Method and device for diagnosing deterioration of exhaust purification catalyst

Abstract

When the temperature of a three-way catalyst (15) is in a first temperature range (200-300°C), the air-fuel ratio in the catalyst is enriched (S2, S3) and the ammonia level is detected with a downstream ammonia sensor 20 (S4). The detected ammonia level is compared with threshold #A (S5). When the catalyst temperature is further in a second temperature range (350-400°C), the air-fuel ratio in the catalyst is similarly enriched (S7, S8) and the ammonia level is detected (S9). The detected ammonia level is compared with threshold #B (S10). When the ammonia level under the first temperature range is lower than threshold #A and the ammonia level under the second temperature range is at or higher than threshold #B, it is determined that the catalyst is deteriorated (S11).

Description

[Technical Field]

[0001] The present invention relates to a deterioration diagnosis for an exhaust purification catalyst, which diagnoses the deterioration of an exhaust purification catalyst provided in an exhaust passage of an internal combustion engine based on the ammonia concentration detected downstream of the exhaust purification catalyst. [Background technology]

[0002] Patent Document 1 discloses a technology in which, when the air-fuel ratio of exhaust gas flowing into a three-way catalyst is richer than the stoichiometric air-fuel ratio, the ammonia concentration in the exhaust gas flowing out from the three-way catalyst is detected by an ammonia sensor, and if the detected ammonia concentration is higher than a reference ammonia concentration corresponding to the engine operating state, the three-way catalyst is determined to be deteriorated.

[0003] However, the ammonia concentration detected by the ammonia sensor downstream of the exhaust purification catalyst fluctuates relatively greatly depending on conditions such as the temperature of the exhaust purification catalyst, so the method of simply comparing with a reference ammonia concentration as described above has low diagnostic accuracy. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-141417 Summary of the Invention

[0005] The present invention provides a method for diagnosing deterioration of an exhaust purification catalyst, which comprises providing an ammonia sensor that is sensitive to the ammonia concentration in exhaust gas downstream of the exhaust purification catalyst in an exhaust passage of an internal combustion engine, and diagnosing deterioration of the exhaust purification catalyst using a detection signal from this ammonia sensor, a first temperature range in which the deteriorated exhaust gas purification catalyst emits relatively less ammonia than a new exhaust gas purification catalyst, and a second temperature range in which the deteriorated exhaust gas purification catalyst emits relatively more ammonia than a new exhaust gas purification catalyst are set in advance; Deterioration of the exhaust purification catalyst is diagnosed based on a first ammonia concentration detected by the ammonia sensor when the exhaust purification catalyst is within a first temperature range, and a second ammonia concentration detected by the ammonia sensor when the exhaust purification catalyst is within a second temperature range.

[0006] In an environment where the inside of the exhaust purification catalyst is richer than the theoretical air-fuel ratio, a catalytic reaction generates ammonia from NOx and hydrogen in the exhaust gas, and some of the generated ammonia is further converted into nitrogen and other substances through an oxidation reaction, with the remaining ammonia flowing out downstream of the exhaust purification catalyst.

[0007] The rates of the ammonia production reaction and the ammonia oxidation reaction in the exhaust purification catalyst differ depending on the temperature conditions of the exhaust purification catalyst. Both of these reactions decrease as the exhaust purification catalyst deteriorates, but the decline in the ammonia production reaction and the ammonia oxidation reaction that accompanies deterioration are different from each other and do not decrease equally.

[0008] Therefore, there may be a temperature range of the exhaust purification catalyst (i.e., a first temperature range) in which a deteriorated exhaust purification catalyst emits relatively less ammonia compared to a new exhaust purification catalyst, and conversely, a temperature range of the exhaust purification catalyst (i.e., a second temperature range) in which a deteriorated exhaust purification catalyst emits relatively more ammonia compared to a new exhaust purification catalyst.

[0009] Therefore, by comparing the first ammonia concentration detected by the ammonia sensor when the exhaust purification catalyst is within a first temperature range and the second ammonia concentration detected by the ammonia sensor when the exhaust purification catalyst is within a second temperature range with the characteristics of, for example, a new exhaust purification catalyst, it is possible to accurately diagnose the deterioration of the exhaust purification catalyst. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram illustrating the configuration of an internal combustion engine equipped with a three-way catalyst according to an embodiment of the present invention; [Figure 2] 4 is a flowchart showing a process flow of a catalyst deterioration diagnosis according to an embodiment; [Figure 3] FIG. 4 is an explanatory diagram showing the relationship between catalyst temperature and the generation and oxidation of ammonia. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is an explanatory diagram showing a schematic configuration of an internal combustion engine 1 of one embodiment to which the present invention is applied. The internal combustion engine 1 of the one embodiment is a four-stroke spark-ignition internal combustion engine (a so-called gasoline engine), and each cylinder is provided with an intake valve 2, an exhaust valve 3, and an ignition plug 4. The illustrated example is configured as a direct injection type engine, and a fuel injection valve 5 that injects fuel into the cylinder is disposed, for example, on the intake valve 2 side. Note that the engine may also be configured as a port injection type that injects fuel toward an intake port 6.

