JPH0680427B2 - Pump type oxygen concentration detector - Google Patents

Description

TECHNICAL FIELD The present invention is set, for example, for an exhaust pipe of an automobile engine, detects the concentration of oxygen contained in the exhaust gas of the engine, and detects the concentration of oxygen in the engine. The present invention relates to a pump-type oxygen concentration detection device that is effectively used for air-fuel ratio control.

BACKGROUND ART For example, in order to execute air-fuel ratio control of an automobile engine, the oxygen concentration contained in the exhaust gas from this engine is detected to monitor the combustion state in the engine,
The fuel injection amount and the like are controlled according to the combustion state. That is, in order to control the air-fuel ratio of the engine, it is necessary to effectively detect the oxygen concentration in the exhaust gas of this engine. There is a concentration detector.

This pump type oxygen concentration detection device has a pump cell and a sensor cell in which electrodes are set on both sides of a solid electrolyte layer, respectively, and a sealed space having a specified volume is set between the pump cell and the sensor cell. is there. In this case, small holes are formed in the solid electrolyte layer forming the pump cell in order to allow gas diffusion between this space and the atmosphere to be measured outside.

In the pump-type oxygen concentration detection device configured as described above, the size of the space and the small holes is a major factor that determines the gas diffusion rate, and the state of the size is the output characteristic of the measuring device. It will greatly affect the response speed.

However, if the solid electrolyte layer constituting the above-mentioned pump cell is manufactured by means such as adhesion of a sintered body, integral sintering using a green sheet, etc. It is extremely difficult to perform stable control of the diffusion rate, and it is substantially difficult to achieve the required detection characteristic accuracy of the oxygen concentration detection device.

[Problems to be Solved by the Invention] The present invention has been made in view of the above points, and in particular, a measured gas chamber corresponding to a space formed between a sensor cell and a pump cell, and an external By making it possible to effectively control and set the gas diffusion rate with the gas atmosphere,
The oxygen concentration detection characteristics can be controlled in a stable manner, and the shape of the detection portion can be set relatively arbitrarily so that it can be effectively used, for example, in detecting the oxygen concentration in the exhaust gas of an engine. The present invention aims to provide a pump type oxygen concentration detecting device.

[Means for Solving the Problems] That is, the pump-type oxygen concentration detecting device according to the present invention is arranged such that electrodes to be formed on both surfaces of the solid electrolyte layer are arranged between the sensor cell and the pump cell, and the gas chamber to be measured is placed between them. In particular, the solid electrolyte layer of the pump cell and the gas chamber to be measured are constructed in a porous state, and the volume of the gas chamber to be measured can be accurately set, and the gas diffusion rate is also set. Is to enable effective setting control.

[Operation] In the pump-type oxygen concentration detecting device configured as described above, the solid electrolyte layer forming the pump cell and the ceramic layer forming the gas chamber to be measured are formed into a porous layer by, for example, plasma spraying. The gas is supplied to and discharged from the external gas atmosphere through the pores of the porous solid electrolyte layer that constitutes the pump cell. In this case, since the volume of the pores and the state of the pore distribution are to be easily controlled during the manufacturing process, the gas diffusion rate can be stably set with high accuracy. The measurement and detection characteristics of the oxygen concentration detection device are effectively and stably set.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 shows the cross-sectional structure. This pump-type oxygen concentration detecting device includes a sensor cell 11 and a pump cell.
A gas chamber 13 to be measured is formed between the sensor cell 11 and the pump cell 12.

The sensor cell 11 includes an oxygen conductive first solid electrolyte layer 111 composed of a dense sintered body such as ZrO ₂ —Y ₂ O _3.
And electrodes 112 and 113 made of porous Pt formed on both surfaces of the electrolytic chamber layer 111. Then, the gas chamber 13 to be measured is constituted by a porous ceramic layer such as Al ₂ O _{3 on} the upper layer of the sensor cell 11 thus configured. In this case, the porous ceramic layer is a layer formed by plasma spraying, the thickness and porosity of the ceramic layer, the type of spray material, particle size, by the choice of the spraying conditions, oxygen (O ₂₎ gas It is controlled so that movement can be performed smoothly. Specifically, the thickness is 50 to 200μ and the porosity is 10 to 20%.

