JP2003214236A - Air/fuel ratio control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform a reducing processing by efficiently releasing NOx and SOx trapped in a catalyst while satisfactorily maintaining the operability of an engine. <P>SOLUTION: When a combustion is changed from a stratified combustion (lean combustion) to a stoichiometric or rich combustion, to perform the reducing processing by releasing the NOx trapped in the NOx trap catalyst, a target air/fuel ratio is steppingly increased, and gradually decreased. To rich the air/ fuel ratio, first fuel is injected by a limit amount not causing a torque variation by only a main injection in an intake stroke, and then an auxiliary injection in an expansion stroke for injecting by an amount short of a requirement for NOx processing is started in combination with the main injection after oxygen accumulated in an exhaust pipe is sufficiently consumed by a main injection rich control and the density of the oxygen is lowered. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an air-fuel ratio control technique for an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, NOx traps NOx (nitrogen oxide) when the air-fuel ratio of the inflowing exhaust gas is lean and desorbs and purifies the trapped NOx when the air-fuel ratio is rich.
In an internal combustion engine equipped with a trap catalyst, after operating at a lean air-fuel ratio, the air-fuel ratio is made rich to reduce NOx.

In Japanese Patent Laid-Open No. 2001-59440, air-fuel ratio enrichment for purifying the catalyst is performed by gradually increasing the main injection amount of the fuel during the intake stroke and expanding the fuel at the same time when the main injection amount starts to increase. It is disclosed that the secondary injection in the stroke is started stepwise.

[0004]

However, in the system in which the sub-injection in the expansion stroke is started stepwise at the same time as the demand for the enrichment of the air-fuel ratio, the afterburn is caused by the oxygen remaining in the exhaust passage and the fuel injected by the sub-injection. Since the air-fuel ratio of the total amount of main injection and sub-injection is rectangular, and the sub-injection amount, which is inefficient compared to the main injection, is not taken into consideration, NOx desorption is likely to occur. The separation efficiency is poor and the fuel efficiency is poor.

It should be noted that the same thing as the above NOx can be said even in the case where a catalyst for trapping SOx (sulfur oxide) is provided. The present invention has been made by paying attention to such a conventional problem, when a request for air-fuel ratio enrichment occurs, by performing the main injection and the sub-injection at an appropriate amount and at an appropriate timing, after-sales An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine that can prevent the occurrence of burn.

[0006]

Therefore, in the invention according to claim 1, the enrichment is performed only by the main injection supplied before the ignition of the fuel for a predetermined period after the request for the enrichment of the air-fuel ratio is generated. After the lapse of the predetermined period of time, the main injection and the sub-injection supplied after ignition are divided and enriched.

According to the first aspect of the present invention, after the air-fuel ratio enrichment request is generated, the excess oxygen in the exhaust gas is consumed by the enrichment by the main injection before ignition to prevent the afterburn, and then the predetermined period elapses. After that, the shortage that is limited by the torque fluctuation limit in the enrichment by the main injection can be supplemented by using the sub-injection after ignition, which has less influence on the torque. It should be noted that the air-fuel ratio enrichment request is issued when a catalyst is provided in the exhaust passage, for example, when NOx or SOx trapped in the catalyst should be released.

The invention according to claim 2 is characterized in that the rich degree by the main injection is increased stepwise. According to the second aspect of the present invention, when the air-fuel ratio is required to be rich and it is desirable to increase the degree of richness in a stepwise manner, the excess oxygen in the exhaust gas is consumed at once, so afterburn is likely to occur. In enrichment by the main injection, the shortage that is limited by the torque fluctuation limit is supplemented by the secondary injection after ignition after the predetermined period has elapsed, so a necessary and sufficient reducing agent is secured in steps while preventing afterburn. can do.

The invention according to claim 3 is characterized in that the rich degree by the main injection is limited to an upper limit value or less. According to the third aspect of the present invention, by limiting the rich degree due to the main injection to the upper limit value or less, it is possible to prevent the torque fluctuation due to the richening from becoming excessive, and it is possible to maintain good drivability.

The invention according to claim 4 is characterized in that the exhaust passage is provided, and the rich degree by the main injection is increased stepwise and then gradually decreased. According to the invention of claim 4, NO trapped by the catalyst
Regarding the emission characteristics of x and SOx, since the emission amount at the start of emission is large and the emission amount is gradually decreased thereafter, the rich degree by the main injection is increased stepwise in accordance with this characteristic and then gradually decreased. By doing so, it is possible to sufficiently enhance the efficiency of the NOx and SOx release processing by the rich fuel.

