Multiple magnetic paths machine

Abstract: Separate multiple flux paths for an electrical generator or motor are provided in a single rotor machine by axially mounting a plurality of pole pieces on the rotor shaft. Each pole piece includes a central disc portion having a plurality of radial pole-forming projections, with the projections of adjacent pole pieces rotated 180 electrical degrees, such that the pole-forming projections of every other pole piece have the same magnetic polarity. Provision of a plurality of separate magnetic flux paths increases the total flux attainable in a machine of given size and therefore improves the machine's output and efficiency.

Description: This invention relates generally to electrical machines and more particularly to an electrical generating machine or motor having multiple magnetic paths in a single rotor machine. According to claim 1, the present invention relates to rotor means for a rotating machine. Particularly for small electrical power generating machines and specifically for use in motor vehicles, the claw pole alternator has achieved wide acceptance as the most efficient means for producing electrical power for use in an automobile. In a claw pole alternator, the pole structure is basically a pair of pole pieces generally made of flat circular metal plates having central bores positioned axially on the rotor shaft on either side of the rotor core and coil. Each pole piece has projecting fingers or claws which are bent over the rotor coil in a direction parallel to the rotor axis. When so bent and positioned, each claw interposes between claws of the opposite pole piece. The pole pieces may be manufactured by metal stamping, forging, machining, or other manufacturing processes. When current is passed through the rotor coil, the claws become electromagnetic poles of opposite polarity. As the rotor is rotated, these poles having opposite polarity produce a magnetic field which alternates in polarity as seen by the stator winding conductors, thus producing alternating current at the output of the alternator. In automotive applications, this alternating current (AC) is generally rectified into direct current (DC) for use in the automotive electrical systems. The AC may also be used directly. The present invention originates from US-A-4,980,595 disclosing a rotor means of this type incorporating bent claws giving much better space efficiency, but making a great deal of mechanical noise. As to a description of further related art, it is therefore referred to the discourse headed "background of the invention" in US-A-4,980,595. US-A-4,916,346 relates to a homopolar machine which is utilized to generate direct current electricity or can be used for motors conducting very high currents. As far as the relevance of this documents with respect to the present invention is concerned, the rotor of this homopolar machine does not contain any source of magnetic flux. Unlike the present invention, the magnetic flux is generated in this stator and passes through the rotor in a single direction. The magnetic coupling between the pole pieces in the homopolar machine is provided by the shaft and a ring of magnetic material. US-A-4,916,346 does not show or suggest means for generating magnetic flux on the rotor. US-A-3,956,650 discloses a synchronous induction motor. The teeth shown on the periphery of the rotor rings are not salient poles but are similar to laminations to reduce iron losses due to changing flux. SUMMARY OF THE INVENTION It is an object of the present invention to increase the achievable output of a generating or motor machine having a given size beyond that presently achievable in conventional designs. It is a further object of the present invention to increase the efficiency of a generating or motor machine significantly beyond that presently achievable in conventional designs. It is a still further object of the present invention to lower rotor noise levels below that presently achievable in conventional designs. According to the invention, the object referred to are solved by the features of claim 1. It has been discovered that a multiple path machine employing pole pieces without axially extending claw portions offers advantages over rotor assemblies having claws. One advantage of such a "clawless" arrangement is significantly reduced magnetic noise which may be caused in claw type rotor assemblies by vibration of the axially extending claws upon rotation of the rotor assembly. Additionally, improved rotor coil cooling is possible if the rotor coils are not totally surrounded by the pole pieces and their respective interleaved claws. Still a further advantage is the simplified construction of the pole pieces resulting in more economical manufacturing and assembly costs for