JP2008309043A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine inhibiting formation of aldehyde and improving cleaning performance of NO<SB>X</SB>by controlling the air fuel ratio in exhaust gas even when fuel containing alcohol components is used. <P>SOLUTION: The exhaust emission control device 30 is provided in an exhaust path 7 of the internal combustion engine 1, and is provided with an upstream side catalyst 11 purifying exhaust gas containing alcohol component and flowing in the exhaust path 7, a downstream side catalyst 12 provided at a downstream side of the upstream side catalyst 11 in an exhaust gas flow direction, an A/F sensor 15 detecting air fuel ratio of exhaust gas, a hydrogen concentration sensor 16 detecting hydrogen concentration of exhaust gas, and a NO<SB>X</SB>sensor 17 detecting nitrogen oxide concentration in exhaust gas. Air fuel ratio of the exhaust gas is controlled based on NO<SB>X</SB>emission quantity and hydrogen concentration, and quantity of hydrogen formation is controlled to keep NO<SB>X</SB>emission quantity not greater than a predetermined value. Consequently, aldehyde formed from alcohol is made react to acid and formation of aldehyde is inhibited. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine that can use a fuel that is a mixture of alcohol and gasoline.

The exhaust gas discharged from the internal combustion engine body contains harmful components such as hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO _x ), and these harmful components need to be removed. There is. For this reason, in a conventional internal combustion engine exhaust purification device, a three-way catalyst that generates hydrogen from hydrocarbons in exhaust gas in an exhaust system and a NO _x adsorption catalyst that adsorbs NO _x discharged during lean operation are provided. Is provided.

In general, when the internal combustion engine is operated at lean than the stoichiometric air-fuel ratio, since the purification of the NO _X discharged becomes difficult in the conventional three-way catalyst, NO _X adsorbing NO _X discharged during lean operation An adsorption catalyst is used. Examples of the NO _x adsorption catalyst include a NO _x storage reduction catalyst. The NO _X storage reduction catalyst is the air-fuel ratio is lean of the exhaust gas flowing into the NO _X occluding and reducing catalyst, when a high oxygen concentration in the exhaust gas is occluded NO _X in the exhaust gas. Further, when the air-fuel ratio of the exhaust gas is substantially stoichiometric or rich, and the oxygen concentration in the exhaust gas is low, the stored NO _x is desorbed. Therefore NO _X is approximately stoichiometric or rich air-fuel ratio of the exhaust gas when being desorbed, the exhaust gas is present HC and CO, desorbed NO _X is HC in the exhaust gas, CO is reduced and purified by the reducing agent and the like, it is removed NO _X in the exhaust gas.

Further, using the hydrogen produced by the three-way catalyst as a reducing agent, by controlling the amount of hydrogen produced from the nitrogen oxide amount discharged performs purification of the NO _X absorbed in the NO _X adsorbing catalyst, NO _X Was efficiently purified (Patent Document 1).

  Further, as fuel, for example, heavy oil has a shorter rich spike (RS) time, light oil has a longer rich spike time, and temperature control is performed when the temperature of the catalyst is raised depending on the fuel properties. I was doing. As a result, harmful exhaust components are efficiently purified by activating the catalyst early regardless of the fuel properties, keeping the air-fuel ratio optimal, and preventing the catalyst bed temperature from decreasing (Patent Document 2).

JP 2001-304031 A Japanese Patent Laid-Open No. 2005-23856

  In recent years, in addition to gasoline fuel, vehicles such as automobiles (FFV) equipped with a system that can simultaneously use alcohol as an alternative fuel have been put into practical use, and gasoline, alcohol, and mixed fuel of these Driving is possible.

  When, for example, alcohol fuel is used as the fuel in the FFV system, the alcohol component contained in the fuel is chemically changed to the following formulas (1) to (3). That is, when the alcohol is oxidized to an aldehyde, the following formula (1) is obtained. When the aldehyde is oxidized to an acid, the following formula (2) is obtained, and when the acid is finally decomposed into water and carbon dioxide. Becomes the following formula (3).

