JP3635474B2 - Piston for internal combustion engine and method for manufacturing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piston for an internal combustion engine, and more particularly to a piston for a two-cycle internal combustion engine in which a concave portion is formed on the surface of a piston head, a piston for a four-cycle internal combustion engine having a concave portion as a valve relief, and a manufacturing method thereof.
[0002]
[Prior art]
In a 4-cycle internal combustion engine, in order to avoid interference between the intake / exhaust valve and the piston and effectively use the combustion chamber volume to increase the compression ratio and improve the output, a piston with a valve escape recess formed on the upper surface of the piston Has been developed.
[0003]
The piston for a four-cycle internal combustion engine having such a valve escape recess requires the following as in the case of a general internal combustion engine piston.
First, it is lightweight, in other words, (i) it has a thin shape (uses a material that is thin and has high fatigue strength at high temperatures, uses a material that is thin and has good forgeability) and (ii) The specific gravity is small (uses a light material).
[0004]
Secondly, the top land above the piston ring of the head portion is thin. This is because the compression ratio is increased and the performance is improved, and the unburned gas is reduced due to the reduction of the clevis, which is effective as an exhaust gas countermeasure. In this case, (i) Even if the top land is thin, the piston does not thermally bond to the piston ring on the lower side of the piston ring (use a material that can maintain hardness even when the upper surface of the piston reaches about 350 ° C. ), And (ii) that the corners of the top land do not sag or deform (use a material that can withstand even if the upper surface of the piston reaches about 350 ° C.).
[0005]
Third, there is little permanent deformation (high rigidity). In other words, (i) it is required to make the head part difficult to bend (to make the head part thick, and to use a material having a high Young's modulus even when the upper surface of the piston reaches about 350 ° C.).
[0006]
As described above, as a piston for an internal combustion engine, it is required to use a material that has high fatigue strength, proof stress, and hardness at high temperatures, and has a formability capable of forming a thin wall shape.
[0007]
However, it is difficult to find one material that meets these requirements. In order to satisfy these requirements, it is conceivable to use a material having high heat resistance for the head part and a material having a different property from the head part for the skirt part as a piston for an internal combustion engine. Three conventional pistons for internal combustion engines based on this idea have been proposed.
[0008]
The first is that the head and skirt are composed of clad materials with different physical properties (comprised of an aluminum alloy and a composite layer (FRM) in which whiskers, short fibers, etc. are mixed in an aluminum alloy), and both are forged. This is a piston for an internal combustion engine that is integrally molded with (see Japanese Patent Laid-Open No. 63-132743).
[0009]
The second is to form a two-layered body by powder-molding a rapidly-quenched powder aluminum alloy (powder metal) with a common composition with different ceramic powder mixing ratios, and pressurizing and heating the two-layered body This is a piston for an internal combustion engine in which this is hot-forged and the layer having the higher ceramic powder content ratio is used as the head part and the lower layer as the skirt part (see JP-A-1-180927) ).
[0010]
The third is a piston for an internal combustion engine in which the head portion is made of a forged product of powder metal or FRM, the skirt portion is made of an aluminum alloy casting, and both are joined by welding (Japanese Patent Laid-Open No. 2-107749). reference).
[0011]
[Problems to be solved by the invention]
However, according to the piston of the first conventional example, it is not possible to obtain a sufficient bonding strength particularly at the central portion of the bonding interface between the head portion and the skirt portion. The reason for this is that, during forging, a sufficient relative slip or an increase in the area of the bonding interface does not occur at the bonding interface between the head part and the skirt, and the oxide film at the bonding interface cannot be destroyed or removed, so that sufficient bonding is achieved. This is because the strength cannot be obtained. That is, according to the piston of the first conventional example, at the time of forging, the relative slip required for the joining action and the increase in the area of the joining interface are unlikely to occur at the joining interface, particularly at the center thereof. If it is going to increase joint strength, the man-hour for it must be increased. Further, in FRM, stress concentration occurs at the interface between the reinforcing material whisker, the short fiber, and the matrix, and sufficient hot fatigue strength cannot be obtained. In addition, the clad material as a forging material has a complicated process and is expensive. Furthermore, the clad material cannot be applied only to a part of the head part, for example, only a ring groove part to which a piston ring is attached or only an upper surface corner part.
