Permanent magnet rotor of brushless motor

A brushless motor includes a stator and a rotor rotatably supported within the stator. The rotor includes a yoke which is formed by laminating many steel sheets so as to provide an even number of magnetic poles projected externally and slots provided in each of or every other said magnetic poles, a permanent magnet for a field inserted in each of said slots and having top, bottom, front, rear, and side faces, and protuberances provided on opposite sides of said slots and brought into contact with the side faces of said permanent magnet for the field, forming spaces on opposite sides of said slots.

TECHNICAL FIELD 
This invention relates to a permanent magnet rotor of a brushless motor, 
and particularly to a permanent magnet rotor of a brushless motor which 
has a yoke made by laminating a large number of steel sheets, an even 
number of magnetic poles protruding outward on the yoke, and a permanent 
magnet for a field inserted in each magnetic pole or every other magnetic 
poles. 
BACKGROUND ART 
Generally known brushless motors consist of a permanent magnet rotor which 
has a plurality of permanent magnets for a field inserted in a yoke made 
by laminating steel sheets and a stator which has magnetic poles opposing 
to the outer periphery of magnetic poles of the above permanent magnet 
rotor with a small space therebetween. 
FIG. 35 is a sectional view in a direction intersecting at right angles 
with the rotatable shaft of a brushless motor using a conventional 
permanent magnet rotor. In this drawing, a conventional brushless motor 51 
consists of a stator 52 and a permanent magnet rotor 53. The stator 52 has 
the permanent magnet rotor 53 rotatably supported therein and many stator 
magnetic poles 54 protruded inward. The stator magnetic poles 54 have a 
coil (not shown) wound thereon. Passing a current through the coil excites 
a prescribed magnetic pole of the stator magnetic poles 54. A magnetic 
pole face 55 at the end of the stator magnetic poles 54 is positioned 
above a cylindrical face at an equal distance from the center of a 
rotatable shaft 56 of the motor. 
The permanent magnet rotor 53 consists of a yoke 57 made by laminating many 
steel sheets and a pair of permanent magnets 58 for a field. The yoke 57 
has four magnetic poles 59 protruded externally on its outer periphery, 
and the permanent magnets 58 for the field are inserted in every other 
bases of the magnetic poles 59 with N poles opposed to each other. A 
magnetic pole face 60 at the end of each magnetic pole 59 is formed to 
have a curved shape at an equal distance from the center of the rotatable 
shaft 56, and opposed to the magnetic pole face 55 at an equal distance at 
every point on the face of the rotatable magnetic pole face 60. 
In the above permanent magnet rotor 53, the repulsion of the N poles of the 
permanent magnets 58 for the field causes the magnetic fluxes to get out 
of the magnetic pole faces 60 without the permanent magnet for the field 
as shown in the drawing, to pass through the stator, and to enter the yoke 
57 from the magnetic pole faces 60 with the permanent magnet for the 
field. Accordingly, the magnetic poles having the permanent magnet of the 
permanent magnet rotor 53 become S pole, and those not having the 
permanent magnet of the permanent magnet rotor 53 become N pole. 
As shown in the drawing, the permanent magnet rotor 53 is rotated by 
exciting the stator magnetic poles 54, which have been slightly deviated 
in the rotating direction from the center of the magnetic poles 59 of the 
permanent magnet rotor 53, to N pole. The permanent magnet rotor 53 is 
rotated by being attracted to the excited stator magnetic poles 54. Then, 
the stator magnetic poles 54 which are further displaced with respect to 
the rotated permanent magnet rotor 53 are excited to N pole. The permanent 
magnet rotor 53 is further rotated by being attracted to the newly excited 
stator magnetic poles 54. This procedure is repeated to continuously 
rotate the permanent magnet rotor 53. 
The known conventional brushless motor uses a back electromotive force 
generated by the rotation of the permanent magnet rotor 53 to determine 
the position of the above permanent magnet rotor. Specifically, the 
rotation of the permanent magnet rotor 53 causes the magnetic fluxes of 
the permanent magnets 58 for the field to cross the coils (not shown) 
wound on the magnetic pole faces 55 of the stator 52 to generate the back 
electromotive force in the coils of the stator 52. The position of the 
back electromotive force is detected to detect the position of each 
permanent magnet for a field of the permanent magnet rotor 53, and the 
position of the magnetic poles to be excited on the stator side is 
determined and excited. 
FIG. 36 shows a conventional permanent magnet rotor in an exploded state. A 
conventional permanent magnet rotor 53 has a yoke 57 and permanent magnets 
58 for a field. The yoke 57 is formed by laminating a large number of 
steel sheets 61. The yoke 57 has magnetic poles 57 formed on the outer 
periphery, and at the bases of the magnetic poles 59, slots 62 are 
respectively formed to insert the permanent magnets 58 for the field. 
Furthermore, each steel sheet 61 is pressed to form caulking sections 63 
recessed in the form of a rectangle. The steel sheets 61 are integrally 
laminated by mutually press-fitting the caulking sections 63. 
The permanent magnets 58 for the field are formed to a size capable of 
being housed in the slots 62. In assembling the permanent magnet rotor 53, 
an adhesive is applied to the surfaces of the permanent magnets 58 for the 
field, which are then inserted in the slots 62 with their same magnetic 
poles opposed to each other as shown in the drawing. Arrows Q in the 
drawing indicate the directions that the permanent magnets 58 for the 
field are inserted. 
On the other hand, for the permanent magnet rotor 53 which cannot use an 
adhesive because of its application conditions, the permanent magnets 58 
for the field are formed so as to be fitted in the slots 62 without 
leaving any gap. To assemble the permanent magnet rotor 53, the permanent 
magnets 58 for the field are pushed in the directions Q shown in the 
drawing by a pneumatic device so as to be forced into the slots 62. 
Therefore, a force is applied, in centrifugal directions R, to bridges 64 
connecting the leading end of the magnetic pole and the base of the 
magnetic pole at both ends of the slot. 
FIG. 37 shows a permanent magnet rotor in an exploded state developed by 
the present applicant. It is shown that engagement pawls 62a are formed to 
protrude to engage with a permanent magnet 58 for a field on the inner 
periphery of slots 62 for inserting the permanent magnet for the field. 
The permanent magnet 58 for the field can be inserted in the slots 62, and 
has a sectional shape to engage with the engagement pawls 62a. 
With the above permanent magnet rotor, the permanent magnet 58 for the 
field is engaged with the engagement pawls 62a only and its frictional 
resistance is small, allowing to press-fit the permanent magnet 58 for the 
field into the yoke 57 by a small pressing force. And, when the permanent 
magnet 58 for the field is press-fitted into the yoke 57, the engagement 
pawls 62a can hold the permanent magnet 58 for the field to prevent it 
from coming out. 
In the above prior arts, the permanent magnet rotors which apply an 
adhesive to the outer periphery of the permanent magnets for the field 
before inserting in the slots of the yoke have disadvantages that the 
adhesive is dissolved with a refrigerant or pressurizing fluid and the 
permanent magnets for the field come out. 
