Stirling engine oil-free lubrication cylinder sleeve and Stirling engine

Abstract

The invention relates to the field of Stirling engines, and provides a Stirling engine oil-free lubrication cylinder sleeve and a Stirling engine, the Stirling engine oil-free lubrication cylinder sleeve comprises a cylinder sleeve body, and the inner hole wall of the cylinder sleeve body is divided into a high-speed section and low-speed sections located on the two sides of the high-speed section in the axial direction of the cylinder sleeve body; continuous net-shaped textures are arranged on the surface of the inner wall of the high-speed section, pit textures distributed in an array mode are arranged on the surface of the inner wall of the low-speed section, and the net-shaped textures and the pit textures form gradient surface textures in the axial direction of the cylinder sleeve body. The gradient surface texture is arranged on the inner surface of the cylinder sleeve according to the reciprocating speed characteristic of a piston, the high-speed section strengthens gas dynamic pressure bearing through the net-shaped texture, the low-speed section optimizes adhesion resistance and abrasive dust storage through the pit texture, the gas lubrication potential is fully released, friction reduction and service life prolonging of a dynamic sealing friction pair are achieved, and the service life is prolonged. The problems that a single surface structure of a traditional cylinder sleeve cannot be matched with the reciprocating speed difference of a piston, and the gas lubrication effect is insufficient are solved.

Description

Technical Field

[0001] This invention relates to the field of Stirling engines, and further to an oil-free lubricated cylinder liner for a Stirling engine and a Stirling engine. Background Technology

[0002] The Stirling engine is an external combustion closed-cycle piston engine. The dynamic sealing friction pair formed by the cylinder liner and piston rings filled with polytetrafluoroethylene (PTFE) is a core component ensuring the sealing of the working fluid (such as hydrogen or helium) and achieving efficient circulation. This friction pair operates under extreme conditions: in a typical double-acting Stirling engine, the temperature at the contact area between the cylinder liner inner wall and the piston rings can reach 100°C, the alternating pressure difference across the piston rings can reach up to 10 MPa, and the average reciprocating speed of the piston is 2-5 m / s. More importantly, to avoid lubricating oil contaminating the working fluid circulation system, oil-free lubrication technology must be employed. Under these conditions, piston ring wear failure has become a key bottleneck restricting the service life and power density improvement of Stirling engines. Currently, industry improvements mainly focus on optimizing the soft materials of piston rings to improve their wear resistance, while innovative research on hard cylinder liner surfaces is relatively scarce. Existing cylinder liner surfaces are typically polished to a single roughness, failing to provide functional surface control to address the uneven speed distribution during piston reciprocating motion. This results in insufficient adaptability of the lubrication state of the dynamic seal friction pair and underutilization of the gas lubrication potential.

[0003] Therefore, although surface texture technology has been applied in the field of liquid lubrication (such as cylinder liner honing of internal combustion engines), the lack of relevant technology for the special scenario of oilless lubrication and uneven reciprocating speed of Stirling engines has led to wear and failure of dynamic seals, which has become a problem restricting the improvement of power density and service life of Stirling engines. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide an oil-free lubricated cylinder liner for a Stirling engine and a Stirling engine. Based on the reciprocating speed characteristics of the piston, a gradient surface texture is set on the inner surface of the cylinder liner. At high speeds, a mesh texture enhances the gas dynamic pressure bearing capacity, while at low speeds, a pitted texture optimizes anti-adhesion and wear debris storage, fully releasing the gas lubrication potential and achieving reduced wear and increased lifespan of the dynamic sealing friction pair. This aims to solve the problems of traditional cylinder liner single-surface structures being unable to adapt to differences in piston reciprocating speeds and insufficient gas lubrication effect.

[0005] To achieve the above objectives, the present invention provides an oil-free lubricated cylinder liner for a Stirling engine, comprising a cylinder liner body, wherein the inner wall of the cylinder liner body is divided along its axial direction into a high-speed section and a low-speed section located on both sides of the high-speed section; the inner wall surface of the high-speed section is provided with a continuous mesh texture, and the inner wall surface of the low-speed section is provided with an array of recessed textures, wherein the mesh texture and the recessed textures form a gradient surface texture along the axial direction of the cylinder liner body.

