Abstract:
An electric circuit breaker ( 10 ) has a toggle mechanism ( 18 ) having two movable over center joints ( 3, 4 ) connected between a push-button ( 16 ) and a movable contact mechanism ( 30 ). When the push-button is depressed a first link rotates bringing the first movable over center joint ( 3 ) across a center position represented by a first imaginary straight line ( 1 ) to a stop surface ( 28 ). A spring member ( 36 ) provides a bias which acts on the second movable over center joint ( 4 ) normally maintaining the second movable joint against the stop surface so that with the two movable over center joints biased against the stop surface the movable contact mechanism is moved to a closed contact position when the push-button is depressed. An overload responsive member transfers motion to the second movable over center joint ( 4 ) upon the occurrence of a selected overload and moves the second over center joint across a center position represented by a second imaginary straight line ( 2 ) allowing the contacts opening spring ( 34 ) to move the movable contact mechanism to the open contacts position providing a trip free operation. The circuit breaker can be formed for a single phase or it can be formed for multiphase operation in which additional ganged phases have no toggle mechanism but do have separate ambient temperature compensated trip arms and overload responsive members which operate through the single toggle mechanism.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to electrical circuit breakers and more particularly to such interrupters used as aircraft circuit breakers. 
     BACKGROUND OF THE INVENTION 
     It is conventional for aircraft circuit breakers to have an overload responsive member such as a current carrying bimetal, typically called a bimetal trip arm, which has a portion which deflects with changes in temperature to move a slidably mounted connecting plate which is adapted to engage and displace a trip arm. One part of a latch mechanism is movable with the trip arm and upon occurrence of an overload the one part of the latch mechanism is separated from a catch portion which allows a collapsible linkage mechanism to move a movable contact into an open contacts position. Such a device is shown, by way of example, in U.S. Pat. Nos. 4,827,233 and 4,837,545, assigned to the assignee of the present invention, the disclosure of which is included a herein by this reference. Typically a high localized contact force exists between the interengaging surfaces of the latch and its catch. Such surfaces are manufactured so that they are extremely smooth and wear resistant, using expensive materials thereby increasing component costs. Although such devices are effective, the friction of the latching mechanism tends to change over time introducing variability and can eventually change the calibration of the circuit breaker. Additionally, such devices require a relatively large number of components, particularly in multiphase breakers where several contact, linkage and latch mechanisms are ganged together. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide circuit breaker free of the prior art limitations noted above. Another object of the invention is the provision of an electrical circuit breaker which performs the same functions as conventional aircraft circuit breakers yet has no latch mechanism with concomitant friction. Yet another object of the invention is to provide an electrical circuit breaker which is trip free, can be made for use with single phase or multiphase applications and which has fewer parts and less weight than prior art devices. 
     Briefly, an electrical circuit breaker made in accordance with the invention comprises a housing in which a stationary electrical contact and a movable contact mechanism having a movable electrical contact are mounted with the movable electrical contact being movable between contacts open and closed positions. The movable contact mechanism is pivotably mounted and is provided with a first spring member urging the movable contact mechanism toward the open contacts position. A push-button is mounted on the housing and is connected to one end of a plurality of end to end interjointed link members with the opposite end connected to the movable contact mechanism. 
     The first link is rotatably connected to the housing at a location intermediate to the first and second ends of the link. One end of the first link is formed with a slot to receive therethrough a pin of the push-button for converting linear motion of the push-button to rotary motion of the first link. The second end of the first link forms a first movable over center joint and is pivotably connected to the first end of a second link. The second end of the second link forms a second movable over center joint and is in turn pivotably jointed to the first end of a third link whose second end is pivotably connected to the movable contact mechanism. A stop surface is disposed on one side of, and closely adjacent to, a first imaginary straight line extending through the rotational connection of the first link to the housing and the second movable over center joint and a second imaginary straight line extending through the first movable over center joint and the pivotable connection of the second end of the third link. 
     A second spring member biases the second movable over center joint toward the stop surface and when the push-button is depressed the first link is rotated against the bias of the first spring member moving the movable contact mechanism toward the contacts closed position with the first movable over center joint moving over center across the first imaginary line and into engagement with the stop surface essentially straightening out the several links and moving the movable contact mechanism into the closed contacts position. 
