JP6504474B2 - Engine exhaust purification system - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus for an engine that reduces and purifies nitrogen oxides (hereinafter referred to as NOx) in exhaust gas.

  Conventionally, a catalyst for reducing and purifying NOx in exhaust gas is disposed in an exhaust passage of an engine. As such a catalyst, NOx storage reduction type catalyst (NOx Storage Catalyst, hereinafter referred to as NOx catalyst), ammonia which stores NOx in exhaust gas in an oxidizing atmosphere and reduces NOx stored in a reducing atmosphere, and ammonia A Selective Catalytic Reduction (hereinafter referred to as an SCR catalyst) is known which reduces NO x in exhaust gas using H 2 as a reducing agent. Since these catalysts have different conditions for achieving their functions, they can be used in combination to constitute an exhaust gas control apparatus for an engine that can cope with a wide range of operating conditions.

  The NOx catalyst occludes NOx in the exhaust gas under an oxidizing atmosphere when the air-fuel ratio of the exhaust gas is in the lean side (air excess ratio λ> 1) larger than the theoretical air-fuel ratio. Further, the NOx catalyst is in a reducing atmosphere when the air-fuel ratio of the exhaust gas is in the vicinity of the stoichiometric air-fuel ratio (λ 又 は 1) or in the rich side (λ <1) where the fuel is larger than the theoretical air-fuel ratio. The NOx stored in the NOx catalyst is reduced using hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas. The SCR catalyst hydrolyzes the supplied urea at high temperature to generate and adsorb ammonia, and reduces the NOx in the exhaust gas with this ammonia.

  For example, when the engine load at which the NOx catalyst travels at a constant speed is low and the air-fuel ratio on the lean side continues, for example, the NOx storage amount reaches its upper limit and NOx in the exhaust gas can not be stored. Also, the NOx storage performance of the NOx catalyst decreases with the increase in the NOx storage capacity. Therefore, if the state of the air-fuel ratio on the lean side continues, it is possible to appropriately execute the NOx reduction processing for regenerating the NOx catalyst by reducing the stored NOx and discharging it before the stored NOx amount reaches the upper limit. Is configured.

  In the NOx reduction process, exhaust is performed by performing post injection that injects additional fuel at a predetermined timing after main injection, in addition to main injection that supplies an amount of fuel corresponding to the torque required for the engine into the engine cylinder. The air-fuel ratio of the gas is set near the stoichiometric air-fuel ratio or on the rich side of the stoichiometric air-fuel ratio to make a reducing atmosphere. Then, the NOx stored in the NOx catalyst is reduced using HC and CO in the exhaust gas, and the NOx is discharged as nitrogen (N2), carbon dioxide (CO2), and water (H2O). This NOx reduction treatment restores the NOx storage performance of the NOx catalyst.

  In order to make full use of the NOx purification performance of the NOx catalyst and the SCR catalyst, it is necessary to have a somewhat high temperature at which each catalyst is activated. For example, immediately after the start of the engine or after the fuel cut by using the engine brake continues for a long time, the temperature of these catalysts is low, so the NOx purification performance can not be sufficiently exhibited. Therefore, the NOx catalyst takes charge of NOx purification while the SCR catalyst, which exhibits NOx purification performance at a higher temperature than the NOx catalyst, can not exhibit its performance.

  Even when the temperature of the NOx catalyst is low, NOx reduction processing is performed after engine start-up to restore the NOx storage performance so that NOx can be stored as much as possible to purify the exhaust gas. For example, as in the exhaust gas purification apparatus for an internal combustion engine described in Patent Document 1, a configuration is known in which the first NOx reduction processing after engine start is performed early by setting the regeneration start temperature according to the NOx storage amount of the NOx catalyst. ing. The NOx reduction treatment has the effect of raising the temperature of the exhaust gas and raising the temperature of the catalyst in the exhaust passage since the additional fuel is post-injected and burned.

JP, 2008-121596, A

  In the NOx reduction process, ammonia (NH3) is generated from HC and NOx in the exhaust gas on the NOx catalyst, and the generated ammonia is consumed for NOx reduction on the NOx catalyst. Since the NOx reduction treatment ends when the NOx stored in the NOx catalyst reaches a predetermined amount (for example, zero), the temperature rise of the catalyst in the exhaust passage may not be sufficient at the end of the NOx reduction treatment. However, if the NOx reduction treatment is continued to raise the temperature of the catalyst, the ammonia generated on the NOx catalyst is not consumed and may be discharged from the exhaust passage to the outside to generate an offensive odor, which is not preferable. Further, the fuel consumption is increased due to the post injection, so the fuel consumption is deteriorated.

  An object of the present invention is to provide an exhaust gas purification apparatus for an engine capable of quickly raising the temperature of the catalyst in the exhaust passage and suppressing the formation of ammonia.

  The exhaust gas purification apparatus for an engine according to claim 1 is characterized in that the NOx catalyst and the SCR catalyst disposed in the exhaust passage of the engine and the exhaust gas empty when the NOx storage amount of the NOx catalyst is equal to or more than a preset reduction start value. In an engine exhaust purification device comprising: NOx reduction control means for performing NOx reduction processing by setting the fuel ratio to a reduction air fuel ratio near the stoichiometric air fuel ratio or on the air fuel ratio rich side, the NOx reduction control means comprises the NOx storage amount If the temperature of the SCR catalyst is lower than the preset SCR catalyst activation temperature when the reduction end value becomes lower than the preset reduction end value, the rich air side and the lean side set to the lean side of the theoretical air fuel ratio It is characterized in that temperature increase control set to a temperature increase air fuel ratio leaner than the reduction air fuel ratio is executed.