[0006] In some embodiments, the parameters of the mesh texture are: a mesh cross angle of 30° to 150°, a groove depth of 0.1 μm to 0.5 μm, a width-to-width ratio of 0.2 to 0.5, a texture line width of 20 μm to 100 μm, and a texture line spacing of 200 μm to 800 μm.

[0007] In some embodiments, the pit texture is a circular pit with the following parameters: pit radius of 100 μm to 300 μm, depth-to-diameter ratio of 0.001 to 0.01, and the area occupancy of all pit textures on the inner surface of the low-speed section is 10% to 40%.

[0008] In some embodiments, the inner wall surface of the low-speed section is also provided with the mesh-like texture, and the mesh-like texture is continuously distributed from the high-speed section to the low-speed section; In the low-speed range, the pit texture and the mesh texture are combined to form a composite texture area, wherein the pit texture is located relative to the closed area enclosed by the mesh lines of the mesh texture.

[0009] In some embodiments, the cylinder liner body is made of ion-nitrided stainless steel.

[0010] In some implementations, the distribution of the high-speed and low-speed segments is based on the reciprocating speed of the Stirling engine piston, with 0° or 360° of crankshaft angle as top dead center, 180° as bottom dead center, and ±45° near dead center as the low-speed segment, and the remainder as the high-speed segment.

[0011] In some embodiments, the mesh texture is integrally formed on the inner bore wall of the cylinder liner body by honing; the pit texture is selectively prepared on the inner bore wall in the low-speed section by laser surface processing.

[0012] According to another aspect of this application, a Stirling engine is further provided, including any of the above-described preferred embodiments of the Stirling engine oil-free lubricated cylinder liners.

[0013] Compared with the prior art, the Stirling engine oilless lubrication cylinder liner and Stirling engine provided by the present invention have at least one of the following beneficial effects: 1. Based on the reciprocating speed characteristics of the piston, a gradient surface texture is set on the inner surface of the cylinder liner. In the high-speed section, the mesh texture enhances the gas dynamic pressure bearing, while in the low-speed section, the pit texture optimizes anti-adhesion and wear debris storage, fully releasing the gas lubrication potential and realizing wear reduction and life extension of the dynamic seal friction pair. This aims to solve the problem that the traditional single surface structure of the cylinder liner cannot adapt to the difference in piston reciprocating speed and the gas lubrication effect is insufficient.

[0014] 2. When the piston moves at high speed, the working gas flows through the convergent wedge region of the mesh texture, generating positive gas film pressure. Each mesh texture forms a tiny gas dynamic pressure lubricating bearing, increasing the gas film bearing capacity and reducing the direct contact between the piston ring and the cylinder liner.

[0015] 3. The circular pit texture can reduce the contact area between the PTFE filler and the cylinder liner. At the same time, the deep valleys of the pit texture can store PTFE wear debris generated by dry friction, preventing the wear debris from plowing the cylinder liner surface. The inner hole wall in the low-speed section provides a stable adhesion point for the transfer film, forming a uniform PTFE transfer film and improving dry friction lubrication conditions. Attached Figure Description

[0016] The preferred embodiments will now be described in a clear and easy-to-understand manner, in conjunction with the accompanying drawings, to further explain the above-mentioned characteristics, technical features, advantages, and implementation methods of the present invention.

[0017] Figure 1 This is a location diagram of an oilless lubrication cylinder liner for a Stirling engine.

[0018] Explanation of icon numbers: Cylinder liner body 1, high-speed section 11, mesh texture 111, low-speed section 12, pit texture 121. Detailed Implementation

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0020] To keep the drawings concise, each figure only schematically shows the parts relevant to the invention, and these do not represent the actual structure of the product. Furthermore, to facilitate understanding, in some figures, only one of components with the same structure or function is schematically depicted, or only one is labeled. In this document, "one" not only means "only one," but can also mean "more than one."

[0021] It should also be further understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0022] In this document, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] Furthermore, in the description of this application, the terms "first," "second," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance. It should be noted that the above embodiments can be freely combined as needed. The above are merely preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

[0024] refer to Figure 1 The present invention provides an oil-free lubricated cylinder liner for a Stirling engine, comprising a cylinder liner body 1, wherein the inner wall of the cylinder liner body 1 is divided along its axial direction into a high-speed section 11 and a low-speed section 12 located on both sides of the high-speed section 11; the inner wall surface of the high-speed section 11 is provided with a continuous mesh texture 111, and the inner wall surface of the low-speed section 12 is provided with an array of recessed textures 121, wherein the mesh texture 111 and the recessed textures 121 form a gradient surface texture along the axial direction of the cylinder liner body 1.

