JP5173577B2 - Particulate filter abnormality judgment method - Google Patents

Description

  The present invention relates to a technique for determining an abnormality of a particulate filter provided in an exhaust passage of an internal combustion engine.

  2. Description of the Related Art In recent years, various techniques for determining an abnormality of a particulate filter have been proposed for an internal combustion engine mounted on a vehicle or the like. As a technique for determining a filter abnormality, a technique is known in which a filter abnormality is determined by comparing an exhaust pressure upstream of a filter after a predetermined time from the start of filter regeneration with a reference pressure determined by an engine operating state at that time. (For example, refer to Patent Document 1).

  In addition, as a technique for determining an abnormality of a filter, a technique for determining an abnormality of a filter by comparing a differential pressure before and after the filter immediately after filter regeneration and a differential pressure at a normal time is known (for example, see Patent Document 2). reference).

Japanese Patent Publication No. 3-38406 JP-A-6-323127 JP-A-6-123216 JP-A-6-330730 JP-A-7-180528 JP 2001-207828 A Japanese Patent Laid-Open No. 5-98941 JP-A-8-121150

  By the way, when a slight abnormality occurs such that a minute amount of particulates (hereinafter referred to as PM) passes through the filter, the exhaust pressure upstream of the filter and the differential pressure before and after the filter slightly change. Difficult to distinguish from changes.

  The present invention has been made in view of the above-described circumstances, and the object thereof is a filter abnormality determination method for collecting PM in exhaust gas, even if a slight abnormality such that a minute amount of PM passes through the filter. An object of the present invention is to provide a technique capable of detecting with high accuracy.

  The feature of the present invention is the temperature behavior of the exhaust gas flowing out from the particulate filter in the particulate filter collecting and oxidizing particulate filter, in other words, the particulate filter abnormality determination method in which the catalyst having oxidation ability is supported. It is in the point which determines abnormality of a filter based on it.

  The inventor of the present application has conducted various experiments and studies to solve the above-described problems, and as a result, when an abnormality that causes PM to pass through the particulate filter occurs, the temperature of the exhaust gas flowing out from the particulate filter (hereinafter, It was found that the effluent exhaust temperature shows a unique behavior.

For example, when the particulate filter is normal, the change in the exhaust gas temperature causes a delay in response to the change in the temperature of the exhaust gas flowing into the particulate filter (hereinafter referred to as the inflow exhaust gas temperature), and the change width is also small. On the other hand, when the particulate filter is abnormal, the response delay of the outflow exhaust gas temperature with respect to the change of the inflow exhaust gas temperature is shortened, and the change width becomes large. That is, when the particulate filter is abnormal, the behavior of the outflow exhaust temperature approximates the behavior of the inflow exhaust temperature.

  The mechanism by which the above behavior appears has not been elucidated, but is presumably due to the following mechanism.

  When exhaust flows through a normal particulate filter, heat exchange is performed between the particulate filter and the exhaust, and oxidation reaction heat such as PM and hydrocarbons is conducted to the exhaust.

  When part of the particulate filter breaks down and PM slips through, the flow resistance of the damaged part is lower than that of the other part (that is, the pressure of the damaged part is lower than that of the other part). Flow concentrates on the damaged part. If the flow of exhaust gas concentrates on the damaged part, the flow rate of the exhaust gas increases, so that the heat exchange rate and the thermal conductivity described above are considered to decrease.

  Furthermore, it is expected that the amount of PM collected at the damaged site will be smaller than normal. When the amount of PM trapped at the damaged portion is reduced, the heat of oxidation reaction generated at the damaged portion is reduced, so that the amount of heat received when the exhaust gas flows through the particulate filter is reduced.

  Therefore, when an abnormality such that PM passes through the particulate filter occurs, the amount of heat exchanged by the exhaust gas in the particulate filter decreases. As a result, when the particulate filter is abnormal, it is presumed that the behavior of the outflow exhaust temperature approximates the behavior of the inflow exhaust temperature.

  Therefore, in the present invention, a change locus of the outflow exhaust temperature with respect to the inflow exhaust temperature of the particulate filter is detected, and abnormality of the particulate filter is determined based on the change locus.

  As a specific determination method at that time, (1) when the response delay time from the start of the change of the inflow exhaust gas temperature to the start of the change of the outflow exhaust gas temperature is less than a predetermined time, it is determined that the particulate filter is abnormal. (2) A method for determining that the particulate filter is abnormal when the relative difference between the change width of the inflow exhaust gas temperature and the change width of the outflow exhaust temperature is less than a predetermined amount, and (3) the change speed of the inflow exhaust gas temperature. A method of determining that the particulate filter is abnormal when the rate of change of the exhaust gas exhaust gas temperature exceeds a predetermined ratio, and (4) when at least two of the above requirements (1) to (3) are satisfied A method for determining that the curate filter is abnormal can be exemplified.

  According to the determination method of the present invention, when PM passes through the particulates, it is possible to detect a peculiar behavior of the outflow exhaust gas temperature.

  Furthermore, since the determination method of the present invention detects the locus of the change in the outflow exhaust gas temperature with respect to the inflow exhaust gas temperature, the determination can be made using the entire change as a parameter. As a result, even if the inflow exhaust gas temperature or the outflow exhaust gas temperature temporarily varies due to disturbance of the engine combustion state or the like, or when the above-mentioned unique behavior appears very small, it is difficult to make an erroneous determination.

In addition, when a part of the particulate filter is damaged, and PM passes through, it is considered that the heat exchange rate and the thermal conductivity are reduced as the flow rate of the exhaust gas flowing through the damaged part is increased. Therefore, the abnormality determination of the present invention may be executed when the intake air amount of the internal combustion engine is equal to or greater than a predetermined amount.

  Another requirement for increasing the flow velocity at the damaged part is a pressure difference between the damaged part and the other part. That is, the higher the pressure of the other part with respect to the damaged part, the higher the flow velocity of the damaged part. Since the pressure at other sites increases as the amount of PM collected increases, the abnormality determination may be performed on the condition that the amount of PM collected is a predetermined amount or more.

  In addition, the abnormality determination according to the present invention is performed when the particulate filter is in a state in which PM can be continuously oxidized (that is, the catalyst supported on the particulate filter is in a state in which PM can be continuously oxidized). May be.

  When the catalyst is not in a state where PM can be continuously oxidized, the amount of heat generated by the oxidation reaction in the particulate filter is reduced, so that the difference between the amount of heat exchanged by the exhaust during normal operation and the amount of heat received by the exhaust during abnormality is small.

  On the other hand, when the catalyst is in a state where PM can be continuously oxidized, the amount of heat generated by the oxidation reaction in the particulate filter increases, so there is a large difference between the amount of heat exchanged by the exhaust during normal operation and the amount of heat received by the exhaust during abnormality. Become.

  Accordingly, the difference between the behavior of the outflow exhaust temperature during normal operation and the behavior of the outflow exhaust temperature during abnormality is more clearly apparent when the catalyst is in the PM continuous oxidizable state than when the catalyst is not in the PM continuous oxidizable state. It can be said.

