JP4868284B2 - Exhaust gas purification method and apparatus - Google Patents

Description

  The present invention relates to a method and an apparatus for controlling an addition amount of a reducing agent using an air-fuel ratio sensor when a catalyst for purifying exhaust gas discharged from an internal combustion engine is regenerated with a reducing agent.

  Exhaust gas purification that incorporates a catalyst device in the exhaust passage of the internal combustion engine to capture and adsorb harmful components contained in the exhaust gas in order to minimize the environmental impact on the exhaust gas emitted from the internal combustion engine The device is known. For example, Patent Document 1 discloses an exhaust gas purification device using a nitrogen reduction catalyst that captures nitrogen oxides (hereinafter referred to as NOx) in exhaust gas.

  In such an exhaust gas purifying apparatus using a catalyst, a function deterioration due to sulfur poisoning or the like occurs, and therefore it is necessary to periodically regenerate the catalyst. In Patent Document 1, in order to detoxify the NOx trapped by the nitrogen reduction catalyst, the fuel is added as a reducing agent in the exhaust passage upstream of the nitrogen reduction catalyst, and the NOx is decomposed. Is removed from the nitrogen reduction catalyst. In this case, the amount of fuel added to the exhaust passage is set based on detection information from an air-fuel ratio sensor that detects the air-fuel ratio of the exhaust gas in the exhaust passage located downstream of the nitrogen reduction catalyst. .

  In a compression ignition type internal combustion engine such as a diesel engine incorporating an exhaust gas purification device, when an unburned component of a high concentration reducing agent, more specifically, a hydrocarbon exists in a detection atmosphere of an air-fuel ratio sensor, It is known that the detection value of the air-fuel ratio sensor shifts to the lean side. For this reason, when feedback control is performed so that the target air-fuel ratio is richer than the stoichiometric air-fuel ratio, that is, the oxygen-deficient side, the amount of reducing agent added is set based on the detected value of the air-fuel ratio sensor As a result, a larger amount of reducing agent than that actually required is added to the nitrogen reduction catalyst. As a result, the unburned reducing agent is discharged as it is into the atmosphere, and accurate feedback control cannot be performed, and white smoke may be generated or fuel consumption may be deteriorated.

  In Patent Document 1 described above, a correction map corresponding to the state of the fuel added to the exhaust gas, that is, the molecular weight thereof and the value detected by the air-fuel ratio sensor is incorporated in advance in the on-vehicle electronic control unit. The air-fuel ratio corresponding to the molecular weight of the fuel in the exhaust gas and the detected value of the air-fuel ratio sensor is read from the correction map, and the addition amount of the reducing agent is set based on this.

JP 2004-316458 A

  In an internal combustion engine that incorporates an air-fuel ratio sensor in the exhaust passage downstream of the nitrogen reduction catalyst, detection due to the characteristics of the air-fuel ratio sensor when regenerating the nitrogen reduction catalyst by adding a reducing agent to the exhaust gas An error inevitably occurs. FIG. 7 is a graph showing the output characteristics of the air-fuel ratio sensor in an atmosphere with a relatively high hydrocarbon concentration. In the figure, the hatched area indicates the amount of additive added, and the alternate long and two short dashes line indicates the actual change in the air-fuel ratio. It can be understood from FIG. 7 that in an atmosphere having a relatively high hydrocarbon concentration, the detected value indicated by the solid line detected by the air-fuel ratio sensor is shifted to the lean side from the actual air-fuel ratio indicated by the two-dot chain line. Such inconveniences may occur when the air-fuel ratio is controlled to be richer than the stoichiometric air-fuel ratio during regeneration of the three-way catalyst, or when the function of the catalyst is reduced due to SOX contained in exhaust gas, that is, sulfur oxide. The same applies to the sulfur poisoning recovery process for recovery.

  As disclosed in Patent Document 1, the value detected by the air-fuel ratio sensor is corrected in accordance with the molecular weight of the fuel added to the exhaust gas, and the amount of fuel added is feedback-controlled based on the corrected value. It is possible to solve the problem that has occurred. However, since Patent Document 1 does not consider the change in the amount of fuel added to the exhaust gas, the corrected air-fuel ratio often does not actually become an appropriate air-fuel ratio.

