JP2007321575A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent blocking-up of a nozzle port of a fuel adding valve, while restraining the deterioration in fuel economy, in an exhaust emission control device having the fuel adding valve for adding fuel to an exhaust passage. <P>SOLUTION: In an environmental change such as an atmospheric pressure change when transferring to highland operation from flatland operation and transfer to transitional operation from steady operation, the final adding interval (a fuel adding quantity per unit time) is set by correcting a reference adding interval (Step ST4 and ST8), by calculating an adding interval correction factor on the basis of a variation in a PM discharge quantity, by taking into consideration a point of increasing the PM discharge quantity more than a flatland steady operation state when the suction air volume of an engine reduces. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an apparatus for purifying exhaust gas of an internal combustion engine with a catalyst, and more particularly to an exhaust purification apparatus provided with a fuel addition valve for adding fuel to an exhaust passage.

  In general, in an internal combustion engine that performs lean combustion, such as a diesel engine, an operation region in which an air-fuel mixture with a high air-fuel ratio (lean atmosphere) is burned occupies most of the entire operation region. For this reason, a NOx storage agent (NOx storage catalyst) for storing (absorbing) nitrogen oxide (hereinafter referred to as NOx) contained in the exhaust gas is disposed in the exhaust passage of this type of engine, and the exhaust gas is disposed. I try to purify it.

  In such a NOx storage catalyst, when the NOx storage amount reaches a saturated state, it is necessary to reduce the NOx and recover the NOx storage catalyst. As a method for reducing NOx, by adding a NOx reducing agent (fuel such as light oil) upstream of the NOx storage catalyst in the exhaust passage, the oxygen concentration in the catalytic converter is lowered, and excess hydrocarbons and carbon monoxide are added. The process (NOx reduction process) which accelerates | stimulates the reduction | restoration of NOx by using etc. as a reducing agent is performed.

  In addition, the exhaust gas of diesel engines includes particulate matter mainly composed of carbon (hereinafter referred to as PM (Particulate Matter)), SOOT (soot), SOF (Soluble Organic Fraction), and the like. Cause air pollution. For the purpose of purifying such PM and the like, a particulate filter is disposed in the exhaust passage of the diesel engine, and the PM contained in the exhaust gas passing through the exhaust passage is collected and released into the atmosphere. There are known exhaust emission control devices that reduce the amount of emissions. As the particulate filter, for example, a DPF (Diesel Particulate Filter) or a DPNR (Diesel Particulate-NOx Reduction system) catalyst is used.

  When collecting particulate matter using a particulate filter, if the amount of collected particulate matter increases and the particulate filter becomes clogged, the pressure loss of the exhaust gas passing through the particulate filter increases. Along with this, an increase in engine exhaust back pressure causes a decrease in engine output and fuel consumption. As a method for solving this problem, there is a process (PM regeneration process) that promotes oxidation (combustion) of PM on the particulate filter by adding fuel to the exhaust passage (upstream of the particulate filter) to raise the exhaust temperature. Has been done.

As described above, in the NOx reduction process and the PM regeneration process that are performed in order to suppress the reduction in the exhaust gas purification effect of the catalyst, the fuel addition valve is disposed in the exhaust passage and the fuel (reducing agent) is supplied into the exhaust passage. is doing. However, since the injection hole of the fuel addition valve is exposed in the exhaust passage, substances such as SOOT and SOF contained in the exhaust gas adhere to and accumulate on the injection hole of the fuel addition valve. Then, there is a concern that the adhered / deposited material may be altered and solidified by exposure to high-temperature exhaust gas, resulting in deposits and blocking the nozzle holes of the fuel addition valve. As a method of preventing such clogging of the fuel addition valve, there is a method of lowering the tip temperature of the fuel addition valve by forcibly adding fuel at a timing other than fuel addition during NOx reduction or PM regeneration. Yes (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2003-222019

  By the way, for example, when the engine intake air amount decreases due to environmental changes such as changes in atmospheric pressure when shifting from flatland operation to highland operation, or when shifting from steady operation to transient operation, it is more than the flatland / normal operation state. PM emissions increase. When the PM discharge amount increases, the amount of PM adhering to / intruding into the nozzle hole of the fuel addition valve increases, and deposits are likely to be generated. Therefore, the nozzle hole of the fuel addition valve may be blocked.

  In order to solve such a problem of injection hole blockage, it is sufficient to adapt the fuel addition amount (addition amount per unit time) at the upper limit of the variation in the PM discharge amount, but the fuel addition amount at the upper limit of the variation in the PM discharge amount. There is a concern that the fuel consumption (fuel consumption) tends to deteriorate if the above is applied.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an exhaust emission control device capable of preventing the fuel injection valve from closing the nozzle hole while suppressing deterioration in fuel consumption.

