JP2000054900A - In-cylinder injection internal combustion engine - Google Patents

Abstract

(57) [Summary] In a cylinder injection type internal combustion engine equipped with a storage NOx catalyst, the storage NOx catalyst is quickly brought to a high temperature state,
Provided is an in-cylinder injection type internal combustion engine capable of always removing occluded SOx without deteriorating fuel economy. SOLUTION: A two-stage injection means (S16, S26) for injecting part of fuel as main injection in one of a compression stroke and an intake stroke and injecting the remainder as sub-injection in an expansion stroke, The rich air-fuel ratio operating means (S2) injecting fuel so that the air-fuel ratio becomes the rich air-fuel ratio
0, S30), and when it is necessary to remove the sulfur component (S component) (S10), the two-stage injection means and the rich air-fuel ratio operating means are alternately operated by the sulfur component removing means (S purge control). Alternatively, it is configured to be performed for each cylinder (S14
~ S24).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a direct injection internal combustion engine, and more particularly, to a technique for raising the temperature of a storage NOx catalyst in a direct injection internal combustion engine provided with a storage NOx catalyst.

[0002]

2. Related Art An in-cylinder injection type internal combustion engine is configured such that fuel can be directly injected into a cylinder not only in an intake stroke but also in a compression stroke, and thereby an air-fuel ratio is set to a stoichiometric air-fuel ratio (value of 14.7). ), The air-fuel ratio is controlled to a super lean air-fuel ratio not less than a target value (for example, value 24) on the super lean side, that is, the lean side.
It is possible to improve the fuel efficiency characteristics of the engine.

However, assuming that the air-fuel ratio is a lean air-fuel ratio, the conventional three-way catalyst has NO
There is a problem that x (nitrogen oxide) cannot be sufficiently purified, and recently, a storage-type NOx catalyst capable of purifying NOx even in an oxygen-excess atmosphere has been developed and put into practical use.
Occlusion-type NOx catalyst, the NOx in the exhaust gas is occluded as nitrate X-NO ₃ in an oxygen excess state (oxidation atmosphere),
The catalyst is configured to have the property of reducing the stored NOx to N ₂ (nitrogen) in a state of excess CO (carbon monoxide) (reducing atmosphere) (carbonate X—CO ₃ is generated at the same time). Speaking of the in-cylinder injection type internal combustion engine, for example, the air-fuel ratio is controlled to the stoichiometric air-fuel ratio or a value close to the stoichiometric air-fuel ratio before the NOx storage amount of the storage NOx catalyst is saturated. (This is referred to as a rich spike), thereby generating a CO-rich reducing atmosphere, purifying and reducing the stored NOx (NOx purge), and regenerating the stored NOx catalyst.

By the way, S (sulfur) component is contained in fuel.
(Sulfur component), and this S component reacts with oxygen
To form SOx (sulfur oxide), which is converted to sulfate X-
SO _FourAs a storage NOx catalyst instead of NOx
It is. In other words, the storage NOx catalyst contains nitrate and sulfate
Will be occluded. However, sulfates are nitrates
Higher salt stability and rich air-fuel ratio
(Reducing atmosphere with reduced oxygen concentration)
Of the sulfate remaining on the NOx storage catalyst
The amount increases with time. Thus, the amount of sulfate increased.
Increases, the storage capacity of the storage NOx catalyst increases over time.
And the performance as a storage NOx catalyst deteriorates.
Is unfavorable (S poisoning).

[0005] However, the thus stored SO 2
It has been found that x is removed (S purge) by raising the catalyst to a high temperature state while generating an excess of CO (reducing atmosphere) by setting the air-fuel ratio to a rich state. Japanese Patent Application Laid-Open No. Hei 7-21747 discloses a technique in which the temperature of exhaust gas is raised by retarding the ignition timing to raise the temperature of the catalyst.
No. 4 and the like.

[0006]

However, the method of raising the catalyst temperature by retarding the ignition timing as disclosed in the above-mentioned publication has a small effect of raising the temperature and reduces the fuel consumption because the combustion is slowed down. As well as aggravating factors,
It is not preferable to increase the retard amount so as to raise the temperature significantly, since deterioration of combustion may lead to deterioration of drivability.

Therefore, in the cylinder injection type internal combustion engine, for example, the target air-fuel ratio is set to a predetermined rich air-fuel ratio (for example, a value of 12), and the fuel injection is performed during the intake stroke (main injection). ) And injection (sub-injection) in the expansion stroke, and the fuel (HC) supplied by the sub-injection is discharged in an unburned state, so that combustion is performed in the exhaust passage or in the storage NOx. It has been considered to raise the exhaust gas temperature in the catalyst to heat the storage NOx catalyst.

