JP4650222B2 - PM trapper failure detection device - Google Patents

Description

  The present invention relates to an apparatus for detecting a failure of a PM trapper provided in an exhaust pipe of an internal combustion engine.

  As a technique for detecting a failure of a PM trapper provided in an exhaust pipe of an internal combustion engine, a differential pressure between exhaust pressure upstream and downstream of the PM trapper is compared with a differential pressure when the PM trapper is normal. A technique for detecting a trapper failure is known (see, for example, Patent Document 1).

Further, as a technique for detecting a failure of the PM trapper, a PM trapper failure is detected by comparing a differential pressure between the exhaust pressure upstream and downstream of the PM trapper and a reference differential pressure determined by an engine operating state. Technology is also known (see, for example, Patent Document 2).
JP-A-6-323127 JP 2003-155920 A JP 2003-35128 A JP 2001-248423 A

  By the way, the differential pressure between the upstream side and the downstream side of the PM trapper varies depending on the deposition site of the particulate matter (hereinafter abbreviated as “PM”) in the PM trapper, and therefore the PM based on the absolute value of the differential pressure. It may be difficult to accurately estimate the amount of deposits. For this reason, there is a possibility that a failure of the PM trapper cannot be detected correctly by the above-described technique that compares the absolute value of the differential pressure with the reference differential pressure.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a technique that makes it possible to detect a failure of a PM trapper with high accuracy.

  In order to achieve the above object, the present invention provides an amount of PM flowing into the PM trapper (hereinafter referred to as “input PM amount”) and an amount of PM flowing out of the PM trapper (hereinafter referred to as “outgoing PM amount”). Is detected directly by the PM sensor, and a failure of the PM trapper is detected based on the ratio of the detected values.

More specifically, the present invention is a PM trapper failure detection device for detecting a failure of a PM trapper provided in an exhaust passage of an internal combustion engine,
An incoming PM sensor that detects the amount of PM flowing into the PM trapper;
A PM sensor for detecting the amount of PM flowing out of the PM trapper;
A failure determination means for detecting a failure of the PM trapper based on a ratio of a detection value by the input PM sensor and a detection value by the output PM sensor;
It is characterized by providing.

  When a failure occurs in the PM trapper, the amount of PM that passes through the PM trapper without being collected by the PM trapper (the amount of PM to be output) may increase.

Therefore, as a method for detecting a PM trapper failure, a method has been proposed in which the absolute amount of the output PM amount is measured, and the PM trapper failure is determined on the condition that the measured output PM amount is greater than normal. It was.

  However, since the output PM amount changes with the fluctuation of the input PM amount even when the PM trapper is normal, the determination accuracy is improved when the failure determination of the PM trapper is performed based only on the absolute amount of the output PM amount. There was a risk of lowering.

  On the other hand, the PM trapper failure detection device of the present invention detects the input PM amount by the input PM sensor and also detects the output PM amount by the output PM sensor, and uses the ratio between the input PM amount and the output PM amount as a parameter. A trapper failure was determined.

  The ratio between the input PM amount and the output PM amount indicates the ratio of the PM amount that has passed through the PM trapper with respect to the PM amount that has flowed into the PM trapper (hereinafter referred to as “PM slip-out rate”).

  The PM slipping rate is less affected by fluctuations in the incoming PM amount than the absolute amount of the outgoing PM amount. This is because the change in the output PM amount accompanying the change in the input PM amount is substantially canceled by dividing the output PM amount by the input PM amount.

  As a result, it is possible to accurately determine the failure of the PM trapper even in a situation where the amount of input PM varies.

  As a specific failure determination method based on the PM slipping rate, a method of determining that the PM trapper has failed when the PM slipping rate exceeds a predetermined reference value can be exemplified. The reference value described above is a value determined based on the PM slipping rate when the PM trapper is normal.

  The reference value described above may be a fixed value obtained experimentally in advance, but the amount of PM collected in the PM trapper at the time when the failure determination is performed (hereinafter referred to as “PM accumulation amount”). The variable value may be changed according to This is because the PM slipping rate of a normal PM trapper tends to change depending on the amount of PM deposition.

  Therefore, the PM trapper failure detection apparatus according to the present invention includes a PM accumulation amount estimating means for estimating the PM amount accumulated on the PM trapper based on the detection value by the input PM sensor and the detection value by the output PM sensor, and this PM accumulation amount. You may make it further provide the reference value setting means which determines a reference value according to PM deposition amount estimated by the estimation means.

