Claims
- 1. A gravity switch comprising:
- (A) a cylindrical shell member of conductive material closed at one end and open at the other end;
- (B) a base member of dielectric material closing the open end of said shell member;
- (C) an electrical contact extending axially through said base member to present a contact tip surface located adjacent the open end of the said shell member on the central axis of that member;
- (D) a ball of conductive material positioned rollably within said shell member and having a diameter which is slightly less than the inner diameter of said shell member and more than half of the shortest distance between said contact tip surface and the inner surface of the closed end of said shell member;
- (E) said shell member and electrical contact cooperating with said base member for hermetrically sealing the interior of said shell member within which said ball is rollable;
- (F) said ball having a surface coating of conductive material different from the interior material of said ball; and
- (G) said contact tip surface and the interior surface of said shell contactable by said ball comprising material having electrical properties comparable to the electrical properties of the material coating said ball.
- 2. A gravity switch according to claim 1, wherein said contact tip surface comprises a spherical surface having a radius comparable to the radius of said ball so as to make a tangent point electrical contact with said ball.
- 3. A gravity switch according to claim 1, wherein said conductive material is a precious metal.
- 4. A gravity switch according to claim 3, wherein said precious metal is silver.
- 5. A gravity switch according to claim 4, wherein said contact tip surface comprises a spherical surface having a radius comparable to the radius of said ball so as to make a tangent point electrical contact with said ball.
- 6. A gravity switch according to claim 1, wherein the material of said ball is brass.
- 7. A gravity switch according to claim 6, wherein said contact tip surface comprises a spherical surface having a radius comparable to the radius of said ball so as to make a tangent point electrical contact with said ball.
- 8. A gravity switch according to claim 6, wherein said conductive material is a precious metal.
- 9. A gravity switch according to claim 8, wherein said precious metal is silver, and said contact tip surface comprises a spherical surface having a radius comparable to the radius of said ball so as to make a tangent point electrical contact with said ball.
- 10. A gravity switch according to claim 8, said base member having an annular flange extending coaxially into the open end of said shell member and having an annular shoulder around said flange, the radial dimension of said shoulder approximating the wall thickness of said shell member, whereby said shell member may be hermetically telescoped over said annular flange portion to position its open end adjacent to said shoulder and define a smooth air-tight switch capsule having a uniform external diameter throughout its length corresponding to that of the shell member.
- 11. A gravity switch for opening or closing an electrical circuit in accordance with the inclination of the axis of the switch from a horizontal position comprising a cup-shaped dielectric member having axially extending sidewalls forming an enclosure, a base closing one axial end of said enclosure, and a mouth opening axially endwise at the opposite axial end of said enclosure; first contact means of electrical conducting material comprising an interior electrical contact within said enclosure adjacent to said base, an exterior electrical contact externally of said enclosure, and means extending through said member and electrically connecting said interior and exterior contacts; second contact means of electrical conducting material spaced from the first contact means and fixed with respect to said enclosure, said second contact means having guide portions extending axially along said sidewalls in the direction from said base toward said mouth and effecting an interference fit with said sidewalls, said guide portions terminating in said direction in portions closing said mouth and defining a second exterior contact; and means for selectively completing an electrical connection between said guide portions and said interior contact comprising gravity actuated contact means movable axially along said guide portions in electrical contact therewith to and from positions of electrical contact with said interior contact in accordance with the inclination of said axis, said gravity actuated contact means comprising a ball rollable within said enclosure, said exterior contact comprising fixed means for effecting a point contact with said ball when the latter is in said position of electrical contact with said interior contact, said first and second contact means cooperating with said dielectric member for hermetrically sealing said enclosure, said ball having a surface coating of conductive material different from the interior material of said ball, the surfaces of said fixed means and said guide portions comprising material having electrical properties comparable to the electrical properties of the material coating said ball.
- 12. A gravity switch according to claim 11, wherein said surface coating is a precious metal.
- 13. A gravity switch according to claim 12, wherein said contact tip surface comprises a spherical surface having a radius comparable to the radius of said ball so as to make a tangent point electrical contact with said ball, and said precious metal is silver.
- 14. A gravity switch according to claim 11, wherein the material of said ball is brass.
- 15. A gravity switch according to claim 14, wherein said contact tip surface comprises a spherical surface having a radius comparable to the radius of said ball so as to make a tangent point electrical contact with said ball, and said surface coating is silver.
BACKGROUND AND OBJECTS OF THE INVENTION
This application is a continuation-in-part of U.S. patent application Ser. No. 491,492, filed on May 4, 1983 now U.S. Pat. No. 4,467,154.
This invention relates to improvements in a gravity operated electrical switch and in particular to such a switch of small size adapted to replace or to be interchangeable with a typical mercury switch of the type adapted to be exposed to the weather and used with an automobile hood or deck lid wherein the switch automatically completes or breaks an electrical circuit when the lid is opened or closed.
