US1948853A

US1948853A - Magneto construction

Info

Publication number: US1948853A
Application number: US630873A
Authority: US
Inventors: William C Heath
Original assignee: Fairbanks Morse and Co
Current assignee: Fairbanks Morse and Co
Priority date: 1932-08-29
Filing date: 1932-08-29
Publication date: 1934-02-27
Anticipated expiration: 1951-02-27

Description

Feb. 27, 1934. w. c. HEATH 1,943,353

MAGNETO CONSTRUCTION Filed mg. 29, 1932 lax Z1,

' A TTORNEY.

Patented Feb. 27, 1934 UNITED STATES MAGNE'EO CONSTRUCTION William 0. Heath, Milwaukee, Wis., assignol' to Fairbanks, Morse & 00., Chicago, 111., a corporation of Illinois Application August 29, 1932. Serial-No. 630.87..

4 Claims.

This invention relates to improvements in magneto construction, and more particularly to improvements in rotors of magnetos of the type employing rotating permanent magnets.

In certain prior types of magnet rotors, it is usual to employ a mass of cast non-magnetic metal, such as brass, for the rotor shaft, and for intimately uniting the laminated pole shoes. Such structures are objectionable, in that a cast shaft is comparatively low in tensile strength and rigidity, and is needlessly expensive for shafting material. In magnetos of this type, it is desirable to employ permanent magnets formed of cobalt steel or other materials having high magnetic retentivity. Such materials have not been widely used in magnetos,- because of the difficulty experienced in machining, and in securing the pole pieces to the rotor. In prior types of rotor constructions it is usual to employ screws or other like fastening means for securing the permanent magnets and the various other parts to the rotor shaft. Such constructions are objectionable in that the screws are very likely to become loose and ineffective after a period of use.

An object of the present invention is to provide an improved rotor for magnetos of the type noted, which includes a rotor shaft formed of steel or othersimila'r material, and a mass of diecast aluminum or zinc alloy for structurally uniting the laminated pole shoes to the shaft. By this provision, a shaft of substantial strength and rigidity is employed in the rotor assembly.

A further object is to provide an improved rotor construction in magnetos of the rotating field type, which includes a mass of die-cast nonmagnetic metal for securing the laminated pole shoes to the rotor shaft, individual masses of nonmagnetic metal for securing suitable bridging members to the pole pieces, and means for removably securing the pole pieces and associated bridging members into intimate contact with the pole shoes.

A still further object is to provide an improved rotor for magnetos of the rotating field type, in which the laminated pole shoes are firmly assembled with the rotor shaft by means of a mass of die-cast non-magnetic metal, and in which the pole pieces and bridging members are removably assembled and more firmly secured to the die cast mass, than is possible through the use of screws, bolts, nuts or like separate fastening and holding elements.

An additional object is to provide an improved rotor for magnetos of the rotating field type, which is rigid and durable in construction, and

is composed of but a. few simple and easily assembled parts, and which results in a substantial reduction of production costs, through minimization of machining operations on the permanent magnets. 69

Further objects and advantages will appear from the following detailed description of parts, and the accompanying drawing of a simple preferred embodiment, and in which:

Fig. 1 is a longitudinal section of a preferred 5 form of rotor for magnetos of the rotating field type, the section being taken' along line 1-1 of Fig. 3; Fig. 2 is a section taken along line 2-2 in Fig. 1; Fig. 3 is a section taken along line 3-3 in Fi 1; Fig. 4 is a fragmentary section taken along line 4-4 in Fig. 3; Fig. 5 is a section taken along line 5-5 in Fig. 1; Fig. 6 is a fragmentary section taken along line 6--6 in Fig. 5, and Fig. '7 is a fragmentary section taken along the line 7--'? in Fig. 6. 7

Referring by reference characters to the drawing the numeral 10 designates, generally, a preferred form of rotor for magnetos of the rotating field type, and which includes a rotor shaft 11 formed, by preference, of mild steel or other similar shafting material of substantial strength and rigidity. A plurality of pole pieces or permanent magnets 12 are, by preference, arranged in spaced relation and substantially parallel to each other, and to the longitudinal axis of the shaft. These pole pieces are, by preference, formed of cobalt steel or other material possessing high magnetic retentivity, and are formed, by preference, of a circular cross section to facilitate machining operations. In the preferred example shown, the rotor 10 includes four such pole pieces, although it will be understood that the number may be varied, depending upon the type and number of poles of the magneto to be constructed.

