JP2017115781A - Internal combustion engine piston, internal combustion engine and process of manufacture of internal combustion engine piston - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine piston, internal combustion engine and process of manufacture of internal combustion engine capable of keeping superior combustion state by maintaining a degree of smoothness at a surface in a cavity while improving a heat shield effect of an entire piston of the internal combustion engine by changing a thickness of Alumite heat shield film in response to a location of the piston and further capable of improving thermal efficiency of the internal combustion engine.SOLUTION: An upper portion Rt of a piston 10 is heat shield coated and at the same time in regard to a thickness of film of this heat shield coating, a thickness of a first area R1 including a lip portion 13 of at least a cavity 12 of the piston 10 is formed not to have that of the lip portion 13. but formed to be thinner than that of a second area R2 including a top surface 14 of the piston 10 and a central portion of the cavity 12.SELECTED DRAWING: Figure 1

Description

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

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

  For example, a highly heat-insulating porous layer (anodized film) having pores by anodizing treatment is formed on the surface of an aluminum alloy base material such as the surface facing the engine combustion chamber. In addition, the heat insulation structure of aluminum alloy products with a coating layer of zirconia, etc., which has a lower thermal conductivity than the base material and a smooth surface by plasma spraying, etc. can be used to reduce engine cooling loss, etc. It has been proposed as a heat insulating structure that can be used (see, for example, 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 covering layer is 0.40 to 0.94 W / ( m · K).

  Also, in order to prevent not only the heat shielding effect but also scuffing and wear, an oxide film is formed on the crown surface portion of the aluminum alloy piston by hard anodizing (for example, patents) Reference 2).

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

  However, if the alumite film is formed thick, its surface becomes rough, and 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. The combustion state in the combustion chamber deteriorates. Therefore, since the combustion state is deteriorated even if the heat shielding effect is increased, there is a problem that the effect of improving the thermal efficiency is reduced as a whole. Regarding the fluidity of the fuel and air, the influence of the roughness of the surface of the lip portion of the cavity is particularly large.

  On the other hand, when an alumite film is formed on a piston made of an aluminum alloy, a large thermal stress is generated at the edge (lip) of the combustion chamber, particularly the opposite edges on both sides in the direction of the piston pin. There is a problem that the durability of the piston and the internal combustion engine using the piston is lowered.

  As a countermeasure, an alumite film is formed on the lip portion on the thrust and anti-thrust sides, the top surface and the bottom surface of the combustion chamber, and the alumite film is not formed on the lip portion and the top surface portion in the front and rear directions. Yes.

  As another method, for example, in an aluminum alloy piston for an internal combustion engine having a concave combustion chamber on the top surface, an alumite treatment applied to the top surface is not performed on the crack generating portion, and the crack generating portion is treated with an inorganic fiber. An aluminum alloy piston for an internal combustion engine that has been reinforced in a composite manner and formed with a hard anodized film in the remaining region has been proposed (see, for example, Patent Document 3).

  However, in these methods, since the combustion temperature inside the cavity is high and the heat loss in the cavity is large, the heat loss of the entire piston cannot be reduced. That is, if only the alumite heat shielding is applied only to the top surface side of the lip portion or more 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 coded with a thermal barrier film such as anodized or zirconia, if the surface is rough, the combustion state deteriorates and the effect of improving thermal efficiency is offset.

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

  On the other hand, the present inventors paid attention to the relationship between the thickness of the alumite film and the roughness of the surface, and obtained the knowledge that the smoothness of the surface is improved when the film is thin.

  The present invention has been made in view of the above, and an object of the present invention is to change the thickness of the thermal barrier coating film in the piston of the internal combustion engine in accordance with the portion of the piston, so that the overall thermal barrier effect of the piston is achieved. The piston of the internal combustion engine, 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 on the surface in the cavity and improving the combustion state. It is to provide a manufacturing method.

  A further object is to suppress the occurrence of cracks in the lip portion (mouth edge) of the cavity where cracks are likely to occur while improving the heat shielding effect of the entire piston by the thermal barrier coating film. An object of the present invention is to provide a piston for an internal combustion engine, an internal combustion engine, and a method for manufacturing the piston for an internal combustion engine that can improve the durability of the piston and the internal combustion engine using the piston.

  In order to achieve the above object, the piston of the internal combustion engine of the present invention has a thermal barrier coating on the upper portion of the piston, and the thickness of the thermal barrier coating is at least the lip of the cavity of the piston. The thickness of the first region including the portion 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.

