JP4630721B2 - Engine exhaust system - Google Patents

Description

  The present invention relates to an exhaust system for an engine of an automobile or the like. More specifically, the present invention relates to an engine exhaust system equipped with an exhaust purification device such as a catalytic converter or a DPF that purifies exhaust discharged from the engine.

  Conventionally, in an engine exhaust system as described above, a catalytic converter is placed in the middle of the exhaust system in order to remove nitrogen oxides, carbon monoxide, hydrocarbons, and the like, which are harmful components in the exhaust discharged from the engine. In general, the diesel engine is provided with DPF (diesel particulate removal) separately from the catalytic converter in order to remove particulate matter (PM) mainly composed of carbon discharged from the engine. It is common to provide a device).

  Catalytic converters purify harmful substances in exhaust gas with catalysts. For example, so-called three-way catalysts are widely used as catalysts for efficiently purifying nitrogen oxides, carbon monoxide, and hydrocarbons in exhaust gas simultaneously. Yes. The three-way catalyst is based on one or more kinds of noble metals such as platinum, palladium, or rhodium, and an oxide such as nickel or cobalt is added to this as a catalyst component. The structure is supported on a heat resistant porous carrier.

  However, the above three-way catalyst generally has low activity in a low temperature region below 300 ° C., and it is difficult to sufficiently purify harmful components in low temperature exhaust discharged immediately after the engine is started. The three-way catalyst can efficiently remove harmful components in a so-called stoichiometric air-fuel ratio operation region where the oxygen concentration in the exhaust gas is approximately 1% or less, but the oxygen concentration in the exhaust gas is several percent or more. In other words, the purification efficiency of harmful components is significantly lower for exhaust emissions from lean combustion regions of Otto cycle engines and diesel engines operating essentially in excess oxygen.

  On the other hand, nitrogen oxides and hydrocarbons can be purified even in the above lean combustion region where the oxygen concentration in the exhaust gas is high by loading a transition metal on a substance having a molecular sieve structure such as various natural zeolites or synthetic zeolites. Catalysts that can be made are being developed. However, a catalyst in which a transition metal is supported on a substance having a molecular sieve structure of this kind generally exhibits excellent activity in a temperature range of about 300 ° C. to 500 ° C., but the temperature is less than 300 ° C. discharged immediately after starting the engine. Efficient purification of harmful components in the exhaust gas has not been achieved with the current technology.

  Therefore, even in an operating region where the exhaust temperature is low, such as immediately after the engine is started, as a means for improving exhaust purification efficiency by the catalyst having the transition metal supported on the three-way catalyst or the molecular sieve structure, an electric heating device is provided around these catalysts. It has been proposed to activate the catalyst with its heat. However, heating with electric heat requires a large amount of power, so it is not suitable for low-powered vehicle engines, etc., and the fuel efficiency of the engine is reduced, or electrical failure leads to durability and reliability. There are problems such as lowering.

  Further, in Patent Document 1 below, a second catalyst such as an oxidation catalyst or a combustion catalyst is used in place of the electric heating device as described above, and a catalyst such as a catalyst in which a transition metal is supported on a material having the above three-way catalyst or molecular sieve structure. An exhaust gas that is disposed around one catalyst, passes through the first catalyst, is guided to the second catalyst, and the first catalyst is heated by an exothermic reaction between the second catalyst and the exhaust gas. Has been proposed. However, the above-described one requires a passage and a control device for guiding the exhaust gas that has passed through the first catalyst to the second catalyst, which increases the manufacturing cost, and the second catalyst is the same as that of the first catalyst. There is a problem that the first catalyst cannot be heated efficiently because it is located outside and on the downstream side with respect to the exhaust flow.

  On the other hand, the DPF removes PM in the exhaust with a filter and regenerates the filter with a regenerator to prevent clogging. There are several types depending on the filter material and the regeneration method. . For example, there are one using a ceramic honeycomb filter called cordierite, one using a ceramic fiber non-woven fabric, and one using a silicon carbide honeycomb filter.

  In any of the above methods, PM clogged in the filter is incinerated to regenerate the filter. As the incineration method, for example, incineration with external heat such as heating wire, or catalyst applied on the filter is used. There are those that lower the combustion temperature of PM by the effect and can burn with about 300 ° exhaust heat, and those that incinerate PM with exhaust heat using nitrogen dioxide in the exhaust.

  However, in any of the above methods, if the incineration temperature is low, PM may not be incinerated well. In particular, those that burn with exhaust heat cannot be incinerated well in cold weather or when the exhaust temperature is low immediately after starting the engine, causing problems such as clogging due to PM remaining on the filter. .

JP-A-10-71324

  The present invention has been proposed in view of the above problems. In an engine exhaust system equipped with an exhaust purification device such as a catalytic converter or a DPF, exhaust gas is exhausted even in a cold state or in an operating state where the exhaust temperature is low immediately after the engine is started. It is an object of the present invention to provide an engine exhaust system that can effectively and efficiently purify harmful components.

