JP6569873B2 - Engine exhaust purification system - Google Patents

Description

  The present invention relates to an engine exhaust purification device that reduces NOx stored in a NOx catalyst by setting an air-fuel ratio of exhaust gas to a target air-fuel ratio that can reduce NOx.

Conventionally, in a lean state where the air-fuel ratio of the exhaust gas is larger than the stoichiometric air-fuel ratio (1 <λ), NOx in the exhaust gas is occluded and the air-fuel ratio of the exhaust gas is in the vicinity of the stoichiometric air-fuel ratio (λ≈ 1) Or, in a state richer than the stoichiometric air-fuel ratio (λ <1), NOx occlusion reduction type that reacts with carbon monoxide (CO) or hydrocarbon (HC) and occluded NOx to reduce it to nitrogen (N ₂ ). NOx catalysts are known.
In the normal operating range, from the viewpoint of improving fuel efficiency, the engine is operated with the air-fuel ratio set to a lean state. However, if the lean operating state continues, the NOx occlusion amount of the NOx catalyst exceeds the allowable amount. And the NOx catalyst cannot store NOx in the exhaust gas.
Therefore, in addition to the main injection amount corresponding to the required torque, the post-injection in which fuel is separately injected in the expansion stroke is performed to set the air-fuel ratio to a state richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio. By reducing the NOx stored in the catalyst, the NOx catalyst is regenerated as appropriate.

By the way, even if it is possible to perform rich spike operation in which the air-fuel ratio is made richer than the theoretical air-fuel ratio by post-injection because the temperature of the NOx catalyst has increased to a reproducible temperature, A relatively large amount of black smoke may be generated as the air-fuel ratio becomes richer.
The engine exhaust gas purification apparatus of Patent Document 1 monitors the exhaust temperature, the supply air temperature, etc. as the temperature correlation value in the cylinder as the operation history, and when this temperature exceeds a predetermined temperature, the temperature in the cylinder rises. It is forbidden to run rich spikes.
Thereby, the generation amount of black smoke is suppressed quickly and reliably.

JP 2004-340003 A

When the exhaust pipe constituting at least a part of the exhaust passage is replaced, a phenomenon occurs in which white smoke is generated over a predetermined period after the new exhaust pipe is attached.
This is because the exhaust pipe is made of a metal material (for example, steel), and in the case of a new exhaust pipe, it is stored in a warehouse or the like with a rust inhibitor applied on the surface. .
That is, the rust preventive agent is composed of the base component solvent and lubricating oil, and the additive component rust preventive additive, oil film conditioner, antioxidant, metal deactivation, etc., and the base component solvent This is because the main component of the lubricating oil corresponds to hydrocarbons.
When post injection is performed to increase the air-fuel ratio in the expansion stroke for regeneration of the NOx catalyst, the rust preventive agent containing a large amount of hydrocarbons evaporates in the exhaust gas as the exhaust gas temperature rises rapidly. This is because the air-fuel ratio of the exhaust gas greatly exceeds the target air-fuel ratio and the hydrocarbons in the exhaust gas increase.

Therefore, it is conceivable to set the post injection amount in consideration of evaporation of the rust preventive agent in advance.
However, this white smoke phenomenon ends when all of the rust preventive agent applied to the exhaust pipe evaporates. Therefore, when the post-injection amount considering the rust preventive agent is set uniformly, the evaporation of the rust preventive agent ends. Thereafter, the hydrocarbons in the exhaust gas necessary for regeneration of the NOx catalyst may be insufficient, resulting in poor regeneration.
In addition, even after the exhaust pipe has been replaced, if a diesel particulate filter (DPF: Diesel Particulate Filter) regeneration process is performed, all of the rust inhibitor is removed by evaporation due to the high exhaust gas temperature. No white smoke is generated.
That is, in terms of emissions, there is a demand for the rapid establishment of a technology that achieves both regeneration of the NOx catalyst and prevention of white smoke.

  An object of the present invention is to provide an engine exhaust purification device and the like that can achieve both regeneration of a NOx catalyst and prevention of white smoke.

The engine exhaust gas purification apparatus according to claim 1 is provided in the exhaust passage of the engine and stores NOx in the exhaust gas and exhausts the stored NOx when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio. The NOx catalyst that reduces when the air-fuel ratio of the gas is near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio, and when the reduction purification condition of the NOx catalyst is satisfied, the air-fuel ratio of the exhaust gas is occluded in the NOx catalyst In the engine exhaust purification apparatus, comprising NOx reduction control means for performing NOx reduction control for setting NOx that has been reduced to a target air-fuel ratio that can be reduced and reducing NOx stored in the NOx catalyst, the reduction purification condition is: includes the NOx occlusion amount occluded in said NOx catalyst becomes equal to or higher than the start threshold, the NOx reduction control means, wherein the NOx reduction control means, before When aged history reflecting the usage state of the exhaust passage is less than a predetermined history, it is characterized in that to change so as to decrease the starting threshold so as to suppress the increase in the exhaust gas temperature due to the NOx reduction.

In this engine exhaust purification system, the reduction purification condition includes that the NOx occlusion amount occluded in the NOx catalyst is equal to or greater than a start threshold value, the NOx reduction control means, the NOx reduction control means, When the aged history reflecting the use state of the exhaust passage is shorter than the predetermined history , the start threshold value is changed to be small so as to suppress an increase in the exhaust gas temperature due to NOx reduction. The removal status of the rust preventive agent applied to the exhaust pipe can be easily determined based on the aging history reflecting the application state of the rust preventive agent. The rise can be suppressed.
Therefore, when the rust inhibitor applied to the exhaust pipe remains, the NOx reduction control period can be shortened to suppress the generation of white smoke, and the rust inhibitor applied to the exhaust pipe is removed. When this is done, the NOx catalyst can be regenerated using an appropriate NOx reduction control period without shortening the NOx reduction control period. In addition, since the NOx catalyst is regenerated with the NOx occlusion amount being small, high purification performance of the NOx catalyst can be ensured.

The invention according to claim 2 is provided in the exhaust passage of the engine and stores NOx in the exhaust gas and stores the stored NOx in the exhaust gas when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio. NOx catalyst that reduces when near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio, and when the NOx catalyst reduction purification condition is satisfied, the NOx occluded in the NOx catalyst is stored in the NOx catalyst. In an exhaust purification apparatus for an engine, comprising NOx reduction control means for performing NOx reduction control for reducing NOx occluded in the NOx catalyst by setting a reducible target air-fuel ratio, the NOx occlusion stored in the NOx catalyst When the NOx reduction control is started when the amount is equal to or greater than the start threshold, and the NOx occlusion amount stored in the NOx catalyst is equal to or less than the end threshold. Said method comprising terminating the serial NOx reduction control the reduction and purification conditions, the NOx reduction control means, when aged history reflecting the usage state of the exhaust passage is less than a predetermined history, rise in exhaust gas temperature due to the NOx reduction The end threshold value is changed so as to increase so as to suppress the above- described problem.
According to this, when the rust preventive agent applied to the exhaust pipe remains, the NOx reduction control period can be shortened to suppress the generation of white smoke, and the rust preventive agent applied to the exhaust pipe. When NO is removed, the NOx catalyst can be regenerated using an appropriate NOx reduction control period without shortening the NOx reduction control period. In addition, since the NOx catalyst is regenerated with a large amount of NOx occluded, high reduction efficiency can be ensured.

According to a third aspect of the present invention, in the first or second aspect of the present invention, a filter that is provided in the exhaust passage and collects particulates in the exhaust gas, and a regeneration unit that burns and removes the collected particulates. And the NOx reduction control means prohibits the change of the reduction purification condition when the filter is regenerated by the regeneration means.
According to this, it is possible to reliably determine the end of evaporation of the rust inhibitor applied to the exhaust pipe using the filter regeneration by the regeneration means as a parameter, and to properly regenerate the NOx catalyst without generating white smoke. it can.

According to a fourth aspect of the present invention, in the third aspect of the present invention, when the cumulative travel distance of the vehicle reaches a predetermined distance, the regeneration means raises the temperature of the filter and burns and removes the collected particulates. The NOx reduction control means prohibits the change of the reduction purification condition when the regeneration means executes the familiar regeneration process.
According to this, it is possible to reliably determine the end of evaporation of the rust preventive agent applied to the exhaust pipe using the familiar regeneration process of the filter by the regeneration means as a parameter.

According to a fifth aspect of the present invention, in the first aspect of the invention, the NOx reduction control means corrects a target air-fuel ratio capable of reducing the NOx based on the aging history using a travel distance of a vehicle as a parameter. It is said.
According to this, the removal situation of a rust preventive agent can be determined with a simple configuration called a travel distance.

According to a sixth aspect of the present invention, in the first aspect of the invention, the NOx reduction control means determines a target air-fuel ratio that can reduce the NOx based on the aging history with a travel distance from when the new exhaust passage is mounted as a parameter. It is characterized by correction.
According to this, the exhaust pipe to which the rust preventive agent is not applied can be excluded from the target, and the removal status of the rust preventive agent can be accurately determined.

  According to the exhaust emission control device for an engine of the present invention, by using the aging history reflecting the state of the exhaust passage, it is possible to easily determine the removal status of the rust inhibitor applied to the exhaust pipe, and the NOx catalyst Both regeneration and white smoke prevention can be achieved.

