JP2884777B2 - Piston for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art During operation of an engine, a piston skirt is permanently deformed inward to a large extent toward its lower end while the piston repeatedly contacts the cylinder bore surface by its lateral force due to crank motion. (It is transformed from A to B in FIG. 6). This increases the clearance between the piston and the cylinder bore wall surface, increases the impact force and slap noise, and finally achieves a small area at the skirt shoulder (C in FIG. 6). As a result, the oil film between the skirt portion and the cylinder bore wall surface breaks, causing seizure. In order to prevent the oil film from being cut off at the skirt shoulder, the skirt has a slightly smaller diameter from the bottom to the top. Normally, the piston has a smaller diameter toward the upper portion in order to escape thermal expansion of the piston crown portion which receives much heat from the engine combustion chamber. In order to maintain the posture of the piston and to form an oil film, the skirt portion has a slightly elliptical planar shape. The skirt shoulder has a smaller diameter for preventing the oil film from breaking, in addition to reducing the diameter for escape of thermal expansion.

[0003]

However, the measure to reduce the diameter of the skirt shoulder is to increase the clearance between the skirt and the cylinder bore wall surface, so that permanent inward deformation occurs at the lower end of the skirt. In such a case, there is a problem that the clearance is further increased, and the impact force and the slap sound are increased.

SUMMARY OF THE INVENTION The present invention provides an improvement in the sidewall structure without increasing the clearance beyond the clearance required for thermal expansion, thereby deforming the lower part of the skirt, thereby increasing the clearance and breaking the oil film at the shoulder of the skirt. The purpose is to reduce such problems.

[0005]

A piston for an internal combustion engine according to the present invention for achieving the above object comprises the following piston. That is, the crown portion, a pair of pin boss portions integrally formed at the lower portion of the crown portion, a pair of skirt portions integrally formed at the lower portion of the crown portion at a position in a direction orthogonal to the axis of the pair of pin boss portions, A piston for an internal combustion engine, comprising: a sidewall portion connecting each skirt portion and each pin boss portion; wherein the sidewall portion is provided at least corresponding to an upper portion of the skirt and is connected to the skirt portion to form the skirt portion. A first portion that extends tangentially in an arc shape and has an outer peripheral surface receded inward from the circumferentially extending surface of the skirt outer peripheral surface, and a second portion that extends in an arc shape from the pin boss portion so as to be continuous with the pin boss portion And the first and second parts
And an arc-shaped third portion connecting the portions of
Both the first portion of the skirt portion and the sidewall portion
To the across support points span of the arcuate beams with small enough skirt bottom toward skirt downward from skirt upper constructed from the side
And the circumferential length of the skirt portion is
From the lower part of the skirt to the lower part of the skirt
In both cases, the circumferential direction of each first portion of the sidewall portion
Spreads from both sides of the skirt to the top of the skirt
Taper the length of the first part in the circumferential direction
A piston for an internal combustion engine, wherein the piston is enlarged from a lower portion to an upper portion of the engine portion.

[0006]

According to the piston of the present invention, the span between the support points at both ends of the arc-shaped beam formed by both the skirt portion and the first portion of the sidewall portion is made smaller from the upper skirt portion to the lower skirt portion. The skirt support rigidity can be reduced as it goes upward from the lower end of the piston. As a result, the skirt portion is less likely to be deformed inward at the lower end, and the skirt shoulder portion is softened so as to come into contact with the cylinder bore wall surface in a large area, so that the collision load per unit area is reduced and the oil film is less likely to break. Also, since the outer peripheral surface of the first portion provided at least in correspondence with the upper part of the skirt is retracted inside the piston to have an oil retaining effect, the seizure of the upper part of the skirt becomes a problem due to high temperature. Can be prevented. In addition, the area of the sliding surface of the skirt increases from the upper part of the skirt to the lower part .
The force per unit area of the sliding surface of the skirt at the lower part of the cart is reduced, and the friction is reduced. Furthermore, each first part
From both sides of the skirt to the top of the skirt
Scratch the circumferential length of the first part
Having increased from the lower portion of the isolation portion in Placing the top, the first
The area of the part increases as it goes upward,
The oil retaining effect of the oil sump by the first portion is increased,
The effect of preventing seizure at the shoulder of the cart is great.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An internal combustion engine piston according to an embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 1, the piston 2 is located in a direction orthogonal to the crown 4, a pair of pin bosses 6, 6 formed integrally with the lower portion of the crown 4, and the axis 8 of the pair of pin bosses. And a pair of skirt portions 10, 10 integrally formed below the crown portion 4, and a sidewall portion 12 connecting each skirt portion 10 and each pin boss portion 6. A piston ring groove 14 and an oil ring groove 16 extending in the circumferential direction are formed in the crown portion 4. A piston pin hole 18 is formed in the pin boss portion 6, into which a piston pin (not shown) is inserted and rotatably connected to a connecting rod (not shown) via the piston pin. The piston 2 swings around a piston pin, that is, a pin boss shaft 8, and a skirt portion 10.
The sliding contact with the inner surface 20 of the cylinder bore (see FIG. 4) maintains the posture.

