JPS61213664A - Oxygen concentration detector - Google Patents

Abstract

PURPOSE:To prevent blackening by providing an oxygen pump element and battery element for measuring an oxygen concn. ratio, detecting oxygen concn. and supplying current to the oxygen pump at the current value meeting the oxygen concn. or below by a limiter means. CONSTITUTION:The oxygen pump element 1 and the battery element 2 for measuring the oxygen concn. ratio are provided in parallel via a spacing 3. The current is inputted to the element 1 and the oxygen in the spacing 3 is fed through the element 1 to the outside by which the oxygen concn. in the spacing 3 is made constant. The air-fuel ratio is detected by the battery element 2 from the difference in the oxygen concn. between the outside and the spacing 3. The voltage detecting the oxygen concn. from the battery element 2 is inputted via an amplifier 25 to an air-fuel ratio control circuit 20 which regulates the opening and closing of secondary air by a solenoid valve 35. The voltage for detecting the oxygen density is fed to the limiter means 26. A constant current circuit 11 is controlled by the limiter means 26 and the current meeting the detected oxygen concn. is supplied to the element 1. Since the supply current is controlled by providing the limiter means, the blackening of the oxygen pump element is prevented and the deterioration of the element is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an oxygen concentration detection device for detecting oxygen concentration in gas such as automobile exhaust gas.

BACKGROUND ART In order to purify the exhaust gas of internal combustion engines and improve fuel efficiency, an air-fuel system detects the oxygen concentration in the exhaust gas and feedback-controls the air-fuel ratio of the air-fuel mixture supplied to the engine to a target air-fuel ratio according to the detection result. There is a fuel ratio control device.

As an oxygen concentration detection device used in such an air-fuel ratio control device, there is one that generates an output proportional to the oxygen concentration in the gas to be measured (Japanese Patent Laid-Open No. 153155/1983). Such an oxygen concentration detection device is provided with an oxygen concentration detector having a pair of flat oxygen ion conductive solid electrolyte materials. The solid electrolyte material is disposed in the gas to be measured, and electrodes are formed on each front and back surface of the solid electrolyte material, and the solid electrolyte materials are arranged in parallel so as to face each other with a predetermined gap in between. It is located. One of the solid electrolyte materials acts as an oxygen pump element, and the other acts as a battery element for oxygen concentration ratio measurement. When a current is supplied between the electrodes of the oxygen pump element so that the electrode on the gap side becomes the negative electrode in the gas to be measured, the oxygen gas in the gas in the gap is ionized on the negative electrode side of the oxygen pump element, and the oxygen pump element The oxygen gas moves to the positive electrode surface and is released as oxygen gas from the positive electrode surface. At this time, the decrease in oxygen gas in the gap causes a difference in oxygen concentration between the gas in the gap and the gas outside the battery element, so if the current supplied to the oxygen pump element is constant, there will be a difference between the electrodes of the battery element. A voltage proportional to the oxygen concentration difference, that is, the oxygen concentration in the gas being measured, is generated.

In such an oxygen concentration detection device, when an excessive current is supplied to the oxygen pump element, a blackening phenomenon occurs in which oxygen is taken away from the solid electrolyte material.

For example, when ZrO (zirconium dioxide) is used as the solid electrolyte material, oxygen O8 is taken away from Zro by excessive current supply to the oxygen pump element, and zirconium Zr is precipitated. This blackening phenomenon causes rapid deterioration of the oxygen pump element and deteriorates its performance as an oxygen concentration detector. The output voltage of the oxygen concentration detection device is set to be equal to a predetermined reference voltage when the air-fuel ratio of the air-fuel mixture that increases in value reaches the target air-fuel ratio. Therefore, by comparing the output voltage of the oxygen concentration detection device with the reference voltage, it is determined whether the air-fuel ratio of the supplied air-fuel mixture is richer or leaner than the target air-fuel ratio.

In the case of a system in which the air-fuel ratio is controlled by secondary air, if the engine is determined to be rich, secondary air is supplied to the engine, and if the engine is determined to be lean, the secondary air supply is stopped. The fuel ratio is controlled to the target air-fuel ratio. However, the richer the air-fuel ratio, that is, the lower the oxygen concentration, the smaller the blackening phenomenon occurrence boundary.
In addition, since the current value supplied to the oxygen pump element is constant, if the air-fuel ratio of the supplied mixture suddenly becomes rich from around the target air-fuel ratio due to fluctuations in the throttle valve, the secondary air, etc. Even if oxygen is supplied, due to the time delay until the control result appears on the exhaust side, the state in which the output voltage of the oxygen concentration detection device is determined to be rich continues for a while, and the value of the current supplied to the oxygen pump element decreases. There has been a problem in that the blackening phenomenon may occur when the value exceeds the threshold value for the occurrence of the blackning phenomenon.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an oxygen concentration detection device that can reliably prevent the blackening phenomenon.