[0025] In this embodiment, a gradient surface texture is set on the inner surface of the cylinder liner according to the reciprocating speed characteristics of the piston. The high-speed section 11 strengthens the gas dynamic pressure bearing through the mesh texture 111, and the low-speed section 12 optimizes anti-adhesion and wear debris storage through the pit texture 121, fully releasing the gas lubrication potential and realizing wear reduction and life extension of the dynamic seal friction pair. It aims to solve the problem that the traditional single surface structure of the cylinder liner cannot adapt to the difference in piston reciprocating speed and the gas lubrication effect is insufficient.

[0026] Specifically, currently, the industry mainly improves wear resistance by optimizing soft piston ring materials (such as improving PTFE filler), while there is little research on hard cylinder liners. Their surfaces are mostly polished with a single roughness, without functional control over the uneven piston reciprocating speed. This results in two core problems for the dynamic seal friction pair: insufficient lubrication adaptability and insufficient exploitation of gas lubrication potential.

[0027] Traditional single smooth surfaces cannot meet the requirements of different speed ranges. Existing smooth polished cylinder liners are prone to insufficient gas film bearing capacity in the high-speed range 11 or adhesive wear in the low-speed range 12. In this application, based on the speed difference of the reciprocating motion of the Stirling engine piston, the inner wall of the cylinder liner body 1 is divided into a high-speed range 11 and a low-speed range 12. The high-speed range 11 needs to enhance the gas dynamic pressure effect to reduce contact friction, while the low-speed range 12 needs to reduce surface adhesion and store wear debris.

[0028] Furthermore, traditional cylinder liner surface processing does not employ gradient morphology designed for gas lubrication characteristics, resulting in large fluctuations in gas film thickness and a significant proportion of power loss due to contact friction. Consequently, the wear life of the piston rings is insufficient to meet the long-term operation requirements of the engine. In this application, the Stirling engine cylinder liner-piston ring friction pair operates in a mixed state of "dry friction + gas lubrication," where the high-pressure working fluid can form a gas film through the tiny pits on the rough surface.

[0029] More specifically, the distribution of high-speed section 11 and low-speed section 12 is based on the reciprocating speed of the Stirling engine piston. Taking a crankshaft angle of 0°-360° as an example, 0° or 360° is the top dead center (TDC), 180° is the bottom dead center (BDC), and the area near BDC ±45° is the low-speed section 12. That is, the area near TDC or BDC is the low-speed section 12, and the rest is the high-speed section 11. The area near BDC is the low-speed section 12 with a speed <1m / s; the area near the midpoint is the high-speed section 11 with a speed >3m / s. On the cylinder liner body 1 itself, high-speed section 11 is located in the middle of the inner wall of the cylinder liner body 1, and low-speed section 12 is located on both sides of high-speed section 11, symmetrically arranged relative to high-speed section 11. High-speed section 11 increases the film bearing capacity, while low-speed section 12 reduces the friction contact area, stores dry friction debris, increases the PTFE transfer film coverage, and avoids localized adhesive wear; the zoned arrangement improves friction and lubrication conditions. Preferably, the high-speed section 11 is the 60% area in the middle of the inner wall of the cylinder liner body 1, and the low-speed section 12 is the 20% area on each side of the inner wall of the cylinder liner body 1.

[0030] It is worth noting that although surface texture technology has been applied in the field of liquid lubrication (such as cylinder liner honing in internal combustion engines), there has been no systematic research on the zonal design criteria, suitable manufacturing process, and gas lubrication enhancement mechanism of the gradient texture on the inner wall of the cylinder liner for the special scenario of oilless lubrication and uneven reciprocating speed of Stirling engines. This technological gap has led to wear and failure of dynamic seals, which has become a problem restricting the improvement of power density and service life of Stirling engines. Therefore, it is urgent to develop a cylinder liner gradient surface texture adapted to the piston reciprocating speed characteristics. By precisely controlling the texture parameters of different regions, the potential of gas lubrication can be fully released, achieving wear reduction and life extension of the dynamic seal friction pair. The gradient surface texture of this invention has significant advantages over traditional untextured or single-textured cylinder liners in terms of lubrication state and sealing performance. In the high-speed section 11, the gas film bearing capacity is improved; in the low-speed section 12, the friction contact area is reduced, dry friction debris is stored, and the PTFE transfer film coverage is improved, avoiding localized adhesive wear. Overall, the gradient surface texture improves friction and lubrication conditions. Moreover, the gradient surface texture does not damage the structural integrity of the cylinder liner body 1. After processing, the inner hole size and roughness of the cylinder liner body 1 meet the sealing requirements of the Stirling engine and satisfy the overall engine operation standards.

