JP2007247405A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve total exhaust emission control performance, by shortening catalyst activity as much as possible through lean forming control of the air-fuel ratio. <P>SOLUTION: From the start of air-fuel ratio feedback control, the target air-fuel ratio A/F is set to lean, and a lean forming degree is set on the basis of the starting time water temperature TWINT. Thus, an HC quantity exhausted from an engine (a combustion chamber) is reduced äFig.5(F)}, and at the same time, catalyst activity time can be shortened, while reducing the residual ratio of a catalyst, in its turn, an HC exhaust quantity from a tail pipe, with an increase in the combustion temperature, accordingly, the exhaust temperature and an increase in reaction heat with HC in the catalyst by surplus oxygen as factors äFig.5(G)}. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for improving exhaust purification performance by promoting catalyst activation in an internal combustion engine equipped with an exhaust purification catalyst.

Patent Document 1 discloses that the air-fuel ratio is enriched immediately after start-up, the air-fuel ratio is gradually converged to stoichiometric (theoretical air-fuel ratio) as time elapses, and then the control proceeds to stoichiometric air-fuel ratio feedback control. Yes.
JP 2001-23479A

However, if the air-fuel ratio is rich or stoichiometric, the heat of reaction with HC in the catalyst due to excess oxygen in the exhaust gas cannot be expected, and the catalyst activation time cannot be shortened, so the exhaust purification performance may be impaired as a whole. It was.
The present invention has been made paying attention to such a conventional problem, and an object of the present invention is to reduce the catalyst activity as much as possible and to improve the exhaust purification performance as a whole by the lean air-fuel ratio control.

Therefore, the present invention is an exhaust purification device for an internal combustion engine provided with an exhaust purification catalyst in an exhaust passage,
After the start, the target air-fuel ratio is set to lean for a predetermined time after the air-fuel ratio feedback control is started when a predetermined air-fuel ratio feedback control condition is satisfied.

  According to the present invention, by setting the target air-fuel ratio to lean for a predetermined time from the start of air-fuel ratio feedback control, the HC remaining rate of the catalyst is reduced while reducing HC (unburned fuel) discharged from the engine (combustion chamber). As a result, the final HC emission amount (oxygen storage amount) from the tail pipe can be reduced, and at the same time, the catalyst activity can be promoted.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system diagram of an engine (internal combustion engine) showing an embodiment of the present invention.
Air is sucked into the combustion chamber of each cylinder of the engine 1 from the air cleaner 2 through the intake duct 3, the throttle valve 4, and the intake manifold 5. Each branch portion of the intake manifold 5 is provided with a fuel injection valve 6 for each cylinder. However, the fuel injection valve 6 may be disposed directly in the combustion chamber.

  The fuel injection valve 6 is an electromagnetic fuel injection valve (injector) that opens when the solenoid is energized and closes when the energization is stopped, and a drive pulse signal from an engine control unit (hereinafter referred to as ECU) 12 described later. The fuel is energized to open the valve, and the fuel is pumped from a fuel pump (not shown) and adjusted to a predetermined pressure by a pressure regulator. Therefore, the fuel injection amount is controlled by the pulse width of the drive pulse signal.

Each combustion chamber of the engine 1 is provided with a spark plug 7, which sparks and ignites and burns the air-fuel mixture.
Exhaust gas from each combustion chamber of the engine 1 is discharged through an exhaust manifold 8. Further, an EGR passage 9 is led out from the exhaust manifold 8, whereby a part of the exhaust is recirculated to the intake manifold 5 via the EGR valve 10.

On the other hand, an exhaust purification catalyst 11 is provided in the exhaust passage so as to be positioned immediately below the exhaust manifold 8.
The ECU 12 includes a microcomputer that includes a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like, receives input signals from various sensors, performs arithmetic processing as described later, and performs fuel injection. 6 is controlled.

  The various sensors include a crank angle sensor 13 that can detect the engine rotational speed Ne together with the crank angle based on the crankshaft or camshaft rotation of the engine 1, an air flow meter 14 that detects the intake air amount Qa in the intake duct 3, and a throttle valve. 4 includes a throttle sensor 15 (including an idle switch that is turned on when the throttle valve 4 is fully closed), a water temperature sensor 16 that detects the cooling water temperature Tw of the engine 1, and an exhaust manifold 8. A wide-range air-fuel ratio sensor 17 or the like that can detect the exhaust air-fuel ratio linearly is provided. A signal is also input to the ECU 12 from the start switch 18 and the like.

2 to 4 are flowcharts of an engine control routine executed by the ECU 12 in time synchronization or rotation synchronization. The engine control will be described according to the flowchart with reference to the time chart of FIG.
In step S1, it is determined whether the start switch 18 is turned on.
When it is determined that the start switch 18 is turned on, the process proceeds to step S2, and the water temperature TWINT at the time of engine start is read.

