US3253172A - Sub-flush commutator - Google Patents

Description

y 24 1966 T. G. TAYLOR, 4R 3,253,172

SUB-FLUSH COMMUTATOR Filed March 5, 1962 I l 5; INVENTOR.

i I 46 THOMAS s. TAYLOR,JR. l BY r; OLSEN Ann STEPHENSON 50 b ATTORNEYS United States Patent Ofifice 3,253,172 Patented May 24, 1966 SUB-FLUSH COMMUTATOR Thomas G. Taylor, Jr., Dayton, Ohio, assignor, by mesne assignments, to Dayton Precision Corporation, Dayton, Ohio, a corporation of Ohio Filed Mar. 5, 1962, Ser. No. 177,387 3 Claims. (Cl. 310-235) This invention relates generally to commutators and more particularly to an improved sub-flush commutator. A commutator of the type to which this invention relates consists generally of an axial bushing, copper com mutator segments which are arranged in a circular formation about the bushing, insulating members which are positioned between the copper segments, and an insulating core which is secured to and extends between the bushing 'and the commutator segments. In a sub-flush commutator, the insulating members are recessed, over at least major portions of their lengths, relative to the radially outer edges of the commutator segments so that the insulating members are below the surface of the com mutator on which the commutator brushes ride. A subflush' commutator is desirable in some instances because commutation is improved and a longer life of the commutator brushes is obtained. However, manufacture of sub-flush commutators has heretofore been difficult to economically carry out because of the d-ifliculty of maintaining an air gap between the copper segments at the outer edges of the insulating members, and the previous solutions to this problem involving internally finned molds and removable steel shims has been expensive and cumbersome. It is an object of this invention, therefore, to provide an improved sub-flush commutator in which the insulating core is molded and in which air gaps are provided between adjacent pairs of copper segments over major portions of their lengths and insulation is provided between adjacent pairs of commutator segments at one of their ends so that the segments will not be moved into engagement when the armature wires are'staked into the segments.

In the manufacture of the improved sub-flush commutator :of this'invention, the copper segments and the mica insulating members, which are recessed at their outer edges, are arranged in a circular formation about an in- 'wardly spaced axial bushing so that the recessed outer edges of the mica members form airgaps between the copper segments. Each air gap extends from one end 'of each segment to a position spaced from but adjacent the opposite end of the segment. The space between the radially inner edges of the segments and insulating members and the bushing is then filled with a hardenable insulating material concurrently with squeezing the segments and members adjacent opposite ends of the air gaps so as to positively prevent flow of insulating material into the air gaps. This sealing off of the air gaps is obtained by providing a squeeze ring which squeezes the segments and insulating members adjacent one end of each air gap Y and a knife edge shutoff ring which is formed in the mold so as to be in sealing engagement with the segments and members adjacent the opposite ends of the air gaps. An improved molded sub-flush commutator is thus obtainable with the method and apparatus of this invention and each FIGURE 2 is a sectional view of the commutator of this invention looking substantially along the line 22 in FIG. 1;

FIGURE 3 is a vertical sectional view of the lower portion of the apparatus used in manufacturing the commutator of this invention, showing the commutator bushing, segments and insulating members as they are initially assembled in the apparatus;

FIGURE 4 is a vertical sectional view of the commutator manufacturing apparatus of this invention showing a completed commutator formed therein;

FIGURE 5 is a vertical sectional View of the commutator manufacturing apparatus of this invention, illus trated similarly to FIG. 4, showing the top half of the apparatus removed and with the completed commutator in a position ejected from the apparatus; and

FIGURE 6 is a sectional view of a portion of the corn mutator manufacturing apparatus of this invention, looking substantially along the line 66 in FIG. 4.

With reference to the drawing, the commutator of this invention, indicated generally at 10, is shown in FIGS. 1 and 2 as including an axial bushing 12, which may be formed of brass or other suitable metal, commutator segments 14, which are usually formed of copper, insulating segments or members 16 which are formed of mica or other suitable non-conducting material and are positioned between the commutator segments 14 so as to insulate the segments 14 from each other, and a molded core 18 of a hardenable plastic material, such as a phenolic or equivalent plastic material. Each of the commutator segments 14 is of a generally trapezoidal shape in cross section, as shown in FIG. 2, and has an outer edge surface 20 which is substantially parallel to the bushing 12. Each segment 14 is also shaped so that it has a pair of ends 22 and 24, which are hereinafter referred to as the upper and lower ends merely for convenience of description, and a radially inner edge 26 which is provided with a substantially dovetail projection 28. Each of the insulating members 16 is of a generally fiat form, and, in longitudinal section, is of generally the same size and shape as a commutator segment 14, as shown in FIG. 1. Each insulating member 16 has a radially inner side 30 which is provided with a substantially dovetail shape projection 32 and opposite ends 34 and 36 which are likewise referred to hereinafter as the upper and lower ends, respectively, for convenience of description.

