exhaust pipe
The exhaust pipe design with a two-layer structure and wire mesh improves heat-shielding and insulation, addressing uncovered flange gaps and maintaining exhaust gas temperature for catalyst efficiency.
Patent Information
- Application Number
- JP2022143602
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2022-09-09
- Publication Date
- 2025-11-06
- Estimated Expiration
- 2042-09-09
AI Technical Summary
Existing exhaust pipes with insulators face gaps due to manufacturing constraints, leaving parts uncovered near flanges, which can lead to ignition of dry grass and reduced catalyst purification efficiency.
An exhaust pipe design with an inner pipe extending beyond the insulator's downstream end to form a two-layer structure with the outer pipe, ensuring complete coverage and improved heat-shielding near flanges, using a jig for precise welding, and incorporating a wire mesh to prevent ignition and maintain heat insulation.
Enhances heat-shielding and heat-insulating properties, preventing ignition and maintaining exhaust gas temperature for effective catalyst operation, even when exposed to unpaved roads.
Smart Images
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Abstract
Description
[Technical Field]
[0001] The present invention relates to an exhaust pipe that forms a part of an exhaust passage that guides exhaust gases from an internal combustion engine. [Background technology]
[0002] Vehicles equipped with internal combustion engines are equipped with an exhaust pipe that guides the combustion gases produced by the internal combustion engine to the outside as exhaust gases. The exhaust pipe is usually located along the underside of the vehicle and is heated to extremely high temperatures by the exhaust gases.
[0003] Therefore, when driving on unpaved roads, there is a risk that dry grass or other materials may come into contact with the exhaust pipe and ignite it. Also, heat emitted from the exhaust pipe can lower the temperature of the exhaust gas, potentially preventing the catalyst from fully utilizing its purification capabilities. To address this issue, a technology is known in which the exhaust pipe is covered with a cylindrical insulator, creating a two-layer or more structure between the inside and outside of the exhaust pipe to provide heat insulation and insulation.
[0004] For example, Patent Document 1 discloses an insulator that covers an exhaust pipe that has one or more bent portions that change the flow direction of the exhaust gas flowing inside. The insulator has a cylindrical shape that circumferentially covers at least one bent portion of the exhaust pipe and the exhaust pipe a predetermined distance forward from the bent portion, and insulates the covered areas from heat from the exhaust pipe. [Prior art documents] [Patent documents]
[0005] [Patent Document 1] Patent Publication No. 2021-76045 Summary of the Invention [Problem to be solved by the invention]
[0006] However, it is difficult to cover the entire exhaust pipe using an insulator such as that described in Patent Document 1, and there is a problem in that, due to manufacturing constraints, some parts of the exhaust pipe are left uncovered by the insulator. Specifically, when connecting a flange on an upstream exhaust pipe to a flange on a downstream exhaust pipe, the insulator cannot be placed close to the flange due to manufacturing constraints. As a result, a gap is created between the insulator and the flange, resulting in some parts not being covered by the insulator. The existence of such parts in the exhaust pipe is undesirable, as it may lead to the aforementioned ignition of dry grass or a decrease in the purification ability of the catalyst.
[0007] The present invention was devised in consideration of these points, and its object is to provide an exhaust pipe that can improve the heat-shielding and heat-insulating properties near the flange, which cannot be covered with an insulator. [Means for solving the problem]
[0008] In order to achieve the above-mentioned object, the exhaust pipe according to the present disclosure is an exhaust pipe that forms part of an exhaust passage that guides exhaust gas from an internal combustion engine, and has an outer pipe, an insulator that covers the periphery of the outer pipe, and an inner pipe provided inside the outer pipe, the inner pipe is connected to the outer pipe at its upstream side and extends downstream from the point of connection with the outer pipe to its downstream end, forming a hollow between itself and the inner surface of the outer pipe, the outer pipe is provided with a flange at its downstream end for connection to another exhaust pipe, the downstream end of the insulator is set at a position a predetermined distance upstream from the flange, the downstream end of the inner pipe extends downstream until it passes beyond the downstream end of the insulator, and the downstream end of the inner pipe extends downstream until just before the flange.
