Combination of piston unit, top land member and parts for piston unit

Abstract

A piston unit that reciprocates in a cylinder comprises a piston and a top bank member attached to the piston, the piston comprising a first portion including an end portion on one end face side of the piston and to which the top bank member is attached, the outer diameter of the first portion being smaller than the outer diameter of a second portion of the piston excluding the first portion, so that a step is formed between the first portion and the second portion, the top bank member comprising a groove wall forming surface, the groove wall forming surface being opposite to a step surface connecting an outer peripheral surface of the first portion and an outer peripheral surface of the second portion, and a first annular groove being defined by the groove wall forming surface, the step surface and the outer peripheral surface of the first portion.

Description

Technical Field

[0001] The present invention relates to a piston unit, a top land component and a combination of parts for the piston unit. Background Art

[0002] As a mechanism for reciprocating a piston in a cylinder, a reciprocating engine, a pneumatic device, etc. are known. In an internal combustion engine as an example of a reciprocating engine, a piston ring that slides on the inner wall surface of the cylinder is attached to one or more annular grooves formed on the outer peripheral surface of the piston from the viewpoint of ensuring sealing performance and reducing friction.

[0003] In a general internal combustion engine, such as a gasoline engine, a combination of piston rings including a compression ring (pressure ring) and an oil ring is used. In the axial direction of the piston, the compression ring is arranged on the combustion chamber side, and the oil ring is arranged on the crank chamber side, and they exert their power by sliding on the inner wall surface of the cylinder. The oil ring farthest from the combustion chamber has an oil sealing function that suppresses the oil from flowing out to the combustion chamber side (oil rise) by scraping off the excess engine oil (lubricating oil) attached to the inner wall surface of the cylinder to the crank side, and prevents the sintering of the piston accompanying the operation of the internal combustion engine by adjusting the oil amount so that the lubricating oil film is properly maintained on the inner wall surface of the cylinder. The compression ring has an air sealing function that suppresses the combustion gas from flowing out (gas leakage) from the combustion chamber side to the crank chamber side by maintaining airtightness, and an oil sealing function that suppresses the oil rise by scraping off the excess oil that the oil ring has not completely scraped off.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 61-232366

[0007] Patent Document 2: Japanese Utility Model Publication No. 61-047456

[0008] Patent Document 3: Japanese Patent Application Publication No. 2020-049536

[0009] Patent Document 4: Japanese Utility Model Publication No. 60-098748 Summary of the invention

[0010] Problems to be solved by the invention

[0011] In the existing piston, a portion (top land) whose outer diameter is larger than the inner diameter of the piston ring is formed between the annular groove closest to the top surface of the piston and the top surface. Therefore, when the piston ring is attached to the annular groove, the joint of the piston ring needs to be expanded so that the inner diameter of the piston ring is larger than the outer diameter of the top land. At this time, if the expansion amount of the joint is too large, the piston ring may be deformed and damaged due to stress. In addition, in the existing piston, due to the existence of the top land, it is difficult to install a piston ring without a joint.

[0012] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a technology that can easily mount a piston ring in a piston unit that reciprocates in a cylinder.

[0013] Solutions for solving problems

[0014] In order to solve the above problems, the present invention adopts the following structure. That is, the present invention is a piston unit that reciprocates in a cylinder, wherein the piston unit comprises: a piston; a top land member attached to the piston; one or more annular grooves formed on the outer periphery of the piston; and one or more piston rings attached to a first annular groove closest to one end face of the piston among the one or more annular grooves, and slides on the inner wall surface of the cylinder, the piston having a first portion, the first portion including an end portion on the one end face side of the piston, and the first portion being attached to the top land member, the outer diameter of the first portion being smaller than the outer diameter of a second portion of the piston other than the first portion, so that a step is formed between the first portion and the second portion, the top land member having a groove wall forming surface, the groove wall forming surface being opposite to a step surface connecting the outer peripheral surface of the first portion and the outer peripheral surface of the second portion, and the first annular groove being defined by the groove wall forming surface, the step surface, and the outer peripheral surface of the first portion.

[0015] That is, the piston unit of the present invention forms the portion between one end face of the piston and the first annular groove, namely the top land, by means of a top land component that is separate from the piston. Therefore, the piston ring can be installed on the piston without the top land component attached. Thus, during installation, there is no need to stretch the piston ring in such a way that the inner diameter of the piston ring becomes larger than the outer diameter of the top land, so even if the piston ring does not have a seam, it can be easily installed. In addition, according to the piston unit of the present invention, even if the piston ring has a seam, during installation, there is no need to stretch the seam in such a way that the inner diameter of each ring becomes larger than the outer diameter of the top land, so deformation and breakage of the ring caused by excessive stretching of the seam can be prevented. Therefore, according to the piston unit of the present invention, the piston ring can be easily installed.

[0016] In addition, the piston unit of the present invention may also include one or more spacer rings, which are attached to the first annular groove in a manner of being arranged along the axial direction of the piston together with the one or more piston rings, and the spacer ring is embedded in the outer peripheral surface of the first part in a manner of leaving a prescribed interval between the spacer ring and the inner wall of the cylinder.

[0017] Furthermore, in the present invention, at least one of the one or more partition rings may not have a seam.

[0018] Furthermore, in the present invention, a plurality of piston rings may be mounted on the first annular groove, and the spacer ring may be arranged between a piston ring closest to the one end face of the piston and a piston ring second closest to the one end face among the plurality of piston rings.

[0019] Furthermore, in the present invention, the land member may be formed as a ring having an inner peripheral surface of an annular piston fitting surface that fits with an outer peripheral surface of the first portion.

[0020] Furthermore, in the present invention, the top bank member may include: an annular portion having an annular piston fitting surface as an inner peripheral surface that fits with the outer peripheral surface of the first portion; and a cover portion that is disposed on the inner side of the annular portion and abuts against the one end surface of the piston.

[0021] Furthermore, the piston unit of the present invention may be attached to a cylinder of an internal combustion engine.

[0022] In addition, the present invention can also be specifically attached to a top bank member of a piston that reciprocates in a cylinder. In the present invention, one or more annular grooves can be formed on the outer periphery of the piston, the piston has a first portion, the first portion includes an end portion on one end face side of the piston, and the first portion is for the top bank member to be attached, the outer diameter of the first portion is smaller than the outer diameter of the second portion of the piston except the first portion, so that a step is formed between the first portion and the second portion, the first annular groove closest to the one end face of the piston among the one or more annular grooves is attached with one or more piston rings that slide on the inner wall surface of the cylinder along the axial arrangement of the piston, the top bank member of the present invention has a groove wall forming surface, the groove wall forming surface is opposite to the step surface that connects the outer peripheral surface of the first portion and the outer peripheral surface of the second portion, and the first annular groove is defined by the groove wall forming surface, the step surface and the outer peripheral surface of the first portion.

