JPH0672864B2 - Oxygen concentration detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to an oxygen concentration detection device for detecting the oxygen concentration in a gas such as engine exhaust gas.

BACKGROUND ART An air-fuel ratio that detects the oxygen concentration in the exhaust gas and purifies the air-fuel ratio of the air-fuel mixture supplied to the engine by feedback control to the target air-fuel ratio according to the detection results for the purpose of purifying exhaust gas from internal combustion engines and improving fuel efficiency. There is a fuel ratio control device.

As an oxygen concentration detecting device used in such an air-fuel ratio control device, there is one which generates an output proportional to the oxygen concentration in the gas to be measured (Japanese Patent Laid-Open No. 153155/1983). In such an oxygen concentration detector, an oxygen concentration detector having a pair of flat plate-shaped oxygen ion conductive solid electrolyte materials is provided. The solid electrolyte material is arranged in the gas to be measured, electrodes are formed on the front and back surfaces of the solid electrolyte material, and the solid electrolyte material is arranged in parallel so as to face each other with a predetermined gap. Has been done. One of the solid electrolyte materials acts as an oxygen pump element and the other acts as an oxygen concentration ratio measuring battery element. When a current is supplied between the electrodes of the oxygen pump element so that the electrode on the gap side becomes negative 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 It moves inside to the positive electrode surface side and is released as oxygen gas from the positive electrode surface. At this time, a decrease in oxygen gas in the gap causes a difference in oxygen concentration between the gas inside the gap and the gas outside the battery element, so that a voltage is generated between the electrodes of the battery element. If the pump current value supplied to the oxygen pump element is changed so that this voltage becomes a constant value, the pump current value at constant temperature becomes almost proportional to the oxygen concentration in the gas to be measured, and it is output as the oxygen concentration detection value. To be done.

In such an oxygen concentration detecting device, when an excessive pump current is supplied to the oxygen pump element, a blackening phenomenon occurs that deprives oxygen from the solid electrolyte material. For example, when ZrO ₂ (zirconium dioxide) is used as the solid electrolyte material, oxygen O ₂ is deprived from ZrO ₂ by excessive current supply to the oxygen pump element and zirconium Zr is deposited. Since this blackening phenomenon rapidly progresses the deterioration of the oxygen pump element and deteriorates the performance as an oxygen concentration detector, the pump current value must be smaller than the value in the blackening occurrence region to prevent the blackening phenomenon. I have to.

FIG. 1 shows the relationship between the oxygen concentration and the pump current to the oxygen pump element and the blackening phenomenon occurrence region with the voltage Vs generated in the battery element as a parameter, and the boundary line with the blackening phenomenon occurrence region is the voltage. Since it is a linear function characteristic like the relational characteristic with Vs as a parameter, the voltage
From Vs, it is possible to determine whether or not the pump current belongs to the value of the blackening phenomenon occurrence region. Therefore, the voltage Vs
When the voltage rises above a predetermined voltage, the pump current to the oxygen pump element becomes a value close to the blackening phenomenon occurrence region, and the pumping current is reduced to prevent the blackening phenomenon from occurring.

However, since the pump current is reduced even if the voltage Vs instantaneously rises above the predetermined voltage, the pump current value fluctuates up and down immediately after the voltage Vs drops below the predetermined voltage, and the oxygen concentration can be accurately detected. There was a problem that it could not be done.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an oxygen concentration proportional current detection type oxygen concentration detection device capable of preventing the occurrence of a blackening phenomenon and accurately detecting the oxygen concentration. .

The oxygen concentration detection device of the present invention is characterized in that the supply current between the electrodes of the oxygen pump element is reduced after a predetermined time has elapsed after the voltage generated between the electrodes of the battery element reached a predetermined voltage or higher.

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

FIG. 2 shows an air-fuel ratio controller using the oxygen concentration detector according to the present invention. In this device, a pair of flat plate-shaped oxygen pump elements 1 and battery elements 2 which are parallel to each other are used.
The oxygen concentration detector consisting of is installed in an exhaust pipe (not shown). The oxygen pump element 1 and the battery element 2 are mainly composed of an oxygen ion conductive solid electrolyte material, a gap portion 3 is formed between one ends thereof, and the other ends thereof are 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 electrode plate 5 is formed on the other end surface.
Lead lines 5a to 8a are formed.

A current is supplied from the current supply circuit 11 between the electrode plates 5 and 6 of the oxygen pump element 1. The current supply circuit 11 is an operational amplifier 12, N
It consists of a PN transistor 13 and resistors 14 and 15. Operational amplifier 1
The output terminal of 2 is connected to the base of the transistor 13 via the resistor 14. The emitter of the transistor 13 is a resistor
Grounded through 15. The resistor 15 is provided to detect the pump current value I _P flowing between the electrode plates 5 and 6 of the oxygen pump element 1, and its terminal voltage is used as the pump current value I _{P to} the I _P input of the air-fuel ratio control circuit 31. Supplied on the edge. The collector of the transistor 13 is the inner electrode plate 6 of the oxygen pump element 1.
To the outer electrode plate 5, and the voltage V _B is supplied to the outer electrode plate 5 via the lead wire 5a.

On the other hand, the inner electrode plate 7 of the battery element 2 is grounded via the lead wire 7a, and the outer electrode plate 8 is connected to the non-inverting amplifier 30 composed of the operational amplifier 26 and resistors 27 to 29 via the lead wire 8a. The output terminal of the non-inverting amplifier 30 is an operational amplifier
Connected to 12 inverting inputs.

The I _C control output of the air-fuel ratio control circuit 31 is connected a D / A converter 32, D / A converter 32 in accordance with the digital signal output from the I _C control output of the air-fuel ratio control circuit 31 Generate voltage. The output terminal of the D / A converter 32 is an operational amplifier via a voltage follower circuit 33 including an operational amplifier, a voltage dividing circuit 36 including resistors 34 and 35, and an integrating circuit 39 including a resistor 37 and a capacitor 38.
Connected to 12 non-inverting inputs.

A limiter circuit 40 is connected to the output terminal of the non-inverting amplifier 30. The limiter circuit 40 includes an operational amplifier 41, resistors 42 to 46, a capacitor 47 and an NPN transistor 48.
The operational amplifier 41 and the resistors 42 and 43 form a non-inverting amplifier 49, and the voltage Vcc is applied to the resistor 44 at the output terminal of the non-inverting amplifier 49.
Is connected via the resistor 45 and the capacitor 47 to the integrating circuit 50. The output terminal of the integrating circuit 50 is connected to the base of the transistor 48 via the resistor 46. The emitter of transistor 48 is grounded and the collector is connected to the base of transistor 13.

Air-fuel ratio control circuit 31 I _C output terminal as described above, A in addition to the I _P input
It has an / F drive end, and is connected to a solenoid valve 51 for secondary air supply adjustment at the A / F drive end. The solenoid valve 51 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, when the digital signal is output from the I _C output terminal of the air-fuel ratio control circuit 31 to the D / A converter 32, the D / A converter 32 converts the digital signal into a voltage, and the converted voltage is The voltage is supplied to the voltage dividing circuit 36 via the voltage follower circuit 33. The voltage dividing circuit 36 divides the output voltage of the voltage follower circuit 33 into a voltage dividing ratio determined by the resistance values of the resistors 34 and 35, and outputs the divided voltage to the integrating circuit 39. The output voltage of the integrating circuit 39 gradually rises due to the integration time constant of the resistor 37 and the capacitor 38, and stabilizes when it reaches the output voltage of the voltage dividing circuit 36. The output voltage of this integrating circuit is supplied to the non-inverting input terminal of the operational amplifier 12 as the reference voltage Vr ₁ . When the supply of the reference voltage Vr ₁ is started, the voltage level at the inverting input terminal of the operational amplifier 12 is lower than the reference voltage Vr ₁ , so the output level of the operational amplifier 12 becomes high and the transistor 13 is turned on. When the transistor 13 is turned on, a pump current flows between the electrode plates 5 and 6 of the oxygen pump element 1.

When the pump current flows, a voltage Vs is generated between the electrode plates 7 and 8 of the battery element 2, and the voltage Vs is supplied to the non-inverting amplifier 30.
The non-inverting amplifier 30 voltage-amplifies the voltage Vs and supplies it to the inverting input terminal of the operational amplifier 12. When the voltage Vs rises, the output voltage Vs' of the non-inverting amplifier 30 also rises. When the output voltage Vs' exceeds the reference voltage Vr ₁ output level of the operational amplifier 12 is inverted to the low level, the transistor 13 is turned off. Since the pump current is reduced by turning off the transistor 13, the battery element 2
The voltage Vs generated between the electrode plates 7 and 8 of the
The voltage Vs' supplied to the inverting input terminal of the operational amplifier 12 also decreases. When the voltage Vs ′ falls below the reference voltage Vr ₁ , the output level of the operational amplifier 12 becomes high again, and the pump current is increased. Since this operation is repeated at high speed, the voltage Vs is controlled to a constant value and becomes a voltage according to the value represented by the digital signal.

The pump current value I _P flowing between the electrode plates 5 and 6 of the oxygen pump element 1 when the reference voltage Vr ₁ is supplied to the operational amplifier 12 is detected by the terminal voltage of the resistor 15, and the terminal voltage is I of the air-fuel ratio control circuit 31. Supplied to _P input. The air-fuel ratio control circuit 31 determines whether the pump current value I _P is smaller than the reference value Ir corresponding to the target air-fuel ratio. If I _P <Ir, it is determined that the air-fuel ratio of the air-fuel mixture supplied to the engine is rich, and the electromagnetic valve 51 is opened to drive the secondary air to the engine. I _P ≧
If Ir, the air-fuel ratio of the supply air-fuel mixture is assumed to be lean, and the valve opening drive of the solenoid valve 51 is stopped to stop the supply of secondary air.

When the voltage Vs between the electrode plates 7 and 8 of the battery element 2 rises,
The output voltage Vs' of the non-inverting amplifier 30 rises. Output voltage V
s'is further voltage-amplified by the non-inverting amplifier 49 and supplied to the integrating circuit 50, and the output voltage of the integrating circuit 50 is supplied to the base of the transistor 48 via the resistor 46. Output voltage V
When s ′ rapidly rises, the output voltage of the integrating circuit 50 gradually rises. The output voltage of the non-inverting amplifier 49 is the reference voltage Vr ₁
That is, when the voltage Vs exceeds a predetermined voltage (for example, 60 V
mV) and the delay time t ₁ elapses before the transistor
48 turns on, causing the base potential of transistor 13 to be approximately equal to ground level, turning off transistor 13 and reducing the pump current. Therefore, when the output voltage Vs ′ of the non-inverting amplifier 30 reaches a voltage close to the blackening phenomenon occurrence region, the output voltage of the integrating circuit 50 gradually rises to reach the blackening phenomenon occurrence region after the delay time t _1. Immediately before belonging, the pump current is reduced.

In the above-described embodiment of the present invention, the integrating circuit including the resistor and the capacitor is used as the delay unit, but the integrating circuit including the resistor and the inductor may be used.

Effects of the Invention As described above, in the oxygen concentration detection device of the present invention, the pump current is reduced after a lapse of a predetermined time after the voltage generated between the electrodes of the battery element reaches a predetermined voltage or more, so that the element is rapidly deteriorated. It is possible to prevent the occurrence of the blackening phenomenon. Further, in order to prevent the occurrence of the blackening phenomenon, it is possible to prevent the fluctuation of the pump current value because it is avoided that the pump current is decreased when the voltage generated between the electrodes of the battery element instantaneously rises to a predetermined voltage or more. Therefore, the accuracy of detecting the oxygen concentration can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a relational characteristic between oxygen concentration and pump current and a blackening phenomenon occurrence region, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. Explanation of symbols of main parts 1 …… Oxygen pump element 2 …… Battery element 3 …… Gap part 4 …… Spacer 11 …… Current supply circuit 30,49 …… Non-inverting amplifier 39,50 …… Integration circuit 40 …… Limiter circuit

Claims (1)

[Claims] 1. A pair of oxygen ion conductive solid electrolyte materials disposed in a gas to be measured, a pair of electrodes being formed on each solid electrolyte material, and the pair of solid electrolyte materials having a predetermined gap. One of the pair of solid electrolyte materials arranged so as to face each other via an oxygen concentration detector each acting as an oxygen concentration ratio measuring battery element as an oxygen pump element, and the voltage between the electrodes of the battery element. Current supply means for supplying a current between the electrodes of the oxygen pump element so as to be constant, and limit means for stopping the excessive current supply between the electrodes of the oxygen pump element by the current supply means, the current An oxygen concentration detection device for outputting a current value supplied to the oxygen pump element by a supply means as an oxygen concentration detection voltage, wherein the limiter means is configured to detect a voltage generated between electrodes of the battery element. Oxygen concentration detecting device, characterized in that it comprises a delay means allowed to reduce the supply current from reaching the above constant voltage between the electrodes of the oxygen pump element after a predetermined time has elapsed.