JP2014141890A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system for an internal combustion engine, for suppressing an increase in the pressure loss due to the accumulation of PMs on a filter.SOLUTION: The exhaust emission control system for an internal combustion engine includes a filter provided in an exhaust passage of the internal combustion engine for trapping particulate matters in exhaust gas. During a time from when the filter is in an initial state until when an ash accumulation amount on the filter reaches a predetermined ash accumulation amount, the exhaust emission control system executes ash amount increasing control so that the amount of ash contained in the exhaust gas from the internal combustion engine is greater than a reference amount.

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine.

  An exhaust passage of the internal combustion engine may be provided with a filter for collecting particulate matter (hereinafter referred to as PM) contained in the exhaust. The collected PM gradually accumulates on the filter. When the PM accumulation amount in the filter increases, the exhaust pressure upstream of the filter increases. Therefore, the pressure loss in the internal combustion engine increases.

  In addition to unburned fuel components and soot, PM contains ash made of a metal compound derived from the lubricating oil of the internal combustion engine.

  Patent Document 1 discloses a particulate matter treatment process in which a filter is heat-treated at a predetermined temperature in order to burn PM each time the amount of PM deposited on the filter exceeds a threshold, and the filter is heat-treated at a temperature higher than the predetermined temperature. An ash treatment method including an ash treatment step of shrinking ash collected by a filter is disclosed.

JP 2010-229927

  An object of the present invention is to suppress an increase in pressure loss due to accumulation of PM on a filter in an exhaust purification system of an internal combustion engine.

An exhaust purification system for an internal combustion engine according to the present invention includes:
A filter provided in the exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
The amount of ash included in the exhaust discharged from the internal combustion engine increases from the reference amount between the time when the filter is in the initial state and the time when the amount of ash accumulated in the filter reaches a predetermined amount of ash. Execute control.

  In the filter, PM is deposited in the pores formed in the partition walls of the filter and on the surfaces of the partition walls of the filter. Hereinafter, the deposition of PM in the pores formed in the partition walls of the filter is referred to as internal deposition, and the deposition of PM on the surface of the partition walls of the filter is referred to as surface deposition.

  Here, the internal deposition of PM has a larger influence on the pressure loss than the surface deposition. That is, when comparing the pressure loss between the case where the same amount of PM is deposited internally and the case where it is deposited on the surface layer, the pressure loss is greater in the case of depositing internally.

  In the present invention, the amount of ash contained in the exhaust gas discharged from the internal combustion engine increases from the reference amount between the time when the filter is in the initial state and the time when the ash accumulation amount in the filter reaches the predetermined ash accumulation amount. The ash amount increase control is executed. Here, the reference amount is the amount of ash contained in the exhaust discharged from the internal combustion engine when the internal combustion engine is normally operated without executing the ash amount increase control.

  When the ash amount increase control is executed, the amount of ash flowing into the filter increases. The ash that has flowed into the filter also accumulates to some extent, but the ash surface layer deposition is promoted by increasing the amount of inflow. Therefore, when the ash amount increase control is executed from the time when the filter is in the initial state, an ash deposition layer is formed on the surface of the partition wall of the filter.

  If an ash deposition layer is formed on the surface of the partition walls of the filter, PM will not easily enter the pores of the partition walls thereafter. Therefore, it becomes difficult to promote the internal deposition of PM. Therefore, according to the present invention, it is possible to suppress an increase in pressure loss due to PM being deposited on the filter.

  However, since ash has a higher melting point than PM other than ash, once it is deposited, it is difficult to remove. Therefore, in the present invention, in order to suppress ash over-deposition, the timing for executing the ash amount increase control is set until the ash accumulation amount in the filter reaches a predetermined ash accumulation amount. Here, the predetermined ash deposition amount is a deposition amount by which it can be determined that a certain amount of ash deposition layer has been formed on the surface of the partition wall of the filter, and is a predetermined value based on experiments or the like.

  In the present invention, the ash amount increase control may be control for increasing the in-cylinder negative pressure of the internal combustion engine. When the in-cylinder negative pressure of the internal combustion engine increases, the amount of lubricating oil drawn into the cylinder through between the bore wall surface and the outer peripheral surface of the piston increases. As a result, the amount of ash generated increases, so the amount of ash contained in the exhaust discharged from the internal combustion engine also increases.

  However, when the ash amount increase control is such control, the consumption amount of the lubricating oil increases when the ash amount increase control is executed. In addition, in a state where the amount of PM deposited on the filter is very small, the ash tends to pass through the pores formed in the partition walls of the filter. Therefore, even if ash amount increase control is executed in such a state, an ash deposit layer is unlikely to be formed.

  Therefore, in the present invention, when the PM accumulation amount in the filter is smaller than the predetermined PM accumulation amount, execution of the ash amount increase control may be prohibited. Here, the predetermined PM deposition amount is a PM deposition amount that prevents ash from passing through the pores formed in the partition walls of the filter, and is a value determined in advance based on experiments or the like.

  According to this, even when the ash accumulation amount in the filter does not reach the predetermined ash accumulation amount, the execution of the ash amount increase control is prohibited when it is difficult to form the ash accumulation layer. Therefore, it is possible to suppress an increase in the consumption amount of the lubricating oil accompanying the execution of the ash amount increase control.

