JP2000097105A - Piston for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piston for internal combustion engine which can realize a light weight as low as possible, while securing a necessary strength. SOLUTION: In a piston 1 for internal combustion engine, a pair of pin bosses extended downward from two position parts on the piston pin axial line C at the lower side of about a disk form head, and a pair of skirt parts extended downward from the front side and the rear side of the above piston pin axial line C, at the outer peripheral edge of the head are connected by plural ribs 5a and 5b extended downward from the lower side of the head. In such a piston 1 for internal combustion engine, when the positioning side of a connecting rod 33 when the piston 1 moves to the bottom dead center side is made as the first area G1, and the positioning side of the con'rod 33 when the piston 1 moves to the top dead center side is made as the second area G2, by making a plane E including the piston pin axial line C and a crank axial line D, as the border, the thickness of the rear side rib 5b at the second area G2, of the above plural ribs, is made thicker than the thickness of the front side rib 5a at the first area G1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston for an internal combustion engine.

[0002]

2. Description of the Related Art In a piston for an internal combustion engine, a pair of pin boss portions extending downward from two portions on the piston pin axis on the lower surface of a substantially disk-shaped head portion and at least the outer peripheral edge of the head portion are provided. A structure is generally adopted in which a skirt portion extending downward from both sides of the piston pin axis is connected by a plurality of rib portions extending downward from the lower surface of the head portion.

[0003]

In order to meet the demand for high speed and high output of the internal combustion engine, it is effective to reduce the weight of the piston as much as possible. However, it is necessary to set the thickness of each part as thin as possible.

SUMMARY OF THE INVENTION The present invention has been made in view of the above demand for high speed and high output of an internal combustion engine, and provides a piston for an internal combustion engine which can reduce the weight as much as possible while securing necessary strength. The challenge is to do.

[0005]

According to a first aspect of the present invention, a pair of pin bosses extending downward from two portions on the lower surface of a substantially disk-shaped head portion on a piston pin axis and a pair of pin bosses are provided. A piston for an internal combustion engine, wherein an outer peripheral edge of the piston is connected to a skirt portion extending downward from at least both side portions of the piston pin axis by a plurality of rib portions extending downward from a lower surface of the head portion; The side where the connecting rod is located when the piston moves in the direction of the bottom dead center with respect to the plane including the axis and the crank axis is defined as a first region,
When the side where the connecting rod is located when the piston moves in the direction of the top dead center is the second area, of the plurality of ribs, the thickness of the rib on the second area is equal to the thickness of the rib on the first area. It is characterized in that it is thicker than the thickness.
The length of the rib portion on the second region side in the piston axial direction is longer than the length of the rib portion on the first region side.

According to a third aspect of the present invention, of the plurality of rib portions, the thickness of the rib portion on the second region side is larger than the thickness of the rib portion on the first region side, and the rib portion on the second region side. Is characterized in that the length in the axial direction of the piston is longer than the length of the rib portion on the first region side.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the piston pin axis is offset to the second region.

[0008]

According to the piston for an internal combustion engine according to the present invention, the rib portions on the first region side and the second region side can be set to a thickness or a length having a strength corresponding to the piston side pressure. The weight can be reduced. That is, when the piston of the present invention is mounted on the engine, in the combustion stroke, that is, in the stroke in which the piston moves in the direction of bottom dead center,
While the piston-side pressure acts on the second region side, the piston-side pressure acts on the first region side during a stroke such as a compression stroke in which the piston moves toward the top dead center, but the piston-side pressure during the combustion stroke is smaller than the compression stroke. Greater than the piston side pressure at. Therefore, in the present invention, the rib portion located on the second region side where the large piston side pressure acts is set to be thicker or longer than the rib portion located on the first region side, so that the rib portion corresponds to the piston side pressure. And, as a result, the weight of the piston can be reduced.

