JPH1136917A - Evaporated fuel processing device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out an appropriate process for evaporating evaporated fuel while maintaining combustion by correlatively controlling an introducing volume of evaporated fuel and a circulating volume of exhaust gas during stratifying combustion with a lean mixture. SOLUTION: In an internal combustion engine in which a burnable mixture stratification is formed in a zone limited around a spark plug 8 in a combustion chamber at least during partial load operation of an engine, and homogeneous mixture is fed into the combustion chamber over its entirety so as to carry out stoichiometric combustion during high load operation of the engine, evaporated fuel generated in a fuel tank 11 is introduced into intake air during lean mixture operation, and a part of exhaust gas is circulated into intake air in accordance with an operating condition of the engine. Meanwhile, a circulating volume of exhaust gas is compensated in accordance with a volume of the evaporated fuel introduced into the intake air, and the larger the volume of the evaporated fuel, the smaller the circulating volume of exhaust gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a device for treating evaporated fuel of a spark ignition internal combustion engine which performs stratified combustion at a partial load or the like.

[0002]

2. Description of the Related Art As a spark ignition type internal combustion engine, fuel is directly injected into a cylinder, and the fuel is ignited and burned by an ignition plug. In particular, the fuel injection timing is set in the latter half of the compression stroke such as during partial load operation. In the vicinity of the compression top dead center, a combustible mixture layer is formed only in the vicinity of the ignition plug and stratified combustion is performed.
As a whole, combustion with a super-lean mixture having an air-fuel ratio exceeding 40 is realized.

[0003] In this internal combustion engine, the recirculation of the evaporated fuel (gas) stored in the fuel tank to the intake system is not performed during stratified combustion but homogeneously, as disclosed in Japanese Patent Application Laid-Open No. Hei 5-223017. By limiting only during the stoichiometric operation with the supply of the air-fuel mixture, the lean operation is prevented from becoming unstable.

[0004] This is because if the evaporated fuel gas is recirculated to the intake system during the lean operation as in the stoichiometric operation, the concentration of the combustible mixture near the spark plug fluctuates greatly due to the effect of the recirculated evaporated fuel. Since the ignition becomes unstable even if the fuel becomes too rich, the recirculation of the evaporated fuel is completely stopped during stratified charge combustion.

[0005]

However, depending on the operating conditions of the vehicle, a large amount of evaporative fuel is generated, for example, at a high outside air temperature, and even when the adsorbing capacity of the carbon canister has reached its limit, the intake system is not connected to the intake system. If you keep the reflux stopped,
The generated evaporated fuel may be released to the atmosphere as it is.

Therefore, it is necessary to recirculate the evaporated fuel to the intake system even during the lean operation. However, if the recirculation is performed in the same manner as in the stoichiometric combustion, deterioration of the combustion is inevitable.

On the other hand, during stratified charge combustion, the amount of NOx emission is relatively small, but it is difficult to reduce NOx with a catalyst of an exhaust system in a lean air-fuel mixture.
The occurrence of x itself is suppressed. By the way, the exhaust gas recirculation has the effect of lowering the combustion temperature and pressure, thereby suppressing the generation of NOx, and the combustion itself is worse than when the exhaust gas is not recirculated. Further, the lean operation becomes unstable.

Therefore, even if the fuel vapor is introduced into the intake system during the stratified charge combustion, the combustion deteriorates and the predetermined lean operation becomes impossible unless the relationship with the exhaust gas recirculation is sufficiently considered. It is possible.

The present invention has been proposed to address such a problem. At the time of stratified charge combustion with a lean mixture, the amount of evaporative fuel introduced and the amount of exhaust gas recirculation are controlled in a correlated manner.
An object of the present invention is to realize proper processing of evaporated fuel while maintaining combustion stability.

