JP2018096313A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of accurately detecting that particulate matters have been burned completely and completing adhered substance removal treatment at suitable timing when the adhered substance removal treatment of an oxidation catalyst deteriorated by adhesion of the particulate matters is performed.SOLUTION: In an exhaust emission control device 6 for an internal combustion engine 2, when determining that performance of an oxidation catalyst 27 has been deteriorated by adhesion of the particulate matters in exhaust gas to the oxidation catalyst 27, a control device 7 starts adhered substance removal treatment for burning the particulate matters by raising a temperature of the exhaust gas. After a predetermined time elapses after start of the adhered substance removal treatment, the control device acquires an outlet part temperature T2 from an outlet part temperature sensor 29, acquires an inlet part temperature T1 from an inlet part temperature sensor 28, and completes the adhered substance removal treatment when a temperature difference between the outlet part temperature T2 and the inlet part temperature T1 is smaller than a predetermined completion threshold value T5.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine that purifies exhaust gas discharged from the internal combustion engine.

An internal combustion engine is provided with an exhaust purification device for purifying exhaust gas. As this exhaust purification device, one having an oxidation catalyst is conventionally known. Due to its catalytic action, this oxidation catalyst changes harmful substances such as carbon monoxide (CO) and hydrocarbons (HC) contained in exhaust gas into harmless substances such as water (H ₂ O) and carbon dioxide (CO ₂ ). To purify the exhaust.

  When such an oxidation catalyst is deteriorated by adhering particulate matter (PM) such as soot contained in exhaust gas, the catalytic action is impaired. Therefore, when deterioration of the oxidation catalyst due to such particulate matter adhesion is detected, the temperature of the exhaust gas exhausted from the internal combustion engine is raised, and the particulate matter adhered to the oxidation catalyst is burned to oxidize. A deposit removing process for recovering the catalytic action of the catalyst is performed.

  Here, in order to detect the deterioration of the oxidation catalyst due to the adhesion of the particulate matter, the temperature difference between the upstream side and the downstream side of the oxidation catalyst is acquired, and when this temperature difference becomes a predetermined threshold value or less, An exhaust gas purification apparatus for an internal combustion engine that determines that an oxidation catalyst has deteriorated has been proposed (see, for example, Patent Document 1).

JP, 2006-053351, A

  However, in conventional exhaust gas purification devices for internal combustion engines, it is difficult to accurately detect that the particulate matter has completely burned when performing the removal treatment of the deposit of the oxidation catalyst that has deteriorated due to the attachment of the particulate matter. There was a problem that it was difficult to finish the deposit removal process at a suitable timing. As a result, if the timing for ending the deposit removal process is too early, deposits remain and the catalytic action of the oxidation catalyst is not sufficiently recovered. On the other hand, if the timing for ending the deposit removal process is too late, the exhaust loss increases due to the exhaust gas temperature rise in the deposit removal process, resulting in a problem that the fuel consumption of the internal combustion engine deteriorates.

  Therefore, the present invention was created in view of such circumstances, and its purpose is to accurately detect that the particulate matter has completely combusted when performing the removal treatment of the deposit of the oxidation catalyst that has deteriorated due to the adhesion of the particulate matter. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine capable of terminating the deposit removal process at a suitable timing.

According to one aspect of the invention,
An exhaust gas purification device for an internal combustion engine that purifies exhaust gas discharged from the internal combustion engine,
An exhaust passage through which exhaust flows;
An oxidation catalyst which is provided in the exhaust passage and oxidizes a substance flowing through the exhaust passage;
An inlet temperature sensor provided at the inlet of the oxidation catalyst in the exhaust passage;
An outlet temperature sensor provided at an outlet of the oxidation catalyst in the exhaust passage;
A control device that acquires the inlet temperature of the exhaust from the inlet temperature sensor, and acquires the outlet temperature of the exhaust from the outlet temperature sensor;
With
The control device is
When it is determined that the performance of the oxidation catalyst has deteriorated due to the particulate matter in the exhaust gas adhering to the oxidation catalyst, the deposit removal process for burning the particulate matter by starting the exhaust temperature is started. And
After a predetermined time has elapsed since the start of the deposit removing process, the outlet temperature is acquired from the outlet temperature sensor and the inlet temperature is acquired from the inlet temperature sensor.
When the temperature difference between the outlet portion temperature and the inlet portion temperature is smaller than a predetermined end threshold, the deposit removing process is ended.

