US2520525A - Magnetic switch - Google Patents

Description

Aug. 29, 1950 H. L. BRousE- 2,520,525

MAGNETIC SWITCH v Filed April 1, 1948 w Hum illllll IN V EN TOR. A AAOZO Z. 6200::

Patented Aug. 29, 1950 2,520,525 FF 1 CE MAGNETIC swi'ron HaroldL. Brouse, Cincinnati, Ohio, assignor, by mesne assignments, to Robot Appliances, Inc., Detroit, Mich, a corporation of Michigan Application April 1, 1948, Serial No. 18,378

3 Claims. (Cl. 200112) Another object of the invention is the provision of a switch of the magnetic type especially adapted for underground use.

A further object of the invention is to provide a hermetically sealed magnetically operated switch suitably adapted for use under extreme conditions of temperature and humidity.

A still further object of this invention is to provide a mercury switch so constructed that the operating efficiency and life expectancy is in no way affected by the presence of the mercury.

Other objects and advantages of the invention will appear upon a thorough consideration of the following detailed description composed with reference to the drawings which constitute a portion of this specification and in which:

Fig. 1 is a perspective view of a switch embodying the instant invention.

Fig. 2 is a front elevation view of the switch with the front cover removed.

Fig. 3 is a rear elevational view of the switch with both the terminal cover and the asphalt packing removed.

Fig. 4 is a vertical sectional view taken substantially on line 4-4 in Fig. 2 with both'covers in place.

In Fig. 1 numeral l0 designates a switch case of non-magnetic and chemically inert conductive material such as stainless steel, having a front cover [2 and a terminal cover l4 provided with an opening NS for the reception of a dual conductor cable l8. The front cover l2 has an outwardly deformed central portion 20 coated on the inside surface with a suitable insulating compound 22, such as plastic adhesive, and rolled along the outer edge thereof into a locking and sealing engagement with the rim of the case It.

The case In is soldered, or otherwise mounted, on a footed bracket 24 having an outstanding annular flange 26 for supporting the terminal cover l4 and providing a case connection terminal 28. The foot of the bracket 24 is welded, or otherwise secured, to a plate 30 so as to provide a convenient base for mounting the switch in an upright position.

An elongated non-magnetic stud 32, of stain- :less "steel or other suitable conductive material, is

mounted centrally in the rear wall of the casing Ill and fixedly held at substantially right angles thereto by a sealing and insulating grommet 34, of an inert resilient material such as a type of chlorinated synthetic elastomer, That portion of the stud 32 within the casing I0 is provided with an annular flange 36 seated against the inner face of the grommet 34 and drilled axially to receive, in a press fit, a non-ma netic pin 38,

I 2 of suitable conductive material, having an enlarged retaining head on the free end thereof.

That portion of the stud 32, outside the case I0, is decreased in cross section to provide an annu larshoulder 39 adjacent the rommet 34 for seating a non-magnetic spacer bushing 40 adapted to imposed a predetermined amount of compression on the resilient rommet 34. The smaller portion of the stud 32'is threaded to receive a nut 42 for holding the spacer bushing 40 in seat against the shoulder 39 and providing lateral support for a central terminal connector 44 locked on the stud by a retaining nut 46. A bar magnet 48 of high permeability material is mounted in a nonmagnetic cradle 50 which is suspended centrally from the pin 38 for balanced rotation thereabout within predetermined angular limits.

The magnet 48 is bonded in the cradle 50 by a suitable cement and further secured therein by means of clips 52 and 54, provided on either end of the cradle 50, and turned down over the top of the magnet 48. The cradle 50 also has a triangular' shaped contact point 56, dependent from each end thereof, adapted to make contact with'a pool of suitable conductive liquid 58, such as triple distilled mercury, when the cradle and magnet assembly is rotated a predetermined distance in either direction.

The rotational limits of the cradle assembly are defined by a cushion stop comprising a section of resilient tubing 60, such as rubber, fitted over a laterally extended bracket 62 supported by a downturned foot wedged between the rear wall of the case I!) and the inner flange of the grommet 34.

The cushion stops, by defining the limits of travel in either direction, prevent the cradle assembly from rotating, under the influence of a strong magnetic field, so as to cause the contacts 56 to float inverted on the surface of the mercury pool rather than remain immersed.

This completes a discussion of the structural details of the invention; however, to facilitate a better understanding of the subject matter involved, a brief discussion will be directed to the manner in which the switch is assembled and the way in which 'it'operates to perform its intended 7 function.

In assembling the switch it is extremely important to remove as much moisture as possible from the airwithinthe casing so as to prevent oxidation of the parts. This reaction, byway of illustration, will. occur readily at a temperature of F.- and relative humidity of 45 percent. However, at this same temperature, the relative humidity must be constantly maintained below 15 percent to avoid the possibility of suchoxidation.