On the other hand, in the conventional permanent magnet rotor which 
directly forces the permanent magnets for the field into the slots of the 
yoke without using an adhesive, a large force is used to press-fit the 
permanent magnets for the field, and this force sometimes breaks the 
permanent magnets for the field, or an inserting force is applied to the 
bridges in the centrifugal directions, possibly resulting in their 
breakage. And, the above permanent magnet rotor is required to have a high 
processing precision for fitting the permanent magnets for the field in 
the slots of the yoke in view of a dimensional tolerance, making it 
difficult to produce the permanent magnet rotor. Besides, the intimate 
contact of the permanent magnets for the field with the bridges at both 
ends of the slots causes the magnetic fluxes of the permanent magnets for 
the field to leak at the bridges and prevent them from passing the outside 
space of the magnetic poles, resulting in no cross of the magnetic fluxes 
with the stator of a motor. Therefore, the magnetic fluxes do not produce 
a force for rotating the permanent magnet rotor. And, the leakage of the 
magnetic fluxes at the bridges generates heat due to a core loss. 
In view of the above, an object of this invention is to provide a permanent 
magnet rotor which prevents the permanent magnets for the field from being 
come out due to a refrigerant or pressurizing fluid, makes positioning of 
the permanent magnets for the field, can be produced easily, and has high 
performance. 
And, the permanent magnet rotor (see FIG. 37) invented by the applicant has 
an advantage that a force for press-fitting the permanent magnets for the 
field is reduced extensively. But, the engagement pawls of each steel 
sheet are gradually bent in the press-fitting direction when the permanent 
magnet for the field is press-fitted, this bending of the engagement pawls 
is accumulated to heavily bend the engagement pawls at the end in the 
laminating direction of the yoke, and this bending exceeds a binding force 
of the caulking sections of the steel sheets to partly separate the steel 
sheets. Besides, in a conventional permanent magnet rotor, because of 
different tolerances of the permanent magnet for the field and the yoke 
length in the axial direction, the leading end of the permanent magnet for 
the field does not completely engage with the engagement pawls of the 
steel sheets at the end of the yoke when the permanent magnet for the 
field is shorter than the yoke, resulting in an unstable press-fitted 
state and sometimes separating the steel sheets due to vibration or the 
like. 
Accordingly, another object of this invention is to remedy the unsolved 
problems of the permanent magnet rotor invented by the present applicant 
and to provide a permanent magnet rotor of a brushless motor in which the 
permanent magnet for the field can be inserted by a small pressing force 
and prevented from coming out, and the steel sheets at the end of the yoke 
are not separated when press-fitting the permanent magnet for the field 
and using, and to provide a method for producing it. 
Furthermore, in the above permanent magnet rotor (see FIG. 37) invented by 
the applicant, part of the magnetic fluxes of the permanent magnet for the 
field getting out from the N poles passes through the bridges of the yoke 
to reach the P poles of the permanent magnet for the field. The magnetic 
fluxes passing through the bridges do not cross the stator of a motor and 
do not contribute to rotate the permanent magnet rotor. Therefore, the 
efficiency of the magnetic force of the permanent magnets for the field is 
lowered in inverse proportion to the magnetic fluxes of the permanent 
magnets for the field passing through the bridges. 
On the other hand, the reduction of the sectional areas of the bridges of 
the yoke can reduce the number of magnetic fluxes passing through the 
bridges. This is because the number of magnetic fluxes passing through the 
bridges is determined from the product of a flux density determined 
according to the yoke material by a sectional area of the bridges. 
But, in the yoke formed by laminating the steel sheets, the steel sheets 
forming the yoke are generally formed by a punch-out process, but it is 
quite difficult to punch out the steel sheets for the yoke having the 
bridges with a very small sectional area. Besides, in the yoke having the 
bridges with a very small sectional area, the bridges of the yoke are 
required to have a high mechanical strength because the magnetic poles and 
the permanent magnets for the field suffer from a centrifugal breakage due 
to the centrifugal force when the yoke is rotated at a high speed. And 
when the bridges have a high mechanical strength, there is a disadvantage 
that the utilization efficiency of the permanent magnets for the field is 
lowered. 
In view of the above, another object of this invention is, in a permanent 
magnet rotor of a brushless motor having permanent magnets for a field, to 
provide a permanent magnet rotor which forms a yoke by a plurality of 
steel sheets laminated, and has an optimum bridge width of the yoke among 
a width which can be punched out, a width allowable in view of the number 
of passing magnetic fluxes, and a width allowable in view of a mechanical 
strength by a centrifugal force. 
Besides, in a conventional permanent magnet rotor, the magnetic fluxes of 
the permanent magnets for the field are concentrated on a position 
deviated in the rotating direction from the circumferential center of the 
magnetic poles due to the relation between the bridge width and the width 
in a radial direction at the magnetic poles, or the relative positional 
relation of the permanent magnet rotor and the stator of the brushless 
motor, the back electromotive force generated by the magnetic fluxes is 
detected earlier than the actual position of the permanent magnets for the 
field, the magnetic poles of the stator are excited earlier than a 
prescribed timing, and the permanent magnet rotor has a failure in its 
rotation. 
In view of the above, another object of the invention is to provide a 
permanent magnet rotor which is formed to concentrate the magnetic fluxes 
of a magnet for a field to a prescribed position of a magnetic pole and 
can accurately detect the position of the magnetic pole. 
SUMMARY OF THE INVENTION 
In a brushless motor comprising a stator and a rotor rotatably supported 
within the stator, wherein the rotor has a yoke which is formed by 
laminating many steel sheets, the yoke has an even number of magnetic 
poles protruded externally, and a permanent magnet for a field is inserted 
in each magnetic pole or every other magnetic poles, this invention is to 
provide a permanent magnet rotor characterized by that the above permanent 
magnet for the field is inserted in slots formed on the magnetic poles, 
and the slots are provided with protrusions at both ends to come in 
contact with the side faces of the permanent magnet for the field. 
And, in a brushless motor comprising a stator and a rotor rotatably 
supported within the stator, wherein the rotor has a yoke which is formed 
by laminating many steel sheets, the yoke has an even number of magnetic 
poles protruded externally, and a permanent magnet for a field is inserted 
in each magnetic pole or every other magnetic poles, this invention is to 
provide a permanent magnet rotor characterized by that the above permanent 
magnet for the field is inserted in slots formed on the magnetic poles, 
the slots have engagement pawls disposed to protrude so as to engage with 
the permanent magnet for the field, and among the laminated steel sheets 
of the yoke, those corresponding to the engagement pawls have reliefs for 
absorbing a bend of the engagement pawls. 
And, in a brushless motor comprising a stator and a rotor rotatably 
supported within the stator, wherein the rotor has a yoke which is formed 
by laminating many steel sheets, the yoke has an even number of magnetic 
poles protruded externally, and a permanent magnet for a field is inserted 
in each magnetic pole or every other magnetic poles, this invention is to 
provide a permanent magnet rotor characterized by that at least one end of 
the yoke has a steel sheet deviated in a rotating direction. 
And, in a brushless motor comprising a stator and a rotor rotatably 
supported within the stator, wherein the rotor has a yoke which is formed 
by laminating many steel sheets, the yoke has an even number of magnetic 
poles protruded externally, and a permanent magnet for a field is inserted 
in each magnetic pole or every other magnetic poles, this invention is 
characterized by that the above permanent magnet for the field is inserted 
in slots formed on the magnetic poles, and a bridge width at either end of 
the slots is determined, among a width which can be punched out, a width 
allowable in view of the number of passing magnetic fluxes, and a width 
allowable in view of a mechanical strength by a centrifugal force, to be a 
larger one between the width which can be punched out and the width 
allowable in view of the mechanical strength by the centrifugal force. 
And, in a brushless motor comprising a stator and a rotor rotatably 
supported within the stator, wherein the rotor has a yoke which is formed 
by laminating many steel sheets, the yoke has an even number of magnetic 
poles protruded externally, and a permanent magnet for a field is inserted 
in each magnetic pole or every other magnetic poles, this invention is to 
provide a permanent magnet rotor characterized by that each magnetic pole 
has at least one connecting portion or gap for laminating the steel 
sheets. 
