JP4687484B2 - Exhaust gas purification system for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine provided with an NOx storage reduction catalyst provided in an exhaust passage of the internal combustion engine.

  In an exhaust gas purification system for an internal combustion engine, a NOx storage reduction catalyst (hereinafter simply referred to as NOx) that stores NOx in exhaust when the ambient atmosphere is an oxidizing atmosphere and reduces NOx that is stored when the ambient atmosphere is a reducing atmosphere. Some of them are called catalysts.

  In such an exhaust gas purification system for an internal combustion engine, in order to restore the NOx occlusion capacity of the NOx catalyst, NOx reduction control for reducing NOx occluded in the NOx catalyst and N for reducing SOx occluded in the Ox catalyst are reduced. SOx poisoning recovery control is performed. Hereinafter, the control for reducing the oxide stored in the NOx catalyst is referred to as oxide reduction control.

Patent Document 1 discloses a technique for executing sub fuel injection at a timing later than main fuel injection in an internal combustion engine for the purpose of increasing the exhaust gas temperature. This patent document 1 also discloses a technique for setting an upper limit value of the auxiliary fuel injection amount so that a torque generated by combustion of the fuel injected by the auxiliary fuel injection becomes equal to or less than an allowable value.
JP 2002-235589 A JP 2003-239789 A JP 2002-276443 A JP 2002-38932 A

  In the oxide reduction control, it is necessary to make the ambient atmosphere of the NOx catalyst a reducing atmosphere by lowering the air-fuel ratio of the exhaust gas to the target air-fuel ratio set according to the oxide to be reduced. Therefore, there is a case where the air-fuel ratio of the exhaust gas is lowered by executing the auxiliary fuel injection in the cylinder of the internal combustion engine at a timing later than the execution timing of the main fuel injection. However, when such sub fuel injection is executed, the fuel injected by the sub fuel injection may burn and the torque of the internal combustion engine may increase.

  The present invention has been made in view of the above problem, and is an exhaust purification system of an internal combustion engine including a NOx catalyst provided in an exhaust passage of the internal combustion engine, and performs oxide injection by performing sub fuel injection. An object of the present invention is to provide a technique capable of suppressing an excessive increase in the torque of the internal combustion engine caused by executing the oxide reduction control in the reduction control.

  The present invention relates to a target sub fuel injection amount in one combustion cycle of an internal combustion engine that is injected to make the ambient atmosphere of the NOx catalyst as a reducing atmosphere during execution of the oxide reduction control, and the torque increase amount of the internal combustion engine is within an allowable range. When the amount is larger than the upper limit auxiliary fuel injection amount, which is the upper limit value, the execution of the oxide reduction control is prohibited.

More specifically, the exhaust gas purification system for an internal combustion engine according to the present invention is:
An NOx storage reduction catalyst that is provided in an exhaust passage of an internal combustion engine and that stores NOx in exhaust when the ambient atmosphere is an oxidizing atmosphere and reduces NOx stored when the ambient atmosphere is a reducing atmosphere;
A fuel injection valve for directly injecting fuel into the cylinder of the internal combustion engine;
By executing the auxiliary fuel injection at a timing later than the execution timing of the main fuel injection by the fuel injection valve, the air-fuel ratio of the exhaust gas is reduced to the target air-fuel ratio, thereby being stored in the NOx storage reduction catalyst. Oxide reduction control execution means for executing oxide reduction control for reducing oxides;
Target sub fuel injection amount calculating means for calculating a target sub fuel injection amount in one combustion cycle of the internal combustion engine when executing the oxide reduction control by the oxide reduction control executing means;
When the oxide reduction control is executed by the oxide reduction control execution means, the upper limit sub-fuel injection amount in one combustion cycle of the internal combustion engine in which the torque increase amount of the internal combustion engine becomes the upper limit value of the allowable range. An upper limit auxiliary fuel injection amount calculating means for calculating the fuel injection amount,
When the target sub fuel injection amount calculated by the target sub fuel injection amount calculating means is larger than the upper limit sub fuel injection amount calculated by the upper limit sub fuel injection amount calculating means, the oxide reduction control is executed. Execution of oxide reduction control by means is prohibited.

