JP3972432B2 - Learning apparatus for oxygen concentration sensor for internal combustion engine control and learning method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an oxygen concentration sensor learning device for controlling an internal combustion engine that learns a reference value of an oxygen concentration sensor that detects an oxygen concentration in exhaust gas discharged from an internal combustion engine, and a learning method thereof.
[0002]
[Prior art]
The oxygen concentration sensor installed in the exhaust passage of the internal combustion engine has a problem that the detection accuracy decreases due to individual differences (variation) in the manufacturing stage and deterioration with time. In order to solve this problem, Japanese Patent Application Laid-Open No. 58-57050 discloses that in a gasoline lean burn engine, it is determined that the exhaust passage is filled with air after a certain period of time during deceleration when fuel is cut, and oxygen at that time is determined. There has been proposed a technique for calibrating the relationship between the output signal of the oxygen concentration sensor and the oxygen concentration using the output signal of the concentration sensor as a reference value.
[0003]
In Japanese Patent Laid-Open No. 62-267544, in a gasoline lean burn engine, it is determined that the exhaust passage is filled with air after a lapse of a certain time after the engine is stopped, and the output signal of the oxygen concentration sensor at that time is used as a reference value. As a technique, a technique for calibrating the relationship between the output signal of the oxygen concentration sensor and the oxygen concentration has been proposed.
[0004]
[Problems to be solved by the invention]
Both of the above-mentioned two technologies have been proposed for gasoline lean burn engines. Recently, diesel engines have also been proposed for EGR (exhaust gas recirculation system) using an oxygen concentration sensor in order to improve the exhaust gas purification rate. ) Etc. are considered.
[0005]
However, when the former technique (Japanese Patent Laid-Open No. 58-57050) is applied to a diesel engine, the oxygen concentration in the atmosphere cannot be accurately detected. The result is shown in FIG. When the fuel is cut during deceleration, the output signal of the oxygen concentration sensor rises and approaches the oxygen concentration in the atmosphere, but the output signal falls before reaching the oxygen concentration in the atmosphere, and then the oxygen in the atmosphere slowly It approached the concentration. The sensor element temperature at this time decreases rapidly after the start of fuel cut and then increases slowly. This is because in gasoline engines, the throttle valve is throttled during deceleration when the fuel is cut, so the exhaust flow rate is small, whereas in diesel engines, the exhaust flow rate for the cylinder volume flows even during deceleration when the fuel is cut. In addition, it is considered that the oxygen concentration sensor is suddenly cooled after the fuel cut is started and the sensor element temperature is suddenly lowered, so that the limit current proportional to the oxygen concentration cannot be detected and the output signal drops.
[0006]
Generally, since an oxygen concentration sensor with a heater that raises the temperature of the sensor element to the activation temperature with a heater is used as the oxygen concentration sensor, even if the sensor element temperature suddenly drops after the fuel cut starts as described above, The sensor element temperature gradually rises due to the heater heating, and the output signal gradually approaches the oxygen concentration in the atmosphere. However, in this case, it takes a long time for the output signal to reach the atmospheric oxygen concentration level by the amount that the output signal temporarily decreases due to the temperature decrease of the sensor element after the start of fuel cut.
[0007]
In a general driving pattern, the deceleration operation is often about several seconds, and fuel injection is resumed when the engine speed falls below a predetermined value during the deceleration operation, so the fuel cut time is less than a few seconds. In many cases, the output signal does not reach the atmospheric oxygen concentration level by the end of the fuel cut, and the atmospheric oxygen concentration cannot be detected accurately.
[0008]
In particular, in a vehicle equipped with an automatic transmission, when the vehicle decelerates, the engine speed quickly decreases to the idle speed and the exhaust (atmospheric) flow rate decreases, so the time required for the exhaust passage to be filled with air. Therefore, it is expected that there will be more and more cases where the oxygen concentration in the atmosphere cannot be accurately detected in combination with the above situation.
[0009]
In addition, the difference in deceleration rate, for example, deceleration from 70 km / h and deceleration from 40 km / h, the time until the exhaust passage is filled with the atmosphere changes. In order to determine that the condition is satisfied, it is necessary to set a sufficiently long time as a certain time. Therefore, this also increases the number of cases where the atmospheric oxygen concentration cannot be accurately detected.
[0010]
When the latter technique (Japanese Patent Laid-Open No. 62-267544) is applied to a diesel engine, it takes a very long time to detect the oxygen concentration in the atmosphere. The result is shown in FIG. When the engine is stopped, the output signal of the oxygen concentration sensor rises a little, but then rises only slowly. The sensor element temperature at this time rapidly decreases after the engine stops when the flow of exhaust stops, and then slowly increases due to heater heating. Although the sensor element temperature is higher in FIG. 17 than in FIG. 16, the output signal rises only slowly, which is considered to be due to the difference in the exhaust gas components when the engine is stopped.
[0011]
In other words, the fuel is cut quickly when the engine is stopped, and after a few revolutions due to the inertia of the engine, the fuel is cut. However, since the fuel is cut during these several revolutions, the air drawn through the intake passage is exhausted. It flows through the passage and approaches the oxygen concentration in the atmosphere in the exhaust passage. On the other hand, in order to reduce vibration when the engine is stopped, the diesel engine greatly reduces the intake air amount by the intake throttle valve before cutting the fuel, and after the injected fuel misfires and the diesel engine stops, Is cut. Therefore, during the period until the diesel engine is stopped, exhaust gas containing a large amount of unburned fuel flows in the exhaust passage. For this reason, it takes a very long time to detect the oxygen concentration in the atmosphere.
[0012]
By the way, as shown in FIG. 3, the relationship between the sensor element applied voltage of the oxygen concentration sensor and the limit current of the oxygen concentration sensor (which will be described later) changes according to the oxygen concentration, and the higher the oxygen concentration, Since the limit current increases, the oxygen concentration can be detected by detecting the limit current. However, in order to accurately detect the limit current corresponding to the oxygen concentration, it is necessary to increase the sensor element applied voltage as the oxygen concentration increases. The oxygen concentration in the atmosphere is considerably higher than the oxygen concentration in the exhaust before the start of the fuel cut, but in the above two publications, the same as when detecting the oxygen concentration in the exhaust before the start of the fuel cut. Since the atmospheric oxygen concentration is detected by the sensor element applied voltage, there is also a drawback that the atmospheric oxygen concentration cannot be accurately detected.
[0013]
The present invention has been made in view of such circumstances. Therefore, the object of the present invention is to accurately detect the oxygen concentration in the atmosphere with an oxygen concentration sensor installed in the exhaust passage and learn it as a reference value. An oxygen concentration sensor learning device for controlling an internal combustion engine and a learning method therefor are provided.
[0014]
[Means for Solving the Problems]
As is apparent from the characteristics of the oxygen concentration sensor shown in FIG. 3, in order to accurately detect the limit current corresponding to the oxygen concentration, it is preferable to increase the sensor element applied voltage as the oxygen concentration increases.
[0015]
  In consideration of this sensor characteristic, in claim 1 of the present invention, when the internal combustion engine is fuel cut,Limit current detection methodA learning period for learning the reference value of the oxygen concentration sensor is set, and the applied voltage of the sensor element of the oxygen concentration sensor is increased during this learning period.In the stateOutput signal of oxygen concentration sensorAs the limit current is detected, itIs learned by learning means with reference value. Thus, by increasing the sensor element applied voltage during the learning period, the reference value of the oxygen concentration sensor (the oxygen concentration in the atmosphere)Limit current corresponding to) With high accuracy.
[0016]
  The invention of claim 1 can be applied to both an oxygen concentration sensor with a heater and an oxygen concentration sensor without a heater. When an oxygen concentration sensor with a heater is used, as in claim 2, A learning period for learning the reference value of the oxygen concentration sensor when the internal combustion engine is fuel cut is set.Increasing the applied voltage to the sensor element andIncrease the power supplied to the heaterIn the stateOutput signal of the oxygen concentration sensorAs the limit current is detected, itYou may make it learn as a reference value. As described above, when the power supplied to the heater of the oxygen concentration sensor is increased during the learning period, the decrease in the sensor element temperature can be suppressed, and the decrease in the sensor element temperature is caused.Limit currentCan be suppressed. As a result, the oxygen concentration sensorLimit currentCan take less time to reach the atmospheric oxygen concentration level, even if the fuel cut time is relatively short,Due to the effects of increased sensor element applied voltage and heater power supplyOxygen concentration sensor reference value (atmospheric oxygen concentrationLimit current corresponding to) With high accuracy.
[0017]
In this case, since the fuel cut is performed when the engine is decelerated and when the engine is stopped, the reference value of the oxygen concentration sensor can be learned both when the engine is decelerated and when the engine is stopped. When the reference value is learned during the fuel cut period during deceleration, the exhaust flow rate flowing through the exhaust passage after the start of the fuel cut is integrated as in claim 3, and when the accumulated exhaust flow rate reaches a predetermined value It is preferable to learn using the output signal of the oxygen concentration sensor as a reference value. In this way, even if there is a situation in which the time until the exhaust passage is filled with the atmosphere changes due to the difference in the deceleration rate, the time can be accurately determined based on the integrated exhaust flow rate. A decrease in learning accuracy due to the difference can be avoided. Moreover, in any deceleration state, the learning period can be set to the minimum necessary, enabling rapid learning of the reference value, as well as oxygen supply by increasing the supply power to the heater and the applied voltage to the sensor element. The load on the concentration sensor can be reduced, leading to improved durability of the oxygen concentration sensor.
[0018]
Further, as in claim 4, an intake throttle valve is provided in the intake passage of the internal combustion engine, and the intake throttle valve is controlled in the closing direction during the learning period during fuel cut during deceleration, so that the intake air flow rate and thus the exhaust gas are controlled. The flow rate may be reduced. In this way, the temperature drop of the oxygen concentration sensor due to the exhaust flow rate during fuel cut can be reduced, and the power supplied to the heater of the oxygen concentration sensor can be saved accordingly.
