JP2000179399A - Forged piston for four-cycle engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a forged piston for four-cycle engine to increase output and reduce weight, while evading problems such as seizures or scuffing due to increase of surface pressure, and to extend life by improving seizure resistance. SOLUTION: This forged piston for four-cycle engine is equipped with a generally disk-like head portion 2, a skirt portion extending downward from at least both sides with respect to the piston pin axis of the outer peripheral edge of the head portion 2, at least two ring grooves 2d, 2e formed on the side peripheral surface of the head portion 2, and an oil hole that is formed in the bottom of the lowest ring groove 2e interconnecting inside of the piston. The piston 1 is manufactured by closed die forging with aluminum alloy containing at least silicone. Fiber flows f are formed on a skirt portion 3 extending in the sliding direction. Between the fiber flows f on the sliding surface of the skirt portion 3, oil retainer grooves 7a are formed by shot peening.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a forged piston used in a four-stroke engine.

[0002]

2. Description of the Related Art As a piston for a four-cycle engine,
A billet made of an aluminum alloy is forged using a mold to produce a piston material having a head portion, a pin boss portion, a skirt portion, and the like. Thereafter, a cylinder sliding surface, a piston pin hole, and a ring are formed on the piston material. In some cases, a forged piston is used as a product by forming a groove or the like by machining.

In the forged piston, at least two ring grooves are formed on the side peripheral surface of the head portion, a pressure ring is fitted in the upper ring groove, and an oil ring is fitted in the lowest ring groove. Generally, a plurality of oil holes communicating with the inside of the piston are formed at the bottom of the lowest oil ring groove.

The piston reciprocates in the cylinder bore under intermittent explosive pressure. In order to ensure lubrication of the sliding surface between the skirt and the cylinder bore, lubricating oil is applied to the sliding surface. To supply.

[0005]

By the way, in the forged piston described above, a higher strength can be obtained as compared with a conventional cast piston or the like, so that the output can be increased by increasing the explosion pressure and the skirt area can be reduced. In some cases, the size is reduced to reduce the weight.

However, when the output and weight of the conventional forged piston are increased and the weight thereof is reduced, the surface pressure of the sliding portion of the piston increases, and in some cases, problems such as scuffing and seizure tend to occur. There is a concern.

[0007] Further, in the forged piston, not only the problem of the increase in the surface pressure of the sliding portion, but also the maintenance of seizure resistance for a longer time commensurate with the strength increase is required.

Further, in the piston for an internal combustion engine, the temperature of the top surface of the head portion tends to rise due to contact with the high temperature burned gas, and the strength of the head portion decreases due to the temperature rise of the head portion depending on the material. In particular, in the case of an aluminum alloy, the strength tends to decrease at high temperatures, and improvement in this respect is required. For this purpose, in addition to increasing the strength of the piston by forging, it is necessary to use a material with a small decrease in strength even at a high temperature, or to increase the heat dissipation to suppress the rise in the temperature of the head.

[0009] However, when a material having a small decrease in strength even at a high temperature is used, there is a problem that the cost is generally high. On the other hand, in the case of the method in which the external cooling is strongly reduced to suppress the rise in the temperature of the piston, there is a concern that the temperature of the burned gas in the entire combustion chamber is reduced and the engine performance is reduced.

The present invention has been made in view of such a situation, and it is possible to avoid the problem of scuffing and seizure due to an increase in surface pressure while improving output and weight, and to improve seizure resistance. It is an object of the present invention to provide a forged piston for a four-stroke engine that can avoid a decrease in strength at high temperatures and can increase strength and reduce weight without using a special material.

[0011]

According to the present invention, there is provided a head portion having a substantially disk shape, a skirt portion extending downward from at least both side portions of the outer peripheral edge of the head portion with respect to the axis of the piston pin, and
4 comprising at least two ring grooves formed on the side peripheral surface of the head portion, and an oil hole formed at the bottom of the lowest ring groove among the ring grooves and communicating with the inside of the piston.
In a forged piston for a sail engine, the piston is made of a die forging made of an aluminum alloy containing at least silicon, and a fiber flow extending in a sliding direction is formed in the skirt portion. Oil retaining grooves extending in the sliding direction are formed by shot peening between the fiber flows of the surfaces.