[0010]

A first aspect of the present invention is to form a combustible air-fuel mixture layer in a limited area near a spark plug of a combustion chamber at least at a partial load of an engine and perform lean combustion, while at a high load, perform combustion. In an internal combustion engine that performs stoichiometric combustion by supplying a homogeneous air-fuel mixture to the entire chamber, evaporative fuel processing means for introducing evaporative fuel generated in a fuel tank into intake air, and a part of exhaust gas during intake according to engine operating conditions. Exhaust recirculation control means for recirculating exhaust gas, and correction means for correcting the exhaust gas recirculation amount in accordance with the amount of evaporated fuel introduced into the intake air during the lean combustion.

According to a second aspect of the present invention, the correction means reduces the exhaust gas recirculation amount as the concentration of the evaporated fuel introduced into the intake air during lean combustion increases.

According to a third aspect of the present invention, there is provided a means for detecting an exhaust air-fuel ratio, a means for calculating an air-fuel ratio feedback correction coefficient based on the detected air-fuel ratio, and a method for introducing evaporative fuel into an intake system in the same operating region. Means for comparing the air-fuel ratio feedback correction coefficient with the non-introduced air-fuel ratio feedback correction coefficient to detect the concentration of evaporated fuel.

According to a fourth aspect of the present invention, the evaporative fuel processing means comprises:
A canister that adsorbs fuel from the fuel tank, a purge control valve that controls the amount of evaporative fuel released from the canister into the intake passage, and an opening degree of the purge control valve that is determined according to the target amount of evaporative fuel to be suctioned. Means for correcting according to the pressure.

According to a fifth aspect of the present invention, a lean NOx catalyst is provided in an exhaust passage, and NOx in exhaust gas is exhausted even in an oxygen-excess atmosphere.
Was reduced.

[0015]

In the first aspect of the present invention, when stratified combustion with a lean air-fuel mixture, when the evaporated fuel is introduced into the intake system, the exhaust gas recirculation amount is adjusted according to the amount of the introduced fuel. For example, when the amount of evaporative fuel introduced increases and stratified combustion tends to become unstable, the amount of exhaust gas recirculation decreases. Conversely, when the amount of evaporative fuel introduced is small and combustion stability increases, the amount of exhaust gas recirculation increases. I do. In this way, it is possible to introduce the evaporated fuel into the intake system and perform the combustion process while suppressing the generation of NOx by the exhaust gas recirculation and without impairing the stability of combustion and, consequently, the operation performance.

In the second aspect of the present invention, the concentration of the combustible gas mixture formed near the spark plug fluctuates depending on the concentration of the introduced fuel vapor, and the stratified combustion tends to be unstable. By reducing the rate, combustion stability can be maintained.

In the third aspect of the invention, the exhaust air-fuel ratio changes between when the evaporated fuel is introduced into the intake system and when it is not introduced, and the air-fuel ratio increases with the introduction. The feedback correction coefficient of the air-fuel ratio controlled so that the air-fuel ratio matches the target value during the stoichiometric operation changes according to the actual air-fuel ratio, and therefore, the feedback correction between when the fuel vapor is introduced and when the fuel vapor is not introduced. By comparing the coefficients, the concentration of the evaporated fuel at the time of introduction can be accurately estimated.

In the fourth aspect of the invention, the amount of fuel vapor introduced into the intake system fluctuates according to the suction negative pressure if the opening of the purge control valve is the same. By performing the correction so as to decrease the opening, even if the suction negative pressure fluctuates during the lean operation, the introduced amount of the evaporated fuel can be accurately maintained at the target value, and the stability of the lean combustion can be maintained.

According to a fifth aspect of the present invention, when the exhaust gas recirculation rate decreases in accordance with the amount of introduced fuel during lean operation,
Although NOx and HC increase in the exhaust gas, since the lean NOx catalyst reduces NOx under the condition where HC is present, the emission amount of NOx can be reduced.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 20 denotes an engine main body;
1 denotes an intake passage, 22 denotes an exhaust passage, and 23 denotes an exhaust gas recirculation passage.

