US3368049A

US3368049A - High current radio frequency switch

Info

Publication number: US3368049A
Application number: US454080A
Authority: US
Inventors: Robert D Mcclaflin; Ted N Tilman
Original assignee: Jennings Radio Manufacturing Corp
Current assignee: Jennings Radio Manufacturing Corp
Priority date: 1965-05-07
Filing date: 1965-05-07
Publication date: 1968-02-06
Anticipated expiration: 1985-02-06
Also published as: GB1135596A; NL6606094A; BE680605A

Description

Feb. 6, 1968 R. D. M CLAFLIN ET HIGH CURRENT RADIO FREQUENCY SWITCH 2 Sheets-Sheet 1 Filed May '7, 1965 INVENTOR$ ROBERT D. MCCLAFLIN TED N. TILMAN Feb. 6, 1968 R D MCCLAFLIN ET AL 3,363,04

HIGH CURRENT RADIO FREQUENCY SWITCH Filed May 7, .1965 2 Sheets-Sheem 2 INVENTORS ROBERT D. Mc CLAFLIN TED N. TILMAN United States Patent 3,368,049 HIGH CURRENT RADIO FREQUENCY SWITCH Robert D. McClafiin and Ted N. Tilman, San Jose, Calif.,

assignors to Jennings Radio Manufacturing Corporation, San Jose, Calif., a corporation of California Filed May 7, 1965, Ser. No. 454,080 5 Claims. (Cl. 200144) ABSTRACT OF THE DISCLOSURE A Vacuum switch structure utilizing an annular lightweight bridge contact and conductor assembly to achieve low inductance transmission through the switch. The conductor assembly is designed to distribute the voltage gradient uniformly across the envelope and reduce the volume within the envelope to facilitate evacuation.

The invention relates to radio frequency switches, and particularly to radio frequency switches of the vacuum type.

Conventional radio frequency switches, both vacuum and air dielectric, have been plagued by two obvious deficiencies. First, it is extremely important in a radio frequency switch that the inductance of the switch be kept to a minimum. Conventional radio frequency vacuum dielectric switches utilizing a bellows in the circuit in the conventional manner are subject to high inductance values due to long current paths and are therefore limited in their application. Secondly, in conventional radio frequency switches little or no consideration is given to the distribution of voltage across the envelope, with the result that non-uniformly distributed high electrostatic stresses are imposed on the envelope, resulting in nonuniform heating of the envelope with attendant rupture thereof and destruction of the switch.

Accordingly, it is one of the principal objects of the invention to provide a high current radio frequency switch which eliminates these deficiencies.

A still further object of the invention is the provision of a high current radio frequency switch designed to provide almost ideal voltage distribution so as to eliminate localized heating of the envelope material.

Still another object of the invention is the provision of a radio frequency switch capable of carrying high currents in the order of 200400 amperes and which incorporates a contact assembly providing a double break so as to withstand high voltages in the order of from 20 kv. to 50 kv.

Another of the problems which has prevented the extensive utilization of vacuum components has been difficulty of fabrication and processing. These factors result in conventional vacuum components being inherently expensive. Therefore, it is a still further object of the present invention to provide a radio frequency vacuum switch which is easily fabricated by production line techniques so as to reduce the ultimate cost to the consumer.

The susceptibility of radio frequency devices to arcing between relatively movable members is well known. This is particularly true in a switch which is utilized in high current applications. One of the factors that initiates such arcing in a switch is contact bounce upon closing of the switch at high closing velocities. Accordingly, it is another important object of the present invention to provide in a high current radio frequency switch a contact and actuator assembly which incorporates a built-in resilience and resistance to contact bounce with resultant arcing.

Among the factors that determine the circuit breaking characteristics of a radio frequency switch is the efliciency with which heat generated in the contact elements is dissipated. It is well known that permitting the contact elements to operate at elevated temperatures increases the electric resistance and thus lowers the current-carrying efficiency of the switch. This problem has been partially solved in the art by fabricating the relatively movable contact member of material possessing a large mass, the thought being that such large mass would function as a heat sink. This solution however introduces a new problem, namely, increased inertial forces when the switch contact of large mass is moved at high velocity into a closed position. Such high inertial forces contribute to contact bounce and to arcing between the contact surfaces. Accordingly, it is another object of the present invention to provide a contact assembly for a high current radio frequency switch in which only the fixed contact members possess a large mass with good thermal conductivity, while the mobile contact is fabricated from light and resilient material having good electrical c011- ductivity but low mass characteristics and therefore imposing low inertial forces upon closing at high velocities.

