Patent Application
20230268807
The present application claims priority to Japanese Application Number 2022-026723, filed Feb. 24, 2022, the disclosure of which is hereby incorporated by reference herein in its entirety.
The present invention relates to a motor.
Known motors include position sensors to detect the position of a rotor. The position sensors may be optical sensors such as optical encoders or magnetic sensors such as Hall devices.
A motor including multiple Hall devices as position sensors may estimate the position of a rotor based on the characteristics of a voltage output from each Hall device (a Hall signal).
The multiple Hall devices incorporated in the single motor are not identical to one another but vary in, for example, their dimensions, shapes, material properties, and mounting positions. Such variations cause the Hall devices to output Hall signals with different characteristics. A microcomputer may learn the characteristics of Hall signals output from the Hall devices to estimate the position of the rotor.
However, the Hall signals can have characteristics that occur randomly based on the varying characteristics of the Hall devices. Two or more Hall devices incorporated in a single motor may coincidentally have either the same or substantially the same characteristics in their output Hall signals. This may cause erroneous estimation of the rotor position.
A motor according to an embodiment includes a stator and a rotor. The rotor includes a rotor core containing a magnetic material, a plurality of magnets located on the rotor core in a rotation direction of the rotor, and a plurality of magnetic sensors located on a mounting surface to detect a magnetic field from the plurality of magnets. The plurality of magnets each have a facing surface facing the mounting surface at a constant distance. The rotor core has a facing surface facing the mounting surface. The rotor core has at least one first area and at least one second area with different distances between the facing surface of the rotor core and the mounting surface. The at least one first area and the at least one second area are located alternately in the rotation direction of the rotor. The at least one first area and the at least one second area include one or more area pairs each including a first area and a second area adjacent to each other. The number of one or more area pairs is determined by the number of pole pairs of the plurality of magnets.
The motor according to the above aspect of the present invention improves the accuracy of position estimation of the rotor.
An embodiment of the present invention will now be described with reference to the drawings. In the drawings used to describe the embodiment, the same reference numerals denote the same or substantially the same components. Such components will not basically be described repeatedly.
The motor 1A includes, for example, a housing 10, a stator 20, a rotor 30, and a substrate 40. The rotor 30 and the stator 20 are housed in the housing 10. The rotor 30 is located radially inward from the stator 20 and rotatable relative to the stator 20. The motor 1A is thus an inner-rotor motor.
The housing 10 includes two parts joined together. More specifically, the housing includes a base 11a and a cover 11b. In
The bottom wall 12 of the base 11a is circular or substantially circular and has a through-hole 15 at the center. A shaft holder 16 that is cylindrical and continuous with the through-hole 15 is located on the bottom wall 12 of the base 11a.
The fasteners 13a and 13b protrude parallel to the bottom wall 12 from the edge of the bottom wall 12. The ribs 14a and 14b extend perpendicularly to the bottom wall 12 from the edge of the bottom wall 12. The fasteners 13a and 13b have threaded holes to receive screws for fastening the motor 1A at a predetermined position. The ribs 14a and 14b are curved along the edge of the bottom wall 12.
The cover 11b includes a cylindrical peripheral wall 17 and a ceiling wall 18 that covers one end of the peripheral wall 17. When the base 11a and the cover 11b are combined together, the peripheral wall 17 of the cover 11b is placed outside the ribs 14a and 14b of the base 11a, and the ceiling wall 18 of the cover 11b faces the bottom wall 12 of the base 11a. The peripheral wall 17 defines an accommodation space between the bottom wall 12 and the ceiling wall 18. The accommodation space is surrounded by the peripheral wall 17 and also by the ribs 14a and 14b partially.
The stator 20 is annular to surround the rotor 30 and is fixed inside the housing 10. The stator 20 and the rotor 30 have a predetermined clearance (air gap) between them.
The stator 20 includes a stator core 21 fixed to an inner circumferential surface of the housing 10. The stator core 21 may be a stack of multiple electromagnetic steel plates or a single electromagnetic steel plate. The stator core 21 includes multiple teeth 22 protruding radially inward (toward the rotor 30), or more specifically, twelve teeth 22 located at intervals of 30 degrees. In other words, the stator 20 has twelve slots.
The stator 20 includes, in addition to the stator core 21, insulators 23 surrounding the respective teeth 22, and coils 24 surrounding the respective insulators 23.
The insulators 23 are formed from an insulating material (e.g., a resin material). The coils 24 are formed from wires (e.g., copper alloy wires) wound around the insulators 23.
The twelve coils 24 include four U-phase coils, four V-phase coils, and four W-phase coils. In other words, the stator 20 receives a three-phase current with phases each shifted by 120 degrees. When energized with a current (coil current), the U-, V-, and W-phase coils 24 generate a magnetic field acting on the rotor 30.
