JP2000227364A - Exhaust gas temperature measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an exhaust gas temperature measuring apparatus employing an air/fuel ratio sensor in order to eliminate a temperature sensor in view point of cost in which the exhaust gas temperature can be measured accurately without limiting the measurement conditions. SOLUTION: In an operating region where conduction to the heater in an air/fuel ratio sensor is not required, exhaust gas temperature is estimated by measuring the element impedance of the air/fuel ratio sensor. In an operating region where conduction to the heater is effected, element temperature drops when conduction to the heater is cut for a predetermined time Δt1 and the element impedance increases. Since increment ΔZ of the element impedance increases as the exhaust gas temperature decreases, exhaust gas temperature can be estimated by measuring ΔZ. Alternatively, exhaust gas temperature may be estimated based on the time Δt2 required for the element impedance increases to be reset to a value before conduction cut after conduction is resumed following to conduction cut.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the temperature of exhaust gas of an internal combustion engine, and more particularly to an apparatus for measuring exhaust gas temperature using a limiting current type air-fuel ratio sensor.

[0002]

2. Description of the Related Art Providing a dedicated temperature sensor for measuring the exhaust gas of an internal combustion engine increases the cost.
On the other hand, estimating the exhaust gas temperature by monitoring the engine speed, the engine load, and the like is also widely performed,
In this case, there is a big problem in accuracy.

Japanese Patent Application Laid-Open No. 58-17351 proposes a technique in which an O ₂ sensor provided for air-fuel ratio control is used for both O ₂ concentration detection and exhaust system temperature detection. That is, this technique, O ₂ from the resistance change by using the O ₂ sensor internal resistance change characteristics as a function of temperature
Is for detecting the temperature of the sensor near an O ₂ sensor does not use the electromotive force time range depends on the oxygen concentration, and, when the oxygen concentration in the measurement gas is in the rich side with respect to the set value (the battery When the output of the O ₂ sensor becomes low due to the structure, the resistance is detected and the exhaust gas temperature is measured.

[0004]

However, the technique disclosed in Japanese Patent Application Laid-Open No. 58-17351 has a problem in that the measurement conditions are limited, so that there are few opportunities for measurement. In addition, since measurement cannot be performed in the rich region, in high-rotation, high-load conditions where overheating of the catalyst (Over Temperature) poses a problem (usually, it is set to rich to prevent overheating of the catalyst). There is a problem that the exhaust gas temperature cannot be measured. Further, a heater may be provided along with the sensor for activating the O ₂ sensor. However, since the above-described prior art does not consider heater control, an accurate exhaust gas temperature is measured when the heater is energized. Have the problem of not being able to do so.

On the other hand, in recent years, an air-fuel ratio sensor has been used instead of the O ₂ sensor.
That is, in order to achieve both a reduction in fuel consumption rate and a reduction in harmful gas emissions in an in-vehicle internal combustion engine, it is necessary to control the air-fuel ratio (A / F) of the air-fuel mixture burned by the engine over a wide range. In order to enable such air-fuel ratio control, an oxygen ion conductive element (sensor element) such as a zirconia solid electrolyte is provided with an atmosphere-side electrode, an exhaust-side electrode, and an exhaust-side diffusion resistor to form a sensor main body. An air-fuel ratio sensor (referred to as a full-range air-fuel ratio sensor, a linear air-fuel ratio sensor, etc.) utilizing the fact that a limit current corresponding to the oxygen concentration or the unburned gas concentration in exhaust is generated with the application of a voltage to the exhaust gas has been put into practical use Feedback control based on the output of the air-fuel ratio sensor is performed.

[0006] In performing the air-fuel ratio feedback control based on the output of the full-range air-fuel ratio sensor, it is essential to maintain the oxygen ion conductive element in an active state. For this purpose, control is performed to heat the element using a heater to maintain the element temperature at a constant value. At that time, it is necessary to detect the element temperature, but since the element resistance has a correlation with the element temperature, it is also proposed to eliminate the necessity of a temperature sensor by detecting the element resistance and estimating the element temperature. Have been.

The present invention has been made in view of the above situation, and an object of the present invention is to provide an exhaust gas temperature measuring apparatus using an air-fuel ratio sensor to eliminate a temperature sensor from the viewpoint of cost. It is an object of the present invention to provide an apparatus capable of accurately measuring an exhaust gas temperature without limiting conditions.

