JP2011083056A - Axial gap motor and electric power steering device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an axial gap motor, along with a power steering device, capable of obtaining a motor torque suitably by ensuring the density of a magnetic flux going from a rotor to a stator or from the stator to the rotor. <P>SOLUTION: The entire flank on the side of the stator 23 of a magnet 35 is covered with a common yoke 36. A curved surface 36a, which is convex to the side of the stator 23, is formed at the flank on the side of the stator 23 of the common yoke 36. Accordingly, the magnetic flux distribution of a magnet 35 can be made into a smooth sine curve. That is, the density of the magnetic flux going from the rotor 30 to the stator 23 is secured suitably. Hereby, the occurrence of torque ripple is suppressed, and a motor can be driven smoothly by a three-phase sine wave driving system. Moreover, the magnetic flux generated from a coil is shut in the common yoke 36, so that it can not pass the magnet 35. Thereby, the density of the magnetic flux of the coil can be secured suitably. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an axial gap type motor and an electric power steering apparatus.

  Conventionally, as described in Patent Document 1, a so-called axial gap type motor is known in which a stator is opposed to a disk-type rotor with an air gap between end faces in the axial direction thereof. The motor obtains a rotational driving force by a magnetic force acting between the surfaces of the rotor and the stator facing each other in the axial direction. The motor has an advantage that the thickness in the axial direction can be reduced as compared with a so-called radial type motor composed of a cylindrical rotor and an annular stator surrounding the peripheral surface thereof. Patent Document 2 describes that such an axial gap type motor is employed as a drive source of an electric power steering apparatus.

JP 2005-341696 A JP 2008-172844 A

  The axial gap type motor as described above is a kind of brushless motor, and it is assumed that a three-phase sine wave driving method is adopted as its driving method. In this case, sinusoidal AC voltages with different phases are applied to the three-phase motor coils through PWM control. The sine wave driving method is said to have high motor winding utilization and good motor efficiency. Further, smooth rotation of the motor and smooth output characteristics can be obtained. For this reason, for example, a sine wave driving method is often adopted as a driving method for a motor used in the above-described electric power steering apparatus.

  However, the conventional motor may not be able to ensure the required motor torque. That is, during sine wave driving, there is a concern that torque ripple (fluctuation in motor torque) is large and smooth rotation becomes difficult. Specifically, since the stator side surface of the rotor is a flat surface, the distribution of the magnetic field (magnetic flux) from the rotor to the stator is also flat. In other words, there is a possibility that a sufficient magnetic flux density from the rotor to the stator cannot be secured. As a result, in the conventional motor, it is difficult to perform smooth sine wave driving, and the required motor torque may not be sufficiently secured. For example, it is difficult to apply to an apparatus that requires a large motor torque such as an electric power steering apparatus, particularly a rack drive type. In the conventional motor, it is conceivable that the rotor is fixed and used as a stator, and the stator is provided so as to be rotatable and used as a rotor. Will occur.

  The present invention has been made to solve the above-described problems, and the object thereof is to suitably obtain motor torque by ensuring the density of magnetic flux from the rotor to the stator or from the stator to the rotor. It is an object of the present invention to provide an axial gap type motor and an electric power steering device that can be used.

  The invention according to claim 1 is an axial gap type motor in which a rotor or a stator including a permanent magnet and a stator or a rotor including an electromagnet are arranged to face each other in the axial direction thereof. The rotor or stator includes a magnetic body that covers the entire surface of the permanent magnet that faces the stator or rotor, and the magnetic field distribution of the permanent magnet is a smooth sine curve. The gist is that the surface of the magnetic body on the stator or rotor side is formed with a curved surface that protrudes toward the stator or rotor.

  For example, when a configuration in which a permanent magnet is provided on the rotor side and an electromagnet is provided on the stator side, the following operations and effects are obtained. That is, by covering the entire surface of the permanent magnet on the stator side with a magnetic material, the magnetic flux generated from the electromagnet (exactly its coil) does not pass through the permanent magnet. For this reason, the magnetic flux density of the electromagnet can be suitably secured. As a result, motor torque can be suitably secured. Further, by forming a curved surface convex toward the stator side on the surface of the magnetic material on the stator side, the magnetic field distribution of the permanent magnet can be a smooth sine curve. That is, the density of the magnetic flux from the rotor to the stator is preferably ensured. Thereby, motor torque can be suitably secured. Moreover, generation | occurrence | production of a torque ripple is suppressed and a motor can be smoothly driven by a three-phase sine wave drive system. In addition, even if it is a case where the structure which provides an electromagnet on the rotor side and a permanent magnet on the stator side is employ | adopted, the effect | action and effect similar to the above-mentioned are acquired.

  The invention according to claim 2 is the axial gap type motor according to claim 1, further comprising a pair of rotors or stators including the permanent magnet and the magnetic body, wherein the rotors or stators are The gist of the present invention is to face each other with a stator or a rotor in between.