According to a second aspect of the present invention, in the first aspect, a fiber flow radially extending from a central portion is formed in the head portion, and the fiber flow on the top surface of the head portion is radially formed by shot peening. Are formed.

According to a third aspect of the present invention, in the first or second aspect, the silicon has an average particle diameter of 50 μm or less.

[0014]

According to the forged piston of the present invention, a piston material made of an aluminum alloy lump or aluminum alloy powder containing Si is forged into a piston shape by a forging die, and then subjected to predetermined machining. Manufactured.

From the difference in the deformation resistance between the aluminum alloy and Si with respect to the forging force during the die forging, Si is converged to form a flow of the material fiber structure, that is, a fiber flow (forging line). The fiber flow is formed along the sliding direction (piston axis) of the skirt portion, and a part thereof is exposed on the outer surface of the skirt portion. The outer surface of the skirt portion thus formed has a structure in which a fiber flow having a high hardness and an aluminum alloy material having a lower hardness are arranged in stripes.

The outer surface of the skirt portion is subjected to shot peening. By this processing, the aluminum alloy ground softer than the fiber flow in the surface texture is preferentially shaved, and thus the oil retaining groove extending in the sliding direction of the present invention is formed.

As described above, according to the forged piston according to the present invention, a fiber flow extending in the sliding direction is formed on the skirt portion of the die forged piston made of an aluminum alloy containing Si, and the fiber flow is formed by shot peening. The lubricating oil supplied to the piston sliding portion is easily held in the oil retaining groove because the oil retaining groove extending in the sliding direction is formed in the oil retaining groove.
As a result, the cooling of the piston is promoted, which suppresses a rise in the surface pressure of the sliding part, thereby preventing scuffing and seizure, and improving the seizure resistance commensurate with the increase in strength, thereby improving the life of the piston. An effect that can be extended can be obtained.

That is, in the four-stroke engine, during the lowering stroke of the piston, oil adhering to the cylinder wall enters the skirt portion and is scraped off by the oil ring, but a part of the oil enters the oil ring structure and passes through the oil hole. From inside the piston, return to the crankcase. This oil circulation lubricates the skirt.

In the present invention, the oil circulation is more reliably performed by the oil retaining groove extending in the above-mentioned sliding direction of the piston, so that the piston is further cooled and the seizure resistance of the piston can be improved.

According to the second aspect of the present invention, a fiber flow is further formed in the head portion. This fiber flow is formed radially from the center of the head part in the radial direction, is continuously formed from the head part to the land part where the ring groove is formed and further to the skirt part, and in the skirt part is parallel to the piston central axis, In addition, a part is exposed on the top surface of the head portion. The top surface of the head thus formed has a structure in which a fiber flow with high hardness and low thermal conductivity and an aluminum alloy material with lower hardness and high thermal conductivity are radially striped. Will be provided.

Then, shot peening is performed on the top surface of the head portion. By this processing, the aluminum alloy ground softer than the fiber flow in the top surface structure is preferentially shaved, and thus the radial heat radiation groove of the present invention is formed.

As described above, according to the forged piston of the present invention, a fiber flow extending radially from the center portion is formed at the head of a die forged piston made of an aluminum alloy containing Si, and the fiber flow is reduced by shot peening. Since the heat radiation grooves extending in the radial direction are formed between the heat radiation grooves, the heat radiation grooves can increase the surface area of the aluminum alloy base on the top surface. While increasing the amount of heat received by this area increase,
Through the aluminum alloy having high radial thermal conductivity, heat can be efficiently guided from the exposed aluminum alloy ground to the inner peripheral wall of the cylinder and from the skirt to the inner peripheral wall of the cylinder, so that heat dissipation can be enhanced. In this way, particularly, the heat of the burned gas that comes into contact with the top surface is taken into the head portion from the heat radiation groove of the head portion, conducted in the radial aluminum alloy ground and in the fiber flow, and transmitted along the piston ring and the skirt portion. It will be transmitted to the cylinder wall.

