JP2017031833A - Catalyst deterioration diagnosis device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst deterioration diagnosis device of an internal combustion engine capable of achieving determination result free from erroneous determination and not lowering frequency of deterioration determination regardless of magnitude of a fluctuation volume of an air-fuel ratio at an upstream side where the air-fuel ratio of the upstream of an exhaust emission control catalyst is alternately changed to lean and rich.SOLUTION: A catalyst deterioration diagnosis device of an internal combustion engine includes an exhaust emission control catalyst 27, air-fuel ratio control means 37 for changing an air-fuel ratio of an exhaust air flowing into the exhaust emission control catalyst 27 between a lean air-fuel ratio and a rich air-fuel ratio, an air-fuel ratio sensor 31 at an upstream side of the catalyst, an oxygen sensor 33 at a downstream side of the catalyst, and catalyst deterioration determination means 39 for determining deterioration of the exhaust emission control catalyst 27 on the basis of the number of times of fluctuations of the lean air-fuel ratio and the rich air-fuel ratio in the air-fuel ratio sensor 31 and the oxygen sensor 33, and counting of the number of times of fluctuations is limited on the basis of a fluctuation amount of an output value of the air-fuel ratio sensor 31 at the upstream side.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a catalyst deterioration diagnosis apparatus for an internal combustion engine, and in particular, a ternary device that purifies carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) contained in exhaust gas discharged from the internal combustion engine. The present invention relates to a catalyst deterioration diagnosis device.

  The exhaust gas discharged from the internal combustion engine of the vehicle mainly contains exhaust gas components of carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx). For this reason, in general, an exhaust purification catalyst such as a three-way catalyst is disposed in an exhaust passage through which exhaust gas discharged from an internal combustion engine passes so that the exhaust gas is released into the atmosphere in a purified state. .

  A three-way catalyst used as an exhaust purification catalyst of an internal combustion engine purifies by reducing NOx in a reducing atmosphere (rich air-fuel ratio atmosphere) while purifying HC and CO in an oxidizing atmosphere (lean air-fuel ratio atmosphere). Is done. For this reason, in order to improve the purification performance of the three-way catalyst, a technique has been proposed that effectively uses the three-way catalyst by controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine while detecting the oxygen concentration of the exhaust gas. ing.

  On the other hand, as a technique for diagnosing the deterioration of the exhaust purification three-way catalyst, oxygen concentration sensors are arranged upstream and downstream of the catalytic converter, and the air-fuel ratio upstream of the catalytic converter is alternately changed lean and rich, A device that determines the deterioration of a catalytic converter based on the fluctuation amount of the output signal of the downstream oxygen concentration sensor is known. This is a determination (diagnosis) method that utilizes the fact that the exhaust gas purification capability of the catalytic converter is highly correlated with the oxygen storage amount of the catalytic converter.

  Patent Documents 1 and 2 are known as prior arts relating to the deterioration diagnosis of a three-way catalyst. The Patent Document 1 discloses a reference point for air-fuel ratio control in which the air-fuel ratio upstream of the catalytic converter is alternately changed lean and rich. It is shown that the frequency of the deterioration diagnosis is increased while correcting the center A / F to prevent erroneous diagnosis of the deterioration diagnosis of the catalytic converter. This center A / F correction amount is applied to the catalytic converter from the time when the fuel supply to the internal combustion engine is prohibited and after the fuel supply is restarted until the output of the oxygen concentration sensor reaches a predetermined value or more. It is shown that the amount of consumed oxygen is calculated and determined based on this oxygen consumption.

  Further, Patent Document 2 discloses a parameter indicating the oxygen balance in the three-way catalyst based on the outputs of the air-fuel ratio sensors installed upstream and downstream of the three-way catalyst (the theoretical air-fuel ratio when the upstream sensor is a linear sensor). When the integral value of the fuel deviation from the corresponding fuel amount exceeds the upper and lower limits, the oxygen balance of the three-way catalyst exceeds the limit, and it is judged that there is a risk of misjudgment during degradation judgment. It is shown whether to stop misidentification and suppress misclassification.

JP 2013-100750 A JP 9-280038 A

  However, in Patent Document 1, as described above, the deterioration of the catalytic converter is diagnosed by correcting the center A / F that is the reference point of the air-fuel ratio control in which the air-fuel ratio upstream of the catalytic converter is alternately changed lean and rich. Because this technology prevents misdiagnosis, the air-fuel ratio upstream of the catalytic converter is lean, and depending on the amount of fluctuation in the rich air-fuel ratio, the downstream air-fuel ratio sensor may be reversed when a normal catalyst is installed, or when a deteriorated catalyst is installed. There is a risk that the downstream air-fuel ratio sensor may not be reversed, resulting in erroneous diagnosis. Therefore, it is necessary to improve the possibility of misdiagnosis due to the size of the upstream A / F fluctuation volume.

  Further, in Patent Document 2, as described above, the integral value of the parameter representing the oxygen balance in the three-way catalyst based on the outputs of the air-fuel ratio sensors installed upstream and downstream of the three-way catalyst is a predetermined upper and lower limit value. When the value exceeds the value, deterioration determination is stopped because there is a possibility that erroneous determination may occur, that is, deterioration determination is prohibited. Therefore, there is a problem that the frequency of deterioration determination is impaired.

  Accordingly, in view of the above-described technical problem, an object of at least one embodiment of the present invention is to provide sensors for detecting the air-fuel ratio upstream and downstream of the exhaust purification catalyst, respectively, and to determine the air-fuel ratio upstream of the catalyst. In a catalyst deterioration diagnosis device that alternately changes between lean and rich and determines catalyst deterioration based on fluctuations in the output signals of the upstream and downstream sensors, the air-fuel ratio upstream of the exhaust purification catalyst is alternately changed to lean and rich. It is to provide a determination result with no erroneous determination regardless of the variation volume of the upstream air-fuel ratio to be changed to the above, and to provide a catalyst deterioration diagnosis device for an internal combustion engine that does not impair the frequency of deterioration determination .

(1) An internal combustion engine catalyst deterioration diagnosis apparatus according to at least one embodiment of the present invention provides an exhaust aftertreatment means provided in an exhaust passage of an internal combustion engine, and an air-fuel ratio of exhaust flowing into the exhaust aftertreatment means with a lean air-fuel ratio. An air-fuel ratio control means that varies between a fuel ratio and a rich air-fuel ratio; and an upstream sensor that detects the air-fuel ratio of the exhaust gas that is provided in the exhaust passage upstream of the exhaust aftertreatment means and flows into the exhaust aftertreatment means A downstream sensor that is provided in the exhaust passage downstream of the exhaust aftertreatment means and detects an air-fuel ratio of the exhaust gas flowing out from the exhaust aftertreatment means, and a lean air-fuel ratio in the upstream sensor and the downstream sensor And catalyst deterioration determination means for determining deterioration of the exhaust aftertreatment means based on the number of times of fluctuation of the rich air-fuel ratio,
The catalyst deterioration determining means limits the count of the number of fluctuations based on the fluctuation amount of the output value of the upstream sensor.

