JP2005207249A - Abnormality diagnosing device for oxygen sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable to accurately determine whether abnormality due to deterioration with an oxygen sensor occurs. <P>SOLUTION: The abnormality diagnosing device is constituted such that a reversal period T of a rich signal and a lean signal from the oxygen sensor 14 and a determination value H used for determination of whether the reversal period T is lengthened due to deterioration of the oxygen sensor 14 are calculated a plurality of times, and the ratio T/H of the reversal period T to the determination value H is determined with every calculation. The ratio T/H is a value being the magnitude of an influence on the reversal period T due to deterioration of the oxygen sensor 14 or being in an operation region where an intake air amount is decreased or a value capable of being represented without being influenced by a difference between a rich skip amount RsR and a lean skip amount RsL of air-fuel ratio feedback control. When an integrated value S obtained by adding the ratio T/H is higher than a threshold set based on the number of calculating times of the reversal period T and the determination value H, it is decided that abnormality due to deterioration with the oxygen sensor 14 occurs. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an abnormality diagnosis device for an oxygen sensor.

  In an internal combustion engine such as an automobile engine, when air-fuel ratio feedback control is performed to control the air-fuel ratio to the stoichiometric air-fuel ratio, an oxygen sensor that outputs a detection signal corresponding to the oxygen concentration in the exhaust gas of the engine is provided.

  This oxygen sensor outputs a rich signal when the oxygen concentration in the exhaust gas is lower than that concentration, based on the oxygen concentration in the exhaust gas when combustion of the air-fuel mixture is performed at the stoichiometric air-fuel ratio. Outputs a lean signal. For this reason, when combustion of the air-fuel mixture richer than the stoichiometric air-fuel ratio is performed, the oxygen concentration in the exhaust gas at that time becomes thinner than that at the time of combustion at the stoichiometric air-fuel ratio, and a rich signal is output from the oxygen sensor. When combustion of the air-fuel mixture leaner than the stoichiometric air-fuel ratio is performed, the oxygen concentration in the exhaust gas at that time becomes higher than that at the time of combustion at the stoichiometric air-fuel ratio, and a lean signal is output from the oxygen sensor.

  In the air-fuel ratio feedback control, the fuel injection amount is corrected to decrease based on the rich signal output from the oxygen sensor, and the fuel injection amount is corrected to increase based on the lean signal output from the oxygen sensor. Is brought close to the stoichiometric air-fuel ratio. During the execution of such air-fuel ratio feedback control, the fuel injection amount is increased or decreased to bring the air-fuel ratio of the internal combustion engine closer to the stoichiometric air-fuel ratio. Therefore, the oxygen concentration in the exhaust gas changes periodically, and the rich signal and lean signal from the oxygen sensor. Signals are output alternately.

  However, in the oxygen sensor, characteristic changes such as internal resistance, electromotive force, and response time occur due to deterioration due to exhaust heat, etc., and the air-fuel ratio of the air-fuel mixture is controlled to the stoichiometric air-fuel ratio by air-fuel ratio feedback control accompanying this characteristic change. The control accuracy at the time deteriorates. Therefore, paying attention to the fact that if the characteristic change due to deterioration occurs in the oxygen sensor, the inversion period of the rich signal and lean signal from the sensor during air-fuel ratio feedback control becomes longer, and the oxygen sensor malfunctions based on the inversion period It has been proposed to make a diagnosis.

  For example, in Patent Document 1, when the actual inversion period between the rich signal and the lean signal from the oxygen sensor is longer than a determination value calculated based on the intake air amount, an abnormality that determines that the oxygen sensor has deteriorated is detected. I have a diagnosis. The determination value is calculated in consideration of the tendency that the inversion period becomes longer as the intake air amount decreases, for example, so as to increase as the intake air amount decreases. It is possible to determine whether or not the oxygen sensor has deteriorated by such an abnormality diagnosis using the determination value and the inversion cycle. When the deterioration has occurred, the accuracy of the air-fuel ratio feedback control is deteriorated due to the deterioration. Measures can be taken.

  However, in the abnormality diagnosis as described above, since it is determined that the oxygen sensor is deteriorated only by the phenomenon that the inversion period becomes longer than the determination value once, the reliability of the determination is reliable. It becomes a problem. For example, if the reversal cycle is longer than the judgment value only once for some reason other than the deterioration of the oxygen sensor, it is erroneously determined that the oxygen sensor has deteriorated. It cannot be said that the nature is high.

For this reason, it is also conceivable to calculate that the oxygen sensor has deteriorated when the inversion period and the determination value are calculated a plurality of times and the sum of the inversion periods is larger than the sum of the determination values. In this case, even if the inversion period is increased only once for some reason, it is unlikely that the sum of the inversion periods is larger than the sum of the determination values. Therefore, when the inversion period becomes larger than the determination value only once, it is not immediately determined that the oxygen sensor has deteriorated, and it is determined whether or not the oxygen sensor has deteriorated. The reliability of the same judgment can be improved.
JP-A-11-166438

  Incidentally, the inversion cycle of the rich signal and the lean signal from the oxygen sensor is not always constant even if the intake air amount is constant, and varies depending on various conditions. For this reason, the reversal cycle determination value is also set to a value that is larger by a predetermined margin than the maximum value of the reversal cycle variation range when the oxygen sensor is normal under the condition that the intake air amount is constant in consideration of the above variation. It is conceivable to calculate such that In this case, when the reversal period varies when the oxygen sensor is normal, the reversal period can be prevented from erroneously exceeding the determination value.

