Trip cross bar and trip armature assembly for a circuit breaker

FIELD OF THE INVENTION

This invention is directed generally to circuit breakers, and more specifically, to the trip cross bar and the trip armature assembly components required to operate the tripping mechanism of a circuit breaker.

BACKGROUND OF THE INVENTION

Circuit breakers are well-known and commonly used to provide automatic circuit interruption to a monitored circuit when undesired overcurrent conditions occur. Some of these overcurrent conditions include, but are not limited to, overload conditions, ground faults, and short-circuit conditions. The current interruption is usually achieved by having a movable contact, which is attached to a movable blade, that separates from a stationary contact, which is attached to a stationary arm or blade. A tripping mechanism is the component that drives the tripping action using, in general, a spring-biased latch mechanism to force the movable blade, and therefore the movable contact, away from the stationary contact.

A part of the tripping mechanism is the trip cross bar that is used as a means to activate a blade mechanism, which automatically moves the movable blade to an open position. The trip cross bar is generally mounted on a frame that is connected directly or indirectly to the circuit breaker housing. For example, in a prior art circuit breaker the trip cross bar must first be riveted to a latch and only then it is possible to attach the trip cross bar to a supporting fitting. Once attached to the supporting fitting the trip cross bar is rotatably supported by a supporting pin which is held in place by the supporting fitting and a side plate of a switch mechanism. A need exists for an improved circuit breaker design that requires fewer parts, is easier to assemble, and is compact in design. Given the position of the trip cross bar in the circuit breaker, the trip cross bar design may affect how other components of the circuit breaker are assembled and, also, how other components are shaped and dimensioned. In particular, space is needed inside the circuit breaker to assemble the various components of the circuit breaker, and the trip cross bar gets in the way.

It is, therefore, an object of this invention to provide easy assembly of a circuit breaker by providing a trip cross bar that is the last component to be assembled, using a top-down assembly method.

One type of tripping mechanism used in a circuit breaker is a thermal tripping unit. When the current reaches a predetermined value, which is generally based on a percentage of the rated current for a period of time, the tripping unit is activated. The tripping unit passes the current through and thereby heats a bimetal, hence, causing the bimetal to bend. As a result, the bimetal, now bent, contacts and activates the trip cross bar. The current also passes through a magnetic trip armature which causes it to rotate into engagement with a magnetized pole, activating the trip cross bar. The trip cross bar, when activated, causes a latch mechanism to rotate on movable blade away from the stationary contact. The end result is that the circuit breaker is in a tripped position, opening the circuit. However, an improved manner of connecting the magnetic trip armature to the armature supporting frame permits the development of a smaller, more efficient, and more economical circuit breaker.

It is, therefore, another object of this invention to provide a magnetic trip armature that can be easily and simply connected to an armature return spring and to an armature supporting frame. This is accomplished by having the magnetic trip armature snap into the armature supporting frame and by being held secure in all orientations by the armature return spring, using a top down assembly wherein late point assembly allows other parts to be placed in the circuit breaker without interference.

SUMMARY OF THE INVENTION

Briefly, in accordance with the foregoing, a circuit breaker for interrupting the flow of current upon the detection of excess current or temperature is provided which comprises a housing, a trip armature plate, a trip armature frame, and a bias spring. The trip armature plate has at least two pivot tabs extending laterally on opposite edges that are inserted into a pivot elongated slot, which is located at an open end of the trip armature frame, and a pivot aperture, which is located at the opposite end of the trip armature frame, respectively. A bias spring is used for securing the pivot tabs into the pivot elongated slot and the pivot aperture, and for urging the trip armature plate pivotably outwardly about the pivot tabs away from the trip armature frame.

Additionally, a trip cross bar is provided in the circuit breaker. The trip cross bar can have, optionally, two fingers that are used to engage optional circuit breaker accessories and that are located asymmetrically to allow the interchangeability of the accessories. During top down assembly, the trip cross bar is the last component that is assembled into the circuit breaker in order to allow the easy installation of other components, including the trip armature frame and trip armature plate. The connecting location of the trip cross bar is in a central position for allowing actuation of the trip cross bar by a central, left, or right bimetal.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1

is a cross-sectional view of a circuit breaker embodying the present invention, shown in the closed position,

FIG. 2

is a cross-sectional view of the circuit breaker of

FIG. 1

, shown in the open position,

FIG. 3

is a cross-sectional view of the circuit breaker of

FIG. 1

, shown in the blown-open position,

FIG. 4

is a cross-sectional view of the circuit breaker of

FIG. 1

, shown in the tripped position,

FIG. 5

is a perspective exploded view of the trip cross bar assembly in the circuit breaker of

FIG. 1

, and

FIG. 6

is a perspective view showing the components of the magnetic trip armature assembly.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Turning now to the drawings, and referring initially to

FIGS. 1

,

2

,

3

, and

4

, a circuit breaker

1

is shown in the “closed,” “open,” “blown-open,” and “tripped” positions, respectively. The circuit breaker

1

contains, generally, a tripping mechanism

3

, a handle mechanism

5

, a blade mechanism

7

, and an arc-extinguishing mechanism

9

.