Adjacent its upper end 34, each commutator insulating member 16 is of a width corresponding substantially to the Width of a commutator segment 14 so that it has an outer edge 38 which is spaced substantially the same distance from the projection 32 as the edge 20 is spaced from the projection 28 on a segment 14. Between the edge 38 and the lower end 36, the insulating member 16 is formed with a longitudinally extending recess or cutout 40 which extends over a major portion of the length of the member 16. The recess 40 extends the full thickness of each insulating member 16 and extends through the end 36 thereof but is spaced from the end 34 for a purpose to appear presently.

The insulating core 18 has the dovetail projections 28 and 32 embedded therein so that the projections 28 and 32 are spaced radially outwardly of the bushing 12 so that they are insulated from the bushing 12. The core 18 is also formed so that it is of a length to extend axially beyond the ends of the segments 14 and the members 16 to thereby additionally strengthen the support of the Segments 14 and members 16 on the bushing 12.

The apparatus for manufacturing the commutator 10, indicated generally at 42, is shown in FIGS. 3 to 6, inclusive, as including upper and lower mold members 44 and 46, respectively. The lower mold member 46 has an opening 48 extended substantially axially thereth-rough and a tubular ejector sleeve 50 is slidably positioned therein. A stationary core pin 52 is positioned in the sleeve 50 and is formed at its upper end with a reduced diameter portion 54 and a horizontal shoulder 56a at the lower end of the reduced portion 54. The lower mold member 46 is formed with an upwardly opening cylindrical cavity 56 which surrounds the pin portion 54, and the lower end of the cavity 56 Communicates with a recess 58 which is of a reduced diameter and is of a shape corresponding to the shape of one end of the insulating core 18. Radially outwardly of the recess 58, the lower mold member 46 is formed with an upwardly projecting shutoff ring 60, which is in the form of a knife edge projection. A steel squeeze ring 62, which is of a predetermined length and diameter, and has an inner surface 64 which is of a diameter corresponding precisely to the desired diameter of the commutator 10, is positioned in the cavity 56 so that it engages the cavity wall 66 and is positioned radially outwardly of the shutoff ring 60.

The top mold member 44 has an axial passage 68 formed therein and in its lower end 70 is formed with a recess 72, which is of the shape desired for one end of the commutator core 18 and communicates with the passage 68. Radially extending vent passages 74 extend between the recess 72 and the outer edge 76 of the upper mold member 44. The passages 74 are illustrated as being four in number, but it is to be understood that the number of passages 74 is dependent upon the viscosity of the material from which the core 18 is molded and may be more or less than four.

'In the use of the apparatus 42 to form the commutator 10, the bushing 12 is initially positioned about the pin portion 54 so that it is supported on the shoulder 56a which is located at the lower end of the recess 58 (FIG. 3). The squeeze ring 62 is positioned in the lower mold cavity 56 and the segments 14 and members 16 are arranged in an alternating relation and in a circular formation or assembly, as shown in FIG. 2, within the squeeze ring 62. By virtue of the trapezoidal shape of the segments 14, the circular formation of a predetermined diameter corresponding to the inner diameter of the squeeze ring 62 is readily obtained, without any tendency of the segments 14 and the members 16 to move radially inwardly of the squeeze ring 62. The engagement of the outer edges 20 and 38 of the segments 14 and members 16, respectively, with the inner surface 64 of the squeeze ring 62 prevents movement of the segments 14 and members 16 radially outwardly of the desired positions.

The segments 14 and members 16 are initially supported on the shutotf ring 60, as shown in FIG. 3, so that they project substantially above the squeeze ring 62. The upper mold member 44 is then moved downwardly so that its lower end 70 engages the upper ends 22 and 34, respectively, of the segments 14 and members 16. Pressure is applied to the upper mold member 44 so as to force the segments 14 and members 16 downwardly on the knife edge shutolf ring 60 so that the shutofi ring 60 bites into the lower ends 24 and 36, respectively, of the segments 14 and members 16, as shown in FIG. 4. The length of the squeeze ring 62 is slightly less than the length of the segments 14 and members 16 so that the squeeze ring 62 does not interfere with the continued application of pressure to the segments 14 and members 16 by the upper mold member 44, as shown in FIG. 4.

With the parts of the apparatus 42 and the parts of the commutator positioned as shown in FIG. 4, the insulating material of which the core 18 is to be formed is injected through the passage 68 into the irregularly shaped cavity 78 formed by the mold recesses 58 and 72 and the space between the segments 14 and 16 and the bushing 12. As shown in FIG. 4, by virtue of. the recess 40 formed in the insulating members 16, an air. gap or space 80 is formed between each adjacent pairof commutator segments 14. The space 80 extends over the major portion of the length of each insulating member 16 between the lower end 36 thereof and a position spaced from and adjacent the upper end 34 thereof.

The projection of the knife edge shutofi ring 60 into the lower ends of the segments 14 and members 16 provides an effective seal to positively prevent any flow of the insulating material from the cavity 78 into the lower ends of the air gaps 80. The upper ends of the air gaps are effectively sealed from the cavity 78 by the tight engagement of the outer edges 20 and 38 of the segments 14 and the members 16 with the inner surface 64 of the squeeze ring 62. The pressure of the insulating material in the cavity 78 additionally effects a tight engagement of the edges 20 and 38 with the inner surface of the squeeze ring 62. The vent passages 7 4 provide for a radially outward flow of any insulating material which might otherwise tend to enter the upper ends of the air gaps 80 since the insulating material will tend to follow the path of least resistance and it is easier for the insulating material to flow through the vent passages 74 than it is for it to flow into the air gaps 80 between the edges 20 and 38 and the squeeze ring surface 64.