The invention possesses other objects and features of advantage, some of which, with the foregoing, will be apparent from the following description and the drawings. It is to be understood however that the invention is not limited to the embodiment illustrated and described but may be embodied in a variety of forms in accordance with the appended claims.

Referring to the drawings:

FIG. 1 is a vertical cross-sectional view taken through the longitudinal axis of the switch;

FIG. 2 is a fragmentary perspective view illustrating the mobile contact and its support shell;

FIG. 3 is a fragmentary plan view illustrating in one embodiment the manner in which the resilient and low mass mobile contact is secured to its support shell;

FIG. 4 is a vertical cross-sectional view taken through the longitudinal axis of another embodiment of the switch; and

FIG. 5 is a cross-sectional view illustrating a modified mobile contact assembly.

In terms of broad inclusion, the high current radio frequency switch of the invention comprises a tubular dielectric portion, preferably fabricated from a ceramic such as aluminum oxide, closed at one end with a generally truncated conically formed end cap having a cylindically flanged portion hermetically bonded to the associated end of the dielectric envelope portion. At its other end the dielectric envelope portion is closed by a generally flat end cap hermetically bonded about its outer periphery to the associated end of the dielectric envelope portion, and having secured thereto a generally truncated conical contact portion extending into the envelope and providing a fixed contact surface radially spaced from a second fixed contact surface associated with the first mentioned end cap assembly. Arranged to bridge the gap between the two fixed contact surfaces is a mobile contact member, annular in form and preferably fabricated from a resilient metallic material having good electrically conductive characteristics and of low mass. The mobile contace member is supported on a truncated conical shell of low mass secured at its apex end on the inner end of an actuator stem slidably journaled on the associated end plate. Means are provided insulating the mobile contact from the actuator assembly.

In terms of greater detail, the high current radio frequency vacuum switch comprises a dielectric envelope portion 2, preferably fabricated from a ceramic such as aluminum oxide, and having its opposite end edges 3 and 4 metalized in a well-known manner. Bonded to the edges 3 and 4 as by brazing are radially extending flanged portions 6 and 7, respectively, of cylindrical seal rings 8 and 9.

As shown best in FIG. 1, in one embodiment of the invention, the seal ring 8 adjacent its outer end is heliarc welded to the cylindrical flange portion 12 which forms an integral continuation of the conical shell portion 13 of an end cap 14 having a transverse wall member 16, on the inner surface 17 of which is brazed a contact ring 18. It will thus be seen that the contact ring 18 provides a flat annular contact surface 19 of relatively small area so as to minimize capacitance and against which a mobile contact may abut, but which possesses the requisite mass and cross sectional area to function as a heat sink to dissipate heat generated in the contact members. The performance of this function is facilitated by the direct connection of the contact ring 18 to the relatively heavy transverse end plate 16, which in turn is connected directly to the conical portion 13, all of these members functioning to provide large radiating surfaces from which heat may be eificiently dissipated. A mounting ring 21 is brazed about its outer periphery within cylindrical portion 12, and is provided with appropriate threaded bores 22 utilized for mounting the switch on a supporting structure. It should be noted that the interconnection of mounting ring 21, cylindrical portion 12 and cylindrical flange 8 is such that thermal expansion and contraction of members 8 and 21 may occur without unduly stressing the union of member 8 with the dielectric 2.

At the other end of the envelope, the seal ring 9 is heliarc welded at its outer end to the cylindrical portion 23 forming an integral extension on conical shell 24, the annular apex end 26 being provided with a fixed flat annular contact surface 28 as shown. The contact surface 28 lies in the same plane as the contact surface 19, and the aperture 27 is proportioned to provide an annular gap between the inner periphery of the annular portion 26 and the outer periphery of the contact ring 18.

To bridge the gap between the

contact surfaces

19 and 28, we provide a mobile contact assembly, designated generally by the numeral 29, and including an annular metallic contact plate 31 having a flat center section 32 and a series of spoon shaped

resilient contact fingers

33 and 34 formed in its outer and inner peripheral portions, respectively. As shown best in FIG. 1, the spoon shaped resilient finger portions 33 are adapted to engage the contact surface 28, while the spoon shaped resilient finger portions 34 are adapted to engage the contact surface 19, thus providing a conductive path between

contact surfaces

19 and 28.

It is important that the series of resilient contact fingers 33 and 34- impinge uniformly on the associated fixed contact surfaces, and it is therefore desirable that the mobile contact plate 31 be mounted on an actuator mechanism in a manner to permit accommodation of the contact fingers to whatever slight irregularities might exist on the contact surfaces or which result from failure to adhere to manufacturing tolerances. Accordingly, the contact plate 31 is loosely secured to the base end 36 of a shallow truncated conical shell 37 having an end wall 38 closing its apex end, the wall 38 being apertured as shown and engaged by the threaded stud portion 39 of a mounting bracket which includes a radially extending skirt portion 41. The end wall 38 is loosely caught between the flange 41 and a nut 42 threaded on the stud 39. As shown best in FIG. 1, the flange 41 and nut 42, on their respective surfaces next adjacent the end wall 38, are tapered to permit a measure of tilting movement of the conical shell 37 therebetween.

