JP2002350242A - Temperature sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-reliability temperature sensor having excellent durability even if it is used in an environment with large temperature change and vibration such as the inside of an exhaust system of an automobile. SOLUTION: This temperature sensor 1 is provided with a metal tube 3 with a tip part closed and with a temperature-sensitive element 2 such as a thermistor housed at the tip part, and a flange 4 with the metal tube 3 jointed to the inside surface and having a radially projecting part. The metal tube 3 is laser-welded to a sheath part 42 on the rear end side of the flange 4 in the circumferential direction. The sheath part 42 is protrusively extended from the rear end face of a flange part 41 of the radially projecting part of the flange 4 toward the rear end thereof, and heat transfer from a heat-sensitive part to the flange 4 or the like is restrained by laser-welding it on the rear end side like this. Since the laser-welded part is easily oxidized, it is preferably airtightly covered with a protective cover formed of stainless steel or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature sensor having a thermistor made of a semiconductor such as a metal oxide as a temperature sensing element. More specifically, it is a temperature sensor having an element sealed at the tip of a metal tube, and can be used for various applications requiring temperature measurement. In addition, it has sufficient durability even in temperature detection in a severe environment such as temperature change and vibration in the exhaust pipe and the like, and also suppresses heat transfer (hereinafter, referred to as “heat drawing”) from the heat-sensitive portion to the flange and the like. And a highly reliable temperature sensor.

[0002]

2. Description of the Related Art Conventionally, a cap is mounted on a distal end portion of a sheath, a thermistor as a temperature sensing element is sealed inside the cap, and the sheath is inserted through a flange and fixed at a predetermined position by caulking or the like. Temperature sensors having a different structure are known. The temperature sensor in which the temperature-sensitive element is sealed in the cap at the distal end of the sheath has a small diameter, is lightweight, suppresses heat from the distal end to the rear end, and has high reliability. Having. This temperature sensor also has excellent heat resistance at high temperatures and can be used for temperature detection in an environment where temperature changes rapidly, such as in a catalytic converter of an automobile or in an exhaust pipe.

[0003]

However, since the temperature sensor formed by the sheath and the cap on the distal end side from the flange in this way has low mechanical strength, it is difficult to assemble it with another member by a spiral, Although assembled, the strength of the entire sensor is not always sufficient. On the other hand, a temperature sensor having a structure in which a thermistor or the like is sealed at the front end of a metal tube having high strength and the rear end of the metal tube is joined to a flange is also used. Although this temperature sensor has sufficient strength and excellent durability, heat is easily drawn from the heat-sensitive portion to the flange and the like, and the reliability and the like may be reduced.

The present invention solves the above-mentioned conventional problems and has excellent mechanical strength and heat resistance, and can be used in a high-temperature and violent environment such as in a catalytic converter of an automobile or an exhaust pipe. It is an object of the present invention to provide a highly reliable temperature sensor which has sufficient durability even when used, and is capable of suppressing the heat from the heat-sensitive portion to the flange and the like.

[0005]

The temperature sensor according to the present invention comprises:
A metal tube in which a tip is closed and an element whose electrical characteristics change depending on temperature is housed in the tip, and a rear end of the metal tube is joined on an inner peripheral surface and a flange having a radially extending portion. The flange comprises a flange portion forming a radially extending portion, and a sheath portion extending to the rear end face of the flange portion and through which the metal tube is inserted. And the metal tube and the sheath are laser-welded in the circumferential direction.

In this temperature sensor, a metal tube having sufficient strength is used, so that the rear end of the metal tube can be press-fitted into a flange and assembled.
Since the rear end of the metal tube housing the elements such as thermistor at the front end thus closed is press-fitted and inserted into the flange, it has sufficient mechanical strength, and thus has the inside of the catalytic converter of the automobile. In addition, even when used in an environment with severe vibration such as in an exhaust pipe, a temperature sensor having excellent durability can be obtained.

[0007] The metal tube and the flange are integrally joined by laser welding, and this laser welding is preferably performed on the rear end side of the flange. It is preferable that the sheath of the flange is extended to protrude to the rear end side from the rear end face of the flange, and the metal tube is laser-welded in the sheath in the circumferential direction. By performing laser welding on the rear end side of the flange in this way, heat drawing is sufficiently suppressed, and the heat sensor has both sufficient mechanical strength and sufficient heat resistance, so that a highly reliable temperature sensor can be obtained. . It is preferable that the size of the flange be as small as possible. Due to the miniaturization, the heat capacity of the flange is reduced, and the heat drawing can be further suppressed.

In a temperature sensor in which an element is hermetically sealed, the inner surface of a metal tube or the like is oxidized at a high temperature, so that the oxygen concentration in the space in which the element is sealed is reduced, and the surface of the element is reduced. For example, the electrical characteristics of the element may change. This oxidation is particularly likely to occur at the laser-welded portion and its back surface, and when the laser welding of the metal tube and the flange is performed at the tip end where the temperature is high, the oxidation is more likely to proceed. Therefore, in order to suppress this oxidation, it is preferable to perform the laser welding on the rear end side of the flange, that is, on the sheath.

