JPH0452895B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a detection device for measuring or controlling the oxygen concentration or air-fuel ratio in the exhaust gas of a combustion device such as an internal combustion engine or gas combustion equipment. .

[Prior Art] Conventionally, oxygen sensors have been used to detect the oxygen content of exhaust gas using an oxygen sensor constructed by adhering a porous electrode layer (e.g., a porous layer made of platinum) to an ion-conducting solid electrolyte (e.g., stabilized zirconia). It is generally known that, for example, an automobile engine can be controlled to operate at the stoichiometric air-fuel ratio by detecting the combustion state near the stoichiometric air-fuel ratio based on the change in electromotive force caused by the difference in pressure. There is.

By the way, the above oxygen sensor can obtain a large output change when the operating air-fuel ratio (A/F), which is the weight ratio of air and fuel, is the stoichiometric air-fuel ratio of 14.7.
There is almost no change in other operating air-fuel ratio ranges, and when the engine is operated at an air-fuel ratio other than the stoichiometric air-fuel ratio, the output of the oxygen sensor cannot be used.

In Japanese Unexamined Patent Publication No. 58-153155, two elements each having an electrode layer provided on both sides of the front side of a plate-shaped oxygen ion conductive solid electrolyte are arranged in parallel with a gap between them, and Oxygen concentration detection in which both elements are fixed by providing a bottom part, one element is an oxygen pump element, and the other element is an oxygen concentration battery element that operates based on the difference in oxygen concentration between the surrounding atmosphere and the bottom part. We are proposing a device. Although such an oxygen concentration detection device has good responsiveness, it has been found that when operated in a fuel-rich region lower than the stoichiometric air-fuel ratio of 14.7 corresponding to the output signal, it generates an output in the same direction as in a fuel-lean region. Ivy. In other words, since two air-fuel ratios correspond to the output, there is a problem that air-fuel ratio control can only be applied when it is clear whether the fuel is in the rich-fuel region or the fuel-lean region. Found out. It has also been found that with this detection device, it is difficult to detect or control the stoichiometric air-fuel ratio or the air-fuel ratio in the vicinity thereof with high accuracy or responsiveness.

[Object of the Invention] The first object of the present invention is to provide an air-fuel ratio that can be detected correctly and with good response in the entire operating air-fuel ratio (A/F) of a combustion device such as an internal combustion engine, from a fuel-rich region to a fuel-lean region. The second object of the present invention is to provide an air-fuel ratio detecting device that has the advantage of being able to perform accurate and easy feedback control when performing air-fuel ratio feedback control within the above air-fuel ratio range. be.

[Configuration of the Invention] In order to achieve the above object, the present invention employs the following configuration.

1 Equipped with a solid electrolyte oxygen concentration battery element and a solid electrolyte oxygen pump element in which porous electrodes are provided on both end faces of an oxygen ion-conducting solid electrolyte, at least one side surface of which is provided with an electric providing an insulating base, and providing a metal oxide semiconductor whose electrical properties change significantly with the stoichiometric air-fuel ratio on the surface of the electrically insulating base of the oxygen concentration battery element or the oxygen pump element;
An air-fuel ratio detecting plug section in which the oxygen concentration cell element and the oxygen pump element are arranged opposite to each other with a booth interposed therebetween, and an output signal from the metal oxide semiconductor determine whether the fuel is in a rich fuel area or in a fuel lean area. a first detection means for detecting, a pump current control means for controlling the supply of pump current to the oxygen pump element so as to keep the electromotive force of the oxygen concentration battery element constant; and a pump current control means controlled by the pump current control means. and an air-fuel ratio detection means for determining the air-fuel ratio by taking into account the pump current value detected by the pump current detection means and the detection result of the first detection means. .

2 A solid electrolyte oxygen concentration element and a solid electrolyte oxygen pump element each having porous electrodes provided on both end faces of an oxygen ion conductive solid electrolyte, and electrically insulated on at least one side of the element except for the porous electrode part. a metal oxide semiconductor whose electrical properties change greatly at the stoichiometric air-fuel ratio is provided on the surface of the electrically insulating substrate of the arithmetic concentration battery element or the oxygen pump element, and the oxygen concentration battery element and the oxygen pump element are arranged opposite to each other with a booth interposed therebetween, and a first air-fuel ratio detecting plug part for detecting whether the fuel is in a rich fuel region or a fuel lean region based on an output signal from the metal oxide semiconductor. a detection means, a constant pump current supply means for supplying a constant pump current to the oxygen pump element, an electromotive force detection means for detecting an electromotive force of the oxygen concentration battery element, and an electromotive force value detected by the electromotive force detection means. and air-fuel ratio detection means for determining the air-fuel ratio by taking into account the detection result of the first detection means.

