Abstract:
A pushbutton resettable circuit breaker is shown having features to prevent manual opening by simply pulling outwardly on the pushbutton. In one embodiment, the pushbutton ( 16 ) is formed with slots ( 16   b ) which are configured to provide a reaction surface essentially inaccessible without a special purpose contact opening tool ( 30 ). The tool is provided with portions that are insertable into the slots and into engagement with the reaction surfaces for pulling the pushbutton out and manually opening the contacts. In a second embodiment, a small aperture  16   k  is formed through the rating tab and top and wall of the button and in alignment with a movable plunger ( 28 ). A special purpose contact opening tool ( 32, 34 ) can be inserted through the aperture to apply a force to the plunger and mechanically trip the circuit breaker.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to electrical circuit breakers and more particulary to aircraft circuit breakers having a pushbutton actuator provided with a manual opening resistant feature. 
     BACKGROUND OF THE INVENTION 
     Aircraft circuit breakers having a pushbutton actuator for closing a set of electrical contacts in a circuit path are well known. By way of example a circuit breaker of this type is shown and described in coassigned U.S. Pat. No. 3,361,882, the subject matter of which is incorporated herein by this reference. Typically, the pushbutton of such circuit breakers when in the dosed or actuated position can be manually grasped and pulled outwardly to open the contacts and de-actuate the circuit breaker. 
     Although this feature has served as a convenient mechanism for opening a circuit path, it also provides an easily accessible means for undesirable tampering with the circuit breaker. 
     SUMMARY OF THE INVENTION 
     An object of the Invention is the provision of a manually resettable circuit breaker which can be manually moved from the closed circuit position to the open circuit position only with the use of a special purpose tool. Another object is the provision of a tamper resistant circuit breaker to prevent undesirable manual opening of the circuit breaker electrical contacts. Yet another object is the provision of a circuit breaker which overcomes the above-noted limitations of the prior art 
     Briefly, in accordance with the invention, a circuit breaker having a manual reset button is configured so that in the operating, dosed contacts position, there is no exposed surface area for grasping to thereby effectively prevent unauthorized personnel or the like from opening the circuit breaker by pulling out the pushbutton. The circuit breaker is provided with a selected opening to provide access for insertion of a special purpose opening tool to engage a reaction surface and apply a contacts opening force. According to a first embodiment, a pair of diametrically opposed generally L-shaped slots are formed in the pushbutton, the slots having a first portion extending in a direction generally parallel to the longitudinal axis of the pushbutton from the top surface thereof and a second portion extending in a common circumferential direction with the surface of the second portion closest to the top surface of the button forming a reaction surface. A special purpose tool used to mechanically trip the circuit breaker is provided with parallelly extending prongs each having a laterally extending foot extending in opposite directions from one another. The prongs and feet are sized to be receivable in respective first portions of the slots and twistable to insert the feet into the respective second portions of the slots and into alignment with the reaction surface. A force can then be applied to the tool to pull out the pushbutton and manually open the circuit breaker. 
     The second embodiment is useful with circuit breakers of the type having a plunger capable of motion relative to the pushbutton and attached to the movable contact assembly and which, when the contacts are in the closed position, selected downward movement of the plunger will release the latch maintaining the contacts in the closed position and allow the pushbutton return spring to move the pushbutton upwardly and the contacts opening spring to move the contacts to the open position. In the second embodiment the top face or outer end surface of the pushbutton is provided with a small aperture aligned with a reaction surface on the plunger of the circuit breaker. A special purpose opening tool having an elongated probe portion receivable through the aperture can be used to open the contacts of the circuit breaker by inserting the probe portion through the aperture in the pushbutton end surface and applying sufficient downward force on the plunger. 
    
    
     Other objects, features and advantages of the present invention will appear from the following detailed description of preferred embodiments taken together with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an aircraft circuit breaker made in accordance with a first preferred embodiment of the invention in an open contacts condition; 
     FIG. 2 is similar to FIG. 1 but shows the circuit breaker in the closed contacts condition, 
     FIG. 3 is a perspective view of a special purpose contact opening tool useful in the FIGS. 1,  2  embodiment; 
     FIGS. 4 and 5 are elevational views of the FIGS. 1,  2  circuit breaker, respectively, with, a case half removed for illustration and with certain parts shown in cross section; 
     FIGS. 6 and 7 are perspective views, similar to FIGS. 1 and 2, respectively, of a circuit breaker made in accordance with a second preferred embodiment of the invention; 
     FIG. 8 is a perspective view of a special purpose contact opening tool useful in the FIGS. 6,  7  embodiment; 
     FIGS. 9 and 10 are elevational views, similar to FIGS. 4 and 5, of the FIGS. 6,  7  circuit breakers, respectively, and 
     FIG. 11 a cross sectional elevational view of an alternative special purpose contact opening tool for use with the FIGS. 6,  7  embodiment. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Turning to FIGS. 1-5 of the drawings, circuit breaker  10  made in accordance with a first preferred embodiment comprises a housing  12  having case halves  12   a ,  12   b , a mounting bushing  14 , a pushbutton  16  slidably movable within the bore of bushing  14  between an open contacts position in which the top surface  16   a  of the pushbutton extends outwardly beyond the open end of bushing  14  as shown in FIGS. 1 and 4, and a dosed contacts position in which the top surface  16   a  of the pushbutton is essentially flush with the end surface  14   a  of the open end of bushing  14 . 
