JP2012215143A - Catalyst deterioration determination device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst deterioration determination device which can properly distinguish and determine uniform deterioration or partial deterioration of an SCR catalyst.SOLUTION: The catalyst deterioration determination device determines deterioration of the SCR for carrying out exhaust emission control using a reducing agent added in an exhaust passage. In a deterioration determination means, a control is carried out in which the reducing agent is added in the exhaust passage so that an equivalent ratio between NOx and NHflowing into the SCR catalyst is changed, and the SCR catalyst is determined to be in either states of the uniform deterioration or the partial deterioration, on the basis of conversion efficiency by the SCR catalyst which is obtained upon the control. Thus, the uniform deterioration and the partial deterioration of the SCR catalyst can be properly distinguished and determined.

Description

  The present invention relates to a technical field of a catalyst deterioration determination device.

Conventionally, a NOx selective reduction catalyst (hereinafter referred to as “SCR (Selective Catalytic Reduction) catalyst” as appropriate) that performs exhaust purification using a reducing agent such as urea added to the exhaust passage is known. For example, Patent Document 1 describes a technique for determining deterioration of an SCR catalyst. Specifically, a technique for determining the deterioration of the SCR catalyst by estimating the NO ₂ ratio in NOx flowing into the SCR catalyst and comparing the NO ₂ ratio when the purification rate reaches a peak with a reference value is described. Has been.

JP 2010-242728 A

  However, Patent Document 1 described above does not describe that when the SCR catalyst is deteriorated, the determination is made by distinguishing whether the SCR catalyst is uniformly deteriorated or partially deteriorated. In the following, the state where the SCR catalyst is uniformly deteriorated as a whole is referred to as “uniform deterioration”, and the state where the SCR catalyst is partially deteriorated is referred to as “partial deterioration”.

  The present invention has been made to solve the above-described problems, and provides a catalyst deterioration determination device capable of appropriately distinguishing and determining uniform deterioration and partial deterioration of an SCR catalyst. Objective.

In one aspect of the present invention, a catalyst deterioration determination device that performs deterioration determination on an SCR catalyst that performs exhaust purification using a reducing agent added in an exhaust passage includes NOx and NH ₃ flowing into the SCR catalyst. Based on the NOx purification rate by the SCR catalyst when the reducing agent is added to the exhaust passage so that the equivalence ratio changes, it is determined whether the SCR catalyst is in a uniform deterioration state or a partial deterioration state. Deterioration determination means for determining is provided.

The catalyst deterioration determination device performs deterioration determination on an SCR catalyst (NOx selective reduction catalyst) that selectively reduces NOx using a reducing agent added in the exhaust passage. Specifically, the deterioration determination means performs control to add a reducing agent into the exhaust passage so that the equivalent ratio of NOx and NH ₃ flowing into the SCR catalyst changes. Then, the deterioration determination means is based on the SCR catalyst NOx purification rate obtained by performing the control (for example, obtained based on the output of the NOx sensor provided on the downstream side of the SCR catalyst). It is determined whether the catalyst is in a deterioration state of uniform deterioration or partial deterioration. The deterioration determination means determines whether the SCR catalyst is uniformly deteriorated or partially deteriorated by utilizing the fact that the mode of change in the NOx purification rate due to the change in the equivalence ratio differs between the case of uniform deterioration and the case of partial deterioration. Thereby, it becomes possible to distinguish and determine between uniform deterioration and partial deterioration of the SCR catalyst. Therefore, it is possible to optimize the reducing agent addition control when the SCR catalyst is deteriorated.

In one aspect of the catalyst deterioration determination device, the deterioration determination unit is configured to change the NOx purification rate when the equivalent ratio of NH _{3 to} NOx is changed between “1” and “0.5”. Whether the SCR catalyst is in the uniform deterioration state or the partial deterioration state is determined based on the slope of the change.

  In this aspect, the deterioration determination means has a change gradient (change gradient) of the NOx purification rate when the equivalence ratio is changed between “1” and “0.5”. It is possible to determine whether the SCR catalyst is in a uniform deterioration state or a partial deterioration state by utilizing the difference between the cases.

1 shows an overall configuration of a system to which a catalyst deterioration determination device according to an embodiment is applied. A specific example of the NOx purification rate when the equivalence ratio is set to “1.0” is shown. A specific example of the NOx purification rate when the equivalence ratio is set to “0.5” is shown. The figure for demonstrating concretely the deterioration determination method which concerns on 1st Embodiment is shown. It is a flowchart which shows the deterioration determination process of the SCR catalyst which concerns on 1st Embodiment. The figure for demonstrating concretely the deterioration determination method which concerns on the modification of 1st Embodiment is shown. A specific example of the NOx purification rate when the NO ₂ ratio is set to “50%” is shown. A specific example of the NOx purification rate when the NO ₂ ratio is set to “30%” is shown. The figure for demonstrating concretely the deterioration determination method which concerns on 2nd Embodiment is shown. It is a flowchart which shows the deterioration determination process of the SCR catalyst which concerns on 2nd Embodiment.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

<Overall configuration>
FIG. 1 is a schematic diagram showing the overall configuration of a system to which a catalyst deterioration determination device according to this embodiment is applied. In FIG. 1, solid arrows indicate the flow of exhaust gas, and broken arrows indicate input / output of control signals and detection signals.

  The engine 11 is an internal combustion engine that generates power for the vehicle by burning an air-fuel mixture of supplied fuel and air (intake air). For example, the engine 11 is a diesel engine. The exhaust gas discharged from the engine 11 flows through the exhaust passage 12.

  On the exhaust passage 12, a first catalyst 13, a urea addition valve 16, an SCR catalyst 14, a second catalyst 15, and a NOx sensor 18 are provided in order from the upstream side to the downstream side. The first catalyst 13 includes an oxidation catalyst called DOC (Diesel Oxidation Catalyst) and a filter called DPF (Diesel Particulate Filter), and performs exhaust gas purification.