And, in a brushless motor comprising a stator and a rotor rotatably 
supported within the stator, wherein the rotor has a yoke which is formed 
by laminating many steel sheets, the yoke has an even number of magnetic 
poles protruded externally, and a permanent magnet for a field is inserted 
in each magnetic pole or every other magnetic poles, this invention is to 
provide a permanent magnet rotor characterized by that the above permanent 
magnet for the field is inserted in slots formed on the magnetic poles, 
and a bridge width at either end of the slots is disposed to be smaller 
than a width between the outside of the permanent magnet for the field and 
the outside edge of the magnetic pole. 
And, in a brushless motor comprising a stator and a rotor rotatably 
supported within the stator, wherein the rotor has a yoke which is formed 
by laminating many steel sheets, the yoke has an even number of magnetic 
poles protruded externally, and a permanent magnet for a field is inserted 
in each magnetic pole or every other magnetic poles, this invention is to 
provide a permanent magnet rotor characterized by that a width of the 
magnetic pole in a radial direction is about 1.5 times of a pole width of 
the stator. 
Furthermore, in a brushless motor comprising a stator and a rotor rotatably 
supported within the stator, wherein the rotor has a yoke which is formed 
by laminating many steel sheets, the yoke has an even number of magnetic 
poles protruded externally, and a permanent magnet for a field is inserted 
in each magnetic pole or every other magnetic poles, this invention is to 
provide a permanent magnet rotor characterized by that the front or back 
of the outer periphery and in a rotating direction of the magnetic pole is 
notched to a certain shape.

BEST MODE FOR CARRYING OUT THE INVENTION 
FIG. 1 shows the permanent magnet rotor in an exploded state of this 
invention. A permanent magnet rotor 1 has a column yoke 2 and a pair of 
plate permanent magnets 3, 3 for a field. The yoke 2 is formed by 
laminating a large number of steel sheets 4, 4 into one body. The yoke 2 
has four magnetic poles 5 (5a, 5b, 5c and 5d) protruding outward radially 
formed on the outer periphery. Among these magnetic poles, the two 
magnetic poles 5a, 5c opposing to each other have at their bases a pair of 
slots 6, 6 for inserting the permanent magnet 3 for the field. 
Furthermore, at the center of the yoke 2, a hole 7 is formed to pass a 
rotatable shaft (not shown) through it. The steel sheet 4 has its part 
recessed to form caulking sections 8, 8, and the caulking sections 8 are 
mutually press-fitted to laminate into one body. 
The steel sheet 4 forming the slots 6, 6 has at both ends of the slots 
formed a plurality of protuberances 9, 9 in the shape of a triangle. 
The permanent magnets 3, 3 for the field are formed into a hexahedron 
having a rectangular cross section, and respectively inserted into the 
slots 6, 6 in the directions P shown in the drawing so that the faces 
having the magnetism of N pole are faced to the hole 7. 
FIG. 2 is a sectional view of a permanent magnet rotor, showing a cross 
section in a direction intersecting at right angles to the rotatable shaft 
of the yoke 2. The slots 6, 6 are bases of the magnetic poles 5a, 5c of 
the yoke 2 and disposed at substantially equal distance from the rotatable 
shaft. The permanent magnets 3, 3 for the field are disposed with their 
faces having the magnetism of N pole opposed to each other, and the 
magnetic fluxes get out of the magnetic poles 5a, 5c of the yoke 2 by the 
repulsion of the magnetic poles and reach the magnetic poles 5b, 5d as 
shown in the drawing. As a result, the magnetic poles 5a, 5c show the 
magnetism of S pole, and the magnetic poles 5b, 5d show the magnetism of N 
pole. Thus, the outer periphery of the yoke 2 has four magnetic poles 
which have N and S poles alternately. 
Furthermore, either end of the slot 6 has a bridge 10 to connect the base 
and the leading end of the magnetic pole 5, and there is a space between 
the bridge 10 and the permanent magnets 3, 3 for the field, so that the 
magnetic fluxes from the N pole side of the permanent magnets for the 
field pass through the bridges 10 to reach the S pole side of the 
permanent magnets for the field, but the magnetic fluxes passing through 
the bridges 10 are reduced because of a large distance from the permanent 
magnets for the field. 
As shown in the drawing, the permanent magnets 3, 3 for the field have 
their surfaces partly engaged with one side of the protuberances 9 when 
press-fitted, and the protuberances 9 suffer from deflection or plastic 
deformation in the outward directions R due to a dimensional difference of 
the magnets and are held within the slots 6, 6. The protuberances 9 
prevent the permanent magnets 3, 3 for the field from contacting to the 
bridges 10 and the inner periphery of the slots 6, 6 on the side of the 
rotatable shaft. Therefore, the friction due to the contact between the 
permanent magnets 3, 3 for the field and the slots 6, 6 is small, and the 
permanent magnets for the field can be inserted by a small force and 
positioned. As shown in the drawing, when press-fitted, the outer 
periphery of the permanent magnets 3, 3 for the field engages with one 
side of the protuberances 9 to prevent the permanent magnets 3, 3 for the 
field from coming out, and no extra force is applied to the bridges 10. 
Since the permanent magnet rotor of this invention does not use an 
adhesive to hold the permanent magnets 3, 3 for the field in the slots 6, 
6, the permanent magnets 3, 3 for the field can be prevented from coming 
out even when the permanent magnet rotor is used in a refrigerant or 
pressurizing fluid because the adhesive does not dissolve in the 
refrigerant or pressurizing fluid. Besides, the permanent magnets for the 
field can be fixed regardless of the processing precision of the permanent 
magnets for the field. 
FIG. 3 shows the yoke of another embodiment of the permanent magnet rotor 
of this invention. 
In this embodiment, protuberances 9 of the steel sheet 4 has a horn shape 
to engage with the permanent magnet for the field (not shown) and a notch 
11 disposed on one side of the bottom of the horn shape of the 
protuberances 9. The protuberances 9 are connected to the inner edge of 
the steel sheet 4 forming the slot 6 via the notch 11. To engage with the 
permanent magnet for the field, the protuberances 9 must be inclined to a 
prescribed level. When the protuberances 9 are excessively large, the 
magnetic flux of the permanent magnet for the field leaks at the 
protuberances 9, resulting in increasing the leaked magnetic fluxes. And, 
when the protuberances 9 are not inclined to the prescribed level, the 
protuberances 9 are deformed by press-fitting the permanent magnet for the 
field. Positioning of the notch 11 on the side of the permanent magnet for 
the field of the protuberances 9 secures an appropriate inclination of the 
protuberances 9, its appropriate deflection reduces a force for inserting 
the permanent magnet for the field and eliminates the necessity of 
chamfering the horn part of the permanent magnet for the field required in 
press-fitting the permanent magnet for the field. In other words, the 
permanent magnet for the field can be inserted in the slots easily. 
Furthermore, either side of the slot has the bridge 10 to connect the base 
and the leading end of the magnetic pole, and there is a space between the 
bridge 10 and the permanent magnets for the field, so that a base 10a of 
the bridge 10 can be made thick, resulting in increasing a strength of the 
bridge 10, and in the production, breakage of the bridge 10 is reduced as 
much as possible. In addition, the space provided reduces the leaked 
magnetic fluxes of the bridge 10 due to the permanent magnets for the 
field and the heat generation due to the core loss at the bridge 10 can be 
reduced because the base 10a has a large area. 