When the piston reaches the top dead center, the direction of inclination of the connecting rod changes, so that the direction of the lateral pressure due to the pressure from the connecting rod changes from the direction F1 to the direction F2. As a result, there is a clearance between the cylinder and the piston, so that a tapping sound (piston slap) is generated. The ignition is performed before the piston reaches the top dead center, and the pressure in the combustion chamber sharply rises, and when the piston reaches the top dead center, the combustion chamber pressure becomes considerably large, which causes The force also increases, which produces a loud tapping sound. However, in the invention of claim 4, since the piston pin axis C is slightly offset to the second region side, the inclination direction of the connecting rod is switched before the piston reaches the conventional top dead center. That is, since the timing at which the directions of the lateral pressures are exchanged is advanced, the pressure in the combustion chamber is correspondingly reduced, and the tapping sound can be reduced.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIGS. 1 to 11 are views for explaining a forged piston for an internal combustion engine and a method of manufacturing the same according to an embodiment of the present invention.
Is a plan view, a right side view, a front view, and a bottom view of the machined forged piston, and FIGS. 5, 6, and 7 are sectional views taken along line VV in FIG.
FIG. 8 is a sectional view taken along a line VII-VII in FIG.
9 and 10 are schematic diagrams for explaining a method for manufacturing the piston, and FIG. 11 is a schematic diagram for explaining a state of action of a force when the piston is mounted on an engine. 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 FIG. 1, reference numeral 1 denotes a forged aluminum alloy piston for a four-cycle, 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.
And two front rib portions 5a and two rear rib portions 5b which extend downward from the front end and connect the pin boss portions 4, the skirt portion 3, and the lower surface 2f of the head portion 2.

The head 2 has a substantially disk shape.
On the upper surface 2a forming the bottom surface of the combustion chamber, three relief recesses 2b for the intake valve and two relief recesses 2c for the exhaust valve are formed. On the side surface 2h, two compression ring grooves 2d and one oil ring are formed. The groove 2e is formed by machining.

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

The skirt portions 3, 3 are for receiving a piston side pressure generated with the rotation of the engine, and are connected to the front and rear sides 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. The outer peripheral surfaces of the skirt portions 3, 3 are in sliding contact with the inner peripheral surface of the cylinder bore, and are machined. As shown in FIG. 5, the thickness of the skirt 3 is set to an inclined thickness that gradually decreases from the upper end 3a near the oil ring groove 2e to the lower end 3b located at the lower end of the piston. I have. When the skirt portion 3 is cut along an arbitrary plane passing through the piston axis A,
The intersection line between the outer peripheral surface and the cut surface, that is, the line formed by the outer peripheral surface is parallel to the piston axis A, and the same intersection line formed by the inner peripheral surface and the cut surface is inclined inward.

Here, a boundary portion 2g between the upper end portion 3a of the skirt portion 3 and the lower surface 2f of the head portion 2 is thick so that a sufficient thickness can be obtained even if the oil ring groove 2e is formed. And has a gentle curved surface without forming an edge shape. The inner surfaces of the head portion 2 and the skirt portion 3 and the surfaces of the pin boss portions 4 and the rib portions 5 remain forged surfaces that have not been machined.

The front rib 5a and the rear rib 5b are
The front and rear edges of the pin boss portions 4 at the substantially axial center thereof and the left and right edges of the front and rear skirt portions 3 and the head portion 2.
Of the front and rear ribs 5
When viewed in the direction of the piston axis A, a and 5b extend leftward and rightward from a straight line perpendicular to the piston pin axis C from the pin boss portion 4 side. Each of the rib portions 5a and 5b is the same as that shown in FIG.
Has a uniform thickness in the direction of the piston axis A, as shown in
Further, as shown in FIG. 8, even when viewed in a direction intersecting the piston pin axis C, it has a uniform thickness.

The front rib 5a and the rear rib 5
b, the thickness of the rear rib 5b is set to be larger than the thickness of the front rib 5a, and
The length of b in the axial direction of the piston is set longer than the length of the front rib portion 5a. Furthermore, the piston pin axis C
Are slightly offset from the rear rib portion 5b.

The piston 1 of this embodiment is mounted on the engine in a state shown in FIG. That is, the piston 1 is slidably inserted into the cylinder bore 31a of the cylinder block 31 to form a combustion chamber with the cylinder bore 31a and the combustion recess 32a of the cylinder head 32.
Crank pin 34a of crankshaft 34 with connecting rod 33
And rotates in the direction of the arrow a shown in the figure.

The piston 1 is separated from a plane E including the axis C of the piston pin and the axis D of the crankshaft 34.
When the side where the connecting rod 33 is located in the direction of bottom dead center is the first area G1 and the side where the connecting rod 33 is located when the piston 1 is moved in the direction of top dead center is the second area G2, the piston 1 The two rear rib portions 5b having the large thickness and the long length in the piston axial direction are formed in the second region G.
The two front rib portions 5a are located on the first region G1 side.