[Effects of the Invention] The air-fuel ratio detection device of the present invention detects the air-fuel ratio (A/F).
can be detected accurately and with good response in the entire range from the fuel rich region to the fuel lean region.

[Example] Next, the present invention will be described based on an example shown in the drawings.

1 to 6 show embodiments of the present invention.

Reference numeral 1 indicates an exhaust pipe of an internal combustion engine, which is a combustion device, and reference numeral 2 indicates a detection plug portion of an air-fuel ratio detection device disposed within the exhaust pipe 1. 3 is the solid electrolyte oxygen pump element of the air-fuel ratio detection plug part 2, which is a flat plate about 0.5 mm thick with porous platinum electrode layers 4 and 5 about 20 μ thick provided on both sides using thick film technology. an ion-conducting solid electrolyte (e.g. stabilized zirconia) 6;
The porous platinum electrode 5 is shaped so as not to block the part of the porous platinum electrode layer 5 attached to one side of the ion-conductive solid electrolyte 6, for example, the side on which the porous platinum electrode layer 5 is provided. Window part a which is an adapted opening
A highly thermally conductive electrically insulating substrate 7 made of a plate-shaped, approximately 0.25 mm thick, highly thermally conductive, electrically insulating material (e.g. alumina, spinel, etc.)
(the substrate can be a formed board or a printed film) and a highly thermally conductive electrically insulating substrate 7
At the outer periphery of the window a on the side opposite to the surface of the ion conductive solid electrolyte 6, there is a gap between the outer periphery of the window a and the outer periphery of the highly thermally conductive electrostatic insulating base 7. An electric heater 8 provided to have
A flat high thermoelectric electrically insulating material 9 having a window b opening a porous platinum electrode layer 5 similar to the highly thermally conductive electrically insulating material 7 which is inscribed in the material and isolated from the outside. It is composed of.

10 is a solid electrolyte oxygen concentration battery element of the air-fuel ratio detection plug portion 2, and the porous platinum electrode layer 4 is provided on both sides.
and a flat ion-conducting solid electrolyte 13 similar to the ion-conducting solid electrolyte 6, which is configured by providing porous platinum electrode layers 11 and 12 using the thick film technology as in 5; Similar to the electrically insulating base 7, a window portion that opens a portion of the porous platinum electrode layer 11 is attached to one side of the ion conductive solid electrolyte 13, which is the side on which the porous platinum electrode layer 11 is provided. A high thermal conductive electrically insulating base 14 having a window c and a window c on the surface opposite to the ion conductive solid electrolyte 13 side of the high thermal conductive electrically insulating base 14, similar to the electric heater 8. An electric heater 15 provided on the outer periphery and an electric heater 15
The porous platinum electrode layer 11 is placed on the surface of the highly thermally conductive electrically insulating substrate 14 provided with the electric heater 15 therein, similar to the highly thermally conductive electrically insulating substrate 14 provided to isolate it from the outside. a flat plate-shaped highly thermally conductive electrically insulating base 16 having an opening window d;
Electric heater 15 made of highly thermally conductive electrically insulating material 16
A metal oxide semiconductor (e.g. titanium element) is formed using thick film technology to a thickness of about 50 μm above the window d on the opposite side to the side where the metal oxide semiconductor is installed.
It consists of 17. In addition, each electric element 4, 5, 8, 11, 12, 15, 17 provided in the oxygen pump element 3 and the oxygen concentration battery element 10
Lead wires 18 are respectively provided by thick film technology to provide electrical continuity to the outside.