  However, since hydrogen is a strong reducing substance, if a large amount of hydrogen is present, this reaction remains as an aldehyde (oxidation reaction of the above formula (1)) or is reduced from an acid to an aldehyde, leaving a highly toxic aldehyde (above) There is a problem that the reduction reaction of formula (2).

In addition, there are water vapor and sulfuric acid mist as the cause of smog, but since sulfuric disulfide is desorbed by hydrogen as shown in the following formula, there is a problem that the presence of hydrogen can also cause photochemical smog There is.
SO ₂ + H ₂ O + 1 / 2O ₂ → H ₂ SO ₄ (4)

The present invention has been made in view of the above problems, and even when a fuel containing an alcohol component is used, by controlling the air-fuel ratio in the exhaust gas, the generation of aldehyde is suppressed, and NO _x is reduced. An object of the present invention is to provide an exhaust gas purification device for an internal combustion engine with improved purification performance.

  In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention includes an upstream catalyst that is provided in an exhaust path of an internal combustion engine that uses alcohol fuel as a fuel and purifies exhaust gas flowing through the exhaust path. An upstream catalyst device to be housed, and provided downstream of the upstream catalyst device in the flow direction of the exhaust gas, and stores nitrogen oxides when the air-fuel ratio of the exhaust gas is lean. At least one downstream catalyst device containing a downstream catalyst that desorbs nitrogen oxides stored when rich, and an air-fuel ratio of the exhaust gas provided upstream of the upstream catalyst device An air-fuel ratio detection means for detecting the exhaust gas, a hydrogen concentration detection means for detecting the hydrogen concentration of the exhaust gas, provided between the upstream catalyst device and the downstream catalyst device in the exhaust path, An exhaust gas purification device provided on the downstream side of the downstream side catalyst device and having a nitrogen oxide concentration detecting means for detecting the nitrogen oxide concentration of the exhaust gas, wherein the air-fuel ratio of the exhaust gas is higher than the stoichiometric air-fuel ratio. When it is lean, hydrogen is generated so that the air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio or rich, and the nitrogen oxide is reduced, and based on the detection result by the nitrogen oxide concentration detection means, The amount of hydrogen generation is controlled so that the concentration of nitrogen oxides is a predetermined value or less.

  In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, when the nitrogen oxide emission amount by the nitrogen oxide concentration detecting means is a predetermined value or more, hydrogen is generated and the nitrogen oxide is reduced. And

  In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, when hydrogen is generated, the catalyst temperature of the upstream catalyst is not more than a predetermined temperature at which a shift reaction from alcohol to acid occurs.

  In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the predetermined temperature is 600 ° C. or less.

  The exhaust gas purification apparatus for an internal combustion engine according to the present invention is characterized in that the generation of hydrogen is controlled when the nitrogen oxide emission amount by the nitrogen oxide concentration detection means is less than a predetermined value.

According to the present invention, even when a fuel containing an alcohol component is used, the air-fuel ratio in the exhaust gas is controlled, and the amount of hydrogen generated is controlled so that the concentration of nitrogen oxides becomes a predetermined value or less. In addition, the generation of aldehyde can be suppressed and the NO _x purification performance can be improved.

  Hereinafter, the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or those that are substantially the same.

[Embodiment]
FIG. 1 is a schematic configuration diagram of an exhaust purification apparatus according to the present embodiment.
As shown in FIG. 1, an exhaust gas purification apparatus 30 for an internal combustion engine according to the present embodiment is provided in an exhaust path 7 of an internal combustion engine 1 that uses alcohol fuel as fuel, and contains exhaust gas containing an alcohol component that flows through the exhaust path 7. An upstream side catalyst device 11 that accommodates an upstream side catalyst that purifies gas, and a downstream side of the upstream side catalyst device 11 in the flow direction of the exhaust gas, and the air-fuel ratio (A / F) of the exhaust gas is lean Of the downstream side catalyst device 12 for storing the downstream side catalyst for storing the nitrogen oxides at the time and desorbing the nitrogen oxides stored at the stoichiometric air-fuel ratio or rich, and the upstream side catalyst device 11 The exhaust gas is provided between an A / F sensor 15 that is provided upstream and detects an air-fuel ratio (A / F) of the exhaust gas, and the upstream catalyst device 11 and the downstream catalyst device 12. Hydrogen concentration A hydrogen concentration sensor 16 for detecting a provided on the downstream side of the downstream catalyst unit 12, and a NO _X sensor 17 for detecting the NOx concentration of the exhaust gas.