  It is an object of the present invention to more accurately control the amount of reducing agent added even when the air-fuel ratio sensor is in an atmosphere with a high hydrocarbon concentration when a reducing agent is added to the exhaust gas and the catalyst is regenerated. An object of the present invention is to provide an exhaust gas purification method and an apparatus therefor.

First embodiment of the present invention, an exhaust gas by adding a reducing agent into the exhaust passage on the upstream side of the catalyst for purifying exhaust gas discharged from the combustion chamber of the internal combustion engine performs the reproduction process of the catalyst A purification method,
Detecting the amount of intake air supplied into the combustion chamber;
Detecting the air-fuel ratio of the exhaust gas flowing in the exhaust passage downstream of the catalyst;
Calculating the amount of reducing agent added to the exhaust passage based on the detected intake air amount and the detected air-fuel ratio;
Comparing the calculated amount of reducing agent added with the amount of reducing agent actually added into the exhaust passage;
Based on this comparison result, correcting the amount of reducing agent added to the exhaust passage so that the air-fuel ratio of the exhaust gas flowing in the exhaust passage downstream of the catalyst becomes the target air-fuel ratio ;
A step of correcting the target air-fuel ratio based on a comparison result between the calculated amount of reducing agent added and the amount of reducing agent actually added to the exhaust passage. The step of correcting the amount is performed with respect to the corrected target air-fuel ratio .

The hydrocarbon concentration in the exhaust passage and the ratio of the calculated reducing agent amount QC to the reducing agent amount QR actually added in the exhaust passage (hereinafter referred to as the addition amount ratio) QC / QR The relationship is schematically shown in FIG. As is apparent from the graph of FIG. 8, it will be understood that as the hydrocarbon concentration in the exhaust passage increases, the addition amount ratio QC / QR becomes a small value that cannot be ignored. In the present invention, the air-fuel ratio of the exhaust gas flowing in the exhaust passage downstream of the catalyst is detected, and added to the exhaust passage based on the detected air-fuel ratio and the intake air amount supplied into the combustion chamber. The amount of the reducing agent applied is calculated. Then, the calculated amount of reducing agent is compared with the amount of reducing agent actually added to the exhaust passage, and based on this comparison result, the exhaust gas flowing in the exhaust passage downstream of the catalyst is emptied. The amount of reducing agent added to the exhaust passage is corrected so that the fuel ratio becomes the target air-fuel ratio. Thus, by adding the reducing agent into the exhaust passage, the air-fuel ratio is corrected during the catalyst regeneration process in which the hydrocarbon concentration increases .

The exhaust gas purification method according to the first aspect of the present invention may further comprise the step of adding a corrected amount of the reducing agent into the exhaust passage.

A second aspect of the invention, the exhaust gas by adding a reducing agent into the exhaust passage on the upstream side of the catalyst for purifying exhaust gas discharged from the combustion chamber of the internal combustion engine performs the reproduction process of the catalyst A purification device,
A reducing agent addition valve for adding a reducing agent into the exhaust passage;
An addition amount setting means for setting the addition amount of the reducing agent from the reducing agent addition valve;
An air flow sensor for detecting the amount of intake air supplied into the combustion chamber;
An air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas flowing in the exhaust passage downstream of the catalyst;
An addition amount calculating means for calculating an addition amount of a reducing agent from the reducing agent addition valve based on an intake air amount detected by the air flow sensor and an air-fuel ratio detected by the air-fuel ratio sensor;
A comparison means for comparing the addition amount of the reducing agent calculated by the addition amount calculation means with the addition amount of the reducing agent set by the addition amount setting means;
Based on the comparison result by the comparison means, the addition amount of the reducing agent set by the addition amount setting means so that the air-fuel ratio of the exhaust gas flowing in the exhaust passage downstream of the catalyst becomes the target air-fuel ratio. and addition amount correcting means for correcting,
Air-fuel ratio correction means for correcting the target air-fuel ratio based on the comparison result by the comparison means, and the addition amount correction means sets the addition amount of the reducing agent with respect to the target air-fuel ratio corrected by the air-fuel ratio correction means. It is characterized by correcting .

