JPH0125418B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a limiting current type oxygen concentration detection device that performs temperature compensation on the output of a limiting current type oxygen sensor. The objective is to compensate for errors and release restrictions on the operating temperature range, enabling high precision and wide operating ranges.

It goes without saying that in today's society, many combustion devices such as thermal power plants and internal combustion engines for automobiles are in practical use and contribute to our lives in various ways. These devices can generate large amounts of harmful gases if operating conditions are not appropriate. There is also a strong demand for lower fuel consumption.

Combustion in the fuel lean (abbreviated as "lean") region is a promising method for purifying exhaust gas and improving fuel efficiency. For example, diesel engines and the like are normally operated in a lean region, but gasoline engines are also expected to be operated in a lean region.

Even in these engines that operate in the lean region, if the air-fuel ratio is improperly adjusted, inconvenient problems such as soot generation, unburned fuel discharge due to misfire, and reduced output occur, which defeats the purpose of operating in the lean region. There is even a fear that it may have the opposite effect. Therefore, adjusting the air-fuel ratio is extremely important. Incidentally, as is common in all types of control, it is necessary to be able to detect the control target (in this case, the air-fuel ratio in the lean region) precisely and at high speed. Until now, suitable sensors have not always existed in this field. For example, magnetic type sensors (oxygen concentration detectors) have slow responses and are unsuitable for use in vehicles, while gas density type or thermal conductivity type sensors have problems such as measurement accuracy being significantly affected by trace amounts of hydrogen (H ₂ ). It was not suitable for engine combustion control.

In response to this, we first proposed a sensor that measures the limiting current and analyzes the oxygen gas concentration (hereinafter referred to as the limiting current oxygen sensor) (Japanese Patent Application Laid-open No. 72286/1986), and also added a porous cathode. Developed an oxygen concentration sensor coated with a carbonaceous layer (Japanese Patent Application No. 123677/1983, Japanese Unexamined Patent Publication No. 1983
-48648 Publication). This limiting current type oxygen sensor solves various difficulties associated with conventional sensors. Although this method is very effective, it cannot be denied that there are some problems. That is, in combustion devices such as automobile engines, the temperature of the exhaust gas usually fluctuates depending on the operating conditions. Therefore, the limiting current type oxygen concentration sensor, which is an exhaust sensor, is also required to operate in a wide temperature range from low to high temperatures. By the way, the limiting current type oxygen sensor has two problems: its internal resistance changes greatly depending on temperature, and the correspondence relationship between oxygen concentration and limiting current changes slightly. The present invention attempts to provide a solution to two problems in which the correspondence relationship between oxygen concentration and limiting current changes depending on temperature.

