JP2014020269A - Catalyst deterioration determination device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst deterioration determination device capable of accurately determining deterioration of a catalyst even when the catalyst is a criterion catalyst which is not detected by complete failure detection because an oxidation catalyst arranged on an exhaust passage of an internal combustion engine is in a state that a degree of deterioration is comparatively small and an oxidation purification function of a certain degree is left.SOLUTION: The catalyst deterioration determination device includes determination means for determining deterioration based on a heat rate of the oxidation catalyst after a lapse of predetermined time from addition of a reductant to the oxidation catalyst. The predetermined time is set to time required for that an estimated bed temperature of an oxidation catalyst model corresponding to a deteriorated oxidation catalyst when supposing addition of the reductant to the oxidation catalyst model is reduced from the start of addition of the supposed reductant up to a predetermined threshold bed temperature due to activation reduction of the oxidation catalyst model.

Description

  The present invention relates to a catalyst deterioration determination device that determines whether or not an oxidation catalyst provided in an exhaust passage of an internal combustion engine has deteriorated.

  In general, an oxidation catalyst (hereinafter sometimes simply referred to as “catalyst”) is provided in an exhaust passage of an internal combustion engine in order to purify exhaust gas. The purpose of the oxidation catalyst is to purify harmful hydrocarbons (HC), carbon monoxide (CO), etc. contained in the exhaust, but when this oxidation catalyst deteriorates due to various causes and the oxidation function decreases, Unpurified exhaust will be released to the atmosphere. In particular, in automobiles, diagnosis of deterioration of an oxidation catalyst by an OBD system is required by the laws and regulations of each country, and therefore, a technology that can more accurately determine the deterioration state of the oxidation catalyst is required.

  For example, Patent Document 1 discloses a technique for performing abnormality determination of an oxidation catalyst installed in an exhaust passage of a diesel engine during regeneration processing of a DPF (diesel particulate filter) installed downstream of the oxidation catalyst. ing. In this technique, after the addition of fuel is started in order to forcibly raise the temperature of the exhaust gas flowing into the DPF, if it is a normal catalyst, it flows into the oxidation catalyst after a lapse of the time when the temperature increase of the exhaust gas is completed. The deterioration is determined by detecting the difference between the temperature of the exhaust gas and the temperature of the exhaust gas flowing out from the oxidation catalyst.

JP 2008-128170 A JP 2009-191789 A JP 2006-291834 A JP 2005-105881 A JP 2009-046988 A JP 2002-339790 A

  In general, an oxidation catalyst deteriorates with time due to an unexpected heat load, and the oxidation purification function is lowered. Conventionally, an oxidation catalyst whose deterioration degree has been remarkably deteriorated and the oxidation purification function has been reduced to a level that requires replacement has been accurately detected by the OBD system and has been judged to be deteriorated (complete failure detection). On the other hand, there is an oxidation catalyst that is not detected by complete failure detection because the degree of deterioration is relatively small and a certain degree of oxidation purification function remains. Hereinafter, such a state is referred to as a criteria state, and an oxidation catalyst in the criteria state is referred to as a criteria catalyst.

For example, when a catalyst used in an exhaust gas purification system for an internal combustion engine that exhausts exhaust containing a relatively large amount of HC and CO, which is highly dependent on the oxidation purification function of the oxidation catalyst, has reached a criteria state due to deterioration. There is a possibility that the emission of the exhausted gas will exceed the OBD regulation value. Therefore, in such a case, it is necessary to accurately determine the deterioration even with the criterion catalyst. However, since a certain degree of oxidation purification function remains even if the criteria catalyst is deteriorated, HC, CO, etc. contained in the exhaust gas when the temperature of the inflowing exhaust gas (inlet temperature) is high to some extent. However, there is a case where the exhaust gas is exhausted at a temperature similar to that of a normal catalyst (normal catalyst) that is not deteriorated due to a certain amount of oxidation heat. That is, D
When fuel is added during the regeneration process of PF, even if it is a criteria catalyst, the exhaust gas whose temperature has been raised to the same level as that of a normal catalyst may be discharged. When such a phenomenon occurs, there is a possibility that an accurate determination cannot be made with the conventional technology in which the normality / abnormality of the catalyst is determined based on the temperature of the exhaust gas flowing out from the oxidation catalyst.

  In addition, with the recent tightening of exhaust gas regulations, an OBD system that can perform deterioration determination of an oxidation catalyst with higher accuracy has been required. In other words, there is an increasing demand for a technique that can accurately detect the above-mentioned criteria catalyst that is in a state where the degree of deterioration is relatively small and a certain degree of oxidation purification function remains.

  In order to solve the above-described problems, an object of the present invention is to provide a catalyst deterioration determination device that can accurately determine deterioration even with a criterion catalyst.

  In order to achieve the above object, a catalyst deterioration determination device according to the present invention includes an oxidation catalyst provided in an exhaust passage of an internal combustion engine, an addition means for adding a reducing agent that generates heat in the oxidation catalyst, and the addition means. Determining means for determining deterioration of the oxidation catalyst based on the heat generation rate of the oxidation catalyst after a predetermined time has elapsed from the start of addition of the reducing agent by the step, wherein the predetermined time corresponds to the deterioration of the oxidation catalyst The estimated bed temperature of the oxidation catalyst model in the case of assuming the addition of the reducing agent to the oxidation catalyst model is increased by the oxidation heat generation of the reducing agent from the start of the assumed addition of the reducing agent. Thereafter, it is set to a time until the oxidation catalyst model decreases to a predetermined threshold bed temperature due to the decrease in the activity of the oxidation catalyst model that progresses with the addition of the reducing agent.

  Reducing agents such as fuel (HC) and CO added to the oxidation catalyst are heated (oxidized) in the oxidation catalyst to raise the bed temperature of the oxidation catalyst. Here, if the oxidation catalyst is a normal catalyst that has not deteriorated, the added fuel is continuously oxidized in the oxidation catalyst, whereby the bed temperature rises, and then the temperature is maintained. On the other hand, when a reducing agent is added to the above-mentioned criteria catalyst that has a relatively low degree of degradation and a certain degree of oxidation purification function, the reducing agent generates a certain amount of oxidation heat at the initial stage of addition. As a result, the bed temperature rises, but after that, the activity of the criteria catalyst is lowered and the bed temperature is lowered (details will be described later). That is, the amount of heat generated by the oxidation exothermic reaction due to the decrease in activity decreases, and as a result, the bed temperature decreases.

  Here, the actual calorific value generated by the exothermic reaction of the reducing agent added to the oxidation catalyst and the target calorific value required to raise the bed temperature of the oxidation catalyst to the target bed temperature are used. Define the heat generation rate represented by "target heat generation". When a reducing agent is added to the normal catalyst, an actual calorific value about the target calorific value can be obtained, so that the heat generation rate is maintained at a high level. On the other hand, when a reducing agent is added to the criteria catalyst, the heat generation rate increases at the initial stage of addition, but as described above, the heat generation rate starts to decrease when the activity decreases. Therefore, the heat generation rate of the criterion catalyst after a predetermined time from the start of fuel addition until the decrease in activity has a clear difference from the heat generation rate of the normal catalyst after the same time has elapsed. Becomes (clearly smaller).

  Therefore, according to the present invention, during the addition of the reducing agent to the oxidation catalyst, if the criterion catalyst is used, the activity decreases from the timing when the activity is reduced and the heat generation rate is clearly reduced, that is, from the start of the addition of the reducing agent by the adding means. After the elapse of a predetermined time until the decrease, the deterioration determination of the oxidation catalyst is executed based on the heat generation rate of the oxidation catalyst. Therefore, in the present invention, the predetermined time is set by the method described below.

