JP4521382B2 - EXHAUST PIPE FOR INTERNAL COMBUSTION ENGINE, INTERNAL COMBUSTION ENGINE EQUIPPED WITH THE SAME - Google Patents

Description

  The present invention relates to an exhaust pipe for an internal combustion engine that guides exhaust gas generated in the internal combustion engine, and more particularly to an exhaust pipe for an internal combustion engine in which at least part of the exhaust pipe appears in the appearance of the vehicle in a vehicle equipped with the internal combustion engine.

  2. Description of the Related Art Many motorcycles equipped with an internal combustion engine expose the internal combustion engine and use the appearance of the motorcycle for the design of the motorcycle. In such a motorcycle, an exhaust pipe for leading exhaust gas from the internal combustion engine also plays an important role in the design of the motorcycle. Even when the internal combustion engine is covered with a cowl or the like, the exhaust pipe is rarely completely covered with a cowl or a protector, and at least a part of the exhaust pipe appears on the exterior, and a part of the design of the motorcycle is displayed. Often configured.

  FIG. 14 is a side view showing an example of a sports type motorcycle. A motorcycle 200 shown in FIG. 14 includes a V-type engine 201 and an exhaust pipe 202 for guiding exhaust gas. The exhaust pipe 202 is led from each of the two cylinders of the V-type engine 201 and assembled into one, and is extended to the rear wheel side so as to eject exhaust gas from the rear part of the vehicle body. In the present specification, the “exhaust pipe” refers to the entire part constituting the flow path for guiding the exhaust gas from the internal combustion engine, and includes the part constituting the silencer 202a.

  Generally, in order to efficiently exhaust the exhaust gas generated in the internal combustion engine 201, the exhaust pipe 202 needs to have a predetermined thickness. Moreover, in the part which comprises the silencer 202a, in order to accommodate the structure for silence, a diameter becomes large. For this reason, the proportion of the exhaust pipe in the overall appearance of the motorcycle is relatively large, and the influence of the shape and color of the exhaust pipe on the design of the entire motorcycle is great.

  For these reasons, the shape and color of the exhaust pipe are important factors in determining the design of the entire motorcycle. For this reason, the exhaust pipe is smoothly bent to create a strong and powerful impression, and the exhaust pipe surface is finished with a glossy metallic color to emphasize contrast with other components. It has been broken. Alternatively, the surface of the exhaust pipe is finished with a color similar to that of the other constituent parts so as to be integrated with the surrounding structure.

  In general, the exhaust pipe is made of carbon steel for mechanical structure (STKM), stainless steel (SUS), titanium or the like. When an exhaust pipe is formed from STKM material, chromium plating is often applied to the surface of the exhaust pipe in order to enhance aesthetics.

  However, since the exhaust gas passing through the exhaust pipe is directly led from the internal combustion engine, the temperature is high. Therefore, when the exhaust gas passes, the exhaust pipe becomes hot, and the surface of the exhaust pipe on which chrome plating has been applied is discolored, oxidized, or deteriorated. In particular, areas that are discolored blue-purple or red-brown appear. Further, even in an exhaust pipe made of SUS or titanium not subjected to chrome plating, the surface is bluish purple or reddish brown due to high temperature, the generated oxide film is peeled off, or the color tone is changed due to the generation of the oxide film.

  In this way, there is a problem that the appearance of the design of the entire motorcycle is impaired due to blue-purple or reddish-colored discoloration or surface deterioration in the exhaust pipe having a metallic luster. In particular, in recent years, the performance of internal combustion engines has improved, and the temperature of exhaust gas has risen, and such problems are likely to occur.

  In order to solve this problem, it is conceivable to form the exhaust pipe in a double or triple cylindrical structure so that the surface of the exhaust pipe does not reach a high temperature. However, even if a double or triple cylindrical structure is adopted, the temperature of the exhaust pipe surface cannot be lowered sufficiently, and oxidation and deterioration of the surface due to heat cannot be completely prevented. Further, in this case, another problem that the outer shape of the exhaust pipe becomes large arises.

  It may be possible to cover the exhaust pipe with a cowl or a protector so that the exhaust pipe does not appear on the appearance against discoloration, oxidation, or deterioration of the exhaust pipe surface. However, in this case, since the exhaust pipe does not appear in the design of the entire motorcycle, it may be difficult to appeal the unique aesthetics of the motorcycle.

In order to solve such problems, the present inventor has proposed that a silicon oxide film be formed on the surface of the exhaust pipe to prevent discoloration of the exhaust pipe (Patent Document 1). As disclosed in Patent Document 1, by forming a silicon oxide film with a thickness of 0.05 μm or more on the surface of the exhaust pipe using a sol-gel method, discoloration hardly occurs even when heated to about 400 ° C. An exhaust pipe can be obtained.
JP 2002-332838 A

  However, in the exhaust pipe obtained by the technique disclosed in Patent Document 1, it has been found that the surface discoloration suddenly occurs when exposed to a temperature exceeding 400 ° C. For this reason, even if the exhaust pipe disclosed in Patent Document 1 is used for a high-performance internal combustion engine in which the temperature of the exhaust gas tends to be high as described above, discoloration may not be sufficiently prevented.