  According to the above configuration, it is possible to raise the temperature of the SCR catalyst early by utilizing the rise of the exhaust gas temperature at the reduction air-fuel ratio. When the NOx storage amount becomes equal to or less than the reduction end value, the exhaust gas temperature is set to a temperature higher than the lean air-fuel ratio because it is set to a temperature increase air-fuel ratio richer than the lean air-fuel ratio during normal operation without performing NOx reduction processing. As it becomes higher, the temperature of the NOx catalyst and the SCR catalyst can be raised earlier. Further, since the temperature-increased air-fuel ratio is set to be leaner than the reduced air-fuel ratio, the generation of ammonia on the NOx catalyst can be suppressed and the fuel consumption can be suppressed more than the state of the reduced air-fuel ratio.

The invention of claim 2 is characterized in that, in the invention of claim 1, the SCR catalyst is disposed downstream of the exhaust gas passage of the engine than the NOx catalyst.
With the above configuration, of the ammonia generated by the NOx catalyst, ammonia that is not consumed can be used in the SCR catalyst, and the emission of ammonia can be suppressed.

The invention according to claim 3 is the invention according to claim 1 or 2, wherein the exhaust passage of the engine is provided with an oxidation catalyst, and the NOx reduction control means makes the temperature increase air fuel ratio richer than the lean air fuel ratio at the time of temperature rise control. It is characterized in that it is set to the side leaner than the stoichiometric air fuel ratio.
With the above configuration, since the temperature-increased air-fuel ratio is set to the lean side of the theoretical air-fuel ratio, the exhaust gas temperature can be increased by the oxidation reaction in the oxidation catalyst, so the temperature of the NOx catalyst and the SCR catalyst can be raised quickly. Can.

The invention according to claim 4 is the invention according to any one of claims 1 to 3, wherein the NOx reduction control means ends the temperature rise control when the exhaust gas temperature downstream of the NOx catalyst becomes equal to or higher than a preset temperature set in advance. It is characterized by
According to the above configuration, high temperature deterioration of the NOx catalyst can be suppressed.

In the invention according to claim 5, according to any one of the inventions according to claims 1 to 4, the NOx reduction control means makes the reduction start value for executing the first NOx reduction process after engine start smaller than the second and subsequent times. The temperature raising control is performed when the temperature of the SCR catalyst is lower than the SCR catalyst activation temperature when the NOx storage amount becomes equal to or less than the reduction end value by the first NOx reduction processing. And
According to the above configuration, the first NOx reduction treatment after the start of the engine can be started early, and the temperature of the SCR catalyst can be raised early.

In the invention of claim 6, in the invention of claim 5, the NOx reduction control means sets the reduction start value for executing the first NOx reduction process smaller as the temperature of the SCR catalyst is lower. It is characterized by
With the above configuration, as the temperature of the SCR catalyst is lower, the first NOx reduction treatment after engine start can be started earlier, and the temperature of the SCR catalyst can be raised earlier according to the temperature condition of the SCR catalyst.

  According to the exhaust gas control apparatus of the engine of the present invention, by performing the NOx reduction process of the NOx catalyst, the temperature of the catalyst in the exhaust passage can be raised early, and the generation of ammonia in the NOx catalyst can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram of the engine system by which the exhaust gas purification device of the engine by embodiment of this invention was applied. FIG. 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 explanatory drawing about the setting method of the air fuel ratio 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. 3 is a flowchart showing fuel injection control according to an embodiment of the present invention. It is a figure which shows the driving | operation area | range of the engine which performs DeNOx in embodiment of this invention. It is a figure which shows the temperature range which implements DeNOx in embodiment of this invention. It is a flow chart which shows post injection amount calculation processing by an embodiment of the present invention. It is a flowchart which shows the setting process of the DeNOx execution flag by embodiment of this invention. 5 is a flowchart showing DeNOx execution control according to an embodiment of the present invention. It is a time chart at the time of DeNOx execution by an embodiment of the present invention. It is a figure which shows the setting example of the reduction | restoration start value (alpha).

  Hereinafter, an exhaust purification system of an engine according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the engine system 200 mainly includes an engine E as a diesel engine, an intake system IN for supplying intake air to the engine E, a fuel supply system FS for supplying fuel to the engine E, and the engine E, the exhaust system EX for exhausting the exhaust gas, the sensors 100 to 119 for detecting various conditions related to the engine system 200, the PCM (Power-train Control Module) 60 for controlling the engine system 200, and the SCR catalyst 47 And a DCU (Dosing Control Unit) 70 that performs control.

  The intake system IN has an intake passage 1 through which intake air passes. On the intake passage 1, an air cleaner 3, a compressor of a turbocharger 5, an intercooler 8 and an intake shutter valve 7 are arranged in this order from the upstream side. A surge tank 12 is provided (corresponding to a throttle valve). The air cleaner 3 purifies air introduced from the outside. The compressor of the turbocharger 5 compresses the intake air passing therethrough to increase the intake pressure. The intercooler 8 cools the intake air using outside air and cooling water. The intake shutter valve 7 regulates the flow rate of intake air passing therethrough. The surge tank 12 temporarily stores intake air in order to efficiently supply the intake air to the engine E.

  An air flow sensor 101 for detecting the amount of intake air and a temperature sensor 102 for detecting an intake temperature are provided on the intake passage 1 on the downstream side of the air cleaner 3. The turbocharger 5 is provided with a pressure sensor 103 for detecting the pressure of intake air. A temperature sensor 106 for detecting the intake air temperature is provided on the intake passage 1 immediately downstream of the intercooler 8. The intake shutter valve 7 is provided with a position sensor 105 for detecting the opening degree of the intake shutter valve 7. The surge tank 12 is provided with a pressure sensor 108 for detecting the pressure of intake air in the intake manifold. The various sensors 101 to 108 provided in the intake system IN respectively output detection signals S101 to S108 corresponding to the detected parameters to the PCM 60.