According to the configuration of (1), the catalyst deterioration determination means limits the count of the number of fluctuations based on the fluctuation amount of the output value of the upstream sensor, so that the air-fuel ratio upstream of the exhaust aftertreatment means is lean, Regardless of the amount of fluctuation of the upstream air-fuel ratio that changes alternately in a rich manner, it is possible to pick up only the fluctuation of the air-fuel ratio suitable for the deterioration determination of the exhaust aftertreatment means, and obtain a determination result without erroneous determination be able to.
Therefore, for example, even if the amplitude and cycle of the air-fuel ratio are set with priority on exhaust gas purification performance and drivability, a determination result without erroneous determination can be obtained.

  Furthermore, since the count of the number of fluctuations is limited based on the fluctuation amount of the output value of the upstream sensor, the count is continued if the restriction based on the fluctuation amount is released. For this reason, the deterioration determination of the exhaust aftertreatment means is performed without impairing the determination frequency and the determination accuracy.

  (2) In some embodiments, in the configuration of (1), the catalyst deterioration determination unit is an upstream air-fuel ratio that is an air-fuel ratio on the upstream side determined based on an output value of the upstream sensor. An upstream inversion detection unit that detects switching between a rich air-fuel ratio and a lean air-fuel ratio, an upstream count unit that counts the number of times of switching detected by the upstream inversion detection unit, and an output of the downstream sensor A downstream inversion detection unit that detects switching between a rich air-fuel ratio of a downstream air-fuel ratio that is an air-fuel ratio on the downstream side that is determined based on a value, and a downstream inversion detection unit that is detected by the downstream inversion detection unit The downstream count unit that counts the number of times of switching, and the ratio between the upstream count number by the upstream count unit and the downstream count number by the downstream count unit A determination unit that performs deterioration determination, and a count control unit that interrupts the counting of the upstream side counting unit and the downstream side counting unit when the fluctuation amount of the output value of the upstream sensor is out of a predetermined range, It is characterized by having.

According to the configuration of (2), the determination unit determines the deterioration based on the ratio between the number of times of switching of the upstream air-fuel ratio by the upstream side counting unit and the number of times of switching of the downstream air-fuel ratio by the downstream side counting unit. Therefore, it is possible to accurately determine the deterioration of the exhaust aftertreatment means.
In addition, when the variation amount of the output value of the upstream sensor is out of the predetermined range in the count control unit, the counting of the upstream counting unit and the downstream counting unit is interrupted, so that the counting is reliably interrupted.

  (3) In some embodiments, in the configuration of (2), the upstream-side inversion detection unit detects the rich air-fuel ratio and the lean air-fuel ratio when the output value of the upstream sensor becomes the stoichiometric air-fuel ratio. While detecting the switching, the downstream inversion detector detects when the output value of the downstream sensor fluctuates from the rich air-fuel ratio to the lean air-fuel ratio and reaches a predetermined lean air-fuel ratio, or from the lean air-fuel ratio to the rich air-fuel ratio. When the air-fuel ratio fluctuates and reaches a predetermined rich air-fuel ratio, switching between the rich air-fuel ratio and the lean air-fuel ratio is detected.

According to the configuration of (3), it is determined that the switching between the rich air-fuel ratio and the lean air-fuel ratio based on the output value of the upstream sensor has been switched when the stoichiometric air-fuel ratio is reached, and the output value of the downstream sensor is determined. It is determined that the switching between the rich air-fuel ratio and the lean air-fuel ratio is switched when the predetermined lean air-fuel ratio is reached or when the predetermined rich air-fuel ratio is reached.
Thus, the timing for detecting the switching between the rich air-fuel ratio based on the output value of the upstream sensor and the lean air-fuel ratio and the timing for detecting the switching between the rich air-fuel ratio based on the output value of the downstream sensor. By combining sensors different from each other, it is possible to accurately detect the number of times of switching of the upstream air-fuel ratio and the number of times of switching of the downstream air-fuel ratio necessary for the deterioration determination.

  (4) In some embodiments, in the configuration of (2), the downstream-side count unit detects the upstream air-fuel ratio detected next after the switching of the upstream air-fuel ratio is detected. Before the switching, when the switching of the downstream air-fuel ratio is detected, the number of switching of the downstream air-fuel ratio is counted.

According to the configuration of the above (4), the number of times of switching of the downstream air-fuel ratio is counted after the upstream air-fuel ratio switching is detected until before the upstream air-fuel ratio switching detected next. By defining the number of times of detection, the number of times of switching of the downstream side air-fuel ratio in accordance with the fluctuation of the air-fuel ratio of the exhaust gas can be accurately counted.
Therefore, even when the exhaust aftertreatment means is deteriorated, if the fluctuation of the exhaust gas air-fuel ratio is small, the fluctuation of the downstream air-fuel ratio is small, and if the downstream air-fuel ratio is not switched, it is mistaken as normal. The problem of judging can be prevented.

  (5) In some embodiments, in the configurations of (2) to (4), the determination by the determination unit is performed by the upstream count number by the upstream count unit and the downstream count unit at a certain time. The determination is based on the ratio with the downstream count.

  According to the configuration of (5), the deterioration determination by the determination unit is performed by calculating a ratio between an upstream count number by the upstream count unit and a downstream count number by the downstream count unit within a predetermined time set in advance. Therefore, information on the deterioration state of the exhaust aftertreatment means is obtained periodically at regular intervals.

  (6) In some embodiments, in the configurations of (2) to (4), the deterioration determination by the determination unit is performed by the upstream count unit in a certain period until the upstream count reaches a predetermined number of times. The determination is made on the basis of the ratio between the upstream count number of the above and the downstream count number of the downstream count unit.

  According to the configuration of (6), the deterioration determination by the determination unit is performed by the upstream count number by the upstream count unit and the downstream count unit by the downstream count unit in a certain period until the upstream count number reaches a predetermined number of times. Since the determination is based on the ratio with the side count number, information on the deterioration state of the exhaust aftertreatment means is obtained periodically each time the upstream side count number reaches a predetermined number.

  (7) In some embodiments, in the configurations of (2) to (4), the deterioration determination by the determination unit is performed based on the upstream count number by the upstream count unit between the start and stop of the engine and the The determination is based on the ratio with the downstream count number by the downstream count unit.

