JP2004324471A - Oxygen sensor deterioration determination device - Google Patents

Abstract

Provided is an oxygen sensor deterioration determination device capable of preventing erroneous determination of deterioration of an oxygen sensor beforehand and performing deterioration determination more appropriately.
An electronic control unit calculates an air-fuel ratio correction coefficient based on an output of an oxygen sensor to perform air-fuel ratio feedback control, and based on an inversion cycle including a rich period and a lean period of the output of the oxygen sensor. To determine whether the oxygen sensor has deteriorated. The electronic control unit 50 prohibits the deterioration determination based on the data of a plurality of continuous periods including the rich period or the lean period of the output of the oxygen sensor 44 corresponding to the time when the air-fuel ratio correction coefficient is reset.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an apparatus for calculating an air-fuel ratio correction coefficient based on an output of an oxygen sensor and performing an air-fuel ratio feedback control on the engine to determine whether the oxygen sensor has deteriorated.
[0002]
[Prior art]
As is well known, many gasoline engines (hereinafter simply referred to as engines) are provided with an oxygen sensor for detecting an oxygen concentration in exhaust gas in an exhaust passage, and an air-fuel ratio is set so that an air-fuel ratio becomes a stoichiometric air-fuel ratio based on its output. Feedback (F / B) control is performed. When it is detected that the air-fuel ratio is richer than the stoichiometric air-fuel ratio based on the output of the oxygen sensor, the fuel injection amount is corrected to be reduced, and it is detected that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio. In such a case, the fuel injection amount is increased and corrected so that the air-fuel ratio is controlled to be the stoichiometric air-fuel ratio.
[0003]
In general, such correction of the fuel injection amount is performed by skip correction for temporarily increasing or decreasing the air-fuel ratio correction coefficient by a predetermined amount when it is confirmed that the air-fuel ratio has been inverted between lean and rich by the output of the oxygen sensor, and the output of the oxygen sensor. During the period in which the air-fuel ratio is lean or rich, the air-fuel ratio correction coefficient is gradually increased or decreased.
[0004]
The characteristics of the oxygen sensor, such as its internal resistance, electromotive force, and response time, may change due to thermal deterioration, and the accuracy of the air-fuel ratio F / B control may decrease due to the change in the characteristics. Therefore, in many engines in which the air-fuel ratio F / B control is performed as described above, it is determined whether or not the oxygen sensor has deteriorated in order to prevent such a decrease in accuracy.
[0005]
Conventionally, such a deterioration determination of the oxygen sensor is performed by comparing an inversion cycle including a rich period and a lean period of the oxygen sensor output with a predetermined deterioration determination value, as described in Patent Document 1. When the inversion cycle is equal to or longer than the deterioration determination value, it is determined that the oxygen sensor is deteriorated.
[0006]
[Patent Document 1]
JP-A-6-50193
[0007]
[Problems to be solved by the invention]
The reversal cycle of the output of the oxygen sensor varies due to the influence of the fuel injection correction control and the operating state of the engine, and there is a possibility that the change in the reversal cycle of the oxygen sensor erroneously determines that the oxygen sensor is deteriorated. There is. In Patent Literature 1, the following preconditions are set in order to exclude the influence of the fuel injection correction control and the operating state. (1) The determination of the activity of the oxygen sensor has been completed. (2) The air-fuel ratio F / B control is being executed. (3) The vehicle speed, the engine speed, the intake air amount, the throttle opening, and the like are within specified ranges, respectively, and the engine is in steady operation.
[0008]
However, in the method for determining deterioration of an oxygen sensor disclosed in Patent Literature 1, in the following cases, the inversion cycle of the output of the oxygen sensor increases, and there is a possibility that an erroneous determination is made. That is, the injection amount of the injector is near the upper and lower limits of the tolerance, and the air-fuel ratio correction coefficient for obtaining the stoichiometric air-fuel ratio is largely shifted to the decrease side or the increase side. Further, the update of the fuel correction learning value based on the air-fuel ratio correction coefficient has never been performed. In these states, when the fuel cut control or the acceleration increase control is executed, the air-fuel ratio F / B control is released and the air-fuel ratio correction coefficient is reset. Further, when the purge control of the fuel vapor generated in the fuel tank is executed and released, the air-fuel ratio F / B control is continued, but the air-fuel ratio correction coefficient is reset. As described above, the output of the oxygen sensor corresponding to the time when the air-fuel ratio correction coefficient is reset is stuck to the rich side or the lean side, and the rich period or the lean period increases. Immediately after the reset of the air-fuel ratio correction coefficient is released, it takes time to return to the original value before the air-fuel ratio correction coefficient was reset, during which a rich period or a lean period of the oxygen sensor output is reduced. Especially increase. Therefore, the reversal cycle composed of data of a plurality of continuous periods including the rich period or the lean period of the output of the oxygen sensor corresponding to the time when the air-fuel ratio correction coefficient is reset is longer than the original reversal period. Therefore, if the deterioration determination of the oxygen sensor is performed based on the inversion cycle of the oxygen sensor corresponding to the time when the air-fuel ratio correction coefficient is reset, the deterioration of the oxygen sensor may be erroneously determined.