  In the present invention, assuming that the oxidation catalyst according to the present invention has deteriorated, that is, a case where a reducing agent is added to an oxidation catalyst model corresponding to an oxidation catalyst that has deteriorated to the criteria state, the predetermined time is determined by the oxidation catalyst model. The oxidation catalyst that progresses with the passage of the addition time of the reducing agent after the estimated bed temperature has been raised by oxidation heat generation of the reducing agent from the time when the assumed addition of the reducing agent is started It is set to the time until the temperature drops to a predetermined threshold bed temperature due to the decrease in the activity of the model.

  By setting the predetermined time as described above, the present invention can execute the deterioration determination of the oxidation catalyst at the timing when the activity is reduced and the heat generation rate is clearly reduced if it is a criteria catalyst. it can. Therefore, according to the present invention, the deterioration determination can be executed at a timing at which the difference between the normal catalyst and the criteria catalyst can be detected reliably and accurately, so that the deterioration determination can be executed with high accuracy.

  Here, in the present invention, the threshold bed temperature is a predetermined threshold heat rate when the estimated heat generation rate of the oxidation catalyst model when the addition of the reducing agent is assumed is caused by a decrease in the activity of the oxidation catalyst model. You may make it be the temperature when it falls to. Thereby, the deterioration determination of the oxidation catalyst can be executed at a timing at which the difference between the normal catalyst and the criteria catalyst can be detected more accurately.

  Further, in the present invention, the threshold bed temperature is a predetermined threshold value due to a decrease in the estimated heat generation rate of the oxidation catalyst model when the addition of the reducing agent is assumed. It may be the temperature when the amount of decrease is reached. That is, even if the threshold bed temperature is set to a temperature at which the estimated heat generation rate decreases relatively rapidly, the difference between the normal catalyst and the criterion catalyst can be detected more accurately at a timing at which the oxidation catalyst is detected. Deterioration determination can be performed.

  In the present invention, the determination unit determines that the oxidation catalyst is deteriorated when the heat generation rate is equal to or lower than a predetermined threshold heat generation rate. That is, according to the present invention, the deterioration determination is performed by comparing the heat generation rate of the oxidation catalyst with the threshold heat generation rate at a timing at which the difference between the normal catalyst and the criteria catalyst can be detected reliably and accurately. can do.

  In the present invention, the determination means calculates a weighted average value of the heat generation rate using a weighting coefficient set based on the estimated bed temperature and the estimated heat generation rate of the oxidation catalyst model. And when the said weighted average value is below a predetermined threshold weighted average value, it determines with the said oxidation catalyst having degraded.

  In other words, when it is necessary to improve the detection accuracy of deterioration determination, instead of comparing the calculated heat generation rate with the threshold heat generation rate, the weighted average value of the heat generation rate is calculated, and the weighted average value and the threshold weighted average are calculated. The values may be compared. Here, the weighting coefficient used when calculating the weighted average value is set based on the estimated bed temperature and the estimated heat generation rate of the oxidation catalyst model. Therefore, for example, when an estimated bed temperature range that is particularly important when making a deterioration determination is known in advance, the accuracy of deterioration determination is further improved by assigning a higher weight to the range. Can do.

  The catalyst deterioration determination device of the present invention further includes a filter that collects particles in the exhaust gas downstream of the oxidation catalyst, and the determination unit performs oxidation processing to remove particles collected by the filter. The deterioration determination of the oxidation catalyst may be performed after the predetermined time has elapsed from the start of addition of the reducing agent by the adding means.

  With such a configuration, it is possible to execute the deterioration determination of the oxidation catalyst when a reducing agent is added for the regeneration process of the filter. Therefore, it is possible to reduce the consumption of the reducing agent (fuel) required for the deterioration determination.

  According to the present invention, it is possible to accurately determine the deterioration of the catalyst.

1 is a diagram illustrating a schematic configuration of an internal combustion engine system according to Embodiment 1. FIG. 3 is a graph showing the relationship between the bed temperature and the heat generation rate of the oxidation catalyst according to Example 1. 3 is a graph showing changes in the bed temperature and heat generation rate of the oxidation catalyst according to Example 1. 4 is a flowchart illustrating a flow of catalyst deterioration determination processing according to the first embodiment. 6 is a flowchart showing a flow of catalyst deterioration determination processing according to Embodiment 2. 6 is a schematic cross-sectional view of a calculation model according to Embodiment 2. FIG. It is a schematic diagram which shows the heat transfer in the i-th cell when the calculation model which concerns on Example 2 assumes that there is no oxidation reaction of a reducing agent. 6 is a schematic diagram illustrating heat transfer in an i-th cell of a calculation model according to Example 2. FIG. 6 is a schematic diagram showing mass transfer during an oxidation reaction in an i-th cell of a calculation model according to Example 2. FIG. 6 is a graph showing heat generation characteristics and a bed temperature region of an oxidation catalyst according to Example 3. 12 is a flowchart illustrating a flow of catalyst deterioration determination processing according to a third embodiment.

[Example 1]
Hereinafter, specific embodiments of a catalyst deterioration determination device according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine system to which a catalyst deterioration determination device according to the present invention is applied. In the present embodiment, an automobile diesel engine is taken as an example of the internal combustion engine, but it may be a diesel engine used for other purposes than an automobile, or an internal combustion engine using another fuel or ignition system. It may be.

  An intake passage 6 for adding intake air to the combustion chamber 4 in each cylinder is connected to the internal combustion engine 2 having four cylinders via an intake manifold 8. Further, an exhaust passage 10 for discharging exhaust gas generated in the combustion chamber 4 is connected to the internal combustion engine 2 via an exhaust manifold 12. In the following, upstream and downstream are defined according to the flow direction of intake and exhaust.

  In the intake passage 6, in order from the upstream side, an air cleaner 14 that removes dust and the like contained in intake air, an air flow sensor 16 that detects the flow rate Ga of the intake air, a compressor housing 18 a of a turbocharger 18 that pressurizes the intake air, and pressurization An intercooler 20 that lowers the temperature of the intake air and a throttle valve 22 that controls the amount of intake air that is added to the combustion chamber based on the driver's accelerator work and the like are provided. The air flow sensor 16 and the throttle valve 22 are electrically connected to an ECU 100 that is an electronic control unit that executes various controls relating to the internal combustion engine 2 (including catalyst deterioration determination processing according to the present invention). Therefore, the intake air flow rate Ga detected by the air flow sensor 16 is output to the ECU 100 as an electrical signal. The throttle valve 22 is controlled by a control signal from the ECU 100.

The fuel injection valve 24 installed in each combustion chamber 4 injects fuel accumulated in advance into each combustion chamber 4 via a common rail or the like (not shown). Each fuel injection valve 24 is electrically connected to the ECU 100, and the timing and amount of fuel injection are controlled by the ECU 100. Further, the ECU 100 stores an injection amount eqfin per stroke of each cylinder in order to calculate an in-cylinder injection flow rate Gaf, which will be described in detail later. The internal combustion engine 2 is provided with a tachometer 26 electrically connected to the ECU 100, and the rotational speed NE of the internal combustion engine is output to the ECU 100.

  Further, in the exhaust passage 10, in order from the upstream side, a fuel addition valve 28 for injecting and adding fuel to the exhaust, the turbine housing 18 b of the turbocharger 18, and a catalyst 30 which is an oxidation catalyst for oxidizing and purifying exhaust passing through the inside. , And a DPF 32 that collects particulate matter (hereinafter referred to as “PM”) present in the exhaust. A first temperature sensor 34 for detecting the temperature of the exhaust gas flowing into the catalyst 30 (hereinafter referred to as “incoming gas”) is installed in the vicinity of the upstream side of the catalyst 30, and the exhaust gas flowing out of the catalyst 30 in the vicinity of the downstream side. A second temperature sensor 36 for detecting the temperature (hereinafter referred to as “outgas”) is installed. Further, an outside air temperature sensor 38 for detecting the temperature around the catalyst 30 is installed in the vicinity of the outside of the catalyst 30. These sensors are electrically connected to the ECU 100, and a detection result is output. Further, a differential pressure sensor 40 that detects a differential pressure between the exhaust gas flowing into the DPF 32 and the exhaust gas flowing out of the DPF 32 is installed, and the detection result is output to the electrically connected ECU 100.

