In the related art, a 3-brush type electric motor that can switch a rotational speed is used as a wiper motor for an automobile. In such an electric motor, a plurality of magnets are disposed on an inner circumferential surface of a bottomed cylindrical yoke at intervals in a circumferential direction, and an armature is rotatably disposed inside the magnets.
The armature includes an armature core fitted onto a rotary shaft, an armature coil wound on the armature core, and a commutator fitted onto the rotary shaft adjacent to the armature core.
In the commutator, a plurality of segments are disposed in a circumferential direction in an insulated state from each other. Distal end sections of the armature coil are respectively connected to the segments.
In addition, a plurality of brushes come into sliding contact with the segments at intervals in the circumferential direction, and electricity is supplied to the armature coils via the brushes.
The brushes are constituted by a brush for a low speed and a brush for a high speed, and a common brush commonly used for the brushes, and are held at brush holder stay via brush holders. In addition, the brush for a low speed and the common brush are disposed at positions spaced 180° from each other at an electrical angle (mechanical angle×the number of pole pairs). The brush for a high speed is disposed to be spaced a predetermined angle from the brush for a low speed in the circumferential direction. Then, as the electrical connection to the brush for a low speed and the brush for a high speed is selectively switched, the speed of the electric motor can be switched.
Here, in the following Patent Literature 1, in an electric motor having a 2-pole-3-brush structure in which the number of magnetic poles is 2 and the number of brushes is 3, a configuration of a so-called hammer brush in which a brush holder is formed in a flat spring shape is disclosed. Specifically, the hammer brush disclosed in Patent Literature 1 includes a U-shaped brush holder stay having a main wall section and a pair of sidewall sections extending from both end sections of the main wall section, a plurality of brush holders extending in the circumferential direction and biased inward in the radial direction, and brushes fixed to protrude inward in the radial direction from front end sections of the brush holders.
In the brush holders, the base end sections are supported on a main wall section of the brush holder stay at intervals in the circumferential direction. And, the brush holders are inclined inward in the radial direction toward the front end sections. Then, in the electric motor of Patent Literature 1, the brush for a low speed and the common brush come into sliding contact with the commutator from positions spaced a mechanical angle of 180° from each other, and the brush for a high speed comes into sliding contact with the commutator from a position spaced a predetermined angle from the brush for a low speed.
When the above-mentioned hammer brush is assembled to the armature, first, as the brush holders are pressed in a direction against a biasing force by a jig or the like, an interval between the brushes is expanded (an opening process). Next, in a state in which the opening section of the brush holder stay (a gap between the sidewall sections) and the commutator are faced to each other in the radial direction, the brush holder stay approaches the commutator in the radial direction (an assembly process). Accordingly, the commutator is inserted into the brush holder stay, and the commutator is disposed between the brushes. After that, as the pressing against the brush holders is released, the brush holders are recovered and the brushes of the brush holders are held in contact with the segments.
In addition, in the related art, in order to wipe out dust, raindrops, or the like, stuck to a windshield or the like of a vehicle such as an automobile, a wiper motor configured to swing a wiper arm, on which a wiper blade is mounted, within a predetermined range on the windshield is known.
Such a wiper motor includes an electric motor serving as a driving source, a speed reduction mechanism configured to reduce a speed of rotational driving force of the electric motor and to output, and a gear housing configured to accommodate the speed reduction mechanism, the brush holders of the electric motor, the commutator, or the like (for example, see the following Patent Literature 2).
The gear housing has a frame section formed of a metal in a bottomed cylindrical shape, and a bottom plate configured to close an opening section of the frame section. A connector, a wiring section configured to electrically connect the connector and the electric motor (the commutator), a contact plate configured to detect a rotational position of the speed reduction mechanism, and so on, are disposed at the bottom plate.