However, when performing two-stage injection in a direct injection type internal combustion engine, although CO is generated by setting the overall air-fuel ratio to a predetermined rich air-fuel ratio, the amount of generated CO is smaller than in a normal rich operation. Therefore, depending on the operation state, the amount of generated CO may be insufficient and the S purge may not be sufficiently performed. The present invention has been made in order to solve such a problem, and an object of the present invention is to provide an in-cylinder injection type internal combustion engine having a storage type NOx catalyst, in which the storage type NOx catalyst is quickly brought to a high temperature state. It is another object of the present invention to provide an in-cylinder injection type internal combustion engine which can always reliably remove occluded SOx without deteriorating fuel efficiency.

[0009]

In order to achieve the above object, according to the present invention, in a cylinder injection type internal combustion engine, a part of fuel is injected by a main injection in one of a compression stroke and an intake stroke. And a rich air-fuel ratio driving means for injecting fuel so that the air-fuel ratio becomes a rich air-fuel ratio in the intake stroke. When removing the sulfur component from the NOx catalyst, the two-stage injection means and the rich air-fuel ratio operation means are configured to be executed alternately or for each cylinder.

Therefore, when the two-stage injection means is implemented,
A large amount of unburned fuel components (combustible substances such as unburned HC) are discharged by the sub-injection, and the unburned fuel components burn in the exhaust passage or the storage NOx catalyst, and the storage NOx catalyst is heated well. When the rich air-fuel ratio operating means is executed, a large amount of CO is generated due to incomplete combustion, and the sulfur component stored in the storage NOx catalyst by the CO, that is, SOx is good. Will be removed. In other words, in the present invention, both the temperature rise of these storage NOx catalysts and the generation of CO, which are necessary for removing the sulfur component, are achieved, whereby the temperature of the storage NOx catalysts rises efficiently and reliably, and CO is reduced. Sufficiently supplied and S purge is surely performed.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, a first embodiment will be described. Referring to FIG. 1, there is shown a schematic configuration diagram of a direct injection internal combustion engine according to the present invention mounted on a vehicle, and the configuration of the direct injection internal combustion engine according to the present invention will be described with reference to FIG. explain.

Engine body (hereinafter simply referred to as engine) 1
For example, in-cylinder injection spark ignition capable of performing fuel injection in an intake stroke (intake stroke injection mode) or fuel injection in a compression stroke (compression stroke injection mode) by switching a fuel injection mode (operation mode), for example. It is an inline 4-cylinder gasoline engine. The in-cylinder injection type engine 1 can be easily operated at a stoichiometric air-fuel ratio (stoichiometric ratio), at a rich air-fuel ratio (rich air-fuel ratio operation), or at a lean air-fuel ratio (lean air-fuel ratio). In particular, in the compression stroke injection mode, it is possible to operate at a super lean air-fuel ratio.

As shown in FIG. 1, the cylinder head 2 of the engine 1 is provided with an electromagnetic fuel injection valve 6 together with a spark plug 4 for each cylinder, whereby fuel is injected into the combustion chamber 8. Direct injection is possible. A fuel supply device (both not shown) having a fuel tank is connected to the fuel injection valve 6 via a fuel pipe. More specifically, the fuel supply device is provided with a low-pressure fuel pump and a high-pressure fuel pump, whereby the fuel in the fuel tank is supplied to the fuel injection valve 6 at a low fuel pressure or a high fuel pressure. From the fuel injection valve 6 into the combustion chamber at a desired fuel pressure. At this time, the fuel injection amount depends on the fuel discharge pressure of the high-pressure fuel pump and the valve opening time of the fuel injection valve 6,
That is, it is determined from the fuel injection time.

An intake port is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 10 is connected to communicate with each intake port. A throttle valve 11 is connected to the other end of the intake manifold 10. The throttle valve 11 is provided with a throttle sensor 11a for detecting a throttle opening θth.

An exhaust port is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of an exhaust manifold 12 is connected to communicate with each exhaust port. Reference numeral 13 in the figure denotes a crank angle sensor for detecting a crank angle, and the crank angle sensor 13 is capable of detecting an engine rotation speed Ne.

The in-cylinder injection type engine 1 is already known, and a detailed description of its configuration is omitted here. As shown in FIG. 1, an exhaust pipe (exhaust passage) 14 is connected to the exhaust manifold 12, and a small close three-way catalyst 20 and an exhaust purification catalyst device 30 close to the engine 1 are connected to the exhaust pipe 14. A muffler (not shown) is connected via the terminal. The exhaust pipe 14 is provided with a high temperature sensor 16 for detecting the exhaust gas temperature.

