Electricity: electrothermally or thermally actuated switches – Electrothermally actuated switches – With longitudinally expansible solid element
Reexamination Certificate
2000-04-26
2001-08-28
Sircus, Brian (Department: 2839)
Electricity: electrothermally or thermally actuated switches
Electrothermally actuated switches
With longitudinally expansible solid element
C337S329000, C337S373000, C337S399000, C337S413000, C200S268000, C174S1170FF, C361S105000
Reexamination Certificate
active
06281780
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an electrical apparatus having electrical contacts that are actuated on the basis of a selected change in temperature or in electric current and to an electrical apparatus which can be suitably employed as a thermostat or surge protector having an expected life of a limited number of cycles.
BACKGROUND OF THE INVENTION
There are many electrical apparatus whose main function lies in opening or closing a pair of electrical contacts in response to physical changes in the environment such as heat, electric current value, pressure or the like. In the case of this kind of electrical apparatus, whenever an anticipated physical change takes place in the apparatus, the electrical contacts are either opened or closed accordingly. Such electrical apparatus includes, for example, battery protectors, motor protectors, thermostats, pressure switches, circuit breakers, relays, etc. A battery protector or a motor protector is installed between the battery or motor and the target electrical product such as a portable computer, camera, communications equipment, automobile control equipment, or the like. In the case where an over-current has been produced in a battery (or in a motor), first and second contacts of the protector are separated from one another, thereby protecting the electrical product involved. In the case of a thermostat, the contacts are opened or closed in response to a selected change in the ambient temperature, thereby shutting off the power source and thus functioning in such a way as to maintain the ambient temperature constant.
A problem common to all of these electrical apparatus having such contacts is erosion or wear of the contacts due to arc discharges which are produced upon opening or closing of the contacts. When contacts that have been in engagement are separated from each other in the state where electric current has been impressed, an arc discharge is produced, with a result that a part of the contact material is eroded. By repeated opening and closing actions of the contacts, the contact material is reduced in a gradual manner and this limits the life of the apparatus.
Manufacturers of this kind of electrical apparatus, determine the expected number of cycles during the useful life of the apparatus due to wearing of the contacts by electric arc discharge and discourage use of the apparatus in excess of this number. In actuality, however, there are cases where these electrical apparatus are used in excess of the expected number. In such cases, it has been impossible to tell with conventional electrical apparatus if the final failure mode will end in contact welding or in a non-conductive state. In the former case, therefore, the electric apparatus does not function as desired and there is a danger of damaging the electrical product for which protection is intended.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is the provision in electrical apparatus possessing a contact which is either opened or closed by a physical change, that the final failure mode ends in electrical non-conductivity.
Another object of the invention is the provision of electrical apparatus caving a useful life of a prescribed number of cycles and also providing apparatus having such a contact in which the circuit containing the contact becomes electrically non-conductive when the apparatus has finally failed.
Still another object of the invention is the provision of electrical apparatus having a circuit with openable and closeable contacts in which the final failure mode of the apparatus becomes electrically non-conductive and which is provided at a low cost and which is highly reliable.
Another object of the invention is the provision of electrical apparatus which overcomes the above noted limitations of the prior art.
Briefly stated, an electrical apparatus according to the invention comprises first and second terminals which are electrically separated and extend into a casing, a first contact which is electrically connected to the first terminal within the casing, a second contact which is electrically connected to the second terminal within the casing and an operating means which electrically connects or disconnects the first and second terminals by relatively connecting or disconnecting the first and second contacts. In accordance with the invention, at least the first contact comprises a first conductive layer of a prescribed thickness containing a surface that is engageable with the second contact, a second conductive layer that is connected to the first terminal, and an insulating fiber that is interposed between the first and second layers and the second contact effecting engagement with the insulating fiber when the insulating fiber has been exposed due to the wearing away of the first layer incident to the closing and opening movement of the first and second contacts.
In accordance with the invention, it is desirable that the first and second layers of the first contact be formed by mutually hot-pressing the layers together. It is also desirable in connection with the material of the contacts that the first layer be composed of a material whose main ingredients are silver (Ag) and nickel (Ni) alloys and whose second layer be composed of a material whose main ingredient is silver (Ag). In addition, it is desirable that the insulating fiber be composed of a suitable glass fiber.
In accordance with one embodiment of the invention, the first contact is a movable contact and the second contact is a stationary contact. It is desirable in connection with the operating means that the movable contact be moved in such a way that the contact surfaces of the contacts come into sliding engagement against each other. In this case, it is desirable for the insulating fiber to extend in a direction which crosses the direction in which the contact surfaces of the contacts slide against each other. According to the invention, moreover, it is desirable for the thickness of the first layer of the first contact to be selected based on the number of openings and closings of the contact that is to be provided.
According to an alternate feature of the invention, the operating means includes a member which is mechanically displaced in response to a selected variation in the ambient temperature, with the first contact being actuated by the mechanical displacement of the member. Accordingly, it is possible to use the electrical apparatus as a thermostat or as a protector that causes either contact engagement or disengagement of the first and second contacts when the ambient temperature has exceeded a prescribed value.
According to another alternate feature of the invention, the operating means contains a member that is mechanically displaced in response to a selected change in electric current, with the first contact being actuated by the mechanical displacement of the member. Accordingly, it becomes possible to use the electrical apparatus as a protector that will separate the first contact from the second contact when the electric current from the power source has exceeded a prescribed value.
According to yet another alternate feature of the invention, the operating means contains a member which is mechanically displaced in response to a selected variation in pressure, with the contacts being actuated by the mechanical displacement of the member. Accordingly, it becomes possible to use the electrical apparatus as a pressure switch that causes engagement or disengagement of the first and second contacts when the pressure of external fluid has exceeded a prescribed value.
The present invention also relates to electrical contacts for opening or closing the electric circuit. At least one electrical contact of a pair of contacts movable into and out of engagement with each other comprises, in accordance with the invention, a first layer having a prescribed thickness and containing a surface that is engageable with the other contact of the pair, a second layer that is connected with the electric circuit, and insulating fiber interposed
Kitada Harumi
Nagano Kouzoh
Sugiyama Akitsugu
Baumann Russell E.
Sircus Brian
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
Webb Brian S.
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