  The present invention relates to an exhaust gas purification apparatus including a catalyst disposed in an exhaust passage of an internal combustion engine and a fuel addition valve for adding fuel to the exhaust passage, and discharging particulate matter from a combustion chamber of the internal combustion engine. A correction means is provided for correcting the addition amount per unit time of the fuel added from the fuel addition valve to the exhaust passage based on the change amount of the amount (PM emission amount).

  In the present invention, when the intake air amount of the engine decreases, such as when the engine intake air amount decreases due to an environmental change such as a change in atmospheric pressure when shifting from flatland operation to highland operation, or when shifting from steady operation to transient operation, In consideration of the increase in PM emission amount, the fuel addition amount per unit time is corrected based on the change amount of PM emission amount (for example, change in actual intake air amount). It becomes possible to add fuel with an appropriate addition amount commensurate with the amount, and excessive fuel addition can be suppressed. As a result, it is possible to prevent the injection hole blockage of the fuel addition valve while suppressing deterioration of fuel consumption.

  In the present invention, as a method of correcting the addition amount per unit time, the final addition interval is set by multiplying the reference addition interval according to the operating state of the internal combustion engine by the correction coefficient according to the change amount of the PM emission amount. A method can be mentioned. In this case, more specifically, the addition interval is short when the actual intake air amount of the internal combustion engine is smaller than the reference intake air amount (when the air amount ratio (actual intake air amount / reference intake air amount) is small). The final addition interval is set by multiplying the reference addition interval by a correction coefficient that is corrected to the side that increases the addition amount per unit time.

  Here, in the exhaust emission control device provided with the fuel addition valve for adding fuel to the exhaust passage, when the atmospheric temperature (exhaust temperature) at the tip of the fuel addition valve is higher than the reference setting, Since the tip temperature also rises, there is a possibility that the injection hole of the fuel addition valve is blocked by the deposit generated by the temperature rise, and in this case also, it is necessary to increase the amount of fuel addition. In consideration of such points, in the present invention, the final addition interval is set in consideration of the tip temperature of the fuel addition valve.

  Specifically, in an exhaust gas purification apparatus comprising a catalyst disposed in an exhaust passage of an internal combustion engine and a fuel addition valve for adding fuel to the exhaust passage, particulate matter from a combustion chamber of the internal combustion engine Compensation means for correcting the addition interval of fuel added to the exhaust passage from the fuel addition valve based on the change amount of the discharge amount (PM change amount), and addition valve temperature estimation means, the correction means, A first correction coefficient for correcting the addition interval to a shorter side when the actual intake air amount of the internal combustion engine is smaller than the reference intake air amount, and the addition valve temperature estimated by the addition valve temperature estimating means is higher from the lower side The second correction coefficient that corrects the addition interval to the short side when the addition interval is changed is compared, and the correction coefficient on the short addition interval is selected as the reference addition interval among the first correction coefficients or the second correction coefficients. Multiply to set the final addition interval.

  As described above, the correction coefficient based on the change amount of the PM exhaust amount or the correction coefficient based on the addition valve tip temperature is selected which has a shorter addition interval (i.e., a larger addition amount per unit time). By correcting the reference addition interval, the fuel addition valve tip temperature rises or the environment changes and the PM emission increases during the transition period. On the other hand, since the addition interval can be corrected, the injection hole blockage of the fuel addition valve can be more effectively suppressed. In addition, fuel can be added at an appropriate amount that matches the changes in the situation, such as an increase in the temperature at the tip of the fuel addition valve, or an increase in PM emissions during environmental changes and transitional periods. Can be suppressed. As a result, it is possible to prevent the injection hole blockage of the fuel addition valve while suppressing deterioration of fuel consumption.

  By the way, when the fuel addition amount per unit time is increased in order to suppress the injection hole blockage of the fuel addition valve, the fuel reacts in the catalyst and the catalyst bed temperature can exceed a predetermined range (for example, 750 ° C.). There is sex. As a method for preventing this, when the temperature of the catalyst exceeds a predetermined value, the amount of fuel added per unit time is set according to the temperature of the catalyst (specifically, the amount of change in the catalyst temperature from the predetermined value). One way to do this is to reduce it. By adopting such a method, it is possible to avoid the problem that the catalyst bed temperature rises excessively due to the increase in the amount of fuel added and the catalyst is thermally deteriorated.

