JP2016145543A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine that enables a reduction in fuel consumption while maintaining an NOelimination ratio at a high level.SOLUTION: An exhaust emission control device includes an exhaust purification catalyst disposed downstream of a hydrocarbon supply valve and a fuel supply device for supplying fuel to the hydrocarbon supply valve, and is formed to perform operation control for supplying hydrocarbon from the hydrocarbon supply valve so that the amplitude of a concentration change of the hydrocarbon flowing into the exhaust purification catalyst during operation of an engine becomes an amplitude within a predetermined range and the concentration of the hydrocarbon is in a cycle within a predetermined range. When the operation control is performed, pressure of fuel to be supplied to the hydrocarbon supply valve is set based on total fuel consumption of the consumption of fuel injected from the hydrocarbon supply valve and fuel consumption for eliminating NO.SELECTED DRAWING: Figure 25

Description

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

For example, carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NO _x ), or particulate matter (PM) may be used as exhaust gas from internal combustion engines such as diesel engines and gasoline engines. Ingredients such as Matter) are included. As a device for purifying NO _X , a reducing catalyst that continuously reduces NO _X contained in the exhaust by supplying a reducing agent to the exhaust purification catalyst, or NO _X is stored when the air-fuel ratio of the exhaust gas is lean. , NO _X storage catalyst is known to reduce with releasing NO _X occluding by the air-fuel ratio of the exhaust gas rich.

In JP 2012-062864 A, a hydrocarbon supply valve is disposed upstream of the exhaust purification catalyst, and further, the hydrocarbon is supplied so that the concentration of hydrocarbon flowing into the exhaust purification catalyst has an amplitude of 200 ppm or more. by feeding hydrocarbons such interval is equal to or less than 5 seconds, an exhaust purifying apparatus for an internal combustion engine for purifying NO _X contained in the exhaust gas is disclosed.

JP 2012-062864 A Special table 2011-504979 gazette JP 2001-152992 A

In the NO _X purification method described in JP 2012-062864 A described above, the fuel of the internal combustion engine can be used as the hydrocarbon for purifying NO _X. This NO _X purification method has a characteristic that it can exhibit excellent NO _X purification performance even when the temperature of the exhaust purification catalyst becomes high. However, it is necessary fuel to purify NO _X, so as to reduce the fuel consumption while maintaining a high purification rate of NO _X, to inject fuel from the hydrocarbon feed valve by adjusting the pressure It is preferable.

On the other hand, a particulate filter for removing particulate matter may be disposed in an exhaust gas purification device for an internal combustion engine. For example, a particulate filter may be disposed downstream of the exhaust purification catalyst that performs the above-described NO _X purification method. Particulate matter accumulates in the particulate filter when the operation is continued. In order to remove the particulate matter accumulated in the particulate filter, the particulate filter is raised to a predetermined temperature or higher. The particulate matter can be oxidized and removed by supplying exhaust gas containing excess air to the particulate filter.

When performing the regeneration of the particulate filter may perform relatively a low temperature of the NO _X purification method. However, when fuel is injected from the hydrocarbon feed valve at a low temperature while maintaining a suitable pressure at a high temperature, there is a problem that the fuel slips through.

The present invention aims to provide an exhaust purification system of an internal combustion engine to reduce fuel consumption while maintaining a high NO _X purification rate.

The exhaust gas purification apparatus for an internal combustion engine according to the present invention includes a hydrocarbon supply valve for supplying hydrocarbons disposed in the engine exhaust passage, and NO _X contained in the exhaust gas in the engine exhaust passage downstream of the hydrocarbon supply valve. An exhaust purification catalyst for reacting the reformed hydrocarbon with the noble metal catalyst is disposed on the exhaust gas flow surface of the exhaust purification catalyst and a basic exhaust around the noble metal catalyst. A gas flow surface portion is formed, and the exhaust purification catalyst emits exhaust gas when the concentration of hydrocarbons flowing into the exhaust purification catalyst is vibrated with a predetermined range of amplitude and a predetermined range of period. which has a property for reducing the NO _X contained in the gas, the vibration period of the hydrocarbon concentration has a property of absorbing the amount of NO _X contained in the exhaust gas to be longer than the range defined the advance is increased The A fuel supply device that supplies fuel to the hydrocarbon supply valve to the internal combustion engine. The fuel supply device is formed so that the pressure of the fuel supplied to the hydrocarbon supply valve can be adjusted, and the exhaust purification catalyst during engine operation. The amount of hydrocarbons supplied from the hydrocarbon supply valve is controlled so that the amplitude of the change in the concentration of hydrocarbons flowing into the exhaust gas falls within the predetermined range, and the amount of hydrocarbons flowing into the exhaust purification catalyst is controlled. It is configured to perform operation control in which the hydrocarbon supply interval from the hydrocarbon supply valve is controlled so that the concentration vibrates with a period within a predetermined range, and the above operation control is performed. In this case, based on the total fuel consumption amount of the fuel consumption amount for driving the fuel supply device and the fuel consumption amount of the fuel injected from the hydrocarbon supply valve by the above operation control, the hydrocarbon supply valve Supply To set the pressure of that fuel.

According to the present invention, it is possible to provide an exhaust purification system of an internal combustion engine to reduce fuel consumption while maintaining a high NO _X purification rate.

1 is an overall view of an internal combustion engine in an embodiment. It is a figure which shows the surface part of the catalyst support | carrier of an exhaust purification catalyst schematically. It is a figure explaining the oxidation reaction of the hydrocarbon in an exhaust purification catalyst. Is a graph showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst in the first NO _X removal method. Is a diagram illustrating a NO _X purification rate of the first NO _X removal method. It is an enlarged view explaining the oxidation-reduction reaction of the exhaust purification catalyst in the first NO _X purification method. It is an enlarged view for explaining the generation of the reducing intermediate in the first NO _X removal method. It is an enlarged view for explaining the storage of the NO _X in the exhaust gas purifying catalyst in the second NO _X removal method. FIG. 6 is an enlarged view for explaining NO _X release and reduction of an exhaust purification catalyst in a second NO _X purification method. Is a graph showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst in the second NO _X removal method. It is a diagram illustrating a NO _X purification rate of the second of the NO _X purification method. 3 is a time chart showing changes in the air-fuel ratio of exhaust gas flowing into the exhaust purification catalyst in the first NO _X purification method. 6 is another time chart showing the change in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst in the first NO _X purification method. FIG. 3 is a diagram showing a relationship between an oxidizing power of an exhaust purification catalyst and a required minimum air-fuel ratio X in the first NO _X purification method. In the first of the NO _X purification method is a diagram showing a relationship between oxygen concentration in the exhaust gas obtained of the same of the NO _X purification rate and the amplitude ΔH of the hydrocarbon concentration. It is a diagram showing a relationship between an amplitude ΔH and NO _X purification rate of the hydrocarbon concentration in the first NO _X removal method. It is a diagram showing the relationship between the vibration period ΔT and NO _X purification rate of the hydrocarbon concentration in the first NO _X removal method. Is a diagram showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst in the second NO _X removal method. It is a diagram showing a map of the NO _X amount NOXA exhausted from the engine body to the engine exhaust passage. It is a figure which shows the fuel-injection time when performing auxiliary injection in a combustion chamber. It is a figure which shows the map of hydrocarbon supply amount WR when performing auxiliary injection. It is a graph illustrating a region of the NO _X purification method based on the operating state of the internal combustion engine. It is a graph of the density | concentration of the hydrocarbon in exhaust gas when fuel is injected from a hydrocarbon feed valve. It is a graph illustrating a region of the NO _X purification method when performing regeneration of the particulate filter. It is a block diagram of the fuel supply apparatus in an embodiment. It is a graph which shows the relationship between the electric current supplied to a fuel pump, and discharge pressure. It is a flowchart of control which sets the pressure of the fuel injected from a hydrocarbon feed valve. It is a graph illustrating the fuel consumption for boosting the fuel by the fuel consumption and the fuel pump for purifying NO _X in the first NO _X removal method.