  According to this configuration, when the thermal barrier coating film is thick, the surface becomes rough, and when the thermal barrier coating film is thin, the surface becomes smooth. Therefore, in the second region where the thermal barrier coating film is thick, the thermal barrier effect per area is large, In the first region where the thermal barrier coating film is thin, the thermal barrier effect per area is less than in the second region, but the thermal barrier effect itself is increased because of the high temperature in the first region, and the surface is smooth, Since it is not rough, the combustion state can be maintained well. Therefore, the thermal efficiency as the whole piston can be improved.

  In addition, while the thermal barrier coating film improves the thermal barrier effect of the entire piston, the thermal stress can reduce the thickness of the thermal barrier coating film at the lip part of the cavity where cracks are likely to occur due to relatively thermal stress. Since it is not thick enough to become large and cracks are generated, it is suppressed to an appropriate thickness, so that generation of cracks due to thermal stress at this part can be suppressed.

  The first region includes a lip portion. However, when the first region is expanded, it is preferable that the first region is extended from the lip portion to the bottom surface side of the cavity so as to include the side surface portion of the cavity.

  In the piston of the internal combustion engine, with respect to the thickness of the thermal barrier coating film, 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 state can be kept smooth to such an extent that the good state can be maintained without deteriorating the combustion state. The heat shielding effect can be demonstrated. In addition, 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 having this thickness can be formed relatively easily by an appropriate anodizing process. Moreover, a relatively large heat shielding effect can be exhibited.

  Also, in the piston of the internal combustion engine, if the lip portion of the piston is formed by composite reinforcement, the lip portions facing each other on both sides in the direction of the piston pin hole of the piston will crack. However, if the alumite film is thick, there is a problem that cracks occur in this alumite film. However, with this configuration, the thickness of the thermal barrier coating film is kept to a level where cracks are unlikely to occur, Can be strengthened by the composite strengthening of the aluminum alloy, and the occurrence of cracks at this portion can be prevented.

  An internal combustion engine of the present invention for achieving the above object is an internal combustion engine including the piston of the internal combustion engine, and has the same effect as the piston of the internal combustion engine. Can do.

  A method for manufacturing a piston for an internal combustion engine according to the present invention for achieving the above object is a method for manufacturing a piston for an internal combustion engine as described above, wherein the piston body is formed of an aluminum alloy, and the first region is reused. After melting, a thermal barrier coating is applied to the upper part of the piston.

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

  Alternatively, a method for manufacturing a piston of an internal combustion engine according to the present invention for achieving the above object is a method for manufacturing a piston of the above internal combustion engine, and when the piston body is formed of an aluminum alloy, It is characterized in that it is formed by composite strengthening of an aluminum alloy, and thereafter, the upper part 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 reinforced with whiskers or ceramic fibers, the growth rate of the thermal barrier coating film such as an alumite film is increased. This is a method utilizing the fact that a thin film can be formed.

  According to the piston of the internal combustion engine, the internal combustion engine, and the manufacturing method of the piston of the internal combustion engine of the present invention, the first region including the lip portion of the cavity also 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 region including the center part of the tee is thermally shielded, the inside temperature becomes high, and the inside of the cavity having a relatively large thermal shielding effect is also shielded by the thermal barrier coating film. In addition, since the thickness of the thermal barrier coating film in the first region is smaller than the thickness of the thermal barrier coating film in the second region, the surface of the first region is smooth and rough. The combustion state can be maintained well. Therefore, the thermal efficiency as the whole piston can be improved.

  In addition, the thermal barrier coating film improves the thermal barrier effect of the entire piston, but the thickness of the thermal barrier coating film at the part where the cracks due to relatively thermal stress of the lip part of the cavity are likely to occur is determined by the thermal stress. Since the crack is not thick enough to cause cracking, it is suppressed to an appropriate thickness, so that cracking due to thermal stress at this part can be suppressed, and a piston and an internal combustion engine using this piston are used. It is possible to improve the durability.

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

  Hereinafter, a piston of an internal combustion engine, an internal combustion engine, and a method of manufacturing the piston of the internal combustion engine according to embodiments of the present invention will be described with reference to the drawings. Note that the internal combustion engine of the embodiment according to the present invention is configured to include the piston 10 of the internal combustion engine of the embodiment according to the present invention, and is similar to the operational effects exhibited by the piston 10 of the internal combustion engine described later. The effect of this 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 is connected to a crankshaft (not shown) via a connecting rod (not shown). Has a function to rotate.

