JP2007315275A - Exhaust gas purifying filter failure diagnosis device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means using a PM sensor for the failure diagnosis of a DPF. <P>SOLUTION: This exhaust gas purifying filter failure diagnosis device comprises an exhaust gas purifying filter provided in an exhaust passage of an internal combustion engine for trapping particulates contained in exhaust gas from the internal combustion engine, and a particulate amount detecting sensor provided on the downstream side of the exhaust gas purifying filter for detecting a particulate amount in the exhaust gas. A failure of the exhaust gas purifying filter is determined in accordance with the particulate amount on the downstream side of the exhaust gas purifying filter, detected by the particulate amount detecting sensor (S106). The trapping efficiency of the exhaust gas purifying filter is considered when determining the failure (S102, S202). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust purification filter failure diagnosis apparatus and method.

  Conventionally, a diesel engine has been equipped with a diesel particulate filter (Diesel Particulate Filter; hereinafter referred to as “DPF”) that collects particulates (hereinafter referred to as “PM”) in the exhaust passage as an exhaust purification measure. Yes. If the DPF continues to collect PM, it will eventually become clogged. Therefore, when PM is accumulated to some extent, the exhaust temperature is raised, and the accumulated PM is forcibly burned and removed to regenerate the DPF.

  As a technique for determining whether or not to regenerate the DPF by detecting clogging of the DPF, a technique for determining based on a differential pressure (front-rear differential pressure) between the inlet and the outlet of the DPF is known (for example, Patent Documents). 1).

There is also known a technique in which a sensor for detecting particulate accumulation is provided on the upstream side of the DPF, and the regeneration start timing of the DPF is determined based on the detection value of the sensor (for example, Patent Documents 2 and 3). reference)
JP 2002-97930 A JP-A-8-68310 JP-A-8-68313

  By the way, when the DPF main body is damaged or the like, PM discharged from the engine cannot be collected. If you continue to drive in that case, emissions may deteriorate and adversely affect the environment. For this reason, when the DPF main body is damaged or the like, it is necessary to notify the driver at an early stage, and to suppress the deterioration of the emission by taking measures such as promptly replacing the DPF.

  However, conventionally, a technique for diagnosing a DPF failure has not been known, and it is therefore desirable to take measures against this. Therefore, it is conceivable to perform a DPF function diagnosis by providing a sensor for detecting the PM amount downstream of the DPF and monitoring the amount of PM discharged downstream of the DPF. However, since the collection efficiency of the DPF is low, it is not possible to identify whether PM is discharged, and there is a possibility that the DPF is erroneously determined to be faulty although the DPF function is normal.

  Accordingly, an object of the present invention is to provide a failure diagnosis of an exhaust purification filter that can accurately perform a failure diagnosis of a DPF.

  An exhaust purification filter that is provided in an exhaust passage of the internal combustion engine and collects particulates contained in exhaust gas discharged from the internal combustion engine, and an amount of particulates that is provided in the exhaust gas provided downstream of the exhaust purification filter A failure of the exhaust gas purification filter is determined based on a particulate amount detection sensor for detecting the amount of particulate matter and a particulate amount downstream of the exhaust gas purification filter detected by the particulate amount detection sensor. And in the case of this failure determination, the structure which considered the collection efficiency of the exhaust gas purification filter was employ | adopted.

  As described above, in consideration of the collection efficiency of the exhaust gas purification filter at the time of failure determination, the influence can be suppressed even if PM is discharged downstream of the DPF due to the low collection efficiency of the DPF. Therefore, the failure diagnosis of the DPF can be executed with high accuracy.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a schematic diagram of a DPF failure diagnosis apparatus according to the present invention. The diesel engine 1 includes an exhaust passage 2. In the exhaust passage 2, a DPF 3 and a soot (SOOT; soot particle constituting PM) sensor 11 are disposed in order from the upstream. The DPF 3 collects PM in the exhaust gas by passing the exhaust gas in the exhaust passage 2 through a porous filter material. The soot sensor 11 detects the amount of PM in the exhaust discharged from the DPF 3.