  In the present invention, when the predetermined ash accumulation amount is the first predetermined ash accumulation amount, a second predetermined ash accumulation amount in the filter is smaller than the first predetermined ash accumulation amount and smaller than the upper limit value of the allowable ash accumulation amount. When the ash accumulation amount is exceeded, the ash amount reduction control may be executed in which the ash amount contained in the exhaust gas discharged from the internal combustion engine is smaller than the reference amount.

When the ash accumulation amount in the filter reaches the first predetermined ash accumulation amount, the ash amount increase control is not performed thereafter. However, the amount of ash deposition on the filter gradually increases thereafter. According to the above, the ash amount reduction control is executed when the ash accumulation amount in the filter reaches the second predetermined ash accumulation amount which is smaller than the upper limit value of the allowable range. When the ash amount reduction control is executed, the amount of ash flowing into the filter decreases. Therefore, the increase rate of the ash deposition amount can be reduced before the ash deposition amount reaches the upper limit of the allowable range. Therefore, ash overdeposition in the filter can be suppressed.

  The timing for determining whether or not the ash accumulation amount in the filter is equal to or greater than the second predetermined ash accumulation amount may be the time when the total travel distance of the vehicle equipped with the internal combustion engine reaches the predetermined determination distance. In this case, the second predetermined ash accumulation amount is set according to the predetermined determination distance.

  In the present invention, the ash amount reduction control may be control for reducing the in-cylinder negative pressure of the internal combustion engine. When the in-cylinder negative pressure of the internal combustion engine decreases, the amount of lubricating oil drawn into the cylinder through the space between the bore wall surface and the outer peripheral surface of the piston decreases. As a result, the amount of ash produced is reduced, and the amount of ash contained in the exhaust discharged from the internal combustion engine is also reduced.

  However, when the ash amount reduction control is such control, when the ash amount reduction control is executed, the effect of the engine brake becomes small (that is, the effect of the engine brake becomes weak). Therefore, in the present invention, when the PM accumulation amount in the filter is smaller than the predetermined PM accumulation amount, execution of the ash amount reduction control may be prohibited. Here, the predetermined PM accumulation amount is a PM accumulation amount that prevents the ash from passing through the pores formed in the partition walls of the filter, similarly to the above-described predetermined PM accumulation amount. Is a predetermined value.

  According to this, even if the ash accumulation amount in the filter is equal to or greater than the second predetermined ash accumulation amount, the execution of the ash amount reduction control is prohibited when the ash accumulation amount is difficult to increase. Accordingly, it is possible to suppress the occurrence frequency of the period when the effect of the engine brake becomes small.

  Further, when the flow rate of the exhaust gas flowing into the filter is large, the ash is more easily deposited in the downstream portion than in the upstream portion of the filter. Therefore, in the present invention, the exhaust flow rate reduction control for reducing the flow rate of the exhaust gas flowing into the filter from the reference flow rate until the ash deposition amount in the filter reaches the predetermined ash deposition amount (first predetermined ash deposition amount). May be executed. Here, the reference flow rate is the flow rate of the exhaust gas flowing into the filter when the internal combustion engine is normally operated without executing the exhaust gas flow rate reduction control.

  According to this, it can suppress that the ash in the filter increased by performing ash amount increase control concentrates and accumulates in the downstream part of this filter. Therefore, the ash deposition layer can be more uniformly formed on the surface of the partition wall of the filter from the upstream side portion to the downstream side portion of the filter. Considering the risk of filter blockage due to ash, the smaller the amount of ash deposition, the better. By forming the ash deposition layer more uniformly on the surface of the filter partition wall, PM internal deposition can be more effectively suppressed. it can.

  Here, in an internal combustion engine, it may be difficult to execute exhaust gas flow reduction control continuously for a long period of time. Also, by increasing the temperature of the filter, when the filter regeneration process is performed to oxidize and remove PM other than the ash accumulated on the filter, the ash aggregates and stabilizes because the filter becomes hot. It is easy to be in a state.

  Therefore, when the exhaust gas purification system according to the present invention further includes a filter regeneration process execution unit that performs the filter regeneration process, the execution period of the exhaust gas flow reduction control is changed from the time when the execution of the ash amount increase control is started. It may be until the execution of the filter regeneration process executed after the execution of the ash amount increasing control is completed. According to this, the flow rate of the exhaust gas flowing into the filter is reduced at the timing at which the ash flowing into the filter aggregates, that is, at the timing at which the ash accumulation layer is easily formed stably. Therefore, it is possible to more uniformly form an ash deposition layer on the surface of the partition wall of the filter.

  The internal combustion engine according to the present invention may be a gasoline engine. In a gasoline engine, the total amount of PM contained in exhaust gas is smaller than that of a diesel engine, but the proportion of ash contained in PM is higher than that of a diesel engine. Therefore, when the internal combustion engine which concerns on this invention is a gasoline engine, the effect at the time of performing each control mentioned above can be acquired more suitably.

  According to the present invention, it is possible to suppress an increase in pressure loss due to PM being deposited on the filter.

