JPH05256175A - Exhaust sensor degradation detecting device for engine - Google Patents

Abstract

PURPOSE:To detect the degradation of a downstream exhaust sensor easily and correctly on the basis of its output value by changing an air-fuel ratio forcibly in the specific operating region of an engine, and detecting the output value of the exhaust sensor disposed downstream of an exhaust gas purifying catalyst at this change time. CONSTITUTION:An exhaust sensor degradation detecting device detects the degradation of a downstream exhaust sensor 12 disposed downstream of an exhaust gas purifying catalyst 10 in the exhaust passage 3 of an engine. In this case, an upstream exhaust sensor 11 for controlling an air-fuel ratio is disposed upstream of the catalyst 10. On the other hand, the operating region of the engine is detected by a means A, and the fuel supply quantity of the engine is controlled by a means B. Further in a specific operating region, the air-fuel ratio is changed by a means C through a means B by the open-loop control based on the output value of the upstream exhaust sensor 11. At this time, the output value of the downstream exhaust sensor 12 is detected by a means D, and the degraded state of the downstream exhaust sensor 12 is judged by a means E on the basis of the detected output value of the downstream exhaust sensor 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a deterioration detecting device for an engine exhaust sensor.

[0002]

2. Description of the Related Art Conventionally, as one of exhaust gas purification methods for an engine, a catalytic converter having a three-way catalyst or the like is arranged in the middle of an exhaust passage, and unburned components in exhaust gas are exhausted by the chemical adsorption of the catalyst. A catalyst type exhaust emission control device for removing the above is widely known.

By the way, in such a catalyst type exhaust emission control device, since the deterioration of the catalyst directly appears as a reduction in exhaust emission purification capability, it is necessary to monitor the deterioration state of the catalyst as appropriate. As a method of detecting such a deterioration state of the exhaust gas purification catalyst, as shown in FIG. 10, between the oxygen storage capacity and the HC purification rate of the end face three-way catalyst, there is a decrease in the oxygen storage ability and the HC purification rate. Attention is paid to the fact that there is a relationship that decreases the exhaust gas, and an exhaust sensor that outputs a predetermined voltage value according to the oxygen concentration in the exhaust gas is arranged on the upstream side and the downstream side of the catalyst provided in the exhaust passage. A technique for detecting catalyst deterioration based on the ratio of the number of output reversals of each exhaust sensor during air-fuel ratio feedback control by an upstream exhaust sensor is known (for example, Japanese Patent Laid-Open No. 63-9785).
No. 2).

As described above, the catalyst deterioration is judged based on the output reversal ratio of the exhaust sensor when the oxygen storage capacity of the catalyst is kept good (that is, when the catalyst is not deteriorated). On the downstream side of the catalyst, the oxygen concentration is lower than on the upstream side, and therefore the output reversal number (Nb) of the downstream side exhaust sensor is smaller than the output reversal number (Na) of the upstream side exhaust sensor, as shown in FIG. This is because it can be determined that the deterioration of the catalyst is advanced as the output reversal ratio (Nb / Na) of the two exhaust sensors on the downstream side and the upstream side is larger.

As a method of disposing exhaust sensors on the upstream and downstream sides of the catalyst and detecting the deterioration of the catalyst by these outputs, the exhaust sensor output reversal ratio (Nb / Na) as in the above-mentioned known example is used. Other than the value, for example, during air-fuel ratio feedback control in the upstream exhaust sensor, the method of determining by the output amplitude of the downstream exhaust sensor, the method of determining by the average output value of the downstream exhaust sensor, or the downstream exhaust A method of making a determination based on the inversion period and the number of inversions with respect to a specific threshold value of the sensor is known.

[0006]

By the way, the accuracy and reliability of the catalyst deterioration detection based on the exhaust sensor output as described above is ensured only when the function of each exhaust sensor is maintained well. However, in a deteriorated state, highly reliable catalyst deterioration detection cannot be performed.

