JPH07104324B2 - Air-fuel ratio detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air-fuel ratio detection device that has an oxygen concentration sensor that produces an output proportional to the oxygen concentration in the exhaust gas of an internal combustion engine and that detects the air-fuel ratio from the output of the oxygen concentration sensor. .

BACKGROUND ART For the purpose of purifying exhaust gas from internal combustion engines and improving fuel efficiency, the oxygen concentration in exhaust gas is detected by an oxygen concentration sensor, and the actual air-fuel ratio is determined according to the output signal of this oxygen concentration sensor. An air-fuel ratio control device for feedback-controlling the air-fuel ratio of an air-fuel mixture supplied to an engine in accordance with the above is known from Japanese Patent Publication No. 55-3533.

As an oxygen concentration sensor 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, that is, the exhaust air-fuel ratio. For example, an electrode pair is provided on each of two flat plate-shaped oxygen ion conductive solid electrolyte materials to form an oxygen pump element and a battery element, and one electrode surface of each of the oxygen pump element and the battery element is a part of a gas retention chamber. JP-A-59-192955 discloses a sensor in which the gas retention chamber communicates with the gas to be measured through an introduction hole so that the other electrode surface of the battery element faces the atmosphere chamber.
In such an oxygen concentration sensor, the generated voltage of the battery element is compared with a predetermined voltage so that the oxygen concentration in the gas retention chamber is always kept at a predetermined concentration (for example, 0), and the oxygen pump element of the oxygen pump element is determined according to the comparison result. A pump current is supplied between the electrodes, and the pump current value is detected as an output proportional to the oxygen concentration. A resistor connected in series with an oxygen pump element is used as a pump current detector, and the voltage across the resistor is obtained as an oxygen concentration output voltage proportional to the pump current value.

Even when performing air-fuel ratio control using an oxygen concentration sensor of the oxygen concentration proportional type in an internal combustion engine equipped with a three-way catalytic converter for exhaust purification, the air-fuel ratio of the supplied mixture is the theoretical air-fuel ratio (14.7). At this time, the three-way catalytic converter operates most effectively, so that the air-fuel ratio of the supply air-fuel mixture is feedback-controlled to the stoichiometric air-fuel ratio in the steady operation state of the engine. Therefore, the air-fuel ratio detection signal corresponding to the deviation of the actual air-fuel ratio from the stoichiometric air-fuel ratio is obtained, and the air-fuel ratio of the supply air-fuel mixture is feedback-controlled by this. However, when the actual air-fuel ratio is close to the stoichiometric air-fuel ratio, the deviation is small, and if the control accuracy to the stoichiometric air-fuel ratio is increased, it is necessary to amplify the deviation. On the other hand, if the amplification factor of the deviation is too large, signal saturation is likely to occur and it is difficult to set the amplification factor.

SUMMARY OF THE INVENTION An object of the present invention is to provide an air-fuel ratio detection device capable of sufficiently improving the accuracy of determining the air-fuel ratio near the stoichiometric air-fuel ratio.

The air-fuel ratio detection device of the present invention is a battery element and a pump element each comprising an oxygen ion conductive solid electrolyte member and an electrode pair facing each other with the solid electrolyte interposed therebetween, and one of the electrode pair of the battery element and the pump element. Gas diffusion limiting means for communicating with the exhaust gas of the internal combustion engine, voltage supply means for applying to the pump element a voltage corresponding to the difference voltage between the voltage between the electrode pair of the battery element and the reference voltage, and the electrode pair of the pump element. An air-fuel ratio detection device comprising signal generation means for generating an air-fuel ratio determination signal according to a pump current value flowing between the signal generation means, the signal generation means comprising voltage generation means for generating a voltage according to the pump current value, and Voltage amplifying means for amplifying the output voltage of the voltage generating means, and output of the voltage amplifying means when the output voltage of the voltage amplifying means is within a predetermined voltage range corresponding to a predetermined air-fuel ratio range including the theoretical air-fuel ratio It is characterized by comprising a determining means for increasing the amplification degree of the voltage amplifying means more than when the pressure is out of the predetermined voltage range and for determining the detected air-fuel ratio from the output voltage of the voltage amplifying means to generate an air-fuel ratio determining signal. I am trying.