  In the present invention, the air flow sensor detects the amount of intake air supplied into the combustion chamber. Then, based on the air-fuel ratio detected by the air-fuel ratio sensor and the intake air amount detected by the airflow sensor, the addition amount calculating means calculates the amount of reducing agent added to the exhaust passage. The comparison means compares the additive addition amount calculated by the addition amount calculation means with the reducing agent addition amount set by the addition amount setting means. The addition amount correction means adjusts the amount of the reducing agent set by the addition amount setting means so that the air-fuel ratio of the exhaust gas flowing in the exhaust passage downstream of the catalyst becomes the target air-fuel ratio based on the comparison result. to correct.

In the exhaust gas purifying apparatus according to the second aspect of the present invention, the addition for controlling the driving of the reducing agent addition valve so that the addition amount of the reducing agent corrected by the addition amount correction means is added into the exhaust passage. Valve drive control means can further be provided.

  According to the exhaust gas purification method of the present invention, the amount of reducing agent added to the exhaust passage is calculated and compared with the amount of reducing agent actually added to the exhaust passage to correct the detected air-fuel ratio. Since the amount of reducing agent added to the exhaust passage is corrected, the catalyst regeneration process can be performed more accurately by adding a particularly corrected amount of reducing agent to the exhaust passage. . In addition, this makes it possible to further improve the composition of the exhaust gas discharged into the atmosphere into a desirable state.

  According to the exhaust gas purification apparatus of the present invention, since the air flow sensor, the addition amount calculation means, the comparison means, the air-fuel ratio correction means, and the addition amount correction means are provided, the reducing agent added in the exhaust passage is provided. The amount can be calculated and compared with the amount of reducing agent actually added to the exhaust passage, and the detected air-fuel ratio can be corrected to correct the amount of reducing agent added to the exhaust passage. In particular, when there is further an addition valve driving means for driving the reducing agent addition valve so that the addition amount of the reducing agent corrected by the addition amount correction means is added into the exhaust passage, the regeneration process of the catalyst is conventional. The composition of the exhaust gas discharged into the atmosphere can be further improved to a desirable state.

  An embodiment in which an exhaust gas purifying apparatus according to the present invention is applied to a compression ignition type internal combustion engine will be described in detail with reference to FIGS. However, the present invention is not limited to such an embodiment, and can be arbitrarily changed according to the use and purpose, and can be applied to any other technique belonging to the spirit of the present invention. it can.

  The concept of the engine system in this embodiment is shown in FIG. 1, and the control block in this engine system is shown in FIG. The engine 10 in the present embodiment is a compression ignition type internal combustion engine that spontaneously ignites by directly injecting light oil as fuel into the combustion chamber 12 in a compressed state from the fuel injection valve 11. Supercharging the combustion chamber 12 using an exhaust gas recirculation (EGR) device 15 for guiding a part of the exhaust gas flowing in the exhaust passage 13 into the intake passage 14 and the kinetic energy of the exhaust gas flowing in the exhaust passage 13 A turbocharger (not shown) that performs the above is incorporated.

  The EGR device 15 has one end communicating with the exhaust pipe 16 defining the main part of the exhaust passage 13 and the other end communicating with the inside of the intake pipe 17 defining the main part of the intake passage 14, and the EGR path 18. An EGR pipe 19 is defined, and an EGR valve 20 is provided in the EGR pipe 19 and controls the flow rate of exhaust gas flowing in the EGR passage 18. In the present embodiment, when the EGR determination unit 22 of the electronic control unit (hereinafter referred to as ECU) 21 determines that the vehicle on which the engine 10 is mounted is in a preset EGR driving region, the driving state of the vehicle is set. Accordingly, the opening degree of the EGR valve 20 is set by the EGR amount setting unit 23 of the ECU 21. The EGR valve drive control unit 24 of the ECU 21 controls the EGR valve 20 to the opening set by the EGR amount setting unit 23, and otherwise keeps the EGR passage 18 closed so as to basically close the EGR passage 18. To do.