1 is a diagram illustrating a schematic configuration of an intake / exhaust system of an internal combustion engine according to Embodiment 1. FIG. It is a figure which shows the relationship between PM deposition amount and pressure loss in a filter. 3 is a flowchart illustrating a flow of ash amount increase control according to the first embodiment. 6 is a flowchart illustrating a flow of ash amount increase control according to the second embodiment. 12 is a flowchart illustrating a flow of ash amount reduction control according to the third embodiment. It is a figure which shows transition of the ash deposition amount in a filter with respect to the total travel distance of a vehicle. 12 is a flowchart illustrating a flow of ash amount reduction control according to the fourth embodiment. It is a figure which shows the state of the accumulation layer of the ash formed on the surface of the partition of a filter by performing ash amount increase control. FIG. 8A shows the state of the ash accumulation layer when the exhaust flow rate reduction control is not executed, and FIG. 8B shows the case where the exhaust flow rate reduction control according to the fifth embodiment is executed. The state of the ash deposition layer is shown.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

<Example 1>
[Schematic configuration of intake and exhaust system of internal combustion engine]
Here, the case where the present invention is applied to an exhaust gas purification system for a gasoline engine for driving a vehicle will be described as an example. However, the present invention can also be applied to an exhaust purification system such as a diesel engine.

  FIG. 1 is a diagram showing a schematic configuration of an intake / exhaust system of an internal combustion engine according to the present embodiment. The internal combustion engine 1 is a gasoline engine for driving a vehicle. An intake passage 2 and an exhaust passage 3 are connected to the internal combustion engine 1.

  An air flow meter 4, a throttle valve 5, and an intake pressure sensor 16 are provided in the intake passage 2. The air flow meter 4 detects the intake air amount of the internal combustion engine 1. The throttle valve 5 adjusts the flow rate of the intake air flowing through the intake passage 2 by changing the cross-sectional area of the intake passage 2. The intake pressure sensor 16 detects the pressure in the intake passage 2 on the downstream side of the throttle valve 5.

The exhaust passage 3 is provided with a filter 6 for collecting PM in the exhaust. The filter 6 is a wall flow type filter having a plurality of cells which are partitioned by a partition made of a porous material and extend in the axial direction of the filter 6. An oxidation catalyst 7 is provided in the exhaust passage 3 upstream of the filter 6 as a pre-stage catalyst. The pre-stage catalyst is not limited to the oxidation catalyst, and may be a catalyst having an oxidation function (for example, an occlusion reduction type NOx catalyst). A fuel addition valve 8 is provided in the exhaust passage 3 upstream of the oxidation catalyst 7. The fuel addition valve 8 adds fuel into the exhaust.

  Further, a differential pressure sensor 13 and an exhaust temperature sensor 14 are provided in the exhaust passage 3. The differential pressure sensor 13 detects a difference between the exhaust pressure upstream of the filter 6 and the exhaust pressure downstream of the filter 6 (hereinafter referred to as front-rear differential pressure). The exhaust temperature sensor 14 is provided in the exhaust passage 3 downstream of the filter 6 and detects the temperature of the exhaust.

  The internal combustion engine 1 is provided with an electronic control unit (ECU) 10 for controlling the internal combustion engine 1. Each sensor such as an air flow meter 4, an intake pressure sensor 16, a differential pressure sensor 13, and an exhaust temperature sensor 14 is electrically connected to the ECU 10. Further, a crank angle sensor 11, an accelerator opening sensor 12, and an oil sensor 15 are electrically connected to the ECU 10. The crank angle sensor 11 detects the crank angle of the internal combustion engine 1. The accelerator opening sensor 12 detects an accelerator opening sensor of a vehicle on which the internal combustion engine 1 is mounted. The oil sensor 15 detects the remaining amount of lubricating oil in the oil pan of the internal combustion engine 1. And the output signal of each sensor is input into ECU10. The ECU 10 can derive the engine speed of the internal combustion engine 1 based on the output signal of the crank angle sensor 11. Further, the ECU 10 can derive the engine load of the internal combustion engine 1 based on the output signal of the accelerator opening sensor 12.

  Further, the throttle valve 5 and the fuel addition valve 8 are electrically connected to the ECU 10. The operation of these devices is controlled by the ECU 10.

[Filter regeneration processing]
For example, the ECU 10 performs filter regeneration processing by adding fuel from the fuel addition valve 8. The PM collected by the filter 6 gradually accumulates on the filter 6. The filter regeneration process is control for removing PM accumulated on the filter 6.

  When fuel is added from the fuel addition valve 8, the fuel is supplied to the oxidation catalyst 7. The fuel supplied to the oxidation catalyst 7 is oxidized by the oxidation catalyst 7, thereby generating oxidation heat. Due to this oxidation heat, the temperature of the exhaust gas flowing into the filter 6 rises, and thereby the temperature of the filter 6 rises. As a result, PM deposited on the filter 6 is oxidized and removed.

  In the filter regeneration process, the temperature of the filter 6 is controlled to a predetermined target temperature by adjusting the amount of fuel added from the fuel addition valve 8. This target temperature is a temperature at which the oxidation of PM is promoted, and is a temperature at which breakage and erosion of the filter 6 can be suppressed, and is predetermined based on experiments and the like. The temperature of the filter 6 can be estimated based on the detection value of the exhaust temperature sensor 14.

  However, since the ash contained in the PM has a higher melting point than other PMs, it is difficult to remove even if the filter regeneration process is executed. Therefore, the ash once deposited on the filter 6 remains deposited.

In this embodiment, the ECU 10 estimates the PM accumulation amount in the filter 6 based on the differential pressure across the filter 6 detected by the differential pressure sensor 13. When the PM accumulation amount in the filter 6 increases, the differential pressure across the filter 6 increases. Therefore, the PM accumulation amount in the filter 6 can be estimated based on the differential pressure across the filter 6. It is also possible to estimate the PM accumulation amount in the filter 6 by estimating the PM amount flowing into the filter 6 based on the operating state of the internal combustion engine 1 and integrating the PM inflow amount. Further, a PM sensor for detecting PM in the exhaust gas can be provided in the exhaust passage 3 on the downstream side of the filter 6, and the PM accumulation amount in the filter 6 can be estimated using the detection value of the PM sensor. Then, after the previous execution of the filter regeneration process is completed, the filter regeneration process is performed again when the estimated value of the PM accumulation amount becomes equal to or greater than the threshold value for starting the filter regeneration process.

