JPH11230931A - Air/fuel ratio-detecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air/fuel ratio-detecting device that can accurately detect an air/fuel ratio in each state of a rich region, a theoretical air/fuel ratio, and a lean region. SOLUTION: A detection part 11 has a zirconium solid electrolyte 102, an atmosphere-side electrode 104, an exhaust-side electrode 105, and a diffusion resistor 106. An atmosphere-side application voltage VAF+ is applied to the non-inverted input terminal of an operational amplifier 82, and an exhaust-side application voltage VAF- is applied to the non-inverted input terminal of an operational amplifier 83. The operational amplifiers 82 and 83 are connected to a plus-side power supply VB and ground, respectively, power is supplied, and operation is made with a single power supply. In an A/D conversion part 84, a voltage V1 at the side of an operational amplifier 83 and a voltage V2 at the side of a detection part 101 are A/D-converted and are outputted to a microcomputer 85. The microcomputer 85 calculates a sensor current IP flowing between the electrodes 104 and 105 based on the voltages V1 and V2 and the resistance value of a resistor R1 and then calculates an air/fuel ratio according to the sensor current IP.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an air-fuel ratio detecting device.

[0002]

2. Description of the Related Art Conventionally, in order to control an air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine to a target value, an air-fuel ratio detecting device is provided in an exhaust pipe of the internal combustion engine, and a fuel supply amount is determined in accordance with the detected air-fuel ratio. Is widely used.

[0003] Such an air-fuel ratio detecting device is for detecting an air-fuel ratio by detecting an air-fuel ratio detecting unit (air-fuel ratio sensor), a driving circuit for driving the detecting unit, and an output signal of the driving circuit. And a microcomputer using a zirconia solid electrolyte as a detection unit.

FIG. 13 is a partial sectional view showing a schematic structure of an example of a detecting section (air-fuel ratio sensor). The detection unit 101
Zirconia solid electrolyte 102, heater 103, electrode 10
4 and 105 and a diffusion resistor 106.

[0005] A cup-shaped detection unit 101 is arranged in an exhaust pipe (not shown) of an internal combustion engine. Atmosphere is introduced into the inside of the tubular tubular zirconia solid electrolyte 102. The rod-shaped heater 103 disposed inside the zirconia solid electrolyte 102 heats the zirconia solid electrolyte 102 to at least 600 ° C. or higher to improve the conductivity of oxygen ions.

An air electrode 104 is formed on the atmosphere side of the zirconia solid electrolyte 102, and an exhaust electrode 105 is formed on the exhaust gas atmosphere side. Each electrode 1
04 and 105 are formed of a porous platinum material having a film thickness of several μm to several tens μm. The diffusion resistor 106 formed on the surface of the electrode 105
The diffusion of oxygen or untwisted gas such as carbon monoxide, which flows into the diffusion layer 5 by diffusion, is suppressed. The diffusion resistor 106 is made porous by plasma spraying spinel or the like, and has a thickness of several hundred μm to increase the diffusion resistivity.
m.

FIG. 14 shows a conventional driving circuit 81 for driving the detecting section 101. The drive circuit 81 includes operational amplifiers 82 and 83 and resistors R1 to R4. The output terminal of the operational amplifier 82 is connected to the electrode 104 of the detection unit 101 via the resistor R1,
1 and R3 are connected to the inverting input terminal of the operational amplifier 82. The output terminal of the operational amplifier 83 is a resistor R
2 and connected to the electrode 105 of the detection unit 101 via the respective resistors R2 and R4. The atmosphere-side applied voltage VAF + is applied to the non-inverting input terminal of the operational amplifier 82, and the exhaust-side applied voltage VAF + is applied to the non-inverting input terminal of the operational amplifier 83.
-Is applied. Here, the operational amplifiers 82 and 83
Are connected to the positive power supply VB and the ground to supply power and perform a single power supply operation. Hereinafter, the resistance values of the resistors R1 to R4 are referred to as “R1” to “R1”, respectively.
Notated as “R4”.

The voltage VAF + is applied to the electrode 104 of the detection unit 101 from the operational amplifier 82, and the voltage VAF− is applied to the electrode 105 from the operational amplifier 83.
4, 105, the difference voltage VR (=
VAF + −VAF−) will be applied.

In a lean region (λ> 1) where the excess air ratio λ is greater than 1, the voltage of the electrode 105 is
, The residual oxygen in the exhaust gas atmosphere is converted into oxygen ions at the electrode 105 via the diffusion resistor 106 by the excitation voltage VR, and the oxygen ions are passed through the zirconia solid electrolyte 102 through an oxygen pump. It is transferred to the electrode 104 side by the action, and is oxidized again by the electrode 104 to become oxygen gas, which is released into the atmosphere. At this time, a sensor current (pump current) Ip flows from the electrode 104 to the electrode 105 in a direction opposite to the flow of the oxygen ions. The sensor current Ip corresponds to the amount of oxygen flowing from the exhaust gas atmosphere into the electrode 105 via the diffusion resistor 106 by diffusion.

The stoichiometric air-fuel ratio when the excess air ratio λ is 1 (λ = 1)
In the above, the amount of residual oxygen in the exhaust gas which diffuses into the electrode 105 via the diffusion resistor 106 and the amount of residual unburned gas such as carbon monoxide are in a chemical equivalent ratio,
Both are completely burned by the catalytic action of 5. for that reason,
Oxygen disappears in the vicinity of the electrode 105, and each electrode 104,
Even if a voltage is excited between 105, no oxygen ions are transferred in the zirconia solid electrolyte 102. Therefore,
The sensor current Ip flowing between the electrodes 104 and 105 becomes zero (Ip = 0).

In the rich region (λ <1) where the excess air ratio λ is smaller than 1, oxygen ions flow from the electrode 104 to the electrode 105, as opposed to the lean region. Acts to increase the oxygen concentration of the oxygen, and is oxidized again by the electrode 105 to become oxygen gas.
This oxygen gas burns unburned gas such as carbon monoxide which flows into the electrode 105 from the exhaust gas atmosphere via the diffusion resistor 106 by diffusion. Therefore, the amount of oxygen ions transferred from the electrode 104 side to the electrode 105 side in the zirconia solid electrolyte 102 has a value corresponding to the amount of unburned gas flowing into the electrode 105 by diffusion. At this time, the sensor current Ip flows from the electrode 105 to the electrode 104 in a direction opposite to the flow of the oxygen ions.

Both ends of the resistor R1 are connected to the A / D converter 8 respectively.
4 is connected. The A / D converter 84 A / D converts the voltage V1 on the operational amplifier 82 side and the voltage V2 on the detection unit 101 side of the resistor R1 under the control of the microcomputer 85, and converts the A / D converted value to the microcomputer. 85. Here, the A / D converter 84
Is connected to a positive power supply VC and a ground to supply power. Hereinafter, the voltages of the power supplies VB and VC are referred to as “VB” and “VC”, respectively.

The microcomputer 85 has a CPU, R
A well-known configuration having OM, RAM, and I / O circuits;
As shown in the equation (1), the voltages V1 and V
2 and the detection unit 101 based on the resistance value R1 of the resistor R1.
The sensor current Ip flowing between the respective electrodes 104 and 105 is calculated.

Ip = (V1−V2) / R1 (Equation 1) The microcomputer 85 calculates the sensor current Ip
The air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is controlled to a target value by feedback-controlling the amount of fuel supplied to the internal combustion engine in accordance with the calculated air-fuel ratio.

In the driving circuit 81, the resistance R
2. When the non-inverting input terminal of the operational amplifier 83 is short-circuited to the power supply VB, an excessive current is prevented from flowing into the non-inverting input terminal of the operational amplifier 83 or flowing out from the output terminal, thereby preventing the operational amplifier 83 from being damaged. , For protecting the output terminal of the operational amplifier 83 from static electricity, and its resistance is set to about 47Ω.

Since the resistor R1 is provided for the operational amplifier 82, by setting the resistance value to 47Ω or more, if the non-inverting input terminal of the operational amplifier 82 is short-circuited to the power supply VB, an excessive current will flow. 82
Of the operational amplifier 82 can be prevented from flowing into the non-inverting input terminal or flowing out of the output terminal of the operational amplifier 82, and the output terminal of the operational amplifier 82 can be protected from static electricity.

