KR840001992B1 - The supply circuit of the basic polar oxygen partial pressure control current for oxygen sensing element - Google Patents

Abstract

An oxygen sensor has a solid electrolyte layer placing a reference electrode and a measurement electrode. A control circuit producing AC current through the electrolyte between the electrodes to establish a reference oxygen partial pressure at the reference electrode- electrolyte interface includes a comparator for reference voltage and output between the electrodes, a multiplier for the output voltage, and a control current regulator utilizing comparator and multiplier outputs so that current intensity depends on output voltage value when one voltage is higher than the other to compensate variations duing to temperature.

Description

Supply circuit of reference electrode oxygen partial pressure control current for oxygen sensing element

1 is a schematic cross-sectional view of a basic membrane structured oxygen sensing element.

2 is a supply circuit diagram of a reference electrode oxygen partial pressure control current for a conventional oxygen sensing element.

3 is a chart showing the relationship between the excess air ratio and the output voltage of the oxygen sensing element.

4 is a table showing the relationship between the conventional oxygen sensing element output voltage and the reference electrode oxygen partial pressure control current.

5 is a schematic diagram of a reference electrode oxygen partial pressure control current supply circuit for an oxygen sensing element according to an embodiment of the present invention.

6 is a supply circuit diagram of a reference electrode oxygen partial pressure control current for an oxygen sensing element in one embodiment of the present invention.

FIG. 7 is a chart showing the relationship between the output voltage of the supply circuit shown in FIG. 6 and the reference electrode oxygen partial pressure control current.

FIG. 8 is a chart showing the relationship between the output voltage in the stable state of the oxygen sensing element supplied with the control current by the supply circuit shown in FIG. 6 and the reference electrode oxygen partial pressure control current.

9 is a supply circuit diagram of a reference electrode oxygen partial pressure control current for an oxygen sensing element according to another embodiment of the present invention.

10A and 10B show an oxygen detector supplied with a control current by the supply circuit shown in FIG.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for supplying a reference electrode oxygen partial pressure control current for an oxygen sensing element. In particular, a reference electrode and a measurement electrode are installed on the surface (both sides or one side) of an oxygen ion conductive solid electrolyte, and are supplied from an external power source. The control current I _S causes the movement of oxygen ions in the solid electrolyte to control the reference electrode oxygen partial pressure, and output voltage V _S according to the difference between the reference electrode oxygen partial pressure and the measured electrode oxygen partial pressure. The present invention relates to a circuit for supplying the reference electrode oxygen partial pressure control current I _S to the oxygen sensing element that is to be generated.

FIG. 1 is a schematic cross-sectional view showing an example of the oxygen sensing element 10 supplied with the above-mentioned reference electrode oxygen partial pressure control current I _S to control the reference electrode oxygen partial pressure, and the diaphragm for maintaining the strength as a structural gas. An insulating heat insulating body 2 is embedded in the sieve 1, and an electron conductive reference electrode 3, an oxygen ion conductive solid electrolyte 4, and an electron conductive measurement electrode 5 are sequentially disposed on the diaphragm body 1. And a porous protective layer 6 around the measuring electrode 5, and at the same time between the reference electrode 3 and the measuring electrode 5, ordinary ions in the solid electrolyte 4 Connect an external power supply (V _C ) for supplying a control current I _S (shown in one of the directions) for controlling the reference electrode oxygen partial pressure to cause movement of the reference electrode, and a measuring device (7) for extracting the output voltage (V _S ). _H on the heat insulating body (2)

FIG. 2 shows an example of a conventional electric circuit diagram in which an external power source V _C and a heating external power source V _H are connected to the oxygen detecting element 10 shown in FIG. Reference numeral E of the sensing element 10 denotes an electromotive force, R denotes an internal resistance, and Rh denotes a resistance of the heat insulating body 2. The external heating power source V _H is applied to the heat insulating body 2 to generate heat. In the supply circuit for the reference pole oxygen partial pressure control current using the external power supply V _C as a voltage source, the drain D axis of the FET (field effect transistor) 11 is connected to the external power supply V _C , and the source is supplied. The (S) side is connected to the reference electrode 3 (or the measuring electrode 5) of the oxygen sensing element 10 via a resistor R _S and a protective resistor R _P , and the other measuring electrode. (5) (or reference electrode 3) is grounded. When the voltage V _GS between the gate G source S in the FET 11 is set to the source current I _S ,