The exhaust purification catalyst device 30 includes two catalysts, that is, a storage type NOx catalyst 30a and a three-way catalyst 30b, and the three-way catalyst 30b has a storage type NOx catalyst 3b.
0a is disposed downstream. The storage NOx catalyst 30a temporarily stores NOx in an oxidizing atmosphere,
It has a function of reducing NOx to N ₂ (nitrogen) or the like mainly in a reducing atmosphere where CO is present. More specifically, the storage NOx catalyst 30a is configured as a catalyst having platinum (Pt), rhodium (Rh) or the like as a noble metal, and an alkali metal such as barium (Ba) or an alkaline earth metal as a storage material. Has been adopted.

A NOx sensor 32 for detecting the NOx concentration is provided between the storage type NOx catalyst 30a and the three-way catalyst 30b.
Is provided. Further, an input / output device, a storage device (R
OM, RAM, nonvolatile RAM, etc.), central processing unit (C
PU), an ECU (electronic control unit) 40 including a timer counter and the like.
With 0, comprehensive control of the direct injection internal combustion engine according to the present invention including the engine 1 is performed. Various sensors such as the high-temperature sensor 16 and the NOx sensor 32 described above are connected to the input side of the ECU 40, and detection information from these sensors is input.

On the other hand, the output side of the ECU 40 is connected to the above-described ignition plug 4 and the fuel injection valve 6 via an ignition coil. The ignition coil, the fuel injection valve 6 and the like are connected to various sensors. The optimum values such as the fuel injection amount and the ignition timing calculated based on the detection information are output.
As a result, an appropriate amount of fuel is injected from the fuel injection valve 6 at an appropriate timing, and ignition is performed by the spark plug 4 at an appropriate timing.

In practice, the ECU 40 determines the target in-cylinder pressure corresponding to the engine load, that is, the target average effective pressure, based on the throttle opening information θth from the throttle sensor 11a and the engine rotation speed information Ne from the crank angle sensor 13. Pe is determined, and the fuel injection mode is set from a map (not shown) according to the target average effective pressure Pe and the engine rotation speed information Ne. For example, when the target average effective pressure Pe and the engine rotation speed Ne are both low, the fuel injection mode is the compression stroke injection mode, and the fuel is injected in the compression stroke, while the target average effective pressure Pe increases or the engine rotation speed increases. When the speed Ne increases, the fuel injection mode is set to the intake stroke injection mode, and fuel is injected during the intake stroke.

The target air-fuel ratio (target A / A) is set as a control target based on the target average effective pressure Pe and the engine speed Ne.
F) is set, and the appropriate amount of fuel injection is set to the target A /
It is determined based on F. The catalyst temperature Tcat is estimated from the exhaust gas temperature information detected by the high temperature sensor 16. Specifically, the high temperature sensor 16 is connected to the storage NOx catalyst 30.
A temperature difference map (not shown) is set in advance by an experiment or the like in accordance with the target average effective pressure Pe and the engine rotation speed information Ne in order to correct an error that occurs due to the inability to directly install the apparatus in the area a. Therefore, the catalyst temperature Tcat is uniquely estimated when the target average effective pressure Pe and the engine speed information Ne are determined.

Hereinafter, the operation of the in-cylinder injection type internal combustion engine according to the present invention will be described. That is,
As described above, SOx is also stored in the storage-type NOx catalyst 30a. Here, the control procedure of the control for removing the SOx, that is, the S purge control (sulfur component removing means) will be described. Referring to FIG. 2, there is shown a flowchart of a control routine for performing the exhaust gas temperature raising control, which will be described below with reference to the flowchart.

First, at step S10, it is determined whether or not the NOx catalyst has deteriorated by S (sulfur), that is, whether or not the amount of SOx occluded by the occlusion type NOx catalyst 30a (poisoned S amount Qs) has reached a predetermined amount. Is determined. Here, the poisoning S amount Qs is a value obtained by estimation. Hereinafter, an estimation method (detection method) of the poisoning S amount Qs will be briefly described. The poisoning S amount Qs is basically set based on the fuel injection integrated amount Qf, and is calculated by the following formula at each execution cycle of a fuel injection control routine (not shown).

Qs = Qs (n−1) + ΔQf · K−Rs (1) where Qs (n−1) is the previous value of the poisoning S amount, and ΔQf is the integrated fuel injection amount per execution cycle. , K is a correction coefficient, Rs
Indicates the reproduction S amount per execution cycle. That is, the current poisoning S amount Qs is obtained by correcting the fuel injection integrated amount ΔQf per execution cycle with the correction coefficient K and integrating the same, and subtracting the regeneration S amount Rs per execution cycle from the integrated value. Can be

The correction coefficient K is, for example, as shown in the following equation (2), the S poisoning coefficient K1 according to the air-fuel ratio A / F, the S poisoning coefficient K2 according to the S content in the fuel, and the catalyst. It consists of the product of three correction coefficients of the S poisoning coefficient K3 according to the temperature Tcat. K = K1, K2, K3 (2) The reproduction S amount Rs per execution cycle is calculated from the following equation (3).