[0012] An electronically controlled throttle valve 10, the opening of which is controlled by a control signal from an engine controller 9, is installed upstream of a collector section 8 in an intake passage 7 connected to the intake port 6 of each cylinder. An air flow meter 11, which detects the amount of intake air, is disposed upstream of the throttle valve 10, and an air cleaner 12 is disposed further upstream.

[0013] The exhaust ports 13 of each cylinder are joined together to form a single exhaust passage 14, which is provided with an exhaust purification catalyst for purifying the exhaust, such as a three-way catalyst 15. The three-way catalyst 15 is, for example, a monolithic ceramic catalyst in which a catalyst layer containing catalytic metal is coated on the surface of a monolithic ceramic body having fine passages formed therein. The three-way catalyst 15 may also be configured to further include a downstream catalyst (a so-called underfloor catalyst) arranged in series.

[0014] An upstream air-fuel ratio sensor 19 for detecting the air-fuel ratio of the exhaust gas discharged by the internal combustion engine 1 (in other words, the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 15) is disposed on the inlet side of the three-way catalyst 15 in the exhaust passage 14, i.e., on the upstream side of the three-way catalyst 15. This upstream air-fuel ratio sensor 19 is a so-called wide-range air-fuel ratio sensor that can obtain an output according to the exhaust air-fuel ratio.

[0015] An ammonia sensor 20, which is sensitive to the ammonia concentration in the exhaust gas flowing out from the three-way catalyst 15, is disposed on the outlet side or downstream side of the three-way catalyst 15. In one embodiment, the ammonia sensor 20 is a so-called NOx sensor capable of detecting NOx in the exhaust gas. That is, it is sensitive to both the ammonia concentration and the NOx concentration, and outputs both as a single detection signal. In a preferred embodiment, the ammonia sensor 20 is configured to output an output signal corresponding to the exhaust air-fuel ratio of the exhaust gas flowing out from the three-way catalyst 15, separately from the ammonia / NOx detection signal. In other words, the ammonia sensor 20 functions as a downstream air-fuel ratio sensor that detects the exhaust air-fuel ratio of the exhaust gas flowing out from the three-way catalyst 15. The exhaust air-fuel ratio of the exhaust gas flowing out from the three-way catalyst 15 is considered to correspond to the air-fuel ratio environment within the three-way catalyst 15. If the exhaust air-fuel ratio of the exhaust gas flowing out from the three-way catalyst 15 is lean, the ammonia / NOx detection signal output by the ammonia sensor 20 is considered to indicate the NOx concentration, and if the exhaust air-fuel ratio of the exhaust gas flowing out from the three-way catalyst 15 is rich, the ammonia / NOx detection signal output by the ammonia sensor 20 is considered to indicate the ammonia concentration.

[0016] It is also possible to configure the system to include a downstream air-fuel ratio sensor that is independent of the ammonia sensor 20. Alternatively, the exhaust air-fuel ratio downstream of the three-way catalyst 15 may not be detected, and the air-fuel ratio environment inside the three-way catalyst 15 may be estimated based on the exhaust air-fuel ratio of the exhaust gas flowing into the three-way catalyst 15 (which is detected by the upstream air-fuel ratio sensor 19).

[0017] Furthermore, the three-way catalyst 15 is equipped with a catalyst temperature sensor 25 for detecting the temperature of the three-way catalyst 15. In one embodiment, the catalyst temperature sensor 25 detects the temperature of the carrier (monolith ceramic body) of the three-way catalyst 15. Note that instead of the catalyst temperature sensor 25 that directly detects the carrier temperature, an exhaust temperature sensor that detects the exhaust gas temperature may be provided on at least one of the upstream and downstream sides of the three-way catalyst 15, and the temperature of the three-way catalyst 15 may be estimated based on the exhaust gas temperature. Alternatively, the temperature of the three-way catalyst 15 may be estimated based on the amount of heat input from the internal combustion engine 1 to the three-way catalyst 15.

