JP2010112251A - Exhaust purification system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust purification system which shortens a regeneration processing time while securing reliability at avoiding overheating. <P>SOLUTION: The system comprises a filter for collecting a PM which is a particulate included in the exhaust of an internal combustion engine; a combustion catalyst carried by the filter, and activated by being heated to a predetermined activating temperature or higher to promote the combustion of the PM; and an ECU 40 (heating control equipment) which controls an exhaust gas temperature by controlling a post injection quantity in order to set the combustion catalyst in an activation temperature or higher. An alkaline catalyst is employed to the fuel catalyst, wherein the alkaline catalyst is activated at a temperature lower than the exhaust gas temperature (overtemperature generation temperature) which may increase the temperature of the filter up to a limit temperature during the idling time of the engine. By means of the regeneration target temperature calculation means 43, according to the accumulation quantity of the PM which is accumulated in the filter, a regeneration target temperature for the filter inlet temperature is calculated, and the exhaust gas temperature is controlled by means of the exhaust gas temperature control means 44 to reach a regeneration target temperature. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification system including a filter that collects PM (particulate matter) contained in exhaust gas of an internal combustion engine, and a catalyst that promotes combustion of PM deposited on the filter.

Conventionally, in this type of exhaust purification system, it is necessary to appropriately regenerate the filter during operation of the internal combustion engine by performing a process (regeneration process) for burning and removing PM accumulated on the filter. In order to burn PM in this way, it is necessary to raise the catalyst supported on the filter to the activation temperature. Therefore, in the conventional regeneration processing, the catalyst temperature can be raised to the activation temperature by performing temperature increase control for increasing the exhaust temperature, such as post injection after the main fuel injection or changing the EGR amount. It is general (refer patent document 1).
JP 2007-170382 A

  Here, once PM combustion occurs, combustion progresses in a chain by combustion propagation. Therefore, the filter temperature becomes high (for example, 900 ° C.) so that the function of the filter is impaired along with PM combustion. It is required to perform temperature rise control so as not to fall into an excessive temperature rise state. In particular, after the PM combustion is started, when the vehicle operating state is switched to an idling state or the like, the exhaust flow rate is decreased, so that the amount of heat taken away from the filter by the exhaust gas is reduced. Therefore, in such a case, there is a particular concern that the above-described excessive temperature rise will occur.

  This concern will be described in more detail using the test results shown in FIG. 2. The horizontal axis in FIG. 2 is the temperature at the filter inlet portion (filter inlet temperature) of the exhaust gas temperature, and the vehicle travels (for example, The temperature at the time of switching from the state of the exhaust flow rate assuming 30 km / h to the state of the exhaust flow rate assuming idling is shown. The vertical axis in FIG. 2 indicates the maximum temperature in the filter after switching to the idling state. A solid line (3) in FIG. 2 shows a test result in the case where a conventional general platinum-based catalyst is used, and the filter inlet temperature is higher than the temperature indicated by the symbol Ms3 (overheating temperature). This indicates that when the state is switched to idling, the filter temperature may fall into an overheated state exceeding the limit temperature To.

  With respect to this concern, in the system described in Patent Document 1, when the filter inlet temperature rises and exceeds a threshold value when the vehicle is running, it is possible to suppress an excessive temperature rise by suppressing the exhaust temperature rise due to the temperature rise control. Ensuring reliability. On the other hand, if the threshold value is set low, the reliability of avoiding excessive temperature rise can be improved, but as a contradiction, the time required for the filter regeneration process becomes longer, leading to problems such as deterioration in fuel consumption. Therefore, it is desirable to set the threshold value high enough to ensure the reliability.

  However, since the activation temperature of the conventional platinum-based catalyst (the temperature indicated by Ts3 in FIG. 2) is higher than the excessive temperature rise generation temperature Ms3, the target temperature with respect to the exhaust temperature is required when the temperature rise control is performed during vehicle travel. Must be set in a temperature range (overheat generation region M3) where overheating may occur. Therefore, in a situation where the exhaust temperature must be controlled in such an excessive temperature rise occurrence region M3, it is not possible to control the exhaust temperature so as to shorten the regeneration processing time while ensuring the reliability of avoiding the excessive temperature rise. It becomes extremely difficult.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide an exhaust purification system that shortens the regeneration processing time while ensuring the reliability of avoiding excessive temperature rise.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

  According to the first aspect of the present invention, a filter that collects PM, which is a particulate matter contained in the exhaust gas of an internal combustion engine, is supported by the filter, and is heated to a predetermined activation temperature or higher. A catalyst that activates and promotes combustion of PM, and a temperature increase control device that controls the exhaust temperature so that the catalyst becomes equal to or higher than the activation temperature. A catalyst that activates at a lower temperature than the exhaust temperature (hereinafter referred to as “overheat generation temperature”) that can raise the filter to the limit temperature is employed. The temperature increase control device includes target temperature calculation means for calculating a target temperature for the temperature of the filter or a temperature correlated with the filter temperature, according to the amount of PM deposited on the filter, and the target And exhaust gas temperature control means for controlling the exhaust gas temperature so as to reach the temperature.

