US 2663810 A
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Description (OCR text may contain errors)
R. A. STEIN 2,663,810
END BELL. OR END BRACKET FOR MOTORS Dec. 22, 1953 Filed Dec. 8, 1950 f JIEZ INVENTOR.
ROBERT A. .STEIN.
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Patented Dec. 22, 1953 UNITED STATES PATENT OFFICE END BELL OR END BRACKET FOR MOTORS Robert A. Stein, Dayton, Ohio, assignor to The Globe Industries, 1110., Dayton, Ohio, a corporation of Ohio 7 Claims.
This invention relates to aeronautical apparatus and more particularly to an electric motor for use in aircraft.
In constructing motors for use on aircraft, it is important to make the parts as small as possible and to arrange the parts as compactly as possible consistent with good electrical design. Consequently, it is important to make the end bells of the motors as small as possible, but the one end bell which serves to support both the bearing for the armature shaft and also the brushes must provide adequate space between the brushes and the bearing to provide sufiicient dielectric strength. The danger of short-circuits is aggravated by the fact that the friction between the brushes and the commutator causes minute particles of conducting material to collect on the surfaces adjacent the brushes and unless the end bell is properly designed, these particles eventually build up a coating of conducting material on the inner surface of the end bell extending between the brushes and the motor bearing.
It is an object of this invention to provide an improved end bell construction which not only lends itself to mass production but also serves to prevent dielectric breakdowns or short-circults.
Thus, it is an object of this invention to provide a very compact end bell wherein the brushes are supported close to the motor hearing and wherein the effective length of the surface between each brush and the hearing has been increased so designed as to reduce the danger of a dielectric breakdown between the brushes and the bearing.
In high speed motors of the type commonly used on aircraft, it is important to provide a uniform air gap between the armature and the stator and. consequently it is important to provide accurately machined reference surfaces on the end bells for engaging complementary reference surfaces on the main motor frame.
It is an object of this invention to provide an improved end bell construction wherein certain of the more accessible portions of the one face of a molded or east end bell are machined to provide a reference plane and wherein other less accessible portions of the same face are not machined but do not extend beyond the machined portions.
Other objects and advantages reside in the constructi n of parts, the combination thereof and the mode of operation, as will become more apparent from the following description,
In the drawing:
Figure 1 is an elevational View, with parts broken away, showing the relationship between the plastic end bell and certain of the other motor parts;
Figure 2 is an elevational view showing the one side of the end bell which faces the motor stator;
Figure 3 is a sectional view or" the end bell taken substantially on line 3-3 of Figure 2 and showin a fragmentary portion of the motor stator frame; and
Figure 4 is a side view of the insulator which is mounted, between the end. bell and the motor frame Referring now to the drawing wherein I have shown a preferred embodiment of my invention, reference numeral I8 designates the main frame or stator of a small direct current motor having an armature or rotor 52 supported for rotation within the stator ii). The rotor I 2 comprises a main shaft it which supports a conventional commutator l 6 in accordance with well established practice. A plastic end bell I8 serves to support the bearing assembly 29 and the motor brushes 22, as best shown in Figure 1.
The plastic end bell is may be made from a cast or molded piece of plastic material, such as a phenol formaldeh de resin, or any other suitable tvpe of insulatin material. It has been found that it is impossible to form the molds accurately enough so as to eliminate the need for machining the reference surfaces on the and bell. The principal reference surfaces whi h must be machined are the surfaces designated by the reference characters 24, 2S and. E9. The reference surfaces 24 are provided. on the one face of the end bell and serve to en'rage a flat insulating disc 3! which fits directly a ainst a comple mentary reference surface it provided on the end of the motor stator it. The surfaces 24 must be perpendicular to the surfaces at and and serve the purpose of proper positioning the bearing assembl 2c and the end bell in proper ali nment with the armature shaft i i. As shown in Figure 4, the insulating disc 35 is provided with a central cut out portion which permits the lugs 32 of the end bell is to pro eot into the motor stator ill. The reference surfaces are pro vided on the outer periphery of the arcuate lugs 32 and cooperate with complementary reference surfaces J provided on the motor stator is (see Figure 3), so as to maintain the rotor in concentric relationship to the stator.
Since the end bell Iii is placed in the lathe while the surfaces 24, 26, 28 and 25 are being machined, it is obvious that the projecting lugs S interfere with machining the surfaces as which lie between the projecting lugs 32. It is desirable to form these relatively inaccessible surfaces so as to be in substantially the same plane as the finished surfaces 24, and in order to achieve this end Without need for resorting vto any complicated machiningv operation and without making it necessary to have the surfaces 3 3 extend beyond the machine surfaces 26, the mold in which the end bell is made is so designed as to form the surfaces 34 slightly lower than the surfaces 2%; so thataflterithel surfaces 2 are machined the surfaces 34 will be in substantial alignment with the surfacesifil... In molding the end bell l8, suitable brush guides Q53 provided as shown. These guides slidably support conventional biiushes' 22 which are biased into engagement with the commutator by any suitable means, such as spring fingers (is. Since the construction of the brushes and the means for holding-the brushes against the commutator may be varied considerably with out' departing from the spirit of my invention, these means will not be described ingreater detail.
