JP2003083031A - Exhaust emission control device of engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device furnished with a continuous regeneration type particulate filter capable of carrying out forced reactivation at more favorable time. SOLUTION: This exhaust emission control device is furnished with an oxidation catalyst, the particulate filter, a control part to judge whether to carry out forced reactivation or not, a temperature raising means, etc. Soot in the particulate filter is burnt by nitrogen oxide continuously generated by the oxidation catalyst when the engine is in a predetermined driving state. The control part judges that the forced reactivation condition is established when assumed accumulated quantity of the soot exceeds a specified value. Thereafter, whether the engine is in the predetermined driving state, that is, in a continuous reactivation region, or not is judged, and only in the case when it is not in the continuous reactivation region, the temperature raising means works and the forced reactivation is performed.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for purifying exhaust gas of a diesel engine. 2. Description of the Related Art In a diesel engine, as a device for purifying exhaust gas, a continuous regeneration type DPF (Diesel parti) using an oxidation catalyst and a particulate filter is used.
culatefilter) is known. This type of purification device
NO in the exhaust gas is oxidized by the oxidation catalyst to be converted into NO ₂ , and soot (mainly carbon) in the particulate filter can be burned in a relatively low temperature range by the NO ₂ . In the continuous regeneration type DPF, if soot is excessively accumulated on the particulate filter, not only the engine output is reduced, but also the particulate filter may be melted and damaged due to abnormally high temperature during soot combustion. For this reason, it is necessary to forcibly burn (that is, forcibly regenerate) the deposited soot at an appropriate timing by some kind of heating means. In this case, it is necessary to accurately estimate the soot accumulation amount and accurately determine the timing of forced regeneration. Conventionally, in order to estimate the soot deposition amount,
The differential pressure across the particulate filter, the filter inlet temperature, the engine speed, etc. are detected, and the soot accumulation at the time of detection is determined based on a map representing the known relationship between the values detected by these sensors and the soot accumulation amount. The amount is estimated. [0005] Conventionally, once the estimated amount of soot deposition exceeds a predetermined value, the mode shifts to a forced regeneration mode.
Even if the engine shifts to a predetermined operating state in which the engine can be continuously regenerated immediately before shifting to the forced regeneration mode, the forced regeneration is executed regardless of a change in the operating state. For this reason, the interval of the forced regeneration tends to be short, and there is room for improvement when it is desired to reduce the frequency of the forced regeneration from the viewpoint of the durability and the fuel efficiency of the filter. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an exhaust gas purifying apparatus provided with a continuous regeneration type particulate filter, capable of performing forced regeneration at a more preferable time. [0007] The exhaust gas purifying apparatus of the present invention is constructed as described in claim 1, and comprises a particulate filter for depositing soot in exhaust gas and an oxidation catalyst having an oxidizing function. Have. When the engine is in a predetermined operating state, NO is continuously generated by the oxidation catalyst.
_{By 2} , the soot deposited on the particulate filter is burned to perform continuous regeneration. Further, when the estimated value or the detected value of the soot deposited on the particulate filter exceeds a set value, the temperature of the particulate filter is raised by the temperature raising means, whereby forced regeneration is performed. In the present invention,
When the deposition amount obtained by the deposition amount estimation means exceeds the set value,
In addition, when it is detected that the engine is in the predetermined operating state, the operation of the temperature raising means is prohibited by the prohibiting means, and the continuous regeneration is continued. The prohibiting means is configured to determine the predetermined operating state (for example, whether or not the engine is in the continuous regeneration enabled area, based on a detected value relating to an engine operating state such as an engine speed or an intake air amount, and a detected value relating to a fuel injection amount, for example. Judge).
