JPS5861455A - Detecting apparatus of air-fuel ratio - Google Patents

Abstract

PURPOSE:To measure the air-fuel ratio quickly and highly accurately in a wide measuring range from rich to lean, by using an oxide semiconductor sensor only on the rich side and switching to a threshold current type oxygen sensor on the lean side. CONSTITUTION:An output of a thermocouple of a TiO2 sensor 1 is introduced into a temperature regulator 23 through an automatic cold junction compensator 19, a measuring amplifier 20, an attenuator 21 and an automatic cold junction compensator 22. A characteristic of resistance of TiO2 to the air-fuel ratio is changed suddenly in about 10<4> times at a boundary of rich and lean. Accordingly, its middle value is set at the standard resistance in a standard resistance setting device 29 and on the other hand, dimensions of the resistance of the sensor are extracted by a temperature compensator 25 and then, both dimensions are compared by a rich and lean decision device 30. When the sensor resistance is small, it is decided as rich and when said resistance is large, it is decided as lean. A threshold current type oxygen sensor 6 is connected to a threshold current voltage and current detection part. The voltage is applied only in case of deciding as lean by the device 30.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio detection device for measuring the air-fuel ratio of exhaust gas from an automobile engine or other combustion device, and particularly relates to an air-fuel ratio detecting device for measuring an air-fuel ratio of exhaust gas from an automobile engine or other combustion device. ) range and a fuel shortage (hereinafter referred to as lean) range.

In today's society, from the viewpoint of environmental protection, it is required to reduce as much as possible harmful components contained in exhaust from various combustion devices including automobile engines.

In order to meet this demand, various adjustments have been made, including ignition timing and EGR, but among these adjustments, the air-fuel ratio adjustment can be said to be the most fundamental. Therefore, there are many opportunities to measure the air-fuel ratio at the Kibi factory, research department, etc. Generally, in Ennon, combustion at near the stoichiometric air-fuel ratio provides high output, and in many cases, there are few harmful components in the exhaust gas.

However, in reality, the air-fuel ratio deviates from the set value due to various reasons, so it becomes necessary to measure and adjust the fc ratio.

The following factors are considered to cause the air-fuel ratio to deviate.

■ When operating the choke during a cold start If the engine runs slowly during a cold start, some of the fuel will adhere to the intake manifold wall and the rate of reaching the inside of the cylinder will decrease. The air-fuel ratio tends to become fuel rich (hereinafter simply referred to as Rich). At this time, a large amount of harmful gas is likely to be generated.

■ Transient states such as acceleration/deceleration Engines experience various fluctuations, so fluctuations are unavoidable even if you try to operate in a steady state.In that sense, the engine is always in a transient state, but particularly large transient states appear during acceleration/deceleration. . The reason why the air-fuel ratio fluctuates during transient conditions is due to the following reasons: In other words, the state of fuel flow in the intake manifold downstream of the carburetor, fuel injection valve, etc. of an engine that uses liquefied fuel such as gasoline is A part of the flow is vaporized and the other part is liquid, creating a so-called gas-liquid two-phase flow.

Assuming that the air-fuel ratio can be adjusted to the stoichiometric air-fuel ratio in a steady state, there will be a certain ratio of gaseous flow and liquid flow in a steady state. Taking deceleration as an example, the fuel from the carburetor decreases, and the fuel in the cylinder must also decrease.

Gaseous flow has a short delay time, so there is no problem, but liquid flow has a long delay time, so the fuel in the cylinder does not decrease immediately and becomes rich.

■ Differences in air-fuel ratio between cylinders It is no exaggeration to say that all practical car engine engines are multi-cylinder engine systems. Since each cylinder inevitably has some kind of asymmetry, variations occur in fuel distribution, resulting in differences in air-fuel ratio between cylinders. The difference between cylinders is relatively small in EFI engines, but it can be quite small in carburetor engines. As cylinder wholesalers become larger, engine characteristics and title components in the exhaust deteriorate, so it cannot be ignored.

As exemplified above, there is a strong demand to easily measure the air-fuel ratio with a short delay time, since fluctuations and variations in the air-fuel ratio occur due to various factors.

Conventionally, as sensors for measuring air-fuel ratios that have been proposed to meet such demands, there are oxide semiconductor sensors, limiting current type oxygen sensors, and the like, which have a relatively high possibility of practical use.

Oxide semiconductor sensors utilize the fact that the resistance of oxide semiconductors changes depending on the air-fuel ratio. As an oxide semiconductor suitable for air-fuel ratio measurement, 'rio2. CeO
2. N-type semiconductors such as Nb2O5, NiO, Co.

There are P-type semiconductors such as

These oxide semiconductor sensors operate without problems even at high temperatures such as exhaust gas from combustion equipment, and can be constructed in a very small size, making it possible to install the sensor directly in the exhaust pipe. Although it has the advantage of being able to measure the air-fuel ratio distribution in an exhaust pipe and other microscopic spaces, it also has the following problems.

As an example, the case of a TiO sensor will be explained.