According to this configuration, a larger motor torque can be obtained by having a pair of rotors or stators.
According to a third aspect of the present invention, in the axial gap type motor according to the first or second aspect, the rotor or the stator is an entire surface of the permanent magnet opposite to the stator or the rotor. The gist of the invention is to have another magnetic body covering the surface.

  For example, when a configuration in which a permanent magnet is provided on the rotor side and an electromagnet is provided on the stator side, the following operations and effects are obtained. That is, the magnetic flux generated from the magnet is prevented from leaking from the surface opposite to the stator. For this reason, while the magnetic circuit of a permanent magnet is formed suitably, the magnetic flux density which goes to the stator side of a permanent magnet can be ensured on a more preferable level. In addition, even if it is a case where the structure which provides an electromagnet on the rotor side and a permanent magnet on the stator side is employ | adopted, the effect | action and effect similar to the above-mentioned are acquired.

  According to a fourth aspect of the present invention, in the axial gap motor according to any one of the first to third aspects, the permanent magnet and the magnetic body on the stator or rotor side are the rotor. The gist of the present invention is that it is divided into a plurality of portions with a gap in the rotation direction.

  For example, when a configuration in which a permanent magnet is provided on the rotor side and an electromagnet is provided on the stator side, the following operations and effects are obtained. That is, by forming a gap between adjacent permanent magnets, it becomes difficult for magnetic flux to be formed between adjacent permanent magnets, and magnetic flux generated from each permanent magnet tends to go to the stator side. For this reason, the magnetic flux density which goes to the stator side of a permanent magnet which concerns on generation | occurrence | production of a motor torque increases. Therefore, further increase in motor torque can be expected. In addition, even if it is a case where the structure which provides an electromagnet on the rotor side and a permanent magnet on the stator side is employ | adopted, the effect | action and effect similar to the above-mentioned are acquired.

  The invention according to claim 5 is the axial gap type motor according to any one of claims 1 to 4, further comprising a casing that accommodates the rotor and the stator, wherein the stator is the While being fixed to the inner peripheral surface of the casing via a fixing member, the rotor is supported so as to be relatively rotatable with respect to the inner peripheral surface of the casing, and the fixing member is made of a nonmagnetic metal material and fixed thereto. The gist is that a slit extending in a direction intersecting with the axial direction of the stator is formed on the surface on the child side.

  Due to the heat generated by energizing the electromagnet, the temperature of the casing rises and its volume increases. At that time, the portion of the fixing member in which the slit is formed is deformed, so that the thermal stress generated in the casing is absorbed and relaxed.

  The gist of the invention described in claim 6 is that, in the electric power steering apparatus, the axial gap motor according to any one of claims 1 to 5 is adopted as a drive source.

  As described above, the axial gap motor according to any one of claims 1 to 4 can be smoothly driven by a three-phase sine wave driving method. Also, the motor torque can be suitably secured. For this reason, it is suitable as a drive source for the electric power steering apparatus.

  According to the present invention, motor torque can be suitably obtained by ensuring the density of magnetic flux from the rotor to the stator or from the stator to the rotor.

1 is a perspective view showing a schematic configuration of a rack assist type electric power steering apparatus. FIG. Sectional drawing along the axis line of the motor of this Embodiment. The exploded perspective view of a motor. Sectional drawing along the axis of a motor similarly. FIG. 3 is a view taken along line AA in FIG. 2. (A) is a developed view of the main part of the rotor showing the shape of the common yoke in the present embodiment, and (b) shows the relationship between the electric angle of the motor and the magnetic flux density from the magnet toward the stator side. Graph. (A) is a perspective view of the rotor and stator which show the magnetic circuit by the permanent magnet of this Embodiment, (b) is a perspective view of the rotor and stator which similarly show the magnetic circuit by an electromagnet (coil). Sectional drawing of the principal part of the rotor in other embodiment. Sectional drawing of the principal part of the rotor in other embodiment. The top view of the magnetic pole member in other embodiment. The principal part side view of the rotor in other embodiment. Sectional drawing along the axial direction of the stator in other embodiment. Sectional drawing along the axial direction of the rotor in other embodiment. Sectional drawing along the axial direction of the rotor in other embodiment.

  Hereinafter, an embodiment in which the present invention is embodied in a so-called rack assist type electric power steering apparatus will be described with reference to FIGS. In this rack assist type electric power steering apparatus, a motor which is a driving source thereof is disposed as a hollow motor coaxially with a rack shaft (exactly, an outer peripheral portion thereof). In this apparatus, the rack shaft is directly assisted through a ball screw mechanism.

<Overall configuration>
As shown in FIG. 1, the steering shaft 12 to which the steering 11 is fixed is connected to a rack and pinion mechanism 13. The rotation of the steering shaft 12 due to the steering operation is converted into a reciprocating linear motion of a rack shaft (not shown) inserted into the rack housing 14 by the rack and pinion mechanism 13. When the rudder angle of the steered wheels 15 is changed by the reciprocating linear motion of the rack shaft, the traveling direction of the vehicle is changed.

