JPH1054228A - Diesel engine exhaust purification system - Google Patents

Abstract

(57) [Summary] The present invention relates to an exhaust gas purification device for a diesel engine, in which a catalyst can be used efficiently over the entire exhaust gas temperature range. A catalyst disposed in an exhaust passage of a diesel engine, and an exhaust passage upstream of the catalyst.
1 and an exhaust turbine 9T.
And a cooling means 14 for cooling the exhaust passage 27 or the catalyst 1 on the upstream side of the catalyst 1 with compressed air obtained from the compressor 9C. Control means S for controlling the flow rate of the compressed air so that the temperature becomes the activation range is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel engine exhaust purification apparatus for purifying exhaust gas by a catalyst in a diesel engine.

[0002]

2. Description of the Related Art Exhaust gas discharged from a diesel engine includes SOF (SoF) such as unburned fuel and unburned oil.
It is generally known that the total amount of particulates emitted can be reduced by oxidizing SOF with a catalyst and then discharging the particulates to the atmosphere.

[0003] As a low-temperature active oxidation catalyst which is effective even at a relatively low temperature, there is a platinum-based catalyst, which is carried on a carrier provided in an exhaust gas flow path to oxidize SOF in particulates. The platinum-based catalyst is effective for reducing HC when the engine is under a low load and reducing SOF of unburned fuel and unburned oil in particulates.

[0004] By the way, at low load, the amount of air is increased relative to the fuel and the generation of "soot" is reduced, but the amount of SOF generated tends to increase as the exhaust temperature decreases. In addition, when the temperature is high and the load is high, even the sulfur contained in the fuel of the diesel engine is oxidized, so that the SOx such as SO ₂ increases, for example, the increased SO ₃
There is also a problem that sulfate (sulfuric acid-based compound) is generated by the reaction between water and water, resulting in an increase in the total amount of particulates.

Therefore, a technique for controlling the temperature of the exhaust gas entering the catalyst has been provided, an example of which is shown in FIGS. That is, FIG. 15 is a schematic view showing the main part, in which a catalyst 1 composed of a catalyst carrier carrying a low-temperature active oxidation catalyst, for example, a platinum-based catalyst, is connected to an exhaust gas passage 2 of a diesel engine and a treated exhaust gas. It is provided between an exhaust gas passage 3 for discharging gas to the atmosphere.

[0006] A bypass passage 4 is branched from the exhaust gas passage 2, and the bypass passage 4 has an inlet 4.
A flow path switching valve 5 is provided at a, and is configured to selectively allow exhaust gas to flow through either the flow path to the catalyst 1 or the bypass flow path 4. The bypass flow path 4 includes flow paths 4b and 4c.
b, 4c surround the catalyst 1, and the exhaust gas passage 3
To join.

The position of the flow path switching valve 5 is adjusted by an actuator 6 controlled by a controller 7, and is set to a required position based on the judgment of a high load state and a low load state of the engine. It is configured to be. With such a configuration, in the operating state of the region A in the graph of FIG. 16, since the amount of sulfate generation is small and the purification region has a high purification temperature, the flow path switching valve 5 is switched to the solid line position in FIG. Then, the exhaust gas is circulated toward the catalyst 1.

The catalyst 1 is heated by the exhaust gas flowing through the bypass passage 4 under a high load condition.
SOF in the particulates is efficiently oxidized. In an operation state such as an idling state with a further low load (region C in FIG. 16), the flow path switching valve 5 is switched to a dotted line position in FIG. Prevent below the proper temperature.

A high load area B where the exhaust gas temperature is high
Then, the exhaust gas is caused to flow through the bypass flow channel 4 by switching the flow channel switching valve 5 so as to suppress the generation of sulfate, so that the exhaust gas does not flow into the catalyst 1.

[0010]

As described above, FIG.
In the conventional configuration shown in FIG. 16, although a device is devised to warm exhaust gas in a low temperature range and flow into the catalyst 1, the catalyst is bypassed in the exhaust gas in a high temperature region in order to suppress sulfate generation. Therefore, exhaust gas is purified only in the temperature range where the generation of sulfate is small and the purification rate is high, and in the high exhaust temperature and low exhaust temperature regions, the polluted exhaust gas is directly discharged to the atmosphere because no catalyst is used. There are issues.

