WO2013005336A1 - Exhaust purification apparatus for internal combustion engine - Google Patents

Abstract

Provided is an exhaust purification apparatus for an internal combustion engine with a DPF disposed in the exhaust system of the internal combustion engine, such that accumulation of ash in the DPF can be suppressed, increases in pressure loss and PM regeneration temperature as well as a decrease in fuel efficiency can be suppressed over a long period, and the suppression of accumulation of ash can be efficiently performed. A surface of the DPF is coated with a solid acid with an acid strength greater than the acid strength of SO₃ and smaller than the acid strength of SO₄. The exhaust purification apparatus is provided with: a PM regeneration operation control; an ash regeneration operation control; and a learning control for determining the interval at which the ash regeneration operation is performed on the basis of a change in back pressure of the DPF before and after the PM regeneration operation is performed a plurality of times.

Description

Exhaust gas purification device for internal combustion engine

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

In order to reduce the number of particles of particulate matter (hereinafter referred to as “PM”) in the exhaust gas of the internal combustion engine, a diesel particulate filter (hereinafter referred to as “DPF”) is installed in the exhaust gas passage of the internal combustion engine, Generally, PM in exhaust gas is collected and removed.

In this case, since the PM collected in the DPF gradually accumulates, regeneration (hereinafter referred to as “PM regeneration”) is performed periodically or by detecting a decrease in the performance of the DPF and burning and removing the PM collected in the DPF. ”).

PM regeneration operation is usually performed by heating the DPF while supplying a reducing agent such as hydrocarbon (HC) to the DPF.

Various improvements have been proposed to improve the performance and reduce the cost of the PM regeneration operation that collects PM in the exhaust gas using the DPF and burns and removes the PM collected in the DPF. Has been.

However, in the conventional DPF, if the use of the DPF is continued, even if the PM regeneration operation is performed, the pressure loss of the DPF gradually increases, and if the PM regeneration temperature is not gradually increased, sufficient regeneration is achieved. There is a problem that it will not be performed, and fuel consumption deteriorates. This problem is caused by the accumulation of ash inside the DPF.

Ash is generated when the engine oil mixed in the cylinder of the engine burns, and the generated ash particles are covered with PM in the DPF. The ash particles covered with PM are exposed to high temperature conditions during the PM regeneration operation in the DPF, and the PM covering the ash particles is burned and removed. Ash deposition occurs because the ash particles are agglomerated and increased in size by further applying heat to the ash particles from which the PM has been burned and removed.

However, there is no effective solution to the accumulation of ash so far, and in order to minimize the influence of the accumulation of ash on the DPF, for example, a large-capacity DPF is installed in advance. Measures were taken.

That is, the improvement to the conventional DPF and the improvement to the regeneration operation of the DPF are intended to improve the collection efficiency of the DPF and improve the performance of the PM regeneration operation, and not to the accumulation of ash. As an object for improving the performance of the PM regeneration operation, for example, there is an invention disclosed in Patent Document 1, and Patent Document 1 shows a configuration of a DPF capable of burning PM at a relatively low temperature. Yes.

The structure of the DPF disclosed in Patent Document 1 is characterized in that, in the DPF and the exhaust gas purification method using the DPF, a catalyst made of a solid superacid having an active metal supported on the DPF is held on the filter surface. is there.

That is, the invention of Patent Document 1 reduces the combustion temperature of PM with a solid super strong acid carrying an active metal, and regenerates DPF at a lower temperature than before, preferably continuously, and CO, HC, NO, NO ₂ can be removed at the same time.

Therefore, the invention of Patent Document 1 is intended to improve the performance of the PM regeneration operation, and does not correspond to the accumulation of ash. If the use of the DPF is continued, the PM regeneration operation is performed. However, this does not solve the problem that the pressure loss of the DPF gradually increases, and unless the PM regeneration temperature is gradually increased, sufficient regeneration cannot be performed and the fuel consumption deteriorates.

Further, as a disclosure of a catalyst structure similar to the invention of Patent Document 1, there is an invention of Patent Document 2, which is selected from platinum, palladium and rhodium as a catalyst for a diesel engine exhaust gas purification device. By using a catalyst having at least one kind of noble metal and a solid super strong acid, it is possible to purify SOF (Soluable Organic Fraction), unburned hydrocarbons, etc. contained in particulate matter in diesel engine exhaust gas from a low temperature range. Further, it is described that the effect of suppressing oxidation of sulfur dioxide is exhibited even in a high temperature range, and the invention of Patent Document 2 aims at an effect similar to the invention of Patent Document 1 and does not relate to DPF. Therefore, it does not correspond to the accumulation of ash on the DPF. If the use of the DPF is continued, the pressure loss of the DPF gradually increases and the PM regeneration temperature gradually increases even if the PM regeneration operation is performed. If this is not done, it will not solve the problem that sufficient regeneration will not be performed and fuel consumption will deteriorate.