The resistors R3 and R4 are provided to protect the output terminals of the operational amplifiers 82 and 83 from static electricity, and have a resistance value of about 1 kΩ. Here, when the voltage VAF + applied to the non-inverting input terminal of the operational amplifier 82 is fixed, the voltage V2 becomes equal to the voltage VAF +. Therefore, the microcomputer 85 stores the value of the voltage V2 in the built-in ROM in advance. It is possible to recognize the voltage V2 at the A / D converter 84.
Need not be A / D converted. However, the operational amplifier 82
In order to accurately detect the sensor current Ip even when the voltage V2 is not equal to the voltage VAF +, for example, when an offset voltage is present, the A / D converter 84 A / D converts the voltage V2 as described above. Is desirable.

Japanese Patent Application Laid-Open No. 61-180131 discloses a circuit similar to the drive circuit 81 shown in FIG. 3 differs from the drive circuit 81 in that the resistors R2 to R4 are omitted and short-circuited, and the output terminal of the operational amplifier 83 and the non-inverting input terminal of the operational amplifier 82 are different. The only difference is that a voltage source for setting the excitation voltage VR is connected therebetween. The operation of each of the resistors R2 to R4 is as described above.
4 does not affect the basic operation of the drive circuit 81 even if it is short-circuited. In the driving circuit 81, the voltages VAF + and VAF- are applied to the non-inverting input terminals of the operational amplifiers 82 and 83, and the difference voltage VR between the voltages VAF + and VAF- becomes the excitation voltage. Functions in the same way as the voltage source. Therefore, the circuit described in the publication performs basically the same operation as the drive circuit 81.

[0019]

In recent years, it has been required to reduce carbon dioxide in exhaust gas for environmental protection.
Further fuel economy is required. Therefore, in addition to the stoichiometric control for controlling the operation of the internal combustion engine at the stoichiometric air-fuel ratio (λ = 1), it is essential to perform the lean burn control for controlling the operation in the lean region (λ> 1). That is,
There is a demand for precise control by switching between stoichiometric control and lean burn control in accordance with the operating state of the internal combustion engine. However, the conventional drive circuit 81 shown in FIG. 14 has a problem that the detection accuracy is reduced when detecting an air-fuel ratio (for example, 25 or more) in a high region for performing the lean burn control.

As described above, in the lean region,
A sensor current Ip flows from the electrode 104 to the electrode 105.
At this time, the lowest voltage that can be output from the operational amplifier 83 is VCE
And It is also assumed that the voltages VAF + and VAF- applied to the non-inverting input terminals of the operational amplifiers 82 and 83 are both variable. Then, the voltage VAF- is expressed by equation (2).

VAF− ≧ VCE + Ip · R2 (Expression 2) Assuming that no offset voltage exists in the operational amplifier 82, the voltage V2 becomes equal to the voltage VAF +, and the voltage applied between the electrodes 104 and 105 of the detection unit 101. VR is each voltage VA
Since it is a difference voltage between F + and VAF-, the voltage V2 is represented by the equation (3).

V2 = VAF + = VAF- + VR (Equation 3) The voltage V1 is represented by the following equation (4). V1 = V2 + Ip · R1 (Equation 4) FIG.
2 shows an example of characteristics of the applied voltage VR and the sensor current Ip in the detection unit 101 when 02 is heated to 700 ° C.

In this characteristic example, the air-fuel ratio (A / F) is 40
, The sensor current Ip becomes 23 mA. Where I
p = 23mA, VCE = 1.5V, VR = 0.9V, R1
= 100Ω and R2 = 47Ω, the values of the voltages V2 and V1 are as shown in the expressions (5) and (6).

V2 ≧ 3.481V (Equation 5) V1 ≧ 5.781V (Equation 6) The A / D converter 84 is connected to the plus-side power supply VC and the ground to supply power. Therefore, the power supply voltage VC
Is 5V, the maximum value of the A / D conversion value is 5V.
Therefore, the voltage V2 can be A / D converted by the A / D converter 84, but the voltage V1 cannot be A / D converted by the A / D converter 84. Therefore, when the air-fuel ratio is 40,
The microcomputer 85 cannot calculate the air-fuel ratio.

Incidentally, the maximum detectable value Ip (max) of the sensor current Ip is expressed by Expression (7) obtained from Expressions (1) to (3). Ip (max) = (VC−VR−VCE) / (R1 + R2) = 17.7 mA (Equation 7) In the detection unit 101 having the characteristic shown in FIG. 15, the sensor current Ip when the air-fuel ratio is 30 is 19 mA. become. Therefore, when the air-fuel ratio is 30, the microcomputer 85 cannot calculate the air-fuel ratio.

As described above, since the conventional drive circuit 81 cannot detect the air-fuel ratio in a high region, it is impossible to perform lean burn control in the air-fuel ratio in a high region. By the way, if the resistance R1 is smaller than 100Ω,
For example, if it is set to 56Ω, the voltage V1 is set to 4.
Since the voltage can be set to 769 V, A / D conversion can be performed by the A / D converter 84. According to the equation (7), Ip (m
Since ax) can be set to 25.24 mA, the detection unit 101 having the characteristics shown in FIG. 15 can also detect an air-fuel ratio in a high region such as 30 or 40. However, when the resistance value of the resistor R1 is reduced, the potential difference between the voltages V1 and V2 is reduced, so that the conversion accuracy of the A / D converter 84 is reduced and the accuracy of the air-fuel ratio calculated by the microcomputer 85 is also reduced. become. Therefore, when the resistance value of the resistor R1 is reduced, the lean burn control in the air-fuel ratio in a high region cannot be precisely controlled.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to detect an air-fuel ratio in each state of a rich region, a stoichiometric air-fuel ratio, and a lean region with high accuracy. It is to provide a device.

[0028]

Means for Solving the Problems In order to achieve the above object, the invention according to claim 1 comprises: a zirconia solid electrolyte; an air electrode formed on the air atmosphere side of the zirconia solid electrolyte; A detection unit is provided that includes an exhaust electrode formed on the exhaust atmosphere side of the zirconia solid electrolyte and a diffusion resistor that suppresses gas flowing from the exhaust atmosphere to the exhaust electrode by diffusion. A drive circuit unit is provided for applying a voltage to each of the atmosphere-side electrode and the exhaust-side electrode of the detection unit. Further, a detection circuit is provided for detecting a current flowing out or flowing in from the exhaust-side electrode of the detection unit, and detecting an air-fuel ratio based on the current value.

Therefore, according to the present invention, the current flowing out or flowing in from the exhaust side electrode, not from the atmosphere side electrode of the detecting section, is detected, and the air-fuel ratio is detected based on the current value. The fuel ratio can be detected with high accuracy, and the detection range of the air-fuel ratio can be expanded from the rich region and the stoichiometric air-fuel ratio to the lean region.

According to the first aspect of the present invention, the driving circuit in the air-fuel ratio detecting device generates an atmosphere-side applied voltage applied to the atmosphere-side electrode of the detecting section. Between the atmosphere-side voltage generation means, the exhaust-side voltage generation means for generating an exhaust-side applied voltage applied to the exhaust-side electrode of the detection unit, and the exhaust-side voltage generation means for the detection unit. , And a current detection resistor connected to the Further, the detection circuit unit includes a voltage detection unit that detects at least a voltage on the exhaust-side voltage generation unit side of a voltage between both ends of a current detection resistor of the drive circuit unit, and a voltage detected by the voltage detection unit. A current detection means for detecting a current flowing from the current detection resistor to the current detection resistor, and an air-fuel ratio calculation means for calculating an air-fuel ratio based on the current detected by the current-voltage detection means.

Therefore, according to the second aspect of the present invention,
Since the air-fuel ratio in a high region can be detected without reducing the resistance value of the current detection resistor, the A / D conversion accuracy when the voltage detection means is embodied by an A / D converter. Can be reduced, and the accuracy of the air-fuel ratio calculated by the air-fuel ratio calculation means can be improved.

Next, a third aspect of the present invention is directed to the second aspect.
In the air-fuel ratio detection device described in (1), both the atmospheric-side applied voltage generated by the atmospheric-side voltage generating means and the exhaust-side applied voltage generated by the exhaust-side voltage generating means are fixed. Therefore, according to the third aspect of the present invention, it is possible to detect the air-fuel ratio in a range necessary for the stoichiometric control with high accuracy.