  Here, the regeneration process of the DPF 32 performed by the ECU 100 will be described. If the combustion of the internal combustion engine 2 continues, PM contained in the exhaust gas that is discharged is accumulated inside the DPF 32, so that the filter function of the DPF 32 is deteriorated. When it is determined that the filter function is lowered based on the detection value of the differential pressure sensor 40, the travel distance of the automobile, or the like, the ECU 100 instructs the fuel addition valve 28 to add fuel in order to execute the regeneration process of the DPF 32. Here, the amount of fuel added from the fuel addition valve 28 increases the temperature of the exhaust gas flowing into the DPF 32 to a desired temperature required for the regeneration process when the entire amount is subjected to the oxidation reaction in the catalyst 30. The amount that can be warmed. Here, when the catalyst 30 is in a normal state that is not deteriorated, the fuel that has flowed into the catalyst 30 together with the input gas is continuously oxidized in the catalyst 30, so that the temperature of the input gas becomes the DPF 32. It is raised to the temperature required for the regeneration process and then maintained. Then, the outflow gas (exhaust gas) flowing out from the catalyst 30 flows into the DPF 32, and PM accumulated in the DPF 32 is sufficiently oxidized and removed.

  1 is only a schematic configuration of the embodiment of the present invention, and does not limit the embodiment. For example, an EGR device that recirculates exhaust gas, a urea SCR system for purifying nitrogen oxide (NOx) in the exhaust gas, or the like may be added as appropriate. Further, fuel may be added to the catalyst 30 by post-injection into the combustion chamber 4 by the fuel injection valve 24 instead of adding fuel by the fuel addition valve 28.

By the way, generally, when the regeneration process of the DPF is executed, as in the present embodiment, fuel is added to the oxidation catalyst installed upstream of the DPF, and the exhaust temperature is forced to the target temperature necessary for the regeneration process. (Forced temperature rise). Here, the actual temperature increase result is affected by the state of the oxidation catalyst, that is, the presence or absence and the degree of deterioration. As described above, when the oxidation catalyst is a normal catalyst that has not deteriorated, the added fuel is continuously oxidized, so that sufficient heat generation continues and the exhaust temperature reaches the target temperature. On the other hand, when the oxidation catalyst is an abnormal catalyst with a remarkable degree of deterioration, the added fuel is hardly oxidized and discharged because the oxidation catalyst does not have a sufficient oxidation function. The exhaust temperature that rises hardly rises. Therefore, a clear difference appears between the exhaust temperature discharged from the normal catalyst and the exhaust temperature discharged from the abnormal catalyst. Therefore, even in the prior art, the deterioration determination of the oxidation catalyst is performed based on the exhaust temperature discharged from the oxidation catalyst. Could be implemented. The above-described complete failure detection by the conventional OBD system and the determination method described in Patent Document 1 are based on such a determination principle.

  Here, even with a deteriorated oxidation catalyst, there is an oxidation catalyst in which the degree of deterioration is relatively small and a certain degree of oxidation purification function remains. Hereinafter, such a deteriorated state of the oxidation catalyst is referred to as “criteria state”, and the oxidation catalyst in the criteria state is referred to as “criteria catalyst”. When an oxidation catalyst used in an exhaust gas purification system for an internal combustion engine that emits a relatively large amount of HC and CO reaches a criteria state, exhaust gas exceeding the emission regulation value may be discharged due to insufficient oxidation ability There is. Therefore, it is necessary to accurately determine that the OBD system is in the criteria state. However, as described above, the criteria catalyst still has some oxidation function, so when the fuel is added during the regeneration process of the DPF. There is a possibility that the exhaust gas, which is exhausted after the fuel is oxidized to some extent, is heated to a target temperature. Therefore, in the conventional OBD system that performs catalyst deterioration determination based on the exhaust gas temperature flowing out from the oxidation catalyst, it is impossible to accurately detect that the oxidation catalyst is in the criteria state.

  Therefore, the present invention makes it possible to accurately detect whether or not the oxidation catalyst to be determined is a criterion catalyst by paying attention to the heat generation characteristics of the criterion catalyst when fuel addition is performed. Hereinafter, the detection method of the criteria catalyst according to the present invention will be described with reference to the drawings.

  First, the heat generation characteristics of the normal catalyst and the criteria catalyst when fuel addition is executed will be described. FIG. 2 is a graph showing a heat generation characteristic which is a relationship between the bed temperature and the heat generation rate when fuel is added to the catalyst 30 which is the oxidation catalyst according to the present invention. Here, the exothermic rate is the actual calorific value actually generated by the exothermic reaction of the reducing agent added to the catalyst 30, and is necessary for raising the bed temperature of the catalyst 30 to the target bed temperature during the regeneration process of the DPF 32. This is a numerical value calculated by “actual heat generation amount / target heat generation amount” using a target heat generation amount.

  In FIG. 2, the graph represented by L1 shows the bed temperature from time ta to te when fuel is continuously added to the catalyst 30 in a normal state without deterioration (hereinafter referred to as “normal catalyst”). It shows the transition of the heat generation characteristics, which is the relationship between and the heat generation rate. On the other hand, the graph represented by L2 shows the relationship between the bed temperature and the heat generation rate from time tf to tm when fuel is continuously added to the catalyst 30 in the criteria state (hereinafter referred to as “criteria catalyst”). This shows the transition of the heat generation characteristics.

  As shown in the graph L1, in the normal catalyst, the bed temperature rises and the heat generation rate changes at about 1 from time ta to te during which fuel addition is performed. This means that the activity of the normal catalyst is stable regardless of the bed temperature. Also, based on the definition of the heat generation rate, this means that the reducing agent added to generate the target heat generation at each bed temperature is sufficiently oxidized, so that a heat generation amount substantially equal to the target heat generation is actually achieved. It means that it has occurred. In other words, when the reducing agent is continuously added to the normal catalyst, the heat generation rate is stable because the catalyst activity does not decrease, so the bed temperature raised to the target bed temperature is maintained at that temperature.

On the other hand, as shown in the graph L2, in the criteria catalyst, both the heat generation rate and the bed temperature are decreased from the time tf to the time tm despite the fuel addition being performed. Hereinafter, this phenomenon will be described in detail. When the fuel is added into the catalyst 30, the fuel generates oxidation heat on the surface of a noble metal such as Pt supported on the catalyst 30. If the catalyst 30 is a normal catalyst without deterioration, the effective surface area of the noble metal is sufficiently present, so that the added fuel is sufficiently oxidized. On the other hand, the effective surface area of the noble metal is reduced due to deterioration in the criteria catalyst. Therefore, although the added fuel is oxidized to some extent, it cannot be fully oxidized, and HC poisoning occurs in which unreacted fuel adheres to the surface of the noble metal. When HC poisoning occurs, the catalytic activity decreases with time, so the heat generation rate and bed temperature also decrease with time. Therefore, when fuel is added to the criteria catalyst, a heat generation characteristic in which the heat generation rate and the bed temperature decrease with time as shown in the graph L2 appears. In the graph L2, at time th when the bed temperature of the criteria catalyst is at a temperature T _0, a decline in the heat rate and bed temperature due to the reduced activity has started is shown.

  As described above, when the fuel is continuously added to the catalyst 30, if the catalyst 30 is a normal catalyst, the catalyst activity does not decrease, so the heat generation rate is stable and the bed temperature does not decrease. If it is a criteria catalyst, a catalyst activity will fall and a heat generation rate and a bed temperature will begin to fall. Therefore, if attention is paid to the time transition of the heat generation characteristic when the catalyst 30 is a normal catalyst and the time transition of the heat generation characteristic when the catalyst 30 is a criteria catalyst, it can be seen that a clear difference appears in both transitions.

