JP2008190470A - Regeneration device for exhaust emission control filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means completing regeneration of a diesel particulate filter (DPF) using a particulate matter (PM) sensor. <P>SOLUTION: This device includes; an exhaust emission control filter provided in an exhaust gas passage of an internal combustion engine and collecting particulate contained in exhaust gas exhausted from the internal combustion engine; a particulate quantity detection sensor provided downstream of the exhaust emission control filter and detecting the particulate quantity contained in the exhaust gas; a regeneration means regenerating the exhaust emission control filter when the collected particulate exceeds a predetermined quantity; and a regeneration completion means S106 completing regeneration of the exhaust emission control filter based on the particulate quantity downstream of the exhaust emission control filter detected by the particulate quantity detection sensor. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust purification filter regeneration device.

  Conventionally, a diesel engine has been fitted 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, DPF regeneration control is performed in which when the PM is accumulated to some extent, the exhaust gas 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).

In addition, a technique is also known in which a sensor for detecting particulate accumulation is provided upstream of the DPF, and whether or not the DPF is to be regenerated is determined based on the detection value of the sensor (for example, Patent Document 2 and Patent Document 2). 3)
JP 2002-97930 A JP-A-8-68310 JP-A-8-68313

  However, the above-described conventional DPF regeneration control end determination is performed by determining the PM remaining amount in the DPF by estimating the PM combustion amount accumulated in the DPF from the regeneration time or by determining the differential pressure across the DPF. Was. In such a conventional end determination, the PM residual amount of the DPF is likely to vary depending on the driving condition and the accuracy is poor. Therefore, a margin is given to the reproduction time in consideration of the variation in the PM remaining amount. Therefore, there is a lot of time for regeneration, and there are problems such as deterioration of fuel consumption, early deterioration of the catalyst, and dilution of engine oil by fuel post injection during filter regeneration.

  The present invention has been made paying attention to such a conventional problem, and an object of the present invention is to provide a DPF regeneration device capable of accurately determining the end of regeneration 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 a particulate matter that is provided downstream of the exhaust purification filter and contained in exhaust gas A particulate quantity detection sensor for detecting the quantity, a regeneration means for regenerating the exhaust purification filter when the collected particulates exceed a predetermined quantity, and a downstream of the exhaust purification filter detected by the particulate quantity detection sensor And a regeneration end means for terminating the regeneration of the exhaust purification filter based on the particulate amount of

  According to the inventors, it was found that when the regeneration of the DPF progresses and the amount of accumulation in the DPF decreases, the collection efficiency of the DPF decreases and PM slightly leaks downstream of the DPF. Therefore, in the present invention, the leaked PM is detected by the particulate amount detection sensor, and the end of regeneration of the DPF is determined. Therefore, wasteful regeneration of the DPF can be prevented.

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

  FIG. 1 is a schematic diagram of a DPF regeneration device 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 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.

  The DPF 3 collects PM in the exhaust gas by passing the exhaust gas flowing through the exhaust passage 2 through a porous filter material. If DPF3 continues collecting PM, it will eventually become clogged.

  Therefore, the controller 10 regenerates the DPF 3 when the amount of accumulated 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 of retarding the fuel injection timing or a method of controlling fuel injection such as execution of post-injection may be applied.

  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 in order to regenerate the DPF 3. Therefore, the controller 10 includes detection from 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, a load sensor 14 that detects the load of the diesel engine 1, and the like. A 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.

  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 PM collection efficiency of the DPF 3 decreases for a while after the regeneration is completed. This is because for a while after the regeneration is finished, PM having a particle size smaller than that of the filter passes through the filter and is discharged downstream of the DPF 3. 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.

  As described above, until a certain amount (reference accumulation amount) of PM is accumulated after the regeneration is completed, the PM having a particle size smaller than the mesh of the filter passes through the filter and is discharged downstream of the DPF 3. Thereafter, when PM accumulates and the filter eyes are filled, PM having a particle size smaller than the filter eyes is also collected. Therefore, the PM collection efficiency of the DPF 3 is restored, and the amount of PM discharged downstream of the DPF 3 is extremely small.