According to a third aspect of the present invention, in the air-fuel ratio detection device, the drive circuit section includes a plurality of resistors connected in series between the voltage source and the ground, as in the fourth aspect of the invention. A resistor voltage dividing circuit is provided. Then, the atmosphere-side voltage generation means generates an atmosphere-side applied voltage based on the voltage divided by the resistance voltage dividing circuit. Also,
The exhaust-side voltage generation means generates an exhaust-side applied voltage based on the voltage divided by the resistance voltage dividing circuit.

Therefore, according to the fourth aspect of the present invention,
Both the atmosphere-side applied voltage and the exhaust-side applied voltage can be generated by a voltage obtained by a simple resistor voltage dividing circuit consisting of only a resistor. Next, the invention according to claim 5 is:
3. The air-fuel ratio detection device according to claim 2, wherein the drive circuit section generates the air-side voltage generation unit based on a voltage applied between an atmosphere-side electrode and an exhaust-side electrode of the detection section. 4. By controlling the applied voltage on the atmosphere side, the current flowing out or flowing from the exhaust side electrode of the detection unit is saturated. Then, the air-fuel ratio calculation unit detects an air-fuel ratio based on the saturated current value.

Therefore, according to the present invention, it is possible to change the voltage applied between the atmosphere-side electrode and the exhaust-side electrode of the detection unit in accordance with the air-fuel ratio, and to cover a wide range of air-fuel ratio in the lean region. Can be detected. By the way, claim 5
The drive circuit unit in the air-fuel ratio detection device according to the invention, as in the invention according to claim 6, a resistance voltage dividing circuit including a plurality of resistors connected in series between a voltage source and a ground,
A variable voltage generation circuit that generates a variable voltage based on a voltage applied between the atmosphere side electrode and the exhaust side electrode of the detection unit. The atmosphere-side voltage generation means generates an atmosphere-side applied voltage based on the variable voltage generated by the variable voltage generation circuit. The exhaust-side voltage generating means generates an exhaust-side applied voltage based on the voltage divided by the resistance voltage dividing circuit.

Therefore, according to the sixth aspect of the present invention,
By fixing the applied voltage on the exhaust side and changing the applied voltage on the atmosphere side, it becomes possible to change the voltage applied between the atmosphere side electrode and the exhaust side electrode of the detection unit according to the air-fuel ratio, It is possible to detect a wide range of air-fuel ratio in the lean region.

Further, the air-fuel ratio detecting device according to the sixth aspect of the present invention is such that the atmospheric-side applied voltage generated by the atmospheric-side voltage generating means is suppressed to a certain value or less, as in the seventh aspect of the present invention. A protection unit is provided for protecting the detection unit by suppressing a voltage applied between the atmosphere-side electrode and the exhaust-side electrode of the detection unit.

Therefore, according to the seventh aspect of the present invention,
By preventing an abnormal voltage from being applied between the electrodes of the detection unit, it is possible to prevent deterioration and destruction of the detection unit. Next, according to an eighth aspect of the present invention, in the air-fuel ratio detection device according to the second aspect, the drive circuit unit is configured to reduce a voltage applied between an atmosphere-side electrode and an exhaust-side electrode of the detection unit. Based on this, by changing both the atmosphere-side applied voltage generated by the atmosphere-side voltage generation unit and the exhaust-side applied voltage generated by the exhaust-side voltage generation unit, the air flows out from the exhaust-side electrode of the detection unit or Saturate the flowing current. Then, the air-fuel ratio calculation unit detects an air-fuel ratio based on the saturated current value.

Therefore, according to the present invention, by changing both the applied voltage on the exhaust side and the applied voltage on the atmosphere side, the applied voltage is applied between the atmosphere side electrode and the exhaust side electrode of the detection unit in accordance with the air-fuel ratio. The voltage can be changed, and an air-fuel ratio in a wide range in a lean region can be detected.

Next, the invention according to claim 9 is based on claim 1
The air-fuel ratio detection device according to any one of claims 1 to 8,
An AC internal resistance between the atmosphere-side electrode and the exhaust-side electrode of the detection unit is detected, and the temperature of the zirconia solid electrolyte of the detection unit is controlled to be constant so that the internal resistance is constant.

Therefore, according to the present invention, the temperature of the zirconia solid electrolyte is always kept constant, and the characteristic variation of the current flowing out or flowing from the exhaust side electrode with respect to the voltage applied between the electrodes of the detecting section is prevented. And the detection accuracy of the air-fuel ratio can be further improved.

According to a ninth aspect of the present invention, there is provided an air-fuel ratio detecting device including a heater for heating the zirconia solid electrolyte of the detecting portion so that the internal resistance is constant. Then, the operation of the heater is controlled.
Further, the air-fuel ratio detecting device according to claim 10 is the first embodiment.
As in the invention described in Item 1, the exhaust-side applied voltage generated by the exhaust-side voltage generating means is changed, and the amount of change in the voltage and whether the voltage flows out of the exhaust-side electrode of the detection unit caused by the change in the voltage. Alternatively, the internal resistance is detected based on the amount of change in the flowing current.

According to a tenth aspect of the present invention, in the air-fuel ratio detecting device, the atmospheric-side applied voltage generated by the atmospheric-side voltage generating means is changed, and the amount of change in the voltage is changed. The internal resistance is detected on the basis of a change in the current flowing or flowing from the exhaust-side electrode of the detection unit caused by the change in the voltage.

In the embodiments of the invention described below, the “detection circuit section” described in the claims or for solving the problems is constituted by an A / D converter 84 and a microcomputer 85. Similarly, the "atmosphere side voltage generation means" is configured by an operational amplifier 82, the "exhaust side voltage generation means" is configured by an operational amplifier 83, the "voltage detection means" is also configured by an A / D converter 84, and the "current The detecting means is a microcomputer 8
5 corresponds to the process of S102, and the “air-fuel ratio calculating means”
Similarly, the "voltage source" corresponds to the power supply VC, the "variable voltage generation circuit" is similarly configured by the D / A converter 32, and the "protection means" is similarly configured by the diode D1.

[0045]

Embodiments of the present invention will be described below with reference to the drawings. In each embodiment,
The same components as those of the conventional embodiment shown in FIGS. 13 to 15 are denoted by the same reference numerals, and detailed description thereof will be omitted.

(First Embodiment) Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 2 shows the overall configuration of a control device for an internal combustion engine for a vehicle using the air-fuel ratio detection device of the present embodiment.

The control device 11 comprises an input buffer 12, an output buffer 13, a drive circuit 14, an A / D converter 84, and a microcomputer 85. A rotation speed detection signal N from a rotation sensor for detecting the rotation speed of the internal combustion engine
E, a digital signal such as a vehicle speed detection signal SPD from a vehicle speed sensor for detecting a vehicle speed of the automobile, and a starter switch operation detection signal STA corresponding to whether or not a starter switch has been operated; Is converted to a signal of 0 V or 5 V,
It is input to the microcomputer 85.

Also, an intake air amount detection signal VG from an air amount sensor for detecting an intake air amount of the internal combustion engine, a throttle opening detection signal VTA from a throttle opening sensor for detecting a throttle opening, a cooling water temperature of the internal combustion engine. An analog signal such as a water temperature detection signal THW from a cooling water temperature sensor for detecting the temperature is converted from analog to digital by an A / D converter 84 and input to a microcomputer 85.

The drive circuit 14 drives the detection unit 101, and the voltages V1 and V2 output from the drive circuit 14 are A / D-converted by the A / D converter 84, and the microcomputer 8
5 is input. The microcomputer 85, based on various signals input from the input buffer 12 and the A / D converter 84, controls the fuel injection amount control signal INJ supplied from the injector to the internal combustion engine and the ignition timing control signal IJ.
GT, a control signal ISC for the idle rotation control valve, and a control signal H for controlling the heater 103 of the detection unit 101.
T or the like is generated. These control signals generated by the microcomputer 85 are output to the outside of the control device 11 via the output buffer 13.

FIG. 1 shows the internal configuration of the drive circuit 14.
In the drive circuit 14 of the present embodiment, the conventional drive circuit 8
The difference from 1 is as follows. (1-1) The output terminal of the operational amplifier 82 is connected to the electrode 104 (atmosphere side) of the detecting unit 101 via the resistor R2, and the operational amplifier 8 is connected via the resistors R2 and R3.
2 inverting input terminals.

