Patent Application
20100301976
1. Field
The disclosed concept relates to electrical switching apparatus and, more particularly, to circuit interrupters, such as, for example and without limitation, aircraft or aerospace circuit breakers including an electronic trip circuit, remote control circuit breakers, and remote power controllers.
2. Background Information
Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition. In small circuit breakers, commonly referred to as miniature circuit breakers, used for residential and light commercial applications, such protection is typically provided by a thermal-magnetic trip device. This trip device includes a bimetal, which heats and bends in response to a persistent overcurrent condition. The bimetal, in turn, unlatches a spring powered operating mechanism, which opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system.
Subminiature circuit breakers are used, for example, in aircraft or aerospace electrical systems where they not only provide overcurrent protection but also serve as switches for turning equipment on and off. Such circuit breakers must be small to accommodate the high-density layout of circuit breaker panels, which make circuit breakers for numerous circuits accessible to a user. Aircraft electrical systems, for example, usually consist of hundreds of circuit breakers, each of which is used for a circuit protection function as well as a circuit disconnection function through a push-pull handle.
In many military applications, moisture resistance, vented and sealed units, and corrosion resistance are key attributes of modern aerospace circuit breakers, which seek to avoid failures resulting from arcing and/or dielectric breakdown. For example, if a molded circuit breaker case absorbs moisture or retains moisture from its molding process, then this could contribute to a premature product failure resulting from arcing and/or dielectric breakdown.
Military specification MIL-83383 for remote control circuit breakers (RCCBs) has dictated the use of thermoset compounds for the molded circuit breaker case.
U.S. Patent Application Publication No. 2009/0027154 discloses a circuit breaker including a trip indicator, which is preferably made of a suitable liquid crystal polymer (LCP), which provides suitable flexibility while also being suitably durable.
U.S. Pat. No. 7,170,376 discloses a circuit breaker housing and a trip circuit forming a composite structure. The housing halves are preferably made from liquid crystal polymer thermoplastic, which may be molded to provide relatively very thin walls (e.g., without limitation, less than about 0.010 in. (about 0.254 mm)) with an irregular wall thickness and a relatively complex geometry, thereby providing superior strength and temperature insulation characteristics. The housing halves also electrically and thermally insulate the arc fault detector (AFD) printed circuit board (PCB) electronics from the current carrying operating mechanism. Over-molding of the AFD PCB electronics provides structural and overall package integrity as may be employed, for example, for aerospace use. The PCBs are made of an FR4 electronics substrate having a thickness of about 0.018 inch.
Vance, Jr., J., “Insert Molding”, Medical Device & Diagnostic Industry Magazine, April 1996, pp. 1-2, discloses that insert molding is an injection molding process whereby plastic is injected into a cavity and around an insert piece placed into the same cavity just prior to molding. The result is a single piece with the insert encapsulated by the plastic. The insert can be made of metal or another plastic. The technique was initially developed to place threaded inserts in molded parts and to encapsulate the wire-plug connection on electrical cords. There are two types of bonding that occur in insert molding, molecular and mechanical. Molecular bonding can occur when the insert material is the same as or similar to the encapsulating resin. This will yield the best results from the joint, both for physical strength and leak resistance. An example would be molding a polyurethane bifurcation to a polyurethane catheter. Mechanical bonding can take place in two ways, by the shrinking of the encapsulating resin around the insert as the resin cools, or by the surrounding of irregularities in the surface of the insert by the encapsulating resin. Although shrinkage always occurs, it is rarely sufficient to produce adequate physical strength or leak resistance of the joint. In general, when insert molding dissimilar materials, the insert should offer some means of mechanical retention such as a sandblasted, flared, or knurled surface.
Insert molding is also known as a process in which plastic is injected into a mold that contains an pre-placed insert. The result of insert molding is a single molded plastic piece with an insert surrounded by the plastic. Inserts can be made of metals or different types of plastic. Insert molding is used in many industries. Applications of insert molding include insert-molded couplings, threaded fasteners, filters, and electrical components.
There is room for improvement in circuit interrupters.
These needs and others are met by embodiments of the disclosed concept, which provide a circuit interrupter including a molded case made of liquid crystal polymer in which a rigid, conductive base is insert molded to the molded case, or where such molded case includes a cavity structured as a mold to receive a number of printed circuit boards and a low pressure molding material to encapsulate the number of printed circuit boards within the cavity.
In accordance with one aspect of the disclosed concept, a circuit interrupter comprises: a housing comprising a molded case made of liquid crystal polymer; separable contacts disposed within the housing; an operating mechanism disposed within the housing and being structured to open and close the separable contacts; and a trip mechanism disposed within the housing and being structured to cooperate with the operating mechanism to trip open the separable contacts, the trip mechanism comprising an electronic trip circuit and a rigid, conductive base providing a ground to the electronic trip circuit, wherein the rigid, conductive base is insert molded to a portion of the molded case.
