JP2006125226A - Three-way catalyst deterioration diagnosis method and exhaust gas purification device - Google Patents

Abstract

The present invention provides a three-way catalyst deterioration diagnosis method capable of performing a three-way catalyst deterioration diagnosis with high accuracy under a wide range of operating conditions including an acceleration operation region.
The method for diagnosing deterioration of a three-way catalyst according to the present invention includes the concentration of nitrogen oxides contained in combustion exhaust gas and / or the upstream and downstream sides of the three-way catalyst 2 inside the exhaust passage 4. A detector 3 capable of continuously measuring the air-fuel ratio of the combustion exhaust gas is disposed, and the concentration of nitrogen oxides contained in the combustion exhaust gas on the upstream side and the downstream side of the three-way catalyst in the exhaust flow path and / or Alternatively, it is a deterioration diagnosis method for a three-way catalyst that obtains an air-fuel ratio of combustion exhaust gas and diagnoses the degree of deterioration of the three-way catalyst 2 based on the obtained concentration of nitrogen oxides and / or fluctuations in the air-fuel ratio of combustion exhaust gas .
[Selection] Figure 1

Description

  The present invention relates to a three-way catalyst deterioration diagnosis method and an exhaust gas purification device. More specifically, a three-way catalyst deterioration diagnosis method capable of performing high-precision deterioration diagnosis of a three-way catalyst under a wide range of operating conditions including an acceleration operation region, and such a three-way catalyst deterioration diagnosis method. The present invention relates to an exhaust gas purification device capable of realizing the above.

  In recent years, a three-way catalyst system that combines a highly accurate air-fuel ratio (hereinafter sometimes referred to as “A / F”) control and a catalyst device with high purification efficiency is often used as an exhaust gas countermeasure for gasoline vehicles. . On the other hand, in-cylinder direct injection type diluted fuel engines are also becoming popular for the purpose of improving the fuel consumption rate. In any case, recent gasoline vehicles have achieved significant exhaust gas purification by using a high-performance catalyst such as the above-described three-way catalyst.

  For this reason, if the catalyst deteriorates in the process of use and the purification performance deteriorates, the exhaust gas cannot be sufficiently purified by the catalyst and is discharged, so the surrounding air is contaminated. . In particular, even if the purification performance of the catalyst is reduced, the driving performance of the vehicle (gasoline vehicle) is hardly affected. Therefore, the vehicle in an abnormal exhaust state is used for a long time without being recognized by the user. There is a danger of continuing to be broken.

  For this reason, in Japan, the introduction of an on-board diagnostic system (OBD) that diagnoses the functions of the catalyst exhaust gas purification system on the vehicle has been studied, and there is a policy of mandatory installation in vehicles after the 2008 model. It is shown.

It is desirable that the deterioration diagnosis of various devices (for example, a purification device) provided with a three-way catalyst has a wide operating range as a diagnosis target and has as few errors as possible. However, at present, there is no technology that can directly detect the deterioration of the catalyst on the vehicle, so the output waveforms of the _two oxygen sensors (O ₂ sensors) attached to the inlet side and the outlet side of the purification device equipped with the catalyst, etc. A method (dual O ₂ sensor method) for indirectly diagnosing deterioration from the above information is used in response to OBD regulations in the United States (see, for example, Patent Document 1).

In this degradation diagnosis method using the dual O ₂ sensor method, for example, the frequencies of the O ₂ sensor signal waveforms on the catalyst inlet side and the outlet side are counted and compared, and the count number on the catalyst outlet side is the count number on the inlet side. This is a method for determining that the deterioration of the catalyst is progressing as it approaches.
Japanese Patent Laid-Open No. 7-305623

However, the above-described dual O ₂ sensor method is accurate in an acceleration operation region in which the deterioration diagnosis result of the three-way catalyst is likely to be affected, that is, in an operation region where the amount of exhaust gas and A / F fluctuate irregularly. Diagnosis is difficult, and there is a problem that only diagnosis in which only a driving range in which deterioration diagnosis is relatively easy can be performed. In particular, in general urban driving, acceleration / deceleration is repeated many times, and the steady driving time that can be diagnosed by the dual O ₂ sensor method is short. Therefore, it is sufficient for diagnosing deterioration of a three-way catalyst under actual use conditions. It was not a thing.

  The present invention has been made in view of the above-described problems, and a three-way catalyst deterioration diagnosis method capable of performing a three-way catalyst deterioration diagnosis with high accuracy under a wide range of operating conditions including an acceleration operation region. And an exhaust gas purifying apparatus capable of realizing such a three-way catalyst deterioration diagnosis method.

