JP2011247195A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit unburned fuel from accumulating in an exhaust passage between an oxidation catalyst provided just after a turbine of a turbo charger and a particulate filter provided at a certain distance from the oxidation catalyst even when the oxidation catalyst deteriorates thermally.SOLUTION: An exhaust emission control device can switch the combustion mode of an internal combustion engine to a first regeneration combustion mode or a second regeneration combustion mode in which exhaust gas temperature just after the internal combustion engine becomes higher than that in the first regeneration combustion mode. The exhaust emission control device sets the combustion mode of the internal combustion engine at the first regeneration combustion mode (ST6) when exhaust gas temperature between the oxidation catalyst and the particulate filter is not smaller than a predetermined threshold Gth or cooling water temperature of the internal combustion engine is not larger than a predetermined threshold Wth (ST3:NO), and sets the combustion mode of the internal combustion engine at the second regeneration combustion mode (ST4) during filter regeneration control when the exhaust gas temperature between the oxidation catalyst and the particulate filter is below the predetermined threshold Gth and the cooling water temperature of the internal combustion engine exceeds the predetermined threshold Wth (ST3:YES).

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly to an exhaust gas purification device that regenerates a particulate filter installed in an exhaust passage by adding unburned fuel to the exhaust passage by a fuel addition valve.

  Conventionally, particulate matter (Particulate Matter: hereinafter referred to as “PM”) containing carbon as a main component is included in exhaust gas discharged when a diesel engine mounted on an automobile or the like is driven. This causes air pollution.

  As a device for preventing PM from being discharged into the atmosphere, a particulate filter installed in an exhaust passage of a diesel engine is known. The particulate filter purifies the exhaust gas by collecting PM contained in the exhaust gas passing through the exhaust passage.

  When PM is collected using a particulate filter, if the amount of collected PM increases, the particulate filter is clogged. When the particulate filter is clogged, the pressure loss of the exhaust gas that passes through the particulate filter increases, resulting in a decrease in engine output and a deterioration in fuel consumption.

  In order to eliminate such clogging, a filter regeneration operation is conventionally performed when the collected amount (deposition amount) of PM collected by the particulate filter reaches a predetermined amount. . In this filter regeneration operation, the PM collected by the particulate filter is burned and removed by raising the filter temperature by a technique such as raising the exhaust gas temperature (see, for example, Patent Document 1). ). For example, post-injection in which a small amount of fuel is sub-injected after main fuel injection into the engine combustion chamber and before the exhaust valve is closed, and an exhaust throttle valve provided downstream of the particulate filter in the engine exhaust passage This is performed in combination with the squeezing operation. As a result, unburned fuel is supplied to the exhaust passage, the exhaust temperature is raised, PM collected by the particulate filter is burned and removed, and the particulate filter is regenerated.

  In addition, in the exhaust gas purification apparatus for an internal combustion engine disclosed in Patent Document 2, a fuel addition valve and a front-stage oxidation catalyst are provided immediately downstream of the turbine of the turbocharger in the exhaust path of the engine. A particulate filter carrying an oxidation catalyst is provided at a certain distance on the downstream side. In this exhaust gas purification apparatus for an internal combustion engine, as a filter regeneration operation, fuel is added from the fuel addition valve to the exhaust passage, and a part of the fuel undergoes an oxidation reaction in the pre-stage oxidation catalyst to raise the exhaust gas temperature. The remaining part causes an oxidation reaction in the downstream particulate filter, raises the temperature of the particulate filter, and burns and removes the collected PM.

JP 2004-162675 A JP 2009-7777 A

  However, in the case of supplying unburned fuel to the exhaust passage during the filter regeneration operation as in the exhaust gas purification device of the internal combustion engine disclosed in Patent Document 2, if the front-stage oxidation catalyst is thermally deteriorated, In the catalyst, an increase in the exhaust temperature due to the oxidation reaction becomes insufficient, and liquefied unburnt fuel may adhere to the exhaust passage between the pre-stage oxidation catalyst and the particulate filter to form a reservoir. In such a case, there are concerns about corrosion of the exhaust pipe forming the exhaust passage, generation of white smoke, and melting of the particulate filter.

  The present invention was devised in view of such problems, and in an exhaust gas purification apparatus for an internal combustion engine in which an exhaust passage is provided with a fuel addition valve, an oxidation catalyst, and a particulate filter in order from the upstream side, the oxidation catalyst is thermally deteriorated. However, an exhaust gas purification apparatus for an internal combustion engine that can prevent unburned fuel from accumulating in an exhaust passage between the oxidation catalyst and the particulate filter provided at a certain distance from the oxidation catalyst is provided. For the purpose.