[0009] With this, the downstream end of the inner pipe is located at the boundary between the outer pipe and the flange, resulting in a two-layer structure across the entire area where the outer pipe is exposed and not covered by the insulator, further improving heat-shielding and heat-insulating properties. Furthermore, when welding a flange to the outer surface of the outer pipe during exhaust pipe manufacturing, a special jig (a jig that is inserted into the outer pipe to adjust the diameter of the outer pipe) is used for welding. When setting such a jig, since the downstream end of the inner pipe is located at the boundary between the outer pipe and the flange, the jig can be inserted from the downstream side of the outer pipe and positioned appropriately simply by pushing it in until it hits the downstream end of the inner pipe.
[0010] In the above exhaust pipe, the flange provided at the downstream end of the outer pipe may be connected to a flange provided at the inlet end of an exhaust gas purification device.
[0011] This results in a two-layer structure over the entire area where the outer pipe is exposed and not covered by the insulator, which provides a high heat retention effect for the exhaust gas in the exhaust pipe just before the exhaust gas purification device. For example, a reaction liquid added toward the exhaust gas purification device can be delivered to the exhaust gas purification device while remaining vaporized at an appropriate temperature. [Brief explanation of the drawings]
[0012] [Figure 1] 1 is a schematic diagram of a vehicle equipped with a diesel engine. [Figure 2] FIG. 2 is a partial cross-sectional view showing a portion of the exhaust system in FIG. [Figure 3] 3 is a cross-sectional view of the vicinity of the connection between the urea water diffusion exhaust pipe and the NOx aftertreatment device in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION
[0013] ●[Overview of a vehicle equipped with a diesel engine (Figure 1)] An exhaust pipe 1 for urea water diffusion as an exhaust pipe according to one embodiment of the present invention will be described below. First, an outline of a vehicle equipped with a diesel engine will be described with reference to FIG.
[0014] As shown in Figure 1, a diesel engine 51 (corresponding to an internal combustion engine) is mounted at the front of a vehicle 50. The diesel engine 51 compresses intake air supplied from an intake manifold 52, causing spontaneous ignition of fuel to generate combustion gases, and converts thermal energy into kinetic energy. The diesel engine 51 has an exhaust system 53, which purifies unnecessary combustion gases and releases them into the atmosphere as exhaust gases.
[0015] The exhaust system 53 forms a series of exhaust passages including an exhaust manifold 54, a turbocharger 55, a first purification device 56, a NOx aftertreatment device 21, a second purification device 57, a silencer 58, and the like, all of which are connected via an exhaust pipe. The exhaust pipe may be provided with a fuel addition valve 59 or a urea addition valve 12. Fuel or urea water is injected from each addition valve. For example, the first purification device 56 has an oxidation catalyst and a particulate collection filter, and purifies CO and HC and captures particulates such as soot. The NOx aftertreatment device 21 has an SCR catalyst and purifies NOx. The second purification device 57 has an oxidation catalyst and purifies ammonia not used for purification.
[0016] The exhaust system 53 is heated to a high temperature by the exhaust gas. Furthermore, most of the exhaust system 53 is arranged along the underside of the vehicle 50. Therefore, when the vehicle 50 travels on unpaved ground, dry grass 60 and the like may come into contact with the exhaust system 53. In particular, the exhaust pipe (the urea water diffusion exhaust pipe 1, see FIG. 2) leading to the NOx aftertreatment device 21 is located relatively upstream in the exhaust system 53 and is close to the road surface, so measures are required to prevent dry grass and the like from catching fire even if it comes into contact with the pipe. Furthermore, it is also necessary to maintain the temperature of the exhaust gas so that the exhaust gas can be delivered to the NOx aftertreatment device 21 (details will be described later).
