JP2010112324A - Piston of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid the occurrence of excessive sliding resistance when bearing pressure of a piston ring to a cylinder bore becomes excessively high on the thrust side. <P>SOLUTION: A ring groove 23 for fitting and inserting the piston ring 15 is arranged on the outer periphery of a piston 3. This ring groove is formed so that the depth becomes larger than a part positioned in the crankshaft direction orthogonal to at least the thrust/anti-thrust direction in a thrust side part. The ring groove is particularly formed so that an external shape of a bottom surface in a view in the piston axis direction forms a substantially elliptic shape with the thrust/anti-trust direction as a short diameter. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a piston of an internal combustion engine.

  The piston of an internal combustion engine is provided with a piston ring for the purpose of a gas seal or an oil seal, and this piston ring is accommodated in a cylinder bore so as to be elastically deformed in the direction of diameter reduction (elastic deformation). The ring groove is recessed in the outer periphery of the piston so that the piston ring is pressed against the cylinder bore and the piston ring surface pressure is secured against movement. Are loosely fitted.

The ring groove in which the piston ring is loosely fitted in this way is generally formed so that the depth (radial width) is uniform over the entire circumference. A technique is known in which an elliptical shape is long in the thrust / anti-thrust direction as viewed in the piston axial direction (Patent Document 1). According to this, there is an advantage that it is possible to avoid interference between the piston ring and the bottom surface of the ring groove due to large thermal expansion that occurs on the side where there is no skirt that promotes heat radiation to the cylinder side.
JP 2004-308568 A

  However, in the piston of an internal combustion engine, when the piston is pressed by the combustion pressure during the expansion stroke, a thrust load (lateral force) in the direction of pressing the piston against the cylinder bore is generated due to the inclination of the connecting rod, and this thrust load is received. On the other hand, on the so-called thrust side, there is a problem that the surface pressure of the piston ring against the cylinder bore increases and excessive sliding resistance occurs.

  To solve this problem, if the outer shape of the bottom surface of the ring groove is an ellipse that is long in the thrust / anti-thrust direction as in the prior art, the ring groove becomes shallow on the thrust side. When the ring is pushed into the ring groove, the piston ring easily abuts against the bottom surface of the ring groove, and the surface pressure of the piston ring against the cylinder bore increases.

  The present invention has been devised to solve such problems of the prior art, and its main purpose is to increase the surface pressure of the piston ring against the cylinder bore on the thrust side, resulting in excessive sliding resistance. An object of the present invention is to provide a piston for an internal combustion engine configured so as to avoid occurrence.

  In order to solve such a problem, in the present invention, as shown in claim 1, a ring groove (23) into which a piston ring (15) is fitted is provided on the outer periphery of the piston (3). However, in the thrust side portion, the depth is at least larger than the portion located in the crankshaft direction orthogonal to the thrust / anti-thrust direction.

  According to this, on the thrust side, the width (diameter dimension) of the gap between the piston ring and the bottom surface of the ring groove is increased, so that a large amount of movement of the piston ring relative to the piston can be ensured, and thereby the piston relative to the cylinder bore. Since an increase in the surface pressure of the ring is suppressed, the occurrence of excessive sliding resistance can be avoided.

  In the piston of the internal combustion engine, as shown in claim 2, the ring groove is formed so that the outer shape of the bottom surface in the piston axial direction has a substantially elliptical shape with a short diameter in the thrust / anti-thrust direction. It can be configured.

  According to this, manufacture is easy and an increase in manufacturing cost can be suppressed.

  In the piston of the internal combustion engine, as shown in claim 3, the ring groove may be formed so that the depth on the thrust side portion is larger than the depth on the anti-thrust side portion.

  According to this, generation | occurrence | production of excessive sliding resistance on the thrust side can be suppressed further reliably.

  In the piston of the internal combustion engine, as shown in claim 4, the piston ring is interposed between an outer ring (21) slidably contacting the cylinder bore (2a), and the outer ring and the bottom surface of the ring groove. And an expander (22) for urging the outer ring outward.

  According to this, since the amount of deformation of the expander changes depending on the width of the gap between the inner peripheral surface of the outer ring and the bottom surface of the ring groove where the expander is sandwiched, the tension of the expander depends on the depth of the ring groove. Can be adjusted. For this reason, the urging force of the expander can be optimized over the entire circumference by changing the depth of the ring groove in accordance with the circumferential position.

