JP4635853B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine. More specifically, in an internal combustion engine having a plurality of cylinder groups, an internal combustion engine that performs sulfur poisoning recovery control that removes sulfur components stored in a lean NOx catalyst in which exhaust passages of each cylinder group are connected together is connected. The present invention relates to a control device.

  Conventionally, Japanese Patent Laid-Open No. 2000-337137 discloses an internal combustion engine having a plurality of banks (cylinder group) and a lean NOx catalyst (rear three-way catalyst) installed in an exhaust passage that collects exhaust gas from the plurality of banks. The agency is disclosed. In this internal combustion engine, the lean NOx catalyst stores NOx in the exhaust gas when the internal combustion engine is operated at a lean air-fuel ratio, and releases and reduces the stored NOx when it is operated at a stoichiometric or rich air-fuel ratio. Has an effect. However, the lean NOx catalyst may occlude NOx and occlude sulfur components contained in the fuel. When the sulfur component occluded in the lean NOx catalyst increases, there may be a problem that the purification rate of the lean NOx catalyst decreases. For this reason, it is necessary to perform sulfur poisoning recovery control for removing the sulfur component occluded in the lean NOx catalyst before the purification rate of the lean NOx catalyst falls below the allowable range.

  The sulfur component stored in the lean NOx catalyst is removed by increasing the temperature of the lean NOx catalyst and controlling the air-fuel ratio to rich or stoichiometric. In the above prior art, during the sulfur poisoning recovery control, the temperature of the lean NOx catalyst is raised to a temperature at which sulfur components can be removed (hereinafter referred to as “sulfur desorption temperature”). Control is performed so that the air-fuel ratio of the other banks becomes lean, and the exhaust gas flowing into the lean NOx catalyst is controlled so that it becomes the stoichiometric air-fuel ratio. As a result, surplus unburned fuel components and oxygen that do not contribute to the catalytic reaction flow out from the front three-way catalyst upstream of the lean NOx catalyst, and these flow into the lean NOx catalyst. As a result, in the lean NOx catalyst, the reaction between unburned fuel and oxygen is promoted, and the catalyst temperature rises. At this time, the entire exhaust gas flowing into the lean NOx catalyst is controlled in the vicinity of the stoichiometric air-fuel ratio. Therefore, according to the above sulfur poisoning recovery control of the prior art, by controlling each bank to rich or lean air-fuel ratio, the catalyst temperature is raised to the sulfur desorption temperature, and the sulfur component is efficiently reduced under the stoichiometric air-fuel ratio. , That can be released.

JP 2000-337137 A JP 2003-120365 A JP 11-351048 A

  However, the exhaust temperature discharged from the bank controlled to a lean air-fuel ratio is particularly low, and the exhaust temperature downstream of the three-way catalyst is low due to exhaust purification by the three-way catalyst. Accordingly, the temperature of the exhaust gas flowing into the lean NOx catalyst becomes low. Under such circumstances, it takes a long time to raise the lean NOx catalyst to the sulfur desorption temperature by the reaction between unburned fuel and oxygen. On the other hand, during the sulfur poisoning recovery control in the above-described prior art, the exhaust gas from each bank is controlled to a rich or lean air-fuel ratio, so that the purification rate of the front three-way catalyst decreases. Therefore, purification of exhaust gas during sulfur poisoning recovery control depends mainly on purification by a lean NOx catalyst. Therefore, taking a long time for sulfur poisoning recovery control is not preferable from the viewpoint of improving the purification rate and reducing emissions.

  Accordingly, the present invention provides an internal combustion engine control device improved so as to shorten the temperature raising time of the lean NOx catalyst during the sulfur poisoning recovery control of the lean NOx catalyst.

In order to achieve the above object, a first invention is an internal combustion engine that controls an internal combustion engine that includes two or more cylinder groups and a lean NOx catalyst in which exhaust passages connected to each of the cylinder groups are connected together. An engine control device,
Sulfur component removal control means for controlling the internal combustion engine to remove the sulfur component stored in the lean NOx catalyst;
Prior to the removal of the sulfur component, the catalyst temperature increase control means for controlling the internal combustion engine to increase the temperature of the lean NOx catalyst,
The sulfur component removal control means includes
When removing the sulfur component stored in the lean NOx catalyst, the control target value of the air-fuel ratio of any one of the cylinder groups is set to be richer than the theoretical air-fuel ratio, and the other cylinder groups A rich / lean air-fuel ratio setting means for setting the control target value of the air-fuel ratio to be leaner than the theoretical air-fuel ratio;
The catalyst temperature raising control means includes ignition timing retarding means for retarding the ignition timing of each cylinder of the cylinder group.

In a second aspect based on the first aspect, the catalyst temperature increase control means comprises:
An opening degree estimating means for estimating the opening degree of the throttle valve when the sulfur component is removed by the sulfur component removal control means;
An opening degree control means for controlling the opening degree of the throttle valve according to the estimated opening degree of the throttle valve;
It is characterized by providing.

In a third aspect based on the second aspect, the catalyst temperature increase control means includes torque estimation means for estimating a generated torque when the sulfur component removal control means removes the sulfur component,
The ignition timing retarding means retards the ignition timing according to the estimated torque.

According to a fourth invention, in any one of the first to third inventions, the internal combustion engine includes an in-cylinder injector disposed in each cylinder of the cylinder group and injecting fuel into the cylinder, respectively.
The catalyst temperature increase control means includes fuel injection timing control means for controlling the fuel to be directly injected into the cylinder during the compression stroke of each cylinder from the in-cylinder injector.

In a fifth aspect based on the fourth aspect, the internal combustion engine comprises:
A fuel tank for holding fuel to be supplied to the in-cylinder injector;
A canister for storing evaporated fuel from the fuel tank;
A purge mechanism for causing the purge gas containing the evaporated fuel to flow into the intake passage from the canister,
Purge gas concentration learning means for learning the purge gas concentration supplied to the intake passage is provided.

According to a sixth invention, in the fifth invention, there is provided purge gas concentration determination means for determining whether or not the purge gas concentration is equal to or lower than a determination concentration,
The catalyst temperature increase control means executes temperature increase control of the lean NOx catalyst only when it is recognized that the purge gas concentration is equal to or lower than a determination concentration.

  According to a seventh aspect, in the sixth aspect, a target purge rate when the purge gas is allowed to flow into the intake passage is set according to operating conditions until the purge gas concentration is recognized to be equal to or less than a determination concentration. And a high purge rate setting means for setting a purge rate higher than the basic target purge rate.

In an eighth aspect based on any one of the fourth to seventh aspects, the internal combustion engine comprises:
A fuel tank for holding fuel to be supplied to the in-cylinder injector;
A canister for storing evaporated fuel from the fuel tank;
A purge mechanism for causing the purge gas containing the evaporated fuel to flow into the intake passage from the canister,
The catalyst temperature raising control means is a low purge rate setting means for setting a target purge rate when the purge gas flows into the intake passage to a lower purge rate than a basic target purge rate set according to operating conditions. It is characterized by providing.

According to a ninth invention, in any one of the first to eighth inventions, the catalyst temperature increase control means includes:
The control target value of the air-fuel ratio of any one of the cylinder groups is set to be richer than the theoretical air-fuel ratio at a ratio smaller than the rich ratio in the sulfur removal control, and the air-fuel ratio of the other cylinder groups Is provided with a weak rich / weak lean air-fuel ratio setting means for setting the control target value to be leaner than the stoichiometric air-fuel ratio at a ratio smaller than the lean ratio in the sulfur removal control.

  According to a tenth aspect of the present invention, in any one of the first to eighth aspects, the catalyst temperature increase control means sets a control target value of the air-fuel ratio of all the cylinder groups in the vicinity of the theoretical air-fuel ratio. A setting means is provided.

  According to the first aspect of the invention, before performing the control to remove the sulfur component stored in the lean NOx catalyst, the ignition timing of each cylinder in the cylinder group is controlled to be retarded. As a result, the temperature of the exhaust gas flowing into the lean NOx catalyst can be raised, and the temperature of the lean NOx catalyst can be raised prior to the control of the sulfur component removal. Therefore, the sulfur component removal time can be shortened, and the exhaust purification rate can be improved.

  According to the second aspect of the invention, prior to the sulfur component removal control, the opening degree of the throttle valve when performing the temperature increase control of the lean NOx catalyst is set according to the throttle valve opening degree during the sulfur component removal control. Set. Therefore, it is possible to suppress fluctuations in the air amount when shifting from the catalyst temperature increase control to the sulfur component removal control, and it is possible to suppress the occurrence of a shock during the transition.

