Piston ring for engine with three-ring structure and engine system

Abstract

The invention provides a piston ring with a three-ring structure for an engine and an engine system.The piston ring comprises a first ring body installed between a piston and the inner wall of a cylinder body, and arc-shaped protrusions extending in the circumferential direction are symmetrically formed on the upper side and the lower side of the first ring body; the cross section area of the arc-shaped bulge is constructed into a trapezoid which is gradually reduced towards the first ring body; and the two second ring bodies are oppositely installed on the upper side and the lower side of the first ring body, and matched arc-shaped protrusions matched with the arc-shaped protrusions are formed on each second ring body so as to limit the two second ring bodies to move in the axial direction relative to the first ring body.

Description

Technical Field

[0001] At least one embodiment of the present invention relates to the technical field of internal combustion engine parts, and in particular to a piston ring with a three-ring structure for an engine and an engine system. Background Art

[0002] The piston ring is a key component of the internal combustion engine. It is an elastic metal ring located in the groove of the piston itself. First, it is used to seal the gas in the combustion chamber to prevent the gas from entering the crankcase through the wall gap; second, since part of the energy during combustion can be transferred to the piston boundary through the piston, its other function is to transfer the heat generated from the piston to the engine cooling system; third, the piston ring has the function of controlling the oil between the piston and the inner wall of the cylinder body, by scraping off the excess oil on the wall and limiting its leakage into the combustion chamber, reducing harmful gas emissions; in addition, the piston ring also has a supporting function.

[0003] Existing piston rings usually adopt a monolithic design mode. Monolithic piston rings are widely used in engines due to their advantages such as simple manufacturing process and convenient installation. However, the upper and lower surfaces of monolithic piston rings are prone to uneven heating and unbalanced thermal expansion, which causes the ring body to deform and then lead to sealing failure.

[0004] In order to solve the above problems, the prior art provides a combined piston ring with two overlapping ring bodies. The overlapping combination of the two ring bodies enhances the flexibility of the piston ring and makes it fit more closely to the inner wall of the cylinder body.

[0005] However, when the cylinder block is operating under high temperature and high pressure, relative movement will occur between the two ring bodies, and they will separate from each other in the axial direction, causing the lubricating oil in the piston ring to flow to the outside of the piston ring. Summary of the invention

[0006] In view of this, the present invention provides a piston ring for an engine with a three-ring structure to prevent a first ring body and two second ring bodies from being separated from each other in the axial direction, and to prevent lubricating oil in the piston ring from flowing to the outside of the piston ring.

[0007] According to an embodiment of the present invention, there is provided a piston ring for an engine with a three-ring structure, comprising: a first ring body, installed between a piston and an inner wall of a cylinder body, wherein arc-shaped protrusions extending in a circumferential direction are symmetrically formed on upper and lower sides of the first ring body, and wherein the cross-sectional area of ​​the arc-shaped protrusions is configured to be a trapezoid which gradually decreases toward the first ring body; and two second ring bodies, installed on upper and lower sides of the first ring body facing each other, wherein each of the second ring bodies is formed with a matching arc-shaped protrusion which matches the arc-shaped protrusion so as to limit the movement of the two second ring bodies in an axial direction relative to the first ring body.

[0008] According to an embodiment of the present invention, the first ring body has a first notch in the circumferential direction, each of the second ring bodies has a second notch in the circumferential direction, the two arc-shaped protrusions are constructed to be aligned with the head and tail ends of the first ring body in the axial direction, the mating arc-shaped protrusions are constructed to be aligned with the head and tail ends of the second ring body in the axial direction, and the mating arc-shaped protrusions of the two second ring bodies are respectively combined with the two arc-shaped protrusions located on both sides of the first ring body, so that the first ring body and the two second ring bodies form a complete circumferential surface in the circumferential direction.