(1-2) The output terminal of the operational amplifier 83 is connected to the electrode 105 (exhaust gas atmosphere side) of the detection unit 101 via the resistor R1, and the inverted input of the operational amplifier 83 via the resistors R1 and R4. Connected to terminal. (1-3) The A / D converter 84 A / D converts the voltage V1 on the operational amplifier 83 side and the voltage V2 on the detection unit 101 side in the resistor R1, and outputs the A / D converted value to the microcomputer 85. Output.

Next, the operation of the drive circuit 14 of the present embodiment will be described. As described above, in the lean region, the sensor current Ip flows from the electrode 104 to the electrode 105. At this time, the minimum output voltage of the operational amplifier 83 is VCE. It is also assumed that the voltages VAF + and VAF- applied to the non-inverting input terminals of the operational amplifiers 82 and 83 are both variable. Then, the voltage V1 is represented by Expression (8).

V1 ≧ VCE (Equation 8) Assuming that there is no offset voltage in the operational amplifier 83, the voltage V2 becomes equal to the voltage VAF−, and the voltage V2 is expressed by Expression (9). V2 = VAF− = V1 + Ip · R1 (Equation 9) Since the voltage VR applied between the electrodes 104 and 105 of the detection unit 101 is a difference voltage between the respective voltages VAF + and VAF−, the voltage VAF + is expressed by the following equation. 10).

VAF + = VAF− + VR (Expression 10) The output voltage VOP of the operational amplifier 82 is expressed by Expression (11). VOP = VAF ++ Ip.R2 (Equation 11) As in the case of the driving circuit 81, Ip = 23 m
A, VCE = 1.5V, VR = 0.9V, R1 = 100
Substituting into equations (8) to (11) assuming that Ω and R2 = 47Ω, the values of the voltages V2, V1, VAF +, and VOP are calculated by equation (12)
To (15).

V1 ≧ 1.5V (Expression 12) V2 = VAF− ≧ 3.8V (Expression 13) VAF + ≧ 4.7V (Expression 14) VOP ≧ 5.781V (Expression 14) (Equation 15) Further, the maximum detectable value Ip (max) of the sensor current Ip
Is represented by Expression (16) obtained from Expressions (8) to (11).

Ip (max) = (VC−VR−VCE) / R1 = 26 mA (Equation 16) Accordingly, each voltage V is set so as to satisfy the equations (13) and (14).
By setting AF + and VAF-, each of the voltages V1 and V2 can be reduced to 5 V or less. The A / D converter 84 is connected to the positive power supply VC and the ground to supply power.
The maximum value of the / D conversion value is 5V. Therefore, equation (12)
From (13), the voltages V1 and V2 can be A / D converted by the A / D converter 84.

In the detecting section 101 having the characteristics shown in FIG. 15, the sensor current Ip when the air-fuel ratio is 40 becomes 23 mA.
Therefore, even when the air-fuel ratio is 40, the microcomputer 85 can calculate the air-fuel ratio from Expression (16). From equation (15), the output voltage VOP of the operational amplifier 82 exceeds 5 V. However, if the power supply VB of each of the operational amplifiers 82 and 83 is supplied from the vehicle-mounted battery, the voltage of the vehicle-mounted battery is 14 V. Operational amplifier 82
The maximum value of the output voltage VOP is 14 V, which is not a problem.

Next, the details of the processing executed by the microcomputer 85 in this embodiment will be described with reference to the flowchart shown in FIG. When the microcomputer 85 is started by turning on the ignition switch and being supplied with power from the vehicle battery, the built-in ROM
In accordance with the control program recorded in the computer, the computer executes the following steps by various types of arithmetic processing.

First, step (hereinafter referred to as S) 101
, The A / D converter 84 performs A / D conversion of the voltages V1 and V2 across the resistor R1, and receives the A / D converted value. Next, in S102, as shown in the above equation (1), the voltages V1 and V output from the drive circuit 14 are output.
The sensor current Ip flowing between the electrodes 104 and 105 of the detection unit 101 is calculated based on 2 and the resistance value of the resistor R1.

Next, in S103, the internal ROM
The air-fuel ratio (A / F) corresponding to the sensor current Ip is calculated by table interpolation using the data table recorded in (1). Here, since the sensor current Ip and the air-fuel ratio do not have a completely linear linear relationship, it is necessary to create a data table in advance by obtaining the air-fuel ratio corresponding to some sensor currents Ip.

Next, returning to S101, in this embodiment, the routine from S101 to S103 is repeated at a timing of 8 ms. And the microcomputer 8
5 controls the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine to a target value by feedback-controlling the fuel injection amount according to the calculated air-fuel ratio to generate a fuel injection amount control signal INJ.

As described above, according to the drive circuit 14 of the present embodiment, it is possible to detect the air-fuel ratio in a high range, and the control device 11 of the internal combustion engine performs lean burn control in the air-fuel ratio in a high range. It can be carried out. Since the resistance value of the resistor R1 does not need to be reduced, the conversion accuracy of the A / D converter 84 does not decrease even when detecting the air-fuel ratio in a high region.
The accuracy of the air-fuel ratio calculated by can be improved. Therefore, the detection range of the air-fuel ratio can be expanded from the rich region and the stoichiometric air-fuel ratio to the lean region without lowering the detection accuracy.

Here, when the voltage VAF- applied to the non-inverting input terminal of the operational amplifier 83 is fixed, the voltage V2 becomes equal to the voltage VAF-, so that the microcomputer 85 stores the value of the voltage V2 in the built-in ROM in advance. By doing so, it is possible to recognize it, and it is not necessary for the A / D converter 84 to A / D convert the voltage V2. However, in order to accurately detect the sensor current Ip even when the voltage V2 is not equal to the voltage VAF-, for example, when an offset voltage is present in the operational amplifier 83, the voltage V2 is set to A in the A / D converter 84 as described above. / D conversion is desirable. However, if the condition that the voltage V2 is equal to the voltage VAF- is satisfied, the A / D of the voltage V2 in the A / D converter 84
It is also possible to omit the D conversion.

(Second Embodiment) Hereinafter, a second embodiment, which is a more specific version of the first embodiment, will be described with reference to the drawings. still,
In the present embodiment, the same components as those in the first embodiment have the same reference numerals, and a detailed description thereof will be omitted.

FIG. 4 shows the internal configuration of the drive circuit 21 of the present embodiment. The drive circuit 21 differs from the drive circuit 14 of the first embodiment shown in FIG. 1 in that the voltages VAF +, VAF- are divided by the resistors R5 to R7 connected in series between the power supply VC and the ground. Is generated.

Next, the operation of the drive circuit 21 of the present embodiment will be described. This embodiment is applied to a case where only stoichiometric control is performed without performing lean burn control. At the time of the stoichiometric control, for example, since the air-fuel ratio (A / F) is substantially controlled between 13 and 18, the detection unit 101 having the characteristic shown in FIG.
Range of 10 mA or less (-10 mA ≦ Ip ≦ 10 m
It suffices to be able to detect in A). Further, as shown by the dotted line (a) in FIG. 15, the applied voltage VR is also constant (= 0.4
V). The sensor current Ip takes a positive value when the sensor current Ip flows from the electrode 104 to the electrode 105 in the lean region, and becomes negative when the sensor current Ip flows from the electrode 105 to the electrode 104 in the rich region. Take a value.

Since the range of the sensor current Ip is -10 mA or more and 10 mA or less, the voltage VAF- is set so that the absolute value IpR of the sensor current in the rich region is equal to the absolute value IpL of the sensor current in the lean region. . Here, assuming that the maximum value of the voltage V1 is V1 (max),
The maximum value IpR (max) of the sensor current IpR is represented by Expression (17). Also, the maximum value IpL of the sensor current IpL (ma
x) is represented by equation (18).

IpR (max) = (V1 (max) −VAF −) / R1 (17) IpL (max) = (VAF−−VCE) / R1 (18) Here, the power supply voltage VC Is 5V, the maximum value V1 (max) becomes 5V. Therefore, IpR (max) = IpL (max), V1 (m
ax) = 5V, VCE = 1.5V, and R1 = 100Ω and substituted into equations (17) and (18), the voltages VAF- and VAF + become as shown in equations (19) and (20). Therefore, Ip
R (max) and IpL (max) are as shown in equation (21).