FIG. 1a shows an example of the cross-sectional structure of a limiting current type oxygen sensor. 1a is a plate or cylinder made of an oxygen ion conductor. Its materials include zirconia, Y ₂ O ₃ , Yb ₂ O ₃ , Gd ₂ O ₃ , MgO, CaO,
Sc ₂ O ₃ etc. as a solid solution as a stabilizer, or Bi ₂ O ₃ as a stabilizer with Y ₂ O ₃ , Er ₂ O ₃ , WO ₃ etc. as a solid solution, or HfO ₂ , ThO ₂ etc. CaO,
It is a dense sintered body containing MgO, Y ₂ O ₃ , Yb ₂ O ₃ , etc. as a solid solution as a stabilizer. An anode 1b is provided on one surface of the ion conductor, and a cathode 1d is provided on the other surface facing the anode. The negative and positive poles are Pt, Ag, Rh, Ir,
It is made of a heat-resistant electron conductor made of Pd or a mixture thereof, and if these materials are used, it is possible to practically reduce the interfacial resistance between the oxygen ion conductor and the electrode. The cathode 1d is covered with a perforated box. FIG. 1a shows an example of a structure covered with a porous layer 1f as one embodiment thereof. This has the function of limiting the flow rate of oxygen flowing into the cathode 1d. Further, in order to prevent the anode 1b from deteriorating due to deposits or the like, the anode was covered with a porous protective layer 1e. The porous layers 1f and 1e are made of a heat-resistant inorganic material such as alumina, magnesia, silica, spinel, or mullite. It is desirable that the porous layer 1e has gas permeability equal to or greater than that of the porous layer 1f. The reason for this is that during operation, the porous layer 1f acts to control the rate of oxygen permeation from the outside world via the cathode 1d to the oxygen ion conductor 1a, whereas the porous layer 1e
This is to discharge oxygen from the oxygen ion conductor 1a to the outside world without resistance via the anode 1b. Lead wires 1i are taken out from both the negative and positive poles. As with the electrodes, the material of the lead wire is Pt, Ag, Rh,
It is a heat-resistant electron conductor made of Ir, Pd, etc. or a mixture of these materials. When a negative voltage is applied to the cathode and a positive voltage is applied to the anode of the limiting current type oxygen sensor configured as described above, and the entire element is brought into contact with the gas to be measured, the oxygen gas in the gas to be measured is reduced by the cathode. The oxygen ions move through the oxygen ion conductor, reach the anode, are oxidized by the anode, become oxygen gas again, and are discharged from the device. If the amount of oxygen gas that reaches the interface between the cathode and the oxygen ion conductor is limited by some method, the amount of oxygen ions generated by reduction at the cathode will be limited, and the charge carried by the oxygen ions will be limited. Since the amount (current) is limited, only a constant current can flow regardless of the voltage, resulting in a limiting current characteristic as shown in FIG. 1b. Therefore, in the limiting current characteristics of an oxygen sensor, when the voltage applied to both the negative and positive electrodes is gradually increased from zero, as shown in Figure 1b, while the voltage is low, the current flowing between the positive and negative electrodes is equal to the voltage. The current increases approximately proportionally to (this voltage region is referred to as the resistance dominated region), but within a certain voltage range, the current remains approximately constant regardless of the voltage (this voltage region is referred to as the overvoltage dominated region). The current in the overvoltage region is called a limiting current, and since the limiting current value is approximately proportional to the oxygen concentration in the gas to be measured, the oxygen concentration in the gas to be measured can be detected by determining the limiting current value. The reason why the limiting current is approximately proportional to the oxygen concentration is that the amount of oxygen that can be moved by diffusion within a gas flow restricting body such as a perforated box is proportional to the difference in oxygen concentration between the inside and outside of the restricting body, and the reason why the limiting current is approximately proportional to the oxygen concentration is that In the dominant region, the oxygen inside the limiting body is sucked into the oxygen ion conductor via the cathode, so the oxygen concentration is close to zero, and the difference in oxygen concentration inside and outside the limiting body is This is due to the oxygen concentration being almost equal to the outside oxygen concentration.

As mentioned above, this example describes a method using a porous layer as the limiting body, but the present invention described below can also be applied to an oxygen sensor using the cathode itself as the limiting body.

Electrolyte (oxygen ion conductor) in the resistance dominated region
The voltage/current ratio is approximately determined by the sum of the internal resistance of the electrode and the resistance of the electrolyte and electrode interface. In a region where the voltage and current are higher than the overvoltage control region, there are parts where the current suddenly increases in response to a small voltage rise. This is because when the applied voltage of the limiting current type oxygen sensor exceeds a certain limit value, part of the carbon dioxide (CO ₂ ) and hydrogen gas (H ₂ O) contained in large amounts in the exhaust gas is decomposed and the oxygen concentration decreases. This is because it appears to have increased. This region will be referred to as an excessive current region. As mentioned above, when the applied voltage is low, the region becomes a resistance-dominated region, and conversely, when the applied voltage is high, the region becomes an excessive current region, so the detection of the limiting current must be performed at a portion sandwiched between the two regions. This range varies depending on the gas composition and the electrode composition. 1.3 to 1.6 in an atmosphere containing some oxygen in an inert gas such as nitrogen or argon.
[V], but in an atmosphere containing a portion of oxygen in a gas containing a large amount of carbon dioxide and water vapor, such as combustion exhaust, it is about 0.6 to 0.8 [V]. In general, it may be advantageous to limit the maximum voltage drop due to internal resistance to about 0.5 [V] and set the applied voltage to 0.6 to 0.75 [V] to avoid being affected by internal resistance and excessive current. many.