  According to such a configuration, since the reference value suitable for the PM accumulation amount when the failure determination means determines the failure of the PM trapper is set, the failure determination of the PM trapper is performed using such a reference value. If this is done, it becomes possible to improve the failure determination accuracy of the PM trapper.

  For example, the reference value may be set to be lower as the PM deposition amount estimated by the PM deposition amount estimation means increases, and may be set to be higher as the estimated PM deposition amount decreases.

  This is because when the amount of accumulated PM increases, the accumulated PM narrows the cross-sectional area of the flow path in the PM trapper so that PM is easily collected.

  In addition, since the PM accumulation amount estimation means according to the present invention estimates the PM accumulation amount based on the actually measured values of the input PM amount and the output PM amount, it is based on the differential pressure between the exhaust pressure upstream and downstream of the PM trapper as in the prior art. Thus, the PM deposition amount estimation accuracy is higher than the method of estimating the PM deposition amount.

  Therefore, if the regeneration process execution timing of the PM trapper is determined using the PM accumulation amount estimated by the PM accumulation amount estimation means, the regeneration process execution timing can be set to a timing commensurate with the PM accumulation amount.

  By the way, in recent years, a catalyst having oxidation ability may be provided along with the PM trapper. In such a case, a part of the PM flowing into the PM trapper is oxidized by the catalyst. Therefore, in order to estimate the net PM accumulation amount, it is necessary to consider the PM amount oxidized by the PM trapper in addition to the input PM amount and the output PM amount.

The amount of PM oxidized by the PM trapper is estimated from the catalyst bed temperature, the amount of oxygen in the exhaust, and the like, but the estimated amount includes an error. If the estimated amount of the PM oxidation amount includes an error, the estimated value of the PM deposition amount also includes an error.

  If the estimated value of the PM accumulation amount includes an error, the reference value determined based on the estimated value of the PM accumulation amount becomes an inappropriate value, which may reduce the failure detection accuracy.

  On the other hand, the inventor of the present application has obtained the knowledge that when the PM accumulation amount increases to some extent, the change amount of the PM slip-through rate with respect to the change amount of the PM accumulation amount decreases.

  According to the above knowledge, if the calculation of the reference value and the PM trapper failure determination are performed when the PM accumulation amount is large, the error included in the estimated PM accumulation amount is difficult to be reflected in the reference value. Therefore, if the calculation of the reference value and the failure determination of the PM trapper are performed when the PM accumulation amount is large, the deterioration of the failure determination accuracy can be suppressed.

  The PM trapper failure detection apparatus according to the present invention can improve the failure detection accuracy of the PM trapper by adopting the following configuration.

That is, the PM trapper failure detection device according to the present invention is a PM trapper failure detection device that detects a failure of the PM trapper provided in the exhaust passage of the internal combustion engine,
An incoming PM sensor that detects the amount of PM flowing into the PM trapper;
A differential pressure sensor for detecting a differential pressure between an exhaust pressure upstream of the PM trapper and an exhaust pressure downstream of the PM trapper;
PM accumulation amount estimation means for estimating the PM accumulation amount in the PM trapper based on the detection value by the input PM sensor;
A failure of the PM trapper is determined based on the amount of increase in the detected value of the differential pressure by the differential pressure sensor during a period until the accumulation amount estimated by the PM accumulation amount estimation means increases from a predetermined reference amount to a predetermined amount. Failure determination means to
You may make it provide.

When the PM trapper is normal, the differential pressure between the upstream side and the downstream side of the PM trapper (hereinafter referred to as “trapper front-rear differential pressure”) tends to increase with an increase in the amount of PM accumulated in the PM trapper.

  On the other hand, when the PM trapper is out of order, the amount of PM passing through the PM trapper increases as compared with the case of a normal PM trapper. Accordingly, the amount of increase in the trapper front-rear differential pressure becomes smaller than that in the normal state.

Therefore, a period (hereinafter referred to as “transition period”) from the state where the estimated PM deposition amount becomes a predetermined reference amount (hereinafter referred to as “reference state”) to the increase of the estimated PM deposition amount by a predetermined amount. A failure of the PM trapper can be determined based on the amount of increase (change) in the differential pressure at.

  Since the differential pressure detected by the differential pressure sensor includes various errors, the detection value of the differential pressure sensor may not accurately reflect the PM accumulation amount of the PM trapper.