  The present invention has been made in view of the above problems, and an object thereof is to provide an exhaust pipe for an internal combustion engine that can prevent discoloration and oxidation due to high-temperature exhaust gas.

  An exhaust pipe for an internal combustion engine according to the present invention covers a metal pipe that surrounds a passage through which exhaust gas from the internal combustion engine passes, and an outside of the metal pipe, and the metal element content mainly contained on the surface of the metal pipe The ceramic film is a SiON film containing 30% by mass or less of O and 10% by mass or more of N, whereby the above object is achieved.

  In a preferred embodiment, the ceramic film contains 5 mass% or less O and 40 mass% or more N.

  In a preferred embodiment, the ceramic film is directly formed on the surface of the metal tube.

  In a preferred embodiment, the ceramic film has a thickness of 5 nm to 300 nm.

  In a preferred embodiment, the ceramic film has a thickness of 5 nm to 30 nm.

  In a preferred embodiment, the metal tube has a surface roughness Ra of 0.4 μm or more and 3.2 μm or less.

  In a preferred embodiment, the metal tube is made of titanium, a titanium alloy or stainless steel.

  In a preferred embodiment, the metal tube has a chromium plating layer on the surface.

  In a preferred embodiment, the exhaust pipe for an internal combustion engine according to the present invention does not substantially include an oxide film of a metal element mainly contained on the surface of the metal tube between the metal tube and the ceramic film. .

  In a preferred embodiment, the ceramic film is a vapor deposition film formed by a vapor deposition method.

  In a preferred embodiment, the ceramic film is a deposited film formed by a sputtering method or an ion plating method.

  In a preferred embodiment, the metal tube has a surface roughness larger than a surface roughness range in which diffracted light by visible light is generated, and the ceramic film has a thickness at which interference fringes by visible light are generated. Have a thickness less than the range.

  An internal combustion engine according to the present invention includes an exhaust pipe for an internal combustion engine having the above-described configuration, thereby achieving the above object.

  The transport device according to the present invention includes the internal combustion engine having the above-described configuration, and thereby the above-described object is achieved.

  The ceramic film provided in the exhaust pipe for an internal combustion engine according to the present invention contains only 0.5% by mass or less of the metal element mainly contained on the surface of the metal pipe, and it can be said that the ceramic film is not substantially contained. Therefore, the exhaust gas is not discolored or the surface is not deteriorated when the metal element is oxidized at a high temperature. Therefore, the exhaust pipe is not discolored by the high-temperature exhaust gas, and an excellent appearance can be maintained. Furthermore, since this ceramic film is a SiON film containing 30% by mass or less of O and 10% by mass or more of N, the effect of preventing discoloration and deterioration of the exhaust pipe is high.

  The inventor of the present application has examined in detail the cause that the silicon oxide film formed by the sol-gel method cannot sufficiently prevent oxidation and discoloration on the exhaust pipe surface. As a result, the silicon oxide film formed by the sol-gel method contains a metal element mainly contained on the surface of the exhaust pipe. When this metal is oxidized at a high temperature, the exhaust pipe is discolored or the surface is deteriorated. It was found that it occurred.

  In addition, in the sol-gel method, since an organic compound bonded to silicon is vaporized and decomposed during firing, fine voids are formed in the obtained silicon oxide film, and the barrier property against gas is reduced. It is thought that there is. Therefore, when the exhaust pipe is exposed to high temperature, the metal on the exhaust pipe surface diffuses into the silicon oxide film and oxidizes by combining with external oxygen, or oxygen passes through the silicon oxide film and the exhaust pipe surface. It is thought to cause metal oxidation. When metal is contained in the silicon oxide film or fine voids are formed in the silicon oxide film in this way, iron of the metal constituting the exhaust pipe is reddish oxide on the surface. It will deposit and damage the appearance of the exhaust pipe.

  The ceramic film provided in the exhaust pipe according to the present invention is such that the content of the metal element mainly contained on the surface of the metal pipe (that is, the metal element that substantially constitutes the surface of the metal pipe) is 0.5% by mass or less. It is formed, and it can be said that the main component elements on the surface of the metal tube are not substantially contained. Therefore, as will be described later, discoloration, oxidation, and deterioration of the surface of the metal tube are prevented.

  In addition, as a result of various studies by the inventor of the present application paying particular attention to a silicon nitride oxide (SiON) film among such ceramic films, the oxygen content and nitrogen content of the SiON film are within a specific range. It was found that the effect of preventing discoloration can be remarkably improved. Specifically, this unexpected effect can be obtained by setting the oxygen content of the SiON film to 30% by mass or less and the nitrogen content to 10% by mass or more as described later.