  Next, the detection principle and determination method of catalyst deterioration based on the time transition of the heat generation characteristics when the catalyst 30 is a normal catalyst and the time transition of the heat generation characteristics when the catalyst 30 is a criteria catalyst will be described.

FIG. 3 shows changes in bed temperature and heat generation rate when fuel is continuously added to the catalyst 30. The graph L3 shows the transition of the bed temperature of the criterion catalyst, and the graph L4 shows the transition of the heat generation rate of the criterion catalyst. Further, the graph L5 shows the transition of the heat generation rate of the normal catalyst. The fuel additive 3 is started to the time t _0.

Here, assuming that the decrease in the activity due to the HC poisoning of the criteria catalyst described above occurs at time t1, as shown in the graphs L3 and L4 during the time t _{0 to} t ₁ which is the initial period of fuel addition. Both the bed temperature and the heat generation rate increase as the added fuel is oxidized to a certain extent. However, when the time t ₁ elapses, the activity starts to decrease, so both the bed temperature and the heating rate start to decrease.

  On the other hand, as described above, since the activity of the normal catalyst does not decrease, the heat generation rate changes in a high state (substantially 1) as indicated by L5.

Here, focusing on the graph L4 and L5, the time t ₁ since the difference in heat rate and criteria catalyst of normal catalyst is increased over time. At time t ₂ , when the bed temperature of the criterion catalyst decreases to Tthresh, the heat generation rate of the criterion catalyst decreases to ηthresh, and the difference from the heat generation rate of the normal catalyst is sufficiently large. Accordingly, the actual heat generation rate of the catalyst 30 after the elapse of time t ₂ , that is, the time (t ₂ −t ₀ ) after the start of fuel addition, which is the timing when the heat generation rate clearly decreases due to the decrease in the activity of the criteria catalyst. If the deterioration determination is performed based on the above, it is possible to clearly detect whether the catalyst is a normal catalyst or a criteria catalyst.

Therefore, in this embodiment, the criterion, which is an oxidation catalyst corresponding to the catalyst 30 that has deteriorated to the criterion state, can be executed after a predetermined time corresponding to the time (t ₂ -t ₀ ) has elapsed since the start of fuel addition. Assume that fuel is added to the model. Then, the predetermined time is set based on the transition of the bed temperature and the transition of the heat generation rate in the criterion model. Specifically, the predetermined time is set to the time from when the bed temperature of the criterion model decreases to Tthresh from the assumed start of addition, that is, until the heat generation rate of the criterion model decreases to ηthresh. Is done.

By setting the predetermined time as described above, in this embodiment, if it is a criteria catalyst, the deterioration determination of the catalyst 30 can be reliably executed at the timing when the heat generation rate is sufficiently lowered. As a result, the deterioration determination can be executed at a timing at which the difference between the normal catalyst and the criteria catalyst can be reliably and accurately detected, so that the deterioration determination can be executed with high accuracy.

  Next, the catalyst deterioration determination process performed by the catalyst deterioration determination apparatus according to the present embodiment will be described using a flowchart. FIG. 4 is a flowchart showing a flow of a catalyst deterioration determination process performed by the ECU 100 corresponding to the catalyst deterioration determination device according to the present invention. The catalyst deterioration determination process (hereinafter simply referred to as “determination process”) according to the present embodiment is based on the assumption that the regeneration process of the DPF 32 has been started.

  When the regeneration process of the DPF 32 is started, first, in step S101, the ECU 100 acquires current information that is information regarding a situation where the catalyst 30 is placed at the time of the current determination process. Here, the current information is, for example, information related to the operating state of the internal combustion engine 2 such as the amount of fuel injected by the fuel injection valve 24, the rotational speed detected by the tachometer 26, or detected by each temperature sensor. The exhaust temperature etc.

  In step S102, the determination processing execution time ts is set based on a criterion model map prepared in advance in the ECU 100. Here, the criteria model map shows that after the temperature of the floor of the criterion model has risen once from the start of fuel addition, which is obtained from an experiment in which fuel addition during the regeneration process of the DPF 32 is performed on the criterion model. The elapsed time until it falls to the threshold bed temperature Tthresh is stored. Note that these elapsed times are stored in correspondence with the situation in which the criterion model at the start of addition is placed (information relating to the operating state of the internal combustion engine 2, exhaust temperature detected by each temperature sensor, etc.). In this step, among these elapsed times, the one corresponding to the current information acquired in the previous step is set as the determination process execution time ts in the current determination process. Note that Tthresh is the bed temperature of the criteria model when the heat generation rate of the criterion model decreases to the threshold heat generation rate ηthresh in the experiment. Here, ηthresh is a heat generation rate when the heat generation rate of the criterion model is lowered to such a degree that there is a clear difference from the heat generation rate of the normal catalyst, and is set to 0.2 in this embodiment. . Further, ηthresh functions as a determination value that is compared with the heat generation rate of the catalyst 30 when the deterioration determination of the catalyst 30 is executed in a later step.

  In step S103, fuel addition to the catalyst 30 is started by the fuel addition valve 28. At this time, the ECU 100 starts counting the fuel addition time ta.

  In step S104, it is determined whether the fuel addition time ta has elapsed until the determination execution time ts. When it has not elapsed, the standby state is entered, and when it has elapsed, the process proceeds to step S105.

  In step S105, the heat generation rate η of the catalyst 30 is calculated. Here, the heat generation rate is obtained by “actual heat generation amount / target heat generation amount” as described above, but more specifically, “(output gas temperature−estimated output gas temperature without heat generation) / (target bed temperature−input). Gas temperature) ”. Here, the outgas temperature is the temperature of the exhaust gas (outlet gas) flowing out from the catalyst 30 detected by the second temperature sensor 36, and the estimated outgas temperature without heat generation is the exhaust gas (inlet gas) flowing into the catalyst 30. This is the estimated temperature of the outgas when it is assumed that the contained fuel has passed through the catalyst 30 without generating any heat of oxidation in the catalyst 30. The target temperature is the exhaust (outgoing gas) temperature necessary for the regeneration process of the DPF 32, and the input gas temperature is the input gas temperature detected by the first temperature sensor 34. The estimated outgas temperature without heat generation is the amount of heat transferred from the exhaust gas to the catalyst 30 when the exhaust gas passes through the catalyst 30, the amount of heat conduction conducted in the base material of the catalyst 30, and the external temperature from the base material. This is a temperature calculated by considering the amount of heat released to the heat source (for details, see step S205 of FIG. 5 according to Example 2 described later).

  In step S106, it is determined whether the calculated heat generation rate η is equal to or less than the above-described threshold heat generation rate ηthresh. When a positive determination is made, it means that the heat generation rate η of the catalyst 30 at the time of the current determination processing has actually decreased to the heat generation rate ηthresh of the criteria catalyst after the elapse of time ts. This means that the activity of the catalyst 30 is actually reduced to the extent of the activity of the criteria catalyst due to deterioration. Therefore, in step S107, it is determined that the catalyst 30 is a criteria catalyst, and this flow ends.

  On the other hand, if a negative determination is made in step S106, the heat generation rate η of the catalyst 30 at the time of the current determination processing has not decreased to the heat generation rate ηthresh of the criteria catalyst after the elapse of time ts, that is, the catalyst 30 means no deterioration to the criteria state. Therefore, in step S108, it is determined that the catalyst 30 is a normal catalyst, and this flow ends.

  In this embodiment, the fuel addition valve 28 corresponds to the adding means in the present invention, and the ECU 100 that executes step S106 corresponds to the determining means in the present invention. In addition, the determination execution time ts set in step S102 corresponds to the predetermined time in the present invention, and the floor temperature and the heat generation rate of the criterion model in the experiment using the criterion model are respectively the estimated bed temperature and the estimated heat generation rate in the present invention. Equivalent to. Further, Tthresh and ηthresh correspond to the threshold bed temperature and the threshold heating rate in the present invention, respectively.

