JP4618069B2 - 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 that removes oxidation of particulate matter deposited on a filter disposed in an exhaust passage of the internal combustion engine by raising the temperature of the filter.

  In an internal combustion engine, an exhaust purification system for an internal combustion engine having a filter in an exhaust passage is known in order to collect particulate matter (PM: Particulate Matter, hereinafter referred to as PM) contained in exhaust gas. It has been. In such a system, a filter regeneration process is performed in which the temperature of the filter is raised to oxidize and remove PM deposited on the filter.

  In the filter regeneration process, heat is generated with the oxidation of PM, and the temperature of the filter may be overheated depending on the relationship between heat generation and heat dissipation in the filter. In order to suppress this excessive temperature rise, a technique is known in which the exhaust flow rate is increased, and the amount of heat taken away by the exhaust downstream of the filter (hereinafter referred to as the amount of removed heat) is increased. In addition, in connection with this, since the floor temperature of the filter is lowered when the exhaust flow rate is excessively increased, a technique for setting an upper limit for the increase amount of the exhaust flow rate is known (see Patent Document 1).

On the other hand, in the filter regeneration process, the calorific value increases as the amount of oxygen when oxidizing the PM increases. For this reason, even if the amount of oxygen increases too much, the filter may overheat. In order to suppress this excessive temperature rise, a technique for reducing the intake flow rate and reducing the amount of oxygen oxidized with PM is known (see Patent Document 2).
JP 2004-190668 A JP 2004-263578 A

  By the way, it cannot be said that the detection accuracy of the PM accumulation amount is necessarily high, but is estimated with a value that allows for some variation. For this reason, the filter regeneration process may be performed in a state where PM is not deposited on the filter. Even in such a case, if a risk condition such as deceleration that overheats the filter is satisfied, the exhaust flow rate may be increased as described above in order to suppress overheating of the filter during the filter regeneration process, The intake flow rate may be decreased.

  In such an increase in the exhaust flow rate, since PM is not deposited, the amount of heat generated due to the oxidation of PM is small, and the temperature rise of the filter does not occur as much as the consideration is made. I will. In addition, if the intake air flow rate is reduced in such a case, the exhaust air flow rate also decreases as the intake air flow rate decreases, and the amount of heat taken away decreases, and the temperature rise of the filter may occur due to the decrease in the amount of heat removed. is there.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technique for more reliably suppressing excessive temperature rise of a filter regardless of the amount of PM deposition.

In the present invention, the following configuration is adopted. That is,
In an exhaust gas purification system for an internal combustion engine that includes a filter that is disposed in an exhaust passage of the internal combustion engine and collects particulate matter in the exhaust gas, and oxidizes and removes particulate matter deposited on the filter by raising the temperature of the filter.
The target flow rate during oxidation removal of the particulate matter is set to a lower limit of the target flow rate based on an oxidation rate of the particulate matter that is oxidized by oxygen supplied by an intake air flow rate that is an upper limit flow rate of the target flow rate. An exhaust gas purification system for an internal combustion engine, comprising target flow rate setting means for determining an exhaust flow rate as a flow rate in a range in which the exhaust gas flow rate is equal to the amount of heat taken away from the filter.

  In other words, in the present invention, the target flow rate during oxidation removal of the particulate matter is determined within a predetermined flow rate range. Here, the predetermined flow rate range is determined based on the calorific value based on the oxidation rate of the particulate matter oxidized with oxygen supplied to the filter when the target flow rate is the upper limit flow rate of the predetermined range, and the target flow rate. The exhaust flow rate when the lower limit flow rate is within the range is determined so that the amount of heat taken away from the filter is equal.

  In the present invention, if the amount of heat generated by oxidation of particulate matter (PM) in the filter is equal to or less than the amount of heat that can be removed from the filter, even if heat generated by the amount of heat generated by the filter is generated by the filter, it is carried away by the exhaust. Therefore, we focused on the fact that the filter does not heat up. In addition, attention is paid to the fact that the intake air flow rate required to supply oxygen for oxidizing PM can be calculated from the calorific value generated in the filter in view of the oxidation rate of PM. Then, combining them, the upper limit flow rate is derived from the calorific value equivalent to the amount of heat taken away at the lower limit flow rate in view of the PM oxidation rate, and the range of the intake flow rate in which the excessive temperature rise of the filter is suppressed is determined. The intake flow rate is determined.

