The present invention relates to a motor including an interior permanent magnet rotor provided with a plurality of permanent magnets in a rotor core.
Conventionally, a motor using a permanent magnet includes a rotor provided on an inner circumference of a stator with a gap interposed between the rotor and the stator.
The stator has substantially a cylindrical shape, and generates a rotating magnetic field.
The rotor includes a rotary shaft and a rotor core. The rotor rotates around the rotary shaft. A magnet hole into which a permanent magnet is inserted is formed on the rotor core. A magnetic pole is formed on the rotor by the permanent magnet inserted into the rotor core.
A motor in which a permanent magnet is embedded into a rotor core as in the configuration described above is also referred to as an interior permanent magnet (IPM) motor.
A small piece of an Nd—Fe—B sintered magnet or a small piece of a ferrite sintered magnet has been widely used for a permanent magnet.
In the case where a small piece of a permanent magnet is used, a magnet hole formed on a rotor core is formed with a size slightly larger than the outer shape of the small piece of the permanent magnet. If the magnet hole has a size slightly larger than the outer shape of the small piece of the permanent magnet, workability in assembling the rotor is enhanced. The reason of the enhancement in workability is as stated below.
Specifically, the magnet hole formed on the rotor core is formed through a process for working a metal. The process for working a metal is referred to as a metal working process below. Therefore, the magnet hole is formed with high-precise working, and thus, a dimensional tolerance is small.
On the other hand, the small piece of the permanent magnet described above is formed through a process for sintering magnet powders or the like. The process for sintering magnet powders or the like is referred to as a sintering process below. The sintering process is similar to a process for firing ceramics or the like in a kiln. Accordingly, a small piece of a permanent magnet which has been subjected to the sintering process may sometimes be deformed, for example, may be warped or bent. If the small piece of the permanent magnet is subjected to a process for grinding the small piece with a grind stone or the like, the deformation occurring on the small piece of the permanent magnet can be eliminated. The process for grinding the small piece with a grind stone or the like is referred to as a grinding process below.
A motor does not employ a grinding process for eliminating deformation on a small piece of a permanent magnet. Alternatively, even if a grinding process is employed for a motor, an amount to be ground of a small piece of a permanent magnet is very small. In addition, precision in grinding a small piece of a permanent magnet is low.
Accordingly, as described above, a motor addresses deformation on a small piece of a permanent magnet by setting a magnet hole to be slightly larger than the outer shape of the small piece of the permanent magnet. It is to be noted that, when the grinding process is employed, the following problems arise. Specifically, the problems include the need of facility and an increase in the number of working processes.
However, in the case where the magnet hole is set to be slightly larger than the outer shape of the small piece of the permanent magnet, a gap is generated between the rotor core and the small piece of the permanent magnet. The gap between the rotor core and the small piece of the permanent magnet acts as magnetic resistance. Therefore, magnetic flux density generated on the surface of the rotor decreases.
Further, a small piece of a permanent magnet formed from an Nd—Fe—B sintered magnet or a ferrite sintered magnet has characteristics of being hard and fragile, like ceramics. In view of this, a small piece of a permanent magnet cannot be formed to have a complex shape.
Specifically, the following shape is employed for a small piece of a permanent magnet. That is, a small piece of a permanent magnet is a columnar body with a rectangular cross-section. The columnar body with a rectangular cross-section is a planar plate. Alternatively, a small piece of a permanent magnet is a columnar body with a trapezoidal cross-section. A small piece of a permanent magnet is a columnar body with an arc cross-section. The columnar body with an arc cross-section is a plate having substantially a U shaped cross section.
Any of the small pieces of permanent magnets formed through the above molding process has a large dimension tolerance. Therefore, when the small pieces of the permanent magnets are used, a gap is formed between the rotor core and the used small piece of the permanent magnet.
To address this problem, PTL 1 discloses an interior permanent magnet rotor including a bonded magnet in a magnet hole. The bonded magnet is formed by filling a mixture constituting the bonded magnet into the magnet hole. The mixture constituting the bonded magnet includes magnet powders, resin material, and a small amount of additives. The mixture constituting the bonded magnet is used in the state in which magnet powders, resin material, and a small amount of additives are melted. The bonded magnet is molded in such a way that, after the mixture constituting the bonded magnet is filled in the magnet hole, a process such as a pressurizing process is performed. The process for molding the bonded magnet is referred to as a molding process below.
