Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1998-10-13
2002-03-05
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S156210
Reexamination Certificate
active
06353275
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to motors for actuating air conditioners, industrial machines, electric vehicles, etc., and, more particularly, the invention relates to the structure of a motor having a rotor inside which permanent magnets are set so that reluctance torque as well as magnetic torque is utilized.
BACKGROUND OF THE INVENTION
A high efficiency motor which utilizes reluctance torque as well as magnetic torque by setting permanent magnets inside a rotor core, viz., so called “an interior permanent magnet motor” is already known.
FIG. 9
is a cross sectional view showing the rotor of such conventional motor. In
FIG. 9
, the rotor is shaped into a cylinder having substantially the same shaft as that of a stator (not illustrated) and is supported by a bearing (not illustrated) for rotating on a shaft
76
. The rotor has eight permanent magnet slits
73
inside a rotor
71
, and these slits are disposed, along the rotating direction of the rotor, at the intervals of substantially same spacing and are extended through the core along the direction of the shaft. To the slits
73
, an adhesive is applied, then plate shaped permanent magnets
72
are inserted, and the magnets
72
are stuck to the rotor core
71
. With this structure, the rotor has eight magnetic poles.
The rotor is disposed inside the stator leaving a narrow annular clearance, then it is rotated by the attracting and repulsing force of the magnetic poles of the rotor to the stator teeth which have rotating magnetic fields created by the electric current which runs through the windings of the stator.
In the above structure, the relation between the inductance “Ld” of a d-shaft direction which meets at right angles with the magnetic poles of the rotor and the inductance “Lq” of a q-shaft direction which runs through the border between adjacent rotor magnetic poles is expressed as Lq>Ld.
Generally, the relation between a motor torque “T” and the parameters of the number of rotor magnetic pole pairs “Pn”, an interlinkage flux “Ma”, a stator winding current “I”, an advanced phase angle (electrical angle) “b” of the current “I” to the induced voltage generated in each phase stator winding by the winding current “I” is expressed as,
T=Pn{Ma·I·cos(b)+0.5(Lq−Ld)I
2
·sin(2b)}
In the above equation, the first term represents a magnetic torque and the second term represents a reluctance torque. In the above described structure, Lq>Ld, so that by controlling to advance the phase of the winding current “I” to the phase of the induced voltage generated in each phase winding, thereby “b” becomes positive, then the reluctance torque is generated. By setting “b” at a predetermined value, the torque “T” can be made larger comparing that of only magnetic torque with the same electric current.
In the above described conventional structure, the rotor has the permanent magnet slits
73
in the rotor core
71
, then the adhesive is applied to the walls of the slits
73
, then the permanent magnets
72
are stuck inside the slits
73
. Then, if the clearances between the slits
73
and the magnets
72
are large, the positions of the magnets
72
become unstable, then the magnetic flux disperses and the characteristic of the motor is deteriorated.
In addition, the big clearances cause the use of thick layers of the adhesive, whereby the effective magnetic flux decreases, which results in a decrease in the torque. Namely, if there are thick adhesive layers between the outer rotor rim
75
and the magnets
72
, the magnetic resistance increases between them, so that the magnetic flux, which is produced by magnets
72
and runs into the stator, decreases, then the magnetic torque decreases and the output power of the motor also decreases.
Therefore, stabilization of the positions of the magnets
73
is tried by decreasing the clearances between the slits
73
and the magnets
72
by adjusting the section size of the magnets
72
and that of the inserting openings of the slits
73
to be substantially the same.
However, if the clearances between the walls of the slits
73
and the magnets
72
are small, the insertion of the magnets
72
is difficult and also the adhesive applied to the walls of the slits
73
is pressed out when the magnets
72
are inserted into the slits
73
. Accordingly, the adhesive layers between the walls of the slits
73
and the magnets
72
mostly disappear, causing concern as to whether the magnets
72
are firmly stuck inside the slits or not. Also, if the adhesive layers are not thick enough, the motor may loose reliability on the problem of the dropping out of the magnets
72
at high speed rotation.
The rotor of “the interior permanent magnet motor” is driven not only by the magnetic torque, which directly contributes for generating the torque by the magnetic flux which is produced by magnets
72
and runs into the stator, but also the motor is driven by utilizing the reluctance torques which is generated by the above described difference between the inductance “Ld” and the inductance “Lq”. While if the space of the outer rotor rim
75
between the magnets
72
and the outer rim edge of the rotor core
71
is narrow, the magnetic flux path becomes also narrow, then the magnetic saturation occurs, and the volume of the magnetic flux which runs there decreases and the reluctance torque becomes small.
It has been suggested to dispose the magnets
72
at positions closer to a shaft
76
for taking wider space of the outer rotor rim
75
, and then for making a larger magnetic flux path so that the magnetic flux runs well and that the large reluctance torque is utilized. However, in that case, the ends of the magnets
72
are more separated from the outer rim edge of the rotor core
71
, then the magnetic flux runs into the adjacent magnets, and the effective volume of the magnetic flux for generating the torque decreases.
While, the structure for preventing the pressing out of the adhesive when permanent magnets are stuck to the rotor of a motor is stated in the Japanese Patent Application Unexamined Publication No. H08-251850. The rotor, as illustrated in
FIG. 10
, has a groove
84
for absorbing the excess of an adhesive
88
applied to a portion where a cylindrical permanent magnet
82
is stuck to a shaft
86
. In the illustration, the thickness of the adhesive layer
88
is enlarged.
However, the structure is not the one in which the permanent magnet is set inside a rotor, but it is the one in which the cylindrical permanent magnet
82
is stuck to the surface of the shaft
86
with an adhesive, that is so called “a surface permanent magnet motor”, namely that is the motor in which the permanent magnet
82
is just stuck to the shaft
86
with the adhesive.
SUMMARY OF THE INVENTION
The present invention aims to provide “an interior permanent magnet motor” having a rotor which has permanent magnets stuck surely inside it so that the reliability is improved, and the rotor also has wide outer rotor rim space between the permanent magnets and the outer rotor rim edge for providing a wide magnetic flux path, still the travels of the magnetic flux into the adjacent magnets are suppressed, so that the efficiency is also improved.
Namely, the present invention provides a motor comprising a stator having a plurality of teeth provided with windings and a rotor including interior permanent magnets, then the rotor has a rotating shaft disposed at the center part, a rotor core fixed to the rotating shaft, permanent magnet slits formed inside the outer rim of the rotor, grooves formed at the walls of the slits, the magnets inserted into the slits, and adhesive layers inside the slits to stick the magnets to the rotor core.
With the structure described above, even if the size of the permanent magnet slits and the section size of the inserted permanent magnets are adjusted to be substantially same, the adhesive remains at least in the grooves, so that the magnets are surely stuck to the rotor core. Also in the present invention, by forming the porti
Nakamura Tomokazu
Nishiyama Noriyoshi
Rossi & Associates
Tamai Karl
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