That is, the deterioration of the exhaust sensor can be roughly classified into two forms, that is, a decrease in the output voltage and a response delay. Regarding the decrease in the output voltage due to the deterioration of the exhaust sensor, as shown in FIG. 7, for example, regarding the output voltage at the time of rich, as shown by the solid line in the figure when the exhaust sensor is not deteriorated. Shows a high voltage value, but after it deteriorates, the output voltage greatly decreases as shown by the chain line in the figure. Therefore, when looking at the relationship between this exhaust sensor output and the air-fuel ratio, As shown in, the output voltage was 0.45 V (threshold value) at the theoretical air-fuel ratio λ = 1 in the initial state, but after deterioration, the actual air-fuel ratio was theoretical air-fuel ratio λ = 1. In this case, the output voltage of the exhaust sensor is about 0.3V, which is lower than the threshold value, so the air-fuel ratio is determined to be lean.

As a result, for example, when the output voltage decreases due to deterioration of the downstream side exhaust sensor, as shown in FIG. 3, the downstream side exhaust sensor is not deteriorated (hereinafter,
In the initial state), a high voltage value is shown as shown by the broken line in the figure, and the number of output inversions is relatively small compared to the initial inversion threshold value, but after deterioration, it is shown by the solid line in the figure. Then, the output voltage decreases and the initial initial inversion threshold value is crossed frequently, and the number of output inversions increases. When the output characteristic of the downstream side exhaust sensor changes in this way, the ratio (Nb / Na) of the output reversal number (Nb) of the downstream side exhaust sensor and the output reversal number (Na) of the upstream side exhaust sensor
Is larger than that in the initial state, so that it is erroneously determined that the catalyst is deteriorated although the catalyst is not deteriorated as a result.

On the other hand, regarding the response delay due to deterioration of the exhaust sensor, as shown in FIG. 9, as the deterioration of the exhaust sensor progresses, a response delay gradually occurs as the deterioration progresses, and for example, the air-fuel ratio is rich. The exhaust sensor output in the case of changing from the side to the lean side gradually shifts from the initial state shown by the solid line in the figure to the deterioration state shown by the broken line. When such a response delay occurs, for example, when the exhaust sensor output changes from the high output side to the low output side due to the change of the air-fuel ratio from the rich side to the lean side, the output of the exhaust sensor output is completely reduced. A change in the air-fuel ratio occurs before it completely changes,
The exhaust sensor output must be reversed during the change, and the output amplitude of the exhaust sensor output becomes smaller accordingly. As a result, for example, when there is a response delay due to deterioration in the downstream side exhaust sensor, the output amplitude is large in the initial state as shown in FIG. On the other hand, it shows a predetermined number of output inversions, but in the state after deterioration, the output is biased toward the rich side as shown by the solid line in the figure due to the decrease of the output amplitude, and the number of output inversions with respect to the initial inversion threshold value decreases accordingly. As a result, the output reversal number ratio (Nb / Na) becomes small, which causes an erroneous determination that the catalyst has not deteriorated although the catalyst has deteriorated considerably. ..

In view of these facts, in the case where the exhaust sensors are arranged on the upstream and downstream sides of the catalyst and the deterioration of the catalyst is detected based on the output of each exhaust sensor, the detection accuracy or reliability thereof is considered. It can be said that it is most important to accurately detect the deterioration state of the exhaust sensor, which is the basis for detecting the catalyst deterioration.

However, since the exhaust gas sensor arranged on the downstream side of the catalyst outputs a predetermined voltage according to the oxygen concentration of the exhaust gas after passing through the catalyst, for example, on the upstream side of the catalyst. Even if the air-fuel ratio is constant,
Different output voltages are generated depending on the oxygen storage capacity of the catalyst, that is, the deterioration state thereof. For this reason, it is extremely difficult to accurately determine the deterioration state from only the output value of the downstream side exhaust sensor with respect to the air-fuel ratio on the upstream side of the catalyst. The current situation is that no technique has been proposed for performing detection.

In view of this, the present invention accurately detects the deterioration of the exhaust sensor itself which is affected by the exhaust gas purification performance of the catalyst due to its arrangement, and in turn, the reliability of the catalyst deterioration detection performed by using the exhaust sensor. It was made to improve.