In the exhaust gas purification apparatus for an internal combustion engine according to one aspect of the present invention,
The control device is
When the temperature difference between the outlet portion temperature and the inlet portion temperature is smaller than a predetermined start threshold value, it is possible to determine that the performance of the oxidation catalyst has deteriorated and start the deposit removing process.

In the exhaust gas purification apparatus for an internal combustion engine according to one aspect of the present invention,
The end threshold value may be determined based on an operating state of the internal combustion engine.

In the exhaust gas purification apparatus for an internal combustion engine according to one aspect of the present invention,
The end threshold value may be determined based on a rotation speed of the internal combustion engine and a target fuel injection amount.

In the exhaust gas purification apparatus for an internal combustion engine according to one aspect of the present invention,
The start threshold value may be determined based on a rotation speed of the internal combustion engine and a target fuel injection amount.

  According to the exhaust gas purification apparatus for an internal combustion engine according to one aspect of the present invention, when the deposit removal process of the oxidation catalyst deteriorated due to the adhesion of the particulate matter is performed, it is accurately detected that the particulate matter is completely burned. Thus, the deposit removal process can be terminated at a suitable timing. Thereby, it is possible to prevent the deposit removal process from being incomplete, and it is possible to avoid deterioration of the fuel consumption of the internal combustion engine by performing the deposit removal process excessively.

1 is a schematic diagram showing an internal combustion engine system including an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention. It is the flowchart which showed the flow of the diagnostic process of an oxidation catalyst. 2 is a diagram conceptually showing a map of a target injection amount Q1 of fuel in a cylinder 11 according to an accelerator opening Ac and a rotational speed Ne of an internal combustion engine 2. FIG. It is a figure which shows notionally the map of the instantaneous value of the phosphorus poisoning amount of the oxidation catalyst 27 according to the target injection quantity Q1 and the rotational speed Ne of an internal combustion engine. 3 is a diagram conceptually showing a map of a deterioration determination threshold value T4 according to a target injection amount Q1 and a rotational speed Ne of the internal combustion engine 2. FIG. It is a graph which shows the relationship between the elapsed time t from the start of a deposit removal process, and the inlet part temperature T1 and outlet part temperature T2 of an oxidation catalyst. FIG. 4 is a diagram conceptually showing a map of an end threshold value T5 according to a target injection amount Q2 and a rotational speed Ne of the internal combustion engine 2.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

(Configuration of internal combustion engine system)
First, the configuration of an internal combustion engine system including an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention will be described. FIG. 1 is a schematic diagram showing an internal combustion engine system according to an embodiment of the present invention. The internal combustion engine system 1 is provided by connecting an internal combustion engine 2, an intake passage 3 connected to the internal combustion engine 2, an exhaust passage 4 connected to the internal combustion engine 2, and an intake passage 3 and an exhaust passage 4. The EGR device 5, the exhaust purification device 6 provided in the exhaust passage 4, and a control device 7 electrically connected to each part are provided.

  The internal combustion engine 2 is a 4-cylinder compression ignition internal combustion engine mounted on a vehicle, that is, a diesel engine. As shown in FIG. 1, the internal combustion engine 2 includes an internal combustion engine main body 8, a fuel injection device 9, and a rotation speed sensor 10. Although the illustrated example shows an in-line four-cylinder internal combustion engine 2, the cylinder arrangement type, the number of cylinders, and the like of the internal combustion engine 2 are arbitrary.

  Although not shown in detail in the figure, the internal combustion engine main body 8 includes structural parts such as a cylinder head, a cylinder block, and a crankcase, and movable parts such as a piston, a crankshaft, and a valve housed therein. As shown in FIG. 1, four cylinders 11 are formed in the internal combustion engine body 8.