  The urea addition valve 16 is a valve that adds (injects) urea as a reducing agent into the exhaust passage 12 between the first catalyst 13 and the SCR catalyst 14. Urea is stored in the urea tank 17 and is supplied into the exhaust passage 12 by the urea addition valve 16 through the urea supply passage 17a. The urea addition valve 16 is controlled by a control signal S16 supplied from the ECU 20.

The SCR catalyst 14 is a low-temperature active catalyst (NOx selective reduction catalyst) that selectively reduces NOx (nitrogen oxide) in the presence of a reducing agent such as urea. Specifically, urea added by the urea addition valve 16 is hydrolyzed by reacting with exhaust gas to generate NH ₃ (ammonia), and the SCR catalyst 14 uses the generated NH _3. NOx is reduced. In addition, it is not limited to using urea as a reducing agent.

The second catalyst 15 is a catalyst (so-called ASC (Ammonia Slip Catalyst)) configured to purify NH ₃ or the like that has been exhausted (slipped) without being reacted by the upstream SCR catalyst 14.

  The NOx sensor 18 is provided on the downstream side of the second catalyst 15 and detects the NOx concentration in the exhaust gas. The NOx sensor 18 supplies a detection signal S18 corresponding to the detected NOx concentration to the ECU 20.

  The ECU (Electronic Control Unit) 20 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like (not shown) and controls the entire vehicle. In the present embodiment, the ECU 20 determines the deterioration of the SCR catalyst 14 based on the NOx concentration corresponding to the detection signal S18 supplied from the NOx sensor 18. Specifically, the ECU 20 determines any deterioration between “uniform deterioration” in which the SCR catalyst 14 is uniformly deteriorated as a whole and “partial deterioration” in which the SCR catalyst 14 is partially deteriorated. Determine if it is in a state. Thus, the ECU 20 corresponds to an example of “deterioration determination means” in the present invention.

  The first catalyst 13 and the second catalyst 15 are not essential components, and the system may not be configured using the first catalyst 13 and / or the second catalyst 15.

<First Embodiment>
Below, the deterioration determination method of the SCR catalyst 14 which concerns on 1st Embodiment is demonstrated. In the first embodiment, the ECU 20 causes the SCR catalyst 14 to be uniformly deteriorated and partially deteriorated based on the NOx purification rate by the SCR catalyst 14 when the equivalent ratio of NOx and NH ₃ flowing into the SCR catalyst 14 is changed. It is determined in which deterioration state.

Here, the “equivalent ratio” corresponds to the ratio of the amount of NH _{3 to the} amount of NOx flowing into the SCR catalyst 14. For example, when the equivalent ratio is “1.0”, the NOx amount and the NH ₃ amount are equal, and when the equivalent ratio is “0.5”, the NH ₃ amount is half of the NOx amount. Such an equivalence ratio is changed by controlling the amount of urea added by the ECU 20 from the urea addition valve 16.

  On the other hand, the “NOx purification rate” corresponds to the ratio of the NOx amount purified by the SCR catalyst 14 to the NOx amount supplied to the SCR catalyst 14. For example, when the NOx purification rate is “100%”, it indicates that the supplied NOx has been completely purified, and when the NOx purification rate is “50%”, the supplied NOx is half. It only shows that it has been purified. Such an NOx purification rate is determined by the ECU 20 between the NOx amount in the exhaust gas on the downstream side of the first catalyst 13 and the upstream side of the SCR catalyst 14 and the NOx amount in the exhaust gas on the downstream side of the second catalyst 15. Ask based. For example, the ECU 20 estimates the NOx amount on the upstream side of the SCR catalyst 14 based on the operating state of the engine 11 and the like, and detects the NOx amount on the downstream side of the second catalyst 15 supplied from the NOx sensor 18. Obtained based on the signal S18. The NOx purification rate thus obtained indicates the total NOx purification rate of the SCR catalyst 14. Note that a NOx sensor may also be provided on the upstream side of the SCR catalyst 14, and the NOx amount on the upstream side of the SCR catalyst 14 may be obtained based on the detection signal supplied from the NOx sensor.

  Next, with reference to FIG. 2 and FIG. 3, the reason for performing the deterioration determination of the SCR catalyst 14 as described above will be described.

FIG. 2 shows a specific example of the NOx purification rate of the SCR catalyst 14 when the equivalence ratio is set to “1.0”. In FIG. 2, for convenience of explanation, the amount of NOx supplied to the SCR catalyst 14 is “100”, and the amount of NH ₃ supplied to the SCR catalyst 14 is “100”.

FIG. 2A shows the NOx purification rate when the SCR catalyst 14 is normal. Specifically, the NOx purification rate when the SCR catalyst 14 as a whole has a NOx purification capacity of “100%” is shown. In this case, the NOx amount is “0” and the NH ₃ amount is “0” on the downstream side of the SCR catalyst 14. Therefore, the NOx purification rate obtained by the ECU 20 is “100%”.

  The equivalent ratio of “1.0” corresponds to the optimal equivalent ratio of the normal SCR catalyst 14. During normal control, the amount of urea to be added from the urea addition valve 16 is controlled so that the equivalent ratio of “1.0” is obtained.

FIG. 2B shows the NOx purification rate when the SCR catalyst 14 is in a uniform deterioration state. Specifically, the NOx purification rate when the SCR catalyst 14 as a whole has only “50%” NOx purification capacity is shown. In this case, the NOx amount is “50” and the NH ₃ amount is “50” on the downstream side of the SCR catalyst 14. Therefore, in the case of uniform degradation as shown in FIG. 2B, the NOx purification rate obtained by the ECU 20 is “50%”.