1 is a schematic configuration diagram of an engine system to which an engine exhaust gas purification apparatus according to an embodiment of the present invention is applied. 1 is a block diagram showing an electrical configuration of an engine exhaust gas purification apparatus according to an embodiment of the present invention. It is a flowchart which shows the fuel-injection control by embodiment of this invention. It is a graph which shows the correlation of the travel distance and start threshold value by embodiment of this invention. It is explanatory drawing about the driving | operation area | region of the engine which performs each of passive DeNOx control and active DeNOx control in embodiment of this invention. It is a flowchart which shows the post injection amount calculation process for DeNOx by embodiment of this invention. It is explanatory drawing about the setting method of the target air fuel ratio by embodiment of this invention. It is a flowchart which shows the setting process of the active DeNOx control execution flag by embodiment of this invention. It is a flowchart which shows the setting process of the passive DeNOx control execution flag by embodiment of this invention. It is a flowchart which shows the fuel injection amount correction | amendment control by embodiment of this invention. It is a block diagram for demonstrating the estimation method of the ammonia adsorption amount by embodiment of this invention. It is a time chart which shows the relationship between the start threshold value by the embodiment of this invention, an end threshold value, and post injection. FIG. 13 is a view corresponding to FIG. 12 according to a modified example.

  Hereinafter, an exhaust emission control device for an engine according to an embodiment of the present invention will be described with reference to the accompanying drawings.

<System configuration>
First, an engine system to which an exhaust emission control device for an engine according to an embodiment of the present invention is applied will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of an engine system to which an engine exhaust gas purification apparatus according to an embodiment of the present invention is applied.

  As shown in FIG. 1, the engine system 200 mainly includes an engine E as a diesel engine, an intake system IN that supplies intake air to the engine E, a fuel supply system FS that supplies fuel to the engine E, An exhaust system EX that exhausts exhaust gas from the engine E, sensors 100 to 119 that detect various states relating to the engine system 200, a PCM (Power-train Control Module) 60 that controls the engine system 200, and an SCR catalyst 47 And a DCU (Dosing Control Unit) 70 for performing control related to the above.

First, the intake system IN has an intake passage 1 through which intake air passes, and an air cleaner 3 that purifies air introduced from the outside in order from the upstream side, and intake air that passes through the intake passage 1. The compressor of the turbocharger 5 that compresses and raises the intake pressure, the intercooler 8 that cools the intake air by outside air or cooling water, and the intake shutter valve 7 that adjusts the intake air flow rate (corresponding to a throttle valve) And a surge tank 12 for temporarily storing the intake air supplied to the engine E.
In the intake system IN, an air flow sensor 101 for detecting the intake air amount and a temperature sensor 102 for detecting the intake air temperature are provided on the intake passage 1 immediately downstream of the air cleaner 3. A pressure sensor 103 for detecting the pressure of the intake air is provided. A temperature sensor 106 for detecting the intake air temperature is provided on the intake passage 1 immediately downstream of the intercooler 8. A position sensor 105 for detecting the opening degree is provided, and the surge tank 12 is provided with a pressure sensor 108 for detecting the pressure of intake air in the intake manifold. Various sensors 101 to 108 provided in the intake system IN output detection signals S101 to S108 corresponding to the detected parameters to the PCM 60, respectively.

  Next, the engine E includes an intake valve 15 that introduces the intake air supplied from the intake passage 1 (including the intake manifold) into the combustion chamber 17, a fuel injection valve 20 that injects fuel toward the combustion chamber 17, A glow plug 21 provided with a heat generating portion in the combustion chamber 17 that generates heat when energized, a piston 23 that reciprocates by combustion of the air-fuel mixture in the combustion chamber 17, and a crankshaft 25 that is rotated by the reciprocating motion of the piston 23 And an exhaust valve 27 that exhausts exhaust gas generated by combustion of the air-fuel mixture in the combustion chamber 17 to a metal exhaust passage 41 (including an exhaust manifold). Further, the engine E is provided with a crank angle sensor 100 that detects a crank angle as a rotation angle with respect to a top dead center in the crankshaft 25, and the crank angle sensor 100 is provided at the detected crank angle. The corresponding detection signal S100 is output to the PCM 60, and the PCM 60 acquires the engine speed based on the detection signal S100.

  The fuel supply system FS includes a fuel tank 30 that stores fuel, and a fuel supply passage 38 that supplies fuel from the fuel tank 30 to the fuel injection valve 20. In the fuel supply passage 38, a low-pressure fuel pump 31, a high-pressure fuel pump 33, and a common rail 35 are provided in order from the upstream side.

  Next, the exhaust system EX has an exhaust passage 41 through which exhaust gas passes. A turbo that is rotated by the exhaust gas passing through the exhaust passage 41 and drives the compressor as described above by this rotation. A turbine of the supercharger 5 is provided. Further, on the exhaust passage 41 on the downstream side of the turbine, NOx catalyst 45 for purifying NOx in the exhaust gas and particulate matter (PM) in the exhaust gas are collected in order from the upstream side. A diesel particulate filter (DPF) 46, a urea injector 51 that injects urea (typically urea water) into the exhaust passage 41 downstream of the DPF 46, and urea injected from the urea injector 51 SCR (Selective Catalytic Reduction) catalyst 47 which purifies NOx by reacting (reducing) this ammonia with NOx in the exhaust gas and oxidizing ammonia released from SCR catalyst 47. And a slip catalyst 48 to be purified. The urea injector 51 is controlled to inject urea into the exhaust passage 41 by a control signal S51 supplied from the DCU 70.

Here, the NOx catalyst 45 and the SCR catalyst 47 will be described more specifically.
The NOx catalyst 45 occludes NOx in the exhaust gas in a lean state (λ> 1) in which the air-fuel ratio of the exhaust gas is larger than the stoichiometric air-fuel ratio. This is a NOx storage reduction catalyst (NSC) that reduces in the vicinity (λ≈1) or in a rich state (λ <1) smaller than the stoichiometric air-fuel ratio. The NOx catalyst 45 generates ammonia when reducing the NOx occluded in this way, and releases the generated ammonia. Specifically, during NOx reduction control, “N” in NOx stored by the NOx catalyst 45 and “H” in “HC” such as unburned fuel supplied as a reducing agent to the NOx catalyst 45. Is combined to produce ammonia (NH3).
The NOx catalyst 45 not only functions as the NSC described above, but also diesel that oxidizes hydrocarbons (HC), carbon monoxide (CO), and the like using oxygen in the exhaust gas to change it into water and carbon dioxide. It also has a function as an oxidation catalyst (DOC: Diesel Oxidation Catalyst). Specifically, the NOx catalyst 45 is made by coating the surface of a DOC catalyst material layer with an NSC catalyst material.
On the other hand, the SCR catalyst 47 adsorbs ammonia produced from urea injected from the urea injector 51 and ammonia produced by NOx reduction in the NOx catalyst 45, and the adsorbed ammonia is adsorbed to NOx in the exhaust gas. To reduce and purify NOx. For example, the SCR catalyst 47 is made by supporting a catalyst metal that reduces NOx with ammonia on zeolite that traps ammonia to form a catalyst component, and supporting this catalyst component on the cell wall of the honeycomb carrier. . Fe, Ti, Ce, W or the like is used as the catalyst metal for NOx reduction.
The DCU 70 described above seems to adsorb an appropriate amount of ammonia to the SCR catalyst 47 from the viewpoint of both ensuring the NOx purification performance by the SCR catalyst 47 and suppressing the release (slip) of ammonia from the SCR catalyst 47. Next, control is performed to inject urea from the urea injector 51. In this case, since the ammonia adsorption capacity changes according to the temperature of the SCR catalyst 47 (specifically, when the temperature of the SCR catalyst 47 becomes high, ammonia is easily released from the SCR catalyst 47), the DCU 70 In consideration of the temperature, control is performed to inject urea from the urea injector 51.

  As shown in FIG. 1, in the exhaust system EX, a pressure sensor 109 that detects the pressure of the exhaust gas and the temperature of the exhaust gas are detected on the exhaust passage 41 upstream of the turbine of the turbocharger 5. A temperature sensor 110 is provided, and an O 2 sensor 111 for detecting the oxygen concentration is provided on the exhaust passage 41 immediately downstream of the turbine of the turbocharger 5. Further, the exhaust system EX includes a temperature sensor 112 for detecting the temperature of the exhaust gas immediately upstream of the NOx catalyst 45, a temperature sensor 113 for detecting the temperature of the exhaust gas between the NOx catalyst 45 and the DPF 46, and the DPF 46. Differential pressure sensor 114 for detecting the pressure difference between the exhaust gas immediately upstream and the downstream side, a temperature sensor 115 for detecting the temperature of the exhaust gas immediately downstream of the DPF 46, and the exhaust gas immediately downstream of the DPF 46 NOx sensor 116 for detecting the concentration of NOx in the exhaust gas, temperature sensor 117 for detecting the temperature of the exhaust gas immediately upstream of the SCR catalyst 47, and the concentration of NOx in the exhaust gas immediately downstream of the SCR catalyst 47 And a PM sensor 119 for detecting PM in the exhaust gas immediately upstream of the slip catalyst 48. Various sensor sensors 109 to 119 provided in the exhaust system EX output detection signals S109 to S119 corresponding to the detected parameters to the PCM 60, respectively.

