JP5708460B2 - 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 in which a particulate filter is disposed in an exhaust passage.

  When the internal combustion engine is in a cold state, moisture contained in the exhaust may be condensed in the exhaust system to generate liquid condensed water. Such condensed water may flow through the exhaust passage along with the exhaust gas and adhere to various exhaust system components.

  In a configuration in which a sensor with a heater is disposed in the exhaust passage of the internal combustion engine, it is determined whether or not the condensed water in the exhaust passage has been vaporized, and when it is determined that the condensed water in the exhaust passage has been vaporized, the sensor A technique for starting energization of a heater has been proposed (see, for example, Patent Document 1).

JP 2010-174657 A JP 2007-162575 A JP 2009-209889 A

  When a particulate filter is disposed in the exhaust passage of the internal combustion engine, if condensed water adheres to the particulate filter, particulate matter (PM) collected in the particulate filter is particulate. There is a possibility of desorption (peeling) from the filter. In that case, the amount of PM discharged into the atmosphere may increase.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to collect the particulate filter by the influence of condensed water in an exhaust gas purification system for an internal combustion engine in which the particulate filter is disposed in the exhaust passage. It is in suppressing the fall of the.

  In order to solve the above-described problems, the present invention provides an exhaust gas purification system for an internal combustion engine in which a particulate filter for collecting particulate matter (PM) in exhaust gas is disposed in an exhaust passage. When condensed water is generated in the exhaust passage upstream of the particulate filter, the decrease in the hydrogen ion index (pH) of the condensed water is suppressed or the hydrogen ion index (pH) is increased.

  As a result of experiments and verifications by the present inventor, when the particulate filter comes into contact with condensed water having high acidity (condensed water having low hydrogen ion index (pH)), condensed water having low acidity (hydrogen ion index) It was found that the amount of PM discharged from the particulate filter is larger than that in the case of contact with (condensed water having a high (pH)). This is expected to be due to the fact that when condensed water having a low hydrogen ion exponent (pH) (for example, condensed water having a pH of less than 5) comes into contact with PM, PM aggregates and desorbs from the particulate filter. .

Therefore, when condensed water can be generated in the particulate filter or the exhaust passage upstream of the particulate filter, it is possible to suppress the decrease in the hydrogen ion index (pH) of the condensed water or increase the hydrogen ion index (pH). If possible, it is possible to suppress an increase in the amount of PM discharged when the particulate filter comes into contact with (contains) condensed water.

Accordingly, the present invention provides an exhaust gas purification system for an internal combustion engine in which a particulate filter that collects particulate matter in exhaust gas is disposed in an exhaust passage.
An increase in the acidity of the condensed water (a decrease in the hydrogen ion index (pH)) is suppressed when a condensed water generation condition, which is a condition in which condensed water can be generated in the exhaust passage upstream of the particulate filter, is satisfied. For this reason, a suppression means for carrying out the acidification suppression treatment is provided.

  When the acidification suppression process is performed when the condensed water generation condition is satisfied, a decrease in the hydrogen ion exponent (pH) of the condensed water is suppressed. As a result, it is possible to suppress an increase in the amount of PM discharged from the particulate filter when the condensed water flows into the particulate filter. In other words, it is possible to suppress a decrease in the collecting ability of the particulate filter due to the influence of the condensed water.

Here, the hydrogen ion exponent of the condensed water (pH) tend to high exhaust of NO _X concentration and SO _X concentration is reduced upon contact with condensed water. Therefore, if the NO _X concentration or SO _X concentration of the exhaust gas can be lowered, the hydrogen ion exponent (pH) of the condensed water is unlikely to decrease (acidity is unlikely to increase).

Therefore, suppression means, as the acidification suppression process, a process for operating an internal combustion engine may be performed as _the amount of NO _X is reduced in the exhaust. As an operation state in which the amount of NO _X in the exhaust gas is reduced, an operation state in which the combustion speed of the air-fuel mixture becomes slow, an operation state in which the combustion temperature of the air-fuel mixture becomes lower, or the like can be considered.