  According to this, since an alkali metal catalyst capable of performing PM combustion at a temperature lower than the excessive temperature rise generation temperature (symbol Ms1 in FIG. 2) is adopted, excessive PM combustion (regeneration processing) is performed. The temperature increase control device can control the exhaust temperature in the region of the temperature increase generation temperature Ms1 or lower. Therefore, the temperature rise control device can easily control the exhaust temperature to be high enough that the filter does not reach the limit temperature. Therefore, it is possible to easily realize a reduction in the regeneration processing time while ensuring the reliability of avoiding overheating of the filter.

  Furthermore, according to a test conducted by the present inventors, it has been clarified that when the filter regeneration process is executed, the overheated temperature is lowered as the PM deposition amount increases. FIG. 2 shows the test results, and solid lines (1) and (2) in the figure show the relationship between the filter inlet temperature (temperature correlated with the filter temperature) and the maximum temperature in the filter. Then, it is clear that the excessive temperature rise occurrence temperature Ms2 when the PM deposition amount is 10 g / L is lower than the overheat rise occurrence temperature Ms1 when 8 g / L.

  In view of this test result, in the invention according to the first aspect, the exhaust temperature is controlled in accordance with the PM deposition amount. Therefore, it is possible to promote increasing the exhaust temperature while ensuring the reliability of avoiding excessive temperature rise. Therefore, it is possible to promote the improvement of reliability for avoiding excessive temperature rise and the shortening of the regeneration processing time. As the regeneration process by PM combustion progresses, the PM deposition amount decreases, but it is easy to increase the target temperature as the PM deposition amount decreases, so the regeneration processing time is shortened. Can be further promoted.

  According to a second aspect of the present invention, detection means for sequentially detecting the temperature of the filter or a temperature correlated with the filter temperature during regeneration processing for burning PM, and detection of the detection means during the regeneration processing. Combustion rate estimation means for sequentially estimating the combustion rate of PM based on the value; and / a PM deposition amount estimation means for sequentially estimating the amount of PM deposited on the filter based on the estimated combustion rate during the regeneration process; The target temperature calculation means sequentially calculates the target temperature during the regeneration process based on the PM accumulation amount estimated by the PM accumulation amount estimation means.

  The present inventors have found the knowledge that “the PM deposition amount is highly correlated with the combustion rate, and the combustion rate is highly correlated with the temperature in the filter”. According to the invention of claim 2 made based on this knowledge, the PM combustion rate is sequentially estimated based on the detected value of the filter temperature, and the PM accumulation amount is sequentially estimated based on the estimated PM combustion rate. It is possible to accurately estimate the amount of PM deposition that changes as the process proceeds. Therefore, shortening of the reproduction processing time can be further promoted.

  According to the third aspect of the present invention, the storage means storing a map representing the relationship between the PM deposition amount or the physical quantity correlated with the deposition amount and the target temperature, and / or the temperature of the filter or the correlation with the filter temperature. Detecting means for detecting a certain temperature, wherein the target temperature calculating means calculates the target temperature based on a detection result by the detecting means and the map. According to this, the target temperature calculation means obtains the optimum value of the target temperature with respect to the PM accumulation amount in advance by testing, and maps and stores the optimum value so that the target temperature calculation means can obtain the optimum value of the target temperature (that is, the filter Can be easily calculated).

  According to a fourth aspect of the present invention, the catalyst has a temperature lower than an exhaust temperature at which the filter can be raised to a limit temperature during the idling operation, and a temperature at which PM starts a rapid temperature increase (reference numeral in FIG. 2). A catalyst that is activated at a lower temperature than that of P1 and P2) is employed.

  Here, according to the test result of FIG. 2 described above, the higher the filter inlet temperature at the time of switching from the running state to the idling operation, the higher the maximum temperature in the filter during the idling operation. It is clear that the maximum temperature in the filter starts to rise rapidly when the filter inlet temperature becomes higher than the temperature indicated by reference signs P1 and P2 (rapid rise start temperature). In view of this point, according to the invention described in claim 4, since the catalyst that is activated at a temperature lower than the sudden rise start temperatures P1 and P2 is employed, the exhaust temperature is set lower than the sudden rise start temperatures P1 and P2. Can be controlled. Therefore, it is possible to more reliably control the exhaust gas temperature so as not to reach the limit temperature To even when the operation is switched to the idling operation, and it is possible to improve the reliability of avoiding the excessive temperature rise.

  In addition, as a specific example of the above-mentioned “catalyst activated at a temperature lower than the exhaust temperature (overheat generation temperature) at which the filter can be raised to the limit temperature during idling operation”, the above-mentioned claim 1 “A catalyst containing at least an alkali metal”. Moreover, according to this alkaline catalyst, the minimum temperature at which PM can combust, that is, the activation temperature (see Ts1 in FIG. 2) can be lowered as compared with the conventional platinum catalyst, and the overheated temperature is also increased. Ms1 can be increased. Therefore, when the temperature rise control device controls the exhaust temperature, even if the operating state of the internal combustion engine is switched to idling, it is possible to improve the reliability of the control in the region where the filter does not reach the limit temperature, and to avoid overheating. Reliability improvement can be promoted.

