CURRENT LIMITING CIRCUIT BREAKER OPERATING MECHANISM INCLUDING LATCHING SYSTEM

Abstract: A circuit breaker includes a stationary contact, a moveable contact, and a blade having the moveable contact attached thereto, the blade being rotatable about a pivot between an OPEN position and an CLOSED position. The moveable contact engages the stationary contact when the blade in the CLOSED position and the circuit breaker is in the ON position. An operating mechanism moves the blade between the OPEN position and the CLOSED position. The operating mechanism includes a frame and a latching system. The latching system includes a cradle having a projection and pivotally coupled to the frame, wherein the cradle is linked to the blade to move the blade to the OPEN position. The latching system also includes a latch pivotally coupled to the frame. The latch has a main latch surface and a latch engagement protuberance. The main latch surface provides for overlapping engagement of the cradle projection when the circuit breaker is in the ON and NON-TRIPPED position. The latch engagement protuberance is biased into an engaged position with the cradle projection when the circuit breaker is in the ON and NON-TRIPPED position and the latch engagement protuberance controls degree of engagement between the main latch surface and the cradle projection. A spring biases the main latch surface in overlapping engagement of the cradle projection.

Description: CURRENT LIMITING CIRCUIT BREAKER OPERATING MECHANISM INCLUDING LATCHING SYSTEM BACKGROUND OF THE INVENTION Field of the Invention The present invention is directed, in general, to current limiting circuit breaker operating mechanisms and, more specifically to latching systems in the operating mechanisms. Description of the Related Art Current limiting circuit breakers are well known in the prior art. Examples of such circuit breakers are disclosed in U.S. Patent Nos. 5,416,291 and 5,633,483 which are assigned to the same assignee as the present application, and which are hereby incorporated by reference. Basically, a current limiting circuit breaker comprises a base and a cover, a stationary contact, a moveable contact secured to a rotatable blade, an interrupting chamber, an operating mechanism for opening and closing the contacts, and a trip unit which releases the operating mechanism when a predetermined amount of current is exceeded. Molded case current limiting circuit breakers have, in the past, typically been large, labor intensive, part intensive devices that had several areas of part limitations. These circuit breakers provide moveable contact arrangements coupled to operating mechanisms that open the circuit at high level short circuits. This is accomplished through the use of thermally responsive tripping elements, and parallel conductor blow open designs. A need therefore, exists for continuing improvement of circuit breaker designs requiring fewer parts, more reliability, easier assembling, and compact design. The circuit breaker of the present invention provides a latching system in an operating mechanism having fewer parts to assemble than prior circuit breaker designs allowing for easier assembly and consistent manufacturing. The latching system of the present invention is also simpler and more reliable in use than prior circuit breaker designs. SUMMARY OF THE INVENTION A circuit breaker is disclosed including a stationary contact, a moveable contact, and a blade having the moveable contact attached thereto, the blade being rotatable about a pivot between an OPEN position and an CLOSED position. The moveable contact engages the stationary contact when the blade in the CLOSED position and the circuit breaker is in the ON position. An operating mechanism moves the blade between the OPEN position and the CLOSED position. The operating mechanism includes a frame and a latching system. The latching system includes a cradle having a projection and pivotally coupled to the frame, wherein the cradle is linked to the blade to move the blade to the OPEN position. The latching system also includes a latch pivotally coupled to the frame. The latch has a main latch surface and a latch engagement protuberance. The main latch surface provides for overlapping engagement of the cradle projection when the circuit breaker is in the ON and NON-TRIPPED positions. The latch engagement protuberance is biased into an engaged position with the cradle projection when the circuit breaker is in the ON and NON-TRIPPED positions, and the latch engagement protuberance controls degree of engagement between the main latch surface and the cradle projection. A spring biases the main latch surface in overlapping engagement of the cradle projection. The cradle is linked to the blade, for example, by a first link, which has a first end, and a second end, wherein the first end is pivotally coupled to the cradle. The first link is coupled to a second link, which has a first end, and a second end, wherein the first end of the second link is pivotally coupled to the second end of the first link. The second link is coupled to a third link having a middle portion between a first end and a second end, wherein the middle portion is pivotally coupled to the frame, the