Further, in the present embodiment, the turbocharger 5 is configured as a two-stage supercharging system that can efficiently obtain high supercharging throughout the entire range from a low rotation range to a high rotation range where the exhaust energy is low.
That is, the turbocharger 5 includes a large turbocharger 5a for supercharging a large amount of air in a high rotation range, a small turbocharger 5b capable of efficiently supercharging with low exhaust energy, and a compressor of the small turbocharger 5b. A compressor bypass valve 5c for controlling the flow of intake air to the turbine, a regulator valve 5d for controlling the flow of exhaust gas to the turbine of the small turbocharger 5b, and a waste gate for controlling the flow of exhaust gas to the turbine of the large turbocharger 5a A valve 5e is provided, and the supercharging by the large turbocharger 5a and the small turbocharger 5b is switched by driving each valve according to the operating state (engine speed and load) of the engine E.

  The engine system 200 according to the present embodiment further includes an EGR device 43. The EGR device 43 connects the exhaust passage 41 upstream of the turbine of the turbocharger 5 and the intake passage 1 downstream of the compressor of the turbocharger 5 (specifically, downstream of the intercooler 8). The passage 43a, the EGR cooler 43b that cools the exhaust gas that passes through the EGR passage 43a, the first EGR valve 43c that adjusts the flow rate of the exhaust gas that passes through the EGR passage 43a, and the EGR cooler 43b are bypassed to flow the exhaust gas. The EGR cooler bypass passage 43d and the second EGR valve 43e for adjusting the flow rate of the exhaust gas passing through the EGR cooler bypass passage 43d are provided.

  Next, with reference to FIG. 2, the electrical configuration of the exhaust emission control device for an engine according to the embodiment of the present invention will be described. FIG. 2 is a block diagram showing an electrical configuration of the engine exhaust gas purification apparatus according to the embodiment of the present invention.

  In addition to the detection signals S100 to S119 of the various sensors 100 to 119 described above, the PCM 60 according to the embodiment of the present invention detects an accelerator opening sensor 150 that detects an accelerator pedal opening (accelerator opening), and a vehicle speed. Based on the detection signals S150 and S151 output from the vehicle speed sensor 151, the control signal S20 is mainly output to control the fuel injection valve 20, and the control signal S7 is output to control the intake shutter valve 7. To do.

  In particular, in the present embodiment, the PCM 60 sets the air-fuel ratio of the exhaust gas from the fuel injection valve 20 so as to set the target air-fuel ratio (specifically, near the stoichiometric air-fuel ratio or a predetermined air-fuel ratio smaller than the stoichiometric air-fuel ratio). Control (NOx reduction control) is performed to reduce the NOx occluded in the NOx catalyst 45 by post injection. That is, the PCM 60 adds to the main injection that injects fuel into the cylinders in order to output the engine torque according to the driver's accelerator operation (basically, the air-fuel ratio of the exhaust gas becomes lean in the main injection). After this main injection, post injection is performed to inject fuel at a timing that does not contribute to engine torque output (specifically, an expansion stroke), and the air-fuel ratio of the exhaust gas is reduced. The NOx occluded in the NOx catalyst 45 is reduced so as to be set to a state close to the theoretical air-fuel ratio (λ≈1) or a rich state smaller than the theoretical air-fuel ratio (λ <1). Hereinafter, such control for reducing the NOx stored in the NOx catalyst 45 is referred to as “DeNOx control”. Note that “De” in the word “DeNOx” is a prefix meaning separation or removal.

Further, although details will be described later, the PCM 60 is divided into “ammonia adsorption amount acquisition means” and “NOx”.
It functions as a “reduction control means”.
The PCM 60 stores a CPU, various programs interpreted and executed on the CPU (including a basic control program such as an OS and an application program that is activated on the OS to realize a specific function), programs, and various data. It is configured by a computer having an internal memory such as a ROM or RAM for storing.

<Fuel injection control>
Next, the fuel injection control according to the embodiment of the present invention will be described with reference to FIG.
FIG. 3 is a flowchart (fuel injection control flow) showing the fuel injection control according to the embodiment of the present invention. This fuel injection control flow is started when the ignition of the vehicle is turned on and the PCM 60 is turned on, and is repeatedly executed at a predetermined cycle.

  First, in step S101, the PCM 60 acquires the driving state of the vehicle. Specifically, the PCM 60 is currently set to at least the accelerator opening detected by the accelerator opening sensor 150, the vehicle speed detected by the vehicle speed sensor 151, the crank angle detected by the crank angle sensor 100, and the transmission of the vehicle. Get the gear position.

  Next, in step S102, the PCM 60 sets a target acceleration based on the driving state of the vehicle including the operation of the accelerator pedal acquired in step S101. Specifically, the PCM 60 determines the acceleration corresponding to the current vehicle speed and gear stage from acceleration characteristic maps (created in advance and stored in a memory or the like) defined for various vehicle speeds and various gear stages. A characteristic map is selected, and a target acceleration corresponding to the current accelerator opening is determined with reference to the selected acceleration characteristic map.

  Next, in step S103, the PCM 60 determines a target torque of the engine E for realizing the target acceleration determined in step S102. In this case, the PCM 60 determines a target torque within the range of torque that can be output by the engine E based on the current vehicle speed, gear stage, road surface gradient, road surface μ, and the like.

  Next, in step S104, the PCM 60 calculates the fuel injection amount to be injected from the fuel injection valve 20 based on the target torque and the engine speed so as to output the target torque determined in step S103 from the engine E. . This fuel injection amount is a fuel injection amount (main injection amount) applied in main injection.

On the other hand, in parallel with the processing of steps S102 to S104 described above, in step S105, the PCM 60 sets a fuel injection pattern according to the operating state of the engine E. Specifically, when performing the above-described DeNOx control, the PCM 60 sets a fuel injection pattern for performing at least post injection in addition to main injection.
In this case, the PCM 60 also determines the fuel injection amount (post injection amount) applied in the post injection and the timing (post injection timing etc.) for performing the post injection. Details of these will be described later.

  After steps S104 and S105, the process proceeds to step S106, where the PCM 60 is based on the main injection amount calculated in step S104 and the fuel injection pattern set in step S105 (when post injection is performed, the post injection amount or post injection). The fuel injection valve 20 is controlled. That is, the PCM 60 controls the fuel injection valve 20 so that a desired amount of fuel is injected in a desired fuel injection pattern.

<DeNOx control>
Hereinafter, DeNOx control according to the embodiment of the present invention will be specifically described.

First, the basic concept of DeNOx control according to an embodiment of the present invention will be described.
In the present embodiment, the PCM 60, when the NOx occlusion amount of the NOx catalyst 45 is equal to or greater than the first occlusion amount determination value α1 corresponding to the start threshold, for example, when the NOx occlusion amount of the NOx catalyst 45 is near the limit, In order to reduce the NOx stored in the NOx catalyst 45 until it becomes substantially zero corresponding to the end threshold value, the air-fuel ratio of the exhaust gas is continuously set to a target air-fuel ratio near the stoichiometric air-fuel ratio or below the stoichiometric air-fuel ratio. DeNOx control for post-injection from the fuel injection valve 20 (hereinafter referred to as “active DeNOx control” as appropriate) is executed.
By so doing, NOx stored in the NOx catalyst 45 in a large amount is forcibly reduced, and the NOx purification performance of the NOx catalyst 45 is reliably ensured.
The basic first occlusion amount determination value α1 corresponds to the vicinity of the limit of the NOx occlusion amount of the NOx catalyst 45, and is thus obtained in advance based on the performance of the NOx catalyst 45.

Here, when at least a part of the exhaust passage 41 including the exhaust manifold is replaced with a new exhaust passage 41 due to breakage or the like, it is applied to the new exhaust passage 41 replaced by a rapid rise in exhaust gas temperature due to post injection. The rust preventive that has been evaporated evaporates, and the air-fuel ratio of the exhaust gas supplied to the NOx catalyst 45 becomes richer than the target air-fuel ratio, which may cause white smoke.
The PCM 60 has a map that defines the correlation between the travel distance of the vehicle and the threshold value β (0 <β ≦ α1), and cumulatively calculates the travel distance from when the new exhaust passage 41 is replaced.
The PCM 60 determines the threshold value β based on the accumulated travel distance from when the new exhaust passage 41 is replaced, and changes the reduction and purification condition for setting the determined threshold value β to the first occlusion amount determination value α1 described above. Is going. Specifically, as shown in FIG. 4, the threshold value β increases in a linear function as the distance increases in a region where the cumulative travel distance from the replacement of the exhaust passage 41 is equal to or less than a predetermined value X. In the region exceeding X, α1 is set regardless of the distance.
The predetermined value X, which is the cumulative travel distance, is obtained in advance through experiments or the like for the travel distance at which the rust inhibitor applied to the exhaust passage 41 is completely evaporated under general travel conditions and environments.

Further, when the DPF 46 is regenerated, the exhaust gas temperature rises abruptly, so that the evaporation of the rust preventive agent applied to the exhaust passage 41 ends even when the cumulative travel distance is in the region of the predetermined value X or less.
Therefore, the PCM 60 prohibits the change of the reduction purification condition described above after the regeneration process of the DPF 46 after the new exhaust pipe is attached.
The regeneration of the DPF 46 includes a familiar regeneration process in which a regeneration process is forcibly performed at the time of completion of a predetermined travel distance (for example, a predetermined distance of 10 km or less) in order to familiarize the DPF characteristics with a new vehicle. .