Rs = α · R1 · R2 · dT (3) where α is a regeneration rate (set value) per unit time, and dT is an execution cycle of the fuel injection control routine. R2 indicates a regeneration capacity coefficient corresponding to the catalyst temperature Tcat and a regeneration capacity coefficient corresponding to the air-fuel ratio A / F, respectively. Then, the determination result of step S10 is false (N
In o), if it is determined that the poisoning S amount Qs obtained as described above has not yet reached the predetermined amount, the routine exits without performing anything.

On the other hand, if the result of the determination in step S10 is true (Y
If it is determined in step es) that the poisoning S amount Qs has reached the predetermined amount, the process proceeds to step S12, and the control mode is set to S.
Switch to purge mode. Thus, the removal of SOx stored in the storage NOx catalyst 30a, that is, the S purge is started. When the S purge is started, it is determined in a step S14 whether or not the target average effective pressure Pe is smaller than a predetermined value Pe1 (a map for the engine rotation speed Ne). Specifically, based on the main injection mode selection map shown in FIG. 3, in relation to the engine rotation speed Ne,
It is determined whether or not the target average effective pressure Pe is within the range of the region A.

The determination result of step S14 is true (Yes).
If the target average effective pressure Pe is smaller than a predetermined value Pe1 (a map for the engine rotation speed Ne), that is, if the engine load and the engine rotation speed are small such as when idling or running at low speed, the next step Proceed to S16. In step S16, the fuel injection mode of the main injection is set to the compression stroke injection mode irrespective of the above-described normal setting, and the sub-injection is performed in the expansion stroke (particularly, in the middle or later stage of the expansion stroke) (two-stage Injection means). That is, as described above, when performing the S purge,
Although the two-stage injection is performed, when the target average effective pressure Pe and the engine rotation speed Ne are in the region A in FIG. 3, the two-stage injection is performed by the compression stroke injection and the expansion stroke injection. I do.

The target A / F, that is, the total target A / F including the main injection and the sub-injection, that is, the total A / F
F is set to a predetermined rich air-fuel ratio (a value suitable for S purge, for example, a value of 12), and the target average effective pressure Pe and the engine rotation speed Ne are determined based on the main injection mode selection map of FIG. Accordingly, the target air-fuel ratio (main A / F) of the main injection is determined. At this time, the main A / F is set while the overall A / F is maintained at the predetermined rich air-fuel ratio (for example, value 12). In other words, the fuel injection ratios of the main injection amount (part) and the sub injection amount (remainder) are properly determined while the entire fuel injection amount is kept constant and the reducing atmosphere is well formed. Is done.

Normally, if the target average effective pressure Pe or the engine rotation speed Ne is small, it can be determined that the temperature of the storage NOx catalyst 30a, that is, the catalyst temperature Tcat is low, and it is not easy to raise the temperature of the storage NOx catalyst 30a. Therefore, in this case,
It is preferable to reduce the main injection amount as much as possible while maintaining the overall A / F at the predetermined rich air-fuel ratio as described above, while increasing the sub injection amount. However, the air-fuel ratio that can be realized in the intake stroke injection mode has an upper limit (for example, value 22). That is, in the intake stroke, the upper limit value (for example,
If the air-fuel ratio is larger than the value 22), combustion is not established.

Therefore, the main A / F is set to the upper limit (for example,
When the value becomes larger than the value 22), the main injection is performed in the compression stroke in which combustion is established at an air-fuel ratio larger than the upper limit (for example, the value 22). By the way, it can be considered that the temperature of the storage NOx catalyst 30a, that is, the catalyst temperature Tcat is lower as the engine load and the engine rotation speed are lower. Therefore, the value of the main A / F increases as the target average effective pressure Pe or the engine rotation speed Ne decreases, and the air-fuel ratio becomes a leaner air-fuel ratio. That is, the lower the catalyst temperature Tcat, the smaller the main injection amount and the larger the sub injection amount.

In particular, when the main injection is the compression stroke injection as described above, the air-fuel ratio can be reduced to a super lean air-fuel ratio (for example, a range up to an upper limit of 50), and the main injection amount can be reduced. On the other hand, it is possible to inject a large amount of fuel by the sub-injection while making the amount extremely small. This allows
When the engine load and the engine rotation speed are low, a large amount of unburned fuel components are discharged into the exhaust pipe 14 and strongly burn in the exhaust pipe 14 or the storage NOx catalyst 30a in the presence of excess oxygen, Even if the catalyst temperature Tcat is low, the storage NOx catalyst 30a is quickly heated to a predetermined high temperature Tcat1 (for example, 650 ° C.) at which S purging is possible. Therefore, even when the engine load and the engine rotational speed are small and the storage type NOx catalyst 30a is in a low temperature state, for example, during low-speed running, the air-fuel ratio of the main injection is set to the super lean air-fuel ratio (for example, the upper limit value). 50, the sub-injection amount contributing to the temperature rise of the exhaust gas can be extremely increased without affecting the operation of the engine 1. Can be rapidly heated up to the high temperature Tcat1.