  The electric power steering apparatus 1 includes a motor 16 that applies an assisting force for assisting a steering operation to a steering system (here, the rack shaft described above), and an electronic control unit (ECU) that controls the operation of the motor 16. 17. The motor 16 is disposed coaxially with the rack shaft in the rack housing 14. The motor torque generated by the motor 16 is transmitted to the rack shaft via a ball screw mechanism (not shown) provided coaxially with the rack shaft, as with the motor 16. In this example, an axial gap type brushless motor is employed as the motor 16. The motor 16 will be described in detail later.

  The electronic control unit 17 calculates a target assist force based on the steering torque τ and the vehicle speed V acquired through the torque sensor 18 and the vehicle speed sensor 19, and uses a motor drive circuit (not shown) to generate the target assist force in the motor 16. Power supply control of the motor 16 is performed. The assist force applied to the steering system is controlled through power supply control of the motor 16. As a driving method of the motor 16, a three-phase (U phase, V phase, W phase) sine wave driving method is employed. That is, sinusoidal AC voltages having different phases are applied to the motor coils of each phase of the motor 16 through PWM control. Thereby, the motor 16 rotates.

<Motor>
Next, the configuration of the motor will be described in detail. As shown in FIG. 2, the casing 21 of the motor 16 is formed in a cylindrical shape whose both end faces are opened by a nonmagnetic metal material such as a stainless steel material. A cylindrical fixing ring 22 is press-fitted and fixed to the inner peripheral surface of the casing 21. A plurality of annular slits 22 b are formed on the inner peripheral surface of the fixing ring 22. In this example, the two slits 22 b are provided at intervals in the axial direction of the fixing ring 22. The cutting depth of the slit 22 b is appropriately set between the inner peripheral surface of the fixing ring 22 and a position near the inner peripheral surface of the casing 21. The slits are provided so that excessive stress is not applied to the base of the magnetic pole portion 27 (in the vicinity of the connecting portion with respect to the core 24) due to the difference in thermal expansion and rigidity between the casing 21 and the core 24 constituting the stator 23 described later. The shape of 22b is determined. The fixing ring 22 is made of a soft nonmagnetic metal material such as aluminum which is also a good heat conductor. That is, the fixing ring 22 functions as a heat passage through which Joule heat generated when a coil 25 constituting a stator 23 described later is energized is transmitted. An annular columnar stator 23 is fixed to the inner peripheral surface of the fixing ring 22.

<Stator>
As shown in FIG. 3, the stator 23 includes a plurality of (18 in this example) electromagnets 26 each including a rod-shaped core 24 and a coil 25 wound around the core 24. Being done. The core 24 is formed in a sector-shaped column shape by a magnetic material such as iron, and fan-shaped plate-shaped magnetic pole portions 27 are provided at both ends thereof. In the core 24, a coil 25 is formed by winding a conductive wire between the magnetic pole portions 27. In addition, as shown in FIG. 2, the magnetic pole portion 27 protrudes outside the coil 25 provided in the core 24. In the pair of upper and lower magnetic pole portions 27 of the core 24, a fixing ring 22 is fitted between the protruding portions 27a that are the protruding portions. Of the pair of upper and lower projecting portions 27 a that sandwich the fixing ring 22, the lower projecting portion 27 a in FIG. 2 is in contact with a step surface 21 a formed on the inner peripheral surface of the casing 21. Thereby, the downward displacement in FIG. 2 of the fixing ring 22 and each electromagnet 26 is regulated. Then, by tightening the annular fixing nut 28 against the inner peripheral surface of the casing 21 through the opening on the opposite side of the stepped surface 21a of the casing 21, the pair of upper and lower protruding portions 27a of each magnetic pole portion 27 is The fixing ring 22 is sandwiched between the step surface 21a and the fixing nut 28 with the fixing ring 22 interposed therebetween. Thereby, the retaining ring 22 and each electromagnet 26 are prevented from coming off from the casing 21.

  Each core 24 is disposed so as to extend in parallel with an axial direction of an output shaft 31 described later. As shown in FIG. 3, the electromagnet 26 includes, for example, three sets of six sets of a U + phase, a V + phase, a W + phase, and U-phase, V-phase, and W-phase corresponding to these. That is, a total of 18 pieces are provided.

<Rotor>
As shown in FIG. 2, a hollow output shaft 31 is rotatably inserted into the insertion hole 23 a of the stator 23. The outer diameter of the output shaft 31 is set smaller than the inner diameter of the insertion hole 23 a of the stator 23. The inner diameter of the output shaft 31 is set to such an extent that the rack shaft described above can be inserted and displaced in the vertical direction in FIG.

