Piston for internal combustion engine

Abstract

To provide a piston capable of reducing oil rising to a combustion chamber due to oil scraping-up of a top ring when the piston rises, while restraining an increase in friction.SOLUTION: The piston 100 includes a flexible auxiliary ring side 35a formed in an annular shape having both end side walls and a side 35b, and a first groove 21 provided on an entire circumference of an outer peripheral portion 14 of the piston 100 and to which the auxiliary ring side 30S is slidably attached, and the first groove 21 has an inclined groove structure inclined with respect to a plane perpendicular to a central axis side X1 of the piston 100 so as to approach the crown surface side from a bottom side 21c toward an opening of the first groove 21. 30S.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a piston for an internal combustion engine, and more particularly to a piston for an internal combustion engine that reciprocates within a cylinder. [Background technology]

[0002] Pistons for internal combustion engines are equipped with multiple piston rings. The multiple piston rings include a compression ring and an oil ring attached to annular grooves on the crown side. The compression ring maintains airtightness and compresses the air-fuel mixture in the combustion chamber. The oil ring properly scrapes off oil to prevent excess oil from entering the combustion chamber. These piston rings are also required to have low friction to reduce fuel consumption, etc.

[0003] Regardless of the orientation of the cylinder, if we define the top dead center side of the piston as "up" and the bottom dead center side as "down," then when the piston descends, a certain amount of oil is scraped off by the oil ring, but when the piston rises, the compression ring, which is closest to the crown, slides across the cylinder bore first. Therefore, when the piston rises, the compression ring scrapes up the oil in the cylinder bore into the combustion chamber. When oil is scraped up into the combustion chamber, it burns, and by repeating this process, the amount of oil decreases.

[0004] Furthermore, the combustion of the oil that is stirred up can increase the amount of particulate matter in the exhaust gas or cause abnormal combustion. Patent Document 1 discloses an invention related to an auxiliary piston ring installed on the top land. It is believed that installing such an auxiliary piston ring has the effect of reducing to some extent the amount of oil that is stirred up into the combustion chamber when the piston rises. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-88104 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the auxiliary piston ring provided on the top land of the piston described in Patent Document 1 is in contact with the cylinder bore, although it has a lower tension than the compression ring, and therefore generates friction. In other words, the installation of the auxiliary piston ring increases friction by that amount. This is undesirable in the current situation where further reduction in piston friction is required to improve energy efficiency.

[0007] In order to solve the above problems, an object of the present invention is to prevent an increase in friction while reducing oil rising into the combustion chamber due to oil being scraped up by the top ring when the piston rises. [Means for solving the problem]

[0008] One embodiment of the present invention comprises: A piston for an internal combustion engine that reciprocates within a cylinder, an auxiliary ring that is an elastically deformable piston ring disposed closest to the piston crown and has both end portions and is formed in an annular shape; a first groove provided on the outer peripheral surface of the piston over the entire circumferential direction, into which the auxiliary ring is fitted, The first groove has an inclined groove structure that is inclined with respect to a plane perpendicular to the central axis of the piston so as to approach the crown surface side from the bottom toward the opening. [Effects of the Invention]

[0009] According to the piston for an internal combustion engine of the present invention, it is possible to prevent an increase in friction and reduce oil rising into the combustion chamber due to oil being scraped up by the top ring when the piston rises. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a partial cross-sectional view of a side surface of a piston according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of the auxiliary ring shown in FIG. [Figure 3] 3 is a cross-sectional view of the auxiliary ring shown in FIG. 2 taken along line BB. [Figure 4] 2 is an enlarged view of part A in FIG. 1, and is a conceptual diagram showing a state when the piston is positioned near the top dead center. [Figure 5] 2 is an enlarged view of part A in FIG. 1, and is a conceptual diagram showing a state when the piston is located near the bottom dead center. DETAILED DESCRIPTION OF THE INVENTION

[0011] <Embodiment> A piston 100 for an internal combustion engine that reciprocates within a cylinder according to an embodiment of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a partial cross-sectional side view of the piston 100, showing the piston 100 at a position between top dead center and bottom dead center. The piston 100 can be used in any type of internal combustion engine, such as an in-line, horizontally opposed, or V-type. The engine (not shown) is, for example, a four-stroke engine that repeats an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke. As is well known, the piston 100 is disposed in a cylinder bore 2 of the engine and is connected to a connecting rod (not shown) by a piston pin. In FIG. 1, the cylinder bore 2 is indicated by a dashed line.

[0012] 1, the piston 100 includes a piston body 10 and a plurality of piston rings attached to the piston body 10. That is, the piston 100 includes a top ring 30-1, a second ring 30-2, and an oil ring 30-3 as normal piston rings, and further includes an auxiliary ring 30S, which will be described later.

[0013] The piston 100 has a central axis X1 and is formed in a generally cylindrical shape. The piston body 10 includes, from the combustion chamber side, a top land portion 11, a second land portion 12, and a skirt portion 13. The piston body 10 also includes an outer circumferential portion 14 that extends from the top land portion 11 to the skirt portion 13. The piston body 10 is formed of metal, for example, an aluminum alloy.

[0014] A first groove 21 is formed in the outer peripheral portion 14 of the piston body 10 on the top land portion 11 side, and is provided around the entire circumferential direction on the outer peripheral surface of the piston 100. The first groove 21 has a first groove first surface 21a, which is an annular surface formed in the top land portion 11, and a first groove second surface 21b, which is an annular surface facing the first groove first surface 21a.

[0015] The entire opening 51 of the first groove 21 opens to the outer circumferential portion 14 of the piston 100, i.e., the side surface of the piston body 10. The first groove first surface 21a and the first groove second surface 21b each form an annular portion of a virtual cone shape centered on the central axis X1, extending toward the top land portion, in a radial range from a predetermined radial position to the opening 51, and covering the entire circumference around the central axis X1.

[0016] 4 and 5, the first groove first surface 21a and the first groove second surface 21b are each formed at an angle e with respect to a plane L perpendicular to the central axis X1. That is, the first groove first surface 21a and the first groove second surface 21b are inclined with respect to the plane L perpendicular to the central axis X1. As a result, the first groove 21 has an inclined groove structure inclined with respect to the plane perpendicular to the central axis X1 of the piston 100 so as to approach the crown surface side of the piston 100 from the bottom portion 21 toward the opening 51. The first groove 21 has a width that allows the auxiliary ring 30S to easily expand in diameter. Specifically, the first groove first surface 21a and the first groove second surface 21b are parallel to each other and are spaced apart so that the auxiliary ring 30S can slide within the groove. The first groove 21 has a depth that allows the tip 45 of the outer diameter portion 44 of the auxiliary ring 30S to move between contact and non-contact with the cylinder bore 2.

[0017] This allows the auxiliary ring 30S to operate as described below, i.e., when the piston 100 is not rising, the auxiliary ring 30S fits into the bottom 21c of the first groove 21, and during the stroke to the top dead center, the auxiliary ring 30S can elastically deform in the radially expanding direction.

[0018] The piston body 10 is provided with grooves 22-1 to 22-3 in which a top ring 30-1, a second ring 30-2, and an oil ring 30-3 are respectively attached. Note that these piston rings can be the same as those in a conventional piston ring installation structure. That is, opposing surfaces in the grooves 22-1 to 22-3 are formed as surfaces parallel to a plane L perpendicular to the central axis X1 shown in FIG. 4.

[0019] The auxiliary ring 30S will be described in detail below with reference to Figures 1, 2, and 3. Figure 2 is a plan view of the auxiliary ring 30S, and Figure 3 is a cross-sectional view taken along line B-B of Figure 2. The auxiliary ring 30S is the piston ring located closest to the top surface and is formed in an annular shape with both ends 35a, 35b. The auxiliary ring 30S is also made of a flexible material, and the auxiliary ring 30S with both ends can expand its outer diameter by bending. This auxiliary ring 30S reduces the amount of oil scraped up by the top ring 30-1 when the piston 100 rises, thereby reducing oil rising into the combustion chamber.

[0020] In its normal state, the auxiliary ring 30S has a shape corresponding to the internal shape of the first groove 21, and is formed in the shape of a generally truncated cone, a short cylinder whose diameter gradually increases from its inner diameter portion to its outer diameter portion. The auxiliary ring 30S has an inner diameter portion 41 and an outer diameter portion 44 that is continuous with the outer diameter side of the inner diameter portion 41. As shown in FIG. 1 , in a cross section of the auxiliary ring 30S taken along a plane parallel to the central axis X1, the inner diameter portion 41 is rectangular, and the outer diameter portion 44 is tapered to a tip portion 45.

[0021] In a cross section of the auxiliary ring 30S taken along a plane parallel to the central axis X1, the radial center axis of the inner diameter portion 41 and the radial center axis of the outer diameter portion 44 are coaxial and are indicated as X2. That is, the auxiliary ring 30S has a central axis X2 in a cross section of the auxiliary ring 30S taken along a plane parallel to the central axis X1. Therefore, the auxiliary ring 30S has a substantially truncated conical short cylindrical shape corresponding to the shape of the first groove 21 having the inclined groove structure as described above, and therefore can move smoothly relative to the first groove first surface 21a and the first groove second surface 21b.

[0022] The outer diameter of the auxiliary ring 30S is the normal outer diameter without deformation due to deflection when it is in a non-diameter-expanded state where no external force such as inertial force is acting on the auxiliary ring 30S. The outer diameter portion 44 of the auxiliary ring 30S is tapered up to the tip end 45, so even when it is in contact with the cylinder bore 2, the contact area is small, and friction can be reduced as much as possible.

[0023] 1 can be of a general structure as described above, and the top ring 30-1 and the second ring 30-2 are formed into annular shapes with opposite ends. Both the top ring 30-1 and the second ring 30-2 are compression rings that, as is well known, keep the combustion chamber airtight and reduce leakage of combustion gas from the combustion chamber to the crankcase (not shown).

[0024] As shown in Fig. 1, the end faces of the top ring 30-1, second ring 30-2, and oil ring 30-3 have the same shape as that of the auxiliary ring 30S, but their cross-sectional shapes are flat, unlike those of the auxiliary ring 30S. These rings have shapes corresponding to the grooves 22-1, 22-2, and 22-3 into which they are fitted. In Fig. 1, reference numerals 52, 53, and 54 denote the openings of the grooves 22-1, 22-2, and 22-3, respectively.

[0025] The oil ring 30-3, like the top ring 30-1 and the second ring 30-2, is formed in an annular shape with both ends. As is well known, the oil ring 30-3 is a ring that scrapes off excess oil adhering to the cylinder bore 2. The oil ring 30-3 also forms an oil film of appropriate thickness between the cylinder bore 2 and the outer circumferential surface of the piston body 10.

[0026] The end faces of the top ring 30-1, second ring 30-2, oil ring 30-3, and auxiliary ring 30S do not necessarily have to be formed in the same shape, and may be oil rings formed in a two-piece structure or a three-piece structure as is well known.

[0027] The top ring 30-1, second ring 30-2, and oil ring 30-3 are elastically deformable in the radial direction and are formed so that they are constantly in contact with the cylinder bore 2 due to tension. Therefore, the top ring 30-1, second ring 30-2, and oil ring 30-3 constantly slide on the inner surface of the cylinder bore 2 when the piston 100 strokes up and down.

[0028] The auxiliary ring 30S, the top ring 30-1, the second ring 30-2, and the oil ring 30-3 are made of metal, such as cast iron or steel. The steel is, for example, stainless steel, silicon chrome steel, or carbon steel.

[0029] [Explanation of the movement of the auxiliary ring 30S] The movement of the auxiliary ring 30S will be described with reference to the relevant figures. When the auxiliary ring 30S is attached to the piston 100, a tension T acts on the auxiliary ring 30S in the direction of its inner diameter. As shown in FIG. 1, when no external force such as an inertial force is acting on the auxiliary ring 30S, the auxiliary ring 30S is formed to have an outer diameter slightly smaller than the cylinder bore 2. In other words, when no external force is acting on the auxiliary ring 30S while it is attached to the piston 100, the auxiliary ring 30S is in a non-contact state where it does not come into contact with the cylinder bore 2.

[0030] In a four-stroke engine, the compression stroke, combustion stroke, exhaust stroke, and intake stroke occur in two revolutions. The compression stroke and exhaust stroke are strokes in which the piston 100 ascends, and the combustion stroke and intake stroke are strokes in which the piston 100 descends. Oil scraping by the top ring 30-1 can occur during the piston's ascending stroke, i.e., the compression stroke and exhaust stroke. The auxiliary ring 30S elastically deforms radially outward and protrudes during the ascending stroke, reducing oil leakage into the combustion chamber. Furthermore, during the descending stroke, the auxiliary ring 30S elastically deforms radially inward, eliminating contact with the cylinder bore 2 and reducing friction. In a two-stroke engine, the ascending and descending strokes occur in one revolution. Even when the present invention is applied to a two-stroke engine, the same effects as those of a four-stroke engine can be obtained during the ascending and descending strokes.

[0031] [When piston 100 is on its upward stroke] FIG. 1 shows the state when the piston 100 is ascending from bottom dead center to top dead center. As the piston 100 moves from bottom dead center to top dead center, the auxiliary ring 30S is loaded into the first groove 21 and moves in the same upward direction as the piston body 10. The piston 100, which has been moving upward, passes the midpoint between top dead center and bottom dead center, where it reaches its maximum speed, and its moving speed temporarily becomes zero at top dead center, so the piston 100 decelerates as it approaches top dead center. At the beginning of this upward stroke, the outer diameter of the auxiliary ring 30S is approximately in its initial state. In this state, as shown in FIG. 1, the auxiliary ring 30S is not in contact with the first groove first surface 21a and is in a non-contact state.

[0032] [When the piston is near top dead center] FIG. 4 is an enlarged view of portion A in FIG. 1, showing the state of the auxiliary ring 30S when the piston 100 is positioned approximately at top dead center. When the piston 100 reaches near top dead center, the piston speed becomes approximately zero. The auxiliary ring 30S, which has been moving upward together with the piston body 10, continues to move due to the inertial force F1 acting on the auxiliary ring 30S even after the piston body 10 stops. Therefore, the auxiliary ring 30S moves upward within the first groove 21 and abuts against the first groove first surface 21a. FIG. 4 shows the state in which the auxiliary ring 30S abuts against the first groove first surface 21a.

[0033] The first groove first surface 21a and the first groove second surface 21b are formed to form an angle e with respect to a plane perpendicular to the central axis X1. The inertial force F1 has a component force F2 parallel to the first groove first surface 21a and a component force F3 perpendicular to the first groove first surface 21a. Therefore, the component force F2 overcomes the tension T acting radially inward, and the auxiliary ring 30S expands in diameter from its initial state over the entire circumference. The auxiliary ring 30S slides on the first groove first surface 21a while contacting the first groove first surface 21a while expanding in diameter. The auxiliary ring 30S in its expanded diameter state has a larger outer diameter than the initial state when no external force is applied, and therefore protrudes radially outward more than the auxiliary ring 30S in its initial state. As a result, the tip 45 of the outer diameter portion 44 of the auxiliary ring 30S approaches the cylinder bore 2 from the initial state and acts as a wall that blocks the oil, thereby blocking the oil scooped up by the top ring 30-1. Finally, the entire circumference of the expanded diameter auxiliary ring 30S abuts against the cylinder bore 2.

[0034] [When piston 100 is on its downward stroke] The piston 100 passes top dead center and begins to move downward. It passes the midpoint between top dead center and bottom dead center, where it reaches its maximum speed, and gradually decelerates as it approaches bottom dead center. Figure 1 shows the state during the upward stroke, as well as the state during the downward stroke. During this downward stroke, the inertial force F1 acting on the auxiliary ring 30S disappears, and the outer diameter of the auxiliary ring 30S is approximately at its initial state. Therefore, the auxiliary ring 30S is not in contact with the cylinder bore 2.

[0035] [When the piston is near bottom dead center] FIG. 5 is an enlarged view of portion A in FIG. 1, showing the state of the auxiliary ring 30S when the piston 100 is positioned approximately at bottom dead center. When the piston 100 reaches approximately bottom dead center, the piston speed becomes approximately zero. The auxiliary ring 30S, which has been moving downward together with the piston body 10, continues to move due to inertial force F4 acting on the auxiliary ring 30S, even after the piston body 10 stops. As a result, the auxiliary ring 30S moves downward within the small gap in the first groove 21 and comes into contact with the first groove second surface 21b. FIG. 5 shows the state in which the auxiliary ring 30S is in contact with the first groove second surface 21b.

[0036] The inertial force F4 has a component F5 parallel to the first groove second surface 21b and a component F6 perpendicular to the first groove second surface 21b. The inertial forces F4, F5, and F6 are opposite in direction to the inertial forces F1, F2, and F3 when the piston is near top dead center. The component F5 is directed inward during the downward stroke. Therefore, the component F5 acts radially inward on the auxiliary ring 30S, causing it to shrink in diameter from its initial state over its entire circumference. The auxiliary ring 30S slides on the first groove second surface 21b while contacting the first groove second surface 21b while shrinking in diameter. The outer diameter of the auxiliary ring 30S in the reduced diameter state is equal to or smaller than the outer diameter in the initial state when no external force is acting, and is therefore pulled inward more than the auxiliary ring 30S in its initial state. The outer diameter of the auxiliary ring 30S becomes smaller than that in the initial state, and the entire circumference does not abut on the cylinder bore 2, resulting in a non-contact state.

[0037] During the downward stroke of combustion, pressure due to combustion (explosion) acts on the auxiliary ring 30S as combustion pressure. The combustion pressure acts primarily in the direction F7, which is the vertical direction, on the top surface of the auxiliary ring 30S, which faces the combustion chamber. Part of the combustion pressure also acts in the direction F8 toward the piston crown surface from the contact point of the tip end 45 of the auxiliary ring 30S with the cylinder bore 2. However, part of the combustion pressure also flows around the gap between the top surface of the auxiliary ring 30S and the first groove first surface 21a, and acts in the direction F9 from the end face of the inner diameter portion 41 of the auxiliary ring 30S that faces the bottom 21c of the first groove 21. Therefore, the combustion pressure only acts in the direction pressing the auxiliary ring 30S against the second surface 21b of the first groove 21, and does not substantially act in either the diameter expansion or contraction direction.

[0038] [Factors influencing the elasticity change of the auxiliary ring 30S] Next, factors that are thought to affect the amount of change in radial elasticity of the auxiliary ring 30S will be described.

[0039] The piston 100 is affected by the angle e between the first groove first surface 21a and the first groove second surface 21b and the plane L perpendicular to the central axis X1, the mass of the auxiliary ring 30S, and the tension of the auxiliary ring 30S. The coefficient of friction between the auxiliary ring 30S and the first groove first surface 21a and the first groove second surface 21b is also influential. It is believed that the larger the angle e, the larger the mass of the auxiliary ring 30S, and the smaller the coefficient of friction, the greater the amount of elastic deformation of the auxiliary ring 30S. The tension of the auxiliary ring 30S is also affected by the material, cross-sectional shape, and other factors.

[0040] With regard to engines, factors such as engine speed, piston stroke, and explosion pressure during combustion have an effect. The higher the engine speed, the greater the deceleration when reaching top dead center, and the greater the amount of elastic change. Also, long-stroke engines with a larger piston stroke have a greater deceleration when reaching top dead center, and the greater the amount of elastic change. Also, the higher the combustion (explosion) pressure during combustion, the greater the component force F8 of the combustion pressure F7, and the greater the force acting in the direction of diameter contraction. Explosion pressure during combustion is related to factors such as the compression ratio.

[0041] Taking the above influencing factors into consideration, it is possible to create the optimal auxiliary ring 30S that combines the effect of preventing oil leakage with low friction.

[0042] As described above, with the piston 100 according to this embodiment, when the piston rises, the auxiliary ring 30S elastically deforms within the first groove 21 and slides in the radially expanding direction due to the inertial force generated when the piston reaches top dead center and is stopped, causing the outer diameter portion 44 to protrude outward from the outer peripheral surface of the piston 100. As a result, the tip end 45 of the outer diameter portion 44 of the auxiliary ring 30S comes into contact or nearly contacts the cylinder bore 2, and if oil is scraped up by the top ring 30-1 during the piston rise, the auxiliary ring 30S can block the oil. This makes it possible to reduce oil spillage into the combustion chamber while suppressing an increase in friction.