  On the other hand, the amount of increase in the differential pressure during the transition period, that is, the difference between the trapper front-rear differential pressure in the reference state and the trapper front-rear differential pressure in the state after transition is a value in which the above-described error is offset.

  As a result, the PM trapper failure detection device according to the present invention can accurately determine the failure of the PM trapper as compared with the conventional failure detection device using the absolute value of the differential pressure as a parameter.

  Further, in this PM trapper failure detection device, the PM trapper failure determination is performed based on the correlation between the increase amount of the differential pressure and the increase amount of the PM accumulation amount, and therefore, the PM trapper failure detection accuracy can be easily improved.

  That is, when the state of the PM trapper is estimated based only on the differential pressure, for example, for the detection result that the differential pressure is small, whether it is due to the failure of the PM trapper or the amount of accumulated PM in the PM trapper is It is difficult to determine whether it is due to less.

  On the other hand, when the PM trapper failure determination is performed based on the correlation between the increase in the PM accumulation amount and the increase in the differential pressure, the PM is increased when the increase in the differential pressure is small with respect to the increase in the PM accumulation amount. It can be determined that the trapper is out of order. On the contrary, even if the increase amount of the differential pressure is small, if the increment of the PM accumulation amount is also small, it can be determined that the PM trapper has not failed.

  Thus, the failure determination accuracy of the PM trapper can be further improved by determining the failure based on the correlation between the increase amount of the differential pressure and the increment of the PM accumulation amount.

  The predetermined increase amount of the differential pressure may be determined based on the increase amount of the differential pressure when the PM accumulation amount is increased by the predetermined amount in a normal PM trapper.

  When the increase amount of the differential pressure detected by the differential pressure sensor is small with respect to the predetermined increase amount determined in this way, it can be considered that the PM slip-through amount is larger than when the PM trapper is normal. As a result, it can be determined that the PM trapper is out of order.

  The PM trapper failure detection apparatus of the present invention can detect a failure of the PM trapper with high accuracy.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings.

  First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows an embodiment of an internal combustion engine to which the present invention is applied.

In FIG. 1, the exhaust discharged from the internal combustion engine 1 flows into a PM trapper 3 provided in the middle of the exhaust pipe 2.

  The PM trapper 3 includes a filter that collects PM in the exhaust, and an oxidation catalyst that is attached to the filter.

  An incoming PM sensor 4 is provided upstream of the PM trapper 3 in the exhaust pipe 2 so that the amount of PM flowing into the PM trapper 3 (incoming PM amount) is detected.

  An outgoing PM sensor 5 is provided downstream of the PM trapper 3 in the exhaust pipe 2 so that the amount of PM flowing out from the PM trapper 3 (outgoing PM amount) is detected.

  An exhaust temperature sensor 10 that detects the temperature of the exhaust gas flowing out from the PM trapper 3 is attached to the exhaust pipe 2 downstream of the PM trapper 3.

  Various sensors such as a crank position sensor 7, an air flow meter 8, and a water temperature sensor 9 are attached to the internal combustion engine 1.

  The incoming PM sensor 4, outgoing PM sensor 5, crank position sensor 7, air flow meter 8, water temperature sensor 9, and exhaust temperature sensor 10 are each electrically connected to the ECU 6, and detection signals from the sensors are input to the ECU 6. It has become.

  The ECU 6 performs known control such as fuel injection control based on the detection signal input from each sensor, and also detects a failure of the PM trapper 3 that is the gist of the present invention.

  Hereinafter, the failure detection of the PM trapper 3 performed by the ECU 6 will be described based on the flowchart of FIG. 2 is a flowchart showing a routine for detecting a failure of the PM trapper 3, and this routine is repeatedly executed by the ECU 6 at predetermined intervals.

  First, in step S201, the ECU 6 calculates the PM accumulation amount Gpmc in the PM trapper 3. Specifically, the ECU 6 calculates the amount of PM Pc oxidized by the oxidation catalyst of the PM trapper 3 (hereinafter referred to as “oxidation”) from the sum of the PM accumulation amount Gpmc and the input PM amount Pi calculated at the previous execution of this routine. Calculated by subtracting the output PM amount Po) (referred to as “PM amount”) (Gpmc ← Gpmc + Pi−Pc−Po).