FIG. 2C shows the NOx purification rate when the SCR catalyst 14 is in a partially deteriorated state. Specifically, half of the SCR catalyst 14 has a NOx purification capacity of “100%”, and the other half of the SCR catalyst 14 has no NOx purification capacity (the NOx purification capacity is “0%”). NOx purification rate in the case). FIG. 2 (c) shows a diagram in which a “50” NOx amount and a “50” NH ₃ amount are supplied for each half of the SCR catalyst 14 for convenience of explanation. In this case, in the portion of the SCR catalyst 14 whose NOx purification capacity is “0%”, the downstream side NOx amount becomes “50” and the NH ₃ amount becomes “50”. On the other hand, in the portion of the SCR catalyst 14 whose NOx purification capacity is “100%”, the downstream side NOx amount is “0” and the NH ₃ amount is “0”. Therefore, in the case of the partial deterioration as shown in FIG. 2C, the NOx purification rate obtained by the ECU 20 is “50%”.

  2 (b) and 2 (c), when the equivalence ratio is “1.0”, NOx obtained when the SCR catalyst 14 is in a state of uniform deterioration and in a state of partial deterioration. The purification rate becomes equal. Therefore, when the equivalence ratio is set to “1.0”, it cannot be distinguished whether the SCR catalyst 14 is in a uniform deterioration state or a partial deterioration state based on the NOx purification rate. It can be said. Note that when the equivalence ratio is set to “1.0”, the NOx purification rate differs depending on whether the SCR catalyst 14 is normal or deteriorated (including both uniform deterioration and partial deterioration). It can be said that it can be appropriately determined whether or not the SCR catalyst 14 is normal (in other words, whether or not the SCR catalyst 14 is deteriorated).

FIG. 3 shows a specific example of the NOx purification rate of the SCR catalyst 14 when the equivalence ratio is set to “0.5”. In FIG. 3, for convenience of explanation, the NOx amount supplied to the SCR catalyst 14 is “100”, and the NH ₃ amount supplied to the SCR catalyst 14 is “50”.

FIG. 3A shows the NOx purification rate when the SCR catalyst 14 is normal. Specifically, the NOx purification rate when the SCR catalyst 14 as a whole has a NOx purification capacity of “100%” is shown. In this case, the NOx amount is “50” and the NH ₃ amount is “0” on the downstream side of the SCR catalyst 14. Therefore, the NOx purification rate obtained by the ECU 20 is “50%”.

FIG. 3B shows the NOx purification rate when the SCR catalyst 14 is in a state of uniform degradation. Specifically, the NOx purification rate when the SCR catalyst 14 as a whole has only “50%” NOx purification capacity is shown. In this case, the NOx amount is “50” and the NH ₃ amount is “0” on the downstream side of the SCR catalyst 14. Therefore, in the case of uniform degradation as shown in FIG. 3B, the NOx purification rate obtained by the ECU 20 is “50%”.

FIG. 3C shows the NOx purification rate when the SCR catalyst 14 is in a partially deteriorated state. Specifically, half of the SCR catalyst 14 has “100%” NOx purification capacity, and the other half of the SCR catalyst 14 has no NOx purification capacity (when the NOx purification capacity is “0%”). The NOx purification rate is shown. FIG. 3C shows a diagram in which “50” NOx amount and “25” NH ₃ amount are supplied for each half of the SCR catalyst 14 for convenience of explanation. In this case, in the portion of the SCR catalyst 14 whose NOx purification capacity is “0%”, the downstream NOx amount is “50” and the NH ₃ amount is “25”. On the other hand, in the portion of the SCR catalyst 14 whose NOx purification capacity is “100%”, the downstream side NOx amount is “25” and the NH ₃ amount is “0”. Therefore, in the case of partial deterioration as shown in FIG. 3C, the NOx purification rate obtained by the ECU 20 is “25%”.

  3 (b) and 3 (c), when the equivalence ratio is “0.5”, the NOx obtained when the SCR catalyst 14 is in a uniform deterioration state and in a partial deterioration state is obtained. The purification rate is different. Therefore, when the equivalence ratio is set to “0.5”, whether the SCR catalyst 14 is in a uniform deterioration state or a partial deterioration state is appropriately distinguished based on the NOx purification rate. Can be said.

From the above, in the first embodiment, ECU 20, based on the amount of NH ₃ NOx purification rate obtained when the equivalent ratio is changed in respect to the NOx amount, SCR catalyst 14 is either uniform degradation and partial degradation Determine if it is in a degraded state. Specifically, the ECU 20 performs control to add urea to the urea addition valve 16 so that the equivalence ratio changes, and based on the mode of change in the NOx purification rate by the SCR catalyst 14 at this time, the SCR catalyst It is determined whether 14 is in a deterioration state of uniform deterioration or partial deterioration.

With reference to FIG. 4, the deterioration determination method of the SCR catalyst 14 according to the first embodiment will be specifically described. In FIG. 4, the horizontal axis represents the equivalent ratio of the NH ₃ amount to the NOx amount supplied to the SCR catalyst 14, and the vertical axis represents the NOx purification rate obtained by the ECU 20.

  A graph 51 (shown by a solid line) shows an example of the relationship between the equivalence ratio and the NOx purification rate in the normal SCR catalyst 14. A graph 52 (shown by a broken line) shows an example of the relationship between the equivalence ratio and the NOx purification rate in the SCR catalyst 14 in the state of uniform deterioration. A graph 53 (shown by an alternate long and short dash line) shows an example of the relationship between the equivalence ratio and the NOx purification rate in the SCR catalyst 14 in a partially deteriorated state. The equivalence ratio A1 is an optimum equivalence ratio of the normal SCR catalyst 14, and the equivalence ratio A2 is an equivalence ratio at which the NOx purification rate of the normal SCR catalyst 14 becomes a predetermined value B. The predetermined value B corresponds to a threshold value for determining whether the SCR catalyst 14 is normal or deteriorated (hereinafter referred to as “degradation determination value” as appropriate). For example, the equivalent ratio A1 is “1.0”, and the equivalent ratio A2 is “0.5”.

