Control device for internal combustion engine

Abstract

To regenerate a filter without complicating a structure.SOLUTION: A control device 70 of an internal combustion engine includes: a fuel injector 51 for supplying fuel to be mixed with intake air flown into an engine 10; and a filter 43 for collecting coals contained in exhaust gas generated by the combustion of mixed gas of the intake air and the fuel in the engine 10. The device has: a fuel cut part 72 for limiting a supply of fuel by the fuel injector 51 when a predefined condition is met; an estimation part 73 for estimating a coal accumulation amount of the filter 43; and a control part 71 for, when a temperature of the filter 43 is higher than a variable predefined temperature defined according to the coal accumulation amount of the filter 43, prohibiting a limit in supply of fuel by the fuel cut part 72 even when the predefined condition is met and controlling an air-fuel ratio at a rich level.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a control device for an internal combustion engine. [Background technology]

[0002] 2. Description of the Related Art Vehicles equipped with filters for trapping particulate matter contained in exhaust gas emitted from an internal combustion engine have been known. The internal combustion engine disclosed in Patent Document 1 has a casing that houses a particulate filter connected to an exhaust port of the engine body via an exhaust pipe, and a secondary air supply device that is further connected to the exhaust pipe. This secondary air supply device supplies secondary air into the exhaust gas flowing into the particulate filter.

[0003] The control device for the internal combustion engine of Patent Document 1 controls the internal combustion engine so that the air-fuel ratio of the exhaust gas discharged from the engine body becomes a rich air-fuel ratio, and executes a process to raise the filter temperature by supplying air from a secondary air supply device.The control device also controls the internal combustion engine so that the air-fuel ratio of the exhaust gas discharged from the engine body becomes a stoichiometric air-fuel ratio, and executes a regeneration process to burn soot accumulated on the filter by supplying air from the secondary air supply device so that the air-fuel ratio of the exhaust gas flowing into the filter becomes a lean air-fuel ratio. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-60137 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the internal combustion engine of Patent Document 1 has a problem in that the structure for regenerating the filter becomes complicated because it needs to be provided with a secondary air supply device.

[0006] The present invention has been made in consideration of the above-mentioned problems, and has as its object to regenerate a filter without complicating the structure. [Means for solving the problem]

[0007] The present invention is a control device for an internal combustion engine comprising a fuel injector that supplies fuel to be mixed with intake air flowing into the internal combustion engine, and a filter that collects soot contained in exhaust gas generated by combustion of the mixture of intake air and fuel in the internal combustion engine, wherein the control device is characterized by having a fuel cut-off means that limits the supply of fuel by the fuel injector when a predetermined condition is met, an estimation means that estimates the amount of soot accumulated in the filter, and a control means that, when the temperature of the filter is higher than a variable predetermined temperature determined according to the amount of soot accumulated in the filter, prohibits the fuel cut-off means from limiting the supply of fuel even if the predetermined condition is met and controls the air-fuel ratio to be rich. [Effects of the Invention]

[0008] According to the present invention, the filter can be regenerated without complicating the structure. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating an example of a schematic configuration of a vehicle. [Figure 2] FIG. 2 is a diagram illustrating an example of a functional configuration of a control device. [Figure 3] FIG. 4 is a diagram showing an example of a map correlating a filter temperature with an amount of soot accumulation. [Figure 4] 10 is a flowchart illustrating an example of a filter regeneration process. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention is a control device 70 for an internal combustion engine including a fuel injector 51 that supplies fuel to be mixed with intake air flowing into the engine 10, and a filter 43 that collects soot contained in exhaust gas generated by combustion of the mixture of intake air and fuel in the engine 10, the control device including a fuel cut unit 72 that limits the supply of fuel by the fuel injector 51 when a predetermined condition is met, an estimation unit 73 that estimates the amount of soot accumulated in the filter 43, and a control unit 71 that prohibits the fuel cut unit 72 from limiting the supply of fuel and controls the air-fuel ratio to be rich when the temperature of the filter 43 is higher than a variable predetermined temperature determined in accordance with the amount of soot accumulated in the filter 43, even if the predetermined condition is met. Therefore, the filter 43 can be regenerated without complicating the structure. [Example]

[0011] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. 1 is a diagram showing a schematic configuration of a vehicle 1 equipped with a control device 70 for an internal combustion engine according to this embodiment. Note that Fig. 1 is simplified for the sake of convenience in explaining this embodiment, and components that are normally included in a vehicle are assumed to be included even if they are not shown in the figure.