The exhaust gas recirculation passage 23 has an exhaust gas recirculation control valve 10
Is provided, and controls the amount of exhaust gas recirculated during intake air according to operating conditions based on a signal from a controller 6 described later.

The exhaust passage 22 is provided with a lean NOx catalyst 19a for reducing NOx in the exhaust gas.
The x catalyst 19 is a catalyst capable of reducing NOx even in an oxygen-excess atmosphere, and a three-way catalyst 1 that performs reduction of NOx in exhaust gas and oxidation of HC and CO at a stoichiometric air-fuel ratio downstream thereof.
9b is installed.

A fuel injection valve 7 for directly injecting fuel into a combustion chamber of the engine body 20 is provided, and the fuel is ignited and burned by an ignition plug 8. The fuel injection amount and the injection timing from the fuel injection valve 7 are also controlled according to the operation state by a signal from the controller 6 as described later.

An evaporative fuel introduction passage 13 is connected to the collector 14 of the intake passage 21 via the purge control valve 9, and the evaporative fuel from the fuel tank 11 adsorbed to the canister 12 is supplied from the controller 6 as described later. Is introduced into the intake system in accordance with the operation state in response to the signal. The canister 12 communicates with the upper space of the fuel tank 11, adsorbs the evaporated fuel generated in the fuel tank 11 to the adsorbent 16, and when the purge control valve 9 is opened, the negative pressure of the collector 14 causes the air to be released from the atmosphere opening port 17. The fuel that has been adsorbed together with the air is released and sucked.

The controller 6, which controls the operation of the fuel injection valve 7, the ignition plug 8, the purge control valve 9, and the exhaust gas recirculation control valve 10, includes a crank angle sensor 2 for detecting an engine crank angle (rotational speed), an intake air Detection signals from an intake air amount sensor 3 for detecting an amount, a throttle opening sensor 4 for detecting a throttle valve opening, an exhaust sensor 5 for detecting an oxygen concentration in exhaust gas, a water temperature sensor 18 for detecting an engine cooling water temperature, and the like. Is input, and according to the operation state based on these, the fuel injection amount, the injection timing, the ignition timing,
The evaporative fuel introduction amount (purge amount), the exhaust gas recirculation amount, and the like are controlled.

In particular, the controller 6 sets the fuel injection timing in the latter half of the compression stroke at the time of partial load or the like, forms a combustible mixture layer only around the ignition plug 8 near the compression top dead center, and performs stratified combustion for the whole. Specifically, the lean air-fuel mixture is stably burned. At this time, when the exhaust gas recirculation control valve 10 is opened to perform exhaust gas recirculation and at the same time the purge control valve 9 is opened to introduce the evaporated fuel into the intake system, The exhaust gas recirculation amount is adjusted according to the introduced amount. For example, when the amount (concentration) of vaporized fuel introduced is large and the air-fuel mixture near the ignition plug becomes too rich, stratified combustion tends to be unstable, and the amount of exhaust gas recirculation is reduced. When the stability of the gas increases, the amount of exhaust gas recirculation increases, and thus,
It is possible to introduce evaporative fuel into the intake system for combustion processing while suppressing generation of NOx by exhaust gas recirculation and without impairing combustion stability and operating performance.

The controller 6 sets the fuel injection timing in the first half of the intake stroke, such as when the load is high, so that the injected fuel is sufficiently premixed with the air before the ignition, so that the fuel is uniformly distributed throughout the combustion chamber. A stoichiometric air-fuel mixture layer is formed, these are homogeneously burned, and high output is ensured. At this time, the fuel supply amount is feedback-controlled based on the output of the exhaust sensor 5 so that the stoichiometric air-fuel ratio is accurately obtained. The purification efficiency of the source catalyst 19b is maintained at the best.

Hereinafter, the contents of the control performed by the controller 6 will be described in detail with reference to FIGS.