  The incoming PM amount Pi and the outgoing PM amount Po are values detected by the incoming PM sensor 4 and the outgoing PM sensor 5, respectively. Since the oxidation PM amount Pc increases as the bed temperature of the oxidation catalyst is high and the amount of oxygen flowing through the oxidation catalyst increases, the oxidation PM amount Pc is estimated based on the detection value Tc by the exhaust temperature sensor 10, the detection value Ga of the air flow meter 8, and the like. be able to.

  In step S202, the ECU 6 determines whether or not the catalyst bed temperature Tc of the oxidation catalyst of the PM trapper 3 is higher than a predetermined temperature C1. That is, the ECU 6 determines whether or not the oxidation ability of the oxidation catalyst is sufficiently activated. This is because, if failure detection is performed when the activation state of the oxidation ability is unstable as in the case where the oxidation catalyst is partially activated, the detection accuracy may be reduced.

  The catalyst bed temperature described above may be directly measured by attaching a temperature sensor to the oxidation catalyst, but may be substituted by the exhaust gas temperature Tc detected by the exhaust gas temperature sensor 10. The predetermined temperature C1 is a temperature at which the entire oxidation catalyst is sufficiently activated.

  If an affirmative determination is made in step S202 described above, the ECU 6 proceeds to step S203. On the other hand, if a negative determination is made in step S202, the ECU 6 ends the execution of this routine.

  In step S203, the ECU 6 determines whether or not the intake air amount Ga detected by the air flow meter 8 is greater than a predetermined amount C2. That is, the ECU 6 determines whether or not the exhaust amount passing through the PM trapper 3 is greater than the predetermined amount C2. This is because when the amount of exhaust gas passing through the PM trapper 3 is small, it is difficult for the PM to slip through due to the failure of the PM trapper 3. In particular, when a minor failure occurs such that a small amount of PM passes through the PM trapper 3, it is difficult for PM to pass through unless the exhaust amount passing through the PM trapper 3 is large to some extent.

  If an affirmative determination is made in step S203, the ECU 6 proceeds to step S204, and if a negative determination is made, the ECU 6 ends the execution of this routine.

  In step S204, the ECU 6 calculates the PM slipping rate Kpm of the PM trapper 3. The PM slipping rate Kpm can be obtained by dividing the incoming PM amount Pi by the outgoing PM amount Po (= Po / Pi).

  The PM slipping rate Kpm obtained in this way is a value in which variations in the output PM amount due to fluctuations in the input PM amount are offset.

  For example, when the incoming PM amount Pi increases, the outgoing PM amount Po may increase as the incoming PM amount Pi increases even if the PM trapper 3 is normal. In this case, if the state of the PM trapper 3 is estimated based only on the absolute amount of the output PM amount Po, the PM trapper 3 breaks down even when the output PM amount Po increases as the input PM amount Pi increases. There is a possibility of misjudging it.

  On the other hand, when the state of the PM trapper 3 is estimated based on the ratio of the output PM amount Po to the input PM amount Pi (that is, the PM slipping rate Kpm), the output PM amount Po associated with the change in the input PM amount Pi The state of the PM trapper 3 can be estimated regardless of fluctuations.

  When the PM slipping rate Kpm is obtained as described above, the ECU 6 proceeds to step S205 and calculates the reference slipping rate Kst. The reference slipping rate Kst is a value corresponding to the PM slipping rate Kpm when the PM trapper is normal.

  The reference slip-through rate Kst depends on the PM accumulation amount of the PM trapper 3, the flow rate (flow rate) of the exhaust gas passing through the PM trapper 3, and the PM amount discharged from the internal combustion engine 1 (hereinafter referred to as “engine exhaust PM amount”). Change. Therefore, the reference slipping rate Kst may be obtained from a function or a map having the PM accumulation amount, the exhaust flow rate, and the engine exhaust PM amount as parameters.

  Since the exhaust flow rate correlates with the intake air amount and engine speed of the internal combustion engine 1, the exhaust flow rate used for calculating the reference slip-through rate Kst is the detected value (intake air amount Ga) of the air flow meter 8 and the engine speed. May be substituted. Since the engine exhaust PM amount correlates with the fuel injection amount and load (accelerator opening) of the internal combustion engine 1, the fuel injection amount and the accelerator opening are used as the engine exhaust PM amount used for calculating the reference slip-through rate Kst. Also good. Further, as the PM deposition amount Gpmc in the PM trapper 3, the PM deposition amount Gpmc calculated in step S201 can be used.

  In step S206, the ECU 6 calculates a difference ΔK between the PM pass-through rate Kpm calculated in step S204 and the reference pass-through rate Kst calculated in step S205.

