JP2010255528A - Exhaust emission control device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively regenerate/reduce NOx by quickly enriching air fuel ratio while suppressing oil dilution and fuel economy deterioration due to fuel increase. <P>SOLUTION: When rich gas supply event occurs, in-cylinder oxygen quantity is dropped by controlling opening of any of a throttle valve, an EGR valve, and a vane of a variable nozzle type turbocharger, and post injection is added to an injection patter of normal control. Consequently, rich gas is quickly formed in response to response delay of an air system, and control for sufficiently reducing and eliminating NOx while avoiding generation of torque shock due to air fuel ratio change over. Injection timing and base quantity of the post injection is gradually changed so as to converge the same to injection timing and injection quantity of target after injection. Injection timing and injection quantity of pilot and main injection is gradually changed. Regeneration/reduction of NOx is effectively done by maintaining a rich state by a target injection pattern corresponding to control of an air system. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an engine exhaust gas purification apparatus that purifies NOx in exhaust gas by disposing a NOx storage reduction catalyst in an exhaust passage.

  In general, in an exhaust gas aftertreatment system for an engine, a NOx occlusion reduction type catalyst is known as a catalyst for nitrogen oxides (NOx). This NOx occlusion reduction type catalyst needs to supply rich gas (HC, CO) serving as a NOx reducing agent to perform NOx regeneration / reduction before NOx is occluded in the catalyst and becomes saturated.

  For this reason, Patent Document 1 proposes a prior art relating to enrichment of the air-fuel ratio for performing regeneration and reduction of NOx trapped in the catalyst. In this prior art, when the catalyst temperature is high, the air-fuel ratio is enriched by controlling the opening degree of the EGR valve. On the other hand, when the catalyst temperature is low, EGR is stopped and the intake air is throttled by the throttle valve. To make it richer.

JP 2003-201890 A

  However, at the initial stage of supplying rich gas to the NOx storage reduction catalyst, the amount of NOx to be regenerated is large, so the air-fuel ratio cannot be quickly enriched with EGR or intake throttle, and NOx is sufficiently reduced. It is not possible.

  For this reason, a technique for enriching the air-fuel ratio by adding fuel injection (post injection) at a timing that does not contribute to combustion is known. However, in post injection, there are problems such as oil dilution due to fuel and fuel consumption deterioration. Arise.

  The present invention has been made in view of the above circumstances, and is an engine that can quickly enrich an air-fuel ratio while effectively suppressing oil dilution and fuel consumption deterioration due to fuel increase, and effectively perform regeneration and reduction of NOx. An object of the present invention is to provide an exhaust purification device.

  In order to achieve the above object, an exhaust emission control device for an engine according to the present invention stores NOx in exhaust when the air-fuel ratio of the exhaust is lean, and stores the stored NOx rich in the air-fuel ratio of the exhaust. In the exhaust purification system for an engine having the NOx occlusion reduction catalyst that is released at the time, the first enrichment control unit that enriches the air-fuel ratio of the exhaust by controlling the air amount of the engine, and the fuel amount of the engine And a second enrichment control unit that enriches the air-fuel ratio of the exhaust, and when the NOx occlusion reduction catalyst releases the NOx occluded by the NOx occlusion reduction catalyst, the first enrichment control unit The enrichment control and the enrichment control by the second enrichment control unit are simultaneously started, and the oxygen concentration in the exhaust gas within a predetermined period after the start of the enrichment control is determined by the second enrichment control unit. And wherein the reducing in rich control.

  According to the present invention, it is possible to rapidly enrich the air-fuel ratio while suppressing oil dilution and fuel consumption deterioration due to fuel increase, and NOx regeneration / reduction can be performed effectively.

Configuration diagram of engine control system Functional block diagram related to enrichment control Explanatory drawing which shows the change of the control state of normal control and rich control Flowchart showing main routine of enrichment control Flowchart showing rich gas generation control subroutine Flowchart showing normal control transition transient control subroutine

Embodiments of the present invention will be described below with reference to the drawings.
In FIG. 1, reference numeral 1 denotes an engine, and in the present embodiment, a diesel engine (hereinafter simply referred to as “engine”). An intake passage 5 and an exhaust passage 6 are communicated with the combustion chamber 2 of the engine 1 through an intake valve 3 and an exhaust valve 4. An intake chamber 40 is formed on the upstream side of the intake passage 5, and a throttle valve 10 is interposed upstream of the intake chamber 40. An intake pressure sensor 37 that detects an air pressure downstream of the throttle valve 10 as an absolute pressure is exposed to the intake chamber 40.

