Abstract:
A relay assembly is provided that includes an intermediate member to aid in coupling a wire to a housing.

Description:
FIELD 
       [0001]    The present disclosure is related generally to relays. The present disclosure is more specifically related to hermetically sealed relays. 
       BACKGROUND AND SUMMARY 
       [0002]    Hermetically sealed electromagnetic relays are used for switching of high electrical currents and/or high voltages, and typically have fixed and movable contacts, and an actuating mechanism supported within a hermetically sealed chamber. To suppress arc formation, and to provide long operating life, air is removed from the sealed chamber by conventional high-vacuum equipment and techniques. In one style of relay, the chamber is then sealed so the fixed and movable contacts contact in a high-vacuum environment. In another common style, the evacuated chamber is backfilled (and sometimes pressurized) with an insulating gas (e.g., sulphur hexafluoride) with good arc-suppressing properties. 
         [0003]    For purposes of this disclosure, a hermetic seal means a seal which is sufficiently strong and impermeable to maintain for a long term a high vacuum of 10 −5  Torr (760 Torr=one atmosphere) or less, and a pressure of at least 1.5 atmospheres. 
         [0004]    In one embodiment described below, a sealed electromagnetic relay assembly is provided comprising a first relay having a plurality of leads for connection to external circuitry; a plurality of permanent magnets coupled to the first relay proximate to first and second contacts; and a hermetically sealed housing assembly enclosing the first relay. The housing assembly comprises: an upper closure including an evacuation tube in fluid communication with an interior chamber of the housing assembly, wherein ambient air may be evacuated from the housing assembly to a vacuum and wherein the housing assembly, after evacuation, is backfilled with an insulative gas to a pressure of greater than 1.5 atmospheres; and an impermeable potting cup surrounding the first relay and permanent magnets, the potting cup being adapted to receive the first relay at one end and being open at the other end for the receipt of encapsulating material and engagement with the upper closure, wherein the encapsulating material seals the housing assembly against ambient air intrusion, and the relay leads extend outwardly from the housing assembly. 
         [0005]    In another embodiment of the present disclosure, a method of producing a relay assembly is provided including the steps of: providing a first relay having a rating of 30V or less for hotswitching; coupling permanent magnets in proximity to fixed and moveable contacts of the first relay so as to create a magnetic field between the fixed and moveable contacts when the fixed and moveable contacts are spaced apart; sealing the first relay within a vessel; evacuating substantially all ambient air from the vessel; and backfilling the vessel with a desired gas. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0006]      FIGS. 1A and 1B  are respectively a sectional side elevation and a top view of an open-frame relay in a plastic cup supported in an outer metal cup, the assembly being shown before encapsulation; 
           [0007]      FIG. 2  shows the assembly of  FIGS. 1A  and B in a closed chamber having evacuation, pressurization and encapsulation-material valves; 
           [0008]      FIG. 3  is a view similar to  FIG. 2 , and showing the relay assembly filled with cured encapsulation material; and 
           [0009]      FIG. 4  is a cross-sectional view of a wire-relay interface. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    A sealed relay according to the disclosure is shown in  FIGS. 1-3 , and this embodiment uses a simple and inexpensive open-frame relay in an open-top housing assembly which is evacuated, encapsulated and backfilled while positioned within a sealed chamber. This manufacturing method eliminates need for an evacuating and backfilling tubulation, and enables use of an inexpensive relay for high-voltage and high-power applications heretofore handled only by more expensive high-vacuum or pressurized units of known types as described in the introductory part of this specification. 
         [0011]    Referring to  FIGS. 1A  and B, relay assembly  70  is shown prior to encapsulation, and the assembly includes a conventional open-frame relay  71  (illustrated as a single-pole single-throw or SPST type, but other conventional contact configurations are equally useful) secured to and suspended from a generally rectangular header  72 . Relay  71  in the present embodiment is rated for 30V or less hotswitching and is not hermetically sealed. 
         [0012]    Elongated metal terminal pins  73   a - d  extend through the header, and pins  73   a  and  b  are connected to a coil  74  of the relay electromagnetic actuator. Pin  73   c  supports a fixed contact  75 , and pin  73   d  is connected to a movable contact  76  which is pulled against the fixed contact when the relay is energized. A coil spring  77  urges the movable contact into an open position in conventional fashion. Permanent magnets  60 ,  61  (shown in phantom so as to not obscure contacts  75 ,  76 ) are added to relay  71  and are positioned on opposing sides of fixed and moveable contacts  75 ,  76 . Magnets  60 ,  61  are oriented to create a magnetic field across the gap, when present, between fixed and moveable contacts  75 ,  76 . Magnets  60 ,  61  are equally distant from fixed and moveable contacts  75 ,  76  and provide arc quenching equally well regardless of current polarity. 
