JP2008232058A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

In an exhaust emission control device provided with a NOx storage catalyst in an exhaust passage of an engine, optimization of fuel consumption, HC emission amount, and NOx emission amount when the catalyst is deteriorated and when the catalyst is not deteriorated is achieved.
An area Sx of a predetermined time range of a current NOx reduction addition A / F waveform is calculated, and the calculated area Sx and an area of the time range of a previously set air-fuel ratio waveform at the time of undeteriorated ( An area difference ΔS with respect to the reference area So) is obtained, and catalyst deterioration of the NOx storage catalyst is determined based on the area difference ΔS. When the determination result based on the NOx reduction addition A / F waveform is catalyst deterioration, a NOx reduction addition amount / addition interval suitable for catalyst deterioration is set. When the NOx storage catalyst is in an undeteriorated state, NOx reduction is performed. By setting the addition amount small with respect to the catalyst deterioration and setting the NOx reduction addition interval longer with respect to the catalyst deterioration, it is possible to avoid deterioration in fuel consumption and increase in HC when the catalyst is not deteriorated.
[Selection] Figure 3

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine (hereinafter also referred to as an engine).

  In general, in an engine that performs lean combustion, such as a diesel engine, an operation region in which an air-fuel mixture with a high air-fuel ratio (lean atmosphere) is burned occupies most of the entire operation region. Therefore, a NOx storage catalyst for storing (absorbing) nitrogen oxide (hereinafter referred to as NOx) contained in the exhaust gas is disposed in the exhaust passage of this type of engine so as to purify the exhaust gas. Yes. As the NOx storage catalyst, for example, an NSR (NOx Storage Reduction) catalyst, a DPNR (Diesel Particulate-NOx Reduction system) catalyst, or the like is used.

  The NOx storage catalyst stores NOx in the exhaust when the exhaust air-fuel ratio (A / F) is lean, that is, when the surrounding atmosphere is in a high oxygen concentration state. On the other hand, when the exhaust air-fuel ratio becomes rich, more specifically, the surrounding atmosphere is in a low oxygen concentration state, and unburned fuel components such as hydrocarbon (HC) and carbon monoxide (CO) are contained in the exhaust. In the case where the NOx storage catalyst is included, the NOx storage catalyst releases and reduces the stored NOx. Specifically, NOx occluded in the NOx occlusion catalyst is released as the oxygen concentration decreases, and the released NOx is reduced and purified by reaction with unburned fuel components contained in the exhaust gas.

In such a NOx occlusion catalyst, when the catalyst deteriorates due to heat load / sulfur poisoning (S poisoning) and the NOx occlusion amount reaches a saturated state, it is necessary to reduce the NOx and recover the NOx occlusion catalyst. There is. As a method of reducing NOx, a NOx reducing agent (fuel such as light oil) is intermittently added to the exhaust passage upstream of the NOx storage catalyst at a predetermined NOx reduction addition amount / addition interval to thereby reduce the NOx storage catalyst. A process (NOx reduction process) that promotes the reduction of NOx by reducing the oxygen concentration and using excess hydrocarbon, carbon monoxide, or the like as a reducing agent (for example, see Patent Documents 1 and 2).
JP 2006-258047 A JP 2005-105881 A JP 2006-138273 A

  By the way, in the current NOx reduction process, the NOx reduction addition amount / addition interval is adapted only when the catalyst is deteriorated. For this reason, since the NOx storage catalyst is in an undegraded state and the NOx reduction performance is high, the NOx reduction process is performed under the same conditions as when the catalyst is deteriorated. There are concerns about deterioration and an increase in HC.

  The present invention has been made in view of such circumstances, and is provided in an exhaust gas purification apparatus for an internal combustion engine in which an NOx storage catalyst is provided in an exhaust passage and a NOx reducing agent is added to an exhaust passage upstream of the NOx storage catalyst. An object is to optimize fuel consumption, HC emission amount, and NOx emission amount when the catalyst is deteriorated and when the catalyst is not deteriorated.