  With reference to FIGS. 1 to 26, an exhaust emission control device for an internal combustion engine in an embodiment will be described. In the present embodiment, a compression ignition type internal combustion engine attached to a vehicle will be described as an example.

  FIG. 1 is an overall view of an internal combustion engine in the present embodiment. The internal combustion engine includes an engine body 1. The internal combustion engine also includes an exhaust purification device that purifies exhaust. The engine body 1 includes a combustion chamber 2 as each cylinder, an electronically controlled fuel injection valve 3 for injecting fuel into each combustion chamber 2, an intake manifold 4, and an exhaust manifold 5.

  The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake duct 6. An inlet of the compressor 7 a is connected to an air cleaner 9 via an intake air amount detector 8. A throttle valve 10 driven by a step motor is disposed in the intake duct 6. Further, a cooling device 11 for cooling the intake air flowing through the intake duct 6 is disposed in the middle of the intake duct 6. In the embodiment shown in FIG. 1, engine cooling water is guided to the cooling device 11. The intake air is cooled by the engine cooling water.

Exhaust purifying apparatus of the present embodiment includes an exhaust purification catalyst 13 for purifying NO _X. In addition, the exhaust purification device includes a particulate filter 14 disposed downstream of the exhaust purification catalyst 13. The exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7. The outlet of the exhaust turbine 7 b is connected to the inlet of the exhaust purification catalyst 13 through the exhaust pipe 12. The outlet of the exhaust purification catalyst 13 is connected to the particulate filter 14.

  A hydrocarbon supply valve 15 for supplying light oil used as fuel for the compression ignition internal combustion engine or hydrocarbons made of other fuel is disposed upstream of the exhaust purification catalyst 13. In the present embodiment, light oil is used as the hydrocarbon supplied from the hydrocarbon supply valve 15. The present invention can also be applied to a spark ignition type internal combustion engine in which the air-fuel ratio at the time of combustion is controlled to be lean. In this case, the hydrocarbon supply valve supplies gasoline used as fuel for the spark ignition type internal combustion engine or hydrocarbons made of other fuels.

  The hydrocarbon supply valve 15 is connected to the fuel chamber 62. The fuel chamber 62 is connected to the fuel tank 22 via the fuel pump 61. When the fuel pump 61 is driven, the fuel in the fuel tank 22 is supplied to the fuel chamber 62. The fuel chamber 62 stores pressurized fuel. A fuel pressure sensor 63 is disposed in the fuel chamber 62 as a pressure detector that detects the pressure of the fuel. The injection pressure of the hydrocarbon supply valve 15 can be detected from the output of the fuel pressure sensor 63.

  An EGR passage 16 is disposed between the exhaust manifold 5 and the intake manifold 4 to perform exhaust gas recirculation (EGR). An electronically controlled EGR control valve 17 is disposed in the EGR passage 16. A cooling device 18 for cooling the EGR gas flowing in the EGR passage 16 is disposed in the middle of the EGR passage 16. In the embodiment shown in FIG. 1, engine cooling water is introduced into the cooling device 18. The EGR gas is cooled by the engine cooling water.

  Each fuel injection valve 3 is connected to a common rail 20 via a fuel supply pipe 19. The fuel stored in the fuel tank 22 is boosted by the electronically controlled fuel pump 61 and the fuel pump 21 and supplied to the common rail 20. The fuel pump 61 is a low pressure pump and raises the fuel to a predetermined pressure. The fuel pump 21 is a high-pressure pump, and further raises the pressure of the fuel boosted by the fuel pump 61. The common rail 20 is supplied with high pressure fuel. The fuel supplied into the common rail 20 is injected into the combustion chamber 2 from the fuel injection valve 3.

  The electronic control unit 30 includes a digital computer. The electronic control unit 30 in the present embodiment functions as a control device for the exhaust purification device. The electronic control unit 30 includes a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35 and an output port 36 that are connected to each other by a bidirectional bus 31.

  A temperature sensor 23 for detecting the temperature of the exhaust purification catalyst 13 is disposed downstream of the exhaust purification catalyst 13. A differential pressure sensor 24 for detecting the differential pressure before and after the particulate filter 14 is attached to the particulate filter 14. Further, a temperature sensor 25 as a temperature detector for detecting the temperature of the particulate filter 14 is disposed downstream of the particulate filter 14. The output signals of the temperature sensors 23 and 25, the differential pressure sensor 24, and the intake air amount detector 8 are input to the input port 35 via corresponding AD converters 37, respectively.

  A load sensor 41 that generates an output voltage proportional to the amount of depression of the accelerator pedal 40 is connected to the accelerator pedal 40. The output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. Further, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 15 °. From the output of the crank angle sensor 42, the crank angle and the engine speed can be detected. On the other hand, the output port 36 is connected to the fuel injection valve 3, the step motor for driving the throttle valve 10, the hydrocarbon supply valve 15, the EGR control valve 17, and the fuel pumps 61 and 21 through corresponding drive circuits 38. . These fuel injection valve 3, throttle valve 10, hydrocarbon feed valve 15, EGR control valve 17, fuel pumps 61, 21, etc. are controlled by an electronic control unit 30.

  An output signal of the fuel pressure sensor 63 is input to the electronic control unit 30. The fuel pump 61 is controlled by the electronic control unit 30. The fuel pump 61 is controlled so that the pressure inside the fuel chamber 62 becomes the required injection pressure of the hydrocarbon feed valve 15.

  The particulate filter 14 is a filter that removes particulate matter (particulates) such as carbon fine particles and sulfate contained in the exhaust gas. The particulate filter 14 has, for example, a honeycomb structure and a plurality of flow paths extending in the gas flow direction. In the plurality of channels, the channels whose downstream ends are sealed and the channels whose upstream ends are sealed are alternately formed. The partition walls of the flow path are formed of a porous material such as cordierite. Particulates are captured when the exhaust passes through the partition wall. Particulate matter is collected by the particulate filter 14. The particulate matter that gradually accumulates on the particulate filter 14 is oxidized and removed by raising the temperature to, for example, about 650 ° C. in an atmosphere with excess air.

  The amount of particulate matter deposited on the particulate filter 14 can be estimated from the output of the differential pressure sensor 24, for example. When the differential pressure across the particulate filter 14 exceeds a predetermined determination value, it can be determined that the amount of particulate matter deposited on the particulate filter 14 exceeds the determination value.