  Here, the main fuel injection is a fuel injection executed near the top dead center of the compression stroke by the fuel injection valve. The auxiliary fuel injection is a fuel injection that is executed in the expansion stroke by the fuel injection valve.

  Further, the target air-fuel ratio is a value determined in advance according to the oxide to be reduced by executing the oxide reduction control. The target sub fuel injection amount is calculated as a sub fuel injection amount for controlling the air-fuel ratio of the exhaust gas to the target air-fuel ratio when the oxide reduction control is executed.

  According to the present invention, when sub fuel injection is performed so that the air-fuel ratio of the exhaust gas becomes the target air-fuel ratio, if the amount of torque increase of the internal combustion engine exceeds the upper limit value of the allowable range, the execution of the oxide reduction control is performed. It is forbidden. That is, the oxide reduction control is executed only when the target sub fuel injection amount is equal to or less than the upper limit sub fuel injection amount. Thereby, it is possible to suppress an excessive increase in the torque of the internal combustion engine caused by executing the oxide reduction control.

  In the present invention, the auxiliary fuel injection may be executed in a plurality of times during one combustion cycle of the internal combustion engine when the oxide reduction control is executed. In this case, there may be further provided a split ratio setting means for setting the ratio of the fuel injection amount in each sub fuel injection performed during one combustion cycle of the internal combustion engine. When the target sub fuel injection amount is relatively large, the fuel in the sub fuel injection executed at a later time in one combustion cycle of the internal combustion engine is compared with when the target sub fuel injection amount is relatively small. The ratio of the injection amount may be increased.

  When the sub fuel injection is executed, the influence of the injected fuel on the torque of the internal combustion engine is reduced as the execution time is delayed. Therefore, when the sub fuel injection is executed a plurality of times during one combustion cycle of the internal combustion engine, the target sub fuel injection amount is increased by controlling the ratio of the fuel injection amount by each sub fuel injection as described above. Even if it exists, it can suppress that the torque increase amount of an internal combustion engine becomes large too much.

  Even in the above case, when the target sub fuel injection amount is equal to or less than the predetermined amount, the number of executions of the sub fuel injection during the execution of the oxide reduction control is set to one time in one combustion cycle of the internal combustion engine. It is also good.

  Here, the predetermined amount is a threshold value of the auxiliary fuel injection amount that causes the torque increase amount of the internal combustion engine to be within an allowable range even if injection is performed by one auxiliary fuel injection during one combustion cycle of the internal combustion engine.

If the target sub fuel injection amount is equal to or less than the predetermined amount, the torque increase amount of the internal combustion engine is suppressed from becoming excessively large even if the number of sub fuel injections is performed only once during one combustion cycle of the internal combustion engine. I can do it. Further, the deterioration of the fuel injection valve can be suppressed by suppressing the number of executions of the auxiliary fuel injection.

  In the present invention, even when the oxide reduction control is executed only when the target sub fuel injection amount is equal to or less than the upper limit sub fuel injection amount, the environmental conditions such as the intake air temperature, the atmospheric pressure, and the temperature of the cooling water vary. As a result, the torque increase amount of the internal combustion engine may exceed the upper limit value of the allowable range during the execution of the oxide reduction control.

  Further, in the present invention, the oxide reduction control is executed even when the main fuel injection is stopped in the internal combustion engine, that is, when the driver of the vehicle equipped with the internal combustion engine requests the deceleration operation. There is a case. At this time, when the torque of the internal combustion engine increases due to combustion of the fuel injected by the auxiliary fuel injection, the rotational speed of the internal combustion engine increases even if the main fuel injection is stopped.