VAF− = 3.25 V (19) VAF + = VAF− + VR = 3.65 V (20) IpR (max) = IpL (max) = 17.5 mA (21) , And each resistance R so as to satisfy the equations (19) and (20).
By setting the resistance values of R5 to R7, stoichiometric control can be performed using the detection unit 101 having the characteristics shown in FIG.

The processing executed by the microcomputer 85 in this embodiment is the same as that in the first embodiment, and a description thereof will be omitted. As described above, according to the drive circuit 21 of the present embodiment, the voltages VAF + and VAF- are generated by using the simple resistor voltage dividing circuits including the resistors R5 to R7, so that the space necessary for the stoichiometric control is obtained. The fuel ratio can be detected with high accuracy.

Further, the drive circuit 21 according to the present embodiment can be formed only by connecting the resistor voltage dividing circuit including the resistors R5 to R7 to the drive circuit 14 according to the first embodiment. Therefore, the printed circuit board on which the operational amplifiers 82 and 83 and the resistors R1 to R4 are mounted in the drive circuit 14 is
1 can be used, and the driving circuits 14 and 21 can be used.
The printed circuit board can be shared. And
In the present embodiment, the processing executed by the microcomputer 85 is the same as that of the first embodiment. Therefore, the control program of the microcomputer 85 can be shared between the present embodiment and the first embodiment. Therefore,
According to the present embodiment, the printed circuit board and the control program (software) can be shared with the first embodiment, so that the cost can be reduced.

(Third Embodiment) Hereinafter, a third embodiment which is a more specific version of the first embodiment will be described with reference to the drawings. still,
In the present embodiment, the same components as those in the first embodiment have the same reference numerals, and a detailed description thereof will be omitted.

FIG. 5 shows the internal configuration of the drive circuit 31 of this embodiment. The drive circuit 31 differs from the drive circuit 14 of the first embodiment shown in FIG. 1 in the following points. (3-1) The drive circuit 31 includes resistors R8 to R10, a diode D1, and a D / A converter 32 in addition to the operational amplifiers 82 and 83 and the resistors R1 to R4.

(3-2) The D / A converter 32 generates a voltage VAF + as a D / A conversion value under the control of the microcomputer 85. Here, the D / A converter 32 is connected to the positive power supply VC and the ground to supply power. (3-3) The non-inverting input terminal of the operational amplifier 82 has D /
The voltage VAF + is applied from the A converter 32 via the resistor R10. The resistor R10 is connected to the operational amplifier 8 from static electricity.
It is provided to protect two non-inverting input terminals.

(3-4) The voltage VAF- generated by the voltage division of the resistors R8 and R9 connected in series between the power supply VC and the ground is applied to the non-inverting input terminal of the operational amplifier 83. I have. The non-inverting input terminal of the operational amplifier 83 is connected to the cathode of the diode D1, and the anode of the diode D1 is connected to the non-inverting input terminal of the operational amplifier.

Next, the operation of the drive circuit 31 of the present embodiment will be described. When the detection unit 101 having the characteristics shown in FIG. 15 is used, a wide range of air-fuel ratios (A / A
In order to detect the sensor current Ip corresponding to F) with a saturation current value, the applied voltage VR must be changed according to the air-fuel ratio as shown by the dotted line (b) in FIG.
Therefore, in the present embodiment, the voltage VAF- is fixed by the voltage division of the resistors R8 and R9, and the voltage VAF- is fixed.
By changing the voltage VAF + by the A converter 32, the applied voltage VR is changed according to the air-fuel ratio.

In the characteristic detecting section 101 shown in FIG.
When the sensor current Ip corresponding to the air-fuel ratio in the range of 2 to 40 is detected by the saturation current value, the sensor current Ip is set to −10.
mA to 25 mA or less (−10 mA ≦ Ip ≦ 25
mA).

From equations (17) and (18), equation (22)
Is required. IpR (max) + IpL (max) = (V1 (max) −VCE) / R1 (22) where IpR (max) = 10 mA, IpL (max) = 25 m
A, V1 (max) = 5V, VCE = 1.5V, and equation (2)
Substituting into 2), the resistance R1 becomes as shown in equation (23).

R1 = (V1 (max) −VCE) / (IpR (max) + IpL (max)) = 100Ω (23) Then, IpR (max) = 10 mA, IpL (max) = 25 m
A, V1 (max) = 5V, VCE = 1.5V, R1 = 100
Substituting into Equations (17) and (18) as Ω, the voltage VAF-
Is as shown in Expression (24).

VAF− = 4.0 V (24) However, it is necessary to confirm whether or not the required applied voltage VR can be obtained from the voltage VAF− obtained by the equation (24). D
Since the / A converter 32 is connected to the positive power supply VC and the ground and is supplied with power, if the power supply voltage VC is 5V, the maximum value of the D / A conversion value is 5V. Here, from the dotted line (b) in FIG. 15, the maximum value VR of the applied voltage VR is obtained.
Assuming that (max) is 0.9 V, the voltage VAF- is 4.0 V from the equation (24). Therefore, the maximum value of the voltage VAF + is 4.9 V according to the equation (10), and the D / A converter 32 There is no problem because it is smaller than 5 V which is the maximum value of the output.

However, the voltage VAF-
If the required applied voltage VR cannot be obtained from the above, the resistor R1 and the voltage VAF- are reset. That is, the values VC, VR (ma) are added to the equation (25) obtained from the equation (16).
x), VCE, and IpL (max) are substituted to determine the resistance R1.

R1 = (VC−VR (max) −VCE) / IpL (max) (25) When the power supply voltage VC is 5 V, the maximum value of the output of the D / A converter 32 (that is, the voltage The maximum value of VAF +) is 5V
Therefore, the voltage VAF- is obtained by substituting VAF + = 5 V and the value of the required applied voltage VR into the above equation (10).

Therefore, by setting the resistance values of the resistors R8 and R9 so that the obtained voltage VAF- is obtained, the detection unit 101 having the characteristic shown in FIG.
The sensor current Ip corresponding to the air-fuel ratio in the range can be detected by the saturation current value. Next, details of processing executed by the microcomputer 85 in the present embodiment will be described with reference to the flowchart shown in FIG.

Steps S101 to S103 shown in FIG. 6 are the same as those shown in FIG. And
In S104 subsequent to S103, the sensor current Ip calculated in S102 based on the characteristic data (dotted line (b) in FIG. 15) of the applied voltage VR and the sensor current Ip in the detection unit 101 recorded in the internal ROM in advance. The applied voltage VR to be applied is calculated.

Next, in S105, the calculated applied voltage VR and the voltage VAF- (= V2) are substituted into the above equation (10) to calculate the voltage VAF +, and the voltage VAF + is output from the D / A converter 32. Generate. Next, the process returns to S101. In this embodiment, the routine from S101 to S105 is performed for 8 ms.
It repeats at the timing of.

As described above, according to the drive circuit 31 of the present embodiment, the fixed voltage VAF− is generated by using the simple resistor voltage dividing circuit including the resistors R8 and R9, and the D / A converter 32 generates the fixed voltage VAF−. By varying the voltage VAF +, the applied voltage VR can be changed according to the air-fuel ratio, and a wide range of air-fuel ratio in the lean region can be detected.

A D / A converter for generating the voltage VAF- may be added to vary the applied voltage VR by varying both the voltages VAF + and VAF-. In this case, the D / A Two converters are required and the cost increases. Incidentally, the diode D1 is provided to protect the detection unit 101. That is, the sensor current Ip
If the detection unit 101 is used in a region where does not reach the saturation current value, the detection unit 101 is deteriorated or destroyed. Therefore, when the detection unit 101 having the characteristics shown in FIG. 15 is used, the applied voltage VR needs to be within ± 1 V. However, the D / A converter 32 or the microcomputer 85
Abnormally operates, or when an abnormality occurs in the wiring connecting the D / A converter 32 and the microcomputer 85, an abnormally high or low voltage VAF + may be generated. , The applied voltage VR may exceed ± 1V.

For example, the generated voltage VAF + is
Lower than VAF + (VAF + <VAF-), the voltage VAF + is calculated by the equation (2)
5). VAF + = VAF−−VF (Equation 25) Therefore, the applied voltage VR (= VAF + −VAF−) becomes equal to the threshold voltage VF. Usually, the threshold voltage VF is 1 V or less. The voltage VR can be kept within ± 1V. Therefore, by clamping the non-inverting input terminals of the operational amplifiers 82 and 83 with the diode D1, the detection unit determines whether the applied voltage VR becomes abnormally high or low when the voltage VAF + is lower than the voltage VAF-. 1
01 can be prevented from being degraded or destroyed.