The surface of the oxygen pump element 3 on the porous platinum electrode layer 4 side and the surface of the oxygen concentration element 10 on the porous platinum electrode layer 12 side form a booth 〓f with an interval of about 0.1 mm to 0.05 mm, and the air is evacuated. A heat-resistant and insulating spacer 19 is provided at the foot of the tube 1 so as to face each other inside the tube 1.
They are fixed to each other via (filling adhesive is fine). A support stand 21 having a threaded portion 20 on the outer periphery of the foot portion of the oxygen pump element 3 and the oxygen concentration battery element 10 fixed to each other by a spacer 19,
It is attached by an adhesive member 22 that is heat resistant and insulating. The air-fuel ratio detection plug portion 2 is attached to the exhaust pipe 1 by screwing the threaded portion 20 of the support base 21 into the mounting screw portion 23 of the air-fuel ratio detection plug portion 2 provided on the exhaust pipe 1.

Here, in order to manufacture the air-fuel ratio detection plug part 2, as shown in FIG. and its lead wires are printed in a predetermined pattern using thick film technology, and on one side, two green sheets of highly thermally conductive and electrically insulating material, such as spinel green sheets with a flat plate shape and a window, are printed. Between,
An oxygen pump element 3 having a ceramic laminated structure obtained by laminating and crimping a platinum resistor used as an electric heater and its lead wires, and then sintering them together;
As shown in FIG. 5, a lead wire for a metal oxide semiconductor such as titania is attached using a thick film technique on the surface of a highly thermally conductive electrically insulating base of the element, which is formed by the same process as the oxygen pump element 3. The oxygen concentration battery element 10 (the thick film of metal oxide is formed by sintering the above element and then firing in an atmosphere) printed in a predetermined pattern and sintered using the above-mentioned element is stacked with a seekness gauge in between. It is advantageous to adhesively fix the foot part with a spacer (heat-resistant ceramic adhesive) 19 in this state.

24 is an example of an attached electronic control device part (corresponding to pump current control means), which controls the electromotive force e generated between the porous platinum electrode layers 11 and 12 of the oxygen concentration battery element 10 through the resistor R1. Operational amplifier A
The transistor Tr is driven by the output of the operational amplifier A which is proportional to the difference between the reference voltage Vr applied to the inverting input terminal of the operational amplifier A and the reference voltage Vr applied to the non-inverting input terminal of the operational amplifier A.
It has a function of controlling the pump current Ip flowing between the porous platinum electrode layers 4 and 5. That is, it functions to supply the pump current Ip necessary to maintain the electromotive force e at a constant value of the reference voltage Vr. C is a capacitor. Further, in order to obtain an output signal corresponding to the pump current Ip supplied from the DC power supply B to the output terminal 25, a resistor R0 is provided (corresponding to pump current detection means). The oxygen concentration battery element 10 also includes an output terminal 26 for detecting a change in the resistance value of the metal oxide semiconductor 17 that occurs in the exhaust pipe 1 in response to a difference in oxygen concentration. Oxide semiconductor 17 and porous platinum electrode layers 4 and 5
and electric heaters 8, 15 that heat 11, 12.
are connected to heating power sources 27 and 28 via lead wires 18 and 18, respectively.

7 and 8 are characteristic diagrams of the air-fuel ratio detection device shown in FIGS. 1 to 6 above.

Figure 7 shows the results of measuring changes in the resistance value of the metal oxide semiconductor 17 at the output terminal 26. In the air-fuel ratio range (fuel rich range) smaller than the stoichiometric air-fuel ratio 14.7, the resistance is small. The value increases rapidly around the stoichiometric air-fuel ratio of 14.7, and the stoichiometric air-fuel ratio
It shows a large resistance value in the air-fuel ratio range greater than 17 (fuel lean range). Characteristic a in Figure 8 is the reference voltage
For example, when Vr is kept constant at 20mV, the electromotive force e
In order to make 20mV, the pump current Ip in the pumping direction decreases as the air-fuel ratio increases in the air-fuel ratio range (fuel rich range) smaller than the stoichiometric air-fuel ratio 14.7,
The stoichiometric air-fuel ratio decreases as the stoichiometric air-fuel ratio increases.
In an air-fuel ratio range greater than 14.7 (fuel lean range), the pump current Ip increases as the air-fuel ratio increases.

This embodiment utilizes the characteristics shown in FIGS. 7 and 8.

For the output terminal 26 that detects changes in resistance value, a point P, which is an arbitrary reference point, is set between the maximum resistance value and the minimum resistance value, and when the resistance value is smaller than point P (fuel rich area) and is larger than point P (fuel range) (corresponding to the first detection means).

