JPS6242367Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Industrial Field of Application] The present invention relates to a resistive gas sensor used primarily to detect the concentration of carbon monoxide in exhaust gas discharged from engines such as automobiles, particularly diesel engines. [Prior Art] In order to reduce nitrogen oxides (NOx) in the exhaust gas of engines, especially diesel engines, it is possible to use a so-called EGR system that returns a portion of the engine exhaust gas to the intake side of the engine. It is valid. However, if the amount of exhaust gas recirculation, the so-called EGR amount, becomes too large, the combustion of intake gas within the engine will become incomplete, and the amount of CO and smoke in the exhaust gas will increase at the same time. Therefore, in the exhaust gas
It is desirable to detect the CO concentration and control the EGR amount based on the signal. Resistive gas sensors have traditionally been used to detect CO concentration in exhaust gas. A resistance-type gas sensor is a linear resistance formed on the surface of a bifurcated substrate with a pair of arms for standard use and detection use, and a linear resistance is formed on the back side of the substrate or inside the substrate. The resistance of the arm for detection is coated with a catalyst layer, and the catalyst layer of the arm for detection comes into contact with the exhaust gas, and the CO in the exhaust gas is absorbed by the catalyst layer. The CO concentration is detected by comparing the change in resistance due to reaction heat during oxidation with the resistance of the standard arm and outputting it as an output. Although it is a type of resistance-type gas sensor, it has a different structure in which the heat generation lead and the O ₂ detection lead are made of a common lead, and the lead is formed into a thin plate shape instead of the above-mentioned linear resistance. A detection device is disclosed in Japanese Patent Application Laid-Open No. 53-45289. [Problems to be solved by the invention] Conventionally, in this type of resistance gas sensor, the detection arm is heated by reaction heat as described above, but the detection arm is heated by reaction heat. The generated heat reaches from the base to the standard arm, that is, tends to spread throughout the entire resistance type gas sensor, which has the disadvantage of causing a delay in response. JP-A No. 53-45289 teaches that the lead and ceramic substrate are squeezed in the middle, but because the cross-sectional area of the thin plate-like lead is large, the amount of heat transmitted through the lead is large, and this technique has not been developed. Due to the fact that it cannot be directly applied to a gas sensor that uses a linear resistance with low heat transfer, and that the effect of squeezing the ceramic base material in a linear resistance gas sensor is not understood, the technique of the above publication cannot be applied directly to a gas sensor that uses a linear resistance type. It could not be applied to gas sensors. The present invention aims to improve the above-mentioned conventional drawbacks and prevent the diffusion of heat applied to the detection arm of a resistive gas sensor by reducing the aperture of the ceramic base material in a resistive type using a linear resistor. The purpose of this project is to study the effects, find an aperture that is effective for heat diffusion, and apply it to a resistive gas sensor, thereby preventing response delays. [Means for Solving the Problems] A resistive gas sensor according to the present invention for achieving the above object includes a plate-shaped substrate made of bifurcated ceramic with a pair of arms extending from the base, and A linear resistance formed on the surface of the substrate, a linear heating element separate from the linear resistance formed on the back surface of the substrate or embedded in the substrate, and one of the substrates. A catalyst layer is coated on the resistor of the arm part, and a narrow part is provided between the root part and the pair of arm parts in the plate-shaped substrate made of ceramic, and the width of the narrow part is the width of the root part. It consists of 1/2 to 1/6 of [Function] In the above resistance type gas sensor of the present invention,
Since the resistance is linear, heat conduction from the arms to the root body is mainly carried out through the ceramic base material, and the amount of heat transfer can be suppressed by squeezing the base material, but the width of the narrow part is the same as that of the root body. Since the aperture is set to 1/2 to 1/6 of the width, it is practically effective in preventing response delays, and an appropriate strength can be maintained. [Example] Figures 1 to 4 show an example of the resistive gas sensor element according to the present invention. It is a substrate of
A narrow portion 1d is formed between the two. The substrate 1 is made of silica, siyamoto, alumina, chromium, forsterite, spinel, chromium-magnesia, magnesia-chromium, carborundum,
The material is preferably a ceramic material such as zircon, zirconia, titanium, or cordierite, which has a low coefficient of thermal expansion and is heat resistant. The above example is
This is not intended to limit the invention. As shown in FIG. 1, linear resistors 2a, 2b are formed along the surfaces of the arm portions 1a, 1b of the substrate 1 in a shape that is reciprocated one or more times. For the resistors 2a and 2b, it is desirable to use a material having corrosion resistance and heat resistance, such as platinum or platinum-rhodium. As shown in FIG. 2, a linear heating element 5 is formed on the back surface of the substrate 1. The heating element 5 is
Platinum (resistance value 1-3Ω) from the viewpoint of corrosion resistance and heat resistance
It is preferable to use The heating element 5 is connected to the substrate 1
It may be buried inside. Resistor 2 excluding the terminal part
On the surfaces of a, 2b and the heating element 5, a coating layer 7 made of ceramic as described above is formed. The coating layer 7 prevents carbon contained in the exhaust gas from depositing on the surfaces of the resistors 2a, 2b and the heating element 5, and thereby preventing the resistors 2a, 2b and the heating element 5 from short-circuiting. As shown in FIG. 3, the coating layer 7 includes a dense layer 7a with a thickness of 5 to 15 microns made of dense ceramic particles with a particle size of about 300 to 500 mesh, and a particle size of 150 to 150 formed on the dense layer 7a at least in the resistor 2a portion. It consists of a coarse layer 7b with a thickness of 10 to 200 microns and made of coarse ceramic particles of about 300 meshes. A catalyst layer 4 is formed on the coating layer 7 of the arm portion 1a. If the surface layer of the coating layer 7 is made into a coarse layer 7b, the adhesion with the catalyst layer 4 will be improved. As the catalyst layer 4, the material contained in the exhaust gas is
It is desirable to use a platinum-based catalyst such as platinum, rhodium, palladium, platinum-rhodium, etc. that can cause a good catalytic reaction with CO. The above-mentioned catalyst is desirably applied to the ceramic as mentioned above.
Thickness of 20 to 300 μ supported at approximately % by weight
Form into a layer. In this way, a sensor body having a layered structure as shown in FIG. 3 is obtained. Cylindrical body 9 whose root part of the sensor body is shown in FIG.
