JP2018042350A - Brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a brushless motor capable of detecting a rotational position of a rotor with high accuracy.SOLUTION: A sensor magnet 40 is configured so that an opposed surface 41 to an MR sensor becomes a convex curved surface from both-side pole boundary parts 40a to a pole center part 40b, and so that an axial thickness becomes thicker as it goes from the pole boundary parts 40a to the pole center part 40b. The sensor magnet is configured so as to have such magnetic characteristics that a magnetic field intensity becomes stronger in a convex curved shape as it goes from both-side pole boundary parts 40a to the pole center part 40b while achieving uniform magnetization in a circumferential direction.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a brushless motor.

Conventionally, a brushless motor having a magnetic sensor for detecting the rotational position of a rotor is known (see, for example, FIG. 13 of Patent Document 1).
Such a brushless motor includes a sensor magnet that rotates integrally with the rotor, and a magnetic sensor that outputs a signal corresponding to a change in the magnetic field of the sensor magnet accompanying the rotation to the control circuit, and rotates based on detection of the rotational position of the rotor. Driving is performed.

JP 2014-81052 A

  By the way, the sensor magnet is alternately magnetized so as to have different polarities in the circumferential direction, for example, and the magnetic sensor controls a signal approximating a sin wave shape or a cosine wave shape corresponding to a change in the magnetic field of the sensor magnet with rotation. Output to. The control circuit detects the rotational position of the rotor based on a signal output from the magnetic sensor.

  However, as the change in the magnetic field in the circumferential direction of the sensor magnet deviates from an ideal wave shape, the distortion generated in the sin wave or cos wave signal output from the magnetic sensor to the control circuit increases. The greater the distortion of this signal, the lower the detection accuracy of the rotational position of the rotor, so improvement is desired.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a brushless motor capable of detecting the rotational position of the rotor with high accuracy.

  A brushless motor that solves the above-mentioned problems is arranged oppositely to a sensor magnet that is magnetized in the axial direction and configured in an annular shape so that the polarity is alternately switched in the circumferential direction, and the circumferential surface on one side in the axial direction of the sensor magnet. A magnetic sensor that outputs a wave-like signal corresponding to a change in the magnetic field of the sensor magnet that rotates integrally with the rotor, and is a brushless motor that is driven to rotate based on detection of the rotational position of the rotor by the magnetic sensor. The sensor magnet has a magnetic characteristic in which the magnetic field strength increases in a convex curve from the pole boundary part on both sides to the pole center part.

  According to this configuration, the sensor magnet has a magnetic characteristic in which the magnetic field strength increases in a convex curve from the pole boundary on both sides to the center of the pole. The change approximates a cos wave shape. Thereby, the distortion of the magnetic flux density in the magnetic sensor is reduced (see FIG. 7), and the distortion of the output signal is also reduced. As a result, the rotational position of the rotor can be detected with high accuracy.

  In the brushless motor, the sensor magnet has a convex curved surface facing the magnetic sensor from the pole boundary part on both sides to the pole center part, and an axial thickness from the pole boundary part to the pole center part. It is preferable that the thickness is increased so that the magnetic characteristics of the convex magnetic field strength are obtained.

  According to this configuration, the sensor magnet has a convex curved surface from the pole boundary on both sides to the pole center, and the axial thickness increases from the pole boundary to the pole center, Even with uniform magnetization in the circumferential direction, it is possible to obtain a magnetic characteristic of a convex magnetic field strength. That is, the sensor magnet can be realized by a method that is easy to magnetize.

  In the brushless motor, the sensor magnet has a flat surface facing the magnetic sensor from the pole boundary part on both sides to the pole center part, and an axial thickness from the pole boundary part to the pole center part. It is preferable that the magnetic field is magnetized so as to have a magnetic characteristic of the convex magnetic field strength.

  According to this configuration, the surface facing the magnetic sensor is a flat surface from the pole boundary on both sides to the pole center, and the thickness in the axial direction is constant from the pole boundary to the pole center. Magnetization is performed so that the magnetic characteristics have a convex curve magnetic field strength. That is, the sensor magnet can be realized in a simple shape with a constant thickness in the circumferential direction.

  According to the brushless motor of the present invention, the rotational position of the rotor can be detected with high accuracy.