[0012]
In addition, according to the piston of the second conventional example, it is not possible to sufficiently obtain the bonding strength particularly in the central portion of the bonding interface between the head portion and the skirt portion. The reason for this is that, as with the piston of the first conventional example, during forging, relative slip and an increase in the area of the joint interface are unlikely to occur at the center of the joint interface. If it is going to increase joint strength, the man-hour for it must be increased. Further, since the head portion and the skirt portion are a common matrix, it is impossible to achieve both the formability of the thin portion required for the skirt portion and the heat resistance required for the head portion. That is, when the hot deformation resistance is lowered in order to ensure moldability, the heat resistance is lowered, and the corners on the upper surface of the head portion are bent and deformed. Furthermore, a preform as a forging material has a low filling rate, and a mold release agent and a lubricant used during hot forging enter and a good molded body cannot be obtained.
[0013]
Further, according to the piston of the third conventional example, when powder metal is used for the head portion and the head portion and the skirt portion are joined by welding, a brittle alloy layer is formed at the weld portion of the powder metal, and the joining strength is lowered. In addition, the original characteristics (fatigue strength, proof stress, hardness, etc.) are lost in the powder metal weld. Furthermore, in the case of friction welding, a burr | flash arises in a junction part. Since this burr causes stress concentration, it is necessary to remove it, but it is difficult to remove because there are irregularities such as pin bosses inside the piston. In addition, when FRM is used for the head portion, stress concentration occurs at the interface between the whisker as a reinforcing material and the short fibers and the matrix, and sufficient hot fatigue strength cannot be obtained.
[0014]
The present invention has been made in view of the above-mentioned drawbacks of the prior art, and in not only a piston for a four-cycle internal combustion engine but also a two-cycle internal combustion engine having a recess on the piston head surface, the bonding strength between the head portion and the skirt portion is An object of the present invention is to provide a piston for an internal combustion engine that is high and has good productivity without increasing the number of processes, and a method for manufacturing the same.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, in a piston for an internal combustion engine comprising a head portion and a skirt portion and having a concave portion in the head portion, at least a part of the head portion is made of a material different from that of other portions. A piston for an internal combustion engine is provided in which a fiber flow by forging corresponding to the shape of the recess is formed in the vicinity of a joint interface between different materials.
[0016]
Further, in the present invention, as a method for manufacturing the piston, the head portion includes a head portion and a skirt portion, the head portion has a recess, and at least a portion of the head portion including the recess is another portion. In the method for manufacturing a piston for an internal combustion engine made of a material different from the above, the piston is constituted At least heat resistance is different Simultaneously forges different materials to form the recesses and joins the different materials together The peripheral part of the head part is made of a material having higher heat resistance than the central part, or the material having high heat resistance is thicker on the intake / exhaust side than the piston pin boss side and thinner on the piston pin boss side than the intake / exhaust side. A method for manufacturing a piston for an internal combustion engine is provided.
[0017]
According to the piston for an internal combustion engine and the method for manufacturing the same, a strong joining action can be obtained by extending both the material layers at the joining surface under pressure welding stress and further by relative sliding.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
In a preferred embodiment, a fiber flow by forging is formed at the center of the surface of the head portion.
[0019]
In another preferred embodiment, the recess is a valve relief and is a piston for a four-cycle internal combustion engine.
[0020]
In a preferred embodiment of the manufacturing method, at the time of forging, a protrusion is formed in the central portion together with the concave portion on the surface of the head portion.
[0021]
Another embodiment of the preferred manufacturing method is characterized in that it is applied to the manufacture of a piston for a four-cycle internal combustion engine in which the concave portion is a valve relief.
[0022]
【Example】
FIG. 1 is an explanatory diagram showing an outline of a four-cycle engine to which a piston for an internal combustion engine of the present invention is applied. The configuration and operation of the four-cycle engine 20 are as follows. That is, when the piston 22 descends from the top dead center in the cylinder 21, the inside of the cylinder 21 becomes negative pressure. At this time, the intake valve 23 is opened, and the air-fuel mixture of the fuel from the injector 24 and the air from the intake passage 25 is sucked into the cylinder 21. Next, when rising from the bottom dead center, the intake and exhaust valves 23 and 26 are both closed, and the air-fuel mixture sucked into the cylinder 21 is compressed by the piston 22.