  As the soot sensor 11, any known soot sensor such as those disclosed in Japanese Patent Application Laid-Open Nos. 8-68313 and 2005-337782 may be applied. The soot sensor disclosed in Japanese Patent Application Laid-Open No. 8-68313 detects the amount of PM in the exhaust gas by measuring the charge that electrically charged PM acts on the measurement electrode. The soot sensor disclosed in Japanese Patent Laid-Open No. 2005-337782 covers two oxygen sensors with porous bodies having different diffusion resistances, and compares the respective oxygen concentrations to detect the amount of PM in the exhaust gas. However, the present invention is not limited thereto, and the PM amount in the exhaust gas can also be detected by detecting the change in the vibration frequency of the measurement membrane due to the change in the PM amount in the exhaust gas.

  When the DPF 3 is functioning normally, the exhaust gas from which PM is removed is discharged from the DPF 3. Therefore, PM is hardly contained in the exhaust gas discharged from the DPF 3.

  On the other hand, when the DPF 3 is broken or melted to cause a functional failure, PM leaks from the DPF 3. Therefore, PM is contained in the exhaust discharged from the DPF 3.

  Therefore, in the present invention, the controller 10 performs failure diagnosis of the DPF 3 based on the detection signal (PM amount) of the soot sensor 11. The controller 10 includes a microcomputer having a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), a nonvolatile memory 20 and an input / output interface (I / O interface).

  Further, the controller 10 estimates the PM accumulation amount in the DPF 3. Therefore, the controller 10 includes an air flow meter 12 that detects the intake air flow rate of the diesel engine 1, a rotation speed sensor 13 that detects the rotation speed of the diesel engine 1, and a load sensor 14 that detects the load of the diesel engine 1. A detection signal is input. The load of the diesel engine 1 can be represented by the accelerator pedal depression amount provided in the vehicle or the fuel injection amount Q of the diesel engine 1.

  Further, the controller 10 regenerates the DPF 3 when the accumulated amount of PM in the DPF 3 reaches a predetermined amount. Therefore, the controller 10 raises the exhaust temperature of the diesel engine 1 and burns the PM accumulated in the DPF 3. In order to raise the exhaust temperature of the diesel engine 1, any known method such as a method based on fuel injection control such as delay of fuel injection timing or execution of post injection may be applied.

  By the way, in order to suppress the exhaust pressure loss and improve the engine output, it is desirable to make the filter of the DPF 3 coarse. However, if the filter is coarsened, the collection efficiency of the DPF 3 will deteriorate for a while after the end of regeneration. This is because for a while after completion of regeneration, PM having a particle size smaller than the eyes of the filter passes through the filter. Note that, after a while after the regeneration, PM having a particle size smaller than that of the filter is also collected. This is because, when PM having a particle size larger than the eyes of the filter is collected after the regeneration is completed, the eyes of the filter are buried accordingly.

  In this way, PM having a particle size smaller than the mesh of the filter passes through the filter until a certain amount (reference deposition amount) of PM is deposited after the regeneration is completed. Therefore, the collection efficiency of the DPF 3 is deteriorated during the period from the end of regeneration until the reference deposition amount of PM is deposited. After that, when the reference accumulation amount of PM is deposited and the filter eyes are filled, PM having a particle size smaller than the filter eyes is also collected. Therefore, the collection efficiency of DPF 3 is recovered, and the PM collection efficiency reaches the failure diagnosis permission efficiency.

  When the amount of accumulated PM in the DPF reaches the diagnosis permission efficiency, if the DPF 3 functions normally, the amount of PM discharged to the downstream side of the DPF 3 is extremely small. On the other hand, when an abnormality occurs due to damage to the DPF 3 main body, the amount of PM discharged downstream of the DPF 3 becomes large. Therefore, it is possible to easily determine whether the DPF 3 is normal or abnormal based on the detection signal of the soot sensor 11.

  However, as described above, when the collection efficiency of DPF 3 is poor, that is, when the amount of PM deposited on DPF 3 is small, PM is discharged to the downstream side of DPF 3. For this reason, it is difficult to determine whether the DPF 3 is actually abnormal or whether the DPF 3 is normal and is simply a region with poor collection efficiency based on the detection signal of the soot sensor 11.