  According to the present invention (first invention), a NOx storage catalyst provided in an exhaust passage of an internal combustion engine, an NOx reducing agent added to an exhaust passage upstream of the NOx storage catalyst, and an addition amount of the NOx reducing agent An exhaust gas purification apparatus for an internal combustion engine, which includes a NOx reduction processing means for setting an addition interval and an air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas downstream of the NOx storage catalyst, is assumed. In such an exhaust purification device, a deterioration determination means for determining deterioration of the NOx storage catalyst based on the output waveform of the air-fuel ratio sensor is provided, and when the determination result by the deterioration determination means is catalyst deterioration, Appropriate NOx reduction addition amount / addition interval is set. When the determination result by the deterioration determining means is that the catalyst is not deteriorated, the NOx reduction addition amount is set smaller than that at the time of catalyst deterioration, and the NOx reduction addition interval is set to the catalyst. It is characterized in that it is set longer than at the time of deterioration.

  As a specific configuration of the present invention, an area of a predetermined time range of the output waveform of the air-fuel ratio sensor (current NOx reduction addition A / F waveform) is calculated, and the calculated area and preset undeteriorated An example is a configuration in which an area difference from an area (reference area) of the time range of the hourly air-fuel ratio waveform is obtained, and catalyst deterioration of the NOx storage catalyst is determined based on the area difference. More specifically, an area of a predetermined time range of the current NOx reduction addition A / F waveform (for example, a time range including a region where the A / F waveform changes from lean to rich) and a reference area collected when the catalyst is new. A configuration in which catalyst deterioration is determined when the area difference between and is larger than a predetermined determination value.

  According to the present invention, it is determined whether the NOx storage catalyst is in a catalyst deterioration state or a catalyst undegraded state based on the output waveform (NOx reduction addition A / F waveform) of the air-fuel ratio sensor, and the NOx storage catalyst is deteriorated. In this state, the additive is added at the NOx reduction addition amount / addition interval suitable for the catalyst deterioration, so that the fuel consumption, HC emission amount, and NOx emission amount at the time of catalyst deterioration can be optimized. Further, when the NOx storage catalyst is in an undegraded state, the NOx reduction addition amount is set to be smaller than that at the time of catalyst deterioration, and the NOx reduction addition interval is set to be longer than that at the time of catalyst deterioration. An increase in HC can be avoided. Thereby, optimization of fuel consumption, HC emission amount, and NOx emission amount when the NOx storage catalyst is not deteriorated can be realized.

  Further, the present invention (second invention) adds a NOx occlusion catalyst provided in an exhaust passage of an internal combustion engine, an NOx reducing agent to an exhaust passage upstream of the NOx occlusion catalyst, and the NOx reducing agent. An exhaust purification device for an internal combustion engine provided with NOx reduction processing means for setting an addition amount and an addition interval is assumed. In such an exhaust purification device, a deterioration determining means for determining deterioration of the NOx storage catalyst based on the catalyst thermal history of the NOx storage catalyst is provided, and when the determination result by the deterioration determination means is catalyst deterioration, the catalyst deterioration NOx reduction addition amount / addition interval suitable for the time is set, and when the determination result by the deterioration determining means is that the catalyst is not deteriorated, the NOx reduction addition amount is set smaller than the catalyst deterioration time, and the NOx reduction addition interval is set to It is characterized in that it is set longer than when the catalyst is deteriorated.

  As a specific configuration of the present invention, there is a configuration in which the catalyst bed temperature of the NOx storage catalyst is estimated, and it is determined that the catalyst is deteriorated when the integrated value of the estimated catalyst bed temperature is larger than a predetermined value. it can. The integrated value of the catalyst bed temperature is, for example, a value obtained by integrating the catalyst bed temperature multiplied by the time during which the temperature has been maintained.

  According to the present invention, based on the catalyst heat history of the NOx storage catalyst (specifically, the integrated value of the catalyst bed temperature of the NOx storage catalyst), the NOx storage catalyst is in a state of catalyst deterioration or catalyst undeterioration. When the NOx storage catalyst is in a deteriorated state, the additive is added at the NOx reduction addition amount / addition interval suitable for the catalyst deterioration, so the fuel consumption, HC emission amount, and NOx emission amount at the time of catalyst deterioration can be calculated. Can be optimized. Further, when the NOx storage catalyst is in an undegraded state, the NOx reduction addition amount is set to be smaller than that at the time of catalyst deterioration, and the NOx reduction addition interval is set to be longer than that at the time of catalyst deterioration. An increase in HC can be avoided. Thereby, optimization of fuel consumption, HC emission amount, and NOx emission amount when the NOx storage catalyst is not deteriorated can be realized.

