JP2018189046A - Heat insulation exhaust pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat insulation exhaust pipe high in heat insulation, capable of reducing its weight, and high in strength reliability against heat strain, compared to conventional arts.SOLUTION: In a heat insulation exhaust pipe 4 with a double pipe structure where a hollow heat insulation layer 3 is interposed between an outer pipe 1 and an inner pipe 2, an end part on an upstream side of the inner pipe 2 is internally fitted and connected to an end part on an upstream side of the outer pipe 1 in a state where an upstream side of the hollow heat insulation layer 3 is sealed; and an end part of a downstream side of the inner pipe 2 is internally fitted to an end part of a downstream side of the outer pipe 1 in a slidable manner, and thermal expansion difference between the outer pipe 1 and the inner pipe 2 can be absorbed in a state where a downstream side of the hollow heat insulation layer 3 is sealed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a heat insulating exhaust pipe.

  Particulate matter (particulate matter) discharged from a diesel engine is mainly composed of soot composed of carbonaceous matter and SOF content (Soluble Organic Fraction) composed of high-boiling hydrocarbon components. Although it has a composition containing a small amount of sulfate (mist-like sulfuric acid component), as a measure to reduce this kind of particulates, a particulate filter is installed in the middle of the exhaust passage through which exhaust gas flows. Has been performed conventionally.

  This type of particulate filter has a porous honeycomb structure made of a ceramic such as cordierite, and the inlets of the flow paths partitioned in a lattice pattern are alternately sealed, and the inlets are not sealed. About the flow path, the exit is sealed, and only the exhaust gas which permeate | transmitted the porous thin wall which divides each flow path is discharged | emitted downstream.

  Then, the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, so that the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging. It is necessary to regenerate, but in normal diesel engine operating conditions, there are few opportunities to obtain exhaust temperatures that are high enough for the particulates to self-combust. It has been studied to adopt a catalyst regeneration type particulate filter that is integrally supported on a particulate filter or that an oxidation catalyst is arranged separately in a stage preceding the particulate filter.

  That is, if such a catalyst regeneration type particulate filter is employed, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates can be burned and removed even at an exhaust temperature lower than the conventional one. It becomes possible.

  In addition to the particulate filter described above, it has also been proposed to equip the exhaust passage with a NOx selective reduction catalyst or NOx occlusion reduction catalyst for the purpose of removing NOx in the exhaust gas as a post-treatment device. Particularly in recent years, an aftertreatment device in which a particulate filter is combined with a NOx storage reduction catalyst has been developed.

  However, even if any of these after-treatment devices is adopted, a relatively high exhaust temperature higher than a predetermined temperature is required in order to obtain reliable combustion removal of particulates and sufficient catalytic activity. It is important to introduce the exhaust gas into the aftertreatment device before the temperature of the exhaust gas discharged from the engine is lowered as much as possible.

  When installing this type of aftertreatment device on a vehicle, depending on the vehicle model, there are cases in which the space for installing the aftertreatment device can be secured only at a position away from the diesel engine. When the outside air temperature is low, the exhaust temperature tends to decrease while the exhaust gas is led from the diesel engine to the aftertreatment device through the exhaust pipe, and there is a concern that the operating region in which the aftertreatment device is active becomes narrower than usual.

  Therefore, in the prior art, as a measure for preventing such a decrease in exhaust temperature, as shown in FIG. 3, a heat insulating exhaust pipe c having a double pipe structure consisting of an outer pipe a and an inner pipe b is used. Between the tube b, an inner blade d formed by braiding a heat-resistant wire rod into a cylindrical shape is interposed. By interposing such an inner blade d having a high porosity, the outer tube a and the inner tube are disposed. Insulation with b is intended.

  Further, the outer pipe a, the inner pipe b, and the inner blade d are welded all around to seal between the outer pipe a and the inner pipe b, and the end of the outer pipe a has flanges e and f. The end of the double-pipe heat insulation exhaust pipe c (especially the upstream end) is the end of another heat insulation exhaust pipe c having the same double pipe structure. Also when connecting to the part, the exhaust gas g is prevented from entering between the outer tube a and the inner tube b.

  As prior art document information related to this type of heat insulating exhaust pipe, there is the following Patent Document 1 and the like.

