JPH0536205Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a gas detector for detecting gas components or their concentrations.

[Prior Art] Conventionally, oxide semiconductors such as SnO2, ZnO, TiO2, and COO are used as gas detection elements as gas detectors for detecting the presence or concentration of gases in the atmosphere. There is a method that detects gas by utilizing the characteristic that its electrical resistance changes when it comes into contact with it. In recent years, in order to simplify the structure and improve productivity of this type of gas detector, hybrid technology has been developed, in which the detection element and its electrodes are thick-film printed on a substrate made of insulating ceramic material. Applications are being developed.

Conventionally, gas detectors are housed in a housing for gripping the detector and can be fixed at the location where the gas is to be detected. In the case of gas detectors equipped with elements, since the ceramic substrate itself has no irregularities, there are problems such as difficulty in determining the fixing position of the spacer used when fixing it in the housing. While the spacer protrudes from the substrate surface, the spacer is attached so as to come into contact with the ceramic substrate surface, so there was a problem in that the spacer came into contact with the detection element during the attachment process and could damage the detection element.

[Purpose of the invention] Therefore, the present invention provides a structure in which the spacer for fixing a gas detector having a detection element on a ceramic substrate in a housing can be easily positioned and the spacer is difficult to come into contact with the detection element. This makes it easy to install the gas detector housing.
Moreover, it is an object of the present invention to provide a gas detector that does not damage the detection element during installation work.

[Structure of the invention] That is, the invention, which has been made to achieve the above object, has the following features: As illustrated in FIG. A sensor electrode for connecting to the element layer to obtain a detection signal, a heat generating part for heating the element layer, and a heater electrode for supplying power to the heat generating part are formed inside. A flat ceramic substrate 2; and a first flat ceramic layer laminated on the same surface as the substrate surface from which the element layer 1 of the ceramic substrate 2 is projected, and having a thickness equal to or greater than the projection thickness of the element layer. 3, and a second ceramic layer 4 laminated on the surface of the first ceramic layer 3 opposite to the ceramic substrate 2, the first ceramic layer 3 and the second
The ceramic layers 4 of the ceramic substrate 2 are laminated in a stepwise manner from the element layer side of the ceramic substrate, and the heat generating portion is stacked on the first ceramic layer 4 of the ceramic substrate 2.
The gist of the present invention is a gas detector characterized in that the second ceramic layers 3 and 4 are formed in a thin wall portion around the element layer where the second ceramic layers 3 and 4 are not laminated.

[Embodiments] Hereinafter, an example in which the gas detector of the present invention is applied to an oxygen sensor for detecting the oxygen concentration in the exhaust gas of an internal combustion engine will be described as an embodiment of the present invention with reference to the drawings.

FIG. 2 is a partial cross-sectional view of the oxygen sensor. In the figure, 10 is a gas detector for detecting oxygen concentration, which includes a detection element 11 as an element layer protruding from a ceramic substrate, and 12 holds the gas detector 10 and connects the sensor to an internal combustion engine. A main metal fitting formed in a cylindrical shape for attachment, 13
is a protector attached to the internal combustion engine tip 12a of the metal shell 12 to protect the gas detector 10; 14 is a protector that protects the gas detector 10 together with the metal shell 12;
The gas detector 10 includes a spacer 15, a filling powder 16, and a glass seal 1.
It is gripped by the metal shell 12 and the inner cylinder 14 via 7. Further, a threaded portion 12b for attaching an internal combustion engine is cut on the outer periphery of the metal shell 12, and a gasket 18 is provided at a portion where the internal combustion engine comes into contact with the wall surface to prevent exhaust gas from leaking.

Here, the filling powder 16 is 1:1 of talc and glass.
The inner cylinder 14 of the gas detector 10 is made of a mixed powder of
The glass seal 17 is made of low melting point glass and is used to prevent leakage of the detection gas and to protect the terminals of the gas detector 10.