■ As is not clear from the characteristics of the T t O2 sensor shown in Figure 1, the resistance on the lean side is significantly higher (108~10
(about [Ω]), making it difficult to measure resistance.

■ Since the resistance of the sensor itself is high, if the insulation resistance of the housing etc. is insufficient, electrical leakage may occur and easily interfere with resistance measurement.

■ On the lean side, the temperature coefficient is many times higher than on the rich side, so a slight temperature change will cause a large resistance change, which will also have a large effect on the air-fuel ratio value.

Temperature compensation should be performed (even if a thermocouple is installed near the TlO2 sensor, there will be a slight temperature source between the TlO2 and the thermocouple, and it will fluctuate, so it is easy to cause errors.) Although embedding solves the problem of temperature difference, the conductivity of T r 02 causes electrical continuity with the thermocouple wire, and the resistance measurement system and temperature measurement system cannot be sufficiently insulated, leading to interference. happen.

■ If the resistance becomes low on the rich side and then returns to the lean side, the resistance increases slowly and is difficult to stabilize.

■ Even if the air-fuel ratio is the same, combustion products (C0
In addition to 2, H2O), the resistance value is greatly affected by the amount and concentration of remaining unburned components.

(2) Since the relationship between the air-fuel ratio of the exhaust gas and the T t O2 sensor resistance is non-linear, calculating the air-fuel ratio from the resistance is likely to involve errors and is inconvenient.

As one solution to these problems, the inventors of the present invention invented an "air-fuel ratio meter" and filed a patent application (Japanese Patent Application No. 165,236/1982).

The invention addresses the above problems as follows.

■ 1 for the problem of resistance measurement of oxide semiconductor sensors.
A unique logarithmic conversion type resistance meter (this was filed as Utility Model Application No. 55-69848) was used, which allows resistances in the range of 0 to 10 [Ω] to be measured accurately and at high speed.

■ Countermeasures will be taken to prevent failures caused by insufficient insulation resistance and stain-like leaks by changing the shape of the housing, changing the gas sealing method, and preventing water vapor solidification by maintaining high temperatures.

(2) To address the temperature issue, in order to avoid errors due to temperature fluctuations, we have made precise temperature adjustments and compensated for even minute fluctuations. Furthermore, since the temperature coefficients are different for the rich side and the intake side, in order to be able to compensate with a temperature coefficient suitable for each side, it is determined whether or not it is on the rich side from the resistance value of the sensor, and the temperature coefficient is determined based on that determination. so that it can be switched.

As a method of detecting the sensor temperature, a thermocouple is embedded within the sensor to prevent a temperature difference between the sensor and the thermocouple. In that case, due to the conductivity of T to 2, insulation between the resistance measurement circuit and the temperature measurement circuit cannot be maintained. ensure proper isolation and eliminate interference.

■ The problem of a slow increase in resistance when the TiO sensor becomes low resistance in a rich atmosphere and then returns to the lean side will be addressed by improving the sensor manufacturing method.

■ For problems that are affected by the type and concentration of unburned components even when the air-fuel ratio is the same, a precatalyst is used to promote the reaction and achieve chemical equilibrium.

■ A linear amplifier (linear live) is provided to solve the problem caused by the non-linear relationship between air-fuel ratio and sensor resistance.

The present invention mainly provides a different solution to the problems (1) and (2) from the above-mentioned solutions to the problems of oxide semiconductors. That is, the problem of the oxide semiconductor sensor is solved by using this oxide semiconductor sensor only on the rich side and switching to the limiting current type oxygen sensor described below for the lean side.

The above-mentioned limiting current type oxygen sensor has electrodes with good oxygen gas permeability on both sides of an oxygen ion conductive plate (for example, stabilized Zilfair, etc.), and a current is passed between the two electrodes.
It pumps up elementary ions, and by installing something that restricts the flow of gas (such as small holes or a porous coating) on the electrode on the side where oxygen gas is sucked, a current proportional to the oxygen concentration in the atmosphere is generated. This is what you get.

FIG. 4 shows an example of current-voltage characteristics of a limiting current type barium sensor. If a voltage of about 0.75 [V] is applied to an element having such characteristics, an output current proportional to the oxygen concentration can be obtained. The saturation current characteristics (referred to as limiting current characteristics) shown in FIG. 1 are caused by the following mechanism.

In an element with a cathode on one side of the oxygen ion conductor plate and an anode on the other side, if a negative voltage is applied to the anode and the cathode and a current is passed, the oxygen gas near the cathode is converted to oxygen by the cathode. It is converted into ions (divalent negative ions), which travel through the barium ion conductor and reach the anode, where they are converted back into oxygen gas and released outside the device.In this case, the device In order for current to flow, oxygen gas must be supplied to the cathode, but if this amount is limited by placing a porous layer on the cathode, the current will be limited.

When the voltage applied to the device is gradually increased from zero, the current can increase while the device current is smaller than the current corresponding to the maximum oxygen flow rate that can be supplied to the cathode; Once the current reaches the amount of supply, the current cannot be increased even if the voltage is increased thereafter.

In this way, voltage-current characteristics as shown in FIG. 4 are produced.