  As described above, in the catalyst deterioration determination device according to the present embodiment, during the addition of fuel during the regeneration process of the DPF 32, if the catalyst 30 is a criterion catalyst, the deterioration determination process is performed at the timing when the activity decreases and the heat generation rate clearly decreases. Is set for a predetermined time until the bed temperature of the criterion model decreases to the threshold bed temperature, and the deterioration determination process for the catalyst 30 is executed after the elapse of the predetermined time from the start of fuel addition. Therefore, according to the present invention, it is possible to execute the deterioration determination at a timing at which the difference between the normal catalyst and the criteria catalyst can be detected reliably and accurately. Further, the catalyst 30 is actually a criteria catalyst by comparing the heat generation rate of the catalyst 30 calculated after the predetermined time with the threshold heat generation rate when the bed temperature of the criteria model is lowered to the threshold bed temperature. It can be clearly distinguished whether or not. Therefore, according to the present invention, it is possible to accurately determine the deterioration of the catalyst.

  Further, the catalyst deterioration device according to this embodiment can reduce the consumption of reducing agent (fuel) required for deterioration determination by executing the determination process during the addition of fuel during the regeneration process of the DPF 32.

  In the present embodiment, Tthresh used in step S102 may be the bed temperature when the amount of decrease in the heat generation rate of the criterion model reaches the threshold decrease amount Δηthresh. Here, Δηthresh is a value obtained in advance by, for example, calculating a difference between two consecutive heat generation rate data based on the result of the experiment using the above-described criterion model. By setting the determination execution time ts in step S102 using Tthresh set in this way, the deterioration determination can be executed at a timing at which the difference between the normal catalyst and the criteria catalyst can be detected reliably and accurately.

[Example 2]
Next, the catalyst deterioration determination process in another embodiment according to the present invention will be described. In the first embodiment, the above-mentioned predetermined time is set using a criteria model map obtained by an experiment carried out in advance using a criteria model. In this embodiment, fuel is added to the catalyst 30. The elapsed time described above is determined by calculating the estimated bed temperature at that time. In addition, since the structure of the internal combustion engine system in a present Example is the same as that of Example 1, description is abbreviate | omitted.

  FIG. 5 is a flowchart showing a flow of a catalyst deterioration determination process (determination process) performed by the catalyst deterioration determination apparatus according to the present embodiment. The determination process is stored as a program in the ECU 100 and is executed, for example, every predetermined execution period Δt.

  First, in step S201, it is confirmed whether or not the post-startup flag of the internal combustion engine 2 is on. If it is on, the process proceeds to step S204. Here, the post-start flag means that a predetermined time has elapsed after the internal combustion engine 2 is started and the warm-up of the internal combustion engine 2 is completed, and the catalyst 30 is also sufficiently warmed up to the catalyst activation start temperature. It is a flag that turns on when heated. If the post-startup flag is off, the process proceeds to step S202, and a standby state is entered until a predetermined warm-up time elapses until the warm-up is completed.

  If it is confirmed in step S202 that the warm-up time has elapsed, the process proceeds to step S203, the post-start flag is turned on, and the process proceeds to step S204.

  In step S204, the incoming gas flow rate Gall [g / s] flowing into the catalyst 30 during the determination process is calculated. Here, Gall is the intake flow rate Ga [g / s] detected by the air flow sensor 16, the in-cylinder injection flow rate Gaf [g / s] injected into the combustion chamber 4 by the fuel injection valve 24, and the fuel addition valve 28. Is calculated by the following mathematical formula using the added fuel flow rate Gad [g / s].

The in-cylinder injection flow rate Gaf is the weight of fuel injected into all four cylinders of the internal combustion engine 2 per unit second, and as shown in Equation (2), the rotational speed NE [rpm] of the internal combustion engine 2 The number of cylinders Ncyl (4 in this embodiment) of the internal combustion engine 2 is obtained from the injection amount eqfin [mm ³ / stroke] per stroke and the fuel density density [g / cm ³ ]. The added fuel flow rate Gad is the fuel weight per unit second added to the exhaust gas flowing into the catalyst 30 by the fuel addition valve 28, and as shown in Equation (3), the determination process execution period Δt [s ], The amount of added fuel eqadf [mm ³ ] added by the fuel addition valve 28 during Δt and the above-mentioned fuel density density.

  Next, in step S205, an estimated outgas temperature Tgas without heat generation at the time of the current determination process is calculated. Note that the estimated outgas temperature without heat generation means that, as described above, the reducing agent contained in the input gas (exhaust gas) flowing into the catalyst 30 passes through the catalyst 30 without any heat generation in the catalyst 30. Is the estimated temperature of the outgas in the case of assuming Here, in the present embodiment, a calculation model assuming various heat transfer generated in the catalyst 30 is used in order to calculate Tgas with higher accuracy. Since the Tgas calculation process in this step is complicated, the calculation process will be described separately.

<About the calculation model>
FIG. 6 is a cross-sectional view schematically showing a calculation model 300 for assuming the heat transfer generated in the catalyst 30 in the present embodiment. The calculation model 300 is assumed to have the same size, weight, heat capacity and the like as the catalyst 30 and is composed of the same parts, and is the same system as the internal combustion engine system to which the catalyst 30 is applied. Has been applied. As shown in FIG. 6, the base material 310 accommodated in the casing 301 of the calculation model 300 is virtually divided into five from the first cell 311 to the fifth cell 315 on a plane perpendicular to the flow direction of the incoming gas. Consider the temperature change in each cell of the incoming gas flowing into the calculation model 300 (hereinafter referred to as “medium gas”). For convenience, the first temperature sensor 34, the second temperature sensor 36, the outside air temperature sensor 38, and the ECU 100 are also illustrated. Here, the inlet gas temperature near the upstream of the calculation model 300 detected by the first temperature sensor 34 is Tin [K], and the outlet gas temperature near the downstream of the calculation model 300 detected by the second temperature sensor 36 is Tout [K]. The temperature in the vicinity of the outside of the calculation model 300 detected by the outside air temperature sensor 38 is defined as Tamb [K].

<About heat transfer in each cell>
Hereinafter, heat transfer generated in each cell from the first cell 311 to the fifth cell 315 will be described with reference to the drawings. FIG. 7 shows this time when it is assumed that the reducing agent contained in the medium gas passes through the calculation model 300 without generating any heat of oxidation in the calculation model 300 (hereinafter referred to as “no heat generation”). It is the figure which showed typically the heat transfer from the i-1 cell to the i-th cell at the time of the determination process (1 <= i <= 5). However, when i = 1, since the i−1th cell does not exist, the case where the input gas directly flows into the first cell 311 is considered. Further, when i = 5, a case is considered where the middle gas that has passed through the fifth cell 315 flows directly into the casing 301 as an outgas.

  A thick arrow X shown in FIG. 7 schematically shows the medium gas passing through the i-th cell. The arrow B indicates the heat transfer amount Qconv (i) [J / s] (= [W]) for transferring heat from the middle gas to the i-th cell, and the arrow C indicates the i-th cell downstream from the i-1 cell. Net heat conduction amount Qcond (i) [W] that conducts heat to the outside, and arrow D represents the heat radiation amount Qloss (i) [W] that is radiated from the i-th cell to the outside through the casing 301. . “Net” means that the amount of heat conducted from the i-th cell to the i + 1-th cell (not shown) is subtracted from the amount of heat conducted from the i-th cell to the i-th cell. I mean. Further, Tin (i) [K] shown in FIG. 7 represents the temperature when the medium gas passes through the virtual end face on the upstream side of the i-th cell, and Tgas (i) [K] It represents the estimated temperature without heat generation when passing through the virtual end face on the downstream side of the i cell. Here, when 2 ≦ i ≦ 5, it may be considered that Tin (i) = Tgas (i−1). Test (i) [K] represents the estimated bed temperature of the i-th cell when there is no heat generation.

