JPH01259252A - Gas sensor - Google Patents

Abstract

PURPOSE:To improve the insulating and sealing characteristics at the time of a high-temp. state by providing sealing glass consisting of 1st glass having a high insulating characteristic and 2nd glass having a prescribed coefft. of thermal expansion between a housing and a sensor element. CONSTITUTION:The sealing glass 10 is provided between the housing 3 which houses the sensor element 1 and sealing rubber 11 which constitutes a lead drawing out part. This sealing glass 10 is constituted of the 1st glass 10a and the 2nd glass 10b and has <=1.0X10<-6>/ deg.C coefft. of thermal expansion. The 1st glass 10a is constituted of a material which maintains the high insulating characteristic of >=1MOMEGA even at a high temp. of 450 deg.C together with the sealing characteristic. The 2nd glass 10b is constituted of a material which has the difference in the coefft. of thermal expansion from the housing within 2.0X10<-6>/ deg.C and surely maintains the sealing characteristic even at the high temp. The high insulating and sealing characteristics are then stably maintained even if the sealing glass part is put into the high-temp. state.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gas sensor, and particularly to an air-fuel ratio sensor used for purifying exhaust gas from an internal combustion engine.

[Prior Art and Problems] Generally, air-fuel ratio sensors maintain sensor characteristics by sealing a metal case and a sensor element using low-temperature adhesive glass.

However, with this type of air-fuel ratio sensor.

When the temperature of the seal reaches a high temperature of 450℃ or higher.

Electrical insulation deteriorates, causing problems with sensor output characteristics.

The present invention aims to solve these problems, namely to develop a gas sensor, especially an air-fuel ratio sensor, which has excellent sealing properties and electrical insulation properties even at high temperatures of 450°C or higher, and can stably maintain accurate sensor output characteristics for a long period of time. With the goal.

[Means for solving the problem] As a result of intensive research in view of the above, the inventors have discovered 1
We were able to complete this invention.

The present invention solves the above-mentioned problems by the following means.

A gas sensor in which a sensor element is housed in a housing, and at least a portion of the space between the housing and the sensor element is sealed with glass.

The sealing glass consists of a first glass located further forward and a second glass located further rearward.

The first glass has high insulation properties of 1 MΩ or more (450° C.).

The difference in thermal expansion coefficient between the housing and the second glass is 2, OX
within 10-6/'C, and the first glass and the second glass
The difference in thermal expansion coefficient with glass is 1. OX 10-6/'C
Within

gas sensor.

[Preferred embodiment and operation] Based on this configuration, even if the sealing glass part reaches a high temperature state (for example, 450°C), the first glass maintains high insulation properties, and the second glass maintains high insulation properties. By specifying the α difference, the sealing performance can be stably maintained.

The present invention is directed to a type of gas sensor in which a sensor element is insulated from a housing. This is because high-temperature insulation between the sensor element and the housing becomes a problem. Also, when the temperature of the seal part is 400℃ or higher during use, especially 450℃
It is preferably applied to gas sensors that are exposed to high temperatures of ℃ or higher. An example is an air-fuel ratio sensor. An air-fuel ratio sensor is one whose element is equipped with a heater to improve detection characteristics in low-temperature conditions, and one whose element is equipped with a heater to improve detection characteristics in low-temperature conditions.
In order to make it possible to use A/Fs other than the above, various types may be used, such as those equipped with pump elements. The sensor element may also be held in place by a high temperature, high strength material such as ceramics, such as alumina. As long as high-temperature insulation in the glass seal portion is a problem, the element shape may be either a plate, a circular tube, or a bag (test tube). When the element is plate-shaped or tubular, it is preferable to adopt a housing having a double structure inside and outside.

The housing and the sensor element must be sealed by a first glass located further forward and a second glass located further rearward. This is to ensure sealing properties and insulation properties, and to maintain highly accurate and stable detection characteristics of the sensor element. The glass seal basically restricts the gas to be measured from passing from the front of the sensor to the rear. Therefore, the sealing site may be at least partially between the housing and the sensor element as long as the gas passage can be restricted. Further, in the case where the sensor element is provided with a pump element or a heater, a glass seal may be similarly applied between the elements or between the element and the heater. Alternatively, a portion where a lead for outputting a signal from an element or the like is present may be sealed. Both 1st and 2nd glasses are 8
It is preferable to use a material that can be sealed at a temperature of 00° C. or lower. Further, it is preferable that the material has good wettability with the housing, elements, etc. to be sealed.