Further, the accumulation amount estimating means in the present invention may estimate the soot accumulation amount based on the pressure difference before and after the particulate filter and the temperature, the engine speed, etc., or from a map of the engine speed and the fuel injection amount, The soot accumulation amount may be estimated. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 schematically shows a diesel engine 11 provided with an exhaust gas purification device 10. The engine 11 includes an engine body 12, an intake system 13 and an exhaust system 14, an EGR device 15, a control unit (control unit) 16 using a microcomputer, and the like. The engine body 12 includes a piston 20, a combustion chamber 21, a fuel injection valve 22, and the like. The EGR device 15 includes an EGR valve 23 and an EGR
A cooler 24 and the like are included. The intake system 13 includes an intake pipe 30, a compressor 31, an intercooler 32, a throttle 33, and the like. The opening of the throttle 33 can be changed by an actuator 34. The exhaust system 14 is
It includes an exhaust pipe 40, a turbine 41, a shutter 42, an oxidation catalyst 43, a particulate filter 44, an envelope 45 functioning as an exhaust passage, and the like. The oxidation catalyst 43 is provided inside the envelope 45 on the upstream side of the particulate filter 44. The compressor 31 and the turbine 41 rotate integrally with each other. The opening of the shutter 42 can be changed by an actuator 46. In order to detect the differential pressure across the particulate filter 44, a first pressure sensor 51 is provided upstream of the particulate filter 44, and a second pressure sensor 52 is provided downstream of the particulate filter 44. Is provided. These sensors 51 and 52 are examples of differential pressure detecting means. A temperature sensor 53 for detecting a filter inlet temperature is provided between the oxidation catalyst 43 and the particulate filter 44. The control unit 16 is constituted by electronic components having an arithmetic function such as a microprocessor, and includes a memory for storing maps M1, M2, and M3 described below. The control unit 16 is connected to an engine speed sensor 54 which is an example of an operation state detecting means, and an injection amount detector 55 which is an example of a fuel injection amount detecting means. As another example of the fuel injection amount detecting means, data relating to the engine load may be input to the control unit 16. As the operating state detecting means, at least one of the intake air amount and the exhaust gas air-fuel ratio may be detected in addition to the engine speed sensor 54. The control section 16 which functions as the accumulation amount estimating means
Is programmed with a logic for estimating the first estimated accumulation amount (a) of the soot of the particulate filter 44 using the three-dimensional map (differential pressure map) M1 shown in FIG. The three-dimensional map M1 includes the pressure sensors 51, 52
, The inlet temperature detected by the temperature sensor 53, the engine speed detected by the engine speed sensor 54 such as a crank sensor, and the relationship between the soot accumulation amount and the map obtained in advance. Sensor 51
The first estimated accumulation amount (a) is obtained based on the detected values from to 54 and the map M1. Further, the control unit 16 controls the map M shown in FIG.
2, the logic for estimating the second estimated deposit amount (b) is programmed. The map M2 includes the engine speed detected by the engine speed sensor 54, the fuel injection amount input from the injection amount detector 55 such as an accelerator position sensor, and the soot accumulation amount (accumulated after the end of the previous forced regeneration. Value) and mapped in advance. Based on this map M2, the second estimated accumulation amount (b) is calculated. Further, the control unit 16 controls the map M shown in FIG.
3 is used to determine whether or not the particulate filter 44 is in the continuously reproducible area. This map M3 is obtained by mapping in advance the relationship among the engine speed, the fuel injection amount, and the continuously reproducible region. Based on this map M3, it is determined whether or not the particulate filter 44 is in the continuously reproducible area. The lines in the map M3 represent the full load characteristics. Next, the operation of the exhaust gas purifying apparatus 10 will be described with reference to a flowchart shown in FIG. This exhaust gas purification device 10 can continuously burn soot deposited in the particulate filter 44 by NO ₂ continuously generated by the oxidation catalyst 43 when the engine is in a predetermined operation state. This state is the continuous reproduction mode. During continuous regeneration, the NO in the exhaust gas is oxidized by the oxidation catalyst 43 to change to NO ₂ , and the NO ₂ causes the soot in the particulate filter 44 to fall in a relatively low temperature range (for example, 270 ° C. to 350 ° C.). ℃). The conversion efficiency of oxygen of the oxidation catalyst 43 is
Since the temperature becomes maximum in a certain temperature range (for example, a conversion peak temperature range around 300 ° C.), if the exhaust gas temperature is in this temperature range, the soot is burned by NO ₂ without any particular control, and continuous regeneration is performed. Can be. When the exhaust gas temperature is lower than the above-mentioned peak temperature range (for example, around 250 ° C.), in order to increase the conversion efficiency of the oxidation catalyst 43, control is performed to raise the temperature of the oxidation catalyst 43 to the above-mentioned peak temperature range (continuous regeneration support). Processing) is performed. The continuous regeneration support processing is performed by, for example, reducing the throttle 33 or the shutter 42 to some extent and raising the exhaust temperature. First, in step S1, the differential pressure map M
1 to obtain the first estimated accumulation amount (a),
The second estimated deposition amount (b) is obtained using the map M2.
Then, in step S2, the first estimated accumulation amount (a)
It is determined whether or not the second estimated accumulation amount (b) exceeds the set value. If both the accumulation amounts (a) and (b) do not exceed the set value (for example, 25 grams), the forced operation is performed. Judge that there is no need for playback. If at least one of the estimated accumulation amounts (a) and (b) exceeds the set value in step S2, the forcing condition is satisfied in step S3. Even if the forced regeneration condition is satisfied, if the operating state of the engine changes after that, there is a possibility that the operation may shift to the continuous regeneration enabled area. Therefore, in step S4, the map M3
It is determined whether or not the current position is in the continuous playable area at this time. Here, when it is in the continuous regeneration possible area, that is, when it is detected that the engine is in the predetermined operation state, it is determined that the forced regeneration is not necessary, and the shift to the forced regeneration mode is prohibited, Perform continuous playback. That is, the control unit 16 also has a function as a prohibition unit referred to in the present invention. If it is determined in step S4 that the area is not in the continuously reproducible area, the control section 16 executes step S4.
The forced regeneration command of 5 is issued. Then, in step S6, the forced regeneration of the particulate filter 44 is performed.