  Here, the upper limit flow rate and the lower limit flow rate are the exhaust flow rate at which the calorific value based on the oxidation rate of the particulate matter oxidized by oxygen supplied by the intake flow rate that becomes the upper limit flow rate becomes the lower limit flow rate. Is equal to the amount of heat removed from the filter.

  Then, since the determined target flow rate is a value that is greater than or equal to the lower limit flow rate and less than or equal to the upper limit flow rate, the actual amount of heat removed in the filter is greater than or equal to the amount of heat removed when the exhaust flow rate is the lower limit flow rate. . Similarly, the amount of heat generated by oxidation of the actual particulate matter in the filter is equal to or less than the amount of heat generated when the exhaust flow rate is the upper limit flow rate.

  For this reason, in the actual filter regeneration processing, the amount of heat taken away by exhausting at the target flow rate can always be greater than or equal to the amount of heat generated by exhausting at the target flow rate.

  According to this configuration, the range of the intake flow rate in which the excessive temperature rise of the filter is suppressed is specified from the viewpoint of the amount of heat and PM oxidation rate. Therefore, the PM accumulation amount does not affect the range of the intake flow rate. Therefore, regardless of the amount of accumulated PM, the excessive temperature rise of the filter can be suppressed if the intake flow rate is in the above range.

  That is, even when the filter regeneration process is performed in a state where PM is not accumulated on the filter, if the intake flow rate is in the above range, the intake flow rate is not excessively increased or decreased. For this reason, it is possible to suppress a decrease in the bed temperature of the filter due to an excessive increase in the exhaust flow rate accompanying an excessive increase in the intake flow rate. In addition, an excessive decrease in the amount of heat taken away due to an excessive decrease in the exhaust flow rate accompanying an excessive decrease in the intake air flow rate can be suppressed, and an excessive temperature rise of the filter caused by the excessive decrease in the amount of heat removed can be suppressed.

  Therefore, the excessive temperature rise of the filter can be more reliably suppressed regardless of the amount of PM accumulation.

In an exhaust gas purification system for an internal combustion engine that includes a filter that is disposed in an exhaust passage of the internal combustion engine and collects particulate matter in the exhaust gas, and oxidizes and removes particulate matter deposited on the filter by raising the temperature of the filter.
Determining a predetermined first flow rate and a second flow rate based on an amount of oxygen derived from an oxidation rate of the particulate matter that is maximally allowed for the amount of heat taken away from the filter by the first flow rate, and Target flow rate setting means for setting the target flow rate during oxidation removal of the particulate matter to a range in which the first flow rate is the lower limit and the second flow rate is the upper limit when the first flow rate is equal to or less than the second flow rate. An exhaust gas purification system for an internal combustion engine, comprising:

  According to this configuration, the second flow rate that is the upper limit flow rate is derived in consideration of the oxidation rate of the particulate matter (PM) based on the calorific value that is determined from the first flow rate that is the lower limit flow rate, and the PM is being oxidized and removed. The target flow rate at which the overheating of the filter is suppressed can be set to a range in which the PM flow rate does not affect the first flow rate and the second flow rate is the upper limit.

The target flow rate setting means includes
The first flow rate is determined as an exhaust flow rate flowing into the filter,
Calculating an allowable maximum oxidation rate that is an oxidation rate of the particulate matter such that the amount of heat taken away based on the first flow rate and the bed temperature of the filter is equal to the total amount of heat of reaction in the filter;
The unit time based on the maximum allowable oxidation rate and the number of moles of the particulate matter oxidized per unit time calculated from the weight per mole of the particulate matter and the weight per mole of oxygen. Calculate the maximum allowable oxygen amount that is the amount of oxygen that reacts with the particulate matter that oxidizes around,
Calculating the second flow rate as the allowable maximum intake flow rate based on the allowable maximum oxygen amount and the amount of oxygen consumed in the cylinder of the internal combustion engine;
Determining whether the first flow rate is less than or equal to the second flow rate;
When the first flow rate is equal to or lower than the second flow rate, the target flow rate during oxidation removal of the particulate matter may be set to a range in which the first flow rate is a lower limit and the second flow rate is an upper limit. .

