Abstract:
A rotary contact circuit breaker employs a crank to couple a switching mechanism to the rotary contact pole structure. The use of a crank allows for the mechanism and pole structure the individually optimized without effecting the performance of the other. In particular the crank allows for a mechanism that is able to achieve maximum torque delivery to the pole structure.

Description:
FIELD OF INVENTION 
     The present invention is directed to mechanism for a molded case circuit breaker capable of switching a rotary contact structure between on, off and tripped positions. 
     BACKGROUND OF THE INVENTION 
     The present invention is directed to a molded case circuit breaker having a mechanism for switching a rotary contact system between on, off and tripped positions. 
     U.S. Pat. No. 5,281,776 (&#39;776) describes a molded case circuit breaker having a toggle type mechanism for switching a rotary contact system. This mechanism utilizes a lower linkage that directly attaches to a drive shaft which extends through and rotates the contact system, as is shown in FIG. 1. A crank attached to the same drive pin is used to drive another pin that also extends through the contact system. Since the drive shaft passes through the contact system, optimum positioning of this shaft may not be possible which may cause geometric constraints on how much force can be transferred from the switching mechanism to the rotor. This often limits the performance level that a circuit breaker which uses the &#39;776 switching mechanism is able to achieve. 
     Therefore, it is desirable to optimize the switching mechanism to transmit an increased amount of force to a rotary contact system. 
     It is also considered desirable in conjunction with the improved switching mechanism to describe an interface between the mechanism and the contact system that allows for flexibility in the placement and design of the mechanism. 
     SUMMARY OF INVENTION 
     In accordance with the present invention a circuit breaker mechanism is provided that comprises a side frame having a cradle attached thereto. A toggle linkage consisting an upper link having a first and second end attaches to the cradle and a lower link attached to the upper link second end by a spring spindle. A crank member attached to the side frame attaches to the lower link. The crank provides the output torque generated by the mechanism. 
     Also in accordance with the present invention, a first and second shaft extend through a rotor assembly. The first shaft connects with the crank to drive the rotor assembly between a closed and open position in response to a change in state of the circuit breaker mechanism. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages and features will become more clearly apparent from the following description of an illustrative embodiment of the invention, given as a non-restrictive example only and represented in the accompanying drawings, in which: 
     FIG. 1 is a cross-sectional view of a prior art mechanism in the closed position. 
     FIG. 2 is a top perspective view of a circuit breaker in accordance with the present invention. 
     FIG. 3 is a front plan view of the elements of the present invention as illustrated in FIG. 2 in the CLOSED position. 
     FIG. 4 is a front plan view of the elements of the present invention as illustrated in FIG. 2 in the OPEN position. 
     FIG. 5 is a front plan view of the elements of the present invention as illustrated in FIG. 2 in the TRIPPED position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG.  2 ,the circuit breaker  10  in accordance with the present invention is comprised of a base  22  and a cover  24 . Enclosed within the base  22  and cover  24  are four poles  14 C,  14 L,  14 R,  14 N each corresponding to a respective phase in an electrical circuit. Each pole  14 C,  14 L,  14 R,  14 N contains a rotary contact assembly  16 C,  16 L,  16 R and  16 N respectively, capable of carrying and interrupting electrical current. A drive shaft  18  connects the four poles  14 C,  14 L,  14 R,  16 N. 
     In addition, the center pole  14 C is straddled by a mechanism assembly  12 . The mechanism  12  connects to the poles  14 C,  14 L,  14 R by the drive shaft  18 . The poles  14 C,  14 L,  14 R are operable to move between three positions open, closed, or tripped in response to operation of the mechanism  12 . 
     As is seen in FIG. 3, each pole  14  is made up of a rotor  60  housing a contact arm  26 , and a pair of movable contacts are  28 ,  28 ′. The movable contacts  28 , 28 ′ mate with the pair of stationary contacts  30 ,  30 ′ when the mechanism is in the CLOSED position shown. The stationary contacts  30 ,  30 ′ are brazed or welded to a load strap  32  and line strap  34  respectively. The rotor  60  pivots on a pin  59  which is either supported by an internal wall (not shown), or a modular cassette (not shown) within the base  22 . The crank  62  connects the mechanism  12  to the rotor assembly  16 C. The crank  62  pivots about the pin  61  which is assembled on the side frames  13 . It should be appreciated that the rotor assemblies  16 R,  16 L,  16 N may be identical to rotor assembly  16 C. The operation of the rotor assembly  16 C operates substantially the same as that described in co-pending U.S. patent application Ser. No. 09/087,038 filed May 29, 1998 which is incorporated herein by reference. 