     An overload responsive trip member in the form of a current carrying bimetal trip arm is caused to deflect upon a selected overload current which deflection is transferred to a rotatably mounted ambient bimetal compensator. Rotation of the bimetal compensator transfers motion through a motion transfer portion of the bimetal compensator to the second movable over center joint moving it over center to the other side of the second imaginary line thereby allowing the first spring member acting on the movable contact mechanism to open the contacts. As long as the overload bimetal member is in the overload deflected position the circuit breaker can not be reset even with the push-button held in the depressed position. 
     According to a feature of the invention, the second movable over center joint is provided with a roller engageable with the stop surface to avoid sliding motion. According to another feature, the movable contact mechanism is preferably formed to provide a preload to obtain a desired level of contact force as by bending a spring member into a generally J-shaped configuration, mounting the movable electrical contact on a stiffened distal free end of the long leg and forming a lost motion pin connection between an intermediate location of the long leg and the distal end portion of the short leg of the J-shaped configuration. The movable contact mechanism is pivotably mounted to the housing adjacent the bight portion between the two legs so that when the third link transfers motion to the contact mechanism and closes the contacts, the pin rides in the slot with the spring member supplying the contact force. According to yet another feature, multiphase circuit breakers made in accordance with the invention have adjacent phase mechanisms which include corresponding contact mechanisms, overload responsive members and motion transfer connecting plates along with an arm of the ambient bimetal compensator but do not include additional toggle mechanisms thereby resulting in a decreased part count and device weight. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and together with the description, serve to explain the objects, advantages and principles of the invention. In the drawings, 
     FIG. 1 is a perspective view of a three phase circuit breaker made in accordance with the invention; 
     FIGS. 2 and 3 are front and rear elevational views of the FIG. 1 breaker shown with the housing broken away for purposes of illustration; 
     FIG. 4 is a side elevational view of the center phase of the FIG. 1 breaker shown without the front wall for purposes of illustration and shown with the push-button depressed and in the overload actuated, contacts open, trip free position; 
     FIG. 5 is a view similar to FIG. 4 but shown in the contacts closed position; 
     FIG. 6 is a view similar to FIG. 5 but showing an outer phase of a multiphase, ganged circuit breaker and shown with the push-button of the center phase; and 
     FIGS. 7-9 are broken away, somewhat simplified side elevational views showing the toggle mechanism in the open, cooled condition (FIG.  7 ), closed contacts position (FIG. 8) and open trip-free position with the push-button depressed (FIG.  9 ). 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Although the drawings show a three phase circuit breaker, breakers made in accordance with the invention can be of a single phase version having only the phase identified herein as the center phase, i.e., as shown in FIGS. 4 and 5, for example, or can be of the version for multiphase applications in which several phases are ganged together as shown in FIGS. 1-3, for example. In either case, an electrical circuit interrupter  10  made in accordance with a first embodiment of the invention comprises a housing  12  having a top wall  12   a  formed with an aperture  12   b  for receipt of a bushing  14  and a push-button  16 . Push-button  16  is linearly movable between inner and outer positions as shown respectively in FIGS. 8 and 7. A push-button return spring  16   a  (see FIG. 4) is mounted within bushing  14  and places a force on the push-button toward the outer position. The bottom portion of the push-button is provided with a pin  16   b  which extends between spaced apart side portions  16   c  (one side portion being shown) for connection with one end of a toggle mechanism  18 . Toggle mechanism  18  has a plurality of links  20 ,  22  and  24  jointed together in end to end fashion to form a chain. First link  20  has first and second ends  20   a ,  20   b  and is rotatably connected to side wall  12   c  of the housing by pin  20   c . Pin  16   b  is received through a slot  20   d  adjacent end  20   a  of the first link, the slot preferably having a wider end furthest from the rotational connection to facilitate transition between linear motion of the push-button and rotational movement of link  20 . Link  20  is generally L-shaped with the rotational connection offset from a straight line joining ends  20   a ,  20   b . It should be understood that other configurations for the link can be employed as long as the actuating force, push-button  16  in the embodiment shown, acts in a direction which is not in line with the rotational connection of the link with the housing. 