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

In the air-fuel ratio detection apparatus equipped with the oxygen concentration sensor according to the embodiment of the present invention shown in FIG. 1, the gas retention chamber 2 is provided in the oxygen ion conductive solid electrolyte material 1 as a gas diffusion limited area.
Are formed. The gas retention chamber 2 communicates with an introduction hole 3 for introducing the exhaust gas of the gas to be measured from outside the solid electrolyte material 1. The introduction hole 3 allows the exhaust gas to flow into the gas retention chamber 2 in the exhaust pipe of an internal combustion engine (not shown). Positioned for ease. Further, the oxygen ion conductive solid electrolyte material 1 is formed with an atmosphere reference chamber 4 for introducing the atmosphere so as to separate the wall from the gas retention chamber 2. An electrode pair is provided on the wall between the gas retention chamber 2 and the atmospheric reference chamber 4 and on the wall opposite to the atmospheric reference chamber 4.
6a, 6b, 5a, 5b are formed respectively. The solid electrolyte material 1 and the electrode pairs 5a, 5b act as the oxygen pump element 7, and the solid electrolyte material 1 and the electrode pairs 6a, 6b act as the battery element 8. A heater element 9 is provided on the outer wall surface of the air reference chamber 4.

As the oxygen ion conductive solid electrolyte material 1, ZrO ₂ (zirconium dioxide) is used, and as the electrodes 5a to 6b,
Pt (platinum) is used.

A differential amplifier circuit 11 is connected to the electrode 6a of the battery element 8 as pump current control means, and the differential amplifier circuit 11 outputs a voltage between the electrodes 6a and 6b of the battery element 8 and a reference voltage output from a reference voltage source 12. It outputs a voltage according to the voltage difference from Vr ₁ . The reference voltage Vr _{1 from the} reference voltage source 12 is a voltage (2.95 [V]) corresponding to the stoichiometric air-fuel ratio. The output terminal of the differential amplifier circuit 11 is connected to the electrode 5a of the oxygen pump element 7. The electrode 5b of the oxygen pump element 7 and the electrode 6b of the battery element 8 are commonly connected and connected to the inverting input terminal of the operational amplifier circuit 13. The reference voltage Vr ₂ output from the reference voltage source 14 is supplied to the non-inverting input terminal of the operational amplifier circuit 13. The reference voltage Vr _{2 from the} reference voltage source 14 is set to 2.5V, for example. A resistor 15 is placed between the inverting input terminal and the output terminal of the operational amplifier circuit 13.
Are connected. Output terminal voltage of operational amplifier circuit 13 V _OUT
And the inverting input terminal voltage Vref are supplied to the differential amplifier circuits 16 and 17. The differential amplifier circuit 16 is comprised of operational amplifier 18 and resistors 19 to 21, the difference voltage between the voltage V _OUT and the voltage Vref V _OUT1
The differential amplifier circuit 17 outputs the operational amplifier circuit 22 and the resistor 23.
Or 25, and the difference voltage V between the voltage V _OUT and the voltage V ref
_It outputs a voltage V _OUT2 that is five times that of _OUT1 . Voltage V _OUT1 and V
_OUT2 is supplied to the A / D converter 26. A / D converter 26 has voltage V
_OUT1 and V _OUT2 are converted into digital signals and supplied to the microprocessor 27.

In such a configuration, the voltage V _S is generated between the electrodes 6a and 6b of the battery element 8 according to the oxygen concentration difference between the gas retention chamber 2 and the atmospheric reference chamber 4. This voltage V _S and the inverting input terminal voltage Vref of the operational amplifier circuit 13 are added and supplied to the inverting input terminal of the differential amplifier circuit 11. On the other hand, the inverting input terminal voltage Vref of the operational amplifier circuit 13 becomes substantially equal to the non-inverting input terminal voltage, that is, the output voltage Vr ₂ of the reference voltage source 14, by the operational amplifier circuit 13 even if the pump current value I _P changes.