  In step S207, the ECU 6 determines whether or not the absolute value of the difference ΔK calculated in step S206 is greater than the reference value C3.

  The reference value C3 may be a fixed value, but is preferably a variable value that is changed according to the PM accumulation amount in the PM trapper 3. This is because the PM slipping rate when the PM trapper 3 is normal varies depending on the PM deposition amount. For example, when the PM trapper 3 is normal, the PM slipping rate Kpm decreases as the PM accumulation amount increases. Therefore, it is preferable that the reference value C3 is determined so as to decrease as the PM deposition amount Gpmc increases as shown in FIG.

  When an affirmative determination is made in S207 (| ΔK |> C3), the amount of PM that has passed through the PM trapper 3 can be considered to be more or less than when the PM trapper 3 is normal.

  In this case, the ECU 6 proceeds to step S208 and sets “1” to the PM trapper failure flag. The PM trapper failure flag is a storage area set in advance in the RAM or backup RAM of the ECU 6, and is set to “1” when it is determined in this routine that the PM trapper 3 has failed. If it is determined that the trapper 3 has not failed, it is reset to “0”.

  On the other hand, if a negative determination is made in step S207, the ECU 6 determines that the PM trapper 3 is normal and proceeds to step S209. In step S209, the PM trapper failure flag is reset to “0” and the execution of this routine is terminated.

  As described above, when the ECU 6 executes the failure detection routine, the failure determination means, the PM accumulation amount estimation means, and the reference value setting means according to the present invention are realized. As a result, it is possible to accurately detect a failure of the PM trapper.

  Incidentally, the incoming PM amount Pi and the outgoing PM amount Po are directly detected by the incoming PM sensor 4 and the outgoing PM sensor 5, but the oxidized PM amount Pc is estimated from the bed temperature of the oxidation catalyst. Therefore, there is a possibility that the estimated value Gpmc of the PM deposition amount includes some errors due to the estimation of the oxidized PM amount Pc. If the estimated value Gpmc of the PM deposition amount includes an error, the reference value C3 determined based on the estimated value Gpmc may be an inappropriate value for the actual PM deposition amount.

  On the other hand, if the above-described failure determination process is performed when the change in the PM slipping rate becomes small with respect to the change in the PM accumulation amount, the reference value C3 is appropriate even if some error occurs in the estimated value of the PM accumulation amount. It is possible to prevent a significant deviation from the correct value.

  For example, when the PM deposition amount of the PM trapper 3 increases, the PM slipping rate decreases, and the PM slipping rate change amount decreases with respect to the PM deposition amount change amount. Therefore, if the failure detection process is performed when the PM accumulation amount is large to some extent, it is possible to prevent the reference value C3 from becoming an inappropriate value even if a slight error occurs in the estimated value of the PM accumulation amount. Accordingly, it is possible to suppress a decrease in failure detection accuracy.

  Next, a second embodiment of the present invention will be described with reference to FIGS. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.

  The difference between the first embodiment described above and the present embodiment is that in the first embodiment described above, the PM trapper is utilized by using the incoming PM sensor 4 and the outgoing PM sensor 5 provided upstream and downstream of the PM trapper 3. In this embodiment, the PM trapper is detected using the differential pressure sensor 11 that detects the differential pressure upstream and downstream of the PM trapper 3 and the input PM sensor 4 provided upstream of the PM trapper 3. 3 is that the failure detection is performed.

  FIG. 4 shows a schematic configuration of an internal combustion engine to which the failure detection apparatus according to this embodiment is applied. In FIG. 4, the same components as those in the first embodiment are denoted by the same reference numerals.

  In FIG. 4, a differential pressure sensor 11 for detecting a differential pressure between an exhaust pressure upstream of the PM trapper 3 and a downstream exhaust pressure is attached to the exhaust pipe 2, and a detection signal from the differential pressure sensor 11 is sent to the ECU 6. It is designed to be entered. Other configurations are the same as those of the first embodiment described above.

  FIG. 5 is a flowchart showing a failure detection routine in this embodiment. This failure detection routine is a routine that is repeatedly executed by the ECU 6 at predetermined intervals.

  In the failure detection routine of FIG. 5, the ECU 6 first determines in step S501 whether or not the determination execution flag is “1”. The determination execution flag is a storage area set in advance in the RAM or backup RAM of the ECU 6, and is set to “1” when the failure determination execution condition is satisfied, and is reset to “0” when the failure determination execution condition is not satisfied. The

  If a negative determination is made in step 501, the ECU 6 executes a reference state setting process in steps S <b> 502 to S <b> 506.