  The throttle valve 10 is connected to an intake actuator 11 that adjusts the opening of the throttle valve 10 by a control signal from an electronic control unit (ECU 50) and controls the intake amount (fresh air amount). Further, an intercooler 12 is interposed upstream of the throttle valve 10, and a compressor 13 a of the turbocharger 13 is interposed upstream of the intercooler 12. Further, an air cleaner 14 is interposed on the upstream side of the compressor 13 a of the turbocharger 13, and an intake air amount sensor 16 incorporating an intake air temperature sensor 15 for detecting the intake air temperature is interposed on the downstream side of the air cleaner 14. Has been.

  On the other hand, the turbine 13 b of the turbocharger 13 is interposed in the exhaust passage 6 of the engine 1, and the exhaust passage 6 on the upstream side of the turbine 13 b is connected to the downstream side of the throttle valve 10 via the exhaust gas recirculation (EGR) passage 17. The intake passage 5 is connected by bypass. The EGR passage 17 is provided with an EGR valve 18 that controls the amount of EGR by a control signal from the ECU 50, and an EGR cooler 19 that cools the EGR gas.

  In the present embodiment, the turbocharger 13 is a well-known variable nozzle turbosupercharger (VGT), and a vane of a variable nozzle provided around the turbine 13b is a link mechanism (see FIG. (Not shown) is connected to the negative pressure actuated actuator 20. A negative pressure control electromagnetic valve 21 controlled by the ECU 50 is connected to the pressure introduction pipe of the actuator 20, and negative pressure from a negative pressure source (not shown) is regulated by the negative pressure control electromagnetic valve 21 to be supplied to the actuator 20. be introduced.

  Thereby, the vane opening degree of the variable nozzle of the turbocharger 13 is varied, the flow rate of the exhaust gas blown to the turbine 13b is adjusted, the turbine rotational speed is varied, and the supercharging pressure is controlled. That is, when the vane opening degree of the variable nozzle is changed in the closing direction by the operation of the actuator 20, the exhaust gas flow rate is increased and the supercharging pressure is increased. On the other hand, when the vane opening degree changes in the opening direction, the exhaust gas flow rate becomes slow and the supercharging pressure decreases.

  The exhaust passage 6 on the downstream side of the turbine 13b is in communication with a diesel oxidation catalyst (DOC) 22 that mainly oxidizes hydrocarbon (HC) and carbon monoxide (CO) in the exhaust gas by a catalytic reaction. . The DOC 22 is formed by supporting a noble metal such as platinum or palladium or a metal oxide such as alumina on the surface of a ceramic carrier made of, for example, a cordierite honeycomb structure.

  Further, a NOx storage reduction catalyst (Lean NOx Trap catalyst; LNT) 23 for storing nitrogen oxide (NOx) in exhaust gas and reducing and purifying it is disposed downstream of the DOC 22. The LNT 23, for example, has a NOx occlusion material such as alkali metal, alkaline earth or rare earth and a noble metal such as platinum supported on a carrier such as alumina, and the oxygen concentration of exhaust gas is reduced by the storage function of NOx and O2. When it is high, it oxidizes and reduces HC and CO and occludes NOx. When the oxygen concentration in the exhaust gas decreases, the stored NOx is released, and NOx is reduced and purified by HC and CO that are left without being oxidized and reduced.

  Further, particulate matter (PM) such as soot, carbon soot, soluble organic components (SOF), sulfate (SO4), etc. in the exhaust gas is captured downstream of the LNT23. A diesel particulate filter (Diesel Particulate Filter; DPF) 24 is arranged. The DPF 24 is formed, for example, by forming heat-resistant ceramics such as cordierite into a honeycomb structure and sealing a large number of cells serving as gas flow paths so that the inlet side or the outlet side are staggered.

  Exhaust gas that has passed through the turbine 13b is purified as it passes through the DOC 22 and LNT 23, and further flows downstream while passing through the porous partition walls of the DPF 24, during which PM in the exhaust gas is collected and deposited. The purified exhaust gas is discharged through an exhaust muffler (not shown).