  When the deterioration of the oxygen sensor occurs, the inversion period becomes longer and the fluctuation range of the inversion period changes as a whole toward the judgment value, so that the maximum value of the fluctuation range takes a value larger than the judgment value. Become. However, the length of the reversal cycle and the magnitude of fluctuation when the oxygen sensor is normal differ depending on the engine operating state. For example, in the operating region where the intake air amount decreases, other operating regions (hereinafter referred to as normal operating regions). ) Has a longer inversion period and a larger fluctuation. Due to this tendency of fluctuation of the inversion period, when the oxygen sensor has deteriorated and the inversion period exceeds the judgment value, the amount of increase in the inversion period with respect to the judgment value, and the inversion period is less than the judgment value. The amount of decrease in the reversal period with respect to the same determination value is greater in the operation region where the intake air amount is smaller than in the normal operation region.

  Therefore, in the process of performing the abnormality diagnosis of the oxygen sensor, when the inversion period is calculated in the operation region in which the intake air amount decreases, the increase amount or the decrease amount with respect to the calculated inversion period determination value is inverted. This greatly affects the total sum of the periods, and may cause erroneous determination when determining whether or not the oxygen sensor has deteriorated.

  Here, as a specific situation in which the misjudgment occurs, for example, out of a plurality of inversion cycle calculations, one calculation is performed in an operating region where the intake air amount is small, and the increase amount is very large. There are situations where the other calculation is performed in the normal operation region and the reversal period takes a value almost smaller than the judgment value. In this case, since most of the inversion periods calculated a plurality of times are smaller than the determination value, there is a high possibility that the oxygen sensor has not deteriorated. However, if the amount of increase with respect to the judgment value of the inversion period becomes very large even once, even if the inversion period becomes less than the judgment value in almost all other cases, the inversion period with respect to the judgment value at that time Since the amount of decrease in the normal operation region is only a very small value, the sum of the inversion periods is larger than the sum of the determination values. As a result, it is erroneously determined that the oxygen sensor has deteriorated.

  In addition, another specific situation in which erroneous determination occurs is, for example, out of a plurality of inversion period calculations, one calculation is performed in an operating region where the intake air amount decreases, and the above reduction amount is very high. In other cases, the other calculation is performed in the normal operation region, and the reversal period takes a value almost larger than the determination value. In this case, since most of the inversion periods calculated a plurality of times are larger than the determination value, there is a high possibility that the oxygen sensor has deteriorated. However, if the amount of decrease with respect to the judgment value of the inversion period becomes very large even once, even if the inversion period becomes larger than the judgment value in almost all other cases, the inversion to the judgment value at that time Since the increase amount of the cycle is only a very small value in the normal operation region, the sum of the inversion cycles is smaller than the sum of the determination values. As a result, it is erroneously determined that the oxygen sensor has not deteriorated.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an oxygen sensor abnormality diagnosis device that can accurately determine whether or not an abnormality has occurred in the sensor due to deterioration of the oxygen sensor. Is to provide.

In the following, means for achieving the above object and its effects are described.
In order to achieve the above object, the invention according to claim 1 is applied to an oxygen sensor that outputs a rich signal or a lean signal in accordance with the oxygen concentration in the exhaust gas of the internal combustion engine, and the air-fuel ratio of the engine is controlled by air-fuel ratio feedback control. Comparing the inversion period of the rich signal and the lean signal from the oxygen sensor when the air-fuel ratio is controlled to the stoichiometric air-fuel ratio with a determination value calculated based on the engine operating state, In the abnormality diagnosis device for the oxygen sensor to be determined, the inversion period and the determination value are calculated at predetermined intervals, and a ratio between the inversion period and the determination value for each calculation is calculated, and this ratio is added. It is determined that an abnormality has occurred in the oxygen sensor based on the fact that the integrated value obtained is greater than a threshold value obtained from the inversion period and the number of times the determination value is calculated. With a cross section.

  The inversion period of the rich signal and the lean signal from the oxygen sensor during the air-fuel ratio feedback control becomes shorter as the deterioration of the oxygen sensor proceeds. Further, the inversion cycle becomes longer as the intake air amount decreases, and tends to fluctuate more greatly in the operation region where the intake air amount decreases than in other operation regions. On the other hand, the determination value calculated based on the engine operating state is set to a larger value as the intake air amount decreases, for example, corresponding to a reversal period that becomes longer as the intake air amount decreases. When the reversal cycle becomes longer due to the deterioration of the oxygen sensor, the fluctuation range of the reversal cycle approaches the determination value, and the reversal cycle fluctuates in the vicinity of the determination value and becomes larger than the determination value or less than the determination value. As described above, the amount of increase in the inversion period with respect to the determination value when the inversion period becomes larger than the determination value, and the amount of decrease in the inversion period with respect to the determination value when the inversion period becomes less than the determination value, In the operation region where the intake air amount decreases, the operation region becomes larger than other operation regions. In other words, the influence on the amount of increase or decrease with respect to the judgment value of the reversal period due to the deterioration of the oxygen sensor is larger in the operation region where the intake air amount is small and the other operation regions under the same deterioration degree. . Without taking this into account, if an oxygen sensor abnormality diagnosis is performed based solely on the amount of increase and decrease in the inversion period with respect to the judgment value, an error may occur in determining whether or not an abnormality has occurred in the sensor due to the deterioration of the oxygen sensor. May occur. However, according to the above configuration, the ratio between the inversion period and the determination value is used for diagnosis of abnormality of the oxygen sensor. This ratio indicates how far the inversion period is from the determination value with reference to the determination value whose magnitude changes as described above. In other words, the ratio between the reversal period and the determination value is a value that can represent the magnitude of the influence on the reversal period due to the deterioration of the oxygen sensor without being influenced by the difference in the operation region (intake air amount). . Therefore, every time the inversion period and the judgment value are calculated, the ratio between the inversion period and the judgment value is calculated, and the integrated value obtained by adding this ratio is larger than the threshold obtained from the number of times the inversion period and the judgment value are calculated. Whether or not an abnormality has occurred in the sensor due to the deterioration of the oxygen sensor can be determined accurately.

