JP2006052727A - Exhaust pipe for internal combustion engines - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust pipe for an internal combustion engine capable of preventing discoloration and oxidation occurring due to high temperature exhaust gas. <P>SOLUTION: The exhaust pipe for an internal combustion engine is provided with a metal tube 5 for surrounding a passage through which exhaust gas from a internal combustion engine 1 passes; and a ceramic membrane 10 which covers the outside of the metal tube 5 and whose content of a metallic element mainly contained in the surface of the metal pipe 5 is 0.5 atom% and less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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.

  Many motorcycles equipped with an internal combustion engine expose the internal combustion engine and use the appearance of the internal combustion engine in the design of the motorcycle. In such a motorcycle, the exhaust pipe for leading the exhaust gas from the internal combustion engine is also automatic. It plays an important role in the design of motorcycles. Even when the internal combustion engine is covered with a cowl or the like, the exhaust pipe is not 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. 11 is a side view showing an example of a sports type motorcycle. A motorcycle 200 shown in FIG. 11 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, for example, creating a strong and powerful impression by bending the exhaust pipe smoothly, or enhancing the contrast with other components by finishing the surface of the exhaust pipe with a shiny metallic color. Yes. On the other hand, it is also practiced to have a unity with the surrounding structure by finishing the color tone similar to that of the other components.

  In general, the exhaust pipe is formed using carbon steel for mechanical structure (STKM), stainless steel (SUS), titanium, or the like. As described above, in order to improve the appearance of the exhaust pipe, when the exhaust pipe is formed of STKM material, the surface of the exhaust pipe is plated with chromium (Cr).

  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 subjected to Cr plating is discolored, oxidized, or deteriorated. In particular, a region discolored in red brown appears. Further, even in an exhaust pipe formed of SUS or titanium not subjected to Cr plating, the surface is reddish 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, a reddish discoloration or surface deterioration occurs in the exhaust pipe having a metallic luster, thereby causing a problem of deteriorating the appearance of the design of the entire motorcycle. 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 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 exhaust pipe of the internal combustion engine to prevent discoloration of the exhaust pipe (Patent Document 1). As disclosed in Patent Document 1, by forming a silicon oxide film by a sol-gel method with a thickness of 0.05 μm or more on an exhaust pipe, it is possible to obtain an exhaust pipe that is not easily discolored even by heating at about 400 ° C. it can.
JP 2002-332838 A

  However, it has been found that the exhaust pipe obtained by the technique disclosed in Patent Document 1 undergoes rapid surface discoloration when exposed to temperatures exceeding 400 ° C. Further, it was found that the silicon oxide film formed by Patent Document 1 is relatively soft and does not have sufficient strength against impact. For this reason, when the exhaust pipe by patent document 1 was used for the internal combustion engine with the high performance in which the temperature of exhaust gas becomes high as mentioned above, it turned out that discoloration may not fully be prevented. It was also found that in motorcycles, stones and sand collide with the exposed exhaust pipe during running, causing scratches on the surface of the exhaust pipe and fading easily from that portion.

  Furthermore, it has been found that interference fringes are likely to appear in the silicon oxide film formed by the sol-gel method, and remarkable interference fringes appear in discoloration caused by exposure to a temperature exceeding 400 ° C.

  An object of the present invention is to solve such problems of the prior art and to provide an exhaust pipe for an internal combustion engine that has high hardness and can prevent discoloration and oxidation due to high-temperature exhaust gas.

  The exhaust pipe for an internal combustion engine of the present invention covers a metal pipe that surrounds a passage through which exhaust gas from the internal combustion engine passes, and a content of a metal element that mainly covers the outside of the metal pipe and is mainly contained on the surface of the metal pipe With a ceramic film of 0.5 atomic% or less.

  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 in the range of 5 nm to 300 nm.

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

  In a preferred embodiment, the metal tube has a surface roughness Ra in the range of 0.4 μm to 3.2 μm.

In a preferred embodiment, the ceramic film is selected from the group consisting of oxides, nitrides, nitride oxides and borides of Si, Ti, Al, Zr, Mo, Nb, W, and V, and B ₄ C 1 Including one or more.

  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, a metal oxide film mainly contained on the surface of the metal tube is not substantially included between the metal tube and the ceramic film.

  In a preferred embodiment, the ceramic film is a deposited film formed by a 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 range in which interference fringes by visible light are generated. Have a smaller thickness.

  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 contains metal elements mainly contained on the surface of the metal pipe. A diamond-like carbon film having a content of 0.5 atomic% or less.

  Alternatively, an exhaust pipe for an internal combustion engine of the present invention includes a metal pipe that surrounds a passage through which exhaust gas from the internal combustion engine passes, and an amorphous film that covers the outside of the metal pipe and is formed by vapor deposition. Prepare.

  The internal combustion engine of the present invention includes the exhaust pipe for an internal combustion engine defined in any one of the above.

  The transport device of the present invention includes the internal combustion engine.

  The method of manufacturing an exhaust pipe for an internal combustion engine according to the present invention includes a step of arranging a metal pipe surrounding a passage through which exhaust gas from the internal combustion engine passes in a vapor deposition apparatus, and a ceramic having a thickness of 5 nm to 300 nm on the metal pipe. Depositing a film.

  In a preferred embodiment, the method further includes etching the surface of the metal tube between the placing step and the depositing step.

  In a preferred embodiment, the etching step is performed by causing plasma particles to collide with the surface of the metal tube.

  In a preferred embodiment, the deposition step is performed by an evaporation method.

  In a preferred embodiment, the deposition step is performed by an ion plating method or a sputtering method.

  The method for manufacturing an exhaust pipe for an internal combustion engine according to the present invention includes a step of disposing a metal pipe surrounding a passage through which exhaust gas from the internal combustion engine passes in a vapor deposition apparatus, and a thickness of 5 to 300 nm on the metal pipe. And depositing the diamond-like carbon film having chemical vapor deposition.

  According to the exhaust pipe of the present invention, the ceramic film contains only 0.5 atomic% or less of the metal mainly contained on the surface of the metal pipe. It does not occur or the surface is not deteriorated. For this reason, the exhaust pipe is not discolored by high-temperature exhaust gas, and an excellent appearance can be maintained. Moreover, since the ceramic film formed by the vapor deposition method is dense, the barrier property is high. For this reason, it is possible to prevent external oxygen from reaching the metal tube and iron contained in the metal tube from being oxidized and deposited on the surface. For this reason, the exhaust pipe is not discolored by high-temperature exhaust gas, and an excellent appearance can be maintained. Moreover, since the ceramic film formed by the vapor deposition method has high hardness, it is also resistant to impact.

  The inventor of the present application has studied in detail the cause of the high-temperature oxidation and discoloration of the surface that cannot be sufficiently prevented in the exhaust pipe formed with the silicon oxide film by the sol-gel method. As a result, the silicon oxide film formed by the sol-gel method contains a metal mainly contained in 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. I found out that Further, in the sol-gel method, since the organic compound bonded to silicon is vaporized and decomposed during firing, fine voids are generated in the obtained silicon oxide film, and the gas barrier property is lowered. Conceivable. For this reason, when the exhaust pipe is exposed to high temperature, the metal on the exhaust pipe surface diffuses into the silicon oxide film and is combined with external oxygen to oxidize, or oxygen penetrates 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, iron in the metal that constitutes the exhaust pipe is deposited as a reddish oxide on the surface. It was found that the appearance of the exhaust pipe was damaged.

  The inventor of the present application paid attention to a ceramic film formed by vapor deposition as an antioxidant film on the surface of the exhaust pipe and conducted various experiments. As a result, it was found that the ceramic film formed by the evaporation method solved the problem of the silicon oxide film formed by the sol-gel method and was suitable as an antioxidant film for the exhaust pipe. Embodiments of the present invention will be described below.

