JP3304663B2 - Degradation diagnosis device for exhaust purification catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for diagnosing deterioration of an exhaust purification catalyst, and more particularly to an apparatus having an air-fuel ratio sensor on each of an upstream side and a downstream side of an exhaust purification catalyst.

[0002]

2. Description of the Related Art In recent years, an exhaust system of an automobile gasoline engine is provided with an oxidation-reduction type exhaust purification catalyst (hereinafter, three-way catalyst) in order to reduce harmful exhaust gas components. The three-way catalyst is a device that purifies exhaust gas by oxidizing hydrocarbons (HC) and carbon monoxide (CO) while reducing nitrogen oxides (NO _x ). Since the redox reaction of the three-way catalyst is performed only in a narrow area (window) near the stoichiometric air-fuel ratio, an air-fuel ratio sensor (O ₂ sensor) is installed in the exhaust manifold or the like, and the air-fuel ratio is fed back based on the output signal. Controlling.
On the other hand, the three-way catalyst deteriorates and its purification efficiency decreases as the service period becomes longer.However, since this deterioration can be confirmed only by a method using an exhaust gas tester at the time of periodic inspection or the like, the purification efficiency is reduced. Nevertheless, there was a risk that the device would continue to be used.

[0003] Therefore, in JP-A-61-286550, etc., on the upstream side and the downstream side of the three-way catalyst provided an O ₂ sensor, respectively, the degradation of the three-way catalyst based on the output signal of the O ₂ sensor Is disclosed. This degradation diagnosis apparatus focuses on the fact that the air-fuel ratio fluctuates in a short cycle around a target air-fuel ratio (for example, a stoichiometric air-fuel ratio) by feedback control, and inverts the upstream O ₂ sensor that changes in response to this. By comparing the frequency with that on the downstream side, deterioration of the three-way catalyst is determined.

[0004] That is, since the three-way catalyst has the ability to store the residual oxygen in the exhaust gas, the exhaust gas that has passed through the three-way catalyst contains only a small amount of oxygen. Therefore, when the three-way catalyst maintains normal purification efficiency, the output signal of the downstream O ₂ sensor is less likely to fluctuate,
As the amplitude becomes smaller, the inversion frequency becomes very low.
Therefore, when calculating the inversion frequency ratio of the upstream O ₂ sensor output signal with the downstream O ₂ sensor and the air-fuel ratio is varied (inversion frequency of the reversal frequency / upstream O ₂ sensor downstream O ₂ sensor), Its value is a very small value.

However, when the three-way catalyst is deteriorated and the purification efficiency is reduced, the purification of harmful exhaust gas components is not carried out, and the capacity for storing oxygen is also reduced. Start passing. As a result, the output signal of the downstream O ₂ sensor also changes in the same manner as the output signal of the upstream O ₂ sensor, and the above-mentioned inversion frequency ratio gradually approaches 1. Therefore, in the above-described deterioration diagnosis device, the deterioration of the three-way catalyst is determined from the relationship between the purification efficiency of the three-way catalyst and the reversal frequency ratio.

[0006]

[SUMMARY OF THE INVENTION Incidentally, if the deterioration of the three-way catalyst does not much headway, the output signal of the downstream O ₂ sensor is not only small amplitude, the rich side and lean at a relatively large period Shift to the side. For this reason, as shown in FIG. 8, when the upper and lower reversal reference values THH and THL for forming the hysteresis are set near the stoichiometric air-fuel ratio to detect the reversal frequency, when the reversal frequency is shifted to the rich side or the lean side, The output signal is the inverted reference value THH,
The inversion frequency is counted lower than the actual value without crossing THL. For example, in FIG. 8, the point indicated by “・” is an inversion detection point, and the signal is output only four times although the inversion is actually performed 16 times. Therefore, even if the deterioration progresses to some extent, the value of the above-mentioned reversal frequency ratio does not easily increase, and the deterioration diagnosis device determines that the three-way catalyst is normal.