Since the piston 2 receives the heat from the combustion chamber at the crown 4, the temperature of the crown 4 becomes highest. In order to escape this thermal expansion, as shown in FIG. 4, the diameter of the crown portion 4 is the smallest, and the diameter is increased toward the lower end of the skirt portion. Further, in order to form an oil film for smooth sliding between the skirt portion 10 and the cylinder bore inner wall surface 20, the piston 2 is slightly elliptical in plan view as shown in FIG. However, in order to maintain the piston attitude, the clearance is minimized at the midpoint of the skirt peripheral surface (the intersection of the ellipse and the major axis of the ellipse).

FIG. 2 shows a cross section of the upper part of the skirt, and FIG. 3 shows a cross section of the lower part of the skirt. As shown in FIG.
The sidewall portion 12 is connected to the skirt portion 10 and extends in a tangential direction of the skirt portion 10 and extends in an arc shape (the center of the arc is the axis of the piston) (as described later, the first portion 12a is It may not be provided at a position corresponding to the lower part of the skirt in the vertical direction, and may be provided at least corresponding to the upper part of the skirt in the vertical direction. The center is formed by arcuately extending the second portion 12b extending to the pin boss portion 6 on the opposite side of the piston center, and the first portion 12a and the second portion 12b (the center of the arc is the side wall portion 1).
2 and a third portion 12c connected to the inner side of the piston and curved concavely toward the inner side of the piston. The outer peripheral surface 22 of the first portion 12a starts from the step portion 24, which is recessed from the skirt outer peripheral surface circumferential extension surface toward the piston center by the interval t (10 microns or more).

2 and 3, when a load is applied to the skirt portion 10 in a direction perpendicular to the axis of the piston boss, the load is transmitted to the pin boss portion 6 through the sidewall portion 12 and received by the piston pin and the connecting rod. Can be Therefore, the skirt portion 10 can be regarded as a both-ends support beam supported at both ends by the sidewall portions 12. The skirt support rigidity of the sidewall portion 12 is changed in the piston axial direction. The skirt support rigidity of the sidewall portion 12 is gradually changed in the vertical direction so as to be large at the lower end portion of the skirt and small at the shoulder portion of the skirt. This gradual change is obtained by the following configuration.

First, among the radii of curvature of the third portion 12c of the sidewall portion 12, the radius of curvature R of the upper part of the skirt portion is set.
Let a be small and let the radius of curvature Rb at the bottom of the skirt be large. In this manner, in the upper part of the skirt portion, as shown in FIG. 2, the beam having the total length of the skirt portion 10 and the first portion 12a of the sidewall portion 12 is supported by the third portion 12c at both ends. The span between the support points at both ends of the beam is increased, and the rigidity of the upper part of the skirt against the lateral force is reduced. In the lower part of the skirt portion, as shown in FIG.
The length of the first portion 12a in the circumferential direction of the piston is reduced, the first portion 12a of the sidewall portion 12 is almost eliminated, and the skirt portion 10 can be regarded as being supported at both ends by the third portion 12c. Therefore, the span between the support points at both ends of the beam is reduced, and the rigidity of the lower portion of the skirt against the lateral force is increased. As shown in FIG. 3, the first portion 12a of the sidewall portion 12 has a gap at both circumferential edges.
The first part 1 has a taper that spreads out toward the top of the
The circumferential length of the piston 2a is smaller at the lower part of the skirt.
It is, the area of the sliding surface of the skirt portion is increased as it goes from the top to the bottom of the skirt.

Further, the distance L between the centers of curvature of the second portions 12b of the side wall portions 12 is gradually changed in the axial direction of the piston so that the distance L becomes larger at the upper part of the skirt and becomes smaller at the lower part of the skirt. . By doing so, the span between the support points at both ends of the arc-shaped beam composed of the skirt portion 10 and the first portion 12a of the sidewall portion 12 can be increased at the upper portion of the skirt portion and reduced at the lower portion of the skirt portion.