  As shown in FIG. 4, the output shaft 31 is relative to the inner surface of the casing 21 via bearings 32 interposed between the outer peripheral surface at both ends and the inner peripheral surface at both ends of the casing 21. It is rotatably supported. As shown in the figure, the motor 16 is coaxially incorporated and connected to an intermediate portion of the rack housing 5 via the casing 21. As described above, a ball screw is inserted into the output shaft 31 and a ball screw nut that is screwed into the ball screw so as to be movable back and forth is fixed in an internally fitted state. For this reason, the ball screw nut rotates together with the output shaft 31. Therefore, the rotational motion of the motor 16 is converted into a linear motion of the ball screw through the ball screw nut. This linear movement of the ball screw is transmitted to the rack shaft in the rack housing 5 as an assist force.

  As shown in FIG. 2, the output shaft 31 is provided with two rotors 30, 30 facing each other with the stator 23 interposed therebetween. The rotor 30 has a magnet support member 33 fixed to the output shaft 31. The magnet support member 33 includes a cylindrical insertion portion 33a, an annular flange portion 33b formed on the outer peripheral surface of the insertion portion 33a, and a cylindrical protection portion 33c formed on the outer peripheral edge of the flange portion 33b. It becomes. The magnet support member 33 is fixed in a state in which the insertion portion 33 a is externally fitted to the output shaft 31. Both magnet support members 33 are attached to the output shaft 31 so that their insertion portions 33a face each other. The magnet support member 33 is integrally formed of a nonmagnetic material such as a stainless steel material.

  An annular plate-shaped magnet yoke 34 is fixed to the insertion portion 33a of the magnet support member 33 in an externally fitted state. The magnet yoke 34 is formed of a magnetic material such as iron, thereby forming a magnetic path for confining a magnetic flux generated from a magnet described later. The magnet yoke 34 is bonded to the inner peripheral surface on the insertion portion 33a side, the outer peripheral surface on the protection portion 33c side, and the side surface on the flange portion 33b side with an adhesive or the like.

  Six magnets (permanent magnets) 35 are fixed to the side surface of the magnet yoke 34 on the stator 23 side. As shown in FIG. 5, each magnet 35 has a fan-plate shape, that is, a shape obtained by dividing a circular flat plate into a plurality of equal parts (in this example, six equal parts) in the circumferential direction. As shown in the figure, each magnet 35 is annularly arranged at a constant interval in the circumferential direction with respect to the side surface of the flange portion 33b on the stator 23 side. As shown in FIG. 5, each magnet 35 is two-pole magnetized in the thickness direction (the axial direction of the output shaft 31). Further, each magnet 35 is provided so that the N pole and the S pole are alternated in the rotation direction of the output shaft 31. Further, the pair of magnets 35 facing each other with the stator 23 interposed therebetween in the axial direction of the output shaft 31 are provided so that different polarities face each other.

  A common yoke 36 is fixed to the side surface of each magnet 35 on the stator 23 side. The common yoke 36 is formed of a magnetic material such as iron, thereby forming a magnetic path for confining the magnetic flux generated from the magnet 35 and the coil 25. The common yoke 36 is bonded to the side surface on the insertion portion 33a side, the side surface on the protection portion 33c side, and the side surface on the magnet 35 side with an adhesive or the like. The common yoke 36 has the same shape as the magnet 35. That is, as shown in FIG. 3, the common yoke 36 has a shape obtained by dividing an annular flat plate into a plurality of equal parts (in this example, six equal parts) in the circumferential direction. As shown in the figure, the outer shape of the common yoke 36 coincides with the magnet 35 when viewed from the direction along the axis of the output shaft 31. In other words, the entire side surface of the magnet 35 on the stator 23 side is covered with the common yoke 36. By means of the common yoke 36 and the magnet yoke 34 described above, each magnet 35 is embedded in a magnetic material. As shown in FIG. 2, a slight gap is formed between each common yoke 36 and the stator 23.

<Motor assembly method>
Next, a method for assembling the motor configured as described above will be described. As shown in FIG. 3, first, the two rotors 30, 30 are assembled in advance by fixing the magnet yoke 34, the magnet 35, and the common yoke 36 to the two magnet support members 33, respectively. The stator 23 is also assembled in advance. The assembly of the stator 23 is performed as follows, for example. That is, the magnetic pole portion 27 is fixed to one end portion of each core 24 by welding or the like. Next, the coil 25 is inserted from the end opposite to the end to which the magnetic pole portion 27 of each core 24 is fixed, and the core 24 and the coil 25 are fixed tightly with an adhesive or the like. And the core 24 and the coil 25 which make these integral are inserted in the fixing ring 22, and the magnetic pole part 27 is fixed to the remaining one end part of each core 24 by welding etc. from the opposite side. Thereby, the assembly of the stator 23 is completed. For example, the fixing ring 22 may be configured by combining semi-cylindrical divided bodies. In this way, after assembling the core 24, the coil 25, and the two magnetic pole portions 27, the fixing ring 22 can be attached to them.