  The engine E has an intake valve 15, a combustion chamber 17, a fuel injection valve 20, a glow plug 21, a piston 23, a crankshaft 25, an exhaust valve 27, and the like. The intake valve 15 introduces the intake air supplied from the intake passage 1 (including the intake manifold) into the combustion chamber 17. The fuel injection valve 20 injects fuel toward the combustion chamber 17. The glow plug 21 is provided with a heat generating portion which generates heat by energization in the combustion chamber 17. The piston 23 reciprocates due to the combustion of the air-fuel mixture in the combustion chamber 17. The crankshaft 25 is rotated by the reciprocating motion of the piston 23. The exhaust valve 27 exhausts the exhaust gas generated by the combustion of the air-fuel mixture in the combustion chamber 17 to a metallic exhaust passage 41 (including an exhaust manifold).

  The engine E is provided with a crank angle sensor 100 that detects a crank angle of the crank shaft 25 on the basis of, for example, a top dead center or the like. The crank angle sensor 100 outputs a detection signal S100 corresponding to the detected crank angle to the PCM 60. The PCM 60 acquires the engine speed based on the detection signal S100.

  The fuel supply system FS has a fuel tank 30 for storing fuel, and a fuel supply passage 38 for supplying 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 this order from the upstream side.

  The exhaust system EX has an exhaust passage 41 through which the exhaust gas passes. On the exhaust passage 41, the turbine of the turbocharger 5 which is rotated by the passing exhaust gas and drives the compressor by this rotation is It is provided. On the exhaust passage 41 on the downstream side of the turbine, a NOx catalyst 45, a diesel particulate filter (hereinafter referred to as DPF) 46, a urea injector 51, and an SCR catalyst 47 are arranged in order from the upstream side. A slip catalyst 48 is provided. The SCR catalyst may be disposed upstream of the NOx catalyst 45.

  The NOx catalyst 45 occludes and purifies NOx in the exhaust gas. The DPF 46 collects particulate matter in the exhaust gas. The urea injector 51 injects urea water stored in a urea water tank (not shown) into the exhaust passage 41 on the downstream side of the DPF 46 to supply urea. The SCR catalyst 47 hydrolyzes the urea injected from the urea injector 51 to generate ammonia, and the ammonia in the exhaust gas is reduced and purified by the ammonia. The slip catalyst 48 oxidizes and purifies the ammonia released from the SCR catalyst 47. The urea injector 51 performs control for injecting urea into the exhaust passage 41 according to a control signal S51 supplied from the DCU 70.

  The NOx catalyst 45 occludes NOx in the exhaust gas in an oxidizing atmosphere in which the air-fuel ratio of the exhaust gas is on the lean side (λ> 1) larger than the stoichiometric air-fuel ratio. Further, the stored NOx is reduced in a reducing atmosphere in which the air-fuel ratio of the exhaust gas is near the stoichiometric air-fuel ratio (λ ≒ 1) or the rich side (λ <1) smaller than the theoretical air-fuel ratio. When the NOx catalyst 45 reduces the stored NOx, “N” in the NOx stored in the NOx catalyst 45 and hydrocarbons (HC) such as unburned fuel supplied to the NOx catalyst 45 as a reducing agent Combine with “H” in it to form ammonia (NH 3). The generated ammonia is consumed for the reduction and purification of NOx.

  In addition to the function as a NOx storage reduction type catalyst, the NOx catalyst 45 functions as a diesel oxidation catalyst (hereinafter referred to as DOC) that oxidizes and purifies HC, CO, etc. in exhaust gas. Also have. For example, the NOx catalyst 45 is formed by coating the surface of the DOC catalyst material with the NSC catalyst material.

  The SCR catalyst 47 adsorbs ammonia generated from urea injected by the urea injector 51 and ammonia generated by reduction of NOx in the NOx catalyst 45 on the upstream side of the exhaust passage 41, and the adsorbed ammonia causes exhaust gas to be contained in the exhaust gas. Reduce and purify NOx. For example, the SCR catalyst 47 is made by supporting a catalyst metal, which reduces NOx with ammonia, on a zeolite that traps ammonia to form a catalyst component, and supporting the catalyst component on the cell wall of a honeycomb carrier. . Fe, Ti, Ce, W, etc. are used as catalyst metals for NOx reduction.

  The DCU 70 controls the urea injector 51 so that an appropriate amount of ammonia is adsorbed to the SCR catalyst 47 in order to ensure both the NOx purification performance by the SCR catalyst 47 and the suppression of the release (slip) of ammonia from the SCR catalyst 47. Perform injection control. Since the SCR catalyst 47 has a property of releasing the adsorbed ammonia as the temperature becomes higher, the ammonia adsorption capacity changes according to the temperature of the SCR catalyst 47. Therefore, the DCU 70 injects the urea injector 51 based on the temperature of the SCR catalyst 47 and the like. Take control.

  The exhaust passage 41 on the upstream side of the turbine of the turbocharger 5 is provided with a pressure sensor 109 for detecting the pressure of the exhaust gas and a temperature sensor 110 for detecting the temperature of the exhaust gas. An O 2 sensor 111 for detecting the oxygen concentration is provided in the exhaust passage 41 on the downstream side of the engine. Further, the exhaust passage 41 includes a temperature sensor 112 for detecting the temperature of exhaust gas on the upstream side of the NOx catalyst 45, a temperature sensor 113 for detecting the temperature of exhaust gas between the NOx catalyst 45 and the DPF 46, and an upstream side of the DPF 46 A differential pressure sensor 114 that detects the pressure difference between the exhaust gas on the downstream side, a temperature sensor 115 that detects the exhaust gas temperature on the downstream side of the DPF 46, and a NOx sensor that detects the NOx concentration in the exhaust gas on the downstream side of the DPF 46 116, a temperature sensor 117 for detecting the exhaust gas temperature upstream of the SCR catalyst 47, an NOx sensor 118 for detecting the concentration of NOx in the exhaust gas downstream of the SCR catalyst 47, and an upstream side of the slip catalyst 48. A PM sensor 119 is provided to detect PM in exhaust gas. The various sensors 109 to 119 of the exhaust system EX output detection signals S109 to S119 respectively corresponding to the detected parameters to the PCM 60.