Japanese Patent Laid-Open No. 2007-9866

  However, although the void ratio of the inner blade d is high, the inner blade d is interposed between the outer tube a and the inner tube b. As a result, it is difficult to obtain the heat retention as expected by increasing the thermal conductivity from the inner tube b side to the outer tube a side. There is a possibility that the mass may be increased by d.

  Further, when the inner tube b is heated by the high-temperature exhaust gas g and thermally expands in the axial direction, a difference in thermal expansion from the outer tube a side that is thermally insulated by the inner blade d occurs. On the other hand, since the inner tube b is constrained at both ends, the difference in thermal expansion is not absorbed, and thermal distortion occurs in the joint portion of the inner tube b with the outer tube a, which may cause damage such as cracks in the welded portion. There was also.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a heat insulating exhaust pipe that has higher heat retention, is lighter, and has higher strength reliability against thermal distortion.

  The present invention is a heat insulating exhaust pipe having a double pipe structure in which a hollow heat insulating layer is interposed between an outer pipe and an inner pipe, and an upstream end portion of the inner pipe with respect to an upstream end portion of the outer pipe Are joined in a state in which the upstream side of the hollow heat insulation layer is sealed, and the downstream end of the inner tube is slidably fitted into the downstream end of the outer tube, and the hollow The present invention is characterized in that it can absorb the difference in thermal expansion between the outer tube and the inner tube while the downstream side of the heat insulating layer is sealed.

  Thus, with this arrangement, the conventional inner blade is not interposed between the outer tube and the inner tube, and the outer tube and the inner tube have a hollow heat insulating layer in most of the portions excluding both ends. Since the heat conductivity from the inner tube side to the outer tube side is lowered, the heat retaining property is improved as compared with the prior art, and the mass is reduced by the amount of eliminating the inner blade. .

  Even if the inner pipe is heated by the high-temperature exhaust gas and thermally expands in the axial direction, resulting in a difference in thermal expansion from the outer pipe side that is insulated by the hollow heat insulating layer, the downstream end of the outer pipe On the other hand, the downstream end of the inner tube slides to absorb the difference in thermal expansion, and thermal distortion does not occur at the joint between the outer tube and the upstream end of the inner tube.

  Furthermore, in concrete implementation of the present invention, hollow insulation is achieved by reducing the diameter of both ends of the outer tube by a predetermined range and expanding the diameter of both ends of the inner tube by a predetermined range to bring them into a fitted state. It is preferable to define a layer and join only the upstream ends of the outer tube and the inner tube.

  According to the above-described heat-insulated exhaust pipe of the present invention, the outer pipe and the inner pipe can be held in a non-contact state only through the hollow heat-insulating layer in most parts except for both ends. The thermal conductivity from the side to the outer tube side can be lowered to significantly improve the heat retention compared to the conventional one, and the inner blade is not required, and a significant weight reduction can be realized. Since the thermal expansion difference between the outer tube and the inner tube can be absorbed without restricting the thermal expansion toward the downstream side of the tube, the thermal strain at the joint between the ends of the outer tube and the upstream side of the inner tube It is possible to obtain an excellent effect that the strength reliability can be greatly improved by avoiding the above-described problem.

It is sectional drawing which shows an example of the form which implements this invention. It is sectional drawing which shows another example of a form of this invention. It is sectional drawing which shows a prior art example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an example of an embodiment for carrying out the present invention. In the example shown here, a double tube structure in which a hollow heat insulating layer 3 is interposed between an outer tube 1 and an inner tube 2 is shown. With respect to the heat insulating exhaust pipe 4, the hollow heat insulating layer is formed by fitting the upstream end of the inner pipe 2 into the upstream end of the outer pipe 1 (upstream in the flow direction of the exhaust gas 5 in FIG. 1). 3 is joined in a sealed state, while the downstream end of the inner tube 2 is slidably fitted to the downstream end of the outer tube 1 so that the downstream side of the hollow heat insulating layer 3 It is characterized in that it is constructed so as to be able to absorb the difference in thermal expansion between the outer tube 1 and the inner tube 2 in a sealed state.

