JP3642194B2 - In-cylinder internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an in-cylinder injection internal combustion engine, and more particularly to a technique for raising the temperature of an occlusion type NOx catalyst in an in-cylinder injection internal combustion engine equipped with an occlusion type NOx catalyst.
[0002]
[Related background]
The in-cylinder injection internal combustion engine is configured to be able to inject fuel directly into the cylinder not only in the intake stroke but also in the compression stroke, so that the air-fuel ratio is set to an extremely lean side from the theoretical air-fuel ratio (value 14.7). In other words, it is possible to improve the fuel efficiency characteristics of the engine by controlling the air / fuel ratio to a super lean air / fuel ratio equal to or higher than the lean target value (for example, value 24).
[0003]
However, when the air-fuel ratio is made lean as described above, there is a problem that the conventional three-way catalyst cannot sufficiently purify NOx (nitrogen oxide) due to its purification characteristics, and recently, NOx is reduced even in an oxygen-excess atmosphere. A storage-type NOx catalyst that can be purified has been developed and put into practical use.
The storage-type NOx catalyst converts NOx in exhaust gas to nitrate X-NO in an oxygen-excess state (oxidizing atmosphere). _Three And stored the NOx in a CO (carbon monoxide) excess state (reducing atmosphere). ₂ Characteristics to reduce to (nitrogen) (at the same time carbonate X-CO _Three Is formed). For a cylinder injection type internal combustion engine, for example, it is regularly performed in a rich air-fuel ratio operation in an intake stroke in which the air-fuel ratio is controlled to the theoretical air-fuel ratio or a value close thereto before the NOx storage amount of the storage-type NOx catalyst is saturated. Thus, a reducing atmosphere with a large amount of CO is generated, and the stored NOx is purified and reduced (NOx purge) to regenerate the stored NOx catalyst.
[0004]
By the way, S (sulfur) component (sulfur component) is contained in the fuel, and this S component reacts with oxygen to become SOx (sulfur oxide), and this SOx is sulfate X-SO. _Four Is stored in the NOx storage catalyst instead of NOx. That is, nitrate and sulfate are stored in the storage-type NOx catalyst. However, sulfate is more stable as nitrate than nitrate, and even when the air-fuel ratio becomes rich (reducing atmosphere with reduced oxygen concentration), only a part of it is decomposed and sulfuric acid remaining in the NOx storage catalyst remains. The amount of salt increases with time. When the amount of sulfate increases in this way, the storage capacity of the storage-type NOx catalyst decreases with time, and the performance as the storage-type NOx catalyst deteriorates, which is not preferable (S poisoning).
[0005]
However, it has been found that the SOx occluded in this way is removed (S purge) by setting the air-fuel ratio to a rich state to generate a CO excess state (reducing atmosphere) and bringing the catalyst to a high temperature state. Japanese Laid-Open Patent Publication No. 7-217474 discloses a technique for raising the temperature of exhaust gas by reducing the ignition timing, for example, under a reducing atmosphere.
[0006]
[Problems to be solved by the invention]
However, as disclosed in the above publication, the method of raising the catalyst temperature by retarding the ignition timing has a small effect of raising the temperature, and slows the combustion, which causes a deterioration in fuel consumption and greatly increases. Increasing the amount of retard to increase the temperature is not preferable because it may lead to worsening of the dribbling due to worsening of combustion.
[0007]
Therefore, in a direct injection internal combustion engine, for example, the overall air-fuel ratio, which is the target air-fuel ratio, is set to a predetermined rich air-fuel ratio (for example, value 12), and fuel injection is performed in the intake stroke (main injection) and expansion. This is divided into two-stage injection, ie, injection in the stroke (sub-injection), and the fuel (HC) supplied by the sub-injection is discharged in an unburned state. It is considered to raise the exhaust temperature and heat the storage-type NOx catalyst.
[0008]
However, when two-stage injection is performed in a direct injection internal combustion engine, CO is generated by setting the total air-fuel ratio to a predetermined rich air-fuel ratio, but the amount of CO generated is smaller than in normal rich operation. Depending on the operating state, the amount of CO produced may be insufficient, and S purge may not be performed sufficiently.