This undesirable oxidation, as well as mercury pollution, resultfrom the'presence of greases and various soldering -or.,welding fluxes present on certain of the component parts. It is, therefore, essential that the case be washed in boilin ater after soldering so:- as to remove all excess flux It is also advisable to immerse all parts in a suitable degreasing solution and then adopt measures in assembling the switch to prevent any deposition of greases on either the enclosed working: parts or the surfaces defining theenclosure.

After the working parts of the switch have been. assembled within the case, the placed; in a dehydrated atmosphere so as to charge the case with moisture-free air. If it is deemed advisable, the case may be charged with a gas. such as nitrogen or hydrogen so as to reduce further the possibility of corrosion. and chemical activity. Caution must.- alsobe exercised. soas to selectsubstantially chemically inert materials to. be. used for the fabrication. of those. elements, in theswitch which are normally exposed eitherto the conductive liquid or its. vapors whenal chemically active substance like mercury is employed,

Before the front cover I7. is placed on. the case It), however, a thin. coating of a rubber cement is preferably applied to the or mating surface thereof and permitted to. dry at a temperature slightly above the. boiling point of water so as to evaporateany moisture present. i

melted asphalt and forced in. place over the terminals. I Y

The. casing isthusv hermetically sealed,- thereby making the switch especially well adapted for use in installations which are-constantly subjected to varying extremes of temperature and moisture. Therefore, barring damage to the. switch caused by impact. or overload, repeated tests have shown 4 would energize the coil temporarily by means of the car battery as the vehicle is passing over the underground magnetic switch. This would cause the switch to close so as to complete a circuit for reference to the details of a single embodiment and: adaptation, it will be appreciated by those skilled in the art that the principles involved, as well as the device itself, are susceptible of numerousother: applications.

Therefore, what I claim and desire to secure by Letters Patent is:

1. A. magnetic switch comprising, an electricall'y conductive non-magnetic and hermetically sealed case,- a conductive. terminal stud having a threaded section on one end anda seating flange on. the other end mountedin one side of the case, insulating means including a resilient grommet sleeved. around the stud and. seated against the stud flange, adjustable means for cooperation V with the threaded section to. compress the gromthat the device will function indefinitely without 7 any loss in sensitivity or efficiency.

In operationv the switch. is. placed in an position on the base- 3flsolthat cradle 50 is free to pivot about the pin 38. Therefore, when the magnet 48, carried by the cradle. 53, is exposed to a magnetic field of sufficie'nt intensity,

the forces of attraction and repulsion are. citedthe switch, and consequently any circuit-in which it is connected, until. it is again. caused to close in one direction or another imder the influence of a magnetic field of sumcient intensity as above described.

One use of the switch as contemplated by the applicant, is in conjimction with. automatic: garage door operating equipment. In this connec tion, the switch may be installed in the ground beneath a driveway so as to be within the operating range or influence of a magnetic on the under side of an automobile or other'sim'rlar vehicle. In such an installation, the dn'yer met a predetermined amount into a sealing engagement with the case, a conductive cradle in the case mounted for limited. rotation. on. the stud a permanent. magnet mounted centrally infthe cradle, and a pool of conductive liquid in the case adapted to immerse one end or the. other of. the cradle and magnet. assembly as it rotates in re.- sponse to a magnetic. stimulus.

2. A magnetically operated switch comprising, an. electrically conductive non-magnetic andhermetically sealedcase, a conductive terminal stud having a threaded section on one end and a seating flange on the opposite end. mounted in one wall of the case by adiustable means including a resilient insulating grommet sleeved on the central portion of v the stud and seated on one end against the stud flange, and non-magnetic for cooperation with the threaded section on the terminal stud to compress the grommet av predetermined amount into a sealing engagement with the case, a. conductive cradle in the case mounted for limited rotation on the terminal stud, a permanent magnet mounted centrally in the cradle, and a. pool of conductive liquid: in the case adapted to immerse one end or the other of. the cradle and magnet assembly as it rotates. in response toa magnetic stimulus.

3. In a magnetic switch having: a sealed case containing an; electric conductin liquid and a conductor member above the level: of. the liquid.

a tiltable. cradle to receive and hold a; bar magnet comprising, an elongated sheet metal base to simport the magnet, a pair of. oppositely disposed REFERENCES CITED 1 The following references are at record in the file of this patent? UNITED STATES PATEN'I'S Number Name Date 1,975,762 Behmer Oct. 9, 1934 1,992,214 H... Feb. 26, 1935 2,052,9-Ll Weathers Sept. 1, 1936 2,240,891 Merchant May c, ion

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