Preferably, a metal sheath wire having one end connected to the element is inserted through the metal tube. The other end of the metal sheath wire is joined to a pair of lead wires by a caulking terminal on the rear end side from the rear end surface of the sheath portion of the flange. In this way, the metal sheath wire is inserted into the metal tube from the element to the lead wire, so that there is no need for a step of separately filling insulating powder between the metal tube and the lead wire, and electrical insulation is achieved. It is definitely done.

Further, since the laser-welded portion is easily oxidized as described above and is easily corroded by various gases contained in automobile exhaust gas, the laser-welded portion is hermetically sealed with a protective cover. It is preferable to cover it. The protective cover can be made of stainless steel, Inconel (registered trademark), etc., and the laser weld is protected from corrosion by joining and fixing the protective cover to the laser weld by a method such as caulking. Can be.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically with reference to examples. (1) Structures of Temperature Sensors of Example and Comparative Example Example 1 (A metal tube was pressed into a sheath of a flange,
FIG. 1 is a cross-sectional view showing an example of the temperature sensor 1 of the present invention. The temperature sensor 1 uses the thermistor element 2 as a temperature-sensitive element, is attached to an exhaust pipe of an automobile, and is used for detecting the temperature of exhaust gas.

The distal end 31 of the metal tube 3 is closed by curling and welding.
Thermistor element 2 is housed inside. The periphery of the thermistor element 2 is filled with the cement 10, thereby preventing the thermistor element 2 from swinging due to vibration or the like during use. The rear end side 32 of the metal tube 3 is open, and this rear end side 32 is
Side, and a sheath 42 on the rear end side of the flange 4
Press fit. The rear end of the metal tube 3 is joined and fixed to the inner peripheral surface of the sheath 42 by laser welding from the outer peripheral surface of the sheath 42 of the flange 4.

A hexagonal nut 5 is provided on the outer peripheral surface of the flange 4.
1 and a nut 5 having a screw portion 52 are rotatably fitted. The temperature sensor 1 is fixed by a nut 5 with the distal end face of the flange 4 abutting on a predetermined position of the exhaust pipe.
A small-diameter portion is formed on the outer peripheral surface of the rear end of the sheath portion 42 of the flange 4, and one end of the joint 6 is fitted into the small-diameter portion and is argon-welded. The outer diameters of the joint 6 and the sheath 42 of the flange 4 are substantially the same, and there is almost no step at the connection.

A pair of metal sheath wires 7 are provided inside the metal tube 3, the flange 4 and the joint 6, and one end of the metal sheath wire 7 is connected to the thermistor element 2 by Pt / R.
It is connected via an h alloy wire 9. This alloy wire 9
The alloy wire 9 is formed by simultaneous firing with the thermistor element 2, and the alloy wire 9 is resistance-welded to the metal sheath wire 7.

On the other hand, the metal sheath wire 7 drawn from the rear end side 32 of the metal tube 3 inside the joint 6 includes:
One ends of a pair of lead wires 12 are connected by caulking terminals 11. The lead wire 12 is included in an auxiliary ring 13 made of heat-resistant rubber, and the other end is drawn out. The auxiliary ring 13 and the joint 6 are fixed to each other by caulking or hexagonal caulking of the joint 6 from the outer peripheral surface side, and are sufficiently adhered to maintain airtightness.
Thus, a sealed space is formed inside the metal tube 3, the flange 4, and the joint 6, and the thermistor element 2 is housed in the sealed space.

Since the temperature sensor 1 is used in a high-temperature environment as high as 1000 ° C., each component must have sufficient heat resistance. Therefore, the metal tube 3 and the metal sheath wire 7 are mainly composed of Fe,
It is formed of SUS310S which is a heat-resistant alloy containing Si, Mn, P, S, Ni and Cr. The flange 4 is made of SUS309S, which is a heat-resistant alloy having the same composition except that the amount ratio of Cr is slightly lower than that of SUS310S.
Is formed. Furthermore, the joint 6 is made of a SUS which is a heat-resistant alloy having the same composition except that the amount ratio of Cr is lower.
304.

The temperature sensor according to the first embodiment is characterized in that the rear end side 32 of the metal tube 3 is
1 is press-fitted into a sheath 42 extending from the rear end face, and the sheath 42 is laser-welded. As a result, a temperature sensor having excellent mechanical strength can be obtained, and heat dissipation can be sufficiently suppressed, so that a highly reliable temperature sensor having excellent heat resistance can be obtained.

Comparative Example 1 (Temperature Sensor without Metal Tube) As shown in FIG. 2, the temperature sensor of Comparative Example 1 does not have a metal tube, and the thermistor element 2 has a sheath 8
Are housed in a metal cap 14 attached to the distal end of the metal cap. Further, the metal sheath wire 7 is inserted inside the sheath 8. The sheath 8 is press-fitted into the sheath 42 of the flange 4 and is fixed by caulking from the outer peripheral surface at the rear end of the sheath 42. The other structure is the same as that of the temperature sensor of the first embodiment.