  In addition, as a specific example of “a catalyst that is activated at a temperature lower than an exhaust temperature (overheat generation temperature) at which the filter can be raised to a limit temperature during idling operation”, an alkali metal is added to the zeolite according to claim 6. Examples thereof include “a composite oxide obtained by supporting and firing at 600 ° C. or higher” and “a catalyst that cannot oxidize carbon monoxide”. By adopting a catalyst that cannot oxidize carbon monoxide, the CO generated during PM combustion is further oxidized to CO2 and is prevented from generating heat, so that the excessive temperature rise generation temperatures Ms1, Ms2 can be increased. Therefore, it is possible to promote the improvement of reliability for avoiding excessive temperature rise and the shortening of the regeneration processing time.

  Hereinafter, an embodiment of an exhaust purification system according to the present invention will be described with reference to the drawings.

  First, an outline of an engine (internal combustion engine) on which the exhaust purification system according to the present embodiment is mounted will be briefly described. In this embodiment, a diesel engine for a four-wheeled vehicle is targeted, and an engine of a system in which high pressure fuel (for example, light oil having an injection pressure of “1000 atm” or more) is directly supplied to the combustion chamber by injection (direct injection supply). is there. The engine is assumed to be a multi-cylinder (for example, in-line four-cylinder) four-stroke, reciprocating diesel engine.

  Next, the configuration of the intake / exhaust system of the engine will be described with reference to FIG.

  The engine includes an EGR pipe 10 that recirculates exhaust gas from the exhaust system to the intake system. By returning a part of the exhaust gas to the intake pipe 11, the combustion temperature in the combustion chamber 12 is lowered to reduce NOX in the exhaust gas. I am trying. The flow rate of EGR gas (EGR flow rate) is adjusted by the EGR valve 13.

  An EGR cooler 14 that cools the EGR gas is provided in a portion of the EGR pipe 10 downstream of the EGR valve 13. By cooling the EGR gas in this way, the volume of the EGR gas is reduced (density increase), thereby improving the charging efficiency of the intake air flowing into the combustion chamber 12.

  The EGR pipe 10 is provided with a bypass pipe 15 that bypasses the EGR gas with respect to the EGR cooler 14. Then, the switching valve 16 adjusts the flow rate of the flow rate for circulating the EGR gas to the EGR cooler 14 and the flow rate for bypassing the EGR cooler 14, and in the portion where the bypass piping 15 joins the downstream side of the EGR cooler 14. The temperature of the EGR gas is adjusted. According to this, it is possible to improve the NOX reduction effect by adjusting the temperature of the EGR gas to the optimum value and refluxing the EGR gas.

  A throttle valve 17 that adjusts the flow rate of fresh air flowing from the air cleaner 21 out of the intake air flowing into the combustion chamber 12 is provided on the upstream side of the portion of the intake pipe 11 to which the EGR pipe 10 is connected.

  A turbocharger 19 (supercharger) is disposed between the intake pipe 11 and the exhaust pipe 18. The turbocharger 19 has a compressor impeller 19a provided in the intake pipe 11 and a turbine wheel 19b provided in the exhaust pipe 18, which are connected by a shaft 19c. In the turbocharger 19, the turbine wheel 19b is rotated by the exhaust gas flowing through the exhaust pipe 18, and the rotational force is transmitted to the compressor impeller 19a via the shaft 19c. Then, the intake air flowing through the intake pipe 11 is compressed by the compressor impeller 19a, and supercharging is performed.

  The turbocharger 19 according to the present embodiment employs a variable capacity turbocharger that can change the ratio of converting the exhaust fluid energy into the rotational driving force of the shaft 19c. Specifically, the turbine wheel 19b is provided with a plurality of variable vanes 19d for making the flow rate of the exhaust gas sprayed variable. These variable vanes 19d open and close in synchronization with each other. Then, the exhaust flow rate is adjusted by changing the size of the gap between the adjacent variable vanes 19d, that is, the opening degree of the variable vane 19d, thereby adjusting the rotational speed of the turbine wheel 19b. Then, by adjusting the rotational speed of the turbine wheel 19b, the amount of air forcibly supplied to the combustion chamber 12, that is, the supercharging pressure is adjusted.

  The air sucked through the air cleaner 21 is supercharged by the turbocharger 19, cooled by the intercooler 20, and then fed downstream. The intake air is cooled by the intercooler 20 to reduce the volume (increase in density), thereby improving the charging efficiency of the intake air flowing into the combustion chamber 12.

  A purification device 30 for purifying exhaust gas is attached to the exhaust pipe 18 on the downstream side of the turbine wheel 19b. The purification device 30 includes a case 31, a filter 32 and an oxidation catalyst 33 housed in the case 31, a temperature sensor 34 (detection means) and a differential pressure sensor 35 attached to the case 31, and the like. The filter 32 is a diesel particulate filter (DPF) that collects particulate matter (PM) contained in the exhaust gas.