FIG. 2 shows a limiting current measuring circuit according to the prior art, which has a configuration in which the current detecting section 3 detects the current when a constant voltage is applied to the limiting current type oxygen sensor 1 from the constant voltage applying section 2. It's summery. Third
The figure shows the relationship between oxygen concentration and limiting current according to the prior art. As is clear from the figure, the correspondence between the oxygen concentration and the limiting current changes depending on the temperature of the sensor, which causes a problem of poor accuracy. Note that in the high oxygen concentration region, there is a region where the oxygen concentration and the limiting current are not proportional, but this is limited to a generally linear range.

FIG. 4 shows the temperature dependence of the limiting current at a given oxygen concentration. This temperature dependence is mainly due to the influence of the temperature dependence of the gas diffusion coefficient.

The characteristics of a limiting current type oxygen sensor using a porous layer to control the rate of oxygen gas flow can be expressed as follows.

Il=4FSDo ₂ effP/RTlln (1/1-Po ₂ /P) (1) Formula where, Il: Limiting current F: Faraday constant S: Area of oxygen flow rate controlling part Do ₂ eff: Effective diffusion coefficient Po ₂ : Oxygen Partial pressure P: Total pressure R: Gas constant T: Absolute temperature l: Porous layer thickness ln: Natural logarithm If oxygen partial pressure ratio Po ₂ /P≪1, approximately Il≒4FSDo ₂ effP/RTl Po ₂ /P Equation (2) is obtained. Here, Do ₂ eff is empirically calculated as Do ₂ eff (T) = Do ₂ eff (T ₀ ) (T/T ₀ ) ^m+1 formula (3) However, T ₀ : Reference temperature Do ₂ eff (T) : Effective diffusion coefficient at T Do ₂ eff (T ₀ ): Represented by the effective diffusion coefficient at T ₀ , the exponent m+1 in this equation is approximately
It is known to be 1.75.

Therefore, the ratio of the output current Il (T) at temperature T to the output current Il (T ₀ ) at temperature T ₀ at the same oxygen partial pressure, that is, the temperature dependence of the output current Il (T)/Il (T ₀ ) is expressed as Il(T)/Il(T ₀ )=(T/T ₀ ) ^m (4).

If only the temperature dependence of the limiting current is due to the change in the gas diffusion coefficient due to temperature, then the output current of the sensor will be linear (T ^0.75 ) depending on the temperature as shown by the broken line in Figure 4, and the change will be small. In reality, the internal resistance increases significantly in the low-temperature region, and the voltage drop caused by this internal resistance acts as a disturbance, resulting in a characteristic in which the limiting current suddenly decreases, as shown by the solid line in the same figure. In some cases. This problem of internal resistance has been solved by the invention of the concurrently filed patent application filed by the present inventors, and by utilizing this, it is possible to improve the characteristics to be straightforward as shown by the broken line. be.

One possible method for eliminating temperature dependence is to measure the oxygen concentration while adjusting the sensor to a constant temperature. The present inventors also devised a specific means for this purpose and filed a separate patent application concurrently with the present application. However, in general, in order to adjust the temperature of the sensor to a constant temperature, a temperature detection section, a heating section, a power adjustment section, etc. are required, resulting in a complicated configuration, resulting in problems such as high cost, large size, and high power consumption.

Therefore, instead of adjusting the temperature to a constant value, we are proposing a device that uses a limiting current sensor that is heated by the temperature of exhaust gas from combustion, etc., and that measures with high precision under fluctuating temperature conditions.

FIG. 5 is a block diagram showing the basic configuration of the present invention. , a temperature measurement section 5 that measures the temperature (internal resistance) of the sensor, a temperature correction coefficient calculation section 6 that calculates a temperature correction coefficient from the measured temperature, and a temperature correction coefficient calculation section that uses the measured value output of the limit current measurement section 4. a correction unit 7 that corrects based on the output of 6;
It is equipped with

The temperature measuring section 5 can be configured to measure the internal resistance of the limiting current type oxygen sensor 1 and calculate the temperature from the measured value. The relationship between the resistivity ρ of the oxygen ion conductor of the sensor and the temperature is as shown in FIGS. 6a and 6b, and can be approximated by the following equation. Incidentally, FIG. 6b shows the case of semi-logarithmic scale.

