JPH07279653A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PURPOSE:To achieve a satisfactory NOx purifying rate in a wide operating region of an internal combustion engine. CONSTITUTION:An exhaust purifier of an internal combustion engine 1 includes a converter 3 in which a catalyst for purifying NOx in the presence of hydrocarbon in the oxygen excess atmosphere is built. In the exhaust purifier, an exhaust pipe 2 extended from the internal combustion engine 1 to the converter 3 is of such a double pipe structure that an outer pipe 5 is put on the outside thereof, and means such as a running wind intake port 6, an intake port 7 for cooling air from a radiator fan and the like are provided for introducing cooling air into the space between the exhaust pipe 2 and the outer pipe 5. Further, flow control valves 8, 9 for controlling the inflow of the cooling air and a control means 11 for controlling the valves are provided, and the exhaust temperature at the inlet of the converter 3 is taken as a NOx purifying effective region. A cooling part which does not bear a catalyst is provided on the middle part of the converter, and the NOx purifying region can be expanded by providing a means for cooling the cooling part by cooling air.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust purification system for an internal combustion engine, and more particularly to an exhaust purification system for an internal combustion engine using a catalyst for purifying NOx in the presence of hydrocarbons in an oxygen excess atmosphere.

[0002]

2. Description of the Related Art NOx contained in exhaust gas of an internal combustion engine
As a device for purifying NO, a catalyst comprising a zeolite supporting a transition metal or a noble metal and using a catalyst for reducing NOx in the presence of hydrocarbons in an oxidizing atmosphere is disclosed, for example, in Japanese Utility Model Publication No. 4-1617. ing. In addition,
In this publication, hydrocarbons are adsorbed when the exhaust gas contains a large amount of hydrocarbons, and when the exhaust gas does not have sufficient hydrocarbons during lean combustion operation, the hydrocarbons are removed and required for the purification reaction. It is disclosed to supply various hydrocarbons.

In an automobile, as shown in FIG. 7, intake air is taken into the internal combustion engine 41 through an air cleaner 42 and a throttle valve 43, and exhaust gas is emitted from the internal combustion engine 41.
After passing through an exhaust pipe 44 extending rearward from the exhaust gas to be purified by a converter 45 having the above-mentioned catalyst built therein disposed in the middle thereof, it is discharged into the atmosphere through a muffler 46 at the rear end.

As shown in FIG. 8, the temperature of the exhaust gas while passing through the exhaust pipe 44 (hereinafter sometimes referred to as the exhaust temperature) is such that the exhaust pipe 44 reaches the converter 45 from the internal combustion engine 41. Is reduced by being cooled by the traveling wind, and is raised in temperature by the purifying reaction in the converter 45, and then is cooled again by the traveling wind while passing through the exhaust pipe 44.

[0005]

By the way, the catalyst of the converter 45 depends on the temperature of the inflowing exhaust gas and NOx.
The purification rate changes greatly. That is, the purification rate of the catalyst is
As shown in FIG. 6, for NOx, the desired purification is performed only in a narrow temperature range of about ± 20 ° C. around a predetermined temperature t (normally in the range of 250 to 350 ° C.) peculiar to the catalyst composition. The effective NOx purification range in which the desired rate of purification of NOx is obtained is very narrow. The purification rate of total hydrocarbons (THC), which is the purification rate of all kinds of hydrocarbons, is due to the oxidation reaction, and a high purification rate can be obtained at a temperature of about 450 ° C or higher.

On the other hand, although the exhaust gas entering the converter 45 is cooled by the traveling wind as described above, the arrangement position of the converter 45 is often limited, and as shown in FIG. However, there is a problem in that it is not possible to cool the NOx to the effective area for NOx purification, and it is often impossible to sufficiently purify NOx. Further, even if the converter can be arranged so that the exhaust temperature at the inlet of the converter 45 is in the NOx purification effective range in a certain operating range of the internal combustion engine, the exhaust temperature depends on the load of the internal combustion engine 41, the traveling speed, The converter 45 changes significantly depending on the outside temperature, etc.
It is impossible to arrange the converter 45 so that the temperature of the exhaust gas flowing into the exhaust gas is always in the NOx purification effective range, and there is a problem that the desired exhaust purification rate cannot be achieved in the entire operating range.