  Such DOC22, LNT23, and DPF24 are provided with sensors for detecting the state of the exhaust gas. That is, a temperature sensor 41 that detects the temperature of the exhaust gas flowing into the DOC 22 is exposed upstream of the DOC 22, and a linear air-fuel ratio sensor 42 that detects the air-fuel ratio of the exhaust gas is exposed between the DOC 22 and the LNT 23. ing. Further, a temperature sensor 43 for detecting the temperature of the exhaust gas and a NOx sensor 44 for detecting the NOx concentration in the exhaust gas are faced between the LNT 23 and the DPF 24. Further, the inlet pressure of the DPF 24 is located upstream and downstream of the DPF 24. A differential pressure sensor 45 for detecting a differential pressure between the outlet pressure and the outlet pressure is provided.

  Next, the fuel injection system of the engine 1 will be described. The engine 1 employs a well-known common rail fuel injection system, and an injector 25 controlled by the ECU 50 is exposed to the combustion chamber 2. A glow plug 26 whose energization is controlled by a glow controller 27 is exposed near the injection nozzle of the injector 25 in the combustion chamber 2.

  The injector 25 is connected to a common rail 29 via a fuel pipe 28 branched to each cylinder. A supply pump 30 that sucks up and pressurizes fuel from a fuel tank (not shown) is connected to the common rail 29. The fuel boosted to a high pressure by the supply pump 30 is accumulated in the common rail 29, and the high-pressure fuel is supplied to the injector 25 of each cylinder via the fuel pipe 28 to each cylinder.

  The supply pump 30 is provided with, for example, an inner cam type pressure feeding system and an intake amount adjustment method using an electromagnetic valve, and an intake adjustment electromagnetic valve 31 for adjusting the intake amount, and a fuel temperature sensor 32 for detecting a fuel temperature are provided in the main body. It is built in. A signal from the fuel temperature sensor 32 of the supply pump 30 is input to the ECU 50 together with a signal from the fuel pressure sensor 33 that detects the fuel pressure (rail pressure) in the common rail 29, and is processed together with signals from other sensors. . Then, the ECU 50 feedback-controls the discharge pressure of the supply pump 30, that is, the fuel pressure of the common rail 29, for example, to an optimum value according to the engine speed and the load via the intake metering solenoid valve 31.

  Next, an electronic control system centering on the ECU 50 will be described. The ECU 50 is configured to include a peripheral circuit such as an A / D converter, a timer, a counter, and various logic circuits, with a microcomputer including a CPU, a ROM, a RAM, an I / O interface and the like as a center.

  The ECU 50 includes an intake air temperature sensor 15, an intake air amount sensor 16, a fuel temperature sensor 32, a fuel pressure sensor 33, a water temperature sensor 34 that faces the cooling water passage of the engine 1 and detects the cooling water temperature, and a rotational position of the crankshaft 1 a. A crank angle sensor 35 that detects the amount of depression, an accelerator pedal sensor 36 that detects the amount of depression of the accelerator pedal, an intake pressure sensor 37 that faces the intake chamber 40, an atmospheric pressure sensor 38 that detects atmospheric pressure, and an exhaust system. Signals from various sensors (temperature sensors 41 and 43, linear air-fuel ratio sensor 42, NOx sensor 44, differential pressure sensor 45) and other various sensors and switches (not shown) are input.

  The ECU 50 is further connected to an in-vehicle network (not shown) based on a communication protocol such as CAN (Controller Area Network). In addition to the ECU 50, a plurality of ECUs such as a transmission ECU that controls the transmission and a brake ECU that controls the brake are connected to the in-vehicle network, and various information is shared by transmitting and receiving data to and from each other.

  The ECU 50 controls the fuel pressure control, the fuel injection control, the intake air control, the supercharging pressure control, the EGR based on signals from the above-described various sensors for detecting the engine operating state and various control information input via the in-vehicle network. Various engine controls such as control are executed, and the operating state of the engine 1 is maintained in an optimum state.

  In this engine control, during normal running, the fuel injection amount and the injection timing are determined by referring to a map or the like according to the engine speed based on the signal from the crank angle sensor 35 and the accelerator opening based on the signal from the accelerator pedal sensor 36. The high pressure fuel is injected from the injector 25 in a multi-stage injection pattern (for example, pilot injection → pre-injection → main injection → after-injection pattern) around the piston top dead center to stabilize combustion and reduce exhaust emissions. I am trying.

