Information
-
Patent Grant
-
6232860
-
Patent Number
6,232,860
-
Date Filed
Friday, June 23, 200024 years ago
-
Date Issued
Tuesday, May 15, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Cantor Colburn LLP
- Horton; Carl B.
-
CPC
-
US Classifications
-
International Classifications
-
Abstract
A latching system for a circuit breaker is arranged to actuate a trip unit and interrupt circuit current upon occurrence of a short circuit or an overcurrent condition. The latching system employs an armature having a recess formed therein and a cradle having a cradle tip arranged to releasably engage the recess. A thermal magnetic trip unit is depicted within the circuit breaker for the purposes of detecting overcurrent conditions through the electric path. During current transport through the circuit breaker, the current is thermally sensed by means of the bimetal and magnetically sensed by means of the magnet. The armature rotates against the return bias of a compression spring to release the cradle tip from the recess and allow counterclockwise rotation of the contact arm. The rotation of the contact arm causes the separation of the movable and fixed contacts under the urgence of a mechanism spring.
Description
BACKGROUND OF THE INVENTION
This invention relates to circuit breaker assemblies with a thermal magnetic trip unit and, more particularly, to circuit breakers utilizing an armature for latching a thermal magnetic trip unit.
Residential circuit breakers are described in U.S. Pat. No. 4,513,268 entitled “Automated Q-Line Circuit Breaker”. The circuit breaker includes a thermalmagnetic trip unit that interrupts the circuit current upon occasion of so-called “instantaneous”, “short time” and “long time” overcurrent conditions. The thermal response of the trip unit is provided by means of an extended bimetal, which is part of the circuit breaker internal current-carrying components, and is separate from the magnet that provides the trip unit magnetic response. The bimetal, in a sense, forms the primary winding of a current transformer with the magnet acting as the transformer core. A separately arranged armature unit responds to the magnetic flux generated by the magnet upon the occurrence of intense overcurrent faults to release the circuit breaker operating mechanism and thereby interrupt the circuit current.
U.S. Pat. No. 4,698,903, entitled “Circuit Breaker High Speed Assembly”, describes a drawback to efficient high speed circuit breaker manufacture. Such a drawback is the time-consuming polishing process required on the latching surfaces. The polishing is required to minimize the amount of tripping force that must be applied to overcome the bias of the operating spring and the static friction of the latch surfaces. Although the polishing can be done in a separate pre-assembly process without affecting the actual circuit breaker assembly operation, the trip force required to overcome the mechanism spring bias and the latch surface friction depends to a certain extent upon the polishing operation. The latch surfaces are fabricated from stamped metal parts which exhibit a rough burr on the edge of one surface and a smooth die roll on the edge of the opposite surface. In the prior art, an opening through the stamped part is formed during the stamping operations. Thus, a die break is produced when the slug pushes into the die during the stamping operation and can tear the work material and consequently produce a rough surface. A rough surface is not suitable for latching as it leads to unpredictable performance between the latching surfaces and is a high friction area. Further, high friction does not lend itself to permit smooth and quick disengagement of the latched part from the latch surface.
In an attempt to reduce the primary latch friction, without requiring either polishing or shaving during the circuit breaker assembly operation, a highly polished shim insert was positioned within the armature-latch arrangement in an offline assembly described in the aforementioned U.S. Pat. No. 4,513,268. The insert was in the form of a highly polished stainless steel shim that was welded or brazed within the cradle retaining slot formed in the armature-latch component. It would be economically advantageous to eliminate the on-line shaving process and to eliminate the off-line polished shim insert without affecting the circuit breaker trip response.
Therefore, it is desirable to provide an armature latch that substantially reduces the static friction existing between the latch surfaces without requiring any shaving or shim insertion operations whatsoever.
BRIEF SUMMARY OF THE INVENTION
In an exemplary embodiment of the invention, a latching system for a circuit breaker is arranged to actuate a trip unit and interrupt circuit current upon occurrence of a short circuit or an overcurrent condition. The latching system employs an armature having a recess formed therein and a cradle having a cradle tip arranged to releasably engage a first side of the recess. The armature is arranged to move upon an overcurrent condition thus causing the cradle tip to be released from the recess.