  Therefore, in the present invention, the collection efficiency of the DPF 3 is estimated based on the operating state of the engine. While the collection efficiency is low, the failure diagnosis of the DPF 3 is prohibited in order to prevent the PM passing through the downstream side of the DPF 3 from being erroneously diagnosed as a functional failure. Below, the specific content of such a failure diagnosis is demonstrated.

  FIG. 2 is a flowchart for explaining the operation of the DPF failure diagnosis according to the first embodiment of the present invention. Hereinafter, the DPF failure diagnosis routine executed by the controller 10 will be described with reference to FIG. The controller 10 repeatedly executes this routine at a predetermined calculation cycle (for example, 10 milliseconds) during operation of the diesel engine 1.

  In step S <b> 101, the controller 10 determines whether PM is discharged from the diesel engine 1. In this embodiment, when fuel injection is performed, it is determined that PM is discharged from the diesel engine 1. The controller 10 proceeds to step S102 when fuel injection is being performed, and ends the current process when fuel injection is not being performed.

  In step S102, the controller 10 calculates the amount of PM accumulated in the DPF by the following method.

Based on the fuel injection amount Q and the rotational speed NE of the diesel engine 1, the controller 10 refers to a characteristic map stored in advance in the ROM and refers to a PM accumulation amount ΔP per unit time.
Find M. The characteristic map of the PM deposition amount per unit time is set in advance through experiments. By setting the unit time equal to the routine calculation cycle in advance, ΔP
M is the PM accumulation amount during the period from the previous routine execution to the current routine execution. Then, the controller 10 adds the PM accumulation amount ΔPM per unit time obtained in the current routine execution to the previous value PMaz of the PM accumulation amount stored in the nonvolatile memory 20, thereby obtaining the DPF.
The PM accumulation amount PMa is calculated.

If the operating condition of the diesel engine 1 is an operating condition in which the PM in the DPF 3 automatically burns, ΔPM may be obtained by subtracting the PM removal amount according to the operating condition. Examples of such operating conditions include operating conditions in which the exhaust temperature rises and the DPF 3 can be regenerated, such as at high speed and high load.

  In step S103, the controller 10 determines whether or not the PM accumulation amount PMa in the DPF exceeds the reference accumulation amount. That is, it is determined whether the PM collection efficiency has reached the failure diagnosis permission efficiency. This is because when the PMa does not exceed the reference deposition amount, the DPF collection efficiency is poor and there is a possibility of erroneous diagnosis.

  In step S103, the controller 10 proceeds to step S104 if the PM accumulation amount PMa in the DPF does not exceed the reference accumulation amount, and proceeds to step S105 if it exceeds.

  In step S104, the controller 10 prohibits DPF failure diagnosis. When the PM accumulation amount PMa in the DPF does not exceed the reference accumulation amount, the DPF collection efficiency is deteriorated as described above. Therefore, it is possible to prevent a fault diagnosis by prohibiting the fault diagnosis during this period, and to perform a fault diagnosis with high accuracy.

  In step S105, the controller 10 starts a DPF failure diagnosis.

In step S106, the controller 10 determines whether or not the output value I SOOT of the _soot sensor 11 exceeds the reference output value. This reference output value is variable according to the operating conditions. For example, the controller 10 determines the reference output value by the following method.

  The controller 10 obtains the exhaust gas flow rate from an exhaust flow rate map set in advance through experiments according to the engine operating conditions. Based on the exhaust flow rate, the controller 10 determines a reference output value from a characteristic table shown in FIG. FIG. 3 is a table for setting a reference output value from the exhaust flow rate. As shown, the reference output value increases as the exhaust flow rate increases. Furthermore, if the exhaust gas flow rate is the same, the reference output value increases as the PM accumulation amount PMa in the DPF increases. The magnitude of the PM deposition amount is determined based on the PM deposition amount PMa.

  The reference output value is not limited to the above method, and may be determined by the following method, for example. FIG. 4 is a table for setting a reference output value from the engine speed. Based on the engine speed, the controller 10 determines a reference output value from a characteristic table shown in FIG. As shown in this table, the reference output value increases as the engine speed increases. Furthermore, if the engine speed is the same, the reference output value increases as the PM emission amount discharged from the diesel engine 1 increases. The PM emission amount discharged from the diesel engine 1 may be obtained from a PM emission amount map set in advance through experiments in accordance with engine operating conditions.

