Method of manufacturing temperature sensor and temperature sensor manufactured thereby

ABSTRACT

A temperature sensor for detecting a temperature of, for example, an exhaust gas of a vehicle is manufactured by inserting a thermistor element into a bottomed metal tube while filling an inside of the metal tube with a filler material, preferably of silicone oil, to reduce a sliding resistance between the thermistor element and the metal tube as an integral temperature sensing structure which is then mounted in a housing.

INFORMATION

DETAILED DESCRIPTION OF THE INVENTION

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a sectional view of a temperature sensor according to a first embodiment of the present invention;

FIG. 2 is an illustration of an outer appearance of an essential portion of the temperature sensor of FIG. 1;

FIG. 3 is an illustration of an essential portion, i.e., temperature sensing structure, of the temperature sensor in a developed state for assembling;

FIG. 4 is an illustration of developed view, similar to FIG. 3, of a temperature sensor according to a second embodiment of the present invention; and

FIG. 5 is an illustration of developed view, similar to FIG. 3, of a temperature sensor according to a third embodiment of the present invention;

DESCRIPTION OF THE PREFERRED EMBODIMENT

Preferred embodiments of the present invention will be described hereunder with reference to the accompanying drawings.

First Embodiment

A first embodiment of the present invention is first described with reference to FIGS. 1 to , in which FIG. 1 shows a sectional view of an entire structure of a temperature sensor, FIG. 2 shows an outer appearance of a temperature sensing portion and a terminal of the temperature sensor, and FIG. 3 is the developed view for the explanation of assembling of the temperature sensing portion.

The temperature sensor of this first embodiment is especially utilized for detecting a temperature of an exhaust gas from an internal combustion engine of a vehicle.

With reference to FIGS. 1 to , the temperature sensor of this embodiment generally comprises a thermistor element , a metal tube , a pair of electrode wires extending from the thermistor element , a pair of lead wires electrically connected to the electrode wires , respectively, and covered by a tube, and terminals connected to the lead wires , as illustrated in FIG. .

The thermistor element is for high temperature use capable of withstanding high temperature of an exhaust gas of a vehicle, for example, more than 1000° C. This thermistor element is formed from ceramics or silicon semiconductor, having a resistance variable in response to variation of the temperature. The thermistor element generally has a shell shape as shown in FIG. .

The thermistor element is inserted into the metal tube , which is made of stainless steel of, for example, SUS 304, SUS 303, or SUS 310. The metal tube has a bottomed cylindrical shape having one end opened and the other end closed.

A pair of electrode wires made of platinum wires, for example, extend from the thermistor element and electrically connected, at the extending ends, to the end portions of the paired lead wires , respectively, by means of, for example, welding.

After the insertion of the thermistor element into the metal tube and the connection of the electrode wires to the lead wires , the metal tube with the thermistor element is inserted into a box , having -shaped (inverted gate-shaped) section, made of resin such as polyphenylene sulfide, and then, the electrode wires and the lead wires are also inserted in the box . Thereafter, the box is filled up with an epoxy resin so as to form an epoxy resin layer in the box as illustrated in FIG. .

Thereafter, end portions of the lead wires extending beyond one end portion of the box are electrically connected, by means of welding, for example, to the paired metal terminals . According to such connection as mentioned above, the thermistor element , the metal tube , the electrode wires , the lead wires and the terminals are integrally connected. This integrated structure is then inserted into a metal cylindrical housing having a staged portion such that the bottom end of the metal tube extends outward over one end of the housing , and thereafter, a resin material such as nylon having an electrical insulating property is injected and molded, thus completing the temperature sensor such as shown in FIG. 1 according to the present invention.

With further reference to FIG. 1, reference numeral denotes a resin mold having an end portion, extending from the housing , to which a connector housing is connected integrally, and one end of each of the terminals extends inside the connector housing .

The housing is formed, on its outer peripheral surface, with male screw thread, and by utilizing this screw thread, the temperature sensor is mounted (i.e. screw-engaged) to an exhaust pipe of an internal combustion engine of a vehicle, not shown, in a manner that the bottom side of the metal tube faces inside the exhaust pipe. According to such mounting of the temperature sensor to the exhaust pipe, the resistance value of the thermistor element varies in response to the temperature of the exhaust gas to thereby detect the temperature of the exhaust gas.