As a method of slowing the combustion speed of the air-fuel mixture, a method of increasing an inert gas (for example, EGR (Exhaust Gas Recirculation) gas) introduced into the cylinder, or a method of retarding the ignition timing of the air-fuel mixture (for example, , A method of delaying fuel injection timing in a compression ignition type internal combustion engine, a method of delaying ignition timing in a spark ignition type internal combustion engine, etc.), a fuel injection valve in a cylinder injection type internal combustion engine A method of reducing the pressure (injection pressure) (suppressing the atomization of the injected fuel) can be used. As a method of lowering the combustion temperature of the air-fuel mixture, in addition to a method similar to the method of lowering the combustion speed, a method of reducing the fuel injection amount, a method of operating premixed compression auto-ignition (HCCI: Homogeneous Charge Compression Ignition) Can be used.

Next, the suppression means may perform a process of supplying a neutralizing agent to the exhaust passage upstream of the particulate filter as the acidification suppression process. As the neutralizing agent, for example, an aqueous solution derived from ammonia (for example, an aqueous solution of urea or ammonium carbamate) can be used. Further, when an oxidation catalyst is disposed in the exhaust passage upstream of the particulate filter, or when the oxidation catalyst is carried on the particulate filter, the internal combustion engine is operated with a rich mixture immediately before the internal combustion engine is stopped. it makes the residence or adsorbed ammonia (NH ₃₎ to the oxidation catalyst, may be work ammonia (NH ₃₎ as a neutralizing agent at the next startup.

Note that the amount of PM discharged from the particulate filter is smaller when the amount of condensed water in contact with the particulate filter is smaller than when the amount is too large. Therefore, as a method of reducing the amount of PM discharged from the particulate filter when the particulate filter comes into contact with the condensed water, the condensed water is used instead of the method of suppressing the decrease in the hydrogen ion exponent (pH) of the condensed water. A method of suppressing the amount of generation of the above may be used, or a method of simultaneously performing these two methods may be used.

As a method of suppressing the amount of condensed water generated, a method of reducing the amount of moisture (H ₂ O) contained in the exhaust gas (the amount of H ₂ O generated when the air-fuel mixture burns) can be considered. As a method for reducing the amount of moisture (H ₂ O) contained in the exhaust, a method for reducing the fuel injection amount can be used.

  The condensate generation condition may be satisfied when, for example, the atmospheric temperature (exhaust temperature) in the exhaust passage or the particulate filter is lower than the temperature at which the condensed water can be vaporized. Even when the condensate generation condition is satisfied, when the amount of PM collected in the particulate filter is sufficiently small, or when PM is not collected in the particulate filter, the acidification is suppressed. Processing may not be executed.

  As the particulate filter, a wall flow type particulate filter having a plurality of passages partitioned by porous partition walls is generally used. The wall flow type particulate filter tends to collect PM in the pores of the partition walls when the amount of collected PM is small and to collect PM on the surface of the partition walls when the amount of collected PM increases. is there. Further, when the particulate filter is wet, the PM collected on the partition wall surface is more easily detached than the PM collected in the pores.

  Therefore, when the amount of PM collected by the particulate filter is small (when PM is collected in the pores of the partition walls and almost no PM is collected on the partition wall surfaces), the particulate filter is wetted. However, it is considered that PM desorption hardly occurs.

  As a result, when the amount of PM collected by the particulate filter is equal to or less than a predetermined amount (the maximum amount of PM collected when PM is collected in the pores of the partition wall and almost no PM is collected on the partition wall surface). The acidification inhibiting treatment may not be performed.

  Next, the exhaust gas purification system for an internal combustion engine of the present invention may further include an adsorbent that is disposed upstream of the particulate filter and adsorbs moisture. According to such a configuration, the moisture contained in the exhaust is adsorbed by the adsorbent before flowing into the particulate filter. In that case, it is possible to suppress the condensed water generated in the exhaust passage upstream of the particulate filter and the gaseous moisture contained in the exhaust from flowing into the particulate filter. As a result, the condensed water generated in the exhaust passage upstream of the particulate filter is prevented from coming into contact with the particulate filter, or the moisture in the exhaust is liquefied in the particulate filter. That is, the moisture content of the particulate filter decreases. When the amount of water covered by the particulate filter decreases, the amount of PM discharged from the particulate filter can be suppressed to a low level.

  The adsorbent is preferably one that generates reaction heat when moisture is adsorbed, such as zeolite. In that case, it is preferable that the adsorbent is disposed in the vicinity of the particulate filter, preferably in contact with the upstream end of the particulate filter, or formed integrally with the particulate filter. According to such a configuration, the reaction heat (adsorption heat) of the adsorbent is easily transmitted to the particulate filter, so that moisture in the exhaust gas is not easily liquefied in the particulate filter and is present in the particulate filter. Moisture is easily vaporized.