  First, in step S502 and step S503, the ECU 6 determines whether or not a failure determination execution condition is satisfied. Specifically, the ECU 6 determines whether or not the catalyst bed temperature Tc of the oxidation catalyst is higher than a predetermined temperature C1 in step S502, and then determines whether or not the intake air amount Ga is higher than a predetermined amount C2 in step S503. To do. The processes in steps S502 and S503 are the same as those in steps S202 and S203 in FIG.

  If a negative determination is made in at least one of step S502 and step S503 described above, the ECU 6 regards that the failure determination execution condition is not satisfied, and proceeds to step S509.

  In step S509, the ECU 6 resets the above-described determination execution flag to “0”. After completing the process of step S509, the ECU 6 skips the processes of steps S504 to S506, which will be described later, and proceeds to step S507.

  On the other hand, if an affirmative determination is made in both step S502 and step S503 described above, the ECU 6 regards that the failure determination execution condition is satisfied, and executes the processing from step S504.

  In step S504 to step S505, the ECU 6 stores the current state of the PM trapper 3 in the RAM or the backup RAM as a reference state.

Specifically, the ECU 6 first stores the detection signal (differential pressure) Pst of the differential pressure sensor 11 in the RAM or the backup RAM as the reference differential pressure Pst in step S504. Subsequently, the ECU 6 sets the estimated value Gpmc of the PM accumulation amount to 0 in step S505.

  When the reference state of the PM trapper 3 is stored in step S504 and step S505 described above, the ECU 6 proceeds to step S506 and sets “1” in the determination execution flag.

  In step S507, the ECU 6 resets the temporary failure flag to “0”. The temporary failure flag is a storage area set in the RAM of the ECU 6 or the backup RAM, and is set to “1” when it is determined in the failure determination process described later that the PM trapper 3 may be broken. .

  Subsequently, the ECU 6 resets the PM trapper failure flag to “0” in step S508, and temporarily ends the execution of this routine. The PM trapper failure flag is a storage area set in the RAM or backup RAM of the ECU 6, and is set to “1” when it is determined that the PM trapper 3 has failed by failure determination processing described later.

  When the execution of this routine is completed with the determination execution flag set to “1”, the ECU 6 makes an affirmative determination (determination execution flag = 1) in step S501 at the next execution of the routine.

  If an affirmative determination is made in step S501, the ECU 6 executes a failure determination process in steps S510 to S517. First, in step S510, the ECU 6 calculates an increase amount of the PM accumulation amount in a period from the above-described reference state to the current time (hereinafter referred to as “failure determination period”).

  At this time, since the estimated value Gpmc of the PM accumulation amount when the PM trapper 3 is in the reference state in step S505 described above is set to “0”, the ECU 6 performs the same method as step S201 in FIG. By calculating the estimated value Gpmc of the PM deposition amount, the calculation result Gpmc can be regarded as the increase amount of the PM deposition amount.

  However, since the internal combustion engine 1 of the present embodiment does not include the output PM sensor, it is necessary to estimate the output PM amount Po. The output PM amount Po when the PM trapper 3 is normal is the input PM amount Pi and the PM accumulation amount (the total amount of PM actually deposited on the PM trapper 3, hereinafter referred to as “total PM accumulation amount”). ). Accordingly, the relationship between the output PM amount Po, the input PM amount Pi, and the total PM deposition amount is experimentally obtained in advance, so that the estimated value of the input PM amount Pi and the total PM deposition amount is used as a parameter. Po can be specified.

  Since the estimated value of the total PM accumulation amount includes some errors, it is preferable to estimate the output PM amount Po when the estimation error of the total PM accumulation amount is difficult to be reflected in the output PM amount. As a case where the estimation error of the total PM deposition amount is difficult to be reflected in the output PM amount, a case where the total PM deposition amount is large to some extent can be exemplified. This is because when the total PM accumulation amount increases to some extent, the trapping ability of the PM trapper 3 becomes substantially uniform, and the output PM amount hardly changes even if the total PM accumulation amount varies somewhat.

  In addition, since the relationship between the total PM deposition amount and the PM slipping rate can be obtained experimentally in advance, the PM slipping rate is calculated from the total PM deposition amount, and is calculated from the calculated PM slipping rate and the input PM amount Pi. The PM amount Po can also be calculated.