         [0013]    Relay  71  is positioned within an open-top plastic cup  79 , with the underside of header  72  supported on short spaced-apart lugs  80  which extend inwardly from the inner perimeter of a sidewall  81  of cup  79  slightly below the top of the cup. The header does not make a snug press fit within the upper end of the cup, and there is instead an intentional narrow gap  82  of say 0.002-0.003 inch between the side edges of the header and the inner surface of sidewall  81 . 
         [0014]    Plastic cup  79  is in turn centrally fitted within an open-top metal cup  84  having a base  85  against which the plastic cup rests, and an upwardly extending sidewall  86 . The plastic cup is smaller in external dimension than the interior of sidewall  86 , creating a space or gap  87  between the plastic and metal cups. Sidewall  86  extends higher than the top of the plastic cup, and pins  73   a - d  in turn extend higher than the top of the metal cup. An acceptable alternative to metal cup  84  is a similarly shaped plastic cup having a separate metal plate resting on the cup bottom for bonding with encapsulation material. 
         [0015]    The thus-assembled components are next placed in a sealed chamber  89  including base  185  as shown in  FIG. 2 . The chamber has an evacuation valve  90  disposed in an evacuation tube  190  connected to a high-vacuum pumping system (not shown) of a conventional type using mechanical and diffusion pumps. The chamber also has a pressurization valve  91  connected to a pressurized source (not shown) of an insulating gas such as SF 6 . The chamber further has a third valve  92  positioned above cup  84 , and connected to a piston-cylinder assembly  93  for holding and delivering a metered amount of uncured viscous, but fluid encapsulating material  94 . 
         [0016]    Evacuation valve  90  is then opened, and the high-vacuum pumping system actuated to withdraw air from the chamber interior to a vacuum which is preferably at least 10 −2  to 10 −3  Torr if the relay is to be backfilled. Ambient air is simultaneously withdrawn from relay assembly  70  through gap  82  between header  72  and sidewall  81 . Valve  90  is closed when a desired vacuum is achieved. 
         [0017]    Open-frame relays are unsuited for long-term vacuum operation due to outgassing of components such as the relay coil which will eventually contaminate and adversely affect a high-vacuum environment. This problem is eliminated by backfilling and pressurizing the chamber and as-yet-unsealed relay assembly with an insulating gas which is admitted by opening pressurization valve  91 . The gas flows freely through gap  82  to fill and pressurize the interior of the relay assembly. 
         [0018]    With the chamber interior stabilized in a high-pressure condition, valve  90  is closed, valve  92  is opened, and piston-cylinder assembly  93  actuated to deliver at a pressure exceeding that of the pressurized chamber a metered amount of fluid encapsulating material into metal cup  84  to completely fill gap  87  and cup  84  to a level just beneath the top of sidewall  86  as shown in  FIG. 3 . The encapsulating material is too viscous to pass through small gap  82 , and the backfilled environment within the relay assembly remains undisturbed. 
         [0019]    Preferably, chamber  89  is of a conventional type which includes a heater such as an induction heater, and heat is applied to the now-encapsulated relay assembly to cross link and cure the encapsulating material. With the chamber vented to atmosphere, the completed relay assembly is removed for testing and packaging. In production, many relay assemblies would be processed in a single loading of the chamber, and the methods of the disclosure can also be adapted for use in a continuous production line. 
         [0020]    The optimum environment in which the relay contacts make and break is dependent upon the required performance of the relay. Vacuum (less than 10 −5  Torr) is generally a good environment for high-voltage applications, but would not be chosen for applications where relay components in the vacuum environment might outgas. There are many gases that can be used to improve electrical performance of a relay. Sulfur hexafluoride (SF 6 ) is a good dielectric gas which at higher pressure will standoff significantly higher voltages than open air. A relay that will standoff 5 kilovolts in open air will standoff 40 kilovolts if it is pressurized with 10 atmospheres of SF 6 . Another characteristic of SF 6  is that once ionized it becomes an excellent conductor. This makes it a good choice for relays that need to make into a load and keep consistent conduction of current while the load is being discharged. 