[0013]

As a concrete means for solving such a problem in the present invention, in the invention described in claim 1, as shown in FIG. 1A, it is arranged in the middle of the exhaust passage 3 of the engine. In an engine exhaust sensor deterioration detecting device for detecting a deterioration state of a downstream side exhaust sensor 12 arranged downstream of an exhaust purification catalyst 10, an upstream side exhaust sensor 11 for air-fuel ratio control is provided upstream of the catalyst 10. On the other hand, when the operating range detecting means A for detecting the operating range of the engine, the fuel control means B for controlling the fuel supply amount to the engine, and the specific operating range are detected by the operating range detecting means A The fuel control means B is controlled by open loop control based on the output value of the upstream side exhaust sensor 11.
And forcibly changing the air-fuel ratio from rich to lean or from lean to rich, and the output of the downstream side exhaust sensor 12 during open-loop control of the air-fuel ratio by the air-fuel ratio changing means C. An output value detecting means D for detecting a value and a deterioration determining means E for judging the deterioration state based on the output value of the downstream side exhaust sensor 12 detected by the output value detecting means D are provided. I am trying.

According to a second aspect of the present invention, as shown in FIG. 1A, in the engine exhaust sensor deterioration detecting apparatus according to the first aspect, the output value detecting means D is set to a rich side or a lean side relative to the theoretical air-fuel ratio. The output voltage value of the downstream side exhaust sensor 12 at the air-fuel ratio is detected, and when the output voltage value of the deterioration determining means E is less than or equal to a preset predetermined value F, the downstream side exhaust sensor is detected. It is characterized in that it is configured so that it is determined that is deteriorated.

According to a third aspect of the present invention, as shown in FIG. 1A, in the deterioration detecting device for an engine exhaust gas sensor according to the first aspect, the output value detecting means D is used to detect the air-fuel ratio of the air-fuel ratio changing means C. The time until the output voltage value of the downstream side exhaust sensor 12 reaches the set voltage value at the time of forced switching is detected, and the deterioration detection means E predicts the detection time by the output value detection means D. The configuration is such that it is determined that the downstream side exhaust sensor 12 is deteriorated when it is equal to or more than the set predetermined value F.

In the invention according to claim 4, as shown in FIG. 1A, in the deterioration detecting device for an exhaust sensor of an engine according to claim 1, 2 or 3, the downstream side exhaust sensor 12
Is characterized in that the output value thereof is input, together with the output value of the upstream side exhaust sensor 11, to the catalyst deterioration determination means G for determining the deterioration state of the catalyst 10 as a determination element.

[0017]

With each of the inventions of the present application, the following effects can be obtained by adopting such a configuration. That is, in the invention according to claim 1, the air-fuel ratio is forcibly changed from rich to lean or from lean to rich by open loop control in the specific operation region, and the output value of the downstream side exhaust sensor in this case is detected. The deterioration state of the downstream side exhaust sensor is detected based on this output value.

In this case, particularly in the invention described in claim 2,
The output value of the downstream side exhaust sensor is detected as its output voltage value in the rich side or lean side of the stoichiometric air-fuel ratio, that is, in the region where the change of the output voltage value with respect to the air-fuel ratio is small, and this is preset. A predetermined value (for example, a value lower than the output voltage value for the same air-fuel ratio in the initial state without deterioration by a predetermined amount), and if the output value is less than or equal to the predetermined value, it is detected as deterioration of the exhaust sensor. Therefore, even if there is some variation in the air-fuel ratio on the downstream side of the catalyst due to the degree of catalyst deterioration, the deterioration state of the exhaust sensor can be accurately determined in a state in which the influence of this variation is eliminated as much as possible. It is a thing.

According to the third aspect of the invention, the time until the voltage value of the downstream side exhaust sensor reaches the set voltage value when the air-fuel ratio is switched between the rich state and the lean state, that is, the air-fuel ratio The response delay time of the downstream side exhaust sensor to the change is detected as the output value of the downstream side exhaust sensor, and this is a predetermined value (for example, after switching the air-fuel ratio in the initial state without deterioration, the output voltage value is the set voltage. If it is longer than the time to reach the value by a predetermined amount), it is judged that the downstream side exhaust sensor is deteriorated. In this case, since the response delay time of the downstream side exhaust sensor is detected with reference to a constant voltage value, the downstream side exhaust sensor does not have a deterioration phenomenon such as a decrease in output voltage. Shows a constant output voltage value, and therefore the response delay time is hardly influenced by the deterioration state of the catalyst.

On the other hand, when the deterioration of the catalyst is detected by the output value of the downstream side exhaust sensor as in the invention of claim 4, the deterioration state of the downstream side exhaust sensor itself is accurately grasped. Therefore, the deterioration state of the catalyst can be detected more accurately by correcting the deterioration detection of the catalyst according to the deterioration state.

[0021]

Therefore, according to the deterioration detecting device for the exhaust gas sensor of the engine of each invention of the present application, the exhaust gas sensor is located on the downstream side of the catalyst and is affected by the purification performance (that is, the deterioration state) of the catalyst. Even if the above condition is satisfied, the deterioration state of the exhaust sensor can be accurately and easily detected regardless of the purification performance of the catalyst. Particularly, the exhaust sensor is used for detecting deterioration of the catalyst. In this case, for example, even if the downstream side exhaust sensor is deteriorated, by performing an appropriate correction in accordance with the deterioration state of the exhaust sensor, the catalyst having the same accuracy as before the deterioration is obtained. If the deterioration can be detected, it is possible to obtain the effect that the exhaust emission of the engine can be favorably maintained for a long period of time.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An engine exhaust gas sensor deterioration detection system according to the present invention will be described below in detail with reference to the accompanying drawings.

First Embodiment FIG. 1B shows an intake / exhaust system of an automobile engine 1 equipped with an exhaust sensor deterioration detecting device according to a first embodiment of the present invention. Is an intake passage, and 3 is an exhaust passage. The intake passage 2 includes a throttle valve 4, an air flow meter 5, and an injector-6.
And an intake air temperature sensor 7 are provided. On the other hand, an exhaust gas purification catalyst 10 is provided in the exhaust passage 3, and an upstream side exhaust sensor 11 is provided on the upstream side of the catalyst 10.
Downstream exhaust sensors 12 are arranged on the downstream side. Each of the exhaust sensors 11 and 12 is composed of, for example, a zirconia solid electrolyte lambda sensor that detects the oxygen concentration in the exhaust gas, and as shown in FIG. It occurs. Of these exhaust sensors 11, 12, the upstream exhaust sensor 11 is used for the air-fuel ratio control of the engine 1 and the deterioration detection control of the catalyst 10, while the downstream exhaust sensor 12 detects the deterioration of the catalyst 10. It is used only for.

The air flow meter 5 and the intake air temperature sensor 7
The detection signals of the exhaust sensors 11 and 12 and the separately installed vehicle speed sensor 9 are input to a control unit 15 described later. The control unit 15 is configured to perform fuel supply control, air-fuel ratio control, deterioration determination control of the catalyst 10, and deterioration determination control of each exhaust sensor on the basis of the input signals, as will be described later.

The above-mentioned respective controls by the control unit 15 will be described below with reference to FIGS. 2, 3 and 8. First, in the flow chart of FIG. 2, the main routine of the air-fuel ratio control will be explained. Execute (step S1).
The air-fuel ratio control is a conventionally known control and controls the fuel supply amount from the injector 6 according to the air-fuel ratio detected by the upstream side exhaust sensor 11, and its detailed description will be given. Is omitted.

Next, the control shifts to the deterioration detection control of the catalyst 10,
First, in step S2, the catalyst deterioration detection condition is determined. For example, it is determined that the catalyst deterioration detection condition is satisfied only when the current operating state is in the feedback control region, the vehicle speed is within the predetermined vehicle speed range, and the change in the vehicle speed is less than or equal to the predetermined value. This is because accurate detection cannot be expected under operating conditions where the air-fuel ratio changes greatly during acceleration, even in the feedback control region.
The purpose is to carry out catalyst deterioration detection control in a specific operation region where the air-fuel ratio does not change significantly.

Then, when the catalyst deterioration detection condition is satisfied, a predetermined catalyst deterioration detection routine is executed (step S3). Note that this catalyst deterioration detection control is also a conventionally known control, and as described above in the section “Prior Art” with reference to FIG. 11, a predetermined reversal threshold value (initial reversal threshold value).
The ratio (Nb) of the output reversal number (Nb) of the upstream side exhaust sensor 11 to the output reversal number (Na) of the downstream side exhaust sensor 12 with respect to
/ Na), it is determined that the catalyst 10 has deteriorated when the ratio (Nb / Na) is larger than a predetermined value.

By the way, as described above, the catalyst deterioration is detected based on the output values of the upstream side exhaust sensor 11 and the downstream side exhaust sensor 12, so that the exhaust sensors 11 and 12 are in the initial state where they are not deteriorated. In this case, it is possible to determine the catalyst deterioration with high reliability without any problem. However, when the exhaust sensors 11 and 12 themselves are deteriorated, an error occurs in the catalyst deterioration detection and the reliability becomes low. That is as described above. For this reason, in this embodiment, subsequent to the above-mentioned catalyst deterioration detection control, deterioration detection control of the downstream side exhaust sensor 12 which will be described later, which is the gist of the present invention, is executed, and the catalyst deterioration is performed according to the deterioration state. By appropriately correcting the reversal threshold value, which is the measurement reference of the number of output reversals that is the basis of the detection control, the accuracy of the catalyst deterioration detection is improved and the reliability is high.

That is, in the flow chart of FIG. 2, first, the exhaust sensor deterioration detection condition is judged (step S4), and when the condition is satisfied, the rich air-fuel ratio control is performed in open loop in step S5. Then, the output value Ed of the downstream side exhaust sensor 12 in this case is sampled (step S6), and the difference between the output value Es of the downstream side exhaust sensor 12 in the initial state and this sample value Ed,
That is, the output reduction value Em of the downstream side exhaust sensor 12 (= Es-E
d) is obtained (step S7). After that, the correction amount of the reversal threshold value (that is, the correction reversal threshold value) corresponding to the output reduction value Em of the downstream side exhaust sensor 12 is obtained from a map (not shown).
(Step S8) Further, as shown in FIG. 3, the inverted threshold value is changed to the corrected inverted threshold value obtained by shifting the initial inverted threshold value to the lean side by a predetermined amount.

As described above, by shifting the reversal threshold value to the lean side, it is possible to prevent the accuracy of the catalyst deterioration detection from being lowered due to the output reduction due to the deterioration of the downstream side exhaust sensor 12. That is, in the initial state where the downstream side exhaust sensor 12 is not deteriorated, a high voltage value is shown as shown by the broken line in FIG. 3, and therefore the number of output inversions with respect to the initial inversion threshold value is also an appropriate number. However, when the output voltage of the downstream side exhaust sensor 12 deteriorates and becomes a state shown by the solid line in the figure, the inversion threshold value is maintained at the initial inversion threshold value. Therefore, the number of output reversals will be greatly increased. This means that the output reversal number ratio (Nb / Na), which is the reference for detecting the catalyst deterioration, becomes larger than that in the initial state before the deterioration, and accordingly, the output reversal number ratio (Nb / N).
When the catalyst deterioration detection control described above is executed using a),
Although the catalyst 10 is not deteriorated, it is erroneously determined that it is deteriorated. In this case, by correcting the reversal threshold value toward the lean side, the same number of output reversals as in the initial state is measured regardless of the output reduction of the downstream side exhaust sensor 12, and the downstream side exhaust sensor 12 is in the initial state. If so, it is possible to detect the catalyst deterioration with high reliability.

Here, in this way, the downstream oxygen sensor 12
The reason why the air-fuel ratio is richly controlled by the open loop when the output reduction value Em is to be detected in order to detect the deterioration state of is due to the following reasons. That is, the downstream oxygen sensor 1
Although the initial output value Es for the specific air-fuel ratio of 2 is easily obtained, the output value (sample value) Ed for the specific air-fuel ratio in the state of being arranged on the downstream side of the catalyst 10 is the oxygen storage action of the catalyst 10. From the influence of the catalyst 1
Various changes occur depending on the deterioration state of 0, and it is difficult to specify this. Therefore, in this embodiment, as shown in FIG. 8, the change in the output voltage with respect to the change in the air-fuel ratio is small, and the residual amount of oxygen is originally small, so that the effect of the oxygen storage capacity of the catalyst 10 (that is, The air-fuel ratio is set to a rich side that is not significantly affected by the deterioration degree of the catalyst 10), and the initial output value Es of the downstream side oxygen sensor 12 and the output value Ed after deterioration at this rich air-fuel ratio are measured and output from these. The decrease value Em is calculated so that the deterioration of the downstream oxygen sensor 12 can be detected while the influence of the deterioration of the catalyst 10 is eliminated.

