JP2010115022A - Brushless motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a brushless motor which meets a demand for motor miniaturization while ensuring the precision of rotor position detection by a resolver. <P>SOLUTION: A resolver stator 23 is housed in a bottomed, cylindrical resolver holder 24, and a magnetic shield 31 made of a magnetic material is attached to the exterior of the resolver holder 24. An air gap 36, which is an air layer, is formed between the resolver holder 24 and the magnetic shield 31. At first, a magnetic flux from the stator 2 is absorbed into the magnetic shield 31. A magnetic flux leaking out of the magnetic shield 31 is then weakend by the air gap 36 and is absorbed into the resolver holder 24. In this manner, the magnetic flux from the stator 2 hardly flows into the resolver stator 23, thereby suppressing the influence of magnetic flux from the stator 2 on the resolver stator 23. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a brushless motor, and more particularly to a technique for improving the accuracy of a resolver sensor signal in a brushless motor using a resolver as a rotor position detection device.
This relates to the mounting structure.

Generally, in a brushless motor, the rotational position of a rotor (rotor) is detected, and based on the detected rotor rotational position, a stator (stator) side coil (stator coil) is sequentially excited to rotate the rotor. . Conventionally, a detection device using an encoder, a Hall IC, or the like has been used for detecting the rotational position of the rotor, but in recent years, a brushless motor using a resolver has also increased. Resolvers are resistant to high temperatures and vibration environments, have a simple structure and are less likely to break down, and are therefore increasingly used for in-vehicle motors. In particular, in an electric power steering device (EPS), a high-performance rotor rotational position detection sensor is required to improve steering feeling, and the use of a resolver that is inexpensive and excellent in assemblage is increasing.
International Publication WO 2008/035755 A1 Publication

  In such a brushless motor using a resolver, a resolver holder for holding the resolver stator is provided between the resolver stator and the motor stator. The resolver holder is made of a magnetic material such as iron, and stores and holds the resolver stator, and also serves to shield the leakage magnetic flux from the motor stator and stabilize the sensor signal.

  However, when the motor is reduced in size, the distance between the field coil of the motor stator and the resolver approaches, so that the magnetic flux from the field coil increases and the magnetic flux cannot be shielded by the resolver holder. If the magnetic flux from the field coil cannot be blocked by the resolver holder, the leaked magnetic flux may affect the resolver and the output accuracy of the resolver may deteriorate. FIG. 6 is an explanatory diagram showing the sensor output when the resolver is disposed close to the field coil.

  In general, the output signal accuracy of the resolver is indicated by an error between the rotor rotation angle and the resolver output signal, and the more accurate the sensor is, the more linear the relationship between the two is as shown by the broken line in FIG. However, when the resolver is disposed close to the field coil, the sensor output is affected by the magnetic field generated by the field coil, and as shown by the solid line in FIG. 6, the linearity is impaired and the sensor accuracy is deteriorated. That is, the resolver output signal (sensor signal), which is essentially a triangular wave, is distorted, and the detection accuracy of the rotor rotational position is lowered.

  When the sensor accuracy deteriorates, a detection error occurs in the rotor rotation position, and there is a problem that the motor cannot be energized at an appropriate timing and torque fluctuation increases. In particular, in the case of a high output motor, the number of winding turns of the field coil and the applied current increase, so that the influence of the magnetic flux on the motor field side increases, and the tendency for the sensing accuracy to decrease increases. For this reason, in EPS using a high-power motor, the steering assist force may change in an unstable manner due to torque fluctuations of the motor, and the steering feeling may deteriorate.

