Rotor for reluctance type rotating machine

A rotor for a reluctance type rotating machine includes a rotor core formed by stacking a number of annular core materials each of which includes magnetic concave and convex portions. The rotor core has two keys which are formed at two positions on an inner circumference of the rotor core. The positions are spaced 180 degrees apart from each other with respect to the rotor core. The rotor core is divided into a plurality of blocks and the core materials constituting at least one block have the magnetic concave and convex portions shifted by a predetermined angle relative to the core materials constituting the other or another block on the basis of a center line passing through the keys. A whole or part of the core materials of at least one block are located circumferentially 180 degrees apart form the core materials constituting the other or another block.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a rotor for a reluctance type electric rotating machine which can achieve the similar effects to those achieved by skew.

2. Description of the Related Art

A reluctance type rotating machine or, for example, a reluctance type rotating machine provided with permanent magnets includes a rotor formed with a magnetic convex portion where a flux is easy to pass (d axis) and a magnetic concave portion where a flux is difficult to pass (q axis) and a permanent magnet which is disposed in a stator provided with a stator winding. The magnetic convex portion (d axis) has a high magnetic flux density in an air gap, whereas the magnetic concave portion (q axis) has a low magnetic flux density in an air gap. These variations in the magnetic flux density produce reluctance torque. Furthermore, torque is also developed by a magnetic attractive force and a magnetic repulsive force between poles of the permanent magnet and stator.

FIGS. 16 and 17illustrate an example of conventional rotor for a reluctance type rotating machine with permanent magnets. The illustrated machine is an 8-pole machine.FIG. 16is a side view of the rotor with an end plate and a rotational shaft being eliminated.FIG. 17is a sectional view taken along line17—17. Referring toFIG. 16, the rotor100includes a rotor core101made by stacking a number of annular silicon steel sheets. The rotor core101has pairs of generally rectangular magnet insertion holes102formed in an outer circumference thereof as shown inFIG. 17. Permanent magnets103are inserted and fixed in the insertion holes102respectively. The outer circumference of the rotor core101is further formed with cavities104located between the respective pairs of permanent magnets103as shown inFIG. 17. Each cavity104is formed into a generally triangular shape. In the rotor100, each pair of insertion holes102, permanent magnets103and each cavity104constitute the aforesaid magnetic concave portion105where a flux is difficult to pass (q axis). Each portion between the concave portions105constitutes the aforesaid magnetic convex portion106where a flux is easy to pass (d axis). The magnetic concave and convex portions105and106are formed alternately with a predetermined angle therebetween. See JP-A-2001-339922, for example.

The rotor core101has keys107formed on an inner circumference thereof. The keys107are adapted to engage key grooves of a rotational shaft respectively. Furthermore, a center line Lo passing the keys107is adapted to pass the center of the magnetic convex portion106. A center line La passes the center of the magnetic convex portion105adjacent to the center line Lo. The center line Lo is adapted to meet the center line La at an angle θ. The angle θ is at 22.5 degrees when the rotor100has 8 poles. The rotor100is adapted to be disposed in a stator (not shown) provided with a stator winding.

It is well known that squirrel-cage induction motors result in crawling due to torque developed by high harmonics. There is a possibility that permanent-magnet reluctance type rotating machines as the reluctance type rotating machine may cause the similar crawling to that caused by the squirrel-cage induction motors. As a result, the crawling results in torque ripple, oscillation, vibration and noise.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a rotor for a reluctance type rotating machine which can achieve the similar effects to those achieved by skew and reduce torque ripple, oscillation, vibration and noise.

The present invention provides a rotor for a reluctance type rotating machine comprising a rotor core formed by stacking a number of annular core materials each of which includes magnetic concave and convex portions alternately formed on an outer circumference thereof and a central through hole, the rotor core having two keys which are formed at two positions on an inner circumference thereof defining the central through hole of the rotor core so as to extend axially, respectively, the positions being spaced 180 degrees apart from each other with respect to the rotor core, the rotor core being divided into a plurality of blocks, the core materials constituting at least one block having the magnetic concave and convex portions shifted by a predetermined angle relative the core materials constituting the other or another block on the basis of a center line passing through the keys, wherein a whole or part of the core materials of the at least one block are located circumferentially 180 degrees apart from the core materials constituting the other or another block, and a rotational shaft inserted through the central hole of the rotor core, the shaft having two key grooves engaging the keys of the rotor core.