FIG. 2 schematically shows the surface portion of the catalyst carrier carried on the substrate of the exhaust purification catalyst. In this exhaust purification catalyst 13, as shown in FIG. 2, noble metal catalysts 51 and 52, which are catalyst particles, are supported on a catalyst carrier 50 made of alumina, for example, and further on this catalyst carrier 50 are potassium K and sodium. Na, donate cesium Cs, barium Ba, alkaline earth metals such as calcium Ca, rare earth and silver Ag, such as lanthanides, copper Cu, iron Fe, electrons in the NO _X as iridium Ir A basic layer 53 containing at least one selected from the metals that can be obtained is formed. Since the exhaust gas flows along the catalyst carrier 50, it can be said that the noble metal catalysts 51 and 52 are supported on the exhaust gas flow surface of the exhaust purification catalyst 13. Further, since the surface of the basic layer 53 is basic, the surface of the basic layer 53 is referred to as a basic exhaust gas flow surface portion 54.

  On the other hand, in FIG. 2, the noble metal catalyst 51 is made of platinum Pt, and the noble metal catalyst 52 is made of rhodium Rh. In this case, any of the noble metal catalysts 51 and 52 can be composed of platinum Pt. In addition to platinum Pt and rhodium Rh, palladium Pd can be further supported on the catalyst carrier 50 of the exhaust purification catalyst 13, or palladium Pd can be supported instead of rhodium Rh. That is, the noble metal catalysts 51 and 52 supported on the catalyst carrier 50 are composed of at least one of platinum Pt, rhodium Rh and palladium Pd.

When hydrocarbons are injected into the exhaust gas from the hydrocarbon supply valve 15, the hydrocarbons are reformed in the exhaust purification catalyst 13. In the present invention, so as to purify the NO _X in the exhaust purification catalyst 13 using the time reformed hydrocarbons. FIG. 3 schematically shows the reforming action performed in the exhaust purification catalyst 13 at this time. As shown in FIG. 3, the hydrocarbon HC injected from the hydrocarbon feed valve 15 is converted into a radical hydrocarbon HC having a small number of carbons by the catalyst 51.

  FIG. 4 shows the supply timing of hydrocarbons from the hydrocarbon supply valve 15 and changes in the air-fuel ratio (A / F) in of the exhaust gas flowing into the exhaust purification catalyst 13. Since the change in the air-fuel ratio (A / F) in depends on the change in the concentration of hydrocarbons in the exhaust gas flowing into the exhaust purification catalyst 13, the air-fuel ratio (A / F) in shown in FIG. It can be said that the change represents a change in hydrocarbon concentration. However, since the air-fuel ratio (A / F) in decreases as the hydrocarbon concentration increases, the hydrocarbon concentration increases as the air-fuel ratio (A / F) in becomes richer in FIG.

FIG. 5 shows a change in the air-fuel ratio (A / F) in of the exhaust gas flowing into the exhaust purification catalyst 13 as shown in FIG. 4 by periodically changing the concentration of hydrocarbons flowing into the exhaust purification catalyst 13. the NO _X purification rate by the exhaust purification catalyst 13 when allowed to indicate for each catalyst temperature TC of the exhaust purification catalyst 13. When the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 is vibrated with an amplitude within a predetermined range and a period within a predetermined range, as shown in FIG. 5, even in a high temperature region of 400 ° C. or higher. An extremely high NO _x purification rate can be obtained.

Further, at this time, a large amount of reducing intermediates containing nitrogen and hydrocarbons are kept or adsorbed on the surface of the basic layer 53, that is, on the basic exhaust gas flow surface portion 54 of the exhaust purification catalyst 13. It has been found that this reducing intermediate plays a central role in obtaining a high NO _x purification rate. Next, this will be described with reference to FIGS. 6A and 6B. 6A and 6B schematically show the surface portion of the catalyst carrier 50 of the exhaust purification catalyst 13, and in these FIGS. 6A and 6B, the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 is predetermined. Shown is a reaction that is presumed to occur when oscillated with an amplitude within a given range and a period within a predetermined range.

  FIG. 6A shows a case where the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 is low, and FIG. 6B shows that the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 when hydrocarbons are supplied from the hydrocarbon supply valve 15 is high. It shows when

As can be seen from FIG. 4, since the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 13 is maintained lean except for a moment, the exhaust gas flowing into the exhaust purification catalyst 13 is usually in an oxygen excess state. At this time, a part of the NO contained in the exhaust gas adheres on the exhaust purification catalyst 13, and a part of the NO contained in the exhaust gas is oxidized on the platinum noble metal catalyst 51 as shown in FIG. 6A. It becomes NO ₂ , and then this NO ₂ is further oxidized to NO ₃ . A part of the NO ₂ is NO ₂ ^- and becomes. Therefore, NO ₂ ⁻ and NO ₃ are produced on the platinum Pt noble metal catalyst 51. NO adhering to the exhaust purification catalyst 13 and NO ₂ ⁻ and NO ₃ produced on the platinum Pt 51 are strongly active, and hence these NO, NO ₂ ⁻ and NO ₃ are hereinafter referred to as active NO _X.

On the other hand, when hydrocarbons are supplied from the hydrocarbon supply valve 15, the hydrocarbons are adsorbed over the entire exhaust purification catalyst 13. Most of these adsorbed hydrocarbons are sequentially reacted with oxygen and burned, and some of the adsorbed hydrocarbons are sequentially reformed in the exhaust purification catalyst 13 as shown in FIG. 3 to become radicals. Therefore, as shown in FIG. 6B, the hydrocarbon concentration around the active NO _X is increased. By the way, after the active NO _X is generated, if the state in which the oxygen concentration around the active NO _X is high continues for a certain time or longer, the active NO _X is oxidized and absorbed in the basic layer 53 in the form of nitrate ions NO ₃ ^−. . However react with radical hydrocarbons HC are active NO _X as the hydrocarbon concentration is high as shown in FIG. 6B on the platinum precious metal catalyst 51 around the active NO _X before the lapse of the certain time, it Produces a reducing intermediate. This reducing intermediate is held or adsorbed on the surface of the basic layer 53.

Incidentally, the first produced reducing intermediate this time is considered to be a nitro compound R-NO _2. When this nitro compound R-NO ₂ is produced, it becomes a nitrile compound R-CN, but since this nitrile compound R-CN can only survive for a moment in that state, it immediately becomes an isocyanate compound R-NCO. This isocyanate compound R-NCO becomes an amine compound R-NH _{2 when} hydrolyzed. However, in this case, it is considered that a part of the isocyanate compound R-NCO is hydrolyzed. Therefore, as shown in FIG. 6B, most of the reducing intermediates retained or adsorbed on the surface of the basic layer 53 are considered to be the isocyanate compound R—NCO and the amine compound R—NH ₂ .

On the other hand, as shown in FIG. 6B, when hydrocarbon HC is adsorbed around the generated reducing intermediate, the reducing intermediate is blocked by hydrocarbon HC and the reaction does not proceed any further. In this case, the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 decreases, and then the hydrocarbon adsorbed around the reducing intermediate is oxidized and disappears, whereby the oxygen concentration around the reducing intermediate is reduced. As is increased, the reducing intermediate reacts with active NO _X as shown in FIG. 6A, reacts with ambient oxygen, or self-decomposes. As a result, the reducing intermediates R—NCO and R—NH ₂ are converted to N ₂ , CO ₂ , and H ₂ O, and thus NO _X is purified.

As described above, in the exhaust purification catalyst 13, a reducing intermediate is generated by increasing the concentration of hydrocarbons flowing into the exhaust purification catalyst 13, and after reducing the concentration of hydrocarbons flowing into the exhaust purification catalyst 13, When the oxygen concentration becomes high, the reducing intermediate reacts with active NO _X or oxygen, or self-decomposes, thereby purifying NO _X. That is, in order to purify the NO _X by the exhaust purification catalyst 13, it is necessary to change the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 periodically.