As a result, the temperature of the layer in contact with the top surface of the burned gas can be lowered, and the temperature rise of the head can be suppressed accordingly. In this case, since the temperature of the burned gas in the entire combustion chamber does not decrease so much, a decrease in engine performance can be avoided.

As described above, since the rise in the temperature of the head portion can be suppressed, the decrease in the strength of the aluminum alloy due to the heat of the burned gas is reduced, and the strength of the head portion is improved by the radial fiber flow. In addition, there is an effect that strength reduction can be avoided without depending on the above-mentioned special material, and thus, the durability of the piston can be improved.

According to the third aspect of the present invention, the average grain size of Si is 5
0 μm or less, S
The i-particles can be prevented from falling off, and the fatigue strength can be improved. From this point, the fatigue life of the piston can be further extended. Further, by setting the Si particles to 50 μm or less, ductility during forging can be increased, and there is an effect that surface roughness can be prevented.

[0026]

Embodiments of the present invention will be described below with reference to the accompanying drawings. 1 to 10 are views for explaining a forged piston for an internal combustion engine according to an embodiment of the present invention, and FIGS. 1 to 4 are a plan view, a right side view, a front view, and a bottom view of the forged piston, respectively. 5, 5 and 6 are sectional views taken along the line VV and VI-VI of FIG. 1, FIGS. 7 and 9 are schematic views of the fiber flow formed on the forged piston, and FIGS. 8 and 10 are FIGS. FIG. 9 is a schematic sectional view taken along line VIII-VIII, XX of FIG. The front, rear, left and right in the present embodiment are as shown in FIG. 1, and the exhaust side is the front and the intake side is the rear in plan view.

In the drawing, reference numeral 1 denotes a forged aluminum alloy piston for a four-stroke, five-valve engine.
Denotes a substantially disk-shaped head portion 2, a pair of pin boss portions 4, 4 extending downward from two portions on the lower surface of the head portion 2 on the piston pin axis C, and an outer peripheral edge of the head portion 2. Skirt portions 3, 3 extending downward from the front and rear portions of the piston pin axis C, and a lower surface 2f of the head portion 2.
Each of the pin bosses 4 and the skirt 3
And four rib portions 5 for integrally connecting the lower portion 2f of the head portion 2 with the lower portion 2f.

The pin bosses 4 and 4 are connected to the head 2
The lower surface 2f extends downward on two axially indented portions from the outer peripheral surface of the head portion 2 on the piston pin axis C. Piston pin holes 4a are formed in the pin boss portions 4, 4 so as to penetrate coaxially. In addition, 4
Reference numeral b denotes a retaining ring groove in which a retaining ring for the piston pin is mounted, and reference numeral 4c denotes a tool insertion hole for attaching / detaching the retaining ring to / from the retaining ring groove 4b.

The head 2 has a substantially disk shape.
On the top surface 2a forming the bottom surface of the combustion chamber, three relief recesses 2b for intake valves and two relief recesses 2c for exhaust valves are formed. On the side surface 2h of the head portion 2, two pressure ring grooves 2d extending in the circumferential direction and one oil ring groove 2e located below the two pressure ring grooves 2d are formed by machining. A plurality of oil holes 2j communicating with the inside of the piston 2 are formed at the bottom of the lowest oil ring groove 2e.

The skirt portions 3, 3 are for receiving a piston side pressure generated with the rotation of the engine, and are connected to a front and rear side of the piston pin axis C, that is, a connecting rod (not shown) connected to the piston pin. Is provided in a portion opposed to the swing direction of. This skirt part 3,3
The outer peripheral surface is in sliding contact with the inner peripheral surface of the cylinder bore, and is machined.

As shown in FIG. 5, the thickness of the skirt portion 3 is an inclined thickness that gradually decreases from the upper end portion 3a adjacent to the oil ring groove 2e to the lower end portion 3b located at the lower end of the piston. Is set. The skirt 3
Has an outer peripheral surface parallel to the piston axis A and an inner peripheral surface inclined inward. The boundary 2g between the upper end 3a of the skirt 3 and the lower surface 2f of the head 2 is thick.
The ring grooves 2d and 2e are formed in the boundary 2g.

