JP2024039217A - Exhaust pipe - Google Patents

Abstract

[Problem] To provide an exhaust pipe that can improve the heat shielding and heat insulating properties in the vicinity of a flange that cannot be covered with an insulator. [Solution] An exhaust pipe 1 has an outer pipe 2, an insulator 4 that covers the periphery of the outer pipe 2, and an inner pipe 3 provided inside the outer pipe 2, the inner pipe 3 is connected to the outer pipe 2 at its upstream side and extends downstream from the connection point with the outer pipe 2 to a downstream end 3d while forming a cavity 3b between the inner pipe 3 and the inner circumferential surface 2a of the outer pipe 2, the outer pipe 2 is provided with a flange 2b at its downstream end 2d for connection to another exhaust pipe, the downstream end 4a of the insulator 4 is set at a position a predetermined distance L upstream from the flange 2b, and the downstream end 3d of the inner pipe 3 extends downstream until it exceeds the downstream end 4a of the insulator 4 and also extends downstream until just before the flange 2b. [Selected Figure] Figure 3

Description

The present invention relates to an exhaust pipe that forms part of an exhaust passage that guides exhaust gas from an internal combustion engine.

A vehicle equipped with an internal combustion engine is equipped with an exhaust pipe that guides combustion gas generated by the internal combustion engine to the outside as exhaust gas. Exhaust pipes are usually located along the underside of a vehicle and are extremely hot due to exhaust gas.

Therefore, when driving on an unpaved area, there is a risk that dry grass or the like may come into contact with the exhaust pipe and catch fire. Furthermore, the temperature of the exhaust gas decreases due to heat radiation from the exhaust pipe, and there is a possibility that the purifying ability of the catalyst cannot be fully demonstrated. Therefore, a known technique is to cover the exhaust pipe with a cylindrical insulator to create a structure of two or more layers between the inside and outside of the exhaust pipe, thereby providing heat shielding and heat insulation.

For example, Patent Document 1 discloses an insulator that covers an exhaust pipe in which one or more bent portions are formed to change the flow direction of exhaust gas flowing inside the pipe. The insulator has a cylindrical shape that circumferentially covers at least one bent part of the exhaust pipe and the exhaust pipe on the front side of the vehicle by a predetermined distance from the bent part, and extends from the covered part of the exhaust pipe. It blocks out the heat.

JP 2021-76045 Publication

However, it is difficult to cover the entire exhaust pipe using the insulator as described in Patent Document 1, and there is a problem in that some parts cannot be covered with the insulator due to manufacturing reasons. Specifically, for manufacturing reasons, when these exhaust pipes are connected by connecting a flange provided on an upstream exhaust pipe and a flange provided on a downstream exhaust pipe, The insulator cannot be placed close to the flange. Therefore, a gap is left between the insulator and the flange, resulting in a portion not covered by the insulator. The presence of such a portion in the exhaust pipe is undesirable because it may cause the dry grass to catch fire as described above or reduce the purification ability of the catalyst.

The present invention has been devised in view of these points, and an object of the present invention is to provide an exhaust pipe that can improve heat shielding properties and heat insulation properties in the vicinity of the flange, which cannot be covered with an insulator.

In order to achieve the above object, an exhaust pipe according to the present disclosure is an exhaust pipe that forms a part of an exhaust passage that guides exhaust gas of an internal combustion engine, and includes an outer pipe, an insulator that covers the outer pipe, and an insulator that covers the outer pipe. an inner tube provided inside the tube, the inner tube having an upstream side connected to the outer tube and extending from the connection point with the outer tube to the downstream end of the inner circumference of the outer tube. The outer pipe is provided with a flange for connection to another exhaust pipe at the downstream end, and the downstream end of the insulator extends downstream from the flange. The downstream end of the inner pipe extends downstream beyond the downstream end of the insulator, and the downstream end of the inner pipe is located a predetermined distance away from the flange. It extends downstream.

According to this, as the downstream end of the inner tube is located at the boundary between the outer tube and the flange, the entire area where the outer tube is exposed without being covered with an insulator becomes a two-layer structure, further improving heat shielding and insulation properties. can do. In addition, when welding the flange to the outer circumferential surface of the outer pipe during the manufacture of exhaust pipes, a special jig (a jig for correcting the diameter of the outer pipe by inserting it into the outer pipe) is used for welding. are doing. When setting such a jig, the downstream end of the inner tube is located at the boundary between the outer tube and the flange, so insert the jig from the downstream side of the outer tube until it hits the downstream end of the inner tube. Simply push it in to position it in the appropriate position.

In the exhaust pipe, the flange provided at the downstream end of the outer pipe may be connected to a flange provided at the inflow end of the exhaust gas purification device.