[Ash increase control]
While the filter regeneration process as described above is not being executed, the PM accumulation amount in the filter 6 gradually increases. When the PM accumulation amount in the filter 6 increases, the exhaust pressure upstream of the filter 6 increases. Therefore, the pressure loss in the internal combustion engine 1 increases.

  FIG. 2 is a diagram illustrating the relationship between the PM accumulation amount and the pressure loss in the filter. In FIG. 2, the horizontal axis represents the PM accumulation amount in the filter, and the vertical axis represents the pressure loss. In FIG. 2, the solid line indicates the relationship between the two in the past, and the broken line indicates the relationship between the two when the ash amount increase control according to the present embodiment as described later is executed.

  The PM deposition in the filter includes an internal deposition that is deposited in pores formed in the partition walls of the filter, and a surface layer deposition that is deposited on the surface of the partition walls of the filter. As shown by the solid line in FIG. 2, the internal deposition of PM has a greater effect on the pressure loss than the surface deposition. That is, when comparing the pressure loss between the case where the same amount of PM is deposited internally and the case where it is deposited on the surface layer, the pressure loss is greater in the case of depositing internally. Therefore, if the increase in the internal deposition of PM is suppressed, the increase in pressure loss can be suppressed.

  Therefore, in this embodiment, in order to suppress the increase in the PM internal accumulation in the filter 6, the filter 6 is in the initial state (that is, the initial state in which the filter 6 is attached to the vehicle, and the PM accumulation amount is substantially zero. Ash in which the amount of ash contained in the exhaust gas discharged from the internal combustion engine 1 increases from the reference amount during the period from the time when the ash accumulation amount in the filter 6 reaches the first predetermined ash accumulation amount. The amount increase control is executed.

  Here, the reference amount is the amount of ash contained in the exhaust discharged from the internal combustion engine 1 when the internal combustion engine 1 is normally operated without executing the ash amount increase control. The reference amount may be an ash amount when the internal combustion engine 1 is operated in an operation state in which the ash amount discharged from the internal combustion engine is maximized as a normal operation.

  When the ash amount increase control is executed, the amount of ash flowing into the filter 6 increases. The ash that has flowed into the filter 6 is also internally deposited to some extent, but by increasing the amount of inflow, ash surface layer deposition in the filter 6 is promoted. Therefore, when the ash amount increase control is executed from the time when the filter 6 is in the initial state, an ash accumulation layer is formed on the surface of the partition wall of the filter 6 while the PM internal accumulation amount is relatively small.

  When an ash deposition layer is formed on the surface of the partition wall of the filter 6, PM becomes difficult to enter the pores of the partition wall thereafter. Therefore, it is difficult to promote the internal deposition of PM, and most of the PM deposition is surface deposition. As a result, as shown by the broken line in FIG. 2, it is possible to suppress an increase in pressure loss due to PM being deposited on the filter 6.

  However, as described above, it is difficult to remove ash once deposited on the filter 6. Therefore, if the ash amount increase control is performed too much, the time when the ash accumulation amount in the filter 6 reaches the upper limit value of the allowable range becomes excessively early.

Therefore, in this embodiment, the period during which the ash amount increase control is executed is set until the ash accumulation amount in the filter 6 reaches the first predetermined ash accumulation amount. Here, the first predetermined ash deposition amount is a deposition amount that can be determined that a certain amount of ash deposition layer has been formed on the surface of the partition wall of the filter 6, and is a value determined in advance based on experiments or the like. . In this way, by limiting the period during which the ash amount increase control is executed, it is possible to suppress ash overdeposition.

  FIG. 3 is a flowchart showing a flow of ash amount increase control according to the present embodiment. This flow is stored in advance in the ECU 10 and is repeatedly executed by the ECU 10.

  In this flow, first, in step S101, the ash accumulation amount Qash in the filter 6 is calculated. The ash accumulation amount Qash in the filter 6 can be calculated based on, for example, the differential pressure before and after the filter when the execution of the filter regeneration process is completed. At the time when the execution of the filter regeneration process is finished, PM other than ash is removed from the filter 6, and almost only ash is deposited on the filter 6. Therefore, the ash deposition amount Qash in the filter 6 can be estimated based on the differential pressure across the filter at this time.

  The ash is generated when the lubricating oil of the internal combustion engine 1 is subjected to combustion in the cylinder. Therefore, the remaining amount of lubricating oil in the oil pan of the internal combustion engine 1 decreases as the integrated amount of ash discharged from the internal combustion engine 1 increases. Therefore, the ash accumulation amount Qash in the filter 6 can be estimated based on the remaining amount of lubricating oil detected by the oil sensor 15.

  Next, in step S102, it is determined whether or not the ash accumulation amount Qash in the filter 6 is smaller than the first predetermined ash accumulation amount Qash1. If a negative determination is made in step S102, that is, if the ash accumulation amount Qash in the filter 6 is equal to or greater than the first predetermined ash accumulation amount Qash1, the execution of this flow is terminated.