<Calculation of estimated outgas temperature without heat generation>
Then, assuming that the time of this determination process is time t, and the estimated bed temperature (estimated bed temperature without heat generation) of the calculation model 300 at time t when there is no heat generation is Test (t) [K], the above-described heat quantity and temperature The following relation holds.

However, h is the heat transfer coefficient [J / (s · m ² · K)] between the inlet gas and the substrate 310, and hamb is the heat transfer coefficient [J / (s) between the substrate 310 and the outside air via the casing 301. · M ² · K)], A is the gas contact area [m ² ] of the substrate 310 in each cell, Aamb is the external surface area (casing contact area) of the substrate 310 in each cell [m ² ], and δx is each cell [M], mssolid is the mass of the base material 310 [kg], Cpsolid is the specific heat [J / (kg · K)] of the base material 310, ε ₁ is the heat transfer coefficient, NTU is the Nusselt number, and Δt is the judgment process Is the execution cycle [s]. ΣQconv is the sum of heat transfer amounts transferred from the medium gas to the cells in each cell, ΣQcond is the sum of net heat transfer amounts conducted from the downstream cells to the upstream cells in each cell, and ΣQloss is This is the total amount of heat released from the cell through the casing 301 to the outside.

  The ECU 100 uses the predetermined initial conditions and boundary conditions in the above mathematical formula, and the estimated heat generation temperature Tgas without heat generation at the time of the current determination process (time t), that is, the medium gas that has passed through the fifth cell 315 is in the casing 301. Tgas (5), which is the temperature at which the gas flows out, is calculated, and the process proceeds to step S206.

  In step S206, a criterion catalyst estimated bed temperature Tmon [K] is calculated. Here, Tmon is the estimated bed temperature of the catalyst 30 when the reducing agent contained in the medium gas in the catalyst 30 generates heat of oxidation. Since the Tmon calculation process in this step is complicated, the calculation process will be described separately.

<About heat transfer in each cell>
In order to calculate Tmon with higher accuracy, it is generated in each cell from the first cell 311 to the fifth cell 315 using the calculation model 300 shown in FIG. 6 in the same manner as the Tgas calculation method in step S205. Consider heat transfer.

  FIG. 8 is a diagram schematically showing heat transfer from the i-1 cell to the i cell at the time of the current determination process when the reducing agent contained in the medium gas in the calculation model 300 generates oxidation heat. (1 ≦ i ≦ 5). However, when i = 1, since the i-1th cell does not exist, the case where the input gas directly flows into the first cell is considered. Further, when i = 5, a case is considered in which the medium gas directly flows out from the fifth cell into the housing 300 as an outgas.

The thick arrow X shown in FIG. 8 schematically shows the medium gas passing through the i-th cell, and the arrows B, C, and D show the same amount of heat transfer as in FIG. On the other hand, an arrow E represents an oxidation heat generation amount Qreac (i) [W] generated when the reducing agent is oxidized by a noble metal such as Pt supported in the i-th cell. Tout (i) [K] represents the temperature when the medium gas passes through the virtual end surface on the downstream side of the i-th cell. When 2 ≦ i ≦ 5, it may be considered that Tin (i) = Tout (i−1).

<About oxidation calorific value Qreac (i)>
Here, in order to calculate Qreac (i), the mass transfer generated around the noble metal supported in each cell is considered. FIG. 9 shows the precious metal (Pt) carried in the i-th cell (1 ≦ i ≦ 5) during the current determination process in order to calculate Qreac (i) represented by arrow E in FIG. It is a figure which shows typically the mass transfer from the gaseous phase currently generated to the solid phase. As shown in FIG. 9, the volume molar concentration of the reducing agents (HC and CO) contained in the medium gas passing near Pt in the i-th cell at a flow rate vg [m / s] is Cg _in (i) [ consider the case of changing from kmol / ^{m 3]} to ^{Cg (i) [kmol / m} 3]. At this time, the mass transfer of the reducing agent to be used in the oxidation reaction around Pt, i.e. mass transfer of the reducing agent to be transferred from the gas phase to the solid phase _{MT = k m · GA · (} Cg (i) -Cs ( i)) [kmol / s / m ³ ] is obtained from the following equation.

However, _{k m} is the mass transfer coefficient, GA contact area per unit volume ^{[m 2 / m 3],} ε 2 is the void ratio, Cg (i) the molarity of the reducing agent in the gas phase in the i-th cell [Kmol / m ³ ], Cs (i) is the volume molar concentration of the reducing agent in the solid phase in the i-th cell [kmol / m ³ ], R ₀ is the reaction rate of the chemical reaction occurring in the solid phase, N (I) is the amount of substance [kmol] provided for the chemical reaction in the i-th cell. Note that the z-axis is an axis with the medium gas flow direction being positive.

  Here, HC and CO can be considered as the reducing agent oxidized around Pt. HC is derived from the fuel added from the fuel addition valve 28 during the regeneration process and unburned fuel discharged from the internal combustion engine 2, and CO is discharged from the internal combustion engine 2. Therefore, the volume molar concentrations of HC and CO in the gas phase in the i-th cell are respectively Cg_hc (i) and Cg_co (i), and the volume molar concentrations of HC and CO in the solid phase in the i-th cell are respectively Cs_hc (i). And Cs_co (i), and when the mass transfer amounts of HC and CO are obtained individually using the above-mentioned mathematical formulas (9) and (10), the thermochemical equation (reaction formula) of the oxidation exothermic reaction generated in the catalyst is It is expressed below.

However, h ₁ and h ₂ are the enthalpies [J / kmol] in the reaction formulas (11) and (12), respectively, and N ₁ (i) and N ₂ (i) are the reaction formulas (11) and (11) in the i-th cell, respectively. It is the amount of substance [kmol] subjected to the chemical reaction shown in (12). R ₁ and R ₂ are reaction rates of chemical reactions represented by reaction formulas (11) and (12), respectively, and are represented by the following formulas.

Here, T is the temperature [K]. Further, k ₁ , k ₂ , and K are chemical reaction rate constants, and are represented by the following equations using the Arrhenius equation.

Here, constants A ₁ and A ₂ are chemical reaction frequency factors represented by reaction formulas (11) and (12), respectively, and constants E ₁ and E ₂ are chemical reactions represented by reaction formulas (11) and (12), respectively. The activation energy of the reaction. A ₃ and E ₃ are a frequency factor and activation energy of a chemical reaction in which CO is generated, respectively.

<About gas concentrations of CO, CH _1.84 and O ₂ >
The gas concentrations [CO], [CH _1.84 ], and [O ₂ ] in Equations (13) and (14) are obtained as follows.

First, the gas concentrations [CO], [CH _1.84 ], and [O ₂ ] of CO, CH _1.84, and O _{2 in} the middle gas passing through the i-th cell are expressed by the following equations from the state equation of gas. Desired.

Here, Cs_hc (i) and Cs_co (i) are the molar molar concentrations of HC and CO in the solid phase in the i-th cell, and Cs_o ₂ (i) is the O ₂ in the solid phase in the i-th cell. It is the volume molarity. R is a gas constant [J / kmol / K], Tin (i) is the temperature [K] of the medium gas flowing into the i-th cell, and P is the pressure [Pa] of the medium gas in the i-th cell.

Here, the volume molar concentrations of HC, CO, and O ₂ in the gas phase in the i-th cell are Cg_hc (i), Cg_co (i), and Cg_o ₂ (i), respectively. Thick arrow F shown in FIG.
, G, it can be seen that Cg_in (i) = Cg (i) + Cs (i) holds, so that the volume molar concentration of each gas in the gas phase and the solid phase in the adjacent cell is 1 ≦ i ≦ The following relationship is established at 4

  From the above, if the volume molar concentration of each gas in the gas phase in the first cell 311 is found, the volume molar concentration of each gas in the gas phase and solid phase in the cell after the second cell 312 can be obtained. Therefore, i = 1, that is, the concentration of each gas in the inlet gas flowing into the first cell 311 is obtained by the following method.