[0012] The vehicle 1 of this embodiment includes an engine 10 as an internal combustion engine, a control device 70, and the like. The engine 10 has an engine body 11, an intake system 30 that takes in intake air for combustion in the engine body 11, an exhaust system 40 that discharges exhaust gas from the engine body 11 to the outside, a fuel system 50 that supplies fuel to the engine body 11, and a sensor system that detects the state of the vehicle 1, etc.

[0013] Engine body 11 performs a series of strokes consisting of an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke. Engine body 11 has a combustion chamber 13 in which a piston 12 is housed so that it can reciprocate, a crank chamber 15 in which a crankshaft 14 is housed so that it can rotate, an intake port 16 which is an inlet for intake air for combustion, and an exhaust port 17 which is an outlet for exhaust gas. Engine body 11 also has an ignition plug 18 arranged so that its tip is located within combustion chamber 13, an intake valve 19 located between combustion chamber 13 and intake port 16, and an exhaust valve 20 located between combustion chamber 13 and exhaust port 17.

[0014] During the intake stroke, the piston 12 descends from top dead center to bottom dead center, the intake valve 19 opens, and the exhaust valve 20 closes. As the piston 12 descends, a mixture of intake air and fuel flows from the intake system 30 into the combustion chamber 13. During the compression stroke, the piston 12 moves upward from the bottom dead center toward the top dead center, and the intake valve 19 and the exhaust valve 20 close. As the piston 12 moves upward, the air-fuel mixture is compressed.

[0015] During the combustion stroke, the compressed air-fuel mixture is ignited by the spark plug 18 and combusted, pushing the piston 12 downward from top dead center to bottom dead center. During the exhaust stroke, the piston 12 rises from bottom dead center to top dead center, the intake valve 19 closes, and the exhaust valve 20 opens. As the piston 12 rises, exhaust gases generated during the combustion stroke are discharged into the exhaust system 40.

[0016] As the engine body 11 repeats a series of processes, driving force is transmitted from the engine body 11 to the drive wheels via the crankshaft 14, causing the vehicle 1 to run. The configuration of the engine body 11 is not particularly limited, and various known engines can be applied. Furthermore, the engine body 11 may be either a gasoline engine or a diesel engine.

[0017] The intake system 30 includes an intake passage 31, an air cleaner 33, and a throttle valve 34. The intake passage 31 is a passage that guides intake air taken in from outside the vehicle 1 to the combustion chamber 13 via the intake port 16. The intake passage 31 is mainly composed of an intake pipe 32. The air cleaner 33 is disposed in the intake passage 31 and purifies the intake air by removing foreign matter such as dust and dirt contained in the intake air. The throttle valve 34 is disposed in the intake passage 31 and adjusts the flow rate of the intake air by opening and closing. The throttle valve 34 adjusts the flow rate of the intake air under the control of the control device 70.

[0018] The exhaust system 40 includes an exhaust passage 41 and a filter 43. The exhaust passage 41 is a passage that exhausts exhaust gas burned in the combustion chamber 13 to the outside of the vehicle 1 via the exhaust port 17. The exhaust passage 41 is mainly composed of an exhaust pipe 42. The filter 43 collects soot (particulate matter) contained in the exhaust gas. The filter 43 may be a gasoline particulate filter (GPF) or a catalyzed gasoline particulate filter (cGPF) that has an integrated catalytic function for purifying harmful substances. If the filter 43 is a gasoline particulate filter (GPF), a catalytic converter is disposed on the exhaust passage 41 between the engine body 11 and the filter 43.

[0019] The fuel system 50 supplies fuel to the engine body 11. The fuel system 50 includes a fuel tank, a fuel pump, and a fuel injector 51. The fuel pump supplies fuel stored in the fuel tank to the fuel injector 51. The fuel injector 51 injects the fuel supplied from the fuel tank into the intake passage 31. The fuel injector 51 adjusts the amount of fuel injected based on the control of the control device 70. Furthermore, the fuel injector 51 is not limited to injecting fuel into the intake passage 31, and may be configured to inject fuel into the combustion chamber 13 or the intake port 16.

[0020] The sensor system detects the state of the vehicle 1 and transmits the detected results to the control device 70. The sensor system includes a crank angle sensor 61, a throttle opening sensor 62, an accelerator opening sensor 63, an air-fuel ratio sensor 64, an exhaust pressure sensor 65, and a filter temperature sensor 66. The sensor system also includes sensors that are normally included in the vehicle 1, such as an intake pressure sensor, an air flow meter, and an engine rotation speed sensor.