  From the graphs 52 and 53, it can be seen that the mode of change in the NOx purification rate with respect to the change in the equivalence ratio differs between the uniform degradation and the partial degradation in the range of the equivalence ratio A1 or less. For example, between the equivalence ratio A1 and the equivalence ratio A2, the NOx purification rate hardly changes in the case of uniform deterioration, whereas the NOx purification rate changes in the case of partial deterioration. Recognize. Therefore, in one example, the ECU 20 uses the difference (absolute value) of the NOx purification rate before and after the change when the equivalent ratio is changed between the equivalent ratio A1 and the equivalent ratio A2. Based on the above, a uniform deterioration and a partial deterioration are discriminated. In this example, the ECU 20 determines that the SCR catalyst 14 is in a state of uniform degradation when the difference in the NOx purification rate before and after the change in the equivalence ratio is less than a predetermined value, and performs the NOx purification before and after the change in the equivalence ratio. When the difference in rate is equal to or greater than a predetermined value, it is determined that the SCR catalyst 14 is in a partially deteriorated state.

  In another example, instead of using the difference in the NOx purification rate as described above, the ECU 20 changes the slope of the change in the NOx purification rate when the equivalent ratio is changed between the equivalent ratio A1 and the equivalent ratio A2 (in other words, And uniform degradation and partial degradation based on the change gradient). In this example, when the slope of the change in the NOx purification rate is less than a predetermined value, the ECU 20 determines that the SCR catalyst 14 is in a uniformly deteriorated state, and the slope of the change in the NOx purification rate is greater than or equal to the predetermined value. If there is, it is determined that the SCR catalyst 14 is in a partially deteriorated state.

  On the other hand, it can be seen from the graphs 51 and 52 that in the case of uniform deterioration, the NOx purification rate in the normal case overlaps within the range of the equivalent ratio A2 or less. On the other hand, it can be seen from the graphs 51 and 53 that in the case of partial deterioration, the NOx purification rate in the normal case does not overlap within the range of the equivalent ratio A2 or less. Therefore, in yet another example, instead of using the difference in NOx purification rate and the gradient of change as described above, the ECU 20 has a normal NOx purification rate within a range equal to or less than the equivalent ratio A2, and the SCR catalyst 14 is normal. The uniform deterioration and the partial deterioration are determined depending on whether or not the NOx purification rate overlaps. In this example, the ECU 20 determines that the SCR catalyst 14 is in a state of uniform deterioration when the NOx purification rate obtained in the range of the equivalence ratio A2 or less overlaps with the NOx purification rate when the SCR catalyst 14 is normal. judge. On the other hand, when the NOx purification rate obtained within the equivalence ratio A2 or less does not overlap with the NOx purification rate when the SCR catalyst 14 is normal, the ECU 20 causes the SCR catalyst 14 to be in a partially deteriorated state. Judge that there is.

(Processing flow)
Next, the deterioration determination process for the SCR catalyst 14 according to the first embodiment will be described with reference to FIG. FIG. 5 is a flowchart showing an example of the deterioration determination process for the SCR catalyst 14 according to the first embodiment. This process is repeatedly executed by the ECU 20 at a predetermined cycle.

First, in step S101, ECU 20 is most suitable amount ratio equivalent ratio of NH ₃ amount to the NOx amount when set to (equivalent ratio A1 of FIG. 4), NOx purification rate by the SCR catalyst 14 (hereinafter, as " Usually referred to as “NOx purification rate”). For example, the ECU 20 estimates the NOx amount on the upstream side of the SCR catalyst 14 based on the operating state of the engine 11, and the downstream side of the second catalyst 15 based on the detection signal S18 supplied from the NOx sensor 18. NOx amount is obtained, and the normal NOx purification rate is obtained based on these NOx amounts. Then, the process proceeds to step S102.

  In step S102, the ECU 20 determines whether or not the normal NOx purification rate is equal to or less than the deterioration determination value. Here, it is determined whether or not the SCR catalyst 14 is normal, in other words, whether or not the SCR catalyst 14 has deteriorated.

  When the normal NOx purification rate is equal to or less than the deterioration determination value (step S102; Yes), the process proceeds to step S103. In this case, the ECU 20 determines that the SCR catalyst 14 has deteriorated, and performs a process for determining whether the SCR catalyst 14 is in a deteriorated state of uniform deterioration or partial deterioration after step S103. Do. On the other hand, when the normal NOx purification rate is larger than the deterioration determination value (step S102; No), the process proceeds to step S108. In this case, the ECU 20 determines that the SCR catalyst 14 is normal (step S108). Then, the process ends.

In step S103, the ECU 20 performs control to reduce the equivalent ratio of the NH ₃ amount to the NOx amount from the optimum equivalent ratio. Specifically, the ECU 20 changes the equivalent ratio of the NH ₃ amount relative to the NOx amount from a predetermined equivalent ratio that is equal to or higher than the equivalent ratio at which the NOx purification rate of the normal SCR catalyst 14 becomes the deterioration determination value from the optimal equivalent ratio (for example, FIG. The amount of urea added from the urea addition valve 16 is controlled so as to reduce the equivalent ratio A2) shown in FIG. Then, the process proceeds to step S104.

  In step S104, ECU20 calculates | requires the NOx purification rate by the SCR catalyst 14 after reducing an equivalence ratio. For example, the ECU 20 estimates the NOx amount on the upstream side of the SCR catalyst 14 based on the operating state of the engine 11, and the downstream side of the second catalyst 15 based on the detection signal S18 supplied from the NOx sensor 18. NOx amount is obtained, and the NOx purification rate after reduction of the equivalence ratio is obtained based on these NOx amounts. Then, the process proceeds to step S105.

  In step S105, the ECU 20 determines whether or not the difference between the normal NOx purification rate and the NOx purification rate after the reduction of the equivalent ratio (the absolute value is used) is equal to or greater than a predetermined value. Here, the ECU 20 determines whether the SCR catalyst 14 is in a uniform deterioration state or a partial deterioration state. As the predetermined value used for the determination, a preset value is used. If the SCR catalyst 14 is in a state of uniform deterioration, basically, the difference between the normal NOx purification rate and the NOx purification rate after the equivalent ratio reduction is substantially “0”, but the predetermined value is a certain amount. A margin is provided and set to a value larger than “0”, for example.