Sectional drawing of the brushless motor of embodiment. The top view of the brushless motor of the same form. The perspective view of the state which attached the end frame and its peripheral member of the same form. The disassembled perspective view which shows the state which removed the peripheral member from the end frame of the same form. The perspective view of the sensor magnet of the same form. (A) is the schematic diagram seen from the side surface side of the sensor magnet of the same form, (b) is a graph which shows the distance of a sensor magnet and a magnetic sensor, (c) is a graph which shows the magnetic field change of a sensor magnet. The graph which shows the relationship between the uneven | corrugated ratio of the opposing surface of a sensor magnet, and the distortion rate of magnetic flux density. The schematic diagram seen from the side of the sensor magnet of another example.

  Hereinafter, an embodiment of the brushless motor will be described. The brushless motor according to the present embodiment is used as a motor for controlling an engine in which the compression ratio is variable, for example, in order to improve the fuel efficiency of a vehicle engine.

  As shown in FIG. 1, the motor case 11 of the brushless motor 10 of this embodiment includes a yoke housing 12 formed in a substantially bottomed cylindrical shape, an end frame 13 that closes an opening of the yoke housing 12, and an end frame. And a cover member 14 covering the 13 openings 13a.

A stator 20 is fixed to the inner peripheral surface of the yoke housing 12. The stator 20 has a stator core 22 having a plurality of teeth 21 extending radially inward.
As shown in FIGS. 1 and 2, the teeth 21 of the stator core 22 are provided at substantially equal intervals in the circumferential direction, and U-phase, V-phase, and W-phase windings 24 are provided on the teeth 21 via insulators 23. It is wound in a concentrated volume.

  As shown in FIG. 1, a rotor 30 is provided inside the stator 20 so as to be fixed to the rotary shaft 25 and rotate integrally with the rotary shaft 25. The rotary shaft 25 is made of, for example, a non-magnetic member, and is fixed to a bearing 26 fixed to a bearing receiving portion 12a provided at a substantially central portion of the bottom of the yoke housing 12 and a bearing receiving portion 13b provided to a substantially central portion of the end frame 13. The bearing 27 is rotatably supported with respect to the motor case 11. A drive transmission member 28 is attached to the tip of the rotary shaft 25.

  As shown in FIG. 2, the rotor 30 is a so-called SPM (Surface Permanent Magnet) type rotor having a rotor core 31 and a rotor magnet 32 provided so that magnetic poles are alternately arranged in the circumferential direction on the outer peripheral surface of the rotor core 31. It is. In the rotor magnet 32 of the present embodiment, an N-pole magnet 32a that is magnetized so that the radially outer side becomes N pole, and an S-pole magnet 32b that is magnetized so that the radially outer side becomes S pole are individually provided. The magnets 32a and 32b are alternately arranged in the circumferential direction so as to have different polarities. The rotor 30 of the present embodiment is configured with eight poles (four pole pairs).

As shown in FIG. 1, the rotor core 31 of the rotor 30 includes a plurality of first and second core sheets 33 and 37 each having an annular plate shape.
As shown in FIGS. 1 and 2, the first core sheet 33 extends in the radial direction from the first annular portion 34 provided with a through hole 34 a for inserting the rotation shaft 25, and the first annular portion 34. A plurality of extending portions 35 and a substantially annular second annular portion 36 (see FIG. 1) located outside the extending portions 35 are included. The second core sheet 37 is configured to have an annular shape that is substantially the same shape as the second annular portion 36 of the first core sheet 33.

  In the rotor core 31, a plurality of first core sheets 33 are stacked on the bottom side (right side in FIG. 1) of the yoke housing 12, and a plurality of second core sheets 37 are stacked on the end frame 13 side (left side in FIG. 1). Composed. At this time, since the second core sheet 37 is configured in substantially the same shape as the second annular portion 36 of the first core sheet 33, the second core sheet 37 penetrates the second core sheet 37 by laminating the second core sheet 37 in the rotor core 31. A recess 31a is formed in the rotor core 31 by the continuous holes 37a.

  A part of the bearing housing part 13 b of the end frame 13 is disposed together with a part of the bearing 27 in the recess 31 a. Thereby, compared with the case where the recessed part 31a is not provided, the bearing 27 and the bearing accommodating part 13b will be offset to the rotor 30 side (bottom part side of the yoke housing 12) in the axial direction.

  A sensor magnet 40 is fixed to an axial end surface of the rotor core 31 on the second core sheet 37 side (on the left side in FIG. 1 and on the end frame 13 side) via a magnet fixing member 38. In this embodiment, the magnet fixing member 38 to which the sensor magnet 40 is fixed is caulked by inserting caulking pins 39 into through holes provided in the rotor core 31 together with the first and second core sheets 33 and 37, respectively. Thus, the rotor core 31 is integrally assembled.