  As a method of reducing the amount of fuel added per unit time, the final addition interval is made shorter than the reference addition interval (for example, the final addition interval obtained by the above correction), and the addition per one time shown in FIG. The method of shortening time can be mentioned. By adopting such a method, it is possible to reduce the total amount of fuel added while ensuring a short addition interval that suppresses the clogging of the injection hole of the fuel addition valve. It is possible to suppress the injection hole blockage of the addition valve.

  Further, as another method for preventing an excessive increase in the catalyst bed temperature, a method of limiting the increase correction of the fuel addition amount per unit time so that the catalyst bed temperature estimated by the exhaust temperature or the like does not exceed a predetermined value. Can be mentioned.

  According to the present invention, the fuel addition amount (addition interval) per unit time is corrected based on the amount of change in the PM emission amount in consideration of the fact that the PM emission amount increases more than the flat ground / normal operation state. Therefore, it is possible to add fuel with an appropriate addition amount commensurate with the amount of change in the PM emission amount, thereby preventing the fuel injection valve from being blocked while the deterioration of fuel consumption is suppressed.

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

-Engine-
A schematic configuration of a diesel engine to which the fuel addition apparatus of the present invention is applied will be described with reference to FIG.

  A diesel engine 1 (hereinafter referred to as “engine 1”) in this example is, for example, a common rail in-cylinder direct injection four-cylinder engine, and includes a fuel supply system 2, a combustion chamber 3, an intake system 6, an exhaust system 7, and the like. Is configured as the main part.

  The fuel supply system 2 includes a supply pump 21, a common rail 22, an injector (fuel injection valve) 23, a shutoff valve 24, a fuel addition valve 25, an engine fuel passage 26, an addition fuel passage 27, and the like.

  The supply pump 21 pumps fuel from the fuel tank, raises the pumped fuel to a high pressure, and supplies the pumped fuel to the common rail 22 via the engine fuel passage 26. The common rail 22 has a function as a pressure accumulation chamber that holds (accumulates) the high-pressure fuel supplied from the supply pump 21 at a predetermined pressure, and distributes the accumulated fuel to each injector 23. The injector 23 is an electromagnetically driven on-off valve that opens when a predetermined voltage is applied and injects fuel into the combustion chamber 3.

  Further, the supply pump 21 supplies a part of the fuel pumped from the fuel tank to the fuel addition valve 25 via the addition fuel passage 27. The fuel addition valve 25 is an electromagnetically driven on-off valve that opens when a predetermined voltage is applied and adds fuel to the exhaust system 7 (from the exhaust port 71 to the exhaust manifold 72). The nozzle hole of the fuel addition valve 25 is exposed in the exhaust system 7. The shutoff valve 24 shuts off the fuel supply by shutting off the added fuel passage 27 in an emergency.

  The intake system 6 includes an intake manifold 63 connected to an intake port formed in the cylinder head, and an intake pipe 64 constituting an intake passage is connected to the intake manifold 63. Further, an air cleaner 65, an air flow meter 32, and a throttle valve 62 are disposed in the intake passage in order from the upstream side. The air flow meter 32 outputs an electrical signal corresponding to the amount of air that flows into the intake passage via the air cleaner 65.

  The exhaust system 7 includes an exhaust manifold 72 connected to an exhaust port 71 formed in the cylinder head, and exhaust pipes 73 and 74 constituting an exhaust passage are connected to the exhaust manifold 72. A catalyst device 4 is disposed in the exhaust passage.

The catalyst device 4 includes a NOx storage reduction catalyst 4a and a DPNR catalyst 4b. The NOx occlusion reduction type catalyst 4a occludes NOx in a state where a large amount of oxygen is present in the exhaust gas, has a low oxygen concentration in the exhaust gas, and has a reducing component (for example, an unburned component (HC) of the fuel). In a state where a large amount exists, NOx is reduced to NO ₂ or NO and released. NO NOx released as NO ₂ or NO, the N ₂ is further reduced due to quickly reacting with HC or CO in the exhaust. Further, HC and CO are oxidized to H ₂ O and CO ₂ by reducing NO ₂ and NO.

  The DPNR catalyst 4b is, for example, a NOx occlusion reduction catalyst supported on a porous ceramic structure, and PM in the exhaust gas is collected when passing through the porous wall. Further, when the air-fuel ratio of the exhaust gas is lean, NOx in the exhaust gas is stored in the NOx storage reduction catalyst, and when the air-fuel ratio becomes rich, the stored NOx is reduced and purified. Further, the DPNR catalyst 4b has a function of oxidizing and burning the collected PM.