  As means for solving the above-described problems, the exhaust gas purification apparatus for an internal combustion engine of the present invention is configured as follows.

  That is, an exhaust purification device for an internal combustion engine according to the present invention includes a fuel addition valve for adding fuel to an exhaust passage of the internal combustion engine, and an oxidation provided downstream of the fuel addition valve in the exhaust passage from where the fuel is added. A catalyst, a particulate filter provided at a certain distance downstream from the oxidation catalyst in the exhaust passage, and collecting particulate matter in the exhaust; and fuel flowing into the exhaust passage by the fuel addition valve A control device having filter regeneration control means for performing filter regeneration control with addition, and the control device detects exhaust gas temperature downstream from the oxidation catalyst, and Fuel that can switch the combustion mode of the internal combustion engine to the first regeneration combustion mode or the second regeneration combustion mode in which the exhaust temperature immediately after the internal combustion engine becomes higher than the first regeneration combustion mode. Further comprising a mode switching means. The combustion mode switching means switches the combustion mode of the internal combustion engine to the first regeneration combustion mode when the exhaust gas temperature detected by the exhaust gas temperature detecting means is equal to or higher than a predetermined threshold during the filter regeneration control. And when the exhaust gas temperature detected by the exhaust gas temperature detecting means is lower than the predetermined threshold value during the filter regeneration control, the combustion mode of the internal combustion engine is set to the second regeneration combustion mode. It is what.

  If the exhaust gas temperature between the oxidation catalyst and the particulate filter is less than the predetermined threshold even though the filter regeneration control is being performed, the oxidation catalyst is thermally deteriorated and the oxidation catalyst and the particulate filter It can be estimated that unburned fuel is attached in the exhaust passage. In such a case, the exhaust gas purification apparatus for an internal combustion engine according to the present invention increases the exhaust temperature between the oxidation catalyst and the particulate filter by setting the combustion mode to the second regeneration combustion mode with a high exhaust temperature, Unburned fuel adhering to the exhaust passage can be vaporized and removed.

  Further, the exhaust gas purification apparatus for an internal combustion engine of the present invention is the exhaust gas purification apparatus for an internal combustion engine having the above configuration, wherein the control device further includes a cooling water temperature detecting means for detecting a temperature of the cooling water of the internal combustion engine, The combustion mode switching means is configured such that, during the filter regeneration control, the exhaust temperature detected by the exhaust temperature detecting means is equal to or higher than a predetermined threshold, or the temperature of the cooling water of the internal combustion engine detected by the cooling water temperature detecting means is a predetermined threshold. When the following is true, the combustion mode of the internal combustion engine is set to the first regeneration combustion mode, and the exhaust gas temperature detected by the exhaust gas temperature detecting means during the filter regeneration control is less than a predetermined threshold value of the exhaust gas temperature, and When the temperature of the cooling water of the internal combustion engine detected by the cooling water temperature detecting means exceeds a predetermined threshold value of the cooling water temperature, the combustion mode of the internal combustion engine is changed to the second regeneration combustion. And over de, it is preferable that.

  When the temperature of the cooling water is low, such as during cold start of the internal combustion engine, the exhaust temperature is naturally low, and the exhaust temperature between the oxidation catalyst and the particulate filter is naturally low even if the oxidation catalyst is not thermally degraded. Therefore, it is not necessary to raise the exhaust temperature at this point. According to the exhaust gas purification apparatus for an internal combustion engine having the above configuration, in such a case, the combustion mode can be set to the first regeneration combustion mode.

  The exhaust gas purification apparatus for an internal combustion engine according to the present invention further includes an exhaust gas recirculation device in the exhaust gas purification apparatus for an internal combustion engine having the above-described configuration, and the exhaust gas recirculation amount in the second regeneration combustion mode is the first regeneration combustion. It is desirable that the amount be less than the exhaust gas recirculation amount in the mode.

  For example, the second regeneration combustion mode is a combustion mode that involves stopping the exhaust gas recirculation.

  The fuel addition valve, for example, adds fuel to the downstream side of the turbocharger turbine in the exhaust passage.

  According to the exhaust gas purification apparatus for an internal combustion engine of the present invention, it is possible to suppress unburned fuel from adhering to the exhaust passage between the oxidation catalyst and the particulate filter and forming a pool.

It is a figure which shows schematic structure of an engine and its intake / exhaust system. It is a block diagram which shows the structure of control systems, such as engine ECU. It is a flowchart which shows procedures, such as filter reproduction | regeneration control. It is a table for judging the execution precondition of the combustion mode which used engine load and engine speed as a parameter.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a case where the present invention is applied to a common rail in-cylinder direct injection multi-cylinder diesel engine (compression self-ignition internal combustion engine) mounted on an automobile will be described.