  The cylinder head 27 formed with the intake port 25 and the exhaust port 26 respectively facing the combustion chamber 12 includes a valve operating mechanism 30 including an intake valve 28 for opening and closing the intake port 25 and an exhaust valve 29 for opening and closing the exhaust port 26; A front fuel injection valve 11 facing the center of the upper end of the combustion chamber 12 is incorporated so as to be sandwiched between the intake valve 28 and the exhaust valve 29. The valve mechanism 30 in the present embodiment can change the opening and closing timings of the intake valve 28 and the exhaust valve 29 according to the operating state of the engine 10, but even if these opening and closing timings are fixed. Good.

  At the upstream end side of the intake pipe 17 that is connected to the cylinder head 27 so as to communicate with the intake port 25 and defines the intake passage 14 together with the intake port 25, dust and the like contained in the atmosphere are removed to remove the intake passage 14. An air cleaner 31 is provided for guiding the air. The other end of the EGR pipe 19 described above is connected to a portion of the intake pipe 17 between the intake valve 28 and a surge tank 32 formed in the middle of the intake pipe 17.

  The fuel injection valve 11 in the present embodiment is a single injection type that injects light oil as fuel into the combustion chamber 12 only in the vicinity of the compression top dead center of the piston 33. In addition to fuel injection in this compression stroke, It is also possible to adopt a multi-injection type that injects during the intake stroke in order to form a more uniform air-fuel mixture. The fuel injection amount and injection timing in the fuel injection valve 11 are set by the fuel injection amount setting unit 34 of the ECU 21 in accordance with the driving state of the vehicle. The injection valve drive control unit 35 of the ECU 21 controls the operation of the fuel injection valve 11 so that the fuel of the injection amount set by the fuel injection amount setting unit 34 is injected at the set injection timing.

In the middle of the exhaust pipe 16 connected to the cylinder head 27 so as to communicate with the inside of the combustion chamber 12 and defining the exhaust passage 13 together with the exhaust port 26, exhaust gas generated by combustion of the air-fuel mixture in the combustion chamber 12. a pretreatment catalyst 36, such as DPF (D iesel P articulate F ilter ) for burning to capture non燃固solid content contained in a nitrogen reducing catalyst 37 for trapping the built in series to NOX in the exhaust gas It is. Further, in the present embodiment, on the downstream side of the exhaust port 26 in the upstream side of the exhaust passage 13 relative to the pretreatment catalyst 36, the nitrogen oxide adsorbed by the nitrogen reduction catalyst 37 is reduced, that is, reduced for burning. The fuel addition valve 38 which supplies the light oil which is a fuel of the engine 10 in this embodiment is provided. The fuel addition position by the fuel addition valve 38 may be anywhere in the exhaust passage 13 upstream of the pretreatment catalyst 36. The fuel addition valve 38 adds a predetermined amount of fuel into the exhaust passage 13 at a predetermined timing, and performs post-heating processing, that is, regeneration of the nitrogen reduction catalyst 37. The fuel addition valve 38 is also used in the recovery process for sulfur poisoning. The addition timing of the fuel from the fuel addition valve 38, the addition amount thereof, and the like are controlled by the addition valve drive control unit 39 of the ECU 21 according to a program preset in the ECU 21, irrespective of the fuel injection timing by the fuel injection valve 11. Is done. Note that one end of the EGR pipe 19 described above is connected to the exhaust pipe 16 on the upstream side of the pretreatment catalyst 36.

  In the present embodiment, the ECU 21 grasps the operating state of the engine 10 and the vehicle on which the engine 10 is mounted, and the ECU 21 opens the EGR valve 20, the fuel injection amount and injection timing from the fuel injection valve 11, and the fuel addition valve 38. In order to control the amount of fuel added and the timing of addition, various sensors as described below are provided. In other words, an accelerator opening sensor 41 is provided that detects the depression amount of the accelerator pedal 40 operated by the driver and outputs the detected depression amount to the ECU 21. An air flow sensor 42 that detects the amount of intake air supplied into the combustion chamber 12 and outputs it to the ECU 21 is attached to a portion of the intake pipe 17 between the air cleaner 31 and the surge tank 32. A crank angle sensor 46 that detects the rotational phase of the crankshaft 45 to which the piston 33 is connected via the connecting rod 44, that is, the crank angle, and outputs it to the ECU 21 is attached to the cylinder block 43 in which the piston 33 reciprocates. It has been. A temperature sensor 47 that detects the temperature of the nitrogen reduction catalyst 37 and outputs it to the ECU 21 and an air-fuel ratio of the exhaust gas flowing in the exhaust passage 13 downstream of the nitrogen reduction catalyst 37 are detected and output to the ECU 21. An air-fuel ratio sensor 48 is incorporated in the exhaust passage 13.