  Next, one rotor 30 is fixed to the output shaft 31. That is, the output shaft 31 is press-fitted into the insertion portion 33a of the magnet support member 33 and fixed with a nut or key (not shown). Next, the stator 23 is inserted into the output shaft 31 to which the one rotor 30 is fixed, and then the remaining rotor 30 is fixed to the output shaft 31. Thereafter, the two rotors 30 and 30 and the stator 23 that are integrated with each other are inserted into the casing 21. Then, the stator 23 is fixed to the casing 21 by tightening the fixing nut 28 with respect to the casing 21. The output shaft 31 is rotatably supported on the casing 21 via bearings 32 at both ends thereof. Thus, the assembly work of the motor 16 is completed. The assembly procedure of the motor 16 may be changed as appropriate.

<Shape of common yoke and magnetic field distribution>
Next, the shape of the common yoke 36 will be described in detail with reference to FIG. FIG. 6A shows a state in which the stator 23 and the rotor 30 are developed by cutting one portion thereof in the axial direction. As shown in the figure, the side surface of the common yoke 36 on the stator 23 side is formed with a curved surface 36a (curved surface) that is curved so as to be convex toward the stator 23 side. The distance L between the curved surface 36a and the stator 23 is the largest at both ends of the curved surface 36a, gradually decreases toward the center, and becomes the minimum at the center. The distance L between the common yoke 36 and the stator 23 greatly affects the magnetic resistance. That is, the smaller the distance L between the common yoke 36 and the stator 23, the smaller the magnetic resistance, and conversely, the larger the distance L, the larger the magnetic resistance. Therefore, as shown in the graph of FIG. 6B, the magnetic field distribution of the magnet 35 when the horizontal axis represents the electrical angle (mechanical angle) and the vertical axis represents the magnetic flux density (Bz) from the magnet 35 toward the stator 23. Draws a sine curve. When attention is paid to one magnet 35, the distance between the centers of the gaps between the adjacent magnets 35 corresponds to an electrical angle of 180 degrees (mechanical angle of 60 degrees). This is because six magnets 35 are used in this example. In this way, by making the side surface of the common yoke 36 on the side of the stator 23 into a curved shape, a so-called sine magnetic field is formed. As a result, motor torque can be suitably obtained through three-phase sine wave drive.

  Incidentally, when the side surface of the common yoke 36 on the stator 23 side is planar, the magnetic field generated by the magnet 35 is also planar. In this case, the motor torque may not be sufficiently obtained. There is also a concern that a large torque ripple may occur. Therefore, when the three-phase sine wave driving method is adopted as the driving method of the motor 16 as in this example, the shape of the side surface of the common yoke 36 on the stator 23 side is set to the stator 23 side as in this example. It is necessary to have a curved shape so as to be convex.

<Magnet magnetic circuit>
Next, the magnetic circuit of each magnet 35 will be described. As shown by the solid arrows in FIG. 7A, the magnetic flux generated from each magnet 35 passes through the inside of the magnet yoke 34 and the common yoke 36 (while being confined), and is provided on opposite sides of each other. It is formed between the magnets 35 of the child 30. The entire side surface of the magnet 35 on the stator 23 side is covered with a magnetic body, that is, the common yoke 36, and a curved surface 36 a that protrudes toward the stator 23 is formed on the side surface of the common yoke 36 on the stator 23 side. As a result, the magnetic flux generated from the magnet 35 is preferably directed toward the stator 23 side. Further, a gap is formed between the magnets 35 adjacent in the rotation direction of the rotor 30. For this reason, it is difficult to form a magnetic flux between the magnets 35 adjacent to each other in the rotation direction, and the magnetic flux of the magnet 35 tends to go toward the stator 23 side. Therefore, the density of the magnetic flux toward the stator 23 side of the magnet 35 is suitably ensured.

<Magnetic circuit of coil>
Next, the magnetic circuit of each coil 25 will be described. As indicated by broken arrows in FIG. 7B, when three-phase AC power is applied to each coil 25, the magnetic flux generated from these coils 25 is formed in a form confined inside the common yoke 36. The Specifically, the magnetic flux passes through each common yoke 36 and each magnetic pole portion 27. That is, the magnetic flux generated from each coil 25 does not interlink with the magnet 35. Since the magnetic flux of the coil 25 does not pass through the magnet 35, the coil magnetic flux is not affected by the magnetic resistance of the magnet 35. For this reason, it becomes possible to generate the magnetic flux of the coil 25 efficiently. The magnetic flux density of the coil 25 is also ensured suitably. In the figure, as an example, magnetic fluxes corresponding to the U + phase and the U− phase are mainly shown. This is due to the following reason. That is, although the magnetic flux is generated also in the coil 25 corresponding to each phase between the U phase and the U− phase, the magnetic fluxes in the opposite directions cancel each other, so that the magnetic flux shown in FIG. It will remain.