  According to the above knowledge, if the abnormality determination is executed when the catalyst is in a state where PM can be continuously oxidized, the determination accuracy can be improved and the catalyst is deteriorated (degradation of the oxidation ability of the catalyst). Can also be determined.

  Next, the inventor of the present application conducted an experiment and examination under various conditions on the unique behavior of the above-described outflow exhaust gas temperature. As a result, when the internal combustion engine is in a decelerating operation state, that is, when the inflow exhaust gas temperature decreases, It was found that the unique behavior of the outflow exhaust temperature appears remarkably.

  Therefore, the abnormality determination according to the present invention may be executed when the internal combustion engine is in a deceleration operation state. If the abnormality determination is performed when the internal combustion engine is in a decelerating operation state, an unusual behavior of the outflow exhaust gas temperature appears remarkably, so that it is possible to improve the determination accuracy. Furthermore, a highly versatile temperature sensor can be used as a temperature sensor used for detecting the inflow exhaust gas temperature and the outflow exhaust gas temperature.

  Note that if the period for detecting the change trajectory of the inflow exhaust gas temperature and the outflow exhaust gas temperature becomes excessively short, the determination accuracy may decrease, so only when the internal combustion engine has performed idle operation for a certain period of time after deceleration operation. The abnormality determination may be performed during a period from before the start of deceleration until the idle operation time becomes equal to or longer than a certain time.

  Further, in the present invention, when the abnormality determination is performed when the internal combustion engine is in a deceleration operation state, the EGR may be stopped and / or the opening of the intake throttle valve may be increased.

  Here, EGR means that the exhaust gas is recirculated from the exhaust passage upstream of the particulate filter to the intake passage, the exhaust gas is recirculated from the exhaust passage downstream of the particulate filter to the intake passage, and a variable valve mechanism. To increase the residual exhaust gas in the combustion chamber.

  As described above, when PM passes through due to a part of the particulate filter being damaged or the like, it is considered that the amount of heat exchanged by the exhaust gas is reduced by increasing the flow velocity of the exhaust gas flowing through the damaged part. For this reason, if the flow velocity of the exhaust gas flowing through the damaged part is increased, the amount of heat given and received by the exhaust gas is further reduced, and the unique behavior of the outflow exhaust gas temperature becomes more prominent. Further, the lower the temperature of the exhaust gas flowing into the particulate filter, in other words, the greater the difference between the particulate filter and the inflow exhaust gas temperature, the more distinctive behavior of the outflow exhaust gas temperature appears.

  Therefore, if the EGR is stopped and the opening of the intake throttle valve is increased when the abnormality determination is performed, the flow rate and flow rate of the exhaust gas flowing into the particulate filter increase, so that the flow rate of the exhaust gas flowing through the damaged portion can be increased. As a result, the inflowing exhaust gas temperature tends to decrease. As a result, the determination accuracy can be further improved.

  In addition, if the flow rate of the exhaust gas flowing through the damaged part is increased and the exhaust gas temperature is lowered, the degree of decrease in the outflow exhaust gas temperature becomes remarkably high. Even if it is shortened, it becomes difficult to make an erroneous determination. As a result, it is possible to increase the execution frequency of abnormality determination.

  Next, the abnormality determination of the present invention may be performed based on the degree of decrease in the outflow exhaust temperature during the deceleration operation.

  When the particulate filter is normal, the degree of decrease in the outflow exhaust temperature during the deceleration operation is slight. However, when the particulate filter is abnormal, the degree of decrease in the outflow exhaust temperature during the deceleration operation is significantly high.

  Therefore, when the difference (decrease temperature) between the outflow exhaust temperature before the start of the deceleration operation and the outflow exhaust temperature after the deceleration operation exceeds the threshold value, it can be determined that the particulate filter is abnormal.

  Next, as a result of further experiments and verifications regarding the behavior of the outflow exhaust gas temperature during deceleration operation, the inventor of the present application has found that when the particulate filter is normal, the amount of PM collected is relatively large and It was also found that the temperature drop when the temperature is relatively small is substantially the same, but when the particulate filter is abnormal, a clear difference appears in the temperature drop between the two.

  Therefore, when the difference between the temperature decrease amount when the PM trapping amount is relatively large and the temperature decrease amount when the PM trapping amount is relatively small exceeds a threshold value, it is determined that the particulate filter is abnormal. It is also possible to do.

  An example of the time when the amount of collected PM is relatively large is immediately before the PM regeneration process of the particulate filter is executed. An example of the time when the amount of collected PM is relatively small is immediately after the PM regeneration process of the particulate filter is executed.

  In the various abnormality determination methods described above, the PM collection amount of the particulate filter may be estimated, and the determination criterion may be changed according to the estimated PM collection amount.

  When the particulate filter is normal, the flow rate of exhaust gas decreases and the amount of heat of oxidation reaction heat increases as the amount of collected PM increases. For this reason, when the particulate filter is normal, the amount of heat exchanged by the exhaust increases as the amount of collected PM increases.

On the other hand, when the particulate filter is abnormal, the flow rate of the exhaust gas flowing through the damaged part of the particulate filter increases as the amount of PM trapped increases, so that the amount of heat exchanged by the exhaust gas in the particulate filter decreases. Conversely, as the amount of PM trapped decreases, the flow rate of the exhaust gas flowing through the damaged portion is less likely to increase, so that the amount of heat transferred by the exhaust gas in the particulate filter is less likely to decrease.

  Therefore, when the amount of collected PM is large, the unique behavior of the outflow exhaust gas temperature becomes more prominent than when the amount of collected PM is small. Therefore, when the amount of collected PM is large, the accuracy of abnormality determination can be increased by raising the determination criterion than when the amount of collected PM is small. On the contrary, when the amount of collected PM is small, it is easier to determine the abnormality of the particulate filter by lowering the determination criterion than when the amount of collected PM is large.

  In addition, the abnormality determination method according to the present invention can be combined with an abnormality determination method using the differential pressure before and after the particulate filter as a parameter. In this case, since the double abnormality determination is performed by the abnormality determination based on the behavior of the outflow exhaust gas temperature and the abnormality determination based on the differential pressure across the particulate filter, it is easy to suppress the occurrence of erroneous determination.

  When the internal combustion engine is in a decelerating operation state, an abnormality determination based on the behavior of the outflow exhaust temperature is performed, and when the internal combustion engine is in a high load / high rotation operation state, an abnormality determination based on the differential pressure across the particulate filter is performed. It may be performed.

  In this case, the particulate filter abnormality can be determined not only in the deceleration operation region but also in the high rotation / high load operation region, so that the operation region where abnormality can be determined is expanded and the frequency of abnormality determination is increased. Is possible.

  Further, the abnormality determination method according to the present invention may perform an abnormality determination by estimating the outflow exhaust gas temperature after the deceleration operation and comparing the estimated calculation value with the actual outflow exhaust gas temperature.