Next, a method of manufacturing the piston 1 will be described. The piston 1 is formed by first forming a piston material (billet) 10 ′ made of an aluminum alloy lump by die forging into a molding material 10 having substantially the same shape as the piston 1 (FIGS. 9 and 10).
) And subjecting the molding material 10 to the required machining.

FIGS. 9 and 10 show a forging die for manufacturing the molding material 10. FIG. FIG. 1 shows the forging die in a cross section along the line VII-V in FIG. In the figure, reference numeral 20 denotes a forging die, which is a first die (upper die) 11 having a shape corresponding to a part of the surface shape of a forming material 10 having substantially the same shape as the piston 1 and the forging die. And a second mold (lower mold) 12 having a shape corresponding to the rest of the surface shape of the material 10. The second mold 12 is fixed to a fixed part of a forging device, the first mold 11 is fixed to a movable part, and the first and second dies 11, 12 are relatively moved with a predetermined forging force. It is possible.

The first mold 11 has a forging die portion 11 a having a shape corresponding to a part of the surface shape of the molding material 10, specifically, the surface shape of the upper surface 2 a of the head portion 2. . Further, the second mold 12 has the remaining surface shape of the molding material 10, specifically, the side outer surface 2 h of the head 2,
Forging mold portions 12a and 12b having a shape corresponding to the lower surface 2f;
A skirt forging die portion 12c having a shape corresponding to the outer surface and inner surface of the skirt portion 3, a forging die portion having a shape corresponding to the surface of the pin boss portion 4, and corresponding to the surfaces of the front rib portion 5a and the rear rib portion 5b. And a rib forging die portion 12db, 12da having a predetermined shape.

Here, the skirt forging die portion 12c of the second die 12 has a draft angle whose thickness dimension is set to be thicker toward the upper side and thinner toward the lower side. 12c at the time of inflow of aluminum alloy
'Is set to a smooth shape having a large curvature.

On the other hand, the rib forging die 1 of the second die 12
2da and 12db do not have a draft angle, the thickness dimension is uniform in the axial direction, and the rib forging die 1
The entrance 12d 'of 2da and 12db is the entrance 1
The edge shape has a smaller curvature than that of 2c '. Furthermore, a forging die portion 12d for the rear rib portion 5b is provided.
“b” is set to be thicker in the thickness direction and longer in the axial direction of the piston than the forging die portion 12da for the front rib portion 5a.

Using the forging die 20, a molding material 10
When the molding material 1 is molded in the second mold 12,
A piston material (billet) 10 'made of an aluminum alloy lump having a volume corresponding to 0 is placed, and the first mold 11 is lowered with a predetermined forging force. In this case, a piston material 10 'is provided by a heater provided in at least one of the first and second molds 11, 12 or by an external heater.
Is heated to 400 to 500 ° C. and hot forged, so that the ductility of the aluminum alloy can be sufficiently utilized to forge the forming material 10 with high dimensional accuracy.

In such a die forging, the second die 1
2 of the skirt forging die portion 12c,
Since the thickness of the side, that is, the side where the piston material 10 'starts flowing in is set to be large and the thickness of the tip side is set to be small, the aluminum alloy is plastically deformed in the skirt forging die portion 12c in the piston axial direction (forging direction). As a result, plastic deformation occurs in the direction perpendicular to the forging direction (thickness direction). In other words, the aluminum alloy continues plastic deformation as the forging progresses, and the required forging load increases accordingly.
However, since the draft of the skirt forging mold portion 12c is set to be thinner toward the tip side and the draft is provided, the die removing load after forging can be reduced.

On the other hand, the rib forging die portions 12da and 12db are set to have a uniform thickness in the piston axial direction (forging direction).
Although plastic deformation occurs in the piston axial direction (forging direction) within 2 db, it does not plastically deform in the direction perpendicular to the forging direction (thickness direction). That is, the aluminum alloy is formed of the rib forging die portions 12 da and 12 db. After passing through the entrance 12d ', there is no further plastic deformation, and the forging load does not increase. On the other hand, the rib forging die portion 12
Since the thicknesses of da and 12 db are set uniformly in the axial direction, there is no draft, and therefore there is a concern that the frictional force at the time of die removal after forging increases. However, the temperature of the aluminum alloy increases due to the plastic deformation described above. Because of this and the axial dimension of the rib portion 5 is shorter than, for example, the skirt portion 3, the die-cutting load does not increase extremely.