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

-Engine-
A schematic configuration of a diesel engine to which the present invention is applied will be described with reference to FIG.

  A diesel engine 1 (hereinafter referred to as “engine 1”) in this example is, for example, a common rail in-cylinder direct injection four-cylinder engine, and includes a fuel supply system 2, a combustion chamber 3, an intake system 6, an exhaust system 7, and the like. Is configured as the main part.

  The fuel supply system 2 includes a supply pump 21, a common rail 22, an injector (fuel injection valve) 23, a shutoff valve 24, a fuel addition valve 25, a fuel pressure control valve 26, a fuel metering valve 27, an engine fuel passage 28, and an added fuel. A passage 29 and the like are provided.

  The supply pump 21 pumps fuel from the fuel tank, makes the pumped fuel high pressure, and then supplies the pumped fuel to the common rail 22 via the engine fuel passage 28. The common rail 22 has a function as a pressure accumulation chamber that holds (accumulates) the high-pressure fuel supplied from the supply pump 21 at a predetermined pressure, and distributes the accumulated fuel to the injectors 23. The injector 23 is an electromagnetically driven on-off valve that opens when a predetermined voltage is applied and injects fuel into the combustion chamber 3.

  Further, the supply pump 21 supplies a part of the fuel pumped from the fuel tank to the fuel addition valve 25 through the addition fuel passage 29. The fuel addition valve 25 opens when a predetermined voltage is applied, and electromagnetically adds fuel from an exhaust port 71 of the exhaust system 7 to an exhaust manifold 72 (an exhaust pipe 73 on the upstream side of the DPNR catalyst 41 described later). It is a drive type on-off valve. The shutoff valve 24 shuts off the fuel supply by shutting off the added fuel passage 29 in an emergency.

  The intake system 6 includes an intake manifold 63 connected to an intake port formed in the cylinder head, and an intake pipe 64 constituting an intake passage is connected to the intake manifold 63. An air cleaner 65, an air flow meter 32, a throttle valve 62, an intake air temperature sensor 33, and an intake air pressure sensor 34 are disposed in the intake passage in order from the upstream side.

  The exhaust system 7 includes an exhaust manifold 72 connected to an exhaust port 71 formed in the cylinder head, and exhaust pipes 73 and 74 constituting an exhaust passage are connected to the exhaust manifold 72. A catalyst device 4 is disposed in the exhaust passage.

  The catalyst device 4 includes a DPNR catalyst 41. The DPNR catalyst 41 is, for example, a NOx occlusion reduction catalyst supported on a porous ceramic structure, and PM in the exhaust gas is collected when passing through the porous wall. Further, when the air-fuel ratio of the exhaust gas is lean, NOx in the exhaust gas is stored in the NOx storage reduction catalyst, and when the air-fuel ratio becomes rich, the stored NOx is reduced and purified.

  The exhaust purification device is configured by the above-described catalyst device 4, the fuel addition valve 25, the added fuel passage 29, and an ECU (Electronic Control Unit) 100 that performs open / close control of the fuel addition valve 25 and the like.

  The engine 1 is provided with a turbocharger (supercharger) 5. The turbocharger 5 includes a turbine wheel 52 and a compressor impeller 53 that are connected via a turbine shaft 51. The compressor impeller 53 is disposed facing the intake pipe 64, and the turbine wheel 52 is disposed facing the exhaust pipe 73. Such a turbocharger 5 supercharges intake air by rotating the compressor impeller 53 using the exhaust flow (exhaust pressure) received by the turbine wheel 52. The turbocharger 5 in this example is a variable nozzle type turbocharger, and a variable nozzle vane mechanism 54 is provided on the turbine wheel 52 side. By adjusting the opening degree of the variable nozzle vane mechanism 54, the engine 1 is overcharged. The supply pressure can be adjusted.

  An intake pipe 64 of the intake system 6 is provided with an intercooler 61 for forcibly cooling the intake air whose temperature has been raised by supercharging in the turbocharger 5. A throttle valve 62 is provided on the downstream side of the intercooler 61. The throttle valve 62 is an electronically controlled on-off valve whose opening degree can be adjusted in a stepless manner, and the flow area of the intake air is reduced under a predetermined condition, and the supply amount of the intake air is adjusted ( It has a function to reduce).