-Engine configuration-
First, a schematic configuration of a diesel engine (hereinafter simply referred to as “engine”) according to the present embodiment will be described. FIG. 1 is a schematic configuration diagram of an engine 1 and its intake and exhaust system according to the present embodiment.

  As shown in FIG. 1, the engine 1 according to this embodiment is basically a mixture obtained by mixing air supplied from an intake system and fuel supplied from a fuel supply system at an appropriate air-fuel ratio. After the gas is burned in the combustion chamber 2, the exhaust gas is discharged to the atmosphere through the exhaust system.

  The intake system includes an intake passage formed by connecting an intake pipe 22 to an intake manifold 21 connected to an intake port 3 formed in the cylinder head, and the intake passage is sequentially arranged from the upstream side in the air flow direction. The air cleaner 23 and the throttle valve 24 are arranged.

  The fuel supply system has a configuration in which a fuel tank 32, a supply pump 33, a common rail 34, and a plurality of fuel injection valves (injectors) 35, 35,... ing. The supply pump 33 is driven by a crankshaft (not shown) of the engine 1, pumps fuel from the fuel tank 32, and supplies the pumped fuel to the common rail 34 via the fuel supply path 31. The common rail 34 functions as a pressure accumulation chamber that holds (accumulates) the high-pressure fuel supplied from the supply pump 33 at a predetermined pressure, and distributes the accumulated fuel to the fuel injection valves 35, 35,. The fuel injection valve 35 is, for example, an electromagnetically driven on-off valve that opens when a predetermined voltage is applied and supplies fuel into the combustion chamber 2.

  The exhaust system has an exhaust passage formed by connecting an exhaust pipe 42 to an exhaust manifold 41 connected to an exhaust port 4 formed in the cylinder head. The exhaust pipe 40 includes an outlet elbow 40a connected immediately downstream of the turbocharger 5, and a front pipe 40b connecting the outlet elbow 40a and the filter device 8b.

  The engine 1 is also equipped with a turbocharger (supercharger) 5, an intercooler 6, an EGR device 7 as an exhaust gas recirculation device, a pre-stage oxidation catalyst (oxidation catalyst) 8a, a filter device 8b, and a fuel addition valve 9. ing.

  As is well known, the turbocharger 5 boosts and supercharges intake air using exhaust gas pressure, and mainly includes a compressor impeller 5a housed in the compressor housing and a turbine wheel 5b housed in the turbine housing. And. The compressor impeller 5a is disposed in the middle of the intake pipe 22, and the turbine wheel 5b is disposed between the collection portion of the exhaust manifold 41 and the exhaust pipe.

  The intercooler 6 forcibly cools the intake air boosted and supercharged by the turbocharger 5, and is disposed between the compressor impeller 5 a of the turbocharger 5 and the throttle valve 24. The throttle valve 24 is an electronically controlled on-off valve whose opening degree can be adjusted steplessly, and the flow area of the intake air is reduced under a predetermined condition, and the supply amount of the intake air is adjusted (reduced). ) Function.

  The EGR device 7 lowers the combustion temperature by returning a part of the exhaust gas (EGR gas) to the intake system and supplying it again to the combustion chamber 2, thereby reducing the amount of NOx generated. The EGR cooler 7b and the EGR valve 7c are arranged from the upstream.

  The EGR cooler 7b includes a heat exchanger that lowers the temperature of the exhaust gas by exchanging heat between the exhaust gas passing through the EGR passage 7a and the cooling water of the engine 1, for example. The EGR valve 7c controls the recirculation amount of the exhaust gas recirculated from the exhaust system side to the intake system side in the EGR passage 7a.

  The front-stage oxidation catalyst 8a is disposed in the exhaust pipe 42 (outlet elbow 40a or front pipe 40b) on the downstream side of the turbine wheel 5b of the turbocharger 5.

  The filter device 8b is provided in the exhaust pipe 42 at a certain distance downstream from the upstream oxidation catalyst 8a. The filter device 8b includes a rear-stage oxidation catalyst 8ba and a particulate filter 8bb connected to the rear-stage oxidation catalyst 8ba with a slight gap.

  The particulate filter 8bb has a configuration in which, for example, a well-known DPF, an oxidation catalyst (for example, a main component of a noble metal such as platinum) is supported on a porous member. In this particulate filter 8bb, harmful substances in the exhaust are oxidized by an oxidation catalyst, converted into carbon dioxide and water vapor, and PM (particulate matter) is collected in the micropores of the porous member.