[0009] According to an embodiment of the present invention, the annular outer wall surface of the first ring body and the annular outer wall surface of the second ring body are both constructed to bulge radially outward in the middle portion, the maximum outer diameters of the first ring body and the second ring body are the same, and at the position where the annular outer wall surface of the first ring body and the annular outer wall surface of the second ring body abut against each other, the outer diameters of the first ring body and the second ring body are the same, so that the first ring body, the two second ring bodies stacked on each other and the inner wall of the cylinder body form a cavity for storing lubricating oil.

[0010] According to an embodiment of the present invention, the width in the radial direction of the end portion where each arc-shaped protrusion is combined with the first ring body is 1 / 2 of the maximum width of the first ring body in the radial direction; the width in the radial direction of the end portion where the mating arc-shaped protrusion is combined with the first ring body in the axial direction is 1 / 2 of the maximum width of the second ring body in the radial direction.

[0011] According to an embodiment of the present invention, two first protrusions extending in the axial direction are respectively formed on the upper and lower sides of the first ring body, and the two first protrusions respectively extend into the second notches of the two second ring bodies to limit the rotation of each second ring body relative to the first ring body.

[0012] According to an embodiment of the present invention, the two first protrusions are symmetrically arranged about a radial extension line of the first ring body where the first notch is located.

[0013] According to an embodiment of the present invention, a second convex portion extending in the axial direction is formed on a side of each second ring body facing the first ring body, and two second convex portions extend into the first notch from upper and lower sides of the first ring body respectively.

[0014] According to an embodiment of the present invention, a groove extending in a circumferential direction is formed on the outer side of the upper surface of the second ring body located on the upper side away from the first ring body, so that in the process of the second ring body located on the upper side moving inside the cylinder body, under the action of the piston, the second ring body located on the upper side generates a torque to adhere to the inner wall of the cylinder body, thereby increasing the contact force between the second ring body located on the upper side and the inner wall of the cylinder body.

[0015] According to an embodiment of the present invention, the thermal expansion coefficient a2 of the second ring body located at the upper side> the thermal expansion coefficient a1 of the first ring body> the thermal expansion coefficient a3 of the second ring body located at the lower side.

[0016] According to an embodiment of the present invention, an engine system is provided, comprising: a cylinder block; a piston installed inside the cylinder block; and a piston ring for an engine having a three-ring structure as described in the above embodiment, installed between the piston and the cylinder block.

[0017] According to the piston ring for an engine with a three-ring structure in the above-mentioned embodiment of the present invention, arc-shaped protrusions extending in the circumferential direction are symmetrically formed on the upper and lower sides of the first ring body, and the cross-sectional area of ​​the arc-shaped protrusions is constructed to be a trapezoid that gradually decreases toward the first ring body. Two second ring bodies are mounted on the upper and lower sides of the first ring body facing each other, and each second ring body is formed with a matching arc-shaped protrusion that matches the arc-shaped protrusion to limit the movement of the two second ring bodies in the axial direction relative to the first ring body, thereby preventing the first ring body and the two second ring bodies from separating from each other in the axial direction and preventing the lubricating oil in the piston ring from flowing to the outside of the piston ring. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a cross-sectional view of a piston ring with a three-ring structure for an engine combined with a piston and a cylinder block according to an embodiment of the present invention;

[0019] Figure 2 yes Figure 1 A partial enlarged view of the middle M part;

[0020] Figure 3 The piston ring for an engine having a three-ring structure according to an embodiment of the present invention is Figure 1 A partial enlarged view of the middle M part;

[0021] Figure 4 is a three-dimensional schematic diagram of a piston ring for an engine with a three-ring structure according to an embodiment of the present invention;

[0022] Figure 5 is a three-dimensional schematic diagram of a second ring body located on the upper side of a piston ring with a three-ring structure for an engine according to an embodiment of the present invention;

[0023] Figure 6 It is a front view of a second notch of a second ring body located on the upper side of a piston ring for an engine with a three-ring structure according to an embodiment of the present invention;

[0024] Figure 7 yes Figure 6 A partial enlarged view of part A;

[0025] Figure 8is a three-dimensional schematic diagram of a first ring body of a piston ring for an engine having a three-ring structure according to an embodiment of the present invention;

