Exhaust gas purification device for internal combustion engine and control method for exhaust gas purification device of internal combustion engine

Abstract

To prevent white smoke from being discharged from a DPF even when a concentration of biofuel in fuel added to an exhaust passage is high during regeneration of the DPF.SOLUTION: During DPF regeneration control, a target intake air amount At is calculated by multiplying a reference intake air amount Anq calculated from a rotational speed NE and a fuel injection amount Qf by a correction coefficient kc. The correction coefficient kc is set to a smaller value as a biofuel concentration is higher (S12). A throttle valve is controlled so that the intake air amount becomes the target intake air amount At (S13). Since a temperature of exhaust gas can be increased while securing an amount of air necessary to burn added fuel and PM accumulated in a DPF, it is possible to promote vaporization of fuel with high biofuel concentration and suppress discharge of white smoke from the DPF.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to an exhaust gas purification device for an internal combustion engine and a method for controlling the exhaust gas purification device for an internal combustion engine.

Background Art

[0002] Towards a decarbonized society, the use of biofuels that are carbon-neutral and have a low environmental impact is expanding. For example, biofuel-blended light oil, which is a mixture of biodiesel fuel made from rapeseed oil or waste cooking oil and light oil, is used as fuel for a compression ignition internal combustion engine (diesel engine).

[0003] By the way, the distillation properties of light oil and biodiesel fuel (hereinafter also referred to as biofuel) are different, and biofuel is less likely to evaporate compared to light oil. Also, the calorific value of biofuel is smaller than that of light oil. For this reason, Japanese Patent Application Laid-Open No. 2010-242664 (Patent Document 1) suggests that when performing temperature rise control of a filter for removing particulate matter in exhaust gas during regeneration of the filter, when the biofuel concentration in the fuel increases, the amount of fuel added (supplied) into the exhaust passage is increased.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When heating up the filter during filter regeneration, fuel is added to the exhaust passage upstream of the oxidation catalyst provided upstream of the filter. The fuel added to the exhaust passage generates heat (burns) in the oxidation catalyst and heats up the downstream filter. When the concentration of biofuel in the fuel added to the exhaust passage increases, since biofuel is difficult to vaporize, the fuel that cannot be vaporized by the oxidation catalyst passes through the oxidation catalyst and flows into the filter, and may be discharged from the filter as white smoke without burning in the filter.

[0006] An object of the present disclosure is to suppress the discharge of white smoke from the filter even when the concentration of biofuel in the fuel added to the exhaust passage is high during filter regeneration.

Means for Solving the Problems

[0007] The exhaust gas purification device of the internal combustion engine of the present disclosure includes a filter provided in the exhaust passage of the internal combustion engine for collecting particulate matter contained in the exhaust gas, an oxidation catalyst provided in the exhaust passage upstream of the filter, a fuel addition valve for adding fuel to the exhaust passage upstream of the oxidation catalyst, a throttle valve provided in the intake passage of the internal combustion engine for controlling the intake air amount, and a control device. The control device executes regeneration control for burning the particulate matter deposited on the filter, and controls the throttle valve so that the amount of air in the exhaust passage decreases as the concentration of biofuel in the fuel added from the fuel addition valve increases when the regeneration control is executed.

[0008] In the regeneration control for burning particulate matter deposited on the filter, in order to raise the temperature of the filter, fuel is added to the exhaust passage, heat is generated by the oxidation catalyst, and the downstream filter is heated. At this time, in order to promote heat generation by the oxidation catalyst, the temperature of the exhaust gas is increased. To increase the exhaust gas temperature, it is preferable to reduce the amount of air in the exhaust gas while ensuring the added fuel and the air (oxygen) necessary for burning the particulate matter deposited on the filter. Biofuel has an oxygen atom in its fuel molecule. Therefore, when the biofuel concentration in the fuel is high, even if the amount of air (oxygen amount) in the exhaust gas is reduced, it is possible to secure the oxygen necessary for burning the added fuel and the particulate matter deposited on the filter.