  According to a second aspect of the present invention, in the first aspect of the present invention, the internal combustion engine is provided with oxygen sensors upstream and downstream of the exhaust gas, and the determination means detects an abnormality in the oxygen sensor upstream of the exhaust gas. The presence or absence was to be judged.

  In an internal combustion engine in which oxygen sensors are provided upstream and downstream of the exhaust, for example, air-fuel ratio feedback control for bringing the air-fuel ratio closer to the stoichiometric air-fuel ratio is performed as follows. That is, main feedback control is performed to correct the fuel injection amount based on a feedback correction value that decreases based on the rich signal from the oxygen sensor upstream of the catalyst and increases based on the lean signal from the sensor. Also, the amount of decrease in the feedback correction value by the main feedback control is increased based on the rich signal from the oxygen sensor downstream of the catalyst, and the amount of increase in the feedback correction value by the main feedback control is increased based on the lean signal from the sensor. Sub feedback control is performed. When such air-fuel ratio feedback control is performed, the inversion period between the rich signal and the lean signal from the oxygen sensor upstream of the catalyst increases as the deviation between the increase amount and the decrease amount of the feedback correction value due to the sub feedback control increases. There is a tendency that the inversion period becomes long and long. For this reason, the determination value calculated based on the engine operating state is set to a larger value as the deviation becomes larger, for example, corresponding to the inversion period that becomes longer as the deviation becomes larger. When the reversal cycle becomes longer due to the deterioration of the oxygen sensor, the fluctuation range of the reversal cycle approaches the determination value, and the reversal cycle fluctuates in the vicinity of the determination value and becomes larger than the determination value or less than the determination value. As described above, the amount of increase in the inversion period with respect to the determination value when the inversion period becomes larger than the determination value, and the amount of decrease in the inversion period with respect to the determination value when the inversion period becomes less than the determination value, When the deviation is large, the deviation is larger than that when the deviation is small. In other words, the influence on the amount of increase or decrease with respect to the judgment value of the reversal period due to the deterioration of the oxygen sensor is greater when the deviation is large than when the deviation is small under the same degree of deterioration. . Without taking this into account, if the abnormality diagnosis of the oxygen sensor is performed based solely on the amount of increase and decrease of the inversion period with respect to the determination value, an error will occur in determining whether or not an abnormality has occurred in the sensor due to the deterioration of the oxygen sensor. May occur. However, according to the above configuration, the ratio between the inversion period and the determination value is used for abnormality diagnosis of the oxygen sensor. This ratio indicates how far the inversion period is from the determination value with reference to the determination value whose magnitude changes as described above. In other words, the ratio between the inversion period and the determination value is a value that can represent the magnitude of the influence on the inversion period due to the deterioration of the oxygen sensor without being influenced by the difference in the magnitude of the deviation. Therefore, every time the inversion period and the judgment value are calculated, the ratio between the inversion period and the judgment value is calculated, and the integrated value obtained by adding this ratio is larger than the threshold obtained from the number of times the inversion period and the judgment value are calculated. Whether or not an abnormality has occurred in the sensor due to the deterioration of the oxygen sensor can be determined accurately.

Hereinafter, an embodiment embodying the present invention will be described with reference to FIGS.
In the engine 1 shown in FIG. 1, the amount of air taken into the combustion chamber 4 is adjusted through opening control of the throttle valve 3 provided in the intake passage 2, and this air and the fuel injection valve 5 are injected. The fuel / air mixture is combusted in the combustion chamber 4. The combusted air-fuel mixture is sent to the exhaust passage 6 as exhaust gas and purified by the three-way catalyst of the catalytic converter 7 provided in the passage 6.

  This three-way catalyst can most effectively remove all harmful components (HC, CO, NOx) in the exhaust when the oxygen concentration in the catalyst atmosphere becomes the value at the time of combustion of the air-fuel mixture at the stoichiometric air-fuel ratio It is. Therefore, the fuel injection amount is corrected according to the oxygen concentration in the exhaust gas so that the oxygen concentration in the catalyst atmosphere is maintained within a predetermined range including the value when the air-fuel mixture is burned at the stoichiometric air-fuel ratio. Fuel ratio feedback control is executed.

  Such air-fuel ratio feedback control is executed through an electronic control unit 8 mounted on the automobile to control the operation of the engine 1. The electronic control device 8 controls the fuel injection valve 5 and inputs detection signals from various sensors described below.

An accelerator position sensor 10 that detects the amount of depression (accelerator depression amount) of the accelerator pedal 9 that is depressed by the driver of the automobile.
A throttle position sensor 11 that detects the opening of the throttle valve 3 (throttle opening).

An air flow meter 12 that detects the amount of air (intake air amount) taken into the combustion chamber 4 through the intake passage 2.
A crank position sensor 13 that outputs a signal corresponding to the rotation of the crankshaft that is the output shaft of the engine 1.

An oxygen sensor 14 that outputs a rich signal or a lean signal according to the oxygen concentration in the exhaust existing upstream from the catalytic converter 7.
An oxygen sensor 15 that outputs a rich signal or a lean signal according to the oxygen concentration in the exhaust gas existing downstream from the catalytic converter 7.

  The electronic control unit 8 calculates the theoretical fuel injection amount required at that time as the injection amount command value Qfin based on the engine operating state, and performs fuel injection in an amount corresponding to the injection amount command value Qfin. The fuel injection valve 5 is driven. The engine speed is obtained based on a detection signal from the crank position sensor 13, and the engine load is obtained based on a parameter corresponding to the intake air amount and the engine speed. As the parameters related to the intake air amount, an actually measured value of the intake air amount, a throttle opening, an accelerator depression amount, and the like are used.