However, c ₁ : Coefficient e : Base of natural logarithm E : Activation energy K : Boltzmann's constant T : Absolute temperature In equation (5), the coefficient c ₁ and activation energy E depend on material composition, firing conditions, impurities, etc. This is a fixed value. If an oxygen ion conductor having the above-mentioned basic structure is used, c ₁ is low and favorable. Regardless of the composition of the oxygen ion conductor, the resistivity increases rapidly as the temperature decreases, as shown in FIG. 6b. The reason is that the activation energy value is 0.5~
This is due to the high voltage of around 1.4 [lV]. In addition to the internal resistance of the electrolyte, there is also resistance at the interface between the electrolyte and the electrode, which varies depending on the surface treatment state of the electrolyte, the electrode material, etc. If a mixed material having the composition described above is used as the electrode material, it is possible to practically reduce the interfacial resistance.

As described above, the internal resistance of the limiting current type oxygen sensor has a large temperature dependence, so the temperature can be determined by measuring the internal resistance.

From equation (5), when T=T ₀ , c ₁ is found by setting ρ=ρ ₀ . ρ=ρ ₀ e ^{E/K(1/T-1/T0)} Equation (7) T=1/K/Elog _e (ρ/ρ ₀ )+1/T ₀ Equation (8) However, log _e : natural logarithm Equation (8) is an equation related to resistivity, but in general it can be assumed that the resistivity and internal resistance of the sensor are proportional, so T = 1/K/Elog _e (R/R ₀ ) + 1/T ₀ Equation (9) However, R: internal resistance R ₀ : internal resistance E at T ₀ and the relationship between T ₀ and R ₀ takes a specific value for each sensor, so the absolute temperature T can be determined from the internal resistance R.

Then, correction is made by multiplying equation (4) by a function (T/T ₀ ) ^-m that makes the temperature-dependent error in FIG. 4 zero with respect to temperature. That is, α(T)=(T/T ₀ ) ^−m (10) where α(T) is the temperature correction coefficient.

In the block diagram of FIG. 5, the temperature correction coefficient calculation unit 6 calculates the temperature correction coefficient α(T), and the correction coefficient α(T) is calculated by the limiting current measurement unit 4.
The correction section 7 multiplies and corrects the output.

In this way, by multiplying the temperature-dependent limiting current value {Equation (4)} by the temperature correction term α(T), the temperature-dependent component is eliminated and the limiting current is proportional only to the oxygen partial pressure. can be found.

Next, the calculation to obtain α(T)=(T/T ₀ ) ^-m from the sensor internal resistance will be explained.

From equations (9) and (10), α(T) = (T/T ₀ ) ^-m = {KT ₀ /Elog _e (R/R ₀ )+
1} ^m Equation (11) It is sufficient to calculate Equation (11) using hardware or software, and perform a product operation on the measured value of the limiting current. However, equation (11) has the disadvantage that the configuration is somewhat complicated because it includes a logarithm operation and a power operation section.

Therefore, when simplicity is more important than accuracy, it is a good idea to use a simple approximation formula instead.

First, by simplifying the logarithm calculation part, (T/T ₀ ) ^-m ≒KT ₀ /E2R/R ₀ -1/R/R ₀ +1+
1 ^m
It becomes equation (12).

Next, if we simplify the power calculation section, (T/T ₀ ) ^-m ≒ 1+2mKT ₀ /E R−R ₀ /R+R ₀ (13)
The formula becomes

_{Figure 7 shows the R /} A study of the applicable range of R ₀ and its accuracy is shown.

It can be seen that in the range of 0.3<R/R ₀ <3, there is an extremely good agreement, and it can be used as an approximate formula for practical use.

The figure also shows the case where the equation is further simplified to y ₃ =R/R ₀ -1 (16). In this case, since it can be configured only by addition and subtraction, the calculation can be significantly simplified.However, the value close to the logarithm is 0.6<R/R ₀ <1.4 compared to the case of equations (14) and (15). limited to a narrow range. However, as will be described later, a good compensation effect is obtained even in the embodiment using this extremely simple formula.