  The fuel injection device 9 is a so-called common rail fuel injection device, and plays a role of injecting fuel into the cylinder 11. As shown in FIG. 1, the fuel injection device 9 includes a common rail 12 that stores fuel in a high-pressure state, four injectors 13 that are connected to the common rail 12 and inject fuel into the four cylinders 11, respectively. have.

  The rotation speed sensor 10 serves to detect a rotation speed (rpm) per unit time that is the rotation speed of the internal combustion engine 2. As shown in FIG. 1, the rotational speed sensor 10 is electrically connected to the control device 7, and the detection result is input to the control device 7.

  The intake passage 3 serves to supply intake air sucked from the outside to each cylinder 11 of the internal combustion engine 2. As shown in FIG. 1, the intake passage 3 includes an intake manifold 14 connected to the internal combustion engine body 8 (particularly a cylinder head), and an intake pipe 16 having one end connected to the intake manifold 14. Yes.

  The exhaust passage 4 serves to discharge the exhaust discharged from the internal combustion engine 2 to the outside. As shown in FIG. 1, the exhaust passage 4 has an exhaust manifold 17 connected to the internal combustion engine body 8 (particularly a cylinder head), and an exhaust pipe 19 having one end connected to the exhaust manifold 17. ing.

  The EGR device 5 serves to recirculate a part of the exhaust gas in the exhaust passage 4 (referred to as “EGR gas”) into the intake passage 3. As shown in FIG. 1, the EGR device 5 includes an EGR passage 20 having one end connected to the exhaust manifold 17 and the other end connected to the intake manifold 14, and an EGR cooler 21 that cools the EGR gas flowing through the EGR passage 20. And an EGR valve 22 provided on the downstream side of the EGR cooler 21 for adjusting the flow rate of the EGR gas. According to such an EGR device 5, the EGR gas is recirculated to reduce the oxygen concentration in the intake air, thereby lowering the combustion temperature in the cylinder 11 and reducing nitrogen oxide in the exhaust gas. it can.

  The exhaust purification device 6 plays a role of purifying exhaust gas flowing through the exhaust pipe 19. The exhaust purification device 6 includes an oxidation catalyst unit 23 provided at a predetermined position of the exhaust pipe 19 and a particulate filter unit 24 (hereinafter referred to as “DPF unit 24”) provided at a position downstream of the oxidation catalyst unit 23. And a NOx catalyst unit 25 provided at a position further downstream from the DPF unit 24 and an ammonia oxidation catalyst 26 provided at a position further downstream from the NOx catalyst unit 25.

  As shown in FIG. 1, the oxidation catalyst unit 23 includes an oxidation catalyst 27, an inlet temperature sensor 28 that is provided at the inlet of the oxidation catalyst 27 and detects the inlet temperature T1, and an outlet of the oxidation catalyst 27. And an outlet temperature sensor 29 that detects the outlet temperature T2. According to the oxidation catalyst unit 23 configured in this way, the exhaust gas is purified by oxidizing the carbon monoxide (CO) and hydrocarbon (HC) in the exhaust gas flowing through the exhaust pipe 19 by the oxidation catalyst 27. In addition, the temperature of the exhaust is raised by oxidizing the fuel and the like in the exhaust by the oxidation catalyst 27.

  As shown in FIG. 1, the DPF unit 24 includes a particulate filter 30 (hereinafter referred to as “DPF 30”) and a differential pressure sensor 31 provided across the upstream side and the downstream side of the DPF 30. Yes. According to the DPF unit 24 configured in this way, particulate matter such as soot contained in the exhaust gas is collected by the DPF 30 and removed from the exhaust gas. Further, the differential pressure of the exhaust gas upstream and downstream of the DPF 30 is detected by the differential pressure sensor 31, and the amount of particulate matter accumulated in the DPF 30 is estimated based on the detection result. When the accumulated amount exceeds a predetermined amount, the control device 7 executes filter regeneration control for recovering the PM collecting ability of the DPF 30 by forcibly burning and removing the accumulated particulate matter.

  As shown in FIG. 1, the NOx catalyst unit 25 includes a selective reduction type NOx catalyst 32 (hereinafter abbreviated as “SCR32: Selective Catalytic Reduction”) and an addition valve 33 provided at the inlet of the SCR 32. doing. According to the NOx catalyst unit 25 configured as described above, when urea water as a reducing agent is added from the addition valve 33 to the SCR 32, ammonia is generated by hydrolysis of the urea water. The ammonia reacts with NOx in the exhaust, whereby NOx is reduced.