Therefore, when the engine is operated in a fuel-rich region, the resistance value of the metal oxide semiconductor 17 is smaller than point P, and this information and the oxygen pump element 3
By detecting the output signal corresponding to the pump current Ip, detailed control or measurement can be performed in the fuel rich region (equivalent to air-fuel ratio detection means).

Further, when the engine is operated in a fuel lean region, the resistance value of the metal oxide semiconductor 17 is greater than point P, and an output signal corresponding to this information and the pump current Ip of the oxygen pump element 3 at this time is By detecting this, fine control or measurement can be performed in the fuel lean region (equivalent to air-fuel ratio detection means).

In addition, when controlling the above engine at a stoichiometric air-fuel ratio of 14.7, the output terminal 26 that detects the resistance value uses the characteristic that the resistance value rapidly decreases around the stoichiometric air-fuel ratio of 14.7 to perform direct or indirect feedback control. It is used as a signal to control the air-fuel ratio (corresponding to air-fuel non-detection means).

With the above configuration, it is possible to obtain an air-fuel ratio detection device capable of accurately and responsively measuring the above-mentioned air-fuel ratio in the entire range of the fuel-rich region, the stoichiometric air-fuel ratio point, and the fuel-lean region. . In addition, by utilizing this fact, once the desired air-fuel ratio is set, the current air-fuel ratio can be quickly detected by the air-fuel ratio detection plug part 2 attached to the exhaust pipe 1, and the desired air-fuel ratio can be continuously detected using the feedback. The air-fuel ratio can be controlled.

As mentioned above, the fact that the pump current Ip changes in proportion to the air-fuel ratio in the fuel lean region is described, for example, in the above-mentioned Japanese Patent Laid-Open No. 153155/1983. That is, by changing the oxygen concentration partial pressure of the exhaust gas introduced into the small gap f by the action of the oxygen pump element 3, it is made to differ from the oxygen partial pressure of the exhaust gas flowing in the exhaust pipe 1, and this oxygen concentration is changed. When controlling the pump current Ip supplied to the oxygen pump element 3 so that the electromotive force e of the oxygen concentration battery element 10 generated in response to the difference in pressure is constant, this pump current Ip is set to It was discovered that the amount of oxygen changes in proportion to the oxygen concentration inside. In addition, in the oxygen pumping mode in the fuel-rich region, the reason for the above operation seems to be that it is sensitive to CO gas.

FIG. 9 shows another embodiment of the air-fuel ratio detection plug part 2.

In this embodiment, high-temperature electrically insulating substrates 7, 9 and 1 have electric heaters 8 and 15 installed therein.
The outer peripheries of 4 and 16 are formed so as to protrude from the portions forming the ion-conductive solid electrolytes 6 and 13, respectively. This increases the area of each of the highly thermally conductive electrically insulating substrates 7, 9 and 14, 16, so the highly thermally conductive electrically insulating substrates 7, 9
and electric heaters 8, 1 provided at 14, 16
5 and metal oxide semiconductor 17 and each lead wire 18
Installation becomes easy.

In the above embodiment, the heater is disposed on the surface of either the oxygen pump element or the oxygen concentration battery element, and is embedded inside a highly thermally conductive electrically insulating base for maintaining the metal oxide semiconductor on the surface. However, if the temperature of the target gas is always sufficiently high and each element and metal oxide semiconductor can be activated without particular heating, the heater can be omitted.

In the above embodiment, the resistance value of the metal oxide semiconductor 17 was used as a criterion for determining the fuel rich region and the fuel lean region, but as shown in FIG. The characteristic of the change in the ratio of voltage (% of applied voltage) passing through the semiconductor 17 may be used (corresponding to the first detection means).

The direction of the pump current Ip of the oxygen pump element 3 was set in the direction of pumping out oxygen from the booth 〓f (IP〓0); ) The pump current Ip, which maintains the output of the oxygen concentration battery element constant even when flowing through the pump, changes in accordance with the air-fuel ratio, as shown in FIG. 1, so the characteristics when doing so may be utilized.

Furthermore, as shown in characteristic b in Fig. 8, when the pump current Ip of the oxygen pump element 3 (including both the case of pumping out oxygen from the booth f and the case of pumping it in) is controlled to be constant, Oxygen concentration battery element 1
Since the generated electromotive force e at 0 also changes in accordance with the air-fuel ratio, the characteristics when doing so can also be utilized (corresponding to constant pump current supply means).