[0019]
By the way, in an internal combustion engine equipped with an exhaust gas recirculation device (hereinafter referred to as “EGR”), part of the exhaust discharged from the internal combustion engine is returned to the intake system during the operation of the EGR. When operating, a part of the combustion gas before the fuel cut will continue to circulate without being discharged indefinitely, and the exhaust passage is prevented from being filled with the atmosphere.
[0020]
As a countermeasure against this, in the internal combustion engine with EGR, it is preferable to set the learning period to a period in which the internal combustion engine is fuel cut and the EGR stops exhaust gas recirculation. In this way, the remaining combustion gas in the internal combustion engine and the exhaust passage can be quickly discharged from the exhaust passage during the learning period without being circulated, and the exhaust passage can be quickly filled with the atmosphere.
[0021]
In general, in a vehicle with an automatic transmission, if the fuel is cut at the time of deceleration, the rotational speed of the internal combustion engine is instantaneously reduced to the idle rotational speed immediately after the fuel cut, so that the intake air flow rate is reduced. It takes a long time to fill the exhaust passage with the atmosphere.
[0022]
As a countermeasure against this, in a vehicle with an automatic transmission, as in claim 6, the automatic transmission may be controlled to reduce the decrease in the rotational speed of the internal combustion engine or increase the rotational speed during the learning period. This control may be performed, for example, by connecting a lockup clutch of an automatic transmission or increasing a gear ratio. In this way, the decrease in the intake air flow rate during the learning period can be reduced, and the time until the exhaust passage is filled with the atmosphere can be shortened accordingly. This makes it possible to quickly learn the reference value and reduce the load on the oxygen concentration sensor due to an increase in power supplied to the heater and an increase in the applied voltage to the sensor element, improving the durability of the oxygen concentration sensor. It also leads to.
[0023]
Further, when the learning period is set when the fuel is cut by the engine stop control, the intake throttle valve may be held at the valve open position during the learning period. In this way, even when the reference value is learned during engine stop control, the flow rate of air (atmosphere) flowing from the intake passage to the exhaust passage through the internal combustion engine can be secured, and the exhaust passage is filled with the atmosphere. Can be shortened, and the same effect as described above can be obtained.
[0024]
  In the case of using an oxygen concentration sensor with a heater, claims1,As shown in Fig. 8, the learning period is set when the fuel is cutToApplied voltage to sensor elementIncreaseLearning using the output signal of the oxygen concentration sensor as a reference valueEvengood. Of course, it goes without saying that the output signal of the oxygen concentration sensor may be learned as a reference value while executing both an increase in the power supplied to the heater and an increase in the applied voltage to the sensor element.
[0025]
Incidentally, as is apparent from the output characteristics of the oxygen concentration sensor shown in FIGS. 19 and 21, the output of the oxygen concentration sensor changes in accordance with changes in the sensor element temperature and the exhaust pressure.
[0026]
  Considering this point, the temperature of the sensor element as in claim 9The temperatureDetected by the detection means, during the fuel cut period of the internal combustion engine,temperatureSensor element temperature detected by the detection meansEvery timeBased on this, the output signal of the oxygen concentration sensor may be corrected, and the learning value may be learned by using the correction value as a reference value.In this case, in consideration of the output change characteristic related to the sensor element temperature shown in FIG. 19, the temperature of the sensor element detected by the temperature detecting means is in a temperature range where the temperature is equal to or lower than a predetermined output stable temperature range. It is preferable that correction is performed so that the output signal of the oxygen concentration sensor increases as the temperature of the sensor element decreases (see FIG. 20).
  Alternatively, the exhaust pressure is detected by the exhaust pressure detecting means, and the output signal of the oxygen concentration sensor is output based on the exhaust pressure detected by the exhaust pressure detecting means during the fuel cut period of the internal combustion engine. Correction may be performed and learning may be performed by the learning unit using the correction value as a reference value. In this case, in consideration of the output change characteristic related to the exhaust pressure shown in FIG. 21, the correction is made so that the output signal of the oxygen concentration sensor decreases as the exhaust pressure detected by the exhaust pressure detecting means becomes higher. It is preferable to do so (see FIG. 22).
  In the invention according to claims 9 to 12,Even if the sensor element temperature and the exhaust pressure change depending on the operating state of the internal combustion engine and the output signal of the oxygen concentration sensor changes due to the change, the change in the output signal due to the sensor element temperature and the exhaust pressure is corrected to The reference value (atmospheric oxygen concentration) of the concentration sensor can be learned with high accuracy.
[0027]
Japanese Patent Publication No. 5-41821 discloses a technique for correcting the target air-fuel ratio in accordance with the exhaust pressure during the operation of the internal combustion engine. There is no function to learn the oxygen concentration), and the reference value is not corrected by the exhaust pressure. For this reason, there is a problem that the detection accuracy of the oxygen concentration is lowered due to individual differences (variation) of the oxygen concentration sensor in the manufacturing stage and deterioration with time. In this respect, the present invention learns the reference value (atmospheric oxygen concentration) of the oxygen concentration sensor during the fuel cut period, so that it is possible to eliminate the influence of individual differences (variation) in the oxygen concentration sensor and deterioration over time at the manufacturing stage. The detection accuracy of oxygen concentration can be improved.
[0028]
  Further, when detecting the exhaust pressure, an exhaust pressure sensor may be installed in the exhaust passage to directly detect the exhaust pressure.13As described above, the exhaust pressure may be estimated based on the operating state of the internal combustion engine. For example, when the operating state of the internal combustion engine changes, such as the engine speed, accelerator opening, vehicle speed, intake pipe pressure, EGR rate, etc., the exhaust pressure changes accordingly, so the exhaust pressure is adjusted based on the operating state of the internal combustion engine. It is possible to estimate. For this reason, it is not necessary to newly provide an exhaust pressure sensor, and it is possible to satisfy the demands for reducing the number of parts and reducing the cost.
[0029]
  Further claims14like,By means of learningBased on the corrected output signal of the oxygen concentration sensor, the presence or absence of abnormality of the oxygen concentration sensor may be determined by the sensor abnormality determination means. In this way, it is possible to accurately determine whether there is an abnormality in the oxygen concentration sensor by eliminating the influence of changes in sensor element temperature and exhaust pressure.
[0030]
  Claims9, 11,As shown in FIG. 15, the degree of clogging of the exhaust passage is determined by the degree-of-clogging determination means based on the difference or ratio between the output signal of the oxygen concentration sensor during the fuel cut period and the output signal of the oxygen concentration sensor while the internal combustion engine is stopped. Anyway. In other words, as the degree of clogging of the exhaust passage (for example, clogging of the catalyst or the like) increases, the exhaust resistance of the exhaust passage increases to increase the exhaust pressure. As the exhaust pressure increases, the oxygen pressure increases as shown in FIG. The output of the density sensor increases. On the other hand, when the internal combustion engine is stopped, the exhaust pressure does not work, so the exhaust passage is filled with atmospheric air regardless of whether the exhaust passage is clogged, and the output signal of the oxygen concentration sensor under atmospheric pressure is obtained. It is done.
[0031]
From this relationship, if the difference or ratio between the output signal of the oxygen concentration sensor during the fuel cut period and the output signal of the oxygen concentration sensor while the internal combustion engine is stopped, the exhaust pressure is high depending on whether the difference or ratio is large. It is possible to determine whether the exhaust passage is clogged.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment (1)]
Hereinafter, an embodiment (1) in which the present invention is applied to a diesel engine will be described with reference to FIGS. 1 to 10.
[0033]
First, the overall configuration of the engine control system will be described with reference to FIG. An airflow sensor 12 for detecting the amount of intake air is installed in an intake pipe 11 (intake passage) of a diesel engine 10 that is an internal combustion engine, and an intake throttle valve 13 is installed on the downstream side of the airflow sensor 12. . This intake throttle valve 13 is not interlocked with the accelerator operation, and for the purpose of reducing vibrations when the engine is stopped, the intake throttle valve 13 is closed before the fuel is cut to greatly reduce the intake air amount. After the fired fuel is misfired and the diesel engine 10 is stopped, the fuel is cut. In addition, when a large amount of EGR flow is recirculated by the EGR 21 described later, the opening degree of the intake throttle valve 13 is decreased to reduce the intake air amount and increase the EGR rate.
[0034]
A fuel injection valve 14 is attached to each cylinder of the diesel engine 10, and fuel accumulated at a high pressure from a high-pressure fuel pump 15 is supplied to each fuel injection valve 14 through a fuel pipe 16. The high-pressure fuel pump 15 is equipped with a fuel injection control valve 40 that controls fuel injection by an injection signal output from an ECU 36 described later.
[0035]
On the other hand, between the exhaust pipe 17 (exhaust passage) of the diesel engine 10 and the intake pipe 11, an EGR pipe 18 that recirculates a part of the exhaust to the intake pipe 11 is connected, and an EGR valve is provided in the middle of the EGR pipe 18. 19 is provided. The EGR valve 19 has its valve opening adjusted by an EGR control valve 20, and the EGR flow rate passing through the EGR pipe 18 is controlled by adjusting the opening. The EGR pipe 18, EGR valve 19, and EGR control valve 20 constitute an exhaust gas recirculation device (EGR) 21.
[0036]
A limit current detection type oxygen concentration sensor 22 for detecting the oxygen concentration in the exhaust gas is installed in the middle of the exhaust pipe 17. The oxygen concentration sensor 22 has a structure as shown in FIG. 2, and the structure will be specifically described below. The oxygen concentration sensor 22 includes a sensor element 23 that generates a limit current corresponding to the oxygen concentration in the exhaust, a heater 24 that heats the sensor element 23 from the inside, and a cover 25 that covers the sensor element 23. A vent hole 25a into which exhaust gas flows is formed in the bottom surface portion of 25.