[0018] Detection signals from the upstream air-fuel ratio sensor 19, ammonia sensor 20, catalyst temperature sensor 25, and air flow meter 11 are input to the engine controller 9. Further detection signals from a number of sensors, such as a crank angle sensor 21 for detecting the engine speed, a water temperature sensor 22 for detecting the coolant temperature, and an accelerator position sensor 23 for detecting the amount of depression of the accelerator pedal operated by the driver, are input to the engine controller 9. Based on these input signals, the engine controller 9 optimally controls the amount and timing of fuel injection by the fuel injection valve 5, the ignition timing by the spark plug 4, the opening of the throttle valve 10, etc.

[0019] As one of various controls for the internal combustion engine 1, the engine controller 9 performs air-fuel ratio control to maintain the oxygen storage amount of the three-way catalyst 15 at a target oxygen storage amount (for example, set to approximately 40 to 60%) in order to optimize the exhaust purification performance of the three-way catalyst 15. In the air-fuel ratio control, the fuel injection amount is feedback-controlled (for example, PID control) so that the exhaust air-fuel ratio detected by the upstream air-fuel ratio sensor 19 (hereinafter referred to as the upstream exhaust air-fuel ratio) is aligned with the target air-fuel ratio. Here, the target air-fuel ratio is calculated so that the oxygen storage amount of the three-way catalyst 15 estimated from the upstream exhaust air-fuel ratio matches the target oxygen storage amount. Therefore, the oxygen storage amount of the three-way catalyst 15 is basically maintained near the target oxygen storage amount. When the oxygen storage amount is near the target oxygen storage amount, the air-fuel ratio environment inside the three-way catalyst 15 is equivalent to the stoichiometric air-fuel ratio. This effectively oxidizes CO and HC in the exhaust and reduces NOx.

[0020] Furthermore, one of the controls performed by the engine controller 9 is to diagnose whether the three-way catalyst 15 has deteriorated. This deterioration diagnosis will be explained below using the flowchart in Fig. 2. In one embodiment, the deterioration diagnosis is performed after the internal combustion engine 1 has started, while the temperature of the three-way catalyst 15 is rising (i.e., while the three-way catalyst 15 is being warmed up).

[0021] First, in step 1, the catalyst temperature is detected, and in step 2, it is determined whether the catalyst temperature is within a first temperature range. The first temperature range is a preset temperature range within which a deteriorated three-way catalyst emits relatively less ammonia than a new three-way catalyst, and in one embodiment, it is 200 to 300°C. If the temperature is outside the first temperature range in step 2, the process returns to step 1 and the detection of the catalyst temperature is repeated. If it is determined in step 2 that the temperature is within the first temperature range, the process proceeds to step 3, and air-fuel ratio control is performed so that the air-fuel ratio environment within the three-way catalyst 15 corresponds to a predetermined rich air-fuel ratio. Then, in step 4, the ammonia concentration is detected via the ammonia sensor 20 under the condition that the air-fuel ratio environment within the three-way catalyst 15 corresponds to a predetermined rich air-fuel ratio. In other words, a first ammonia concentration is calculated. As described above, in one embodiment, the exhaust air-fuel ratio downstream of the three-way catalyst 15, which is simultaneously detected by the ammonia sensor 20, is considered to be the air-fuel ratio within the three-way catalyst 15. Alternatively, the air-fuel ratio environment inside the three-way catalyst 15 may be estimated based on the upstream exhaust air-fuel ratio. Note that the rich-side air-fuel ratio inside the three-way catalyst 15 for detecting the ammonia concentration is desirably set so that the deviation from the stoichiometric air-fuel ratio is as small as possible within a range where the ammonia concentration required for deterioration diagnosis can be measured. Also, after measuring the ammonia concentration, it is desirably to terminate enrichment and return the target air-fuel ratio to the stoichiometric air-fuel ratio.

[0022] In step 5, it is determined whether the first ammonia concentration under the first temperature range is higher than a predetermined threshold value #A. The threshold value #A is appropriately set so that, under the condition that the temperature is within the first temperature range and the air-fuel ratio environment inside the three-way catalyst is the same rich-side air-fuel ratio, the ammonia concentration discharged will be higher than the threshold value #A in the case of a new three-way catalyst and will be equal to or lower than the threshold value #A in the case of a three-way catalyst that has deteriorated to a predetermined level. For example, the threshold value #A is set to a value that separates the average value of a large number of data points for a new three-way catalyst from the average value of a large number of data points for a three-way catalyst that has deteriorated to a predetermined level.