  On the other hand, when a positive determination is made in step S102, ash amount increase control is executed in step S103. The ash amount increase control according to the present embodiment is specifically control for increasing the in-cylinder negative pressure of the internal combustion engine 1. For example, in this embodiment, the in-cylinder negative pressure during the intake stroke of the internal combustion engine 1 is reduced by reducing the opening of the throttle valve 5 during execution of so-called fuel cut control for stopping fuel injection in the internal combustion engine 1. The ash amount increase control is realized by increasing the ash amount. Note that the in-cylinder negative pressure of the internal combustion engine 1 may be increased by reducing the opening of the idle speed control valve (ISC valve) instead of the throttle valve 5 during execution of the fuel cut control.

  When the in-cylinder negative pressure of the internal combustion engine 1 increases, the amount of lubricating oil drawn into the cylinder through between the bore wall surface and the outer peripheral surface of the piston increases. As a result, the amount of lubricating oil used for combustion in the cylinder increases. As a result, the amount of ash generated increases, so the amount of ash contained in the exhaust discharged from the internal combustion engine 1 increases.

  In the above case, the ash amount increase control is actually executed during the fuel cut control when the ash accumulation amount Qash in the filter 6 is smaller than the first predetermined ash accumulation amount Qash1. When the ash accumulation amount Qash in the filter 6 is equal to or greater than the first predetermined ash accumulation amount Qash1, execution of the ash amount increase control is prohibited.

<Example 2>
[Ash increase control]
The schematic configuration of the intake and exhaust system of the internal combustion engine according to the present embodiment is the same as that of the first embodiment. Hereinafter, the points different from the first embodiment regarding the ash amount increase control according to the present embodiment will be mainly described.

  As with the first embodiment, the ash amount increasing control according to the present embodiment is also a control that increases the in-cylinder negative pressure of the internal combustion engine 1 and thereby increases the amount of lubricating oil provided for combustion in the cylinder. is there. In this case, if the ash amount increase control is executed, the consumption amount of the lubricating oil increases.

  Therefore, in this embodiment, the execution condition of the ash amount increase control is further limited in order to suppress the consumption amount of the lubricating oil. Specifically, when the PM accumulation amount in the filter 6 is smaller than the predetermined PM accumulation amount, execution of the ash amount increase control is prohibited.

  Even when the ash accumulation amount Qash in the filter 6 is smaller than the first predetermined ash accumulation amount Qash1, if the PM accumulation amount in the filter 6 is equal to or greater than the threshold value for starting the filter regeneration process, the filter regeneration process is executed. When the filter regeneration process is executed, PM other than ash is almost removed from the filter 6.

  Here, in a state where the PM accumulation amount in the filter 6 is very small, the ash that has flowed into the filter 6 tends to pass through the pores formed in the partition walls of the filter 6. Therefore, even if the ash amount increase control is executed in such a state, an ash deposit layer is hardly formed on the surface of the partition wall of the filter 6.

  Therefore, in this embodiment, as described above, when the PM accumulation amount in the filter 6 is smaller than the predetermined PM accumulation amount, execution of the ash amount increase control is prohibited. Here, the predetermined PM deposition amount is a PM deposition amount that prevents ash from passing through the pores formed in the partition walls of the filter 6 and is a value determined in advance based on experiments or the like. . It should be noted that the predetermined PM accumulation amount is naturally a value smaller than the threshold value for starting the filter regeneration process.

  According to this, even when the ash accumulation amount in the filter 6 does not reach the first predetermined ash accumulation amount, the execution of the ash amount increase control is prohibited when it is difficult to form the ash accumulation layer. That is, the ash amount increase control is executed only when the ash deposition layer is easily formed. Therefore, it is possible to suppress an increase in the consumption amount of the lubricating oil accompanying the execution of the ash amount increase control.

  FIG. 4 is a flowchart showing a flow of ash amount increase control according to the present embodiment. This flow is stored in advance in the ECU 10 and is repeatedly executed by the ECU 10. This flow is obtained by adding step S202 to the flowchart shown in FIG. Therefore, only the process in step S202 will be described, and the description of the processes in other steps will be omitted.

  In this flow, if an affirmative determination is made in step S102, it is then determined in step S202 whether or not the PM accumulation amount Qpm in the filter 6 is equal to or greater than the predetermined PM accumulation amount Qpm0. Note that the PM accumulation amount Qpm in the filter 6 is estimated based on the differential pressure across the filter 6 as described above.

  When a negative determination is made in step S202, that is, when the PM accumulation amount Qpm in the filter 6 is smaller than the predetermined PM accumulation amount Qpm0, the execution of this flow is terminated. That is, execution of ash amount increase control is prohibited. On the other hand, if an affirmative determination is made in step S202, ash amount increase control is then executed in step S103.

<Example 3>
The schematic configuration of the intake and exhaust system of the internal combustion engine according to the present embodiment is the same as that of the first embodiment. Also in the present embodiment, as in the first or second embodiment, the ash amount increase control is executed.

[Ash amount reduction control]
When the ash accumulation amount in the filter 6 reaches the first predetermined ash accumulation amount, the ash amount increase control is not performed thereafter. However, the ash deposition amount in the filter 6 gradually increases thereafter. Further, when the ash amount increase control is executed, the ash accumulation amount in the filter 6 reaches the first predetermined ash accumulation amount when the total traveling distance of the vehicle is shorter than when the ash amount increase control is not executed. . Therefore, after the time when the ash accumulation amount in the filter 6 reaches the first predetermined ash accumulation amount, when the internal combustion engine 1 is normally operated in an operation state in which the ash discharge amount is large, the total travel distance of the vehicle is the guaranteed distance. There is a high possibility that the amount of ash deposited on the filter 6 will reach the upper limit of the allowable range before reaching.