FIG. 2 is a flowchart for controlling the fuel injection amount. In step 1, the intake air amount Qa and the engine speed Ne are detected. In step 2, the basic fuel is calculated from the intake air amount Qa and the engine speed Ne. The injection amount Tp is
= K × (Qa / Ne).

In step 3, it is determined whether lean operation by stratified combustion is permitted by the routine of FIG. 10 described later. When the lean operation is not permitted, the stoichiometric operation based on the stoichiometric air-fuel ratio is performed.
Are performed, and when the lean operation is permitted, the process proceeds to Steps 7 and 8.

In step 4, for the air-fuel ratio feedback control in the stoichiometric operation, the air-fuel ratio feedback correction coefficient α by the known PI control is set from the output of the exhaust (O ₂ ) sensor as shown in FIG. The learning value LALPHA of the air-fuel ratio is obtained based on FIGS. 3 and 4 described later, and the fuel injection amount Ti for obtaining the stoichiometric (theoretical) air-fuel ratio is calculated as Ti = Tp × α × LALPHA (step 6). ).

On the other hand, when the lean operation is permitted, the air-fuel ratio feedback control is stopped in step 7 and the feedback correction coefficient α is clamped to the reference value (1.0) to perform the open control. Step 8
Then, based on the basic fuel injection amount Tp, the air-fuel ratio feedback correction coefficient α, and the basic learning value BS, the fuel injection amount Ti is adjusted to a target air-fuel ratio (for example, the air-fuel ratio 22).
Is calculated according to the following equation.

Ti = (14.7 / 22) × Tp × α × BS Then, in order to inject fuel during the intake stroke during stoichiometric operation and during the compression stroke during lean operation, a predetermined amount is synchronized with engine rotation. The fuel injection is performed at the timing.

FIGS. 3 and 4 are flowcharts for learning the air-fuel ratio correction coefficient.

In step 1, it is determined whether or not initialization has been performed after the engine is started. When initialization has been performed, the process proceeds to step 3. When initialization has not been performed, in step 2, the basic learning convergence flag FBSLTTD, the normal learning convergence flag FLRNTD, and the basic learning counter CBSLTD are determined. , Normal learning counter CLR
Reset each NTD to 0. That is, these initializations are performed only once after startup. In step 3, it is determined whether or not the basic learning has converged (FBSLTD = 1) based on the value of the basic learning convergence flag FBSLTD.

When FBSLTD = 0 (basic learning not converged), the process proceeds to step 4 to perform basic learning, and the learning map, the lattice of the learning map (Ne lattice, Tp lattice), the learning convergence counter, and the learning area designation are set. Set the flag to the one for basic learning. That is, basic learning map: TBS
LM, basic learning map Ne lattice: TBSLN, basic learning map Tp lattice: TBSLP, basic learning convergence counter:
CBSLTD, basic learning area designation flag: FBLMAD
Make a selection.

As shown in FIG. 5, the learning map assigns a learning value and a learning convergence counter to each area (0 to F) of the engine operating state based on the engine speed Ne and the basic fuel injection amount Tp. is there. Further, as shown in FIG. 6, the learning area designation flag indicates an area of the engine operating state (0 to 0).
F) is provided corresponding to F), and among the learning counters in each area, those used for the learning convergence determination are set to 1.

In step 5, a learning value LALPHA corresponding to the area of the current engine operating state (Ne, Tp) is searched from the selected basic learning map. In the next step 6, the learning value LALPHA is updated according to a learning value updating routine (learning value updating means) of FIG. 7 described later.

Here, the learning value update will be described with reference to the flowchart of FIG.

In step 1, it is determined whether or not the learning value update condition (that is, the water temperature Tw is equal to or more than a predetermined value during the air-fuel ratio feedback control) is satisfied. Move to

In step 2, the average value Mα of the air-fuel ratio feedback correction coefficient α is calculated by the following equation.

Mα = (α1 + α2) / 2 Here, α1 is the air-fuel ratio feedback correction coefficient immediately before inversion from lean to rich, and α2 is the feedback correction coefficient immediately before inversion from rich to lean (FIG. 8). reference).