[0023] If the first ammonia concentration is higher than the threshold value #A, it is determined that the deterioration has not reached the predetermined level, and the diagnostic process is terminated. If the first ammonia concentration is equal to or lower than the threshold value #A, proceed to step 6.

[0024] In step 6, the catalyst temperature is detected again, and in step 7, it is determined whether the catalyst temperature is within a second temperature range. The second temperature range is a preset temperature range in which a deteriorated three-way catalyst emits relatively more ammonia than a new three-way catalyst, and in one embodiment, it is 350 to 400°C. If the temperature is outside the second temperature range in step 7, the process returns to step 6 and the detection of the catalyst temperature is repeated. If it is determined in step 7 that the temperature is within the second temperature range, the process proceeds to step 8, and air-fuel ratio control is performed so that the air-fuel ratio environment inside the three-way catalyst 15 corresponds to a predetermined rich air-fuel ratio. Then, in step 9, the ammonia concentration is detected via the ammonia sensor 20 under the condition that the air-fuel ratio environment inside the three-way catalyst 15 corresponds to the predetermined rich air-fuel ratio. That is, a second ammonia concentration is calculated. In one embodiment, the rich air-fuel ratio when measuring the first ammonia concentration within the first temperature range and the rich air-fuel ratio when measuring the second ammonia concentration within the second temperature range are set to be equal to each other. After measuring the ammonia concentration, it is desirable to terminate the enrichment and return the target air-fuel ratio to the stoichiometric air-fuel ratio.

[0025] Next, in step 10, it is determined whether the second ammonia concentration under the second temperature range is less than a predetermined threshold value #B. Threshold value #B is appropriately set so that, under the condition that the temperature is within the second temperature range and the air-fuel ratio environment inside the three-way catalyst is the same rich-side air-fuel ratio, the ammonia concentration discharged will be less than threshold value #B for a new three-way catalyst and will be equal to or greater than threshold value #B for a three-way catalyst that has deteriorated to a predetermined level. For example, threshold value #B is set to a value that separates the average value of a large number of data for a new three-way catalyst from the average value of a large number of data for a three-way catalyst that has deteriorated to a predetermined level.

[0026] If the second ammonia concentration is less than the threshold value #B, it is determined that the catalyst has not deteriorated to a predetermined level, and the diagnostic process is terminated. If the second ammonia concentration is equal to or greater than the threshold value #B, the process proceeds to step 11, where it is determined that the three-way catalyst 15 has deteriorated to a predetermined level.

[0027] In this way, in the above embodiment, it is determined that the three-way catalyst 15 has deteriorated to a predetermined level based on a combination of two conditions: "the first ammonia concentration within the first temperature range is equal to or lower than threshold value #A" and "the second ammonia concentration within the second temperature range is equal to or higher than threshold value #B." Therefore, deterioration diagnosis can be performed with higher accuracy.

[0028] In addition, in the above embodiment, after the internal combustion engine 1 is started, while the temperature of the three-way catalyst 15 is rising (i.e., while the three-way catalyst 15 is warming up), when the temperature reaches the relatively low first temperature range, a judgment is made under the first temperature range, and then when the temperature reaches the second temperature range, a judgment is made under the second temperature range, so that diagnosis can be performed efficiently under two conditions.

[0029] 2, when the first ammonia concentration measured within a first temperature range (e.g., 200-300°C) is higher than threshold value #A, the second ammonia concentration within a second temperature range (e.g., 350-400°C) is not measured and compared with threshold value #B, but it is also possible to measure the second ammonia concentration within the second temperature range and compare it with threshold value #B even when the first ammonia concentration is higher than threshold value #A. For example, when the first ammonia concentration is higher than threshold value #A and the second ammonia concentration is less than threshold value #B, it can be determined more reliably that degradation has not progressed.

[0030] Although threshold value #A and threshold value #B depend on the characteristics of the three-way catalyst and the temperatures in the first and second temperature ranges, threshold value #A is usually the larger value.

[0031] Next, the diagnostic principle of the above-mentioned deterioration diagnosis will be explained with reference to the explanatory diagram of FIG.

[0032] When the inside of a three-way catalyst is in an environment richer than the stoichiometric air-fuel ratio, a catalytic reaction occurs, producing ammonia from the NOx and hydrogen in the exhaust gas. For example, the reaction occurs as shown in the following formula:

[0033] NO, CO, H2 → NH3, H2O, CO2 Such an ammonia production reaction is initiated at a relatively low catalyst temperature of, for example, 200° C. or higher, as indicated by the arrow labeled "production" in FIG.