  Further, the engine 1 is provided with an EGR passage (exhaust gas recirculation passage) 8 that connects the intake system 6 and the exhaust system 7. The EGR passage 8 is configured to reduce the combustion temperature by recirculating a part of the exhaust gas to the intake system 6 and supplying it again to the combustion chamber 3, thereby reducing the amount of NOx generated. Further, the EGR passage 8 is provided with an EGR valve 81 and an EGR cooler 82 for cooling the exhaust gas passing through (refluxing) the EGR passage 8, and by adjusting the opening degree of the EGR valve 81, The amount of EGR (exhaust gas recirculation amount) introduced from the exhaust system 7 to the intake system 6 can be adjusted.

-Sensors-
Various sensors are attached to each part of the engine 1, and signals related to the environmental conditions of each part and the operating state of the engine 1 are output.

  For example, the air flow meter 32 is disposed on the upstream side of the throttle valve 62 of the intake system 6 and outputs a detection signal corresponding to the intake air amount. The intake air temperature sensor 33 is disposed in the intake manifold 63 and outputs a detection signal corresponding to the intake air temperature. The intake pressure sensor 34 is disposed in the intake manifold 63 and outputs a detection signal corresponding to the intake air pressure.

  The A / F sensor 35 is disposed in the exhaust pipe 74 on the downstream side of the catalyst device 4 of the exhaust system 7 and outputs a detection signal corresponding to the exhaust air-fuel ratio (exhaust A / F). The exhaust temperature sensor 36 is disposed in the exhaust pipe 74 on the downstream side of the catalyst device 4 of the exhaust system 7 and outputs a detection signal corresponding to the temperature of exhaust gas (exhaust temperature). The rail pressure sensor 37 outputs a detection signal corresponding to the fuel pressure stored in the common rail 22.

-ECU-
As shown in FIG. 2, the ECU 100 includes a CPU 101, a ROM 102, a RAM 103, a backup RAM 104, and the like.

  The ROM 102 stores various control programs, maps that are referred to when the various control programs are executed, and the like. The CPU 101 executes various arithmetic processes based on various control programs and maps stored in the ROM 102. The RAM 103 is a memory that temporarily stores calculation results of the CPU 101, data input from each sensor, and the like. The backup RAM 104 is a nonvolatile memory that stores data to be saved when the engine 1 is stopped, for example. Memory.

  The ROM 102, CPU 101, RAM 103, and backup RAM 104 are connected to each other via a bus 107 and are connected to an input interface 105 and an output interface 106.

  The input interface 105 includes a water temperature sensor 31 that outputs a detection signal corresponding to the cooling water temperature of the engine 1, an air flow meter 32, an intake air temperature sensor 33, an intake air pressure sensor 34, an A / F sensor 35, an exhaust gas temperature sensor 36, a rail pressure. A sensor 37, an accelerator opening sensor 38 that outputs a detection signal corresponding to the amount of depression of the accelerator pedal, a crank position sensor 39 that detects the rotation speed (engine rotation speed) of the crankshaft that is the output shaft of the engine 1, and the like Is connected. On the other hand, to the output interface 106, an injector 23, a shutoff valve 24, a fuel addition valve 25, a variable nozzle vane mechanism 54, a throttle valve 62, an EGR valve 81, and the like are connected.

  The ECU 100 executes various controls of the engine 1 including fuel injection amount control and the like based on the outputs of the various sensors described above. Further, the ECU 100 executes the following NOx reduction control.

-NOx reduction control-
First, in a diesel engine, the exhaust air-fuel ratio is a lean air-fuel ratio in most operating regions, so that the ambient atmosphere of the DPNR catalyst 41 is in a high oxygen concentration state in a normal operating state. For this reason, NOx in the exhaust gas is occluded in the NOx of the DPNR catalyst 41. However, when the catalyst deteriorates due to heat load / sulfur poisoning (S poisoning) and the NOx reduction performance decreases, NOx is reduced. It is necessary to reduce and recover the NOx storage catalyst. Therefore, in this example, the fuel is intermittently supplied to the exhaust passage (exhaust pipe 73) on the upstream side of the DPNR catalyst 41 at a predetermined NOx reduction addition amount / addition interval (see FIG. 8) by opening / closing control of the fuel addition valve 25. By adding, the air-fuel ratio of the exhaust gas is controlled to make the ambient atmosphere of the DPNR catalyst 41 high temperature or reducing atmosphere, so that NOx occluded in the DPNR catalyst 41 is converted into N ₂ , CO _2, and H ₂ O. Reduce and release.