Here, in the present embodiment, the second mold 1 is used.
The entrance portion 12c 'of the skirt forging die portion 12c is set to have a smooth shape with a large curvature, while the entrance portion 12d' of the rib forging die portions 12da and 12db has a curvature smaller than that of the entrance portion 12c '. It is set to a small edge shape. Thereby, the thin rib forging die portion 12d is formed.
The inflow of the aluminum alloy into the a and 12db is relatively easy as compared with the inflow into the thick skirt forging die portion 12c, and the two forging die portions 12 have the same forging load as a whole.
The aluminum alloy can be caused to flow into c, 12da, and 12db without underfill.

This will be described in more detail below. That is, when the entrance has an edge shape with a small curvature like the 12d ', the inclined shear plane (maximum shear stress surface) toward the entrance of the molding material 10' with respect to the main stress direction (forging direction). The angle becomes smaller, and the temperature of the aluminum alloy rises due to plastic deformation, thereby reducing the shear fracture stress. As a result, the inflow of the aluminum alloy becomes easy even in a thin-walled forging die.

On the other hand, when the entrance has a corner cut shape having a large curvature as shown in 12c ', the molding material 1
Inclined shear surface toward the entrance of 0 '(maximum shear stress surface)
The angle with respect to the main stress direction (forging direction) becomes as large as 45 °, and frictional heat and compression heat due to plastic deformation are diffused, making it difficult for the aluminum alloy to rise in temperature.
As a result, the aluminum alloy easily adheres to the mold surface, and it becomes difficult to flow the aluminum alloy unless the thickness of the forged mold portion is increased.

As shown by a two-dot chain line in FIGS. 9 and 10, the second die 12 of the forging die 20 is replaced with a skirt forging die portion 12c, rib forging die portions 12da, 12db and a pin boss portion. It is also possible to divide the mold into a mold b inside and a mold c outside the division surface a passing through the lower end of the corresponding forging die. In this case, when the aluminum alloy flows into the skirt forging die portion 12c and the rib forging die portions 12da, 12db, the forging die portions 12c, 12da, 12db are formed.
The occurrence of cracks at the bottom can be avoided by slightly opening the divided surface a, and as a result, the life of the mold can be extended.

The piston 1 of this embodiment is mounted on an engine as shown in FIG. In this case, in the combustion stroke, that is, in the stroke in which the piston 1 moves in the direction of the bottom dead center (stroke indicated by a solid line in the drawing), the piston-side pressure F2 acts on the second region G2 side, while the piston in the compression stroke and the like operates. In the process of moving toward the top dead center (the process indicated by the two-dot chain line in the figure), the piston-side pressure F1 acts on the first region G1 side, but the piston-side pressure F2 in the combustion stroke is larger than F1.

Therefore, in the present embodiment, the rear rib portion 5b located on the second region G2 side where the large piston side pressure F2 acts is made thicker than the front rib portion 5a located on the first region G1 side. Since the axial length is set long, the thickness and length can be set corresponding to the piston side pressures F1 and F2 acting on the front and rear rib portions 5a and 5b, and as a result, the weight of the piston 1 is reduced. can do.

In this embodiment, the piston pin axis C
Is slightly offset to the second area G2 side, so that the inclination direction of the connecting rod 33 is switched before the piston 1 reaches the top dead center when there is no conventional offset. That is, since the timing at which the direction of the lateral pressure is switched from the direction F1 to the direction F2 is advanced, the pressure in the combustion chamber at which the ignition and ignition start before the top dead center becomes smaller at the timing at which the direction of the lateral pressure is switched, and the cylinder 31a The tapping sound due to the movement of the piston 1 in the F2 direction due to the clearance between the pistons 1 can be reduced.

Here, the piston material (buret) 10 'used for manufacturing the forged piston as described above is, for example, made of aluminum (Al) as a base material, silicon (Si) at 10 to 25% by weight, iron 1% by weight of (Fe)
Hereinafter, copper (Cu) is 0.5 to 7% by weight, magnesium (Mg) is 0.1 to 2% by weight, and manganese (Mn) is 1.
5% by weight or less, nickel (Ni) 1.5% by weight or less,
An aluminum alloy containing chromium (Cr) in a range of 1.5% by weight or less is used by cutting an ingot that is continuously cast into a cylindrical rod.

Further, an aluminum alloy having the above composition is drawn out from the bottom of the melting furnace as a continuous cast having a columnar shape, and a stirrer comprising an electromagnet or an ultrasonic oscillator is provided on the outer periphery of a portion where the solidification starts after leaving the melting furnace. Is arranged and solidified while stirring and mixing the central portion and the outer peripheral portion of the cylindrical continuous cast body, thereby suppressing the growth of precipitated crystal particles to reduce the particle size, and from the outer peripheral portion to the central portion. A solid circular aluminum alloy rod-like body in which crystal grains are uniformly dispersed may be cut into a suitable size and used as the piston material 10 '.

