JP2002371843A - Exhaust pipe for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust pipe for an internal combustion engine requiring satisfactory appearance and capable of preventing the discoloration on an outer face of the exhaust pipe due to the influence of a temperature of exhaust gas and the occurrence of thermal oxidation. SOLUTION: A plated layer having luster is formed on an inner face of at least any of steel pipe 11 among steel pipes except an innermost pipe 12 of the exhaust pipe 1 constituted by multiple steel pipes, and the inner face (the inner face of the steel pipe 11) on which the plated layer is formed is made apart from the steel pipe 12 on its inner side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust pipe through which exhaust gas from an internal combustion engine passes, and more particularly, to an exhaust pipe suitable for a case where a good external appearance is required by being exposed to the outside. Regarding exhaust pipe.

[0002]

2. Description of the Related Art In a motorcycle, a single pipe or a double pipe of a steel pipe such as STKM or SUS is generally used as an exhaust pipe extending from an engine and exposed to the outside. Exhaust pipe made of STKM material single pipe, S
In order to improve the appearance and enhance the decorativeness of the entire vehicle, STKM is used as a double-pipe exhaust pipe having an outer pipe made of TKM material.
Conventionally, Cr plating is applied to the outer surface of the exhaust pipe (the outer surface of the single tube or the outer surface of the double tube) which is a material.

[0003]

By the way, in the above-mentioned conventional exhaust pipe of an internal combustion engine, when the temperature of the exhaust gas becomes high due to the improvement of the engine output, the single pipe made of STKM steel pipe whose outer surface is plated with Cr is used. In the case of the exhaust pipe described above, direct exposure to high-temperature exhaust gas causes discoloration of the Cr plating applied to the outer surface of the exhaust pipe, and further causes deterioration and thermal oxidation. Further, even in the case of a single exhaust pipe made of a SUS material whose outer surface is not subjected to Cr plating, if the temperature of the exhaust gas is high, discoloration or, in some cases, scale formation and peeling due to high-temperature oxidation may occur.

On the other hand, in the case of an exhaust pipe of a double pipe having a space portion between an outer pipe and an inner pipe (including a pipe having an inner pipe or an outer pipe itself having a multilayer structure), an outer pipe is provided. Since the pipe is not directly exposed to high-temperature exhaust gas, discoloration and thermal oxidation on the outer surface of the exhaust pipe are less likely to occur than in the case of a single pipe exhaust pipe, but in recent years the performance of internal combustion engines has improved. As the output per exhaust volume increases, the temperature of the exhaust gas further rises due to the introduction of the secondary air. Therefore, even in the case of a double-pipe exhaust pipe, the exhaust pipe is radiated by heat radiation from the inner pipe. Discoloration and thermal oxidation may occur on the outer surface (the outer surface of the outer tube), and scale formation and peeling may occur due to high-temperature oxidation.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems. More specifically, an exhaust pipe of an internal combustion engine, which needs to have good appearance, has an exhaust gas affected by the temperature of exhaust gas. It is an object to prevent discoloration and thermal oxidation from occurring on the outer surface of the tube.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an exhaust pipe for passing exhaust gas from an internal combustion engine, the innermost one of an exhaust pipe composed of multiple steel pipes. A glossy plating layer is formed on the inner surface of at least one of the steel pipes other than the pipe, and the inner surface on which the plating layer is formed is separated from the inner steel pipe. It is characterized by the following.

According to the exhaust pipe of an internal combustion engine as described above,
In the exhaust pipe by multiple steel pipes, the glossy plating layer is formed on the inner surface of at least one of the steel pipes outside the innermost pipe in contact with the exhaust gas,
Even if the innermost pipe in contact with the exhaust gas becomes hot and radiates heat to the surroundings, the outer plating layer on the inner surface of the steel pipe that reflects this heat radiation will become hotter than this plating layer. As a result, discoloration and thermal oxidation due to high temperature on the outer surface of the exhaust pipe (the outer surface of the outermost pipe) can be prevented.

In addition, the plating layer formed on the inner surface of the steel pipe outside the innermost pipe is separated from the inner steel pipe and has no direct heat conduction from the inner steel pipe. Since the heat transfer is small through the gas (including a substantially vacuum) in the space between the steel pipe and the inner steel pipe, the plating layer and the base material are unlikely to be heated to a high temperature. No discoloration or thermal oxidation occurs in the layer, and a low emissivity (that is, high reflectance) in the plating layer can be maintained.