In the next step S18, step S16
Then, it is determined whether or not a predetermined time t2 (for example, 2 seconds) has elapsed since the start of the two-stage injection. If the determination result is false (No) and it is determined that the predetermined time t2 has not yet elapsed, the two-stage injection is continued until the predetermined time t2 has elapsed. On the other hand, if the result of the determination is true (Yes) and it is determined that the predetermined time t2 has elapsed, the process proceeds to step S20.

In step S20, the rich air-fuel ratio operation is performed without performing the two-stage injection by setting the fuel injection mode to the intake stroke injection mode (rich air-fuel ratio operation means). In this case, the target A / F is set to a predetermined rich air-fuel ratio (for example, a value of 12), similarly to the overall A / F. When the rich air-fuel ratio operation is performed as described above, since the fuel is in an excessive fuel state, the fuel causes incomplete combustion, and a large amount of CO is emitted. That is, by performing the rich air-fuel ratio operation, a large amount of CO required for reducing and removing SOx is stored in the NOx storage type.
It is supplied to the catalyst 30a, and the S purge is promoted.

Then, in step S22, step S
At 20, it is determined whether or not a predetermined time t3 (for example, 2 seconds) has elapsed since the start of the rich air-fuel ratio operation.
If the determination result is false (No) and it is determined that the predetermined time t3 has not yet elapsed, the rich air-fuel ratio operation is continued until the predetermined time t3 has elapsed. On the other hand, if it is determined that the determination result is true (Yes) and the predetermined time t3 has elapsed,
Next, the process proceeds to step S24.

On the other hand, if the result of the determination in step S14 is false (No), and the target average effective pressure Pe is determined to be equal to or higher than the predetermined value Pe1 (a map for the engine speed Ne), that is, when the vehicle is running at a middle speed, If the engine load and the engine speed are relatively large, the process proceeds to step S26. In step S26, the fuel injection mode of the main injection is set to the intake stroke injection mode regardless of the normal setting described above, and the sub-injection is performed during the expansion stroke.
That is, when the engine load and the engine rotation speed are relatively large and the target average effective pressure Pe and the engine rotation speed Ne are in the region B in FIG. 3, the two-stage injection is performed by the intake stroke injection and the expansion stroke injection. I do.

Then, similarly to the above, the overall A / F is set to a predetermined rich air-fuel ratio (for example, value 12), and the overall A / F is set to the predetermined rich air-fuel ratio (for example,
While maintaining the value 12), the target air-fuel ratio (main A / F) of the main injection is determined, and the respective fuel injection ratios of the main injection amount (part) and the sub injection amount (remainder) are properly determined. . Normally, if the engine load and the engine rotation speed are relatively large, the storage NOx catalyst 30a is heated to a certain high temperature, and reaches a predetermined high temperature Tcat1 (for example, 650 ° C.) at which the storage NOx catalyst 30a can be S-purged. It can be easily determined that the temperature can be raised. Therefore, in this case, it is preferable to reduce the sub-injection amount while increasing the main injection amount to maintain the overall A / F at a predetermined rich air-fuel ratio. However, the air-fuel ratio that can be realized in the compression stroke injection mode has a lower limit (for example, value 22). That is, in the compression stroke, contrary to the above case, combustion is not established at an air-fuel ratio equal to or lower than the lower limit (for example, value 22).

Therefore, when the air-fuel ratio of the main injection is equal to or lower than the lower limit (for example, value 22), the main injection is performed in the intake stroke in which combustion is established at the air-fuel ratio equal to or lower than the lower limit (for example, value 22). Injection should be performed. As a result, the main fuel injection amount (partly) is maintained while the overall fuel injection amount is maintained constant and the reducing atmosphere is well formed.
And the fuel injection ratio of the sub-injection amount (remainder) is properly determined, and the storage NOx catalyst 30a
Is a predetermined high temperature Tcat1 that can be S purged (for example, 650).
(° C).

When the vehicle is running at a high speed, the engine speed Ne and the target average effective pressure Pe are large, and the main A / F is smaller than the lower limit value 16 and is in the vicinity of stoichio. When Pe and the engine rotation speed Ne are in the region C in FIG. 3, two-stage injection is difficult due to restrictions of the injector driver and the like,
It can be determined that the combustion heat is large, the exhaust gas temperature is sufficiently high, and it is possible to heat the storage NOx catalyst 30a to a predetermined high temperature Tcat1 at which S purging can be performed only by retarding the ignition timing. Therefore, in this case, only the main injection is performed in the intake stroke instead of the two-stage injection in step S26, and the temperature rise control is performed by retarding the ignition timing. Note that, also in this case, the overall A / F is set to a predetermined rich air-fuel ratio (for example, a value of 12).