Note that, for example, Japanese Patent Application Laid-Open Nos. 5-263628 and 6-264732, and JP-A-6-825
Japanese Patent Application Publication No. 9 and Japanese Utility Model Publication No. 5-1616 also disclose related techniques, but these techniques do not solve the above-mentioned problems. The present invention has been made in view of the above-described problems, and in order to effectively utilize the catalyst in a wider operating range, the exhaust gas temperature is controlled, and the catalyst can be used efficiently over the entire area. An object of the present invention is to provide an exhaust gas purification device for an engine.

[0012]

According to a first aspect of the present invention, there is provided an exhaust gas purifying apparatus for a diesel engine, comprising: a catalyst disposed in an exhaust passage of the diesel engine for purifying harmful components in exhaust gas; An exhaust turbine provided in the exhaust passage on the upstream side of the exhaust passage and driven by exhaust pressure, and a compressor connected to the exhaust turbine and rotated by the exhaust turbine. A cooling means for cooling the exhaust passage or the catalyst upstream of the catalyst, and a control means for controlling a flow rate of the compressed air so that an exhaust gas temperature flowing into the catalyst becomes an optimum activation range temperature of the catalyst. It is characterized by:

According to a second aspect of the present invention, there is provided the exhaust gas purifying apparatus for a diesel engine according to the present invention, in addition to the configuration of the first aspect, wherein a bypass passage for bypassing the exhaust gas to the exhaust turbine is provided in the exhaust passage. A bypass valve for controlling a flow rate of exhaust gas flowing through the bypass passage, wherein the control means controls an open / close state of the bypass valve in accordance with an exhaust gas temperature and an engine operating state upstream of the catalyst. It is characterized by being configured to control.

According to a third aspect of the present invention, there is provided an exhaust gas purifying apparatus for a diesel engine according to the first aspect of the present invention, further comprising an engine intake passage downstream of the compressor and a cooling passage to the cooling means. The cooling passage is provided with a valve device for controlling the flow rate of air flowing through the cooling passage, and the control means is provided in accordance with an exhaust gas temperature or an engine operating state upstream of the catalyst. It is characterized in that it is configured to control the open / close state of the valve device.

According to a fourth aspect of the present invention, there is provided an exhaust gas purifying apparatus for a diesel engine according to the third aspect of the present invention, in addition to the configuration of the third aspect, wherein the engine intake passage and the cooling passage are located downstream of the compressor. An intercooler for cooling the air compressed by the compressor is provided upstream of the branch portion.

According to a fifth aspect of the present invention, there is provided an exhaust gas purifying apparatus for a diesel engine according to the present invention, wherein the cooling means includes an upstream side of the catalyst. A heat exchanger having a double-pipe structure formed of an inner pipe and an outer pipe formed in an exhaust passage, wherein compressed air from the compressor is supplied to the outer pipe of the double-pipe structure; It is characterized in that the exhaust gas is made to flow through the inner pipe of the structure.

According to a sixth aspect of the present invention, there is provided an exhaust gas purifying apparatus for a diesel engine according to the present invention, wherein the catalyst has a plurality of catalyst layers in addition to the configuration according to any one of the first to fourth aspects. The catalyst is characterized in that the catalyst is formed by alternately polymerizing the catalyst layer and an air flow path portion for flowing compressed air from the compressor. According to a seventh aspect of the present invention, there is provided the exhaust gas purifying apparatus for a diesel engine according to the present invention, in addition to the configuration according to any one of the first to sixth aspects, wherein the catalyst is configured as an oxidation catalyst, and the purification action by the oxidation catalyst is performed. Wherein the control means controls the flow rate of the compressed air so that the temperature of exhaust gas flowing into the catalyst falls within a temperature range in which sulfate is not generated in the oxidation catalyst. .

[0018]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an exhaust gas purifying apparatus for a diesel engine according to a first embodiment of the present invention; FIG. FIG. 2 is a schematic view showing the configuration of the main part of the air-cooled heat exchanger, FIG. 2 is a schematic cross-sectional view showing the configuration of the main part of the air-cooled heat exchanger, and FIGS. FIGS. 7 to 9 are schematic cross-sectional views showing the main parts of another example of the air-cooled heat exchanger, FIGS. 7 to 9 are diagrams showing the operation characteristics thereof, and FIGS. FIG. 10 is a schematic diagram showing a configuration of a main part of the exhaust gas purification device, FIGS. 11 and 12 are diagrams showing its operation characteristics, and FIGS. 13 and 14 are diesel engines as a third embodiment of the present invention. FIG.
FIG. 14 is a schematic view showing the configuration of the main part, and FIG. 14 is a schematic perspective view showing the catalyst structure. (A) Description of First Embodiment First, a first embodiment will be described. As shown in FIG. 1, a catalyst 1 for purifying harmful components in exhaust gas is provided in an exhaust system 100 of a diesel engine E. Has been established.

The exhaust system 100 upstream of the catalyst 1
, An exhaust turbine 8T of the first supercharger 8 and an exhaust turbine 9T of the second supercharger 9 are interposed, and each of the exhaust turbines 8T, 9T is configured to be rotationally driven by exhaust gas. Have been. A compressor 8C and a compressor 9C are connected to the exhaust turbine 8T and the exhaust turbine 9T, respectively.
Are rotatably driven on coaxial cores with the exhaust turbines 8T and 9T respectively connected thereto.

Here, the first supercharger 8 is a general turbocharger provided for improving the output of the engine E. When the compressor 8C is driven, the first supercharger 8 is introduced through the air cleaner 15. The intake air is pressurized and supplied to the engine E. Also, the first supercharger 8
The exhaust turbine 8T is disposed between the exhaust passage 2 and the exhaust passage 16 of the exhaust system 100 of the engine E. The exhaust gas after driving the exhaust turbine 8T is
Is to be discharged.

The downstream side of the exhaust passage 16 is branched into an exhaust passage 11 and a bypass passage 13, and a branch portion between the exhaust passage 11 and the bypass passage 13 is provided with a passage switching valve (by-pass valve). ) 10 is interposed. The exhaust passage 11 is provided with an exhaust turbine 9T of the second supercharger 9.
The exhaust turbine 9T is driven by flowing exhaust gas through the exhaust passage 11.

The exhaust turbine 9T in the exhaust passage 11
Downstream of the exhaust passage 11 and the bypass passage 1
3 form an exhaust passage 27. Also,
The compressor 9C of the second supercharger 9 takes in air from the air supply passage 12 that is open to the atmosphere, pressurizes (compresses) the air, and supplies pressurized air to a downstream cooling air passage (cooling passage) 17. It has become. The pressurized air (or compressed air) supplied in this manner is passed through a cooling air passage 17 to a cooler (heat exchanger) 14 as a cooling means.
It is configured to be fed to

Here, the cooler 14 has a structure as shown in FIG. 3, for example. That is, in the structure shown in FIG. 3, the cooler 14 is configured to have a double pipe structure including the inner pipe 20 and the outer pipe 21, and the outer pipe 21 is supplied with compressed air from the compressor 9C. ing.
Further, the inner pipe 20 is connected to an exhaust passage 27, and the inner pipe 20 is supplied with exhaust gas.
By providing the cooler 14 in this way, the inner pipe 2
The exhaust gas flowing through the outer tube 21 is configured as a heat exchange structure in which the exhaust gas is cooled by compressed air in the outer tube 21.

By the way, a control means S is provided to control the flow rate of the compressed air so that the temperature of the exhaust gas flowing into the catalyst 1 becomes the optimum activation range temperature of the catalyst 1. That is, the control means S is composed of the flow path switching valve 10 and the controller 7, and the flow path switching valve 10 adjusts the outflow opening from the exhaust passage 16 to the exhaust passage 11 from fully closed to fully open. It is configured to adjust the flow rate of exhaust gas from the exhaust passage 16 to the exhaust passage 11. At this time, of the exhaust gas flowing from the exhaust passage 16, the remainder not flowing out to the exhaust passage 11 flows out of the exhaust passage 16 to the bypass passage 13.

On the other hand, information from a sensor (not shown) capable of detecting the exhaust gas temperature and the engine speed is input to the controller 7, and the controller 7 constituted by a computer or the like receives the information from each sensor. The control signal based on the input signal is output to control the opening and closing of the flow path switching valve 10 in accordance with the exhaust gas temperature upstream of the catalyst 1 and the operating state of the engine.

Here, the flow path switching valve 10 is configured as shown in FIG. 2, and the valve body 10A is driven by an actuator (not shown) so that the opening degree for the bypass passage 13 and the opening degree for the exhaust passage 11 are determined. Is adjusted so that a desired state of shunting is performed. As described above, the control means S controls the flow path switching valve 10 by the control signal from the controller 7 to perform desired cooling in the cooler 14, so that the temperature range is high in the activity of the catalyst 1 and high in purification efficiency. The exhaust gas temperature is controlled in advance. When the catalyst 1 is an oxidation catalyst, control is performed so that the catalyst inlet temperature is in a range where sulfate is not generated.

Since the exhaust gas purifying apparatus for a diesel engine according to the first embodiment of the present invention is configured as described above, the following operation is performed. First, engine E
Is operated, the compressor 8C is driven by the exhaust gas from the exhaust passage 2 via the exhaust turbine 8T, and the intake air flowing from the air cleaner 15 is pressurized by the compressor 8C to perform the supercharging operation.

On the other hand, the exhaust gas discharged from the engine E drives the exhaust turbine 8T of the first supercharger 8, and then flows into the catalyst 1 through the exhaust passage 16 and the bypass passage 13. Here, a part of the exhaust gas in the exhaust passage 16 flows through the exhaust passage 11 via the flow passage switching valve 10,
After driving the exhaust turbine 9T of the second supercharger 9, it joins the bypass passage 13. By driving the exhaust turbine 9T with the exhaust energy in this way, the exhaust gas works and the exhaust temperature decreases.

The flow rate of the exhaust passage 11 is controlled by the control means S
Is controlled by That is, the opening degree of the flow path switching valve 10 is adjusted by the control signal from the controller 7,
The flow rate of the exhaust passage 11 is adjusted, and the driving state of the exhaust turbine 9T is controlled. Then, the compressor 9C is driven by the driving of the exhaust turbine 9T, whereby the air flowing from the air supply passage 12 is compressed and flows into the cooler 14 through the cooling air passage 17.

In the cooler 14, the exhaust gas in the inner tube 20 is cooled by the cooling air in the outer tube 21 to perform heat exchange. The temperature of the exhaust gas is controlled by adjusting the supply amount of the cooling air. That is, catalyst 1
The temperature of the exhaust gas is controlled so as to be in a temperature range where the activity of the exhaust gas is high and the purification efficiency is high. When the catalyst 1 is an oxidation catalyst, the temperature of the exhaust gas is controlled so that the catalyst inlet temperature does not generate sulfate.

The operating characteristics obtained by such an operation will be described with reference to FIGS. 7 to 9. First, as shown in FIG. 7, when the inlet temperature of the exhaust turbine 9T is low (at a light load), the flow path is switched. The operation is controlled with the valve 10 closed (see FIG. 2). When the inlet temperature of the exhaust turbine 9T rises and the inlet temperature of the catalyst 1 reaches the first predetermined temperature,
The flow switching valve 10 starts to open based on a control signal from the controller 7. As a result, a part of the exhaust gas flows through the exhaust passage 11, the exhaust turbine 9T is driven, the compressor 9C operates, and air is supplied to the cooler 14.

As a result, the temperature of the exhaust gas in the inner pipe 20 in the bypass passage 13 decreases, and the inlet temperature of the catalyst 1 decreases. By controlling the flow path switching valve 10 in this manner, the catalyst 1 is efficiently purified. By the way, regarding the oxidation catalyst,
The relationship between the catalyst inlet temperature, the sulfate production amount, and the catalyst efficiency as described above has characteristics as shown in FIG. For this reason, based on information from an exhaust temperature sensor (not shown), the catalyst inlet temperature is adjusted to a central appropriate range (for example, 250 to 4).
The operation of the flow path switching valve 10 is controlled to be 50 ° C.).

Further, the relationship between the catalyst inlet temperature and the catalyst efficiency of the NOx catalyst has characteristics as shown in FIG. 9. In this case, the relationship between the catalyst inlet temperature and the catalyst efficiency is determined based on information from an exhaust temperature sensor (not shown). The inlet temperature is in the central appropriate range (3
(500 ° to 500 °). Further, when the temperature of the exhaust gas in the exhaust passage 27 is too low, the flow path switching valve 10 is closed and the operation of the compressor 9C is prohibited, so that the cooler 14 having the double pipe structure functions as a heat retaining device. The exhaust gas temperature can be kept in a desired temperature range.

As described above, according to the present apparatus, since the exhaust gas temperature can be controlled to the maximum efficiency temperature of the catalyst, the exhaust gas reduction effect and the amount of sulfate generated can be greatly improved. Further, since the temperature of the catalyst 1 does not become too high, thermal deterioration of the catalyst 1 can be prevented. Further, since the compressed air produced by the compressor 9c is not returned to the engine intake, the residual oxygen in the exhaust does not increase. For example, in the case of a NOx catalyst, there is an advantage that the catalyst efficiency does not decrease.

Incidentally, the structure of the cooler 14 is not limited to that shown in FIG.
You may comprise by the structure as shown in FIG. And
Even with such a configuration, the same operation as described above can be realized. Here, what is shown in FIG. 4 is one in which an inner tube 20 composed of a plurality of small tubes is provided in one outer tube 21. And according to such a structure, the inner pipe 20
Has an advantage that the temperature of the exhaust gas passing through the inner tube 20 can be efficiently reduced.

The nozzle shown in FIG. 5 is provided with a nozzle 17A at the tip of the cooling air passage 17 and blows compressed air (cooling air) from the nozzle 17A into the exhaust passage 27, thereby forming the inside of the exhaust passage 27. The exhaust gas is configured to be cooled. According to such a structure, there is an advantage that the cooler 14 can be easily configured.

FIG. 6 shows a turbine 22 driven by a nozzle 17A.
The cooling air is supplied to the exhaust passage 27 by the propeller 23. According to such a structure,
Even when the amount of air supplied from the nozzle 17A is small, there is an advantage that more air can be supplied to the exhaust passage 27 and the cooling efficiency of the cooler 14 can be improved. (B) Description of Second Embodiment Next, a second embodiment of the present invention will be described. In the present embodiment, as shown in FIG. In the passage 25, an intercooler 24 for cooling the intake air pressurized by the compressor 9C is interposed.

The intake passage 25 is provided with a cooling air passage 17 downstream of the intercooler 24 and an intake passage 25A.
The cooling air passage 17 is connected to the cooler 14. A part of the compressed air cooled by the intercooler 24 is guided to the cooler 14 through the cooling air passage 17 so as to cool the exhaust gas in the exhaust passage 27 downstream of the exhaust turbine 9T. It is configured.

Further, the present apparatus is provided with control means S for controlling the inlet temperature of the catalyst 1 within a predetermined range. The control means S is mainly composed of the controller 7 and a valve (valve device) 26 connected to the controller 7, and controls the opening degree of the valve 26 to a desired state to thereby supply cooling to the cooler 14. The amount of air for use is adjusted.

The controller 7 also receives information such as engine speed information, engine load information, boost pressure information of the supercharger 9, and exhaust temperature information at the inlet of the catalyst 1 from various sensors (not shown). And the valve 26
Is adjusted in accordance with a control amount based on each of these pieces of information. Thus, the exhaust gas temperature at the catalyst inlet is controlled so as to be within a predetermined temperature range.

The cooler 14 has the same structure as that of the first embodiment, and for example, has a double pipe structure as shown in FIG. Since the exhaust gas purifying apparatus for a diesel engine according to the second embodiment of the present invention is configured as described above, the exhaust gas in the exhaust passage 27 is cooled by the cooling air cooled by the intercooler 24. Cooled by. At this time, the exhaust passage 27 is cooled by controlling the opening degree of the valve 26 based on the control signal of the controller 7.

