JP2009293572A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure a high NO<SB>X</SB>storage rate of an NO<SB>X</SB>storage reduction catalyst. <P>SOLUTION: The NO<SB>X</SB>storage reduction catalyst 16 is arranged in an engine exhaust passage, and a particulate filter 14 is arranged in the upstream of the NO<SB>X</SB>storage reduction catalyst 16. A temperature range where the NO<SB>X</SB>storage rate to the NO<SB>X</SB>storage reduction catalyst 16 is equal to or more than an allowable storage rate RX exists in a temperature TC of the NO<SB>X</SB>storage reduction catalyst 16, and when the temperature TC of the NO<SB>X</SB>storage reduction catalyst 16 is lower than a lower limit temperature TC<SB>0</SB>of the temperature range, ozone is supplied from an ozone supply device 17 into the engine exhaust passage, and NO in exhaust gas flowing into the NO<SB>X</SB>storage reduction catalyst 16 is converted to NO<SB>2</SB>. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

An NO _x storage catalyst for storing NO _x contained in the exhaust gas is disposed in the engine exhaust passage, and particulates contained in the exhaust gas are collected in the engine exhaust passage upstream of the NO _x storage catalyst. An internal combustion engine in which a particulate filter is disposed and ozone is supplied upstream of the particulate filter and between the particulate filter and the NO _x storage catalyst is known (see, for example, Patent Document 1).

In this internal combustion engine, the particulates accumulated on the particulate filter are burned and removed by supplying ozone upstream of the particulate filter, and further, the particulates are supplied by supplying ozone between the particulate filter and the NO _x storage catalyst. NO in the exhaust gas flowing out from the filter by converting to NO ₂ is the NO _x in the exhaust gas so as to better occluded in _the NO _x storage catalyst.
JP 2005-538295 A

Meanwhile as _the NO _x storage catalyst, releasing the NO _x air-fuel ratio of the exhaust gas which is occluded when the air-fuel ratio of the exhaust gas by occluding NO _x contained in the exhaust gas flowing becomes the stoichiometric air-fuel ratio or rich when the lean flowing when using _the NO _x storage catalyst, effectively increasing the storage action of the NO _x by the supply of ozone it is necessary to control the supply of ozone in accordance with the temperature of the NO _x storage catalyst. However, the above-mentioned internal combustion engine makes no suggestion about such ozone supply control.
An object of the present invention is to provide an exhaust purification device for an internal combustion engine that can effectively enhance the NO _x storage function.

According to the present invention, in the engine exhaust passage, when the air-fuel ratio of the exhaust gas flowing into the lean air-fuel ratio of the exhaust gas by occluding NO _x contained in the exhaust gas flowing becomes the stoichiometric air-fuel ratio or rich storage in the NO _x arranged _the NO _x storage catalyst to release, the NO _x storage catalytic internal combustion engine which is arranged a particulate filter for trapping particulate matter upstream contained in the exhaust gas in the engine exhaust passage, Patti filter and is provided with an ozone supplying device for supplying ozone to the engine exhaust passage between _the NO _x storage catalyst, the temperature of the NO _x storage catalytic NO adsorption rate is predetermined to _the NO _x storage catalyst When there is a temperature range that exceeds the allowable storage rate and the temperature of the NO _x storage catalyst is lower than the lower limit temperature of this temperature range, the ozone supply device enters the engine exhaust passage. When ozone is supplied and NO in the exhaust gas flowing into the NO _x storage catalyst is converted into NO ₂ , ozone supply from the ozone supply device is performed when the temperature of the NO _x storage catalyst is higher than the lower limit temperature of this temperature range. I try to stop.

By supplying ozone when low NO absorbing rate increases the occlusion rate of the NO _x, when NO adsorption rate is high, i.e. ozone by supplying NO _x storage rate is high ozone when unnecessary to stop the supply of the ozone Thus, it is possible to ensure a good storage effect of NO _x while avoiding unnecessary consumption.