By keeping the space between the steel pipes arranged in multiple layers in a substantially vacuum state, it is possible to reduce the heat convection in that part, and to exhaust air to the outer surface side of the exhaust pipe. The effect of heat from the gas can be more effectively reduced.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an exhaust pipe of an internal combustion engine according to the present invention will be described below with reference to the drawings. In addition,
FIG. 1 shows a motorcycle which is an example of an exhaust pipe, FIG. 2 shows an internal structure near both ends of an exhaust pipe composed of an outer pipe and an inner pipe, and FIG. FIG. 4 shows an example of a method for forming a plating layer on both the inner and outer surfaces, and FIG.
(A) Differences in emissivity with and without plating and (B) Relationships between glossiness, emissivity, and surface roughness are shown in graphs.

As shown in FIG. 1, the exhaust pipe of this embodiment is used as a part of an exhaust pipe 1 connected to an engine 2 of a motorcycle. The structure of the exhaust pipe is shown in FIG. As shown, the outer pipe 11 made of one steel pipe
And an inner pipe 12 having a two-layered structure in which two steel pipes 12a and 12b are overlapped with one without any gap in most of the longitudinal direction.
And the steel pipes 12a and 12b constituting the inner pipe 12 are each made of a SUS material.
The outer tube 11 is a steel tube made of STKM material whose outer surface is plated with Cr.

With respect to the exhaust pipe 1 composed of the outer pipe 11 and the inner pipe 12 as described above, in the present embodiment, not only the outer face of the outer pipe 11 but also the inner face of the outer pipe 11 is used. The inner tube 12 (a single tube of a multilayer structure composed of the steel pipes 12a and 12b) is provided with a two-layer chromium plating as a glossy plating layer on both the inner and outer surfaces thereof. Fe), a nickel (Ni) plating layer is formed thereon, and a chromium (Cr) plating layer is formed thereon. The thickness of the nickel plating layer is 20 to 30 μm, and the thickness of the chromium plating layer is It is 0.15 μm or more.

An example of the composition of a plating solution for forming such a nickel plating layer or a chromium plating layer is as follows. [Nickel Plating Solution Composition] Nickel sulfate _{(NiSO 4 6H 2 O) 220~370g} / l nickel chloride _{(NiCl 2 6H 2 O) 30~60g} / l boric acid _{(H 3 BO 3) 30~60g /} l [chrome plating solution Composition] Chromic anhydride (CrO ₃ ) 200-400 g / l Sulfuric acid (H ₂ SO ₄ ) 0.5-2.5 g / l

An example of a method of manufacturing the exhaust pipe 1 of the present embodiment in which the plating layer is formed as described above will be described. First, a pipe that becomes an outer pipe or an inner pipe of the exhaust pipe (two pipes are used for the inner pipe). Each of the steel pipes is made into a single pipe with a multilayer structure), polished, bent and formed into a predetermined shape, and then degreased and dried. After forming a plating layer on both the inner and outer surfaces of each of the inner tubes, the ends of each tube are integrally joined by welding, and air is extracted from the space between the outer tube and the inner tube to substantially vacuum. In the state.

When plating is performed on the inner and outer surfaces of the outer tube and the inner tube in the plating process, for example, as shown in FIG. The anode member 21 is inserted while being electrically insulated from (12), and the anode member 21 and the steel pipe 1 are inserted.
1 (12) is immersed in the plating solution 23, and another anode member 24 is immersed in the plating solution 23 outside the steel tube 11 (12). The electrodes are energized, and a positive electrode of DC electricity is applied to each of the anode members 21 and 24.

According to such a plating method, when forming a plating layer on both the inner and outer surfaces of the outer tube 11, first, the anode member 21 and the outer tube 11 are immersed in a plating solution 23, and a current is applied to each of them. Thereafter, another anode member 24 is immersed in the plating solution 23, and current is applied to each of the anode members 21, 24 and the outer tube 11, so that the inner surface of the outer tube 11 is longer than the outer surface. The plating can be performed for a long time, so that the plating layer formed on the inner surface of the outer tube 11 can be formed to be thicker than the plating layer formed on the outer surface.

Unlike the case of the present embodiment, for example, when a SUS material whose outer surface is not plated with Cr is used as the outer tube 11, another anode member 24 is provided outside the tube 11. Without being immersed in the plating solution 23, and electrically insulated from the tube 11 by the insulating ring 22,
The anode member 21 and the tube 11 are immersed in the plating solution 23 by inserting the anode member 21 into the inner central portion of the tube 11, and the anode member 21 and the outer tube 11 are energized, respectively. 11 can be plated only on the inner surface side.

According to the exhaust pipe 1 of the internal combustion engine of the present embodiment in which plating layers are respectively formed on the inner surface of the outer pipe 11 and the inner and outer surfaces of the inner pipe 12 by the above-described method, the inner pipe 12 of the exhaust pipe is formed. Even if the temperature of the exhaust gas passing through the inside becomes high, the heat radiation from the inner pipe 12 which comes in contact with the exhaust gas and becomes high temperature due to the formation of the glossy plating layer on the inner surface of the outer pipe 11 The light can be reflected on the inner surface of the outer pipe 11, and as a result, the influence of heat from the exhaust gas is reduced on the outer surface of the outer pipe 11 of the exhaust pipe 1. This can prevent discoloration and thermal oxidation from occurring due to the high temperature of the exhaust pipe 1, and can maintain a good appearance of the exhaust pipe 1 in which the outer surface of the outer pipe 11 is plated with Cr.