[0017] ●[Outline of the urea water diffusion exhaust pipe 1 (Fig. 2)] Fig. 2 is a partial cross-sectional view showing a part of the exhaust system in Fig. 1. As shown in Fig. 2, an exhaust pipe 1 for urea water diffusion according to the present invention forms part of an exhaust passage that guides exhaust gas from a diesel engine 51 (see Fig. 1). An exhaust pipe 11 for urea water mixing is connected to the upstream side of the exhaust pipe 1 for urea water diffusion, and a NOx aftertreatment device 21 (corresponding to an exhaust gas purification device) is connected to the downstream side. Exhaust gas emitted from the diesel engine 51 flows into the exhaust pipe 11 for urea water mixing, passes through the exhaust pipe 1 for urea water diffusion according to the present invention, and is guided to the NOx aftertreatment device 21.
[0018] 2, the urea water mixing exhaust pipe 11 located at the most upstream position is connected to the urea water diffusion exhaust pipe 1 via a dispersion device 13. The urea water mixing exhaust pipe 11 has a urea addition valve 12, and urea water is injected from the urea addition valve 12 toward the dispersion device 13. The urea water is atomized when it hits the dispersion device 13, and exhaust gas mixed with the atomized urea water flows into the urea water diffusion exhaust pipe 1.
[0019] The urea-water diffusion exhaust pipe 1 vaporizes atomized urea water, diffuses the urea into the exhaust gas, and guides it to the NOx aftertreatment device 21. Therefore, the urea-water diffusion exhaust pipe 1 is preferably an exhaust passage that maintains the temperature of the exhaust gas to promote the vaporization of the urea water and maintains the SCR catalyst 26 of the NOx aftertreatment device 21 at its activation temperature. It has an outer pipe 2 and an inner pipe 3 disposed inside the outer pipe 2 to enhance thermal insulation. The urea-water diffusion exhaust pipe 1 also has an insulator 4 surrounding the outer pipe 2 to prevent dry grass or the like from coming into contact with the outer pipe 2 and igniting it, enhancing thermal insulation. In the urea-water diffusion exhaust pipe 1 with this three-layer structure, the atomized urea water vaporizes as it flows through the inner pipe 3, and the urea diffuses into the exhaust gas. The urea-water diffusion exhaust pipe 1 has a flange 2b disposed at its downstream end 2d. The flange 2b is connected to a flange 27 disposed at the inlet end of the NOx aftertreatment device 21. The NOx aftertreatment device 21 receives exhaust gas containing urea.
[0020] The NOx aftertreatment device 21 has an SCR catalyst 26, and reduces and removes NOx in the exhaust gas using urea diffused in the exhaust gas. The purified exhaust gas is then guided further downstream and finally emitted into the atmosphere.
[0021] ●[Structure of the exhaust pipe 1 for urea water diffusion (Fig. 2, Fig. 3)] As shown in Figure 2, in the exhaust pipe 1 for urea water diffusion, the inner pipe 3 is connected to the outer pipe 2 on its upstream side. Specifically, the outer peripheral surface 3a of the inner pipe 3 is connected to the inner peripheral surface 2a of the outer pipe 2, for example, by spot welding. In this way, the outer pipe 2 and the inner pipe 3 are connected together on their upstream sides and are integrated. Note that in Figure 2, the exhaust pipe 1 for urea water diffusion is depicted as extending almost straight, but it may be bent. When bending the exhaust pipe 1 for urea water diffusion, in order to maintain the hollow portions 3b of the outer pipe 2 and the inner pipe 3, the hollow portions 3b are filled with granular material such as sand, and then the outer pipe 2 and the inner pipe 3 are bent together.
[0022] As shown in Figures 2 and 3, the inner pipe 3 extends downstream from its connection with the outer pipe 2 to its downstream end 3d (see Figure 3), forming a cavity 3b between itself and the inner circumferential surface 2a of the outer pipe 2. The presence of this cavity 3b allows for a temperature drop of approximately 100°C between the outer pipe 2 and the inner pipe 3. As a result, the temperature of the outer circumferential surface 2c of the outer pipe 2 can be increased to approximately 300°C. As shown in Figure 3, the downstream end 3d of the inner pipe 3 is supported by a wire mesh 6 without contacting the inner circumferential surface 2a of the outer pipe 2. The wire mesh 6 is positioned in the cavity 3b to stably support the inner pipe 3 without contacting the outer pipe 2. The wire mesh 6 is sandwiched between an annular protrusion 3c formed on the inner pipe 3, restricting axial movement of the inner pipe 3.