FIG. 1 shows an overall view of a compression ignition type internal combustion engine.
Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electronically controlled fuel injection valve for injecting fuel into each combustion chamber 2, 4 is an intake manifold, and 5 is an exhaust manifold. Respectively. The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 9 via the intake air amount detector 8. A throttle valve 10 driven by a step motor is disposed in the intake duct 6, and a cooling device 11 for cooling intake air flowing through the intake duct 6 is disposed around the intake duct 6. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 11, and the intake air is cooled by the engine cooling water.

On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7, and the outlet of the exhaust turbine 7 b is connected to the inlet of the oxidation catalyst 12. The outlet of the oxidation catalyst 12 is connected to a particulate filter 14 for collecting particulate matter contained in the exhaust gas, i.e., particulates, through an exhaust pipe 13, and the outlet of the particulate filter 14 is connected to the exhaust pipe. 15 is connected to the inlet of the NO _x storage catalyst 16.

As shown in FIG. 1, an ozone supply device 17 is provided in the embodiment according to the present invention. The ozone supply device 17 includes an air pump 18, an ozone generator 19 that generates ozone by applying a high voltage, for example, and an ozone flow rate control disposed in an ozone supply pipe 20 that extends from the ozone generator 19 to the exhaust pipe 15. And a valve 21. The outside air is sent into the ozone generator 19 by the air pump 18, and the ozone generated in the ozone generator 19 is passed through the ozone supply pipe 20 and the ozone flow rate control valve 21 between the particulate filter 14 and the NO _x storage catalyst 16. Supplied in between.

  The exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 22, and an electronically controlled EGR control valve 23 is disposed in the EGR passage 22. A cooling device 24 for cooling the EGR gas flowing in the EGR passage 22 is disposed around the EGR passage 22. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 24, and the EGR gas is cooled by the engine cooling water. Further, a fuel supply valve 25 for supplying a fuel made of hydrocarbons, for example, light oil, in the exhaust gas is disposed in the exhaust manifold 5.

  On the other hand, each fuel injection valve 3 is connected to a common rail 27 via a fuel supply pipe 26, and this common rail 27 is connected to a fuel tank 29 via an electronically controlled variable discharge pump 28. The fuel stored in the fuel tank 29 is supplied into the common rail 27 by the fuel pump 28, and the fuel supplied into the common rail 27 is supplied to the fuel injection valve 3 through each fuel supply pipe 26.

The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. 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. It comprises. A temperature sensor 39 for detecting the temperature of the oxidation catalyst 12 is attached to the oxidation catalyst 12, and a temperature sensor 40 for detecting the temperature of the particulate filter 14 is attached to the particulate filter 14. Further, a differential pressure sensor 41 for detecting the differential pressure across the particulate filter 14 is attached to the particulate filter 14. Also, the _the NO _x storage catalyst 16 the temperature sensor 42 for detecting the temperature of the NO _x storage catalyst 16 is mounted. The output signals of these temperature sensors 39, 40, 42, differential pressure sensor 41 and intake air amount detector 8 are input to the input port 35 via corresponding AD converters 37, respectively.

  A load sensor 44 that generates an output voltage proportional to the depression amount L of the accelerator pedal 43 is connected to the accelerator pedal 43, and the output voltage of the load sensor 44 is input to the input port 35 via the corresponding AD converter 37. Is done. Further, a crank angle sensor 45 that generates an output pulse every time the crankshaft rotates, for example, 15 ° is connected to the input port 35. On the other hand, the output port 36 is connected through a corresponding drive circuit 38 to the fuel injection valve 3, the step motor for driving the throttle valve 10, the air pump 18, the ozone generator 19, the ozone flow rate control valve 21, the EGR control valve 23, and the fuel pump 28. Connected to.

The oxidation catalyst 12 shown in FIG. 1 carries a noble metal catalyst such as platinum. On the other hand, the particulate filter 14 may be a particulate filter that does not carry a catalyst, or may be a particulate filter that carries a precious metal catalyst such as platinum. Further, a catalyst carrier made of alumina, for example, is supported on the base of the NO _x storage catalyst 16, and FIG. 2 schematically shows a cross section of the surface portion of the catalyst carrier 48. As shown in FIG. 2, a noble metal catalyst 46 is dispersed and supported on the surface of the catalyst carrier 48, and a layer of NO _x absorbent 47 is formed on the surface of the catalyst carrier 48.