In step S106, when the output value I SOOT of the _soot sensor 11 is within the reference output value, that is, when the PM contained in the exhaust discharged from the _{DPF 3} is equal to or less than the reference value, the controller 10 proceeds to step S107. .

In step S106, when the output value ISOOT of the _soot sensor 11 exceeds the reference output value, that is, when PM exceeding the reference value is included in the exhaust gas discharged from the DPF 3, the controller 10 proceeds to step S108. Migrate processing.

  In step S107, the controller 10 determines that the DPF 3 is functioning normally.

  In step S108, the controller 10 determines that the DPF 3 has a functional failure.

  FIG. 5 is a graph showing the relationship between the amount of PM deposited on DPF 3 and the PM collection efficiency. As described above, the PM having a particle size smaller than the eyes of the filter passes through the filter until a certain amount (reference deposition amount) of PM is deposited after the regeneration is completed. Therefore, as shown by hatching in FIG. 5, the collection efficiency of the DPF 3 is deteriorated during the period from the end of regeneration until the reference deposition amount of PM is deposited. After that, when the reference accumulation amount of PM is deposited and the filter eyes are filled, PM having a particle size smaller than the filter eyes is also collected. Therefore, the collection efficiency of DPF 3 is recovered, and the PM collection efficiency reaches the failure diagnosis permission efficiency. If the PM accumulation amount PMa in the DPF exceeds the reference accumulation amount, the DPF collection efficiency is almost 100% as shown in FIG. In the present embodiment, the reference deposition amount is set to about 10% of the PM collection capacity of the DPF 3, but it is not limited thereto.

  In the region where the PM collection efficiency is poor as shown in FIG. 5 (the region where the PM collection efficiency is less than the failure diagnosis permission efficiency), the exhaust gas containing a relatively large amount of PM is discharged from the DPF 3. Therefore, when the failure diagnosis of the DPF 3 is performed in this region, the controller 10 may diagnose that the DPF 3 is a functional failure even though the DPF 3 has not caused the functional failure. Therefore, in the present invention, in such an area where PM collection efficiency is poor, DPF failure diagnosis is prohibited to prevent erroneous diagnosis.

  According to this embodiment described above, failure diagnosis of the DPF 3 can be performed, and the failure can be detected reliably and early. Further, failure diagnosis of the DPF 3 is prohibited during a period when the collection efficiency of the DPF 3 is deteriorated after the regeneration is completed until the reference amount of PM is deposited on the DPF 3. Therefore, it is possible to prevent erroneous diagnosis of failure diagnosis and perform failure diagnosis with high accuracy.

(Second Embodiment)
Next, the DPF failure diagnosis operation according to the second embodiment of the present invention will be described. The second embodiment of the present invention is that the failure diagnosis is prohibited until the predetermined time is reached after the regeneration is completed, and the failure diagnosis is prohibited until the reference amount of PM is accumulated in the DPF 3 after the regeneration is completed. Is different. The difference will be described below. Note that in the second embodiment, the same reference numerals are used for portions that perform the same functions as those in the first embodiment described above, and redundant descriptions are omitted as appropriate.

  FIG. 6 is a flowchart for explaining the operation of the DPF failure diagnosis according to the second embodiment of the present invention. Hereinafter, the DPF failure diagnosis routine according to the second embodiment of the present invention executed by the controller 10 will be described with reference to FIG.

In step S202, the controller 10 calculates an elapsed time (hereinafter referred to as “counter value”) CTa from the end of reproduction. The fuel cut time is excluded from the counter value CTa (step S101). The controller 10 calculates CTa by adding the calculation cycle Δt to the previous value CTaz of the counter value stored in the nonvolatile memory 20. The controller 10 returns CTa to 0 with the end of regeneration of the DPF 3 as a trigger, and starts counting again.

  In step S203, the controller 10 determines whether or not the counter value CTa exceeds the reference value. The reference value is set by the following method.