  Thus, according to the present invention, on the thrust side, since the width (diameter dimension) of the gap between the piston ring and the bottom surface of the ring groove is increased, it is possible to ensure a large amount of movement of the piston ring relative to the piston, As a result, an increase in the surface pressure of the piston ring with respect to the cylinder bore is suppressed, so that an excessive sliding resistance can be avoided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a main part of an internal combustion engine to which a piston according to the present invention is applied. In this internal combustion engine, a cylindrical sleeve 2 forming a cylinder bore 2 a is provided in a cylinder block 1, and a piston 3 is slidably accommodated in the sleeve 2. An upper end of a connecting rod 5 is connected to the piston 3 via a piston pin 4, and a lower end of the connecting rod 5 is connected to a crankshaft 7 via a crank pin 6.

  A cylinder head (not shown) provided with an intake port and an exhaust port that are opened and closed by an intake valve and an exhaust valve, respectively, is coupled to the upper side of the cylinder block 1. A combustion chamber 9 is defined by the cylinder bore 2a.

  The piston 3 includes a top portion 11 on which the pressure of the combustion gas acts, a pair of skirt portions 12 provided in a manner suspended from the top portion 11, and a pair of portions provided in a manner to connect the pair of skirt portions 12 to each other. A side wall portion 13 and a pair of pin boss portions 14 provided on the pair of side wall portions 13 are provided. Piston rings 15 to 17 are respectively attached to the outer periphery of the top portion 11. The piston rings 15 and 16 are compression rings, and the piston ring 17 is an oil ring.

  In such an internal combustion engine, when the piston 3 is pressed by the combustion pressure during the expansion stroke, the connecting rod 5 is inclined to generate a thrust load (lateral force) in a direction in which the piston 3 is pressed against the cylinder bore 2a. On the side receiving the thrust load, the so-called thrust side, the surface pressure of the piston rings 15 to 17 with respect to the cylinder bore 2a increases, and the sliding resistance increases.

  FIG. 2 is a cross-sectional view showing the piston shown in FIG. 1 cut along a plane perpendicular to the center line and passing through the ring groove. FIG. 3 is a longitudinal sectional view showing a main part on the thrust side of the piston shown in FIG. 2 cut along a plane along the center line of the piston.

  The piston ring 15 is fitted and inserted into a ring groove 23 that is annularly recessed on the outer peripheral surface of the piston 3, and an outer ring 21 that is in sliding contact with the cylinder bore 2 a and a space between the outer ring 21 and the bottom surface of the ring groove 23. And an expander 22 that urges the outer ring 21 radially outward. Both the outer ring 21 and the expander 22 have a C shape with a part cut away.

  The expander 22 has a polygonal shape in which a plurality of bent portions 22a are formed at a predetermined interval. The expander 22 is elastically deformed by being sandwiched between the outer ring 21 and the bottom surface of the ring groove 23, so that the outer Tension (spring urging force) that urges the ring 21 in the direction in which the ring 21 is pressed against the cylinder bore 2a is generated, and the outer ring 51 itself that is elastically deformed in the diameter reducing direction by being accommodated in the cylinder bore 2a cooperates with the tension generated. Thus, the surface pressure of the outer ring 21 against the cylinder bore 2a is secured.

  In this way, the outer ring 21 is pressed against the cylinder bore 2a by the tension of the outer ring 21 itself and the tension of the expander 22, but when a thrust load is applied to the piston 3, the outer ring 21 and the expander are on the thrust side. Since the thrust load is added to the tension of 22, the surface pressure of the outer ring 21 against the cylinder bore 2a increases.

  4 is a schematic cross-sectional view showing the outer shape of the bottom surface of the ring groove shown in FIG. The ring groove 23 is formed so that the depth on the thrust side portion is greater than at least the portion located in the axial direction of the crankshaft 7 orthogonal to the thrust / anti-thrust direction. In particular, here, the outer shape of the bottom surface of the ring groove 23 when viewed in the piston axial direction is formed so as to form a substantially elliptical shape having a short diameter in the thrust / anti-thrust direction. It has a substantially elliptical shape at the center, and the depth of the ring groove 23 is the same in the thrust side portion and the anti-thrust side portion. The piston axial direction is the direction in which the piston 3 slides, and is the axial direction of the cylinder bore 2a.

