JP6701726B2 - Internal combustion engine piston, internal combustion engine, and method of manufacturing internal combustion engine piston - Google Patents

Description

  The present invention relates to a piston for an internal combustion engine, an internal combustion engine, and a method for manufacturing a piston for an internal combustion engine. More specifically, the heat loss in the cavity can be reduced, and the combustion state can be favorably maintained to improve thermal efficiency. The present invention relates to an improved internal combustion engine piston, an internal combustion engine, and a method of manufacturing an internal combustion engine piston.

  Generally, in a piston of an internal combustion engine such as a diesel engine mounted on a vehicle, in order to improve the fuel efficiency of the engine, in order to maintain the temperature of the combustion chamber including a cavity provided at the top of the piston, It is known that an effective method is to apply a thermal barrier coating around the combustion chamber.

  For example, on a surface of an aluminum alloy base material such as the surface facing the engine combustion chamber, a porous layer (alumite film) with high heat insulation having pores by anodization is formed, and the porous layer having this uneven surface is formed. In addition, the adiabatic structure of aluminum alloy products, which has a structure with a coating layer such as zirconia that has a lower thermal conductivity than the base material and has a smooth surface by plasma spraying, can be used for reducing engine cooling loss. It has been proposed as a heat insulating structure that can be made (for example, see Patent Document 1). In this heat insulating structure, the thermal conductivity of the aluminum alloy base material is 150 W/(m·K), the porous side is 24 to 53 W/(m·K), and the coating layer is 0.40 to 0.94 W/( m・K).

  Further, in addition to the heat shield effect, in order to prevent the occurrence of scuffing and wear, it is performed to form an oxide film by hard alumite treatment on the crown surface of the aluminum alloy piston (for example, patent Reference 2).

  By forming the alumite film as the thermal barrier coating on the cavity having a concave shape around the combustion chamber and the top surface around the cavity, cooling loss of the engine can be reduced and thermal efficiency can be improved. It is generally desired to form a thick alumite film in order to improve the heat shielding effect in forming the alumite film.

  However, if the alumite film is thickly formed, its surface becomes rough, so if the entire cavity is coated with a thick alumite film, the surface of the cavity becomes rough, which adversely affects the flow state of air and fuel in the cavity. This causes the combustion state in the combustion chamber to deteriorate. Therefore, even if the heat shielding effect is increased, the combustion state is deteriorated, and there is a problem that the effect of improving the thermal efficiency is reduced as a whole. The roughness of the surface of the lip portion of the cavity has a great influence on the fluidity of the fuel and air.

  On the other hand, when an alumite coating is formed on a piston made of aluminum alloy, large thermal stress is generated at the edges of the combustion chamber (lips), especially at the edges facing each other in the direction of the piston pin, and cracks often occur. When it occurs, there is a problem that the durability of the piston and the internal combustion engine that uses this piston deteriorates.

  As a countermeasure against this, a method of forming an alumite film on the thrust and anti-thrust side lip parts, the top surface and the bottom of the combustion chamber, and not forming the alumite film on the front and rear lip parts and the top surface part has been taken. There is.

  Further, as another method, for example, in an aluminum alloy piston for an internal combustion engine having a concave combustion chamber on the top surface, without performing the alumite treatment applied to the top surface to the crack generation portion, the crack generation portion is an inorganic fiber There has been proposed an aluminum alloy piston for an internal combustion engine, which has been subjected to composite strengthening by means such as the above, and has a hard alumite coating formed on the remaining region (see, for example, Patent Document 3).

  However, these methods cannot reduce the heat loss of the entire piston because the combustion temperature inside the cavity is high and the heat loss in this cavity is large. In other words, if the alumite heat is shielded only on the top surface side above the lip portion of the piston, the heat loss in the cavity is large and the improvement of the thermal efficiency is limited. Moreover, even if the cavity is simply coated with a heat shield film such as alumite or zirconia, if the surface is rough, the combustion state deteriorates and the effect of improving the thermal efficiency is offset.