  The internal combustion engine 1 has a cylinder block 2, and the cylinder block 2 is provided with a piston 4 that can reciprocate inside the cylinder block 2. A combustion chamber 5 is formed above the piston 4. A cylinder head 3 is provided above the cylinder block 2. An intake pipe 6 and an exhaust pipe (exhaust path) 7 are connected to the cylinder head 3. An intake valve 8 is provided at a connection portion between the intake pipe 6 and the combustion chamber 5. An exhaust valve 9 is provided at a connection portion between the exhaust path 7 and the combustion chamber 5. The intake pipe 6 is provided with a fuel injection valve 10 that injects fuel into the intake air.

The exhaust path 7 is provided with an upstream catalyst device 11 that houses an upstream catalyst for purifying exhaust gas and a downstream catalyst device 12 that houses a downstream catalyst. The upstream catalyst in the upstream catalyst device 11 is a ternary that can simultaneously remove three substances of hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NO _x ) by an oxidation / reduction reaction. It is a catalyst. That is, harmful HC in the exhaust gas, CO and NO _X harmless H ₂ O, into CO _2, N ₂ reduced or oxidized.

Further, the downstream catalyst of the downstream catalytic converter 12, oxidation-reduction reaction HC air-fuel ratio of the exhaust gas (A / F) is contained in the exhaust gas when the stoichiometric air-fuel ratio of the (stoichiometric), CO, and NO _X Simultaneously purifies H ₂ O, CO ₂ and N ₂ , and temporarily stores NO _x contained in the exhaust gas when the air-fuel ratio (A / F) of the exhaust gas is lean. when the oxygen concentration is in the rich burn zone of reduced emits occluded NO _X, in which the reduction of NO _X by the fuel as the additive reducing agent. As the downstream catalyst 12, _{specifically,} NSR (NO X Storage Reduction) and DPNR (Diesel Particulate-NOx Reduction System ) is known. NSR is a NOx occlusion reduction type catalyst that stores NOx in the form of nitrate in the catalyst during operation in the lean operation mode and reduces the nitrate to N ₂ in a reducing atmosphere with a reduced oxygen concentration. DPNR is a system capable of purifying particulate matter (PM) and NOx continuously at the same time. For example, DPF (Diesel Particulate Filter), which is a PM collection device, stores NO _{X in a} reduced manner. A type catalyst is supported. In this embodiment, a NO _x storage reduction catalyst (NSR) is applied as the downstream catalyst in the downstream catalyst device 12.

Here, the downstream catalyst unit 12 of the upstream catalytic converter 11 is disposed in an exhaust gas flow direction downstream, to oxidize HC and NO _X in the upstream side catalyst of the upstream-side catalytic converter 11, the upstream catalyst in adsorbing NO _X which has not been purified by the downstream catalyst. Further, whether or not the upstream catalyst in the upstream catalyst device 11 and the downstream catalyst in the downstream catalyst device 12 are in an active state may be determined by detecting the respective catalyst bed temperatures. Further, it may be determined from the cooling water temperature of the internal combustion engine detected from a water temperature sensor (not shown).

Further, a NO _x sensor 17 is provided on the downstream side of the downstream side catalyst device 12 in the exhaust gas flow direction. The downstream catalyst in the downstream catalyst device 12 is an NO _x storage reduction catalyst (NSR). Therefore, there is a limit to _the amount of NO _X can be adsorbed and absorbed a certain amount, NO _X that has not been adsorbed in the exhaust gas is increased, the NO _X sensor 17, and flows out from the downstream-side catalyst unit 12 concentration of NO _X exhaust gas is detected.

  A hydrogen sensor 16 is provided between the upstream catalyst device 11 and the downstream catalyst device 12. The hydrogen sensor 16 detects the hydrogen concentration in the exhaust gas flowing out from the upstream side catalyst device 11.

