JP3952109B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification apparatus for an internal combustion engine. More specifically, the present invention relates to hydrogen sulfide (H generated by desorption of sulfur components in exhaust gas stored on a catalyst. ₂ The present invention relates to a technique for preventing release of S) into the atmosphere.
[0002]
[Related background]
Generally, fuel contains an S (sulfur) component (sulfur component), which reacts with oxygen to form SOx (sulfur oxide), which is, for example, sulfate X-SO. _Four As a catalyst converter (three-way catalyst, NOx catalyst, etc., hereinafter abbreviated as catalyst) (S poisoning). The SOx occluded in the catalyst as described above is, as disclosed in JP-A-7-217474, etc., the catalyst is at a predetermined high temperature and the exhaust air-fuel ratio is rich (a reducing atmosphere in which the oxygen concentration is reduced). Sulfur dioxide (SO ₂ ) And released (S purge).
[0003]
By the way, if the amount of stored SOx is large and the richness of the rich air-fuel ratio is large, the released SOx ₂ Part of and H ₂ Chemical reaction with reducing substances such as hydrogen sulfide (H ₂ S) is generated and SO ₂ Together with the H ₂ S is also discharged into the atmosphere. However, as is well known, H ₂ S has the characteristic of giving off a strange odor, and the H ₂ It has been a problem to suppress the discharge of S.
[0004]
Therefore, for example, as disclosed in Japanese Patent Application Laid-Open No. 8-294618, H is provided downstream of the upstream catalyst provided in the exhaust passage. ₂ When a downstream catalyst containing an S trap agent is disposed and the S component (sulfur component) storage amount of the upstream catalyst reaches a set value, O ₂ The air / fuel ratio is alternately changed between the rich region and the lean region (air / fuel ratio perturbation) based on the stoichiometric air / fuel ratio based on the sensor output. ₂ Reduced to S and the H ₂ S was captured by the downstream catalyst, and the captured H in the lean region ₂ S is oxidized to H ₂ Techniques for suppressing the release of S into the atmosphere have been proposed.
[0005]
[Problems to be solved by the invention]
However, in the technique disclosed in the above publication, O ₂ Desorption of S component and H by air-fuel ratio perturbation based on the theoretical air-fuel ratio based on sensor output ₂ Because it is an oxidation of S, H only in a specific operating range ₂ S release cannot be suppressed.
[0006]
That is, according to the technique disclosed in the above publication, for example, in an engine operating state where the catalyst temperature is equal to or higher than a predetermined temperature and the exhaust air-fuel ratio is a rich air-fuel ratio, the S component is desorbed from the catalyst and H ₂ S is generated, but because there is a concern about a decrease in output, air-fuel ratio perturbation based on the theoretical air-fuel ratio cannot be performed, that is, H ₂ S that cannot be oxidized and produced H ₂ S will continue to be captured by the downstream catalyst.
[0007]
Therefore, H more than the capture capacity of the downstream catalyst. ₂ If S is generated, overflow H ₂ S is released into the atmosphere and the released H ₂ S is not preferable because it also gives off a strange odor.
In the case of this technology, H ₂ There is a problem that a special catalyst containing a trapping agent for capturing S must be used, leading to high costs.
[0008]
The present invention has been made in order to solve such problems, and the object of the present invention is to ensure H in a wide operating range without incurring high costs. ₂ An object of the present invention is to provide an exhaust purification device for an internal combustion engine capable of suppressing the release of S into the atmosphere.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, there is provided an exhaust purification device for an internal combustion engine having an injection valve capable of directly injecting fuel into a cylinder, wherein the exhaust air-fuel ratio becomes a lean air-fuel ratio. It has an oxygen storage function downstream of the first catalyst that stores the sulfur component in the exhaust in one operating state and releases the stored sulfur component in the second operating state in which the exhaust air-fuel ratio becomes a high temperature and the exhaust air-fuel ratio becomes rich. A second catalyst is provided, and further intermittently during the second operating state. While ensuring that the exhaust air / fuel ratio becomes a lean air / fuel ratio as a whole In the intake stroke or compression stroke Fuel In the expansion stroke while performing the main injection Fuel An operating state changing means for performing the sub-injection is provided.