[0009] According to this configuration, when the control device of the exhaust gas purification device of the internal combustion engine executes the regeneration control for burning the particulate matter deposited on the filter, the throttle valve is controlled so that the higher the biofuel concentration in the fuel added from the fuel addition valve, the less the amount of air in the exhaust passage. During the regeneration control of the filter, since the higher the biofuel concentration in the fuel, the less the amount of air in the exhaust gas, it becomes possible to increase the temperature of the exhaust gas while securing the oxygen necessary for burning the added fuel and the particulate matter deposited on the filter. Therefore, the temperature of the oxidation catalyst can be increased, the vaporization of the fuel with a high biofuel concentration can be promoted, and the discharge of white smoke from the filter can be suppressed.

[0010] Preferably, during the execution of the regeneration control, the control device may calculate a target intake air amount based on the rotational speed of the internal combustion engine, the fuel injection amount of the internal combustion engine, and the biofuel concentration in the fuel, and control the throttle valve so that the intake air amount becomes the target intake air amount.

[0011] According to this configuration, since the target intake air amount is calculated based on the rotational speed of the internal combustion engine, the fuel injection amount of the internal combustion engine, and the biofuel concentration in the fuel, the air-fuel ratio (air amount) of the exhaust gas can be appropriately controlled according to the operating state of the internal combustion engine.

[0012] Preferably, when the regeneration control is executed, the control device may add fuel from the fuel addition valve when the temperature of the oxidation catalyst is equal to or higher than a first predetermined value.

[0013] According to this configuration, when the temperature of the oxidation catalyst is equal to or higher than the first predetermined temperature, fuel is added from the fuel addition valve, so that the fuel surely vaporizes in the oxidation catalyst and then flows into the filter, and the emission of white smoke from the filter can be more surely suppressed.

[0014] Preferably, when the regeneration control is executed, the control device may stop adding fuel from the fuel addition valve when the temperature of the filter is equal to or higher than a second predetermined value greater than the first predetermined value.

[0015] According to this configuration, when the temperature of the filter is equal to or higher than the second predetermined value and is a temperature sufficient for the particulate matter to burn, the addition of fuel from the fuel addition valve is stopped, so that the fuel consumption can be reduced.

[0016] The control method of the present disclosure is a control method for an exhaust gas purification device of an internal combustion engine, including a filter provided in an exhaust passage of the internal combustion engine to collect particulate matter contained in exhaust gas, an oxidation catalyst provided in the exhaust passage upstream of the filter, and a fuel addition valve for adding fuel to the exhaust passage upstream of the oxidation catalyst. When performing regeneration control to burn the particulate matter deposited on the filter, the intake air amount of the internal combustion engine is controlled so that the higher the biofuel concentration in the fuel added from the fuel addition valve, the less the air amount in the exhaust passage.

[0017] According to this control method, when performing regeneration control to burn particulate matter deposited on the filter, the intake air amount of the internal combustion engine is controlled such that the higher the biofuel concentration in the fuel added from the fuel addition valve, the less the amount of air in the exhaust passage. During the regeneration control of the filter, since the higher the biofuel concentration in the fuel, the less the amount of air in the exhaust gas, it becomes possible to increase the temperature of the exhaust gas while ensuring the oxygen necessary to burn the particulate matter deposited on the filter. Therefore, the temperature of the oxidation catalyst can be increased, the vaporization of the fuel with a high biofuel concentration can be promoted, and the emission of white smoke from the filter can be suppressed.

Advantages of the Invention

[0018] According to the present disclosure, even when the biofuel concentration in the fuel added to the exhaust passage is high during the regeneration of the filter, it is possible to suppress the emission of white smoke from the filter.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and their description will not be repeated.