  According to the third aspect of the present invention, the ignition timing retardation amount when performing the temperature increase control of the lean NOx catalyst is set to the torque estimated to be generated during the sulfur component removal control prior to the sulfur component removal control. Decide accordingly. Therefore, it is possible to suppress torque fluctuations when shifting from the catalyst temperature increase control to the sulfur component removal control, and it is possible to suppress the occurrence of shock during the transition.

  According to the fourth aspect of the invention, during the temperature rise control of the catalyst, control is performed so that the fuel is directly injected into the cylinder from the in-cylinder injector during the compression stroke of the cylinder. Therefore, combustion can be stabilized even when the ignition timing is significantly retarded in the catalyst temperature rise control.

  According to the fifth aspect, it is possible to learn the purge gas concentration supplied to the intake passage. Accordingly, the air-fuel ratio in the cylinder can be predicted during the temperature rise control of the catalyst, and the operating conditions can be selected so as to stabilize the combustion according to the predicted air-fuel ratio.

  According to the sixth aspect of the invention, the temperature increase control of the lean NOx catalyst is prohibited until the purge gas concentration supplied to the intake passage becomes equal to or lower than the determination concentration. Therefore, it is possible to suppress the occurrence of defective combustion due to the overrich state near the spark plug during the temperature rise control of the catalyst.

  According to the seventh aspect of the invention, the target purge rate is set to a high purge rate until it is recognized that the purge gas concentration is equal to or lower than the determination concentration. Therefore, the purge gas concentration can be lowered at an earlier stage, and the time required for sulfur poisoning recovery control can be shortened.

  According to the eighth aspect of the invention, the target purge rate is set to a low purge rate during the temperature rise control of the catalyst. Therefore, it is possible to prevent the air-fuel ratio in the cylinder from being over-rich, and to suppress the occurrence of poor combustion.

  According to the ninth aspect of the invention, during the catalyst temperature increase control, the control target value of the air-fuel ratio of any one of the cylinder groups is set to the stoichiometric air-fuel ratio at a ratio smaller than the rich ratio in the sulfur removal control. The air-fuel ratio control target value of the other cylinder group is set to be leaner than the stoichiometric air-fuel ratio at a ratio smaller than the lean ratio in the sulfur removal control. Accordingly, in the catalyst temperature increase control, the temperature increase effect of the lean NOx catalyst due to the retard of the ignition timing can be raised by the reaction of the unburned components and oxygen in the lean NOx catalyst, and the lean NOx catalyst can be obtained at an earlier stage. Can be heated.

  According to the tenth aspect, during the catalyst temperature increase control, the control target value of the air-fuel ratio of all the cylinder groups is set in the vicinity of the theoretical air-fuel ratio. Therefore, the exhaust purification rate can be increased until the temperature of the lean NOx catalyst is raised to a predetermined temperature, and emission can be reduced.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is simplified or omitted.

Embodiment 1 FIG.
[System configuration of the first embodiment]
FIG. 1 is a schematic diagram for explaining a control system according to Embodiment 1 of the present invention. The system shown in FIG. 1 includes an internal combustion engine 2. The internal combustion engine 2 includes two banks, a first bank and a second bank, and each of the two banks has cylinders 4a and 4b. In FIG. 1, only the cross sections of the cylinders 4a and 4b belonging to the first and second banks are shown, but the first and second banks each have a plurality of cylinders. A piston 6 is disposed in each of the cylinders 4a and 4b. The piston 6 has a depression on its surface. The piston 6 is connected to a crankshaft (not shown) via a connecting rod 8. In the vicinity of the crankshaft, a rotational speed sensor 10 that emits an output corresponding to the engine rotational speed of the internal combustion engine 2 is disposed.

  A combustion chamber 12 is provided above the piston 6 in the cylinders 4a and 4b. A spark plug 14 is assembled at the center of the ceiling (cylinder head) of the combustion chamber 12 so that the gap at the tip thereof protrudes into the combustion chamber 12. An in-cylinder injector 16 is assembled to the side of the combustion chamber 12 so as to protrude into the combustion chamber 12. Intake ports 18a and 18b and exhaust ports 20a and 20b communicate with the ceiling of the combustion chamber 12 of each cylinder 4a and 4b. The intake ports 18a and 18b are each provided with an intake valve 22 for opening and closing the intake ports 18a and 18b. The exhaust ports 20a and 20b are provided with exhaust valves 24 that open and close the exhaust ports 20a and 20b, respectively.

  As described above, the intake port 18a of each cylinder 4a belonging to the first bank of the internal combustion engine 2 is connected to a common intake manifold 26a. The intake port 18b of each cylinder 4b belonging to the second bank is connected to a common intake manifold 26b. The intake manifolds 26 a and 26 b are connected to a common intake passage 28. An electronically controlled throttle valve 30 is provided in the intake passage 28. The throttle valve 30 adjusts the amount of air flowing into the intake passage 28 by changing its opening. The opening degree of the throttle valve 30 is electrically controlled based on an acceleration / deceleration request by an accelerator operation or the like via an actuator. That is, the throttle opening can be controlled independently of the accelerator opening. An air flow meter 32 is disposed in the intake passage 28 upstream of the throttle valve 30. The air flow meter 32 generates an output corresponding to the flow rate of air flowing into the intake passage 28.

  The internal combustion engine 2 includes a high-pressure fuel pump 34 connected to the in-cylinder injector 16. The high pressure fuel pump 34 is connected to the fuel tank 36. The fuel tank 36 is connected to a canister 40 via a vapor passage 38. A purge passage 42 is connected to the canister 40. A VSV (purge control valve) 44 is provided in the purge passage 42. One end of the purge passage 42 is connected to the intake passage 28. In this system, part of the evaporated fuel (vapor) generated in the fuel tank 36 is introduced into the canister 40 through the vapor passage 38. The canister 40 adsorbs and holds the evaporated fuel. The evaporated fuel adsorbed in the canister 40 is supplied to the intake passage 28 via the purge passage 42 during operation of the internal combustion engine 2.

  The exhaust port 20a of each cylinder 4a belonging to the first bank is connected to a common exhaust manifold 50a. The exhaust ports 20b belonging to the second bank are connected to a common exhaust manifold 50b. Air-fuel ratio sensors 52a and 52b are attached to the exhaust manifolds 50a and 50b, respectively. The air-fuel ratio sensors 52a and 52b emit an output corresponding to the exhaust air-fuel ratio. The exhaust manifolds 50a and 50b are connected to the three-way catalysts 54a and 54b, respectively. One ends of exhaust passages 56a and 56b are connected to the downstream sides of the three-way catalysts 54a and 54b, respectively. Air-fuel ratio sensors 58a and 58b are attached to the exhaust passages 56a and 56b, respectively. The air / fuel ratio sensors 58a and 58b emit an output corresponding to the exhaust air / fuel ratio. The downstream ends of the exhaust passages 56a and 56b are gathered and connected to a common lean NOx catalyst 60. One end of an exhaust passage 62 is connected to the downstream side of the lean NOx catalyst 60. An air-fuel ratio sensor 64 is attached to the exhaust passage 62.

  The internal combustion engine 2 includes an ECU (Electronic Control Unit) 70. The ECU 70 acquires information necessary for controlling the internal combustion engine 2 from the rotation speed sensor 10, the throttle valve 30, the air flow meter 32, the air-fuel ratio sensors 52a, 52b, 58a, 58b, 64, the accelerator position sensor, and the like. Further, based on the acquired information, the crankshaft, the VVT mechanism, the ignition timing of the spark plug 14, the fuel injection amount and injection timing from the in-cylinder injector 16, the opening degree of the throttle valve 30, the opening degree of the VSV 44, and the like are controlled. To do.

  In the internal combustion engine 2 configured as described above, the three-way catalysts 54a and 54b reduce NOx in the exhaust gas and oxidize HC and CO with the maximum conversion efficiency at the stoichiometric air-fuel ratio. On the other hand, the lean NOx catalyst 60 reduces NOx and oxidizes HC and CO at the maximum conversion efficiency at the stoichiometric air-fuel ratio, and stores NOx contained in the exhaust inside the stoichiometric air-fuel ratio at the lean air-fuel ratio. Alternatively, when the oxygen concentration in the exhaust gas decreases, such as at the time of a rich air-fuel ratio, NOx is desorbed and the desorbed NOx is reduced by HC and CO contained in the exhaust gas.

[Basic sulfur poisoning recovery control in Embodiment 1]
However, the lean NOx catalyst 60 occludes sulfur components such as SOx (hereinafter referred to as “S component”) contained in the fuel as sulfates instead of NOx. If the lean NOx catalyst 60 occludes the S component, NOx in the exhaust gas becomes difficult to occlude, and the purification rate of the catalyst may decrease. Therefore, in order to maintain the purification performance of the lean NOx catalyst 60, the control to remove the S component (sulfur poisoning recovery control) is executed before the storage amount of the S component exceeds the allowable range.