  An A / F sensor 15 is provided upstream of the upstream catalyst device 11 in the exhaust gas flow direction. The A / F sensor 15 detects the air-fuel ratio (A / F) of the exhaust gas discharged from the engine 1.

Based on the value of the NO _x concentration of the exhaust gas flowing out from the downstream catalyst in the downstream side catalyst device 12 detected by the NO _x sensor 17 and the value of the hydrogen concentration of the exhaust gas detected by the hydrogen sensor 16, The catalyst bed temperature of the upstream catalyst in the upstream catalyst device 11 is adjusted. Thereby, the amount of hydrogen generated in the upstream catalyst is adjusted.

Further, in the upstream catalyst in the upstream catalyst device 11, hydrogen is generated by a partial oxidation reaction and a steam reforming reaction as in the following formulas (I) and (II). The partial oxidation reaction is a reaction in which a mixed gas of CO and H ₂ is produced when hydrocarbons and oxygen are reacted at a high temperature as shown in the following formula (I). For example, 2 moles of hydrogen are produced from 1 mole of methane. Is done. Further, in the steam reforming reaction, for example, 3 moles of hydrogen are generated from 1 mole of methane as shown in the following formula (II).
2CH ₄ + O ₂ → 2CO + 4H ₂ (I)
CH ₄ + H ₂ O → CO + 3H ₂ (II)

The exhaust gas air-fuel ratio (A / F) is temporarily made rich, the amount of hydrogen generated is feedback controlled, and the exhaust gas adjusted for hydrogen concentration is supplied to the upstream side catalyst device 11 and detected by the A / F sensor 15. The value of the air / fuel ratio (A / F) is controlled to be within a predetermined range.
Here, the predetermined range refers to an air-fuel ratio in which NO _x is desorbed and hydrogen is not generated.

That is, based on the detection result by the A / F sensor 15, when the air-fuel ratio (A / F) of the exhaust gas is leaner than the stoichiometric air-fuel ratio, the air-fuel ratio (A / F) of the exhaust gas is calculated from the stoichiometric air-fuel ratio. Hydrogen is generated as rich and nitrogen oxides are reduced. Further, based on the detection result by the NO _X sensor 17, controls the generation amount of hydrogen such that the concentration of nitrogen oxides is equal to or less than a predetermined value.

When the NO _X concentration detected by the NO _X sensor 17 is equal to or greater than a predetermined value and lean, the air-fuel ratio (A / F) of the exhaust gas is corrected to a rich value. As a result, the exhaust gas enriched in the air-fuel ratio flows into the upstream side catalyst device 11, and the HC in the exhaust gas is partially oxidized to generate hydrogen.

Further, based on the hydrogen concentration detected by the hydrogen sensor 16, for example, when the hydrogen concentration is equal to or higher than a predetermined value, NO _x can be desorbed. Similarly, the air-fuel ratio of the exhaust gas is a rich value as it is. Maintain with.

  If the catalyst bed temperature of the upstream catalyst in the upstream catalyst device 11 is a predetermined temperature (for example, 600 ° C.) or less, a shift reaction from alcohol to acid in the upstream catalyst in the upstream catalyst device 11 proceeds. As it can, keep it as it is.

  Further, when hydrogen is generated, the catalyst bed temperature needs to be lowered, so that the advance angle control is performed. On the other hand, when hydrogen is not generated, the catalyst bed temperature may be increased and the retard angle control may be performed.

  An oxygen sensor 18 is provided between the upstream catalyst device 11 and the downstream catalyst device 12. The oxygen sensor 18 detects the oxygen concentration in the exhaust gas flowing out from the upstream side catalyst device 11. When the oxygen concentration detected by the oxygen sensor 18 is low based on the detection result of the oxygen sensor 18, the air-fuel ratio (A / F) of the exhaust gas is substantially the stoichiometric air-fuel ratio or rich, so the downstream side catalyst device It is also possible to control the enrichment of the downstream catalyst in the cylinder 12 so that it becomes lean. Further, when the oxygen concentration detected by the oxygen sensor 18 is high, the air-fuel ratio (A / F) of the exhaust gas is lean, so that the enrichment of the downstream catalyst 12 is controlled, and the stoichiometric air-fuel ratio or rich It may be made to become.