  Furthermore, the inventor of the present application has found that a vapor deposition method such as a sputtering method or an ion plating method is particularly suitable for forming a ceramic film (SiON film) having an excellent discoloration prevention effect as described above. Conventionally, thin film formation using a vapor deposition method such as sputtering has been performed for a small scale material such as a semiconductor device, but for a large scale material such as an exhaust pipe, a vapor deposition device is used. It was not industrially performed because of the difficulty of securing the degree of vacuum inside. This inventor acquired the said knowledge by accumulating examination without being caught by such technical common sense.

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

  FIG. 1 shows a motorcycle 100 using an exhaust pipe for an internal combustion engine (hereinafter also simply referred to as an exhaust pipe) of the present invention. The motorcycle 100 includes an internal combustion engine 1 and an exhaust pipe 2 connected to the internal combustion engine 1.

  The exhaust pipe 2 is provided to exhaust exhaust gas generated in the internal combustion engine 1 from the rear of the vehicle body. The exhaust pipe 2 includes a portion 2a constituting a greatly bent exhaust path so as to guide exhaust gas discharged from the front of the internal combustion engine 1 to the rear, and a silencer 2b. The exhaust pipe 2 may be integrally configured by one component, or may be configured by joining a plurality of components.

  In the present embodiment, the entire exhaust pipe 2 is exposed so as to appear in the appearance of the motorcycle 100, and constitutes a part of the design of the entire motorcycle 100. As will be described in detail below, when the entire exhaust pipe 2 is exposed, discoloration of the exhaust pipe 2 does not occur over a long period of time, and the effect of the present invention that maintains the appearance of a new car appears remarkably. However, as long as at least a part of the exhaust pipe 2 appears on the exterior, a part of the exhaust pipe 2 may be covered with a cowl or a protector depending on the design of the motorcycle. Further, the shape of the motorcycle in which the exhaust pipe for an internal combustion engine of the present invention is used is not limited to that shown in FIG. For example, the exhaust pipe of the present invention may be employed in a motorcycle having a structure as shown in FIG.

  FIG. 2 is a cross-sectional view showing a part (part 2 a) of the exhaust pipe 2. The exhaust pipe 2 includes a metal pipe 5 that surrounds the passage 6 through which the exhaust gas passes, and a ceramic film 10 that covers the outside of the metal pipe 5. In other words, exhaust gas flows inside the metal tube 5, and the ceramic film 10 is provided outside the metal tube 5.

  The metal tube 5 only needs to surround the passage 6, and may adopt a double tube structure including an inner tube that directly surrounds the passage 6 and an outer tube that is held so as to surround the outer side of the inner tube. Good. However, the effect of using the present invention is higher in the single tube structure that directly surrounds the passage 6 because the outside of the metal tube 5 tends to be hot. Further, the ceramic film 10 may be disposed so as to cover the outside of the metal tube 5 and prevent outside air such as oxygen from coming into contact with the metal tube 5 in a portion where oxidation prevention is required. Another film or layer may be formed between the two, or another film may cover the outside of the ceramic film 10.

  The metal pipe 5 is formed of carbon steel for mechanical structure (STKM), stainless steel (SUS), titanium, a titanium alloy, a nickel alloy, an aluminum alloy, or the like. In order to enhance the metallic luster and decorativeness of the surface, the surface of the metal tube 5 may be plated with chromium or the like to form a plating layer. Since STKM material does not have sufficient metallic luster with high decorativeness, when using metal tube 5 formed of STKM material, either chrome plating or both nickel plating and chrome plating are applied to the surface of metal tube 5. It is preferable that Moreover, when using the metal tube 5 formed from SUS, the surface may be electropolished.

  The ceramic film 10 is made of an amorphous material that is dense and hardly oxidizes or decomposes even at high temperatures. “Ceramics” in the present specification refers to solid materials such as metal or non-metal oxides, nitrides, nitride oxides, etc., and only those formed by a technique including a firing process that has been used frequently in the past. Of course, those formed by vapor deposition as will be described later are included.

  The ceramic film 10 in the present embodiment does not contain more than 0.5 mass% of the metal element that is mainly included (typically included at a ratio of 50% or more) on the surface of the metal tube 5. When the main component element on the surface of the metal tube 5 is contained in the ceramic film 10 in an amount of more than 0.5% by mass, the metal element is oxidized from the surface of the ceramic film 10 due to high heat, and the surface of the exhaust pipe may be discolored. There is. Further, there is a possibility that the oxidation proceeds from the oxidized metal to the inside of the metal tube 5. On the other hand, the ceramic film 10 according to the present embodiment has a content of main component elements on the surface of the metal tube 5 of 0.5% by mass or less, thereby preventing discoloration and oxidation due to high heat. Considering the appearance of the exhaust pipe 2 when the metal contained in the ceramic film 10 is oxidized, the content of the main component elements on the surface of the metal pipe 5 is more preferably 0.4% by mass or less, and 0.3% by mass. More preferably, it is% or less.