[0023] As shown in Fig. 2, the outer pipe 2 has an expanded diameter on the upstream side so that the dispersion device 13 can be fitted into it. The dispersion device 13 is fitted into and welded to the upstream side of the outer pipe 2. Meanwhile, as shown in Fig. 3, the outer pipe 2 is provided with a connection flange 2b at its downstream end 2d so that it can be connected to a NOx aftertreatment device 21 on the downstream side. Specifically, the flange 2b is welded to the outer peripheral surface 2c of the downstream end 2d of the outer pipe 2. A flange 27 is also provided at the inlet end (another exhaust pipe) of the exhaust gas in the NOx aftertreatment device 21.
[0024] As shown in Figures 2 and 3, the insulator 4 covers the periphery of the outer pipe 2. The insulator 4 is formed, for example, by joining two halves split along the longitudinal direction of the outer pipe 2 together to form a cylindrical shape. The welding of the outer pipe 2 to the flange 2b described above is performed after the outer pipe 2 is covered with the insulator 4. Therefore, as shown in Figure 3, the downstream end 4a of the insulator 4 is set at a position a predetermined distance L upstream from the flange 2b. In other words, the insulator 4 does not cover the outer pipe 2 from the downstream end 4a to the flange 2b. The wire mesh 5 is arranged inside the downstream end 4a of the insulator 4 to prevent dead grass and the like from entering through the gap between the insulator 4 and the outer pipe 2.
[0025] As shown in FIG. 3, the downstream end 3d of the inner pipe 3 extends downstream beyond the downstream end 4a of the insulator 4 and stops just before the flange 2b (the inner pipe 3 does not overlap the flange 2b in the longitudinal direction of the exhaust pipe). As a result, the area near the flange 2b, where the outer pipe 2 is exposed and not covered by the insulator 4, has a two-layer structure of the outer pipe 2 and the inner pipe 3, improving the heat insulation and thermal insulation properties of the urea water diffusion exhaust pipe 1. In other words, even if dry grass or the like comes into direct contact with the outer pipe 2 between the downstream end 4a of the insulator 4 and the flange 2b, it will not ignite (improved heat insulation). Furthermore, because heat radiation from the outer pipe 2 is prevented, the exhaust gas flows into the NOx aftertreatment device 21 while maintaining its temperature (improved thermal insulation).
[0026] In addition, the downstream end 3d of the inner pipe 3 is located at the boundary between the outer pipe 2 and the flange 2b. Therefore, the jig used when welding the flange 2b to the outer peripheral surface 2c of the outer pipe 2 during the manufacture of the exhaust pipe 1 for urea water diffusion, and used to correct the diameter of the outer pipe 2, can be positioned at an appropriate position simply by inserting the jig from the downstream side of the outer pipe 2 and pushing it in until it hits the downstream end 3d of the inner pipe 3.
[0027] ●[Upstream structure of the NOx aftertreatment device 21 (Figure 3)] The exhaust gas in which urea has been diffused in the urea water diffusion exhaust pipe 1 is led to a NOx aftertreatment device 21. In the NOx aftertreatment device 21, measures are also taken to prevent withering and to keep the exhaust gas warm.
[0028] 3, the upstream side of the inner pipe 23 is connected to the outer pipe 22 by, for example, spot welding. As shown in FIG. 3, the inner pipe 23 extends downstream from the connection point with the outer pipe 22 to the downstream end, forming a cavity 23a between itself and the inner circumferential surface 2a of the outer pipe 2.
[0029] 3, the outer pipe 22 is provided with a connecting flange 27 at its upstream end 22a so that it can be connected to the urea water diffusion exhaust pipe 1 on the upstream side. Specifically, the flange 27 is welded to the outer peripheral surface 22c of the upstream end 22a of the outer pipe 22. The flange 27 is connected to a flange 2b provided at the downstream end of the urea water diffusion exhaust pipe 1.