same. Additionally, larger rotor coils may be provided in the same space where no claws are used since the coils can extend to the outer periphery of the pole pieces which, in the claw type rotor assembly, would be taken up by the claw material itself. Further objects, features and advantages of this invention will become apparent from reading of the following detailed description, taken in conjunction with accompanying drawings, in which: Fig. 1 is a side view of a multiple magnetic path alternator which is a second alternative embodiment of the invention; Fig. 2 is a view of the alternative embodiment of Fig. 5 taken along line 6-6-; and Fig. 3 is an alternator assembly having rotor pole pieces similar to those of the embodiment of Figs. 5 and 6, but including both rotor electromagnets and permanent magnets as sources of excitation. DETAILED DESCRIPTION While the following description specifically refers to alternators arranged according to principles of the present invention, the present invention applies equally well to motors. The teachings in the detailed description that follows are merely illustrative, showing two preferred embodiments of the present invention. With reference to Figs. 1 and 2, a side view of a rotor assembly 500 arranged in accordance with the principles of the invention, is set forth in Fig. 1 and an end view of the same assembly taken along line 2-2 of Fig.l is set forth in Fig. 2. Rotor assembly 500 is mounted for rotation with rotor shaft 502 and is surrounded by a stator assembly 501. The rotor assembly is principally comprised of a plurality of pole pieces 510, 520, 530, and 540 axially spaced along rotor shaft 502 such that excitation flux elements may be spaced between adjacent pole pieces. In the embodiment of Figs. 5 and 6, the flux elements are comprised of a magnetically permeable core such as 530a surrounded by a current carrying coil 531a. Similar elements bearing the last letter b and c are shown interposed between succeeding pole pieces of Fig. 5. Each of the plurality of pole pieces, such as pole piece 510, are comprised of a central disc portion 512 for receipt of rotor shaft 502 such that the pole pieces fixedly attached for rotation therewith. Radially extending from the central disc portion 512 is a plurality of radial pole forming projections 514a through 514f, each separated by gaps 516a through 516f. It is to be noted that these pole forming radial projections 514a through 514f extend in the radial direction only and have no bent portions or claws extending in a direction normal to a plane of the pole piece disc. As seen from Fig. 6, each pole piece is rotationally displaced 180 electrical degrees from its adjacent neighbors such that the radial pole forming projections are disposed in axial alignment with the gaps of adjacent pole pieces. Hence, the pole forming projections 524a through 524f of pole piece 520 are axially aligned with gaps 516a through 516f, respectively, of pole piece 510. With this arrangement, when a excitation flux is provided by the coils 531a, etc. circulating around cores 530a, etc., it will be seen that each radial pole forming projection on each pole piece will assume the same magnetic polarity and that this magnetic polarity will be of an opposite sense as one proceeds axially along the stack of pole pieces in the rotor assembly 500. For example, as seen from Figs. 5 and 6, the radial projections of pole piece 510 have north, N, magnetic polarity, the pole projections of pole piece 520 have south, S, polarity, the projections of pole piece 530 have N polarity, etc., in alternating fashion along the stack. In the arrangement of Fig. 5, it is seen that a plurality of separate magnetic paths are supported by adjacent pairs of pole pieces in conjunction with the stator core in stator assembly 501 and a portion of rotor shaft 502. These flux paths 540a, 540b, 540c, etc. are seen passing flux out of north pole segments and into a south pole segment of an adjacent pole piece. Likewise, two examples of flux paths are shown at 620 and 630 of Fig. 6. It is to be understood that the actual flux paths shown are not contained within the plane of the drawing figures in which they are presented. For example, it will be seen that at flux path 620, as the magnetic flux leaves radial pole forming projection 514f and enters into stator core material of stator assembly 501, the flux will actually flow somewhat into the page as one views Fig. 6, such that it will exit the stator in the vicinity of pole projection 524e of adjacent pole piece 520. It is also seen from Fig. 6 that a portion of the rotor shaft itself may form a part of the magnetic paths where the flux excitation means comprises an electromagnet utilizing coils such as 531a and cores such as 530a. Yet another version of the