JP5607582B2 - Manufacturing method of engine valve - Google Patents

Description

  The present invention relates to a method for manufacturing an engine valve constituting an internal combustion engine.

  An internal combustion engine such as a gasoline engine or a diesel engine is mainly composed of an engine block and a cylinder head, and its combustion chamber has a bore surface of the cylinder block, a piston top surface incorporated in the bore, and a cylinder head. It is defined by a bottom surface and a top surface of each intake and exhaust engine valve disposed in the cylinder head. It is important to reduce the cooling loss with the increase in output required for recent internal combustion engines. As one of the measures to reduce this cooling loss, the inner wall of the combustion chamber is insulated with ceramics. The method of forming a film can be mentioned.

  However, the ceramics mentioned above generally have a low thermal conductivity and a high heat capacity, so that the intake efficiency decreases and knocks due to a steady increase in surface temperature (knocking abnormal combustion due to heat generated in the combustion chamber). As a result, the present situation is that it is not widely used as a coating material on the inner wall of the combustion chamber.

  Therefore, it is desirable that the heat insulating coating formed on the wall surface of the combustion chamber is formed of a material having low heat conductivity and low heat capacity as well as heat resistance and heat insulating properties. Furthermore, in addition to the low thermal conductivity and low heat capacity, a coating is formed from a material that can withstand repeated stresses of explosion pressure and injection pressure, thermal expansion and thermal contraction during combustion in the combustion chamber, and It is desirable that the coating is formed from a material having high adhesion to a base material such as a cylinder block.

  Here, turning to the prior art, there is a microporous silicon dioxide or aluminum oxide coating on both the bottom surface of the cylinder head and the inner surface of the water jacket defined in the cylinder head. A cylinder head formed by anodization is disclosed in Patent Document 1. According to this cylinder head, since the microporous film is provided on both the bottom surface of the head and the inner surface of the jacket, the surface area of the bottom surface of the head and the inner surface of the jacket is expanded by this coating, and the heat generated in the combustion chamber. Can be efficiently absorbed into the inside through the coating, and the heat absorbed inside is efficiently released to the cooling water through the coating on the inner surface of the jacket. For this reason, the cylinder head is easily warmed by heat absorption and easily cooled by heat radiation, and the temperature rise is suppressed.

  By the way, since the engine valve which comprises an internal combustion engine has especially large heat load, it is common to form from heat-resistant steel, such as SUH1,3 (SUH: Steel Heat Resisting). In particular, in an exhaust engine valve, the atmosphere temperature of the exhaust gas to be exposed is 900 ° C. or higher, which is considerably higher than 600 to 660 ° C., which is the melting point of aluminum. For this reason, it is extremely difficult to form the above-described anodized film on the surface of the engine valve.

  Therefore, it is conceivable to apply the method disclosed in Patent Document 2 as a method of forming an anodized film on the engine valve. In the technique disclosed in Patent Document 2, an aluminum coating layer is formed by performing aluminum plating on the surface of a bolt or nut whose base material is made of carbon steel, and then the aluminum coating layer is oxidized by an anodic oxidation method. This is a method of forming an oxide film.

  Thus, for an engine valve made of a steel material, an anodized film can be formed by applying aluminum plating to the surface of the engine valve. However, simply forming an anodic oxide film on the surface of the engine valve cannot satisfy both the heat dissipation and the swing characteristics. Here, the “swing characteristic” is a characteristic in which the temperature of the anodized film follows the gas temperature in the combustion chamber while having heat insulation performance.

  The engine valve is composed of an umbrella portion facing the combustion chamber of the internal combustion engine and a shaft portion that is integral with the umbrella portion and extends into the intake valve or the exhaust valve, but faces the internal combustion engine. When attempting to require the swing characteristics described above for the umbrella, only the anodized film is present on the surface and no aluminum plating remains, and the anodized film having voids is further shielded against heat. It is desirable to take measures to make a coating film.

