JP2008182862A - Brushless motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent dimension variance and inconsistent treatment of a magnet cover by eliminating anneal treatment after press in the magnet cover, to improve the ease of assembly, and to reduce cogging torque. <P>SOLUTION: The roughly cylindrical magnet cover 28 formed in stainless steel is attached to a rotor 3 of a brushless motor 1. The magnet cover 28 is formed by means of drawing within a drawing ratio of 0.5-1 and used in a magnetized state. The cogging torque is restrained to be a predetermined reference value or less in the drawing ratio of 0.5-1 regardless of with/without anneal treatment. The anneal treatment while is thereby eliminated, while restraining the cogging torque to be the reference value or less. It is preferable that relative plate thickness of the magnet cover 28 is 0.8% or less from a viewpoint of output decrease prevention, and the plate thickness of the magnet cover 28 is 0.35 mm or less from a viewpoint of cogging torque decrease. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a brushless motor, and more particularly, to a magnet cover used for a brushless motor.

Conventionally, in a brushless motor, in particular, a brushless motor for an electric power steering device (EPS), a magnet cover is externally provided on the outside of the magnet so that even if the magnet is broken, the motor is not locked by the broken pieces. . This magnet cover is made of a non-magnetic material such as stainless steel, so that output reduction due to leakage magnetic flux is prevented. Moreover, the magnet cover attached to the outer periphery of the rotor magnet is usually formed in a substantially cylindrical shape, and is generally formed by using a metal pipe or drawing by a press to reduce manufacturing costs. It is. For example, Patent Document 1 discloses a rotating electrical machine in which a substantially cylindrical nonmagnetic member (magnet cover) using a metal pipe is mounted outside a permanent magnet of a rotor.
JP 2004-129369 A

  On the other hand, when such a magnet cover is pressed, stainless steel, which is originally a non-magnetic material, may become martensite and become a magnetic material. For this reason, conventionally, when manufacturing a magnet cover, annealing is performed after press working to make the stainless steel non-magnetic. However, when the annealing process is performed on the magnet cover, there is a problem in that the size varies and the workability at the time of assembling deteriorates. In addition, when unevenness occurs in the annealing process, there is a possibility that a magnetized portion is unevenly formed on the magnet cover, and the cogging torque increases accordingly. In particular, in an EPS motor, since an increase in cogging torque leads to deterioration in steering feeling, it is necessary to suppress it to a predetermined value or less, and a countermeasure for this is required.

  An object of the present invention is to suppress an increase in cogging torque due to magnetization of a magnet cover used in a brushless motor. Another object of the present invention is to eliminate the annealing process after press working and reduce the variation in the dimensions of the magnet cover.

  The brushless motor of the present invention is a brushless motor comprising a stator and a rotor rotatably disposed inside the stator, wherein the rotor is formed of a magnetic material, and the rotor core. A magnet attached to the outer periphery of the magnet and a substantially cylindrical magnet cover attached to the outside of the magnet, and the magnet cover draws a stainless steel material in a drawing ratio range of 0.5 to 1. It is formed.

  In the present invention, a stainless steel material is drawn at a drawing ratio of 0.5 to 1 to form a magnet cover, whereby the stainless steel material is martensitic transformed and the magnet cover is magnetized. On the other hand, within the range of the drawing ratio, the cogging torque can be suppressed to a predetermined reference value or less regardless of the presence or absence of annealing, so that the annealing process can be omitted while keeping the cogging torque below the reference value. For this reason, the increase in the cogging torque resulting from the variation in the dimension by annealing and the nonuniformity of annealing treatment can be prevented. Moreover, a time crack can also be prevented by performing a drawing process in the said range.

  In the brushless motor, the relative plate thickness of the magnet cover may be set to 0.8% or less, thereby suppressing a decrease in output due to leakage magnetic flux and reducing friction. Further, the plate thickness of the magnet cover may be set to 0.35 mm or less, which also reduces the cogging torque.