Particularly, in the case of lean burn operation, a large amount of NOx is generated during acceleration.
When accelerating, the air-fuel ratio is returned to the theoretical air-fuel ratio, or the air-fuel ratio is set to NO.
It is necessary to adopt a complicated combustion control system such as severely controlling just before the irregular combustion where x does not occur.
There is a problem that the cost becomes high and it is difficult to obtain a sufficient effect.

Further, even if the exhaust gas in the NOx purification effective region flows into the converter 45, as shown in FIG. 9, the exhaust gas temperature rises due to the NOx purification reaction in the converter 45, and the exhaust gas moves out of the NOx purification effective region. Therefore, the NOx purification is performed only at the inlet of the converter 45, and there is also a problem that good NOx purification cannot be expected.

In view of such conventional problems, an object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine which can achieve a sufficient NOx purification rate in a wide operating range of the internal combustion engine.

[0010]

The first invention of the present application is an exhaust gas purification apparatus for an internal combustion engine, which comprises a converter incorporating a catalyst for purifying NOx in the presence of hydrocarbons in an oxygen excess atmosphere. Has a double pipe structure in which at least a part of the exhaust pipe is fitted with an outer pipe on the outside thereof, and a means for introducing cooling air into the space between the exhaust pipe and the outer pipe is provided and the inflow amount of the cooling air is controlled. It is characterized in that means for performing is provided.

In the second invention of the present application, the converter is divided in the exhaust gas flow direction and a cooling section which does not carry a catalyst is provided in an intermediate portion thereof, and a means for cooling the cooling section with cooling air is provided and the converter is cooled. It is characterized in that means for controlling the flow rate of wind is provided.

[0012]

According to the first invention of the present application, since the outer pipe is fitted on the outer side of the exhaust pipe between the internal combustion engine and the converter to introduce the cooling air between them, the exhaust pipe is The flowing exhaust gas can be efficiently cooled, and the inflow amount of the cooling air is controlled according to the exhaust temperature at the inlet of the converter, etc., so that the exhaust temperature flowing into the converter is reliably
It is possible to control in the Ox purification effective range, and it is possible to achieve a sufficient NOx purification rate in a wide operating range of the internal combustion engine.

Further, according to the second invention of the present application, by providing a cooling portion not carrying a catalyst in the middle portion of the converter and cooling with cooling air, the temperature rises due to the NOx purification reaction, and the NOx purification effective region is increased. Since the exhaust temperature can be lowered at a position outside the range, NOx purification can be performed again downstream thereof, and the exhaust temperature can be reliably controlled within the NOx purification effective region by controlling the flow rate of the cooling air. The NOx purification range, which was limited to the inlet of the converter, can be expanded and a high NOx purification rate can be achieved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG.

In FIG. 1, reference numeral 1 denotes an internal combustion engine mounted on an automobile, and an exhaust pipe 2 thereof extends downward from the front side of the internal combustion engine 1 and extends downward from the lower part of the vehicle body toward the rear part of the vehicle body. Along the way, a converter 3 having a built-in catalyst for purifying NOx in the presence of hydrocarbons in an oxygen excess atmosphere is arranged. A muffler 4 is arranged at the rear end of the exhaust pipe 2.

The portion of the exhaust pipe 2 from the exhaust manifold to the converter 3 is fitted with an outer pipe 5 on the outer side of the exhaust pipe 2.
It has a heavy pipe structure. A traveling air intake 6 for taking in traveling air is connected to the lower part of the front end of the outer pipe 5, and a cooling air intake 7 for taking in the cooling air generated by the radiator fan 10 is connected to the upper part thereof. The traveling air intake 6 and the cooling air intake 7 are provided with flow rate adjusting valves 8 and 9 for adjusting their opening degrees, respectively. The flow rate adjusting valves 8 and 9 and the radiator fan 10 are controlled by an engine control unit or a separately provided control means 11, and the control means 11 includes an exhaust temperature sensor 12 arranged immediately before the inlet of the converter 3. The detection signal is input.

Further, at an appropriate portion of the portion of the exhaust pipe 2 having the double pipe structure, particularly at an appropriate portion in the vicinity of the converter 3, cooling which projects toward the space between the exhaust pipe 2 and the outer pipe 5. The fins 13 are provided and configured to efficiently cool the exhaust gas flowing in the exhaust pipe 2. The outer tube 5 is fitted onto the outer circumference of the converter 3 and is open to the atmosphere at its rear end.

