1. Field of the Invention
The present invention relates to a temperature fuse for use in an electric circuit provided in an automobile or the like and, in more particular, to such a temperature fuse which allows a signal current to be taken out from a circuit wiring the temperature of which is to be detected.
2. Description of the Related Art
Conventionally, in an electric circuit for use in an automobile or the like, a cartridge type of fuse 1 as shown in FIG. 3 is used. This fuse 1 is structured such that a pair of terminals 3 and 3 is connected to each other by a fuse element 5, the connected terminals are mounted within a housing 7 formed of insulating heat-resistant resin, and an opening 9 formed in the top portion of the housing 7 is closed by a transparent cover 11. In the interior portion of the housing 7, a terminal receiving chamber for receiving the terminals 3, 3 therein, and an element receiving space which communicates with the terminal receiving chamber there are formed. When the terminals 3, 3 are received into the terminal receiving chamber, the fuse element 5 is thereby situated in the element receiving space, so that whether the fuse element 5 is fused or not can be visually confirmed through the transparent cover 11. In particular, the fuse element 5 includes a fusible portion formed of low fusing-point metal such as lead, tin or the like which, when a current of a rated level or more flows therein, is heated by such a current and is thereby fused due to the thus generated heat. In other words, if the fusible portion is fused, then the electric circuit is opened to thereby protect electric wires and devices.
The above-mentioned conventional fuse 1, generally, has such a correlation between an energizing current and a prearcing time as shown in FIG. 4. Meaning, when a current 200% or more than a fuse rating flows, the fusible portion of the fuse 1 is fused immediately; and, when a current 200% or less than the fuse rating flows, the fusing time of the fusible portion is relatively long because the fuse 1 has durability against a rush current. Also, when there flows a short current which is not continuous but intermittent as in a rare short circuit, the fusible portion of the fuse element 5 generates and radiates heat alternately and repetitively in the element receiving space, so that the fusing time of the fusible portion can be made longer. On the other hand, in an electric wire forming the electric circuit, even if the intermittent short current flows, heat is not radiated in the fusible portion even in the current cut-off time because the electric wire is covered with a wire cover, but the temperature of the electric wire continues to rise due to storage of heat and, in the worst case, there is a fear that the electric wire may give off smoke or the like.
In order to eliminate the drawbacks found in the above-mentioned conventional cartridge type fuse, conventionally, there has been sometimes used a temperature fuse which is able to detect the temperature of an electric wire used in an electric circuit. In particular, a temperature fuse 13 is structured such that, as shown in FIG. 5, two lead wires 17 and 17 are respectively connected to the two ends of a low fusing-point metal member 15, the low fusing-point metal member 15 is covered with a film 19 having a lower fusing point than the low fusing-point metal member 15, and the film 19 is in turn covered with an insulating case 21. According to the temperature fuse 13, the low fusing-point metal member 15 portion is mounted on a circuit wiring the temperature of which is to be detected, and the lead wires 17, 17 are connected by soldering to an alarm circuit or a forced cutoff circuit, whereby, when the circuit wiring reaches a temperature which is equal to or higher than a given temperature, the low fusing-point metal member 15 is fused at the current temperature, and the alarm circuit or forced cutoff circuit is operated to turn on an alarm light or cut off the circuit, thereby protecting the circuit.
However, when such a temperature fuse 13 is used, there two electric wires are required, an exclusive power supply wire and a signal wire. Also, when the space for provision of an electric wire is limited, there is a fear that the temperature fuse 13 cannot be mounted onto the circuit wiring using to a method of winding tape around the same. Further, since the power supply wire is necessary, when a proper power supply terminal is not provided near the circuit wiring, the temperature fuse 13 cannot be mounted onto the circuit wiring.