[0030] As shown in Figure 3, the insulator 24 covers the periphery of the outer pipe 22. As with the urea water diffusion exhaust pipe 1, the upstream end 24a of the insulator 24 is located at a predetermined distance downstream from the flange 27. In other words, the insulator 24 does not cover the outer pipe 22 from the upstream end 24a to the flange 27. However, in the vicinity of the flange 27 where the outer pipe 22 is exposed and not covered by the insulator 24, a two-layer structure of the outer pipe 22 and the inner pipe 23 is formed, and heat-shielding and heat-insulating properties are not reduced. In addition, the wire mesh 25 is arranged inside the upstream end 24a of the insulator 24 to prevent dead grass and the like from entering through the gap between the insulator 24 and the outer pipe 22.
[0031] The exhaust pipe 1 for urea water diffusion of the present invention is not limited to the appearance, configuration, structure, etc. described in this embodiment, and various modifications, additions, and deletions are possible within the scope that does not change the gist of the present invention.
[0032] In the description of this embodiment, the exhaust pipe according to the present invention has been described by taking as an example the exhaust pipe 1 for urea water diffusion connected to the upstream side of the NOx aftertreatment device 21. However, the exhaust pipe is not limited to the exhaust pipe 1 for urea water diffusion, and may be an exhaust pipe located in any part of the exhaust system, as long as the vicinity of the flange cannot be covered with an insulator and the outer pipe is exposed.
[0033] In the description of this embodiment, an example (see FIG. 3) has been given in which the downstream end 3d of the inner pipe 3 extends to just before the flange 2b. However, if the downstream end 3d of the inner pipe 3 extends downstream beyond the downstream end 4a of the insulator 4, the portion of the single-layer structure consisting of only the outer pipe 2 is reduced, thereby improving the heat-shielding and heat-insulating properties accordingly. Therefore, for example, the downstream end 3d of the inner pipe 3 may extend to between the downstream end 4a of the insulator 4 and the flange 2b. Alternatively, the downstream end 3d of the inner pipe 3 may extend until it overlaps with the flange 2b. [Explanation of symbols]
[0034] 1. Urea water diffusion exhaust pipe 2, 22 outer tube 2a Inner surface 2b, 27 flange 2c, 3a, 22c outer surface 2d, 3d, 4a downstream end 3 Inner tube 3b, 23a Cavity 3c Annular convex part 4, 24 Insulator 4a Downstream end 5, 6, 25 wire mesh 11. Exhaust pipe for mixing urea water 12 Urea addition valve 13 Dispersion device 21 NOx aftertreatment device 26 SCR catalyst 50 vehicles 51 Diesel engine 52 Intake manifold 53 Exhaust System 54 Exhaust manifold 55 Supercharger 56 First Purification Device 57 Second Purification Device 58 silencer 59 Fuel addition valve 60 dried grass
Claims
1. An exhaust pipe forming a part of an exhaust passage that guides exhaust gas from an internal combustion engine, The outer tube and an insulator that covers the outer tube; an inner tube provided inside the outer tube; and the inner pipe is connected to the outer pipe at its upstream side, and extends downstream from the connection point with the outer pipe to its downstream end while forming a cavity between itself and an inner circumferential surface of the outer pipe, The outer pipe has a flange at its downstream end for connection to another exhaust pipe, The downstream end of the insulator is set at a position spaced a predetermined distance upstream from the flange, a downstream end of the inner pipe extends downstream beyond the downstream end of the insulator, The downstream end of the inner pipe extends downstream to just before the flange. Exhaust pipe.
2. The exhaust pipe according to claim 1, The flange provided at the downstream end of the outer pipe is connected to a flange provided at the inlet end of an exhaust gas purification device. Exhaust pipe.
Citation Information
Patent Citations
Exhaust system of vehicular engine
JP2006070705A
Vehicular exhaust pipe
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Insulator
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Muffler Heat Protection Assembly
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