  In this case, if the difference between the estimated calculation value and the actual exhaust gas temperature does not exceed the threshold value, it is determined that the particulate filter is normal. If the difference exceeds the threshold value, the particulate filter is abnormal. May be determined.

  According to such an abnormality determination method, it is possible to perform abnormality determination easily and in a short time.

  According to the present invention, by using the behavior of the exhaust gas temperature of the particulate filter as a parameter, it is possible to accurately determine the occurrence of an abnormality even if a slight abnormality such that a minute amount of PM passes through the particulate filter. Can do.

Hereinafter, specific embodiments of 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 to which the present invention is applied. In FIG. 1, an internal combustion engine 1 is a compression ignition type diesel engine.

  An intake passage 2 and an exhaust passage 3 are connected to the internal combustion engine 1. An intake throttle valve 4 and an air flow meter 12 are provided in the intake passage 2. A particulate filter 5 is disposed in the exhaust passage 3.

The particulate filter 5 has a wall flow type carrier and is configured to collect particulate matter (PM) in the exhaust gas. A catalyst having an oxidizing ability is supported on the carrier of the particulate filter 5 so that the collected PM and the PM in the exhaust can be oxidized.

  A pre-stage catalyst 6 is disposed in the exhaust passage 3 upstream of the particulate filter 5. An upstream exhaust temperature sensor 7 is disposed in the exhaust passage 3 between the particulate filter 5 and the front catalyst 6. A downstream exhaust temperature sensor 8 is disposed in the exhaust passage 3 downstream from the particulate filter 5. In addition, since the pre-stage catalyst 6 is not an essential component of the present invention, it may not be arranged upstream of the particulate filter 5.

  An EGR passage 9 is provided between the intake passage 2 downstream of the intake throttle valve 4 and the exhaust passage 3 upstream of the front catalyst 6. An EGR valve 10 is provided in the middle of the EGR passage 9. When the turbine housing of the centrifugal supercharger is disposed in the exhaust passage 3, the EGR passage 9 is connected to the exhaust passage 3 upstream from the turbine housing.

  The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 11. The ECU 11 is an arithmetic logic circuit that includes a CPU, ROM, RAM, backup RAM, and the like.

  The ECU 11 is electrically connected to various sensors such as the accelerator position sensor 11 in addition to the upstream exhaust temperature sensor 7, the downstream exhaust temperature sensor 8, and the air flow meter 12. The ECU 11 is electrically connected to the intake throttle valve 4 and the EGR valve 10 and can control the opening degree of each.

  ECU11 performs filter abnormality determination control used as the summary of this invention in addition to known control, such as fuel injection control. Hereinafter, filter abnormality determination control will be described.

  The filter abnormality determination control of the present invention is an abnormality in which PM passes through the particulate filter 5 with the output signal value (outflow exhaust gas temperature) of the downstream side exhaust temperature sensor 8 as a parameter, for example, a passage wall surface in the particulate filter 5 This is a control for detecting abnormalities in which cracks and holes are generated.

  The inventor of the present application has conducted intensive experiments and verifications in the process of searching for a suitable abnormality determination method for the particulate filter 5. As a result, if an abnormality such that PM passes through occurs in the particulate filter 5, It was found that the exhaust gas exhaust temperature shows a peculiar behavior from the normal operation period during the deceleration operation period to the idle operation period.

  FIG. 2 is a diagram showing the results of measuring the inflow exhaust gas temperature and the outflow exhaust gas temperature under the same conditions for each of the normal particulate filter 5 and the particulate filter 5 in which an abnormality that allows PM to pass through occurs.

  In FIG. 2, the dotted lines in the figure indicate the inflow exhaust gas temperature and the outflow exhaust temperature when the particulate filter 5 is normal, and the solid lines in the figure indicate the case where an abnormality that causes PM to slip through the particulate filter 5 occurs. The inflow exhaust temperature and the outflow exhaust temperature are shown.

  In addition, as the particulate filter 5 in which an abnormality occurred, a particulate filter having a fine hole formed on the wall surface of the passage in the normal particulate filter was used.

  According to the measurement result of FIG. 2, when the particulate filter 5 is normal, the change in the outflow exhaust temperature causes a response delay with respect to the change in the inflow exhaust temperature, and the change width is small.

  On the other hand, when the particulate filter 5 is abnormal, the inflow occurs when the internal combustion engine 1 performs the idle operation following the deceleration operation, particularly when the idle operation state after the deceleration operation is continued for a relatively long time. The response delay of the outflow exhaust gas temperature with respect to the decrease in the exhaust gas temperature is shortened and the range of change is large.

  That is, when the particulate filter 5 is normal, the outflow exhaust temperature hardly decreases with respect to the decrease in the inflow exhaust temperature, but when the particulate filter 5 is abnormal, the outflow exhaust follows the decrease in the inflow exhaust temperature. The temperature is also greatly reduced.

  Furthermore, as a result of experiments and verifications of the above unique behavior under various conditions, the present inventors have found the following characteristics. That is, the above-mentioned unique behavior is more prominent when (1) the catalyst supported on the particulate filter 5 is in a PM continuous oxidizable state than when it is not in a PM acid continuable state, (2) It appears more prominently as the exhaust flow rate flowing into the particulate filter 5 increases. (3) The effect appears more prominently as the amount of PM trapped by the particulate filter 5 increases.

  Although the specific mechanism of such behavior and characteristics of the exhaust gas temperature has not been elucidated, it is presumed that it depends on the following mechanism.

  When the particulate filter 5 is normal, the heat of the particulate filter 5 is conducted to the exhaust gas in the particulate filter 5, and PM, hydrocarbon (HC), carbon monoxide (CO), etc. Heat (oxidation heat) generated when being oxidized by the catalytic action is conducted to the exhaust.

  For this reason, when the particulate filter 5 is normal, it is considered that the outflow exhaust gas temperature is unlikely to decrease even when the inflow exhaust gas temperature decreases.

  On the other hand, when a part of the particulate filter 5 is damaged and PM passes through, the flow resistance at the damaged part is lower than that at the other part (that is, the pressure at the damaged part is lower than the other part). As a result, the exhaust flow concentrates on the damaged part. When the flow of exhaust gas concentrates on the damaged part, the flow rate of the exhaust gas increases, so that the thermal conductivity decreases.

  That is, when a part of the particulate filter 5 is damaged, most of the exhaust gas flowing into the particulate filter 5 flows through the damaged portion at a high speed, so that the amount of heat received by the exhaust gas in the particulate filter 5 decreases.

  Furthermore, since the amount of collected PM in the vicinity of the damaged portion is smaller than normal, the generation amount of oxidation reaction heat is reduced. When the amount of heat of oxidation reaction in the vicinity of the damaged portion decreases, the amount of heat received by the exhaust gas further decreases in combination with the increase in the flow velocity described above.