It is inserted into a rectangular slit 10 extending in the axial direction. The cylindrical body 9 is made of the same ceramic as the substrate 1, and both ends thereof are cut off to form tapered portions 9a and 9b. The sensor body is made by printing electronic circuit printing ink on the surface of a base material made by mixing ceramic powder with synthetic resin as a primary binder and forming parts corresponding to resistors 2a and 2b and heating element 5. The resistors 2a and 2a are formed using ceramic slurry.
2b and the heating element 5 to form a portion corresponding to the coating layer, the cylindrical body 9 is manufactured by molding ceramic in the same manner as described above, pre-sintering the ceramic, and inserting the unfired sensor into the cylindrical body 9. By inserting it into the main body and firing it simultaneously, it can be made integral with the sensor main body as shown in FIG. The base end of the sensor body is exposed from the cylindrical body 9, the output of the resistor 2 is taken out from terminals 3a, 3b, 3c provided at the base end of the sensor body, and the heating element 5 is exposed at the base end of the sensor body. The signal is input from terminals 6a and 6b provided in the section. That is, the fourth
As shown in the figure, terminals 3a, 3b, 3c, 6a, 6
Ribbon-shaped lead wires 12a, 12b, 12
c, 12d, and 12e are connected, respectively. The lead wires 12a, 12b, 12c, 12d, and 12e are each made of a corrosion-resistant alloy such as Hastelloy, Inconel, Colmonoy, stainless steel, or the like. The above examples are not intended to limit the invention. The lead wires 12a, 12b, 12c, 12
d, 12e and terminals 3a, 3b, 3c, 6a, 6b
To connect platinum, gold, or
An ohmic connection can be obtained by applying a conductive paste made by kneading conductive metal powder such as silver with squeegee oil, polymerizing it to each terminal, and then covering it with the conductive paste. In order to protect the above-mentioned connection parts, it is desirable to further coat the connection parts with an inorganic adhesive 8. Examples of inorganic adhesives include glass-based adhesives, phosphoric acid polymer-based adhesives, ceramic-based adhesives, etc., and ceramic-based adhesives are preferable from the viewpoint of heat resistance and corrosion resistance. As described above, the sensor body includes ribbon-shaped lead wires 12a, 12b, 12c, 12d, 1
2e are connected, the connected portions are covered with an inorganic adhesive 8, and then housed in a protective cover 13 as shown in FIG. The protective cover 13 has a flange 14A
a mounting cylinder 14 which bulges out to the middle part and has a tapered stepped part 14B formed inside thereof in a shape corresponding to the tapered part 9b of the cylinder body 9 of the sensor body;
It consists of a cover part 15 attached to the tip of 4,
The cover portion 15 is provided with a large number of ventilation holes 15a. Insert the sensor main body into the protective cover 13, position the arm parts 1a and 1b inside the cover part 15, and press the tapered part 9b of the cylinder 9 into contact with the stepped part 14B of the mounting cylinder 14 via the metal packing 16. and then insert the cap 17 again.
A tapered portion 17 formed inside the tip portion in a shape corresponding to the tapered portion 9a of the cylindrical body 9 of the sensor body.
A is brought into contact with the tapered portion of the cylinder 9, and the ceramic packing 18 is inserted around the tapered portion 17A. Next, the nut 19 is screwed onto the outer periphery of the mounting tube 14, and the cap nut-shaped presser nut 20 is screwed onto the nut 19, so that the peripheral surface of the flange portion 20A, which is erected at the center inside the presser nut 20, is screwed onto the nut 19. It contacts and presses the ceramic packing 18 via the metal packing 21. In this way, the sensor main body is attached via the metal packing 16 at the tapered portions 9a and 9b of both ends of the cylindrical body 9, and the tapered stepped portion 14B of the mounting tube 14, the ceramic packing 18, and the metal packing 21. It is held between the peripheral edge surface of the flange portion 20A of the holding nut 20 and the tapered portion 17A of the cap 17, which is pressed. Therefore, the sensor main body is securely inserted into the protective cover 13 without wobbling due to the above-described tapered fixation of the cylindrical body 9. Furthermore,
The nut 19 screwed onto the outer periphery of the mounting tube 14 is tightened in the direction of the holding nut 20 to prevent the holding nut 20 from loosening. The sensor set as described above is attached to an appropriate location on the engine exhaust side and brought into contact with the exhaust gas. At this time, the flow direction of the exhaust gas is
Adjust the mounting position of the sensor so that it is perpendicular to the surface. At the same time, lead wires 12d and 12e
is input to the heat generating layer 5 via terminals 6a and 6b.
Substrate 1 to the extent that the catalytic reaction of CO occurs easily.
Heat it up. The heating temperature of the substrate 1 must be such that the hydrocarbon components HC and CO in the exhaust gas do not self-combust. Exhaust gas is substrate 1
When the exhaust gas comes into contact with the catalyst layer 4 in the arm 1a, CO in the exhaust gas reacts to become _CO2 , and the heat of reaction causes a temperature rise. The catalyst layer 4 is not present in the arm portion 1b, so the temperature does not rise due to reaction heat and is maintained at the reference temperature. Therefore,
The resistor 2a of the arm portion 1a has a higher temperature than the resistor 2b of the arm portion 1b, resulting in a difference in resistance value between the resistor 2a and the resistor 2b. As shown in FIG. 8, the resistors 2a and 2b are connected together with a fixed resistor 22 and a variable resistor 23 to form a bridge circuit in which a voltage E is applied, and the balance of the circuit is maintained by adjusting the variable resistor 23 as appropriate. However, if a difference occurs in the resistance values of the resistors 2a and 2b as described above, the balance of the bridge circuit is broken and the output voltage changes. This change in output voltage is drawn out from the lead wires 12a, 12b, 12c and detected as a sensor output, and the EGR amount is controlled based on the detected value. Other than the above-mentioned embodiments, in the present invention, as shown in FIG.
The shape of d may take various shapes. As described above, in the present invention, a bifurcated substrate with a pair of arms extended from the base, a linear resistor formed on the surface of the substrate, and a resistor formed on the back surface of the substrate or In a resistive gas sensor consisting of a linear heating element embedded within the substrate and a catalyst layer coated on a resistor on one arm of the substrate, a width is provided between the base of the substrate and the arm, respectively. Since the narrow width portion with a set ratio is provided, the heat applied to the arm portion is prevented from dispersing throughout the resistive gas sensor, and therefore, response delay is effectively prevented. be. In addition, the width of this narrow part
The ratio W ₁ /W between W ₁ and the width W of the root body needs to be 1/2 to 1/6. The reason is that when W ₁ /W > 1/2, the response delay prevention effect is small, and when W ₁ /W <
This is because the strength of the board decreases when it is 1/6, making it unsuitable for applications that are subject to vibrations and shocks in automobiles. FIG. 9 shows the relationship between W ₁ /W and sensor response speed. In FIG. 9, the vertical axis represents sensor output (mV), the horizontal axis represents time (sec), and the samples used are shown in Table 1.