  The content of the main component element on the surface of the metal tube 5 may vary locally in the ceramic film 10, but at least 0.5% by mass or less in the central portion in the thickness direction of the ceramic film 10. Is preferred. Further, the content ratio of the main component elements on the surface of the metal tube 5 is 10% of the thickness near the inner surface (on the metal tube 5 side) and near the outer surface of the ceramic film 10 (respectively the thickness of the entire ceramic film 10). It is preferable that it is 0.5 mass% or less in the part (namely, the part equivalent to 80% of the whole ceramic film 10) except the part which has).

  In order to make the content of the main component element on the surface of the metal tube 5 0.5 mass% or less, when the ceramic film 10 is formed outside the metal tube 5, the main component element on the surface of the metal tube 5 is the ceramic film 10. It is preferable to use a method that hardly diffuses into the inside. As a result of various studies, the inventor of the present application has found that when the vapor deposition method is used for forming the ceramic film 10, the main component elements on the surface of the metal tube 5 are difficult to diffuse into the ceramic film 10. Moreover, since the ceramic film formed by the vapor deposition method is dense, it was found that even at a temperature of about 500 ° C., it has a high gas barrier property and can prevent the surface of the metal tube 5 from being oxidized.

  In the present specification, “vapor deposition” refers to a CVD (chemical vapor deposition) method and a PVD (physical vapor deposition) method in which a substance to be deposited is deposited in a gaseous state. Of the vapor deposition methods, it is more preferable to use the physical vapor deposition method. In particular, since the film formed by the ion plating method and the sputtering method is generally dense, the ceramic film 10 is formed by the ion plating method or sputtering. More preferably, it is formed by the method.

  When the sputtering method is used, a DC sputtering apparatus, an RF sputtering apparatus, a magnetron sputtering apparatus, an ion beam sputtering apparatus, or the like can be used. When these methods are used, the surface of the metal tube 5 can be etched by causing plasma particles to collide with the surface of the metal tube 5 on which the ceramic film 10 is deposited. By utilizing this, the natural oxide film formed on the surface of the metal tube 5 can be removed, and the adhesion between the ceramic film 10 and the metal tube 5 can be improved. That is, it is preferable that a metal element oxide film mainly contained on the surface of the metal tube 5 is not substantially formed between the ceramic film 10 and the metal tube 5. Even when the ceramic film 10 is formed by a deposition method that does not use plasma, the natural oxide film formed on the surface of the metal tube 5 is removed before the ceramic film 10 is formed by a physical or chemical method. It is preferable to keep it.

  The ceramic film 10 formed by the vapor deposition method is basically an amorphous film, and remains amorphous even when heated to a high temperature by the operation of the engine. The amorphous film here refers to a film that does not have a long-period structure as observed as a diffraction peak by X-ray diffraction. Depending on the formation conditions, a part of the film may crystallize when heated, but there is practically no problem with gas barrier properties.

  Specifically, the ceramic film 10 in this embodiment is a silicon nitride oxide (SiON) film containing oxygen (O) of 30% by mass or less and nitrogen (N) of 10% by mass or more. The inventor of the present application focused on the SiON film among the ceramic films, and verified the characteristics from various viewpoints. As a result, the inventors have found that when the content of oxygen and nitrogen in the SiON film is within the above range, the effect of preventing discoloration of the SiON film is remarkably increased, and the present invention has been conceived. Although the verification result about the relationship between the content rate of oxygen and nitrogen and the anti-discoloration effect will be described in detail later, the manufacturing method of the exhaust pipe 2 will be described before that. Below, the example which forms the ceramic film 10 by sputtering method is demonstrated.

  First, a metal tube 5 is prepared. When an STKM material is used as the material of the metal tube 5, it is preferable to apply chrome plating to the surface of the metal tube 5 in order to improve the metallic luster and decorativeness.

  Next, as shown in FIGS. 3A and 3B, the metal tube 5 is introduced into the chamber 21 of the sputtering apparatus 20. The sputtering apparatus 20 illustrated in FIGS. 3A and 3B suspends and holds two metal tubes 5 vertically so that the ceramic film 10 can be simultaneously formed on many metal tubes 5. A plurality of holders 24 are provided. Each holder 24 revolves in the chamber 21 while rotating around the rotation shaft 23. A plurality of targets 22 are provided outside the track on which the holder 24 rotates. In this embodiment, since a silicon nitride oxide film is formed as the ceramic film 10, a silicon (or silicon nitride) target 22 is used. The inner diameter φ1 of the chamber 21 is, for example, 1200 mm, and an effective region where a film can be formed is, for example, a cylindrical shape having a diameter φ2 of 1080 mm and a height of 1800 mm. By using the sputtering apparatus 20 having such a structure, the ceramic film 10 having a uniform thickness can be formed on the entire outside of the metal tube 5 having a three-dimensional shape. Moreover, many metal tubes 5 can be processed in one batch.