The above protuberances 9 engaging with the permanent magnets for the field 
have been described with reference to the shape of a horn, but the shape 
is not limited to it, and may be formed into a round shape. 
FIG. 4 shows the permanent magnet rotor 1 of a second embodiment in an 
exploded state. In the same way as in the first embodiment, the yoke 2 is 
formed by laminating a large number of steel sheets 4 (4a, 4b) so as to 
match one another. The steel sheets 4b at the middle in the laminated 
direction of the yoke 2 have engagement pawls 12 disposed to protrude from 
the inner periphery of the slots 6 so as to engage with the permanent 
magnet 3 for the field. On the other hand, the several number of the steel 
sheets 4a at either end in the laminated direction of the yoke 2 have 
reliefs 13 disposed to absorb a bend of the engagement pawls 12 on the 
inner periphery of the slots 6 corresponding to the engagement pawls 12 of 
the steel sheets 4b at the middle. 
FIG. 5 shows a sectional view at the middle of the yoke 2 having the 
permanent magnets 3 for the field inserted. In the steel sheets 4b at the 
middle in the laminated direction of the yoke 2, the engagement pawls 12 
engage with the permanent magnets 3 for the field to reduce a 
press-fitting resistance of the permanent magnets 3 for the field and 
prevent them from coming out. 
FIG. 6 shows a sectional view of the end portion in the press-fitting 
direction of the yoke 2 having the permanent magnets 3 for the field 
inserted. The leading end of the permanent magnet 3 for the field which is 
first press-fitted has the inclined faces to reduce its sectional area, 
and the steel sheets 4a at the ends of the yoke 2 in the press-fitting 
direction have only the reliefs 13 on the inner periphery of the slot 6, 
so that the leading end of the permanent magnet for the field is not in 
contact with the inner periphery of the slot 6 of the steel sheets 4a as 
shown in FIG. 6. 
The operation of the permanent magnet rotor of the second embodiment will 
be described based on the above structure with reference to FIG. 7. 
FIG. 7 shows the yoke 2 with its part expanded, illustrating the laminated 
state of the steel sheets 4b at the middle part and the steel sheet 4a at 
the end in the laminated direction, and the engaged state of the steel 
sheets 4a, 4b and the permanent magnet 3 for the field. 
FIG. 7 shows that the permanent magnet 3 for the field is slightly engaged 
with the engagement pawls 12 of the steel sheets 4b at the middle of the 
yoke 2, so that the permanent magnet 3 for the field can be press-fitted 
in the yoke 2 by a small pressing force with a small frictional resistance 
at the leading end of the engagement pawls 12. It is experimentally known 
that when the permanent magnet for the field is being press-fitted, the 
engagement pawls 12 of each steel sheet 4b is gradually bent in the 
press-fitting direction due to the engagement and friction with the 
permanent magnet 3 for the field, and the bends of the engagement pawls 12 
are accumulated to be great at the end of the yoke 2. As shown in FIG. 7, 
the steel sheet 4a at the end in the laminated direction of the yoke 2 of 
this embodiment has the reliefs 13 positionally matching the engagement 
pawls 12 formed on the inner periphery of the slot 6 to absorb the bends 
of the engagement pawls 12, resulting in preventing the steel sheet 4a 
from separating. And, by inserting the permanent magnet 3 for the field, 
the engagement pawls 12 and the permanent magnet 3 for the field are 
mutually engaged, enabling to prevent the permanent magnet 3 for the field 
from coming out. 
According to this embodiment, the steel sheets 4a having the reliefs 13 are 
laminated at the ends of the yoke 2 to make the permanent magnet 3 for the 
field always longer than those having the engagement pawls 12 of the yoke 
2, so that all engagement pawls 12 are completely engaged with the 
permanent magnet 3 for the field to provide a stable press-fitted state. 
Thus, the disadvantages of a conventional permanent magnet rotor in which 
some engagement pawls at the ends of the yoke do not engage with the 
permanent magnet for the field, falling in an unstable press-fitted state 
and causing the separation of the steel sheets by vibration or the like 
can be remedied. 
A method for easily producing the permanent magnet rotor of this embodiment 
will be described with reference to FIG. 8 and FIG. 9. 
FIG. 8 shows one process for punching out the steel sheets to be laminated 
to form the yoke from a belt steel sheet. As shown in FIG. 8, the steel 
sheets 4a, 4b of this embodiment are punched out by sending a belt steel 
sheet material 14 through a punch die in the direction P at a prescribed 
pitch. Punch-out position A punches out the slots 6 having the engagement 
pawls 12 or the slots 6 having the reliefs 13, punch-out position B 
punches out the rotatable shaft hole 7, and punch-out position C punches 
out an outward form of the steel sheet 4a or 4b to be laminated and 
laminates at the same time. The steel sheet punch-out process of this 
embodiment uses a punch die which punches out the slots 6 with different 
shapes according to a driving depth. 
FIG. 9 shows the punch die which punches out the slots with different 
shapes according to a driving depth. The punch die consists of a male mold 
15 and a female mold 16, the male mold 15 of the punch die is supported to 
be vertically movable above the steel sheet material 14, and the female 
mold 16 of the punch die is fixed below the steel sheet material 14. After 
the steel sheet material 14 is sent at a prescribed pitch and stopped at a 
prescribed position, the male mold 15 of the punch die is brought down to 
punch out through the steel sheet material 14 and to enter the female mold 
16 of the punch die. Thus, the steel sheet material 14 is punched out into 
the shape of the male mold 15 of the punch die. 
As shown in FIG. 9, the male mold 15 of the punch die of this embodiment 
has different-shaped bottom and top ends, a lower part 15a has a shape to 
punch out the slots 6 and the engagement pawls 12, and an upper part 15b 
which is above the part 15a has a shape to punch out the reliefs 13. Thus, 
when a driving depth is in a range to the part 15a, the slots 6 having the 
engagement pawls 12 can be punched out and, when the driving depth reaches 
the part 15b, the slots 6 having the reliefs 13 can be punched out. 
The production method of this embodiment first punches out a prescribed 
number of the steel sheets 4a for one end of the yoke 2 at a driving depth 
in a range using the part 15b and laminates them, punches out the steel 
sheets 4b for the middle of the yoke 2 at a driving depth in a range using 
the part 15a and laminates them, and punches out a prescribed number of 
the steel sheets 4a for the other end of the yoke 2 at a driving depth in 
a range using the part 15b and laminates them to complete the production 
of the yoke 2. 
According to the above production method, the yoke 2 which has the steel 
sheets 4a having the reliefs 13 at the ends and the yoke 2 which has the 
steel sheets 4b having the engagement pawls 12 at the middle can be 
continuously produced by the same production device, the production device 
can be simplified, and work efficiency can be improved extensively. 
But, it is obvious that this invention is not limited to the above but can 
also be applied to a permanent magnet rotor in which the permanent magnets 
for the field are inserted into the yoke formed of the steel sheets having 
a prescribed shape. 
In the above description about the production method, three punch dies are 
used to successively punch out one steel sheet, but it is to be understood 
that one punch die may be used to punch out steel sheets with different 
shapes in the driving depth. 