first end of the third link is pivotally coupled to the second end of the second link, and the second end of the third link is coupled to the blade to move the blade to the OPEN position. BRIEF DESCRIPTION OF THE DRAWINGS The present invention may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings. Figure 1 is a perspective view of a three-pole current limiting circuit breaker constructed in accordance with the present invention; Figure 2 is a longitudinal sectional view of the current limiting circuit breaker of Figure 1 , taken generally along the line 2-2 of Figure 1 and showing a center pole thereof with parts in an ON/CLOSED position; Figure 3 is side cross sectional views of the operating mechanism of the current limiting circuit breaker of Figure 2 in an ON/CLOSED position; Figure 4 is side cross sectional views of the operating mechanism of the current limiting circuit breaker of Figure 2 in an OFF and NON-TRIPPED position; Figure 5 is side cross sectional views of the operating mechanism of the current limiting circuit breaker of Figure 2 in a TRIPPED/OPEN position; Figure 6A is a perspective view of the latching system of mechanism of Figure 2; and Figure 6B is a side view of the latching system of Figure 6A. The use of the same reference symbols in different drawings indicates similar or identical items. DESCRIPTION OF THE PREFERRED EMBODIMENT(S) For exemplary purposes, the present invention is illustrated and described with respect to a three-pole circuit breaker, although the circuit breaker latching system of the present invention is equally applicable to circuit breakers of a different number of poles. The circuit breaker disclosed in the present application is designed for a top down assembly in which all of the parts are inserted in a circuit breaker base from the top and are secured to the base by threading screws into threaded inserts that are molded into the base. Referring to Figure 1, a circuit breaker 10 is shown having a base 12, cover 14, shroud 11 , trim cover 16, access cover 17, escutcheon 15, and operating handle 18, all preferably made of molded insulating material. The cover 14 secures the circuit breaker components in the base 12 and the cover 14 is secured in place from the top using screws. Referring now to Figure 2, an interrupter assembly is illustrated for the circuit breaker 10 including a handle arm 61, a blade 20, a blade stop 32, a moveable contact 26, a stationary contact 28, an arc runner 30, an over-molded magnet 34, an arc stack 36, a baffle stack 38, a chamber liner 40, and a current path 42. The current path 42 is shown running along the bottom of the base 12 and then bending into a generally U-shape around the bottom portion of an over-molded magnet 34 having a stationary contact 28 secured thereto using a typical securing method. The over-molded magnet 34 comprises a plurality of steel plates grouped together and being over molded with thermoplastic. The over-molded magnet 34 physically surrounds the blade 20, the blade stop 32, the stationary and moveable contacts 28 and 26, respectively, a portion of the current path 42, and the arc runner 30. An insulator 190 is placed between the current path 42 and the over-molded magnet 34. An arc runner 30 is secured between the over-molded magnet 34 and the current path 42. The arc runner 30 is automatically connected to the current path 42 at the time of assembly without a brazing or welding operation and requires no added fasteners to effect the electrical connection. A T-shaped insulator 191 is placed above the current path 42 and generally adjacent to the stationary contact 28. Moveable contact 26 is secured to the blade 20. The moveable contact 26 engages the stationary contact 28, which is secured to the upper portion of the current path 42, when the circuit breaker is in the ON position and the blade 20 is in the CLOSED position. In the operating mechanism 50 of the present invention, a roller latch, as taught by U.S. Patent Nos. 5,416,291 and 5,633,483 which is assigned to the assignee of the present application and has been incorporated herewith by reference, has been eliminated. The roller latch of the prior circuit breaker designs is very difficult to manufacture and assemble, and is unreliable when used. The latching system of the present invention provides a more reliable and easier assembling circuit breaker design. The operating mechanism 50, as illustrated in Figures 3, 4, and 5, is shown including a ' pair of upper toggle links 52, a pair of lower toggle links 54, a pair of bell cranks 56, a cradle 58, a main latch 62, a pair of tension springs 66 (shown in phantom lines), a blade catcher 70, and a torsion spring 72 positioned between two mechanism sides 53 (only one side is shown). The latching system of the present invention, illustrated in greater detail in Figures 6A and 613, includes a main latch surface 63 for overlapping engagement of a cradle projection 102 on the cradle 5 8 when the circuit breaker 10 is in the ON and NON- TRIPPED positions. The main latch 62 also includes a latch engagement protuberance 100 biased into an engaged position with the cradle projection 102 when the circuit breaker 10 is in the ON and NON-TRIPPED positions and