The oxygen concentration detection device of the present invention is characterized by having a limiter means for limiting the current supplied to the oxygen pump element below a current value corresponding to the detected oxygen concentration.

Example Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an air-fuel ratio control device using an oxygen concentration detection device according to the present invention. In this device, a pair of planar elements, an oxygen pump element 1 and a battery element 2, are arranged in parallel to each other. The main body of the oxygen pump element 1 and the battery element 2 is made of an oxygen ion conductive solid electrolyte material, and a gap 3 is formed between one end thereof, and the other end thereof is connected to each other via a spacer 4. Further, rectangular electrode plates 5 to 8 made of porous heat-resistant metal are provided on the front and back surfaces of one end of the oxygen pump element 1 and the battery element 2, and the lead wires 5α of the electrode plates 5 to 8 are provided on the other end surface. 8 cL is formed.

A constant current circuit 11 is connected between the electrode plates 5 and 6 of the oxygen pump element 1.
A constant current is supplied from the The constant current circuit 11 is a sink type circuit, and the operational amplifier 12. NPN transistor 13
．． It consists of a diode 14 and resistors 15 to 18. That is, the output terminal of the operational amplifier 12 is connected to the base of the transistor 13 via the resistor 15. The emitter of the transistor 13 is grounded via a resistor 16, connected to the inverting input terminal of the operational amplifier 12 via a resistor 17, and further connected to the output terminal of the operational amplifier 12 via a diode 14 in the forward direction.

The collector of the transistor 13 is connected to the inner electrode plate 6 of the oxygen pump element 1 via a lead wire 6α, and the voltage VB is supplied to the outer electrode plate 5 via the lead wire 5α.

A programmable voltage generation circuit 19 is connected to the non-inverting input terminal of the operational amplifier 12 via a resistor 18. The programmable voltage generation circuit 19 is connected to I of the air-fuel ratio control circuit 20.
Generates a voltage according to the digital signal output from the P output terminal.

On the other hand, the inner electrode plate 7 of the battery element 2 is grounded via a lead wire 7α, and the outer electrode plate 8 is connected to the operational amplifier 21. It is connected to a non-inverting amplifier 25 consisting of resistors 22-24. The output terminal of the non-inverting amplifier 25 is connected to the ■s input terminal of the air-fuel ratio control circuit 20. Also, a limiter circuit 2 is connected to the output terminal of the non-inverting amplifier 25.
6 is connected. The limiter circuit 26 is the operational amplifier 2
7° resistance 28 to 31. It consists of a variable resistor 32 and a diode 33. The resistors 28 and 29 and the variable resistor 32 are connected in series to form a voltage dividing circuit 34 for voltage VB, and the movable end of the variable resistor 32, which is the voltage dividing output terminal, is connected to the inverting input terminal of the operational amplifier 27. ing. operational amplifier 27
The output terminal of the non-inverting amplifier 25 is connected to the non-inverting input terminal of the operational amplifier 2.
7 from the output end of resistor 30. The signal is supplied to the inverting input terminal of the operational amplifier 12 via the diode 33 in the top direction.

The air-fuel ratio control circuit 20 has an A/F drive end in addition to the above-mentioned I, output end, and (8) input end, and a solenoid valve 35 for adjusting secondary air supply is connected to the A/F drive end. There is. Solenoid valve 35
is provided in the intake secondary air supply passage communicating with the intake passage downstream of the carburetor throttle valve of the engine.

In such a configuration, a digital signal is output from the output terminal I of the air-fuel ratio control circuit 20 to the programmable voltage generation circuit 1.
9, the digital signal represents
11. A voltage is supplied as a reference voltage vr1 to the non-inverting input terminal of the operational amplifier 12 via the resistor 18. The pump current value IP flowing between the electrode plates 5 , 6 of the oxygen pump element 1 is detected by the terminal voltage vP of the resistor 16 , and the terminal voltage vP is supplied via the resistor 17 to the inverting input terminal of the operational amplifier 12 . When the terminal voltage ■P is smaller than the reference voltage vr1, the output level of the operational amplifier 12 becomes high level and increases the base current of the transistor 150, so the pump current increases. When the terminal voltage ■P is higher than the reference voltage v71, the output level of the operational amplifier 12 increases. The output level becomes a low level and reduces the base current of the transistor 15, so that the pump current /b -C bonno'ton redundancy 1
En has a Kenden accent of 11, which is 1 of 1.