  Therefore, when an abnormality such that PM passes through the particulate filter 5 occurs, it is considered that the outflow exhaust gas temperature also decreases following the decrease in the inflow exhaust gas temperature.

  The flow rate of the exhaust gas flowing through the damaged part of the particulate filter 5 increases as the exhaust flow rate flowing into the particulate filter 5 increases and / or the flow resistance difference between the damaged part and other parts increases.

The exhaust flow rate flowing into the particulate filter 5 increases in proportion to the intake air amount of the internal combustion engine 1. The difference in flow resistance between the damaged portion and other portions increases as the amount of PM trapped by the particulate filter 5 increases.

  Therefore, it is considered that the degree of decrease in the outflow exhaust gas temperature becomes more remarkable as the intake air amount of the internal combustion engine 1 is increased and / or the PM trapping amount of the particulate filter 5 is increased.

  According to the behavior and characteristics of the outflow exhaust gas temperature described above, when the internal combustion engine 1 continues the idle operation for a predetermined time or more after the deceleration operation, the period from the start of the deceleration operation until the idle operation time reaches a certain time (hereinafter referred to as the idle operation time) It is possible to detect the behavior of the outflow exhaust temperature during the deceleration idle period) and determine the abnormality of the particulate filter 5 using the behavior as a parameter.

  Hereinafter, specific examples of the abnormality determination control will be described.

  First, an example in which an abnormality of the particulate filter 5 is determined based on the relative relationship between the inflow exhaust gas temperature and the outflow exhaust gas temperature during the deceleration idle period will be described.

  As described above, the relative relationship between the amount of decrease in the inflow exhaust temperature and the amount of decrease in the outflow exhaust temperature during the deceleration idle period differs between when the particulate filter 5 is normal and when it is abnormal.

  When the particulate filter 5 is normal, the inflow exhaust temperature decreases during the deceleration idle period, but the outflow exhaust temperature hardly changes. That is, the amount of decrease in the outflow exhaust temperature with respect to the amount of decrease in the inflow exhaust temperature during the deceleration idle period is sufficiently reduced.

  On the other hand, when the particulate filter 5 is abnormal, the outflow exhaust temperature also decreases following the decrease in the inflow exhaust temperature during the deceleration idle period. That is, during the deceleration idle period, the amount of decrease in the outflow exhaust temperature with respect to the amount of decrease in the inflow exhaust temperature increases.

  Therefore, when the particulate filter 5 is abnormal, as shown in FIG. 3, the relative difference between the inflow exhaust gas temperature and the outflow exhaust gas temperature during the deceleration idle period becomes larger than that during normal operation.

  Therefore, the relative difference between the inflow exhaust gas temperature and the outflow exhaust gas temperature during the deceleration idle period is calculated, and when the relative difference becomes larger than the threshold value, it can be determined that the particulate filter 5 is abnormal.

  By the way, when the abnormality of the particulate filter 5 is minor (when the amount of PM passing through is small), or when the amount of PM trapped by the particulate filter 5 is small, there is a possibility that the amount of decrease in the outflow exhaust gas temperature is reduced. is there. Furthermore, the inflow exhaust gas temperature and the outflow exhaust gas temperature are irregular due to various factors such as a response delay of the upstream side exhaust temperature sensor 7 and the downstream side exhaust temperature sensor 8, a response delay of the exhaust gas, or a disturbance in the combustion state of the internal combustion engine 1. There is a possibility that it will change.

  For this reason, if the relative difference between the inflow exhaust gas temperature and the outflow exhaust gas temperature during one period of the deceleration idle period is used as a parameter, an erroneous determination may be induced.

  On the other hand, in the present embodiment, the relative difference between both is integrated from the locus of the inflow exhaust temperature and the outflow exhaust temperature during the deceleration idle period, and if the integrated value is larger than the threshold value, it is determined that the particulate filter 5 is abnormal. I tried to do it. That is, the area of the hatched portion in FIG. 4 is calculated, and if the area is larger than the threshold value, it is determined that the particulate filter 5 is abnormal.

  As described above, when the abnormality determination is performed based on the locus of the inflow exhaust gas temperature and the outflow exhaust gas temperature, when the decrease amount of the outflow exhaust gas temperature at the time of abnormality is small, temporary fluctuation of the inflow exhaust gas temperature and the outflow exhaust gas temperature, etc. Even if it occurs, an erroneous determination is less likely to occur.

  Hereinafter, the abnormality determination control of this embodiment will be described with reference to FIG. FIG. 5 is a flowchart illustrating an abnormality determination control routine according to the first embodiment. This abnormality determination control is a routine stored in advance in the ROM of the ECU 11 and is executed by the ECU 11.

  In the abnormality determination control routine, the ECU 11 first determines in S101 whether or not the inflow exhaust gas temperature Tin is equal to or higher than a predetermined temperature. The predetermined temperature corresponds to the lowest temperature in a temperature range in which the catalyst of the particulate filter 5 is in a state where PM can be continuously oxidized.

  When it is determined in S101 that the inflow exhaust gas temperature Tin is equal to or higher than the predetermined temperature, the ECU 11 proceeds to S102 and determines whether or not the value of the deceleration flag is “1”.

  The deceleration flag is a storage area set in the RAM or the like, and is “1” when the engine speed is equal to or higher than the predetermined speed and the accelerator opening is fully closed, in other words, when the deceleration fuel cut condition is satisfied. Is stored, and “0” is stored when the deceleration fuel cut condition is not satisfied.

  When it is determined in S102 that the value of the deceleration flag is “1”, the ECU 11 proceeds to S103. In S103, the ECU 11 closes the EGR valve 10 and controls the intake throttle valve 4 to fully open. In this case, the intake air amount of the internal combustion engine 1 increases, and the exhaust gas flow rate flowing into the particulate filter 5 increases accordingly.

  In S104, the output signal (inflow exhaust temperature: Tin) of the upstream side exhaust temperature sensor 7 and the output signal (outflow exhaust temperature: Tout) of the downstream side exhaust temperature sensor 8 are input.

  In S105, the ECU 11 calculates a relative difference: ΔT (= Tin−Tout) between the inflow exhaust gas temperature: Tin and the outflow exhaust gas temperature: Tout input in S104.

In S106, the ECU 11 calculates a new integrated value: ΣΔT by adding the relative difference: ΔT calculated in S105 to the integrated value: ΣΔTold calculated in the previous execution of S106. The default value of the previous integrated value: ΣΔTold is “0”.

  In S107, the ECU 11 determines whether or not the value of the idle flag is “1”.

  The idle flag is a storage area set in a RAM or the like, and stores “1” when the engine speed is less than a predetermined speed and the accelerator opening is fully closed, and the engine speed is a predetermined speed. When the accelerator opening is not fully closed, “0” is stored.

  When it is determined in S107 that the value of the idle flag is “0”, that is, when the internal combustion engine 1 is still continuing the deceleration operation, or the internal combustion engine 1 has shifted to the acceleration operation or the steady operation from the middle of the deceleration operation. In this case, the ECU 11 executes the processes after S102 described above again.