More specifically, when the circuit breaker

1

is in the “closed” position, as shown in

FIG. 1

, a movable contact

11

attached to a blade

13

, which in turn is part of the blade mechanism

7

, engages a stationary contact

15

. The connection that occurs between the movable contact

11

and the stationary contact

15

results in normal operation of the electrical system to which the circuit breaker

1

is connected. A handle

17

is a part of the handle mechanism

5

and protrudes through the circuit breaker's housing for manually resetting the circuit breaker

1

. The handle

17

can also serve as a visual indication of the status of the circuit breaker

1

. In the “closed” position, see

FIG. 1

, the handle

17

is shown at the closed edge

19

of a handle slot, which is at the counterclockwise end of the handle slot as viewed in FIG.

1

. Also, a trip cross bar

21

, which is part of the tripping mechanism

3

, is shown in its untripped position having the long surface of a finger

47

positioned horizontally.

The “open” position is a manually controlled position that allows an operator of circuit breaker

1

to interrupt the flow of current by separating the movable contact

11

from the stationary contact

15

. The operator moves the handle

17

to the most clockwise position, as shown in FIG.

2

. In this position the blade

13

swings in a clockwise direction so that the movable contact

11

is spaced well away from the stationary contact

15

. The trip cross bar

21

remains unchanged from its closed position.

In the “blown-open” position, shown in

FIG. 3

, an electric current that has a higher value than the preset acceptable threshold by a certain percentage, i.e., 35%, produces electromagnetic forces which are high enough to overcome pre-applied forces on the blade

13

. This causes the blade

13

to swing across the arc-extinguishing mechanism

9

to the maximum clockwise position of the blade

13

. In this position the blade housing

22

and trip cross bar

21

remain in the same position as in the “closed” and “open” positions. Similarly, the handle

17

remains in the same position as in the “closed” position.

The “tripped” position is caused by the presence of a higher current than the assigned current for the circuit breaker

1

over a specified period of time. The exposure of the circuit breaker

1

to a longer period of high current activates the tripping mechanism

3

that, as shown in

FIG. 4

, causes the blade

13

and the blade housing

22

to swing across the arc-extinguishing mechanism

9

in the clockwise direction, as viewed in

FIG. 4

, and therefore interrupt the current flow. The handle

17

remains in an intermediate position between the “closed” and “open” positions, wherein the operator must reset the circuit breaker

1

by first moving the handle

17

to its “open” position before moving the handle

17

to its “closed” position. In this position the trip cross bar

21

is shown in its activated state.

One aspect of the invention is the trip cross bar

21

, which is more clearly shown in FIG.

5

. The trip cross bar

21

is a molded plastic part that is separated into three segments, which are integrated into one single part. A middle segment

23

acts as a bridge between a left segment

25

and a right segment

27

, being connected to each segment by a semicircular rod

29

. The middle segment

23

is molded, generally, in the shape of a rectangular cube, with various cuts and notches that will be explained below. Centered with respect to both the long and the narrow dimensions, along the top surface, the middle segment

23

has a drilled-through counterbored hole. A screw

31

is used to secure the trip cross bar

21

to a latch

33

by inserting the screw

31

through the counterbored hole of the middle segment

23

and threading the screw

31

into a threaded hole in the latch.

Two identical latch slots

35

are cut into the bottom of the middle segment

23

of the trip cross bar

21

to allow the mating of the latch main body

37

with the middle segment

23

. Specifically, the latch slots

35

of the middle segment

23

fit over mating walls on the latch main body

37

. Also on the bottom of the middle segment

23

, two major circular slots are cut to accommodate the curved vertical frame ends

39

, and two minor circular slots are cut to accommodate the pin ends

41

of the supporting pin

42

. Plastic material is molded to the middle segment

23

next to each semicircular rod

29

in order to engulf most of the metal area near the curved ends

39

of the frame

43

. Furthermore, the semicircular rods

29

, which are formed on both sides of the middle segment

23

, serve as a lock to prevent the supporting pin

42

from sliding out of the frame

43

.