     With particular reference to FIG. 4 (showing open contacts) and FIG. 5 (showing closed contacts), circuit breaker  10  has a movable contact assembly  18  which mounts a movable bridging electrical contact  21  for movement between an open contacts position and a closed contacts position with a pair of stationary electrical contacts  20 , one of which being indicated in the drawings. The circuit breaker has first and second electrical terminals T 1 , T 2  mounted in and extending out of housing  12 . Terminal T 2  is electrically connected to a first of the pair of electrical contacts  20  while terminal T 1  is connected to a current carrying bimetal element  22  mounted in housing  12  and configured, for example, as a generally U-shaped element. The free end  22   a  of one leg of the U-shaped element is fixedly mounted in the housing and electrically connected to terminal T 1  while the other end of the U-shaped element, also fixedly mounted in the housing, is electrically connected to the second of the pair of stationary electrical contacts  20  by means of a strap (not shown) and with the bight portion  22   c  of the U-shaped element arranged to deflect to the left relative to the position shown in FIGS. 4,  5 , with an increase in temperature of the element. Movable bridging electrical contact  21  is mounted on contact leaf spring  21   a  which in turn is mounted on bell crank  18   a  pivotably mounted on plunger  28 . Plunger  28  is slidingly received in a bore of pushbutton  16  (see bore  16   g  in FIGS. 9 and 10) and operatively connected thereto by a plunger latch, discussed in detail in U.S. Pat. No. 3,361,882 referenced above, but not shown in FIGS. 4 and 5, except for latch ball receiving opening  16   f.    
     A non-current carrying ambient compensation bimetal element  24  has one end pivotably mounted in housing  12  and a distal free end  24   a  disposed in selected spaced apart alignment with bight  22   c  of current carrying bimetal  24  with the spacing between free end  24   a  and bight  22   c  remaining constant with changes in ambient temperature. A catch member  24   b  having a ledge  24   c  is attached to the ambient compensating bimetal element only at the base thereof so that the position of ledge  24   c  is unaffected by ambient temperature variations. 
     When in the contacts closed position with the pushbutton and plunger depressed and latched by the plunger latch, the bell crank latch  18   b  engages ledge  24   c  of catch member  24   b  limiting counterclockwise rotation of bell crank  18   a  about the pivot connection  18   c  with plunger  28 . Upon a selected overload in current passing through bimetal element  22 , the element will increase in temperature and bight  22   c  will deflect to the left compared to the position shown in FIGS. 4,  5 . This motion is transferred to ambient compensation bimetal  24  through a slidably mounted motion transfer plate  26  which also moves catch member  24   b  and ledge  24   c  to the left to trip the circuit breaker by allowing contact opening spring  18   d  to pivot the bell crank  18   a  counterclockwise as seen in the drawings about pivot connection  18   c  on plunger  28  and move the movable contact to the open (FIG. 4) position with plunger  28  moving upwardly along with pushbutton  16  under the influence of pushbutton return spring  16   m  to a position with top surface  16   a  of pushbutton  16  spaced from and above end surface  14   a  of bushing  14 . The outer cylindrical surface of pushbutton button  16  can be provided with a selected color contrasting with the surrounding structure, e.g., white, to enhance visibility of a tripped circuit breaker, if desired. 
     As long as bight  22   c  is in the overload deflected position, the circuit breaker cannot be reset due to the displaced ledge. Upon cooling of the bimetal element  22  and a return of bight  22   c  to the FIG. 4 position pushbutton  16  can be depressed with latch  18   b  engaging ledge  24   c  of catch member  24   b  and permitting closure of the contacts. 
     Further details of the operation of the circuit breaker can be obtained in U.S. Pat. No. 3,361,882 referenced supra. In that patent, the pushbutton extends above the mounting bushing when the contacts are in the closed position so that the pushbutton can be grasped and pulled in an outward direction allowing the disengagement of the plunger latch which allows the contacts to move to the open contacts position. In accordance with the present invention as described above, the top end surface  16   a  of pushbutton  16 , when in the contacts closed position, is essentially flush with the open end surface  14   a  of bushing  14  thereby preventing anyone from grasping the pushbutton In order to pull out the pushbutton and de-actuate the circuit controlled by the circuit breaker. 