Engine exhaust system according to the present invention, in the engine exhaust system of an exhaust gas purification apparatus provided in an exhaust pipe for purifying the exhaust gas discharged from the engine, constitute the exhaust pipe between the inner and outer tubes, the As an exhaust purification device, it has a catalytic converter and a diesel particulate removal device connected in order from the exhaust upstream side, and generates heat in contact with exhaust exhausted from the engine in the inner pipe upstream of the catalytic converter And a cylindrical heating element having a large number of through-holes on the peripheral wall surface is disposed substantially concentrically with the exhaust pipe, and the exhaust upstream end of the heating element is fixed to the inner surface of the inner pipe, the portion other than the end portion of the heating element causes away from the inner surface of the inner tube, within said tube upstream of the diesel particulate filter downstream of the catalytic converter, the exhaust of the engine Another cylindrical heating element that generates heat upon contact with the exhaust and has a large number of through-holes on the peripheral wall surface is arranged substantially concentrically with the exhaust pipe, and the exhaust upstream end of the additional heating element Is fixed to the inner surface of the inner tube, and a portion other than the end portion of the another heat generating element is separated from the inner surface of the inner tube, and the heat generating element in the inner tube and the exhaust heat upstream side of the other heat generating element Providing an inclined portion that expands toward the exhaust upstream side and the end portion that is expanded in diameter, and forming the through hole in the inclined portion and a portion on the exhaust downstream side of the inclined portion. Features. The exhaust system of the engine of the present invention, the feature that the projection hole or cut-and-raised hole protrudes through the small hole before Symbol heating element and said another heating element in said tube, on the outside or inside To do .

  Examples of the heating element include at least one of a calcium oxide / calcium carbonate (CaO / CaCO3) substance, a noble metal such as platinum (Pt), rhodium (Rh), palladium (Pd), or an alloy mainly composed of these. Either one can be selected and used. Moreover, as a shape of the said heat generating body, the cylindrical thing which has many through-holes in a surrounding wall surface is suitable for installing in exhaust_gas | exhaustion, for example. In that case, the heating element itself is formed in a cylindrical shape having a large number of through holes, or the heating element is provided on the surface of a carrier made of a cylindrical metal or ceramic having a large number of through holes on the peripheral wall surface. A supported structure may be used.

  As described above, the exhaust system of the engine according to the present invention is in contact with the exhaust discharged from the engine in the exhaust system upstream of the exhaust purification device such as a catalytic converter or DPF provided in the middle of the system. By providing the heat generating element that generates heat, the exhaust gas introduced into the exhaust gas purification device such as the catalytic converter or the DPF can be heated in advance. In particular, in Patent Document 1, the first catalyst is indirectly heated from the outside by the second catalyst, whereas the present invention allows the exhaust gas introduced into the exhaust purification device such as the catalytic converter to be sent from the engine to the catalytic converter. It is efficient because it is directly heated by the heating element in the middle of the exhaust system. Further, when an exothermic catalyst such as an oxidation catalyst or a combustion catalyst that generates heat upon contact with exhaust gas is used as the heating element, the exhaust gas purification efficiency can be further improved by the catalyst.

  Hereinafter, the present invention will be specifically described based on embodiments shown in the drawings. FIG. 1 is a perspective view of a schematic configuration showing an embodiment of an exhaust system according to the present invention, and FIGS. 2A and 2B are partially enlarged sectional views of a part and b part in FIG.

  The embodiment shown in the figure is applied to an exhaust system of a diesel engine. The exhaust system 1 is arranged in the middle of an exhaust pipe (exhaust pipe) 3 extending from the exhaust manifold 2 of the engine to the muffler 5 (not shown). As the purification device 4, a catalytic converter 41 and a DPF (diesel particulate removal device) 42 are connected in communication in that order. In the figure, 6 is a flange joint.

  As the catalyst used in the catalytic converter 41, for example, the above-described three-way catalyst or a catalyst in which a transition metal is supported on a substance having a molecular sieve structure can be used. As the three-way catalyst, for example, one or more kinds of noble metals such as platinum (Pt), rhodium (Rh), palladium (Pd), etc. are used as a base, and nickel (Ni), iron (Fe) may be used as necessary. , Cobalt (Co), manganese (Mn), cerium (Ce) and other oxides added as catalyst components, which are supported on granular or monolithic carriers with excellent heat resistance such as alumina and cordierite Can be used.

  In addition, as a catalyst in which a transition metal is supported on a substance having the above molecular sieve structure, it is generally called zeolite, the main components are silica and alumina, the Si / A1 ratio is about 5 to 100, and the crystal structure is X-type. , Y-type and ZSM-type metallosilicates, etc., and zeolites and metallosilicates obtained by ion exchange with transition metals can be used.