[0008]

According to the present invention, in order to achieve the above object, according to the present invention, a sensor body for generating a limit current according to the concentration of oxygen or unburned gas in exhaust gas upon application of a voltage, and An air-fuel ratio sensor having a heater for heating and activating the oxygen ion conductive element in the sensor body, an element impedance detecting means for detecting an element impedance of the oxygen ion conductive element, and a power supply to the heater. Energizing exhaust temperature estimating means for temporarily cutting energization during execution, and estimating the exhaust temperature based on a state of change accompanying the cut of the element impedance detected by the element impedance detecting means. A temperature measurement device is provided.

According to the present invention, preferably, a non-energized exhaust temperature estimating step of estimating an exhaust temperature based on an element impedance detected by the element impedance detecting means while energizing the heater is not performed. Means.

Further, according to the present invention, preferably, the power-supply-time exhaust gas temperature estimating means estimates the exhaust gas temperature based on a rise rate of the element impedance when the power supply is cut off.

Further, according to the present invention, preferably, the energized exhaust gas temperature estimating means estimates the exhaust gas temperature based on an increase in the element impedance when the energized electric power is cut off for a certain period of time.

According to the present invention, preferably, the power supply exhaust temperature estimating means estimates the exhaust gas temperature based on a decreasing rate of the element impedance when the power supply is started again after the power supply is cut off.

Further, according to the present invention, preferably, the exhaust gas temperature estimating means at the time of energization cuts the energization for a certain period of time, and then returns to a value before the energization is cut off from the time when the energization is started again. The exhaust temperature is estimated based on the required time up to the time point.

[0014]

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

First, the principle of the air-fuel ratio sensor will be described. FIG. 1 is a characteristic diagram showing the relationship between the air-fuel ratio and the oxygen (O ₂ ) concentration in the exhaust gas and the relationship between the air-fuel ratio and the carbon monoxide (CO) concentration in the exhaust gas. As shown in this figure, in the air-fuel ratio region leaner than the stoichiometric air-fuel ratio, the O ₂ concentration changes almost linearly with respect to the air-fuel ratio, while the air-fuel ratio region richer than the stoichiometric air-fuel ratio is increased. In this case, the concentration of unburned gas, CO, changes almost linearly with the air-fuel ratio. The air-fuel ratio sensor utilizes this relationship, as described later.

FIG. 2 is a sectional view showing an example of the configuration of the air-fuel ratio sensor. The air-fuel ratio sensor 10 is connected to the exhaust pipe 9 of the internal combustion engine.
It is used in a state protruding toward the inside of the zero. The air-fuel ratio sensor 10 is roughly divided into a cover 11, a sensor body 13
And a heater 18. The cover 11 has a cup-shaped cross section, and a plurality of small holes 12 communicating with the inside and outside of the cover are formed in a peripheral wall thereof.

In the sensor body 13, an exhaust-side electrode layer 16 is fixed to the outer surface of the oxygen ion-conductive solid electrolyte layer 14 formed in a test tube, while an atmosphere-side electrode layer 17 is fixed to the inner surface. Have been. The diffusion resistance layer 1 is formed on the outside of the exhaust side electrode layer 16 by a plasma spraying method or the like.
5 are formed. For example, in the present embodiment, the solid electrolyte layer 14 is made of ZrO ₂ (zirconia element).
It is formed of an oxygen ion conductive oxide sintered body in which aO or the like is dissolved as a solid solution (hereinafter, the solid electrolyte layer 14 is also referred to as a sensor element). The diffusion resistance layer 15 is made of a heat-resistant inorganic substance such as alumina. The exhaust-side electrode layer 16 and the atmosphere-side electrode layer 17 are both made of a noble metal having high catalytic activity such as platinum, and the surfaces thereof are subjected to porous chemical plating or the like.

The heater 18 is housed in the atmosphere-side electrode layer 17 and generates heat from the sensor body 13 by the heat generated by the heater 18.
Is heated to activate the zirconia element 14. The heater 18 has a sufficient heat generating capacity to activate the zirconia element 14.