JP 2006-289175 A Japanese Patent Laid-Open No. 10-033985

The present invention suppresses ash accumulation on the DPF, and can suppress an increase in pressure loss, an increase in PM regeneration temperature, and a decrease in fuel consumption over a long period of time. An object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can be performed.

That is, the present invention provides a configuration in which the ash deposited on the DPF is discharged with a reduced particle size and the DPF is regenerated (hereinafter referred to as “ash regeneration”). With this configuration, an increase in pressure loss and PM regeneration over a long period of time are provided. It is an object of the present invention to provide an epoch-making DPF capable of suppressing an increase in temperature and a decrease in fuel consumption and further achieving an advantageous effect that an ash regeneration operation can be efficiently performed.

According to the present invention, the accumulated ash can be discharged with a reduced particle size. As a further effect, a DPF that is smaller than the conventional DPF can be used from the beginning of the installation of the DPF. Not only cost reduction, but also energy cost of PM regeneration operation can be reduced. In addition, the fact that a small DPF can be used means that the space for mounting the DPF on the vehicle can be reduced, and the weight of the vehicle on which the DPF is mounted can be reduced.

The inventor of the present application studied the problem of ash accumulation inside the DPF, analyzed the cause of ash accumulation, and the main components of ash were calcium (Ca) contained in engine oil and SOx in exhaust gas. It was found that ash is ion-bonded, CaSO ₄ is the main component, and Ca salt has a high melting point, so that in the exhaust gas, ash flows into the DPF as a solid and aggregates to increase the particle size.

Furthermore, the inventors of the present application have confirmed by experiments that the size of ash is on the order of submicrons, and that the ash slips through the DPF when the ash size is reduced to the order of nanomicrons.

Furthermore, the inventors of the present application, a CaSO ₄ that large grain size to the size of submicron, when placed in a reducing atmosphere, it becomes SO ₃ SO ₄ of CaSO ₄ is reduced, the bond between Ca weakened, At this time, if an acid stronger than SO ₃ is present on the surface of the DPF, the bond between Ca and SO _{3 in} the CaSO ₃ is cleaved, and the Ca ions are stronger than the SO ₃ on the surface of the DPF. It was confirmed by experiments that the atoms were dispersed and bonded in an atomic form.

Furthermore, the inventors of the present application, Ca ions associated with stronger acid than SO ₃ on the surface of the DPF is different from the stronger acid than SO ₃ on the surface of the DPF, if a stronger acid is present in the atmosphere It was confirmed by an experiment that it binds to a stronger acid in the atmosphere, is released from the DPF, and passes through the DPF to be discharged.

To summarize the above, if the acid strength of this acid is stronger than SO ₃ on the surface of the DPF and the acid strength of this acid is stronger than SO ₃ and weaker than SO ₄ , the particle size will be submicron. CaSO ₄ deposited in the DPF turned into, in a reducing atmosphere, becomes CaSO ₃ SO ₄ is reduced in CaSO _4, Ca ions CaSO ₃ is bonded with the acid on the surface of the DPF, on the surface of the DPF Disperse in atomic form. Next, if SO ₄ is present in the atmosphere, the Ca on the surface of the DPF combines with the SO _{4 in} the atmosphere and becomes sub-nanometer-sized CaSO ₄ and is released from the DPF.

When the exhaust gas atmosphere is a stoichiometric or rich atmosphere, it is the above-described reducing atmosphere, and when it is a lean atmosphere, the lean atmosphere contains SO ₄ . Therefore, if control for making the atmosphere stoichiometric or rich and control for making the lean atmosphere next are performed on the above-mentioned DPF, ash Ca ions deposited on the DPF in the stoichiometric or rich atmosphere are converted to DPF. Then, in a lean atmosphere, Ca on the surface of the DPF is combined with SO ₄ in the lean atmosphere and released from the DPF, and the fine particle size is reduced to a sub-nanometer size. CaSO ₄ is converted to pass through the DPF and discharged.

That is, in the above process, the first CaSO ₄ having a large particle size of submicron and deposited on the DPF is finally released again from the DPF as CaSO _4. No. ₄ is reduced in size to a sub-nanometer size and passes through the DPF and is discharged.