Further, since the space portion 13 is formed between the outer tube 11 and the inner tube 12, there is no direct heat conduction from the inner tube 12 to the outer tube 11, and the gas in the space portion 13 is removed. Since the heat transfer from the inner tube 12 to the outer tube 11 through the inner tube 12 is small, the plating layer formed on the inner surface of the outer tube 11 does not become hot and does not cause discoloration or thermal oxidation. Rate (ie, high reflectivity) can be maintained. FIG. 4A shows STKM which is a base metal of the outer tube 11.
FIG. 4B shows the difference between the emissivity when the material is plated and when it is not plated, and FIG. 4B shows the relationship between the glossiness and the emissivity and the surface roughness.

In the exhaust pipe 1 of the present embodiment, the outer pipe 1
The space 13 between the inner tube 1 and the inner tube 12 is substantially in a vacuum state (0.1
(Atmospheric pressure or less), heat convection hardly occurs in this space portion 13, and thus heat conduction by air from the inner tube 12 heated by the exhaust gas and the outer tube 11 by convection
The heat transfer to the exhaust pipe 1 can be almost eliminated, and discoloration and thermal oxidation due to high temperature on the outer surface of the outer pipe 11 of the exhaust pipe 1 can be more effectively prevented.

Further, in the exhaust pipe 1 of the present embodiment, not only the inner surface of the outer tube 11 but also the inner and outer surfaces of the inner tube 12 are formed with plating layers by two-layer chrome plating. Base metal (each steel pipe 12a, 1 constituting the inner pipe 12)
The SUS material is used as the material 2b). Therefore, in the inner tube 12 (particularly, the inner surface of the inner tube 12a) directly exposed to the high-temperature exhaust gas, the plating layer is discolored and further deteriorates to generate thermal oxidation. By using a high SUS material for the underlying metal of the plating layer, it is possible to prevent the thermally oxidized plating layer from peeling off from the underlying metal.
The emissivity is increased (that is, the reflectance is decreased) due to discoloration and thermal oxidation, but the inner tube 12 can be protected as an oxide film unless peeling occurs.

In the exhaust pipe 1 of the present embodiment, how the heat of the exhaust gas passing through the inner pipe 12 is transferred to the surface of the outer pipe 11 will be described in detail below. The hot exhaust gas molecules flowing along the inner surface of the inner tube 12a of the tube 12
While heating (heat transfer) the inner surface of the inner tube 2a, the radiant heat of the exhaust gas molecules heats the inner surface of the inner tube 12a of the inner tube 12.

The heat (thermal energy) of the inner surface of the inner tube 12a of the inner tube 12 causes the metal elements of the crystal lattice constituting the inner tube 12a to sequentially vibrate, and the heat reaches the outer surface of the inner tube 12a (heat conduction). I do. The outer tube 12b of the inner tube 12 is heated (heat transferred) by the temperature rise of the outer surface of the inner tube 12a, and the heat reaches the outer surface of the outer tube 12b through the inside of the outer tube 12b of the inner tube 12.

The heat on the outer surface of the outer tube 12b of the inner tube 12 is transferred to the air molecules which are very slightly present in the space portion 13,
The heated air molecules move (convection), reach the inner surface of the outer tube 11, and heat (heat transfer) the inner surface. Radiation heat is radiated from the outer surface of the outer tube 12b of the inner tube 12, and the inner surface of the outer tube 11 is heated by the radiant heat. And
The heat (thermal energy) on the inner surface of the outer tube 11 is thermally conducted in the outer tube 11 and transmitted to the outer surface of the outer tube 11.

Here, the magnitude of radiant heat from the outer surface of the outer tube 12b of the inner tube 12 is represented by radiant power E (radiant heat energy per unit surface area / time). E = εEb = ε × 4.88 × (T / 100) ⁴ E: Unit is Kca1 / (m ² h) m: Length meter h: Time ε: Emissivity on outer surface of outer tube 12b (dimensionless Eb: Emissivity of black body (Kca1 / (m ² h) T: Absolute temperature of outer surface of outer tube 12b (° K)

The inner surface of the outer tube 11 absorbs the radiant heat and rises in temperature. At this time, the heat absorption rate α (dimensionless) is
It is substantially equal to ε on that surface. Outer tube 1 of inner tube 12
Since the outer surface of the outer tube 2b and the inner surface of the outer tube 11 are parallel and the distance between both surfaces is short, the radiant heat reaching the inner surface of the outer tube 11 is substantially equal to the radiant heat on the outer surface of the outer tube 12b of the inner tube 12. Therefore, the heat receiving capacity = αE = αεEb. A part of the radiant heat is reflected on the inner surface of the outer tube 11. This reflectance is represented by (1−α).