[0010]
For example, in the second operating state, the stored sulfur component is released and simultaneously H ₂ S may be generated, but at this time, intermittently While ensuring that the exhaust air / fuel ratio becomes a lean air / fuel ratio as a whole The main injection is performed in the intake stroke or the compression stroke, and the sub-injection is performed in the expansion stroke, and surplus oxygen is supplied to the second catalyst provided downstream while increasing the temperature of the first catalyst by increasing the temperature of the exhaust gas. It is stored as appropriate and H is stored by the stored oxygen. ₂ S is oxidized well. This reliably prevents the exhaust gas from giving off a bad odor.
[0011]
Preferably, the second operation is performed when the sulfur component occluded in the first catalyst reaches a predetermined amount, and intermittently by the operation state changing means in accordance with this. Main injection is performed in the intake stroke or compression stroke, and sub-injection is performed in the expansion stroke Should be implemented. In this case, SOx is released at once and a large amount of H ₂ S is produced, but since the second catalyst is intermittently replenished with oxygen and constantly stored, H ₂ Even when a large amount of S is generated, H ₂ S is reliably oxidized and brominated without oxygen.
[0012]
Preferably, the operation state changing means periodically performs the main injection in the intake stroke or the compression stroke and performs the sub-injection in the expansion stroke in the second operation state. No. 2 catalyst continues to be stored without deficiency, ₂ S is more reliably oxidized and non-brominated.
According to a second aspect of the present invention, the operating state changing means is configured to perform a compression stroke when the load of the internal combustion engine is smaller than a predetermined value. Fuel In the expansion stroke while performing the main injection Fuel When sub-injection is performed and the load on the internal combustion engine is greater than the predetermined value, the intake stroke Fuel In the expansion stroke while performing the main injection Fuel Sub-injection is performed.
That is, the fuel injection mode is appropriately set according to the load of the internal combustion engine.
According to a third aspect of the present invention, the internal combustion engine is a multi-cylinder internal combustion engine, and the operating state changing means is partially in the second operating state. While injecting fuel so that the exhaust air-fuel ratio becomes a rich air-fuel ratio in the cylinder, On the cylinder Oh And While ensuring that the exhaust air / fuel ratio becomes a lean air / fuel ratio as a whole In the intake stroke or compression stroke Fuel In the expansion stroke while performing the main injection Fuel Sub-injection is performed.
That is, some While injecting fuel so that the exhaust air-fuel ratio becomes a rich air-fuel ratio in the cylinder, On the cylinder Oh And While ensuring that the exhaust air / fuel ratio becomes a lean air / fuel ratio as a whole The main injection is performed in the intake stroke or the compression stroke, and the sub-injection is performed in the expansion stroke. As in the case of claim 1, surplus oxygen is provided downstream while increasing the temperature of the first catalyst by increasing the temperature of the exhaust gas. Supplied to the second catalyst and appropriately stored, and the stored oxygen causes H ₂ S is oxidized well. This reliably prevents the exhaust gas from giving off a bad odor.
[0013]
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 an exhaust gas purification apparatus for an internal combustion engine according to the present invention mounted on a vehicle, and the configuration of the exhaust gas purification apparatus according to the present invention will be described based on the same figure.
[0014]
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.
[0015]
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.
[0016]
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.
[0017]
Further, 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 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.
[0018]
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.
[0019]
The exhaust purification catalyst device 30 includes two catalysts, a storage type NOx catalyst (first catalyst) 30a and a three-way catalyst (second catalyst) 30b, and the three-way catalyst 30b stores more. It is arranged downstream of the type NOx catalyst 30a.