[0021] The crank angle sensor 61 detects the crank angle (the rotation angle of the crankshaft 14) and transmits information about the detected crank angle to the control device 70. The control device 70 controls the ignition timing of the spark plug 18 based on the information about the crank angle detected by the crank angle sensor 61.

[0022] The throttle opening sensor 62 detects the throttle opening of the throttle valve 34 and transmits information on the detected throttle opening of the throttle valve 34 to the control device 70 . The accelerator opening sensor 63 detects the stroke amount of the accelerator pedal and transmits information about the detected accelerator pedal stroke amount to the control device 70.

[0023] The air-fuel ratio sensor 64 detects the air-fuel ratio of the exhaust gas and transmits information on the detected air-fuel ratio of the exhaust gas to the control device 70. The exhaust pressure sensor 65 detects the pressure of the exhaust gas and transmits information on the detected exhaust gas pressure to the control device 70. The filter temperature sensor 66 detects the filter temperature of the filter 43 and transmits information on the detected filter temperature to the control device 70.

[0024] The control device 70 controls the entire vehicle 1 and the engine 10. For example, an ECU (Electronic Control Unit) can be used as the control device 70. The control device 70 has a CPU, ROM, RAM, etc. as its hardware configuration. The ROM stores programs and predetermined information for controlling the vehicle 1, the engine 10, etc. The RAM is a work memory that temporarily stores programs and data. The CPU reads out programs stored in the ROM, expands them into the RAM, and executes them to control the vehicle 1, the engine 10, etc.

[0025] FIG. 2 is a diagram illustrating an example of the functional configuration of the control device 70. As shown in FIG. The control device 70 includes a control unit 71 , a fuel cut unit 72 , and an estimation unit 73 . The control unit 71 controls the entire vehicle 1 and engine 10. The control unit 71 drives the engine 10 by controlling the injection timing and injection amount of fuel from the fuel injector 51, the ignition timing of the spark plug 18, the amount of intake air taken in by the intake system 30, and the like, in accordance with the amount of accelerator pedal stroke detected by the accelerator opening sensor 63. The control unit 71 also performs air-fuel ratio control based on information detected by the air-fuel ratio sensor 64, to control the air-fuel ratio to the stoichiometric air-fuel ratio, rich, or lean.

[0026] When a predetermined condition is met, fuel cut unit 72 limits the supply of fuel by fuel injector 51. Specifically, as an example of the predetermined condition, fuel cut unit 72 cuts off fuel injection by fuel injector 51 (hereinafter referred to as fuel cut) when the accelerator pedal is not operated and the engine speed is equal to or higher than a predetermined engine speed.

[0027] The estimation unit 73 estimates the soot accumulation amount of soot accumulated on the filter 43. Specifically, the estimation unit 73 estimates the soot accumulation amount based on information about the exhaust pressure detected by the exhaust pressure sensor 65. Note that the estimation unit 73 is not limited to estimating the soot accumulation amount based on information about the exhaust pressure detected by the exhaust pressure sensor 65, and can estimate the soot accumulation amount using an ultrasonic sensor or the like that can directly detect the soot accumulation amount on the filter 43, or can estimate the soot accumulation amount using a known method.

[0028] The control device 70 of this embodiment efficiently regenerates the filter 43 while preventing the filter temperature from rising excessively by performing air-fuel ratio control or control to prohibit fuel cutoff in accordance with the filter temperature and the amount of soot accumulated on the filter 43. The control device 70 stores a map that associates the filter temperature with the amount of soot accumulated. The map is divided into multiple regions according to the filter temperature and the amount of soot accumulated.

[0029] 3 is a diagram showing an example of a map divided into a plurality of regions according to the filter temperature and the amount of soot accumulation, where the vertical axis represents the filter temperature and the horizontal axis represents the amount of soot accumulation.

[0030] The first region is a region where the filter temperature is equal to or higher than a first predetermined temperature and the amount of soot accumulation is smaller than a second predetermined amount. When the filter temperature and the amount of soot accumulation correspond to the first region, the amount of soot accumulation is small, so there is no reduction in engine output, and there is little need to regenerate the filter 43.

[0031] The second region is a region where the filter temperature is lower than the first predetermined temperature and the amount of soot accumulation is equal to or less than the first predetermined amount. When the filter temperature is lower than the first temperature, it is difficult or impossible to burn the soot, so to regenerate the filter 43, the filter temperature needs to be equal to or higher than the first predetermined temperature.