As described later, the piston 1 is formed by forging a piston material made of an aluminum alloy lump containing Si having an average particle diameter of 50 μm or less into a piston shape by a forging die, and subjecting the piston material to shot peening. And then subject to a predetermined machining process. The shot ball used in this shot peening has a hardness higher than the hardness of the aluminum alloy ground and lower than the hardness of the fiber flow portion. Si
Is mainly about Hv = 1200, the hardness of the aluminum alloy ground whose hardness is increased by forging is about Hv = 200, and Hv = 30 as a shot ball.
Approximately 0 to 1000 steel balls, glass balls and the like are selectively used.

As shown in FIGS. 7 and 8, the head portion 2 is formed with a fiber flow f extending radially from the center of the piston (the portion of the piston axis A) in the radial direction. The fiber flow f means a flow of a material fiber structure appearing in die forging, that is, a forging line. A part of the fiber flow f is exposed on the top surface 2a of the head portion 2, and the fiber flow f and the aluminum alloy material Al form radial stripes on the top surface 2a.

On the top surface 2a of the head portion 2, there is formed a radiation groove 7 which also extends in the radial direction between the fiber flows f. The heat radiation groove 7 is formed by shaving off an aluminum alloy material Al having a lower hardness than the fiber flow f during the shot peening process.

As shown in FIGS. 9 and 10, the skirt portion 3 further includes a fiber flow f extending in the sliding direction (the direction of the piston axis A) as a further extension of the radially extending fiber flow f in the head portion. Is formed. The fiber flow f means a flow of a material fiber structure appearing in die forging, that is, a forging line. A part of the fiber flow f is exposed on the outer surface of the skirt portion 3, and on the outer surface, the fiber flow f and the aluminum alloy material Al form stripes extending in the sliding direction.

An oil retaining groove 7a is formed on the outer surface of the skirt portion 3 between the fiber flows f, f and extends in the same sliding direction. The oil retaining groove 7a is formed by shaving off an aluminum alloy base Al having a lower hardness than the fiber flow f during the shot peening.

Next, one manufacturing method of the piston 1 is shown in FIG.
This will be described with reference to FIG. Here, in FIG. 11, reference numeral 20 denotes a continuous casting apparatus for producing the piston blank W1, and reference numeral 21c denotes an outlet. An ingot G of an aluminum alloy and a Si powder having an average particle diameter of 50 μm or less are charged, or an ingot G of an aluminum alloy containing a Si powder having an average particle diameter of 50 μm or less is charged, and the melting temperature of the aluminum alloy is higher than the melting temperature of the aluminum alloy. After melting at the following temperature, continuous casting is carried out by taking out continuously from the outlet 21c and cooling and solidifying, and the taken out continuous cast body is cut into a predetermined size, thereby forging the piston forging material (buret) W1. To manufacture. It is desirable to control the amount of the Si powder charged so that the Si content is 10 to 22% by weight, or to feed the aluminum alloy ingot G having the Si content of this weight ratio.

In the continuous casting apparatus shown in FIG. 11, a temperature difference occurs between the periphery and the center of the continuous casting material during the cooling and solidification process.
When the solidification of the central portion is delayed, the crystal grain size of the aluminum alloy increases in the central portion, and the particle size tends to be non-uniform inside and outside. FIG. 12 shows a continuous casting apparatus capable of making the particle size uniform inside and outside.
A melting furnace 21 having an inlet 21a at an upper part and a heater 21b wound therearound, and a stirrer 22 provided with an outlet 21c formed at the bottom of the melting furnace 21 and formed of an electromagnet.
And a roller 23 for continuously drawing the casting.

In the continuous casting apparatus shown in FIG. 12, the ingot G of the aluminum alloy and the
0 μm or less of Si powder,
An ingot G of an aluminum alloy containing Si powder of not more than μm is charged, and the molten metal is stirred by the stirrer 22 to disperse the nuclei (Si particles) while preventing the difference in cooling temperature between inside and outside. The solidified and cooled continuous cast body W is drawn out by the roller 23 and cut into a size corresponding to one piston to produce a piston raw material W1. Similarly to the above, it is desirable to control the content of Si in the continuous casting W to be 10 to 22% by weight.