  The above-described catalyst device 4, the fuel addition valve 25, the added fuel passage 27, the shut-off valve 24, the ECU (electronic control unit) 100 that performs opening / closing control of the fuel addition valve 25, and the like constitute an exhaust purification device.

  The engine 1 is provided with a turbocharger (supercharger) 5. The turbocharger 5 includes a turbine wheel 5b and a compressor impeller 5c connected via a turbine shaft 5a. The compressor impeller 5c is arranged facing the inside of the intake pipe 64, and the turbine wheel 5b is arranged facing the inside of the exhaust pipe 73. Such a turbocharger 5 supercharges intake air by rotating the compressor impeller 5c using an exhaust flow (exhaust pressure) received by the turbine wheel 5b. The turbocharger 5 of this example is a variable nozzle type turbocharger, and is provided with a variable nozzle vane mechanism 5d on the turbine wheel 5b side. The supply pressure can be adjusted.

  An intake pipe 64 of the intake system 6 is provided with an intercooler 61 for forcibly cooling the intake air whose temperature has been raised by supercharging in the turbocharger 5. A throttle valve 62 is provided further downstream than the intercooler 61. The throttle valve 62 is an electronically controlled on-off valve whose opening degree can be adjusted in a stepless manner, and the flow area of the intake air is reduced under a predetermined condition, and the supply amount of the intake air is adjusted ( It has a function to reduce).

  Further, the engine 1 is provided with an EGR passage (exhaust gas recirculation passage) 8 that connects the intake system 6 and the exhaust system 7. The EGR passage 8 is configured to reduce the combustion temperature by recirculating a part of the exhaust gas to the intake system 6 and supplying it again to the combustion chamber 3, thereby reducing the amount of NOx generated. Further, the EGR passage 8 is provided with an EGR valve 81 and an EGR cooler 82 for cooling the exhaust gas passing (refluxing) through the EGR passage 8, and by adjusting the opening degree of the EGR valve 81, The amount of EGR (exhaust gas recirculation amount) introduced from the exhaust system 7 to the intake system 6 can be adjusted.

-Sensors-
Various sensors are attached to each part of the engine 1, and signals related to the environmental conditions of each part and the operating state of the engine 1 are output.

  For example, the air flow meter 32 outputs a detection signal corresponding to the flow rate (intake air amount) of intake air upstream of the throttle valve 62 in the intake system 6. The intake air temperature sensor 33 is disposed in the intake manifold 63 and outputs a detection signal corresponding to the intake air temperature. The intake pressure sensor 34 is disposed in the intake manifold 63 and outputs a detection signal corresponding to the intake air pressure. The A / F (air-fuel ratio) sensor 35 outputs a detection signal that continuously changes in accordance with the oxygen concentration in the exhaust gas downstream of the catalyst device 4 of the exhaust system 7. Similarly, the exhaust temperature sensor 36 outputs a detection signal corresponding to the temperature of exhaust gas (exhaust temperature) downstream of the catalyst device 4 of the exhaust system 7. The rail pressure sensor 37 outputs a detection signal corresponding to the fuel pressure stored in the common rail 22. The fuel pressure sensor 38 outputs a detection signal corresponding to the pressure (fuel pressure) of the fuel flowing through the added fuel passage 27.

-ECU-
As shown in FIG. 2, the ECU 100 includes a CPU 101, a ROM 102, a RAM 103, a backup RAM 104, and the like. 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 bus 107 and are connected to an input interface 105 and an output interface 106.

  An air flow meter 32, an intake air temperature sensor 33, an intake air pressure sensor 34, an A / F sensor 35, an exhaust gas temperature sensor 36, a rail pressure sensor 37, and a fuel pressure sensor 38 are connected to the input interface 105. A water temperature sensor 31 that outputs a detection signal corresponding to the cooling water temperature, an atmospheric pressure sensor 39 that detects an atmospheric pressure that fluctuates due to an environment such as altitude, and an accelerator opening that outputs a detection signal corresponding to the amount of depression of the accelerator pedal A degree sensor 40 and a crank position sensor 41 that outputs a detection signal (pulse) each time the output shaft (crankshaft) of the engine 1 rotates by a certain angle are connected. On the other hand, the injector 23, the shutoff valve 24, the fuel addition valve 25, the variable nozzle vane mechanism 5d, the throttle valve 62, the EGR valve 81, and the like are connected to the output interface 106.

  The ECU 100 executes various controls of the engine 1 based on the outputs of the various sensors described above. Further, the ECU 100 executes the following PM regeneration control and addition interval correction processing.