Further, the invention according to claim 5 is characterized in that the rich degree by the main injection is increased stepwise, maintained at a constant degree, and then gradually decreased. According to the fifth aspect of the present invention, at the initial stage of the enrichment control, the rich degree due to the main injection is held at a stepwise large value to maintain high NOx and SOx release processing efficiency, and also increase the torque. NO in the second half while suppressing
Wasteful fuel injection can be suppressed by gradually reducing the rich degree so as to correspond to the decrease in the release amount of x and SOx.

The invention according to claim 6 is characterized in that the degree of richness due to the sub injection is increased stepwise. Further, the invention according to claim 7 is characterized in that the rich degree by the auxiliary injection is increased stepwise and then gradually decreased.

The invention according to claim 8 is characterized in that the overall rich degree of the main injection and the sub-injection is increased stepwise and then gradually reduced to a substantially triangular wave state. According to the inventions of claims 6 to 8, NOx and SOx are also applied to the sub-injection as in the main injection.
By setting so as to match the emission characteristics of NOx, NOx and SOx can be efficiently released and reduction treatment can be performed.
Furthermore, by setting the overall rich degree of the main injection and the sub-injection in a substantially triangular wave state, the most efficient processing can be performed.

Further, the invention according to claim 9 is characterized in that the oxygen concentration in the exhaust passage is estimated, and when the oxygen concentration falls below a predetermined value, the auxiliary injection is started assuming that the predetermined period has elapsed. According to the ninth aspect of the invention, when the estimated oxygen concentration falls below the predetermined value, it is determined that the afterburn will not occur, and the auxiliary injection is started, whereby the auxiliary injection can be started quickly.

The invention according to claim 10 is characterized in that the oxygen concentration in the exhaust passage is estimated based on the amount of main injection and the engine speed. According to the tenth aspect of the present invention, the supply amount of the reducing agent (CO) capable of reducing and consuming oxygen in the exhaust passage can be obtained from the amount of main injection and the engine rotation speed. The oxygen concentration can be estimated by subtracting the amount.

According to the eleventh aspect of the present invention, when the air-fuel ratio downstream of the catalyst provided in the exhaust passage is detected and it is detected that the air-fuel ratio becomes rich, it is determined that the predetermined period has elapsed. It is characterized by starting the sub-injection. According to the invention of claim 11, the sensor used for the air-fuel ratio feedback control is used to detect the rich air-fuel ratio, so that the decrease in the oxygen concentration in the exhaust gas can be detected and the secondary injection can be started. .

The invention according to claim 12 is characterized in that the predetermined period is set on the basis of a parameter correlated with the exhaust temperature. The invention according to claim 13 is
The predetermined period is set to be shorter as the parameter correlated to the exhaust gas temperature is lower.

According to the twelfth and thirteenth aspects of the present invention, since the afterburn is more likely to occur as the exhaust gas temperature becomes higher, it is set based on a parameter correlated with the exhaust gas temperature. By setting the predetermined period to be shorter as shown, the predetermined period for starting the secondary injection can be appropriately set.

The invention according to claim 14 is characterized in that the enrichment of the air-fuel ratio is required when the NOx trapped in the catalyst provided in the exhaust passage is released. The invention according to claim 15 is characterized in that the enrichment of the air-fuel ratio is required when the SOx trapped in the catalyst provided in the exhaust passage is released.

According to the fourteenth and fifteenth aspects of the present invention, when NOx and SOx are released from the catalyst for reduction treatment, they can be treated by enriching the air-fuel ratio. Further, the invention according to claim 16 is characterized in that the main injection is performed in an intake stroke.

According to the sixteenth aspect of the present invention, the main injection is performed in the intake stroke before ignition to enrich the fuel by homogeneous combustion. The invention according to claim 17 is characterized in that the sub-injection is performed in an expansion stroke. Secondary injection is performed in the expansion stroke after ignition.

In the eighteenth aspect of the present invention, the rich degree due to the main injection is limited to a predetermined degree, and the insufficient enrichment in other than some cylinders is covered by the sub-injection of the some cylinders. Is characterized by. According to the eighteenth aspect of the present invention, the sub-injection amount is increased in only some of the cylinders by performing the sub-injection so as to cover the shortage amount in the main injection. Since the injection can be performed in the region where the linearity of the fuel injection valve opening period-injection amount characteristic is ensured, good injection amount accuracy can be obtained and the injection amount that is sufficient to meet the required NOx and SOx emission amount can be supplied. can do.

The invention according to claim 19 is characterized in that it has a plurality of cylinder groups, each cylinder group is provided with a catalyst, and each of the cylinder groups is provided with a part of the cylinders. Claim 1
According to the invention of No. 9, by performing the enrichment control according to the present invention on the catalysts for each cylinder group, it is possible to sufficiently perform the release and reduction processing of NOx and SOx from each catalyst.