  According to the configuration of (7), the deterioration determination by the determination unit is based on the ratio between the upstream count number by the upstream count unit and the downstream count number by the downstream count unit between engine start and stop. Therefore, every time the engine is stopped, information on the deterioration state of the exhaust aftertreatment means is obtained periodically.

  (8) In some embodiments, in any one of the configurations (2) to (7), the catalyst deterioration determination unit further determines the upstream air-fuel ratio based on the output of the upstream sensor. An upstream oxygen amount integrating unit that calculates an integrated value of the oxygen amount after the switching is detected and before the switching of the upstream air-fuel ratio detected next, the count control unit; When the integrated value by the upstream oxygen amount integrating unit is outside the predetermined upper and lower limit integrated range, the upstream air-fuel ratio is counted by the upstream counting unit and the downstream counting unit by the downstream counting unit. The counting of the number of times of switching of the side air-fuel ratio is interrupted.

  According to the configuration of (8), when the integrated value by the upstream oxygen amount integrating unit is outside the predetermined upper and lower limit integrated range, the number of times of switching of the upstream air-fuel ratio by the upstream counting unit is increased. Since the count and the count of the number of times the downstream air-fuel ratio is switched by the downstream-side count unit are interrupted, only the fluctuation of the air-fuel ratio on the upstream side of the catalyst suitable for determining the deterioration of the catalyst is ensured by using the oxygen amount integrated value. Can be picked up and counted.

  (9) In some embodiments, in the configuration of (8), the upstream oxygen amount integrating unit resets the integrated value to zero after the switching of the upstream air-fuel ratio is detected. The calculation of the integrated value is started from the above.

  According to the configuration of (9), the calculation of the integrated value of the oxygen amount by the upstream oxygen amount integrating unit becomes clear, and a comparison with a predetermined upper and lower limit value can be performed reliably.

  (10) In some embodiments, in the configuration of (8) or (9), the count control unit uses the count value by the upstream count unit and the downstream count unit at the time of the interruption. And a count value.

  According to the configuration of (10), when the counting of the number of times of switching of the upstream air-fuel ratio and the counting of the number of times of switching of the downstream air-fuel ratio by the downstream counting unit are interrupted, the result before counting is retained. Therefore, when the interruption is canceled, it is added to the held count value, so that the frequency of deterioration determination and the accuracy are not lowered.

  According to at least one embodiment of the present invention, sensors for detecting an air-fuel ratio are provided upstream and downstream of the exhaust purification catalyst, respectively, and the air-fuel ratio upstream of the catalyst is alternately changed to lean and rich, and the upstream side In a catalyst deterioration diagnosis device that determines catalyst deterioration based on fluctuations in output signals of sensors and downstream sensors, an upstream air-fuel ratio fluctuation volume that alternately changes the air-fuel ratio upstream of the exhaust purification catalyst to lean and rich Regardless of the size, it is possible to obtain a determination result without erroneous determination. Furthermore, determination results can be provided without deteriorating the frequency of deterioration determination.

1 is an overall configuration diagram of a catalyst deterioration diagnosis device for an internal combustion engine according to an embodiment of the present invention. It is a block diagram of the catalyst deterioration determination means according to an embodiment of the present invention. It is a block diagram of the configuration of the catalyst deterioration determination means according to an embodiment of the present invention. It is a block diagram of the configuration of the catalyst deterioration determination means according to an embodiment of the present invention. It is a block diagram of the configuration of the catalyst deterioration determination means according to an embodiment of the present invention. It is a block diagram of the configuration of the catalyst deterioration determination means according to an embodiment of the present invention. It is a control flowchart of the catalyst deterioration diagnosis of one Embodiment of this invention. 4 is a flowchart of a subroutine of an embodiment of the present invention, in which a rich air-fuel ratio and a lean air-fuel ratio on the upstream side of the catalyst are reversed NF, and a rich air-fuel ratio on the downstream side of the catalyst and the number of inversions NR of the lean air-fuel ratio are counted up. It is a flowchart. FIG. 6 is an explanatory diagram of counting up the number of inversions NF of the rich air-fuel ratio and lean air-fuel ratio upstream of the catalyst and the number of inversions NR of the rich air-fuel ratio and lean air-fuel ratio downstream of the catalyst. It is explanatory drawing of the output signal of the oxygen sensor of a normal catalyst and a deterioration catalyst.

Several embodiments of the present invention will be described below with reference to the accompanying drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in these embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples. Only.
For example, expressions expressing relative or absolute arrangements such as “in a certain direction”, “along a certain direction”, “parallel”, “orthogonal”, “center”, “concentric” or “coaxial” are strictly In addition to such an arrangement, it is also possible to represent a state of relative displacement with an angle or a distance such that tolerance or the same function can be obtained.
For example, an expression indicating that things such as “identical”, “equal”, and “homogeneous” are in an equal state not only represents an exactly equal state, but also has a tolerance or a difference that can provide the same function. It also represents the existing state.
For example, expressions representing shapes such as quadrangular shapes and cylindrical shapes represent not only geometrically strict shapes such as quadrangular shapes and cylindrical shapes, but also irregularities and chamfers as long as the same effects can be obtained. A shape including a part or the like is also expressed.
On the other hand, the expressions “comprising”, “comprising”, “comprising”, “including”, or “having” one constituent element are not exclusive expressions for excluding the existence of other constituent elements.

  FIG. 1 is an overall configuration diagram of a catalyst deterioration diagnosis device for an internal combustion engine according to some embodiments of the present invention. As shown in FIG. 1, a gasoline engine (hereinafter referred to as an engine) 1 as an internal combustion engine is shown, and an intake port injection type engine that injects fuel into an intake port 3 is shown. It may be an engine that injects fuel into the collecting portion of the intake pipe, or an in-cylinder injection engine that directly injects into the combustion chamber.

In FIG. 1, the engine 1 includes a cylinder head 5 and a cylinder block 7. A cylinder 9 is formed in the cylinder block 7. A piston 11 is accommodated in the cylinder 9 so as to be reciprocally movable. 11, the cylinder 9, and the cylinder head 5 form a combustion chamber 13.
An intake port 3 is formed in the cylinder head 5, and an intake manifold (not shown) is connected to the intake port 3. Further, an intake valve 15 is provided in the intake port 3 so that the combustion chamber 13 and the intake port 3 are communicated and blocked by the intake valve 15. The intake manifold 17 is provided with a port injection injector 17 that injects fuel into the intake port 3.

  On the other hand, an exhaust port 19 is formed in the cylinder head 5, and an exhaust pipe (exhaust passage) 23 is connected to the exhaust port 19 via an exhaust manifold 21. Further, the exhaust port 19 is provided with an exhaust valve 25 so that the combustion chamber 13 and the exhaust port 19 are communicated and blocked by the exhaust valve 25. The exhaust pipe 23 has a three-way catalyst (exhaust aftertreatment means) that purifies mainly hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) in the exhaust gas. (Hereinafter referred to as catalyst) 27 is installed.