When the increase amount Gpmc of the PM accumulation amount during the failure determination period is calculated in this way, the ECU 6 proceeds to step S511. In step S511, the ECU 6 determines whether or not the PM accumulation amount increase amount Gpmc is greater than a predetermined amount C4.

  The predetermined amount C4 is an amount by which the detection signal of the differential pressure sensor 11 can be clearly changed (increased) when the PM accumulation amount increases by the predetermined amount C4 in the normal PM trapper 3, and is obtained experimentally in advance. .

  If a negative determination is made in step S511 (Gpmc ≦ C4), the ECU 6 once ends the execution of this routine. On the other hand, when an affirmative determination is made in step S511 (Gpmc> C4), the ECU 6 proceeds to step S512.

  In step S512, the ECU 6 calculates a difference ΔP (= P−Pst) between the reference differential pressure Pst stored in the RAM or the backup RAM in step S504 and the current detected value P of the differential pressure sensor 11.

  In step S513, the ECU 6 determines whether or not the difference ΔP calculated in step S512 is smaller than a predetermined value C5. The predetermined value C5 is a value determined based on the amount of increase in the differential pressure when the PM accumulation amount increases by the predetermined amount C4 in a normal PM trapper.

  If a negative determination is made in step S513 (ΔP ≧ C5), the ECU 6 considers that the PM trapper 3 has not failed and ends the execution of this routine.

  On the other hand, if an affirmative determination is made in step S513 (ΔP <C5), the ECU 6 proceeds to step S514. In step S514, the ECU 6 determines whether or not “1” is set in the temporary failure flag.

  If a negative determination is made in step S514 (temporary failure flag = 0), the ECU 6 executes PM regeneration processing of the PM trapper 3 in step S515, and then sets “1” in the temporary failure flag in step S516.

  Although a method of immediately determining that the PM trapper 3 is out of order when an affirmative determination is made in step S513 described above can be considered, an estimation error of the total PM accumulation amount, an estimation error of an increase amount of the PM accumulation amount during the failure determination period Even if the PM trapper 3 is normal, the difference ΔP is a predetermined value due to various factors such as a difference in pressure difference caused by a difference in the PM deposition site in the PM trapper 3 or a measurement error of the differential pressure sensor 11. The case where it becomes smaller than C5 is assumed.

  In order to prevent erroneous determination due to the factors as described above, the ECU 6 may not have determined that the PM trapper 3 has failed immediately when an affirmative determination is made in step S513, and the PM trapper 3 may have failed. It was decided to keep the judgment (provisional failure) that there is.

  Further, the ECU 6 regenerates and removes the PM deposited on the PM trapper 3 and then performs a failure determination process after step S511 to suppress the occurrence of erroneous determination due to the difference in the PM deposition site. ing.

  When the process after step S511 is executed again in the state where the temporary failure flag is set to “1”, if an affirmative determination is made again (ΔP <C5) in step S513, the ECU 6 determines that the difference ΔP is a predetermined value. The process proceeds to step S517, assuming that the factor smaller than the value C5 is the failure of the PM trapper 3. In step S517, the ECU 6 sets “1” in the failure flag.

According to the embodiment described above, the difference ΔP between two different states is used as a parameter P
Since the failure determination of the M trapper 3 is performed, it is possible to perform an accurate failure determination without considering various errors included in the differential pressure.

  In the present embodiment, the PM slipping rate may be obtained from the estimated value of the total PM deposition amount in the process of estimating the output PM amount, but the estimated value of the total PM deposition amount may include an error. . If the estimated value of the total PM deposition amount includes an error, the PM slipping rate may become an inappropriate value.

  FIG. 6 is a diagram showing the relationship between the PM deposition amount and the PM slipping rate. The horizontal axis in FIG. 6 indicates the total PM deposition amount, and the vertical axis indicates the PM slipping rate.

  In FIG. 6, when the total PM deposition amount belongs to the region B, the amount of change in the PM slipping rate with respect to the total PM deposition amount is larger than when the total PM deposition amount belongs to the region A (<B). Is getting smaller. That is, when the total PM deposition amount increases to some extent, the PM slip-through rate hardly changes even if the total PM deposition amount slightly changes.

  Therefore, if the PM slipping rate is calculated when the total PM deposition amount belongs to the region B in FIG. 6, the PM slipping rate is inappropriate even if the estimated value of the total PM deposition amount includes an error. It can be suppressed from becoming a value.