When the exhaust gas purification system for an internal combustion engine of the present invention includes an adsorbent, the suppression means is an acidification suppression process when the condensed water generation condition is satisfied and the moisture adsorption amount of the adsorbent is saturated. May be executed. According to such a configuration, when moisture that cannot be adsorbed by the adsorbent flows into the particulate filter, an increase in the amount of PM discharged from the particulate filter can be suppressed.

  In addition, when the exhaust gas purification system for an internal combustion engine of the present invention includes an adsorbent, the apparatus further includes a temperature raising unit that performs a process of raising the temperature of the adsorbent before the operation of the internal combustion engine is stopped. Good. According to such a configuration, when the internal combustion engine is restarted, the moisture adsorption amount of the adsorbent can be made substantially zero. As a result, when the internal combustion engine is restarted, even if the condensate generation condition is satisfied, the time from when the internal combustion engine is started until the moisture adsorption amount of the adsorbent is saturated becomes longer. As a result, the possibility that the warm-up of the internal combustion engine is completed before the moisture adsorption amount of the adsorbent is saturated increases. If warming up of the internal combustion engine is completed before the moisture adsorption amount of the adsorbent is saturated, it is possible to avoid liquid moisture from flowing into the particulate filter. Note that if the amount of moisture adsorbed by the adsorbent is substantially zero when the internal combustion engine is restarted, the accuracy in estimating (calculating) the amount of moisture adsorbed by the adsorbent can be increased. It is also possible to more accurately determine when the amount of moisture adsorbed becomes saturated.

  Here, as a method for raising the temperature of the adsorbent, the temperature of the adsorbent is indirectly increased by increasing the exhaust temperature, or the temperature of the adsorbent is directly increased using a heater such as a heater. The method can be used. As a method of increasing the exhaust temperature, a method of retarding the ignition timing in a spark ignition internal combustion engine, a method of retarding the fuel injection timing in a compression ignition internal combustion engine, or the like can be used.

  According to the present invention, in the exhaust gas purification system for an internal combustion engine in which the particulate filter is disposed in the exhaust passage, it is possible to suppress a decrease in the collecting ability of the particulate filter due to the influence of condensed water.

1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied and an intake / exhaust system thereof in a first embodiment. It is a figure which shows the time-dependent change of PM amount discharged | emitted from a particulate filter when an internal combustion engine is cold-started. It is a flowchart which shows the acidification suppression processing routine in a 1st Example. It is a figure which shows schematic structure of the internal combustion engine to which this invention is applied in 2nd Example, and its intake / exhaust system. It is a flowchart which shows the acidification suppression processing routine in a 2nd Example. It is a figure which shows the correlation with the adsorption capacity of an adsorbent, and a pressure. It is a figure which shows the correlation with the adsorption capacity of an adsorbent, and humidity. It is a figure which shows the correlation with the adsorption capacity of adsorbent, and temperature.

  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>
First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied and its intake / exhaust system. Internal combustion engine 1 shown in FIG.
Is a four-stroke cycle spark ignition internal combustion engine having a plurality of cylinders. In FIG. 1, only one cylinder among a plurality of cylinders is shown. The internal combustion engine to which the present invention is applied is not limited to a spark ignition type internal combustion engine, and may be a compression ignition type internal combustion engine.

  A piston 3 is slidably inserted into the cylinder 2 of the internal combustion engine 1. The piston 3 is connected to a crankshaft (not shown) via a connecting rod 4. The internal combustion engine 1 includes an intake port 7 for taking fresh air (air) into the cylinder 2, a fuel injection valve 6 for injecting fuel into the intake port 7, and air introduced into the cylinder 2 from the intake port 7. And an ignition plug 5 for igniting the fuel-air mixture, and an exhaust port 8 for discharging the gas burned in the cylinder 2 (burned gas). The internal combustion engine 1 further includes an intake valve 9 for opening and closing the intake port 7 and an exhaust valve 10 for opening and closing the exhaust port 8.

  An intake passage 70 is connected to the intake port 7. The intake passage 70 is a passage that guides air taken from the atmosphere to the intake port 7. In the middle of the intake passage 70, a throttle valve 71 for changing the passage cross-sectional area of the intake passage 70 and an air flow meter 72 that outputs an electric signal correlated with the amount (mass) of air flowing in the intake passage 70. Is attached.