  The fuel addition valve 9 is provided so as to add fuel on the downstream side of the turbine wheel 5b of the turbocharger 5 in the exhaust pipe 42 and on the upstream side of the pre-stage oxidation catalyst 8a. Fuel is supplied to the fuel addition valve 9 from the supply pump 33 via the additive supply path 52. The unburned fuel added from the fuel addition valve 9 causes an oxidation reaction in the pre-stage oxidation catalyst 8a, and raises the exhaust gas temperature by the reaction heat. Further, the unburned fuel injected from the fuel addition valve 9 also undergoes an oxidation reaction in the rear-stage oxidation catalyst 8ba of the filter device 8b, and the exhaust gas temperature is raised by the reaction heat to be collected in the particulate filter 8bb. Burn away PM.

  Various operations of the engine 1 configured as described above are controlled by the engine ECU (Electronic Control Unit) 10.

  The engine ECU 10 includes, for example, a CPU 101, a ROM 102, a RAM 103, a backup RAM 104, and the like as shown in FIG. The ROM 102 stores various control programs, maps that are referred to when the various control programs are executed, and the like. The CPU 101 executes various arithmetic processes based on various control programs and maps stored in the ROM 102. The RAM 103 is a memory that temporarily stores calculation results of the CPU 101, data input from each sensor, and the like. The backup RAM 104 is a nonvolatile memory that stores data to be saved when the engine 1 is stopped, for example. Memory. The ROM 102, CPU 101, RAM 103, and backup RAM 104 are connected to each other via a bidirectional bus 107 and are connected to an input interface 105 and an output interface 106.

  The engine ECU 10 controls various operations of the engine 1 based on signals from various sensors (operation parameters: signals according to the vehicle running state and the engine 1 driving state). Only the regeneration control of the particulate filter 8bb will be mainly described.

  As shown in FIG. 2, the input interface 105 includes a water temperature sensor 71, an air flow meter 72, an intake air temperature sensor 73, an intake air pressure sensor 74, an A / F (air / fuel ratio) sensor 76, exhaust gas temperature sensors 77a, 77b, 77c, A rail pressure sensor 78, a throttle opening sensor 79, an accelerator opening sensor 80, a crank position sensor 81, a differential pressure sensor 82, and the like are connected.

  The water temperature sensor 71 outputs a detection signal corresponding to the cooling water temperature of the engine 1. The air flow meter 72 outputs a detection signal corresponding to the flow rate (intake air amount) of intake air upstream from the throttle valve 24 of the intake system. The intake air temperature sensor 73 is disposed in the intake manifold 21 and outputs a detection signal corresponding to the intake air temperature. The intake pressure sensor 74 is disposed in the intake manifold 21 and outputs a detection signal corresponding to the intake air pressure. The A / F sensor 76 outputs a detection signal that continuously changes in accordance with the oxygen concentration in the exhaust gas on the downstream side of the exhaust system filter device 8b.

  The exhaust temperature sensor 77a is provided to detect the exhaust temperature downstream of the upstream oxidation catalyst 8a and upstream of the particulate filter 8bb in the exhaust passage. In the present embodiment, a detection signal is output according to the inlet exhaust temperature of the rear-stage oxidation catalyst 8ba, provided upstream in the vicinity of the rear-stage oxidation catalyst 8ba. Exhaust temperature sensors 77b and 77c are also provided between the downstream oxidation catalyst 8ba and the particulate filter 8bb in the exhaust passage and on the downstream side in the vicinity of the particulate filter 8bb.

  The rail pressure sensor 78 outputs a detection signal corresponding to the fuel pressure stored in the common rail 34. The throttle opening sensor 79 detects the opening of the throttle valve 24. The accelerator opening sensor 80 outputs a detection signal corresponding to the depression amount of the accelerator pedal. The crank position sensor 81 outputs a detection signal (pulse signal) every time a crankshaft (not shown) of the engine 1 rotates by a certain angle. The differential pressure sensor 82 is provided between the post-stage oxidation catalyst 8ba and the particulate filter 8bb and in the vicinity of the particulate filter 8bb, and outputs a detection signal corresponding to each pressure in the engine ECU 10. A differential pressure before and after the particulate filter 8bb is detected.

  On the other hand, the throttle valve 24, the fuel injection valve 35, the EGR valve 7c, the fuel addition valve 9 and the like are connected to the output interface 106, and these valves are controlled according to the operating state of the engine 1 and the like. .