[0026] Fig. 9 is a front view of a first notch of a first ring body of a piston ring with a three-ring structure for an engine according to an embodiment of the present invention;

[0027] Fig.10 yes Fig. 9 A partial enlarged view of part B;

[0028] Fig.11 It is a three-dimensional schematic diagram of a second ring body located at the lower side of a piston ring with a three-ring structure for an engine according to an embodiment of the present invention;

[0029] Fig.12 It is a front view of a second notch of a second ring body located at a lower side of a piston ring with a three-ring structure for an engine according to an embodiment of the present invention;

[0030] Fig.13 yes Fig.12 A partial enlarged view of part C in the middle;

[0031] Fig.14 is a three-dimensional schematic diagram of a piston ring for an engine with a three-ring structure according to an embodiment of the present invention, in which two first protrusions of a first ring body extend into second notches of two second ring bodies respectively; and

[0032] Fig.15 It is a three-dimensional schematic diagram of a piston ring for an engine with a three-ring structure in which the second convex parts of the two second ring bodies extend into the first notch of the first ring body respectively according to an embodiment of the present invention.

[0033] In the figure:

[0034] 1-first ring body; 11-arc-shaped protrusion; 12-first notch; 13-first convex part;

[0035] 2-second ring body; 21-matching arc-shaped protrusion; 22-second notch; 23-second convex part; 24-groove;

[0036] 3-piston; 31-first ring groove; 32-second ring groove; 33-third ring groove; 34-fourth ring groove;

[0037] 4-cylinder block;

[0038] 5- Cavity. DETAILED DESCRIPTION

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0040] According to the inventive concept of one aspect of the present invention, there is provided a piston ring for an engine with a three-ring structure, comprising: a first ring body, installed between a piston and an inner wall of a cylinder body, the first ring body having symmetrically formed upper and lower sides with arc-shaped protrusions extending in a circumferential direction, the cross-sectional area of ​​the arc-shaped protrusions being configured to be a trapezoid which gradually decreases toward the first ring body; and two second ring bodies, installed on the upper and lower sides of the first ring body facing each other, each second ring body having formed thereon a matching arc-shaped protrusion matched with the arc-shaped protrusion so as to limit the axial movement of the two second ring bodies relative to the first ring body.

[0041] Figure 1 is a cross-sectional view of a piston ring with a three-ring structure for an engine combined with a piston and a cylinder block according to an embodiment of the present invention; Figure 2 yes Figure 1 A partial enlarged view of the middle M part; Figure 3 The piston ring for an engine having a three-ring structure according to an embodiment of the present invention is Figure 1 A partial enlarged view of the middle M part; Figure 4 It is a three-dimensional schematic diagram of a piston ring for an engine with a three-ring structure according to an embodiment of the present invention.

[0042] According to an exemplary embodiment of the present invention, please refer to Figure 1-Figure 4 , a piston ring for an engine with a three-ring structure is provided, comprising a first ring body 1 and two second ring bodies 2. The first ring body 1 is installed between the piston 3 and the inner wall of the cylinder body 4, and arc-shaped protrusions 11 extending in the circumferential direction are symmetrically formed on the upper and lower sides of the first ring body 1, and the cross-sectional area of ​​the arc-shaped protrusions 11 is configured to be a trapezoid that gradually decreases toward the first ring body 1. The two second ring bodies 2 are installed on the upper and lower sides of the first ring body 1 facing each other, and a matching arc-shaped protrusion 21 that matches the arc-shaped protrusion 11 is formed on each second ring body 2, and the matching arc-shaped protrusion 21 of each second ring body 2 is respectively combined with the two arc-shaped protrusions 11 of the first ring body 1 to limit the movement of the two second ring bodies 2 relative to the first ring body 1 in the axial direction.