  [1] A deterioration diagnosis method for a three-way catalyst that is disposed inside an exhaust passage for combustion exhaust gas discharged from an internal combustion engine and diagnoses the degree of deterioration of the three-way catalyst that purifies the combustion exhaust gas. The concentration of nitrogen oxides contained in the combustion exhaust gas and / or the air-fuel ratio of the combustion exhaust gas can be continuously measured upstream and downstream of the three-way catalyst in the exhaust passage. A detector is provided to obtain the concentration of nitrogen oxides contained in the combustion exhaust gas and / or the air-fuel ratio of the combustion exhaust gas on the upstream side and the downstream side of the three-way catalyst in the exhaust flow path; A three-way catalyst deterioration diagnosis method (hereinafter referred to as “first invention”) for diagnosing the degree of deterioration of the three-way catalyst based on the concentration of the obtained nitrogen oxides and / or fluctuations in the air-fuel ratio of the combustion exhaust gas. Sometimes).

  [2] When the internal combustion engine is in a lean combustion state, the concentration of the nitrogen oxides contained in the combustion exhaust gas at the upstream side and the downstream side of the three-way catalyst in the exhaust passage is measured and obtained. The method for diagnosing deterioration of a three-way catalyst according to [1], wherein the degree of deterioration of the three-way catalyst is diagnosed based on a change in the concentration of nitrogen oxides.

[3] The air-fuel ratio of the combustion exhaust gas at the upstream side and the downstream side of the three-way catalyst in the exhaust passage is measured, and the cross-correlation coefficient R _xy (τ) shown in the following equation (1) The deterioration diagnosis method for a three-way catalyst according to [1] or [2], wherein the degree of deterioration of the three-way catalyst is diagnosed.

（但し、ｔは時間、τは上流側と下流側とにおいて測定した信号間の遅れ時間、ｘ（ｔ）は時間ｔでの前記排気流路の前記三元触媒より上流側における前記燃焼排気ガスの空燃比、ｙ（ｔ＋τ）は時間（ｔ＋τ）での前記排気流路の前記三元触媒より下流側における前記燃焼排気ガスの空燃比、Ｒ_xy（τ）は相互相関係数を示す）

(Where t is a time, τ is a delay time between signals measured on the upstream side and the downstream side, and x (t) is the combustion exhaust gas upstream of the three-way catalyst in the exhaust passage at time t. The air-fuel ratio of the combustion exhaust gas at the downstream side of the three-way catalyst in the exhaust passage at time (t + τ) at the time (t + τ), and R _xy (τ) represents the cross-correlation coefficient)

  [4] The deterioration diagnosis method for a three-way catalyst according to any one of [1] to [3], wherein a zirconia solid electrolyte type detector is used as the detector.

  [5] Diagnosing the degree of deterioration of the three-way catalyst in a state where the temperature of the three-way catalyst is equal to or higher than the activation temperature in the purification reaction for purifying the combustion exhaust gas. The deterioration diagnosis method for a three-way catalyst according to any one of the above.

  [6] An exhaust gas purifying device for purifying combustion exhaust gas discharged from an internal combustion engine, the three-way catalyst disposed inside the exhaust passage of the internal combustion engine, and the three-way of the exhaust passage A detector capable of continuously measuring the concentration of nitrogen oxides contained in the combustion exhaust gas and / or the air-fuel ratio of the combustion exhaust gas, which are respectively disposed upstream and downstream of the catalyst. Exhaust gas purifying device (hereinafter sometimes referred to as “second invention”).

  [7] The exhaust gas purification device according to [6], wherein the detector is a zirconia solid electrolyte type detector.

  The deterioration diagnosis of the three-way catalyst of the present invention can perform the deterioration diagnosis of the three-way catalyst with high accuracy under a wide range of operating conditions including the acceleration operation region. Moreover, since the exhaust gas purification apparatus of the present invention can realize the above-described deterioration diagnosis of the three-way catalyst, it is possible to accurately grasp the degree of deterioration of the three-way catalyst.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a three-way catalyst deterioration diagnosis method and an exhaust gas purification apparatus of the present invention (first and second inventions) will be described in detail with reference to the drawings. The present invention is not construed as being limited, and various changes, modifications, and improvements can be made based on the knowledge of those skilled in the art without departing from the scope of the present invention.