The pump cell 12 is formed on the upper layer of the measured gas chamber 13, and the measured gas chamber 13 is formed so as to be enclosed between the pump cell 12 and the sensor cell 11. is there. The pump cell 12 is composed of a porous oxygen-conductive second solid electrolyte layer.
121, and porous electrodes 122 and 123 made of Pt or the like formed on both surfaces of the electrolyte layer 121. That is, the electrode 122 is formed on the upper surface of the ceramic layer forming the gas chamber 13 to be measured, and then the second solid electrolyte layer 121 is formed by plasma spraying or the like.
Then, the porous electrode 123 is formed on the surface of the second solid electrolyte layer 121.

Here, the second solid electrolyte layer 121 constituting the pump cell 12 needs to enable stable gas diffusion between the measured gas chamber 13 and the external gas atmosphere. Therefore, when forming the solid electrolyte layer 121, depending on the type of the spray material, the particle size, the selection of the spray conditions, the thickness 50 ~ 100μ,
Make sure that a porous state with a porosity of 3 to 10% is set.

In the oxygen concentration detection device, the measured gas chamber 13
And the first solid electrolyte layer 111 forming the sensor cell 11 for preventing diffusion of gas from the side surface of the pump cell 12.
Is a structure having a pair of walls 114 and 115 rising up on both sides of the measured gas chamber 13 and the pump cell 12.

That is, in the pump-type oxygen concentration detection device configured as described above, with respect to the pump cell 12, when the voltage V _P is applied and set from the DC power supply 14, and the current I _{P is made} to flow, by the oxygen pumping action, _A difference occurs between the oxygen partial pressure P _V of the measured gas chamber 13 and the external oxygen partial pressure P _A. Then, in this state, the shade electromotive force V _S is generated in the sensor cell 11 according to the Nernst equation. this
V _S is given by the following equation.

V _S = V ₀ ln (P _A / P _V ) (1) However, V ₀ = RT / 4F, R: gas constant, F: Faraday constant, T: temperature Also, at this time, oxygen molecules are pump cells. It moves between the measured gas chamber 13 and the external gas atmosphere through the pores of the second solid electrolyte layer 121. Now, if the number of oxygen molecules in the measurement gas chamber 13 and N _V, the following equation holds.

dN _V / dt = (−I _P / 4e) + σ _L (P _A −P _V ) ... (2) where σ _L is the oxygen diffusion coefficient and the measured gas chamber 1
3, a value determined by the diffusion resistance (thickness, porosity, etc.) in the second solid electrolyte layer 121. Also, the state equation P _V = NR
From T and the above equation (2), the following equation is established.

dP _V / dt =-(V ₀ I _P / V) + (P _A -P _V ) / τ _P ...... (3) However, τ _P = V / σ _L kT In the steady state, (dP _V / dt = 0), the following equation holds from the above equations (1) and (3).

I _P = 4eτ _L P _A [1-e × P (-V _S / V ₀ )] (4) In other words, if I _P is controlled so that V _S has a certain value, this
Since I _P and P _A have a proportional relationship, the oxygen concentration P _A in the external gas atmosphere can be detected from the measurement of I _P.

Such an oxygen concentration detecting device can be arbitrarily formed in shape, and can be formed in a cylindrical shape as shown in FIG. 2, for example. That is, the sensor cell
11 is molded into a cylindrical state, and the walls 114 and 115 are formed at both ends thereof by forming a brim. Then, the ceramic layer forming the gas chamber 13 to be measured and the pump cell 12 are wound around the outer circumference of the sensor cell 11 in a layered state.

With such a cylindrical or columnar configuration, for example, when measuring the oxygen concentration of the exhaust gas of an engine, fluctuations in the detection characteristics due to the directionality of the exhaust gas can be effectively suppressed. The attachability is also improved.

Here, the electrodes 112, 113, 122, and 123 may be appropriately formed by means such as chemical plating, paste application, sputtering, and vapor deposition, and the material of the porous layer forming the gas chamber 13 to be measured. In addition to Al ₂ O ₃ mentioned above, MgO
・ It is possible to use heat resistant ceramics such as Al ₂ O ₃ spinel. Further, the material constituting the solid electrolyte layer, ZrO ₂ -Yb ₂ O ₃ , CaO, MgO and the like in addition to the above-mentioned materials, further oxygen conductive material can be used as appropriate, vapor deposition, CVD It may be configured by such means.