  The ammonia oxidation catalyst 26 plays a role of purifying exhaust gas by oxidizing excess ammonia discharged from the SCR 32. Thereby, it is suppressed that ammonia is discharged outside the internal combustion engine system 1.

  The control device 7 plays a role of acquiring detection results from various sensors and controlling the operation of each unit based on the detection results. As shown in FIG. 1, the control device 7 includes various parts constituting the internal combustion engine system 1, for example, a rotational speed sensor 10 of the internal combustion engine 2, an EGR valve 22 of the EGR device 5, and an inlet temperature sensor of the oxidation catalyst unit 23. 28, the outlet temperature sensor 29, the differential pressure sensor 31 of the DPF unit 24, and the addition valve 33 of the NOx catalyst unit 25 are electrically connected. The control device 7 is also electrically connected to an accelerator opening sensor 34 that detects the accelerator opening. The detection result of the accelerator opening sensor 34 can be acquired. Then, the control device 7 acquires detection results from the rotation speed sensor 10, the inlet temperature sensor 28, the outlet temperature sensor 29, the differential pressure sensor 31, and the accelerator opening sensor 34, and based on the detection results, the injector 7 13, the operation of the EGR valve 22, the addition valve 33 and the like are controlled.

(Oxidation catalyst diagnostic process)
Next, the flow of diagnostic processing for the oxidation catalyst 27 constituting the exhaust gas purification device 6 will be described. FIG. 2 is a flowchart showing the flow of diagnostic processing for the oxidation catalyst 27. When the diagnosis process is started, the control device 7 first acquires the exhaust inlet temperature T1 from the inlet temperature sensor 28 of the oxidation catalyst unit 23 (S1).

  Then, the control device 7 determines whether or not the acquired inlet portion temperature T1 is greater than a predetermined deterioration determination start threshold T3 (S2). As a result, when it is determined that the inlet temperature T1 is equal to or lower than the deterioration determination start threshold T3 (S2: No), the control device 7 returns to S1 and acquires the exhaust inlet temperature T1 again, and then in S2. The process of determining whether the inlet temperature T1 is greater than the deterioration determination start threshold T3 is repeated. This deterioration determination start threshold T3 is set to be equal to or higher than the activation start temperature of the oxidation catalyst 27.

  Thereafter, when it is determined in S2 that the inlet temperature T1 is higher than the deterioration determination start temperature T3 (S2: Yes), the control device 7 acquires the exhaust outlet temperature T2 from the outlet temperature sensor 29 of the oxidation catalyst unit 23. At the same time, the phosphorus poisoning amount integrated value P1 of the oxidation catalyst 27 is acquired (S3). For example, when an engine oil additive containing phosphorus is used, phosphorus may be contained in the exhaust gas. In such a case, the oxidation catalyst 27 may be deteriorated due to poisoning of the oxidation catalyst 27 by phosphorus in the exhaust gas. Therefore, when the oxidation catalyst 27 is deteriorated, the phosphorus poisoning amount integrated value P1 is acquired in this step S3 in order to determine whether the deterioration is due to phosphorus poisoning in a later step S5.