In the above-described construction, the core materials constituting at least one block are formed so that the magnetic concave and convex portions are shifted by a predetermined angle from the core materials constituting the other or another block relative to a center line passing the key. Accordingly, for example, a center line passing the center of the magnetic concave portion of at least one block has a locus shifted from one of another or the other block. Consequently, since the similar effects to those achieved by skew can be achieved, the torque ripple, oscillation, vibration and noise can be reduced.

Each block may include the magnetic concave portions each of which is provided with a pair of magnet insertion holes which are opposed to each other so that a distance therebetween is gradually rendered longer as the insertion holes approach the outer circumference of the rotor, and permanent magnets may be inserted and fixed in the insertion holes respectively.

A magnetic torque by the permanent magnets can also be achieved in addition to reluctance torque. Furthermore, harmonic values of counter electromotive force can be reduced by the similar effects to those achieved by skew.

DETAILED DESCRIPTION OF THE INVENTION

Several embodiments of the present invention will be described.FIGS. 1A to 5illustrate a first embodiment in which the invention is applied to a reluctance type rotating machine with permanent magnets. The reluctance type rotating machine possesses eight poles. A rotor1of the reluctance type rotating machine includes a rotor core2made by stacking a number of annular silicon steel sheets serving as a core material. The rotor core2is divided into four blocks3and4having the same thickness as shown inFIG. 2. The blocks3and4are stacked alternately.

Each block3or the silicon steel sheets composing each block3will be described with reference toFIG. 1A. Each block3has a number of pairs of generally rectangular magnet insertion holes5formed in an outer circumferential portion thereof. The paired magnet insertion holes5are opposed to each other so that a distance therebetween is gradually rendered longer as the magnet insertion holes5approach an outer circumferential edge. Permanent magnets6are inserted into the paired magnet insertion holes5respectively and fixed by an adhesive agent, filler or the like. The outer circumferential portion of each block3also has cavities7formed between the permanent magnets6of each pair. Each cavity7is formed into a generally triangular shape having two sides parallel to the paired permanent magnets6and the other side extending along the outer circumference. The two sides of each cavity7may or may not be parallel to the paired permanent magnets6.

Each block3includes each portion thereof corresponding to the paired magnet insertion holes5, permanent magnets6and cavity7and serving as a magnetic concave portion8(q axis) where a flux is difficult to pass. Each block3further includes each portion thereof located between the magnetic concave portion8and serving as a magnetic convex portion9(d axis) where a flux is easy to pass. The magnetic concave and convex portions8and9are formed alternately so that each of the magnetic concave and convex portions8and9meets the other at a predetermined angle. Each block3further has two keys10and11which are formed on the inner circumference thereof so as to be 180-degree apart from each other and so as to extend axially.

A center line Lo passing the centers of the keys10and11also passes the magnetic convex portions9in each block3. Now, assume a center line Loa shifted from the center line Lo by a predetermined angle Δθ in the direction opposite the direction of rotation of the rotor (clockwise). The center line Loa forms a predetermined angle θ with a center line Lb passing the center of the magnetic concave portion8adjacent to the center line Loa. Accordingly, the center line Loa passes the center of the magnetic convex portion9. The angle θ is represented as 180/n when n is the number of poles of the rotor1. Furthermore, when a stator50(seeFIG. 5) has slots the number of which is represented as 6×n, the magnetic concave and convex portions8and9representative of a pole position of each block3are shifted by the slot pitch a relative to the center line Lo. Accordingly, the angle Δθ is obtained from:
Δθ=(360×a)/(6×n)=(60×a)/n
Thus, the angle Δθ is represented as −(60×a)/n in degree. The minus sign indicates shift in the direction opposite the direction of rotation of the rotor (clockwise).