  The ECU 21 includes a microcomputer including a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like (not shown), and the above-described sensors 41, 42, 46- Predetermined arithmetic processing is performed based on detection signals from 48 and the like, and operations of the EGR valve 20, the fuel injection valve 11, the fuel addition valve 38, and the like are controlled in accordance with a preset program. For this reason, the ECU 21 in this embodiment includes a catalyst regeneration determination unit in addition to the above-described EGR determination unit 22, EGR amount setting unit 23, EGR valve drive control unit 24, fuel injection amount setting unit 34, and injection valve drive control unit 35. 49, an addition amount calculation unit 50, an addition amount setting unit 51, a comparison unit 52, an air-fuel ratio correction unit 53, an addition amount correction unit 54, and the previous addition valve drive control unit 39.

  The catalyst regeneration determination unit 49 integrates the amount of fuel injected from the fuel injection valve 11, and determines that it is in the SOX catalyst regeneration mode when this amount exceeds a preset amount. In the catalyst regeneration mode for this sulfur poisoning, a predetermined amount of fuel is added as a sulfur component reducing agent from the fuel addition valve 38 into the exhaust passage 13 to reduce SOX adsorbed on the nitrogen reduction catalyst 37 to harmless sulfur. In the atmosphere. The catalyst regeneration determination unit 49 also detects the amount of fuel injected from the fuel injection valve 11, the engine speed calculated based on the detection signal from the crank angle sensor 46, and the accelerator opening detected by the accelerator opening sensor 41. When the integrated amount of NOx trapped by the nitrogen reduction catalyst 37 is read from a map set in advance based on the temperature of the nitrogen reduction catalyst 37 detected by the catalyst temperature sensor 47, and this exceeds a predetermined amount It is determined that the catalyst regeneration mode for NOx is in use. In this NOx catalyst regeneration mode, a predetermined amount of fuel is added to the exhaust passage 13 from the fuel addition valve 38 as a NOx reducing agent, and NOx is reduced to harmless nitrogen gas and discharged to the atmosphere.

  In this case, as is well known, the addition of fuel in the NOx catalyst regeneration mode is completed once or twice, whereas the fuel addition in the SOx catalyst regeneration mode is performed three or more times. However, in each case, the regeneration process is basically different so that the temperature of the nitrogen reduction catalyst 37 does not exceed a predetermined value. The addition amount and the addition timing of are appropriately set.

  The addition amount calculation unit 50 serves as a reducing agent added from the fuel addition valve 38 into the exhaust passage 13 based on the air-fuel ratio detected by the air-fuel ratio sensor 48 and the intake air amount detected by the airflow sensor 42. Calculate the amount of fuel. When fuel is also injected from the fuel injection valve 11 when the fuel addition valve 38 is driven, it is necessary to subtract and correct the fuel injection amount from the fuel injection valve 11 using information from the fuel injection amount setting unit 34. It goes without saying that there is.

  The addition amount setting unit 51 starts from the fuel addition valve 38 based on the value detected by the air / fuel ratio sensor 48 so that the air / fuel ratio of the exhaust gas flowing in the exhaust passage 13 downstream of the nitrogen reduction catalyst 37 becomes the target air / fuel ratio. Set the amount of fuel added. The set fuel addition amount is output to the addition amount correction unit 54. Note that, immediately after the start of the catalyst regeneration mode, the amount of fuel initially supplied from the fuel addition valve 38 into the exhaust passage 13 is set in advance to a predetermined amount that is leaner than the target air-fuel ratio.