The piston blank 1 solidified while stirring and mixing the central portion and the outer peripheral portion of the cylindrical continuous cast body as described above.
When 0 ′ is used, cracks are less likely to occur during forging because the crystal grains are small and uniformly dispersed, so that the yield during forging can be improved, and the piston 1 can be used. It is possible to increase the fatigue strength of the skirt portion 3 when the engine is assembled and operated.

Further, regarding the piston material 10 ',
An aluminum alloy obtained by solidifying rapidly solidified powder containing 10 to 22% by weight of silicon (Si) having an average particle diameter of primary crystal silicon of 10 μm or less may be used.

As such a rapidly solidified powdered aluminum alloy, for example, aluminum (Al) is used as a base material, silicon (Si) is 10 to 22% by weight, and iron (Fe) is 1 to 10%.
Weight%, copper (Cu) 0.5-5% by weight, magnesium (Mg) 0.5-5% by weight, manganese (Mn) 1% by weight or less, nickel (Ni) 1% by weight or less, chromium There is a material that surrounds (Cr) in a range of 1% by weight or less, zirconium (Zr) in a range of 2% by weight or less, and molybdenum (Mo) in a range of 1% by weight or less.

Among the components contained in the above-mentioned rapidly solidified powdered aluminum alloy, silicon (Si) is used to enhance wear resistance and seizure resistance by crystallizing hard primary crystals and eutectic silicon grains in the metal structure. Iron (Fe) is added to disperse and strengthen the metal structure to obtain a high strength at 200 ° C. or higher, and also to add copper (Cu) and magnesium (M
g) is added in order to increase the strength at 200 ° C. or less, and the amount of these added is out of the above range, so that the desired abrasion resistance and seizure resistance and the required strength at high temperature are obtained. Can not get.

In the piston material 10 'made of the rapidly solidified powdered aluminum alloy as described above, the melted aluminum alloy is sprayed in the form of a mist, rapidly solidified, and then powdered and then solidified. About 1 in average particle size
The silicon (Si) contained therein is hard primary crystal silicon crystallized in a metal structure of an aluminum alloy that solidifies while being powdered, and has an average particle diameter of 10 μm.
It is finely divided so as to be not more than μm, and is dispersed for each aluminum alloy particle.

Since silicon (Si) is finely divided and dispersed as described above, when the piston material 10 'is forged into a substantially piston-shaped molding material 10',
In particular, even if the material is forged so that the material is stretched thinly at the skirt portion 3, the primary crystal silicon particles do not crack and crack at that portion, and as a result, the piston 1 formed by forging is Thus, the fatigue strength of the skirt portion 3 is high.

The rapidly solidified powdered aluminum alloy used as the piston material 10 'is not limited to the above-mentioned ones. For example, in order to further increase its wear resistance, carbonized material which is harder than silicon (Si) is used. Silicon (Si
Those containing a predetermined amount of C) are also used.

As an example of the above-mentioned rapidly solidified powdered aluminum alloy containing silicon carbide (SiC), aluminum (Al) is used as a base material, silicon (Si) is 10 to 22% by weight, and iron (Fe) is 1 to 10%. % By weight of copper (Cu).
5-5 wt%, magnesium (Mg) 0.5-5 wt%, manganese (Mn) 1 wt% or less, nickel (N
i) not more than 1% by weight, chromium (Cr) not more than 1% by weight,
2% by weight or less of zirconium (Zr), molybdenum (M
In some cases, o) is contained in a range of 1% by weight or less and further, silicon carbide (SiC) is contained in a range of 1 to 10% by weight.

Piston material 1 made of rapidly solidified powdered aluminum alloy containing silicon carbide (SiC) as described above
In the case of 0 ', silicon (Si) is finely contained so that the average grain size of primary crystal silicon is 10 μm or less, and in order to further enhance wear resistance and seizure resistance,
Silicon carbide (SiC), which is a harder and more insoluble non-metallic material than silicon (Si), is dispersed and contained in the metal structure in a finely divided state so that the average particle size is 10 μm or less. In the piston 1 forged from the piston material 10, fine silicon carbide (SiC) is evenly dispersed in the aluminum alloy structure, whereby high wear resistance can be obtained.