  That is, a DPF with a coarse filter to suppress exhaust pressure loss has a characteristic that the PM collection efficiency decreases as the PM accumulation amount decreases.

  Therefore, the present invention makes a reproduction end determination using this characteristic of the DPF.

  For some time after the start of regeneration, the filter eyes of the DPF 3 are filled, so that PM is hardly discharged downstream of the DPF 3. Therefore, the soot sensor 11 hardly detects PM during this period. However, when the regeneration of the DPF 3 progresses and the amount of accumulated PM decreases, PM with a small particle size leaks downstream of the DPF 3. Then, the soot sensor 11 detects PM leaking downstream of the DPF 3. In the present invention, when the soot sensor 11 detects this leaked PM, it is determined that the regeneration of the DPF 3 is completed. By making such a determination, it is possible to prevent the DPF 3 from being wasted.

  That is, when the regeneration of the DPF 3 progresses and the amount of accumulated PM decreases, PM with a small particle size leaks downstream of the DPF 3. Therefore, when the soot sensor 11 detects this leaked PM, it is determined that the regeneration of the DPF 3 has ended. By making such a determination, it is possible to prevent the DPF 3 from being wasted.

  Hereinafter, the specific contents of the above-described DPF 3 regeneration end determination will be described with reference to FIG.

  FIG. 2 is a flowchart for explaining the regeneration end determination of the DPF 3 according to the present embodiment. The controller 10 repeatedly executes this flow 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 detects whether or not the soot sensor 11 detects PM during PM deposition. When the soot sensor 11 detects PM, the controller 10 proceeds to step S103, and when not detected, the controller 10 proceeds to step S105.

  In step S103, the controller 10 determines whether or not the PM accumulation amount PMa exceeds the reference accumulation amount. Here, the PM accumulation amount PMa indicates the total amount of PM accumulated in the DPF. If the PM accumulation amount PMa does not exceed the reference accumulation amount, the controller 10 ends the current process, and if it exceeds, the process proceeds to step S104.

  The controller 10 calculates the PM accumulation amount PMa in the DPF 3 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 obtains the PM accumulation amount ΔPM per unit time. 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 period in advance, ΔPM becomes 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 by the current routine execution to the previous value PMaz of the PM accumulation amount stored in the nonvolatile memory 20, thereby obtaining the PM accumulation amount PMa in the DPF. calculate. 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 reducing 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 S104, the controller 10 determines that the DPF 3 main body is damaged or the like and a functional failure has occurred. This is because the soot sensor 11 detects the PM discharged from the DPF 3 even though the PM accumulation amount PMa in the DPF 3 reaches the reference accumulation amount and the PM collection efficiency is recovered.

In step S105, the controller 10 determines whether or not the DPF 3 is being regenerated. Specifically, the controller 10 determines the value of the playing flag. If 1 (playing), the controller 10 proceeds to step S106, and if it is 0 (not playing), the current processing ends. The during-regeneration flag takes into account the engine operating conditions and the like. For example, the regeneration condition is not satisfied when the engine is idling, decelerating, or at a very low vehicle speed (for example, less than 20 km / h).

In step S106, the controller 10 determines whether or not the output value I SOOT of the _soot sensor 11 exceeds the reproduction end determination value (predetermined value). If the output value I SOOT of the _soot sensor 11 exceeds the regeneration end determination value during regeneration, the regeneration of the _{DPF 3} proceeds, and the PM collection efficiency is lowered, so that the soot sensor 11 detects PM discharged from the DPF 3. This is because it can be determined.

  Note that the regeneration end determination value is variable according to the operating conditions. The controller 10 determines the reproduction end determination value by the following method, for example.

  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 the regeneration end determination value from the characteristic table shown in FIG. 3 stored in advance in the ROM. FIG. 3 is a table for setting the regeneration end determination value from the exhaust flow rate. As shown, the regeneration end determination value increases as the exhaust flow rate increases.