Particularly in the case where thermosetting resin is used as the resin material, the molding process includes the following processes. Specifically, the molding process includes a heating process for heating the mixture and melting the heated mixture. Since a thermosetting reaction is caused in the heated mixture, the mixture is cured. The cured mixture is cooled through a cooling process. The cooled mixture constitutes the bonded magnets.
In addition, in the case where thermoplastic resin is used as the resin material, the molding process includes the following processes. Specifically, the molding process includes a heating process for heating the mixture and melting the heated mixture. The heated mixture is cooled through a cooling process. The cooled mixture is re-cured to constitute the bonded magnets.
Note that, in the description below, a mixture constituting a bonded magnet is also referred to as a bonded magnet in some cases.
According to this configuration, the bonded magnet is filled without a gap along the shape of the magnet hole formed on the rotor core. Since there is no gap generated between the rotor core and the bonded magnet, the reduction in a magnetic flux generated on the rotor is suppressed.
Further, PTL 2 discloses a manufacturing method of an interior permanent magnet rotor using an insert die having a plurality of gates. The gate is an inlet opening from which a bonded magnet is inserted. In PTL 2, a mixture constituting a bonded magnet is inserted from both ends of a magnet hole using the above-mentioned insert die.
PTL 1: Unexamined Japanese Patent Publication No. H10-304610
PTL 2: Unexamined Japanese Patent Publication No. 2013-121240
A motor according to the present invention includes a stator and a rotor.
The stator includes a winding through which a drive current flows and a stator core around which the winding is wound.
The rotor includes a rotary shaft, a rotor core, and a plurality of bonded magnets.
The rotor core is mounted to the rotary shaft to form a columnar body in a direction of a shaft center of the rotary shaft. The rotor core includes an outer circumferential surface formed along the shaft center, and a plurality of magnet holes. Each of the plurality of magnet holes is located along the outer circumferential surface. Each of the plurality of magnet holes has a convex surface located on a side of the rotary shaft and a concave surface located on a side of the outer circumferential surface. Each of the plurality of magnet holes has a shape of projecting from the outer circumferential surface toward a position where the rotary shaft is located. Here, α1 is a distance between the convex surface and the concave surface on an end part located on the side of the outer circumferential surface. β1 is a distance between the convex surface and the concave surface on a central part located on the side of the rotary shaft. In each of the plurality of magnet holes, α1 is larger than β1.
Each of the plurality of bonded magnets is filled in each of the magnet holes. Here, α2 is a thickness of a magnet component located on the end part in an oriented direction of the magnet component. β2 is a thickness of a magnet component located on the central part in an oriented direction of the magnet component. In each of the plurality of bonded magnets, α2 is larger than β2.
In addition, the rotor has a plurality of d-axis magnetic flux paths and a plurality of q-axis magnetic flux paths. A plurality of d-axis magnetic flux paths generates magnet torque out of rotary torques generated on the rotor due to a rotating magnetic field generated by the stator, when a drive current flows through the winding. Similarly, a plurality of q-axis magnetic flux paths generates reluctance torque out of rotary torques.
Each of the d-axis magnetic flux paths is located to cross each of the plurality of bonded magnets. Each of the q-axis magnetic flux paths is located along each of the plurality of bonded magnets.
A motor according to the exemplary embodiment of the present invention can suppress deterioration in magnetic characteristics at low cost without increasing the size of the motor by the configuration described below.
Specifically, there is the problem described below in employing the bonded magnet disclosed in PTL 1 in an interior permanent magnet rotor used in a conventional motor by using the manufacturing method disclosed in PTL 2. That is, a mixture filled in each of magnet holes from both ends thereof to constitute a bonded magnet generates a flow toward the central part of each magnet hole. The mixture filled from both ends of each magnet hole forms a weld on the location where the flows of the bonded magnet merge. The mixture cured through a molding process constitutes the bonded magnet in the state of including the weld. Therefore, in the bonded magnet manufactured by the manufacturing process described above, the magnetic characteristics are deteriorated on the central part of the magnet hole where the weld occurs.