Thus, the temperature of the exhaust gas flowing into the catalyst 1 is controlled to a desired state, and high purification efficiency can be obtained. Then, with the present apparatus, characteristics as shown in FIGS. 11 and 12 can be obtained. this house,
The graph shown in FIG. 11 shows the relationship between the exhaust gas temperature at the inlet of the catalyst and the load factor of the engine E. In addition,
The load factor of the engine E corresponds to the exhaust temperature of the engine E. As shown in FIG. 11, in a low load region, the exhaust gas temperature cannot be sufficiently increased by the conventional device. On the other hand, in the present apparatus, when the exhaust gas temperature is low, the exhaust gas is kept warm by the double pipe of the cooler 14 by closing the valve 26, so that the exhaust gas temperature at the catalyst inlet is kept within a predetermined range ( For example, 250 for an oxidation catalyst
４５０450 ° C.).

In the high load range, the exhaust gas temperature has conventionally been too high. However, according to the present apparatus, in the high load range, the valve 26 is controlled to be in the open state, and the cooler 14 is controlled.
As a result, a rise in the exhaust gas temperature can be suppressed, and the catalyst inlet temperature can be maintained in a desired state. The graph shown in FIG. 12 shows the characteristics of the catalyst efficiency, and the horizontal axis corresponds to the exhaust temperature of the engine E. In FIG. 12, the dotted line shows the catalyst efficiency in the conventional exhaust gas purification device, and the solid line shows the catalyst efficiency in the present device.

According to the present apparatus, by performing the temperature control as shown in FIG. 11, as shown in FIG. 12, the catalyst efficiency can be increased in almost all load regions as compared with the conventional apparatus. It is. Thus, in the present embodiment, substantially the same effects as in the first embodiment can be obtained. Further, in addition to the effects of the first embodiment, there is an advantage that deterioration of fuel efficiency can be suppressed by bypassing the intake air in a medium-speed high-load region where air is excessive in the supercharged engine.

The structure of the cooler 14 may be a double pipe structure as shown in FIG. 3 or a structure as shown in FIGS. (C) Description of Third Embodiment Next, a third embodiment of the present invention will be described. As shown in FIG. 13, an exhaust turbine 9T of a supercharger 9 is provided downstream of an exhaust passage 2 of an engine E. The catalyst 1 is provided downstream of the exhaust turbine 9 </ b> T via an exhaust passage 16.

A bypass passage 13 is provided between the exhaust passage 2 and the exhaust passage 16 for bypassing the exhaust gas from the exhaust turbine 9T.
A flow path switching valve (bypass valve) 10 is provided therein. The flow path switching valve 10 is controlled based on a control signal from the controller 7, so that the amount of exhaust flowing through the bypass 13 can be adjusted.

A compressor 9C is connected to the exhaust turbine 9T, and the compressor 9C is driven to rotate as the exhaust turbine 9T rotates. When the controller 9C is driven, the air taken in through the air cleaner 15 is pressurized, and the air is cooled through the cooling air passage 17 into the cooler 14.
It is supplied to.

Incidentally, the flow rate of the air supplied to the cooler 14 is controlled by the control means S so that the temperature of the exhaust gas flowing into the catalyst 1 becomes the temperature of the optimum activation range of the catalyst 1. . Here, the control means S includes a flow path switching valve 10 and a controller 7, and controls the driving state of the exhaust turbine 9T by adjusting the opening degree of the flow path switching valve 10, and also controls the compressor 9C. The operation is controlled to adjust the flow rate of the air supplied to the cooler 14.

The control means S performs the same control as in the first and second embodiments. That is, various information such as the exhaust gas temperature and the engine speed are input to the controller 7.
The controller 7 outputs a control signal based on an input signal from each sensor, and controls opening and closing of the flow path switching valve 10 according to the exhaust gas temperature at the inlet of the catalyst 1 and the engine operating state. It is.

On the other hand, as shown in FIG. 14, in the present embodiment, the catalyst 1 is configured to have a function as a cooler 14. That is, as shown in FIG.
Are catalyst layers 1A to 1C for purifying exhaust gas and cooling passage layers (air flow path portions) 17A to 1C for flowing compressed air.
7C are alternately polymerized. Also,
Exhaust gas flow passing through catalyst 1 and cooling passage layers 17A-
The respective catalyst layers 1A to 1C and the cooling passage layers 17A to 17C are arranged so that the cooling air passing through the inside of the 17C is substantially orthogonal.

With such a structure, the exhaust gas can be cooled through the catalyst 1. Since the exhaust gas purifying apparatus for a diesel engine according to the third embodiment of the present invention is configured as described above, the following operation is performed. First, the exhaust gas discharged from the engine E passes through the exhaust passage 2 to drive the exhaust turbine 9T, and then flows into the catalyst 1 through the exhaust passage 16.

When the exhaust gas drives the exhaust turbine 9T, the rotational driving force causes the compressor 9C to rotate.
Is driven. Then, the air taken in through the air cleaner 15 is pressurized and sent to the cooler 14 through the cooling air passage 17. Here, since the cooler 14 is configured as the catalyst 1 having a cooling function, the compressed air is applied to the cooling passage layers (air flow path portions) 17A to 17 of the catalyst 1.
By passing C, the temperature of the exhaust gas in the catalyst 1 is reduced.

The controller 7 controls the flow path switching valve 10 according to the exhaust gas temperature of the catalyst 1 and the operating state of the engine.
Is controlled, the amount of exhaust gas flowing through the bypass 13 is adjusted. Thereby, the exhaust turbine 9
The flow rate of the exhaust gas for driving the T is adjusted, the flow rate of the compressed air flowing through the cooling passage layers 17A to 17C is adjusted, and the temperature of the exhaust gas in the catalyst 1 is controlled to be within an appropriate range. It is done.

Therefore, in this embodiment, substantially the same effects as those of the first and second embodiments can be obtained. Note that the cooler 14 of the present embodiment is not limited to the above-described one, and for example, the cooler 14 described in the first and second embodiments may be applied. Further, the coolers 14 of the first and second embodiments may be configured using the coolers 14 described in the third embodiment.

[0055]

As described above in detail, according to the exhaust purification system for a diesel engine of the present invention, the exhaust gas temperature is
Since the temperature can be controlled to the highest efficiency temperature of the catalyst, exhaust gas reduction effect, thermal deterioration characteristics, sulfate generation amount, added HC amount, and the like can all be significantly improved.

Also, unlike the conventional supercharging technique, the compressed air produced by the compressor is not returned to the engine intake, so that the residual oxygen in the exhaust does not increase. For example, in the case of a NOx catalyst, the catalyst efficiency decreases. There is also the advantage of not doing it.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a main configuration of an exhaust gas purification device for a diesel engine as a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a flow path switching valve of the exhaust gas purification device for a diesel engine as the first embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view showing a main configuration of an air-cooled heat exchanger of the exhaust gas purification device for a diesel engine as the first embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view illustrating a main configuration of another example of the air-cooling heat exchanger of the exhaust gas purification device for a diesel engine as the first embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view illustrating a main configuration of another example of the air-cooling heat exchanger of the exhaust gas purification device for a diesel engine as the first embodiment of the present invention.

FIG. 6 is a schematic cross-sectional view showing a main configuration of another example of the air-cooling heat exchanger of the exhaust gas purification device for a diesel engine as the first embodiment of the present invention.

FIG. 7 is a diagram illustrating operating characteristics of the exhaust gas purification device for a diesel engine as the first embodiment of the present invention.

FIG. 8 is a diagram illustrating operating characteristics of the exhaust gas purification device for a diesel engine as the first embodiment of the present invention.

FIG. 9 is a diagram illustrating operating characteristics of the exhaust gas purification device for a diesel engine as the first embodiment of the present invention.

FIG. 10 is a schematic diagram showing a main configuration of a diesel engine exhaust gas purification apparatus according to a second embodiment of the present invention.

FIG. 11 is a diagram illustrating operating characteristics of an exhaust gas purification device for a diesel engine as a second embodiment of the present invention.

FIG. 12 is a diagram illustrating operating characteristics of an exhaust gas purification device for a diesel engine as a second embodiment of the present invention.