With the temperature sensor of the structure mentioned above, the inserting and assembling processes of the thermistor element to the metal tube will be explained with reference to FIG. .

An operator holds the electrode wires so that the front end of the thermistor element is positioned to the opened end of the metal tube with a clearance between the inner peripheral surface of the metal tube and the outer peripheral surface of the thermistor element in a state now illustrated in FIG. . Then, while feeding a filler inside the metal tube , as shown with a letter A in FIG. 3, through the clearance, the electrode wires are pushed so that the thermistor element is inserted into the metal tube to a position that the inserted front end of the thermistor element abuts against the bottom portion of the metal tube .

As the filler, silicone oil is preferably utilized in this embodiment for reducing a sliding resistance between the thermistor element and the metal tube , and the silicone oil fills the metal tube by using an injector, for example. This silicon oil may be being injected till the entire structure of the thermistor element is inserted into the metal tube or the front end of the thermistor element abuts against the bottom portion of the metal tube .

Further, in order to sufficiently reduce the sliding resistance between the thermistor element and the metal tube , it is preferred to set viscosity of the silicone oil of 100 to 1500 cSt (cm·stokes) or to use silicone oil having viscosity of 100 to 1500 cSt (cm·stokes), and more preferably, of 500 to 800 cSt. In a case when silicone oil having viscosity in a range other than that mentioned above is used, it will be difficult to sufficiently reduce the sliding resistance, and in such case, it will be necessary to control or manage temperature and moisture.

In a preferred example, the gap between the thermistor element and the metal tube is desired to be about 0.01 to 0.5 mm in diametrical direction. In a case of less than 0.1 mm, it is difficult to insert the thermistor element into the metal tube regardless of the presence the filler, and in a case of more than 0.5 mm, the thermistor element will engage without the filler.

Further, it will be also desired that the silicone oil as the filler applied to the metal tube surface has a thin thickness in form of film.

According to the embodiment described above, the sliding resistance between the thermistor element and the metal tube is made small by the silicone oil, so that only a small force is applied to the electrode wires , and hence, it is prevented for the electrode wires from being bent and it becomes possible to insert the thermistor element to the bottom portion of the metal tube . Accordingly, the thermistor element is surely positioned to the bottom portion of the metal tube , thus improving the measuring performance.

In one example of a temperature sensor adapted to detect a temperature of an exhaust gas from a vehicle, an outer diameter (φ) of the metal tube is set to 0.5 to 1.5 mm, a depth of the metal tube from its opened end to its bottom portion is set to 5 to 25 mm, and a temperature ambient of the temperature of an inside portion of an exhaust tube, at which the bottom portion of the metal tube is positioned (i.e., a portion at which a temperature is detected), is about −40 to 1000° C.

As mentioned above, in the case of severe ambient of the temperature at the portion to be detected, it is difficult to make small the thermistor element , and in addition, since the outer diameter of the metal tube is small, the clearance between the thermistor element and the metal tube inevitably becomes small.

On the contrary, according to the described first embodiment of the present invention, in which the silicone oil is utilized as filler, the thermistor element can be surely inserted into the bottom portion of the metal tube even in the case of the small clearance between the thermistor element and the metal tube . Accordingly, the present invention is preferably applicable to a temperature sensor, for detecting a temperature of an exhaust gas, having a small clearance therebetween.

Second Embodiment

In this second embodiment, silicone oil fills the inner space of the metal tube before the thermistor element is inserted therein, and the technology other than this matter is substantially the same as that of the first embodiment.

In this second embodiment, with reference to FIG. 4, the silicone oil is first fed into the metal tube to thereby form a silicone oil film layer so as to cover the inner peripheral wall surface of the metal tube . Thereafter, the thermistor element is positioned by holding the electrode wires so that the front end of the thermistor element is positioned to, the opened end portion of the metal tube . Under the state, while pouring the silicone oil into the metal tube through the clearance as shown with letter A in FIG. 4 between the outer peripheral surface of the thermistor element and the inner peripheral surface of the metal tube , the thermistor element is pushed forward by holding the electrode wires and inserted into the metal tube till the inserted front end of the thermistor element abuts against the bottom portion of the metal tube .