[0023] In addition, the present invention can also be specifically a combination of the above-mentioned parts for the piston unit. That is, the present invention can also be a combination of parts for the piston unit, which comprises: a top bank member, which is attached to a piston that reciprocates in a cylinder; and one or more piston rings, which are attached to a first annular groove closest to one end face of the piston among one or more annular grooves formed on the outer periphery of the piston, and slide on the inner wall surface of the cylinder, the piston having a first portion, the first portion including an end portion on the side of the one end face of the piston, and the first portion is for the top bank member to be attached, the outer diameter of the first portion is smaller than the outer diameter of a second portion of the piston other than the first portion, so that a step is formed between the first portion and the second portion, the top bank member having a groove wall forming surface, the groove wall forming surface is opposite to a step surface connecting the outer peripheral surface of the first portion and the outer peripheral surface of the second portion, and the first annular groove is defined by the groove wall forming surface, the step surface, and the outer peripheral surface of the first portion.

[0024] Effects of the Invention

[0025] According to the present invention, a piston ring can be easily installed in a piston unit that reciprocates in a cylinder. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a cross-sectional view of an internal combustion engine including a piston unit according to an embodiment.

[0027] Figure 2 It is a partial cross-sectional view of an internal combustion engine including a piston unit according to an embodiment.

[0028] Figure 3 It is a cross-sectional view for explaining the first annular groove in the embodiment.

[0029] Figure 4 The diagram is for illustrating variations of the fitting method between the top land member and the piston.

[0030] Figure 5 It is a plan view schematically illustrating the shape of a partition ring according to the embodiment.

[0031] Figure 6 It is a partial cross-sectional view of an internal combustion engine including a piston unit according to Modification 1 of the embodiment.

[0032] Figure 7 It is a partial cross-sectional view of an internal combustion engine including a piston unit according to a second modification of the embodiment.

[0033] Figure 8 It is a partial cross-sectional view of an internal combustion engine including a piston unit according to a third modification of the embodiment.

[0034] Fig. 9It is a cross-sectional view of an internal combustion engine including a piston unit according to a fourth modification of the embodiment.

[0035] Fig.10 It is a partial cross-sectional view of an internal combustion engine including a piston unit according to a fourth modification of the embodiment.

[0036] Fig.11 The diagram is for illustrating variations of the fitting method between the top land member and the piston. DETAILED DESCRIPTION

[0037] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are embodiments in which the technology of the present invention is applied to an internal combustion engine as an example of a reciprocating engine. However, the technology of the present invention is not limited to application to internal combustion engines, and the technology of the present invention can be applied to any mechanism in which a piston reciprocates in a cylinder. As application objects of the technology of the present invention, for example, reciprocating engines such as internal combustion engines, pneumatic equipment such as compressors, etc. can be listed. In addition, unless otherwise specified, the configurations described in the following embodiments are not intended to limit the technical scope of the invention to only this.

[0038] [Overall composition]

[0039] Figure 1 It is a cross-sectional view of an internal combustion engine 100 including a piston unit 20 according to the embodiment. Figure 2 It is a partial cross-sectional view of an internal combustion engine 100 including a piston unit 20 according to the embodiment. Figure 1 and Figure 2 The middle figure shows a cross section along the central axis A1 of the piston 1. Figure 1 and Figure 2 As shown, the internal combustion engine 100 of the embodiment includes a cylinder 10 and a piston unit 20 attached to the cylinder 10. The internal combustion engine 100 is configured such that the piston unit 20 reciprocates in the cylinder 10. Hereinafter, in the internal combustion engine 100, the combustion chamber side indicated by the reference numeral 30 is set as the upper side, and the crank chamber side indicated by the reference numeral 40 is set as the lower side.

[0040] like Figure 1 and Figure 2 As shown, the piston unit 20 comprises: a piston 1; a top bank member 2, attached to the piston 1; a first annular groove 3, formed on the outer periphery of the piston 1; a plurality of piston rings 4, 5, 6, attached to the first annular groove 3; and a plurality of separator rings 7, 8, attached to the first annular groove 3 in a manner of being arranged along the axial direction of the piston 1 together with the plurality of piston rings 4, 5, 6. The top bank member 2, the piston rings 4, 5, 6, and the separator rings 7, 8 can be referred to as parts for the piston unit. The details will be described later. The first annular groove 3 is formed on the outer periphery of the piston 1 as a space surrounded by the groove wall forming surface 24 of the top bank member 2, the step surface 14 of the piston 1, and the first outer peripheral surface 12 (refer to Figure 3 The piston unit 20 of the embodiment is configured such that a combination of three piston rings, including two compression rings (pressure rings) and one oil ring 6 , is mounted in the first annular groove 3 , wherein the two compression rings include a top ring 4 and a second ring 5 .

[0041] In this specification, when explaining without distinguishing the top ring 4, the second ring 5, and the oil ring 6, they are simply referred to as "piston rings". Figure 1 , Figure 2 The state in which the piston 1 (piston unit 20) with the piston rings and the separator rings installed as shown is attached (inserted) to the cylinder 10 is referred to as the "use state". Figure 2 As shown in FIG. 1 , the direction along the central axis of the piston 1 (axial direction) is defined as the “up-down direction”. In addition, in the axial direction of the piston 1, the combustion chamber 30 side ( Figure 1 The upper side in the figure is defined as the “upper side”, and the opposite side of the combustion chamber 30 side, that is, the crank chamber 40 side ( Figure 1 The lower side in (a) is defined as the “lower side”. Hereinafter, each structure of the piston unit 20 will be described.

[0042] [piston]

[0043] like Figure 1 As shown, the piston 1 has a roughly stepped cylindrical shape. The reference symbol A1 represents the central axis of the piston 1. The end surface on the combustion chamber 30 side (that is, the upper end surface) of the two axial end surfaces of the piston 1 forms the top surface 11 of the piston 1. The top surface 11 is formed as a flat surface orthogonal to the axial direction of the piston 1, facing the combustion chamber 30. The top surface 11 is equivalent to the "one end surface of the piston" in the present invention. However, the "one end surface of the piston" in the present invention is not limited to the top surface, as long as it is any end surface of the two axial end surfaces of the piston. A hollow portion 1c opening at the lower end surface and a pin hole 1d penetrating from the hollow portion 1c to the outside of the piston 1 are formed in the piston 1. A piston pin (not shown) is embedded in the pin hole 1d. The piston 1 is connected to the crankshaft via the piston pin. It should be noted that in the present invention, the mechanism for transmitting the power of the piston is not particularly limited. It can be a mechanism that converts the reciprocating motion of the piston into rotational motion through a piston / crank mechanism (slider crank mechanism) and a yoke mechanism, or it can be a crankless mechanism that does not use a connecting rod or a crank.

[0044] like Figure 1As shown, the piston 1 is divided into a first portion 1a and a second portion 1b in the axial direction thereof. The first portion 1a is a cylindrical portion including the upper end portion (the end portion on the top surface 11 side) of the piston 1 and having a predetermined length. The second portion 1b is a cylindrical portion of the piston 1 other than the first portion 1a, and is formed at a position lower than the first portion 1a. The outer peripheral surface of the first portion 1a is referred to as the first outer peripheral surface and is indicated by the reference numeral 12. In addition, the outer peripheral surface of the second portion 1b is referred to as the second outer peripheral surface and is indicated by the reference numeral 13. Here, the outer diameter of the first portion 1a (i.e., the maximum diameter of the first outer peripheral surface 12) is set to D1, and the outer diameter of the second portion 1b (i.e., the maximum diameter of the second outer peripheral surface 13) is set to D2. At this time, in the piston 1, D1<D2. That is, the outer diameter of the first portion 1a is smaller than the outer diameter of the second portion 1b. Therefore, as Figure 1 As shown, a radial step is formed between the first outer peripheral surface 12 and the second outer peripheral surface 13. The first outer peripheral surface 12 is located radially inward of the second outer peripheral surface 13. The first outer peripheral surface 12 and the second outer peripheral surface 13 are connected via a step surface 14. The step surface 14 of this example is formed as a flat surface that is orthogonal to the axial direction of the piston 1. However, the step surface of the present invention is not limited to this. It should be noted that the connecting portion (corner) between the first outer peripheral surface 12 and the step surface 14 can also be a rounded surface shape or a chamfered surface shape.