When the exhaust air / fuel ratio becomes an oxidizing atmosphere (lean air / fuel ratio), the catalyst 27 is oxidized and purified by oxidizing HC and CO and until the exhaust air / fuel ratio becomes a reducing atmosphere (rich air / fuel ratio). (O ₂ ) is stored. When the air-fuel ratio becomes rich, NOx is reduced and purified, and stored O ₂ is released, and HC and CO are oxidized and purified.

  The cylinder head 5 is provided with an ignition plug 29 for each cylinder, and an ignition coil (not shown) that outputs a high voltage is connected to the ignition plug 29.

The exhaust pipe 23 on the upstream side of the catalyst 27 is provided with an air-fuel ratio (A / F) sensor 31 as an upstream sensor for detecting the air-fuel ratio of the exhaust gas flowing into the catalyst 27. The exhaust pipe 23 on the downstream side of the catalyst 27 is provided with an oxygen (O ₂ ) sensor 33 as a downstream sensor that detects the air-fuel ratio of the exhaust discharged from the catalyst 27.
The upstream air-fuel ratio sensor 31 is composed of a linear air-fuel ratio sensor (LAFS) that generates an output signal substantially proportional to the residual oxygen concentration in the exhaust gas. The downstream oxygen sensor 33 generates a binary signal corresponding to the residual oxygen concentration in the exhaust gas, that is, a binary value indicating whether the property in the exhaust gas is lean or rich with respect to the stoichiometric air-fuel ratio. Generate a signal.

The ECU (electronic control unit) 35 includes an input / output device, a storage device (ROM, RAM, etc.), a central processing unit (CPU), a timer counter, and the like. The ECU 35 performs overall control of the engine 1.
In addition to the air-fuel ratio sensor 31 and the oxygen sensor 33 described above, detection information from various sensors such as a crank angle sensor 36 that detects the crank angle of the engine 1 is input to the input side of the ECU 35.

  The output side of the ECU 35 is connected to various output devices such as the port injector 17 and the spark plug 29 described above. The various output devices output the fuel injection amount, fuel injection timing, ignition timing, and the like calculated by the ECU 35 based on detection information from the sensors. An appropriate target air-fuel ratio is set based on detection information from various sensors, and an appropriate amount of fuel is injected from the port injector 17 at an appropriate timing so that the actual air-fuel ratio becomes the target air-fuel ratio. The amount of air introduced into the combustion chamber 13 is adjusted by a throttle valve (not shown), and spark ignition is performed at an appropriate timing by the spark plug 29.

Further, the ECU 35 controls the amount of fuel from the port injector 17 and the throttle valve so that the air-fuel ratio of the exhaust gas flowing into the catalyst 27 varies between the lean air-fuel ratio and the rich air-fuel ratio with the stoichiometric air-fuel ratio as a boundary. The air-fuel ratio control means 37 for controlling the opening degree of the catalyst and the catalyst deterioration determination means 39 for determining the deterioration of the purification performance of the catalyst 27 are provided.
In order to maintain the purification performance of the catalyst 27, it is necessary to maintain the air-fuel ratio of the exhaust gas in the stoichiometric air-fuel ratio state. For this reason, the air-fuel ratio control means 37 uses the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 13. Is controlled alternately with a predetermined target amplitude between the rich side and the lean side around the theoretical air-fuel ratio. Further, based on the output of the air-fuel ratio sensor 31, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 13 is feedback-controlled so that the air-fuel ratio upstream of the catalyst 27 becomes the stoichiometric air-fuel ratio.

Further, the catalyst deterioration determination means 39 determines the number of inversions (fluctuations) of the lean air-fuel ratio and the rich air-fuel ratio in the air-fuel ratio sensor 31 provided on the upstream side of the catalyst 27 and the oxygen sensor 33 provided on the downstream side of the catalyst 27. Based on this, the deterioration of the catalyst 27 is determined. Here, more preferably, the lean air-fuel ratio and the rich air-fuel ratio are preferably the lean air-fuel ratio and the rich air-fuel ratio with respect to the stoichiometric air-fuel ratio.
For example, the number of inversions NF of the air-fuel ratio sensor 31 on the upstream side of the catalyst 27 and the number of inversions NR of the oxygen sensor 33 on the downstream side of the catalyst 27 are calculated, and the ratio (NR / NF) is calculated. Is larger than a predetermined reference value, it is determined that the catalyst 27 has deteriorated.
Further, when the fluctuation amount of the output signal of the air-fuel ratio sensor 31 is large or small outside the predetermined range, the catalyst deterioration determination unit 39 temporarily stops the deterioration determination by limiting the count-up as the number of inversions. Like to do.

According to the above configuration, the catalyst deterioration determination unit 39 determines the deterioration by limiting the count up of the number of inversions (the number of fluctuations) when the fluctuation amount of the output signal of the upstream air-fuel ratio sensor 31 is out of the predetermined range. Therefore, regardless of the amount of variation in the air-fuel ratio upstream of the catalyst 27, only the variation in the air-fuel ratio suitable for determining the deterioration of the catalyst 27 is picked up and determined, so that a determination result without erroneous determination is obtained. be able to.
Therefore, even if the amplitude and period of the air-fuel ratio are set with priority on exhaust gas purification performance and drivability, a determination result without erroneous determination can be obtained.

  Further, when the fluctuation amount of the output signal of the upstream air-fuel ratio sensor 31 is out of the predetermined range, the deterioration determination is temporarily interrupted by limiting the number of determinations, so that the output signal of the air-fuel ratio sensor 31 is When the fluctuation amount of the current value falls within the predetermined range, the interruption is canceled, the count-up is continued, and the deterioration determination is continued. For this reason, the frequency and accuracy of deterioration determination of the catalyst 27 are not impaired. Compared with the case where the deterioration determination is stopped and a new determination condition is awaited, a decrease in the frequency and accuracy of deterioration determination is prevented.

In some embodiments, the catalyst deterioration determination means 39 shown in FIG. 1 is configured as shown in FIG.
As shown in FIG. 2, the catalyst deterioration determination means 39 is an upstream inversion detection unit that detects a change between rich and lean air-fuel ratio upstream of the catalyst 27 that is determined based on the output of the air-fuel ratio sensor 31. 41, an upstream side count unit 43 that counts up the number of times of switching of the upstream side air-fuel ratio detected by the upstream side inversion detection unit 41, and the downstream side air-fuel ratio that is determined based on the output of the oxygen sensor 33 A downstream inversion detector 45 that detects a change between rich and lean, a downstream counter 47 that counts up the number of downstream air-fuel ratio changes detected by the downstream inversion detector 45, and the upstream side The ratio (NR / NF) of the upstream count number (NF) by the count unit 43 and the downstream count number (NR) by the downstream count unit 47 A determination unit 49 that performs deterioration determination based on the determination result, a determination result output unit 51 that outputs a determination result by the determination unit 49 to notify the driver, etc. A count control unit 53 that interrupts the count-up of the upstream-side count unit 43 and the downstream-side count unit 47.