[0032] The third region is a region where the filter temperature is higher than a variable predetermined temperature Tv determined according to the amount of soot accumulation, and the amount of soot accumulation is equal to or less than a first predetermined amount and equal to or greater than a second predetermined amount. Here, the variable predetermined temperature Tv is a threshold temperature that decreases as the amount of soot accumulation increases. When the filter temperature and the amount of soot accumulation correspond to the third region, the filter 43 needs to be regenerated, but the filter temperature needs to be lowered because the high filter temperature causes a reaction between fuel and oxygen at a temperature at which so-called afterburning is likely to occur.

[0033] The fourth region is a region where the amount of soot accumulation is greater than the first predetermined amount. When the amount of soot accumulation is greater than the first predetermined amount, the filter 43 is clogged, causing a decrease in engine output, and so the filter 43 needs to be regenerated. However, since burning the soot to regenerate the filter 43 tends to cause the filter temperature to overheat, it is necessary to suppress the overheating.

[0034] The fifth region is a region where the filter temperature is equal to or higher than the first predetermined temperature and equal to or lower than the variable predetermined temperature Tv, and the amount of soot is equal to or lower than the first predetermined amount and equal to or higher than the second predetermined amount. Since the amount of soot is equal to or higher than the second predetermined amount, it is necessary to regenerate the filter 43 so as not to reduce the engine output.

[0035] The information on the first predetermined temperature, the variable predetermined temperature Tv, the first predetermined amount, and the second predetermined amount in the map 80 shown in Figure 3 is set, for example, for each type of vehicle 1 and is stored in advance in the control device 70.

[0036] Fig. 4 is a flowchart showing an example of a regeneration process of the filter 43 by the control device 70. The flowchart of Fig. 4 is realized, for example, by the ECU, which is the control device 70, executing a program. The flowchart of Fig. 4 is initiated when the engine 10 is started.

[0037] In S10, the estimation unit 73 of the control device 70 estimates the amount of soot accumulated on the filter 43 based on information on the exhaust pressure detected by the exhaust pressure sensor 65. In S11, the control unit 71 of the control device 70 determines whether the soot accumulation amount estimated by the estimation unit 73 is greater than a first predetermined amount. If it is determined that the soot accumulation amount is greater than the first predetermined amount, the process proceeds to S12, and if not, the process proceeds to S13. Here, the case where the process proceeds to S12 is when the relationship between the filter temperature and the soot accumulation amount corresponds to the fourth region in the map 80 shown in FIG. 3.

[0038] In S12, the control unit 71 of the control device 70 executes air-fuel ratio control (lean control) so that the air-fuel ratio becomes lean. The control unit 71 also controls the fuel cut unit 72 to prohibit fuel cut. Therefore, even if a predetermined condition for fuel cut is met, the fuel cut unit 72 does not cut fuel, and thus exhaust gas always flows into the filter 43.

[0039] 3, in the fourth region where the amount of soot accumulation is large, by executing lean control, the oxygen contained in the exhaust gas increases above the stoichiometric air-fuel ratio, thereby increasing the amount of oxygen supplied to the filter 43 and raising the temperature of the exhaust gas. Therefore, the soot can be burned by the oxygen contained in the exhaust gas and the heated exhaust gas, thereby regenerating the filter 43. Furthermore, although the filter temperature is likely to rise excessively when the soot accumulation amount is large, prohibiting fuel cut prevents excessive supply of air (oxygen) to the filter 43, thereby suppressing the excessive rise in the filter temperature.

[0040] In S13, the control unit 71 of the control device 70 determines whether the filter temperature is lower than a first predetermined temperature. If it is determined that the filter temperature is lower than the first predetermined temperature, the process proceeds to S14, and if not, the process proceeds to S15. Here, the case where the process proceeds to S14 is when the relationship between the filter temperature and the amount of soot accumulation corresponds to the second region in the map 80 shown in FIG. 3.

[0041] In S14, the control section 71 of the control device 70 executes air-fuel ratio control (lean control) so that the air-fuel ratio becomes lean. In the second region where the filter temperature is low and soot is difficult or impossible to burn, as shown in Figure 3, the temperature of the exhaust gas can be raised by executing lean control. Therefore, the heated exhaust gas can quickly raise the filter temperature to a temperature at which soot can be burned. Furthermore, when a predetermined condition is met, the fuel cut unit 72 cuts fuel, thereby improving fuel efficiency.