  Therefore, in this embodiment, in order to suppress such excessive accumulation of ash, the ash accumulation amount in the filter 6 is equal to or greater than the second predetermined ash accumulation amount when the total traveling distance of the vehicle reaches a predetermined determination distance. In this case, ash amount reduction control is executed in which the amount of ash contained in the exhaust discharged from the internal combustion engine 1 is smaller than the reference amount.

  Here, the second predetermined ash accumulation amount is an amount larger than the first predetermined ash accumulation amount and smaller than the upper limit value of the allowable range of the ash accumulation amount. The predetermined determination distance is a distance shorter than the guaranteed traveling distance of the vehicle. The second predetermined ash accumulation amount is a value determined according to the predetermined determination distance. That is, if the ash accumulation amount in the filter 6 is the second predetermined ash accumulation amount when the total travel distance of the vehicle reaches the predetermined determination distance, then, in an operating state in which the ash emission amount from the internal combustion engine 1 is maximized thereafter. When the internal combustion engine 1 is normally operated, the ash accumulation amount in the filter 6 becomes the upper limit value of the allowable range when the total traveling distance of the vehicle becomes the guaranteed distance. Such a predetermined determination distance and the second predetermined ash accumulation amount can be obtained based on experiments or the like, and are stored in the ECU 10 in advance.

  When the ash amount reduction control is executed, the amount of ash flowing into the filter 6 decreases. Therefore, according to the present embodiment, it is possible to reduce the increase rate of the ash deposition amount before the ash deposition amount reaches the upper limit value of the allowable range. Therefore, ash overdeposition in the filter 6 can be suppressed. That is, it is possible to prevent the ash accumulation amount in the filter 6 from reaching the upper limit value of the allowable range before the total travel distance of the vehicle reaches the guaranteed distance.

  FIG. 5 is a flowchart illustrating a flow of ash amount reduction control according to the present embodiment. This flow is stored in advance in the ECU 10 and is repeatedly executed by the ECU 10.

  In this flow, first, in step S301, it is determined whether or not the total travel distance Dv of the vehicle equipped with the internal combustion engine 1 has reached the predetermined determination distance Dv0. If a negative determination is made in step S301, that is, if the total travel distance Dv of the vehicle has not reached the predetermined determination distance Dv0, the execution of this flow is temporarily terminated.

  On the other hand, if an affirmative determination is made in step S301, the ash accumulation amount Qash in the filter 6 is then calculated in step S302. The calculation method of the ash deposition amount here is the same as the calculation method in step S101 of the flowchart shown in FIG.

Next, in step S303, it is determined whether or not the ash accumulation amount Qash in the filter 6 is equal to or greater than the second predetermined ash accumulation amount Qash2. If a negative determination is made in step S303, that is, if the ash accumulation amount Qash in the filter 6 is smaller than the second predetermined ash accumulation amount Qash2, the execution of this flow is terminated.

  On the other hand, when a positive determination is made in step S303, ash amount reduction control is executed in step S304. The ash amount reduction control according to the present embodiment is specifically control for reducing the in-cylinder negative pressure of the internal combustion engine 1. For example, in this embodiment, by increasing the opening degree of the throttle valve 5 during the execution of the fuel cut control, the in-cylinder negative pressure during the intake stroke of the internal combustion engine 1 is reduced, thereby performing the ash amount reduction control. Realize. Note that the in-cylinder negative pressure of the internal combustion engine 1 may be reduced by increasing the opening of the ISC valve instead of the throttle valve 5 during execution of the fuel cut control.

  When the in-cylinder negative pressure of the internal combustion engine 1 is reduced, the amount of lubricating oil drawn into the cylinder through between the bore wall surface and the outer peripheral surface of the piston is reduced. As a result, the amount of lubricating oil used for combustion in the cylinder is reduced. As a result, the amount of ash produced is reduced, so that the amount of ash contained in the exhaust discharged from the internal combustion engine 1 is reduced.

  In the above case, the ash amount reduction control is actually executed during the fuel cut control when the ash accumulation amount Qash in the filter 6 is equal to or larger than the second predetermined ash accumulation amount Qash2.

  FIG. 6 is a diagram showing the transition of the ash accumulation amount in the filter 6 with respect to the total travel distance of the vehicle. In FIG. 6, the horizontal axis represents the total travel distance of the vehicle, and the vertical axis represents the ash accumulation amount in the filter 6. In FIG. 6, the alternate long and short dash line indicates the transition of the ash accumulation amount in the filter 6 when the internal combustion engine 1 is continuously operated normally in the operation state in which the ash discharge amount is maximum from the time when the filter 6 is in the initial state. Is shown. In this case, as shown in FIG. 6, when the total travel distance of the vehicle reaches the guaranteed distance, the ash accumulation amount in the filter 6 becomes the upper limit value of the allowable range.

  In this embodiment, the ash amount increases from the time when the filter 6 is in the initial state, that is, from when the total travel distance of the vehicle is zero until the ash accumulation amount in the filter 6 reaches the first predetermined ash accumulation amount Qash1. Control is executed. Then, after the time point when the ash accumulation amount in the filter 6 reaches the first ash predetermined accumulation amount Qash1, the ash amount increase control is not performed, and the internal combustion engine 1 is normally operated.

