US2192073A - Electric generator - Google Patents

Description

Feb. 27, 1940. w G|5KE$ ET AL 2,192,073

ELECTRI C GENERATOR Filed Feb. 4, 1938 foa By Petenfed Feb. 21, 1940 UNITED STATES PATENT OFFICE ELECTRIC GENERATOR Netherlands Application February 4, 1938, Serial No. 188,790 In Germany February 5, 1937 8 Claims.

Our invention relates to electric generators which have a permanent-magnet rotor, and are adapted for operation at greatly varying speeds.

As the invention is particularly adapted to l generators for use on bicycles, we shall describe the same in this connection, although it is not limited thereto.

In generators of the above type, the coils are usually arranged in slots of a soft iron stator. However, it is dicult to introduce the coils into the slots, and the construction must be comparatively heavy. It is also known to use a permanent-magnet rotor and to use as the stator a number of solid soft iron members arranged around the rotor and connected to a frame which also serves as part of the magnetic circuit. Although a single coil ca'n be used in such a construction, the magnetic circuit is comparatively complicated and the construction is relatively expensive.

The object of our invention is to overcome the above difficulties and to provide a generator of simple and inexpensive construction, which even at a comparatively low speed, supplies a voltage which is suiilciently high and which varies only slightly with the speed.

According to the invention We use a permanent-magnet cylindrically-shaped rotor, and va stator whose core has at least four legs arranged around the rotor and extending substantially parallel to the axis of rotation thereof. The rotor preferably has a length at least as large as its diameter, whereas the winding is arranged on those parts of the core legs which ex- 35 tend beyond the rotor in the direction of its longitudinal axis.

Such a construction results in a reduction in the overall dimensions of the generator, as well as in its volume, and because of the arrangement 40 of the coil relative to the rotor, a. simple and a highly eicient magnetic circuit is obtained.- In

addition it is possible to reduce the iron losses in the magnetic circuit to a very low value because all of the circuit through which a vary- 45 ing ilux passes can be made in avery simple manner from laminations of transformer steel.

The rotor is preferably given an axial length at least as large as its diameter. Because of this 50 relative great length, it is possible to give the that the cross-sectional area of the air gap,

whicharea is determined by the length and width of the portions of the core legs opposing the rotor, will be larger than the cross-sectional area `permanent magnet steel. Rotor 2 preferably has diameter.

lis formed of U-shaped bundles of laminations core legs a relative great length with the result of the core and consequently the reluctance of the air, gap will be considerably reduced.

In vorder that the invention may be clearly understood and'readily carried into effect, we shall describe the same in more detail with reference 5 to the Vaccompanying drawing, in which:

- Figure l is a longitudinal sectional view ofl an B-pole bicycle generator;

Fig. 21s a sectional view along line II-II of Fig. l; and 10 Fig. 3 is a development of a portion of the stator shown in Figs. l and 2.

As shown in Fig. l, the generator comprises a frame 5 provided with a bore into which is tted bearings 25 and 26. Rotatably mounted on 15 bearings 25 and 26 is a driving spindle 2| having a threaded end to which is secured by means of a nut 29, a driving Wheel 28 provided with a grooved surface adapted to engage the surface of a bicycle tire. A member 2l of suitable pack- 2G ing material, for instance felt, lits into a counterbore in the end of frame 5 and tightly engages spindle 2| to prevent the entrance of dirt.

Spindle 2| carries a cylindrical member 32 of non-magnetic material, such as brass, and for 25 this purpose is provided with a ridged portion 3| upon which member 32 is forced. A cupshaped cover 4, for instance of pressed metal, is secured to frame 5 by a screw 9, and carries a lea-f spring |'l which presses on the end of spindle to prevent vibration of the same in an axial direction.

Secured to member 3| by means of a shrink t is a hollow cylindrically-shaped rotor 2 of a smooth outer surface and is magnetized so'that 35 the lines of force extend substantially perpendieular to thev axis, i. e., with the north and south poles, as shown in Fig. 2. FThe rotor 2 preferably has a length which is equal to or greater than its o The stator of the generator comprises a core having eight legs 1 extending parallel to the yaxis of rotor 2 and equidistantly spaced around the rotor. As shown more clearly in Fig. 3, the core whose extending portions are secured together to form the legs 1. This gives a very advantageous and sturdy construction, and the assembly of the core may be very readily effected. More particularly, strips of transformer steel are assembled in a bundle and the bundle given a U-shape, after which they are riveted together to form the complete core.

As the core legs l are parallel to each other through their relatively great length, a comparatively high leakage flux is set up.y We have found that among other factors, such as the number of turns of the coil and the frequency which is the product of the number of poles and the speed of rotation, it is necessary that the iiux produced in the core by the passage of ycurrent through the winding should be high in order to obtain a substantially flat speed-voltage characteristic. To increase this iiux, we so arrange the legs that the magnetic eld of the winding can pass from one leg to another instead of passing through the permanent magnet rotor.

Referring now to Fig. l, the core is secured by means of rivets 8 to a ring 6 of non-magnetic material secured to frame by screws I0. Annular plates I2 and I4 of insulating material provided with apertures for legs l, serve to hold the legs in position. Fitting over each leg 1 is a U-shaped member I5 of magnetic material having bent ends 33 (see Fig. 2), which serve to distribute more evenly the magnetic field around the inner circumference of the core, and to hold the laminations of the legs together.