Further, the above-mentioned shift to the rich side or the lean side has a problem that the period and amplitude of the shift are different depending on the state of the engine body and the auxiliary equipment, and the value of the reversal frequency ratio greatly varies depending on each engine. There was also. Therefore, conventionally, it is impossible to set the reversal frequency ratio, which is the reference for the deterioration determination, to a very high value, and even if the purification efficiency is within the allowable limit, the three-way catalyst may be determined to be deteriorated and replaced. was there. As is well known, a three-way catalyst is a very expensive part using a precious metal such as platinum, and
Not only increased maintenance man-hours, but also resource saving and running cost were problems.

[0008] The present invention has been made in view of the above situation,
It is an object of the present invention to provide an exhaust gas purifying catalyst deterioration diagnosis device capable of determining the deterioration of the three-way catalyst with high accuracy even if the output signal of the downstream O ₂ sensor shifts to the rich side or the lean side.

[0009]

SUMMARY OF THE INVENTION Therefore, according to a first aspect of the present invention, there is provided a fuel cell system based on an output signal of a downstream air-fuel ratio sensor provided downstream of an exhaust purification catalyst in an exhaust passage of an internal combustion engine.
Of the exhaust gas purifying catalyst for diagnosing the deterioration of the exhaust gas purifying catalyst.
The output signal of the downstream air-fuel ratio sensor is
The signal is rich or rich depending on the operating state of the internal combustion engine.
In the exhaust gas purifying catalyst.
An average value calculating means for calculating an average value of the output signal output from the downstream air-fuel ratio sensor during the deterioration diagnosis, and an inversion reference value using the average value calculated by the average value calculating means. And a deterioration determining means for determining the deterioration of the exhaust purification catalyst based on the number of times the output signal of the downstream air-fuel ratio sensor crosses the inversion reference value set by the reference value setting means. The present invention proposes a device for diagnosing deterioration of an exhaust purification catalyst, which is provided with the device.

According to a second aspect of the present invention, in the deterioration diagnosing apparatus according to the first aspect, the deterioration judging means uses the inverted reference value set by the reference value setting means as an output signal of the downstream air-fuel ratio sensor. A first inversion frequency calculating means for calculating an inversion frequency of the output signal of the downstream side air-fuel ratio sensor from the number of times that
It is proposed that the deterioration of the exhaust purification catalyst is determined based on the inversion frequency of the output signal of the downstream air-fuel ratio sensor calculated by the inversion frequency calculation means.

According to a third aspect of the present invention, in the deterioration diagnosis apparatus according to the second aspect, an upstream air-fuel ratio sensor provided upstream of the exhaust gas purification catalyst in the exhaust passage; A second inversion frequency calculating means for calculating an inversion frequency of the output signal; wherein the deterioration determining means includes an inversion frequency of the output signal of the downstream air-fuel ratio sensor calculated by the first inversion frequency calculation means; It is proposed that the deterioration of the exhaust gas purification catalyst is determined by comparing the output signal of the upstream air-fuel ratio sensor with the inversion frequency calculated by the second inversion frequency calculation means.

According to a fourth aspect of the present invention, in the deterioration diagnosis apparatus according to the first aspect, the average value calculating means calculates an average value O ₂ ave of an output signal of the downstream air-fuel ratio sensor and a previous average value. Assuming that O ₂ ave (n−1), the value of the current output signal of the downstream air-fuel ratio sensor is O ₂ real, and the filter constant is a, the following equation is used: O ₂ ave = a × O ₂ ave (n− 1) We propose a method characterized by calculating by + (1-a) × O ₂ real.

[0013]

According to the first aspect of the present invention, when the output signal of the downstream air-fuel ratio sensor shifts to the rich side or the lean side,
The average value and the inversion reference value also follow and shift. Therefore, even if the output signal is inverted with a relatively small amplitude, it crosses the inversion reference value, and the number of inversions is accurately measured.

Further, in the deterioration diagnosis apparatus according to the present invention, for example, when the inversion frequency of the output signal of the downstream air-fuel ratio sensor calculated by the first inversion frequency calculation means becomes larger than a predetermined value, the deterioration judgment is performed. The means determines that the exhaust purification catalyst has deteriorated. Further, in the deterioration diagnosis device of claim 3, for example, the inversion frequency of the output signal of the downstream air-fuel ratio sensor calculated by the first inversion frequency calculation means and the inversion frequency of the upstream air-fuel ratio sensor calculated by the second inversion frequency calculation means. When the ratio of the output signal to the reversal frequency approaches 1, the exhaust gas purification efficiency of the exhaust gas purification catalyst has decreased below the limit, and the deterioration determination means has determined that the exhaust gas purification catalyst has deteriorated. Is determined.