The present invention has been made to solve such problems, and an object of the present invention is to quickly bring the storage-type NOx catalyst into a high-temperature state in a cylinder injection internal combustion engine equipped with the storage-type NOx catalyst. Another object of the present invention is to provide a cylinder injection type internal combustion engine that can always reliably remove the stored SOx without deteriorating fuel consumption.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, in a direct injection internal combustion engine, a part of the fuel is injected as a main injection in one of the compression stroke and the intake stroke, and the remaining portion is expanded. And a rich air-fuel ratio operating 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-type NOx catalyst These two-stage injection means and rich air-fuel ratio operation means are configured to be implemented alternately or for each cylinder.
[0010]
For this reason, when the two-stage injection means is implemented, a large amount of unburned fuel components (combustible materials such as unburned HC) are discharged by sub-injection, and the unburned fuel components are exhausted in the exhaust passage or in the storage NOx catalyst. When the rich NO.sub.x catalyst is heated and heated, the rich air-fuel ratio operation means generates a large amount of CO due to incomplete combustion. The sulfur component occluded in the NOx catalyst, that is, SOx can be removed well. That is, in the present invention, both the temperature rise of the storage type NOx catalyst necessary for the removal of the sulfur component and the generation of CO are made compatible. Sufficient supply will ensure that S purge is performed.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
First, Example 1 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. Hereinafter, the configuration of the direct injection internal combustion engine according to the present invention will be described based on the same drawing. explain.
[0012]
The engine main body (hereinafter simply referred to as an engine) 1 is, for example, a fuel injection in an intake stroke (intake stroke injection mode) or a fuel injection in a compression stroke (compression stroke injection mode) by switching a fuel injection mode (operation mode). Is an in-cylinder injection type spark ignition type in-line four-cylinder gasoline engine. The in-cylinder injection type engine 1 can be easily operated at a stoichiometric air fuel ratio (stoichio) or 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.
[0013]
As shown in the figure, 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, so that fuel can be directly injected into the combustion chamber 8. It is said that.
A fuel supply device (both not shown) having a fuel tank is connected to the fuel injection valve 6 through a fuel pipe. More specifically, the fuel supply device is provided with a low pressure fuel pump and a high pressure fuel pump, whereby fuel in the fuel tank is supplied to the fuel injection valve 6 at a low fuel pressure or a high fuel pressure. Can be injected from the fuel injection valve 6 into the combustion chamber at a desired fuel pressure. At this time, the fuel injection amount is determined from the fuel discharge pressure of the high-pressure fuel pump and the opening time of the fuel injection valve 6, that is, the fuel injection time.
[0014]
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 so as to communicate with each intake port. A throttle valve 11 is connected to the other end of the intake manifold 10, and the throttle valve 11 is provided with a throttle sensor 11a for detecting the throttle opening θth.
[0015]
Further, an exhaust port is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of the exhaust manifold 12 is connected so as to communicate with each exhaust port.
In the figure, reference numeral 13 denotes a crank angle sensor that detects a crank angle, and the crank angle sensor 13 can detect the engine rotational speed Ne.
[0016]
Note that the in-cylinder injection type engine 1 is already known, and the description of the configuration thereof is omitted here.
As shown in the drawing, an exhaust pipe (exhaust passage) 14 is connected to the exhaust manifold 12, and a small 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 cable. The exhaust pipe 14 is provided with a high temperature sensor 16 for detecting the exhaust temperature.
[0017]
The exhaust purification catalyst device 30 includes two catalysts, a storage type NOx catalyst 30a and a three-way catalyst 30b, and the three-way catalyst 30b is disposed downstream of the storage type NOx catalyst 30a. ing.
The storage-type NOx catalyst 30a temporarily stores NOx in an oxidizing atmosphere, and stores NOx in a reducing atmosphere mainly containing CO. ₂ It has a function of reducing to (nitrogen) or the like. Specifically, the storage type NOx catalyst 30a is configured as a catalyst having platinum (Pt), rhodium (Rh) or the like as a noble metal, and as the storage material, an alkali metal such as barium (Ba) or an alkaline earth metal is used. It has been adopted.
[0018]
Further, a NOx sensor 32 for detecting the NOx concentration is provided between the storage type NOx catalyst 30a and the three-way catalyst 30b.
Further, an ECU (electronic control unit) 40 including an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a central processing unit (CPU), a timer counter, and the like is installed. The overall control of the direct injection internal combustion engine according to the present invention including 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.