  Therefore, the depth d of the ring groove 23 becomes maximum at the angular position (α = 0 °) in the thrust direction, and the angle α away from this center, that is, the angle α formed with the thrust direction becomes large. And becomes minimum at the angular position (α = 90 °) in the axial direction of the crankshaft 7 orthogonal to the thrust direction. Since the outer ring 21 has a uniform cross section in the circumferential direction and the width (diameter dimension) is uniform in the circumferential direction, the outer ring 21 on the thrust side according to the depth d of the ring groove 23. The gap between the inner surface of the outer ring 21 and the bottom surface of the ring groove 23 (radial dimension) is in the thrust direction and the anti-thrust direction, as shown in FIG. The maximum value Cmax is obtained at the angular position, and the value C becomes smaller as the distance from the angular position increases.

  FIG. 5 is a cross-sectional view showing the main part on the thrust side of the piston according to the present invention shown in FIG. 2 and a comparative example according to the conventional configuration. FIG. 5A shows the case according to the present invention, and FIG. Each case is shown.

  In the expander 22, the inner surface of the straight portion 22 b corresponding to the polygon side abuts against the bottom surface of the ring groove 23, and the outer surface of the bent portion 22 a corresponding to the apex of the polygon abuts against the inner surface of the outer ring 21. The outer ring 21 is bent and deformed by being sandwiched between the inner surface of the outer ring 21 and the bottom surface of the ring groove 23 to generate a tension that urges the outer ring 21 outward, and the bottom surface of the ring groove 23 and the inner surface of the outer ring 21 are As the gap distance (diameter dimension) C increases, the amount of flexure deformation of the expander 22 decreases, and the tension of the expander 22 decreases accordingly.

  As shown in FIG. 5 (B), in the piston 51 according to the conventional configuration, the depth d of the ring groove 52 and the gap C between the bottom surface of the ring groove 52 and the inner surface of the outer ring 21 are uniform over the entire circumference. On the other hand, as shown in FIG. 5 (A), in the piston 3 according to the present invention, the depth d of the ring groove 23 is formed on the thrust side so that the outer ring 21 and the ring groove 23 The clearance C between the bottom surface and the bottom surface is increased, whereby the amount of deformation of the expander 22 on the thrust side is reduced, and the tension of the expander 22 is reduced. For this reason, on the thrust side, the surface pressure of the outer ring 21 with respect to the cylinder bore 2a becomes low, and it can be avoided that excessive sliding resistance is generated.

  As described above, the width of the gap between the outer ring 21 having a substantially circular shape and the bottom surface of the ring groove 23 having a substantially elliptical shape is maximum at the center position in the minor axis direction, that is, the thrust / anti-thrust direction. Since it becomes a state that becomes narrower as it moves away from here, the surface pressure distribution that changes according to the width of the gap becomes smooth, and it is avoided that the sliding resistance of the outer ring 21 with respect to the sleeve 2 is locally increased. Can do.

  FIG. 6 is a schematic cross-sectional view showing another example of the outer shape of the bottom surface of the ring groove according to the present invention. In the example shown in FIG. 4, the outer shape of the bottom surface of the ring groove 23 is formed in a substantially elliptical shape with a short axis in the thrust / anti-thrust direction, and the depth of the ring groove 23 is between the thrust side portion and the anti-thrust side. 6A, in the example shown in FIG. 6A, the outer shape of the bottom surface of the ring groove 23 is a substantially elliptical shape centered on the center O1 that is shifted from the center O of the piston 3 to the anti-thrust side. The depth d of the ring groove 23 is larger at the thrust side than at the anti-thrust side and gradually decreases from the thrust side to the anti-thrust side.

  In the example shown in FIG. 6B, the outer shape of the bottom surface of the ring groove 23 is a half region on the thrust side, and is a substantially semi-elliptical shape with the center O of the piston as the center and the short axis in the thrust / anti-thrust direction. In the half region on the anti-thrust side, it has a substantially semicircular shape centered on the center O of the piston. On the thrust side half surface where α = 0 to 90 °, the depth d of the ring groove 23 is While gradually decreasing from the thrust side to the anti-thrust side, the depth d of the ring groove 23 is constant on the anti-thrust side half of α = 90 to 180 °.