  When the difference between the normal NOx purification rate and the NOx purification rate after the equivalent ratio reduction is equal to or greater than a predetermined value (step S105; Yes), the process proceeds to step S106. In this case, the ECU 20 determines that the SCR catalyst 14 is in a partially deteriorated state (step S106). Then, the process ends. On the other hand, when the difference between the normal NOx purification rate and the NOx purification rate after the equivalent ratio reduction is less than the predetermined value (step S105; No), the process proceeds to step S107. In this case, the ECU 20 determines that the SCR catalyst 14 is in a state of uniform deterioration (step S107). Then, the process ends.

  According to the first embodiment described above, it is possible to appropriately distinguish and determine uniform degradation and partial degradation of the SCR catalyst 14 based on the NOx purification rate when the equivalence ratio is changed. This makes it possible to optimize urea addition control when the SCR catalyst 14 is deteriorated.

  In the above processing flow, an example is shown in which the determination is performed using the normal NOx purification rate obtained when the equivalence ratio is set to the optimum equivalence ratio. However, the present invention is not limited to this. Even if it is not the optimum equivalence ratio, if the NOx purification rate of the normal SCR catalyst 14 is an equivalence ratio equal to or higher than the equivalence ratio that becomes the deterioration judgment value, the determination is made using the NOx purification rate obtained when the equivalent ratio is set. May be performed.

(Modification of the first embodiment)
Here, a modified example of the first embodiment will be described. The modification relates to a deterioration determination method for the SCR catalyst 14 that is performed when the second catalyst 15 is not provided on the downstream side of the SCR catalyst 14. In this case, since it is influenced by NH ₃ discharged (slipped) without being reacted by the SCR catalyst 14, a deterioration determination method different from that in the first embodiment described above is performed.

FIG. 6 is a diagram for specifically explaining the deterioration determination method for the SCR catalyst 14 according to a modification of the first embodiment. In FIG. 6, the horizontal axis indicates the equivalent ratio of the NH ₃ amount to the NOx amount supplied to the SCR catalyst 14, and the vertical axis indicates the NOx purification rate obtained by the ECU 20.

A graph 61 (shown by a solid line) shows an example of the relationship between the equivalence ratio and the NOx purification rate in the normal SCR catalyst 14. A graph 62 (shown by a broken line) shows an example of the relationship between the equivalence ratio and the NOx purification rate in the SCR catalyst 14 in the state of uniform deterioration. A graph 63 (shown by a one-dot chain line) shows an example of the relationship between the equivalent ratio and the NOx purification rate in the SCR catalyst 14 in a partially deteriorated state. The equivalence ratio A1 is the optimum equivalence ratio of the normal SCR catalyst 14, and is, for example, “1.0”. Comparing FIG. 6 and FIG. 4, the change in the NOx purification rate with respect to the change in the equivalence ratio is different between the case where the second catalyst 15 is not provided and the case where the second catalyst 15 is provided. Recognize. This is due to the effect of NH ₃ slip.

  From the graphs 62 and 63, it can be seen that the mode of change of the NOx purification rate with respect to the change of the equivalence ratio is different between the uniform deterioration and the partial deterioration in the range of the equivalence ratio A1 or less. For example, in the range of the equivalence ratio A1 or less, the NOx purification rate hardly changes in the case of partial deterioration (the NOx purification rate is generally “0”), whereas in the case of uniform deterioration. It can be seen that the NOx purification rate is changing. Therefore, in one example, the ECU 20 determines that the uniform deterioration is based on the difference in the NOx purification rate before and after the change (assuming that an absolute value is used) when the equivalent ratio is changed in the range of the equivalent ratio A1 or less. Discriminated from partial deterioration. In this example, when the difference in the NOx purification rate before and after the change in the equivalence ratio is less than a predetermined value, the ECU 20 determines that the SCR catalyst 14 is in a partially deteriorated state, and the NOx purification before and after the change in the equivalence ratio. When the difference in rate is equal to or greater than a predetermined value, it is determined that the SCR catalyst 14 is in a state of uniform deterioration.

  Further, from the graphs 62 and 63, in the range of the equivalence ratio A1 or less, the NOx purification rate peak exists in the case of uniform deterioration, but such NOx purification rate peak does not exist in the case of partial deterioration. I understand. Therefore, in another example, when the equivalent ratio is changed within a range equal to or less than the equivalent ratio A1, the ECU 20 discriminates between uniform deterioration and partial deterioration based on whether or not the peak of the NOx purification rate exists. . In this example, the ECU 20 determines that the SCR catalyst 14 is in a state of uniform deterioration when the peak of the NOx purification rate exists, and if the peak of the NOx purification rate does not exist, the ECU 20 Determined to be in a degraded state.

  Further, from the graphs 61, 62, and 63, in the equivalence ratio A1 or less, there is a range of equivalence ratio that overlaps the NOx purification rate in the normal case in the case of uniform degradation, but in the case of normal in the case of partial degradation It can be seen that there is no equivalent ratio range overlapping the NOx purification rate. Therefore, in yet another example, when the ECU 20 changes the equivalence ratio within the equivalence ratio A1 or less, there is an equivalence ratio range that overlaps with the NOx purification rate obtained when the SCR catalyst 14 is normal. Based on whether or not, uniform deterioration and partial deterioration are discriminated. In this example, the ECU 20 determines that the SCR catalyst 14 is in a state of uniform deterioration when there is an equivalent ratio range that overlaps with the normal NOx purification rate, and overlaps with the normal NOx purification rate. When the equivalence ratio range does not exist, it is determined that the SCR catalyst 14 is in a partially deteriorated state.

  According to the modification of the first embodiment described above, when the second catalyst 15 is not provided on the downstream side of the SCR catalyst 14, the uniform degradation and the partial degradation of the SCR catalyst 14 are appropriately distinguished and determined. It becomes possible.

