US2422379A - Electric bushing - Google Patents

Description

June 17, 1947. s, E. WESTMAN ELECTRIC BUSHING Filed Aug. 50, 1944 INVENTOR.

N A M T s E W E Y E N D Y s ATTORNEY Patented June 17, 1947 UNITED STATES PATENT OFFICE ELECTRIC BUSHING Sydney Edward Westman, Los Angeles, =Calif., as-

signor to Bendix Aviation Corporation, South Bend, Ind, a corporation of Delaware Application August 30, 1944, Serial No. 551,887

2 Claims. 1

This invention relates to electric insulating bushings for extending electrical leads through electrically conducting walls and it has to do particularly with insulating bushings for hydraulic devices and the like in which there is a substantialpressure differential across the wall so that the bushing must not only insulate the lead from the wall, but must be fluid tight.

An object of the invention is to provide a bushing of simple and inexpensive construction that is fluid tight particularly at high pressures.

It has been common practice in the past to formelectrical bushings by molding central conductors or electrodes in an insulating block and then mounting the block in an annular casing having screw threads or other means for securing it to the wall through which electrical connection is to be made. In such structures it is common to rely upon the bonding between the central conductor and the insulating block to prevent fluid leakage therebetween and to employ a gasket of some type between the insulating block and the outer casing to prevent leakage there between. A typical example of such structures is the spark plug in common use on gasoline engines. Similar bushing structures have been employed in other devices. An objection to the type of structure in which a bond between the central conductor and the insulating block is relied upon to prevent leakage therebetween is that it is relatively expensive to so join the conductor and the insulating block so that a leak-proof bond is obtained, and it may be impossible to produce a leak-proof bond between conductor and insulating materials that would otherwise be desirable. It is, of course, ossible to also employ some type of gasket structure for producing a fluidtight joint between the conductor and the insulating block but such structures become more expensive and are particularly difficult to incr porate in small size bushings.

In accordance with the present invention, I provide a single flexible or resilient annular sealing element between the central conductor and the outer casing of an electric bushing, which sealing element bridges the entire gap between the electrode and casing and makes. it unnecessary to provide a fluid-tight bond between either the insulator and the conductor or the insulator and the outer casing. The seal employed is of the type that seals more tightly as the pressure increases so that it is adaptable for use under extreme pressures. At the same time it is also effective at lower pressures without imposing unnecessary heavy strains on the rest of the structure, as isthe case with gaskets that are mechanically compressed at the time of assembly.

A full understanding of the invention may be had from the following detailed description or a preferred embodiment of the invention as disclosedin the drawing, in which:

Fig. 1 is a side elevation view of a bushing with portions broken away and shown in section; and

Fig. 2 is a view similar to Fig. l, but showing the device connected to a wall and. exposed to pressure fluid.

Referring to Fig. 1, there is shown a bushing comprising a tubular body member [0 which may be of ny desired material, either electrically conductive or non-conductive, which is adapted to be mounted in a wall through which an electrical conductor is'to be extended. In the particular form shown, the member ill has threads H on one end adapted to be screwed into a threaded opening in a hydraulic fixture or the like, indicated at 12 in Fig. 2. Near its mid-por tion, the body member 19 may be provided with a hexagonal shoulder l3 for the application of a wrench. At its left end, the body is provided with external threads 14 for attachment, to a suitable electrical connector. It is to be understood, however, that it is immaterial to the present invention what specific shape is employed on the left end, or what specific structure is employedto connect the body member l3 to the wall in which it is positioned.

Positioned centrally within the tubular body member H), is an electrically conducting rod l5, which is insulatingly supported within the body member by an annular insulating block 16, which is preferably press-fitted into the body.

The particular fitting shown is adapted to seal against pressure at the right end, and to prevent longitudinal displacement of the insulator IS, the latter fits against the annular face I! of an internal shoulder la in the body l0. As shown, the insulator is provided with a reduced neck 19 extending past the shoulder l8.