[0043] In this embodiment, arc-shaped protrusions 11 extending in the circumferential direction are symmetrically formed on the upper and lower sides of the first ring body 1, and the cross-sectional area of ​​the arc-shaped protrusion 11 is constructed into a trapezoid that gradually decreases toward the first ring body 1. The two second ring bodies 2 are installed on the upper and lower sides of the first ring body 1 facing each other, and each second ring body 2 is formed with a matching arc-shaped protrusion 21 that matches the arc-shaped protrusion 11 to limit the axial movement of the two second ring bodies 2 relative to the first ring body 1, thereby preventing the first ring body 1 and the two second ring bodies 2 from separating from each other in the axial direction, and preventing the lubricating oil in the piston ring from flowing to the outside of the piston ring.

[0044] Furthermore, through the above-mentioned arrangement, the positive torsional force and elastic force formed between the two second ring bodies 2 and the first ring body 1 strengthen the axial connection between the two second ring bodies 2 and the first ring body 1, and have better sealing and stability.

[0045] Figure 5 is a three-dimensional schematic diagram of a second ring body located on the upper side of a piston ring with a three-ring structure for an engine according to an embodiment of the present invention; Figure 6 It is a front view of a second notch of a second ring body located on the upper side of a piston ring for an engine with a three-ring structure according to an embodiment of the present invention; Figure 7 yes Figure 6 A partial enlarged view of part A; Figure 8 is a three-dimensional schematic diagram of a first ring body of a piston ring for an engine having a three-ring structure according to an embodiment of the present invention; Fig. 9 is a front view of a first notch of a first ring body of a piston ring with a three-ring structure for an engine according to an embodiment of the present invention; Fig.10 yes Fig. 9 A partial enlarged view of part B; Fig.11 It is a three-dimensional schematic diagram of a second ring body located at the lower side of a piston ring with a three-ring structure for an engine according to an embodiment of the present invention; Fig.12 It is a front view of a second notch of a second ring body located at a lower side of a piston ring with a three-ring structure for an engine according to an embodiment of the present invention; Fig.13 yes Fig.12 A partial enlarged view of part C.

[0046] In some exemplary embodiments, referring to Figure 4-Figure 13 The first ring body 1 has a first notch 12 in the circumferential direction, and each second ring body 2 has a second notch 22 in the circumferential direction. The two arc-shaped protrusions 11 are constructed to be aligned with the first and second ends of the first ring body 1 in the axial direction at their ends, and the matching arc-shaped protrusions 21 are constructed to be aligned with the first and second ends of the second ring body 2 in the axial direction at their ends. The matching arc-shaped protrusions 21 of the two second ring bodies 2 are respectively combined with the two arc-shaped protrusions 11 located on both sides of the first ring body 1, so that the first ring body 1 and the two second ring bodies 2 form a complete circumferential surface in the circumferential direction.

[0047] Through the above-mentioned setting method, the matching arc-shaped protrusions 21 of the two second ring bodies 2 are respectively combined with the two arc-shaped protrusions 11 of the first ring body 1, so that the dimensions of the outer wall surface of the piston ring in the circumferential direction at each point in the axial direction after the two second ring bodies 2 are combined with the first ring body 1 remain consistent, and a complete circumferential surface is formed, thereby preventing the lubricating oil from flowing to the outside of the piston ring and improving the sealing effect of the piston ring on the internal lubricating oil.

[0048] In some exemplary embodiments, referring to Figure 2-Figure 3The annular outer wall surface of the first ring body 1 and the annular outer wall surface of the second ring body 2 are both constructed to bulge radially outward in the middle part, the maximum outer diameters of the first ring body 1 and the second ring body 2 are the same, and at the position where the annular outer wall surface of the first ring body 1 and the annular outer wall surface of the second ring body 2 abut against each other, the outer diameters of the first ring body 1 and the second ring body 2 are the same, so that the stacked first ring body 1, the two second ring bodies 2 and the inner wall of the cylinder body 4 form a cavity 5 for storing lubricating oil.

[0049] Through the above arrangement, the first ring body 1 and the two second ring bodies 2 are stacked and installed between the piston 3 and the cylinder body 4, and the first ring body 1 and the two second ring bodies 2 respectively form a cavity 5 for storing lubricating oil with the inner wall of the cylinder body 4. The cavity 5 for storing lubricating oil is formed between the first ring body 1 and the two second ring bodies 2 and the inner wall of the cylinder body 4, which can effectively improve the lubrication of the piston ring at the top dead center and prevent the lubricating oil from running up, thereby improving the carbon deposition problem of particulate matter entering the crankcase, and preventing the wear of the cylinder body 4 caused by carbon deposition while increasing the life of the lubricating oil.