  The filter 32 has a cylindrical porous partition wall structure made of a heat-resistant ceramic such as cordierite, and is constituted by a wall flow type filter base material (monolith carrier) in which honeycomb-shaped holes are alternately sealed. Has been. Alternatively, instead of a heat-resistant ceramic, a metal powder is applied to a lattice formed of a heat-resistant metal and fired, and pores are generated inside, so that the above-described wall flow type filter base material is configured. Also good.

  When the exhaust gas passes through the porous partition walls of the filter 32, PM in the exhaust gas is collected and accumulated in the honeycomb-shaped holes. The deposited PM is burned by being regenerated periodically (or irregularly according to the amount of accumulated PM) and discharged as harmless carbon dioxide.

  The filter 32 carries a combustion catalyst for PM combustion (corresponding to “catalyst” described in claims). Specifically, the combustion catalyst is coated on the base material of the filter 32. This combustion catalyst functions to promote PM combustion when the carbon component in PM is oxidized and burned. Therefore, when the combustion catalyst is heated by the high-temperature exhaust gas and reaches the activation temperature, the deposited PM starts to burn. However, this combustion catalyst does not have the ability to oxidize carbon monoxide. Therefore, a reaction in which CO generated during PM combustion is further oxidized to CO2 to generate heat is suppressed, and as a result, the temperature of PM during combustion is suppressed from rapidly rising.

  A specific example of the combustion catalyst of the present embodiment is to employ a composite oxide obtained by supporting an alkali metal on zeolite and calcining at 600 ° C. or higher. Specific examples of the zeolite include A-type sodalite, Y-type sodalite, and mordenite. Specific examples of the alkali metal include potassium, cesium, and rubidium. By adopting the alkaline combustion catalyst in this way, when performing the regeneration process for raising the exhaust gas temperature flowing into the filter 32 and burning PM, the combustion catalyst is used for the excessive temperature rise generation temperature Ms1 described in detail later. , Activated at a lower temperature than Ms2.

  The oxidation catalyst 33 is supported on a base material disposed on the upstream side of the filter 32, and is a platinum-based catalyst or an alkaline catalyst. The oxidation catalyst 33 functions to oxidize and purify unburned HC and CO in the exhaust gas.

  When the regeneration process is performed, post-injection is performed after main injection for engine output in one combustion cycle in injecting fuel from the fuel injection valve 22. As a result, unburned HC is caused to flow into the oxidation catalyst 33, and the amount of heat generated during the oxidation reaction of unburned HC at the oxidation catalyst 33 is increased. As a result, the temperature of the exhaust gas flowing into the filter 32 rises, and the combustion catalyst can be raised to the activation temperature. As a result, the forced regeneration of the filter 32 is performed such that the PM accumulated on the filter 32 is combusted.

  The temperature sensor 34 is arranged in the case 31 on the downstream side of the oxidation catalyst 33 and the upstream side of the filter 32, and detects the temperature of the inlet portion of the filter 32 (filter inlet temperature). The differential pressure sensor 35 detects a pressure difference between the upstream side and the downstream side of the filter 32 in the case 31.

  The engine ECU 40 (electronic control unit) receives detection signals from the temperature sensor 34 and the differential pressure sensor 35, and from various sensors such as a crank angle sensor 28, an air flow sensor (not shown), an intake pressure sensor, and an A / F sensor. An output detection signal is input. Based on these detection signals, the ECU 40 performs engine control by controlling the fuel injection amount, the supercharging pressure, the EGR amount, the intake air amount, and the like as follows.

  The microcomputer 40a provided in the ECU 40 calculates the rotation speed (engine rotation speed NE) of the engine output shaft (crankshaft) based on the detection signal input from the crank angle sensor 28. Further, based on a detection signal input from an accelerator sensor (not shown), an operation amount (depression amount) of the accelerator pedal by the driver is calculated. The microcomputer 40a calculates the target fuel injection amount based on the engine operating state (for example, the engine speed NE), the accelerator pedal operation amount, etc., and controls the operation of the fuel injection valve 22 so that the target injection amount is obtained. .

  The microcomputer 40 a controls the supercharging pressure by adjusting the capacity of the variable capacity turbocharger 19. That is, the target opening of the variable vane 19d is calculated using a map or the like using the target injection amount and the engine rotational speed NE as parameters. Then, the variable vane 19d is controlled to have the target opening by driving and controlling an actuator (not shown) so as to have the target opening. It should be noted that the higher the engine speed NE or the greater the target injection amount, the larger the target opening is set, and consequently the supercharging pressure increases.

  The microcomputer 40a controls the opening degree of the EGR valve 13a, thereby controlling the EGR flow rate that flows into the EGR pipe 10 from the exhaust pipe 18 and returns. That is, the target value (target exhaust oxygen concentration) of the oxygen concentration (exhaust oxygen concentration) in the exhaust gas is calculated using a map or the like using the target injection amount and the engine rotational speed NE as parameters. Then, the target EGR flow rate is set so that the exhaust oxygen concentration detected by the A / F sensor approaches the target exhaust oxygen concentration, and the operation of the EGR valve 13a is feedback-controlled so as to be the target EGR flow rate.