In addition, a vehicle (not shown) on which the engine 1 is mounted is provided with a vehicle control unit 20 having an ECU (Electronic Control Unit) that controls each part of the vehicle. The A / F sensor 15, the hydrogen sensor 16, the oxygen sensor 18, and the NO _X sensor 17 are connected to the vehicle control unit 20, and each measurement result is input to the vehicle control unit 20. The fuel injection valve 10 and a flow rate control valve (not shown) are connected to the vehicle control unit 20, and their operations are controlled by the vehicle control unit 20.

Thereby, even when a fuel containing an alcohol component is used, the amount of hydrogen generated so that the NO _x concentration becomes a predetermined value or less based on the detection results of the A / F sensor 15, the hydrogen sensor 16, and the NOx sensor 17. By controlling the air-fuel ratio (A / F) in the exhaust gas, the reaction can be advanced to the acid all at once without leaving the aldehyde generated from the alcohol as it is. As a result, even when an alcohol-containing fuel is used, the generation of aldehyde can be significantly suppressed while controlling the NO _x emission amount.

  Here, a control method using the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment will be described.

FIGS. 2-1 to 2-3 are flowcharts showing the operation of the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment. FIG. 2-1 is a flowchart illustrating an example of the original control operation, FIG. 2-2 is a flowchart illustrating an example of the control operation at the time of Step S11, and FIG. 2-3 illustrates the operation at the time of Step S12. It is a flowchart which shows an example of control operation.
As shown in FIG. 2A, first, in step S11, the NO _X sensor 17 determines whether or not the NO _X emission amount in the exhaust gas is a predetermined value or more. Result of the determination in step S11, if NO _X emissions is determined to a predetermined value or more (step S11: Yes), the process proceeds to step S12.

  In step S12, the hydrogen sensor 16 determines whether or not the hydrogen concentration is equal to or higher than a predetermined value. As a result of the determination in step S12, when it is determined that the hydrogen concentration is equal to or higher than the predetermined value (Yes in step S12), the process proceeds to step S13.

  In step S13, the air-fuel ratio (A / F) of the exhaust gas is controlled and adjusted to an air-fuel ratio (A / F) within a predetermined range.

Here, control of the air-fuel ratio (A / F) will be described.
Adjustment of the air-fuel ratio (A / F) when the air-fuel ratio (A / F) detected by the A / F sensor 15 is rich and lean is determined with reference to a predetermined map.

3 and 4 show the relationship among the air-fuel ratio, nitrogen oxide emission amount, and hydrogen concentration when alcohol fuel is used.
FIGS. 3 and 4 are relationship diagrams showing the relationship among exhaust gas air-fuel ratio (A / F), nitrogen oxide concentration, and hydrogen concentration when E13 (fuel in which 13% ethanol is mixed in gasoline) is used. . FIG. 3 shows a case where the exhaust gas temperature is 600 ° C., and FIG. 4 shows a case where the exhaust gas temperature is 700 ° C.

  At 600 ° C. shown in FIG. 3, the air-fuel ratio (A / F) of the exhaust gas from which hydrogen is generated is, for example, from the rich side from around 14.5, and the air-fuel ratio (A / F) of the exhaust gas is, for example, 14 It was confirmed that no hydrogen was generated in the lean atmosphere on the lean side from around .5.

  At 700 ° C. shown in FIG. 4, the air-fuel ratio (A / F) of the exhaust gas from which hydrogen is generated is, for example, from the rich side from around 15.0, and the air-fuel ratio (A / F) of the exhaust gas is, for example, 15 It was confirmed that no hydrogen was generated in the lean atmosphere on the lean side from around 0.0.

Therefore, A / F sensor 11, the detection result of the hydrogen sensor 16 and the NO _X sensor 17, the air-fuel ratio of the predetermined fuel (A / F), based on a map showing the nitrogen oxide concentration and the hydrogen concentration of the relationship Then, it is determined whether or not the feedback control of hydrogen is performed, and the air-fuel ratio (A / F) of the exhaust gas is controlled.