The first glass has sealing properties as well as high temperature (for example, 400
℃ or higher), it maintains high insulation properties. Therefore, it is preferable that the first glass be present in a portion of the glass seal portion that is exposed to a high temperature of 400° C. or higher during use. Insulation resistance according to the measurement method described later is 4500
The resistance at C is preferably 1 MΩ or more, preferably 5 MΩ or more. Also, 1 volume resistivity (450℃) is 107.3Ω
It is more than the mark, preferably more than the 10 g·2 Ω mark. This type of glass has PBO as its main component (60 to 70 v
't%), S i O15~25wt%, B2
ZrO, A as a plaster to something consisting of about 20 wt% O3
j! 203, spinel, zircon, mullite, silica (
It is preferable to use a mixture containing about 10 to 20 wt % of powder such as crystalline powder. The basic glass composition is the above PbO-
In addition to the 8iO-B O system, S t 02-BaO-
NaO-KO system, S i02 Z n O-
BO system, 5iO128a O-Ca O system, Si02-
It may also have a composition such as B203 series. Amorphous glass is preferred, but crystallized glass may also be used. The porosity is preferably 10% or less.

However, if it is in a closed pore state, it may exceed 10%.

The second glass reliably maintains sealing properties even under high temperatures. The difference in thermal expansion causes distortion between the housing (metal) and the sealing glass due to cooling and heating cycles when the sensor is used.

Considering long-term use, the seal glass part becomes brittle.

Is it necessary to prevent seal collapse due to cracks? Therefore, it is important to select and combine materials within a first-order thermal expansion difference. That is, the difference in thermal expansion coefficient with the housing (α difference) or 2. Within OX 10”/℃, preferably 1
．． It is recommended that the temperature be within 5×10′/°C. Also, the α difference with the first glass is 1. It is recommended that the temperature be within OX 10-6/°C, preferably within 0.5 x 10''/°C.

As this kind of glass, one having the same composition as the first glass is preferably used. The type and amount of supplementary rules may be adjusted as appropriate to achieve the above α difference. In order to ensure sealing performance, it is preferable to use a material with a small α difference from the metal material. The presence of the second glass reliably prevents exhaust gas from escaping from the front of the sensor to the rear even if the sealing performance of the first glass deteriorates under high temperature conditions. The second glass is preferably used in a glass seal portion whose temperature is 4008C or less during use.

This is because if the temperature exceeds 400° C., the insulation resistance will decrease, which may adversely affect the conductivity and sensor output characteristics. Preferably, it is used in a region with a temperature of 350° C. or lower.

[Example] Two aspects of the present invention will be described in detail below.

FIG. 1.2 is a diagram showing an embodiment in which the present invention is applied to an air-fuel ratio sensor A. In each figure, the air-fuel ratio sensor A generally includes a sensor element 1, a lead 2 for outputting a signal from the element 1, a housing 3 that houses the element 1, and a housing 3, the element 1, and the lead 2. and an intervening member 4 that is held apart. The sensor element 1 is plate-shaped and includes a pump element and a heater. The leads 2 are connected to the rear end of the element 1, extend rearward, and extend outside the housing 3. The housing 3 has an inner-outer double structure and includes a mounting bracket 5 as an outer cylinder and an inner cylinder 6. Further, a protective cap 7 is provided at the front of the mounting bracket 5, and a rear cylinder 8 is provided at the rear.

The intervening part side 4 has a ceramic holder 9. which holds the element 1 in a predetermined position. A sealing glass 10 that surrounds and insulates the rear end of the element 1 and the leading end of the lead 2. and a sealing rubber 1 that surrounds and insulates the lead 2 at the rear.
Consists of 1. The ceramic holder 9 has a front part 9a, a middle part 9b, and a rear part 9c whose restraints are slightly different, so that the coefficient of thermal expansion is adapted to the inner cylinder 6. The seal rubber 11 is also the front part 11
a, and a rear portion 11b.

The sealing glass 10 is a first glass lo located further forward.
a and a second glass lOb located further back,
Here, the axial distance of the first glass LOa is 13m+n,
The second glass is 1Ob or 7 dragons.

Further, an example of the sensor element is shown in FIG. FIG. 3 is a diagram showing a plate-shaped sensor element A obtained by laminated printing technology in a state before integration.

This example is of a closed chamber type equipped with a pump element. Laminated printing technology prints each component of the sensor element on a predetermined green sheet.

This refers to the technology of attaching this printed green sheet to a base material and baking it into one piece. For details, see JP-A No. 82-1501.
See 56. In FIG. 3, from below, the base material 12. − side electrode layer 13. First solid electrolyte layer (Green Sea 1-) 14. Other side electrode layer 15. Gas rate controlling layer 1B, spacer 17. − side electrode layer 18. Second solid electrolyte layer 19
．． Other side electrode layer 20. Electrode protective layer 21. The insulating layer 22 is positioned, the elements 12 to 22 are laminated, and fired and integrated.

Further, 17a is a measurement gas chamber, 23 and 24 are terminals for connecting the other side electrode to the outside, and 25 is a conduction port for connecting the other side electrode layer 15 and the terminal 23.

Reference numeral 22a indicates an opening formed corresponding to the position of the protective layer 21. For example, the dimensions of each element are as follows.