-PM regeneration control-
First, the ECU 100 estimates the amount of PM deposited on the DPNR catalyst 4b. As a method for estimating the PM accumulation amount, for example, a PM adhesion amount corresponding to the operating state of the engine 1 (for example, exhaust temperature, fuel injection amount, engine speed, etc.) is obtained in advance through experiments or the like and mapped. A method for accumulating the PM adhesion amount obtained from this map to obtain the PM accumulation amount, a method for estimating the PM accumulation amount according to the vehicle travel distance or travel time, or the upstream of the DPNR catalyst 4b in the catalyst device 4 Examples include a method in which a differential pressure sensor that detects a differential pressure between the side pressure and the downstream pressure is provided, and the amount of PM collected in the DPNR catalyst 4b is estimated based on the sensor output.

Then, the ECU 100 determines that it is time to regenerate the DPNR catalyst 4b when the estimated PM amount is equal to or greater than a predetermined reference value (limit accumulation amount), and executes PM regeneration control. Specifically, based on the engine speed read from the output of the crank position sensor 41, the required addition amount and addition interval of fuel are calculated with reference to a map created in advance through experiments, etc. Then, the opening and closing of the fuel addition valve 25 is controlled, and fuel addition to the exhaust system 7 is repeated intermittently. By such fuel addition, the catalyst bed temperature of the DPNR catalyst 4b rises, and the PM deposited on the DPNR catalyst 4b is oxidized and discharged as H ₂ O or CO ₂ .

In addition to the above PM regeneration control, the ECU 100 may execute S poison recovery control and NOx reduction control. The S poison recovery control is to intermittently repeat the fuel addition from the fuel addition valve 25 to increase the catalyst bed temperature, and to make the air-fuel ratio of the exhaust gas stoichiometric or rich so that the NOx occlusion reduction type catalyst 4a and DPNR In this control, sulfur is released from the NOx occlusion reduction catalyst in the catalyst 4b. In addition, the NOx reduction control is performed by intermittently adding fuel from the fuel addition valve 25 to store NOx stored in the NOx storage reduction catalyst 4a and the NOx storage reduction catalyst in the DPNR catalyst 4b as N ₂ , CO ₂ and This is control to reduce to H ₂ O and purify.

  These PM regeneration control, S poison recovery control and NOx reduction control are performed when there is a request for execution of each, but when the execution of each control overlaps, PM regeneration control → S poison recovery control → NOx. Prioritized in the order of reduction control.

-Addition interval correction processing-
First, in the engine 1 mounted on the vehicle, as described above, the engine changes when the environment changes, such as a change in atmospheric pressure when the operation is changed from the flat operation to the high operation, or when the operation changes from the steady operation state to the transient operation state. When the intake air amount decreases, the PM emission amount increases more than in the flat ground / normal operation state. When the PM discharge amount increases, the amount of PM adhering to and intruding into the nozzle hole of the fuel addition valve 25 increases, and deposits are easily generated. Therefore, the nozzle hole of the fuel addition valve 25 may be blocked. Further, when the atmospheric temperature (exhaust temperature) at the front end of the fuel addition valve 25 is higher than that at the reference setting, the front end temperature of the fuel addition valve 25 also increases, so that the deposit generated by the temperature rise is increased. As a result, the nozzle hole of the fuel addition valve 25 may be blocked.

  In order to solve such a problem, in this embodiment, an addition interval correction coefficient eminttemp for correcting the addition interval of the fuel based on the tip temperature of the fuel addition valve 25 is calculated. Further, an addition interval correction coefficient emintpm for correcting the addition interval of fuel is calculated based on the change amount of the PM emission amount in the environmental change / transition period, and the unit time of the addition interval correction coefficient eminttemp or the addition interval correction coefficient emintpm is calculated. A feature is that the injection hole blockage of the fuel addition valve 25 is prevented while suppressing the deterioration of fuel consumption by selecting the correction coefficient that increases the fuel addition amount per hit and setting the final fuel addition interval. is there.

  A specific example of the addition interval correction process will be described with reference to the flowchart of FIG. This addition interval correction process is a process executed by the ECU 100. This correction processing routine is repeatedly executed at a predetermined time period.

  First, in step ST1, the engine speed Ne is read from the output of the crank position sensor 41, and the required addition amount Q is calculated with reference to a map based on the engine speed Ne. The map for calculating the required addition amount Q is a map in which the relationship between the engine speed Ne and the required addition amount Q is obtained in advance through experiments and calculations, and is stored in the ROM 102 of the ECU 100 in advance. ing.

