Abstract:
A rotary contact arrangement for circuit breakers of the type including a pair of movable contacts ( 30,36 ), one arranged on each end of the rotary contact arm ( 32 ), utilizes a single pair of contact springs ( 38 ), one spring on each side of the rotary contact arm ( 32 ). The springs ( 38 ) are aligned to intersect the axis of rotation of the rotary contact arm ( 32 ) for automatic uniform contact force adjustment throughout the operating life of the circuit breaker.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to circuit breakers, and, more particularly, to a circuit breaker rotary contact arm arrangement. 
     U.S. Pat. No. 4,616,198 entitled CONTACT ARRANGEMENT FOR A CURRENT LIMITING CIRCUIT BREAKER describes the early use of a first and second pair of circuit breaker contacts arranged in series to substantially reduce the amount of current let-through upon the occurrence of an overcurrent condition. 
     When the contact pairs are arranged upon one movable rotary contact arm such as described within U.S. Pat. No. 4,910,485 entitled MULTIPLE CIRCUIT BREAKER WITH DOUBLE BREAK ROTARY CONTACT, some means must be provided to insure that the opposing contact pairs exhibit the same contact pressure to reduce contact wear and erosion. 
     One arrangement for providing uniform contact wear is described in U.S. Pat. No. 5,310,971 entitled ROTARY CONTACT SYSTEM FOR CIRCUIT BREAKERS. This arrangement includes a rotary contact arm that employs rollers between the movable contact arm and spring pins to reduce contact arm friction. A rotor assembly with four contact springs, two on each side of the rotor, offset from the center of the rotor to impart contact force between the fixed and movable contacts is also disclosed. However, the roller system used in this arrangement can cause friction between the rollers and contact arm, which will result in uneven contact forces and, therefore, uneven contact wear. In addition, a rotor with springs offset from the rotor&#39;s axis of rotation can cause a non-uniform force distribution between the fixed and movable contact pairs if one pair of contacts erodes more than the other pair. The erosion of the contact pair with lower force results in a further reduction in force that continues to accelerate the erosion process. 
     BRIEF SUMMARY OF THE INVENTION 
     In an exemplary embodiment of the invention, a circuit breaker rotary contact arrangement includes a rotor having first and second opposing sides with pin retainer slots formed on the first side and a movable contact arm disposed intermediate the first and second sides. The movable contact arm has movable contacts at opposite ends of the contact arm, with each movable contact arranged opposite a fixed contact. A pivot pin is arranged on a central portion of the movable contact arm, with the pivot pin extending within an aperture formed on a central portion of the rotor. The pivot pin allows rotation of the movable contact arm with respect to the rotor. First and second links are pivotally secured to a first side of the movable contact arm. A first spring pin extends from the first link through the first pin retainer slot, and a second spring pin extends from the second link through the second pin retainer slot. A spring is arranged proximate the first side of the rotor and extends from the first spring pin to the second spring pin. The spring exerts a spring force directed to intersect the axis of rotation of the pivot pin. The spring force urges the movable contacts towards the fixed contacts. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front perspective view of a circuit breaker rotary cassette assembly employing the rotary contact assembly of the present invention; 
     FIG. 2 is a partially exploded perspective view of a cassette assembly with the cassette cover in isometric projection with the rotary contact arrangement of FIG. 1; 
     FIG. 3 is an enlarged side view of the rotary contact assembly of FIG. 1 with the circuit breaker contacts in an initial, undamaged condition; and 
     FIG. 4 is an enlarged side view of the rotary contact assembly of FIG. 1 with the circuit breaker contacts in an eroded condition. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a rotary contact assembly  12  in a circuit breaker cassette assembly  10  is shown in an electrically-insulative cassette half piece  14  intermediate a line-side contact strap  16 , load-side contact strap  18  and associated arc chutes  20 ,  22 . In the embodiment shown, line-side contact strap  16  would be electrically connected to line-side wiring (not shown) in an electrical distribution circuit, and loadside contact strap  18  would be electrically connected to load-side wiring (not shown) via a lug (not shown) or some device such as a bimetallic element or current sensor (not shown). Electrically-insulative shields  24 ,  26  separate load-side contact strap  18  and line-side contact strap  16  from the associated arc chutes  20 ,  22  respectively. Although a single rotary contact assembly  12  is shown, it is understood that a separate rotary contact assembly is employed within each pole of a multi-pole circuit breaker and operate in a similar manner. The arc chutes  20 ,  22  are similar to that described within U.S. Pat. No. 4,375,021 entitled RAPID ELECTRIC ARC EXTINGUISHING ASSEMBLY IN CIRCUIT BREAKING DEVICES SUCH AS ELECTRIC CIRCUIT BREAKERS. Electrical transport through the circuit breaker interior proceeds from the line-side contact strap  16  to associated fixed and moveable contacts,  28 ,  30  at one end of a movable contact arm  32 , to the fixed contacts and movable contacts  34 ,  36  at the opposite end thereof, to the associated load-side contact strap  18 . The movable contact arm  32  is arranged between two halves of a circular rotor  37 . Moveable contact arm  32  moves in unison with the rotor  37  upon manual articulation of the circuit breaker operating mechanism (not shown) to drive the movable contacts  30 ,  36  between CLOSED and OPEN positions. A first contact spring  38  extends between a pair of spring pins  40 ,  42  within the contact spring slot  48  formed within one side of the rotor  37  and a second contact spring (not shown) extends between pins  40 ,  42  in a similar manner on the opposite side of rotor  37 . An aperture  46  extends through the rotor  37 . Aperture  46  allows for a link connection with the circuit breaker operating mechanism to allow manual intervention for opening and closing the circuit breaker contacts in the manner described within the aforementioned U.S. patent application Ser. No. 09/087,038 entitled ROTARY CONTACT ASSEMBLY FOR HIGH AMPERE-RATED CIRCUIT BREAKERS, filed May 29, 1998, which is incorporated by reference. 