Second Embodiment
Next, a method for determining the deterioration of the SCR catalyst 14 according to the second embodiment will be described. In the first embodiment, based on the NOx purification rate when the equivalent ratio of NOx and NH ₃ flowing into the SCR catalyst 14 is changed, whether the SCR catalyst 14 is in a deterioration state of uniform deterioration or partial deterioration. Was judged. In contrast, in the second embodiment, instead of the equivalent ratio, the NO ₂ ratio indicating the ratio of NO (nitrogen monoxide) and NO ₂ (nitrogen dioxide) flowing into the SCR catalyst 14 is changed. Whether the SCR catalyst 14 is in a deteriorated state, that is, a uniform deterioration or a partial deterioration, is determined based on the NOx purification rate obtained.

Here, the “NO ₂ ratio” corresponds to the ratio of the NO ₂ amount to the NO x amount (an amount including both NO and NO ₂ ) flowing into the SCR catalyst 14. For example, when the NO ₂ ratio is “50%”, the ratio between the NO amount and the NO ₂ amount is “1: 1”, and when the NO ₂ ratio is “30%”, the NO amount and the NO ₂ The ratio to the amount is “7: 3”. Such a NO ₂ ratio is changed, for example, by the ECU 20 controlling the operating state of the engine 11 and the like.

  In the following, a method for determining the deterioration of the SCR catalyst 14 performed when the second catalyst 15 is provided on the downstream side of the SCR catalyst 14 will be described.

  With reference to FIGS. 7 and 8, the reason for performing the deterioration determination of the SCR catalyst 14 as described above will be described.

FIG. 7 shows a specific example of the NOx purification rate of the SCR catalyst 14 when the NO ₂ ratio is set to “50%”. In FIG. 7, for convenience of explanation, the NO amount supplied to the SCR catalyst 14 is “50”, and the NO ₂ amount supplied to the SCR catalyst 14 is “50”. Further, in FIG. 7, the NOx amount change (in other words, NOx concentration change) in the SCR catalyst 14 is schematically represented by the line segment shown in the hatched region. This change in the NOx amount indicates a change in both the NO amount and the NO ₂ amount (because the NO amount change and the NO ₂ amount change are the same in the example shown in FIG. 7).

FIG. 7A shows the NOx purification rate when the SCR catalyst 14 is normal. Specifically, the NOx purification rate when the SCR catalyst 14 as a whole has a NOx purification capacity of “100%” is shown. In this case, the NO amount becomes “0” and the NO ₂ amount becomes “0” on the downstream side of the SCR catalyst 14. Therefore, the NOx purification rate obtained by the ECU 20 is “100%”.

Note that the NO ₂ ratio of “50%” corresponds to the optimum NO ₂ ratio of the normal SCR catalyst 14. During normal control, control is performed so that the NO ₂ ratio is “50%”. Basically, the NOx purification by the SCR catalyst 14 is only a reaction for purification when the ratio of the NO amount to the NO ₂ amount is “1: 1”, and no purification reaction with NO alone or NO ₂ alone occurs.

FIG. 7B shows the NOx purification rate when the SCR catalyst 14 is in a state of uniform degradation. Specifically, the NOx purification rate when the SCR catalyst 14 as a whole has only “50%” NOx purification capacity is shown. In this case, the NO amount becomes “25” and the NO ₂ amount becomes “25” on the downstream side of the SCR catalyst 14. Therefore, in the case of uniform degradation as shown in FIG. 7B, the NOx purification rate obtained by the ECU 20 is “50%”.

FIG. 7C shows the NOx purification rate when the SCR catalyst 14 is in a partially deteriorated state. Specifically, half of the SCR catalyst 14 has a NOx purification capacity of “100%”, and the other half of the SCR catalyst 14 has no NOx purification capacity (the NOx purification capacity is “0%”). NOx purification rate in the case). FIG. 7 (c) shows a diagram in which a “25” NO amount and a “25” NO ₂ amount are supplied for each half of the SCR catalyst 14 for convenience of explanation. In this case, in the portion of the SCR catalyst 14 whose NOx purification capacity is “0%”, the downstream side NO amount is “25” and the NO ₂ amount is “25”. On the other hand, in the portion of the SCR catalyst 14 whose NOx purification capacity is “100%”, the downstream side NO amount is “0” and the NO ₂ amount is “0”. Therefore, in the case of the partial deterioration as shown in FIG. 7C, the NOx purification rate obtained by the ECU 20 is “50%”.

7B and 7C, when the NO ₂ ratio is “50%”, the NOx obtained when the SCR catalyst 14 is in a uniform deterioration state and in a partial deterioration state is obtained. The purification rate becomes equal. Therefore, when the NO ₂ ratio is set to “50%”, it cannot be distinguished whether the SCR catalyst 14 is in a uniform deterioration state or a partial deterioration state based on the NOx purification rate. It can be said. When the NO ₂ ratio is set to “50%”, the NOx purification rate differs between when the SCR catalyst 14 is normal and when it is deteriorated (including both uniform deterioration and partial deterioration). It can be said that it can be appropriately determined whether or not the SCR catalyst 14 is normal (in other words, whether or not the SCR catalyst 14 is deteriorated).

FIG. 8 shows a specific example of the NOx purification rate of the SCR catalyst 14 when the NO ₂ ratio is set to “30%”. In FIG. 8, for convenience of explanation, the amount of NO supplied to the SCR catalyst 14 is “70”, and the amount of NO ₂ supplied to the SCR catalyst 14 is “30”. Further, in FIG. 8, the NOx amount change (in other words, NOx concentration change) in the SCR catalyst 14 is schematically represented by the line segment shown in the hatched region. Specifically, the broken line indicates a change in NO amount, and the solid line indicates a change in NO ₂ amount.

FIG. 8A shows the NOx purification rate when the SCR catalyst 14 is normal. Specifically, the NOx purification rate when the SCR catalyst 14 as a whole has a NOx purification capacity of “100%” is shown. In this case, the NO amount is “40” and the NO ₂ amount is “0” on the downstream side of the SCR catalyst 14. Therefore, the NOx purification rate obtained by the ECU 20 is “60%”.

