Hybrid excitation rotating electrical machine

A hybrid excitation rotating electrical machine configured with a rotor having a shaft extended on at least one side in an axial direction, and first and second cores that are separated in the axial direction with a gap between the cores. First magnetic poles that are excited by a permanent magnet and second magnetic poles that are not excited by the permanent magnet are alternately arranged in a circumferential direction in each of the first and second cores. The first magnetic poles of the first core have a different polarity from that of the first magnetic poles of the second core, and the first magnetic poles of one of the first and second cores are placed so as to face the second magnetic poles of the other of the first and second cores in the axial direction with the gap between the magnetic poles.

TECHNICAL FIELD

The present invention relates to hybrid excitation rotating electrical machines, and more particularly to hybrid excitation rotating electrical machines using both a permanent magnet and an electromagnet as an exciting circuit.

BACKGROUND ART

Conventionally, hybrid excitation rotating electrical machines including a permanent magnet and an electromagnet are known in the art (see, e.g., Patent Documents 1 and 2). Such a rotating electrical machine includes a rotor and a stator placed radially outward of the rotor to generate a rotating magnetic field rotating the rotor. The stator has a stator core and a stator coil. The rotor has a shaft extending in the axial direction, and first and second cores separated in the axial direction. Each of the first and second cores has permanent magnet excitation magnetic poles that are excited by a permanent magnet, and non-excited permanent magnet non-excitation magnetic poles that are not excited by the permanent magnet, and the permanent magnet excitation magnetic poles and the permanent magnet non-excitation magnetic poles are alternately arranged in the circumferential direction in the radial end of each of the first and second cores. The permanent magnet excitation magnetic poles in the first core and the permanent magnet excitation magnetic poles in the second core have polarities that are inverted with respect to each other. The permanent magnet excitation magnetic poles in the first core are placed so as to face the permanent magnet non-excitation magnetic poles in the second core in the axial direction, and the permanent magnet non-excitation magnetic poles in the first core are placed so as to face the permanent magnet excitation magnetic poles in the second core in the axial direction.

The amount of magnetic flux of the permanent magnet is substantially constant. The rotating electrical machine further includes an exciting coil that excites the permanent magnet non-excitation magnetic poles. When current is applied from the outside to the exciting coil, the exciting coil excites the permanent magnet non-excitation magnetic poles to generate magnetic flux that weakens or strengthen the magnetic flux generated by the permanent magnet. Thus, according to the above rotating electrical machine, the rotor can be appropriately rotated by combined magnetic flux of the magnetic flux of the permanent magnet and the magnetic flux of the electromagnet.

PRIOR ART DOCUMENTS

Patent Documents

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

In the rotating electrical machine of Patent Document 1, the exciting coil is placed in a gap formed in the axial direction between the first core and the second core that are separated in the axial direction. In this case, when current is applied to the exciting coil, magnetic flux flows to the shaft on the radially inner side of the exciting coil. In the rotating electrical machine of Patent Document 2, the exciting coil is placed on the outer side in the radial direction between the first core and the second core that are separated in the axial direction. In this case, when current is applied to the exciting coil, magnetic flux flows to the shaft or the first and second cores on the radially inner side of the exciting coil. In the structures of these rotating electrical machines, iron loss that is caused when the magnetic flux is generated by the exciting coil is increased. Thus, the size of the device itself is increased in order to generate large torque.

The present invention was developed in view of the above problems, and it is an object of the present invention to provide a hybrid excitation rotating electrical machine capable of suppressing iron loss that is caused when magnetic flux is generated by an exciting coil exciting magnetic poles that are not excited by a permanent magnet.

Means for Solving the Problem

The above object is achieved by a hybrid excitation rotating electrical machine including: a rotor having a shaft extended on at least one side in an axial direction, and first and second cores that are separated in the axial direction with a gap therebetween, wherein first magnetic poles that are excited by a permanent magnet and second magnetic poles that are not excited by the permanent magnet are alternately arranged in a circumferential direction in each of the first and second cores, the first magnetic poles of the first core have a different polarity from that of the first magnetic poles of the second core, and the first magnetic poles of one of the first and second cores are placed so as to face the second magnetic poles of the other of the first and second cores in the axial direction with the gap therebetween, the hybrid excitation rotating electrical machine further including: a stator that is placed radially outward of the rotor, and that generates a rotating magnetic field rotating the rotor; an exciting coil that is placed in the gap, and that excites the second magnetic poles; and a third core that is placed radially inward of the first core, the second core, and the exciting coil, and that is made of a material having smaller iron loss than the shaft.

Effects of the Invention

According to the present invention, iron loss can be suppressed which is caused when magnetic flux is generated by an exciting coil exciting magnetic poles that are not excited by a permanent magnet.

MODES FOR CARRYING OUT THE INVENTION

A specific embodiment of a hybrid excitation rotating electrical machine according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1is a perspective view showing the structure of a hybrid excitation rotating electrical machine10according to an embodiment of the present invention. The hybrid excitation rotating electrical machine10is shown partially cutaway inFIG. 1.FIG. 2is a sectional view of the hybrid excitation rotating electrical machine10of the present embodiment taken along a plane including an axis line.FIG. 3is a sectional view of the hybrid excitation rotating electrical machine10of the present embodiment taken along line III-III inFIG. 2.FIG. 4is a sectional view of the hybrid excitation rotating electrical machine10of the present embodiment taken along line IV-IV inFIG. 2.FIG. 5shows sectional views showing the shapes of a rotor core of the hybrid excitation rotating electrical machine10of the present embodiment.FIG. 6is an exploded perspective view of the hybrid excitation rotating electrical machine10of the present embodiment.