As is clear from Figure 4, the excess air ratio is larger than l,
A clear limiting current characteristic can be seen in the lean region, and if a constant voltage of about 0.7 to 0.8 [V] is applied to the d-sensor element, the limiting current corresponding to the excess air ratio λ, that is, the sensor output Current can be obtained. However, in the range where the excess air ratio λ is smaller than 1, that is, in the region 1, the current only increases monotonically with respect to the voltage applied to the element, and no limiting current characteristics are observed.

FIG. 5 shows the results of recording the current flowing by applying a constant voltage of 0.7 [V] to the limiting current type oxygen sensor while continuously changing the excess air ratio of the combustion system. On the lean side, oxygen concentration and current have a nearly proportional relationship. However, on the rich side, a large current flows even though the oxygen concentration is close to zero. This is due to the following reasons. In other words, by applying a voltage, CO2 and H2 in the atmosphere can be removed.
This is due to the fact that in a cold atmosphere where some of the O is decomposed and oxygen is generated, the electrolyte exhibits electronic conductivity and an electron current flows.

When the decomposition of CO2 occurs, carbon precipitation occurs at the interface between the electrode and the electrolyte, causing deterioration of the electrode.

Therefore, since passing current on the rich side is a serious cause of inducing deterioration of the electrodes and electrolyte, current should not be passed on the rich side.

However, as shown in FIG. 5, since the output current is a bivalent function with respect to the air-fuel ratio, it was not possible to know from the current value whether it was on the rich side or on the one-in side. Therefore,
There has been a problem in that the air-fuel ratio can only be known when it is known that it is on the lean side using some method. In addition, when there is a possibility that the air-fuel ratio is divided into rich and lean, it is not only impossible to accurately determine the air-fuel ratio on the Lynch side, but also there is a serious problem of deterioration. Further, since the characteristics change depending on temperature, measures against temperature are required, as in the case of the oxide semiconductor sensor.

In order to solve the above-mentioned problems in the conventional technology, the present invention combines an oxide semiconductor sensor and a limiting current type oxygen sensor, and selects a favorable range of the characteristics of each, thereby providing a wide range from rich to lean. This realizes an air-fuel ratio detection device that can measure air-fuel ratios over a wide range.

The present invention determines whether a gas to be measured is in a rich region or a lean region based on the resistance value of an oxide semiconductor sensor. That is, the resistance value of the oxide semiconductor sensor is compared with a certain resistance value, and if it is thicker than that, it is determined to be lean, and if not, it is determined to be rich. If it is determined that the limit current is negative, a voltage for measuring the limit current is applied to the limit current sensor, the value of the limit current is determined, and this is converted into an air-fuel ratio and output. If it is determined to be rich, the resistance value of the oxide semiconductor sensor is converted into an air-fuel ratio and output. The output may be selected using a changeover switch such as a relay, but it is better to use an electronic circuit to avoid switching noise.

Hereinafter, embodiments will be described in detail with reference to the drawings.

First, an oxide semiconductor sensor and a limiting current type oxygen sensor used in the sensor section of this embodiment will be described.

Figure 2 shows T + using TiO2 as an oxide semiconductor.
This shows an example of the structure of the 02 sensor 1, and T i O
2 Two platinum (Pt)')-do wires 3 in the sintered body 2
, 4 and platinum-platinum 87 tyrosium 13% (PH10)
It has a structure in which a thermocouple 5 is embedded. Its manufacture was carried out as follows. T with a diameter of 0.1 to 0.8 [μm]
The iO2 powder was calcined at a temperature of 900 to 1100 (°C),
Calcinate for 1° to 2 (hr). Then, the calcined powder is pulverized to a diameter of 0.5 to 0.2 [μm], mixed with platinum black, and granulated using polyvinyl alcohol as a binder. The size of the particles after granulation is 1 to 3 [μm] in diameter. The appropriate proportion of platinum black is 10 to 50 (wt%).The granulated powder, Pt lead wire, and PR13 thermocouple are placed in a mold and pressed to form.The pressure during molding is 700
[kg/crn2]. The appropriate diameter of the T+02 sensor is 065 to 5 mm. The appropriate thickness of the sensor is 0.3 to 3. The diameter of the Pt lead wire is suitably 50 to 500 [μm]. The diameter of the PR13 thermocouple wire is suitably 50 to 100 [μm]. Appropriate firing conditions are 900 to 1200 [°C] and 1 to 3 [hr].

The appropriate porosity after firing is 30-60'l:%).

The purpose of adding platinum black is to help the resistance value of the sensor quickly reach its final value (normal value) and improve responsiveness.