wherein the latch engagement protuberance 100 controls the degree of engagement between the main latch surface 63 and the cradle projection 102. The upper ends of the upper toggle links 52 are pivotally connected to the cradle 58 with pivot pin 78. The lower portions of the upper toggle links 52 are pivotally connected to the upper portion of the lower toggle links 54 with toggle pin 79. Lower portions of lower toggle links 54 are pivotally connected to the lower ends of boomerang shaped bell cranks 56 at pivot pin 55 that is attached to corresponding bell crank 56. The upper ends of the bell cranks 56 have cramming pins 59 that attached thereto that cooperate with a beil crank drive pin slot 67 in the frame sides 53 and engage a positioning slot in the blade carrier 70. The middle of the bell cranks is pivotally mounted about a catcher pivot pin 51 , which is secured to the frame sides 53. The cradle 58 rotates about a cradle pivot pin 60 that is secured to the frame sides 53 at one end. The middle of the main latch 62 is rotatably mounted to the frame sides 53 with main latch pivot pin 75. The main latch surface 63 provides for overlapping engagement of the cradle projection 102 on the cradle 58 when the circuit breaker 10 is in the ON and NON-TRIPPED positions as shown in Figures 3 and 4. The latch engagement protuberance 100 on the main latch 62 is biased into an engaged position with the cradle projection 102 when the circuit breaker 10 is in the ON and NON- TRIPPED positions. The latch engagement protuberance 100 controls the degree of engagement between the main latch surface 63 and the cradle projection 102 and provides consistent engagement between the main latch surface 63 and the cradle projection 102. The main latch 62 includes a torsion spring 104 providing a force on the main latch 62 and for biasing the main latch surface 63 for overlapping engagement of a cradle projection 102. A nub surface 65 is formed at an end of the main latch 62 for cooperating with the trip unit 80 hammer. A blade cross bar 76 is connected to the blade carrier 70 of all three poles to cause all three blade carriers 70 to move simultaneously in response to the opening or closing of the operating mechanism 50. When the operating handle 18 is in the ON/CLOSED position the operating mechanism 50 parts are in position as shown in Figure 3. The upper and lower links 52 and 54 respectively, are in the overcenter position as shown and having tension springs 66 supplying an upward tension on toggle pin 79. The spring force that is applied to toggle pin 79 is transferred to the cradle 58, through the upper toggle links 52, forcing the cradle projection 102 to engage latching surface 63 and maintain the operating mechanism 50 in the ON/CLOSED position. Figure 4 illustrates the operating mechanism 50 when the operating handle is in the OFF and NON-TRIPPED position. As illustrated the main latch surface 63 and the latch engagement protuberance 100 on the main latch 62 are biased into an engaged position with the cradle projection 102. Figure 5 illustrates the operating mechanism 50 in a TRIPPED position. When the trip unit 80 senses an overcurrent or fault condition it releases the hammer (not shown) which in turn strikes the nub surface 65 on the main latch 62 wherein the main latch 62 rotates about the main latch pivot pin 75 causing the latch engagement protuberance 100 and the latch surface 63 to disengage from the cradle projection 102. The tension from the tension springs 66 forces the cradle 58 to swing upward pulling upper toggle links 52 upward. As a result, the upper toggle links 52 and lower toggle links 54 bend at their common point at toggle pin 79, thereby resulting in the upper toggle links 52 pulling the lower toggle links 54 upward which in turn rotates the bell cranks 56 about catcher-pivot pin 51. The upper end of bell cranks 56 translates into the positioning slot 71, as shown in Figure 5, forcing the blade carrier 70 to rotate about the blade pivot 74 and separate the moveable and stationary contacts 26 and 28, respectively. The trip unit 80 (shown in Figure 2) is illustrated enclosed in a molded plastic trip unit housing and is, for example, a thermally responsive magnetic trip unit including an adjustable magnetic tripping range, a bimetal thermal portion, and a tripping mechanism having a hammer for striking the main latch 62 nub surface 65. The trip unit 80 is, for example, the trip unit as taught by U.S. Patent Nos. 5,416,291 and 5,633,483 which is assigned to the assignee of the present application and has been incorporated herewith by reference. The circuit breaker of the present invention provides a latching system in an operating mechanism having fewer parts to assemble than prior circuit breaker designs providing for easier assembly and consistent manufacturing. The latching system of the present invention, including the cradle projection, main latch surface and latch engagement protuberance, is also simpler and more reliable in use than prior circuit breaker designs, such as those designs including a roller latch in addition to a main latch. While preferred embodiments have 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 illustrations and not limitations.