In the present embodiment, the hybrid excitation rotating electrical machine10includes a rotor12that is rotatable about an axis, and a stator14that generates a rotating magnetic field rotating the rotor12. The rotor12is rotatably supported by a case20via bearings16,18at both axial ends. The stator14is placed radially outward of the rotor12, and is fixed to the case20. The rotor12and the stator14face each other in the radial direction with an air gap22of a predetermined length therebetween.

The stator14has a stator core24and a stator coil28. The stator core24is formed in a hollow cylindrical shape. A stator tooth26is formed on the inner peripheral surface of the stator core24. The stator tooth26protrudes inward in the radial direction of the stator core24, namely toward the axis. A plurality (e.g.,18) of the stator teeth26are provided in the circumferential direction on the inner peripheral surface of the stator core24, and are arranged at regular intervals along the circumferential direction. The stator coil28is wound around each stator tooth26. A plurality (e.g.,18) of the stator coils28are provided in the circumferential direction on the inner peripheral surface of the stator core24, and are arranged at regular intervals along the circumferential direction. In the case where the hybrid excitation rotating electrical machine10is applied to, e.g., a three-phase alternating current (AC) motor, each stator coil28forms one of a U-phase coil, a V-phase coil, and a W-phase coil.

The stator core24is divided in the axial direction, and has a first stator core30, a second stator core32, and a third stator core34. The first to third stator cores30to34are formed in a hollow cylindrical shape, and are arranged in the axial direction. The first to third stator cores30to34have substantially the same inner diameter. The first and third stator cores30,34are placed at both axial ends. The second stator core32is placed in the center in the axial direction. The second stator core32is interposed between the first stator core30and the third stator core34in the axial direction, and is bonded and fixed to the end faces of the first and third stator cores30,34which are located closer to the center in the axial direction.

Each of the first and third stator cores30,34is formed by stacking a plurality of insulation coated electromagnetic steel plates in the axial direction. The second stator core32is made of a soft magnetic material, specifically a material produced by compression molding insulation coated soft magnetic material powder. The magnetic resistance in the axial direction of the second stator core32is lower than that in the axial direction of the first and third stator cores30,34.

A cylindrical yoke36that supports the first to third stator cores30to34is provided radially outward of the stator core24. Like the second stator core32, the yoke36is made of a material produced by compression molding insulation coated soft magnetic material powder. The magnetic resistance in the axial direction of the yoke36is lower than that in the axial direction of the first and third stator cores30,34. The yoke36may be integral with the second stator core32. The yoke36is bonded and fixed to the radially outer surfaces of the first stator core30and the third stator core34. The first stator core30and the third stator core34are magnetically coupled together by the yoke36. The stator teeth26are provided in each of the first to third stator cores30to34, and the stator teeth26of each of the first to third stator cores30to34are provided so as to be arranged next to each other in the axial direction. Each stator coil28is formed so as to extend through the first to third stator cores30to34in the axial direction.

The stator core24has an attachment portion38that protrudes to the radially outer side and that attaches and fixes the stator14to the case20. The attachment portion38is formed by a plurality of electromagnetic steel plates that are stacked in the axial direction. The attachment portion38has an attachment portion38aformed integrally with the first stator core30, an attachment portion38bformed integrally with the third stator core34, and an attachment portion38cinterposed between the attachment portions38a,38b. The attachment portion38cis placed radially outward of the second stator core32. The attachment portion38cmay be formed integrally with the second stator core32instead of being formed by the plurality of electromagnetic steel plates that are stacked in the axial direction. A plurality (e.g., 3) of the attachment portions38are provided in the circumferential direction. A through hole40is provided in each attachment portion38so as to extend therethrough in the axial direction. The stator14is fixed to the case20by tightening into the case20bolts42extending through the through holes40of the attachment portions38.

The rotor12is placed radially inward of the stator14. The rotor12has a shaft50and a rotor core52. The shaft50extends in the axial direction, and extends beyond the axial ends of the stator14at its both axial ends. The shaft50need only be formed so that at least one axial end of the shaft50extends beyond the axial end of the stator14. The shaft50is made of a material having predetermined iron loss, specifically carbon steel such as S45C. The rotor core52has a radially outer rotor core54that is placed radially outward of the shaft50so as to be supported by the shaft50. The radially outer rotor core54is formed in a hollow cylindrical shape, and is fixed to the radially outer surface of the shaft50.

The radially outer rotor core54is divided in the axial direction, and has a first radially outer rotor core56and a second radially outer rotor core58. The first and second radially outer rotor cores56,58are formed in a hollow cylindrical shape, and are placed radially outward of the shaft50so as to be supported by the shaft50. Each of the first and second radially outer rotor cores56,58is formed by a plurality of insulation coated electromagnetic steel plates that are stacked in the axial direction. The first radially outer rotor core56and the second radially outer rotor core58are separated from each other in the axial direction with an annular gap60therebetween.