-Filter regeneration control-
When the engine ECU 10 estimates the amount of PM accumulated in the particulate filter 8bb and determines that the estimated amount exceeds a predetermined threshold (a value that requires regeneration of the particulate filter 8bb), the filter The regeneration flag is turned on, and the filter regeneration mode is entered. In the filter regeneration mode, filter regeneration control is executed to remove PM collected by the particulate filter 8bb. In this filter regeneration control, fuel is injected from the fuel addition valve 9 into the exhaust passage in order to burn and remove the PM collected by the particulate filter 8bb. When fuel is injected into the exhaust passage, a part thereof causes an oxidation reaction (combustion) in the pre-stage oxidation catalyst 8a to raise the exhaust temperature. Further, the surplus fuel that has not undergone the oxidation reaction at the front-stage oxidation catalyst 8a undergoes an oxidation reaction (combustion) in the rear-stage oxidation catalyst 8ba and the particulate filter 8bb to raise the exhaust temperature again. Thereby, the particulate filter 8bb rises to a temperature necessary for burning PM, and the PM collected by the particulate filter 8bb is burned and removed.

  The fuel addition from the fuel addition valve 9 to the exhaust passage is performed by referring to a map prepared beforehand through experiments or the like based on the engine speed Ne read by the engine ECU 10 from the output of the crank position sensor 81 and The addition interval is calculated, and the opening of the fuel addition valve 9 is controlled according to the calculation result.

  During the filter regeneration control, the combustion mode of the engine 1 is switched between the first regeneration combustion mode and the second regeneration combustion mode in which the exhaust gas temperature immediately after the engine 1 is higher than the first regeneration combustion mode. That is, the engine ECU 10 determines that the temperature of the engine coolant obtained from the output of the water temperature sensor 71 is equal to or higher than the predetermined threshold Gth when the exhaust gas temperature immediately before flowing into the filter device 8b is obtained from the output of the exhaust temperature sensor 77. When the temperature is equal to or lower than the threshold value Wth, the second regeneration combustion mode is set, and the second temperature when the exhaust gas temperature immediately before flowing into the filter device 8b is lower than the threshold value Gth and the engine coolant temperature exceeds the threshold value Wth. The regeneration combustion mode is set.

  In the present embodiment, the engine ECU 10 closes the EGR valve 7c of the EGR device 7 in the second regeneration combustion mode to stop exhaust gas recirculation, and opens the EGR valve 7c in the first regeneration combustion mode to exhaust the exhaust gas. Recirculation is to be performed. As a result, the exhaust temperature immediately after the engine 1 is higher in the second regeneration combustion mode than in the first regeneration combustion mode. Instead of stopping the exhaust gas recirculation by the EGR device 7 in the second regeneration combustion mode, the exhaust gas recirculation amount in the second regeneration combustion mode is made smaller than the exhaust gas recirculation amount in the first regeneration combustion mode, The exhaust temperature immediately after the engine 1 may be higher in the second regeneration combustion mode than in the first regeneration combustion mode.

  When engine ECU 10 determines that the amount of PM estimated to be accumulated in particulate filter 8bb is less than a predetermined threshold, it sets the filter regeneration mode to the OFF state. When the filter regeneration mode is turned off, the normal combustion mode in which the exhaust gas temperature immediately after the engine 1 is lower than both the first regeneration combustion mode and the second regeneration combustion mode is switched.

-Combustion mode switching control-
Hereinafter, a procedure such as switching control of the regenerative combustion mode executed by the engine ECU 10 will be described based on a flowchart shown in FIG.

  First, in step ST1, it is determined whether or not the filter regeneration mode is in effect based on whether or not the filter regeneration flag is in an ON state. If an affirmative determination is made here, the process proceeds to step ST2, and if a negative determination is made, the process proceeds to step ST7.

  As described above, the filter regeneration flag is turned ON when it is determined that the amount of PM estimated to be deposited on the particulate filter 8bb exceeds a predetermined threshold. For example, as is well known, the PM accumulation amount is estimated by mapping the PM adhesion amount according to the operating conditions of the engine 1 (for example, exhaust temperature, fuel injection amount, engine speed, etc.) in advance through experiments or the like. In addition, a method for accumulating the PM deposition amount obtained from this map to obtain a PM deposition amount, a method for estimating the PM deposition amount according to the vehicle travel distance or travel time, and the inlet (upstream side) pressure of the particulate filter 8bb And a method of estimating the PM accumulation amount collected by the particulate filter 8bb based on the output of the differential pressure sensor 82 that detects the differential pressure between the outlet pressure and the outlet (downstream side) pressure.