FIG. 3 shows an example in which a concrete exhaust gas sensor device is configured by the cylindrical detection device as shown in FIG. 2. The detection device 20 as shown in FIG. It is set to be stored in. The housing 21 is attached and set to the exhaust pipe of the engine by a flange 22, and is a cover that covers the portion of the measuring device 20.
The 23 parts are exposed to the exhaust gas in the exhaust pipe.

The detecting device 20 is connected to the insulating tube via the spring 24.
25, the metal pipe 26 is set to hold down,
The metal cover 27 is used for caulking and fixing.
Further, the lead wire 28 of the pump cell and the lead wire 29 of the sensor cell of the detection device 20 are taken out through the wall portion of the solid electrolyte layer of the sensor cell and fixedly set by a paste or the like. In this case, a sealing material is filled in the penetrating portion of the lead wire. Further, in this case, the lead wire inside the sensor cell is set by welding to the metal stem 30, and the metal stem 30 is fitted in the hollow portion of the detection element 20 so that an electrical contact state is set. To do.

The pump type oxygen concentration detecting device 20 may be configured in a cup shape as shown in FIG. That is,
The first solid electrolyte 111 that forms the sensor cell 11 forms a tubular body, and one opening of the tubular body is closed, and an external gas atmosphere is introduced from the other opening. The electrode 112 is formed on the inner surface. Then, a cut step portion is formed on the outer periphery of this cylindrical solid electrolyte 11, and an electrode 113, a porous gas chamber 13 to be measured, an electrode 122, a porous second electrolyte layer 121, and an electrode 123 are formed in this portion. It is formed by sequentially laminating.

[Advantages of the Invention] As described above, in the pump-type oxygen concentration detection device according to the present invention, the volume of the gas chamber to be measured is controlled, and the thickness and porosity of the porous ceramic layer constituting this chamber are controlled. Therefore, it can be set with high accuracy, and by controlling the thickness and porosity of the porous second solid electrolytic chamber layer constituting the pump sensor,
The gas diffusion rate can be effectively set and controlled. That is, since it is possible to manufacture the above-mentioned porous second solid electrolytic chamber layer while controlling the pore volume and pore distribution, it is possible to adjust the gas diffusion rate of this detection device to a highly accurate state. In this case, the detection characteristics can be effectively set within the required accuracy.

[Brief description of drawings]

FIG. 1 is a sectional view for explaining the structure of a pump type oxygen concentration detecting apparatus according to an embodiment of the present invention, FIG. 2 is a sectional view showing a state of another embodiment of the detecting apparatus, and FIG. Sectional configuration diagram showing an example of an exhaust gas sensor device using a detection device,
FIG. 4 is a diagram showing still another embodiment of the present invention. 11 ... Sensor cell, 111 ... First solid electrolytic chamber layer (dense sintered body), 12 ... Pump sensor, 121 ... Second solid electrolytic chamber layer (porous structure), 13 ... Gas chamber to be measured (porous ceramic) Layers), 112, 113, 122, 123 ... Electrodes.

Claims (1)

[Claims] 1. A sensor cell formed by an oxygen-conductive first solid electrolyte layer made of a dense sintered body and porous electrodes formed on both surfaces of the electrolyte layer, and one of the sensor cells. Of the measurement target gas chamber formed in a state of being laminated on the surface of the first solid electrolyte layer, and a measurement target gas chamber configured to be composed of a porous layer, and being formed in a state of being stacked in the measurement target gas chamber. Surrounded by some,
A second solid electrolyte layer composed of a porous layer in which the movement of oxygen is restricted only in the thickness direction, and a pump cell composed of a porous electrode formed on both surfaces of the electrolyte layer, A voltage is set to be applied to the electrodes on both sides of the solid electrolyte layer of the pump cell, a pump current corresponding to the moving state of oxygen is generated in the solid electrolyte layer, and oxygen is sucked and discharged between the gas chamber and the outside. A pump type oxygen concentration detector characterized in that the above is performed.