  On the other hand, in order to prevent the resolver from being affected by the motor field, many techniques for separating the resolver from the motor stator have been conventionally employed. However, if the distance between the two is increased, the physique of the motor increases correspondingly, which hinders miniaturization of the motor. In particular, in the above-described EPS brushless motor, it is necessary to store the device in a narrow space in the automobile. Therefore, the motor itself is also required to be reduced in outer dimensions, which leads to an increase in the size of the motor. The configuration is difficult to adopt. Although the influence on the resolver can be reduced by increasing the plate thickness of the resolver holder, it is necessary to increase the plate thickness of the holder significantly in order to effectively block the leakage magnetic flux. As the plate thickness increases, the holder processing itself becomes very difficult.For example, in the case of a resolver holder formed by drawing, it is unavoidable that the number of processing steps increases exponentially and causes a cost increase. I want.

  An object of the present invention is to provide a brushless motor capable of satisfying the demand for miniaturization of the motor while ensuring the rotor position detection accuracy by the resolver.

  The brushless motor of the present invention is a stator having a stator core and a field coil wound around the stator core, and is rotatably disposed inside the stator, and is attached to the outer periphery of the rotor core and the rotor core. A brushless motor comprising: a rotor including a magnet; a resolver rotor that rotates together with the rotor; and a resolver stator disposed outside the resolver rotor, wherein the resolver stator and the field coil A first magnetic shielding member that covers the resolver stator and a second magnetic shielding member that is disposed outside the first magnetic shielding member and covers the first magnetic shielding member. .

  In the present invention, the first magnetic shielding member and the second magnetic shielding member magnetic body are interposed between the resolver stator and the field coil. For this reason, the magnetic flux on the stator side is first absorbed by the second magnetic shielding member, and only the magnetic flux leaked without being absorbed there reaches the first magnetic shielding member magnetic body and is absorbed there. Accordingly, the stator side magnetic flux hardly flows into the resolver stator, the influence of the stator side magnetic flux on the resolver stator is suppressed, and the linearity of the resolver output signal is ensured even when the resolver stator and the field coil are brought close to each other.

  In the brushless motor, a gap may be provided between the first magnetic shielding member and the second magnetic shielding member, and by arranging a gap formed of such an air layer between the two magnetic shielding members, The magnetic flux leaking from the second magnetic shielding member is weakened by the nonmagnetic air layer and reaches the first magnetic shielding member magnetic body. For this reason, the magnetic flux on the stator side is more difficult to flow into the resolver stator.

  As the second magnetic shielding member, a bottomed cylindrical magnetic shield made of a magnetic material and disposed so as to surround the outside of the first magnetic shielding member may be provided. Further, as the first magnetic shielding member, a resolver holder made of a magnetic material and accommodating and holding the resolver stator may be provided. The brushless motor is further provided with a cylindrical case for accommodating the stator and a bracket attached to an end of the case, and the resolver stator is accommodated and held in the bracket as the first magnetic shielding member. A cylindrical resolver fixing portion may be provided. In this case, the bracket may be formed of a nonmagnetic material such as aluminum.

  According to the brushless motor of the present invention, the first magnetic shielding member and the second magnetic shielding member are provided between the resolver stator and the field coil. Thus, the magnetic flux on the stator side can be absorbed more effectively. For this reason, it can suppress that a stator side magnetic flux flows into a resolver stator, and it becomes possible to suppress the influence of the magnetic flux of the stator side with respect to a resolver stator. Therefore, even when the resolver stator and the field coil are brought close to each other, the linearity of the resolver output signal is ensured, and the brushless motor can be miniaturized while ensuring the rotor position detection accuracy.

  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 that is Embodiment 1 of the present invention. 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 (field coil, hereinafter abbreviated as coil 6), and a bus bar unit (terminal unit) attached to the stator core 5. 7). The case 4 is formed in a bottomed cylindrical shape with iron or the like, and an aluminum die-cast bracket 8 is attached to an opening of the case 4 with a fixing screw 9. A synthetic resin insulator 11 is attached to the stator core 5, and a coil 6 is wound around the insulator 11.