In the above structure, the exhaust pipe 2 and the outer pipe 5
By introducing the traveling wind or the cooling air by the radiator fan 10 from the traveling air intake 6 or the cooling air intake 7 into the space between the exhaust pipes from the internal combustion engine 1 to the converter 3 by these cooling winds. The outer peripheral surface of 2 is cooled, and the exhaust gas flowing in the exhaust pipe 2 is efficiently cooled. Also,
Since the cooling fins 13 are provided at appropriate places near the converter 3, the exhaust gas is efficiently cooled even after the temperature of the exhaust gas is lowered to some extent. Then, based on the exhaust temperature detected by the exhaust temperature sensor 12 immediately before the converter 3, the control means 11 operates the flow rate adjusting valves 8 and 9 to control the inflow amount of the traveling wind or the cooling wind. The exhaust gas temperature at the inlet of the converter 3 can be accurately controlled. In the control, the traveling wind is preferentially taken in from the traveling wind intake 6, and when the cooling capacity is insufficient only by the traveling wind, for example, at a low speed and a high load such as an uphill, there is a relation with the cooling water temperature. Instead, the radiator fan 10 is driven to take in cooling air from the radiator fan 10.

In this way, by introducing cooling air into the space between the exhaust pipe 2 and the outer pipe 5 to cool the exhaust gas based on the exhaust gas temperature immediately before the converter 3, as shown in FIG. To ensure that the exhaust temperature flowing into the converter 3 is N
It is possible to control in the Ox purification effective range, and it is possible to achieve a sufficient NOx purification rate in a wide operating range of the internal combustion engine 1.

Next, a second embodiment of the present invention will be described with reference to FIG.
-It demonstrates, referring FIG.

In FIG. 2, intake air is taken into the internal combustion engine 1 through an air cleaner 21 and a throttle valve 22,
A converter 23 is arranged in the middle of an exhaust pipe 2 extending rearward from the internal combustion engine 1. Traveling air is introduced into the outer peripheral surface of the converter 23 by a traveling air introducing duct 24, and the flow rate adjusting valve 2 is provided in the middle of the traveling air introducing duct 24.
5 is provided, and the throttle valve 22 and the flow rate adjusting valve 25 are interlockingly connected by an interlocking wire 26.

As shown in FIGS. 3 and 4, the converter 23 is constructed by arranging a catalyst body 32 in an outer cylinder 31, and the catalyst body 32 is constructed by supporting a catalyst on a metal honeycomb 33 and the converter 23. A cooling unit 35, on which no catalyst is supported, is provided between the catalyst supporting unit 34a on the inlet side and the catalyst supporting unit 34b on the outlet side. A heat radiation fin 36 is fixed to a portion of the outer circumference of the outer cylinder 31 corresponding to the cooling portion 35, and an air cooling jacket 37 is provided so as to surround the periphery of the heat radiation fin 36. One side of the air-cooling jacket 37 is open, and the traveling wind introducing duct 24 is connected to the other side portion.

In the above structure, the cooling portion 35 that does not carry the catalyst is provided in the middle portion of the converter 23 to cool it by the running wind. Therefore, as shown in FIG. When the exhaust temperature rises due to the NOx purification reaction in the portion 34a and goes out of the NOx purification effective range, the exhaust temperature is lowered in the cooling portion 35, so that the NO again occurs at the inlet portion of the catalyst supporting portion 34b downstream thereof.
x purification is performed, the NOx purification range limited to the inlet portion of the converter 23 can be expanded, and a high NOx purification rate can be achieved. Further, since the radiation fins 36 are provided on the outer peripheral portion of the cooling unit 35 to enable efficient cooling, the converter 23 can be made compact and the restrictions on the vehicle can be eliminated.

When the load is low during constant speed traveling, the throttle valve 22 is closed and the flow rate adjusting valve 25 is closed by the interlocking wire 26, so that supercooling can be prevented. The catalyst performance can be effectively exhibited in the entire operating region of the internal combustion engine 1. The cooling unit 3
A temperature sensor may be arranged in the vicinity of 5, and the flow control valve 25 may be opened / closed based on the detected temperature to control the introduction of traveling wind.