Each block4or the silicon steel sheets composing each block4will be described with reference toFIG. 1B. Each block4has magnet insertion holes12which are similar to the magnet insertion holes5and formed in an outer circumferential portion thereof. Permanent magnets13are inserted into the paired magnet insertion holes12respectively and fixed by an adhesive agent, filler or the like. The outer circumferential portion of each block4also has cavities14which are similar to the cavities7and are formed between the permanent magnets13of each pair.

Each block4includes each portion thereof corresponding to the paired magnet insertion holes12, permanent magnets13and cavity14and serving as a magnetic concave portion15(q axis) where a flux is difficult to pass. Each block4further includes each portion thereof located between the magnetic concave portion15and serving as a magnetic convex portion16(d axis) where a flux is easy to pass. The magnetic concave and convex portions8and9are formed alternately so that each of the magnetic concave and convex portions8and9meets the other at a predetermined angle. Each block4further has two keys10and11which are formed on the inner circumference thereof so as to be 180-degree apart from each other and so as to extend axially.

A center line Lo passing the centers of the keys10and11also passes the magnetic convex portions16in each block4. Now, assume a center line Lob shifted from the center line Lo by a predetermined angle Δθ in the rotation direction X of the rotor (counterclockwise). The center line Lob forms a predetermined angle θ with a center line Lc passing the center of the magnetic concave portion15adjacent to the center line Lob. Accordingly, the center line Lob passes the center of the magnetic convex portion16. The angle θ is represented as 180/n when n is the number of poles of the rotor1. The angle Δθ is represented as +(60×a)/n in degree. The plus sign indicates deviation in the rotation direction X of the rotor (counterclockwise).

As obvious fromFIGS. 1A and 1B, the block4is made by stacking the silicon steel sheets which are the same as those of the block3and reversed inside out. Accordingly, the blocks3and4of the rotor core2can be composed of a single type of silicon steel sheets. Two annular end plates17and18are attached to both ends of the rotor core2respectively as shown inFIG. 4.

The rotating shaft19, rotor core2and end plates17and18are integrated together by shrinkage fitting thereby to be assembled. In this case, as shown inFIG. 4, the keys10and11of the rotor core2are adapted to correspond with key grooves20of the rotating shaft19respectively. Only one of the key grooves20is shown inFIG. 4. The rotating shaft19is formed with a flange21for positioning the rotor core2and end plates17and18.

Upon completion of assembly of the rotor1, the magnetic concave and convex portions8and9of the block3are shifted by the predetermined angle Δθ in the direction opposite the rotation direction X (clockwise) on the basis of the center line Lo. Further, the magnetic concave and convex portions15and16of the block4are also shifted by the predetermined angle Δθ in the rotation direction X (counterclockwise) on the basis of the center line Lo. As a result, the center lines Lb and Lc of the blocks3and4have linear loci which are zigzagged but not straightforward as in the conventional reluctance type rotating machines, as shown inFIG. 3. Accordingly, the rotor1can achieve the effects similar to those of skew in the rotors for squirrel-cage induction motors. In this case, an amount of shift is required to be ±0 between the center lines Lb and the center lines Lc. More specifically, the sum total of a shift angle Δθ (−) of the center lines Lb and a shift angle Δθ (+) of the center lines Lc is required to be ±0 and the sum total of loci lengths of the center lines Lb (total thickness of the block3) is required to be equal to the sum total of loci lengths of the center lines Lc (total thickness of the block4) or the difference between both sums is required to be ±0.

The permanent-magnet reluctance type rotating machine60comprises the rotor1disposed in the stator provided with stator winding (not shown) as shown inFIG. 5. The rotor1includes the magnetic concave portions8and15(q axis) where a flux is difficult to pass and the magnetic convex portions9and16(d axis) where a flux is easy to pass. By causing electric current to flow into the stator winding, magnetic energy is stored in air gaps over the magnetic concave and convex portions8and15, and9and16respectively. The magnetic energy differs from one air gap to another. The changes in the magnetic energy develop reluctance torque. Furthermore, since the rotor1is provided with the permanent magnets6and13, torque is also developed by a magnetic attractive force and magnetic repulsive force between the permanent magnets6and13and magnetic poles of the stator. Consequently, the rotor1is rotated.