  On the other hand, when the above-mentioned heat dissipation performance is required for the shaft portion of the engine valve, it is desirable to take measures such as opening the void of the anodized film on the surface to the outside.

JP 2003-113737 A JP 2008-232366 A

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for manufacturing an engine valve constituting an internal combustion engine having excellent swing characteristics and heat dissipation.

  In order to achieve the above object, a method of manufacturing an engine valve according to the present invention includes an umbrella part facing a combustion chamber of an internal combustion engine, a shaft part integrally extending with the umbrella part and extending into an intake valve or an exhaust valve, A method for manufacturing an engine valve made of an iron-based material, the first step of forming an aluminum plating film on the entire circumference of the engine valve, anodizing the aluminum plating film The second step of forming a film comprises a third step of forming a sealing film by performing a sealing process on the surface of the anodized film in the umbrella portion. In the first step, the film thickness of the aluminum plating film Is adjusted to ½ or less of the film thickness of the anodic oxide film to be formed.

  The engine valve to be manufactured by the manufacturing method of the present invention is made of an iron-based material, and this iron-based material means heat-resistant steel, carbon steel, titanium material, or the like. Further, the internal combustion engine to which the engine valve is applied may be either a gasoline engine or a diesel engine, and the configuration is mainly composed of an engine block and a cylinder head, as described above. The combustion chamber is defined by the bore surface of the cylinder block, the top surface of the piston incorporated in the bore, the bottom surface of the cylinder head, and the top surfaces of the intake and exhaust engine valves disposed in the cylinder head. The constituent members other than the engine valve are generally made of aluminum or an alloy thereof, so that an anodic oxide coating can be formed on the surface without forming an aluminum plating coating.

  As described above, an engine valve made of an iron-based material and having an umbrella portion facing the combustion chamber of the internal combustion engine and a shaft portion integrally formed with the umbrella portion and extending into the intake valve or the exhaust valve. In order to form the anodized film on the surface, first, as a first step, an aluminum plating film is formed on the entire circumference of the engine valve.

  Here, the film thickness of the aluminum plating film is adjusted to be ½ or less of the film thickness of the anodized film to be finally formed, so that the aluminum plating film is formed on the surface of the engine valve finally manufactured. Has been specified by the present inventors. More specifically, it is sufficient that the aluminum plating film does not remain in the umbrella portion of the engine valve that requires swing characteristics. In this aluminum plating, either aluminum or an alloy thereof is plated.

  When the aluminum plating film is formed on the entire circumference of the engine valve in the first step, as the second step, this is subjected to an anodic oxidation treatment to make the aluminum plating film an anodic oxidation film.

  With this anodic oxide coating, the engine valve has low thermal conductivity and low heat capacity, and can withstand repeated pressures of explosion pressure, injection pressure, thermal expansion and thermal contraction during combustion in the combustion chamber.

  Next, as a third step, an engine valve is manufactured by forming a sealing film by performing a sealing process on the surface of the anodized film in the umbrella portion. Here, the sealing treatment means that the surface of the void (pore) is sealed with a sealing film, and the deep void is maintained as it is, and the surface is thus sealed. However, the anodized film of the umbrella portion can exhibit excellent swing characteristics due to the internal structure having a large number of voids.

  Here, examples of the sealing treatment method include a method of performing sealing treatment with boiling water or steam, coating treatment of a heat-resistant sealing material, or both treatments.

  By performing the sealing treatment only on the umbrella portion, the void of the anodic oxide coating on the surface of the umbrella portion is sealed with the sealing coating, and the heat shielding performance of the engine valve is guaranteed.

  On the other hand, since the shaft portion is not sealed, the heat dissipation of the engine valve is guaranteed.

  In the case where importance is attached to the heat dissipation of the shaft portion, it is preferable that the thickness of the anodic oxide coating on the shaft portion is smaller than that of the anodic oxide coating on the umbrella portion.