JP 2012-72745 A JP, 11-267929, A JP-A 61-294159

  On the other hand, the present inventor paid attention to the relationship between the thickness of the alumite film and the roughness of the surface, and found that the thinner the film, the better the smoothness of the surface.

  The present invention has been made in view of the above, and an object thereof is, in a piston of an internal combustion engine, a heat shield effect of the entire piston by changing the thickness of the heat shield coating film according to the portion of the piston. Of the internal combustion engine piston, the internal combustion engine, and the piston of the internal combustion engine can improve the thermal efficiency of the internal combustion engine by maintaining the smoothness of the surface in the cavity while maintaining a good combustion state. It is to provide a manufacturing method.

  A further object is to improve the heat-shielding effect of the entire piston by the heat-shielding coating film, while suppressing the occurrence of cracks in the lip portion (rim of the cavity) where cracks are likely to occur. An object of the present invention is to provide a piston of an internal combustion engine, an internal combustion engine, and a method of manufacturing the piston of the internal combustion engine, which can improve the durability of the piston and the internal combustion engine using the piston.

The piston of the internal combustion engine of the present invention for achieving the above object is a piston of an internal combustion engine, the upper part of the piston is heat-shielding coated, and with respect to the thickness of the heat-shielding coating film, The thickness of the first region including at least the lip portion of the cavity of the piston is formed thinner than the thickness of the second region not including the lip portion and including the top surface of the piston and the central portion of the cavity. There is.

  According to this configuration, if the thermal barrier coating film is thick, the surface becomes rough, and if it is thin, the surface becomes smooth, so that the thermal barrier effect per area is large in the second region where the thermal barrier coating film is thick, while In the first region where the thermal barrier coating film is thin, the heat shielding effect per area is smaller than in the second region, but since the temperature becomes higher in the first region, the heat shielding effect itself becomes large, and the surface is smooth, Since it is not rough, it is possible to maintain a good combustion state. Therefore, the thermal efficiency of the piston as a whole can be improved.

  In addition, the thermal barrier coating improves the thermal barrier effect of the entire piston, but the thickness of the thermal barrier coating at the portion where cracks are likely to occur due to the thermal stress of the lip portion of the cavity Since the thickness is suppressed to an appropriate thickness without increasing the thickness so that the crack becomes large and cracks are generated, it is possible to suppress the generation of cracks due to thermal stress in this portion.

  The first region includes a lip portion, but when the first region is widened, it is preferable to extend the lip region from the lip portion to the bottom surface side of the cavity and to include the side surface portion of the cavity.

  In the piston of the internal combustion engine, the thickness of the thermal barrier coating film is formed such that the thickness of the first region is 5 μm or more and less than 50 μm, and the thickness of the second region is 50 μm or more and 500 μm or less. Configured to be.

  When the thickness of the thermal barrier coating film in the first region is 5 μm or more and less than 50 μm, the surface condition can be kept smooth to such an extent that the combustion condition does not deteriorate and a good condition can be maintained. The heat shield effect can be exhibited. When the thickness of the thermal barrier coating film in the second region is 50 μm or more and 500 μm or less, the thermal barrier coating film of this thickness can be relatively easily formed by an appropriate alumite film forming treatment. Moreover, a relatively large heat shield effect can be exhibited.

  In addition, in the piston of the internal combustion engine, when the lip portion of the piston is formed by composite strengthening, cracks occur at the lip portion portions on both sides of the piston in the direction of the piston pin hole. Since it is easy, if you thicken the alumite film etc., there will be a problem that cracks will occur in this alumite film, but with this configuration the thickness of the thermal barrier coating film is kept to a thickness where cracks do not easily occur, Can be strengthened by the composite strengthening of the aluminum alloy, and the occurrence of cracks at this portion can be prevented.