The radially outer surface of the first radially outer rotor core56faces the radially inner surface of the first stator core30in the radial direction. That is, the radially outer surface of the first radially outer rotor core56and the radially inner surface of the first stator core30face each other in the radial direction. The radially outer surface of the second radially outer rotor core58faces the radially inner surface of the third stator core34in the radial direction. That is, the radially outer surface of the second radially outer rotor core58and the radially inner surface of the third stator core34face each other in the radial direction. The gap60faces the radially inner surface of the second stator core32, and is provided radially inward of the second stator core32.

A rotor tooth62is formed in the outer periphery of the first radially outer rotor core56. The rotor tooth62protrudes outward in the radial direction of the first radially outer rotor core56. A plurality (e.g., 6) of the rotor teeth62are provided in the circumferential direction on the outer peripheral surface of the first radially outer rotor core56, and are arranged at regular intervals along the circumferential direction.

A permanent magnet64is attached between the rotor teeth62adjoining each other in the circumferential direction, so as to adjoin the rotor teeth62. The permanent magnet64is placed radially outward of the first radially outer rotor core56. The permanent magnet64is, e.g., a ferrite magnet. A plurality (e.g., 6) of the permanent magnets64are provided in the circumferential direction, and are provided at regular intervals along the circumferential direction. Each permanent magnet64has a predetermined width (angle) in the circumferential direction, and has a predetermined radial thickness. Each permanent magnet64is magnetized with a predetermined polarity (e.g., the radially outer side is N pole and the radially inner side is S pole).

The radially outer end face of the permanent magnet64and the radially outer end face of the rotor tooth62are formed at substantially the same distance from the axis. The first radially outer rotor core56has permanent magnet excitation magnetic poles that are excited by the permanent magnets64, and non-excited permanent magnet non-excitation magnetic poles that are not excited by the permanent magnets64. The permanent magnet non-excitation magnetic poles are formed in the rotor teeth62. The permanent magnet excitation magnetic poles and the permanent magnet non-excitation magnetic poles are alternately arranged in the circumferential direction. The first radially outer rotor core56has a magnetic pole of a different polarity at every predetermined angle, and has a predetermined number (e.g., 12) of magnetic poles in the circumferential direction by the permanent magnet excitation magnetic poles and the permanent magnet non-excitation magnetic poles.

A rotor tooth66is formed in the outer periphery of the second radially outer rotor core58. The rotor tooth66protrudes outward in the radial direction of the second radially outer rotor core58. A plurality (e.g., 6) of the rotor teeth66are provided in the circumferential direction on the outer peripheral surface of the second radially outer rotor core58, and are arranged at regular intervals along the circumferential direction.

A permanent magnet68is attached between the rotor teeth66adjoining each other in the circumferential direction, so as to adjoin the rotor teeth66. The permanent magnet68is placed radially outward of the second radially outer rotor core58. The permanent magnet68is, e.g., a ferrite magnet. A plurality (e.g., 6) of the permanent magnets68are provided in the circumferential direction, and are provided at regular intervals along the circumferential direction. Each permanent magnet68has a predetermined width (angle) in the circumferential direction, and has a predetermined radial thickness. Each permanent magnet68is magnetized with a predetermined polarity different from that of the permanent magnet64(e.g., the radially outer side is S pole and the radially inner side is N pole). That is, the permanent magnet68and the permanent magnet64have polarities that are inverted with respect to each other.

The radially outer end face of the permanent magnet68and the radially outer end face of the rotor tooth66are formed at substantially the same distance from the axis. The second radially outer rotor core58has permanent magnet excitation magnetic poles that are excited by the permanent magnets68, and non-excited permanent magnet non-excitation magnetic poles that are not excited by the permanent magnets68. The permanent magnet non-excitation magnetic poles are formed in the rotor teeth66. The permanent magnet excitation magnetic poles and the permanent magnet non-excitation magnetic poles are alternately arranged in the circumferential direction. The second radially outer rotor core58has a magnetic pole of a different polarity at every predetermined angle, and has the same predetermined number (e.g., 12) of magnetic poles as the first radially outer rotor core56in the circumferential direction by the permanent magnet excitation magnetic poles and the permanent magnet non-excitation magnetic poles.

The permanent magnet excitation magnetic poles of the first radially outer rotor core56are arranged so as to face the permanent magnet non-excitation magnetic poles of the second radially outer rotor core58in the axial direction with the gap60therebetween. That is, the permanent magnets64of the first radially outer rotor core56are arranged so as to face the rotor teeth66of the second radially outer rotor core58in the axial direction with the gap60therebetween. The permanent magnet non-excitation magnetic poles of the first radially outer rotor core56are arranged so as to face the permanent magnet excitation magnetic poles of the second radially outer rotor core58in the axial direction with the gap60therebetween. That is, the rotor teeth62of the first radially outer rotor core56are arranged so as to face the permanent magnets68of the second radially outer rotor core58in the axial direction with the gap60therebetween.

