator bar surface in contact 4with the brushes -of the dynamoelectric machine. It ,also provides for `the wide cut necessary to free the slot vof all the insulating material.

The dovetail slot may be achieved by -means of a 4circular milling cutter that is inclined at a slight angle with respect to the insulator segment. A lirsticut is then taken along the length of the insulator segment. A circular milling cutter is then inclined at a similar angle in the opposite direction with respect to 'the insulator segrnent and `a 'secondcut is taken. 'This produces a `dovetail slot at each insulator segment.

'In the preferred manner of performing the method of the invention, `the dovetail slots may be formed by the use of two circular milling cutters that are mounted on a common shaft or arbor. One circular milling cutter will make all of the cuts at the insulator segments inclined in one direction and the other circular milling cutter will make all ofthe cuts inclined in the'opposite direction. After the two circular fmilling cutters have 'made a pair of Acuts into a set of insulator segments, the commutator is rotated about its axis to bring the next set of insulator segments into proper cutting relationship with these circular milling cutters. Mounting the two circular milling cutters on a common lshaft will assist greatly in holding the exact location of the second cut at 'sulator segment 12.

3,279,041. Patented Oct. 18, 19,65

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each of the insulator .segments relative to the rst cut at each of the insulator segments.

An object of the invention is the provision of Ia method for undercutting the vinsulator segments on commutators that will remove all of the insulator at the undercut area and that will leave `a maximum amount of commutator bar surface in contact with the brushes -of the dynamoelectric machine.

Another object of the invention is to provide a method for undercutting the insulator segments of commutators that forms an undercut slot in a commutator at each insulator segment that is narrow .at the surface of the commutator and that is wide at the portion of the slot positioned nearest the center of the commutator.

A further object of the invention is the provision yof a commutator that provides a maximum amount of commutator bar surface in .contact with the brushes of a dynamoelectric machine and that simultaneously has all of the insulating material `of `the insulator .segments removed in the `area of the undercut slots of the insulator segments.

Other objects and attendant advantages of the invention will become more apparent as the specification is considered in connection with the attached drawings in which:

FIGURE i is a perspective view of the .commutator of the present invention;

FIGURE 2 is an enlarged sectional view of a portion of the commutator prior to Aundercut'ting showing adjacent conductive bars or segments separated by an insulator segment;

FIGURE 3 is a view similar to FIGURE 2 and l,showing how the commutator is undercut, and

FIGURE 4 is a partial schematic view of a means for carrying out the methods of the invention.

Referring now to FIGURE l, there is shown the cornmutator 10 of the present invention that is formed of a plurality of commutator bars or conductive segments 11 that are separated by a plurality of insulator segments 12. As conventional incommutator structures, the conductive segments 11 are formed of copper bars while the insulator segments 12 are formed of Ia mica base insulating material. The commutator is formed so that the alternating conductive bars -or segments 11 and insulator segments 12 form a cylindrical array in which the insulator segments 12 extend radially inwardly from the surface V13 of the commutator toward the center of the cylindrical array. The commutator 10 is undercut at each of the insulator segments 12 to form a dovetail slot 14 that extends, through the length of the commutator that is adapted to contact an electrical contact brush. This dovetail slot is narrow at the surface v13 vof the commutator and -is wider at the bottom thereof `toward the center of the commutator 10. This type of `slot or undercut has the advantages pointed out in the introductory portion of the specification. It `provides a maximum amount of commutator segments or bars in contact -with the electrical`brushes of (the dynamoelectric machine and it insures that all ofthe insulating material is removed in the area -of the undercut.