A thermal-magnetic trip unit is depicted within the circuit breaker for the purposes of detecting overcurrent conditions through the electric path. During current transport through the circuit breaker, the current is thermally sensed by means of the bimetal and magnetically sensed by means of the magnet. The armature rotates to release the cradle tip from the recess and allow counterclockwise rotation of the contact arm. The rotation of the contact arm causes the separation of the movable and fixed contacts under the urgence of a mechanism spring.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is an internal front side view of a circuit breaker according to an embodiment of the present invention;
FIG. 2
is a rear side view of the armature, bimetal and magnet embodied by the present invention;
FIG. 3
is an isometric view of the armature and recess embodied by the present invention; and
FIG. 4
is an isometric view of a magnet and an armature embodied by the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Referring to
FIG. 1
, a residential type circuit breaker
10
is shown in the OPEN position and consists of a molded plastic case
12
with a load terminal lug
14
arranged at one end. Although a residential circuit breaker is shown, the use of commercial or industrial circuit breakers, as well as other types of residential circuit breakers, is within the scope of this invention. An operating handle
27
extends through an opening
25
in the case
12
. The operating handle
27
is movable between OFF and ON positions. Moving the operating handle
27
to the OFF position separates a fixed contact
26
from a movable contact
24
. Thus, the flow of electrical current through the circuit breaker
10
is stopped when the operating handle
27
is in the OFF position. Moving the operating handle
27
to the ON position brings the fixed and movable contacts
26
,
24
into contact to allow the electrical current to flow through the fixed and movable contacts
26
,
24
to a protected load.
In the ON position, the current path proceeds from the load terminal lug
14
through a load strap
16
, a current carrying bimetal (bimetal)
18
, and a braid conductor (conductor)
20
to a movable contact arm
22
that supports movable contact
24
at one end. The electrical path is completed through fixed contact
26
, which engages an external electric circuit by means of a line terminal stab
28
. The circuit current transfers between the fixed and movable contacts
26
,
24
until an overcurrent condition is sensed by means of the bimetal
18
or a magnetic trip unit
30
.
Referring to
FIGS. 1 and 2
, bimetal
18
is welded or brazed at one end to the top part of the load strap
16
. The opposite end of the bimetal
18
is welded or brazed to one end of the braid conductor
20
. The opposite end of the braid conductor
20
is welded or brazed to the movable contact arm
22
. The magnetic trip unit
30
includes a magnet
32
that interacts with an armature
34
that is pivotally arranged within the case
12
. The armature
34
and the magnet
32
are positioned at the top of the case
12
and are held together by means of a compression spring (spring)
80
. The magnet
32
is press-fitted into a slot (not shown) within the case
12
between the bimetal
18
and the load strap
16
. The magnet
32
is shaped to provide a structure, preferably L-shaped, in order to surround the bimetal
18
. A pair of tabs
50
is positioned on the armature
34
and provides a pivot for the armature
34
.
Referring again to
FIG. 1
, a latching system, shown generally at
68
, comprises a cradle
23
and the armature
34
. Cradle
23
is formed from a single Ushaped body configuration formed to include a radiused end
38
. Radiused end
38
is pivotally secured in a hemispherical recess (not shown) formed within the case
12
for allowing the cradle
23
to rotate between a latched position (shown in
FIG. 1
) to an unlatched position about a cradle pivot
52
. An offset tab
40
at one end of the top part of the cradle
23
interacts with one part of a shoulder
42
integrally formed with the operating handle
27
. A tab
44
extending parallel and opposite offset tab
40
interacts with an opposite part of the shoulder
42
when the operating handle
27
is moved between the ON and OFF positions. A cradle tip
46
is located at an end of the cradle
23
opposite the end where the radiused end
38
.