V _GS = -I _S ㆍ R _S ... … … … … … … … … … [One]

The control current I _S , which is the same as the source current I _S shown in Equation [1], flows into the solid electrolyte 4 of the oxygen sensing element 10, and the solid electrolyte 4 The movement of oxygen ions causes the movement of oxygen ions to control the reference electrode oxygen partial pressure, and generates an electromotive force E corresponding to the difference between the reference electrode oxygen partial pressure and the measured electrode oxygen partial pressure, thereby outputting the output voltage used for the internal resistance R. Output (V _S )

In more detail, for example, it is assumed that an external power source V _C is connected such that the control current I _S flows from the reference electrode 3 toward the measurement electrode 5 in the solid electrolyte 4. Movement of oxygen ions occurs from the measuring electrode 5 toward the reference electrode 3 in the electrolyte 4 to force the introduction of oxygen ions into the reference electrode 3 and from the reference electrode 3. The reference electrode oxygen partial pressure is kept slightly high (for example, about 10 ⁻¹ atm) in the state of being balanced with the diffusion of oxygen molecules through the solid electrolyte 4 or the diaphragm 1 (if breathable). When the measuring electrode 5 has a catalytic action, as shown in FIG. 3, a large output voltage V _S occurs at the λ <1 side (that is, the rich side with excessive fuel), in the vicinity of λ = 1 output voltage (V _S) is dramatically reduced, output from the excess air ratio λ> 1 side (that is the air is over-lean side) Voltage (V _S) is shown the characteristic is reduced.

On the contrary, assuming that the external power source Vc is connected so that the control current Is flows from the measuring electrode 5 toward the reference electrode 3, the measuring electrode (1) from the reference electrode 3 in the solid electrolyte 4 As oxygen ions move toward 5), the reference electrode oxygen partial pressure is kept slightly lower (e.g., about 10 ^-20 atm). It shows the characteristic which produces (Vs).

4 shows control of the case where the control current I _S flows from the reference electrode 3 toward the measurement electrode 5 in the solid electrolyte 4 (characteristics shown in FIG. 3). Current (Is) and Oxygen _S

On the other hand, the control current I _S by the conventional circuit shown in FIG. 2 is constant as indicated by the dotted line in FIG. 4, and each intersection becomes an output voltage V _S.

However, in the conventional case, since the control current Is is constant, the output voltage V _S (V _AL ', V _BL ', V _CL 'and V _AR ', V _BR according to the change of the oxygen sensing element temperature). The imbalance of ', V _CR ') becomes considerably large, for example, air-fuel ratio control centered on? That is, in the example of FIG. 4, the line CR has the control current I _S because the diffusion of the above-mentioned oxygen molecules increases when the device temperature is 550 ° C. and λ = 0.9 or when the device temperature becomes 650 ° C., for example. ) Is constant, the reference electrode oxygen partial pressure decreases, the output voltage is lowered from (V _CR ') to (V _BR ) and becomes a characteristic of the line BR, and the output voltage is considerably reduced compared to the line CR. . Therefore, when the oxygen sensing element temperature rises, it is necessary to increase the control current I _S to increase the amount of oxygen ions serving as the reference electrode 3 so that the reference polar oxygen partial pressure does not decrease. Further, the diffusion of the oxygen molecules increases even when the porosity of the solid electrolyte 4 or the like increases as in the case where the temperature rises, and the output _{S S} when the control current I _S is constant.

As described above, in the conventional case, since the reference electrode oxygen partial pressure control current I _S is constant, the output voltage V _S varies greatly depending on the oxygen sensing element temperature, the porosity of the solid electrolyte, the gas to be measured, and the like. The problem was that the accuracy was lowered when judging the excess air ratio λ> 1 or λ <1 using the predetermined voltage (0.55V) as the comparison voltage.