When the engine speed Ne and the target average effective pressure Pe are extremely large and the main A / F has a rich air-fuel ratio, that is, when the target average effective pressure Pe and the engine rotation speed Ne in FIG. When it is in the D region, it can be determined that the combustion heat is extremely large and the exhaust gas temperature is high enough to perform the S purge without performing the temperature increase control. In this case,
Step S26 is skipped.

In the next step S28, the above step S
Similarly to 18, it is determined whether or not a predetermined time t2 (for example, 2 seconds) has elapsed since the start of the two-stage injection in step S26. If the determination result is false (No) and it is determined that the predetermined time t2 has not yet elapsed, the two-stage injection is continued until the predetermined time t2 has elapsed. On the other hand, if the result of the determination is true (Yes) and it is determined that the predetermined time t2 has elapsed, then the flow proceeds to step S30.

In step S30, step S20
Similarly to the above, the fuel injection mode is set to the intake stroke injection mode, and the rich air-fuel ratio operation is performed without performing the two-stage injection. As a result, a large amount of CO is discharged and S purge is promoted. In step S32, similarly to step S22, it is determined whether or not a predetermined time t3 (for example, 2 seconds) has elapsed since the start of the rich air-fuel ratio operation in step S30. If the determination result is false (No) and it is determined that the predetermined time t3 has not yet elapsed, the rich air-fuel ratio operation is continued until the predetermined time t3 has elapsed. On the other hand, if the determination result is true (Yes) and the predetermined time t3
Is determined to have elapsed, the process proceeds to step S24.

In step S24, the storage NOx catalyst 3
It is determined whether 0a has reached a high temperature (for example, 650 ° C.) suitable for SOx removal and a predetermined time t4 has elapsed. The predetermined time t4 is a time set in advance by an experiment or the like as a time capable of sufficiently removing SOx when the storage NOx catalyst 30a is maintained at a predetermined high temperature Tcat1 in a reducing atmosphere.

The determination result of step S24 is false (No)
If it is determined that the predetermined time t4 has not elapsed, the process returns to step S14 to continue the operation in the S purge mode. That is, step S16 and step S2
6, two-stage injection and steps S20 and S3
0 is repeatedly performed alternately with the rich air-fuel ratio operation at 0, and the storage type NOx catalyst 3
0a does not fall below a high temperature suitable for SOx removal.

That is, in the S purge control, the two-stage injection having a large temperature raising effect and the rich air-fuel ratio operation for discharging a large amount of CO are alternately repeated for a predetermined time t2 and a predetermined time t3. In the process, the temperature of the storage NOx catalyst 30a is raised to a predetermined high temperature Tcat1 early while removing SOx from the storage NOx catalyst 30a.
It is possible to maintain a high temperature suitable for removal.

On the other hand, if the decision result in the step S24 is true (Y
If it is determined to be es), it is considered that SOx has been sufficiently removed, and the routine exits from the routine and ends the S purge control.
In the above embodiment, the two-stage injection and the rich air-fuel ratio operation are always performed alternately during the entire period from the start of the catalyst temperature rise to the SOx removal. However, even when the catalyst temperature Tcat is equal to or lower than the predetermined high temperature Tcat1, CO is not changed. When the catalyst is supplied, S purge is performed to some extent according to the temperature. Therefore, first, two-stage injection is continuously performed, and after the catalyst temperature Tcat reaches a predetermined high temperature Tcat1, the two-stage injection and the rich air-fuel ratio operation are alternately performed. May be implemented.

In this case, referring to FIG. 4, a part of the control routine of the S purge control in which steps S19 and S29 are added to the flowchart of FIG. 2 is shown as a modified example.
In step S19 and step S29, it is determined whether the catalyst temperature Tcat has become equal to or higher than the predetermined high temperature Tcat1 after the two-stage injection is performed in step S6. If the predetermined high temperature Tcat1 has not yet been reached, the two-stage injection is continuously performed without performing the two-stage injection of step S21 and the rich air-fuel ratio operation.

If the result of the determination in steps S19 and S29 is true (Yes), in step S21 the catalyst temperature Tcat is maintained at a predetermined high temperature Tcat1 based on the output of the high temperature sensor 16 as in the above embodiment. While, for example, the two-stage injection and the rich air-fuel ratio operation are performed alternately, for example, the storage NOx catalyst 30a is kept in the SOx removal atmosphere.
Then, in step S24, it is determined whether or not a predetermined time t4 has elapsed, and the control in step S21 is continued until the determination result becomes true (Yes).