[0050] It should be noted that, in this embodiment, the annular outer wall surfaces of the first ring body 1 and the second ring body 2 are radially contracted inwardly at portions close to both ends in the axial direction, and the cone angles thereof are 20°-70°, preferably 45°.

[0051] In some exemplary embodiments, referring to Figure 2-Figure 3 The width of the end of each arc-shaped protrusion 11 combined with the first ring body 1 in the radial direction is 1 / 2 of the maximum width of the first ring body 1 in the radial direction. The width of the end of the matching arc-shaped protrusion 21 combined with the first ring body 1 in the axial direction in the radial direction is 1 / 2 of the maximum width of the second ring body 2 in the radial direction.

[0052] Through the above-mentioned setting method, the bonding area between the matching arc-shaped protrusions 21 of the two second ring bodies 2 and the two arc-shaped protrusions 11 of the first ring body 1 is increased, so as to improve the bonding strength between the two second ring bodies 2 and the first ring body 1 in the axial direction, so as to further prevent the two second ring bodies 2 from moving in the axial direction relative to the first ring body 1.

[0053] Fig.14 It is a three-dimensional schematic diagram of a piston ring for an engine with a three-ring structure in which two first protrusions of a first ring body extend into second notches of two second ring bodies respectively according to an embodiment of the present invention.

[0054] In some exemplary embodiments, referring to Figure 4 , Figure 5 , Figure 8 , Fig.11 as well as Fig.14Two first protrusions 13 extending in the axial direction are respectively formed on the upper and lower sides of the first ring body 1. The two first protrusions 13 extend into the second notches 22 of the two second ring bodies 2 respectively to limit the rotation of each second ring body 2 relative to the first ring body 1, prevent the first notch 12 from being aligned with the two second notches 22 in the axial direction, and the lubricating oil flows to the outside of the piston ring through the first notch 12 and the two second notches 22.

[0055] In this embodiment, two first protrusions 13 extending in the axial direction are respectively formed on the upper and lower sides of the first ring body 1, and the two first protrusions 13 respectively extend into the second notches 22 of the two second ring bodies 2 to limit the rotation of each second ring body 2 relative to the first ring body 1, thereby preventing the two second notches 22 from being aligned with the first notch 12 in the axial direction, and the lubricating oil flows to the outside of the piston ring through the first notch 12 and the two second notches 22.

[0056] In some exemplary embodiments, referring to Figure 8 The two first protrusions 13 are symmetrically arranged about the radial extension line of the first ring body 1 where the first notch 12 is located.

[0057] With the above arrangement, when the two first protrusions 13 of the first ring body 1 are respectively extended into the two second notches 22 of the two second ring bodies 2, the torque formed by the limiting resistance provided by the two first protrusions 13 to the two second ring bodies 2 in the circumferential direction is balanced.

[0058] Fig.15 It is a three-dimensional schematic diagram of a piston ring for an engine with a three-ring structure in which the second convex parts of the two second ring bodies extend into the first notch of the first ring body respectively according to an embodiment of the present invention.

[0059] In some exemplary embodiments, referring to Figure 4 , Figure 5 , Figure 8 , Fig.11 as well as Fig.15 A second protrusion 23 extending in the axial direction is formed on one side of each second ring body 2 facing the first ring body 1. The two second protrusions 23 extend into the first notch 12 from the upper and lower sides of the first ring body 1 respectively to limit the rotation of the two second ring bodies 2 relative to the first ring body 1.

[0060] In this embodiment, a second protrusion 23 extending in the axial direction is formed on the side of each second ring body 2 facing the first ring body 1, and the two second protrusions 23 extend into the first notch 12 from the upper and lower sides of the first ring body 1 respectively to further limit the rotation of each second ring body 2 relative to the first ring body 1.

