JP2001082133A - Exhaust emission control device for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To clean both NOx and PM efficiently. SOLUTION: A catalyst oxide 4 for producing NO2 by the oxidization of an engine exhaust gas and NO and a reduction component adsorption catalyst 5 having the action adsorbing/releasing the reduction component (HC) in the exhaust gas by the temperature change of the catalyst or exhaust gas are arranged in a line in the exhaust passage 2 of a diesel engine 1. PM in the exhaust gas in collected in these down streamside and DPF 6 for reacting the collected PM to NO2 in the exhaust gas and a reduction component density change type NOx cleaning catalyst 7 for absorbing NOx in the exhaust gas when the reduction component density in the flow in exhaust gas is low and discharging and reducing NOx when the reduction component density in the flow in exhaust gas is high are arranged in series.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for a diesel engine, and more particularly, to particulates (particulate matter; typified by NOx (nitrogen oxide) and soot contained in exhaust gas).
The present invention relates to an exhaust gas purifying apparatus capable of removing both of them.

[0002]

2. Description of the Related Art A three-way catalyst is widely used as a catalyst for purifying exhaust gas containing an oxidizing component and a reducing component substantially equal to each other as in a conventional automobile gasoline engine. This is a catalyst mainly composed of activated alumina carrying various components including a noble metal component such as platinum (Pt), palladium (Pd) and rhodium (Rh) and a ceria (Ce) component. HC, a harmful component
(Hydrocarbon), CO (carbon monoxide) and NOx (nitrogen oxide) can be purified with high efficiency.

On the other hand, in recent years, a so-called lean burn engine that operates even at an air-fuel ratio higher than the stoichiometric air-fuel ratio has attracted attention from the viewpoints of improving fuel efficiency and reducing CO ₂ (carbon dioxide) emissions. The exhaust gas of this type of engine at the time of lean combustion has a higher oxygen content than the exhaust gas of a conventional engine that is operated near the stoichiometric air-fuel ratio. Become. Therefore, a new catalyst that can efficiently remove NOx in exhaust gas during lean burn in a lean burn engine has been desired.

As one of them, Japanese Patent No. 2604002 discloses a NOx absorbing material that absorbs NOx when the inflowing exhaust gas has a lean air-fuel ratio and releases NOx when the inflowing exhaust gas has a reduced oxygen concentration. The device used has been proposed.

[0005]

However, in this device, in a high oxygen concentration range above a certain level, even if control is performed to lower the oxygen concentration by lowering the lean degree of the air-fuel ratio to release NOx. In addition, there has been a problem that the amount of released NOx is extremely reduced, and a NOx absorption-release purification cycle cannot be obtained.

Therefore, in the case of using the exhaust gas of an actual internal combustion engine, in order to obtain an effective NOx absorption-release purification cycle, the stoichiometric air-fuel ratio or the rich air-fuel ratio in which the oxygen concentration is close to 0% is obtained. Operating an internal combustion engine with
Or secondary supply of fuel or fuel into the exhaust passage, which sacrifices fuel efficiency of the internal combustion engine.

[0007] Further, in a diesel engine that performs compression ignition, combustion is always performed under an excess air condition, and operation at a stoichiometric air-fuel ratio or a rich state is normally impossible. When NOx is to be released from the NOx absorption catalyst in order to reduce and purify the NOx released from the NOx absorption catalyst, the air-fuel ratio of the inflowing exhaust gas must be a stoichiometric air-fuel ratio or a rich state.
For example, a complicated device such as supplying a gaseous reducing agent into the exhaust passage and reducing NOx accumulated in the catalyst by the reducing agent is required. Accompany.

Therefore, in an oxygen-excess atmosphere having an oxygen concentration of 4.5% or more, the concentration of reducing components in the inflowing exhaust gas is 100 p.
A NOx purifying catalyst that absorbs NOx in exhaust when the pressure is lower than pm and releases and reduces NOx when the concentration of reducing components in the inflowing exhaust gas is higher than 200 ppm is disclosed in
No. 319689, which was previously proposed to facilitate application to diesel engines. Hereinafter, the catalyst of the prior application is referred to as a NOx purification catalyst with a variable concentration of reducing components.

[0009] This NOx purification catalyst with variable reducing component concentration can be prepared by the following method. Basically, the NOx purification catalyst is prepared by supporting a noble metal and a NOx absorbent on a honeycomb carrier.
A catalyst having an Ox absorption-release reduction reaction can be obtained.

An alumina sol obtained by mixing and stirring 10 g of boehmite alumina with 900 g of a 1% aqueous nitric acid solution and an activated γ-alumina powder were charged into a magnetic ball mill and pulverized to obtain an alumina slurry. This slurry liquid was adhered to a cordierite-based monolithic carrier (1 L, 400 cells) and baked at 400 ° C. for 1 hour to obtain a coat layer weight of 100 g /
L carrier was obtained. The obtained carrier material was impregnated with a barium acetate aqueous solution, dried, and then calcined in air at 400 ° C. for 1 hour. The barium content in the material is 1
It was 5.0 g / L. The resulting carrier material was impregnated with a mixed aqueous solution of dinitrodiamine platinum, dried, and then calcined at 400 ° C. for 1 hour in air to obtain a NOx purification catalyst. The platinum content in this catalyst was 1.18 g / L.

Further, a NOx purification catalyst with a variable concentration of reducing components can be prepared by using the following compounds instead of the aqueous barium acetate solution. Barium _{Ba (CH 3 COO) 2 ·} H 2 O Potassium KCH ₃ COO · 2H ₂ O Sodium NaNO ₃ lithium LiNO ₃ cesium Cs (CH ₃ COO) Magnesium _{Mg (NO 3) 2 · 6H} 2 O Calcium Ca (NO _{3) 3} strontium Sr (CH ₃ COO) lanthanum La (NO _{3) 3} cerium Ce (CH ₃ COO) ₃ yttrium _{Y (NO 3) 3 · 6H} 2 O praseodymium Pr (NO _{3) 3} neodymium Nd (CH ₃ COO) ₃ samarium _{sm (NO 3) 3 · 6H} 2 O zirconium _{ZrO (NO 3) 2 · 2H} 2 O , manganese Mn (NO _{3) 2} iron _{Fe (NO 3) 3 · 9H} 2 O nickel _{Ni (NO 3) 2 · 6H} 2 O cobalt _{Co (NO 3) 2 · 6H} 2 O tungsten _{(NH 4) 10 [W 12} O 42 H 2] 10H 2 O molybdenum (NH _{4) 6} [Mo ₇ O ₂₄ ] 4H ₂ O Further, instead of the aqueous solution of dinitrodiamine platinum,
It can be similarly prepared using rhodium nitrate, palladium nitrate, and iridium nitrate.

After platinum (Pt) and barium (Ba) are supported on alumina, the catalyst obtained by changing the noble metal, which is an oxidizing agent for NO, and the absorbent into the Pt-Ba absorption catalyst coated on the honeycomb carrier is variously changed. Like the Pt-Ba catalyst, it has a high NOx release rate and a reduction performance of absorbed NOx.