[0021] FIG. 1 is a schematic configuration diagram of an exhaust gas purification device for an internal combustion engine according to this embodiment. The engine 1 is a compression self-ignition type internal combustion engine (diesel engine) equipped with an exhaust gas purification device. The engine 1 is an internal combustion engine that injects fuel from a fuel injection valve (injector) 14 into a combustion chamber formed in a cylinder 12 of the engine body 10 and performs compression self-ignition. In this embodiment, the engine 1 has four cylinders. An air cleaner 22, an intercooler 24, and a throttle valve (diesel throttle valve) 26 are provided in the intake passage 20 of the engine 1. Fresh air (air) from which foreign substances have been removed by the air cleaner 22 is supercharged (compressed) by a compressor 32 of a turbocharger 30, cooled by the intercooler 24, supplied to the intake manifold 28, and supplied from the intake port to each combustion chamber.

[0022] Exhaust (exhaust gas) discharged from the combustion chamber is collected in the exhaust manifold 50 and discharged to the outside air through the exhaust passage 52. Also, a part of the exhaust is refluxed to the intake manifold 28 through an EGR (Exhaust Gas Recirculation) passage 60. An EGR cooler 62 and an EGR valve 64 are provided in the EGR passage 60.

[0023] In the exhaust passage 52, a turbine 34 of a turbocharger 30, an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 70, and a DPF (Diesel Particulate Filter) 72 are provided from the upstream side. The DPF 72 is a filter that collects particulate matter (PM: Particulate Matter) in the exhaust gas and purifies it by appropriately burning and removing the collected PM. Although not shown, a urea addition valve and a selective reduction catalyst may be provided downstream of the DPF 72. Note that instead of or in addition to the urea addition valve and the selective reduction catalyst, a NOx storage reduction catalyst (NSR (NOx Storage-Reduction) catalyst) may be provided.

[0024] Fuel is stored in the fuel tank 40. The fuel in the fuel tank 40 is supplied to the high-pressure fuel pump 42 by the feed pump 41, and the high-pressure fuel discharged from the high-pressure fuel pump 42 is pumped to the common rail 44 through the fuel passage 43. The high-pressure fuel stored in the common rail 44 is injected from the injector 14 into the combustion chamber (inside the cylinder).

[0025] A fuel addition valve 80 is provided in the exhaust passage 52 upstream of the oxidation catalyst 70 (in this embodiment, the exhaust passage 52 upstream of the turbine 34). Fuel in the fuel tank 40 is supplied to the fuel addition valve 80 by the feed pump 41 through the fuel passage 45. When the fuel addition valve 80 is opened, fuel is added (injected) into the exhaust passage 52.

[0026] The engine ECU 100 (Electronic Control Unit) includes a CPU 101, a memory 102 composed of a ROM and a RAM, an input / output port (not shown) for inputting and outputting various signals, etc. Based on the information stored in the memory 102 and the information from various sensors, it executes predetermined arithmetic processing and controls the injector 14, the throttle valve 26, the high-pressure fuel pump 42, the fuel addition valve 80, etc. Note that the engine ECU 100 corresponds to the "control device" of the present disclosure.

[0027] As various sensors input to the engine ECU 100, for example, there are an engine speed sensor 111, an accelerator pedal sensor 112, an air flow meter 113, an oxidation catalyst temperature sensor 114, a DPF temperature sensor 115, a pressure sensor 116, and the like. The engine speed sensor 111 detects the rotational speed NE of the engine 1. The accelerator pedal sensor 112 detects the amount of accelerator pedal operation (hereinafter also referred to as "accelerator opening") AP by the user. The air flow meter 113 detects the intake air amount (inhaled air amount) Ga of the engine 1. The oxidation catalyst temperature sensor 114 detects the temperature Tc of the oxidation catalyst 70. Note that it is desirable for the oxidation catalyst temperature sensor 114 to detect the inlet temperature of the oxidation catalyst 70. The DPF temperature sensor 115 detects the temperature Tf (the bed temperature of the DPF 72) of the DPF 72. The pressure sensor 116 detects the pressure difference ΔP in the exhaust passage 52 upstream and downstream of the DPF 72.