Figure 3 shows an example of the structure of the limiting current type barium sensor f6 of this example, where 7 is an oxygen ion conductor, 8 is a cathode,
9 is an anode, 10 is a porous layer, 11 is a porous gorge layer, 12
is the lead wire. The silicon ion conductor 7 has a composition (zrO
z) o, 92 (Y2O3) 0.081) A dense sintered disk was manufactured by the following method. First, high purity (99
, 9% or more) Nozro2 powder and Y2O powder were mixed at a molar ratio of 92:8, ground in a wet sol mill for 10 hours, and dried. The obtained mixed powder was heated to 1250 [
t, calcined for 110 hours, and then further ground into fine powder in an agate mortar. Add 0 polyvinyl alcohol to this powder.
．． 5% by weight in an aqueous solution, granulated, and pressed using a mold to form a disc with a thickness of approximately 0.4 mm and a diameter of 4 at a load of 700 kg/cm2. This was sintered in air at 2000°C for 12 hours.
Disc dimensions after sintering are diameter 3.5 [-) and thickness 0.3 to 0.
．． 35. A dense sintered body was obtained.The cathode 8 and the anode 9 were made by sputtering platinum onto the center of the upper and lower surfaces of the oxygen ion conductor to a thickness of 1 μm and a diameter of 1.9 mm.
It collapsed into a (+w+) disk shape.

Furthermore, the anode had the same thickness as the cathode, and was formed to face the cathode. The lead wire 12 was a platinum wire with a diameter of 0.3 (-) and was connected to the cathode and anode by thermocompression bonding, respectively. The porous layer 10 covers the cathode 8 and has 4p and 6
The porous layer was formed to a thickness of 40 (μm) by plasma spraying using spinel powder as a raw material.The average particle size of the spinel powder was 47 cm), and the volume porosity of the porous layer after formation was It was 9 [chi]. FIG. 4 shows the current-voltage characteristics of the limiting current type oxygen sensor manufactured in this way.

FIG. 6 shows the structure of the housing of the sensor unit including the T102 sensor 1 and the limiting current type oxygen sensor 6 described above. The lead wire portions of the T102 sensor 1 and the limiting current type oxygen sensor 6 are fixed to the 7 flange 14 via a ceramic insulator 13, and a precatalyst 15 is provided around both sensors.

The precatalyst 15 is used to accelerate the reaction of some unburned components contained in the exhaust gas, and to constantly supply a gas close to chemical equilibrium to the sensor. The method for manufacturing the catalyst is to use alumina as a carrier, and to support chlorides of noble metals such as platinum (PT), rhodium (Rh), palladium (Pd), etc. alone or in combination on the carrier and then to sinter the catalyst.

The weight of the carrier is 2 to 3 [gr], and the catalyst metal is 0.01 to 0.
, o 3 (gr), firing conditions are 600-800 [
C processing time of 0.5 to 1 [hr] is appropriate.

A heater 16 is installed outside the precatalyst 15.

This is to maintain the temperature of sensors 1 and 6 at a constant high temperature. The heater 16 is a sheathed heater, and has a diameter of 1 mm and a length of 150 mm.

The reason why a sheathed heater is used is that exhaust gas is highly corrosive, and ordinary heater materials such as nichrome and kanthal deteriorate so much that they are not practical. Any material other than the sheathed heater may be used as long as it is resistant to corrosion in exhaust gas, such as platinum. The power of the heater is about 30~SO(W),
It is used at 400-800[°C].

A current limiting cover 17 is attached to the outside of the heater 16 to prevent the speed at which exhaust gas is blown onto the sensors 1 and 6 from becoming excessive. Considering the balance between response time and power consumption, the opening area of the hole provided in the current limiting cover 17 is 0.3 to 30 (■).
It is.

FIG. 7 is a system diagram of an embodiment of the present invention. Figure 2,
The sensor section described in FIGS. 3 and 6 is attached to a part of the exhaust pipe 18. The output of the thermocouple of sensor 1 is an automatic cold junction compensator 19, a measurement amplifier 20, and an attenuator 21.
, an automatic cold junction compensator 22, and a temperature regulator 23. The temperature regulator 23 controls the temperature of the sensor section to be kept constant by adjusting the power applied to the heater 16 in accordance with the temperature detection of the sensor section by a thermocouple. As mentioned above, the electromotive force of the thermocouple is measured through the automatic cold junction compensator (e.g., Chino Seisakusho 615E) 19 and the i-jyaku angle 20 to detect the temperature, and the reason for this is as mentioned above. Due to the conductivity of TlO2, the resistance measurement circuit and thermoelectromotive force measurement circuit cannot be insulated, causing interference between the two circuits, so this is to avoid this on the amplifier side. As a total I11 amplifier 20 IC, 9-
Braun's 3670K was used. Figure 8 shows the internal circuit of the measurement amplifier. The range in which insulation can be obtained with the measurement amplifier 20 is limited to a range in which each input terminal voltage is within about 10 V from the output ground. By commonly connecting the ground of k), one side of the resistor ill constant terminal of the TlO2 sensor becomes a virtual ground, and the other side is separated by the applied voltage for resistance measurement. Maximum applied voltage is 5 [■
] can be kept within the permissible range of the measurement amplifier.