The invention according to claim 20 is characterized in that, after the lapse of the predetermined period, the cylinders that first reach the timing of the sub-injection are the partial cylinders. According to the twentieth aspect of the present invention, the cylinders that are in the first expansion stroke after the sub-injection is enabled are some of the cylinders that perform the sub-injection, so that NOx and SOx are released as quickly as possible. The reduction process can be performed.

Further, the invention according to claim 21 is characterized in that the cylinders having the shortest distance to the catalyst provided in the exhaust passage are the partial cylinders. According to the twenty-first aspect of the present invention, the cylinder closest to the catalyst is a part of the cylinders that perform the sub-injection, so that the sub-injected fuel can be promptly discharged and the loss due to the adhesion to the exhaust passage wall can be reduced. NOx and SOx can be released and reduced by reaching the catalyst.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a system configuration of an embodiment of an air-fuel ratio control device according to the present invention. Internal combustion engine 1
Is a cylinder injection type spark ignition gasoline internal combustion engine capable of performing intake stroke injection or compression stroke injection (main injection) by switching operation modes. The internal combustion engine 1 can be operated at a stoichiometric air-fuel ratio (stoichiometric ratio), a rich air-fuel ratio operation, and a lean air-fuel ratio operation.

An ignition plug 3 and a fuel injection valve 4 are attached to the cylinder head 2 of the internal combustion engine 1 for each cylinder. A fuel pump 5 is connected upstream of the fuel injection valve 4, and fuel discharged from the fuel pump 5 can be directly injected from the fuel injection valve 4 into the combustion chamber at an arbitrary fuel pressure. The fuel injection amount is determined by the fuel discharge pressure of the fuel pump 5 and the valve opening time of the fuel injection valve 4.

An intake port 6 is formed in the cylinder head 2 for each cylinder, and an intake manifold 7 is connected in communication with the intake port 6. An intake pipe 20 connected upstream of the intake manifold 7 includes an air cleaner 21 from an upstream side, an air flow meter 22 for detecting an intake air amount,
An electronically controlled throttle valve 23 for controlling the intake air amount is provided, and a throttle sensor 24 for detecting the opening of the throttle valve is attached to the throttle valve 23. An exhaust port 8 is formed for each cylinder on the opposite side of the cylinder head 2, and an exhaust manifold 9 is connected in communication with the exhaust port 8. Cylinder block 2
5, a water temperature sensor 26 for detecting the engine cooling water temperature, a crank angle sensor 2 for detecting the engine rotation speed Ne, etc.
7 are provided.

An EGR passage 10 is connected between the intake manifold 7 and the exhaust manifold 9, and the opening degree of the EGR valve 11 interposed in the EGR passage 10 is controlled in accordance with the operating condition, so that the EGR ( The amount of exhaust gas recirculation) is controlled. The exhaust manifold 9 is provided with an air-fuel ratio sensor 12 that detects the air-fuel ratio in the combustion chamber based on the amount of oxygen in the exhaust, and a three-way catalyst 13 is provided downstream of the air-fuel ratio sensor 12 and is connected downstream thereof. The NOx trap catalyst 15 is attached to the exhaust pipe 14.
Is installed. The three-way catalyst 13 oxidizes HC and CO when the air-fuel ratio of the inflowing exhaust gas is stoichiometric, and NO
It has a function of reducing and purifying x. The NOx trap catalyst 15 traps NOx in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and releases and reduces the NOx when the air-fuel ratio of the inflowing exhaust gas is stoichiometric or rich. Typically, a coat layer of a base material carrying a noble metal such as platinum (Pt) and a NOx trapping agent is formed on a honeycomb carrier. The NOx trap agent is an alkali metal such as cesium (Cs), sodium (Na), potassium (K), lithium (Li), an alkaline earth such as barium (Ba), calcium (Ca), lanthanum (La), It contains at least one selected from rare earth elements such as yttrium (Y).

Further, an input / output device, a storage device (ROM,
A C / U (control unit) 16 including a RAM), a central processing unit (CPU), a timer counter, etc. is installed. By this C / U 16, comprehensive control of the exhaust emission control device including the internal combustion engine according to the present invention is performed.
The detection information from the various sensors is input to the input side of the C / U 6, and the fuel injection valve 4, the spark plug 5 and the like are connected to the output side of the C / U 6, which are calculated based on the detection information from the various sensors. Values such as the fuel injection amount and ignition timing are output.

