Electricity: electrothermally or thermally actuated switches – Electrothermally actuated switches – Fusible element actuated
Reexamination Certificate
2000-06-21
2002-09-03
Vortman, Anatoly (Department: 2835)
Electricity: electrothermally or thermally actuated switches
Electrothermally actuated switches
Fusible element actuated
C337S290000, C337S401000, C337S404000, C337S405000, C361S104000
Reexamination Certificate
active
06445277
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a safety device of an electric circuit for preventing an accident due to an overcurrent from occurring and a process for producing the same and, more specifically, to a safety device of an electric circuit containing first and second protective devices, wherein an accident is securely prevented from occurring by using the second protective device such as a thermal fuse even when the first protective device such as an overcurrent protective element is extraordinarily overheated.
(2) Description of the Related Art
An overcurrent protector is employed in an electric circuit of a power unit and the like mounted on an electric vehicle in order to prevent an accident due to overcurrent from occurring. For example, a positive temperature coefficient (hereinafter, called PTC) element, a variable resistor (hereinafter, called varistor) and an aluminum electrolytic capacitor are used as the overcurrent protector that generates heat to increase its electrical resistance when an overcurrent flows therethrough and then, reduces or cuts off the overcurrent, thereby keeping the electric circuit in secure condition.
However, when the overcurrent is kept flowing to overheat the overcurrent protector extraordinarily and is left as it goes, the overcurrent protector might catch fire to cause a vehicle fire.
Therefore, various measures to cope with the extraordinary overheating of the overcurrent protector have hitherto been proposed.
For example, Japanese Patent Application Laid-Open No. H8-250304 has proposed a safety device
110
of an electric circuit, in which one of a pair of leads
112
and
113
soldered to a PTC element
111
having a spring characteristic with respect to a direction apart from the PTC element
111
as shown in FIG.
13
.
According to the above construction, when the PTC element
111
is extraordinarily overheated due to overcurrent, the solder is brought into melted condition and one lead
112
is lifted up to be apart from the PTC element
111
, thereby the overcurrent flowing through an electric circuit is cut off.
Japanese Utility Model Application Laid-Open No. H1-129744 has proposed a safety device
120
of an electric circuit, in which a voltage-dependent type varistor (hereinafter, called ZNR)
121
is employed as shown in FIG.
14
A.
In the safety device
120
, a lead
122
of the ZNR
121
is bended at right angles and soldered to one conductor pattern
123
and another conductor pattern
124
that are separated and insulated from each other on an circuit board, thereby the conductor pattern
123
is connected to the other conductor pattern
124
.
According to the above construction, as shown in
FIGS. 14A
,
14
B and
14
C, when the ZNR
121
is extraordinarily overheated, solder for fixing the lead
122
melts to force the ZNR
121
to be left out by its own weight, thereby breaking an electrical connection between the conductor pattern
123
and the other conductor pattern
124
and also breaking the overcurrent flowing in the electrical circuit.
The above conventional safety devices
110
and
120
of an electric circuit can prevent an accident due to an extraordinary overheating of an overcurrent protector, however causing the following problems.
In the safety device
110
shown in
FIG. 13
, the soldering must be done against an elastic force of the lead
112
, resulting in time consuming for soldering and that the safety device
110
can not be produced easily by employing an automatic soldering machine and the like.
In the safety device
120
shown in
FIG. 14
, the soldering must be done with holding the ZNR
121
so that the ZNR
121
is left out by its own weight upon the extraordinary overheating, also resulting in that a lot of time is required for soldering and that the safety device
120
can not be produced easily by employing an automatic soldering machine and the like.
As a result of study, the present inventors have reached a technological idea that a thermal fuse be situated in the vicinity of the overcurrent protector and the thermal fuse detects an extraordinary overheating of the overcurrent protector, thereby the electric circuit is cut off.
In the following, an ordinary thermal fuse is explained with reference to
FIGS. 15A
,
15
B and
15
C.
As shown in
FIG. 15A
, one conductor pattern
132
and another conductor pattern
133
are formed on a circuit board
131
, then electrodes
132
a
and
133
a
of the conductor pattern
132
and other conductor pattern
133
, respectively, are insulated from each other by a gap
134
. Then, as shown in
FIG. 15B
, the electrodes
132
a
and
133
a
are connected by bridging the gap
134
with solder
135
, thereby a thermal fuse
130
is formed.
According to the above construction, when a temperature of the conductor pattern
132
, the other conductor pattern
133
or an atmosphere around the solder
135
rises high, the solder
135
completely melts.
Then, as shown in
FIG. 15C
, the solder
135
is repeled by an surface of the circuit board, which is hard to be wetted by solder, at the gap
134
and then, splits into two parts toward each electrode
132
a
and
133
a
, which are easily wetted by solder, by surface tension.
As a result, the electrical connection between the electrodes
132
a
and
133
a
is cut off and an accident due to an extraordinary overheating of the electric circuit can be prevented from occurring.
When the above conventional thermal fuse
130
is formed, the solder
135
must be put on the gap
134
between the electrodes
132
a
and
133
a
on such a condition that the solder
135
is nearly completely melted. However, at this time, the solder
135
splits into two parts toward each electrode
132
a
and
133
a
, that is, it is very hard to put the solder
135
that is nearly completely melted on the gap
134
between the electrodes
132
a
and
133
a.
Therefore, there has been a problem that the thermal fuse
130
can not be easily formed by soldering simultaneously with soldering of other electric components by employing an automatic soldering machine and the like.
As shown in
FIG. 15A
, the gap
134
between the electrodes
132
a
and
133
a
extends in a direction along an arrow shown in the figure, in another word, there is no electrode that can stop the molten solder
135
along the direction, therefore, the molten solder
135
can not stay steadily on the surface of the circuit board at the gap
134
, causing the above problem.
However, the nature that the molten solder
135
easily splits into two parts toward each electrode
132
a
and
133
a
essentially contributes to reliability of the thermal fuse upon the extraordinary overheating of the electric circuit, it is required that the molten solder
135
should not split into two parts toward each electrode
132
a
and
133
a
only when the thermal fuse
130
is formed.
In order to solve the above problem, Japanese Patent Application Laid-Open No. H4-56028 has proposed a thermal fuse, in which an electrode of one conductor pattern and an electrode of another conductor pattern, which are separated and insulated from each other on a circuit board, are connected by using porous solder layer in which openings among the solder grain remain.
According to the above idea, however, in order to form the porous solder layer, particular steps including printing solder cream on a circuit board and half-melting the solder cream are required, causing a problem that the thermal fuse can not be easily formed by soldering simultaneously with soldering of other electric components by employing an automatic soldering machine and the like.
SUMMARY OF THE INVENTION
It is therefore an objective of the present invention to solve the above problems and to provide a safety device of an electric circuit and a process for producing the same, the safety device containing first and second protective devices, wherein an accident is securely prevented from occurring by using the second protective device such as a thermal fuse even when the first protective devic
Ishikawa Satoshi
Maruo Hisafumi
Soda Osamu
Armstrong Westerman & Hattori, LLP
Yazaki -Corporation
LandOfFree
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