In the present embodiment, the PCM 60 determines that the NOx occlusion amount of the NOx catalyst 45 is less than the first occlusion amount judgment value α1, but is greater than or equal to the second occlusion amount judgment value α2 corresponding to the start threshold value. When the air-fuel ratio of the exhaust gas changes to the rich side due to acceleration, the fuel injection valve 20 is set so that the air-fuel ratio of the exhaust gas is temporarily set to the target air-fuel ratio in order to reduce the NOx stored in the NOx catalyst 45. DeNOx control (hereinafter, referred to as “passive DeNOx control” as appropriate) is executed. For example, the second storage amount determination value α2 is set to a value of about 1/3 of the limit value of the NOx storage amount (first storage amount determination value α1). Therefore, in the passive DeNOx control, the reduction and purification conditions are not changed as in the active DeNOx control.
In this passive DeNOx control, the air-fuel ratio is adjusted to a target air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio or below the stoichiometric air-fuel ratio by taking advantage of the situation where the main injection amount increases during acceleration and the air-fuel ratio of the exhaust gas decreases. Since the post-injection is performed so as to be set, the post-injection amount for setting the air-fuel ratio to the target air-fuel ratio is smaller than in the case where the DeNOx control is performed in a situation where the air-fuel ratio of the exhaust gas does not decrease (that is, during non-acceleration) Become.
Further, since the passive DeNOx control is performed by taking advantage of acceleration of the vehicle, it is performed at a relatively high frequency.

In the present embodiment, by applying such passive DeNOx control, DeNOx is performed at a high frequency while suppressing deterioration in fuel consumption due to DeNOx. Although the passive DeNOx control is performed only for a relatively short period, it is performed at a high frequency, so that the NOx occlusion amount of the NOx catalyst 45 can be efficiently reduced.
As a result, the NOx occlusion amount of the NOx catalyst 45 is less likely to exceed a predetermined amount, so that the frequency of execution of active DeNOx control that requires a larger amount of post-injection than passive DeNOx control can be reduced, and fuel consumption deterioration due to DeNOx can be reduced. It becomes possible to improve effectively.

Further, in the present embodiment, when the above-described active DeNOx control is executed, the post-injected fuel is burned in the cylinder of the engine E, so that the air-fuel ratio of the exhaust gas is set to the target air-fuel ratio. In this case, the PCM 60 performs the post-injection at the timing when the post-injected fuel is combusted in the cylinder.
Specifically, the PCM 60 sets a predetermined timing in the first half of the expansion stroke of the engine E as a post injection timing in the active DeNOx control.
By applying such post injection timing in the active DeNOx control, the post-injected fuel is discharged as it is as unburned fuel (that is, HC), and the oil dilution by the post-injected fuel is suppressed. ing.

On the other hand, in the present embodiment, when the above-described passive DeNOx control is performed, the PCM 60 causes the post-injected fuel to be discharged into the exhaust passage 41 as unburned fuel without burning in the cylinder of the engine E. Thus, the air-fuel ratio of the exhaust gas is set to the target air-fuel ratio.
In this case, the PCM 60 performs the post-injection at the timing when the post-injected fuel is discharged into the exhaust passage 41 as unburned fuel without being burned in the cylinder.
Specifically, the PCM 60 sets a predetermined timing in the latter half of the expansion stroke of the engine E as a post injection timing in the passive DeNOx control.
By applying such post-injection timing in passive DeNOx control, it is possible to prevent the post-injected fuel from burning in the cylinder and generating smoke.

Here, with reference to FIG. 5, the operation area | region of the engine E which performs each of passive DeNOx control and active DeNOx control in embodiment of this invention is demonstrated.
FIG. 5 shows the engine speed on the horizontal axis and the engine load on the vertical axis.
In FIG. 5, a curve L1 indicates the maximum torque line of the engine E.

  As shown in FIG. 5, in the present embodiment, the PCM 60 is in an intermediate load range where the engine load is equal to or higher than the first predetermined load Lo1 and lower than the second predetermined load Lo2 (> first predetermined load Lo1), and When the engine speed is in the middle engine speed range that is greater than or equal to the first predetermined engine speed N1 and less than the second predetermined engine speed N2 (> the first predetermined engine speed N1), that is, the engine load and the engine engine speed are indicated by reference numeral R12 When included in the region (hereinafter referred to as “active DeNOx execution region R12”), the active DeNOx control is executed. The reason for adopting such an active DeNOx execution region R12 is as follows.

  As described above, when executing the active DeNOx control, the post-injected fuel is reduced from the viewpoint of suppressing the generation of HC due to the post-injected fuel being discharged as it is or the oil dilution by the post-injected fuel. Post injection is performed at the timing of combustion in the cylinder. In this case, in this embodiment, when the post-injected fuel is burned, the generation of smoke is suppressed and the generation of HC (that is, the discharge of unburned fuel due to incomplete combustion) is suppressed. Specifically, the time until the post-injected fuel burns is made as much as possible, that is, ignition occurs in a state where air and fuel are properly mixed to suppress the generation of smoke and HC. Yes. For this reason, the ignition of post-injected fuel is effectively delayed by introducing an appropriate amount of EGR gas during active DeNOx control.

The reason for suppressing the generation of HC during the active DeNOx control is that when EGR gas is introduced as described above, HC is also recirculated to the intake system IN as EGR gas, and this HC becomes a binder and is combined with soot. This is to prevent the gas passage from being blocked.
In addition, when active DeNOx control is performed in an area where the temperature of the NOx catalyst 45 is low and HC purification performance (HC purification performance by DOC in the NOx catalyst 45) is not ensured, HC is not purified. This is to prevent discharge.
Incidentally, the active DeNOx execution region R12 includes a region where the temperature of the NOx catalyst 45 where the HC purification performance is not ensured is relatively low.
The reason for suppressing the generation of smoke during active DeNOx control is that PM corresponding to the smoke is collected by the DPF 46, but DPF regeneration for burning and removing the PM collected by the DPF 46 (similar to DeNOx control). This is to prevent the fuel efficiency and the like from being deteriorated by frequently performing post-injection control).

By the way, when the engine load increases, the air introduced into the engine E in order to achieve the target air-fuel ratio is reduced, so that there is not enough oxygen necessary to properly burn the post-injected fuel, so that smoke and HC Tend to occur. In particular, when the engine load increases, the in-cylinder temperature rises and the time until the post-injected fuel is ignited cannot be properly secured, and ignition occurs midway, that is, the air and fuel are mixed properly. Combustion occurs in a state where it is not performed, and smoke and HC are generated. On the other hand, in a region where the engine load is considerably low, the temperature of the NOx catalyst 45 is low, and the NOx reduction function of the NOx catalyst 45 is not sufficiently exhibited.
In addition, in this region, the post-injected fuel does not burn properly, that is, misfire occurs. In addition, although the phenomenon regarding an engine load was described above, the same phenomenon arises also about an engine speed.

  From the above, in this embodiment, the operation region of the engine E corresponding to the medium load region and the medium rotation region is employed as the active DeNOx execution region R12 for executing the active DeNOx control. In other words, in this embodiment, the active DeNOx control is executed only in the active DeNOx execution region R12, and the execution of the active DeNOx control is prohibited in the operation region other than the active DeNOx execution region R12. Thus, in the operation region of the engine E for which execution of the active DeNOx control is prohibited, particularly in the region on the higher load side or the higher rotation side than the active DeNOx execution region R12 (region denoted by reference numeral R13), the SCR Since the NOx purification performance of the catalyst 47 is sufficiently secured, the SCR catalyst 47 purifies NOx, and NOx emission from the vehicle can be prevented without executing DeNOx control.

Further, in this embodiment, in the region on the higher load side than the region R13 in which the SCR catalyst 47 purifies NOx (the region denoted by reference numeral R11, hereinafter referred to as “passive DeNOx execution region R11”). Since the amount of exhaust gas increases and the SCR catalyst 47 cannot completely purify NOx, passive DeNOx control is executed. In this passive DeNOx control, as described above, post-injection is performed at a timing at which the post-injected fuel is discharged into the exhaust passage 41 as unburned fuel without being combusted in the cylinder.
In the passive DeNOx execution region R11, the temperature of the NOx catalyst 45 is sufficiently high, and the HC purification performance (HC purification performance by DOC in the NOx catalyst 45) is ensured, so the unburned fuel discharged in this way Can be appropriately purified by the NOx catalyst 45.
In passive DeNOx control, smoke is generated when post-injected fuel is burned in the cylinder as in active DeNOx control. As described above, the reason is the same as the reason why the execution of the active DeNOx control is prohibited when the engine load increases. Therefore, in passive DeNOx control, the post-injected fuel is discharged into the exhaust passage 41 as unburned fuel without burning in the cylinder.