[0009]
The present invention has been made in view of such circumstances, and it is an object of the present invention to provide an oxygen sensor deterioration determination device capable of preventing erroneous determination of deterioration determination of an oxygen sensor beforehand and performing deterioration determination more appropriately. .
[0010]
[Means for Solving the Problems]
Hereinafter, means for solving the above-described problems and the effects thereof will be described.
The invention according to claim 1 is applied to an engine that performs an air-fuel ratio feedback control by calculating an air-fuel ratio correction coefficient based on an output of an oxygen sensor that detects rich or lean at a stoichiometric air-fuel ratio. The air-fuel ratio correction coefficient is reset in an oxygen sensor deterioration determination device including a determination unit that determines whether or not the oxygen sensor has deteriorated based on a reversal cycle including a rich period and a lean period of the output of the oxygen sensor. A prohibition unit for prohibiting a determination by the determination unit based on data of a plurality of periods that are continuous to the period including a rich period or a lean period of the output of the oxygen sensor corresponding to a period is provided.
[0011]
During the air-fuel ratio feedback control, when the air-fuel ratio correction coefficient for setting the air-fuel ratio to the stoichiometric air-fuel ratio is largely shifted to the decrease side or the increase side, if the air-fuel ratio correction coefficient is reset, it corresponds to that time. The output of the oxygen sensor will stick to the rich side or the lean side, and the rich period or the lean period will increase. Immediately after the reset of the air-fuel ratio correction coefficient is released, it takes time to return to the original value before the air-fuel ratio correction coefficient was reset, during which a rich period or a lean period of the oxygen sensor output is reduced. Especially increase. Therefore, the reversal cycle composed of data of a plurality of continuous periods including the rich period or the lean period of the output of the oxygen sensor corresponding to the time when the air-fuel ratio correction coefficient is reset is longer than the original reversal period. Therefore, if the deterioration determination of the oxygen sensor is performed based on the inversion cycle of the oxygen sensor corresponding to the time when the air-fuel ratio correction coefficient is reset, the deterioration of the oxygen sensor may be erroneously determined.
[0012]
In this regard, according to the first aspect of the present invention, the determination based on the data of a plurality of continuous periods including the rich period or the lean period of the output of the oxygen sensor corresponding to the period when the air-fuel ratio correction coefficient is reset. Is prohibited, erroneous determination of deterioration of the oxygen sensor can be prevented before it occurs.
[0013]
As in the invention according to claim 2, the prohibiting means includes a rich period or a lean period of the output of the oxygen sensor corresponding to a time when the air-fuel ratio correction coefficient is reset, and a lean period or a lean period immediately after the period. The determination by the determination unit based on the data of the two rich periods can be prohibited.
[0014]
The invention according to claim 3 is applied to an engine that performs an air-fuel ratio feedback control by calculating an air-fuel ratio correction coefficient based on an output of an oxygen sensor that detects rich or lean at a stoichiometric air-fuel ratio. An oxygen sensor deterioration determining device comprising a determination unit for determining the presence or absence of deterioration of the oxygen sensor based on an inversion cycle including a rich period and a lean period of the output of the oxygen sensor. When the deviation between the period and the lean period does not fall within the range of the specified value, the control device includes a prohibition unit that prohibits the determination by the determination unit based on the inversion cycle including the rich period and the lean period.
[0015]
The change in the reversal cycle of the oxygen sensor is due to aging, and the output characteristics of the oxygen sensor do not suddenly change. Therefore, when the inversion cycle of the output of the oxygen sensor is partially extended, the inversion cycle is not increased due to the deterioration of the oxygen sensor, but is temporarily increased due to the influence of the air-fuel ratio feedback control. Can be determined as a typical phenomenon.
[0016]
According to the above configuration, when the deviation of the output of the oxygen sensor from the continuous rich period and lean period does not fall within the range of the specified value, the determination based on the inversion cycle including the rich period and the lean period is prohibited. Therefore, erroneous determination of deterioration of the oxygen sensor can be prevented before it occurs.
[0017]
The invention according to claim 4 is applied to an engine that performs an air-fuel ratio feedback control by calculating an air-fuel ratio correction coefficient based on an output of an oxygen sensor that detects an air-fuel ratio. In the oxygen sensor deterioration determination device provided with determination means for determining the presence or absence of deterioration of the oxygen sensor based on the fuel for compensating for a steady deviation between the air-fuel ratio detected by the oxygen sensor and the stoichiometric air-fuel ratio. A learning means for learning a correction learning value based on the air-fuel ratio correction coefficient is further provided, and a prohibiting means for prohibiting the determination by the determining means when the learning of the air-fuel ratio is not performed is provided.
