US2400968A - Commutator cap construction - Google Patents

Description

C. A. ATWELL ETAL May 28, 1946.

COMMUTATOR CAP CONSTRUCTION Filed April I14. 1944 allllalapllllll INVENTORS Varenne/9 /7we// anal/Vorman MY/y.

BY 9 2 Z ATTORNEY Patented May 28, 1946 UNITED STATES PATENT OFFICE COMMUTATOR CAP CONSTRUCTION Application April 14, 1944, Serial No. 530,960

(Cl. YY1- 321) 2 Claims.

Our invention relates to molded V-ring caps for motor commutatore; and in particular, our invention relates to a more suitable means for taking the place of the string-bands or wrappings which have been commonly utilized on the extending ends of insulating V-rings for approximately four decades, or ever since there has been any occasion for retaining these ends against centrifugal force. These string-bands have had a number of objectionable features, being somewhat costly to apply, subject to breakage if but a single strand of the string is broken, and somewhat difficult to coat with a smooth, glossy, insulating paint-surface so that it can be easily wiped off and will not so readily accumulate dirt which would impair the insulation creepage surface. In the case of a motor-flash, between one of the commutator-bars and the metal clamping V-ring under the insulating V-ring, a slight damage to a string-band allows all of it to come loose. Many corrective proposals have been brought forward and tried out, during the course of the years, but in spite of its obvious disadvantages, the string-band has so far proven to be the most successful and acceptable bindingmeans for the free end of the insulating V-rings, up until the time of our present invention.

The object of our present invention is to provide a novel method and means for retaining the free ends of insulating V-rings, utilizing a rigid insulating cap which has suicient mechanical strength to resist centrifugal forces, and which is slid on axially over the end of the insulating V-ring, in substantial Contact with the large end thereof, after which, the space between the cap and the extended portion of the insulating V-ring is substantially filled with a plastic heat-hardenable insulating cement, which is iinally hardened by means of a suitable heatetreatment.

With the foregoing and other objects in View, our invention consists in the combinations, systems, structures, parts, and methods hereinafter described and claimed, and illustrated in the accompanying drawing, wherein Figure 1 is a fragmentary view of a portion of a motor embodying our invention, on a slightly reduced scale, and

Fig. 2 is a considerably enlarged detail of the commutator cap assembly.

In Fig. l, we have shown our invention applied to a commutator-type dynamo-electric machine in the form of a direct-current railway tractionmotor, comprising a statormember 3 and a rotormember 4, the latter being mounted on a shaft 5 and carrying a commutator-assembly 6 embodying our invention. The commutator-assembly is made up of a number of copper commutator-bars 'l separated by mica or other insulating bars 8, the two kinds of bars being of similar size and shape, except that the insulating bars are thinner and commonly project back about one-eighth of an inch behind the commutator-bars, as indicated by the numeral 8, that is, the mica bars 8 are longer than the copper bars 1. The bars 'I and 8 are provided with V-grooves 9 in the ends thereof, said V-grooves having inclined, an inner, arch-binding surface II, usually at a angle, and an outer surface I 2, usually at a 3 angle, or sometimes a 6 angle.

The V-grooves 9 are insulatingly engaged by clamping V-rings I3 and I3', usually of steel, having conical surfaces inclined at the same angles as the surfaces of the V-grooves. The insulating engagement is provided through the intermediary of insulating V-rings I4, preferably made of sheet-mica of suieient thickness towithstand the maximum voltage which is applied to the commutator-member.

At least the outer clamping V-ring I3', or the one at the end of the machine, has an outer conical surface I5 which extends out of the associated V-groove 9, beyond the end of the commutator-bars l. The corresponding insulating V-ring I 4 likewise has an extended outer conical portion I6 which lits against the extended portion I5 of the clamping V-ring, and which preferably extends out substantially to the large end of the outer conical surface I5 of the clamping V-ringT I3. It is this free or extended portion I6 of the insulating V-ring I4 which was formerly held down by a string-band.

