JP2612889B2 - Semiconductor exhaust gas sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention includes an n-type or p-type semiconductor element, and detects an oxygen concentration in exhaust gas based on a change in resistance value of the semiconductor element due to oxygen adsorption. The improvement of semiconductor exhaust gas sensors.

(Prior Art) The present applicant has proposed a semiconductor exhaust gas sensor of this type disclosed in Japanese Patent Application No. 61-230292 and drawings. In this device, as shown in FIG. 9, after a semiconductor element a made of an n-type semiconductor or a p-type semiconductor is embedded in the surface of a substrate b, the semiconductor element a can adsorb oxygen in the exhaust gas. As shown, except for the center portion, a ceramic material or the like is sprayed on a portion surrounded by a dashed line in the figure around the periphery to form a sprayed layer, and the semiconductor element a is held on the surface of the substrate b with the sprayed layer. The semiconductor element a is prevented from falling off from the substrate b.

Further, as disclosed in the specification and drawings proposed by the applicant of the present invention, particularly in FIGS. 1 (c) and (d) and FIG. 2 (c), the semiconductor exhaust gas sensor includes the semiconductor element a. The heater (20) is built in because the characteristic of the resistance value change of the semiconductor exhaust gas sensor changes according to the temperature, and the semiconductor heater a is heated by the built-in heater to set the semiconductor exhaust gas sensor within a set temperature range. Has been made to use.

Here, as for the specific configuration of arranging the heater, as shown in FIG.
Is printed, and the two substrates b and c are adhered to each other with an adhesive such as a cement material while the print heater d on the surface of the other substrate c is positioned on the back of the substrate b holding the semiconductor element a. And built into the semiconductor exhaust gas sensor.

By arranging the semiconductor exhaust gas sensor in the exhaust passage of the engine and forming a series circuit in which a predetermined voltage is electrically applied by the semiconductor element a and the additional resistor, the semiconductor element a is exhausted. When the resistance value changes by adsorbing oxygen in the gas, the partial pressure (output voltage) generated in the additional resistance of the series circuit is measured to detect the oxygen concentration in the exhaust gas (air-fuel ratio of the air-fuel mixture). It was done.

(Problems to be Solved by the Invention) In the above-described semiconductor exhaust gas sensor, the reason why the print heater d is located between the two substrates b and c is that when the print heater d comes into contact with the exhaust gas, its thermal influence is reduced. This is for the purpose of suppressing an exothermic function due to the reaction.

However, since the two substrates b and c are bonded with an adhesive such as a cement material, the adhesive layer is interposed between the substrate b having the semiconductor element a and the print heater d, and the thickness of the adhesive layer is Is different for each semiconductor exhaust gas sensor, the heat transfer from the print heater d to the semiconductor element a is different for each sensor, and the semiconductor element a
Cannot be heated to the same temperature range, and there is a disadvantage that the output characteristics are different for each sensor.

The present invention has been made in view of such a point, and its object is to provide a semiconductor exhaust gas sensor as described above,
By arranging the print heater in the vicinity of the semiconductor element while preventing its oxidation reaction, the print heater is prevented from contacting with the exhaust gas, and its heat generating function is sufficiently ensured. Effectively demonstrate the heating performance of the element and make it uniform between each sensor,
It is to improve the temperature characteristics of the semiconductor element for each sensor.

(Means for Solving the Problems) In order to achieve the above object, a solution of the present invention includes, as a semiconductor exhaust sensor, a semiconductor element housed in a hollow portion provided on a substrate surface, and oxygen adsorption of the semiconductor element is performed. It is assumed that the oxygen concentration in the exhaust gas is detected based on the change in the resistance value due to. A print heater for heating the semiconductor element is arranged on the substrate surface around the semiconductor element, and a part and the print heater are both formed on the surface of the semiconductor element by a dense thermal spray layer sprayed from above. It is configured to be held on the substrate surface.

(Operation) With the above configuration, in the semiconductor exhaust gas sensor according to the present invention, the semiconductor element is heated by the print heater disposed on the surface of the same substrate as the semiconductor element and around the semiconductor element. Since there is no adhesive layer such as a cement layer between the print heater and the semiconductor element, the semiconductor element can be heated to substantially the same temperature under the same heat generation condition of the print heater, and there is no variation between the semiconductor exhaust gas sensors. .