The exhaust gas is controlled so as to become a stoichiometric air-fuel ratio or rich to generate hydrogen to reduce the nitrogen oxides, and based on the detection result by the NO _x sensor 17, the concentration of the nitrogen oxides is a predetermined value. The amount of hydrogen generated is controlled so as to be as follows.

  By controlling the amount of hydrogen generated, the reduction from acid to aldehyde can be suppressed, and the reaction from alcohol to acid can proceed at a stretch, so that the generation of aldehyde can be suppressed.

  Thereafter, in step S14 shown in FIG. 2A, it is determined whether or not the catalyst temperature is equal to or lower than a predetermined temperature (for example, 600 ° C.). This is because the catalyst temperature of the upstream catalyst needs to be not more than a predetermined temperature at which the shift reaction from alcohol to acid occurs, and this shift reaction occurs at, for example, 600 ° C. or less.

  As a result of the determination in step S14, when it is determined that the catalyst temperature rise is equal to or lower than a predetermined temperature (for example, 600 ° C.) (Yes in step S14), the control of the air-fuel ratio (A / F) of the exhaust gas is ended.

  If it is determined in step S14 that the catalyst bed temperature is equal to or higher than the predetermined temperature (No in step S14), the process proceeds to step S15. In step S15, the catalyst bed temperature of the upstream catalyst 11 is lowered to a predetermined temperature (for example, 600 ° C.) or less, and the control of the air-fuel ratio (A / F) of the exhaust gas is finished.

  Moreover, as a result of the determination in step S11, when it is determined that the NOx emission amount is equal to or less than the predetermined value (No in step S11), the process proceeds to step S21 shown in FIG.

  In step S21, it is determined in the hydrogen sensor 16 whether the hydrogen concentration is equal to or higher than a predetermined value. As a result of the determination in step S21, when it is determined that the hydrogen concentration is equal to or higher than the predetermined value (Yes in step S21), the process proceeds to step S22.

  In step S22, the catalyst bed temperature of the upstream catalyst in the upstream catalyst device 11 is raised to reduce the amount of hydrogen generated, and the process proceeds to step S23.

  In step S23, it is determined whether or not the catalyst bed temperature of the upstream catalyst in the upstream catalyst device 11 is equal to or lower than a predetermined temperature (for example, 600 ° C.). As a result of the determination in step S23, when it is determined that the catalyst bed temperature of the upstream catalyst in the upstream catalyst device 11 is equal to or lower than a predetermined temperature (for example, 600 ° C.) (Yes in step S23), the air-fuel ratio of the exhaust gas ( A / F) is terminated.

  If it is determined in step S21 that the hydrogen concentration is equal to or lower than the predetermined value (No in step S21), the process proceeds to step S24 to control the air-fuel ratio (A / F) of the exhaust gas, and in step S23. Migrate to

  In step S23, it is determined whether or not the catalyst bed temperature of the upstream catalyst in the upstream catalyst device 11 is equal to or lower than a predetermined temperature (for example, 600 ° C.) as described above, and as a result of the determination, the upstream catalyst device 11 is determined. If it is determined that the catalyst temperature rise of the upstream catalyst is equal to or lower than the predetermined temperature (Yes at step S23), the control of the air-fuel ratio (A / F) of the exhaust gas is terminated.

  If it is determined in step S23 that the catalyst temperature rise is equal to or higher than the predetermined temperature (No in step S23), the process proceeds to step S25, and the catalyst bed temperature of the upstream catalyst in the upstream catalyst device 11 is determined. Then, the control of the air-fuel ratio (A / F) of the exhaust gas is finished.

  If the hydrogen concentration is determined to be equal to or lower than the predetermined value as a result of the determination in step S12 in FIG. 2-1 (No in step S12), the process proceeds to step S31 shown in FIG. (A / F) is controlled and adjusted to a predetermined air-fuel ratio (A / F).

  Thereafter, in step S32, it is determined whether or not the catalyst temperature of the upstream catalyst in the upstream catalyst device 11 is equal to or lower than a predetermined temperature (for example, 600 ° C.). As a result of the determination in step S32, when it is determined that the catalyst bed temperature of the upstream catalyst in the upstream catalyst device 11 is equal to or lower than a predetermined temperature (for example, 600 ° C.) (Yes in step S32), the air-fuel ratio of the exhaust gas ( A / F) is terminated.