  And an internal combustion engine of the present invention for achieving the above object is an internal combustion engine characterized by including the piston of the above internal combustion engine, and has the same effect as the piston of the above internal combustion engine. You can

A method for manufacturing a piston for an internal combustion engine according to the present invention to achieve the above object is the method for manufacturing a piston for an internal combustion engine, wherein the piston body of the piston is formed of an aluminum alloy, and the first After remelting the area, a thermal barrier coating is applied to the upper portion of the piston .

  This method is a method of adjusting the film thickness by controlling the alloy composition, and when the aluminum alloy is remelted (remelted) by using a laser or an arc, its structure (particle size) becomes finer and the alumite film is formed. It is a method that utilizes the fact that the film formation rate can be slowed down and a thin film can be formed.

Alternatively, a method of manufacturing a piston of an internal combustion engine of the present invention for achieving the above object is a method of manufacturing a piston of the internal combustion engine, wherein the piston main body of the piston is formed of an aluminum alloy, the It is characterized in that the aluminum alloy in one region is formed by composite strengthening, and then the upper portion of the piston is subjected to thermal barrier coating.

  This method is a method of adjusting the film thickness by compounding an aluminum alloy.If the aluminum alloy is compounded and strengthened with whiskers or ceramic fibers, the growth rate of a thermal barrier coating such as an alumite film will increase. It is a method that utilizes the fact that it is possible to slow down the process and form a thin film.

  According to the piston of the internal combustion engine, the internal combustion engine, and the method for manufacturing the piston of the internal combustion engine of the present invention, the first region including the lip portion of the cavity does not include the lip portion of the cavity, and the top surface of the piston and the cavity Since the upper part of both pistons in the second area including the central part of the tee is heat shield coated, the internal temperature becomes high, and the heat shield coating film also shields heat inside the cavity where the heat shield effect is relatively large. In addition, since the thickness of the thermal barrier coating film in the first region is formed thinner than the thickness of the thermal barrier coating film in the second region, the surface of the first region is smooth and rough. Since it does not, it is possible to maintain a good combustion state. Therefore, the thermal efficiency of the piston as a whole can be improved.

  Also, while improving the heat shield effect of the entire piston by the heat shield coating film, the thickness of the heat shield coating film on the lip portion of the cavity where cracks are likely to occur due to heat stress The thickness of the piston and the internal combustion engine that uses this piston can be suppressed because the thickness is suppressed to an appropriate thickness without being thick enough to cause cracks. The durability of can be improved.

It is a sectional side view which shows typically the structure of the piston of embodiment which concerns on this invention. It is a top view which shows the structure of the piston of FIG. 1 typically. It is an expansion side sectional view showing typically an example of the 1st field and the 2nd field in a piston.

  Hereinafter, a piston for an internal combustion engine, an internal combustion engine, and a method for manufacturing the piston for the internal combustion engine according to embodiments of the present invention will be described with reference to the drawings. The internal combustion engine according to the embodiment of the present invention has a configuration including the piston 10 of the internal combustion engine according to the embodiment of the present invention, and has the same operation effect as the piston 10 of the internal combustion engine described below. The effect of can be achieved.

  As shown in FIG. 1, a piston (hereinafter, piston) 10 of an internal combustion engine according to an embodiment of the present invention moves up and down in a cylinder (not shown), and a crankshaft (not shown) via a connecting rod (not shown). Not) has the function of rotating.

  A concave-shaped cavity 12 (combustion chamber) is formed in an upper portion (piston crown: piston crown) Rt of the piston body 11 of the piston 10, and a flat top surface is provided outside a lip portion (rim portion) 13 thereof. 14 is formed. Further, piston ring grooves 15a and 15b for the compression ring and a piston ring groove 15c for the oil ring are formed on the outer peripheral surface of the piston body 11 below that, and the piston skirt 16 is formed on the lower side thereof. There is. Further, the piston body 11 is provided with a piston pin hole 18 into which a piston pin 17 that connects the piston body 11 and a connecting rod (not shown) is inserted.