In the deterioration diagnosis apparatus according to the present invention, for example, by appropriately setting the filter constant a, when the output signal shifts to the rich side or the lean side, the average value and the inversion reference value follow. The precision and response when shifting are adjusted. Become.

[0016]

An embodiment of the present invention will be described below with reference to the drawings.
I will tell. FIG. 1 shows an inside view of the apparatus provided with the deterioration diagnosis apparatus according to the present invention.
It is a schematic structure figure showing a fuel engine. In FIG.
The fuel injection valve 3 is installed in the intake port 2 of each cylinder 1 for each cylinder.
Air cleaning via the attached intake manifold 4
Na 5, Karman vortex air flow sensor 6, throttle
Valve 7, ISC (idle speed controller) 8
Are connected. Also, exhaust port
An exhaust pipe 12 is provided at 10 through an exhaust manifold 11.
The exhaust pipe 12 is connected to a three-way catalyst 13 and
A muffler (not shown) is attached. Exhaust pipe 12
In the pipeline, upstream and downstream of the three-way catalyst 13 are provided, respectively.
Upstream O_TwoSensor 14 and downstream O _TwoSensor 15 and
Is being worn. These O_TwoSensors 14 and 15 are three-way
Reacts with the oxygen in the exhaust gas before and after passing through the medium 13,
Generates a voltage corresponding to the concentration of

The engine 1 has a crank angle sensor 20 for detecting the engine rotation speed Ne and the like, and a cooling water temperature TW.
A throttle sensor 22 for detecting the opening θTH of the throttle valve 7 and an atmospheric pressure sensor 2 for detecting the atmospheric pressure Ta are provided in the intake system.
3. Various sensors such as an intake air temperature sensor 24 for detecting the intake air temperature Ta are connected. In the figure, reference numeral 30 denotes a spark plug disposed above a combustion chamber 31;
This is an ignition coil that outputs a high voltage to the ignition coil.

On the other hand, in the cabin, an input / output device (not shown) and a storage device (RO) containing a large number of control programs are provided.
M, RAM, nonvolatile RAM, etc.), central processing unit (CP
U), an ECU (engine control unit) 40 including a timer counter and the like is provided. ECU40
On the input side, various sensors other than the O ₂ sensors 14 and 15 are connected, and detection information from these is input. On the output side, the fuel injection valve 3, ISC8,
The ignition coil 32 and the like are connected, and an optimum value calculated based on input information from various sensors is output to these. Then, ECU 40 includes a fuel injection, ignition timing, in addition to performing the control of ISC, etc., both O ₂ sensor 14,
The catalyst deterioration determination is also performed based on the 15 output signals. In the figure, reference numeral 41 denotes a warning light installed in the vehicle compartment, which is turned on when the three-way catalyst 13 is deteriorated, and alerts the driver.

First, the fuel injection control in this embodiment will be briefly described. At the same time as the driver starts the engine 1, the fuel injection control by the ECU 40 is executed. When this control is started, the ECU 40 obtains the intake air amount information A / N per intake stroke based on the output signals of the air flow sensor 6 and the crank angle sensor 20, and determines the value and the target air-fuel ratio (normally, the stoichiometric air-fuel ratio). ) To calculate the basic fuel injection time TBASE. Next, the ECU 40 corrects the basic fuel injection time TBASE based on the output signals of the atmospheric pressure sensor 23 and the intake temperature sensor 24, and further warms up based on the output signals of the water temperature sensor 21, the throttle sensor 22, and the like. The fuel injection time TINJ is calculated by performing a correction for increasing the amount of the engine or a correction for increasing the acceleration. Then, the ECU 40 adds the invalid injection time TD for complementing the valve opening delay of the fuel injection valve 3 to the fuel injection time TINJ obtained in this way, and then adds the fuel injection valve via a fuel injection valve driver (not shown). 3 is driven.