  First, an embodiment of the three-way catalyst deterioration diagnosis method of the first invention will be described. FIG. 1 is an explanatory view schematically showing a configuration of an exhaust gas purification apparatus using the three-way catalyst deterioration diagnosis method of the present embodiment. As shown in FIG. 1, the three-way catalyst deterioration diagnosis method according to the present embodiment uses an exhaust flow path 4 for combustion exhaust gas (hereinafter, simply referred to as “exhaust gas”) discharged from the internal combustion engine 5. This is a three-way catalyst deterioration diagnosis method that diagnoses the degree of deterioration of the three-way catalyst 2 disposed inside and purifying the combustion exhaust gas. The three-way catalyst 2 is a catalyst that simultaneously purifies three components of carbon monoxide (CO), hydrocarbon (HC), and nitrogen oxide (NOx) when the internal combustion engine 5 such as a gasoline engine is in a stoichiometric air-fuel ratio state. In general, it is used by being disposed inside the exhaust flow path 4 of the combustion exhaust gas discharged from the internal combustion engine 5. When the three-way catalyst 2 has been used for a long period of time, its performance gradually deteriorates. Therefore, it is necessary to diagnose the degree of deterioration and replace the one that has deteriorated.

  The deterioration diagnosis method for the three-way catalyst according to the present embodiment is a method for diagnosing the concentration of nitrogen oxides contained in the combustion exhaust gas and / or the combustion exhaust gas upstream and downstream of the three-way catalyst 2 inside the exhaust passage 4. A detector 3 capable of continuously measuring the air-fuel ratio of the gas is provided, and the concentration and / or combustion of nitrogen oxides contained in the combustion exhaust gas upstream and downstream of the three-way catalyst in the exhaust passage. This is a three-way catalyst deterioration diagnosis method that obtains the air-fuel ratio of exhaust gas and diagnoses the degree of deterioration of the three-way catalyst 2 based on the concentration of the obtained nitrogen oxides and / or fluctuations in the air-fuel ratio of the combustion exhaust gas. With this configuration, the deterioration diagnosis of the three-way catalyst 2 can be performed with high accuracy under a wide range of operating conditions including the acceleration operation region. In the three-way catalyst deterioration diagnosis method of the present embodiment, the “air-fuel ratio of combustion exhaust gas” refers to an oxygen concentration converted value.

  The three-way catalyst deterioration diagnosis method of the present embodiment obtains the concentration of nitrogen oxides contained in the combustion exhaust gas and / or the air-fuel ratio of the combustion exhaust gases, and the concentration of nitrogen oxides obtained and / or the combustion exhaust gas. This is a three-way catalyst deterioration diagnosis method for diagnosing the degree of deterioration of the three-way catalyst 2 based on fluctuations in the air-fuel ratio of the gas. Here, the detector 3 described above can measure the concentration of nitrogen oxides. A case where deterioration diagnosis is performed by measuring the concentration of nitrogen oxide contained in combustion exhaust gas using a concentration detector will be described. FIG. 2 shows a case where a new three-way catalyst and a deteriorated three-way catalyst are disposed in the exhaust passage of the engine and the 10.15 mode (exhaust gas test mode performed at the time of new vehicle certification) is performed. 4 is a graph showing emissions of carbon monoxide, hydrocarbons, and nitrogen oxides in exhaust gas downstream from the three-way catalyst. Each emission amount in the exhaust gas discharged from the deteriorated three-way catalyst in FIG. 2 is shown as a ratio with respect to a case where the emission amount in a new three-way catalyst is 1.0. As can be seen from FIG. 2, the emission of all three components continues to increase up to a travel distance of 80,000 km, which indicates that the deterioration of the three-way catalyst is progressing. However, when the mileage is equivalent to 100,000 km, the nitrogen oxides continue to increase, but the emissions of carbon monoxide and hydrocarbons are slightly lower than when they are equivalent to 80,000 km. There is a tendency for the progress of For this reason, the deterioration diagnosis of the three-way catalyst can be performed with high accuracy by measuring the concentration of nitrogen oxides in the exhaust gas. In the three-way catalyst deterioration diagnosis method of the present embodiment, the nitrogen oxide concentration is measured, and the degree of deterioration of the three-way catalyst 2 is diagnosed from the obtained nitrogen oxide concentration. The degree of deterioration of the three-way catalyst 2 can also be diagnosed by the fluctuation of the nitrogen oxide emission amount calculated from the nitrogen oxide concentration and the instantaneous exhaust gas amount.

In the three-way catalyst deterioration diagnosis method of the present embodiment, when measuring the concentration of nitrogen oxides, the measured value may be affected by other substances contained in the exhaust gas. For this reason, in order to perform a more accurate diagnosis, it is preferable to measure the concentration of nitrogen oxides in an operating state in which the measured value is not easily affected. For example, in a three-way catalyst, hydrogen (H ₂ ) contained in exhaust gas reacts with nitrogen oxides to generate ammonia (NH ₃ ). Ammonia varies depending on the type of detector, but may affect the measured concentration of nitrogen oxides obtained.