  Therefore, in the present invention, when the main fuel injection is stopped in the internal combustion engine and the oxide reduction control is executed, the torque of the internal combustion engine is transmitted to the drive system of the vehicle. If the rotational speed of the internal combustion engine is higher than the rotational speed at the time when the main fuel injection is stopped and the oxide reduction control is executed, the oxide reduction control is performed. May be stopped.

  Here, the predetermined rotational speed is a threshold value of the rotational speed increase amount that can be determined that the torque increase amount of the internal combustion engine has exceeded the upper limit of the allowable range.

  As a result, even if the torque of the internal combustion engine fluctuates due to variations in environmental conditions, it is possible to suppress an excessive increase in the torque of the internal combustion engine.

  In the present invention, when the execution of the oxide reduction control by the oxide reduction control execution means is stopped, the sub fuel injection amount in one combustion cycle of the internal combustion engine may be gradually decreased.

  As a result, it is possible to suppress sudden fluctuations in the torque of the internal combustion engine when the execution of the oxide reduction control is stopped.

  According to the present invention, an exhaust gas purification system for an internal combustion engine provided with an NOx catalyst provided in an exhaust passage of the internal combustion engine, which performs oxide reduction control by executing sub fuel injection, oxide reduction It is possible to suppress an excessive increase in the torque of the internal combustion engine caused by executing the control.

  Hereinafter, specific embodiments of an exhaust gas purification system for an internal combustion engine according to the present invention will be described with reference to the drawings.

<Schematic configuration of internal combustion engine and intake / exhaust system thereof>
Here, a case where the present invention is applied to a diesel engine for driving a vehicle will be described as an example. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its intake / exhaust system according to the present embodiment.

The internal combustion engine 1 is a diesel engine for driving a vehicle. A piston 3 is slidably provided in the cylinder 2 of the internal combustion engine 1. An intake port 4 and an exhaust port 5 are connected to the combustion chamber in the upper part of the cylinder 2. The openings of the intake port 4 and the exhaust port 5 to the combustion chamber are opened and closed by an intake valve 6 and an exhaust valve 7, respectively. The intake port 4 and the exhaust port 5 are connected to an intake passage 8 and an exhaust passage 9, respectively. The cylinder 2 is provided with a fuel injection valve 10 that directly injects fuel into the cylinder 2.

  An air flow meter 11 is provided in the intake passage 8. The exhaust passage 9 is provided with an NOx storage reduction catalyst 12 (hereinafter simply referred to as the NOx catalyst 12). The NOx catalyst 12 is a catalyst that stores NOx in the exhaust when the ambient atmosphere is an oxidizing atmosphere and reduces the NOx that is stored when the ambient atmosphere is a reducing atmosphere.

  Further, an air-fuel ratio sensor 13 for detecting the air-fuel ratio of the exhaust is provided upstream of the NOx catalyst 12 in the exhaust passage 9. Further, an exhaust gas temperature sensor 14 for detecting the temperature of the exhaust gas is provided downstream of the NOx catalyst 12 in the exhaust gas passage 9.

  The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 20 for controlling the internal combustion engine 1. An air flow meter 11, an air-fuel ratio sensor 13, and an exhaust temperature sensor 14 are electrically connected to the ECU 20. Further, the ECU 20 is connected to a crank position sensor 15, an accelerator opening sensor 16 that detects an accelerator opening of a vehicle on which the internal combustion engine 1 is mounted, and a clutch switch 18. These output signals are input to the ECU 20. The ECU 20 calculates the rotational speed of the internal combustion engine 1 based on the detection value of the crank position sensor 15. Further, the ECU 20 estimates the temperature of the NOx catalyst 12 based on the detected value of the exhaust temperature sensor 14.

  The ECU 20 is electrically connected to a transmission 17 of a vehicle on which the fuel injection valve 10 and the internal combustion engine 1 are mounted. This is controlled by the ECU 20.