[0045] like Figure 2 As shown, the first outer peripheral surface 12 includes a straight surface 121 and a tapered surface 122. The straight surface 121 is connected to the inner peripheral edge of the step surface 14 and extends from the inner peripheral edge of the step surface 14 to the upper side along the axial direction of the piston 1. The tapered surface 122 connects the upper end of the straight surface 121 to the outer peripheral edge of the top surface 11 of the piston 1 and is inclined in a manner that the diameter decreases as it approaches the top surface 11 side (approaching the center axis A1). In addition, the second outer peripheral surface 13 is connected to the outer peripheral edge of the step surface 14 and extends to the lower side along the axial direction of the piston 1. In the internal combustion engine 100, a predetermined separation distance is ensured between the second outer peripheral surface 13 of the piston 1 and the inner wall surface 101 of the cylinder 10, thereby forming a piston gap PC1.

[0046] [Top shore components]

[0047] The top bank member 2 is a member that functions as a substitute for the top bank by being attached to the first portion 1a of the piston 1. The top bank member 2 of the embodiment is formed into a ring. However, the shape of the top bank member of the present invention is not limited to a ring shape. The top bank member 2 of this example does not have a seam, but is continuous throughout the entire circumference. The top bank member 2 has a bank outer peripheral surface 21, a piston fitting surface 22, a bank end surface 23, and a groove wall forming surface 24.

[0048] The land end surface 23 is formed as the upper end surface of the top land member 2, and faces the combustion chamber 30. The top surface (upper end surface) of the piston unit 20 is composed of the land end surface 23 of the top land member 2 and the top surface 11 of the piston 1. The land end surface 23 of this example is formed as a flat surface orthogonal to the axial direction of the piston 1, but the present invention is not limited to this.

[0049] The groove wall forming surface 24 is formed as the lower end surface of the top land member 2 and faces the crank chamber 40 side. Figure 2 As shown, the groove wall forming surface 24 is spaced apart from the step surface 14 of the piston 1 and faces the step surface 14. The groove wall forming surface 24 of this example is formed parallel to the step surface 14, but the present invention is not limited thereto and may be inclined relative to the step surface 14.

[0050] The piston fitting surface 22 is formed in an annular shape as the inner peripheral surface of the top bank member 2. The piston fitting surface 22 fits into the conical surface 122 in the first outer peripheral surface 12 of the first portion 1a, thereby fixing the top bank member 2 to the first portion 1a of the piston 1. The piston fitting surface 22 of the top bank member 2 is in close contact with the first outer peripheral surface 12 of the piston 1. The piston fitting surface 22 is in contact with the first outer peripheral surface 12 throughout the entire circumference. It should be noted that as a method of installing the top bank member 2 to the piston, examples thereof include heat press fitting, friction joining, screw fastening, screwing in, bonding, welding, etc., but are not limited thereto.

[0051] The piston fitting surface 22 is inclined in a manner that the diameter decreases as it approaches the upper side corresponding to the shape of the tapered surface 122. By fitting the piston fitting surface 22 and the tapered surface 122 in this way, the top bank member 2 is supported from the lower side by the tapered surface 122. As a result, the top bank member 2 can be restricted from moving in a direction away from the top surface 11 (downward), and a predetermined separation distance can be ensured between the groove wall forming surface 24 and the step surface 14.

[0052] Figure 4 2 is a diagram for illustrating a variation of the engagement method between the top bank member 2 and the piston 1. Figure 4 As shown in (A), the first outer peripheral surface 12 of the piston 1 and the piston fitting surface 22 of the top bank member 2 can also be formed as a surface extending along the axial direction. Figure 4 As shown in (B), the downward movement of the top bank member 2 can also be restricted by providing a radial step that can receive the top bank member 2 at the first portion 1a. Figure 4 As shown in (C), the downward movement of the top bank member 2 can also be restricted by making a portion of the inner circumference of the top bank member 2 protrude radially inward and providing a radial step at the first portion 1a that can receive the portion of the top bank member 2. Figure 4 As shown in (D), the piston fitting surface 22 of the top land member 2 may be formed to be partially inclined so that a portion fits in the straight surface 121 and another portion fits in the tapered surface 122 .

[0053] The bank outer peripheral surface 21 is formed as the outer peripheral surface of the top bank member 2. A part of the outer peripheral surface of the piston unit 20 is constituted by the bank outer peripheral surface 21. In more detail, the bank outer peripheral surface 21 functions as the outer peripheral surface of the top bank. Here, the outer diameter of the top bank member 2 (that is, the maximum diameter of the bank outer peripheral surface 21) is set to be smaller than the inner diameter of the inner wall surface 101 of the cylinder 10. Therefore, a prescribed separation distance is ensured between the bank outer peripheral surface 21 of the top bank member 2 and the inner wall surface 101 of the cylinder 10. In other words, the top bank member 2 is separated from the inner wall surface 101 of the cylinder 10. In addition, the outer diameter of the top bank member 2 is set to be larger than the inner diameter of the piston rings 4, 5, and 6.

[0054] like Figure 2 As shown, the top bank member 2 is attached to the first portion 1a in a manner that ensures a specified separation distance between the groove wall forming surface 24 and the step surface 14 in the axial direction of the piston 1, and a first annular groove 3 that can attach a piston ring and a separator ring is formed on the outer periphery of the piston 1. Figure 3 It is a cross-sectional view for explaining the first annular groove 3 according to the embodiment. Figure 3 The area shown by the dot pattern in FIG. 1 is the first annular groove 3. Figure 3 As shown, the first annular groove 3 is defined by the groove wall forming surface 24 of the top bank member 2, the step surface 14 of the piston 1, and the first outer peripheral surface 12 (more specifically, the straight surface 121). In the first annular groove 3, the groove wall forming surface 24 functions as the inner wall on the upper side, the step surface 14 functions as the inner wall on the lower side, and the straight surface 121 of the first outer peripheral surface 12 functions as the bottom wall. Such a first annular groove 3 is formed on the entire circumference of the piston 1 as a groove with a rectangular cross section extending in an annular shape around the axis of the piston 1. Since the piston fitting surface 22 contacts the first outer peripheral surface 12 in a manner throughout the entire circumference, the oil in the first annular groove 3 can be prevented from flowing out from between the piston 1 and the top bank member 2.

[0055] The material of the top land member 2 is not particularly limited, and for example, steel, cast iron, Cu alloy, or aluminum alloy can be used. For example, the material of the top land member 2 can also be a material having a linear expansion coefficient different from that of the material of the piston 1.