The tapered flange 41 is brazed to one end of a dielectric tube 43 the other end of which is brazed to a header block 44 having a radially extending heliarc flange 46 thereon, the outer periphery of which is heliarc welded to the inner convolution 47 of a flexible metallic bellows 48. The other end of the bellows is heliarc welded to a heliarc flange 49, the inner periphery 51 of which is brazed to tubular bearing sleeve 52 secured as by brazing within an aperture 53 formed in end plate 54. The bearing tube 52 extends into the bellows 48 and slidably supports an actuating stem 56, the inner end 57 of which is brazed to the header 44. The outer peripheral edge portion of end plate 54 is heliarc welded as at 59 to the cylindrical shell portion 23. Actuation of the switch is accomplished by a stem 61 engaged in an appropriately threaded section 62 of the actuator 56.

In the embodiment of the switch illustrated in FIGS. 1 through 3, the central section 32 of the mobile contact plate 31 is loosely fastened to the base end 36 of conical shell 37 by upstanding tabs 63, shown best in FIGS. 2 and 3, which tabs project through an appropriate aperture 64 in the central section 32 of the mobile contact plate and are then twisted'as shown to lock the mobile contact plate loosely to the conical shell. In this embodiment of the switch one of the advantages is that the conical shell 13 functions as an end cap and projects inwardly to reduce the volume which must be evacuated, thus reducing the cost of processing the switch. The shell 13 also cooperates with the conical section 24 there-opposed to control the voltage distribution across the dielectric member 2 so that no section of the dielectric member is subjected to localized stress. Additionally, due to the proportions of the parts, the inner periphery of portion 26 which defines the aperture 27 in the conical shell 24 cooperates with the adjacent corner of end wall 16 to shield the interior surface of the dielectric member 2 against the deposition of vaporized contact material. A further advantage of the construction is that because of the spoon shaped resilient contact fingers abutting the associated fixed contact surfaces in line contact, the distributed capacitance in the contact assembly is reduced to a negligible amount.

In the embodiment of the switch illustrated in FIGS. 4 and 5, the seal flange 6 has been extended radially outwardly and formed as shown to provide a toroidal corona ring 71 arcuate in cross section as shown to provide a smooth rounded surface 72 opposing a complementary surface 73 on the corona ring 74 which forms an extension of the seal flange 7 at the other end of the envelope. It is important that the toroidal corona rings be offset as shown from the respective planes of the seal rings 6 and 7 in order to remove the mass of the corona ring from the plane of the seal flanges. The functional significance of such offset lies in the desirability of reducing the amount of stress imposed on the adjacent ceramic member due to differences in thethe-rmal co-efficiency of expansion and contraction inherent in the materials use.

As indicated in FIG. 4, in this embodiment of the switch, the contact surface 19 is formed by the inner end of the conical shell which has been formed to correspond with the surface configuration shown in FIG. 1 for the

members

13 and 18. This reduces the weight of the unit and simplifies fabrication, thus lowering the cost to the consumer. The mobile contact plate 31 thus still makes contact with fixed contact surfaces 19 and 28 lying in the same plane.

Under some circumstances it has been found desirable to utilize a different method of loosely fastening the con-' tact plate 31 to the conical shell 37. In this embodiment rivets 76 (preferably four in number and circumferentially evenly spaced about the contact plate) including shank portions 77, extend through appropriately positioned apertures in the mobile contact plate and each is provided on its inner end with a head 78 as shown. Suflicient clearance is provided between the shank and the aperture through which it extends and between the head 78 and the upper surface of the central plate portion 32 of the mobile contact plate to permit loose accommodation of the contact plate to irregularities as pre viously explained.

While it is desirable that the conical shell 37 be loosely caught between flange 41 and nut 42, it has been found that under certain vibration conditions it is desirable that the conical shell 37 be resiliently held in a central position. Accordingly, in the embodiment illustrated in FIG. 4

spring washers

79 and 80 are positioned respectively above and below the shell 37 as shown so as to resiliently resist tilting movement of the conical shell.