[0042] In S15, the control unit 71 of the control device 70 determines whether the filter temperature is higher than the variable predetermined temperature Tv. If it is determined that the filter temperature is higher than the variable predetermined temperature Tv, the process proceeds to S16, and if not, the process proceeds to S17. Here, the case where the process proceeds to S16 is when the relationship between the filter temperature and the amount of soot accumulation corresponds to the third region in the map 80 shown in FIG. 3.

[0043] In S16, the control unit 71 of the control device 70 executes air-fuel ratio control (rich control) so that the air-fuel ratio becomes rich. The control unit 71 also controls the fuel cut unit 72 to prohibit fuel cut. Therefore, even if the predetermined conditions for fuel cut are met, the fuel cut unit 72 does not cut fuel, and thus exhaust gas always flows into the filter 43.

[0044] In the state of the third region as shown in Fig. 3, the filter temperature is high, so that the soot accumulated on the filter 43 is burned, thereby regenerating the filter 43. In addition, by performing rich control, the temperature of the exhaust gas can be lowered, and the lowered exhaust gas temperature can lower the filter temperature to a temperature at which fuel cut is possible. Furthermore, by prohibiting fuel cut, a large amount of air (oxygen) is not supplied to the filter 43, so afterburning caused by supplying a large amount of air to the filter 43 can be prevented.

[0045] In S17, the control unit 71 of the control device 70 determines whether the soot accumulation amount estimated by the estimation unit 73 is equal to or greater than a second predetermined amount. If it is determined that the soot accumulation amount is equal to or greater than the second predetermined amount, the process proceeds to S18, and if not, the process proceeds to S19. Here, the case where the process proceeds to S18 is when the relationship between the filter temperature and the soot accumulation amount corresponds to the fifth region in the map 80 shown in FIG. 3. On the other hand, the case where the process proceeds to S19 is when the relationship between the filter temperature and the soot accumulation amount corresponds to the first region in the map 80 shown in FIG. 3.

[0046] In S18, the control section 71 of the control device 70 executes air-fuel ratio control (lean control) so that the air-fuel ratio becomes lean. 3, in the fifth region where the amount of soot accumulation is large, executing lean control increases the amount of oxygen contained in the exhaust gas compared to the stoichiometric air-fuel ratio, which not only increases the amount of oxygen supplied to the filter 43 but also raises the temperature of the exhaust gas. Therefore, the soot can be burned by the oxygen contained in the exhaust gas and the heated exhaust gas, thereby regenerating the filter 43. Furthermore, when a predetermined condition is met, the fuel cut unit 72 cuts fuel, thereby improving fuel efficiency.

[0047] In S19, the control section 71 of the control device 70 executes air-fuel ratio control so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. In the first region state where the amount of soot accumulation is small as shown in Figure 3, there is no need to regenerate the filter 43, so by performing air-fuel ratio control based on the stoichiometric air-fuel ratio, it is possible to achieve both improved fuel efficiency and reduced harmful substances in the exhaust gas.

[0048] After executing steps S12, S14, S16, S18, and S19 in the flowchart of FIG. 4, the process returns to S10 and is repeated until the engine 10 is stopped, thereby preventing the filter temperature from rising excessively and efficiently regenerating the filter 43.

[0049] Thus, according to this embodiment, the control device 70 includes a fuel cut unit 72 that limits the supply of fuel by the fuel injector 51 when predetermined conditions are met, an estimation unit 73 that estimates the amount of soot accumulated in the filter 43, and a control unit 71 that prohibits the fuel cut unit 72 from limiting the supply of fuel even when the predetermined conditions are met, and controls the air-fuel ratio to be rich when the filter temperature of the filter 43 is higher than a variable predetermined temperature Tv that is determined according to the amount of soot accumulated in the filter 43 (S16). Therefore, the high filter temperature of the filter 43 burns the soot accumulated on the filter 43, and the filter 43 can be regenerated without complicating the structure. Also, by performing rich control, the temperature of the exhaust gas can be lowered, and the filter temperature can be lowered to a temperature at which fuel cut is possible. Furthermore, by prohibiting fuel cut, afterburning caused by supplying a large amount of air to the filter 43 can be prevented.

[0050] Furthermore, according to this embodiment, when the filter temperature of the filter 43 is lower than the first predetermined temperature, the control unit 71 controls the air-fuel ratio to be lean (S14). By controlling the air-fuel ratio to be lean, the temperature of the exhaust gas can be raised, and the heated exhaust gas can quickly raise the filter temperature to a temperature at which soot can be burned.