[0056] In addition, a coating including at least one of a resin coating, a nitriding coating, an anodized coating, a plating coating, a PVD (Physical Vapor Deposition) coating, a coating, and a DLC (Diamond Like Carbon) coating may be formed on the surface of the top bank member 2. It should be noted that a "resin coating" refers to a coating formed by a resin material. In addition, a "nitriding coating" refers to a coating formed by allowing nitrogen to penetrate into the metal surface through a nitriding treatment. In addition, a "plating coating" refers to a coating formed by plating, and examples thereof include a "Ni-P plating coating" and a "chrome plating coating". A "Ni-P plating coating" refers to a coating formed by plating Ni-P. "Ni-P plating" is, for example, electroless Ni-P plating, but is not limited thereto. In addition, a "chrome plating coating" refers to a coating formed by chrome plating. Chromium plating is also referred to as industrial chrome plating. In addition, "PVD (physical vapor deposition) treatment coating" refers to a coating formed by the PVD method. In addition, "DLC (Diamond Like Carbon) coating" refers to an amorphous hard carbon film mainly composed of hydrocarbons and carbon allotropes. Such a coating is preferably formed on the contact portion between the top bank member 2 and other components, namely, the piston fitting surface 22 and the groove wall forming surface 24. By forming such a coating, the wear resistance of the top bank member 2 can be improved, and the adhesion of the top bank member 2 and other components can be prevented. Defects caused by direct contact between the base materials can be prevented.

[0057] In addition, a heat insulating layer may be provided on the bank end surface 23 and the bank outer peripheral surface 21 of the top bank member 2 facing the combustion chamber 30. The "heat insulating layer" mentioned here is formed of a raw material that can make the heat transfer between the combustion chamber 30 and the top bank member 2 lower than the state in which the heat insulating layer is not formed. The heat insulating layer may be composed of, for example, a hot-dip layer of a ceramic material (alumina, zirconia, etc.). By providing the heat insulating layer on the bank end surface 23 of the top bank member 2, the temperature rise of the piston 1 can be suppressed.

[0058] [Piston ring]

[0059] The piston rings 4, 5, 6 are sliding members mounted on the piston 1 attached to the cylinder 10 of the internal combustion engine 100 and sliding on the inner wall surface 101 of the cylinder 10 as the piston 1 reciprocates. In the piston unit 20 of the embodiment, three piston rings 4, 5, 6 are attached to one first annular groove 3.

[0060] like Figure 2As shown, the top ring 4 is a compression ring installed at the position closest to the top surface 11 of the piston 1 (that is, the uppermost position) among the three piston rings. The top ring 4 of this example is formed in a so-called rectangular shape, and its cross section is rectangular. The top ring 4 has an outer peripheral surface 41, an inner peripheral surface 42, an upper surface 43 and a lower surface 44. The axial width of the top ring 4 is defined by the upper surface 43 and the lower surface 44. The outer peripheral surface 41 is formed as a curved barrel surface in a manner protruding radially outward. The top ring 4 is installed on the piston 1 in the internal combustion engine 100 in the following manner: the upper surface 43, which is one of the two end surfaces in the axial direction, faces the upper side, and the lower surface 44, which is the other end surface in the axial direction, faces the lower side, and the outer peripheral surface 41 is in sliding contact with the inner wall surface 101 of the cylinder 10. In addition, the top ring 4 has self-tensioning force, so that the outer peripheral surface 41 presses the inner wall surface 101 of the cylinder 10 in the use state. As a result, an air sealing function and an oil sealing function can be obtained. It should be noted that the shape of the top ring of the present invention is not limited to the above. Various shapes can be used as the top ring. For example, the outer peripheral surface of the top ring can also be a straight surface or a cone. In addition, the cross-sectional shape of the top ring can also be a keystone, a half keystone, or an internal bevel.

[0061] like Figure 2 As shown, the second ring 5 is a compression ring installed at the second position closest to the top surface 11 of the piston 1 among the three piston rings. That is, the second ring 5 is installed between the top ring 4 and the oil ring 6. The second ring 5 has an outer peripheral surface 51, an inner peripheral surface 52, an upper surface 53 and a lower surface 54. The axial width of the second ring 5 is defined by the upper surface 53 and the lower surface 54. The second ring 5 is formed in a so-called rectangular shape, and the outer peripheral surface 51 of the second ring 5 has a tapered shape inclined in a manner that increases in diameter as it approaches the lower side. The second ring 5 is installed on the piston 1 in the internal combustion engine 100 in the following manner: the upper surface 53, which is one of the two end surfaces in the axial direction, faces the upper side, and the lower surface 54, which is the other of the two end surfaces in the axial direction, faces the lower side, and the outer peripheral surface 51 is in sliding contact with the inner wall surface 101 of the cylinder 10. In addition, the second ring 5 has self-tensioning force, so that the outer peripheral surface 51 presses the inner wall surface 101 of the cylinder 10 in the use state. As a result, the gas sealing function and the oil sealing function can be obtained. It should be noted that the shape of the second ring of the present invention is not limited to the above. Various shapes can be used as the second ring. For example, the outer peripheral surface of the second ring can also be a barrel surface, or a straight surface. In addition, the second ring can also be an oil scraper ring with an undercut, or a nose ring (Napier Ring). In addition, the cross-sectional shape of the second ring can also be a trapezoid, a semi-trapezoid, or an inner bevel.

[0062] like Figure 2As shown, the oil ring 6 is the piston ring installed at the position farthest from the top surface 11 of the piston 1 (that is, the lowermost position) among the three piston rings. The oil ring 6 is a so-called three-piece combined oil ring, such as Figure 2 As shown, the oil ring 6 includes a pair of scrapers 61U and 61L (an example of a pair of sliding portions) and a spacer expander 62 (an example of an expander).

[0063] A pair of scrapers 61U, 61L are formed into a ring shape around the axis of the oil ring 6, and are independently arranged along the axial direction. The upper scraper 61U is arranged on the upper side of the spacer expander 62, and the lower scraper 61L is arranged on the lower side of the spacer expander 62. The oil ring 6 of this example has a pair of scrapers 61U, 61L of the same shape. However, the shapes of the pair of scrapers of the present invention can also be different. Hereinafter, when the pair of scrapers 61U, 61L are not distinguished, they are simply referred to as scrapers 61. Figure 2 As shown, the scraper 61 has an outer peripheral surface 611, an inner peripheral surface 612, an upper surface 613 and a lower surface 614. The axial width of the scraper 61 is defined by the upper surface 613 and the lower surface 614. The scraper 61 is mounted on the piston 1 in the internal combustion engine 100 in the following manner: the upper surface 613, which is one of the two axial end surfaces, faces upward, and the lower surface 614, which is the other of the two axial end surfaces, faces downward, and the outer peripheral surface 611 is in sliding contact with the inner wall surface 101 of the cylinder 10. The spacer expander 62 is provided between a pair of scrapers 61U and 61L, and has a self-tensioning force so as to expand the diameter in the use state. As a result, the upper scraper 61U and the lower scraper 61L are urged radially outward by the spacer expander 62, and the outer peripheral surface 611 presses the inner wall surface 101 of the cylinder 10. As a result, the oil sealing function can be obtained. It should be noted that the shape of the oil ring of the present invention is not limited to the above content. The oil ring may be a so-called two-piece oil ring, for example. A two-piece oil ring refers to an oil ring that has an oil ring body formed in an annular shape around an axis and a spiral expander (an example of an expander) that applies force to the oil ring body radially outward, and a pair of rails (an example of a pair of sliding parts) that protrude radially outward are formed on the oil ring body along the axial direction of the oil ring. In addition, the oil ring may be a form that does not have a spacer expander or a spiral expander and functions as a single body.