  A concave cavity 12 (combustion chamber) is formed in the upper portion (piston head portion: piston crown) Rt of the piston 10 of the piston 10, and a flat top surface is formed outside the lip portion (mouth edge portion) 13. 14 is formed. Further, compression ring piston ring grooves 15a and 15b and an oil ring piston ring groove 15c are formed on the outer peripheral surface of the piston body 11 below the piston main body 11, and a piston skirt 16 is formed on the lower side thereof. Yes. 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 that the piston 10 does not come into contact with the piston 10 even when the exhaust valve or the intake valve is opened when the piston 10 is raised. These are omitted for the sake of simplicity. Also, an engine oil cooling passage (cooling channel) for cooling the piston body 11 and an injection mechanism for injecting engine oil to the back side of the piston are not shown.

  As shown in FIGS. 1-3, in this invention, the surface of the upper part Rt of this piston 10 is heat-shielding-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 release the heat of the piston upper portion Rt and has excellent cooling performance. However, in an engine, in order to maintain a good combustion state and maintain high thermal efficiency in combustion, It is important to shield the area where the fuel burns. Therefore, in order to improve the heat shielding property of the piston upper portion Rt, a heat shielding coating is formed on the upper portion Rt of the piston 10 by heat shielding coating.

  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 is formed by immersing an aluminum alloy piston as an anode in an electrolytic solution that is an aqueous solution of oxalic acid, sulfuric acid, chromic acid, etc. It can be easily formed by anodizing treatment by oxidizing and growing aluminum oxide on the surface of the aluminum alloy in this portion to form an oxide film. In general, a piston of an engine is formed with an alumite film called “hard anodized” having excellent film hardness and wear resistance. The thermal conductivity of this anodized film is about one third of that of aluminum.

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

  In the present invention, in the upper portion Rt of the piston 10, a first region (cross-hatched portion in FIGS. 1 to 3) R 1 including at least the lip portion 13 of the cavity 12 of the piston 10, and the cavity 12. The lip portion 13 is not included, and the top surface 14 of the piston 10 and the second region (the hatched portion in FIGS. 1 to 3) R2 including the central portion of the cavity 12 are divided. And regarding the thickness of the film of the thermal barrier coating, the thickness of the first region R1 is formed to be thinner than the thickness of the second region R2.

  The first region includes a lip portion. However, when the first region is expanded, it is preferable that the first region is extended from the lip portion to the bottom surface side of the cavity so as to include the side surface portion of the cavity.

  Further, regarding the thickness of the thermal barrier coating film, 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 state can be kept smooth to such an extent that the good state can be maintained without deteriorating the combustion state. And can exert a heat shielding effect. Further, when the thickness of the thermal barrier coating film in the second region R2 is set to 50 μm or more and 500 μm or less, the thermal barrier coating film having this thickness can be formed relatively easily by an appropriate anodizing process. In addition, a relatively large heat shielding effect can be exhibited.

  With the above configuration, when the thermal barrier coating film is thick, the surface becomes rough, and when the thermal barrier coating film is thin, the surface becomes smooth. Therefore, in the second region R2 where the thermal barrier coating film is thick, the thermal barrier effect per area is large, On the other hand, in the first region R1 where the thermal barrier coating film is thin, the heat shielding effect per area is less than in the second region R2, but in the first region R1, since the temperature is high, the heat shielding effect itself is increased.

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

  Further, since the thickness of the thermal barrier coating film in the first region R1 is formed 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. Therefore, the combustion state in the cylinder can be maintained satisfactorily. Therefore, the thermal efficiency as the whole piston 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 cracking due to relatively thermal stress is likely to occur. Since it is not thick enough to cause cracks due to thermal stress, it is kept at an appropriate thickness, so that the portion of this lip portion 13, in particular, the piston pin of the piston 10 surrounded by a one-dot chain line in FIG. It is possible to suppress the occurrence of cracks due to thermal stress in the mutually facing portions Rc on both sides in the direction of the hole 18, and to improve the durability of the piston 10 and the internal combustion engine using the piston 10. it can.

  Furthermore, since this part can be strengthened by the composite strengthening of the aluminum alloy, the occurrence of cracks due to thermal stress in this part Rc can be prevented.

  Next, a method for manufacturing the piston of the internal combustion engine according to the embodiment of the present invention will be described. The piston manufacturing method of the internal combustion engine is a method for manufacturing the above-described piston 10, and here, the method of remelting the first region R1 as the first embodiment and the second embodiment. And a method of strengthening the first region R1 as a composite.

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

  This method is a method of adjusting the film thickness by controlling the alloy composition. When the aluminum alloy is remelted by applying a laser or blowing an arc, the structure (particle size) becomes finer. In this method, the film forming speed of the alumite film can be slowed and a thin film can be formed.