Further, the determination unit 49 that performs deterioration determination calculates a ratio (NR / NF), and determines that the catalyst 27 is deteriorated when the ratio is larger than a preset reference value, and the result is output as a determination result output unit. By 51, the deterioration state of the catalyst 27 is notified to the driver or the like. That is, the determination result is output when the catalyst 27 is deteriorated.
The determination by the determination unit 49 is constant every time it counts up, every fixed time as described later, every time it is operated, or every time the upstream count number (NF) reaches a predetermined number of times. It may be calculated for each condition and output as a determination result.

According to the above configuration, the upstream count number (NF) of the number of times of switching of the upstream air-fuel ratio by the upstream side count unit 43 and the downstream count number of the number of times of switching of the downstream air-fuel ratio by the downstream side count unit 47 ( Since the deterioration determination is performed based on the ratio (NR / NF) to (NR), the deterioration of the catalyst 27 can be determined easily and accurately.
Further, the count control unit 53 interrupts the count-up of the upstream count unit 43 and the downstream count unit 47 when the fluctuation amount of the output signal of the air-fuel ratio sensor 31 is out of the predetermined range. Surely done.
In addition, since the determination result output unit 51 notifies the driver or the like that the catalyst 27 is in a deteriorated state, it is possible to prompt subsequent treatment.

  In some embodiments, the downstream count unit 47 of the catalyst deterioration determination means 39 shown in FIG. 2 performs the next after the upstream air-fuel ratio switching by the upstream air-fuel ratio sensor (LAFS) 31 is detected. When the air-fuel ratio switching of the downstream oxygen sensor 33 is detected before the detected upstream air-fuel ratio switching, the number of times of switching (NR) of the downstream air-fuel ratio is counted up. It is configured.

FIG. 9 shows the count-up state of the upstream count number (NF) by the upstream count unit 43 and the downstream count number (NR) by the downstream count unit 47.
FIG. 9A shows changes in the oxygen concentration output signal by the upstream air-fuel ratio sensor (LAFS) 31. FIG. 9B shows a change state of the integrated value of the upstream oxygen amount calculated based on the oxygen concentration output signal. After the upstream air-fuel ratio switching is detected, the integrated value is reset to zero. Indicates the accumulated state. FIG. 9C shows an output signal from the oxygen sensor 33 in the case of a deteriorated catalyst. FIG. 9D shows an output signal from the oxygen sensor 33 in the case of a normal catalyst. FIG. 9E shows a count-up state of the number of times of switching of the upstream side air-fuel ratio (NF), showing that it increases stepwise. FIG. 9F shows the downstream in the case of a deteriorated catalyst. It shows the count-up state of the number of times of switching (NR) of the side air-fuel ratio, and shows that it increases corresponding to the upstream count-up state. FIG. 9G shows the case of a normal catalyst, and oxygen is absorbed by the catalyst and consumed in the reaction. Therefore, the downstream oxygen sensor 33 does not recognize the inversion and does not count up.

In FIG. 9 (A), after the upstream air-fuel ratio switch (LAFS) 31 is detected by the upstream air-fuel ratio sensor (LAFS) 31 until before the next upstream air-fuel ratio switch detected, that is, Between t _{1 and} t ₂ , the output of the air-fuel ratio sensor 31 shows a rich state, and the oxygen amount integrated value ΣdO ₂ during that time finally has an upper limit determination threshold value R2 and a lower limit determination threshold value on the rich side at time t _2. It is located between R1. For this reason, when the output change of the downstream oxygen sensor (RO ₂ S) is in the count permissible region, the change from the lean region to the rich region is detected at point P in the case of the deteriorated catalyst, so the downstream air-fuel ratio is detected. The number of times of switching (NR) is counted up.

The number of times of switching (NR) by the downstream oxygen sensor 33 is defined as the number of detections from when the upstream air-fuel ratio sensor 31 by the upstream air-fuel ratio sensor 31 is detected until it is next detected. As a result, the number of switching of the air-fuel ratio on the downstream side of the catalyst in accordance with the fluctuation of the air-fuel ratio of the exhaust gas can be accurately counted up. That is, by counting the inversion by the downstream oxygen sensor 33 within the inversion cycle by the upstream air-fuel ratio sensor 31, it is possible to accurately count up the number of times the air-fuel ratio on the downstream side of the catalyst is switched.
Thus, even when the catalyst 27 is deteriorated, if the fluctuation of the exhaust gas air-fuel ratio is small, it is erroneously determined as normal when the fluctuation of the downstream air-fuel ratio is small and the downstream air-fuel ratio does not change. Can prevent problems.

The switching of the upstream air-fuel ratio by the upstream air-fuel ratio sensor (LAFS) 31 detects the switching between the rich air-fuel ratio and the lean air-fuel ratio when the output value of the air-fuel ratio sensor 31 becomes the stoichiometric air-fuel ratio. It is like that.
In addition, the downstream air-fuel ratio is switched by the downstream oxygen sensor 33 when the output value of the oxygen sensor 33 changes from the rich air-fuel ratio to the lean air-fuel ratio to reach a predetermined lean air-fuel ratio, or from the lean air-fuel ratio. When the air-fuel ratio is changed to a predetermined rich air-fuel ratio, switching between the rich air-fuel ratio and the lean air-fuel ratio is detected.
The timing for detecting the switching between the rich air-fuel ratio and the lean air-fuel ratio based on the output value of the upstream air-fuel ratio sensor 31 and the switching between the rich air-fuel ratio based on the output value of the downstream oxygen sensor 33 and the lean air-fuel ratio are detected. By combining sensors having different timings, it is possible to accurately detect the number of times of switching of the upstream air-fuel ratio and the number of times of switching of the downstream air-fuel ratio necessary for determining deterioration.

In some embodiments, the catalyst deterioration determination unit 57 shown in FIG. 3 detects the switching of the upstream air-fuel ratio based on the output of the upstream air-fuel ratio sensor 31 in the catalyst deterioration determination unit 39 of FIG. And an upstream oxygen amount integrating unit 59 for calculating an integrated value of the oxygen amount from the time it is detected to the next time.
In the count control unit 61, when the integrated value by the upstream oxygen amount integrating unit 59 is outside the predetermined upper and lower limit integration range, the upstream count unit 43 counts up the number of times the upstream air-fuel ratio is switched and the downstream The counting of the number of times of switching of the downstream air-fuel ratio by the side counting unit 47 is interrupted.