Now, the activation of the upstream O ₂ sensor 14 is completed, the engine 1 is not in a high-load, high-speed operation state, etc.
When predetermined operating conditions are satisfied, the ECU 40 starts air-fuel ratio feedback control. When this control starts, EC
U40, the output voltage VOF with a predetermined threshold value VTH of the upstream O ₂ sensor 14 (e.g., 0.5V) to compare the magnitude of the performs feedback correction of the air-fuel ratio. That is, the upstream O
_{The two} sensors 14 determine that the air-fuel ratio of the mixture is the stoichiometric air-fuel ratio (14.
7) before and after the output voltage VOF reaches the minimum voltage (for example, 0 V).
V) to the maximum voltage (for example, 1.0 V), and when the output voltage VOF falls below the threshold value VTH (for example, 0.5 V), the fuel injection time TINJ is gradually increased to shift to the rich side. Conversely, when the output voltage VOF exceeds the threshold value VTH, the fuel injection time TINJ is gradually shortened to shift to the lean side. As a result, the air-fuel ratio of the air-fuel mixture is always kept close to the stoichiometric air-fuel ratio, and the three-way catalyst 13 purifies the exhaust gas with high efficiency.

In the air-fuel ratio feedback control in this embodiment, learning correction is performed so that the central value of the feedback correction coefficient becomes 1.0, and the learning correction amount is stored in the nonvolatile RAM.
To be stored. Then, by using the learning correction amount,
The accuracy of the above-described open loop control is improved, and the amount of deviation at the start of feedback control is reduced.

The procedure for diagnosing catalyst deterioration in this embodiment will be described below with reference to the flowcharts of FIGS. 2 to 5 and the graphs of FIGS. When the driver turns on the ignition switch and starts the engine 1, the catalyst deterioration diagnosis subroutine shown in FIGS. 2 and 3 is executed. When this subroutine is started, the ECU 40 first determines whether or not a normal flag FOK indicating that the three-way catalyst 13 is functioning normally is 1 in step S2 of FIG. Normal flag F
OK is 0 each time the ignition switch is turned off
And is set to 1 when the three-way catalyst 13 is diagnosed as normal. Therefore, immediately after the start of the engine 1, the normal flag FOK always becomes 0, and the ECU 4
0 means that the determination in step S2 is No (negative),
Proceed to step S4.

In step S4, the ECU 40 determines whether a condition for performing a catalyst deterioration diagnosis is satisfied. Here, it is sequentially confirmed that the air-fuel ratio feedback control is performed, the engine speed Ne and the volumetric efficiency ηv are within predetermined ranges, and that both the O ₂ sensors 14 and 15 are operating normally. When all the conditions are satisfied, the determination result is Yes (Yes). Here, the reason for confirming that the engine speed Ne and the volumetric efficiency ηv are within predetermined ranges is that when these are not stable, the O ₂ concentration of the exhaust gas is not stable, and normal feedback control is performed. The condition is that the engine speed Ne and the volumetric efficiency ηv are within the ranges of the following equations (1) and (2). In the following formula, Ne1, Ne2, ηv1, ηv2
Indicates a determination threshold value, and specific values thereof are, for example, when the engine 1 is connected to an automatic transmission, Ne1 is 1400 rpm, Ne2 is 3000 rpm,
ηv1 is 25% and ηv2 is 60%.

Ne1 <Ne <Ne2 (1) ηv1 <ηv <ηv2 (2) If the result of the determination in step S4 is Yes, the ECU 40
Is then in step S6, to calculate the upstream-side reversing frequency fF, based on an output signal from the upstream O ₂ sensor 14.
As a calculation method, for example, a predetermined time (for example, 1
0 seconds) within obtains the number of times the output voltage VOF of the upstream O ₂ sensor 14 has crossed the threshold VTH (e.g., 0.5V), to the number of the upstream-side reversing frequency fF.

Next, in step S8, the ECU 40 determines whether or not the upstream inversion frequency fF is smaller than a predetermined value THp. This determination is for stopping the catalyst deterioration diagnosis when the upstream O ₂ sensor 14 deteriorates and does not function normally. That is, since the upstream O ₂ sensor 14 is always exposed to high-temperature exhaust gas, the downstream O ₂ sensor 1
5 is more likely to deteriorate due to heat, the response is reduced, and a normal electromotive force is no longer output. For this reason, the output voltage from the upstream O ₂ sensor 14 may not clearly change, and in this case, the upstream inversion frequency fF is lower than that in the normal state. Thus, the upstream inversion frequency f
When F decreases, the reversal frequency ratio fR / fF with respect to the downstream reversal frequency fR increases, and there is a possibility that the three-way catalyst 13 is erroneously determined to be deteriorated. The predetermined value THp used here is a judgment threshold value THc of the inversion frequency ratio fR / fF described later.
Is a value (for example, 0.1 Hz) set in advance based on the experimental data.