Another modification in the embodiment of the switch illustrated in FIG. 4, lies in the cooperative relationship between the cylindrical flanges S and 9 and

cylindrical sections

12 and 23 of

shells

13 and 24 respectively. In this embodiment the outer end of the

cylindrical portions

12 and 23 are brazed to the inner cylindrical surface of the members 8 and 9 respectively, with the outer ends 81 and 82 of flanges 8 and 9, respectively, heliarc welded to the outer periphery of an end plate 83 in the case of flange 8, and an end plate 84 in the case of flange 9. The plate 83 is provided with a tubulation 85 for evacuating the interior of the envelope and appropriate apertures 86 are provided in the shell 13 to facilitate this operation.

Plate 84, as shown best in FIG. 4, is provided with an aperture 87 the inner periphery of which is rabbeted to receive the inner end 88 of a tubular housing portion 89, coaxially arranged with respect to the end plate 84 and the longitudinal axis of the switch, and having on its outer end 91 a mounting cap or plate 92 having a radially extending flange 93 as shown, and a cylindrically extending flange 94. Heliarc welded within the cylindrical flange 94 is a bearing member 96 having a cylindrical inwardly extending bearing extension 97 within which the actuator stem 98 is journaled. The inner end of the actuator stem is brazed to a header block 99 about which is brazed a seal flange 101, to the outer periphery of which is heliarc welded the last convolution 102 of a bellows 103. On the end of the header 99 opposite actuator stem 98 is brazed a dielectric stem 104 which is axially aligned with the actuator stem 98 and which engages one end of a metal contact support block 106. As in the embodiment illustrated in FIG. 1 the support block 106 serves to support the conical mobile contact support shell 37.

In operation an actuator mechanism of any suitable design, for example a solenoid device, is attached to the

actuator stem

61 or 98 and energized to open the switch contacts against atmospheric pressure to break a circuit therethrough. Closing movement of the switch contacts is eflected by atmospheric pressure acting on the interior of the

bellows

48 and 104 in both embodiments. It will of course be apparent to those skilled in the art that a spring (not shown) could be interposed between the

actuator stem

61 or 98 and the envelope to overcome atmospheric pressure and thus render the switch normally open instead of normally closed as shown.

We claim:

1. A high current radio frequency switch comprising:

(a) an evacuated envelope including a tubular dielectric portion symmetrical about a longitudinal axis and heremetically closed at each opposite end by a metallic end cap assembly,

(b) means associated with each said end cap assembly including an electrically conductive metallic surface extending into the tubular dielectric portion to a point adjacent the mid-portion thereof from adjacent each end thereof to provide spaced fixed contact surfaces in substantial planar alignment within the tubular dielectric portion.

(c) a mobile contact plate movably supported within the envelope and movable in a direction generally along said longitudinal axis to engage or disengage said spaced fixed contact surfaces, and

(d) an actuator assembly operatively connected to said mobile contact plate and operable to effect selective movement of said mobile contact plate.

2. The combination according to claim 1, in which one of said electrically conductive metallic surfaces extending into the tubular dielectric portion constitutes the inner surface portion of at least one of said metallic end cap assemblies.

3. The combination according to claim 1, in which said mobile contact plate includes an annular flat metallic plate having a center mounting section and inner and outer peripheral resilient finger portions adapted to engage and disengage the fixed contact surfaces.

4. A high current radio frequency switch comprising:

(a) an evacuated envelope including a tubular dielectric portion hermetically closed at each opposite end by a metallic end cap assembly,

(b) means associated with each said end cap assembly including an electrically conductive metallic surface extending into the tubular dielectric portion to a point adjacent the mid-portion thereof from adjacent each end thereof to provide spaced fixed contact surfaces in substantial planar alignment within the tubular dielectric portion,

(c) a mobile contact plate movably supported Within the envelope and movable to engage or disengage said spaced fixed contact surfaces, and

(d) an actuator assembly operatively connected to said mobile contact plate and including a truncated conical shell having an end Wall closing its apex end and its base end loosely secured to the contact plate and operable to effect selective movement of the mobile contact plate.

5. A high current radio frequency switch comprising:

(d) an actuator assembly operatively connected to said mobile contact plate and operable to effect selective movement of said mobile contact plate, said assembly including a bearing member supported on one of said end cap assemblies, a stem slidably supported in the bearing member and including a metallic portion outside the envelope and a dielectric portion inside the envelope, and a conical shell mounted on the inner end of the stem within the envelope and engaging the contact plate.

References Cited UNITED STATES PATENTS 2,981,813 4/1961 Jennings 200144 3,178,541 4/1965 Jennings 200144 3,200,222 8/1965 Hawkins 200144 3,247,347 4/1966 Lindsay 200144 3,261,953 7/1966 Tilman et a1 200144 ROBERT S. MACON, Primary Examiner.