[0037]
The sensor element 23 includes a solid electrolyte layer 26 formed in a test tube, an atmosphere-side electrode 27 and an exhaust-side electrode 28 fixed to the inner and outer peripheral surfaces of the solid electrolyte layer 26, and an outer peripheral surface of the solid electrolyte layer 26. The diffusion layer 29 is formed, air is introduced into the solid electrolyte layer 26, and the outer peripheral surface of the diffusion layer 29 is exposed to exhaust gas. The solid electrolyte layer 26 is made of ZrO.₂(Zirconia), HfO₂, ThO₂, Bi₂O_ThreeEtc. CaO, MgO, Y₂O_Three, Yb₂O_ThreeOr the like as a stabilizer. The diffusion layer 29 is formed of a porous sintered body of a heat resistant inorganic material such as alumina, magnesia, siliceous, spinel, mullite or the like. Both the atmosphere side electrode 27 and the exhaust side electrode 28 are formed of a noble metal having high catalytic activity such as platinum.
[0038]
On the other hand, the heater 24 is accommodated in the sensor element 23, and the sensor element 23 (atmosphere side electrode 27, solid electrolyte layer 26, exhaust side electrode 28, and diffusion layer 29) is heated by the amount of heat generated thereby. Activate.
[0039]
The atmosphere side electrode 27 and the exhaust side electrode 28 are connected to a voltage control unit 31 via lead wires 30a and 30b, and the voltage applied between the electrodes 27 and 28 is controlled by the voltage control unit 31. Further, an oxygen ion current flowing through the solid electrolyte layer 26 is detected by the current detection unit 32 via the voltage control unit 31 with a voltage applied between the electrodes 27 and 28. The heater 24 is connected to the power control unit 34 via lead wires 33a and 33b, and the power control unit 34 controls the power supplied to the heater 24. The power control unit 34, the voltage control unit 31, and the current detection unit 32 constitute a sensor control circuit 35. The sensor control circuit 35 performs the above-described control based on an applied voltage command and a supply power command from an engine control electronic control unit (hereinafter referred to as “ECU”) 36.
[0040]
On the other hand, the ECU 36 detects the operating state of the diesel engine 10 based on signals read from the airflow sensor 12, the accelerator sensor 37, the engine speed sensor 38, and the vehicle speed sensor 39 shown in FIG. The timing is calculated, the injection signal is output to the fuel injection control valve 40, and the oxygen concentration in the exhaust gas is detected based on the limit current of the oxygen concentration sensor 22 detected by the current detection unit 32 of the sensor control circuit 35. Based on the detected value, the flow rate of the EGR 21 is controlled so that the oxygen concentration in the exhaust gas matches the target exhaust oxygen concentration, thereby reducing the NOx emission amount.
[0041]
Next, the operation of the limiting current detection type oxygen concentration sensor 22 will be described with reference to FIG. FIG. 3 shows sensor characteristics when the temperature of the sensor element 23 is constant at a predetermined temperature (eg, 700 ° C.) within the active temperature range. The horizontal axis represents the voltage applied to the solid electrolyte layer 26, and the vertical axis represents The oxygen ion current detected by the oxygen concentration sensor 22 is taken. For convenience of explanation, the case where the oxygen concentration is 7% will be described as an example. When the applied voltage is a, the detected current increases corresponding to the increase of the applied voltage, and when the applied voltage is between a and b, the applied voltage is Even if it increases, the detected current becomes almost constant (this becomes the limit current). Therefore, when the applied voltage is between a and b, a limit current limited by the diffusion speed of the gas diffusing inside the diffusion layer 29 can be detected.
[0042]
Further, the resistance value of the sensor element 23 can be calculated from the detected current when the applied voltage is a, and the temperature of the sensor element 23 can be estimated from the temperature characteristics of the sensor element 23 based on this resistance value. When the applied voltage exceeds b, the detection current increases again. This is because water vapor in the gas diffusing inside the diffusion layer 29 is decomposed to generate oxygen ions. Therefore, the limit current corresponding to the oxygen concentration in the gas can be detected when the applied voltage is between a and b. Usually, in order to perform stable detection, the applied voltage is set to c, which is between a and b.
[0043]
Further, the relationship between the applied voltage and the limit current changes according to the oxygen concentration, and the limit current increases as the oxygen concentration increases. Therefore, the oxygen concentration can be detected by detecting the limit current. However, in order to detect the limit current corresponding to the oxygen concentration stably and accurately, it is necessary to increase the applied voltage as the oxygen concentration increases. From this viewpoint, for example, the applied voltage d is set at an oxygen concentration of 13%, and the applied voltage e is set at an oxygen concentration of 20%.
[0044]
Next, sensor characteristics when the sensor element temperature changes will be described with reference to FIG. In FIG. 4, the sensor characteristic when the oxygen concentration is 20% and the sensor element temperature is 700 ° C. is indicated by a solid line, and the sensor characteristic when the sensor element temperature is 550 ° C. is indicated by a dotted line. When the sensor element temperature decreases, the resistance value of the sensor element 23 increases, so the rate of increase in the detected current with respect to the increase in applied voltage decreases, and the gas diffusion rate in the diffusion layer 29 is also somewhat affected by temperature. The limit current also changes slightly. Therefore, in order to detect the oxygen concentration with high accuracy, it is necessary to reliably maintain the sensor element temperature at a certain temperature or higher, or to set the applied voltage higher than usual. For example, even when the sensor element temperature is 550 ° C., the detection accuracy is improved by setting the applied voltage from normal e to higher f. Here, it is necessary to increase the power supplied to the heater 24 in order to ensure that the sensor element temperature is kept above a certain temperature during deceleration or the like, but avoid excessive power increase due to the high temperature durability of the heater 24. In addition, it is necessary to shorten the time when the temperature of the heater 24 is higher than usual.
[0045]
In addition, setting the applied voltage higher than usual may degrade the oxygen concentration detection accuracy due to the decomposition of water vapor as described above. It is preferable to set it to 2.0V. If the diesel engine 10 is in a normal operating state, several percent of water vapor is contained in the exhaust, but when the fuel is cut, the water vapor concentration in the exhaust becomes the same level as the water vapor concentration in the atmosphere. The water vapor concentration in the exhaust gas is extremely low compared to the water vapor concentration in the exhaust gas during normal operation. Therefore, even if the applied voltage is set higher than usual during fuel cut, the decrease in detection accuracy of oxygen concentration due to decomposition of water vapor is relatively small.
[0046]
Considering the characteristics of the oxygen concentration sensor 22 described above, the ECU 36 has a learning period during which the reference value of the oxygen concentration sensor 22 is learned during the period in which the diesel engine 10 is fuel-cut in the deceleration state (fuel cut during deceleration). The output signal of the oxygen concentration sensor 22 (limit current corresponding to the oxygen concentration in the atmosphere) is set as a reference value while increasing the supply power to the heater 24 and increasing the voltage applied to the sensor element 23 during this learning period. learn. The ROM (storage medium) built in the ECU 36 stores the atmospheric oxygen concentration learning program shown in FIGS. 5 and 6 in order to execute the learning process described above. The ECU 36 plays a role as a learning means in the claims by repeatedly executing this atmospheric oxygen concentration learning program every predetermined time or every predetermined crank angle.
[0047]
The contents of the atmospheric oxygen concentration learning program shown in FIGS. 5 and 6 will be described below. When this program is started, first, in step 101, signals output from the accelerator sensor 37, the engine speed sensor 38, and the airflow sensor 12 are read in order to detect the engine operating state. Thereafter, in step 102, it is determined from the signals from the accelerator sensor 37 and the engine speed sensor 38 whether the fuel cut condition during deceleration is satisfied. Here, the fuel cut condition for deceleration is, for example, that the accelerator is fully closed and the engine speed is 1500 rpm or more. When these two conditions are satisfied, the fuel cut condition for deceleration is satisfied. If the fuel cut condition during deceleration is not satisfied, the learning process is not performed, the process jumps from step 102 to step 113, the normal power is supplied to the heater 24 of the oxygen concentration sensor 22, and the sensor element 23 is normally supplied. The oxygen concentration sensor 22 is controlled in a normal control mode in which a voltage is applied.
[0048]
On the other hand, if the fuel cut condition during deceleration is satisfied, the process proceeds from step 102 to step 103, the output of the injection signal to the fuel injection control valve 40 is stopped, and the fuel cut is executed. At 104, it is determined whether or not atmospheric oxygen concentration learning is necessary. For example, when atmospheric oxygen concentration learning has never been performed until now, or when a predetermined total travel distance has been reached since the previous atmospheric oxygen concentration learning has been performed, it is determined that atmospheric oxygen concentration learning is necessary. The When the atmospheric oxygen concentration learning is unnecessary, the process proceeds to step 113, and the oxygen concentration sensor 22 is controlled in the normal control mode.
[0049]
If atmospheric oxygen concentration learning is necessary, the process proceeds from step 104 to step 105, where the temperature of the heater 24 of the oxygen concentration sensor 22 is estimated as follows. For example, the resistance value of the heater 24 is calculated from the voltage and current of the heater 24, and the heater temperature is estimated from the temperature characteristics of the heater 24 based on the resistance value. Thereafter, in step 106, it is determined whether or not the heater temperature of the oxygen concentration sensor 22 is not more than a limit temperature (for example, 1100 ° C.). If it is not more than the limit temperature, the process proceeds to step 107 and the heater 24 is within an allowable range. By supplying the maximum power and maximizing the amount of heat generated by the heater 24, the sensor reduces the temperature drop of the oxygen concentration sensor 22 due to the low temperature exhaust, and can detect the high concentration oxygen concentration in the atmosphere with high accuracy. The applied voltage of the element 23 is set to a voltage higher than normal, and the process proceeds to Step 109.
[0050]
If the temperature of the heater 24 is higher than the limit temperature, the process proceeds from step 106 to step 108, the power supplied to the heater 24 is set to zero, the heat generation of the heater 24 is stopped, and the applied voltage of the sensor element 23 is set to a voltage higher than normal. And go to step 109.