[0028] In the engine 1 configured as described above, PM contained in the exhaust gas discharged from the engine 1 is collected by the DPF 72. When the amount of PM deposited on the DPF 72 reaches a predetermined value or more, the engine ECU 100 executes a regeneration control to regenerate the DPF 72 by raising the temperature of the DPF 72 and burning and removing the deposited PM. When executing the regeneration control, in order to raise the temperature of the DPF 72, fuel is added from the fuel addition valve 80. The added fuel causes the oxidation catalyst 70 to generate heat (burn), and the temperature of the exhaust gas flowing into the DPF 72 rises.

[0029] As the fuel stored in the fuel tank 40, a biofuel - blended gas oil obtained by mixing gas oil and biofuel may be used. FIG. 2 is a diagram showing the relationship between the biofuel concentration (mixing ratio of biofuel to gas oil) in the fuel and the distillation ratio. In FIG. 2, the vertical axis represents the distillation ratio (%), and the horizontal axis represents the temperature. The distillation ratio indicates the ratio (%) of the vaporized fuel. In FIG. 2, the dashed line is the distillation ratio of the fuel (B7) in which 7% biofuel is mixed with gas oil, the one - dotted line is the distillation ratio of the fuel (B50) in which 50% biofuel is mixed with gas oil, and the two - dotted line is the distillation ratio of the 100% biofuel (B100). As shown in FIG. 2, the higher the biofuel concentration in the fuel, the more difficult it is to vaporize. Therefore, when a fuel with a high biofuel concentration is added from the fuel addition valve 80 to the exhaust passage 52, the fuel that cannot be vaporized by the oxidation catalyst 70 may flow through the oxidation catalyst 70 and into the DPF72, and may be discharged from the DPF72 as white smoke without burning in the DPF72.

[0030] In order to promote the vaporization of the fuel added from the fuel addition valve 80 to the exhaust passage 52, it is preferable to raise the temperature of the exhaust gas to increase the temperature of the oxidation catalyst 70. To raise the exhaust gas temperature, it is preferable to reduce the amount of air in the exhaust gas while ensuring the air (oxygen) necessary for burning the added fuel and the PM deposited on the DPF72. Biofuel has oxygen atoms in its fuel molecules and a large oxygen content. Therefore, when the biofuel concentration in the fuel is high, even if the amount of air (oxygen amount) in the exhaust gas is reduced, it is possible to ensure the oxygen necessary for burning the added fuel and the particulate matter deposited on the DPF72.

[0031] In the present embodiment, when the regeneration control of the DPF72 is executed, the more the biofuel concentration in the fuel added from the fuel addition valve 80 is high, the more the throttle valve 26 is controlled so that the amount of air in the exhaust passage 52 decreases, the amount of air in the exhaust gas is reduced, the temperature of the exhaust gas is raised to increase the temperature of the oxidation catalyst 70, the vaporization of the fuel with a high biofuel concentration is promoted, and the discharge of white smoke from the DPF72 is suppressed.

[0032] Figure 3 is a flowchart showing an example of the process of DPF regeneration control executed by the engine ECU 100. This flowchart is repeatedly processed at predetermined intervals during the operation of the engine 1. In step (hereinafter, steps are abbreviated as "S") 10, it is determined whether or not the PM deposition amount ΣPmd of the DPF 72 is equal to or greater than the regeneration start threshold value A. If the PM deposition amount ΣPmd is equal to or greater than the regeneration start threshold value A and regeneration of the DPF 72 (combustion removal of the deposited PM) is necessary, an affirmative determination is made and the process proceeds to S11. After setting the flag Fr to 1, the process proceeds to S12. If the PM deposition amount ΣPmd is less than the regeneration start threshold value A and regeneration of the DPF 72 is unnecessary, a negative determination is made and the process proceeds to S18. After setting the flag Fr to 0, the current routine is terminated.