  In step ST2, the fuel reference addition interval Tb (see FIG. 8) is calculated with reference to the map of FIG. 4 based on the required addition amount Q and the engine speed Ne. The reference addition interval calculation map is a map in which the relationship between the required addition amount Q and the engine speed Ne and the reference addition interval Tb is obtained in advance through experiments and calculations, and is mapped in the ROM 102 of the ECU 100 in advance. It is remembered. In step ST2, a reference exhaust temperature (a temperature around the fuel addition valve 25) when the reference addition interval Tb is calculated is acquired.

  In step ST3, an addition interval correction coefficient eminttemp for correcting the addition interval of the fuel based on the tip temperature of the fuel addition valve 25 is calculated.

  Specifically, the addition interval correction coefficient eminttemp is calculated with reference to the map of FIG. 5 based on the difference (exhaust temperature change amount ΔTh) between the reference exhaust temperature obtained in step ST2 and the current exhaust temperature. The addition interval correction coefficient map shown in FIG. 5 is obtained by previously obtaining the relationship between the exhaust gas temperature change amount ΔTh and the addition interval correction coefficient einttemp by experiment / calculation and the like, and mapping these relationships in the ROM 102 of the ECU 100. Stored in advance. The addition interval correction coefficient eminttemp is set to be smaller as the exhaust gas temperature change amount ΔTh is larger, and the fuel addition interval is shortened as the addition interval correction coefficient eminttemp based on the addition valve tip temperature is smaller.

  As for the exhaust temperature (ambient temperature of the fuel addition valve 25), an exhaust temperature calculation map using the engine speed Ne, the intake air temperature, the atmospheric pressure, and the like as parameters is created in advance through experiments and calculations and stored in the ROM 102 of the ECU 100. In addition, the exhaust temperature calculation map may be used for calculation, or, for example, a pre-turbo exhaust temperature sensor that detects the exhaust temperature upstream of the turbocharger 5 is installed, and the sensor output is calculated from the sensor output. The exhaust temperature may be obtained.

  In step ST4, an addition interval correction coefficient emintpm for correcting the fuel addition interval is calculated based on the amount of change in the PM emission amount in the environmental change / transition period.

  Specifically, first, the following air amount ratio calculation and PM emission coefficient λ correction coefficient are calculated.

Calculation of the air amount ratio Based on the actual intake air amount of the engine 1 obtained from the output signal of the air flow meter 32 and the reference intake air amount on flat ground, the air amount ratio gnr (air amount ratio = intake air amount / reference Intake air amount) is calculated.

Calculation of λ correction coefficient for PM emission amount Based on the air amount ratio gnr calculated by the above processing and the atmospheric pressure (detected value) obtained from the output signal of the atmospheric pressure sensor 39, the PM shown in FIG. A discharge amount λ (excess air ratio) correction coefficient imgpmmld is calculated. The λ correction coefficient map in FIG. 6 is a map of λ correction coefficients obtained in advance through experiments and calculations using the air amount ratio gnr and atmospheric pressure as parameters, and is stored in advance in the ROM 102 of the ECU 100. The λ correction coefficient imgpmmld is set so as to increase as the air amount ratio gnr and the atmospheric pressure decrease.

  Then, based on the λ correction coefficient empgmlmd calculated in this way, the addition interval correction coefficient emintpm is calculated with reference to the map shown in FIG. The addition interval correction coefficient map of FIG. 7 is obtained by previously obtaining the relationship between the λ correction coefficient empgpmmd and the addition interval correction coefficient emintpm by experiments and calculations, and mapping those relationships, and storing them in the ROM 102 of the ECU 100 in advance. Has been. The addition interval correction coefficient emintpm is set so as to be smaller as the amount of change in the PM discharge amount (λ correction coefficient empgmlmd) is larger. The smaller the addition interval correction coefficient emintpm is, the shorter the fuel addition interval is. .

  In steps ST5 to ST7, the addition interval correction coefficient eminttemp calculated in step ST3 is compared with the addition interval correction coefficient emintpm calculated in step ST4, and the addition interval correction coefficient is smaller, that is, the fuel addition amount per unit time. The addition interval correction coefficient with the larger value is selected. Specifically, when the addition interval correction coefficient eminttemp due to the addition valve tip temperature is smaller than the addition interval correction coefficient emintpm due to the change in the PM discharge amount (when the determination result of step ST5 is affirmative determination), the addition valve The addition interval correction coefficient eminttemp according to the tip temperature is selected as the final addition interval correction coefficient emintad (step ST6). On the other hand, when the addition interval correction coefficient emintpm due to the change in the PM discharge amount is smaller than the addition interval correction coefficient eminttemp due to the addition valve tip temperature (when the determination result of step ST5 is negative), the addition due to the change in the PM discharge amount The interval correction coefficient emintpm is selected as the final addition interval correction coefficient emintad (step ST7).