  For example, when the thickness of the anodized film is about 40 μm, the surface of the anodized film has almost the same roughness as the surface of the aluminum alloy before processing. That is, in the first region that requires a thermal barrier coating film having a highly smooth surface, the thermal barrier coating is performed after the aluminum alloy is remelted. As a result, a thermal barrier coating film having a smooth surface and a certain level of thermal barrier effect can be obtained.

  Further, in the method of manufacturing the piston of the internal combustion engine according to the second embodiment, when the piston body 11 is formed of an aluminum alloy, the aluminum alloy of the first region R1 is formed by composite strengthening, and thereafter, the piston 10 This is a method of applying a thermal barrier coating to the upper portion Rt.

  This method is a method of adjusting the film thickness by compounding an aluminum alloy. If the aluminum alloy is reinforced with whiskers or ceramic fibers, the growth rate of the thermal barrier coating film such as an alumite film is increased. This is a method utilizing the fact that a thin film can be formed.

  This compounding process is performed by, for example, placing a preform formed of silicon carbide (SiC) whisker, aluminum borate whisker, alumina fiber, or the like in the first region R1, and casting a piston with an aluminum alloy. The first region R1 can be combined and strengthened.

  For example, in an aluminum alloy composite material in which the first region R1 is reinforced with aluminum borate whiskers, the first region is obtained when the thickness of the alumite film of an aluminum alloy portion without normal strengthening is about 180 μm in the same processing time. In the composite material portion of R1, the thickness of the alumite film was about 20 μm, and the surface was the same roughness as before the alumite processing.

  In particular, in this method, even in the portion Rc where the lip portion 13 of the cavity 12 is relatively liable to be cracked, it is possible to suppress the occurrence of cracking due to thermal stress because the composite reinforcement can be performed. The durability of the internal combustion engine using the piston 10 can be improved.

  According to the piston 10 of the internal combustion engine configured as described above, the internal combustion engine, and the piston manufacturing method, 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. 13, including the second region R 2 formed including the top surface 14 of the piston 10, the upper portion Rt of the piston 10 is subjected to thermal barrier coating, so that the internal temperature becomes high and the thermal barrier effect is achieved. The inside of the relatively large cavity 12 can also be shielded from heat, and the surface of the first region R1 is smooth by forming the first region R1 thinner than the second region R2. And since it is not rough, the combustion state can be maintained well. Therefore, the thermal efficiency as the whole piston can be improved.

  Accordingly, in the piston 19 of the internal combustion engine, by changing the thickness of the thermal barrier coating film according to the part of the piston 10, the degree of smoothness on the surface in the cavity 12 is improved while improving the thermal barrier effect of the entire piston. Thus, the combustion state can be maintained well, and the thermal efficiency of the internal combustion engine can be improved.

  In addition, the thermal barrier coating film improves the overall thermal barrier effect of the piston, but the lip portion (mouth edge) 13 of the cavity 12 cracks due to thermal stress in the portion Rc where cracks 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 having the stepped anodized heat shielding film of the present invention, the piston of the comparative example 1 in which the prior art anodized heat shielding film is not formed at all, the anodized heat shielding film only on the top surface, When compared with the piston of Comparative Example 2 in which the anodized thermal barrier film is not formed on the tee, although it is an experimental example, the piston 10 of the example of the present invention has a thermal efficiency of about 3.5% compared to the piston of Comparative Example 1. The result shows that the efficiency is improved by 1% in comparison with the piston of Comparative Example 2.

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

Claims (6)

The upper portion of the piston is coated with a thermal barrier coating, and the thickness of the thermal barrier coating film is the thickness of the first region including at least the lip portion of the cavity of the piston without including the lip portion. The piston of the internal combustion engine, wherein 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.   2. The internal combustion engine according to claim 1, wherein the thickness of the thermal barrier coating film is 5 μm or more and less than 50 μm, and the second region is 50 μm or more and 500 μm or less. Engine piston.   The piston of the internal combustion engine according to claim 1 or 2, wherein a portion of 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.   The method for manufacturing a piston of an internal combustion engine according to any one of claims 1 to 3, wherein the piston body is formed of an aluminum alloy and re-melted in the first region, and then the upper portion of the piston is shielded. A method of manufacturing a piston of an internal combustion engine, characterized by performing thermal coating.   The method for manufacturing a piston of an internal combustion engine according to any one of claims 1 to 3, wherein when the piston body is formed of an aluminum alloy, the aluminum alloy in the first region is formed by composite strengthening. A method of manufacturing a piston for an internal combustion engine, characterized in that an upper portion of the piston is thermally coated later.

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