  The air-fuel ratio feedback control by the electronic control unit 8 is realized by main feedback control and sub feedback control. Here, the main feedback control is to reduce the feedback correction value FAF based on the rich signal from the oxygen sensor 14 upstream of the catalyst, and to increase the feedback correction value FAF based on the lean signal from the sensor 14, so that the correction value The fuel injection amount is corrected using FAF. The sub-feedback control is based on the rich signal from the oxygen sensor 15 downstream of the catalyst and increases the amount of decrease in the feedback correction value FAF by the main feedback control, and is based on the main feedback control based on the lean signal from the sensor 15. The increase amount of the feedback correction value FAF is increased.

  By the air / fuel ratio feedback control realized through the main feedback control and the sub feedback control, the air / fuel ratio of the engine 1 is controlled to the stoichiometric air / fuel ratio. The sub-feedback control is performed to compensate for variations in output characteristics of the oxygen sensor 14 upstream of the catalyst used for main feedback control, and to suppress a decrease in control accuracy of air-fuel ratio feedback control due to the variations.

  Next, the main feedback control will be described in detail with reference to the flowchart of FIG. 3 showing an injection amount command value calculation routine. This routine is executed through the electronic control unit 8 by, for example, a time interruption every predetermined time.

  In the injection amount command value calculation routine, first, based on the engine speed and the engine load, a basic fuel injection amount Qbase that is a theoretical value of the fuel injection amount required in the current operating state is calculated (S101). ). Subsequently, on the premise that the main feedback execution condition is satisfied (S102: YES), the processing after step S103 related to the main feedback control is executed.

  In this series of processing, it is first determined whether or not the detection signal from the oxygen sensor 14 upstream of the catalyst is inverted between the rich signal and the lean signal (S103). As shown in FIG. 2, when the oxygen concentration in the exhaust gas upstream of the catalyst is a value (oxygen concentration x) when the air-fuel mixture is burned at the stoichiometric air-fuel ratio, as shown in FIG. 5v "is output. When the oxygen concentration in the exhaust gas upstream of the catalyst becomes higher than the above-described oxygen concentration x due to the lean combustion or the like, a value smaller than “0.5 v” is obtained from the oxygen sensor 14 as the lean signal. Is output. Further, when the oxygen concentration in the exhaust gas upstream of the catalyst becomes thinner than the above-described oxygen concentration x due to rich combustion or the like, a value larger than “0.5 v” is output from the oxygen sensor 14 as a rich signal. Is output.

  If it is determined in step S103 that the inversion of the rich signal and the lean signal has occurred, skip control is performed to increase or decrease the feedback correction value FAF by the amount of skip at the time of the inversion. That is, if it is determined in step S104 that the lean signal is currently output from the oxygen sensor 14, the inversion from the rich signal to the lean signal has occurred, and the feedback correction value FAF has the rich skip amount RsR. The amount is increased by the amount (S105). If it is determined in step S104 that the lean signal is not currently output from the oxygen sensor 14, the lean signal has been inverted to the rich signal, and the feedback correction value FAF is equal to the lean skip amount RsL. The amount is reduced only by S106.

  On the other hand, if it is determined in step S103 that the inversion of the rich signal and the lean signal has not occurred, the integration control for gradually increasing or decreasing the feedback correction value FAF by the amount of integration is executed. That is, if it is determined in step S01 that the current lean signal is output, the lean signal is output, and the rich integration in which the feedback correction value FAF is smaller than the rich skip amount RsR described above. The amount is increased by the amount KiR (S108). For this reason, while the lean signal is output, the feedback correction value FAF is gradually increased by the rich integration amount KiR every predetermined time. If it is determined in step S107 that the lean signal is not currently output, the rich signal continues, and the feedback correction value FAF is the lean integral amount KiL smaller than the lean skip amount RsL described above. The amount is reduced only by S109. For this reason, while the rich signal is output, the feedback correction value FAF is gradually reduced by the lean integral amount KiL every predetermined time.

  The rich skip amount RsR and the rich integral amount KiR are used to increase the feedback correction value FAF, and are values representing the increase amount of the correction value FAF in the main feedback control. Further, the lean skip amount RsL and the lean integral amount KiL are used to decrease the feedback correction value FAF, and are values representing the decrease amount of the correction value FAF in the main feedback control. Then, based on the feedback correction value FAF calculated as described above, the basic fuel injection amount Qbase, and the like, the injection amount command value Qfin is calculated using the following equation (1) (S111).

Qfin = Qbase · FAF · A (1)
Qfin: Injection amount command value
Qbase: Basic fuel injection amount
FAF: Feedback correction value
A: Other correction value The injection amount command value Qfin calculated in this way is corrected based on the feedback correction value FAF. Then, by increasing or decreasing the feedback correction value FAF based on the detection signal from the oxygen sensor 14 upstream of the catalyst as described above, the air-fuel ratio of the air-fuel mixture is controlled to the stoichiometric air-fuel ratio by main feedback control. . When it is determined in step S102 that the main feedback execution condition is not satisfied, the feedback correction value FAF is set to “1.0” (S110), so that the main feedback control is executed. There is no.

  Next, the sub feedback control will be described with reference to the flowcharts of FIGS. 4 and 5 showing the skip amount / integration amount calculation routine. This routine is executed through the electronic control unit 8 by, for example, a time interruption every predetermined time.

  In the skip amount / integration amount calculation routine, the processing of steps S202 to S206 related to the sub feedback control is executed on the premise that the sub feedback execution condition is satisfied (S201: YES in FIG. 4). In this series of processing, it is first determined whether or not the detection signal from the oxygen sensor 15 downstream of the catalyst is inverted between the rich signal and the lean signal (S202). The oxygen sensor 15 has an output characteristic similar to that of the oxygen sensor 14 shown in FIG. Therefore, when the oxygen concentration in the exhaust gas downstream of the catalyst becomes higher than the oxygen concentration x described above, a value smaller than “0.5 v” is output from the oxygen sensor 15 as a lean signal. When the oxygen concentration in the exhaust gas downstream of the catalyst becomes lower than the oxygen concentration x described above, a value larger than “0.5 v” is output from the oxygen sensor 15 as a rich signal.