Also, regarding the power calculation z ₁ = (1 + x) ^m (17) being replaced by z ₂ ≒ (1 + mx) (18), the operating temperature of this sensor is
In the range of 600° to 1000°C, x≪1, and equation (18) can be approximated with high accuracy within 1%, so there is no problem at all. According to the approximation of equation (16), (T/T ₀ ) ^-m ≒1+mKT ₀ /E(R/R ₀ -1) (19)
It is a formula.

When simplified in this way, unlike equation (11), equation (13) does not include logarithms or power numbers, and equation (13) involves addition, subtraction, and quotient operations, while equation (19) only requires addition and subtraction, so the equipment for the operations is It is extremely simple to construct and low cost.

Temperature can be measured using methods other than the internal resistance of the sensor.
For example, a method using a thermistor or thermocouple as a temperature sensing element may be used.

Alternating current can be used to measure the internal resistance of the limiting current type oxygen sensor.

FIG. 8 shows a trajectory of impedance according to frequency in the overvoltage control region of the limit current sensor. i.e. direct current (DC) and infinity (∞)
At the frequency, there is only a resistance component and the reactance component is zero, but at intermediate frequencies there is also a reactance component. The electrical equivalent circuit of a sensor that draws such a nearly semicircular locus can be expressed as shown in FIG. In FIG. 9, Rb corresponds to the internal resistance in the resistance dominated region. Further, R _D represents the resistance existing at the interface between the electrolyte and the electrode in the overvoltage region, and C _D similarly represents the capacitance at the interface.

Therefore, in the overvoltage dominant region, the internal resistance Rb
There may be several ways to find it.

a 1/2πC _D Find the absolute value of impedance at a frequency equal to or close to Rb and use it as an approximate value of Rb.

b Calculate the resistance component from the AC impedance absolute value and phase angle using the same method as above.

c Measure the absolute value and phase angle of impedance at multiple frequencies and find each constant of the equivalent circuit.

Among these methods, method a) is the simplest. The frequency depends on the size of the sensor element,
It is necessary to set it optimally depending on the manufacturing method, etc., but usually
Approximately 500 [Hz] to 100 [KHz] is appropriate.

FIG. 10 shows the basic circuit configuration of an embodiment in which internal resistance is measured using alternating current and temperature compensation of the output is performed based on the measured internal resistance.

The limiting current type oxygen sensor has the same construction as that shown in FIG. 1a. The voltage of the AC/DC superimposed voltage applying section 12 is supplied to the sensor 1 via the current detecting section 13 . The current signal detected by the current detection section 13 is guided to the AC/DC separation section 14 . This separation can be achieved by using high pass filters and low pass filters. The DC current component separated by the AC/DC separator 14 is a limiting current and corresponds to the oxygen concentration. The internal resistance calculation unit 15 calculates an internal resistance value from the output voltage of the AC oscillator 18 and the AC current component separated by the AC/DC separation unit 14. Based on the obtained internal resistance value, a temperature correction coefficient α(t) is calculated in the temperature correction coefficient calculating section 16. To calculate α(t), the above formula (11) is used.
Equations (13), (19), etc. are used. Based on the obtained temperature correction coefficient α(t), in the correction unit 17,
Corrections are made to the measurement limit current. In the above configuration, the internal resistance calculating section 15, the temperature correction coefficient calculating section 16, and the correcting section 17 constitute a compensating section 20 for the temperature dependence of the output.

Note that the logarithmic operation of log _e (R/R ₀ ) in the first term on the right side of equation (11) can be easily configured using, for example, the logarithmic conversion module 4366 (or 4367) manufactured by Teledyne Film Corporation.

Furthermore, the power calculation on the right side of equation (14) can be easily configured using the company's power function module 4371 or the like.

FIG. 11 shows an example in which equation (13) is used to calculate the temperature correction coefficient.