[0033] The PM deposition amount ΣPmd is the amount of PM deposited (collected) on the DPF 72 and is calculated based on the operating state of the engine 1. Figure 4 is a flowchart showing an example of the PM deposition amount calculation process executed by the engine ECU 100. This flowchart is repeatedly processed at predetermined times during the operation of the engine 1. First, in S20, it is determined whether or not the flag Fr is 1. If the DPF 72 is not under regeneration control and the flag Fr is 0, a negative determination is made and the process proceeds to S21.

[0034] In S21, the PM emission amount Pad, which is the amount of PM emitted from the engine 1, is calculated based on the engine speed NE, fuel injection amount Qf, etc. of the engine 1. For example, in the memory 102, the amount of PM emitted from the engine 1 per unit time is stored in advance as a map using the engine speed NE, fuel injection amount Qf, engine coolant temperature, etc. as parameters. The PM emission amount Pad is calculated by multiplying the amount of PM emitted per unit time read from this map by the time interval Δt between the previous process and the current process. Note that the fuel injection amount Qf is the amount of fuel injected into the combustion chamber from the injector 14 and is calculated in the engine ECU 100 based on the accelerator opening AP, engine speed NE, etc.

[0035] In S22, the PM emission amount Pad is added to the previously calculated PM deposition amount ΣPmd to calculate the (current) PM deposition amount ΣPmd, and this routine is terminated.

[0036] In S20, when the DPF 72 is being regenerated, the flag Fr is 1, so an affirmative determination is made and the process proceeds to S23. In S23, during the regeneration control of the DPF 72, the PM removal amount Psu, which is the amount of PM removed by combustion, is calculated based on the temperature Tf of the DPF 72. For example, in the memory 102, the amount of PM removed from the DPF 72 per unit time is stored in advance as a map with the temperature Tf of the DPF 72 as a parameter. The PM removal amount Psu is calculated by multiplying the amount of PM removed by combustion per unit time read from this map by the time interval Δt between the previous process and the current process.

[0037] In S24, the PM removal amount Psu is subtracted from the previously calculated PM deposition amount ΣPmd to calculate the (current) PM deposition amount ΣPmd, and this routine is terminated.

[0038] Referring to FIG. 3, in S12 following S11, the target intake air amount At is calculated based on the rotational speed NE, the fuel injection amount Qf, and the biofuel concentration Cf in the fuel. For example, in advance through experiments or the like, with the rotational speed NE and the fuel injection amount Qf as parameters, when using light oil as the fuel (when using fuel with a biofuel concentration Cf of 0%), the reference intake air amount Anq is obtained, which can ensure the air (oxygen) required to burn the fuel added from the fuel addition valve 80 to the exhaust passage 52 and the PM deposited on the DPF 72 and raise the exhaust gas temperature to a level at which the added fuel can burn (generate heat) in the oxidation catalyst 70. Then, this reference intake air amount Anq is stored in the memory 102 as a map with the rotational speed NE and the fuel injection amount Qf as parameters.

[0039] Further, a correction coefficient kc is obtained based on the biofuel concentration Cf. FIG. 5 is a diagram showing an example of a map for obtaining the correction coefficient kc in the present embodiment. As shown in FIG. 5, the correction coefficient kc is a value of 1.0 or less, and the smaller the biofuel concentration Cf, the smaller the value. The correction coefficient kc is set in advance by experiments or the like so that even if the amount of air (oxygen amount) in the exhaust gas is reduced, the oxygen contained in the biofuel can secure the air (oxygen) necessary for burning the added fuel and the PM deposited on the DPF 72.