[0034] Furthermore, in the three-way catalyst, a purification effect is achieved in which the generated ammonia is converted into nitrogen and the like through an oxidation reaction at the same time as the generation of ammonia. For example, an oxidation reaction occurs as shown in the following formula.

[0035] NH3, O2 → N2, NO, H2O Such an ammonia oxidation reaction begins at a relatively high catalyst temperature, for example, 350° C. or higher, as indicated by the arrow labeled "oxidation" in FIG.

[0036] The concentration of ammonia flowing out from the three-way catalyst depends on the balance between ammonia production and ammonia oxidation, and the portion of the produced ammonia that is not oxidized flows downstream.

[0037] As is clear from FIG. 3, there is a catalyst temperature range in which the ammonia production reaction has begun but the ammonia oxidation reaction cannot occur. This temperature range can be the first temperature range, and in the above embodiment, the first temperature range is set to 200 to 300°C. In this temperature range, the produced ammonia flows out downstream of the three-way catalyst without being oxidized. When the catalyst deteriorates, its ammonia production ability at relatively low catalyst temperatures such as this first temperature range decreases, so that a deteriorated three-way catalyst will produce less ammonia downstream than a new three-way catalyst. Therefore, by appropriately setting threshold value #A, it can be determined that the catalyst is deteriorated if the detected ammonia concentration is below threshold value #A.

[0038] On the other hand, at relatively high catalyst temperatures, both the ammonia production reaction and the oxidation reaction occur actively. This temperature range can be the second temperature range, and in the above embodiment, the second temperature range is set to 350 to 400°C. In this temperature range, most of the produced ammonia is oxidized, so the amount of ammonia flowing downstream of the three-way catalyst is relatively small if the three-way catalyst is new. When the catalyst deteriorates, both the ammonia production reaction and the oxidation reaction weaken, but the ability of the oxidation reaction is relatively greatly reduced, resulting in an increase in the amount of ammonia that flows downstream of the catalyst without being oxidized. Therefore, by appropriately setting threshold value #B, it can be determined that the catalyst has deteriorated if the detected ammonia concentration is equal to or greater than threshold value #B.

[0039] Here, in the first temperature range, ammonia emissions decrease with catalyst degradation, and in the second temperature range, ammonia emissions increase with catalyst degradation. In the present invention, by combining these two characteristics with different increasing and decreasing trends, it is possible to reduce the number of times a non-degraded three-way catalyst is erroneously diagnosed as degraded, thereby improving diagnostic accuracy.

[0040] In the above embodiment, the enrichment in step 3 and step 8 is performed at the same air-fuel ratio, but different rich air-fuel ratios may be set.

[0041] In the above embodiment, the first temperature range is set to 200 to 300°C and the second temperature range is set to 350 to 400°C, but these specific temperatures are set according to the characteristics of the exhaust purification catalyst used (the characteristics of the ammonia production reaction and oxidation reaction as shown in Figure 3), and may be different numerical ranges depending on the catalyst. However, to facilitate control, it is desirable that the two temperature ranges are not continuous, that is, that they are appropriately separated.

[0042] The results of the catalyst deterioration diagnosis according to the present invention can be used in any manner. For example, if a catalyst deterioration is diagnosed, it is desirable to change the air-fuel ratio of the rich spike executed to optimize the oxygen storage amount when the internal combustion engine restarts combustion operation so that it approaches the stoichiometric air-fuel ratio. In this case, it is also desirable to lengthen the time for which the rich spike is applied. In other words, since the oxygen absorption and desorption rate of a deteriorated catalyst is slow, it is desirable to apply a relatively weak rich spike for a long period of time.

[0043] In the above embodiment, the catalyst is classified into two types, non-degraded and deteriorated, using two temperature ranges and two corresponding thresholds. However, in the present invention, it is possible to classify catalyst deterioration into even more levels by using three or more temperature ranges and appropriate corresponding thresholds. For example, in Figure 3, even within the temperature range where the ammonia production reaction and the oxidation reaction occur simultaneously, if attention is focused on several different temperatures, the change in the balance between the ammonia production reaction and the oxidation reaction due to catalyst deterioration may be different for each temperature. Therefore, by appropriately setting the temperature ranges and the corresponding thresholds, it is possible to classify the degree of deterioration into multiple levels.