If the result of the determination in step S8 is also No, the ECU 40 proceeds to step S10 where the downstream O ₂
Based on the output voltage VOR of the sensor 15, its average value VOR
ave is calculated by the following equation. In the following formulas, VORave (n-1) is the previous average value, VOR the present output voltage of the downstream O ₂ sensor 15, a denotes a filter constant. VORave = a × VORave (n−1) + (1−a) × VOR By this calculation, the output voltage VOR of the downstream O ₂ sensor 15 is obtained.
Is shifted to rich side or lean side, the average value VORave
Will shift accordingly. The filter constant a
Is appropriately set, the accuracy and response when the average value VORave shifts following the output voltage VOR are determined.

When the calculation of the average value VORave is completed in step S10, the ECU 40 calculates the upper and lower inversion reference values THH and THL in step S12 according to the following equations. here,
α is a hysteresis constant, and is set to, for example, about 0.05 V in this embodiment. THH = VORave + α THL = VORave -α Next, ECU 40, at step S14, in a predetermined aforementioned time, inversion reference value output voltage VOR of the upper and lower downstream O ₂ sensor 15 THH, the number of times across the THL This number is determined as the downstream inversion frequency fR. FIG. 6 is a graph showing the relationship between the inversion reference values THH and THL and the output voltage VOR. In FIG. 6, the number of inversion detection points indicated by "・" becomes equal to the actual number of inversions of the output voltage VOR. I have. That is, even if the output voltage VOR of the downstream O ₂ sensor 15 shifts to the rich side or the lean side, the inversion reference value THH
, THL are similarly shifted, so that the downstream inversion frequency fR is accurately measured. The downstream-side reversal frequency fR of the measurement above and below the inversion reference value THH, the reason for using a value THL, the amplitude of the output voltage VOR of the downstream O ₂ sensor 15 is small, the output voltage VOR than a single inversion reference value This is because there is a risk of excessive measurement due to minute vibration.

Next, the ECU 40 executes step S1 in FIG.
In step 6, an inversion frequency ratio fR / fF is calculated from the upstream inversion frequency fF and the downstream inversion frequency fR.
(For example, 0.8) is determined. If the result of this determination is No, the three-way catalyst 13 has not deteriorated and, as shown in FIG. 7, normally functions at or above the lower limit E1 (for example, about 85%) of the purification efficiency ECAT. Is diagnosed, and the normal processing subroutine of FIG. 4 is executed in step S18.

In the normal processing subroutine, first, in step S32, the warning lamp 41 is turned off and the three-way catalyst 1 is turned off.
3 indicates to the driver that it is functioning properly. Next, in step S34, the ECU 40 performs an operation of deleting the failure code so that the failure code corresponding to the deterioration of the three-way catalyst 13 does not remain in the RAM. Then, in step S36, the normality flag FOK is set to 1 and the three-way catalyst 13
Remember that is functioning normally.

As described above, once the normal flag FOK is set to 1, the determination in step S2 becomes Yes at the next execution of the catalyst deterioration diagnosis subroutine. Therefore, in this case, the subroutine ends without performing the catalyst deterioration determination again until the ignition switch is turned off. On the other hand, the inversion frequency ratio f
If R / fF exceeds the predetermined value THc (0.8), step S16
If the determination result is Yes, it is diagnosed that the three-way catalyst 13 has deteriorated and the purification efficiency ECAT has fallen below the lower limit value E1 (about 85%). In step S20, the deterioration processing subroutine shown in FIG. Execute

In the deterioration processing subroutine, first, in step S42, the warning lamp 41 is turned on to notify the driver of the deterioration of the three-way catalyst 13 and urge the driver to repair it. Then, in step S44, the ECU 40 stores a failure code corresponding to the deterioration of the three-way catalyst 13 in the RAM. Thus, when performing repair, the details of the failure can be easily known by reading out the failure code, and the response such as replacement of the three-way catalyst 13 can be promptly performed.

