JPH0743221A - Thermistor temperature sensor - Google Patents

Abstract

PURPOSE:To provide a thermistor temperature sensor the thermo-unit of which can be easily incorporated in a metallic tube and, at the same time, does not yield temperature errors, because it cannot be erroneously incorporated in the tube. CONSTITUTION:A thermistor temperature sensor is provided with a metallic tube 11, thermo-unit 20 housed in the tube 11, with the front end of the tube 11 being brought into contact with the front end section 111 of the tube, and lead wires 15. The unit 20 is provided with an insulated tube 21 and thermistor element 22 fixed to the front end section of the tube 21 and the front part of the tube 21 is fixed in the metallic tube 11 with cement 30. The maximum cross-sectional area Sa of the buried part 23 of the unit 20 in the cement 30 is set at 55-85% of the minimum hollow cross-sectional area of the part 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to automobile exhaust gas E
The present invention relates to a thermistor temperature sensor that measures the temperature of GR gas or the like.

[0002]

2. Description of the Related Art There are various types of temperature sensors, and one of them is a thermistor temperature sensor that utilizes the resistance change of the thermistor with respect to temperature. The thermistor temperature sensor measures the temperature by, for example, projecting the thermistor element from the tip of the insulating tube and bringing it close to the inspection object. In addition, in order to protect the thermistor element, the one in which the thermistor element and the insulating tube are housed in a metal tube is often used.

A structure using heat-resistant cement has been proposed as a method for fixing the thermistor element and the insulating tube to the metal tube (see Japanese Patent Laid-Open No. 62-278421). That is, the temperature sensor 9 is, as shown in FIG.
The thermo unit 90 in which the thermistor element 91 is projected from the tip of the insulating tube 922 and fixed to each other with an adhesive 921 is housed in a metal tube 93, and the thermo unit 90 is embedded in a heat-resistant cement 94 injected into the metal tube 93 and the thermo unit 90 described above. To fix.

Then, the lead wire 95 of the thermo unit 90 connected to the thermistor element 91 is connected to the lead wire 96 for taking out the signal in the metal tube 93. As described above, the method of fixing the thermo unit 90 to the metal tube 93 with the heat-resistant cement 94 (hereinafter, simply referred to as “cement”) has advantages that the number of constituent parts is small, the structure is simple, and the cost is low.

The cement 94 also serves to transmit the temperature of the fluid to be measured to the thermo unit 90 via the metal tube 93. Therefore, the cement 94 having relatively good thermal conductivity is used. In FIG. 8, reference numeral 97
Is a screw fitting for fixing the temperature sensor 9 near the temperature measuring unit.

That is, as shown in FIG. 9, in the temperature sensor 9, the temperature sensitive portion at the tip of the temperature sensor 9 is inserted from the screw hole provided in the accommodating portion 98 accommodating the fluid to be measured, and the screw fitting 97 is screwed into the screw hole. It is screwed onto and fixed to the accommodation portion 98. For example, when measuring the exhaust gas temperature of the engine, the tip of the temperature sensor 9 is inserted from the screw hole provided in the exhaust pipe of the engine, and the screw fitting 97 is screwed into the screw hole of the exhaust pipe. In FIG. 9, reference numeral 971 is a gasket.

[0007]

[Problems to be Solved] However, the thermistor temperature sensor for fixing the thermo unit using cement has the following problems. It is a workability problem of assembly in which the thermo unit is embedded and fixed in a metal pipe with cement.

The first point is that if the outer diameter of the thermo unit is made smaller than the inner diameter of the metal pipe, the thermo unit can be easily inserted and embedded in the cement, but the axis of the thermo unit is the shaft of the metal pipe. It means tilting with respect to the heart, or both axes deviating in parallel directions. If the axis of the thermo unit and the axis of the metal pipe are misaligned or tilted, the temperature detection value may vary and the response speed may change when measuring the temperature of the flowing fluid. Occurs.

That is, as shown in FIG. 9, when the temperature of the exhaust gas 99 flowing in the exhaust pipe as indicated by the arrow is measured, the axis 931 of the metal tube 93 and the axis 90 of the thermo unit 90 are measured.
If there is a deviation δ in 1, the response characteristic of the measured value changes depending on the mounting direction.

When the thermo unit 90 is inclinedly inserted into the metal pipe 93, the cement 94 enters rearward in a place where the gap between the thermo unit 90 and the inner wall 93 of the metal pipe is small, while in the place where the gap is large. Then the cement does not penetrate to the rear of the metal pipe. That is, the cement 94 does not uniformly cover the outer periphery of the thermo unit 90, and thus the heat conduction characteristics in the outer peripheral portion of the thermo unit 90 change, causing variations in the characteristics for each product.