By the way, when performing the above ash reproduction | regeneration operation | movement, the ash is normally in the state buried in PM deposited in DPF. Therefore, even trying to ash reproduced in this state, in order to CaSO ₄ deposited in the DPF with large grain size to the size of the sub-micron can not be in contact with a reducing atmosphere, SO ₄ of CaSO ₄ is reduced Not. Alternatively, the ash reduced to CaSO ₃ cannot contact the solid acid on the surface of the DPF. Therefore, in order to effectively decompose the ash, it is preferable to perform the ash regeneration operation after burning and removing PM by the PM regeneration operation.

The ash regeneration operation and the PM regeneration operation are performed in accordance with the ash accumulation state and the PM accumulation state, respectively. Usually, the frequency of the ash regeneration operation may be less than the frequency of the PM regeneration operation. In addition, since the ash regeneration operation and the PM regeneration operation can be performed at substantially the same temperature, it is efficient that the ash regeneration operation is performed following the PM regeneration operation using the temperature increase of the PM regeneration operation. Is.

Therefore, there is a problem that it is effective to perform the ash regeneration operation subsequent to the PM regeneration operation when the PM regeneration operation is performed.

According to the present invention, in order to solve this problem, the control system of the ash regeneration operation learns the relationship between the implementation time of the ash regeneration operation and the implementation time of the PM regeneration operation during vehicle operation, and the optimum ash regeneration operation is performed. The learning control is provided for determining the interval.

According to the first aspect of the present invention, there is provided an exhaust purification device for an internal combustion engine in which a DPF is disposed in an exhaust system of the internal combustion engine, wherein the DPF is a DPF whose surface is coated with a solid acid, Control of the PM regeneration operation in which the acid strength is larger than the acid strength of SO ₃ and smaller than the acid strength of SO ₄ , and the PM accumulated in the DPF is burned and removed by raising the temperature of the DPF, and in the DPF The ash regeneration operation is controlled by reducing the particle size of the deposited ash and allowing the DPF to pass through and removing, and the detection means for detecting the back pressure of the DPF. The control of the ash regeneration operation increases the temperature of the DPF. Control for controlling the air-fuel ratio of the atmosphere in the DPF, and learning control for determining an execution interval of the ash regeneration operation based on a change in the back pressure of the DPF before and after the PM regeneration operation is performed a plurality of times. Wherein the exhaust gas purification apparatus is provided for an internal combustion engine.

That is, in the invention of claim 1, the DPF is constituted by applying a solid acid having an acid strength stronger than SO _{3 and} weaker than SO ₄ on the surface of the DPF. A PM regeneration operation and an ash regeneration operation are performed on the DPF configured in this manner in accordance with the PM accumulation state and the ash accumulation state. The timing of the ash regeneration operation and the implementation of the PM regeneration operation are performed. The control system of the ash regeneration operation learns the relationship with the time during the vehicle operation, and determines the optimum ash regeneration operation interval.

Therefore, the CaSO ₄ having a large particle size that was buried in the PM is exposed to the reducing atmosphere by the PM regeneration operation, and the ash that is reduced to CaSO ₃ is converted into the DPF. It comes into contact with the solid acid on the surface, and the ash regeneration operation proceeds effectively, and the ash regeneration operation proceeds at an optimum ash regeneration operation interval. As a result, the ash is completely removed, an increase in pressure loss, an increase in the PM regeneration temperature, and a decrease in fuel consumption can be suppressed over a long period of time, and further, ash accumulation can be efficiently suppressed. An exhaust purification device for an internal combustion engine is provided.

According to the first aspect of the present invention, an ash regeneration configuration is provided, and the ash is completely removed in the ash regeneration operation, and an increase in pressure loss, an increase in PM regeneration temperature, and a decrease in fuel consumption are suppressed over a long period of time. In addition, there is an effect of providing an exhaust emission control device for an internal combustion engine that can efficiently suppress ash accumulation.

FIG. 1 is a flowchart illustrating a schematic configuration of an embodiment of control when the present invention is applied to an exhaust gas purification apparatus for an internal combustion engine.
2A and 2B are diagrams for explaining the control of the present invention. FIG. 2A is a diagram for explaining a case where the ash regeneration operation is not performed, and FIG. 2B is a diagram for explaining a case where the ash regeneration operation is performed.
FIG. 3 is a diagram for explaining the principle of control of the present invention.
FIG. 4 is a diagram for explaining the principle of control of the present invention.
FIG. 5 is a diagram for explaining the control of the present invention.
FIG. 6 is a diagram illustrating a schematic configuration of an embodiment of the apparatus arrangement when the present invention is applied to an exhaust gas purification apparatus for an internal combustion engine.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the plurality of accompanying drawings, the same or corresponding members are denoted by the same reference numerals.