On the other hand, the oxygen concentration detection voltage generated between the electrode plates 6 and 7 of the battery element 2 is amplified by the non-inverting amplifier 25 and is applied to the Vs input terminal of the air-fuel ratio control circuit 20 for comparison. The output voltage vs increases as the air-fuel ratio of the supplied air-fuel mixture becomes richer, so if Vs > Vr2, it is rich and the solenoid valve 35 is driven to open and secondary air is supplied to the engine, and if v8≦vr2 Solenoid valve 35 as lean
By stopping the valve opening drive, the supply of secondary air is stopped.

Here, it is assumed that the air-fuel ratio of the supplied air-fuel mixture changes greatly toward the rich side due to the sudden closing of the throttle valve. Then, battery element 2
The voltage between the electrode plates 7 and 8, that is, the output voltage s of the non-inverting amplifier 25 increases. Output voltage vs is divided voltage vL
When the output voltage V obtained by the operational amplifier 27 exceeds
The voltage corresponding to the difference voltage between s and the divided voltage VL is the terminal voltage ■
Since it is higher than P, the resistor 30 is connected to the operational amplifier 27. A current flows through the diode 33, resistor 17, and resistor 16, raising the voltage at the inverting input of the operation switch 1120.

Therefore, the output voltage of the operational amplifier 12 decreases and the base current of the transistor 13 decreases, so that the oxygen pump element 1
The pump current I also decreases.

Since the divided voltage vL is set slightly higher than the reference voltage v1, when the output voltage vs of the non-inverting amplifier 25 reaches the divided voltage vL, it indicates that the blackening phenomenon has approached the region where the blackening phenomenon occurs. When Vs > Vt, the richer the air-fuel ratio is, the higher the output voltage of the operational amplifier 27 becomes, reducing the pump current I, thereby preventing the blackning phenomenon from occurring.

Now, in steady air-fuel ratio control, the pump electrician and the oxygen concentration in the exhaust gas are 0. The relationship with is the reference voltage V.

is determined as the characteristic A in FIG. 2 using as a parameter, the oxygen concentration corresponding to the target air-fuel ratio A/Fα becomes 0. (In L, the pump current I becomes IPl. The upper limit value of the pump current I for each oxygen concentration O8 is set as in characteristic B using the partial pressure voltage vL as a parameter. If the oxygen concentration in the exhaust gas detected at that time fluctuates greatly and the oxygen concentration in the exhaust gas is O3b, the pump current I becomes IPI.
If it remains as it is, it will be included in the area where blackening phenomenon occurs, but
The limiter circuit 26 reduces the pump current I to IPt.

Effects of the Invention As described above, in the oxygen concentration detection device of the present invention, the current supplied to the oxygen pump element is limited to a value below the current value corresponding to the detected oxygen concentration. Even if there is a time delay until the control result is detected based on the oxygen concentration in the exhaust gas, the blackening phenomenon can be reliably prevented from occurring.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an air-fuel ratio control device using an oxygen concentration detection device according to the present invention, and FIG. 2 is a diagram showing the relationship between pump current and oxygen concentration. Explanation of symbols of main parts 1...Oxygen pump element 2...Battery element 3...
・Gap portion 4...Spacer 5 to 8・
... Electrode plate 11 ... Constant current circuit 25 ... Non-inverting amplifier 26 ... Limiter circuit 34 ...
voltage divider circuit

Claims (2)

[Claims] (1) It has a pair of flat oxygen ion conductive solid electrolyte materials disposed in the gas to be measured, electrodes are formed on each of the front and back surfaces, and the solid electrolyte materials are connected to each other through a predetermined gap. An electric current is applied between the electrodes of the oxygen pump element and the oxygen concentration detection means, which are arranged in parallel so as to face each other, one of the solid electrolyte materials acts as an oxygen pump element, and the other acts as a battery element for measuring the oxygen concentration ratio. an oxygen concentration detection device that outputs the voltage generated between the electrodes of the battery element as an oxygen concentration detection voltage, the current supply means supplying a current value below a current value corresponding to the detected oxygen concentration. An oxygen concentration detection device comprising a limiter means for limiting the current supplied to the oxygen pump element. (2) The oxygen concentration detecting device according to claim 1, wherein the limiter means sets the limiting current value to be smaller as the oxygen concentration in the gas to be measured becomes smaller.