<Effect of Embodiment>
Therefore, according to the present embodiment, the following effects can be obtained.
(1) The entire side surface of the magnet 35 on the stator 23 side is covered with the common yoke 36. Then, a curved surface 36 a that protrudes toward the stator 23 is formed on the side surface of the common yoke 36 on the stator 23 side. For this reason, the magnetic field distribution of the magnet 35 can be a smooth sine curve. That is, the density of the magnetic flux from the rotor 30 toward the stator 23 is preferably ensured. Thereby, generation | occurrence | production of a torque ripple is suppressed and the motor 16 can be smoothly driven by a three-phase sine wave drive system. Generation of noise is also suppressed. Further, since the entire side surface of the magnet 35 on the stator 23 side is covered with the common yoke 36, the magnetic flux generated from the coil 25 does not pass through the magnet 35. For this reason, the magnetic flux density of the coil 25 can be suitably secured. As a result, a motor torque can be ensured.

(2) The pair of rotors 30 are opposed to each other with the stator 23 interposed therebetween. For this reason, compared with what has the single rotor 30, a larger motor torque can be obtained.
(3) The rotor 30 includes a common yoke 36 that covers the entire surface of the magnet 35 on the stator 23 side, and a magnet yoke 34 that covers the entire surface on the side opposite to the stator 23. For this reason, it is suppressed that the magnetic flux emitted from the magnet 35 leaks from the surface opposite to the stator 23. Therefore, the magnetic circuit of the magnet 35 is suitably formed, and the density of the magnetic flux toward the stator 23 side of the magnet 35 can be secured at a more preferable level.

(4) In one rotor 30, the plurality of magnets 35 and the plurality of common yokes 36 are annularly arranged with a gap in the rotation direction of the rotor 30.
By forming a gap between the adjacent magnets 35, it becomes difficult to form a magnetic flux between the adjacent magnets 35, and the magnetic flux generated from each magnet 35 is easily directed to the stator 23 side. For this reason, the density of the magnetic flux which goes to the stator 23 side of the magnet 35 concerning generation | occurrence | production of a motor torque increases. Therefore, further increase in motor torque can be expected.

  (5) An annular slit 22 b is formed on the inner peripheral surface of the fixing ring 22. Due to changes in the ambient temperature (rise and fall) and heat generated by energization of the coil 25, the stress at the base portion of the magnetic pole portion 27 due to the difference in linear expansion coefficient due to the difference in material may be excessive. In order to relieve the stress, the fixing ring 22 is deformed by the slit 22b that lowers the rigidity in the axial direction of the fixing ring 22 that presses the magnetic pole portion 27, and the stress is relieved.

  (6) The magnet 35, the magnet yoke 34, and the common yoke 36 are connected to the output shaft 31 via the magnet support member 33 formed of a nonmagnetic material. For this reason, it is suppressed that the magnetic flux emitted from the magnet 35 leaks to the output shaft 31 side. Therefore, the magnetic flux density to the stator 23 side of the magnet 35 is suitably ensured.

  (7) Further, the side surface on the casing 21 side of the magnet 35, the magnet yoke 34, and the common yoke 36 is covered by the protection portion 33 c of the magnet support member 33. For this reason, it is suppressed that the magnetic flux emitted from the magnet 35 leaks to the casing 21 side. Therefore, the density of the magnetic flux toward the stator 23 side of the magnet 35 can be suitably ensured.

  (8) According to the motor 16 of this example, as described above, smooth driving by the three-phase sine wave driving method is realized. Also, the motor torque can be suitably secured. For this reason, it is suitable as a drive source of the electric power steering apparatus 1.

  (9) In the axial gap type motor 16, the stator 23 made of an electromagnet is sandwiched between two rotors 30 made of magnets (permanent magnets) 35. For this reason, compared with what is called a radial gap type motor, the opposing area of the rotor 30 (magnet 35) and the stator 23 (electromagnet) can be taken large. Therefore, the physique can be downsized or the output can be increased.

<Other embodiments>
The embodiment described above may be modified as follows.
In this example, six magnets 35 are used, but four may be used, for example. In this way, the iron loss of the stator 23 is reduced.

  In this example, the protection part 33c of the magnet support member 33 may be omitted. That is, as shown in FIG. 8, the magnet support member 33 includes an insertion portion 33a and a flange portion 33b. Even in this case, the magnet 35, the magnet yoke 34, and the common yoke 36 are connected to the output shaft 31 via the magnet support member 33 formed of a nonmagnetic material such as stainless steel. Absent. For this reason, it is suppressed that the magnetic flux emitted from the magnet 35 leaks to the output shaft 31 side. As a result, the magnetic flux density to the stator 23 side of the magnet 35 is suitably ensured.

  As shown in FIG. 9, a synthetic resin layer 42 that covers the entire magnet yoke 34, magnet 35, and common yoke 36 may be formed. By molding the magnet yoke 34, the magnet 35, and the common yoke 36 with a synthetic resin material, the magnet 35 can be prevented from being separated from the magnet yoke 34 or the common yoke 36.