  As shown in FIG. 5, the annular sensor magnet 40 is magnetized in the axial direction, and N poles and S poles are alternately configured in the circumferential direction. Here, a portion where the polarity is switched in the circumferential direction is defined as a pole boundary portion 40a, and a central portion of the N or S pole located in the middle between the pole boundary portions 40a is defined as a pole center portion 40b. In addition, the sensor magnet 40 of this embodiment is comprised by 8 poles (4 pole pairs) like the rotor magnet 32. FIG.

  Further, as shown in FIG. 6A, the circumferential surface on one side (end frame 13 side) in the axial direction of the sensor magnet 40, that is, the facing surface 41 with the MR sensor 62 described later, is from the pole boundary portions 40a on both sides. It is comprised so that it may become a convex curve toward the pole center part 40b. The sensor magnet 40 is formed such that the axial thickness gradually increases from the pole boundary portion 40a to the pole center portion 40b.

  If the thickness of the pole center portion 40b of the sensor magnet 40 is H1, and the thickness of the pole boundary portion 40a is H2, the sensor magnet 40 of this embodiment has a thickness H2 of the pole boundary portion 40a of the pole center portion 40b. For example, the thickness H1 is set to 85%. In addition, the sensor magnet 40 of the present embodiment has a concavity and convexity on the opposing surface 41, and is uniformly magnetized regardless of the circumferential position such as the pole boundary portion 40a and the pole center portion 40b.

  Such a sensor magnet 40 is shifted in the circumferential direction by 90 degrees in electrical angle with respect to the rotor magnet 32 (see FIG. 2). As described above, since the number of poles of the sensor magnet 40 and the rotor magnet 32 is eight, the sensor magnet 40 and the rotor magnet 32 are shifted in the circumferential direction by 22.5 degrees in terms of mechanical angle.

Next, the end frame 13 and the detailed configuration around it will be described.
As shown in FIGS. 3 and 4, a circuit board 60 having an MR sensor 62 is attached to the end frame 13 of the motor 10 of the present embodiment so as to face the sensor magnet 40 in the axial direction, and the stator 20. A connector 70 for supplying power to the circuit board 60 is attached.

  As shown in FIG. 3, the circuit board 60 is screwed into mounting holes 51 and 61 formed in the end frame 13 and the circuit board 60, respectively, so that the inner surface of the end frame 13 (sensor magnet 40. It is attached to the opposite surface. As shown in FIGS. 1 and 3, the circuit board 60 is provided with a plurality (three in this embodiment) of MR sensors 62.

  The MR sensor 62 is a sensor using a magnetoresistive effect element, and outputs different signals according to a magnetic field change (magnetic flux amount change). In the present embodiment, since the sensor magnet 40 is alternately magnetized so as to have different polarities in the circumferential direction, a wave-like signal is output from the MR sensor 62.

  Here, as described above with reference to FIG. 6A, the sensor magnet 40 of the present embodiment has a gradually convex curved surface from the pole boundary portion 40a toward the pole center portion 40b. That is, the MR sensor 62 is close to the pole center portion 40b of the sensor magnet 40, is separated from the pole boundary portion 40a, and has a curvilinear shape as shown in FIG. 6B, which follows the curved shape of the facing surface 41 of the sensor magnet 40. Therefore, the magnetic field change of the sensor magnet 40 received by the MR sensor 62 approximates a sin wave shape (or a cosine wave shape) as shown in FIG.

  Further, as apparent from FIG. 7, the harmonic component of the axial magnetic flux density detected by the MR sensor 62 is compared with the case where the opposing surface 41 is a single plane (H2 / H1 ratio is 100%). Thus, in the sensor magnet 40 of the present embodiment having the curved opposing surface 41, the distortion rate of the magnetic flux density can be kept small. For this reason, distortion of the signal output from the MR sensor 62 to the control circuit is also reduced, and the output signal from the MR sensor 62 is a signal that approximates a sin wave shape or a cosine wave shape.

  As shown in FIG. 7, the ratio (concave / convex ratio) H2 / H1 between the thickness H2 of the pole boundary portion 40a and the thickness H1 of the pole center portion 40b decreases as the ratio decreases, that is, the pole center portion 40b. As the difference between the magnetic field and the pole boundary 40a is relatively increased, the distortion rate of the magnetic flux density detected by the MR sensor 62 is reduced. In consideration of the structure (strength) of the sensor magnet 40, the strength of the generated magnetic field, the ease of manufacture, etc., the ratio H2 of the thickness H2 of the pole boundary 40a and the thickness H1 of the pole center 40b of the sensor magnet 40 / H1 is determined.