Although the description of a specific embodiment has been completed above, embodiments of the present invention are not limited to this embodiment. That is, in the above-described embodiment, the catalyst deterioration determination is stopped only when the upstream O ₂ sensor, which is easily deteriorated by heat, is deteriorated. However, a similar measure may be taken when the downstream O ₂ sensor is deteriorated. Further, in the above embodiment, the upstream and downstream air-fuel ratio sensors are both voltage output type O ₂ sensors.
A current output type sensor such as a linear air-fuel ratio sensor may be used. Furthermore, starting the specific procedure of control,
Specific values such as the thresholds can be changed without departing from the gist of the present invention.

[0033]

According to the first aspect of the present invention, there is provided a downstream air-fuel ratio sensor provided downstream of an exhaust purification catalyst in an exhaust passage of an internal combustion engine, and an output of the downstream air-fuel ratio sensor. Mean value calculating means for calculating an average value of the signal, reference value setting means for setting an inversion reference value using the average value calculated by the average value calculating means, and inversion reference set by the reference value setting means And a deterioration determination unit that determines the deterioration of the exhaust gas purification catalyst based on the number of times the output signal of the downstream air-fuel ratio sensor crosses the output signal, so that the output signal of the downstream air-fuel ratio sensor becomes richer or leaner. Even if the shift is performed, the average value and the inversion reference value are also shifted so that the number of inversions of the output signal is accurately measured. As a result, the deterioration determination accuracy of the exhaust gas purification catalyst is improved, so that the reference value for the deterioration determination can be set high,
Replacing an exhaust purification catalyst whose purification efficiency is within an allowable limit is reduced.

Further, according to the deterioration diagnosis apparatus of the second aspect,
2. The deterioration diagnosis device according to claim 1, wherein the deterioration determination unit determines the output of the downstream air-fuel ratio sensor based on the number of times the output signal of the downstream air-fuel ratio sensor crosses the inversion reference value set by the reference value setting unit. A first inversion frequency calculating means for calculating an inversion frequency of the signal, wherein the deterioration determination means is configured to determine the deterioration of the exhaust purification catalyst based on the inversion frequency of the output signal of the downstream air-fuel ratio sensor calculated by the first inversion frequency calculation means. Is determined, the deterioration can be quantitatively determined. As a result, the deterioration determination accuracy of the exhaust gas purification catalyst is further improved, so that the reference value for the deterioration determination can be set high, and replacement of the exhaust gas purification catalyst whose purification efficiency is within an allowable limit is reduced.

According to a third aspect of the present invention, there is provided a deterioration diagnosis apparatus.
3. The deterioration diagnosis apparatus according to claim 2, wherein an upstream air-fuel ratio sensor provided upstream of the exhaust gas purification catalyst in the exhaust passage, and a second inversion frequency for calculating an inversion frequency of an output signal of the upstream air-fuel ratio sensor. Further comprising arithmetic means,
The deterioration determining means includes an inversion frequency of an output signal of the downstream air-fuel ratio sensor calculated by the first inversion frequency calculation means and an output signal of the upstream air-fuel ratio sensor calculated by the second inversion frequency calculation means. Since the deterioration of the exhaust gas purification catalyst is determined by comparing with the reversal frequency, the purification efficiency of the exhaust gas purification catalyst can be directly and quantitatively determined. Less to do.

Further, according to the deterioration diagnosis apparatus of the fourth aspect,
2. The deterioration diagnostic apparatus according to claim 1, wherein the average value calculating means includes an average value O ₂ ave of an output signal of the downstream air-fuel ratio sensor.
And the last average value _{O 2 ave (n-1)} , when the value of the O ₂ real of this output signal of the downstream air-fuel ratio sensor, the filter constant was a, the following calculation formula O ₂ ave = a × O ₂ ave (n−1) + (1−a) × O ₂ real, so that the average value and the inverted reference value are shifted following the output signal by appropriately setting the filter constant a. This makes it possible to adjust the accuracy and response of the exhaust gas purifying catalyst, and it is possible to make a deterioration determination in accordance with the layout, operating conditions, and the like of the exhaust gas purification catalyst.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an internal combustion engine including a deterioration diagnosis device according to the present invention.