  When it is determined in step S202 that the inversion of the rich signal and the lean signal from the oxygen sensor 15 has occurred, the rich skip amount RsR and the lean skip amount RsL used in the main feedback control (skip control) are increased or decreased. Steps S203 to S206 are executed.

  If it is determined in step S203 that the lean signal is currently output from the oxygen sensor 15, the rich signal is inverted to the lean signal, and the rich skip amount RsR is increased by the constant ΔRsR. (S204). If it is determined in step S203 that the lean signal is not currently output from the oxygen sensor 15, the lean signal has been inverted to the rich signal, and the rich skip amount RsR is reduced by ΔRsR. (S205). The rich skip amount RsR that is increased or decreased in this way is subjected to a guard process so as to change within a predetermined range such as “2” to “8”.

  Subsequently, in step S206, the lean skip amount RsL is calculated by subtracting the rich skip amount RsR from “10”. Therefore, the lean skip amount RsL takes a smaller value as the rich skip amount RsR increases, and also changes within a predetermined range of “2” to “8”, similar to the rich skip amount RsR.

  As described above, the sub feedback control that compensates for variations in the output characteristics of the oxygen sensor 14 upstream of the catalyst by increasing or decreasing the rich skip amount RsR and the lean skip amount RsL based on the detection signal from the oxygen sensor 15 downstream of the catalyst. Is done.

  On the other hand, if it is determined in step S202 that the inversion of the rich signal and the lean signal has not occurred, processing for calculating the rich integration amount KiR and the lean integration amount KiL used in the main feedback control (integration control) is executed. .

  That is, when it is determined in the subsequent step S207 (FIG. 5) that the lean signal is currently output, the lean signal output is continued. In this case, the rich integration amount KiR is calculated with reference to a predetermined rich map based on the intake air amount (S208). If it is determined in step S207 that the lean signal is not currently output, the rich signal continues, and the lean integral amount KiL is determined based on the intake air amount. It is calculated with reference to (S209).

  By the way, when the air-fuel ratio feedback control including the above-described main feedback control and sub-feedback control is performed, the oxygen concentration upstream of the catalyst increases and decreases in a predetermined cycle centering on the oxygen concentration x described above, and from the oxygen sensor 14 upstream of the catalyst. Is output with a lean signal and a rich signal alternately with a predetermined period. The inversion period T between the rich signal and the lean signal from the oxygen sensor 14 upstream of the catalyst becomes longer with changes in characteristics such as internal resistance, electromotive force, and response time due to deterioration of the sensor 14. Here, the inversion period T between the rich signal and the lean signal from the oxygen sensor 14 is a time from when the rich signal and the lean signal are inverted to when the inversion is further performed twice. .

  In the present embodiment, the oxygen upstream of the catalyst is utilized by utilizing the fact that the inversion period T between the rich signal and the lean signal from the oxygen sensor 14 during the air-fuel ratio feedback control becomes longer with the deterioration of the oxygen sensor 14 upstream of the catalyst. An abnormality diagnosis such as deterioration in the sensor 14 is performed. Hereinafter, the abnormality diagnosis procedure of the oxygen sensor 14 will be described with reference to the flowchart of FIG. 6 showing the abnormality diagnosis routine. This abnormality diagnosis routine is executed, for example, by interruption at predetermined intervals through the electronic control unit 8.

  In the abnormality diagnosis routine, first, it is determined whether or not a precondition for performing abnormality diagnosis of the oxygen sensor 14 is satisfied (S301). The determination as to whether or not these preconditions are satisfied is made based on whether or not all of the following conditions are satisfied, for example.

-The main feedback control and the sub feedback control are being executed.
・ Do not be idle.
-The intake air amount of the engine 1 is within a predetermined range excluding near the minimum and maximum.

-The engine speed must be within a specified range excluding near the minimum speed and near the maximum speed.
・ Do not cut fuel.

  When it is determined that the above preconditions are satisfied based on the fact that all these conditions are satisfied, it is determined whether or not the diagnosis permission conditions for subsequent abnormality diagnosis are satisfied. (S302). The determination as to whether or not such a diagnosis permission condition is satisfied is made based on whether or not all of the following conditions are satisfied, for example.

The rich signal output period from the oxygen sensor 14 and the lean signal output period are not excessively deviated.
The variation amount of the intake air amount within one rich signal output period or one lean signal output period of the oxygen sensor 14 is small.

  If it is determined that the diagnosis permission condition is satisfied based on the satisfaction of these conditions, the process proceeds to step S303. Subsequently, in step S303, whether or not the inversion of the rich signal and the lean signal from the oxygen sensor 14 has been performed four times or more after the diagnosis permission condition is satisfied, that is, whether or not the inversion has been performed stably. To be judged. If the determination is affirmative, the inversion period T and the determination value H are calculated every time the inversion of the rich signal and the lean signal is performed twice (S304).

  For this inversion period T, whether the oxygen sensor 14 is deteriorated or not, the intake air amount of the engine 1 and the difference in the size of the rich skip amount RsR and lean skip amount RsL (hereinafter referred to as skip amount difference X) Influenced by. That is, the inversion period T becomes longer as the intake air amount decreases, and tends to fluctuate more in the operation region where the intake air amount decreases than in other operation regions. Further, the inversion period T becomes longer as the skip amount difference X increases, and tends to vary greatly.

  Here, the above-described tendency of the inversion period T is shown in the timing chart of FIG. In the figure, the horizontal axis represents the calculation timing of the inversion period T, and the vertical axis represents the length of the inversion period T. As can be seen from the figure, when in the operating region where the intake air amount decreases, or when the skip amount difference X is large, the inversion period T calculated at each calculation timing is long, and the fluctuation between the inversion periods T is long. It will be big. On the other hand, when the vehicle is in an operation region other than the operation region where the intake air amount decreases (hereinafter referred to as a normal operation region), or when the skip amount difference X is small, the inversion period T calculated at each calculation timing is short, Variations between the inversion periods T are small.

  Further, as described above, the inversion period T also tends to become longer as the deterioration of the oxygen sensor 14 upstream of the catalyst proceeds. For this reason, when the oxygen sensor 14 is not deteriorated (normal time), for example, a value shown in the region A of FIG. 7 is obtained as the inversion period T by calculating the inversion period T at each calculation timing. Become. On the other hand, when the deterioration of the oxygen sensor 14 progresses, as shown in the region B of FIG. Long value. The increase of the reversal period with respect to the deterioration of the oxygen sensor 14 is in the operation region where the intake air amount decreases, or when the skip amount difference X is large, when it is in the normal operation region, or when the skip amount difference X is small. Bigger than that.

  The determination value H calculated in step S304 is a value used to determine whether or not the reversal period T is longer than usual due to deterioration of the oxygen sensor 14, and includes a difference between the intake air amount and the skip amount. It is calculated based on the engine operating state represented by a parameter such as X. The determination value H calculated in this way is a value that is larger by a predetermined margin α than the maximum value Tmax of the normal fluctuation range W of the reversal period T when the oxygen sensor 14 is normal (region A). Note that the determination value H shown in FIG. 7 is a value in a state where the intake air amount and the skip amount difference X are always held constant at each calculation timing.

  After the inversion period T and the determination value H are calculated in step S304, the ratio T / H between the inversion period T and the determination value H is calculated (S305). Subsequently, the integrated value S obtained by adding the ratio T / H is calculated (S306). That is, a value obtained by adding the calculated ratio T / H to the integrated value S is set as a new integrated value S.

  Then, when the number of calculation of the inversion period T and the determination value H after the start of the addition of the ratio T / H to the integrated value S is 10 times or more (S307: YES), that is, the ratio T / H to the integrated value S. Is added ten times or more, it is determined whether or not the integrated value S is larger than a threshold value (in this case, “10”) set based on the number of calculations (S308). If the integrated value S is larger than this threshold (S308: YES), it is determined that an abnormality due to deterioration has occurred in the oxygen sensor 14 upstream of the catalyst (S309), and if the integrated value S is smaller than the threshold (S308). : NO), it is determined that the above-mentioned abnormality has not occurred in the oxygen sensor 14 and is normal (S310). When it is determined that the oxygen sensor 14 is normal or abnormal, the integrated value S is reset to the initial value “0” (S311).

  When it is determined that an abnormality due to deterioration has occurred in the oxygen sensor 14 (S309: YES), for example, the determination result is stored in the backup RAM of the electronic control unit 8, and the oxygen sensor is turned on by lighting the abnormal lamp. 14 abnormalities will be notified to the driver.

Next, advantages of the abnormality diagnosis of the oxygen sensor 14 in the present embodiment will be described in detail based on a comparison with the abnormality diagnosis of the conventional oxygen sensor.
Now, it is assumed that the inversion period T and the determination value H are calculated at a total of ten timings t1, t2, t3,. Then, as shown in FIG. 8, the values of a1, a2, a3... A10 are obtained as the inversion periods T calculated at each timing, and b1 as the determination value H calculated at each calculation timing. Assume that values b2, b3... b10 are obtained.

[Conventional diagnosis]
In the conventional abnormality diagnosis, the sum “a1 + a2 + a3... + A10” of the inversion period T calculated at each timing is more than the sum “b1 + b2 + b3. Based on whether it is large or not, it is determined whether or not an abnormality due to deterioration has occurred in the oxygen sensor 14. In other words, whether or not an abnormality due to deterioration has occurred in the oxygen sensor 14 is determined based on whether or not the sum of the inversion periods T and the sum of the determination values H have the relationship of the following equation (2). The

(A1 + a2 + a3 ... + a10)
> (B1 + b2 + b3... + B10) (2)
This equation (2) can be modified as shown in the following equation (3).

(A1-b1) + (a2-b2) + (a3-b3)... + (A10-b10)> 0 (3)
The terms “a1-b1”, “a2-b2”, “a3-b3”... “A10-b10” in Expression (3) are the inversion period T and the determination value H calculated at the same timing. The difference “TH” is expressed. When the above terms representing the difference “T−H” are replaced with the terms c1, c2, c3... C10, the equation (3) is represented by the following equation (4).

c1 + c2 + c3... + c10> 0 (4)
Here, as the deterioration of the oxygen sensor 14 progresses, the reversal period T becomes longer, so the fluctuation range W of the reversal period T is also displaced to the increasing side, and approaches the determination value H as shown in region B in FIG. In the vicinity of the determination value H, the inversion period T varies and becomes larger than the determination value H or less than the determination value H. Then, the values a1, a2, a3,..., A10 calculated as the inversion period T at each calculation timing are calculated as determination values H at the same time as the values b1, b2, b3,. The sign of c1, c2, c3... C10 used for the left side of the equation (4) is determined depending on whether it is larger or smaller than the value b10. When the left side becomes a positive value and the relationship of Expression (4) is obtained, it is determined that an abnormality due to deterioration has occurred in the oxygen sensor 14.