[0019]
On the other hand, the ignition plug 4 and the fuel injection valve 6 described above are connected to the output side of the ECU 40 via an ignition coil. The ignition coil, the fuel injection valve 6 and the like are detected information from various sensors. The optimum values such as the fuel injection amount and ignition timing calculated based on the above 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 at an appropriate timing by the spark plug 4.
[0020]
In practice, the ECU 40 obtains the target in-cylinder pressure corresponding to the engine load, that is, the target average effective pressure Pe, based on the throttle opening information θth from the throttle sensor 11a and the engine rotational speed information Ne from the crank angle sensor 13. Further, the fuel injection mode is set from a map (not shown) according to the target average effective pressure Pe and the engine rotational speed information Ne. For example, when both the target average effective pressure Pe and the engine speed Ne are small, the fuel injection mode is set to the compression stroke injection mode, and fuel is injected in the compression stroke, while the target average effective pressure Pe increases or the engine rotation When the speed Ne increases, the fuel injection mode is changed to the intake stroke injection mode, and fuel is injected in the intake stroke.
[0021]
Then, a target air-fuel ratio (target A / F) as a control target is set from the target average effective pressure Pe and the engine speed Ne, and the appropriate fuel injection amount is determined based on the target A / F. .
The catalyst temperature Tcat is estimated from the exhaust gas temperature information detected by the high temperature sensor 16. Specifically, in order to correct an error caused by the fact that the high temperature sensor 16 cannot be directly installed on the occlusion-type NOx catalyst 30a, the temperature is experimentally determined in advance according to the target average effective pressure Pe and the engine rotational speed information Ne. A difference map (not shown) is set, and therefore the catalyst temperature Tcat is uniquely estimated when the target average effective pressure Pe and the engine speed information Ne are determined.
[0022]
Hereinafter, the operation of the direct injection internal combustion engine according to the present invention configured as described above 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 exhaust gas temperature raising control, which will be described below along the flowchart.
[0023]
First, in 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 stored in the storage type NOx catalyst 30a (poisoned S amount Qs) has reached a predetermined amount. To do. Here, the poisoned S amount Qs is a value obtained by estimation. Hereinafter, the estimation method (detection method) of the poisoned 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 equation for each execution cycle of a fuel injection control routine (not shown).
[0024]
Qs = Qs (n-1) +. DELTA.Qf.K-Rs (1)
Here, Qs (n-1) is the previous value of the poisoning S amount, ΔQf is the fuel injection integrated amount per execution cycle, K is a correction coefficient, and Rs is the regeneration S amount per execution cycle.
That is, the current poisoning S amount Qs is obtained by correcting and integrating the fuel injection integrated amount ΔQf per execution cycle with the correction coefficient K, and subtracting the regeneration S amount Rs per execution cycle from the integrated value. It is done.
[0025]
For example, as shown in the following equation (2), the correction coefficient K includes an S poisoning coefficient K1 corresponding to the air-fuel ratio A / F, an S poisoning coefficient K2 corresponding to the S content in the fuel, and the catalyst temperature Tcat. It consists of the product of three correction coefficients of the corresponding S poison coefficient K3.
K = K1, K2, K3 (2)
Further, the reproduction S amount Rs per execution cycle is calculated from the following equation (3).
[0026]
Rs = α ・ R1 ・ R2 ・ dT (3)
Here, α is the regeneration rate (set value) per unit time, dT indicates the execution period of the fuel injection control routine, and R1 and R2 are the regeneration capacity coefficient and air-fuel ratio A corresponding to the catalyst temperature Tcat, respectively. The reproduction capability coefficient according to / F is shown.
If the determination result in step S10 is false (No) and it is determined that the poisoning S amount Qs obtained as described above has not yet reached the predetermined amount, the routine is terminated without doing anything.
[0027]
On the other hand, if the determination result in step S10 is true (Yes) and it is determined that the poisoning S amount Qs has reached the predetermined amount, the process proceeds to step S12, and the control mode is switched to the S purge mode. As a result, removal of SOx stored in the storage-type NOx catalyst 30a, that is, S purge is started.
When the S purge is started, in step S14, it is determined whether or not the target average effective pressure Pe is smaller than a predetermined value Pe1 (map for the engine speed Ne). Specifically, based on the main injection mode selection map shown in FIG. 3, it is determined whether or not the target average effective pressure Pe is within the range of the region A in relation to the engine speed Ne.