Comparing unit 52, the reducing agent is calculated by the addition amount calculating section 50, i.e. a measurement amount Q _C of the fuel, is actually added to the exhaust passage 13 from the set by the addition amount setting unit 51 fuel addition valve 38 and calculating the amount ratio _{Q C} / _{Q R} from the amount _{Q R} of the fuel.

A graph as shown in FIG. 3 representing the relationship between the addition amount ratio Q _C / Q _R and the air-fuel ratio error is stored in advance in the air-fuel ratio correction unit 53, and the air-fuel ratio correction unit 53 includes the comparison unit described above. Based on the comparison result by 52, the air-fuel ratio error acquired from the graph as shown in FIG.

The addition amount correction unit 54 corrects the fuel addition amount set by the addition amount setting unit 51 based on the air / fuel ratio corrected by the air / fuel ratio correction unit 53 and outputs the target addition amount to the addition valve drive control unit 39. To do. In the present embodiment, the calculating the target amount Q _O as follows. First air-fuel ratio determining the minimum value R _m of the air-fuel ratio which is corrected by the correction unit 53 calculates the amount Q _m of fuel at this time from _{Q m = (A / R m} ) G. Here, A is the amount of intake air detected by the air flow sensor 42, and G is the specific gravity of the fuel set in advance. Further, since the target fuel addition amount Q _O corresponding to the target air-fuel ratio RO is (A / RO) G, the corrected addition amount ΔQ _C can be expressed by Q _O -Q _m . Therefore, the target addition amount Q _O is Q _R + ΔQ _C.

The addition valve drive control unit 39 controls the operation of the fuel addition valve 38 so that the target addition amount of fuel output from the addition amount correction unit 54 is added into the exhaust passage 13 at the set addition time. FIG. 6 schematically shows a change in the output of the air-fuel ratio sensor 48 in the catalyst regeneration mode. _{t 1,} t _2, the minimum value R _m of the detected air-fuel ratio by the air-fuel ratio sensor 48 for each addition time t ₃ but approaches gradually to the target air-fuel ratio RO, to an amount corresponding target air-fuel ratio RO of air-fuel ratio error It will be understood that the minimum value R _m converges in a state of being separated.

  FIG. 4 shows a control procedure of the exhaust gas purification method in the present embodiment. First, in step S1, the air-fuel ratio sensor 48 is calibrated. This is completed when the ECU 21 sets that the output of the air-fuel ratio sensor 48 in the operation state in which the fuel injection from the fuel injection valve 11 is stopped indicates an oxygen concentration of 20.9%. Therefore, thereafter, the detected value of the air-fuel ratio sensor 48 is read into the ECU 21 with this output value as a reference.

  Next, if the ECU 21 determines in step S2 whether or not the fuel addition valve 38 is normal and determines that the fuel addition valve 38 is abnormal, no proper catalyst regeneration control can be performed, so nothing is done. To finish. In this case, some warning may be issued as necessary. In the case of the present embodiment, a region where the detection error of the air-fuel ratio sensor 48 is small, that is, a specific lean region which is not significantly affected by the hydrocarbon concentration, for example, the air-fuel ratio detected by the air-fuel ratio sensor 48 is about 18. In addition, when the fuel is added from the fuel addition valve 38 to the exhaust passage 13 in advance by the addition valve drive control unit 39 for a short time and the detected value of the air-fuel ratio sensor 48 is within a predetermined range centering on 18, The ECU 21 determines that the fuel addition valve 38 is normal.

  When the ECU 21 determines that the fuel addition valve 38 is normal in step S2 described above, the process proceeds to step S3, and the catalyst regeneration determination unit 49 determines whether or not the catalyst regeneration mode is in effect. If it is determined that the catalyst regeneration mode is not set, it is not necessary to control the fuel addition valve 38, and thus this control flow ends.

  On the other hand, when the catalyst regeneration determination unit 49 determines that the catalyst regeneration mode is set in step S3, the process proceeds to step S4, and the regeneration process for SOX or NOX is performed on the nitrogen reduction catalyst 37 according to the determination result. Do it.