  The turbocharger 5 is configured as a two-stage supercharging system capable of efficiently obtaining high supercharging over the entire range from a low rotation region to a high rotation region where exhaust energy is low. The turbocharger 5 includes a large turbocharger 5a for supercharging a large amount of air in a high speed range, a small turbocharger 5b capable of efficiently supercharging even with low exhaust energy, a compressor bypass valve 5c, and regulation. A valve 5 d and a waste gate valve 5 e are provided. The compressor bypass valve 5c controls the flow of intake air to the compressor of the small turbocharger 5b. The regulating valve 5d controls the flow of exhaust to the turbine of the small turbocharger 5b. The waste gate valve 5e controls the flow of exhaust to the turbine of the large turbocharger 5a. By driving each valve according to the operating state (engine speed and load) of the engine E, supercharging by the large turbocharger 5 a and the small turbocharger 5 b is switched.

  The engine system 200 also has an EGR device 43. The EGR device 43 includes an EGR passage 43a, an EGR cooler 43b, a first EGR valve 43c, an EGR cooler bypass passage 43d, and a second EGR valve 43e. The EGR passage 43 a connects the exhaust passage 41 on the upstream side of the turbine of the turbocharger 5 and the intake passage 1 on the downstream side (downstream of the intercooler 8) of the compressor of the turbocharger 5. The EGR cooler 43b cools the exhaust gas passing through the EGR passage 43a. The first EGR valve 43c adjusts the flow rate of the exhaust gas to be passed through the EGR passage 43a. The EGR cooler bypass passage 43d bypasses the EGR cooler 43b to circulate the exhaust gas. The second EGR valve 43e adjusts the flow rate of the exhaust gas to be passed through the EGR cooler bypass passage 43d.

  FIG. 2 is a block diagram showing an electrical configuration of an exhaust gas purification apparatus of an engine. The PCM 60 includes detection signals S100 to S119 of the various sensors 100 to 119, a detection signal S150 of an accelerator opening degree sensor 150 for detecting an accelerator opening degree reflecting the depression amount of an accelerator pedal, and a vehicle speed sensor 151 for detecting a vehicle speed. Based on the detection signal S151, the control signal S20 that mainly controls the fuel injection valve 20 is output, and the control signal S7 that controls the intake shutter valve 7 is output.

  The PCM 60 performs main injection to inject fuel toward the combustion chamber 17 in order to output an engine torque corresponding to the accelerator pedal operation of the driver. In order to improve fuel consumption mainly, the main injection basically sets the fuel injection amount and the like so that the air-fuel ratio of the exhaust gas becomes lean. Further, when reducing the NOx stored in the NOx catalyst 45, the PCM 60 sets the air-fuel ratio of the exhaust gas to near the stoichiometric air-fuel ratio or to the rich reduced air-fuel ratio smaller than the stoichiometric air-fuel ratio. 20 is a NOx reduction control means for performing NOx reduction control to post-inject additional fuel from 20.

  The PCM 60 includes a CPU, various programs to be interpreted and executed on the CPU (including a basic control program such as an OS, and an application program activated on the OS to realize a specific function), operating conditions of programs and engines, etc. It is comprised by a computer provided with internal memories, such as ROM for storing various information, and RAM.

Next, setting of the air-fuel ratio by the PCM 60 will be described.
In FIG. 3, the vertical axis indicates the excess air ratio λ, and the horizontal axis indicates the ammonia adsorption amount of the SCR catalyst 47 described later. In the case where the amount of air actually supplied is the same as that at the theoretical air fuel ratio, that is, when the air fuel ratio is set to the theoretical air fuel ratio, λ = 1 and the region R21 of λ <1 on the rich side is a NOx catalyst The range 45 where the stored NOx can be reduced is shown, and the region R22 of λ> 1 on the lean side of the air fuel ratio shows the range where the NOx catalyst 45 stores NOx. During normal travel, the air-fuel ratio is set so that λ basically falls within the range R22 mainly to improve fuel consumption. A line G11 indicates λ set in accordance with the ammonia adsorption amount of the SCR catalyst 47 at the time of NOx reduction control. This line G11 corresponds to a map that defines the air-fuel ratio set according to the ammonia adsorption amount.

  Post injection for setting the air-fuel ratio at the time of NOx reduction control injects additional fuel at a timing (for example, an expansion stroke) which does not contribute to the output of the engine torque after the main injection. By this post injection, the NOx occluded in the NOx catalyst 45 is brought into the state where the air fuel ratio of the exhaust gas is in the vicinity of the stoichiometric air fuel ratio (λ ≒ 1) or in the rich side (λ <1) smaller than the theoretical air fuel ratio. The NOx reduction process to reduce is performed. Hereinafter, this NOx reduction process is referred to as "DeNOx". "De" is a prefix meaning separation or removal.

Next, estimation of the ammonia adsorption amount of the SCR catalyst 47 by the PCM 60 will be described.
FIG. 4 is a block diagram for explaining a method of estimating the amount of adsorbed ammonia. First, ammonia supply 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 exhaust gas temperature, and the SCR catalyst temperature and the like. Determine the quantity. Further, the amount of ammonia generated per unit time generated from the NOx catalyst 45 at the time of DeNOx is determined based on the operating state of the engine E and the state of the NOx catalyst 45 such as NOx catalyst temperature and NOx storage amount. In addition, the unit time consumed by the reduction and purification of NOx in the SCR catalyst 47 based on the exhaust gas state, the exhaust gas state such as the exhaust gas temperature and the NOx concentration in the exhaust gas, and the SCR catalyst 47 such as the SCR catalyst temperature Determine the per capita ammonia consumption.

  Thereafter, the amount of change in adsorbed ammonia per unit time (the amount of change in the amount of adsorbed ammonia) in the SCR catalyst 47 is determined from the amount of supplied ammonia, the amount of generated ammonia and the amount of consumed ammonia. Then, the present (current) ammonia adsorption amount is obtained by adding the obtained adsorption ammonia change amount to the current ammonia adsorption amount, that is, the ammonia adsorption amount estimated last time.