  A bus bar unit 7 is attached to one end side of the stator core 5. The bus bar unit 7 has a structure in which a copper bus bar is insert-molded in a synthetic resin main body. Around the bus bar unit 7, a plurality of power supply terminals 12 protrude in the radial direction and are welded to the end of the coil 6 when the bus bar unit 7 is attached. 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. 12 is electrically connected. The stator core 5 is fixed in the case 4 after the bus bar unit 7 is attached.

  A rotor 3 is inserted inside the stator 2. The rotor 3 has a rotor shaft 13, and the rotor shaft 13 is rotatably supported by bearings 14a and 14b. The bearing 14 a is press-fitted and fixed at the bottom center of the case 4. The bearing 14 b is fixed to the center portion of the bracket 8 by a metal bearing holder 19. A cylindrical rotor core 15 is fixed to the rotor shaft 13, and a segment type magnet (permanent magnet) 16 is attached to the outer periphery thereof. A magnet cover 18 having a bottomed cylindrical shape is attached to the outside of the magnet 16. A magnet holder 17 made of synthetic resin is attached to the outside of the magnet 16. The magnet 16 is disposed on the outer periphery of the rotor core 15 so as to be held by the magnet holder 17.

  A rotor (resolver rotor) 22 of a resolver 21 serving as a rotation angle detection means is attached to the left end of the magnet holder 17 in FIG. On the other hand, the stator (resolver stator) 23 of the resolver 21 is press-fitted into a metal resolver holder 24 formed of a magnetic material and is accommodated in a bracket holder 25 made of synthetic resin. The resolver holder 24 is formed in a bottomed cylindrical shape, and is lightly press-fitted into the outer periphery of the end portion of the rib 26 provided in the center portion of the bracket 8. The bracket holder 25 is fixed to the inside of the bracket 8 by a tapping screw (not shown).

  The bracket holder 25 and the bracket 8 are fixed by the aforementioned tapping screw in a form in which the flange portion 24a of the resolver holder 24 is interposed therebetween. The flange portion 24a is attached between the bracket holder 25 and the bracket 8 so as to be slightly movable in the circumferential direction. After the position of the stator 23 is adjusted, the resolver holder 24 is attached to the bracket holder 25 by a resolver fixing screw 28. Fixed. A metal resolver fixing nut 27 is attached to the bracket holder 25, and a screw 28 is screwed into the nut 27 from the outside of the bracket 8. As a result, the bearing holder 19 and the resolver holder 24 are fastened together with the bracket 8, and the resolver holder 24 is fixed to the inside of the bracket 8 with the circumferential position adjusted. In the motor 1, the resolver 21 is thus arranged on the inner side of the motor than the bearing 14 b of the bracket 8, and the dead space generated inside the bracket 8 is also effectively utilized. Therefore, the motor can be reduced in size, but on the other hand, the resolver stator 23 and the coil 6 are close to each other, and as described above, there is a problem that the sensor accuracy is lowered due to magnetic flux leakage.

  Therefore, in the motor 1 according to the present invention, a magnetic shield (second magnetic shielding member) 31 formed of a magnetic material such as iron is further attached to the outside of the resolver holder (first magnetic shielding member) 24 to improve the sensor accuracy. The decline is prevented. FIG. 2 is a perspective view showing the configuration of the magnetic shield 31. As shown in FIG. 2, the magnetic shield 31 is also formed in a bottomed cylindrical shape like the resolver holder 24, and is attached so as to surround the outside of the resolver holder 24. The magnetic shield 31 includes a bottom wall portion 33 on one end side of a cylindrical side wall portion 32, and a through hole 34 is provided in the center of the bottom wall portion 33. A mounting piece 35 is provided on the other end side of the side wall portion 32 so as to extend in the radial direction, and is fixed to the bracket 8 together with the resolver holder 24 by the screw 28 described above.