The present invention is not limited to the above embodiment. For example, by combining the above first and second embodiments, the exhaust gas temperature at the inlet of the converter is controlled to ensure the operation in all operating regions. NOx purification is performed, and exhaust gas is cooled in the middle of the converter to reduce NOx.
The x purification reaction region can be expanded to achieve a high NOx purification rate.

[0026]

As described above, according to the exhaust gas purifying apparatus for an internal combustion engine of the first invention of the present application, the outer pipe is fitted on the outer side of the exhaust pipe between the exhaust manifold and the converter, and cooling is performed between them. Since the air is introduced, the exhaust gas flowing through the exhaust pipe can be efficiently cooled, and by controlling the inflow amount of the cooling air according to the exhaust temperature at the converter inlet, the exhaust gas flowing into the converter can be controlled. The temperature of the gas can be reliably controlled within the effective NOx purification range, a sufficient NOx purification rate can be achieved in a wide operating range of the internal combustion engine, and the degree of freedom in the location of the converter is increased. The degree of freedom in design is increased, and even if a large amount of NOx is generated during acceleration during lean burn operation, severe combustion control can be relaxed and the cost of the combustion control system can be reduced. Effect is exhibited.

Further, according to the exhaust gas purifying apparatus for an internal combustion engine of the second invention of the present application, by providing a cooling portion not carrying a catalyst in the middle portion of the converter and cooling with a cooling air, NO
Since the temperature rises due to the x purification reaction and the temperature of the exhaust gas falls below the NOx purification effective range, the NOx purification can be performed again downstream thereof, and the exhaust flow rate can be controlled by controlling the flow rate of the cooling air. The temperature is definitely N
Since the control can be performed within the Ox purification effective range, the NOx purification range limited to the inlet of the converter can be expanded and a high NOx purification rate can be achieved.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of an exhaust gas purification apparatus for an internal combustion engine of the present invention and a change in exhaust gas temperature along an exhaust pipe thereof.

FIG. 2 is a diagram showing an overall configuration of a second embodiment of an exhaust purification system for an internal combustion engine of the present invention.

FIG. 3 is a vertical sectional view showing a configuration of a converter according to the embodiment.

4 is a cross-sectional view taken along the line AA of FIG.

FIG. 5 is a diagram showing exhaust gas temperature at each position of the converter of the embodiment.

FIG. 6 is a characteristic diagram of a purification rate with respect to an exhaust temperature of a catalyst built in a converter.

FIG. 7 is a diagram showing an overall configuration of an exhaust gas purification device for an internal combustion engine of a conventional example.

FIG. 8 is a diagram showing a configuration of an exhaust emission control device in a conventional example and a change in exhaust gas temperature along an exhaust pipe thereof.

FIG. 9 is a diagram showing a converter in a conventional example and exhaust gas temperatures at respective positions thereof.

[Explanation of symbols]

 1 Internal Combustion Engine 2 Exhaust Pipe 3 Converter 5 Outer Pipe 6 Traveling Wind Inlet 7 Cooling Wind Inlet 8 Flow Rate Control Valve 9 Flow Rate Control Valve 11 Control Means 23 Converter 24 Traveling Wind Inlet Duct 25 Flow Rate Control Valve 34a Inlet Side Catalyst Carrier 34b Outlet side catalyst support part 35 Cooling part

Claims (2)

[Claims] 1. An exhaust gas purifying apparatus for an internal combustion engine, comprising a converter having a built-in catalyst for purifying NOx in the presence of hydrocarbons in an oxygen excess atmosphere, wherein at least a part of an exhaust pipe from the internal combustion engine to the converter is provided outside the exhaust pipe. An internal combustion engine having a double pipe structure in which an outer pipe is fitted over the outer pipe, means for introducing cooling air into the space between the exhaust pipe and the outer pipe, and means for controlling the inflow amount of the cooling air. Exhaust gas purification device for engines. 2. In an exhaust gas purification apparatus for an internal combustion engine equipped with a converter that contains a catalyst for purifying NOx in the presence of hydrocarbons in an oxygen excess atmosphere, the converter is divided in the exhaust gas flow direction and the catalyst is provided in the middle portion. An exhaust gas purification apparatus for an internal combustion engine, comprising: a cooling section that does not carry the cooling air; and a means for cooling the cooling section with cooling air and a means for controlling the flow rate of the cooling air.