[0023]
Next, when the air-fuel mixture is compressed, electric sparks fly to the spark plug 27 and the air-fuel mixture burns. The gas in the cylinder 21 is expanded by this combustion, and the piston 22 is pushed down by the expansion pressure. When the piston 22 is sufficiently pushed down, the exhaust valve 26 is opened, and the burned gas is discharged from the exhaust passage 28 while the piston 22 moves up.
[0024]
In the four-cycle engine 20 based on this principle, when the piston 22 reciprocates twice, the crankshaft 32 rotates twice via the piston pin 29, the connecting rod 30, and the crank arm 31, and one combustion cycle is completed. If the rotation of the crankshaft 32 is, for example, a motorcycle, it is transmitted to the rear wheels via a chain. The amount of air-fuel mixture is increased or decreased by adjusting the opening of the throttle valve 33 interposed in the intake passage 25.
[0025]
In such a piston 22 of the engine 20, a recess 70 for escaping the valve is formed on the upper surface corresponding to each intake valve 23 and the exhaust valve 26. The valve escape recess 70 is for avoiding interference with the piston when the intake and exhaust valves 23 and 26 are lifted.
[0026]
FIG. 2 is a cross-sectional view of an example of a piston 58 for an internal combustion engine according to the present invention. The left half shows the piston pin boss 36 below the piston ring groove 65 as viewed from the front, and the right half shows the piston pin boss. The state which looked at 36 from the side is shown. In this example, as shown in the drawing, the thickness on the side where the piston pin boss 36 is present is increased to increase the strength for supporting the piston pin. As can be seen from the left half of the figure, the skirt portion (piston side surface) continuous to the head portion constituting the upper surface of the piston gradually decreases in thickness toward the lower side. Further, the valve escape recesses 70 are formed at two positions on the center left and right of the head portion in the case of a two-valve engine, and are formed at four or five locations corresponding to the valves in the case of a four-valve or five-valve engine.
[0027]
FIG. 3 is an explanatory view showing the manufacturing process of the piston for the internal combustion engine of FIG. 2 in order. Hereinafter, an example of a method for manufacturing a piston for an internal combustion engine according to the present invention will be described with reference to the drawing.
[0028]
First, in step (A), an alloy ingot made of aluminum (Al), silicon (Si), copper (Cu), and magnesium (Mg) is prepared for the skirt portion. Here, silicon is added to increase the wear resistance and seizure resistance required for the sliding surface of the piston skirt by crystallizing hard primary or eutectic silicon grains in the metal structure. Is. Copper and magnesium are both added to increase the alloy strength at high temperatures. In this case, it is preferable that the silicon content is 5 to 25%, the copper content is 0.5 to 5%, and the magnesium content is 0.5 to 1.5%. This is because the desired wear resistance, seizure resistance, and the required strength at high temperatures cannot be obtained outside this range. Instead of aluminum, silicon, copper, magnesium alloy ingots, aluminum ingots or powders, silicon ingots or powders, copper ingots or powders, and magnesium ingots or powders are prepared separately and mixed. And may be melted.
[0029]
Next, in the step (B), the ingot is melted, and the skirt block is manufactured by continuous casting or extrusion. The Al—Si based alloy block obtained in this way has a lower deformation resistance in the hot state than the Al—Fe based alloy block described later (the yield strength at 400 ° C. is approximately the same as that of the Al—Fe based powder metal). 50%), and good moldability in the thin portion can be obtained.
[0030]
Next, in the step (C), the block is cut into a size required for the skirt portion, and the piston alloy 50 is formed.
[0031]
On the other hand, in step (D), an alloy ingot made of aluminum (Al), iron (Fe), and silicon (Si) for the head portion is prepared. Here, iron is added to disperse and strengthen the metal structure to obtain high fatigue strength at 200 ° C. or higher. In addition, as described above, silicon has the effects of increasing wear resistance and seizure resistance, increasing ductility, and lowering the melting point. Therefore, if the amount of silicon added is large, the elongation becomes too large and the strength is lowered, and the heat resistance is lowered by lowering the melting point. Therefore, only the minimum amount necessary for the moldability and wear resistance of the head is added. To do. As described above, iron is effective in improving high-temperature strength and fatigue strength at high temperature, and the mixing ratio of iron in the head alloy is 5% or more.