[0064] [Separator Ring]

[0065] The spacer rings 7 and 8 are annular members that are attached to the first annular groove 3 in a manner arranged along the axial direction of the piston 1 together with one or more piston rings (piston rings 4, 5, and 6 in this example), thereby functioning as a substitute for the piston land. The spacer rings 7 and 8 in this example are formed into a so-called rectangular shape, and their cross-sections orthogonal to the circumferential direction are rectangular. However, the present invention is not limited to this.

[0066] like Figure 2 As shown, in the piston unit 20 , a spacer ring 7 is arranged between the top ring 4 and the second ring 5 , and a spacer ring 8 is arranged between the second ring 5 and the oil ring 6 , whereby the first annular groove 3 is divided.

[0067] like Figure 2 As shown, the partition rings 7 and 8 each have an outer peripheral separation surface S1, an inner peripheral fitting surface S2, an upper side partition wall surface S3 and a lower side partition wall surface S4. In the use state, the upper side partition wall surface S3 faces the combustion chamber 30 side, and the lower side partition wall surface S4 faces the crank chamber 40 side. The inner peripheral fitting surface S2 is provided on the inner peripheral portion of the partition rings 7 and 8, and is fitted into the straight surface 121 in the first outer peripheral surface 12 of the first portion 1a in the use state, thereby forming a contact state between it and the first outer peripheral surface 12. The inner peripheral fitting surface S2 of this example contacts the first outer peripheral surface 12 in a manner that covers the entire circumference. However, the present invention is not limited to this, and the inner peripheral fitting surface only needs to have at least a portion thereof contact the outer peripheral surface of the first portion. In addition, the inner peripheral fitting surface S2 of this example is fitted with the first outer peripheral surface 12 in a manner that the partition rings 7 and 8 can slide on the first outer peripheral surface 12 along the axial direction. Therefore, the partition rings 7 and 8 can move along the axial direction together with the piston rings 4, 5, and 6. However, the present invention is not limited to this, and the inner peripheral fitting surface may also fit with the outer peripheral surface of the first portion to such an extent that the partition ring cannot move in the axial direction. The outer peripheral separation surface S1 is provided on the outer peripheral portion of the partition rings 7 and 8, connecting the outer peripheral edge of the upper partition surface S3 with the outer peripheral edge of the lower partition surface S4. In addition, the outer peripheral separation surface S1 ensures a predetermined separation distance between the outer peripheral separation surface S1 and the inner wall surface 101 of the cylinder 10 in the use state. In other words, the partition rings 7 and 8 are separated from the inner wall surface 101 of the cylinder 10.

[0068] It should be noted that the upper wall surface S3 of the spacer rings 7 and 8 may be parallel to the groove wall forming surface 24 of the top bank member 2 or may be inclined relative to the groove wall forming surface 24. Similarly, the lower wall surface S4 of the spacer rings 7 and 8 may be parallel to the step surface 14 of the piston 1 or may be inclined relative to the step surface 14. In addition, chamfers, step cuts, etc. may be formed at the corners of the spacer rings 7 and 8.

[0069] Furthermore, the partition rings 7 and 8 may or may not have a joint. Figure 5 FIG. 2 is a top view schematically illustrating the shapes of the spacer rings 7 and 8 according to the embodiment (a view when visually confirmed from the upper side in the axial direction). Figure 5 As shown in (A), the partition rings 7 and 8 may also have a joint shown by reference numeral G1. The joint G1 is formed between a pair of joint ends facing each other. Figure 5 As shown in (B), the partition rings 7 and 8 may have a shape that is continuous over the entire circumference without having a joint.

[0070] like Figure 2 As shown, a space for attaching the top ring 4 is defined between the groove wall forming surface 24 of the top bank member 2 and the upper side partition wall surface S3 of the partition ring 7, a space for attaching the second ring 5 is defined between the lower side partition wall surface S4 of the partition ring 7 and the upper side partition wall surface S3 of the partition ring 8, and a space for attaching the oil ring 6 is defined between the lower side partition wall surface S4 of the partition ring 8 and the step surface 14 of the piston 1. That is, by sandwiching the partition ring 7 between the top ring 4 and the second ring 5, the top ring 4 and the second ring 5 are separated. In addition, by sandwiching the partition ring 8 between the second ring 5 and the oil ring 6, the second ring 5 and the oil ring 6 are separated. In this way, by arranging the partition rings 7 and 8 between the piston rings 4, 5, and 6 to divide the first annular groove 3, three piston rings 4, 5, and 6 can be attached to one first annular groove 3. In the piston unit 20, the partition ring 7 functions as a substitute for the second bank, and the partition ring 8 functions as a substitute for the third bank.

[0071] The material of the separator rings 7 and 8 is not particularly limited. For example, separator rings made of steel, cast iron, Cu alloy, and aluminum alloy can be used. In addition, a coating including at least any one of a resin coating, a nitriding coating, an anodized coating, a plated coating, a PVD coating, a coating, and a DLC coating can be formed on the surface of the separator rings 7 and 8. Such a coating is preferably formed on the contact portion between the separator rings 7 and 8 and other components, namely, the inner peripheral fitting surface S2, the upper side wall surface S3, and the lower side wall surface S4. By forming such a coating, the wear resistance of the separator rings 7 and 8 can be improved, and the adhesion of the separator rings 7 and 8 to other components and other adverse conditions caused by direct contact between the base materials can be prevented.

[0072] [Assembly method of piston unit]

[0073] The piston unit 20 of the embodiment is assembled according to the following process. First, the piston rings 4, 5, 6 and the spacer rings 7, 8 are installed on the piston 1 to which the top bank member 2 is not attached. The piston rings 4, 5, 6 and the spacer rings 7, 8 are attached to the first portion 1a of the piston 1 in order from the ring (the oil ring 6 in this example) farthest from the top surface 11 of the piston 1. After that, the top bank member 2 is attached to the first portion 1a of the piston 1, thereby forming the first annular groove 3, as shown in FIG. Figure 1 The piston unit 20 shown is assembled. As the method of mounting the spacer rings 7 and 8, shrink fit, friction bonding, screw fixing, screwing, bonding, welding, etc. can be exemplified, but not limited to these. In the case of friction bonding, the spacer rings 7 and 8 are fixed by sliding the spacer rings 7 and 8 relative to the piston 1 after being embedded in the piston 1.