At this time, if the internal combustion engine 1 continues the deceleration operation, it is determined in S102 that the value of the deceleration flag is “1”. On the other hand, if the internal combustion engine 1 has shifted to the acceleration operation or the steady operation from the middle of the deceleration operation, it is determined in S102 that the value of the deceleration flag is “0”. If it is determined in S102 that the value of the deceleration flag is “0”, the ECU 11 ends the execution of this routine after executing the processing of S113 described later.

  When it is determined in S107 that the value of the idle flag is “1”, in other words, when the internal combustion engine 1 shifts from the deceleration operation to the idle operation, the ECU 11 activates the idle counter in S108. The idle counter is a counter that measures idle operation time.

In S109, the ECU 11 determines whether or not the time counted by the idle counter (idle operation time) is equal to or longer than a predetermined time: tidl, that is, whether or not the idle operation time is continued for a predetermined time or more.

When it is determined in S109 that the time counted by the idle counter is less than the predetermined time: tidl, the ECU 11 repeatedly executes the processes after S103.

At this time, if the internal combustion engine 1 has transitioned from the idle operation state to the non-idle operation state (the internal combustion engine 1 has transitioned to another operation state without continuing the idle operation for a predetermined time or longer), the idle flag is set in S107. It is determined that the value is “0”, and then it is determined in S102 that the value of the deceleration flag is “0”. If it is determined in S102 that the value of the deceleration flag is “0”, the ECU 11 defaults the integrated value: ΣΔTold in S113 (= 0).
And the time of the idle counter is reset and the execution of this routine is terminated.

On the other hand, if it is determined in S109 that the time measured by the idle counter is equal to or longer than the predetermined time: tidl, the ECU 11 proceeds to S110, and whether the integrated value: ΣΔT calculated in S106 is greater than the threshold value: Ts. Is determined. The above-described threshold value: Ts is a value corresponding to the maximum value that can be taken by the integrated value: ΣΔT when the particulate filter 5 is normal, and has been experimentally obtained in advance.

  If it is determined in S110 that the integrated value: ΣΔT is greater than the threshold value: Ts, the ECU 11 considers that the particulate filter 5 is abnormal and stores “1” in the failure flag in S111.

  If it is determined in S110 that the integrated value: ΣΔT is not larger than the threshold value: Ts, the ECU 11 considers that the particulate filter 5 is normal and stores “0” in the failure flag in S112.

When the ECU 11 finishes executing the process of S111 or S112, the ECU 11 proceeds to S113, resets the integrated value: ΣΔTold to the default (= 0), resets the time counted by the idle counter, and ends the execution of this routine. To do.

  According to the abnormality determination method of the present embodiment, it is possible to detect the behavior of the outflow exhaust gas temperature when the particulate filter 5 is abnormal. Therefore, it is possible to accurately determine the abnormality of the particulate filter 5. Become. Further, when the abnormality determination control is executed when the catalyst carried on the particulate filter 5 is in a state where PM can be continuously oxidized, it is possible to detect deterioration of the oxidation function of the catalyst.

  Furthermore, since the abnormality determination method of the present embodiment uses the change locus of the inflow exhaust gas temperature and the outflow exhaust gas temperature as a parameter, the abnormality determination can be performed with high accuracy even when the amount of PM trapped by the particulate filter 5 is small. Can do.

  Next, an example in which the abnormality of the particulate filter 5 is determined based on the degree of decrease in the outflow exhaust gas temperature during the deceleration idle period will be described.

  FIG. 6 is a diagram showing the behavior of the outflow exhaust gas temperature during the deceleration idle period. The dotted line in FIG. 6 shows the outflow exhaust temperature when the particulate filter 5 is normal, and the solid line in FIG. 6 shows the outflow exhaust temperature when the particulate filter 5 is abnormal.

  When the particulate filter 5 is normal, the amount of decrease in the outflow exhaust gas temperature during the deceleration idle period is slight. On the other hand, when the particulate filter 5 is abnormal, the amount of decrease in the outflow exhaust gas temperature during the deceleration idle period increases. That is, the amount of decrease in the outflow exhaust gas temperature differs between when the particulate filter 5 is normal and when it is abnormal.

  Therefore, in this embodiment, the difference (temperature decrease amount) between the outflow exhaust temperature at the start of the deceleration idle period and the outflow exhaust temperature at the end of the deceleration idle period (temperature decrease amount) is calculated, and if the difference exceeds a threshold value, the particulate filter 5 was determined to be abnormal.

  In addition, when the abnormality of the particulate filter 5 is minor or when the amount of PM trapped by the particulate filter 5 is small, the amount of decrease in the outflow exhaust gas temperature may be reduced. The abnormality determination is performed under the condition that the prepared catalyst is in a state in which PM can be continuously oxidized and the intake air amount at the start of the deceleration idle period is a predetermined amount or more.

  Hereinafter, the abnormality determination control of this embodiment will be described with reference to FIG. FIG. 7 is a flowchart illustrating an abnormality determination control routine according to the second embodiment.

  In the abnormality determination control routine, the ECU 11 first inputs an output signal (inflow exhaust gas temperature): Tin and an output signal (intake air amount): Ga of the air flow meter 12 in S201.

  In S202, the ECU 11 determines whether or not the inflow exhaust gas temperature Tin input in S201 is equal to or higher than a predetermined temperature. The predetermined temperature corresponds to the lowest temperature in a temperature range in which the catalyst of the particulate filter 5 is in a state where PM can be continuously oxidized.

  When it is determined in S202 that the inflow exhaust gas temperature Tin is less than the predetermined temperature, the ECU 11 regards that the particulate filter 5 is not in a state in which PM can be continuously oxidized, and ends the execution of this routine.

  If it is determined in S202 that the inflow exhaust gas temperature Tin is equal to or higher than the predetermined temperature, the ECU 11 regards the particulate filter 5 as being in a state where PM can be continuously oxidized, and proceeds to S203.

  In S203, the ECU 11 determines whether or not the intake air amount: Ga input in S201 is equal to or greater than a predetermined amount: Gas. Predetermined amount: Gas is a value determined so that the exhaust gas temperature in the particulate filter 5 shows a behavior different from that in the normal state even if the amount of PM passing through the particulate filter 5 is very small and the amount of PM trapped is small. Have been experimentally determined in advance.

  When it is determined in S203 that the intake air amount: Ga is less than the predetermined amount: Gas, the ECU 11 ends the execution of this routine. On the other hand, if it is determined in S203 that the intake air amount: Ga is equal to or greater than the predetermined amount: Gas, the ECU 11 proceeds to S204.

  In S204, the ECU 11 inputs the output signal of the downstream side exhaust temperature sensor 8, and stores the output signal in the RAM as the outflow exhaust temperature at the start of the deceleration idle period: Tout1.