[0051]
In this step 109, in order to determine whether or not the exhaust pipe 17 is filled with the atmosphere by the intake air after the start of the fuel cut, it is determined whether or not the integrated exhaust flow rate after the start of the fuel cut has exceeded a predetermined value. To do. The calculation of the integrated exhaust flow rate after the start of fuel cut is performed by, for example, integrating the signal of the air flow sensor 12 with respect to time, or integrating the exhaust flow rate obtained from the engine speed sensor 38 and the engine exhaust amount with respect to time. The predetermined value is set to a sufficient value necessary for the combustion gas in the exhaust pipe 17 to be swept away by the atmosphere (intake air).
[0052]
If the accumulated exhaust flow after the start of fuel cut does not reach a predetermined value, the combustion gas remains in the exhaust pipe 17, and the program is terminated without performing the subsequent learning process.
[0053]
Thereafter, when the integrated exhaust flow rate after the fuel cut starts reaches a predetermined value or more, it is determined that the exhaust pipe 17 is filled with the atmosphere, and the routine proceeds from step 109 to step 110, where the sensor element temperature is set as follows. presume. For example, the resistance value of the sensor element 23 is calculated from the output current of the sensor element 23, and the sensor element temperature is estimated from the temperature characteristics of the sensor element 23 based on the resistance value. Thereafter, in step 111, it is determined whether or not the sensor element temperature is equal to or higher than a predetermined temperature at which the limit current can be detected (for example, 600 ° C. or higher). Then, the power supplied to the heater 24 of the oxygen concentration sensor 22 and the applied voltage of the sensor element 23 are returned to normal values.
[0054]
On the other hand, when the sensor element temperature is equal to or higher than a predetermined temperature at which the limit current can be detected, the reference value can be learned. Therefore, the process proceeds to step 112, and the atmosphere output from the oxygen concentration sensor 22 at this time A learning process for resetting a signal (limit current) corresponding to the oxygen concentration as a reference value is performed. Thereafter, the process proceeds to step 113, where the power supplied to the heater 24 of the oxygen concentration sensor 22 and the applied voltage of the sensor element 23 are returned to normal values.
[0055]
A control example when the above-described atmospheric oxygen concentration learning program is executed will be described with reference to the time chart of FIG. When the fuel is cut at time 0 seconds during deceleration, the maximum power is instantaneously supplied to the heater 24, the heater temperature rises rapidly, and the heating amount of the sensor element 23 is increased. Therefore, although the sensor element 23 is cooled by the low temperature exhaust gas after the fuel cut, unlike the prior art shown in FIG. 16, the sensor element temperature does not decrease and is kept at the activation temperature of around 700 ° C. Be drunk. Furthermore, after the fuel cut is started, the applied voltage of the sensor element 23 is increased more than usual so that a high-concentration oxygen concentration in the atmosphere can be accurately detected. For this reason, an output corresponding to the oxygen concentration in the exhaust gas after the fuel cut is obtained as the output of the oxygen concentration sensor 22.
[0056]
Since the heater temperature reaches the limit temperature in about 2 seconds from the start of fuel cut, the heater power becomes zero. However, when the heater power becomes zero, the heater temperature immediately falls below the limit temperature, so that the heater power becomes maximum again. Therefore, the maximum electric power and zero time average electric power are applied to the heater 24, but it is larger than the normal heater electric power, and the sensor element temperature is not greatly lowered, but is kept at a predetermined temperature or higher. Then, in about 4 seconds from the start of the fuel cut, the integrated exhaust flow rate after the start of the fuel cut obtained by integrating the signals of the air flow sensor 12 with respect to time becomes equal to or greater than a predetermined value. At this time, the output signal of the oxygen concentration sensor 22 (limit current corresponding to the atmospheric oxygen concentration) is reset as a reference value. Thereafter, the heater power of the oxygen concentration sensor 22 and the sensor element applied voltage are returned to normal values. Thereafter, the sensor element 23 is cooled by the low-temperature exhaust gas, the sensor element temperature decreases, and the output of the oxygen concentration sensor 22 becomes a value lower than the actual oxygen concentration in the exhaust gas.
[0057]
In this case, when the durability of the heater 24 is taken into consideration, it is better to shorten the time during which the heater 24 is near the limit temperature as much as possible. In the present embodiment (1), the exhaust flow rate that has flowed through the exhaust pipe 17 after the start of fuel cut is integrated, and the time when the exhaust pipe 17 is filled with the atmosphere is determined based on the integrated exhaust flow rate. Atmospheric oxygen concentration) is learned, so even if there is a situation in which the time until the exhaust pipe 17 is filled with the air changes due to the difference in the deceleration rate, the time is accurately determined by the integrated exhaust flow rate. It is possible to avoid a decrease in learning accuracy due to a difference in the deceleration rate. In addition, in any deceleration state, the time from the start of fuel cut to the end of learning can be set to the minimum necessary, and a quick reference value can be learned.
[0058]
Furthermore, in order to shorten the time from the start of fuel cut to the end of learning, the engine speed when the fuel is cut may be set higher than usual. When the transmission is a manual transmission, in the fuel cut area during deceleration, the engine brake is applied and the engine speed increases unless the driver disengages the clutch, but an automatic transmission using a fluid coupling is installed. In such a vehicle, since the engine speed is instantaneously reduced to the idle speed after the fuel cut is started, the exhaust flow rate is reduced, and it takes a long time until the exhaust pipe 17 is filled with the atmosphere. End up.
[0059]
As a countermeasure against this, in a vehicle with an automatic transmission, if the automatic transmission is controlled to reduce the decrease in the engine speed or increase the engine speed during the period from when the fuel is cut until the oxygen concentration in the atmosphere is detected, good. For this control, for example, a lock-up clutch of an automatic transmission may be connected or a gear ratio may be increased. In this way, it is possible to reduce the decrease in the exhaust flow rate after the start of the fuel cut, and accordingly, it is possible to shorten the time until the exhaust pipe 17 is filled with the atmosphere. As a result, the reference value can be quickly learned, and the time during which the heater 24 is in the vicinity of the limit temperature can be shortened, and the load on the oxygen concentration sensor 22 can be reduced correspondingly. A decrease in sensor durability can be avoided.
[0060]
In this case, the automatic transmission is not limited to the one that transmits engine power through a fluid coupling, and there is no need to control the transmission ratio by transmitting the engine power using a belt and a pulley and changing the effective radius of the pulley. It may be one using a step transmission.
[0061]
Further, as in the present embodiment (1), in the diesel engine 10 equipped with the EGR 21, part of the exhaust discharged from the diesel engine 10 is returned to the intake system during the operation of the EGR 21. If the EGR 21 continues to operate, a part of the combustion gas before the fuel cut will continue to circulate without being discharged indefinitely, and the exhaust pipe 17 is prevented from being filled with the atmosphere.
[0062]
As a countermeasure, in the diesel engine 10 with the EGR 21, when the reference value is learned during the fuel cut during deceleration, it is preferable to learn the reference value during the period when the EGR 21 stops exhaust gas recirculation. In this way, at the time of learning, the residual combustion gas in the diesel engine 10 and the exhaust pipe 17 can be quickly exhausted from the exhaust passage without being circulated, and a quick reference value can be learned.
[0063]
The reference value (atmospheric oxygen concentration) learned by the above-described atmospheric oxygen concentration learning program of FIGS. 5 and 6 is used to correct the output signal of the oxygen concentration sensor 22. The corrected output signal of the oxygen concentration sensor 22 is used for controlling the EGR 21, for example.
[0064]
The control of the EGR 21 is executed by the EGR control program shown in FIG. This EGR control program is stored in the ROM of the ECU 36 and is repeatedly executed by the ECU 36 at predetermined time intervals or at predetermined crank angles. When the EGR control program is started, first, in step 131, signals output from the engine speed sensor 38, the accelerator sensor 37, and the oxygen concentration sensor 22 are read, and then in step 132, the engine speed sensor 38 and the accelerator are read. A target exhaust oxygen concentration and a reference drive signal for the EGR control valve 20 are calculated from the output signal of the sensor 37.
[0065]
Thereafter, in step 133, the reference value K1 learned in step 112 of FIG. 6, that is, the atmospheric oxygen concentration detected by the actual oxygen concentration sensor 22 having individual differences and deterioration with time, and ideal with no individual differences and deterioration with time. The correction coefficient K1 / K0 is calculated from the ratio with the atmospheric oxygen concentration (ideal sensor output K0) detected by a simple oxygen concentration sensor. For reference, FIG. 9 shows the output relationship between an actual oxygen concentration sensor 22 having errors due to individual differences and deterioration over time and an ideal oxygen concentration sensor without errors.
[0066]
Thereafter, the process proceeds to step 134, where the actual oxygen concentration is obtained by correcting the output of the oxygen concentration sensor 22 by dividing the current output of the oxygen concentration sensor 22 by the correction coefficient K1 / K0 [actual oxygen concentration = current. Oxygen concentration sensor output ÷ (K1 / K0)].
[0067]
In the next step 135, the actual oxygen concentration is compared with the target exhaust oxygen concentration calculated in step 132, and the EGR 21 is controlled as follows according to the comparison result. That is, when the actual oxygen concentration is lower than the target exhaust oxygen concentration, the routine proceeds to step 136 where the reference drive signal is corrected so as to decrease the EGR flow rate, and is output to the EGR control valve 20, and the opening degree of the EGR valve 19 is increased. Decrease. When the actual oxygen concentration matches the target exhaust oxygen concentration, the routine proceeds to step 137, where the reference drive signal is output to the EGR control valve 20 without correction, and the current opening degree of the EGR valve 19 is continuously maintained. If the actual oxygen concentration is higher than the target exhaust oxygen concentration, the routine proceeds to step 138 where the reference drive signal is corrected to increase the EGR flow rate and output to the EGR control valve 20, and the opening degree of the EGR valve 19 is increased. Increase. For reference, the relationship between the drive signal of the EGR control valve 20 and the EGR flow rate is shown in FIG.