  An exhaust passage 80 is connected to the exhaust port 8. The exhaust passage 80 is a passage for discharging burned gas (exhaust gas) discharged from the cylinder 2 to the exhaust port 8 into the atmosphere after passing through a silencer or the like. In the middle of the exhaust passage 80, an exhaust purification device such as a particulate filter 81 and an exhaust purification catalyst (not shown) is disposed. The particulate filter 81 collects particulate matter (PM) contained in the exhaust gas, and is, for example, a wall flow type filter. Further, an exhaust temperature sensor 82 that outputs an electrical signal correlated with the temperature of the exhaust is attached to the exhaust passage 80 downstream of the particulate filter 81.

  An intake passage 70 downstream of the throttle valve 71 and an exhaust passage 80 upstream of the particulate filter 81 are connected to each other by an EGR passage 100. The EGR passage 100 is a passage that guides a part of exhaust gas (EGR gas) from the exhaust passage 80 to the intake passage 70. An EGR valve 101 that changes the cross-sectional area of the EGR passage 100 is disposed in the middle of the EGR passage 100.

  The internal combustion engine 1 configured as described above is provided with an ECU 20. The ECU 20 is an electronic control unit that includes a CPU, a ROM, a RAM, a backup RAM, and the like. In addition to the air flow meter 72 and the exhaust gas temperature sensor 82, the ECU 20 is electrically connected with various sensors such as the water temperature sensor 12, the crank position sensor 21, and the accelerator position sensor 22. The water temperature sensor 12 is a sensor that outputs an electrical signal that correlates with the temperature of the cooling water circulating in the internal combustion engine 1. The crank position sensor 21 is a sensor that outputs an electrical signal correlated with the rotational position of the crankshaft. The accelerator position sensor 22 is a sensor that outputs an electrical signal correlated with the amount of operation of the accelerator pedal (accelerator opening).

Various devices such as the spark plug 5, the fuel injection valve 6, the throttle valve 71, and the EGR valve 101 are electrically connected to the ECU 20. The ECU 20 electrically controls the various devices according to output signals from the various sensors. For example, the ECU 20 parameters the engine speed calculated based on the output signal of the crank position sensor 21, the output signal of the accelerator position sensor 22 (accelerator opening), the output signal of the water temperature sensor 12 (cooling water temperature), and the like. Calculated by calculating the opening of the throttle valve 71 (throttle opening), the fuel injection amount per cylinder (fuel injection time), the ignition timing, or the opening of the EGR valve 101 (EGR opening), etc. The throttle valve 71, the fuel injection valve 6, the spark plug 5, or the EGR valve 101 is controlled according to the throttle opening, fuel injection timing, ignition timing, EGR opening, or the like.

  Further, the ECU 20 determines that the acidity of the condensed water increases (hydrogen ion index (pH) decreases) when condensed water may be present in the particulate filter 81 or the exhaust passage 80 upstream of the particulate filter 81. The acidification suppression process for suppressing is implemented. Hereinafter, the execution method of the acidification suppression process in a present Example is described.

  When moisture in the exhaust is condensed in the exhaust passage 80 upstream from the particulate filter 81, or when moisture in the exhaust is condensed inside the particulate filter 81, the PM trapped in the particulate filter 81 is reduced. May come into contact with condensed water.

  When the PM collected by the particulate filter 81 comes into contact with the condensed water, the amount of PM discharged from the particulate filter 81 may increase. This is considered to be because PM accumulated on the passage wall surface of the particulate filter 81 aggregates and desorbs from the particulate filter 81 when it contacts the condensed water. This phenomenon becomes more prominent as the acidity of the condensed water becomes higher (for example, when the hydrogen ion index (pH) is smaller than “5”).

The hydrogen ion exponent (pH) of the condensed water tends to decrease as the amount of nitrogen oxide (NO _X ) or sulfur oxide (SO _X ) contained in the exhaust gas increases. Therefore, if the condition that condensate can exist in the exhaust passage 80 upstream of the particulate filter 81 (condensate generation condition) is satisfied, if the NO _X amount or the SO _X amount in the exhaust gas is reduced, the particulates Even if the filter 81 is flooded with condensed water, an increase in the amount of PM discharged from the particulate filter 81 can be suppressed.