In particular, the above-described ammonia (NH ₃ ) is generated in a larger amount under the operating conditions where the A / F is rich. Therefore, in the three-way catalyst deterioration diagnosis method of the present embodiment, A / F feedback is performed. When the internal combustion engine is in a lean combustion state, such as when the lean region changes during control or when the fuel is cut during deceleration, the nitrogen oxides contained in the combustion exhaust gas upstream and downstream of the three-way catalyst in the exhaust flow path It is preferable to measure the concentration or calculate the emission amount, and diagnose the degree of deterioration of the three-way catalyst based on fluctuations in the concentration or emission amount of the obtained nitrogen oxides. FIGS. 3A and 3B are graphs showing the concentration of nitrogen oxides in the exhaust gas after passing through the three-way catalyst when the 10.15 mode operation is performed. FIG. 3 (a) shows the result for a new three-way catalyst, and FIG. 3 (b) shows the result for a deteriorated three-way catalyst corresponding to 100,000 km travel. In FIGS. 3A and 3B, the continuous data (NOx sensor output) of the obtained nitrogen oxide concentration (NOx concentration) is converted to nitrogen oxide by limiting the A / F to the lean region. It is shown as an object concentration appearance rate (%) (number of data in the corresponding area / number of data in the entire lean area during mode operation). The exhaust gas to be measured has an oxygen concentration (O ₂ concentration) of 0 to 4.5%, 4.5 to 9.0%, 9.0 to 13.5%, 13.5 to 18%, and 18 Measurements were made by classifying into five types of more than 5%.

By comparing FIG. 3 (a) and FIG. 3 (b), nitrogen oxidation during feedback control in which the O ₂ concentration is 0 to 4.5% (corresponding to 14.6 to 18.5 as A / F). It can be seen that the substance concentration appearance rate is widely dispersed in the high concentration region due to the deterioration of the three-way catalyst. Further, it can be seen that the nitrogen oxide concentration appearance rate in the region estimated as the fuel cut region during deceleration with an O ₂ concentration of 4.5% or more increases in the high concentration region due to the deterioration of the three-way catalyst. From these results, the degree of deterioration of the three-way catalyst is diagnosed with high accuracy by examining the appearance rate of nitrogen oxide concentration in the lean combustion state of the internal combustion engine, that is, measuring the concentration or emission amount of nitrogen oxide. can do.

  Here, the reason why the concentration of nitrogen oxides changes due to the deterioration of the three-way catalyst will be described. FIGS. 4A and 4B are graphs showing the nitrogen oxide concentration on the downstream side of the three-way catalyst in the deceleration fuel cut region (lean combustion state). FIG. 4 (a) shows the results for a new three-way catalyst, and FIG. 4 (b) shows the results for a degraded three-way catalyst corresponding to 100,000 km travel. From the graphs shown in FIG. 4 (a) and FIG. 4 (b), nitrogen oxide flowing from the upstream side of the three-way catalyst, carbon monoxide, hydrocarbons, etc. adsorbed on the three-way catalyst during feedback control before fuel cut It can be seen that the exhaust gas is being purified by the reaction with the reducing components. When the three-way catalyst deteriorates, the reducing component adsorption ability decreases, and the nitrogen oxide concentration on the downstream side of the three-way catalyst in the fuel cut region (lean combustion state) during deceleration or the like increases. For this reason, the degree of deterioration of the three-way catalyst can be diagnosed by measuring the fluctuation of the nitrogen oxide concentration.

  FIG. 5 is a graph showing the nitrogen oxide purification rate (%) in the fuel cut region during deceleration (lean combustion state) when the 10.15 mode and the actual travel mode operation are performed. FIG. 5 shows nitrogen oxide purification rates for a new three-way catalyst and two types of deteriorated three-way catalysts (corresponding to 30,000 km travel and 100,000 km travel). It can be seen that in both modes of operation, the nitrogen oxide purification rate decreases as the three-way catalyst deteriorates. This also indicates that the degree of deterioration of the three-way catalyst can be diagnosed by measuring the change in the concentration of nitrogen oxides. This nitrogen oxide purification rate (%) is the reduction of nitrogen oxides due to the purification reaction in the layer composed of the three-way catalyst with respect to the nitrogen oxide emission (g / sec) upstream of the three-way catalyst. The ratio of the amount (g / sec) is expressed as a percentage (%). Note that the reduction amount (g / sec) of nitrogen oxides due to the purification reaction in the layer constituted by the three-way catalyst is calculated from the nitrogen oxide discharge amount (g / sec) on the upstream side to the nitrogen oxide on the downstream side. Can be obtained by subtracting the discharge amount (g / sec). Further, the nitrogen oxide emission amount (g / sec) on the upstream side and the downstream side includes the instantaneous nitrogen oxide concentration, the instantaneous exhaust gas flow rate (l / sec), and the nitrogen oxide density (g / L). The reason for using such nitrogen oxide purification rate (%) is that carbon monoxide, hydrocarbons and other reducing components adsorbed on the three-way catalyst during feedback control before the fuel cut and flowed into the catalyst during the fuel cut This is because the reaction with nitrogen oxides is handled, and the comparison based on emission is effective rather than the comparison based on concentration.