As described above, the yoke of the permanent magnet rotor according to the 
second embodiment disposes the steel sheets having the engagement pawls 
for reducing a resistance at press-fitting of the permanent magnets for 
the field and preventing them from coming out at the middle in the 
laminated direction, and disposes the steel sheets having the reliefs to 
absorb the bend of the engagement pawls at press-fitting of the permanent 
magnets for the field at the ends in the laminated direction, to allow the 
press-fitting of the permanent magnets for the field by a small pressing 
force. And, the steel sheets at the ends of the yoke are not separated by 
the press-fitting, and after the insertion, the permanent magnets for the 
field are prevented from coming out. And, the permanent magnet rotor of 
this embodiment can easily set the permanent magnets for the field to be 
longer than the part having the engagement pawls of the yoke, so that all 
engagement pawls engage with the permanent magnets for the field to 
provide a stable press-fitted state, and the possibility of the steel 
sheets from being separated by vibration can be reduced. 
And, the method for producing the permanent magnet rotor of this embodiment 
has the punch die which can punch out the steel sheets with different 
shapes according to a driving depth, and can vary only the driving depth 
to continuously produce the yoke having the steel sheets having the 
reliefs at the ends and the steel sheets having the engagement pawls at 
the middle by the same production device, so that the production device 
can be simplified, and the work efficiency can be improved extensively. 
FIG. 10 shows the permanent magnet rotor in an exploded state of a third 
embodiment. A permanent magnet rotor 1 has two pairs of plate permanent 
magnets 3, 3 in this case. The yoke 2 is formed by punching out many steel 
sheets 4 by a die and laminating in the same way as in the above 
embodiment. One end of the yoke 2 is made of a steel sheet 4' by having 
the steel sheet 4 deviated in a rotating direction. The steel sheets 4 
have caulking sections 8 which are formed by denting the steel sheets in 
part, and the caulking sections 8 are mutually press-fitted to be 
laminated into one body. The permanent magnets 3, 3 for the field are 
moved in the direction R shown in the drawing to be respectively inserted 
into the slots 6, 6d. Then a steel sheet 4" deviated in a rotating 
direction with the hole 7 as the center integrally press-fitted by the 
caulking sections 8. 
FIG. 11 shows a sectional view of the steel sheet 4. The slots 6, 6 are at 
bases of the magnetic poles 5a, 5b, 5c and 5d of the steel sheet 4 and 
disposed at substantially equal distance from the rotatable shaft of the 
yoke. The permanent magnets 3, 3 for the field are respectively inserted 
in the slots 6, 6, The permanent magnets 3, 3 for the field are disposed 
so that the outer periphery of the yoke 2 has the magnetisms of N and S 
poles alternately. Furthermore, the steel sheet 4 has caulking sections 
8a, 8b, 8c and 8d inside of the permanent magnets for the field to 
mutually press-fit the steel sheets, and the caulking sections 8a, 8b, 8c 
and 8d are mutually press-fitted for laminating. 
Furthermore, intervals of the caulking sections 8a, 8b, 8c and 8d with 
respect to the rotatable shaft are m between the caulking sections 8a and 
8b, between the caulking sections 8b and 8c, and between the caulking 
sections 8c and 8d; and k between the caulking sections 8d and 8a, and 
determined to be p.times.m.noteq.360.degree. (p is the number of 
caulkings) and m.noteq.k. 
And, a gap 8'a is close to the caulking section 8a so as to be able to be 
press-fitted with one of the caulking sections 8a, 8b, 8c and 8d, and a 
gap 8'b is close to the caulking section 8d so as to be able to be 
press-fitted with one of the caulking sections 8a, 8b, 8c and 8d. An 
interval T (an angle with respect to the rotatable shaft) between the gap 
9a and the caulking section 8a is set to be T=p.times.m-360.degree. 
(p.times.m&gt;360.degree.), and an interval q (an angle with respect to the 
rotatable shaft) between the gap 8'b and the caulking section 8d is set to 
be q=360.degree.-p.times.m (p.times.m&gt;360.degree.). And, the caulking 
sections 8a, 8b, 8c and 8d and the gaps 8'a, 8'b are on the same 
circumference with respect to the rotatable shaft. 
FIG. 12 shows a sectional view (steel sheet 4") of the steel sheet 4 
deviated in a rotating direction by m.degree.. Caulking sections 18a, 18b, 
18c and 18d of the steel sheet 4" correspond to the caulking sections 8a, 
8b, 8c and 8d which are not deviated, and gaps 18'a, 18'b correspond to 
the gaps 8'a, 8'b which are not deviated. 
FIG. 13 shows a sectional view (steel sheet 4') of the steel sheet 4 
deviated in a rotating direction by m.degree. and all caulking sections 
8a, 8b, 8c and 8d pulled out to leave gaps. Gaps 19a, 19b, 19c and 19d of 
the steel sheet 4' correspond to the caulking sections 8a. 8b, 8c and 8d 
which are not deviated, and the gaps 19'a, 19'b correspond to the gaps 
8'a, 8'b which are not deviated. The gaps 19a, 19b, 19c and 19d, when a 
die is lowered deeper to press the steel sheets, provide completely hollow 
caulking sections, and when lowered shallow, provide caulkings. 
FIG. 14 shows that the steel sheet 4 is caulked to the steel sheet 4" from 
above. The caulking sections 20d, 20a, 20b and 20c of the steel sheet 4" 
are placed on the gap 8'a and the caulking sections 8b, 8c and 8d of the 
steel sheet 4. And, the steel sheet 4" can be turned in the opposite 
direction to place the caulking sections 20b, 20c, 20d and 20a of the 
steel sheet 4" on the caulking sections 8a, 8b and 8c and the gap 8'b. 
The gap 8'b of the steel sheet 4 is required to be put on the above steel 
sheet by turning in the opposite direction and eliminates directionality 
in laminating the steel sheets. In addition, when the steel sheet 4" is 
stacked, the permanent magnets 3, 3 for the field have the slots 6", 6" of 
the steel sheet 4" held inclined with respect to the slots of the steel 
sheet 4 as shown in the drawing. Since the inclination of the slots 
slightly interfere with a part of the outer periphery of the end faces of 
the permanent magnets 3, 3 for the field, magnetic fluxes substantially do 
not leak from the magnet end faces. Furthermore, since the permanent 
magnets 3, 3 for the field are inserted in the slots 6, 6 of the steel 
sheet 4 in the same way as in prior art, no extra force is applied to the 
slots. And, even when an adhesive is used to fix the permanent magnets 3, 
3 for the field and the rotor is used in a refrigerant or pressurizing 
fluid, the dissolution of the adhesive in the refrigerant or pressurizing 
fluid does not cause the permanent magnets 3, 3 for the field to come out 
by virtue of the steel sheet 4". Besides, the permanent magnets for the 
field can be fixed regardless of the processing precision of the permanent 
magnets for the field. 
FIG. 15 shows that the steel sheet 4 is caulked to a steel sheet 4' from 
above. In the drawing, the caulking sections 8a, 8b, 8c and 8d of the 
steel sheet 4 are placed on gaps 19a, 19b, 19c and 19'b of the steel sheet 
4'. The stacking of the steel sheet 4 can result in the same effect as in 
FIG. 14. 
FIG. 16 shows an exploded view of the permanent magnet rotor according to 
another embodiment of the permanent magnet rotor. A yoke 2 is divided into 
two, steel sheets 4 are caulked to each steel sheet 4' from above, and 
these yokes 2 are moved in directions R to insert the permanent magnets 3, 
3 for the field. Positioning of the magnetic poles of each yoke 2 is 
determined by the permanent magnets 3, 3 for the field and, in this case, 
the positioning can be made easily because plate permanent magnets for the 
field are used. Since the permanent magnets for the field have a deviated 
steel sheet and slot at either end of the yokes, they do not come out by 
being prevented by them. And the same effect can be obtained when the 
slots of the end steel sheet of the yokes have a different shape. 