  According to this configuration, the target flow rate at which the excessive temperature rise of the filter during PM oxidation removal is suppressed by a simpler calculation process, the PM accumulation amount does not affect, the first flow rate is set as the lower limit, and the second flow rate is set as the upper limit. The range can be set.

  The target flow rate setting means may bring the target flow rate closer to the second flow rate as the amount of the particulate matter deposited on the filter increases.

  According to this configuration, the greater the amount of PM deposited, the faster the oxidation rate, and PM oxidation removal can be terminated earlier. Thereby, it is possible to reduce the temperature raising time of the filter that occurs during the oxidation removal of PM. And since the temperature rising time of a filter can be reduced, the time which a filter is exposed to high temperature can be reduced, and the thermal deterioration of a filter can be suppressed.

  The target flow rate setting means may set the target flow rate to the second flow rate in order to maximize the oxidation rate and end oxidation removal of the particulate matter at an early stage.

  According to this configuration, the oxidation rate can be maximized and PM oxidation removal can be terminated early. Thereby, it is possible to reduce the temperature raising time of the filter that occurs during the oxidation removal of PM. And since the temperature rising time of a filter can be reduced, the time which a filter is exposed to high temperature can be reduced, and the thermal deterioration of a filter can be suppressed.

  According to the present invention, the excessive temperature rise of the filter can be more reliably suppressed regardless of the amount of PM accumulation.

  Specific examples of the present invention will be described below.

  FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which an exhaust purification system according to Embodiment 1 of the present invention is applied and its intake / exhaust system.

  An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders.

  An intake passage 2 is connected to the internal combustion engine 1. An air flow meter 3 that outputs an electrical signal corresponding to the mass of intake air (intake flow rate) flowing through the intake passage 2 is attached to the intake passage 2.

  A compressor housing for the supercharger 4 is provided in a portion of the intake passage 2 downstream of the air flow meter 3. An intake throttle valve 5 is provided in the intake passage 2 downstream of the compressor housing to adjust the flow rate of intake air flowing through the intake passage 2. An intake throttle actuator 6 is attached to the intake throttle valve 5.

  An exhaust passage 7 is connected to the internal combustion engine 1. The exhaust passage 7 is connected to a muffler (not shown) downstream. A turbine housing of the supercharger 4 is arranged in the middle of the exhaust passage 7, and a filter 8 for collecting PM in the exhaust discharged from the cylinder is arranged downstream of the turbine housing. ing. The filter 8 is a particulate filter in which a catalyst such as an oxidation catalyst, a NOx storage reduction catalyst, or a three-way catalyst is supported.

  An upstream exhaust temperature sensor 9 and a downstream exhaust temperature sensor 10 for outputting an electrical signal corresponding to the temperature of the exhaust gas flowing through the exhaust passage 7 are attached to the upstream side and the downstream side of the filter 8 in the exhaust passage 7. Yes.

The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 11 for controlling the internal combustion engine 1. The ECU 11 is a control computer including a CPU, a ROM, a RAM, a backup RAM, and the like.

  The ECU 11 includes a crank position sensor and a water temperature sensor attached to the internal combustion engine 1 in addition to the air flow meter 3, the upstream exhaust temperature sensor 9, and the downstream exhaust temperature sensor 10, and the interior of the vehicle in which the internal combustion engine 1 is mounted. Various sensors such as an accelerator position sensor attached to the vehicle are connected, and output signals of the various sensors are input to the ECU 11.

  On the other hand, an intake throttle actuator 6, a fuel injection valve, a fuel addition valve, and the like are connected to the ECU 11, and the ECU 11 can control them.

  Here, the ECU 11 oxidizes PM accumulated in the filter 8 by periodically raising the temperature of the filter 8 as described below as an interruption process based on the crank position sensor or an interruption process at regular intervals. The filter regeneration process to be removed is executed.