Of course, that this case, it is necessary to increase the concentration of hydrocarbons to a sufficiently high concentration to generate a reducing intermediate, the generated reducing intermediate is reacted with the active NO _X and oxygen, or to autolysis It is necessary to reduce the hydrocarbon concentration to a sufficiently low concentration. That is, it is necessary to vibrate the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 with an amplitude within a predetermined range. In this case, the reducing intermediates are formed on the basic layer 53 until the generated reducing intermediates R—NCO and R—NH ₂ react with active NO _X and oxygen, or until they self-decompose, that is, It must be retained on the basic exhaust gas flow surface portion 54, for which a basic exhaust gas flow surface portion 54 is provided.

On the other hand, if the hydrocarbon supply interval is lengthened, the period during which the oxygen concentration becomes high after the hydrocarbon is supplied and before the next hydrocarbon is supplied becomes longer, so that the active NO _X has a reducing intermediate. It is absorbed in the basic layer 53 in the form of nitrate without being formed. In order to avoid this, it is necessary to oscillate the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 with a period within a predetermined range.

Therefore, in the embodiment according to the present invention, NO _X contained in the exhaust gas is reacted with the reformed hydrocarbon to produce reducing intermediates R-NCO and R-NH ₂ containing nitrogen and hydrocarbons. Further, noble metal catalysts 51 and 52 are supported on the exhaust gas flow surface of the exhaust purification catalyst 13, and the generated reducing intermediates R-NCO and R-NH ₂ are held in the exhaust purification catalyst 13. Therefore, a basic exhaust gas flow surface portion 54 is formed around the noble metal catalysts 51 and 52, and the reducing intermediates R-NCO and R-NH held on the basic exhaust gas flow surface portion 54 are formed. ₂ is converted into N ₂ , CO ₂ , and H ₂ O, and the vibration period of the hydrocarbon concentration is the vibration period necessary to continue to produce the reducing intermediates R-NCO and R-NH ₂ . In the example shown in FIG. 4, the supply interval is 3 seconds.

If the oscillation period of the hydrocarbon concentration, that is, the supply interval of the hydrocarbon HC is longer than the period within the above-mentioned predetermined range, the reducing intermediates R-NCO and R-NH ₂ are formed on the surface of the basic layer 53. At this time, the active NO _X produced on the platinum Pt noble metal catalyst 51 diffuses into the basic layer 53 in the form of nitrate ions NO ₃ ⁻ as shown in FIG. 7A and becomes nitrates. That is, at this time, NO _X in the exhaust gas is absorbed into the basic layer 53 in the form of nitrate.

On the other hand, FIG. 7B shows a case where the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 13 is made the stoichiometric air-fuel ratio or rich when NO _X is absorbed in the basic layer 53 in the form of nitrate. Is shown. In this case, since the oxygen concentration in the exhaust gas decreases, the reaction proceeds in the reverse direction (NO ₃ ⁻ → NO ₂ ), and thus the nitrates absorbed in the basic layer 53 are successively converted into nitrate ions NO _3. ⁻ And released from the basic layer 53 in the form of NO ₂ as shown in FIG. 7B. Next, the released NO ₂ is reduced by the hydrocarbons HC and CO contained in the exhaust gas.

Figure 8 shows a case where NO _X absorbing capacity of the basic layer 53 is to be temporarily rich air-fuel ratio (A / F) in of the exhaust gas flowing into the exhaust purification catalyst 13 shortly before saturation Yes. In the example shown in FIG. 8, the time interval of this rich control is 1 minute or more. NO _X the air-fuel ratio (A / F) in of the exhaust gas is absorbed in the basic layer 53 when the lean in this case, the air-fuel ratio (A / F) in temporarily rich exhaust gas When released, it is released from the basic layer 53 at once and reduced. Therefore, in this case, the basic layer 53 serves as an absorbent for temporarily absorbing NO _X.

Incidentally, at this time, sometimes the basic layer 53 temporarily adsorbs the NO _X, thus using term of storage as a term including both absorption and adsorption In this case the basic layer 53 temporarily the NO _X It plays the role of NO _X storage agent for storage. That is, in this case, the ratio of the air and fuel (hydrocarbon) of the exhaust gas supplied into the engine intake passage, the combustion chamber 2 and the exhaust passage upstream of the exhaust purification catalyst 13 is the air-fuel ratio (A / F) of the exhaust gas. ) and the referred, the exhaust purification catalyst 13, the air-fuel ratio of the exhaust gas is occluded NO _X when the lean, and functions as the NO _X storing catalyst the oxygen concentration in the exhaust gas to release NO _X occluding the drops Yes.

Figure 9 shows the NO _X purification rate when making the exhaust purification catalyst 13 was thus function as _the NO _X storage catalyst. The horizontal axis in FIG. 9 indicates the catalyst temperature TC of the exhaust purification catalyst 13. When the exhaust purification catalyst 13 functions as a NO _X storage catalyst, as shown in FIG. 9, when the catalyst temperature TC is 300 ° C. to 400 ° C., an extremely high NO _X purification rate is obtained, but the catalyst temperature TC is 400 ° C. NO _X purification rate decreases when a high temperature of more.

The reason why the the catalyst temperature TC becomes equal to or higher than 400 ° C. NO _X purification rate is lowered, nitrate when the catalyst temperature TC becomes equal to or higher than 400 ° C. is released from the exhaust purification catalyst 13 in the form of NO ₂ by thermal decomposition Because. That is, so long as storing NO _X in the form of nitrates, it is difficult to obtain a high NO _X purification rate when the catalyst temperature TC is high. However, in the new NO _X purification method shown in FIGS. 4 to 6A and 6B, nitrate is not generated or is very small even if generated as shown in FIGS. 6A and 6B. catalyst temperature TC as shown is that even high NO _X purification rate is obtained when high.

In this invention, the hydrocarbon feed valve 15 for feeding hydrocarbons disposed in the engine exhaust passage, the reformed NO _X and reforming contained in the exhaust gas to the hydrocarbon feed valve 15 downstream of the engine exhaust passage An exhaust purification catalyst 13 for reacting with the hydrocarbons is disposed, and noble metal catalysts 51 and 52 are supported on the exhaust gas flow surface of the exhaust purification catalyst 13 and basic around the noble metal catalysts 51 and 52. The exhaust gas flow surface portion 54 is formed, and the exhaust gas purification catalyst 13 has a concentration of hydrocarbons flowing into the exhaust gas purification catalyst 13 with an amplitude within a predetermined range and a period within a predetermined range. which has a property for reducing the NO _X contained in the exhaust gas and to vibrate, of the NO _X contained the vibration period of the hydrocarbon concentration in the exhaust gas to be longer than the predetermined range It has a property of increasing the storage amount, and vibrates the hydrocarbon concentration flowing into the exhaust purification catalyst 13 during engine operation with an amplitude within a predetermined range and a period within a predetermined range, Thus, NO _X contained in the exhaust gas is reduced by the exhaust purification catalyst 13.

