JP2008274892A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique regenerating a particulate filter in the further proper timing, in an exhaust emission control device of an internal combustion engine. <P>SOLUTION: This exhaust emission control device of the internal combustion engine mixes and uses a plurality of fuels including at least bio-fuel, and has: a fuel concentration detecting means 7 detecting the concentration of the bio-fuel; the particulate filter 9; a collecting quantity estimating means 12 estimating quantity of particulate matter collected in the particulate filter 9 based on an operation state of at least the internal combustion engine 1; a filter regenerating means 12 regenerating the particulate filter 9 when the quantity of particulate matter collected in the articulate filter 9 is a specified quantity or more; and a collecting quantity correcting means 12 correcting the quantity of particulate matter estimated by the collecting quantity estimating means 12 in response to the concentration of the bio-fuel. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  The particulate matter collected in the particulate filter (hereinafter referred to as “filter”) can be oxidized by raising the temperature of the particulate filter to regenerate the filter. For example, the filter is regenerated when the amount of PM collected by the filter becomes a specified value or more.

Here, a technique for suppressing the discharge amount of particulate matter (hereinafter referred to as “PM”) by supplying hydrogen gas to the combustion chamber is known (for example, see Patent Document 1).
JP 2001-323823 A Japanese Patent Laid-Open No. 2006-177311

  By the way, an internal combustion engine that can use a biofuel made of rapeseed or palm as a raw material is known. This biofuel can also be used by mixing with other fuels (for example, light oil).

  Here, since the biofuel is a fuel containing oxygen, the higher the concentration, the more the combustion is promoted, and the SOOT emission amount is reduced. Thereby, the amount of particulate matter collected by the particulate filter is reduced. In addition, since biofuel has a higher proportion of high-boiling components than light oil or the like, the higher the concentration of biofuel, the more difficult the fuel evaporates and the greater the amount of SOF emitted. That is, the higher the concentration of biofuel, the smaller the amount of particulate matter deposited on the particulate filter, and the higher the proportion of SOF in the deposited particulate matter.

  And since SOF is mainly unburned fuel, compared with SOOT which is mainly soot, the temperature which oxidizes is low. Therefore, depending on the operating state of the internal combustion engine, PM is oxidized without performing filter regeneration control, so the amount of PM collected in the filter decreases. That is, if the amount of PM collected in the filter is estimated based on the operating state of the internal combustion engine when the concentration of biofuel is high, there is a risk that an erroneous estimation is made. Thereby, if the regeneration control of the filter is performed more than necessary, the fuel consumption is deteriorated or the thermal deterioration of the filter is advanced.

  Here, it is conceivable to estimate the amount of collected PM by giving a map for each concentration of biofuel or changing the estimation logic, but it is difficult because it is necessary to install a large capacity memory in the ECU. It is. Also, many experiments must be conducted during the development process, resulting in a huge development cost.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of performing regeneration of a particulate filter at a more appropriate time in an exhaust purification device of an internal combustion engine. To do.

In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention employs the following means. That is, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is
In an exhaust emission control device for an internal combustion engine capable of mixing and using a plurality of fuels including at least biofuel,
Fuel concentration detection means for detecting the concentration of the biofuel;
A particulate filter provided in an exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
A collection amount estimating means for estimating an amount of particulate matter collected in the particulate filter based on at least an operating state of the internal combustion engine;
Filter regeneration means for regenerating the particulate filter when the amount of the particulate matter collected in the particulate filter is a specified amount or more;
A collection amount correction means for correcting the amount of particulate matter estimated by the collection amount estimation means according to the concentration of biofuel detected by the fuel concentration detection means;
It is characterized by comprising.

  The internal combustion engine can be used only with biofuel or only with other fuel (for example, light oil). In addition, the biofuel may be a fuel containing oxygen and having a predetermined high boiling point component ratio of a predetermined value or more.

  The collected amount estimating means estimates the amount of particulate matter discharged from the internal combustion engine based on, for example, the amount of fuel supplied, the engine speed, etc., and integrates the estimated amount of particulate matter collected by the particulate filter. Estimate the amount of substance. The fuel supply amount may be a value related to the fuel supply amount, and may be, for example, a load of an internal combustion engine, a throttle opening, or an engine generated torque. That is, the collection amount estimation means may estimate the amount of particulate matter collected by the particulate filter based on at least a value related to the fuel supply amount.

  The filter regeneration means regenerates the particulate filter when the amount of the particulate matter is equal to or more than the specified amount. As the amount of the particulate matter, a value obtained by means other than the collected amount estimation means can be used. That is, in addition to the collected amount estimating means, there may be provided means for estimating the amount of particulate matter collected by the particulate filter without using the operating state of the internal combustion engine. The prescribed amount can be determined in consideration of a decrease in the ability of the particulate filter to collect particulate matter or a decrease in the function of the internal combustion engine.