The occlusion-type NOx catalyst 30a temporarily converts NOx into nitrate X-NO in an oxidizing atmosphere. _Three In the 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 the storage material is an alkali metal such as barium (Ba) or an alkaline earth metal. It has been adopted.
[0020]
By the way, the storage type NOx catalyst 30a includes not only NOx but also an oxide of S (sulfur) component (sulfur component) in the fuel contained in the exhaust gas, that is, SOx, as described above, sulfate X-SO. _Four As occluded. And the sulfate X-SO _Four Is nitrate X-NO _Three As described above, the NOx storage catalyst 30a needs to have a predetermined high temperature and a reducing atmosphere in order to reduce and remove the salt.
[0021]
The three-way catalyst 30b is a commonly used three-way catalyst, and has a function of storing oxygen therein as a general characteristic. In addition, it is preferable that ceria (Ce) is added as an additive to the three-way catalyst 30b, so that the oxygen storage capacity is higher.
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.
[0022]
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 exhaust gas purification apparatus for an internal combustion engine according to the present invention including 1 is performed. Various sensors such as the throttle sensor 11a, the crank angle sensor 13, and the high temperature sensor 16 described above are connected to the input side of the ECU 40, and detection information from these sensors is input.
[0023]
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.
[0024]
Incidentally, 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. The intake stroke injection mode includes an intake lean mode that is a lean air-fuel ratio, a stoichiometric feedback mode that is a stoichiometric air-fuel ratio, and an open loop mode that is a rich air-fuel ratio.
[0025]
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.
[0026]
The operation of the exhaust gas purification apparatus for an internal combustion engine according to the present invention configured as described above will be described below. That is, as described above, the storage-type NOx catalyst 30a mainly stores SOx during the lean air-fuel ratio operation (first operation state) (the air-fuel ratio region in which SOx is stored differs depending on the catalyst characteristics). When removing, that is, when purging S ₂ S is generated. Here, the control procedure of the S purge control will be described and the H according to the present invention will be described. ₂ The S bromide-free method will be described.
[0027]
Referring to FIG. 2, there is shown a flowchart of an S purge control routine, which will be described along the flowchart.
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.
[0028]
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).
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 released S amount per execution cycle.
[0029]
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 released S amount Rs per execution cycle from the integrated value. It is done.
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.
[0030]
K = K1, K2, K3 (2)
Further, the released S amount Rs per execution cycle is calculated from the following equation (3).
Rs = α ・ R1 ・ R2 ・ dT (3)
Here, α is the release rate (set value) per unit time, dT indicates the execution cycle of the fuel injection control routine, and R1 and R2 are the discharge capacity coefficient and air-fuel ratio A corresponding to the catalyst temperature Tcat, respectively. The release capacity coefficient according to / F is shown.
[0031]
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.
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. Thereby, removal of SOx stored in the storage type NOx catalyst 30a, that is, S purge is started (second operation state).
[0032]
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.
[0033]
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 rich air-fuel ratio operation is performed with the fuel injection mode as the intake stroke injection mode.
[0034]
In order to perform the S purge, it is necessary to make the storage-type NOx catalyst 30 in the reducing atmosphere as described above. Here, first, the rich air-fuel ratio operation is performed so that the exhaust air-fuel ratio becomes the rich air-fuel ratio. . In this case, the target A / F is set to a predetermined rich air-fuel ratio (for example, value 12).
As a result, incomplete combustion occurs in an excessive fuel state, and a large amount of CO (carbon monoxide) and HC (hydrocarbon) (reducing agent) necessary for the reduction and removal of SOx is generated in the storage-type NOx catalyst 30a. This will promote S purge.
[0035]
By the way, when the S purge is promoted in this way and the reduction of SOx proceeds, under high temperature and a rich air-fuel ratio, a strange odor is emitted at the same time. ₂ S is generated. However, H generated in this way ₂ Since the three-way catalyst 30b provided downstream of the storage-type NOx catalyst 30a has an oxygen storage capacity as described above, S is satisfactorily oxidized and non-brominated by the stored oxygen. This suitably prevents the exhaust gas from giving off an odor.