  After the metal tube 5 is placed in the holder 24, the chamber 21 is evacuated using a pump (not shown). When the degree of vacuum in the chamber 21 reaches a predetermined value, argon is introduced into the chamber 21 and discharge is started. While rotating and revolving the holder 24, a bias voltage is applied so that plasma particles generated by discharge collide with the metal tube 5, and the surface of the metal tube 5 is etched by reverse sputtering. The reverse sputtering is preferably performed until the natural oxide film formed on the surface of the metal tube 5 is completely removed. The thickness of the natural oxide film is generally about 2 nm to 3 nm. By removing the natural oxide film, the adhesion between the metal tube 5 and the ceramic film 10 can be enhanced.

  After removing the natural oxide film, nitrogen gas and oxygen gas are introduced into the chamber 21 to start discharging. A bias voltage is applied so that the plasma particles collide with the target, and deposition of the ceramic film 10 is started. In the present embodiment, silicon particles that have jumped out of the target react with nitrogen plasma or oxygen plasma, and a silicon nitride oxide film is deposited on the surface of the metal tube 5. The deposition time is determined according to the target film thickness of the ceramic film to be generated, taking into account conditions such as the number of targets, the pressure during reaction, and the bias voltage. By performing sputtering for a predetermined time and forming the ceramic film 10 having a predetermined thickness outside the metal tube 5, the exhaust pipe 2 is obtained.

  The ceramic film 10 formed as described above contains only 0.5% by mass or less of the metal element mainly contained on the surface of the metal tube 5, and the main component element on the surface of the metal tube 5 is substantially contained. It can be said that it is not included. For this reason, when this metal element is oxidized at a high temperature, the exhaust pipe 5 is not discolored or the surface is not deteriorated. For this reason, the exhaust pipe 5 is not discolored by high-temperature exhaust gas, and an excellent appearance can be maintained. Since the ceramic film 10 formed by the vapor deposition method is dense, it has a high barrier property, and external oxygen reaches the metal tube 5 or iron contained in the metal tube 5 is oxidized and deposited on the surface. Can be effectively prevented.

  The thickness of the ceramic film 10 is preferably 5 nm or more and 300 nm or less. When the thickness is less than 5 nm, it is difficult to form the ceramic film 10 that uniformly covers the metal tube 5. Moreover, since sufficient gas barrier property cannot be ensured, it becomes difficult to completely prevent oxidation and discoloration of the surface of the metal tube 5. On the other hand, if it is thicker than 300 nm, it takes a long time to form the ceramic film 10 and the productivity is lowered, which is not preferable. Moreover, when it is thicker than 300 nm, or when the ceramic film 10 does not have a completely uniform thickness, an interference color such as rainbow is likely to be seen, and the decorativeness of the appearance is deteriorated. From the viewpoint of productivity of the ceramic film 10, the thickness of the ceramic film 10 is preferably 50 nm or less, and more preferably 40 nm or less. When the thickness of the ceramic film 10 is in the range of 5 nm to 30 nm, a colorless and transparent ceramic film 10 that does not generate an interference color is obtained regardless of the material and the refractive index.

  As shown in FIG. 4, the surface of the metal tube 5 preferably has a surface roughness that is greater than the thickness of the ceramic film 10. Specifically, the average roughness Ra of the surface of the metal tube 5 is preferably 0.4 μm or more. When the average roughness is less than 0.4 μm, when visible light is reflected on the surface of the metal tube 5, diffracted light is strengthened when the optical path difference between wavefronts reflected from adjacent grooves is an integral multiple of the wavelength. As a result, the appearance of the exhaust pipe 2 may be impaired. In addition, when the average roughness is reduced and the surface of the metal tube 5 is smooth, the adhesion of the ceramic film 10 may be reduced. There is no particular upper limit to the value of the average roughness Ra on the surface of the metal tube 5, but if the average roughness Ra on the surface of the metal tube 5 is 3.2 μm or more, the light reflectivity is reduced and the merchantability and aesthetics are impaired. It is not preferable.

  Thus, ceramics having a thickness smaller than the range of thickness where interference fringes due to visible light are generated on the surface of a metal tube having a surface roughness larger than the range of surface roughness where diffracted light due to visible light is generated A film is formed. As a result, even when hot exhaust gas passes, surface oxidation or discoloration does not occur, and it is possible to obtain an exhaust pipe having a uniform metallic luster with excellent adhesion and no occurrence of interference fringes. it can.

(Analysis and experimental examples)
First, the distribution in the depth direction of elements in the exhaust pipe according to the present invention and the exhaust pipe disclosed in Patent Document 1 was examined. A metal tube formed of SUS304 was prepared as an exhaust pipe of the present invention, and a silicon nitride oxide film was formed as a ceramic film by a sputtering method. In order to form a silicon oxynitride film, a chromium-plated metal tube was placed in a chamber of a magnetron sputtering apparatus and evacuated until a vacuum degree of 3 × 10 ⁻³ Pa was reached. Thereafter, argon was introduced into the chamber at a flow rate of 100 sccm, and while maintaining a pressure of 3 × 10 ⁻¹ Pa, 800 V, 5 A (4 KW) power was applied, and reverse sputtering was performed for 10 minutes, so that the natural surface of the metal tube The oxide film was removed. Then, using silicon as a target, nitrogen and oxygen are introduced into the chamber, and while maintaining a pressure of 3 × 10 ⁻¹ Pa, power of 800 V, 5 A (4 KW) is applied, and sputtering is performed for 5 minutes to form a metal tube surface. A silicon nitride oxide film having a thickness of 50 nm was formed.