An exciting coil70that excites the permanent magnet non-excitation magnetic poles of the rotor teeth62,66is placed in the gap60, namely between the first radially outer rotor core56and the second radially outer rotor core58in the axial direction. The exciting coil70fills almost the entire region of the gap60. The exciting coil70is formed in an annular shape around the shaft50, and is wound in a toroidal form. The exciting coil70is placed radially outward of the shaft50, is placed radially inward of the second stator core32, and faces the second stator core32in the radial direction. The exciting coil70is attached and fixed to the stator14(specifically, the stator core24thereof). A direct current (DC exciting current) is supplied to the exciting coil70. When the direct current is supplied to the exciting coil70, magnetic flux (DC exciting magnetic flux) is generated which extends through the radially inner side (the axis side) of the exciting coil70in the axial direction. The magnetic flux is generated in an amount corresponding to the direct current supplied to the exciting coil70.

Fixing of the exciting coil70to the stator14may be implemented by direct bonding of the exciting coil70and the stator14. Fixing of the exciting coil70to the stator14may be implemented by providing in the circumferential direction a plurality of U-shaped holding members (clips)71that hold the annular exciting coil70from the radially inner side, and inserting and hanging pawl portions on both sides of each holding member71in holes that are formed in the radially inner surface of the second stator core32or holes that are formed in the opposing axial end faces of the first and third stator cores30,34of the stator core24.FIG. 6shows the state where the exciting coil70is fixed to the stator14by the plurality of holding members71provided in the circumferential direction.

The shaft50is formed in a hollow shape. The shaft50has a large diameter cylindrical portion72having a relatively large diameter, and small diameter cylindrical portions74,76having a relatively small diameter. The small diameter cylindrical portions74,76are provided at both axial ends. The small diameter cylindrical portions74,76of the shaft50are supported by the case20via the bearings16,18. The large diameter cylindrical portion72is provided in the center in the axial direction, and is interposed between the small diameter cylindrical portions74,76at both axial ends. The first and second radially outer rotor cores56,58are placed radially outward of the large diameter cylindrical portion72so as to be supported by the large diameter cylindrical portion72, and are fixed to the radially outer surface of the large diameter cylindrical portion72.

The rotor core52has a radially inner rotor core80that is placed radially inward of the shaft50so as to be supported by the shaft50. The radially inner rotor core80is placed radially inward of the first radially outer rotor core56and the second radially outer rotor core58of the rotor core52and the exciting coil70. A hollow space82is formed in the large diameter cylindrical portion72of the shaft50. The radially inner rotor core80is accommodated in the hollow space82of the large diameter cylindrical portion72, and is bonded and fixed to the radially inner surface of the large diameter cylindrical portion72. The radially inner rotor core80is made of a material produced by compression molding a soft magnetic material, specifically insulation coated soft magnetic material powder. The radially inner rotor core80is made of a material having smaller iron loss than the shaft50.

The radially inner rotor core80is divided in the circumferential direction, and is formed by a plurality (e.g., 6) of rotor core pieces84each formed in a sector shape as viewed in the axial direction. The division of the radially inner rotor core80in the circumferential direction is performed at regular intervals (equal angles) in the circumferential direction, and the rotor core pieces84have the same shape. The number of pieces into which the radially inner rotor core80is divided in the circumferential direction, namely the number of rotor core pieces84, is the number of poles of the first and second radially outer rotor cores56,58in the radially outer rotor core54, or a divisor of the number of poles. For example, in the case where the number of poles is “12,” the radially inner rotor core80is divided into “2,” “3,” “4,” “6,” or “12” pieces (inFIGS. 3 and 4, the radially inner rotor core80is divided into “6” pieces).

The division of the radially inner rotor core80in the circumferential direction is performed along the lines extending through the axis of the rotor12and the shaft50and the circumferential centers of at least two of the permanent magnets64,68and the rotor teeth62,66(that is, the permanent magnet excitation magnetic poles and the permanent magnet non-excitation magnetic poles) which are alternately arranged in the circumferential direction in the first and second radially outer rotor cores56,58of the rotor12. That is, each plane including the plane that divides the radially inner rotor core80in the circumferential direction extends through the axis of the rotor12and the shaft50and through the circumferential center of any of the permanent magnets64,68and the rotor teeth62,66(that is, the permanent magnet excitation magnetic poles and the permanent magnet non-excitation magnetic poles).

The radially inner rotor core80has notch holes86,88extending in the axial direction in its axial ends. The notch holes86,88are provided at both axial ends. Each of the notch holes86,88is formed in a tapered shape as shown inFIG. 5Aor in a stair-like shape as shown inFIG. 5Bso that its diameter decreases from the axial end face toward the axial center. The diameter at the axial end (the shallowest portion) of the notch hole86,88substantially matches the inner diameter of the large diameter cylindrical portion72of the shaft50, and the diameter in the axial central portion (the deepest portion) of the notch hole86,88is a predetermined diameter. The radially inner rotor core80has a predetermined radial thickness in the axial central portion, and has a smaller radial thickness at both axial ends than in the axial central portion. The radial thickness of the large diameter cylindrical portion72of the shaft50is set so as to maintain the strength required to transfer motor torque, and the radial thickness of the axial central portion of the radially inner rotor core80is set to the predetermined thickness that does not allow the magnetic flux generated by the exciting coil70to be saturated. Thus, the radial thickness of the axial central portion of the radially inner rotor core80is larger than that of the large diameter cylindrical portion72of the shaft50.