  On the other hand, as a result of the determination in step S32, when it is determined that the catalyst bed temperature of the upstream catalyst in the upstream catalyst device 11 is equal to or higher than the predetermined temperature (No in step S23), the process proceeds to step S33, and the catalyst bed temperature. Is lowered to a predetermined temperature (for example, 600 ° C.) or less, and the control of the air-fuel ratio (A / F) of the exhaust gas is finished.

  Further, in the present embodiment, the case where E13 (fuel in which 13% of ethanol is mixed in gasoline) is used as a fuel containing an alcohol component in the series of control methods has been described, but the present invention is limited to this. Instead, a fuel containing another alcohol component may be used.

With this series of control methods, even when a fuel containing an alcohol component is used, the amount of hydrogen generated is adjusted so that the NO _x concentration becomes a predetermined value or less, and the air-fuel ratio (A / F) in the exhaust gas is adjusted. By controlling, it is possible to suppress the generation of alcohol by reducing the acid with hydrogen, and to proceed to the acid at once without stopping the reaction of the aldehyde generated from the alcohol in the aldehyde state. . As a result, the generation of aldehyde can be significantly suppressed while controlling the NO _x emission amount.

Further, although one downstream catalyst device 12 is provided, the present invention is not limited to this, and two or more downstream catalyst devices 12 may be provided.
When alcohol fuel is used as fuel in the FFV system, usually two downstream side catalyst devices 12 are provided. After adjusting the air-fuel ratio (A / F) of the exhaust gas to be richer than the stoichiometric air-fuel ratio in the downstream downstream catalytic device in the exhaust gas flow direction, the air-fuel ratio ( The air-fuel ratio (A / F) of the exhaust gas obtained by adjusting the A / F) with the downstream side catalyst device is adjusted to be on the lean side from, for example, 14.1. Thereby, hydrogen can be prevented from being generated.

  FIG. 5 shows an exhaust emission control device for an internal combustion engine in which two downstream catalyst devices 12 are arranged. As shown in FIG. 5, a first downstream catalyst device 12-1 and a second downstream catalyst device 12-2 are provided as the downstream catalyst device 12.

  The first downstream catalyst device 12-1 adjusts the air-fuel ratio (A / F) of the exhaust gas so as to be richer than the stoichiometric air-fuel ratio. Further, the second downstream catalyst device 12-2 adjusts the air-fuel ratio (A / F) of the exhaust gas that is rich on the first downstream catalyst device 12-1 to the lean side.

  In the first downstream side catalyst device 12-1, the air-fuel ratio (A / F) of the exhaust gas is adjusted to be on the rich side, for example, about 12.0 to 13.0 from the theoretical air-fuel ratio.

  In the second downstream catalyst device 12-2, the air-fuel ratio (A / F) of the exhaust gas adjusted by the first downstream catalyst device 12-1 is adjusted to a lean side from about 14.1, for example. I have to.

When E13 (fuel in which 13% ethanol is mixed in gasoline) is used and the catalyst bed temperature of the upstream catalyst in the upstream catalyst device 11 is a predetermined temperature (for example, 600 ° C.), as shown in FIGS. The air-fuel ratio (A / F) of the exhaust gas at which hydrogen starts to be generated is around 14.5. Therefore, the air-fuel ratio on the discharge side of the second downstream side catalyst device 12-2 is set to, for example, 14.5 or 14.6, which is a value on the lean side from 14.5, for example, and the stoichiometric air-fuel ratio (stoichiometric) or rich. As a result, NO _x can be desorbed and reacted, and an air-fuel ratio that does not generate hydrogen can be obtained.

As described above, according to the exhaust gas purification apparatus for an internal combustion engine of the present embodiment, the air-fuel ratio in the exhaust gas is controlled from the NO _x emission amount and the hydrogen concentration, and hydrogen is generated so that the NO _x emission amount becomes a predetermined value or less. The amount can be controlled. For this reason, even when a fuel containing an alcohol component is used, the reaction of the aldehyde generated from the alcohol to the acid can be advanced at once, so that the generation of aldehyde is greatly reduced while controlling the NO _x emission amount. Can be suppressed.