[0036]
In step S18, it is determined whether or not a predetermined time t1 (for example, 2 seconds) has elapsed since the rich air-fuel ratio operation was started in step S16. If the determination result is false (No) and it is determined that the predetermined time t1 has not yet elapsed, the rich air-fuel ratio operation is continued until the predetermined time t1 has elapsed. On the other hand, if it is determined that the determination result is true (Yes) and the predetermined time t1 has elapsed, the process proceeds to step S20.
[0037]
In step S20, 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). Injection is performed (operating state changing means).
In order to perform the S purge, as described above, it is necessary to raise the storage-type NOx catalyst 30 to a predetermined high temperature along with the execution of the rich air-fuel ratio operation. Here, in order to increase the temperature of the storage-type NOx catalyst 30, two stages are required. Perform the injection. That is, the temperature of exhaust gas is raised by burning unburned fuel components (unburned HC, etc.) by sub-injection in the exhaust pipe 14 or in the proximity three-way catalyst 20, thereby raising the temperature of the storage NOx catalyst 30. To. When the target average effective pressure Pe and the engine rotational 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.
[0038]
Normally, if the target average effective pressure Pe or the engine 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 overall A / F at the predetermined 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).
[0039]
Therefore, when the target air-fuel ratio (main A / F) of main injection becomes larger than the upper limit value (for example, value 22), combustion is established at an air-fuel ratio larger than the upper limit value (for example, value 22). The main injection is performed during the compression stroke.
Further, it can be considered that the temperature of the storage-type 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.
[0040]
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 are exhausted by powerful combustion in the exhaust pipe 14 or the adjacent three-way catalyst 20 in the presence of oxygen. Therefore, even if the catalyst temperature Tcat is low, the storage-type NOx catalyst 30a rapidly rises to a predetermined high temperature Tcat1 (for example, 650 ° C.) that can be purged with S.
[0041]
Incidentally, at this time, the overall target A / F of the main injection and the sub-injection, that is, the overall A / F is set to a predetermined lean air-fuel ratio (for example, value 15). That is, in step S20, unlike the case of step S16, the target A / F, that is, the overall A / F is set to a lean air-fuel ratio (first operation). Then, with the overall A / F maintained at the predetermined lean air-fuel ratio (for example, value 15), the main A / F is based on the target average effective pressure Pe and the engine speed based on the main injection mode selection map of FIG. It is determined according to the speed Ne, and the fuel injection ratios of the main injection amount and the sub injection amount are appropriately determined.
[0042]
When the entire A / F is set to the lean air-fuel ratio in this manner, oxygen is excessive as a whole during the two-stage injection, so that the exhaust gas contains excess oxygen. The surplus oxygen discharged as exhaust gas in this way is the above-mentioned H because the three-way catalyst 30b has an oxygen storage capacity as described above. ₂ The three-way catalyst 30b is well stored so as to make up for the amount corresponding to the reduced oxygen used for the oxidation of S.
[0043]
In other words, in step S20, the temperature of the storage NOx catalyst 30 is raised by performing two-stage injection, and at the same time, the lean air-fuel ratio operation is performed. ₂ The oxygen in the reduced three-way catalyst 30b used for the oxidation of S is replenished.
In the next step S22, 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 S20. 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 S24.
[0044]
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, as in step S16, the rich air-fuel ratio operation is performed with the fuel injection mode as the intake stroke injection mode. As a result, a large amount of CO and HC (reducing agent) is discharged, and S purge is promoted.
[0045]
At this time, as described above, H ₂ S will occur, but the H ₂ As described above, S is satisfactorily oxidized and non-brominated by oxygen stored in the three-way catalyst 30b. This suitably prevents the exhaust gas from giving off an odor.