The radius of curvature R of the upper part of the skirt portion of the radius of curvature of the second portion 12b of the sidewall portion 12 is
c is small, and the radius of curvature Rd at the lower part of the skirt is large. By doing so, the span between the support points at both ends of the arc-shaped beam composed of the skirt portion 10 and the first portion 12a of the sidewall portion 12 can be increased at the upper portion of the skirt portion and reduced at the lower portion of the skirt portion.

In FIG. 2, the boundary between the first portion 12a of the sidewall portion 12 and the skirt portion 10 is a step portion 24. Outer peripheral surface 2 of first portion 12a at skirt shoulder
As shown in FIG. 5, 2 is retracted by t toward the center of the piston from the extended surface of the outer surface of the skirt portion, which is slightly elliptical. It functions as an oil film forming surface that forms and holds an oil film.
The interval t is uniform along the first portion 12a in the circumferential direction. If the skirt 10 is retracted inside the piston, the posture of the piston 2 cannot be maintained and the swing becomes large,
The first portion 12a of the side wall portion which does not retreat and does not affect the attitude of the piston apart from the skirt portion 10 is used as an oil film forming surface. Here, a sufficient oil film is held and supplied to the skirt portion 10 and the inner wall surface 20 of the cylinder bore to prevent seizure of the skirt portion 10. The reason why the interval t is made uniform is that the thickness of the oil film is made uniform, heat conduction and heat transfer from the skirt shoulder to the cylinder bore inner wall surface 20 are improved, and the temperature of the piston shoulder is lowered.
This is for the purpose of effectively preventing image sticking. Since there is no first portion 12a of the sidewall at the lower part of the skirt portion,
Although the outer peripheral surface 22 retreated for forming the oil film is not formed,
Since the temperature of the lower part of the skirt is relatively low, no problem occurs.

Next, the operation will be described. It is said that the ideal shape of the piston is such that the area between the piston skirt and the inner wall surface of the cylinder bore is １ ／ of the bore diameter at the upper part of the skirt and ／ of the bore diameter at the lower part of the skirt. In addition, in order to maintain the normal posture of the piston and prevent the oil film from being cut off at the shoulder of the piston skirt, the rigidity of the piston at the shoulder of the skirt is small, and the rigidity of the piston at the bottom of the skirt is large. Sufficient oil must be supplied to the skirt outer peripheral surface at the skirt shoulder.

The piston 2 according to the embodiment of the present invention can satisfy all the above requirements. First portion 12 of sidewall portion 12
a does not hit the cylinder bore inner wall surface 20 because the outer peripheral surface is recessed inside the piston,
Only the skirt portion 10 contacts the cylinder bore inner wall surface 20. Therefore, by appropriately selecting the position of the step portion 24, the area of the skirt portion 10 corresponding to the bore inner wall surface 20 can be easily set to の of the bore diameter at the upper part of the skirt. Further, since the outer peripheral surface of the sidewall first portion 12a functions as the oil film forming surface 22, the oil can be sufficiently supplied to the outer peripheral surface of the upper part of the skirt, and the oil film can be prevented from being cut. The heat can be released to the cylinder bore through the through hole, so that seizure can be prevented.

Since the skirt support rigidity of the sidewall portion 12 is gradually changed in the vertical direction of the piston, an ideal skirt rigidity can be obtained. Conventionally, there has been no device in which the skirt rigidity is changed by changing the rigidity of the sidewall portion itself or the pitch of the sidewall portion. For example, if the skirt rigidity is changed by changing the thickness of the skirt portion 1 itself, problems such as insufficient running of the molten metal at the time of casting the piston occur. Then, problems such as insufficient running of the molten metal during casting do not occur. Further, since the area of the sliding surface of the skirt portion increases from the upper portion to the lower portion of the skirt portion, the force per unit area of the sliding surface of the skirt portion decreases, and the friction decreases. In addition, each first
Te which spreads upward at both circumferential edges of the portion 12a
Around the first portion 12a of the sidewall portion.
As the length and area in the direction increase,
Of the oil sump by the first portion 12a of the
Larger, the effect of preventing seizure on the skirt shoulder
It will be great.