As mentioned above, by preliminarily filling the inside of the metal tube with the silicone oil and forming the silicone oil film layer , the siding resistance between the thermistor element and the metal tube can be surely reduced and the thermistor element can be surely and easily inserted into the bottom portion of the metal tube .

Further, in this embodiment, since the silicone oil film layer is preliminarily formed on the inner wall section of the metal tube , the feeding of the silicone oil at the thermistor element insertion time through the clearance may be eliminated.

Third Embodiment

This third embodiment represents another inserting and assembling process of the thermistor element to the metal tube , and descriptions on processes or steps substantially equal to those of the first embodiment will be omitted hereunder.

In this third embodiment, with reference to FIG. 5, the front end portion of the thermistor element is inserted into the metal tube by holding the electrode wires so that the lower side of the thermistor element contacts the lower inner peripheral surface of the metal tube as just shown in FIG. . Under the state, the silicone oil is fed inside the metal tube shown with the letter A through the clearance between the thermistor element and the metal tube at the upper side to thereby surely apply the silicone oil to the upper side inner peripheral surface of the metal tube and the outer peripheral surface of the thermistor element .

Then, the thermistor element is raised upward and then inserted into the metal tube till the front end of the thermistor element abuts against the bottom portion of the metal tube .

As mentioned above, according to this embodiment, since the thermistor element is inserted in contact to the portion to which the silicone oil is surely applied, the siding resistance between the thermistor element and the metal tube can be surely reduced and the thermistor element can be surely and easily inserted into the bottom portion of the metal tube .

Hereunder, fourth embodiment and fifth embodiment of the present invention will be further described, which additionally include processes or steps after those of the first to third embodiments mentioned above.

Fourth Embodiment

The fourth embodiment includes further step after the inserting and assembling the thermistor element in the metal tube .

That is, the metal tube of the temperature sensor into which the thermistor element has been inserted in accordance with any one of the first to third embodiments is then heated at a temperature of more than 400° C. for more than 5 minutes. Through this heating process, oil component of the silicone oil volatiles, and hence, silica (SiO2) exists in the metal tube in solid powder state, whereby any liquid state material does not remain therein and hence does not leak during the usage of the temperature sensor.

Fifth Embodiment

In this fifth embodiment, ceramics powder such as Al2O3, MgO, SiO2 or like is preliminarily added to the silicone oil before the filling into the metal tube . The processes or steps carried out in any one of the first to third embodiments are then applied. Thereafter, the metal tube is then heated at a temperature of more than a ceramics sintering temperature for a predetermined time. Through this heating process, the ceramics is sintered in the metal tube and the thermistor element is hence secured to the metal tube .

As mentioned hereinbefore, according to the present invention, the required objects can be achieved.

It is further to be noted that the present invention is not limited to the described embodiments and many other changes and modifications may be made without departing from the scopes of the appended claims.

CLAIMS

1. A method of manufacturing a temperature sensor which comprises a bottomed metal tube and a thermistor element inserted into the metal tube, comprising the steps of: preparing a metal tube and a thermistor element; and inserting the thermistor element into the metal tube while filling an inside of the metal tube with a filler material to reduce a sliding resistance between the thermistor element and the metal tube.

2. The method of manufacturing a temperature sensor according to claim 1, wherein said filler material is a silicone oil.

3. The method of manufacturing a temperature sensor according to claim 2, wherein said silicone oil has a viscosity of 100 to 1500 cm • stokes.

4. The method of manufacturing a temperature sensor according to claim 1, wherein said metal tube has an outer diameter of 0.5 to 1.5 mm.

5. The method of manufacturing a temperature sensor according to claim 1, wherein an ambient temperature of a portion to be detected is −40 to 1000° C.

6. The method of manufacturing a temperature sensor according to claim 1, wherein said metal tube has a depth of 5 to 25 mm from an opened end of the bottomed metal tube to the bottom portion thereof.

7. The method of manufacturing a temperature sensor according to claim 1, wherein said filler material is a silicone oil and said metal tube is heated after the insertion of the thermistor element thereinto so as to volatilize an oil component of the silicone oil.