In the embodiment according to the present invention, platinum Pt is used as the noble metal catalyst 46, and the constituents of the NO _x absorbent 47 are, for example, alkali metals such as potassium K, sodium Na, cesium Cs, barium Ba, calcium Ca. At least one selected from alkaline earths such as these, lanthanum La, and rare earths such as yttrium Y is used.

When the ratio of air and fuel (hydrocarbon) supplied to the engine intake passage, the combustion chamber 2 and the exhaust passage upstream of the NO _x storage catalyst 16 is referred to as the air-fuel ratio of the exhaust gas, the NO _x absorbent 47 air absorbs NO _x when the lean, the oxygen concentration in the exhaust gas performs the absorbing and releasing action of the NO _x that releases NO _x absorbed to decrease.

That is, the case where barium Ba is used as a component constituting the NO _x absorbent 47 will be described as an example. When the air-fuel ratio of the exhaust gas is lean, that is, when the oxygen concentration in the exhaust gas is high, it is contained in the exhaust gas. NO is oxidized to NO ₂ becomes on the platinum Pt46 as shown in FIG. 2, then nitrate ions NO ₃ while being absorbed in the NO _x absorbent 47 and bonds with the barium carbonate BaCO ₃ ^- absorption of NO _x in the form of It diffuses into the agent 47. Further, as shown in FIG. 2, NO ₂ contained in the exhaust gas is directly absorbed into the NO _x absorbent 47 and combined with barium carbonate BaCO _3, and in the form of nitrate ions NO ₃ ⁻ , the NO _x absorbent 47. Diffuses in. In this way, the NO _x absorption of NO _x capacity NO _x unless saturation of the absorbent 47 is absorbed in the NO _x absorbent 47.

On the other hand, if the air-fuel ratio of the exhaust gas is made rich or stoichiometric by supplying additional fuel into the combustion chamber 2 or by supplying fuel from the fuel supply valve 25, the oxygen concentration in the exhaust gas decreases. proceeds to ^{_{- (→ NO 2 NO 3)}} , thus to _the NO _x absorbent in the 47 nitrate ions NO ₃ by ^- reaction reverse to be released from _the NO _x absorbent 47 in the form of NO _2. Next, the released NO _x is reduced by unburned HC and CO contained in the exhaust gas.

In this way, when the air-fuel ratio of the exhaust gas is lean, that is, when combustion is performed under the lean air-fuel ratio, NO _x in the exhaust gas is absorbed into the NO _x absorbent 47. However becomes saturated the absorption of NO _x capacity of the NO _x absorbent 47 during the combustion of the fuel under a lean air-fuel ratio is continued, no longer able to absorb NO _x by _the NO _x absorbent 47 and thus End up. Therefore, in the embodiment according to the present invention, the air-fuel ratio of the exhaust gas is supplied by supplying additional fuel into the combustion chamber 2 before the absorption capacity of the NO _x absorbent 47 is saturated or by supplying fuel from the fuel supply valve 25. temporarily made rich and thereby so that to release the NO _x from the NO _x absorbent 47.

Next, FIG. 3 will be described. The solid line represents the NO storage ratio indicating the ratio of NO stored in the NO _x storage catalyst 16 out of the total NO contained in the exhaust gas, and the broken line represents the exhaust gas in the exhaust gas. The NO ₂ occlusion rate indicating the ratio of NO ₂ occluded by the NO _x occlusion catalyst 16 in the total NO ₂ contained in the NO ₂ is shown. In FIG. 3, the horizontal axis TC indicates the temperature of the NO _x storage catalyst 16.