  -As shown in FIG. 10, you may integrally form each magnetic pole part 27. As shown in FIG. In other words, a single annular plate-shaped magnetic pole member 43 is provided, and each core 24 is connected thereto. In this case, from the viewpoint of securing the assembly workability of the coil 25, as shown in the figure, the notch groove 44 is formed corresponding to each core 24. Each cutout groove 44 may be formed to extend in the radial direction of the magnetic pole member 43, or may be formed as a diagonal cutout groove extending in a direction intersecting with the radial direction as a countermeasure against cogging.

  In the magnetic pole member 43, the remaining portion 44 a of the notch groove 44 (inner peripheral edge portion of the magnetic pole member 43) may be thinner than other portions of the magnetic pole member 43. For example, the magnetic pole member 43 is formed so that the thickness thereof becomes smaller toward the center of the magnetic pole member 43, or simply, the thickness of the remaining portion 44a is thinner than other portions. In this way, when the coil 25 is excited, the magnetic pole member 43 is saturated with a slight magnetic flux. For this reason, high efficiency of the motor 16 is achieved. Further, when the remaining portion 44a has insufficient rigidity, a thinned remaining portion may be formed on the outer peripheral side of the notch groove 44 in the same manner as the remaining portion 44a on the inner peripheral side of the magnetic pole member 43. . In this way, since the outer peripheral edge of the magnetic pole member 43 is connected by the thin portion on the outer peripheral side, the rigidity of the magnetic pole member 43 can be ensured.

  As shown in FIG. 11, another magnet 45 may be interposed in the gap between each magnet 35. In this case, the other magnet 45 is provided so as to have the same polarity as the polarity of the magnet 35 adjacent to the other magnet 45. In the example of the figure, the magnet 45 is provided so as to be N pole, N pole, S pole, and S pole from the left. By utilizing the repulsive force between the magnet 35 and the magnet 45, it becomes difficult for the magnetic flux to go back and forth between the adjacent magnets 35 with a gap therebetween, and the magnetic flux generated from the 35 tends to go to the stator 23 side. . For this reason, the density of the magnetic flux which goes to the stator 23 side of the magnet 35 can be suitably ensured.

  In this example, the core 24 has one stage, but it may have a plurality of stages (N stages: N is a natural number of 2 or more). The magnetic pole part 27 has N + 1 stages. For example, as shown in FIG. 12, when the core 24 has two stages, the magnetic pole part 27 has three stages. However, in this case, the central magnetic pole portion 27 in the axial direction of the stator 23 does not function as a magnetic pole. In this way, the total cross-sectional area of the coil 25 can be greatly increased in the axial direction of the stator 23. For this reason, a significant increase in the magnetic flux density emitted from the coil 25 can be expected. As the magnet 35, it is not necessary to employ a neodymium magnet or the like that has a larger magnet energy product than, for example, a bond magnet (plastic magnet) or a ferrite magnet. A bond magnet or ferrite magnet is sufficient.

  In addition, in this example, the stator 23 is sandwiched between the two rotors 30, but three or more rotors 30 may be provided. For example, as shown in FIG. 13, when three rotors 30 are provided, between the two adjacent rotors 30 in the axial direction of the output shaft 31, that is, the upper rotor 30 and the central rotor 30. The stators 23 are interposed between the intermediate rotor 30 and the central rotor 30 and the lower rotor 30. Here, the central rotor 30 is formed in such a manner that the same ones as the upper and lower two rotors 30 are integrated in the opposite direction. However, in the central rotor 30, unlike the two upper and lower rotors 30, the magnet yoke 34 is omitted. Moreover, the magnet support member 33 is integrally formed. For this reason, the central rotor 30 sandwiched between the two stators 23 can pass the magnetic flux from the S pole to the N pole. That is, the central rotor 30 is shared as the rotor of the upper and lower two stators 23. In this way, the motor torque can be increased. In addition, although it is possible to simply provide a plurality of so-called twin rotor types shown in FIG. 2 in this case, it is necessary to provide two rotors 30 between the two stators 23 in this case. In this regard, according to the configuration shown in FIG. 13, it is only necessary to interpose a single rotor 30 between the two stators 23 and without the magnet yoke 34. For this reason, an increase in the axial length of the motor 16 can be suppressed. If an increase in the axial length of the motor 16 is not a problem, a so-called twin rotor type as shown in FIG. 2 may be provided in a plurality of stages. Even in this case, it is possible to increase the motor torque.

  In this example, an annular slit 22b extending in the direction intersecting the axial direction of the stator 23 is formed on the inner peripheral surface of the fixing ring 22, that is, the surface on the stator 23 side. It does not have to be. For example, the slit 22b may be divided into a plurality. As long as the difference in linear expansion due to the difference in material between the casing 21 and the stator 23 (more precisely, the core 24) can be absorbed, it is possible to adopt other configurations in addition to the slit 22b. Further, when the linear expansion of the casing 21 can be absorbed by the axial thickness of the fixing ring 22, the slit 22b may be omitted.

