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EP-4270743-B1 - ELECTRIC MOTOR

EP4270743B1EP 4270743 B1EP4270743 B1EP 4270743B1EP-4270743-B1

Inventors

  • YOSHIOKA, Yuuki

Dates

Publication Date
20260506
Application Date
20211116

Claims (11)

  1. An electric motor (2) comprising: a rotor (10) including a rotary shaft (13) and a commutator (14) mounted to the rotary shaft (13); a brush (60) including a first end (61) in contact with the commutator (14) and a second end (62) positioned on a side opposite to the first end (61); and a constant load spring (80) including a strip-shaped wire material and configured to press the brush (60) against the commutator (14), wherein the constant load spring (80) includes a spiral part (81) around which the strip-shaped wire material is wound, and the spiral part (81) and the second end (62) are in contact with each other at two or more locations, characterized in that the brush (60) is held in a brush holder (70), the brush holder (70) includes a tubular part (71) having a tubular shape surrounding the brush (60), the constant load spring (80) has a fold-back structure (82) in which one end (80a) drawn out from the spiral part (81) is bent to be folded back outward, the fold-back structure (82) includes a first fold-back part (82a) in which the one end (80a) is folded back outward, and an opposing part (82b) opposing to the first fold-back part (82a), the constant load spring (80) is fixed to an opening end (71a) of the tubular part (71) by the fold-back structure (82) being inserted into the opening end (71a) of the brush holder to cause the first fold-back part (82a) and the opposing part (82b) to sandwich the opening end (71a) of the tubular part (71), the brush holder (70) accommodates the constant load spring (80) together with the brush (60) in the tubular part (71). the first fold-back part (82a) includes a first slit (83a) extending along an insertion direction of the fold-back structure (82), the brush holder (70) has a protrusion (71b) erected on an outer surface of an outer wall of the tubular part (71) and extending along the insertion direction, and the constant load spring (80) is fixed to the tubular part (71) by the fold-back structure (82) being inserted into an opening end (71a) of the tubular part (71) and the first slit (83a) being inserted into the protrusion (71b).
  2. The electric motor (2) according to Claim 1, wherein the second end (62) includes a recess (63), and the spiral part (81) is in contact with the recess (63) at two or more locations.
  3. The electric motor (2) according to Claim 2, wherein in a cross-section taken along a plane orthogonal to an axial center direction of the rotary shaft (13) , the recess (63) has a V shape, an arc shape, a U shape, or a backwards C shape.
  4. The electric motor (2) according to any one of Claims 1 to 3, wherein in the cross-section taken along the plane orthogonal to the axial center direction of the rotary shaft (13), the spiral part (81) and the second end (62) are in contact with each other at two points of a first point (P1) and a second point (P2), and a line connecting the first point (P1) and the second point (P2) is parallel to a direction orthogonal to a longitudinal direction of the brush (60).
  5. The electric motor (2) according to Claim 4, wherein in a circle centered on a center of the spiral part (81), a center angle formed by the first point (P1) and the second point (P2) as a chord is θ, θ ≥ 40° is true.
  6. The electric motor (2) according to Claim 4, wherein in a circle centered on a center of the spiral part (81), a center angle formed by the first point (P1) and the second point (P2) as a chord is θ, θ ≥ 48° is true.
  7. The electric motor (2) according to any one of Claims 1 to 6, wherein the second end (62) includes a restriction part (64) that restricts the spiral part (81) from moving in an axial center direction of the rotary shaft (13).
  8. The electric motor (2) according to any one of Claims 1 to 7, wherein the brush (60) includes a carbon brush (60a) and a mounting component (60b) mounted to a rear end of the carbon brush (60a), and the second end (62) is a rear end of the mounting component (60b).
  9. The electric motor (2) according to Claim 1, wherein the fold-back structure (82) further includes a second fold-back part (82c) erected on the first fold-back part (82a), the second fold-back part (82c) includes a second slit (83b) continuous with the first slit (83a), and the second slit (83b) is without being cut out up to a tip end of the second fold-back part (82c).
  10. The electric motor (2) according to Claim 1, wherein a gap between the first fold-back part (82a) and the opposing part (82b) becomes narrower as a distance from a fold-back position of the fold-back structure (82) increases.
  11. The electric motor (2) according to any one of Claims 1 to 10, further comprising a conductive wire (91) having one end connected to the brush (60) and another end connected to an electrode terminal (92) that provides the brush (60) with electric power, wherein a length of the conductive wire (91) is set to cause the constant load spring (80) to apply a pressing force to the brush (60) even when the brush (60) is maximally worn.