In step 3, based on the deviation of the average value Mα of the air-fuel ratio feedback correction coefficient α from the reference value (1.0), the learning value LALPHA is updated according to the following equation.

LALPHA = LALPHA + (Mα−
1.0) × GAIN Note that GAIN is a predetermined value, and 0 <GAIN <1.
In step 4, the updated LALPHA is stored in a predetermined position of the selected learning map. In step 5, the selected learning convergence counter (CB) corresponding to the updated area
SLTDi or CLRNTDi) is counted up, and the learning value update routine ends.

Returning to the flow of FIG. 3 and FIG.
Now, for example, all the regions designated by the basic learning region designation flag FBLMAD as shown in FIG.
In (a), the learning convergence counter CBSLTD
It is determined whether or not i is equal to or more than a predetermined value. If i is equal to or more than the predetermined value, it is determined that the basic learning has converged, and in step 8, the basic learning convergence flag FBSLTD is set to 1 and the process is terminated.

In order to make the basic learning converge quickly, the grid of the basic learning map is set such that the entire operation area is covered by a small number (one or more) of the learning areas as shown in FIG. 9B. Then, only that region is designated as the learning region. If accuracy is not required, this allows a quick transition to lean operation.

In the determination in step 3, FBSLTD = 1
If (basic learning convergence), the process proceeds to step 9 to perform normal learning.

In step 9, the learning map, the learning map lattice (Ne lattice, Tp lattice), the learning convergence counter, and the learning area designation flag are set to those for normal learning.
That is, the normal learning map: TLRNM, the normal learning map Ne lattice: TLRNN, the normal learning map Tp lattice: T
LRNP, a normal learning convergence counter: CLRNTD, and a normal learning area designation flag: FLRMAD are selected.

In the next step 10, a learning value LALPHA corresponding to the area of the current engine operating state (Ne, Tp) is searched from the selected normal learning map. In step 11, the learning value LALPHA is updated according to the learning value updating routine of FIG. Next Step 1
2, in all the regions specified by the normal learning region specification flag FLRMAD (see FIG. 16A),
It is determined whether the learning convergence counter CLRNTDi is equal to or greater than a predetermined value. If the learning convergence counter CLRNTDi is equal to or greater than the predetermined value, it is determined that the normal learning has converged.
This processing is ended with D = 1.

As a normal learning designated area, for example, FIG.
If the designation is made as shown in (a), the air-fuel ratio accuracy at the time of the lean operation is increased. However, if only the flat ground steady running region is designated as shown in FIG. 9 (b), the purge start and the lean operation start can be accelerated. it can.

FIG. 10 is a flowchart of the lean operation permission determination. In step 1, it is determined whether or not a predetermined lean operation condition is established based on the engine speed Ne, the basic fuel injection amount Tp, the water temperature Tw, and the like. If it is an operation condition, the process proceeds to step 2.

In step 2, the basic learning convergence flag FB
It is determined whether or not SLTD = 1, and the process proceeds to step 3 if YES. In step 3, the normal learning convergence flag FLRN
It is determined whether TD = 1 or not. If the flag = 1, the process proceeds to step 4.

In step 4, the accumulated purge amount PR after the start calculated by the accumulated purge amount calculation routine of FIG.
It is determined whether or not GQ is equal to or greater than a predetermined value. In step 5, lean operation is permitted (lean operation permission flag set). If any of the determinations in steps 1 to 4 are NO, the process proceeds to step 6 and the lean operation is not permitted (lean operation permission flag reset).

The reason that the lean operation is permitted only when the accumulated purge amount PRGQ after the start is equal to or more than a predetermined value is to prevent the operation from shifting to the lean operation while the purge gas concentration is very high and the stratified combustion from becoming unstable. It is.

FIG. 11 is a flowchart for obtaining the accumulated purge amount of the evaporated fuel.