In step S28, as in step S18, it is determined whether or not a predetermined time t1 (for example, 2 seconds) has elapsed since the rich air-fuel ratio operation was started in step S26. If the determination result is false (No) and it is determined that the predetermined time t1 has not yet elapsed, the rich air-fuel ratio operation is continued until the predetermined time t1 has elapsed. On the other hand, if it is determined that the determination result is true (Yes) and the predetermined time t1 has elapsed, the process proceeds to step S30.
[0046]
In step S30, the fuel injection mode of the main injection is set to the intake stroke injection mode regardless of the above-described normal setting, 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. (Operating state changing means).
[0047]
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).
[0048]
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 occlusion-type NOx catalyst 30a is rapidly heated to a predetermined high temperature Tcat1 (for example, 650 ° C.) at which S purge can be performed during medium speed running.
[0049]
At this time, as in the case of step S20, the overall target A / F of the main injection and the sub-injection, that is, the overall A / F is set to a predetermined lean air-fuel ratio (for example, value 15). . That is, also in step S30, unlike the case of step S26, the target A / F, that is, the overall A / F is set to the lean air-fuel ratio (first operation). Then, with the overall A / F maintained at the predetermined lean air-fuel ratio (for example, value 15), the main A / F is based on the target average effective pressure Pe and the engine speed based on the main injection mode selection map of FIG. It is determined according to the speed Ne, and the fuel injection ratios of the main injection amount and the sub injection amount are appropriately determined.
[0050]
As a result, the above H ₂ The three-way catalyst 30b stores oxygen well so as to make up for the amount corresponding to the reduced oxygen used for the oxidation of S.
That is, in step S30 as well, in the same manner as in step S20, the NOx catalyst 30 is heated by performing two-stage injection, and at the same time, the lean air-fuel ratio operation is performed. ₂ The oxygen in the reduced three-way catalyst 30b used for the oxidation of S is replenished.
[0051]
In the next step S32, as in step S22, 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 S30. 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 S24.
[0052]
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 t3 has elapsed. This predetermined time t3 is a time set in advance by experiment 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.
[0053]
If the determination result in step S24 is false (No) and it is determined that the predetermined time t3 has not yet elapsed, the process returns to step S14 and the operation in the S purge mode is continued. That is, the rich air-fuel ratio operation in step S16 and step S26 and the two-stage injection in step S20 and step S30, that is, the lean air-fuel ratio operation are alternately repeated, so that the storage type NOx catalyst 30a has a predetermined high temperature suitable for SOx removal. The S purge is continued while the catalyst temperature feedback control is performed so that it does not fall below Tcat1. In the catalyst temperature feedback control, in order to maintain a predetermined high temperature Tcat1, H H is based on information from the high temperature sensor 16. ₂ The main A / F and the ignition timing are changed within a range that does not affect the oxidation treatment of S. In this case, the sub-injection amount of the two-stage injection may be adjusted, and the predetermined time t2 may be changed.
[0054]
As a result, the rich NO.sub.x catalyst 30a can be efficiently supplied to the predetermined high temperature Tcat1 by alternately repeating the rich air-fuel ratio operation in which a large amount of CO is discharged and the two-stage injection having a large temperature rise effect by the predetermined time t1 and the predetermined time t2. The temperature can be raised, SOx can be removed, and further, oxygen can always be stored in the three-way catalyst 30b by performing the two-stage injection so that the entire A / F becomes the lean air-fuel ratio. Therefore, H generated during the execution of S purge ₂ It is possible to oxidize S almost completely and reliably and to make it non-brominated.
[0055]
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.
Actually, an air bypass valve or a drive-by-wire type (not shown) is used so that the output torque is equal between the rich air-fuel ratio operation (steps S16 and S26) and the two-stage injection (steps S20 and S30). The throttle valve adjusts the intake air amount and the ignition timing.
[0056]
Further, here, whether or not SOx has been sufficiently removed is determined based on whether or not the predetermined time t3 has elapsed. However, the poisoning S amount Qs is calculated from the above equation (1) to obtain the poisoning S. You may make it discriminate | determine by whether the quantity Qs became below predetermined value.