[0068]
In this case, since the output of the oxygen concentration sensor 22 is corrected based on the reference value learned with high accuracy, it is possible to accurately correct deviations in the output of the oxygen concentration sensor 22 due to individual differences in the oxygen concentration sensor 22 and deterioration over time. In addition, by controlling the EGR 21 with this correction output, the EGR flow rate can be controlled with high accuracy, and the NOx emission amount can be reduced.
[0069]
The target controlled by the output of the oxygen concentration sensor 22 is not limited to the EGR flow rate, and for example, the fuel injection amount, the intake air amount, and the like may be controlled. The intake air amount may be controlled by adjusting the opening of the intake throttle valve 13.
[0070]
[Embodiment (2)]
11 and 12 are flowcharts showing the flow of processing of the atmospheric oxygen concentration learning program executed in the embodiment (2) of the present invention. The difference from the embodiment (1) is that the intake throttle valve 13 is closed and the intake air is throttled (step 104a) to reduce the exhaust flow rate during the period from the start of fuel cut to the learning of the reference value. This is to reduce the temperature drop of the oxygen concentration sensor 22 due to exhaust. In this case as well, the power supplied to the heater 24 of the oxygen concentration sensor 22 is increased to suppress the temperature drop of the oxygen concentration sensor 22 due to exhaust, but the exhaust flow rate is reduced by the intake throttle valve 13 and the oxygen concentration sensor 22 Since the temperature drop is small, the power supplied to the heater 24 can be less than that of the embodiment (1). After completion of learning, the intake throttle valve 13 is opened to the normal opening (step 113a). The other processes are the same as the processes in FIGS. 5 and 6 of the embodiment (1).
[0071]
[Embodiment (3)]
An embodiment (3) of the present invention will be described with reference to FIGS. In the above-described embodiments (1) and (2), the reference value is learned during the fuel cut during deceleration, but in this embodiment (3), when the fuel is cut by the engine stop control, the intake throttle valve It is characterized in that the reference value is learned after a predetermined time while holding 13 in the open state.
[0072]
As described above, the intake throttle valve 13 is not interlocked with the accelerator operation, and in normal engine stop control, the intake throttle valve 13 is closed before the fuel is cut for the purpose of reducing vibration during engine stop. Thus, the amount of intake air is greatly reduced, and the fuel is cut after the injected fuel is misfired and the diesel engine 10 is stopped. For this reason, in normal engine stop control, exhaust gas in which a large amount of unburned fuel is flowing in the exhaust pipe 17 flows during the period until the diesel engine 10 stops. Therefore, when trying to learn the reference value in normal engine stop control, it takes an extremely long time to detect the oxygen concentration in the atmosphere, which is undesirable from the durability of the oxygen concentration sensor 22.
[0073]
As a countermeasure, in this embodiment (3), when the fuel is cut by the engine stop control by the engine stop control program with the atmospheric oxygen concentration learning function shown in FIGS. 13 and 14, the intake throttle valve 13 is opened. While maintaining, the reference value is learned after a predetermined time. This engine stop control program is stored in the ROM of the ECU 36, and is repeatedly executed by the ECU 36 at predetermined time intervals or at predetermined crank angles. When the engine stop control program is started, first, in step 201, it is determined whether the ignition switch is turned off (that is, whether the engine stop control is performed). If the ignition switch is not turned off, the subsequent processing is performed. End this program.
[0074]
Thereafter, when the ignition switch is turned off, the routine proceeds from step 201 to step 202, where it is determined whether or not atmospheric oxygen concentration learning is necessary. For example, when atmospheric oxygen concentration learning has never been performed until now, or when a predetermined total travel distance has been reached since the previous atmospheric oxygen concentration learning has been performed, it is determined that atmospheric oxygen concentration learning is necessary. The
[0075]
When the atmospheric oxygen concentration learning is unnecessary, normal engine stop control in steps 203 to 206 is performed as follows. That is, before the fuel is cut, the intake throttle valve 13 is closed (step 203), thereby greatly reducing the amount of intake air, causing the injected fuel to misfire and stopping the diesel engine 10 before the fuel cut. Perform (steps 205 and 206). When performing normal engine stop control, it is not necessary to detect the oxygen concentration in the exhaust gas. Therefore, the energization of the heater 24 and the sensor element 23 of the oxygen concentration sensor 22 is stopped after the intake throttle valve 13 is closed. (Step 204).
[0076]
On the other hand, if atmospheric oxygen concentration learning is necessary, the routine proceeds from step 202 to step 207, where the fuel is cut while the intake throttle valve 13 is kept open. Thereafter, in step 208, the maximum electric power within the allowable range is supplied to the heater 24 to maximize the amount of heat generated by the heater 24, thereby suppressing the temperature drop of the oxygen concentration sensor 22 and the high concentration oxygen in the atmosphere. The applied voltage of the sensor element 23 is set to a higher voltage than usual so that the concentration can be detected with high accuracy.
[0077]
In the next step 209, the process waits until the diesel engine 10 stops due to the fuel cut described above. After the engine stops, the process proceeds to step 210, and the heater temperature is estimated by the same method as in the first embodiment (1). Thereafter, in step 211, it is determined whether or not the heater temperature is equal to or lower than a limit temperature (for example, 1100 ° C.). If the limit temperature is exceeded, the power supplied to the heater 24 is set to zero (step 212). The heat generation at 24 is stopped and the routine proceeds to step 213. If the heater temperature is below the limit temperature, the process proceeds to step 213 as it is.
[0078]
In this step 213, it is determined whether or not a predetermined time has elapsed since the engine was stopped. Here, the predetermined time is a time required for the residual combustion gas in the exhaust pipe 17 to be swept out to the atmosphere. If the predetermined time has not elapsed, the process returns to step 210, and the processing from step 210 to step 213 is repeated. Thereafter, when a predetermined time elapses after the engine is stopped, the process proceeds from step 213 to step 214. After the sensor element temperature is estimated by the same method as in the embodiment (1), the sensor element temperature is limited in step 215. It is determined whether or not the temperature is higher than a predetermined temperature at which current can be detected (for example, 600 ° C. or higher). If the temperature is lower than the predetermined temperature, the learning process is not performed and the process proceeds to step 217 to The energization of the element 23 is stopped and this program is terminated.
[0079]
On the other hand, when the sensor element temperature is equal to or higher than a predetermined temperature at which the limit current can be detected, the reference value can be learned. Therefore, the process proceeds to step 216, and the atmosphere output from the oxygen concentration sensor 22 at this time A learning process for resetting a signal (limit current) corresponding to the oxygen concentration as a reference value is performed. Thereafter, the process proceeds to step 217, the energization of the heater 24 and the sensor element 23 of the oxygen concentration sensor 22 is stopped, and this program is terminated.
[0080]
A control example during learning when the engine stop control program described above is executed will be described with reference to the time chart of FIG. When the ignition switch is turned off at time 0 seconds, the fuel is cut while the intake throttle valve 13 is kept open, the maximum power is supplied to the heater 24 of the oxygen concentration sensor 22, and the sensor element 23 is applied. Set the voltage higher than normal. Further, after the fuel cut is started, the applied voltage of the sensor element 23 is set to a higher voltage than usual so that a high-concentration oxygen concentration in the atmosphere can be accurately detected.
[0081]
Since the fuel is cut until the diesel engine 10 is stopped, the air sucked through the intake pipe 11 flows through the exhaust pipe 17, and the inside of the exhaust pipe 17 approaches the oxygen concentration in the atmosphere. At this time, since the maximum power is supplied to the heater 24, the sensor element temperature is not lowered by the heating of the heater 24 even though the sensor element 23 is cooled by the low-temperature exhaust. Therefore, an output corresponding to the oxygen concentration in the exhaust gas can be obtained from the oxygen concentration sensor 22.
[0082]
Since the heater temperature reaches the limit temperature immediately after the fuel cut, the heater power becomes zero. However, as soon as the heater power becomes zero, the heater temperature decreases and the heater power becomes maximum again. Therefore, the maximum electric power and zero time average electric power are applied to the heater 24, but it is larger than the normal heater electric power, and the sensor element temperature is not greatly lowered, but is kept at a predetermined temperature or higher. Then, in about 30 seconds from the start of the fuel cut, the residual combustion gas in the exhaust pipe 17 is purged with the atmosphere. At this time, the output signal of the oxygen concentration sensor 22 (limit current corresponding to the atmospheric oxygen concentration) is reset as a reference value. Thereafter, energization of the heater 24 and the sensor element 23 of the oxygen concentration sensor 22 is stopped. Therefore, the heater 22 and the sensor element 24 are naturally cooled and the temperature is lowered.
[0083]
In this embodiment (3), when the reference value is learned during the engine stop control, the air (from the intake pipe 11 to the exhaust pipe 17 through the diesel engine 10 to keep the intake throttle valve 13 in the open position) ( Air) flow rate can be ensured, and the time until the exhaust pipe 17 is filled with air can be shortened. Thereby, the reference value can be quickly learned, and the load on the oxygen concentration sensor 22 due to the increase in the power supplied to the heater 24 and the increase in the applied voltage to the sensor element 23 can be reduced. Leads to improved durability.
[0084]
  In each of the above embodiments, both the heater supply power and the sensor element applied voltage are increased during the learning period in which the reference value of the oxygen concentration sensor 22 is learned.Increase in sensor element applied voltageIn this case, the learning accuracy can be improved as compared with the prior art.
[0085]
[Embodiment (4)]
  Embodiment (4) of this invention is demonstrated using FIG. 18 thru | or FIG. In this embodiment (4), a catalyst 41 such as an oxidation catalyst, a reduction catalyst, or a three-way catalyst is installed on the downstream side of the oxygen concentration sensor 22, and an exhaust pressure sensor 42 (Exhaust pressureDetection means). The other system configuration is the same as the configuration of FIG. 1 described in the embodiment (1).