  FIG. 1 shows a motorcycle 100 in which an exhaust pipe for an internal combustion engine of the present invention (hereinafter sometimes simply referred to as an exhaust pipe) is used. 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 using the exhaust pipe for the internal combustion engine of the present invention is not limited to that shown in FIG. 1. For example, the exhaust pipe of the present invention is adopted for a motorcycle having a structure as shown in FIG. May be.

  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 outside of the inner tube. . 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 tube 5 is made of carbon steel for mechanical structure (STKM), stainless steel (SUS), titanium, a titanium alloy, a nickel alloy, an aluminum alloy, or the like. A plating layer such as chrome plating may be formed in order to enhance the surface metallic luster and decorativeness. Since the STKM material does not have a decorative and sufficient metallic luster, when the metal tube 5 made of STKM is used, it is preferable that chrome plating or nickel plating and chrome plating are applied. Moreover, when using the metal tube 5 which consists of 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. Specifically, the ceramic film 10 includes silicon (Si), titanium (Ti), aluminum (Al), zirconium (Zr), molybdenum (Mo), niobium (Nb), tungsten (W), vanadium (V), and the like. And at least one selected from oxides, nitrides, nitride oxides or borides of the above elements. These materials do not necessarily contain elements in a stoichiometric ratio. The ceramic film 10 may contain B ₄ C (boron carbide). The ceramic film 10 includes one or more layers made of these materials.

  “Ceramics” widely refers to solid materials such as metal or non-metal oxides, nitrides, nitride oxides, borides, carbides, etc., and are formed by a technique that includes a firing process that has been often used in the past. As a matter of course, not only those formed by vapor deposition as already described, but also those included.

  In view of easy formation and easy availability of materials, it is preferable to use an oxide, nitride, or nitride oxide of Si. That is, the ceramic film 10 is preferably made of silicon oxide, silicon nitride, or silicon nitride oxide. In general, nitrides are denser and harder than oxides. From the same viewpoint, it is also preferable to use an oxide, nitride or nitride oxide of Al. That is, the ceramic film 10 is preferably made of aluminum oxide, aluminum nitride, or aluminum nitride oxide.

  It is preferable that the ceramic film 10 does not contain more than 0.5 atomic% of metal contained mainly (typically in a ratio of 50% or more) on the surface of the metal tube 5. When the metal contained mainly on the surface of the metal tube 5 (that is, substantially constituting the surface of the metal tube 5) is more than 0.5 atomic%, the metal is oxidized from the surface of the ceramic film 10 due to high heat. As a result, the surface of the exhaust pipe 2 may be discolored. Further, there is a possibility that the oxidation proceeds from the oxidized metal into the metal tube 5. Considering the appearance of the exhaust pipe when the metal contained in the ceramic film 10 is oxidized, the content of the metal contained mainly in the surface of the metal pipe 5 in the ceramic film 10 is more preferably 0.4 atomic% or less. Preferably, it is 0.3 atomic% or less.

  The content of the metal mainly contained on the surface of the metal tube 5 may locally vary in the ceramic film 10, but the content is at least 0.5 atomic% at the central portion in the thickness direction of the ceramic film 10. The following is preferable. Further, the portion (that is, the entire ceramic film 10) excluding the vicinity of the inner surface (the metal tube 5 side) and the outer surface of the ceramic film 10 (each having a thickness of 10% with respect to the entire thickness of the ceramic film 10). The content is preferably 0.5 atomic% or less in a portion corresponding to 80% of the above.

  When the ceramic film 10 is formed outside the metal tube 5, the ceramic film 10 is formed by a method in which the metal mainly contained on the surface of the metal tube 5 diffuses into the formed ceramic film 10 and is not contained in the film. Specifically, it is preferably formed by a vapor deposition method. In this specification, “evaporation method” refers to a CVD (chemical vapor deposition) method and a physical vapor deposition method in which a substance to be deposited is deposited in a gaseous state. In the present invention, it is more preferable to use a physical vapor deposition method as the 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 more preferably formed by the ion plating method or the sputtering 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. 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 formed before the ceramic film 10 is formed by a physical or chemical method. It is preferable to remove it.