On the other hand, when the difference between the outer diameter of the thermo unit 90 and the inner diameter of the metal tube 93 is small, that is, when the gap between the two is small, when the thermo unit is inserted into the metal tube, the resistance of the cement increases, It becomes difficult to insert the thermo unit. As a result, the thermo unit may not be inserted all the way to the front end of the metal tube, and similarly, temperature errors and response characteristics may change.

That is, when the thermo unit can be smoothly inserted into the cement, the operator can easily detect that the tip of the thermo unit has come into contact with the inner wall of the metal tube. However, if the cement insertion resistance increases, it becomes difficult to detect whether or not the tip of the thermo unit abuts the inner wall of the metal tube, and the gap g (Fig. 4) occurs.

When the above-described gap g occurs and the thermistor element retracts to the rear of the metal tube, heat transfer from the tip of the metal tube to the thermistor element is delayed, and the measured value is affected by the outside air temperature from the rear of the metal tube. There will be fluctuations. In view of the problems of the conventional thermistor temperature sensor, the present invention aims to provide a thermistor temperature sensor which is easy to assemble a thermo unit to a metal tube and which does not cause a temperature error due to a defective assembly. Is.

[0014]

According to the present invention, a metal pipe having a closed front end, a thermo unit housed close to the front end of the metal pipe, and a thermo unit connected in the metal pipe from the rear of the metal pipe. A thermistor temperature sensor having a lead wire pulled out, wherein the thermo unit has an insulating tube through which the lead wire is inserted and a thermistor element fixed to a front end portion of the insulating tube, and a front portion thereof. Is embedded and fixed in cement in the metal pipe, and the maximum cross-sectional area Sa in the cement-embedded portion of the thermo unit is
Is in the thermistor temperature sensor, which is between 55% and 85% of the minimum inner air cross-sectional area Sn in the cement embedding portion of the metal pipe excluding the front end portion.

What is most noticeable in the present invention is that the thermo unit is embedded and fixed in cement in the metal pipe, and the maximum cross-sectional area Sa in the cement burying portion of the thermo unit is the minimum inner space in the cement burying portion of the metal pipe. It is between 55 and 85% of the cross-sectional area Sn.

Since the front end portion of the metal pipe is closed, the tip portion of the metal pipe is not included in the range of the above-mentioned minimum inner empty cross-sectional area Sn. For example, when the cross-sectional area of the thermo unit and the inner air cross-sectional area of the metal pipe are both circular, the above numerical condition is that the ratio of the diameter d of the thermo unit to the inner air diameter D of the metal pipe is 0.74 to 0.92. Corresponding to being between.

[0017]

[Operation and effect] The maximum cross-sectional area Sa in the cement-embedded portion of the thermo unit is 85% or less of the minimum inner-air cross-sectional area Sn in the cement-embedded portion of the metal pipe. As a result, the cement resistance at the time of inserting the thermo unit is suppressed, and as shown in the experimental example (Fig. 3) described later, the thermo unit can be inserted (assembled) smoothly into the cement, and the tip of the thermo unit and the metal pipe The gap g (FIG. 4) between the tip inner wall is suppressed to a low level. That is, the thermistor element is inserted up to the tip of the metal tube, which enables accurate temperature measurement.

On the other hand, the maximum cross-sectional area Sa in the cement-embedded portion of the thermo unit is 55% or more of the minimum internal void cross-sectional area Sn in the cement-embedded portion of the metal pipe. this is,
As mentioned above, the outer diameter ratio of the circular cross section is 7
Equivalent to 4% or more. As a result, as shown in an experimental example to be described later, axial misalignment between the thermo unit and the metallic tube in the metal tube is suppressed, and temperature error due to axial misalignment and fluctuations in response characteristics can be suppressed to a low level ( See above, FIG. 9 etc.).

As described above, according to the present invention, a thermistor temperature sensor is provided which is easy to assemble the thermo unit to the metal tube and which does not cause a temperature error due to a failure in assembling the thermo unit to the metal tube. can do.

[0020]

EXAMPLE A thermistor temperature sensor according to an example of the present invention will be described with reference to FIGS. This example is a thermistor temperature sensor that measures the EGR gas temperature of the engine exhaust system. In this example, as shown in FIG.
And a front end portion 111 of the metal pipe 11
The thermistor temperature sensor 10 includes a thermo unit 20 that is housed in close proximity to the thermo unit 20 and a lead wire 15 that is connected to the thermo unit 20 in the metal tube 11 and pulled out from the rear of the metal tube 11.