In view of this, the motor according to the exemplary embodiment of the present invention is configured to allow a mixture constituting a bonded magnet to easily flow by the configuration described below, thereby being capable of suppressing the reduction in the density of the bonded magnet. Therefore, even if a mixture constituting a bonded magnet is filled from a central part of a magnet hole, the motor can suppress deterioration in magnetic characteristics of the bonded magnet on an end part of the magnet hole.
In addition, in the motor according to the exemplary embodiment of the present invention, only a thickness α2 on a magnet end part, which is located on a position distant from a position where a gate is located and which is included in the bonded magnet, is set large. The present configuration can prevent a large increase in an amount of a material to be used for forming a bonded magnet. Thus, an inexpensive motor can be provided without increasing the size of the motor.
An exemplary embodiment of the present invention will be described below with reference to the drawings. Note that the exemplary embodiment described below is merely illustrative of implementing the present invention, and not restrictive of the technical scope of the present invention.
In addition,
In addition,
Firstly, one example of a process of assembling motor 100 according to the exemplary embodiment of the present invention will briefly be described with reference to
As illustrated in
As illustrated in
Firstly, rotor core 11 is prepared for rotor 10 (S1). Thin steel plates constituting rotor core 11 are punched by a die. Each of the steel plates is punched by a die to form a magnet hole. Rotary shaft 12 is inserted into each of a plurality of steel plates punched out by the die. The plurality of steel plates is laminated along the shaft center of rotary shaft 12 to form rotor core 11.
Then, a mixture constituting a bonded magnet is filled in a magnet hole formed on rotor core 11 (S2). The mixture constituting the bonded magnet is used in the state in which magnet powders, resin material, and a small amount of additives are melted. The mixture constituting the bonded magnet is filled in the magnet hole from a gate included in an insert die.
The mixture filled in rotor 10 is cured through a molding process to constitute a bonded magnet. During the molding process, a process according to the characteristic of the resin material included in the mixture is performed (S3).
On the other hand, stator core 41 is prepared for stator 40 (S4). As in rotor core 11, stator core 41 is formed by laminating thin steel plates. Insulator 42 which is an insulating member is attached to stator core 41 (S5).
Next, a winding 43 through which a current is to flow is wound around stator core 41 to which insulator 42 is attached (S6).
Rotor 10 and stator 40, which are individually prepared, are combined to each other (S7). As illustrated in
Next, the motor according to the exemplary embodiment of the present invention will be described in detail with reference to
As illustrated in
Stator 40 includes winding (43) through which a drive current flows and stator core 41 around which winding (43) is wound.
Rotor 10 includes rotary shaft 12, rotor core 11, and a plurality of bonded magnets 14.
Rotor core 11 is mounted to rotary shaft 12 to form a columnar body in a direction of shaft center 12a of rotary shaft 12. Rotor core 11 includes outer circumferential surface 11b formed along shaft center 12a, and a plurality of magnet holes 13. Each of the plurality of magnet holes 13 is located along outer circumferential surface 11b.
As illustrated in
Each of the plurality of bonded magnets 14 is filled in each of the plurality of magnet holes 13. Here, α2 is a thickness of a magnet component located on end part 15a in an oriented direction of the magnet component. β2 is a thickness of a magnet component located on central part 16a in an oriented direction of the magnet component. In each of the plurality of bonded magnets 14, α2 is larger than β2.
In addition, as illustrated in
Each of d-axis magnetic flux paths 20 is located to cross each of the plurality of bonded magnets 14. Each of q-axis magnetic flux paths 21 is located along each of the plurality of bonded magnets 14.
Notably, in the present exemplary embodiment, bonded magnets 14 are filled in magnet holes 13. Therefore, α1 and β1 indicating the thickness of magnet hole 13 and α2 and β2 indicating the thickness of bonded magnet 14 have substantially the following relation. That is, α1=α2 and β1=β2 are established.
The motor providing particularly significant operation and effects is as stated below.