As a result, although the SOx cannot be sufficiently removed in the catalyst temperature increasing process, the occlusion type NOx catalyst 30a can quickly reach the predetermined high temperature Tcat1 at which the SOx can be reliably removed. You can do it. In the above embodiment, the two-stage injection is performed for a predetermined time t2.
After performing (for example, 2 seconds), the rich air-fuel ratio operation is performed for a predetermined time t3 (for example, 2 seconds).
The stage injection and the rich air-fuel ratio operation may be alternately performed every predetermined number of strokes (one or more strokes). That is, the two-stage injection and the rich air-fuel ratio operation may be repeated each time the predetermined number of strokes elapses in each cylinder.

Here, the predetermined time t2 and the predetermined time t3 are both set to, for example, 2 seconds. However, the predetermined time t2 and the predetermined time t3 are separately set in accordance with a required temperature increase amount and a required CO amount. It may be. Further, these may be varied according to operating conditions (target average effective pressure Pe, engine rotation speed Ne, etc.) and catalyst temperature Tcat. As a result, the S purge can be performed more appropriately.

Next, a second embodiment will be described. In the first embodiment, the two-stage injection and the rich air-fuel ratio operation are switched every predetermined time or every predetermined number of strokes. However, in the second embodiment, when the engine 1 is a multi-cylinder engine,
For the predetermined time, the two-stage injection and the rich air-fuel ratio operation are repeated for each cylinder instead of the predetermined number of strokes.

Referring to FIG. 5, there is shown a part of a flowchart showing a control routine of the S purge control (sulfur component removing means) according to the second embodiment following the flowchart of FIG. Only parts different from the first embodiment will be described. In the second embodiment, in step S14, it is determined whether or not the target average effective pressure Pe is smaller than a predetermined value Pe1, and if the determination result is true (Yes), then step S16 'is performed.
Proceed to.

In step S16 ', rich air-fuel ratio operation is performed in some cylinders, and two-stage injection is performed in the remaining cylinders. That is, here, since the engine 1 is, for example, an in-cylinder injection spark ignition type in-line four-cylinder gasoline engine, the rich air-fuel ratio operation is performed in some of the four cylinders (for example, two cylinders), and the remaining cylinders (for example, Two-stage injection is performed in two cylinders). In this case, for the two-stage injection, the main injection is performed in the compression stroke and the sub-injection is performed in the expansion stroke, as in the first embodiment, based on the determination in step S14.

When the engine 1 is, for example, a V-type gasoline engine, the rich air-fuel ratio operation is performed in each cylinder of one bank, and the two-stage injection is performed in each cylinder of the other bank. Good to do. On the other hand, step S
When the determination result of No. 14 is false (No), the process proceeds to step S26 '.

In step S26 ', the rich air-fuel ratio operation is performed in some cylinders and two-stage injection is performed in the remaining cylinders in the same manner as described above. In this case, the first embodiment is performed based on the determination in step S14. As in the case of, the main injection is performed in the intake stroke and the sub-injection is performed in the expansion stroke. Then, in step S24, it is determined whether the SOx removal atmosphere has passed a predetermined time t4.

The determination result of step S24 is false (No)
If it is determined that the predetermined time t4 has not elapsed, the process returns to step S14. In this case, step S
16 ′ and step S26 ′, the high temperature sensor 16
In accordance with the output, the two-stage injection and the rich air-fuel ratio operation are continuously performed for each cylinder so that the catalyst temperature Tcat is maintained at the predetermined high temperature Tcat1 and the storage NOx catalyst 30a is maintained in the SOx removal atmosphere.

In this manner, the two-stage injection having a large temperature-raising effect and the rich air-fuel ratio operation capable of discharging a large amount of CO are carried out in a well-balanced manner. , The SOx can be surely removed. Therefore, also in the case of the second embodiment, the S purge, that is, the removal of SOx is reliably performed while preventing the deterioration of the fuel economy, and the storage NOx catalyst 30
It is possible to always keep the NOx purification efficiency of a high.

In this case, both the partial cylinder and the remaining cylinder are, for example, two cylinders. However, as in the case where the predetermined time t2 and the predetermined time t3 are set separately in the first embodiment, the necessary temperature increase The number of partial cylinders and the number of remaining cylinders may be set to different numbers of cylinders according to the required CO amount. Further, these may be varied according to operating conditions (target average effective pressure Pe, engine rotation speed Ne, etc.) and catalyst temperature Tcat. As a result, the S purge can be performed more appropriately.

Further, after performing the two-stage injection in the remaining cylinders or all the cylinders, the rich air-fuel ratio operation may be started in some of the cylinders when the catalyst temperature Tcat rises to a predetermined high temperature Tcat1. . As a result, in the same manner as described above, in the catalyst heating process until the catalyst reaches the predetermined high temperature Tcat1, SOx
Although removal of NOx cannot be expected, the storage NOx catalyst 30a can quickly reach a predetermined high temperature Tcat1 at which SOx can be removed reliably.