FIG. 2 is a flowchart showing a procedure of a catalyst deterioration diagnosis subroutine.

FIG. 3 is a flowchart illustrating a procedure of a catalyst deterioration diagnosis subroutine.

FIG. 4 is a flowchart illustrating a procedure of a normal processing subroutine.

FIG. 5 is a flowchart illustrating a procedure of a degradation processing subroutine.

FIG. 6 is a graph showing a relationship between inversion reference values THH and THL and an output voltage VOR in the embodiment.

FIG. 7 is a graph showing the relationship between the reversal frequency ratio fR / fF and the purification efficiency ECAT.

FIG. 8 is a graph showing the relationship between the inversion reference values THH and THL and the output voltage VOR in the conventional device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine 12 Exhaust pipe 13 Three-way catalyst 14 Upstream O ₂ sensor 15 Downstream O ₂ sensor 40 ECU 41 Warning light

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI F02D 45/00 368 F02D 45/00 368G (72) Inventor Toshiro Nomura 5-33-8 Shiba 5-chome, Minato-ku, Tokyo Mitsubishi Motors Inside the Company (72) Inventor Eiji Kanao 5-33-8 Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Corporation (56) References JP-A-3-249357 (JP, A) JP-A-5-249 JP-A-5-256125 (JP, A) JP-A-5-280402 (JP, A) JP-A-5-179935 (JP, A) JP-A-5-288106 (JP, A) JP-A-7-34860 (JP, A) JP-A-5-312025 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 3/08-3/38 F01N 9/00 -11/00 F02D 41/00-41/40 F02D 43/00-45/00

Claims (4)

(57) [Claims] 1. An output signal of a downstream air-fuel ratio sensor provided downstream of an exhaust purification catalyst in an exhaust passage of an internal combustion engine.
An exhaust purification catalyst that diagnoses deterioration of the exhaust purification catalyst based on
In the medium deterioration diagnosis apparatus, the output signal of the downstream air-fuel ratio sensor is used to control the operation of the internal combustion engine.
The gear shifts to rich or lean depending on the rotation state.
Wherein during the deterioration diagnosis of the exhaust purification catalyst,
Average value calculating means for calculating an average value of the output signal output from the side air-fuel ratio sensor ; reference value setting means for setting an inversion reference value using the average value calculated by the average value calculating means; Deterioration determination means for determining deterioration of the exhaust gas purification catalyst based on the number of times the output signal of the downstream air-fuel ratio sensor crosses the inversion reference value set by the value setting means. Deterioration diagnosis device. 2. The deterioration judging means determines the inversion frequency of the output signal of the downstream air-fuel ratio sensor from the number of times the output signal of the downstream air-fuel ratio sensor crosses the inversion reference value set by the reference value setting means. A first inversion frequency calculating means for calculating, the deterioration determining means determining deterioration of the exhaust purification catalyst based on the inversion frequency of the output signal of the downstream air-fuel ratio sensor calculated by the first inversion frequency calculating means. The device for diagnosing deterioration of an exhaust purification catalyst according to claim 1, wherein: 3. An upstream air-fuel ratio sensor provided upstream of an exhaust purification catalyst in the exhaust passage, and a second inversion frequency calculating means for calculating an inversion frequency of an output signal of the upstream air-fuel ratio sensor. The deterioration determining means comprises: an inversion frequency of an output signal of the downstream air-fuel ratio sensor calculated by the first inversion frequency calculation means; and an output of the upstream air-fuel ratio sensor calculated by the second inversion frequency calculation means. 3. The deterioration diagnosis device for an exhaust gas purification catalyst according to claim 2, wherein the deterioration of the exhaust gas purification catalyst is determined by comparing the inversion frequency of the signal. 4. The average value calculating means calculates an average value O ₂ ave of an output signal of the downstream air-fuel ratio sensor, calculates a previous average value of O ₂ ave (n−1), When the value of the output signal is O ₂ real and the filter constant is a, the calculation is performed by the following equation: O ₂ ave = a × O ₂ ave (n−1) + (1−a) × O ₂ real The degradation diagnosis device for an exhaust purification catalyst according to claim 1, wherein: