JP5551541B2 - Piston of internal combustion engine - Google Patents

Description

  The present invention relates to a piston of an internal combustion engine, and more particularly to a technique for improving lubricity in a piston skirt portion.

  In a reciprocating type internal combustion engine, combustion resistance and inertial force act alternately on the piston, so that frictional resistance and striking noise are likely to occur on the thrust side and anti-thrust side of the piston skirt. The thrust side and the anti-thrust side are both orthogonal to the axis of the piston pin. The thrust force acts on the thrust side when the piston descends, and the thrust force acts on the anti-thrust side when the piston rises. To do.

  In order to reduce friction loss and hammering sound of the piston, the cross section of the piston skirt is formed along an ellipse having a focal point on the piston axial center orthogonal to the piston pin, and the ellipticity of this piston skirt is at least the piston. There has been proposed a piston which is changed from the lower side to the upper side within a range facing the side of the pin so as to approach a perfect circle (see Patent Document 1). According to this piston, when the upper part of the piston skirt part approaches a perfect circle, the surface pressure of the part is reduced, while the contact area in the circumferential direction is reduced by increasing the ellipticity of the lower part of the piston skirt part. This reduces friction loss.

Japanese Patent Laid-Open No. 3-199655

  In the piston of Patent Document 1, the problem related to lubrication as described below may occur due to the large ellipticity of the lower portion of the piston skirt. That is, on the thrust side of the piston skirt, when the piston pressed against the cylinder moves from the top dead center side to the bottom dead center side, the engine oil flows from the central portion to the side, and the central portion at the bottom dead center. The oil film becomes very thin. As a result, when the piston moves from the bottom dead center side to the top dead center side, an oil film break occurs, the piston skirt portion and the cylinder inner wall are likely to be worn, and the friction loss may also increase.

  The present invention has been made in view of such a background, and an object of the present invention is to provide a piston of an internal combustion engine that realizes improved lubricity in a piston skirt portion.

  In the first aspect of the present invention, a piston (1) of an internal combustion engine that reciprocates in a cylinder (2) and has a thrust side skirt (7) below a piston ring (4-6) on the thrust side. The thrust-side skirt portion (7) has a vertical cross-sectional shape having different profiles at a circumferential center and a circumferential side, and the longitudinal-sectional shape at the circumferential center is different from that of the cylinder (2). A central-side bulging portion (11) having the smallest clearance is provided, and is formed so that the clearance with the cylinder (2) increases from the central-side bulging portion (11) upward, and the circumferential direction The lateral longitudinal cross-sectional shape is such that side bulging portions (12, 13) having the smallest clearance with the cylinder (2) are provided above the central bulging portion (11), and the side Side bulge 12, 13) and a cross section passing through the side bulging portion (12, 13) of the thrust side skirt portion (7) so that the clearance with the cylinder (2) increases from the bottom toward the bottom. The shape is formed such that the clearance with the cylinder (2) increases from the side bulged portion (12, 13) toward the center in the circumferential direction.

  According to the present invention, in the thrust side skirt portion (7), when the piston (1) moves from the top dead center side to the bottom dead center side, the central bulge portion (11) and the lateral bulge portion ( 12, 13), the engine oil is guided, and the oil film breakage hardly occurs when the piston (1) moves from the bottom dead center side to the top dead center side.

It is a perspective view which shows the piston which concerns on embodiment. It is a front view which shows the piston which concerns on embodiment. FIG. 3 is a sectional view taken along line III-III in FIG. 2. It is IV-IV sectional drawing in FIG. It is VV sectional drawing in FIG. It is VI-VI sectional drawing in FIG. It is VII-VII sectional drawing in FIG. It is explanatory drawing which shows the effect | action of embodiment.

  Hereinafter, an embodiment in which the present invention is applied to a piston for a reciprocating engine will be described in detail with reference to the drawings. In the description of the embodiment, the upper side in FIG. 2 is the upper side, the left side is the left side, and the front side of the page is the front side.

<< Configuration of Embodiment >>
As shown in FIGS. 1 and 2, the piston 1 of the present embodiment is slidably held by a cylinder 2 and is connected to a crankshaft (not shown) via a connecting rod 3. The piston 1 has three piston rings 4 to 6 (4 and 5 are compression rings, and 6 is an oil ring) mounted on the upper part thereof. The piston 1 has a thrust side skirt 7 formed below the piston rings 4 to 6 at the front thereof, and is connected to the connecting rod 3 by a piston pin 8.

<Center side bulge>
At the lower part of the thrust side skirt portion 7, a central side bulging portion 11 bulging in the radial direction is provided at the center in the circumferential direction. As shown in FIGS. 3 and 5, the central side bulging portion 11 bulges a predetermined amount (for example, about 10 μm) from the thrust side skirt portion 7 toward the inner wall surface 2 a of the cylinder 2 (that is, the central side bulging portion). The clearance with the inner wall surface 2a of the cylinder 2 is reduced at the protruding portion 11). Then, at the center in the circumferential direction of the thrust side skirt portion 7, the clearance gradually increases from the center side bulging portion 11 upward. The bulging amount of the central bulging portion 11 is very small, but is schematically illustrated in FIGS. 1 to 3 and 5.

<Side bulge>
On the upper side of the thrust side skirt portion 7 (that is, the side closer to the piston rings 4 to 6 than the central side bulging portion 11), the left and right side bulging portions bulging in the radial direction on both circumferential side edges. 12 and 13 are provided. As shown in FIGS. 4 and 6, the left and right side bulging portions 12 and 13 are also formed from the thrust side skirt portion 7 to the inner wall surface 2 a of the cylinder 2 in the same manner as the outer peripheral surface 11 a of the central bulging portion 11 described above. A predetermined amount (for example, about 10 μm) bulges to the side (that is, the clearance with the inner wall surface 2a of the cylinder 2 is reduced at the left and right side bulging portions 12 and 13). Then, on the side in the circumferential direction of the thrust side skirt portion 7, the clearance gradually increases downward from the side side bulging portions 12 and 13. In addition, although the bulging amount of the side bulging parts 12 and 13 is very small, like the central bulging part 11, it is typically drawn in FIGS.

  As shown in FIG. 7, the center-side bulging portion 11 and the right-side bulging portion 13 are smoothly continuous with the clearance slightly increased in the middle. In addition, between the center side bulging part 11 and the left side bulging part 12 is also smoothly continuous, as between the center side bulging part 11 and the right side bulging part 13.

<< Operation of Embodiment >>
When the piston starts to reciprocate in the cylinder 2 by starting the engine and the piston 1 descends from the top dead center side to the bottom dead center side in the intake stroke and the expansion stroke, the thrust side skirt portion 7 is moved to the inner wall surface 2a of the cylinder 2. It is pressed by thrust force. At this time, in the present embodiment, as shown by smudging in FIG. 8, the engine oil present between the inner wall surface 2 a of the cylinder 2 and the thrust side skirt portion 7 is left and right side bulging portions 12, After being guided to the center in the circumferential direction of the thrust side skirt portion 7 by 13, it is held above the center side bulging portion 11. When the piston 1 rises from the bottom dead center side to the top dead center side in the compression stroke and the exhaust stroke, the engine oil held above the central bulging portion 11 of the thrust side skirt portion 7 is retained in the cylinder 2. Flows between the inner wall surface 2a and the thrust side skirt 7.

  In this embodiment, by adopting such a configuration, the oil film breakage during the ascent of the piston 1 is effectively suppressed, and wear of the thrust side skirt portion 7 and the inner wall surface 2a of the cylinder 2 is less likely to occur. Friction loss can also be reduced.

  Although the description of the specific embodiment is finished as described above, the present invention is not limited to the above embodiment and can be widely modified. For example, the bulging amount from the thrust side skirt portion of the central side bulging portion or the side side bulging portion can be appropriately set according to the properties of the engine oil and the like. In addition, the specific shape and the like of the piston can be appropriately changed depending on the design and manufacturing convenience.

DESCRIPTION OF SYMBOLS 1 Piston 2 Cylinder 4 Piston ring 7 Thrust side skirt part 11 Center side bulging part 12, 13 Side side bulging part

Claims (1)

A piston of an internal combustion engine that reciprocates in a cylinder and has a thrust side skirt portion below a piston ring on the thrust side,
Vertical cross section of the thrust side skirt portion has a different profile in the circumferential direction central and circumferential both sides edge,
The longitudinal cross-sectional shape at the center in the circumferential direction is provided with a central bulging portion that provides the smallest clearance with the cylinder, and from the central bulging portion toward the upper side that is closer to the piston ring . Formed so that the clearance gradually increases,
Longitudinal sectional shape of the circumferential both side edge, said central-side protruding portion lateral side expansion clearance smallest left and right with the cylinder upwards is provided than the left and right lateral side Rise It is formed so that the clearance with the cylinder gradually increases downward from the protruding portion,
The center side bulge and the left and right side bulges are smoothly continuous,
The cross-sectional shape passing through the left and right side bulges of the thrust side skirt is formed so that the clearance from the cylinder increases from each side bulge toward the center in the circumferential direction. A piston for an internal combustion engine characterized by the above.

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