Although not shown in FIG. 2, the vehicle is traveling at a high speed, 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 is close to stoichiometric. In other words, that is, when the determination result in step S14 is false (No), and the target average effective pressure Pe and the engine rotational speed Ne are in the region C in FIG. 3, it is difficult to perform the two-stage injection due to the restriction of the injector driver or the like. On the other hand, it can be determined that the combustion heat is large and the exhaust temperature is sufficiently high, so that the storage-type NOx catalyst 30a can be heated to a predetermined high temperature Tcat1 that can be S purged only by the ignition timing retard. Therefore, in this case, the rich air-fuel ratio operation is performed in step S26, and in step S30, only the main injection is performed in the intake stroke instead of the two-stage injection, and the exhaust gas temperature is increased by retarding the ignition timing. To do. Also in this case, the entire A / F is set to a predetermined lean air-fuel ratio (for example, value 15) (first operation), and surplus oxygen is well supplemented and stored in the three-way catalyst 30b. After all H ₂ S is reliably oxidized and non-brominated.
[0057]
Similarly, when the engine speed Ne and the target average effective pressure Pe are extremely large and the main A / F is a rich air-fuel ratio, that is, the determination result of step S14 is false (No) and the target When the average effective pressure Pe and the engine rotational speed Ne are in the region D in FIG. 3, it can be determined that the combustion heat is extremely high and the exhaust temperature is high enough to allow S purge even without performing the temperature rise control. Therefore, in this case, the rich air-fuel ratio operation is performed in step S26, and only the main injection is performed in the intake stroke instead of the two-stage injection in step S30. In this case as well, the entire A / F is set to a predetermined lean air-fuel ratio (for example, value 15) (first operation), and surplus oxygen is well supplemented and stored in the three-way catalyst 30b. After all H ₂ S is reliably oxidized and non-brominated.
[0058]
In the first embodiment, after the rich air-fuel ratio operation is performed for a predetermined time t1 (for example, 2 seconds), the two-stage injection (lean air-fuel ratio operation) is performed for the predetermined time t1 (for example, 2 seconds). The rich air-fuel ratio operation and the two-stage injection (lean air-fuel ratio operation) may be performed alternately every predetermined number of strokes (one or more strokes). That is, the rich air-fuel ratio operation and the two-stage injection may be repeated every time a predetermined number of strokes elapses in each cylinder.
[0059]
Here, the predetermined time t1 and the predetermined time t2 are both set to 2 seconds, for example. However, the predetermined time t1 and the predetermined time t2 are set in consideration of the balance between the required temperature increase amount, the required CO amount, and the required oxygen amount. Each may be set separately. 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, and the H ₂ S can be more reliably oxidized and non-brominated.
[0060]
Next, Example 2 will be described.
In the first embodiment, the rich air-fuel ratio operation and the two-stage injection (lean air-fuel ratio operation) are switched every predetermined time or every predetermined number of strokes. However, in the second embodiment, the engine 1 has multiple cylinders. In this case, the rich air-fuel ratio operation and the two-stage injection (lean air-fuel ratio operation) are repeated for each cylinder instead of the predetermined number of strokes for a predetermined time.
[0061]
Referring to FIG. 4, a part of a flowchart showing an S purge control routine according to the second embodiment following the flowchart of FIG. 2 is shown. Only parts different from the first embodiment will be described based on this flowchart.
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 ′.
[0062]
In step S16 ′, a rich air-fuel ratio operation is performed with some cylinders. In step S20 ′, the remaining cylinder performs two-stage injection (lean air-fuel ratio operation) (first operation). 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 (lean air-fuel ratio operation) is performed. 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.
[0063]
It should be noted that the rich air-fuel ratio operation and the two-stage injection are preferably performed alternately and evenly. 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 side bank. The two-stage injection may be performed in each cylinder of the other one-side bank.
On the other hand, if it is determined that the determination result in step S14 is false (No), the process proceeds to step S26 ′.