Therefore, in this embodiment, ECU 20, when the condensed water generation conditions is satisfied, NO _X amount in the exhaust gas is so as to operate the internal combustion engine 1 so as to reduce. Note that the NO _X amount in the exhaust gas is likely to be generated when the air-fuel mixture is burned under high pressure and high temperature. Thus, the operating state of the combustion velocity of the mixture is slow, or by operating conditions the combustion temperature of the mixture is lowered if the internal combustion engine 1 is operated, it is possible to reduce the amount of NO _X in the exhaust gas.

  As a method of slowing down the combustion speed of the air-fuel mixture, a method of increasing the EGR gas introduced into the cylinder 2, a method of retarding the ignition timing, or the injection pressure of the fuel injection valve in the in-cylinder injection internal combustion engine is used. A method of reducing the level can be used. As a method of lowering the combustion temperature of the air-fuel mixture, in addition to a method similar to the method of slowing down the combustion speed, a method of reducing the fuel injection amount, a method of operating premixed compression auto-ignition (HCCI) Can be used. In this embodiment, an example will be described in which a decrease in the hydrogen ion exponent (pH) of condensed water is suppressed by a method of increasing the amount of EGR gas introduced into the cylinder 2.

Condensed water has a low temperature (cooling water temperature or oil temperature) of the internal combustion engine 1 as in the case where the internal combustion engine 1 is cold started, and the ambient temperature in the exhaust passage 80 or the particulate filter 81 is moisture ( It is likely to occur when the temperature is lower than the temperature at which H ₂ O) can be vaporized (hereinafter referred to as “vaporization temperature”). Here, FIG. 2 shows the amount of PM discharged from the particulate filter 81 (PM discharge amount) when the internal combustion engine 1 is cold-started. In FIG. 2, the horizontal axis indicates the elapsed time from the start of the internal combustion engine 1, and the vertical axis indicates the amount of PM discharged from the particulate filter 81. At the start of the internal combustion engine 1 or immediately after the start, the amount of PM discharged from the particulate filter 81 (PM discharge amount) increases, and the PM discharge amount becomes substantially zero after a certain period of time has elapsed. This is presumably because the moisture in the exhaust gas is cooled in the exhaust passage 80 and the particulate filter 81 upstream of the particulate filter 81 and becomes liquid condensed water at the start of the internal combustion engine 1 and immediately after the startup. .

  Therefore, when the internal combustion engine 1 is in a cold state, in other words, if the acidification suppression process is performed during the period from when the internal combustion engine 1 is cold started to when the exhaust gas temperature is equal to or higher than the vaporization temperature, The amount of PM discharged from the curate filter 81 can be reduced. That is, the ECU 20 satisfies the condensate generation condition on condition that the temperature of the internal combustion engine 1 (cooling water temperature or oil temperature) is lower than the temperature after the warm-up is completed and the exhaust gas temperature is lower than the vaporization temperature. What is necessary is just to determine with it.

  Hereinafter, the execution procedure of the acidification suppression process in a present Example is demonstrated along FIG. FIG. 3 is a flowchart showing an acidification suppression processing routine. This routine is stored in advance in the ROM of the ECU 20 and is executed by the ECU 20 when the internal combustion engine 1 is started.

  In S101, the ECU 20 reads the output signal (cooling water temperature) thw of the water temperature sensor 12 and the output signal (exhaust temperature) Tex of the exhaust temperature sensor 82.

  In S102, the ECU 20 determines whether or not the cooling water temperature thw is lower than the cooling water temperature thwh after completion of warm-up, and the exhaust temperature Tex is lower than the exhaust temperature (vaporization temperature) Texh at which the condensed water evaporates. Determine. If an affirmative determination is made in S102, the condensed water generation condition is established. Therefore, the ECU 20 executes an acidification suppression process in S103.

  In S103, the ECU 20 increases the opening of the EGR valve 101. For example, the ECU 20 increases the opening degree of the EGR valve 101 as compared with a case where the operation state determined from the accelerator opening degree and the engine speed is equivalent and the condensed water generation condition is not satisfied. At that time, the ECU 20 calculates the amount of condensed water generated using the fuel injection amount, the intake air amount, the exhaust gas temperature, and the like as parameters, and the EGR valve 101 when the calculated amount of condensed water is large compared to when it is small. The opening degree may be set large. Note that the amount of condensed water generated may vary depending on the amount of alcohol component (for example, ethanol) contained in the fuel. Therefore, the ECU 20 may correct the amount of condensed water generated according to the concentration of the alcohol component contained in the fuel. For example, the amount of condensed water generated is higher when the concentration of the alcohol component is high than when the concentration is low. Therefore, the ECU 20 may perform correction so that the amount of condensed water generated is larger when the concentration of the alcohol component is high than when the concentration is low.