[0018]
When the air-fuel ratio learning is performed, the steady-state deviation between the air-fuel ratio and the stoichiometric air-fuel ratio is corrected based on the fuel correction learning value, and the air-fuel ratio correction coefficient does not shift to the increasing side and the decreasing side, and the correction amount is corrected. It changes around 0%. In this case, immediately after the reset of the air-fuel ratio correction coefficient is released, the time until the air-fuel ratio correction coefficient returns to the original value before the reset is shortened, and the rich period or the lean period of the oxygen sensor output is shortened. Is less likely to increase, and erroneous determination of deterioration of the oxygen sensor can be prevented. Conversely, when the air-fuel ratio learning is not performed, the steady-state deviation between the air-fuel ratio and the stoichiometric air-fuel ratio is not corrected, and the air-fuel ratio correction coefficient shifts to the increasing side and the decreasing side. In this case, immediately after the reset of the air-fuel ratio correction coefficient is released, it takes time to return to the original value before the air-fuel ratio correction coefficient was reset, during which a rich period of the oxygen sensor output or The lean period is particularly increased. Therefore, the reversal cycle composed of data of a plurality of continuous periods including the rich period or the lean period of the output of the oxygen sensor corresponding to the time when the air-fuel ratio correction coefficient is reset is longer than the original reversal period. Therefore, if the deterioration determination of the oxygen sensor is performed based on the inversion cycle of the oxygen sensor corresponding to the time when the air-fuel ratio correction coefficient is reset, the deterioration of the oxygen sensor may be erroneously determined.
[0019]
In this regard, according to the above configuration, the determination is prohibited when the learning of the fuel correction learning value for compensating for the steady deviation between the air-fuel ratio and the stoichiometric air-fuel ratio is not performed. Erroneous determination can be prevented beforehand.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
(1st Embodiment)
Hereinafter, a first embodiment of a deterioration determination device for an oxygen sensor according to the present invention will be described with reference to FIGS.
[0021]
FIG. 1 shows a schematic configuration of an oxygen sensor deterioration determination device according to the present embodiment, a vehicle engine to which the device is applied, and the like. As shown in FIG. 1, an intake passage 20 is connected to the engine 10. The intake passage 20 is provided with a throttle valve 24 that is opened and closed by a throttle motor 22.
[0022]
The intake air supplied to the engine 10 through the intake passage 20 is metered based on the opening of the throttle valve 24. An injector 26 for injecting fuel is provided near the engine 10 in the intake passage 20.
[0023]
On the other hand, a three-way catalyst 32 is provided in the exhaust passage 30 connected to the engine 10. The three-way catalyst 32 purifies HC (hydrocarbon), CO (carbon monoxide), and NOx (nitrogen oxide) contained in the exhaust gas.
[0024]
Further, the engine 10 is provided with various sensors for detecting its operating state. For example, a rotation speed sensor 41 that detects an engine rotation speed signal NE is provided near the crankshaft of the engine 10. A throttle sensor 42 is provided near the throttle valve 24 for detecting the throttle valve opening TA and performing feedback control of the throttle valve opening TA to a target opening. Further, an air flow meter 43 for detecting an intake air amount QA passing through the intake passage 20 is mounted upstream of the throttle valve 24. In the exhaust passage 30, an upstream oxygen sensor 44 and a downstream oxygen sensor 45 for detecting the respective oxygen concentration signals ODU and ODD are provided upstream and downstream of the three-way catalyst 32, respectively. The detection signals of these sensors 41 to 45 are input to an electronic control unit 50 that executes various controls of the engine.
[0025]
The electronic control unit 50 includes an arithmetic unit (CPU), a memory for storing various control programs, an arithmetic map, data calculated at the time of executing control, and the like. The electronic control unit 50 executes air-fuel ratio feedback control according to the oxygen concentration of exhaust gas, rotation speed control during idling operation, and the like, based on the operating state of the engine 10 detected by the various sensors 41 to 45 and the like. .
[0026]
Further, in the engine 10 of the present embodiment, the electronic control unit 50 calculates the fuel injection time τfin by the injector 26 based on the following equation (1).
τfin = Qbase (1 + KG + FAF) × KINJ (1)
In the above equation (1), “Qbase” is supplied to the cylinder in order to set the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio based on the intake air amount calculated based on the output of the air flow meter 43 and the stoichiometric air-fuel ratio. This is the basic injection quantity to be performed. “KINJ” is a basic fuel injection time. Specifically, it is determined based on the engine speed and the intake air amount QA such that the air-fuel ratio, which is the mixture ratio of the intake air and the fuel, becomes the stoichiometric air-fuel ratio.
[0027]
“KG” is a fuel correction learning value of the fuel injection time, and is set so that the air-fuel ratio becomes equivalent to stoichiometric according to the operating state of the engine 10. That is, after the learning for correcting the fuel injection amount (time) is completed, the feedback center in the air-fuel ratio feedback control basically matches the stoichiometric equivalent value. Note that the learning of the fuel correction learning value KG is performed for each engine operation region classified by the engine load or the like.