As described above, the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment controls the air-fuel ratio in the exhaust gas, and controls the amount of hydrogen generated so that the NO _x emission amount becomes a predetermined value or less. use the reaction proceeded aldehyde generated from the alcohol in the fuel to the acid, while controlling the NO _X emissions, which attempt to suppress the generation of aldehydes, gasoline engine mounted on a motor vehicle, in particular an alcohol fuel This is useful for FFV systems.

It is the schematic which shows the structure of the exhaust gas purification apparatus which concerns on this Embodiment. It is a flowchart which shows an example of the original control operation | movement of this embodiment. It is a flowchart which shows an example of the control action at the time of step S11. It is a flowchart which shows an example of the control action at the time of step S12. It is a related figure which shows the relationship between an air fuel ratio, nitrogen oxide discharge | emission amount, and hydrogen concentration at the time of using E13. It is another relationship figure which shows the relationship between the air fuel ratio at the time of using E13, nitrogen oxide concentration, and hydrogen concentration. It is the schematic which shows the other structure of the exhaust gas purification apparatus which concerns on this Embodiment.

Explanation of symbols

1 Internal combustion engine
2 Cylinder block 3 Cylinder head 4 Piston 5 Combustion chamber 6 Intake pipe 7 Exhaust pipe (exhaust path)
8 Intake Valve 9 Exhaust Valve 10 Fuel Injection Valve 11 Upstream Catalyst 12 Downstream Catalyst 12-1 First Downstream Catalyst Device 12-2 Second Downstream Catalyst Device 15 A / F Sensor 16 Hydrogen Concentration Sensor 17 NO _X Sensor 20 Vehicle control unit 30 Exhaust purification device

Claims (5)

An upstream catalyst device that is provided in an exhaust path of an internal combustion engine that uses alcohol fuel as a fuel, and that contains an upstream catalyst that purifies exhaust gas flowing through the exhaust path;
Provided on the downstream side in the exhaust gas flow direction from the upstream side catalyst device, and stores nitrogen oxide when the air-fuel ratio of the exhaust gas is lean and also stores when the stoichiometric air-fuel ratio or rich. At least one downstream catalyst device containing a downstream catalyst for desorbing nitrogen oxides;
An air-fuel ratio detecting means provided on the upstream side of the upstream side catalyst device for detecting an air-fuel ratio of the exhaust gas;
A hydrogen concentration detection means provided between the upstream catalyst device and the downstream catalyst device in the exhaust path, for detecting the hydrogen concentration of the exhaust gas;
An exhaust gas purification device provided on the downstream side of the downstream side catalyst device and having nitrogen oxide concentration detection means for detecting the nitrogen oxide concentration of the exhaust gas,
When the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, hydrogen is generated so that the air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio or rich, and the nitrogen oxides are reduced.
An exhaust gas purification apparatus for an internal combustion engine, wherein the amount of hydrogen generation is controlled based on a detection result by the nitrogen oxide concentration detection means so that the concentration of the nitrogen oxide is not more than a predetermined value. In claim 1,
An exhaust gas purifying apparatus for an internal combustion engine, characterized in that when the amount of nitrogen oxide discharged by the nitrogen oxide concentration detecting means is a predetermined value or more, hydrogen is generated and the nitrogen oxide is reduced. In claim 1 or 2,
An exhaust gas purifying apparatus for an internal combustion engine, wherein when generating hydrogen, the catalyst temperature of the upstream catalyst is not more than a predetermined temperature at which a shift reaction from alcohol to acid occurs. In claim 2 or 3,
The exhaust gas purification apparatus for an internal combustion engine, wherein the predetermined temperature is 600 ° C or lower. In any one of claims 1 to 4,
An exhaust gas purification apparatus for an internal combustion engine, wherein generation of hydrogen is controlled when the nitrogen oxide emission amount by the nitrogen oxide concentration detection means is less than a predetermined value.

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