19 is an outer cylinder attached to the metal shell 12 so as to cover the inner cylinder 14; 20 is a sealing material made of silicone rubber; and lead wires 21 to 23;
This is for insulating and protecting the connection portions from the gas detector 10 that protrude from the glass seal 17 shown in FIG. 3 to the terminals 31 to 33. In addition, to connect the lead wires 21 to 23 and the terminals 31 to 33, as shown in FIG. Connect the tip with the crimping fittings 24 to 26, and then attach the crimping fitting 2.
This is done by caulking the terminals 4 to 26 to the terminals 31 to 33.

Next, the gas detector 10 of this embodiment is manufactured according to the procedure shown in FIGS. 5 to 10. In Figures 5 to 10, A is a front view of the gas detector 10 in the assembly process, and B is its A.
-A cross-sectional views are shown respectively. Furthermore, since these Figures 5 to 10 are for explaining the manufacturing process of the gas detector 10, the dimensions of each part are not made to correspond to the gas detector shown in Figure 2 for ease of understanding. The same applies to FIGS. 11 and 12, which will be described later.

Here, in each of the above figures 5 to 10, 40 to 43 are A12O3 with an average particle size of 1.5 μm.
92% by weight, SiO2 4% by weight, CaO2% by weight and
12 parts by weight of butyral resin and 6 parts by weight of dibutyl phthalate (DBP) were added to 100 parts by weight of a mixed powder consisting of 2% by weight of MgO, mixed in an organic solvent to form a slurry, and green was formed using a doctor plate. The green sheet 40 has a thickness of 1 mm, and the green sheet 41 has a thickness of 1 mm.
0.2mm, green sheets 42 and 43 are 0.8mm thick
It was created in advance.

44 to 49 are 7% Al203 to Pt.
44 and 45 are electrode patterns directly connected to the detection element 11 by stacking the detection element 11 on top, and 46 is an electrode pattern of these electrode patterns 44 and 45. A heating resistor pattern is formed around the heating resistor pattern 47 as a heat generating part that heats the detection element 11, and 47 to 49 are electrode patterns for printing a power supply on the heating resistor pattern 46 and extracting a detection signal from the detection element 11. . In addition, electrode pattern 4
Reference numerals 7 and 49 serve as the aforementioned heater electrodes that generate heat by applying power to the heat generating resistor pattern 46 as a heat generating part, and electrode patterns 44 and 45 that are directly connected to the detection element 11, and the electrode patterns 44. , 45 connected to the electrode pattern 48,
49 functions as the aforementioned sensor electrode for extracting a detection signal from the detection element 11.

As shown in FIG. 5, the production of the present gas detector 10 begins by printing each of the patterns 44 to 49 as a thick film on a green sheet 40 using platinum paste, and then, as shown in FIG.
Platinum lead wires 51 to 53 each having a diameter of 0.2 mm are disposed on the electrode patterns 47 to 49, respectively.

Next, as is clear from FIG. 7, openings 55 are formed in the green sheet 41 by punching to expose the tips of the electrode patterns 44 and 45. A green sheet 41 is laminated and thermocompressed onto the green sheet 40 to cover the green sheet 40. Here, the laminated body of the green sheet 40 and the green sheet 41 which are laminated and pressed together corresponds to the aforementioned ceramic substrate constituting the present invention, and later the detection element 11 which corresponds to the element layer is laminated within the opening 55. That will happen.

Subsequently, as shown in FIG. 8, a green sheet 42 is placed on top of the green sheet 41 of the laminate produced above.
The green sheets 43 are laminated and thermocompressed in a stepped manner on top of the green sheet 42 as shown in FIG. 9. Here, the above green sheet 4
2 corresponds to the above-mentioned first ceramic layer, and green sheet 43 corresponds to the second ceramic layer.