  Further, the ECU 50 intentionally enriches the exhaust air-fuel ratio at a predetermined timing and supplies rich gas to the LNT 23 with respect to normal engine control so that NOx and SOx can be effectively regenerated and reduced in the LNT 23. Control. The supply of the rich gas is basically mainly an additional post injection after the after injection in the normal injection pattern. However, the post injection is limited only to the initial stage of supplying the rich gas, and thereafter the EGR valve 18. By controlling the in-cylinder oxygen amount by controlling the vane opening degree of the throttle valve 10 and the variable nozzle turbocharger 13, the rich gas can be supplied without depending on the post injection.

  Therefore, as shown in FIG. 2, the ECU 50 functions as a function related to the enrichment control, as shown in FIG. 2, the enrichment determination unit 51 that determines whether to execute / stop the enrichment control, or the first rich that performs the enrichment control based on the air amount restriction. The control unit 52 mainly includes a second enrichment control unit 53 that performs enrichment control based on fuel increase.

  The enrichment determination unit 51 determines execution / stop of the enrichment control that supplies the rich gas to the LNT 23, and instructs the first enrichment control unit 52 and the second enrichment control unit 53 to execute the enrichment control. In the present embodiment, the execution / stop of the enrichment control is treated as the occurrence of an event in the real-time control, and when the occurrence condition of the event for supplying the rich gas is satisfied, the rich gas supply event is issued to enrich from the normal control. When the condition for generating an event for stopping the rich gas supply is satisfied, the rich gas stop event is issued to shift (return) from the rich control to the normal control.

The rich gas generation event is issued when a condition shown in the following (A) is satisfied.
(A) NOx occlusion amount> set threshold (upper limit side)
In this case, the NOx occlusion amount NOXabsorb can be obtained by the following equation (1) using the NOx emission amount NOXexh, the trap rate NOXtrap, and the NOx regeneration amount NOXregen. In the following expression, the subscript (n) indicates the value in the current calculation cycle, and (n-1) indicates the value in the previous calculation cycle.
NOXabsorb (n) = NOXabsorb (n-1) + (NOXexh × NOXtrap−NOXregen) (1)

However, the NOx emission amount, the trap rate, and the NOx regeneration amount are calculated as map values depending on the following parameters, respectively.
・ NOx emission amount: Map value with parameters of engine speed, fuel injection amount, intake pressure, intake air amount, EGR amount, intake air temperature, water temperature ・ Trap rate: previous NOx occlusion amount NOXabsorb (n-1 ), SOx occlusion amount SOXabsorb (n-1), air-fuel ratio, catalyst temperature, map value using any one of catalyst deterioration indicators as parameters ・ NOx regeneration amount: map value using either catalyst temperature or air-fuel ratio as parameters

Here, the catalyst deterioration index can be calculated based on any of travel distance, catalyst temperature history, and total fuel injection amount. The SOx occlusion amount SOXabsorb (n) is the SOx emission amount SOXexh (value based on the fuel injection amount), trap rate SOXtrap (previous NOx occlusion amount NOXabsorb (n-1), SOx occlusion amount SOXabsorb (n-1), Using the air-fuel ratio, catalyst temperature, or catalyst deterioration index as a parameter) and SOx regeneration amount SOXregen (map value using either the catalyst temperature or air-fuel ratio as a parameter), the following equation (2) Can be calculated.
SOXabsorb (n) = SOXabsorb (n-1) + (SOXexh * SOXtrap-SOXregen) (2)

On the other hand, the rich gas stop event is issued when any of the following conditions (B1) to (B3) is satisfied.
(B1) Elapsed time after issuing a rich event> set threshold (B2) NOx occlusion amount <set threshold (lower limit side)
(B3) (engine speed> setting threshold) and (fuel injection amount> setting threshold)

  As shown in FIG. 3, the first enrichment control unit 52 is notified of the occurrence of a rich gas supply event from the enrichment determination unit 51, and includes a throttle valve 10, an EGR valve 18, a variable nozzle type, which are air system control devices. Control is made so as to reduce the in-cylinder oxygen amount by controlling any one of the vane openings of the turbocharger 13 and supply rich gas to the LNT 23.