[0028]
If the determination result in step S14 is true (Yes) and the target average effective pressure Pe is smaller than a predetermined value Pe1 (map for engine speed Ne), that is, engine load and engine speed as during idling or low speed running. If the speed is low, the process proceeds to step S16.
In step S16, the fuel injection mode of the main injection is set to the compression stroke injection mode regardless of the above-described normal setting, and the sub-injection is performed in the expansion stroke (particularly, in the middle of the expansion stroke or thereafter) (two-stage). Injection means). That is, as described above, when performing the S purge, the two-stage injection is performed, but when the target average effective pressure Pe and the engine rotational speed Ne are in the region A in FIG. 3, the compression stroke is performed. Two-stage injection is performed by injection and expansion stroke injection.
[0029]
The target A / F, that is, the target A / F as a whole of the main injection and the sub-injection, that is, the entire A / F is a predetermined rich air-fuel ratio (a value suitable for S purge, for example, a value 12), and the target air-fuel ratio (main A / F) of the main injection is determined according to the target average effective pressure Pe and the engine speed Ne based on the main injection mode selection map of FIG. At this time, the main A / F is set while the entire 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 appropriately determined while the overall fuel injection amount is maintained constant and the reducing atmosphere is well formed. Is done.
[0030]
Normally, if the target average effective pressure Pe or the engine rotational 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 increase the sub-injection amount while reducing the main injection amount as much as possible while maintaining the entire A / F at the predetermined rich air-fuel ratio as described above. However, there is an upper limit value (for example, value 22) in the air-fuel ratio that can be realized in the intake stroke injection mode. That is, in the intake stroke, combustion is not established at an air-fuel ratio greater than the upper limit value (for example, value 22).
[0031]
Therefore, when the main A / F is larger than the upper limit value (for example, 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 value (for example, value 22). To do.
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 speed are lower. Accordingly, the main A / F has a larger value as the target average effective pressure Pe or the engine rotational speed Ne is smaller, so that the air-fuel ratio becomes a leaner air-fuel ratio side. That is, the lower the catalyst temperature Tcat, the smaller the main injection amount and the larger the sub injection amount.
[0032]
In particular, when the main injection is compression stroke injection in this way, the air-fuel ratio can be diluted to an ultra-lean air-fuel ratio (for example, a range up to the upper limit value 50), and the main injection amount is extremely reduced. On the other hand, a large amount of fuel can be injected by the sub-injection.
As a result, when the engine load and the engine speed are low, a large amount of unburned fuel components are discharged into the exhaust pipe 14 and burned strongly in the exhaust pipe 14 or in the storage type NOx catalyst 30a in the presence of excess oxygen. Thus, even if the catalyst temperature Tcat is low, the storage-type NOx catalyst 30a is rapidly heated to a predetermined high temperature Tcat1 (for example, 650 ° C.) that can be purged with S. Accordingly, even when the engine load and engine speed are small, such as during low-speed running, and the storage-type NOx catalyst 30a is in a low temperature state, 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 exhaust gas temperature increase can be greatly increased without affecting the operation of the engine 1, and the storage-type NOx catalyst 30a can be subjected to the above S purge. It becomes possible to rapidly heat up to the high temperature Tcat1.
[0033]
In the next step S18, 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 S16. 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 it is determined that the determination result is true (Yes) and the predetermined time t2 has elapsed, the process proceeds to step S20.
[0034]
In step S20, the rich air-fuel ratio operation is performed without performing the two-stage injection with the fuel injection mode as 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) in the same manner as the overall A / F. When the rich air-fuel ratio operation is performed in this way, since the fuel is in an excessive state, the fuel causes incomplete combustion and a large amount of CO is discharged. That is, by performing the rich air-fuel ratio operation, a large amount of CO required for reducing and removing SOx is supplied to the storage-type NOx catalyst 30a, and S purge is promoted.
[0035]
In step S22, it is determined whether or not a predetermined time t3 (for example, 2 seconds) has elapsed since the rich air-fuel ratio operation was started in step S20. 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, the process proceeds to step S24.
[0036]
On the other hand, if the determination result 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 (map for the engine rotational speed Ne), that is, the engine load, If the engine speed is relatively high, 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 in the expansion stroke. That is, when the engine load and the engine rotational speed are relatively large, and the target average effective pressure Pe and the engine rotational speed Ne are in the region B in FIG. 3, two-stage injection is performed by the intake stroke injection and the expansion stroke injection. To do.