In the foregoing embodiment, the magnetic concave and convex portions8and9of the block3are shifted by the predetermined angle Δθ in the direction opposite the rotation direction X (clockwise) on the basis of the center line Lo. Further, the magnetic concave and convex portions15and16of the block4are also shifted by the predetermined angle Δθ in the rotation direction X (counterclockwise) on the basis of the center line Lo. As a result, the linear loci of the center lines Lb and Lc of the blocks3and4are zigzagged and accordingly, the rotor1can achieve the effects similar to those of skew in the rotors for squirrel-cage induction motors. Consequently, torque ripple, oscillation, vibration and noise can be reduced in the permanent-magnet reluctance type rotating machine, and a peak value of back electromotive force can be reduced in the stator winding.

Additionally, an amount of shift is set so as to be ±0 between the center lines Lb and the center lines Lc in the rotor core2. Consequently, magnetic obstacle can be prevented although the rotor1can achieve the effects similar to those of skew in the rotors for squirrel-cage induction motors.

FIGS. 6 to 8illustrate a second embodiment of the invention. Describing the difference of the second embodiment from the first embodiment, the rotor core26employed instead of the rotor core2includes blocks3and27stacked alternately. Each block27is configured as shown inFIG. 8. This configuration is obtained by turning the silicon steel sheets of each block4circumferentially by 180 degrees and then stacking the sheets so that the key10of the block3as shown inFIG. 1Aand the key11of the block27overlap each other. The other construction of the rotor of the second embodiment is the same as that of the first embodiment.

In the construction of the second embodiment as shown inFIG. 7, too, the linear loci of the center lines Lb and Lc of the blocks3and27are zigzagged in the same manner as in the first embodiment. Consequently, the rotor of the second embodiment can achieve the same effects as those of the first embodiment.

The annular silicon steel sheets constituting the rotor core26are formed by punching a rolled elongated silicon steel sheet. It is well known that the rolling results in shift in the thickness in the rolling direction and in the direction perpendicular to the rolling direction. In the second embodiment, however, the blocks27obtained by turning the blocks4circumferentially by 180 degrees. Consequently, since the deviation in the thickness is absorbed, the thickness of the rotor core26can be rendered uniform.

The thicknesses of the four blocks3and27are equal to one another in the second embodiment. However, the total thickness of the blocks having the respective center lines Lb may be equal to the total thickness of the blocks having the respective center lines Lc.

FIGS. 9 to 11illustrate a third embodiment of the invention. Describing the difference of the third embodiment from the first embodiment, the rotor core28employed instead of the rotor core2is divided into four blocks29,30and31. Each block29has a thickness set to be equal to or less than one half of that of each of blocks30and31. The thickness of each block29is set at one half of that of each of the blocks30and31in the embodiment. The block30is formed by stacking the same silicon steel sheets as those of each block4(seeFIG. 1B). The block31is formed by stacking the same silicon steel sheets as those of each block3(seeFIG. 1A). The block30has a thickness equal to one of the block31and larger than the blocks3and4. The rotor core28has a thickness equal to that of the rotor core2.

Each block29or the silicon steel sheets composing each block29will be described with reference toFIG. 11. Each block29has a number of pairs of generally rectangular magnet insertion holes32which are formed in an outer circumferential portion thereof and are similar to the insertion holes5. The permanent magnets33are inserted into the paired magnet insertion holes32respectively and fixed by an adhesive agent, filler or the like. The outer circumferential portion of each block29also has cavities34which are formed between the permanent magnets33of each pair and are similar to the cavities7.