  By the way, in such NOx reduction processing, in the conventional control, the NOx reduction addition amount / addition interval is adapted only when the DPNR catalyst 41 is deteriorated as described above. For this reason, even when the catalyst is not deteriorated, the NOx reduction treatment is performed under the same conditions as when the catalyst is deteriorated, and there is a concern that the fuel consumption deteriorates and the HC increases when the catalyst is not deteriorated.

  In order to solve this problem, in this example, the NOx reduction addition amount when the catalyst is not deteriorated is set smaller than that when the catalyst is deteriorated, and the NOx reduction addition interval is set longer than that when the catalyst is deteriorated. It is characterized in that optimization of fuel consumption, HC emission amount, and NOx emission amount when the catalyst is not deteriorated is realized by avoiding deterioration in fuel consumption and increase in HC.

  In this example, the indexes of “NOx reduction addition A / F waveform” and “catalyst thermal deterioration history” are used as indexes for determining catalyst deterioration of the DPNR catalyst 41. An example of NOx reduction control to which catalyst deterioration determination based on each index is applied will be described below.

-NOx reduction control by NOx reduction addition A / F waveform judgment-
First, the reference area So of the NOx reduction addition A / F waveform when the catalyst is not deteriorated used in the NOx reduction control of this example will be described.

  The NOx reduction addition A / F waveform (the output waveform of the A / F sensor 35) is, for example, a waveform that repeats lean and rich in synchronization with fuel addition in which fuel is intermittently added, as shown in FIG. In this example, first, the NOx reduction addition A / F waveform Wo when the DPNR catalyst 41 is new is collected in advance. Next, with respect to the collected NOx reduction addition A / F waveform Wo, as shown in FIG. 4, a determination time range and a determination threshold (A) from a point t1 at which a change starts from lean to a rich side to a point t2 after a predetermined time. / F waveform lean level) is calculated, and the calculated area is stored in the ROM 102 of the ECU 100 as the reference area So of the NOx reduction addition A / F waveform when the catalyst is not deteriorated. Note that t2 that defines the determination time range is, for example, the median value (or the peak position on the rich side) of the time when the NOx reduction addition A / F waveform Wo is rich.

  Further, in this example, the NOx reduction addition amount / addition interval during catalyst deterioration adapted to optimize the fuel consumption / HC emission amount / NOx emission amount when the catalyst deteriorates, and the fuel consumption / HC emission amount when the catalyst is not deteriorated. The NOx reduction addition amount / addition interval when the catalyst is not deteriorated and adapted to optimize the NOx emission amount is stored in the ROM 102 of the ECU 100. However, considering that the NOx reduction performance is high when the catalyst is not deteriorated, the NOx reduction addition amount when the catalyst is not deteriorated is smaller than that when the catalyst is deteriorated, and the NOx reduction addition interval when the catalyst is not deteriorated is also deteriorated. It is longer than time.

  Next, the NOx reduction control will be described with reference to the flowchart of FIG. The control routine of FIG. 3 is repeatedly executed in the ECU 100 at predetermined time intervals.

  In step ST11, the current output waveform of the A / F sensor 35, that is, the area Sx of the determination time range of the NOx reduction addition A / F waveform Wx is obtained. Specifically, as shown in FIG. 5, the determination time range and the determination threshold value (A) from the point t1 at which the NOx reduction addition A / F waveform Wx starts to change from the lean side to the rich side to the point t2 after a certain time. The area Sx of the region surrounded by the / F waveform lean level) is calculated, and the calculated area Sx, the above-described reference area So, and the area difference ΔS are calculated. The determination time ranges t1 to t2 and the determination threshold set for the NOx reduction addition A / F waveform Wx are the same as the determination time ranges t1 to t2 and the determination threshold when the reference area So is obtained in FIG. .

  In step ST12, it is determined whether or not the area difference ΔS obtained in step ST11 exceeds a predetermined determination value α, and based on the determination result, it is determined whether the DPNR catalyst 41 is deteriorated or not. The determination process in step ST12 will be described below.