The object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to significantly reduce the temperature of the oxygen sensing element in use and the porosity of the solid electrolyte of the oxygen sensing element (when the diaphragm body is breathable, Even when there is scattering, the external output voltage V _S of the oxygen sensing element can be maintained at a substantially constant level at each of the excess air ratios λ> 1 and λ <1. In the case of determining λ> 1 or λ <1 by the excess of air, the relative position between the comparison voltage and the output voltage V _S can be kept substantially constant, and the accuracy of the judgment can be significantly improved. In other words, it is possible to obtain good output voltage characteristics even if the temperature of the oxygen sensing element and the porosity of the solid electrolyte are not very strictly.

In the present invention, in supplying the reference electrode oxygen partial pressure control current to the oxygen sensing element, the _S corresponds to a change in the output voltage V _S of the oxygen sensing element.

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

FIG. 5 is a system diagram showing a supply circuit for the reference electrode oxygen partial pressure control current for the oxygen sensing element in the embodiment of the present invention, and the measuring electrode 5 of the oxygen sensing element 10 in FIG. A heating external power source (V _H ) is connected to the heat insulating body 2 (which may be an oxygen sensing element 10 that is not installed) and is capable of generating heat.

In addition, the supply circuit includes a comparator 15 comparing the output voltage V _S of the oxygen sensing element 10 with a predetermined voltage V _T and an output voltage V _S of the oxygen sensing element 10. and a computing unit (16) for an integral multiple of, the comparison unit 15, the reference electrode an oxygen partial pressure control current corresponding to the output, and the output voltage (V _S) of the oxygen sensing element 10 in accordance with an output from the computing unit 16 from A current control unit 17 for supplying I _S is provided. The comparison unit 15 compares the predetermined voltage V _T with the output voltage V _S of the oxygen sensing element 10, converts a divalent signal, and controls the current control unit 17. . Here, in the solid electrolyte 4 of the oxygen sensing element 10, the control current I _S flows from the reference electrode 3 toward the measurement electrode 5 so that the excess air has a large output voltage of λ <1. (V _S ) is generated. Tables 3 and 4 in Figures 3 and 4 _{T S S S T S S S S S}

FIG. 6 shows an example of the specific circuit of FIG. 5, in which a predetermined voltage V _T is input to the + input side of the operational amplifier 21 constituting the comparator 15, and an oxygen sensing element on the-input side. the output voltage (V _S) of 10 is input. The output side of the operational amplifier 21 is connected to the base of the PNP transistor Tr constituting the current control unit 17 via the diode D ₁ in the forward direction. On the other hand, the output voltage V _S of the oxygen sensing element 10 is input to the + input side of the operational amplifier 22 constituting the operation unit 16, and the output voltage of the operational amplifier 22 is applied to the input side of the resistor R _1. ) And the voltage divided by the resistor (R ₂ ) is input. The output voltage is input to the + input side of the operational amplifier 23 constituting the current control unit 17. On the input side of the operational amplifier 23, a resistor R ₃ and a transistor _{4 C} having a voltage V _C applied to one side thereof.

In the circuit configuration shown in FIG. 6, a heating external power supply V _H is connected to the heat transfer element 2 of the oxygen sensing element 10 so as to generate heat. In addition, in the oxygen sensing element 10 having no heat transfer element 2, there is naturally no connection of such a negative power supply V _H for heating.

Here, when the output voltage V _S of the oxygen sensing element 10 (the predetermined voltage V _T ), the operational amplifier 21 outputs (V _T ) and makes the transistor Tr in an inoperative state. Therefore, in this case jejeo current (is) is only a minute current (I _V). the small current (I _V) is

Is indicated, and as shown in FIG. 7, there is a substantially constant small current.

In addition, when the output voltage V _S of the oxygen sensing element 10 is a predetermined voltage V _T , the operational amplifier 21 outputs OV, so that the diode D ₁ becomes inoperative and the transistor Tr It becomes the operation state. On the other hand, the output voltage (V _S) of the oxygen detection element 10 inputted to the operational amplifier 22 of the operation unit 16 is, integer times the following equation by the operational amplifier 22.

Then, an integer multiple of the voltage μ · V _S is input to the current control unit 17. Operational amplifier 23 constituting the current control unit 17

The transistor Tr is controlled to be.