Important objects of the present invention are to provide an improved switch of the above type characterized by simplified low cost design and construction and that is light in weight, compact, highly reliable, and capable of economical manufacture by automated mass production procedures; to provide such a switch having improved contact elements including a spherical contact member or metallic ball movable by gravity within a cylindrical electrical conductor such that operation of the switch is assured regardless of the rotational position of the housing axis; to provide an improved economical and automated method of manufacturing such a switch wherein dimensional tolerances between the external electrical contacts are closely maintained without recourse to precise and expensively maintained dimensions for the component parts.
Among the problems involved in the substitution of such a gravity switch for a mercury switch are ball sticking or a welding effect and high millivolt drop across the electrical contacts. Ball sticking or welding of the ball to the contacts at the "on" or a closed circuit position impairs gravity induced movement of the ball to the "off" or open circuit condition. Also a comparatively high voltage drop between the ball and the switch contacts at the closed circuit condition results in loss of electrical power, or luminous intensity when the switch is employed with an electric light.
The above problems are overcome in accordance with the present invention by providing means for significantly increasing the contact pressure between the ball and the switch contact elements. Inasmuch as the overall switch dimensions are severely limited by the requirement of maintaining interchangeability with customarily employed mercury switches, the design of the ball switch is critical.
Other objects accordingly are to provide an improved switch design which, without increasing the external dimensions of the switch, enables use of a larger diameter ball contact element of correspondingly greater weight, which in turn has been found to reduce the voltage drop across the ball contacts materially when the switch is tilted to the "on" position. In consequence, a comparatively costly lead ball, which has been heretofore preferred in small switches because of its high specific gravity, can be replaced by a larger, heavier, and less costly brass ball which reduces voltage loss across the contacts and likewise the welding effect and enables efficient operation of the switch with larger current flow than heretofore. By suitably plating the switch elements, as for example with silver, and by thoroughly cleansing all the switch elements immediately prior to their assembly, the welding effect and consequent ball sticking are further reduced and optimum electrical conductivity through the switch is achieved.
Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.
Although applicant is not aware of any switch comparable in simplicity and effectiveness to the present invention, sealed gravity actuated switches comprising a conducting shell arranged coaxially within an insulating shell are common, as illustrated for example in Hobbs, U.S. Pat. No. 2,206,094 and U.S. Pat. No. 2,228,456 and in Zink U.S. Pat. No. 4,042,796. In particular, the prior art does not teach the construction of a cup-shaped dielectric member and a cup-shaped conductor pressed together in axially telescoping relationship at an interference fit, whereby the two cup-shaped members are fixed with respect to each other to comprise an integrated dimensionally stable sealed housing for a contact element movable axially within the members and adapted for selectively making or breaking an electrical connection between the cup-shaped conductor and a second conductor extending axially through the base of the cup-shaped dielectric member whereby the axially outer surfaces of the electrical contacts for the switch, comprising the base of the cup-shaped conductor and the second conductor, are available for making electrical contact with a pair of axially spaced contacts within a container for the switch, and also whereby the overall axial dimension between said axially outer surfaces of the switch contacts may be readily preselected and maintained in production without recourse to closely maintained and costly axial tolerances in the fabrication of the cup-shaped members. Likewise there is no suggestion in the prior art of such a switch wherein the dielectric cup-shaped member has a cylindrical portion of reduced outer diameter with respect to its base and extending therefrom for a comparatively short axial extent to its open end, and wherein the conducting member is sleeved or telescoped over said reduced outer diameter portion in tightly fitting sealing engagement, thereby to reduce the costly dielectric plastic material to a minimum and achieve the maximum internal diameter for the conducting member without increasing the overall outer diameter of the switch.
The prior art also does not teach the combination of a cylindrical shell member of conductive material closed at one end and open at the other end; a base member of dielectric material closing the open end of the shell member; an electrical contact extending axially through the base member to present a contact tip surface within the open end of the shell member; and a ball of conductive material positioned rollably within the shell member and having a diameter which is slightly less than the inner diameter of the shell member and more than half of the shortest distance between the contact tip surface and the inner surface of the closed end of the shell member.
The prior art also does not teach the further feature of the invention whereby the ball, the contact, and the interior surface of the shell member are plated with a common conductive material which is different from the material of either the ball, the contact, or the shell member. This feature has been found to minimize the welding effect and consequent ball sticking and produce a gravity switch having an extremely long effective switching life. In the disclosed embodiment of the invention, the common conductive material is silver.
The prior art also does not teach the still further feature of the invention whereby the various elements of the switch are thoroughly cleansed immediately prior to their assembly and the assembly is performed in a clean room environment. This feature has been found to further minimize the welding and sticking effect and further contribute to a long effective switching life.
US Referenced Citations (10)
Continuation in Parts (1)
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491492 |
May 1983 |
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Patent Grant
4513183