  On the other hand, the DPF 42 can be applied to any of the conventional systems. Particularly, as a filter regeneration system, the PM combustion temperature is lowered by the effect of the catalyst applied on the filter, and is about 300 °. Combustible with the heat of exhaust gas and an oxidation catalyst placed in front of the filter to increase the amount of nitrogen dioxide in the exhaust gas. It can be applied well to what is incinerated.

  In the present invention, a heating element 7 is provided in the exhaust system 1 on the exhaust upstream side of the exhaust purification device 4 such as the catalytic converter 41 or the DPF 42 to generate heat by contact with the exhaust discharged from the engine. In the present embodiment, the heating element 7 as shown in FIG. 2A is provided in the exhaust pipe 3 at the portion a in FIG. 1 upstream from the catalytic converter 41, and b in FIG. 1 upstream from the DPF 42. The heating elements 7 as shown in FIG. 2B are respectively provided in the exhaust pipe 3 of the part.

In particular, in the case of the figure, a cylindrical heating element 7 having a large number of small through- holes 7 a on the peripheral wall surface is disposed substantially concentrically with the exhaust pipe 3 in the inner pipe 31 of the exhaust pipe 3 formed in the inner and outer doubles 31 and 32. The end of the heating element 7 on the upstream side of the exhaust is enlarged and fixed to the inner surface of the inner pipe 31 by welding or the like, and the other end than the upstream side is from the inner surface of the inner pipe 31. By separating them, the exhaust gas flows through the small through holes 7a and both the inner and outer surfaces of the heating element 7 so that the heating element 7 and the exhaust gas are in contact with each other on a wide surface.

  The heating element 7 may be made of any material as long as it generates heat upon contact with exhaust from the engine. For example, as described above, a calcium oxide / calcium carbonate (CaO / CaCO3) substance or platinum ( Pt), rhodium (Rh), noble metals such as palladium (Pd) or alloys mainly composed thereof, for example, platinum-palladium alloy (Pt-Pd), or those obtained by adding a small amount of rhodium (Rh) It is possible to select and use at least one of them.

  The shape of the heating element is also appropriate. For example, as described above, a cylindrical member having a large number of through holes on the peripheral wall surface is suitable for installation in the exhaust. In that case, the heating element itself is formed in a cylindrical shape having a large number of through-holes, or on the substantially entire surface of a carrier made of a cylindrical metal or ceramic having a large number of through-holes on the peripheral wall surface. The structure which carried the said heat generating body may be sufficient.

  In the above configuration, the exhaust discharged from the engine 1 not shown in the figure is introduced into the exhaust pipe 3 through the exhaust manifold 2 and then first provided in the exhaust pipe 3 in FIG. It flows into the heating element 7 of (a) from the direction of the arrow in the figure. As a result, exhaust is brought into contact with the heating element 7 and both react (exothermic reaction), and the exhaust is heated by the heat. In particular, in the illustrated example, the heating element 7 has a large number of through-holes 7a on the peripheral wall surface. And the heating element 7 and the exhaust are separated from each other on a wider surface by separating the exhaust pipe 3 (inner pipe 31) from the exhaust pipe 3 (inner pipe 31). Can be contacted.

  That is, the exhaust gas that has entered from the upstream side of the heating element 7 contacts the inner peripheral surface of the heating element 7 and flows into the outer peripheral surface side of the heating element 7 from the through small hole 7a. In particular, in FIG. 2A, by forming the through small hole 7a in the upstream inclined portion 7b, more exhaust gas can flow into the outer peripheral surface side of the heating element 7. The exhaust gas flowing into the outer peripheral surface side of the heating element 7 comes into contact with the outer peripheral surface of the heating element 7, and a part of the exhaust gas is moved again to the inner peripheral surface side of the heating element 7 through the through small holes 7a. To do. By repeating this, the heating element 7 and the exhaust are uniformly contacted on a wider surface, and the above reaction is promoted, and the exhaust passing through the vicinity of the heating element 7 can be efficiently heated. is there.

  The exhaust gas heated as described above is continuously introduced into the catalytic converter 41 as an exhaust gas purification device to purify the exhaust gas. At that time, the exhaust gas is discharged from the engine, for example, when it is cold or when the engine is started. Even when the temperature of the exhaust gas is low, it can be introduced into the converter 41 in a state of being heated to a predetermined temperature or higher by the heating element 7 in advance. As a result, the exhaust gas purification performance of the catalytic converter 4 can be improved. In particular, in the present invention, the exhaust gas introduced into the catalytic converter 4 can be directly heated on the upstream side thereof, so that the thermal efficiency and the exhaust gas purification efficiency are high. The exhaust can be purified extremely efficiently.