[0032]
Next, in step (E), the ingot is melted and rapidly solidified at a cooling rate of 100 ° C./sec or more to produce an Al—Fe-based alloy powder. Next, in the step (F), it is molded and solidified and further hot extruded. The thus obtained quenched powder aluminum alloy block has a uniform metal structure free from a portion that causes stress concentration, and a high fatigue strength. This is because in the cooling by the normal casting process, a coarse composition of iron is formed in the alloy and the strength is lowered. However, the Al-Fe alloy powder is formed and solidified by rapid solidification and further hot extruded. By forming an alloy with the above, the formation of a coarse composition of iron is prevented, and a uniform metal structure without a coarse composition part of the iron component that causes stress concentration can be obtained, so a large amount of iron component should be added This is because an alloy with high fatigue strength can be obtained. Instead of an alloy ingot made of aluminum, iron, or silicon, an aluminum ingot or powder, an iron ingot or powder, and a silicon ingot or powder may be separately prepared and mixed to melt. .
[0033]
Next, in the step (G), the block is cut into the size of the head portion to form a powder metal alloy (PM alloy) 51.
[0034]
The skirt part alloy (piston alloy) 50 and the head part alloy (PM alloy) 51 obtained through the above steps are overlapped and coated with a release agent in the step (H). Next, in step (K), heating is performed to improve moldability. Next, in the step (L), the heated two-layer alloy is sandwiched between a pair of upper and lower molds, and integrally formed into a piston shape by forging that strongly presses. At this time, as will be described later, both the alloys are joined together.
[0035]
Next, in the step (M), heat treatment is performed to increase the strength. Finally, in the step (N), the piston ring groove 65 is formed by machining, and a processing process such as scraping off unnecessary portions is performed and the process ends. Thereafter, as necessary, for example, surface treatment such as plating on the side surface of the skirt portion is performed in order to improve sliding characteristics and wear resistance. The completed piston 58 is composed of a forged joined body of different materials in which the head portion 40 is made of a quenched powder aluminum alloy (PM alloy) and the skirt portion 41 is made of an alloy (piston alloy) made of aluminum, silicon, copper, and magnesium. Is done.
[0036]
FIG. 4 is a diagram for explaining the details of steps (K) to (N) in FIG. FIG. 4A corresponds to step (K) of FIG. 3 and is composed of an alloy composed of aluminum, silicon, copper, and magnesium with a PM alloy 51 for the head portion composed of a quenched powder aluminum alloy. Piston alloy for skirt 50 The two layers of the heated alloy are placed in the recessed portion 56 of the preheated lower die 55 and pressed with a punch 57, which is a preheated upper die, and forged into a piston shape. A protrusion 71 for forming a valve escape recess 70 is provided in the recess 56 of the lower die 55. Further, a recess 72 is formed on the lower surface of the punch 57 in correspondence with the lower mold protrusion 71.
[0037]
4B corresponds to the step (L) of FIG. 3, and the forged piston 58 is formed with a recess 70 for valve escape on the surface of the head portion 40 by the projection 71 formed on the lower die 55. Further, a protrusion 73 is formed on the inner surface side of the head portion 40 corresponding to the concave portion 72 on the punch side.
[0038]
In the step (L) of FIG. 3, as the tip of the punch 57 bites into the upper skirt alloy 50, the outer periphery of the skirt alloy 50 rises to form a skirt. On the other hand, the head portion alloy 51 receives a pressing force of the punch 57 acting via the skirt portion alloy 50 and a reaction force from the lower die 55 which is a reaction thereof. The reaction force generated by the protrusion 71 of the lower die 55 pushes a part of the skirt alloy 50 into the recess 72 of the punch 57 via the head alloy 51. The boundary surface 100 before forging between the skirt portion alloy 50 and the head portion alloy 51, which was flat before forging, is such that the protrusion 71 is pushed into the head portion alloy 51, and a part of the skirt portion alloy 50 is recessed. When it enters into 72, it deforms and protrudes upward in a convex shape. This is the protrusion 200d on the boundary surface after forging. The other part 200e of the boundary surface after forging is almost flat. By the forging, the boundary surface is deformed, and the area increases at the protrusion 200d. As the area increases, the skirt alloy 50 Not only The head portion alloy 51 also extends greatly at the boundary surface. The oxide film is broken at the portion where the elongation is large, and the skirt alloy 50 and the head alloy 51 are in direct contact and joined. If there is a difference in easiness of elongation between the alloys 50 and 51, not only the area of the boundary surface is increased, but also a relative slip occurs between the alloys 50 and 51, which also contributes to the destruction of the oxide film. Different metals join more firmly. In addition, since elongation occurs in a state where the pressing force by the punch 57 and the reaction force act, a fiber flow in the stretching direction is formed at least in the vicinity of the boundary surface 200d of both alloys.