  Here, in FIG. 6, L1 represents a transition of the ash accumulation amount in the filter 6 when the internal combustion engine 1 is normally operated in an operation state in which the ash discharge amount is relatively small after the execution period of the ash amount increase control ends. Show. On the other hand, L2 shows the transition of the ash accumulation amount in the filter 6 when the internal combustion engine 1 is normally operated in the operation state in which the ash discharge amount becomes maximum after the execution period of the ash amount increase control ends.

  When the ash accumulation amount in the filter 6 changes as indicated by L1, the ash accumulation amount does not reach the upper limit of the allowable range even when the total traveling distance of the vehicle reaches the guaranteed distance. On the other hand, when the ash accumulation amount in the filter 6 changes as indicated by L2, the ash accumulation amount reaches the upper limit of the allowable range before the total travel distance of the vehicle reaches the guaranteed distance. In this case, the ash accumulation amount in the filter 6 when the total traveling distance of the vehicle reaches the predetermined determination distance Dv0 is equal to or greater than the second predetermined ash accumulation amount Qash2.

Therefore, in this embodiment, in this case, the ash amount reduction control is executed from the time when the total travel distance of the vehicle reaches the predetermined determination distance Dv0. L3 in FIG. 6 indicates the transition of the ash accumulation amount in the filter 6 when this ash amount reduction control is executed. As indicated by L3, the ash amount reduction control is executed, so that the increase rate of the ash accumulation amount in the filter 6 is reduced. As a result, the ash accumulation amount in the filter 6 is prevented from reaching the upper limit value of the allowable range before the traveling distance of the vehicle reaches the guaranteed distance.

  In this embodiment, after the execution of the ash amount reduction control is started, the ash amount is reached when the total travel distance of the vehicle and the ash accumulation amount in the filter 6 reach the values shown on the alternate long and short dash line in FIG. The execution of the amount reduction control may be stopped. If the total mileage of the vehicle and the ash accumulation amount in the filter 6 reach the values represented on the one-dot chain line in FIG. 6, then the internal combustion engine 1 is normally operated in an operation state in which the ash discharge amount is maximum. Even in this case, the ash accumulation amount in the filter 6 is suppressed from reaching the upper limit value of the allowable range before the total traveling distance of the vehicle reaches the guaranteed distance.

  Further, the ash amount reduction control is executed when the ash accumulation amount in the filter 6 reaches a predetermined ash accumulation amount that is larger than the first predetermined ash accumulation amount and smaller than the upper limit value of the allowable range regardless of the total travel distance of the vehicle. By doing so, ash overdeposition may be suppressed.

<Example 4>
The schematic configuration of the intake and exhaust system of the internal combustion engine according to the present embodiment is the same as that of the first embodiment. Also in the present embodiment, as in the first or second embodiment, the ash amount increase control is executed. Hereinafter, the difference from the third embodiment regarding the ash amount reduction control according to the present embodiment will be mainly described.

[Ash amount reduction control]
As with the third embodiment, the ash amount reduction control according to the present embodiment is a control that reduces the in-cylinder negative pressure of the internal combustion engine 1 and thereby reduces the amount of lubricating oil used for combustion in the cylinder. is there. In this case, when the ash amount reduction control is executed, the effect of the engine brake becomes small (that is, the effect of the engine brake becomes weak).

  Therefore, in this embodiment, the execution condition of the ash amount reduction control is further limited in order to suppress the occurrence frequency of the period when the effect of the engine brake becomes small. Specifically, when the PM accumulation amount in the filter 6 is smaller than the predetermined PM accumulation amount, execution of the ash amount reduction control is prohibited. Here, the predetermined PM deposition amount is a PM deposition amount to the extent that ash is prevented from passing through the pores formed in the partition walls of the filter 6 as in the case of the predetermined PM deposition amount according to the second embodiment.

  According to this, when the ash accumulation amount in the filter 6 is not less than the second predetermined ash accumulation amount when the total traveling distance of the vehicle reaches the predetermined determination distance, the ash amount is difficult to increase. Execution of reduction control is prohibited. That is, during the execution period of the ash amount reduction control as shown in FIG. 6, the ash amount reduction control is executed only when the ash deposit layer is easily formed. Accordingly, it is possible to suppress the occurrence frequency of the period when the effect of the engine brake becomes small.

  FIG. 7 is a flowchart illustrating a flow of ash amount reduction control according to the present embodiment. This flow is stored in advance in the ECU 10 and is repeatedly executed by the ECU 10. In this flow, step S404 is added to the flowchart shown in FIG. Therefore, only the process in step S404 will be described, and the description of the processes in other steps will be omitted.

In this flow, if an affirmative determination is made in step S303, it is then determined in step S404 whether or not the PM accumulation amount Qpm in the filter 6 is equal to or greater than a predetermined PM accumulation amount Qpm0. Also in this case, the PM accumulation amount Qpm in the filter 6 is estimated based on the differential pressure across the filter 6 as described above.

  If a negative determination is made in step S404, that is, if the PM accumulation amount Qpm in the filter 6 is smaller than the predetermined PM accumulation amount Qpm0, the process of step S404 is executed again. That is, the execution of the ash amount reduction control is prohibited. On the other hand, if an affirmative determination is made in step S404, ash amount reduction control is executed next in step S304.