(a) Sample 12: 0.36X 3.8X 44mm
(b) Solid electrolyte layer 14.19: 0.3Bx 3
．． [iX 45+++n(c) electrode 13.15.18
．． 20: 2. OX4. Omm(d) Spacer 17
: 80g+n X 3. OX 44n+n+(e
) Measurement gas chamber 17a: 2. OX4. Omm again,
As for the material, the solid electrolyte layer 14.19 is Z r O2
Y 203 series, electrodes 13.15.18.20 are platinum/1
Consists of 6% ceramic.

[Test Example] In the air-fuel ratio sensor of the above example, four types of glasses A, B, C, and D shown in the table below were used alone or in combination as the seal glass.

The sealing properties and insulation properties were investigated. In addition, the inner cylinder is 5US403 (α=io, ox 10-6/℃)
.

Two types of 5US430 (α = lO, 4X 10-6/°C) were employed.

(Left below) *1: ``Yui'' indicates crystallized glass, and ``non'' indicates amorphous glass.

*2: Value measured with a 50 VMΩ meter at 450°C.

*3 Nigaras A and C are about 15w as a plaster on glass D.
t% ZrO, Aj70, spinel, zircon,
It is made by adding and mixing one or both of powders such as mullite and silica.

*4: The volume resistivity (Ωm) value at 450°C is calculated from the graph in Figure 4 based on the volume resistivity value at 250°C.

(a) Heat the tip part of the electrically insulating air-fuel ratio sensor with a Bunsen burner, change the temperature (°C) of the glass seal part to 450°C, check the insulation resistance (MΩ), and evaluate the insulation properties. do.

To measure the insulation resistance, connect a 50 VMQ meter between the mounting bracket 5 and the lead 2, and measure the temperature at the interface between the ceramic insulator 9 and the seal glass 10 as the glass seal temperature ('C).
The test was conducted with the heater not energized.

(b) Install the sealable air-fuel ratio sensor in a predetermined position on the actual engine vehicle,
The glass seal part was subjected to 100 hr durability at 400℃,
Evaluate sealing performance. That is, the front end face of the sealing rubber 11 is checked for white change and rubber hardening due to thermal decomposition (in the case of silicone rubber, generation of rubber crosslinking agent and further decomposition of siloxane bonds) due to gas leakage from the sealing glass portion IO.

The results for each evaluation item (a) and (b) are shown in Section 4.
They are shown in Figure 5.

As is clear from FIGS. 4 and 5, the first glass 10a is glass A or glass C1.
Only the combination using glass B as the second glass shows excellent results in terms of insulation and sealing properties.

That is, the air-fuel ratio sensor of the embodiment related to this combination is 450
Insulation resistance is 1M even at high temperatures of ℃! 2 or more” 2,
Maintains high sealing performance even after 100 hours of durability. Glass A, B.

When C and D are used alone or in combinations other than the examples listed in (g) above, neither the insulation nor the sealing performance satisfies a practical level. For example, if Glass D, which is a highly insulating glass, is used alone, the following problems may occur in terms of sealing performance. That is, the α difference between this highly insulating glass and the inner cylinder is 3. OX to -6/°C. Therefore, when using the air-fuel ratio sensor, if the tip of the sensor is exposed to exhaust gas and the exhaust gas reaches the rear glass seal, the difference in thermal expansion coefficient between the metal case and the highly insulating glass will result in high insulation. This causes cracks in the glass and reduces sealing performance. Then, exhaust gas passes through this crack and carbonizes the rubber seal portion located further back, causing poor conduction and deteriorating sensor output characteristics.

[Effects] As described in -1- below, according to the present invention, excellent sealing properties and electrical insulation properties are achieved even at high temperatures of 450°C or higher.

Accurate sensor output characteristics can be maintained stably for a long period of time.
This is extremely useful in the field of gas sensors.

[Brief explanation of the drawing]

FIG. 1 is a front half-sectional view and a plan view showing an air-fuel ratio sensor according to an embodiment of the present invention. Figure 2 is an enlarged view of Figure 1. FIG. 3 is an exploded perspective view of a sensor element according to one embodiment. FIG. 4 is a graph showing the relationship between glass seal temperature and insulation resistance (MΩ) for various glass seals. FIG. 5 is a graph showing the sealing properties of various glass seals when the temperature of the glass seal portion was maintained at 400° C. for durability. respectively. 1 Sensor element 3...Housing 10...Seal glass 10a...First glass 10b...Second glass Applicant NGK Spark Plug Co., Ltd. Agent Patent attorney Asami Kato (1 other person) Figure 3/ Fuko 21 Fig. 4 Glass enclosure section Onryo (0C)

Claims (1)

[Claims] A gas sensor in which a sensor element is housed in a housing, and at least a portion of the space between the housing and the sensor element is sealed with glass, comprising: a first glass in which the sealing glass is located further forward; It consists of a second glass located at the rear, and the first glass is 1M.
It has high insulation properties of Ω or more (450℃), and the difference in thermal expansion coefficient between the housing and the second glass is 2.0×1.
0^-^6/°C or less, and the difference in thermal expansion coefficient between the first glass and the second glass is within 1.0x10^-^6/°C.