  More specifically, both ends of the outer tube 1 are reduced in diameter by a predetermined range to form a reduced diameter portion 1a, and both ends of the inner tube 2 are enlarged by a predetermined range to form an enlarged diameter portion 2a. The hollow heat insulating layer 3 is defined by fitting the upstream and downstream reduced-diameter portions 1a and the enlarged-diameter portions 2a to each other, and the reduced-diameter portion 1a of the outer pipe 1 on the upstream side. Only the enlarged diameter portion 2a of the inner pipe 2 is joined by spot welding at four positions every 90 ° in the circumferential direction, and the reduced diameter portion 1a of the outer pipe 1 on the downstream side and the enlarged diameter portion 2a of the inner pipe 2 are welded. It is in a state where it is simply abutted without being used.

  Further, flanges 6 and 7 are respectively fitted to both ends of the outer pipe 1 and welded to the entire circumference, and another heat insulating exhaust pipe 4 manufactured in the same manner is connected to the flanges 6 and 7. It can be connected by bolt fastening or the like.

  Thus, in this way, the conventional inner blade is not interposed between the outer tube 1 and the inner tube 2, and most of the outer tube 1 and the inner tube 2 except for both ends. In this case, the heat conductivity from the inner tube 2 side to the outer tube 1 side is lowered and the heat retaining property is improved as compared with the prior art, and the inner blade is eliminated. The mass can be reduced by that amount.

  Further, even if the inner pipe 2 is heated by the high-temperature exhaust gas 5 and thermally expands in the axial direction, and a thermal expansion difference from the outer pipe 1 side insulated by the hollow heat insulating layer 3 occurs, The downstream end of the inner tube 2 slides with respect to the downstream end to absorb the thermal expansion difference, and thermal distortion occurs at the joint between the outer tube 1 and the upstream end of the inner tube 2. Disappear.

  Therefore, according to the above-described embodiment, the outer tube 1 and the inner tube 2 can be held in a non-contact state only through the hollow heat insulating layer 3 in most parts except for the both ends. The thermal conductivity from the 2 side to the outer tube 1 side can be lowered to significantly improve the heat retention compared to the prior art, and the inner blade is not required, and a significant weight reduction can be realized. On the other hand, the thermal expansion difference between the outer tube 1 and the inner tube 2 can be absorbed without restricting the thermal expansion toward the downstream side of the inner tube 2, so that the upstream end of the outer tube 1 and the inner tube 2 can be absorbed. Strength reliability can be greatly improved by avoiding thermal distortion at the joint between the parts.

  FIG. 2 shows another embodiment of the present invention. In the embodiment shown in FIG. 1 described above, an example of the heat insulating exhaust pipe 4 having a straight extension shape is shown. Shows an example of a bent heat insulating exhaust pipe 4 for constituting a corner portion or the like of an exhaust system. Even in such a shape, the straight extending heat insulating exhaust pipe 4 described in FIG. Needless to say, the same operational effects as the case can be obtained.

  However, when such a heat insulating exhaust pipe 4 having a bent shape is manufactured by restricting both ends of the inner pipe 2 with respect to the outer pipe 1 as in the prior art, a difference in thermal expansion between the outer pipe 1 and the inner pipe 2 is simply achieved. Not only occurs, but also a difference in thermal extension occurs between the outer side and the inner side in the bending direction, and a large thermal distortion appears. Therefore, it is significant to apply the heat insulating exhaust pipe 4 of the present invention. The heat insulating exhaust pipe 4 having a bent shape that is very useful can be obtained.

  In addition, the heat insulation exhaust pipe of this invention is not limited only to the above-mentioned example, Of course, a various change can be added in the range which does not deviate from the summary of this invention.

1 Outer pipe 2 Inner pipe 3 Hollow heat insulation layer 4 Heat insulation exhaust pipe

Claims (2)

  A heat insulation exhaust pipe having a double-pipe structure in which a hollow heat insulation layer is interposed between the outer pipe and the inner pipe, and the end on the upstream side of the inner pipe is fitted into the end on the upstream side of the outer pipe. And the downstream end of the inner tube is slidably fitted into the downstream end of the outer tube to slidably fit the downstream end of the hollow heat insulating layer. A heat-insulated exhaust pipe characterized by being configured to absorb a difference in thermal expansion between the outer pipe and the inner pipe in a state where the side is sealed.   A hollow heat insulating layer is formed by reducing both ends of the outer tube by a predetermined range and expanding both ends of the inner tube by a predetermined range so as to be fitted to each other, and upstream of the outer tube and the inner tube. The heat-insulated exhaust pipe according to claim 1, wherein only end portions on the side are joined.

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