  Here, when the amount of particulate matter collected is estimated based on the operating state of the internal combustion engine, the amount of particulate matter discharged and the amount of oxidation change according to the concentration of biofuel in the fuel. However, the collection amount estimation means estimates the amount of particulate matter collected by the particulate filter based on the operating state of the internal combustion engine, so even if the concentration of biofuel changes, the collection amount estimation The estimated value by means does not change.

  For this reason, there is a difference between the estimated value of the amount of the particulate matter collected by the particulate filter and the actual value, and the collected amount correction means corrects the difference so that the difference is reduced. Here, since the amount of the particulate matter collected by the particulate filter is correlated with the concentration of the biofuel, the amount of the particulate matter can be corrected based on the concentration of the biofuel. Thereby, it can suppress that regeneration of a particulate filter is performed more than necessary.

  Instead of correcting the trapped amount of particulate matter, the specified amount may be corrected.

  In the present invention, the collection amount correction means can correct the amount of particulate matter to be smaller as the biofuel concentration is higher.

The higher the concentration of biofuel, the higher the SOF ratio, so that the particulate matter is oxidized at a lower temperature. In addition, the higher the concentration of biofuel, the higher the proportion of fuel containing oxygen, so the emission of particulate matter decreases. That is, as the biofuel concentration increases, the amount of particulate matter deposited on the particulate filter decreases. By performing the correction according to this relationship, the difference between the estimated value of the particulate matter collected in the particulate film and the actual value can be reduced.

  In addition, you may correct | amend so that a regulation amount may increase, so that the density | concentration of biofuel is high.

  According to the present invention, the particulate filter can be regenerated at a more appropriate time.

  Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 to which an exhaust gas purification apparatus for an internal combustion engine according to this embodiment is applied, and its exhaust system. The internal combustion engine 1 is a diesel engine, and a mixed fuel obtained by mixing light oil and biofuel can be used. The concentration of the biofuel in the mixed fuel may be any value from 0 to 100%.

  In addition, a fuel injection valve 3 for injecting fuel into the cylinder 2 is attached to the internal combustion engine 1. The fuel injection valve 3 is connected via a fuel pipe 5 and a fuel tank 4 for storing fuel. A fuel pump 6 is provided in the middle of the fuel pipe 5 to increase the fuel pressure.

  A biofuel concentration sensor 7 for detecting the concentration of biofuel in the fuel stored in the fuel tank 4 is attached to the fuel tank 4. In this embodiment, the biofuel concentration sensor 7 corresponds to the fuel concentration detection means in the present invention.

On the other hand, an exhaust passage 8 leading to the cylinder 2 is connected to the internal combustion engine 1. A particulate filter 9 (hereinafter referred to as filter 9) carrying an NOx storage reduction catalyst (hereinafter referred to as NOx catalyst) is provided in the middle of the exhaust passage 8. The NOx catalyst has a function of storing NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reducing the stored NOx when the oxygen concentration of the inflowing exhaust gas is reduced and a reducing agent is present. . Further, the filter 9 collects PM contained in the exhaust gas.

Furthermore, in this embodiment, a fuel addition valve 10 is provided for adding fuel as a reducing agent to the exhaust gas flowing through the exhaust passage 8 upstream of the filter 9. The fuel addition valve 10 is connected to the fuel pump 6. The fuel addition valve 10 is opened by a signal from the ECU 12 described later to inject fuel. This fuel reacts with the NOx catalyst and raises the temperature of the filter 9.

  Then, the PM trapped in the filter 9 is oxidized by raising the temperature of the filter 9 to a temperature necessary for the oxidation of PM. That is, the filter 9 can be regenerated. Thus, when raising the temperature of the filter 9, the amount of fuel injected from the fuel addition valve 10 is determined so that the temperature of the filter 9 becomes the target temperature. In this embodiment, the ECU 12 that regenerates the filter 9 corresponds to the filter regeneration means in the present invention. The regeneration of the filter 9 may be performed by increasing the temperature of the filter 9 using a heater or the like.

  An air-fuel ratio sensor 11 that measures the air-fuel ratio of the exhaust gas flowing through the exhaust passage 8 is attached to the exhaust passage 8 downstream of the filter 9. Further, a differential pressure sensor 13 for detecting a pressure difference between the upstream side and the downstream side of the filter 9 is attached to the exhaust passage 8.

  The internal combustion engine 1 configured as described above is provided with an ECU 12 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 12 controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.

  An output signal of the sensor is input to the ECU 12. Further, the fuel injection valve 3 and the fuel addition valve 10 are connected to the ECU 12 via electric wiring, and these are controlled by the ECU 12.