[0074] [Function / Effect]

[0075] As described above, the piston unit 20 of the embodiment comprises: a piston 1; a top bank member 2 attached to the piston 1; a first annular groove 3 formed on the outer periphery of the piston 1; a plurality of piston rings 4, 5, 6 attached to the first annular groove 3 and sliding on the inner wall surface 101 of the cylinder 10; and a plurality of spacer rings 7, 8 attached to the first annular groove 3 in a manner arranged along the axial direction of the piston 1 together with the plurality of piston rings 4, 5, 6. In addition, the piston 1 has a first portion 1a including an end portion on the top surface 11 side and to which the top bank member 2 is attached, and the outer diameter of the first portion 1a is smaller than the outer diameter of the second portion 1b of the piston 1 excluding the first portion 1a, so that a step is formed between the first portion 1a and the second portion 1b. In addition, the top bank member 2 has a groove wall forming surface 24, which is opposite to the step surface 14 connecting the first outer peripheral surface 12 of the first portion 1a and the second outer peripheral surface 13 of the second portion 1b. Furthermore, in the piston unit 20 , the first annular groove 3 is defined by the groove wall forming surface 24 , the step surface 14 , and the first outer peripheral surface 12 .

[0076] That is, the piston unit 20 forms the top land between the top surface 11 of the piston 1 and the first annular groove 3 by means of the top land member 2 which is separate from the piston 1, and the top land member 2 is set to be detachable relative to the piston 1. Therefore, the piston rings 4, 5, 6, and the spacer rings 7, 8 can be installed on the piston 1 in a state where the top land member 2 is not attached. Therefore, during installation, it is not necessary to expand the piston rings 4, 5, 6, and the spacer rings 7, 8 in such a way that the inner diameter of each ring is larger than the outer diameter of the top land, so even if the piston rings 4, 5, 6, and the spacer rings 7, 8 do not have a seam, they can be easily installed. That is, the piston rings and spacer rings without a seam (hereinafter also referred to as seamless) can be easily installed on the piston. In addition, according to the piston unit 20, even if the piston rings 4, 5, 6, and the spacer rings 7, 8 have a seam, during installation, it is not necessary to expand the seam in such a way that the inner diameter of each ring is larger than the outer diameter of the top land, so deformation and breakage of the rings caused by excessive expansion of the seam can be prevented.

[0077] Thus, according to the piston unit 20, it is easy to install the piston rings 4, 5, 6, and the spacer rings 7, 8. This also applies to the removal of the piston rings 4, 5, 6, and the spacer rings 7, 8. As a result, according to the piston unit 20, the piston rings 4, 5, 6, and the spacer rings 7, 8 can be easily replaced, and the life of the internal combustion engine 100 can be extended.

[0078] It should be noted that the present invention can also set at least one of the one or more separator rings installed in the first annular groove to be seamless, and can also set at least one of the one or more piston rings installed in the first annular groove to be seamless. In this way, air leakage and oil rise through the seam can be prevented. In addition, by setting the separator ring to be seamless, it is easy to manufacture the separator ring. As a result, the manufacturing cost can be suppressed. In addition, it is also expected that the dimensional accuracy of the separator ring will be improved.

[0079] Furthermore, the piston unit 20 is constituted of the top land by the top land member 2 which is separate from the piston 1, thereby making it easy to make the material and surface treatment of the top land different from those of the piston 1. By appropriately selecting the material and surface treatment of the top land member 2, it is possible to prevent the occurrence of aluminum adhesion and other undesirable conditions at the contact portion between the top ring 4 and the top land member 2, and improve the wear resistance and heat resistance of the top land member 2.

[0080] It should be noted that, in the piston unit 20 of the embodiment, there is only one annular groove (only the first annular groove 3), but the piston unit of the present invention can also form multiple annular grooves on the outer circumference of the piston. The present invention only needs to attach one or more piston rings to the first annular groove closest to one end face of the piston (the top face 11 in this example) among the multiple annular grooves. Therefore, the number of piston rings attached to the first annular groove is not limited to three, and can also be less than two or more than four. For example, as in the modified example 2 described later, two annular grooves can be formed on the outer circumference of the piston, and a separator ring and two piston rings (top ring and second ring) can be attached to the annular groove (first annular groove) closest to one end face of the piston, and a piston ring (oil ring) can be attached to the second annular groove (second annular groove) close to one end face of the piston. In addition, the types of piston rings are not limited to the above-mentioned top ring, second ring and oil ring.

[0081] Here, in an internal combustion engine in which a plurality of piston rings are mounted on a piston, in the case where an annular groove is formed for each piston ring, in order to shorten the axial length of the piston, the interval between the annular grooves needs to be shortened. However, when the interval between the annular grooves is shortened, the piston banks between the adjacent annular grooves in the axial direction become thin-walled, so it is difficult to maintain the strength of the piston. In addition, from the perspective of the processing accuracy of the annular groove, it is also difficult to shorten the axial length of the piston. In contrast, in the piston unit 20 of the embodiment, the separator rings 7 and 8, which are fitted to the first outer peripheral surface 12 of the first portion 1a in a manner of leaving a predetermined interval between the inner wall surface 101 of the cylinder 10, function as substitutes for the piston banks that separate the piston rings 4, 5, and 6 in the first annular groove 3. Therefore, it is not necessary to form an annular groove for attaching the piston rings 4, 5, and 6 in the piston 1 for each ring. That is, according to the piston unit 20 of the embodiment, a plurality of piston rings (in this case, the piston rings 4, 5, and 6) can be attached to one annular groove (the first annular groove 3). Thus, in an internal combustion engine in which a plurality of piston rings are mounted on a piston, the number of annular grooves can be reduced compared to a case where annular grooves are formed for each piston ring. Thus, the axial length of the piston 1 can be easily shortened. As a result, according to the piston unit 20, it is possible to contribute to the lightweighting of the piston and thus the lightweighting of the internal combustion engine. In addition, the axial length of the piston 1 can be shortened by thinning the piston rings and the separator rings. In addition, by reducing the number of annular grooves to be formed on the piston 1, the strength of the piston can be increased compared to a case where annular grooves are formed for each piston ring. Therefore, it can contribute to the high output of the internal combustion engine.

[0082] Furthermore, according to the piston unit 20 provided with the spacer rings 7 and 8, the restriction on the design of the bank volume can be eased. Here, the "bank volume" refers to the volume of the space (bank space) surrounded by the piston rings, the outer peripheral surface of the piston, and the inner wall surface of the cylinder, which are adjacent to the piston in the upward direction of the axis. In this example, the spacer rings 7 and 8 function as a substitute for the piston bank, so the space surrounded by the lower surface 44 of the top ring 4, the upper surface 53 of the second ring 5, the outer peripheral separation surface S1 of the spacer ring 7, and the inner wall surface 101 of the cylinder 10 is the second bank space, and the space surrounded by the lower surface 54 of the second ring 5, the upper surface 613 of the upper scraper 61U of the oil ring 6, the outer peripheral separation surface S1 of the spacer ring 8, and the inner wall surface 101 of the cylinder 10 is the third bank space. The spacer rings 7 and 8 are formed as a member separate from the piston 1, so from the viewpoint of strength, the restriction on making the width in the axial direction thinner is smaller than the piston bank. Therefore, according to the piston unit 20, the degree of freedom in the design of the bank volume can be increased. This can improve the pressure adjustment function of the shore space and the degree of freedom in design in terms of the function as an oil reservoir.