  Next, a playback process control method, which is a main part of the present embodiment, will be described.

  When the differential pressure of the filter 32 detected by the differential pressure sensor 35 increases beyond the threshold, the microcomputer 40a determines that the PM 32 is in a deposition state where a predetermined amount or more of PM is deposited. When it is determined that the fuel is in the accumulated state, the post injection described above is performed so as to raise the exhaust gas temperature. Then, the filter inlet temperature rises, the combustion catalyst rises to the activation temperature, and PM starts combustion. However, if the temperature in the filter 32 becomes excessively high due to PM combustion, there is a concern that the filter 32 is damaged and the function is impaired. On the other hand, if the temperature in the filter is low, it takes time for PM combustion and the time required for the filter regeneration process becomes long, leading to problems such as deterioration in fuel consumption.

  Therefore, the microcomputer 40a sets a target temperature (regeneration target temperature) at the filter inlet so as to make the filter inlet temperature as high as possible without causing the damage of the filter 32, and sets the post temperature so that the filter inlet temperature approaches the regeneration target temperature. By controlling the injection amount, the regeneration processing time is shortened while ensuring the reliability of avoiding damage to the filter 32. Hereinafter, a method for setting the regeneration target temperature will be described.

  The solid lines (1) and (2) in FIG. 2 indicate the filter inlet temperature during PM combustion according to the present embodiment using an alkaline combustion catalyst and the temperature of the highest temperature in the filter 32 (the highest in the filter). Test data showing the relationship with (temperature). Incidentally, the solid line (1) is test data when the PM deposition amount per unit volume in the filter 32 is 8 g, and the solid line (2) is test data when 10 g. The solid line (3) represents test data when the PM deposition amount is 8 g / L in a conventional exhaust purification system using a platinum combustion catalyst.

  Further, in this test, the exhaust flow rate is reduced by switching the engine operating state from the exhaust flow velocity state assuming vehicle travel (for example, 30 km / h) to the exhaust flow velocity state assuming idling. The horizontal axis in FIG. 2 indicates the filter inlet temperature measured at the time of switching to the idling state (at the start of exhaust gas flow reduction), and the vertical axis in FIG. 2 shows the maximum temperature in the filter after switching to the idling state. The temperature at the time of the measurement (maximum temperature in the filter)

  A symbol To in FIG. 2 indicates a maximum temperature in the filter (for example, 900 ° C.) at which the filter 32 may be damaged. In other words, the solid lines (1), (2), and (3) in FIG. 2 indicate that the filter inlet temperature is changed to the idling operation when the filter inlet temperature is higher than the temperatures indicated by the symbols Ms1, Ms2, and Ms3 (overheat generation temperature) This indicates that the temperature may fall into an excessive temperature rise state exceeding the limit temperature To. When the combustion catalyst is an alkaline system, the overheating temperature Ms1, Ms2 (starting temperature of the overheating area M1, M2) is the overheating temperature Ms3 (overheating area when the platinum catalyst is used). Higher than the starting temperature of M3). In addition, the activation temperature Ts1 of the combustion catalyst when the combustion catalyst is an alkaline system, that is, the lowest temperature at which PM can burn is lower than the activation temperature Ts3 of the combustion catalyst when the combustion catalyst is a platinum system. Become.

  In short, by making the combustion catalyst alkaline, it is possible to increase the overheat generation temperature Ms1, Ms2 and to lower the activation temperature Ts1. Therefore, according to the present embodiment in which the combustion catalyst is an alkaline system, the combustion catalyst can be activated at a temperature lower than the excessive temperature rise generation regions M1 and M2 to start PM combustion. Therefore, the regeneration target temperature can be set in a temperature range lower than the excessive temperature rise occurrence regions M1 and M2 during vehicle travel.

  The regeneration target temperature during vehicle travel needs to be set to a temperature at which the maximum temperature in the filter does not exceed the limit temperature To even if the idling operation is switched. According to this embodiment in which the regeneration target temperature can be set at a low temperature, it is possible to easily realize control of the filter inlet temperature so as to make the filter inlet temperature as high as possible without causing the filter 32 to be damaged.

  On the other hand, in the case of a conventional system in which the combustion catalyst is platinum-based, since the activation temperature Ts3 is within the overheat generation region M3, the regeneration target temperature is set in a temperature region in which overheating does not occur. I can't.

  Incidentally, when the filter inlet temperature is the activation temperature Ts1 of the alkaline combustion catalyst, the reason why the maximum temperature Ta in the filter indicated by the solid lines (1) and (2) is higher than the maximum temperature Tb in the filter indicated by the solid lines (3). Is described below. In the solid lines (1) and (2) with the alkaline combustion catalyst, the maximum temperature Ta in the filter increases as PM burns, whereas in the solid line (3) with the platinum combustion catalyst, the alkaline combustion This is because PM does not burn at the catalyst activation temperature Ts1.

  2, the higher the filter inlet temperature at the time when the exhaust flow rate is reduced, the higher the maximum temperature in the filter. However, the filter inlet temperature is higher than the temperatures indicated by symbols P1 and P2 (rapid increase start temperature). If the temperature is too high, the maximum temperature in the filter rises rapidly. In the present embodiment, the activation temperature Ts1 is made lower than the rapid rise start temperatures P1 and P2 by using an alkaline combustion catalyst.

  By the way, comparing the solid lines (1) and (2), it can be seen that the higher the PM accumulation amount, the lower the excessive temperature rise generation temperatures Ms1 and Ms2. Therefore, in this embodiment, when setting the regeneration target temperature, it is variably set according to the PM accumulation amount. Hereinafter, a procedure for setting the regeneration target temperature in accordance with the PM deposition amount so as to shorten the regeneration processing time while ensuring the reliability of avoiding damage to the filter 32 will be described with reference to FIG.

  FIG. 3 is a functional block diagram when the ECU 40 is functioning to set the regeneration target temperature. The microcomputer 40a performs the combustion speed estimation means 41, the PM accumulation amount estimation means 42, and the regeneration target temperature calculation described below. Means 43 and exhaust temperature control means 44 are provided.

  First, the ECU 40 acquires the filter inlet temperature from the detection signal of the temperature sensor 34. The combustion speed estimation means 41 estimates the PM combustion speed generated in the filter 32 based on the acquired filter inlet temperature. That is, the filter inlet temperature and the PM combustion rate are highly correlated, and it can be estimated that the PM combustion rate increases as the filter inlet temperature increases. For example, the correlation between the filter inlet temperature and the PM combustion rate is acquired in advance by testing, and the correlation is mapped and stored in the memory 40b of the microcomputer 40a. And the combustion speed estimation means 41 should just calculate PM combustion speed based on filter inlet temperature with reference to the map.

  Next, the PM accumulation amount estimation means 42 estimates the PM accumulation amount based on the estimated PM combustion speed. That is, there is a high correlation between the PM combustion rate and the PM accumulation amount, and it can be estimated that the PM accumulation amount decreases faster as the PM combustion rate increases. For example, the correlation between the PM combustion rate and the PM accumulation amount is acquired in advance by a test, and the correlation is mapped and stored in the memory 40b. Then, the PM accumulation amount estimation means 42 may calculate the PM accumulation amount based on the PM combustion speed with reference to the map.

  The combustion rate estimating means 41 and the PM accumulation amount estimating means 42 are used as one means, and the correlation between the filter inlet temperature and the PM accumulation amount is mapped and stored in the memory 40b, and the filter inlet temperature is referred to by referring to the map. The PM accumulation amount may be calculated based on the above.

  Next, the regeneration target temperature calculation unit 43 calculates the regeneration target temperature based on the calculated PM accumulation amount so that the filter inlet temperature is increased to the extent that the maximum temperature in the filter does not exceed the limit temperature To. Specifically, the map M shown in FIG. 4 is stored in the memory 40b (storage means), and the regeneration target temperature is calculated based on the PM accumulation amount with reference to the map M. Hereinafter, the contents of the map M will be described.

  The map M shown in FIG. 4 shows the relationship between the PM deposition amount and the regeneration target temperature, and is acquired and set in advance by a test. A solid line L1 in the map M is a test result indicating a line (overheat generation occurrence line) where the maximum temperature in the filter reaches the limit temperature To. This test result shows that the filter inlet temperature when reaching the limit temperature To becomes lower as the PM deposition amount increases.

  The region on the side where the amount of accumulated PM is larger than the excessive temperature rise generation line L1 (the region indicated by the slanted line R1) is an excessive temperature rise risk region R1 where the maximum temperature in the filter exceeds the limit temperature To. On the other hand, the region where the amount of accumulated PM is smaller than the excessive temperature rise generation line L1 (the region indicated by the oblique line S1) is the safety region S1 in which the maximum temperature in the filter does not exceed the limit temperature To. Therefore, the regeneration target temperature is set so as to exist in a region (regeneration target temperature region Strg shown by the halftone hatch) adjacent to the overheat generation line L1 in the safety region S1. In the safety region S1, the regeneration target temperature does not enter the excessive temperature rise occurrence region M1 (see FIG. 2).

  Incidentally, FIG. 5 is a test result showing an excessive temperature increase generation line L2, an excessive temperature increase risk region R2, and a safety region S2 in a conventional system using a platinum-based combustion catalyst. However, in this conventional system, the activation temperature Ts3 (see FIG. 2) of the platinum-based combustion catalyst is higher than the activation temperature Ts1 of the alkaline combustion catalyst. Therefore, in the safety region S2, the activation temperature Ts3 of the platinum-based combustion catalyst is set. Not reach. Therefore, even if the regeneration target temperature is set in the safety region S2, PM does not burn and filter regeneration processing is not performed. Therefore, in order to burn PM, the regeneration target temperature must be set in the practical region S3 that is higher than the safe region S2 (for example, 600 ° C. or higher). In the practical area S3, the regeneration target temperature enters the excessive temperature rise occurrence area M3 (see FIG. 2).