FIG. 17 shows a sectional view of the steel sheet according to another 
embodiment of the permanent magnet rotor. Slots 6, 6 are disposed in bases 
of magnetic poles 5a, 5b, 5c and 5d of a steel sheet 4 at substantially 
equal distance from the rotatable shaft of the yoke. A permanent magnet 
for a field is inserted in these slots 6, 6. Furthermore, the steel sheet 
4 has caulking sections 21a, 21b, 21c and 21d formed inside of the 
permanent magnets for the field to mutually press-fit the steel sheets and 
gaps 22a, 22b, 22c and 22d capable of press-fitting the caulking sections 
21a, 21b, 21c and 21d even when the steel sheets are turned, and by 
turning the above caulking sections 21a, 21b, 21c and 21d by m.degree., 
the caulking sections 21a, 21b, 21c and 21d are fitted in the gaps 22a, 
22b, 22c and 22d. An interval m between the caulking section 21a and the 
gap 22b is determined to be p.times.m.noteq.360.degree. (p is the number 
of caulkings, m an interval between the caulking and the gap). And the 
caulking and the gap are point symmetrical with respect to the rotatable 
shaft and they are on the same circumference with the rotatable shaft at 
the center, so that the steel sheets are well balanced at a high-speed 
rotation. 
FIG. 18 shows a sectional view of the steel sheet according to another 
embodiment of the permanent magnet rotor. In this embodiment, the steel 
sheet has caulking sections 23a, 23b, 23c and 23d and oval gaps 24a, 24b, 
24c and 24d capable of press-fitting the caulking sections 23a, 23b, 23c 
and 23d by turning the steel sheet, and is laminated by mutually 
press-fitting the caulking sections 23a, 23b, 23c and 23d. The caulking 
sections 23a, 23c and the gaps 24b, 24d are on the same circumference, and 
the caulking sections 23b, 23d and the gaps 24a, 24c are on a 
circumference different from the above circumference, so that the gap area 
can be made long on the circumference, thus forming an oval shape in FIG. 
18. Forming the gaps to an oval shape further enables to rotate at a 
desired very small angle. Furthermore, the caulkings and the gaps are 
point symmetrical with respect to the rotatable center and the steel 
sheets are well balanced at a high-speed rotation. In addition, the 
position of the gaps and the caulkings on a plurality of circumferences 
enables to form the gaps into a desired shape, thus allowing to reduce a 
weight of the yoke itself. The above caulkings are round, but not limited 
to it. They may be a rectangular V-shaped caulking for example. The yoke 
is not limited to the laminated steel sheets, but can be made of one solid 
metal. 
FIG. 19 shows another embodiment of the permanent magnet rotor. In this 
embodiment, a yoke 2 has a twist at a very small angle formed by a 
deviation of the pitch between the caulkings with the rotatable shaft 7a 
as the center, and the slots 6, 6 of the permanent magnet rotor 1 are also 
deviated by a very small angle within the permanent magnet rotor 1, making 
it possible to fix the permanent magnets for the field; and at the 
magnetic poles, the highest back electromotive force is always generated 
at the circumferential center of each rotating magnetic pole face, thus 
allowing to hold tile-shaped permanent magnets 3, 3 in the slots 6, 6. 
FIG. 20 shows an exploded view of the permanent magnet rotor according to 
another embodiment. A permanent magnet rotor 1 forms a yoke 2 by 
laminating a large number of steel sheets 4 into one body by the same way 
as above, the steel sheets 4 have caulking sections 8 formed by denting 
them partly, and the caulking sections 8 are mutually press-fitted to 
laminate into one body. Permanent magnets 3, 3 for the field are formed 
into a hexahedron having a rectangular cross section, and respectively 
inserted into the slots. Then a round iron sheet 25 having caulking 
sections 8 is attached to slightly cover with its outer periphery the 
permanent magnets 3, 3 for the field to integrally press-fit by the 
caulking sections 8 (see FIG. 21). The structure as described above allows 
to caulk the gaps in the yoke through a positioning pin in a rotating 
direction when caulking the steel sheets, preventing the permanent magnets 
for the field from coming out axially, and after shrinkage fitting of the 
yoke to the rotatable shaft, the permanent magnets for the field can be 
inserted, then the iron sheet 25 can be caulked last. Besides, even when 
an adhesive is used to fix the permanent magnets for the field and the 
rotor is used in a refrigerant or pressurizing fluid, the dissolution of 
the adhesive in the refrigerant or pressurizing fluid does not cause the 
permanent magnets for the field to come out from the slots by virtue of 
the steel sheet 25. And, the permanent magnets for the field can be fixed 
regardless of the processing precision of the permanent magnets for the 
field. 
Thus, the permanent magnet rotor of the third embodiment has the deviated 
steel sheet having the same shape with the steel sheets of the yoke by a 
pitch of the caulking at least at one end of the slots for inserting the 
permanent magnet for the field to enable to axially fix the permanent 
magnet for the field, and can set the deviated degree of the steel sheets 
by a pitch of the caulking; this deviation can be set to a very small 
angle and prevents the magnetic fluxes at the end face of the permanent 
magnet for the field from leaking. And, since the steel sheet at one end 
is deviated, it has an effect of preventing the steel sheets from falling 
in the axial direction. Furthermore, the gaps in the steel sheets make it 
easy to press-fit and position the caulkings of the steel sheets. Since 
the gaps can be formed to a desired shape, the yoke itself can be made 
lightweighted, and the caulkings and the gaps are point symmetrical with 
respect to the rotatable shaft, thus making the yoke well balanced. After 
shrinkage fitting of the yoke to the rotatable shaft, the permanent 
magnets for the field can be inserted easily, and after inserting, 
another-shaped iron sheet can be easily fixed by caulking with reference 
to the gap. In addition, since high processing precision is not required 
thanks to the positional matching of the slots and the permanent magnets 
for the field, the permanent magnet rotor can be produced easily. And, the 
permanent magnets for the field can be prevented from coming out even when 
used in a refrigerant or pressurizing fluid, and the permanent magnet 
rotor which can be easily produced and assembled can be obtained. 
FIG. 22 shows a perspective view of the permanent magnet rotor of a fourth 
embodiment, and FIG. 23 shows a cross section intersecting at right angles 
to the rotatable shaft of the permanent magnet rotor. The permanent magnet 
rotor 1 has a pair of plate permanent magnets 3, 3 in this case. The yoke 
2 is formed by punching out a large number of steel sheets 4 by a die and 
laminating. The steel sheets 4 have caulking sections 8 which are formed 
by partly denting the steel sheets, and are laminated into one body by 
mutually press-fitting the caulking sections 8. And, in this embodiment, 
bridges 10, 10 are produced to have a width of 0.35 mm. 
In FIG. 23, the magnetic fluxes passing through the bridges 10 do not cross 
the stator of a motor because they do not pass the outer space of the yoke 
23. Therefore, a force for rotating the permanent magnet rotor is not 
produced. The reduction of the magnetic fluxes passing through the bridges 
10 can use the magnetic force of the permanent magnet 3 for the field more 
effectively. 
The magnetic fluxes .phi. passing through the bridges 10 are calculated 
from the following formula. Assuming that the sectional area of the 
bridges 10 is S and the magnetic flux density of the steel sheet 4 is B, 
the following formula is established. 