When using a smooth-surfaced cylindrical rotor, there is likely to be irregular operation due to excessive attraction between the rotor and each leg 1. This, however, is eliminated by the portions 33. of member I5. A similar eifect may be obtained by inclining legs 'I slightly with respect to the axis of the rotor or by so magnetizing the rotor that the poles do not extend parallel to the axis of the rotor, or by a combinatio of these means.

Arranged above rotor 2 is a winding in the form of a single coil I3, which is wound in a circular or quadratic manner and then shaped so that it may be slipped over legs 1 in such a manner that it extends on the outside of each second core leg, as shown in Fig. 2. Although it is possible to use separate coils one on each of the core legs and connected in series, the use of a singlecoil is preferable, as it simplifies the construction and reduces the cost of manufacture.

Winding 3 has one end II connected to the frame 5, for instance by means of a lug secured under screw I0 (not shown), and its other end 35 connected to a lug I9. Lug I9 is connected to a screw I8 insulated from vframe 5 by insulating washers 2l] and secured thereto by a nut 23. A suitable terminal nut 24 serves to hold a connecting lug 36.

The tgenerator shown is adapted to be supported from the frame of a bicycle (not shown) so that wheel 28 may be placed in engagement with the side of the tire. For this purpose a strap I is riveted to cover 4 by means of rivets 30 and is secured to a device which allows for the adjustment of the position of the generator. As such adjusting devices are well known inthe art and do not form part of the present invention, a detailed description ofthe same is believed unnecessary.

It will be noted that by removing screw 9, the entire mechanism can be removed from cover 4 and is accessible for inspection or repair.

Furthermore, rotorv2 may be slipped into the generator directlyfrom the magnetizing apparatus, and hence there will be little'loss in the magnetic intensity.

While we have described our invention in connection with specific examples and applications,

. we do not wish to be limited thereto, but desire the appended claims to be construed as broadly aspermissible in view of the prior art.

What we lclaim is: 1. An electric generator for operation at greatly varying speeds, comprising a permanentmagnet rotorof cylindrical shape, and a stator comprising a core of magnetic material having at least four legs arranged at relatively short distances from each other around said rotor and having at least four legs arranged at relatively short distances from each other around said rotor and extending substantially parallel to the axis thereof, each of said legs having a length equal to at least the distance between two diametrically-opposite legs, and a winding arranged on those parts of said legs which extend beyond the rotor in the direction of its axis.

3. An electric generator for operation atv greatly varying speeds, comprising a permanentmagnet rotor of cylindrical shape, and a stator comprising a core having at least four legs arranged at relatively short distances from each other around said rotor and extending substantially parallel to the axis thereof, each of said legs having a length equal to at least the distance between two diametrically opposite legs, said core comprising a plurality of bundles of U-shaped strips of magnetic material, each leg of the core comprising an extending portion of two adjacent bundles, and a winding arranged on those parts of said legs which extend beyond the rotor in the direction of its axis.

4. An electric generator for voperation at greatly varying speeds, comprising a permanentmagnet rotor of cylindrical shape and having a length at least equal to its diameter, and a stator comprising a core having at least four legs arranged at relatively short distances. from each other around said rotor and extending substantially parallel to the axis thereof, each of said legs having a length equal to at least the distance between two diametrically-opposite legs, said core comprising a plurality of bundles of strips of magnetic material bent in a U-shape, each leg comprising an extending portion of two bundles, and a windingarranged on those parts of said legs which extend beyond the rotor in the direction of its axis.

5. An electric generator for operation at greatly varying speeds, comprising a permanentmagnet rotor of cylindrical shape, and a stator comprising a core having at least eight bundles of laminations of magnetic material bent in a U-shape, said bundles being arranged 4with their extending portions around the surface of the rotor and with the bottom portions of all bundles at one end of the rotor, the adjacent extending portions of two successive bundles 'being secured together to form legs arranged around said rotor and extending substantially parallel to the axis thereof, and a winding arranged on those parts of said legs which extend beyond -the rotor irl/the direction of its axis.

6. An electric generator for operation at greatly varying speeds, comprising a permanentmagnet rotor of cylindrical shape, and a stator comprising a core having at least four legs of magnetic material arranged around said rotor and extending substantially parallel to the axis thereof, a winding arranged on those parts oi. said legs which extend beyond the rotor in the direction of its axis, and means to prevent sudden changes in the magnetic ileld comprising a member of magnetic material on the part of each of said legs adjacent the rotor.

7. An electric. generator for operation at greatly varying speeds, comprising a permanentmagnet rotor of cylindrical shape, and a stator comprising a core of magnetic material having at least four legs arranged around said rotor and extending substantially parallel to the axis thereof, and a vsingle coil arranged on those parts of said legs which extend beyond the rotor in the direction of its axis, said coil being of sinuous shape and passing on the outside of every second leg and on the inside of every remaining leg.

8. An electric generator for operation at greatly varying speeds comprising supporting means, a permanent-magnet rotor of cylindrical shape rotatably supported by said means, va stator comprising a core of magnetic material having at least four legs arranged around said rotor and extending substantially parallel to the axis thereof, said core being supported at one end from said supporting means with the legs extending therefrom, and a single coil of sinuous shape arranged on portions of the legs at one side of the rotor, said coil passing on the ontside oi every second leg andron the inside of each of the remaining legs.

WILLEM (SAISKES.` y

HENDRIK AREND GODARD HAZEU.

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