8. The method of manufacturing a temperature sensor according to claim 1, wherein said filler material is a silicone oil, ceramics powder is mixed with the silicone oil and said metal tube is heated after the insertion of the thermistor element thereinto so as to volatilize an oil component of the silicone oil and to sinter the ceramics powder to thereby secure the thermistor element to the metal tube.

9. A method of manufacturing a temperature sensor which comprises a bottomed metal tube and a thermistor element inserted into the metal tube, comprising the steps of: preparing a metal tube and a thermistor element; positioning an insertion side front end of the thermistor element to an open end portion of the metal tube; filling an inside of the metal tube with a filler material through a clearance between the front end of the thermistor element and the metal tube to reduce a sliding resistance between the thermistor element and the metal tube; and inserting the thermistor element into the metal tube.

10. The method of manufacturing a temperature sensor according to claim 9, wherein said filler material is a silicone oil.

11. The method of manufacturing a temperature sensor according to claim 10, wherein said silicone oil has a viscosity of 100 to 1500 cm • stokes.

12. The method of manufacturing a temperature sensor according to claim 9, wherein said metal tube has an outer diameter of 0.5 to 1.5 mm.

13. The method of manufacturing a temperature sensor according to claim 9, wherein an ambient temperature of a portion to be detected is −40 to 1000° C.

14. The method of manufacturing a temperature sensor according to claim 9, wherein said metal tube has a depth of 5 to 25 mm from an opened end of the bottomed metal tube to the bottom portion thereof.

15. The method of manufacturing a temperature sensor according to claim 9, wherein said filler material is a silicone oil and said metal tube is heated after the insertion of the thermistor element thereinto so as to volatilize an oil component of the silicone oil.

16. The method of manufacturing a temperature sensor according to claim 9, wherein said filler material is a silicone oil, ceramics powder is mixed with the silicone oil and said metal tube is heated after the insertion of the thermistor element thereinto so as to volatilize an oil component of the silicone oil and to sinter the ceramics powder to thereby secure the thermistor element to the metal tube.

17. A method of manufacturing a temperature sensor which comprises a bottomed metal tube and a thermistor element inserted into the metal tube, comprising the steps of: preparing a metal tube and a thermistor element; filling an inside of the metal tube with a filler material; positioning an insertion side front end of the thermistor element to an open end portion of the metal tube; and inserting the thermistor element into the metal tube while further filling the inside of the metal tube with the filler material through a clearance between the front end of the thermistor element and the metal tube to reduce a sliding resistance between the thermistor element and the metal tube.

18. The method of manufacturing a temperature sensor according to claim 17, wherein said filler material is a silicone oil.

19. The method of manufacturing a temperature sensor according to claim 18, wherein said silicone oil has a viscosity of 100 to 1500 cm • stokes.

20. The method of manufacturing a temperature sensor according to claim 17, wherein said metal tube has an outer diameter of 0.5 to 1.5 mm.

21. The method of manufacturing a temperature sensor according to claim 17, wherein an ambient temperature of a portion to be detected is −40 to 1000° C.

22. The method of manufacturing a temperature sensor according to claim 17, wherein said metal tube has a depth of 5 to 25 mm from an opened end of the bottomed metal tube to the bottom portion thereof.

23. The method of manufacturing a temperature sensor according to claim 17, wherein said filler material is a silicone oil and said metal tube is heated after the insertion of the thermistor element thereinto so as to volatilize an oil component of the silicone oil.

24. The method of manufacturing a temperature sensor according to claim 17, wherein said filler material is a silicone oil, ceramics powder is mixed with the silicone oil and said metal tube is heated after the insertion of the thermistor element thereinto so as to volatilize an oil component of the silicone oil and to sinter the ceramics powder to thereby secure the thermistor element to the metal tube.

25. A method of manufacturing a temperature sensor which comprises a bottomed metal tube and a thermistor element inserted into the metal tube, comprising the steps of: preparing a metal tube and a thermistor element provided with an electrode wire from which a lead wire extends, a terminal being connected to the lead wire; inserting the thermistor element into the metal tube while filling an inside of the metal tube with a filler material to thereby form an integral structure of the metal tube and the thermistor element; mounting said integral structure to a housing from which the bottomed end portion of the metal tube extends outward; and feeding an electrical insulating material into the housing.

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