  An output signal from the MR sensor 62 is output to a control circuit (not shown) provided on the circuit board 60. The control circuit detects the rotational position of the rotor 30 for rotationally driving the brushless motor 10 based on the signal output from the MR sensor 62. Since the output signal from the MR sensor 62 is a signal that approximates a sin wave shape or a cosine wave shape, the control circuit can detect the rotational position of the rotor 30 with high accuracy. In the present embodiment, the MR sensor 62 is used as the magnetic sensor, but a linear Hall IC can also be used.

  In addition, a plurality of (five in the present embodiment) through holes 63 into which signal terminals 73 of connectors 70 described later are fitted are formed in the circuit board 60 in one row. Positioning holes 64 for positioning the circuit board 60 with respect to the connector 70 (signal terminal 73) are formed at both ends of the row of through holes 63.

  As shown in FIG. 1, the connector 70 is attached to the outer side surface of the end frame 13 (the side surface opposite to the surface to which the circuit board 60 is attached). The connector 70 includes a connector part 70a exposed to the outside of the motor 10, an inner extension part 70b extending inward from the connector part 70a, and a terminal 71 disposed across the connector part 70a and the inner extension part 70b. Have An external connector for power supply (not shown) is connected to the connector portion 70a.

  The terminal 71 includes a power supply terminal 72 for supplying power to the winding 24 of the stator 20 from the outside, and a signal terminal 73 for transferring signals between the circuit board 60 and the outside. In the present embodiment, three power supply terminals 72 and five signal terminals 73 are provided.

  The distal end portion of the power supply terminal 72 has a connection portion 72 a for connecting to the terminal portion of the winding 24. A first through hole 52 is formed at a portion of the end frame 13 corresponding to the connection portion 72a of the power supply terminal 72 so that the connection portion 72a faces the inner side in the axial direction (winding 24 side) from the end frame 13. .

  The signal terminal 73 is disposed along the connector part 70a and the inner extension part 70b. The distal end portion 73a on the inner extension portion 70b side of the signal terminal 73 is bent in the axial direction (end frame 13 side) and arranged in one row. A second through-hole 53 is formed in a portion of the end frame 13 corresponding to the distal end portion 73a of the signal terminal 73 so that the distal end portion 73a faces the inner side in the axial direction (circuit board 60 side) from the end frame 13. .

  Positioning pins 74 for positioning the connector 70 with respect to the end frame 13 and the circuit board 60 are provided at both ends of the row of the signal terminals 73 at the distal end portion of the inner extending portion 70b. It extends in the same direction as the bending direction. A positioning hole 54 is formed in the part of the end frame 13 corresponding to the positioning pin 74, and a positioning hole 64 is further formed in the circuit board 60.

  Then, the positioning of the circuit board 60 and the connector 70 through the end frame 13 is performed by inserting the positioning pins 74 of the connector 70 into the positioning holes 54 of the end frame 13 and inserting into the positioning holes 64 of the circuit board 60. Is done. By positioning the connector 70 and the circuit board 60, the signal terminal 73 of the connector 70 is smoothly inserted into the through hole 63 of the circuit board 60 through the second through hole 53 of the end frame 13.

  When the connector 70 is attached to the end frame 13, the terminal portion of the winding 24 of the stator 20 is positioned in the first through hole 52 of the end frame 13, and the connection between the terminal portion of the winding 24 and the power supply terminal 72 is connected. Connection with the part 72a is achieved. A cover member 14 is attached to the end frame 13 so as to cover the first and second through holes 52 and 53 and the inner extending portion 70 b of the connector 70. Thus, the periphery of the end frame 13 is configured.

Next, the effect of this embodiment will be described.
(1) In the sensor magnet 40, the surface 41 facing the MR sensor 62 has a convex curved surface from the pole boundary part 40a on both sides to the pole center part 40b, and the axial thickness extends from the pole boundary part 40a to the pole center part 40b. Constructed thick. That is, the sensor magnet 40 has a magnetic characteristic in which the magnetic field strength increases in a convex curve from the pole boundary portion 40a on both sides to the pole center portion 40b while being uniformly magnetized in the circumferential direction. Therefore, the magnetic field change of the sensor magnet 40 received by the MR sensor 62 is a change that approximates a sin wave shape or a cos wave shape, and the distortion of the magnetic flux density in the MR sensor 62 is reduced (see FIG. 7). As a result, distortion of a sin wave-like or cos wave-like signal from the MR sensor 62 output to the control circuit is also reduced, and the rotational position of the rotor 30 can be detected with high accuracy.