  The S component occluded in the lean NOx catalyst 60 is reduced and released when the lean NOx catalyst 60 is at a high temperature and the introduced exhaust gas has a stoichiometric air-fuel ratio or a rich air-fuel ratio. Therefore, when performing sulfur poisoning recovery control of the lean NOx catalyst 60, the temperature of the lean NOx catalyst 60 is raised to a temperature at which the S component can be reduced (hereinafter referred to as "sulfur desorption temperature"), The air-fuel ratio of the gas flowing into the lean NOx catalyst 60 (hereinafter referred to as “input gas”) is controlled to become the stoichiometric air-fuel ratio or the rich air-fuel ratio. Specifically, in the first embodiment, control is performed so that the air-fuel ratio of the exhaust gas from one of the first and second banks becomes rich, and the air-fuel ratio of the exhaust gas from the other bank is made lean. In addition, the air-fuel ratio after both exhaust gas merges is controlled to be close to the stoichiometric air-fuel ratio (hereinafter referred to as “bank control”). As a result, surplus unfueled fuel including oxygen and HC that do not contribute to the catalytic reaction or oxygen flows out from the three-way catalysts 54a and 54b connected to the first and second banks, respectively, and these flow into the lean NOx catalyst 60. Flows in. In the lean NOx catalyst 60, the reaction between the unburned fuel and oxygen is promoted, whereby the temperature of the lean NOx catalyst 60 rises. At this time, the exhaust gas merged in the lean NOx catalyst 60 is controlled in the vicinity of the stoichiometric air-fuel ratio. Therefore, the S component occluded in the lean NOx catalyst 60 can be removed by the above bank control.

  However, during the bank control, the exhaust temperature is low particularly in a bank operated at a lean air-fuel ratio (hereinafter referred to as “lean bank”. Also, a bank operated at a rich air-fuel ratio is referred to as “rich bank”). In addition, the temperature of the gas entering the lean NOx catalyst 60 is low due to exhaust purification by the three-way catalysts 54a and 54b. Under such circumstances, it is considered that it takes a long time to raise the lean NOx catalyst 60 to about 650 to 700 ° C. which is the sulfur desorption temperature by the reaction between unburned fuel and oxygen. Further, the S component cannot be desorbed until the sulfur desorption temperature is reached. Accordingly, if the S component is removed only by bank control as described above, it takes a long time to complete the removal of the S component.

  As described above, the three-way catalysts 54a and 54b purify the exhaust gas with the maximum conversion efficiency at the stoichiometric air-fuel ratio. However, when bank control is performed, the exhaust gas flowing into each of the three-way catalysts 54a and 54b connected downstream of the exhaust manifolds 50a and 50b for each bank is biased to a rich air-fuel ratio or a lean air-fuel ratio. Therefore, during the bank control, the exhaust gas purification rate by the three-way catalyst 54a, 54b becomes low, and the purification of the exhaust gas mainly depends on the lean NOx catalyst 60. Therefore, the exhaust gas purification rate is reduced and the emission characteristics are reduced as compared with the normal stoichiometric control in which the three-way catalysts 54a and 54b and the lean NOx catalyst 60 both function efficiently. Further, during the bank control, the rich gas and the lean gas are mixed immediately before the lean NOx catalyst 60, so that the air-fuel ratio controllability is also disadvantageous. From the above, it is preferable that the bank control be performed in a short time. For this reason, when there is a request for sulfur poisoning recovery control, the temperature of the lean NOx catalyst 60 is raised to the sulfur desorption temperature as quickly as possible. Is preferred.

[Characteristic control of the system of the first embodiment]
As described above, when the sulfur poisoning recovery control is performed in the system of the first embodiment, the catalyst temperature increase control is executed so that the catalyst temperature is raised to some extent in advance prior to the bank control. Specifically, before the bank control, and during the normal stoichiometric operation of each of the first and second banks, the ignition timing is retarded significantly from the normal case. By retarding the ignition timing in this manner, the combustion efficiency in each of the cylinders 4a and 4b is lowered, and the exhaust gas temperature discharged to the exhaust ports 20a and 20b is increased. Further, since combustion is delayed, a large amount of unburned components are discharged to the exhaust ports 20a and 20b, and the unburned components are burned at the exhaust ports 20a and 20b or downstream thereof. As a result, the inlet gas temperature to the lean NOx catalyst 60 can be raised, and thereby the temperature of the lean NOx catalyst 60 can be raised at an early stage.

  Further, during the catalyst temperature increase control that greatly retards the ignition timing in this way, the fuel is directly injected from the in-cylinder injector 16 into the cylinders 4a and 4b at the timing of the compression stroke. The fuel thus injected is guided to the vicinity of the spark plug 14 along a recess formed in the upper surface of the piston 6. As a result, a region (stratification) where the fuel density is higher than the surrounding atmosphere is formed around the spark plug 14. Thereby, it can ignite in the state which the ignitability by the ignition plug 14 was improved, and what is called stratified combustion is implement | achieved. By using stratified combustion in this way, combustion can be stabilized even when the ignition timing is greatly retarded. The timing of fuel injection during the compression stroke during catalyst temperature rise control is determined based on the engine speed and the engine load factor. Further, during the catalyst temperature increase control, the control is performed so that the stoichiometric air-fuel ratio is set for each bank and the stratified stoichiometric operation is performed.

  The basic ignition timing during the compression stroke and stratified stoichiometric operation is set according to the engine speed and the engine load factor. Further, with respect to this basic ignition timing, an ignition timing retardation amount for raising the catalyst temperature is obtained in accordance with the engine speed and the engine load factor. The ignition timing during the catalyst temperature increase control is obtained by correcting the basic ignition timing during the compression stroke and stratified stoichiometric operation according to the ignition timing retard amount obtained in accordance with the engine speed and the engine load factor. The ECU 70 stores in advance a map of the basic ignition timing during the compression stroke and the stratified stoichiometric operation and a map of the ignition timing retard amount during the catalyst temperature increase control using the engine speed and the engine load factor as parameters. . The ignition timing in the catalyst temperature increase control is set according to the engine speed and the engine load factor according to these maps.

  Further, if the ignition timing is simply retarded during the catalyst temperature increase control, a large torque fluctuation occurs when shifting from the normal stoichiometric operation to the catalyst temperature increase control. In order to suppress this variation in torque, the opening of the throttle valve 30 is corrected so that the generated torque is substantially the same before and after the shift to the catalyst temperature increase control. That is, the opening degree of the throttle valve 30 (throttle opening degree) is determined by correcting the basic throttle valve opening degree (basic throttle opening degree) by the opening degree correction value corresponding to the ignition timing retardation amount.

  FIG. 2 is a graph showing the relationship between the ignition timing retardation amount and the opening correction value. In FIG. 2, the horizontal axis represents the ignition timing retard amount, and the vertical axis represents the opening correction value. The basic throttle opening is an opening determined according to the required torque according to the accelerator opening and the engine speed during normal operation. The opening correction value for the basic throttle opening is set so as to compensate for the torque decrease due to the ignition timing retardation during the catalyst temperature increase control with the intake air amount. That is, as shown in FIG. 2, the opening correction value is set to increase as the ignition timing retardation amount increases. When determining the throttle opening, an opening correction value is added to the basic throttle opening.

  By correcting the basic throttle opening in this way, it is possible to compensate for the lower portion of the torque due to the ignition timing significant retard, and to suppress the torque fluctuation before and after the shift to the catalyst temperature increase control. In addition, since the throttle opening is largely adjusted, the intake air amount increases. As a result, the exhaust temperature can be made higher. Accordingly, in combination with the temperature rise effect of the exhaust gas due to the ignition timing retardation, the exhaust temperature can be increased, the temperature of the gas entering the lean NOx catalyst 60 can be further increased, and the lean NOx can be increased in a short time. The temperature of the catalyst 60 can be raised.

  The ECU 70 stores a map of an opening correction value using the ignition timing retard amount based on the relationship shown in FIG. 2 as a parameter together with a basic throttle opening map using the required torque and the engine speed as parameters. is doing. The throttle opening during the catalyst temperature increase control is determined by correcting the basic throttle opening by the opening correction value obtained according to the ignition timing retard amount.

[Specific Control Routine of Embodiment 1]
3 and 4 are flowcharts for illustrating a control routine executed by the system according to the first embodiment of the present invention. In the routine of FIG. 3, first, in step S102, the required torque is obtained. The required torque is calculated according to information such as the output of the air flow meter 32 and the accelerator opening. Next, the engine speed is obtained (step S104). The engine speed is obtained based on an output generated by the speed sensor 10. Next, the engine load factor is obtained (step S106). The engine load factor is calculated according to information such as the intake air amount from the air flow meter 32.