This flow is repeated every 0.1 second,
The cumulative purge amount PRGQ is obtained as follows by integrating the target purge flow rate Qf every 0.1 second.

PRGQ = PRGQ + Qf / 600 The accumulated purge amount is cleared each time the engine is started. The target purge flow rate Qf is used to calculate the purge control valve opening degree as shown in FIG.
2 in the canister purge control routine.

FIG. 12 is a flowchart of canister purge control. In step 1, it is determined whether or not predetermined canister purge conditions are satisfied based on cooling water temperature, air-fuel ratio feedback control (λ control), fuel cut state, and the like.
If the predetermined condition is satisfied, it is determined in step 2 whether or not the basic learning flag FBSLTD = 1. When the basic learning has converged (FBSLTD = 1), the intake air amount Qa, the throttle opening TVO, and the engine speed Ne are detected in step 3. Then, in step 4, based on these, the target purge amount Qe is calculated by the following equation.

Qe = Qa × β × (14.7 / target air-fuel ratio) Note that β is a constant determined by operating conditions, and the target air-fuel ratio is also determined by operating conditions at that time.

In step 5, the throttle opening area ATV
O is calculated as ATVO = ATH × (1-cosTVO). ATH is a throttle diameter.

In step 6, an intake negative pressure Boost is calculated from the engine speed Ne and the throttle opening area ATVO with reference to a map. In step 7, the negative suction pressure Boost and the target purge amount Qe are calculated. The purge control valve opening is calculated from the map. In this case, for the same target purge amount, when the suction negative pressure Boost is high, the purge control valve opening becomes relatively small.

If none of the conditions is satisfied in steps 1 and 2, the process proceeds to step 8, where the target purge amount Qe is set to 0, and the introduction (purge) of the evaporated fuel into the intake system is stopped.

Next, FIG. 13 is a flowchart for estimating the concentration of the evaporated fuel purged to the intake system.

First, in step 1, the fuel injection amount Tp and the engine speed Ne are detected, and in step 2, it is detected whether the air-fuel ratio feedback correction coefficient α has been inverted twice in the grid area divided in the engine operating state. If the inversion has not been performed twice, the routine is terminated because the purge gas concentration cannot be determined. It should be noted that the case where there is two reversals in the same region is during the stoichiometric operation in which the air-fuel ratio is feedback-controlled.

When the gas is reversed twice, the purge gas concentration can be determined. In step 3, the air-fuel ratio feedback correction coefficient average value Mα is calculated as Mα = (α1 + α2) / 2.
This is compared with the basic learning value BS of the air-fuel ratio feedback correction coefficient in the same operating region (based on Tp and Ne) obtained at the time of non-purge, and the evaporated fuel concentration De is calculated as follows.

De = (Mα−BS) × k where k is a constant.

The air-fuel ratio of the air-fuel mixture changes depending on the concentration of the evaporated fuel, assuming that the amount of the introduced fuel is constant.
Output changes according to the air-fuel ratio. Therefore, if the fuel vapor concentration is low, the air-fuel ratio feedback correction coefficient average value Mα approaches the learning value BS at the time of non-purge, and if the fuel fuel concentration is high, the difference increases. Therefore, the density De can be calculated by multiplying these differences by a predetermined constant. Then, using the concentration De, the exhaust gas recirculation rate at the time of the next shift to the lean operation is corrected.

FIG. 14 is a flowchart for controlling the exhaust gas recirculation amount. Here, the exhaust gas recirculation amount is corrected based on the relationship with the concentration of the evaporated fuel (purge gas) introduced into the intake system.

In step 1, the fuel injection amount Tp and the engine speed Ne are detected, and in step 2, the exhaust gas recirculation control valve (EGR valve) opening EVO is calculated based on these by referring to a map. EVO is set to be large in a low load and low rotation range.