Now, as shown in FIG. 2, in order for NO contained in the exhaust gas to be absorbed by the NO _x absorbent 47, it is necessary to oxidize NO to NO ₂ by the noble metal catalyst 45. However oxidizing power of the noble metal catalyst 45 decreases as the temperature TC of the NO _x storage catalyst 16 is lowered, NO occlusion rate decreases the thus temperature TC of the NO _x storage catalyst 16 becomes lower. In the embodiment shown in FIG. 3, when the temperature TC of the NO _x storage catalyst 16 becomes lower than about 300 ° C., the NO storage rate decreases.

On the other hand, NO ₂ contained in the exhaust gas is absorbed in the NO _x absorbent 47 regardless of the oxidizing power of the noble metal catalyst 45, and therefore, the NO ₂ occlusion rate of the NO _x occlusion catalyst 16 is as shown in FIG. Even if the temperature TC is lowered, it is kept high. Therefore, when the temperature TC of the NO _x storage catalyst 16 is low, a high NO _x storage rate can be secured by converting NO occupying most of the exhaust gas into NO ₂ . In this case, when ozone is supplied into the exhaust gas, NO in the exhaust gas is converted to NO ₂ . Accordingly, in the present invention, ozone is supplied into the exhaust gas when NO in the exhaust gas is to be converted to NO ₂ .

On the other hand, when the temperature TC of the NO _x storage catalyst 16 is increased, NO _x is spontaneously released from the NO _x storage catalyst 16, and therefore both the NO storage rate and the NO ₂ storage rate are lowered as shown in FIG. In this case, in order to ensure a good NO _x purification rate, it is necessary to maintain a higher NO storage rate and NO ₂ storage rate than the allowable storage rate during engine operation. In FIG. 3, RX indicates the allowable storage rate. In the embodiment shown in FIG. 3, the allowable storage rate RX is 80% of the peak value of the NO storage rate.

As can be seen from FIG. 3, when the NO storage rate is higher than the allowable storage rate RX, a sufficiently high NO _x storage rate can be obtained without supplying ozone. On the other hand, there are a temperature range of NO adsorption rate to _the NO _x storage catalyst 16 is the predetermined allowable occlusion rate RX than the temperature of the NO _x storage catalyst 16 as can be seen from Fig. 3, NO _x When the temperature TC of the storage catalyst 16 becomes lower than the lower limit temperature TC ₀ of this temperature range, the NO storage rate decreases.

Therefore, in the present invention, when the temperature TC of the NO _x storage catalyst 16 becomes lower than the lower limit temperature TC ₀ of this temperature range, ozone is supplied from the ozone supply device 17 into the engine exhaust passage and flows into the NO _x storage catalyst 16. NO in the exhaust gas is converted into NO ₂ , and when the temperature TC of the NO _x storage catalyst 16 is higher than the lower limit temperature TC ₀ of this temperature range, the supply of ozone from the ozone supply device 17 is stopped. .

By the way, when supplying ozone from the ozone supply device 17, even if an unnecessarily large amount of ozone is supplied, there is no point in consuming wasteful energy necessary for generating ozone, and supplying the required amount of ozone. It is preferable to do. Therefore, in the present invention, a calculation means for calculating the amount of NO in the exhaust gas flowing out from the particulate filter 14 is provided. When the temperature TC of the NO _x storage catalyst 16 is lower than the lower limit temperature TC ₀ , the particulate filter The amount of ozone required to convert NO in the exhaust gas flowing out from 14 into NO ₂ is calculated, and this calculated amount of ozone is supplied.

Next, an example of a method for calculating the amount of NO in the exhaust gas will be described. Generally speaking, the amount of NO discharged from the engine is larger than the amount of NO ₂ , and these NO amount and NO ₂ amount are determined accordingly when the operating state of the engine is determined. Therefore, in the embodiment according to the present invention, the NO amount NOXA discharged from the engine per unit time is previously stored in the ROM 32 in the form of a map as shown in FIG. 4A as a function of the required torque TQ of the engine and the engine speed N. are stored, in advance ROM32 in the memory in the form of a map as shown in FIG. 4 (B) as a function of the NO ₂ amount NOXB is the engine required torque TQ and engine speed N which is discharged from the engine per unit time Has been.