If it is determined in step S1 that the start switch 18 has been turned off after the engine is started, the process proceeds to step S3, where the starting water temperature TWINT is within a set water temperature range in which the target air-fuel ratio can be made lean -L ≦ TWINT. It is determined whether or not ≦ K.
If it is determined that it is not within the set water temperature range, it is determined that there is no effect of the target air-fuel ratio leaning, and the routine proceeds to step S4 where air-fuel ratio feedforward control for starting is performed.

  When it is determined that the starting water temperature TWINT is within the set range, the process proceeds to step S5, where it is determined whether the air-fuel ratio feedback control is started. Air-fuel ratio feedforward control according to The target air-fuel ratio is set to an initial stoichiometric value, but does not function for air-fuel ratio control {part A in FIG. 5B}.

When it is determined that the air-fuel ratio feedback control has been started, the target air-fuel ratio lean set value C is determined based on the starting water temperature TWINT in step S6.
In step S7, it is determined whether the catalyst 11 has reached the activation temperature. This activity determination may be a method of determining by time by providing a timer.
When it is determined that the catalyst 11 is not active, it is determined in step S8 whether the current target air-fuel ratio A / F is less than the lean set value C, and is determined to be equal to or less than the set value C. In this case, the control shifts to a control for gradually shifting the target air-fuel ratio from stoichiometric to lean {B portion in FIG. 5B}.

Specifically, in step S9, the target air-fuel ratio A / F is set by the following equation.
A / F = A / Fo + T1 × a
A / Fo; previous target air-fuel ratio T1; time from previous time when target air-fuel ratio A / F is calculated a; A / F increase / decrease value per unit time T1 In step S10, from target air-fuel ratio A / F, An ignition timing correction amount is calculated. Specifically, calculation is performed so that the ignition timing is advanced in accordance with the gradient of the target air-fuel ratio A / F {B portion in FIG. 5B} {B portion in FIG. 5D}. Thereby, the deterioration of the combustion degree at the time of the transition from stoichiometric to lean can be prevented.

In step S11, an intake air amount correction amount is calculated from the target air-fuel ratio A / F and ignition timing. Specifically, it is calculated so as to increase the air amount in accordance with the leaning of the target air-fuel ratio {B portion in FIG. 5 (E)}. Thereby, the fall of rotation by A / F leaning can be prevented.
When the target air-fuel ratio A / F reaches the lean set value C and the water temperature starts to rise {C portion in FIG. 5 (A)}, the combustion stability is improved and the ignition timing can be retarded. Therefore, while maintaining the target air-fuel ratio A / F at the lean set value C in step S12, the water temperature TWN is read in step S13, and the ignition timing is retarded in accordance with the water temperature increased in step S14 {FIG. C part}, leading to an increase in exhaust temperature.

Since the torque becomes insufficient due to the retarded ignition timing and the rotation is reduced as it is, the process proceeds to step S15 to calculate the insufficient air amount from the target air-fuel ratio A / F and the ignition timing to prevent the rotation from falling {FIG. E) C part}.
If it is determined in step S7 that the catalyst has been activated, the control shifts to gradually returning the target air-fuel ratio from lean to stoichiometric.

Specifically, in step S16, the target air-fuel ratio A / F is set by the following equation {D portion in FIG. 5B}.
A / F = A / Fo + T2 × (−a)
A / Fo: Previous target air-fuel ratio (initial value = C)
T2: Time from the previous time when calculating the target air-fuel ratio A / F (D portion in the figure) -a; A / F increase / decrease value per unit time T2 In step S17, the target air-fuel ratio A / F is F (stoichiometric air). It is determined whether or not the fuel ratio is less than F, and if it is greater than F, the routine proceeds to step S18 where the ignition timing correction amount is calculated from the target A / F. Specifically, calculation is performed so that the ignition timing is retarded in accordance with the inclination of the target air-fuel ratio A / F {D portion in FIG. 5B} {D portion in FIG. 5D}. Thereby, the combustion at the time of the transition from lean to stoichiometric can be favorably maintained.

Next, the routine proceeds to step S19, where the intake air amount correction amount is calculated from the target air-fuel ratio A / F and the ignition timing. Specifically, calculation is performed so as to decrease the air amount in accordance with the enrichment of the target air-fuel ratio {D portion in FIG. 5E}.
When it is determined in step S17 that the target air-fuel ratio A / F is equal to or less than F, the process proceeds to step S20 to enrich the target air-fuel ratio A / F to E {E portion in FIG. 5B}, So-called rich spike control is performed.