Following hardening of the insulating material in the cavity 78, so as to form the core 18, the completed commutator is removed from the apparatus 42 by first removing the upper mold member 44. The ejector sleeve 50 is then moved upwardly relative to the stationary pin 52 so as to move the commutator 10 with the squeeze ring 62 thereon out of the lower mold 46. After final hardening and any heat treating operations which may be desirable, the squeeze ring 62 is removed from the commutator 10.

From the above description it is seen that this invention provides a mica molded commutator in which an air gap 80 is provided between each pair of adjacent commutator segments 14. The configuration of the insulating members 16 so that they project outwardly, adjacent the ends 22 of the segments 14, distances sufficient to position their outer edges 38 such that they are flush with the outer edges 20 of the segments 14 is advantageous because the insulating members 16 then prevent the segments from being deformed into engagement when the armature wires are staked into the segments 14 adjacent their ends 22. By virtue of the provision of the squeeze ring 62 and the shutoff ring 60 the air gaps 80, which are desirable in a subflush commutator, are maintained free of restrictions during manufacture of the commutator 10. The cavity 78 is shaped so that the core 18 extends axially outwardly be yond the ends of the segments 14 to thereby provide in-v creased support for the segments 14 on the bushing 12 to prevent accidental separation of the segments 14 from the bushing 12.

It will be understood that the sub-flush commutator which is herein disclosed and described is presented for purposes of explanation and illustration and is not intended to indicate limits of the invention, the scope of which is defined by the following claims. 1

What is claimed is:

1. In a commutator having an axis, a plurality of spaced commutator segments arranged in a circular formation about said axis and spaced radially outwardly from said axis, each of said segments being shaped so that it has an inner edge and an outer edge which is substantially parallel to said axis, a projection on said inner edge, a plurality of insulating members disposed between said commutator segments, each of said insulating members being shaped so that it has an inner edge and an outer edge which over a minor portion of its length adjacent one end of the member is substantially flush with the outer edges of the segments on opposite sides thereof and over the remainder and major portion of its length is recessed relative to said portion, a projection on the inner edge of each of said insulating members, and a one-piece generally tubular shape core having said projections embedded therein for retaining said segments and members in pre determined fixed positions relative to said axis, said core being formed of a moldable insulating material.

2. The invention according to claim 1 in which said segments and insulating members are formed with an annular knife edge groove at the end of said commutator remote from the end at which said insulating members are substantially flush with the outer edges of said segments, said groove being continuous and substantially concentric with said axis.

3. The invention according to claim 1 further including an axial bushing secured to and positioned concentrically within said core, said core extending axially outwardly of said bushing at the end of said core corresponding to the ends of said insulating members which are substantially flush with the outer edges of said segments.

References Cited by the Examiner UNITED STATES PATENTS Priest et al. 310-236 Zabriskie et al 310--236 Fitzgerald 310236 Kaegi 310236 Apple 1836 Apple 18-36 10 MILTON 0. HIRSHFIELD, Primary Examiner.

Claims (1)

1. IN A COMMUTATOR HAVING AN AXIS, A PLURALITY OF SPACED COMMUTATOR SEGMENTS ARRANGED IN A CIRCULAR FORMATION ABOUT SAID AXIS AND SPACED RADIALLY OUTWARDLY FROM SAID AXIS, EACH OF SAID SEGMENTS BEING SHAPED SO THAT IT HAS AN INNER EDGE AND AN OUTER EDGE WHICH IS SUBSTANTIALLY PARALLEL TO SAID AXIS, A PROJECTION ON SAID INNER EDGE, A PLURALITY OF INSULATING MEMBERS DISPOSED BETWEEN SAID COMMUTATOR SEGMENTS, EACH OF SAID INSULATLING MEMBERS BEING SHAPED SO THAT IT HAS AN INNER EDGE AND AN OUTER EDGE WHICH OVER A MINOR PORTION OF ITS LENGTH ADJACENT ONE END OF THE MEMBER IS SUBSTANTIALLY FLUSH WITH THE OUTER EDGES OF THE SEGMENTS ON OPPOSITE SIDES THEREOF AND OVER THE REMAINDER AND MAJOR PORTION OF ITS LENGTH IS RECESSED RELATIVE TO SAID PORTION, A PROJECTION ON THE INNER EDGE OF EACH OF SAID INSULATING MEMBERS, AND A ONE-PIECE GENERALLY TUBULAR SHAPE CORE HAVING SAID PROJECTIONS EMBEDDED THEREIN FOR RETAINING SAID SEGMENTS AND MEMBERS IN PREDETERMINED FIXED POSITIONS RELATIVE TO SAID AXIS, SAID CORE BEING FORMED OF A MOLDABLE INSULATING MATERIAL.

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