Specifically, as illustrated in
In addition, as illustrated in
In addition, as illustrated in
Further, as illustrated in
In addition, as illustrated in
The interior permanent magnet rotor used in the motor according to the present exemplary embodiment will be described in more detail with reference to the drawings.
As illustrated in
Rotor 10 includes rotor core 11, a plurality of magnet holes 13, and a plurality of bonded magnets 14. Rotor core 11 is formed by laminating steel plates 11a, which are punched out, in the direction of shaft center 12a of rotary shaft 12. Mixture (14a) constituting bonded magnets 14 is filled in magnet holes 13.
As illustrated in
As illustrated in
Notably, as illustrated in
Specifically, in each bonded magnet 14, the radius of arc 18 included in concave surface 18a includes two or more different curvatures 1/R1a and 1/R1b. That is, the radius of arc 18 included in concave surface 18a is formed by connecting arcs having different curvatures of 1/R1a and 1/R1b to each other.
Meanwhile, in the case where a mixture constituting a bonded magnet is filled from a central part of a magnet hole using a gate included in an insert die, problems described below may arise.
Specifically, there may be the case where the density of the bonded magnet obtained by curing the mixture constituting the bonded magnet is different between the location near the gate from which the mixture is inserted and the location distant from the gate. That is, the result similar to the case where the filling pressure for the mixture constituting the bonded magnet is lowered is obtained on the location distant from the gate, that is, on the magnet end part.
Consequently, the bonded magnet obtained by curing the mixture may have deterioration in magnetic characteristics on the portion having low density.
In view of this, as illustrated in
According to this configuration, mixture 14a constituting bonded magnets 14 is filled in magnet holes 13 from gate 50 included in an insert die. In the present exemplary embodiment, mixture 14a constituting bonded magnets 14 is filled from central part 16a of each magnet hole 13. Mixture 14a to be filled to constitute bonded magnets 14 includes magnet powders, resin material, and a plurality of additives.
In this case, in rotor 10, magnet thickness α2 on magnet end part 15 located on end part 15a distant from gate 50 is larger than magnet thickness β2 on magnet central part 16 located on central part 16a where gate 50 is provided. Therefore, mixture 14a constituting bonded magnets 14 is easy to flow on end part 15a. Accordingly, the variation in density of mixture 14a constituting bonded magnets 14 is reduced more than conventionally in the region from central part 16a of magnet hole 13 to end part 15a of magnet hole 13. Since the variation in density of mixture 14a is reduced, an extreme density variation does not occur on bonded magnet 14 obtained by curing mixture 14a. Consequently, in bonded magnet 14, local deterioration in magnetic characteristics is not caused.
In addition, in the present configuration, only magnet thickness α2 on magnet end part 15 distant from gate 50 is set larger. Thus, the amount of the material to be used to constitute bonded magnet 14 can be decreased, in addition to the above-mentioned operation and effect. Accordingly, rotor 10 according to the present exemplary embodiment can suppress deterioration in magnetic characteristics at low cost without increasing the size of motor 100.
Specifically, the rotor used in the motor according to the present exemplary embodiment is configured to satisfy the following relation. That is, the decrease rate of the density of bonded magnet 14 is defined as A. In this case, bonded magnet 14 satisfies equation (1) with respect to magnet thickness α2 on magnet end part 15 and magnet thickness β2 on magnet central part 16.
β2=A×α2 (1)
Here, decrease rate A indicating the density of bonded magnet 14 is represented by the following equation. That is, as illustrated in
A=X/(Y×C) (2)
Then, as illustrated in
As illustrated in
As apparent from
In view of this, according to the rotor used in the motor according to the present exemplary embodiment, magnet thickness α2 on magnet end part 15 can be adjusted in proportion to the decrease rate of the density of bonded magnet 14. Specifically, magnet thickness α2 is set larger on magnet end part 15 where the density of bonded magnet 14 is lowered. Magnet thickness α2 may be increased in proportion to the decrease in the density of bonded magnet 14.