  First, when the catalyst deterioration of the DPNR catalyst 41 progresses and the NOx reduction performance decreases, as shown in FIG. 6, the current NOx reduction addition A / F waveform Wx is changed to a NOx reduction addition A / F waveform Wo when new. On the other hand, it shifts to the rich side. When such a shift to the rich side occurs, the area Sx (see FIG. 5) of the determination time range t1 to t2 of the current NOx reduction addition A / F waveform Wx is larger than the reference area So (see FIG. 4) when new. Also grows. Moreover, as the degree of deterioration of the DPNR catalyst 41 increases, the area difference ΔS between the area Sx of the current NOx reduction addition A / F waveform Wx and the reference area So increases.

  Focusing on this point, in this example, the catalyst deterioration or non-degradation of the DPNR catalyst 41 is determined using the area difference ΔS of the NOx reduction addition A / F waveform as an index. Specifically, the relationship between the degree of deterioration of the DPNR catalyst 41 and the area difference ΔS of the NOx reduction addition A / F waveform is sampled in advance by experiments and calculations, and a determination value for determining catalyst deterioration based on the result. α (determination value for the area difference ΔS) is determined empirically, and if the area difference ΔS is larger than the determination value α (ΔS> α), the DPNR catalyst 41 is determined to be catalyst deteriorated. On the other hand, when the area difference ΔS is equal to or less than the determination value α (ΔS ≦ α), it is determined that the DPNR catalyst 41 is undegraded.

  If the determination result in step ST12 is affirmative, that is, if the DPNR catalyst 41 is at the time of catalyst deterioration, in step ST13, the above-described NOx reduction addition amount / addition interval at the time of catalyst deterioration is selected, and the DPNR catalyst 41 is selected. Fuel is intermittently added from the fuel addition valve 25 to the upstream exhaust passage (exhaust pipe 73).

  On the other hand, if the determination result in step ST12 is negative, that is, if the DPNR catalyst 41 is in the catalyst undegraded state, in step ST14, the above-described NOx reduction addition amount / addition interval in the catalyst undegraded state is selected, and the DPNR Fuel is intermittently added to the exhaust passage upstream of the catalyst 41 from the fuel addition valve 25.

  According to the NOx reduction control of this example, it is determined based on the NOx reduction addition A / F waveform whether the DPNR catalyst 41 is in a catalyst deterioration state or a catalyst undeterioration state, and the NOx storage catalyst 41 is in a deterioration state. Sometimes, the additive is added at the NOx reduction addition amount / addition interval suitable for the catalyst deterioration, so that the fuel consumption, HC emission amount, and NOx emission amount at the time of catalyst deterioration can be optimized. Further, when the NOx storage catalyst 41 is in an undegraded state, the NOx reduction addition amount is set to be smaller than that at the time of catalyst deterioration, and the NOx reduction addition interval is set to be longer than that at the time of catalyst deterioration. Deterioration of fuel consumption and increase in HC can be avoided. Thereby, optimization of fuel consumption, HC emission amount, and NOx emission amount when the NOx storage catalyst is not deteriorated can be realized.

-NOx reduction control based on catalyst thermal degradation determination-
First, thermal degradation that affects the NOx reduction ability of the DPNR catalyst 41 is correlated with the temperature history of the heat received by the DPNR catalyst 41, in other words, the integrated value of the catalyst bed temperature, which is the temperature of the DPNR catalyst 41, It can be determined that the thermal deterioration of the DPNR catalyst 41 is progressing as the integrated value of the catalyst bed temperature increases. Focusing on this point, in this example, the catalyst deterioration of the DPNR catalyst 41 or the catalyst undegraded is determined using the integrated value of the catalyst bed temperature as an index, and NOx reduction control is executed.

  A specific control routine is shown in FIG. The control routine of FIG. 7 is repeatedly executed in the ECU 100 at predetermined time intervals.

  In this example as well, as in the above-described example of NOx reduction control, the NOx reduction addition amount / addition interval during catalyst deterioration adapted to optimize the fuel consumption, HC emission amount, and NOx emission amount during catalyst deterioration. Further, the NOx reduction addition amount / addition interval when the catalyst is not deteriorated, which is adapted to optimize the fuel consumption, the HC emission amount, and the NOx emission amount when the catalyst is not deteriorated, is stored in the ROM 102 of the ECU 100. Similarly, regarding the NOx reduction addition amount / addition interval when the catalyst is not deteriorated, in consideration of the high NOx reduction performance, the NOx reduction addition amount is made smaller than that at the time of catalyst deterioration, and the NOx reduction addition interval is reduced. It is longer than the time.