  Here, the phosphorus poisoning amount integrated value P <b> 1 is estimated by the control device 7 based on the operating conditions of the internal combustion engine 2. More specifically, the control device 7 first acquires the rotational speed Ne of the internal combustion engine 2 from the rotational speed sensor 10 shown in FIG. 1 and also acquires the accelerator opening Ac from the accelerator opening sensor 34. On the other hand, the map shown in FIG. 3 is stored in advance in the storage unit 35 included in the control device 7. In this map, details are not shown, but the fuel injection amount of the injector 13, specifically, at each lattice point of the rotational speed Ne of the internal combustion engine 2 shown on the horizontal axis and the accelerator opening degree Ac shown on the vertical axis. Specifically, the fuel target injection amount Q1 (calculated in advance by experiments or the like), which is an instruction value to the injector 13, is input. By referring to this map, the control device 7 acquires the target injection amount Q1 corresponding to the acquired accelerator opening Ac and the rotational speed Ne of the internal combustion engine. Further, a map shown in FIG. 4 is also stored in advance in the storage unit 35 of the control device 7. In this map, details are not shown in the figure, but the phosphorus poisoning amount received by the oxidation catalyst 27 at the lattice point between the rotational speed Ne of the internal combustion engine shown on the horizontal axis and the target injection amount Q1 shown on the vertical axis. Each instantaneous value is input. By referring to this map, the control device 7 acquires the instantaneous value of the phosphorus poisoning amount at the calculation time of the control device 7, and acquires the acquired instantaneous value for each calculation cycle of the control device 7 (for example, every 10 milliseconds). ) To estimate the phosphorus poisoning amount integrated value P1. In addition, the acquisition method of phosphorus poisoning amount integrated value P1 is not restricted to this. For example, a map is created in which the phosphorus poisoning amount per unit cycle (for example, 1 second) according to various operating conditions (rotational speed Ne, fuel injection amount, inlet temperature T1, etc.) is created. On the other hand, an operation condition is acquired for each calculation cycle (for example, every 10 milliseconds), an average value in the unit cycle is calculated, and a phosphorus poisoning amount corresponding to the average value is acquired from the map. Then, the phosphorus poisoning amount integrated value P1 may be acquired by integrating the phosphorus poisoning amount acquired in this way every time the unit period elapses.

  Next, the control device 7 determines whether or not the value of the temperature difference T2-T1 between the acquired outlet temperature T2 and the previously acquired inlet temperature T1 is smaller than a predetermined deterioration determination threshold value T4 (S4). ). As a result, when it is determined that the value of the temperature difference T2-T1 is equal to or greater than the deterioration determination threshold value T4 (S4: No), the control device 7 determines that the oxidation catalyst 27 has not deteriorated and ends the diagnosis process. . On the other hand, when it is determined that the value of the temperature difference T2-T1 is smaller than the deterioration determination threshold T4 (S4: Yes), the control device 7 determines that the oxidation catalyst 27 has deteriorated and proceeds to the next step S5. .

  The deterioration determination threshold value T4 may be changed according to the operating state of the internal combustion engine 2, the exhaust component, the temperature, and the like. The map shown in FIG. 5 is stored in the storage unit 35 of the control device 7 shown in FIG. Although details are not shown in this map, the deterioration determination threshold value T4 (experiment or the like) is set at each lattice point of the rotational speed Ne of the internal combustion engine 2 shown on the horizontal axis and the target injection amount Q1 shown on the vertical axis. Are calculated in advance). The control device 7 obtains the rotational speed Ne of the internal combustion engine 2 from the rotational speed sensor 10 shown in FIG. 1 and the accelerator opening degree Ac from the accelerator opening sensor 34, and refers to the map of FIG. The optimum target injection amount Q1 in the state is acquired. Further, the control device 7 refers to the map of FIG. 5 based on the rotational speed of the internal combustion engine 2 detected by the rotational speed sensor 10 and the target injection amount Q1 obtained from the map of FIG. An optimum deterioration determination threshold value T4 in the state is acquired. The method for obtaining the deterioration determination threshold value T4 is not limited to this. For example, a map in which the deterioration determination threshold value T4 corresponding to the inlet temperature T1 and the rotation speed Ne is input, or the inlet temperature T1 and the cylinder 11 are used. It is also possible to obtain a deterioration determination threshold value T4 by creating a map in which the deterioration determination threshold value T4 corresponding to the fuel injection amount (command value) is input and referring to the map.