On the other hand, the oxidation action for NO can be performed not only by the oxidation catalyst 12 but also by the particulate filter 14, but in the example shown in FIG. 1, the oxidation action for NO is performed only by the oxidation catalyst 12. Therefore, in the example shown in FIG. 1, NO is converted to NO ₂ in the oxidation catalyst 12, and FIG. 5A shows the NO ₂ conversion rate R from NO to NO ₂ by the oxidation catalyst 12. As shown in FIG. 5A, the NO ₂ conversion rate R peaks when the temperature TB of the oxidation catalyst 12 is between approximately 300 ° C. and approximately 400 ° C.

The peak value of the NO ₂ conversion rate R depends on the platinum loading amount of the oxidation catalyst 12, and in the embodiment according to the present invention, the platinum loading amount is set so that the peak value of the NO ₂ conversion rate R is approximately 0.5. Has been. The NO amount in the exhaust gas flowing into the oxidation catalyst 12 per unit time is NOXA shown in FIG. 4A. Therefore, when this NOXA is multiplied by the NO ₂ conversion rate R, it is generated in the oxidation catalyst 12 per unit time. An amount of NO ₂ is obtained.

On the other hand, in the example shown in FIG. 1, NO ₂ is reduced on the particulate filter 14 and converted to NO. The NO conversion rate RR from NO ₂ to NO is shown in FIG. As can be seen from FIG. 5B, this NO conversion rate RR is a function of the temperature TD of the particulate filter 14, and the NO conversion rate RR increases as the temperature TD of the particulate filter 14 increases.

As described above, the NO amount discharged from the engine per unit time is NOXA, the NO ₂ amount discharged from the engine per unit time is NOXB, and the NO ₂ conversion rate in the oxidation catalyst 12 is R. The amount of NO flowing into the curative filter 14 per unit time is represented by NOXA · (1-R), and the amount of NO ₂ flowing into the particulate filter 14 per unit time is represented by NOXA · R + NOXB. On the other hand, NO ₂ flowing into the particulate filter 14 is converted into NO with the NO conversion rate RR shown in FIG. 5B, so the NO amount WNO in the exhaust gas flowing out from the particulate filter per unit time is It is expressed by the following formula.
WNO = NOXA. (1-R) + RR. (NOXA.R + NOXB)

On the other hand, in the embodiment according to the present invention, NO and NO ₂ contained in the exhaust gas, that is, NO _x is occluded in the NO _x occlusion catalyst 16, and when this NO _x occlusion amount exceeds the allowable amount, the NO _x occlusion catalyst. The air-fuel ratio of the exhaust gas flowing into the NO _x storage catalyst 16 to release NO _x from the engine 16 is made rich. In this case, in a specific example according to the present invention, calculation means for calculating the amount of NO _{x in} the exhaust gas flowing out from the particulate filter 14 is provided, and an integrated value of this NO _x amount is predetermined. In order to release NO _x from the NO _x storage catalyst 16 when the allowable amount is exceeded, the air-fuel ratio of the exhaust gas flowing into the NO _x storage catalyst 16 is made rich.

Next, the exhaust purification control routine shown in FIG. 5 will be described. This routine is executed by interruption every predetermined time.
Referring to FIG. 5, first, at step 50, the NOx emission amount NOXA per unit time is calculated from the map shown in FIG. 4A, and then at step 51, the emission per unit time is calculated from the map shown in FIG. 4B. The NO ₂ amount NOXB is calculated.

  Next, at step 52, it is judged if the regeneration condition for the particulate filter 14 is satisfied. When the differential pressure across the particulate filter 14 detected by the differential pressure sensor 41 exceeds a predetermined differential pressure, it is determined that the regeneration condition for the particulate filter 14 is satisfied, and then the longitudinal difference between the particulate filters 14 is determined. The regeneration condition of the particulate filter 14 is satisfied until the pressure becomes equal to or lower than a predetermined differential pressure or until a certain time elapses, that is, until the particulates accumulated on the particulate filter 14 are removed by combustion. To be judged. When the regeneration condition for the particulate filter 14 is not satisfied, the routine proceeds to step 53.