  Since the ceramic film formed by the vapor deposition method is dense, it has a high gas barrier property even at a temperature of about 500 ° C. and can prevent the surface of the metal tube 5 from being oxidized.

  In addition, most of the ceramic films formed by vapor deposition using the materials exemplified in the above description are amorphous films, and remain 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 material, a part of the film may be crystallized, but there is practically no problem in gas barrier properties.

  FIG. 3 is an enlarged sectional view showing the vicinity of the surface of the exhaust pipe 2. As shown in the figure, the surface of the metal tube 5 has a larger surface roughness 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 smaller 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.

  As far as these reasons are concerned, there is no upper limit to the value of the average roughness Ra of the surface of the metal tube 5. However, when the average roughness Ra of the surface of the metal tube 5 is 3.2 μm or more, the light reflectance is lowered, and the merchantability and aesthetics are impaired.

  The thickness of the ceramic film 10 is preferably in the range of 5 nm to 300 nm. 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, interference colors are 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.

  In this range, the color and transparency of the ceramic film 10 can be arbitrarily selected by appropriately selecting the thickness in consideration of the refractive index of the ceramic film to be formed. For example, when the refractive index of the ceramic film 10 is 1.7 to 2.0, the ceramic film 10 is colorless and transparent in the thickness range of 5 nm to 30 nm. The ceramic film 10 is colored and transparent in the thickness range of 30 to 120 nm, and is colored and opaque in the thickness range of 120 to 300 nm. Therefore, by making the thickness of the ceramic film 10 from 5 nm to 30 nm, it is possible to obtain an exhaust pipe that takes advantage of the color tone of the surface of the metal pipe 5 and that is not oxidized by exhaust gas. By setting the thickness of the ceramic film 10 to 30 nm to 120 nm, the color tone of the ceramic film 10 is superimposed on the color tone of the surface of the metal tube 5, and an exhaust pipe having a color that cannot be obtained with a conventional exhaust pipe is obtained. In this range, as the thickness increases, the color of the ceramic film 10 itself changes in the order of gold-red-blue-gold. Furthermore, by setting the thickness of the ceramic film 10 to 120 nm to 300 nm, it is possible to obtain an exhaust pipe having the color generated by the ceramic film 10 and excellent in wear resistance and impact resistance.

  If 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 interference color can be obtained regardless of the material and the refractive index. In other words, a ceramic film having a thickness smaller than the range in which the interference fringes are generated on the surface of the metal tube having a surface roughness larger than the range of the surface roughness in which the diffracted light by visible light is generated is formed. By doing so, even if high-temperature exhaust gas passes, surface oxidation or discoloration does not occur, and an exhaust pipe having a uniform metallic luster with excellent adhesion and no interference fringes is obtained. Can do.

  Next, a method for manufacturing the exhaust pipe 2 will be described. In the following description, an example in which the ceramic film 10 is formed by sputtering will be described.

  First, a metal tube 5 is prepared. As described above, when the metal tube 5 is formed using the STKM material, chrome plating is applied in order to improve the metallic luster and decorativeness of the surface. Next, as shown in FIGS. 4A and 4B, the metal tube 5 is introduced into the chamber 21 of the sputter deposition apparatus 20. The sputter deposition apparatus 20 includes a plurality of holders 24 that can hold, for example, two metal tubes 5 suspended vertically so that a film can be formed on many metal tubes 5 simultaneously. Each holder 24 revolves in the chamber 21 while rotating around the rotation shaft 23. The sputter deposition apparatus 20 includes a plurality of targets 22 outside the track on which the holder 24 rotates. When a silicon nitride film is formed as the ceramic film 10, a silicon target 22 is used. A silicon nitride target may be 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 sputter deposition 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.

  The metal tube 5 is placed in the holder 24, and the inside of 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 in the range of 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, argon and nitrogen gas are introduced into the chamber 21 to start discharge. 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 case of this embodiment, the silicon particles jumping out of the target react with nitrogen plasma and are deposited on the surface of the metal tube 5 as a silicon nitride film. 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.