  As a method for making the shaft anodized film relatively thin, the shaft portion anodizing time is relatively shortened compared to the umbrella portion, or the umbrella portion and the shaft portion are anodized in the same processing time. For example, after the treatment, a part of the anodized film on the shaft portion is scraped to relatively reduce the film thickness.

  Here, the microstructure of the anodized film is outlined. The anodized film is composed of a large number of cells having the thickness, and a structure in which voids are provided between the cells, or a separate void is provided in the cell itself. It has a structured.

  In particular, the thickness of the anodic oxide coating on the umbrella is preferably adjusted in the range of 100 to 500 μm because of the swing characteristics. If the thickness of the anodic oxide coating having the heat insulation performance is less than 100 μm, the temperature rise on the coating surface during the combustion cycle is insufficient and the heat insulation performance becomes insufficient, and the fuel efficiency improvement described later cannot be achieved. On the other hand, if the thickness of the anodic oxide coating exceeds 500 μm, the heat capacity becomes large, and the anodic oxide coating itself tends to accumulate heat, thereby inhibiting the swing characteristics. However, it is very difficult to form an anodic oxide film thicker than 500 μm.

In the second step of anodic oxidation, the engine valve is immersed in an acidic electrolyte solution to form an anode, a cathode is formed in the acidic electrolyte solution, and the maximum voltage is in the range of 130 to 200 V between both electrodes. The adjusted voltage can be applied and the electrolysis can be performed at a heat removal rate adjusted to a range of 1.6 to 2.4 cal / s / cm ² .

This is one method of anodizing treatment for forming a microstructured anodic oxide coating on the surface of an engine valve in which cells having vacant spaces in the anodic oxide coating further have voids in the interior thereof. A voltage adjusted to a maximum voltage in the range of 50 to 200 V is applied between the anode and the cathode in the acidic electrolyte in which the engine valve is immersed, and in the range of 1.6 to 2.4 cal / s / cm ² . Electrolysis should be performed at a controlled heat removal rate. That is, by performing the electrolysis under the above-described conditions, the acid can be penetrated to the bottom (deep part) of the anodized film to be formed, and the gap to the bottom of the anodized film can be formed in a desired size. Can be generated. The “heat removal rate” is the amount of heat taken by the electrolytic solution per unit time and unit area, and the heat removal rate is in the range of 1.6 to 2.4 cal / s / cm ² . The temperature of the electrolytic solution is adjusted to a range of, for example, -5 to 15 ° C.

  As can be understood from the above description, according to the method for manufacturing an engine valve of the present invention, the thickness of the anodic oxide film to be formed with respect to the engine valve formed of an iron-based material is not more than 1/2. The aluminum plating film is formed, and then the aluminum film is made an anodized film, and the sealing part is formed on the surface of the anodized film in the umbrella part of the engine valve, thereby forming the sealing film. It is possible to manufacture an engine valve that constitutes an internal combustion engine that is excellent in both the swing characteristics and the heat dissipation as well as the heat insulation performance.

It is a flowchart explaining the manufacturing method of the engine valve of this invention. It is a schematic diagram explaining the 1st step of a manufacturing method. (A) is a schematic diagram explaining the 2nd step of a manufacturing method, (b) is an enlarged view of the b section of (a). (A) is a schematic diagram explaining the 3rd step of a manufacturing method, (b) is an enlarged view of the b section of (a). (A) is a schematic diagram explaining the outline of a cooling test, (b) is a figure which shows the cooling curve based on a cooling test result, and the 40 degreeC fall time calculated | required from this. It is a figure which shows the correlation graph of a 40 degreeC fall time in a fuel consumption improvement rate and a cooling test. It is a graph which shows a cooling test. It is a graph which shows a heat dissipation test result.

  Embodiments of an engine valve manufacturing method of the present invention will be described below with reference to the drawings.