  In addition, if necessary, a valve recess serving as a relief portion is provided so as not to contact the piston 10 even when the exhaust valve and the intake valve are opened when the piston 10 is lifted. These have been omitted for simplicity. Further, an engine oil cooling passage (cooling channel) for cooling the piston body 11 and an injection mechanism for injecting the engine oil to the back side of the piston are not shown.

  As shown in FIGS. 1 to 3, in the present invention, the surface of the upper portion Rt of the piston 10 is heat shield coated. That is, the piston body 11 is often made of an aluminum alloy because it has a low coefficient of thermal expansion, excellent heat resistance, and is lightweight. This aluminum alloy has a high thermal conductivity and can quickly dissipate the heat of the piston upper portion Rt and has an excellent cooling property. However, in order to maintain a good combustion state in the engine and maintain a high thermal efficiency in combustion, It is important to shield the area where the fuel burns. Therefore, in order to improve the heat insulating property of the piston upper portion Rt, the heat insulating coating is performed to form the heat insulating coating film on the upper portion Rt of the piston 10.

  As a method of forming this thermal barrier coating film, there is a method of forming an alumite film or a zirconia film. The thermal barrier coating film of the alumite layer uses the piston made of an aluminum alloy as an anode and is immersed in an electrolytic solution which is an aqueous solution of oxalic acid, sulfuric acid, chromic acid or the like to carry out electrolysis, so that the upper portion Rt of the piston 10 is removed. It can be easily formed by anodizing by oxidizing and growing aluminum oxide on the surface of the aluminum alloy in this portion to form an oxide film. Generally, in an engine piston, an alumite coating called "hard alumite" having excellent coating hardness and wear resistance is formed. The thermal conductivity of this alumite coating is about one third of that of aluminum.

The thermal barrier coating of the zirconia layer is generally formed by thermal spraying such as plasma spraying, and a thermal barrier coating of a ceramic material such as zirconia (ZrO ₂ ) is deposited on engine parts such as pistons. The internal porosity of the thermal barrier coating film such as zirconia is 20% to 30%, and the thermal conductivity of the zirconia film is as low as about 1 W/mK.

  In the present invention, further, in the upper portion Rt of the piston 10, the first region (cross-hatched portion of FIGS. 1 to 3) R1 including at least the lip portion 13 of the cavity 12 of the piston 10 and the cavity 12 are formed. It is divided into a top surface 14 of the piston 10 and a second region (hatched portion in FIG. 1 to FIG. 3) R2 that does not include the lip portion 13 and includes the central portion of the cavity 12. Then, regarding the thickness of the film of the thermal barrier coating, the thickness of the first region R1 is formed to be smaller than the thickness of the second region R2.

  The first region includes a lip portion, but when the first region is widened, it is preferable to extend the lip region from the lip portion to the bottom surface side of the cavity and to include the side surface portion of the cavity.

  Regarding the thickness of the thermal barrier coating, it is preferable that the thickness of the first region R1 is 5 μm or more and less than 50 μm, and the thickness of the second region R2 is 50 μm or more and 500 μm or less.

  When the thickness of the thermal barrier coating film in the first region R1 is 5 μm or more and less than 50 μm, the surface condition can be kept smooth to such an extent that the combustion condition is not deteriorated and a good condition can be maintained. It is possible to exert the heat shield effect. In addition, when the thickness of the thermal barrier coating film in the second region R2 is 50 μm or more and 500 μm or less, the thermal barrier coating film of this thickness can be formed relatively easily by an appropriate alumite film forming process. In addition, a relatively large heat shield effect can be exhibited.

  With the above configuration, if the film of the thermal barrier coating is thick, the surface becomes rough, and if it is thin, the surface becomes smooth, so that the thermal barrier effect per area is large in the second region R2 where the film of the thermal barrier coating is thick, On the other hand, in the first region R1 where the film of the thermal barrier coating is thin, the heat shielding effect per area is smaller than in the second region R2, but in the first region R1, the temperature is high and the heat shielding effect itself is large.