Comparative Example 2 (Temperature Sensor in which Metal Tube is Laser Welded on the Tip Surface of Flange) As shown in FIG. The structure is the same as that of the temperature sensor of the first embodiment except that the surface is laser-welded.

(2) Evaluation of Durability of Temperature Sensors of Examples and Comparative Examples The durability of each of the temperature sensors of Example 1 and Comparative Examples 1 and 2 was evaluated using actual vehicles. As a result, it was found that the temperature sensors of Example 1 and Comparative Example 2 did not have any cracks or the like and had excellent durability. On the other hand, in the temperature sensor of Comparative Example 1, it was found that cracks and the like occurred, mechanical strength was low, and durability was poor.

(3) Evaluation of Heat Removal of Temperature Sensors of Examples and Comparative Examples The heat removal of the temperature sensors of Example 1 and Comparative Examples 1 and 2 was evaluated. As a result, it was found that in the temperature sensor of Example 1, heat extraction was sufficiently suppressed. Comparative Example 1
Similarly, the temperature sensor was excellent without any problem regarding heat removal. On the other hand, in the temperature sensor of Comparative Example 2, since the metal tube and the flange were laser-welded on the high temperature side, it was found that heat was easily generated.

The present invention is not limited to the above-described specific embodiments, but can be variously modified within the scope of the present invention according to the purpose and application. For example, it is also possible to use a metal tube whose tip is closed by deep drawing of a steel sheet, instead of being closed by welding after curling the tip of the metal tube.
This metal tube has a uniform thickness at the distal end, and can be used as a more reliable temperature sensor. In addition, the response of the temperature sensor can be improved by making the thickness of the tip portion thinner than other portions.

Further, the inner peripheral surface of the front end of the flange can be tapered by inclining from the front end to the rear end, so that the operation of pressing the rear end of the metal tube into the flange can be easily performed. In other words, heat can be suppressed. In addition, in the vicinity of the tip of the flange, to increase the outer diameter of the metal tube, to cover the metal tube with a sheath,
Alternatively, the resonance frequency of the metal tube can be shifted to a higher frequency side by covering the metal tube with a sheath extending from the distal end of the flange. As a result, when used for detecting the temperature of the exhaust system of an automobile or the like, a temperature sensor that is more durable and does not cause cracks or the like due to vibration can be provided.

[0024]

According to the present invention, even when used in an environment in which temperature changes and vibrations are severe, such as inside a catalytic converter of an automobile and an exhaust pipe, the durability is excellent, the heat dissipation is sufficiently suppressed, and the reliability is improved. It is possible to provide a highly sensitive temperature sensor. Further, in the temperature sensor of the present invention, since the metal tube is used instead of covering the distal end side of the sheath with a cap, the strength is improved, and the metal tube can be easily pressed into the flange. Then, the metal tube and the flange are laser-welded to the sheath portion on the rear end side of the flange, so that heat drawing can be sufficiently suppressed.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of a temperature sensor of the present invention in which a metal tube is press-fitted into a sheath portion of a flange and laser-welded at the sheath portion.

FIG. 2 is a partial cross-sectional view of a temperature sensor in which a sheath is used instead of a metal tube, and a sheath portion of a flange and a sheath are fixed by caulking;

FIG. 3 is a partial cross-sectional view of a temperature sensor in which a metal tube is laser-welded at a distal end portion of a flange portion.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1; Temperature sensor, 2; Thermistor element, 3; Metal tube, 31; Front end side of metal tube, 32; Rear end side of metal tube, 4; Flange, 41; Flange part, 42; Sheath part, L ₁ ; Laser welded portion, L ₂ ; laser welded portion at the tip of flange portion, K; caulked portion between sheath and sheath, 5; nut, 51; hexagonal nut portion, 52; screw portion, 6; A metal sheath core wire; 8; a sheath;
9; Pt / Rh alloy wire, 10; cement, 11; caulking terminal, 12; a pair of lead wires, 13;
4: cap.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takaaki Nagasokabe 14-18 Takatsuji-cho, Mizuho-ku, Nagoya Japan F-term (reference) 2F056 QC04 QC06 3G004 DA25 GA01 GA04 GA06 3G091 AA02 AB01 DB10 EA17 HA35

Claims (4)

[Claims] 1. A metal tube in which a tip is closed and an element whose electrical characteristics change depending on temperature is housed in the tip, and a rear end of the metal tube is joined on an inner peripheral surface to protrude in a radial direction. A flange having a flange portion forming a projecting portion in the radial direction, and a sheath portion extending to the rear end face of the flange portion and through which the metal tube is inserted. A temperature sensor, wherein a tube is press-fitted into the sheath, and the metal tube and the sheath are laser-welded in a circumferential direction. 2. The metal tube and the sheath portion are laser-welded in a circumferential direction, wherein the sheath portion extends so as to protrude rearward from a rear end surface of the flange portion. A temperature sensor as described. 3. The temperature sensor according to claim 1, wherein a metal sheath wire connected to the element is inserted through the metal tube. 4. The temperature sensor according to claim 1, wherein a protective cover is provided to hermetically cover a portion where the metal tube and the sheath portion are laser-welded. .