When the opening degree of the EGR valve 101 is increased by the various methods described above, the amount of EGR gas introduced into the cylinder 2 of the internal combustion engine 1 increases, so that the combustion speed of the air-fuel mixture becomes slow and the air-fuel mixture burns. The temperature goes down. As a result, the amount of NO _X contained in the exhaust is reduced. When the amount of NO _X contained in the exhaust gas decreases, the decrease in the hydrogen ion exponent (pH) of the condensed water is suppressed, and the increase in the PM amount discharged from the particulate filter 81 is suppressed. After executing the process of S103, the ECU 20 returns to S101.

  When a negative determination is made in S102, the ECU 20 proceeds to S104, and sets the opening of the EGR valve 101 to a normal opening (an opening when the condensed water generation condition is not satisfied).

  Thus, when the ECU 20 executes the routine of FIG. 3, the suppression means according to the present invention is realized. As a result, a decrease in the collection capacity of the particulate filter 81 due to the influence of condensed water is suppressed.

In the present embodiment, as an example of the acidification suppression process, a process of reducing the amount of NO _{X in} the exhaust gas is taken as an example, but a process of supplying a neutralizing agent into the exhaust gas upstream of the particulate filter may be used. Alternatively, a process of electrolyzing condensed water may be used. As the neutralizing agent, an aqueous solution derived from ammonia (for example, an aqueous solution of urea or ammonium carbamate) can be used. When the neutralizing agent is added or the condensed water is electrolyzed, the hydrogen ion exponent (pH) of the condensed water becomes high (the acidity becomes low). Therefore, when the particulate filter gets wet, the particulate filter The amount of PM desorbed from can be suppressed. Further, when an oxidation catalyst is disposed in the exhaust passage 80 upstream of the particulate filter 81 or when the oxidation catalyst is carried on the particulate filter 81, the internal combustion engine 1 is made rich immediately before the operation of the internal combustion engine 1 is stopped. Do mixing be operated in air, residence or adsorbed ammonia (NH ₃₎ on the oxide catalyst, the ammonia (NH ₃₎ may be serve as a neutralizing agent in the next startup.

  By the way, when the hydrogen ion exponent (pH) of the condensed water is smaller than “5”, PM is easily desorbed from the particulate filter 81. Therefore, when the hydrogen ion exponent (pH) is smaller than “5”, the amount of EGR gas is reduced. Acidification suppression treatment such as increase, addition of a neutralizing agent, or electrolysis of condensed water may be performed. At that time, as the hydrogen ion exponent (pH) of the condensed water is smaller, the amount of EGR gas may be increased or the amount of neutralizing agent added may be increased. The hydrogen ion index (pH) of the condensed water may be measured by placing a measuring device in the exhaust passage 80 or may be calculated from the operation history of the internal combustion engine 1.

<Example 2>
Next, a second embodiment of the present invention will be described with reference to FIGS. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.

  The difference between the first embodiment described above and the present embodiment is that an adsorbent that adsorbs moisture in the exhaust gas is disposed upstream of the particulate filter 81. FIG. 4 is a diagram showing a schematic configuration of an internal combustion engine to which the present invention is applied and its intake / exhaust system. In FIG. 4, an adsorbent 810 is disposed on the upstream side of the particulate filter 81. The adsorbent 810 is made of a substance that generates reaction heat (adsorption heat) when moisture in exhaust gas is adsorbed, such as zeolite. Further, the adsorbent 810 is disposed in the same casing as the particulate filter 81, and the downstream end of the adsorbent 810 is disposed in contact with the upstream end of the particulate filter 81. At that time, the adsorbent 810 and the particulate filter 81 may be integrally formed.

  When the adsorbent 810 is disposed on the upstream side of the particulate filter 81, condensed water generated in the exhaust passage 80 upstream from the particulate filter 81 is generated in the adsorbent 810 when the internal combustion engine 1 is in a cold state. Since it is adsorbed, the particulate filter 81 is not covered with condensed water. As a result, it is possible to suppress an increase in the amount of PM discharged due to the wetness of the particulate filter 81.