FIG. 8B shows the NOx purification rate when the SCR catalyst 14 is in a state of uniform degradation. Specifically, the NOx purification rate when the SCR catalyst 14 as a whole has only “50%” NOx purification capacity is shown. In this case, the NO amount is “45” and the NO ₂ amount is “5” on the downstream side of the SCR catalyst 14. Therefore, in the case of uniform deterioration as shown in FIG. 8B, the NOx purification rate obtained by the ECU 20 is “50%”.

FIG. 8C shows the NOx purification rate when the SCR catalyst 14 is in a partially deteriorated state. Specifically, half of the SCR catalyst 14 has “100%” NOx purification capacity, and the other half of the SCR catalyst 14 has no NOx purification capacity (when the NOx purification capacity is “0%”). The NOx purification rate is shown. FIG. 8C shows a diagram in which the NO amount of “35” and the NO ₂ amount of “15” are supplied for each half of the SCR catalyst 14 for convenience of explanation. In this case, in the portion of the SCR catalyst 14 whose NOx purification capacity is “0%”, the downstream side NO amount is “35” and the NH ₃ amount is “15”. On the other hand, in the portion of the SCR catalyst 14 whose NOx purification capacity is “100%”, the downstream side NO amount is “20” and the NO ₂ amount is “0”. Therefore, in the case of the partial deterioration as shown in FIG. 8C, the NOx purification rate obtained by the ECU 20 is “30%”.

8B and 8C, when the NO ₂ ratio is “30%”, the NOx obtained when the SCR catalyst 14 is in a uniform deterioration state and in a partial deterioration state is obtained. The purification rate is different. Therefore, when the NO ₂ ratio is set to “30%”, it is necessary to appropriately distinguish whether the SCR catalyst 14 is in a uniform deterioration state or a partial deterioration state based on the NOx purification rate. Can be said.

From the above, in the second embodiment, the ECU ₂₀ determines whether the SCR catalyst 14 is in a uniform deterioration state or a partial deterioration state based on the NOx purification rate obtained when the NO ₂ ratio is changed. judge.

With reference to FIG. 9, the deterioration determination method of the SCR catalyst 14 according to the second embodiment will be specifically described. FIG. 9 shows the NO ₂ ratio on the horizontal axis and the NOx purification rate obtained by the ECU 20 on the vertical axis.

A graph 71 (shown by a solid line) shows an example of the relationship between the NO ₂ ratio and the NOx purification rate in the normal SCR catalyst 14. A graph 72 (shown by a broken line) shows an example of the relationship between the NO ₂ ratio and the NOx purification rate in the SCR catalyst 14 in a uniform deterioration state. A graph 73 (shown by a one-dot chain line) shows an example of the relationship between the NO ₂ ratio and the NOx purification rate in the SCR catalyst 14 in the partially deteriorated state. The NO ₂ ratio C1 is the optimum NO ₂ ratio of the normal SCR catalyst 14, and is “50%”, for example. On the other hand, the NO ₂ ratio C2 is a NO ₂ ratio at which the NOx purification rate of the normal SCR catalyst 14 becomes the deterioration determination value B, for example, a value smaller than “50%”.

From the graphs 72 and 73, it can be seen that the mode of change of the NOx purification rate with respect to the change of the NO ₂ ratio differs between uniform deterioration and partial deterioration. For example, between the NO ₂ ratio C1 and the NO ₂ ratio C2, the NOx purification rate hardly changes in the case of uniform deterioration, whereas the NOx purification rate changes in the case of partial deterioration. I understand that. Therefore, in one example, ECU 20 is at the time of changing a NO ₂ ratio between NO ₂ ratio C1 and NO ₂ ratio C2, and those using the difference (absolute value of the NOx purification rate before and after the change. The same shall apply hereinafter) to determine whether there is uniform deterioration or partial deterioration. In this example, the ECU ₂₀ determines that the SCR catalyst 14 is in a state of uniform deterioration when the difference in the NOx purification rate before and after the change in the NO ₂ ratio is less than a predetermined value, and before and after the change in the NO ₂ ratio. When the difference in the NOx purification rates is equal to or greater than a predetermined value, it is determined that the SCR catalyst 14 is in a partially deteriorated state.

In another example, ECU 20, instead of using the difference between the NOx purification rate as described above, NO ₂ ratio C1 and the NOx purification rate of change definitive when changing the NO ₂ ratio between NO ₂ ratio C2 Uniform deterioration and partial deterioration are discriminated based on the inclination (in other words, the change gradient). In this example, when the slope of the change in the NOx purification rate is less than a predetermined value, the ECU 20 determines that the SCR catalyst 14 is in a uniformly deteriorated state, and the slope of the change in the NOx purification rate is greater than or equal to the predetermined value. If there is, it is determined that the SCR catalyst 14 is in a partially deteriorated state.

On the other hand, it can be seen from the graphs 71 and 72 that in the case of uniform deterioration, the NOx purification rate overlaps with the normal case within the range of the NO ₂ ratio C2 or less. On the other hand, it can be seen from the graphs 71 and 73 that in the case of the partial deterioration, the NOx purification rate does not overlap with the normal case within the range of the NO ₂ ratio C2 or less. Therefore, in yet another example, instead of using the difference in NOx purification rate and the gradient of change as described above, the ECU 20 has a NOx purification rate obtained in a range of the NO ₂ ratio C2 or less and the SCR catalyst 14 is normal. Uniform deterioration and partial deterioration are determined depending on whether or not the NOx purification rate overlaps in some cases. In this example, the ECU 20 indicates that the SCR catalyst 14 is in a state of uniform deterioration when the NOx purification rate obtained in the range of the NO ₂ ratio C2 or less overlaps with the NOx purification rate when the SCR catalyst 14 is normal. Is determined. On the other hand, the ECU ₂₀ determines that the SCR catalyst 14 is in a partially deteriorated state when the NOx purification rate obtained in the range of the NO ₂ ratio C2 or less does not overlap with the NOx purification rate when the SCR catalyst 14 is normal. It is determined that

(Processing flow)
Next, with reference to FIG. 10, the deterioration determination process of the SCR catalyst 14 according to the second embodiment will be described. FIG. 10 is a flowchart showing an example of the deterioration determination process of the SCR catalyst 14 according to the second embodiment. This process is repeatedly executed by the ECU 20 at a predetermined cycle.