  FIG. 7 is a characteristic diagram showing the PM accumulation amount in the DPF with respect to the elapsed time under the operating condition in which the PM emission amount from the diesel engine 1 becomes the minimum value. This characteristic diagram is set in advance through experiments. Based on this characteristic diagram, in the operating condition where the PM emission amount from the diesel engine 1 is the minimum value, the time until the reference deposition amount of PM is deposited on the DPF 3 is obtained in advance. When the time determined from this characteristic diagram has elapsed, PM equal to or greater than the reference deposition amount is necessarily deposited in the DPF 3.

  Therefore, in this embodiment, the time obtained in this way is set as a reference value and stored in the ROM in advance. If the counter value CTa exceeds the reference value, it can be estimated that the reference accumulation amount of PM has accumulated in the DPF 3. That is, it can be estimated that the PM collection efficiency has reached the failure diagnosis permission efficiency. Conversely, if the counter value does not exceed the reference value, it can be estimated that the reference accumulation amount of PM is not accumulated in the DPF 3. Therefore, in step S103, the controller 10 prohibits the DPF failure diagnosis if the counter value CTa does not exceed the reference value (step S104), and permits the DPF failure diagnosis if it exceeds (step S105). Thus, by diagnosing failure diagnosis during a period when the collection efficiency of the DPF is deteriorated, erroneous diagnosis can be prevented and highly accurate failure diagnosis can be performed.

  According to the present embodiment described above, failure diagnosis can be performed when the DPF 3 has a functional failure, as in the first embodiment. At that time, failure diagnosis of the DPF 3 is prohibited during a period in which the collection efficiency of the DPF 3 is deteriorated after the regeneration is completed until the reference amount of PM is deposited on the DPF 3. Therefore, it is possible to prevent erroneous diagnosis of failure diagnosis and perform failure diagnosis with high accuracy.

  Note that the present invention is not limited to the above-described embodiment, and it is obvious that various modifications can be made within the scope of the technical idea. For example, in the present invention, as a method of calculating the PM accumulation amount in the DPF 3, an operation history method for calculating the PM accumulation amount by integrating the PM accumulation amount per unit time determined by the operation condition of the diesel engine 1 is integrated. Applied. However, the present invention is not limited to this method, and the PM accumulation amount may be estimated from the differential pressure upstream and downstream of the DPF 3 or the absolute pressure near the inlet of the DPF 3 according to the exhaust flow rate determined by the operating conditions of the diesel engine 1. When the exhaust gas flow rate is constant, the differential pressure or the absolute pressure increases as the PM deposition amount increases. Therefore, the PM accumulation amount can be obtained from a map set in advance through experiments from the relationship between the exhaust gas flow rate and the differential pressure or absolute pressure. In this case, a detection signal of a differential pressure sensor that detects a differential pressure upstream and downstream of the DPF 3 or a detection signal of a pressure sensor that detects a pressure upstream of the DPF 3 is input to the controller 10.

  In the present embodiment, the conditions for low DPF3 collection efficiency are specified by the estimated amount of DPF3 deposition or the elapsed time from the end of regeneration. However, the present invention is not limited to this, and a soot sensor is separately provided upstream of the DPF3. You may identify the conditions with low collection efficiency by detecting PM deposition amount of DPF3.

  In the present embodiment, the DPF 3 failure diagnosis is prohibited under the condition that the DPF 3 collection efficiency is low. However, even if the diagnosis is once executed and the diagnosis result is reset at a predetermined timing after the failure is determined. good.

In addition, when the failure diagnosis of the _{DPF 3} is executed under the condition that the collection efficiency of the DPF 3 is low, the output reference value for determining the failure of the _{DPF 3 with} respect to the output value I SOOT of the _soot sensor 11 may be corrected. Specifically, the output reference value is corrected to a large value. This makes it difficult to determine the failure of the DPF 3 under conditions where the collection efficiency is low, and the failure can be diagnosed when the degree of failure of the DPF 3 is severe and a large amount of PM is discharged downstream of the DPF 3.