FIG. 6 is a diagram showing a basic configuration of the present invention. A solid acid corresponding to an acid strength of SO ₃ or more and SO ₄ or less is formed on the surface of DPF 2, specifically, on the surface of the DPF substrate of DPF 2. Apply. The exhaust gas from the internal combustion engine is guided to the DPF 2, and the PM in the exhaust gas is collected and removed by the DPF 2, and the exhaust gas from which the PM has been removed is discharged. Since the PM collected in the DPF gradually accumulates, PM regeneration operation is performed periodically or by detecting a decrease in the performance of the DPF and burning and removing the PM collected in the DPF.

However, if the PM regeneration operation is repeatedly performed, the ash 3 accumulates in the DPF, and even if the PM regeneration operation is performed, the pressure loss of the DPF gradually increases, and it is sufficient if the PM regeneration temperature is not increased gradually. There is a problem that proper regeneration is not performed, and fuel consumption deteriorates.

In the present invention, the ash 3 accumulated in the DPF is reduced in particle size by the ash regeneration operation, so that the reduced particle size 4 passes through the filter gap of the DPF and is discharged together with the exhaust gas, which causes a problem of ash accumulation. Further, learning control is performed in which the control system for the ash regeneration operation learns the relationship between the execution timing of the ash regeneration operation and the execution timing of the PM regeneration operation and determines the optimum ash regeneration operation interval during vehicle operation. As a result, the ash regeneration operation is performed efficiently.

That is, according to the present invention, the PM regeneration operation and the ash regeneration operation are performed on the DPF configured as shown in FIG. 6 according to the PM accumulation state and the ash accumulation state, and the ash regeneration operation is further performed. The control system of the ash regeneration operation learns the relationship between the implementation time and the PM regeneration operation time during vehicle operation, determines the optimum ash regeneration operation interval, and determines the optimum ash based on the determined interval. Regeneration operation is performed.

FIG. 1 is a flowchart of learning control for determining an optimum ash regeneration operation interval, and FIGS. 2 to 4 are diagrams for explaining the principle of determining the optimum ash regeneration operation interval of FIG. In FIGS. 1 to 4 and the description thereof, “increase in back pressure” is “increase in pressure drop” from the initial value of the outlet pressure of the DPF, but in order to simplify the explanation, the following explanation will be given. So, it is expressed as “an increase in back pressure”. Therefore, the detection value P _O of the back pressure of the ash regeneration operation before the DPF in the description of FIG. 1 is a pressure lower than the detection value P of the back pressure of the ash regeneration operation at the end of the DPF, Pd described below = P- _PO is a positive numerical value.

First, as shown in FIG. 2A, when the PM regeneration operation is repeated in the DPF, the back pressure of the DPF after the PM regeneration operation ends gradually increases. Each of the serrated peaks in FIG. 2A gradually increases the back pressure of the DPF due to the accumulation of PM, and when the PM regeneration operation is performed on this, the back pressure of the DPF recovers, that is, rises. However, if the PM regeneration operation is repeated, the back pressure of the DPF after the PM regeneration operation is increased like _{ΔP OT} and completely Will not recover. Broken line in FIG. 2 (a), is a back pressure rise based on the burning remaining PM, based on the ash is gradually deposited, back pressure, △ P _OA only increases, PM regeneration operation after completion of the The back pressure of the DPF increases as indicated by a solid line indicated by ΔP _OT .

Therefore, the ash regeneration operation is intended to recover the back pressure increase indicated by _ΔPOA , and after the ash regeneration operation is performed and the back pressure is recovered, as shown in FIG. The PM regeneration operation is repeated. The broken line on the lower side of FIG. 2B is a back pressure increase based on the PM remaining unburned, and even if the ash regeneration operation is performed and the back pressure recovers, the back pressure increase based on the PM unburned remains. However, the increase in the back pressure based on the unburned PM remains large in the initial stage of using the DPF, and then converges to a substantially constant value.

Based on the above knowledge, the present invention performs learning for determining the interval of the ash regeneration operation in order to optimally recover the back pressure by the ash regeneration operation. That is, the back pressure increase indicated by _ΔPOA in FIG. 2A is recovered at an optimum interval.

This principle will be described with reference to FIGS. 3 and 4. For example, as shown in FIG. 3, after performing the PM regeneration operation once, performed twice, performed three times, performed four times, As described above, the ash regeneration operation is performed by changing the interval. When the ash regeneration operation is performed in this manner, the back pressure recovery value by the ash regeneration operation after performing the PM regeneration operation twice is larger than the back pressure recovery value by the ash regeneration operation after performing the PM regeneration operation once. Although the change is such that the back pressure recovery value by the ash regeneration operation after performing the PM regeneration operation three times is further increased, the back pressure recovery value converges to a substantially constant value.