When the generated voltage VAF + is abnormally high, the maximum value VR (max) of the applied voltage VR that does not cause deterioration or destruction in the detection unit 101 is set to 1 V, and the power supply voltage VC is set to 5 V, and the D / A conversion is performed. Assuming that the maximum value of the output of the detector 32 (that is, the maximum value of the voltage VAF +) is 5 V, if the voltage VAF- is set to 4 V or more according to the equation (10), the maximum value VR is obtained.
(max) can be reduced to 1 V or less. Here, since the voltage VAF- is 4.0 V from the equation (24), the maximum value VR (max) can be set to 1 V or less in practical use.
Therefore, by optimally setting the voltage VAF- according to the maximum value VR (max) and the maximum value of the voltage VAF +, whether the applied voltage VR becomes abnormally high or low when the voltage VAF + is abnormally high. As a result, it is possible to prevent the detection unit 101 from being deteriorated or destroyed.

(Fourth Embodiment) Hereinafter, a fourth embodiment in which the third embodiment is partially modified will be described with reference to the drawings. In the present embodiment, the same components as those in the third embodiment have the same reference numerals, and a detailed description thereof will be omitted.

FIG. 7 shows the internal configuration of the drive circuit 41 of this embodiment. The drive circuit 41 differs from the drive circuit 31 of the third embodiment shown in FIG. 5 in the following points. (4-1) The drive circuit 41 includes operational amplifiers 82 and 83, resistors R1 to R4, R8 to R10, diodes D1, and D / A.
In addition to the converter 32, it comprises resistors R11 to R14, a capacitor C1, and transistors Tr1 and Tr2.

(4-2) The capacitor C1 is connected between the non-inverting input terminal of the operational amplifier 83 and the ground. (4-3) PNP transistor Tr1 connected in series
And a resistor R11 connected in parallel with the resistor R8, and an NPN transistor Tr2 and a resistor R12 connected in series.
Are connected in parallel with the resistor R9. Each transistor T
r1 and Tr2 are connected to a microcomputer 85 via resistors R13 and R14, respectively.
5. The resistors R13 and R14 are provided to protect the transistors Tr1 and Tr2 from static electricity.

Next, the operation of the drive circuit 41 of the present embodiment will be described. When the temperature of the zirconia solid electrolyte 102 changes in the detection unit 101, the characteristic of the sensor current Ip with respect to the applied voltage VR fluctuates, and thus there is a problem that the detection accuracy of the air-fuel ratio decreases. In order to keep the temperature of the zirconia solid electrolyte 102 constant, the AC internal resistance of the detection unit 101 may be detected, and the heater 103 may be turned on and off so that the internal resistance becomes a constant value.

In the drive circuit 41, when detecting the sensor current Ip for detecting the air-fuel ratio, both the transistors Tr1 and Tr2 are turned off. Then, the driving circuit 4
Reference numeral 1 denotes the same configuration as the drive circuit 31 of the third embodiment. A voltage VAF- generated by resistance division by the resistors R8 and R9 is applied to a non-inverting input terminal of an operational amplifier 83. The voltage VAF + is applied to the terminal from the D / A converter 32 via the resistor R10.
Therefore, in the drive circuit 41, similarly to the drive circuit 31, the fixed voltage VAF- is generated by using a simple resistor voltage dividing circuit including the resistors R8 and R9, and the voltage VAF + is generated by the D / A converter 32. By varying, it becomes possible to change the applied voltage VR in accordance with the air-fuel ratio,
It is possible to detect a wide range of air-fuel ratio in the lean region.

In this embodiment, the processing executed by the microcomputer 85 when detecting the air-fuel ratio is the same as that in the third embodiment, and a description thereof will be omitted. Next, in the present embodiment, details of the processing executed by the microcomputer 85 when detecting the AC internal resistance of the detection unit 101 will be described with reference to the flowchart shown in FIG.

FIG. 9 shows that each of the transistors Tr1 and Tr2 when detecting the AC internal resistance of the detecting unit 101.
ON / OFF state and each voltage VAF-(= V2), V1
Shows the time displacement of. Since the operational amplifier 83 has no offset voltage, the voltage VAF- is equal to the voltage V2.
Becomes equal to

As shown in FIG. 8, first, in S201, A / D conversion of the voltages V1 and V2 across the resistor R1 is performed by A / D conversion.
The A / D converter 84 executes the A / D conversion and receives the A / D converted value. At this time, the transistors Tr1 and Tr2 are both turned off. As shown in FIG. 9, the voltage value of the voltage V1 detected here is expressed as a voltage V10, and the voltage value of the voltage V2 is expressed as a voltage V20. Further, the sensor current Ip flowing at this time (hereinafter, described as “I0”) is expressed by the following equation (2).
6).

Ip = I0 = (V20−V10) / R1 (Equation 26) Next, in S202, the transistor Tr2 is turned on, and the counter value of the built-in counter of the microcomputer 85 is cleared. Next, in S203,
In S202, it is determined whether 135 μs has elapsed since the count value of the built-in counter was cleared, and the process proceeds to S204 when 135 μs has elapsed.

In S204, the A / D converter 84 executes A / D conversion of the voltages V1 and V2 across the resistor R1, and receives the A / D converted value. At this time, since the transistor Tr1 is off and the transistor Tr2 is on, the resistors R9 and R12 are connected in parallel. As a result, the voltage VAF- becomes a voltage value calculated by the series-parallel circuit of the resistors R8, R9, and R12, and the voltage value becomes a voltage V21 lower than the voltage V20 as shown in FIG. Further, as the voltage VAF- decreases, the voltage value of the voltage V1 also decreases to a voltage V11 lower than the voltage V10. Therefore, the sensor current Ip flows from the electrode 105 to the electrode 104 as in the case of the rich region. The sensor current Ip flowing at this time (hereinafter referred to as “I1”) is
It is represented by equation (27).

Ip = I1 = (V21−V11) / R1 (Expression 27) From Expressions (26) and (27), the amount of change ΔI of the sensor current Ip due to the change in the voltage VAF− is calculated by Expression (28). expressed.
Further, the change amount ΔV of the voltage VAF− is expressed by Expression (29).

ΔI = I1−I0 (Expression 28) ΔV = V21−V20 (Expression 29) From Expressions (28) and (29), the AC internal resistance Z of the detection unit 101 is expressed by Expression (30). ).

Z = ΔV / ΔI (Equation 30) Accordingly, the detection unit 10 is set so that the internal resistance Z becomes a constant value.
A control signal HT for on / off control of one heater 103 is generated. Next, in S205, after the counter value of the built-in counter is cleared in S202, 200 μm
It is determined whether or not s has elapsed, and the process proceeds to S206 when 200 μs has elapsed.

Next, in S206, the transistor T
While turning on r1 and turning off the transistor Tr2,
Clear the counter value of the built-in counter. At this time, the resistors R8 and R11 are connected in parallel, and the voltage VAF- is a voltage value calculated by a series-parallel circuit of the resistors R8, R9 and R11. The voltage value is, as shown in FIG. The voltage V22 is higher than the voltage V20. The voltage VAF-
Increases, the voltage value of the voltage V1 also increases,
The voltage becomes higher than V10.

Next, in S207, it is determined whether or not 200 μs has elapsed since the counter value of the built-in counter was cleared in S202.
Shift to 06. Next, in S208, the transistor Tr1 is turned off.

At this time, in steps S206, the voltages VAF-, VAF
1 has a high voltage value of each of the voltages V22 and V12, so that the sensor current Ip quickly returns to the original current value I0.
Return to. That is, in S204, the voltages VAF-, V
1 is set to a voltage value as low as each of the voltages V21 and V11.
Even if both are turned off, the sensor current Ip does not immediately return to the original current value I0. Thus, the sensor current Ip can be quickly returned to the original current value I0 by increasing each of the voltages VAF- and V1 once decreased in S204 and oscillating them in the opposite direction in S206.