In the completed circuit breaker
10
, the line terminal stab
28
, a stab spring
58
and fixed contact
26
are arranged within a slot (not shown) within the case
12
. An arc chute
51
is shown located intermediate the fixed and movable contacts
26
,
24
. A mechanism spring
36
is supported by means of a spring tab
56
on the contact arm
22
and a spring tab
54
on cradle
23
. Spring tabs
54
,
56
move with the cradle
23
and contact arm
22
. When the circuit breaker contacts
24
,
26
are in the closed position, the mechanism spring
36
provides pressure on the cradle tip
46
to maintain engagement within a recess
48
of armature
34
. This pressure ensures the movable contact
24
maintains contact with the fixed contact
26
thus preventing nuisance tripping.
Referring to
FIG. 3
, armature
34
is formed from a single piece of steel, having a first section
62
and a second section
64
having a first end
90
. First section
62
includes a first end
74
and a second end
76
. Second section
64
includes a first end
90
proximate to first end
74
of first section
62
. The second section
64
is integral with the first section
62
and extends generally perpendicular from the first section
62
. Preferably, the armature
34
is generally L-shaped for promoting magnetic transfer between the armature
34
and the magnet
32
. The first section contains a narrow top portion
60
having two notches
70
for which are press-fitted into corresponding slots (not shown) within case
12
(FIG.
1
). Tabs
50
are located proximate to the second end
76
of first section
62
. Tabs
50
project outward, preferably perpendicular, from the first section
62
. At the first end
74
of the first section
62
, recess
48
is formed. A conventional die stamping process forms the recess
48
. Preferably, the recess
48
forms a four-sided depression on one side of the first section
62
and a protrusion (not shown) on the opposite side of the flat bottom piece
62
, preferably protruding in the same general direction as the tabs
50
. At the first end
90
of second section
64
, leg
96
extends in a direction parallel to second section
64
. Preferably, leg
96
is angled inward and positioned proximate to the bimetal
18
. Proximate to the leg
96
and located on second section
64
is an elongated, depression
72
.
Recess
48
has a first side
82
, a second side
84
, a third side
86
and a fourth side
88
. First side
82
is formed by stamping the first section
62
of armature
34
to about ninety percent of the -first section
62
. First side
82
is fabricated with a straight edge, preferably perpendicular with the flat bottom piece
62
. Second side
84
is inwardly beveled, preferably at a forty-five degree angle. Second side is located adjacent to the first side
82
. Third and fourth sides
86
,
88
are also inwardly beveled, preferably at a forty-five degree angle. Third side
84
is located adjacent to the second side
84
and opposite the first side
82
. Fourth side
88
is located between the first and third sides
82
,
86
. First, second, third and fourth sides
82
,
84
,
86
,
88
form the sides of the recess
48
. The cradle tip
46
is releasably engaged within recess
48
. The surface of the first side
82
that engages the cradle tip
46
is smooth and straight minimizing friction between the cradle tip
46
and the surface of the first side
82
of the armature
34
. A smooth surface thus permits the cradle tip
46
to smoothly and quickly slide away from the recess
48
. The depth of the recess
48
ensures that the cradle tip
46
sufficiently engages within the recess
48
.
Referring to
FIG. 4
, the armature
34
and magnet
32
are shown in detail. The magnet
32
includes an angled top piece
66
integral with a flat bottom piece
63
and an angled bottom piece
69
. Angled top piece
66
is positioned between a slot (not shown) within case
12
(
FIG. 1
) and one end of the armature
34
and rests on tabs
50
of the armature
34
. Spring
80
is pressed against a protrusion
78
located on first section
62
of the armature
34
. Protrusion
78
is located proximate the tabs
50
of the armature
34
. Spring
80
defines a line of force “F”, designated by an arrow, “F”, acting on the armature
34
and the magnet
32
at a predetermined point of contact indicated by protrusion
78
. Thus, spring
80
supports the magnet
32
and the armature
34
within the case
12
(FIG.