  According to the exhaust pipe of the present invention, the ceramic film contains only 0.5 atomic% or less of the metal mainly contained on the surface of the metal tube, and the metal that is the main component of the surface of the metal tube is substantially contained. It can be said that it is not included. For this reason, when this metal is oxidized at a high temperature, the exhaust pipe is not discolored or the surface is not deteriorated. For this reason, the exhaust pipe is not discolored by high-temperature exhaust gas, and an excellent appearance can be maintained.

  In particular, since the ceramic film formed by the vapor deposition method is dense, it has a high barrier property, and external oxygen reaches the metal tube, or iron contained in the metal tube is oxidized and deposited on the surface. Can be prevented. For this reason, the exhaust pipe is not discolored by high-temperature exhaust gas, and an excellent appearance can be maintained.

  As described above, the method of directly forming the ceramic film by the vapor deposition method is more dense than the method of forming the metal oxide film by heat treatment after forming the metal film once by the sputtering method or the ion plating method. It is excellent in that it can be formed. In the technique of performing oxidation after forming a metal film once, the density of the film decreases due to oxidation, and oxidation proceeds more and more during subsequent use. On the other hand, in the method of directly forming the ceramic film by the vapor deposition method, a film that has already been oxidized or nitrided is formed. Therefore, the film does not deteriorate after film formation, and a dense state is maintained.

  Further, by changing the thickness of the ceramic film, the transparency and color tone of the ceramic film can be arbitrarily selected. For this reason, it is possible to obtain an exhaust pipe having a color tone that could not be obtained by the conventional method and that can maintain the color tone for a long time without being changed by the heat of the exhaust gas.

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

  Note that, instead of the one exemplified in the above description, a film made of diamond-like carbon (DLC) may be formed so as to cover the outside of the metal tube 5, thereby preventing oxidation of the exhaust pipe surface. . Since the DLC film is made of amorphous carbon and is excellent in thermal conductivity and gas barrier properties, it can be used in the same manner as the exemplified film. When using a DLC film, it is preferable to form the DLC film by a CVD method (chemical vapor deposition method).

(Analysis and experimental examples)
First, the distribution in the depth direction of elements in the exhaust pipe of the present invention and the exhaust pipe of Patent Document 1 was examined. As the exhaust pipe of the present invention, a metal pipe made of STKM material with nickel plating and chromium plating was prepared, and a silicon oxide film was formed as a ceramic film by sputtering. In order to form a silicon oxide film, a nickel-plated and chromium-plated metal tube was placed in a magnetron sputtering apparatus chamber and evacuated until a vacuum degree of 3 × 10 ⁻⁴ Pa was reached. After that, argon was introduced into the chamber at a flow rate of 25 sccm, and while maintaining a pressure of 0.4 Pa, 500 V, 4 A (2 KW) power was applied and reverse sputtering was performed for 1.5 minutes to naturally oxidize the metal tube surface. The membrane was removed. Then, using silicon as a target, silicon and oxygen are introduced into the chamber, and while maintaining a pressure of 0.2 Pa, 700 V, 4 A (4.9 kW) power is applied, and sputtering is performed for 1 minute. A silicon oxide film having a thickness of 25 nm was formed. Similarly, using a sputtering method, a silicon oxide film having a thickness of 250 nm was formed on the surface of the metal tube by changing the film forming conditions.

  As a conventional example, a metal tube similar to that described above was prepared, and a ceramic film was formed 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. 5A and FIG. 6A show the element distribution in the depth direction of the exhaust pipe of the present invention. 5 (b) and 6 (b) are enlarged views showing the vicinity of the surface of FIGS. 5 (a) and 6 (a), respectively. As is apparent from these drawings, in the exhaust pipe of the present invention, the silicon oxide film, which is a ceramic film, contains almost no chromium, which is the main component metal on the surface of the metal pipe. Specifically, the elemental concentration of chromium is 0.5% or less (for example, 0.1% in FIG. 6B), and the chromium concentration rapidly increases at the boundary between the silicon oxide film and the chromium plating. ing. Further, the profiles indicating the concentrations of silicon and oxygen decrease with substantially the same gradient in the vicinity of the boundary between the silicon oxide film and the chromium plating. This is because chromium is not diffused into the silicon oxide film, and oxygen is bonded to silicon at the boundary between the silicon oxide film and the chromium plating, and the chromium oxide film, that is, the natural oxide film of chromium is almost all. Indicates that it does not exist.