The thermo unit 20 has an insulating tube 21 through which the lead wire 14 is inserted, and a thermistor element 22 fixed to the front end of the insulating tube 21, the front portion of which is the metal tube 1.
It is embedded and fixed in the cement 30 within 1. The maximum cross-sectional area Sa in the cement-buried portion 23 of the thermo unit 20 is 72%, which is between 55-85% of the minimum inner-air cross-sectional area Sn in the cement-buried portion 23 of the metal pipe 11 excluding the front end 111.

Each of these will be described in detail below. As shown in FIG. 9, the thermistor temperature sensor 10 of the present example is attached by screwing a metal fitting into a screw hole of the exhaust system EGR gas passage pipe of the engine. In the thermistor temperature sensor 10, as shown in FIG. 1, a cylindrical thermo unit 20 is housed in a cylindrical metal tube 11, and a front end portion 1 of the metal tube 11 is accommodated.
A thermistor element 22, which is a temperature measuring element, is arranged so as to be in contact with 11.

The thermo unit 20 is fixed to the metal tube 11 by the following steps. First, the MgO-based cement is mixed with water to form a mud. Then, a predetermined amount of the muddy cement 30 is injected into the front end portion 111 of the metal pipe 11 by using a dispenser or the like. The dispenser is an injector provided with a needle-like pipe.

Then, the thermo unit 20 is inserted straight into the cement 30 until the tip of the thermo unit 20 hits the metal tube 11. As the thermo unit 20 is inserted, the cement 30 is pushed backward,
Crawl up the gap between the outer periphery of the inner wall 113 and the inner wall 113 of the metal tube 11.

As a result, in front of the thermo unit 20, a cement embedding portion 23 covered with the cement 30 is formed. Then, cement 30 at room temperature to 200 ℃
The thermo unit 20 to the metal tube 11
Fixed to.

In the thermo unit 20, a thermistor element 22 is attached to the front end of an insulating tube 21, and as shown in FIG. 2, the insulating tube 21 has a lead hole 211 through which the lead wire 14 of the thermistor element 22 is inserted. Has been drilled. The lead wire 14 is fixed to the lead hole 211 with an adhesive 212. The insulating tube 21 is a cylindrical insulating tube made of magnesia ceramic and has a total length of about 21 mm.

The thermistor element 22 is a thermistor sealed with glass, and is attached to the insulating tube 21 by glass welding. The total length of the thermistor element 22 is about 3.8 mm. Then, as shown in FIG. 1, the lead wire 14 drawn out from the rear of the insulating tube 21 is connected to a lead wire 15 having a coating, and the lead wire 15 is
The thermistor temperature sensor 10 is pulled out from the rear side.

The lead-out portion of the lead wire 15 is provided with a rubber bush 16 and a protective tube 18, and the metal tube 1
1 is crimped and sealed. On the other hand, a screw fitting 12 is brazed to the outer circumference of the metal tube 11 at a position 5 to 10 mm from the tip of the metal tube 11. The front and rear length of the screw fitting 12 is about 15 mm.

The outer diameter d of the insulating tube 21 is 4 mm, and the inner diameter D of the metal tube 11 is 4.7 mm. Therefore,
Cross-sectional area Sa of the cement burying portion 23 of the insulating pipe 21
Is the inner cross-sectional area Sn of the cement burying portion 23 of the metal pipe 11.
72% of that. Further, the cement 30 is injected into the metal pipe 11 by a predetermined amount so that the length of the cement burying portion 23 of the thermo unit 20 is 5 mm or more.

Next, the function and effect of the thermistor temperature sensor 10 of this example will be described. In this example, the cement-embedded portion 23 of the thermo unit 20 has a length of 5 mm or more, and the thermo unit 20 (25 mm in total length, excluding the protruding portion of the lead wire 14) is embedded in the metal pipe 11 with required strength. Can be fixed. That is, while satisfying the vibration resistance of 490 m / S ² (50 G) or more required for automobile parts, a static tensile strength of 49 N (5 kgf) by the lead wire 15 is satisfied.

On the other hand, the outer diameter d of the insulating pipe 21 is equal to that of the metal pipe 11.
It is less than 85% of the inner diameter D of the cement, and the cement resistance becomes a reasonable value.
Can be inserted deep enough to the tip of the metal tube 11. That is, when the thermo unit 20 is manually inserted into the cement 30 in the metal tube 11, the gap g between the tip of the thermo unit 20 and the tip of the inner wall of the metal tube 11 shown in FIG. 4 can be suppressed to an extremely small value. .