[Effect of idea]

When using the resistance type gas sensor of the present invention, in the gas sensor using a linear resistance, a narrow part is provided between the root part and the bifurcated arm part, and the width of the narrow part is set to 1/2 to 1/2 of the root part. 6, the amount of heat transmitted through the ceramic base material to the root trunk can be suppressed to a small level, the delay in response can be suppressed to a small level, and there are no problems with strength.

[Brief explanation of the drawing]

The figures show one embodiment of the present invention, in which Fig. 1 is a plan view of the resistive gas sensor body, Fig. 2 is a back view, Fig. 3 is an enlarged side cross-sectional view of an arm covered with a catalyst layer, and Fig. 4 The figure is an enlarged partial plan view of the state in which the lead wire and terminal are connected, Figure 5 is a perspective view of the cylinder, Figure 6 is a sectional view taken along line A-A' in Figure 1 with the cylinder attached, and Figure 7 is a cross-sectional view of Figure 1 with the cylinder attached. The figure is a side sectional view of the resistive gas sensor body housed in the protective cover, Figure 8 is the circuit diagram, Figure 9 is a graph showing the relationship between W ₁ /W and response speed, and Figure 10 A and B. , C, D, and E are plan views showing other embodiments of the substrate. In the figure, 1... board, 1a, 1b... arm, 1d
...Narrow portion, 2a, 2b...Resistor, 4...Catalyst layer, 5...Heating element.

Claims (1)

[Scope of utility model registration request] A plate-shaped substrate made of bifurcated ceramic with a pair of arms extended from the base, a linear resistor formed on the surface of the substrate, and a resistor formed on the back surface of the substrate or embedded in the substrate. It consists of a linear heating element separate from the linear resistor, and a catalyst layer coated on the resistor on one arm of the substrate, and is paired with the root body in the plate-shaped substrate made of ceramic. A resistance type gas sensor characterized in that a narrow part is provided between each arm part of the body, and the width of the narrow part is 1/2 to 1/6 of the base part.