[0018]

According to the present invention, the span between the supporting points at both ends of the arc-shaped beam composed of the skirt portion and the first portion provided at least corresponding to the upper portion of the skirt extends from the upper skirt portion to the lower skirt portion. Since the skirt portion is small, the rigidity of the skirt portion against the lateral force becomes large at the lower portion of the skirt, and becomes smaller as it goes upward. Due to this, the deformation of the lower part of the skirt when the piston skirt portion hits the cylinder bore wall surface is small, it is difficult to hit at the skirt shoulder, and even if it is the skirt shoulder, the skirt shoulder is relatively softly supported As a result, it is possible to prevent the oil film from being broken due to a large area. Also, since the retracted to the outer circumferential surface of the first portion of the sub id wall portion to the piston inside the circumferential direction extending surface of the skirt portion outer peripheral surface, the outer peripheral surface of the first portion functions as an oil groove,
Seizure of the upper part of the skirt portion, which becomes a problem due to high temperature, can be prevented. The clearance between the skirt and the cylinder bore wall escapes as in the prior art by preventing the deformation due to the skirt support rigidity of the sidewall portion, preventing the oil film from breaking, and preventing the seizure due to the oil groove effect on the outer peripheral surface of the first portion. Since it is no longer necessary to make the clearance larger than the required clearance, the clearance can be made substantially smaller than before, and the effects such as stability of the posture of the piston, reduction of the hitting force, reduction of the slap noise and the like can be obtained. In addition, because the oil film does not break, in addition to preventing seizure, heat escapes from the piston to the cylinder bore through the oil film, reducing the heat load on the piston.
The reliability of the piston is improved. Further, since the area of the sliding surface of the skirt is increased from the upper part of the skirt to the lower part, the friction at the lower part of the skirt is reduced. In addition, each
The taper that spreads upward at both circumferential edges of the part 1
, And the circumferential length of the first part was increased toward the top.
Therefore, the area of the first portion of the sidewall portion is larger as it goes upward.
The sump by the first part of the side wall part
Oil retention effect increases, and the skirt shoulder burns
The effect of preventing sticking is great.

[Brief description of the drawings]

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

FIG. 2 is a sectional view taken along line 2-2 of FIG.

FIG. 3 is a sectional view taken along line 3-3 in FIG. 1;

FIG. 4 is a schematic elevation view showing the relationship between the outer shape of the piston as viewed from the elevation and the cylinder bore wall surface.

FIG. 5 is a schematic plan view showing the relationship between the external shape of the piston in plan view and the cylinder bore wall surface.

FIG. 6 is a schematic elevation view showing a deformation of a conventional piston.

[Explanation of symbols]

Reference Signs List 2 piston for internal combustion engine 4 crown portion 6 pin boss portion 8 pin boss portion shaft core 10 skirt portion 12 sidewall portion 12a first portion 12b second portion 12c third portion (portion concavely curved toward the inside of the piston) Reference Signs List 20 inner wall surface of cylinder bore 22 outer peripheral surface of first portion 24 stepped portion

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A 2-99245 (JP, U) JP-A 2-80747 (JP, U) JP-A 57-156050 (JP, U) JP-A 62- 87147 (JP, U) JP-A 61-125646 (JP, U) JP-A 63-50445 (JP, Y2) (58) Fields investigated (Int. Cl. ⁶ , DB name) F16J 1/00-1 / 24 F02F 3/00

Claims (1)

(57) [Claims] 1. A crown portion, a pair of pin bosses formed integrally with a lower portion of the crown portion, and a pair of pin bosses formed integrally with a lower portion of the crown portion at a position orthogonal to the axis of the pair of pin boss portions. A piston for an internal combustion engine comprising a skirt portion, a sidewall portion connecting each skirt portion and each pin boss portion, wherein the sidewall portion is provided corresponding to at least an upper portion of the skirt and connected to the skirt portion. A first portion that extends in an arc shape in a tangential direction of the skirt portion and has an outer peripheral surface receded inward from a circumferential extension surface of the outer peripheral surface of the skirt portion, and a first portion that extends in an arc shape from the pin boss portion in connection with the pin boss portion 2
And portions, a third portion of the arc connecting the first and second portions have a both a first portion of said skirt portion and the sidewall portion
To the across support points span of the arcuate beams with small enough skirt bottom toward skirt downward from skirt upper constructed from the side
And the circumferential length of the skirt portion is
From the lower part of the skirt to the lower part of the skirt
In both cases, the circumferential direction of each first portion of the sidewall portion
Spreads from both sides of the skirt to the top of the skirt
Taper the length of the first part in the circumferential direction
A piston for an internal combustion engine, which is enlarged from a lower portion to an upper portion of a piston portion.