According to this configuration, fluidity of mixture 14a constituting bonded magnet 14 is enhanced. Therefore, in rotor 10 used in the motor according to the present exemplary embodiment, the density of bonded magnet 14 can be made uniform, regardless of the shape of magnet hole 13. Thus, rotor 10 can three-dimensionally suppress deterioration in magnetic characteristics.
Particularly, in rotor 10 used in the motor according to the present exemplary embodiment, magnet thickness γ on the side of end face 11d of magnet hole 13, at which the density of bonded magnet 14 obtained by curing mixture 14a is lowered, is increased, as illustrated in
According to this configuration, fluidity of mixture 14a constituting bonded magnet 14 is enhanced. Thus, in rotor 10 used in the motor according to the present exemplary embodiment, the variation in the density of mixture 14a is reduced more than conventionally in the region of magnet hole 13 from end face 11c located on the side of gate 50 to end face 11d located on the side opposite to gate 50, regardless of the shape of magnet hole 13. Since the variation in density of mixture 14a is reduced, an extreme density variation does not occur on bonded magnet 14 obtained by curing mixture 14a. Thus, rotor 10 can three-dimensionally suppress deterioration in magnetic characteristics.
In addition, as illustrated in
If resistance to demagnetization D1 and resistance to demagnetization D2 are equal to each other, the magnetic characteristics of bonded magnet 14 become uniform.
That is, in the case where the magnetic characteristics of bonded magnet vary, it is considered, for example, that demagnetization occurs on the portion of the bonded magnet where the magnetic characteristics are deteriorated.
In view of this, if the magnetic characteristics of bonded magnet 14 are made uniform as described above, the occurrence of problems such as demagnetization can be prevented.
As illustrated in
In this case, demagnetizing field is applied to bonded magnet 14 in the direction of reducing the magnetic flux of bonded magnet 14 from winding 43 on the portion of magnet hole 13 near the side of outer circumferential surface 11b. Therefore, bonded magnet 14 is required to increase resistance to demagnetization so as not to generate demagnetization.
In principle, the resistance to demagnetization of bonded magnet 14 increases in proportion to the magnet thickness. Therefore, the resistance to demagnetization of bonded magnet 14 can be increased by increasing the magnet thickness. However, if the magnet thickness is increased, the amount of magnet powders to be used for bonded magnet 14 is increased, which increases cost.
In view of this, in rotor 10 in the present exemplary embodiment, only the magnet thickness of bonded magnet 14 on magnet end part 15 where demagnetizing field is applied is increased. Thus, in rotor 10, the magnet thickness of bonded magnet 14 is increased only on a portion which is required to have increased resistance to demagnetization. In other words, rotor 10 according to the present exemplary embodiment enables an increase in resistance to demagnetization of bonded magnet 14 by increasing magnet powders at minimum to the optimum portion which is required to have increased resistance to demagnetization.
Accordingly, a motor having excellent magnetic characteristics can be provided at low cost without increasing the size of motor 100 by using rotor 10 according to the present exemplary embodiment.
Note that, in the above exemplary embodiment, the number of poles of rotor 10 is six. That is, the above exemplary embodiment indicates that the number of magnet holes 13 is six. The technical scope of the present invention is not limited to this number. When n is defined as a natural number, and if the number of poles of rotor 10 is 2n, the technical scope of the present invention encompasses rotor 10 having the present configuration.
In addition, the motor described above has a specification of 6-pole 9-slot concentrated winding. According to the technical scope of the present invention, the similar operation and effect can be obtained, even if other specifications are used. For example, the technical scope of the present invention encompasses a concentrated winding motor with other combinations. Further, the technical scope of the present invention also encompasses a distributed winding motor or a wave winding motor with respect to a winding of a slot.
In addition, similarly, the shape of bonded magnet 14 is not limited to the above-described shape. For example, the cross-section of bonded magnet 14 orthogonal to shaft center 12a may have a V shape or a U shape. If so, the similar operation and effect can be obtained.
The interior permanent magnet rotor according to the present invention and a motor using this rotor are widely applicable to motors using permanent magnets, such as electrical apparatuses or industrial machines.
Number | Date | Country | Kind |
---|---|---|---|
2014-187368 | Sep 2014 | JP | national |
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/JP2015/004451 | 9/2/2015 | WO | 00 |