The oxygen amount (dO ₂ ) [g] based on the output of the air-fuel ratio sensor 31 is calculated by calculating the output signal (A / F) of the air-fuel ratio sensor 31, the fuel amount signal (Qf) from the port injection injector 17, the crank It is calculated using the engine speed signal from the output of the angle sensor 36. Specifically, it is calculated by the following equation (1).
dO ₂ = {(A / F) − (A / F) c} × Qf × d × T × {Ne / (120 / N)}
× 0.23 (1)
Here, (A / F) is the actual air-fuel ratio obtained from the air-fuel ratio sensor 31, (A / F) c is the center A / F, Qf is the fuel injection amount per ignition [g], and d is the gasoline specific gravity. , T is the calculation cycle [sec], Ne is the engine speed [rpm], and N is the number of cylinders.
(A / F) c is basically the value of the stoichiometric air-fuel ratio, but is appropriately corrected by sub A / F feedback based on the output of the oxygen sensor 33.

Then, the upstream oxygen amount integrating unit 59 integrates the oxygen amount calculated for each calculation cycle in the ECU 35 to calculate an upstream oxygen amount integrated value (ΣdO ₂ ). If this oxygen amount integrated value (ΣdO ₂ ) is an upper / lower limit value, for example, a value between L1 and L2 on the lean side and a value between R1 and R2 on the rich side, as shown in FIG. Permits counting up, and stops counting up when the value falls outside the upper and lower limits.
The upstream oxygen amount integrating unit 59 resets the integrated value to zero after the switching of the upstream air / fuel ratio of the air / fuel ratio sensor 31 is detected, and then starts calculating the integrated value. Since the air-fuel ratio is reset to zero when the air-fuel ratio is switched between rich and lean, the calculation of the integrated value of the oxygen amount by the upstream oxygen amount integrating unit 59 becomes clear, and the comparison with a predetermined upper and lower limit value is ensured. It can be carried out.

According to the above configuration, the integrated value of the oxygen amount flowing into the catalyst until the switching of the upstream air-fuel ratio is detected based on the output of the upstream air-fuel ratio sensor 31 is a predetermined upper and lower limit value. When out of the integration range, the counting up of the number of switching of the upstream air-fuel ratio by the upstream counting unit and the counting up of the number of switching of the downstream air-fuel ratio by the downstream counting unit are interrupted.
Therefore, only the change in the air-fuel ratio suitable for determining the deterioration of the catalyst 27 can be reliably picked up and counted up by using the integrated value of the oxygen amount.

  Further, based on the output of the upstream air-fuel ratio sensor 31, the integrated value of the oxygen amount flowing into the catalyst until the switching of the upstream air-fuel ratio is detected, the rich value is rich between L1 and L2 on the lean side. Since the determination is made based on the range defined by using the upper limit value and the lower limit value, such as between R1 and R2, the downstream side when the fluctuation of the exhaust gas air-fuel ratio is small even when the catalyst 27 is deteriorated. When the fluctuation of the side air-fuel ratio is small and there is no switching of the downstream side air-fuel ratio, there is a problem of misjudging as normal, or when the fluctuation of the exhaust gas air-fuel ratio is large even when the catalyst 27 is normal Can prevent the problem of erroneous determination of deterioration when the downstream air-fuel ratio varies greatly and the downstream air-fuel ratio is switched.

That is, FIG. 10 shows misjudgment when the fluctuation of the exhaust gas air-fuel ratio is large and when it is small.
When the variation of the exhaust gas air-fuel ratio is large, as shown in FIG. 10 (B), it exceeds L2 on the lean side, and when it exceeds R2 on the rich side, even when the normal catalyst is mounted as shown in FIG. The change in the side air-fuel ratio is large, and the switching of the downstream side air-fuel ratio by the oxygen sensor 33 is detected, and there is a possibility that the failure is erroneously determined as in the case of the deteriorated catalyst shown in FIG.
When the fluctuation of the exhaust gas air-fuel ratio is small, as shown in FIG. 10 (B), it is less than L1 on the lean side, and when it is less than R1 on the rich side, even when the deteriorated catalyst shown in FIG. The change in the side air-fuel ratio is small, and the switching of the downstream side air-fuel ratio by the oxygen sensor 33 is not detected, and there is a possibility that it is erroneously determined as normal as in the case of mounting the normal catalyst shown in FIG.

  Further, the count control unit 61 holds the count-up value by the upstream-side count unit 43 and the count-up value by the downstream-side count unit 47 when the count-up is interrupted, and when the interrupt is released, Since it is added to the held count value, the frequency of deterioration determination and the accuracy do not decrease.

  In some embodiments, in the catalyst deterioration determination means 39 and 57 shown in FIGS. 2 and 3, the determination unit 49 includes an upstream count number (NF) by the upstream count unit 43 and a downstream by the downstream count unit 47. Based on the ratio (NR / NF) to the side count number (NR), when the ratio becomes larger than a predetermined reference value, it is determined that the catalyst 27 has deteriorated and a determination result is output. However, as shown in FIG. 4, the timer 55 is provided, and the determination unit 69 for deterioration determination is based on the upstream count number (NF) by the upstream count unit 43 at a certain time based on the time from the timer 55. The determination may be made based on the ratio (NR / NF) with the downstream count number (NR) by the downstream count unit 47.

  According to the configuration shown in FIG. 4, the determination is based on the ratio between the upstream count number (NF) by the upstream count unit 43 and the downstream count number (NR) by the downstream count unit 47 at a certain time. Information on the deterioration state of the catalyst 27 is obtained periodically at regular intervals.

  In some embodiments, the catalyst deterioration determination means 39 and 57 shown in FIGS. 2 and 3 include an upstream count number determination unit 73 as shown in FIG. Based on the signal that the upstream count number (NF) has reached the predetermined number of times, the determination unit 69 for deterioration determination is performed by the upstream count unit 43 during the period until the upstream count number (NF) reaches the predetermined number of times. The determination may be based on the ratio between the upstream count number (NF) and the downstream count number (NR) by the downstream count unit 47.

  According to the configuration shown in FIG. 5, the upstream count number (NF) by the upstream count unit 43 and the downstream count by the downstream count unit 47 in the period until the upstream count number (NF) reaches a predetermined number of times. Since the determination is based on the ratio to the number (NR), information on the deterioration state of the catalyst 27 is obtained periodically every time until the upstream count number (NF) reaches a predetermined number.