The electromotive force of PRIa thermocouple 5 is 8 [mV] at 800 [℃].
], so if the gain of the measurement amplifier 20 is multiplied by 1000, it will be 8 [V], and the drift of the amplifier can be used with minimum symmetry. Instead, the temperature controller 23 is attenuated by 171,000 by the attenuator 21 to restore the original 8
(mV) and connect the automatic cold junction compensator 22 in the opposite direction before supplying it. Here, the automatic cold junction compensator was used in the opposite direction because the temperature controller 23 had a built-in cold junction compensator to avoid duplication with the compensator 19 installed before the measurement amplifier 20. It's for a reason. If a temperature controller without a built-in cold junction compensator is used, it must be connected directly to the attenuator 21.

As mentioned above, the temperature controller 23 is designed to keep the temperature of the sensor constant, and in order to avoid steady-state deviations, it uses proportional-integral operation (P-I type) and minimizes temperature pulsations. The one with phase control to hold down (mostly electric EC7
6AO4) was used.

As described above, the temperature of the sensor section is detected by the thermocouple 5, and according to the detection, the temperature regulator 23 controls the power of the heater 6 to adjust the temperature of the sensor section to a constant value.

The resistance of the TiO□ sensor in an atmosphere whose temperature has been adjusted to a constant value is measured by a logarithmic conversion type resistance meter 24, and its output is subjected to temperature compensation by a temperature compensator 25, and then calculated as an air-fuel ratio. After passing through a linearization amplifier (resistance to air-fuel ratio converter) 26 that linearizes the non-linear relationship with the sensor resistance, the air-fuel ratio is output.

The resistance of the TiO sensor increases from 10' to 1 as the air-fuel ratio changes.
It changes at a rate as large as 0.05 times. In order to measure it continuously and accurately without changing the range, the present invention newly develops a dedicated logarithmic conversion type resistance meter and uses it as the logarithmic conversion type resistance meter 24. FIG. 9 shows the relationship between the resistance and output voltage of the logarithmic conversion type resistance meter. This is 105 [Ω] as a standard resistance, and the gain is 1 (V/de
This is the characteristic when set to cade). As a resistance meter, even a resistance meter other than a logarithmic conversion type, such as a root conversion type or a negative power conversion type, is suitable for the above purpose. These are collectively referred to as compression type resistance conversion.

Further, the resistance meter does not need to be a compression type as long as it can measure the JO range using a range switching table.

As described above, even if highly accurate temperature control is performed on the sensor section, it is inevitable that slight transient temperature fluctuations will occur when the amount of heat generated in the precatalyst section suddenly changes. In order to correct the resulting error, temperature compensation is performed by the temperature compensator 25. The temperature fluctuation is calculated by a temperature deviation calculator 28 from the output of the measurement amplifier 2o and the set value of the standard temperature setting device 27, and is provided to the temperature compensator 25.

Sintered TiO sensors usually have a temperature coefficient of resistance of 0.001 to 0.007 on the rich side [: decade/deg
, l, the temperature coefficient of resistance on the lean side is 0.03 to 0.
．． 01 (deeade/deg). As described above, since the temperature coefficients on the rich side and the intake side are different in magnitude, it is difficult to obtain good results even if temperature compensation is attempted using a common temperature coefficient for both the rich side and the intake side. but,
Since the TIO2 sensor is used only on the rich side, temperature compensation can be performed by adjusting the temperature coefficient to match the rich side. The resistance characteristic of TiO2 with respect to the air-fuel ratio is the first
As shown in the figure, it suddenly changes about 10 times at the boundary between rich and lean. Therefore, the intermediate value is set as a reference resistance in the standard resistance setter 29, the magnitude of the resistance of the other sensor is extracted in the temperature compensator 25, and both are compared in the rich lean determiner 3o. When the sensor resistance is small, it is judged as rich, and when it is small, it is judged as high.

The temperature-compensated resistance value is converted to a voltage proportional to the air-fuel ratio through the linearization amplifier 26 and output.

As for the linearization amplifier 26, a functional type, a polygonal type (diode type, microcomputer operation type), etc. are suitable, and a polygonal type is slightly inferior to a functional type in terms of smoothness, but there are fewer restrictions on curve setting. Therefore, it is convenient. Figure 9 shows an example of the linearized linear amplifier, using 5 units on each side.
Linearization is performed by specifying 0 break points.

Next, the limiting current type oxygen sensor 6 is connected to the limiting current detecting section 31. As described above, the limiting current detection section 31 consists of a section to which a constant voltage (approximately 0.75 [V]) is applied and a current detection section. Then, a voltage is applied only when the rich/lean determining section determines that the fuel is lean/lean.

The output of the limit current detection section 31 is connected to the temperature compensation section 32. The output current of the limiting current type oxygen sensor 6 is approximately 0 at the feed temperature.
．． Since it is proportional to the 75th power, we compensate for it.

The output of the temperature compensator 32 is the current to air-fuel ratio (A/F'
) Connect to the conversion section 33. This converter 33 calculates the air-fuel ratio from the limit current value.

To determine the air-fuel ratio from the current value of the limit current sensor, proceed as follows. FIG. 4 shows the limit current sensor v-1 characteristics. The current in the horizontal part of the characteristic is approximately proportional to the oxygen concentration (partial pressure).