  FIG. 1 is a flowchart for explaining a method for manufacturing an engine valve according to the present invention, and FIG. 2 is a schematic diagram for explaining a first step of the manufacturing method. 3a is a schematic diagram for explaining the second step of the manufacturing method, FIG. 3b is an enlarged view of part b of FIG. 3a, and FIG. 4a is a schematic diagram for explaining the third step of the manufacturing method. FIG. 4b is an enlarged view of part b of FIG. 4a.

  The engine valve targeted by the production method of the present invention is based on heat-resistant steel, carbon steel, titanium material, etc., and the internal combustion engine to which this engine valve is applied targets either a gasoline engine or a diesel engine. It may be what.

  As shown in FIG. 1, in this engine valve manufacturing method, first, an aluminum plating film is formed on the entire circumference of the engine valve (first step S1).

  Here, as shown in FIG. 2, the engine valve 3 includes an umbrella part 1 facing a combustion chamber of an internal combustion engine (not shown), and extends into an intake valve or an exhaust valve (not shown) integrally with the umbrella part 1. The shaft portion 2 is configured to be configured.

  An aluminum plating film 4 made of aluminum or an alloy thereof is formed on the entire circumference of the umbrella portion 1 and the shaft portion 2 (more specifically, the upper end region of the shaft portion 2 is not plated in the illustrated example). The thickness of the aluminum plating film 4 is t1.

  Returning to FIG. 1, when the aluminum plating film 4 having a film thickness t1 is formed on the entire circumference of the engine valve 3, the aluminum plating film 4 is anodized to form an anodized film (second step S2).

  As shown in FIG. 3a, by this anodizing treatment, the aluminum plating film 4 having a film thickness t1 becomes an anodized film 5 having a film thickness t2 that is twice or more of that, that is, the condition of t2 ≧ 2 × t1. By forming the anodic oxide coating 5 having a film thickness that satisfies the above condition, the engine valve 3 covered only with the anodic oxide coating 5 can be manufactured without the aluminum plating coating 4 remaining on the surface thereof.

  As shown in FIG. 3b, the microstructure of the anodic oxide coating 5 is composed of a large number of cells 5a,... And gaps 5b between the cells 5a, 5a. There is also a form in which is formed.

  By providing such a microstructured anodic oxide coating 5 on the surface, the engine valve has excellent heat dissipation as well as heat resistance and heat insulation performance.

  Returning to FIG. 1, when the anodic oxide coating 5 is formed on the surface of the engine valve 3, the sealing process is performed only on the umbrella portion 1 of the engine valve (third step S3).

  This sealing treatment is performed by performing sealing treatment with boiling water or steam, coating treatment with a heat-resistant sealing material such as water glass, or both treatments, as shown in FIGS. 4a and 4b. The sealing coating 6 is formed only on the surface of the anodic oxide coating 5 on the entire surface from the front surface of the umbrella portion 1, that is, from the front surface where the umbrella portion 1 faces the combustion chamber to the rear surface connected to the shaft portion 2.

  Here, as shown in FIG. 4b, the sealing coating 6 is formed from the surface of the cell 5a constituting the anodic oxide coating 5 to a part of the gap 5b between the cells 5a and 5a, but deeper than that. Since the gap 5b has a film structure in which the air gap 5b is maintained as it is, the anodized film 5 on the surface of the umbrella 1 has a heat shielding performance and becomes an engine valve 10 having excellent swing characteristics.

  The manufactured engine valve 10 can be applied to an internal combustion engine (not shown). A specific configuration of the internal combustion engine includes a cylinder block in which a cooling water jacket is formed, a cylinder head disposed on the cylinder block, an intake port and an exhaust port defined in the cylinder head. They are composed of an intake engine valve 10 and an exhaust engine valve 10 which are mounted so as to be movable up and down in an opening facing the combustion chamber, and a piston formed so as to be movable up and down from the lower opening of the cylinder block.

[Cooling test and results]
The present inventors made four types of test bodies of Examples 1 and 2, Comparative Example and Reference Example by the following method, and conducted a cooling test on them.