[0064]
In step S26 ′, the rich air-fuel ratio operation is performed with some cylinders as described above. In step S30 ′, the remaining cylinder performs two-stage injection (lean air-fuel ratio operation) (first operation). In this case, for the two-stage injection, the main injection is performed in the intake stroke and the sub-injection is performed in the expansion stroke based on the determination in step S14.
[0065]
In step S24, it is determined whether or not the storage-type NOx catalyst 30a has reached a high temperature suitable for SOx removal (for example, 650 ° C.) and a predetermined time t3 has elapsed. Also in this case, the poisoned S amount Qs is obtained from the above equation (1), and it is determined whether or not SOx is sufficiently removed depending on whether or not the poisoned S amount Qs has become a predetermined value or less. Good.
[0066]
If the determination result in step S24 is false (No) and it is determined that the predetermined time t3 has not yet elapsed, the process returns to step S14. As a result, in step S16 ′ and step S20 ′ or step S26 ′ and step S30 ′, the catalyst temperature Tcat is maintained at a predetermined high temperature Tcat1 by catalyst temperature feedback control, and the storage type NOx catalyst 30a is rich so as to maintain the SOx removal atmosphere. The air-fuel ratio operation and the two-stage injection (lean air-fuel ratio operation) are continuously performed for each cylinder.
[0067]
In this way, the rich air-fuel ratio operation in which a large amount of CO and HC are discharged and the two-stage injection with a large temperature rise effect are carried out in a well-balanced manner. It is possible to raise the temperature well to the high temperature Tcat1, and it is possible to surely remove SOx, and furthermore, by performing the two-stage injection so that the entire A / F becomes the lean air-fuel ratio, the S purge is performed. H generated ₂ As in the case of Example 1 above, S can be oxidized almost completely and reliably without any bromination.
[0068]
Note that, here, for example, two cylinders are used for both the partial cylinder and the remaining cylinder. However, as in the case where the predetermined time t1 and the predetermined time t2 are set separately in the first embodiment, the necessary temperature increase amount and the necessary cylinder are set. The number of partial cylinders and the number of remaining cylinders may be set to different numbers of cylinders in consideration of the balance between the CO amount and the necessary oxygen amount. 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, S purge can be performed more appropriately, and H ₂ S can be more reliably oxidized and non-brominated.
[0069]
Further, in the rich air-fuel ratio operation, the ignition timing may be retarded, so that the temperature raising effect can be obtained not only during the two-stage injection operation but also during the rich air-fuel ratio operation.
By the way, in the above embodiment, the two-stage injection is performed in step S20 and step S30 as the exhaust gas temperature raising control, but instead of the two-stage injection, the entire A / F is set to a predetermined lean air-fuel ratio (for example, value 15). However, the ignition timing may be retarded as the exhaust gas temperature raising control. Even in this case, H ₂ S is reliably oxidized and non-brominated.
[0070]
In the above embodiment, the rich air-fuel ratio operation (steps S16, S26, S16 ′, S26 ′) is first performed, and then the lean air-fuel ratio operation (steps S20, S30, S20 ′, S30 ′) by two-stage injection is performed. On the contrary, firstly, the lean air-fuel ratio operation is performed after the lean air-fuel ratio operation by the two-stage injection, and the subsequent operation is repeated. Also good.
[0071]
In the above embodiment, the three-way catalyst 30b is disposed downstream of the storage-type NOx catalyst 30a, and the proximity three-way catalyst 20 is disposed upstream of the storage-type NOx catalyst 30a. An S (sulfur) trap capable of storing SOx and releasing it in a reducing atmosphere may be disposed upstream of the NOx storage catalyst (which may be a selective reduction NOx catalyst).
[0072]
In this case, the NOx catalyst and the three-way catalyst may be individually arranged in order downstream of the S trap, or the NOx catalyst may be a NOx catalyst with a three-way catalyst and no separate three-way catalyst may be provided. . Further, instead of the S trap, a two-layer trap having both the S trap function and the NOx catalyst function may be provided, and a three-way catalyst may be provided downstream of the two-layer trap.