In this way, the platinum lead wires 51 to 53
Once a step-shaped laminate is created in which a portion of the electrode patterns 44 and 45 are exposed and the tips of the electrode patterns 44 and 45 are exposed, the laminate will be left in an atmosphere at 1500°C for 2 hours. , a ceramic substrate on which a first ceramic layer and a second ceramic layer are laminated is fired.

Thereafter, as shown in FIG. 10, a detection element 11 is provided in the opening 55 of the fired ceramic substrate. of platinum black is added, and further 3 parts of platinum black are added to the total powder.
The opening 55 is filled with a TiO2 paste which has been mixed in butyl carbitol (a trade name of 2-(2-butoxyethoxy)ethanol) to which ethyl cellulose has been added in an amount of 30% by weight and the viscosity is adjusted to 300 poise. It is formed by printing a thick film so that it adheres to the tip, and then leaving it in the air at 1200°C for 1 hour and baking it. Note that the protruding portion of the detection element 11 from the substrate is made thinner than the laminated and sintered green sheet 42 by 0.3.
mm or less.

The connections between the platinum lead wires 51 to 53 protruding to the outside of the gas detector 10 thus created and the terminals 31 to 33 are made by etching on a nickel plate with a thickness of 0.3 mm, as shown in FIG. Terminals 31 to 33 integrally formed by processing,
This is done by respectively disposing and welding the platinum lead wires 51 to 53. Note that the gas detector 10 is fixed to the metal shell 12 on the nickel plate on which the terminals 31 to 33 are integrally formed, and then a part of the substrate of the gas detector 10, the platinum lead wires 51 to 53, and the terminals 31 to 33 are connected to each other. The joint portion is protected by a glass seal 17, and after being fixed in the inner tube 14, it is cut into a predetermined length. In addition, A in FIG. 11 is a front view of the present gas detector 10,
B shows its right side view.

As explained above, in the oxygen sensor of this embodiment, since the substrate surface on the detection element 11 side of the gas detector 10 is formed in a stepped shape, the spacer 15 is attached to the gas detector 10 as shown in FIG. 10, positioning can be performed reliably at the stepped portion between the ceramic layer formed by the green sheet 42 and the ceramic layer formed by the green sheet 43. Furthermore, since the part of the gas detector 10 where the spacer 15 is fitted has a thickness greater than that of the detection element 11, the fitting hole of the spacer 15 is naturally larger than the part where the detection element 11 is fitted.
It will be possible to install it without damaging it. Therefore, the work efficiency of attaching the metal shell 12 of the present gas detector 10 is improved, and damage to the detection element 11 can also be prevented.

In the oxygen sensor created above, the heating resistor pattern 46 is heated by applying a heating power source between the lead wires 21 and 23;
Activate the detection element 11 and connect the leads 22 and 23.
The oxygen concentration can be detected by detecting the change in resistance between the two.

Next, the gas detector 10 of this embodiment is formed stepwise from the detection element 11 side by stacking the plate-shaped green sheets 40 to 43, so the detection element is simply mounted on the plate-shaped substrate. Compared to the case where the metal shell 12 is provided, earthquake resistance can be improved, and breakage at the attachment part to the metal shell 12 due to an external impact can be prevented. Further, the plate thickness of the tip portion of the gas detector 10 from which the detection element 11 protrudes is thinner, and the detection element 1
Since the heating resistor pattern 46 for heating the detection element 11 is formed, the detection element 11 can be quickly heated.

Furthermore, the electrode patterns 44 to 49 including the heating resistor pattern 46 are connected to the green sheet 41.
The opening 55 is formed between the green sheet 40 and the green sheet 41 except for the opening 55.
An element layer 11 is formed thereon. Therefore, the electrode patterns 44 to 49 are not exposed to the outside and are not corroded by the gas components to be measured.
The life of the sensor can be extended.