  Further, as a conventional example, a metal tube made of STKM material with nickel plating and chrome plating applied thereto was prepared, and a silicon oxide film was formed as a ceramic film by a sol-gel method. The element distribution in the depth direction of the obtained exhaust pipe of the present invention and the conventional exhaust pipe was measured using a GDS method (glow discharge emission spectroscopy).

  Fig.5 (a) has shown the element distribution of the depth direction of the exhaust pipe of this invention. FIG. 5B is an enlarged view showing the vicinity of the surface of FIG. As is apparent from these drawings, in the exhaust pipe of the present invention, the silicon nitride oxide film, which is a ceramic film, contains almost no iron, which is the main component element on the surface of the metal pipe. Specifically, the elemental concentration of iron in the silicon nitride oxide film is about 0.5% or less as shown in FIG. 5B, and the iron concentration is at the boundary between the silicon nitride oxide film and the metal tube. It is increasing rapidly.

  FIG. 6A shows an element distribution in the depth direction of a conventional exhaust pipe. FIG. 6B is an enlarged view showing the vicinity of the surface of FIG. As is apparent from these figures, in the conventional exhaust pipe, a silicon oxide film formed by the sol-gel method contains a relatively large amount of chromium, which is a main component metal on the surface of the metal pipe. Specifically, the elemental concentration of chromium in the silicon oxide film is about 4% by mass, and the chromium concentration slightly increases at the boundary between the silicon oxide film and the chromium plating. Further, the profile indicating the concentration of oxygen is present at a higher ratio to the inside than silicon. This is because chromium diffuses into the silicon oxide film formed by the sol-gel method, and there is oxygen bonded to chromium at the boundary between the silicon oxide film and chromium plating, that is, chromium oxide. This is considered to indicate that

  In order to investigate the state of the boundary between the silicon oxide film and chromium plating in the conventional exhaust pipe, the depth profile of the element concentration in the conventional exhaust pipe is further measured by XPS (X-ray photoelectron spectroscopy). It was. First, a chrome-plated sample was prepared in order to examine the thickness of the chrome-plated natural oxide film, and the element concentration in the depth direction was examined using the XPS method. As shown in FIG. 7, the natural oxide film of chromium has a thickness of about 5 minutes in terms of sputtering time.

  FIG. 8A shows the element distribution in the depth direction of a conventional exhaust pipe by the XPS method. As is apparent from the figure, the concentration of oxygen (O1s) is constant in the silicon oxide film, but decreases in two steps so as to be surrounded by broken lines C1 and C2 at the interface with the chromium plating. The oxygen concentration change (C2) on the side close to the interface with the chromium plating is considered to indicate oxygen contained in the natural oxide film of chromium because the change is about 5 minutes in terms of sputtering time. It is done.

  On the other hand, in order to investigate the state of chromium in the region where the change in oxygen concentration indicated by C1 occurs, the binding energy of chromium 2p valence electrons at the sputtering times T1 and T2 was measured. The measurement results are shown in FIG. In the sputtering time T2, elements other than chromium are substantially not detected, and it is considered that only chromium exists at the depth indicated by the sputtering time T2. Therefore, the profile of T2 in FIG.8 (b) has shown the (metal bond) bond energy of chromium. On the other hand, the profile of T1 is shifted to the high energy side, indicating that chromium is in an oxidized state. This chromium oxide is considered to be generated when the silicon oxide film is formed by the sol-gel method.

  Thus, in the exhaust pipe 2 of this invention, it turned out that the metal element mainly contained in the surface of the metal pipe 5 is not substantially contained in the ceramic film 10 (it is 0.5 mass% or less). .

  FIG. 9 is a schematic diagram showing an example of the distribution of the thickness of the exhaust pipe formed by the above-described method. FIG. 9 shows the percentage of the thickness indicated by the arrow relative to the target value. As is apparent from the figure, the ceramic film 10 can be formed with a variation of about ± 30% even in an exhaust pipe having a three-dimensional shape bent into a complicated shape. This shows that the uniform ceramic film 10 can be formed by physical vapor deposition.

  Here, as a conventional example, a silicon oxide film formed by a sol-gel method is mentioned. However, other methods conventionally used for coating exhaust pipes, for example, metal oxide films formed by a method of firing after applying a solution containing a metal compound to the exhaust pipe surface using a coating method or dipping method However, like a silicon oxide film formed by a sol-gel method, it is not dense. For example, when the solution of the metal compound contains an organic compound, vaporization and decomposition of the organic compound bonded to the metal occurs during firing, and fine voids are generated, whereby the film is porous. Become. In addition, since the technique described above is a technique in which the metal contained in the film once formed is oxidized later by firing, the density of the film decreases due to the oxidation, and the oxidation proceeds more and more during subsequent use. End up.