  In S205, the ECU 11 determines whether or not the value of the deceleration flag is “1”. If it is determined in S205 that the value of the deceleration flag is “0”, the ECU 11 ends the execution of this routine. On the other hand, if it is determined in S205 that the value of the deceleration flag is “1”, the ECU 11 proceeds to S206.

  In S206, the ECU 11 closes the EGR valve 10 and opens the intake throttle valve 4 in order to increase the amount of intake air during the deceleration idle period (in other words, the exhaust flow rate flowing into the particulate filter 5 during the deceleration idle period). Control fully open.

  In S207, the ECU 11 determines whether or not the value of the idle flag is “1”. If it is determined in S207 that the value of the idle flag is “0”, the ECU 11 executes the processes subsequent to S205 again.

  If it is determined in S207 that the value of the idle flag is “1”, the ECU 11 proceeds to S208. In S208, the ECU 11 activates the idle counter.

  In S209, the ECU 11 determines whether or not the time counted by the idle counter (idle operation time) is equal to or longer than a predetermined time: tidl.

If it is determined in S209 that the time counted by the idle counter is less than the predetermined time: tidl, the ECU 11 repeatedly executes the processes after S207.

If it is determined in S209 that the time measured by the idle counter is equal to or longer than the predetermined time: tidl, the ECU 11 proceeds to S210. In S210, the ECU 11 inputs the output signal of the downstream side exhaust temperature sensor 8, and stores the output signal as the outflow exhaust temperature at the end of the deceleration idle period: Tout2.

In S211, the ECU 11 calculates a temperature decrease amount: ΔTout (= Tout1−Tout2) by subtracting the outflow exhaust temperature at the end of the deceleration idle period: Tout2 from the outflow exhaust temperature at the start of the deceleration idle period: Tout1.

In S212, the ECU 11 determines that the temperature decrease amount calculated in S211: ΔTout is a threshold value:
It is determined whether or not it is larger than ΔTj. The above-described threshold value: ΔTj is a value corresponding to the maximum value that the temperature drop amount: ΔTout can take when the particulate filter 5 is normal, and is obtained experimentally in advance.

  If it is determined in S212 that the temperature drop amount: ΔTout is greater than the threshold value: ΔTj, the ECU 11 considers that the particulate filter 5 is abnormal, and stores “1” in the failure flag in S213.

  If it is determined in S212 that the temperature drop amount: ΔTout is not greater than the threshold value: ΔTj, the ECU 11 considers that the particulate filter 5 is normal and stores “0” in the failure flag in S214.

According to the abnormality determination method of the present embodiment, it is possible to detect the behavior of the outflow exhaust gas temperature when the particulate filter 5 is abnormal, based on the amount of decrease in the outflow exhaust air temperature during the deceleration idle period. For this reason, it is possible to perform abnormality determination with simpler logic than in the first embodiment described above.

  Next, an example will be described in which the outflow exhaust gas temperature at the end of the deceleration idle period is estimated and the abnormality of the particulate filter 5 is determined based on the difference between the estimated value and the actually measured value.

  As a method for estimating and calculating the exhaust gas temperature at the end of the deceleration idle period, the heat balance of the exhaust system from the upstream exhaust gas temperature sensor 7 to the downstream exhaust gas temperature sensor 8 is modeled, and the exhaust gas temperature is calculated using the model. An example of the estimation calculation method can be exemplified.

  The model includes a first model that models the heat balance of the exhaust system from the upstream side exhaust temperature sensor 7 to the particulate filter 5, a second model that models the heat balance in the particulate filter 5, It can be divided into a third model that models the heat balance of the exhaust system from the curate filter 5 to the downstream exhaust temperature sensor 8.

  The first model is a model for calculating the heat energy (hereinafter referred to as filter inflow heat energy) of the exhaust gas at the inlet of the particulate filter 5. In the first model, the constant pressure molar specific heat of the exhaust passage 3 from the upstream exhaust temperature sensor 7 to the particulate filter 5, the temperature of the exhaust gas passing through the upstream exhaust temperature sensor 7, and the upstream exhaust temperature sensor 7 are passed. This is a model that schematically shows the relationship between the exhaust gas flow rate and the heat energy flowing into the filter.

  The second model is a model for calculating the thermal energy of the exhaust gas at the outlet of the particulate filter 5 (hereinafter referred to as filter outflow heat energy). This second model includes the filter inflow heat energy, the heat transfer coefficient of the particulate filter 5, the constant volume molar specific heat of the particulate filter 5, and the temperature of the catalyst supported on the particulate filter 5 (catalyst bed temperature). The mass of the catalyst and the heat energy generated when the reducing components in the exhaust (hydrocarbon (HC), carbon monoxide (CO), etc.) are oxidized (when the catalyst is in a state where PM can be continuously oxidized, PM is This is a model that schematically shows the relationship between the heat energy generated when oxidized and the heat energy that flows out of the filter.

  The third model is a model for calculating the thermal energy (hereinafter referred to as sensor passing thermal energy) that the exhaust has when passing through the downstream side exhaust temperature sensor 8. This third model includes the filter outflow heat energy, the heat release coefficient of the exhaust passage 3 from the particulate filter 5 to the downstream side exhaust temperature sensor 8, and the exhaust passage 3 from the particulate filter 5 to the downstream side exhaust temperature sensor 8. It is a model that schematically shows the relationship among the constant pressure molar specific heat, the exhaust gas flow rate passing through the downstream side exhaust temperature sensor 8, the atmospheric temperature, and the sensor passing heat energy.

  When the first to third models are sequentially calculated, the exhaust gas temperature at the end of the deceleration idle period when the particulate filter 5 is normal is estimated. The outflow exhaust temperature thus estimated (hereinafter referred to as the estimated outflow exhaust temperature) is compared with the output signal (hereinafter referred to as the actually measured outflow exhaust temperature) of the downstream side exhaust temperature sensor 8 at the end of the deceleration idle period. The

  As described above, when the particulate filter 5 is normal, the outflow exhaust temperature hardly decreases during the deceleration idle period, whereas when the particulate filter 5 is abnormal, the outflow exhaust temperature greatly increases during the deceleration idle period. descend.

Therefore, when the measured outflow exhaust temperature is lower than the estimated outflow exhaust temperature by a predetermined temperature or more, it is possible to determine that the particulate filter 5 is abnormal.

  Hereinafter, the abnormality determination control of this embodiment will be described with reference to FIG. FIG. 8 is a flowchart illustrating an abnormality determination control routine according to the third embodiment.

  In S301 to S303 of the abnormality determination control routine, the ECU 11 executes the same processing as S201 to S202 of the abnormality determination control routine in the second embodiment described above.

  In S304, the ECU 11 determines whether or not the value of the deceleration flag is “1”. If it is determined in S304 that the value of the deceleration flag is “0”, the ECU 11 ends the execution of this routine. On the other hand, when it is determined in S304 that the value of the deceleration flag is “1”, the ECU 11 proceeds to S305.

  In S305, the ECU 11 closes the EGR valve 10 and controls the intake throttle valve 4 to fully open.