Next, fuel injection control by the PCM 60 will be described.
FIG. 5 is a flowchart showing fuel injection control. The fuel injection control is started when the ignition of the vehicle is turned on and the PCM 60 is started, and is repeatedly executed in a predetermined cycle. Si (i = 201, 202,...) In the figure represents a step.

  First, in S201, the driving state of the vehicle, for example, 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 are currently set Get information such as the current gear position.

  Next, in S202, a target acceleration is set based on the driving state of the vehicle acquired in S201. For example, an acceleration characteristic map corresponding to the current vehicle speed and gear is selected from among the acceleration characteristic maps defined for various vehicle speeds and gear stages stored in advance in the internal memory, and the selected acceleration characteristic map is selected. Reference is made to determine a target acceleration corresponding to the current accelerator opening.

  Next, in S203, a target torque of the engine E for achieving the target acceleration determined in S202 is determined. In this case, the target torque is determined within the range of torque that the engine E can output based on the current vehicle speed, gear, road surface gradient, road surface μ and the like.

  Next, in S204, in order to output the target torque determined in S203 from the engine E, the amount of fuel injection of the main injection to be injected from the fuel injection valve 20 based on the target torque and the engine speed derived from the crank angle Calculate the main injection amount).

  In parallel to the above-described processing of S202 to S204, the fuel injection pattern according to the operating state of the engine E is set in S205. In the case of performing DeNOx, a fuel injection pattern for performing post injection in addition to main injection is set, and the fuel injection amount (post injection amount) for post injection and the timing of post injection are set. When DeNOx is not performed, a fuel injection pattern of only main injection is set.

  Next, in S206, the fuel injection valve 20 is controlled based on the main injection amount calculated in S204 and the fuel injection pattern set in S205 (including post injection amount and post injection timing when performing post injection) Do.

Next, DeNOx will be described.
The NOx catalyst 45 occludes NOx in the exhaust gas in an oxidizing atmosphere in which the air-fuel ratio of the exhaust gas is set to the lean side. The NOx storage amount of the NOx catalyst 45 has an upper limit, and the NOx storage performance decreases as the NOx storage amount increases. Therefore, when the NOx storage amount exceeds the reduction start value α, DeNOx that reduces the NOx stored in the NOx catalyst 45 is executed and discharged to the outside to regenerate the NOx catalyst 45 and restore the NOx storage performance. I am doing it.

  When performing DeNOx, the PCM 60 sets a predetermined timing in the expansion stroke of the engine E in which the post-injected fuel is burned in the combustion chamber 17 (within the cylinder) as the post injection timing. At that timing, post injection is performed from the fuel injection valve 20, and combustion is performed in the cylinder to perform control to set the air-fuel ratio of the exhaust gas to the reduction side air-fuel ratio on the rich side. At this time, an appropriate amount of EGR gas is introduced at the time of DeNOx execution to effectively delay the ignition of the post-injected fuel so that ignition occurs in a state where air and fuel are appropriately mixed. Thus, the post-injected fuel is discharged as HC of a large amount of unburned fuel as it is, and oil dilution by the post-injected fuel is suppressed.

  Here, with reference to FIG. 6, the operating range of the engine E that executes DeNOx will be described. In FIG. 6, the horizontal axis represents the engine speed, and the vertical axis represents the engine load. The curve L1 shows the maximum torque line of the engine E. The PCM 60 has an engine load equal to or greater than a first predetermined load Lo1 and equal to or less than a second predetermined load Lo2, and has an engine speed equal to or greater than a first predetermined speed N1 and equal to or less than a second predetermined speed N2. And, when the engine speed is within the operating range R12, the DeNOx is executed. The air-fuel ratio of the exhaust gas at this time is set to a lean air-fuel ratio leaner than the stoichiometric air-fuel ratio.

  As the engine load increases, the cylinder temperature increases, and post-injection fuel burns in a state where it is not properly mixed with air, and a large amount of HC is generated. On the contrary, in the region where the engine load such as idling is considerably low, the temperature of the NOx catalyst 45 is lowered and the NOx purification performance is not sufficiently exhibited. In addition, in this region, post-injected fuel does not burn properly and a misfire occurs. A phenomenon similar to this also occurs for the engine speed.

  From the above, the operation range R12 of the engine E corresponding to the medium load range and the medium rotation range is set as the DeNOx execution range for executing the DeNOx process, and the DeNOx process is prohibited in the other operation ranges. As described above, in the operation range R13 of the engine E in which the DeNOx process is prohibited, the SCR catalyst 47 prevents the exhaust of NOx.

  Next, the temperature range in which the DeNOx process is performed will be described based on FIG. In FIG. 7, the horizontal axis indicates the temperature, and the vertical axis indicates the NOx purification rate. The NOx catalyst 45 exhibits NOx purification performance in a low temperature range as compared with the SCR catalyst 47, and the SCR catalyst 47 exhibits NOx purification performance in a high temperature range as compared with the NOx catalyst 45. The temperature range in which the NOx purification performance of the NOx catalyst 45 is exhibited partially overlaps the low temperature side of the temperature range in which the NOx purification performance of the SCR catalyst 47 is exhibited.

  The boundary temperatures on the low temperature side of the temperature range where the NOx purification rate above a certain level can be obtained by the NOx catalyst 45 and the SCR catalyst 47 are respectively the NOx catalyst activation temperature Tn and the SCR catalyst activation temperature (activation temperature) Ts. The PCM 60 executes DeNOx when the temperature of the NOx catalyst 45 is equal to or higher than the NOx catalyst activation temperature Tn and the temperature of the SCR catalyst 47 is lower than the SCR catalyst activation temperature Ts. If the temperature of the NOx catalyst 45 is lower than the NOx catalyst activation temperature Tn or the SCR catalyst temperature is equal to or higher than the SCR catalyst activation temperature Ts, DeNOx is prohibited. This is because DeNOx is not efficient when it is less than the NOx catalyst activation temperature Tn, and there is no need to regenerate the NOx catalyst 45 because the SCR catalyst 47 purifies NOx when it is more than the SCR catalyst activation temperature Ts.