[0037]
Similarly to the above, the entire A / F is set to a predetermined rich air-fuel ratio (for example, value 12), and the entire A / F is maintained at the predetermined rich air-fuel ratio (for example, value 12). Then, the target air-fuel ratio (main A / F) of the main injection is determined, and the fuel injection ratios of the main injection amount (part) and the sub-injection amount (remainder) are appropriately determined.
Normally, if the engine load and the engine speed are relatively large, the storage-type NOx catalyst 30a is heated to a certain high temperature, up to a predetermined high temperature Tcat1 (for example, 650 ° C.) at which the storage-type NOx catalyst 30a can be purged with S. It can be easily determined that the temperature can be raised. Therefore, in this case, it is preferable to increase the main injection amount in order to keep the entire A / F at a predetermined rich air-fuel ratio while reducing the sub-injection amount. However, there is a lower limit value (for example, value 22) in the air-fuel ratio that can be realized in the compression stroke injection mode. That is, in the compression stroke, contrary to the above case, combustion is not established at an air-fuel ratio that is equal to or lower than the lower limit value (for example, value 22).
[0038]
Therefore, when the air-fuel ratio of the main injection is lower than the lower limit value (for example, value 22), the main injection is performed in the intake stroke in which combustion is established at the air-fuel ratio of the lower limit value (for example, value 22) or lower. To do.
As a result, the fuel injection ratios of the main injection amount (part) and the sub injection amount (remainder) are appropriately adjusted while the overall fuel injection amount is maintained constant and the reducing atmosphere is well formed. Thus, the storage-type NOx catalyst 30a is rapidly heated to a predetermined high temperature Tcat1 (for example, 650 ° C.) that can be S-purged during medium-speed traveling.
[0039]
By the way, when the vehicle is traveling at high speed and the engine rotational 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 close to stoichiometric, that is, the target average effective pressure Pe, the engine When the rotational speed Ne is in the region C in FIG. 3, two-stage injection is difficult due to the restrictions of the injector driver and the like, while the combustion heat is large and the exhaust temperature is sufficiently high. Can be heated to a predetermined high temperature Tcat1 that can be purged with S. Therefore, in this case, instead of the two-stage injection in step S26, only the main injection is performed in the intake stroke, and the temperature rise control is performed by retarding the ignition timing. Even in this case, the entire A / F is set to a predetermined rich air-fuel ratio (for example, value 12).
[0040]
Further, 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, the target average effective pressure Pe and the engine speed Ne are in the D region in FIG. In some cases, it can be determined that the combustion heat is extremely high and the exhaust temperature is high enough to be purged without performing temperature rise control. In this case, step S26 is skipped.
[0041]
In the next step S28, as in step S18, 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 it is determined that the determination result is true (Yes) and the predetermined time t2 has elapsed, the process proceeds to step S30.
[0042]
In step S30, similarly to step S20, the rich air-fuel ratio operation is performed without performing the two-stage injection with the fuel injection mode as the intake stroke injection mode. As a result, a large amount of CO is discharged and S purge is promoted.
In step S32, as in step S22, it is determined whether or not a predetermined time t3 (for example, 2 seconds) has elapsed since the rich air-fuel ratio operation was started 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 it is determined that the determination result is true (Yes) and the predetermined time t3 has elapsed, the process proceeds to step S24.
[0043]
In step S24, it is determined whether or not the storage-type NOx catalyst 30a has reached a high temperature (for example, 650 ° C.) suitable for SOx removal and a predetermined time t4 has elapsed. This predetermined time t4 is a time set in advance by experiments or the like as a time during which SOx can be sufficiently removed when the storage-type NOx catalyst 30a is held at a predetermined high temperature Tcat1 in a reducing atmosphere.
[0044]
If the determination result in step S24 is false (No) and it is determined that the predetermined time t4 has not yet elapsed, the process returns to step S14 and the operation in the S purge mode is continued. In other words, the two-stage injection in step S16 and step S26 and the rich air-fuel ratio operation in step S20 and step S30 are alternately performed repeatedly, and based on the output of the high temperature sensor 16, the storage type NOx catalyst 30a is below a high temperature suitable for SOx removal. Do not become.
