JP6622110B2 - Exhaust gas purification control device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification control apparatus for an internal combustion engine, which is applied to an internal combustion engine provided with an exhaust aftertreatment device in an exhaust passage and having an addition portion for adding fuel to exhaust gas flowing into the aftertreatment device.

  For example, in Patent Document 1, in order to purify a NOx catalyst (post-treatment device), a process of intermittently adding fuel is performed by an addition valve that adds fuel to the exhaust gas in the exhaust passage, and the temperature of the NOx catalyst is determined. An apparatus for raising the height is described. Further, in this apparatus, at the end of the purification process of the NOx catalyst, the above-mentioned fuel before the middle period is intermittently added in order to burn and remove the particulate matter (PM) remaining on the upstream end face of the NOx catalyst. It has been proposed to execute the process of intermittently adding the same amount of fuel as the process of intermittently adding the fuel before the middle period in a shorter period of time than the process to be performed. This is because the temperature of the NOx catalyst is increased more rapidly and at a higher temperature than before the middle period in view of the fact that PM does not completely burn on the upstream end face of the NOx catalyst depending on the purification process before the middle period. It aims at burning PM on the same end face.

JP 2006-291817 A

  However, in the above-described control, since the above-described series of purification processing of the NOx catalyst is performed in order to reduce or eliminate clogging due to PM on the upstream end face of the NOx catalyst, the period during which the temperature of the NOx catalyst is increased. However, there is a concern that the catalyst will deteriorate over a long period of time.

  The present invention has been made in view of such circumstances, and its purpose is to reduce or eliminate clogging of the end face on the upstream side of the post-processing apparatus while shortening the temperature rise period of the post-processing apparatus. An object of the present invention is to provide an exhaust purification control device for an internal combustion engine.

Hereinafter, in order to solve the above-described problem, an exhaust gas purification control apparatus for an internal combustion engine is provided with an exhaust aftertreatment device in an exhaust passage, and an addition engine for adding fuel to exhaust gas flowing into the aftertreatment device. Applied to the determination processing unit that determines whether or not there is a PM removal request on the upstream end face of the post-processing device, and when the determination processing unit determines that there is the removal request, flows into the post-processing device On condition that the temperature of the exhaust gas is lower than the maximum boiling point of the fuel, an addition processing unit that operates the adding unit to add the fuel to the exhaust gas to attach the fuel to the end surface; and And an increase processing unit for increasing the temperature of the exhaust gas flowing into the end surface to a target temperature that is a temperature equal to or higher than the maximum value of the boiling point while the fuel adhering to the end surface remains by the addition processing unit. In the invention described in the claims, the “maximum value of the boiling point of the fuel” is corrected to “the maximum value of the boiling points of the components of the fuel”.

  In the above configuration, the fuel is added to the exhaust gas by the addition processing unit on the condition that the temperature of the exhaust gas is lower than the maximum value of the boiling point. Thereby, at least a part of the fuel added to the exhaust gas adheres to the upstream end face of the aftertreatment device without boiling. In such a state, the fuel adhering to the upstream end face of the aftertreatment device is combusted by raising the temperature of the exhaust gas to the target temperature by the ascending processor. At this time, the temperature of the end face is higher than the temperature of the exhaust. For this reason, clogging of the end face can be alleviated or eliminated in a short time compared with the case where the temperature of the exhaust gas is raised to the target temperature without attaching fuel to the end face in advance. For this reason, it is possible to reduce or eliminate clogging of the end face on the upstream side of the post-processing apparatus while shortening the temperature rise period of the post-processing apparatus.

The figure which shows one Embodiment of the exhaust gas purification control apparatus, and its control object. The flowchart which shows the procedure of the removal process of PM adhering to the end surface concerning the embodiment. The figure which shows the relationship between the amount of intake air and the amount of added fuel, and HC slipping amount concerning the embodiment. The figure which shows the ratio of the soluble organic component in the upstream end surface of the oxidation catalyst by fuel addition. The figure which shows the effect of the said embodiment.

Hereinafter, an embodiment of an exhaust gas purification control device for an internal combustion engine will be described with reference to the drawings.
As shown in FIG. 1, the air sucked from the intake passage 12 of the diesel engine (internal combustion engine 10) is sucked into the combustion chamber 14 of each cylinder. A fuel injection valve 16 is provided in the combustion chamber 14 and injects fuel into the combustion chamber 14. An air-fuel mixture of the fuel injected by the fuel injection valve 16 and the air sucked from the intake passage 12 is combusted and then discharged as exhaust gas into the exhaust passage 18. The exhaust passage 18 is provided with an oxidation catalyst 20 and a diesel particulate filter (DPF 22) in order from the upstream side.