The present invention utilizes various characteristics obtained from the air-fuel ratio detection plug portion 2, etc., singly or in combination, to perform feedback control, and continuously performs air-fuel ratio control within the entire operating range while frequently switching modes as needed. This is to perform feedback control of the fuel ratio.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the air-fuel ratio detection device of the present invention, FIG. 2 is a cross-sectional view taken along the line - in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line - in FIG. Figure 4 is a cross-sectional view taken along the - line in Figure 2, Figure 5 is an exploded view of the oxygen concentration battery element, Figure 6 is an exploded view of the oxygen pump element, and Figure 7 is the air-fuel ratio and resistance of the metal oxide semiconductor. Figure 8 shows the change in the pumping current Ip of the oxygen pump element with respect to the air-fuel ratio when the electromotive force e of the oxygen concentration battery element is constant, and the characteristic diagram showing the change in the pump current Ip of the oxygen concentration battery element with the constant pump current. FIG. 9 is a cross-sectional view showing another embodiment of the air-fuel ratio detection section, and FIG. 10 is a characteristic diagram showing changes in air-fuel ratio and applied voltage %. , No. 11 is a characteristic diagram showing the change in the forced pump current Ip of the oxygen pump element with respect to the air-fuel ratio when the electromotive force e of the oxygen concentration cell element is constant. In the figure, 2...Air-fuel ratio detection plug part, 3...Solid electrolyte oxygen pump element, 4, 5...Porous platinum electrode layer (porous electrode), 6...Ion conductive solid electrolyte (oxygen ion conductive solid electrolyte), 7, 9, 1
4, 16...High thermal conductivity electrically insulating base (electrically insulating base), 10...Solid electrolyte oxygen concentration battery element, 17...Metal oxide semiconductor, 24...Electronic control device (pump current control means), e...electromotive force,
f... Booth =, Ip... Pump current.

Claims (1)

[Scope of Claims] 1. A solid electrolyte oxygen concentration battery element and a solid electrolyte oxygen pump element each having a porous electrode on both end faces of an oxygen ion conductive solid electrolyte, the porous electrode on at least one side thereof An electrically insulating base is provided in a portion other than the stoichiometric air-fuel ratio, and a metal oxide semiconductor whose electrical properties change significantly at the stoichiometric air-fuel ratio is provided on the surface of the electrically insulating base of the oxygen concentration battery element or the oxygen pump element. , an air-fuel ratio detection stopper formed by arranging the oxygen concentration battery element and the oxygen pump element to face each other with a booth interposed therebetween; and an output signal from the metal oxide semiconductor.
a first detection means for detecting whether the fuel is in a rich fuel region or a fuel lean region; a pump current control means for controlling the supply of pump current to the oxygen pump element so as to keep the electromotive force of the oxygen concentration cell element constant; a pump current detection means for detecting the magnitude of the pump current controlled by the pump current control means; and an air-fuel ratio that takes into account the pump current value detected by the pump current detection means and the detection result of the first detection means. An air-fuel ratio detection device comprising an air-fuel ratio detection means for determining the air-fuel ratio. 2 Equipped with a solid electrolyte oxygen concentration battery element and a solid electrolyte oxygen pump element in which porous electrodes are provided on both end faces of an oxygen ion-conducting solid electrolyte, and at least one side surface of the battery element is provided with an electrically conductive part other than the porous electrode part. An insulating base is provided, and a metal oxide semiconductor whose electrical properties change significantly at the stoichiometric air-fuel ratio is provided on the surface of the electrically insulating base of the oxygen concentration battery element or the oxygen pump element, and the oxygen concentration battery element and the oxygen pump element are disposed opposite to each other with a booth interposed therebetween; and an output signal from the metal oxide semiconductor,
a first detection means for detecting whether the fuel is in a rich fuel region or a fuel lean region; a constant pump current supply means for supplying a constant pump current to the oxygen pump element; and an electromotive force for detecting an electromotive force of the oxygen concentration cell element. An air-fuel ratio detection device comprising: a power detection means; and an air-fuel ratio detection means for determining an air-fuel ratio by taking into consideration the electromotive force value detected by the electromotive force detection means and the detection result of the first detection means.