     Mechanism  12  consists of a lower link  38  connected to the crank  62  by connector pin  39 . The opposite end of the lower link  38  from the crank is connected to an upper link  40  by a spring spindle  48 . The upper link  40  in turn is connected to cradle  42  by pin  56 , to which is attached to a latch mechanism (not shown). The mechanism spring  50  is connected between the spring spindle  48  and a pin  52  in handle  46 . The mechanism  12  is prevented from further counter-clockwise rotation when the pin  58  attached to the upper link  40  comes into contact with the cradle  42 . 
     The amount of torque that can be generated by the mechanism  12  is determined by the amount force F transferred from mechanism spring  50  through the lower link  38  and the moment arm. The moment arm is shown in FIG. 3 as the perpendicular distance d. The perpendicular distance d is the length of a perpendicular line from the crank pivot  61  to the line of action of the force F. Since torque is the product of the force F times the distance d, it should be apparent that for a given mechanism, the greater the distance d the more torque is generated. This distance d and thus the torque will be maximized when the distance d is coincident with the connecting pin  39 . In the present invention, the pin  39  only connects the lower link  38  to the crank  62 . It should be noted that in prior art mechanisms, the pin  39  was also the drive pin that extended through and connected all the rotors. 
     The components of the rotor assembly  16 C often do not allow the drive pin to be placed in this optimal position. For example, as seen in FIG. 3, if the pin  39  is used as the drive shaft to connect all the rotor assemblies, then it would need to pass directly through the contact arm  26 . Thus, if an optimized mechanism arrangement is desired, the lower link  38  needs to be decoupled from the drive shaft and the rotor assembly  16 C. The present invention accomplishes this by attaching the lower link  38  to a crank  62  which in turn transmits the force to the drive shaft  18 . The drive shaft  18  can then be positioned anywhere on the rotor without effecting the amount of torque the mechanism can create. By using the crank  62 , either the rotor assembly  16 C, or the mechanism assembly  12  may be optimized without compromising the performance of the other, thus allowing for the maximum amount of flexibility in the design of the circuit breaker while still maintaining optimized subassemblies. 
     Referring to FIG. 4, under normal switching operation, the handle  46 , is rotated counter-clockwise to switch the circuit breaker  10  from ON to OFF. As the handle  46  is rotated, the line-of-action of the spring  50  will move from the right side to the left side of the pivot  56 . This movement “over-centers ” the mechanism  12  and the force stored in the spring causes the mechanism  12  to open the rotor assemblies  16 C,  16 R,  16 L,  16 N. This opening movement separates the movable contacts  28 ,  28 ′ from the stationary contacts  30 ,  30 ′ thereby preventing any flow of current through the circuit breaker  10 . 
     When an abnormal condition is detected by a circuit breaker trip unit (not shown), the latching mechanism (not shown) is released allowing the cradle  42  to rotate in a clockwise direction. The latch and trip unit are similar to U.S. Pat. No. 4,789,848 which is incorporated herein by reference. The resulting movement of the cradle  42  causes the rotor assembly  16 C via the upper link  40  and the lower link  38  to rotate separating the movable contacts  28 , 28 ′ from the stationary contacts  30 , 30 ′. The separation of the contacts stops the flow of current through the circuit breaker  10 . 
     It should be appreciated that large loads are applied to the drive shaft  18  by the mechanism  12  and the rotor assemblies  16 C,  16 L,  16 R,  16 N when the circuit breaker  10  is in the closed position. These loads tend to either deflect the drive shaft  18 , or twist the rotor assemblies  16 C,  16 L,  16 R,  16 N. This deflection of the shaft  18  tends to greatly reduce the either the contact depression, or the contact pressure between the stationary contact  30 ,  30 ′ and the moveable contacts  28 ,  28  resulting lower than expected performance. To compensate, or correct this bending, a second shaft  19  is added to provide the additional strength. 
     Referring to FIGS. 2 and 3, shaft  19  is similar to drive shaft  18  in that it extends through and rotationally connects rotor assemblies  16 C,  16 L,  16 R, and  16 N. However, shaft  19  is not connected to the crank  62  which allows it to be connected to the rotor assemblies  16 C,  16 L,  16 R,  16 N in any convenient location without effecting the optimal crank loading described herein above. Even though the shaft  19  is not attached to the crank  62 , significantly greater contact depression has been observed. For example, when the contact depression was measured on a 480V, 600 A industrial circuit breaker, the contact depression with the shaft  19  added was as much as 75% greater in the extreme outer pole  14 N than that with only the drive shaft  18 . 
     Although a preferred embodiment of this invention has been described, many variations and modifications will now be apparent to those skilled in the art, and it is therefore preferred that the instant invention be limited not by the specific disclosure herein but only by the following claims.