[0073]
Further, the present invention can be carried out satisfactorily even if the proximity three-way catalyst 20 is omitted.
Further, in the above embodiment, it is determined whether or not the poisoning S amount Qs of the storage NOx catalyst 30a has reached a predetermined amount. If the poisoning S amount Qs exceeds a predetermined amount, the S purge of the storage NOx catalyst 30a is performed. However, in practice, the occlusion-type NOx catalyst 30a naturally becomes hot during high-load operation or the like, and the exhaust air-fuel ratio is a rich air-fuel ratio even during normal driving. Even in such a case, the first operation in which the exhaust air-fuel ratio becomes the lean air-fuel ratio is intermittently performed to perform H purge. ₂ S discharge can be suppressed.
[0074]
Specifically, when the storage NOx catalyst 30a reaches a predetermined high temperature Tcat1 and the target A / F reaches a predetermined rich air-fuel ratio (for example, value 12) regardless of the poisoning S amount Qs, the lean as described above. The air-fuel ratio operation may be performed periodically. This ensures that H is always good when S purge is performed. ₂ S is oxidized and not brominated. In this case, the entire A / F during the lean air-fuel ratio operation is a predetermined lean air-fuel ratio (for example, about 15) near the stoichio and the lean air-fuel ratio operation is a short time. Even if it exists, the output torque fall hardly occurs.
[0075]
【The invention's effect】
As explained in detail above, claim 1 of the present invention. Thru 3 According to the exhaust gas purification apparatus for an internal combustion engine of the present invention, the H in a wide operating range without incurring high costs. ₂ It is possible to satisfactorily prevent the exhaust gas from giving off a bad odor by oxidizing S satisfactorily.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an exhaust gas purification apparatus for an internal combustion engine according to the present invention.
FIG. 2 is a flowchart showing a control routine of the exhaust gas purification apparatus for an 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 control routine of an exhaust gas purification apparatus for an internal combustion engine according to a second embodiment.
[Explanation of symbols]
1 engine (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 type catalyst (first catalyst)
30b Three-way catalyst (second catalyst)
40 Electronic Control Unit (ECU)

Claims (3)

An exhaust purification device for an internal combustion engine having an injection valve capable of directly injecting fuel into a cylinder,
The sulfur component stored in the exhaust passage is stored in the second operation state, which is provided in the exhaust passage and occludes the sulfur component in the exhaust in the first operation state where the exhaust air-fuel ratio becomes a lean air-fuel ratio, and the exhaust air-fuel ratio becomes a rich air-fuel ratio A first catalyst that releases
A second catalyst provided downstream of the first catalyst in the exhaust passage and having an oxygen storage function;
In the second operating state, an operating state in which the main injection of the fuel is performed in the intake stroke or the compression stroke and the sub-injection of the fuel is performed in the expansion stroke while the exhaust air-fuel ratio becomes the entire lean air-fuel ratio intermittently. Change means,
An exhaust emission control device for an internal combustion engine, comprising: The operating state changing means performs main injection of fuel during the compression stroke and sub-injection of fuel during the expansion stroke when the load of the internal combustion engine is smaller than a predetermined value, and when the load of the internal combustion engine is larger than the predetermined value. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the main injection of fuel is performed in the intake stroke and the sub-injection of fuel is performed in the expansion stroke. The internal combustion engine is a multi-cylinder internal combustion engine,
The operating state changing means, when the second operating condition, whereas the air-fuel ratio of exhaust gas in the partial-cylinder injects fuel so that a rich air-fuel ratio, the lean air-fuel ratio in the entire exhaust air-fuel ratio have you to balance the cylinders 2. An exhaust emission control device for an internal combustion engine according to claim 1, wherein the main injection of the fuel is performed in the intake stroke or the compression stroke while the sub injection of the fuel is performed in the expansion stroke.

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