  On the other hand, as described above, the filter regeneration flag is turned off when it is determined that the amount of PM estimated to be accumulated in the particulate filter 8bb is less than a predetermined threshold. For example, as is well known, the PM remaining amount is estimated by mapping the combustion rate of PM according to the exhaust temperature by experimentation and the amount of combustion removal estimated based on this map from the initial PM accumulation amount. Can be obtained by subtracting.

  In step ST2, it is determined whether or not a precondition for executing the second regeneration combustion mode is satisfied. If a positive determination is made here, the process proceeds to step ST3. If a negative determination is made, the process proceeds to step ST5.

  The determination of step ST2 is relatively easy to switch to the second regeneration combustion mode when the exhaust temperature is difficult to rise, such as when the intake air temperature (outside air temperature) is low, as when the intake air temperature is high. In addition, it is relatively easy to switch to the first regeneration combustion mode when the exhaust temperature is likely to rise. Specifically, the engine ECU 10 is based on the intake air temperature obtained from the output signal from the intake air temperature sensor 73, and the first to third tables described later using the engine load (fuel injection amount) and the engine speed as parameters. 1 is selected, and the precondition is determined based on the selected table. These first to third tables are stored in the ROM 102 in advance.

  The engine ECU 10 selects the first table as shown in FIG. 4A when the intake air temperature obtained from the output signal from the intake air temperature sensor 73 is equal to or higher than a predetermined threshold temperature T1, and the intake air temperature is equal to or higher than the predetermined threshold temperature T2. When the temperature is lower than the threshold temperature T1, the second table as shown in FIG. 4B is selected. When the intake air temperature is lower than the threshold temperature T2, the third table as shown in FIG. 4C is selected. The hysteresis is set so that the threshold temperature when the intake air temperature changes from the low temperature side to the high temperature side is higher by a predetermined value than the threshold temperature T1 and T2 when the intake air temperature changes from the high temperature side to the low temperature side. It may be provided.

  In the present embodiment, the first table, the second table, and the third table are selected in order as the intake air temperature is shifted from the high temperature side to the low temperature side. Any one of the first table, the second table, and the third table may be selected by using the atmospheric pressure obtained from the output signal of the atmospheric pressure sensor as a parameter instead of the intake air temperature. In this case, the first table, the second table, and the third table are sequentially selected as the atmospheric pressure moves from the high pressure side to the low pressure side.

  The first table shown in FIG. 4A is a table selected in an environment in which the exhaust gas temperature is relatively easy to rise (when the intake air temperature is relatively high and when the atmospheric pressure is relatively high). An executable region of the first regeneration combustion mode is set. The normal combustion mode is set in a region where the fuel injection amount of the fuel injection valve 35 is Q1 or less and the rotational speed of the engine 1 is Ne1 or less. In the first regeneration combustion mode, the fuel injection amount of the fuel injection valve 35 is set to an area where Q2 or less and the rotational speed of the engine 1 is Ne2 or less. Here, Q1> Q2 and Ne1> Ne2. When the first table is selected, the engine ECU 10 makes a negative determination in step ST2 because the executable region of the second regeneration combustion mode is not set. The fuel injection amount of the fuel injection valve 35 can be calculated based on, for example, a map for setting the fuel injection amount with the engine speed and the intake air amount as parameters. Can be calculated based on the output signal of the crank position sensor 81, for example.

  The second table shown in FIG. 4B sets the feasible regions for the normal combustion mode, the first regeneration combustion mode, and the second regeneration combustion mode. The normal combustion mode is set in a region where the fuel injection amount of the fuel injection valve 35 is Q3 or less and the rotational speed of the engine 1 is Ne3 or less. In the first regeneration combustion mode, the fuel injection amount of the fuel injection valve 35 is set to an area where Q4 or less and the rotation speed of the engine 1 is Ne4 or less. The second combustion mode is set in a region where the fuel injection amount of the fuel injection valve 35 is Q5 or less and the rotational speed of the engine 1 is Ne5 or less. Here, Q3> Q4> Q5 and Ne3> Ne4> Ne5. When this second table is selected, the engine ECU 10 makes an affirmative determination in step ST2 when the fuel injection amount of the fuel injection valve 35 is Q5 or less and the rotation speed of the engine 1 is Ne5 or less, and otherwise Make a negative decision.