     Referring to FIG. 2, the circuit breaker cassette assembly  10  is shown prior to attaching a cassette half piece  50  with cassette half piece  14  to form a complete enclosure. The contact spring  38  proximate rotor  37  is protected from contamination by the attachment of a rotor cap  52 . A cap aperture  54  in rotor cap  52  aligns with the rotor aperture  46 . A radial protrusion  56  extending from the exterior of the cap  52  sits within an aperture  58  formed within the cassette half piece  50  and acts as a bearing surface, which allows the rotor  37  to rotate freely within a slotted aperture  60  formed within the cassette half piece  50 . A side (not shown) of rotor  37  proximate cassette half piece  14  is similar to the side of rotor  37  shown in FIG. 2, including a spring  38 , rotor cap  52  and aperture  46 . The rotor cap  52  proximate cassette half piece  14  also includes a radial protrusion  56  and aperture  54 . The radial protrusion  56  proximate cassette half piece  14  extends within an aperture  58  in cassette half piece  14 , which also acts as a bearing surface. 
     With the cassette half piece  50  attached to the cassette half piece  14  by means of apertures  62 ,  64  and rivets (not shown), a pair of circuit breaker operating mechanism sideframes  66 ,  67  are next attached to cassette half pieces  50 ,  14  by pins extending through apertures  68 ,  70 . Operating mechanism lever links (side arms)  72 , on opposing sides of the sideframes  14 ,  50  each connect with a crank lever  74  by a pin  76  extending through a slot  86  formed in sideframes  66 ,  67 . The lever links  72  each connect with the circuit breaker operating mechanism (not shown) in the manner described within the aforementioned U.S. patent application Ser. No. 09/087,038. Crank levers  74  pivotally connect with sideframes  66 ,  67  by pivots  80  for rotation of crank levers  74  in response to rotation of lever links  72 . Operative connection with crank levers  74  and the rotor  37  is provided by means of the extended rotor pin  82  that passes through the apertures  84  in the crank levers  74 , slots  86  in sideframes  66 ,  67 , slotted apertures  60  in cassette half pieces  50 ,  14 , the apertures  54  in the rotor caps  52  and the aperture  46  within the rotor  37 , as indicated by dashed lines. 
     Upon activation of lever links  72  by the circuit breaker operating mechanism (not shown), lever links  72  force crank levers  74  to pivot about pivot  80 . Extended rotor pin  82  moves in conjunction with lever links  72 , thereby rotating rotor  37  and movable contact arm  32  for driving the movable contacts  30 ,  36  (FIG. 1) between CLOSED and OPEN positions. 