FIGS. 13 and 14 show another method of manufacturing three piston blanks W1. In the process (1) of FIG. 13, an ingot G of an aluminum alloy containing Si having an average particle diameter of 50 μm or less is prepared. In the process (2),
This ingot G is put into a melting furnace and is heated to about 700 ° C.
After melting at a temperature equal to or lower than the melting temperature of Si, the aluminum alloy containing Si is rapidly dispersed and sprayed in a mist state and rapidly cooled and solidified at a cooling rate of 100 ° C./sec or more (atomizing method). Solidified powder (powder metal). An ingot G of an aluminum alloy containing no Si was melted, and a rapidly solidified powder of an aluminum alloy was produced by an atomizing method.
The powder may be mixed and stirred to form a powder material of an aluminum alloy containing Si.

Thereafter, in the step (3) of FIG.
Either the process (1) or the process (3 '') shown in FIG. 14 is employed. In the step (3), the cylindrical rod-shaped body formed by heating and extruding the powdered material of the aluminum alloy containing Si is cut into a predetermined size in the step (4) to produce the piston material W1.

In the case of adopting the step (3 '), the mold is filled with a powder material of an aluminum alloy containing Si, and then pressed (cold pressed) at room temperature to be solidified. , 4
By heating to 00 to 500 ° C. and pressing (hot pressing 4 ′), a piston material W1 of a desired size is manufactured.

When the step (3 '') is adopted, the aluminum alloy powder material containing Si is accommodated in a thin aluminum alloy cylindrical container, vacuum degassed, and then the process (4 '') is carried out. In the process, the cylindrical container is housed in a mold and extruded in a heated state, and in the process (5 ''), the extruded rod is cut into a predetermined size to produce a piston material W1.

15 and 16, reference numeral 25 denotes a forging die for forming the piston material W1 into a forming material 10 by die forging. The mold 25 includes a first mold (upper mold) 11 having a shape corresponding to a part of the surface shape of the molding material 10 having substantially the same shape as the piston 1, and a remaining portion of the surface shape of the molding material 10. Second of corresponding shape
And a mold (lower mold) 12. The first and second dies 11, 12 are relatively movable with a predetermined forging force.

Then, in the second mold 12 of the mold 25,
A release agent is applied to the outer surface of the piston material W1 and placed thereon, and the first mold 11 is lowered with a predetermined forging force.
In this case, the piston material W1 is heated to a predetermined temperature by a heater or the like and hot forged. By performing the hot forging, the forming material 10 can be forged with good dimensional accuracy by making full use of the ductility of the aluminum alloy (see FIGS. 17 (1) to (4)).

Thus, the piston material W1 is
It is formed into a forming material 10 corresponding to the piston 1 by crushing while applying an impact force by a mold 11. Here, the mold surface 11 a of the first mold 11 corresponds to the top surface 2 a ′ of the head part 2 ′, and the mold surfaces 12 a, 1 of the second mold 12.
2b is a side outer surface 2h 'and a lower surface 2f' of the head 2 '.
It corresponds to. The mold surface 12c corresponds to the skirt 3 ', and the mold surface 12d corresponds to the rib 5'.

In the above-mentioned die forging, the first forging force is applied.
When the piston material W1 is plastically deformed by being pressed by the mold surface 11a of the mold 11 and the mold surface 12b of the second mold 12, Si accumulates due to a difference in deformation resistance between the aluminum alloy and Si. A radial fiber flow is formed. Accordingly, a fiber flow f having high hardness and small thermal conductivity and an aluminum alloy base Al having low hardness and high thermal conductivity are alternately arranged on the top surface 2a 'of the head portion 2'. (See FIGS. 7 and 8A).

Further, in the above-described die forging, when the piston material W1 plastically deforms and flows into the die surface 12c of the second die 12 due to the forging force, the two Sis are separated from each other due to the difference in deformation resistance between the aluminum alloy and the Si. The striped fiber flow f is formed by accumulation. As a result, a stripe pattern is formed on the outer surface of the skirt portion 3 'in which the fiber flow f having a high hardness and the aluminum alloy material Al having a lower hardness are alternately arranged (FIGS. 9 and 10). (A)).