[0086]
As shown in FIG. 19, the atmospheric oxygen concentration output voltage (hereinafter simply referred to as “sensor output”) of the oxygen concentration sensor 22 depends on the sensor element temperature, and in the region where the sensor element temperature is 720 ° C. or less, the sensor element temperature The sensor output decreases as the value decreases, and in the region of 720 ° C. to 760 ° C., the sensor output becomes substantially constant even if the sensor element temperature changes. Normally, control of the sensor element temperature (energization control of the heater 24) by the ECU 36 is performed with the sensor output starting to stabilize, for example, 720 ° C. as a target temperature. 760 ° C.), the sensor output changes accordingly.
[0087]
As a countermeasure, in this embodiment (4), the sensor output is corrected using the correction coefficient shown in FIG. 20 according to the sensor element temperature. The characteristic of the correction coefficient is set to be a value corresponding to the sensor output at the target temperature (720 ° C.) when the sensor output is multiplied by the correction coefficient, and in the region below the target temperature (720 ° C.). The lower the sensor element temperature, the larger the correction coefficient. In the region of 720 ° C. to 760 ° C., the correction coefficient becomes a substantially constant value (1.0).
[0088]
Further, as shown in FIG. 21, the sensor output also depends on the exhaust pressure, and the sensor output increases as the exhaust pressure increases. That is, as the exhaust gas pressure increases, the diffusion rate of the gas in the diffusion layer 29 of the sensor element 23 increases and the limit current increases. Therefore, the sensor output increases as the exhaust gas pressure increases, and the rate of increase is increased. Is proportional to approximately the 0.8th power of the exhaust pressure.
[0089]
Therefore, in this embodiment (4), the sensor output is corrected using the correction coefficient shown in FIG. 22 according to the exhaust pressure. The characteristic of the correction coefficient is set to be a value corresponding to the sensor output at the reference exhaust pressure (1 atm) when the sensor output is multiplied by the correction coefficient. The higher the exhaust pressure is, the smaller the correction coefficient is. Become.
[0090]
Correction of the sensor output based on the sensor element temperature and the exhaust pressure described above is performed by the ECU 36. The ECU 36 corrects the output signal of the oxygen concentration sensor 22 based on the sensor element temperature and the exhaust pressure when the diesel engine 10 is decelerated and the fuel is cut, and outputs the corrected output signal (to the oxygen concentration in the atmosphere). The corresponding limit current) is learned as a reference value. A ROM (storage medium) built in the ECU 36 stores the correction coefficient maps shown in FIGS. 20 and 22 and the atmospheric oxygen concentration learning program shown in FIG. 23 in order to execute the learning process described above. The ECU 36 plays the role of learning means in the claims by repeatedly executing this atmospheric oxygen concentration learning program every predetermined period or every predetermined distance.
[0091]
The contents of the atmospheric oxygen concentration learning program in FIG. 23 will be described below. When the program is started, first, in steps 301 to 304, it is determined whether or not the following learning execution conditions (a) to (d) are satisfied.
[0092]
(A) The engine speed is, for example, 1000 rpm or more (step 301).
(B) The accelerator is fully closed (step 302).
(C) The fuel is being cut (step 303).
(D) A predetermined time, for example, 1 second or more has elapsed since the start of fuel cut (step 304)
Here, (a) to (c) are conditions for establishing the fuel cut during deceleration, and (d) is because the exhaust pipe 17 is filled with the atmosphere (intake air) during the fuel cut during deceleration. This is a necessary condition.
[0093]
The learning execution condition is satisfied when all of the conditions (a) to (d) are satisfied, but there is a condition that does not satisfy any one of the conditions (determine “No” in any one of steps 301 to 304). When the learning execution condition is not satisfied, the program is terminated without performing the subsequent processing.
[0094]
When the learning execution condition is satisfied (when all the determinations are “Yes” in steps 301 to 304), that is, when one second or more has elapsed from the start of the fuel cut during deceleration fuel cut, the exhaust pipe 17 , The process proceeds to step 305, and the output of the oxygen concentration sensor 22, the sensor element temperature, and the exhaust pressure (the output of the exhaust pressure sensor 42) are read. Here, the sensor element temperature may be directly detected by the temperature sensor. For example, the resistance value of the sensor element 23 is calculated from the voltage applied to the sensor element 23 and the output current, and the sensor element is based on the resistance value. It may be estimated from the 23 temperature characteristics. Further, in a system without the exhaust pressure sensor 42, the exhaust pressure is detected by, for example, output signals from the air flow sensor 12 (or intake pipe pressure sensor), the accelerator sensor 37, the engine speed sensor 38, the vehicle speed sensor, and the like. You may make it estimate from the engine operating state detected based on an EGR rate.
[0095]
In the next step 306, it is determined whether or not the sensor element temperature is within an output stable temperature range (720 to 760 ° C.) where the limit current can be detected stably and accurately, and the sensor element temperature is determined from the output stable temperature range. If not, the process proceeds to step 307, a correction coefficient corresponding to the sensor element temperature is searched from the correction coefficient map shown in FIG. 20, and the correction coefficient is multiplied by the output of the oxygen concentration sensor 22 to obtain the oxygen concentration. The output of the sensor 22 is corrected according to the sensor element temperature. Thereafter, in step 308, a correction coefficient corresponding to the exhaust pressure is retrieved from the correction coefficient map shown in FIG. 22, and this correction coefficient is multiplied by the output of the oxygen concentration sensor 22 to output the oxygen concentration sensor 22. Is corrected according to the exhaust pressure.
[0096]
On the other hand, if the sensor element temperature is within the stable output temperature range in step 306, there is no need for correction based on the sensor element temperature, so the process proceeds directly to step 308, where only correction based on the exhaust pressure is performed.
[0097]
In this way, after correcting the output signal of the oxygen concentration sensor 22 according to the sensor element temperature and the exhaust pressure, in step 309, the corrected output signal (atmospheric oxygen concentration) of the oxygen concentration sensor 22 is set as a reference value. The learning process is performed again, and this program ends. Thereafter, until the next learning process is performed, the relationship between the output signal of the oxygen concentration sensor 22 and the oxygen concentration is calibrated using this reference value.
[0098]
An execution example of the atmospheric oxygen concentration learning program described above will be described with reference to the time chart of FIG. In the example of FIG. 24, the fuel injection amount is 20 mm when the vehicle is traveling at a steady speed at a vehicle speed of 40 km / h and an engine speed of 1400 rpm.^Three/ St, EGR rate is controlled to 40%. At this time, the sensor element temperature is controlled to the target temperature of 720 ° C. by the heater 24, the output of the oxygen concentration sensor 22 is 3 V, and the exhaust pressure is 1.02 atm.
[0099]
Thereafter, when the accelerator is fully closed at time t, the vehicle is decelerated, and both the vehicle speed and the engine speed decrease. At this time, since the accelerator is fully closed when the engine speed is 1000 rpm or more, fuel cut during deceleration is started, and at the same time, exhaust gas recirculation (EGR) by the EGR 21 is stopped. When the EGR is stopped, the residual combustion gas in the diesel engine 10 and the exhaust pipe 17 is quickly exhausted from the exhaust pipe 17 without being circulated.
[0100]
After the fuel cut is started, the atmosphere is introduced into the exhaust pipe 17 by the pumping effect of the engine 10, and the output of the oxygen concentration sensor 22 increases as the oxygen concentration in the exhaust pipe 17 increases. Further, stopping EGR has the effect of increasing the flow rate of the air flowing into the exhaust pipe 17, so that the exhaust pressure rises at the start of fuel cut. Thereafter, as the engine speed decreases, the flow rate of the air flowing into the exhaust pipe 17 decreases, so that the exhaust pressure also gradually decreases. At this time, the sensor element temperature is maintained at a target temperature of 720 ° C. or higher.
[0101]
One second after the start of the fuel cut, it is determined that the exhaust pipe 17 is filled with the atmosphere, and the learning process is started. At this time, the output of the oxygen concentration sensor 22 indicates, for example, 4.9V. In this case, since the sensor element temperature is within the stable output temperature range (720 to 760 ° C.), the correction of the output of the oxygen concentration sensor 22 is not performed based on the sensor element temperature, but is corrected based on the exhaust pressure. Only done. Thereafter, the corrected output signal (atmospheric oxygen concentration) of the oxygen concentration sensor 22 is learned as a reference value, and thereafter the output signal of the oxygen concentration sensor 22 is used using this reference value until the next learning process is performed. And the oxygen concentration are calibrated. This makes it possible to detect the oxygen concentration that is not affected by fluctuations in the exhaust pressure.
[0102]
In the example of FIG. 24 described above, the sensor element temperature is maintained in the output stable temperature range (720 to 760 ° C.). However, the sensor element temperature is just below the output stable temperature range in order to ensure the durability of the heater 24. It is often controlled at a temperature of 720 ° C. For this reason, when a large amount of air is introduced into the exhaust pipe 17, the sensor element 23 may be cooled and the sensor element temperature may be lowered to less than 720 ° C. In such a case, based on the atmospheric oxygen concentration learning program, the output of the oxygen concentration sensor 22 is corrected based on the sensor element temperature at the time of learning. As a result, it is possible to learn the atmospheric oxygen concentration without being affected by variations in the sensor element temperature.
[0103]
In the above atmospheric oxygen concentration learning program, the output of the oxygen concentration sensor 22 is corrected based on both the exhaust pressure and the sensor element temperature. However, the oxygen concentration sensor is based on only one of the exhaust pressure and the sensor element temperature. The output of 22 may be corrected.
[0104]
Further, in this embodiment (4), the ECU 36 repeatedly executes the exhaust pipe clogging determination program shown in FIG. 25 stored in the ROM every predetermined period or every predetermined distance, thereby the exhaust pipe 17 (exhaust passage). It plays a role as a clogging degree judging means for judging the clogging degree.
[0105]
Here, a method for determining the degree of clogging of the exhaust pipe 17 will be described. As the degree of clogging of the exhaust pipe 17 (for example, clogging of the catalyst 42, etc.) increases, the exhaust resistance of the exhaust pipe 17 increases and the exhaust pressure increases. As the exhaust pressure increases, as shown in FIG. The output signal of the oxygen concentration sensor 22 increases. On the other hand, since the exhaust pressure does not work while the engine is stopped, the exhaust pipe 17 is filled with atmospheric air regardless of whether the exhaust pipe 17 is clogged, and the output signal of the oxygen concentration sensor 22 under atmospheric pressure. Is obtained.
[0106]
From this relationship, if the difference or ratio between the output signal of the oxygen concentration sensor 22 during the fuel cut period and the output signal of the oxygen concentration sensor 22 when the engine is stopped is considered, the exhaust pressure will depend on whether the difference or ratio is large. It can be determined whether or not it is high, whereby the degree of clogging of the exhaust pipe 17 can be determined.
[0107]
The determination of the degree of clogging of the exhaust pipe 17 is executed as follows by the exhaust pipe clogging determination program of FIG. First, in step 311, it is determined whether the engine speed is 1000 rpm or more. In the case of 1000 rpm or more, as in steps 302 to 304 of the atmospheric oxygen concentration learning program of FIG. 23 described above, whether or not 1 second or more has elapsed since the start of the fuel cut during deceleration fuel cut in steps 312 to 314. If one second or more has elapsed, it is determined that the exhaust pipe 17 is filled with the atmosphere, and the process proceeds to step 315. The output S1 of the oxygen concentration sensor 22 at that time is read, and at the time of fuel cut Store as output S1 and proceed to step 319.
[0108]
On the other hand, if it is determined in step 311 that the engine speed is lower than 1000 rpm, the process proceeds to step 316 to determine whether or not the engine is stopped. If the engine is stopped, the process proceeds to step 317 to determine whether or not a predetermined time has elapsed since the engine was stopped. Here, the predetermined time is set to a time sufficient for the exhaust pipe 17 to be filled with the atmosphere after the engine is stopped. If the predetermined time has not elapsed, this program is terminated, and when the predetermined time has elapsed, the process proceeds to the next step 318, where the output S2 of the oxygen concentration sensor 22 at that time is read and used as the engine stop output S2 Store and proceed to step 319.
[0109]
In step 319, an output difference ΔS (= S1−S2) between the fuel cut output S1 of the oxygen concentration sensor 22 and the engine stop output S2 is calculated. Thereafter, in step 320, the degree of clogging of the exhaust pipe 17 is calculated from the output difference ΔS by a mathematical formula, a map, or the like. At this time, the larger the output difference ΔS, the greater the degree of clogging of the exhaust pipe 17 (that is, the exhaust flow becomes worse). Thereafter, in step 321, it is determined whether or not the degree of clogging of the exhaust pipe 17 is within the allowable range. If it is within the allowable range, the program is terminated as it is. Proceeding to 322, it is determined that the exhaust pipe 17 is clogged, and this program ends. When it is determined that the exhaust pipe 17 is clogged, a warning lamp (not shown) is lit to warn the driver.
[0110]
As described above, since the exhaust pipe 17 is filled with the atmosphere during fuel cut during deceleration and when the engine is stopped, the oxygen concentration sensor 22 detects the oxygen concentration (the same oxygen concentration) in the atmosphere. While the engine is stopped, the exhaust flow rate becomes zero, so the exhaust pressure becomes equal to the atmospheric pressure (1 atm). However, at the time of deceleration, the exhaust pressure increases due to an increase in the exhaust flow rate due to EGR cut and exhaust resistance due to the catalyst 41, etc. Bigger than inside. Due to this difference in exhaust pressure, as shown in FIG. 26, the output of the oxygen concentration sensor 22 changes, the fuel cut output S1 is 5V, the engine stop output S2 is 4.8V, and the fuel cut output S1 is The higher the exhaust pressure, the higher the engine stop output S2.
[0111]
When exhaust resistance increases due to clogging of the exhaust pipe 17 due to soot accumulation in the catalyst 41, the exhaust pressure during fuel cut during deceleration increases, and the output of the oxygen concentration sensor 22 also increases accordingly. Accordingly, as the clogging of the exhaust pipe 17 becomes more serious, the output difference ΔS between the fuel cut output S1 and the engine stop output S2 becomes larger. Therefore, the degree of clogging of the exhaust pipe 17 can be determined based on this output difference S. It is possible to determine whether or not the exhaust pipe 17 is clogged by determining whether or not the degree of clogging is within a preset allowable range.
[0112]
In this case, the degree of clogging of the exhaust pipe 17 may be determined by the ratio of S1 and S2 (= S1 / S2) instead of the output difference ΔS between the fuel cut output S1 and the engine stop output S2. .
[0113]
25 may be omitted, and the output of the oxygen concentration sensor 22 read in step 305 in FIG. 23 may be used as the fuel cut output S1.
[0114]
Further, in addition to the catalyst 41, the exhaust pipe 17 may be provided with a particulate trap, an exhaust throttle valve, a silencer, and the like. Even when the exhaust pipe 17 is clogged by these, FIG. The exhaust pipe clogging determination program can determine whether the exhaust pipe 17 is clogged.
[0115]
[Embodiment (5)]
In the embodiment (5) of the present invention shown in FIG. 27, the presence or absence of abnormality of the oxygen concentration sensor 22 is determined based on the output of the oxygen concentration sensor 22 corrected according to the sensor element temperature and the exhaust pressure. Also in this embodiment (5), the output of the oxygen concentration sensor 22 is corrected according to the sensor element temperature and the exhaust pressure by the processes of steps 301 to 308 in the same manner as in the embodiment (4). Thereafter, in step 308a, it is determined whether or not the corrected output of the oxygen concentration sensor 22 is larger than the abnormality determination value. If the corrected output is larger than the abnormality determination value, the process proceeds to step 108b and the oxygen concentration is increased. It is determined that the sensor 22 is abnormal, and the program ends. In this case, a warning lamp (not shown) is lit to warn the driver. The processing of steps 108a and 108b serves as sensor abnormality determination means in the claims.
[0116]
On the other hand, if the corrected output of the oxygen concentration sensor 22 is equal to or less than the abnormality determination value, it is determined that the oxygen concentration sensor 22 is normal, and the process proceeds to step 309 to output the corrected output signal (atmospheric oxygen concentration) of the oxygen concentration sensor 22 ) Is used as the reference value, and the learning process is completed, and the program ends.
[0117]
As described above, if an abnormality of the oxygen concentration sensor 22 is determined using the corrected output of the oxygen concentration sensor 22, the sensor element temperature caused by the engine operating state and the traveling environment (atmospheric pressure change and outside air temperature change due to altitude difference). In addition, it is possible to accurately determine the presence or absence of abnormality of the oxygen concentration sensor 22 by eliminating the influence due to the change of the exhaust pressure or the exhaust pressure, and to improve the accuracy of the abnormality determination of the oxygen concentration sensor 22.
[0118]
In this embodiment (5), the corrected output of the oxygen concentration sensor 22 is compared with the abnormality determination value to determine whether the oxygen concentration sensor 22 is abnormal. However, the corrected output of the oxygen concentration sensor 22 The presence or absence of abnormality of the oxygen concentration sensor 22 may be determined by comparing the difference or ratio with the initial reference value with the abnormality determination value. Here, the initial reference value may be the corrected output of the oxygen concentration sensor 22 in the initial state of the vehicle, or may be an atmospheric oxygen concentration reference value in advance.
[0119]
In other words, the correction of the output signal of the oxygen concentration sensor 22 corrects individual differences (variations) in manufacturing, deterioration with time, and deviation of the output signal due to changes in sensor element temperature and exhaust pressure. If 22 is normal, the output signal will not change significantly before and after the correction. Accordingly, by comparing the correction amount or correction rate of the output signal of the oxygen concentration sensor 22 (that is, the difference or ratio between the corrected output signal and the initial reference value) with a predetermined abnormality determination value, the abnormality of the oxygen concentration sensor 22 is detected. The presence or absence of can be accurately determined.
[0120]
In the above embodiments (1) to (5), the oxygen concentration sensor 22 is not limited to the one with the heater 24, and an oxygen concentration sensor without a heater may be used.
In addition, the internal combustion engine to which the present invention can be applied is not limited to a diesel engine, but can also be applied to an in-cylinder injection (direct injection) gasoline engine, a gasoline lean burn engine, or the like.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an entire diesel engine control system showing an embodiment (1) of the present invention.
FIG. 2 is an enlarged sectional view of the main part of the oxygen concentration sensor.
FIG. 3 is a sensor characteristic diagram showing the relationship between the sensor element applied voltage, the limit current, and the oxygen concentration of the oxygen concentration sensor.
FIG. 4 is a sensor characteristic diagram showing the relationship between the sensor element applied voltage, the limit current, and the sensor element temperature of the oxygen concentration sensor.
FIG. 5 is a flowchart showing a processing flow of an atmospheric oxygen concentration learning program used in the embodiment (1).
FIG. 6 is a flowchart continued from FIG. 5;
FIG. 7 is a time chart showing an example of control when the atmospheric oxygen concentration learning program of the embodiment (1) is executed.
FIG. 8 is a flowchart showing a flow of processing of an EGR control program used in the embodiment (1).
FIG. 9 is a diagram for explaining a difference in sensor characteristics depending on individual differences of oxygen concentration sensors and deterioration with time;
FIG. 10 is a diagram showing a relationship between an EGR control valve drive signal and an EGR flow rate.
FIG. 11 is a flowchart showing a processing flow of an atmospheric oxygen concentration learning program used in the embodiment (2) of the present invention.