I#, kPo2 ・・・・・・・・・・・・・・・(1
) However, in the limit current: Proportionality coefficient Po2: Oxygen partial pressure And the excess air ratio (λ) and oxygen partial pressure have a relationship as shown in the following equation.

Po2= 0.21 (1-7) ・= −−(2)
In equation (2), the constant 0.21 represents the oxygen partial pressure in the air. However, the excess air ratio (λ) is a value obtained by normalizing the air-fuel ratio by the stoichiometric air-fuel ratio.

However, A/F: air-fuel ratio (A/F) stoich: stoichiometric fuel ratio According to this equation (4), the air-fuel ratio A/F can be determined from the limit current I. The proportionality coefficient includes the element shape, dimensions,
In addition to the porosity of the porous layer covering the cathode, it is also affected by temperature. Therefore, in order to eliminate the influence of warm tears, it is necessary to use the product at a constant temperature. Note that if slight temperature fluctuations are unavoidable, it is necessary to measure the temperature with a temperature detection element such as a thermocouple and compensate for it. Further, in FIG. 4, the slope (tan θ) of the VI characteristic represents the resistance of the ionic conductor. If a constant voltage is applied to determine the limiting current value, the load line will be vertical like the broken line in Figure 4, but the horizontal part of the characteristic curve (limiting current part) at each oxygen concentration
Since only the range where the resistance intersects with the load line can be used, the larger the resistance, the narrower the detectable oxygen concentration range. The lower the temperature, the higher the resistance, so the operating temperature must be relatively high. For example, when stabilized norconia is used as the electrolyte, a temperature of 600 [°C] or higher is appropriate.

One of the air-fuel ratio obtained from the T102 sensor and the air-fuel ratio obtained from the limiting current type oxygen sensor is outputted to the output terminal 35 by the output switch 34. The switching output device 34 is controlled by the output of the rich-lean determiner 30, and when the rich-lean determiner 30 determines that it is rich, the switching output device 34 is controlled by the output of the rich-lean determiner 30.
The air-fuel ratio from the 102 sensor is selected, and in the case of Lee/, the air-fuel ratio from the limiting current type oxygen sensor is selected and output.

FIG. 11 shows more specifically the temperature compensator 25, rich lean determiner 30, etc. of the TiO□ sensor in FIG. 7. Note that the description of parts related to temperature adjustment is omitted.

The standard temperature setting device 27 consists of a +IOV power supply and a potentiometer P1 with an inverting amplifier.

The coefficient i- of this potentiometer P1 with an inverting amplifier is used to set the standard temperature.

10・a=v・1000・・・・・・・・・・・・・・・
・(5) However, ■ is the electromotive force at the set temperature of the PR13 thermocouple from formula (5), a=v・100 ・・・・・・・・・・・・・・・
・(6) The temperature deviation calculator 28 is the adder A3,
Dyne is -1, and the output of the measurement amplifier 20 and the output of the potentiometer P1 with inverting amplifier of the standard temperature setting device 27 are input, and the output is the inverting a/f of the temperature compensator 25.
It is input to the attached potentiometer P2. The coefficient of this potentiometer P2 with inverting amplifier is rich T I
Gives the temperature coefficient of resistance of O2.

From the gain of the logarithmic conversion type resistance meter 24, I V = 1 (decade) -==”
(7) The temperature coefficient of resistance of the TiO□ sensor on the rich side is Tc
R[jiecILde/deg), in the rich case, the output fluctuation Δ~ of the resistance meter at the slight/J% temperature difference Δt (deg:) is ΔRM=Δt−Tc8[decade
]1.510109000000. (8) The output value ΔRP of the potentiometer P2 at the same time is the temperature coefficient of the electromotive force T. c[v/deg] as ΔR,=ha・T,oXl
ooO・b・・・・・・・・・・・・ (9) For temperature compensation, equations (8) and (9) must be equal.

Δt, TcR; Δt-Tcc×1000·b... Therefore, the coefficient is as follows.

The coefficients are set by this equation (10).

The rich-lean determiner 3o consists of a comparator c, the negative input of which is connected to the output of the standard resistance setting device 29, the positive input of which is connected to the output of the adder A2, and the output of the comparator C is connected to the output of the adder A2. to drive. The comparator C is configured to turn on when the positive input is higher than the negative input, that is, when it is on the output signal side of the adder A2.

Standard resistance setting device 29, 7 yometer P with reversing knob
The coefficient d of 4 is set so that the output of P4 becomes an intermediate value between the output of the adder A2 when the fuel is rich and the output of the adder A2 when the fuel is lean.

By setting in this manner, in the case of Con-Greak C, it is possible to judge whether the sensor is rich or leached if the sensor resistance value, which is the output of the adder A2, is lower than the set value but higher than the set value.

When the comparator C is ON, that is, when it is determined that the lean side is on, the limit current detection section 31 is
It is driven so that the limiting current measuring voltage is applied to the limiting current type oxygen sensor 6. At the same time, the relay R of the output switching device 34 is driven by the output of the converter and the relay R, and its contact is connected to the No side. The air-fuel ratio value determined by the sensor is output from the output terminal 35.