Next, the operation of the exhaust gas purification device according to the present invention will be described. In addition, here, the case where the main injection is performed in the compression stroke of the internal combustion engine and the lean air-fuel ratio operation is performed will be described as an example. In the case of an oxidizing atmosphere when operating at a lean air-fuel ratio, the NOx trap catalyst 15 is
However, the trapped NOx amount decreases when it approaches the saturation amount, so it is necessary to release and reduce the trapped NOx. Therefore, in the exhaust gas purification device having the NOx trap catalyst, for example, the target air-fuel ratio is reduced at a preset predetermined cycle to perform the rich air-fuel ratio operation for a predetermined period (hereinafter referred to as rich spike).
A reducing atmosphere is forcibly created in the x-trap catalyst to desorb and reduce trapped NOx.

In the present invention, the air-fuel ratio is made rich by the following method on the premise of the above control. In the first embodiment, N
The amount of fuel increase for the Ox process is calculated, and the amount of fuel injection in the intake stroke, which is the main injection, is increased to a level where there is no torque fluctuation or an operationally permissible level. After starting the main injection amount increase, this state is maintained for a certain period of time until the oxygen concentration in the exhaust pipe falls below a predetermined value.

After the lapse of the predetermined time, the fuel which could not be increased in order to avoid the torque fluctuation is compensated by the fuel injection in the expansion stroke which is the secondary injection. The rich spike control of the first embodiment will be described according to the flowchart of FIG. 2 and with reference to the time chart of FIG. In step 1, the operating state detection values such as the engine speed, load (accelerator opening, etc.) are read.

At step 2, the target air-fuel ratio is calculated based on the detected operating state value. The target air-fuel ratio here is set corresponding to the fuel injection amount that does not include the fuel increase amount even during the rich spike described later. Step 3
Then, the fuel injection amount according to the target air-fuel ratio is calculated.
This fuel injection amount is the main injection amount TP1 injected in the intake stroke (or compression stroke) before ignition.

In step 4, it is determined based on the value of the combustion switching flag whether the stratified combustion (lean combustion) is switched to the stoichiometric combustion (or rich combustion, which will be hereinafter referred to as stoichiometric combustion). When it is determined that the combustion has been changed to stoichiometric combustion (see a in FIG. 3), rich spike control is performed for a predetermined period, so in step 5, NOx desorption /
A required value TP20 for increasing the main injection amount required for the reduction is calculated. Here, the N trapped in the NOx trap catalyst
Since the reduction efficiency of Ox gradually decreases at the beginning, the increase request value TP20 also increases the initial value stepwise according to this characteristic, and is set in a triangular shape so as to decrease with time (FIG. 3). B)).

In step 6, the increase in the main injection that is injected before ignition causes a torque increase (fluctuation) because it is used for combustion. Therefore, the torque fluctuation that is the main injection increment corresponding to the allowable torque fluctuation limit. Allowable increase limit TP
21 (see c in FIG. 3) is calculated. In step 7, the main injection increase demand value TP20 calculated in step 5 is
It is determined whether the torque fluctuation limit is TP21 or less calculated in step 6.

When it is determined in step 7 that TP20≤TP21, the torque fluctuation can be kept within the limit even if the main injection amount is increased according to the required value TP20. Therefore, in step 8, the main injection amount TP1 is increased. The main injection is performed with the fuel injection amount obtained by increasing the required value TP20. In this case, the secondary injection after ignition is not performed. On the other hand, in step 7, the increase amount demand value TP
When it is determined that 20 exceeds the torque fluctuation limit TP21, the increased amount of the main injection is set to the torque fluctuation limit TP21 in step 9, and then the increased amount is suppressed to the torque fluctuation limit TP21 in step 10. The increase shortage TP22 due to this is calculated by subtracting TP21 from TP20.

In step 11, the auxiliary injection amount TP3 for covering the insufficient increase amount TP22 in the main injection by the auxiliary injection in the expansion stroke is calculated. In the case of main injection, NOx is reduced mainly by CO produced by combustion,
In the case of secondary injection in the expansion stroke after ignition, the proportion of HC (unburned fuel) that could not contribute to combustion increases, and at this HC, NO
Since x is reduced, the reduction efficiency is inferior to the main injection.

Therefore, as shown in the following equation, the amount TP22 of insufficient increase in the main injection has a coefficient K (> 1, for example, NOx reduction efficiency by K = CO / NOx reduction efficiency by HC) corresponding to the decrease of the NOx reduction efficiency. ) Is calculated to calculate the sub injection amount TP3. In addition, since the insufficient increase amount TP22 becomes a triangular shape that decreases with time, the auxiliary injection amount TP
3 also has a triangular shape (see d in FIG. 3).

TP3 = TP22 × K In step 12, it is determined whether the delay time td for starting the sub injection has elapsed. Before the lapse of time, this routine is ended and only the main injection is performed. After the main injection in the intake stroke, the fuel of TP3 calculated above is sub-injected in the expansion stroke.

