US2261521A - Commutator for electric motors - Google Patents

Description

1941- J. E. MORROW 2,261,521

COMMU TATOR FOR ELECTRIC MOTORS Filed Jan. 27, 1941 as" 3, '93 a5 50 W W|TNE%7% ATTORNEYS Patented Nov, 4, 1941 COMMUTATOR FOR ELECTRIC MOTORS James E. Morrow, Butler, Pa assignmof forty per cent to John F. Thomas, Butler, Pa.

Application January 27, 1941, Serial No. 376,200

2 Claims.

This invention relates to commute-tors for electric motors and has for an object to provide a commutator which has increased life due to elimination of grounding of the commutator bars through the V ring which clamps the copper bars and the insulating mica strips in position.

Ninety per cent of short circuits causing commutator failure occur at the outer'ends of the commutator bars and the present invention contemplates increasing the thickness of the insulation at this point by grooving the sides of the outer ends oi the copper segment bars and cutting away the inner walls of the grooves at an angle of about 45, and also cutting away the mica insulating segment in a similar manner, thus providing a radial space between the outer ends of the adjacent copper segment bars termiouting at the bottom in a triangular space, such space being filled with insulating cement and providing effective insulation to prevent short circuiting.

A further object is to provide a device of this after fully described and claimed, it being understood that various modifications may be resorted to within the scope of the appended claims without departing :rom the spirit or sacrificing any of the advantages of the invention.

In the accompanying drawing forming a part of this specification:

Figure 1 isa side elevation, partly in section, of a commutator constructed in accordance with the invention.

Figure 21s an end elevation of the commutator looking toward the outer end or left side of Figure 1, and showing insulating cement between some of the copper segment rings and showing some of the rings in end elevation without the cement in the grooves thereof.

Figure 3 is a fragmentary plan view or the commutator looking in the direction of the arrows 3-3 of Figure 2.

Figure 4 is a diagrammatic view showln! copper segments provided with grooves at the outer ends, widened by being cut back at an angle 0! 45 at the bottom or the inner walls, and showing in dot and dash lines how the mica segment between the rings is undercut below the wear surfaces 0! the rings and cut away at its outer end.

Referring now to the drawing in which like characters'of reference designate similar parts in the various views, l0 designates copper conducting segments arranged in the form of a cylinder and separated by mica segments ll disposed between adjacent copper segments and extending only part way from the bottom of the copper segments to the tops or the wear sur% faces of the copper segments as indicated diagrammatically by dotted lines in Figure 4, which dotted lines represent the planes of the outer end faces I! of the copper-segments and the cylindrical surface in which the wear surfaces l3 of the copper segments extend. The copper segments and the mica segments are undercut in the usual manner to provide dovetail base portions M, a flange i5 oi V-shape cross sectlon, carried by the cylindricai body W of the commutator engaging the inner side, that is the side toward the electric motor, of the dovetail projection, while the conventional V ring ll engages the other side of the dovetail projection of all of the copper segment bars and mica segment bars, the V ring being held in place by a clamp ring 18 which is threaded on to the end of the cylindrical body It of the commutator. So far the construction may be said to be conventional.

The invention, or improvement in commutator constructions, consists in forming grooves is on each end face I2 of the copper segment bars H, the grooves opening through the side faces of the bars, The inner wall of each groove is cut back obliquely at an angle of about 45 to provide an inclined lower portion 20 of the bottom wall of the groove. The mica segment I! is cut away obliquelyvat the lower end of the front edge to provide an inclined wall 2| which extends flush with the inclined portion 20 of the bottom wall of the groove I!) of the adjacent copper segment when the copper segments and mica segments are assembled.

The grooves l9, as well as the triangular spaces at the lower ends of the grooves formed by the inclined walls ll of the copper segments and 2| 0! the mica segments are filled with insulatlng cement or other suitable insulating material of any type. By thus insulating the front ends of the copper segments from each other by insulation or greater thickness than a single mica the V ring I1 and copper segment bars is eliminated and longer service greatly promoted.

In completing the construction of the com mutator above described, insulating cement 22 of any suitable type is disposed between the copper segments and on top of the mica seg ments for a short distance at the front ends thereof. A band of cords 23 is disposed upon insulating material 24 interpolatedlbetween the V ring and the copper and mica segments, and an insulating layer of paint 25 is disposed upon the band. A ring of cement I6. is disposed between the inner end of the band and the lower ends of the outer faces H of the copper segment bars at the triangular spaces at thelower ends 2,261,521 bottoms of the grooves, short circuiting between segments, said segments and said sheets having dovetail extensions. means engaging said dovetail extensions and holding the segmentsand sheets assembled, the outer end .faces of the of the grooves of the bars, which spaces and which grooves are, as previously stated, illled with cement 29 and 30, or any desired insulate ing material.

From the above description it is thought that the construction and operation of the invention will be fully understood without further explanation.

What is claimed is:

1, A cylindrical commutator comprising conducting segments having outer peripheral brush engaging faces and radially disposed outer end faces, sheets of insulating material between the segments being provided with radially disposed grooves opening through the side faces of the segments, said grooves having portions of the inner walls inclined at about an angle of 45 to said outer end faces to provide triangular spaces opening through the inner peripheral faces of the segments, andinsulating material in said grooves and in said triangular spaces coacting ing cutaway obliquely at the outer ends adJa-g cent to said opposite surface to form substantially triangular spaces, and additional insulation between the segments in said spaces extending through said opposite surface.

- JAMES E. ormow.

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