Conversely, when it is determined that the controller C is on the rich side, the relay R is deenergized and its contact is connected to the NC side,
The output of the linearization amplifier 26, which outputs the air-fuel ratio value detected by the TiO2 sensor, is output from the output terminal 35.

Correction for temperature compensation to the output of the logarithmic conversion type resistance meter 24 is performed by the adder AI in the temperature compensator 25. Since the output of the potentiometer P2 with an inverting angle is a compensation amount according to the characteristics shown in FIG.
1, temperature compensation is performed by adding the output of the logarithmic conversion resistance meter 24 and the compensation amount. Incidentally, since the dyne of the adder A1 is -1, the signal is further passed through the adder A2 having a gain of -1, and the polarity is returned to its original value before being output.

The output of adder A2 is sent to linearizing amplifier (function generator F) 26
to get the output of the air-fuel ratio value. The air-fuel ratio value is output from the output terminal 35 via the output switch 34 as described above.

FIG. 12 shows another embodiment. Functional parts that are the same as those in the embodiment shown in FIG. 7 are indicated using the same symbols. In this embodiment, in order to prevent noise in the part where the air-fuel ratio obtained from the TiO2 sensor and the air-fuel ratio obtained from the limiting current oxygen sensor are switched, a large output value is used instead of switching using a contact such as a relay. A maximum value detection circuit is used that outputs the maximum value. FIG. 13 shows the characteristics required for each air-fuel ratio output value in this embodiment. In other words, the air-fuel ratio output voltage of each cell receiver maintains linearity with respect to the input in the range where it has power, and the linearization amplifier ( The output characteristics of the resistance-to-air-fuel ratio converter 26 and the current-to-air-fuel ratio converter 33 are set as shown by the solid line and broken line in FIG. 13. The maximum value detection circuit 39 selects the larger value of the output voltages of the linearization amplifier 26 and the current-to-air-fuel ratio converter 39 and outputs it to the output terminal 35.

FIG. 14 shows the configuration of the maximum value detection circuit. As shown in the figure, the two diodes 41 and 420B are connected to the operational amplifier 4.
Connect to the positive input terminal of No.3. Then, the output of the operational amplifier 43 is connected to the negative input terminal of the operational amplifier 43.

The two inputs to be selected are connected one each to the anodes of the diodes. By connecting in this way, the higher input voltage of the two input voltages is output, and the lower input voltage is not concerned.

A resistor 44 is connected between the positive input terminal of the operational amplifier 43 and ground. This is to improve the speed when lowering the potential of the positive input terminal.

In addition, in this embodiment, a temperature adjustment circuit with a simple configuration in the case where no thermocouple is embedded in the TIO2 sensor is shown.

In each of the above embodiments, T is used as an oxide semiconductor sensor.
Although a sensor using an sO2 sensor is shown, it is of course possible to use a sensor using other N-type oxide semiconductors (Nb205, CeOs, etc.).

In addition, an oxygen concentration battery type oxygen sensor may be used as a substitute for the atomized compound semiconductor, and in that case, an electromotive force measuring section may be used as the resistance measuring section in each embodiment, and the standard resistance setting device may be replaced with an electromotive force measuring section. Use a standard electromotive force setting device.

Further, a non-contact type relay such as an analog switch can be used instead of the contact type relay shown in FIG. 7 or FIG. 11. This makes it possible to reduce noise during switching.

As described above in detail with reference to the embodiments, the present invention provides an oxide semiconductor sensor that exhibits extremely excellent air-fuel ratio detection characteristics on the Lynch side and is capable of determining rich lean, and an oxide semiconductor sensor that exhibits excellent characteristics on the lean side. The sensor is combined with a limiting current type oxygen sensor that indicates the air-fuel ratio, and is configured to select the measured value output depending on whether the gas being measured is in the rich region or the gas region, allowing for a wide measurement range from rich to rich. It can be measured quickly and with high precision.

[Brief explanation of drawings]