A pair of bridging members 13 of stamped soft iron or steel, are disposed near one end of the rotor and each in contact-with the end portions of a pair of the pole pieces 12 of opposed polarity. Each bridging member forms a flux path between the paired pole pieces of opposite polarity, to provide a structure which is, in effect, a permanent magnet of U shape or horseshoe type. .By this arrangement there are provided two distinct magnetic circuits within the rotor, where'a two pole machine is desired. Each bridging member 13 is provided with an intermediate semi-circular recessed portion 14. By reason of this construction, there results an annular space 15, which separates the shaft 11 from 'the opposed recessed inner margins of the members 13. Pole shoes 16 no because of the shape and formation of the slotted portion 18 of the laminations.

In assembling the rotor, the laminated pole shoes and rotor shaft, are suitably positioned in a die-casting mold, the mold, prior to casting, being provided with cores corresponding in size and shape with, and so as to result in openings 20. In similar manner, paired, tapered transverse slots 21 are provided by suitable cores in the die-casting mold. A mass of nonmagnetic metal 22, such as a suitable aluminum or zinc alloy, is then poured into the mold for intimately uniting to the shaft, the assembled pole-shoe laminaticns. after the die-casting process, the resulting rigid, integral structure is removed from the mold, and the cores corresponding to openings 20 and slots 21, removed from the casting. The body of cast metal, thus formed, serves securely to embrace the laminations constituting the pole shoes 16, and is provided with peripheral channels 20 therethrough, extending parallel to the shaft, but substantially spaced therefrom, these openings serving, as will hereinafter appear to receive the pole pieces 12.

The pole piece assembly in the preferred example shown, may, if desired, be constructed entirely separately from the body of cast metal containing the shaft and pole shoes. The magnets, or pole pieces are, by preference, peripherally grooved or channelled near one end as indicated at 23. Prior to casting, the pole shoes are disposed in spaced parallel relation, as suggested in Figs. 2 and 3, with their correspondingly grooved ends extending into a suitable die casting mold which may be substantially smaller than that employed by the body of metal 22, the mold for the pole piece assembly serving to contain, prior to casting, the desired number of bridging elements 13 arranged for example, as suggested in Figs. 5 and 6. Cast metal 24 is then poured about the bridging pieces 13 and the adjacent grooved .ends of the pole pieces, so as firmly and permanently to unite, and magnetically connect, the end faces of the pole pieces to the bridging elements therefor. The cast structure, including the body of metal 24, firmly embraces the bridging member 13 and the ends of the pole pieces, as will appear as shown in Figs. 1 and 6, it being noted that each body of metal 24 is provided with opposed recessed portions 25, so that after application of the pole assembly to the remaining elements heretofore described, the single steel shaft 11 projects endwise of and beyond each of the opposite ends of the assembled rotor as shown in Fig. 1. Assembly of the several parts embraced, respectively, by the bodies of

metal

24 and 22, may be effected by inserting the pole pieces endwise into the openings 20 therefor to an extent sufficient to bring the pole pieces through both the cored openings 20 and the pole shoe apertures 1'7. It will be noted (Figs. 3 and 4) that each pole piece is provided with a slotted or notched portion 26 which, in assembly, are brought into register with the transverse slots 21 reviou y cored in the body of metal 22.

With the parts in this position, a tapered wedge pin 27 is driven or pressed into each slot therefor so as snugly to engage the walls of the corresponding passage 21 and at the same time wedgingly engage at least a pair of seats 26 in the pole pieces. The wedge pins 27 may be formed of a suitable non-magnetic material and, as illustrated, each of such pins serves to position a pair of the pole pieces of opposite polarity, in the assembly.

The rotor is now completely assembled and ready for use in a magneto, and it will be apparent that by the above arrangement all screws or threaded fastening means for assembling the rotor, are eliminated, a much simpler and more secure assembly expedient being provided by the wedge pins. 7 r

In the construction above described, it will be seen that the mass of cast, non-magnetic metal secures the various parts of the rotor to the shaft, and that a web of non-magnetic metal, magnetically insulates the bridging members 13 from the shaft. The tapered slots 21 are, by preference, formed with a tapered wall portion 30 and an opposite straight wall portion 31. By this provision, the slots in the pole pieces may be ground without taper to facilitate machining and assembling. It will be readily seen that the entire pole piece assembly, including a pair of the pole pieces 12 and the bridging member 13 therefor, may be removed, as a unit, for remagnetizing purposes, simply by withdrawing the wedge pins .27. After remagnetization, the poles may be reinserted and again secured in place by the pins 27. The use of these wedge pins eliminates expensive and diflicult machining operations on the hard steel magnets. The only operation, viz., that of grinding the straight slots 21 and grooves 26, is simple and inexpensive, as compared to the machining necessary with prior types of rotors.