  FIG. 3 is an explanatory diagram showing a simplified configuration of the motor 1 to which the magnetic shield 31 is attached. As shown in FIG. 3, when such a magnetic shield 31 is attached, the resolver stator 23 is disposed in the motor 1 so as to be surrounded by the resolver holder 24 and the magnetic shield 31. An air gap 36 is formed between the resolver holder 24 and the magnetic shield 31. The air gap 36 is a magnetic gap formed by an air layer that is a nonmagnetic material. That is, two magnetic shielding members are installed between the resolver stator 23 and the coil 6 with the air gap 36 interposed therebetween, and the resolver stator 23 has triple magnetic shielding by two shielding walls and an air layer. It is isolated from the coil 6 by its structure.

  FIG. 4 is an explanatory diagram showing the magnetic shielding action of the resolver holder 24 and the magnetic shield 31. In the motor 1, as shown in FIG. 4, the magnetic flux from the coil 6 is first absorbed by a magnetic shield 31 that is a shielding member close to the field side. On the other hand, the magnetic flux leaked outside without being absorbed by the magnetic shield 31 is weakened by the gap 36 and then flows into the resolver holder 24. At this time, since the magnetic flux flows into the resolver holder 24 only by the leakage magnetic flux of the magnetic shield 31, most of the magnetic flux is absorbed by the resolver holder 24 and almost no magnetic flux flows into the resolver stator 23. For this reason, even if the coil 6 and the resolver stator 23 are arranged close to each other, the magnetic flux from the coil 6 is effectively absorbed as compared with the conventional brushless motor, and the field magnetic flux is prevented from flowing into the resolver stator 23. Can do. Therefore, the influence of the field magnetic flux on the resolver stator 23 can be suppressed, and the sensor accuracy can be improved.

  Thus, in the motor 1 according to the present invention, the linearity of the resolver output signal can be ensured, torque fluctuation can be suppressed, and the motor can be downsized while ensuring the rotor position detection accuracy. It becomes possible. Further, in the EPS motor 1, the steering assist force is stabilized by reducing the torque fluctuation, and the steering feeling can be improved. That is, the motor 1 can satisfy the request for miniaturization of the motor without impairing the steering feeling in the EPS. Furthermore, since the plate thickness of the magnetic shield 31 itself can be suppressed by the triple magnetic shield structure with an air layer interposed (for example, about 1.6 mm), member processing is easy, while suppressing an increase in cost. The influence of the magnetic flux on the field side can be effectively suppressed. In addition, it is not necessary to use a thick plate for the resolver holder 24, and the resolver holder 24 can be easily processed. Note that the effect of the field magnetic flux is less when the gap between the resolver holder 24 and the magnetic shield 31 is increased (when the gap 36 is made larger) than when the plate thickness of the resolver holder 24 and the magnetic shield 31 is increased.

  Next, a brushless motor 41 that is Embodiment 2 of the present invention will be described. FIG. 3 is an explanatory diagram showing the configuration in a simplified manner. In the following embodiments, the same members and portions as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  As shown in FIG. 5, here, the resolver stator 23 is held by an aluminum bracket 42. A cylindrical resolver fixing portion 43 projects from the bracket 42 in the axial direction, and the resolver stator 23 is housed and fixed inside the resolver fixing portion 43. That is, in the brushless motor 41, instead of the resolver holder 24, the resolver fixing portion 43 is provided as the first magnetic shielding member. Similar to the motor 1 of the first embodiment, the magnetic shield 31 is attached to the outside of the resolver fixing portion 43. A gap 36 is formed between the resolver fixing portion 43 and the magnetic shield 31.

  In such a brushless motor 41, the resolver stator 23 is first magnetically shielded by aluminum which is a nonmagnetic material. The brushless motor 41 is magnetically isolated from the coil 6 by the air gap 36 and the magnetic shield 31 thereon. The magnetic flux from the coil 6 is first absorbed by the magnetic shield 31, and the magnetic flux leaking from the magnetic flux is weakened by the gap 36 and then flows into the resolver fixing portion 43. As described above, since the magnetic flux flows into the resolver fixing portion 43 only by the leakage magnetic flux of the magnetic shield 31, most of the magnetic flux is absorbed by the resolver fixing portion 43 and almost no magnetic flux flows into the resolver stator 23. For this reason, even if the coil 6 and the resolver stator 23 are arranged close to each other, the magnetic flux from the coil 6 can be prevented from flowing into the resolver stator 23, the influence of the field magnetic flux on the resolver stator 23 can be suppressed, and the sensor accuracy can be improved. It is possible to improve.