Next, the skirt portion 3 'of the molding material 10
17 (5) is subjected to a shot peening process on the outer surface and the top 2a of the head portion. This shot peening process is a process in which a shot (steel grain or the like) is pressurized by air pressure or centrifugal force and is sprayed onto the outer surface, and is mainly intended to increase the surface hardness and extend the fatigue life. I do. By this shot peening process, the soft aluminum alloy material on the surface of the skirt portion 3 'and the top surface 2a of the head portion is preferentially scraped off, so that the radiation grooves 7 and the piston extending radially from the center of the piston between the fiber flows f, f An oil retaining groove 7a extending in the axial direction is formed (see FIGS. 8 and 10B).

During the shot peening, the side surface 2h, that is, the upper side surface on which the ring grooves 2d and 2e are formed is masked so that the ring grooves 2d and 2e are protected and the aluminum alloy ground exposed on the side surface 2h is scraped off. Not to be.

Thereafter, the molding material 10 is subjected to machining, and the sliding surface, each of the ring grooves 2d and 2e, and the piston pin hole 4 are formed.
a etc. are formed. Thereafter, a surface treatment is performed, for example, an inner chemical conversion film of Al ₂ O ₃ of about 1 μm is formed or tin plating is applied (see FIG. 17 (6)). Thereby, the forged piston 1 of the present embodiment is manufactured. The inner surface of the skirt portion 3 of the piston 1 and the surfaces of the pin boss portions 4 and the rib portions 5 are subjected to a surface treatment without forging without machining. Regarding the head portion 21, the heat radiation groove 7 by shot peening is used even when the forged skin is left as it is or when machining is performed.
So that it remains.

Here, a center boss (not shown) for machining is formed by forging at a portion corresponding to the center of the top surface of the head portion of the molding material 10. This center boss was removed during machining. Due to the removal of the center boss, a boss mark A ′ remains at the center of the top surface, and the terminal end of the fiber flow f is exposed to the boss mark A ′.

Next, the operation and effect of this embodiment will be described. The forged piston 1 of the present embodiment is slidably inserted into a cylinder bore of a four-cycle engine. The head portion 2 of the piston 1 is exposed to the high heat of the burned gas and rises in temperature during the explosion combustion stroke.
Transmitted to the inside of the piston, is transmitted from the piston ring and the skirt portion 3 to the inner peripheral wall of the cylinder bore, thereby preventing the head portion 2 from overheating.

According to the present embodiment, a fiber flow f extending radially in the radial direction from the center portion is formed in the head portion 2 of the forged piston 1 made of an aluminum alloy containing Si, and the head portion 2 is formed by shot peening. Top 2
a, the heat dissipation groove 7 is formed on the top surface 2 by the heat dissipation groove 7.
a, the surface area of the aluminum alloy ground can be increased, the amount of heat received is increased by the increased area, and heat is efficiently transferred directly from the exposed aluminum alloy ground on the side surface 2h through an aluminum alloy having a high radial thermal conductivity. Are ring grooves 2d, 2
e can be guided from the exposed portion of the aluminum alloy ground to the cylinder inner peripheral wall via the piston ring, and further from the skirt portion to the cylinder inner peripheral wall, so that heat radiation can be improved. Thereby, the temperature of the layer in contact with the top surface 2a of the burned gas can be reduced, and the temperature rise of the head portion 2 can be suppressed accordingly. In this case, since the temperature of the burned gas in the entire combustion chamber does not decrease so much, a decrease in engine performance is avoided.

As described above, since the rise in the temperature of the head portion 2 due to the heat of the burned gas can be suppressed, a decrease in the strength of the piston can be avoided without using a special material, and the durability of the piston can be improved.

In this embodiment, since the end of the fiber flow f is exposed at the center boss mark A ', more heat of the burned gas in contact with the top surface is transferred from the exposed portion to the cylinder wall. The temperature of the boss mark portion of the burned gas in contact with the top surface is more reliably reduced.