  On the other hand, in the relationship between the differential pressure between the upstream and downstream of the PM trapper 3 and the total PM deposition amount, the change amount of the differential pressure with respect to the change of the total PM deposition amount becomes smaller as the total PM deposition amount increases. FIG. 7 is a diagram showing the relationship between the total PM deposition amount and the differential pressure. The horizontal axis in FIG. 7 indicates the total PM deposition amount, and the vertical axis indicates the differential pressure.

  In this embodiment, the failure of the PM trapper is determined based on the characteristic that the increase amount of the corresponding differential pressure differs between the normal PM trapper and the failed PM trapper even when the PM accumulation amount increases by the same amount. Judgment.

  The difference between when the PM trapper is normal and when it is malfunctioning appears more prominently in a region (approximately the region indicated by C in FIG. 7) where the amount of increase in the differential pressure with respect to the increment of the PM deposition amount is larger. In a state where the accumulation amount belongs to the region C, the PM trapper failure can be determined with higher accuracy.

  Therefore, if the PM trapper failure determination process according to the present embodiment is executed when the total PM accumulation amount belongs to the region B in FIG. 6 and the region C in FIG. 7, the failure detection accuracy is further improved. It becomes possible.

  The above-described embodiment is an example for explaining the present invention, and various modifications can be made to the above-described embodiment without departing from the spirit of the present invention.

1 is a diagram illustrating a schematic configuration of an internal combustion engine in Embodiment 1. FIG. 3 is a flowchart illustrating a failure detection routine according to the first embodiment. It is a figure which shows the map for defining the reference value in Example 1. FIG. FIG. 3 is a diagram showing a schematic configuration of an internal combustion engine in a second embodiment. 7 is a flowchart illustrating a failure detection routine according to a second embodiment. It is a figure which shows the relationship between PM deposit amount of PM trapper in Example 2, and PM slip-through rate. It is a figure which shows the relationship between PM deposition amount of PM trapper in Example 2, and differential pressure | voltage upstream and downstream of PM trapper.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Exhaust pipe 3 ... PM trapper 4 ... PM sensor 5 ... PM sensor 6 ... ECU
7 ... Crank position sensor 8 ... Air flow meter 9 ... Water temperature sensor 10 ... Exhaust temperature sensor 11 ... Differential pressure sensor 12 ... Oxidation catalyst

Claims (4)

A PM trapper failure detection device for detecting a failure of a PM trapper provided in an exhaust passage of an internal combustion engine,
An incoming PM sensor for detecting the amount of particulate matter flowing into the PM trapper;
A PM sensor for detecting the amount of particulate matter flowing out of the PM trapper;
Failure determination means for determining that the PM trapper is in failure when the ratio of the detection value by the output PM sensor to the detection value by the input PM sensor exceeds a predetermined reference value;
PM deposition amount estimation means for estimating a deposition amount of particulate matter in the PM trapper based on a detection value by the input PM sensor and a detection value by the output PM sensor;
A reference value setting means for determining the reference value in accordance with the accumulation amount estimated by the PM accumulation amount estimation means;
A PM trapper failure detection apparatus comprising: 2. The reference value setting means according to claim 1 , wherein the reference value setting means sets the reference value lower as the accumulation amount estimated by the PM accumulation amount estimation means increases, and the accumulation amount estimated by the PM accumulation amount estimation means decreases. A PM trapper failure detection apparatus, wherein the reference value is set high. A PM trapper failure detection device for detecting a failure of a PM trapper provided in an exhaust passage of an internal combustion engine,
An incoming PM sensor for detecting the amount of particulate matter flowing into the PM trapper;
A differential pressure sensor for detecting a differential pressure between an exhaust pressure upstream of the PM trapper and an exhaust pressure downstream of the PM trapper;
PM deposition amount estimation means for estimating the amount of particulate matter deposited on the PM trapper based on the detection value by the input PM sensor;
A failure of the PM trapper is determined based on an increase amount of the differential pressure detected by the differential pressure sensor during a period until the accumulation amount estimated by the PM accumulation amount estimating means increases by a predetermined amount from a predetermined reference amount. Failure determination means;
A PM trapper failure detection apparatus comprising: 4. The PM trapper failure detection device according to claim 3 , wherein the failure determination means determines that the PM trapper is in failure when the increase amount of the differential pressure is less than a predetermined increase amount.

Images