Although the trip cross bar

21

is allowed to rotate around the supporting pin

42

, a stop tab

45

is formed on the left side of the middle segment

23

to engage the flat metal edge of the frame

43

that continues from the curved frame end

39

. Alternatively, the stop tab

45

can also be formed on the right side of the middle segment

23

.

The segments

25

and

27

are identical in shape, having a generally V-shaped profile that continues throughout the entire segment length. A finger

47

is formed on the bottom side of each segment

25

and

27

for activating the blade mechanism

7

. Each finger

47

has an L-shaped profile with the activating side

49

being longer than finger-connecting side

51

. The segment

27

is connected to the middle segment

23

on the finger

47

side, while the segment

25

is connected to the middle segment

23

on the side opposite where the finger

47

is located, thus giving a non-symmetrical shape to the trip cross bar

21

. When enough heat is generated in the circuit breaker

1

, i.e., a temperature above a predetermined threshold temperature that is considered adequate for the normal operation of the circuit breaker

1

, a bimetal (not shown) bends and engages and pivots the trip cross bar

21

. The handle mechanism

5

and the blade mechanism

7

are both affected by the pivoting motion of the trip cross bar

21

which rotates slightly in a counterclockwise direction, as viewed in FIG.

4

. The handle

17

resumes its “tripped” position, and the movable contact

11

separates from the stationary contact

15

, thereby interrupting the flow of electric current in the electrical system controlled by circuit breaker

1

.

Using top down assembly, the trip cross bar

21

is the last component to be installed by securing it with only one screw

31

to the latch

33

, which can be preassembled to the frame

43

by using the supporting pin

42

. Because the trip cross bar

21

is the last component to be installed, this invention allows other components to be installed when assembly in tight spaces is required. This is particularly useful in the assembly of circuit breakers that have a relatively small size. The size and shape of the trip cross bar

21

allows its easy insertion after all components have been installed, and with the use of a simple tool, such as a screwdriver, it can be securely attached to the frame

43

by using the screw

31

. Furthermore, given the simplicity of this assembly method, automated assembly is facilitated.

Another aspect of the invention involves the tripping mechanism

3

and, more specifically, one of its components, namely, a magnetic trip armature

53

, which is shown in FIG.

6

. The trip armature

53

is connected to an armature frame

55

in three locations that allow an easy assembly and securing method. The first connecting location is a pivoting projection

57

that is located on the pivoting side

59

of the trip armature

53

. Although pivoting projection

57

constrains translational motion of the pivoting side

59

, it allows rotational motion of the trip armature

53

. The dimensions of the projection

57

are small enough to allow its insertion into a mating pivoting hole

63

in the armature frame

55

. Located next to the pivoting projection

57

is a rectangular stop protrusion

65

, which abuts a stop surface

67

on the armature frame

55

to prevent the trip armature

53

from rotating in the clockwise direction.

The second connecting location is a constraining protrusion

69

that is located opposite the pivoting projection

57

on the trip armature

53

, and that is similar in size and shape to the pivoting projection

57

. The constraining protrusion

69

is slipped into a armature slot

71

in the armature frame

55

during assembly in order to constrain translation motion of the trip armature

53

in a horizontal direction and in a downward direction, away from the return spring

73

.

The third connecting location is provided by a spring arm

75

that has a first end

77

near the constraining protrusion

69

, and that extends upward, away from the main body of trip armature

53

, in an inverted L-shaped configuration. A second end

79

, forming the short, bottom end of the inverted L-shaped configuration, has a small spring notch

81

on the side farthest away from the main body of the trip armature

53

for accommodating a return spring

73

. Hooking one end of the return spring

73

into the spring notch

81

prevents the trip armature

53

from sliding out of the armature slot

71

, while allowing the trip armature

53

to function rotationally as required by the tripping mechanism

3

.

When the current is higher than the preset current level of the circuit breaker

1

and the current intensity is sustained over a specified period of time, an electromagnetic force is generated that allows a magnetized pole (not shown) to attract a main armature surface

83

causing it to rotate in a counterclockwise direction as viewed in FIG.

1

. The electromagnetic force is strong enough to overcome the force applied by the return spring

73

on the trip armature

53

and, therefore, to cause the spring arm

75

to engage the trip cross bar

21

which, in turn, actuates the handle mechanism

5

and the blade mechanism

7

. The end result is that the handle

17

responds by moving to the “tripped” position and the movable contact

11

separates from the stationary contact

15

, thereby interrupting the flow of electric current.

While particular embodiments and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and compositions disclosed herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.