Each block29includes each portion thereof corresponding to the paired magnet insertion holes32, permanent magnets33and cavity34and serving as the magnetic concave portion35(q axis) where a flux is difficult to pass. Each block29further includes each portion thereof located between the magnetic concave portion35and serving as a magnetic convex portion36(d axis) where a flux is easy to pass. The magnetic concave and convex portions35and36are formed alternately with a predetermined angle therebetween. Each block29further has two keys10and11which are formed on the inner circumference thereof so as to be 180-degree apart from each other and so as to extend axially.

The center line Lo passing the centers of the keys10and11also passes the magnetic convex portions36in each block29. The center line Lo forms a predetermined angle θ with a center line Ld passing the center of the magnetic concave portion35adjacent to the center line Lo. The angle θ is represented as 180/n when n is the number of poles of the rotor1. Thus, the silicon steel sheets constituting each block29are similar to those employed in the conventional rotor core as shown inFIG. 17.

In the above-described construction, the center lines Lb and Lc of the blocks31and30have linear loci which are zigzagged. Accordingly, the rotor can achieve the effects similar to those of skew in the rotors for squirrel-cage induction motors as in the first embodiment. In particular, the center lines Ld of the blocks29located at both ends of the rotor core28have loci are located between the loci of the center lines Lc and Lb. Accordingly, since the mechanical balance can be improved between the rotor core28and the stator winding, the waveform characteristic of the back electromotive force can be improved in the stator winding.

FIGS. 12 and 13illustrate a fourth embodiment of the invention. The difference of the fourth embodiment from the first embodiment will be described. The rotor core39employed instead of the rotor core2includes a block40formed by integrating the blocks3and a block41formed by integrating the blocks4.

In the foregoing construction, the loci of the center lines Lb and Lc of the respective blocks40and41are as shown inFIG. 13. Accordingly, the fourth embodiment can achieve the same effects as those of the first embodiment.

FIGS. 14 and 15illustrate a fifth embodiment of the invention. The difference of the fifth embodiment from the fourth embodiment will be described. The rotor core42employed in the fifth embodiment includes blocks43and44. One half44aof the block44is formed by stacking the silicon steel sheets (seeFIG. 1B) which are the same as those of the block41. The other half44bof the block44is formed by stacking the silicon steel sheets (seeFIG. 8) which are the same as those of the block27. Furthermore, one half43aof the block43is formed by stacking the silicon steel sheets (FIG. 1A) which are the same as those of the block40. The other half43bis formed by turning circumferentially by 180 degrees and stacking the silicon steel sheets which are the same as those of the block40or more specifically, by turning the portion43acircumferentially by 180 degrees. The other construction of the rotor of the fifth embodiment is the same as that of the first embodiment. Consequently, the fifth embodiment can achieve the same effects as those of the fourth and second embodiments.

The portions43aand43band the portions44aand44bconstituting the respective blocks43and44are set at one halves of the thicknesses of the blocks43and44respectively in the fifth embodiment. However, these portions may be set substantially at one halves respectively.

The permanent magnets are provided on the rotor core in each of the foregoing embodiments. However, the permanent magnets may or may not be provided on the rotor core. Further, the generally triangular cavities are formed in the rotor core so as to compose the concave and convex portions in each of the foregoing embodiments. However, the cavities may be circular, elliptic, rectangular or rhombic. Additionally, the rotor core may have mechanical concave and convex portions formed therein so that the magnetic concave and convex portions are formed.

The number of poles of the rotor should not be limited to eight. The same effect can be achieved even when the number of poles is any other number. Furthermore, the number of slots of the stator may be set at any suitable number. Additionally, the number of blocks of the rotor should not be limited to two and four. Five or more blocks may be provided by stacking the silicon steel sheets having the magnetic concave and convex portions shifted. In this case, an amount of shift of the center line is required to be ±0.

The foregoing description and drawings are merely illustrative of the principles of the present invention and are not to be construed in a limiting sense. Various changes and modifications will become apparent to those of ordinary skill in the art. All such changes and modifications are seen to fall within the scope of the invention as defined by the appended claims.