FIG. 3 shows the change range of the gap g (upper and lower double arrows) and the thermistor temperature sensor 10 when the thermounit 20 is inserted while changing the outer diameter ratio d / D. It is a characteristic view which shows the change of a response characteristic. The response delay degree R in the figure is the delay degree (when the gap g is zero) of the time required for the thermistor temperature sensor 10 to reach a predetermined measurement value (63% value) when the temperature is changed in a step function. %).

Point A (13%) in the figure shows the allowable limit of the response delay degree in the specification,
As is known from the figure, the outer diameter ratio d / D is 0.92.
If it is below, the gap g is suppressed to 1 mm or less,
The response delay degree R can be suppressed within the allowable limit of 13%.

If the outer diameter ratio d / D is 0.74 or more, when the thermo unit 20 is embedded in the cement 30, the response characteristic of the thermistor temperature sensor 10 is greatly affected. It was possible to confirm by trial production that there was no axial misalignment between the metal tube 11 and the metal tube 11. As described above, according to this example, the thermo unit 2
It is possible to provide a thermistor temperature sensor which can be easily assembled to the metal tube 11 of 0 and which does not cause a temperature error due to a failure in assembling the thermo unit 20 to the metal tube 11.

Example 2 In this example, as shown in FIG.
4 is another embodiment in which 4 is composed of a small diameter insulating pipe 241 and a large diameter insulating pipe 242. That is, the insulating pipe 24 is composed of a small-diameter insulating pipe 241 having a diameter smaller than that of the insulating pipe 21 of the first embodiment and a large-diameter insulating pipe 242 having a diameter slightly larger than that of the insulating pipe 21 of the first embodiment. Has been done.

The cement 30 is a small diameter insulating pipe 241.
Since only the periphery of the thermocouple 200 is buried, the assembling work for inserting the thermo unit 200 into the metal tube 11 is easy, and the gap g hardly occurs. In addition, the large-diameter insulation pipe 242
Since the gap between the metal tube 11 and the inner wall of the metal tube 11 is small, it can be assembled so that the axis of the thermo unit 200 and the axis of the metal tube 11 are hardly misaligned. as a result,
The thermo unit 200 can be accurately assembled to the metal tube 11. Others are the same as those in the first embodiment.

Example 3 In this example, as shown in FIG. 6 and FIG.
This is another embodiment in which the insulating tubes 25 and 26 are not circular in cross-sectional shape (see FIG. 2). That is, the cross-sectional shape of the insulating tubes 25 and 26 of the thermo unit of this example is a partial circle (FIG. 6) or a rhombus shape (FIG. 7) whose side surfaces are cut.

However, in each of the insulating pipes 25 and 26, the cross-sectional area Sa is the inner cross-sectional area Sn of the metal pipe 11.
Is between 55 and 85%. Others are the same as those in the first embodiment.

[Brief description of drawings]

FIG. 1 is a sectional view of a thermistor temperature sensor according to a first embodiment.

FIG. 2 is a sectional view taken along the line BB of FIG.

FIG. 3 is a characteristic change diagram when the ratio of the outer diameter of the insulating pipe to the inner diameter of the metal pipe is changed in the first embodiment.

FIG. 4 is an explanatory diagram of a gap g in FIG.

FIG. 5 is a sectional view of a thermistor temperature sensor according to a second embodiment.

FIG. 6 is a sectional view taken along the line BB of FIG. 1 according to the third embodiment.

FIG. 7 is another sectional view taken along the line BB of FIG. 1 according to the third embodiment.

FIG. 8 is a sectional view of a conventional thermistor temperature sensor.

FIG. 9 is an explanatory view of a mounting state of a conventional thermistor temperature sensor.

[Explanation of symbols]

 10. ． ． Thermistor temperature sensor, 11. ． ． Metal tube, 111. ． ． Front end, 15. ． ． Lead wire, 20. ． ． Thermo unit, 21. ． ． Insulating tube, 22. ． ． Thermistor element, 23. ． ． Cement burial section, 30. ． ． cement,

Claims (1)

[Claims] 1. A metal pipe having a closed front end, a thermo unit housed near the front end of the metal pipe, and a lead wire connected to the thermo unit in the metal pipe and pulled out from the rear of the metal pipe. And a thermo unit having an insulating tube through which a lead wire is inserted and a thermistor element fixed to a front end portion of the insulating tube, the front portion of which is cemented in a metal tube. The maximum cross-sectional area Sa in the cement-buried portion of the thermo unit is the minimum inner-air cross-sectional area Sn in the cement-buried portion of the metal pipe excluding the front end.
Of the thermistor temperature sensor.