Further, the adsorbent 810 generates heat of adsorption when moisture in the exhaust is adsorbed. The heat of adsorption is transmitted from the adsorbent 810 to the particulate filter 81. As a result, the particulate filter 81 is heated by receiving the heat of adsorption. At this time, if condensed water exists in the particulate filter 81, the condensed water is vaporized by the temperature rise of the particulate filter 81. Therefore, even when condensed water is generated in the particulate filter 81 while the operation of the internal combustion engine 1 is stopped, the amount of water covered by the particulate filter 81 can be suppressed to a low level.

  By the way, since the adsorption capacity of the adsorbent 810 is limited, when the amount of moisture adsorbed by the adsorbent 810 is saturated, moisture that cannot be adsorbed by the adsorbent 810 flows into the particulate filter 81. At this time, if the acidity of the water is high, the amount of PM discharged from the particulate filter 81 may increase.

  Therefore, in the present embodiment, the ECU 20 is configured to perform the acidification suppression process when the moisture adsorption amount of the adsorbent 810 is saturated. Hereinafter, the execution procedure of the acidification suppression process in a present Example is demonstrated along FIG. FIG. 5 is a flowchart showing an acidification suppression processing routine in the present embodiment. The acidification suppression processing routine of FIG. 5 is a routine that is executed when the internal combustion engine 1 is started. In FIG. 5, the same reference numerals are assigned to the same processes as those in the acidification suppression process routine of the first embodiment described above.

In the acidification suppression processing routine of FIG. 5, the ECU 20 first calculates the amount of condensed water generation (water generation amount) Wl in S201. For example, the ECU ₂₀ calculates the amount of H ₂ O contained in the exhaust gas from the fuel injection amount and the intake air amount. Subsequently, the ECU ₂₀ calculates the amount (moisture generation amount) Wl of liquid condensed water in H ₂ O contained in the exhaust gas using the exhaust gas temperature Tex as a parameter.

  In S202, the ECU 20 calculates the amount of water (adsorbable amount) Wc that the adsorbent 810 can adsorb. The adsorbable amount Wc is an amount obtained by subtracting the amount of moisture already adsorbed by the adsorbent 810 from the adsorption capacity of the adsorbent 810.

The adsorption capacity of the adsorbent 810 can be experimentally obtained in advance. However, the adsorption capacity of the adsorbent 810 is the pressure acting on the adsorbent 810 (exhaust pressure), the humidity of the atmosphere to which the adsorbent 810 is exposed (moisture concentration in the exhaust), or the adsorbent 810 is exposed. Varies depending on the ambient temperature (exhaust temperature). For example, as shown in FIG. 6, the adsorption capacity of the adsorbent 810 is larger when the pressure acting on the adsorbent 810 is high than when the pressure is low. Further, as shown in FIG. 7, the adsorption capacity of the adsorbent 810 is larger when the humidity of the atmosphere to which the adsorbent 810 is exposed is higher than when the humidity is low. Furthermore, as shown in FIG. 8, the adsorption capacity of the adsorbent 810 is smaller when the temperature of the atmosphere to which the adsorbent 810 is exposed is higher than when the temperature is low. Therefore, the ECU ₂₀ may obtain the adsorption capacity of the adsorbent 810 using the exhaust temperature Tex, the exhaust pressure, the amount of H ₂ 0 contained in the exhaust, and the like as parameters. On the other hand, the amount of water already adsorbed by the adsorbent 810 is a value obtained by integrating the water generation amount Wl.

  Here, returning to FIG. 5, in S203, the ECU 20 determines whether or not the water generation amount Wl calculated in S201 is larger than the adsorbable amount Wc calculated in S202. When the moisture generation amount Wl is larger than the adsorbable amount Wc, moisture that cannot be adsorbed by the adsorbent 810 flows into the particulate filter 81. Therefore, if an affirmative determination is made in S203 (Wl> Wc), the ECU 20 proceeds to S103 and executes an acidification suppression process (a process for increasing the opening degree of the EGR valve 101). When the acidification suppression process is executed, an increase in the acidity of water that is adsorbed by the adsorbent 810 and is not clean (a decrease in the hydrogen ion exponent (pH)) is suppressed. As a result, an increase in the amount of PM discharged from the particulate filter 81 is suppressed. The ECU 20 returns to S201 after completing the process of S103.