Therefore, the control current I _S when the output voltage V _S > constant voltage V _{T of the} oxygen sensing element 10 is

Is represented by, as shown in the Figure 7, the output voltage (V _S) is obtained the characteristics becomes small gradually the control current (Is) in accordance with the larger than the predetermined voltage (V _T).

FIG. 8 shows the relationship between the output voltage V _S and the reference electrode oxygen partial pressure control current I _{S in} the stable state of the oxygen sensing element 10, and denotes AL, BL, and CL. ) And (AR), (BR) and (CR) are the same as in the case of FIG.

This stable state means that in (AL), (BL), and (CL), the control current (I _S ) and the output voltage (V _S ) in the state where λ = 1.1 (see FIG. 3) continues. (AR), (BR) and (CR), the relationship between the control current I _S and the output voltage V _S when the state of λ = 0.9 (see FIG. 3) is continued. It is shown. In addition, as in the case of FIG. 4, the relationship between the control current I _S and the output voltage V _S also varies depending on the porosity of the solid electrolyte 4.

In the stable state, the characteristic curves AL, BL, CL and AR between the control current I _S and the output voltage V _S of the oxygen sensing element indicated by solid lines in FIG. 8. The intersection of (BR), (CR) and the characteristic curve between the control current (I _S ) and the output voltage (V _S ) of the control current supply circuit shown in FIG. The control current I _S and the output voltage V _S corresponding to changes in the temperature or porosity of each oxygen sensing element are obtained.

Therefore, for example, in the case of the output voltage V _S and the predetermined voltage V _T , the temperature of the oxygen sensing element is increased or the porosity of the solid electrolyte 4 of the oxygen sensing element is large due to unbalance at the time of manufacture. In this case, the diffusion of oxygen molecules from the reference electrode 3 increases and the output voltage V _S decreases. However, as indicated by the dotted line in FIG. 8, the control voltage is reduced along with the decrease in the output voltage V _S. Since I _S increases, the fall of the output voltage V _S can be considerably reduced, and the output voltages V _AR and V in the respective curves AR, BR, and CR are reduced. _BR ) and (V _CR ) can be regarded as stable with a relatively small fluctuation range compared to the values of output voltages V _AR ', (V _BR '), (V _CR ') shown in FIG. have.

In addition, in the case of the output voltage V _S (predetermined voltage V _T ), since only a small current I _V is supplied to the oxygen sensing element, the curves AL, BL, and CL correspond to each other. Output voltage (V _AL ), _{BL CL AL BL CL}

Therefore, by based on the predetermined voltage (V _T), the output voltage (V _S) are all greater jakeunga the thus-measured environment fuel rich side (rich side) is the excess air side (lean side) is applied in which the determination that It is possible to significantly increase the accuracy of the case.

Thus, in the case of the steady state, i.e., the excess air side (e.g. λ = 1.1) or the fuel excess side (e.g. λ = 0.9) is continued, the temperature change of the oxygen sensing element or the porosity of the solid electrolyte 4 Although the fluctuation range of the output voltage V _S due to unevenness can be made considerably smaller than in the conventional case, the excess air ratio λ is achieved by performing feedback control of the air-fuel ratio as exhaust gas of the internal combustion engine for automobiles. In the case where control is maintained so that combustion in the vicinity of = 1 is always maintained, the rich (λ <1) and lean (λ> 1) states are constantly repeated based on the excess air ratio λ = 1. And, for example, because the third also a rich state in which the output voltage (V _S), even when moving to a lean state decreases from the display to, and in this case, as the characteristics shown in the seventh degree, the output voltage (V _S In response to the decrease of), the control current I _S increases rapidly and acts in the direction of preventing the decrease of the output voltage V _S , and at the same time, the excessive control current with respect to the oxygen sensing element 10 temporarily ( I _S ) (up to about 120 μA in the case of FIG. 7) may be supplied to deteriorate the oxygen sensing element 10. Therefore, the sudden drop in the output voltage V _S when moving from the rich state to the lean state remains as output _{S S S} of the current control unit 17.