In step 53, it is judged if the temperature TC of the NO _x storage catalyst 16 is lower than the lower limit temperature TC ₀ shown in FIG. When TC <TC _0, the routine proceeds to step 54, where the NO ₂ conversion rate R is calculated from the relationship shown in FIG. 5A, and the NO conversion rate RR is calculated from the relationship shown in FIG. 5B. Next, at step 55, the NO amount WNO in the exhaust gas discharged per unit time from the particulate filter 14 is calculated based on the following equation.
WNO = NOXA. (1-R) + RR. (NOXA.R + NOXB)
Next, at step 56, the ozone amount Q to be supplied is calculated by multiplying the NO amount WNO by the proportional constant K, and the calculated amount Q of ozone is supplied upstream of the NO _x storage catalyst 16.

Next, at step 57, a NO _x releasing process from the NO _x storage catalyst 16 is performed. A routine for performing this NO _x releasing process is shown in FIG. This routine will be described later. On the other hand, when it is judged at step 53 that TC ≧ TC ₀ , the routine jumps to step 57. Therefore, the supply of ozone is stopped at this time.

On the other hand, when it is determined in step 52 that the regeneration condition of the particulate filter 14 is satisfied, the routine proceeds to step 58 where fuel is supplied by supplying additional fuel into the combustion chamber 2 or from the fuel supply valve 25. Thus, the temperature raising control is performed to raise the temperature of the particulate filter 14 to about 600 ° C., and then the routine proceeds to step 53, where the temperature TC of the NO _x storage catalyst 16 is lower than the lower limit temperature TC ₀ shown in FIG. Is determined.

When the temperature rise control is started and the temperature of the particulate filter 14 rises, the temperature of the NO _x storage catalyst 16 rises accordingly, and while the temperature of the particulate filter 14 rises toward 600 ° C., NO _x The temperature TC of the storage catalyst 16 becomes higher than the lower limit temperature TC ₀ shown in FIG. When it is determined in step 53 that TC ≧ TC ₀ , the supply of ozone is stopped, so that the supply of ozone is stopped during the temperature rise of the particulate filter 14 and is kept stopped during the temperature rise control period. Become.

Referring now to _the NO _x releasing processing routine shown in FIG. 7, the discharge amount of NO NOXA and discharge amount of NO _x NOXB is _the exhaust NO _x which are respectively calculated from the map shown in step 70 FIG. 4 (A) and (B) Is added to the integrated value ΣNOX. Then whether the integrated value ΣNOX of step 71 exhaust NO _x has exceeded the allowable value MAX or not. When the integrated value ΣNOX of the exhausted NO _x exceeds the allowable value MAX, the routine proceeds to step 72 where it is judged if the temperature TC of the NO _x storage catalyst 16 is higher than the lower limit temperature TC ₀ shown in FIG.

When TC ≦ TC _0, the routine proceeds to step 73 where temperature increase control is performed to increase the temperature TC of the NO _x storage catalyst 16 by supplying additional fuel into the combustion chamber 2 or by supplying fuel from the fuel supply valve 25. Is done. Next, when it is judged at step 72 that TC> TC ₀ , the routine proceeds to step 74 where the additional fuel is supplied into the combustion chamber 2 or the fuel is supplied from the fuel supply valve 25 to thereby store the NO _x storage catalyst 16. Rich control is performed to temporarily enrich the air-fuel ratio of the exhaust gas flowing into the engine. Next, at step 75, ΣNOX is cleared.

  FIG. 8 shows a second embodiment in which ozone can also be supplied upstream of the particulate filter 14. In this second embodiment, the ozone generator 19 is supplied to the exhaust pipe 13 between the oxidation catalyst 12 and the particulate filter 14 via the second ozone supply pipe 76 in order to supply ozone also upstream of the particulate filter 14. The second ozone flow rate control valve 77 is arranged in the second ozone supply pipe 76.