<Example 5>
The schematic configuration of the intake and exhaust system of the internal combustion engine according to the present embodiment is the same as that of the first embodiment. Also in the present embodiment, as in the first or second embodiment, the ash amount increase control is executed.

[Exhaust flow reduction control]
When the flow rate of the exhaust gas flowing into the filter 6 is large, the ash flowing into the filter 6 does not stay in the upstream portion of the filter 6 but easily flows into the downstream portion. Therefore, ash is more easily deposited in the downstream portion of the filter 6 than in the upstream portion thereof. Therefore, by executing the ash amount increase control, the ash deposition layer formed on the surface of the partition wall of the filter 6 tends to be non-uniform.

  In addition, since the filter 6 is at a high temperature during the filter regeneration process, the ash tends to aggregate and become stable. Therefore, in this embodiment, exhaust flow rate reduction control is executed to reduce the flow rate of the exhaust gas flowing into the filter 6 from the reference flow rate until the ash deposition amount in the filter 6 reaches the first predetermined ash deposition amount. . At this time, the execution period of the exhaust gas flow reduction control is executed after the completion of the execution of the ash amount increase control from the start of execution of the ash amount increase control executed during the execution of the fuel cut control as described above. Until the end of execution of the filter regeneration process.

  Here, the reference flow rate is the flow rate of the exhaust gas flowing into the filter 6 when the internal combustion engine 1 is normally operated without executing the exhaust gas flow rate reduction control.

  According to this, it is possible to suppress the ash in the filter 6 increased by executing the ash amount increase control from being concentrated in the downstream portion of the filter 6. Further, the flow rate of the exhaust gas flowing into the filter 6 is reduced at the timing when the ash flowing into the filter 6 aggregates, that is, at the timing when the ash accumulation layer is easily formed stably.

  FIG. 8 is a diagram showing the state of the ash deposition layer formed on the surface of the partition wall of the filter by executing the ash amount increase control. FIG. 8A shows the state of the ash accumulation layer when the exhaust flow rate reduction control is not executed, and FIG. 8B shows the case when the exhaust flow rate reduction control according to this embodiment is executed. The state of the ash deposition layer is shown.

  As shown in FIG. 8B, by performing the exhaust flow rate reduction control as described above, an ash deposition layer is formed on the surface of the partition wall of the filter 6 from the upstream side portion to the downstream side portion of the filter 6. It becomes possible to form more uniformly. Thereby, also in the upstream part of the filter 6, the increase in internal deposition of PM can be suppressed more. Therefore, according to the present embodiment, PM internal deposition can be more effectively suppressed.

  The execution period of the exhaust flow rate reduction control is not necessarily limited to the above period. For example, the exhaust flow rate reduction control may be continuously executed until the ash accumulation amount in the filter 6 reaches the first predetermined ash accumulation amount.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Intake passage 3 ... Exhaust passage 4 ... Air flow meter 5 ... Throttle valve 6 ... Particulate filter 7 ... Oxidation catalyst 8 ... Fuel addition valve 10. ・ ECU
13 .... Differential pressure sensor 14 ... Exhaust temperature sensor 15 ... Oil sensor 16 ... Intake pressure sensor

Claims (8)

A filter provided in the exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust;
The amount of ash included in the exhaust discharged from the internal combustion engine increases from the reference amount between the time when the filter is in the initial state and the time when the amount of ash accumulated in the filter reaches a predetermined amount of ash. An exhaust purification system for an internal combustion engine that executes control. The ash amount increasing control is control for increasing the in-cylinder negative pressure of the internal combustion engine,
2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein execution of the ash amount increase control is prohibited when the accumulation amount of particulate matter in the filter is smaller than a predetermined PM accumulation amount. The predetermined ash accumulation amount is a first predetermined ash accumulation amount,
Included in the exhaust discharged from the internal combustion engine when the ash accumulation amount in the filter is greater than the first predetermined ash accumulation amount and greater than or equal to a second predetermined ash accumulation amount that is less than the upper limit value of the allowable ash accumulation amount. The exhaust gas purification system for an internal combustion engine according to claim 1 or 2, wherein an ash amount reduction control is performed so that an ash amount to be reduced is smaller than the reference amount.   4. The internal combustion engine according to claim 3, wherein whether or not an ash accumulation amount in the filter is equal to or greater than the second predetermined ash accumulation amount is determined when a total traveling distance of a vehicle equipped with the internal combustion engine reaches a predetermined determination distance. Exhaust purification system. The ash amount reduction control is control for reducing the in-cylinder negative pressure of the internal combustion engine,
The exhaust gas purification system for an internal combustion engine according to claim 3 or 4, wherein execution of the ash amount reduction control is prohibited when the amount of particulate matter deposited on the filter is less than a predetermined amount of PM deposited.   6. The exhaust flow rate reduction control is executed to reduce the flow rate of the exhaust gas flowing into the filter from a reference flow rate until the ash deposition amount in the filter reaches the predetermined ash deposition amount. An exhaust gas purification system for an internal combustion engine according to the item. A filter regeneration processing execution unit that performs a filter regeneration process for oxidizing and removing particulate matter other than ash deposited on the filter by increasing the temperature of the filter;
The internal combustion engine according to claim 6, wherein the exhaust gas flow reduction control is executed from a start time of execution of the ash amount increase control to an end of execution of the filter regeneration process executed after the execution of the ash amount increase control. Engine exhaust purification system.   The exhaust purification system for an internal combustion engine according to claim 1, wherein the internal combustion engine is a gasoline engine.

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