The reason why the start of the sub-injection is delayed is that the sub-injected HC (unburned fuel) reacts with the excess oxygen accumulated in the exhaust pipe during lean combustion before combustion switching before it is used for NOx reduction. To prevent the afterburn from occurring, and C generated by the main injection amount increase TP21
Excess oxygen content in the exhaust pipe is consumed by O (e in FIG. 3).
(See reference), and the secondary injection is started.

In this way, the torque fluctuation is suppressed within the allowable value by the increase in the main injection with high NOx reduction efficiency, and the occurrence of afterburn is avoided while the shortage of the required value is covered by the secondary injection. As a result, the NOx trapped by the NOx trap catalyst can be sufficiently desorbed and reduced, and NOx emission during this period can be effectively suppressed (see f in FIG. 3).

In this embodiment, the delay time td for preventing the afterburn is set to a fixed value, and in this case, a large afterburn is surely avoided even when the amount of oxygen remaining in the exhaust pipe is large. Must be set to a value. Therefore, in the second embodiment, while estimating the residual oxygen amount in the exhaust pipe, the sub-injection is started when the oxygen amount decreases below a predetermined value.

FIG. 4 shows a flow chart of the rich spike control in the second embodiment. Instead of the delay time elapse determination in step 11 of FIG. 2 showing the first embodiment, a sub injection permission determination is performed in step 11 ′. The sub-injection permission determination is made based on the value of the sub-injection permission flag. When it is 1, the sub-injection is performed in step 12, and when it is 0, the sub-injection is stopped.

FIG. 5 is a flow chart of a subroutine for setting the value of the sub injection permission flag. Step two
At 1, the engine speed Ne is read. In step 22, the oxygen consumption amount O2d in the exhaust pipe due to the main injection increase amount TP21 is calculated by the following equation.

O2d = TP21 × Ne × A Here, the coefficient A is a value corresponding to the oxygen consumption efficiency, and is a value proportional to the fuel amount (TP21 × Ne) increased per unit time, per unit time. The oxygen consumption amount O2d is calculated. In step 23, the total amount O2dt of the oxygen amount in the exhaust pipe that is consumed after the start of the rich spike control, that is, the main injection amount increase, is calculated by the following equation by integrating the oxygen consumption amount O2d per unit time.

O2dt = O2dt (previous value) + O2d At step 24, at the start of the rich spike control, the initial value O2s of the oxygen amount remaining in the exhaust pipe due to the lean combustion until then is read. Since the lean air-fuel ratio in the immediately preceding lean combustion is often constant, it is sufficient to read the pre-calculated initial value O2s at that time. However, when the lean air-fuel ratio becomes variable, it depends on the lean air-fuel ratio. It may be variably calculated (see map, etc.).

In step 25, the initial value O of the oxygen amount is
The current exhaust pipe oxygen amount O2r is calculated by subtracting the total oxygen consumption amount O2dt from 2s (see the following equation). O2r = O2s-O2dt In step 26, it is determined whether or not the oxygen amount O2r in the exhaust pipe has decreased to the allowable value B or less at which afterburn does not occur even if the secondary injection is started.

When it is determined in step 26 that the exhaust pipe oxygen amount O2r has decreased to the allowable value B or less, step 2
If the sub injection permission flag FTP3 is set to 1 in step 7 and it is determined that the allowable value B is still exceeded, step 28
The sub-injection permission flag FTP3 is maintained at 0. By doing this, since the sub-injection is started while estimating the amount of oxygen remaining in the exhaust pipe, the start of the sub-injection can be accelerated compared to the case where the delay time is set to a certain large value, and the fuel consumption, The exhaust emission can be improved.

In the second embodiment, the start timing of the sub-injection is determined only by the amount of oxygen in the exhaust pipe, but afterburn is more likely to occur as the exhaust temperature is higher. Therefore,
It is necessary to set the allowable value B on the assumption that the exhaust gas temperature is the highest, and when the exhaust gas temperature is low, the start of the secondary injection is delayed more than necessary. Therefore, in the third embodiment, the start timing of the sub-injection is determined in consideration of the exhaust gas temperature as well.

The flow chart (main routine) of the rich spike control in the third embodiment is the same as that in FIG. 4 of the second embodiment, and the flow chart of the subroutine for setting the value of the sub injection permission flag is shown in FIG. Show.
FIG. 6 is partially different from FIG. That is, steps 21 to
Steps 25 are the same, and in step 31, the exhaust gas temperature TEMP detected by the sensor or estimated based on the engine operating state is read, and in step 32, the set characteristic as shown based on the exhaust gas temperature TEMP is read. The allowable value B of the residual oxygen amount is referred to from the map. Here, since the afterburn is more likely to occur as the exhaust temperature is higher, the allowable value B is set to a smaller value. Similarly to the second embodiment, the values of the sub-injection permission flag FTP3 are set while comparing the current exhaust pipe oxygen amount O2r with the allowable value B in steps 26 to 28.

