Exhaust emission control system for internal combustion engine

Abstract

To provide an exhaust emission control system for an internal combustion engine, which when estimating the deposition amount of particulate matters in a filter based on the differential pressure across the filter, can further improve the estimation accuracy by appropriately correcting the differential pressure across the filter.SOLUTION: An exhaust emission control system for an internal combustion engine has a filter 43 that collects particulate matters in exhaust gas, a differential pressure detection device 35 that detects a differential pressure across the filter between the inflow side and the outflow side of the filter, and a control device 50. The control device executes filter regeneration processing of burning and removing the particulate matters deposited in the filter when determining that the particulate matters exceeding a predetermined amount deposits in the filter and when a predetermined condition is satisfied; obtains, based on an operation state, an increase side correction amount by which the differential pressure across the filter is corrected to an increase side; obtains a corrected differential pressure in which the differential pressure across the filter is corrected using the increase side correction amount; and determines that the particulate matters exceeding the predetermined amount deposits in the filter when the corrected differential pressure exceeds a predetermined threshold set in accordance with the predetermined amount.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an exhaust gas purification system for an internal combustion engine.

Background Art

[0002] Conventionally, vehicles equipped with a diesel engine as an internal combustion engine collect fine particulate matter (PM) in exhaust gas with a filter (DPF: Diesel Particulate Filter) provided in the exhaust passage so as not to be released into the atmosphere. The filter has a wall provided with a large number of micropores that do not allow particulate matter to pass through, and exhaust gas is passed through the micropores of the wall to collect particulate matter.

[0003] Particulate matter collected by the filter accumulates, and if the accumulated particulate matter is not removed regularly, the filter will become clogged. For this reason, a filter regeneration process for burning and removing the particulate matter accumulated in the filter is regularly performed. In the filter regeneration process, the temperature of the exhaust gas, which is about 300 to 400 [°C] under normal operating conditions, is forcibly raised to about 600 [°C] or higher to burn and remove the particulate matter accumulated in the filter. When the exhaust gas is forcibly heated, fuel is added to the exhaust gas, and the fuel is reacted with an oxidation catalyst disposed upstream of the filter to heat the exhaust gas, which involves fuel consumption.

[0004] Executing the filter regeneration process too frequently is not preferable because it deteriorates fuel efficiency, and too infrequently is not preferable because the filter may become clogged. Therefore, it is necessary to perform the filter regeneration process at an appropriate frequency, and for this purpose, it is necessary to accurately detect the amount of particulate matter accumulated in the filter.

[0005] It is not possible to directly detect the amount of particulate matter accumulated in the filter, and the following methods (1) and (2) are generally used as methods for estimating the accumulated amount. (1) Using an actual vehicle, measure the amount of particulate matter generated according to the operating state of the internal combustion engine, create a map or the like, and estimate the deposition amount of particulate matter by obtaining and integrating the generation amount according to the operating state at predetermined time intervals, an integrated formula estimation method. (2) Measure the differential pressure before and after the filter (the pressure difference between the inlet side and the outlet side of the filter), and estimate the deposition amount of particulate matter based on this differential pressure before and after the filter, a differential pressure type estimation method.

[0006] The above integrated formula estimation method in (1) has relatively large errors due to variations and deterioration of the internal combustion engine, and is less preferable because its estimation accuracy is lower than that of the differential pressure type estimation method in (2). Also, in the differential pressure type estimation method in (2) above, there are cases where the differential pressure before and after the filter deviates to the higher side or the lower side with respect to the reference differential pressure before and after the filter with respect to the deposition amount of particulate matter. For this reason, it is desired to appropriately correct the detected differential pressure before and after the filter.

[0007] The deviation (error) to the higher side with respect to the characteristics serving as the reference for the differential pressure before and after the filter occurs due to the phenomenon described below. The particulate matter deposited on the filter includes particulate matter that has entered the micropores in the filter wall (micropore-deposited particulate matter) and particulate matter that has deposited on the surface of the filter wall (wall-surface-deposited particulate matter). Depending on the amount of micropore-deposited particulate matter, it becomes difficult for the exhaust gas to pass through (see Fig. 6), and the differential pressure before and after the filter deviates to the higher side. In a filter on which no particulate matter has been deposited immediately after the completion of the filter regeneration process, first, particulate matter (micropore-deposited particulate matter) enters the micropores in the filter wall until it reaches a saturated state (initial amount of micropore deposition), and then particulate matter (wall-surface-deposited particulate matter) deposits on the surface of the filter wall. When particulate matter deposits on the surface of the filter wall, particulate matter cannot enter the micropores in the filter wall, so the amount of micropore-deposited particulate matter does not increase beyond the initial amount of micropore deposition. Then, the micropore-deposited particulate matter gradually burns and decreases according to the operating state of the internal combustion engine, and the deviation to the higher side of the differential pressure before and after the filter gradually becomes smaller. That is, the deviation to the higher side of the differential pressure before and after the filter is large at the initial stage and then gradually becomes smaller (see characteristic B that deviates to the higher side with respect to the reference characteristic A shown in Fig. 8).

[0008] The deviation (error) to the lower side with respect to the characteristics serving as the reference for the differential pressure before and after the filter is caused by the phenomenon described below. When cracks or the like occur in the layer of particulate matter deposited on the wall surface of the filter (wall surface deposited particulate matter) based on the operating state of the internal combustion engine, the exhaust gas becomes more likely to pass through according to the amount of cracks or the like (see Fig. 7), and the differential pressure before and after the filter deviates to the lower side. When the filter regeneration process is performed and particulate matter (wall surface deposited particulate matter) accumulates on the surface of the filter wall, cracks, fissures, or the like may occur depending on the operating state of the internal combustion engine. Since these cracks, fissures, or the like do not recover, if the cracks, fissures, or the like increase according to the operating state of the internal combustion engine, the deviation to the lower side of the differential pressure before and after the filter gradually increases. That is, the deviation to the lower side of the differential pressure before and after the filter is small at first, and then the deviation amount gradually increases (see characteristic C deviated to the lower side with respect to the reference characteristic A shown in Fig. 8).

[0009] For example, Patent Document 1 discloses an exhaust gas purification device that corrects the differential pressure before and after the filter deviated to the higher side with respect to the reference characteristics by the particulate matter deposited in the micropores, thereby further improving the estimation accuracy of the deposition amount of the particulate matter in the filter. In Patent Document 1, after the completion of the filter regeneration process, first, the initial amount of deposition in the micropores is obtained, and then the combustion amount of the particulate matter deposited in the micropores according to the operating state is obtained, and the differential pressure before and after the filter is corrected based on the remaining amount obtained by subtracting the combustion amount from the initial amount of deposition in the micropores.

[0010] Also, for example, in Patent Document 2, after the completion of the filter regeneration process, first, the deposition amount of the particulate matter is estimated by a differential pressure type estimation method. Then, when an index for determining the deterioration of the estimation accuracy in which the differential pressure before and after the filter deviates to the lower side with respect to the reference characteristics due to cracks generated in the particulate matter deposited on the wall surface exceeds the threshold value, the estimation method of the deposition amount of the particulate matter is switched from the differential pressure type estimation method to the integration type estimation method. However, it does not correct the differential pressure before and after the filter deviated to the lower side.

Prior Art Documents

Patent Documents

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-170193 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-190120 [Summary of the Invention] [Problems to be Solved by the Invention]

[0012] The deposition of particulate matter (micropore-deposited particulate matter) into the micropores of the filter wall and the combustion of the micropore-deposited particulate matter, as well as the occurrence of cracks and fissures in the wall surface-deposited particulate matter, vary depending on the operating state of the internal combustion engine, and either one may occur or both may occur. That is, depending on the operating state of the internal combustion engine, the differential pressure across the filter may deviate to the higher side or may deviate significantly to the lower side with respect to the reference characteristics. Therefore, when correcting the differential pressure across the filter, it is preferable to perform both corrections for the deviation to the higher side and the deviation to the lower side, but it is at least preferable to perform a correction for the deviation to the lower side where the deviation amount gradually increases.

[0013] The invention described in Patent Document 1 addresses the deviation of the differential pressure across the filter to the higher side due to the deposition and combustion of particulate matter (micropore-deposited particulate matter) into the micropores of the filter wall. However, since it does not consider the occurrence of cracks and fissures in the wall surface-deposited particulate matter, it cannot address the deviation of the differential pressure across the filter to the lower side, and there is a possibility that the estimation accuracy of the deposition amount of particulate matter may decrease. Also, as described above, since the deviation amount to the lower side of the differential pressure across the filter gradually increases, there is a possibility that the estimation accuracy may significantly decrease.

[0014] The invention described in Patent Document 2 addresses the deviation of the differential pressure across the filter towards the lower side due to cracks or fissures in the particulate matter deposited on the wall surface. However, although the invention described in Patent Document 2 switches the estimation method of the deposition amount of particulate matter from the differential pressure estimation method to the integration estimation method, it does not correct the differential pressure across the filter. Further, since it does not consider the deposition and combustion of particulate matter (fine pore deposited particulate matter) in the fine pores of the filter wall, it cannot address the deviation of the differential pressure across the filter towards the higher side.

[0015] In view of such points, the present invention was devised, and an object thereof is to provide an exhaust gas purification system for an internal combustion engine that can appropriately correct the differential pressure across the filter and improve the estimation accuracy when estimating the deposition amount of particulate matter in the filter based on the differential pressure across the filter.

Means for Solving the Problems

[0016] To solve the above problems, a first invention is an exhaust gas purification system for an internal combustion engine, comprising a filter disposed in an exhaust passage of the internal combustion engine for collecting particulate matter contained in exhaust gas from the internal combustion engine, a differential pressure detection device for detecting a differential pressure across the filter, which is the pressure difference between the inflow side and the outflow side of the exhaust gas in the filter, and a control device for detecting an operating state of the internal combustion engine and controlling the internal combustion engine based on the detected operating state. When the control device determines that the particulate matter exceeding a predetermined amount has accumulated in the filter and satisfies a predetermined condition, it executes a filter regeneration process for burning and removing the particulate matter accumulated in the filter. Based on the operating state, it obtains an increase-side correction amount for correcting the differential pressure across the filter detected using the differential pressure detection device towards the increasing side, obtains a corrected differential pressure across the filter by correcting the differential pressure across the filter using the increase-side correction amount, and when the corrected differential pressure across the filter exceeds a predetermined threshold value set according to the predetermined amount, determines that the particulate matter exceeding the predetermined amount has accumulated in the filter. It is an exhaust gas purification system for an internal combustion engine.

[0017] Next, a second invention is an exhaust gas purification system for an internal combustion engine, comprising a filter disposed in an exhaust passage of the internal combustion engine to collect particulate matter contained in exhaust gas from the internal combustion engine, a differential pressure detection device that detects a differential pressure across the filter, which is a pressure difference between an inflow side and an outflow side of the exhaust gas in the filter, and a control device that detects an operating state of the internal combustion engine and controls the internal combustion engine based on the detected operating state. When the control device determines that the particulate matter exceeding a predetermined amount has accumulated in the filter and satisfies a predetermined condition, the control device executes a filter regeneration process for burning and removing the particulate matter accumulated in the filter. Based on the operating state, both an increase-side correction amount for correcting the differential pressure across the filter detected using the differential pressure detection device to the increasing side and a decrease-side correction amount for correcting the differential pressure across the filter to the decreasing side are obtained. A corrected differential pressure across the filter is obtained by correcting the differential pressure across the filter using both the increase-side correction amount and the decrease-side correction amount. When the corrected differential pressure across the filter exceeds a predetermined threshold value set according to the predetermined amount, it is determined that the particulate matter exceeding the predetermined amount has accumulated in the filter. This is an exhaust gas purification system for an internal combustion engine.

[0018] Next, a third invention is an exhaust gas purification system for an internal combustion engine according to the first or second invention above, wherein when obtaining the increase-side correction amount, the control device determines an increase-side correction base amount set according to a filter temperature, which is a temperature of the filter estimated based on at least one of an exhaust gas temperature on the inflow side of the filter and an exhaust gas temperature on the outflow side of the filter, or an exhaust gas temperature on the inflow side of the filter, and an amount of particulate matter accumulation in the filter estimated based on the operating state. This is an exhaust gas purification system for an internal combustion engine.

[0019] Next, a fourth invention is an exhaust gas purification system for an internal combustion engine according to the second invention, wherein when obtaining the reduction-side correction amount, after completion of the filter regeneration process, the control device obtains a reduction-side initial amount which is an initial amount of the reduction-side correction amount, and based on at least one of the exhaust gas temperature on the inflow side of the filter and the exhaust gas temperature on the outflow side of the filter, a filter temperature which is the temperature of the filter estimated, or the exhaust gas temperature on the inflow side of the filter, the reduction-side correction base amount set accordingly, and the reduction-side initial amount, an exhaust gas purification system for an internal combustion engine is obtained.

Advantages of the Invention

[0020] According to the first invention, when the differential pressure across the filter is shifted to the lower side, by obtaining the corrected differential pressure across the filter using the increase-side correction amount for correcting the differential pressure across the filter to the increase side, the differential pressure across the filter can be appropriately corrected. And since the shift to the lower side of the differential pressure across the filter where the shift amount gradually increases is corrected, it is possible to avoid a significant decrease in estimation accuracy. Therefore, when estimating the deposition amount of particulate matter in the filter based on the differential pressure across the filter, the differential pressure across the filter can be appropriately corrected to achieve higher estimation accuracy.

[0021] According to the second invention, when the differential pressure across the filter is shifted to the lower side, when the differential pressure across the filter is shifted to the higher side, in either case, or when both occur, by obtaining the corrected differential pressure across the filter using the increase-side correction amount and the reduction-side correction amount, the differential pressure across the filter can be appropriately corrected. Therefore, when estimating the deposition amount of particulate matter in the filter based on the differential pressure across the filter, the differential pressure across the filter can be appropriately corrected to achieve higher estimation accuracy.

[0022] According to the third invention, the increase-side correction amount can be obtained more specifically and appropriately.

[0023] According to the fourth invention, the reduction-side correction amount can be obtained more specifically and appropriately.

Brief Description of the Drawings

[0024]

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Embodiments for Carrying Out the Invention

[0025] <Overall Configuration of the Internal Combustion Engine System 1 (Fig. 1)> Hereinafter, the internal combustion engine system 1 including the exhaust purification system 2 of the present invention will be described with reference to the drawings. First, an example of the overall configuration of the internal combustion engine system 1 will be described with reference to Fig. 1. Note that the internal combustion engine 10 of the internal combustion engine system 1 in the example of Fig. 1 is a so-called diesel engine. The exhaust purification system 2 includes a control device 50, a filter 43 (particulate matter collection filter), and a differential pressure detection device 35. Hereinafter, the configuration etc. of the internal combustion engine system 1 will be described in order from the intake side to the exhaust side.

[0026] An air flow rate detection device 31 is provided in the intake pipe 11A. The air flow rate detection device 31 (for example, an intake air flow sensor) outputs a detection signal corresponding to the flow rate [g / sec] of the air inhaled by the internal combustion engine 10 to the control device 50. The air flow rate detection device 31 is also provided with an intake air temperature detection device 32A and an atmospheric pressure detection device 33A. The intake air temperature detection device 32A (for example, an intake air temperature sensor) outputs a detection signal corresponding to the temperature of the intake air (in this case, outside air) to the control device 50. The atmospheric pressure detection device 33A (for example, a pressure sensor) outputs a detection signal corresponding to the atmospheric pressure to the control device 50. The intake pipe 11A is also connected to the compressor 82 of the supercharger 80.

[0027] The intake pipe 11A is connected to the inlet side of the compressor 82, and the intake pipe 11C is connected to the outlet side of the compressor 82. The compressor 82 is rotationally driven by the turbine 81 and pumps the intake air flowing in from the intake pipe 11A to the intake pipe 11C. A pressure detection device 33B is provided in the intake pipe 11A on the upstream side of the compressor 82. The pressure detection device 33B (for example, a pressure sensor) outputs a detection signal corresponding to the pressure of the air before being compressed by the compressor 82 to the control device 50.

[0028] The downstream side of the intake pipe 11C is connected to the intake manifold 11D. The intake pipe 11C is provided with a pressure detection device 33C, an intercooler 84, a throttle device 64, and an intake air temperature detection device 32B. The pressure detection device 33C (for example, a pressure sensor) outputs a detection signal corresponding to the pressure of the intake air pressurized by the compressor 82 to the control device 50. The intercooler 84 reduces the temperature of the intake air pressurized by the compressor 82 to increase the oxygen density. The throttle device 64 adjusts the opening degree of the throttle valve to the target throttle opening degree based on a control signal from the control device 50. The intake air temperature detection device 32B (for example, an intake air temperature sensor) outputs a detection signal corresponding to the temperature of the intake air reduced by the intercooler 84 to the control device 50.

[0029] The downstream side of the intake manifold 11D is connected to an intake port that guides the intake air to each cylinder of the internal combustion engine 10. The intake air guided to the intake manifold 11D is sucked into each cylinder of the internal combustion engine 10 and used for combustion together with the fuel injected from the injector 21. The intake manifold 11D is provided with a pressure detection device 33D. The pressure detection device 33D (for example, a pressure sensor) outputs a detection signal corresponding to the pressure of the intake air in the intake manifold 11D to the control device 50.

[0030] The internal combustion engine 10 is provided with a rotation detection device 34A and a cylinder detection device 34B. The rotation detection device 34A (for example, a crankshaft rotation sensor) outputs a detection signal (crank angle signal) corresponding to the rotation angle of the crankshaft of the internal combustion engine 10 to the control device 50. Further, the cylinder detection device 34B (for example, a camshaft rotation sensor) outputs a detection signal (cylinder discrimination signal) to the control device 50 when, for example, the piston of the first cylinder reaches top dead center of compression. The internal combustion engine 10 is also provided with a load device 63 capable of adjusting the load of the internal combustion engine 10. The load device 63 is, for example, an alternator, and changes the load of the internal combustion engine 10 based on a load control signal (power generation control signal) from the control device 50. The internal combustion engine 10 is also provided with a coolant temperature detection device 32C. The coolant temperature detection device 32C (for example, a water temperature sensor) outputs a detection signal corresponding to the temperature of the coolant (cooling water) that cools the internal combustion engine to the control device 50.

[0031] The accelerator pedal depression amount detection device 38 (for example, an accelerator pedal depression amount sensor) outputs a detection signal corresponding to the depression amount of the accelerator pedal operated by the driver to the control device 50. The ignition switch 39 is an input device for receiving an instruction from the driver to start or stop the internal combustion engine.

[0032] The control device 50 calculates a required load based on the rotational speed of the internal combustion engine based on the detection signal from the rotation detection device 34A and the depression amount of the accelerator pedal based on the detection signal from the accelerator pedal depression amount detection device 38, and calculates a fuel amount corresponding to the required load. Then, the control device 50 controls the injector 21 at a predetermined timing based on the detection signals from the rotation detection device 34A and the cylinder detection device 34B, and injects the fuel amount corresponding to the required load into each of the cylinders of cylinders #1 to #4 of the internal combustion engine 10.

[0033] An exhaust manifold 12A is connected to the exhaust port of the internal combustion engine 10. The exhaust from the internal combustion engine 10 is guided through the exhaust manifold 12A, the exhaust pipe 12B, and the turbine 81 of the supercharger 80, rotates the turbine 81 to drive it, and is discharged into the exhaust pipe 12C. The exhaust from the internal combustion engine 10 contains carbon monoxide (CO), hydrocarbons (HC), particulate matter (PM), nitrogen oxides (NOx), etc.

[0034] The inlet side of the EGR pipe 13 for returning a part of the exhaust gas to the intake air is connected to the exhaust manifold 12A or the exhaust pipe 12B. And the outlet side of the EGR pipe 13 is connected to the intake pipe 11C or the intake manifold 11D. And an EGR valve 13A that is controlled by the control device 50 to adjust the opening degree of the EGR pipe is provided in the EGR pipe 13.

[0035] An exhaust pipe 12B is connected to the outlet side of the exhaust manifold 12A. Also, the inlet side of the turbine 81 of the supercharger 80 is connected to the downstream side of the exhaust pipe 12B. And an exhaust pipe 12C is connected to the outlet side of the turbine 81, and an exhaust purification device 40 is connected to the downstream side of the exhaust pipe 12C.

[0036] The exhaust purification device 40 is composed of an upstream exhaust purification device 41 and a downstream exhaust purification device 45 arranged on the downstream side of the upstream exhaust purification device 41. The upstream exhaust purification device 41 has, from the upstream side, a first oxidation catalyst 42 (DOC: Diesel Oxidation Catalyst) and a filter 43 (DPF: Diesel Particulate Filter). The downstream exhaust purification device 45 has, from the upstream side, a urea SCR 46 (SCR: Selective Catalytic Reduction, SCR catalyst) and a second oxidation catalyst 47 (DOC: Diesel Oxidation Catalyst).

[0037] The first oxidation catalyst 42 purifies carbon monoxide (CO), hydrocarbons (HC), etc. contained in the exhaust gas through an oxidation reaction. The filter 43 collects particulate matter (PM) contained in the exhaust gas and allows only the exhaust gas to flow out to the downstream side. Note that the filter 43 also has a function of purifying carbon monoxide and hydrocarbons through an oxidation reaction.

[0038] On the exhaust pipe 12C upstream of the first oxidation catalyst 42, a fuel addition valve 61A, an exhaust temperature detection device 36A (for example, an exhaust temperature sensor), etc. are provided. The fuel addition valve 61A can add (inject) fuel, and when performing a filter regeneration process for regenerating the filter 43 on which the collected particulate matter has accumulated (when burning and removing the particulate matter), fuel (reaction liquid) for raising the temperature of the exhaust gas through an oxidation reaction in the first oxidation catalyst 42 is injected into the exhaust pipe 12C. Also, a dispersion device 61B for colliding and dispersing the fuel injected from the fuel addition valve 61A is arranged in the exhaust pipe 12C. Note that fuel is supplied to the fuel addition valve 61A from a fuel tank 90.

[0039] An exhaust temperature detection device 36B (for example, an exhaust temperature sensor) is provided downstream of the first oxidation catalyst 42 and upstream of the filter 43. An exhaust temperature detection device 36C (for example, an exhaust temperature sensor) is provided downstream of the filter 43. The exhaust temperature detection devices 36A, 36B, and 36C output detection signals corresponding to the temperature of the exhaust gas to the control device 50.

[0040] A differential pressure detection device 35 (for example, a differential pressure sensor) for detecting the differential pressure (pressure difference) between the exhaust pressure upstream of the first oxidation catalyst 42 and upstream of the filter 43 and the exhaust pressure downstream of the filter 43 is provided. The differential pressure detection device 35 outputs a detection signal corresponding to the differential pressure across the filter, which is the pressure difference between the pressure upstream and downstream of the filter 43, to the control device 50.

[0041] On the other hand, the downstream exhaust gas purification device 45 is provided with a urea aqueous solution addition valve 62A, a dispersion device 62B, a urea SCR 46, a second oxidation catalyst 47, etc. from the upstream side. The urea SCR 46 is connected to the downstream side of the filter 43 via the exhaust pipe 12D. The urea aqueous solution addition valve 62A can add (inject) urea aqueous solution, and is arranged in the exhaust pipe 12D which is on the downstream side of the filter 43 and upstream of the urea SCR 46, and injects urea aqueous solution (reaction liquid) into the exhaust gas at a predetermined timing. The injected urea aqueous solution collides with and scatters on the dispersion device 62B and is atomized, diffuses in the exhaust pipe 12D, and reaches the urea SCR 46. The urea aqueous solution addition valve 62A is supplied with urea aqueous solution from a urea aqueous solution tank (not shown). The urea SCR 46 uses the ammonia gas generated from the added urea aqueous solution to reduce and purify nitrogen oxides (NOx) contained in the exhaust gas.

[0042] In addition, a NOx detection device 37A (for example, a NOx sensor) is provided in the exhaust pipe 12D upstream of the urea SCR 46. Also, in the exhaust pipe 12E downstream of the urea SCR 46, a NOx detection device 37B (for example, a NOx sensor) and an exhaust gas temperature detection device 36D (for example, an exhaust gas temperature sensor) are provided. The NOx detection devices 37A and 37B output detection signals corresponding to the concentration of NOx in the exhaust gas to the control device 50, and the exhaust gas temperature detection device 36D outputs a detection signal corresponding to the temperature of the exhaust gas to the control device 50. The control device 50 calculates the NOx purification rate of the urea SCR 46 based on the detection signals of the NOx detection devices 37A and 37B, the exhaust gas temperature detection device 36D, etc., and controls the urea aqueous solution addition valve 62A based on the calculated NOx purification rate. Note that the exhaust pipes 12B, 12C, 12D, and 12E correspond to the exhaust passage.

[0043] The second oxidation catalyst 47 is connected to the downstream side of the urea SCR 46 via the exhaust pipe 12E. The second oxidation catalyst 47 oxidizes and purifies the ammonia gas remaining in the exhaust gas. Note that the second oxidation catalyst 47 also has a function of oxidizing and purifying carbon monoxide and hydrocarbons through an oxidation reaction.

[0044] The control device 50 is a known device including a CPU 51, a RAM 52, a ROM 53 (storage device), a timer 54, a non-volatile storage device 55 (e.g., EEPROM), etc. The CPU 51 executes various arithmetic processes based on various programs and maps stored in the ROM 53 (e.g., Flash-ROM). Also, the RAM 52 temporarily stores the arithmetic results in the CPU and the data input from each detection device, etc., and the non-volatile storage device 55 stores, for example, the data to be saved when the internal combustion engine 10 stops.

[0045] And the control device 50 can detect the operating state of the internal combustion engine 10 based on the input detection signal. Also, the control device 50 outputs a control signal for controlling various actuators such as an injector 21 that injects fuel into the cylinder, a fuel addition valve 61A, an aqueous urea solution addition valve 62A, and an EGR valve 13A according to the detected operating state of the internal combustion engine 10 and the request from the driver based on the detection signal from the accelerator depression amount detection device 38.

[0046] The control device 50 detects the differential pressure across the filter 43, which is the pressure difference between the upstream side and the downstream side of the filter 43, based on the detection signal from the differential pressure detection device 35, and can estimate the deposition amount of the particulate matter collected in the filter 43 based on the detected differential pressure across the filter. And when the estimated deposition amount exceeds the threshold value, the control device 50 executes a filter regeneration process to inject fuel (reaction liquid) from the fuel addition valve 61A to raise the exhaust temperature, and burns and removes the particulate matter deposited in the filter 43 to regenerate the filter 43.

[0047] Since the above filter regeneration process consumes fuel, if the filter regeneration process is executed more frequently than necessary, the fuel consumption deteriorates, and if the frequency is low, the filter 43 may become clogged. In order to execute the filter regeneration process at an appropriate frequency, it is necessary to accurately estimate the deposition amount of the particulate matter deposited in the filter 43. However, the differential pressure across the filter based on the detection signal from the differential pressure detection device 35 may deviate to the higher side or the lower side with respect to the characteristic serving as a reference, as described below.

[0048] <Structure of Filter 43 (Figs. 2 to 4) and Factors Causing Deviation in Differential Pressure before and after Filter (Figs. 5 to 8)> First, the structure of filter 43 will be described with reference to Figs. 2 to 4. Fig. 2 shows the overall schematic structure of filter 43, Fig. 3 is an enlarged view of portion AA shown in Fig. 2, and Fig. 4 is an enlarged view of portion BB shown in Fig. 3.

[0049] As shown in Fig. 2, filter 43 is arranged such that the inflow passage 43a with the inflow side of the exhaust open and the outflow side of the exhaust closed by the lid portion 43c and the outflow passage 43b with the inflow side of the exhaust closed by the lid portion 43d and the outflow side of the exhaust open are alternately adjacent to each other.

[0050] As shown in Fig. 3, the exhaust that has flowed into the inflow passage 43a flows out from the outflow passage 43b after passing through the filter wall 43e between the inflow passage 43a and the outflow passage 43b.

[0051] As shown in Fig. 4, the filter wall 43e is formed with a plurality of fine pores 43f through which particulate matter P cannot pass. Therefore, the exhaust can pass through the filter wall 43e, but the particulate matter P contained in the exhaust cannot pass through the filter wall 43e and is collected.

[0052] FIG. 5 shows the state in which particulate matter (wall surface deposited particulate matter Pb) collected without passing through the filter wall 43e is deposited on the surface of the filter wall 43e. In the deposition state shown in FIG. 5, the relationship between the deposition amount of particulate matter in the filter 43 and the differential pressure across the filter becomes characteristic A (reference characteristic) shown in FIG. 8. The storage device of the control device 50 stores the deposition amount-differential pressure characteristic of characteristic A shown in FIG. 8. And the control device 50 determines (estimates) that the deposition amount = deposition amount Ma when the differential pressure across the filter = differential pressure threshold value ΔP based on characteristic A shown in FIG. 8. When the deposition state of the particulate matter is the deposition state shown in FIG. 5, the estimation accuracy of the deposition amount estimated from the differential pressure across the filter based on characteristic A shown in FIG. 8 is sufficiently high. However, the deposition state of the particulate matter deposited in the filter 43 and the characteristics of the differential pressure across the filter do not necessarily become the deposition state shown in FIG. 5 and characteristic A of FIG. 8. Depending on the operating state of the internal combustion engine, there may be cases where the deposition state shown in FIG. 6 and characteristic B of FIG. 8, cases where the deposition state shown in FIG. 7 and characteristic C of FIG. 8, or cases where both are mixed.

[0053] The deposition state shown in FIG. 6 shows a deposition state of characteristic B in which the differential pressure across the filter is shifted to the higher side with respect to characteristic A (reference characteristic) of FIG. 8. The deposition state shown in FIG. 6 has particulate matter (fine pore deposited particulate matter Pa) entering at least a part of the fine pores 43f in the filter wall 43e compared to the deposition state shown in FIG. 5. In the filter 43 where no particulate matter is deposited by performing the filter regeneration process, first, particulate matter (fine pore deposited particulate matter Pa) enters the fine pores 43f of the filter wall 43e until it reaches a saturated state (initial fine pore deposition amount), and then particulate matter (wall surface deposited particulate matter Pb) is deposited on the surface of the filter wall 43e. As particulate matter (wall surface deposited particulate matter Pb) is deposited on the surface of the filter wall 43e, particulate matter (fine pore deposited particulate matter Pa) cannot enter the fine pores 43f of the filter wall 43e, so the fine pore deposited particulate matter Pa does not increase beyond the initial fine pore deposition amount. And the fine pore deposited particulate matter Pa gradually burns and decreases according to the operating state of the internal combustion engine.

[0054] Since the fine pore deposited particulate matter Pa blocks the fine pores 43f through which the exhaust gas passes, the differential pressure across the filter shifts to the higher side. Therefore, the differential pressure across the filter in this case becomes the characteristic B shown in FIG. 8. In characteristic B, first, while the fine pore deposited particulate matter Pa is depositing in the fine pores 43f until it reaches the saturation state (initial amount of deposition in the fine pores) (while the deposition amount shown in FIG. 8 is from 0 to Mx), the differential pressure across the filter shifts to a higher value than characteristic A. After that, the shift to the higher side gradually becomes smaller due to the incineration by combustion of the fine pore deposited particulate matter Pa in the fine pores 43f, and it approaches characteristic A. That is, the shift to the higher side of the differential pressure across the filter (the difference between characteristic A and characteristic B shown in FIG. 8) is large at the initial stage of deposition after the completion of filter regeneration, and the subsequent shift amount gradually becomes smaller.

[0055] The deposition state shown in FIG. 7 shows a deposition state of characteristic C in which the differential pressure across the filter shifts to the lower side with respect to characteristic A (reference characteristic) in FIG. 8. The deposition state shown in FIG. 7 has cracks 43g, etc. generated in the layer of particulate matter (wall surface deposited particulate matter Pb) deposited on the surface of the filter wall 43e compared to the deposition state shown in FIG. 5. As particulate matter (wall surface deposited particulate matter Pb) deposits on the surface of the filter wall 43e as shown in FIG. 5, cracks 43g may occur depending on the operating state. In particular, cracks 43g are likely to occur when the exhaust gas temperature becomes high at a predetermined temperature or higher.

[0056] When cracks 43g occur according to the operating state of the internal combustion engine, the exhaust gas becomes more likely to pass through according to the amount of cracks 43g, and the differential pressure across the filter shifts to the lower side. Since these cracks 43g do not recover, if the cracks 43g increase according to the operating state of the internal combustion engine, the shift to the lower side of the differential pressure across the filter gradually becomes larger. That is, the shift to the lower side of the differential pressure across the filter (the difference between characteristic A and characteristic C shown in FIG. 8) is small at first, and then the shift amount gradually becomes larger.

[0057] The control device 50 of the exhaust gas purification system 2 described in this embodiment can estimate a more accurate deposition amount (the deposition amount of particulate matter in the filter 43) by using the corrected differential pressure before and after the filter, which corrects the deviation to the higher side and the deviation to the lower side of the differential pressure before and after the filter, through the processes described below. In the description of this embodiment, "deviating to the higher side" means that "the differential pressure before and after the filter deviates to the higher side as shown in characteristic B in FIG. 8 with respect to the reference characteristic (characteristic A shown in FIG. 8)". Also, "deviating to the lower side" means that "the differential pressure before and after the filter deviates to the lower side as shown in characteristic C in FIG. 8 with respect to the reference characteristic (characteristic A shown in FIG. 8)".

[0058] <Processing procedures, etc. of the control device 50 in the first embodiment (FIGS. 9 to 15)> <Overall processing (FIG. 9)> Next, the processing of the control device 50 (CPU 51) in the first embodiment will be described with reference to the flowcharts and the like shown in FIGS. 9 to 15. In the first embodiment, the corrected differential pressure before and after the filter is obtained by using both the increasing side correction amount for correcting the deviation to the lower side of the differential pressure before and after the filter and the decreasing side correction amount for correcting the deviation to the higher side of the differential pressure before and after the filter.

[0059] The control device 50 (CPU 51) starts the processing shown in FIG. 9 at a predetermined time interval of about several tens of [ms] to several hundreds of [ms], and proceeds to step S10. In the following description, "PM" refers to "particulate matter".

[0060] In step S10, the control device 50 estimates the PM emission amount according to the operating state of the internal combustion engine. For example, the control device 50 stores a map in which the PM emission amount corresponding to the rotational speed of the internal combustion engine and the load (or fuel injection amount) of the internal combustion engine is set, and obtains the PM emission amount based on the map and the operating state of the internal combustion engine. Then, the control device 50 adds the PM emission amount to the PM estimated deposition amount (corresponding to the particulate matter deposition amount) to update the PM estimated deposition amount, and proceeds to step S20 for processing. The PM estimated deposition amount is an integrated value of the PM emission amount, and is used for calculating the increasing-side instantaneous correction amount in step T25 of FIG. 10 which is the process of step S20 described later, and is reduced in step S75 described later.

[0061] In step S20, the control device 50 executes [calculating the increasing-side correction amount (correction amount for the deviation to the side with a lower differential pressure before and after the filter)], and proceeds to step S30 for processing. The details of [calculating the increasing-side correction amount] will be described later.

[0062] In step S30, the control device 50 executes [calculating the decreasing-side correction amount (correction amount for the deviation to the side with a higher differential pressure before and after the filter)], and proceeds to step S40 for processing. The details of [calculating the decreasing-side correction amount] will be described later.

[0063] In step S40, the control device 50 adds the increasing-side correction amount obtained in step S20 to the differential pressure before and after the filter obtained based on the detection signal from the differential pressure detection device 35, and subtracts the decreasing-side correction amount obtained in step S30 to obtain the corrected differential pressure before and after. Then, the control device 50 proceeds to step S60 for processing.

[0064] In step S60, the control device 50 determines whether the DPF regeneration execution flag is ON. When the DPF regeneration execution flag is ON (Yes), the control device 50 proceeds to step S75, and when the DPF regeneration execution flag is not ON (No), the control device 50 proceeds to step S65. The DPF regeneration execution flag is a flag that is set to ON during the execution of the "filter regeneration process (a process of raising the temperature of the exhaust gas to burn and remove the particulate matter deposited in the filter 43 to regenerate the filter 43)", which will be described later. The DPF regeneration execution flag is set to ON in step S70 and set to OFF in step S85.

[0065] When the process proceeds to step S65, the control device 50 determines whether the corrected differential pressure before and after exceeds a predetermined threshold value. For example, when determining whether it exceeds the deposition amount Ma (corresponding to a predetermined amount) shown in FIG. 8, the control device 50 determines whether the corrected differential pressure before and after exceeds the differential pressure threshold value ΔP (corresponding to a predetermined threshold value). The differential pressure threshold value ΔP (predetermined threshold value) is set to a value corresponding to the deposition amount Ma (predetermined amount). When the corrected differential pressure before and after exceeds the predetermined threshold value (Yes), the control device 50 proceeds to step S70, and when the corrected differential pressure before and after does not exceed the predetermined threshold value (No), the process shown in FIG. 9 ends.

[0066] In the example of FIG. 9, an example is shown in which the filter regeneration processes of steps S70 and S75 are executed when the corrected differential pressure before and after exceeds the predetermined threshold value in step S65. However, other predetermined conditions are omitted. For example, when all other predetermined conditions such as the engine speed being within a predetermined range, the fuel injection amount being within a predetermined range, and the accelerator pedal depression amount being within a predetermined range are satisfied, the filter regeneration processes of steps S70 and S75 are executed. The other predetermined conditions are not limited to the above example, and various conditions are set, but since they are existing conditions, they are omitted.

[0067] As shown in FIG. 8, when the characteristic of the differential pressure before and after the filter is characteristic A, if the differential pressure before and after the filter = differential pressure threshold value ΔP, the deposition amount of particulate matter in the filter 43 = deposition amount Ma. However, in the case of characteristic B where the differential pressure before and after the filter is shifted to the higher side, when the differential pressure before and after the filter = differential pressure threshold value ΔP, the deposition amount of particulate matter in the filter 43 = deposition amount Mb. Since the frequency of the filter regeneration process increases and the fuel consumption increases, this is not very preferable. Also, in the case of characteristic C where the differential pressure before and after the filter is shifted to the lower side, when the differential pressure before and after the filter = differential pressure threshold value ΔP, the deposition amount of particulate matter in the filter 43 = deposition amount Mc. Since the deposition amount is more than the assumed amount and there is a possibility that clogging or the like may occur in the filter 43, this is not preferable.

[0068] As will be described later, the corrected differential pressure before and after is corrected to be characteristic Ch in the case of characteristic C where the differential pressure before and after the filter is shifted to the lower side with respect to characteristic A as shown in FIG. 12. Further, as will be described later, the corrected differential pressure before and after is corrected to be characteristic Bh in the case of characteristic B where the differential pressure before and after the filter is shifted to the higher side with respect to characteristic A as shown in FIG. 15. By using this corrected differential pressure before and after, it becomes possible to more accurately estimate the deposition amount of particulate matter in the filter 43, and it becomes possible to execute the filter regeneration process at an appropriate frequency, contributing to the improvement of fuel efficiency.

[0069] When the process proceeds to step S70, the control device 50 sets the DPF regeneration execution flag to ON, resets the PM estimated deposition amount, and proceeds to step S75. In step S10, the control device 50 obtained the PM estimated deposition amount by the integration formula estimation method, but in step S70, it is corrected and the PM estimated deposition amount is reset by the differential pressure formula estimation method using the more accurate corrected differential pressure before and after (note that the resetting of the PM estimated deposition amount may be omitted).

[0070] When the process proceeds to step S75, the control device 50 executes a filter regeneration process (an existing process) and proceeds to step S80. Since the filter regeneration process is an existing process, detailed description thereof is omitted. Briefly, fuel is injected from the fuel addition valve 61A shown in FIG. 1, reacted by the first oxidation catalyst 42 to raise the temperature of the exhaust gas, and PM in the DPF (filter 43) is burned and removed to regenerate the DPF (filter 43). Then, the control device 50 obtains the amount of PM burned and removed according to the exhaust gas temperature, regeneration time, etc., and updates (decreases) the PM estimated deposition amount.

[0071] When the process proceeds to step S80, the control device 50 determines whether the filter regeneration is completed. For example, the control device 50 determines that the filter regeneration is completed when the PM estimated deposition amount updated in step S75 becomes substantially zero (or below a predetermined amount). If the control device 50 determines that the filter regeneration is completed (Yes), the process proceeds to step S85. If the control device 50 determines that the filter regeneration is not completed (No), the process shown in FIG. 9 ends.

[0072] When the process proceeds to step S85, the control device 50 sets the DPF regeneration execution flag to OFF, sets the DPF regeneration completion flag to ON, initializes (initializes to zero) the increase-side correction amount and the decrease-side correction amount, and ends the process shown in FIG. 9. The DPF regeneration completion flag is used in [Calculating the decrease-side correction amount] described later.

[0073] <Calculate the increase-side correction amount (correction amount for the deviation to the side with a lower differential pressure before and after the filter) (FIGS. 10 to 12)> When the control device 50 executes [Calculate the increase-side correction amount (correction amount for the deviation to the side with a lower differential pressure before and after the filter)] in step S20 shown in FIG. 9, the process proceeds to step T20 of [Calculating the increase-side correction amount] shown in FIG. 10.

[0074] In step T20, the control device 50 calculates the increase-side correction base amount and advances the process to step T25. In the storage device (ROM53) of the control device 50, for example, the [temperature - increase-side correction base amount characteristic] shown in FIG. 11 is stored. In the [temperature - increase-side correction base amount characteristic], the increase-side correction base amount corresponding to the temperature is set. Note that this temperature is the exhaust gas temperature on the inlet side of the filter 43, or the filter temperature (filter bed temperature), etc., which is the temperature of the filter 43 estimated based on at least one of the exhaust gas temperature on the inlet side of the filter 43 and the exhaust gas temperature on the outlet side of the filter 43. The control device 50 calculates the increase-side correction base amount based on the [temperature - increase-side correction base amount characteristic] and the operating state of the internal combustion engine. Note that the increase-side correction base amount is set as the correction amount per unit PM amount per unit time.

[0075] In step T25, the control device 50 calculates the increase-side instantaneous correction amount and advances the process to step T40. The control device 50 calculates the increase-side instantaneous correction amount, for example, by the following (Equation 1). Note that the constant Fc is set to an appropriate value obtained through experiments or simulations using an actual vehicle. As described above, since the increase-side correction base amount is the correction amount per unit PM amount per unit time, the increase-side instantaneous correction amount obtained by multiplying the PM estimated deposition amount obtained in step S10 of FIG. 9 is the correction amount per unit time. Increase-side instantaneous correction amount = constant Fc * increase-side correction base amount * PM estimated deposition amount (Equation 1)

[0076] Note that the PM estimated deposition amount (the PM deposition amount in the filter 43 recognized by the control device 50) has been described by taking the example of being obtained by the integration formula estimation method in step S10 shown in FIG. 9, but it may be obtained using a known method such as the differential pressure type estimation method or a method using a counter according to the elapsed time.

[0077] In step T40, the control device 50 adds the increasing-side instantaneous correction amount to the increasing-side correction amount to update the increasing-side correction amount, and proceeds to step T50. Note that the increasing-side correction amount is initialized (to zero) in step S85 shown in FIG. 9, and is the integrated value of the increasing-side instantaneous correction amount after the completion of the filter reproduction. As described above, since the increasing-side instantaneous correction amount is an amount per unit time, the increasing-side correction amount obtained by integrating the increasing-side instantaneous correction amount is the correction amount at the current time after the completion of the filter reproduction process.

[0078] In step T50, the control device 50 determines whether the increasing-side correction amount is less than or equal to the upper guard amount. If the increasing-side correction amount is less than or equal to the upper guard amount (Yes), the control device 50 ends the process shown in FIG. 10 and returns the process to below step S20 shown in FIG. 9. If the increasing-side correction amount is greater than the upper guard amount (No), the control device 50 proceeds to step T60. Note that the value of the upper guard amount is set to an appropriate value obtained through experiments or simulations using an actual vehicle.

[0079] When proceeding to step T60, the control device 50 sets the upper guard amount to the increasing-side correction amount, ends the process shown in FIG. 10, and returns the process to below step S20 shown in FIG. 9.

[0080] Through the process shown in FIG. 10 above, in the example of FIG. 12, when the differential pressure before and after the filter is characteristic C which is shifted to the lower side with respect to characteristic A, the characteristic C is corrected to characteristic Ch by the increasing-side correction amount Hc. In the case of characteristic C, when the differential pressure = differential pressure threshold value ΔP, the deposition amount of particulate matter in the filter 43 = deposition amount Mc. However, in the case of characteristic Ch, when the differential pressure = differential pressure threshold value ΔP, the deposition amount of particulate matter in the filter 43 = deposition amount Mch, and it becomes closer to the deposition amount Ma which is the correct deposition amount.

[0081] <Calculate the decreasing-side correction amount (correction amount for the shift to the higher differential pressure side before and after the filter) (FIGS. 13 to 15)> When the control device 50 executes [calculating the correction amount on the decreasing side (the correction amount for the deviation toward the side with a higher differential pressure before and after the filter)] in step S30 shown in FIG. 9, the process proceeds to step U10 of [calculating the correction amount on the decreasing side] shown in FIG. 13.

[0082] In step U10, the control device 50 determines whether the DPF regeneration completion flag is set to ON. The DPF regeneration completion flag is a flag that is set to ON when the filter regeneration is completed in step S85 shown in FIG. 9. When the DPF regeneration completion flag is set to ON (Yes), the control device 50 proceeds to step U15, and when the DPF regeneration completion flag is not set to ON, the control device 50 proceeds to step U20.

[0083] When the process proceeds to step U15, the control device 50 calculates the initial amount Hbi on the decreasing side, initializes the integrated amount on the decreasing side (initializes it to zero), sets the DPF regeneration completion flag to OFF, and proceeds to step U20. For example, the initial amount Hbi on the decreasing side is set as a constant corresponding to the internal combustion engine and the filter 43. The integrated amount on the decreasing side is the amount obtained by integrating the instantaneous correction amount on the decreasing side in step U30.

[0084] In step U20, the control device 50 calculates the correction base amount on the decreasing side and proceeds to step U25. In the storage device (ROM53) of the control device 50, for example, [temperature - correction base amount characteristic on the decreasing side] shown in FIG. 14 is stored. In the [temperature - correction base amount characteristic on the decreasing side], the correction base amount on the decreasing side corresponding to the temperature is set. This temperature is the filter temperature (filter bed temperature), etc., which is the temperature of the filter 43 estimated based on at least one of the exhaust gas temperature on the inlet side of the filter 43 or the exhaust gas temperature on the inlet side of the filter 43 and the exhaust gas temperature on the outlet side of the filter 43. The control device 50 calculates the correction base amount on the decreasing side based on the [temperature - correction base amount characteristic on the decreasing side] and the operating state of the internal combustion engine. The correction base amount on the decreasing side has a correction amount per unit time set.

[0085] In step U25, the control device 50 calculates the decreasing-side instantaneous correction amount and proceeds with the process to step U30. The control device 50 calculates the decreasing-side instantaneous correction amount, for example, using the following (Equation 2). The constant Fb is set to an appropriate value obtained through experiments, simulations, etc. using an actual vehicle. Decreasing-side instantaneous correction amount = Constant Fb * Decreasing-side correction base amount (Equation 2)

[0086] In step U30, the control device adds the decreasing-side instantaneous correction amount to the decreasing-side integrated amount to update the decreasing-side integrated amount, and proceeds with the process to step U40. The decreasing-side integrated amount is initialized (to zero) in step U15 shown in FIG. 13, and is the integrated value of the decreasing-side instantaneous correction amount after the completion of filter reproduction. As described above, since the decreasing-side instantaneous correction amount obtained by multiplying the decreasing-side correction base amount by the constant Fb is the correction amount per unit time, the decreasing-side integrated amount obtained by integrating the decreasing-side instantaneous correction amount is the amount at the current time after the completion of the filter reproduction process.

[0087] In step U40, the control device 50 sets the value obtained by subtracting the decreasing-side integrated amount obtained in step U30 from the decreasing-side initial amount obtained in step U15 as the decreasing-side correction amount, and proceeds with the process to step U50.

[0088] In step U50, the control device 50 determines whether the decreasing-side correction amount is equal to or greater than the lower guard amount. When the decreasing-side correction amount is equal to or greater than the lower guard amount (Yes), the control device 50 ends the process shown in FIG. 13 and returns the process to below step S30 shown in FIG. 9. When the decreasing-side correction amount is less than the lower guard amount (No), the control device proceeds with the process to step U60. The value of the lower guard amount is set to an appropriate value obtained through experiments, simulations, etc. using an actual vehicle.

[0089] When proceeding with the process to step U60, the control device 50 sets the lower guard amount as the decreasing-side correction amount, ends the process shown in FIG. 13, and returns the process to below step S30 shown in FIG. 9.

[0090] By the process shown in FIG. 13 above, in the example of FIG. 15, when the differential pressure before and after the filter deviates to the higher side with respect to characteristic A and becomes characteristic B, characteristic B is corrected to characteristic Bh by the decrease-side correction amount Hb. In the case of characteristic B, when the differential pressure = differential pressure threshold value ΔP, the deposition amount of particulate matter in the filter 43 = deposition amount Mb, but in the case of characteristic Bh, when the differential pressure = differential pressure threshold value ΔP, the deposition amount of particulate matter in the filter 43 = deposition amount Mbh, and it becomes a deposition amount closer to the correct deposition amount Ma.

[0091] In the processing procedure of the control device 50 described in this embodiment, as shown in FIGS. 12 and 15, for characteristic C where the differential pressure before and after the filter deviates to the lower side with respect to characteristic A (reference characteristic), and for characteristic B where it deviates to the higher side, the corrected differential pressure before and after is obtained so as to approach characteristic A. That is, the corrected differential pressure before and after is obtained using both the increase-side correction amount in step S20 and the decrease-side correction amount in step S30. Then, by estimating the deposition amount of particulate matter deposited in the filter 43 using the corrected differential pressure before and after, the deposition amount can be estimated with higher accuracy. For this reason, it is possible to avoid performing the filter regeneration process more frequently than necessary, which can contribute to improving fuel efficiency. Also, it is possible to avoid the filter regeneration process not being performed until the deposition amount becomes more than necessary, and clogging of the filter can be avoided.