The filter regeneration process starts when the ECU 11 satisfies a filter regeneration process condition (hereinafter referred to as “filter regeneration process condition”) of the filter 8. Examples of the filter regeneration processing condition include a condition that the PM accumulation amount collected by the filter 8 is a predetermined amount or more. Note that the predetermined amount is lower than the amount that causes the filter 8 to be clogged when PM is deposited on the filter 8, and this clogging causes an increase in exhaust resistance and a decrease in the output of the internal combustion engine. Is an amount set in advance for each internal combustion engine.

  When it is determined that the filter regeneration processing condition is satisfied, the ECU 11 executes a temperature raising process for raising the temperature of the filter 8 to a high target temperature at which PM undergoes an oxidation reaction.

  As a method of executing the temperature raising process, a method is employed in which unburned fuel is oxidized in the catalyst supported on the filter 8 and the temperature of the filter 8 is raised by the reaction heat generated at that time. As a specific method, fuel is added into the exhaust from the fuel addition valve, or sub-injection is performed from the fuel injection valve of the cylinder during the exhaust stroke of the internal combustion engine 1.

  When such filter regeneration processing is executed, PM accumulated on the filter 8 is oxidized and PM is removed from the filter 8.

  By the way, in the filter regeneration process, heat is generated with the oxidation of PM, and the filter 8 may be overheated depending on the relationship between heat generation and heat dissipation in the filter. In order to suppress this excessive temperature rise, the exhaust flow rate is increased, and the amount of heat taken away by the exhaust among the heat generated by the oxidation of PM is increased, or the intake flow rate is decreased to oxidize the PM contained in the intake air and the amount of oxygen that is oxidized There is a known technique for reducing the above.

  However, the detection accuracy of the PM accumulation amount is not necessarily high, and is estimated with a value that allows for some variation. Therefore, the filter regeneration process may be performed in a state where PM is not accumulated on the filter 8. . In such a case, if a risk condition such as deceleration that overheats the filter 8 is satisfied, the exhaust flow rate is increased or the intake flow rate is decreased in order to suppress the excessive temperature rise of the filter 8 during the filter regeneration process. Control is performed.

  Then, the increase in the exhaust gas flow rate at this time is not generated as much as considering the temperature rise of the filter 8 because the amount of heat generated by the oxidation of the PM is small because PM is not deposited, and the floor temperature of the filter 8 is lowered. Invite a trade-off. In addition, the decrease in the intake flow rate at this time causes a decrease in the amount of heat taken away due to a decrease in the exhaust flow rate accompanying a decrease in the intake flow rate, and the excessive temperature rise of the filter 8 is caused by the decrease in the amount of heat taken away. May occur.

  Therefore, in this embodiment, the range of the intake air flow rate at which the filter 8 does not overheat regardless of the amount of PM accumulated on the filter 8 is set.

  Hereinafter, the flow rate setting process for setting the range of the intake flow rate at which the filter 8 does not overheat is referred to as “target flow rate setting process”. In addition, this process is a process which ECU11 performs, and corresponds to the target flow volume setting means of this invention.

  Specifically, in this embodiment, the ECU 11 executes the target flow rate setting process according to the following process. This process is periodically executed as an interrupt process based on the crank position sensor or an interrupt process at regular intervals during the filter regeneration process. Hereinafter, it demonstrates along the flowchart of FIG.

This intake flow rate setting routine is a routine stored in advance in the ROM of the ECU 11. First, in step (hereinafter simply referred to as “S”) 101, the ECU 11 is the exhaust flow rate flowing into the filter 8, and the target A flow rate Ggas (g / s) as a first flow rate, which is a lower limit flow rate, is set. Then, the process proceeds to S102.

  Note that Ggas at the start of this routine is a minimum value determined from various viewpoints such as fuel efficiency and noise, or a value when the intake throttle valve 5 is at the minimum opening. For example, Ggas = 5 is set in the idling state.

  In S102, the ECU 11 determines the allowable maximum oxidation that is the oxidation rate of PM based on Ggas and the bed temperature of the filter 8 so that the amount of heat removed from the filter 8 and the total reaction heat in the filter 15 are equal. The PM oxidation rate Grgn (g / s) as a rate is calculated.