  Specifically, target values for throttle opening, EGR valve opening, and vane opening are set using each map centered on driver demand torque and engine speed calculated with reference to accelerator opening. Each control device is controlled to converge to these target values. These target values are set so as to be the in-cylinder oxygen amount necessary for generating the driver required torque when the exhaust air-fuel ratio is enriched.

  Further, when the rich enrichment determination unit 51 is notified of the occurrence of the rich gas stop event, the first enrichment control unit 52 resets the control target value for each control device in the air system to the target value during normal control. . Then, each control device is controlled to converge to the target value at the time of normal control, and the in-cylinder oxygen amount is returned to the value at the time of normal control.

  The control for converging to the above target value includes a target value (target throttle opening, target EGR valve opening, target vane opening) and an actual value (actual throttle opening, actual EGR valve opening, actual vane opening) Open control using a gradual change amount set based on the deviation, and control is performed so that the target value is gradually converged by this gradual change amount.

  On the other hand, the second enrichment control unit 53, when notified of the occurrence of the rich gas supply event from the enrichment determination unit 51, pilot injection → pre injection → main injection → after. The fuel is immediately increased by adding post injection that does not contribute to the torque to the injection pattern of the normal control of the injection, and the rich gas is quickly generated. In the following description, for convenience, pilot and pre-injection are described as pilot injection.

  That is, at the initial stage of supplying rich gas to the LNT 23, the amount of NOx to be regenerated is large, and there is a response delay until the air-fuel ratio becomes rich due to the restriction of the air amount by the first enrichment control unit 52. Therefore, as shown in FIG. 3, the second enrichment control unit 53 quickly supplies rich gas to the LNT 23 by adding post-injection simultaneously with the occurrence of the rich gas supply event, and the torque due to the switching of lean ← → rich. Control is made so that NOx released from the LNT 23 is sufficiently reduced and purified while avoiding the occurrence of shock.

  The post-injection injection amount is set to a value obtained by adding a correction amount for PID control to the target air-fuel ratio λ (during rich control) to a basic amount calculated from a map of driver required torque and engine speed. Is done. The target air-fuel ratio λ during the enrichment control is calculated from a map of driver request torque and engine speed. At this time, the target injection pattern (injection amount and injection timing of pilot injection, main injection, and after injection) in the enrichment control is also calculated from the map of the driver required torque and the engine speed.

  The second enrichment control unit 53 adds the post injection composed of the basic amount and the correction amount due to the occurrence of the rich gas supply event, and then, as shown in FIG. 3, sets the injection timing / basic amount of the post injection to the target after injection. Gradually change to converge to the injection timing and injection amount. Further, the injection timing and injection amount of the pilot and main injections are gradually changed so as to converge to the target injection pattern. By converging on the injection timing and the injection amount of the target injection pattern, the target air-fuel ratio λ and the driver required torque are set.

  The gradual change amount of the injection timing / injection amount for converging to the target injection pattern includes the above-described throttle opening, EGR valve opening, time delay of in-cylinder oxygen amount reduction by open control of the vane opening, and target injection timing / Calculation is made with reference to the deviation between the target injection amount and the actual injection timing / actual injection amount. Due to the convergence to the target injection pattern, the post-injection composed of the initial basic amount and the correction amount is shifted to the after-injection timing and the injection amount, and becomes only the correction amount. The amount of post-injection at this time is a small amount of fuel for correcting feedback to the target air-fuel ratio λ by PID control. Therefore, thereafter, the enrichment of the exhaust air-fuel ratio is maintained by the control of the in-cylinder oxygen amount via the air system control device by the first enrichment control unit 52 and the fuel amount in the target injection pattern corresponding thereto. The

  In addition, when the occurrence of the rich gas stop event is notified to the above enrichment control, the second enrichment control unit 53 performs the transition control from the enrichment control to the normal control. In this transition control, first, post-injection is reset to zero simultaneously with the occurrence of a rich gas stop event, and then the injection timing and injection amount of pilot, main, and after injection are set to the target injection timing and target in normal control. Gradually change to converge to the injection amount. The gradual change amount at this time is the cylinder oxygen response delay due to the gradual change of the throttle opening, the EGR valve opening, and the vane opening, and the target injection timing / target injection amount and the actual injection timing / actual injection amount during normal control. Calculate with reference to the deviation.

  Next, program processing related to enrichment control by the ECU 50 will be described with reference to the flowcharts of FIGS.