In the manufacture of the piston material 10 from the above-mentioned rapidly solidified powdered aluminum alloy, first, an aluminum (A1) base material containing aluminum (A1) containing necessary components (silicon, silicon carbide and the like) in advance. Prepare an alloy ingot, melt it at about 700 ° C or more, spray it in a mist, cool it rapidly at a cooling rate of 100 ° C / sec or more to solidify it into a powder, or Aluminum alloy powder formed by melting and quenching and solidifying an aluminum alloy that does not have an average particle size of 1 to 10 μm
An aluminum alloy powder before solidification is obtained by, for example, mixing a predetermined amount of powder of a necessary component that has been refined so as to obtain an aluminum alloy powder before solidification.

With respect to the aluminum alloy powder as described above, the mold is filled with the aluminum alloy powder,
C. (a temperature of less than 700.degree. C.) and pressurize to directly form the piston material 10 'having a desired size and shape, or to extrude the aluminum alloy powder by heating to 400 to 500.degree. After solidification as a round bar by
This round bar is cut into a thick disk shape of an appropriate size corresponding to one piston to obtain a thick disk-shaped piston material 10 '.

In order to form the piston blank 10 'from the aluminum alloy powder, the aluminum alloy powder must be
After being guided between a pair of rolling rolls while being heated to 500 ° C. and rolled, it is formed into a thick disk-shaped piston material by punching out with a press, or cut into a desired size by shearing to obtain a rectangular piston material. It is also possible to form the material into a rectangular shape, and then to form a thick disk-shaped piston material by pre-forging.

[Brief description of the drawings]

FIG. 1 is a plan view of a forged piston for an internal combustion engine according to an embodiment of the present invention.

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

FIG. 3 is a front view of the piston.

FIG. 4 is a bottom view of the piston.

FIG. 5 is a sectional side view (a sectional view taken along line VV in FIG. 1) of the piston.

6 is a sectional front view of the piston (a sectional view taken along line VI-VI in FIG. 1).

FIG. 7 is a sectional front view of the piston (a sectional view taken along line VII-VII in FIG. 1).

FIG. 8 is a sectional plan view of the piston (VIII-VIII in FIG. 2).
FIG.

FIG. 9 is a schematic diagram showing a state of die forging of the piston.

FIG. 10 is a schematic view showing a state of die forging of the piston.

FIG. 11 is a schematic view showing a state in which the piston is mounted on the engine.

[Explanation of symbols]

 Reference Signs List 1 piston 2 head 2f lower surface 3 skirt 4 pin boss 5a front rib 5b rear rib 33 connecting rod C piston pin axis D crank axis E plane G1 first area G2 second area

Claims (4)

[Claims] 1. A pair of pin bosses extending downward from two portions on a lower surface of a substantially disk-shaped head portion on a piston pin axis, and at least both side portions of an outer peripheral edge of the head portion on the piston pin axis. In a piston for an internal combustion engine in which a skirt portion extending downward from the lower portion of the head portion is connected by a plurality of rib portions extending downward from a lower surface of the head portion, a plane including the piston pin axis and the crank axis is used as a boundary,
When the side where the connecting rod is located when the piston moves in the direction of bottom dead center is the first region, and when the side where the connecting rod is located when the piston moves in the direction of top dead center is the second region, the plurality of rib portions , The thickness of the rib portion on the second region side is set to the first
A piston for an internal combustion engine, characterized in that the thickness is greater than the thickness of a rib on the region side. 2. A pair of pin bosses extending downward from two portions on the piston pin axis on the lower surface of the substantially disk-shaped head portion, and at least both side portions of the outer peripheral edge of the head portion on the piston pin axis. In a piston for an internal combustion engine in which a skirt portion extending downward from the lower portion of the head portion is connected by a plurality of rib portions extending downward from a lower surface of the head portion, a plane including the piston pin axis and the crank axis is used as a boundary,
When the side where the connecting rod is located when the piston moves in the direction of bottom dead center is the first region, and when the side where the connecting rod is located when the piston moves in the direction of top dead center is the second region, the plurality of rib portions A piston for an internal combustion engine, wherein the length of the rib portion in the second region side in the axial direction of the piston is longer than the length of the rib portion in the first region. 3. The piston for an internal combustion engine according to claim 1, wherein the length of the rib portion on the second region side in the axial direction of the piston is longer than the length of the rib portion on the first region side. 4. The piston for an internal combustion engine according to claim 1, wherein the axis of the piston pin is offset toward the second region.