[0028]
“FAF” is an air-fuel ratio correction coefficient calculated based on the outputs of the oxygen sensors 44 and 45, and is supplied to the engine 10 based on the outputs of the oxygen sensors 44 and 45 during the air-fuel ratio feedback control. The air-fuel ratio of the air-fuel mixture is set to match the target air-fuel ratio. More specifically, the air-fuel ratio correction coefficient FAF is repeatedly set based on the following equation (2).
[0029]
FAF ← FAF + RS + KI (2)
“RS” in the above equation (2) is a skip correction amount. The skip correction amount RS is set to a predetermined negative value Rd when the output of the upstream oxygen sensor 44 indicates the reversal of the air-fuel ratio from lean to rich, and indicates the reversal of the air-fuel ratio from rich to lean. Sometimes it is set to a predetermined positive value Ri. Thus, when the output of the upstream oxygen sensor 44 is inverted, the air-fuel ratio correction coefficient FAF is increased or decreased in a skip shape.
[0030]
The values Rd and Ri are adjusted so that the overall air-fuel ratio becomes stoichiometric according to the lean-rich tendency of the air-fuel ratio obtained from the oxygen concentration signal ODD of the downstream oxygen sensor 45. That is, here, by setting the set value (value Ri) of the skip correction amount RS at the time of the increase correction and the same set value (Rd) at the time of the decrease correction to be symmetric, the overall air-fuel ratio is calculated from the stoichiometric air-fuel ratio. The deviation is compensated.
[0031]
“KI” in the above equation (2) is an integral correction amount. The integral correction amount KI is set to a predetermined negative value Kd while the oxygen sensor 44 on the upstream side is outputting a signal indicating that the air-fuel ratio is rich, and a signal indicating lean is set. During output, it is set to a predetermined positive value Ki. As a result, the air-fuel ratio correction coefficient FAF is decremented by the value Kd at predetermined time intervals during a period in which the air-fuel ratio is indicated to be rich, and is decreased by a predetermined time period during a period indicated to be lean. The value is gradually increased by Ki every time. Therefore, the larger the values Kd and Ki are, the larger the changing speed of the fuel injection time τfin, that is, the changing speed of the fuel injection amount.
[0032]
The values Kd and Ki are variably set according to the intake air amount QA and the like, and the air-fuel ratio control is adapted to the change in the response of the oxygen sensor 44 according to the intake air amount QA. Like that.
[0033]
Hereinafter, the deterioration determination processing of the oxygen sensor according to the present embodiment will be described with reference to FIGS.
In the present embodiment, the inversion cycle of the output of the upstream oxygen sensor 44 is measured, and when the measured inversion cycle exceeds a predetermined deterioration determination value, it is determined that the oxygen sensor 44 has deteriorated, and the deterioration is determined. Judgment is being performed. FIG. 2 is a flowchart showing a procedure for determining deterioration of the oxygen sensor 44 executed by the electronic control unit 50.
[0034]
In this series of processing, first, it is determined in step 102 whether the preconditions for the deterioration determination are satisfied. That is, when all of the following conditions are satisfied, the deterioration determination processing of the oxygen sensor 44 is permitted.
(1) The air-fuel ratio F / B control is being executed.
(2) The oxygen sensor 44 is in an active state.
(3) The vehicle speed, the engine speed, the intake air amount, the throttle opening, and the like are within specified ranges, respectively, and the engine is in steady operation.
(4) A predetermined time or more has elapsed since the engine was started, and the fuel injection amount has not been increased after the start.
(5) The engine cooling water temperature is equal to or higher than a predetermined temperature, and the fuel injection amount is not warmed up.
[0035]
When all of the above conditions are satisfied and the deterioration determination control of the oxygen sensor 44 is permitted, an affirmative determination is made in step 102 and the process proceeds to step 104. If any of the conditions (1) to (5) is not satisfied, a negative determination is made in step 102 and the routine proceeds to step 124, in which all the data calculated for determining the deterioration of the oxygen sensor 44 are cleared. The routine ends.
[0036]
In step 104, it is determined whether the cycle calculation permission condition is satisfied. If it is determined that the cycle calculation permission condition is satisfied (step 104: YES), the process proceeds to the oxygen sensor cycle calculation process of step 106, and if it is determined that the cycle calculation permission condition is not satisfied (step 104: NO), the process proceeds to step 116.
[0037]
In step 116, it is determined whether or not the output of the oxygen sensor 44 has reversed from the rich side to the lean side or from the lean side to the rich side. If it is determined that the output of the oxygen sensor has not been inverted (step 116: NO), this process is temporarily terminated. If it is determined that the oxygen sensor output has been inverted (step 116: YES), the cycle calculation permission condition is satisfied in step 118, and the flow proceeds to the oxygen sensor cycle calculation processing in step 106. That is, the time when the output of the oxygen sensor 44 is inverted is used as a starting point for measuring the inversion cycle of the output of the oxygen sensor 44, so that it is determined whether or not the output has been inverted.
[0038]
In step 106, the inversion cycle calculation processing of the oxygen sensor shown in the flowchart of FIG. 3 is executed.