  First, the main routine of the enrichment control shown in the flowchart of FIG. 4 will be described. In this main routine, initial processing is executed in the first step S1, a rich gas supply flag F1 for instructing supply of rich gas, a normal control transition transition flag F2 for stopping the supply of rich gas and instructing transition to normal control, Each is initialized to 0. Next, the process proceeds to step S2, and it is checked whether or not an event generation condition is satisfied. If the condition is satisfied, a rich gas generation event or a rich gas stop event is issued.

  In a succeeding step S3, it is determined whether or not a rich gas generation event has occurred. If the determination result is true (T), the process proceeds to step S4, 1 is set to the rich gas supply flag F1, and the process proceeds to step S5. On the other hand, if the determination result is false (F), the process jumps from step S3 to step S5.

  Step S5 is a step for determining the occurrence of a rich gas stop event. If the determination result is true (T), the process proceeds to step S6, the rich gas supply flag F1 is cleared to 0, and the normal control transition transition flag F2 is set to 1. Is set, and the process proceeds to step S7. On the other hand, if the determination result is false (F), the process jumps from step S5 to step S7.

  In step S7, it is determined with reference to the rich gas supply flag F1 whether F1 = 1. As a result, if F1 = 1, that is, if a rich gas generation event has occurred and a rich gas stop event has not yet occurred, the process proceeds from step S7 to step S7_1 to execute the rich gas generation control subroutine of FIG. To do. And it returns to step S2 and prepares for the next event announcement.

  On the other hand, if F1 = 0 in step S7, that is, if a rich gas stop event has occurred, the process proceeds from step S7 to step S8 to determine whether the normal control transition transition flag F2 is F2 = 1. To do. This is to determine whether or not the shift to the normal control is completed after the supply of the rich gas is stopped by the occurrence of the rich gas stop event.

  As a result, when the normal control transition transition flag F2 is F2 = 0 and the determination result in step S8 is false (F), that is, when the transition from the rich gas generation control to the normal control has already been completed, The process proceeds from step S8 to step S9. In step S9, normal control is executed, and in step S2, the next event is issued.

  On the other hand, if the normal control transition transition flag F2 is F2 = 1 and the determination result in step S8 is true (T), the process proceeds from step S8 to step S8_1, and the normal control transition transient control subroutine of FIG. Execute. After the execution of the normal control transition transient control, it is determined in step S8-2 whether or not the termination condition for the normal control transition transient control is satisfied.

  Completion of normal control transition transient control is determined by comparing the difference between the actual value and target value of each parameter in the normal control transition transient control with a predetermined threshold, and when each difference converges below the threshold, normal control transition transient control It is determined that the end. If the result of the end determination in step S8_2 is false (F), the next event is issued in step S2. If true (T), the normal control transition transition flag F2 is cleared to 0 in step S8_3. Then, the process returns to step S2.

  Next, the rich gas generation control in step S7-1 of the above-described rich control main routine will be described with reference to the flowchart of FIG.

  In the first steps S101 and S102, the rich gas generation control subroutine includes a fuel injection amount, a fuel injection timing, and a target value of the air system control amount based on the driver requested torque calculated with reference to the accelerator opening and the engine speed. The amount of gradual change to the target value is calculated. As for fuel injection, post injection is added to the normal control injection pattern, and the target value and gradual change amount of the post injection are calculated. Next, it progresses to step S103 and the control value gradually changed by the gradual change amount calculated previously is calculated.

  As a result, control by the air system control device (throttle opening, EGR valve opening, and vane opening to the target values) is started, and calculated from a map of driver required torque and engine speed. The post-injection is executed by adding the correction amount for PID control to the target air-fuel ratio λ to the basic amount to quickly generate rich gas. After the post-injection is executed, as shown in FIG. 3, the post-injection injection timing / basic amount is gradually converged to the target after-injection injection timing / injection amount in synchronization with the in-cylinder oxygen reduction speed. Further, the injection timing and injection amount of the pilot and main injections are gradually changed so as to converge to the target injection pattern.

  Then, it progresses to step S104 and the convergence determination of a rich gas production | generation driving | operation is performed. This convergence determination is determined as convergence when the injection amount / injection timing of the main injection falls within the set range with respect to the target injection timing / injection amount. Control to the fuel ratio λ is performed.

  The rich gas generation control described above shifts to normal control when a rich gas stop event occurs. Next, the normal control transition transient control in step S8_1 of the main routine of the enrichment control will be described using the flowchart of FIG.