Moreover, the print heater is held on the substrate surface together with the semiconductor element by a sprayed layer that is sprayed on a part of the surface of the semiconductor element and holds the semiconductor element on the substrate surface,
Since this thermal spray layer is a dense thermal spray layer, the print heater is reliably shut off from the exhaust gas by the dense thermal spray layer and does not come into contact with the exhaust gas, so that the oxidation reaction is effectively suppressed and prevented. Is done. As a result, the temperature of the semiconductor element is reliably maintained within the set temperature range while the heating performance of the semiconductor element by the print heater is secured well, and the temperature characteristics can be improved.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a semiconductor exhaust gas sensor A according to the present invention. Reference numeral 1 denotes a substrate made of alumina, and a surface near the side of the substrate 1 has a surface as shown in FIGS. A recess 1a having a rectangular cross section for accommodating a semiconductor element is formed, and the recess 1a has a semiconductor element 2 made of, for example, an n-type semiconductor (Ba Sn O _{3 by a} chemical symbol) having substantially the same shape as this.
However, it is embedded with its surface exposed to the outside.
The semiconductor element 2 has a resistance characteristic in which the resistance value changes when oxygen is adsorbed.

Around the semiconductor element 2 on the surface of the substrate 1, a print heater 3 made of W / MO (tungsten / molybdenum) is disposed so as to surround the semiconductor element 2 from outside. The semiconductor element 2 is heated through the heating.

In addition, immediately above the surface of the semiconductor element 2, a fourth
As shown in FIG. 5 and FIG. 5, an elastic alumina fiber 4 formed in a hollow square shape is disposed so as to cover only the periphery of the semiconductor element 2.

Thus, Mg Al ₂ O ₄ was formed on the surface of the substrate 1 by spraying Mg Al ₂ O ₄ from above the substrate 1 except for the central portion of the semiconductor element 2 within a range indicated by a chain line in FIG. Two thermal spray layers 5 and 6 are provided, and the two thermal spray layers 5 and 6
The entire surface of the print heater 3 and the alumina battle area 4 and the peripheral portion that is a part of the surface of the semiconductor element 2 are covered and held on the surface of the substrate 1.

In the two thermal spray layers 5, 6, the lower thermal spray layer 5 is made of porous MgAl ₂ O ₄ having a large particle size (for example, 30 μm or less), and the upper thermal spray layer 6 is Small (eg 1-10
It is composed of dense Mg Al ₂ O ₄ (about μ).

Thus, the semiconductor exhaust gas sensor A as described above is electrically connected in series with an additional resistor (not shown) separately provided by the semiconductor element 2 to form a series circuit to which a predetermined voltage is applied. When the semiconductor element 2 is disposed, for example, in an exhaust gas passage of an engine and adsorbs oxygen in the exhaust gas and its resistance value changes, the voltage (partial voltage) generated across the additional resistance of the series circuit changes. By detecting the partial pressure signal (output voltage), the oxygen concentration in the exhaust gas, that is, the air-fuel ratio of the air-fuel mixture supplied to the engine is detected.

Next, FIGS. 6 to 8 show a specific example configuration in which the semiconductor exhaust gas sensor A as described above is disposed in the exhaust passage of the engine. In FIG. 6, a pair of lead wires 8 connected to the semiconductor element 2 to form a series circuit are arranged at the rear end of the substrate 1 in the axial direction of the substrate 1, and each of the lead wires 8 A pair of copper wires 9 is connected to the rear end portion on an extension thereof. Similarly, the print heater 3
At the rear end, a pair of lead wires 10 is connected to the print heater 3 so as to energize the print heater 3, and at the rear end of each lead wire 10, a pair of copper wires 11 are provided. It is connected.

As shown in FIG. 7, the rear of the substrate 1 from the center is protected by a ceramic protective tube 12 covering the substrate, and the respective lead wires 8, 10 and the conductive wires 9, 11 are respectively provided for preventing contact. Are protected by the spacers 13 and 14.

In addition, as shown in FIG. 8, the outside of the semiconductor exhaust gas sensor is surrounded by a holder 15 except for a portion ahead of the central portion of the substrate 1 (the portion where the semiconductor element 2 is located). At the tip of the head portion 15a, double inner and outer protectors 16, 17 covering the semiconductor element 2 are disposed to prevent unburned components in the exhaust gas from adhering to the semiconductor element 2. .