  Therefore, the first region R1 including the lip portion 13 of the cavity 12 does not include the lip portion 13 of the cavity 12, and the upper portion Rt of both pistons 10 in the second region R2 including the top surface 14 of the piston 10 is not included. Since the thermal barrier coating is applied, the internal temperature becomes high, and the inside of the cavity 12, which has a relatively large thermal barrier effect, can be shielded by the thermal barrier coating film.

  Further, since the thickness of the thermal barrier coating film in the first region R1 is made thinner than the thickness of the thermal barrier coating film in the second region R2, the surface of the first region R1 is smooth and rough. Since it is not present, the combustion state in the cylinder can be maintained well. Therefore, the thermal efficiency of the piston as a whole can be improved.

  In addition, the thermal barrier coating improves the overall thermal barrier effect of the piston 10, while reducing the thickness of the thermal barrier coating on the lip portion 13 of the cavity 12 where cracks are likely to occur due to thermal stress. The thickness of the lip portion 13 is not so thick as to cause the generation of cracks due to thermal stress, but is kept at a proper thickness. Therefore, the piston pin of the piston 10 shown in FIG. It is possible to suppress the occurrence of cracks due to thermal stress in the opposing portions Rc on both sides in the direction of the hole 18, and improve the durability of the piston 10 and the internal combustion engine using the piston 10. it can.

  Further, since this portion can be strengthened by the composite strengthening of the aluminum alloy, it becomes possible to prevent the occurrence of cracks in this portion Rc due to thermal stress.

  Next, a method for manufacturing the piston of the internal combustion engine according to the embodiment of the present invention will be described. This piston manufacturing method for an internal combustion engine is a method for manufacturing the piston 10 described above, and here, a method for remelting the first region R1 as the first embodiment and a second embodiment are used. A method for compositely strengthening the first region R1 will be described.

  In the method of manufacturing a piston for an internal combustion engine according to the first embodiment, the piston body 11 is formed of an aluminum alloy, the first region R1 is remelted, and then the upper portion Rt of the piston 10 is subjected to thermal barrier coating. Is the way.

  This method is a method of adjusting the film thickness by controlling the alloy composition, and when the aluminum alloy is irradiated with a laser or an arc is blown to remelt it, the structure (grain size) becomes finer. It is a method that utilizes the fact that the film forming rate of the alumite film can be slowed down and a thin film can be formed.

  For example, when the thickness of the alumite coating is about 40 μm, the surface of the alumite coating has almost the same roughness as the surface of the aluminum alloy before processing. That is, in the first region requiring the thermal barrier coating film having a surface with a high smoothness, the aluminum alloy is remelted before thermal barrier coating. This makes it possible to obtain a thermal barrier coating film having a smooth surface and having a thermal barrier effect to some extent.

  In addition, in the method for manufacturing the piston for the internal combustion engine of the second embodiment, when the piston body 11 is formed of an aluminum alloy, the aluminum alloy of the first region R1 is compounded and strengthened, and then the piston 10 is formed. This is a method of thermal barrier coating the upper portion Rt.

  This method is a method of adjusting the film thickness by compounding an aluminum alloy.If the aluminum alloy is compounded and strengthened with whiskers or ceramic fibers, the growth rate of a thermal barrier coating such as an alumite film will increase. It is a method that utilizes the fact that the film can be slowed down and a thin film is formed.

  This composite treatment is performed by, for example, disposing a preform formed of silicon carbide (SiC) whiskers, aluminum borate whiskers, alumina fibers, or the like in the first region R1, and casting a piston with an aluminum alloy, The first region R1 can be compositely strengthened.

  For example, in the case of an aluminum alloy composite material in which the first region R1 is reinforced with aluminum borate whiskers, when the thickness of the alumite film of the normal non-reinforced aluminum alloy part is about 180 μm in the same treatment time, In the composite material portion of R1, the thickness of the alumite film was about 20 μm, and the surface had the same roughness as before the alumite processing.