According to this, the entire area where the outer pipe is exposed without being covered by the insulator has a two-layer structure, and the heat retention effect of the exhaust gas in the exhaust pipe immediately before the exhaust gas purification device is high, so it can be used, for example, in the exhaust gas purification device. The reaction liquid added to the exhaust gas purifier can be delivered to the exhaust gas purification device while being vaporized at an appropriate temperature.

1 is a schematic diagram of a vehicle equipped with a diesel engine. 2 is a partial cross-sectional view showing a part of the exhaust system in FIG. 1. FIG. FIG. 3 is a sectional view of the vicinity of the connection between the urea water diffusion exhaust pipe and the NOx after-treatment device in FIG. 2;

●[Overview of a vehicle equipped with a diesel engine (Figure 1)]
Hereinafter, a urea water diffusion exhaust pipe 1 as an exhaust pipe according to an embodiment of the present invention will be described. First, an overview of a vehicle equipped with a diesel engine will be explained using FIG.

As shown in FIG. 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, causes spontaneous ignition of fuel, generates combustion gas, and converts thermal energy into kinetic energy. The diesel engine 51 has an exhaust system 53 that purifies the combustion gas that is no longer needed and releases it into the atmosphere as exhaust gas.

The exhaust system 53 includes an exhaust manifold 54, a supercharger 55, a first purification device 56, a NOx aftertreatment device 21, a second purification device 57, a silencer 58, etc., forming a series of exhaust passages, each of which has an exhaust pipe. are connected via. Some exhaust pipes are provided with a fuel addition valve 59 and a urea addition valve 12. Fuel and urea water are injected from each addition valve. For example, the first purification device 56 includes an oxidation catalyst and a particulate collection filter, and purifies CO and HC and collects particulates such as soot. Further, the NOx after-treatment device 21 includes an SCR catalyst and purifies NOx. Further, the second purification device 57 has an oxidation catalyst and purifies ammonia that is not used for purification.

The exhaust system 53 has a high temperature due to exhaust gas. Further, most of the exhaust system 53 is arranged along the lower surface of the vehicle 50. Therefore, when the vehicle 50 travels on an unpaved area, the dry grass 60 and the like may come into contact with the exhaust system 53. In particular, the exhaust pipe leading to the NOx after-treatment device 21 (exhaust pipe 1 for urea water diffusion, see Figure 2) is located relatively upstream in the exhaust system 53 and is close to the road surface, so dry grass etc. This is a part that requires measures to prevent it from catching fire if touched. It is also necessary to maintain the temperature of the exhaust gas and deliver the exhaust gas to the NOx aftertreatment device 21 (details will be described later).

● [Outline of exhaust pipe 1 for urea water diffusion (Figure 2)]
FIG. 2 is a partial sectional view showing a part of the exhaust system in FIG. 1. FIG. As shown in FIG. 2, the urea water diffusion exhaust pipe 1 according to the present invention forms part of an exhaust passage that guides exhaust gas from a diesel engine 51 (see FIG. 1). A urea water mixing exhaust pipe 11 is connected to the upstream side of the urea water diffusion exhaust pipe 1, and a NOx after-treatment device 21 (corresponding to an exhaust gas purification device) is connected to the downstream side. Exhaust gas discharged from the diesel engine 51 flows into the urea water mixing exhaust pipe 11, passes through the urea water diffusion exhaust pipe 1 according to the present invention, and is guided to the NOx aftertreatment device 21.

The urea water mixing exhaust pipe 11 located at the most upstream position in FIG. 2 is connected to the urea water diffusion exhaust pipe 1 via the dispersion device 13. The urea water mixing exhaust pipe 11 has a urea addition valve 12 , and the urea water is injected from the urea addition valve 12 toward the dispersion device 13 . The urea water is atomized by the dispersion device 13, and the exhaust gas mixed with the atomized urea water flows into the urea water diffusion exhaust pipe 1.

The urea water diffusion exhaust pipe 1 vaporizes the atomized urea water, diffuses the urea into the exhaust gas, and guides it to the NOx after-treatment device 21 . Therefore, the urea water diffusion exhaust pipe 1 is an exhaust passage that maintains the temperature of the exhaust gas and promotes the vaporization of the urea water, and maintains the SCR catalyst 26 of the NOx after-treatment device 21 at the activation temperature. It is desirable to have an outer tube 2 and an inner tube 3 provided inside the outer tube 2 to improve heat insulation. Further, the urea water diffusion exhaust pipe 1 has an insulator 4 that covers the outer tube 2 to prevent dry grass or the like from touching the outer tube 2 and catching fire, thereby improving heat shielding properties. In the urea water diffusion exhaust pipe 1 having such a three-layer structure, the atomized urea water vaporizes while flowing through the inner pipe 3, and the urea diffuses into the exhaust gas. The urea water diffusion exhaust pipe 1 is provided with a flange 2b at the downstream end 2d. The flange 2b is connected to a flange 27 provided at the inflow end of the NOx aftertreatment device 21. Exhaust gas containing urea flows into the NOx aftertreatment device 21 .