The rotor 30 includes a rotor core 31, a rotor hub 32, magnets 33, and a shaft 34, and is rotatable about a central axis C as the rotation axis. The central axis C extends in a direction defined herein as a vertical direction. In this definition, the base 11a and the cover 11b included in the housing 10 face each other in the vertical direction. More specifically, the bottom wall 12 of the base 11a and the ceiling wall 18 of the cover 11b face each other in the vertical direction. For ease of explanation, a portion of the structure adjacent to the bottom wall 12 may be hereafter referred to as being lower or downward, and a portion adjacent to the ceiling wall 18 as being upper or upward. The rotation direction of the rotor 30 that rotates about the central axis C as the rotation axis may be referred to as a circumferential direction.
The rotor core 31 is formed from a magnetic material and is a cylinder extending in the vertical direction. The rotor hub 32 is located inward from the rotor core 31, and the multiple magnets 33 are located outside the rotor core 31.
The rotor hub 32 has a side surface 32a and an upper surface 32b. The side surface 32a is cylindrical and has an outer diameter smaller than the inner diameter of the rotor core 31. The upper surface 32b is disk-shaped and covers one end of the side surface 32a. The side surface 32a and the upper surface 32b are formed integrally using a non-magnetic material.
The rotor hub 32 is fitted to the inner circumference of the rotor core 31. The rotor hub 32 and the rotor core 31 are nonrotatable relative to each other. More specifically, with the inner circumferential surface of the rotor core 31 and the outer circumferential surface of the rotor hub 32 fixed to each other, the rotor core 31 and the rotor hub 32 are integral with each other.
The multiple magnets 33 are located on the rotor core 31 in the rotation direction (circumferential direction) of the rotor 30. More specifically, ten magnets 33 are located on the rotor core 31 at equal intervals in the circumferential direction. The ten magnets 33 have their N poles and S poles alternating in the circumferential direction. The magnets 33 are fixed (bonded) on the outer circumferential surface of the rotor core 31.
The shaft 34 is fixed to the rotor hub 32. More specifically, the shaft 34 has a basal end extending through and protruding from the shaft holder 16. The basal end of the shaft 34 protruding from the shaft holder 16 is press-fitted at the center of the rotor hub 32.
The shaft 34 is supported by bearings 35a and 35b located in the shaft holder 16 in a rotatable manner. The bearing 35b is vertically stacked on the bearing 35a with a spring washer 36 between them.
The distal end of the shaft 34 extends through the bottom wall 12 of the base 11a and protrudes from the housing 10. A pinion gear 37 is attached to the distal end of the shaft 34 protruding from the housing 10.
The substrate 40 is a flexible substrate. The substrate 40 has a part located inside the housing 10, and another part extending outside the housing 10. For ease of explanation, the part of the substrate 40 located inside the housing 10 may be hereafter referred to as a body 41, and the other part of the substrate 40 extending outside the housing 10 may be hereafter referred to as an extension 42.
The body 41 of the substrate 40 is a disk that covers the substantially entire bottom wall 12 of the base 11a except the shaft holder 16. The extension 42 is a strip that extends between the fastener 13a and the rib 14b of the base 11a and then outside the housing 10.
Multiple magnetic sensors are mounted on the substrate 40 to detect magnetic fields from the magnets 33 on the rotor 30. More specifically, three Hall devices 50u, 50v, and 50w are mounted on the substrate 40. The Hall devices 50u, 50v, and 50w are mounted on a surface 41a of the body 41 at equal intervals in the circumferential direction. In other words, the surface 41a of the body 41 is a mounting surface commonly for the three Hall devices 50u, 50v, and 50w. Thus, the surface 41a of the body 41 may be hereafter referred to as a mounting surface 41a. The Hall devices 50u, 50v, and 50w may be hereafter collectively referred to as Hall devices 50.
The Hall device 50u is a magnetic sensor for detecting the magnetic field strength of a U phase and outputs a voltage (a Hall signal or a differential signal) corresponding to the magnetic field strength of the U phase. The Hall device 50v is a magnetic sensor for detecting the magnetic field strength of a V phase and outputs a voltage (a Hall signal or a differential signal) corresponding to the magnetic field strength of the V phase. The Hall device 50w is a magnetic sensor for detecting the magnetic field strength of a W phase and outputs a voltage (a Hall signal or a differential signal) corresponding to the magnetic field strength of the W phase.
Each of the Hall devices 50u, 50v, and 50w is electrically connected to the wiring on the substrate 40. The Hall signals output from the Hall devices 50u, 50v, and 50w are input into, for example, a predetermined device, a processor, or a controller through the wiring on the substrate 40.
The position estimator 61 is an information processor for estimating the position of the rotor 30. The position estimator 61 includes a calculator and a storage. The position estimator 61 estimates the position of the rotor 30 using values calculated based on the input Hall signals and information prestored in the storage, and outputs the estimation result to the controller 62. The position estimator 61 can estimate the position of the rotor 30 that may be stopped or rotating.
The controller 62 generates a control signal based on the position of the rotor 30 estimated by the position estimator 61 and an instruction signal received from an external device, and outputs the control signal to the drive 63. The instruction signal indicates, for example, the rotation direction, rotational force, rotation angle, or rotational speed of the rotor 30. The control signal indicates, for example, a register value in accordance with the rotation direction indicated by the instruction signal, or a current value of the current output from the drive 63 to the stator 20.