  The intake passage 12 is provided with an air flow meter 30 for detecting the intake air amount Ga, and an upstream side exhaust temperature sensor 32 for detecting the exhaust temperature Texu is provided upstream of the oxidation catalyst 20 in the exhaust passage 18. ing. Further, on the upstream side and the downstream side of the oxidation catalyst 20, a differential pressure sensor 34 that detects a difference in pressure on the upstream side (differential pressure ΔP) with respect to the pressure on the downstream side is provided. Further, a downstream side exhaust temperature sensor 36 for detecting the exhaust temperature Texd is provided between the oxidation catalyst 20 and the DPF 22.

  The control device 40 includes a CPU 42 and a memory 44. The control device 40 is a control device that controls the control amount (torque, exhaust component, etc.) of the internal combustion engine 10 by operating an actuator such as the fuel injection valve 16 while referring to the detection value of the sensor. In particular, the control device 40 executes processing for removing PM on the end face when clogging occurs due to PM on the end face on the upstream side of the oxidation catalyst 20.

  FIG. 2 shows a procedure for removing PM from the upstream end face of the oxidation catalyst 20. This process is realized by the CPU 42 executing a program stored in the memory 44. This process is executed every time a predetermined execution condition is satisfied.

  In the series of processes shown in FIG. 2, the CPU 42 first detects the presence or absence of clogging of the upstream end face of the oxidation catalyst 20 (S10). Here, the clogging is caused by the temperature increase performance of the oxidation catalyst 20 based on the fact that the differential pressure ΔP detected by the differential pressure sensor 34 is not less than a predetermined value and the exhaust temperature Texd detected by the downstream side exhaust temperature sensor 36. It is determined that clogging has occurred when the logical product with the detection of a decrease is true. Here, in the temperature rise performance determination processing, the exhaust temperature assumed downstream of the oxidation catalyst 20 when post-injection is performed by operating the fuel injection valve 16 and unburned fuel is supplied to the oxidation catalyst 20. On the other hand, when the exhaust temperature Texd is lower than the specified value, it may be determined that the temperature rise performance has deteriorated. This is because the outlet temperature of the oxidation catalyst 20 does not increase as expected when the upstream end face of the oxidation catalyst 20 is clogged.

  Then, the CPU 42 determines whether clogging of the end face is detected and whether a request for removing PM on the end face has occurred (S12). Here, when the CPU 42 determines that clogging has occurred in step S10 and is in an operation state in which the exhaust gas temperature can be raised to a target temperature at which PM can be removed by processing described later, there is a removal request. judge. When determining that there is no removal request (S12: NO), the CPU 42 returns to step S10. On the other hand, when determining that there is a removal request (S12: YES), the CPU 42 acquires the exhaust gas temperature Texu detected by the upstream exhaust gas temperature sensor 32 (S14). Then, the CPU 42 determines whether or not the exhaust temperature Texu is lower than the lowest boiling point value of the fuel (soluble organic component) injected from the fuel injection valve 16 (S16). That is, the fuel is a mixture, and components having a low boiling point and components having a high boiling point are mixed, and there are minimum and maximum boiling points. When the CPU 42 determines that the boiling point is equal to or higher than the minimum value of the boiling point (S16: NO), the CPU 42 returns to the process of step S14.

  On the other hand, if the CPU 42 determines that the boiling point is lower than the minimum value (S16: YES), the fuel injection valve 16 is operated to perform post injection, whereby unburned fuel is discharged into the exhaust gas discharged to the exhaust passage 18. The process which adds is performed (S18). This treatment is for adhering fuel to the upstream end face of the oxidation catalyst 20. That is, by adding unburned fuel to the exhaust when the exhaust temperature Texu is lower than the minimum boiling point, the fuel reaches the upstream end face of the oxidation catalyst 20, and the reached fuel does not burn nor vaporize. The attached state can be maintained. Here, the amount of fuel added per unit time is set so that the amount of the added fuel amount that passes through the oxidation catalyst 20 is not more than a predetermined amount.