  In some embodiments, the catalyst deterioration determination means 39 and 57 shown in FIGS. 2 and 3 include an engine ON / OFF signal transmitter 71 as shown in FIG. The determination unit 69 for deterioration determination is based on the ratio between the upstream count number (NF) by the upstream count unit 43 and the downstream count number (NR) by the downstream count unit 47 between the start and stop of the engine 1. The determination may be made based on (NR / NF).

  According to the configuration shown in FIG. 6, based on the ratio between the upstream count number (NF) by the upstream count unit 43 and the downstream count number (NR) by the downstream count unit 47 between the start and stop of the engine. Since the determination is made, information on the deterioration state of the catalyst 27 is obtained periodically every time the engine is stopped.

In some embodiments, for example, in the configuration block diagram of the catalyst deterioration determination unit 57 shown in FIG. 3, the control flow of catalyst determination is shown in FIGS.
As shown in FIG. 7, when the control of the catalyst deterioration diagnosis is started, in step S21, the lean air-fuel ratio on the upstream side of the catalyst 27 and the count number (NF) of the number of inversions of the rich air-fuel ratio, and the downstream side of the catalyst 27 are counted. The lean air-fuel ratio and the count number (NR) of the number of inversions of the rich air-fuel ratio are counted up. Therefore, first, the “NF, NR count up” subroutine of step S21 will be described with reference to FIG.

In step S41 of FIG. 8, it is determined whether the reversal of the air-fuel ratio on the upstream side of the catalyst 27 has occurred. That is, it is determined whether the rich lean has been switched based on the output signal of the air-fuel ratio sensor 31. If not, the process proceeds to step S42, and the oxygen amount dO ₂ supplied to the catalyst 27 is calculated. This oxygen amount dO ₂ is calculated using the above-described equation (1).
In step S43, the oxygen amount calculated in step S42 is integrated to calculate an oxygen amount integrated value (ΣdO ₂ ). That is, by adding the current oxygen content in the oxygen amount in the previous operation cycle _{(ΣdO 2 (n) = ΣdO} 2 (n-1) + dO 2), to calculate the amount of oxygen accumulated value (ΣdO _2). That is, the oxygen amount integrated value (ΣdO ₂ ) is an oxygen integrated amount integrated from the previous upstream air-fuel ratio inversion to the current upstream air-fuel ratio switching.

On the other hand, if the reversal of the air-fuel ratio on the upstream side of the catalyst 27 has occurred in step S41, the determination becomes Yes, and the process proceeds to step S44. In step S44, it is determined whether the oxygen amount integrated value (ΣdO ₂ ) calculated in step S43 until the inversion occurs is within a predetermined range. That is, the integrated oxygen amount accumulated from the previous inversion of the upstream air-fuel ratio to the current upstream air-fuel ratio switching is specifically the upper and lower limits of the predetermined range are the lean side shown in FIG. Is between L1 and L2, and between R1 and R2 on the rich side.
If it is within this range, the routine proceeds to step S45, where the lean air fuel ratio upstream of the catalyst 27 and the count number (NF) of the number of inversions of the rich air fuel ratio are counted up. If it exceeds or falls below the predetermined range, the process ends without counting up.

Next, in step S46, it is determined whether the reverse flag of the oxygen sensor (RO ₂ S) 33 on the downstream side of the catalyst 27 is established. If it is determined that the condition is satisfied, the routine proceeds to step S47, where the lean air / fuel ratio downstream of the catalyst 27 and the number of inversions of the rich air / fuel ratio (NR) are counted up, and at step S48, the amount of oxygen is increased. The integrated value (ΣdO ₂ ) is reset to zero.
If the inversion flag is not set, the process ends without counting up. The establishment of the reverse flag of the oxygen sensor (RO ₂ S) 33 will be described later.

  After the “NF, NR count up” subroutine shown in steps S41 to S48 is completed, the process returns to FIG. 7 again. In step S22 of FIG. 7, the reversal of the air-fuel ratio on the upstream side of the catalyst 27 occurs again. Determine whether. That is, it is determined whether the rich lean has been switched based on the output signal of the air-fuel ratio sensor 31.

If it is determined that the switch has been made, the process proceeds to step S23 where the lean flag (RO ₂ S lean flag) of the oxygen sensor 33, the rich flag (RO ₂ S rich flag) of the oxygen sensor 33, and the reverse flag of the oxygen sensor 33 (RO ₂ S inversion flag) are all reset.

In step S24, it is determined whether the air-fuel ratio sensor 31 is rich and the oxygen sensor 33 is equal to or less than the lean determination value (lean region). That is, it is determined whether or not it is in the area A shown in FIGS. This region A means that the oxygen sensor 33 will be inverted from lean to rich from now on. When the determination in step S24 is Yes, the process proceeds to step S25 and the lean flag (RO ₂ of the oxygen sensor 33). S lean flag) is established.

On the other hand, if the determination in step S24 is No, the process proceeds to step S26 to determine whether the air-fuel ratio sensor 31 is lean and the oxygen sensor 33 is greater than or equal to the rich determination value (rich region). That is, it is determined whether or not it is in the region B shown in FIGS. This region B means that the oxygen sensor 33 will be reversed from rich to lean from now on. If the determination in step S26 is Yes, the process proceeds to step S27 and the rich flag (RO ₂₎ of the oxygen sensor 33 is reached. S rich flag) is established.

If it is determined in step S22 that the air-fuel ratio sensor 31 is not inverted and the determination is No, the process proceeds to step S28, the lean flag (RO ₂ S lean flag) of the oxygen sensor 33 is established, and the oxygen sensor 33 is rich. It is determined whether it is equal to or greater than the determination value (rich region). In other words, it is determined whether or not the region A is shifted to the region C shown in FIG. If the determination in step S28 is yes, the process proceeds to step S30, and the reverse flag of the oxygen sensor 33 is established.

If the determination in step S28 is No, the process proceeds to step S29, whether the rich flag (RO ₂ S rich flag) of the oxygen sensor 33 is established, and whether the oxygen sensor 33 is equal to or greater than the lean determination value (lean region). Determine. In other words, it is determined whether or not the region D shown in FIG. If the determination in step S29 is yes, the process proceeds to step S30, and the reverse flag of the oxygen sensor 33 is established.

  As described above, the information that establishes the inversion flag of the oxygen sensor 33 in step S30 is used in step S46 of the “NF, NR count-up” subroutine in the next calculation cycle, and the NR number is counted up in step S47. Is executed.

Therefore, in the flowcharts shown in FIGS. 7 and 8, as shown in FIGS. 9A and 9C, the output of the oxygen sensor 33 changes from lean to rich while the output of the air-fuel ratio sensor 31 is between t _{1 and} t _2. In the case of inversion, the inversion of the oxygen sensor 33 is counted up. Similarly, when the output of the oxygen sensor 33 is inverted from rich to lean during the period from t ₂ to t ₃ , the oxygen sensor 33 It shows that the sensor 33 counts up inversion.