FIG. 9 shows an embodiment in which a peak holding unit is provided in the calculation unit of the supply circuit for the control current I _S shown in FIG. 6, and the same reference numerals are used for the same parts as in FIG. The output voltage V _S of the oxygen sensing element 10 input to the operational amplifier 22 of the calculation unit 16 is integer-multiplied by the operational amplifier 22 as in the formula [3], and the output (μV _S ) is increased. It is input to the + input terminal of the operational amplifier 24. In the peak holding section composed of the operational amplifier 24, the diode D ₂ , the capacitor C ₁ , and the resistor R ₆ , the above μ μV _S is converted into a peak voltage V _P as follows. .

(Where V _max is the maximum value of V _S )

This peak voltage V _P is input to the + input terminal of the operational amplifier 23 of the current control unit 17 instead of (μV _S ) in FIG. 6 to determine (I _C ) shown in the following equation. .

Therefore, when the output voltage (V _S) (a predetermined voltage (V _T) in the case [2] smiling (V _S, only the output current-voltage (I _V) obtained from the formula given) a predetermined voltage (V _T) is, (I _V ) And (I _C ) by the formula [7] are supplied to the oxygen sensing element 10.

However, the time constant of the discharge in the peak holding portion would be displayed as (R ₆ × C _1), for example, in the case of the air-fuel ratio control of the internal combustion engine for automobiles, it is suitably about 5 to 15 seconds. That is, the track of time taken for the output voltage (V _S) if the sudden decrease in the third degree displayed with status be changed lean side from the rich side, the oxygen sensing element 10, as in the 0.5 seconds or less, or the The transition time also varies depending on differences in the solid state of the oxygen sensing element 10 or changes over time. Here, if the time constant of the discharge is made slightly longer in consideration of the shifting time, the excessive control current I _C caused by the decrease of the output voltage V _S when the state changes from the rich side to the lean side is Supply can be prevented. On the other hand, if the time constant of the discharge is too large, and the reference electrode an oxygen partial pressure between the lack of a relatively short period of time is impossible in case that the output voltage (V _S) decrease, can compensate for this.

FIG. 10 shows the oxygen concentration in the exhaust gas of the internal combustion engine for automobiles by using the oxygen sensing element 10 to which the reference electrode oxygen partial pressure control current I _S is supplied by the circuit shown in FIG. The operating state when the feedback control is performed is shown. At this time, the oxygen detecting element 10 has a large _S <>< _S at an excess air ratio λ <1, as shown in FIG.

In addition, the solid line in FIG. 10 shows the peak voltage V _P (attenuates according to the time constant R ₆ × C ₁ of discharge), but the peak voltage V _P is actually the output voltage V _S. ) Is an integer multiplier (see equation [3] and equation [6] above).

It has to be partially overlapped with the output voltage (V _S) substituted with.

In the case of the excess air ratio λ <1, the output voltage V _S becomes a large value and is temporarily held in the peak holding portion to be V _S = V _P ', as shown by the point A in FIG. The control current I _S A is supplied to the oxygen detecting element 10. Subsequently, when the state changes to the lean side and becomes λ> 1, the output voltage V _S drops rapidly. On the other hand, the holding voltage (V _P ') will be gradually reduced as described in correspondence with the discharge time constant can be maintained negative peaks shown by the solid line in the Figure 10b. At the same time as the voltage V _P ′ decreases, as shown in FIG. 10A, the control current I _S increases toward the current electrode I _S B. Next, when the output voltage V _S reaches point b in FIG. 10 and becomes smaller than the predetermined voltage V _T , the output of the operational amplifier 21 becomes an OV signal. _{S V S V} < _S

At this time, the control current I _S C (= I _W ) maintains the micro state until the output voltage V _S exceeds the predetermined voltage V _T (up to the point d in FIG. 10B). Next, when the output voltage V _S exceeds the predetermined voltage V _T , the control current from the arithmetic circuit (peak holding circuit) shown in FIG. 9 is supplied again, and the control current I _S shown in FIG. While the voltage is rapidly increased up to D) and the voltage V _P 'from the point D to the point E is attenuated, it is (V _P ') (V _S ), and thus increases to the control current I _S E. At the point E, (V _P ') = (V _S ), while the output voltage V _S rises again, the voltage V _P ' similarly increases, so that the control current I _S is a current value. The reduction is continued by maximizing (I _S E) and returning to the state corresponding to the above-mentioned point (A) via the point (F). Therefore, even when the output voltage V _S suddenly decreases when the state changes from λ <1 to λ> 1, the output voltage V _S is temporarily maintained as the peak voltage V _P (V _P ′). Since it gradually falls with the time constant of the discharge of the peak holding circuit, it is possible to prevent excessive control current I _S from flowing through the oxygen sensing element 10.