  Further, the third table shown in FIG. 4C is a table selected under an environment where the exhaust temperature is relatively difficult to rise, and sets the executable region of the normal combustion mode and the second regeneration combustion mode. The normal combustion mode is set in a region where the fuel injection amount of the fuel injection valve 35 is Q6 or less and the rotational speed of the engine 1 is Ne6 or less. In the second regeneration combustion mode, the fuel injection amount of the fuel injection valve 35 is set to an area where Q7 or less and the engine speed is Ne7 or less. Here, Q6> Q7 and Ne6> Ne7. When this third table is selected, the engine ECU 10 makes an affirmative determination in step ST2 when the fuel injection amount of the fuel injection valve 35 is equal to or less than Q7 and the rotational speed of the engine 1 is equal to or less than Ne7, and otherwise Make a negative decision.

  In step ST3, it is determined whether or not the exhaust gas temperature detected from the exhaust gas temperature sensor 77 is less than a predetermined threshold value Gth and the coolant temperature detected from the water temperature sensor 71 exceeds a predetermined threshold value Wth. . If an affirmative determination is made here, the process proceeds to step ST4, and if a negative determination is made, the process proceeds to step ST5. If the exhaust temperature immediately before flowing into the filter device 8b is lower than the threshold value Gth even though the fuel is added to the upstream oxidation catalyst 8a from the fuel addition valve 9 by entering the filter regeneration mode, the upstream oxidation catalyst 8a is heated. It is assumed that liquefied unburned fuel is attached to the exhaust passage between the pre-stage oxidation catalyst 8a and the filter device 8b, or that a pool of unburned fuel is formed. This step ST3 is for making an affirmative determination in such a case and switching to the second regeneration combustion mode in which the exhaust gas temperature is relatively high in step ST4 described later. The exhaust gas temperature threshold Gth is a value that can be estimated that the front-stage oxidation catalyst 8a is in an inactive state when the exhaust temperature is lower than the threshold during the filter regeneration mode, or the front-stage oxidation catalyst 8a is thermally deteriorated. A value that can be estimated that liquefied unburned fuel is attached to the exhaust passage between the front-stage oxidation catalyst 8a and the filter device 8b is set. Such a threshold value is obtained by experiments or the like.

  In step ST3, the cooling water temperature of the engine 1 is used as the determination parameter for the following reason. That is, when the temperature of the cooling water is low as in the case where the engine 1 is started at the time of cold start, the exhaust temperature is naturally low and the conditions for enabling the front-stage oxidation catalyst 8a are not satisfied. Even if 8a is not thermally deteriorated, the exhaust temperature detected by the exhaust temperature sensor 77 is naturally low. In such a case, the combustion mode is set to the first regeneration combustion mode in order to prevent the emission from deteriorating.

  Further, when the temperature of the cooling water is low, the temperature in the combustion chamber 2 is also low. In such a case, if the exhaust gas recirculation amount is set to zero or less in the second regeneration combustion mode, the pilot injected fuel becomes difficult to warm up. In addition, the ignitability of the pilot injection fuel or the like tends to deteriorate. In order to prevent such deterioration of ignitability and maintain a suitable combustion state, the combustion mode is set to the first regeneration combustion mode.

  In step ST4, the combustion mode is switched to the second regeneration combustion mode in which the exhaust temperature is higher than that in the first regeneration combustion mode. If the combustion mode is already set, the combustion mode is maintained. By setting the combustion mode to the second regeneration combustion mode with a relatively high exhaust temperature, the exhaust temperature passing through the exhaust passage between the front-stage oxidation catalyst 8a and the filter device 8ba rises and does not adhere to the exhaust passage. The accumulated liquefied unburnt fuel is vaporized and sent to the downstream side of the exhaust passage. Further, since the temperature of the exhaust gas supplied to the pre-stage oxidation catalyst 8a rises, the pre-stage oxidation catalyst 8a that is thermally deteriorated is activated and the exhaust temperature passing through the pre-stage oxidation catalyst 8a is likely to rise. The exhaust temperature passing through the exhaust passage between 8a and the filter device 8ba is more likely to rise. Of course, if the particulate filter 8bb has not been heated to a temperature required for filter regeneration due to thermal degradation of the pre-stage oxidation catalyst 8a, the temperature is increased to that temperature, so that the filter regeneration is performed well. Will come to be.

  In step ST5, it is determined whether or not a precondition for executing the first regeneration combustion mode is satisfied. If an affirmative determination is made here, the process proceeds to step ST6. If a negative determination is made, the process proceeds to step ST7. Note that the determination in step ST5 is based on the first table to the third table shown in FIGS. 4 (a) to 4 (c) based on the intake air temperature by the engine ECU 10 as in the description in step ST2. Any one is selected, and this is performed based on the selected table. For example, when the engine ECU 10 selects the first table shown in FIG. 4A, when the fuel injection amount of the fuel injection valve 35 is Q2 or less and the rotation speed of the engine 1 is Ne2 or less, an affirmative determination is made in step ST5. Otherwise, a negative determination is made. Further, for example, when the engine ECU 10 selects the second table shown in FIG. 4B, when the fuel injection amount of the fuel injection valve 35 is Q4 or less and the rotation speed of the engine 1 is Ne4 or less, in step ST5 An affirmative determination is made, and a negative determination is made otherwise. Further, for example, when the engine ECU 10 selects the third table shown in FIG. 4C, a negative determination is made in step ST5 because the executable region of the first regeneration combustion mode is not set.