[0045]
That is, in the S purge control, the two-stage injection having a large temperature rising effect and the rich air-fuel ratio operation in which a large amount of CO is discharged are alternately repeated by the predetermined time t2 and the predetermined time t3. While removing SOx from the occlusion-type NOx catalyst 30a, the occlusion-type NOx catalyst 30a can be quickly heated to a predetermined high temperature Tcat1 and maintained at a high temperature suitable for SOx removal.
[0046]
On the other hand, if it is determined that the determination result in step S24 is true (Yes), it is considered that SOx has been sufficiently removed, and the routine exits 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 alternately performed in the entire period from the start of the catalyst temperature rise to the SOx removal. However, even if the catalyst temperature Tcat is equal to or lower than the predetermined high temperature Tcat1, the CO is reduced. Since it is purged to some extent depending on the temperature when it is supplied, first, the 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.
[0047]
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, but two steps are performed in steps S16 and S26. It is determined in step S19 and step S29 whether or not the catalyst temperature Tcat has become equal to or higher than a predetermined high temperature Tcat1 after the injection is performed. These determination results are false (No) and the catalyst temperature Tcat is still a predetermined high temperature. As long as Tcat1 has not been reached, the two-stage injection is continuously performed without performing the two-stage injection and the rich air-fuel ratio operation in step S21.
[0048]
When the determination results of step S19 and step S29 are true (Yes), in step S21, while maintaining the catalyst temperature Tcat at a predetermined high temperature Tcat1 based on the output of the high temperature sensor 16 as in the above embodiment, 2 Stage injection and rich air-fuel ratio operation are performed alternately, for example, and the storage-type NOx catalyst 30a is maintained in the SOx removal atmosphere. In step S24, it is determined whether or not the predetermined time t4 has elapsed, and the control in step S21 is continued until the determination result is true (Yes).
[0049]
As a result, although the SOx removal cannot be sufficiently performed in the catalyst temperature raising process as compared with the above-described embodiment, the storage-type NOx catalyst 30a can quickly reach the predetermined high temperature Tcat1 that can reliably remove SOx. .
In the above embodiment, the rich air-fuel ratio operation is performed for a predetermined time t3 (for example, 2 seconds) after the second-stage injection is performed for a predetermined time t2 (for example, 2 seconds). The operation may be performed alternately 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 every time a predetermined number of strokes elapses in each cylinder.
[0050]
Here, both the predetermined time t2 and the predetermined time t3 are set to 2 seconds, for example, but the predetermined time t2 and the predetermined time t3 may be set separately according to the required temperature increase amount and the required CO amount. Good. Furthermore, these may be varied in accordance with operating conditions (target average effective pressure Pe, engine speed Ne, etc.) and catalyst temperature Tcat. As a result, the S purge can be performed more appropriately.
[0051]
Next, Example 2 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 multi-cylinder, a predetermined time, Instead of the predetermined number of strokes, the two-stage injection and the rich air-fuel ratio operation are repeated for each cylinder.
[0052]
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. 2. Hereinafter, the first embodiment will be described based on this flowchart. Only different parts will be described.
In the second embodiment, whether or not the target average effective pressure Pe is smaller than the predetermined value Pe1 is determined in step S14, and if the determination result is determined to be true (Yes), the process proceeds to step S16 ′.
[0053]
In step S16 ′, the rich air-fuel ratio operation is performed in some cylinders, and the two-stage injection is performed in the remaining cylinders. That is, here, the engine 1 is, for example, an in-cylinder injection type spark ignition type in-line four-cylinder gasoline engine, and therefore, rich air-fuel ratio operation is performed in a part of the four cylinders (for example, two cylinders), and the remaining cylinders (for example, Two-stage injection is performed with 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 based on the determination in step S14.
[0054]
When the engine 1 is a V-type gasoline engine, for example, the rich air-fuel ratio operation is performed in each cylinder of one side bank, and the two-stage injection is performed in each cylinder of the other side bank. Good.
On the other hand, if it is determined that the determination result in step S14 is false (No), the process proceeds to step S26 ′.
[0055]
In step S26 ′, as described above, the rich air-fuel ratio operation is performed for some cylinders, and the two-stage injection is performed for the remaining cylinders. In this case, based on the determination in step S14, the case of the first embodiment is also performed. Similarly, the main injection is performed in the intake stroke and the sub-injection is performed in the expansion stroke.
In step S24, it is determined whether or not the SOx removal atmosphere has passed a predetermined time t4.