  FIG. 7A shows the element distribution in the depth direction of the conventional exhaust pipe. FIG. 7B is an enlarged view showing the vicinity of the surface of FIG. As is apparent from these figures, in the conventional exhaust pipe, the silicon oxide film formed by the sol-gel method contains chromium, which is the main component metal on the surface of the metal pipe, at a ratio of about 4 atomic%. At the boundary between the silicon oxide film and the chromium plating, the chromium concentration slightly increases. 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. 8, the natural oxide film of chromium has a thickness of about 5 minutes in terms of sputtering time.

  FIG. 9A shows the element distribution in the depth direction of a conventional exhaust pipe by the XPS method. As is clear from the figure, the concentration of oxygen (O1s) is constant in the silicon film, but at the interface with the chromium plating, the oxygen concentration decreases in two steps so as to be surrounded by broken lines C1 and C2. . Among these, the change (C2) in the oxygen concentration on the side close to the interface with the chromium plating indicates oxygen contained in the natural oxide film of chromium because the change is about 5 minutes in terms of sputtering time. It is thought that there is.

  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.9 (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 of the present invention, compared to the conventional exhaust pipe, the ceramic film contains substantially no metal mainly contained on the surface of the metal pipe, and the ceramic film and the metal pipe It was found that the metal oxide that substantially constitutes the surface of the metal tube was not present at the interface.

  Here, as a conventional example, a silicon oxide film formed by a sol-gel method has been described. However, other methods conventionally used for coating exhaust pipes, for example, a solution containing a metal compound using a coating method or a dipping method are used. The metal oxide film formed by the method of firing after being applied to the surface of the exhaust pipe also lacks the denseness like the silicon oxide film formed by the sol-gel method. 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, the exhaust pipe of the present invention was produced under various conditions and subjected to a high temperature heating test. As the metal tube, a material made of SUS304, titanium, STKM material plated with chromium was used. As the ceramic film, a single layer film of silicon nitride, silicon oxide and silicon nitride oxide, and a double layer film of silicon nitride and silicon oxide were formed. The produced exhaust pipe was left in the atmosphere at 500 ° C. for 24 hours, and the oxidation state and discoloration state of the exhaust pipe surface were examined. The results are shown in Table 1.

  As shown in Table 1, it was found that even if the substrate on which the ceramic film is formed is any one of chrome plating, stainless steel, and titanium, there is no oxidation or discoloration of the surface at a high temperature and an excellent appearance can be maintained. It can also be seen that any of the silicon nitride film, silicon oxide film, and silicon nitride oxide film functions to prevent oxidation and discoloration. Further, it has been found that these films are effective in the thickness range of 10 nm to 120 nm.

  Next, a corrosion resistance evaluation test was performed on some of the samples shown in Table 1. The test was performed based on JIS-Z2371, and the degree of corrosion was evaluated by RN (Rating Number). RN is a score indicating the degree of corrosion according to the ratio of the corrosion area and the effective area, and is classified into 10 to 0. The larger the number, the smaller the corrosion area ratio and the less the corrosion. The results are shown in Table 2.

  As shown in Table 2, according to the present invention, both the heated sample and the non-heated sample exhibit excellent corrosion resistance. That is, since the surface is completely protected by the ceramic film, corrosion does not occur. On the other hand, if a ceramic tube is not formed on the surface of the metal tube as a comparative example, corrosion can be prevented to some extent by chromium formed on the surface unless heating is performed. However, by heating, iron precipitates from the base STKM material and oxidizes. For this reason, it is thought that corrosion resistance falls and corrosion arises over a large area of the surface.