The notch hole86and the notch hole88communicate with each other in the center in the axial direction, and are connected together at their deepest portions through a through hole89extending through the rotor core80in the axial direction. That is, the radially inner rotor core80is formed in a hollow shape so as to have the through hole89. All of the notch holes86,88and the through hole89of the radially inner rotor core80are provided on the axis line of the shaft50. The through hole89of the radially inner rotor core80has substantially the same diameter as the deepest portions of the notch holes86,88.

The rotor12is divided into two portions in the axial direction. The shaft50is divided into two portions in the axial direction, and is formed by two cup-shaped members90,92that are fitted together. The shaft50is divided in the axial direction substantially along the center in the axial direction. The cup-shaped member90has the small diameter cylindrical portion74and a part of the large diameter cylindrical portion72(specifically, a half connected to the small diameter cylindrical portion74). The cup-shaped member92has the small diameter cylindrical portion76and a part of the large diameter cylindrical portion72(specifically, a half connected to the small diameter cylindrical portion76). The shaft50is formed by fitting the cup-shaped member90and the cup-shaped member92together. The first radially outer rotor core56is supported by the cup-shaped member90, and the second radially outer rotor core58is supported by the cup-shaped member92. The first radially outer rotor core56is fixed to the radially outer surface of the cup-shaped member90, and the second radially outer rotor core58is fixed to the radially outer surface of the cup-shaped member92.

Bolt holes94,96extending in the axial direction on the axis are formed in the cup-shaped members90,92, respectively. The bolt holes94,96have substantially the same diameter as the through hole89of the radially inner rotor core80. A bolt98is inserted in the bolt holes94,96of the cup-shaped members90,92and the through hole89of the radially inner rotor core80. The cup-shaped member90and the cup-shaped member92are fitted together, and are fastened together by the bolt98.

The radially inner rotor core80may be divided into two portions in the axial direction. In this case, the radially inner rotor core80may be divided in the axial direction at a position corresponding to the position where the shaft50is divided in the axial direction, or substantially along the center in the axial direction. One of the divided two portions of the radially inner rotor core80is bonded and fixed to the radially inner surface of the cup-shaped member90of the shaft50, and the other divided portion of the radially inner rotor core80is bonded and fixed to the radially inner surface of the cup-shaped member92.

If a direct current is supplied to the annular exciting coil70in the above structure of the hybrid excitation rotating electrical machine10, magnetic flux is generated which extends through the radially inner side (the axis side) of the exciting coil70in the axial direction. The magnetic flux generated by the electromagnet using the exciting coil70flows through the permanent magnet non-excitation magnetic poles of the first or second radially outer rotor core56,58, the radially inner rotor core80, the permanent magnet non-excitation magnetic poles of the second or first radially outer rotor core58,56, the air gap22, the stator core24, the air gap22, and the permanent magnet non-excitation magnetic poles of the first or second radially outer rotor core56,58in this order. If such magnetic flux is generated, the permanent magnet non-excitation magnetic poles of the first and second radially outer rotor cores56,58are excited. The magnetic flux thus generated by the electromagnet weakens or strengthens the magnetic flux generated by the permanent magnets46,68. The amount of magnetic flux generated by the electromagnet is adjusted according to the magnitude of the direct current that is applied to the exciting coil70.

Thus, according to the present embodiment, torque that rotates the rotor12about the stator14can be adjusted by the combined magnetic flux of the magnetic flux generated by the permanent magnets64,68and the magnetic flux generated by the electromagnet using the exciting coil70, whereby the rotor12can be appropriately rotated.

In the structure of the hybrid excitation rotating electrical machine10of the present embodiment, the magnetic flux that is generated by excitation of the exciting coil70flows through the radially inner rotor core80placed radially inward of the shaft50, on the radially inner side (the axis side) of the radially outer rotor core54(specifically, the first and second radially outer rotor cores56,58) and the exciting coil70that are placed radially outward of the shaft50. Unlike the structure in which the radially inner rotor core80is not provided radially inward of the shaft50, this structure suppress flowing of the magnetic flux, which flows in the axial direction on the radially inner side of the exciting coil70by excitation of the exciting coil70, in the shaft50itself (specifically, the large diameter cylindrical portion72etc.).

Since the radially inner rotor core80is made of a material having smaller iron loss than the shaft50, iron loss of the radially inner rotor core80is smaller than that of the shaft50. Thus, the structure of the hybrid excitation rotating electrical machine10of the present embodiment can suppress iron loss that is caused when the magnetic flux is generated by the exciting coil70. Accordingly, torque that rotates the rotor12can be efficiently generated, and a torque increase upon rotating the rotor12can be implemented. This can suppress an increase in size of the device itself in order to generate large torque.

In the structure of the hybrid excitation rotating electrical machine10of the present embodiment, the radially inner rotor core80having smaller iron loss than the shaft50is made of a soft magnetic material (specifically, compressed soft magnetic material powder). This radially inner rotor core80is placed radially inward of the shaft50, and is bonded and fixed to the radially inner surface of the large diameter cylindrical portion72of the shaft50. In this structure, the radially inner rotor core80is not interposed in a portion where large load (torque, centrifugal force, axial force, etc.) is generated. Specifically, the radially inner rotor core80is present outside a torque transfer path in the rotor12. This can prevent breakage of the radially inner rotor core80due to torque transfer. The radially inner rotor core80is present radially inward of the shaft50. Thus, the radially inner rotor core80is less susceptible to centrifugal force as compared to the structure in which the radially inner rotor core80is disposed radially outward of the rotor12. This can prevent breakage or scattering of the radially inner rotor core80due to the centrifugal force.