That is, the NO _X purification methods shown in FIGS. 4 to 6A and 6B almost form nitrates when an exhaust purification catalyst supporting a noble metal catalyst and forming a basic layer capable of absorbing NO _X is used. It can be said that this is a new NO _X purification method that purifies NO _X without having to do so. In fact, when this new NO _X purification method is used, the amount of nitrate detected from the basic layer 53 is extremely small compared to the case where the exhaust purification catalyst 13 functions as a NO _X storage catalyst. Incidentally, this new NO _X purification method hereinafter referred to as a first NO _X removal method.

Next, the first NO _x purification method will be described in a little more detail with reference to FIGS. 10 to 15.

  FIG. 10 shows an enlarged view of the change in the air-fuel ratio (A / F) in shown in FIG. As described above, the change in the air-fuel ratio (A / F) in of the exhaust gas flowing into the exhaust purification catalyst 13 indicates the change in the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 at the same time. In FIG. 10, ΔH indicates the amplitude of the change in the concentration of hydrocarbon HC flowing into the exhaust purification catalyst 13, and ΔT indicates the oscillation period of the concentration of hydrocarbon flowing into the exhaust purification catalyst 13.

Further, in FIG. 10, (A / F) b represents the base air-fuel ratio indicating the air-fuel ratio of the combustion gas for generating the engine output. In other words, the base air-fuel ratio (A / F) b represents the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 13 when the supply of hydrocarbons is stopped. On the other hand, in FIG. 10, X is an air-fuel ratio (A / F) in used for generating a reducing intermediate without the generated active NO _X being occluded in the basic layer 53 in the form of nitrate. The air-fuel ratio (A / F) in is made lower than the upper limit X of the air-fuel ratio in order to react the active NO _X with the reformed hydrocarbon to produce a reducing intermediate. It will be necessary.

In other words, X in FIG. 10 represents the lower limit of the concentration of hydrocarbons required for reacting active NO _X with the reformed hydrocarbon to form a reducing intermediate, and the reducing intermediate In order to produce a body, it is necessary to make the hydrocarbon concentration higher than the lower limit X. In this case, the ratio of the oxygen concentration and the hydrocarbon concentration of whether around the active NO _X reducing intermediate is produced, i.e. determined by the air-fuel ratio (A / F) in, for producing the reducing intermediate The above-mentioned upper limit X of the air-fuel ratio necessary for the above is hereinafter referred to as a required minimum air-fuel ratio.

  In the example shown in FIG. 10, the required minimum air-fuel ratio X is rich. Therefore, in this case, the air-fuel ratio (A / F) in is instantaneously required to generate the reducing intermediate. The following is made rich: On the other hand, in the example shown in FIG. 11, the required minimum air-fuel ratio X is lean. In this case, the reducing intermediate is generated by periodically reducing the air-fuel ratio (A / F) in while maintaining the air-fuel ratio (A / F) in lean.

  In this case, whether the required minimum air-fuel ratio X becomes rich or lean depends on the oxidizing power of the exhaust purification catalyst 13. In this case, for example, if the amount of the precious metal catalyst 51 supported is increased, the exhaust purification catalyst 13 becomes stronger in oxidizing power, and if it becomes more acidic, the oxidizing power becomes stronger. Therefore, the oxidizing power of the exhaust purification catalyst 13 varies depending on the amount of the noble metal catalyst 51 supported and the acidity.

  When the exhaust purification catalyst 13 having a strong oxidizing power is used, the air-fuel ratio (A / F) in is periodically decreased while maintaining the air-fuel ratio (A / F) in lean as shown in FIG. When the air-fuel ratio (A / F) in is lowered, the hydrocarbon is completely oxidized, and as a result, a reducing intermediate cannot be generated. On the other hand, when the exhaust purification catalyst 13 having strong oxidizing power is used, if the air-fuel ratio (A / F) in is periodically made rich as shown in FIG. 10, the air-fuel ratio (A / F) in is rich. When selected, some hydrocarbons are partially oxidized without being completely oxidized, i.e., the hydrocarbon is reformed, thus producing a reducing intermediate. Therefore, when the exhaust purification catalyst 13 having a strong oxidizing power is used, the required minimum air-fuel ratio X needs to be made rich.

  On the other hand, when the exhaust purification catalyst 13 having a weak oxidizing power is used, the air-fuel ratio (A / F) in is periodically decreased while maintaining the air-fuel ratio (A / F) in lean as shown in FIG. As a result, some of the hydrocarbons are not completely oxidized but are partially oxidized, that is, the hydrocarbons are reformed, thus producing a reducing intermediate. On the other hand, when the exhaust purification catalyst 13 having a weak oxidizing power is used, if the air-fuel ratio (A / F) in is periodically made rich as shown in FIG. 10, a large amount of hydrocarbons are not oxidized. The exhaust gas is simply exhausted from the exhaust purification catalyst 13, and the amount of hydrocarbons that are wasted is increased. Therefore, when the exhaust purification catalyst 13 having a weak oxidizing power is used, the required minimum air-fuel ratio X needs to be made lean.

  That is, it can be seen that the required minimum air-fuel ratio X needs to be lowered as the oxidizing power of the exhaust purification catalyst 13 becomes stronger, as shown in FIG. As described above, the required minimum air-fuel ratio X becomes lean or rich due to the oxidizing power of the exhaust purification catalyst 13, but the case where the required minimum air-fuel ratio X is rich will be described as an example. The amplitude of the change in the concentration of the inflowing hydrocarbon and the oscillation period of the concentration of the hydrocarbon flowing into the exhaust purification catalyst 13 will be described.

When the base air-fuel ratio (A / F) b increases, that is, when the oxygen concentration in the exhaust gas before the hydrocarbons are supplied increases, the air-fuel ratio (A / F) in is set to be equal to or less than the required minimum air-fuel ratio X. As a result, the amount of hydrocarbons necessary for the increase increases, and the amount of excess hydrocarbons that did not contribute to the production of the reducing intermediate also increases. In this case, in order to satisfactorily purify NO _X must oxidize the excess hydrocarbons as described above, therefore in order to satisfactorily purify NO _X amounts of higher hydrocarbons the amount of the surplus is large Oxygen is needed.

In this case, the amount of oxygen can be increased by increasing the oxygen concentration in the exhaust gas. To satisfactorily purify NO _X, therefore, it is necessary to increase the oxygen concentration in the exhaust gas after the hydrocarbon feed when the oxygen concentration in the exhaust gas before the hydrocarbons are fed is high. That is, it is necessary to increase the amplitude of the hydrocarbon concentration as the oxygen concentration in the exhaust gas before the hydrocarbon is supplied is higher.

FIG. 13 shows the relationship between the oxygen concentration in the exhaust gas before the hydrocarbon is supplied and the amplitude ΔH of the hydrocarbon concentration when the same NO _X purification rate is obtained. From FIG. 13, it can be seen that in order to obtain the same NO _x purification rate, the higher the oxygen concentration in the exhaust gas before the hydrocarbons are supplied, the more the amplitude ΔH of the hydrocarbon concentration needs to be increased. That is, it is necessary to increase the amplitude ΔH of the hydrocarbon concentration as the base air-fuel ratio (A / F) b is increased to obtain the same of the NO _X purification rate. In other words, in order to satisfactorily purify NO _X can be reduced the amplitude ΔH of the hydrocarbon concentration as the base air-fuel ratio (A / F) b becomes lower.

By the way, the base air-fuel ratio (A / F) b becomes the lowest during acceleration operation. At this time, if the amplitude ΔH of the hydrocarbon concentration is about 200 ppm, NO _X can be purified well. The base air-fuel ratio (A / F) b is usually larger than that during acceleration operation. Therefore, as shown in FIG. 14, if the hydrocarbon concentration amplitude ΔH is 200 ppm or more, a good NO _x purification rate can be obtained. become.