It has been found that it is possible to reduce the axial distance between the brushes Z2 and the bearing assembly 2% without reducing the distance which must be traversed any shortcircuiting current by providing circumferentially extending grooves as '(see Figure l) in the end. bell surface between the brushes 22- the bearing assembly Zll. The side walls of the groove 48 are parallel and lie in planes substantially perpendicular to the axis of rotation of the rotor. The groove not only serves to increase the effective length of thesurface between each brush and the bearing assembly- 28, so as to elongate the path of anyshort-circui't ing current, but also serves to establishes. pocket between each brush and the bearing assembly into which particles emanating'frorn'the brushes do not readily pass. Thus, the provision of the grooves as. very materially increasesthe length of time that a motor of this type can be operated without the formation of 'a coating of short-circuiting material between the bearing assembly 2i! and one or more of the brushes 22.
Although the preferred embodiment of the device has been described, it. will be understood that within the purview of. this invention various changes may be made in the form, de tails, proportion and arrangement of parts, the combination thereof and mode of operation, which generally stated consist in a device capa-v ble of carrying out the objects set forth, as disclosed and defined in theappended claims.
Having thus described my inventioml claim:
1. In speed motor for use in. aircraft the like, a stator, a rotor, said rotor having a sha t, a commutator supportedonlsaid shaft, ulating end bellcarried by stator, said end bell having brush guides formed therein, a shaft bearing carried by said end bell, brushes slidably supported within brush guides, and circumferentiallyextending groove means provided in the inner surface of said end bell between said brushes and said shaft bearing, the side walls of the groove means lying in planes substantially perpendicular to the axis of rotation of the rotor and offset from the end of the commutator.
2. In a small high speed motor for use in aircraft and the like, a stator having reference surfaces formed thereon for engagement by an end bell, a rotor, said rotor having a shaft, a commutator supported on said shaft, an end bell carried by said stator and having reference surfaces complementary to said first named surfaces, certain of said reference surfaces being arranged at right angles to other of said referencersurfaces; said end'bell comprising a molded insulating member having machined reference surfaces and having brush guides molded therein, a shaft bearing carried by said end bell, and brushes" slidahly supported within said brush guides, said end bell having circumferentially extending-groove means provided in the surface betweensaid brushes and said shaft bearing, the
side walls of the groove means lying in planes substanti'ally papendicular to the axis of rotation of the rotor, said planes being offset from the-end of the commutator.
3. An end bell for a brush type of motor having aacommutator; said end bellcomprising a one-piece molded insulating m mber, brush guides formed in the one face of said member, said member having a substantially centrally located? aperture therein,a first portion of said aperture being adapted to support a shaft hearing;. said member having a circumferentially extending. groove formed in the walls of said central aperture between saidbrush guides and said first portion, saidgroove being onset, from the end of the commutator and having a pair of parallelfside Walls lying, in. planes substan tiallypei pendi'cular to the axis of rotation, of the motor whereby the effective length of the surface between; said first portion and the. brushes operating inesaid brush guides isincreased.
4.: Anend bellfor, a brush type. of motor havingga commutator, said end bellcomprising aone-piece: molded insulating member, brush guides; formed. the, oneface of said member, said member having a substantially centrally located aperture therein, a first portion of. said aperture. being adapted to support ashaftl bearsaid -member having a circumferentially extending groove formedin, thewallsof said central aperture between said brush guides and said first pcmtion, said groove being off-setv from the end of the commutator and having a pairv of parallel side walls lying in planes substantially perpendicular to the axis of rotation of the motor whereby the effective length of the surfacebetween said first portion and the brushes operating in said brush guides is increasedand positioning lugs formed integrally with said end bell and proiecting from said one face for engagement with a motor frame.
5. An end bell for a brush type of motor comprising a one-piece molded insulating member, brush guides formed in the one face of said member; a*substantiallycentrally located aperture in said member, afirst portion of said aperture being adaptedto support a shaft bearing, a circumferentially' extendinggroove formed in the walls of said central aperture between said brush guides and said shaft bearing supporting portion whereby the effective length of the surface between, the bearing and the brushes operating in said brush guides is increased, the sides of the groove-being parallel and lying in a plane substantially normal to the axis of rotation of the armature so that the groove forms a pocket into which particles emanating from the brushes do not readily pass, said one face of said member having a machined reference surface formed thereon, said'machined 5 reference surface projecting slightly beyond the face of member adjacent said central aperture, and projecting reference lugs extending beyond said machined surface and having machined surfaces formed thereon at right angles to said named machined surfaces.
5. An end bell for a brush type of motor cor. prising a one-piece molded insulating member, crush guides formed in the one face of said member, a substantially centrally located aperture in said member, a first portion of said aperture being adapted to support a shaft bearing, said one face of said member having a machined reference surface formed thereon, said machined reference surface projecting slightly beyond the face or" said member adjacent said central aperture, and projecting reference lugs extending beyond said machined surface and having machined surfaces formed thereon at right angles to said first named machined surfaces.
7. A method of manufacturing an end bell for a brush type of motor having brush guides formed in one face thereof, said method including the steps of molding the end bell from insulating materiai, forming brush guides therein and a central- References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,408,738 Hiii Mar. 7, 1922 2,012,290 Spengler Aug. 27, 1935 2,177,472 Barrett Oct. 24, 1939 2,479,455 Aronoff Aug. 16, 1949 FOREIGN PATENTS Number Country Date 130,981 Switzerland Mar, 16, 1929 358,226 Germany Sept. 7, 1922