Next, returning to S201, in the present embodiment, the routine from S201 to S208 is repeated at a timing of 128 ms. The timing to start the routine from S201 is set to an intermediate timing of the timing to start the routine from S101 shown in FIG. That is, since the routine from S101 shown in FIG. 6 is repeated at a timing of 8 ms, the timing to start the routine from S201 is set 4 ms after the start of the routine from S101. This is S
This is because it takes a certain amount of time for each voltage VAF-, V1 to change and stabilize according to the routine from 201. After each voltage VAF-, V1 is stabilized, S101 is executed.
, The sensor current Ip can be accurately detected.

As shown in FIG. 9, the capacitor C1 is provided to slow down the falling of the waveforms of the voltages VAF- and V1. That is, the capacitor C1
Is omitted, overshoot and ringing occur in the waveforms of the voltages VAF- and V1, and the voltage values of the voltages V21 and V11 may fluctuate due to the overshoot and ringing. Therefore, by providing the capacitor C1, each of the voltages VAF-, VAF-,
The voltage V21 and V11 can be stabilized by slowing down the fall of the waveform of V1 and preventing the occurrence of overshoot and ringing.

As described above, according to the drive circuit 41 of the present embodiment, the AC internal resistance Z of the detection unit 101 is detected,
The zirconia solid electrolyte 1 is controlled by turning on and off the heater 103 so that the internal resistance Z becomes a constant value.
02 can be kept constant, and the characteristic fluctuation of the sensor current Ip with respect to the applied voltage VR can be prevented.
Therefore, in addition to the effect of the drive circuit 31 of the third embodiment, the accuracy of the air-fuel ratio calculated by the microcomputer 85 can be further improved.

In the present embodiment, the transistor Tr1 is turned off and the transistor Tr2 is turned on to lower the voltages VAF- and V1, and the sensor current Ip flows from the electrode 105 to the electrode 104 as in the rich region. Thus, the change amounts ΔI and ΔV are obtained. However, contrary to the present embodiment, the transistors Tr1 are turned on and the transistor Tr2 is turned off to increase the voltages VAF- and V1.
5, the change amount Δ
I and ΔV may be obtained.

However, as described above, the detection range of the sensor current Ip is limited. Therefore, when the sensor current Ip flows from the electrode 105 to the electrode 104 as in the lean region when detecting the air-fuel ratio corresponding to the lean region, the sensor current Ip may exceed the detection range. Also,
When detecting the air-fuel ratio corresponding to the rich region, if the sensor current Ip flows from the electrode 104 to the electrode 105 as in the rich region, the sensor current Ip may exceed the detection range.

Therefore, when detecting the air-fuel ratio corresponding to the lean region, the change amounts ΔI, ΔV are obtained by flowing the sensor current Ip in the same direction as in the rich region as in the present embodiment. It is desirable. Further, when detecting the air-fuel ratio corresponding to the rich region, it is desirable to obtain the change amounts ΔI, ΔV by flowing the sensor current Ip in the same direction as in the lean region.

By the way, in the drive circuit 31 of the third embodiment, when the voltage VAF + is varied by the D / A converter 32, the voltage at both ends of the resistor R1 and the detecting section 10 of the resistor R2 are detected.
By detecting the voltage on one side, the change amounts ΔI, Δ
V may be obtained.

However, in this case, the detection unit 1 of the resistor R2
It is necessary to add an A / D converter for detecting the voltage on the 01 side, which increases the cost. Also, in this case,
The microcomputer 85 detects the resistance R2 when the voltage VAF + is varied by the D / A converter 32.
It is also possible to recognize by storing the amount of change ΔV of the voltage value of the resistor R2 in advance in the built-in ROM.
There is no need to add a D converter. However, considering the case where there is an error in the output of the D / A converter 32, the case where an offset voltage exists in the operational amplifier 82, and the like, in order to accurately obtain the change amounts ΔI and ΔV, the detection unit of the resistor R2 It is desirable that the voltage on the 101 side be detected by an A / D converter.

Incidentally, the AC internal resistance of the detecting section 101 is detected, and the heater 103 is set so that the internal resistance becomes a constant value.
The technology for controlling the pressure is disclosed in JP-A-59-214756.
No. 6,086,045. However, according to the technique described in the publication, a bias voltage of a predetermined frequency is applied to the output side of an oxygen sensor (corresponding to the detection unit 101 of the present embodiment) via a resistor, and the amplitude level of the combined output voltage of the oxygen sensor is Is detected and the operation of the heater is controlled based on the amplitude level, which is completely different from the present embodiment.

(Fifth Embodiment) A fifth embodiment in which the second embodiment is partially modified will be described below with reference to the drawings. In the present embodiment, the same components as those in the second and fourth embodiments have the same reference numerals, and a detailed description thereof will be omitted.

FIG. 10 shows the internal configuration of the drive circuit 51 of this embodiment. In the drive circuit 51, similarly to the drive circuit 21 of the second embodiment, the voltage VAF + is generated using a resistor voltage dividing circuit including the resistors R5 to R7, and similarly to the drive circuit 41 of the fourth embodiment, Resistance R8, R9, R1
1 to R14, capacitor C1, transistors Tr1, T
r2, and when detecting the sensor current Ip to detect the air-fuel ratio, each of the transistors Tr1, Tr2
Are turned off, and a voltage VAF- is generated using a resistor voltage dividing circuit formed by the resistors R8 and R9. Then, the driving circuit 51
In detecting the AC internal resistance of the detection unit 101, the on / off control of the transistors Tr1 and Tr2 is performed as described with reference to FIGS. 8 and 9 as in the fourth embodiment.

Therefore, according to the drive circuit 51 of the present embodiment, in addition to the effects of the drive circuit 21 of the second embodiment, the fourth
Similarly to the drive circuit 41 of the embodiment, the accuracy of the air-fuel ratio calculated by the microcomputer 85 can be further improved by controlling the heater 103 on / off to keep the temperature of the zirconia solid electrolyte 102 constant.

(Sixth Embodiment) Hereinafter, a sixth embodiment in which the fifth embodiment is partially modified will be described with reference to the drawings. In this embodiment, the same components as those in the fifth embodiment have the same reference numerals, and a detailed description thereof will be omitted.

FIG. 11 shows the internal configuration of the drive circuit 61 of this embodiment. In the drive circuit 61, each resistor R5
Each of the voltages VAF + and VAF- is generated by using a resistor voltage dividing circuit by R7, and the voltage VAF- is applied from the voltage follower including the operational amplifier 62 to the non-inverting input terminal of the operational amplifier 83 via the resistor R15. ing. The drive circuit 61 is similar to the drive circuit 51 of the fifth embodiment,
R11 to R14, capacitor C1, transistor Tr
1 and Tr2, and when detecting the AC internal resistance of the detection unit 101, the transistors Tr1 and Tr2 are turned on and off as described with reference to FIGS.

In the driving circuit 51 of the fifth embodiment, the voltage VAF + is generated by using a resistor voltage dividing circuit composed of the resistors R5 to R7, and the voltage VAF− is divided by the resistor R8 and R9. It is generated using a circuit. Therefore, in order to accurately set the voltages VAF + and VAF-, it is necessary to set the resistance values of the resistors R5 to R8 accurately. If there is an error in the resistance values of the resistors R5 to R8, Voltages VAF + and VAF- cannot be set accurately, and the detection accuracy of sensor current Ip is reduced.

On the other hand, the driving circuit 61 of the present embodiment
Since the voltages VAF + and VAF- are generated using a resistor voltage dividing circuit including the resistors R5 to R7,
AF + and VAF- can be set accurately, and the detection accuracy of the sensor current Ip can be improved. However,
In order to prevent the resistances R5 to R7 from affecting each other during the on / off control of each of the transistors Tr1 and Tr2, it is necessary to provide a voltage follower composed of an operational amplifier 62. The cost will increase compared to. The resistor R15 is provided to protect the non-inverting input terminal of the operational amplifier 83 from static electricity.

The present invention is not limited to the above embodiments, but may be modified as follows. Even in such a case, the same operation and effect as those of the above embodiments can be obtained. [1] Each operational amplifier 82, 83 with respect to the sensor current Ip
If the output current supply capability of the amplifiers is insufficient, a current amplifier circuit composed of a push-pull transistor is connected to the output terminal of each of the operational amplifiers 82 and 83, and the output current of each of the operational amplifiers 82 and 83 is May be amplified to a required level.

[2] The shape of the zirconia solid electrolyte 102 of the detection unit 101 is not limited to a tubular shape,
Any shape may be used as long as air can be introduced into the electrode 104, and for example, a flat plate shape as shown in FIG. In the detection unit 101 shown in FIG. 12, the same components as those shown in FIG. 13 are denoted by the same reference numerals.