Although the embodiment of the exhaust pipe of the internal combustion engine according to the present invention has been described above, the present invention is not limited to the above-described embodiment. For example, the structure of the exhaust pipe is described above. The present invention is not limited to the double pipe composed of the outer pipe and the inner pipe as shown in the embodiment, but may include other multiple pipes (such as a triple pipe).
For the outermost pipe of the exhaust pipe, C
SU-plated STKM material
S material or other materials may be used, and the application of the exhaust pipe is not limited to the exhaust pipe used for motorcycles,
The exhaust pipe may be an exhaust pipe used for an automobile or another vehicle, or may be an exhaust pipe connected to an engine other than the engine of the vehicle.

The plating applied to each surface of the exhaust pipe is not limited to the two-layer chromium plating as shown in the above embodiment, but may be other plating such as, for example, molten aluminum plating. When the plating layers on both the inner and outer surfaces of the inner tube 12 are two-layer chromium plating, when the plating layer on the inner surface of the inner tube 12 is discolored to increase the emissivity, the plating layer on the outer surface of the inner tube 12 also becomes hot. By using molten aluminum plating for the plating layer of the inner tube 12, the molten aluminum plating is inferior in appearance, but hardly generates thermal oxidation (emissivity is hardly increased even if thermally oxidized), The emissivity of the plating layer on the outer surface of the inner tube 12 can be kept low,
It is possible to prevent the outer tube 11 from becoming high temperature due to the radiant heat from 2.

In the exhaust pipe shown in the above embodiment, the inner pipe 1 is a double pipe composed of the outer pipe 11 and the inner pipe 12.
2 has a two-layer structure in which the inner tube 12a and the outer tube 12b are stacked together without any gap.
With a gap between the outer tube 12b and the outer tube 12b.
A plating layer may be applied to both the inner and outer surfaces of the inner tube, so that it is possible to prevent the plating layer from discoloring due to a high temperature on the outer surface of the inner tube 12 (the outer surface of the outer tube 12b) and increase the emissivity. As a result, it is possible to suppress the temperature of the outer tube 11 becoming high due to the radiant heat from the inner tube 12.

Further, in the exhaust pipe shown in the above embodiment, the plating layer is formed on both the inner surface of the outer tube and both the inner and outer surfaces of the inner tube in the double tube. A plating layer is formed on at least one of the inner surfaces of the steel pipes other than the innermost tube, and the inner surface on which the plating layer is formed is separated from the outer surface of the inner steel pipe. Is also good. Furthermore, in an exhaust pipe having a bent portion, a centrifugal force acts on the exhaust gas flow to increase a heat load on an outer wall of the bent portion. Therefore, not only a large portion in the longitudinal direction of the pipe but only the bent portion. A plating layer may be formed, and by performing such partial treatment, the cost can be reduced even if the effect is slightly reduced.

[0031]

According to the exhaust pipe of the internal combustion engine of the present invention as described above, the influence of the heat from the exhaust gas on the outer surface of the exhaust pipe is reduced by the plating layer formed inside the exhaust pipe. Accordingly, discoloration and thermal oxidation due to high temperature on the outer surface of the exhaust pipe can be prevented, and the appearance of the exhaust pipe can be maintained in a good state.

[Brief description of the drawings]

FIG. 1 is a side view showing a motorcycle which is an example of use of an exhaust pipe of an internal combustion engine of the present invention.

FIG. 2 is a partial cross-sectional view showing an internal structure of an exhaust pipe according to one embodiment of the present invention.

FIG. 3 is an explanatory sectional view showing an example of a method for forming plating layers having different thicknesses on both inner and outer surfaces of a steel pipe constituting an exhaust pipe.

4A is a graph showing a difference in emissivity between when plating is performed on an STKM material and when it is not, and FIG. 4B is a graph showing a relationship between glossiness, emissivity, and surface roughness.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Exhaust pipe 2 Engine (internal combustion engine) 11 Outer pipe (of exhaust pipe) 12 Inner pipe (of exhaust pipe) 13 Space part (of exhaust pipe)

Claims (2)

[Claims] 1. An exhaust pipe for passing exhaust gas from an internal combustion engine, wherein at least one of the steel pipes other than the innermost pipe of the exhaust pipe composed of multiple steel pipes has a glossy surface. With a plated layer with
An exhaust pipe for an internal combustion engine, wherein an inner surface on which the plating layer is formed is separated from a steel pipe inside the plating layer. 2. The exhaust pipe of an internal combustion engine according to claim 1, wherein a space between the respective pipes in the multi-pipe is substantially in a vacuum state.