Each gas concentration in the incoming gas flowing into the first cell 311 can be obtained by specifically obtaining the incoming gas flow rate Gall and the flow rates of HC, CO, and O ₂ contained in the incoming gas. First, the incoming gas flow rate Gall is calculated from the above mathematical formulas (1) to (3).

Next, Ghc, Gco, and Go ₂ (all units are [g / s]), which are the flow rates of HC, CO, and O ₂ contained in the input gas, are the exhaust gas discharged from the internal combustion engine 2. of CO, HC, is the flow rate of _{O 2 Ghc_out,} Gco_out, using Go 2 _out (in units of [g / s]), is expressed by the following equation.

Incidentally, on the basis _{Ghc_out,} Gco_out, Go 2 _out, for example the operating state of the internal combustion engine 2 at the time the map data composed of experimental results using internal combustion engine 2 is prepared in advance in the ECU 100, the current determination process The appropriate value may be selected as appropriate. Then, the volume molar concentrations Cg_hc (i), Cg_co (i), and Cg_o ₂ (i) of each gas component in the inlet gas flowing into the first cell 311 are obtained by the following equations.

However, Mhc, Mco, and Mo ₂ are molar masses [kg / kmol] of each substance, R is a gas constant [J / kg / K], P is an exhaust pressure [Pa], and Tin is an inlet gas temperature [K]. .

<Summary>
By obtaining the reaction rates R ₁ and R ₂ of the chemical reaction represented by the reaction formulas (11) and (12) as described above, the calorific value generated by the oxidative exothermic reaction of HC and CO represented by the reaction formula. h ₁ · R ₁ · N ₁ (i) and h ₂ · R ₂ · N ₂ (i) are determined. Then, the oxidation heat generation amount Qreac (i) generated by the oxidation reaction of HC and CO in the i-th cell is expressed by the following equation.

  Further, the heat transfer amount Qconv (i), the heat conduction amount Qcond (i), and the heat dissipation amount Qloss (i) in the i-th cell are expressed by the equations (4), (5), and (6) used in step S205. This is obtained by replacing Test (i) with the estimated bed temperature Tmon (i) [K] of the i-th cell in this step (when the reducing agent contained in the medium gas generates heat of oxidation). Then, in step S205, the total heat transfer amount ΣQconv that is transferred from the medium gas to the cell in each cell, and the total heat transfer amount that is transferred from the downstream cell to the upstream cell in each cell. Using ΣQcond, the sum ΣQloss of the amount of heat radiated to the outside through the casing 301 in each cell, and the sum ΣQreac of the amount of oxidative heat generated in each cell, a calculation model at the time of this determination processing (time t) The estimated bed temperature Tmon (t) [K] of 300 is obtained by the following equation.

  The ECU 100 calculates the estimated bed temperature Tmon (t) of the calculation model 300 at the time of the current determination process, that is, the criterion catalyst estimated bed temperature Tmon of the catalyst 30 by using predetermined initial conditions and boundary conditions in the above formula. Then, the process proceeds to step S207.

  Next, in step S207, it is determined whether the regeneration process of the DPF 32 is being executed. If it is already being executed, the process proceeds to step S210. On the other hand, if it is not being executed, the process proceeds to step S208 to determine whether or not the regeneration process of the DPF 32 is necessary.

  In step S208, the ECU 100 determines whether or not the regeneration process of the DPF 32 is necessary based on the detection value of the differential pressure sensor 40, the travel distance of the automobile, and the like. If it is determined that regeneration processing is necessary, the process proceeds to step S209, where fuel addition is commanded to the fuel addition valve 28, and fuel addition is started. On the other hand, if it is determined that it is not necessary, the process returns to step S201.

  In step S210, it is determined whether or not Tmon calculated in step S206 is equal to or lower than the above-described threshold bed temperature Tthresh. If a positive determination is made in this step, the process proceeds to step S105, which is the same as that in the first embodiment, in order to calculate the heat generation rate in the current determination process. On the other hand, if a negative determination is made, it is determined that it is not necessary to perform the deterioration determination, and the process returns to step S201.

After step S105, the same process as described in the first embodiment is executed to determine the deterioration of the catalyst 30. The heat generation rate η calculated in step S105 is calculated by the following equation using the estimated no-heat generation output gas temperature Tgas calculated in step S205 described above.

  Here, Tout is the outlet gas temperature detected by the first temperature sensor 34, Ttarget is the target bed temperature of the regeneration process that is being performed during the current determination process, and Tin is the inlet gas temperature detected by the second temperature sensor 36. It is. Note that Ttarget is selected in advance from a data map prepared in the ECU 100, for example.

  By the way, in the present embodiment, the process of the deterioration determination itself in step S106 is performed after the internal combustion engine 2 is started and after it is determined that the DPF regeneration process is necessary in step S208 and the regeneration process is started in step S209. . That is, in this embodiment, the time from the start of fuel addition for regeneration processing in step S209 to the positive determination in step S210 corresponds to the predetermined time in the present invention. Thereby, the catalyst deterioration determination apparatus according to the present embodiment can reliably execute the deterioration determination of the catalyst 30 at the timing when the heat generation rate is sufficiently lowered if the catalyst 30 is a criteria catalyst. Therefore, since the difference between the normal catalyst and the criterion catalyst can be clarified by performing the deterioration determination based on the heat generation rate of the oxidation catalyst that is the determination target at this timing, the deterioration determination of the oxidation catalyst is accurately performed. be able to.

[Example 3]
In this embodiment, in order to improve the detection accuracy of the catalyst deterioration determination, a weighted average of the heat generation rate of the determination target catalyst using a weighting coefficient set based on a heat generation characteristic that is a relationship between the bed temperature of the criteria catalyst and the heat generation rate. A value is calculated, and when the weighted average value is equal to or less than a predetermined threshold weighted average value, it is determined that the determination target catalyst is deteriorated. That is, as shown in FIG. 10, paying attention to the heat generation characteristics that are the relationship between the bed temperature of the criteria catalyst and the heat generation rate when the catalyst activity starts to decrease during the fuel addition during the regeneration process, it decreases with the bed temperature. Calculate the weighted average value of the heat generation rate. The catalyst deterioration determination process according to the present embodiment is different from the determination process flow shown in FIG. 5 according to the second embodiment in steps after step S105. Only that will be described.

  FIG. 10 is a graph for explaining the weighting coefficient of the heat generation characteristic of the oxidation catalyst according to the present embodiment. In FIG. 10, the graph represented by L6 is a graph showing the heat generation characteristics when both the bed temperature and the heat generation rate decrease due to the decrease in activity when fuel is continuously added to the criterion catalyst for a certain period. Each point on the graph L6 is a plot of the bed temperature and the heat generation rate detected every predetermined time, and changes from the upper right to the lower left with the passage of time.

  Here, the weighted heat generation rate ηav in the present embodiment is obtained as follows after dividing a predetermined range of the bed temperature T into n bed temperature regions. First, for each of the divided bed temperature regions, the average value of the heat generation rates belonging to the bed temperature region is obtained, and these are set as x1, x2,. In addition, the weighting coefficients corresponding to the respective bed temperature regions are sequentially set as w1, w2,. Then, the weighted heat generation rate ηav is expressed by the following equation.