  According to the brushless motor of the present invention, as a magnet cover to be mounted on the rotor of the brushless motor, a stainless steel material drawn with a drawing ratio of 0.5 to 1 is used, so that the cogging torque is less than the reference value. Thus, it is possible to omit the annealing process. For this reason, it is possible to reduce the processing steps and reduce the cost, to prevent variation in dimensions due to annealing, and to improve the assemblability. Further, unevenness in the annealing process can be prevented, and an increase in cogging torque due to the process unevenness can be prevented.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view of a brushless motor according to an embodiment of the present invention, and FIG. 2 is an exploded perspective view of the brushless motor of FIG. As shown in FIG. 1, a brushless motor 1 (hereinafter abbreviated as “motor 1”) is an inner rotor type brushless motor having a stator (stator) 2 on the outside and a rotor (rotor) 3 on the inside. Yes. The motor 1 is used, for example, as a power source of a column assist type electric power steering device (EPS), and applies an operation assisting force to a steering shaft of an automobile. The motor 1 is attached to a speed reduction mechanism provided on the steering shaft, and the rotation of the motor 1 is transmitted to the steering shaft by being decelerated by the speed reduction mechanism.

  The stator 2 includes a bottomed cylindrical case 4, a stator core 5, a stator coil 6 wound around the stator core 5 (hereinafter abbreviated as coil 6), and a bus bar unit (terminal unit) 7 attached to the stator core 5. It is configured. The case 4 is formed in a bottomed cylindrical shape with iron or the like, and a bracket 24 made of aluminum die cast is attached to an opening of the case 4 with a fixing screw 23. The stator core 5 includes a plurality of divided cores 8 and has a configuration in which nine divided cores 8 are assembled in the circumferential direction. The split core 8 is formed by stacking core pieces made of electromagnetic steel plates, and an insulator 9 made of synthetic resin is attached around the core.

  A coil 6 is wound around the outside of the insulator 9, and an end portion 6 a of the coil 6 is drawn out in the radial direction on one end side of the stator core 5. A bus bar unit 7 in which a copper bus bar is insert-molded in a synthetic resin main body is attached to one end side of the stator core 5. Around the bus bar unit 7, a plurality of power supply terminals 11 protrude in the radial direction, and when the bus bar unit 7 is attached, the coil end 6 a is welded to the power supply terminal 11. In the bus bar unit 7, the number of bus bars corresponding to the number of phases of the motor 1 (here, three for U phase, V phase, W phase) is provided, and each coil 6 is a power supply terminal corresponding to that phase. 11 is electrically connected. After the bus bar unit 7 is attached, the stator core 5 is press-fitted into the case 4 and bonded and fixed to the inner peripheral surface of the case.

  A rotor 3 is inserted inside the stator 2. The rotor 3 has a rotor shaft 21, and the rotor shaft 21 is rotatably supported by bearings 22a and 22b. The bearing 22 a is fixed to the center of the bottom of the case 4, and the bearing 22 b is fixed to the center of the bracket 24. A cylindrical rotor core 25 is fixed to the rotor shaft 21, and a segment type magnet (permanent magnet) 26 is attached to the outer periphery thereof. A magnet holder 27 made of synthetic resin is inserted on the rotor shaft 21, and the magnet 26 is disposed on the outer periphery of the rotor core 25 in a form held by the magnet holder 27. In the motor 1, six magnets 26 are arranged along the circumferential direction, and a bottomed cylindrical magnet cover 28 is attached to the outside of the magnet 26.

  The magnet cover 28 is formed of stainless steel such as SUS304, and is formed by drawing from a disk-shaped blank material as described above. In the motor 1 according to the present invention, the draw ratio m (punch diameter of the magnet cover 28). / Blank diameter) is set to 0.5 to 1.0. FIG. 3 is an explanatory view showing the relationship between the magnet cover drawing ratio m and cogging torque in the case of SUS304 plate thickness 0.2 mm and drawing process: 5 drawing. As shown in FIG. 3, according to the experiments by the inventors, the cogging torque increases rapidly as the aperture ratio m decreases. This is considered to be because when the drawing ratio m is small, the punch diameter is small with respect to the blank, the deformation amount of the blank material is large, and the martensitic transformation induced by processing is large.

