Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2002-06-05
2004-01-06
Lam, Thanh (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S044000, C310S219000, C310S237000
Reexamination Certificate
active
06674212
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon, and claims the benefit of priority of, prior Japanese Patent Application 2001-169673, filed on Jun. 5, 2001, the contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-layer current-carrying member (a brush portion or a commutator portion) for a direct-current motor in a fuel pump, a method for producing the member, and a fuel pump employing the member.
2. Description of Related Art
Engines in automobiles, and the like, are normally equipped with low pressure fuel pumps for pumping fuel from a fuel tank to a delivery pipe or to a high pressure pump of a fuel injection valve or device. Such a fuel pump is generally driven by a direct-current (DC) motor using a battery or other power supply source. In the case of the DC motor, it is necessary to keep a direction of a current constant with a rotational position of an armature coil, and for this reason, rectification is carried out by a brush and a commutator.
Additionally, resistance to fuel erosion (resistance to a fuel that causes erosion) is required for a fuel pump, whether it is an in-tank type or other type, and, in particular, for its DC motor. Japanese Laid-Open Patent Publication No. Hei. 8-308183 discloses a commutator (carbon commutator segments) containing a carbon layer in a sliding portion for a brush. Further, the publication describes that by forming a metal carbon layer beneath the carbon layer, the bonding to a conductive metal terminal (riser) can be ensured. The conductive metal terminal is connected to the metal carbon layer at one end thereof, and to the armature coil at the other end. Similar descriptions are disclosed in Japanese Laid-Open Patent Publication No. Hei. 9-46978 and International Publication No. WO99/08367.
The metal carbon layers disclosed in Japanese Laid-Open Patent Publication Nos. Hei. 8-308183 and Hei. 9-46978 are formed by sintering a copper powder with a carbon powder. Also, the metal carbon layer disclosed in the International Publication No. WO99/08367 is formed by sintering a mixed powder of a copper powder, a tin powder, and a carbon powder. International Publication No. WO99/08367 describes bonding between the carbon layer and the conductive metal terminal as being improved due to a liquid phase of the tin powder having a low melting point. A composition ratio of copper to tin in this publication is about Cu-10 Sn (wt %).
The inventor of the present invention, however, has found that a current-carrying member, such as a commutator and a brush, using copper or copper alloy with a high content of copper has poor resistance to a fuel. To be more specific, the current-carrying member has poor resistance to erosion because of sulfur in the fuel. Erosion of the current-carrying member is not acceptable because it deteriorates the durability and performance of the fuel pump. Hence, the current-carrying member is required to have satisfactory resistance to sulfidation.
SUMMARY OF THE INVENTION
The present invention was devised in view of the foregoing disadvantages. Therefore, it is an object of the present invention to provide a sulfidation-resistant current-carrying member for a DC motor in a fuel pump. It is another object of the present invention to provide a method for producing such a fuel pump. The present invention has yet another object which is to provide a fuel pump employing the current-carrying member.
(Current-carrying Member for a DC Motor in a Fuel Pump)
In order to achieve the above and other objects, sulfidation-resistant brass is used as the metal in the metal carbon layer of a current-carrying member composed of a carbon layer and a metal carbon layer. That is, a current-carrying member for a DC motor in a fuel pump of the present invention comprises a brush having a sliding surface at one end and fed with a current from a power supply source. Additionally, the member has a commutator with a sliding surface that slides on a sliding surface of the brush for feeding an armature coil with the current received from the brush. At least one of the brush and the commutator is composed of a carbon layer having carbon as a principal component and forming the sliding surface at one end, and a metal carbon layer fixedly bound with the carbon layer at the other end and comprising 55 to 90 wt % of metal having brass as a principal component and a remaining portion having carbon as a principal component.
According to the current-carrying member of the present invention, because metal in the metal carbon layer has brass as a principal component, resistance to sulfidation is enhanced, making it possible to enhance durability of the current-carrying member, and hence, that of the fuel pump. The reason why a weight ratio of the metal in the metal carbon layer (out of a total of 100 wt %) is set to a range from 55 to 90 wt % is as follows. A weight ratio less than 55 wt % is not preferable because a specific resistance value of the metal carbon layer increases.
Generally, a conductive metal terminal is connected to the metal carbon layer, and the armature coil is fed with a current through the conductive metal terminal. For this reason, it is preferable that the metal carbon layer has a small resistance value. Also, a weight ratio of the metal less than 55 wt % is not preferable, because the metal carbon layer has poor strength, which deteriorates the retentivity of the current-carrying member. In particular, in a case where the conductive metal terminal is connected to the metal carbon layer mechanically (for example, in the case of press-fitting or fastening), the metal carbon layer needs to have the strength of a certain or greater degree in order to secure a stable connection therebetween.
Likewise, a weight ratio of the metal higher than 90 wt % is also not preferable because the bonding strength in the vicinity of the boundary of the carbon layer and the metal carbon layer becomes poor. When the bonding strength becomes poor, an overall resistance value increases, which deteriorates the retentivity of the current-carrying member. Further, when a weight ratio of the metal exceeds 90 wt %, the metal carbon layer becomes too rigid and hard. Hence, for example, in a case where the conductive metal terminal is connected to the metal carbon layer by press-fit or the like, the machining load required to achieve the press-fit, or the like, increases. Then, the load reaches the carbon layer, having a relatively poor toughness, which may possibly cause cracking or the like in the carbon layer.
In view of the foregoing, it is preferable to set a weight ratio of the metal to a range from 55 to 90 wt % and more preferably to a range from 70 to 80 wt %. The current-carrying member of the present invention includes a type in which the conductive metal terminal is embedded into the metal carbon layer and the metal carbon layer and the conductive metal terminal are integrally sintered.
The metal carbon layer is composed of, for example, a porous metal skeleton having brass as a principal component, and a filling material present in the porous metal skeleton having carbon as a principal component. The metal carbon layer may be integrally formed by sintering a mixture of a brass powder, a carbon powder, etc. or formed by filling foamed metal (porous metal skeleton) prepared in advance to have brass as a principal component with a filling material having carbon as a principal component.
Brass used in the metal carbon layer is an alloy having Cu and Zn as principal components. For example, a copper alloy containing 25 to 45 wt % of Zn on a basis of 100 wt % of brass is favorable as brass. Zn has a larger sulfide-producing free energy than Cu, and is an effective sulfidation-resistant element. When a weight ratio of Zn is less than 25 wt %, resistance to sulfidation of the metal carbon layer becomes insufficient. A weight ratio of Zn higher than 45 wt % is not preferable, because of the &bgr; phase precipitates, which deteriorate the work
Hotta Tokio
Inukai Kyoji
Kiyose Kenzo
Kokuryu Etsuo
Matsumoto Ken-ichi
Denso Corporation
Lam Thanh
Nixon & Vanderhye P.C.
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