  Next, the exhaust gas purified by the catalytic converter 41 is continuously processed in the same manner as described above by the heating element 7 shown in FIG. 2B provided in the exhaust pipe 3 of the b part in FIG. It is heated in the DPF 42 and guided into the DPF 42, for example, PM that is clogged in the filter in the DPF 42 can be surely incinerated and the filter can be regenerated well, and is discharged from the engine during cold or engine start. Even when the temperature of the exhaust gas is low, the exhaust gas purification performance by the DPF 42 can be improved satisfactorily and the performance can be maintained stably for a long period of time.

  In the above embodiment, the heating elements 7 are provided at two locations on the upstream side of the catalytic converter 41 and the upstream side of the DPF 42. However, the arrangement position and the number of arrangements are appropriate. It may be provided at one upstream side, for example, at a part or c part in FIG. Further, three or more portions a to c in FIG. 1 may be provided.

  2A, the cylindrical heating element 7 is spaced apart in the exhaust pipe 3, particularly in the inner pipe 31 of the exhaust pipe 3 formed in the inner and outer duplex 31, 32 as shown in the example. If the exhaust resistance is increased when the diameter of the heating element 7 becomes too small, the diameter of the exhaust pipe 3 (inner and outer pipes 31, 32) is, for example, as shown in FIG. 3 (a) or (b). And the diameter of the heating element 7 may be increased accordingly. The same applies to the exhaust pipe and the heating element 7 in FIG.

Further, the through hole 7a of the heating element 7 may be a protruding hole or a cut-and- raised hole protruding outside or inside the cylindrical heating element 7 as shown in FIG. It is possible to increase the contact area with the exhaust. The shape of the heating element 7 is not limited to a cylindrical shape, but may be a semi-cylindrical shape, a rod shape, or any other appropriate shape, and may be formed in a protruding shape on the inner surface of the exhaust pipe 3 (inner pipe 31).

  Moreover, although the said embodiment was applied to the exhaust system provided with both the catalytic converter 41 and DPF42, it is applicable also to what is provided with only one of the catalytic converter 41 and DPF42. Although the illustrated example is applied to a diesel engine such as an automobile, it can also be applied to an ordinary four-cycle engine, an engine for a motorcycle, and the like.

  As described above, the exhaust system of the engine according to the present invention preheats the exhaust introduced into the exhaust purification device such as the catalytic converter and the DPF even in a cold state or in an operating state where the exhaust temperature is low immediately after starting the engine. The exhaust purification efficiency can be increased by this, and the degree of freedom of design and industrial applicability of this type of muffler can be increased.

The perspective view which shows one Embodiment of the exhaust system of the engine by this invention. (A) And (b) is an expanded sectional view of the a part and b part in FIG. (A) And (b) is an expanded sectional view of the a part in FIG. 1 of the modification. (A) And (b) is the perspective view and sectional drawing which show the example of a change of a heat generating body.

DESCRIPTION OF SYMBOLS 1 Engine exhaust system 2 Exhaust manifold 3 Exhaust pipe 31 Inner pipe 32 Outer pipe 4 Exhaust purification device 41 Catalytic converter 42 DPF
5 Muffler 6 Flange joint 7 Heating element 7a Through hole

Claims (2)

In an engine exhaust system in which an exhaust purification device for purifying exhaust exhausted from the engine is provided in the middle of the exhaust pipe,
The exhaust pipe is composed of an inner pipe and an outer pipe,
As the exhaust purification device, having a catalytic converter and a diesel particulate removal device connected in order from the exhaust upstream side,
A cylindrical heating element that generates heat in contact with the exhaust discharged from the engine and has a large number of through-holes on the peripheral wall surface in the inner pipe upstream of the catalytic converter is substantially concentric with the exhaust pipe. Placed in
An end portion on the exhaust upstream side of the heating element is fixed to the inner surface of the inner tube, and a portion other than the end portion of the heating element is separated from the inner surface of the inner tube ,
Another cylindrical heat generating in the inner pipe on the downstream side of the catalytic converter and in the upstream side of the diesel particulate removing device in contact with the exhaust discharged from the engine and having a large number of through holes on the peripheral wall surface Arranging the body substantially concentrically with the exhaust pipe,
The exhaust heat upstream end of the another heating element is fixed to the inner surface of the inner tube, and the other heating element other than the end is separated from the inner surface of the inner tube,
Provided on the exhaust upstream side of the heating element and the other heating element in the inner pipe is an inclined portion that expands toward the exhaust upstream side and the end that is expanded, and the inclined portion and the inclined An exhaust system for an engine , wherein the through hole is formed in a portion on the exhaust downstream side of the portion . 2. The engine exhaust system according to claim 1, wherein the small through-holes of the heating element and the other heating element in the inner pipe are formed as a protruding hole or a cut-and-raised hole protruding outward or inward .

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