Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-02-23
2001-12-04
Waks, Joseph (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S242000, C074S006000
Reexamination Certificate
active
06326716
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
The present application is based on and claims priority from Japanese Patent Applications: Hei 11-48599, filed Feb. 25, 1999; Hei 11-320436, filed Nov. 11, 1999; and Hei 11-363770, filed Dec. 22, 1999; the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a DC motor which is suitable for a vehicle starter.
2. Description of the Related Art
As a prior art, a starter is disclosed in JP-U-63-143040. The motor of this starter has a face-contact commutator. The face-contact commutator has a surface perpendicular to an armature shaft to be in contact with a pair of brushes. There is a difference between this face-contact commutator and a common cylindrical commutator in that: it is necessary for the cylindrical commutator to have an axial marginal length for receiving the brushes, while it is not necessary for the face-contact commutator to have the same. In other words, the face-contact commutator is effective to shorten the axial length of the motor.
The motor disclosed in the publication has compression coil springs for biasing the brushes against a commutator. Compression coil springs are disposed at the rear end of brushes opposite to the commutator. If the spring constant of the coil spring is lowered and the initial spring is increased to provide a sufficient spring force for a long time until the brushes are worn away, the total length of springs is increased. That is, although the face-contact commutator shortens the length of the armature, the total length of the motor can not be reduced.
If the spring force is increased to shorten its length, the springs may be fatigued shortly due to heat of the motor.
As disclosed in JP-A-7-194066, a resinous holder holding a brush holder thereon is fastened to a bracket by a bolt, and the bracket together with a torque sensor unit disposed thereon is also fastened to a flange of motor casing by bolts. Through holes are formed in the bracket and the flange and female screw holes are formed in the torque sensor unit. Because the inside diameter of the through holes is larger than the outside diameter of the bolts, clearances are formed between the bolts and the bracket's through holes. As a result, the bracket may move in the clearances, and this makes the circumferential positioning difficult.
Even after the motor casing and the brush holder have been assembled, the bracket may move within the clearance due to vibration. This changes circumferential position of the brush holder relative to the yoke.
In addition, the torque sensor and the motor casing with the bracket interposed therebetween necessitate to align three through holes thereof with each other.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above circumstances and has a main object to reduce the total length of a DC motor.
According to a main feature of the invention, each brush spring has a springy spring body and a spring arm extending from the brush body to bias the rear end of one of the brushes, and the spring body is disposed at a side of the one of the brushes within the axial length of the one of the brushes. Accordingly, the total length of the DC motor can be reduced.
Another object of the invention is to provide a DC motor which is easy to position the yoke and brush holder accurately.
The brush holder unit is comprised of a metal brush holder and a resinous holder having a plurality of cavities for respectively accommodating the blush holders. Each of the brush holders has a stopper means for preventing the same from falling away from one of the cavities.
Therefore, the brush holders can be fixed to the resinous holder easily without screws or rivets. Because the mental brush holder is surrounded by resinous material and a distance between the brush holder and an end frame can be provided, sufficient insulation can be provided even if abrasion powders of the brushes due to long use stick to the brush holder. Because the brushes are accommodated by the mental brush holder, the resinous holder is protected from thermal damage even if the brushes are over-heated.
The stopper means may have a support arm which has an edge in engagement with a groove formed in the resinous holder. If the support arm is applied reaction force of the brush spring, the support arm and the brush holder are prevented by the edge of the support arm from deforming.
The commutator of the DC motor may be a face-contact commutator whose surface is perpendicular to a shaft of the armature.
According to another feature of the invention, a rubber bushing is fixed to the brush holder unit so that the yoke and the brush holder unit are positioned with the rubber bushing interposed therebetween. This, prevents slippage of the brush holder unit in the circumferential direction.
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Hosoya Akifumi
Niimi Masami
Denso Corporation
Pillsbury & Winthrop LLP
Waks Joseph
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