On the other hand, a larger stress is generated at the center of the piston top surface due to the explosion pressure than at the other parts. However, in the present embodiment, as described above, since a rise in temperature at the center of the piston top surface is suppressed, a decrease in strength can be reduced, a large stress can be endured, and durability can be improved.

In the forged piston 1 of the present embodiment, during the descending stroke, the lubricating oil adhering to the inner peripheral surface of the cylinder bore enters the skirt portion 3 to lubricate the piston sliding portion. The lubricating oil that has entered the skirt portion 3 is scraped off by the oil ring and collected in the crank chamber. A part of the lubricating oil enters the oil ring groove 2e and passes through the oil hole 2j from the inside of the piston 1 into the crank chamber. Will be collected. The lubrication of the piston sliding portion is performed by such oil circulation.

According to the piston of this embodiment, a fiber flow f extending in the sliding direction is formed on the skirt 3 of the forged piston 1 made of an aluminum alloy containing Si, and the sliding surface of the skirt 3 is formed by shot peening. Oil retaining groove 7a
Is formed, the lubricating oil that has entered the skirt portion 3 is easily retained in the oil retaining groove 7a, and the oil retaining groove 7 functions as a circulation passage, thereby reliably lubricating the piston sliding portion. be able to. As a result, piston 1
Is promoted, the surface pressure of the sliding portion can be reduced, and problems such as scuffing and seizure can be prevented. Further, since the cooling property of the piston 1 can be improved, the improvement in seizure resistance corresponding to the increase in strength by forging can be obtained, and the life of the piston can be extended.

The skirt 3 has a fiber flow f
Is formed, the stiffness and strength of the skirt portion 3 itself can be increased, and from this point, abrasion resistance and seizure resistance can be improved. Since the fiber flow f of the skirt portion is formed as a continuous flow of the radial fiber flow f of the head portion, the forged piston 1 has high strength and rigidity as a whole.

In this embodiment, the average particle size of Si is 50 μm.
m or less, the Si particles can be prevented from falling off during shot peening, and the fatigue strength can be improved. In this respect, the durability can be improved and the life of the piston can be extended. In addition, since the Si particle size is set to 50 μm or less, ductility during die forging can be increased, and surface roughness can be prevented.

FIG. 18 is a characteristic diagram showing the relationship between the average Si grain size and the fatigue life to show the results of an experiment conducted to confirm the effect of this embodiment. In this experiment, a piston sample with a high outer surface hardness and a piston sample with a lower surface hardness were prepared with different Si particle sizes.
The fatigue life when shot peening was performed on each sample was measured and performed.

As is clear from the figure, when the average grain size of Si exceeds 50 μm, the fatigue strength of all samples is extremely reduced. This is considered to be because if the Si average particle diameter exceeds 50 μm, the hardness reduction rate due to shot peening sharply increases. On the other hand, when the average particle size of Si is set to 50 μm or less, the rate of decrease in hardness does not increase because there is no dropout of Si by shot peening, and as a result, fatigue strength can be improved. Conceivable.

[0064]

[Table 1]

Table 1 shows the results of measuring the hardness and fatigue strength of the forged piston of the present invention. Column II of Table 1 above shows the piston of the present invention obtained by die forging an aluminum alloy (AHSG) lump having a Si particle size of 30 μm manufactured by continuous casting.
Column III shows the Si particle size of 10 μm produced by atomization.
The piston of the present invention obtained by die-forging the following aluminum alloy (PM1) powder is shown. Column IV shows the piston of the present invention (PM2) having a different chemical composition by the same manufacturing method as that of column III. I
The column shows a conventional die casting piston (AC9B).

As is clear from the table, the conventional piston has a low hardness of 65 HRB and a low fatigue strength of 140 MPa (see column I). On the other hand, each of the pistons of the present invention has a hardness of 70 to 80 HRB and a fatigue strength of 180 to 22.
It can be seen that it is 0 Mpa, which is much higher than that of the conventional piston (see columns II to IV).