  Next, calculation of the post injection amount applied to DeNOx by the PCM 60 will be described. FIG. 8 is a flowchart (post injection amount calculation flow) of calculation processing of the post injection amount. Si (i = 211, 212,...) In the figure represents a step. The post injection amount calculation flow is repeatedly performed by the PCM 60 in a predetermined cycle, and is performed in parallel with the fuel injection control flow shown in FIG. 5, and the post injection amount is calculated while the fuel injection control is being performed. Calculated at any time.

  First, in S211, the operating state of the engine E is acquired. For example, the intake air amount detected by the air flow sensor 101, the oxygen concentration of the exhaust gas detected by the O 2 sensor 111, the main injection amount calculated in S204 of FIG. 5, and the like are acquired. Further, the amount of EGR gas recirculated to the intake system IN by the EGR device 43 and the amount of adsorbed ammonia, which is the amount of ammonia adsorbed by the SCR catalyst 47, are acquired.

  Next, in S212, based on the ammonia adsorption amount acquired in S211, the rich side air-fuel ratio applied to reduce the NOx stored in the NOx catalyst 45 is set. The reduction air-fuel ratio is set based on a map (see FIG. 3) specified according to the ammonia adsorption amount of the SCR catalyst 47.

  Next, in S213, the amount of air introduced into the engine E (that is, the amount of charge) is calculated based on the amount of intake air and the amount of EGR gas acquired in S211. Then, in S214, the oxygen concentration of the air introduced into the engine E is calculated from the filling amount calculated in S213.

  Next, at S215, based on the oxygen concentration calculated at S214 and the oxygen concentration detected by the O2 sensor 111, a post injection amount for making the air-fuel ratio set at S212 is calculated. 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 is empty The post injection amount for making the fuel ratio to the set air-fuel ratio is calculated. The air-fuel ratio of the exhaust gas is controlled to the air-fuel ratio accurately set by the post-injection for injecting the fuel of the calculated post-injection amount, so that the NOx stored in the NOx catalyst 45 is reliably reduced.

  While the SCR catalyst 47 is at a low temperature immediately after the start of the engine, etc., the NOx catalyst 45 plays a role of NOx purification, but the NOx catalyst 45 can not sufficiently exhibit the NOx storage performance because of the low temperature. At this time, if the NOx catalyst 45 is regenerated, the NOx storage performance may be recovered and the NOx emission may be reduced. Therefore, the first DeNOx after the start of the engine is executed early. The first DeNOx after engine start is started when the NOx storage amount of the NOx catalyst 45 exceeds α1 which is preset as the reduction start value α. Since the exhaust gas temperature rises due to DeNOx, temperature rise of the NOx catalyst 45 and the SCR catalyst 47 can also be expected.

  The second and subsequent DeNOx is started when it exceeds α2 which is preset as the reduction start value α. Since there is no need for early execution as in the first time, α2 is set to a value larger than α1. Further, in consideration of the fact that the NOx storage performance of the NOx catalyst 45 decreases with an increase in the NOx storage amount, α2 is set to a value smaller than the maximum storage amount of the NOx catalyst 45. For example, α2 is set to 90% of the maximum storage amount, and α1 is set to 1/3 of α2. These α1 and α2 are appropriately set according to the specification of the engine system 200 and the like.

  When the NOx storage amount of the NOx catalyst 45 is the reduction start value α or more, the PCM 60 reduces the air-fuel ratio of the exhaust gas to near the theoretical air-fuel ratio or to reduce the NOx storage amount to the predetermined reduction end value β or less. It is set to the rich side reduction air-fuel ratio below the stoichiometric air-fuel ratio, and DeNOx to be post-injected from the fuel injection valve 20 is performed. Although the reduction end value β is set to substantially zero, it may be set between zero and the reduction start value α.

Next, with reference to FIG. 9, the setting of the DeNOx execution flag that determines whether or not the DeNOx execution is required by the PCM 60 will be described.
FIG. 9 is a flowchart showing a DeNOx execution flag setting flow. Si (i = 301, 302,...) In the figure represents a step. The DeNOx execution flag setting flow is repeatedly executed in a predetermined cycle in parallel with the fuel injection control flow of FIG.

  First, in S301, various information in the vehicle is acquired. Specifically, the temperature of the NOx catalyst 45, the temperature of the SCR catalyst 47, the NOx storage amount of the NOx catalyst 45, and the like are acquired. The temperature of the NOx catalyst 45 is estimated based on, for example, the temperature detected by the temperature sensor 112 on the upstream side of the NOx catalyst 45. The temperature of the NOx catalyst 45 may be estimated based on the temperature detected by the temperature sensor 113 between the NOx catalyst 45 and the DPF 46, or by combining the temperatures detected by the temperature sensors 112 and 113. Further, the temperature of the SCR catalyst 47 is estimated, for example, based on the temperature detected by the temperature sensor 117 provided on the upstream side of the SCR catalyst 47. The NOx storage amount can be obtained by, for example, estimating the NOx amount in the exhaust gas based on the operating state of the engine E, the flow rate of the exhaust gas, the temperature of the exhaust gas, etc. and integrating the NOx amount. The NOx storage amount may be determined based on the estimated NOx amount in the exhaust gas and the concentration detected by the NOx sensor 116.

  Next, in S302, it is determined whether the temperature of the SCR catalyst 47 acquired in S301 is less than the SCR catalyst activation temperature Ts. If the determination is No, the NOx in the exhaust gas can be appropriately purified by the SCR catalyst 47. Therefore, the process proceeds to S310, the DeNOx execution flag F is set to "0" to prohibit execution of DeNOx, and the process is ended. Do. If the determination is Yes, the process proceeds to S303.