In step S21, it is determined whether the integration time Te of the rich spike control has reached a predetermined time T3, and when it reaches, the process proceeds to step S22 to return to the control in which the normal target air-fuel ratio is stoichiometric {FIG. F part of (B)}.
The rich spike control is performed to suppress the deterioration of the NOx emission amount when returning from the target air-fuel ratio lean to the stoichiometric condition. However, if the execution time is too long, the HC emission amount will be deteriorated. Return to stoichiometric at T3.

  As described above, by making the target air-fuel ratio A / F lean from the start of the air-fuel ratio feedback control, the amount of HC discharged from the engine (combustion chamber) is simultaneously reduced {FIG. 5 (F)}, The catalyst activation time can be shortened while reducing the HC residual rate of the catalyst and hence the HC emission amount from the tail pipe due to an increase in the combustion temperature and therefore the exhaust temperature and an increase in the reaction heat with HC due to excess oxygen. Yes {Fig. 5 (G)}.

Further, by setting the degree of leaning of the target air-fuel ratio A / F based on the starting water temperature TWINT, the degree of leaning is increased when the water temperature is low, and the degree of leaning is decreased when the water temperature is relatively high. By doing so, the catalyst activity can be accelerated by leaning as much as necessary according to the water temperature while maintaining operability.
Further, when the target air-fuel ratio A / F is changed from stoichiometric to lean and returned from lean to stoichiometric, it is gradually changed over a predetermined time, so that deterioration of drivability can be suppressed.

Similarly, the ignition timing is advanced during lean control to prevent deterioration of combustibility, and the amount of air can be increased to prevent the engine from falling off. In addition, the ignition timing, which has been advanced to stabilize combustibility as described above, is retarded as the combustibility improves as the water temperature rises, thereby raising the exhaust temperature and promoting catalyst activity. To do.
The target air-fuel ratio A / F leaning deteriorates the NOx remaining rate of the catalyst and increases the NOx emission amount from the tail pipe. As described above, the target air-fuel ratio leaning is performed at the catalyst activation temperature ( By using control that can be arbitrarily set by time) or represented by time, it is possible to prevent NOx deterioration as much as possible. Further, the deterioration of the NOx emission amount from the catalyst when the target air-fuel ratio A / F is returned from lean to stoichiometric can be avoided by performing the rich spike {FIG. 5 (H)}.

Engine system diagram showing an embodiment of the present invention Air-fuel ratio control routine flowchart Air-fuel ratio control routine flowchart Air-fuel ratio control routine flowchart Time chart showing various state changes during air-fuel ratio control after startup

Explanation of symbols

1 engine
6 Fuel injection valve
12 ECU
17 O2 sensor

Claims (10)

An exhaust gas purification apparatus for an internal combustion engine having an exhaust gas purification catalyst in an exhaust passage,
An exhaust gas purification control apparatus for an internal combustion engine, wherein after a start, a target air-fuel ratio is set to lean for a predetermined time after the air-fuel ratio feedback control is started when a predetermined air-fuel ratio feedback control condition is satisfied.   The exhaust gas purification control apparatus for an internal combustion engine according to claim 1, wherein the lean degree of the target air-fuel ratio in the predetermined time is set according to the engine water temperature.   3. The exhaust gas purification control for an internal combustion engine according to claim 1, wherein, in the air-fuel ratio feedback control after the predetermined time has elapsed, when the target air-fuel ratio is changed, the target air-fuel ratio is set to change gradually. apparatus.   The exhaust gas purification control apparatus for an internal combustion engine according to any one of claims 1 to 3, wherein the predetermined time is measured by a timer.   The exhaust purification control device for an internal combustion engine according to any one of claims 1 to 3, wherein the end of the predetermined time is detected as a time when the exhaust purification catalyst is activated.   6. The exhaust gas purification control apparatus for an internal combustion engine according to claim 1, wherein the target air-fuel ratio is set to be rich for a predetermined time after the target air-fuel ratio is set to lean for the predetermined time. .   The exhaust gas purification control apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein when the target air-fuel ratio is set to be lean for the predetermined time, the ignition timing is set in accordance with the lean degree. .   The exhaust gas purification control device for an internal combustion engine according to any one of claims 1 to 7, wherein a change amount of the ignition timing according to the lean degree is set according to an engine water temperature.   The exhaust gas purification control apparatus for an internal combustion engine according to any one of claims 1 to 8, wherein the air-fuel ratio lean control for the predetermined time is performed by increasing and correcting the intake air amount.   The exhaust purification control apparatus for an internal combustion engine according to any one of claims 1 to 9, wherein the increase correction amount of the intake air amount is set based on a target air-fuel ratio and ignition timing.

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