The drive 63 drives the stator 20 based on the input control signal. The drive 63 rotates the rotor 30 in an instructed direction at an instructed speed by, for example, supplying a three-phase current with a current value indicated by the control signal to each coil 24 of the stator 20.
As described above, the ten magnets 33 are located to have their N poles and S poles alternating in the circumferential direction and attached on the outer circumferential surface 31a of the rotor core 31. The rotor core 31 is thus located on the rear of (inward from) the ten magnets 33 placed annularly, and functions as a back yoke. A magnet 33 with the N pole and a magnet 33 with the S pole adjacent to each other may be hereafter referred to as a pole pair. The rotor core 31 thus includes five pole pairs of magnets 33 attached (the number of pole pairs being five).
The ten magnets 33 are located at constant intervals in the circumferential direction (in the direction of the array) and have the same height from the mounting surface 41a. The height of each magnet 33 from the mounting surface 41a refers to the shortest linear distance from the mounting surface 41a to a facing surface 38 of the magnet 33 facing the mounting surface 41a.
For ease of explanation, the ten magnets 33 may be identified by referring to them as, for example, a magnet 33a, a magnet 33b, and a magnet 33c.
Whereas the ten magnets 33 have the same height from the mounting surface 41a, the rotor core 31 has a varying height from the mounting surface 41a. More specifically, the height of the rotor core 31 from the mounting surface 41a varies in the circumferential direction. The height of the rotor core 31 from the mounting surface 41a refers to the shortest linear distance from the mounting surface 41a to a facing surface 31b of the rotor core 31 facing the mounting surface 41a.
In other words, the rotor core 31 has areas (first areas) R1 with its width continuously narrower upward in the circumferential direction of the rotor core 31 and then continuously wider toward the facing surface 31b in the circumferential direction of the rotor core 31. The rotor core 31 also has areas (second areas) R2 in which the width is constant. The first areas R1 and the second areas R2 are located alternately in the circumferential direction of the rotor core 31. One first area R1 and one second area R2 adjacent to the first area R1 are referred to as an area pair. When the rotor core 31 has multiple first areas R1 and multiple second areas R2, multiple area pairs are located adjacent to one another in the circumferential direction of the rotor core 31. In
The number of area pairs (or a cycle) is determined by the number of pole pairs of magnets 33. The number of area pairs and the number of pole pairs of magnets 33 satisfy conditions (1) to (3) below.
(1) The number of area pairs and the number of pole pairs of magnets 33 have no common factor other than one.
(2) The number of area pairs and the number of pole pairs of magnets 33 are both positive integers.
(3) When either the number of area pairs or the number of pole pairs of magnets 33 is one, the other number is other than one.
The magnets 33 have the same height, whereas the rotor core 31 has the varying height as described above. Thus, the magnets 33 have different areas of overlaps with the rotor core 31. More specifically, the magnets 33a, 33b, 33c, 33d, 33e, 33f, 33g, 33h, 33i, and 33j are located in this order in the circumferential direction. The magnet 33a at one end of the array is located in the second area R2 with a wider portion of the rotor core 31. The magnet 33j at the other end of the array is located in the first area R1 with a portion of the rotor core 31 narrower than that in the second area R2. The area of overlap between the magnet 33j and the rotor core 31 is thus smaller than the area of overlap between the magnet 33a and the rotor core 31. Also, as described above, the first areas R1 are continuously narrower upward in the circumferential direction of the rotor core 31 and then continuously wider toward the facing surface 31b in the circumferential direction of the rotor core 31. The magnets 33b to 33i thus have different areas of overlaps with the rotor core 31.
As described above, the magnets 33 have different areas of overlaps with the rotor core 31, which functions as a back yoke. The magnetoresistance of a magnetic circuit including the magnetic flux of a magnet 33 and a Hall device 50 does not match the magnetoresistance of another magnetic circuit including the magnetic flux of another magnet 33 and the Hall device 50.
The Hall devices 50 thus output a Hall signal with a different magnitude (voltage) for each magnet 33. More specifically, when the three Hall devices 50u, 50v, and 50w incorporated in the motor 1A coincidentally have the same characteristics, the maximum and minimum values and the waveforms of Hall signals output from the Hall devices 50u, 50v, and 50w differ from each other for each magnet 33.
The rotor core 31 with an example shape described above includes four area pairs and five pole pairs of magnets 33. However, the rotor core 31 may have other numbers of area pairs and pole pairs. For example, the rotor core 31 may have one area pair and two pole pairs of magnets 33 satisfying the above conditions (1) to (3).
In the above embodiments, the rotor core 31 has a shape satisfying the above conditions (1) to (3) to cause no combination of the waveforms s1, s2 and s3 at a rotation angle to match another combination at another rotation angle as shown in
The present invention is not limited to the above embodiments, but may be modified variously without departing from the spirit and scope of the invention. For example, the numbers of teeth 22, magnets 33, and Hall devices 50 may be changed as appropriate.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-026723 | Feb 2022 | JP | national |
