Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-02-03
2001-04-24
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S044000, C310S235000, C310S236000, C310S237000, C029S597000
Reexamination Certificate
active
06222298
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a commutator in a motor, and more particularly to a carbon commutator in which a member for sliding on a motor brush contains carbon.
BACKGROUND ART
In fuel feed pumps in automobiles, there has been known a so-called in-tank-type system having a motor and a pump integrated in a fuel tank, in which a commutator of the motor directly contacts the fuel because the fuel in the tank is fed through a motor housing to outside devices. In automobiles using gasoline including alcohol, the problem arises that copper in the sliding member of the commutator, which contacts with the brush, is eroded by the alcohol in the gasoline. To avoid this, Japanese Patent Application, First Publication No. Hei 8-308183 discloses a carbon commutator which contains carbon in the member for sliding on the brush.
In the carbon commutator described in the publication, a plurality of segments (commutator pieces), which are produced by compacting and sintering a carbon powder, are arranged to be insulated from each other in a circumferential direction on an insulating boss member made of a synthetic resin. Copper riser pieces which are conductive terminal members are integrally sintered together with the segments. This publication discloses that, in order to ensure electrical connection between the conductive terminal members and the segments, conductive metal powder may be compacted and sintered around the conductive terminal members, or a mixture of the metal powder and the carbon powder is stratified and sintered so that the ratio of the carbon powder may be increased from the conductive terminal members toward the sliding member for the brush. In order for the coefficient of thermal expansion to approximate that of the riser pieces, the same copper material as the riser pieces or nickel-plated copper powder is selected for the metal powder.
However, the above copper powder and the nickel-plated copper powder are not integrated with the riser piece during sintering in a range of 700° C. to 900° C., which is the sintering temperature range for the carbon powder. The riser pieces merely come in contact with the copper powder in the sintered segments, which may therefore become unstable. It is known that the green compact of the metal powder contracts during the sintering, so even when the same copper material as the riser pieces is selected as the metal powder to approximate the coefficient of thermal expansion, the problem arises that gaps may be occur between the sintered compact of the copper powder and the riser pieces.
When the carbon powder and the copper powder are stratified and sintered, binder added to the carbon powder is thermally decomposed and carbonized so that in the carbon powder portion the contraction ratio is greater than the expansion ratio. The contraction ratio of the copper powder is less than the contraction ratio of the carbon powder portion, while the thermal expansion in the copper powder during the sintering is greater than that in the carbon powder. Therefore, slippage may occur at the boundary between the carbon powder and the copper powder, so the sintered segments are apt to separate at the boundaries. It is impossible in the conventional carbon commutator to achieve a long-term stable electrical and mechanical connection especially in fuel which contains alcohol as mentioned above.
It is therefore an object of the present invention to provide a carbon commutator which contains carbon in the sliding members and which achieve long-term stable electrical and mechanical connection between the segments and the conductive terminal members.
DISCLOSURE OF INVENTION
In order to solve the problem, a carbon commutator according to the present invention comprises a plurality of segments having ends which are sliding members on a brush and the other ends to which conductive terminal members are attached, wherein the segments are arranged in a circumferential direction on an insulating boss member and are insulated from each other, carbon layers being formed on the sliding member sides of the segments, metal layers being formed between the carbon layers and the conductive terminal members by sintering a first material of a principal component of the conductive terminal member with a second material which can alloy with the first material. Zinc, antimony, or lead may be substituted for tin which is the second material in the metal layer. The carbon commutator is produced by filling a space around the conductive terminal members with a metal powder to form the metal layer, filling the space on the side of the sliding members with a carbon powder, and then compacting and sintering the powders. During the sintering, the tin powder which has a low melting point of 232° C. melts such that copper particles and the conductive terminal members become wet with tin, thereby liquid phase sintering occurs.
During the liquid phase sintering, the copper melts into the liquid phase of the molten tin, and the amount of the liquid phase increased so as to increase the ratio of the copper content until it is saturated with the solid phase component, while the tin has been diffused in the copper solid phase. The particles are rearranged so as to relax compressive stress arising from thermal expansion of the conductive terminal members. The small copper particles preferentially melt in the liquid phase and are deposited on the large copper particles as a solid phase. The grain growth is promoted during the dissolution and deposition process, so that the copper component in the metal layer alloys with the tin component (production of bronze) to integrate the conductive terminal members with the carbon layers, relaxing the compressive stress. Thus, the segments and the conductive terminal members are reliably integrated electrically and mechanically. By sintering in which the tin component in the metal layer forms the liquid phase, even when gaps and slippage occur between the conductive terminal member and the carbon layer because of the difference in ratio of the contraction and the thermal expansion, the gap is filled with the liquid phase and the compressive stress is relaxed, thus preventing separation between the metal layer, the conductive terminal member, and the carbon layer and ensuring reliable bonding therebetween. When the metal layer is arranged only on the side of the carbon layer with respect to the conductive terminal member, the sufficient electrical and mechanical bonding can be achieved.
When the ratio of the tin component to the copper component in the metal layer is too high, an undesirable brittle phase of the intermetallic compound may form during the sintering, and depending on the sintering temperature the concentration of tin component may exceed the upper limit of the concentration of tin in a stable a solid solution in the copper tin alloy series. On the other hand, when the tin component ratio is too low, the molten tin alloys preferentially with the copper powder particles which have small diameters. This reduces the ratio of alloy with the conductive terminal member and inhibits the relaxation of the compressive stress against the carbon layer, so that sufficient bonding between the metal layer, the conductive terminal layer, and the carbon layer is not achieved. To avoid this, a weight ratio of the copper to the tin in the metal layer is in a range from 98.0:2.0 to 86.5:13.5, and more preferably in a range from 95.0:5.0 to 90.0:10.0.
To produce the segments, the carbon powder forming the carbon layer and the mixed powder of copper and tin are pressed and sintered as mentioned above. When the sintering temperature is too low, the above mentioned effect is not obtained, making the bonding of the segments with the conductive terminal members unstable. When the sintering temperature is too high, the liquid phase may increase so that the shape of the compact cannot be maintained, and may flow out along the conductive terminal member depending on the circumstances. To solve the problem, the sintering temperature is preferably set in
Kumagai Shunji
Saito Junichi
Darby & Darby
Mitsuba Corporation
Mullins Burton
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