     Referring to FIG. 3, rotary contact assembly  12  is shown with contact springs  38  arranged on each side of rotor  37 , and movable contact arm  32  having fixed and movable contacts  28 ,  30 ,  34 ,  36  arranged between load and line-side contact straps  18 ,  16 . The contact springs  38  are attached between the movable contact arm  32  and the spring pins  40 ,  42  by means of a pair of links  100 ,  102  in the manner described within the aforementioned U.S. patent application Ser. No. 09/087,038. One end of a spring pin  40  attaches to one end of the contact spring  38 , via link  100  and is positioned within a pin retainer slot  112  formed in the rotor  37 . The other end of the spring pin  40  connects with a similar link and retainer slot (not shown) on the opposite side of the contact arm  32  and the other contact spring  38  on the opposite side of rotor  37 . One end of the spring pin  42  attaches to one end of the contact spring  38 , via link  102  and is positioned within a pin retainer slot  114  formed in the rotor  37 . The other end of the spring pin  42  connects with a similar link and retainer slot (not shown) on the opposite side of the contact arm  32  and the other contact spring  38  on the opposite side of rotor  37 . A contact arm pivot pin  104  extends from central portion of rotary contact arm  32  and is captured within the rotor  37  via an elongated clearance slot  106  disposed in rotor  37  to allow contact arm  32  to rotate and translate relative to the rotor  37 , in the manner to be described with reference to FIG. 4. A contact arm pin  108  connects the link  100  with the contact arm  32  and a contact arm pin  110  connects the link  102  with the contact arm  32 . The contact arm pins  108 ,  110  connect the other links, although not shown, with the contact arm  32  on the other side of the contact arm  32 . Spring pins  40 ,  42  are positioned in line (co-linear) with the central pivot pin  104  so that the spring force H, exerted between spring pins  40 ,  42  is directed to intersect the axis of rotation of the movable contact arm  32 . The force H is transferred to the movable contact arm  32  via pins  40 ,  42 , links  100 ,  102  and pins  108 ,  110 . Pins  108  and  110  are offset from the line created by pins  40 ,  42  and pivot pin  104 , allowing the force H to rotate movable contact arm  32 . The rotation of movable contact arm  32  urges movable contacts  30 ,  36  toward fixed contacts  28 ,  34 . Because the force H is centered through the rotational axis of movable contact arm  32 , the force of movable contacts  30 ,  36  onto fixed contacts  28 ,  34  is substantially equal. The fixed and movable contacts  28 ,  30 ,  34 ,  36  are depicted herein in an undamaged condition, that is, free from any surface erosion. 
     FIG. 3 shows contact arm  32  in the CLOSED position. Upon an overcurrent condition, fixed contacts  28 ,  34  and movable contacts  30 ,  36  are separated by magnetic repulsion that occurs between the fixed contacts  28 ,  34  and movable contacts  30 ,  36 , as is known the art. The force caused by magnetic repulsion acts against the force created by the contact springs  38 , which tends to maintain the fixed and movable contacts  28 ,  30 ,  34 ,  36  in a CLOSED position. If the repulsive force exceeds the force created by springs  38 , contact arm  32  rotates in a clockwise direction, while rotor  37  remains stationary. The rotation of contact arm  32  moves pins  108  and  110  around pivot pin  104  and towards the line of force H. The motion of pins  108  and  110  is translated to spring pins  40  and  42  via links  100  and  102 , causing pins  40  and  42  to translate within slots  112  and  114  towards the perimeter of rotor  37 . The translation of pins  40  and  42  acts against the force of springs  38 . If rotary contact arm  32  rotates in a clockwise correction such that pins  108  and  110  move past the line force created by springs  38 , springs  38  will act to maintain contact arm  32  in a detented open position, with fixed and movable contacts  28 ,  30 ,  34 ,  36  separated. Once in the detented open position, contact arm is reset to the CLOSED position by rotating the rotor  37  in a counterclockwise direction until pins  108  and  110  are returned to the position shown in FIG.  3 . 
     Referring to FIG. 4, the rotary contact assembly  12  is shown after extended use and subjected to severe contact erosion between the fixed contact  28 , and the movable contact  30 , for example, at on end of the movable contact arm  32  within the rotor  37 . It is noted that the rotor  37  has rotated in the counter-clockwise direction as indicated, driving the central pivot pin  104  downward within the elongated clearance slot  106  such that the spring force, as now indicated by H′, remains directed through the rotational axis of central pivot pin  104 , similar to the spring force depicted at H in the undamaged contacts condition shown earlier in FIG.  3 . The slight movement of the central pivot pin  104  allows the slight rotation of the spring links  100 ,  102  attached to the moveable contact arm  32  by means of the spring pins  108 ,  110 , which translate within the retainer links slots  112 ,  114 . Elongated clearance slot  106  and pin retainer slots  112 ,  114  extend along rotor  37  in the same direction (i.e. substantially parallel to each other) to allow contact arm  32  and spring pins  40  and  42  to translate in the same direction relative to rotor  37 . The arrangement of the elongated clearance slot  106  and pin retainer slots  112 ,  114  allow contact arm  32  and spring pins  40  and  42  to remain in line, which allows the spring force H′ to continue to be directed through the axis of rotation of central pivot pin  104 . The arrangement of the spring force through the central pivot pin  104  causes the forces between the fixed and moveable contacts  28 ,  30 ,  34 ,  36  to remain constant such as when the fixed and movable contacts  28 ,  30 ,  34 ,  36  were in the undamaged condition depicted earlier in FIG.  3 . The constant force between the fixed and movable contacts  28 ,  30 ,  34 ,  36  ensures a uniform transfer of current between the fixed and movable contacts  28 ,  30 ,  34 ,  36 , which, in turn, prevents further erosion of the contact surfaces. 
     A simple arrangement of a single contact spring  38  on each side of a movable contact arm  32  in a lineal relation with the movable contact arm pivot pin  104  has herein been shown to provide an inexpensive means for reducing the effects of contact erosion over long periods of operation. 
     While a preferred embodiment has been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.