EQU .phi.=B.times.S 
It is obvious from the above formula that the magnetic fluxes passing 
through the bridges 10 can be reduced by making the sectional area S of 
the bridges 10 smaller. On the other hand, a centrifugal breakage applied 
to the bridges is calculated from the following formula. Assuming that the 
centrifugal force is F and the yielding point of the steel sheet is D, the 
following formula is established. 
EQU F/S&lt;D 
And, the sectional area S is calculated from the following formula. In FIG. 
22, assuming that the bridge width is M, the steel sheet thickness is T, 
and the yoke thickness is N, the following formula is established. 
EQU S=M.times.T.times.(N/T).times.2 
It is obvious from the above formula that when the yoke length is fixed, 
the allowable width M should be increased according to the necessary 
strength of the bridges 10. In the above formula, (N/T) is the number of 
steel sheets 4, and (.times.2) means that one magnetic pole has two 
bridges 10. 
FIG. 24 shows a relation among the bridge width, the magnetic flux density 
of the bridges, and the mechanical strength of the bridges. More 
specifically, the horizontal axis shows the bridge width, and the vertical 
axis shows the magnetic flux density of the bridges and the mechanical 
strength against the centrifugal force. And, curve L1 indicates a magnetic 
flux density curve, and L2 indicates a mechanical strength curve against 
the centrifugal force. The curve L1 forms a straight line without any 
change between point a or a minimum width capable of being punched out by 
a die and point b or a minimum width of an allowable magnetic flux 
density, and shows that the magnetic flux density is gradually lowered 
with a width larger than the width of the point b. 
The width of the point a capable of being punched out by a die depends on 
the steel sheet thickness, and the thickness is 0.1 mm, 0.35 mm or 0.5 mm. 
And the relation of the bridge width capable of being produced by a die is 
expressed as M/T.gtoreq.1. For example, when the steel sheet thickness is 
0.35 mm and the bridge width is 0.35 mm or more, the production can be 
made easily. But, the bridge width is influenced by the minimum width 
allowed from the mechanical strength against the centrifugal force. 
Therefore, when the width allowed from the mechanical strength due to the 
centrifugal force is within the width capable of being produced by a die, 
highly efficient performance with a less loss of the magnetic fluxes of 
the permanent magnets for the field and the minimum width capable of being 
produced by a die can be obtained by determining to either of the width 
capable of being produced by a die or the width allowed from the magnetic 
flux density. 
And, when the width allowed from the mechanical strength due to the 
centrifugal force is between the width capable of being produced by a die 
and the width allowed from the magnetic flux density, by determining to 
either of the width allowed from the mechanical strength due to the 
centrifugal force or the width allowed from the magnetic flux density, 
highly efficient performance with a less loss of the magnetic fluxes of 
the permanent magnets for the field and capable of punching out quickly by 
a die can be realized. 
And, when the width allowed from the mechanical strength due to the 
centrifugal force is equal to or greater than the width allowed from the 
magnetic flux density, the width allowed from the mechanical strength due 
to the centrifugal force is selected. In this case, it is advantageous 
that the production is easy by virtue of rigidity against the punching out 
by the die and the production cost is lowered because the steel sheet 
material can be a low-saturated steel sheet material. 
In summary, among the width capable of being punched out, the width allowed 
in view of the number of passing magnetic fluxes, and the width allowed 
from the mechanical strength due to the centrifugal force, the bridge 
width at either end of the slot is determined to be equal to or larger 
than larger one of the width capable of being punched out or the width 
allowed from the mechanical strength due to the centrifugal force and 
equal to or smaller than the width allowed in view of the number of 
passing magnetic fluxes. Exceptionally, when the width capable of being 
punched out and the width allowed from the mechanical strength due to the 
centrifugal force are equal to or larger than the width allowed in view of 
the magnetic flux density, it is determined to be a larger one or more 
between the width capable of being punched out and the width allowed from 
the mechanical strength due to the centrifugal force. 
FIG. 25 shows a perspective view of the permanent magnet rotor of a fifth 
embodiment, and FIG. 26 shows a cross section intersecting at right angles 
to the rotatable shaft of the permanent magnet rotor. The permanent magnet 
rotor 1 has a pair of plate permanent magnets 3, 3 in this case. The yoke 
2 is formed by punching out a large number of steel sheets 4 by a die and 
laminating. In this embodiment, the steel sheets 4 have caulking sections 
8, which are formed by partly denting the steel sheets, disposed on each 
magnetic pole. The caulking sections 8 are formed by partly denting the 
steel sheet by pressing by means of a die. Therefore, each magnetic pole 
has gaps formed by the dented portions of the caulking sections 8. 
In FIG. 26, arrows in the drawing show the flow of magnetic fluxes between 
each magnetic pole and stator magnetic poles. The stator 26 has a 
permanent magnet rotor 3 therein, and stator magnetic poles 27 are excited 
by coils not shown. Slots 6, 6 are in the bases of magnetic poles 5a, 5c 
of a yoke 2 and positioned at an equal distance from the rotatable shaft 
of the yoke 2. As described above, the permanent magnets 3, 3 for the 
field are inserted in these slots 6, 6 with the faces having the magnetism 
of N pole opposed to each other, and the magnetic fluxes get out of the 
magnetic poles 5a, 5c of the yoke 2 due to the repulsion of the magnetic 
poles as shown and reach the magnetic poles 5b, 5d. As a result, the 
magnetic poles 5a, 5c bear the magnetism of S pole, and the magnetic poles 
5b, 5d the magnetism of N pole. And, the outer periphery of the yoke 2 has 
the four magnetic poles alternately having N and S poles. 
The yoke 2 has on each magnetic pole a caulking section 8 for laminating 
steel sheets, and the flow of the magnetic fluxes of each magnetic pole 
detours around the caulking section 8 and reaches the magnetic pole face 
of the yoke 2 as indicated by the arrows in FIG. 26. This is because the 
caulking section 8 is formed by denting the steel sheet to form a space by 
the dented portion, so that the space has a low magnetic permeability with 
respect to the steel sheet, increasing a magnetic resistance at the 
caulking section 8. Therefore, the magnetic fluxes are divided to pass 
both sides of the caulking section 8 of the magnetic pole and not 
concentrated toward the rotating direction. Thus, the back electromotive 
force generated by the magnetic fluxes is largest at the center of the 
magnetic pole, allowing to prevent an erroneous detection of the position 
of each magnetic pole of the permanent magnet rotor. 
And, the caulking section 8 disposed on the magnetic poles 5a to 5d makes 
an external force difficult to be applied to bridges 10 connecting the 
base and the leading end of the magnetic pole. And even when an unexpected 
external force is applied to the leading end of the magnetic pole, the 
steel sheets of the yoke 2 do not suffer from the occurrence of separation 
and gaps. 
FIG. 27 and FIG. 28 are explanatory views of another embodiment of the 
permanent magnet rotor, showing a front view and a sectional view of the 
yoke 2. The above embodiment has used caulkings by denting the steel 
sheets for connecting the steel sheets 4. But, this embodiment forms a 
through hole in magnetic poles 5a, 5b, 5c and 5d, and inserts a shaft 28 
to connect the laminated steel sheets 4, thereby forming the yoke 2. The 
shaft 28 is aluminum, stainless steel or other nonmagnetic materials to 
increase a magnetic resistance at the shaft, resulting in obtaining the 
same effect as in the above embodiment. In this embodiment, each end of 
the connection shaft 28 is fixed by caulking, but desired ways such as 
screwing and welding can be adopted. 