[0061] It should be noted that, in this embodiment, the first notch 12 and the two second notches 22 are dispersedly arranged in the circumferential direction. Furthermore, due to the three-layer design, the piston ring has an increased thickness, making it easier to meet the high-efficiency operation of the engine under high-load conditions, and improving the high sealing, high oil control and low friction capabilities. In addition, the piston ring of this embodiment overcomes the problem of ring body deformation caused by uneven heating and unbalanced thermal expansion of the upper and lower surfaces of the monolithic piston ring, and can better disperse heat and improve the sealing effect. It also has the characteristics of simple structure and easy installation.

[0062] In some exemplary embodiments, referring to Figure 2-Figure 3 A groove 24 extending in the circumferential direction is formed on the outer side of the upper surface of the second ring body 2 located on the upper side away from the first ring body 1, so that when the second ring body 2 located on the upper side moves inside the cylinder body 4, under the action of the piston 3, the second ring body 2 located on the upper side generates a torque to fit tightly against the inner wall of the cylinder body 4, thereby increasing the contact force between the second ring body 2 located on the upper side and the inner wall of the cylinder body 4.

[0063] In this embodiment, a groove 24 extending in the circumferential direction is formed on the outer side of the upper surface of the second ring body 2 located on the upper side of the first ring body 1 and away from the first ring body 1, so that when the second ring body 2 moves inside the cylinder body 4, under the action of the piston 3, the moments generated between the two sides of the second ring body 2 facing each other are unequal, so that the second ring body 2 generates torque, so that the second ring body 2 is tightly attached to the inner wall of the cylinder body 4, increasing the contact force between the second ring body 2 and the inner wall of the cylinder body 4.

[0064] In some exemplary embodiments, the thermal expansion coefficient a2 of the second ring body 2 located at the upper side is greater than the thermal expansion coefficient a1 of the first ring body 1 and greater than the thermal expansion coefficient a3 of the second ring body 2 located at the lower side.

[0065] In this embodiment, the second ring body 2 located on the upper side is located close to the combustion chamber, has a large surface heat, and is usually in a high-temperature environment. The first ring body 1 plays a role in further sealing the gas and controlling the oil, and can serve as a buffer for the two second ring bodies 2 located on the upper and lower sides. The second ring body 2 located on the lower side mainly plays a role in controlling the oil and further sealing. Based on the installation position and function of the above-mentioned first ring body 1 and the two second ring bodies 2, the thermal expansion coefficient a2 of the second ring body 2 located on the upper side> the thermal expansion coefficient a1 of the first ring body 1> the thermal expansion coefficient a3 of the second ring body 2 located on the lower side, so as to meet the working conditions of the first ring body 1 and the two second ring bodies 2.

[0066] According to an exemplary embodiment of the present invention, please refer to Figure 1, an engine system is provided, comprising a cylinder body 4, a piston 3 and a piston ring for an engine with a three-ring structure as described in the above embodiment. The piston 3 is installed inside the cylinder body 4. The piston ring for an engine with a three-ring structure as described in the above embodiment is installed between the piston 3 and the cylinder body 4.

[0067] In this embodiment, the piston ring for the engine with the three-ring structure described in the above embodiment is installed between the piston 3 and the cylinder block 4 to prevent the lubricating oil inside the piston ring from flowing to the outside of the piston ring.

[0068] It should be noted that in this embodiment, the piston 3 is formed with a first ring groove 31, a second ring groove 32, a third ring groove 33 and a fourth ring groove 34 suitable for installing piston rings. For example, the piston ring of the embodiment of the present invention is installed inside the first ring groove 31.

[0069] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A piston ring for an engine having a three-ring structure, comprising: A first ring body (1) is installed between the piston (3) and the inner wall of the cylinder body (4), wherein arc-shaped protrusions (11) extending in the circumferential direction are symmetrically formed on the upper and lower sides of the first ring body (1), and the cross-sectional area of ​​the arc-shaped protrusions (11) is configured to be a trapezoid that gradually decreases toward the first ring body (1); and Two second ring bodies (2) are mounted facing each other on the upper and lower sides of the first ring body (1), and each of the second ring bodies (2) is formed with a matching arc-shaped protrusion (21) that matches the arc-shaped protrusion (11) to limit the movement of the two second ring bodies (2) in the axial direction relative to the first ring body (1).