The radially inner rotor core80is divided in the circumferential direction. Thus, the radially inner rotor core80is less susceptible to centrifugal force as compared to the structure in which the radially inner rotor core80is integrated along the entire circumference. This can prevent breakage or scattering of the radially inner rotor core80due to the centrifugal force.

The radially inner rotor core80is divided at regular intervals in the circumferential direction, and the number of pieces into which the radially inner rotor core80is divided in the circumferential direction is the number of poles of the first and second radially outer rotor cores56,58in the radially outer rotor core54, or a divisor of the number of poles. The division of the radially inner rotor core80in the circumferential direction is performed along the lines extending through the axis of the rotor12and the shaft50and the circumferential centers of at least two of the permanent magnets64,68and the rotor teeth62,66(that is, the permanent magnet excitation magnetic poles and the permanent magnet non-excitation magnetic poles) which are alternately arranged in the circumferential direction in the first and second radially outer rotor cores56,58of the rotor12. In this structure, a gap is formed between the two rotor core pieces84adjoining each other in the circumferential direction of the radially inner rotor core80, but a magnetic path that is desirable to rotate the rotor12can be maintained without blocking the path of the magnetic flux that is generated by the permanent magnets64,68and the path of the magnetic flux that is generated by the electromagnet using the exciting coil70.

The magnetic flux that flows radially inward of the exciting coil70by excitation of the exciting coil70flows through the first or second radially outer rotor core56,58of the radially outer rotor core54, the radially inner rotor core80, the second or first radially outer rotor core58,56, the air gap22, the stator core24, the air gap22, and the first or second radially outer rotor core56,58. At this time, the axial ends of the radially inner rotor core80which face the first and second radially outer rotor cores56,58in the radial direction have high magnetic flux density in a radially outer portion, and have low magnetic flux in a radially inner portion (in a portion near the axis).

In the present embodiment, the radially inner rotor core80has the notch holes86,88extending in the axial direction in its axial ends. This can eliminate an unnecessary portion of the radially inner rotor core80which does not perform the function of the radially inner rotor core80. Thus, as compared to the structure in which the notch holes86,88are not present, the weight of the inner-side rotor core80can be reduced while minimizing the influence on the flow of the magnetic flux, and the cost can be reduced.

In the present embodiment, the rotor core52is divided in the axial direction, and the shaft50is divided in the axial direction. In this structure, after manufacturing the stator14including the exciting coil70that protrudes from the radially inner surface of the stator core24toward the axis, the rotor12can be attached from both sides of the stator14so that the stator14is interposed between the divided portions of the rotor core52and the divided portions of the shaft50. This facilitates assembly of the hybrid excitation rotating electrical machine10.

FIGS. 7 and 8are diagrams illustrating a phenomenon that can occur in the structure of such a hybrid excitation rotating electrical machine10as in the present embodiment.FIG. 7Ais a perspective view of the shaft50of the rotor12, andFIG. 7Bis a sectional view of the shaft50and its surrounding portion, taken along line A-A inFIG. 7A.FIG. 8Ais a diagram showing how magnetic flux flows in the shaft50and the radially inner rotor core80after an exciting current to the exciting coil70is decreased suddenly.FIG. 8Bis a diagram showing how an eddy current is generated in the shaft50after the exciting current to the exciting coil70is decreased suddenly.FIG. 9shows diagrams showing a portion in which an eddy current generated in the shaft50flows.FIG. 9Ais a side view of the shaft50and its surrounding portion, andFIG. 9Bis a sectional view of the shaft and its surrounding portion, taken along line B-B inFIG. 9A.

In the present embodiment, as described above, the exciting coil70that excites the permanent magnet non-excitation magnetic poles of the rotor teeth62,66is placed between the first radially outer rotor core56and the second radially outer core58of the radially outer rotor core54in the axial direction, and this exciting coil70is formed in an annular shape around the shaft50. The radially inner rotor core80, which is made of a material produced by compression molding insulation coated soft magnetic material powder, is placed radially inward of the shaft50formed in a hollow shape. The radially outer rotor core54, which is formed by stacking a plurality of insulation coated electromagnetic steel plates in the axial direction, is placed radially outward of the shaft50. The radially inner rotor core80is made of a material having smaller iron loss than the shaft50.

In the above structure, if a DC exciting current is supplied to the exciting coil70, DC exciting magnetic flux is generated which extends through the radially inner side (the axis side) of the exciting coil70in the axial direction, and this DC exciting magnetic flux flows through the shaft50. Since the DC exciting current that is supplied to the exciting coil70is controlled to a predetermined magnitude by switching, it includes a harmonic component. Accordingly, as the DC exciting magnetic flux that is generated around the exciting coil70fluctuates according to a change in DC exciting current, an eddy current may be generated in a part of the magnetic path which has small electrical resistance (specifically, the shaft50) (seeFIG. 7). This may increase loss.