The zirconia element 14 is characterized in that when an oxygen concentration difference occurs at both ends of the element in a high-temperature active state, oxygen ions (O ²⁻ ) pass from the higher concentration side to the lower concentration side (oxygen battery characteristic).
Having. Further, the zirconia element 14 has a characteristic (oxygen pump characteristic) in which, when a potential difference is applied to both ends thereof, movement of oxygen ions (O ²⁻ ) according to the potential difference is caused to move from the cathode to the anode. .

As shown in FIG. 2, a constant bias voltage is applied to the sensor body 13 such that the atmosphere side electrode layer 17 has a positive polarity and the exhaust side electrode layer 16 has a negative polarity. When the exhaust air-fuel ratio is lean, oxygen ions (O ²⁻ ) move from the exhaust-side electrode layer 16 to the atmosphere-side electrode layer 17 due to the oxygen pump characteristics. As a result, current flows from the positive electrode of the bias voltage source to the negative electrode of the bias voltage source via the atmosphere-side electrode layer 17, the solid electrolyte layer 14, and the exhaust-side electrode layer 16. The magnitude of the current flowing at this time can be reduced from the exhaust gas to the diffusion resistance layer
Corresponding to the amount of oxygen flowing into the exhaust-side electrode layer 16 by diffusion. Therefore, by detecting the magnitude of the limit current, the oxygen concentration can be known, and the air-fuel ratio in the lean region can be known as described with reference to FIG.

On the other hand, when the air-fuel ratio of the exhaust gas is rich, the oxygen cell characteristics operate.
To move oxygen ions (O ²⁻ ) from the gas to the exhaust side electrode layer 16. That is, the oxygen cell characteristics act in the opposite direction to the bias voltage. Since the air-fuel ratio sensor is configured such that the electromotive force due to the characteristics of the oxygen cell overcomes the bias voltage, a current flows from the atmosphere-side electrode layer 17 to the exhaust-side electrode layer 16 through the bias voltage source. The magnitude of the current flowing at this time is determined by the amount of oxygen ions (O ²⁻ ) transferred from the atmosphere side electrode layer 17 to the exhaust side electrode layer 16 in the solid electrolyte layer 14. The oxygen ions pass from the exhaust through the diffusion resistance layer 15 to the exhaust-side electrode layer 1.
6 reacts (combustes) in the exhaust-side electrode layer 16 with unburned gas such as carbon monoxide flowing by diffusion to 6, and the oxygen ion transfer amount corresponds to the concentration of unburned gas. Therefore, by detecting the magnitude of this limit current, it is possible to know the unburned gas concentration, and hence to know the air-fuel ratio in the rich region as described with reference to FIG.

When the exhaust air-fuel ratio is the stoichiometric air-fuel ratio, the amounts of oxygen and unburned gas flowing into the exhaust-side electrode layer 16 have a chemical equivalent ratio. Burns completely. Therefore, oxygen is eliminated in the exhaust-side electrode layer 16, and oxygen ions to be transferred are not generated due to the oxygen cell characteristics and the oxygen pump characteristics. As a result, when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio, no current flows through the circuit.

Thus, the voltage-current (V) of the air-fuel ratio sensor
-I) The characteristic indicates a limit current corresponding to the air-fuel ratio (A / F) of the exhaust gas to which the sensor is exposed, as shown in FIG. In FIG. 3, a straight line parallel to the V axis represents the limit current. The direction in which the limit current flows in the lean region and the rich region is reversed. As the air-fuel ratio increases in the lean region and the air-fuel ratio decreases in the rich region, the absolute value of the limit current increases. Becomes larger.
According to the characteristic diagram of FIG. 3, when the applied voltage is set to about 0.3 V, a wide range of air-fuel ratio can be detected. Note that a region where the voltage is smaller than the voltage of the linear portion parallel to the V axis is a resistance dominating region.

Next, an example of a hardware configuration of an air-fuel ratio detecting device having a function as an exhaust gas temperature measuring device according to the present invention will be described with reference to FIG. The air-fuel ratio detection device is roughly divided into an air-fuel ratio sensor 10, a sensor main body drive circuit 20, a heater drive circuit 30, and a central processing unit (C
PU) 40. The air-fuel ratio sensor 10 is shown in FIG.
As described above, the sensor body 13 and the heater 18 are provided. Further, the heater drive circuit 30 is a circuit that receives a duty ratio signal and applies the voltage of the battery 32 to the heater 18 on / off in accordance with the duty ratio. The CPU 40 performs fuel injection control, ignition timing control, and the like as a center of an electronic control unit (ECU) of the internal combustion engine, and includes an A / D converter (ADC), a D / A converter (DAC), and a memory. Built-in.