It is a schematic diagram of a DPF failure diagnostic device. It is a flowchart explaining the operation | movement of the DPF failure diagnosis by 1st Embodiment. It is a table which sets a standard output value from exhaust flow. It is a table which sets a standard output value from engine rotation speed. It is the figure which showed the relationship between PM deposit amount of DPF, and PM collection efficiency. It is a flowchart explaining the operation | movement of the DPF failure diagnosis by 2nd Embodiment. It is the characteristic figure which showed the PM deposit amount in DPF with respect to the elapsed time on the driving | running condition in which PM emission amount from a diesel engine becomes the minimum value.

Explanation of symbols

1 Diesel engine (internal combustion engine)
2 Exhaust passage 3 DPF (Exhaust gas purification filter)
11 PM sensor (particulate amount detection sensor)
S102, S203 Collection efficiency estimation means S103, S203 Failure diagnosis prohibition means S106 Failure diagnosis means

Claims (10)

An exhaust purification filter that is provided in an exhaust passage of the internal combustion engine and collects particulates contained in exhaust gas discharged from the internal combustion engine;
A particulate quantity detection sensor that is provided downstream of the exhaust purification filter and detects the particulate quantity contained in the exhaust;
Failure diagnosis means for determining a failure of the exhaust purification filter based on the particulate amount downstream of the exhaust purification filter detected by the particulate quantity detection sensor;
The failure diagnosis device of the exhaust gas purification filter is characterized in that the failure diagnosis means considers the collection efficiency of the exhaust gas purification filter. 2. The exhaust gas purification according to claim 1, further comprising failure diagnosis prohibiting means for prohibiting failure diagnosis of the exhaust purification filter by the failure diagnosis means under a condition in which the collection efficiency of the exhaust purification filter is lower than a predetermined value. Filter fault diagnosis device. A collection efficiency estimating means for estimating the collection efficiency of the exhaust gas purification filter based on the operating condition of the internal combustion engine;
The failure diagnosis prohibiting means prohibits failure diagnosis of the exhaust purification filter by the failure diagnosis means when the collection efficiency of the exhaust purification filter estimated by the collection efficiency estimation means falls below a predetermined value. The failure diagnosis device for an exhaust purification filter according to claim 2. The exhaust purification filter according to claim 3, wherein the collection efficiency estimating means calculates the accumulation amount of particulates accumulated in the exhaust purification filter, and estimates the collection efficiency based on the accumulation amount. Fault diagnosis device. 5. The collection efficiency estimating unit calculates the amount of accumulation by calculating an increase amount of particulates deposited on the exhaust gas purification filter at regular intervals and accumulating the increase amount. The exhaust gas purification filter failure diagnosis device according to claim 1. The exhaust purification filter failure according to claim 4, wherein the collection efficiency estimating means detects a differential pressure across the exhaust purification filter, and calculates the particulate accumulation amount based on the differential pressure across the exhaust purification filter. Diagnostic device. The exhaust purification filter according to claim 4, wherein the collection efficiency estimating means detects an absolute pressure in the vicinity of an inlet of the exhaust purification filter, and calculates the particulate accumulation amount based on the absolute pressure. Fault diagnosis device. The said collection efficiency estimation means calculates the elapsed time from the completion | finish time of the reproduction | regeneration of the said exhaust gas purification filter as a count value, and estimates a collection efficiency based on the count value. Exhaust gas purification filter failure diagnosis device. The exhaust purification filter failure diagnosis device according to claim 8, wherein the collection efficiency estimation means does not calculate a time during fuel cut out of the elapsed time as the count value. An exhaust purification filter that is provided in the exhaust passage of the internal combustion engine and collects particulates contained in the exhaust, and a particulate amount detection that is provided downstream of the exhaust purification filter and detects the amount of particulates contained in the exhaust. A sensor, and
A failure diagnosis step of performing a failure diagnosis of the exhaust purification filter based on a detection value of the particulate amount detection sensor;
A collection efficiency estimating step of estimating the collection efficiency of the exhaust purification filter in accordance with operating conditions of the internal combustion engine;
A failure diagnosis prohibiting step for prohibiting failure diagnosis of the exhaust purification filter based on the collection efficiency;
An exhaust purification filter failure diagnosis method comprising: