Exhaust emission control system for internal combustion engine

Abstract

To provide an exhaust emission control system for an internal combustion engine, which, in filter regeneration control for burning off the particulate matter accumulated on a filter by heating exhaust gas so that a filter bed temperature approaches a target bed temperature, can set the target bed temperature to a higher temperature, and when thermal runaway is predicted to occur, can temporarily lower the target bed temperature to prevent occurrence of thermal runaway and can shorten the period of the filter regeneration control by more appropriately predicting the occurrence of thermal runaway.SOLUTION: An exhaust emission control system has a filter that collects particulate matter in exhaust gas, an exhaust heating device, and a control device. The control device acquires a temperature gradient within the filter on the basis of a temperature distribution within the filter, which is based on the operation state of an internal combustion engine, sets a target bed temperature, controls the exhaust heating device so that a filter bed temperature approaches the target bed temperature, and lowers the target bed temperature when the temperature gradient exceeds a temperature gradient threshold and the intake volume of the internal combustion engine is less than an intake volume threshold for a predetermined period of time or longer.SELECTED DRAWING: Figure 12

Description

[Technical Field]

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

[0002] Vehicles equipped with diesel engines as their internal combustion engines have traditionally used a diesel particulate filter (DPF) installed in the exhaust passage to capture fine particulate matter (PM) in the exhaust gas to prevent it from being released into the atmosphere. Since the particulate matter accumulated in the filter must be periodically removed, the filter will become clogged, and so filter regeneration control is periodically performed to burn and remove the particulate matter accumulated in the filter.

[0003] In filter regeneration control, the exhaust gas temperature, which is about 300-400°C under normal driving conditions, is forcibly raised to about 600°C or higher to burn and remove particulate matter accumulated in the filter. When forcibly raising the exhaust gas temperature, fuel is added to the exhaust gas and the fuel is reacted in an oxidation catalyst located upstream of the filter to raise the exhaust gas temperature, which involves fuel consumption. Therefore, fuel efficiency deteriorates while filter regeneration control is being executed, so it is desirable to shorten the filter regeneration time and the period during which fuel efficiency deteriorates.

[0004] When filter regeneration control is performed, a target bed temperature for the filter is set according to the amount of particulate matter deposited in the filter, and the amount of fuel added to the exhaust gas is adjusted so that the filter bed temperature approaches the target bed temperature. To shorten the filter regeneration time, the target bed temperature can be set higher; however, if the target bed temperature is too high, the accumulated particulate matter may be burned too quickly, resulting in a sudden temperature rise (so-called thermal runaway), which may cause cracks in the filter and damage it. To reliably prevent these cracks from occurring, conventional systems have had no choice but to set the target bed temperature low to allow for a safety margin, resulting in longer filter regeneration times.

[0005] For example, Patent Document 1 discloses an exhaust gas purification device for an internal combustion engine that estimates the temperature distribution within a filter from the exhaust gas flow rate, the differential pressure across the filter, the center temperatures across the filter, the A / F (air-fuel ratio) within the filter, the distribution of particulate matter within the filter, the heat generation rate of the exhaust gas, the heat generation rate of the heating fuel, and the heat radiation rate of the filter, calculates the temperature gradient within the filter based on the estimated temperature distribution, and lowers the target bed temperature if the temperature gradient exceeds a set value (critical value α). According to Patent Document 1, the target bed temperature can be set higher than conventionally, and the occurrence of thermal runaway can be predicted and prevented before it occurs. As a result, a period during which the target bed temperature is higher than conventionally can be secured, thereby shortening the period of filter regeneration control. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-203280 Summary of the Invention [Problem to be solved by the invention]

[0007] In the exhaust gas purification device for an internal combustion engine of Patent Document 1, when the temperature gradient in the filter exceeds a set value (risk value α), it predicts that thermal runaway will occur and unconditionally lowers the target bed temperature, which results in lowering the target bed temperature more than necessary, and the period of filter regeneration control becomes longer by the amount of the lowering of the target bed temperature more than necessary.

[0008] Even when the temperature gradient in the filter exceeds a set value (risk value α), there are operating states of the internal combustion engine in which thermal runaway occurs and operating states in which thermal runaway does not occur. If the target bed temperature is lowered only when the temperature gradient in the filter exceeds the set value and the internal combustion engine is operating states in which thermal runaway occurs, the period of filter regeneration control can be further shortened while preventing the occurrence of thermal runaway.

[0009] The present invention was devised in consideration of these points, and aims to provide an exhaust purification system for an internal combustion engine that, in filter regeneration control, heats the exhaust gas to bring the filter bed temperature closer to a target bed temperature and burns off particulate matter accumulated on the filter, can set the target bed temperature to a higher temperature, and if thermal runaway is predicted to occur, can temporarily lower the target bed temperature to prevent thermal runaway from occurring, and can shorten the period of filter regeneration control by more appropriately predicting the occurrence of thermal runaway. [Means for solving the problem]

[0010] In order to solve the above problems, a first invention is an exhaust purification system for an internal combustion engine, comprising: a filter provided in an exhaust path of the internal combustion engine to capture particulate matter in the exhaust; an exhaust heating device provided upstream of the filter to heat the exhaust; and a control device capable of detecting the operating state of the internal combustion engine and controlling the exhaust heating device. The control device, in filter regeneration control that controls the exhaust heating device to heat the exhaust and burn off and remove particulate matter trapped on the filter to regenerate the filter, acquires a temperature distribution within the filter based on the operating state including the filter upstream exhaust temperature, which is the exhaust temperature upstream of the filter, and the filter downstream exhaust temperature, which is the exhaust temperature downstream of the filter, acquires a temperature gradient within the filter based on the temperature distribution, sets a target bed temperature, which is the target temperature of the filter, according to the PM accumulation amount, which is the amount of particulate matter accumulated on the filter, controls the exhaust heating device so that the filter bed temperature, which is the temperature of the filter, approaches the target bed temperature, and lowers the target bed temperature when the temperature gradient exceeds a temperature gradient threshold and the state in which the intake amount of the internal combustion engine is less than the intake amount threshold continues for a predetermined time or more. This is an exhaust purification system for an internal combustion engine.

[0011] Next, a second invention is an exhaust purification system for an internal combustion engine according to the first invention, wherein the temperature gradient threshold is set according to the amount of PM accumulation, and is set to become smaller as the amount of PM accumulation increases.

[0012] Next, a third invention is an exhaust purification system for an internal combustion engine according to the first or second invention, wherein the predetermined time is set according to the temperature gradient and the amount of PM accumulation, and is set to be shorter as the temperature gradient increases and shorter as the amount of PM accumulation increases.

[0013] Next, a fourth invention is an exhaust purification system for an internal combustion engine according to the first or second invention, wherein the internal combustion engine is mounted on a vehicle, and the control device determines the temperatures at multiple positions in the direction of exhaust flow within the filter as the filter bed temperature based on the operating state including the exhaust temperature upstream of the filter, the exhaust temperature downstream of the filter, the outside air temperature, the speed of the vehicle, the flow rate of the exhaust passing through the filter, and the heat capacity of the filter, and obtains the temperature gradient as the temperature difference between the temperature at the position most upstream of the exhaust and the temperature at the position most downstream of the exhaust among the multiple positions. [Effects of the Invention]

[0014] According to the first aspect of the present invention, the target bed temperature is not lowered unconditionally when the temperature gradient in the filter exceeds the temperature gradient threshold. Instead, even if the temperature gradient exceeds the temperature gradient threshold, the target bed temperature is maintained without being lowered until the intake air volume remains below the intake air volume threshold for a predetermined period of time. When the intake air volume is small, heated exhaust gas passes through the filter, concentrating near the center of the filter and causing a localized temperature rise near the center, making thermal runaway more likely. Therefore, the target bed temperature is lowered. However, when the intake air volume is large, heated exhaust gas passes through the entire filter without concentrating near the center, preventing a localized temperature rise near the center of the filter. This makes thermal runaway less likely to occur. Therefore, the target bed temperature is maintained without being lowered. This allows the target bed temperature to be set higher, and when thermal runaway is predicted, the target bed temperature can be temporarily lowered to prevent thermal runaway from occurring. By more accurately predicting the occurrence of thermal runaway, the filter regeneration control period can be shortened.

[0015] According to the second aspect of the present invention, by setting the temperature gradient threshold to an appropriate value depending on the amount of PM accumulation, it is possible to more appropriately predict the occurrence of thermal runaway of the filter, thereby shortening the period of filter regeneration control.

[0016] According to the third aspect of the present invention, by setting the predetermined time to an appropriate value depending on the temperature gradient and the amount of PM accumulation, it is possible to more appropriately predict the occurrence of thermal runaway of the filter, thereby shortening the period of filter regeneration control.

[0017] According to the fourth aspect of the present invention, an appropriate temperature gradient can be obtained. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a diagram illustrating an example of the overall configuration of an internal combustion engine system. [Figure 2] FIG. 2 is a diagram illustrating an example in which a filter (DPF) is composed of a plurality of segments. [Figure 3]3 is an enlarged view of the AA portion shown in FIG. 2, illustrating an example of the structure of cells that make up a segment. FIG. [Figure 4] 10A and 10B are diagrams illustrating an example of a plurality of positions when determining the temperature distribution in a filter. [Figure 5] FIG. 10 shows an example (1) of the temperature distribution in the filter, and is a diagram illustrating an example in which the temperature gradient exceeds the temperature gradient threshold value after filter regeneration control is started. [Figure 6] 10A and 10B are diagrams illustrating an example in which the temperature gradient does not exceed the temperature gradient threshold value after the start of filter regeneration control. [Figure 7] 10A and 10B are diagrams illustrating an example in which the temperature gradient does not exceed the temperature gradient threshold value after the start of filter regeneration control. [Figure 8] FIG. 7 is an image diagram of the temperature distribution on the inlet and outlet surfaces of the filter at time Tb (immediately after the start of the PM oxidation reaction) in FIGS. 5 and 6. [Figure 9] FIG. 6 is an image diagram of the temperature distribution on the inlet and outlet surfaces of the filter at time Tc in FIG. 5 (when the PM oxidation reaction (combustion) has progressed sufficiently). [Figure 10] FIG. 7 is an image diagram of the temperature distribution on the inlet and outlet surfaces of the filter at time Tc in FIG. 6 (when the PM oxidation reaction (combustion) has progressed sufficiently). [Figure 11] 10 is a flowchart illustrating an example of a processing procedure of an "overall process" in filter regeneration control by the control device. [Figure 12] 12 is a flowchart illustrating an example of a processing procedure for "calculating target bed temperature" in the flowchart shown in FIG. [Figure 13] FIG. 10 is a diagram illustrating an example of the target bed temperature characteristic. [Figure 14] FIG. 10 is a diagram illustrating an example of the temperature gradient threshold characteristic. [Figure 15] FIG. 10 is a diagram illustrating an example of the intake air amount counter threshold characteristic. [Figure 16] 10 is an example (1) of an operating waveform when the target bed temperature is lowered. [Figure 17]10 is an example (2) of an operational waveform illustrating that the period of filter regeneration control is shorter than in the past. DETAILED DESCRIPTION OF THE INVENTION

[0019] <Overall configuration of internal combustion engine system 1 (Fig. 1)> An internal combustion engine system 1 including an exhaust gas purification system 2 of the present invention will be described below with reference to the drawings. First, an example of the overall configuration of the internal combustion engine system 1 will be described using 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 gas purification system 2 also has a control device 50, a filter 43 (particulate matter collection filter), and a fuel addition valve 61A (corresponding to an exhaust gas heating device). Below, the configuration of the internal combustion engine system 1 will be described in order from the intake side to the exhaust side.

[0020] An air flow rate detecting device 31 is provided in the intake pipe 11A. The air flow rate detecting device 31 (for example, an intake air flow rate sensor) outputs a detection signal corresponding to the flow rate [g / sec] of air taken in by the internal combustion engine 10 to the control device 50. The air flow rate detecting device 31 is also provided with an intake air temperature detecting device 32A and an atmospheric pressure detecting device 33A. The intake air temperature detecting device 32A (for example, an intake air temperature sensor) outputs a detection signal corresponding to the temperature of the intake air (in this case, the temperature of outside air) to the control device 50. The atmospheric pressure detecting 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 a compressor 82 of a turbocharger 80.

[0021] An intake pipe 11A is connected to the inflow side of the compressor 82, and an intake pipe 11C is connected to the discharge side of the compressor 82. The compressor 82 is rotationally driven by a turbine 81, and compresses and sends the intake air that flows in from the intake pipe 11A to the intake pipe 11C. A pressure detection device 33B is provided in the intake pipe 11A, which is upstream of the compressor 82. The pressure detection device 33B (e.g., 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.

[0022] The downstream side of the intake pipe 11C is connected to an 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 (e.g., a pressure sensor) outputs a detection signal corresponding to the pressure of the intake air compressed by the compressor 82 to the control device 50. The intercooler 84 reduces the temperature of the intake air compressed by the compressor 82 to increase the oxygen density. The throttle device 64 adjusts the opening of the throttle valve to a target throttle opening based on a control signal from the control device 50. The intake air temperature detection device 32B (e.g., 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.

[0023] The downstream side of the intake manifold 11D is connected to an intake port that guides intake air to each cylinder of the internal combustion engine 10. The intake air guided to the intake manifold 11D is drawn into each cylinder of the internal combustion engine 10 and used for combustion together with fuel injected from the injector 21. The intake manifold 11D is also provided with a pressure detection device 33D. The pressure detection device 33D (e.g., 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.

[0024] The internal combustion engine 10 is provided with a rotation detection device 34A and a cylinder detection device 34B. The rotation detection device 34A (e.g., 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. The cylinder detection device 34B (e.g., a camshaft rotation sensor) outputs a detection signal (cylinder discrimination signal) to the control device 50, for example, when 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 that can adjust 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 (e.g., 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.

[0025] An accelerator depression amount detection device 38 (for example, an accelerator 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. An ignition switch 39 is an input device for the driver to input commands to start or stop the internal combustion engine.

[0026] The control device 50 calculates the required load based on the rotation 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 depression amount detection device 38, and calculates the amount of fuel corresponding to the required load.The control device 50 then 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 amount of fuel corresponding to the required load into each of the #1 to #4 cylinders of the internal combustion engine 10.

[0027] An exhaust manifold 12A is connected to an exhaust port of the internal combustion engine 10. Exhaust gas from the internal combustion engine 10 is guided through the exhaust manifold 12A, an exhaust pipe 12B, and a turbine 81 of a turbocharger 80, where it drives the turbine 81 to rotate and is then discharged into an exhaust pipe 12C. The exhaust gas from the internal combustion engine 10 contains carbon monoxide (CO), hydrocarbons (HC), particulate matter (PM), nitrogen oxides (NOx), and the like.

[0028] An inlet side of an EGR pipe 13 for returning a portion of the exhaust gas to the intake air is connected to the exhaust manifold 12A or the exhaust pipe 12B. The outlet side of the EGR pipe 13 is connected to the intake pipe 11C or the intake manifold 11D. The EGR pipe 13 is provided with an EGR valve 13A that is controlled by the control device 50 to adjust the opening degree of the EGR pipe.

[0029] An exhaust pipe 12B is connected to the outflow side of the exhaust manifold 12A. The inflow side of a turbine 81 of a turbocharger 80 is connected to the downstream side of the exhaust pipe 12B. An exhaust pipe 12C is connected to the outflow side of the turbine 81, and the exhaust purification device 40 is connected to the downstream side of the exhaust pipe 12C.

[0030] The exhaust purification device 40 is composed of an upstream exhaust purification device 41 and a downstream exhaust purification device 45 located downstream 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).

[0031] The first oxidation catalyst 42 purifies carbon monoxide (CO), hydrocarbons (HC), and other substances 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 downstream. The filter 43 also has the function of purifying carbon monoxide and hydrocarbons through an oxidation reaction.

[0032] The exhaust pipe 12C upstream of the first oxidation catalyst 42 is provided with a fuel addition valve 61A (corresponding to an exhaust heating device), an exhaust temperature detection device 36A (e.g., an exhaust temperature sensor), and the like. The fuel addition valve 61A is capable of adding (injecting) fuel and raising the temperature of the exhaust gas, and when filter regeneration control is performed to regenerate the filter 43 on which trapped particulate matter has accumulated (when burning and removing the particulate matter), the fuel addition valve 61A injects fuel (reaction liquid) into the exhaust pipe 12C to cause an oxidation reaction in the first oxidation catalyst 42 and raise the temperature of the exhaust gas. A dispersion device 61B is also disposed in the exhaust pipe 12C, which causes the fuel injected from the fuel addition valve 61A to collide and disperse the fuel. The fuel addition valve 61A is supplied with fuel from a fuel tank 90.

[0033] An exhaust gas temperature detecting device 36B (e.g., an exhaust gas temperature sensor) is provided downstream of the first oxidation catalyst 42 and upstream of the filter 43. An exhaust gas temperature detecting device 36C (e.g., an exhaust gas temperature sensor) is provided downstream of the filter 43. The exhaust gas temperature detecting devices 36A, 36B, and 36C output detection signals according to the exhaust gas temperatures to the control device 50.

[0034] A differential pressure detection device 35 (e.g., a differential pressure sensor) is provided downstream of the first oxidation catalyst 42 and upstream of the filter 43 to detect the differential pressure (pressure difference) between the exhaust pressure on the downstream side of the filter 43. The differential pressure detection device 35 outputs a detection signal to the control device 50 in accordance with the differential pressure across the filter, which is the pressure difference between the pressure on the upstream side and the pressure on the downstream side of the filter 43.

[0035] The downstream exhaust purification device 45 is provided with, from upstream to downstream, a urea water addition valve 62A, a dispersion device 62B, a urea SCR 46, a second oxidation catalyst 47, and the like. The urea SCR 46 is connected to the downstream side of the filter 43 via the exhaust pipe 12D. The urea water addition valve 62A is capable of adding (injecting) urea water and is disposed in the exhaust pipe 12D downstream of the filter 43 and upstream of the urea SCR 46. The urea water addition valve 62A injects urea water (reaction liquid) into the exhaust at a predetermined timing. The injected urea water collides with and scatters against the dispersion device 62B, where it is atomized, and then diffuses within the exhaust pipe 12D to reach the urea SCR 46. The urea water addition valve 62A is supplied with urea water from a urea water tank (not shown). The urea SCR 46 reduces and purifies nitrogen oxides (NOx) contained in the exhaust using ammonia gas generated from the added urea water.

[0036] Furthermore, a NOx detection device 37A (e.g., a NOx sensor) is provided in the exhaust pipe 12D upstream of the urea SCR 46. Furthermore, a NOx detection device 37B (e.g., a NOx sensor) and an exhaust gas temperature detection device 36D (e.g., an exhaust gas temperature sensor) are provided in the exhaust pipe 12E downstream of the urea SCR 46. 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 from the NOx detection devices 37A and 37B and the exhaust gas temperature detection device 36D, and controls the urea water addition valve 62A based on the calculated NOx purification rate. The exhaust pipes 12B, 12C, 12D, and 12E correspond to exhaust passages.

[0037] The second oxidation catalyst 47 is connected downstream of the urea SCR 46 via the exhaust pipe 12E. The second oxidation catalyst 47 oxidizes and purifies ammonia gas remaining in the exhaust gas. The second oxidation catalyst 47 also has the function of purifying carbon monoxide and hydrocarbons through an oxidation reaction.

[0038] The control device 50 is a known device that includes a CPU 51, a RAM 52, a ROM 53 (storage device), a timer 54, a nonvolatile storage device 55 (for example, an EEPROM), etc. The CPU 51 executes various calculation processes based on various programs and maps stored in the ROM 53 (for example, a Flash-ROM). The RAM 52 temporarily stores the calculation results of the CPU and data input from each detection device, and the nonvolatile storage device 55 stores data that should be saved when the internal combustion engine 10 is stopped, for example.

[0039] Based on the input detection signals, the control device 50 can detect various operating states of the internal combustion engine 10. Furthermore, in response to the detected operating state of the internal combustion engine 10 and a request from the driver based on a detection signal from the accelerator depression amount detection device 38, the control device 50 outputs control signals for controlling various actuators such as the injector 21 that injects fuel into the cylinder, the fuel addition valve 61A, the urea water addition valve 62A, and the EGR valve 13A.

[0040] The control device 50 detects the filter differential pressure, which is the pressure difference between the upstream and downstream sides of the filter 43, based on a detection signal from the differential pressure detection device 35, and can estimate the amount of particulate matter deposited in the filter 43 based on the detected filter differential pressure. When the estimated amount of deposition exceeds a threshold, the control device 50 executes filter regeneration control to inject fuel (reaction liquid) from the fuel addition valve 61A to increase the exhaust temperature, and raises the filter bed temperature, which is the temperature of the filter 43, to approach the target bed temperature, which is the target temperature of the filter, thereby burning and removing the particulate matter deposited in the filter 43 and regenerating the filter 43. The above filter regeneration control consumes fuel, so it is preferable that the period of the filter regeneration control be as short as possible.

[0041] <Structure of filter 43 (Fig. 2, Fig. 3)> First, the structure of the filter 43 will be described with reference to Figures 2 and 3. Figure 2 shows a schematic overall structure of the filter 43, with a portion shown in cross section. Figure 3 is an enlarged view of the AA portion shown in Figure 2.

[0042] As shown in Figures 2 and 3, the filter 43 is arranged so that cells 43a, each having an open exhaust inlet side and a closed exhaust outlet side with a lid portion 43c, and cells 43b, each having an open exhaust inlet side and a closed exhaust outlet side with a lid portion 43d, are arranged alternately next to each other.

[0043] As shown in Fig. 3, exhaust gas that flows into cell 43a passes through filter wall 43e between cell 43a and cell 43b and flows out of cell 43b. Filter wall 43e has a plurality of micropores that particulate matter cannot pass through. Therefore, the exhaust gas can pass through filter wall 43e, but the particulate matter contained in the exhaust gas cannot pass through filter wall 43e and is trapped.

[0044] As shown in FIG. 2, a plurality of cells 43a and a plurality of cells 43b form a segment 43s, and a filter 43 is formed by the plurality of segments 43s.

[0045] <Example of temperature distribution inside the filter during filter regeneration control according to the operating state of the internal combustion engine (Figs. 4 to 10)> In order to obtain the temperature distribution within the filter 43 during filter regeneration control, as shown in FIG. 4, the filter 43 has conventionally been virtually divided into multiple sections on a plane perpendicular to the exhaust gas flow direction, and the temperature at the center of each divided virtual divided filter (positions CF1 to CF4) has been estimated (temperatures at multiple positions have been estimated). Note that an existing method is used for calculating the estimated temperatures at positions CF1 to CF4, and detailed explanations will be omitted. In the example shown in FIG. 4, the filter 43 is virtually divided into virtual divided filters F1 to F4. In the following explanation, the estimated temperature of virtual divided filter F1 in FIG. 4 is the estimated temperature at position CF1, the estimated temperature of virtual divided filter F2 is the estimated temperature at position CF2, the estimated temperature of virtual divided filter F3 is the estimated temperature at position CF3, and the estimated temperature of virtual divided filter F4 is the estimated temperature at position CF4.

[0046] 5 to 7 below show different operating conditions (exhaust flow rate) of the internal combustion engine during execution of filter regeneration control, and [Temperature distribution example (1)] in Fig. 5 shows an example in which thermal runaway occurred in the filter 43. Also, [Temperature distribution example (2)] in Fig. 6 and [Temperature distribution example (3)] in Fig. 7 show examples in which thermal runaway did not occur in the filter 43.

[0047] <Example of temperature distribution (1) (Fig. 5)> 5 shows an example of estimated temperatures at the exhaust-most upstream position CF1 and the exhaust-most downstream position CF4 (see FIG. 4) of the filter 43 when filter regeneration control is started (exhaust gas temperature increase is started) at time Ta and the oxidation reaction (combustion) of PM (particulate matter) accumulated in the filter 43 is started at time Tb. Also, FIG. 5 shows an example in which the vehicle is operating at a medium exhaust flow rate at a constant speed of, for example, about 40 to 50 km / h from time Ta to time Tb, and then transitions to a low exhaust flow rate, such as an idle state, from time Tb to time Tc. Also shown is an example in which the target bed temperature in the filter regeneration control is set to a temperature that is a predetermined temperature higher than the conventional target bed temperature.

[0048] 5, the temperatures of positions CF1 and CF4 of filter 43 gradually increase from time Ta to time Tb, with the temperature at position CF1 on the exhaust inflow side being higher than the temperature at position CF4 on the exhaust outflow side, and the temperature difference (temperature gradient) gradually increasing. Note that the temperature image at time Tb in FIG. 5 is as shown in FIG. 8, and the temperature difference between the central portion M1a and the outer peripheral portion M1b on the bottom surface M1 of segment 43s in FIG. 8 is not very large.

[0049] In Figure 5, between time Tb and time Tc, the exhaust flow rate drops to a low level, causing the temperature at position CF4 on filter 43 to rise sharply. The temperature image at time Tc in Figure 5 is shown in Figure 9. Because the exhaust flow rate drops to a low level, the exhaust gas flows primarily near the center of filter 43, rapidly burning PM accumulated near the center of filter 43, resulting in a significant temperature difference (temperature gradient) between the center and outer periphery of filter outlet surface Mb. In the state shown in Figure 9, the temperature difference between center portion M1a and outer periphery M1b on bottom surface M1 of segment 43s (temperature difference ΔT1 shown in Figure 5) becomes very large, which may result in cracks occurring in segment 43s.

[0050] <Example of temperature distribution (2) (Fig. 6)> Figure 6 is the same as Figure 5 up to time Tb (operating state with medium exhaust flow rate), but differs in that after time Tb, the exhaust flow rate transitions to a high flow rate operating state due to factors such as depressing the accelerator.

[0051] In Fig. 6, from time Ta to time Tb, the temperatures at positions CF1 and CF4 are both the same as the temperatures in Fig. 5. Therefore, the temperature image at time Tb in Fig. 6 is the same as Fig. 8, and the temperature difference between the central portion M1a and the outer peripheral portion M1b on the bottom surface M1 of the segment 43s in Fig. 8 is not very large.

[0052] In Figure 6, from time Tb to time Tc, the exhaust flow rate increases, causing the temperature at position CF4 of filter 43 to rise gradually. Note that the temperature image at time Tc in Figure 6 is as shown in Figure 10, where the high exhaust flow rate causes the exhaust to flow almost uniformly throughout the entire filter 43, and the combustion of PM accumulated inside filter 43 also progresses almost uniformly, resulting in a small temperature difference between positions CF1 and CF4. For this reason, in the state shown in Figure 10, the temperature difference between center portion M1a and outer peripheral portion M1b on bottom surface M1 of segment 43s (temperature difference ΔT2 shown in Figure 6) is much smaller than temperature difference ΔT1 shown in Figure 5, and no cracks will occur in segment 43s.

[0053] <Example of temperature distribution (3) (Fig. 7)> FIG. 7 differs from FIG. 5 in that the operating state is one in which the exhaust flow rate is high until time Tb, but is the same in that after time Tb the operating state shifts to one in which the exhaust flow rate is low, such as an idle state.

[0054] In FIG. 7, from time Ta to time Tb, the exhaust gas flow rate is high, so the exhaust gas flows almost uniformly over the entire filter 43, and therefore the temperature difference between positions CF1 and CF4 is very small.

[0055] In Fig. 7, from time Tb to time Tc, the temperature at position CF4 at time Tb is sufficiently higher than the temperature at position CF4 at time Tb in Fig. 5, and the combustion of PM does not proceed rapidly but rather proceeds relatively slowly. Therefore, the temperature difference between the central portion M1a and the outer peripheral portion M1b of the bottom surface M1 of segment 43s (temperature difference ΔT3 shown in Fig. 7) is smaller than the temperature difference ΔT1 shown in Fig. 5, and cracks do not occur in segment 43s.

[0056] From the above, the state shown in Fig. 5 is a case where cracks occur in the filter, and the states shown in Fig. 6 and Fig. 7 are states where cracks do not occur. Therefore, in the state shown in Fig. 5, it is sufficient to predict that a temperature difference ΔT1 will occur between time Ta and time Td (before a sudden temperature rise occurs at position CF4 in Fig. 5) and lower the target bed temperature. The processing procedure of the control device 50 for this purpose will be described below.

[0057] <Processing Procedures of the Control Device 50 (FIGS. 11 and 12) and Examples of Each Characteristic (FIGS. 13 to 15)> <Overall processing (Fig. 11)> Next, the processing of the control device 50 (CPU 51) will be described using the flowcharts shown in Figures 11 to 15. The control device 50 (CPU 51) starts the processing shown in Figure 11 at a predetermined time interval of, for example, several [ms] to several hundred [ms], and proceeds to step S10. In the following description, "PM" refers to "particulate matter." In this embodiment, the "calculation of target bed temperature" in Figure 12, which corresponds to the details of "calculating target bed temperature" in step S40 of the flowchart in Figure 11, is different from the conventional method, and the steps other than step S40 in Figure 11 are almost the same as the conventional method.

[0058] In step S10, the control device 50 acquires various operating states of the internal combustion engine (internal combustion engine system 1), and proceeds to step S15. The operating states to be acquired include, for example, physical quantities (such as rotation speed) based on detection signals from the various detection devices described above, such as the internal combustion engine rotation speed, intake air amount, fuel injection amount, accelerator pedal depression amount, filter upstream side exhaust temperature, filter downstream side exhaust temperature, and outside air temperature, physical quantities (such as fuel injection amount) based on control amounts of actuators controlled by the control device 50 itself, and physical quantities (such as exhaust flow velocity) calculated using these physical quantities.

[0059] In step S15, the control device 50 estimates the amount of particulate matter (PM accumulation amount) accumulated in the filter 43, and then proceeds to step S20. The PM accumulation amount is estimated using an existing estimation method, such as an integration method in which the amount of PM generated per predetermined time is calculated and integrated using a PM generation amount map corresponding to the operating state (rotation speed and fuel injection amount), or a differential pressure method in which the PM accumulation amount is estimated based on the differential pressure before and after the filter 43.

[0060] In step S20, the control device 50 determines whether the regeneration in progress flag is ON, and if the regeneration in progress flag is ON (Yes), the process proceeds to step S25, and if the regeneration in progress flag is not ON (No), the process proceeds to step S32. The regeneration in progress flag is a flag that is set ON in step S35 in Fig. 11 and set OFF in step S60, and is set ON while filter regeneration control is being executed.

[0061] If the process proceeds to step S25, the control device 50 determines whether the PM accumulation amount exceeds the accumulation threshold. If the PM accumulation amount exceeds the accumulation threshold (Yes), the control device 50 proceeds to step S30, and if the PM accumulation amount does not exceed the accumulation threshold (No), the control device 50 proceeds to step S60.

[0062] When the process proceeds to step S30, the control device 50 determines whether or not the regeneration start conditions (the regeneration start conditions other than step S25) are satisfied. If the regeneration start conditions of the filter regeneration control (the regeneration start conditions other than step S25) are satisfied (Yes), the control device 50 proceeds to step S35, and if the regeneration start conditions are not satisfied (No), the control device 50 proceeds to step S60. Note that the regeneration start conditions other than step S25 are the same as those in existing processes, so details will be omitted.

[0063] When the process proceeds to step S32, the control device 50 determines whether the regeneration continuation condition is satisfied. If the regeneration continuation condition for the filter regeneration control is satisfied (Yes), the control device 50 proceeds to step S40, and if the regeneration continuation condition is not satisfied (No), the control device 50 proceeds to step S60. Note that the regeneration continuation condition is the same as the existing condition, so details will be omitted.

[0064] If the process proceeds to step S35, the playback in progress flag is set to ON, and the process proceeds to step S40.

[0065] In step S40, the controller 50 executes "calculate target bed temperature" and proceeds to step S45. Details of "calculate target bed temperature" will be described later.

[0066] In step S45, the control device 50 adjusts the amount of fuel added from the fuel addition valve 61A so that the filter bed temperature (the temperature of the filter 43, for example, the estimated temperature at position CF4 shown in FIG. 4) approaches the target bed temperature, and then proceeds to step S50.

[0067] In step S50, the control device 50 estimates the amount of PM removed by combustion based on the filter bed temperature, etc., updates the PM accumulation amount by subtracting the amount of PM removed by combustion from the PM accumulation amount, and proceeds to step S55. Note that, when the PM accumulation amount is estimated using the integration method in step S15, the update in step S50 is essential, but when the PM accumulation amount is estimated using the differential pressure method, this step may be omitted. Note that the "PM accumulation amount" is stored in a non-volatile storage device.

[0068] In step S55, the control device 50 determines whether filter regeneration is complete. For example, the control device 50 determines that filter regeneration is complete when the PM accumulation amount is equal to or less than the regeneration completion threshold (for example, when the PM accumulation amount is approximately zero). If the control device 50 determines that filter regeneration is complete (Yes), the control device 50 proceeds to step S60, and if the control device 50 determines that filter regeneration is not complete (No), the control device 50 ends the process shown in FIG. 11.

[0069] When the process proceeds to step S60, the control device 50 sets the regeneration in progress flag to OFF, initializes (resets to zero) the intake air amount counter, sets the gradient threshold flag to OFF, and ends the process shown in Fig. 11. Note that the "intake air amount counter" and the "gradient threshold flag" are a counter and a flag used in <Calculation of target bed temperature (Fig. 12)>, which will be described later, and will be explained in <Calculation of target bed temperature (Fig. 12)>.

[0070] <Calculating the target bed temperature (Figure 12)> After executing the "Calculation of target bed temperature" in step S40 shown in FIG. 11, the control device 50 advances the process to step U10 of the "Calculation of target bed temperature" in FIG.

[0071] In step U10, the control device 50 acquires and stores a (tentative) target bed temperature according to the PM accumulation amount, and proceeds to step U15. For example, the control device 50 stores the target bed temperature acquired using the [target bed temperature characteristics] shown in FIG. 13 and the PM accumulation amount in the "(tentative) target bed temperature." The [target bed temperature characteristics] are set so that the target bed temperature decreases as the PM accumulation amount increases. Note that in the [target bed temperature characteristics], the target bed temperature used in this embodiment is set to a temperature higher than the conventional target bed temperature, and an appropriate value confirmed by experiments, simulations, etc. using an actual vehicle is set.

[0072] In step U15, the control device 50 acquires the temperature gradient in the filter 43 and the temperature gradient threshold, and proceeds to step U20. For example, the temperature gradient is the temperature gradient ΔD between the temperature at position CF1 on the most upstream side of the exhaust gas and the temperature at position CF4 on the most downstream side of the exhaust gas, as shown in FIG. 4 (temperature at position CF1 - temperature at position CF4 (temperature difference)). The control device 50 also stores the value acquired using the [temperature gradient threshold characteristic] shown in FIG. 14 and the amount of PM accumulation in the "temperature gradient threshold." The [temperature gradient threshold characteristic] is set so that the temperature gradient threshold decreases as the amount of PM accumulation increases.

[0073] Regarding the "temperature gradient," for example, the control device 50 estimates the temperatures at positions CF1 and CF4 of the filter 43 based on the exhaust temperature upstream of the filter detected using the exhaust temperature detection device 36B, the exhaust temperature downstream of the filter [°C] detected using the exhaust temperature detection device 36C, the outside air temperature [°C] detected using the intake air temperature detection device 32A, the exhaust gas flow rate [g / sec] calculated based on the intake air amount, the rotation speed of the internal combustion engine, the exhaust temperature, etc., and the operating state of the internal combustion engine including the heat capacity of the filter 43. Note that the method for estimating the temperatures at positions CF1 and CF4 uses an existing method, so details will be omitted.

[0074] In step U20, the control device 50 determines whether the temperature gradient exceeds the temperature gradient threshold. If the temperature gradient exceeds the temperature gradient threshold (Yes), the control device 50 proceeds to step U25. If the temperature gradient does not exceed the temperature gradient threshold (No), the control device 50 proceeds to step U32.

[0075] If the process proceeds to step U25, the control device 50 determines whether the gradient threshold flag is OFF. If the gradient threshold flag is OFF (Yes), the control device 50 proceeds to step U30, and if the gradient threshold flag is not OFF (No), the control device 50 proceeds to step U35.

[0076] If the process proceeds to step U30, the control device 50 initializes (resets to zero) the intake air amount counter, sets the gradient threshold flag to ON, and proceeds to step U35. When the temperature gradient exceeds the temperature gradient threshold, the gradient threshold flag is set from OFF to ON, and the intake air amount counter is initialized to zero. The intake air amount counter is a counter that measures the accumulated time during which the temperature gradient exceeds the temperature gradient threshold and the intake air amount is less than the intake air amount threshold.

[0077] If the process proceeds to step U32, the control device 50 sets the gradient threshold flag to OFF and proceeds to step U60. The "gradient threshold flag" is a flag for determining when the temperature gradient exceeds the temperature gradient threshold from below the temperature gradient threshold, and is set to ON in step U30 of Fig. 12, and set to OFF in step U32 of Fig. 12 and step S60 of Fig. 11.

[0078] If the process proceeds to step U35, the control device 50 determines whether the intake air amount is less than the intake air amount threshold. If the intake air amount is less than the intake air amount threshold (Yes), the control device 50 proceeds to step U40, and if the intake air amount is not less than the intake air amount threshold (No), the control device 50 proceeds to step U45. The intake air amount threshold is, for example, a constant value, but may be variable depending on the amount of PM accumulation, etc.

[0079] If the process proceeds to step U40, the control device 50 increments the intake air amount counter (+1) and proceeds to step U45.

[0080] If the process proceeds to step U45, the control device 50 acquires an intake air amount counter threshold and proceeds to step U50. For example, the control device 50 stores a value acquired using the [intake air amount counter threshold characteristics] shown in FIG. 15, the PM accumulation amount, and the temperature gradient in the "intake air amount counter threshold." The [intake air amount counter threshold] is set so that the intake air amount counter threshold decreases as the PM accumulation amount increases, and also decreases as the temperature gradient increases. The "intake air amount counter threshold" corresponds to a "predetermined time."

[0081] In step U50, the control device 50 determines whether the intake amount counter is equal to or greater than the intake amount counter threshold. If the intake amount is equal to or greater than the intake amount counter threshold (Yes), the control device 50 proceeds to step U55. If the intake amount is less than the intake amount counter threshold (No), the control device 50 proceeds to step U60.

[0082] If the process proceeds to step U55, the control device 50 updates the (tentative) target bed temperature to a temperature obtained by subtracting the decrease temperature from the (tentative) target bed temperature (a temperature lower than the (tentative) target bed temperature), stores the updated temperature, and proceeds to step U60. The "decrease temperature" may be a constant temperature or may be a variable temperature depending on the amount of PM accumulation, etc. The "decrease temperature" is set to an appropriate value confirmed by experiments, simulations, etc. using an actual vehicle.

[0083] If the process proceeds to step U60, the controller 50 sets the value (temperature) stored in the (provisional) target bed temperature as the "target bed temperature," and ends the process shown in FIG.

[0084] <Example of operating waveform (1) (Fig. 16) and example of operating waveform (2) (Fig. 17)> The example (1) of the operational waveform in FIG. 16 shows an example of the operational waveform for lowering the target bed temperature by the process of [Calculating the target bed temperature] in FIG. 12. When the filter regeneration control is executed and the temperature at positions CF1 and CF4 of the filter rises as shown from time Ta to time Tb in FIG. 5, and the temperature gradient ΔD (temperature at position CF1 - temperature at position CF4 (temperature difference)) increases, the "temperature gradient" in FIG. 16 increases. Then, at time T11 when the "temperature gradient" in FIG. 16 exceeds the "temperature gradient threshold V1," the "target bed temperature" is not yet lowered. After time T11, from time T12 when the "intake air amount" becomes less than the "intake air amount threshold V2," to time T13 when the "intake air amount counter" becomes equal to or greater than the "intake air amount counter threshold V3," the "target bed temperature" is lowered by the "decreasing temperature."

[0085] As a result, in the case of the operating state of [Temperature distribution example (1)] shown in Figure 5, thermal runaway of the filter is predicted and the target bed temperature is lowered to prevent thermal runaway. Also, in the case of the operating state of [Temperature distribution example (2)] shown in Figure 6 and the operating state of [Temperature distribution example (3)] shown in Figure 7, thermal runaway of the filter does not occur, so the target bed temperature is maintained without being lowered.

[0086] 17 shows an outline of the entire process from the start to the completion of filter regeneration control. In contrast to the conventional example, in the present embodiment, the target bed temperature is set to a high temperature, and when thermal runaway of the filter is predicted, the target bed temperature is temporarily lowered at the timing of symbol Tz in FIG. 17, thereby preventing thermal runaway and shortening the period of filter regeneration control.

[0087] <Effects etc.> As described above, the exhaust gas purification system 2 described in this embodiment can shorten the period of filter regeneration control by setting the target bed temperature higher than conventionally. Furthermore, if thermal runaway of the filter is predicted during filter regeneration, the target bed temperature is temporarily lowered to prevent thermal runaway before it occurs. Furthermore, the condition for predicting thermal runaway and lowering the target bed temperature is not only "when the temperature gradient exceeds the temperature gradient threshold," but also "when the intake air volume remains less than the intake air volume threshold for a predetermined period of time or longer." This allows for more accurate prediction of thermal runaway and prevents the target bed temperature from being lowered more than necessary, thereby shortening the period of filter regeneration control.

[0088] <Other> The exhaust purification system 2 for an internal combustion engine of the present invention is not limited to the configuration, structure, processing procedures, etc. described in this embodiment, and various modifications, additions, and deletions are possible within the scope that does not change the gist of the present invention.

[0089] In the description of this embodiment, an example has been given in which a fuel addition valve provided in the exhaust path is used as the exhaust temperature raising device, but the fuel addition valve may be omitted and post injection from the injector may be used to raise the temperature of the exhaust.

[0090] The exhaust gas purification system 2 for an internal combustion engine of the present invention is not limited to vehicles equipped with a diesel engine, and the present invention can be applied to various devices equipped with a diesel engine.

[0091] Furthermore, when expressions such as "greater than or equal to (≧)," "less than or equal to (≦)," "greater than," "exceeds (>)," and "less than (<)" are used, the equal sign may or may not be included. Furthermore, when numerical values ​​are used in the description of this embodiment, they are merely examples and are not limited to these numerical values. [Explanation of symbols]

[0092] 1 Internal combustion engine system 2. Exhaust purification system 10 Internal combustion engine 11A, 11C intake pipe 11D Intake manifold 12A Exhaust manifold 12B, 12C, 12D, 12E exhaust pipes 13 EGR piping 13A EGR valve 21 Injector 31 Air flow detection device 32A, 32B Intake air temperature detection device 32C Coolant temperature detector 33A Atmospheric pressure detector 33B, 33C, 33D Pressure detection device 34A Rotation detector 34B Cylinder detection device 35 Differential pressure detection device 36A~36D Exhaust temperature detector 37A, 37B NOx detector 38 Accelerator pedal depression amount detection device 39 Ignition switch 40 Exhaust gas purification device 41 Upstream exhaust purification device 42 First oxidation catalyst 43 Filters 43a, 43b cells 43c, 43d Lid 43e Filter Wall 43s segment 45 Downstream exhaust purification device 46 Urea SCR 47 Secondary oxidation catalyst 50 Control device 51 CPU 55 Non-volatile storage 61A Fuel addition valve (exhaust gas heating device) 61B Dispersion device 62A Urea solution addition valve 62B Dispersion device 63 Load device (alternator) 64 Throttle device 80 Supercharger 81 Turbine 82 Compressor 84 Intercooler 90 Fuel Tank CF1, CF2, CF3, CF4 position F1, F2, F3, F4 Virtual division filters V1 Temperature Gradient Threshold V2 Inspiratory Volume Threshold V3 Intake volume counter threshold (predetermined time)

Claims

1. An exhaust gas purification system for an internal combustion engine, a filter provided in an exhaust path of the internal combustion engine to capture particulate matter in the exhaust; an exhaust gas heating device that is provided upstream of the filter and is capable of heating the exhaust gas; a control device capable of detecting an operating state of the internal combustion engine and controlling the exhaust gas heating device; and The control device In a filter regeneration control in which the exhaust gas heating device is controlled to heat the exhaust gas and burn and remove particulate matter trapped on the filter to regenerate the filter, a temperature distribution in the filter is obtained based on the operating state including a filter upstream exhaust temperature, which is the exhaust temperature upstream of the filter, and a filter downstream exhaust temperature, which is the exhaust temperature downstream of the filter; obtaining a temperature gradient in the filter based on the temperature distribution; a target bed temperature of the filter is set according to a PM accumulation amount, which is the amount of particulate matter accumulated on the filter; controlling the exhaust gas temperature raising device so that a filter bed temperature, which is the temperature of the filter, approaches the target bed temperature; When the temperature gradient exceeds a temperature gradient threshold and the intake air amount of the internal combustion engine is less than an intake air amount threshold for a predetermined period of time or longer, the target bed temperature is reduced. Exhaust gas purification system for internal combustion engines.

2. 2. An exhaust gas purification system for an internal combustion engine according to claim 1, The temperature gradient threshold is set according to the amount of PM accumulation, and is set to be smaller as the amount of PM accumulation increases. Exhaust gas purification system for internal combustion engines.

3. 3. An exhaust gas purification system for an internal combustion engine according to claim 1 or 2, The predetermined time is set according to the temperature gradient and the amount of PM accumulation, and is set to be shorter as the temperature gradient increases and as the amount of PM accumulation increases. Exhaust gas purification system for internal combustion engines.

4. 3. An exhaust gas purification system for an internal combustion engine according to claim 1 or 2, The internal combustion engine is mounted on a vehicle, The control device determining, as the filter bed temperature, temperatures at a plurality of positions in the direction in which the exhaust gas flows within the filter based on the operating conditions including the filter upstream side exhaust temperature, the filter downstream side exhaust temperature, an outside air temperature, the vehicle speed, the flow velocity of the exhaust gas passing through the filter, and the heat capacity of the filter; A temperature difference between a temperature at a position on the most upstream side of the exhaust gas and a temperature at a position on the most downstream side of the exhaust gas among the plurality of positions is acquired as the temperature gradient. Exhaust gas purification system for internal combustion engines.

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