That is, the temperature Tcat (° C.) detected by the downstream exhaust temperature sensor 10, the temperature Tgas (° C.) detected by the upstream exhaust temperature sensor 9, the unburned HC amount Ghc (g / g) in the filter 8 calculated by the ECU 11. s), and using these,
(Tcat−Tgas) × Ggas × Rgas = Ghc × Rhc + Grgn × Rrgn (1)
However, Rgas: Gas specific heat (constant value) (J / (g ° C.))
Rhc: HC lower heating value (constant value) (J / g)
Rrgn: PM lower heating value (constant value) (J / g)
The PM oxidation rate Grgn is calculated by the following equation. Then, the process proceeds to S103.

  Further, since the numerical values of parameters other than Ggas can be determined in the equation (1), Grgn can be expressed as Grgn = f (Ggas) as a function of Ggas.

  In the above equation (1), if the exhaust flow rate is equal to the amount of heat that can be taken away from the filter 8, even if the amount of heat generated by the filter 8 is generated by the filter 8, Focusing on the fact that the temperature does not rise, this is an equation in which the amount of heat taken away and the total amount of reaction heat in the filter 8 are connected by an equal sign.

  As for the left side of the equation (1), the temperature rise of the exhaust gas before and after passing through the filter 8 is derived by (Tcat−Tgas), and the temperature rise of the exhaust gas before and after passing through the filter 8 is integrated with Ggas and Rgas. Thus, the amount of heat that can be taken away by Ggas is derived.

  For the right side of the equation (1), the heat generation amount for the HC reaction in the filter 8 is derived by (Ghc × Rhc), and the heat generation amount for the PM reaction in the filter 8 is derived by (Grgn × Rrgn). The total reaction heat quantity in the filter 8 is derived by the sum of

  In S103, the ECU 11 oxidizes per unit time based on the number of moles of PM oxidized per unit time calculated from the weight per mole of Grgn and PM and the weight per mole of oxygen. The oxygen amount Go2 (g / s) is calculated as the allowable maximum oxygen amount that is the amount of oxygen that reacts with PM.

That is,
(Go2 / Ro) / (Grgn / Rc) = Ro / c (2)
However, Ro: weight per mole of oxygen (O2) (constant value) (g / mol)
Rc: weight per PM (C) (constant value) (g / mol)
Ro / c: Reaction molar ratio of oxygen and PM (constant value)
The oxygen amount Go2 is calculated by the following formula. Then, the process proceeds to S104.

  In addition, in the equation (2), since parameters other than Grgn are constant values, Go2 can be represented as Go2 = g (Grgn) = g ′ (Ggas) as a function of Grgn or Ggas.

  In S104, the ECU 11 calculates the allowable maximum flow rate Gmax (g / s), which is the second maximum flow rate that is the allowable maximum intake flow rate and is the upper limit flow rate of the target flow rate, based on the amount of oxygen consumed by Go2 and the internal combustion engine 1. calculate.

That is, the fuel injection amount Gfuel (g / s) in the cylinder of the internal combustion engine 1 calculated by the ECU 11 is read and used.
Gmax × Rair = Gfuel × Rst + Go2 (3)
However, Rair: atmospheric oxygen concentration (constant value) (% wt)
Rst: Theoretical air-fuel ratio (constant value)
The allowable maximum flow rate Gmax is calculated by the following formula. Then, the process proceeds to S105.

  Further, since the numerical values of parameters other than Go2 can be determined in the expression (3), Gmax can be expressed as Gmax = h (Go2) = h ′ (Ggas) as a function of Go2 or Ggas. Eventually, Gmax can be derived using Ggas as a parameter.

  In S105, the ECU 11 determines whether Ggas is equal to or less than Gmax (Ggas ≦ Gmax).

  When an affirmative determination is made in S105 (Ggas ≦ Gmax), in S106, the ECU 11 sets the target flow rate G of the intake air flow rate in the filter regeneration processing to a range (Ggas ≦ G ≦ Gmax) in which Ggas is the lower limit and Gmax is the upper limit. Set. As long as it is within the range, the value of G may be any value.

  On the other hand, if a negative determination is made in S105 (Ggas ≦ Gmax is not satisfied), the ECU 11 increases the value of Ggas and resets it in S107 (Ggas (i) = Ggas (i−1) +1: i is Integer) and return to S102.