[0092] <Processing Procedure of Control Device 50 in the Second Embodiment (FIG. 16)> <Overall Processing (FIG. 16)> Next, the processing of the control device 50 (CPU 51) in the second embodiment will be described using the flowchart shown in FIG. 16. In the second embodiment, the calculation of the decrease-side correction amount for correcting the deviation of the differential pressure before and after the filter to the higher side is omitted, and the corrected differential pressure before and after is obtained using only the increase-side correction amount for correcting the deviation of the differential pressure before and after the filter to the lower side.

[0093] In the second embodiment, as shown in the flowchart of FIG. 16, step S30 (calculation of the reduction-side correction amount) is omitted compared to the first embodiment (FIG. 9). Further, step S40 is changed to step S42 in which the reduction-side correction amount is omitted, and step S85 is changed to step S87 in which the process of setting the DPF regeneration completion flag to ON and the process of initializing the reduction-side correction amount are omitted. The other steps are the same as those in the first embodiment.

[0094] That is, among the increase-side correction amount in step S20 and the reduction-side correction amount in step S30 in the first embodiment shown in FIG. 9, only the increase-side correction amount in step S20 is obtained, and the differential pressure before and after correction is obtained. As shown in FIG. 8, for characteristic A of the differential pressure before and after the filter, characteristic C shifted to the lower side has an increasing deviation amount, so an increase-side correction amount is required. However, for characteristic B shifted to the higher side, the deviation amount gradually decreases, so the reduction-side correction amount is omitted.

[0095] In the second embodiment, it is possible to avoid performing the filter regeneration process until the deposition amount exceeds the necessary level, and to avoid clogging of the filter.

[0096] <Others> The exhaust gas purification system 2 of the internal combustion engine of the present invention is not limited to the configurations, structures, processing procedures, etc. described in this embodiment, and various changes, additions, and deletions are possible without changing the gist of the present invention.

[0097] The exhaust gas purification system 2 of the internal combustion engine of the present invention is not limited to a vehicle equipped with a diesel engine, and the present invention can be applied to various devices equipped with a diesel engine.

[0098] Also, when expressions such as greater than or equal to (≧), less than or equal to (≦), greater than, exceeding (>), less than (<), etc. are described, the equality sign may or may not be included. Further, when numerical values are given in the description of this embodiment, the numerical values are examples and are not limited to these numerical values.

Description of Reference Numerals

[0099] 1 Internal combustion engine system 2 Exhaust gas purification system 10 Internal combustion engine 11A, 11C Intake pipes 11D Intake manifold 12A Exhaust manifold 12B, 12C, 12D, 12E Exhaust pipes 13 EGR pipe 13A EGR valve 21 Injector 31 Air flow detection device 32A, 32B Intake air temperature detection devices 32C Coolant temperature detection device 33A Atmospheric pressure detection device 33B, 33C, 33D Pressure detection devices 34A Rotation detection device 34B Cylinder detection device 35 Differential pressure detection device 36A - 36D Exhaust gas temperature detection devices 37A, 37B NOx detection devices 38 Accelerator pedal depression amount detection device 39 Ignition switch 40 Exhaust gas purification device 41 Upstream exhaust gas purification device 42 First oxidation catalyst 43 Filter 43a Inflow passage 43b Outflow passage 43c, 43d Cover parts 43e Filter wall 43f Micro - pores 45 Downstream exhaust gas purification device 46 Urea SCR 47 Second oxidation catalyst 50 Control device 51 CPU 55 Non - volatile memory device 61A Fuel addition valve 61B Dispersion device 62A Urea - water addition valve 62B Dispersion device 63 Load device (alternator) 80 Supercharger 81 Turbine 82 Compressor 84 Intercooler 90 Fuel tank Hb decrease side correction amount Initial amount on the Hbi decrease side Hc increase side correction amount Ma deposition amount (predetermined amount) ΔP differential pressure threshold value (predetermined threshold value)

Claims

1. An exhaust gas purification system for an internal combustion engine, a filter disposed in an exhaust passage of the internal combustion engine to collect particulate matter contained in exhaust gas from the internal combustion engine, a differential pressure detection device that detects a differential pressure across the filter, which is a pressure difference between an inflow side and an outflow side of exhaust gas in the filter, a control device that detects an operating state of the internal combustion engine and controls the internal combustion engine based on the detected operating state, comprising: the control device: when it is determined that the particulate matter exceeding a predetermined amount has accumulated in the filter and a predetermined condition is satisfied, executes a filter regeneration process for burning and removing the particulate matter accumulated in the filter, obtains an increase-side correction amount for correcting the differential pressure across the filter detected using the differential pressure detection device to the increase side based on the operating state, obtains a corrected differential pressure across the filter by correcting the differential pressure across the filter using the increase-side correction amount, when the corrected differential pressure across the filter exceeds a predetermined threshold value set according to the predetermined amount, determines that the particulate matter exceeding the predetermined amount has accumulated in the filter, an exhaust gas purification system for an internal combustion engine.

2. An exhaust gas purification system for an internal combustion engine, a filter disposed in an exhaust passage of the internal combustion engine to collect particulate matter contained in exhaust gas from the internal combustion engine, a differential pressure detection device that detects a differential pressure across the filter, which is a pressure difference between an inflow side and an outflow side of exhaust gas in the filter, a control device that detects an operating state of the internal combustion engine and controls the internal combustion engine based on the detected operating state, comprising: the control device: when it is determined that the particulate matter exceeding a predetermined amount has accumulated in the filter and a predetermined condition is satisfied, executes a filter regeneration process for burning and removing the particulate matter accumulated in the filter, obtains both an increase-side correction amount for correcting the differential pressure across the filter detected using the differential pressure detection device to the increase side and a decrease-side correction amount for correcting the differential pressure across the filter to the decrease side based on the operating state, obtains a corrected differential pressure across the filter by correcting the differential pressure across the filter using both the increase-side correction amount and the decrease-side correction amount, when the corrected differential pressure across the filter exceeds a predetermined threshold value set according to the predetermined amount, determines that the particulate matter exceeding the predetermined amount has accumulated in the filter, an exhaust gas purification system for an internal combustion engine.

3. An exhaust gas purification system for an internal combustion engine according to claim 1 or 2, wherein the control device when obtaining the increase-side correction amount, a filter temperature which is the temperature of the filter estimated based on at least one of the exhaust gas temperature on the inlet side of the filter and the exhaust gas temperature on the outlet side of the filter, or the exhaust gas temperature on the inlet side of the filter, and an increase-side correction base amount set according to the temperature; a particulate matter deposition amount which is the deposition amount of the particulate matter in the filter estimated based on the operating state; are used to obtain an exhaust gas purification system for an internal combustion engine.

4. An exhaust gas purification system for an internal combustion engine according to claim 2, wherein the control device when obtaining the decrease-side correction amount, after completion of the filter regeneration process, obtains a decrease-side initial amount which is an initial amount of the decrease-side correction amount, a filter temperature which is the temperature of the filter estimated based on at least one of the exhaust gas temperature on the inlet side of the filter and the exhaust gas temperature on the outlet side of the filter, or the exhaust gas temperature on the inlet side of the filter, and a decrease-side correction base amount set according to the temperature; the decrease-side initial amount; are used to obtain an exhaust gas purification system for an internal combustion engine.

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