In the above embodiment (Examples 1 and 2), the total A / F is set to a predetermined rich air-fuel ratio (for example, a value of 12) when performing two-stage injection. Is to purge the S even at the time of the two-stage injection. Even if the two-stage injection is considered to be used only as a means for raising the temperature of the storage NOx catalyst 30a, when the two-stage injection is performed, The overall A / F may be stoichiometric or lean air-fuel ratio. By doing so, it is possible to further prevent deterioration of fuel efficiency.

In the rich air-fuel ratio operation, the ignition timing may be retarded. This gives 2
Not only in the stage injection operation but also in the rich air-fuel ratio operation, the temperature increasing effect can be obtained as much as possible.
This is effective when it is desired to raise the temperature of the Ox catalyst 30a earlier. Further, in the present embodiment, the storage NOx
Although the poisoning S amount of the catalyst 30a is estimated, the two-stage injection and the rich air-fuel ratio operation are performed alternately or for each cylinder.
For example, immediately after the start, the S purge control may be performed by always performing the two-stage injection and the rich air-fuel ratio operation alternately or for each cylinder without estimating the poisoning S amount.

[0062]

As described above in detail, according to the in-cylinder injection type internal combustion engine of the first aspect of the present invention, the temperature rise of these storage NOx catalysts and the generation of the reducing atmosphere required for the removal of the sulfur component are performed. Thus, the temperature of the storage NOx catalyst can be efficiently and reliably raised, and a sufficient atmosphere of CO can be supplied to ensure a reducing atmosphere.

Accordingly, the amount of sulfur stored in the storage NOx catalyst
Ox can be reliably removed without deterioration in fuel efficiency, and the NOx purification efficiency of the storage NOx catalyst can be constantly maintained at a high level.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a direct injection internal combustion engine according to the present invention.

FIG. 2 is a flowchart illustrating a control routine of the direct injection internal combustion engine according to the first embodiment of the present invention.

FIG. 3 is a main injection mode selection map when performing two-stage injection.

FIG. 4 is a part of a flowchart showing a modification of the control routine of FIG. 2;

FIG. 5 is a part of a flowchart showing a control routine of the direct injection internal combustion engine according to the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine (in-cylinder injection type internal combustion engine) 4 Spark plug 6 Fuel injection valve 11 Throttle valve 11a Throttle sensor 13 Crank angle sensor 16 High temperature sensor 30a Storage type NOx catalyst 40 Electronic control unit (ECU)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) F01N 3/24 ZAB F01N 3/24 ZABE 3/28 301 3/28 301C 3/36 ZAB 3/36 ZABB F02D 41/02 325 F02D 41/02 325A 41/04 305 41/04 305Z 41/36 41/36 B 45/00 301 45/00 301G (72) Inventor Takashi Dogahara 5-33 Shiba 5-chome, Minato-ku, Tokyo No. 8 Inside Mitsubishi Motors Corporation (72) Yuki Tamura, Inventor 5-33-8 Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Corporation (72) Takashi Kawabe 5-33-8, Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation (72) Inventor Satoshi Yoshikawa 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation F-term (reference) 3G084 AA03 AA04 BA09 BA13 BA15 BA24 CA00 CA03 CA04 CA09 DA02 DA10 EB02 EC02 EC03 3G091 AA02 AA12 AA13 AA17 AA24 AA28 AB03 AB06 AB09 AB11 BA02 BA13 BA14 BA17 CA18 CA26 CB02 CB03 CB05 DA02 DA06 DB07 DC00 DC06 EA01 EA02 EA07 EA12 FA13 EA12 EA17 EA12 FA17 GB02W GB03W GB05W GB06W HA08 HA12 HA19 HA20 HA35 3G301 HA01 HA04 HA06 HA16 JA02 JA21 JA25 KA00 KA07 KA08 KA09 KA24 KA25 LA00 LB04 MA01 MA11 MA19 MA23 MA26 MA27 NA06 NA08 NB02 NC02 NE13 NE14 NE15 NE16 NE17ZZZZZZZZZZZZZZWZ

Claims (1)

[Claims] 1. An exhaust passage, which stores NOx in exhaust gas when the internal combustion engine is in a lean air-fuel ratio operating state,
A storage-type NOx catalyst that reduces the stored NOx when in a stoichiometric air-fuel ratio operation or a rich air-fuel ratio operation state; and a part of fuel is injected as main injection in one of a compression stroke and an intake stroke, and the remainder is Two-stage injection means for injecting as a sub-injection in the expansion stroke, rich air-fuel ratio operation means for injecting fuel so that the air-fuel ratio becomes a rich air-fuel ratio in the intake stroke, and removing sulfur components from the storage NOx catalyst. A direct injection type internal combustion engine comprising: a two-stage injection unit and a rich air-fuel ratio operating unit, alternately or for each cylinder.