The molded case may include a first cavity, a separate second cavity and a wall separating the first cavity from the separate second cavity; the separable contacts and the operating mechanism may be disposed within the separate second cavity; and the electronic trip circuit may comprise a number of printed circuit boards disposed within the first cavity. The first cavity may be structured as a mold and may receive the number of printed circuit boards and a low pressure molding material to encapsulate the number of printed circuit boards within the first cavity.
The rigid, conductive base may include a planar portion disposed adjacent the molded case, the planar portion including a plurality of openings, the molded case including a plurality of protrusions disposed through the plurality of openings, in order to mechanically interlock the planar portion to the molded case when the rigid, conductive base is insert molded to the portion of the molded case.
The low pressure molding material may be a low pressure moldable polymide.
As another aspect of the disclosed concept, a circuit interrupter comprises: a housing comprising a molded case made of liquid crystal polymer, the molded case including a first cavity, a separate second cavity and a wall separating the first cavity from the separate second cavity; separable contacts disposed within the separate second cavity; an operating mechanism disposed within the separate second cavity and being structured to open and close the separable contacts; and a trip mechanism disposed within the housing and being structured to cooperate with the operating mechanism to trip open the separable contacts, the trip mechanism comprising a number of printed circuit boards disposed within the first cavity, wherein the first cavity is structured as a mold and receives the number of printed circuit boards and a low pressure molding material to encapsulate the number of printed circuit boards within the first cavity.
The low pressure molding material may be a low pressure moldable polymide.
As another aspect of the disclosed concept, a circuit interrupter comprises: a plurality of poles, each of the poles comprising: a housing comprising a molded case made of liquid crystal polymer, separable contacts disposed within the housing, an operating mechanism disposed within the housing and being structured to open and close the separable contacts, and a trip mechanism disposed within the housing and being structured to cooperate with the operating mechanism to trip open the separable contacts, the trip mechanism comprising an electronic trip circuit and a rigid, conductive base providing a ground to the electronic trip circuit, wherein the rigid, conductive base is insert molded to a portion of the molded case; and a plurality of fasteners coupling the plurality of poles together.
A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
As employed herein, the term “to encapsulate” means to at least substantially surround a number of conductive or partially conductive structures by a number of insulative structures.
As employed herein, the statement that two or more parts are “coupled” together means that the parts are joined together either directly or joined through one or more intermediate parts.
The disclosed concept is described in association with a remote control circuit breaker (RCCB), although the disclosed concept is applicable to a wide range of circuit interrupters including, but not limited to, single-phase and plural-phase RCCBs, single-phase and plural-phase circuit breakers, and single-phase and plural-phase remote power controllers (RPCs). Such circuit breakers can be, for example and without limitation, subminiature circuit breakers, and aircraft or aerospace circuit breakers.
Referring to
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The low pressure molding material 30 can be, for example and without limitation, a suitable low pressure moldable polymide.
The circuit interrupter 6 (
The example aluminum mounting base 4 can be about 2.25 inches, by about 1.125 inches, by about 0.625 inches in size.
The example aluminum mounting base 4 includes a planar portion 32 disposed adjacent the molded case 3. The planar portion 32 includes a plurality of openings 34 (
The cross-drilled openings 34 of the aluminum mounting base 4 mechanically interlock the molded case 3 to the aluminum mounting base 4 during the insert molding process. This occurs when the molding LCP plastic material fills/flows into the voids in the aluminum mounting base 4. In the bottom of the molded case 3, there are two example rows 38 of five of the protrusions 36 in the molded case 3 that interlock with two example rows 39 of five of the openings 34 in the aluminum mounting base 4. The protrusions 36 of the molded case 3 are disposed in the rows 38, with each of the rows 38 including a plurality of the protrusions 36. The openings 34 of the planar portion 32 are disposed in the rows 39, with each of the rows 39 including a plurality of the openings 34.
The example insert molding process consists of a suitably machined, metal injection molded or die-cast aluminum mounting base 4 that is “inserted/loaded” into a conventional thermoplastic molding press (not shown). The mold cavity precisely locates the aluminum mounting base 4. The mold core (or plug) (not shown) closes to define the molded geometry. The LCP plastic material fills the voided area within the mold, which includes the cross drilled openings 34 in the aluminum mounting base 4. The insert molding cycle is complete resulting in plastic mechanically interlocking the aluminum mounting base 4 to the molded case 3. The LCP material preferably requires no post secondary operations to become a final product, such as de-flashing or post moisture baking. This does not require epoxying of the aluminum mounting base 4 to the molded case 3.
There are also two example protrusions 40 and two example corresponding openings 42 on each side of the molded case 3 and aluminum mounting base 4, respectively. There are two example relatively larger openings 44 and 46 in the molded case 3 and the aluminum mounting base 4, respectively. Two fasteners, such as screws 48, are installed to mount a coil/motor assembly 50 (
The example aluminum mounting base 4 further includes two side portions 56,57 normal to the planar portion 32. The two side portions 56,57 are disposed adjacent the molded case 3, with each of the two side portions 56,57 including the two example openings 42. The molded case 3 further includes the protrusions 40 disposed through the openings 42 of each of the two side portions 56,57 in order to mechanically interlock the two side portions 56,57 to the molded case 3 when the aluminum mounting base 4 is insert molded to the molded case 3.