  FIG. 3 shows the relationship between the amount of fuel added, the bed temperature of the oxidation catalyst 20 and the amount of intake air, and the amount of slipping out of the added fuel (HC slipping amount). As shown in FIG. 3, the slip-through amount increases as the bed temperature of the oxidation catalyst 20 decreases, the slip-through amount increases as the intake air amount increases, and the slip-through amount increases as the fuel addition amount increases. Therefore, when the bed temperature of the oxidation catalyst 20 is low, the amount of addition per unit time is less than when it is high, and when the amount of intake air is large, the amount of addition per unit time is less than when it is small. To do.

  And CPU42 determines whether the elapsed time (addition time) from the start of the process to add became more than a threshold value (S20). Here, the threshold value is that the amount of fuel adhering to the upstream end face of the oxidation catalyst 20 removes the PM on the end face to some extent even when the addition amount per unit time set in relation to the slip-through amount is the smallest. Is set to the amount of time that can be. CPU42 continues the process to add until it becomes more than a threshold value (S20: NO), and when it becomes more than a threshold value (S20: YES), the process to add is complete | finished (S22).

  Next, the CPU 42 acquires the exhaust temperature Textex detected by the upstream side exhaust temperature sensor 32 and the exhaust flow rate (S24). Here, the exhaust flow rate is an amount grasped by the CPU 42 based on the intake air amount Ga detected by the air flow meter 30. Then, the CPU 42 calculates the rate of increase of the exhaust temperature when executing the process of delaying the injection timing of the main injection by the fuel injection valve 16 to lower the efficiency and raising the exhaust temperature to the target temperature (S26). Here, the higher the exhaust gas temperature Texu, the lower the rate of increase, and the higher the exhaust gas flow rate, the lower the rate of increase. This is because if the rising speed is increased while the exhaust temperature Texu is high or the exhaust flow rate is large, the temperature of the end face on the upstream side of the oxidation catalyst 20 may become excessively high. The target temperature is set to an exhaust temperature at which PM can be combusted together with the fuel on the end face in a state where the fuel is attached to the end face on the upstream side of the oxidation catalyst 20 by the processing in step S18. However, the target temperature is set to a temperature at which it is difficult to quickly burn the PM on the end face when the process of step S18 is not performed to attach fuel to the upstream end face of the oxidation catalyst 20. .

  Then, the CPU 42 determines whether or not the calculated ascending speed is equal to or higher than the threshold speed (S28). Here, the threshold speed is set to a speed at which the target temperature can be reached before the unburned fuel attached to the end face on the upstream side of the oxidation catalyst 20 by the processing in step S18 is completely combusted. The threshold speed is set to a higher speed as the amount of fuel added until the determination in step S20 is affirmative is smaller. When determining that the speed is less than the threshold speed (S28: NO), the CPU 42 returns to the process of step S24. On the other hand, if the CPU 42 determines that the speed is equal to or higher than the threshold speed (S28: YES), the CPU 42 delays the injection timing of the main injection by the fuel injection valve 16 to reduce the efficiency, and increases the exhaust gas temperature to the target temperature. Start (S30). When the exhaust temperature Texu reaches the target temperature after executing the process of increasing the exhaust temperature Texu, the CPU 42 executes the process of maintaining that temperature. Then, the CPU 42 determines whether or not a set time has elapsed since the start of the process of increasing the exhaust gas temperature Texu (S32). Here, the set time is set to a time necessary for removing PM on the upstream end face of the oxidation catalyst 20. The set time is longer than the time until the exhaust temperature reaches the target temperature.

  When determining that the set time has not elapsed (S32: NO), the CPU 42 waits until the set time has elapsed. On the other hand, when determining that the set time has elapsed (S32: YES), the CPU 42 ends the process of delaying the injection timing of the main injection by the fuel injection valve 16 and reducing the efficiency (S34). In addition, when the process of step S34 is completed, CPU42 once complete | finishes a series of processes shown in FIG.

Here, the operation of the present embodiment will be described.
When the CPU 42 determines that a request to remove the PM on the upstream end face of the oxidation catalyst 20 has occurred, the CPU 42 is discharged into the exhaust passage 18 by post injection on the condition that the exhaust temperature Texu is lower than the minimum value of the boiling point of the fuel. Add fuel to the exhaust.

  FIG. 4 shows fuel (soluble organic matter) for PM on the end face of the oxidation catalyst 20 when the process of adding fuel is executed by the process of step S18 of FIG. 2 (after the addition control) and when not executed (before the addition control). The ratio of component) is shown. As shown in FIG. 4, the ratio of the soluble organic component in the oxidation catalyst 20 can be increased by the process of step S18 of FIG.