[0013] Further, the reducing component concentration fluctuating NOx purifying catalyst contains at least one selected from the group consisting of tungsten and platinum, palladium, rhodium and iridium.

With this catalyst, the NOx reduction rate is further improved. The reason is not clear, but when the concentration of HC is controlled from a low concentration to a high concentration, the reaction between HC and oxygen, which is a side reaction, is delayed, and the reaction between HC and NOx is relatively promoted. Conceivable. Also, the reason that the reaction between HC and oxygen is delayed is that when the concentration of HC is controlled from a low concentration to a high concentration, the reaction heat generated when the reaction between HC and oxygen is absorbed by the catalyst. , The catalyst will be heated. Tungsten in the catalyst is considered to be an oxide, but because of its large atomic weight and large heat capacity, the absorption of heat into the catalyst is large and the heating of the catalyst is delayed, so the reaction between HC and oxygen is delayed. It is estimated that this was done.

Further, the reducing component concentration variable NOx purification catalyst contains at least one selected from the group consisting of an oxide obtained by compounding tungsten and zirconia, and platinum, palladium, rhodium and iridium.

As described above, by combining tungsten with zirconia, the NOx reduction rate is further improved.
This is because the dispersibility of tungsten is improved by compounding tungsten with zirconia, and the contact with the noble metal in the catalyst is improved.As a result, the heat absorption efficiency of the catalyst is improved, and the HC and oxygen It is considered that the reaction was delayed.

On the other hand, even if the catalyst can remove NOx,
Since M (especially soot, that is, dry soot containing carbon as a main component) cannot be removed, a diesel particulate filter (hereinafter referred to as “DPF”) for trapping PM in exhaust gas is provided, and an oxidation catalyst is provided upstream of the DPF. The oxidation catalyst oxidizes NO (nitrogen monoxide) in the exhaust gas to generate NO ₂ (nitrogen dioxide) (see FIG. 3).
By removing the PM trapped in the DPF by burning with the generated high oxidizing NO ₂ ,
There is one that regenerates a DPF (Japanese Patent Laid-Open No. 1-3
No. 18715). This PM removal device is hereinafter referred to as C
It is called RT (Continuously Regenerating Trap).

The reaction principle of the conventional CRT for removing PM is as follows: "NO ₂ + C → NO + CO, 2NO ₂ + C → 2
NO + CO ₂ and 2NO ₂ + 2C → N ₂ + 2CO
₂ ), which is equivalent to the amount of PM generated from the engine.
_{If two} amounts are present, even if the oxidation catalyst is at a relatively low temperature, the PM trapped in the DPF is continuously removed and no PM is deposited on the DPF, so a special heating device for regenerating the DPF is used. There is no need to provide such a device. This has been confirmed in the applicant's research.

However, NO from the oxidation catalyst to N
The conversion to O ₂ is dependent on the catalyst temperature, from NO to NO
The conversion to ₂ starts around 150 ° C. at the exhaust temperature at the catalyst inlet. In addition, the above “NO ₂ + C → NO + CO, 2
NO ₂ + C → 2NO + CO ₂ and 2NO ₂ + 2C
Since the reaction of “→ N ₂ + 2CO ₂ ” also depends on the temperature, the exhaust temperature of a diesel engine is often relatively low in practice, so the above 2NO ₂ + 2C → N ₂
The reaction of + 2CO ₂ hardly occurs, and most of the reaction is NO ₂ + C → NO + CO, 2NO ₂ + C → 2NO 10 CO
₂ For this reason, in the conventional CRT, when soot on the DPF is treated, there is a problem that NO is released into the atmosphere together with exhaust gas.

For this reason, Japanese Patent Application Laid-Open No. 9-53442 discloses that when the air-fuel ratio of the inflowing exhaust gas is lean, NOx
Is absorbed and the oxygen concentration of the inflowing exhaust gas is reduced.
NOx absorber that releases x (Japanese Patent No. 260049)
(Similar to Japanese Patent Publication No. 2) has been proposed.

In this device, the exhaust air-fuel ratio is made richer than the stoichiometric air-fuel ratio for a short time in order to release the NOx absorbed by the conventional NOx absorbent and restore the NOx absorption capacity (referred to as NOx absorbent regeneration operation). To the side. This conventional NO
The regeneration operation of the x-absorbing material is realized by periodically performing fuel injection in the exhaust stroke in addition to the normal fuel injection of the diesel engine, and discharging unburned components of the fuel to the exhaust passage. That is, the unburned components of the fuel discharged into the exhaust passage are oxidized by the oxidation catalyst, and the oxygen in the exhaust is almost consumed, and the oxygen concentration is reduced to about the same level as when the diesel engine is operated at the stoichiometric mixture ratio. Also, because the exhaust air-fuel ratio is rich,
Many unburned components, that is, HC and CO are allowed to flow into the conventional NOx absorbent without being oxidized. Then, NOx is released from the conventional NOx absorbent, and NOx is reduced and purified by the reducing components HC and CO.

However, even with this device, NO
When NOx is released from the x-absorbent to reduce and purify, the above-described reaction does not occur unless the air-fuel ratio of the inflow exhaust gas is in a rich state. Therefore, when applied to a diesel engine, there is a substantial sacrifice in fuel efficiency. Problem cannot be solved.

The present invention solves the above-mentioned problems and provides a CRT
A function (a function of burning and removing PM with NO ₂ having a high oxidizing power) treats the PM trapped in the DPF, and efficiently absorbs, releases and reduces NOx even in a state where oxygen is always excessive. It is an object of the present invention to provide an exhaust gas purifying apparatus which can be applied to a diesel engine without significant sacrifice of fuel efficiency.

[0024]

According to the first aspect of the present invention, there is provided an exhaust gas purifying apparatus disposed in an exhaust passage of a diesel engine, wherein the exhaust gas purifying apparatus acts on a part of engine exhaust gas.
An oxidation catalyst that oxidizes NO at least to generate NO ₂ , a reducing component adsorbing catalyst having a function of adsorbing and desorbing a reducing component in exhaust gas by a change in temperature of the catalyst or the exhaust gas, and PM (particulate) in the exhaust gas (Diesel Particulate Filter) that collects PM and reacts the collected PM with NO ₂ in the exhaust gas, and absorbs NOx in the exhaust gas when the concentration of the reducing component in the exhaust gas flowing in is low and flows in And a reducing component concentration-variable NOx purification catalyst that releases and reduces NOx when the reducing component concentration in the exhaust gas is high.

According to the second aspect of the present invention, the oxidation catalyst and the reducing component adsorption catalyst are arranged in parallel in an exhaust passage, and the DPF and the reducing component concentration-variable NOx purification catalyst are connected in series downstream of these. It is characterized by being arranged in.

According to the third aspect of the present invention, a bypass passage is provided in parallel with the oxidation catalyst for allowing exhaust gas to pass through the oxidation catalyst without being oxidized, and the reduction component adsorption catalyst, the DPF, and the reduction component are provided downstream of these bypass passages. It is characterized in that concentration-variable NOx purification catalysts are arranged in series. Note that this bypass passage may be provided inside the oxidation catalyst or may be provided outside.

The invention according to claim 4 is characterized in that a bypass valve that opens only under a predetermined temperature condition is interposed in the bypass passage. In the invention according to claim 5, in the invention according to claim 1, 3, or 4, the DPF carries a reducing component adsorption catalyst, and the reducing component adsorption catalyst and the DPF are integrated. It is characterized by. That is, a DPF with a reducing component adsorption catalyst is used.

[0028] The invention according to claim 6 is characterized in that a reducing component adsorption catalyst is carried on the carrier of the oxidation catalyst. In the invention according to claim 7, the reduced component adsorption catalyst supported on the carrier of the oxidation catalyst is different from another reduced component adsorption catalyst (a reduced component adsorption catalyst provided alone or a reduced component adsorption catalyst supported on DPF). At a low temperature.

In the invention according to claim 8, a metal (copper or palladium or the like) is ion-exchanged on the carrier of the reducing component adsorption catalyst (a reducing component adsorption catalyst provided alone or a reducing component adsorption catalyst supported on DPF). Characterized in that the zeolite-based selective reduction catalyst is supported.

[0030]

According to the first aspect of the present invention, an oxidation catalyst that acts on a part of the engine exhaust gas to oxidize NO to generate NO ₂ , and adsorbs and desorbs a reducing component in the exhaust gas. And a DPF for trapping PM in the exhaust gas and reacting the trapped PM with NO ₂ in the exhaust gas
NOx in the exhaust when the concentration of the reducing component in the exhaust is low
Absorb, and the reducing component concentration change type NOx purifying catalyst to release reducing NOx when a high reducing component concentration in the exhaust gas, that and a oxidation of NO to NO ₂ by the oxidation catalyst, reducing component adsorption catalyst Of reducing component (HC) by
In addition to enabling both desorption and regeneration, DPF can be regenerated with NO ₂ , and NOx can be purified by a NOx purification catalyst by a change in the concentration of reducing components (HC) without making the exhaust air-fuel ratio rich. can do. Therefore, since it is not necessary to make the exhaust air-fuel ratio rich, the present invention can be applied to a diesel engine without sacrificing great fuel efficiency.

According to the second aspect of the present invention, since the oxidation catalyst and the reducing component adsorption catalyst are arranged in parallel in the exhaust passage, the oxidation of NO to NO ₂ by the oxidation catalyst and the reduction by the reducing component adsorption catalyst are performed. Both the adsorption and desorption of the component (HC) can be reliably expressed.

According to the invention of claim 3, with respect to the oxidation catalyst, since the bypass passage for passing the exhaust without oxidizing is arranged, and oxidation of NO to NO ₂ by the oxidation catalyst, the reducing component adsorption Adsorption of reducing component (HC) by catalyst
Both elimination and elimination can be reliably expressed.

According to the fourth aspect of the present invention, the bypass passage is provided with a bypass valve that opens only under a predetermined temperature condition, and the exhaust gas is bypassed at a predetermined temperature (HC desorption temperature) or lower. Thus, the concentration fluctuation of the reducing component (HC) can be enhanced.

According to the fifth aspect of the present invention, the use of the DPF with a reducing component adsorption catalyst eliminates the need for a specially arranged reducing component adsorption catalyst, thereby reducing the mounting space of the entire exhaust gas purification apparatus and reducing the mountability. And the cost can be reduced by simplification.

According to the sixth aspect of the present invention, by adsorbing the reducing component adsorption catalyst also on the carrier of the oxidation catalyst, the adsorbing power of the reducing component (HC) can be enhanced. According to the invention according to claim 7, the reducing component adsorbing catalyst supported on the carrier of the oxidation catalyst is configured to desorb the reducing component at a lower temperature than other reducing component adsorbing catalysts. HC) concentration fluctuation can be enhanced.

According to the eighth aspect of the present invention, the NOx reduction / purification performance at high temperatures is achieved by supporting a zeolite-based selective reduction catalyst obtained by ion-exchanging a metal such as Cu or Pd on the carrier of the reducing component adsorption catalyst. Is improved.

[0037]

Embodiments of the present invention will be described below with reference to the drawings. First, a first embodiment of the present invention will be described with reference to FIG.

In FIG. 1, 1 is a main body of a diesel engine (engine), and 2 is an exhaust passage. An oxidation catalyst 4 and a reducing component adsorption catalyst 5 are divided and arranged in parallel in the exhaust gas flow direction in one casing 2a in a casing 2a arranged in the exhaust passage 2.

In a casing 2b disposed downstream of the casing 2a, a DPF (Diesel Particulate Filter) 6 and a reducing component concentration variable NO
The x purification catalyst 7 is arranged in series.

Here, the oxidation catalyst 4 oxidizes engine exhaust and oxidizes NO to produce NO ₂ . Specifically, for example, a monolithic carrier made of cordierite is
It is coated with activated alumina supporting noble metal components such as t and Pd, and can oxidize and purify HC and CO, which are unburned components in exhaust gas, with high efficiency.
The O component is oxidized to produce the NO ₂ component.

The reducing component adsorption catalyst 5 has a function of adsorbing and desorbing the reducing component (HC) in the exhaust gas by changing the temperature of the catalyst or the exhaust gas. Specifically, for example, a zeolite component is supported on a cordierite monolithic carrier, and the zeolite includes ZSM-
5, β, USY, and mordenite types are known, and it is desirable to use these alone or in combination.

The DPF 6 collects PM (particulates; especially soot) in the exhaust gas, and removes the collected PM from the NO in the exhaust gas.
_This is a filter for collecting and processing PM that reacts with ₂ .
Specifically, ceramic fibers 6b are wound around the core member 6a having a bottom and having a cylindrical shape and provided with a large number of holes, and the bottom side is attached to the downstream side. . At this time, the exhaust gas flows as shown by the arrow in the figure, and PM in the exhaust gas is collected by the ceramic fiber 6b. DP
F is not limited to this type, and may be a conventionally known wall flow honeycomb type.

The NOx purifying catalyst 7 with a variable reducing component concentration is
When the concentration of the reducing component in the inflowing exhaust gas is low, the N
It absorbs Ox and releases and reduces NOx when the concentration of the reducing component in the inflowing exhaust gas is high. Specifically, in an oxygen-excess atmosphere having an oxygen concentration of 4.5% or more, when the concentration of the reducing component in the inflowing exhaust gas is lower than 100 ppm, it absorbs NOx in the exhaust gas and reduces the concentration of the reducing component in the inflowing exhaust gas. Is a catalyst of the prior application (Japanese Patent Application No. 10-319689), which releases and reduces NOx when is higher than 200 ppm.
Basically, by supporting a noble metal such as Pt, Rh, Pd, and Ir and a NOx absorbent such as barium, potassium, and sodium on a honeycomb carrier, a catalyst having a NOx absorption-release reduction reaction can be obtained.

An oxidation catalyst 4 is provided upstream of the DPF 6, and the oxidation catalyst 4 oxidizes NO in the exhaust gas to produce NO ₂
(The ratio of NO ₂ in NOx increases), and DPF
By burning the PM trapped in the NO. ₆ by the generated high oxidizing NO ₂ and removing the PM, the DP
F6 is regenerated, but the reaction principle of PM removal is “NO ₂ +
C → NO + CO, 2NO ₂ + C → 2NO 10 CO ₂ , and 2NO ₂ + 2C → N ₂ + 2CO ₂ ”, and if there is an NO ₂ amount corresponding to the PM generation amount from the engine,
Even if the temperature is relatively low, PM trapped in the DPF 6 is continuously removed, and no PM is deposited on the DPF 6, so that D
There is no need to provide a special heating device or the like for regenerating the PF6.

However, the conversion of NO to NO ₂ by the oxidation catalyst 4 depends on the temperature of the exhaust gas flowing into the catalyst or the temperature of the catalyst as shown in FIG. The conversion from NO to NO ₂ takes about 15 at the exhaust temperature at the inlet of the oxidation catalyst 4.
Start around 0 ° C. In addition, the above “NO ₂ + C → N
O + CO, 2NO ₂ + C → 2NO 10 CO ₂ , and 2
Since the reaction of “NO ₂ + 2C → N ₂ + 2CO ₂ ” also depends on the temperature of the oxidation catalyst 4, about 250 to 3
If the temperature is not higher than 00 ° C, PM collected in DPF6
Does not result in a situation that is continuously removed.

Accordingly, when the exhaust gas is at a low temperature such as during a traffic congestion operation in which the idling operation ratio becomes high, the PPF 6 is gradually supplied to the DPF 6.
If traffic congestion continued because M was accumulating,
The power performance of the engine deteriorates due to the rise of the back pressure. Further, when the PM deposition conditions are met, if the deposition amount of PM is large, the heat generated by the PM combustion becomes excessive and the DPF 6 may be burned out.
It is necessary to increase the frequency at which the exhaust temperature becomes higher than ℃.

In general, diesel engines have NO
The emission amount of HC is relatively small with respect to the emission amount of x. In a diesel engine using a high-pressure fuel injection device such as a common rail type fuel injection device, this tendency is particularly remarkable, and the HC emission in a state where the engine has been warmed up is about 200 ppm or less under no-load conditions. Approx. 1 under maximum load conditions
Only about 00 ppm.

As described above, the reducing component concentration variable NO
In order to increase the NOx purification efficiency of the x purification catalyst 7, it is necessary to change the concentration of HC as a reducing agent. That is, the reducing component concentration variable NOx purification catalyst 7 absorbs NOx in the exhaust gas when the reducing component concentration in the inflowing exhaust gas is lower than 100 ppm, and absorbs the NOx in the inflowing exhaust gas when the reducing component concentration in the inflowing exhaust gas is higher than 200 ppm. NOx is released and reduced.

For this reason, for example, in a diesel engine using a common rail type fuel injection device, the concentration of HC discharged from the engine is reduced by a reducing component concentration type NO.
If it can be reduced by about half at the time of flowing into the x purification catalyst 7, NOx absorption performance can be exhibited.

However, conversely, in order to exhibit the performance of releasing and reducing the absorbed NOx, the amount of H
The NOx purification catalyst 7 with a variable concentration of reducing component relative to the C concentration
It is necessary to be able to generate a concentration increase of 100 ppm or more at the time of flowing into the water.

Here, FIG. 4 shows an oxidation catalyst in which Pt-supported active alumina is coated on a cordierite monolithic carrier, and a reducing component adsorption catalyst in which β-zeolite is supported on a cordierite monolithic carrier. (HC adsorption catalyst), when the exhaust temperature changes by 20 ° C./sec, the temperature rises continuously from the no-load state to the maximum load, and when the maximum load is reached, the temperature decreases continuously to the no-load state. H at each catalyst outlet relative to the HC concentration of
The C reduction rate is shown.

This will be described. First, a Pt-based oxidation catalyst does not exhibit oxidizing activity until the temperature reaches about 200 ° C. or higher. Heavy components in HC (hereinafter referred to as SOF)
Does not completely evaporate unless it exceeds about 200 ° C. For this reason, at 100 ° C., the oxidation activity of the catalyst does not appear,
F is adsorbed and the HC concentration decreases by about 40%. When the temperature rises from this state, the SOF evaporates as the temperature rises, and the adsorption rate decreases and the adsorbed SOF desorbs, so that the HC reduction rate decreases.

At about 250 ° C., the peak of desorption of HC is reached, and the outlet concentration becomes higher by about 100% than the inlet HC.
When the temperature is further increased, the amount of HC that is oxidized and reduced exceeds the amount of desorbed HC, so that the HC reduction rate increases. At about 400 ° C. or higher, the desorbed HC disappears, so that the very high HC due to the original oxidation activity of the oxidation catalyst is used.
A reduction rate is obtained.

When the temperature decreases when the maximum load is reached,
Since SOF is not adsorbed on the oxidation catalyst, a high HC reduction rate can be obtained up to about 300 ° C. due to the high oxidation activity of the catalyst.
Since the reduction rate decreases and the SOF starts to be adsorbed again at about 200 ° C., the performance becomes almost the same as the performance at the time of temperature rise.

Next, the reducing component adsorption catalyst (HC adsorption catalyst) supporting β zeolite has almost no oxidizing activity.
Further, since gaseous light HC is trapped in the pores of zeolite, it has a characteristic that the adsorption rate of HC is extremely high. Therefore, at a low temperature of about 100 ° C., a high HC reduction rate of about 80% can be obtained by adsorption of SOF and trapping of light HC. As the temperature rises from this state, the SOF vaporizes at about 200 ° C. or higher, and the HC vaporization rate increases at 250 ° C. or higher, so that the adsorbed SOF and light HC begin to desorb, and the HC reduction rate decreases. descend.

At about 400 ° C., the peak of HC desorption is reached, and the outlet concentration is about 500% higher than that of the inlet HC.
HC desorbs at about 500 ° C or more when the temperature is further increased
And the increase in outlet concentration is reduced.

When the maximum load is reached, no HC is desorbed, so that the outlet HC is slightly reduced with respect to the inlet HC. This is probably due to the adsorption of heavy HC or the oxidation of light HC.

When the temperature is further decreased, the reduced component adsorption catalyst does not adsorb HC, so that the H
The state shifts to the state of the C reduction rate, and when the temperature is further lowered, the HC vaporization rate decreases, and at about 350 ° C., the HC is again captured in the pores of the zeolite, and the HC reduction rate starts to increase. Then, at about 250 ° C., the performance becomes almost the same as that at the time of temperature rise.

In the first embodiment of the present invention, the oxidation catalyst 4
The reduction component adsorption catalyst 5 is divided and arranged in parallel in the exhaust gas flow direction in one casing 2a. For example, FIG. 5 shows a configuration in which an equal amount of exhaust gas flows into the oxidation catalyst 4 and the reduction component adsorption catalyst 5, and, as described above,
The temperature rises continuously from the no-load state to the maximum load with the exhaust gas temperature change of ° C./sec. Shows the HC reduction rate.

Here, the oxidation catalyst 4 is obtained by coating a monolithic carrier made of cordierite with activated alumina carrying Pt. Further, the reducing component adsorption catalyst 5 has a β-zeolite supported on a cordierite monolithic carrier.

As shown in FIG. 5, in the first embodiment of the present invention, the characteristics of the oxidation catalyst 4 and the reduction component adsorption catalyst 5 are combined. That is, at a low exhaust gas temperature of about 100 ° C., the amount of HC decreases by about 60% from the outlet HC of the engine 1, and as the temperature rises from this state, the HC becomes about 400 ° C.
Desorption peak, which is 20 times higher than HC at the exit of engine 1.
The inlet HC of the DPF 6 increases by about 0%. When the load reaches the maximum load, there is no HC desorbed from the reducing component adsorption catalyst 5, and the inlet HC of the DPF 6 is reduced by about 60% with respect to the outlet HC of the engine 1 due to the effect of the oxidation performance of the oxidation catalyst 4.

At the same time, NO ₂ is generated by the oxidation catalyst 4 (at the same time, adsorption and desorption of HC and oxidation also occur). By the way, in practical operation, acceleration and deceleration from no load to high load are frequently performed, so that the temperature of the exhaust gas rises and falls frequently, and the exhaust gas is trapped by the DPF 6 by NO ₂ generated by the oxidation catalyst 4. PM can also be removed, and the concentration of the HC flowing into the reducing component concentration-variable NOx purification catalyst 7 fluctuates, so that NOx absorption and emission reduction in the reducing component concentration-variable NOx purification catalyst 7 are efficiently performed.

On the other hand, in a state where the operation is continuously performed for a long time at a low exhaust temperature or a high exhaust temperature, for example, when the operation is continuously performed at a low exhaust temperature, HC is removed from the reducing component adsorption catalyst 5. It is necessary to raise the temperature for desorption.

On the other hand, when the exhaust gas is continuously operated at a high exhaust gas temperature, the NOx purification catalyst 7 of the reducing component concentration fluctuating type
In order to release and reduce the absorbed NOx, it is necessary to forcibly increase HC as a reducing agent.

To achieve this, a small amount of fuel is post-injected in the expansion stroke or the exhaust stroke of each cylinder using a common rail type fuel injection device to generate an increase in unburned HC and an increase in temperature at the engine outlet. It is valid.

Here, the timing of the post-injection is less affected by the combustion of the main injected fuel as the crank angle interval from the compression top dead center is larger, so that the post-injected fuel becomes unburned HC and is discharged. Will be increased. Conversely, the timing of the post-injection is more susceptible to the combustion of the main injected fuel as the crank angle interval from the compression top dead center becomes smaller, and therefore the proportion of the post-injected fuel that burns increases, Although the exhaust gas temperature rises, the proportion of unburned HC and exhausted decreases.

For this reason, as shown in FIGS. 6 and 7,
As the engine load and the number of revolutions increase, the temperature increases mainly due to the post-injection under low exhaust temperature conditions and the HC increases under high exhaust temperature conditions.
The delay interval from the main injection is set to increase,
If possible, it is desirable to carry out the post-injection in the expansion stroke. Furthermore, even if the post-injection is performed at an extremely low exhaust temperature, HC is not easily desorbed from the reducing component adsorption catalyst 5, so that the exhaust temperature at which the post-injection is performed is preferably, for example, 200 ° C. or higher.

Also, the exhaust temperature depends on the state of the engine (load,
Therefore, the engine torque and the number of revolutions are set as parameters, and matching may be performed under steady-state conditions after the engine is warmed up.

Therefore, a sensor for detecting the temperature of the catalyst is provided, and the determination is made based not only on the load and the number of revolutions of the engine but also on the catalyst temperature. Next, a common rail type fuel injection device used for post-injection will be outlined with reference to FIG. 2 (for details, refer to Japanese Patent Application Laid-Open No. 9-112251).

The fuel injection device 10 mainly includes a fuel tank 11, a fuel supply passage 12, a supply pump 14, a common rail (accumulator) 16, and a fuel injection valve 17 provided for each cylinder. The stored fuel is temporarily stored in the common rail 16 via the fuel supply passage 15, and then the high-pressure fuel in the common rail 16 is distributed to the fuel injection valves 17 for the number of cylinders.

The fuel injection valve 17 includes the needle valve 18 and the nozzle chamber 1
9, fuel supply passage 20 to nozzle chamber 19, retainer 2
1. A return spring 23 for urging the hydraulic piston 22, the needle valve 18 in the valve closing direction (downward in the figure), a fuel supply passage 24 to the hydraulic piston 22, and a three-way valve (electromagnetic Valve 25).

Here, the passages 20 and 24 in the valve body
When the three-way valve 25 through which the high-pressure fuel is guided to both the upper part of the hydraulic piston 22 and the nozzle chamber 19 is turned off (when the ports A and B are connected and the ports B and C are shut off), the pressure of the hydraulic piston 22 is received. Since the area is larger than the pressure receiving area of the needle valve 18, the needle valve 18 is in a seated state.

On the other hand, when the three-way valve 25 is turned ON (the ports A and B are shut off and the ports B and C are in communication), the fuel above the hydraulic piston 22 is transferred to the fuel tank 11 via the return passage 28. The fuel pressure acting on the hydraulic piston 22 is reduced. As a result, the needle valve 18 rises and fuel is injected from the injection hole at the tip of the fuel injection valve 17.

When the three-way valve 25 is returned to the OFF state again, the high-pressure fuel in the common rail (accumulator) 16 is guided to the hydraulic piston 22, and the fuel injection ends. That is, the three-way valve 2
The fuel injection amount is adjusted by the ON time of No. 5, and if the pressure of the common rail 16 is the same, the longer the ON time, the larger the fuel injection amount. 26 is a check valve, and 27 is an orifice.

The fuel injection device 10 is further provided with a pressure control valve 31 in the return passage 13 in which the fuel discharged from the supply pump 14 can be returned in order to control the common rail pressure.

The pressure control valve 31 is connected to the electronic control unit 4
The common rail pressure is controlled by adjusting the amount of fuel discharged to the common rail 16 in order to change the flow area of the return passage 13 according to the duty signal from 1. The fuel injection amount also changes depending on the fuel pressure of the common rail 16. If the ON time of the three-way valve 25 is the same, the fuel injection amount increases as the fuel pressure of the common rail 16 increases.

The electronic control unit 41 receives signals from a sensor 32 for detecting the common rail pressure PCR1 and a sensor 37 for detecting the exhaust gas temperature T1 on the inlet side of the oxidation catalyst 4 and the reducing component adsorption catalyst 5, and an accelerator opening sensor 33. (Generates an output L proportional to the amount of depression of the accelerator pedal),
Crank angle sensor 34 (detects engine speed Ne and crank angle), cylinder discriminating sensor 35 (cylinder discriminating signal Cy
1), together with the signal from the water temperature sensor 36.

The electronic control unit 41 calculates the target fuel injection amount of the main injection and the target pressure of the common rail 16 according to the engine speed Ne and the engine load (accelerator opening) L, and the common rail detected by the pressure sensor 32. The fuel pressure of the common rail 16 is feedback-controlled via the pressure control valve 31 so that the pressure matches the target pressure. Further, in addition to controlling the ON time of the three-way valve 25 in accordance with the calculated target fuel injection amount of the main injection, the post-injection described above is performed in the expansion stroke of each cylinder separately from the main injection to increase the temperature and increase the unburned fuel. Causes an increase in HC.

The control performed by the electronic control unit 41 will be described with reference to the flowcharts of FIGS.
FIG. 9 is a main routine of the fuel injection control, and FIGS.
1, FIG. 12 is a subroutine showing a part of the main routine in detail.

In the main routine of FIG. 9, in step 100, the common rail pressure PCR1, the engine speed Ne, the cylinder discrimination signal Cyl, the engine load L, and the exhaust temperature T1 are read.
At 00, the common rail pressure control, main injection control for engine output control, and exhaust post-processing control (post-injection control) for generating an increase in temperature and an increase in unburned HC are executed.

The subroutine of FIG. 10 is for performing common rail pressure control. Step 201, 202
Then, a predetermined map is searched from the engine speed Ne and the engine load L, and the target reference pressure P of the common rail 16 is obtained.
CR0 and a reference duty ratio (reference control signal) Dut of the pressure control valve 31 for obtaining the target reference pressure PCR0.
Find y0. These maps show the engine speed Ne.
And the engine load L as parameters stored in the ROM of the electronic control unit 41 in advance.

At step 203, the target reference pressure PCR
Absolute value of difference between zero and actual common rail pressure PCR1 |
PCR0-PCR1 | is obtained, and this is set as the target reference pressure PC.
R0 is compared with a preset allowable pressure difference ΔPCR0.

If | PCR0-PCR1 | is within the allowable range, the routine proceeds to step 206, where the reference duty ratio Du is set.
The same duty ratio is maintained by setting ty0 to the valve opening duty ratio Duty.
A duty signal is generated from the duty ratio Duty to drive the pressure control valve 31.

On the other hand, if | PCR0-PCR1 | is not within the allowable range, the process proceeds from step 203 to step 204, where a preset ROM table is searched for PCR0-PCR1 (= ΔP). To calculate the duty ratio correction coefficient KDuty. For example, when ΔP is minus (PCR1 is larger than PCR0), KDu
ty is smaller than 1 and ΔP is plus (P
KD Duty when PCR1 is smaller than CR0)
Becomes a value larger than 1. Specifically, the pressure control valve 31
The table data of the duty ratio correction coefficient KDuty is set in accordance with the characteristics of (1).

Then, in step 205, after the reference duty ratio Duty0 is corrected by this correction coefficient KDuty, a value (Duty0 × KDuty) is set as the valve opening duty ratio Duty, and then the operation of step 207 is executed.

The subroutine of FIG. 11 is for performing main injection control. In step 301, a predetermined map is searched from the engine speed Ne and the engine load L,
The main injection amount Qmain is obtained.

In step 302, the main injection amount Qma
A predetermined map is searched from in and the common rail pressure PCR1 to determine the main injection period Mperiod. here,
The main injection period Mperiod is set in msec.
As shown in the above, if the main injection amount Qmain is the same, the higher the common rail pressure PCR1 is, the higher the main injection period Mperio is
If d is shorter and the common rail pressure PCR1 is the same, the larger the main injection amount Qmain, the larger the main injection period Mperio
d becomes longer.

At step 303, the engine speed Ne
And a predetermined map is searched from the engine load L to determine the main injection start timing Mstart. In step 304,
During the period of Mperiod from the main injection start timing Mstart to supply the main injection amount Qmain, the fuel injection valve 17 of the cylinder to be main-injected is driven to open based on the signals from the crank angle sensor 34 and the cylinder discrimination sensor 35. I do.

The subroutine of FIG. 12 is for performing exhaust post-processing control (post-injection control) for generating a rise in temperature and an increase in unburned HC in this embodiment. First, in step 401, the exhaust gas temperature T1 on the inlet side of the oxidation catalyst 4 and the reducing component adsorption catalyst 5 is adjusted to a temperature suitable for performing post-injection and desorbing HC from the reducing component adsorption catalyst 5;
Alternatively, it is determined whether or not the temperature is equal to or higher than a temperature (predetermined temperature a) suitable for increasing the supply of HC to the NOx purification catalyst 7 with a reduced component concentration, for example, 200 ° C or higher.

If the temperature is lower than 200 ° C., it is not suitable for the post-injection.
If the temperature is 200 ° C. or more, the effect of the post-injection can be expected, so the process proceeds to step 402, and the continuous operation time ΔTime at 200 ° C. or more is calculated (if the temperature falls below 200 ° C. during the calculation, the time is reset to 0). . And step 4
03, the continuous operation time ΔTime above 200 ° C.
Whether the time to execute the post-injection has been reached, for example, 10 seconds
It is determined whether or not c has elapsed.

If the time to execute the post-injection has not been reached, the routine proceeds to step 407, where the post-injection is stopped. If the time to execute the post-injection has been reached, the engine speed Ne is determined at step 404, as in the case of the main injection control.
And a post-injection condition, that is, a post-injection amount Qa, from a map stored in the ROM in advance corresponding to the engine load L.
ft and the post-injection period Aperiod (see FIG. 8) corresponding to the common rail pressure PCR1 and the post-injection start timing A
In step 405, post-injection is executed.

In step 406, it is determined whether or not the post-injection has been executed for a predetermined time. If the post-injection has not been executed for a predetermined time, the process returns to step 404, and
If the post-injection has been performed, in step 407, the post-injection is stopped.

Here, the post-injection during the expansion stroke reaches the cylinder wall of the combustion chamber and dilutes the oil film, and if the vehicle is running for a long time, lubricity may be impaired and engine wear may occur. Therefore, 1
The amount of post-injection fuel to be injected each time is desirably about 10% at the maximum with respect to the main injection fuel quantity, and it is desirable to set the number of injections to an upper limit of 2% in terms of fuel consumption on average on average ( For example, at most, 10
%, The post-injection is executed every 2 seconds for 10 seconds).

FIG. 13 shows a second embodiment. Note that the same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In the casing 2a, only the oxidation catalyst 4A is disposed. The oxidation catalyst 4A is provided with an internal bypass passage 45, and a part (for example, about half) of exhaust gas
Without passing through the oxidation catalyst 4A (without treatment).

In the casing 2b disposed downstream of the casing 2a, the reducing component adsorbing catalyst 5A is provided from the upstream side.
, DPF 6, NOx purification catalyst 7 with reduced concentration of reducing component
And are arranged in series.

The reducing component adsorption catalyst 5A has a zeolite component supported on a cordierite monolithic carrier in the same manner as in the first embodiment.
ZSM-5, β, USY, and mordenite types are known, and it is desirable to use these alone or in combination. In the second embodiment, for example, β zeolite is supported.

When the oxidation catalyst 4A having the internal bypass passage 45 and the reducing component adsorbing catalyst 5A are formed in a tandem configuration, the exhaust gas temperature is about 250.degree.
Since the HC adsorption performance of the reducing component adsorption catalyst 5A is integrated with the HC adsorption performance of A, the HC reduction rate at low exhaust temperatures is improved as shown in FIG. The amount increases.

Therefore, in a practical operation in which acceleration and deceleration from no load to high load are frequently performed, PM trapped in the DPF 6 by NO ₂ generated by the oxidation catalyst 4A can be removed, and the concentration of the reducing component changes. Fluctuations in the concentration of HC flowing into the NOx purification catalyst 7 are further amplified, and NOx absorption and emission reduction in the NOx purification catalyst 7 with reduced component concentration are efficiently performed.

FIG. 14 shows a third embodiment. The same parts as those in the first and second embodiments are denoted by the same reference numerals, and description thereof will be omitted. As in the second embodiment, an oxidation catalyst 4A provided with an internal bypass passage 45 is disposed in the casing 2a.

A casing 2b disposed downstream of the casing 2a is provided with a reducing component adsorption catalyst D
The PF 8 and the NOx purification catalyst 7 with the variable concentration of reducing components are
They are arranged in series.

DPF 8 is equipped with a reducing component adsorption catalyst,
Bottomed cylindrical core member 8a having a large number of holes in a cylindrical portion
The ceramic fiber 8b is wound in several layers, and a zeolite component (for example, β zeolite) is supported on the ceramic fiber 8b as a reducing component adsorption catalyst. The DPF is not limited to this type, and a zeolite component may be supported on a conventionally known wall flow honeycomb type.

With such a configuration, the DPF 8 is provided with the ability to adsorb a reducing component, so that there is no need to arrange a special reducing component adsorption catalyst as in the first and second embodiments. Therefore, the mounting space of the entire exhaust gas purification device is reduced, so that the mountability is improved, and the cost can be reduced by simplification.

FIG. 15 shows a fourth embodiment. The same parts as those in the first, second, and third embodiments are denoted by the same reference numerals, and description thereof is omitted. Only the oxidation catalyst 4B is arranged in the casing 2a. A bypass passage 2c that bypasses the casing 2a (oxidation catalyst 4B).
The bypass passage 2c is provided with a bypass valve 9 that is opened and closed by an electronic control unit 41 via an actuator (not shown).

In the casing 2b disposed downstream of the casing 2a, as in the third embodiment, a DPF 8 with a reducing component adsorption catalyst and a reducing component concentration-variable NOx purification catalyst 7 are arranged from the upstream side in the same manner as in the third embodiment. They are arranged in series.

In this embodiment, the electronic control unit 4
The exhaust post-processing control performed in step 1 will be described with reference to the flowchart of FIG. Basically, opening / closing control of the bypass valve 9 shown in steps 501, 502, and 503 is added to the flowchart of FIG.

First, in step 401, the exhaust gas temperature T1 on the inlet side of the oxidation catalyst 4B is adjusted to a temperature suitable for desorbing HC from the reducing component adsorption catalyst of the DPF 8 by performing post-injection.
Alternatively, it is determined whether or not the temperature is equal to or higher than a temperature (predetermined temperature a) suitable for increasing the supply of HC to the NOx purification catalyst 7 with a reduced component concentration, for example, 200 ° C or higher.

If the temperature is lower than 200 ° C., it is not suitable for the post-injection. Therefore, the process proceeds to step 502, the bypass valve 9 is opened, and the post-injection is stopped in step 407. By doing so, most of the exhaust gas flows into the DPF 8 via the bypass passage 2c without passing through the oxidation catalyst 4B, and PM is collected and HC is adsorbed and reduced.

If the temperature is equal to or higher than 200 ° C., the effect of the post-injection can be expected, so the routine proceeds to step 402, where the continuous operation time ΔTime at 200 ° C. or higher is calculated. Then, in step 403, the time for executing post-injection (for example, 10 seconds)
It is determined whether or not c) has been reached.

If the time to execute the post-injection has not been reached, the routine proceeds to step 503, where the bypass 9 is closed.
In step 407, the post injection is stopped. Where 200 ° C
When the bypass valve 9 is closed as described above, almost all of the exhaust gas flows into the oxidation catalyst 4B, and is changed from NO to NO by the oxidation catalyst 4B.
Oxidation to ₂ is promoted, and PM of DPM
Removal by O ₂ is promoted.

On the other hand, if the temperature rises due to acceleration from less than 200 ° C., desorption of HC adsorbed on the DPF 8 occurs, and the HC flows into the NOx purification catalyst 7 with a variable concentration of reduced components. The concentration of the generated HC fluctuates, and the NOx absorption and release reduction of the NOx purifying catalyst 7 with reduced component concentration are efficiently performed.

If it is determined in step 403 that the time to execute the post-injection has reached (for example, 10 seconds), in step 404, the engine speed Ne and the engine load L
According to the map stored in the ROM in advance,
The post-injection conditions, that is, the post-injection period and the post-injection start timing are obtained, and in step 405, post-injection is executed, and the routine proceeds to step 501, where the bypass valve 9 is opened.

That is, after the exhaust gas raises the temperature of the exhaust gas and the unburned HC by the post-injection, most of the exhaust gas does not pass through the oxidation catalyst 4B but passes through the bypass passage 2c through the DPF 2c.
Flow into 8.

At this time, PM is trapped in the DPF 8 (combustes when the exhaust gas temperature is about 500 ° C. or higher), but unburned HC passes through the DPF 8 and flows into the NOx purification catalyst 7 with a variable concentration of reducing components. Concentration fluctuations occur in the HC
The NOx absorption and emission reduction in the NOx purification catalyst 7 with the variable reducing component concentration are efficiently performed.

In step 406, it is determined whether or not the post-injection has been performed for a predetermined time. If the post-injection has not been performed for a predetermined time, the process returns to step 404, where
If the post-injection has been executed, the bypass valve 9 is closed in step 503, and the post-injection is stopped in step 407.

In the first to fourth embodiments,
Although the reducing component adsorption catalysts 5 and 5A or the DPF 8 with the reducing component adsorption catalyst have the function of adsorbing HC,
4A and 4B may also have HC adsorption performance.

That is, the oxidation catalyst is, for example, a monolithic carrier made of cordierite coated with activated alumina carrying noble metal components such as Pt and Pd, and a zeolite component as a reduction component adsorption catalyst is mixed. Alternatively, it can be prepared by coating each layer.

As a result, the HC adsorbing performance at low exhaust temperatures is further improved, the HC reduction rate at low exhaust temperatures is improved, the amount of HC desorbed at elevated temperatures is increased, and no load is applied to high load. In a practical operation in which acceleration and deceleration up to the maximum are performed, fluctuations in the concentration of HC flowing into the NOx purification catalyst 7 with a variable concentration of reducing components are further amplified, and the NOx purification catalyst 7 with a variable concentration of a reducing component 7
NOx absorption and emission reduction are efficiently performed.

Zeolite includes ZSM-5, β, U
It is desirable to use these alone or in combination from among SY, mordenite type and the like. However, the zeolite (for example, β) used for the reducing component adsorption catalysts 5, 5A or the DPF 8 with the reducing component adsorption catalyst, Zeolite having low adsorption power (desorption temperature is relatively low, for example, ZS
M-5) is carried, and it is desirable that HC be desorbed at a temperature at which the oxidation activity of the oxidation catalyst becomes strong so as not to oxidize and burn with the catalyst (because the HC concentration fluctuation does not become strong).

In the first to fourth embodiments, the reducing component adsorbing catalysts 5, 5A or the DPF 8 with the reducing component adsorbing catalyst have only the HC adsorption performance. Zeolite-based selective reduction catalysts obtained by ion-exchange of metals such as these may be supported together. Thereby, the NOx reduction / purification performance at high temperatures is improved.

As described above, according to the exhaust gas purification apparatus of the present invention, NOx can be efficiently absorbed, released, and released when the exhaust gas is always in an excessive oxygen state like a diesel engine.
It is possible to perform reduction purification. In addition, the CRT function (a function of burning and removing PM with NO ₂ having a high oxidizing power) can process the PM collected by the DPF. Therefore, for example, even in the case of performing post-injection using a fuel injection device such as a common rail, it is not necessary to make the exhaust air-fuel ratio rich, so that it is possible to avoid a great sacrifice in fuel efficiency.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a diesel engine and an exhaust gas purification device according to a first embodiment.

FIG. 2 is a configuration diagram of a common rail type fuel injection device.

FIG. 3 is a characteristic diagram of NO → NO ₂ conversion of an oxidation catalyst.

Fig. 4 Characteristic diagram of HC adsorption / desorption

FIG. 5 is a characteristic diagram of the HC reduction rate.

FIG. 6 is a characteristic diagram of setting of post-injection timing.

FIG. 7 is a characteristic diagram of setting of a post-injection timing.

FIG. 8 is a characteristic diagram of fuel injection periods of main injection and post-injection.

FIG. 9 is a flowchart of a main routine of fuel injection control.

FIG. 10 is a flowchart of a common rail pressure control subroutine.

FIG. 11 is a flowchart of a subroutine of main injection control.

FIG. 12 is a flowchart of a subroutine of exhaust post-processing control.

FIG. 13 is a configuration diagram of an exhaust gas purification device according to a second embodiment.

FIG. 14 is a configuration diagram of an exhaust gas purification device according to a third embodiment.

FIG. 15 is a configuration diagram of an exhaust emission control device according to a fourth embodiment.

FIG. 16 is a flowchart of a subroutine of exhaust post-processing control according to a fourth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Exhaust passage 2a Casing 2b Casing 2c Bypass passage 4,4A, 4B Oxidation catalyst 5,5A Reduction component adsorption catalyst 6 DPF 7 Reduction component concentration variation type NOx purification catalyst 8 DPF with reduction component adsorption catalyst 9 Bypass valve 10 Fuel Injector 16 Common rail 17 Fuel injector 41 Electronic control unit 45 Internal bypass passage

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Hiroshi Akama, Nissan Motor Co., Ltd., 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Prefecture (72) Motohisa Kamijo 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa, Nissan Motor Co., Ltd. Terms (reference) 3G090 AA01 CB04 CB22 DA12 DA14 DA18 DA20 DB01 DB02 3G091 AA18 AA28 AB02 AB06 AB09 BA00 BA01 CA12 CA13 CB02 CB06 DC05 EA00 EA01 EA03 EA07 EA16 EA17 EA18 FA02 FB02 GA04 GB06W HA11 HA19 HA20

Claims (8)

[Claims] An exhaust purification device disposed in an exhaust passage of a diesel engine, the oxidation catalyst acting on a part of engine exhaust and oxidizing at least NO to generate NO ₂ , a catalyst or exhaust gas and reducing component adsorption catalyst having an effect of adsorption and desorption of reducing components in the exhaust gas by temperature change, and of collecting particulates in exhaust, diesel reacted with NO ₂ in the exhaust gas trapped particulates A curable filter, and N in the exhaust gas when the concentration of the reducing component in the exhaust gas is low.
Reduced component concentration variable NO that absorbs Ox and releases and reduces NOx when the concentration of the reduced component in the inflowing exhaust gas is high.
An exhaust purification device for a diesel engine, comprising: a x purification catalyst; 2. The oxidation catalyst and the reduction component adsorption catalyst are arranged in parallel in an exhaust passage, and the diesel particulate filter and the reduction component concentration-variable NOx purification catalyst are arranged in series on the downstream side of the oxidation catalyst and the reduction component adsorption catalyst. The exhaust gas purifying apparatus for a diesel engine according to claim 1, wherein: 3. A bypass passage through which exhaust gas passes without being oxidized with respect to the oxidation catalyst is provided in parallel, and downstream of these bypass passages, the reduction component adsorption catalyst, the diesel particulate filter, and the reduction component concentration type The exhaust gas purifying apparatus for a diesel engine according to claim 1, wherein the NOx purifying catalyst is arranged in series. 4. The exhaust gas purifying apparatus for a diesel engine according to claim 3, wherein a bypass valve that opens only under a predetermined temperature condition is interposed in the bypass passage. 5. The diesel particulate filter having a reducing component adsorption catalyst supported thereon, and the reducing component adsorption catalyst and the diesel particulate filter are integrated with each other. Item 4
An exhaust gas purification device for a diesel engine according to any one of the above. 6. The exhaust gas purifying apparatus for a diesel engine according to claim 1, wherein a reduction component adsorption catalyst is carried on a carrier of the oxidation catalyst. 7. The reduction component adsorption catalyst carried on the carrier of the oxidation catalyst, wherein the reduction component is desorbed at a lower temperature than other reduction component adsorption catalysts.
An exhaust purification device for a diesel engine as described in the above. 8. The diesel engine according to claim 1, wherein a zeolite-based selective reduction catalyst obtained by ion-exchange of a metal is carried on a carrier of the reducing component adsorption catalyst. Engine exhaust purification device.