The DC voltage application section 21 and the AC constant current application section 22 apply a superimposed DC and AC voltage or current to the limiting current type oxygen sensor 1, and the current/voltage conversion circuit 23 converts the current flowing through the sensor or the current being displayed on the sensor. Detects the voltage applied. Among the detected components, a limiting current component, which is a direct current component, separated by a low-pass filter 24 is guided to a product calculation section 26 . The AC component is separated by a high-pass filter 25, and a voltage proportional to the internal resistance is obtained from the rectified value by a rectifier 27. Since the alternating current applied to the sensor 1 is a constant voltage, the internal resistance calculating section 15 shown in FIG. 10 can be omitted. As a setting condition, the frequency of AC is 500 to 50 [K
Hz], and the magnitude of the alternating current is preferably about 1 to 100 [mV] in terms of the terminal voltage of the limiting current type oxygen sensor.

In this embodiment, an AC constant current applying section is used as the AC constant current applying section 22, but an AC constant voltage applying section may be used. In that case, when the input of the high-pass filter 25 is taken from the output of the current-voltage conversion circuit 23 and the reciprocal of the rectified output is taken, it is proportional to the internal resistance.

The temperature correction coefficient calculating section is configured to calculate equation (13). That is, R+R ₀ of equation (13) is obtained by the three elements of voltage source 28 and resistors 29 and 30.
is calculated approximately. Voltage source 31, resistor 32
and R- of formula (13) by the three elements of 33
R ₀ is calculated approximately. The quotient calculation unit 34 calculates R−R ₀ /R+R ₀ in equation (13). By using four elements such as voltage source 28, resistors 35 and 36, and potentiometer 37, 1+2m of equation (13)
KT ₀ /E R−R ₀ /R+R ₀ is approximately calculated.

Incidentally, instead of using a resistor network, an adder can be used to perform more precise calculations.

A temperature-compensated output can be obtained by introducing the temperature correction coefficient obtained by the calculation of equation (13) to the product calculation section 26 and performing the product calculation with the measured limit current. Sensors with different temperature coefficients can be easily accommodated by adjusting the potentiometer 37.

FIG. 12 shows another embodiment. 1st
The difference from the configuration of the embodiment shown in FIG. 1 is that the temperature correction coefficient calculating section is configured to use equation (19).
That is, the temperature correction term in equation (19) is
and resistor 39, resistor 40 and potentiometer 4
1 to simplify the configuration of the temperature correction coefficient calculation section. For sensors with different temperature coefficients, a constant voltage applying section 38 or a potentiometer 41 is used.
This can be easily adjusted by adjusting the

FIG. 13 shows an embodiment in which the following is used as the limiting current type oxygen sensor 1A. That is, a cathode layer 42a is provided on one surface of the oxygen ion conductor for detecting the limiting current shown in FIG.
A configuration in which an anode layer is provided on the other side facing this,
Or, in addition to the basic configuration of the part in which the cathode layer is covered with a member for restricting gas diffusion to the cathode (referred to as the part for detecting the limiting current), the following parts, i.e., internal resistance detection. An electrode 42b is provided on one surface of the oxygen ion conductor for performing this, and a portion having an electrode (referred to as a portion for detecting internal resistance) is provided on the other surface facing the electrode 42b, and a portion for detecting a limiting current is provided with an electrode 42b. limit current measuring sections 43, 44, and 45 that apply a voltage in the overvoltage control region to measure the limit current; and a section for detecting internal resistance that applies a current or voltage in the resistance control region to measure the internal resistance. internal resistance measuring section 46 to measure;
47, there is no need to switch, superimpose, or separate the applied voltage or current.

FIG. 14 also shows an example of the results obtained by the present invention. As is clear from the figure, when the conventional technology is used in a region where the temperature changes, it has a large temperature dependence, which causes loss of accuracy and is a factor that restricts the operating temperature range. On the other hand, when using the device of the present invention, the temperature dependence is compensated for, so the accuracy can be improved and the usable temperature range can be widened.