[0051] Furthermore, according to this embodiment, when the amount of soot accumulated on the filter 43 is greater than a first predetermined amount, the control unit 71 prohibits the fuel cut by the fuel cut unit 72 and controls the air-fuel ratio to be lean even if a predetermined condition is met (S12). By controlling the air-fuel ratio to be lean, it is possible to increase the oxygen supplied to the filter 43 and to raise the temperature of the exhaust gas. Therefore, the soot can be burned by the oxygen contained in the exhaust gas and the heated exhaust gas, and the filter 43 can be regenerated. Furthermore, prohibiting the fuel cut prevents an excessive supply of air (oxygen) to the filter 43, thereby suppressing an excessive rise in the filter temperature.

[0052] Furthermore, according to this embodiment, the control unit 71 controls the air-fuel ratio to be lean when the filter temperature of the filter 43 is equal to or higher than the first predetermined temperature and equal to or lower than the variable predetermined temperature Tv, and when the amount of soot accumulated on the filter 43 is equal to or lower than the first predetermined amount and equal to or higher than the second predetermined amount (S18). By controlling the air-fuel ratio to be lean, it is possible to increase the amount of oxygen supplied to the filter 43 and to raise the temperature of the exhaust gas. Therefore, the soot can be burned by the oxygen contained in the exhaust gas and the heated exhaust gas, and the filter 43 can be regenerated.

[0053] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and modifications and the like are possible within the scope of the present invention.

[0054] 3 in the above-described embodiment, the fifth region is described as a region where the filter temperature is equal to or higher than the first predetermined temperature, but this is not limited to this case and may be a region where the filter temperature is higher than the first predetermined temperature and higher than a second predetermined temperature that is lower than the variable predetermined temperature Tv. Also, the fifth region is described as a region where the filter temperature is equal to or higher than the second predetermined amount, but this second predetermined amount may be a soot accumulation amount that is greater than zero.

[0055] In the above-described embodiment, when the air-fuel ratio is controlled to be lean, the control unit 71 may control the air-fuel ratio so that the amount of oxygen supplied to the filter 43 increases as the amount of soot deposition increases. Furthermore, in the above-described embodiment, when the temperature of the engine body 11 is low, soot is likely to accumulate on the filter 43. Therefore, when the coolant temperature is lower than a predetermined temperature, the control unit 71 may control the air-fuel ratio to be lean, thereby raising the temperature of the exhaust gas and promoting the combustion of the soot accumulated on the filter 43. [Explanation of symbols]

[0056] 1: Vehicle 10: Engine (internal combustion engine) 11: Engine body 12: Piston 13: Combustion chamber 19: Intake valve 20: Exhaust valve 30: Intake system 34: Throttle valve 40: Exhaust system 43: Filter 50: Fuel system 51: Fuel injector 61: Crank angle sensor 62: Throttle opening sensor 63: Accelerator opening sensor 64: Air-fuel ratio sensor 65: Exhaust pressure sensor 66: Filter temperature sensor 70: Control device 71: Control unit 72: Fuel cut unit 73: Estimation unit

Claims

1. a fuel injector for supplying fuel to be mixed with intake air entering the internal combustion engine; a filter that collects soot contained in exhaust gas generated by combustion of a mixture of intake air and fuel in the internal combustion engine, The control device a fuel cutoff means for limiting the supply of fuel by the fuel injector when a predetermined condition is met; an estimation means for estimating the amount of soot accumulated on the filter; and a control means for prohibiting the fuel cut means from restricting the fuel supply and controlling the air-fuel ratio to be rich when the temperature of the filter is higher than a variable predetermined temperature determined in accordance with the amount of soot accumulated on the filter, even if the predetermined condition is met.

2. The control means 2. The control device for an internal combustion engine according to claim 1, wherein when the temperature of said filter is lower than a first predetermined temperature which is lower than said variable predetermined temperature, the air-fuel ratio is controlled to be lean.

3. The control means 3. The control device for an internal combustion engine according to claim 1, wherein when the amount of soot accumulated on the filter is greater than a first predetermined amount, the control device prohibits the fuel cut means from restricting the fuel supply and controls the air-fuel ratio to be lean even when the predetermined condition is met.

4. The control means 4. The control device for an internal combustion engine according to claim 3, wherein the air-fuel ratio is controlled to be lean when the temperature of the filter is equal to or higher than the first predetermined temperature and the amount of soot deposited on the filter is equal to or lower than the first predetermined amount but equal to or higher than a second predetermined amount that is smaller than the first predetermined amount.

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