First, in step 202, it is determined whether or not the air-fuel ratio is rich based on whether or not the output of the oxygen sensor 44 is equal to or higher than a reference voltage 0.45V corresponding to the stoichiometric air-fuel ratio. When the output of the oxygen sensor 44 is 0.45 V or more, it is determined that the air-fuel ratio is rich, and when the output of the oxygen sensor 44 is less than 0.45 V, it is determined that the air-fuel ratio is lean. If it is determined that the output of the oxygen sensor 44 is 0.45 V or more and the air-fuel ratio is rich (step 202: YES), the process proceeds to step 204. On the other hand, if it is determined that the output of the oxygen sensor 44 is less than 0.45 V and the air-fuel ratio is lean (step 202: NO), the process proceeds to step 214.
[0039]
In step 204, it is determined whether or not there is a lean history. If it is determined that there is a lean history (step 204: YES), the process proceeds to step 206, and if it is determined that there is no lean history (step 204: NO), the process proceeds to step 208.
[0040]
In step 206, the current value of the cycle counter is determined as the lean period TL, and the value of the cycle counter is cleared. In this step 206, the lean history is cleared.
[0041]
In step 208, the period counter is incremented for calculating the rich period.
In the next step 210, it is determined whether or not the state where the output of the oxygen sensor 44 is equal to or more than a specified value (for example, 0.48 V) has continued for a predetermined time or more. If a negative determination is made in step 210, the present routine is terminated. If an affirmative determination is made in step 210, the process proceeds to step 212, where the rich history is set to ON, and this routine is temporarily ended. The rich history indicates a state in which the oxygen sensor 44 is detecting a rich air-fuel ratio, not due to noise.
[0042]
When a negative determination is made in step 202 and the process proceeds to step 214, in step 214, it is determined whether or not there is a rich history. If it is determined that there is a rich history (step 214: YES), the process proceeds to step 216. If it is determined that there is no rich history (step 214: NO), the process proceeds to step 218.
[0043]
In step 216, the current value of the cycle counter is determined as the rich period TR, and the value of the cycle counter is cleared. In this step 216, the rich history is cleared.
[0044]
In step 218, the cycle counter is incremented for calculating the lean period TL.
In the next step 220, it is determined whether or not the state where the output of the oxygen sensor 44 is less than a specified value (for example, 0.42 V) has continued for a predetermined time or more. If a negative determination is made in step 220, this routine is temporarily ended. If an affirmative determination is made in step 220, the routine proceeds to step 222, where the lean history is set to ON, and this routine is temporarily ended. The lean history indicates a state in which the oxygen sensor 44 is not detecting noise but detecting a lean air-fuel ratio.
[0045]
Accordingly, as shown in FIG. 6, when the output of the oxygen sensor 44 is inverted from the rich side to the lean side to become less than 0.45 V at the time t1, when there is a rich history, the rich period TR is changed to the time t1. And the rich history is cleared. With the determination of the rich period TR, the lean period TL of the oxygen sensor output starts at time t1, and the measurement is started by the cycle counter. Then, when the output of the oxygen sensor 44 becomes less than 0.42 V at time t2 and a predetermined time T1 has elapsed, the lean history is set to ON at time t3.
[0046]
Thereafter, at time t4, when the output of the oxygen sensor 44 reverses from the lean side to the rich side and becomes 0.45 V or more, the lean period is determined at the time t4 because the lean history exists, and the lean history is cleared. . In addition, even if noise is applied to the output of the oxygen sensor 44 and becomes 0.45 V or more between the time t1 and the time t2, since the noise does not continue for the predetermined time T1 or more, the noise output time is also reduced to the lean period TL. It is measured as
[0047]
The rich period TR of the oxygen sensor output starts at the time t4 by the determination of the lean period TL, and the measurement is started by the cycle counter. Then, when the output of the oxygen sensor 44 becomes 0.48 V or more at time t5 and a predetermined time T2 elapses, the rich history is set to ON at time t6. The rich period TR of the oxygen sensor output starts, and measurement is started by the cycle counter.
[0048]
Thereafter, at time t7, when the output of the oxygen sensor 44 reverses from the rich side to the lean side and becomes less than 0.45 V, the rich period TR is determined at the time t7 because the rich history exists, and the rich history is cleared. .
[0049]
When the rich period TR is determined, the lean period TL of the oxygen sensor output starts at time t7, and measurement is started by the cycle counter. Thereafter, the lean period TL and the rich period TR of the output of the oxygen sensor 44 are similarly measured.
[0050]
Next, returning to FIG. 2, in step 108, a process of calculating the counter after the FAF reset is executed. FIG. 4 is a flowchart showing the process of calculating the counter after the FAF reset.