1
). The angled bottom piece
69
of the magnet
32
cooperates with the first section
62
and the second section
64
of the armature
34
to provide a closed magnetic loop which increase the magnetic coupling between the armature
34
and the magnet
32
. An elongated depression
73
is formed in the flat bottom piece
63
. Depression
73
of magnet
32
and depression
72
of armature
34
provide a bearing surface to the bimetal
18
as the bimetal
18
deflects during an overcurrent condition.
Referring to
FIGS. 1 and 2
, the operation of the armature
34
during a trip event will now be described in detail. A thermal-magnetic trip unit is depicted within the circuit breaker
10
for the purposes of detecting overcurrent conditions through the electric path. During current transport through the circuit breaker
10
, the current is thermally sensed by means of the bimetal
18
and magnetically sensed by means of the magnet
32
.
The thermal portion of the thermal-magnetic trip unit utilizes cradle
23
that is biased by mechanism spring
36
in a counterclockwise direction about cradle pivot
52
. The armature
34
is biased in a clockwise direction (shown in
FIG. 1
) by spring
80
. The engagement of the cradle tip
46
within recess
48
prevents the cradle
23
from rotating, thus maintaining the movable contact
24
of the contact arm
22
in contact with the fixed contact
26
. When movable contact
24
is in contact with fixed contact
26
a current path through circuit breaker
10
is created.
When an overcurrent condition occurs, the temperature of the bimetal
18
increases due to the current passing through the bimetal
18
. If the temperature of the bimetal
18
increases sufficiently due to the overcurrent condition thus exceeding a predefined current level, the bimetal
18
will deflect from an initial position and engage the leg
96
of the armature
34
. The armature
34
rotates in a counterclockwise direction in response to the force of the bimetal
18
applied to the leg
96
. The armature
34
moves in a direction away from cradle
23
thereby displacing the cradle tip
46
out of the recess
48
. The cradle
23
is thus released from the recess
48
and rotates in a clockwise direction thereby releasing the mechanism spring
36
. The mechanism spring
36
, once released, rapidly pulls the contact arm
22
and movable contact
24
away from the fixed contact
26
. Thus, the current through the circuit is interrupted.
The magnetic trip portion of the thermal-magnetic trip unit includes the armature
34
and magnet
32
. Upon the occurrence of a “short time” overcurrent condition of a predetermined magnitude and duration, the armature
34
is magnetically drawn towards the magnet
32
in a direction away from cradle
23
. The cradle tip
46
is displaced out of the recess
48
. The cradle
23
is thus released from the recess
48
and rotates in a clockwise direction thereby releasing the mechanism spring
36
. The mechanism spring
36
, once released, rapidly pulls the contact arm
22
and movable contact
24
away from the fixed contact
26
. Thus, the current through the circuit is interrupted.
When the circuit breaker is not under overcurrent of short circuit conditions, the movable and fixed contacts
24
,
26
can be separated by manually moving the operating handle
27
. Under short circuit or overcurrent conditions, the thermal magnetic trip unit will trip the circuit breaker
10
and unlatch the latching system
68
as described herein above. To re-latch the circuit breaker
10
, the operating handle
27
is manually moved to the OFF position and then back to the ON position. The operation of the operating handle
27
to the OFF position resets the cradle tip
46
within the recess
48
of the armature
34
. The motion of the operating handle
27
to the ON position will bias the mechanism spring
36
forcing the cradle tip
46
to engage the recess
48
.
As described herein, the recess
48
is fabricated with a straight die punch in a conventional steel stamping process. The first side
82
of the recess
48
provides an even surface for engagement with the cradle tip
46
. Thus, a superior material surface area is achieved for the latching surface. The second, third and fourth sides
84
,
86
,
88
of the recess
48
are beveled and ensure the structural integrity of the recess
48
. Therefore, all the advantages inherent in the recess
48
contribute to reliable latching forces that ensure that the circuit breaker
10
will trip at all designed overcurrent levels. To assist with the slippage of the cradle tip
46
from the recess
48
, grease is applied to the recess
48
and will be retained within the recess
48
for extended use. Finally, the recess
48
of the armature
34
does not require any additional calibration or post processing machining operations. Once the recess
48
is formed in the armature
34
, the armature
34
is ready to be assembled into the circuit breaker
10
.