[0031] Furthermore, the parameters of the mesh texture 111 are as follows: the mesh cross angle is 30° to 150°, the groove depth is 0.1μm to 0.5μm, the width-to-width ratio is 0.2 to 0.5, the texture line width is 20μm to 100μm, and the texture line spacing is 200μm to 800μm. In this embodiment, when the piston moves at high speed, the working gas flows through the converging wedge region of the mesh texture 111, generating positive gas film pressure. Each mesh texture 111 forms a tiny gas dynamic pressure lubricating bearing, increasing the gas film bearing capacity and reducing the direct contact between the piston ring and the cylinder liner.

[0032] Furthermore, the recessed texture 121 is a circular recess with the following parameters: recess radius of 100μm to 300μm, depth-to-diameter ratio of 0.001 to 0.01, and the area occupancy of all recessed textures 121 on the inner surface of the low-speed section 12 is 10% to 40%. In this embodiment, the small size and high areal density of the circular recesses can reduce the contact area between the PTFE filler and the cylinder liner. At the same time, the deep valleys of the recessed texture 121 can store PTFE wear debris generated by dry friction, preventing the wear debris from plowing the cylinder liner surface. The inner wall of the low-speed section 12 provides a stable adhesion point for the transfer film, forming a uniform PTFE transfer film and improving dry friction lubrication conditions. It is worth noting that the recessed texture 121 can also be square, rhomboid, elliptical, oval, or other shapes, which are not further limited in this application. It is worth noting that the parameters of the mesh texture 111 in the high-speed section 11 and the parameters of the recessed texture 121 in the low-speed section 12 are determined through simulation and experimental optimization using a gas dynamic lubrication model. Specifically, a gas dynamic lubrication model of the Stirling engine cylinder liner-piston ring was established, and the influence of parameters such as texture form, depth, and density on the air film bearing capacity at different speeds was simulated and analyzed. The optimal texture form for high-speed section 11 and low-speed section 12 was determined using air film thickness, friction coefficient, and wear rate as evaluation indicators.

[0033] Furthermore, the inner wall surface of the low-speed section 12 is also provided with a mesh texture, and the mesh texture 111 is continuously distributed from the high-speed section 11 to the low-speed section 12; in the low-speed section 12, the pit texture 121 is combined with the mesh texture 111 to form a composite texture area, wherein the pit texture 121 is located in a closed area surrounded by the mesh lines of the mesh texture 111.

[0034] In this embodiment, the gradient surface texture can enhance the gas dynamic pressure bearing capacity of the high-speed section 11, optimize the anti-adhesion and wear debris storage of the low-speed section 12, and when paired with the filled PTFE piston ring, it can improve the friction and lubrication conditions of the piston ring, thereby reducing wear and extending its service life.

[0035] Specifically, in the composite texture region, the continuous mesh texture 111 serves as the basic bearing surface. Its regular mesh lines help guide the flow of working gas in the high-speed section 11. Utilizing the gas dynamic pressure effect generated by the high-speed piston movement, a uniformly distributed and stronger micro-gas film is formed, effectively isolating the piston rings from direct contact with the cylinder liner surface and significantly reducing the friction coefficient. Simultaneously, in the low-speed section 12, the recessed texture 121 is precisely fabricated within the mesh of the mesh texture 111. These recesses serve two purposes: firstly, as micro-chip storage grooves, effectively capturing PTFE wear debris generated during friction and preventing it from participating in secondary wear; secondly, under boundary lubrication conditions, they also act as temporary storage points for solid lubricant (PTFE from the piston rings) and form localized pressure micro-zones, further optimizing the friction state in that region.