  Next, it is determined whether or not a sulfur poisoning recovery request has been made (step S108). The presence or absence of a sulfur poisoning recovery request is determined based on, for example, whether or not the estimated sulfur poisoning amount has reached a determination amount or more. Here, the sulfur poisoning amount is estimated based on, for example, information such as engine rotation, engine load, catalyst temperature, and elapsed time since the previous sulfur poisoning recovery control. Further, the determination amount is stored in advance in the ECU 70 as a limit amount that the NOx purification rate by the lean NOx catalyst 60 is considered to fall below the allowable range when the sulfur poisoning amount further increases. If it is not confirmed in step S108 that the sulfur poisoning amount ≧ the determination amount is satisfied, it is assumed that there is no sulfur poisoning recovery request, and this process is once ended and normal control is performed.

  If it is determined in step S108 that the sulfur poisoning amount ≧ the determination amount is established, the fuel injection timing is set to the compression stroke injection timing when the stratified stoichiometric operation is performed (step S110). The fuel injection timing is set according to the engine load factor and the engine speed obtained in steps S104 and S106 according to a map using the engine load factor and the engine speed as parameters. Thereby, the fuel injection timing from the in-cylinder injector 16 is set to the timing at the time of the stratified stoichiometric operation, and the stratified stoichiometric operation is executed.

  Next, an ignition timing retardation amount is obtained (step S112). The ignition timing retardation amount is obtained according to the engine speed and the dangerous load factor according to a map using the engine speed and the engine load factor as parameters. Next, the ignition timing is set (step S114). The ignition timing is set to a timing obtained by correcting the basic ignition timing in the case of performing stratified stoichiometry and compression stroke injection according to the ignition timing retardation amount obtained in step S112.

  Next, a throttle opening correction value is obtained in accordance with the ignition timing retardation amount obtained in step S112 (step S116). The throttle opening correction value is obtained as a value corresponding to the ignition timing retardation amount according to a map using the ignition timing retardation amount as a parameter. Next, the throttle opening is set (step S118). The throttle opening is calculated by adding the throttle opening correction value obtained in step S116 to the basic throttle opening obtained according to the engine speed and the required torque. A signal corresponding to the calculated throttle opening is issued from the ECU 70 to the throttle valve 30 to set the throttle opening. By the settings in steps S110 to S118, the internal combustion engine 2 is operated under the conditions of stratified stoichiometric operation of compression stroke injection, ignition timing retardation, and throttle opening increase. As a result, the exhaust gas temperature rises, whereby the temperature of the lean NOx catalyst 60 can be raised.

  Next, the temperature of the lean NOx catalyst 60 is obtained (step S120). The temperature of the lean NOx catalyst 60 is estimated from operating conditions such as the engine speed and the engine load. Next, it is determined whether or not the estimated temperature of the lean NOx catalyst is equal to or higher than a determination temperature (step S122). The determination temperature is a temperature stored in the ECU 70 in advance so as to reach a temperature that can sufficiently remove sulfur components in a short period of time after the start of bank control, and is, for example, about 550 ° C. to 600 ° C. In step S122, if it is not recognized that the lean NOx catalyst 60 is equal to or higher than the determination temperature, the operating conditions of the stratified stoichiometric combustion and the ignition timing retarded by the compression stroke injection until the lean NOx catalyst temperature is equal to or higher than the determination temperature Thus, the catalyst temperature increase control is continued. During this time, the air-fuel ratio is detected from the outputs from the air-fuel ratio sensors 52a and 52b (step S124), the air-fuel ratio feedback correction value is obtained, and thereby the air-fuel ratio feedback control is executed (step S126).

  On the other hand, if it is determined in step S122 that lean NOx catalyst temperature ≧ determination temperature is established, bank control is executed (step S130). Bank control is executed according to the bank control execution routine shown in FIG. In the routine shown in FIG. 4, first, the valve opening is set to the opening of the throttle valve during bank control (step S132). The opening degree of the throttle valve is determined in accordance with a throttle valve opening degree map at the time of bank control using the required torque and the engine speed as parameters stored in the ECU 70 in advance.

  Next, measurement of the S component purge time is started (step S134). The S component purge time is measured as an elapsed time from the start of bank control. Next, the rich / lean air-fuel ratio setting mode flag in the bank control is read (step S136). This flag designates a mode in which when the flag = 0, the target air-fuel ratio of the first bank is set to a predetermined rich air-fuel ratio and the target air-fuel ratio of the second bank is set to a predetermined lean air-fuel ratio. A flag for designating a mode in which the target air-fuel ratio of the first bank is set to a predetermined lean air-fuel ratio and the target air-fuel ratio of the second bank is set to a predetermined rich air-fuel ratio when = 1. At the initial setting stage, flag = 0 is set.

  Next, the target air-fuel ratio of each bank is set (step S138). The target air-fuel ratio is set according to the flag read in step S134. Specifically, since flag = 0 at the present stage, the target air-fuel ratio is set to the rich air-fuel ratio in the first bank and the lean air-fuel ratio in the second bank. Next, the ignition timing for each bank is set (step S140). The ignition timing is a predetermined timing such that the output torques of the rich bank and the lean bank are approximately the same, and is set so that the ignition timing of the rich bank is retarded. That is, here, the ignition timing of each cylinder 4a of the first bank is set to a timing delayed from the ignition timing of the second bank. Next, measurement of the mode elapsed time is started (step S142). The mode elapsed time is an elapsed time after the target air-fuel ratio, ignition timing, throttle valve opening, etc. of each bank are set as operating conditions corresponding to the mode setting flag.

  Next, it is determined whether or not the removal of the S component has been completed (step S144). Completion of removal of the S component is determined based on, for example, whether or not a predetermined time has elapsed since the start of bank control, that is, whether or not S component purge time ≧ predetermined time is satisfied. If the completion of the S component removal is not recognized, it is next determined whether or not the mode elapsed time is equal to or longer than the determination time (step S146). Here, the determination time is stored in advance in the ECU 70 as a time during which the operation in the mode is continued. If the establishment of the mode elapsed time ≧ the determination time is not recognized in step S146, this mode is maintained until either the S component removal completion (step S144) or the mode elapsed time ≧ the determination time is established (step S146). Continue driving at.

  On the other hand, if it is recognized in step S146 that the mode elapsed time ≧ the determination time is satisfied, the mode flag is changed (step S148). That is, when the current flag = 0, the flag is changed to 1, and when the current flag = 1, the flag is changed to 0. Next, the mode elapsed time = 0 is set (step S150). In this state, the mode setting flag is read again in step S136, and the target air-fuel ratio of each bank is set to the reverse lean / rich air-fuel ratio so far (step S138), and set to the respective ignition timings. (Step S140). It is again determined whether or not the S component removal is completed (step S144). If the completion is not recognized, the bank control is continued in the same manner as described above. On the other hand, when the S component removal completion is recognized, this process is terminated. During the above bank control, the air-fuel ratio sensors 58a and 58b are the main air-fuel ratio sensors and the air-fuel ratio sensor 64 is the sub air-fuel ratio sensor, and the air-fuel ratio feedback correction value is calculated based on the outputs from these sensors. Air-fuel ratio feedback control is being executed.

  As described above, in the first embodiment, in the sulfur poisoning recovery control, the catalyst temperature increase control is performed by significantly retarding the ignition timing prior to the bank control. Thus, the exhaust gas temperature rises by performing a significant retardation of the ignition timing, and the incoming gas temperature when flowing into the lean NOx catalyst 60 can be raised. Therefore, prior to bank control, the temperature of the lean NOx catalyst 60 can be raised to the sulfur desorption temperature or a temperature close thereto. Therefore, the bank control time can be reduced to a short time, the efficiency of sulfur poisoning control can be improved, and the emission can be reduced.

  In the present invention, means such as determination of sulfur poisoning recovery control request (step S108), detection of catalyst temperature (step S120) and determination of completion of bank control (step S144) are the same as those described in the first embodiment. It is not limited. Also, the bank control execution routine is not limited to that described in the first embodiment, and any other control routine can be used as long as it removes the S component by controlling each bank to a rich air-fuel ratio and a lean air-fuel ratio. It may be executed according to a routine.

  For example, in the first embodiment, by executing steps S102 to S126, the “catalyst temperature increase control means” of the present invention is realized, and by executing the bank control execution routine of step S130, the present invention "Sulfur component removal control means" is realized. Also, by executing step S138, the “rich / lean air-fuel ratio setting means” of the present invention is realized, and by executing steps S112 and S114, the “ignition timing retarding means” of the present invention is realized, By executing step S110, the “fuel injection timing control means” is realized.