arrangement of Figs. 5 and 6 is set forth in Fig. 7. The only difference in the arrangement of Fig. 7 from that of Fig. 5 is that the flux excitation means provided between certain of the pole pieces comprises a permanent magnet with an isolation sleeve separating the permanent magnet from the rotor shaft. In combination with the permanent magnet type excitation element, an electromagnet is provided between two of the pole pieces such that the total excitation of the rotor assembly may be varied. With reference to Fig. 7, rotor assembly 700 which is surrounded by stator assembly 701 is comprised of a plurality of pole pieces 710, 720, 730 and 740 axially spaced along rotor shaft 702, such that permanent magnet 760a lies between pole pieces 710 and 720, permanent magnet 760b lies between pole pieces 720 and 730, and an electro magnet utilizing coil 731 and magnetically permeable core 730 lies between pole pieces 730 and 740. Isolating magnetically each permanent magnet from rotor shaft 702 is a non-magnetic sleeve. Sleeve 770a surrounds shaft 702 radially inwardly of annular magnet 760a, while sleeve 770b surrounds shaft 702 radially inwardly of annular magnet 760b. As with the arrangement of Fig. 5, alternating pole pieces along the axial stack assume alternating magnetic polarities. Additionally, each pole piece in the stack has the identical configuration to that shown in Fig. 6 - namely, a central disc portion from which extends a plurality of radial pole forming projections extending only in a radial direction. The rotor assemblies of these embodiments of the present invention provide several important benefits to alternator design. Because the rotor pole structure is smaller, the alternator will produce more output per unit weight. Also, lower magnetic noise will be generated at a given speed. Because of the reduced size of the pole pieces required in this invention, the cost for producing stampings for use as pole pieces is reduced and therefore machinings or forgings are not required in order to minimize the bend radius problem so as to maximize the surface area of the claw or claws adjacent the stator core. Another advantage of this invention is that as more flux is produced, for a given output required, the smaller the number of stator winding turns that are required. As losses are primarily due to heating in the stator winding, reducing the winding turns will reduce this heating loss and therefore will increase alternator efficiency. This in turn will then require less power input for a given electrical power output. From the above description it is seen this invention provides an improved rotor design in an electrical machine, either motor or generator, utilizing multiple magnetic flux paths, to facilitate increased electrical output, efficiency, and versatility. The instant invention has been described in an illustrative manner and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Modifications and variations are possible within the scope of the appended claims.

Claims: A rotor means (500) for a rotating machine having a stationary housing, said rotor means being supported by said housing, and stator windings and a stator core (501) in the housing, the rotor means comprising: a rotor shaft (502) rotatably mounted in the housing; at least three pole pieces (510, 520, 530, 540) axially spaced along the shaft; a plurality of magnetic flux generating means (531a, 531b, 531c;760a, 760b); each mounted for rotation with the shaft between adjacent pole pieces and each pole piece comprising a central disc portion (512) surrounding the shaft and having a plurality of pole forming projections (514a-514f) extending only radially from the central disc portion with gaps therebetween, the pole forming projections of each pole piece being rotationally positioned 180 electrical degrees from the pole-forming projections of axially adjacent-pole pieces, such that the pole-forming projections of every other pole piece have a like magnetic polarity; whereby a plurality of separate magnetic flux paths is established, each flux path supported by a pair of the adjacent pole pieces and the stator core. The rotor means according to claim 1, wherein at least one of the magnetic flux means comprises: a magnetically permeable core (530a, 530b, 530c) mounted on said shaft; and a current carrying coil (531a, 531b, 531c) encircling the core. The rotor means according to claim 1 or 2, wherein at least another one of the magnetic flux means comprises: a non-magnetic sleeve (770a, 770b) surrounding said shaft; and a permanent magnet (760a, 760b) surrounding said sleeve.

Inventors: ARORA RAM SARAN, ARORA, RAM SARAN
Applicants: CHRYSLER CORP, CHRYSLER CORPORATION
Application year: 1992
Main classification: H02K19
IPC codes: H02K21, H02K1, H02K16, H02K19