  7 and 8, the upstream count number (NF) by the upstream count unit 43 and the downstream count number (NR) by the downstream count unit 47 can be calculated.

  According to one embodiment of the present invention, it is possible to obtain a determination result with no erroneous determination regardless of the amount of fluctuation in the upstream air-fuel ratio that changes the air-fuel ratio upstream of the exhaust purification catalyst alternately lean and rich. In addition, since the determination result can be obtained without impairing the frequency of deterioration determination, sensors for detecting the air-fuel ratio are provided upstream and downstream of the exhaust purification catalyst, respectively, and the air-fuel ratio upstream of the catalyst is made lean. It is effective for application to a catalyst deterioration diagnosis device that changes the output alternately in a rich manner and determines deterioration of the catalyst based on fluctuations in the output signals of the upstream sensor and the downstream sensor.

1 engine (internal combustion engine)
17 Port injection injector 23 Exhaust passage 27 Catalyst (exhaust aftertreatment means)
31 Air-fuel ratio sensor (upstream sensor)
33 Oxygen sensor (downstream sensor)
35 ECU (Electronic Control Unit)
36 Crank angle sensor 37 Air-fuel ratio control means 39, 57 Catalyst deterioration determination means 41 Upstream inversion detection section 43 Upstream count section 45 Downstream inversion detection section 47 Downstream count section 49 Determination section 51 Determination result output sections 53, 61 Control unit 55 Timer 59 Upstream oxygen amount integration unit 71 Engine ON / OFF signal transmission unit 73 Upstream count number determination unit

Claims (10)

Exhaust aftertreatment means provided in the exhaust passage of the internal combustion engine;
Air-fuel ratio control means for varying the air-fuel ratio of the exhaust gas flowing into the exhaust after-treatment means between a lean air-fuel ratio and a rich air-fuel ratio;
An upstream sensor that is provided in the exhaust passage upstream of the exhaust aftertreatment means and detects an air-fuel ratio of exhaust flowing into the exhaust aftertreatment means;
A downstream sensor that is provided in the exhaust passage downstream of the exhaust aftertreatment means and detects an air-fuel ratio of the exhaust gas flowing out from the exhaust aftertreatment means;
Catalyst deterioration determination means for determining deterioration of the exhaust aftertreatment means based on the number of fluctuations of the lean air-fuel ratio and the rich air-fuel ratio in the upstream sensor and the downstream sensor,
The catalyst deterioration diagnosing device for an internal combustion engine, wherein the catalyst deterioration determining means limits the count of the number of fluctuations based on a fluctuation amount of an output value of the upstream sensor. The catalyst deterioration determination means includes
An upstream inversion detection unit that detects switching between a rich air-fuel ratio of an upstream air-fuel ratio that is an air-fuel ratio on the upstream side that is determined based on an output value of the upstream sensor, and a lean air-fuel ratio;
An upstream counting unit that counts the number of times of switching detected by the upstream inversion detection unit;
A downstream inversion detection unit that detects switching between a rich air-fuel ratio of a downstream air-fuel ratio that is an air-fuel ratio on the downstream side that is determined based on an output value of the downstream sensor, and a lean air-fuel ratio;
A downstream counting unit that counts the number of times of switching detected by the downstream inversion detection unit;
A determination unit that performs deterioration determination based on a ratio between an upstream count number by the upstream count unit and a downstream count number by the downstream count unit;
2. The counter according to claim 1, further comprising: a count control unit that interrupts counting of the upstream side count unit and the downstream side count unit when a fluctuation amount of the output value of the upstream side sensor is out of a predetermined range. Catalyst deterioration diagnosis device for internal combustion engines. The upstream inversion detection unit detects a change between the rich air-fuel ratio and the lean air-fuel ratio when the output value of the upstream sensor becomes the stoichiometric air-fuel ratio,
The downstream inversion detection unit changes when the output value of the downstream sensor changes from a rich air-fuel ratio to a lean air-fuel ratio to a predetermined lean air-fuel ratio, or changes from a lean air-fuel ratio to a rich air-fuel ratio and changes to a predetermined rich air-fuel ratio. 3. The catalyst deterioration diagnosis apparatus for an internal combustion engine according to claim 2, wherein when the air-fuel ratio is reached, switching between the rich air-fuel ratio and the lean air-fuel ratio is detected.   The downstream count unit performs the switching of the downstream air-fuel ratio after the switching of the upstream air-fuel ratio is detected and before the switching of the upstream air-fuel ratio detected next. 3. The catalyst deterioration diagnosis device for an internal combustion engine according to claim 2, wherein the number of times of switching of the downstream air-fuel ratio is counted when detected.   5. The deterioration determination by the determination unit is determined based on a ratio between an upstream count number by the upstream count unit and a downstream count number by the downstream count unit in a certain time. The catalyst deterioration diagnosis device for an internal combustion engine according to any one of the above.   The deterioration determination by the determination unit is based on the ratio of the upstream count number by the upstream count unit and the downstream count number by the downstream count unit in a certain period until the upstream count number reaches a predetermined number of times. The catalyst deterioration diagnosis apparatus for an internal combustion engine according to any one of claims 2 to 4, wherein the determination is made.   The deterioration determination by the determination unit is determined based on a ratio between an upstream count number by the upstream count unit and a downstream count number by the downstream count unit between engine start and stop. The catalyst deterioration diagnosis apparatus for an internal combustion engine according to any one of claims 2 to 4. Further, the catalyst deterioration determining means is based on the output of the upstream sensor, and from the time when the switching of the upstream air-fuel ratio is detected to the time before the switching of the upstream air-fuel ratio detected next. An upstream oxygen amount integrating unit that calculates an integrated value of the oxygen amount between
The count control unit counts the number of times of switching of the upstream air-fuel ratio by the upstream count unit and the downstream when the integrated value by the upstream oxygen amount integrating unit is outside a predetermined upper and lower limit integration range. The catalyst deterioration diagnosis apparatus for an internal combustion engine according to any one of claims 2 to 7, wherein the counting of the number of times the downstream air-fuel ratio is switched by the side counting unit is interrupted.   9. The upstream oxygen amount integrating unit, after detecting the switching of the upstream air-fuel ratio, resets the integrated value to zero and starts calculating the integrated value. A catalyst deterioration diagnosis device for an internal combustion engine as described.   10. The internal combustion engine according to claim 8, wherein the count control unit holds a count value by the upstream count unit and a count value by the downstream count unit during the interruption. Engine catalyst deterioration diagnosis device.

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