In addition, in the above-described embodiment, the oxygen sensing element 10 that generates a large output voltage V _S at the excess air ratio? <1 has been described as an example, but the oxygen in the solid electrolyte 4> _S

Although the case where the predetermined voltage V _T is about 0.55 V as shown in Fig. 7, the predetermined voltage V _T can be changed as appropriate. That is, in this type of oxygen sensing element, the internal resistance R of the solid electrolyte 4 increases when the element temperature decreases, so that the value of (internal resistance R) x (control current I _S ) is increased. more large, appearance of the output voltage (V _S) is a further increase. Therefore, if the predetermined voltage V _T is not increased in accordance with it, for example, in the oxygen sensing element having the characteristic shown in FIG. 3, the output voltage V _S at the lambda> 1 side also exceeds the predetermined voltage V _T. A situation arises that it becomes impossible to perform good control. Therefore, specifically in the case of a car, while revolution high, and there while driving, a predetermined voltage (V _T) and to a low predetermined voltage (V _T), In addition, when the smaller of the internal combustion engine load, a predetermined voltage (V _T) when high, the load is large, it is also preferable to change according to the operating state of the vehicle so as to decrease the predetermined voltage (V _T).

In addition, in the supply circuit in the above embodiment, when the output voltage V _S is lower than the predetermined voltage V _T , the control current I _S decreases only slightly with respect to the increase in the output voltage V _S , When the output voltage V _S exceeds the predetermined voltage V _T , the control current I _S discontinuously increases _{S T S S S S}

Furthermore, the diaphragm body 1, the heat transfer body 2, the reference electrode 3, the oxygen ion conductive solid electrolyte 4, the measurement electrode 5, and the protective layer 6 which constitute the oxygen sensing element 10, etc. As a raw material, it is preferable to suitably select and use from a variety of conventionally known oxygen sensing element materials.

Or more, as described above, according to the present invention, in response to the change in the output voltage (V _S) of the oxygen sensing element by changing the reference electrode an oxygen partial pressure of the control current (I _S), the output voltage (V _S of the oxygen-sensing element Since the control current (I _S ) corresponding to) is supplied, when the temperature of the oxygen sensing element changes considerably in use or when there is a significant non-uniformity in the porosity of the solid electrolyte of the oxygen sensing element, Therefore, even when the output voltage is susceptible to fluctuation, the output voltage V _S of the oxygen sensing element can be maintained at a substantially constant level at each of the excess air ratios λ> 1 and λ <1, and in particular, the predetermined voltage is compared with the comparison voltage. Then, the excess air ratio λ> 1 or λ <1 is judged and the ratio of fuel is increased when the excess air ratio λ> 1, and the ratio of air is increased when λ <1 is always around the excess air ratio λ = 1. Air and kite In the control to perform a combustion with the excess air ratio λ> 1 or λ <1

Claims (1)

A reference electrode and a measurement electrode are installed on the surface of the oxygen ion conductive solid electrolyte, and the oxygen current is controlled in the solid electrolyte by the control current I _S supplied from an external power source to control the oxygen partial pressure of the reference electrode. In a circuit for supplying the reference electrode oxygen partial pressure control current (I _S ) to an oxygen sensing element that generates an output voltage (V _S ) corresponding to the difference between the reference electrode oxygen partial pressure and the measured electrode oxygen partial pressure. And a comparator for comparing the output voltage V _S of the oxygen sensing element with a predetermined voltage V _T , an arithmetic unit for multiplying the output voltage V _S of the oxygen sensing element, the output of the comparator and the arithmetic unit Therefore, the reference electrode an oxygen partial pressure of the control current (I _S) of oxygen comprising the current control for supplying the sensing element based on the oxygen partial pressure-pole control currents for corresponding to the output voltage (V _S) of the oxygen sensing element Supply circuit.

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