FIG. 4 is a graph schematically explaining the convergence of the back pressure recovery value. When control is performed to gradually extend the ash regeneration operation interval as shown in the uppermost graph of FIG. 4, FIG. As shown in the middle graph, the back pressure recovery value ΔP _OT eventually converges to a substantially constant value. Therefore, the optimum ash regeneration operation interval I _opt is determined from the middle graph of FIG. The lowermost graph in FIG. 4 shows an interval until control of each ash regeneration operation. The interval is ideally an accumulated distance through which the exhaust gas passes through the DPF, but in actual control, for example, the travel distance of the vehicle is substituted.

FIG. 1 is a flowchart showing learning control for determining the optimum ash regeneration operation interval. When the learning condition of the control system is satisfied, the control of FIG. 1 starts, and in step 100, the interval counter for ash regeneration operation control counts the interval from the previous ash regeneration operation to the current ash regeneration operation. Furthermore the process proceeds to step 200, ash regeneration operation before the back pressure, i.e., detects the back pressure P _O immediately after PM regeneration operation, in step 300, starts the ash regeneration operation.

When ash regeneration operation is completed, at step 400, detects the back pressure P of the ash regeneration operation at the end of the DPF, the routine proceeds to step 500 to calculate the pressure difference Pd = _{P-P O} P and _{P O.}

Next, in step 600, the difference between Pd by the previous ash regeneration operation and Pd by the current ash regeneration operation, that is, the increment of the differential pressure Pd is set to ΔPd, the interval by the previous ash regeneration operation, It is determined whether the difference between the intervals due to the ash regeneration operation, that is, the increment of the interval is ΔInt, and the ratio of ΔPd and ΔInt is equal to or less than a certain value K.

FIG. 5 is a diagram for explaining the increment ΔPd of the differential pressure Pd and the increment ΔInt of the interval. If the ratio of ΔPd and ΔInt does not become a certain value K or less in step 600 of FIG. 1, the process proceeds to step 800 and steps 100 to 600 are repeated.

In step 600, when the ratio of ΔPd to ΔInt becomes a constant value K or less, that is, as shown by Iopt in FIG. It is determined that the recovery has converged, the process proceeds to step 700, and the interval at this time is stored as the optimum interval value. That is, when there is an interval value learned last time, the interval value is updated and the learning control is terminated. Therefore, the ash regeneration operation after learning is performed at the updated interval.

As described above, in the control of the ash regeneration operation in which the learning control of the present invention is performed, the ash regeneration operation proceeds at an optimum ash regeneration operation interval. As a result, the ash is completely removed, an increase in pressure loss, an increase in the PM regeneration temperature, and a decrease in fuel consumption can be suppressed over a long period of time, and further, ash accumulation can be efficiently suppressed. An exhaust purification device for an internal combustion engine is provided.

Therefore, according to the present invention, it is possible to configure an exhaust gas purification apparatus for an internal combustion engine having a DPF whose performance does not deteriorate indefinitely, and the present invention can dramatically improve the performance of the DPF over a long period of time. There is an advantageous effect. Furthermore, as a further effect that accompanies this effect, a DPF smaller than the conventional one can be used from the beginning of the installation of the DPF, which not only reduces the manufacturing cost of the DPF but also reduces the energy cost of the PM regeneration operation. be able to. Furthermore, the fact that a small DPF can be used has the effect that the space for mounting the DPF on the vehicle can be reduced, and the weight of the vehicle on which the DPF is mounted can be reduced. It should be noted.

1 Internal combustion engine 2 DPF
3 Ash 4 Fine particle size

Claims (1)

1. An exhaust purification device for an internal combustion engine in which a DPF is disposed in an exhaust system of the internal combustion engine,
   The DPF is a DPF having a surface coated with a solid acid,
   The acid strength of the solid acid is greater than the acid strength of SO ₃ and less than the acid strength of SO ₄ ;
   Control of PM regeneration operation in which the temperature of the DPF is raised to burn and remove PM accumulated in the DPF;
   Control of the ash regeneration operation, which reduces the ash deposited in the DPF and passes the DPF to remove it;
   Detecting means for detecting the back pressure of the DPF,
   The control of the ash regeneration operation is
   Control for increasing the temperature of the DPF;
   Control of the air-fuel ratio of the atmosphere in the DPF;
   Learning control for determining an execution interval of the ash regeneration operation based on a change in the back pressure of the DPF before and after the PM regeneration operation is performed a plurality of times.
   An exhaust purification device for an internal combustion engine.

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