  In particular, in this method, even in the region Rc of the lip portion 13 of the cavity 12 where cracks are relatively likely to occur, composite strengthening can be performed, so that cracking due to thermal stress can be suppressed, and the piston 10 and this The durability of an internal combustion engine using the piston 10 can be improved.

  According to the piston 10 of the internal combustion engine, the internal combustion engine, and the method for manufacturing the piston of the internal combustion engine having the above-described configurations, the first region R1 including at least the lip portion 13 of the cavity 12 of the piston 10 is also the lip portion of the cavity 12. Since the upper part Rt of the piston 10 including the second region R2 formed not including 13 but including the top surface 14 of the piston 10 is subjected to thermal barrier coating, the internal temperature becomes high and the thermal barrier effect is obtained. The relatively large cavity 12 can also be shielded from heat, and the thickness of the first region R1 is made thinner than that of the second region R2, so that the surface of the first region R1 is smooth. And, since it is not rough, it is possible to maintain a good combustion state. Therefore, the thermal efficiency of the piston as a whole can be improved.

  Therefore, in the piston 19 of the internal combustion engine, by changing the thickness of the thermal barrier coating film according to the site of the piston 10, while improving the thermal barrier effect of the entire piston, the degree of smoothness of the surface inside the cavity 12 is improved. Can be maintained to maintain a good combustion state, and the thermal efficiency of the internal combustion engine can be improved.

  Further, the thermal barrier coating film improves the thermal barrier effect of the entire piston, but cracks due to thermal stress in the region Rc where cracks due to thermal stress in the lip portion (rim portion) 13 of the cavity 12 are relatively likely to occur. Can be suppressed, and the durability of the piston 10 and the internal combustion engine using the piston 10 can be improved.

  Then, the piston 10 formed with the stepped alumite heat shield film of the present invention, the piston of Comparative Example 1 in which no prior art alumite heat shield film is formed, and the alumite heat shield film formed only on the top face Comparing the piston of Comparative Example 2 in which the alumite heat shield film is not formed on the tee, which is an experimental example, the piston 10 of the example of the present invention has a thermal efficiency of about 3.5% as compared with the piston of Comparative Example 1. The result is that the thermal efficiency is improved by 1% compared with the piston of Comparative Example 2.

10 piston (piston of internal combustion engine)
11 Piston body 12 Cavity 13 Lip part 14 Top surfaces 15a, 15b, 15c Piston ring groove 16 Piston skirt 17 Piston pin 18 Piston pin hole

Claims (6)

A piston of an internal combustion engine, wherein the upper portion of the piston has a thermal barrier coating, and the thickness of the thermal barrier coating is the thickness of a first region including at least the lip portion of the cavity of the piston. Is formed thinner than the thickness of the second region including the top surface of the piston and the central portion of the cavity without including the lip portion.   The internal combustion engine according to claim 1, wherein the thickness of the thermal barrier coating film is set such that the thickness of the first region is 5 μm or more and less than 50 μm, and the thickness of the second region is 50 μm or more and 500 μm or less. Engine piston.   The piston for an internal combustion engine according to claim 1 or 2, wherein the lip portion of the piston is formed by composite reinforcement.   An internal combustion engine comprising the piston of the internal combustion engine according to any one of claims 1 to 3. It is a manufacturing method of the piston of the internal combustion engine according to any one of claims 1 to 3, and forms the piston main body of the piston with an aluminum alloy, and after re-melting the 1st field , the upper part of the piston . A method for manufacturing a piston for an internal combustion engine, characterized in that a part of the piston is subjected to thermal barrier coating. It is a manufacturing method of the piston of the internal combustion engine according to any one of claims 1 to 3, and when forming the piston main body of the piston with an aluminum alloy, it forms by carrying out compound strengthening of the aluminum alloy of the 1st field. and method for producing a piston for an internal combustion engine, which comprises a thermal barrier coating an upper portion of the piston thereafter.

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