Embodiment 2. FIG.
[Control executed by the system of the second embodiment]
The system according to the second embodiment has the same configuration as the system according to the first embodiment. The system of the second embodiment is the same as that of the second embodiment except that the throttle opening at the time of catalyst temperature increase control and the bank control is made the same, and the ignition timing retardation amount is set according to the throttle opening. The same control as the system 1 is performed.

  As described above, in bank control, each bank is controlled to a lean air-fuel ratio or a rich air-fuel ratio. At this time, if the lean bank and the rich bank are controlled in the same manner, the torque generated between the banks varies. In the bank control, in order to compensate for this torque variation, the ignition timing of the rich bank is retarded, and the torque generated in the rich bank is controlled to coincide with the generated torque of the lean bank. The ignition retard amount of the rich bank is determined based on the engine speed and the engine load so that the torque generated in the rich bank matches the generated torque of the lean bank. The ECU 70 stores in advance a rich bank ignition delay amount map using the engine load and the engine speed as parameters, and during bank control, the rich control is performed according to the engine speed and the engine load according to this map. The retard amount of the bank ignition timing is determined.

  On the other hand, if the control is performed so that the generated torque of the rich bank and the generated torque of the lean bank coincide with each other simply by the ignition retard, the generated torque of the entire internal combustion engine 2 is reduced. Therefore, the opening degree of the throttle valve 30 is corrected in order to compensate for torque reduction during bank control. That is, the opening degree of the throttle valve 30 is adjusted so that the opening degree is larger than that during the normal stoichiometric operation in order to compensate for the decrease in the generated torque. Such a correction value for the opening of the throttle valve is obtained according to a map using the required torque and the engine speed as parameters.

  As described above, at the time of bank control, the ignition timing is retarded and the opening of the throttle valve 30 is adjusted in order to suppress the variation in the generated torque for each bank and the decrease in the generated torque of the entire internal combustion engine 2. However, if the opening degree of the throttle valve 30 is changed during the transition from the catalyst temperature raising control to the bank control, the air amount and the torque change during the transition. For this reason, it is conceivable that shocks due to air amount fluctuations and torque fluctuations occur during the transition from the catalyst temperature raising control time to the bank control time.

[Characteristic control of the second embodiment]
For this reason, in the second embodiment, when performing the catalyst temperature increase control, the throttle opening during the subsequent bank control is estimated in advance, and the throttle opening during the catalyst temperature increase control is set to the estimated throttle opening. It will be set. That is, the throttle opening during the catalyst temperature increase control is set to be the same as the throttle opening during the bank control corrected by the correction value determined from the required torque and the engine speed.

  In addition, stratified stoichiometric combustion by compression stroke injection is realized during catalyst temperature rise control. For this reason, if the throttle opening during the catalyst temperature increase control is simply adjusted to be the same as the opening during the bank control, a larger torque is generated during the catalyst temperature increase control than during the bank control. As a result, the torque varies between the catalyst temperature increase control and the bank control, and a shock is generated when switching to the bank control. Therefore, in order to suppress the torque fluctuation at the time of transition from the catalyst temperature increase control to the bank control, the ignition timing retardation amount at the catalyst temperature increase control is set to the same timing as the torque generated at the bank control. Set to. As a result, it is possible to suppress the occurrence of shock due to torque fluctuation when switching from the catalyst temperature raising control to the bank control. Further, since the ignition timing is retarded also in this control, the effect of raising the temperature of the lean NOx catalyst 60 by the ignition timing retardation can be obtained as in the first embodiment.

  Specifically, the ignition timing retardation amount during the catalyst temperature increase control is set so as to increase as the opening correction value increases. As a result, the combustion efficiency can be lowered to reduce the torque during the catalyst temperature increase control, and can be made to coincide with the generated torque during the bank control. A map of the ignition timing retardation amount based on such a relationship and using the throttle valve opening correction value as a parameter is stored in the ECU 70 in advance. In the catalyst temperature increase control, the ignition timing retard amount corresponding to the opening correction value of the throttle valve 30 is calculated according to this map, and the basic ignition timing is retarded according to the ignition timing retard amount. Ignition timing is required. By setting the ignition timing in this way, it is possible to suppress torque fluctuations when switching from the catalyst temperature increase control to the bank control, and at the same time, the temperature of the gas entering the lean NOx catalyst 60 is increased, and the lean NOx catalyst 60 is increased. Can be efficiently heated.

[Specific Control Routine of Embodiment 2]
5 and 6 are flowcharts for illustrating a control routine executed by the system according to the second embodiment of the present invention. The routine of FIG. 5 is the same as the routine of FIG. 3 except that steps S202 to S208 are executed instead of steps S112 to S118. The routine of FIG. 6 is the same as the routine of FIG. 4 except that step S132 is not executed.

  Specifically, after the required torque, engine speed, and engine load factor are obtained in the routine of FIG. 5 (steps S102 to S106), if a sulfur poisoning recovery request is recognized in step S108, first, the fuel injection timing Is set (step S114), and then a throttle opening correction value for performing bank control is obtained (step S202). The throttle opening correction value is obtained according to the required torque and the engine speed according to a map using the required torque and the engine speed as parameters. Next, the throttle opening is set (step S204). The throttle opening is set to a value obtained by adding the throttle opening correction value at the time of bank control obtained in step S202 to the basic throttle opening determined according to the engine speed and the required torque. This throttle opening is the same as the throttle opening during the subsequent bank control.

  Next, the ignition timing retard amount is set (step S206). Here, the ignition timing retard amount corresponding to the throttle opening correction value Δfa obtained in step S202 is obtained according to the ignition timing retard amount map using the throttle opening correction value stored in the ECU 70 as a parameter in advance. . Next, the ignition timing is set (step S208). The ignition timing is set to a timing obtained by correcting (retarding) the basic ignition timing in the case of performing stratified stoichiometry and compression stroke injection according to the ignition timing retardation amount obtained in step S206. Depending on the throttle opening and ignition timing set in steps S204 and S208, the output torque in the catalyst temperature increase control and the bank control can be made substantially the same, and when the catalyst temperature increase control shifts to the bank control, a shock is generated. Occurrence can be suppressed. Further, since the ignition timing is greatly retarded, the temperature of the exhaust gas can be raised to raise the temperature of the gas entering the lean NOx catalyst.

  Next, the temperature of the lean NOx catalyst 60 is obtained, and it is determined whether or not the estimated temperature of the lean NOx catalyst 60 is equal to or higher than a determination temperature (steps S120 and S122). In step S122, when it is recognized that lean NOx catalyst temperature ≧ determination temperature is established, bank control is executed. In the bank control routine of FIG. 6, the opening of the throttle valve for changing to bank control is not changed (step S132 of FIG. 4), and the purge time measurement is immediately started in step S134 and the mode setting flag is read. (Step S136) is performed, and bank control is executed until completion of removal of the S component is recognized.

  As described above, in the second embodiment, in the sulfur poisoning recovery control, the throttle opening during the bank control and the throttle opening during the catalyst temperature increase control are made the same, and the bank control is performed. The ignition timing is retarded so that the generated torque becomes equal to the generated torque during the catalyst temperature increase control. Therefore, when shifting from catalyst temperature increase control to bank control, it is possible to prevent the occurrence of shocks due to air amount changes, vibration due to torque fluctuation, etc., and smooth transition from catalyst temperature increase control to bank control. it can.

  Further, since the combustion efficiency is lowered by retarding the ignition timing during the catalyst temperature increase control, the temperature of the exhaust gas discharged to the exhaust passage rises. Further, due to the ignition timing retardation, the unburned components are burned after being discharged to the exhaust ports 20a and 20b, thereby increasing the temperature of the exhaust gas. For this reason, the temperature of the exhaust gas flowing into the lean NOx catalyst 60 can be increased as compared with the normal stoichiometric operation or lean operation. Therefore, prior to bank control, the lean NOx catalyst 60 can be efficiently raised to the sulfur desorption temperature or a temperature close thereto. Therefore, the time for bank control can be reduced to a short time, and the efficiency of sulfur poisoning control can be improved and the emission can be improved.

  For example, in the second embodiment, by executing step S202, the “opening degree estimation means” of the present invention is realized, and by executing step S204, the “opening degree control means” is realized, By executing S206, "torque estimation means" and "ignition timing retarding means" are realized.

Embodiment 3 FIG.
The system of the third embodiment has the same configuration as the system of the first embodiment. The system according to the third embodiment performs the same control as the system according to the first embodiment except that when the evaporation purge is performed during the catalyst temperature increase control, the control is performed in consideration of the concentration of the purge gas. That is, in the third embodiment, similarly to the first embodiment, in the catalyst temperature increase control before the bank control, the stratified stoichiometric combustion is performed only by the direct fuel injection from the in-cylinder injector 16, and the ignition timing is further increased. The lean NOx catalyst 60 is raised in temperature by being retarded.