The connecting portion and the space of the magnetic poles 5a to 5d are not 
required to be positioned at the center of the magnetic poles. They may be 
positioned on the side of the rotating direction of the rotor with respect 
to the center of the magnetic pole and approached just next to the leading 
end of the magnetic pole. Disposition of the space or connecting portion 
on the side of the rotating direction interrupts the flow of the magnetic 
fluxes which are concentrated toward the rotating direction, thus 
enhancing the effect of accelerating the concentration of the magnetic 
fluxes on the center of the magnetic pole. The magnetic fluxes which are 
prevented from concentrating toward the rotating direction are dispersed 
at the space or connecting portion, and again concentrated toward the 
rotating direction on the magnetic pole. But, the disposition of the space 
or connecting portion at the position immediately next to the leading end 
of the magnetic pole in the rotating direction of the rotor causes the 
dispersed magnetic fluxes to reach the leading end of the magnetic pole 
prior to concentrating toward the rotating direction, resulting in 
concentrating the magnetic fluxes on the center of the magnetic pole. 
Thus, it is more assured that an erroneous detection of the position of 
each magnetic pole is prevented. 
The connecting portion or space is not limited to be one on each magnetic 
pole and may be disposed in more than one. The above embodiment has been 
described using the rotor having the structure that the four magnetic 
poles are formed on the outer periphery of the yoke and the permanent 
magnet for the field is inserted in every other magnetic poles. But, this 
embodiment is not limited to the above structure and can be applied to a 
case that a desired even number of magnetic poles is formed and the 
permanent magnet for the field is inserted in each magnetic pole. 
In the permanent magnet rotor of this embodiment, the portion for 
connecting the steel sheets is disposed on each magnetic pole, so that the 
magnetic resistance at the connecting portion is increased to suppress the 
concentration of the magnetic fluxes toward the rotating direction. And 
the disposition of the connecting portion on each magnetic pole so as to 
accelerate the magnetic fluxes to concentrate on the center of each 
magnetic pole generates the back electromotive force largest at the center 
of the magnetic pole, thus enabling to obtain a position sensorless 
brushless motor which can accurately detect the position of the magnetic 
pole of the permanent magnet rotor. 
Besides, the disposition of the connecting portion on each magnetic pole 
makes the external force hard to be transmitted to the bridges connecting 
the base and the leading end of the magnetic pole, and even when the 
unexpected external force is applied to the leading end of the magnetic 
pole, the steel sheets of the yoke forming the permanent magnet rotor are 
prevented from suffering the occurrence of separation and gaps, thus 
capable of providing the permanent magnet rotor excelling in strength. 
FIG. 29 is a computer-analyzed diagram showing the flow of magnetic fluxes 
on a cross section intersecting at right angles to the rotatable shaft of 
the permanent magnet rotor of a three-phase, four-pole motor (24 poles) 
with the rotor rotating satisfactorily. It is seen from the flow of the 
magnetic fluxes that the magnetic pole above the permanent magnet for the 
field bends the magnetic fluxes from the stator magnetic pole (pole) and 
the magnetic fluxes from three stator magnetic poles flow to one permanent 
magnet for the field. Since a half of the quantity of magnetic fluxes of 
the magnet passes through the magnetic pole above the permanent magnet for 
the field, a width a between the permanent magnet for the field and the 
outer periphery edge of the magnetic pole is preferably in a relation of 
(a=1.5.times.b) (including a case that a is almost (1.5.times.b)) with 
respect to a width b of the stator magnetic pole. In other words, a half 
of the quantity of magnetic fluxes of the magnet passes through the part a 
and enters 1.5 stator magnetic poles. In the case of the above 
(a=1.5.times.b), the magnetic fluxes flow easily and do not leak many 
because both magnetic flux densities are equal, resulting in a remarkable 
motor efficiency with a less loss. 
Since the width b of the stator magnetic pole is generally fixed, when the 
width a is larger than (1.5.times.b), the permanent magnet for the field 
is relatively close to the rotatable shaft because the gap between the 
rotor and the stator is fixed and the magnetic pole outside the permanent 
magnet for the field has a large area, reducing a gap magnetic flux 
density outside the rotor. Furthermore, when the magnetic pole has a large 
area, the bridge width is increased to retain the magnitude of a 
centrifugal force, increasing a loss and lowering a motor efficiency. 
Besides, the magnet has a long magnetic path, and a leakage quantity is 
increased. 
Conversely, when the width a is smaller than (1.5.times.b), the permanent 
magnet for the field is relatively away from the rotatable shaft and 
approaches to the stator, the magnetic pole outside the permanent magnet 
for the field has a small area, making the magnetic fluxes difficult to 
bend and easy to be saturated. Thus, the magnetic flux density increases 
and a loss (core loss) is increased, making the magnet demagnetized easily 
by heat. 
As described above, when a is almost equal to (1.5.times.b), the above 
disadvantages can be remedied, and a cutoff can be disposed on the rotor 
magnetic poles (removing a local concentration of magnetic fluxes) to be 
described afterward while securing the strength of the bridges. It is to 
be understood that the above width a is larger than the bridge width. 
FIG. 30 and FIG. 31 are computer-analyzed diagrams showing the flow of 
magnetic fluxes on a cross section intersecting at right angles to the 
rotatable shaft of the permanent magnet rotor of a three-phase, four-pole 
motor (24 poles) with the rotor rotating. FIG. 30 shows the rotor magnet 
pole with a cutoff 29, and FIG. 31 shows it without the same. FIG. 32 and 
FIG. 33 are graphs showing a gap magnetic flux density, corresponding to 
FIG. 30 and FIG. 31 respectively. When the cutoff 29 is not disposed, the 
magnetic fluxes concentrate on stator magnetic poles 103, 104, and 105 
respectively, and the quantity of magnetic fluxes is in order of the 
magnetic flux of the magnetic pole 103, the magnetic flux of the magnetic 
pole 104, and the magnetic flux of the magnetic pole 105 in proportion to 
the passage (torque magnitude) of a current through the stator winding, 
the magnetic fluxes are locally saturated, the torque between the 
respective stator magnetic poles is not uniform, and the rotation of the 
rotor is varied. 
On the other hand, when the cutoff 29 is disposed, substantially an equal 
quantity of magnetic fluxes enters stator magnetic poles 203, 204 and 205, 
the magnetic fluxes do not bend extremely at the rotor magnetic poles, 
saturation is not much at the magnetic poles, each stator magnetic pole 
has the same torque, and the rotor rotates without many changes or 
vibrations. FIG. 34 is a diagram showing a relation between the permanent 
magnet rotor and the stator of a three-phase, four-pole motor (24 poles), 
where A is an interval between the ends of two stator magnetic poles (2 
poles), and a width of the cutoff 29 corresponds to the above interval. In 
other words, the angle A is a cutoff angle. In FIG. 34, a gap G at a 
non-cutoff part is 0.5 mm, a maximum gap B at the cutoff part is 1.3 mm, 
an angle of the maximum gap B from the rotor center is 25.degree., and an 
angle of the cutoff end part from the rotor center is 34.degree.. The 
above values are same in the cases of 12 poles and 36 poles of a 
three-phase, four-pole motor. In the cases of 18 poles and 36 poles of a 
three-phase, six-pole motor, the cutoff angle A is 16.7.degree., and an 
angle of the cutoff end part from the rotor center is 22.7.degree.. 
Industrial Applicability 
This invention is suitable for a rotor of a brushless motor used for 
compact disc players, various types of acoustic equipment, OA equipment 
and others which need accurate rotation and durability.