Even in the case of temperature compensation with a simple configuration using equation (19), an effect comparable to that of a configuration for precise temperature compensation is obtained. 7th
As shown in the figure, the approximation equation (16) is an insufficient approximation to the original logarithmic operation equation (14) in both the regions of 0.6>R/R ₀ and R/R ₀ >1.4. Nevertheless, the reason why the result is as good as the example shown in FIG. 8 using equation (14) and the example shown in FIG. 9 using equation (15) is that the temperature shown in FIG. The characteristics are not ideal characteristics as shown by the broken line, but are characteristics that rapidly decrease on the low temperature side as shown in the solid line.The slope of equation (16) is adjusted so that it becomes close to a logarithmic function on the high temperature side, and on the low temperature side This is because the correction was made by setting the correction amount to be larger than the logarithm. Note that the product calculation unit 21 in the embodiment shown in FIG. 9 and the embodiment shown in FIG.
Instead of using a, it is also possible to use an element such as a FET whose internal resistance is modulated by the gate input voltage.

In summary, by using the two regions of the limiting current type oxygen sensor, the limiting current is detected from the overvoltage dominant region, the internal resistance is measured from the resistance dominant region, the temperature is determined from the internal resistance, and the temperature dependence of the limiting current is detected. By correcting and correctly detecting the limiting current, that is, the oxygen concentration, the measurement accuracy can be improved and the operating temperature range can be expanded. The present invention can provide such an industrially extremely useful and highly useful technology.

[Brief explanation of drawings]

Figure 1a is an example of the cross-sectional structure of a limiting current type oxygen sensor, Figure 1b is an example of a typical voltage vs. current characteristic of a limiting current type oxygen sensor, and Figure 2 is a conventional limiting current type oxygen sensor. Example of measurement circuit, 3rd
The figure shows the relationship between oxygen concentration and limiting current of a limiting current type oxygen sensor at two temperatures, Figure 4 shows the relationship between temperature and limiting current at a constant oxygen concentration, Figure 5 shows the basic configuration of the present invention, and Figure 6 shows the relationship between temperature and limiting current at a constant oxygen concentration. Figures a and b show the temperature dependence of internal resistance, and Figure 7 shows the accuracy and applicable range of the simple function approximation method.
Figure 8 is a diagram showing the locus of impedance with respect to the frequency of a minute AC input voltage when a voltage (current) in the overvoltage control region is applied to the limiting current type oxygen sensor, and Figure 9 is a diagram showing the locus of impedance with respect to the frequency of the minute AC input voltage when a voltage (current) in the overvoltage control region is applied to the limiting current type oxygen sensor. This shows the equivalent circuit. FIGS. 10 to 13 show embodiments of the present invention, and FIG. 14 shows an example of limiting current compensation characteristics according to the present invention. FIGS. 10 to 13 show embodiments of the present invention, and FIG. 14 shows an example of limiting current compensation characteristics according to the present invention. 1...Limiting current type oxygen sensor (cross section shown), 4
...Limiting current measuring section, 5...Temperature (internal resistance) measuring section, 6...Temperature correction coefficient calculating section, 7...Correction section, 12
...AC/DC superimposed voltage application section, 13...current detection section,
14... AC/DC separation section, 15... Internal resistance calculation section,
16...Temperature correction coefficient calculation section, 17...Correction section, 18
...AC oscillator, 19...DC voltage application section, 20...temperature dependence compensation section, 21...DC constant voltage application section, 22
...AC constant current applying section, 23...current voltage conversion circuit,
24...Low pass filter, 25...High pass filter, 26...Product calculation section, 27... Rectification section, 28, 31
... Constant voltage application section, 29, 30, 32, 33, 3
5, 36, 39, 40, 44...resistance, 34...quotient calculation section, 37, 41...potentiometer, 1A...limiting current detection electrode 42a and internal resistance detection electrode 4
2b, a limiting current type oxygen sensor (cross section shown), 43...voltage application section for limiting current detection, 45...
Potential difference detection section.