Therefore, in the above-described embodiment, in the semiconductor exhaust gas sensor A, the print heater 3 is arranged on the substrate 1 in which the semiconductor element 2 is embedded and around the semiconductor element 2, so that the conventional two-dimensional sensor is used. Since there is no cement layer for bonding the substrate, the heat transfer from the print heater 3 to the semiconductor element 2 is improved, and the temperature characteristics of the semiconductor element 2 can be improved. In addition, even when the exhaust gas sensor A is mass-produced, the heat transfer between the sensors is made uniform, the variation is prevented, and the output characteristics of the semiconductor element 2 can be made substantially the same between the sensors. .

The print heater 3 is held on the surface of the substrate 1 together with the semiconductor element 2 by spraying layers 5 and 6 for preventing the semiconductor element 2 from being pulled out of the substrate 1. The sprayed layer 6 serves as a partition wall between the print heater 3 and the exhaust gas, so that the contact of the print heater 3 with the exhaust gas is effectively suppressed or prevented. Is sufficiently suppressed and prevented, and the heat generation performance is effectively maintained. Therefore, the preheater 3 is arranged near the semiconductor element 2 on the surface of the substrate 1 while reliably preventing the oxidation reaction of the print heater 3, and the temperature characteristics of the semiconductor element 2 are made uniform among the sensors to improve the same. Can be.

Moreover, since the thermal sprayed layers 5 and 6 have a two-layer structure and the lower thermal sprayed layer 5 is porous, the adhesive force is increased by the buffer effect, and the semiconductor element 2 and the print heater 3 are attached to the surface of the substrate 1. It can be securely held. In addition, the semiconductor element 2
Is thermally affected by the temperature of the exhaust gas, the thermal expansion of the semiconductor element 2 is absorbed by the alumina fibers 4 because the alumina fibers 4 on the outer surface of the thermal spray layer have elasticity. No peeling of 5,6 occurs.

In the above embodiment, an n-type semiconductor is used as the semiconductor element 2. However, the present invention can be applied to a p-type semiconductor or a semiconductor exhaust gas sensor that uses both of them to linearly detect the oxygen concentration in the exhaust gas. Of course, the spray material is Mg A
The material is not limited to l ₂ O ₄ and may be another spray material.

(Effect of the Invention) As described above, according to the semiconductor exhaust gas sensor of the present invention, a print heater is arranged on the surface of the substrate containing the semiconductor element and around the semiconductor element, and the print heater is held by the semiconductor element. The thermal spray layer is held on the substrate surface together with the semiconductor element by a thermal spray layer, and this thermal spray layer is formed of a dense thermal spray layer, so that the oxidation reaction caused by the contact with the exhaust gas of the print heater can be effectively suppressed and prevented. By improving the heat transfer to the element, the output characteristics of the semiconductor element among the sensors can be made uniform, and the temperature characteristic of the semiconductor element can be improved.

[Brief description of the drawings]

1 to 8 show an embodiment of the present invention, FIG. 1 is a perspective view showing a main part of a semiconductor exhaust gas sensor, FIG. 2 is an enlarged view of the main part, and FIG. FIG. 4 is a plan view of the essential part, and FIG. 5 is a vertical sectional view of the same. 6 to 8 show a specific structure of the semiconductor exhaust gas sensor when it is arranged in the exhaust passage of the engine. FIG. 6 is a side view of the main part, and FIG. FIG. 8 is a plan view of a main part with a holder added. The ninth
FIG. 1 is a perspective view of a main part of a semiconductor exhaust gas sensor showing a conventional example. DESCRIPTION OF SYMBOLS 1 ... board | substrate, 2 ... semiconductor element, 3 ... print heater, 5 ... inner thermal spray layer, 6 ... outer thermal spray layer.

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-292049 (JP, A) JP-A-63-83649 (JP, A) JP-A-1-203954 (JP, A)

Claims (1)

(57) [Claims] 1. A semiconductor exhaust gas sensor comprising: a semiconductor element housed in a recess provided on a surface of a substrate; and detecting an oxygen concentration in exhaust gas based on a change in resistance value of the semiconductor element due to oxygen adsorption. A print heater for heating the semiconductor element is disposed on the surface of the substrate around the semiconductor element. A part of the surface of the semiconductor element and the print heater are both formed by a dense thermal spray layer sprayed from above. A semiconductor exhaust gas sensor characterized by being held in a semiconductor exhaust gas sensor.