FIG. 13 is a schematic diagram showing a configuration of a main part of an exhaust gas purification device for a diesel engine as a third embodiment of the present invention.

FIG. 14 is a schematic perspective view showing a configuration of a catalyst of an exhaust gas purification device for a diesel engine as a third embodiment of the present invention.

FIG. 15 is a schematic diagram showing a configuration of a main part of a conventional exhaust gas purifying apparatus for a diesel engine.

FIG. 16 is a schematic diagram showing operating characteristics of a conventional exhaust purification device for a diesel engine.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Catalyst 1A-1C Catalyst layer 2, 11, 16, 27 Exhaust passage 4 Bypass flow path 5 Flow path switching valve 7 Controller 8 First supercharger 8C Compressor 8T Exhaust turbine 9 Second supercharger 9C Compressor 9T Exhaust turbine 10 Flow path switching valve (bypass valve) 12 Air supply passage 13 Bypass passage 14 Cooler (heat exchanger) as cooling means 15 Air cleaner 17 Cooling air passage (cooling passage) 17A to 17C Cooling passage layer (air passage portion) Reference Signs List 20 inner pipe 21 outer pipe 22 turbine 23 propeller 24 intercooler 25, 25A intake passage 26 valve 100 exhaust system S control means

Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location F01N 3/24 F01N 3/24 T ZAB ZABL 5/04 5/04 A 7/08 7/08 A F02B 37 / 00 ZAB F02B 37/00 ZAB 302 302D 303H (72) Inventor Toshiharu Murota 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation

Claims (7)

[Claims] 1. A catalyst disposed in an exhaust passage of a diesel engine for purifying harmful components in exhaust gas, an exhaust turbine provided in the exhaust passage upstream of the catalyst and driven by exhaust pressure, and the exhaust gas A compressor connected to a turbine and rotationally driven by the exhaust turbine; cooling means for cooling an exhaust passage upstream of the catalyst or the catalyst by compressed air obtained from the compressor; and an exhaust gas temperature flowing into the catalyst. And control means for controlling the flow rate of the compressed air so that the temperature of the compressed air becomes the optimum activation range of the catalyst. 2. The exhaust passage is provided with a bypass passage for bypassing the exhaust gas to the exhaust turbine, and a bypass valve for controlling a flow rate of the exhaust gas flowing through the bypass passage is provided. 2. The exhaust gas purifying apparatus for a diesel engine according to claim 1, wherein the open / close state of the bypass valve is controlled according to an exhaust gas temperature and an engine operating state upstream of the catalyst. 3. A downstream side of the compressor is formed by branching into an engine intake passage and a cooling passage to the cooling means, and the cooling passage is provided with a valve device for controlling a flow rate of air flowing through the cooling passage. 2. The diesel engine according to claim 1, wherein the control unit is configured to control an opening / closing state of the valve device in accordance with an exhaust gas temperature or an engine operating state upstream of the catalyst. 3. Engine exhaust purification device. 4. An intercooler for cooling air compressed by the compressor is provided downstream of the compressor and upstream of a branch between the engine intake passage and the cooling passage. The exhaust gas purifying apparatus for a diesel engine according to claim 3, characterized in that: 5. The cooling means is configured as a heat exchanger having a double pipe structure including an inner pipe and an outer pipe formed in an exhaust passage upstream of the catalyst. The compressed air from the compressor is supplied to the outer pipe, and the exhaust gas is circulated through the inner pipe of the double pipe structure.
5. The exhaust gas purifying apparatus for a diesel engine according to any one of 4. 6. The method according to claim 1, wherein the catalyst has a plurality of catalyst layers, and the catalyst is formed by alternately polymerizing the catalyst layers and an air flow path portion for flowing compressed air from the compressor. The exhaust gas purifying apparatus for a diesel engine according to any one of claims 1 to 4, characterized in that: 7. The catalyst is constituted as an oxidation catalyst, and in the purifying action of the oxidation catalyst, the control means controls the exhaust gas flowing into the catalyst to a temperature range in which sulfate is not generated in the oxidation catalyst. The exhaust gas purifying apparatus for a diesel engine according to any one of claims 1 to 6, wherein a flow rate of the compressed air is controlled.