It is within the scope of this invention and understood by those skilled in the art that the armature
34
and recess
48
can be utilized with various magnet
32
and bimetal
18
configurations within a trip unit.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments failings within the scope of the appended claims.
Claims
- 1. A latching system suitable for actuating a thermal magnetic trip unit to trip a circuit breaker upon an overcurrent condition, the latching system comprising;an armature having a recess formed therein, wherein said armature being arranged to move upon the overcurrent condition; and a cradle having a cradle tip arranged to releasably engage from said recess, wherein movement of said armature in response to the overcurrent condition releases said cradle tip from said recess.
- 2. The latching system of claim 1 wherein said recess includes:a first side, said cradle tip releasably engaging said first side; a second side positioned adjacent to said first side; a third side positioned adjacent to said second side and opposite said first side; and a fourth side positioned between said first and third sides.
- 3. The latching system of claim 2 wherein said second, third and fourth sides are inwardly beveled.
- 4. The latching system of claim 2 wherein said armature being formed from a single L-shaped metal piece having a first section and a second section, said recess formed in said first section proximate a first end.
- 5. The latching system of claim 4 wherein said first side of said recess is perpendicular to said first section of said armature.
- 6. The latching system of claim 4 further including:a magnet having an angled top piece positioned proximate to a second end of said first section of said armature and an angled bottom piece positioned proximate said second section of said armature, wherein said armature is attracted to said magnet during a short circuit condition thereby releasing said cradle tip from said recess.
- 7. The latching system of claim 6 wherein said magnet is formed from a single L-shaped metal piece.
- 8. The latching system of claim 6 further including:a bimetal positioned between said magnet and said armature; and said armature includes: a leg extending from a first end of said second section of said armature; wherein said bimetal pivots said leg of said armature in response to an overcurrent condition thereby releasing said cradle tip from said recess.
- 9. A circuit breaker comprising:a molded case; a fixed contact and a moveable contact arranged within said case to separate upon an overcurrent condition, said moveable contact being arranged at one end of a moveable contact arm and said fixed contact electrically connected to a line terminal stab; a trip unit configured to separate said fixed and movable contacts; and a latching system including: an armature having a recess formed therein, wherein said armature being arranged to move upon the overcurrent condition; and a cradle having a cradle tip arranged to releasably engage from recess, wherein movement of said armature in response to the overcurrent condition releases said cradle tip from said recess.
- 10. The circuit breaker of claim 9 wherein said recess includes:a first side, said cradle tip releasably engaging said first side; a second side positioned adjacent to said first side; a third side positioned adjacent to said second side and opposite said first side; and a fourth side positioned between said first and third sides.
- 11. The circuit breaker of claim 10 wherein said second, third and fourth sides are inwardly beveled.
- 12. The circuit breaker of claim 9 wherein said armature being formed from a single L-shaped metal piece having a first section and a second section, said recess formed in said first section proximate a first end.
- 13. The circuit breaker of claim 12 wherein said first side of said recess is perpendicular to said first section of said armature.
- 14. The circuit breaker of claim 12 further including:a magnet having an angled top piece positioned proximate to a second end of said first section of said armature and an angled bottom piece positioned proximate said second section of said armature, wherein said armature is attracted to said magnet during a short circuit condition thereby releasing said cradle tip from said recess.
- 15. The circuit breaker of claim 14 wherein said magnet is formed from a single L-shaped metal piece.
- 16. The circuit breaker of claim 14 further including:a bimetal positioned between said magnet and said armature; and saqid armature includes: a leg extending from a first end of said second section of said armature; wherein said bimetal pivots said leg of said armature in response to an overcurrent condition thereby releasing said cradle tip from said recess.
US Referenced Citations (8)