The region in which the eddy current may be generated in this case is a region near a part of the shaft50which is sandwiched in the axial direction between the first radially outer rotor core56and the second radially outer rotor core58of the radially outer rotor core54(specifically, a part where the cup-shaped member90and the cup-shaped member92as the two parts into which the shaft50is divided in the axial direction are fitted together) (a shaded region S1surrounded by broken line inFIG. 9A), regions near those parts of the shaft50which are located radially inward of and face the axial ends of the first and second radially outer rotor cores56,58(shaded regions S2surrounded by broken line inFIG. 9A), and/or a region near a part of the shaft50which is located radially inward of and faces the first and second radially outer rotor cores56,58and which is located on a line (centerline L between protruding poles shown inFIG. 9B) extending through the axis and the middle point between the rotor teeth62,66adjoining each other in the circumferential direction of the first and second radially outer rotor cores56,58(shaded regions S3surrounded by broken line inFIGS. 9A and 9B).

If the DC exciting current to the exciting coil70is reduced to zero in the situation where a counter electromotive voltage needs to be reduced instantly during DC excitation of the exciting coil70(e.g., in the event of failure due to an abnormal condition of the three-phase system), an eddy current is generated in the shaft50in the magnetic path, and the DC exciting magnetic flux generated around the exciting coil70may not immediately disappear and remain (seeFIG. 8), and therefore the counter electromotive voltage may not easily decrease.

The region in which the eddy current may flow in this case is especially the region near the part of the shaft50which is sandwiched in the axial direction between the first radially outer rotor core56and the second radially outer rotor core58of the radially outer rotor core54(specifically, the part where the cup-shaped member90and the cup-shaped member92as the two parts into which the shaft50is divided in the axial direction are fitted together) (the shaded region S1surrounded by broken line inFIG. 9A).

Such an eddy current flows in the circumferential direction of the shaft in the region near the part of the shaft50which is sandwiched in the axial direction between the first radially outer rotor core56and the second radially outer rotor core58of the radially outer rotor core54, flows in the circumferential direction of the shaft in the regions near those parts of the shaft50which are located radially inward of the first and second radially outer rotor cores56,58and face the axial ends of the first and second radially outer rotor cores56,58, and flows in the axial direction of the shaft in the region near the part of the shaft50which is located radially inward of and faces the first and second radially outer rotor cores56,58and which is located on the centerline L between protruding poles in the circumferential direction of the first and second radially outer rotor cores56,58.

FIG. 10shows diagrams showing the position of means for suppressing an eddy current that is generated in the shaft50in the hybrid excitation rotating electrical machine10of the present embodiment.FIG. 10Ais a perspective view of the shaft50, andFIG. 10Bis a sectional view of the shaft50and its surrounding portion.FIG. 11shows diagrams illustrating effects of the hybrid excitation rotating electrical machine10of the present embodiment.FIG. 11Ashows a change with time in a current that is supplied to the exciting coil70,FIG. 11Bshows a change with time in a counter electromotive voltage in a comparative example that is compared with the present embodiment, andFIG. 11Cis a change with time in a counter electromotive voltage in the present embodiment.

The hybrid excitation rotating electrical machine10of the present embodiment has eddy current suppressing means100for suppressing an eddy current that is generated in the shaft50as described above. That is, in the hybrid excitation rotating electrical machine10, the shaft50is provided with the eddy current suppressing means100for suppressing an eddy current.

The eddy current suppressing means100is placed in the region of the shaft50in which an eddy current may flow, specifically, in the region near the part of the shaft50which is sandwiched in the axial direction between the first radially outer rotor core56and the second radially outer rotor core58of the radially outer rotor core54(specifically, the part where the cup-shaped member90and the cup-shaped member92are fitted together) (the shaded region S1), the regions near those parts of the shaft50which are located radially inward of the first and second radially outer rotor cores56,58and face the axial ends of the first and second radially outer rotor cores56,58(the shaded regions S2), and/or the region near the part of the shaft50which is located radially inward of and faces the first and second radially outer rotor cores56,58and which is located on the centerline L between protruding poles extending through the axis and the middle point between the rotor teeth62,66adjoining each other in the circumferential direction of the first and second radially outer rotor cores56,58(the shaded regions S3).

For example, the eddy current suppressing means100is a slit102that is provided in the region near the part of the shaft50which is sandwiched in the axial direction between the first radially outer rotor core56and the second radially outer rotor core58of the radially outer rotor core54. As shown inFIG. 10, this slit102opens in the direction toward the axis from the surface of the region near the part of the shaft50which is sandwiched in the axial direction between the first radially outer rotor core56and the second radially outer rotor core58, and extends linearly in the axial direction. The slit102may be provided at one position in the circumferential direction of the shaft50, but is preferably provided at a plurality of positions in the circumferential direction of the shaft50.

With this slit102, the electrical resistance at the time a current flows in the circumferential direction of the shaft in the region near the part of the shaft50which is sandwiched in the axial direction between the first radially outer rotor core56and the second radially outer rotor core58is larger than in the case where the slit102is not provided. Accordingly, an eddy current flowing in the circumferential direction of the shaft is suppressed in the region near this part.