Figure 1 is the characteristic diagram of T io 2 senna, Figure 2 is TiO
It is a figure showing an example of the composition of two sensors. Figure 3 shows an example of the structure of a limiting current type oxygen sensor, Figure 4 shows the relationship between applied voltage and current using the oxygen concentration as a parameter, and Figure 5 shows the limiting current type oxygen sensor. FIG. 6 is a diagram showing the relationship between the air-fuel ratio and current when a constant voltage is applied to the oxygen sensor. FIG. 6 is a diagram showing an example of the senna section used in the present invention. Fig. 7 is a block diagram of an embodiment of the present invention, Fig. 8 is a circuit diagram of a measuring amplifier, Fig. 9 is a diagram showing an example of the characteristics of a logarithmic conversion type resistance meter, and Fig. 10 is a circuit of a linearizing amplifier. Figure, 11th
The figure is a circuit diagram showing the temperature compensator etc. in detail. Fig. 12 is a Zorock diagram showing another embodiment of the present invention, and Fig. 13 is a diagram showing the setting of the characteristics of the linearization amplifier (resistance to air-fuel ratio converter) and current to air-fuel ratio converter in this embodiment. be. FIG. 14 shows a maximum value detection circuit. 1... T s O2 sensor, 2... TiO2 sintered body, 3, 4... Pt lead wire, 5, 5'... thermocouple,
6... Limiting current type oxygen sensor, 7... Oxygen ion conductor, 8... Cathode, 9... Anode, 10... Porous layer, 11... Porous protective layer, 12...・Lead wire, 1
3...Ceramic insulator, 14...7 Ranno, 15
...Pre-catalyst, 16...Heater, 17...Current limiting cover, 18...Exhaust pipe, 19...Automatic cold junction compensator, 20...Measuring amplifier, 21...Attenuation Vessel, 22...
・Automatic cold junction compensator, 23...Temperature regulator, 24...
・Logarithmic conversion type resistance meter, 25...Temperature compensator, 26...
- Linearization amplifier (resistance to air-fuel ratio converter), 27... Standard temperature setting device, 28... Temperature deviation calculator, 29...
Standard resistance setter, 30... Rich, lean judge, 3
1...Limiting current detection section, 32...Temperature compensation section, 33
...Current-to-air-fuel ratio converter, 34...Output switch, 3
5... Output terminal, 36... Pump, 37... Gas inlet, 38... Gas outlet, 39... Maximum value detection circuit, 40... Thermocouple amplifier, 41.42. ...Diode, 43...Operation amplifier, 44...Resistor. Fig. 1 Fig. 2 Fig. 3 9 11 12 4m 555 Excessive exchange, excess rod work 6 Fig. (1 1◆2nXV+2-Vn)) 911 - TiO2 begging grandson 49th 10th Garden Figure 13 One Guest Meretsu 1 and (A/F) Great Sword (Ga's Qυ 1st +■

Claims (4)

[Claims] (1) An oxide semiconductor sensor that causes resistance changes depending on the air-fuel ratio, a cathode layer on one side of a plate or cylinder made of an oxygen ion conductor, and an anode l- on the opposite side, and the cathode layer is porous. A sensor that detects the air-fuel ratio because the size of the current that flows by applying a positive voltage to the anode layer and a negative voltage to the cathode layer changes depending on the acid concentration a resistance measuring section that measures the i resistance over a wide range of the oxide semiconductor; and a resistance measuring section that measures the i resistance of the oxide semiconductor over a wide range; a limiting current detection section that applies a voltage to the limiting current type oxygen sensor and detects the limiting current only in the case of fuel shortage; and a limiting current detection section that detects the limiting current by applying a voltage to the limiting current type oxygen sensor only when fuel is insufficient; an air-fuel ratio detection device comprising: a selection unit that selects an air-fuel ratio obtained from a limiting current type oxygen sensor if there is a fuel shortage; (2) The air-fuel ratio output determined based on the oxide semiconductor sensor is set to an output characteristic such that it becomes a normal value in a fuel excess region and a value smaller than the normal value in a fuel shortage region, and The air-fuel ratio output determined based on the limiting current type oxygen sensor is set to an output characteristic such that it does not take a normal value in a fuel shortage region, and becomes a value smaller than the normal value in a fuel excess region. (FIG. 13), the air-fuel ratio according to claim (1), characterized in that the selection section is configured with a maximum value detection circuit that selects the larger value among the two inputs. Detection device. (3) An oxygen concentration battery-type oxygen sensor that generates an electromotive force change depending on the air-fuel ratio, a cathode layer on one side of a plate or cylinder made of an oxygen ion conductor, and an anode layer on the other side facing the cathode. Cover the electrode with a porous layer or a perforated box, apply a positive voltage to the anode layer and a negative voltage to the cathode layer, and detect the air-fuel ratio because the magnitude of the flowing current changes depending on the dispersion concentration. (hereinafter referred to as a limiting current type oxygen sensor); an electromotive force measurement unit that measures the electromotive force of the oxygen concentration battery type oxygen sensor; and an electromotive force measurement unit that measures the electromotive force of the oxygen concentration battery type enzyme sensor. a portion that determines whether there is excess fuel or insufficient fuel based on the stoichiometric air-fuel ratio; a limiting current detection portion that applies voltage to the limiting current type cumulative sensor to detect a limiting current only in the case of fuel shortage; If there is an excess of fuel, we select one fc air-fuel ratio obtained from the oxygen concentration battery type sensor, and if there is insufficient fuel, we select the air-fuel ratio obtained from the limit current type sensor. An air-fuel ratio detection device characterized by: (4) An output such that the air-fuel ratio output determined based on the dazzle concentration battery type cumulative sensor is a normal value in a fuel excess region9, and a value smaller than the normal value in a fuel shortage region. The air-fuel ratio output set in the characteristic and determined based on the limiting current type oxygen sensor is a normal value in a fuel shortage region, and a value slightly smaller than the normal value in a fuel excess region. Claim (3) characterized in that the output characteristic is set as follows, and the selection section is configured with a maximum value detection circuit that selects the larger value among the two inputs. The air-fuel ratio detection device described in .