[0040] The biofuel concentration Cf may be estimated from the calorific value of the fuel. FIG. 6 is a flowchart showing an example of biofuel concentration estimation processing executed by the ECU 100. This flowchart is executed every time the engine 1 is started. For example, when the ignition switch (start switch) is turned ON and the engine 1 is started, it is determined in S30 whether or not fuel has been supplied to the fuel tank 40. In the present embodiment, it is determined whether or not fuel has been supplied using the fuel amount of the fuel tank 40 detected by a fuel level gauge (not shown). For example, when the fuel amount at the start of the engine 1 this time is greater than the fuel amount when the engine 1 stopped last time (when the ignition switch was turned OFF), it is determined that fuel has been supplied. Note that if there is a history of the fuel lid (fail lid) being opened between the stop of the engine 1 and the start of the engine 1 this time, it may be determined that fuel has been supplied. When it is determined in S30 that fuel has been supplied to the fuel tank 40, the process proceeds to S31. When it is determined that fuel has not been supplied to the fuel tank 40, the present routine ends.

[0041] In S31, after the engine 1 is started, it is determined whether a predetermined period has elapsed. The predetermined period is set to a time sufficient for the fuel stored in the fuel tank 40 before fuel supply and the supplied fuel to mix. When the engine 1 is mounted on a vehicle, due to the vibration during driving, stirring of the fuel in the fuel tank 40 can be expected, so the predetermined period may be several minutes after the engine 1 is started. After the engine 1 is started, S31 is repeatedly processed until the predetermined period elapses. When the predetermined period elapses after the engine 1 is started, an affirmative determination is made in S31 and the process proceeds to S32.

[0042] In S32, the calorific value of the fuel (calorific value per unit mass) is calculated from the combustion pressure (in-cylinder pressure) detected by a combustion pressure sensor (not shown) and the fuel injection amount Qf, and based on the calorific value, the biofuel concentration Cf is estimated. Since the calorific value of biofuel is smaller than that of light oil, the biofuel concentration Cf can be estimated based on the calorific value of the fuel.

[0043] Referring to FIG. 3, in S12, the target intake air amount At is calculated (At = Anq × kc) by multiplying the reference intake air amount Anq calculated from the rotational speed NE and the fuel injection amount Qf by the correction coefficient kc calculated from the biofuel concentration Cf. The target intake air amount At becomes a smaller value as the biofuel concentration Cf is higher.

[0044] In S13, intake air amount control is performed to control the opening degree of the throttle valve 26 so that the intake air amount of the engine 1 becomes the target intake air amount At. The intake air amount control is, for example, feedback control of the opening degree of the throttle valve 26 so that the intake air amount Ga detected by the air flow meter 113 becomes the target intake air amount At.

[0045] In the subsequent S14, it is determined whether the temperature Tc of the oxidation catalyst 70 (preferably, the inlet temperature of the oxidation catalyst 70) is equal to or higher than a first predetermined value T1. The first predetermined value T1 is a temperature sufficient for the fuel flowing into the oxidation catalyst 70 to vaporize and then burn (generate heat) to raise the temperature of the exhaust gas, and is set in advance by experiments or the like. When the temperature Tc is lower than the first predetermined value T1, a negative determination is made and the process returns to S12 to continue the intake air amount control. By the intake air amount control, the exhaust gas temperature rises. When the temperature Tc becomes equal to or higher than the first predetermined value T1, an affirmative determination is made in S14 and the process proceeds to S15.

[0046] In S15, it is determined whether the temperature Tf of the DPF 72 is equal to or higher than a second predetermined value T2. The second predetermined value T2 is a temperature at which the PM deposited on the DPF 72 is sufficiently burned and removed, and is set in advance by experiments or the like. When the temperature Tf is equal to or higher than the second predetermined value T2, an affirmative determination is made and the process returns to S12 to continue the intake air amount control. Thus, when the PM deposited on the DPF 72 can be sufficiently burned and removed without adding fuel to the exhaust passage 52 to raise the exhaust gas temperature, the addition of fuel from the fuel addition valve 80 is not performed, so that fuel consumption can be reduced. When the temperature Tf is lower than the second predetermined value T2, a negative determination is made and the process proceeds to S16.