  Next, in S303, it is determined whether the temperature of the NOx catalyst 45 acquired in S301 is equal to or higher than the NOx catalyst activation temperature Tn. If the temperature of the NOx catalyst 45 is less than the NOx catalyst activation temperature Tn, the stored NOx can not be reduced efficiently even if the air-fuel ratio of the exhaust gas is set to the rich side reduction air-fuel ratio. In this case, the process proceeds to S310, in which the DeNOx execution flag F is set to "0" to prohibit the execution of DeNOx, and the process returns. If the determination in step S303 is yes, the process proceeds to step S304.

  Next, in S304, it is determined whether the operating condition of the engine E is within the operating range R12 (see FIG. 6). If the determination is No, the process proceeds to S310, the DeNOx execution flag F is set to "0" to prohibit execution of DeNOx, and the process returns. If the determination is Yes, the process proceeds to S305.

  Next, in S305, based on the information stored in the internal memory, it is determined whether or not the first DeNOx after engine start has not been implemented. If the determination is Yes, the process proceeds to S306, the reduction start value α is set to α1 so that the first DeNOx can be performed early after engine start, and the process proceeds to S308. If the determination is No, the process proceeds to S307, the reduction start value α is set to α2, and the process proceeds to S308.

  Next, in S308, it is determined whether the NOx storage amount is equal to or more than the reduction start value α. If the determination is No, the DeNOx process is not performed, so the process proceeds to S310, the DeNOx execution flag F is set to "0", and the process returns. If the determination is Yes, the process proceeds to step S309 to execute the DeNOx process, the DeNOx execution flag F is set to "1", and the process returns.

Next, DeNOx execution control by the PCM 60 will be described with reference to FIG.
FIG. 10 is a flowchart of DeNOx execution control. Si (i = 311, 312,...) In the figure represents a step. This DeNOx execution control is also repeatedly executed in a predetermined cycle in parallel with the fuel injection control flow of FIG.

  First, in S311, it is determined whether the DeNOx execution flag F is "1". If the determination is No, since DeNOx is not performed, the process proceeds to S315, the lean air-fuel ratio is set, and main injection is performed and the process returns. If the determination is Yes, the process proceeds to S312, the rich side reduction air-fuel ratio, the post injection amount, and the like are set, and main injection and post injection are executed, and the process proceeds to S313.

  Next, in S313, it is determined whether or not the reduction of the stored NOx is completed. Specifically, the NOx storage amount estimated based on the operating state of the engine E, the flow rate of the exhaust gas, the temperature of the exhaust gas, etc. becomes equal to or less than the reduction end value β, and the NOx sensor provided immediately downstream of the DPF 46 When the detected value of 116 changes, it is determined that the reduction is completed. When the determination is No, the process returns to S311, and when the determination is Yes, the process proceeds to S314.

  Next, in S314, it is determined whether the current DeNOx is the first DeNOx after engine start. If the determination is No, the process proceeds to S319, sets the DeNOx execution flag F to "0", ends DeNOx, and returns. If the determination is Yes, the process proceeds to S316.

  Next, in S316, it is determined whether the temperature of the SCR catalyst 47 is equal to or higher than the SCR catalyst activation temperature Ts. If the determination is Yes, there is no need to raise the temperature of the SCR catalyst 47, so the process proceeds to S319, sets the DeNOx execution flag F to "0", ends DeNOx, and returns. If the determination is No, the process proceeds to S317 to raise the temperature of the SCR catalyst 47, sets the temperature-increased air-fuel ratio, the post injection amount, and the like, executes main injection and post injection, and proceeds to S318. The temperature-increased air-fuel ratio is set to the lean side of the stoichiometric air-fuel ratio and to the rich side of the lean air-fuel ratio, and the oxidation of HC or the like in the NOx catalyst 45 also contributes to the temperature rise.

  Next, in S318, it is determined whether the temperature of the SCR catalyst 47 is equal to or higher than the SCR catalyst activation temperature Ts. If the determination is No, the process returns to S316 to raise the temperature of the SCR catalyst 47. If the determination is Yes, there is no need to raise the temperature of the SCR catalyst 47, so the process proceeds to S319, the DeNOx execution flag F is set to “0”, and DeNOx is ended and the process returns.

Next, the first DeNOx after engine start will be described based on the time chart shown in FIG.
After starting the engine E at time t0, the exhaust gas is discharged to the exhaust passage 41, and the temperatures of the NOx catalyst 45 and the SCR catalyst 47 gradually increase. Further, the NOx catalyst 45 occludes NOx in the exhaust gas, and the NOx occlusion amount gradually increases. During this time, the PCM 60 executes the above-mentioned DeNOx execution flag setting flow. The engine E is in the operating state in the region R12 of FIG. 6, and is set to a lean air fuel ratio.

  When the NOx storage amount exceeds the reduction start value α at time t1 and the DeNOx execution flag F is set to "1", the PCM 60 starts the above-mentioned DeNOx execution control, and the air fuel ratio of the exhaust gas is theoretical until the reduction ends. The post-injection is performed by setting the reduction air-fuel ratio richer than the air-fuel ratio and setting the post injection amount for achieving the reduction air-fuel ratio. Since the NOx stored in the NOx catalyst is reduced at the reducing air-fuel ratio, the NOx storage amount gradually decreases. Further, since the exhaust gas temperature is raised by the post injection, the temperature rise of the NOx catalyst 45 and the SCR catalyst 47 becomes faster.

  When reduction ends at time t2, the current DeNOx is the first DeNOx after engine start and the temperature of the SCR catalyst 47 is lower than the SCR catalyst activation temperature Ts, so the temperature is raised to further raise the temperature of the SCR catalyst 47 Execute control. In the temperature raising control, the air fuel ratio of the exhaust gas is set to a temperature increasing air fuel ratio leaner than the reduction air fuel ratio and richer than the lean air fuel ratio, and a post injection amount is set to make the temperature raising air fuel ratio Perform an injection.