In the forced regeneration, post-injection is performed as an example of the temperature raising means. In the post injection, fuel is injected into the combustion chamber 21 during the exhaust stroke of the engine body 12. The injected fuel reaches the oxidation catalyst 43 and the fuel (HC) is oxidized, so that the soot is generated by the particulate filter 44 in a higher temperature range (for example, 500 ° C. to 550 ° C. or higher) than in the continuous operation. It is directly oxidized (combusted) by O ₂ . The fuel (HC) not consumed by the oxidation catalyst 43 adheres to the soot on the particulate filter 44, and the combustion is further activated. When the forced regeneration is performed, the second estimated deposition amount (b) is initialized in step S7, and the second
Of the estimated accumulation amount (b) is started. As described above, the exhaust gas purifying apparatus 10 of this embodiment uses two types of estimated accumulation amounts (a) and (b) having different properties from each other, and when at least one of the accumulation amounts exceeds a set value. To perform forced regeneration. That is, the first estimated accumulation amount (a) is determined by the sensors 51 and 5 at the time of determining whether to perform forced regeneration (at the time of detecting the differential pressure).
Since the value is based on the differential pressure of 2, the soot accumulation amount can be estimated without being affected by the history of the operating state of the engine up to the time of determination. On the other hand, since the second estimated accumulation amount (b) is a value based on the integrated value from the time when the previous forced regeneration is completed to immediately before the current judgment time, the second estimated accumulation amount (b) should be Even if the sensors 51 to 55 break down and their functions are lost, an estimated amount of deposit that can be used as a criterion for determining whether or not to perform forced regeneration can be obtained based on the integrated value obtained so far. When the engine is in a predetermined operating state and can be continuously regenerated after detecting that the estimated amount of soot exceeds a set value (for example, 25 grams), the exhaust gas purifying apparatus 10 The transition to the playback mode is prohibited. For this reason, the forced regeneration interval can be lengthened, and the frequency of forced regeneration is reduced, thereby reducing the load on the particulate filter 44 and avoiding wasting energy for forced regeneration. Can be. In practicing the present invention, the constituent elements of the present invention, such as a specific form of a particulate filter, a temperature raising means for performing forced regeneration, a deposition amount estimating means, and a prohibiting means, are summarized in the summary of the invention. It goes without saying that various changes can be made without departing from the scope of the present invention. According to the present invention, in an exhaust gas purification apparatus provided with a continuous regeneration type particulate filter, forced regeneration can be performed at a more favorable timing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of an exhaust gas purification device provided with a particulate filter. FIG. 2 is a flowchart showing the processing content of the exhaust gas purification apparatus according to one embodiment of the present invention. FIG. 3 is a diagram showing a three-dimensional map used for obtaining a first estimated accumulation amount based on an engine speed, a differential pressure across the DPF, and an inlet temperature. FIG. 4 is a diagram showing a map used for obtaining a second estimated accumulation amount based on an engine speed and a fuel injection amount. FIG. 5 is a diagram showing a map representing a relationship among an engine speed, a fuel injection amount, and a continuously reproducible region. [Description of Signs] 16: control unit (accumulation amount estimation means, inhibition means) 43: oxidation catalyst 44: particulate filter

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) F02D 41/38 B01D 46/42 B // B01D 46/42 53/36 103C (72) Inventor Hiroki Taniguchi Minato-ku, Tokyo 3-3-8 Shiba 5-Chome Mitsubishi Motors Corporation (72) Inventor Kiyoshi Hatano 5-33-8 Shiba 5-Chome Minato-ku, Tokyo Mitsubishi Motors Corporation F-term (reference) 3G090 AA02 BA02 CA01 CB02 CB04 CB23 DA04 DA09 DA10 DA13 DA18 DB02 EA02 EA05 EA06 EA07 3G091 AA10 AA11 AA18 AB02 AB13 BA02 BA04 CA02 CA18 CA27 DA02 DC01 EA01 EA05 EA07 EA08 EA09 EA19 EA21 EA32 FA01 FA04 FB02 GA06 HA15 HA36 HA37 H0125 HA06 HA37 H013 ND02 NE01 PA01Z PA07Z PA11A PD11Z PD14Z PE01Z 4D048 AA06 AA14 AB01 CC38 CD05 DA01 DA02 DA03 DA07 DA13 DA20 4D058 MA41 SA08 TA06

Claims (1)

Claims: 1. A particulate filter for accumulating soot in exhaust gas and burning the accumulated soot when the temperature exceeds a regeneration temperature, and an oxidizer provided in an exhaust passage upstream of the particulate filter. An exhaust purification device that burns soot deposited on the particulate filter with an oxidation catalyst having a function and NO ₂ continuously generated by the oxidation catalyst in a predetermined operating state of the engine, wherein the particulate matter is deposited on the particulate filter. A deposit amount estimating means for estimating or detecting the accumulated amount of soot; a temperature increasing means for increasing the temperature of the particulate filter when the soot accumulation amount obtained by the accumulated amount estimating means exceeds a set value; It is detected that the soot accumulation amount obtained by the accumulation amount estimation means has exceeded the set value Prohibiting means for prohibiting the operation of the temperature raising means when it is detected that the engine is in the predetermined operating state.