  Next, the temperature range in which passive DeNOx control and active DeNOx control are performed in the embodiment of the present invention will be described. Basically, the NOx catalyst 45 exhibits NOx purification performance in a relatively low temperature range, and the SCR catalyst 47 has a relatively high temperature range, specifically, a temperature range where the NOx purification performance of the NOx catalyst 45 is exhibited. It exhibits NOx purification performance in a high temperature range. In the present embodiment, the temperature near the lower boundary value of the temperature range in which the NOx purification rate equal to or higher than a predetermined value is obtained by the SCR catalyst 47 is used as the determination temperature (hereinafter referred to as “SCR determination temperature”). Passive DeNOx control or active DeNOx control is executed only when the temperature of the SCR catalyst 47 (hereinafter referred to as “SCR temperature”) is lower than the SCR determination temperature, and when the SCR temperature is equal to or higher than the SCR determination temperature. The execution of the passive DeNOx control and the active DeNOx control is prohibited. This is because, when the SCR temperature is equal to or higher than the SCR determination temperature, the NOx in the exhaust gas can be appropriately purified by the SCR catalyst 47, so that the NOx purification performance by the NOx catalyst 45 is ensured. This is because there is no need to perform control. Therefore, in the present embodiment, when the SCR temperature is equal to or higher than the SCR determination temperature, the execution of DeNOx control is prohibited, and the deterioration of fuel consumption due to the execution of DeNOx control is suppressed.

Next, a method for calculating a post injection amount (hereinafter referred to as “DeNOx post injection amount”) applied during DeNOx control in the embodiment of the present invention will be described with reference to FIG. 6.
FIG. 6 is a flowchart (DeNOx post injection amount calculation flow) showing the DeNOx post injection amount calculation processing according to the embodiment of the present invention. This DeNOx post-injection amount calculation flow is repeatedly executed by the PCM 60 at a predetermined cycle, and is executed in parallel with the fuel injection control flow shown in FIG. That is, while the fuel injection control is being performed, the post injection amount for DeNOx is calculated as needed.

First, in step S111, the PCM 60 acquires the operating state of the engine E. Specifically, the PCM 60 performs at least the intake air amount (fresh air amount) detected by the airflow sensor 101, the oxygen concentration of the exhaust gas detected by the O2 sensor 111, and the main injection calculated in step S104 of FIG. Get the quantity.
Further, the PCM 60 also acquires an exhaust gas amount (EGR gas amount) recirculated to the intake system IN by the EGR device 43, which is obtained by a predetermined model or the like. In addition, an ammonia adsorption amount that is the amount of ammonia adsorbed on the SCR catalyst 47 is acquired. In this case, the PCM 60 acquires the estimated ammonia adsorption amount. The method for estimating the ammonia adsorption amount will be described later in detail (see FIG. 11).

  Next, in step S112, the PCM 60 sets a target air-fuel ratio to be applied to reduce NOx stored in the NOx catalyst 45 based on the ammonia adsorption amount of the SCR catalyst 47 acquired in step S111. Specifically, the PCM 60 sets the target air-fuel ratio applied when executing the active DeNOx control and the target air-fuel ratio applied when executing the passive DeNOx control based on the ammonia adsorption amount of the SCR catalyst 47. To do. A method for setting the target air-fuel ratio will be specifically described with reference to FIG.

FIG. 7 is an explanatory diagram for a target air-fuel ratio setting method according to the embodiment of the present invention.
In FIG. 7, the horizontal axis indicates the ammonia adsorption amount of the SCR catalyst 47, and the vertical axis indicates the target air-fuel ratio.

In FIG. 7, “λ1” indicates the stoichiometric air-fuel ratio, and an air-fuel ratio region R21 richer than the stoichiometric air-fuel ratio λ1 indicates an air-fuel ratio range in which NOx stored in the NOx catalyst 45 can be reduced. An air-fuel ratio region R22 that is leaner than the theoretical air-fuel ratio λ1 indicates an air-fuel ratio range in which NOx stored in the NOx catalyst 45 cannot be reduced. The graph G11 shows the target air-fuel ratio that should be set according to the ammonia adsorption amount of the SCR catalyst 47 when the passive DeNOx control is executed, and the graph G12 shows the SCR catalyst 47 when the active DeNOx control is executed. The target air-fuel ratio to be set according to the ammonia adsorption amount is shown.
These graphs G11 and G12 correspond to maps defining the target air-fuel ratio to be set according to the ammonia adsorption amount.

Basically, when the target air-fuel ratio is set to the lean side in the region R21, the amount of reducing agent (HC, etc.) supplied to the NOx catalyst 45 decreases, and the NOx reduction efficiency (NOx catalyst 45) in the NOx catalyst 45 decreases. This corresponds to the rate at which NOx occluded in the catalyst is reduced. The same applies hereinafter), but the amount of ammonia generated from the NOx catalyst 45 decreases. In consideration of this, in the present embodiment, as shown in the graphs G11 and G12, as the ammonia adsorption amount of the SCR catalyst 47 increases in both the case where the passive DeNOx control is executed and the case where the active DeNOx control is executed, The target air-fuel ratio is set to the lean side within the air-fuel ratio range (region R21) in which NOx stored in the NOx catalyst 45 can be reduced. For example, the target air-fuel ratio is set to about 0.98.
When the ammonia adsorption amount of the SCR catalyst 47 is large, such a target air-fuel ratio on the lean side is applied to the DeNOx control, so that the NOx reduction efficiency in the NOx catalyst 45 is secured to some extent and the NOx catalyst 45 is obtained by this NOx reduction. The SCR catalyst 47 prevents the ammonia generated from the catalyst from being completely absorbed and released.

  On the other hand, when the target air-fuel ratio is set to the rich side, the amount of reducing agent (such as HC) supplied to the NOx catalyst 45 increases and the amount of ammonia generated from the NOx catalyst 45 increases, but the NOx catalyst 45 NOx reduction efficiency is improved. Therefore, in the present embodiment, as shown in the graphs G11 and G12, the target air-fuel ratio is reduced as the ammonia adsorption amount of the SCR catalyst 47 decreases in both the case where the passive DeNOx control is executed and the case where the active DeNOx control is executed. Set to rich side. For example, the target air-fuel ratio is set to about 0.96. When the amount of ammonia adsorbed by the SCR catalyst 47 is small, it takes time until the ammonia generated from the NOx catalyst 45 due to NOx reduction is not completely adsorbed by the SCR catalyst 47 and is released. In this case, the rich side By applying this target air-fuel ratio to DeNOx control, priority is given to improving the NOx reduction efficiency in the NOx catalyst 45 rather than suppressing the generation of ammonia from the NOx catalyst 45.

  In this embodiment, as shown in the graphs G11 and G12, when the passive DeNOx control is executed, the target air-fuel ratio to be applied at the same ammonia adsorption amount is made richer than when the active DeNOx control is executed. Set to. The reason for this is as follows. Since the passive DeNOx control is performed at the time of acceleration when the air-fuel ratio temporarily decreases, the amount of ammonia (integrated amount) generated from the NOx catalyst 45 is reduced because the execution duration is shorter than that of the active DeNOx control. . Therefore, there is a low possibility that ammonia is not completely absorbed by the SCR catalyst 47 and is released. On the other hand, at the start of DeNOx control, “H” in “HC” such as unburned fuel supplied as a reducing agent to the NOx catalyst 45 by DeNOx control is replaced by “O” of oxygen stored in the NOx catalyst 45. ”And is consumed first, and ammonia is not generated from the NOx catalyst 45. The passive DeNOx control with a short execution duration ends within a period until the oxygen stored in the NOx catalyst 45 is consumed, and the ammonia amount is hardly generated from the NOx catalyst 45, or the passive DeNOx control is performed. Most of the control execution period is included in the period until the oxygen stored in the NOx catalyst 45 is consumed, and the amount of ammonia generated from the NOx catalyst 45 is reduced.

For the above reasons, in the present embodiment, when the passive DeNOx control is executed, the target air-fuel ratio to be applied at the same ammonia adsorption amount is set to the richer side than when the active DeNOx control is executed. In this way, when passive DeNOx control is executed, priority is given to improving the NOx reduction efficiency in the NOx catalyst 45 over suppression of ammonia generation from the NOx catalyst 45.
Note that the maximum value of the target air-fuel ratio on the rich side applied in the passive DeNOx control is such that the amount of HC generated corresponding to the post-injected fuel is less than a predetermined amount in order to suppress the blockage of the gas passage by HC during the DeNOx control. It is better to set the air-fuel ratio so that

In this embodiment, as shown in the graphs G11 and G12, the target air-fuel ratio to be applied in a region where the ammonia adsorption amount is relatively large in both the case where the passive DeNOx control is executed and the case where the active DeNOx control is executed. It is almost constant. Specifically, the target air-fuel ratio is set to the minimum value on the lean side in the entire region where the ammonia adsorption amount is relatively large. The reason for this is as follows.
The ammonia adsorption capacity of the SCR catalyst 47 varies depending on the operating state of the engine E, the SCR temperature, and the like. For example, when the SCR temperature increases, the ammonia adsorption capacity of the SCR catalyst 47 decreases, and the maximum ammonia adsorption amount of the SCR catalyst 47 tends to decrease.
Therefore, in the present embodiment, even in a situation where the ammonia adsorption capacity is lowered, it is possible to reliably suppress that the ammonia generated from the NOx catalyst 45 by DeNOx is not completely adsorbed by the SCR catalyst 47 and is released. Therefore, with a margin, the target air-fuel ratio is set to the minimum value on the lean side for a relatively wide range regarding the ammonia adsorption amount.