     The second end  20   b  of first link  20  is pivotably connected at  20   b  to the first end  22   a  of second link  22  and forms a first movable over center joint  3 . Second link  22  preferably is formed as a pair of overlying links members received on either side of first link  20  to allow uninhibited pivotal motion between the first and second link. The second ends  22   b  of second link members  22  receive therebetween and are pivotably connected to the first end  24   a  of third link  24  and form a second movable over center joint  4 . Preferably, freely rotatable rollers  26  are mounted at the pivotable connection at ends  22   b  at movable joint  4  for rolling engagement with a stop surface  28  to be discussed. The second end  24   b  of third link  24  is pivotably connected to a movable contact mechanism  30 . Movable contact mechanism  30  is pivotably connected to housing  12  at one end of the mechanism by pin  30   h . Movable electrical contact  30   a  is movable into and out of electrical engagement with a stationary electrical contact  32   a  between respective contacts closed and open positions. Preferably, movable electrical contact  30   a  is provided with a preload as by forming the movable contact arm  30   b  out of a strip of suitable spring material and bending the strip back over itself to form a generally J-shaped configuration having two legs extending from a bight portion with one end on the upper, shorter leg formed with two spaced apart, downwardly extending legs  30   c  formed with pin receiving aperture  30   d  and two spaced apart, upwardly (after bending) extending legs  30   e  on the lower, longer leg having a generally vertically extending pin receiving slot  30   f  formed in each leg. The legs extending from the bight portion are rigidized as by turning over the outer side margins. A pin  24   c  is placed through the aperture, slots and an aperture in the second end  24   b  of third link  24 . In the open contacts position, the spring strip causes the pin to move to the uppermost extremity of the slots and when the movable electrical contact mounted at the distal end  30   g  of the longer leg engages the stationary electrical contact the pin moves downwardly in the slots placing a selected force on the stationary electrical contact. The movable contact mechanism is pivotably mounted on pin  30   h  adjacent to the bight portion connecting the two legs. 
     With particular reference to FIGS. 7-9, as push-button  16  is moved down or pulled up, first link  20  rotates about pin  20   c  with rivet  20   e  joining links  20 ,  22  forming a first movable over center joint  3  as mentioned above and being movable between opposite sides of an imaginary line  1  extending through pin  20   c  and rollers  26 . A second movable over center joint  4  is formed at rollers  26  which is movable between opposite sides of an imaginary line  2  extending through over center joint  3  and pin  24   c  at second end  24   b  of third link  24 . 
     A generally vertically extending stop surface  28  is formed in housing  12  and is placed so that it limits motion of first and second movable over center joints  3 ,  4  on one side of their respective imaginary lines closely adjacent thereto. 
     When push-button  16  is pulled outwardly, as shown in FIG. 7, link  20  is rotated (counterclockwise as seen in the drawing) so that movable over center joint  3  is moved away from stop surface  28  to the other side of imaginary line  1 . First spring members  34  connected between movable contact mechanism  30  and a stationary portion of the breaker provide a bias to the movable contact mechanism, as well as the toggle mechanism, in the open contacts direction. Thus pulling the push-button outwardly opens the contacts. A second spring member, torsion spring  36 , engages third link  24  reacting against pin  24   c , and biases link  24  towards stop surface  28  to normally maintain second movable over center joint  4  on the stop surface side of imaginary line  2 . 
     When push-button  16  is pushed inwardly as shown in FIG. 8, link  20  is rotated (clockwise as seen in the drawing) in the opposite direction against an increasing force of spring member  34  as it is stretched, tending to straighten the toggle mechanism until movable joint  3  passes a center point having a maximum resisting spring force when movable joint  3  is aligned with imaginary line  1 , and then the movable joint snaps over to the stop surface  28 . 
     With regard to a single phase circuit breaker discussed thus far, electrical circuit breaker  10 , is connected to a circuit to be protected through terminals L 1 , L 2 . Terminal L 1  mounts stationary electrical contact  32   a  and movable contact  30   a  is connected to load terminal L 2  through an overload sensing mechanism to be described. A short current carrying wire or pigtail  38  is connected between terminal L 2  and a current carrying bimetallic trip arm  40 . Trip arm  40  is generally U-shaped with the end of one leg being fixedly mounted in housing  12  and connected to pigtail  38  and the end of the other leg being fixedly mounted in housing  12  and connected to a long, current carrying, flexible wire or pigtail  42  having an opposite end connected to movable contact assembly  30  and movable electrical contact  30   a . The bight portion  40   a  of the trip arm is disposed adjacent one end  44   a  of a connecting plate  44  horizontally slidable in housing  12 . 