At step 3, it is determined whether or not the stratified operation is currently being performed. If the stratified operation is not being performed, the routine is terminated because no correction is required. If the stratified operation is being performed, the exhaust gas recirculation amount needs to be corrected. Proceed to. In step 4, an EGR valve correction coefficient EGRHOS is calculated based on the set air-fuel ratio at that time and the latest evaporated fuel concentration De with reference to the map. The correction coefficient is 1 ≧ EGRHOS> 0,
The correction coefficient decreases as De increases. As for the air-fuel ratio, the correction amount of the EGR valve is reduced as the air-fuel ratio becomes thinner.

Then, in step 5, the EGR valve opening EVO is corrected as follows. EVO = EVO × EGRHOS Accordingly, the opening degree of the exhaust gas recirculation control valve is corrected in a decreasing direction as the concentration of the evaporated fuel introduced into the intake system is higher, so that the exhaust gas recirculation amount is reduced.

The configuration is as described above. Next, the operation will be described.

When the condition for introducing the evaporated fuel into the intake system, that is, the purge condition is satisfied during the lean operation, the purge control valve 9
Is opened to purge the evaporated fuel.

During the stratified operation, the introduced fuel vapor affects the concentration of the combustible mixture layer formed only in the vicinity of the ignition plug 8, and for example, if the concentration is too high, the stratified combustion becomes unstable. Therefore, the target value of the purge amount is determined so as not to impair the lean operation, whereby the stability of the stratified combustion is maintained.

Since the opening of the purge control valve 9 is determined by the target value of the purge amount, the suction negative pressure at that time is estimated, and the opening is corrected according to the suction negative pressure. Can be maintained at the target value.

On the other hand, during stratified operation, the exhaust gas recirculation control valve 10
To open a part of the exhaust gas to recirculate it into the intake air.
x generation amount is suppressed.

The exhaust gas recirculation lowers the maximum combustion temperature and pressure,
By suppressing combustion, the amount of generated NOx is reduced.
Therefore, the combustion conditions are worse during the exhaust gas recirculation than when the exhaust gas is not recirculated. If the above purge conditions are satisfied during such exhaust gas recirculation, combustion tends to be particularly unstable.

Even if the amount of evaporative fuel introduced as described above is accurately maintained at the target value, if the concentration of the purge gas is high, the mixture layer formed mainly in the vicinity of the spark plug becomes excessively richer than the flammable range. When the purge gas concentration is low, the air-fuel mixture is in the flammable region, and the stability is maintained.

Therefore, the exhaust gas recirculation amount is corrected in accordance with the purge gas concentration. The exhaust gas recirculation ratio is reduced from the target value as the purge gas concentration becomes higher, and the exhaust gas recirculation ratio is brought closer to the target value when the concentration is low. I have.

As described above, the exhaust gas recirculation rate is corrected in accordance with the concentration of the evaporated fuel introduced into the intake system during the lean operation, that is, the concentration of the purge gas. Therefore, NOx can be reduced while maintaining favorable stratified combustion, and By processing the evaporated fuel, it is possible to prevent unburned HC and the like from being released to the outside as it is.

By the way, the evaporated fuel introduced into the intake system,
In other words, when the concentration of the purge gas is high, the exhaust gas recirculation rate is lowered to avoid the deterioration of stratified combustion, but the amount of generated NOx increases, and at the same time, the amount of HC generated due to the dense purge gas also increases. .

However, a lean NOx catalyst 19a is provided in the exhaust passage 22, and this lean NOx catalyst 19a can reduce NOx not only in a stoichiometric air-fuel mixture but also in an oxygen-excess atmosphere due to the lean air-fuel mixture. As shown in FIG. 15, this lean NOx catalyst 19a
The higher the / NOx ratio, the higher the NOx conversion rate. For this reason, it is possible to treat the increased NOx emission amount due to the high purge gas concentration and the lowered exhaust gas recirculation rate by the lean NOx catalyst 19a, and as a result, it is possible to achieve both good stratified combustion and exhaust performance during lean operation. .