  As described with reference to FIG. 1, in this system, during operation of the internal combustion engine 2, the evaporated fuel adsorbed in the canister 40 is discharged into the intake passage 28 according to the state (evaporation purge). As a result, the evaporated fuel is mixed with the atmosphere in the intake passage 28 and supplied into the cylinders 4a and 4b. On the other hand, fuel injection from a port injector (not shown) into the intake ports 18a and 18b is not performed during the catalyst temperature increase control. That is, during catalyst temperature increase control, fuel is supplied only by injecting fuel directly from the in-cylinder injector 16 into the cylinder, thereby concentrating the fuel around the spark plug 14 to form a stratified region, and stratified stoichiometric operation. It is carried out. During the stratified combustion, if the evaporation purge is executed and the atmosphere in which the evaporated fuel is mixed is supplied from the intake ports 18a and 18b, the stratified region formed around the spark plug 14 becomes over-rich, resulting in poor combustion. Can be caused.

  Therefore, in order to prevent combustion failure, in the third embodiment, learning of the purge gas concentration (hereinafter referred to as “evaporation concentration”) in the evaporation purge is executed until the evaporation concentration is determined. The catalyst temperature increase control is prohibited while the evaporation concentration is higher than the determination concentration, and normal stoichiometric control is executed until the evaporation concentration becomes equal to or less than the determination concentration. Note that the evaporation concentration in the third embodiment is obtained based on the amount of change in the feedback correction value when the air-fuel ratio is stoichiometrically controlled, for example. Further, the determination concentration is set to an upper limit value in a range where it is considered that no combustion failure occurs during stratified stoichiometric combustion.

  FIG. 7 is a flowchart for illustrating a specific control routine according to the third embodiment of the present invention. The routine shown in FIG. 7 is the same as the routine of FIG. 3 except that steps S302 to S306 are executed after step S108 of FIG. Specifically, if it is determined in step S108 that there is a request for sulfur poisoning recovery control, it is determined in step S302 whether the evaporation purge is being performed. If it is not recognized in step S302 that the evaporation purge is being performed, the fuel injection timing is determined in step S110, the ignition timing and the throttle valve opening are then set (steps S112 to S118), and the catalyst temperature increase control is performed.

  On the other hand, if it is determined in step S302 that the evaporation purge is being performed, evaporation concentration learning is executed (step S304). Specifically, the air-fuel ratio learning is stopped, and the change amount of the air-fuel ratio feedback correction value from that stage is obtained. The evaporation density is obtained as a value corresponding to the change amount of the correction value.

  Next, it is determined whether or not the evaporation concentration is less than or equal to the determination concentration (step S306). The determination concentration is a value stored in the ECU 70 in advance, which is set to the upper limit of a range in which no combustion failure occurs even if the compression stroke injection and stratified stoichiometric combustion are started. That is, if it is recognized that the evaporation concentration ≦ the determination concentration, it can be determined that no combustion failure occurs even if the catalyst temperature increase control is started. If it is determined in step S306 that the evaporation concentration ≦ the determination concentration is not satisfied, the process returns to step S304, and the learning of the evaporation concentration and the determination in step S306 are repeated until the evaporation concentration ≦ the determination value is recognized. On the other hand, if it is determined in step S306 that the evaporation concentration ≦ the determination concentration, the process proceeds to step S110, where the catalyst temperature raising control is performed in the same manner as in the first embodiment, and then the bank control is performed according to the routine of FIG. I do.

  As described above, in the third embodiment, the catalyst temperature increase control is prohibited until the evaporation concentration is equal to or lower than the determination concentration. As a result, even when stratified stoichiometric combustion is performed in the catalyst temperature increase control, it is possible to prevent the vicinity of the spark plug 14 from becoming an overrich state and prevent combustion failure.

  In the third embodiment, the case where the evaporation concentration is learned by the change amount of the air-fuel ratio feedback control correction value in step S304 has been described. However, learning of the evaporation concentration in the present invention is not limited to this method, and the evaporation concentration may be detected by another method.

  In the third embodiment, the case where the catalyst temperature increase control is prohibited until the evaporation concentration is reduced to the determination concentration has been described. However, the present invention is not limited to this. For example, after evaporative concentration learning, combustion failure may be prevented by a technique such as controlling the temperature of the fuel injection from the in-cylinder injector 16 according to the evaporated concentration and performing catalyst temperature rise control.

  Further, in the third embodiment, the case where the catalyst temperature increase control is performed by the significant delay of the ignition timing is described as in the first embodiment when the evaporation concentration falls below the determination concentration. However, the present invention is not limited to this, and the catalyst temperature increase control described in the second embodiment may be performed when it is recognized that the evaporation concentration has decreased below the determination value. As a specific routine, steps S302 to S306 are executed after step S108 in FIG. 5. When it is determined that the evaporation concentration ≦ the determination concentration is established in step S306, the process proceeds to step S110 in FIG. What is necessary is just to obtain | require the correction value of an opening degree.

  For example, in the third embodiment, “purge gas concentration learning means” is realized by executing step S304, and “purge gas concentration determining means” is realized by executing step S306.

Embodiment 4 FIG.
The system of the fourth embodiment has the same configuration as the system of the first embodiment. In the fourth embodiment, the same control as that of the system of the third embodiment is performed except that the target purge rate is switched to a large value during the evaporation purge, and the evaporation concentration is controlled to be low at an early stage. . That is, while the system of the third embodiment waits for the concentration learning value to fall to the determination concentration during the evaporative purge and performs the catalyst temperature increase control, the system of the fourth embodiment has the catalyst temperature increase control. Before, the evaporation purge rate is set to a high high purge rate, and the evaporation concentration is controlled to decrease to the determination concentration at an early stage.

  Here, the purge rate is a value obtained as purge flow rate / intake air amount. Further, the purge flow rate is obtained from the valve opening time and the opening degree of the VSV 44, the negative pressure in the intake passage 28, and the like. In the fourth embodiment, the target purge rate is set to a high purge rate during the evaporation purge before the catalyst temperature increase control, and the opening degree and the valve opening time of the VSV 44 are adjusted according to the set high purge rate. As a result, the amount of evaporated fuel flowing from the purge passage 42 into the intake passage 28 increases, and the evaporated fuel in the canister 40 can be discharged into the intake passage 28 at an earlier stage. Therefore, when there is a request for sulfur poisoning recovery control, the evaporation concentration can be quickly lowered to a low concentration, and the catalyst temperature increase control can be started in a short time.

  FIG. 8 is a flowchart for illustrating a control routine executed by the system in the fourth embodiment of the present invention. The routine shown in FIG. 8 is the same as the routine shown in FIG. 7 except that step S402 is executed after step S302, and step S404 is executed after step S306. Specifically, when the request for sulfur poisoning recovery control is recognized in step S108 and it is recognized that the evaporation purge is being performed in step S302, the target purge rate of the evaporation purge is switched to a high purge rate (step S402). The high purge rate is determined according to the engine speed and the load factor according to a map stored in the ECU 70 in advance.

  Thereafter, the evaporation concentration learning is executed (step S304), and if the evaporation concentration ≦ the determination concentration is confirmed in step S306, the target purge rate is returned to the purge rate during normal operation (step S404). Thereafter, the catalyst temperature increase control is executed in accordance with steps S110 to S122.

  As described above, according to the fourth embodiment, when there is a sulfur poisoning recovery control request, the target purge rate for the evaporative purge is larger than the target purge rate for the normal stoichiometric control before the catalyst temperature increase control. A high purge rate is set so that evaporation purge is performed at a high purge rate. Therefore, the evaporation concentration can be lowered in a short time, and the catalyst temperature increase control can be started at an early stage after the sulfur poisoning recovery control request is made.

  In the fourth embodiment, as in the third embodiment, the case where the catalyst temperature increase control similar to that in the first embodiment is performed when the evaporation concentration is reduced to the determination concentration has been described. However, the present invention is not limited to this, and as in the second embodiment, the throttle valve opening at the time of bank control and at the time of catalyst temperature rise control is set to be the same, and further according to the throttle opening. The catalyst temperature increase control may be performed by setting the ignition timing retardation amount.

  In the fourth embodiment, the “high purge rate setting means” of the present invention is realized by executing step S402.

Embodiment 5. FIG.
The system of the fifth embodiment has the same configuration as the system of the first embodiment. The system of the fifth embodiment performs the same control as the system of the first embodiment except that the evaporation purge is performed by setting the target purge rate of the evaporation purge to be smaller than normal during the catalyst temperature increase control. . As described above, when the catalyst temperature raising control is performed during the evaporation purge, if the concentration of the evaporated fuel supplied together with the atmosphere is too high, the vicinity of the spark plug 14 may be overrich and cause combustion failure. . For this reason, in the fifth embodiment, the target purge rate of the evaporation purge is set to a low purge rate smaller than the purge rate at the time of normal stoichiometric control so that the evaporation concentration is kept low.