2. The piston ring for an engine having a three-ring structure according to claim 1, wherein: The first ring body (1) has a first notch (12) in the circumferential direction, and each of the second ring bodies (2) has a second notch (22) in the circumferential direction. The two arc-shaped protrusions (11) are configured to be aligned with the first and second ends of the first ring body (1) in the axial direction at their ends, and the matching arc-shaped protrusions (21) are configured to be aligned with the first and second ends of the second ring body (2) in the axial direction at their ends. The matching arc-shaped protrusions (21) of the two second ring bodies (2) are respectively combined with the two arc-shaped protrusions (11) located on both sides of the first ring body (1), so that the first ring body (1) and the two second ring bodies (2) respectively form a complete circumferential surface in the circumferential direction.

3. The piston ring for an engine having a three-ring structure according to claim 1, wherein: The annular outer wall surface of the first ring body (1) and the annular outer wall surface of the second ring body (2) are both constructed to bulge radially outward at the middle part, the maximum outer diameters of the first ring body (1) and the second ring body (2) are the same, and at the position where the annular outer wall surface of the first ring body (1) and the annular outer wall surface of the second ring body (2) abut against each other, the outer diameters of the first ring body (1) and the second ring body (2) are the same, so that the first ring body (1), the two second ring bodies (2) and the inner wall of the cylinder body (4) stacked on each other form a cavity (5) for storing lubricating oil.

4. The piston ring for an engine having a three-ring structure according to claim 3, wherein: The width of the end portion of each arc-shaped protrusion (11) connected to the first ring body (1) in the radial direction is 1 / 2 of the maximum width of the first ring body (1) in the radial direction; The width in the radial direction of the end portion of the matching arc-shaped protrusion (21) coupled to the first ring body (1) in the axial direction is 1 / 2 of the maximum width of the second ring body (2) in the radial direction.

5. The piston ring for an engine having a three-ring structure according to claim 2, wherein: Two first protrusions (13) extending in the axial direction are respectively formed on the upper and lower sides of the first ring body (1), and the two first protrusions (13) respectively extend into the second notches (22) of the two second ring bodies (2) to limit the rotation of each second ring body (2) relative to the first ring body (1).

6. The piston ring for an engine having a three-ring structure according to claim 5, wherein: The two first protrusions (13) are symmetrically arranged about a radial extension line of the first ring body (1) where the first notch (12) is located.

7. The piston ring for an engine having a three-ring structure according to claim 6, wherein: A second convex portion (23) extending in the axial direction is also formed on one side of each second ring body (2) facing the first ring body (1), and the two second convex portions (23) extend into the first notch (12) from the upper and lower sides of the first ring body (1), respectively.

8. The piston ring for an engine having a three-ring structure according to any one of claims 1 to 7, wherein: A groove (24) extending in the circumferential direction is formed on the outer side of the upper surface of the second ring body (2) located on the upper side, which is away from the upper surface of the first ring body (1), so that when the second ring body (2) located on the upper side moves inside the cylinder body (4), under the action of the piston (3), the second ring body (2) located on the upper side generates a torque to adhere closely to the inner wall of the cylinder body (4), thereby increasing the contact force between the second ring body (2) located on the upper side and the inner wall of the cylinder body (4).

9. The piston ring for an engine having a three-ring structure according to claim 1, wherein: The thermal expansion coefficient a2 of the second ring body (2) located on the upper side> the thermal expansion coefficient a1 of the first ring body (1)> the thermal expansion coefficient a3 of the second ring body (2) located on the lower side.

10. An engine system comprising: Cylinder body (4); A piston (3) installed inside the cylinder (4); as well as The piston ring for an engine with a three-ring structure according to any one of claims 1 to 9 is installed between the piston (3) and the cylinder block (4).

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