Referring now to FIGURES 2 iand V3, the method of undercutting the insulator segments i the commutator 10 and forming the dovetail slots 14 will nowbe described. The method comprises making a :first cut Vinto the commutatorat the insulator :segment 13 that is inclined in one `directionewithrrespect to the insulator segment. This rst cut -is directed into `theconductive `segment 11 positioned on one side of the -insnlator segment. A second cut is then made at the insulatorsegment i12 in a direction that is inclined to the insulator segment in a direction opposite to the first cut. This ysecondcutfisdirected into the conductive segment 1-1 positionedon the other side of the in- It can be appreciated that these two cuts form the dovetail slot 14 at the insulator segment and that the narrow portion of the dovetail slot at the surface 13 of the commutator spans or is wider than the mica segment at this position. Although the method is not so limited, it is preferred that the two inclined cuts be made of the same width (wider than the insulator segment 12) and be in the same position on the surface 13 of the commutator as shown in FIGURES 2 and 3. Itis to be understood that the first and second cuts described above extend through the length of the commutator that may come into contact with the electrical brushes of the dynamoelectric machine.

A practical means for making the dovetail slots 14 in the commutator 10 and for carrying out the method of the invention is shown in FIGURE 4. A first circular milling cutter 21 and a second circular milling cutter 22 are mounted on a common rotatable shaft 23. This shaft is adapted for movement downwardly, as shown in FIG- URE 4, to make the first and second cuts described above and for movement in a direction perpendicular to the plane of the drawings so that the cuts are made through a desired length of the commutator. The circular milling cutter 21 makes-the rst cut, as described above, and the circular milling cutter 22 makes the second cut, as described above, since the circular milling cutter 22 is inclined at an angle with respect to the conductive segments undergoing cutting opposite to the angle of the circular milling cutter 21. In practice, the commutator assembly is rotated through one conductive segment 11 after the circular milling cutters A21 and 22 each makes a cut. It can be seen that the dovetail slot 14 will be completed at each of the insulator segments 12 when the circular milling cutter 21 has made a first cut at each of the insulator segments 12 and the second circular milling cutter 22 has made a second cut at each of the insulator segments 12.`

It can be readily appreciated by an inspection of FIG- URE 4 that the

circular milling cutters

21 and 22 are rotatable about an axis that is substantially normal to the direction of the radially extending insulator segment 12A that is positioned between the

circular milling cutters

21 and 22 and the insulator segments 12B and 12C that are being cut by these cutters.

Considered in a broader aspect, it can be appreciated that the first cut at an insulator segment 12 is made by a circular milling cutter that is rotatable about an axis that is substantially normal to the adjacent insulator segment positioned on one side of the insulator segment undergoing cutting. The second cut is made by a milling cutter that is rotatable about an axis that is substantially normal to the adjacent insulator segment positioned on the other side of the insulator segment undergoing cutting. This can be appreciated by an inspection of FIGURE 4 and by consideringthat the commutator 10 is rotated or indexed in a counterclockwise direction.

As viewed in FIGURE 4, the insulator segment 12C is being cut by the circular milling cutter 22. The circular milling cutter 22 is rotatable about an axis that is substantially normal to the insulator segment 12A positioned to the left of the insulator segment 12C. After this cutting operation is performed, the second cut in the insulatorV segment 12C will be made by the circular milling cutter 21 after the commutator assembly has been rotated or indexed counterclockwise to bring the insulator segment 12C under the circular milling cutter 21. In this position, the circular milling cutter 21 is rotatable about an axis that is substantially normal to the insulator segment 12D that is now positioned between the

circular milling cutters

21 and 22. The insulator segment 12D is the insulator segment adjacent the insulator segment 12C and positioned on the other side thereof from the insulator segment 12A. From this description of the methodof cutting the dovetail slots 14 at the insulator segments 12 of the commutator 10 to undercut the commutator, it can be seen that the commutator assembly may remain stationary and that both

circular milling cutters

21 and 22 may be revolved about the commutator assembly 10 to make the cuts in the directions described above. It can also be appreciated that a single milling cutter could be employed to cut the dovetail slots.

The advantage of using two circular milling cutters on a common shaft is that this assembly will assist greatly in holding the exact location of the second cut1relative to the first cut.