First, in step S201, the ECU 20 sets the NO ₂ ratio to the optimum NO ₂ ratio (the NO ₂ ratio C1 shown in FIG. 9). The NOx purification rate by the SCR catalyst 14 (this NOx purification rate is also described below). Then, it is called “normal NOx purification rate”). For example, the ECU 20 estimates the NOx amount on the upstream side of the SCR catalyst 14 based on the operating state of the engine 11, and the downstream side of the second catalyst 15 based on the detection signal S18 supplied from the NOx sensor 18. NOx amount is obtained, and the normal NOx purification rate is obtained based on these NOx amounts. Then, the process proceeds to step S202.

  In step S202, the ECU 20 determines whether or not the normal NOx purification rate is equal to or less than the deterioration determination value. Here, it is determined whether or not the SCR catalyst 14 is normal, in other words, whether or not the SCR catalyst 14 has deteriorated.

  When the normal NOx purification rate is equal to or less than the deterioration determination value (step S202; Yes), the process proceeds to step S203. In this case, the ECU 20 determines that the SCR catalyst 14 has deteriorated, and performs a process for determining whether the SCR catalyst 14 is in a deteriorated state of uniform deterioration or partial deterioration after step S203. Do. On the other hand, when the normal NOx purification rate is larger than the deterioration determination value (step S202; No), the process proceeds to step S208. In this case, the ECU 20 determines that the SCR catalyst 14 is normal (step S208). Then, the process ends.

In step S203, the ECU ₂₀ performs control to change the set NO ₂ ratio from the optimum NO ₂ ratio. For example, the ECU ₂₀ changes from the optimal NO ₂ ratio to a predetermined NO ₂ ratio (for example, the NO ₂ ratio C2 shown in FIG. 9) that is equal to or higher than the NO ₂ ratio at which the NOx purification rate of the normal SCR catalyst 14 becomes the deterioration determination value. The operating state of the engine 11 and the like are controlled so as to decrease the operating state. Then, the process proceeds to step S204.

In step S204, the ECU ₂₀ obtains the NOx purification rate by the SCR catalyst 14 after changing the NO ₂ ratio. For example, the ECU 20 estimates the NOx amount on the upstream side of the SCR catalyst 14 based on the operating state of the engine 11, and the downstream side of the second catalyst 15 based on the detection signal S18 supplied from the NOx sensor 18. NOx amount is obtained, and the NOx purification rate after changing the NO ₂ ratio is obtained based on these NOx amounts. Then, the process proceeds to step S205.

In step S205, the ECU ₂₀ determines whether or not the difference between the normal NOx purification rate and the NOx purification rate after changing the NO ₂ ratio (assuming that an absolute value is used) is equal to or greater than a predetermined value. Here, the ECU 20 determines whether the SCR catalyst 14 is in a uniform deterioration state or a partial deterioration state. As the predetermined value used for the determination, a preset value is used. If the SCR catalyst 14 is in a state of uniform deterioration, basically, the difference between the normal NOx purification rate and the NOx purification rate after changing the NO ₂ ratio is approximately “0”, but the predetermined value is somewhat Is set to a value larger than “0”, for example.

If the difference between the normal NOx purification rate and NO ₂ ratio NOx purification rate after the change is equal to or larger than the predetermined value (step S205; Yes), the process proceeds to step S206. In this case, the ECU 20 determines that the SCR catalyst 14 is in a partially deteriorated state (step S206). Then, the process ends. In contrast, when the difference between the normal NOx purification rate and NO ₂ ratio NOx purification rate after the change is smaller than the predetermined value (step S205; No), the process proceeds to step S207. In this case, the ECU 20 determines that the SCR catalyst 14 is in a state of uniform deterioration (step S207). Then, the process ends.

Also according to the second embodiment described above, it is possible to appropriately distinguish and determine uniform deterioration and partial deterioration of the SCR catalyst 14 based on the NOx purification rate when the NO ₂ ratio is changed. This makes it possible to optimize urea addition control when the SCR catalyst 14 is deteriorated.

In the process flow described above, an example in which determination is performed using a conventional NOx purification rate obtained when setting the NO ₂ proportion in the optimum NO ₂ ratio, limited to this are not. Even not optimal NO ₂ ratio, if normal NO ₂ ratio NOx purification rate becomes deterioration determination value NO ₂ ratio or more of the SCR catalyst 14, NOx purification rate obtained when set to the NO ₂ ratio The determination may be made using.

11 Engine 12 Exhaust passage 13 First catalyst 14 SCR catalyst (NOx selective reduction catalyst)
15 Second catalyst 16 Urea addition valve 18 NOx sensor 20 ECU

Claims (2)

A catalyst deterioration determination device that performs deterioration determination on an SCR catalyst that performs exhaust purification using a reducing agent added in an exhaust passage,
Based on the NOx purification rate by the SCR catalyst when the reducing agent is added to the exhaust passage so that the equivalent ratio of NOx and NH ₃ flowing into the SCR catalyst changes, the SCR catalyst is uniformly deteriorated And a deterioration determination device for a catalyst, comprising deterioration determination means for determining whether the deterioration state is partial deterioration or partial deterioration. The deterioration determining means, wherein the equivalent ratio of the NH ₃ for NOx from "1" when changing between "0.5" based on the inclination of the change of the NOx purification rate, the SCR catalyst The catalyst deterioration determination device according to claim 1, wherein it is determined which of the uniform deterioration and the partial deterioration is present.

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