Description

TECHNICAL FIELD The present disclosure relates to an electric motor. BACKGROUND ART Examples of the electric motor include a commutator electric motor with a brush and a brushless electric motor without a brush. In a commutator electric motor, a brush spring is used to press a brush against the commutator. The brush spring applies pressure to the brush using spring elasticity. Conventionally, a coil spring or a torsion spring has been used as a brush spring of a commutator electric motor. However, the coil spring or the torsion spring has a large difference between the pressure (initial pressure) before the brush wear and the pressure (final pressure) after the brush wear, and therefore it is necessary to set the initial pressure high in order to secure at least a certain final pressure or more. For this reason, in the initial stage, friction between the brush and the commutator increases during rotation of the rotor, and sliding loss of the brush may increase. This results in a decrease in efficiency of the electric motor and a decrease in brush life. Therefore, in order to reduce the difference between the initial pressure and the final pressure and apply uniform pressure (load) to the brush, a technique using a constant load spring as a brush spring has been proposed. For example, PTL 1 discloses an electric motor that applies a constant load to a brush by bringing a spiral part of a spiral spring into contact with a rear end surface of the brush using the spiral spring having the spiral part in which a strip-shaped wire material is spirally wound as a constant load spring. However, it has been found that in the conventional spiral spring, the spiral part moves left and right as the brush wears. In this case, with the brush wear, the contact part between the rear end surface of the brush and the spiral part also moves left and right. This may cause the load applied to the brush by the spiral spring to be unstable. In particular, when the spiral part moves left and right, the spiral spring is accommodated in a brush holder together with the brush, and therefore the spiral part of the spiral spring may come into contact with the inner surface of the brush holder. In this case, the load applied to the brush by the spiral spring greatly decreases. As described above, when the spiral part of the spiral spring moves left and right, it becomes no longer possible to apply a stable load to the brush. As a result, the efficiency of the electric motor decreases, or the life of the brush decreases due to unstable mechanical wear. Citation List Patent Literature PTL 1: Unexamined Japanese Patent Publication No. S61-118987PTL 2: JP 2008 125202 APTL 3: US 2009/230813 A1 SUMMARY OF THE INVENTION The present disclosure has been made to solve the above problems. An object of the present disclosure is to provide an electric motor capable of suppressing a decrease in efficiency of the electric motor and a decrease in life of the brush by applying a stable load to the brush even when a constant load spring is used. In order to achieve the above object, one aspect of an electric motor according to the present disclosure includes: a rotor including a rotary shaft and a commutator mounted to the rotary shaft; a brush including a first end in contact with the commutator and a second end positioned on a side opposite to the first end; and a constant load spring including a strip-shaped wire material and configured to press the brush against the commutator, wherein the constant load spring includes a spiral part around which the strip-shaped wire material is wound, and the spiral part and the second end are in contact with each other at two or more locations, the brush is held in a brush holder, the brush holder includes a tubular part having a tubular shape surrounding the brush, the constant load spring has a fold-back structure in which one end drawn out from the spiral part is bent to be folded back outward, the fold-back structure includes a first fold-back part in which the one end is folded back outward, and an opposing part opposing to the first fold-back part, the constant load spring is fixed to an opening end of the tubular part by the fold-back structure being inserted into the opening end of the brush holder to cause the first fold-back part and the opposing part to sandwich the opening end of the tubular part, the brush holder accommodates the constant load spring together with the brush in the tubular part the first fold-back part includes a first slit extending along an insertion direction of the fold-back structure,the brush holder has a protrusion erected on an outer surface of an outer wall of the tubular part and extending along the insertion direction, and the constant load spring is fixed to the tubular part by the fold-back structure being inserted into an opening end of the tubular part and the first slit being inserted into the protrusion. It is preferable that the second end includes a recess, and the spi