<SOx poisoning recovery control>
The NOx catalyst 12 stores not only NOx in exhaust gas but also SOx. When the SOx occlusion amount in the NOx catalyst 12 increases, the NOx occlusion capacity in the NOx catalyst 12 decreases. Therefore, in this embodiment, SOx poisoning recovery control for reducing the SOx stored in the NOx catalyst 12 is performed. In this embodiment, the SOx poisoning recovery control corresponds to the oxide reduction control according to the present invention.

  In the SOx poisoning recovery control, the temperature of the NOx catalyst 12 is raised to a target temperature at which SOx can be reduced, and the air-fuel ratio in the ambient atmosphere of the NOx catalyst 12 is lowered to a target air-fuel ratio at which SOx can be reduced. The ambient atmosphere around the NOx catalyst 12 needs to be a reducing atmosphere. Therefore, in the SOx poisoning recovery control according to the present embodiment, the fuel injection valve 10 performs the auxiliary fuel injection at a timing later than the main fuel injection executed near the top dead center of the compression stroke.

  When such sub fuel injection is executed, the fuel injected by the sub fuel injection is supplied to the NOx catalyst 12. The temperature of the NOx catalyst 12 rises due to the heat of oxidation generated when the supplied fuel is oxidized in the NOx catalyst 12. Further, when the auxiliary fuel injection is executed, the air-fuel ratio of the exhaust discharged from the internal combustion engine 1, that is, the exhaust flowing into the NOx catalyst 12, is lowered. Then, by controlling the sub fuel injection amount in one combustion cycle in the internal combustion engine 1, the temperature of the NOx catalyst 12 is controlled to the target temperature, and the air-fuel ratio of the ambient atmosphere of the NOx catalyst 12 is controlled to the target air-fuel ratio. To do.

  Here, during the execution of the SOx poisoning recovery control, the temperature of the NOx catalyst 12 becomes the target temperature, and the air-fuel ratio of the ambient atmosphere of the NOx catalyst 12 becomes the target air-fuel ratio. The fuel injection amount is set as a target sub fuel injection amount. The target auxiliary fuel injection amount is calculated based on the intake air amount, the main fuel injection amount, the target temperature, and the target air-fuel ratio.

  As described above, in this embodiment, the SOx poisoning recovery control is performed by executing the auxiliary fuel injection. However, when the auxiliary fuel injection is executed, the torque of the internal combustion engine 1 may increase due to combustion of the fuel injected by the auxiliary fuel injection. If the torque fluctuation amount at this time is excessively large, the drivability may be deteriorated.

  Therefore, in this embodiment, when the SOx poisoning recovery control is executed, the torque increase amount of the internal combustion engine 1 becomes the upper limit value of the allowable range (hereinafter, the torque increase upper limit value) in one combustion cycle. An upper limit auxiliary fuel injection amount that is an auxiliary fuel injection amount is calculated. The upper limit value of torque increase is determined in advance according to the rotational speed of the internal combustion engine 1 and the gear ratio of the transmission 17. An upper limit auxiliary fuel injection amount is calculated based on the torque increase upper limit value.

  When the SOx poisoning recovery control is executed, if the target auxiliary fuel injection amount is larger than the upper limit auxiliary fuel injection amount, the execution of the SOx poisoning recovery control is prohibited. In other words, the SOx poisoning recovery control is executed only when the target sub fuel injection amount is equal to or less than the upper limit sub fuel injection amount.

  Thereby, even when the SOx poisoning recovery control is performed by executing the auxiliary fuel injection, it is possible to suppress an excessive increase in the torque of the internal combustion engine 1 by executing the SOx poisoning recovery control. I can do it.

  Next, the control routine of the SOx poisoning recovery control according to this embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 20 and is a routine that is repeatedly executed at predetermined intervals during the operation of the internal combustion engine 1.