In the fourth embodiment, based on the detection value of the air-fuel ratio sensor 12 upstream of the three-way catalyst, the auxiliary injection permission flag F is set.
The value of TP3 is set, and the flow chart (main routine) of rich spike control is the same as that of FIG. 4 of the second embodiment. In the flowchart of the subroutine for setting the value of the auxiliary injection permission flag shown in FIG. 7, the detection value of the air-fuel ratio sensor is read in step 41,
In step 42, it is determined whether the detected value is inverted to rich, and when it is determined to be inverted to rich, step 4
The value of the sub-injection permission flag FTP3 is set to 1 at 3, and is maintained at 0 otherwise.

As described above, the auxiliary injection can be started by simply detecting the decrease in the amount of oxygen in the exhaust pipe by using the air-fuel ratio sensor used for the air-fuel ratio feedback control. The fifth embodiment uses only the exhaust gas temperature to determine the start timing of the sub-injection, and the flow chart (main routine) of the rich spike control is the same as in FIG. 2 of the first embodiment.

In the flowchart of the subroutine for setting the value of the sub injection permission flag shown in FIG.
In step 1, the engine speed and load are read, in step 52, the exhaust temperature TEMP in the exhaust pipe is estimated based on the operating state detected based on these engine speed and load, and in step 53, the sub injection start delay time tde is calculated based on the exhaust gas temperature TEMP by referring to a map or the like. As described above, as the exhaust temperature is higher, afterburn is more likely to occur, so the delay time tde is calculated to be a large value.

In the above embodiment, the sub-injection is performed in all cylinders. However, since the sub-injection amount enough to cover the shortage of the main injection is small, the sub-injection is performed by dividing into all the cylinders. Further, the sub injection amount per cylinder becomes even smaller, and the injection amount error increases by using the small injection amount region in which the injection amount variation of the fuel injection valve in FIG. 9 is large. Therefore, in the following embodiment, the injection amount error is suppressed by performing the sub-injection in only some of the cylinders.

FIG. 10 shows a flow chart of the rich spike control in the sixth embodiment. Steps 1 to 10 'are the same as those in FIG. 2, but step 1
The sub-injection amount TP3 ′ calculated by 0 ′ is calculated by the following equation, and is set for each cylinder when the sub-injection is performed in each cylinder as in the first to fifth embodiments. It is a value obtained by multiplying TP3 by the number of cylinders.

TP3 '= TP22 (Insufficient amount of increase in main injection) × K × number of cylinders After it is determined in step 11 that the sub injection start delay time has elapsed (or the sub injection as in the second to fourth embodiments). After the injection permission is determined), the cylinder for which the sub-injection is performed is specified in step 61, and the sub-injection for the sub-injection amount TP3 ′ is performed only in the specific cylinder in step 62.

FIG. 11 is a flow chart of a subroutine for identifying the cylinder to be sub-injected in step 61. In step 71, the signal from the crank angle sensor 27 is input. In step 72, immediately after it is determined that the sub injection start delay time has elapsed based on the signal from the crank angle sensor 27 (or the second to the second).
Immediately after the sub-injection permission determination as in the fourth embodiment), the cylinder having the next expansion stroke is specified as the cylinder that performs the sub-injection.

FIG. 12 shows a state in which the cylinder for which the secondary injection is performed is specified and the secondary injection is started when this embodiment is applied to an in-line four-cylinder engine, and FIG. 13 similarly shows the rich spike control start. The state from to the end is shown. As described above, by performing the secondary injection only in the specific cylinder, the secondary injection amount in the specific cylinder can be increased, and the linearity of the fuel injection valve opening period-injection amount characteristic shown in FIG. Since the injection can be performed in the secured region, it is possible to obtain a good injection amount accuracy and supply an injection amount that is sufficient in proportion to the required NOx desorption amount. In addition, the desorption reduction process of NOx can be performed as quickly as possible by setting the cylinder that is in the first expansion stroke after the secondary injection becomes possible as the specific cylinder that performs the secondary injection.