  In this case, when annealing is performed after processing, a decrease in cogging torque is recognized as shown by a broken line in FIG. However, although the effect of such an annealing process is remarkable when the drawing ratio is low, there is almost no effect when the drawing ratio is increased. When the drawing ratio is 0.5 or more, the presence or absence of annealing treatment is not present. Regardless of the value, it is below the reference value (10 Nm) required by EPS. On the other hand, when the drawing ratio is less than 0.5, the reference value is exceeded even if annealing is performed.

  That is, from the results of FIG. 3, when the drawing ratio m is 0.5 or more, stainless steel, which is an austenitic steel, is magnetized by martensitic transformation after drawing, but the presence or absence of annealing does not affect the cogging torque. I understand that. It was also found that if the drawing ratio m was set to 0.5 or more, the cogging torque was kept below the reference value even if the annealing process was omitted. Therefore, in the motor 1 according to the present invention, the aperture ratio m of the magnet cover 28 is set to 0.5 to 1.0, the cogging torque is kept below the reference value, the annealing process is omitted, the dimensional variation due to annealing, Unevenness of annealing treatment is prevented. Thereby, in the motor 1, the dimensional accuracy of the magnet cover 28 is stabilized, the workability at the time of assembling the cover is improved, and an increase in cogging torque due to processing unevenness is also suppressed.

  In stainless steel, a so-called “time crack” may occur when several days have passed after drawing, and a vertical crack may occur in the axial direction. Such a time crack is said to easily occur when the drawing ratio m is in the range of 0.43 to 0.38. As described above, if the drawing ratio m is set to 0.5 to 1.0, This period cracking can also be prevented.

  On the other hand, even when the aperture ratio m is set in the above range, the plate thickness increases as the relative plate thickness of the magnet cover 28 ((plate thickness t / cover outer diameter D) × 100) increases, and the magnetic flux of the magnet 26 increases. Is transmitted through the magnet cover 28, and the leakage magnetic flux increases. For this reason, when the relative plate thickness increases, the effective magnetic flux decreases and the motor output decreases. FIG. 4 is an explanatory diagram showing the relationship between the relative plate thickness and the motor torque when the aperture ratio m = 0.6. As shown in FIG. 4, according to the experiments by the inventors, when the relative plate thickness exceeds 0.8%, the torque rapidly decreases. Therefore, in the motor 1, the plate thickness of the magnet cover 28 is set so that the relative plate thickness is 0.8% or less while satisfying the above-described condition of the drawing ratio m.

  However, if the plate thickness of the magnet cover 28 is increased, as described above, the leakage magnetic flux increases and affects the cogging torque. Therefore, it is preferable to limit the plate thickness itself. FIG. 5 is an explanatory diagram showing the relationship between the magnet cover plate thickness and the cogging torque when the cover outer diameter D = 45.5 mm and the drawing ratio m = 0.5, 0.6, 0.8. As shown in FIG. 5, according to the experiments by the inventors, when the drawing ratio m = 0.5, 0.6, when the plate thickness is substantially larger than 0.35 mm, the drawing ratio m = 0.8. In this case, it was found that the cogging torque exceeded the reference value when the plate thickness was made larger than 0.4 mm. That is, even when the drawing ratio m is set to 0.5 or more, in order to keep the cogging torque below the reference value, it is basically necessary to set the plate thickness to 0.35 mm or less. Therefore, in the motor 1, the thickness of the magnet cover 28 is set to 0.35 mm or less while satisfying the above-described conditions, and the cogging torque is suppressed to a reference value or less.