  In the above example, the outer shape of the bottom surface of the ring groove is substantially elliptical, but the present invention is not limited to this. Here, the ring groove 23 is deepened on the thrust side so that the surface pressure of the outer ring 21 with respect to the cylinder bore 2a does not become excessive on the thrust side, and the ring groove so that the surface pressure does not change abruptly according to the circumferential position. What is necessary is just to make it the depth of 23 change gradually, and various curves are possible.

  FIG. 7 is a schematic longitudinal sectional view of a main part showing another example of a piston according to the present invention and a comparative example according to a conventional configuration, and (A-1) and (A-2) are cases according to the present invention. , (A-1) shows a normal state, and (A-2) shows a state in which a thrust load is applied. (B-1) and (B-2) are cases according to the conventional configuration, and (B-1) shows a normal state and (B-2) shows a state in which a thrust load is applied.

  In the above example, the combination piston ring including the outer ring 21 and the expander 22 is used. However, here, the structure does not include the expander. In such a configuration, the air layer 74 in the gap between the bottom surface of the ring groove 72 formed in the piston 71 and the piston ring 73 functions as an air spring, and when a thrust load is applied to the piston 71, the piston ring 73 is moved inward. Since it is pushed in and the air layer 74 is compressed accordingly, a compression reaction force is generated by the air spring.

  Here, as shown in FIG. 7 (B-1), in the conventional configuration in which the gap between the bottom surface of the ring groove 77 formed in the piston 75 and the piston ring 78 is small, the bottom surface of the ring groove 77 and the piston ring 78 Since the air layer 79 in the gap is small, as shown in FIG. 7B-2, when the piston ring 78 is pushed inward by the thrust load, the compression reaction force by the air spring increases rapidly, and the piston ring 78 A high surface pressure is generated between the cylinder bore 2a and an excessive sliding resistance.

  On the other hand, as shown in FIG. 7A-1, in the configuration according to the present invention, the air layer 74 in the gap between the piston ring 73 and the bottom surface of the ring groove 72 is large. Furthermore, when the piston ring 73 is pushed inward by thrust load, even if the piston ring 73 moves as much as the example of FIG. 7 (B-2), the volume reduction rate from the example of FIG. 7 (B-2). Therefore, the compression reaction force by the air spring is also reduced, the surface pressure between the piston ring 73 and the cylinder bore 2a is low, and it is possible to avoid the occurrence of excessive sliding resistance.

  As mentioned above, although the example regarding the top ring which is a compression ring by the side of a combustion chamber among piston rings with which a piston is mounted was demonstrated, the same structure can be employ | adopted also about a second ring.

It is sectional drawing which shows the principal part of the internal combustion engine to which the piston by this invention is applied. FIG. 2 is a cross-sectional view showing the piston shown in FIG. 1 cut along a plane perpendicular to the center line and passing through the ring groove. FIG. 3 is a longitudinal sectional view showing a main part on the thrust side of the piston shown in FIG. 2 cut along a plane along the center line of the piston. FIG. 3 is a schematic cross-sectional view showing the outer shape of the bottom surface of the ring groove shown in FIG. 2. It is a cross-sectional view which shows the principal part by the side of the thrust of the piston by this invention shown in FIG. 2, and the comparative example by a conventional structure. It is a typical cross-sectional view which shows another example regarding the external shape of the bottom face of the ring groove | channel by this invention. It is a typical principal part longitudinal cross-sectional view which shows another example of the piston by this invention, and the comparative example by a conventional structure.

Explanation of symbols

2 Sleeve, 2a Cylinder bore 3 Piston 4 Piston pin 7 Crankshaft 15-17 Piston ring 21 Outer ring 22 Expander, 22a Bent part, 22b Straight part 23 Ring groove

Claims (4)

  A ring groove into which the piston ring is inserted is provided on the outer periphery, and this ring groove is formed so that the depth on the thrust side is greater than at least the part located in the crankshaft direction perpendicular to the thrust / anti-thrust direction. Piston characterized by being made.   2. The piston according to claim 1, wherein the ring groove is formed so that an outer shape of a bottom surface when viewed in the piston axial direction has a substantially elliptical shape with a short diameter in a thrust / anti-thrust direction.   3. The piston according to claim 1, wherein the ring groove is formed to have a depth greater in a thrust side portion than in an anti-thrust side portion. 4.   The piston ring includes an outer ring that is in sliding contact with a cylinder bore, and an expander that is interposed between the outer ring and a bottom surface of the ring groove and biases the outer ring outward. The piston according to any one of claims 1 to 3.

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