  In this routine, the ECU 20 first determines in S101 whether or not the SOx occlusion amount in the NOx catalyst 12 is equal to or greater than a predetermined occlusion amount Qse. Here, the predetermined storage amount Qse is a value that serves as a threshold with which it can be determined that the NOx storage amount of the NOx catalyst 12 may be excessively reduced. Here, the NOx catalyst 12 is based on the integrated amount of fuel injection in the internal combustion engine 1 or the travel distance of the vehicle on which the internal combustion engine 1 is mounted after the previous execution of the SOx poisoning recovery control is stopped. The SOx occlusion amount may be estimated. If an affirmative determination is made in S101, the ECU 20 proceeds to S102, and if a negative determination is made, the ECU 20 ends the execution of this routine.

  In S102, the ECU 20 calculates a target auxiliary fuel injection amount Qfst when executing the SOx poisoning recovery control.

  Next, the ECU 20 proceeds to S103, and calculates an upper limit auxiliary fuel injection amount Qfsmax when the SOx poisoning recovery control is executed.

  Next, the ECU 20 proceeds to S104, and determines whether or not the target sub fuel injection amount Qfst is equal to or less than the upper limit sub fuel injection amount Qfsmax. If an affirmative determination is made in S104, the ECU 20 proceeds to S105, and if a negative determination is made, the ECU 20 proceeds to S110.

  The ECU 20 having advanced to S110 prohibits the execution of the auxiliary fuel injection. That is, the execution of the SOx poisoning recovery control at the present time is prohibited.

On the other hand, the ECU 20 having proceeded to S105 determines whether or not the target auxiliary fuel injection amount Qfst is equal to or less than the predetermined injection amount Qfs1. Here, the predetermined injection amount Qfs1 is the upper limit of the auxiliary fuel injection amount at which the torque increase amount of the internal combustion engine 1 is equal to or less than the torque increase upper limit value even if injection is performed by one sub fuel injection during one combustion cycle of the internal combustion engine 1. Value. If a positive determination is made in S105, the EC
If U20 proceeds to S106 and a negative determination is made, the ECU 20 proceeds to S108.

  The ECU 20 that has proceeded to S106 sets the number Nf of sub fuel injections during one combustion cycle of the internal combustion engine 1 to one.

  Next, the ECU 20 proceeds to S107 and executes sub fuel injection. That is, the SOx poisoning recovery control is executed. In this case, the auxiliary fuel injection is executed once in the expansion stroke, and the fuel for the target auxiliary fuel injection amount Qfst is injected by this one auxiliary fuel injection. Thereafter, the ECU 20 ends the execution of this routine.

  The ECU 20 having proceeded to S108 sets the number of executions Nf of the auxiliary fuel injection in one combustion cycle of the internal combustion engine 1 to 2 times. Here, the auxiliary fuel injection that is performed earlier, that is, closer to the compression stroke top dead center is referred to as the first auxiliary fuel injection, and is later, that is, farther from the compression stroke top dead center. The auxiliary fuel injection that is performed at the time is referred to as a second auxiliary fuel injection. In this case, each sub fuel injection is executed such that the sum of the fuel injection amount by the first sub fuel injection and the fuel injection amount by the second sub fuel injection becomes the target sub fuel injection amount.

  Next, the ECU 20 proceeds to S109 and sets a ratio Rd (hereinafter simply referred to as a division ratio Rd) between the fuel injection amount by the first sub fuel injection and the fuel injection amount by the second sub fuel injection. At this time, when the target sub fuel injection amount Qfst is relatively large, the division ratio is set so that the ratio of the fuel injection amount by the second sub fuel injection is higher than when the target sub fuel injection amount Qfst is relatively small. Rd is set.

  Next, the ECU 20 proceeds to S107 and executes sub fuel injection. That is, the SOx poisoning recovery control is executed. In this case, the auxiliary fuel injection is executed twice in the expansion stroke. The fuel for the target auxiliary fuel injection amount Qfst is injected by the two auxiliary fuel injections. Further, the fuel injection amount by each sub fuel injection is an amount obtained by dividing the target sub fuel injection amount Qfst by the division ratio set in S109. Thereafter, the ECU 20 ends the execution of this routine.