  When the exhaust temperature immediately downstream of the NOx catalyst 45 becomes equal to or higher than the preset temperature at time t3, the temperature raising control is ended, the air fuel ratio of the exhaust gas is set to the lean air fuel ratio, and the post injection is ended. The first DeNOx is ended after startup. In the case of DeNOx after the second time, when reduction ends at time t2, the air-fuel ratio of the exhaust gas is set to a lean air-fuel ratio, post injection is ended, and DeNOx is ended.

Next, the operation and effects of the exhaust gas purification apparatus for an engine according to the embodiment of the present invention will be described.
Since DeNOx is executed earlier than usual when the temperature of the SCR catalyst 47 is less than the SCR catalyst activation temperature Ts, the temperature of the SCR catalyst is raised early by utilizing the fact that the exhaust gas temperature is set and the exhaust gas temperature rises. can do. Then, even if the NOx storage amount becomes equal to or less than the reduction end value β, the SCR is set to the temperature-increased air-fuel ratio richer than the lean air-fuel ratio, and the exhaust gas temperature becomes higher than at the lean air-fuel ratio. The temperature of the catalyst 47 can be raised early. Moreover, since the temperature-increased air-fuel ratio is set to be leaner than the reduced air-fuel ratio, generation of ammonia on the NOx catalyst 45 can be suppressed and fuel consumption can be suppressed as compared with the reduced air-fuel ratio. .

  Further, since the SCR catalyst 47 is disposed downstream of the NOx catalyst 45 on the downstream side of the exhaust passage 41, ammonia not consumed among the ammonia generated by the NOx catalyst 45 is used in the SCR catalyst 47. Can reduce the emission of ammonia to the outside.

  The NOx catalyst 45 also has a DOC function, and in order to set the temperature-increased air-fuel ratio during temperature rise control richer than the lean air-fuel ratio and leaner than the theoretical air-fuel ratio, the exhaust gas temperature is increased by the oxidation reaction at the oxidation catalyst. Since the temperature can be raised, the temperature of the NOx catalyst and the SCR catalyst can be raised quickly. Further, since the temperature rise control ends when the exhaust gas temperature downstream of the NOx catalyst reaches a preset temperature, the high temperature deterioration of the NOx catalyst can be suppressed.

  The reduction start value α is set to α1 for the first DeNOx after engine start, and is set to α2 for the second and subsequent DeNOx, and α1 is set smaller than α2, so the first DeNOx is early The temperature of the SCR catalyst 47 can be raised early. Since the temperature rise control is executed when the temperature of the SCR catalyst 47 is less than the SCR catalyst activation temperature Ts when the NOx storage amount of the NOx catalyst 45 becomes less than or equal to the reduction end value β due to the first DeNOx, SCR is performed. The temperature of the catalyst 47 can be raised early.

  As shown in FIG. 12, α1 which is the reduction start value α for starting the first DeNOx after engine start is set according to the temperature of the SCR catalyst 47 so as to decrease as the temperature of the SCR catalyst 47 decreases. It is also possible. As the temperature of the SCR catalyst 47 is lower, the first DeNOx after engine start can be started earlier, and the temperature of the SCR catalyst 47 can be raised earlier according to the temperature condition of the SCR catalyst 47.

  If the fuel cut continues for a long time due to the use of the engine brake or if the travel of the electric motor continues for a long time in a so-called hybrid vehicle powered by the electric motor and the engine, the exhaust system of the engine is cooled. In the same manner as described above, it is also possible to execute DeNOx early.

  In addition, those skilled in the art can carry out the embodiments in which various modifications are added to the embodiments or a combination of the embodiments without departing from the spirit of the present invention, and the present invention is not limited to such modifications It also includes the form.

7 intake shutter valve 17 combustion chamber 20 fuel injection valve 41 exhaust passage 43 EGR device 45 NOx catalyst 47 SCR catalyst 51 urea injector 60 PCM (NOx reduction control means)
111 O2 sensor 112 temperature sensor 113 temperature sensor 115 temperature sensor 116 NOx sensor 117 temperature sensor 200 engine system E engine EX exhaust system

Claims (6)

The NOx catalyst and the SCR catalyst disposed in the exhaust passage of the engine, and the air-fuel ratio of the exhaust gas near the theoretical air-fuel ratio or the air-fuel ratio rich side when the NOx storage amount of the NOx catalyst is equal to or more than the preset reduction start value. An engine exhaust purification device comprising: NOx reduction control means for performing NOx reduction processing by setting the reduction air-fuel ratio of
The NOx reduction control means is leaner than the theoretical air fuel ratio if the temperature of the SCR catalyst when the NOx storage amount falls below the preset reduction end value is lower than the preset SCR catalyst activation temperature. An engine exhaust gas purification apparatus that executes temperature increase control set to a temperature increase air-fuel ratio that is richer than the lean air-fuel ratio set to and leaner than the reduced air-fuel ratio.   The engine exhaust gas purification apparatus according to claim 1, wherein the SCR catalyst is disposed downstream of an exhaust passage of the engine than the NOx catalyst.   The exhaust passage of the engine includes an oxidation catalyst, and the NOx reduction control means sets the temperature-increased air-fuel ratio to be richer than the lean air-fuel ratio and leaner than the theoretical air-fuel ratio during the temperature increase control. An exhaust purification system of an engine according to claim 1 or 2.   The engine according to any one of claims 1 to 3, wherein the NOx reduction control means terminates the temperature increase control when the exhaust gas temperature downstream of the NOx catalyst becomes equal to or higher than a preset temperature set in advance. Exhaust purification system.   The NOx reduction control means sets the reduction start value for executing the first NOx reduction process after engine start smaller than that after the second time, and the NOx storage amount is the reduction end value by the first NOx reduction process The exhaust gas purification system according to any one of claims 1 to 4, wherein the temperature raising control is executed when the temperature of the SCR catalyst at the time of becoming lower than the SCR catalyst activation temperature. apparatus.   6. The exhaust gas purification system according to claim 5, wherein the NOx reduction control means sets the reduction start value for executing the first NOx reduction process to be smaller as the temperature of the SCR catalyst is lower. apparatus.