  In consideration of the fact that the ammonia adsorption capacity of the SCR catalyst 47 varies with the SCR temperature as described above, the target air-fuel ratio to be set according to the ammonia adsorption amount may be further varied based on the SCR temperature. Specifically, when the SCR temperature is high, it is better to set the target air-fuel ratio to be applied at the same ammonia adsorption amount to the lean side in the region R21 than when the SCR temperature is low. This is because when the SCR temperature increases, the ammonia adsorption ability of the SCR catalyst 47 decreases and ammonia is easily released from the SCR catalyst 47.

  Returning to FIG. 6, the processing after step S113 will be described. In step S113, the PCM 60 calculates the amount of air (that is, the charging amount) introduced into the engine E based on the fresh air amount and the EGR gas amount acquired in step S111. In step S114, the PCM 60 calculates the oxygen concentration of the air introduced into the engine E from the filling amount calculated in step S113.

Next, in step S115, the PCM 60 calculates a post injection amount (DeNOx post injection amount) necessary to realize the target air-fuel ratio set in step S112.
That is, the PCM 60 determines how much post-injection amount should be applied in addition to the main injection amount in order to set the air-fuel ratio of the exhaust gas to the target air-fuel ratio.
In this case, the PCM 60 realizes the post-injection amount for realizing the target air-fuel ratio when the active DeNOx control set in step S112 is performed and the target air-fuel ratio when the passive DeNOx control set in step S112 is performed. The post-injection amount is calculated respectively.

  Then, the PCM 60 appropriately performs feedback processing according to the difference between the detected oxygen concentration and the calculated oxygen concentration from the air-fuel ratio of the exhaust gas generated when the main injected fuel is burned, and the exhaust gas The post-injection amount for DeNOx for setting the air / fuel ratio of the engine to the target air / fuel ratio is calculated. By calculating the post-injection amount for DeNOx in this way, the air-fuel ratio of the exhaust gas is accurately set to the target air-fuel ratio while suppressing the generation of white smoke at the time of exhaust pipe replacement by post-injection in DeNOx control. The NOx occluded in the NOx catalyst 45 is reliably reduced.

  Hereinafter, the active DeNOx control and the passive DeNOx control according to the embodiment of the present invention will be specifically described.

  First, with reference to FIG. 8, the setting process of the active DeNOx control execution flag used for determining whether or not the execution of the active DeNOx control according to the embodiment of the present invention is necessary will be described. FIG. 8 is a flowchart (active DeNOx control execution flag setting flow) showing the setting process of the active DeNOx control execution flag. This active DeNOx control execution flag setting flow is repeatedly executed by the PCM 60 at a predetermined cycle, and is executed in parallel with the fuel injection control flow shown in FIG.

  First, in step S201, the PCM 60 acquires various information on the vehicle. Specifically, the PCM 60 includes at least the NOx catalyst temperature, the SCR temperature, the NOx occlusion amount of the NOx catalyst 45, the first occlusion amount determination value α1, the travel distance from when the new exhaust pipe is attached, and the travel distance. And the correlation between the start threshold value β and the like. In this case, the NOx catalyst temperature is estimated based on, for example, the temperature detected by the temperature sensor 112 provided immediately upstream of the NOx catalyst 45 (a temperature sensor provided between the NOx catalyst 45 and the DPF 46). The temperature detected by 113 may be used). The SCR temperature is estimated based on the temperature detected by the temperature sensor 117 provided immediately upstream of the SCR catalyst 47, for example. The NOx occlusion amount is obtained by, for example, estimating the NOx amount in the exhaust gas based on the operating state of the engine E, the exhaust gas flow rate, the exhaust gas temperature, and the like, and integrating the NOx amount. It is done.

  Next, in step S202, the PCM 60 determines whether or not the SCR temperature acquired in step S201 is lower than the SCR determination temperature. As a result of this determination, when the SCR temperature is lower than the SCR determination temperature (step S202: Yes), the process proceeds to step S203. On the other hand, when the SCR temperature is equal to or higher than the SCR determination temperature (step S202: No), the process proceeds to step S209. In this case, since NOx in the exhaust gas can be appropriately purified by the SCR catalyst 47, the PCM 60 sets the active DeNOx control execution flag to “0” in order to prohibit the execution of the active DeNOx control ( Step S206). Then, the process ends.

  Next, in step S203, the PCM 60 determines whether or not the NOx catalyst temperature acquired in step S201 exceeds a predetermined temperature. When the NOx catalyst temperature is low, the NOx catalyst 45 hardly reduces the stored NOx even if the air-fuel ratio of the exhaust gas is set to the target air-fuel ratio. Therefore, in step S203, it is determined whether or not the NOx stored in the NOx catalyst 45 can be reduced. Therefore, the predetermined temperature used in the determination in step S203 is set based on the NOx catalyst temperature that can reduce the NOx stored in the NOx catalyst 45. As a result of the determination in step S203, if the NOx catalyst temperature exceeds the predetermined temperature (step S203: Yes), the process proceeds to step S204. On the other hand, when the NOx catalyst temperature is equal to or lower than the predetermined temperature (step S203: No), the process proceeds to step S209.

Next, in step S204, the PCM 60 determines whether or not the travel distance from when the new exhaust pipe is mounted is less than a predetermined value X. When the travel distance from when the new exhaust pipe is mounted is less than the predetermined value X, the rust preventive agent applied to the exhaust pipe constituting a part of the exhaust passage 41 remains, so the DeNOx post injection is executed. As a result, the exhaust gas temperature rises and the rust preventive agent containing a large amount of hydrocarbons evaporates, causing white smoke to be generated. For this purpose, the aging history reflecting the state of the exhaust passage 41, that is, the state of the so-called rust inhibitor remaining in the exhaust pipe is determined using the cumulative travel distance as a parameter. As a result of this determination, when the travel distance from when the new exhaust pipe is mounted is less than the predetermined value X (step S204: Yes), the process proceeds to step S205.
On the other hand, when the travel distance from when the new exhaust pipe is mounted is equal to or greater than the predetermined value X (step S204: No), the process proceeds to step S210.

Next, in step S205, the PCM 60 determines whether or not the regeneration process of the DPF 46 has not been performed after the new exhaust pipe is attached. When the normal regeneration process or the familiar regeneration process of the DPF 46 is executed, the exhaust gas temperature becomes high. Therefore, even if the travel distance from when the new exhaust pipe is installed is less than the predetermined value X, the rust inhibitor Evaporates completely and does not remain in the exhaust passage 41. Therefore, the regeneration process of the DPF 46 is determined.
As a result of this determination, when the regeneration process of the DPF 46 has not been performed yet (step S205: Yes), the process proceeds to step S206. In this case, since the cumulative travel distance from when the new exhaust pipe is attached is short and the DPF regeneration process is not executed, the rust preventive agent remains in the new exhaust pipe. Therefore, in order to change the reduction and purification condition, the threshold value β based on the cumulative travel distance from when the new exhaust pipe is attached is set to the first occlusion amount determination value α1 (step S206).
On the other hand, when the regeneration process of the DPF 46 has already been executed (step S205: No), the process proceeds to step S210. In this case, since there is no rust preventive agent remaining in the exhaust passage 41, the preset first storage amount determination value α1 is maintained without changing the reduction purification condition (step S210). The basic first occlusion amount determination value α1 before the reduction and purification condition change is held in advance.

Next, in step S207, the PCM 60 determines whether the NOx storage amount acquired in step S201 exceeds the first storage amount determination value α1.
As a result of this determination, when the NOx storage amount exceeds the first storage amount determination value α1 (step S208: Yes), the process proceeds to step S208. In this case, the PCM 60 sets an active DeNOx control execution flag to “1” in order to allow execution of active DeNOx control (step S208). In this way, the active DeNOx control is executed after the engine is started to forcibly reduce NOx occluded in the NOx catalyst 45 to some extent, thereby ensuring the NOx purification performance of the NOx catalyst 45 reliably.
On the other hand, when the NOx occlusion amount is equal to or less than the first occlusion amount determination value α1 (step S209: No), the process proceeds to step S209. In this case, the PCM 60 sets the active DeNOx control execution flag to “0” in order to prohibit execution of useless active DeNOx control (step S209). Then, the process ends.

Next, with reference to FIG. 9, the setting process of the passive DeNOx control execution flag used in order to determine the necessity of execution of the passive DeNOx control according to the embodiment of the present invention will be described.
FIG. 9 is a flowchart (passive DeNOx control execution flag setting flow) showing the setting process of the passive DeNOx control execution flag according to the embodiment of the present invention. This passive DeNOx control execution flag setting flow is repeatedly executed by the PCM 60 at a predetermined cycle, and is executed in parallel with the fuel injection control flow shown in FIG. 3, the active DeNOx control execution flag setting flow shown in FIG. Is done.