On the other hand, when the base air-fuel ratio (A / F) b is the highest is found that good NO _X purification rate when the amplitude ΔH of the hydrocarbon concentration of about 10000ppm is obtained. Therefore, in the present invention, the predetermined range of the amplitude of the hydrocarbon concentration is set to 200 ppm to 10,000 ppm.

In addition, when the vibration period ΔT of the hydrocarbon concentration becomes longer, the period during which the oxygen concentration around the active NO _X becomes higher after the hydrocarbon is supplied and then the hydrocarbon is supplied next becomes longer. In this case, when the vibration period ΔT of the hydrocarbon concentration becomes longer than about 5 seconds, the active NO _X begins to be absorbed in the basic layer 53 in the form of nitrate, and therefore the vibration period of the hydrocarbon concentration as shown in FIG. ΔT is longer than about 5 seconds, the NO _X purification rate falls. Therefore, the vibration period ΔT of the hydrocarbon concentration needs to be 5 seconds or less.

On the other hand, when the vibration period ΔT of the hydrocarbon concentration becomes approximately 0.3 seconds or less, the supplied hydrocarbon starts to accumulate on the exhaust gas flow surface of the exhaust purification catalyst 13, and therefore, as shown in FIG. NO _X purification rate decreases the vibration period ΔT approximately 0.3 seconds becomes below. Therefore, in the present invention, the vibration period of the hydrocarbon concentration is set to be between 0.3 seconds and 5 seconds.

  Now, in the embodiment according to the present invention, the amplitude ΔH and the vibration period ΔT of the hydrocarbon concentration correspond to the operating state of the engine by changing the supply amount and supply interval of one hydrocarbon from the hydrocarbon supply valve 15. It can be controlled to be an optimum value. The supply amount of hydrocarbons capable of obtaining the amplitude ΔH of the hydrocarbon concentration is stored in advance in the ROM 32 of the electronic control unit 30 in the form of a map as a function of the fuel injection amount Q of the fuel injection valve 3 and the engine speed N. ing. Further, the hydrocarbon concentration oscillation period ΔT, that is, the hydrocarbon supply interval can also be stored in advance in the ROM 32 in the form of a map in which the fuel injection amount Q of the fuel injection valve 3 and the engine speed N are functions.

Next, the NO _X purification method when the exhaust purification catalyst 13 is caused to function as a NO _X storage catalyst will be specifically described with reference to FIGS. 16 to 19. Hereinafter, the NO _X purification method in the case where the exhaust purification catalyst 13 functions as the NO _X storage catalyst is referred to as a second NO _X purification method.

In this second NO _X purification method, as shown in FIG. 16, the exhaust gas flowing into the exhaust purification catalyst 13 when the stored NO _X amount ΣNOX stored in the basic layer 53 exceeds a predetermined allowable amount MAX. The air-fuel ratio (A / F) in of the gas is temporarily made rich. When the air-fuel ratio (A / F) in of the exhaust gas is made rich, NO _X occluded in the basic layer 53 from the basic layer 53 when the air-fuel ratio (A / F) in of the exhaust gas is lean. It is released at once and reduced. Thereby, NO _X is purified.

Occluded amount of NO _X ΣNOX is calculated from the amount of NO _X discharged from the engine, for example. As a function of the injection quantity Q and engine speed N from the discharge amount of NO _X NOXA the fuel injection valve 3 in the embodiment according to the present invention, which is discharged from the engine per unit time, in advance in the form of a map as shown in FIG. 17 ROM 32 The stored NO _X amount ΣNOX is calculated from this exhausted NO _X amount NOXA. In this case, as described above, the period during which the air-fuel ratio (A / F) in of the exhaust gas is made rich is usually 1 minute or more.

In this second NO _X purification method, as shown in FIG. 18, in addition to the injection quantity Q of main injection as fuel for combustion from the fuel injection valve 3 into the combustion chamber 2, additional fuel as auxiliary injection is injected. By injecting at WR, the air-fuel ratio (A / F) in of the exhaust gas flowing into the exhaust purification catalyst 13 is made rich. The horizontal axis in FIG. 18 indicates the crank angle. This additional fuel WR is injected when it burns but does not appear as engine output, that is, slightly before ATDC 90 ° after compression top dead center. The injection amount WR of auxiliary injection is stored in advance in the ROM 32 in the form of a map as shown in FIG. 19 as a function of the injection amount Q from the fuel injection valve 3 and the engine speed N. Of course, the air-fuel ratio (A / F) in of the exhaust gas can be made rich by increasing the amount of hydrocarbons supplied from the hydrocarbon supply valve 15 in this case.

FIG. 20 shows a graph for explaining a NO _x purification method of the exhaust purification device during normal operation. The horizontal axis is the engine speed, and the vertical axis is the in-cylinder injection amount from the fuel injection valve 3. In the exhaust purification device of the present embodiment, a region for performing the first NO _X purification method and a region for performing the second NO _X purification method are determined based on the engine speed and the in-cylinder injection amount. . To perform purification of the NO _X at a high purification rate at the first NO _X removal method, it is preferable that the exhaust purification catalyst 13 is activated. That is, generation of active NO _X from NO _X flowing into the exhaust purification catalyst 13, partial oxidation of hydrocarbons, and in order to perform sufficiently the generation or the like of the reducing intermediates that exhaust purification catalyst is activated preferable. Further, it is known that the catalyst is activated when the temperature of the exhaust purification catalyst becomes high. For this reason, in the region where the engine speed is very low and the region where the in-cylinder injection amount is very low, NO _X is purified by the second NO _X purification method. Even in a region where the engine speed is relatively low and the in-cylinder injection amount is also relatively low, NO _X is purified by the second NO _X purification method. On the other hand, in other regions, NO _X is purified by the first NO _X purification method.

Next, in the first NO _X purification method in the present embodiment, the pressure of fuel supplied from the hydrocarbon supply valve and the amount of fuel necessary for NO _X purification will be described. FIG. 21 shows a graph for explaining the relationship between the pressure of the fuel supplied from the hydrocarbon supply valve and the concentration of hydrocarbons contained in the exhaust gas. The horizontal axis is time, and the vertical axis is the concentration of hydrocarbons contained in the exhaust gas. FIG. 21 shows changes in the hydrocarbon concentration when injected from the hydrocarbon feed valve 15 at a low pressure and changes in the hydrocarbon concentration when fuel is injected at a high pressure.

  The internal combustion engine in the present embodiment is a compression self-ignition type. During normal operation, combustion is performed in the combustion chamber 2 in a leaner state than the stoichiometric air-fuel ratio. For this reason, the exhaust gas is in an excess air state.

When hydrocarbons are supplied to the exhaust gas, the hydrocarbons are oxidized by excess air. Of concentration of hydrocarbons in the exhaust gas, hydrocarbons concentration WHC following areas indicated by the arrow 91 is not used for reduction of the NO _X to become completely oxidized. On the other hand, the hydrocarbons of the upper portion than the concentration WHC, functions as a reducing agent for purifying NO _X.