The present invention thus provides a method for undercutting the insulator segments of a commutator in which the undercut is narrow at the surface to preserve the maximum amount of conductive bars or segments in contact' with the brushes and is wider as the undercut deepens to` insure that .all the insulator in the area of the undercut is removed.

It will be understood that the invention is not to be limited to the exact construction shown and described,`

but that various changes and modifications may be made without departing from the spirit and scope of the inven-` tion as defined in the appended claims.

I claim:

1. A method of undercutting a commutator for a dynamo-electric machine that includes a first and a second conductive segment separated by an insulator segment comprising, making a first cut into said commutator at said insulator, said first cut spanning said insulator seg-` ment at the surface of said insulator and being directed at an angle to said insulator and into said first conductive segment, and making a second cut into said commutator at the same position on the surface of said commutator as said first cut, said second cut y'being directed atan angle! to said insulator and into said second conductive segment. 2. A method of undercutting a commutator for a` spanning the insulator segments atthe surface of said` commutator, and being inclined to said insulator segments toward a conductive segment positioned on one side of each lnsulator segment, making second cuts into said com-` mutator at each of said insulator segments and at the same position on the surface of said commutator at each in- -sulator segment as said first cuts, said second cuts being 1 inclined toward a conductive segment positioned on the other side of each insulator segment.

3. A method of undercutting a commutator for a dynamo-electric machine that includes a pair of conductive segments separated by an insulator segment comprising, making a first cut into said insulator segment of said commutator at an angle to said insulator and making:

a second cut into said insulator segment at an angle to form a dovetail slot in said commutator at said insulat tor segment that spans said insulator segment at the surt face of said commutator.

4. A method of undercutting a commutator for a dynamo-electn'c machine that includes a cylindrical array of conductive commutator segments separated by insulator segments that are directed radially inwardly from the sur. face of said commutator toward the center of said cylin` t making a first cut into a pair of: spaced insulator segments that are separated Iby an n`` termediate pair of conductive segments and an insulator drical array comprising,

segment by a pair of milling cutters rotating about an axis that is substantially normal to the direction of said intermediate insulator segment, rotating said commutator about its cylindrical axis and making a second cut into` each of said spaced insulator segments by the milling cut-` ter that made the first cut in the other of the spaced in-` sulator segments.

5. A method of undercutting a commutator for a dynamo-electric machine that includes a cylindrical array of conductive commutator segments separated by insulator segments that are directed radially inwardly from the surface of ysaid commutator toward the center of ysaid cylindrical array comprising, making a first cut into said commutator at one of said insulator segments of a Width greater than said insulator segment by a milling cutter that is rotatable about an axis substantially normal to the adjacent insulator segment positioned on one side of said one insulator segment, and making a second cut into said commutator at said one insulator segment of approximately the same width las said rst cut by a milling cutter that is rotatable about an axis that is substantially normal to the adjacent insulator segment positioned on the other side of said one insulator segment.

References Cited bythe Examiner UNITED STATES PATENTS 1,614,558 1/1927 Kasle'y 90-11 3,010,182 11/1961 Quinlan 29-155.54 `3,066,387 12/ 1962 Herbst 29-155.54

10 JOHN F. CAMPBELL, Primary Examiner.

J. M. ROMANCHIK, Assistant Examiner.

Claims

1. A METHOD OF UNDERCUTTING A COMMUTATOR FOR A DYNAMO-ELECTRIC MACHINE THAT INCLUDES A FIRST AND A SECOND CONDUCTIVE SEGMENT SEPARATED BY AN INSULATOR SEGMENT COMPRISING, MAKING A FIRST CUT INTO SAID COMMUTATOR AT SAID INSULATOR, SAID FIRST CUT SPANNING SAID INSULATOR SEGMENT AT THE SURFACE OF SAID INSULATOR AND BEING DIRECTED