The sensor body drive circuit 20 is roughly divided into a low-pass filter (LPF) 21 and a first voltage follower (v
(voltage follower) circuit 22, a reference voltage generation circuit 25, and a second voltage follower circuit 26. LPF2
1 is for removing high frequency components of the analog signal voltage output from the CPU 40. The first voltage follower circuit 22 includes an operational amplifier, a resistor, a diode, a transistor, and the like, and maintains the potential of the atmosphere-side electrode layer 17 of the sensor body 13 at the same potential as the output potential of the LPF 21. The potential is 3.3 when the air-fuel ratio is detected.
V.

The reference voltage generation circuit 25 _divides the constant voltage V _CC to generate a reference voltage of 3.0V. The second voltage follower circuit 26 includes the first voltage follower circuit 22
And the potential of the exhaust-side electrode layer 16 of the sensor body 13 is maintained at the reference voltage of 3.0 V. Therefore,
At the time of detecting the air-fuel ratio, a value of 0.1 is applied between both electrode layers of the sensor body 13.
The voltage V of 3 V is applied, and as described with reference to the characteristic diagram of FIG. 3, the limit current can be measured to detect the air-fuel ratio over a wide range. The resistor 23 in the first voltage follower circuit 22 functions as a current detection circuit.
The potential V ₀ of the sensor side terminal of the resistor 23 and the potential V ₁ of the other terminal are supplied to the CPU 40. The CPU 40 calculates the analog potential V at both ends of the resistor 23.
₀ and V ₁ are A / D converted and the potential difference “V ₁ −
V ₀ ”is calculated, and based on the potential difference and the resistance value of the resistor 23, a current I is calculated so that the direction flowing from the first voltage follower circuit 22 to the atmosphere-side electrode layer 17 of the sensor body 13 is positive. I do.

As will be understood from the above description with reference to FIG. 3, the calculated current value and the air-fuel ratio have a relationship as shown in FIG. Therefore, the CPU 40 can detect the air-fuel ratio of the exhaust based on the detected current value, and can realize air-fuel ratio feedback control.

Now, in order to detect the air-fuel ratio, it is necessary to maintain the sensor element (zirconia element) 14 in an active state. The active state is such that the element temperature is kept at a constant value, for example, 7
Maintained by maintaining at 00 ° C. By the way, since the element temperature and the element resistance have a certain correlation as shown in FIG. 6, in order to keep the element temperature at 700 ° C., it is necessary to set the element resistance to 30Ω. Good.
Therefore, the element resistance is detected, and the heater drive circuit 30 is feedback-controlled based on the detected resistance value, thereby performing control to maintain the element active state.

FIGS. 7A and 7B are views showing the structure of the sensor body 13, wherein FIG. 7A is a sectional view and FIG. 7B is a partially enlarged view of the solid electrolyte 14. FIG. 8 is a diagram showing an equivalent circuit of the sensor body 13. In FIG. 8, R1 is the bulk resistance of the solid electrolyte made of zirconia.
Corresponds to the (grain) part. R2 is the grain boundary resistance of the solid electrolyte, and corresponds to the grain boundary part in FIG. R3 is the interface resistance of the electrode made of platinum. C
2 is a capacity component of a grain boundary of the solid electrolyte. C3 is a capacitance component at the electrode interface. Z (W) is an impedance component (Wirble impedance) generated when the interface concentration periodically changes when polarization occurs due to alternating current.

As can be seen from FIG.
Then, when a voltage in the resistance dominant region (see FIG. 3) is applied and the output current is measured, “R1 + R2 + R3” can be detected. However, since R3 changes greatly due to deterioration of the electrodes and the like, it is not possible to extract only the element resistance "R1 + R2". Moreover, as shown in FIG. 3, since the resistance dominant region changes according to the air-fuel ratio, it is extremely difficult to detect the element resistance based on the DC characteristics of the sensor body.
Therefore, an element resistance detection method using AC characteristics has been proposed.