         [0021]    Hydrogen (and hydrogen-nitrogen blends) has been shown to effectively cool the electrical arc that is created when the electrical contacts move away from each other while breaking a load. The difficulty with hydrogen is that not only is it the smallest molecule so that it will propagate through the smallest cracks, but it can also chemically propagate through many materials. The design of the present disclosure using cross-linked polymers, unlike other designs, will hold pressurized hydrogen gas for many years. 
         [0022]    There are several kinds of epoxy materials which bond satisfactorily with metal and, which are impermeable to prevent leakage of air into a vacuum relay, or loss of insulating gas in a pressurized relay. A material that is commercially available is provided under the trademark Resinform RF-5407 (75% alumina filled) mixed 100:12 by weight with Resinform RF-24 hardener. Alternative epoxy materials may provide these characteristics: 
         [0023]    a. Low gas permeability (less than 10 −10  standard cubic centimeters of air per second). 
         [0024]    b. High dielectric strength (greater than 100 volts per mil). 
         [0025]    c. Low outgassing (to maintain a vacuum of 10 −5  Torr or better). 
         [0026]    d. Good mechanical strength. 
         [0027]    e. Thermal expansion characteristics reasonably matched to those of the metal with which the epoxy forms a hermetic seal. 
         [0028]    Whereas initial relay  71  is rated for 30V or less hotswitching, the resulting relay assembly  70 , via the pressurization and permanent magnets  60 ,  61 , is rated for 48V or greater hotswitching. Accordingly, a relatively inexpensive high performance relay assembly  70  is provided. 
         [0029]      FIG. 4  shows relay  100  having a dielectric seal for coupling electrical leads to relay  100 .  FIG. 4  shows relay  100  where space or gap  187  between inner cup  179  and outer potting cup  184 , similar to space/gap  87  of relay assembly  70 , is filled with epoxy material  101 . 
         [0030]    Relay  100  receives jacketed wires  102 ,  104  secured in the epoxy. The relay mechanism in relay  100  is standard, and as such, is not shown. Wires  102 ,  104  have conductive cores  106 ,  108  and non-conductive sheaths  110 ,  112 . Conductive cores  106 ,  108  electrically couple to terminal pins  173   c,    173   d.  Non-conductive sheaths  110 ,  112  are exemplarily shown as either plastic or silicone. Plastic and silicone are relatively pliable and compressible. Accordingly, subsequent to being secured within epoxy  101 , sheaths  110 ,  112  may distort and allow foreign material, including conductive material (not shown) to enter any gaps between sheaths  110 ,  112  and epoxy fill/shell  101 . Infiltration of such conductive material may allow arcing and circuit completion between wires  102 ,  104  outside of relay  100 . 
         [0031]    Metal rings  150  are provided proximate ends of wires  102 ,  104 . Metal rings  150  generally approximate flat washers. Metal rings  150  have an outer diameter approximately equal to the outer diameter of wires  102 ,  104  and inner diameters greater than inner diameters of non-conductive sheaths  110 ,  112 . Accordingly, metal rings  150  are electrically isolated from conductive cores  106 ,  108 . 
         [0032]    The bonding properties between metal and epoxy as well as between metal and silicone/plastic are superior in strength and reliability to the bonding properties between epoxy and silicone/plastic. Accordingly, metal rings  150  provide an intermediary to which both epoxy and sheaths  110 ,  112  may adhere more reliably than an epoxy-sheath direct bond. 
         [0033]    If foreign material infiltrates from the exterior of relay  100  between epoxy  101  and non-conductive sheaths  110 ,  112 , such foreign material is prevented from extending beyond metal rings  150  due to the superior bonding between rings  150  and epoxy  101  and sheaths  110 ,  112 . Furthermore, rings  150  are positioned at such a distance from conductive cores  106 ,  108  and with non-conductive intermediaries therebetween to maintain electrical isolation of cores  106 ,  108  in most all applications. 
         [0034]    Whereas rings  150  have been described as being disposed within epoxy filled gaps of relay  100 , such rings  150  may also be disposed within an exterior wall of sealed chamber  89  of relay assembly  70  or other similar structures in other relays. 
         [0035]    There have been described several embodiments of epoxy envelopes for hermetically sealing standard relay designs in a special atmosphere for improved performance. These envelopes provide significant cost savings in the manufacture of vacuum or pressurized sealed relays, and have performance characteristics at least equivalent to relays of this type using glass or ceramic envelopes. The disclosure is not limited to the specific relay types described above, and is equally useful with other switching devices such as reed-style relays and the like.