  FIG. 10 is a schematic diagram showing an example of the distribution of the thickness of the exhaust pipe formed by the above-described method. In FIG. 10, the percentage of the thickness indicated by the arrow relative to the target value is shown as a percentage. 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 a uniform ceramic film can be formed by physical vapor deposition.

  As described above, according to the exhaust pipe of the present invention, when the ceramic film is in the above-described film thickness range, it prevents surface oxidation and discoloration of the surface at high temperature and has excellent corrosion resistance. I understood.

  INDUSTRIAL APPLICABILITY 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. 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 the side sectional view and upper sectional view which show typically the structure of the sputter deposition apparatus used for manufacture of the exhaust pipe for internal-combustion engines of the present 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 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. 1 is a side view showing the appearance of a motorcycle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,201 Internal combustion engine 2,202 Exhaust pipe 5 Metal pipe 6 Passage 10 Ceramic film 20 Sputter deposition apparatus 21 Chamber 22 Target 23 Shaft 24 Holder 100, 200 Motorcycle

Claims (21)

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 atomic% or less mainly contained on the surface of the metal tube;
An exhaust pipe for an internal combustion engine comprising:   The exhaust pipe for an internal combustion engine according to claim 1, wherein the ceramic film is directly formed on a surface of the metal pipe.   The exhaust pipe for an internal combustion engine according to claim 1 or 2, wherein the ceramic film has a thickness in a range of 5 nm to 300 nm.   The exhaust pipe for an internal combustion engine according to claim 1 or 2, wherein the ceramic film has a thickness in a range of 5 nm to 30 nm.   The exhaust pipe for an internal combustion engine according to claim 3 or 4, wherein the metal pipe has a surface roughness Ra within a range of 0.4 µm to 3.2 µm. The ceramic film includes one or more selected from the group consisting of oxides, nitrides, nitride oxides and borides of Si, Ti, Al, Zr, Mo, Nb, W, and V, and B ₄ C. The exhaust pipe for an internal combustion engine according to any one of 1 to 5.   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, which does not substantially include a metal oxide film mainly contained on a surface of the metal pipe 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 vapor deposition film formed by a vapor deposition method.   The exhaust pipe for an internal combustion engine according to claim 10, 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 4. A metal tube surrounding a passage through which exhaust gas from the internal combustion engine passes;
A diamond-like carbon film that covers the outside of the metal tube and has a metal element content of 0.5 atomic% or less mainly contained on the surface of the metal tube;
An exhaust pipe for an internal combustion engine.   An internal combustion engine comprising an exhaust pipe for an internal combustion engine as defined in any one of claims 1 to 13.   A transportation device comprising an internal combustion engine as defined in claim 14. Arranging a metal tube surrounding a passage through which exhaust gas from the internal combustion engine passes in the vapor deposition apparatus;
Depositing a ceramic film having a thickness of 5 nm to 300 nm on the metal tube;
Of manufacturing an exhaust pipe for an internal combustion engine. Etching the surface of the metal tube between the placing step and the depositing step;
The manufacturing method of the exhaust pipe for internal combustion engines of Claim 16 which further contains these.   The method of manufacturing an exhaust pipe for an internal combustion engine according to claim 17, wherein the etching step is performed by causing plasma particles to collide with a surface of the metal pipe.   The method for manufacturing an exhaust pipe for an internal combustion engine according to any one of claims 16 to 18, wherein the deposition step is performed by an evaporation method.   The method for manufacturing an exhaust pipe for an internal combustion engine according to claim 19, wherein the deposition step is performed by an ion plating method or a sputtering method. Arranging a metal tube surrounding a passage through which exhaust gas from the internal combustion engine passes in the vapor deposition apparatus;
Depositing a diamond-like carbon film having a thickness of 5 nm to 300 nm on the metal tube by chemical vapor deposition;
Of manufacturing an exhaust pipe for an internal combustion engine.

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