  In S306, the ECU 11 determines whether or not the value of the idle flag is “1”. If it is determined in S306 that the value of the idle flag is “0”, the ECU 11 executes the processes after S304 again.

  If it is determined in S306 that the value of the idle flag is “1”, the ECU 11 proceeds to S307. In S307, the ECU 11 activates the idle counter.

  In S308, the ECU 11 determines whether or not the time counted by the idle counter (idle operation time) is equal to or longer than a predetermined time: tidl.

If it is determined in S308 that the time counted by the idle counter is less than the predetermined time: tidl, the ECU 11 repeatedly executes the processes after S306.

If it is determined in S308 that the time counted by the idle counter is equal to or longer than the predetermined time: tidl, the ECU 11 proceeds to S309. In S309, the ECU 11 calculates an estimated outflow exhaust gas temperature Toutc at the end of the deceleration idle period according to the above-described model.

  In S310, the ECU 11 inputs the output signal of the downstream side exhaust temperature sensor 8, and stores the output signal in the RAM as the actually measured outflow exhaust gas temperature Touta at the end of the deceleration idle period.

  In S311, the ECU 11 calculates a temperature difference: ΔTd by subtracting the measured outflow exhaust temperature: Touta from the estimated outflow exhaust temperature: Toout.

In S312, the ECU 11 determines whether or not the temperature difference: ΔTd is greater than a threshold value: ΔTdj. The above-mentioned threshold value: ΔTdj is a value determined on the basis of the error range of the estimated outflow exhaust gas temperature: Toutc when the particulate filter 5 is normal, and is obtained experimentally in advance.

If it is determined in S312 that the temperature difference: ΔTd is greater than the threshold value: ΔTdj, the ECU 11 considers that the particulate filter 5 is abnormal, and stores “1” in the failure flag in S313.

If it is determined in S312 that the temperature difference: ΔTd is not greater than the threshold value: ΔTdj, the ECU 11 considers that the particulate filter 5 is normal and stores “0” in the failure flag in S314.

  According to the abnormality determination method of the present embodiment, abnormality determination of the particulate filter 5 can be performed using the outflow exhaust gas temperature at the end of the deceleration idle period as a parameter.

  In the second embodiment described above, an example in which the abnormality of the particulate filter 5 is determined based on the amount of decrease in the outflow exhaust gas temperature during the deceleration idle period has been described, but in this embodiment, the amount of decrease when the amount of PM trapped is small. An example in which an abnormality of the particulate filter 5 is determined based on a relative difference from a decrease amount when the amount of PM trapped is large will be described.

  The inventor of the present application has verified the correlation with the PM trapping amount with respect to the specific behavior of the outflow exhaust gas temperature when abnormality occurs in the particulate filter 5, and as a result, has derived the following characteristics.

  FIG. 9 is a diagram showing the measurement results of the outflow exhaust temperature before and after PM collection for each of the normal particulate filter and the abnormal particulate filter. The exhaust gas temperature before PM collection is measured immediately after the execution of the process for forcibly regenerating the PM collection ability of the particulate filter (PM regeneration process). The outflow exhaust gas temperature after PM collection is measured immediately before the execution of the PM regeneration process.

  The solid line and dotted line in FIG. 9 indicate the outflow exhaust gas temperature before and after PM collection by a normal particulate filter. The one-dot chain line in FIG. 9 shows the outflow exhaust temperature after PM collection of the abnormal particulate filter, and the two-dot chain line in FIG. 6 shows the outflow exhaust temperature before PM collection of the abnormal particulate filter. .

  When the particulate filter is normal, the exhaust gas temperature before PM collection and after PM collection shows substantially the same behavior, and the amount of decrease during the deceleration idle period hardly changes.

  On the other hand, when the particulate filter is abnormal, the exhaust gas temperature before PM collection and after PM collection show completely different behaviors, and the amount of decrease during the deceleration idle period is also clearly different.

  That is, when the particulate filter is abnormal, the outflow exhaust temperature after PM collection is lower than the outflow exhaust temperature before PM collection, and the amount of decrease in the outflow exhaust temperature during the deceleration idle period is also before PM collection. On the other hand, the number after PM collection increases.

  This is considered to be caused by the fact that when the particulate filter is abnormal, the amount of heat exchanged by the exhaust gas in the particulate filter decreases as the amount of collected PM increases.

  In view of such characteristics of the outflow exhaust temperature, a comparison between the amount of decrease in the outflow exhaust temperature before PM collection and the amount of decrease in the outflow exhaust temperature after PM collection, or the outflow exhaust temperature and PM before PM collection It is possible to determine the abnormality of the particulate filter 5 by comparison with the outflow exhaust gas temperature after collection.

  That is, when the relative difference between the amount of decrease in the outflow exhaust temperature before PM collection and the amount of decrease in the outflow exhaust temperature after PM collection exceeds the threshold value, or the outflow exhaust temperature before PM collection and after PM collection When the relative temperature difference with the outflow exhaust gas temperature exceeds the threshold value, it can be determined that the particulate filter 5 is abnormal.

  Hereinafter, an abnormality determination method based on the relative difference between the amount of decrease in the outflow exhaust temperature before PM collection and the amount of decrease in the outflow exhaust temperature after PM collection will be specifically described.

  FIG. 10 is a flowchart illustrating an abnormality determination control routine according to the fourth embodiment. In this abnormality determination control routine, the ECU 11 first determines whether or not a PM regeneration process execution condition is satisfied in S401.

  The PM regeneration process execution condition is that the amount of PM trapped by the particulate filter 5 exceeds a predetermined value. The amount of PM trapped is estimated by a known estimation method using the integrated intake air amount, the integrated fuel injection amount, the integrated operation time, or the like of the internal combustion engine 1 as a parameter.

  If the PM regeneration process execution condition is not satisfied in S401, the ECU 11 ends the execution of this routine.

  If the PM regeneration process execution condition is satisfied in S401, the ECU 11 changes the value of the PM regeneration process standby flag to “1” in S402. The PM regeneration process standby flag is a storage area previously set in the RAM or the like, and “1” is stored when the PM regeneration process execution condition is satisfied, and the amount of decrease in the outflow exhaust temperature after PM collection is calculated. “0” is stored in the memory.

  When the PM regeneration process standby flag is “1”, execution of the PM regeneration process is prohibited in a separate PM regeneration process execution routine, and when the PM regeneration process standby flag is “0”, the PM regeneration process is performed. It is assumed that execution of the PM regeneration process is permitted in the execution routine.

In S403, the ECU 11 calculates a decrease amount of the outflow exhaust gas temperature after PM collection (a decrease amount after PM collection): ΔTout1. This calculation method is the same as S201 to S211 of the abnormality determination control routine in the second embodiment.

  In S404, the ECU 11 rewrites the value of the PM regeneration process standby flag to “0”. In this case, the PM regeneration process is executed in a separate PM regeneration process execution routine.