  First, in step ST21, the catalyst bed temperature of the DPNR catalyst 41 is estimated based on the exhaust temperature read from the output signal of the exhaust temperature sensor 36.

  In step ST22, an integrated value of the catalyst bed temperature of the DPNR catalyst 41 estimated in step ST21 is calculated. Here, the integrated value of the catalyst bed temperature of the DPNR catalyst 41 is, for example, a value obtained by integrating the catalyst bed temperature multiplied by the time during which the temperature lasts. It should be noted that the calculation of the integrated value of the catalyst bed temperature is sequentially repeated every time exhaust gas temperature data is collected.

  In step ST23, it is determined whether or not the integrated value of the catalyst bed temperature of the DPNR catalyst 41 calculated in step ST22 exceeds a predetermined determination value β. If the determination result is an affirmative determination (accumulated catalyst bed temperature). Value> β), it is determined that the DPNR catalyst 41 is at the time of catalyst deterioration. In step ST24, the above-described NOx reduction addition amount / addition interval at the time of catalyst deterioration is selected, and the exhaust passage (exhaust gas) on the upstream side of the DPNR catalyst 41 is selected. Fuel is intermittently added from the fuel addition valve 25 to the pipe 73).

  On the other hand, if the determination result in step ST23 is negative (integrated value of catalyst bed temperature ≦ β), it is determined that the DPNR catalyst 41 is undegraded, and in step ST25, the above-described NOx reduction when the catalyst is undegraded. The addition amount / addition interval is selected, and fuel is intermittently added from the fuel addition valve 25 to the exhaust passage upstream of the DPNR catalyst 41.

  Note that the determination value β used in the determination process of step ST23 is obtained empirically based on the result obtained by previously obtaining the relationship between the degree of deterioration of the DPNR catalyst 41 and the integrated value of the catalyst bed temperature through experiments and calculations. Set the value.

  According to the NOx reduction control of this example, it is determined based on the integrated value of the catalyst bed temperature of the DPNR catalyst 41 whether the DPNR catalyst 41 is in a catalyst deterioration state or a catalyst undegraded state, and the NOx storage catalyst is in a deterioration state. In this case, since the additive is added at the NOx reduction addition amount / addition interval suitable for the catalyst deterioration, the fuel consumption, HC emission amount, and NOx emission amount at the time of catalyst deterioration can be optimized. Further, when the NOx storage catalyst is in an undegraded state, the NOx reduction addition amount is set to be smaller than that at the time of catalyst deterioration, and the NOx reduction addition interval is set to be longer than that at the time of catalyst deterioration. Deterioration and HC increase can be avoided. Thereby, optimization of fuel consumption, HC emission amount, and NOx emission amount when the NOx storage catalyst is not deteriorated can be realized.

-Other embodiments-
In the above example, it is preferable to set both the NOx reduction addition amount and the addition interval when the catalyst is not deteriorated with respect to the catalyst deterioration time. However, the NOx reduction addition amount when the catalyst is not deteriorated is more than that when the catalyst is deteriorated. May be set to be smaller, or the NOx reduction addition interval when the catalyst is not deteriorated may be set longer than when the catalyst is deteriorated.

  In the above example, the NOx reduction addition amount / addition interval when the catalyst is deteriorated and the NOx reduction addition amount / addition interval when the catalyst is not deteriorated are mapped using the engine operating state (for example, the engine speed) as a parameter, respectively. Alternatively, it may be set with reference to each map according to the engine operating state.

  Further, regarding the NOx reduction addition amount / addition interval when the catalyst is not deteriorated, when the determination result of step ST12 of FIG. 3 or the determination result of step ST23 of FIG. In accordance with the degree of catalyst deterioration, the NOx reduction addition amount may be reduced and the NOx reduction addition interval may be lengthened as the catalyst deterioration degree is smaller. The NOx reduction additive is not limited to fuel (light oil), and other additives capable of reducing the NOx storage catalyst may be added to the exhaust passage upstream of the NOx storage catalyst.

  In the above example, the exhaust purification apparatus of the present invention is applied to an in-cylinder direct injection 4-cylinder diesel engine. However, the present invention is not limited to this, and other examples such as an in-cylinder direct injection 6-cylinder diesel engine, etc. It can also be applied to diesel engines with any number of cylinders. Further, the present invention is not limited to an in-cylinder direct injection diesel engine, but can be applied to other types of diesel engines. Moreover, it is applicable not only for vehicles but also for engines used for other purposes.

