Circuit breaker with shift guide

Details Circuit breaker with shift guide Circuit breaker with shift guide

2001-08-30

2003-01-28

Donovan, Lincoln (Department: 2836)

Electricity: magnetically operated switches, magnets, and electr

Electromagnetically actuated switches

Automatic circuit-interrupting devices

C337S360000, C337S392000

Reexamination Certificate

active

06512434

ABSTRACT:

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a circuit breaker incorporating a thermal overload open-phase tripping device used in a molded case circuit breaker applied to an electric-motor feeding circuit or the like.
The structure of a conventional circuit breaker, in this example, a molded case circuit breaker, which incorporates a bimetal-type thermal overload open-phase tripping device, is shown in
FIGS. 6
,
7
(
a
) and
7
(
b
). In these figures, reference numeral
1
denotes a breaker case (resin molding), reference numeral
2
denotes a case cover (resin molding) placed on the case
1
, reference numerals
3
and
4
denote load-side main circuit terminals and power-supply-side main circuit terminals, reference numeral
5
denotes an opening and closing mechanism section for a main circuit contact shoe, reference numeral
6
denotes an opening and closing operating handle, reference numeral
7
denotes a bimetal-type thermal overload open-phase tripping device incorporated in the case
1
, and reference numeral
8
denotes an instantaneous-operation-type solenoid-based overload tripping device. Although not shown, a main circuit breaking section composed of movable and fixed contact shoes and an arc extinguishing chamber is incorporated into a bottom side of the case
1
.
Further, the thermal overload open-phase tripping device
7
includes bimetals
9
U,
9
V and
9
W corresponding to different phases of a main circuit, a differential shifter mechanism
10
, a compensating bimetal
11
also acting as a lever for linking the differential shifter mechanism
10
and a latch receiver
5
a
of the opening and closing mechanism section
5
, an adjustable dial
11
a
for the compensating bimetal
11
and the like.
The interior of the case
1
is partitioned into chambers corresponding to the U, V, and W phases by interphase partition walls
1
a
. The bimetals
9
U,
9
V and
9
W are laterally arranged in the chambers for the respective phases and have lower ends fixed to and supported by the case
1
, as shown in FIG.
7
(
a
). Heater wires
9
a
wound around the corresponding bimetals are connected to the main circuit to cause the bimetals to bend when a current is conducted through the heater wires to generate heat.
On the other hand, the differential shifter mechanism
10
is composed of an assembly of a plate-shaped push shifter
10
a
and a plate-shaped pull shifter
10
b
, arranged alongside the bimetals
9
U,
9
V and
9
W, and an interlocking plate
10
c
extending over the top surfaces of the push shifter
10
a
and the pull shifter
10
b
. Each of the L-shaped arm portions extending laterally from the push shifter
10
a
and a corresponding L-shaped arm portion extending laterally from the pull shifter lob face each other across a top portion of the corresponding bimetal
9
U,
9
V or
9
W, and the corresponding bimetal then acts as an operating end. Further, the interlocking plate
10
c
has an output end or projecting portion
10
c
-
1
located at a side opposite to a side surface of the compensating bimetal
11
.
The interphase partition walls
1
a
of the case
1
have recesses
1
a
-
1
formed at upper edges thereof, in which the push shifter
10
a
and the pull shifter
10
b
are fitted, as shown in FIG.
7
(
b
). The push shifter
10
a
and the pull shifter
10
b
extend over the interphase partition walls
1
a
and lie within the recesses
1
a
-
1
so as to be loosely fitted therein to permit sliding. In an assembled state in which the case cover
2
is installed on the case
1
, as shown in FIG.
7
(
a
), the case cover
2
holds the differential shifter mechanism
10
to keep it from slipping from the recesses
1
a
-
1
in the interphase partition walls
1
a.
Since the operation of the thermal overload open-phase tripping device configured as described above is well known, a detailed description thereof is omitted. When an overcurrent flows through the main circuit to bend and displace the bimetals
9
U,
9
V and
9
W in the direction of arrow P in FIG.
7
(
a
), the push shifter
10
a
of the differential shifter mechanism
10
correspondingly slides in the direction of arrow Q to cause the output end of the interlocking plate
10
c
to push the compensating bimetal
11
, thereby driving the latch receiver
5
a
(see
FIG. 6
) of the opening and closing mechanism section
5
to a release position. The opening and closing mechanism section
5
thereby performs a trip operation to open the contact shoes of the main circuit of the breaker, thereby shutting off the current.
The circuit breaker of the above conventional configuration has the problem such that overload open-phase tripping operation characteristics change, resulting in failure to operate as specified. The inventors' study has demonstrated that this problem originates from the support structure of the differential shifter mechanism. That is, in the differential shifter mechanism
10
, the interlocking plate
10
c
is placed on the top surfaces of the push shifter
10
a
and the pull shifter
10
b
so as to extend over these surfaces, as previously described. Thus, in the conventional assembled structure, a gap corresponding to the thickness of the interlocking plate
10
c
remains between the top surfaces of the push shifter
10
a
and the pull shifter
10
b
and an inner wall surface of the case cover
2
, as shown in FIG.
7
(
a
).
Consequently, when the push shifter
10
a
of the differential shifter mechanism
10
is pushed due to the bending displacement of the bimetals
9
U,
9
V and
9
W, it is inclined, using as a support point the abutting point between the output end of the interlocking plate
10
c
and the compensating bimetal
11
, so that its rear end (right end in the figure) is raised. Thus, the rear edge of the raised shifter rubs against the inner surface of the case cover
2
to produce the sliding friction, and the inclined position of the shifter reduces the force for laterally pushing the compensating bimetal
11
via the interlocking plate
10
c
. As a result, the bending displacement of the bimetals
9
is not accurately transmitted to the compensating bimetal
11
via the differential shifter mechanism
10
, varying the tripping operation characteristics of the breaker.
It is thus an object of the present invention to provide a circuit breaker that provides an improved support structure for a differential shifter mechanism so as to accurately transmit the bending displacement of bimetals to a compensating bimetal via a differential shifter mechanism without any loss, in order to stabilize the operational characteristics of a thermal overload open-phase tripping device.
Further objects and advantages of the invention will be apparent from the following description of the invention.
SUMMARY OF THE INVENTION
To attain the above object, the present invention provides a circuit breaker including a thermal overload open-phase tripping device. The tripping device is composed of bimetals corresponding to different phases of a main circuit; a differential shifter mechanism composed of a combination of a plate-shaped push shifter and a plate-shaped pull shifter linked to operating ends of the bimetals of the respective phases, and an interlocking plate extending over the top surfaces of both shifters; and a compensating bimetal also acting as a lever to transmit an output from the shifter mechanism to an opening and closing mechanism section to release a latch receiver. The push and pull shifters of the differential shifter mechanism extend over interphase partition walls in a breaker case and are loosely fitted into recesses formed at the upper edges of the interphase partition walls to permit sliding support. A case cover is placed and held over the push and pull shifters of the differential shifter mechanism.
In the invention, shifter position guides are provided on an inner surface side of the case cover opposite to the push and pull shifters to restrain inclination of the shifters moving in accordance with bending displacement

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