  When the execution of the process of step S106 is completed, the ECU 20 ends the execution of this routine.

  In this way, the range of the intake flow rate in which the excessive temperature rise of the filter 8 in the filter regeneration process is suppressed is specified from the viewpoint of the amount of heat removed and the oxidation rate of PM. Therefore, the PM accumulation amount does not affect the range of the intake flow rate. Therefore, regardless of the amount of accumulated PM, the excessive temperature rise of the filter 8 can be suppressed if the intake flow rate is in the above range. Therefore, the excessive temperature rise of the filter 15 can be more reliably suppressed regardless of the amount of PM accumulation.

  In the above-described embodiment, the range of the intake flow rate in which the excessive temperature rise of the filter in the filter regeneration process is suppressed is set, but the range of Ggas ≦ G ≦ Gmax may be further limited from another viewpoint.

(Embodiment 1)
In the present embodiment, the set flow rate is made closer to Gmax as the PM accumulation amount in the filter 8 increases in the range of Ggas ≦ G ≦ Gmax.

  In this way, the greater the amount of PM deposited, the faster the oxidation rate for PM during the filter regeneration process, and the PM oxidation removal (filter regeneration process) can be terminated earlier. Thereby, the temperature raising time of the filter 8 generated during the filter regeneration process can be reduced. And since the temperature rising time of the filter 8 can be reduced, the time which the filter 8 is exposed to high temperature can be reduced, and the thermal deterioration of the filter 8 can be suppressed.

(Embodiment 2)
In the present embodiment, the set flow rate is set to Gmax (G = Gmax) so that the oxidation rate for PM is maximized and the filter regeneration process is terminated early in the range of Ggas ≦ G ≦ Gmax.

  In this way, the oxidation rate for PM can be maximized in the range of Ggas ≦ G ≦ Gmax, and the filter regeneration process can be terminated early. Thereby, the temperature raising time of the filter 8 generated during the filter regeneration process can be reduced. And since the temperature rising time of the filter 8 can be reduced, the time which the filter 8 is exposed to high temperature can be reduced, and the thermal deterioration of the filter 8 can be suppressed.

(Embodiment 3)
In the present embodiment, the set flow rate is set to Ggas (G = Ggas) in order to further suppress deterioration in fuel consumption in the range of Ggas ≦ G ≦ Gmax.

  In this way, the intake flow rate can be minimized within the range of Ggas ≦ G ≦ Gmax, and the amount of fuel to be supplied can be reduced. Thereby, the fuel consumption deterioration during the filter regeneration process can be suppressed.

(Embodiment 4)
In the present embodiment, the set flow rate is within the range of Ggas ≦ G ≦ Gmax, as long as the value of the set flow rate G does not become Ggas or less or Gmax or more so that the temporal variation is reduced as shown in FIG. (Average) (G (i) = G (i−1) + (Gmax−G (i−1)) × α: 0 <α ≦ 1).

  In this way, the change in the temporal flow rate can be reduced in consideration of the response delay of the change in the state of the filter 8 in the intake flow rate control due to the time difference from the supply of fuel to the arrival of the filter 8 and the arrival thereof. The state of the filter 8 such as the temperature during the transient operation can be stabilized.

(Embodiment 5)
In the present embodiment, the set flow rate is within the range of Ggas ≦ G ≦ Gmax, as long as the value of the set flow rate G does not become less than Ggas or more than Gmax so as to reduce temporal variation as shown in FIG. The previous value is held (G (i) = G (i-1)).

  In this way, the change in the temporal flow rate can be reduced in consideration of the response delay of the change in the state of the filter 8 in the intake flow rate control due to the time difference from the supply of fuel to the arrival of the filter 8 and the arrival thereof. The state of the filter 8 such as the temperature during the transient operation can be stabilized.

(Embodiment 6)
In the present embodiment, the set flow rate is further limited within the range of Ggas ≦ G ≦ Gmax, and the upper limit flow rate of the intake flow rate is limited due to the NOx restriction during the filter regeneration process (Ggas ≦ G ≦ Gm).
ax ′ (NOx)). Note that Gmax ′ (NOx) is the upper limit flow rate of the intake flow rate due to the NOx restriction during the filter regeneration process, and satisfies Ggas ≦ Gmax ′ (NOx) ≦ Gmax.

