Electricity: circuit makers and breakers – Electric switch details – Contact
Reexamination Certificate
1999-02-23
2001-06-12
Leubke, Renee (Department: 2833)
Electricity: circuit makers and breakers
Electric switch details
Contact
C200S265000
Reexamination Certificate
active
06246020
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a micro switch, particularly, a micro switch for use in an air conditioner, a freezer, a heater, and the like.
BACKGROUND ART
In electrical equipment such as air conditioners, freezers, and heaters, micro switches have found advantageous application in temperature control including thermostat control, which enables on-off control of large amounts of electrical power without using a relay. Such micro switches have a fixed contact, a movable contact, and a snap-action device. The snap-action device moves the movable contact in or out of contact with the fixed contact to open and close an associated electric circuit.
The fixed and movable contacts of the micro switch have been conventionally made of silver, a silver-carbon sintered metal, a silver-metal oxide alloy, or the like. Particularly, most micro switches have been made of a silver-metal oxide alloy that exhibits outstanding performance with respect to mutual welding of the contacts and consumption of the contacts due to arc discharge.
Japanese Patent Application Laid-open No. 59-123108 discloses a pair of contacts each of which is made of a material having a different characteristic. One of the contacts is made of a silver-tungsten carbide (Ag-WC) sintered metal, while the other is made of an Ag-SnO
2
alloy (viz., a silver-metal oxide compound alloy.
A commonly used micro switch for a large current has been made of a silver-metal oxide alloy that has an outstanding performance against mutual welding of the contacts and against consumption by arc discharge. However, the alloy has the disadvantage of a larger contact resistance to cause a substantial temperature rise at its associated contacts when energized as compared with silver or a silver-carbon sintered metal.
Thus, when both the movable contact and the fixed contact are made of silver-metal oxide alloy, a contact point temperature of the pair of contacts becomes elevated because of a larger contact resistance, disadvantageously affecting an electrical performance thereof. To solve this problem, it is required that the pair of contacts have a larger diameter to increase the contact area thereof for reducing the contact resistance, or that there is provided with an auxiliary plate having a high thermal conductivity for heat radiation.
The enlargement in diameter of the contacts without modifying the switch case in size, decreases clearances between the contacts and other parts, causing a possibility of an arc discharge therebetween. Particularly, a micro switch having a snap-action device consisting of a resilient plate and a U-shaped, snap-action spring raises the problem that the snap-action spring is located very close to the fixed contact, inviting an arc discharge therebetween. Since the snap-action spring is joined to a free end portion of the resilient plate supported by the switch case at one end thereof, and is joined to a movable contact supporting plate having a contact at the other end thereof, the fixed contact must be partially cut away in a side thereof opposed to the snap-action spring, for example, into a D-shape configuration.
Meanwhile, contacts which are both made of a silver-carbon sintered metal do not encounter the above problems. However, the silver-carbon sintered metal, is disadvantageous as compared with a silver-metal oxide alloy in connection with mutual welding of the contacts and consumption of the contacts due to arc discharge. The contacts made of a silver-carbon sintered metal thus have a shorter life. In addition, a silver-carbon sintered metal has a comparatively higher toughness, which hinders plastic molding and is not suitable for a die-cut flat conductor or a contact plate because they can not be directly crimped onto a contact supporting plate.
Japanese Patent Application Laid-open No. 59-123108 discloses a pair of contacts, one of which is made of a silver-tungsten carbide sintered metal, while the other is made of a silver-metal oxide compound alloys. However, this combination is not suitable with respect to preventing mutual welding of the contacts and contact resistance to obviate heating of the contacts. Moreover, it requires a tungsten carbide that has been heat-treated at a high temperature.
SUMMARY OF THE INVENTION
In view of the above problems, an object of the invention is to provide a micro switch having an acceptable performance with respect to mutual welding and against consumption by arc discharge. Moreover, the micro switch does not require an auxiliary contact support and improves its contact elements with respect to miniaturization and electrical life. The contact elements can be directly crimped on a contact supporting plate, which simplifies mounting.
For achieving this and other objects, a first aspect of the invention resides in a micro switch including a fixed contact, a movable contact, and a snap-action device, the snap-action device moving the movable contact in or out of contact with the fixed contact.
In addition, one of the fixed and movable contacts is made of a silver-carbon sintered metal, and the other is made of a silver-metal oxide alloy.
A second aspect of the invention resides in a specified micro switch of the above-mentioned type, wherein the silver-carbon sintered metal includes a carbon power that consists of particles sufficiently small in average size to enable plastic molding of the silver-carbon sintered metal.
One of these contacts is directly crimped and secured to a contact supporting plate.
A third aspect of the invention is a micro switch similar to the second aspect but wherein the silver-carbon sintered metal is made of a silver powder mixed with a carbon powder having an average particle size not more than 1 &mgr;m, the carbon powder being 0.01 to 0.5% in weight to the silver powder.
A fourth aspect of the invention resides in a micro switch similar to the first configuration but which further includes: a switch case enclosing the fixed and the movable contacts, a pair of first and second terminal pieces respectively electrically connected with the fixed contact or the movable contact, and a movable-contact supporting plate resiliently cantilevered from the switch case,
wherein the movable contact is secured to a free end portion of the movable-contact supporting plate, and the snap-action device comprises a resilient plate and a U-shaped, snap-action spring, one end of the resilient plate being secured to the switch case, the snap-action spring being joined at one end thereof to a free end portion of the resilient plate and being joined at the other end thereof to a free end portion of the movable contact supporting plate.
In accordance with the first aspect of the invention, one of the fixed and movable contacts is made of a silver-carbon sintered metal, while the other is made of a silver-metal oxide alloy. This combination of materials having different characteristics compensates for the respective weakness and/or shortcomings of the materials compared with a pair of contacts made of a single material, providing adequate resistance with respect to mutual welding of the contacts and with respect to consumption of the contacts due to arc discharge. This compatibly allows a reduction in contact resistance of the pair of contacts.
In the second aspect of the invention, the micro switch has one contact made of a silver-carbon sintered metal which is capable of plastic molding. The contact is directly crimped on the contact supporting plate.
In the third aspect of the invention, the silver-carbon sintered metal is made of a silver powder mixed with a carbon powder having an average particle size not more than 1 &mgr;m, the carbon powder being 0.01 to 0.5% in weight to the silver powder.
In the fourth aspect of the invention, the fixed contact connects to the first terminal piece so as to be secured to the switch case. The movable contact is secured to the free end portion of the movable-contact supporting plate, and the snap-action device comprises the resilient plate and the U-shaped, snap-action spring, one end of the resilient
Kabushiki Kaisha Saginomiya Seisakusho
Leubke Renee
McDermott & Will & Emery
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