FIG. 9 shows a DC voltage (0.3
V), the impedance Z of the sensor body is changed according to the change of the frequency f of the input AC voltage.
Is a diagram showing a locus drawn by the horizontal axis, where the horizontal axis represents the real part R of the impedance Z and the vertical axis represents the imaginary part X. This trajectory does not depend on the air-fuel ratio. The impedance Z of the sensor body is Z = R +
It is represented by jX. As shown in FIG. 9, the impedance Z converges on the element resistance “R1 + R2” as the frequency f approaches 1 kHz.

FIG. 10 is a diagram showing the relationship between the frequency f of the input AC voltage and the absolute value | Z | of the impedance Z.
From FIG. 10, it can be seen that | Z | is substantially “R1 + R2” at frequencies of 1 kHz to 10 MHz, and | Z | decreases at frequencies higher than 10 MHz and converges to R1.
Accordingly, in order to detect the element resistance “R1 + R2”, it is desirable to apply an AC voltage of about 1 kHz to 10 MHz, measure the output AC current, and obtain the impedance.

FIGS. 11A, 11B and 11C show the LP
Input voltage to F21, output voltage from LPF21, that is, voltage applied to atmosphere-side electrode layer 17 of air-fuel ratio sensor 10,
FIG. 4 is a diagram showing waveforms of an output current of an air-fuel ratio sensor and an output current of the air-fuel ratio sensor. The horizontal axis represents time, and the vertical axis represents voltage or current.
As described above, since the exhaust-side electrode layer 16 is maintained at the reference voltage of 3.0 V and the atmosphere-side electrode layer 17 is normally maintained at 3.3 V as shown in FIG. Normally, a DC voltage of 0.3 V is applied between both electrodes of the main body. The output DC current with respect to the input DC voltage indicates the air-fuel ratio.

Then, the CPU 40 measures L as shown in FIG. 11A to measure the element impedance.
The input voltage to the PF 21 is changed by ΔV. LPF2
As shown in FIG. 11B, the output voltage from No. 1, that is, the voltage applied to the atmosphere-side electrode layer 17 of the air-fuel ratio sensor 10 is a smoothed waveform mainly composed of a specific frequency component (for example, 5 kHz). 2. The AC voltage pulse of 3.
It is superimposed on 3V. In response to this AC voltage pulse, the output current becomes ΔI as shown in FIG.
Only change. Then, ΔV / ΔI gives the element impedance (absolute value) Z. The element temperature is detected by referring to the characteristic curve of FIG. 6 based on Z. The reason why the applied voltage is changed to both positive and negative sides is to expedite the discharge of the electric charge accumulated in the capacitance component.

The sensor element is heated by the exhaust gas and the heater. That is, the element temperature is determined by the exhaust gas temperature and the amount of electricity supplied to the heater. As described above, since the element temperature needs to be maintained at 700 ° C., in a region where the exhaust gas temperature is 700 ° C. or more, heating by the heater is unnecessary.

The following shows how the exhaust gas temperature THEG changes in accordance with the engine speed NE and the engine load LD.
A characteristic diagram as shown in FIG. 12 is obtained. The engine load LD may be any of an engine intake air flow rate, an intake pipe pressure, an intake air flow rate / rotational speed ratio, and the like. In this figure, THEG = 700 °
In a region REG2 above the curve C, the exhaust gas temperature TH
Since EG is 700 ° C. or higher, it is not necessary to energize the heater, and the duty ratio of the signal supplied to the heater drive circuit 30 is 0%. Therefore, in REG2, the element temperature is determined only by the exhaust gas temperature THEG. That is, the exhaust gas temperature can be estimated by measuring the element temperature.

On the other hand, in FIG. 12, THEG = 700 °
In the region REG1 below the curve C, since the element temperature cannot be maintained at 700 ° C. only with the exhaust gas, the heater is energized. by the way,
While the power is being supplied to the heater, as shown in FIG. 13, a flag HF indicating that the heater control is permitted is performed.
If the LG is turned off for a certain period of time Δt ₁ and energization of the heater is cut off (duty ratio 0%), the element temperature decreases accordingly. Therefore, the element impedance Z increases from the relationship shown in FIG. The element temperature decrease amount becomes larger as the exhaust gas temperature THEG is lower.
Therefore, the element impedance increase ΔZ increases as the exhaust gas temperature THEG decreases. Therefore, ΔZ
, The exhaust gas temperature can be estimated.