When ozone O ₃ or NO ₂ is contained in the exhaust gas, the oxidation reaction of the particulates deposited on the particulate filter 14 is promoted, so that the particulates deposited on the particulate filter 14 are burned and removed. That is, in order to regenerate the particulate filter 14, it is preferable to increase the amount of O ₃ or NO _{2 in} the exhaust gas as much as possible. Therefore, in the second embodiment, ozone is supplied also from the ozone supply device 17 to the upstream of the particulate filter 14 during regeneration of the particulate filter 14.

By the way, in order to promote the oxidation reaction of the particulates deposited on the particulate filter 14, it is preferable that the amount of ozone is larger as long as it does not become excessive. Therefore, in this second embodiment, the particulate filter 14 should be regenerated. Sometimes as much ozone as possible is supplied upstream of the particulate filter 14 from the ozone supply device 17. However, ozone does not exist stably unless the temperature TD of the particulate filter 14 is equal to or lower than a constant temperature TD _{0 of} about 300 ° C., and ozone is decomposed when TD> TD ₀ . Therefore, in this second embodiment, when the particulate filter 14 is regenerated, the temperature of the particulate filter 14 is controlled to be kept below 300 ° C. as much as possible, unlike the first embodiment. Absent.

On the other hand, in the second embodiment, NO ₂ is converted to NO on the particulate filter 14 during regeneration of the particulate filter 14. Therefore, in the second embodiment, during regeneration of the particulate filter 14, an amount of ozone necessary for converting NO in the exhaust gas flowing out from the particulate filter 14 into NO ₂ is supplied from the ozone supply pipe 20 to the particulate filter 14. Continue to be supplied downstream.

FIG. 9 shows an exhaust purification control routine for executing the second embodiment. This routine is also executed by interruption every predetermined time.
Referring to FIG. 9, first, at step 80, the NOx emission amount NOXA per unit time is calculated from the map shown in FIG. 4A, and then at step 81, the emission per unit time is calculated from the map shown in FIG. 4B. The NO ₂ amount NOXB is calculated.

  Next, at step 82, it is judged if the regeneration condition for the particulate filter 14 is satisfied. As described above, when the differential pressure across the particulate filter 14 detected by the differential pressure sensor 41 exceeds a predetermined differential pressure, it is determined that the regeneration condition for the particulate filter 14 is satisfied, and then the particulate filter The regeneration condition of the particulate filter 14 is satisfied until the differential pressure before and after the pressure drops below a predetermined differential pressure or until a certain time has elapsed, that is, until the particulate accumulated on the particulate filter 14 is removed by combustion. It is judged that When the regeneration condition for the particulate filter 14 is not satisfied, the routine proceeds to step 83.

In step 83, it is judged if the temperature TC of the NO _x storage catalyst 16 is lower than the lower limit temperature TC ₀ shown in FIG. When TC <TC _0, the routine proceeds to step 84, where the NO ₂ conversion rate R is calculated from the relationship shown in FIG. 5A, and the NO conversion rate RR is calculated from the relationship shown in FIG. 5B. Next, at step 85, the NO amount WNO in the exhaust gas discharged per unit time from the particulate filter 14 is calculated based on the following equation.
WNO = NOXA. (1-R) + RR. (NOXA.R + NOXB)
Next, at step 86, the ozone amount Q to be supplied is calculated by multiplying the NO amount WNO by a proportional constant K, and this calculated amount Q of ozone is supplied from the ozone supply pipe 20 to the upstream of the NO _x storage catalyst 16. Is done.

Next, at step 87 NO _x releasing processing from _the NO _x storage catalyst 16 shown in FIG. 7 is performed. On the other hand, when it is determined in step 83 that TC ≧ TC ₀ , the routine jumps to step 87. Therefore, the supply of ozone is stopped at this time.

On the other hand, when it is determined in step 82 that the regeneration condition of the particulate filter 14 is satisfied, the routine proceeds to step 88, where it is determined whether or not the temperature TD of the particulate filter 14 is lower than a certain temperature TD ₀ , that is, 300 ° C. Determined. When TD <TD _0, the routine proceeds to step 89 where as much ozone Qa as possible is supplied from the second ozone supply pipe 76 to the upstream side of the particulate filter 14. Next, the routine proceeds to step 83. At this time, conversion from NO ₂ to NO in the particulate filter 14 is suppressed as compared with the case where ozone is not supplied upstream of the particulate filter 14, and therefore the NO conversion rate shown in FIG. A value obtained by multiplying the conversion rate RR by a predetermined reduction rate S (0 <S <1.0) can also be used.