FIG. 5 shows the procedure for the regeneration treatment of the nitrogen reduction catalyst 37. That is, based on the detected value from the air-fuel ratio sensor 48, the fuel addition is performed so that the air-fuel ratio of the exhaust gas flowing in the exhaust passage 13 downstream of the nitrogen reduction catalyst 37 becomes the target air-fuel ratio RO in the step of S11. amount Q _R of the fuel from the valve 38 is set at amount setting unit 51. Information about the setting amount Q _R are output to the comparator 52 and the addition valve drive control unit 39.

On the other hand, based on the air-fuel ratio detected by the air-fuel ratio sensor 48 in step S12 and the intake air amount detected by the airflow sensor 42, the amount of fuel added to the exhaust passage 13 by the addition amount calculation unit 50. to calculate the Q _C. Fuel addition amount Q _C The calculated are also output to the comparator 52.

Next, a measurement amount Q _C of the calculated fuel quantity Q comparator 52 and _R of the fuel added in the actual exhaust passage 13 from the fuel addition valve 38 is compared at S13 in step, the The air-fuel ratio detected by the air-fuel ratio sensor 48 is corrected using the air-fuel ratio error read from the air-fuel ratio correction unit 53 based on the addition amount ratio Q _C / Q _R which is the comparison result.

Thereafter, the process proceeds to step S14 on the basis of the corrected air-fuel ratio, the addition amount correcting section 54 calculates the correction amount Delta] Q _C, set by the addition amount setting unit 51 in addition step S15 correcting the fuel amount Q _R, and outputs the amount of fuel added to the exhaust passage 13, that is, the target addition amount Q _O the addition valve drive control unit 39. The addition valve drive control unit 39 adds the fuel of the target addition amount Q _O output from the addition amount correction unit 54 into the exhaust passage 13 at the set addition timing.

  In this way, an appropriate amount of fuel is added from the fuel addition valve 38 into the exhaust passage 13, and the regeneration process of the nitrogen reduction catalyst 37 is appropriately performed.

In the embodiment described above, the value of the air-fuel ratio detected by the air-fuel ratio sensor 48 is corrected according to the value of the addition amount ratio Q _C / Q _R based on the comparison result in the comparison unit 52, and The fuel corresponding to the difference is supplied from the fuel addition valve 38 into the exhaust passage 13 by feedback control. However, the reducing agent corresponding to the difference from the air-fuel ratio detected by the air-fuel ratio sensor 48 by correcting the target air-fuel ratio based on the value of the addition amount ratio Q _C / Q _R based on the comparison result in the comparison unit 52. The same result can be obtained by correcting the amount of fuel added.

  It should be noted that the present invention should be construed only from the matters described in the claims, and in the above-described embodiment, all the changes and modifications included in the concept of the present invention are other than those described. Is possible. That is, all matters in the above-described embodiment are not intended to limit the present invention, and include any configuration not directly related to the present invention. To get. For example, in the above-described embodiment, the regeneration process of the nitrogen reduction catalyst 37 has been described. However, when the three-way catalyst equipped in the spark ignition type internal combustion engine is regenerated, the fuel is added to obtain the theoretical air-fuel ratio. Also, the present invention can be applied to a rich state or to sulfur poisoning recovery processing.