  The ECU 12 estimates the PM amount discharged from the internal combustion engine 1 based on the rotational speed of the internal combustion engine 1 and the fuel supply amount, and accumulates the discharged PM amount to thereby collect the PM collected in the filter 9. The amount is estimated. The fuel supply amount may be replaced with the load or torque of the internal combustion engine 1. The estimation of the PM amount in this way is hereinafter referred to as “estimation of the PM amount based on the operating state”. In this embodiment, the ECU 12 that estimates the PM amount according to the operating state corresponds to the collection amount estimating means in the present invention.

  On the other hand, the ECU 12 estimates the amount of PM collected by the filter 9 based on the differential pressure obtained by the differential pressure sensor 13. The estimation of the PM amount in this way is hereinafter referred to as “estimation of the PM amount by the differential pressure”.

  That is, in this embodiment, the PM amount is estimated by two means. When the value obtained as a result of the estimation of the PM amount due to the operating state becomes equal to or greater than the first specified value, or when the value obtained as a result of the estimation of the PM amount due to the differential pressure becomes equal to or greater than the second specified value. The filter 9 is regenerated. In this embodiment, the ECU 12 that regenerates the filter 9 corresponds to the filter regeneration means in the present invention.

  Here, the first specified value is a value smaller than the second specified value, and the estimated value of the PM amount according to the operating state usually reaches the first specified value earlier. Even if there is an error in the estimation of the PM amount based on the operating state, the regeneration timing of the filter 9 can be determined by estimating the PM amount based on the differential pressure. In this way, even if one of the two fails, the regeneration timing of the filter 9 can be determined by the other, so that a decrease in the function of the internal combustion engine 1 due to clogging of the filter 9 can be suppressed.

  Here, FIG. 2 is a diagram showing the relationship between the biofuel concentration and the PM and SOF emissions. A solid line indicates PM, and a broken line indicates SOF. When biofuel is mixed with light oil and used, the higher the concentration of biofuel, the higher the proportion of oxygenated fuel, so the PM emission from the internal combustion engine 1 decreases. Moreover, since the ratio of a high boiling point component becomes so high that the density | concentration of biofuel is high, the ratio of SOF in PM becomes high. Since SOF is oxidized at a temperature lower than that of SOOT, the amount of PM collected by the filter 9 decreases when the proportion of SOF in PM increases.

  Thus, when the concentration of biofuel increases, the amount of PM collected by the filter 9 decreases. For this reason, the value obtained as a result of the estimation of the PM amount according to the operating state becomes larger than the actual PM amount. As a result, the regeneration of the filter 9 is performed at a time when it is not necessary, and the fuel consumption is deteriorated or the heat deterioration is advanced.

  Therefore, in this embodiment, the estimated value of the PM amount according to the operating state is corrected based on the biofuel concentration.

  Here, FIG. 3 is a diagram showing the relationship between the biofuel concentration and the PM amount correction value. This relationship can be obtained in advance through experiments or the like. The PM amount is corrected by multiplying this correction value by the estimated value of the PM amount according to the operating state. Then, the higher the biofuel concentration, the lower the PM emission from the internal combustion engine 1 and the higher the SOF component ratio, so that the PM amount is corrected to be smaller. That is, the correction value is a value of 1 or less, and the correction value decreases as the biofuel concentration increases.

  In the present embodiment, the correction value is a value of 1 or less. However, even when the correction value exceeds 1, the same can be applied.

  Next, FIG. 4 is a flowchart showing the regeneration flow of the filter 9. This routine is executed when the ignition switch is turned on.

  In step S <b> 101, the biofuel concentration L is measured by the biofuel concentration sensor 7. In addition, the kind of biofuel supplied is limited. Here, the biofuel concentration L may be estimated from the air-fuel ratio obtained by the air-fuel ratio sensor 11. Alternatively, the biofuel concentration L may be estimated by measuring the fuel concentration or temperature.

  In step S102, a PM amount correction coefficient K is calculated. That is, the correction value K is calculated from the biofuel concentration L obtained in step S101 and FIG.

  In step S103, when it is assumed that only light oil is used as the fuel, the PM amount A collected by the filter 9 is calculated. That is, the PM amount is estimated based on the operating state. This is a value before correction of the PM amount collected by the filter 9. As described above, the PM amount discharged from the internal combustion engine 1 is estimated based on the rotational speed of the internal combustion engine 1 and the fuel supply amount, and the exhausted PM amount is integrated to be collected by the filter 9. The amount of PM A is estimated.