  In S405, the ECU 11 determines whether or not the execution of the PM regeneration process has ended. If it is determined in S405 that the PM regeneration process has not been completed, the ECU 11 repeatedly executes S405 until the PM regeneration process is completed.

When it is determined in S405 that the PM regeneration process has been completed, the ECU 11 proceeds to S406. In S406, the ECU 11 calculates a decrease amount of the outflow exhaust gas temperature before PM collection (a decrease amount before PM collection): ΔTout2. This calculation method is also the same as S201 to S211 of the abnormality determination control routine in the second embodiment.

  In S407, the ECU 11 subtracts the decrease amount after PM collection: ΔTout1 calculated in S403 from the decrease amount before PM collection: ΔTout2 calculated in S406, and sets the relative difference between them: ΔToutd. calculate.

In S408, the ECU 11 determines whether or not the relative difference: ΔToutd calculated in S407 is larger than a threshold value: ΔToutdj. The threshold value: ΔToutdj is a value corresponding to the maximum value that the relative difference: ΔToutd can take when the particulate filter 5 is normal, and has been experimentally obtained in advance.

If it is determined in S408 that the relative difference: ΔToutd is greater than the threshold: ΔToutdj, the ECU 11 considers that the particulate filter 5 is abnormal and stores “1” in the failure flag in S409.

  If it is determined in S408 that the relative difference: ΔToutd is not greater than the threshold value: ΔToutdj, the ECU 11 considers that the particulate filter 5 is normal and stores “0” in the failure flag in S410.

  According to the abnormality determination method of the present embodiment, since the abnormality of the particulate filter 5 is determined based on the relative difference between the decrease amount before PM collection and the decrease amount after PM collection, the determination accuracy can be improved. .

  In the first to third embodiments described above, the thresholds that serve as the basis for abnormality determination (threshold value of the first embodiment: Ts, threshold value of the second embodiment: ΔTj, threshold value of the third embodiment: ΔTdj) are fixed values. However, it is good also as a variable value increased / decreased according to PM collection amount of the particulate filter 5. FIG.

  The peculiar behavior of the outflow exhaust temperature when the particulate filter 5 is abnormal becomes more prominent as the amount of PM trapped increases. On the contrary, the unusual behavior of the outflow exhaust gas temperature when the particulate filter 5 is abnormal is less likely to appear as the amount of collected PM decreases.

  Therefore, when the amount of collected PM is small, the criterion may be lowered (that is, the threshold value is made smaller) than when the amount of collected PM is large.

  When the determination criterion is made variable in this way, it is possible to determine the abnormality of the particulate filter 5 even under a condition where the amount of collected PM is small, and also when the amount of collected PM is large. It is possible to suppress the occurrence of erroneous determination.

  In the above-described first to third embodiments, the example in which the abnormality determination is performed without considering the PM collection amount of the particulate filter 5 is described. However, the abnormality determination is performed on the condition that the PM collection amount is a predetermined amount or more. May be executed.

  The unusual behavior of the exhaust gas temperature when the particulate filter 5 is abnormal appears more significantly when the amount of PM trapped is larger than when the amount of trapped PM is small. If determination control is executed, determination accuracy can be increased.

  In the above-described first to fourth embodiments, the example in which the abnormality of the particulate filter 5 is determined based on the behavior of the outflow exhaust gas temperature during the deceleration idle period has been described. You may make it combine the abnormality determination method and any one of the abnormality determination methods of Examples 1-4.

  When an abnormality such that PM passes through the particulate filter 5 occurs, the front-rear differential pressure is smaller than when the particulate filter 5 is normal. For this reason, when the differential pressure before and after falls below a predetermined value, it can be determined that the particulate filter 5 is abnormal.

  However, since the differential pressure across the particulate filter 5 is unlikely to occur when the exhaust flow rate flowing into the particulate filter 5 is small, the abnormality determination method based on the longitudinal differential pressure is executed in the high rotation / high load operation region where the exhaust flow rate increases. It is preferred that

  On the other hand, the abnormality determination methods of the first to fourth embodiments described above are performed in the deceleration operation region and the idle operation region to improve the determination accuracy.

  Therefore, when the abnormality determination method according to any one of the first to fourth embodiments described above and the abnormality determination method based on the front-rear differential pressure are combined, the accuracy is improved in the high rotation / high load operation region in addition to the deceleration / idle operation region. Since a high abnormality determination can be performed, the determination frequency can be increased.

  Further, only when it is determined that the particulate filter 5 is abnormal in each abnormality determination method, if the abnormality determination of the particulate filter 5 is determined, the determination accuracy can be further improved. .

The figure which shows schematic structure of the internal combustion engine to which this invention is applied. The figure which shows the result of having measured the inflow exhaust temperature and outflow exhaust temperature of a particulate filter Diagram showing the relative difference between the inflow exhaust temperature and the outflow exhaust temperature during the deceleration idle period Diagram showing the accumulated relative difference between the inflow exhaust temperature and the outflow exhaust temperature during the deceleration idle period The flowchart figure which shows the abnormality determination control routine in Example 1 A diagram showing the amount of decrease in the outflow exhaust temperature during the deceleration idle period The flowchart figure which shows the abnormality determination control routine in Example 2. The flowchart figure which shows the abnormality determination control routine in Example 3 The figure which shows the result of having measured the outflow exhaust gas temperature before PM collection, and the outflow exhaust gas temperature after PM collection The flowchart figure which shows the abnormality determination control routine in Example 4

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 3 ... Exhaust passage 4 ... Intake throttle valve 5 ... Particulate filter 7 ... Upstream side exhaust temperature sensor 8 ...・ Downstream exhaust temperature sensor 9 ... EGR passage 10 ... EGR valve 11 ... ECU

Claims (5)

In an abnormality determination method for abnormalities such as PM passing through a part of a particulate filter that is disposed in an exhaust passage of an internal combustion engine and collects and oxidizes particulates,
It is determined that the particulate filter is abnormal when the degree of decrease in the outflow exhaust temperature lower than the inflow exhaust temperature relative to the inflow exhaust temperature of the particulate filter during the deceleration operation or the integrated value of the decrease exceeds a predetermined value. A particulate filter abnormality determination method characterized by: 2. The particulate filter abnormality determination method according to claim 1, wherein the EGR is stopped when the degree of decrease in the outflow exhaust temperature with respect to the inflow exhaust temperature is detected. 3. The particulate filter abnormality determination method according to claim 1, wherein the degree of opening of the intake throttle valve is increased when detecting the degree of decrease in the outflow exhaust temperature relative to the inflow exhaust temperature. The particulate filter according to any one of claims 1 to 3 , wherein the particulate collection amount of the particulate filter is estimated, and when the estimated particulate collection amount is large, the determination criterion is set higher than when the particulate collection amount is small. Curate filter abnormality determination method. 5. The method according to claim 1, wherein the particulate collection amount of the particulate filter is estimated, and the abnormality determination is performed on the condition that the estimated particulate collection amount is equal to or greater than a predetermined amount. A particulate filter abnormality determination method.

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