  The CPU 42 increases the exhaust temperature Texu to the target temperature by retarding the injection timing of the main injection in a state where the fuel is attached to the upstream end face of the oxidation catalyst 20. Thereby, the fuel adhering to the upstream end face of the oxidation catalyst 20 burns, and the temperature of the end face rises higher than the exhaust temperature Texu. Thereby, PM of an end surface can be burned and removed quickly.

  FIG. 5 shows a case before the exhaust temperature is raised to the target temperature (here, 500 ° C.) (initial) and when the exhaust temperature is raised to the target temperature without executing the process of step S18 of FIG. 2 (no fuel addition control). ) And the clogging degree (blocking rate) of the end face in each of the case where the temperature is raised to the target temperature after the process of step S18 of FIG. 2 is performed (with fuel addition control). Specifically, FIG. 5 shows an experimental result when the process of removing PM as the target temperature is performed for 5 minutes.

  As shown in FIG. 5, according to the present embodiment in which the temperature is raised to the target temperature after executing the process of step S <b> 18 of FIG. 2, the case where the temperature is raised to the target temperature without executing the process of step S <b> 18 of FIG. In comparison, more PM on the end face on the upstream side of the oxidation catalyst 20 can be removed. Even when the temperature is raised to the target temperature without executing the processing of step S18 in FIG. 2, the amount of PM removal can be increased by extending the time for the target temperature. However, in this case, the time for setting the target temperature is longer than that in the present embodiment.

  Incidentally, if the exhaust temperature Texd is controlled to a temperature higher than the target temperature in the present embodiment, the PM on the end face on the upstream side of the oxidation catalyst 20 is sufficiently and quickly removed without executing the process of step S18 of FIG. It is also possible to do. However, in this case, there is a concern that the deterioration of the oxidation catalyst 20 is promoted.

  As described above, in the present embodiment, the PM on the upstream end face of the oxidation catalyst 20 is removed while suppressing the target temperature from becoming excessively high and suppressing the period of the target temperature from becoming long. be able to.

According to the embodiment described above, the following effects can be obtained.
(1) The addition amount per unit time was variably set according to the intake air amount and the temperature of the oxidation catalyst 20. Thereby, the addition amount can be controlled so that the slip-through amount is not more than a predetermined amount.

  (2) It is uncertain when the transition to the operating state in which the exhaust gas temperature is equal to or higher than the maximum boiling point depends on the torque request to the internal combustion engine 10 by the user. For this reason, when the addition process is performed until the amount of fuel adhering to the upstream end face of the oxidation catalyst 20 reaches a predetermined amount, the exhaust temperature becomes higher than the maximum boiling point during the process, and the oxidation catalyst 20 There is a possibility that the process of removing the PM on the upstream end face cannot be completed. In contrast, in the present embodiment, when the addition time is equal to or greater than the threshold value, the addition process is terminated, and the process proceeds to the exhaust gas temperature increase process, thereby removing PM on the upstream end face of the oxidation catalyst 20. Can increase the possibility of completing.

  (3) The threshold speed of the rising speed of the exhaust temperature Texu is variably set according to the amount of fuel adhering to the upstream end face of the oxidation catalyst 20. Accordingly, it is possible to prevent the exhaust temperature Texu from reaching the target temperature before the fuel on the upstream end face of the oxidation catalyst 20 disappears, but to be determined to be less than the threshold speed.

<Correspondence>
Correspondences between the items described in the column of “Means for Solving the Problems” and items in the embodiment are as follows. In the following, “CPU 42 that executes a predetermined process according to a program stored in memory 44” will be referred to as “CPU 42 that executes a predetermined process” in order to simplify the description. The post-processing device corresponds to the oxidation catalyst 20, and the addition unit corresponds to the CPU 42 that operates the fuel injection valve 16 and the fuel injection valve 16 to perform post injection. Further, the determination processing unit corresponds to the CPU 42 that executes the process of step S12 in FIG. 2, the addition processing unit corresponds to the CPU 42 that executes the processes of steps S16 to S22, and the ascending processing unit corresponds to the steps S24 to S34. This corresponds to the CPU 42 that executes the process. The exhaust purification control device corresponds to the control device 40.

<Other embodiments>
In addition, you may change at least 1 of each matter of the said embodiment as follows.
・ About the additive part
The configuration is not limited to the configuration including the fuel injection valve 16 and the CPU 42. For example, you may comprise by the addition valve which adds a fuel to the exhaust_gas | exhaustion in the exhaust passage 18 upstream of the oxidation catalyst 20. FIG.

・ "About post-processing equipment"
The post-processing device from which the PM on the upstream end face is to be removed is not limited to the oxidation catalyst 20. For example, the post-treatment device positioned in the uppermost stream in the exhaust passage 18 may be a NOx storage reduction catalyst or a NOx selective reduction catalyst, and this post-treatment device may be the post-treatment device to be removed. Further, for example, instead of FIG. 1, the post-processing device located in the uppermost stream in the exhaust passage 18 may be the DPF 22, and the PM on the upstream end face may be the removal target.

・ About the additive processing section
In the said embodiment, when it was temperature lower than the minimum value of the boiling point of a fuel, although the process of step S18 was performed, it does not restrict to this. For example, when the temperature is lower than a predetermined temperature that is lower than the highest value and higher than the lowest value among the boiling points of the components of the fuel, the process of step S18 may be executed. In short, if the process of step S18 is executed on condition that the temperature is lower than the maximum boiling point, it is possible to avoid a situation in which it is impossible to expect that all of the fuel is vaporized and the fuel adheres to the end face. it can.

  In the above embodiment, it is not considered that the slip-through amount depends on the PM deposition amount in the oxidation catalyst 20. However, when the PM deposition amount of the oxidation catalyst 20 at the time of executing the process of removing the PM on the upstream end face of the oxidation catalyst 20 takes various values, it is desirable to consider this.

  It is not essential to variably set the addition amount per unit time according to the intake air amount and the bed temperature of the oxidation catalyst 20. For example, it may be variably set according to either the intake air amount or the bed temperature of the oxidation catalyst 20, and the addition amount per unit time may be a fixed value.

It is not restricted to what performs an addition process until addition time becomes more than a threshold value. For example, the addition process may be executed until the total addition amount from the start of the addition process becomes equal to or greater than a threshold value.
・ About "Rise Processing Department"
In the above embodiment, when the process of step S28 is replaced with a positive determination from the negative determination, a process of increasing the exhaust temperature Texu is performed. A process of determining whether or not may be performed, and a process of increasing the exhaust gas temperature Texu may be performed on the condition that it has not disappeared. Here, the determination of whether or not it has disappeared can be executed based on whether or not the exhaust gas temperature Texu has become equal to or higher than the maximum boiling point. In this case, if it is determined that it has disappeared, the processing from step S12 may be performed again.

  In the above-described embodiment, it is determined whether or not the exhaust temperature can be increased at the threshold speed or higher after performing the process (S18) of attaching the fuel to the upstream end face of the oxidation catalyst 20, but this is not limitative. Absent. For example, a condition that the exhaust temperature can be raised at a threshold speed or higher may be added to the execution condition of the process for attaching the fuel to the upstream end face of the oxidation catalyst 20. However, even in this case, can the exhaust temperature be increased at the threshold speed or higher before the exhaust temperature is increased after the process of attaching the fuel to the upstream end face of the oxidation catalyst 20 is performed? It is desirable to execute again the process of determining whether or not.

  The process for raising the exhaust gas temperature to the target temperature is not limited to retarding the injection timing of the main injection. For example, a process of burning unburned fuel in the burned mixture by so-called after injection in which fuel is injected by the fuel injection valve 16 with respect to the mixture burned along with the main injection may be used.

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 12 ... Intake passage, 14 ... Combustion chamber, 16 ... Fuel injection valve, 18 ... Exhaust passage, 20 ... Oxidation catalyst, 22 ... DPF, 30 ... Air flow meter, 32 ... Upstream side exhaust temperature sensor, 34 ... Differential pressure sensor 36 ... downstream exhaust temperature sensor 40 ... control device 42 ... CPU 44 ... memory

Claims (1)

An exhaust aftertreatment device is provided in the exhaust passage, and is applied to an internal combustion engine including an addition unit for adding fuel to the exhaust gas flowing into the aftertreatment device,
A determination processing unit for determining whether or not there is a PM removal request on the upstream end face of the post-processing device;
When the determination processing unit determines that there is the removal request, the addition unit is provided on the condition that the temperature of the exhaust gas flowing into the aftertreatment device is lower than the highest value among the boiling points of the components of the fuel. And an addition processing unit for attaching the fuel to the end surface by adding the fuel to the exhaust by operating
An internal combustion engine comprising: an increase processing unit configured to increase a temperature of exhaust gas flowing into the end surface to a target temperature that is a temperature equal to or higher than the maximum value of the boiling point while the fuel adhering to the end surface remains by the addition processing unit. Engine exhaust purification control device.