[0039]
FIG. 4C corresponds to step (N) of FIG. 3 and shows a state after various machining processes for forming the piston are performed. That is, the piston ring groove 65 is formed, and a processing process such as surface treatment or shape finishing is performed as necessary. At this time, the fiber flow formed in FIG. 4B remains. The concave portion 72 on the punch 57 side may be omitted. In this case, as shown in FIG. 4D, the protrusion 71 is formed between the side surface of the punch 57 and the side surface of the recess 56 by the amount of the area that is eliminated by being pushed into the head portion alloy 50. It enters the skirt portion, and the vicinity of the inner protrusion 71 around the boundary surface rises in a convex shape to form a protrusion 200f. Even in the projection 200f on the boundary surface, an increase or slippage of the boundary surface area occurs, the oxide film is broken, and the alloys 50 and 51 are firmly bonded to each other.
[0040]
FIG. 5 is a process explanatory diagram of another embodiment of the present invention, and FIG. 6 is a detailed explanatory diagram of a part thereof. In this embodiment, the step (L) is different from the embodiment of FIG. 3, and the subsequent steps (M) and (N) are different accordingly.
[0041]
In the figure, reference numeral 100 denotes a boundary surface of the two-layer alloy before forging, and is a flat surface in this embodiment. The two layers of alloy are in contact with each other across the boundary surface 100. A mold release agent is applied to the cylindrical outer peripheral surface before forging. The shape of the punch 57 is determined so as to give a necessary thickness to each part of the piston 58. On the other hand, a recess 59 is formed at the center of the bottom surface of the recess 56 of the lower die 55 so as to face the protrusion 57 a of the punch 57.
[0042]
As the protrusion 57a of the punch 57 bites into the upper skirt alloy 50, the outer periphery of the skirt alloy 50 rises to form a skirt. On the other hand, the head portion alloy 51 is pushed by the protrusion 57 a of the punch 57 through the skirt portion alloy 50 and enters the recess 59 formed in the lower die 55 to form the protrusion 42. By entering into the recess 59, the boundary surface 100 is deformed, and a portion corresponding to the recess 59 is deformed in a convex shape toward the head portion alloy 51 side. Further, the protrusion 57a of the punch 57 further descends from the position of the boundary surface 100 before forging, so that the outer periphery of the head part alloy 51 rises and the skirt part alloy 50 below the protrusion 57a has a thickness. As the thickness decreases, the outer periphery of the skirt alloy 50 is further raised.
The boundary surface 200 after forging includes an outer peripheral portion 200a that is higher than the boundary surface 100 before forging, and a first dome portion 200b that protrudes downward along the protruding portion 57a to a position lower than the boundary surface 100 before forging. The second dome 200c that protrudes further downward in the central portion and the area that is eliminated when the projection 71 is pushed into the head portion alloy 51 are formed between the side surface of the punch 57 and the side surface of the recess 56. The skirt portion is formed by a protrusion 200f formed so as to protrude in the vicinity of the inner protrusion 71 around the boundary surface. The flat boundary surface 100 before forging changes to a boundary surface 200 having a dome shape after forging. That is, since the area of the boundary surface 100 is increased by forging, not only the skirt portion alloy 50 but also the head portion alloy 51 is greatly extended at the boundary surface. The oxide film is broken at the portion where the elongation is large, and the skirt alloy 50 and the head alloy 51 are in direct contact and joined. Further, if there is a difference in easiness of elongation between the alloys 50 and 51, not only the area of the boundary surface is increased, but also relative slip occurs between the alloys 50 and 51, which also contributes to the destruction of the oxide film, Different metals join more firmly. That is, the oxide film breaks and joins due to the increase in the area of the boundary surface or the occurrence of relative slip in a plurality and a wide range of the first dome part 200b, the second dome part 200c, and the protrusion 200f, and sufficient joining strength is obtained. .