  Next, the control device 7 determines whether or not the phosphorus poisoning amount integrated value P1 of the oxidation catalyst 27 acquired in S3 shown in FIG. 2 is larger than a preset phosphorus poisoning amount threshold value P2 (S5). ). As a result, when it is determined that the phosphorus poisoning amount integrated value P1 is larger than the phosphorus poisoning amount threshold value P2 (S5: Yes), the control device 7 determines that the cause of the deterioration of the oxidation catalyst 27 is phosphorus poisoning. Then, a harmful substance emission reduction process is executed (S6). That is, since deterioration due to phosphorus poisoning is irreversible deterioration, the control device 7 determines that it is difficult to recover the performance of the oxidation catalyst 27, and is included in the exhaust discharged from the internal combustion engine 2 instead of the performance recovery. Execute hazardous substance emission reduction processing for the purpose of reducing the amount of harmful substances produced. The phosphorus poisoning amount threshold value P2 is set to an appropriate value in advance through experiments, simulations, and the like, and is stored in the storage unit 35 of the control device 7.

  Here, the control device 7 executes both so-called EGR gas reduction processing and combustion advance processing as the harmful substance emission reduction processing. Note that the harmful substance emission reduction process is not limited to this, and for example, one of the EGR gas reduction process and the combustion advance process may be executed, or another method may be executed.

  The EGR gas reduction process is a process of reducing the amount of EGR gas recirculated to the intake passage 3 by the EGR device 5 shown in FIG. More specifically, during normal operation of the internal combustion engine system 1, the control device 7 controls the opening degree of the EGR valve 22 according to a predetermined EGR valve opening degree map (not shown) stored in advance in the storage unit 35. By doing so, the recirculation amount of the EGR gas to the intake passage 3 is controlled. On the other hand, when the EGR gas reduction process is executed, the control device 7 corrects the opening degree of the EGR valve 22 in the EGR valve opening degree map to a valve closing side by a predetermined amount from that in the normal operation. Thereby, the opening degree of the EGR valve 22 is controlled to the valve closing side by a predetermined amount, and the recirculation amount of the EGR gas to the intake passage 3 is reduced from the value during normal operation. According to such an EGR gas reduction process, the amount of EGR gas introduced into the cylinder 11 shown in FIG. 1 is reduced, so that the fuel combustion temperature in the cylinder 11 rises and the oxygen supply amount to the cylinder 11 also increases. Therefore, the combustion state of the fuel in the cylinder 11 becomes good. And since the combustion state of a fuel becomes favorable in this way, the discharge | emission amount of the harmful substance which should be processed with the oxidation catalyst 27, such as carbon monoxide and a hydrocarbon, is reduced.

  The combustion advance process is a process for advancing the fuel start timing of the fuel in the cylinder 11 by advancing the fuel supply timing to the cylinder 11 shown in FIG. More specifically, during normal operation of the internal combustion engine system 1, the control device 7 performs main fuel injection into the cylinder 11 according to a predetermined fuel injection timing map (not shown) stored in advance in the storage unit 35. The timing is controlled. On the other hand, when the combustion advance processing is executed, the control device 7 corrects the start timing of the main injection of the fuel in the fuel injection timing map by a predetermined amount from the normal operation to the advance side, so that The start timing of fuel supply is advanced from the value during normal operation. As a result, the combustion time of the fuel in the cylinder 11 becomes longer, and the combustion state of the fuel becomes better. And since the combustion state of a fuel becomes favorable in this way, the discharge | emission amount of the harmful substance which should be processed with the oxidation catalyst 27, such as carbon monoxide and a hydrocarbon, is reduced.

  On the other hand, as a result of the determination in S5 of FIG. 2, when it is determined that the phosphorus poisoning amount integrated value P1 is equal to or less than the phosphorus poisoning amount threshold value P2 (S5: No), the control device 7 indicates that the oxidation catalyst 27 has deteriorated. Is determined not to be due to phosphorus poisoning but to cause particulate matter such as soot in the exhaust to adhere to the oxidation catalyst 27. As a result, the control device 7 starts a deposit removal process, that is, a process of removing particulate matter from the oxidation catalyst 27 (S7). This deposit removal process is performed by raising the temperature of the exhaust discharged from the internal combustion engine 2 and burning the particulate matter adhered to the oxidation catalyst 27.

  Here, as an example of means for increasing the temperature of the exhaust, the control device 7 delays the start timing of the main injection of fuel into the cylinder 11 shown in FIG. Delay). According to this, the exhaust gas temperature in the internal combustion engine 2 increases, so that the temperature of the exhaust gas can be raised.