For example, the eddy current suppressing means100is a hole104that is provided in the regions near those parts of the shaft50which are located radially inward of the first and second radially outer rotor cores56,58and face the axial ends of the first and second radially outer rotor cores56,58. As shown inFIG. 10, the hole104is a void that extends in the direction toward the axis from the surfaces of the regions near those parts of the shaft50which are located radially inward of the first and second radially outer rotor cores56,58and faces the axial ends of the first and second radially outer rotor cores56,58.

The hole104may extend linearly in the axial direction of the shaft50. The hole104may be provided at one position in the circumferential direction of the shaft50for each of the axial ends of the first and second radially outer rotor cores56,58, but is preferably provided at a plurality of positions in the circumferential direction of the shaft50. In order to suppress an eddy current, the hole104is preferably provided in the region near the part of the shaft50which is located on the centerline L between protruding poles in the circumferential direction of the first and second radially outer rotor cores56,58.

With the hole104, the electrical resistance at the time a current flows in the circumferential direction of the shaft in the regions near those parts of the shaft50which are located radially inward of the first and second radially outer rotor cores56,58and face the axial ends of the first and second radially outer rotor cores56,58is larger than in the case where the hole104is not provided. Accordingly, an eddy current flowing in the circumferential direction of the shaft is suppressed in the regions near these parts.

Moreover, for example, the eddy current suppressing means100is a resin106that is provided in the region near the part of the shaft50which is located radially inward of and faces the first and second radially outer rotor cores56,58and which is located on the centerline L between protruding poles extending through the axis and the middle point between the rotor teeth62,66adjoining each other in the circumferential direction of the first and second radially outer rotor cores56,58. The resin106has higher electrical resistance than the body of the shaft50. As shown inFIG. 10, the resin106is embedded in the region near this part of the shaft50.

The resin106may extend linearly in the axial direction of the shaft50. The resin106may be provided at one position in the circumferential direction of the shaft50, but is preferably provided at a plurality of positions in the circumferential direction of the shaft50. The resin106may be provided for each centerline L between protruding poles.

With the resin106, the electrical resistance at the time a current flows in the axial direction of the shaft in the region near the part of the shaft50which is located radially inward of and faces the first and second radially outer rotor cores56,58and which is located on the centerline L between protruding poles in the circumferential direction of the first and second radially outer rotor cores56,58is larger than in the case where the resin106is not provided. Accordingly, an eddy current flowing in the axial direction of the shaft is suppressed in the region near this part.

As described above, according to the structure of the hybrid excitation rotating electrical machine10of the present embodiment, the slit102, the hole104, and/or the resin106as the eddy current suppressing means100is provided at the predetermined position on the shaft50. This can suppress an eddy current that is generated in the shaft50.

Accordingly, the present embodiment can reduce eddy current loss in the shaft50when the DC exciting magnetic flux fluctuates according to a change in DC exciting current including a harmonic component and supplied to the exciting coil70, and can improve efficiency of the rotating electrical machine10. Moreover, as compared to the configuration having no eddy current suppressing means100, the present embodiment can reduce the DC exciting magnetic flux remaining around the exciting coil70when the DC exciting current to the exciting coil70is suddenly decreased to zero etc. (time t=t1inFIG. 11), and thus can quickly reduce the counter electromotive voltage (seeFIG. 11).

In the above embodiment, the permanent magnet excitation magnetic poles that are excited by the permanent magnets64,68of the first and second radially outer rotor cores56,58correspond to the “first magnetic poles” described in the claims, the permanent magnet non-excitation magnetic poles that are not excited by the permanent magnets64,68correspond to the “second magnetic poles” described in the claims, the first and second radially outer rotor cores56,58correspond to the “first and second cores” described in the claims, and the radially inner rotor core80corresponds to the “third core” described in the claims.

In the above embodiment, the rotor12and the shaft50are divided in the axial direction. However, the present invention is not limited to this, and each of the rotor12and the shaft50may be an integral member. In this modification, the notch holes86,88extending in the axial direction need only be formed in both axial ends of the radially inner rotor core80. The radially inner rotor core80need not be formed in a hollow shape in order to insert the bolt98that fastens the cup-shaped member90and the cup-shaped member92of the shaft50together, and the notch holes86,88need not communicate with each other.

In the above embodiment, the radially inner rotor core80is fixed to the radially inner surface of the shaft50and rotates together with the rotor12. However, the radially inner rotor core80may be, e.g., a non-rotating member placed in the shaft50.

In the above embodiment, the slit102and the hole104which are formed at a predetermined position on the shaft50so as to extend from the surface of the shaft50toward the axis and the resin106that is embedded at a predetermined position on the shaft50are used as the eddy current suppressing means100for suppressing an eddy current that is generated in the shaft50. However, any of the slit, hole, and resin may be used at any position as long as the eddy current is suppressed, and anything other than the slit, hole, and resin may be used as long as it has higher electrical resistance than the body of the shaft50.

In order to suppress an eddy current that is generated in the shaft50, it is desirable to place the eddy current suppressing means100in all of the shaded regions S1, S2, S3shown inFIG. 9. However, the eddy current suppressing means100may be placed in any one or more of these regions.

This international application claims priority to Japanese Patent Application No. 2012-044851 filed on Feb. 29, 2012, and the disclosure of which is incorporated herein by reference in its entirety.

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