The NOx after-treatment device 21 includes an SCR catalyst 26, and reduces and removes NOx in the exhaust gas using urea diffused into the exhaust gas. The purified exhaust gas is guided further downstream and finally discharged into the atmosphere.

● [Structure of exhaust pipe 1 for urea water diffusion (Figures 2 and 3)]
As shown in FIG. 2, in the exhaust pipe 1 for urea water diffusion, the inner pipe 3 is connected to the outer pipe 2 on the upstream side. Specifically, the outer circumferential surface 3a of the inner tube 3 is connected to the inner circumferential surface 2a of the outer tube 2 by, for example, spot welding. In this way, the outer tube 2 and the inner tube 3 are connected on the upstream side and are integrated. In addition, in FIG. 2, the exhaust pipe 1 for urea water diffusion is drawn in a substantially straight shape, but it may be bent. When bending the exhaust pipe 1 for urea water diffusion, in order to hold the hollow parts 3b of the outer pipe 2 and the inner pipe 3, fill the hollow parts 3b with sand or other particles, and then bend the outer pipe 2 and the inner pipe 3. Bending the inner tube 3 together.

As shown in FIGS. 2 and 3, the inner tube 3 has a cavity 3b between it and the inner peripheral surface 2a of the outer tube 2 from the connection point with the outer tube 2 to the downstream end 3d (see FIG. 3). While forming, it extends downstream. By providing such a cavity 3b, a temperature drop of about 100° C. can be expected between the outer tube 2 and the inner tube 3. As a result, the temperature of the outer circumferential surface 2c of the outer tube 2 can be approximately 300°C. As shown in FIG. 3, the downstream end 3d of the inner tube 3 is held by the wire mesh 6 without contacting the inner circumferential surface 2a of the outer tube 2. The wire mesh 6 is arranged in the cavity 3b in order to stably hold the inner tube 3 without contacting the outer tube 2. The wire mesh 6 is sandwiched between the annular protrusions 3c formed on the inner tube 3, and movement of the inner tube 3 in the axial direction is restricted.

As shown in FIG. 2, the outer tube 2 has an enlarged diameter so that the dispersion device 13 can be fitted on the upstream side. The dispersion device 13 is fitted and welded to the upstream side of the outer tube 2. On the other hand, as shown in FIG. 3, the outer tube 2 is provided with a connecting flange 2b at the downstream end 2d so that it can be connected to the 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 tube 2. Note that a flange 27 is also provided at the exhaust gas inflow end (another exhaust pipe) of the NOx aftertreatment device 21.

As shown in FIGS. 2 and 3, the insulator 4 covers the outer tube 2. As shown in FIGS. The insulator 4 is, for example, divided into halves along the longitudinal direction of the outer tube 2 and joined together to form a cylindrical shape. The above-described welding of the outer tube 2 and the flange 2b is performed after the outer tube 2 is covered with the insulator 4. Therefore, as shown in FIG. 3, the downstream end 4a of the insulator 4 is set upstream from the flange 2b by a predetermined distance L. That is, the insulator 4 does not cover the outer tube 2 from the downstream end 4a to the flange 2b. Note that the wire mesh 5 is arranged inside the downstream end 4a of the insulator 4 so that dried grass and the like do not enter through the gap formed between the insulator 4 and the outer tube 2.

As shown in FIG. 3, the downstream end 3d of the inner pipe 3 extends downstream until it exceeds the downstream end 4a of the insulator 4, and stops just before the flange 2b (the inner pipe 3 is connected to the exhaust pipe with respect to the flange 2b). do not overlap in the longitudinal direction). As a result, the vicinity of the flange 2b where the outer tube 2 is exposed without being covered with the insulator 4 becomes a two-layer structure of the outer tube 2 and the inner tube 3, improving the heat shielding and heat insulation properties of the urea water diffusion exhaust pipe 1. can do. That is, even if dried grass or the like comes into direct contact with the outer tube 2 between the downstream end 4a of the insulator 4 and the flange 2b, it will not catch fire (improvement of heat shielding properties). Further, since heat radiation from the outer tube 2 is prevented, the exhaust gas flows into the NOx aftertreatment device 21 while maintaining its temperature (improvement of heat insulation).