First, in step S301, the PCM 60 acquires various information on the vehicle. Specifically, the PCM 60 has at least the NOx catalyst temperature, the SCR temperature, the target torque determined by the fuel injection control flow shown in FIG. 3, the NOx occlusion amount of the NOx catalyst 45, and the values shown in FIG. The value of the active DeNOx control execution flag set in the active DeNOx control execution flag setting flow is acquired. The method for obtaining the NOx catalyst temperature, the SCR temperature, and the NOx occlusion amount is as described above.
In addition, in step S301, the PCM 60 also acquires the execution frequency of passive DeNOx control within a predetermined period. Specifically, the PCM 60 acquires, as the execution frequency of the passive DeNOx control, the number of times that the passive DeNOx control has been executed during a predetermined period (for example, several seconds or several minutes).

  Next, in step S302, the PCM 60 determines whether or not the SCR temperature acquired in step S301 is lower than the SCR determination temperature. As a result of this determination, when the SCR temperature is lower than the SCR determination temperature (step S302: Yes), the process proceeds to step S303. On the other hand, when the SCR temperature is equal to or higher than the SCR determination temperature (step S302: No), the process proceeds to step S307. In this case, since NOx in the exhaust gas can be appropriately purified by the SCR catalyst 47, the PCM 60 sets the passive DeNOx control execution flag to “0” in order to prohibit the execution of the passive DeNOx control ( Step S307). Then, the process ends.

  Next, in step S303, the PCM 60 determines whether or not the execution frequency of the passive DeNOx control acquired in step S301 is less than a predetermined value that is a frequency determination value. If the execution frequency of the passive DeNOx control is less than the predetermined value as a result of the determination in step S303 (step S303: Yes), the process proceeds to step S304. On the other hand, when the execution frequency of the passive DeNOx control is equal to or higher than the predetermined value (step S303: No), the process proceeds to step S307. In this case, the PCM 60 sets the passive DeNOx control execution flag to “0” in order to prohibit the execution of the passive DeNOx control (step S307).

When the passive DeNOx control has been performed relatively frequently so far, when the passive DeNOx control is executed from now on, there is a high possibility that oil dilution due to post injection occurs. Therefore, in this embodiment, when the execution frequency of the passive DeNOx control is equal to or higher than the predetermined value (step S303: No), the execution of the passive DeNOx control is prohibited and the oil dilution caused by the post injection in the passive DeNOx control is performed. I try to suppress it. On the other hand, when passive DeNOx control has hardly been performed so far (that is, when the frequency of passive DeNOx control is relatively low), even if passive DeNOx control is executed from now on, oil dilution caused by post injection will occur. Is unlikely to occur. Therefore, in this embodiment, when the execution frequency of passive DeNOx control is less than a predetermined value (step S303: Yes), execution of passive DeNOx control is not prohibited.
In this embodiment, the predetermined value for frequency determination used in step S303 is set to a larger value as the in-cylinder temperature becomes higher. When the predetermined value is a large value, the possibility that the execution frequency of the passive DeNOx control is less than the predetermined value (step S303: Yes) is higher than when the predetermined value is a small value. Therefore, in this embodiment, the higher the in-cylinder temperature is, the more the restriction on the control according to the execution frequency of the passive DeNOx control is relaxed. This is because as the in-cylinder temperature increases, the post-injected fuel is more vaporized and oil dilution is less likely to occur.

Next, in step S304, it is determined whether or not the NOx storage amount acquired in step S301 exceeds the second storage amount determination value α2. For example, the second storage amount determination value α2 is set to a fixed value of about 1/3 of the limit value of the NOx storage amount. Therefore, the reduction purification condition for changing the occlusion amount determination value is not changed as in the active DeNOx control.
As a result of this determination, if the NOx storage amount exceeds the second storage amount determination value α2 (step S304: Yes), the process proceeds to step S305.
On the other hand, when the NOx occlusion amount is equal to or less than the second occlusion amount determination value α2 (step S304: No), the process proceeds to step S307. In this case, the PCM 60 prohibits the execution of useless passive DeNOx control and sets the passive DeNOx control execution flag to “0” in order to suppress fuel consumption deterioration caused by the execution of the passive DeNOx control (step S307). ). Then, the process ends.

Next, in step S305, the PCM 60 determines whether or not the active DeNOx control execution flag acquired in step S301 is “0”. That is, the PCM 60 determines whether or not the situation is that the active DeNOx control should be executed. As a result of this determination, when the active DeNOx control execution flag is “0” (step S305: Yes), the process proceeds to step S306. In this case, since all of the above-described conditions of steps S302 to S305 are satisfied, the PCM 60 sets the passive DeNOx control execution flag to “1” in order to permit the execution of the passive DeNOx control (step S306). Then, the process ends.
On the other hand, when the active DeNOx control execution flag is not “0”, that is, “1” (step S305: No), the process proceeds to step S308. In this case, the PCM 60 prohibits the execution of the passive DeNOx control and sets the passive DeNOx control execution flag to “0” in order to preferentially execute the active DeNOx control (step S307). That is, even if the execution condition for the passive DeNOx control is satisfied, if the execution condition for the active DeNOx control is satisfied, the active DeNOx control is executed with priority. Then, the process ends.

  Next, the fuel injection amount correction control for main injection and post injection according to the embodiment of the present invention will be described with reference to FIG. FIG. 10 is a flowchart (fuel injection amount correction control flow) showing the fuel injection amount correction control processing according to the embodiment of the present invention. This fuel injection amount correction control flow is repeatedly executed by the PCM 60 at a predetermined cycle, and is shown in FIG. 3, the fuel injection control flow shown in FIG. 6, the DeNOx post injection control flow shown in FIG. It is executed in parallel with each DeNOx control execution flag setting flow.

  First, in step S401, the PCM 60 acquires various information on the vehicle. Specifically, the PCM 60, at least, the engine speed, the engine load, the value of the active DeNOx control execution flag, the value of the passive DeNOx control execution flag, the main injection amount, and the DeNOx post injection amount (specifically Is obtained as a post-injection amount for DeNOx calculated as applied during active DeNOx control and passive DeNOx control.

Next, in step S402, the PCM 60 determines whether or not the active DeNOx control execution flag acquired in step S401 is “1”. That is, the PCM 60 determines whether or not it is a situation in which active DeNOx control should be executed.
As a result of this determination, if the active DeNOx control execution flag is “1” (step S402: Yes), the process proceeds to step S403 because active DeNOx control is to be executed. The PCM 60 executes the already set main injection and post-injection for active DeNOx (step S403), and proceeds to step S404.
On the other hand, when the active DeNOx control execution flag is “0” (step S402: No), the process proceeds to step S405.

Next, in step S404, the PCM 60 determines whether or not the NOx occlusion amount of the NOx catalyst has become substantially zero. Specifically, the PCM 60 has a NOx occlusion amount estimated based on the operating state of the engine E, the flow rate of exhaust gas, the temperature of exhaust gas, and the like, and is provided on the downstream side of the DPF 46. When the detected value 116 changes, it is determined that the NOx occlusion amount of the NOx catalyst 45 has become substantially zero. When the NOx occlusion amount of the NOx catalyst 45 becomes substantially zero (step S404: Yes), the process ends. In this case, the PCM 60 resets the NOx occlusion amount used in each control flow to zero.
On the other hand, when the NOx occlusion amount of the NOx catalyst 45 is not substantially zero (step S404: No), the process returns to step S402.

Next, in step S405, the PCM 60 determines whether or not the passive DeNOx control execution flag acquired in step S401 is “1”. That is, the PCM 60 determines whether or not it is a situation where passive DeNOx control should be executed.
If the result of this determination is that the passive DeNOx control execution flag is “1” (step S405: Yes), the process proceeds to step S403 because passive DeNOx control is to be executed. The PCM 60 executes the already set main injection and passive DeNOx post-injection (step S403).
On the other hand, when the passive DeNOx control execution flag is “0” (step S405: No), the process proceeds to step S406 because the DeNOx control is not to be executed. The PCM 60 executes the already set main injection (step S406) and ends.

<Ammonia adsorption amount estimation method>
Next, a method for estimating the ammonia adsorption amount of the SCR catalyst 47 according to the embodiment of the present invention will be described with reference to FIG. FIG. 11 is a block diagram for explaining an ammonia adsorption amount estimation method according to an embodiment of the present invention. This ammonia adsorption amount estimation method is executed by the PCM 60.

  First, the PCM 60 per unit time supplied to the SCR catalyst 47 by urea injection from the urea injector 51 based on the exhaust gas state such as the exhaust gas amount and the exhaust gas temperature and the state of the SCR catalyst 47 such as the SCR temperature. Find the ammonia supply. Further, the PCM 60 obtains the ammonia generation amount per unit time generated from the NOx catalyst 45 during DeNOx control based on the operating state of the engine E and the state of the NOx catalyst 45 such as the NOx catalyst temperature and the NOx occlusion amount. Further, the PCM 60 is consumed by the reduction and purification of NOx in the SCR catalyst 47 based on the exhaust gas state such as the exhaust gas amount, the exhaust gas temperature and the NOx concentration in the exhaust gas, and the state of the SCR catalyst 47 such as the SCR temperature. Find the ammonia consumption per unit time.