Next, another embodiment (seventh embodiment) in which the sub injection is performed only in some of the cylinders will be described. In this embodiment, each cylinder group has a specific cylinder that performs sub injection, and the cylinder closest to the catalyst is a specific cylinder.
The one applied to a V-type internal combustion engine is shown. FIG. 14 shows the positional relationship between the catalyst and the cylinders in the system of this embodiment.
In the figure, a V-type 6-cylinder internal combustion engine 1 ′ has three-way catalysts 33, 34 and NOs on the downstream sides of the exhaust manifolds 31, 32 connected to the left and right banks, respectively.
The x trap catalysts 35 and 36 are provided.

In the cylinder group (# 1, # 3, # 5) of the left bank, the cylinder closest to the catalyst is the # 5 cylinder. Therefore, the specific cylinder of the cylinder group is the # 5 cylinder, and the cylinder group of the right bank is In (# 2, # 4, # 6), the cylinder closest to the catalyst is the # 6 cylinder, so the specific cylinder of the cylinder group is set to the # 6 cylinder. The flow chart of the rich spike control in this embodiment is the same as that of FIG. 10 of the sixth embodiment. The specific cylinders that perform the secondary injection are determined as described above, and the secondary injection is performed during the expansion stroke of these cylinders.

By doing so, the rich spike control according to the present invention can be carried out for each catalyst in each cylinder group, and in the V-type internal combustion engine, the distance from the catalyst is greatly different between the cylinders, so that the catalyst is most suitable. By making the near cylinder a specific cylinder, the auxiliary injected fuel can reach the catalyst quickly and with less loss due to adhesion to the exhaust passage wall and NOx.
Can be eliminated and reduced.

If the auxiliary injection in the cylinder that is in the first expansion stroke after the secondary injection becomes possible, such as at high speed, reaches the catalyst earlier, the cylinder is set as the specific cylinder,
Otherwise, the specific cylinder may be switched depending on the operating state so that the cylinder close to the catalyst is set as the specific cylinder. Further, in the embodiment described above, the specific cylinder is fixed during the rich spike control, but it may be variable. For example, with respect to the first cylinder to be sub-injected, which has a large effect of the sub-injection, the specific cylinder is set as in the above-described embodiment, but after the second time, the specific cylinder is set for each number of expansion strokes different from the number of cylinders. You may do it. For example, 4
In the cylinder engine, sub-injection may be performed every three cylinders to accelerate the sub-injection cycle, or conversely, sub-injection may be performed every five cylinders to increase the initial sub-injection amount. .

Further, in the above-mentioned embodiment, the NOx trapped by the NOx trap catalyst is released by the enrichment of the air-fuel ratio for reduction treatment. However, a catalyst for trapping SOx is provided and the SOx trapped by the catalyst is provided. To
It can also be applied to the one that is released by the enrichment of the air-fuel ratio and reduced.

[Brief description of drawings]

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

FIG. 2 is a flowchart of rich spike control in the first embodiment.

FIG. 3 is a time chart showing a state during the rich spike control.

FIG. 4 is a flowchart of a main routine of rich spike control in the second embodiment.

FIG. 5 is a flowchart of a sub-injection permission flag setting routine in the same rich spike control.

FIG. 6 is a flowchart of a sub-injection permission flag setting routine according to the third embodiment.

FIG. 7 is a flowchart of a sub-injection permission flag setting routine according to the fourth embodiment.

FIG. 8 is a flowchart of a delay time setting routine in the fifth embodiment.

FIG. 9 is a diagram showing an injection amount characteristic of a fuel injection valve.

FIG. 10 is a flowchart of a main routine of rich spike control in the sixth embodiment.

FIG. 11 is a flowchart of a routine for identifying a cylinder that performs secondary injection in the same rich spike control.

FIG. 12 is a time chart showing a state at the time of starting sub injection during the rich spike control of the sixth embodiment.

FIG. 13 is a time chart showing a state during rich spike control according to the sixth embodiment.

FIG. 14 is a plan view showing the positional relationship between the catalyst and each cylinder in the seventh embodiment.

[Explanation of symbols]

1 Internal combustion engine 1'V type internal combustion engine 4 Fuel injection valve 9 Exhaust manifold 13 three-way catalyst 15 NOx trap catalyst 16 control unit 22 Air flow meter 26 Water temperature sensor 27 Crank angle sensor 33,34 three-way catalyst 35,36 NOx trap catalyst