  As a detector (concentration detector) capable of continuously measuring the concentration of nitrogen oxide used in the method for diagnosing deterioration of the three-way catalyst of the present embodiment, for example, a zirconia solid electrolyte type detector is a preferred example. Can be mentioned. Furthermore, when measuring the concentration of nitrogen oxides, it is affected by other components contained in the exhaust gas, such as ammonia, so use a detector in which the influence of such other components is reduced. In addition, more accurate diagnosis can be performed.

  Next, in the three-way catalyst deterioration diagnosis method of the present embodiment, a case where deterioration diagnosis is performed by measuring the air-fuel ratio of the combustion exhaust gas upstream and downstream of the three-way catalyst in the exhaust passage will be described. FIG. 6 is a graph showing the air-fuel ratio of the combustion exhaust gas measured by the respective detectors disposed on the upstream side and the downstream side of the three-way catalyst when the 10.15 mode operation is performed. As shown in FIG. 6, the air-fuel ratio of the combustion exhaust gas upstream of the three-way catalyst fluctuates between the lean region and the rich region due to the influence of feedback control. On the other hand, when the air-fuel ratio of the combustion exhaust gas is in a lean region, the three-way catalyst adsorbs an oxidizing substance (for example, oxygen, nitric oxide, etc.) and is in a rich region. Has the property of adsorbing reducing substances (for example, carbon monoxide, hydrocarbons, etc.). As a result, the air-fuel ratio of the combustion exhaust gas downstream of the three-way catalyst is the same as that of the upstream combustion exhaust gas. The fluctuation amount is much smaller than the air-fuel ratio. The deterioration of the three-way catalyst is caused by a decrease in the adsorption ability of the oxidizing substance in the lean region and the adsorption ability of the reducing substance in the rich region. From this, the degree of deterioration of the three-way catalyst can be diagnosed by comparing the air-fuel ratio of the combustion exhaust gas on the upstream side and downstream side of the three-way catalyst. Specifically, for example, the degree of deterioration of the three-way catalyst can be diagnosed by quantifying the attenuation effect of the three-way catalyst. In addition, the speed shown in FIG. 6 is the same as that when driving on an actual road in a laboratory, when a test vehicle is installed on a device such as a chassis dynamometer and the vehicle is driven in 10.15 mode operation. It shows the change in speed of the test vehicle.

In the method for diagnosing deterioration of the three-way catalyst of the present embodiment, although not particularly limited, the difference in the fluctuation state of the air-fuel ratio of the combustion exhaust gas between the upstream side and the downstream side of the three-way catalyst (that is, the three-way catalyst) A cross correlation coefficient R _xy (τ) can be cited as a method for indicating the similar degree of the waveform indicated by the change in the air-fuel ratio of the combustion exhaust gas on the upstream side and downstream side of the catalyst. Specifically, the air-fuel ratio of the combustion exhaust gas at the upstream side and the downstream side from the three-way catalyst in the exhaust passage is measured, and the three-way is obtained by the cross-correlation coefficient R _xy (τ) shown in the following equation (2). It is preferable to diagnose the degree of catalyst degradation.

（但し、ｔは時間、τは上流側と下流側とにおいて測定した信号間の遅れ時間、ｘ（ｔ）は時間ｔでの排気流路の三元触媒より上流側における燃焼排気ガスの空燃比、ｙ（ｔ＋τ）は時間（ｔ＋τ）での排気流路の三元触媒より下流側における燃焼排気ガスの空燃比、Ｒ_xy（τ）は相互相関係数を示す）

(Where t is the time, τ is the delay time between the signals measured on the upstream side and downstream side, and x (t) is the air-fuel ratio of the combustion exhaust gas upstream of the three-way catalyst in the exhaust passage at time t. Y (t + τ) is the air-fuel ratio of the combustion exhaust gas downstream of the three-way catalyst in the exhaust passage at time (t + τ), and R _xy (τ) indicates the cross-correlation coefficient)

By using such a cross-correlation coefficient R _xy (τ), it becomes possible to quantify the damping effect of the three-way catalyst, and the air-fuel ratios of the respective combustion exhaust gases upstream and downstream of the three-way catalyst Thus, the degree of deterioration of the three-way catalyst can be diagnosed with high accuracy.