Here, the case where the fuel is supplied from the hydrocarbon supply valve 15 at a high pressure is compared with the case where the fuel is supplied at a low pressure. It can be seen that in order to obtain the same amount of reducing agent, it takes longer to inject fuel when injected at low pressure. For this reason, it can be seen that when the fuel is injected at a low pressure, the amount of fuel contained in the region of the concentration WHC or less increases. On the other hand, it can be seen that when the pressure is increased, the time during which the fuel is injected is shortened and the amount of fuel contained in the region of the concentration WHC or less is reduced. That is, the amount of fully oxidized not used for the reduction of the NO _X and hydrocarbon is reduced. In a region where the reducing agent is insufficient, the NO _x purification rate increases as the amount of reducing agent increases. For this reason, in the first NO _x purification method, it is preferable to increase the pressure of the fuel injected from the hydrocarbon supply valve 15.

By the way, as described above, when the amount of particulate matter accumulated in the particulate filter 14 exceeds a predetermined determination value, regeneration is performed to raise the particulate filter to a high temperature in an excess air state. By regenerating the particulate filter 14, the particulate matter can be oxidized and removed. FIG. 22 shows a graph for explaining the NO _x purification method when the particulate filter is regenerated. When performing the regeneration of the particulate filter filters, regardless of cylinder injection amount, to purify NO _X from the lower the engine speed range at purifying method of the first NO _X. That is, the first NO _x purification method is performed from a region where the exhaust purification catalyst 13 is relatively low temperature.

  When the exhaust purification catalyst 13 is in a relatively low temperature region, the ability to partially oxidize hydrocarbons or generate a reducing intermediate is reduced. When fuel is supplied from the hydrocarbon supply valve 15 at a high pressure in such a state, a part of the hydrocarbons may pass through the exhaust purification catalyst 13. The exhaust purification device of the present embodiment performs control to reduce the pressure of the fuel supplied from the hydrocarbon supply valve 15 in an operating state where hydrocarbons may pass through the exhaust purification catalyst 13.

  FIG. 23 shows a schematic diagram of a fuel supply device for an internal combustion engine in the present embodiment. The fuel discharged from the low-pressure fuel pump 61 is low-pressure fuel, and the fuel discharged from the high-pressure fuel pump 21 is high-pressure fuel. Then, very low pressure fuel leaking from the fuel pumps 21 and 61 and the common rail 20 is returned to the fuel tank 22.

  The fuel supplied to the fuel injection valve 3 is high pressure fuel. On the other hand, a part of the low-pressure fuel discharged from the low-pressure fuel pump 61 is supplied to the hydrocarbon supply valve 15. Of the low-pressure fuel discharged from the low-pressure fuel pump 61, excess fuel is returned to the fuel tank 22 after the pressure is reduced by the throttle member 75 such as an orifice. The fuel supply device of the present embodiment is formed so that the pressure of the fuel discharged from the low-pressure fuel pump 61 can be adjusted.

  FIG. 24 is a graph showing the relationship between the current supplied to the fuel pump and the pressure of the fuel discharged from the fuel pump. It can be seen that when the current supplied to the fuel pump 61 is increased, the pressure of the fuel discharged from the fuel pump 61 increases. In the present embodiment, the pressure of the fuel supplied from the fuel pump 61 to the hydrocarbon supply valve 15 is adjusted by adjusting the current supplied to the fuel pump 61. The current supplied to the fuel pump 61 is controlled by the electronic control unit 30. Referring to FIG. 21, in the present embodiment, the pressure of the fuel supplied from hydrocarbon supply valve 15 is lowered in an operating state where hydrocarbons may pass through exhaust purification catalyst 13. By this control, the maximum value of the hydrocarbon concentration of the exhaust gas becomes low, and the exhaust purification catalyst 13 can be prevented from slipping through.

Thus, the exhaust emission control device in the present embodiment is formed so that the pressure of hydrocarbons injected from the hydrocarbon supply valve 15 can be adjusted. However, when the pressure is lowered as described above, hydrocarbons that are completely oxidized increase and the fuel consumption increases. Therefore, the exhaust purification apparatus of the present embodiment performs control to reduce the amount of fuel consumed when performing the first NO _x purification method.

FIG. 25 shows a flowchart of control for setting the pressure of the fuel discharged from the low-pressure fuel pump when the first NO _X purification method in the present embodiment is performed. In other words, the flowchart of FIG. 25 is a control flowchart for setting the pressure of the fuel injected from the hydrocarbon supply valve 15.

In step 101, it is determined whether or not there is a request to supply fuel from the hydrocarbon supply valve 15. When there is a request to supply fuel, for example, when the regeneration of the particulate filter described above is performed, when the first NO _x purification method is performed, and the hydrocarbon supply valve 15 is prevented from being clogged. Therefore, the case where hydrocarbon is periodically injected from the hydrocarbon supply valve 15 is included. Furthermore, the case where control for releasing sulfur oxide (SO _x ) stored in the exhaust purification catalyst 13 is included is included.

  In step 101, when there is no request to supply fuel from the hydrocarbon supply valve 15, this control is repeated. If there is a request to supply fuel from the hydrocarbon supply valve 15 in step 101, the process proceeds to step 102.

In step 102, it is determined whether or not there is a request for the first NO _x purification method. That is, it is determined whether or not to implement the first NO _X purification method. The case where there is a request to implement the first NO _X purification method includes the case where the internal combustion engine is in a predetermined operating region during the above-described normal operation, the case where there is a request for regeneration of the particulate filter, and the like. Here, the temperature of the exhaust purification catalyst 13 is detected, and if it is lower than the predetermined temperature, control for prohibiting the first NO _x purification method can be performed. In addition to this, it is possible to perform control for implementing the first NO _X purification method when the amount of NO _X flowing into the exhaust purification catalyst is a predetermined value or more. Or, if _the NO _X storage amount is large in the exhaust purification catalyst 13, on an implementation of the first NO _X removal method, there is a possibility that NO _X that was stored is not completely purified is released at a time. Therefore, if greater than the determination value _the NO _X storage amount is a predetermined in the exhaust purification catalyst 13 can be carried out a control for prohibiting the first NO _X removal method. In this way, it is possible to determine whether or not to implement the first NO _x purification method by setting an arbitrary condition.

If there is no request for the first NO _x purification method in step 102, the process proceeds to step 103. In this case, NO _X is purified by the second NO _X purification method. In step 103, the pressure of the fuel supplied from the hydrocarbon supply valve 15 is set to a predetermined pressure. For example, it is set to a predetermined low pressure. In step 106, the current supplied to the low-pressure fuel pump 61 is calculated based on the set fuel pressure. The low-pressure fuel pump 61 is driven with the calculated current.

On the other hand, when the first NO _X purification method is requested in step 102, the routine proceeds to step 104. In step 104, it calculates a required amount of the reducing agent for purifying NO _X. Referring to FIG. 21, the required amount of reducing agent here corresponds to the amount of hydrocarbon in the region above the concentration WHC. Here, the supply interval of hydrocarbons can be set according to the operating state of the internal combustion engine. For example, the hydrocarbon supply interval can be set based on the time during which the reducing intermediate can be held or adsorbed on the surface of the basic layer 53. Alternatively, the hydrocarbon supply interval may be set based on the operating state of the internal combustion engine.