  In step ST6, the combustion mode is switched to the first regeneration combustion mode in which the exhaust temperature is lower than that in the second regeneration combustion mode. If the combustion mode is already set, the combustion mode is maintained.

  In step ST7, the combustion mode is switched to the normal combustion mode having a lower exhaust temperature than both the first and second regeneration combustion modes. If the same combustion mode has already been set, the setting is maintained.

  The present invention can be applied to, for example, an exhaust purification device that regenerates a particulate filter installed in an exhaust passage by adding unburned fuel to the exhaust passage by a fuel addition valve.

1 engine (internal combustion engine)
5 Turbocharger (supercharger)
5b Turbine wheel (turbine)
7 EGR device (exhaust gas recirculation device)
8a Pre-stage oxidation catalyst (oxidation catalyst)
8b Filter device 8ba Post-stage oxidation catalyst 8bb Particulate filter 9 Fuel addition valve 10 Engine ECU (control device)
42 Exhaust pipe (exhaust passage)
71 Water temperature sensor (cooling water temperature detection means)
77a, 77b, 77c Exhaust temperature sensor (exhaust temperature detection means)

Claims (5)

A fuel addition valve for adding fuel to the exhaust passage of the internal combustion engine;
An oxidation catalyst provided downstream of the fuel addition valve in the exhaust passage from the position where the fuel is added;
A particulate filter that is provided at a certain distance downstream of the oxidation catalyst in the exhaust passage and collects particulate matter in the exhaust;
A control device having filter regeneration control means for performing filter regeneration control accompanied by addition of fuel into the exhaust passage by the fuel addition valve;
An exhaust gas purification apparatus for an internal combustion engine comprising:
The controller is
Exhaust temperature detection means for detecting the exhaust temperature downstream of the oxidation catalyst, and the combustion mode of the internal combustion engine in the first regeneration combustion mode or the second regeneration in which the exhaust temperature immediately after the internal combustion engine is higher than in the first regeneration combustion mode Combustion mode switching means that can be switched to the combustion mode,
The combustion mode switching means sets the combustion mode of the internal combustion engine to the first regeneration combustion mode when the exhaust gas temperature detected by the exhaust gas temperature detection means is equal to or higher than a predetermined threshold during the filter regeneration control, When the exhaust gas temperature detected by the exhaust gas temperature detecting means during the filter regeneration control is less than the predetermined threshold value, the combustion mode of the internal combustion engine is set to the second regeneration combustion mode. An exhaust purification device for an internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
The controller is
A cooling water temperature detecting means for detecting the temperature of the cooling water of the internal combustion engine;
The combustion mode switching means is configured such that, during the filter regeneration control, the exhaust gas temperature detected by the exhaust gas temperature detecting means is equal to or higher than a predetermined threshold value, or the temperature of the cooling water of the internal combustion engine detected by the cooling water temperature detecting means is a predetermined When it is equal to or lower than the threshold value, the combustion mode of the internal combustion engine is set to the first regeneration combustion mode, and the exhaust gas temperature detected by the exhaust gas temperature detecting means during the filter regeneration control is less than a predetermined threshold value of the exhaust gas temperature. And when the temperature of the cooling water of the internal combustion engine detected by the cooling water temperature detecting means exceeds a predetermined threshold value of the cooling water temperature, the combustion mode of the internal combustion engine is set to the second regeneration combustion mode. An exhaust purification device for an internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2,
An exhaust gas purification apparatus for an internal combustion engine, further comprising an exhaust gas recirculation device, wherein an exhaust gas recirculation amount in the second regeneration combustion mode is smaller than an exhaust gas recirculation amount in the first regeneration combustion mode. The exhaust gas purification apparatus for an internal combustion engine according to claim 3,
The exhaust gas purification apparatus for an internal combustion engine, wherein the second regeneration combustion mode is a combustion mode accompanied by stop of exhaust gas recirculation. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 4,
The exhaust gas purification apparatus for an internal combustion engine, wherein the fuel addition valve is configured to add fuel to the downstream side of the turbocharger turbine in the exhaust passage.

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