  On the other hand, when the water generation amount Wl is equal to or less than the adsorbable amount Wc, the wetness of the particulate filter 81 is suppressed. Therefore, if a negative determination is made in S203 (Wl ≦ Wc), the ECU 20 proceeds to S104 and sets the opening of the EGR valve 101 to a normal opening. Subsequently, the ECU 20 proceeds to S204, and determines whether or not the water generation amount Wl calculated in S201 is smaller than the allowable amount a. Here, the allowable amount a is an amount in which the amount of PM discharged from the particulate filter 81 hardly increases even if a smaller amount of moisture than the allowable amount a flows into the particulate filter 81, and is experimentally determined in advance. This is the amount required. If an affirmative determination is made in S204 (Wl <a), the ECU 20 ends the execution of this routine. If a negative determination is made in S204 (Wl ≧ a), the ECU 20 returns to S201.

  According to the embodiment described above, it is possible to more reliably prevent the condensed water having high acidity from flowing into the particulate filter 81. As a result, it is possible to more reliably suppress an increase in the PM emission amount due to the particulate filter 81 getting wet.

  It is preferable that the period from when the internal combustion engine 1 is started until the moisture adsorption amount of the adsorbent 810 is saturated (hereinafter referred to as “moisture adsorption period”) is as long as possible. If the moisture adsorption period is long, the atmospheric temperature in the exhaust passage 80 and the particulate filter 81 is likely to rise above the temperature at which moisture can be vaporized before the moisture adsorption amount of the adsorbent 810 is saturated. As a result, the liquid phase moisture (condensed water) is prevented from flowing into the particulate filter 81 after the moisture adsorption amount of the adsorbent 810 is saturated. Therefore, the temperature of the adsorbent 810 may be raised before the operation of the internal combustion engine 1 is stopped to vaporize the moisture adsorbed on the adsorbent 810.

  As a method of raising the temperature of the adsorbent 810, the temperature of the adsorbent 810 is indirectly increased by raising the exhaust temperature, or the temperature of the adsorbent 810 is directly increased using a heater such as a heater. The method can be used. As a method for raising the exhaust gas temperature, a method for retarding the ignition timing can be used.

  Further, in the present embodiment, the example in which the acidification suppression process is performed when the moisture adsorption amount of the adsorbent 810 is saturated is described. However, before the moisture adsorption amount of the adsorbent 810 is saturated, the generation of condensed water is performed. You may make it implement an acidification suppression process, when conditions are satisfied.

  In the first and second embodiments, the method of increasing the opening of the EGR valve 101 is used as a method of increasing the amount of EGR gas introduced into the cylinder 2, but the opening / closing timing of at least one of the intake valve and the exhaust valve is used. It is also possible to use a method of increasing the amount of burnt gas (internal EGR gas) remaining in the cylinder 2 by adjusting.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder 5 Spark plug 6 Fuel injection valve 7 Intake port 8 Exhaust port 9 Intake valve 10 Exhaust valve 12 Water temperature sensor 20 ECU
21 Crank position sensor 22 Accelerator position sensor 70 Intake passage 71 Throttle valve 72 Air flow meter 80 Exhaust passage 81 Particulate filter 82 Exhaust temperature sensor 100 EGR passage 101 EGR valve 810 Adsorbent

Claims (7)

In an exhaust gas purification system for an internal combustion engine in which a particulate filter that collects particulate matter in exhaust gas is disposed in an exhaust passage,
Suppression means for performing an acidification suppression process for suppressing a decrease in the hydrogen ion index of the condensed water when a condensed water generation condition is established, which is a condition in which condensed water can be generated in the exhaust passage upstream of the particulate filter. An exhaust gas purification system for an internal combustion engine.   2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the acidification suppression process is a process for reducing the amount of nitrogen oxides contained in the exhaust gas of the internal combustion engine. According to claim 1, before Symbol acidification suppression processing, an exhaust gas purification system for an internal combustion engine is a process for supplying a neutralizer in an upstream of the exhaust gas from the particulate filter.   The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 3, further comprising an adsorbent that is disposed upstream of the particulate filter and adsorbs moisture.   5. The exhaust gas purification system for an internal combustion engine according to claim 4, wherein the suppression means executes the acidification suppression process when a condensed water generation condition is satisfied and a moisture adsorption amount of the adsorbent is saturated. .   6. The exhaust gas purification system for an internal combustion engine according to claim 5, further comprising a temperature raising unit that executes a process of raising the temperature of the adsorbent before the operation of the internal combustion engine is stopped.   7. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the condensed water generation condition is established when the exhaust gas temperature is lower than a temperature at which the condensed water can be vaporized.

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