  The specific purge rate is determined in consideration of the engine speed and the engine load factor, but the purge rate is kept at a low purge rate of around 2%. As a result, even when the evaporative purge is performed during the stratified stoichiometric combustion in the catalyst temperature rise control, it is possible to prevent the stratified region formed in the vicinity of the spark plug 14 from becoming over-rich and to prevent combustion failure. Can do.

  FIG. 9 is a flowchart for illustrating a control routine executed by the system according to the fifth embodiment of the present invention. The routine shown in FIG. 9 is the same as the routine of FIG. 3 except that steps S502 and S504 are executed after step S108 of the routine of FIG. Specifically, after the sulfur poisoning recovery request is accepted in step S108, it is determined in step S502 whether the evaporation purge is being performed. When it is not recognized that the evaporation purge is being performed, the process proceeds to step S110, and the catalyst temperature increase control is performed as in the first embodiment.

  On the other hand, if it is determined in step S502 that the evaporation purge is being performed, the target purge rate of the evaporation purge is set to a low purge rate in step S504. The low purge rate is set in accordance with a low purge rate map stored in the ECU 70 in advance during catalyst temperature increase control. The low purge rate to be set is a value within a range where it is considered that the evaporation concentration is kept low to some extent and the stratified region around the spark plug 14 can be suppressed from being overrich even when the stratified stoichiometric operation is performed. Yes, and a value corresponding to the engine speed and engine load factor. Thereafter, the catalyst temperature increase control is performed according to steps S110 to S118. When it is recognized that the lean NOx catalyst is equal to or higher than the determination temperature (step S122), the bank control is performed according to step S130 (see FIG. 4).

  As described above, according to the fifth embodiment, the target purge rate of evaporation purge is set to a low purge rate during catalyst temperature increase control. Accordingly, it is possible to suppress the occurrence of combustion failure due to over-riching in the vicinity of the spark plug 14 during the stratified stoichiometric operation of the catalyst temperature increase control.

  In the fifth embodiment, the case where the target purge rate of the evaporation purge is set to the low purge rate when the control of the first embodiment is performed has been described. However, the present invention is not limited to this, and the evaporation purge rate may be set to a low purge rate even when the control of the second embodiment is performed. Specifically, before step S202 of the routine of FIG. 5, steps S502 and S504 are performed to set the evaporation purge rate to a low purge rate, and then the catalyst temperature increase control may be performed.

  In the fifth embodiment, the case where the bank control is performed in step S504 while the target purge rate is set to the low purge rate has been described. However, the present invention is not limited to this, for example, a low purge rate is set during the catalyst temperature increase control, and after it is recognized in step S122 that the temperature of the lean NOx catalyst is equal to or higher than the determination temperature, the target purge rate is set. May be reset to the basic purge rate during normal operation and bank control may be performed.

  For example, by executing step S504 in the fifth embodiment, the “low purge rate setting means” of the present invention is realized.

Embodiment 6 FIG.
The system of the sixth embodiment has the same configuration as the system of the first embodiment. The system of the sixth embodiment performs the same control as the system of the first embodiment except that the air-fuel ratio of each bank is controlled to be weak rich / weak lean at the time of catalyst temperature increase control. That is, in the catalyst temperature increase control in the fifth embodiment, the compression stroke is performed in a state where the target air-fuel ratio for each bank is set to a weak rich / weak lean ratio that is smaller than the stoichiometric rich ratio and lean ratio during the bank control. Performs stratified charge combustion and ignition delay. At this time, the weak rich / weak lean is set so that the air-fuel ratio of the combined exhaust gas flowing into the lean NOx catalyst 60 becomes stoichiometric.

  Specifically, the weak rich ratio is determined according to a predetermined map according to the engine speed and the throttle opening. The weak lean ratio is determined by weak lean ratio = 14.6 / (2-weak rich ratio) so that the internal combustion engine 2 has a stoichiometric air-fuel ratio in accordance with the weak rich ratio. Here, the weak rich / weak lean ratio is set in a range where the torque change due to the air-fuel ratio change is small. Specifically, as the weak rich air-fuel ratio, A / F is from 14.2 to about the stoichiometric air-fuel ratio, and the weak lean air-fuel ratio is set to a value from about 15.0 to the stoichiometric air-fuel ratio.

  In this way, by setting the target air-fuel ratio to weak rich / weak lean at the stage of catalyst temperature rise control, a catalytic reaction can be caused in the lean NOx catalyst 60 as in the bank control. As a result, even during the catalyst temperature increase control, the temperature increase due to the catalytic reaction in the lean NOx catalyst 60 can be achieved. That is, according to the control of the sixth embodiment, the target air-fuel ratio is increased at the same time that the temperature of the gas entering the lean NOx catalyst 60 is raised by the stratified stoichiometric combustion of the compression stroke injection and the ignition timing retarded to raise the catalyst temperature. With this weak rich / weak lean control, the temperature of the catalyst can be raised by the catalytic reaction in the lean NOx catalyst 60. Therefore, the lean NOx catalyst 60 can be raised to the determination temperature in a shorter time.

  FIG. 10 is a flowchart for illustrating a control routine executed by the system in the sixth embodiment of the present invention. The routine shown in FIG. 10 is executed except that steps S602 to S608 are executed after step S108, and steps S610 to S616 are executed when the catalyst temperature ≧ the determination temperature is not established in step S122. This is the same as the routine of FIG. That is, after the sulfur poisoning recovery request is recognized in step S108, the mode setting flag is read (step S602). Similar to the mode setting flag in the bank control, this flag is a mode in which when the flag = 0, the target air-fuel ratio of the first bank is set to a weak rich air-fuel ratio and the target air-fuel ratio of the second bank is set to a weak lean air-fuel ratio. This flag specifies a mode in which the target air-fuel ratio of the first bank is set to a weak lean air-fuel ratio and the target air-fuel ratio of the second bank is set to a weak rich air-fuel ratio when the flag = 1. At the initial setting stage, flag = 0 is set.

  Next, the rich rich ratio of the rich bank is set according to the mode setting flag (step S604). The weak rich ratio is calculated and set, for example, according to a map using engine speed and required torque as parameters. Next, the weak lean ratio of the lean bank is set (step S606). The weak lean ratio of the lean bank is calculated and set according to the calculation formula (14.6 / (2-rich ratio)) from the weak rich ratio obtained in step S604. Next, the measurement of the weak rich / weak lean mode elapsed time is started (step S608). The weak rich / weak lean mode elapsed time is an elapsed time after the target air-fuel ratio of each bank is set as the operating condition corresponding to the mode setting flag.

  Thereafter, the throttle valve opening, the fuel injection timing, and the ignition timing retard amount are set (steps S110 to S118), and the operation of the internal combustion engine 2 is started in the weak rich / weak lean state set as described above. . Next, in step s120, it is determined whether or not the temperature of the lean NOx catalyst 60 has risen to the determination temperature. In step S122, if it is not recognized that the lean NOx catalyst temperature ≧ the determination temperature is satisfied, it is determined whether or not the weak rich / weak lean mode elapsed time is equal to or longer than a predetermined determination time (step S610). If it is not recognized that the weak rich / weak lean mode elapsed time ≧ determination time is satisfied, air-fuel ratio feedback control is performed according to the outputs of the main air-fuel ratio sensors 58a and 58b and the sub air-fuel ratio sensor 64 (step S612). Returning to step S120, the lean NOx catalyst temperature is detected.

  On the other hand, if it is determined in step S610 that the weak rich / weak lean mode elapsed time ≧ determination time is satisfied, the flag is changed (step S614). That is, when the current mode setting flag = 0, the flag = 1, and when the flag = 1, the flag = 0. Next, the weak rich / weak lean mode time = 0 is set (step S616), and the process returns to step S602 to read the flag. By repeating the above-described steps, when it is recognized in step S122 that the lean NOx catalyst has reached the determination temperature, bank control (step S130) is performed thereafter.

  As described above, according to the system of the sixth embodiment, during the catalyst temperature increase control of the lean NOx catalyst 60, in addition to the temperature increase due to the stratified stoichiometric combustion of the compression stroke injection and the ignition timing delay control, the weak rich / The catalyst temperature rise is controlled by weak lean control. Therefore, the sulfur poisoning recovery can be completed at an earlier stage, and the emission can be improved.