  Here, as an example, consider the case where n = 3 in Equation (33). As shown in FIG. 10, the three bed temperature areas A, B, and C for the bed temperature T are divided into the bed temperature area A: Ta ≦ T ≦ Tb, the bed temperature area B: Tb ≦ T ≦ Tc, and the bed temperature area C: It is defined as Tc ≦ T ≦ Td. Further, if the average value of the heat generation rate of the data belonging to the bed temperature region obtained for each bed temperature region is xa, xb, xc, and the weighting coefficients corresponding to each bed temperature region are wa, wb, wc, In this case, the weighted heat generation rate ηav is expressed by the following equation.

  Next, in order to explain the setting method of the weighting coefficients wa, wb, and wc, the heat generation characteristic data as shown in FIG. 10 is obtained in advance from the result of the fuel addition experiment performed on the criteria catalyst. Assuming that Here, for example, when the importance of data belonging to a predetermined bed temperature region is found to be relatively high, such as a bed temperature region where the activity of the criteria catalyst starts to decrease, the importance of the data (ηav The weighting coefficient corresponding to the floor temperature region may be set so that the degree of contribution) increases.

  Next, the catalyst deterioration determination process according to the present embodiment will be described using a flowchart. FIG. 11 is a flowchart illustrating a flow of determination processing performed by the catalyst deterioration determination device according to the present embodiment. As described above, the steps from step S201 to step S105 shown in FIG. 11 are the same as the steps shown in FIG.

  In step S105, when the heat generation rate η at the time of the current determination process is calculated using the above mathematical formula (32), the ECU 100 uses the heat generation rates η calculated in the current and past determination processes in step S306, An average heat generation rate xi (i = 1, 2,..., N) for each bed temperature region is calculated. Specifically, based on the criterion catalyst estimated bed temperature Tmon calculated in step S206 in each determination process, the bed temperature region to which η calculated in the determination process belongs is determined, which is similar to the calculation of the moving average. The average heat rate in the floor temperature region is calculated by the calculation method.

  In step S307, the ECU 100 calculates the weighted average heat rate ηav of the catalyst 30 during the current determination process from the equation (33) using the average heat rate xi calculated in the previous step. Note that the weighting coefficient wi used in the equation (33) is set in advance according to the importance of each bed temperature region as described above.

In step S308, it is determined whether or not ηav calculated in the previous step is equal to or less than a threshold-weighted heat generation rate ηav_thresh. Here, ηav_thresh is a weighted heat generation rate when the activity decreases after elapse of a certain time when fuel is added to the criterion catalyst, and the heat generation rate of the criterion catalyst is clear relative to the heat generation rate of the normal catalyst. It is the heat generation rate when it decreases to such an extent that it has a significant difference. Note that ηav_thresh is a value set in advance based on, for example, the results of an experiment performed in advance using a criteria catalyst, and is set to 0.2 in this embodiment. If an affirmative determination is made in this step, it means that the activity of the catalyst 30 during the current determination process has actually decreased to the activity of the criteria catalyst or below. Accordingly, in this case, the process proceeds to step S309, where it is determined that the catalyst 30 is a criteria catalyst, and the flow is terminated.

  On the other hand, if a negative determination is made in step S308, it means that the activity of the catalyst 30 during the current determination process has not decreased to the level of the criterion catalyst. Therefore, it progresses to step S310, it determines with the catalyst 30 being a normal catalyst, and this flow is complete | finished.

  As described above, in the present embodiment, when the bed temperature region that is important and the bed temperature region that is not important when the catalyst deterioration determination is made are known in advance, the weighting set for each of these bed temperature regions. By calculating the weighted average heat rate using the coefficient, it is possible to improve the accuracy of detecting the deterioration of the oxidation catalyst.

[Other Examples]
In the above-described first to third embodiments, the catalyst deterioration determination process is performed while fuel is being added from the fuel addition valve 28 during the regeneration process of the DPF 32. As another example of the present invention, For example, this determination process may be executed during post injection by the fuel injection valve 24 of the internal combustion engine 2. In this case, the fuel injection valve 24 corresponds to the adding means in the present invention. Further, the determination process according to the present invention may be executed by adding fuel to the catalyst 30 for the purpose of determining the deterioration itself without assuming that the regeneration process of the DPF 32 is being executed.

  Further, a catalyst deterioration determination device installed in an exhaust gas purification system for an internal combustion engine that does not include a DPF can also estimate the amount of unburned fuel and CO or other reducing agent that is discharged from the internal combustion engine and reaches the catalyst. Insofar as possible, the determination processing according to the present invention can be applied.

  In addition, in the internal combustion engine system to which the catalyst deterioration determination device of the present invention is applied regardless of the presence or absence of the DPF, the oxidation catalyst in the criterion state can be reliably detected, so that the undetected criterion catalyst is left unattended. Such a situation can be avoided. In other words, when a criterion catalyst is detected, it can be dealt with promptly, so that the emission restriction of exhaust gas discharged from the internal combustion engine is greatly relaxed during normal times when the oxidation catalyst is in a normal state. As a result, restrictions on the combustion conditions in the internal combustion engine are alleviated and the degree of freedom of engine adaptation is greatly improved. For example, it is possible to set the combustion conditions that are further shifted to the fuel efficiency side.

2 Internal combustion engine 6 Intake passage 10 Exhaust passage 24 Fuel injection valve 28 Fuel addition valve 30 Catalyst 32 DPF
34 1st temperature sensor 36 2nd temperature sensor 100 ECU
300 Calculation model 310 Base material

Claims (7)

An oxidation catalyst provided in the exhaust passage of the internal combustion engine;
An adding means for adding a reducing agent that generates oxidation heat in the oxidation catalyst;
Determination means for performing deterioration determination of the oxidation catalyst based on a heat generation rate of the oxidation catalyst after a predetermined time has elapsed from the start of addition of the reducing agent by the addition means,
The predetermined time is
The estimated bed temperature of the oxidation catalyst model in the case of assuming the addition of the reducing agent to the oxidation catalyst model corresponding to the deterioration of the oxidation catalyst is from the time when the assumed addition of the reducing agent is started. It is set to the time until the temperature drops to a predetermined threshold bed temperature due to the decrease in the activity of the oxidation catalyst model that progresses with the passage of the addition time of the reducing agent after the temperature is raised by the oxidation heat of the reducing agent. The catalyst deterioration determination apparatus characterized by the above-mentioned. The threshold bed temperature is
The estimated heat generation rate of the oxidation catalyst model when the addition of the reducing agent is assumed is a temperature at which the heat generation rate of the oxidation catalyst model decreases to a predetermined threshold heat generation rate due to a decrease in activity of the oxidation catalyst model. Item 4. The catalyst deterioration determination device according to Item 1. The determination means includes
The catalyst deterioration determination device according to claim 2, wherein when the heat generation rate is equal to or less than the threshold heat generation rate, it is determined that the oxidation catalyst is deteriorated. The threshold bed temperature is
The amount of decrease in the estimated heat generation rate of the oxidation catalyst model when the addition of the reducing agent is assumed is a temperature when a predetermined threshold decrease amount is reached due to the decrease in activity of the oxidation catalyst model. The catalyst deterioration determination apparatus according to claim 1. The determination means includes
The catalyst deterioration determination device according to claim 4, wherein when the heat generation rate is equal to or lower than a predetermined threshold heat generation rate, it is determined that the oxidation catalyst is deteriorated. The determination means includes
When the weighted average value of the heat generation rate is calculated using a weighting coefficient set based on the estimated bed temperature and the estimated heat generation rate of the oxidation catalyst model, and the weighted average value is equal to or less than a predetermined threshold weighted average value 5. The catalyst deterioration determination device according to claim 2, wherein the determination is made that the oxidation catalyst has deteriorated. Further comprising a filter for collecting particles in the exhaust gas downstream of the oxidation catalyst;
The determination means is
2. The deterioration determination of the oxidation catalyst is performed after the predetermined time has elapsed from the start of the addition of the reducing agent by the adding means during the regeneration process for oxidizing and removing the particles collected by the filter. The catalyst deterioration determination apparatus according to any one of claims 6 to 6.

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