  As another means for increasing the temperature of the exhaust gas, the control device 7 increases the fuel injection amount in the after-injection in the cylinder 11 after the main fuel injection than in the normal operation. Let According to this, the heat generation amount in the expansion process inside the cylinder 11 is increased, and the exhaust loss in the internal combustion engine 2 is increased, whereby the temperature of the exhaust can be raised.

  Further, as another means for increasing the temperature of the exhaust, the control device 7 decreases the fuel pressure inside the common rail 12 shown in FIG. 1, that is, the common rail 12 pressure. According to this, when the fuel injection amount into the cylinder 11 is fixed, the time required for fuel injection becomes longer and the fuel combustion time becomes longer, so that the exhaust loss increases. Therefore, the exhaust gas temperature can be raised as in the case of retarding at the start of main injection.

  Next, the control device 7 determines whether or not the elapsed time t from the start of the deposit removal process is greater than a predetermined time threshold t1 (S8). As a result, when it is determined that the value of the elapsed time t is equal to or less than the time threshold t1 (S8: No), the control device 7 returns to S8 and waits until the elapsed time t becomes larger than the time threshold t1. On the other hand, if it is determined in S8 that the elapsed time t is greater than the time threshold t1 (S8: Yes), the control device 7 proceeds to the next step S9.

  Next, the control device 7 obtains the inlet temperature T1 again from the inlet temperature sensor 28 shown in FIG. 1 and also obtains the outlet temperature T2 from the outlet temperature sensor 29 again (S9). Then, the control device 7 determines whether or not the value of the temperature difference T2-T1 between the inlet temperature T1 and the outlet temperature T2 acquired in S9 is smaller than a predetermined end threshold T5 (S10). As a result, when it is determined that the value of the temperature difference T2-T1 is equal to or greater than the end threshold value T5 (S10: No), the control device 7 returns to S9 and repeats the subsequent processing. On the other hand, as a result of the determination in S10, when it is determined that the value of the temperature difference T2-T1 is smaller than the end threshold value T5 (S10: Yes), the control device 7 ends the deposit removal process, Returning to the control state during operation, the temperature rise of the exhaust is stopped (S11).

  Here, FIG. 6 is a graph showing the relationship between the elapsed time t from the start time tst of the deposit removal process and the inlet temperature T1 and outlet temperature T2 of the oxidation catalyst 27. When the deposit removing process is started at tst, the inlet temperature T1 in the illustrated example continues to be a constant value, but the outlet temperature T2 gradually increases as the burning of the deposit progresses inside the oxidation catalyst 27. It rises. Thereby, the value of temperature difference T2-T1 becomes large gradually as time passes. However, when the deposits are burned and the remaining amount of deposits decreases, the burnout of deposits gradually converges, and the outlet temperature T2 gradually decreases. Thereby, the value of temperature difference T2-T1 becomes small gradually with progress of time. Based on such a tendency, the control device 7 is after the time threshold t1 has elapsed from the start of the deposit removal process, that is, the outlet temperature T2 is decreasing, and the temperature difference T2 At t2 where −T1 becomes smaller than the end threshold value T5, it is determined that most of the deposits burned and the performance of the oxidation catalyst 27 has almost recovered, and the deposit removal process is terminated. As a result, as shown in FIG. 4, the controller 7 erroneously determines that the performance of the oxidation catalyst 27 has recovered before t0, which is a region where the temperature difference T2-T1 is smaller than the end threshold value T5, and performs the deposit removal process. Termination is prevented.

  The end threshold value T5 may be changed according to the operating state of the internal combustion engine 2, the exhaust component, the temperature, and the like. The map shown in FIG. 7 is stored in the storage unit 35 of the control device 7 shown in FIG. Although not shown in detail in this map, an end threshold value T5 (by experiment or the like) is set at each lattice point of the rotational speed Ne of the internal combustion engine 2 shown on the horizontal axis and the target injection amount Q1 shown on the vertical axis. (Calculated in advance) are input respectively. The control device 7 obtains the rotational speed Ne of the internal combustion engine 2 from the rotational speed sensor 10 shown in FIG. 1 and the accelerator opening degree Ac from the accelerator opening sensor 34, and refers to the map of FIG. The optimum target injection amount Q1 in the state is acquired. Then, the control device 7 refers to the map of FIG. 7 based on the rotational speed Ne of the internal combustion engine 2 detected by the rotational speed sensor 10 and the target injection amount Q1 obtained from the map of FIG. An optimal end threshold value T5 in the driving state is acquired.