To support the conductor [5 longitudinally, it is provided with a flange 20 of circular cross section, one face or shoulder, 2|, of which rests against the end of the insulator l6. Positioned against the other face, or shoulder, 22 of flange 29 is an insulating washer 23, which is secured in place with a snap ring 24, which snaps into an annular groove 25 formed on the inner surface of the member Hi.

It will be observed that, irrespective of the tightness of fit between the conducting rod l5 and the insulator IS, the rod is mechanically supported against either axial or radial movement with respect to the body member 10. Although it might be desirable to press-fit the rod l5 into the insulator l5, it is not essential to do so, because separate sealing means is provided for preventing fluid leakage through the body [0, both between the rod l5 and the insulator is and between the latter and the body member. This sealing means comprises a resilient ring 26 of rubber or the like positioned in the annular space defined by the flange 20 on the rod l5, the body member 10, the insulator l6, and the insulating washer 23. The sealing ring 26 is dimensioned to completely fill the space between the flange 20 and the body 13, and when it is exposed to fluid pressure, as shown in Fig. 2, it is compressed to conform to and fill the corners defined between the flange 2B and the insulator i6 and between the latter and the body Hi, and positively prevent leakage. The length of the annular passage in which the sealing ring 26 is positioned is not important, but it may be made greater than the thickness of the ring.

Obviously, the structure will also seal against pressure from the left, such pressure forcing the sealing ring 25 from the right against the washer 23. The washer 23 can be made as thick as necessary to withstand forces resulting from pressure applied from the left end.

In the particular structure shown, the ends of the rod I 5 are adapted to make contact with cooperating electrical conductors, not shown. Obviously, any desired type of structure can be employed while still utilizing the present invention, which relates only to that portion of the electrical conductor which extends through the insulating block and the sealing structure.

Numerous variations from the exact construction shown can be made while still utilizing the advantages of the invention. The invention, therefore, is only to be limited to the extent set forth in the appended claims.

I claim:

1. A fluid-tight bushing comprising a body member having a cylindrical bore therein, an annular, rigid, electrical insulating member positioned within and radially supported by said bore, means for axially supporting said insulating member with respect to said body member, a. central electrical conducting element extending through and radially supported by said insulating member and having a flange with a cylindrical peripheral face, one end of said flange resting against one end of said insulating member, a second, rigid, insulating member within and radially supported by said bore and resting against the other end of said flange, and a resilient sealing ring of insulating material surrounding said flange and dimensioned to contact both the peripheral surface of the flange and the surface of said bore, the axial dimension of said ring being less than the axial length of said flange.

2. A fluid-tight bushing for extending an electrical connection through a wall exposed to different fluid pressures on opposite sides, said bushing comprising: a body member adapted to be mounted in said wall and having a cylindrical passage therein; an internal shoulder in said passage; an annular electrical insulating member of substantially rigid material positioned within said passage and having a shoulder resting against said shoulder on the body member for axially supporting said insulating member; a central electrical conducting element extending through and supported by said insulating member and having an annular shoulder resting against the end of said insulating member opposite the shoulder thereon; said conducting element having a peripheral surface of the same diameter as and extending from the outer edge of the shoulder thereon and a single resilient annular sealing ring of electrical insulating material surrounding and dimensioned to directly contact said peripheral surface of said conducting element and the inner surface of said body member, for effecting a fluid seal both between said annular member and the wall of said passage, and between said annular member and said conducting element, when said annular member is compressed axially against said end of said insulating member by pressure fluid, the axial dimension of said peripheral surface being of the same order of magnitude as the radial spacing between said peripheral surface and the said inner surface of said body member, and the axial dimension of said sealing ring being less than the axial dimen-- sion of said peripheral surface.

SYDNEY EDWARD WESTMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,314,683 Berry Mar. 23, 1943 1,941,397 Grier Dec. 26, 1933 2,287,163 Bishop June 23, 1942 2,110,457 Wentz Mar. 8, 1938 1,610,442 Gorton Dec. 14, 1926

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