  Incidentally, the fluctuation range W of the reversal period T (FIG. 7) is larger when the operating range is the intake air amount is smaller and when the skip amount difference X is larger than when the normal operating region is and when the skip amount difference X is small. See) is particularly large. For this reason, when the oxygen sensor 14 is deteriorated, if the inversion period T becomes larger than the determination value H and the difference “T−H” becomes a positive value, the increase amount of the inversion period T with respect to the determination value H (The absolute value of the difference “T−H”) becomes large. That is, the increase amount is larger when the operation range is such that the intake air amount is smaller and when the skip amount difference X is larger than when it is the normal operation region and when the skip amount difference X is small. Further, when the oxygen sensor 14 is deteriorated, if the inversion period T becomes smaller than the determination value H and the difference “T−H” becomes a negative value, the decrease amount (difference of the inversion period with respect to the determination value H) The absolute value of “TH” is large. That is, the decrease amount has the same tendency as the increase amount.

  From this, the influence on the increase amount and the decrease amount (the absolute value of the difference “T−H”) of the inversion period T with respect to the determination value H due to the deterioration of the oxygen sensor 14 is the intake air under the condition that the deterioration degree is the same. When it is in the operation region where the amount is small, it becomes larger than when it is in the normal operation region. In addition, the above-described influence is greater when the skip amount difference X is large than when the skip amount difference X is small. For this reason, the reversal period T is calculated in the operation region where the intake air amount is small, and the reversal period T is calculated in a state where the skip amount difference X is large, and the difference “T−H” obtained based on the calculation result is calculated. "Is used in the expression (4), it greatly affects the left side of the expression (4). And it may cause misjudgment when judging the presence or absence of abnormality of the oxygen sensor 14 resulting from that.

  For example, when a plurality of reversal periods T are calculated at timings t1 to t10 as a process of performing an abnormality diagnosis, the calculation at timing t1 is performed in an operating region where the intake air amount decreases or the skip amount difference X is large. Suppose that c1 which is performed in the state and is the difference “TH” becomes a positive value. The calculation of the inversion period T at other timings t2 to t10 is performed in the normal operation region or in a state where the skip amount difference X is small, and many of c2 to c10 having the difference “T−H” are obtained. Suppose that it becomes negative. In this case, since many of c1-c10 become a negative value, possibility that the oxygen sensor 14 has not deteriorated is high.

  However, since c1 is calculated as a positive value in a situation where the fluctuation range W of the reversal period T becomes large, that is, in an operation region where the intake air amount decreases, or in a state where the skip amount difference X is large, the following formula ( As shown in 5), it is much larger than c2 to c10.

c1 >> c2, c3,..., c10 (5)
Thus, when c1 becomes very large, even if most of c1 to c10 have negative values, the left side of Expression (4) becomes a value larger than “0”. As a result, the relationship of Expression (4) is established, and an erroneous determination is made that an abnormality due to deterioration has occurred in the oxygen sensor 14.

  On the other hand, when the reversal period T is calculated a plurality of times from timing t to t10, the calculation at timing t1 is performed in an operating region where the intake air amount decreases or in a state where the skip amount difference X is large. It is assumed that c1 which is “TH” becomes a negative value. The calculation of the inversion period T at other timings t2 to t10 is performed in the normal operation region or in a state where the skip amount difference X is small, and many of c2 to c10 having the difference “T−H” are obtained. Suppose that it becomes a positive value. In this case, since many of c1 to c10 have positive values, there is a high possibility that the oxygen sensor 14 has deteriorated.

  However, since c1 is calculated as a negative value in a situation where the fluctuation range W of the reversal period T is large, that is, in an operation region where the intake air amount is small, or in a state where the skip amount difference X is large, the following equation ( As shown in 6), it is much smaller than c2 to c10.

c1 << c2, c3,..., c10 (6)
Thus, when c1 becomes very small, even if most of c1 to c10 are positive values, the left side of Equation (4) is a value smaller than “0”. As a result, the relationship of Expression (4) is not established, and an erroneous determination is made that no abnormality due to deterioration has occurred in the oxygen sensor 14.

[Abnormality diagnosis of this embodiment]
In contrast to the conventional abnormality diagnosis as described above, in the abnormality diagnosis of the present embodiment, the inversion period T and the determination value H are calculated every time the inversion period T and the determination value H are calculated at the timings t1 to t10 shown in FIG. The ratio T / H is calculated. The ratios T / H calculated at the respective timings t1 to t10 have values of “a1 / b1”, “a2 / b2”, “a3 / b3”,... “A10 / b10”, respectively. It becomes like this. Then, as shown in the following equation (7), the sum of these values is taken as the integrated value S.

S = (a1 / b1) + (a2 / b2) + (a3 / b3) ... + (a10 / b10) (7)
The terms “a1 / b1”, “a2 / b2”, “a3 / b3”,... “A10 / b10” in the formula (7) are the terms d1, d2, d3. In other words, equation (7) is expressed by the following equation (8).

S = d1 + d2 + d3 ... + d10 (8)
Based on whether or not the integrated value S is larger than a threshold value (in this case, “10”) set based on the number of calculations (ten times) of the inversion period T and the determination value H, the oxygen sensor 14 causes deterioration. It is determined whether an abnormality has occurred. In other words, based on whether or not the integrated value S and the threshold have a relationship represented by the following formula (9), it is determined whether or not an abnormality due to deterioration has occurred in the oxygen sensor 14.

S> 10 (9)
By substituting the right side of the equation (8) into the left side of the equation (9), the equation (8) is expressed by the following equation (10).

d1 + d2 + d3... + d10> 10 (10)
In equation (10), the values d1, d2, d3..., D10 represent the ratio T / H between the inversion period T calculated at each calculation timing t1 to t10 and the determination value H. . This ratio T / H is a value with which the reversal period T calculated simultaneously with the determination value H with respect to the determination value H that changes in accordance with the intake air amount and the skip amount difference X is a value. It indicates whether or not In other words, the ratio T / H is a value that can represent the magnitude of the influence on the inversion period T due to the deterioration of the oxygen sensor 14 without being influenced by the difference between the intake air amount and the skip amount difference X. .