  As shown in FIG. 5A, the valve base material is JIS standard SUH3 as a test body having a diameter of 25 mm × thickness of 1 mm. After sufficiently melting as described above, the specimen was immersed in this molten metal for 2 minutes and then pulled up.

  Subsequently, it was cooled at room temperature, the masking and the impurity layer on the surface of the aluminum plating were removed, and the surface of the aluminum plating film was smoothly finished by polishing (surface roughness Ra = 1 μm or less).

  Regarding the test bodies of Examples 1 and 2, anodizing treatment was further performed, and finally a sealing process was performed to prepare a test body.

  On the other hand, a comparative example is a test body that does not have an anodized film, and a reference example is a test body that has an anodized film but whose umbrella portion is not sealed.

  Table 1 below shows the results regarding the thickness of the aluminum plating film by the aluminum plating treatment, the detailed conditions of the anodizing treatment, the presence or absence of the sealing treatment, and the thickness of the aluminum plating film remaining in the finally manufactured specimen. It is shown in 2.

  As shown in FIG. 5a, the outline of the cooling test is as follows. A test body TP having an anodized film only on one surface is used, and the back surface (the surface not having the anodized film) is heated by high temperature injection at 750 ° C. (Heat in the figure) The entire test piece TP is stabilized at about 250 ° C., and a nozzle that has been flown at room temperature at a predetermined flow rate in advance is a front surface of the test piece TP (surface on which an anodized film is applied). ) To start cooling (providing cooling air at 25 ° C. (Air in the figure), and high-temperature injection on the back surface continues at this time). The temperature of the anodic oxide coating surface of the test piece TP is measured with a radiation thermometer located outside the test piece TP, and the temperature drop during cooling is measured to create the cooling curve shown in FIG. 5b. This cooling test is a test method that simulates the intake stroke of the combustion chamber wall, and evaluates the cooling rate of the surface of the heated insulation coating. In the case of a heat insulating coating having a low thermal conductivity and a low heat capacity, the rapid cooling rate tends to increase.

  The time required to decrease by 40 ° C. is read from the created cooling curve, and the thermal characteristics of the coating are evaluated as 40 ° C. drop time.

On the other hand, according to the present inventors, during the experiment, it clearly demonstrated the fuel economy improvement ratio without being buried as a measurement error, and to shorten the warm-up time of the NO _X reduction catalyst by increasing the exhaust gas temperature, NO _{As a} value that can achieve _X reduction, a fuel efficiency improvement rate (fuel efficiency improvement rate) of 5% at the best combustion point of a diesel engine is one target value that is achieved when the anodic oxide coating in the present invention is formed on the entire combustion chamber wall surface. Yes. Here, FIG. 6 shows a correlation graph between the fuel consumption improvement rate specified by the present inventors and the 40 ° C. drop time in the cooling test.

  An approximated curve (secondary curve) is created as shown in FIG. 6 based on the result of obtaining the 40 ° C. descent time corresponding to the fuel efficiency improvement rates of 8%, 5%, 2.5%, and 1.3%. Note that the 40 ° C. descent time corresponding to the fuel efficiency improvement rate of 5% coincides with the 45 ms specified in FIG.

  The cooling test results are shown in FIG. From the figure, the comparative example cannot satisfy the fuel efficiency improvement rate of 5%, and the results of Examples 1 and 2 sufficiently satisfy the fuel efficiency improvement rate of 5%.

  As shown in Table 2, in addition to the specimens of Examples 1 and 2 having an anodic oxide film having voids, the surface of the anodic oxide film voids is sealed by a sealing treatment. Is due to. In Examples 1 and 2, it can also be confirmed that the thickness of the aluminum plating film is 1/2 or less of the thickness of the anodized film, and by adjusting the thickness of the aluminum plating film in this way. It has also been demonstrated that the aluminum plating film does not remain on the surface of the engine valve finally obtained.