  The reproduction end determination 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 the regeneration end determination value from the engine speed. Based on the engine rotation speed, the controller 10 determines the reproduction end determination value from the characteristic table shown in FIG. 4 stored in advance in the ROM. As shown in this table, the regeneration end determination value increases as the engine speed increases. Furthermore, if the engine rotation speed is the same, the regeneration end determination 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 exceeds the regeneration end determination value, that is, when the exhaust gas discharged from the DPF 3 contains PM equal to or higher than the reference value, the controller 10 performs step S107. The process is transferred to.

In step S106, when the output value I SOOT of the _soot sensor 11 is within the regeneration end determination 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 ends the current process. .

  In step S107, the controller 10 ends the regeneration of the DPF 3.

  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 indicated by hatching in FIG. 5, the collection efficiency of the DPF 3 decreases 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 DPF3 is recovered. 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.

  FIG. 6 is a diagram showing the relationship between the amount of PM discharged from the DPF 3 and the output value of the soot sensor 11.

  As shown in FIG. 5, when the regeneration of the DPF 3 progresses and the PM deposition amount decreases, the PM collection efficiency reaches the PM low collection efficiency region. In the PM low collection efficiency region, exhaust gas containing a relatively large amount of PM is discharged from the DPF 3. The output value of the soot sensor 11 when the discharged PM exceeds a predetermined amount is set as a regeneration end determination value.

  According to the present invention described above, the regeneration end determination is performed by using the characteristic that the PM collection efficiency decreases as the amount of PM accumulated in the DPF with a coarse filter is reduced in order to suppress exhaust pressure loss. That is, as the regeneration of the DPF 3 proceeds, the PM collection efficiency decreases, so the DPF 3 exhausts exhaust gas containing a relatively large amount of PM. By determining that the regeneration of the DPF 3 is completed when the soot sensor 11 detects the discharged PM, it is possible to prevent the regeneration of the DPF 3 in vain. Therefore, deterioration of fuel consumption, dilution of engine oil, and early deterioration of the catalyst can be prevented. In addition, since the time for collecting PM is reduced in the PM low collection efficiency region, the emission of PM can be suppressed as compared with the case where the DPF is completely regenerated.

  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 embodiment, as a method for calculating the PM accumulation amount in the DPF 3, an operation history for calculating the PM accumulation amount by integrating the PM accumulation amount per unit time determined by the operation conditions of the diesel engine 1 is integrated. The law was 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, when fuel injection is not performed, it is determined that PM is not discharged from the diesel engine 1. In addition to this, it may be determined that PM is not discharged even in a high-load operation condition in which PM discharged from the engine 1 automatically burns.

  In the present embodiment, one soot sensor 11 is provided downstream of the DPF 3, but two soot sensors 11 may be provided. When a certain amount of PM adheres to the soot sensor 11, it is necessary to burn and remove the PM on the sensor surface with a heater. While the soot sensor 11 is being reproduced, PM cannot be detected. Therefore, PM detection cannot be performed continuously with a single soot sensor. Therefore, two soot sensors 11 are provided downstream of the DPF 3 and are alternately regenerated. Thereby, detection of PM can be performed continuously.

It is the schematic of a DPF reproduction | regeneration apparatus. It is a flowchart explaining the reproduction | regeneration end determination of DPF. 6 is a table for setting a regeneration end determination value from an exhaust flow rate. It is a table which sets a reproduction end judgment 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 the figure which showed the relationship between PM amount discharged | emitted from DPF, and the output value of the soot sensor 11. FIG.

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)
S106 Playback end determination means

Claims (4)

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;
Regeneration start means for starting regeneration of the exhaust purification filter when the collected particulates exceed a predetermined amount;
Regeneration end means for ending regeneration of the exhaust purification filter based on the particulate quantity downstream of the exhaust purification filter detected by the particulate quantity detection sensor;
An exhaust purification filter regenerator. The exhaust purification filter regeneration device according to claim 1, wherein the regeneration end means terminates regeneration of the exhaust purification filter when a detection value of the particulate quantity detection sensor exceeds a predetermined value. The exhaust purification filter regeneration device according to claim 2, wherein the predetermined value is larger as the operating condition of the internal combustion engine is higher. The exhaust gas purification filter regeneration device according to any one of claims 1 to 3, wherein two of the particulate quantity detection sensors are provided and used alternately.

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