[0051]
As shown in FIG. 4, first, in step 302, it is determined whether the FAF reset flag is ON. The FAF reset flag is a flag for resetting the air-fuel ratio correction coefficient FAF. The FAF reset flag is used when the air-fuel ratio F / B control based on the fuel cut control or the acceleration increase control is released, or when the purge control is executed and released. The reset flag is set to ON. If it is determined that the FAF reset flag is ON (step 302: YES), the process proceeds to step 304. If it is determined that the FAF reset flag is OFF (step 302: NO), the process proceeds to step 306. move on.
[0052]
In step 304, “2” is set as an initial value in the post-FAF reset counter, and the FAF reset flag is set to OFF.
In the next step 306, it is determined whether the lean period TL or the rich period TR has been determined based on the processing result of the step 206 or step 216. If it is determined that the lean period TL or the rich period TR has been determined (step 306: YES), the process proceeds to step 308, and if it is determined that the lean period TL and the rich period TR have not been determined (step 306: NO), this routine is temporarily ended.
[0053]
Then, in step 308, the counter after the FAF reset is decremented, and this routine is temporarily ended.
Returning to FIG. 2 again, in step 110, it is determined whether or not the value of the counter after the FAF reset is “0”. If it is determined that the value of the post-FAF reset counter is “0” (step 110: YES), the process proceeds to step 112, and if it is determined that the value of the post-FAF reset counter is not “0” (step 110). : NO), the process proceeds to step 122. In step 122, since the two periods of the output of the oxygen sensor have not elapsed after the FAF reset, the cycle data is cleared, and this routine ends.
[0054]
In step 112, it is determined whether or not the average value of the reversal cycle obtained by adding the rich period TR and the lean period TL of the oxygen sensor output is less than a predetermined value Tref for determining deterioration. If it is determined that the average value of the inversion cycle is less than the specified value Tref (step 112: YES), the process proceeds to step 114, where it is determined that the oxygen sensor 44 has not deteriorated, and the routine ends. Is done. On the other hand, if it is determined that the average value of the inversion cycle is equal to or greater than the specified value Tref (step 112: NO), the process proceeds to step 120, where it is determined that the oxygen sensor 44 has deteriorated, and the present routine is performed. Is terminated.
[0055]
FIG. 5 is a timing chart showing a process of measuring the inversion cycle of the output of the oxygen sensor according to the present embodiment.
Now, the injection amount of the injector 26 is near the upper limit of the tolerance, and the air-fuel ratio correction coefficient FAF for setting the air-fuel ratio to the stoichiometric air-fuel ratio is largely shifted to the reduction side. Further, the learning update of the fuel correction learning value KG based on the air-fuel ratio correction coefficient FAF has never been performed.
[0056]
In such a state, when the air-fuel ratio correction coefficient FAF is reset at time t11 based on, for example, execution of the fuel cut control, the output of the oxygen sensor 44 corresponding to the time when the air-fuel ratio correction coefficient FAF is reset becomes lean. Side, and its lean period TLR will increase.
[0057]
Further, when the fuel cut control is released at time t12 and the reset of the air-fuel ratio correction coefficient FAF is released, the air-fuel ratio correction coefficient FAF becomes a predetermined skip correction amount Ri and an integral correction amount KI during the period from time t12 to t13. Is increased. Then, the air-fuel ratio correction coefficient FAF is overcorrected, so that at time t13, the output of the oxygen sensor 44 reverses to the rich side and sticks. It takes time before time t14 when the air-fuel ratio correction coefficient FAF returns to the original value before the reset, and the rich period TRR of the output of the oxygen sensor 44 increases. As described above, the inversion cycle including the lean period TL and the rich period TRR of the output of the oxygen sensor 44 corresponding to the time when the air-fuel ratio correction coefficient FAF is reset is extremely likely to be longer than the specified reference value Tref.
[0058]
According to the present embodiment, the data of the inversion cycle (TLR + TRR) of the output of the oxygen sensor 44 corresponding to the time when the air-fuel ratio correction coefficient FAF is reset is discarded until the count value of the counter after the FAF reset becomes “0”. (Cleared). Therefore, in the deterioration determination process of the oxygen sensor 44, the deterioration determination based on the reversal cycle (TLR + TRR) of the output of the oxygen sensor 44 corresponding to the time when the air-fuel ratio correction coefficient FAF is reset is prohibited, and the oxygen sensor 44 is determined. It is possible to prevent erroneous determination of the deterioration of the device beforehand.
[0059]
(2nd Embodiment)
Hereinafter, a second embodiment that embodies the oxygen sensor deterioration determination apparatus according to the present invention will be described, focusing on differences from the first embodiment.
[0060]
The change in the inversion cycle of the output of the oxygen sensor 44 is due to aging, and the output characteristics of the oxygen sensor do not suddenly change. Therefore, when the inversion cycle of the output of the oxygen sensor 44 is partially extended, the inversion cycle is not increased due to the deterioration of the oxygen sensor 44, but is caused by the influence of the air-fuel ratio F / B control. It can be determined that this is a temporary phenomenon in which the period has increased.
[0061]
Therefore, in the present embodiment, when the deterioration of the oxygen sensor 44 is determined, the deviation between the rich period and the lean period of the output of the oxygen sensor 44 that are continuous with each other is calculated, and the deviation does not fall within the range of the specified value. , The determination of deterioration of the oxygen sensor 44 based on the inversion cycle including the rich period and the lean period is prohibited.
[0062]
FIG. 7 is a flowchart showing a process of determining deterioration of the oxygen sensor according to the present embodiment.
Subsequent to the oxygen sensor inversion cycle calculation process of step 106 shown in FIG. 2, in step 400, the deviation of the output of the oxygen sensor 44 between the rich period TR and the lean period TL (the rich period TR / the lean period TL). Is determined between the lower limit specified value and the upper limit specified value. If an affirmative determination is made in step 400, the process proceeds to step 112, and if a negative determination is made in step 400, the process proceeds to step 122.
[0063]
According to the present embodiment, when the deviation of the output of the oxygen sensor 44 between the continuous rich period TR and the lean period TL does not fall within the range of the specified value, the data of the inversion cycle composed of the rich period TR and the lean period TL. Is discarded (cleared), so that an erroneous determination of deterioration of the oxygen sensor 44 can be prevented.
[0064]
As shown in FIG. 8, when the response of the air-fuel ratio correction coefficient FAF to the output of the oxygen sensor 44 is rich, the skip correction amount Rd during the decrease correction is set to be large on the rich side, and the skip correction during the increase correction is set on the lean side. The amount Ri may be set to be small. In this case, the rich period TR of the output of the oxygen sensor 44 is short, the lean period TL is long, and the deviation between the rich period TR and the lean period TL greatly changes.
[0065]
Therefore, when the response of the air-fuel ratio correction coefficient FAF to the output of the oxygen sensor 44 is set to be different between the rich side and the lean side, the deviation between the rich period TR and the lean period TL is determined. Is also variably set in accordance with the response of the air-fuel ratio correction coefficient FAF.
[0066]
(Third embodiment)
Hereinafter, a third embodiment that embodies the oxygen sensor deterioration determination apparatus according to the present invention will be described, focusing on differences from the first embodiment.
[0067]
In the present embodiment, when the learning of the fuel correction learning value KG is not performed, the deterioration determination of the oxygen sensor 44 is prohibited.
FIG. 9 is a flowchart showing a process of determining deterioration of the oxygen sensor according to the present embodiment.
[0068]
If it is determined in step 102 shown in FIG. 2 that the precondition is satisfied, it is determined in step 410 whether or not there is a fuel correction learning execution history. If an affirmative determination is made in step 410, the process proceeds to step 104, and if a negative determination is made in step 410, the process proceeds to step 124.
[0069]
When the learning of the fuel correction learning value KG is performed, the steady deviation between the air-fuel ratio and the stoichiometric air-fuel ratio is corrected based on the fuel correction learning value KG, and the air-fuel ratio correction coefficient FAF in the air-fuel ratio F / B control. Changes around the correction amount 0% without shifting to the increasing side and the decreasing side. In this case, even if the air-fuel ratio correction coefficient FAF is reset, immediately after the FAF reset is released, the air-fuel ratio correction coefficient FAF can be corrected based on the fuel correction learning value KG. Therefore, the time required for the air-fuel ratio correction coefficient FAF to return to the original value before the reset is shortened, and the rich period TR or the lean period TL of the output of the oxygen sensor 44 is unlikely to be extended. The inversion cycle including the lean period TL does not become long. Therefore, the deterioration determination of the oxygen sensor 44 can be performed based on the inversion cycle of the output of the oxygen sensor 44.
[0070]
Conversely, when the learning of the fuel correction learning value KG has not been performed, the steady deviation between the air-fuel ratio and the stoichiometric air-fuel ratio is not corrected, and the air-fuel ratio correction coefficient FAF is increased in the air-fuel ratio F / B control. Side and weight loss side. In this case, immediately after the reset of the air-fuel ratio correction coefficient FAF is released, it takes time until the air-fuel ratio correction coefficient FAF returns to the original value before the reset, and during that time, the richness of the oxygen sensor output is reduced. In particular, the period TR or the lean period TL increases. Therefore, the reversal cycle consisting of data of a plurality of continuous periods including the rich period TR or the lean period TL of the output of the oxygen sensor 44 corresponding to the time when the air-fuel ratio correction coefficient FAF is reset is smaller than the reference value Tref. It is likely to be longer. Therefore, if the deterioration determination of the oxygen sensor 44 is performed based on the inversion cycle of the output of the oxygen sensor 44 corresponding to the time when the air-fuel ratio correction coefficient FAF is reset, the deterioration of the oxygen sensor 44 may be erroneously determined. .
[0071]
According to the present embodiment, when the learning of the fuel correction learning value KG is not performed, the deterioration determination based on the inversion cycle of the output of the oxygen sensor 44 is prohibited, so that the erroneous determination of the deterioration of the oxygen sensor 44 is prevented beforehand. be able to.
[0072]
The oxygen sensor deterioration determination device according to the present invention is not limited to the above embodiments, and may be implemented as, for example, the following embodiments.