  Moreover, when the thickness of an aluminum plating film is thicker than 1/2 of the thickness of an anodized film, the present inventors have found that an aluminum plated film remains after anodizing treatment. More specifically, an aluminum plating film that remains without being fully anodized is interposed between the aluminum base material and the anodized film. If the aluminum plating film remains in this way, the remaining aluminum plating film melts when the combustion chamber is placed in a high-temperature atmosphere higher than the melting point of aluminum, which causes the anodized film to be removed from the aluminum base material. It has also been specified by the present inventors that there is a problem of easy peeling. Based on this knowledge, the thickness of the aluminum plating film is set to 1/2 or less of the thickness of the anodized film.

[Heat dissipation test and results]
The present inventors further measured the temperature of the surface of the test body by bringing the base material side into close contact with a ceramic heater as a heat source (100 W) for each of the test bodies of Example 2, Comparative Example, and Reference Example. Here, the surroundings of the heater were in a natural convection state, and the thermocouple was measured in contact with the anodized film surface and the heater heating surface, respectively. The test results are shown in FIG.

  From the figure, for example, when the heater temperature is about 200 ° C., the surface temperature of the comparative example is about 190 ° C., whereas the surface temperature of Example 2 is about 150 to 160 ° C., which is about 40 ° C. lower. Has been demonstrated. This is because the specimen of Example 2 has an anodic oxide coating with low thermal conductivity on its surface. When only heat dissipation is taken into account, it has been confirmed that the surface temperature of the reference example in which the umbrella portion is not sealed is the most excellent at about 130 ° C.

[Heat resistance test and results]
The inventors further placed each specimen of Examples 1 and 2 in a high-temperature furnace heated to 900 ° C. and held it for 5 hours, and left the specimen removed from the high-temperature furnace at room temperature to cool naturally. An experiment was conducted to observe the state of the test specimen.

  As a result of the observation, no change was observed on the surface of any of the test bodies of Examples 1 and 2. This is because in the specimens of Examples 1 and 2, no aluminum plating film remained on the surfaces thereof.

  From the various test results described above, it is necessary to form an aluminum plating film on the surface of the engine valve for the engine valve using heat resistant steel or carbon steel as a base material. By adjusting the film thickness of the aluminum plating film to ½ or less of the film thickness of the anodized film so that the aluminum plating film does not remain on the surface of the engine valve obtained in the above, good heat dissipation and heat resistance It becomes an engine valve.

  In addition, by forming a sealing film on the anodized film on the surface of the umbrella part constituting the engine valve, the swing characteristic resulting from the cooling performance of the engine valve is improved, which can contribute to an increase in fuel efficiency improvement rate. It will be a thing.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and there are design changes and the like without departing from the gist of the present invention. They are also included in the present invention.

DESCRIPTION OF SYMBOLS 1 ... Umbrella part, 2 ... Shaft part, 3 ... Engine valve, 4 ... Aluminum plating film, 5 ... Anodized film, 5a ... Cell, 5b ... Air gap (pore), 6 ... Sealing film, 10 ... Engine valve

Claims (3)

An engine valve manufacturing method comprising an umbrella part facing a combustion chamber of an internal combustion engine and a shaft part integrally formed with the umbrella part and extending into an intake valve or an exhaust valve, and formed of an iron-based material. There,
A first step of forming an aluminum plating film on the entire circumference of the engine valve;
A second step of anodizing the aluminum plating film into an anodized film;
In the umbrella part, the surface of the anodic oxide coating is subjected to a sealing process to form a sealing coating,
In the first step, the engine valve manufacturing method is such that the film thickness of the aluminum plating film is adjusted to ½ or less of the film thickness of the anodized film to be formed.   The method for manufacturing an engine valve according to claim 1, wherein a thickness of the anodic oxide coating on the shaft portion is smaller than that of the anodic oxide coating on the umbrella portion.   The method for manufacturing an engine valve according to claim 1 or 2, wherein the sealing treatment includes a sealing treatment with boiling water or steam, a coating treatment with a heat-resistant sealing material, or both treatments.

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