1 is a conceptual diagram schematically showing a main part of a vehicle in an embodiment in which an exhaust gas purifying apparatus according to the present invention is applied to a compression ignition engine. FIG. 2 is a control block diagram in the embodiment shown in FIG. 1. It is a graph showing the relationship between the ratio of the fuel addition amount calculated from the detection value of the sensor with respect to the actual fuel addition amount, and the air-fuel ratio. It is a flowchart of the main control procedure in embodiment shown in FIG. 5 is a flowchart showing a detailed work procedure in the catalyst regeneration process shown in FIG. 4. 2 is a graph schematically showing a change in a detected value by an air-fuel ratio sensor during the catalyst regeneration process of the embodiment shown in FIG. It is a graph showing the detection characteristic of an air fuel ratio sensor. It is a graph showing the relationship between the density | concentration of the hydrocarbon in exhaust gas, and the ratio of the fuel addition amount calculated from the detected value of the sensor with respect to the actual fuel addition amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 11 Fuel injection valve 12 Combustion chamber 13 Exhaust passage 14 Intake passage 15 Exhaust gas recirculation (EGR) device 16 Exhaust pipe 17 Intake pipe 18 EGR passage 19 EGR pipe 20 EGR valve 21 Electronic control unit (ECU)
DESCRIPTION OF SYMBOLS 22 EGR determination part 23 EGR amount setting part 24 EGR valve drive control part 25 Intake port 26 Exhaust port 27 Cylinder head 28 Intake valve 29 Exhaust valve 30 Valve mechanism 31 Air cleaner 32 Surge tank 33 Piston 34 Fuel injection amount setting part 35 Injection valve Drive control unit 36 Pretreatment catalyst 37 Nitrogen reduction catalyst 38 Fuel addition valve 39 Addition valve drive control unit 40 Accelerator pedal 41 Accelerator opening sensor 42 Airflow sensor 43 Cylinder block 44 Connecting rod 45 Crankshaft 46 Crank angle sensor 47 Catalyst temperature sensor 48 Air-fuel ratio sensor 49 Catalyst regeneration determination unit 50 Addition amount calculation unit 51 Addition amount setting unit 52 Comparison unit 53 Air-fuel ratio correction unit 54 Addition amount correction unit QC Addition amount calculated by the _QC addition amount calculation unit _QR addition amount amount Q of fuel that is set by the setting unit Target amount Delta] Q _C correction amount t _{1, t 2, t 3} fuel addition timing of

Claims (4)

A exhaust gas purification method by adding a reducing agent into the exhaust passage on the upstream side of the catalyst for purifying exhaust gas discharged from the combustion chamber of the internal combustion engine performs the reproduction process of the catalyst,
Detecting the amount of intake air supplied into the combustion chamber;
Detecting the air-fuel ratio of the exhaust gas flowing in the exhaust passage downstream of the catalyst;
Calculating the amount of reducing agent added to the exhaust passage based on the detected intake air amount and the detected air-fuel ratio;
Comparing the calculated amount of reducing agent added with the amount of reducing agent actually added into the exhaust passage;
Based on this comparison result, correcting the amount of reducing agent added to the exhaust passage so that the air-fuel ratio of the exhaust gas flowing in the exhaust passage downstream of the catalyst becomes the target air-fuel ratio ;
A step of correcting the target air-fuel ratio based on a comparison result between the calculated amount of reducing agent added and the amount of reducing agent actually added to the exhaust passage. The method for purifying exhaust gas, wherein the step of correcting the amount is performed with respect to the corrected target air-fuel ratio .   2. The exhaust gas purification method according to claim 1, further comprising the step of adding a corrected amount of the reducing agent into the exhaust passage. A exhaust gas purification device which performs a reproduction process of a catalyst by adding a reducing agent into the exhaust passage on the upstream side of the catalyst for purifying exhaust gas discharged from the combustion chamber of an internal combustion engine,
A reducing agent addition valve for adding a reducing agent into the exhaust passage;
An addition amount setting means for setting the addition amount of the reducing agent from the reducing agent addition valve;
An air flow sensor for detecting the amount of intake air supplied into the combustion chamber;
An air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas flowing in the exhaust passage downstream of the catalyst;
An addition amount calculating means for calculating an addition amount of a reducing agent from the reducing agent addition valve based on an intake air amount detected by the air flow sensor and an air-fuel ratio detected by the air-fuel ratio sensor;
A comparison means for comparing the addition amount of the reducing agent calculated by the addition amount calculation means with the addition amount of the reducing agent set by the addition amount setting means;
Based on the comparison result by the comparison means, the addition amount of the reducing agent set by the addition amount setting means so that the air-fuel ratio of the exhaust gas flowing in the exhaust passage downstream of the catalyst becomes the target air-fuel ratio. and addition amount correcting means for correcting,
Air-fuel ratio correction means for correcting the target air-fuel ratio based on the comparison result by the comparison means, and the addition amount correction means sets the addition amount of the reducing agent with respect to the target air-fuel ratio corrected by the air-fuel ratio correction means. An exhaust gas purifying device characterized by correcting . An addition valve drive control means for controlling the drive of the reducing agent addition valve is further provided so that the addition amount of the reducing agent corrected by the addition amount correction means is added into the exhaust passage. The exhaust gas purifying device according to claim 3 .

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