  As described above, in the motor 1 according to the present invention, the drawing rate m is set to 0.5 to 1.0, and the magnet cover 28 magnetized by the drawing process is used, thereby suppressing the cogging torque and annealing treatment. Can be omitted. Therefore, it is possible to improve the dimensional accuracy of the magnet cover 28, reduce the cost by reducing the number of processes, and provide an inexpensive magnet cover. Moreover, the time cracking peculiar to stainless steel can also be prevented by setting the drawing ratio m to 0.5 to 1.0. Furthermore, by setting the relative plate thickness of the magnet cover 28 to be equal to or less than 0.8%, it is possible to suppress a decrease in output due to leakage magnetic flux and reduce friction. In addition, the cogging torque can be reduced by setting the plate thickness of the magnet cover 28 to 0.35 mm or less.

  On the other hand, a rotor (resolver rotor) 32 of a resolver 31 that is a rotation angle detecting means is attached to the end of the magnet holder 27. On the other hand, the stator (resolver stator) 33 of the resolver 31 is press-fitted into a metal resolver holder 34 and is fixed to the bracket holder unit 35 in that state. A sensor harness 36 for transmitting a signal output as the rotor 32 rotates is fixed to the resolver stator 33. The sensor harness 36 is welded to the terminal portion 33a of the stator 33, and an insulator 37 made of synthetic resin is attached to the terminal portion 33a. The sensor harness 36 is drawn between the bracket 24 and the bracket holder unit 35 along the circumferential direction, and is drawn out of the apparatus from the outer peripheral portion of the bracket 24 via the rubber grommet 38.

  In the motor 1, the resolver holder 34 is formed in a bottomed cylindrical shape, and is inserted and mounted in the central portion of the bracket holder unit 35. On the other hand, the opening side end portion where the flange portion 34 a is formed is lightly press-fitted into the outer periphery of the end portion of the rib 39 provided on the bracket 24. The rib 39 projects in a cylindrical shape toward the axial direction at the center of the bracket 24, and a bearing 22 b that supports the rotor shaft 21 is fixed to the inside of the rib 39. Therefore, by lightly press-fitting the resolver holder 34 into the rib 39, the resolver stator 33 is mounted concentrically with the rotor shaft 21, the core accuracy of the stator 33 and the rotor 32 of the resolver 31 is improved, and the rotor position detection accuracy is improved. Is planned.

  The bracket holder unit 35 is formed of synthetic resin, and a metal female screw portion 41 is insert-molded. A mounting screw 42 is screwed into the female screw portion 41 from the outside of the bracket 24, whereby the resolver holder 34 is fixed to the inside of the bracket 24. The attachment hole 34b formed in the flange portion 34a of the resolver holder 34 is a long hole extending in the circumferential direction, and the position of the resolver holder 34 can be finely adjusted in the circumferential direction. The bracket holder unit 35 is also provided with three external power feeding terminals 43. The external power supply terminal 43 is provided for each phase of U, V, and W, and when the bracket holder unit 35 is assembled to the bracket 24, the external power supply terminal 43 is provided so as to protrude in the radial direction from the side surface of the bracket 24. It has been.

  Each external power feeding terminal 43 (43U, 43V, 43W) is electrically connected to a connection terminal 44 (44U, 44V, 44W) provided in the bracket holder unit 35. Each connection terminal 44 protrudes from the main body 45 of the bracket holder unit 35 in the axial direction, and is welded to a bus bar terminal 46 (46U, 46V, 46W) provided on the bus bar unit 7. The bus bar terminal 46 also projects from the main body 47 of the bus bar unit 7 in the axial direction, and when the motor 1 is assembled, the bus bar terminal 46 and the connection terminal 44 face each other in parallel. In the motor 1, after the bracket 24 is attached to the case 4, the bus bar terminal 46 and the connection terminal 44 are fixed by welding. A work hole 48 is formed in the bracket 24, and a bracket cap 49 is attached to the work hole 48 after the welding process.