[0043] Furthermore, during the reciprocating motion of the piston 100, the auxiliary ring 30S is in an expanded-diameter state in which the outer diameter portion 44 moves in a direction toward contact with the cylinder bore 2 within a predetermined piston stroke range including top dead center, and is in a contracted-diameter state in a direction away from the cylinder bore 2 within a predetermined piston stroke range including bottom dead center. In this manner, the auxiliary ring 30S contracts in diameter and fits into the bottom portion 21c of the first groove 21 when the piston 100 is not ascending, thereby being out of contact with the cylinder bore 2 and suppressing an increase in friction. Furthermore, with the piston 100 of this embodiment, the inertial force generated when stroking toward top dead center allows the auxiliary ring 30S to smoothly elastically deform in the expanded diameter direction.

[0044] In addition, the auxiliary ring 30S in this embodiment is elastically deformable and has a shape that corresponds to the internal shape of the first groove 21, so that under normal conditions when no load is applied, it is housed within the first groove 21. Furthermore, the auxiliary ring 30S is formed symmetrically with respect to the central axis X1, so that it can stably abut against the cylinder bore 2 without wobbling even during high-speed rotation.

[0045] Furthermore, the auxiliary ring 30S of this embodiment has a tapered outer diameter portion 44, and therefore, even when the auxiliary ring 30S is in contact with the cylinder bore 2, the contact area is small, thereby minimizing friction.

[0046] [Modifications of the present invention] In addition to the configurations described above, the present invention can be partially modified as follows.

[0047] In the above explanation, the expanded diameter of the auxiliary ring 30S is such that the entire circumference of the tip end 45 of the outer diameter portion 44 of the auxiliary ring 30S contacts the cylinder bore 2. However, this amount of elastic deformation may be changed. For example, the amount of expansion of the auxiliary ring 30S may be reduced by reducing the amount of elastic deformation, so that only a portion of the auxiliary ring 30S comes into contact when expanded. Alternatively, even if the entire circumference of the tip end 45 of the auxiliary ring 30S does not contact the cylinder bore 2 when an external force, i.e., an inertial force, is applied, the effect of reducing oil leakage can be achieved by simply narrowing the gap between the auxiliary ring 30S and the cylinder bore 2 to a certain extent.

[0048] If the auxiliary ring 30S is not in complete contact as described above, there is an advantage that there is greater freedom in designing it to meet other performance requirements that the auxiliary ring 30S must meet, such as wear resistance.

[0049] The present invention is not limited to the above-described embodiment and modifications, and various modifications are possible without departing from the spirit of the invention. [Explanation of symbols]

[0050] 1 engine 2 cylinder bore 10 piston body, 11 Topland Department 21 First groove 21a 1st groove 1st surface 21b 1st groove 2nd surface 30 Piston rings 30S auxiliary ring 41 Inner diameter 44 Outer diameter part 45 Tip 100 pistons

Claims

1. A piston for an internal combustion engine that reciprocates within a cylinder, an auxiliary ring that is an elastically deformable piston ring disposed closest to the piston crown and has both end portions and is formed in an annular shape; a first groove provided on the outer peripheral surface of the piston over the entire circumferential direction, and into which the auxiliary ring is fitted, a piston for an internal combustion engine, characterized in that the first groove has an inclined groove structure inclined with respect to a plane perpendicular to a central axis of the piston so as to approach the crown surface side from the bottom toward the opening thereof.

2. 2. The piston for an internal combustion engine according to claim 1, wherein the first groove has a width that allows the auxiliary ring to easily expand in diameter and a depth that allows the outer edge of the auxiliary ring to move between contact and non-contact with the cylinder bore.

3. 3. The piston for an internal combustion engine according to claim 1, wherein the auxiliary ring has a shape corresponding to the internal shape of the first groove in a normal state, and is formed in a substantially truncated conical, short cylindrical shape whose diameter gradually increases from an inner diameter portion to an outer diameter portion.

4. 3. The piston for an internal combustion engine according to claim 1, wherein the outer diameter portion of the auxiliary ring is formed so that a cross section taken along a plane parallel to a central axis of the auxiliary ring is tapered.

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