  In the above example, the catalyst device including the DPNR catalyst is provided in the exhaust passage. However, the catalyst device including the NSR catalyst and the DPNR catalyst may be provided in the exhaust passage. In addition, a catalyst device including a NOx storage catalyst other than the DPNR catalyst and the NSR catalyst may be provided in the exhaust passage.

As the NSR catalyst, for example, alumina (Al ₂ O ₃ ) is used as a carrier, and an alkali metal such as potassium (K), sodium (Na), lithium (Li), or cesium (Cs) is used on the carrier, List those in which an alkaline earth such as barium (Ba) and calcium (Ca), a rare earth such as lanthanum (La) and yttrium (Y), and a noble metal such as platinum (Pt) are supported. Can do.

It is a schematic structure figure showing an example of a diesel engine to which the present invention is applied. It is a block diagram which shows the structure of control systems, such as ECU. It is a flowchart which shows an example of NOx reduction | restoration control which ECU performs. It is a wave form diagram which shows NOx reduction addition A / F waveform at the time of a new catalyst. It is a wave form diagram which shows NOx reduction addition A / F waveform at the time of catalyst deterioration. FIG. 6 is a waveform diagram in which a NOx reduction addition A / F waveform when the catalyst is new and a NOx reduction addition A / F waveform when the catalyst is deteriorated are superimposed. 6 is a flowchart showing another example of NOx reduction control executed by the ECU. It is a figure which shows the NOx reduction addition amount and addition interval of a fuel.

Explanation of symbols

1 engine (internal combustion engine)
DESCRIPTION OF SYMBOLS 2 Fuel supply system 21 Supply pump 23 Injector 24 Shutoff valve 25 Fuel addition valve 29 Addition fuel passage 4 Catalytic device 41 DPNR catalyst 7 Exhaust system 71 Exhaust port 72 Exhaust manifold 73, 74 Exhaust pipe 35 A / F sensor (air-fuel ratio sensor)
100 ECU

Claims (4)

NOx storage catalyst provided in the exhaust passage of the internal combustion engine, and NOx reduction processing means for adding the NOx reducing agent to the exhaust passage upstream of the NOx storage catalyst and setting the addition amount and addition interval of the NOx reducing agent An air-fuel ratio sensor that detects an air-fuel ratio of the exhaust downstream of the NOx storage catalyst, and a deterioration determination means that determines deterioration of the NOx storage catalyst based on an output waveform of the air-fuel ratio sensor,
The NOx reduction processing means sets a NOx reduction addition amount / addition interval suitable for catalyst deterioration when the determination result by the deterioration determination means is catalyst deterioration, and the determination result by the deterioration determination means is that the catalyst has not deteriorated. Sometimes, the NOx reduction addition amount is set smaller than that at the time of catalyst deterioration, and the NOx reduction addition interval is set longer than that at the time of catalyst deterioration. The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
The deterioration determining means calculates an area of a predetermined time range of the output waveform of the air-fuel ratio sensor, and an area between the calculated area and an area of the time range of a preset undegraded air-fuel ratio waveform An exhaust purification device for an internal combustion engine, wherein a difference is obtained and catalyst deterioration of the NOx storage catalyst is determined based on the area difference. NOx storage catalyst provided in the exhaust passage of the internal combustion engine, and NOx reduction processing means for adding the NOx reducing agent to the exhaust passage upstream of the NOx storage catalyst and setting the addition amount and addition interval of the NOx reducing agent And deterioration determination means for determining deterioration of the NOx storage catalyst based on the catalyst heat history of the NOx storage catalyst,
The NOx reduction processing means sets a NOx reduction addition amount / addition interval suitable for catalyst deterioration when the determination result by the deterioration determination means is catalyst deterioration, and the determination result by the deterioration determination means is that the catalyst has not deteriorated. Sometimes, the NOx reduction addition amount is set smaller than that at the time of catalyst deterioration, and the NOx reduction addition interval is set longer than that at the time of catalyst deterioration. The exhaust gas purification apparatus for an internal combustion engine according to claim 3,
The deterioration determining means estimates the catalyst bed temperature of the NOx storage catalyst, and determines that the deterioration of the catalyst is caused when the integrated value of the estimated catalyst bed temperature is larger than a predetermined value. Exhaust purification device.

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