  Returning to FIG. 3, the exhaust temperature control means 44 controls the post injection amount so that the filter inlet temperature approaches the regeneration target temperature set as described above. For example, it is desirable to feedback-control the post injection amount so that the deviation between the actual filter inlet temperature detected by the temperature sensor 34 and the regeneration target temperature approaches zero. Then, the calculation of the regeneration target temperature and the exhaust gas temperature control by the various means 41 to 44 shown in FIG. 3 are repeatedly executed every predetermined cycle (for example, the calculation cycle of the microcomputer 40a or the predetermined crank angle cycle).

  According to the embodiment described in detail above, the following effects can be obtained.

  (1) Since an alkali metal combustion catalyst capable of performing PM combustion at a temperature lower than the overheat generation temperature Ms1, Ms2 is employed, the filter regeneration process is performed within the safe region S1 where the overheat is not generated. Even if the regeneration target temperature is set, PM can be burned. Therefore, it is possible to easily set the regeneration target temperature so as to make the filter inlet temperature as high as possible so that the filter 32 is not damaged even when the idling operation is switched. Therefore, it is possible to easily realize a reduction in the regeneration processing time while ensuring the reliability of avoiding damage to the filter 32.

  (2) Since the regeneration target temperature is set lower as the PM accumulation amount is larger, the regeneration target temperature can be set as close as possible to the over-temperature rise generation line L1 when setting the regeneration target temperature within the safety region S1. Accordingly, it is possible to promote shortening of the regeneration processing time while ensuring the reliability of avoiding damage to the filter 32.

  (3) Since the amount of accumulated PM decreases as the filter regeneration process proceeds, the regeneration target temperature can be raised as the regeneration process proceeds. In view of this point, in the above embodiment, the calculation of the regeneration target temperature and the exhaust gas temperature control by the various means 41 to 44 in FIG. Therefore, since the regeneration target temperature is updated so as to approach the excessive temperature rise generation line L1 in accordance with the PM deposition amount that changes as the regeneration process proceeds, the regeneration process time can be further shortened.

  (4) The relationship between the regeneration target temperature set in the regeneration target temperature region Strg and the PM deposition amount is obtained by testing in advance, and the regeneration based on the PM deposition amount is performed with reference to a map M that specifies the relationship. Since the target temperature is calculated, the regeneration target temperature is calculated so as to be within the regeneration target temperature region Strg as compared with the case where the regeneration target temperature is calculated by substituting the PM deposition amount into the arithmetic expression without using the map M. The calculation processing load can be reduced.

  (5) Since the PM accumulation amount used for calculating the regeneration target temperature is estimated based on the combustion speed, it is possible to easily estimate the PM accumulation amount with high accuracy. In addition, since the combustion speed used for calculating the PM accumulation amount is estimated based on the filter inlet temperature, it is possible to easily estimate the combustion speed with high accuracy.

  (6) Since an alkali metal combustion catalyst capable of burning PM at a temperature lower than the sudden rise start temperatures P1 and P2 is employed, regeneration is performed in a region lower than the sudden rise start temperatures P1 and P2 when the vehicle is running. The target temperature can be set. Therefore, the filter 32 is not damaged even when the idling operation is switched, compared with the case where the regeneration target temperature is set at a temperature higher than the sudden rise start temperatures P1 and P2 although it is lower than the excessive temperature rise occurrence temperatures Ms1 and Ms2. It is possible to reliably control the exhaust temperature as high as possible. Therefore, it is possible to improve the reliability of avoiding overheating.

  (7) In the conventional exhaust purification system, the filter inlet temperature must be controlled at a temperature lower than the catalyst activation temperature Ts3 during the idling operation of the engine. Therefore, the exhaust temperature is controlled so as not to cause PM combustion during the idling operation. It takes a thing. In contrast, in this embodiment, the filter inlet temperature can be controlled at a temperature higher than the catalyst activation temperature Ts1 even during the idling operation of the engine. Therefore, PM combustion is performed even during the idling operation. The exhaust temperature can be controlled.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be modified as follows. Moreover, you may make it combine the characteristic structure of each embodiment arbitrarily, respectively.

  In the above embodiment, the post-injection amount is controlled so that the filter inlet temperature becomes the target temperature. However, the target temperature according to the present invention may be a temperature correlated with the temperature of the filter 32, for example, the filter The target temperature may be set for the filter outlet temperature instead of the inlet temperature. Further, the temperature of the filter base material (filter bed temperature) may be estimated based on the filter inlet temperature and the filter outlet temperature, and the target temperature may be set for the estimated filter bed temperature. Further, the target temperature may be set with respect to the inlet temperature of the oxidation catalyst 33. In these cases, a temperature sensor 37 (see FIG. 1) for detecting the filter outlet temperature and a temperature sensor 36 (see FIG. 1) for detecting the inlet temperature of the oxidation catalyst 33 are provided and detected by these temperature sensors 36, 37. It is desirable to perform feedback control of the post-injection amount in accordance with the deviation between the actual temperature or the filter bed temperature estimated from the detected temperature and the target temperature.