By reason of simplifying the description of a single embodiment of the invention, the drawing shows an arrangement in which only two pole pieces of opposite polarity are held in assembly including a bridging element cast into the body of metal 24. It will appear that the body of metal 24 may be formed to embrace the ends, say, of four or any other desired number of the pole pieces so as toenable their application to, and removal from the body 22, as a unit. While the present drawing illustrates the rotor for a twopole machine, by the expedient last described the rotor may be formed suitably for either a two or four-pole machine, or a machine having any other usual and desired number of poles.

The rotor shaft 111s, by preference, provided with a knurled portion 32 to insure good interengaging coherence between the mass of cast metal 22 and the shaft. This knurled portion prevents any relative movement, due to an improved bond between the cast metal 22 and the shaft. It will be apparent that the present improved rotor is neat and compact in construction, and forms practically a rigid, solid, rotating mass.

- It will, of course, be understood that the present sembly,

nuaeos v 3 spaced from said shalt, a body of non-magnetic metal cast about a portion of the shaft and the pole shoes, the pole shoes and body of cast metal having preformed longitudinal openings, arranged to receive a plurality of pole pieces; an assembly of parallel pole pieces including an element bridging a plurality of the pole pieces near one end thereof, a second body of non-magnetic metal cast about the bridging element and adjacent ends of the pole pieces engaged thereby; the pole pieces and the first named body of cast metal having preformed openings, and locking pins extending through the openings in the first named body of cast metal and said pole pieces for securing the assembly thereof in predetermined detachable relation to said first named body of cast metal and the pole shoes.

2. In a magnet structure for magnetos of the rotating-field type, a rotor shaft, a body of nonmagnetic metal cast onto said shaft, pole shoes carried by said body, the pole shoes and body having openings formed therein arranged to receive a plurality of pole pieces, disposed parallel to the shaft; an assembly of pole pieces having peripheral grooves near their corresponding ends, a bridging member engaging the ends of the pole pieces, a body of non-magnetic metal cast about the bridging element and the grooved ends of the pole pieces for securing them in assembled relation, and means for securing the pole piece assembly to the pole shoe and shaft assaid means consisting of transverse tapered channels in the first named body of cast metal and transverse grooves in said pole pieces, and pins of tapered section coacting with said channels and grooves to position the pole piece assembly with respect to the shaft and pole shoe assembly.

3. A magnet structure for magnetos of the rotating-fleld type, including a shaft of ferrous metal, a body of non-ferrous metal die-cast onto said shaft, laminated pole shoes carried by said body, a second die-cast body of non-ferrous metal, spaced along the shaft from said first named body, pole pieces and a'bridging element therefor, carried by the second named body, the last named body being die-cast into interlocking relation with the bridging element and corresponding ends of the pole pieces, whereby the pole pieces are mounted as an assembled unit, and means for relatively positioning the pole pieces within said 86 first named cast body, said means including tapered transverse passages in the first named body of cast metal, and grooves in the pole pieces, and tapered locking elements disposable in said passages, an interlocking engagement with the 90 grooves in the pole pieces.

4. In. a magnet structure for magnetos of the rotating-field type, a pole piece assembly including aplurality of endwise peripherally grooved pole pieces, a bridging element for a plurality of 98 said pole pieces, and a body of cast non-magnetic metal interengaging said grooves and securing the pole pieces in contacting relation with said bridging element; a second body of cast nonmagnetic metal, a plurality of laminated pole 100 shoes secured by said second cast body, the pole shoes and second named body having preformed pole-piece openings longitudinally thereof, and

-a shaft of ferrous metal united, by casting, to

one of said bodies of cast metal and projecting 106 endwise beyond both of said bodies, and means for securing the pole piece assembly, into assembled relation with said last named cast body, said means including a preformed tapered bore in said last named body of cast metal, and grooves 110 in said pole pieces, registerable with said bore when the pole pieces and said last named body are in assembled relation, and tapered pins disposable in the bore and grooves, to secure the pole pieces and pole piece assembly against end- 118 wise movement. WILLIAM C. HEATH.

III