  In this example, the magnet 35, the magnet yoke 34, and the common yoke 36 are connected to the output shaft 31 via the magnet support member 33 formed of a non-magnetic material. However, leakage of magnetic flux to the output shaft 31 is prevented. If it does not matter, the magnet support member 33 may be omitted. In this case, for example, as shown in FIG. 14, the magnet yoke 34 is directly connected to the output shaft 31, and the magnet 35 and the common yoke 36 are bonded and fixed to the magnet yoke 34. In this case, it is preferable to provide a slight gap D between the magnet 35 and the common yoke 36 and the output shaft 31.

  In this example, the magnet 35 is sandwiched between the magnet yoke 34 and the common yoke 36. However, if some magnetic flux leakage does not become a problem, the entire magnet 35 may be covered with a magnetic material. Conversely, only the entire side surface of the magnet 35 on the stator 23 side may be covered with the magnetic material. That is, the magnet yoke 34 may be omitted.

  In this example, the plurality of magnets 35 are annularly arranged with a gap therebetween, but may be configured as a single annular permanent magnet. Similarly, in this example, the same number of common yokes 36 as the magnets 35 are provided, but they may be configured as a single annular common yoke. Such a configuration can be employed when a sufficient magnetic flux toward the stator 23 is obtained.

  In the present example, a so-called twin rotor type motor in which the stator 23 is sandwiched between the two rotors 30 is used. However, a single rotor type in which the single rotor 30 is disposed opposite to the stator 23 is configured. May be.

  In this example, the magnetic pole portions 27 are arranged at equal intervals in the circumferential direction of the stator 23, but the magnetic pole pitches may be slightly shifted. In this example, the gap formed between the magnetic pole portions 27 adjacent to each other in the circumferential direction of the stator 23 is formed so as to extend along the radial direction of the stator 23, so that the gap is skewed. It may be. That is, each magnetic pole portion 27 is formed such that a gap formed between two magnetic pole portions 27 adjacent to each other in the circumferential direction of the stator 23 extends in a direction intersecting with the radial direction of the stator 23. In this way, torque ripple or cogging torque can be reduced.

  The rotor 30 in this example may be a stator, and the stator 23 may be a rotor. That is, the rotor 30 is fixed to the casing 21 and provided so as to be rotatable relative to the output shaft 31. In addition, the stator 23 is provided so as to be rotatable relative to the casing 21 and the rotor 30 and is provided so as to be integrally rotatable with the output shaft 31. Even in this case, the magnetic field distribution of the magnet 35 can be a smooth sine curve, as in the above embodiment. In this case, the rotor 30 (here, the stator) can be fixed to the casing 21 using the fixing ring 22 as shown in FIG. A slit 22b may be provided.

  -In this example, although the motor 16 was applied as a drive source of the electric power steering apparatus 1, the use is not ask | required.

  DESCRIPTION OF SYMBOLS 1 ... Electric power steering apparatus, 16 ... Motor, 21 ... Casing, 22 ... Fixing ring (fixing member), 22b ... Slit, 23 ... Stator, 26 ... Electromagnet, 30 ... Rotor, 34 ... Magnet yoke (magnetic body) 35 ... magnet, 36 ... common yoke (other magnetic body), 36a ... curved surface.

Claims (6)

In an axial gap type motor in which a rotor or a stator including a permanent magnet and a stator or a rotor including an electromagnet are arranged to face each other in the axial direction thereof,
The rotor or stator includes a magnetic body that covers the entire surface of the permanent magnet that faces the stator or rotor, and the magnetic body has a magnetic field distribution of the permanent magnet so as to have a smooth sine curve. An axial gap type motor in which a curved surface convex toward the stator or the rotor is formed on the surface of the stator or the rotor. The axial gap type motor according to claim 1,
An axial gap type motor comprising a pair of rotors or stators each including the permanent magnet and the magnetic body, the rotors or stators facing each other with the stator or rotor interposed therebetween. In the axial gap type motor according to claim 1 or 2,
The rotor or stator is an axial gap type motor having another magnetic body that covers the entire surface of the permanent magnet opposite to the stator or rotor. In the axial gap type motor according to any one of claims 1 to 3,
An axial gap type motor in which the permanent magnet and the magnetic body on the stator or rotor side are divided into a plurality with a gap in the rotation direction of the rotor. In the axial gap type motor according to any one of claims 1 to 4,
A casing for housing the rotor and the stator; the stator is fixed to an inner peripheral surface of the casing via a fixing member; and the rotor is rotatable relative to the inner peripheral surface of the casing To support
The axial member of the axial gap type, wherein the fixing member is made of a non-magnetic metal material, and a slit extending in a direction intersecting with the axial direction of the stator is formed on the surface of the stator.   An electric power steering apparatus in which the axial gap motor according to any one of claims 1 to 5 is employed as a drive source.

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