Claims (1)

[Scope of Claims] 1. A limiting current type oxygen sensor, a limiting current measuring section that measures a limiting current by applying a voltage for limiting current measurement to the limiting current type oxygen sensor, and a limiting current measuring unit that measures an internal resistance of the limiting current type oxygen sensor. an internal resistance measuring section that measures the internal resistance by applying a voltage or current for the purpose of measurement; a temperature correction coefficient calculation section that calculates a temperature correction coefficient from the output of the internal resistance measurement section; and a temperature correction coefficient calculation section that calculates the temperature correction coefficient from the output of the limit current measurement section. A limiting current type oxygen concentration detection device comprising: a correction unit that corrects based on the output of the calculation unit; and the internal resistance measuring unit applies a voltage or current that is a superimposition of direct current and alternating current to the limiting current type oxygen sensor. and a means for separating the DC and AC components from the superimposed DC and AC current or voltage flowing through the limiting current type oxygen sensor, the limiting current is determined from the DC component, and the internal resistance is determined from the AC component. Limiting current type oxygen concentration detection device. 2. A filter section in which the temperature correction coefficient calculation section obtains an alternating current proportional to the internal resistance; a rectifying section that rectifies the alternating current to obtain a direct current proportional to the internal resistance;
A first addition section that adds a voltage or current of the same polarity to the rectified output, a second addition section that adds a voltage or current of the opposite polarity to the rectification output, and an output of the first addition section and the second addition section. an arithmetic unit that calculates the ratio of outputs;
The limiting current oxygen concentration detection device according to claim 1, further comprising a third addition section that adds a fixed value to the output of the calculation section. 3. The temperature correction coefficient calculating section includes a filter section that calculates an alternating current proportional to the internal resistance, a rectifying section that rectifies the alternating current and outputs a direct current voltage or current proportional to the internal resistance, and a rectifying section that calculates an alternating current proportional to the internal resistance, and a rectifying section that calculates an alternating current that is proportional to the internal resistance. The limiting current type oxygen concentration detecting device according to claim 1, further comprising: or an adding section for adding current. 4. The limiting current type oxygen concentration detection device according to claim 2 or 3, wherein each of the adding sections is constituted by a resistor. 5 A limiting current type oxygen sensor, a limiting current measuring section that applies a voltage for limiting current measurement to the limiting current type oxygen sensor to measure the limiting current, and a limiting current measuring unit that applies a voltage or current for internal resistance measurement to the limiting current type oxygen sensor. an internal resistance measuring section that measures the internal resistance by applying voltage, a temperature correction coefficient calculating section that calculates a temperature correction coefficient from the output of the internal resistance measuring section, and a temperature correction coefficient calculating section that calculates the temperature correction coefficient from the output of the limiting current measuring section. In the limiting current type oxygen concentration detection device, the limiting current type oxygen sensor has a cathode layer on one side of a plate or cylinder made of an oxygen ion conductor, and the other side facing the cathode layer. a part for detecting a limiting current, which is configured by providing an anode layer on a part of the oxygen ion conductor, and a part for detecting internal resistance, which is configured by further providing an additional electrode layer on a part of the oxygen ion conductor; The part for detecting the internal resistance measures the limiting current by applying the voltage in the overvoltage dominated region, and the part for detecting the internal resistance measures the internal resistance by applying the voltage or current in the resistance dominated region. A limiting current type oxygen concentration detection device. 6. A filter section in which the temperature correction coefficient calculation section obtains an alternating current proportional to the internal resistance; a rectifying section that rectifies the alternating current to obtain a direct current proportional to the internal resistance;
A first addition section that adds a voltage or current of the same polarity to the rectified output, a second addition section that adds a voltage or current of the opposite polarity to the rectification output, and an output of the first addition section and the second addition section. an arithmetic unit that calculates the ratio of outputs;
6. The limiting current type oxygen concentration detection device according to claim 5, further comprising a third addition section that adds a constant value to the output of the calculation section. 7. The temperature correction coefficient calculating section includes a filter section that calculates an alternating current proportional to the internal resistance, a rectifying section that rectifies the alternating current and outputs a direct current voltage or current proportional to the internal resistance, and a rectifying section that calculates an alternating current proportional to the internal resistance. The limiting current type oxygen concentration detecting device according to claim 5, further comprising: or an adding section for adding current. 8. The limiting current type oxygen concentration detection device according to claim 6 or 7, wherein each of the adding sections is constituted by a resistor.