Claims

1. 1. A method for diagnosing deterioration of an exhaust purification catalyst, comprising: providing an ammonia sensor that is sensitive to the ammonia concentration in exhaust gas downstream of an exhaust purification catalyst in an exhaust passage of an internal combustion engine; and diagnosing deterioration of the exhaust purification catalyst using a detection signal of this ammonia sensor, a first temperature range in which the deteriorated exhaust gas purification catalyst emits relatively less ammonia than a new exhaust gas purification catalyst, and a second temperature range in which the deteriorated exhaust gas purification catalyst emits relatively more ammonia than a new exhaust gas purification catalyst are set in advance; diagnosing deterioration of the exhaust purification catalyst based on a first ammonia concentration detected by the ammonia sensor when the exhaust purification catalyst is within a first temperature range and a second ammonia concentration detected by the ammonia sensor when the exhaust purification catalyst is within a second temperature range; Here, the first ammonia concentration detection and the second ammonia concentration detection are performed under the same air-fuel ratio inside the exhaust purification catalyst that is on the rich side. A method for diagnosing deterioration of an exhaust purification catalyst.

2. When the first ammonia concentration is equal to or less than a first threshold and the second ammonia concentration is equal to or greater than a second threshold, a diagnosis of deterioration is made.

2. The method for diagnosing deterioration of an exhaust purification catalyst according to claim 1.

3. When the deterioration is diagnosed, the air-fuel ratio of the rich spike executed when the combustion operation of the internal combustion engine is restarted is changed so as to be relatively closer to the stoichiometric air-fuel ratio.

2. The method for diagnosing deterioration of an exhaust purification catalyst according to claim 1.

4. detecting a first ammonia concentration and a second ammonia concentration while the temperature of the exhaust gas purification catalyst is rising after the internal combustion engine is started; 2. The method for diagnosing deterioration of an exhaust purification catalyst according to claim 1.

5. The first temperature range is lower than the second temperature range, and the two are not continuous.

2. The method for diagnosing deterioration of an exhaust purification catalyst according to claim 1.

6. The first temperature range is 200 to 300°C, and the second temperature range is 350 to 400°C.

6. The method for diagnosing deterioration of an exhaust purification catalyst according to claim 5.

7. an exhaust purification catalyst provided in an exhaust passage of the internal combustion engine; an ammonia sensor that is provided downstream of the exhaust purification catalyst and is sensitive to the ammonia concentration in the exhaust gas; a controller that performs a deterioration diagnosis of an exhaust purification catalyst using a detection signal from the ammonia sensor; Equipped with The above controller is a first temperature range in which the deteriorated exhaust gas purification catalyst emits relatively less ammonia than a new exhaust gas purification catalyst, and a second temperature range in which the deteriorated exhaust gas purification catalyst emits relatively more ammonia than a new exhaust gas purification catalyst are set in advance; diagnosing deterioration of the exhaust purification catalyst based on a first ammonia concentration detected by the ammonia sensor when the exhaust purification catalyst is within a first temperature range and a second ammonia concentration detected by the ammonia sensor when the exhaust purification catalyst is within a second temperature range; Here, the first ammonia concentration detection and the second ammonia concentration detection are performed under the same air-fuel ratio inside the exhaust purification catalyst that is on the rich side. A deterioration diagnosis device for exhaust purification catalysts.

8. A method for diagnosing deterioration of an exhaust purification catalyst, comprising providing an ammonia sensor that is sensitive to the ammonia concentration in exhaust gas downstream of the exhaust purification catalyst in the exhaust passage of an internal combustion engine, and diagnosing deterioration of the exhaust purification catalyst using the detection signal of this ammonia sensor, a first temperature range in which the deteriorated exhaust gas purification catalyst emits relatively less ammonia than a new exhaust gas purification catalyst, and a second temperature range in which the deteriorated exhaust gas purification catalyst emits relatively more ammonia than a new exhaust gas purification catalyst are set in advance; diagnosing deterioration of the exhaust purification catalyst based on a first ammonia concentration detected by the ammonia sensor when the exhaust purification catalyst is within a first temperature range and a second ammonia concentration detected by the ammonia sensor when the exhaust purification catalyst is within a second temperature range; Here, the first temperature range is lower than the second temperature range, and the two are not continuous. A method for diagnosing deterioration of an exhaust purification catalyst.

9. The first temperature range is 200 to 300°C, and the second temperature range is 350 to 400°C.

9. The method for diagnosing deterioration of an exhaust purification catalyst according to claim 8.

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