The clamping-rings I3 and I3 are held in clamping-position by means of a bolt I2! applied to the ring I3 so as to hold the inner conical surface I8 of each clamping-ring in arch-binding clamping-engagement with the corresponding surface Il of the respective V-grooves.

The commutator-bars l are provided with armature-connections 20 which cause the ccm-- mutator-bars to operate at such voltage as to involve the danger of flashovers to ground, under operating conditions of the machine, particularly when the machine is utilized as a street-car or electric-locomotive motor which is operated close to the ground, in wet, dirty weather. Such iiashovers may take the form of arcs from the free ends of one o1' more commutator-bars l, to any adjacent grounded surface, such as the end of the associated clamping V-ring I3', or, as shown, we provide flashing-sectors 2I which are carried by the bearing-cartridge 22, between the brushhoider-supporting structures 25 which support the brushholders 26 for carrying the brushes 2l which bear on the cylindrical surface of the commutator.

In accordance with our invention, the free extending ends I6 of the insulating V-rings I4 are held down, and at the same time protected against flashings, by means of a rigid insulating cap 3S, which is preferably molded of layers of impreg nated asbestos-paper, so as to provide a rigid structure of sufficient mechanical strength to re sist centrifugal forces. Said cap 30 has a substantially cylindrical portion 3| which extends over said extending portion I6 of the insulating V-ring I4. The cap also has a radial flange-pon tion 32 which extends over the end of the associated clamping V-ring I3.'. Preferably, the substantially cylindrical portion 3| of the cap 3D is of such diameter that its inner surface is substantially in direct contact with the end-portion cr largest end of the extended portion I6 of the insulating V-ring I4, or at least in contact in spots. or in certain motors, in case of variation in the diameter of the insulating V-rings in different motors.

In utilizing our invention, the cap 30 is slid on axially over the extended end I6 of the insulating V-ring i4. If the insulating V-ring end I6 is of too large a diameter, as by reason of a slight roughening of the mica sheet-material or surface, its outer surface may be rst sandpapered slightly in order to admit of the application of the cap 3U. The inside of the cap or ring 30 is first smeared with cement, and then the cap is pushed in place, so that after it is in place, the space underneath its cylindrical portion 3l, between the same and the inclined or conical outer surface of the extended portion I6 of the insulating V- ring I4, is substantiatlly filled with plastic heathardenable insulating cement, such as a polymerizing cement 33. This operation is preferably performed before the usual dipping and baking operation which is applied to the armature 35 of the machine. The entire machine, or just the rotor-member thereof, is then subjected to a suitable heat-treating operation, such as baking for several hours, which sets or hardens the cement 33 at the same time that it sets the dipping-compound with which the armature 35 is treated.

It will be obvious, from the foregoing description, that our invention has several advantages, among which may be mentioned the following:

(1) It is simple, thus differing markedly from many other elaborate schemes which have been suggested for avoiding some of the difficulties of the string-bands.

(2) Our cap 3D provides increased creepagedistance to ground, because of its end-flange 32 which extends downward over the end of the metal V-ring I3. This permits a more compact commutator-design, by making it possible to use a shorter axial distance between the end of the commutator and the end of the metal V-ring.

(3) It has ease of application. The labor of cementing the cap or ring 30 in place requires much less time than the application f a stringband.

4) It is effective. The centrifugal force of the motor-revolution does not loosen the cap, as it often does the string-bands, because the cap is all one solid piece. This makes it possible to successfully operate the motor under modern conditions of high-speed street-car service.

(5) The outside of the cap provides a smoother surface than is provided by a string-band, even though the string-band is covered with a thick application of glossy paint, The surface of the cap can be painted with a smooth glossy finish of insulating paint, which can be kept clean very easily, and which provides a much better insulating creepage-surface than formerly.