  In step ST8, the final addition interval correction coefficient emintad selected in the above step ST6 or step ST7 is used, and the final addition interval correction coefficient emintad is multiplied by the reference addition interval calculated in step ST2 to obtain the final addition interval (final interval). (Addition interval = [reference addition interval before correction] × emintad) is calculated, and this routine is terminated.

  According to the addition interval correction process described above, the addition interval is short among the addition interval correction coefficient eminttemp calculated based on the addition valve tip temperature or the addition interval correction coefficient emintpm calculated based on the change amount of the PM exhaust amount. Since the final addition interval is set by selecting the one (that is, the correction coefficient with the larger amount of fuel addition per unit time), the rise of the tip temperature of the fuel addition valve 25 or the environmental change / transition period It becomes possible to correct the addition interval with respect to the change in the situation where the injection hole clogging of the fuel addition valve 25 is likely to occur in the increase in the PM discharge amount, and the injection hole clogging of the fuel addition valve 25 is effectively suppressed. be able to. Moreover, it is possible to add fuel at an appropriate addition amount (addition amount per unit time) commensurate with each situation change such as a rise in the temperature of the tip of the fuel addition valve 25 or an increase in the PM emission amount during an environmental change or transition period. Therefore, deterioration of fuel consumption can be suppressed as compared with, for example, the case where the addition amount is adapted at the upper limit of variation in the PM emission amount.

  By the way, if the fuel addition amount per unit time is increased in order to suppress the injection hole clogging of the fuel addition valve 25, the fuel reacts in the catalyst and the catalyst bed temperature may exceed a predetermined range (for example, 750 ° C.). There is sex. As a method of avoiding this, when the catalyst bed temperature of the DPNR catalyst 4b is estimated based on the exhaust temperature obtained from the output of the exhaust temperature sensor 35, and the estimated catalyst bed temperature becomes equal to or higher than a predetermined set value, A method of preventing an excessive increase in the catalyst bed temperature by reducing the amount of fuel added per unit time according to the catalyst bed temperature (specifically, the amount of change in the catalyst temperature from a predetermined value) is mentioned. be able to. In addition, the value calculated | required empirically considering the setting range (for example, 750 degreeC) of a catalyst bed temperature is employ | adopted for the setting value with respect to a catalyst bed temperature.

  Here, as a method of reducing the fuel addition amount per unit time, there is a method of shortening the addition time per one time shown in FIG. 8 while keeping the final addition interval obtained by the addition interval correction processing described above. be able to. By adopting such a method, it is possible to reduce the total amount of fuel added while securing a short addition interval that suppresses the injection hole clogging of the fuel addition valve 25, while suppressing an excessive increase in the catalyst bed temperature, It is possible to suppress the injection hole blockage of the fuel addition valve 25.

  Further, as another method for preventing an excessive increase in the catalyst bed temperature, the catalyst bed temperature of the DPNR catalyst 4b is estimated based on the exhaust temperature obtained from the output of the exhaust temperature sensor 35, and the estimated current catalyst bed temperature and Based on the final addition interval calculated in the addition interval correction process described above, the rising temperature of the catalyst bed temperature when fuel is added at the final addition interval is estimated, and the estimated catalyst bed temperature is set to a set value (catalyst bed). A method of limiting the increase correction of the fuel addition amount per unit time so as not to exceed the set value in consideration of the allowable upper limit temperature of the temperature can be mentioned.

-Other embodiments-
In the above example, the final addition interval is set using the addition interval correction coefficient eminttemp calculated based on the addition valve tip temperature or the addition interval correction coefficient eintpm calculated based on the change amount of the PM exhaust amount. The present invention is not limited to this, and the final addition interval may be set by calculating only the addition interval correction coefficient emintpm corresponding to the amount of change in the PM exhaust amount.

  In the above example, the fuel addition amount is corrected by multiplying the reference addition interval Tb by the addition interval correction coefficient eminttemp or the addition interval correction coefficient emintpm. Instead, the reference addition time (see FIG. 8) is used instead. ) May be multiplied by the addition interval correction coefficient eminttemp or the addition interval correction coefficient emintpm to correct the addition amount of fuel per unit time. In addition, when correcting the reference addition time per time, the addition interval correction coefficient eminttemp is set so as to increase as the exhaust gas temperature change amount ΔTh increases. Also, the addition interval correction coefficient emintpm is set so as to increase as the change amount of the PM discharge amount (λ correction coefficient empgmlmd) increases.