Then, in this way, the downstream side exhaust sensor 12
Of the downstream side exhaust sensor 12 by accurately detecting the deterioration state of the exhaust gas and correcting the reverse threshold value appropriately based on the detected deterioration state.
It is possible to detect the catalyst deterioration with higher accuracy despite the deterioration.

Second Embodiment FIG. 4 shows a control flow chart of an engine exhaust sensor deterioration detecting device according to a second embodiment of the present invention. In the present embodiment, the deterioration form of the output voltage decrease is targeted in the deterioration form of the downstream side exhaust sensor 12 in the first embodiment, whereas the deterioration form of response delay is targeted. It was done. Then, the number of output inversions decreases due to the decrease in output amplitude due to the response delay of the downstream side exhaust sensor 12 (see FIG. 5), and thus it is possible to erroneously determine that the deteriorated catalyst 10 is not deteriorated. It is something to avoid.

This will be described below with reference to the flow chart of FIG. 4. First, air-fuel ratio control is performed based on the output values of the upstream side exhaust sensor 11 and the downstream side exhaust sensor 12 (step S21), and further. When the catalyst deterioration detection condition is satisfied, the ratio (Nb / N) of the number of output reversals (Nb) of the downstream side exhaust sensor 12 and the number of output reversals (Na) of the upstream side exhaust sensor 11 is performed.
Determining the deterioration state of the catalyst 10 based on the value of a) (steps S22 and S23) is the same as in the case of the first embodiment.

Next, the process proceeds to the deterioration detection control of the downstream side exhaust sensor 12, and if it is determined in step S24 that the exhaust sensor deterioration detection condition is satisfied, first, in step S25, the open-loop control of the air-fuel ratio is executed. Then
Switch air-fuel ratio between rich and lean. When the air-fuel ratio is switched by the open loop control in this way, as shown in FIG. 6, a characteristic diagram when the output voltage rises from lean to rich and a characteristic diagram when the output voltage drops from rich to lean are displayed. can get. Here, in the initial state where the downstream side exhaust sensor 12 is not deteriorated, the change shown by the solid line in the figure is shown, and when it is deteriorated, the change shown by the broken line is shown in the figure. In this case, in the deteriorated state, compared to the initial state,
After switching the air-fuel ratio, the time (a: during lean → rich switching) and the time (b: during rich → lean switching) shift until the output voltage value reaches a predetermined threshold value (for example, 0.45 V) ( That is, a response delay) occurs.

Therefore, in order to detect the deterioration of the catalyst 10 on the basis of the output value of the downstream side exhaust sensor 12, the response delay (that is, the deterioration state) of the downstream side exhaust sensor 12 is quantitatively grasped and is determined. It is necessary to take this into consideration when detecting catalyst deterioration.

Therefore, in this embodiment, the response delay times (a) and (b) of the downstream side exhaust sensor 12 are measured in step S26 of the flow chart, and further, these responses are received in step S27. Based on the delay time, the bias value M (= b−a) of the response delay is obtained from the rich side to the lean side or from the lean side to the rich side. further,
The bias value M is compared with the predetermined bias value M ₀ set in advance (step S28), and if M ₀ <M, it is determined that the downstream side exhaust sensor 12 is deteriorated. Then, in this case, a correction value of the inversion threshold value corresponding to the bias value M is obtained from the map (step S29), and the initial inversion threshold value is changed to this correction inversion threshold value as shown in FIG. (Step S30).

Thus, by correcting the reverse threshold value of the downstream side exhaust sensor 12 to the lean side in response to the response delay due to the deterioration of the downstream side exhaust sensor 12, even if the output amplitude of the downstream side exhaust sensor 12 deteriorates. Even if it decreases, the same number of output reversals as in the initial state without deterioration is obtained, and as a result, the catalyst 10 judged based on the ratio of the number of output reversals of the downstream side exhaust sensor 12 and the upstream side exhaust sensor 11 is used as a reference. The accuracy of deterioration detection is kept good.

Here, in the case where the response delay due to the deterioration of the downstream side exhaust sensor 12 is directly detected from the output value in the initial state and the output value after deterioration as in this embodiment, the above is applied. Since the response delay itself is hardly affected by the change in the air-fuel ratio, it is assumed that the catalyst 10 whose oxygen storage capacity changes depending on the deterioration state exists upstream of the downstream side exhaust sensor 12. Also, the catalyst 1
The deterioration state of the downstream side exhaust sensor 12 can be detected more accurately without being affected by the deterioration state of 0.

[Brief description of drawings]

FIG. 1A is a diagram corresponding to a claim of the present invention.

FIG. 1B is a system diagram of an engine including an exhaust sensor deterioration detection device according to a first embodiment of the present invention.

FIG. 2 is a control flow chart of the deterioration detecting device for the exhaust sensor shown in FIG. 1B.

FIG. 3 is an explanatory diagram of reverse threshold value correction control of an exhaust sensor output in the control of FIG. 2.

FIG. 4 is a control flow chart of a deterioration detecting device for an exhaust sensor according to a second embodiment of the present invention.

FIG. 5 is an explanatory diagram of reverse threshold value correction control in the control of FIG.

FIG. 6 is a diagram illustrating detection of a response delay time of an exhaust sensor.

FIG. 7 is an explanatory diagram of a state in which the output is reduced due to deterioration of the exhaust sensor.

FIG. 8 is an explanatory diagram of an output change with respect to an air-fuel ratio due to deterioration of an exhaust sensor.

FIG. 9 is an explanatory diagram of a response delay state due to deterioration of the exhaust sensor.

FIG. 10 is a correlation diagram between the oxygen storage capacity of the three-way catalyst and the HC purification rate.

FIG. 11 is a correlation diagram between the HC purification rate and the reversal frequency ratio of the exhaust sensors arranged on the upstream and downstream sides of the catalyst.

[Explanation of symbols]

1 is an engine, 2 is an intake passage, 3 is an exhaust passage, 4 is a throttle valve, 5 is an air flow meter, 6 is an injector, 10 is an exhaust purification catalyst, 11 is an upstream exhaust sensor, 12 is a downstream exhaust sensor, Reference numeral 15 is a control unit.

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location F02D 45/00 368 H 7536-3G

Claims (4)

[Claims] 1. A deterioration detecting device for an exhaust sensor of an engine, which detects a deterioration state of a downstream side exhaust sensor arranged on a downstream side of an exhaust gas purifying catalyst arranged midway in an exhaust passage of the engine. While arranging an upstream side exhaust sensor for air-fuel ratio control on the upstream side, an operating area detecting means for detecting an operating area of the engine, a fuel control means for controlling a fuel supply amount to the engine, and the operating area detecting means. The air-fuel ratio forcibly switching the air-fuel ratio from rich to lean or from lean to rich by the fuel control means by the open loop control based on the output value of the upstream side exhaust sensor when a specific operating region is detected. Changing means, and an output value detecting means for detecting an output value of the downstream side exhaust sensor during open-loop control of the air-fuel ratio by the air-fuel ratio changing means, Deterioration detecting device for an exhaust sensor of the engine, characterized in that a degradation determiner means the deteriorated state based on the output value of the downstream exhaust sensor that is detected by the output value detecting means. 2. The output value detection means according to claim 1, wherein the output voltage value of the downstream side exhaust sensor at an air-fuel ratio richer or leaner than the stoichiometric air-fuel ratio is detected, and the deterioration determination means is further provided. Is configured to determine that the downstream side exhaust sensor is deteriorated when the output voltage value is equal to or less than a preset predetermined value. 3. The output value detecting means according to claim 1, wherein when the air-fuel ratio changing means forcibly switches the air-fuel ratio, the output value detecting means detects a time until the output voltage value of the downstream side exhaust sensor reaches a set voltage value. Further, the deterioration detecting means is configured to judge that the downstream side exhaust sensor is deteriorated when the detection time by the output value detecting means is equal to or more than a predetermined preset value. A device for detecting deterioration of an exhaust sensor of an engine, characterized by: 4. The catalyst deterioration determining means according to claim 1, 2 or 3, wherein the output value of the downstream side exhaust sensor is the same as the output value of the upstream side exhaust sensor, and the catalyst deterioration determining means determines the deterioration state of the catalyst. A deterioration detecting device for an exhaust sensor of an engine, characterized by being input as.