When the supply of the pump current to the oxygen pump element 7 is started, if the mixture supplied to the engine and the air-fuel ratio are in the lean region, the voltage V _S generated between the electrodes 6a, 6b of the battery element 8
Is decreased and the voltage V _S + Vref becomes the output voltage Vr _{1 of the} reference voltage source 12.
Since it becomes lower, the output level of the differential amplifier circuit 11 becomes a positive level, and this positive level voltage is applied to the electrode of the oxygen pump element 7.
Applied to 5a. Therefore, the pump current flows through the oxygen pump element 7 and the resistor 15 and then into the operational amplifier circuit 13. A pump current flows from the electrode 5a to the electrode 5b in the oxygen pump element 7, so that oxygen in the gas retention chamber 2 is ionized at the electrode 5b and moves in the oxygen pump element 7 to be released as oxygen gas from the electrode 5a. Then, oxygen in the gas retention chamber 2 is pumped out.

By pumping out oxygen in the gas retention chamber 2, an oxygen concentration difference occurs between the exhaust gas in the gas retention chamber 2 and the atmosphere in the atmosphere reference chamber 4. A voltage V _S according to this oxygen concentration difference is generated between the electrodes 6a and 6b of the battery element 8, and this voltage V _S is added to the voltage Vref and supplied to the inverting input terminal of the differential amplifier circuit 11. Since the output voltage of the differential amplifier circuit 11 is a voltage proportional to the difference voltage between the voltage V _S + Vref and the output voltage Vr ₁ of the reference voltage source 12, the pump current value I _P is proportional to the oxygen concentration in the exhaust gas.

When the air-fuel ratio is in the rich region, the voltage V _S + Vref exceeds the output voltage Vr ₁ of the reference voltage source 12. Therefore, the differential amplifier circuit 11
The output level of is inverted from the positive level to the negative level. Due to this negative level, the pump current flowing between the electrodes 5a and 5b of the oxygen pump element 7 decreases and the current direction is reversed. That is, since the pump current flows in the direction from the electrode 5b to the electrode 5a, the external oxygen is ionized at the electrode 5a and moves in the oxygen pump element 7 to be released as oxygen gas from the electrode b into the gas retention chamber 2 to generate oxygen. Are pumped into the gas retention chamber 2. Therefore, pumping oxygen by supplying a pump current so that the oxygen concentration in the gas retention chamber 2 is always constant,
Since it is pumped out, the pump current value I _P is proportional to the oxygen concentration in the exhaust gas in the lean and rich regions, respectively.

On the other hand, the output terminal voltage V _OUT and the inverting input terminal voltage Vref of the operational amplifier circuit 13 are supplied to the differential amplifier circuits 16 and 17. The differential amplifier circuit 16 outputs the voltage V _OUT −Vref as the voltage V _OUT1 , and the differential amplifier circuit 17 outputs a voltage V 5 times the voltage V _OUT −Vref.
Output _OUT2 . Pump current value I _P is I _P = (V _OUT −Vref)
Because represented by / R _P becomes Formula voltage V _OUT1 and V _OUT2
Is a voltage proportional to the pump current value I _P. Note that R _P is the resistance value of the resistor 15. The voltages V _OUT1 and V _OUT2 are converted into digital signals by the A / D converter 26 and supplied to the microprocessor 27.

The microprocessor 27 first reads the digitized voltage V _OUT2 from the A / D converter 26 (step 51) at a predetermined cycle or in synchronization with the engine rotation as shown in the flow chart of FIG. It is determined whether _OUT2 is smaller than the predetermined value V ₁ (step 52). When V _OUT2 ≧ V ₁ , it is determined whether the read V _OUT2 is larger than a predetermined value V ₂ (however, V ₂ > V ₁ ) (step 53). V ₁ ≤ V _OUT2
If ≦ V _2, it means that it is within the dynamic range of the differential amplifier circuit 17, and the detected air-fuel ratio is determined from the read V _OUT2 (step 54). On the other hand, if V _OUT2 <V ₁ or V _OUT2 > V _2, then it is outside the proper reading range of the voltage V _OUT2.
The digitized voltage V _OUT1 is read from the converter 26 (step 55), and the detected air-fuel ratio is determined from the read V _OUT1 (step 56). For example, the predetermined voltage V
_The air-fuel ratio corresponding to the read voltage is retrieved from the different data map for each _OUT1 and V _OUT2 , and it is used as the detected air-fuel ratio. When the detected air-fuel ratio is the theoretical air-fuel ratio, I _P =
0 and V _OUT = V ref, so V _OUT1 = V _OUT2 = 0
[V]. Therefore, V ₁ <0 [V] and V ₂ > 0 [V] are set.

When the microprocessor 27 obtains the detected air-fuel ratio, it sets the air-fuel ratio correction value according to the deviation between the detected air-fuel ratio and the target air-fuel ratio in another routine (not shown), and the intake secondary air according to the air-fuel ratio correction value. The supply amount or fuel supply amount can be adjusted. In this way, the air-fuel ratio feedback control is performed.

As described above, in the air-fuel ratio detecting device of the present invention, the voltage according to the pump current value is output to the voltage generating means, the output voltage of the voltage generating means is amplified and output from the voltage amplifying means. It When the output voltage of the voltage amplifying means is within a predetermined voltage range that does not exceed the dynamic range of the voltage amplifying means for the vicinity of the stoichiometric air-fuel ratio, the amplification degree of the voltage amplifying means is increased and the voltage amplification is performed than when the output voltage is outside the predetermined voltage range. By determining the detected air-fuel ratio from the output voltage of the means, it is possible to detect the air-fuel ratio in a wide range and improve the accuracy of determining the air-fuel ratio when the air-fuel ratio exists near the stoichiometric air-fuel ratio. Therefore, the air-fuel ratio of the supply air-fuel mixture can be feedback-controlled to the stoichiometric air-fuel ratio with high accuracy, and the exhaust purification efficiency of the three-way catalytic converter can be improved.

In the case of digitizing by the A / D converter as in the above-described embodiment, it is prevented that the conversion range of the A / D converter is exceeded.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a flow chart showing the operation of the microprocessor in the circuit of FIG. Explanation of symbols of main parts 1 …… Oxygen ion conductive solid electrolyte material 2 …… Gas retention chamber 3 …… Introduction hole 4 …… Atmosphere reference chamber 7 …… Oxygen pump element 8 …… Battery element 11,16,17… … Differential amplifier circuit 12,14 …… Reference voltage source 13,18,22 …… Operational amplifier circuit

Claims (1)

[Claims] 1. A battery element and a pump element each comprising an oxygen ion conductive solid electrolyte member and a pair of electrodes facing each other with the solid electrolyte interposed therebetween, and one of the electrode pair of each of the battery element and the pump element is an internal combustion engine. Gas diffusion limiting means for communicating with the exhaust gas, voltage supply means for applying a voltage according to the difference voltage between the voltage between the electrode pair of the battery element and the reference voltage to the pump element, and the electrode pair of the pump element. An air-fuel ratio detecting device comprising a signal generating means for generating an air-fuel ratio determination signal according to a pump current value flowing between the signal generating means and the signal generating means, and a voltage generating means for generating a voltage according to the pump current value. A voltage amplifying means for amplifying an output voltage of the voltage generating means, and an output voltage of the voltage amplifying means when the output voltage is within a predetermined voltage range corresponding to a predetermined air-fuel ratio range including a theoretical air-fuel ratio, The amplification degree of the voltage amplifying means is increased more than when the output voltage of the voltage amplifying means is out of the predetermined voltage range, and the detected air-fuel ratio is discriminated from the output voltage of the voltage amplifying means to generate the air-fuel ratio discrimination signal. And an air-fuel ratio detecting device.