Further, the downstream end 3d of the inner tube 3 is located at the boundary between the outer tube 2 and the flange 2b. Therefore, the jig used for welding the flange 2b to the outer circumferential surface 2c of the outer tube 2 during the manufacture of the exhaust pipe 1 for urea water diffusion, and the jig for correcting the diameter of the outer tube 2, is The jig can be positioned at an appropriate position by simply inserting it from the downstream side of the tube 2 and pushing it until it hits the downstream end 3d of the inner tube 3.

● [Structure of the upstream side 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 guided to the NOx after-treatment device 21 . Also in the NOx after-treatment device 21, measures are taken to prevent dry grass and to keep the exhaust gas warm.

As shown in FIG. 3, the upstream side of the inner tube 23 is connected to the outer tube 22 by, for example, spot welding. As shown in FIG. 3, the inner tube 23 extends downstream from the connection point with the outer tube 22 to the downstream end while forming a cavity 23a between it and the inner peripheral surface 2a of the outer tube 2. .

As shown in FIG. 3, the outer tube 22 is provided with a connecting flange 27 at the upstream end 22a so that it can be connected to the urea water diffusion exhaust pipe 1 on the upstream side. Specifically, a flange 27 is welded to the outer peripheral surface 22c of the upstream end 22a of the outer tube 22. The flange 27 is connected to a flange 2b provided at the downstream end of the urea water diffusion exhaust pipe 1.

As shown in FIG. 3, the insulator 24 covers the outer tube 22. Similar to the urea water diffusion exhaust pipe 1, the upstream end 24a of the insulator 24 is set at a position downstream from the flange 27 by a predetermined distance. That is, the insulator 24 does not cover the outer tube 22 from the upstream end 24a to the flange 27. However, the vicinity of the flange 27 where the outer tube 22 is exposed without being covered with the insulator 24 has a two-layer structure of the outer tube 22 and the inner tube 23, and the heat shielding properties and heat insulation properties are not deteriorated. Further, the wire mesh 25 is arranged inside the upstream end 24a of the insulator 4 to prevent dried grass and the like from entering through the gap formed between the insulator 24 and the outer tube 22.

The urea water diffusion exhaust pipe 1 of the present invention is not limited to the appearance, configuration, structure, etc. described in this embodiment, and various changes, additions, and deletions can be made without changing the gist of the present invention. .

In the description of this embodiment, the urea water diffusion exhaust pipe 1 connected to the upstream side of the NOx after-treatment device 21 was used as an example of the exhaust pipe according to the present invention. However, if the exhaust pipe is such that the vicinity of the flange cannot be covered with an insulator and the outer pipe is exposed, the exhaust pipe is not limited to the urea water diffusion exhaust pipe 1, but can be placed in any part of the exhaust system. It's okay to have one.

In the description of this embodiment, an example has been described in which the downstream end 3d of the inner tube 3 extends to just before the flange 2b (see FIG. 3). However, if the downstream end 3d of the inner tube 3 extends beyond the downstream end 4a of the insulator 4 to the downstream side, the portion of the outer tube 2 that has a single layer structure is reduced, and the heat shielding property is improved accordingly. It is possible to improve insulation. Therefore, for example, the downstream end 3d of the inner tube 3 may extend between the downstream end 4a of the insulator 4 and the flange 2b. Furthermore, the downstream end 3d of the inner tube 3 may extend until it overlaps the flange 2b.

1 Exhaust pipe for urea water diffusion 2, 22 Outer pipe 2a Inner peripheral surface 2b, 27 Flange 2c, 3a, 22c Outer peripheral surface 2d, 3d, 4a Downstream end 3 Inner pipe 3b, 23a Cavity part 3c Annular convex part 4, 24 Insulator 4a Downstream end 5, 6, 25 Wire mesh 11 Exhaust pipe for urea water mixing 12 Urea addition valve 13 Dispersion device 21 NOx after-treatment device 26 SCR catalyst 50 Vehicle 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 Hay

Claims (2)

An exhaust pipe forming part of an exhaust passage that guides exhaust gas from an internal combustion engine,
an outer tube;
an insulator that covers the outer tube;
an inner tube provided inside the outer tube;
has
The inner tube has an upstream side connected to the outer tube, and extends downstream from the connection point with the outer tube to the downstream end while forming a cavity between it and the inner peripheral surface of the outer tube. ,
The outer pipe is provided with a flange for connection to another exhaust pipe at the downstream end,
The downstream end of the insulator is set upstream from the flange by a predetermined distance,
The downstream end of the inner tube extends downstream beyond the downstream end of the insulator,
The downstream end of the inner tube extends downstream to just before the flange.
Exhaust pipe. 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 inflow end of the exhaust gas purification device.
Exhaust pipe.

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