(6) In case 0f motor-flash, the only possibility of damage to the cap will be a slightly damaged surface, but the flash will seldom burn the cap suiciently to necessitate its replacement. It may be smoothed with sandpaper and repainted and will be practically as good as new. On the contrary, with the old string-band construction, a slight damage to a string-band allows all of it to come loose.

We claim as our invention:

l. A V-ring commutator-assembly of commutator-bars and, insulating bars separating the commutator-bars, said bars having V-grooves in the ends thereof, insulating V-rings, clamping V -rings having a conical surface tightly engaging a corresponding surface of the V -grooves, with the insulating V-rings interposed in between, at least one of said clamping V--rings having an outer conical surface which extends out of the associated Vg1'oove, beyond the end of the commutator-bars, the outer conical `portion of the corresponding insulating V-ring likewise having an extended portion fitting against the extended portion of the clamping Vring, a separately formed rigid insulating cap having sufficient rnechanical strength to resist centrifugal forces, said cap having a substantially cylindrical portion extending over said extended portion of the insulating V-ring and further having an inte- ,eral flange-portion extending over the end of the associated clamping V-ring. whereby said flangeporticn mechanically stifens and strengthens said cylindrical portion and electrically extends the insulation creepage surface of said cylindrical portion radially inwardly along said flangeportion, and a filling of a hard insulating cement substantially filling the space between said. cylindrical portion and said extended portion of the insulating V-ring, characterized by the extended portion of the insulating V-ring extending substantially out to the end of the clamping V-ring, and further characterized by the substantially cylindrical portion of the cap being substantially in direct contact with the end-portion of the extended portion of the insulating V-ring, whereby the cap and the intervening cement constitute the sole encompassing means around said extended portion of the insulating i/ring for holding the latter against radial displacement due to centrifugal force, and whereby the insulating V-ringr and the intervening cement and the close t between the substantially cylindrical portion of the cap and the end-portion of the extended portion of the insulating V-ring constitute the sole means for holding the flangeportion of the cap against axial displacement away from the end of the clamping vaine.

2. A commutator-type dynamo-electric ma chine characterized by having a V-ring commutator-assernbly of commutator-bars and insulating bars separating the commutator-bars, said bars having V-grooves in the ends thereof, insulating V-rings, clamping V-rings having a conical surface tightly engaging a corresponding surface of the V-grooves, with the insulating V- rings interposed in between, at least one of said clamping V-rings having an outer conical surface which extends out of the associated V-groove, beyond the end of the commutator-bars, the outer conical portion of the corresponding insulating V-ring likewise having an extended portion fitting against the extended portion of the clamping V-ring, a separately formed rigid insulating cap` having sufficient mechanical strength to resist centrifugal forces, said cap having a substantially cylindrical portion extending over said extended portion of the insulating V-ring and further having an integral flange-portion extending over the end of the associated clamping V-ring, whereby said flange-portion mechanically stiens and strengthens said cylindrical portion and electrically extends the insulation creepage surface of said cylindrical portionl radially inwardly along said flange-portion, a lling of a hard insulating cement substantially filling the space between said cylindrical portion and said extended portion of the insulating V-ring, and armature-connections to said commutator-bars for causing the same to operate at such voltage as to involve the danger of flashovers to ground, under operating conditions of the machine, except for the presence of said cap, characterized by the extended portion of the insulating V-ring extending substantially out to the end of the clamping V-ring, and further characterized by the substantially cylindrical portion of the cap being substantially in direct Contact with. the end-portion of the extended portion of the insulating V-ring, whereby the cap and the intervening cernentbonstitute the sole encompassing means around said extended portion of the insulating V-ring for holding the latter against radial displacement due to cen trifugal force, and whereby the insulating V- ring and the intervening cement and the close iit between the substantially cylindrical portion of the cap and the end-portion of the extended portion of the insulating V-ring constitute the sole means for holding the iiange-portion of the cap against axial displacement away from the end of the clamping V-ring.

CLARENCE A. ATWELL. NORMAN H. WILLBY.

Images