In FIG. 12, a passage 111 and a diffusion chamber 112 are provided in a flat zirconia solid electrolyte 102. An electrode 104 is formed on the zirconia solid electrolyte 102 on the inner wall of the passage 111, and the diffusion chamber 11
An electrode 105 is formed on the zirconia solid electrolyte 102 on the inner wall 2. Further, the diffusion chamber 112 is provided with one hole communicating with the outside, and the hole constitutes the diffusion resistor 106. Then, the atmosphere is introduced into the electrode 104 through the passage 111, and the residual oxygen and unburned gas in the exhaust gas are transferred from the diffusion resistor 106 to the diffusion chamber 112.
And flows into the electrode 105 by diffusion. The zirconia solid electrolyte 102 has an insulating layer 113 made of alumina.
Is fixed, and a linear heater 10 is provided in the insulating layer 113.
3 are arranged. Then, the heater 103 heats the zirconia solid electrolyte 102 via the insulating layer 113 to improve the conductivity of oxygen ions.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a drive circuit according to a first embodiment of the invention.

FIG. 2 is a block diagram showing a control device of an internal combustion engine for a vehicle using the air-fuel ratio detection device according to the first to sixth embodiments of the present invention;

FIG. 3 is a flowchart for explaining processing contents of a microcomputer according to the first, second, fifth, and sixth embodiments.

FIG. 4 is a circuit diagram showing a drive circuit according to a second embodiment.

FIG. 5 is a circuit diagram showing a drive circuit according to a third embodiment.

FIG. 6 is a flowchart for explaining processing contents of a microcomputer according to the third and fourth embodiments.

FIG. 7 is a circuit diagram showing a drive circuit according to a fourth embodiment.

FIG. 8 is a flowchart for explaining processing contents of a microcomputer according to the fourth, fifth, and sixth embodiments.

FIG. 9 is a timing chart for explaining the operation of the fourth, fifth, and sixth embodiments.

FIG. 10 is a circuit diagram showing a drive circuit according to a fifth embodiment.

FIG. 11 is a circuit diagram showing a drive circuit according to a sixth embodiment.

FIG. 12 is a partial cross-sectional view illustrating a schematic structure of a detection unit.

FIG. 13 is a partial cross-sectional view illustrating a schematic structure of a detection unit.

FIG. 14 is a circuit diagram showing a conventional driving circuit.

FIG. 15 is a characteristic diagram of the detection unit.

[Explanation of symbols]

14, 21, 31, 41, 51, 61 ... drive circuit 3
2 D / A converters 82 and 83 Operational amplifier 84 A / D converter 85 Microcomputer 101 Detection unit 102 Zirconia solid electrolyte 103 Heater
104 ... atmosphere side electrode 105 ... exhaust side electrode 106 ... diffusion resistor D1 ...
Diodes R1 to R15: resistors Tr1, Tr2: transistors

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Akira Tachiki 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside DENSO Corporation

Claims (12)

[Claims] 1. A zirconia solid electrolyte, an atmosphere-side electrode formed on the atmosphere side of the zirconia solid electrolyte,
An exhaust-side electrode formed on the exhaust atmosphere side of the zirconia solid electrolyte; a detection unit including a diffusion resistor for suppressing gas flowing from the exhaust atmosphere to the exhaust-side electrode by diffusion; A drive circuit unit that applies a voltage to each of the electrode and the exhaust-side electrode, and a detection circuit unit that detects a current flowing out or flowing from the exhaust-side electrode of the detection unit, and detects an air-fuel ratio based on the current value. An air-fuel ratio detection device comprising: 2. The air-fuel ratio detection device according to claim 1, wherein the drive circuit unit is configured to generate an atmosphere-side voltage applied to an atmosphere-side electrode of the detection unit. Exhaust-side voltage generation means for generating an exhaust-side applied voltage applied to the exhaust-side electrode of the unit; and a current-detecting resistor connected between the exhaust-side electrode of the detection unit and the exhaust-side voltage generation means. The detection circuit unit includes: a voltage detection unit that detects at least a voltage on the exhaust-side voltage generation unit side of a voltage across a current detection resistor of the drive circuit unit; and a voltage detected by the voltage detection unit. A current detection means for detecting a current flowing from the current detection resistor to the current detection resistor; and an air-fuel ratio calculation means for calculating an air-fuel ratio based on the current detected by the current-voltage detection means. Inspection Apparatus. 3. The air-fuel ratio detecting device according to claim 2, wherein an atmospheric-side applied voltage generated by the atmospheric-side voltage generating means,
An air-fuel ratio detecting device, wherein an exhaust-side applied voltage generated by the exhaust-side voltage generating means is fixed together. 4. The air-fuel ratio detection device according to claim 3, wherein the drive circuit unit includes a resistance voltage dividing circuit including a plurality of resistors connected in series between a voltage source and a ground, and the air side. The voltage generating means generates an atmosphere-side applied voltage by the voltage divided by the resistance voltage dividing circuit, and the exhaust-side voltage generating means: applies the exhaust-side voltage by the voltage divided by the resistance voltage dividing circuit. An air-fuel ratio detection device for generating a voltage. 5. The air-fuel ratio detection device according to claim 2, wherein the drive circuit unit is configured to control the air-side voltage based on a voltage applied between an air-side electrode and an exhaust-side electrode of the detection unit. By controlling the atmosphere-side applied voltage generated by the generation unit, the current flowing out or flowing out of the exhaust-side electrode of the detection unit is saturated. An air-fuel ratio detecting device, characterized by detecting the following. 6. The air-fuel ratio detection device according to claim 5, wherein the drive circuit unit includes a resistance voltage dividing circuit including a plurality of resistors connected in series between a voltage source and a ground; A variable voltage generation circuit that generates a variable voltage based on a voltage applied between the atmosphere-side electrode and the exhaust-side electrode, wherein the atmosphere-side voltage generation unit uses a variable voltage generated by the variable voltage generation circuit. An air-fuel ratio detecting device, wherein an air-side applied voltage is generated, and the exhaust-side voltage generating means generates an exhaust-side applied voltage by a voltage divided by the resistance voltage dividing circuit. 7. The air-fuel ratio detecting device according to claim 6, wherein the atmospheric-side applied voltage generated by the atmospheric-side voltage generating means is suppressed to a certain value or less, so that an atmospheric-side electrode and an exhaust-side electrode of the detecting unit are provided. An air-fuel ratio detection device, comprising: protection means for suppressing a voltage applied between the detection portion and the protection portion to protect the detection portion. 8. The air-fuel ratio detection device according to claim 2, wherein the drive circuit unit is configured to control the air-side voltage based on a voltage applied between an air-side electrode and an exhaust-side electrode of the detection unit. By changing both the atmosphere-side applied voltage generated by the generating unit and the exhaust-side applied voltage generated by the exhaust-side voltage generating unit, the current flowing out or flowing from the exhaust-side electrode of the detection unit is saturated, An air-fuel ratio detection device, wherein the air-fuel ratio calculation unit detects an air-fuel ratio based on the saturated current value. 9. The air-fuel ratio detection device according to claim 1, wherein an AC internal resistance between an atmosphere-side electrode and an exhaust-side electrode of the detection unit is detected, and the inside thereof is detected. An air-fuel ratio detecting device, wherein the temperature of the zirconia solid electrolyte of the detecting section is controlled to be constant so that the resistance becomes constant. 10. The air-fuel ratio detection device according to claim 9, further comprising a heater for heating the zirconia solid electrolyte of the detection unit, wherein the operation of the heater is controlled so that the internal resistance becomes constant. Air-fuel ratio detecting device. 11. The air-fuel ratio detecting device according to claim 10, wherein an exhaust-side applied voltage generated by the exhaust-side voltage generating means is changed, and the amount of change in the voltage and the detection caused by the change in the voltage are changed. The internal resistance is detected based on a change amount of a current flowing out or flowing in from an exhaust side electrode of the unit. 12. The air-fuel ratio detecting device according to claim 10, wherein the atmospheric-side applied voltage generated by the atmospheric-side voltage generating means is changed, and the amount of change in the voltage and the detection caused by the change in the voltage are changed. The internal resistance is detected based on a change amount of a current flowing out or flowing in from an exhaust side electrode of the unit.