[0047] In S16, fuel is added (injected) from the fuel addition valve 80 to the exhaust passage 52. As a result, the fuel added to the exhaust passage 52 generates heat (burns), so that the exhaust gas temperature rises and the DPF 72 is heated, whereby the PM deposited on the DPF 72 can be burned and removed. The amount of fuel added (injection amount) by the fuel addition valve 80 may be calculated based on, for example, the rotational speed NE, the fuel injection amount Qf, the intake air amount Ga, etc., so that the air-fuel ratio of the exhaust gas becomes a predetermined value.

[0048] In the subsequent S17, it is determined whether the PM deposition amount ΣPmd is less than or equal to the regeneration end threshold B. If the PM deposition amount ΣPmd is greater than the regeneration end threshold B, a negative determination is made and the process returns to S12, where intake air amount control and fuel addition to the exhaust passage 52 are performed to increase the exhaust gas temperature and continue the combustion removal of the PM deposited on the DPF72. As the combustion removal of the PM progresses and the PM deposition amount ΣPmd becomes less than or equal to the regeneration end threshold B, an affirmative determination is made in S17 and the process proceeds to S18. After setting the flag Fr to 0, the current routine ends.

[0049] In the present embodiment, the correction coefficient kc is set to a smaller value as the biofuel concentration Cf in the fuel added from the fuel addition valve 80 is higher. The higher the biofuel concentration Cf, the smaller the target intake air amount At. The throttle valve 26 is controlled so that the higher the biofuel concentration Cf in the fuel added from the fuel addition valve 80, the less the amount of air in the exhaust passage 52. The correction coefficient kc is set so that even if the amount of air (oxygen amount) in the exhaust gas is reduced, the oxygen contained in the biofuel can ensure the air (oxygen) necessary for burning the added fuel and the PM deposited on the DPF72. Therefore, during the PM regeneration control of the DPF72, it becomes possible to increase the temperature of the exhaust gas while ensuring the amount of air (oxygen amount) necessary for burning the added fuel and the PM deposited on the DPF72, increase the temperature of the oxidation catalyst 70, promote the vaporization of the fuel with a high biofuel concentration, and suppress the discharge of white smoke from the DPF72.

[0050] In the above embodiment, the target intake air amount At (= Anq × kc) was calculated by multiplying the reference intake air amount Anq calculated from the rotational speed NE and the fuel injection amount Qf by the correction coefficient kc calculated from the biofuel concentration Cf. The method for calculating the target intake air amount At is not limited to this. For example, based on the biofuel concentration Cf, a correction amount Ak that becomes larger as the biofuel concentration Cf is higher can be calculated, and the target intake air amount At (= Anq - Ak) can be calculated by subtracting the correction amount Ak from the reference intake air amount Anq. The target intake air amount At may be obtained from a three-dimensional map using the rotational speed NE, the fuel injection amount Qf, and the biofuel concentration Cf as parameters.

[0051] Also, in the above-described embodiment, the correction coefficient kc continuously decreased as the biofuel concentration Cf increased (see FIG. 5), but it may be a value that decreases in multiple steps. For example, the correction coefficient kc may be set in two steps, when the biofuel concentration Cf is low and when it is high. In the present disclosure, "the higher the biofuel concentration Cf in the fuel added from the fuel addition valve 80, the less the amount of air in the exhaust passage 52" includes "when the biofuel concentration Cf in the fuel added from the fuel addition valve 80 is high, the amount of air in the exhaust passage 52 is less than when the biofuel concentration Cf is low".