  According to the control routine described above, when the target sub fuel injection amount Qfst is larger than the upper limit sub fuel injection amount Qfsmax, the execution of the SOx poisoning recovery control is prohibited. Therefore, it is possible to suppress an excessive increase in the torque increase amount of the internal combustion engine 1 by executing the SOx poisoning recovery control.

  Further, according to the above control routine, when the target auxiliary fuel injection amount Qfst is larger than the predetermined injection amount Qfs1, the auxiliary fuel injection is divided and executed twice in one combustion cycle of the internal combustion engine 1. At this time, when the target sub fuel injection amount Qfst is relatively large, the ratio of the fuel injection amount by the second sub fuel injection is made higher than when the target sub fuel injection amount Qfst is relatively small.

  When the sub fuel injection is executed, the influence of the injected fuel on the torque of the internal combustion engine 1 becomes smaller as the execution time becomes farther from the top dead center of the compression stroke. That is, the influence on the torque of the internal combustion engine 1 when the fuel injected by the second auxiliary fuel injection is burned is the influence on the torque of the internal combustion engine 1 when the fuel injected by the first auxiliary fuel injection is burned. Smaller than.

  Therefore, as described above, by controlling the ratio of the fuel injection amount by each of the first sub fuel injection and the second sub fuel injection, even if the target sub fuel injection amount Qfst increases, the torque of the internal combustion engine 1 increases. An excessive increase in the amount can be suppressed.

  Further, according to the above control routine, when the target auxiliary fuel injection amount Qfst is equal to or less than the predetermined injection amount Qfs1, the number of executions of the auxiliary fuel injection is only once during one combustion cycle of the internal combustion engine. Thereby, the frequency | count of execution of sub fuel injection can be suppressed, and, therefore, deterioration of the fuel injection valve 10 can be suppressed.

  In the present embodiment, when the target sub fuel injection amount is larger than the predetermined injection amount, the number of executions of the sub fuel injection in one combustion cycle of the internal combustion engine is set to two. It is good also as 3 times or more. Also in this case, each sub fuel injection is executed such that the sum of the fuel injection amounts injected by each sub fuel injection becomes the target sub fuel injection amount. Also in this case, when the target sub fuel injection amount is relatively large, the sub fuel executed at a later time in one combustion cycle of the internal combustion engine than when the target sub fuel injection amount is relatively small. Increase the ratio of fuel injection amount in injection. As a result, as described above, even when the target auxiliary fuel injection amount Qfst increases, it is possible to suppress an excessive increase in the torque of the internal combustion engine 1.

  Further, in the present embodiment, when the execution of the SOx poisoning recovery control is stopped after the execution, the sub fuel injection amount in one combustion cycle of the internal combustion engine is gradually decreased.

  As a result, it is possible to suppress sudden fluctuations in the torque of the internal combustion engine 1 when the execution of the SOx poisoning recovery control is stopped.

  The schematic configuration of the internal combustion engine and its intake / exhaust system according to this embodiment is the same as that of the first embodiment. Also in the present embodiment, the SOx poisoning recovery control similar to that in the first embodiment is performed.

<Torque increase suppression control after execution of SOx poisoning recovery control>
As described above, even when the SOx poisoning recovery control is executed only when the target auxiliary fuel injection amount is equal to or less than the upper limit auxiliary fuel injection amount, the environmental conditions such as the intake air temperature, the atmospheric pressure, the cooling water temperature, and the like. Due to the influence of the variation of the engine, the amount of increase in the torque of the internal combustion engine 1 that rises due to the combustion of the fuel injected by the auxiliary fuel injection during the execution of the SOx poisoning recovery control may exceed the torque increase upper limit value. There is.

In addition, the SOx poisoning regeneration control is executed even when the main fuel injection is stopped in the internal combustion engine 1, that is, when the driver of the vehicle equipped with the internal combustion engine 1 is requesting a deceleration operation. There is. At this time, when the torque of the internal combustion engine 1 increases due to combustion of the fuel injected by the auxiliary fuel injection, the rotational speed of the internal combustion engine 1 increases even when the main fuel injection is stopped. In such a case, the rotational speed of the internal combustion engine 1 rises even though the driver of the vehicle requests a deceleration operation, which may lead to a deterioration in drivability.