[0056]
If the determination result in step S24 is false (No) and it is determined that the predetermined time t4 has not yet elapsed, the process returns to step S14. In this case, in step S16 ′ and step S26 ′, in accordance with the output of the high temperature sensor 16, the two-stage injection and the rich are performed so as to maintain the catalyst temperature Tcat at a predetermined high temperature Tcat1 and maintain the storage NOx catalyst 30a in the SOx removal atmosphere. The air-fuel ratio operation is continuously performed for each cylinder.
[0057]
In this way, the two-stage injection having a large temperature rise effect and the rich air-fuel ratio operation in which a large amount of CO is discharged are performed in a balanced manner, and the storage-type NOx catalyst 30a is moved to a predetermined high temperature Tcat1 while performing SOx removal. As a result, the temperature can be satisfactorily increased, and then SOx can be reliably removed.
Therefore, also in the case of the second embodiment, the S purge, that is, the removal of SOx is surely performed while preventing the deterioration of fuel consumption, and the NOx purification efficiency of the storage type NOx catalyst 30a is always kept high. Is possible.
[0058]
In this example, both the part cylinders and the remaining cylinders 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 required temperature increase amount and the required cylinder are set. Depending on the amount of CO, the number of partial cylinders and the number of remaining cylinders may be set to different numbers. Furthermore, these may be varied in accordance with operating conditions (target average effective pressure Pe, engine speed Ne, etc.) and catalyst temperature Tcat. As a result, the S purge can be performed more appropriately.
[0059]
Alternatively, 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 cylinders when the catalyst temperature Tcat is raised to a predetermined high temperature Tcat1. Thus, as described above, the removal of SOx cannot be expected in the process of raising the catalyst temperature until the catalyst reaches the predetermined high temperature Tcat1, but the occlusion-type NOx catalyst 30a is promptly reached to the predetermined high temperature Tcat1 that can reliably remove SOx. It can be reached.
[0060]
By the way, in the above embodiment (Example 1 and Example 2), the entire A / F is set to a predetermined rich air-fuel ratio (for example, value 12) when performing the two-stage injection. This is because the S-purging is performed even a little at the time of injection, and when considering using the two-stage injection only as a means for raising the temperature of the storage-type NOx catalyst 30a, the entire A / F may be stoichiometric or a lean air-fuel ratio. In this way, fuel consumption can be further prevented from deteriorating.
[0061]
Further, the ignition timing may be retarded in the rich air-fuel ratio operation. As a result, a temperature increase effect can be obtained as much as possible not only during the two-stage injection operation but also during the rich air-fuel ratio operation, which is effective when it is desired to increase the temperature of the storage NOx catalyst 30a earlier. is there.
Further, in the present embodiment, the poisoning S amount of the storage type NOx catalyst 30a is estimated and the two-stage injection and the rich air-fuel ratio operation are performed alternately or for each cylinder. 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 poison S amount.
[0062]
【The invention's effect】
As described above in detail, according to the in-cylinder injection internal combustion engine of claim 1 of the present invention, it is possible to achieve both the temperature increase of these occlusion-type NOx catalysts necessary for the removal of sulfur components and the generation of a reducing atmosphere. Thus, the temperature of the storage-type NOx catalyst can be increased efficiently and reliably, and CO can be sufficiently supplied to ensure a reducing atmosphere.
[0063]
Therefore, the SOx stored in the storage type NOx catalyst can be surely removed without deteriorating the fuel consumption, and the NOx purification efficiency of the storage type NOx catalyst can always be 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 showing 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.
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]
1 Engine (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 NOx storage catalyst
40 Electronic Control Unit (ECU)

Claims (1)

An NOx storage catalyst that is provided in the exhaust passage and stores NOx in the exhaust when the internal combustion engine is in a lean air-fuel ratio operation state, and reduces the stored NOx when in a stoichiometric air-fuel ratio operation or rich air-fuel ratio operation state When,
Two-stage injection means for injecting part of the fuel as main injection in one of the compression stroke and the intake stroke and the remaining portion as sub-injection in the expansion stroke, and the air-fuel ratio to be a rich air-fuel ratio in the intake stroke Rich air-fuel ratio operation means for injecting fuel;
When removing the sulfur component from the storage-type NOx catalyst, the sulfur component removing unit that performs the two-stage injection unit and the rich air-fuel ratio operation unit alternately or for each cylinder;
A cylinder injection type internal combustion engine characterized by comprising:

Images