FIG. 12 is a flowchart continued from FIG.
FIG. 13 is a flowchart showing a processing flow of an engine stop control program used in the embodiment (3) of the present invention.
FIG. 14 is a flowchart continued from FIG. 13;
FIG. 15 is a time chart showing a control example when the engine stop control program of the embodiment (3) is executed.
FIG. 16 is a time chart showing the behavior of the output of the oxygen concentration sensor and the sensor element temperature after fuel cut during deceleration.
FIG. 17 is a time chart showing the behavior of the output of the oxygen concentration sensor and the sensor element temperature after the engine stops.
FIG. 18 is a configuration diagram of the entire diesel engine control system showing the embodiment (4) of the present invention.
FIG. 19 is a graph showing the relationship between the sensor element temperature of the oxygen concentration sensor and the sensor output.
FIG. 20 is a diagram showing the relationship between the sensor element temperature of the oxygen concentration sensor and the correction coefficient.
FIG. 21 is a graph showing the relationship between the exhaust pressure and the output ratio of the oxygen concentration sensor.
FIG. 22 is a diagram showing the relationship between exhaust pressure and correction coefficient
FIG. 23 is a flowchart showing a processing flow of an atmospheric oxygen concentration learning program used in the embodiment (4) of the present invention.
FIG. 24 is a time chart showing an example of control after fuel cut during deceleration (part 1).
FIG. 25 is a flowchart showing the flow of processing of an exhaust pipe clogging determination program.
FIG. 26 is a time chart showing an example of control after fuel cut during deceleration (part 2).
FIG. 27 is a flowchart showing a processing flow of an atmospheric oxygen concentration learning program used in the embodiment (5) of the present invention.
[Explanation of symbols]
  DESCRIPTION OF SYMBOLS 10 ... Diesel engine (internal combustion engine), 11 ... Intake pipe (intake passage), 12 ... Air flow sensor, 13 ... Intake throttle valve, 14 ... Fuel injection valve, 17 ... Exhaust pipe (exhaust passage), 18 ... EGR piping, 19 ... EGR valve, 20 ... EGR control valve, 21 ... EGR (exhaust gas recirculation device), 22 ... oxygen concentration sensor, 23 ... sensor element, 24 ... heater, 26 ... solid electrolyte layer, 27 ... atmosphere side electrode, 28 ... exhaust side Electrode, 29 ... diffusion layer, 31 ... voltage control unit, 32 ... current detection unit, 34 ... power control unit, 35 ... sensor control circuit, 36 ... ECU (learning means, sensor abnormality determination means, clogging degree determination means), 37 Accelerator sensor, 38 Engine speed sensor, 39 Vehicle speed sensor, 41 Catalyst, 42 Exhaust pressure sensor (Exhaust pressureDetection means).

Claims (15)

In an oxygen concentration sensor learning device for controlling an internal combustion engine that learns a reference value of an oxygen concentration sensor of a limiting current detection method that detects an oxygen concentration in exhaust gas discharged from an internal combustion engine,
The oxygen concentration sensor has a sensor element that outputs a limit current corresponding to the oxygen concentration in the exhaust gas,
Means for controlling the voltage applied to the sensor element;
When the internal combustion engine is fuel cut, a learning period for learning the reference value of the oxygen concentration sensor is set, and an output signal of the oxygen concentration sensor is set in a state where the applied voltage to the sensor element is increased during the learning period. A learning device for an oxygen concentration sensor for controlling an internal combustion engine, comprising learning means for detecting a limit current as a reference value and learning using the limit current as a reference value. In an oxygen concentration sensor learning device for controlling an internal combustion engine that learns a reference value of an oxygen concentration sensor of a limiting current detection method that detects an oxygen concentration in exhaust gas discharged from an internal combustion engine,
The oxygen concentration sensor has a sensor element that outputs a limit current corresponding to the oxygen concentration in the exhaust, and a heater that heats the sensor element,
Means for controlling the voltage applied to the sensor element;
Means for controlling the power supplied to the heater;
A learning period for learning the reference value of the oxygen concentration sensor is set when the fuel in the internal combustion engine is cut, and the applied voltage to the sensor element is increased and the power supplied to the heater is increased during the learning period. A learning device for an oxygen concentration sensor for controlling an internal combustion engine, comprising learning means for detecting a limit current as an output signal of the oxygen concentration sensor in a state of learning and learning the limit current as a reference value.   The learning means sets the learning period to a period in which the internal combustion engine is decelerated in a deceleration state, integrates the exhaust flow rate flowing through the exhaust passage after the fuel cut starts, and the accumulated exhaust flow rate is a predetermined value 3. The learning device for an oxygen concentration sensor for controlling an internal combustion engine according to claim 1, wherein the learning is performed using an output signal of the oxygen concentration sensor as a reference value when the value reaches the reference value. An intake throttle valve is installed in the intake passage of the internal combustion engine;
The learning device for an oxygen concentration sensor for controlling an internal combustion engine according to claim 3, wherein the learning means controls the intake throttle valve in a valve closing direction during the learning period. An exhaust gas recirculation device for recirculating a part of the exhaust gas discharged from the internal combustion engine to the intake system;
5. The learning device according to claim 1, wherein the learning unit sets the learning period to a period in which the internal combustion engine is fuel cut and the exhaust gas recirculation device stops exhaust gas recirculation. A learning device for an oxygen concentration sensor for controlling an internal combustion engine. An automatic transmission is provided in the power transmission system of the internal combustion engine,
When the learning means sets the learning period to a period in which the internal combustion engine is decelerated and fuel is cut, the learning means reduces the decrease in the rotational speed of the internal combustion engine during the learning period. 6. The learning apparatus for an oxygen concentration sensor for controlling an internal combustion engine according to claim 1, wherein control is performed so as to increase the rotational speed. An intake throttle valve is installed in the intake passage of the internal combustion engine;
2. The learning unit sets the learning period when the internal combustion engine is fuel cut by engine stop control, and holds the intake throttle valve in a valve open position during the learning period. Or an oxygen concentration sensor learning device for controlling an internal combustion engine according to 2; In a learning method of an oxygen concentration sensor for controlling an internal combustion engine that learns a reference value of an oxygen concentration sensor of a limiting current detection method that detects an oxygen concentration in exhaust gas discharged from the internal combustion engine,
The oxygen concentration sensor has a sensor element that outputs a limit current corresponding to the oxygen concentration in the exhaust gas,
When the internal combustion engine is fuel cut, a learning period for learning the reference value of the oxygen concentration sensor is set, and an output signal of the oxygen concentration sensor is set in a state where the applied voltage to the sensor element is increased during the learning period. A method for learning an oxygen concentration sensor for controlling an internal combustion engine, characterized in that a limit current is detected and learned as a reference value. In an oxygen concentration sensor learning device for controlling an internal combustion engine that learns a reference value of an oxygen concentration sensor that detects an oxygen concentration in exhaust gas discharged from an internal combustion engine,
The oxygen concentration sensor has a sensor element that outputs an output signal corresponding to the oxygen concentration in the exhaust,
Temperature detecting means for detecting the temperature of the sensor element;
Learning means for correcting the output signal of the oxygen concentration sensor based on the temperature of the sensor element detected by the temperature detection means during the fuel cut period of the internal combustion engine, and learning the correction value as a reference value ;
Clogging degree determination for determining the degree of clogging of the exhaust passage based on the difference or ratio between the output signal of the oxygen concentration sensor during the fuel cut period of the internal combustion engine and the output signal of the oxygen concentration sensor while the internal combustion engine is stopped learning device of the oxygen concentration sensor for an internal combustion engine control, characterized by comprising a means.   The learning means increases the output signal of the oxygen concentration sensor as the temperature of the sensor element decreases in a temperature range where the temperature of the sensor element detected by the temperature detection means is equal to or lower than a predetermined output stable temperature range. The oxygen concentration sensor learning device for controlling an internal combustion engine according to claim 9, wherein the oxygen concentration sensor learning device according to claim 9 is corrected. In an oxygen concentration sensor learning device for controlling an internal combustion engine that learns a reference value of an oxygen concentration sensor that detects an oxygen concentration in exhaust gas discharged from an internal combustion engine,
The oxygen concentration sensor has a sensor element that outputs an output signal corresponding to the oxygen concentration in the exhaust,
Exhaust pressure detection means for detecting the exhaust pressure;
Learning means for correcting the output signal of the oxygen concentration sensor based on the exhaust pressure detected by the exhaust pressure detecting means during the fuel cut period of the internal combustion engine, and learning the correction value as a reference value ;
Clogging degree determination for determining the degree of clogging of the exhaust passage based on the difference or ratio between the output signal of the oxygen concentration sensor during the fuel cut period of the internal combustion engine and the output signal of the oxygen concentration sensor while the internal combustion engine is stopped learning device of the oxygen concentration sensor for an internal combustion engine control, characterized by comprising a means.   10. The oxygen concentration for controlling an internal combustion engine according to claim 9, wherein the learning unit corrects the output signal of the oxygen concentration sensor to decrease as the exhaust pressure detected by the exhaust pressure detection unit increases. Sensor learning device.   13. The learning apparatus for an oxygen concentration sensor for controlling an internal combustion engine according to claim 11 or 12, wherein the exhaust pressure detection means estimates the exhaust pressure based on an operating state of the internal combustion engine.   14. A sensor abnormality determination unit that determines whether or not the oxygen concentration sensor is abnormal based on an output signal of the oxygen concentration sensor corrected by the learning unit. An oxygen concentration sensor learning device for controlling an internal combustion engine as described. Clogging degree determination for determining the degree of clogging of the exhaust passage based on the difference or ratio between the output signal of the oxygen concentration sensor during the fuel cut period of the internal combustion engine and the output signal of the oxygen concentration sensor while the internal combustion engine is stopped An oxygen concentration sensor learning device for controlling an internal combustion engine according to any one of claims 1 to 7, further comprising: means.

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