(2) The distortion of the signal output from the MR sensor 62 can be reduced by an easy method such as forming the opposing surface 41 of the sensor magnet 40 into a convex curved surface.
(3) Since the connector 70 and the circuit board 60 are positioned by the positioning pins 74 formed in the connector 70 (inner extending portion 70b) and the positioning holes 64 formed in the circuit board 60, the signal for the connector 70 is used. The positional accuracy between the terminal 73 (tip portion 73a) and the through hole 63 of the circuit board 60 is improved. Thereby, the front-end | tip part 73a of the signal terminal 73 can be easily inserted in the through hole 63. FIG.

  (4) By positioning the positioning pin 74 of the connector 70 (inner extending portion 70b) into the positioning hole 54 formed in the end frame 13, the positioning pin 74 is inserted into the positioning hole 64 of the circuit board 60. The end frame 13 and the MR sensor 62 of the circuit board 60 are positioned. As a result, the MR sensor 62 can contribute to improving the detection accuracy of the rotational position of the rotor 30.

In addition, you may change the said embodiment as follows.
In the above embodiment, the ratio H2 / H1 between the thickness H2 of the pole boundary portion 40a and the thickness H1 of the pole center portion 40b is set to 85% in the sensor magnet 40, but the ratio H2 / H1 is not limited to this. , May be changed as appropriate.

  In the above embodiment, the sensor magnet 40 has a magnetic field strength that is convexly curved from the pole boundary portion 40a on both sides to the pole center portion 40b, for example, by making the surface 41 facing the MR sensor 62 a convex curved surface. It had magnetic properties. On the other hand, for example, as shown in FIG. 8, the surface 41 facing the MR sensor 62 is a flat surface, and the sensor magnet 45 having a constant axial thickness in the circumferential direction is positioned from the pole boundary 40 a to the pole center. The portion 40b is magnetized so as to have a magnetic characteristic of a convex magnetic field strength. Even in this case, similarly to the above embodiment, the distortion of the signal output from the MR sensor 62 can be reduced, and the detection accuracy of the rotational position of the rotor 30 can be improved. In this aspect, the sensor magnet 45 can be realized in a simple shape having a constant thickness in the circumferential direction.

In the above embodiment, the number of poles of the sensor magnet 40 is eight (four pole pairs), but the number of poles may be changed as appropriate.
In the above embodiment, three MR sensors 62 (magnetic sensors) are provided, but the number may be changed as appropriate.

Next, a technical idea that can be grasped from the above embodiment and another example will be added below.
(A) A magnetic sensor that outputs a signal in response to a magnetic field change of a sensor magnet that rotates integrally with the rotor, an end frame that covers the opening of the yoke housing, and a bottomed cylindrical yoke housing that houses the rotor and stator. And a connector having a terminal that is electrically connected to the winding of the stator and the circuit board, and the circuit board and the connector are provided with positioning portions that position each other. Brushless motor characterized by

  (B) The brushless motor according to (a), wherein the positioning portion is intended to position the circuit board with respect to the end frame.

  DESCRIPTION OF SYMBOLS 30 ... Rotor, 40, 45 ... Sensor magnet, 40a ... Polar boundary part, 40b ... Polar center part, 41 ... Opposite surface, 62 ... MR sensor (magnetic sensor).

Claims (3)

A sensor magnet which is magnetized in the axial direction and configured in an annular shape so that the polarity is alternately switched in the circumferential direction;
A magnetic sensor that is disposed opposite to the circumferential surface on one side in the axial direction of the sensor magnet and that outputs a wave-like signal corresponding to a change in the magnetic field of the sensor magnet that rotates integrally with the rotor;
A brushless motor that is driven to rotate based on detection of the rotational position of the rotor by the magnetic sensor,
The sensor magnet has a magnetic characteristic in which the magnetic field strength increases in a convex curve from the pole boundary portion on both sides to the pole center portion. The brushless motor according to claim 1,
The sensor magnet has a convex curved surface facing the magnetic sensor from the pole boundary part on both sides to the pole center part, and the thickness in the axial direction is increased from the pole boundary part to the pole center part, A brushless motor, wherein the brushless motor is configured to have magnetic characteristics of the convex curve magnetic field strength. The brushless motor according to claim 1,
The sensor magnet has a flat surface facing the magnetic sensor from the pole boundary on both sides to the pole center, and the axial thickness is constant from the pole boundary to the pole center, A brushless motor characterized by being magnetized so as to have a magnetic characteristic of a convex magnetic field strength.

Images