Electricity: electrical systems and devices – Igniting systems – For explosive devices
Reexamination Certificate
2000-08-24
2002-09-03
Huynh, Kim (Department: 2836)
Electricity: electrical systems and devices
Igniting systems
For explosive devices
C337S401000, C337S412000, C337S298000, C337S157000, C361S104000, C361S249000, C361S103000, C200S061080
Reexamination Certificate
active
06445563
ABSTRACT:
The present patent application claims the benefit of earlier Japanese Patent Application No. H11-237956 filed Aug. 25, 1999, the disclosure of which is entirely incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a power circuit breaker, which can instantaneously interrupt a power source circuit by disconnecting a fuse element from the circuit making use of a gas pressure of an igniter.
2. Description of the Related Art
FIG. 1
illustrates a conventional fuse
61
used to break a high-current circuit. The fuse
61
includes a housing
62
made of a synthetic resin, a fuse element
63
made of a conductive metal and accommodated in the housing
62
, and a cover
64
for capping the top opening of the housing
62
.
The fuse element
63
comprises a base body
65
bent into an inverse U-shape, a pair of female terminal pieces
66
extending from both ends of the base body
65
, and a tin chip (i.e., a heat storage)
67
placed on the top face of the base body
65
. Each female terminal piece
66
is combined with an elastic contact piece
68
, which is positioned separate from the baseboard
63
. The female terminal piece
66
and the elastic contact piece
68
constitute a female terminal to receive a male terminal of a fuse box or the like (not shown). The male terminal is inserted from the lower opening
69
, and it comes into contact with the elastic contact piece
68
of the female terminal.
The base body
65
also has a pair of stoppers
70
that are formed monolithically with the base body
65
. Each stopper
70
catches the shoulder of the inner wall of the housing
62
, thereby preventing the fuse element
63
from coming off the housing
62
. The base body
65
of the fuse element
63
blows out if an excessive amount of electric current flows through it. The blowout of the fuse element
63
causes the power source circuit to be cut off.
FIG. 2
is a graph showing the breaking characteristics of the conventional fuse
61
shown in FIG.
1
. The horizontal axis denotes an electric current, and the vertical axis denotes a blowout time T, which is indicated in a logarithmic scale.
As an electric current I flowing through the fuse
61
increases, the blowout time T of the fuse
61
decreases along a quadratic curve. The blowout time T becomes very long at a lower range of excessive current.
In the example shown in
FIG. 2
, the fuse
61
is designed so that the electric current through it in the normal use is 60 Amp, which are about 50% of the rated current. If the excessive current is small, that is, if an electric current of 70 Amp or 80 Amp flows through the fuse
61
, then the fuse
61
does not blow out for a long time, as indicated by the circle A in
FIG. 2
, even through some faults occur in the circuit.
This means that it is difficult for the conventional fuse
61
to instantaneously break the circuit when the quantity of excessive current is small because the fuse element does not blow out immediately. The same defect applies to a situation in which an intermittent short circuit, such as a rare short, occurs. As still anther situation, if a short circuit has occurred in a load circuit, the temperature of the fuse element
63
does not rise up to the blowout temperature in spite of the overcurrent. This also prevents the fuse element
63
from blow out promptly.
To overcome these problems, a power circuit breaker
76
shown in
FIG. 3
was proposed. The prior art power circuit breaker
76
electrically senses an overcurrent, and shuts off the circuit forcibly by means of an ignition pressure of the igniter.
The power circuit breaker
76
has a pair of terminals
77
and
78
, each of which has a multi-contact-point spring
80
. A conductive shaft
79
is in contact with the multi-contact-point springs
80
in a slidable manner. An igniter
81
is placed behind one of the multi-contact-point spring
80
of the terminal
78
.
The base of the shaft
79
is secured to an operation shaft
82
, which is furnished with a torsion spring
83
. The igniter
81
is filled with a gas-blasting agent, and a heater is placed inside it. The heater is connected to a lead
84
. Both the shaft
79
and the operation shaft
82
are placed in the housing
85
in a slidable manner.
The terminals
77
and
78
are electrically connected with the shaft
79
via the multi-contact-point springs
80
. If an excessive current flows through the terminals
77
and
78
, the sensor (not shown) senses the change, and causes an electric current to flow through the lead
84
to the heater. The heater heats the gas-blasting agent, and the shaft
79
is pushed toward the disconnected position under a gas pressure of the igniter, as shown in FIG.
2
B. The electric conductivity between the terminals
77
and
78
are now cut off. The shaft
79
is prevented from returning to the original position because the torsion spring
83
forces a stopper
86
to project outward and catch the edge of the housing
85
.
However, a problem in the power circuit breaker
76
is that the igniter
81
is not be activated when the quantity of excessive current is below the minimum sensible current of the sensor, as in the conventional fuse
61
shown in FIG.
1
. This situation often occurs, for example, if a rare short happens, a short circuit occurs in the load circuit, or no excessive current flows through the terminals
77
and
78
. In these cases, the power source circuit can not be appropriately interrupted.
SUMMARY OF THE INVENTION
The present invention was conceived to overcome these problems in the prior art, and it is an object of the invention to provide a power circuit breaker that can break the power source circuit without fail even under a small amount of excessive current. The power circuit breaker also reliably works if a short circuit occurs in the load circuit.
In order to achieve the object, a power circuit breaker according to the invention has a housing, a fuse element placed in the housing, and a temperature sensitive fuse attached to the fuse element. The power circuit breaker also has switching means connected to the temperature sensitive fuse, and an igniter connected to the switching means. The fuse element has a pair of tab terminals, which are received in trunk terminals connected to an external circuit.
Preferably, the switching means is a transistor. The igniter is filled with a gas-blasting agent, and a heater is placed in the gas-blasting agent. The transistor is connected to the heater.
If an excessive current flows through the fuse element due to a short circuit having occurred in a load circuit, the temperature of the fuse element rises, but still below the blowout temperature of the fuse element. The temperature sensitive fuse attached to this fuse element is sensitive to a change in the temperature of the fuse element, and it blows out in response to a small rise of the temperature. The blowout of the temperature sensitive fuse immediately causes the transistor to turn on, and the heater is electrically connected. The gas-blasting agent is heated, and a gas pressure causes the tab terminals of the fuse element to be detached from the trunk terminal, whereby the power source circuit is cut off.
Preferably, a circuit board, on which the switching means is incorporated, is accommodated in the housing. The melted temperature sensitive fuse is easily replaced with a new one.
REFERENCES:
patent: 3873786 (1975-03-01), Lagofun
patent: 4292611 (1981-09-01), Bresson et al.
patent: 5502612 (1996-03-01), Osterhout et al.
patent: 5990572 (1999-11-01), Yasukuni et al.
patent: 6194988 (2001-02-01), Yamaguchi et al.
patent: 5-274995 (1993-10-01), None
patent: 10-55742 (1998-02-01), None
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Huynh Kim
Yazaki -Corporation
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