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/24 F01N 3/24 R 3/28 301 3/28 301C 3/36 3/36 B F02D 41/04 305 F02D 41/04 305A 41/14 310 41/14 310L 45/00 312 45/00 312R 314 314Z 362 362H 364 364N 368 368F (72) Inventor Kenichi Sato 2 Takaracho, Kanagawa-ku, Kanagawa Prefecture Nissan Motor Co., Ltd. F Term (reference) 3G084 AA04 BA09 BA13 BA15 BA20 DA02 DA07 DA10 DA11 DA25 EA07 EB08 EB11 EC01 FA07 FA10 FA20 FA27 FA29 FA33 FA38 FA39 3G091 AA02 AA11 AA12 AA17 AA24 AA28 ACB29 BA01 CB01 CB01 CB03 CB01 CB03 CB03 BA05 BA03 BA32 BA02 BA32 BA02 BA32 BA32 BA02 BA32 BA32 BA32 DA02 DA04 DA05 DB10 DC01 EA01 EA05 EA07 EA16 EA30 EA31 EA34 FB10 FB11 FB12 GA06 GB02Y GB03Y GB04Y GB06W HA08 HA10 HA36 HB05 3G301 HA04 HA08 HA13 HA16 JA02 JA04 JA25 LB04 MA01 MA11 MA19 MA02 NC02 NE27 NB02 E14 NE16 NE17 NE22 NE23 PA01Z PA11Z PB03Z PD02Z PD11Z PE01Z PE03Z PE05Z PE07Z PE08Z PF03Z

Claims (21)

[Claims] 1. A main injection that is supplied before ignition of fuel for a predetermined period after an air-fuel ratio enrichment request is made, and after the predetermined period has elapsed, the main injection and a sub injection that is supplied after ignition are performed. An air-fuel ratio control device for an internal combustion engine, characterized in that it is divided into injection and enrichment. 2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the rich degree due to the main injection is increased stepwise. 3. The rich degree by the main injection is limited to an upper limit value or less.
An air-fuel ratio control device for an internal combustion engine as set forth in. 4. The catalyst according to claim 1, wherein the exhaust passage is provided with a catalyst, and the rich degree by the main injection is increased stepwise and then gradually decreased. Air-fuel ratio controller for internal combustion engine. 5. The air-fuel ratio control apparatus for an internal combustion engine according to claim 4, wherein the rich degree by the main injection is increased stepwise, maintained at a constant degree, and then gradually decreased. 6. The air-fuel ratio control device for an internal combustion engine according to claim 4, wherein the rich degree due to the auxiliary injection is increased stepwise. 7. The air-fuel ratio control of an internal combustion engine according to claim 4, wherein the rich degree due to the auxiliary injection is increased stepwise and then gradually decreased. apparatus. 8. A substantially triangular wave state in which the overall rich degree of the main injection and the sub-injection is increased stepwise and then gradually decreased.
An air-fuel ratio control device for an internal combustion engine according to claim 7. 9. The method according to claim 1, wherein the oxygen concentration in the exhaust passage is estimated, and when the oxygen concentration falls below a predetermined value, the sub injection is started assuming that the predetermined period has elapsed. An air-fuel ratio control device for an internal combustion engine as set forth in. 10. The air-fuel ratio control device for an internal combustion engine according to claim 9, wherein the oxygen concentration in the exhaust passage is estimated based on the amount of the main injection and the engine rotation speed. 11. A sub-injection is started assuming that the predetermined period has elapsed when an air-fuel ratio downstream of a catalyst provided in an exhaust passage is detected and when the air-fuel ratio becomes rich. The air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 8. 12. The predetermined period is set based on a parameter that correlates with exhaust temperature.
An air-fuel ratio control device for an internal combustion engine according to claim 11. 13. The air-fuel ratio control apparatus for an internal combustion engine according to claim 11, wherein the predetermined period is set shorter as the parameter correlated to the exhaust gas temperature becomes lower. 14. The enrichment of the air-fuel ratio is required because NOx trapped in a catalyst provided in an exhaust passage.
The air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 13, characterized in that it is the time to release. 15. The enrichment of the air-fuel ratio is required for SOx trapped in a catalyst provided in an exhaust passage.
The air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 13, characterized in that it is the time to release. 16. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the main injection is performed in an intake stroke. 17. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the sub-injection is performed in an expansion stroke. 18. The method according to claim 1, wherein the rich degree of the main injection is limited to a predetermined degree, and the shortage of the enrichment in some cylinders is covered by the sub-injection of the some cylinders. An air-fuel ratio control device for an internal combustion engine according to claim 17. 19. The air-fuel ratio control for an internal combustion engine according to claim 18, wherein the cylinder-by-cylinder group has a plurality of cylinder groups, a catalyst is provided for each cylinder group, and each of the cylinder groups is provided with a part of the cylinders. apparatus. 20. The air-fuel ratio control apparatus for an internal combustion engine according to claim 18 or 19, wherein the cylinders that first reach the timing of the sub-injection after the lapse of the predetermined period are the partial cylinders. . 21. The internal combustion engine according to any one of claims 18 to 20, characterized in that the cylinders closest to the catalyst provided in the exhaust passage are the partial cylinders. Air-fuel ratio controller.