  In the above example, the addition interval correction coefficient eminttemp correction coefficient due to the tip temperature of the fuel addition valve 25 is calculated based on the exhaust temperature change amount ΔTh, but instead, it is obtained from the output signal of the water temperature sensor 31. Based on the coolant temperature of the engine 1, the addition interval correction coefficient eminttemp may be calculated with reference to the map shown in FIG.

  In the above example, the exhaust purification apparatus of the present invention is applied to an in-cylinder direct injection 4-cylinder diesel engine. However, the present invention is not limited to this, and other examples such as an in-cylinder direct injection 6-cylinder diesel engine, etc. It can also be applied to diesel engines with any number of cylinders. Further, the present invention is not limited to an in-cylinder direct injection diesel engine, but can be applied to other types of diesel engines. Moreover, it is applicable not only for vehicles but also for engines used for other purposes.

  In the above example, the catalyst device 4 includes the NOx storage reduction catalyst 4a and the DPNR catalyst 4b. However, the catalyst device 4 may include the NOx storage reduction catalyst 4a or the oxidation catalyst and the DPF.

It is a schematic structure figure showing an example of a diesel engine to which the present invention is applied. It is a block diagram which shows the structure of control systems, such as ECU. It is a flowchart which shows an example of the addition space | interval correction | amendment process which ECU performs. It is a figure which shows the reference | standard addition space | interval calculation map used with the addition space | interval correction | amendment process of FIG. It is a figure which shows the addition space | interval correction coefficient map used with the addition space | interval correction | amendment process of FIG. It is a figure which shows (lambda) correction coefficient map of PM discharge amount used with the addition space | interval correction | amendment process of FIG. It is a figure which shows the addition space | interval correction coefficient map used with the addition space | interval correction | amendment process of FIG. It is a figure which shows the addition interval and addition time of a fuel. It is a figure which shows the other example of the addition space | interval correction coefficient map by the addition tip temperature.

Explanation of symbols

1 engine (internal combustion engine)
DESCRIPTION OF SYMBOLS 2 Fuel supply system 21 Supply pump 22 Common rail 24 Shutoff valve 23 Injector 25 Fuel addition valve 27 Additional fuel passage 4 Catalytic device 4a NOx occlusion reduction type catalyst 4b DPNR catalyst 6 Intake system 7 Exhaust system 31 Water temperature sensor 33 Intake temperature sensor 36 Exhaust temperature Sensor 39 Atmospheric pressure sensor 41 Crank position sensor 100 ECU

Claims (6)

In an exhaust purification device comprising a catalyst disposed in an exhaust passage of an internal combustion engine and a fuel addition valve for adding fuel to the exhaust passage,
Correction means for correcting an addition amount per unit time of the fuel added from the fuel addition valve to the exhaust passage based on a change amount of the discharge amount of the particulate matter from the combustion chamber of the internal combustion engine. A featured exhaust purification device. The exhaust emission control device according to claim 1,
The exhaust gas purification apparatus according to claim 1, wherein the correction means sets a final addition interval by multiplying a reference addition interval by a correction coefficient corresponding to a change amount of the particulate matter discharge amount. The exhaust emission control device according to claim 2,
The correction means sets the final addition interval by multiplying the reference addition interval by a correction coefficient for correcting the addition interval to a shorter side when the actual intake air amount of the internal combustion engine is smaller than the reference intake air amount. A featured exhaust purification device. In an exhaust purification device comprising a catalyst disposed in an exhaust passage of an internal combustion engine and a fuel addition valve for adding fuel to the exhaust passage,
Correction means for correcting the addition interval of fuel added from the fuel addition valve to the exhaust passage based on the amount of change in the discharge amount of particulate matter from the combustion chamber of the internal combustion engine, and addition valve temperature estimation means,
The correction means includes a first correction coefficient for correcting an addition interval to a shorter side when the actual intake air amount of the internal combustion engine is smaller than a reference intake air amount, and an addition valve estimated by the addition valve temperature estimation means Compared with the second correction coefficient that corrects the addition interval to the short side when the temperature changes from the low side to the high side, of the first correction coefficient or the second correction coefficient, the correction on the short addition interval side An exhaust emission control device that sets a final addition interval by multiplying a reference addition interval by a coefficient. The exhaust emission control device according to any one of claims 1 to 4,
The exhaust gas purification apparatus according to claim 1, wherein when the temperature of the catalyst becomes equal to or higher than a predetermined value, the correction means reduces the fuel addition amount per unit time according to the temperature of the catalyst. The exhaust emission control device according to claim 5,
An exhaust emission control device that reduces the addition time per fuel addition and corrects the addition interval to a shorter side to reduce the fuel injection amount per unit time.

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