  Thus, the diagnostic process for the oxidation catalyst 27 is completed.

  According to such a diagnostic process of the oxidation catalyst 27, when the deposit removal process of the oxidation catalyst 27 deteriorated due to the adhesion of the particulate matter is performed, the temperature difference T2-T1 between the inlet temperature T1 and the outlet temperature T2 is By detecting that it has become smaller than the end threshold value T5, it is possible to accurately detect that the particulate matter has completely combusted. Therefore, the catalytic action of the oxidation catalyst 27 can be quickly and reliably recovered by terminating the deposit removal process at a suitable timing.

(Modification)
As mentioned above, although embodiment of this invention was described in detail, the modification as shown below is also considered as embodiment of this invention.

  (1) In the present embodiment, the timing for ending the deposit removal process is determined based on the temperature difference between the outlet temperature T2 and the inlet temperature T1 of the oxidation catalyst 27. If the inlet temperature T1 is limited to some extent, the timing for ending the deposit removal process may be determined based only on the outlet temperature T2.

  (2) In the present embodiment, as shown in FIG. 2, when it is determined that the inlet temperature T1 is larger than a predetermined deterioration determination start threshold T3, the outlet temperature T2 and the phosphorus poisoning amount integrated value P1 are acquired. did. However, the timing for obtaining the outlet temperature T2 and the phosphorus poisoning amount integrated value P1 may be the same as the time when the inlet temperature T1 is obtained in S1.

2 Internal combustion engine 4 Exhaust passage 6 Exhaust purification device 7 Control device 27 Oxidation catalyst 28 Inlet temperature sensor 29 Outlet temperature sensor T1 Inlet temperature T2 Outlet temperature T3 Start threshold T5 End threshold Ne Rotational speed Q1 of internal combustion engine Target injection amount

Claims (5)

An exhaust gas purification device for an internal combustion engine that purifies exhaust gas discharged from the internal combustion engine,
An exhaust passage through which exhaust flows;
An oxidation catalyst which is provided in the exhaust passage and oxidizes a substance flowing through the exhaust passage;
An inlet temperature sensor provided at the inlet of the oxidation catalyst in the exhaust passage;
An outlet temperature sensor provided at an outlet of the oxidation catalyst in the exhaust passage;
A control device that acquires the inlet temperature of the exhaust from the inlet temperature sensor, and acquires the outlet temperature of the exhaust from the outlet temperature sensor;
With
The control device is
When it is determined that the performance of the oxidation catalyst has deteriorated due to the particulate matter in the exhaust gas adhering to the oxidation catalyst, the deposit removal process for burning the particulate matter by starting the exhaust temperature is started. And
After a predetermined time has elapsed since the start of the deposit removing process, the outlet temperature is acquired from the outlet temperature sensor and the inlet temperature is acquired from the inlet temperature sensor.
The exhaust gas purification apparatus for an internal combustion engine, wherein when the temperature difference between the outlet portion temperature and the inlet portion temperature is smaller than a predetermined end threshold value, the deposit removing process is ended. The control device is
When the temperature difference between the outlet portion temperature and the inlet portion temperature is smaller than a predetermined start threshold value, it is determined that the performance of the oxidation catalyst has deteriorated, and the deposit removing process is started. 2. An exhaust emission control device for an internal combustion engine according to 1.   The exhaust purification device for an internal combustion engine according to claim 1 or 2, wherein the end threshold value is determined based on an operating state of the internal combustion engine.   The exhaust purification device for an internal combustion engine according to claim 3, wherein the end threshold value is determined based on a rotation speed of the internal combustion engine and a target injection amount of fuel.   The exhaust purification device for an internal combustion engine according to any one of claims 2 to 4, wherein the start threshold value is determined based on a rotation speed of the internal combustion engine and a target fuel injection amount.

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