[0043]
As shown in FIG. 6C, the protrusion 42 is deleted by machining in the step (N).
[0044]
If the contact interface between the skirt alloy 50 and the head alloy 51 before forging is increased after forging, a fiber flow accompanying elongation is formed in the vicinity of the contact interface after forging. Increases strength against external forces that bend the flow. In other words, while the piston is used in an actual engine, even if the gas pressure acting on the head acts, the fiber flow formed radially toward the outer periphery of the head supports this force and transmits it to the piston pin boss. Increase the strength of the head.
[0045]
FIG. 7 is an explanatory view showing another example of the composition distribution of the quenched powder aluminum alloy constituting the head portion of the piston.
[0046]
(A) shows the example which comprised only the peripheral part containing the piston ring groove | channel 65 of the head part 40 with the quenching powder aluminum alloy (PM alloy). According to this example, the peripheral portion of the head portion 40 that is particularly required to have heat resistance is formed of a PM alloy having excellent heat resistance, and other portions are formed of a piston alloy having good moldability. This improves the workability, and makes the joint surface curved so that relative slip is likely to occur, thereby improving the joint strength. As a result, the top land above the piston ring groove 65 can be made thinner as in the above embodiment, and the unburned gas is reduced by reducing the clevis, which is effective as an exhaust gas countermeasure. It can withstand even when the temperature of the portion reaches about 350 ° C., and the corner portion will not be bent or deformed. (C) is a development view of the piston of (A). In this case, the quenched powder aluminum alloy 51 is formed to the same thickness over the entire circumference of the piston outer peripheral surface.
[0047]
(B) shows an example in which the quenched powder aluminum alloy 51 is made thicker on the intake / exhaust side and thinner on the piston pin boss side. According to this example, the heat resistance is selectively enhanced in the portion on the intake and exhaust side where the heat load is severe. (D) is a development view of the piston outer peripheral surface of (B). In this case, the thickness of the quenched powder aluminum alloy 51 is thin above the piston ring groove 65 above the piston pin boss 66 and thick below the piston ring groove 65 above the piston pin boss 66. As a whole, a waveform is formed.
[0048]
FIG. 8 is a cross-sectional view showing still another method for manufacturing a piston according to the present invention. According to this manufacturing method, it can be used for forging of the piston 40 shown in FIG. 7 (A), and the bond between the skirt portion alloy 50 and the head portion alloy 51 can be strengthened on the outer periphery of the piston. Of the reference numerals in FIG. 8, those common to FIG. 4 are not described. The periphery of the bottom surface of the concave portion 56 of the lower mold 55 is formed as a protrusion 95 protruding upward in a donut shape. Or the center part of the bottom face of the recessed part 56 of the lower mold | type 55 is made into the recessed part 98 dented below.
[0049]
The central portion of the head portion alloy 51 enters the recess 96 by forging (when the viewpoint is changed, the periphery of the head portion alloy 51 is pushed up by the protrusion 95), and the boundary surface 100 before forging is the boundary surface 200 after forging. To change. When the pre-processed material after forging is processed from below to X as shown in FIG. 8B, the piston 40 shown in FIG. 7A is obtained.
[0050]
Also in this piston, the area of the boundary surface is greatly increased, and if the elongation rates of both alloys 50 and 51 are different, further relative slip occurs and they are firmly joined to each other.
[0051]
The piston 58 of the above-described embodiment is effective when used in an engine that is used at high rotation and high output, such as an automobile, a motorcycle, a snow vehicle, and an outboard motor. Moreover, it can be used not only for a piston of a 4-cycle engine but also for a piston for a 2-cycle engine in which a recess is provided at the top of the piston head.
