Brushless motor

• US 10,644,552 B2
• Filed: 06/29/2016
• Issued: 05/05/2020
• Est. Priority Date: 06/29/2015
• Status: Active Grant

• Current Assignee: Mitsuba Corporation
• Original Assignee: Mitsuba Corporation
• Inventors: Ohori, Ryo, Shioda, Naoki
• Primary Examiner(s): Hollington, Jermele M
• Assistant Examiner(s): Elnakib, Ahmed
• Application Number:
  US15/739,754
• Publication Number:
  US 20180198333A1
• Time in Patent Office: 1,406 Days
• Field of Search: 31015638, 31015601, 31015623, 31015628, 31015631, 31015643, 31015647, 31015668, 310216055, 310216069, 310216071, 310216072, 310216073, 310 4939
• CPC Class Codes: H02K 1/2773 consisting of tangentially magnetized radial magnets
• CPC Class Codes: H02K 1/278 Surface mounted magnets; Inset magnets
• CPC Class Codes: H02K 21/14 with magnets rotating within the armatures
• CPC Class Codes: H02K 29/03 with a magnetic circuit specially adapted for avoiding torque ripples or self-starting problems

Abstract

A rotor of a brushless motor includes permanent magnets formed on the outer circumference of a rotating shaft to have a fan shape in an axial cross section, magnetized from the inner radial surface toward the outer radial surface, and arranged at even intervals so that magnetic poles of the outer radial surfaces are disposed alternately with respect to the polarities thereof in the circumferential direction. The outer radial surface of each of the permanent magnets includes a center of curvature on a line segment connecting a center point in the circumferential width on the outer radial surface with the axial center of the rotating shaft, and formed as a cylindrical surface having a radius of curvature smaller than the distance of the line segment. Each of the permanent magnets is magnetized in a parallel orientation so that the orientation of magnetized magnetic flux is parallel to the line segment.

Claims

1. A brushless motor, which is an inner rotor type brushless motor, comprising:

a rotating shaft,

a stator that is cylindrical and concentrically disposed with respect to the rotating shaft and on which a coil is wound, wherein the stator includes a stator core, and the stator core includes a ring yoke portion, wherein the ring yoke portion includes a plurality of flat portions connected to each other, and each two of the flat portions symmetrically disposed at opposite sides of the rotating shaft are mutually parallel,

wherein an outermost surface of each of the flat portions is a flat surface, and

a rotor integrally formed with the rotating shaft and disposed on an inner circumferential side of the stator with a gap,

wherein the rotor includes a plurality of permanent magnets that are segment-typed and formed on an outer circumference of the rotating shaft to have a fan-shaped axial cross section, magnetized from an inner radial surface toward an outer radial surface and disposed at regular intervals so that magnetic poles of the outer radial surfaces are alternately disposed in a circumferential direction, and

the outer radial surface of each of the permanent magnets has a center of curvature on a line segment connecting a center point of a circumferential width on the outer radial surface and an axial center of the rotating shaft and is formed as a cylindrical surface having a radius of curvature smaller than a distance of the line segment connecting the center point of the circumferential width on the outer radial surface and the axial center of the rotating shaft, and each of the permanent magnets is magnetized in a parallel orientation so that a direction of a magnetized magnetic flux is in parallel with the line segment connecting the center point of the circumferential width on the outer radial surface and the axial center of the rotating shaft,

wherein a rotor core that is cylindrical is fitted and fixed to the outer circumference of the rotating shaft, the permanent magnets are disposed on an outer circumference of the rotor core, and a maximum thickness of each of the permanent magnets in a radial direction is set to be greater than a maximum thickness of the rotor core in the radial direction.

2. The brushless motor according to claim 1, wherein the ring yoke portion formed in a regular polygonal cylindrical shape and a tooth portion configured to protrude radially inward from a central position of a circumferential width of an inner circumference of each of the plurality of flat portions of the ring yoke portion corresponding to a side of the regular polygonal shape and on which the coil is wound.

3. The brushless motor according to claim 1, wherein each of the permanent magnets is a ferrite magnet.

4. The brushless motor according to claim 1, wherein a cylindrical magnet cover formed of a nonmagnetic material is fitted to outer circumferences of the permanent magnets arranged in the circumferential direction.

5. The brushless motor according to claim 1, wherein an axial length of each of the permanent magnets is set to be longer than an axial length of the stator.