Abstract:
A rotary contact arrangement for circuit breakers of the type including a pair of contact springs arranged on each side of a rotary contact arm, as the contact springs interconnect between the rotors and the contact arm via a pair of U-shaped levers. The provision of the U-shaped levers provides uniform contact pressure between both pairs of fixed and moveable contacts to prevent contact erosion.

Description:
BACKGROUND OF INVENTION 
     This invention relates to circuit breaker, and, more particularly, to a circuit breaker rotary contact arm arrangement. 
     Circuit breakers having a current interrupting module within a rotary contact arm arrangement whereby the circuit breaker movable contact arms are arranged at the opposite ends of the movable contact carrier are able to interrupt circuit current at a faster rate than circuit breakers having a movable contact carrier with a contact arranged at one end. U.S. Pat. No. 5,310,971 entitled Rotary Contact System for Circuit Breakers, describes a rotary contact arm that employs rollers between the contact springs and the contact arm to provide a uniform force distribution between the fixed contacts attached to the circuit breaker line and load straps and the movable contacts arranged at the opposite ends of the movable contact arm. One problem associated with a non-uniform force distribution between the fixed and movable contacts is the possibility of excessive contact erosion on the pair of contacts at the lower force points along the fixed contact surface. 
     U.S. patent application Ser. No. 09/384,908 filed Aug. 27, 1999 entitled Rotary Contact Assembly For High Ampere-Rated Circuit Breakers describes connecting the circuit breaker contact springs with the movable contact arm by means of pivotally-arranged links to compensate for contact wear and erosion over long periods of extensive circuit interruption. 
     SUMMARY OF THE INVENTION 
     In an exemplary embodiment of the invention, a rotary contact arrangement for circuit breakers of the type including a pair of contact springs arranged on each side of the rotary contact arm, has the contact springs interconnected between the rotors and the contact arm via a pair of U-shaped levers. The U-shaped lever sidearms interact with the perimeter surfaces of the rotors whereas the bights of the U-shaped levers interact with the shaped surfaces of the contact arm to insure uniform spring force between the fixed and movable contacts. 
     Uniform contact pressure between both pairs of fixed and movable contacts in a rotary type circuit breaker is provided without having to interpose rollers between the contact springs and the movable contact arm, especially when used in multi-pole circuit breakers that require a separate movable contact arm in each of the separate poles 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front perspective view of a rotary contact circuit breaker interior employing the rotary contact assembly according to one embodiment of the invention; 
     FIG. 2 is an enlarged front perspective view of the rotor assembly contained within the circuit breaker interior of FIG. 1; and 
     FIG. 3 is an enlarged front perspective view of the rotor assembly contained within the circuit breaker interior of FIG. 2 with the rotor plate removed to depict the U-shaped levers in greater detail. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, a rotor assembly  20  in a circuit breaker interior assembly is generally shown intermediate a line strap  11  and a load strap  12  and associated arc chutes  16 A,  16 B. Although a single rotor assembly is shown, it is to be understood that a seperate rotor assembly is employed within each pole of a multi-pole circuit breaker and that each operates in a similar manner. The arc chutes  16 A,  16 B are similar to that described in U.S. Pat. No. 4,375,021 entitled Rapid Electric Arc Extinguishing Assembly in Circuit Breaking Devices Such as Electric Circuit Breakers, which is incorporated by reference. Electrical transport through the circuit breaker interior proceeds from the line strap  11  to an associated fixed contact  13 B to a movable contact  14 B connected to one end of a movable contact arm  15 . The current transfers then to the opposite end of movable and fixed contacts  14 A,  13 A to the associated load strap  12 . The movable contact arm  15  moves a pivot  18  (pin) in unison with a rotor  17  upon articulation of the circuit breaker operating mechanism (not shown) by links  19 A,  19 B to move the movable contacts  14 A,  14 B between, CLOSED and OPEN positions. The rotor  17  responds to the rotational movement of the pivot  18  to effect the contact closing and opening function. An extended pin  25  provides attachment of the rotor  17  with the circuit breaker operating mechanism through links  19 A,  19 B 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. 09/384,908 filed Aug. 27, 2000. 
     Referring to FIG. 2, a rotor assembly  20  a first embodiment of the invention is generally shown as a single unitary assembly comprising a pair of opposing rotor plates  17 A,  17 B joined by a pair of extended cylinders  21 A,  21 B each having a passageway as shown at  22 . The rotor plates and cylinders are preferably fabricated from a glass-filled thermoset resin having good structural and electrical insulative properties and the central operating pivot  18  extends through both of the rotor plates as well as the movable contact arm  15 . The rotor plates  17 A,  17 B each include, on their opposing perimeters, a U-shaped retainer slot  28  and a sloping carrier slot  29  which includes a raised radial stop as shown at  30 . An opposing pair of contact springs  23 A,  23 B are guided along shaped carrier slots  29  at one end by spring pins  26 A, to which one end of the springs is attached and are retained at an opposite end by means of spring pins  27 B that are captured within U-shaped retainer slots  28 . An opposing pair of contact springs  24 A,  24 B are guided along shaped carrier slots  29  at one end by spring pins  26 B to which one end of the springs is attached and are retained at an opposite end by spring pins  27 A that are captured within U-shaped retainer slots  28 . The spring pins  26 A,  26 B and  27 A,  27 B cooperate with a pair of U-shaped levers  31 A,  31 B in the manner best seen by now referring to the rotor assembly  20  shown in FIG. 3 with the rotor plate  17 A removed and the cylinders  21 A,  21 B sectioned to depict the U-shaped levers  31 A,  31 B in greater detail. 
     Referring now to FIG. 3, the U-shaped levers  31 A,  31 B connect with the central pivot  18  through apertures  41 ,  42  and each define a pair of opposing sidearms  32 A,  32 B and  34 A,  34 B joined by bights  33 ,  35  respectively. The spring pins  26 A,  27 A at the ends of the contact springs  23 A,  23 B extend through openings  36  at the ends of the sidearms  32 A,  32 B and terminate on the surface of the carrier slot  29 , as indicated at  39 . The bight  33  joining the sidearms  32 A,  32 B rides along the surface  1  SB of one end of the movable contact arm  15 . The bight  35  joining the sidearms  34 A,  34 B rides along the surface  15 A of the opposite end of the movable contact arm. It is to be understood that the spring pins  26 B,  27 B are arranged in as similar manner on the rotor plate  17 A, shown earlier in FIG.  2 . 
     The provision of the U-shaped levers  31 A,  31 B intermediate the rotor plates  17 A,  17 B and the surfaces  15 A,  15 B on the opposing ends of the movable contact arm  15  thereby allows the forces of the contact springs  23 A,  23 B and  24 A,  24 B to interact in feed-back relation, whereby a generally constant force is applied between the fixed and movable contacts  13 A,  14 A and  13 B,  14 B of FIG.  1 . The forces exhibited by the contact springs at one end of the movable contact arm are transmitted via interaction with the bight associated with the one end to the bight associated with the other end of the movable contact arm to adjust the position of the bight associated with the other end thereof. An increase in force between one pair of fixed and movable contacts at one end of the movable contact arms is accordingly reflected in a corresponding increase in force between the other pair of fixed and movable contacts resulting in a constant force between both pair of fixed and movable contacts through-out the operational life of the associated circuit breaker