The NO _x purification rate of the exhaust purification catalyst 13 is determined in advance. The purification rate of the required NO _X, by multiplying the amount of the NO _X flowing from the engine body 1 to the exhaust purification catalyst 13, purification of the required NO _X is calculated. The amount of NO _x flowing into the exhaust purification catalyst 13 from the engine body 1 can be estimated from, for example, a map having a function of the engine speed and the load as a function. Then, based on the hydrocarbon feed interval, the amount of NO _x flowing from the engine body 1 into the exhaust purification catalyst 13 for one fuel injection of the hydrocarbon feed valve 15, that is, the required purification of NO _x . The amount can be calculated. Then, the required amount of reducing agent can be calculated based on the required NO _X purification amount. The required amount of reducing agent may be stored in the electronic control unit 30 in advance, for example, by creating a map using the engine speed and load as a function. The engine speed and load may be detected, and the required amount of reducing agent may be set based on the engine speed and load.

  Next, in step 105, the pressure of the fuel injected from the hydrocarbon supply valve 15 is set based on the set required amount of reducing agent.

FIG. 26 shows a graph of fuel consumption consumed when the first NO _x purification method is performed. The horizontal axis represents the pressure of fuel injected from the hydrocarbon supply valve 15. When performing the first NO _x purification method, the amount of fuel supplied from the hydrocarbon supply valve 15 can be reduced as the pressure increases. For this reason, the higher the pressure of the fuel injected from the hydrocarbon supply valve 15, the smaller the amount of fuel consumed by fuel injection from the hydrocarbon supply valve 15.

  On the other hand, the low-pressure fuel pump 61 of the present embodiment is driven by electricity. When the pressure of the fuel discharged from the low-pressure fuel pump 61 is increased, the power consumption increases. The electric power for driving the fuel pump 61 is generated by generating electric power using the rotational force output from the engine body 1. For this reason, when the power consumption of the fuel pump 61 increases, the fuel consumption in the combustion chamber 2 increases. Thus, the fuel consumption for driving the fuel pump 61 increases as the pressure of the fuel injected from the hydrocarbon supply valve 15 increases.

  FIG. 26 shows a total fuel consumption amount obtained by adding the fuel consumption amount due to fuel injection from the hydrocarbon supply valve 15 and the fuel consumption amount due to driving of the fuel pump 61. It can be seen that the total fuel consumption is minimized at the pressure Pa of the fuel injected from the hydrocarbon feed valve 15. For this purpose, referring to FIG. 25, in step 105, the pressure of the fuel injected from the hydrocarbon supply valve 15 is set to the pressure Pa.

  Next, in step 106, the low-pressure fuel pump 61 is driven so that the pressure of the fuel injected from the hydrocarbon supply valve 15 becomes the pressure Pa. That is, the current at which the discharge pressure of the low-pressure fuel pump 61 becomes the pressure Pa is set, and the fuel pump 61 is driven with the set current.

As described above, the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment is configured to reduce the amount of fuel consumed for driving the fuel supply device that supplies hydrocarbons to the engine exhaust passage and the fuel injected from the hydrocarbon supply valve 15. The pressure of the fuel supplied to the hydrocarbon supply valve 15 is set based on the total fuel consumption with the fuel consumption. This control makes it possible to reduce fuel consumption while maintaining a high NO _x purification rate.

The control for setting the pressure of the fuel injected from the hydrocarbon supply valve 15 of the present embodiment is not limited to the regeneration of the particulates, but is an arbitrary case where NO _x is purified by the first NO _x purification method. Can be applied to.

  Note that regarding the passing of hydrocarbons in the exhaust purification catalyst 13, an upper limit of the concentration of hydrocarbons contained in the exhaust gas may be set based on the temperature of the exhaust purification catalyst 13. For example, the upper limit of the hydrocarbon concentration or the upper limit of the pressure of the fuel injected from the hydrocarbon supply valve 15 can be determined in advance using the engine speed and the load as a function. When the pressure of the low-pressure fuel pump 61 set by the above control exceeds the upper limit of the pressure based on the passage of hydrocarbon, the hydrocarbon is supplied at the upper limit of the pressure based on the passage of hydrocarbon. It doesn't matter.

Further, when the particulate filter 14 is regenerated, it is necessary to raise the temperature of the exhaust gas so that the temperature of the particulate filter 14 is increased. For this reason, hydrocarbons supplied to the exhaust purification catalyst 13 may be increased. By causing an oxidation reaction of hydrocarbons inside the exhaust purification catalyst 13, the temperature of the exhaust gas rises. The amount of hydrocarbons supplied to raise the temperature of the exhaust gas can be calculated in consideration of the amount of hydrocarbons that are completely oxidized in the above-described method for purifying NO _x .

  The fuel supply device in the present embodiment is formed such that the pressure of fuel injected from the hydrocarbon supply valve is variably changed by changing the discharge pressure of the fuel pump. Any fuel supply device that makes the pressure of the fuel injected from the fuel variable can be employed. For example, the fuel supply device may be formed so that the pressure of the fuel supplied to the hydrocarbon supply valve can be adjusted by disposing a variable flow nozzle or the like in the flow path for supplying fuel to the hydrocarbon supply valve. Absent.

  In addition, the above-mentioned control can change the order of steps suitably within the range which has each effect | action and function. In the respective drawings described above, the same or equivalent parts are denoted by the same reference numerals. In addition, said embodiment is an illustration and does not limit invention. Further, in the embodiment, changes in the implementation shown in the claims are included.

DESCRIPTION OF SYMBOLS 1 Engine body 2 Combustion chamber 3 Fuel injection valve 13 Exhaust purification catalyst 14 Particulate filter 15 Hydrocarbon supply valve 21, 61 Fuel pump 30 Electronic control unit 50 Catalyst support 51, 52 Precious metal catalyst 53 Basic layer 54 Exhaust gas distribution surface portion 62 Fuel chamber 63 Fuel pressure sensor

Claims (1)

A hydrocarbon supply valve for supplying hydrocarbons is arranged in the engine exhaust passage, and NO _X contained in the exhaust gas reacts with the reformed hydrocarbon in the engine exhaust passage downstream of the hydrocarbon supply valve. An exhaust gas purification catalyst is disposed, a noble metal catalyst is supported on the exhaust gas flow surface of the exhaust gas purification catalyst, and a basic exhaust gas flow surface portion is formed around the noble metal catalyst,
The exhaust purification catalyst reduces NO _X contained in the exhaust gas when the concentration of hydrocarbons flowing into the exhaust purification catalyst is vibrated with an amplitude within a predetermined range and a period within the predetermined range. And has the property of increasing the amount of NO _x stored in the exhaust gas when the vibration period of the hydrocarbon concentration is longer than the predetermined range,
A fuel supply device for supplying fuel of the internal combustion engine to the hydrocarbon supply valve;
The fuel supply device is formed so that the pressure of the fuel supplied to the hydrocarbon supply valve can be adjusted,
The amount of hydrocarbons supplied from the hydrocarbon supply valve is controlled so that the amplitude of the change in the concentration of hydrocarbons flowing into the exhaust purification catalyst during engine operation becomes an amplitude within the predetermined range, and the exhaust purification catalyst Is configured to carry out operation control in which the hydrocarbon supply interval from the hydrocarbon supply valve is controlled so that the concentration of the hydrocarbon flowing into the cylinder vibrates with a period within a predetermined range.
When performing the operation control, based on the total fuel consumption of the fuel consumption for driving the fuel supply device and the fuel consumption of the fuel injected from the hydrocarbon supply valve by the operation control, An exhaust purification device for an internal combustion engine, characterized in that the pressure of fuel supplied to the hydrocarbon supply valve is set.

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