  Next, in order to verify the relationship between the nitrogen content and oxygen content of the silicon nitride oxide film (SiON film) and the anti-discoloration effect, a SiON film is formed on the surface of the metal tube 5 under various conditions and heated at high temperature. A test was conducted. The nitrogen content and oxygen content of the SiON film were changed by adjusting the flow rate ratio of nitrogen gas and oxygen gas introduced into the chamber 21 of the sputtering apparatus 20. As the metal tube 5, one formed from SUS304 was used. The high temperature heating test was conducted by leaving the exhaust pipe 2 in the atmosphere at 500 ° C. for 24 hours and examining the discoloration of the surface of the exhaust pipe 2. The results are shown in Table 1 below.

For heating evaluation, the color difference ΔE ^* in the L ^* a ^* b ^* color system is measured, and “◎” indicates that the color difference ΔE ^* is 1 or less before and after heating. The case of exceeding 2 and 3 or less was evaluated as “Δ”, and the case of exceeding 3 was determined as “X”, and the state of discoloration was evaluated in 4 stages. Table 1 also shows the chemical composition of the obtained SiON film. The relationship between the chemical composition and the gas flow rate ratio is shown in FIG. As shown in FIG. 10, the higher the nitrogen gas ratio, the higher the nitrogen content of the SiON film and the lower the oxygen content.

  From Table 1, the higher the ratio of nitrogen gas, that is, the higher the nitrogen content of the silicon nitride oxide film and the lower the oxygen content, the more the surface can be oxidized and not discolored at a high temperature and the excellent appearance can be maintained. Recognize. Specifically, as can be seen from Table 1 and FIG. 10, when the nitrogen content is 10% by mass or more and the oxygen content is 30% by mass or less, a very excellent antioxidant effect is obtained, and the exhaust gas is exhausted. Discoloration and deterioration of the tube 2 surface are prevented.

Here, paying attention to the color difference ΔE ^* in Table 1, it can be seen that when the nitrogen and oxygen content exceeds the above range, the color difference ΔE ^* increases rapidly. FIG. 11 shows the relationship between the concentrations of nitrogen gas and oxygen gas and the color difference ΔE ^* . As shown in FIG. 11, when the concentration of nitrogen gas falls below a certain value (that is, when the concentration of oxygen gas exceeds a certain value), ΔE ^* suddenly increases. This is because the characteristics of the silicon nitride oxide film are critically changed, and the effect of preventing discoloration and oxidation is remarkably improved by setting the nitrogen content and the oxygen content within the above-described ranges. It is shown that.

FIG. 12 shows the relationship between the oxygen content of the SiON film and the color difference ΔE ^*, and FIG. 13 shows the relationship between the nitrogen content of the SiON film and the color difference ΔE ^* . From FIG. 12 and FIG. 13, by setting the oxygen content of the SiON film to 30% by mass or less and the nitrogen content to 10% by mass or more, the color difference ΔE ^* before and after heating can be sufficiently reduced, and excellent oxidation is achieved ^. It turns out that the prevention effect is acquired.

  The reason why such an unexpected effect was obtained is not clear. However, during high-temperature heating, there is a phenomenon in which silicon in the silicon nitride oxide film binds to external oxygen and releases the oxygen that was originally bound to the metal tube side. It is speculated that this phenomenon is less likely to occur as the nitrogen content is higher.

  From the viewpoint of increasing the effect of preventing discoloration, it is preferable to make the oxygen content of the SiON film as low as possible and the nitrogen content as high as possible. Specifically, it is more preferable that the oxygen content is 5% by mass or less and the nitrogen content is 40% by mass or more.

However, in order to sufficiently reduce the oxygen content of the SiON film, the chamber 21 is evacuated so that the degree of vacuum is sufficiently high, and then substantially only nitrogen gas is introduced into the chamber 21. Sputtering is necessary. For example, in order to set the oxygen content rate to 5% by mass or less, the degree of vacuum in the chamber 21 needs to be about 1 × 10 ⁻⁴ Pa or less. Setting the degree of vacuum in the large chamber 21 that can accommodate large parts such as the exhaust pipe 5 to a high value as described above increases the time required for production, which may be disadvantageous in production. . Moreover, even if evacuation is performed for a long time using a high-performance pump, residual oxygen and oxygen that exudes from a workpiece, jig, or device cannot be made zero, so the oxygen content is 1 mass. Setting it to less than% is extremely difficult in actual production.

On the other hand, when the oxygen content is more than 5% by mass and 30% by mass or less and the nitrogen content is in the range of 10% by mass to less than 40% by mass, the degree of vacuum in the chamber 21 is 1 × 10 ⁻ It may be about ³ Pa. Therefore, setting the oxygen and nitrogen content in such a range can reduce the time required for production, which is very advantageous in production. Even if the oxygen and nitrogen contents are set within such a range, the color difference ΔE ^* can be made sufficiently small (for example, 1 or less) as shown in Table 1, and sufficiently high oxidation prevention can be achieved. An effect is obtained. This is because, as already described, the present invention utilizes the unique property of the SiON film that the antioxidant effect is remarkably improved by setting the oxygen and nitrogen content in a specific range.