[0083] In addition, usually, the piston is made of aluminum alloy, so aluminum adhesion may occur at the contact point between the piston ring and the piston. In addition, the piston may be worn due to the sliding between the piston ring and the piston. In this regard, in the piston unit 20, a separator ring 7 is sandwiched between the top ring 4 and the second ring 5 instead of the second bank, and a separator ring 8 is sandwiched between the second ring 5 and the oil ring 6 instead of the third bank. Therefore, compared with the case where the piston rings are separated from each other by the piston bank, the contact point between the piston rings 4, 5, 6 and the piston 1 can be reduced. Therefore, it is possible to suppress the adverse conditions such as aluminum adhesion caused by the direct contact between the piston rings 4, 5, 6 and the piston 1. In addition, by appropriately selecting the material and surface treatment of the separator rings 7, 8, it is possible to prevent the adverse conditions such as aluminum adhesion from occurring at the contact point between the piston rings 4, 5, 6 and the separator rings 7, 8, and improve the wear resistance and heat resistance of the separator rings 7, 8.

[0084] In addition, in the piston unit 20, a contact state is formed between the first outer peripheral surface 12 of the piston 1 and the inner peripheral fitting surface S2 of the spacer rings 7 and 8, so that the oil rise and the gas outflow from the inner peripheral side of the spacer rings 7 and 8 in the first annular groove 3 can be suppressed. In addition, since the first outer peripheral surface 12 of the piston 1 is in contact with the inner peripheral fitting surface S2 of the spacer rings 7 and 8, the heat of the piston 1 can be transferred from the first outer peripheral surface 12 to the piston rings 4, 5, and 6 via the inner peripheral fitting surface S2 of the spacer rings 7 and 8, and the heat can be discharged to the cylinder 10 with which the piston rings 4, 5, and 6 are in sliding contact. It should be noted that from the perspective of the cooling effect of the piston 1, at least a part of the inner peripheral fitting surface S2 only needs to be in contact with the first outer peripheral surface 12 of the piston 1.

[0085] It should be noted that, in this example, a plurality of separator rings (separator rings 7, 8) are attached to the first annular groove 3, but the number of separator rings attached to the first annular groove is not limited to two, and may be one, or may be more than three. In other words, one or more separator rings may be attached to the first annular groove. For example, as in the modified example 2 described later, two piston rings (a top ring and a second ring) and a separator ring may be attached to the first annular groove, and the separator ring may be arranged between the two piston rings. In addition, for example, a piston ring (a top ring) and a separator ring may be attached to each of the first annular grooves, and the separator ring may be arranged between the lower surface of the piston ring and the step surface of the piston (the inner wall on the lower side of the annular groove). Through these structures, the contact area between the piston ring and the piston can also be reduced. In addition, in the present invention, the separator ring is not a necessary structure. In other words, the piston unit of the present invention may also not have a separator ring as in the modified example 3 described later.

[0086] [Modifications]

[0087] In the following description, the differences from the above-mentioned piston unit 20 are mainly described, and the same components are denoted by the same reference numerals, and detailed descriptions thereof are omitted.

[0088] [Modification 1]

[0089] Figure 6 1 is a partial cross-sectional view of an internal combustion engine 100A including a piston unit 20A according to a first modification of the embodiment. The piston unit 20A according to the first modification is different from the above-described piston unit 20 in the shape of a spacer ring.

[0090] like Figure 6 As shown, the cross section of the spacer ring 7A of the modification example 1 orthogonal to the circumferential direction is formed into a T-shape. The spacer ring 7A has an outer peripheral separation surface S1, an inner peripheral fitting surface S2, an upper side bulkhead surface S3, a lower side bulkhead surface S4, an upper side protrusion UP1, and a lower side protrusion LP1. In addition, the cross section of the spacer ring 8A of the modification example 1 orthogonal to the circumferential direction is formed into an L-shape. The spacer ring 8A has an outer peripheral separation surface S1, an inner peripheral fitting surface S2, an upper side bulkhead surface S3, a lower side bulkhead surface S4, and a lower side protrusion LP1. The upper side protrusion UP1 is provided at a position closer to the inside than the upper side bulkhead surface S3 in the radial direction of the piston 1, and protrudes to the upper side (combustion chamber 30 side) relative to the upper side bulkhead surface S3. The lower side protrusion LP1 is provided at a position closer to the inside than the lower side bulkhead surface S4 in the radial direction of the piston 1, and protrudes to the lower side (crank chamber 40 side) relative to the lower side bulkhead surface S4.

[0091] The upper protrusion UP1 of the spacer ring 7A abuts against the groove wall forming surface 24 of the top land member 2 on the inner peripheral surface 42 side of the top ring 4, thereby limiting the upward movement of the spacer ring 7A. In addition, the lower protrusion LP1 of the spacer ring 7A abuts against the upper partition wall surface S3 of the spacer ring 8A on the inner peripheral surface 52 side of the second ring 5, thereby limiting the downward movement of the spacer ring 7A and the upward movement of the spacer ring 8A. Furthermore, the lower protrusion LP1 of the spacer ring 8A abuts against the step surface 14 of the piston 1 on the inner peripheral surface side of the oil ring 6, thereby limiting the downward movement of the spacer ring 8A. In this way, the spacer rings 7A and 8A are supported in the axial direction of the piston 1, and their axial movement is limited.

[0092] According to the piston unit 20A of the modification 1, the axial movement of the spacer rings 7A and 8A is limited by the upper protrusion UP1 and the lower protrusion LP1, thereby ensuring the side clearance of the piston rings 4, 5, and 6. It should be noted that the side clearance here refers to the gap formed between the other components (top land component, spacer ring, piston) adjacent to the piston ring in the axial direction of the piston and the piston ring.

[0093] [Modification 2]

[0094] Figure 7 1 is a partial cross-sectional view of an internal combustion engine 100B having a piston unit 20B of a second modification of the embodiment. In the piston unit 20B of the second modification, a second annular groove 102 is formed on the second outer peripheral surface 13 of the piston 1. That is, in the piston unit 20B, a plurality of (two) annular grooves are formed on the outer periphery of the piston 1. In addition, a top ring 4, a second ring 5, and a spacer ring 7 are attached to the first annular groove 3, and the spacer ring 7 is arranged between the top ring 4 and the second ring 5. In addition, an oil ring 6 is attached to the second annular groove 102.

[0095] [Variation 3]

[0096] Figure 8 It is a partial cross-sectional view of an internal combustion engine 100C having a piston unit 20C of a modified example 3 of the embodiment. The piston unit 20C of the modified example 3 does not have a separator ring. In addition, in the piston unit 20C of the modified example 3, a second annular groove 102 and a third annular groove 103 are formed on the second outer peripheral surface 13 of the piston 1 in the order from near to far from the top surface 11 of the piston 1. That is, in the piston unit 20C, a plurality of (three) annular grooves are formed on the outer periphery of the piston 1. In addition, a top ring 4 is attached to the first annular groove 3, a second ring 5 is attached to the second annular groove 102, and an oil ring 6 is attached to the third annular groove 103.