[0052]
【The invention's effect】
As described above, in the present invention, the piston head portion and the skirt portion are made of different materials, and these different materials are simultaneously integrally formed by forging and simultaneously formed a recess for valve escape. Corresponding to the recess for valve escape, relative slip occurs between different materials and fiber flow is formed. Therefore, at the same time as molding by forging, the oxide film at the joint interface between different materials is destroyed and removed, and different materials are joined firmly Is done. That is, a strong bonding action can be obtained by the extension of the two material layers at the bonding surface under the pressure stress and the relative sliding. As a result, the alloy of the head part, which requires heat resistance and rigidity, and the alloy of the skirt part, which requires formability and slidability, are formed of different members, and these different alloys can be used without increasing the number of processes. The top land is made thinner and lighter, the output is increased by increasing the compression ratio in the combustion chamber, the emission of unburned HC gas is reduced by reducing the clevis volume, and the piston inertia force is reduced. Reduction of the weight and durability of the bearing portion due to the reduction, and reduction of engine vibration due to the weight reduction are achieved.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing the outline of a four-cycle engine to which a piston for an internal combustion engine of the present invention is applied.
FIG. 2 is a cross-sectional view of an example of a piston for an internal combustion engine according to the present invention, in which the left half shows the piston pin boss below the piston ring groove as viewed from the front, and the right half shows the piston pin boss from the side. Shows the state of viewing.
FIG. 3 is an explanatory view showing the manufacturing process of 23 pistons for a 4-cycle internal combustion engine in order.
FIG. 4 is a diagram for explaining details of steps (K) to (N) in FIG. 3;
FIG. 5 is an explanatory view showing in sequence the steps of a piston manufacturing method according to another embodiment of the present invention.
6 is a diagram illustrating details of steps (K) to (N) in FIG. 5;
FIG. 7 is an explanatory diagram of a distribution state of the heat-resistant alloy of the piston of the present invention.
FIG. 8 is a cross-sectional view showing still another method for manufacturing a piston according to the present invention.
[Explanation of symbols]
20: 4-cycle engine, 21: cylinder, 22: piston, 23: intake valve, 24: jet nozzle, 25: intake passage, 26: exhaust valve, 27: spark plug, 28: exhaust passage, 29: piston pin, 30 : Connecting rod, 31: crank arm, 32: crankshaft, 33: throttle valve, 36: piston pin boss, 40: head part, 41: skirt part, 42: extrusion protrusion, 50: piston alloy, 51: PM alloy, 55: Lower mold, 56: recess, 57: punch, 57a: protrusion, 58: piston, 59: recess, 65: piston ring groove, 66: piston pin boss, 70: recess for valve escape, 71: protrusion, 72: recess, 73: Protrusions, 74: Fiber flow, 95: Protrusions, 96: Recesses, 100, 200: Interface, 200a: Outer periphery 200b: first dome, 200c: second dome, 200d: projection, 200f: projection.

Claims (8)

  In an internal combustion engine piston comprising a head portion and a skirt portion and having a recess in the head portion, at least a portion of the head portion is made of a material different from other portions, A piston for an internal combustion engine, wherein a fiber flow is formed by forging corresponding to the shape of the recess.   2. The piston for an internal combustion engine according to claim 1, wherein a fiber flow by forging is formed at a central portion of the surface of the head portion.   The piston for an internal combustion engine according to claim 1 or 2, wherein the recess is a valve relief and is a piston for a four-cycle internal combustion engine. Manufacture of a piston for an internal combustion engine comprising a head portion and a skirt portion, the head portion having a recess, and at least a portion of the head portion including the recess made of a material different from other portions In the method, at least the dissimilar materials different in heat resistance constituting the piston are simultaneously forged to form the concave portion, and the dissimilar materials are joined and integrated, and the peripheral portion of the head portion has higher heat resistance than the central portion. A method for manufacturing a piston for an internal combustion engine, characterized by comprising a material . Manufacture of a piston for an internal combustion engine comprising a head portion and a skirt portion, the head portion having a recess, and at least a portion of the head portion including the recess made of a material different from other portions In the method, at least the different materials constituting the piston are forged at the same time to form the recesses, and the different materials are joined and integrated so that the material having higher heat resistance is on the intake / exhaust side than the piston pin boss side. A method for manufacturing a piston for an internal combustion engine , wherein the piston pin boss is thicker and thinner than the intake and exhaust sides . 6. The method for manufacturing a piston for an internal combustion engine according to claim 5 , wherein a projection is formed in the central portion together with the concave portion on the surface of the head portion during forging. The method for manufacturing a piston for an internal combustion engine according to any one of claims 4 to 6, which is applied to manufacture of a piston for a four-cycle internal combustion engine in which the concave portion is a valve relief. The internal combustion engine provided with the piston manufactured by the manufacturing method in any one of Claims 4-6.

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