Thereafter, the PCM 60 obtains an adsorption ammonia change amount (amount of change in the ammonia adsorption amount) per unit time in the SCR catalyst 47 from these ammonia supply amount, ammonia generation amount, and ammonia consumption amount. Specifically, the PCM 60 calculates the amount of change in adsorbed ammonia per unit time from “ammonia supply amount + ammonia generation amount−ammonia consumption amount”. Then, the PCM 60 obtains the current ammonia adsorption amount by applying the obtained adsorption ammonia change amount to the current ammonia adsorption amount, that is, the previously estimated ammonia adsorption amount. Specifically, if the amount of change in adsorbed ammonia is a positive value, the PCM 60 adds the amount of adsorbed ammonia to the previously estimated amount of adsorbed ammonia to obtain the current amount of adsorbed ammonia (in this case, ammonia adsorbed amount). If the amount of change in adsorbed ammonia is negative, the amount of adsorbed ammonia is subtracted from the amount of adsorbed ammonia estimated last time to obtain the current amount of adsorbed ammonia (in this case, the amount of adsorbed ammonia is Decrease).
In addition, although the example which estimates the ammonia adsorption amount of the SCR catalyst 47 was shown, you may detect the ammonia adsorption amount of the SCR catalyst 47 using a predetermined sensor.

Next, the operation and effect of the engine exhaust gas purification apparatus according to the embodiment of the present invention will be described.
According to the present embodiment, the reduction purification condition (start of NOx reduction control) is performed so as to suppress an increase in the exhaust gas temperature due to NOx reduction based on the travel distance of the vehicle corresponding to the aging history reflecting the usage state of the exhaust passage 41. (Occupation amount determination value that is a threshold value) is changed, and the removal status of the rust preventive agent applied to the exhaust passage 41 can be easily determined based on the travel distance of the vehicle reflecting the use state of the exhaust passage 41. An increase in exhaust gas temperature due to NOx reduction can be suppressed based on the removal status of the rust inhibitor. Therefore, as shown in FIG. 12, when the rust inhibitor applied to the exhaust passage 41 remains (see the left side in the figure), the NOx reduction control period is shortened to suppress the generation of white smoke. When the rust preventive agent applied to the exhaust passage 41 is removed (see the right side in the figure), the NOx catalyst is regenerated using an appropriate NOx reduction control period without shortening the NOx reduction control period. be able to.

The reduction purification condition includes that the NOx occlusion amount occluded in the NOx catalyst 45 is equal to or greater than the occlusion amount judgment value that is the start threshold value, and the NOx reduction control means occludes when the travel distance of the vehicle is shorter than the predetermined distance. The amount judgment value is changed to be smaller.
Thereby, since the NOx catalyst 45 is regenerated in a state where the amount of NOx stored is small, it is possible to ensure high purification performance of the NOx catalyst.

  A DPF 46 provided in the exhaust passage 41 and collecting particulates in the exhaust gas, and a regeneration means for burning and removing the collected particulates, and the PCM 60 is reduced when the DPF 46 is regenerated by the regeneration means. In order to prohibit the change of the purification conditions, it is possible to reliably determine the end of evaporation of the rust preventive agent applied to the exhaust passage 41 using the regeneration of the DPF 46 by the regeneration means as a parameter, and appropriately NOx without generating white smoke. The catalyst 45 can be regenerated.

  The regeneration means is configured to execute a familiar regeneration process in which the collected particulates are burned and removed by raising the temperature of the DPF 46 when the cumulative travel distance of the vehicle reaches a predetermined distance. When the familiar regeneration process is executed, it is possible to reliably determine the end of evaporation of the rust inhibitor applied to the exhaust passage 41 using the familiar regeneration process of the DPF 46 by the regeneration means as a parameter in order to prohibit the change of the reduction purification condition. it can.

Next, a modified example in which the embodiment is partially changed will be described.
1] In the above embodiment, an example in which an aged history reflecting the use state of the exhaust passage is detected using the travel distance from when the new exhaust passage (exhaust pipe) is mounted as a parameter has been described. It is only necessary to be able to detect (application state of rust preventive agent), and it is possible to detect any parameters such as the elapsed time since the installation of a new exhaust passage, the cumulative time of ignition ON, the cumulative flow rate of exhaust gas, etc. It is also possible to do.

2] In the embodiment changes the start threshold of the NOx reduction control (storage amount judgment value), a description has been given of an example in which the end threshold value to a fixed value, may be changed to exit threshold. Specifically, when the NOx occlusion amount stored in the NOx catalyst 45 becomes equal to or higher than the start threshold value, the NOx reduction control is started and the NOx occlusion amount occluded in the NOx catalyst 45 becomes equal to or less than the end threshold value. Completing the NOx reduction control is included in the reduction purification condition, and the PCM 60 changes the end threshold value to be larger when the travel distance of the vehicle is shorter than a predetermined distance.
As a result, as shown in FIG. 13, when the rust inhibitor applied to the exhaust pipe remains (see the left side in the figure), the NOx reduction control period can be shortened to suppress the generation of white smoke. When the rust inhibitor applied to the exhaust pipe is removed (see the right side in the figure), the NOx catalyst can be regenerated using an appropriate NOx reduction control period without shortening the NOx reduction control period. it can. In addition, since the NOx catalyst is regenerated with a large amount of NOx occluded, high reduction efficiency can be ensured.

3] In the above-described embodiment, the example in which the NOx reduction control period is changed has been described. However, the PCM 60 may correct the target air-fuel ratio that can reduce NOx based on the aging history using the travel distance of the vehicle as a parameter. good. Thereby, the removal condition of a rust preventive agent can be determined with the simple structure of a travel distance.
Further, the PCM 60 may correct the target air-fuel ratio that can reduce NOx based on the aging history with the travel distance from when the new exhaust pipe is mounted as a parameter. Thereby, the exhaust pipe to which the rust preventive agent is not applied can be excluded from the target, and the removal status of the rust preventive agent can be accurately determined.

4) In the above-described embodiment, the first occlusion determination threshold that is the active DeNOx determination threshold is corrected based on the aging history, and the second occlusion determination threshold that is the passive DeNOx determination threshold is not corrected. The second occlusion determination threshold value may be corrected based on the aging history in the same manner as the first occlusion determination threshold value. At this time, the second occlusion determination threshold is also set to a characteristic that increases in proportion to the travel distance up to a predetermined distance in the same manner as the first occlusion determination threshold and becomes a constant value after the predetermined distance.

5] In addition, those skilled in the art can implement the present invention in a form in which various modifications are added to the above-described embodiment or in a form in which each embodiment is combined without departing from the spirit of the present invention. Various modifications are also included.

20 Fuel injection valve 41 Exhaust passage 45 NOx catalyst 46 DPF
60 PCM
E engine

Claims (6)

NOx in the exhaust gas is stored when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, and is stored in the exhaust passage of the engine. The NOx catalyst that reduces when it is richer than the air-fuel ratio, and when the reduction purification condition of the NOx catalyst is satisfied, the air-fuel ratio of the exhaust gas is changed to a target air-fuel ratio that can reduce NOx stored in the NOx catalyst In an engine exhaust purification device comprising NOx reduction control means for performing NOx reduction control for setting and reducing NOx stored in the NOx catalyst,
The reduction purification condition includes that the NOx occlusion amount occluded in the NOx catalyst is equal to or greater than a start threshold value,
The NOx reduction control means changes the start threshold value to be small so as to suppress an increase in exhaust gas temperature due to NOx reduction when an aged history reflecting the use state of the exhaust passage is shorter than a predetermined history. An exhaust purification device for an engine characterized by the above. NOx in the exhaust gas is stored when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, and is stored in the exhaust passage of the engine. The NOx catalyst that reduces when it is richer than the air-fuel ratio, and when the reduction purification condition of the NOx catalyst is satisfied, the air-fuel ratio of the exhaust gas is changed to a target air-fuel ratio that can reduce NOx stored in the NOx catalyst In an engine exhaust purification device comprising NOx reduction control means for performing NOx reduction control for setting and reducing NOx stored in the NOx catalyst,
The NOx reduction control is started when the NOx occlusion amount stored in the NOx catalyst becomes equal to or higher than the start threshold value, and the NOx reduction control is performed when the NOx occlusion amount stored in the NOx catalyst becomes equal to or less than the end threshold value. Including termination in the reduction and purification conditions,
The NOx reduction control means changes the end threshold value so as to increase so as to suppress an increase in exhaust gas temperature due to NOx reduction when an aged history reflecting the use state of the exhaust passage is shorter than a predetermined history. exhaust purification device characteristics and to Rue engine a. A filter that is provided in the exhaust passage and collects particulates in the exhaust gas;
Regenerating means for burning and removing the collected particulates,
3. The engine exhaust purification system according to claim 1, wherein the NOx reduction control unit prohibits the change of the reduction purification condition when the filter is regenerated by the regeneration unit. The regeneration means is configured to execute a familiar regeneration process in which when the cumulative travel distance of the vehicle reaches a predetermined distance, the temperature of the filter is increased to burn and remove the collected particulates.
4. The engine exhaust gas purification apparatus according to claim 3 , wherein the NOx reduction control unit prohibits the change of the reduction purification condition when the regeneration unit executes a familiar regeneration process . 2. The engine exhaust gas purification apparatus according to claim 1 , wherein the NOx reduction control unit corrects a target air-fuel ratio capable of reducing the NOx based on the aging history using a travel distance of a vehicle as a parameter . 2. The engine according to claim 1 , wherein the NOx reduction control unit corrects a target air-fuel ratio capable of reducing the NOx based on the aging history using a travel distance from when the new exhaust passage is mounted as a parameter. Exhaust purification equipment.