  ADVANTAGE OF THE INVENTION According to this invention, the exhaust pipe for internal combustion engines which can prevent discoloration and oxidation by high temperature exhaust gas is provided.

  The exhaust pipe for an internal combustion engine according to the present invention can be widely used in vehicles such as motorcycles equipped with an internal combustion engine and all-weather four-wheeled vehicles, ships such as ships equipped with an internal combustion engine, and airplanes.

1 is a side view of a motorcycle in which an exhaust pipe for an internal combustion engine of the present invention is used. It is sectional drawing of the exhaust pipe for internal combustion engines of this invention. (A) And (b) is the sectional side view and upper sectional view which show typically the structure of the sputtering device used for manufacture of the exhaust pipe for internal combustion engines of this invention. It is a schematic diagram which shows the structure of the surface vicinity of the exhaust pipe for internal combustion engines of this invention. (A) And (b) is a figure which shows the element distribution in the depth direction of the exhaust pipe for internal combustion engines of this invention by GDS analysis, respectively. (A) And (b) is a figure which shows the element distribution in the depth direction of the conventional exhaust pipe for internal combustion engines by GDS analysis, respectively. It is a figure which shows element distribution in the depth direction by XPS analysis of a chromium plating film. (A) And (b) is a figure which shows the element distribution in the depth direction of the conventional exhaust pipe for internal combustion engines by XPS analysis, and the binding energy of chromium in two points shown to (a), respectively. It is a figure explaining distribution of the ceramic film of the exhaust pipe for internal-combustion engines of the present invention. It is a graph which shows the relationship between the flow rate ratio of the gas introduce | transduced in a chamber, and the chemical composition of a SiON film | membrane. It is a graph which shows the relationship between nitrogen and oxygen gas density | concentration and color difference (DELTA ⁾ E ^* . It is a graph which shows the relationship between the oxygen content rate of a SiON film | membrane, and color difference (DELTA ⁾ E ^* . It is a graph which shows the relationship between the nitrogen content rate of a SiON film | membrane, and color difference (DELTA ⁾ E ^* . 1 is a side view showing the appearance of a motorcycle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Exhaust pipe 5 Metal pipe 6 Passage 10 Ceramics film 20 Sputtering apparatus 21 Chamber 22 Target 23 Axis 24 Holder 100 Motorcycle

Claims (13)

A metal tube surrounding a passage through which exhaust gas from the internal combustion engine passes;
A ceramic film covering the outside of the metal tube and having a metal element content of 0.5% by mass or less mainly contained on the surface of the metal tube;
With
The ceramic film, Ri SiON Makudea containing 30 wt% or less of O and 10 mass% or more of N,
The exhaust pipe for an internal combustion engine , wherein the ceramic film is a vapor deposition film formed by a vapor deposition method .   The exhaust pipe for an internal combustion engine according to claim 1, wherein the ceramic film contains 5 mass% or less of O and 40 mass% or more of N.   The exhaust pipe for an internal combustion engine according to claim 1 or 2, wherein the ceramic film is directly formed on a surface of the metal pipe.   The exhaust pipe for an internal combustion engine according to any one of claims 1 to 3, wherein the ceramic film has a thickness of 5 nm to 300 nm.   The exhaust pipe for an internal combustion engine according to any one of claims 1 to 3, wherein the ceramic film has a thickness of 5 nm to 30 nm.   The exhaust pipe for an internal combustion engine according to claim 4 or 5, wherein the metal pipe has a surface roughness Ra of 0.4 µm or more and 3.2 µm or less.   The exhaust pipe for an internal combustion engine according to any one of claims 1 to 6, wherein the metal pipe is made of titanium, a titanium alloy, or stainless steel.   The exhaust pipe for an internal combustion engine according to any one of claims 1 to 6, wherein the metal pipe has a chromium plating layer on a surface thereof.   The exhaust pipe for an internal combustion engine according to any one of claims 1 to 8, wherein an oxide film of a metal element mainly contained on a surface of the metal pipe is substantially not included between the metal pipe and the ceramic film. The exhaust pipe for an internal combustion engine according to any one of claims 1 to 9, wherein the ceramic film is a deposited film formed by a sputtering method or an ion plating method. The metal tube has a surface roughness larger than a surface roughness range in which diffracted light by visible light is generated, and the ceramic film has a thickness smaller than a thickness range in which interference fringes by visible light are generated. An exhaust pipe for an internal combustion engine according to any one of claims 1 to 10 . The internal combustion engine provided with the exhaust pipe for internal combustion engines in any one of Claim 1 to 11 . A transportation device comprising the internal combustion engine according to claim 12 .

Images