  Therefore, in this embodiment, torque increase suppression control is performed to suppress an excessive increase in torque of the internal combustion engine 1 when SOx poisoning recovery control is executed at the time of a deceleration operation request.

  Here, the control routine of the torque increase suppression control according to the present embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 20 and is a routine that is repeatedly executed at predetermined intervals during the operation of the internal combustion engine 1.

In this routine, the ECU 20 first determines in S201 whether or not the accelerator opening Raopen of the vehicle on which the internal combustion engine 1 is mounted is zero. When the accelerator opening Raopen is zero, the main fuel injection by the fuel injection valve 10 is stopped. That is, it is possible to determine whether or not the driver of the vehicle is requesting a deceleration operation by determining whether or not the accelerator opening Raopen is zero. If an affirmative determination is made in S201, the ECU 20 proceeds to S202, and if a negative determination is made, the ECU 20 ends the execution of this routine.

  In S202, the ECU 20 determines whether the SOx poisoning recovery control is being executed, that is, whether the sub fuel injection is being executed. If an affirmative determination is made in S202, the ECU 20 proceeds to S203, and if a negative determination is made, the ECU 20 ends the execution of this routine.

  In S203, the ECU 20 determines the rotational speed Ne0 of the internal combustion engine 1 when the accelerator opening degree Raopen is zero and the SOx poisoning recovery control is being executed from the current rotational speed Ne of the internal combustion engine 1. Is subtracted to calculate the rotation speed increase amount ΔNe. Here, when the execution of the SOx poisoning recovery control is started when the accelerator opening Raopen is zero, that is, when the main fuel injection by the fuel injection valve 10 is stopped, the rotational speed Ne0 Is the rotational speed of the internal combustion engine 1 at the time when execution of the SOx poisoning recovery control is started. Further, when the accelerator opening degree Raopen becomes zero when the SOx poisoning recovery control is being executed, the rotational speed Ne0 is the rotational speed of the internal combustion engine 1 when the accelerator opening degree Raopen becomes zero. In the present embodiment, the rotational speed Ne0 is stored in the ECU 20 according to each case.

  Next, the ECU 20 proceeds to S204, where the clutch switch 18 is OFF, that is, the clutch of the vehicle on which the internal combustion engine 1 is mounted is kept engaged, and the rotational speed increase amount ΔNe is equal to the predetermined rotational speed. It is determined whether or not the increase amount is ΔNe0 or more. Here, the predetermined rotational speed increase amount ΔNe0 is a threshold value of the rotational speed increase amount at which it can be determined that the torque increase amount of the internal combustion engine 1 has exceeded the torque increase upper limit value. If an affirmative determination is made in S204, the ECU 20 proceeds to S205, and if a negative determination is made, the ECU 20 ends the execution of this routine.

  When the clutch is engaged in the vehicle, the torque of the internal combustion engine 1 is transmitted to the drive system of the vehicle. In such a state, when there is no increase in torque due to combustion of fuel in the internal combustion engine 1, the rotational speed of the internal combustion engine 1 usually does not increase. Therefore, when the rotational speed increase amount ΔNe becomes equal to or greater than the predetermined rotational speed increase amount ΔNe0 even though the clutch remains engaged, the fuel injected by the auxiliary fuel injection is burned. It can be judged that the influence on the torque is excessively large. Therefore, in S205, the ECU 20 stops the execution of the auxiliary fuel injection. That is, the execution of the SOx poisoning recovery control is stopped. Thereafter, the ECU 20 ends the execution of this routine.

  According to the control routine described above, even if the torque of the internal combustion engine 1 fluctuates due to variations in environmental conditions, it is possible to suppress an excessive increase in the torque of the internal combustion engine 1. .