The openings 34 of the example aluminum mounting base 4 can be a first plurality of openings 34, and the planar portion 32 can further include the second openings 46, which are larger in diameter than the first openings 34. The molded case 3 includes the corresponding relatively larger openings 44. A number of fasteners 48 couple the planar portion 32 to the molded case 3 at the number of openings 44,46.
The circuit interrupter 6 can be, for example and without limitation, a subminiature circuit breaker, or an aircraft or aerospace circuit breaker.
The disclosed molded case 3 has the insert molded aluminum mounting base 4 provided by a corresponding insert molding process as compared to prior known circuit breakers in which an aluminum base is epoxy bonded to a circuit breaker case.
A conventional printed circuit board (not shown) is conventionally overmolded or, otherwise, encapsulated to protect the corresponding electronics (not shown) from heat, moisture and mechanical damage. That alone, however, is not mechanically robust.
It is believed that using the disclosed molded case 3 as a mold to further encapsulate the number of PCBs 28 (
The low pressure molding material 30 can be, for example and without limitation, Macromelt 687 marketed by Henkel Corporation of Düsseldorf, Germany, or any suitable low pressure moldable polymide suitable for high humidity applications and designed to overmold electronic components.
The molded case 3 can be made of, for example and without limitation, Vectra® A130 LCP made by Ticona of Florence, Ky.; DuPont™ Zenite® LCP made by E. I. du Pont de Nemours and Company of Wilmington, Del.; or any suitable LCP material.
The example molded case 3 can include a plurality of threaded inserts (not shown), a molded terminal barrier (not shown) and a plurality of internal insulators (not shown). All of these structures are preferably insert molded at one time.
Referring to
The molded case 3 includes the back portion 52, four side portions 80,82,84,86 disposed from the back portion 52 and an open front portion 88. For each of the poles 72,74,76, a planar cover 90 is coupled to the molded case 3 at the open front portion 88. Each of the covers includes a tab 92 disposed into a corresponding tab-receiving opening 94.
There are five example electronics interconnect pins 68 (shown in
A multi-circuit protection device is, for example, four single-phase loads (not shown) that are opened during a fault, such as a three-phase load and a single-phase avionics load, a two-pole, a three-pole, or a four-pole DC device. Regardless whether there is a “single-phase” or one-pole circuit interrupter as opposed to a “three-phase” or three-pole circuit interrupter, there are preferably no differences between the three single-pole circuit interrupters 6 (
As is conventional, the disclosed three-pole RCCB or three-pole RPC 70 includes an intelligent interconnect between individual poles 72,74,76. This trips all poles/phases when a thermal overload is detected on any pole or phase.
The RCCB or RPC 70 is a combination relay and circuit breaker, which can be tripped or set by applying a trip or set coil pulse current. The RCCB is preferably used in conjunction with an indicator control unit (ICU) (e.g., without limitation, a one-half ampere, fast trip, push-pull, thermal circuit breaker) (not shown). With the ICU closed, and power available to a line terminal (not shown), the RCCB assumes a set (closed) state. The RCCB assumes a trip (open) state if the ICU is open. If power is removed from the RCCB, then it will remain in the same state it was in prior to power removal. When power is reapplied, the RCCB will assume the state dictated by the ICU. With the RCCB closed, an overload or fault current (e.g., without limitation, 138% or greater of rated current), will cause the RCCB to trip within the time limits of an applicable trip time curve, and, in turn, cause a controlled overloading of the ICU, causing it to trip also. The ICU provides indication that the RCCB has opened. The ICU opens and reconnects before the RCCB can be reset.
The disclosed molded case 3, which is made of LCP, provides superior moisture resistance characteristics as contrasted with thermoset compounds, which are believed to be notorious for varying dielectric characteristics based on post-bake temperatures and times. The molded case 3 is stronger from an installation standpoint, lighter, and far more repeatable from an environmental or dielectric withstand capability. The molded case 3 also reduces terminal torque out failures since LCP is about ten times stronger in tensile than thermoset compounds.
The disclosed molded case 3 and the insert molded aluminum mounting base 4 provide various improvements in circuit interrupters and are believed to be a departure from known prior technology. For example, the use of LCP permits: (1) molding relatively very thin walls, such as 26 (
The disclosed circuit interrupter 6 is preferably sealed and vented. For example, all covers are gasketed or bonded for the seal. A vent tube (not shown) with a relatively very small hole is place on the side of the circuit interrupter 6 facing “down” when installed. This allows for an internal expansion during electrical overloads or pressure differences, and drives/pushes moisture out of the circuit interrupter 6 during normal operation.
While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.