The lean NOx catalyst 19aa may be of a type that reduces NOx even during operation with a stoichiometric mixture. In this case, NOx can be reduced during stoichiometric operation without the three-way catalyst 19b.

In the above embodiment, the exhaust gas recirculation amount is corrected according to the purge gas concentration. However, when the target purge gas flow rate changes, the exhaust gas recirculation rate may be corrected according to the purge gas flow rate.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart for calculating a fuel injection amount.

FIG. 3 is a flowchart illustrating learning of an air-fuel ratio correction coefficient.

FIG. 4 is also a flowchart.

FIG. 5 is an explanatory diagram showing a learning area.

FIG. 6 is an explanatory diagram showing a learning area designation flag.

FIG. 7 is a flowchart illustrating updating of a learning value.

FIG. 8 is an explanatory diagram showing a relationship between an output of an exhaust sensor and an air-fuel ratio feedback correction coefficient.

FIG. 9 is an explanatory diagram showing a learning convergence determination area.

FIG. 10 is a flowchart showing a lean operation condition determination.

FIG. 11 is a flowchart illustrating calculation of an accumulated purge amount.

FIG. 12 is a flowchart illustrating calculation of an opening of a purge control valve.

FIG. 13 is a flowchart showing calculation of a purge gas concentration.

FIG. 14 is a flowchart showing calculation of an opening degree of an exhaust gas recirculation control valve.

FIG. 15 is a characteristic diagram showing a NOx conversion rate of a catalyst.

[Explanation of symbols]

 Reference Signs List 2 crank angle sensor 3 intake air amount sensor 4 throttle opening sensor 5 exhaust sensor 6 controller 7 fuel injection valve 8 spark plug 9 purge control valve 10 exhaust recirculation control valve 11 fuel tank 12 canister 13 introduction passage 19a lean NOx catalyst 20 engine body 21 intake passage 22 exhaust passage 23 exhaust recirculation passage

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 41/04 301 F02D 41/04 301C 43/00 301 43/00 301N 45/00 301 45/00 301L 301G F02M 25/07 550 F02M 25/07 550R 25/08 25/08 P 301 301U 301J

Claims (5)

[Claims] At least when the engine is partially loaded, a combustible mixture layer is formed in a limited area near the ignition plug of the combustion chamber to perform lean combustion, while at a high load, a homogeneous mixture is supplied to the entire combustion chamber. In an internal combustion engine that performs stoichiometric combustion, evaporative fuel processing means for introducing evaporative fuel generated in a fuel tank into intake air, exhaust gas recirculation control means for recirculating a part of exhaust gas into the intake air according to operating conditions of the engine, A correction means for correcting the exhaust gas recirculation amount in accordance with the amount of evaporative fuel introduced into the intake air during lean combustion. 2. The evaporative fuel processing apparatus for an internal combustion engine according to claim 1, wherein said correction means reduces the exhaust gas recirculation amount as the concentration of the evaporative fuel introduced into the intake air during lean combustion increases. 3. A means for detecting an exhaust air-fuel ratio, a means for calculating an air-fuel ratio feedback correction coefficient based on the detected air-fuel ratio, and an air-fuel ratio feedback correction when introducing evaporated fuel into an intake system in the same operation region. The evaporative fuel processing apparatus for an internal combustion engine according to claim 2, further comprising means for comparing the coefficient with an air-fuel ratio feedback correction coefficient at the time of non-introduction to detect the concentration of evaporative fuel. 4. A fuel supply system comprising: a canister for adsorbing fuel in a fuel tank; a purge control valve for controlling an amount of evaporated fuel released from the canister into an intake passage; The evaporative fuel processing apparatus for an internal combustion engine according to any one of claims 1 to 3, further comprising means for correcting an opening degree of the purge control valve determined according to the suction negative pressure. 5. An evaporative fuel processing apparatus for an internal combustion engine according to claim 1, wherein a lean NOx catalyst is provided in the exhaust passage to reduce NOx in the exhaust gas even in an oxygen-excess atmosphere. .