  When the difference “TH” is used for the diagnosis as in the case of the conventional abnormality diagnosis, the difference “TH” indicates that the intake air amount and the skip amount even if the deterioration of the oxygen sensor 14 is constant. Different values are taken depending on the difference X. As a result, in the situation illustrated in the column of [Conventional abnormality diagnosis], the difference “T−H” calculated at the timing t1 is c1, and the difference “T−H” calculated at the timing t2 to t10 is “ Compared with c2 to c10, which is the value of “TH”, the value is very large as shown by the equation (5) or very small value as shown by the equation (6). As a result, an erroneous determination is made regarding whether or not an abnormality has occurred in the oxygen sensor 14.

  However, in the abnormality diagnosis of the present embodiment, the ratio T that can represent the magnitude of the influence on the reversal period T due to the deterioration of the oxygen sensor 14 regardless of the difference between the intake air amount and the skip amount difference X. An abnormality diagnosis of the oxygen sensor 14 is performed using / H. For this reason, even in the situation exemplified in [Conventional abnormality diagnosis], d1 which is the value of the ratio T / H calculated at timing t1 is the value of the ratio T / H calculated at timings t2 to t10. It does not become an excessively large value or a small value as compared with certain d2 to d10. Therefore, it is possible to accurately determine whether or not an abnormality has occurred due to deterioration in the oxygen sensor 14 based on whether or not the integrated value S obtained by adding d1 to d10 is larger than the threshold value.

According to the embodiment described in detail above, the following effects can be obtained.
(1) The inversion period T and the determination value H are calculated a plurality of times, and the integrated value S obtained by adding the ratio T / H between the inversion period T and the determination value H for each calculation is the inversion period T and the determination value. When it is larger than the threshold value set based on the number of times H is calculated, it is determined that an abnormality due to deterioration has occurred in the oxygen sensor 14 upstream of the catalyst. Thus, by using the ratio T / H for abnormality diagnosis of the oxygen sensor 14, it is possible to accurately determine whether or not an abnormality has occurred in the sensor 14.

  (2) With respect to the integrated value S, even if the ratio T / H is increased only once for some reason other than the deterioration of the oxygen sensor 14, it is unlikely that the integrated value S is larger than the threshold value by itself. Therefore, when the ratio T / H increases only once as described above, it is not immediately determined that an abnormality due to deterioration has occurred in the oxygen sensor 14, and an abnormality has occurred in the oxygen sensor 14. It is possible to increase the reliability of the determination when the determination is made.

In addition, each said embodiment can also be changed as follows, for example.
Although the threshold value is set to a value equal to the number of times of calculation of the inversion period T and the determination value H, it may be set to a value slightly larger or smaller than that value.

As the parameter for calculating the determination value H, it is not always necessary to use both the intake air amount and the skip amount difference X.
Although the oxygen sensor 14 is provided upstream of the catalyst, the oxygen sensor 15 is provided downstream of the exhaust, and the present invention is applied to the engine 1 that performs main feedback control and sub feedback control as air-fuel ratio feedback control, the oxygen sensor downstream of the catalyst The present invention may be applied to an engine that does not include 15. In this case, since the rich skip amount RsR and the lean skip amount RsL are not changed by the sub feedback control, the skip amount difference X is not used as a parameter used for calculating the determination value H.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the whole engine with which the abnormality diagnosis apparatus of the oxygen sensor of this embodiment is applied. The graph which shows the output characteristic of an oxygen sensor. The flowchart which shows the calculation procedure of injection amount command value. The flowchart which shows the calculation procedure of rich skip amount, lean skip amount, rich integral amount, and lean integral amount. The flowchart which shows the calculation procedure of rich skip amount, lean skip amount, rich integral amount, and lean integral amount. The flowchart which shows the abnormality diagnosis procedure of the oxygen sensor upstream of a catalyst. The timing chart which shows the change for every calculation timing of the inversion period calculated several times. The table | surface which shows the inversion period calculated at each calculation timing, the judgment value, and those differences and ratios.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Intake passage, 3 ... Throttle valve, 4 ... Combustion chamber, 5 ... Fuel injection valve, 6 ... Exhaust passage, 7 ... Catalytic converter, 8 ... Electronic control unit (determination means), 9 ... Accelerator pedal, DESCRIPTION OF SYMBOLS 10 ... Accelerator position sensor, 11 ... Throttle position sensor, 12 ... Air flow meter, 13 ... Crank position sensor, 14 ... Oxygen sensor, 15 ... Oxygen sensor

Claims (2)

Applied to an oxygen sensor that outputs a rich signal or a lean signal according to the oxygen concentration in the exhaust gas of the internal combustion engine, from the oxygen sensor when the air-fuel ratio of the engine is controlled to the stoichiometric air-fuel ratio by air-fuel ratio feedback control In the oxygen sensor abnormality diagnosis device for comparing the inversion cycle of the rich signal and the lean signal with a determination value calculated based on the engine operating state to determine whether or not an abnormality has occurred in the oxygen sensor,
The reversal period and the determination value are calculated at predetermined intervals, a ratio between the reversal period and the determination value for each calculation is calculated, and an integrated value obtained by adding this ratio is the reversal period. And an oxygen sensor abnormality diagnosing device, comprising: a determination unit configured to determine that an abnormality has occurred in the oxygen sensor based on being larger than a threshold value obtained from the number of calculation of the determination value. 2. The oxygen sensor abnormality according to claim 1, wherein the internal combustion engine is provided with oxygen sensors respectively upstream and downstream of the exhaust gas, and the determination means determines whether or not an abnormality has occurred in the oxygen sensor upstream of the exhaust gas. Diagnostic device.

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