  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 gap 36 is interposed between the resolver holder 24 and the magnetic shield 31, but the resolver holder 24 and the magnetic shield 31 are in close contact with each other without providing the gap 36 therebetween. You may let them. Also in this case, a double magnetic shielding member is installed between the coil 6 and the resolver stator 23, and magnetic flux inflow from the coil 6 to the resolver stator 23 is suppressed.

  On the other hand, in the above-described embodiment, the brushless motor used in the column assist type EPS is shown. However, the present invention can be applied to other types of EPS motors. Further, the present invention can be widely applied to general brushless motors as well as motors for EPS and various in-vehicle electric products.

It is sectional drawing of the brushless motor which is Example 1 of this invention. It is a perspective view which shows the structure of a magnetic shield. It is explanatory drawing which simplified and showed the structure of the said motor which attached the magnetic shield. It is explanatory drawing which shows the magnetic shielding effect | action of a resolver holder and a magnetic shield. It is explanatory drawing which simplified and showed the structure of the brushless motor which is Example 2 of this invention. It is explanatory drawing which shows a sensor output at the time of arrange | positioning a resolver close to a field coil.

Explanation of symbols

1 Brushless motor 2 Stator (stator)
3 Rotor (rotor)
4 Case 5 Stator core 6 Stator coil (field coil)
7 Busbar unit 8 Bracket 9 Fixing screw 11 Insulator 12 Power supply terminal 13 Rotor shaft 14a, 14b Bearing 15 Rotor core 16 Magnet 17 Magnet holder 18 Magnet cover 19 Bearing holder 21 Resolver 22 Resolver rotor 23 Resolver stator 24 Resolver holder (first magnetic shield) Element)
24a Flange 25 Bracket holder 26 Rib 27 Resolver fixing nut 28 Resolver fixing screw 31 Magnetic shield (second magnetic shielding member)
32 Side wall portion 33 Bottom wall portion 34 Through hole 35 Mounting piece 36 Air gap 41 Brushless motor 42 Bracket 43 Resolver fixing portion

Claims (6)

A stator comprising a stator core and a field coil wound around the stator core;
A rotor that is rotatably arranged inside the stator and includes a rotor core and a magnet attached to an outer periphery of the rotor core;
A resolver rotor that rotates with the rotor;
A resolver stator disposed outside the resolver rotor, and a brushless motor comprising:
A first magnetic shielding member that covers the resolver stator between the resolver stator and the field coil; and a second magnetic shielding member that is disposed outside the first magnetic shielding member and covers the first magnetic shielding member. A brushless motor, characterized in that   2. The brushless motor according to claim 1, wherein a gap is provided between the first magnetic shielding member and the second magnetic shielding member.   3. The brushless motor according to claim 1, wherein the second magnetic shielding member is provided with a bottomed cylindrical magnetic shield formed of a magnetic material and disposed so as to surround the outside of the first magnetic shielding member. A brushless motor characterized by that.   4. The brushless motor according to claim 1, wherein a resolver holder that is formed of a magnetic material and accommodates and holds the resolver stator is provided as the first magnetic shielding member. 5. motor. The brushless motor according to any one of claims 1 to 3, wherein the brushless motor further includes a cylindrical case that accommodates the stator, and a bracket that is attached to an end of the case.
A brushless motor as the first magnetic shielding member, wherein the bracket is provided with a cylindrical resolver fixing portion that accommodates and holds the resolver stator.   6. The brushless motor according to claim 5, wherein the bracket is made of a non-magnetic material.

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