[0097] [Variation 4]

[0098] Fig. 9 It is a cross-sectional view of an internal combustion engine 100D including a piston unit 20D according to a fourth modification of the embodiment. Fig.10 FIG. 1 is a partial cross-sectional view of an internal combustion engine 100D including a piston unit 20D according to a fourth modification of the embodiment. Fig. 9 As shown, a piston unit 20D according to Modification 4 is different from the above-described piston unit 20 in that a top land member is formed in a cap shape.

[0099] like Fig. 9 and Fig.10 As shown, the top bank member 2D of the modification example 4 has an annular portion 2a and a cover portion 2b. Fig.10As shown, the annular portion 2a is an annular portion having an annular piston fitting surface 22 as an inner circumferential surface that fits with the first outer circumferential surface 12 of the first portion 1a of the piston 1. In Modification 4, the groove wall forming surface 24 is formed as the lower end surface of the annular portion 2a. In addition, in Modification 4, the bank outer circumferential surface 21 is formed as the outer circumferential surface of the annular portion 2a. The cover portion 2b is provided on the inner side of the annular portion 2a. The cover portion 2b closes the inner side of the annular portion 2a in a manner excluding a specified area including the lower end of the annular portion 2a. Thus, the piston fitting surface 22 is formed on the inner side of the annular portion 2a. In Modification 4, the bank end surface 23 is formed to include the upper end surface of the annular portion 2a and the upper end surface of the cover portion 2b. In addition, in Modification 4, the top surface (upper end surface) of the piston unit 20D is composed of the bank end surface 23 of the top bank member 2D.

[0100] like Fig.10 As shown, the cover portion 2b of the top bank member 2D covers the top surface 11 of the piston 1. The cover portion 2b abuts against the top surface 11 of the piston 1, whereby the top bank member 2D is supported from the bottom by the top surface 11. Thus, the top bank member 2D can be restricted from moving in a direction away from the top surface 11 (downward), and a predetermined separation distance can be ensured between the groove wall forming surface 24 and the step surface 14.

[0101] Fig.11 2D is a diagram for illustrating a variation of the fitting method between the top bank member 2D and the piston 1. Fig.11 As shown in (A), a radial step may be provided at the first portion 1a so that the piston fitting surface 22 can be fitted. Fig.11 As shown in (B), the piston fitting surface 22 of the top bank member 2D may also be formed to be inclined as a whole so as to fit into the tapered surface 122. Fig.11 As shown in (C), the piston fitting surface 22 may be formed partially inclined so that a portion fits in the straight surface 121 and another portion fits in the tapered surface 122 .

[0102] <Other>

[0103] As mentioned above, although the preferred embodiment of the present invention was described, the above-mentioned various aspects can be combined as much as possible.

[0104] Description of Reference Numerals

[0105] 100, 100A, 100B, 100C, 100D: internal combustion engine;

[0106] 10: cylinder;

[0107] 20, 20A, 20B, 20C, 20D: piston unit;

[0108] 30: Combustion chamber;

[0109] 40: crank chamber;

[0110] 1: Piston;

[0111] 2. 2D: top bank member;

[0112] 3: first annular groove;

[0113] 4, 5, 6: piston ring;

[0114] 7, 7A, 8, 8A: Separator ring.

Claims

1. A piston unit reciprocates in a cylinder, wherein: The piston unit comprises: piston; A top land member, mounted on the piston; one or more annular grooves formed on the outer circumference of the piston; and One or more piston rings are mounted in a first annular groove closest to an end face of the piston among the one or more annular grooves and slide on the inner wall surface of the cylinder. The piston has a first portion, the first portion includes an end portion on the one end surface side of the piston, and the first portion is for the top bank member to be attached, and the outer diameter of the first portion is smaller than the outer diameter of a second portion of the piston other than the first portion, so that a step is formed between the first portion and the second portion, The top bank member has a groove wall forming surface, the groove wall forming surface facing a step surface connecting the outer peripheral surface of the first portion and the outer peripheral surface of the second portion, The first annular groove is defined by the groove wall forming surface, the step surface and the outer peripheral surface of the first portion. The top land member is formed as a ring having an inner peripheral surface of an annular piston fitting surface that fits with the outer peripheral surface of the first portion. The piston fitting surface is fitted to the outer peripheral surface of the first portion in such a manner that the land member is supported by the outer peripheral surface of the first portion from the other end surface side of the piston.

2. The piston unit according to claim 1, wherein: The piston unit further comprises one or more spacer rings, and the one or more spacer rings are attached to the first annular groove in a manner of being arranged along the axial direction of the piston together with the one or more piston rings. The one or more spacer rings are fitted to the outer peripheral surface of the first portion with a predetermined gap between them and the inner wall of the cylinder.

3. The piston unit according to claim 2, wherein: At least one of the one or more spacer rings has no seam.

4. The piston unit according to claim 2 or 3, wherein: A plurality of piston rings are mounted in the first annular groove. The spacer ring is arranged between a piston ring closest to the one end surface of the piston and a piston ring second closest to the one end surface among the plurality of piston rings.

5. The piston unit according to claim 1, wherein: The piston unit is attached to a cylinder of an internal combustion engine.

6. A top land member, attached to a piston reciprocating in a cylinder, wherein: One or more annular grooves are formed on the outer circumference of the piston. The piston has a first portion, the first portion includes an end portion on one end surface side of the piston, and the first portion is for the top bank member to be attached, and the outer diameter of the first portion is smaller than the outer diameter of a second portion of the piston other than the first portion, so that a step is formed between the first portion and the second portion. One or more piston rings sliding on the inner wall surface of the cylinder are mounted on the first annular groove closest to the one end surface of the piston among the one or more annular grooves. The top bank member has a groove wall forming surface, the groove wall forming surface facing a step surface connecting the outer peripheral surface of the first portion and the outer peripheral surface of the second portion, The first annular groove is defined by the groove wall forming surface, the step surface and the outer peripheral surface of the first portion. The top land member is formed as a ring having an inner peripheral surface of an annular piston fitting surface that fits with the outer peripheral surface of the first portion. The piston fitting surface is fitted to the outer peripheral surface of the first portion in such a manner that the land member is supported by the outer peripheral surface of the first portion from the other end surface side of the piston.

7. A combination of parts for a piston unit, comprising: A top land member mounted on a piston that reciprocates in the cylinder; and One or more piston rings are attached to a first annular groove closest to one end surface of the piston among one or more annular grooves formed on the outer circumference of the piston, and slide on the inner wall surface of the cylinder. The piston has a first portion, the first portion includes an end portion on the one end surface side of the piston, and the first portion is for the top bank member to be attached, and the outer diameter of the first portion is smaller than the outer diameter of a second portion of the piston other than the first portion, so that a step is formed between the first portion and the second portion, The top bank member has a groove wall forming surface, the groove wall forming surface facing a step surface connecting the outer peripheral surface of the first portion and the outer peripheral surface of the second portion, The first annular groove is defined by the groove wall forming surface, the step surface and the outer peripheral surface of the first portion. The top land member is formed as a ring having an inner peripheral surface of an annular piston fitting surface that fits with the outer peripheral surface of the first portion. The piston fitting surface is fitted to the outer peripheral surface of the first portion in such a manner that the land member is supported by the outer peripheral surface of the first portion from the other end surface side of the piston.

Images