[Effects of the invention] As detailed above, in the gas detector of the invention, the first and second ceramic layers are laminated in a stepped manner on the protruding surface of the element layer of the ceramic substrate from the element layer side. Therefore, the gas detector can be easily positioned and fixed to a housing etc. by using the step between the first ceramic layer and the second ceramic layer, and the first ceramic layer is free from the ceramic substrate. Since it is thicker than the protruding thickness of the element layer, it is possible to prevent the spacer from coming into contact with the element layer and damaging the element layer when attaching a spacer for fixing the gas detector to a housing or the like.

Furthermore, in the gas detector of the present invention, the first and second ceramic layers are stacked on the ceramic substrate to form a step-like structure from the element layer side. Compared to the case where element layers are laminated on the substrate, earthquake resistance can be improved, and when the gas detector is housed in the housing, there is no risk of damage to the gas detector inside the housing due to external shocks, etc. can also be prevented.

Furthermore, since the heat generating part that heats the element layer is formed around the element layer or in the thin part of the ceramic substrate where the first and second ceramic layers are not laminated,
It becomes possible to quickly heat the element layer.

In other words, in a gas detector that has an element layer on a plate-shaped ceramic substrate, if the thickness of the ceramic substrate is increased in order to maintain its strength, the thermal conductivity from the heat generating part to the element layer will deteriorate, and conversely, heat generation will occur. If the thickness of the ceramic substrate is reduced in order to ensure thermal conductivity from the top to the element layer, the strength cannot be ensured, but in the present invention, the first and second ceramic layers are formed on the ceramic substrate in a step-like manner. In the ceramic substrate, the first and second ceramic layers are not laminated and the heat generating part is formed in the thin part, so while ensuring the strength of the gas detector itself, it is possible to reduce the heat transfer from the heat generating part to the element layer. This improves thermal conductivity so that the element layer can be heated quickly.

Furthermore, in the gas detector of the present invention, the heat generating part, the sensor electrode, and the heater electrode are formed inside the ceramic substrate, so there is no possibility that these parts will corrode when exposed to the gas to be measured. It is possible to prevent this and extend the life of the gas detector.

[Brief explanation of the drawing]

Figure 1 is a side view showing an example of the configuration of the gas detector of the present invention, and Figures 2 to 12 are examples of the gas detector of the present invention being applied to an oxygen sensor for detecting the oxygen concentration in the exhaust gas of an internal combustion engine. Figure 2 shows the entire structure of this oxygen sensor, Figure 3 shows the terminal part of the gas detector fixed inside the inner cylinder, and Figure 4 shows the lead wire connected to the terminal. 5 to 10 show the assembly procedure of the gas detector 10, and in each figure, A is a front view, B is an end view taken along line A-A, and FIG. 1 shows the connection of the terminals of the gas detector 10, A is a front view, B is a right side view, and FIG. 12 is a perspective view of the gas detector 10 with a spacer 15 attached thereto. 1... Element layer, 2... Ceramic substrate, 3...
First ceramic layer, 4... Second ceramic layer, 10... Gas detector, 11... Detection element, 1
2... Metal shell, 15... Spacer, 40, 4
1, 42, 43...green sheet.

Claims (1)

[Claims for Utility Model Registration] An element layer whose electrical resistance value changes depending on the gas component and its concentration is provided protruding from the substrate surface, and a sensor electrode connected to the element layer to obtain a detection signal; A flat ceramic substrate having a heat generating part for heating the element layer and a heater electrode for supplying power to the heat generating part formed therein; and a substrate surface of the ceramic substrate from which the element layer is protruded. a flat first ceramic layer laminated on the same surface as and having a thickness equal to or greater than the protrusion thickness of the element layer; and a flat first ceramic layer laminated on the surface of the first ceramic layer opposite to the ceramic substrate. a second ceramic layer; the first ceramic layer and the second ceramic layer are laminated in a stepwise manner from the element layer side of the ceramic substrate; . A gas detector characterized in that the first and second ceramic layers are formed in a thin portion around the element layer where the first and second ceramic layers are not laminated.