  In the first and second embodiments, the case where the present invention is applied to SOx poisoning recovery control has been described. However, the present invention can also be applied to a case where NOx reduction control for reducing NOx stored in the NOx catalyst 12 is performed by executing sub fuel injection by the fuel injection valve 10.

BRIEF DESCRIPTION OF THE DRAWINGS The figure which shows schematic structure of the internal combustion engine which concerns on Example 1 of this invention, and its intake / exhaust system. The flowchart which shows the control routine of SOx poisoning recovery control which concerns on Example 1 of this invention. The flowchart which shows the control routine of the torque rise suppression control which concerns on Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 8 ... Intake passage 9 ... Exhaust passage 10 ... Fuel injection valve 11 ... Air flow meter 12 ... NOx storage reduction catalyst 13 ... Air-fuel ratio sensor 14 ...・ Exhaust temperature sensor 15 ・ Crank position sensor 16 ・ Accelerator opening sensor 17 ・ Transmission 18 ・ Clutch switch 20 ・ ECU

Claims (4)

An NOx storage reduction catalyst that is provided in an exhaust passage of an internal combustion engine and that stores NOx in exhaust when the ambient atmosphere is an oxidizing atmosphere and reduces NOx stored when the ambient atmosphere is a reducing atmosphere;
A fuel injection valve for directly injecting fuel into the cylinder of the internal combustion engine;
The fuel injection valve reduces the air / fuel ratio of the exhaust gas to the target air / fuel ratio by performing sub fuel injection in a plurality of times during one combustion cycle of the internal combustion engine at a time later than the execution time of the main fuel injection. And oxide reduction control execution means for executing oxide reduction control for reducing oxides stored in the NOx storage reduction catalyst.
Target sub fuel injection amount calculating means for calculating a target sub fuel injection amount in one combustion cycle of the internal combustion engine when executing the oxide reduction control by the oxide reduction control executing means;
When the oxide reduction control is executed by the oxide reduction control execution means, the upper limit sub-fuel injection amount in one combustion cycle of the internal combustion engine in which the torque increase amount of the internal combustion engine becomes the upper limit value of the allowable range. Upper limit auxiliary fuel injection amount calculating means for calculating the fuel injection amount;
Split ratio setting means for setting a ratio of the fuel injection amount in each sub fuel injection performed during one combustion cycle of the internal combustion engine ,
When the target sub fuel injection amount calculated by the target sub fuel injection amount calculating means is larger than the upper limit sub fuel injection amount calculated by the upper limit sub fuel injection amount calculating means, the oxide reduction control is executed. Prohibit the execution of oxide reduction control by means ,
The division ratio setting means is configured to reduce the internal combustion engine when the target sub fuel injection amount calculated by the target sub fuel injection amount calculation means is relatively large compared to when the target sub fuel injection amount is relatively small. An exhaust gas purification system for an internal combustion engine, wherein a ratio of a fuel injection amount in sub fuel injection executed at a later time in one combustion cycle is increased . When the target sub fuel injection amount calculated by the target sub fuel injection amount calculating means is less than or equal to a predetermined amount, the oxide reduction control execution means executes the number of times of sub fuel injection during execution of the oxide reduction control. 2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the exhaust gas is only once during one combustion cycle of the internal combustion engine. When the main fuel injection is stopped in the internal combustion engine and the oxide reduction control is executed by the oxide reduction means, the torque of the internal combustion engine is also transmitted to the drive system of the vehicle. Regardless, if the rotational speed of the internal combustion engine is higher than the rotational speed at the time when the main fuel injection is stopped and the oxide reduction control is performed, the oxidation 3. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein execution of oxide reduction control by the substance reduction control execution means is stopped. Wherein when stopping the execution of the oxide reduction control by oxide reduction control execution means, the claims 1 to 3, characterized in that to reduce gradually the auxiliary fuel injection amount in one combustion cycle of the internal combustion engine An exhaust purification system for an internal combustion engine according to any one of the above.

Images