In each of the above embodiments, the engine 10 in which the fuel is injected by the injector 26 in the intake passage 20 is embodied. However, the engine 10 may be embodied as a type in which the fuel is directly injected into the combustion chamber.
[0073]
Next, other technical ideas that can be grasped from the above embodiments will be described below.
(A) In the oxygen sensor deterioration determination device according to claim 1 or 2, the prohibiting means sets a rich period or a lean period of the output of the oxygen sensor corresponding to a time when the air-fuel ratio correction coefficient is reset. The determination is prohibited by discarding data for a plurality of periods including the period.
[0074]
(B) In the oxygen sensor deterioration judging device according to claim 3, wherein the prohibition means is configured to set the rich period and the lean period when deviations of the continuous rich period and the lean period are not within a range of a specified value. The determination is prohibited by discarding the data of the inversion cycle including the period.
[Brief description of the drawings]
FIG. 1 is a block diagram schematically showing a first embodiment of an oxygen sensor deterioration determination apparatus according to the present invention.
FIG. 2 is an exemplary flowchart showing a processing procedure for determining deterioration of the oxygen sensor according to the embodiment;
FIG. 3 is an exemplary flowchart showing a process of measuring the inversion cycle of the output of the oxygen sensor according to the embodiment;
FIG. 4 is an exemplary flowchart showing a process of calculating a post-FAF reset counter according to the embodiment;
FIG. 5 is a timing chart showing changes in the output of the oxygen sensor and the air-fuel ratio correction coefficient of the embodiment.
FIG. 6 is a timing chart showing a process of measuring the inversion cycle of the output of the oxygen sensor according to the embodiment;
FIG. 7 is a flowchart showing a process for determining deterioration of the oxygen sensor according to the second embodiment;
FIG. 8 is a timing chart showing changes in the output of the oxygen sensor and the air-fuel ratio correction coefficient for the embodiment.
FIG. 9 is a flowchart illustrating a process of determining deterioration of the oxygen sensor according to the third embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Engine, 20 ... Intake passage, 22 ... Throttle motor, 24 ... Throttle valve, 26 ... Injector, 30 ... Exhaust passage, 32 ... Three-way catalyst, 41 ... Rotation speed sensor, 42 ... Throttle sensor, 43 ... Air flow meter, 44: oxygen sensor, 45: oxygen sensor, 50: electronic control device as determination means, prohibition means and learning means.

Claims (4)

The present invention is applied to an engine that performs an air-fuel ratio feedback control by calculating an air-fuel ratio correction coefficient based on an output of an oxygen sensor that detects rich or lean at a stoichiometric air-fuel ratio, and performs a rich period and a lean period of the oxygen sensor output. In the oxygen sensor deterioration determination device including a determination unit that determines the presence or absence of deterioration of the oxygen sensor based on a reversal cycle consisting of a period,
Prohibition means for prohibiting the determination by the determination means based on data of a plurality of periods continuous to the period including the rich period or the lean period of the output of the oxygen sensor corresponding to the time when the air-fuel ratio correction coefficient is reset. An oxygen sensor deterioration determination device, comprising: The deterioration determination device for an oxygen sensor according to claim 1,
The prohibiting unit is configured to perform the above-described operation based on data of two periods of a rich period or a lean period of the output of the oxygen sensor corresponding to a time when the air-fuel ratio correction coefficient is reset, and a lean period or a rich period immediately after the rich period. An apparatus for determining deterioration of an oxygen sensor, wherein a determination by a determination unit is prohibited. The present invention is applied to an engine that performs an air-fuel ratio feedback control by calculating an air-fuel ratio correction coefficient based on an output of an oxygen sensor that detects rich or lean at a stoichiometric air-fuel ratio, and performs a rich period and a lean period of the oxygen sensor output. In the oxygen sensor deterioration determination device including a determination unit that determines the presence or absence of deterioration of the oxygen sensor based on a reversal cycle consisting of a period,
If the deviation between the continuous rich period and lean period of the output of the oxygen sensor does not fall within the range of the specified value, prohibition of prohibiting the determination by the determining means based on the inversion cycle including the rich period and lean period. An oxygen sensor deterioration judging device characterized by comprising means. Applied to an engine that performs an air-fuel ratio feedback control by calculating an air-fuel ratio correction coefficient based on an output of an oxygen sensor that detects an air-fuel ratio, and determines whether the oxygen sensor has deteriorated based on an inversion cycle of the output of the oxygen sensor. In the oxygen sensor deterioration determination device comprising a determination means for determining
A learning unit for learning a fuel correction learning value based on the air-fuel ratio correction coefficient for compensating for a steady-state deviation between the air-fuel ratio and the stoichiometric air-fuel ratio detected by the oxygen sensor,
An apparatus for determining deterioration of an oxygen sensor, comprising: a prohibition unit that prohibits the determination by the determination unit when the air-fuel ratio learning by the learning unit is not performed.

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