  Such a motor 1 is assembled as follows. First, the stator 2, the rotor 3, and the bracket assembly 51 are assembled individually. In this case, the bracket assembly 51 is an assembly product in which the bracket 24 in which the bearing 22 b is incorporated and the bracket holder unit 35 in which components related to the resolver stator 33 are assembled, and are fixed by a tapping screw 52. The stator 2 is an assembly product in which a bus bar unit 7 is attached to a stator core 5 around which a coil 6 is wound, and a power supply terminal 11 and a coil end 6 a are welded and accommodated in a case 4. The rotor 3 is an assembly product in which the rotor core 25 is fixed to the rotor shaft 21 and the magnet holder 27 is attached, then the magnet 26 is press-fitted and the magnet cover 28 is attached, and the resolver rotor 32 is press-fitted and fixed to the magnet holder 27. It is.

  After assembling such assemblies, the rotor 3 is attached to the bracket assembly 51, the stator 2 is externally mounted thereon, and the case 4 and the bracket 24 are fastened by the fixing screws 23. Next, the bus bar terminal 46 and the connection terminal 44 are fixed by welding through the work hole 48. In this state, motor resistance, insulation check, etc. are performed, and then the origin of the resolver 31 is adjusted. The origin adjustment is performed by finely adjusting the position of the resolver holder 34 from the outside of the bracket 24 in the circumferential direction by using the long attachment hole 34b. After adjusting the origin, the mounting screw 42 is inserted from the outside of the bracket 24 and is fixed to the female screw portion 41 by screwing. As a result, the flange portion 34 a of the resolver holder 34 is fixed so as to be sandwiched between the bracket 24 and the bracket holder unit 35. After tightening the attachment screw 42, the bracket cap 49 is attached. Thus, the assembly work of the motor 1 is completed, after which various characteristic checks and the like are performed to obtain a finished product.

It goes without saying that the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.
For example, in the above-described embodiment, the brushless motor used for the column assist type EPS is shown. However, the present invention can be applied to other types of EPS motors. In addition, the present invention is widely applicable not only to EPS and motors for various on-vehicle electric products, but also to general brushless motors.
Moreover, in the above-mentioned Example, although the example which used SUS304 as a stainless steel material was shown, you may use other austenitic stainless steel materials, such as SUS302.

It is sectional drawing of the brushless motor which is one Example of this invention. It is a disassembled perspective view of the brushless motor of FIG. It is explanatory drawing which shows the relationship between the aperture ratio m of a magnet cover, and a cogging torque. It is explanatory drawing which shows the relationship between relative board thickness and a motor torque. It is explanatory drawing which shows the relationship between magnet cover board thickness and cogging torque.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Brushless motor 2 Stator 3 Rotor 4 Case 5 Stator core 6 Stator coil 6a Coil end 7 Bus bar unit 8 Divided core 9 Insulator 11 Feeding terminal 21 Rotor shaft 22a, 22b Bearing 23 Fixing screw 24 Bracket 25 Rotor core 26 Magnet 27 Magnet holder 28 Magnet cover 31 Resolver 32 Rotor 33 Stator 33a Terminal portion 34 Resolver holder 34a Flange portion 34b Mounting hole 35 Bracket holder unit 36 Sensor harness 37 Insulator 38 Rubber grommet 39 Rib 41 Female screw portion 42 Mounting screw 43 External power supply terminal 44 Connection terminal 45 Main body Portion 46 Busbar terminal 47 Body 48 Working hole 49 Bracket cap 51 Bracket assembly 52 Tapping screw m Rate (punch diameter / blank diameter)

Claims (3)

A brushless motor having a stator and a rotor rotatably disposed inside the stator,
The rotor includes a rotor core formed of a magnetic material, a magnet attached to the outer periphery of the rotor core, and a substantially cylindrical magnet cover attached to the outside of the magnet.
The magnet cover is formed by drawing a stainless steel material in a drawing ratio of 0.5 to 1.   2. The brushless motor according to claim 1, wherein the magnet cover has a relative plate thickness of 0.8% or less.   3. The brushless motor according to claim 1, wherein the magnet cover has a thickness of 0.35 mm or less.

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