In the continuous casting shown in FIGS. 11 and 12, silicon carbide (Sic) or aluminum oxide (Al
_The burette may be manufactured by adding powder having an average particle size of 50 μm or less of a hard component such as ₂ O ₃ ) or aluminum oxide (AlN) singly or in a plurality of melting furnaces. In this case, the total content of these components is about 5% by weight.

Similarly to the above, powder having an average particle size of a hard component such as silicon carbide (Sic) having a particle diameter of 50 μm or less alone or a plurality of additional powders is added to the rapidly solidified powder of the aluminum alloy shown in FIG. The burette may be manufactured through the process shown in FIG.

Even when a burette containing a hard component in addition to the above Si is subjected to die forging shown in FIGS. 15 and 16, the fiber flows shown in FIGS. 7 to 10 are formed. This fiber flow is formed by gathering Si particles and hard components. Thereby, the strength of the head portion 2 and the skirt portion 3 can be further improved, the temperature rise of the head portion 2 can be suppressed, and the lubricity of the skirt portion 3 can be improved.

[Brief description of the drawings]

FIG. 1 is a plan view illustrating a forged piston according to an embodiment of the present invention.

FIG. 2 is a right side view of the forged piston.

FIG. 3 is a front view of the forged piston.

FIG. 4 is a bottom view of the forged piston.

5 is a sectional side view of the forged piston (FIG. 1)
VV line cross section).

6 is a sectional front view of the forged piston (FIG. 1)
VI-VI sectional view).

FIG. 7 is a schematic diagram showing a fiber flow of a head portion of the forged piston.

FIG. 8 is a schematic view showing a heat radiation groove of the forged piston (a sectional view taken along line VIII-VIII in FIG. 7).

FIG. 9 is a schematic view showing a fiber flow in a skirt portion of the forged piston.

FIG. 10 is a schematic view (a sectional view taken along line XX in FIG. 9) showing an oil retaining groove of the forged piston.

FIG. 11 is a schematic view showing a manufacturing process of the forged piston.

FIG. 12 is a schematic view of a continuous casting apparatus in a process of manufacturing the forged piston.

FIG. 13 is a schematic view showing a process for manufacturing the forged piston.

FIG. 14 is a schematic view showing a manufacturing process of the forged piston.

FIG. 15 is a schematic view showing a state of die forging of the forged piston.

FIG. 16 is a schematic diagram showing a state of die forging of the forged piston.

FIG. 17 is a schematic view showing a manufacturing process of the forged piston.

FIG. 18 is a characteristic diagram showing an effect of the embodiment.

[Description of Signs] 1 Forged Piston 2 Head 2a Top 2d, 2e Ring Groove 2j Oil Hole 3 Skirt 7 Heat Radiation Groove 7a Oil Retaining Groove f Fiber Flow C Piston Pin Axis

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) F16J 1/02 F16J 1/02 F term (reference) 3J044 AA06 AA08 BB39 CA13 CA40 EA10 4E087 AA02 AA10 BA04 CA11 CA33 CB07 CB11 DB18 DB24 EC12 EC22 HA62

Claims (3)

[Claims] 1. A substantially disk-shaped head portion, a skirt portion extending downward from at least both side portions of an outer peripheral edge of the head portion with respect to a piston pin axis, and a side peripheral surface of the head portion. A forged piston for a four-sile engine having at least two ring grooves and an oil hole formed at the bottom of the lowest ring groove among the ring grooves and communicating with the inside of the piston, wherein the piston has at least silicon-containing aluminum. It is made of a die forging made of an alloy, and a fiber flow extending in the sliding direction is formed on the skirt portion, and extends in the sliding direction by shot peening between the fiber flows on the outer surface of the skirt portion. A forged piston for a four-stroke engine, wherein an oil retaining groove is formed. 2. The head according to claim 1, wherein a fiber flow extending radially from a central portion is formed in the head portion, and a radial heat radiation groove is formed by shot peening between the fiber flows on the top surface of the head portion. A forged piston for an internal combustion engine, comprising: 3. The forged piston for a four-stroke engine according to claim 1, wherein the silicon has an average particle diameter of 50 μm or less.