  The normal control transition transient control subroutine stops the post-injection in the first step S201, and in steps S202 and 203, the target value of the fuel injection amount, the fuel injection timing, the air system control amount, and the gradual change amount to these target values. Is calculated. Next, in step S204, a control value gradually changed by the previously calculated gradual change amount is calculated.

  As a result, the control amount (throttle opening, EGR valve opening, vane opening) for the control device of the air system during the enrichment control is the gradual amount calculated previously so as to converge to the target value during the normal control. While gradually changing, the injection pattern (injection timing / injection amount) at the time of enrichment control is gradually changed by the previously calculated gradual change amount so as to converge to the target injection pattern at the time of normal control. The injection pattern at this time is gradually changed in consideration of the response delay of the air system, and synchronizes with the in-cylinder oxygen increase rate as shown in FIG.

  As described above, in the present embodiment, when the NOx occluded in the LNT 23 is released to reduce and purify, the enrichment control by controlling the air system of the throttle opening, the EGR valve opening, and the vane opening, and the combustion The enrichment control by additional post injection that does not contribute to the start is simultaneously started, and the rich gas is rapidly supplied by post injection in the initial stage, and thereafter, the in-cylinder oxygen amount is mainly controlled by the air system.

  As a result, NOx can be effectively regenerated / reduced at an initial stage where the amount of NOx to be regenerated is large, and the engine is operated at a lean air-fuel ratio and is operated at a rich air-fuel ratio. It is possible to minimize the occurrence of oil dilution due to the supply of rich gas and the deterioration of fuel consumption while avoiding torque shocks associated with switching to the state.

DESCRIPTION OF SYMBOLS 1 Engine 23 NOx occlusion reduction type | mold catalyst 50 Electronic controller 51 Enrichment determination part 52 1st enrichment control part 53 2nd enrichment control part

Claims (7)

An engine exhaust purification apparatus having a NOx occlusion reduction type catalyst that stores NOx in exhaust when the air-fuel ratio of the exhaust is lean and releases the stored NOx when the air-fuel ratio of the exhaust is rich in the exhaust passage of the engine In
A first enrichment control unit that enriches the air-fuel ratio of the exhaust by controlling the air amount of the engine;
A second enrichment control unit for controlling the fuel amount of the engine to enrich the air-fuel ratio of the exhaust,
When NOx occluded by the NOx occlusion reduction catalyst is released to reduce and purify,
The enrichment control by the first enrichment control unit and the enrichment control by the second enrichment control unit are started simultaneously, and the oxygen concentration in the exhaust gas within a predetermined period after the start of the enrichment control is set to the second An exhaust gas purification apparatus for an internal combustion engine, characterized by being reduced by enrichment control by an enrichment control unit. After the oxygen concentration in the exhaust gas is reduced by the enrichment control by the second enrichment control unit, the enrichment control by the first enrichment control unit mainly converges the oxygen concentration in the exhaust gas to a target value. The engine exhaust gas purification apparatus according to claim 1. The first enrichment control unit executes enrichment control for reducing the in-cylinder oxygen amount by controlling any one of the throttle opening, the exhaust gas recirculation amount, and the vane opening of the variable nozzle turbocharger. ,
3. The engine exhaust gas purification apparatus according to claim 1, wherein the second enrichment control unit performs enrichment control by injection of invalid fuel at a timing that does not contribute to combustion.   The second enrichment control unit controls the injection amount of the invalid fuel by a basic amount based on an engine operating state and a correction amount for converging the air-fuel ratio of the exhaust gas to the target air-fuel ratio. The exhaust emission control device for an engine according to claim 3. The first enrichment control unit controls the throttle opening, the exhaust gas recirculation amount, and the vane opening of the variable nozzle turbocharger so as to become target values at the time of enrichment control. The exhaust emission control device for an engine according to claim 3.   The engine exhaust gas purification apparatus according to claim 4, wherein the second enrichment control unit gradually changes the basic amount by a predetermined gradual change amount so as to converge to the target injection amount at the time of the enrichment control. .   The gradual change amount is calculated in consideration of a response delay of the in-cylinder oxygen amount by controlling the throttle opening, the exhaust gas recirculation valve opening, and the vane opening of the variable nozzle turbocharger. The exhaust emission control device for an engine according to claim 6.

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