On the other hand, when it is determined at step 88 that TD ≧ TD ₀ , the routine proceeds to step 90 where the supply of ozone Qa from the second ozone supply pipe 76 is stopped. Next, the routine proceeds to step 83. That is, in the second embodiment, even when the particulate filter 14 is being regenerated, the supply of ozone from the second ozone supply pipe 76 is stopped when TD ≧ TD ₀ .

1 is an overall view of a compression ignition type internal combustion engine. 2 is a cross-sectional view of a surface portion of a catalyst carrier of an NO _x storage catalyst. FIG. Is a diagram illustrating a NO adsorption rate and NO ₂ adsorption rate. It is a figure which shows the map etc. of NO amount NOXA discharged | emitted per unit time from an engine. Is a diagram illustrating a NO ₂ conversion rate R and NO conversion rate RR. It is a flowchart for performing exhaust purification control. Is a flow chart for executing the NO _x releasing processing. It is a general view which shows another Example of a compression ignition type internal combustion engine. It is a flowchart for performing exhaust purification control.

Explanation of symbols

4 intake manifold 5 exhaust manifold 7 exhaust turbocharger 12 oxidation catalyst 14 particulate filter 16 NO _x storage catalyst 17 ozone supply device 18 air pump 19 ozone generator 20,76 ozone supply pipe

Claims (5)

When the air-fuel ratio of the exhaust gas flowing into the engine exhaust passage is lean, the NO _x contained in the exhaust gas is occluded, and when the air-fuel ratio of the exhaust gas flowing in becomes the stoichiometric air-fuel ratio or rich, the stored NO _x is released. An internal combustion engine in which an NO _x storage catalyst is disposed and a particulate filter for collecting particulates contained in exhaust gas is disposed in an engine exhaust passage upstream of the NO _x storage catalyst. and comprising an ozone supply device for supplying ozone to the engine exhaust passage between _the NO _x storage catalyst, the allowable occlusion to a temperature of _the NO _x storage catalyst NO adsorption rate to _the NO _x storage catalyst is predetermined there exists a temperature range in which a rate above, when the temperature of the NO _x storage catalyst is lower than the lower limit temperature of the temperature range the ozone into the engine exhaust passage from the ozone supply device The NO gas in the exhaust gas that is supplied and flows into the NO _x storage catalyst is converted to NO _2, and the supply of ozone from the ozone supply device is stopped when the temperature of the NO _x storage catalyst is higher than the lower limit temperature of the temperature range An exhaust emission control device for an internal combustion engine. Computation means for calculating the amount of NO in the exhaust gas flowing out from the particulate filter is provided, and in the exhaust gas flowing out from the particulate filter when the temperature of the NO _x storage catalyst is lower than the lower limit temperature of the above temperature range _2. An exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein an amount of ozone necessary for converting NO of NO into NO2 is supplied. And comprising a calculating means for calculating the amount of the NO _x in the exhaust gas flowing out from the particulate filter, NO from _the NO _x storage catalyst when the integrated value of the amount of NO _x has exceeded a predetermined allowable amount _The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the air-fuel ratio of the exhaust gas flowing into the NO _x storage catalyst to release _x is made rich.   2. The internal combustion engine according to claim 1, wherein the ozone supply device can supply ozone also upstream of the particulate filter, and ozone is also supplied from the ozone supply device upstream of the particulate filter during regeneration of the particulate filter. Engine exhaust purification system. During regeneration of the particulate filter, as much ozone as possible is supplied upstream from the particulate filter from the ozone supply device. At this time, NO in the exhaust gas flowing out from the particulate filter is NO in the downstream of the particulate filter. The exhaust emission control device for an internal combustion engine according to claim 4, wherein an amount of ozone necessary for conversion to ₂ is supplied.

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