Although not particularly limited, when calculating the cross-correlation coefficient R _xy (τ) by applying the equation (2), in order to improve the accuracy of the deterioration diagnosis of the three-way catalyst, As the air-fuel ratio fluctuation data used for the calculation, it is preferable to use data composed of a large number of short trips (traveling sections from start to stop of the vehicle), for example, air-fuel ratio fluctuation data over the entire 10.15 mode operation. . Here, the purification reaction in the three-way catalyst is caused by the reaction between the material adsorbed on the catalyst in the past and the material that has flowed into the catalyst in the layer composed of the three-way catalyst, so it always affects the past operation history. Will be. For this reason, by using the air-fuel ratio fluctuation data for a relatively long time, the influence of the operation history can be mitigated, and a more accurate deterioration diagnosis of the three-way catalyst can be realized.

  As a detector capable of continuously measuring the air-fuel ratio of combustion exhaust gas used in the method for diagnosing deterioration of the three-way catalyst of the present embodiment, for example, a zirconia solid electrolyte type detector may be cited as a preferred example. it can.

  Further, in the three-way catalyst deterioration diagnosis method of the present embodiment, the method of diagnosing the degree of deterioration of the three-way catalyst based on the nitrogen oxide concentration or emission amount described so far, and the air-fuel ratio of the combustion exhaust gas By performing in combination with a method for diagnosing the degree of deterioration of the three-way catalyst, it is possible to realize a more accurate diagnosis. For example, a zirconia solid electrolyte type detector can measure both with a single detector.

  Further, in the three-way catalyst deterioration diagnosis method of the present embodiment, the three-way catalyst degradation is performed in a state where the temperature of the three-way catalyst to be diagnosed is equal to or higher than the activation temperature in the purification reaction for purifying the combustion exhaust gas. It is preferable to diagnose the degree. By configuring in this way, it is possible to realize a more accurate diagnosis.

  In the three-way catalyst deterioration diagnosis method of the present embodiment, it is preferably used as an OBD device. For example, the degree of deterioration of the three-way catalyst is determined from the results obtained by the respective diagnosis methods described above. If the three-way catalyst has deteriorated beyond a certain level, an external signal such as an alarm may be transmitted. In particular, when the three-way catalyst deterioration diagnosis method of the present embodiment is used for an exhaust gas purification apparatus such as an automobile, the degree of deterioration of the three-way catalyst can be confirmed at the driver's seat, When the alarm has deteriorated over a certain level, a warning is given to the driver by an alarm device such as a lamp, so that the deterioration of the three-way catalyst can be detected accurately, and environmental pollution caused by the deteriorated three-way catalyst can be detected. Risk can be avoided. The obtained diagnosis results are stored in a storage means such as a computer so that the diagnosis results can be confirmed later, thereby confirming the state of the vehicle for a long period of time or abnormalities in the vehicle. It can also be used for discovery.

  Next, an embodiment of the exhaust gas purification apparatus of the second invention will be specifically described. The exhaust gas treatment apparatus of the present embodiment is an exhaust gas purification apparatus 1 capable of realizing one embodiment of the first invention (deterioration diagnosis method for a three-way catalyst) as shown in FIG. The deterioration diagnosis of the three-way catalyst 2 can be performed with high accuracy under a wide range of operating conditions including the acceleration operating range.

  As shown in FIG. 1, an exhaust gas purification device 1 according to the present embodiment is an exhaust gas purification device 1 that purifies combustion exhaust gas discharged from an internal combustion engine 5 (for example, a gasoline engine). The three-way catalyst 2 disposed inside the exhaust passage 4 and the nitrogen oxides contained in the combustion exhaust gas respectively disposed upstream and downstream of the three-way catalyst 2 of the exhaust passage 4 And / or a detector 3 capable of continuously measuring the air-fuel ratio of the combustion exhaust gas. In this way, the concentration of nitrogen oxides contained in the combustion exhaust gas and / or the air-fuel ratio of the combustion exhaust gas, which are respectively disposed upstream and downstream of the three-way catalyst 2 in the exhaust flow path 4, are continuously set. The degree of deterioration of the three-way catalyst 3 by using the three-way catalyst deterioration diagnosis method described in one embodiment of the first invention (three-way catalyst deterioration diagnosis method). Can be diagnosed.

  Although there is no restriction | limiting in particular as the detector 3 used for the exhaust gas purification apparatus 1 of this Embodiment, The detector of a zirconia solid electrolyte system can be used suitably.