[0052] In the above-described embodiment, by comparing the PM deposition amount ΣPmd with thresholds (the regeneration start threshold A and the regeneration end threshold B), it was determined whether combustion removal (regeneration of the DPF 72) of the PM deposited on the DPF 72 was necessary. However, instead of this, or in addition, the pressure difference ΔP between the upstream and downstream of the DPF 72 in the exhaust passage 52 detected by the pressure sensor 116 may be used to determine whether combustion removal of the PM is necessary. In this case, for example, when the pressure difference ΔP is equal to or greater than a predetermined value, combustion removal of the PM may be performed.

[0053] In the above-described embodiment, the temperature Tf of the DPF 72 (the bed temperature of the DPF 72) was detected using the DPF temperature sensor 115, but the temperature of the DPF 72 may be estimated using the rotational speed NE, the fuel injection amount Qf, the engine coolant temperature, etc.

[0054] The embodiments disclosed this time should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the description of the above-described embodiments but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims are included.

Explanation of Reference Numerals

[0055] 1 Engine, 10 Engine block, 12 Cylinder, 14 Fuel injection valve (Injector), 20 Intake passage, 22 Air cleaner, 24 Intercooler, 26 Throttle valve (Diesel throttle valve), 28 Intake manifold, 30 Turbocharger, 32 Compressor, 34 Turbine, 40 Fuel tank, 41 Feed pump, 42 High-pressure fuel pump, 43 Fuel passage, 44 Common rail, 45 Fuel passage, 50 Exhaust manifold, 52 Exhaust passage, 60 ERG passage, 62 EGR cooler, 64 EGR valve, 70 Oxidation catalyst (DOC), 72 DPF, 80 Fuel addition valve, 100 Engine ECU, 101 CPU, 102 Memory, 111 Engine speed sensor, 112 Accelerator pedal sensor, 113 Airflow meter, 114 Oxidation catalyst temperature sensor, 115 DPF temperature sensor, 116 Pressure sensor, 117 Biofuel concentration sensor.

Claims

1. A filter provided in an exhaust passage of an internal combustion engine for collecting particulate matter contained in exhaust gas, an oxidation catalyst provided in the exhaust passage upstream of the filter, a fuel addition valve for adding fuel to the exhaust passage upstream of the oxidation catalyst, a throttle valve provided in an intake passage of the internal combustion engine for controlling an intake air amount, and a control device, and the control device executes a regeneration control for burning the particulate matter deposited on the filter, and controls the throttle valve so that the air amount in the exhaust passage decreases as the biofuel concentration in the fuel added from the fuel addition valve is higher during the execution of the regeneration control. An exhaust gas purification device for an internal combustion engine.

2. The control device calculates a target intake air amount based on the rotational speed of the internal combustion engine, the fuel injection amount of the internal combustion engine, and the biofuel concentration in the fuel during the execution of the regeneration control, and controls the throttle valve so that the intake air amount becomes the target intake air amount. The exhaust gas purification device for an internal combustion engine according to Claim 1.

3. The control device adds the fuel from the fuel addition valve when the temperature of the oxidation catalyst is equal to or higher than a first predetermined value during the execution of the regeneration control. The exhaust gas purification device for an internal combustion engine according to Claim 1 or Claim 2.

4. The control device stops the addition of the fuel from the fuel addition valve when the temperature of the filter is equal to or higher than a second predetermined value which is larger than the first predetermined value during the execution of the regeneration control. The exhaust gas purification device for an internal combustion engine according to Claim 3.

5. A control method for an exhaust gas purification device of an internal combustion engine, including a filter provided in an exhaust passage of the internal combustion engine for collecting particulate matter contained in exhaust gas, an oxidation catalyst provided in the exhaust passage upstream of the filter, and a fuel addition valve for adding fuel to the exhaust passage upstream of the oxidation catalyst, wherein during the execution of a regeneration control for burning the particulate matter deposited on the filter, the intake air amount of the internal combustion engine is controlled so that the air amount in the exhaust passage decreases as the biofuel concentration in the fuel added from the fuel addition valve is higher. A control method for an exhaust gas purification device of an internal combustion engine.

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