Claims: WHAT IS CLAIMED IS: 1. A circuit breaker comprising: a stationary contact; a moveable contact; a blade having the moveable contact attached thereto, the blade being rotatable about a pivot between an OPEN position and a CLOSED position, wherein the moveable contact engages the stationary contact when the blade in the CLOSED position and the circuit breaker is in an ON position; and an operating mechanism for moving the blade between the OPEN position and the CLOSED position, the operating mechanism including; a frame; a cradle having a projection and pivotally coupled to the frame and wherein the cradle is linked to the blade to move the blade to the OPEN position; and a latch pivotally coupled to the frame, the latch including; a main latch surface for overlapping engagement of the cradle projection when the circuit breaker is in the ON and NON- TRIPPED position; and a latch engagement protuberance biased into an engaged position with the cradle projection when the circuit breaker is in the ON and NON-TRIPPED position and wherein the latch engagement protuberance controls degree of engagement between the main latch surface and the cradle projection. 2. A circuit breaker, as recited in claim 1 , further comprising: a spring for biasing the main latch surface in overlapping engagement of the cradle projection. 3 A circuit breaker, as recited in claim 1 , wherein the linking of the cradle to the blade further comprises: a first link having a first end and a second end, the first end pivotally coupled to the cradle; a second link having a first end and a second end, the first end of the second link pivotally coupled to the second end of the first link; and a third link having a middle portion between a first end and a second end, the middle portion pivotally coupled to the frame, the first end of the third link pivotally coupled to the second end of the second link, and the second end of the third link coupled to the blade to move the blade to the OPEN position. 4. A latching system for use in an operating mechanism of a circuit breaker, wherein the operating mechanism includes a frame and a cradle pivotally coupled to the frame, and wherein the cradle is linked to a blade for moving the blade from a CLOSED position to an OPEN position, the latching system comprising: a latch pivotally coupled to the frame, the latch including; a main latch surface for overlapping engagement of a projection on the cradle when the circuit breaker is in the ON and NON-TRIPPED position; and a latch engagement protuberance biased into an engaged position with the projection on the cradle when the circuit breaker is in the ON and NON-TRIPPED position and wherein the latch engagement protuberance controls degree of engagement between the main latch surface and the projection on the cradle. 5. A latching system, as recited in claim 4, further comprising: a spring for biasing the main latch surface in overlapping engagement of the projection on the cradle. 6. A latching system, as recited in claim 4, further comprising: a stationary contact; a moveable contact; and wherein the moveable contact is attached to the blade, the blade being rotatable about a pivot between an OPEN position and a CLOSED position and wherein the moveable contact engages the stationary contact when the blade in the CLOSED position. 7. A circuit breaker comprising: a stationary contact; a moveable contact; a blade having the moveable contact attached thereto, the blade being rotatable about a pivot between an OPEN position and a CLOSED position, wherein the moveable contact engages the stationary contact when the blade in the CLOSED position and the circuit breaker is in the ON position; and an operating mechanism for moving the blade between the OPEN position and the CLOSED position, the operating mechanism including; a frame; a cradle having a projection and pivotally coupled to the frame and wherein the cradle is linked to the blade to move the blade to the OPEN position; and a latch pivotally coupled to the frame, the latch including; a main latch surface for overlapping engagement of the cradle projection when the circuit breaker is in the ON and NON- TRIPPED position; and a latch engagement protuberance biased into an engaged position with the cradle projection when the circuit breaker is in the ON and NON-TRIPPED position and wherein the latch engagement protuberance controls degree of engagement between the main latch surface and the cradle projection; and a spring for biasing the main latch surface in overlapping engagement of the cradle projection.

Inventors: GREEN KEVIN J, POWELL RODNEY G, SPANIER ERIC M, WONG TAK MAN, GREEN, KEVIN, J., POWELL, RODNEY, G., SPANIER, ERIC, M., WONG, TAK, MAN
Applicants: SQUARE D CO, SQUARE D COMPANY
Application year: 1999
Main classification: H01H71
IPC codes: H01H71