     Ambient temperature compensation is provided in circuit breaker  10  by an ambient temperature bimetal compensator member  46 . Member  46  has an upper deflectable compensator arm  46   a  in the form of a strip of bimetallic material and a lower, rigid motion transfer portion  46   b  having side walls or the like to provide rigidity and may be formed of bimetal as a one piece member if desired. Member  46  is mounted on rod  46   c  which is rotatably mounted in housing  12 . The distal end of compensator arm  46   a  is disposed adjacent to end  44   b  of connecting plate  44 , opposite to end  44   a . A current overload in trip arm  40  will cause the bight portion thereof to deflect to the left as seen in the drawings resulting in opening of the contacts of the circuit breaker as will be explained below. However, a change in ambient temperature will cause both the bight portion of trip arm  40  and the distal free end of the upper compensator arm  46   a  to deflect similarly to maintain essentially the same spatial relationship therebetween. 
     A calibration assembly  48  comprising calibration arm  48   a , calibration screw  48   a  and calibration plate  48   c  cooperate to allow adjustment of the circuit breaker to perform properly for given over currents and ambient temperatures. Plate  48   c  is fixedly mounted in housing  12  and screw  48   a  is received therethrough so that rotation of screw  48   a  can cause rotation of calibration arm  48   a  about pivot  48   d  which transfers motion through connecting plate  44  to rotate compensator arm  46   a  of ambient compensator member  46  a corresponding amount. 
     Third link  24  is preferably formed with extension  24 e, adjacent to second movable over center joint  22   c  and extending toward motion transfer portion  46   b  of compensated trip member  46 . When an overload occurs and bight  40   a  deflects to thereby move connecting plate  44 , the connecting plate will cause bimetal compensator  46  to rotate counterclockwise as viewed in the drawings and transfer motion and force to extension  24   e  thereby moving the second movable joint  4  away from stop surface  28  and past the center, imaginary line  2 , allowing spring member  34  to open the contacts. 
     Using the second movable over center joint to trip the circuit breaker results in a trip free device. That is, even if the push-button is held down in the depressed position as shown in FIGS. 4 and 9, motion transfer portion  24   e  prevents the second movable joint  4  from moving back over imaginary line  2 . Both movable joints must on the stop surface side of their respective imaginary lines  1 ,  2  in order for the contacts to be in the closed contacts position. 
     In the above description a single phase has been described, however, it applies as well to a multiphase device in which devices for more than one phase are ganged together to protect two or more phases. In such a ganged device, the toggle mechanism and push-button remains the same for the phase described above with the devices for the other phases provided with similar tripping mechanisms cooperating through the single toggle mechanism. With reference to FIGS. 2 and 3 which show a circuit breaker having three ganged phase devices  5 ,  6  and  7 , shown without housing  12 , center phase  6  is the same as described above. Ambient temperature bimetal compensator member  46  has spaced apart compensator arms  46   a , one aligned with each phase extending upwardly from transversely extending portion  46   d  with motion transfer portion  46   b  extending downwardly from the center compensator arm  46   a . The compensator arms and transversely extending portion  46   d  are fixedly attached to rotatable rod  46   c . Each phase is provided with a connecting plate  44 , trip arm  40  and calibration mechanism  48  as in the center phase. Thus an overload in a trip arm  40  of any of the phases will cause the respective connecting plate to slide over and push the distal end portion of the respective upper compensator arm  46   a  causing rod  46   c  to rotate and in turn move motion transfer portion  46   b  which moves extension  24   e  of third link  24  and second movable over center joint  4  away from the stop surface  28  across imaginary line  2  to trip the circuit breaker to the open contacts position. 
     A circuit breaker made in accordance with the invention as described above does not have a latch mechanism as used in typical prior art devices which results in avoiding friction associated with latches and concomitant problems with changing frictional forces over time which adversely affect calibration of the device. In circuit breaker devices made in accordance with the invention in which a plurality of phases are ganged together, further advantages are obtained by reducing the complexity of the design and significantly decreasing the number of parts needed along with an accompanying savings in weight by virtue of employing only one toggle mechanism. The toggle mechanism movable over center joints provide repeatable operational forces while the reset and pull-out forces can be independently adjusted without affecting the trip of contact forces. 
     Although the invention has been described with regard to certain preferred embodiments thereof, variations and modifications will become apparent to those skilled in the art. For example, although a push-button is shown and described for rotating first link  20 , other force applying members can be used if desired, such as a toggle or rocker mechanism, known in the art. The particular configurations and lengths of the several links of the toggle mechanism can be varied to provide different contact set and reset forces, amount of contact opening and the like. Further, the toggle mechanism of the invention can be used with other circuit interrupting devices such as thermostats for example. Various actuation mechanisms can be used such as solenoid, piezo, thermal, magnetic and the like. The movable contact mechanism can be pre-loaded as described, snap acting, spring loaded cantilever, dual contact and the like. It is, therefore, the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.