  In the above embodiment, when performing the filter regeneration process, the unburned HC is supplied to the oxidation catalyst 33 by post injection to increase the temperature of the filter inlet, but the exhaust pipe 18 is upstream of the oxidation catalyst 33. An oxidant supply valve (not shown) for supplying an oxidant (for example, HC) to the side portion may be provided, and the temperature at the filter inlet may be increased by supplying the oxidant. In this case, the filter inlet temperature is controlled by adjusting the supply amount of the oxidizing agent.

  -Alternatively, when performing the filter regeneration process, the intake air amount is reduced by the intake valve, the exhaust pressure is increased by the exhaust valve, or the injection amount of the main injection so as to increase the exhaust gas temperature discharged from the combustion chamber 12 The filter inlet temperature may be increased by increasing the EGR amount or the EGR amount. In this case, the filter inlet temperature is controlled by adjusting the intake air amount, the exhaust pressure, the fuel injection amount, the EGR amount, and the like.

  In the above embodiment, the PM accumulation amount is calculated based on the combustion speed. For example, the PM accumulation amount is calculated based on the differential pressure detected by the differential pressure sensor 35, the engine operating time, and the vehicle running The PM accumulation amount may be estimated based on the distance or the like.

  The combustion catalyst used in the present invention is not limited to an alkaline catalyst, and may be a catalyst other than an alkaline catalyst as long as it is activated at a temperature lower than the excessively high temperature generation temperatures Ms1, Ms2.

1 is a configuration diagram showing an engine intake / exhaust system to which an exhaust purification system according to an embodiment of the present invention is applied. Test data showing the relationship between the filter inlet temperature during PM combustion and the maximum temperature in the filter when the exhaust flow rate decreases during filter regeneration. FIG. 2 is a functional block diagram when the ECU shown in FIG. 1 functions to set a regeneration target temperature. FIG. 4 is a map used by the regeneration target temperature calculation unit shown in FIG. 3 for calculating the regeneration target temperature. FIG. 3 is a diagram showing an excessive temperature rise generation line and the like in a conventional exhaust purification system employing a platinum-based combustion catalyst.

Explanation of symbols

  32 ... Filter, 34 ... Temperature sensor (detection means), 40 ... ECU (temperature increase control device), 41 ... Combustion rate estimation means, 42 ... PM accumulation amount estimation means, 43 ... Regeneration target temperature calculation means (target temperature calculation means) ), 44 (exhaust temperature control means).

Claims (7)

A filter that collects PM, which is particulate matter contained in the exhaust gas of the internal combustion engine;
A catalyst carried on the filter and activated by being heated to a predetermined activation temperature or higher to promote PM combustion;
A temperature increase control device for controlling the exhaust temperature so that the catalyst is equal to or higher than the activation temperature;
With
The catalyst employs a catalyst that is activated at a temperature lower than an exhaust temperature at which the filter can be raised to a limit temperature during idling operation of the internal combustion engine,
The temperature increase control device includes:
Target temperature calculation means for calculating a target temperature for the temperature of the filter or a temperature correlated with the filter temperature according to the amount of PM deposited on the filter;
Exhaust temperature control means for controlling the exhaust temperature so as to be the target temperature;
An exhaust purification system characterized by comprising: Detecting means for successively detecting the temperature of the filter or a temperature correlated with the filter temperature during the regeneration process for burning PM;
Combustion speed estimation means for sequentially estimating the combustion speed of PM based on the detection value of the detection means during the regeneration process;
PM accumulation amount estimation means for sequentially estimating the accumulation amount of PM accumulated on the filter based on the estimated combustion rate during the regeneration process;
With
The exhaust purification system according to claim 1, wherein the target temperature calculation means sequentially calculates the target temperature during the regeneration process based on the PM accumulation amount estimated by the PM accumulation amount estimation means. A storage means for storing a map representing a relationship between the PM deposition amount or a physical quantity correlated with the deposition amount and the target temperature;
Detecting means for detecting the temperature of the filter or a temperature correlated with the filter temperature;
With
The exhaust gas purification system according to claim 1 or 2, wherein the target temperature calculation means calculates the target temperature based on a detection result by the detection means and the map.   As the catalyst, a catalyst that is activated at a temperature lower than an exhaust temperature at which the filter can be raised to a limit temperature during the idling operation and at a temperature lower than a temperature at which PM starts a rapid temperature increase is employed. The exhaust gas purification system according to any one of claims 1 to 3.   The exhaust purification system according to any one of claims 1 to 4, wherein the catalyst contains at least an alkali metal.   The exhaust purification system according to claim 5, wherein the catalyst is a composite oxide obtained by supporting an alkali metal on zeolite and calcining at 600 ° C or higher.   The exhaust purification system according to any one of claims 1 to 6, wherein the catalyst is a catalyst that cannot oxidize carbon monoxide.

Images