  In step S104, a value obtained by multiplying the PM amount A obtained in step S103 by the correction value K obtained in step S102 is set as a new PM amount A. That is, the PM amount A is corrected. Thereafter, the regeneration timing of the filter 9 is determined using the PM amount A obtained in this step. In this embodiment, the ECU 12 that executes step S103 and step S104 corresponds to the collection amount correction means in the present invention.

  In step S105, it is determined whether or not the ignition switch is OFF. When the ignition switch is turned off, the filter 9 cannot be regenerated until the ignition switch is turned on next time, and thus this routine is terminated. Even if the ignition switch is turned off, the PM amount A is stored in the ECU 12.

  If a negative determination is made in step S105, the process proceeds to step S106. If an affirmative determination is made, the present routine is temporarily terminated.

  In step S106, it is determined whether or not the PM amount A obtained in step S104 is greater than or equal to the specified amount B. The specified amount B is a value that is set to determine whether or not to start regeneration of the filter 9, and takes into account a decrease in the ability of the filter 9 to collect PM or a decrease in the function of the internal combustion engine 1 in advance. Find it by experiment.

  If an affirmative determination is made in step S106, the process proceeds to step S107, whereas if a negative determination is made, the process returns to step S103.

  In step S107, the regeneration of the filter 9 is started. That is, removal is performed by oxidizing the PM by raising the temperature of the filter 9 by adding fuel from the fuel addition valve 10.

  In step S108, it is determined whether the regeneration of the filter 9 has been completed. For example, when the regeneration of the filter 9 is performed for a predetermined time or more, it is determined that the regeneration of the filter 9 is completed. Further, it may be determined that the regeneration of the filter 9 is completed when the differential pressure of the exhaust gas upstream and downstream of the filter 9 becomes equal to or less than a specified value.

  If an affirmative determination is made in step S108, the process proceeds to step S109, whereas if a negative determination is made, the process returns to step S108.

  In step S109, the PM amount A is set to zero. That is, when the regeneration of the filter 9 is completed, the amount of PM accumulated on the filter 9 is set to zero. When the regeneration of the filter 9 is stopped halfway, the amount of PM collected by the filter 9 at that time is substituted.

  In step S110, it is determined whether or not the ignition switch is OFF. Here, the same determination as in step S105 is performed.

  In this way, the amount of PM is estimated according to the biofuel concentration, and the filter 9 is regenerated based on this estimated value.

  As described above, in the present embodiment, it is possible to suppress the regeneration of the filter 9 more than necessary by estimating the amount of PM trapped in the filter 9 as the biofuel concentration is higher. Thereby, deterioration of a fuel consumption can be suppressed or progress of the heat deterioration (sintering of noble metals, such as platinum) of the filter 9 can be suppressed.

  In addition, since it is not necessary to change the map or logic for estimating the PM amount for each concentration of biofuel, the burden during development can be reduced. Furthermore, the memory capacity of the ECU 12 can be small.

  In this embodiment, since the PM amount is simply corrected, a difference may be caused between the estimated PM amount and the actual PM amount, but the PM amount is estimated based on the differential pressure. Thus, the regeneration time of the filter 9 can be determined. Since the number of regenerations of the filter 9 can be reduced by correcting the PM amount according to the present embodiment, it is possible to suppress the deterioration of the fuel consumption or the progress of the thermal deterioration of the filter 9.

It is a figure which shows schematic structure of the internal combustion engine which applies the exhaust gas purification apparatus of the internal combustion engine which concerns on an Example, and its exhaust system. It is the figure which showed the relationship between the density | concentration of biofuel, and the discharge amount of PM and SOF. It is the figure which showed the relationship between the density | concentration of biofuel, and the correction value of PM amount. It is the flowchart which showed the reproduction | regeneration flow of a filter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 3 Fuel injection valve 4 Fuel tank 5 Fuel pipe 6 Fuel pump 7 Bio fuel concentration sensor 8 Exhaust passage 9 Particulate filter 10 Fuel addition valve 11 Air-fuel ratio sensor 12 ECU
13 Differential pressure sensor

Claims (2)

In an exhaust emission control device for an internal combustion engine capable of mixing and using a plurality of fuels including at least biofuel,
Fuel concentration detection means for detecting the concentration of the biofuel;
A particulate filter provided in an exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
A collection amount estimating means for estimating an amount of particulate matter collected in the particulate filter based on at least an operating state of the internal combustion engine;
Filter regeneration means for regenerating the particulate filter when the amount of particulate matter trapped in the particulate filter is greater than or equal to a specified amount;
A collection amount correction means for correcting the amount of the particulate matter estimated by the collection amount estimation means according to the concentration of the biofuel detected by the fuel concentration detection means;
An exhaust emission control device for an internal combustion engine, comprising:   2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the collection amount correction unit corrects the amount of particulate matter to be smaller as the concentration of biofuel is higher.

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