  The three-way catalyst 2 is not particularly limited, and a conventionally known three-way catalyst containing a metal such as platinum, rhodium, or palladium can be used. Further, the exhaust gas purification apparatus 1 of the present embodiment includes a case body that becomes a part of the exhaust flow path of the combustion exhaust gas, and the three-way catalyst 2 is disposed inside the case body. May be. By using the case body configured as described above connected to the exhaust flow path 4 of the combustion exhaust gas, for example, when the three-way catalyst 2 is deteriorated, the three-way catalyst 2 can be exchanged together with the case body. Thus, the replacement work of the three-way catalyst 2 can be easily performed.

  Although not shown in the drawings, the exhaust gas purifying apparatus of the present embodiment can be used as an OBD apparatus so that the degree of deterioration of the three-way catalyst is determined from the results obtained by the respective detectors. If it is determined that the three-way catalyst has deteriorated beyond a certain level, an external signal transmission means for transmitting an external signal such as an alarm may be further provided. As this external signal transmission means, there is a monitor that can confirm the degree of deterioration of the three-way catalyst in the driver's seat, and an alarm device such as a lamp that issues an alarm when the three-way catalyst has deteriorated over a certain level. It can be mentioned as a suitable example. By providing such an external signal transmission means, the degree of deterioration of the three-way catalyst can be accurately detected, and the risk of environmental contamination due to the deteriorated three-way catalyst can be avoided.

  Further, the exhaust gas purification apparatus of the present embodiment is not particularly limited, but may further include a storage means such as a computer that can store the obtained diagnostic result. Good. By configuring in this way, the diagnosis result can be confirmed later, and the vehicle state can be confirmed for a long period of time, or it can be used for finding a vehicle abnormality or the like.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Using a new three-way catalyst and a three-way catalyst equivalent to 30,000 km travel, 50,000 km travel, 80,000 km travel, and 100,000 km travel, The air-fuel ratio of the upstream and downstream exhaust gases was measured, and the cross-correlation coefficient R _xy (τ) was calculated from the obtained air-fuel ratio of each exhaust gas. The cross-correlation coefficient R _xy (τ) is calculated by the equation (2). FIG. 7 shows the relationship between the cross-correlation coefficient R _xy (τ) thus obtained and the delay time τ between signals measured on the upstream side and downstream side of the three-way catalyst. FIG. 7 also shows the cross-correlation coefficient R _xy (τ) calculated by measuring the air-fuel ratio of the exhaust gas when no three-way catalyst is provided.

  The detector that measured the air-fuel ratio of the exhaust gas was a zirconia solid electrolyte type detector. The exhaust gas used for the measurement was exhausted from an electronic fuel injection type, theoretical air-fuel ratio control type gasoline engine (4 cycles, 2200 cc), and the main gas components were nitrogen, moisture, carbon dioxide, oxygen, and monoxide. Gasoline combustion exhaust gas composed of carbon, unburned hydrocarbons and nitrogen oxides was used.

As shown in FIG. 7, it can be seen that the deterioration of the three-way catalyst proceeds as the value of the cross-correlation coefficient R _xy (τ) increases. Specifically, for example, when the delay time τ between signals measured on the upstream side and the downstream side is 0.2 seconds, the cross-correlation coefficient R _xy (τ) in each three-way catalyst is The degree of deterioration of the three-way catalyst is diagnosed by the cross-correlation coefficient R _xy (τ), which is increased corresponding to the distance and indicated by the air-fuel ratio of the exhaust gas upstream and downstream of the three-way catalyst. I was able to.

  The three-way catalyst deterioration diagnosis method of the present invention can perform deterioration diagnosis of the three-way catalyst with high accuracy under a wide range of operating conditions including an acceleration operation region. It can be suitably used for deterioration diagnosis of the three-way catalyst to be purified. The exhaust gas purifying apparatus of the present invention is an exhaust gas purifying apparatus capable of realizing the above-described three-way catalyst deterioration diagnosis method of the present invention.