FIGS. 14 and 15 are flowcharts showing the processing procedure of an exhaust gas temperature estimation routine that embodies the above findings. This routine is executed by the CPU 40 at predetermined time intervals (for example, several tens of milliseconds). First, in step 102, an operation region in which the element temperature is currently higher than the exhaust gas temperature, that is, REG1 shown in FIG.
Is determined based on the engine speed NE and the engine load LD.

If the decision result in the step 102 is YES, that is, if it is in the REG1 of FIG. 12, the process proceeds to a step 104. In step 104, the counter CN
While incrementing T1, the counter CNT2
Is cleared to 0. The counter CNT1 is provided for estimating the exhaust gas temperature at a constant time period when it is in the REG1, while the counter CNT2 is provided for the REG1.
2 is provided for estimating the exhaust gas temperature in a fixed time cycle when it is at 2.

Steps executed after step 104
In step 106, CNT1 is set to a predetermined value C ₀Or not,
That is, after the shift to REG1 or the previous exhaust temperature
Determine if a certain time has passed since the estimation
You. CNT1 = C₀Is established, first, the current
The element impedance Z is measured, and the value is expressed as Z₀Note as
(Step 108), and then sets the flag HFLG to 0.
(Step 110), and this routine ends. Separately
The heater control routine being executed determines that HFLG is 0.
The signal supplied to the heater drive circuit 30
The duty ratio of the signal is forcibly set to 0%.

[0041] In step 112 is executed when it is determined that CNT1 ≠ C ₀ in step 106, determines the counter CNT1 is whether reaches the predetermined value C ₁ (> C _0). “C ₁ −C ₀ ” is an amount corresponding to the energization cut time Δt ₁ in FIG. And Δt
₁ is set as a time during which the element temperature, that is, the element impedance changes, to a certain extent without cooling the element much, and is, for example, about several seconds. In step 112, CNT1 ≠ C ₁
When the determination is made, this routine ends.

On the other hand, in step 112, CNT1 =
When it is determined that C ₁ is first measured element impedance Z, is the measured value and Z ₁ (Step 11
4). Next, the flag HFLG is set to 1 (step 1).
16). The separately executed heater control routine is H
When FLG is set to 1, the power supply to the heater is restarted. Next, an increase amount ΔZ of the element impedance is obtained by an operation of Z ₁ −Z ₀ (step 118). This ΔZ is an amount that increases as the exhaust gas temperature THEG decreases.

Next, an operation of ΔZ × K1 is performed, and ΔZ × K1 is calculated.
The exhaust gas temperature THEG is estimated by referring to a map as shown in FIG. 16 based on × K1 (step 120). Here, the map of FIG. 16 is a standard map for obtaining the exhaust gas temperature based on the increase amount ΔZ of the element impedance, and is obtained experimentally in advance. K1 is the structure of the internal combustion engine, the structure of the sensor,
This is a correction coefficient for absorbing a difference in a sensor mounting position and the like, and is a constant obtained in advance by an experiment. Finally, the counter CNT1 is cleared to 0, and this routine ends (step 122).

If the decision result in the step 102 is NO,
That is, when the heater is not energized in the operation region of REG2 in FIG. In step 130, the counter CNT1 is cleared to 0, and the counter CNT2 is incremented. Next, at step 132, whether CNT2 reaches a predetermined value C _0, that is, determines whether or not the lapse of a predetermined time from the estimated migration to or from previous exhaust temperature REG2, CNT2 When ≠ C ₀ , this routine ends.

On the other hand, in step 132, CNT2 =
When C ₀ holds, first, the element impedance Z
Is measured, and the element temperature TH is calculated based on the Z value and the relationship shown in FIG.
The SE is determined (step 134). Next, an exhaust gas temperature THEG is calculated based on the element temperature THSE and a map as shown in FIG. 17 (step 136). Note that the map of FIG. 17 shows the relationship between the element temperature THSE and the exhaust gas temperature THEG when the heater is not driven, and is a map that is experimentally obtained in advance. Since the element temperature THSE is substantially equal to the exhaust temperature THEG, the obtained element temperature THSE may be directly used as the exhaust temperature THEG. Finally, CNT2 is cleared to 0, and this routine ends (step 138).

According to the processing shown in FIGS. 14 and 15, it is possible to measure the exhaust gas temperature using the air-fuel ratio sensor in all operating regions.

In the above embodiment, when the heater is energized, the exhaust gas temperature is reduced based on the decrease in the element temperature (ie, the increase in the element impedance) when the energization is cut off for a certain period of time. In other words, the exhaust temperature is estimated on the basis of the rate of decrease in element temperature when current is cut off (that is, the rate of increase in element impedance). On the other hand, if the rise rate of the element temperature (that is, the fall rate of the element impedance) at the time when the electricity supply is started again after the energization is cut off is detected, the temperature rise rate (ie, the impedance fall rate) is detected.
Becomes smaller as the exhaust gas temperature is lower. Therefore, it is possible to estimate the exhaust gas temperature from the decreasing rate of the element impedance. Accordingly, as shown in FIG. 13, the second embodiment of the present invention is configured such that after the energization is cut off for a certain time Δt ₁ , the energization is started again, and the element impedance returns to the value before the energization cut. It is intended to estimate the exhaust gas temperature based on the required time Δt _{2 up} to this point.

FIGS. 18 and 19 are flowcharts showing the processing procedure of the exhaust gas temperature estimation routine according to the second embodiment. Steps 202 to 210 are the same as steps 102 to 110 described above, and steps 230 to 238 are the same as steps 130 to 138 described above.

In step 212, it is determined whether or not the counter CNT1 has reached a predetermined value C ₁ (> C ₀ ).
When it is determined that 1 = C ₁ , that is, when it is time to restart the heater energization, the routine proceeds to step 214, where the flag H
FLG is set to 1 and this routine ends. On the other hand, CN
When it is determined that T1 ≠ C _1, the process proceeds to step 216, determines whether the CNT1 is greater than C _1. CN
While the routine ends when the T1 ≦ C _1, CN
When T1> C ₁ proceeds to step 218. In step 218, the element impedance Z is measured. Next, at step 220, it is determined whether or not Z ≦ Z ₀ holds.
That is, it is determined whether or not the element impedance has returned to the value before the energization cut. When Z> Z ₀ , that is, when the element impedance has not yet returned, this routine ends.

On the other hand, when Z ≦ Z ₀ is satisfied in step 220, that is, when the element impedance has returned to the value before the energization cut, first, the time Δt ₂ required for “CNT1−C ₁ ” to return is expressed. Therefore, Δt ₂ is calculated (step 222). Next, an operation of Δt ₂ × K2 is performed, and the exhaust gas temperature THEG is estimated by referring to a map as shown in FIG. 20 based on Δt ₂ × K2 (step 224). Here, the map in FIG. 20 is a standard map for obtaining the exhaust gas temperature based on the required time for returning the element impedance Δt ₂ , and is obtained in advance by experiment. K2 is a correction coefficient for absorbing differences in the structure of the internal combustion engine, the structure of the sensor, the mounting position of the sensor, and the like, similarly to the above-described K1.
This is a constant that is obtained in advance by experiments. Finally,
The counter CNT1 is cleared to 0, and this routine ends (step 226).

The two embodiments have been described above. By combining them, the exhaust temperature is obtained from the increase in the element impedance at the time of energization cut, and the exhaust temperature is also obtained from the time required to recover the element impedance when the energization is restarted. By averaging the exhaust gas temperatures, the accuracy of the measurement of the exhaust gas temperature may be improved.

[0052]

As described above, according to the present invention,
The use of the air-fuel ratio sensor can accurately measure the exhaust gas temperature without increasing the cost and without limiting the measurement conditions.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a relationship between an air-fuel ratio and an exhaust component concentration.

FIG. 2 is a cross-sectional view showing one configuration example of an air-fuel ratio sensor.

FIG. 3 is a characteristic diagram illustrating an example of a voltage-current characteristic of the air-fuel ratio sensor.

FIG. 4 is an electric circuit diagram showing an example of a hardware configuration of an air-fuel ratio detection device having a function as an exhaust gas temperature measurement device according to the present invention.

FIG. 5 is a characteristic diagram showing a relationship between an air-fuel ratio and an output current of an air-fuel ratio sensor.

FIG. 6 is a characteristic diagram showing a relationship between element temperature and element resistance.

FIGS. 7A and 7B are diagrams showing a structure of a sensor main body, wherein FIG. 7A is a cross-sectional view and FIG. 7B is a partially enlarged view of a solid electrolyte.

FIG. 8 is a diagram showing an equivalent circuit of the sensor body.

FIG. 9 is a diagram showing a locus drawn by the impedance of the sensor main body when the frequency of the input AC voltage superimposed on the DC voltage for air-fuel ratio detection is changed.

FIG. 10 is a diagram showing a relationship between a frequency of an input AC voltage and an element impedance.

FIG. 11 is a diagram illustrating waveforms of an input voltage to an LPF, an input voltage to an atmosphere-side electrode of an air-fuel ratio sensor, and an output current from an air-fuel ratio sensor.

FIG. 12 is a characteristic diagram showing how the exhaust gas temperature THEG changes according to the engine speed NE and the engine load LD.

FIG. 13 is a time chart showing a change in element temperature and a change in element impedance when energization is temporarily cut off during energization of the heater.

FIG. 14 is a flowchart (1/2) showing a processing procedure of an exhaust gas temperature estimation routine according to the first embodiment.

FIG. 15 is a flowchart (2/2) showing a processing procedure of an exhaust gas temperature estimation routine according to the first embodiment.

FIG. 16 is a diagram showing a map for obtaining an exhaust gas temperature from an increase in element impedance when current supply to a heater is cut off for a certain period of time.

FIG. 17 shows a map for obtaining the exhaust gas temperature THEG from the element temperature THSE when the heater is not driven.

FIG. 18 is a flowchart (1/2) showing a processing procedure of an exhaust gas temperature estimation routine according to the second embodiment.

FIG. 19 is a flowchart (2/2) showing a processing procedure of an exhaust gas temperature estimation routine according to the second embodiment.

FIG. 20 is a diagram showing a map for obtaining an exhaust gas temperature from a required time for restoring element impedance when energization of a heater is cut off for a predetermined time.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Air-fuel ratio sensor (A / F sensor) 11 ... Cover 12 ... Small hole 13 ... Sensor main body 14 ... Oxygen ion conductive solid electrolyte layer (sensor element) 15 ... Diffusion resistance layer 16 ... Exhaust side electrode layer 17 ... Atmospheric side Electrode layer 18 Heater 20 Sensor main body drive circuit 21 Low-pass filter (LPF) 22 First voltage follower circuit 23 Current detection circuit 25 Reference voltage generation circuit 26 Second voltage follower circuit 30 Heater drive circuit 32 battery 40 CPU 90 exhaust pipe of internal combustion engine

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) G01N 27/46 325E 325N (72) Inventor Shinsuke Inagaki 1 Toyota Town, Toyota City, Aichi Prefecture F-term (in Toyota Motor Corporation) Reference) 3G084 BA00 DA13 DA25 EA05 EA07 EB08 FA18 FA27 FA29 FA33

Claims (6)

[Claims] 1. A sensor main body for generating a limit current according to an oxygen concentration or an unburned gas concentration in exhaust gas with the application of a voltage, and an oxygen ion conductive element in the sensor main body for heating and activating the oxygen ion conductive element. An air-fuel ratio sensor having a heater, an element impedance detecting means for detecting an element impedance of the oxygen ion conductive element, and temporarily stopping energization while the energization to the heater is being performed, and detecting the element impedance by the element impedance detecting means. An exhaust gas temperature estimating means for estimating the exhaust gas temperature based on the state of the change in the element impedance to be performed in accordance with the cut. 2. A non-energizing exhaust temperature estimating means for estimating an exhaust temperature based on an element impedance detected by the element impedance detecting means while energization of the heater is not being performed. 2. The exhaust gas temperature measuring device according to 1. 3. The exhaust gas temperature measuring device according to claim 1, wherein said exhaust gas temperature estimating means at the time of energization estimates the exhaust gas temperature based on a rise rate of the element impedance when the energization is cut off. 4. The exhaust gas temperature measuring device according to claim 1, wherein said energized exhaust gas temperature estimating means estimates the exhaust gas temperature based on an increase in element impedance when energization is cut off for a predetermined time. 5. The exhaust gas temperature measuring device according to claim 1, wherein said exhaust gas temperature estimating means at the time of energization estimates the exhaust temperature based on a decrease rate of the element impedance when the energization is started again after the energization is cut. apparatus. 6. The energization-time exhaust temperature estimating means, after cutting energization for a certain period of time, from the time when energization is started again,
The exhaust temperature measuring device according to claim 1, wherein the exhaust temperature is estimated based on a time required until the element impedance returns to a value before the energization cut.