  In this way, the maximum amount of NOx discharged from the filter 8 can be regulated, and the amount of NOx discharged from the filter 8 can be managed.

  As in the above embodiment, a better intake flow rate can be set by further limiting the range of Ggas ≦ G ≦ Gmax from another viewpoint. In addition, each embodiment can also be implemented in combination.

1 is a diagram illustrating a schematic configuration of an internal combustion engine to which an exhaust purification system according to Embodiment 1 is applied and an intake / exhaust system thereof. 6 is a flowchart illustrating a control routine for setting an intake air flow rate in the filter regeneration process according to the first embodiment. 10 is a graph showing an averaged set flow rate according to the fourth embodiment. It is a graph which shows the setting flow volume which held last time value concerning Embodiment 5. FIG.

Explanation of symbols

1 Internal combustion engine 2 Intake passage 5 Intake throttle valve 7 Exhaust passage 8 Filter 9 Upstream exhaust temperature sensor 10 Downstream exhaust temperature sensor

Claims (5)

In an exhaust gas purification system for an internal combustion engine that includes a filter that is disposed in an exhaust passage of the internal combustion engine and collects particulate matter in the exhaust gas, and oxidizes and removes particulate matter deposited on the filter by raising the temperature of the filter.
The target flow rate during oxidation removal of the particulate matter is set to a lower limit of the target flow rate based on an oxidation rate of the particulate matter that is oxidized by oxygen supplied by an intake air flow rate that is an upper limit flow rate of the target flow rate. An exhaust gas purification system for an internal combustion engine, comprising target flow rate setting means for determining an exhaust gas flow rate as a flow rate within a range in which the exhaust gas flow rate is equal to the amount of heat taken away from the filter. In an exhaust gas purification system for an internal combustion engine that includes a filter that is disposed in an exhaust passage of the internal combustion engine and collects particulate matter in the exhaust gas, and oxidizes and removes particulate matter deposited on the filter by raising the temperature of the filter.
Determining a predetermined first flow rate and a second flow rate based on an amount of oxygen derived from an oxidation rate of the particulate matter that is maximally allowed for the amount of heat taken away from the filter by the first flow rate, and Target flow rate setting means for setting the target flow rate during oxidation removal of the particulate matter to a range in which the first flow rate is the lower limit and the second flow rate is the upper limit when the first flow rate is equal to or less than the second flow rate. An exhaust gas purification system for an internal combustion engine, comprising: The target flow rate setting means includes
The first flow rate is determined as an exhaust flow rate flowing into the filter,
Calculating an allowable maximum oxidation rate that is an oxidation rate of the particulate matter such that the amount of heat taken away based on the first flow rate and the bed temperature of the filter is equal to the total amount of heat of reaction in the filter;
The unit time based on the maximum allowable oxidation rate and the number of moles of the particulate matter oxidized per unit time calculated from the weight per mole of the particulate matter and the weight per mole of oxygen. Calculate the maximum allowable oxygen amount that is the amount of oxygen that reacts with the particulate matter that oxidizes around,
Calculating the second flow rate as the allowable maximum intake flow rate based on the allowable maximum oxygen amount and the amount of oxygen consumed in the cylinder of the internal combustion engine;
Determining whether the first flow rate is less than or equal to the second flow rate;
When the first flow rate is equal to or lower than the second flow rate, the target flow rate during oxidation removal of the particulate matter is set to a range in which the first flow rate is a lower limit and the second flow rate is an upper limit. The exhaust gas purification system for an internal combustion engine according to claim 2.   The exhaust purification of an internal combustion engine according to claim 2 or 3, wherein the target flow rate setting means brings the target flow rate closer to the second flow rate as the amount of the particulate matter accumulated in the filter increases. system.   The target flow rate setting means sets the target flow rate to the second flow rate in order to maximize the oxidation rate and end oxidation removal of the particulate matter at an early stage. An exhaust purification system for an internal combustion engine.

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