It is explanatory drawing which shows typically the structure of the exhaust-gas purification apparatus using one Embodiment of the deterioration diagnosis method of the three way catalyst of this invention (1st invention). Carbon monoxide in the exhaust gas downstream of the three-way catalyst when a new three-way catalyst and a deteriorated three-way catalyst are disposed in the exhaust passage of the engine and operated in 10.15 mode, It is a graph which shows the discharge | emission amount of a hydrocarbon and nitrogen oxides. It is a graph which shows the density | concentration of the nitrogen oxide in exhaust gas after passing a three-way catalyst when a new three-way catalyst is arrange | positioned inside an exhaust flow path, and 10.15 mode driving | running is performed. The concentration of nitrogen oxides in the exhaust gas after passing through the three-way catalyst when a deteriorated three-way catalyst equivalent to 100,000 km travel is disposed inside the exhaust passage and the 10.15 mode operation is performed. It is a graph to show. A graph showing the nitrogen oxide concentration downstream of the three-way catalyst in the fuel cut region (lean combustion state) when a new three-way catalyst is disposed inside the exhaust passage and the 10.15 mode operation is performed. is there. Nitrogen on the downstream side of the three-way catalyst in the fuel cut region (lean combustion state) when a deteriorated three-way catalyst equivalent to 100,000 km travel is disposed inside the exhaust passage and the 10.15 mode operation is performed It is a graph which shows an oxide density | concentration. It is a graph which shows the nitrogen oxide purification | cleaning rate (%) in a fuel cut area (lean combustion state) when performing 10 * 15 mode and real driving | running | working mode driving | operation. It is a graph which shows the air-fuel ratio of the combustion exhaust gas measured by each detector arrange | positioned in the upstream and downstream of a three-way catalyst at the time of 10.15 mode operation. The cross-correlation coefficient R _xy (τ) when a new three-way catalyst and a deteriorated three-way catalyst are arranged in the exhaust passage and the 10.15 mode operation is performed, and the upstream side of the three-way catalyst It is a graph which shows the relationship with the delay time (tau) between the signals measured in the downstream.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Exhaust gas purification apparatus, 2 ... Three way catalyst, 3 ... Detector, 4 ... Exhaust flow path, 5 ... Internal combustion engine.

Claims (7)

A three-way catalyst deterioration diagnosis method for diagnosing the degree of deterioration of a three-way catalyst disposed inside an exhaust passage of combustion exhaust gas discharged from an internal combustion engine and purifying the combustion exhaust gas,
Detection capable of continuously measuring the concentration of nitrogen oxides contained in the combustion exhaust gas and / or the air-fuel ratio of the combustion exhaust gas on the upstream side and the downstream side of the three-way catalyst inside the exhaust passage To obtain the concentration of nitrogen oxides contained in the combustion exhaust gas and / or the air-fuel ratio of the combustion exhaust gas on the upstream side and the downstream side of the three-way catalyst in the exhaust passage. A three-way catalyst deterioration diagnosis method for diagnosing the degree of deterioration of the three-way catalyst based on the concentration of the nitrogen oxide and / or the change in the air-fuel ratio of the combustion exhaust gas.   When the internal combustion engine is in a lean combustion state, the concentration of the nitrogen oxides contained in the combustion exhaust gas at the upstream side and the downstream side of the three-way catalyst in the exhaust passage is measured, and the obtained nitrogen oxides The method for diagnosing deterioration of a three-way catalyst according to claim 1, wherein the degree of deterioration of the three-way catalyst is diagnosed by fluctuations in the concentration of the catalyst. The air-fuel ratio of the combustion exhaust gas at the upstream side and the downstream side of the three-way catalyst in the exhaust passage is measured, and the three-way catalyst is obtained by a cross-correlation coefficient R _xy (τ) shown in the following equation (1). The deterioration diagnosis method for a three-way catalyst according to claim 1 or 2, wherein the degree of deterioration of the three-way catalyst is diagnosed.

(Where t is a time, τ is a delay time between signals measured on the upstream side and the downstream side, and x (t) is the combustion exhaust gas upstream of the three-way catalyst in the exhaust passage at time t. The air-fuel ratio of the combustion exhaust gas at the downstream side of the three-way catalyst in the exhaust passage at time (t + τ) at the time (t + τ), and R _xy (τ) represents the cross-correlation coefficient)   The three-way catalyst deterioration diagnosis method according to claim 1, wherein a zirconia solid electrolyte type detector is used as the detector.   The degree of deterioration of the three-way catalyst is diagnosed in a state where the temperature of the three-way catalyst is equal to or higher than an activation temperature in a purification reaction for purifying the combustion exhaust gas. Three-way catalyst deterioration diagnosis method. An exhaust gas purification device for purifying combustion exhaust gas discharged from an internal combustion engine,
Nitrogen contained in the combustion exhaust gas disposed in the exhaust passage of the internal combustion engine, and upstream and downstream of the three-way catalyst in the exhaust passage. An exhaust gas purification apparatus comprising: a detector capable of continuously measuring the concentration of oxide and / or the air-fuel ratio of the combustion exhaust gas.   The exhaust gas purifying device according to claim 6, wherein the detector is a zirconia solid electrolyte type detector.

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