  In the sixth embodiment, the case where the temperature increase control is performed by correcting the ignition timing greatly retarded and the opening of the throttle valve 30 as in the first embodiment has been described. However, the present invention is not limited to this, and the control of the second embodiment may be combined with the weak rich / weak lean control of the sixth embodiment. In this case, specifically, in step S108 of the routine of FIG. 5, the target air-fuel ratio is set to weak rich / weak lean as in steps S602 to 608, and steps S610 to S616 are performed after step S122. The catalyst temperature increase control described in the second embodiment may be performed.

  In the sixth embodiment, the mode setting flag is read, weak rich / weak lean is set according to the flag, and the weak rich bank and the weak lean bank are periodically reversed. Thereby, degradation of the three-way catalysts 54a and 54b can be prevented. However, in the present invention, the present invention is not limited to the case where the rich bank and the lean bank are reversed as described above, and even if the rich bank and the lean bank are fixed and weak rich / weak lean control is performed. Good.

  In the sixth embodiment, the “weak rich / weak lean air-fuel ratio setting means” of the present invention is realized by executing steps S604 and S606.

  In the above embodiment, when referring to the number of each element, quantity, quantity, range, etc., unless otherwise specified or clearly specified in principle, the number referred to It is not limited. Further, the structures described in the embodiments, steps in the method, and the like are not necessarily essential to the present invention unless otherwise specified or clearly specified in principle.

It is a schematic diagram for demonstrating the structure of the system in Embodiment 1 of this invention. 6 is a graph for explaining a relationship between an ignition timing retardation amount and a throttle valve opening correction value in Embodiment 1 of the present invention; It is a flowchart for demonstrating the routine of sulfur poisoning recovery | restoration control which the system of Embodiment 1 of this invention performs. It is a flowchart for demonstrating the routine of the bank control which the system of Embodiment 1 of this invention performs. It is a flowchart for demonstrating the routine of sulfur poisoning recovery | restoration control which the system of Embodiment 2 of this invention performs. It is a flowchart for demonstrating the routine of the bank control which the system of Embodiment 2 of this invention performs. It is a flowchart for demonstrating the routine of sulfur poisoning recovery | restoration control which the system of Embodiment 3 of this invention performs. It is a flowchart for demonstrating the routine of sulfur poisoning recovery | restoration control which the system of Embodiment 4 of this invention performs. It is a flowchart for demonstrating the routine of sulfur poisoning recovery control which the system of Embodiment 5 of this invention performs. It is a flowchart for demonstrating the routine of sulfur poisoning recovery control which the system of Embodiment 6 of this invention performs.

Explanation of symbols

2 Internal combustion engine 4a, 4b Cylinder 14 Spark plug 16 In-cylinder injector 18a, 18b Intake port 20a, 20b Exhaust port 26a, 26b Intake manifold 28 Intake passage 30 Throttle valve 32 Air flow meter 34 High pressure fuel pump 36 Fuel tank 38 Vapor passage 40 Canister 42 Purge passage 44 VSV
50a, 50b Exhaust manifold 54a, 54b Three way catalyst 56a, 56b Exhaust passage 60 Lean NOx catalyst

Claims (9)

An internal combustion engine control device for controlling an internal combustion engine comprising two or more cylinder groups and a lean NOx catalyst in which exhaust passages connected to each of the cylinder groups are connected together,
Sulfur component removal control means for performing sulfur component removal control for removing sulfur components stored in the lean NOx catalyst;
Prior to the sulfur component removal control , a catalyst temperature increase control means for performing a catalyst temperature increase control for increasing the temperature of the lean NOx catalyst, and
The sulfur component removal control means includes
In the sulfur component removal control, the control target value of the air-fuel ratio of one of the cylinder groups is set to be richer than the theoretical air-fuel ratio, and the control target value of the air-fuel ratio of the other cylinder group is theoretically set. Rich / lean air-fuel ratio setting means for setting to be leaner than the air-fuel ratio,
The catalyst temperature rise control means includes
An opening degree estimating means for estimating the opening degree of the throttle valve when the sulfur component removal control is executed;
In the catalyst temperature increase control, an opening control means for controlling the opening of the throttle valve to the same opening as the estimated opening of the throttle valve;
Ignition timing retarding means for retarding the ignition timing of each cylinder of the cylinder group , so that the torque generated in the catalyst temperature increase control is the same as the torque generated in the sulfur component removal control ;
A control device for an internal combustion engine, comprising: The internal combustion engine includes an in-cylinder injector that is disposed in each cylinder of the cylinder group and injects fuel into the cylinder.
The catalyst temperature increase control means includes a fuel injection timing control means for controlling the fuel to be directly injected from the in- cylinder injector into the cylinder during the compression stroke of each cylinder during the catalyst temperature increase control. The control apparatus for an internal combustion engine according to claim 1, further comprising: The internal combustion engine
A fuel tank for holding fuel to be supplied to the in-cylinder injector;
A canister for storing evaporated fuel from the fuel tank;
A purge mechanism for causing the purge gas containing the evaporated fuel to flow into the intake passage from the canister,
The control apparatus for an internal combustion engine according to claim 2 , further comprising purge gas concentration learning means for learning a purge gas concentration supplied to the intake passage. Purge gas concentration determination means for determining whether or not the purge gas concentration is equal to or lower than a determination concentration;
4. The control device for an internal combustion engine according to claim 3 , wherein the catalyst temperature increase control means executes the catalyst temperature increase control only when the purge gas concentration is recognized to be equal to or lower than a determination concentration. Two or more cylinder groups,
An in-cylinder injector that is disposed in each cylinder of the cylinder group and injects fuel into the cylinder;
A fuel tank for holding fuel to be supplied to the in-cylinder injector;
A canister for storing evaporated fuel from the fuel tank;
A purge mechanism for causing the purge gas containing the evaporated fuel to flow into the intake passage from the canister;
A lean NOx catalyst in which exhaust passages connected to each of the cylinder groups are connected together;
An internal combustion engine control device for controlling an internal combustion engine comprising:
Sulfur component removal control means for performing sulfur component removal control for removing sulfur components stored in the lean NOx catalyst;
Prior to the sulfur component removal control, catalyst temperature increase control means for performing catalyst temperature increase control for increasing the temperature of the lean NOx catalyst;
Purge gas concentration learning means for learning the concentration of purge gas supplied to the intake passage;
Purge gas concentration determination means for determining whether the purge gas concentration is equal to or lower than a determination concentration ;
With
The sulfur component removal control means includes
In the sulfur component removal control, the control target value of the air-fuel ratio of one of the cylinder groups is set to be richer than the theoretical air-fuel ratio, and the control target value of the air-fuel ratio of the other cylinder group is theoretically set. Rich / lean air-fuel ratio setting means for setting to be leaner than the air-fuel ratio,
The catalyst temperature rise control means includes
The catalyst temperature increase control is executed only when the purge gas concentration is found to be equal to or lower than the determination concentration , and
In the catalyst temperature increase control, ignition timing retarding means for retarding the ignition timing of each cylinder of the cylinder group;
Fuel injection control means for controlling so that fuel is directly injected into the cylinder from the in-cylinder injector in the compression stroke of each cylinder during the catalyst temperature increase control;
Control device for the internal combustion engine you comprising: a. Until the purge gas concentration is found to be equal to or lower than the determination concentration, the target purge rate when the purge gas flows into the intake passage is higher than the basic target purge rate set according to the operating conditions. 6. The control device for an internal combustion engine according to claim 4 , further comprising high purge rate setting means for setting to The internal combustion engine
A fuel tank for holding fuel to be supplied to the in-cylinder injector;
A canister for storing evaporated fuel from the fuel tank;
A purge mechanism for causing the purge gas containing the evaporated fuel to flow into the intake passage from the canister,
The catalyst temperature rise control means sets a target purge rate when the purge gas is allowed to flow into the intake passage in the catalyst temperature rise control to a purge rate lower than a basic target purge rate set according to operating conditions. control apparatus for an internal combustion engine according to any one of the low purge rate setting means for setting, claim 2, characterized in that it comprises 6. In the catalyst temperature increase control, the catalyst temperature increase control means theoretically sets a control target value of the air-fuel ratio of any one of the cylinder groups at a ratio smaller than a rich rate in the sulfur removal control. Set to richer than the air-fuel ratio, and set the control target value of the air-fuel ratio of the other cylinder group to a leaner than the stoichiometric air-fuel ratio at a ratio smaller than the lean ratio at the time of the sulfur removal control. control apparatus for an internal combustion engine according to any one of claims 1 7, characterized in that it comprises a lean air-fuel ratio setting means. The catalyst temperature increase control means includes theoretical air / fuel ratio setting means for setting a control target value of the air / fuel ratio of all the cylinder groups in the vicinity of the theoretical air / fuel ratio in the catalyst temperature increase control. the control device according to any one of 1 to 7.

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