     In accordance with the first preferred embodiment of the invention, pushbutton  16  is formed with a pair of spaced apart diametrically opposed, generally L-shaped slots  16   b . Each slot comprises a first slot portion  16   c  which extends in a direction generally parallel with the longitudinal axis of pushbutton  16  and having a selected width and a second communicating arcuate slot portion  16   d  extending in a common circumferential direction, i.e., the arcuate slots extend along a line, lying in a plane generally perpendicular to the longitudinal axis. The surface defining the upper extremity of the second slot portion serves as a reaction surface  16   e  for a purpose to be described. 
     With reference to FIG. 3, a special purpose contact opening tool  30  is shown comprising a body portion  30   a  from which a pair of prongs  30   b  extend in generally parallel directions and being spaced, apart a distance selected to be receivable in slots  16   b . A foot  30   c  extends laterally from the free distal end of each prong  30   b  in opposite directions from one another. Preferably, the feet are arc shaped so that the feet extend from the prongs in a common circumferential direction relative to an imaginary circle of which the arcs form separate segments thereof. The length l of each arc is selected to be accommodated along with its respective prong in first slot portion  16   c  and the height h of each foot is selected to be accommodated in second slot portion  16   d.    
     In order to open the circuit breaker contacts, prongs  30   b  are inserted into respective first slot portions  16   c  and the tool is then twisted so that feet  30   c  enter into respective second slot portions  16   d  and then the tool is pulled outwardly with feet  30   c  placing a force on reaction surface  16   e  to pull out the pushbutton. 
     It will be appreciated that although a pair of slots is preferred and has been described, it is within the purview of the invention to use a different number of slot and prong combinations, such as three equally spaced slots and prongs for example. Further, although it is preferred to form the feet arcuately, feet extending in a straight line could be used as long as the slot is sufficiently deep to accommodate the feel As shown, slots  16   b  have a further slot extending from the extremity of second slot portion  16   d  opposite to first slot portion  16   b ; however, that is shown for the convenience of forming slot portion  16   d  and does not relate to the opening procedure itself. 
     A second preferred embodiment is shown in FIGS. 6-10 which comprises the same circuit breaker as in the FIGS. 1-5 embodiment described above with a modified pushbutton  16 ′. Pushbutton  16 ′ is formed so that top surface  16   a ′, as in the first embodiment, is essentially flush with the open end surface  14   a  of mounting bushing  14  when the contacts are in the closed position. Pushbutton  16 ′ is formed with an opening  16   g  open at its inner end for slidable reception of plunger  28  and having an end wall  16   h . According to the second embodiment, a relatively small aperture  16   k  is formed through the end wall  16   h  and rating tab  17  and aligned with plunger  28 . 
     Special purpose contact opening tool  32 , useful with the circuit breaker of the second embodiment, is shown in FIG.  8  and comprises a body portion  32   a  having a single rigid prong  32   b  extending therefrom having a size slightly smaller than aperture  16   k  to allow sliding reception of prong  32   b  through aperture  16   k . A force applied to reaction surface  28   a  will depress the plunger relative to the pushbutton releasing the plunger and resulting in a mechanical trip of the circuit breaker. 
     With reference to FIG. 11, an alterative special purpose contact opening tool  34  is shown comprising a body portion  34   a  having a bushing receiving opening  34   b  for reception on an open end of mounting bushing  14  of a circuit breaker  10 ′. Opening  34   b  may be threaded for threaded engagement with the threads of bushing  14  or not as desired. An elongated, rigid, vertically movable probe  34   c  extends from pushbutton  34   d  which is spring loaded by coil spring  34   e  disposed between the pushbutton bottom surface and a probe alignment shelf  34   f  of body portion  34   f  and shown in the drawing in the normal, at rest recessed condition. Tool  34  can be placed on bushing  14  of a circuit breaker to be manually tripped, as shown, with probe  34   c  automatically aligned with aperture  16   k  so that pushing down on pushbutton  34   d  will cause probe  34   c  to move downwardly into aperture  16   k  striking reaction surface  28   a  to cause a mechanical trip of the circuit breaker. 
     It should be understood that although particular embodiments of the invention have been described by way of illustrating the invention, other embodiments and variations are possible. It Will be understood that the first embodiment of the invention applies to any manually resettable circuit breaker having a push-pull pushbutton. The second embodiment of the invention applies to any circuit breaker in which downward movement of a movable contact assembly plunger aligned with a pushbutton causes a mechanical trip. It is intended that the invention include all modifications and equivalents of the disclosed embodiments within the scope of the claims.