[0036] Furthermore, the cylinder liner body 1 is made of ion-nitrided stainless steel. Specifically, the cylinder liner is made of high-temperature ion-nitrided duplex stainless steel, which combines corrosion resistance and wear resistance, and has excellent compatibility with PTFE-filled piston rings. The pretreatment process is as follows: rough machining to preliminary dimensions → solution treatment → aging treatment → ion nitriding, to ensure that the cylinder liner substrate has high hardness and provides a stable base material for subsequent texturing.

[0037] Furthermore, the mesh texture 111 is integrally formed on the inner wall of the cylinder liner body 1 through a honing process; the pit texture 121 is selectively prepared on the inner wall of the low-speed section 12 through a laser surface processing process. Specifically, the inner surface of the cylinder liner is honed using a honing machine to form a uniform plateau mesh texture 111, providing a reference surface for subsequent laser processing; a pit texture is processed in the low-speed section 12 using laser processing equipment. The honing and laser processing processes are mature and controllable, suitable for mass production, and the post-processing steps are simple, requiring no additional coating, reducing manufacturing costs and facilitating engineering applications. It is worth noting that the cylinder liner stainless steel undergoes rough turning → solution treatment → aging → ion nitriding treatment; a honing machine equipped with cubic boron nitride strips is used to process the honing mesh texture on the inner surface of the cylinder liner. Since it is difficult to completely guarantee that the mesh texture parameters are consistent with the design parameters in actual processing, the actual processed mesh texture mainly controls the two core parameters, cross angle and roughness (groove depth), to be consistent with the design values. Then, a nanosecond laser is used to process a circular pit-like texture on the low-speed section 12 of the cylinder liner; a three-dimensional optical surface morphology instrument is used to detect the texture parameters to ensure that the actual texture parameters deviate from the design parameters by less than 20%.

[0038] Furthermore, this application provides a Stirling engine, including the oil-free lubricated cylinder liner of the Stirling engine in any of the above embodiments.

[0039] It should be noted that the above embodiments can be freely combined as needed. The above are merely preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A Stirling engine oil-free lubricated cylinder liner, characterized in that, Includes a cylinder liner body, wherein the inner wall of the cylinder liner body is divided along its axial direction into a high-speed section and a low-speed section located on both sides of the high-speed section; The inner wall surface of the high-speed section is provided with a continuous mesh texture, and the inner wall surface of the low-speed section is provided with an array of pit textures. The mesh texture and the pit textures form a gradient surface texture along the axial direction of the cylinder liner body.

2. The oilless lubricated cylinder liner for a Stirling engine according to claim 1, characterized in that, The parameters of the mesh texture are as follows: the mesh cross angle is 30° to 150°, the groove depth is 0.1μm to 0.5μm, the width-to-width ratio is 0.2 to 0.5, the texture line width is 20μm to 100μm, and the texture line spacing is 200μm to 800μm.

3. A Stirling engine oil-free lubricated cylinder liner according to any one of claims 1 or 2, characterized in that, The pit texture is a circular pit with the following parameters: pit radius of 100μm to 300μm, depth-to-diameter ratio of 0.001 to 0.01, and the area occupancy of all pit textures on the inner surface of the low-speed section is 10% to 40%.

4. The Stirling engine oil-free lubricated cylinder liner according to claim 3, characterized in that, The inner wall surface of the low-speed section is also provided with the mesh-like texture, and the mesh-like texture is continuously distributed from the high-speed section to the low-speed section; In the low-speed range, the pit texture and the mesh texture are combined to form a composite texture area, wherein the pit texture is located relative to the closed area enclosed by the mesh lines of the mesh texture.

5. The oilless lubricated cylinder liner for a Stirling engine according to claim 1, characterized in that, The cylinder liner body is made of ion-nitrided stainless steel.

6. The oilless lubricated cylinder liner for a Stirling engine according to claim 1, characterized in that, The distribution of the high-speed and low-speed segments is based on the reciprocating speed of the Stirling engine piston. The top dead center is defined as 0° or 360° of the crankshaft angle, the bottom dead center is defined as 180°, the low-speed segment is defined as the near dead center ±45°, and the rest is defined as the high-speed segment.

7. The oilless lubricated cylinder liner for a Stirling engine according to claim 1, characterized in that, The mesh texture is integrally formed on the inner bore wall of the cylinder liner body through a honing process; the pit texture is selectively prepared on the inner bore wall in the low-speed section through a laser surface processing process.

8. A Stirling engine, characterized in that, Including the oilless lubricated cylinder liner for a Stirling engine as described in any one of claims 1-7.

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