Cylinder block structure and connection method for air-cooled two-stroke aviation piston engine

Abstract

The present application belongs to the technical field of aviation piston engine. The present application discloses a kind of cylinder body structure and connecting method of air-cooled two-stroke aviation piston engine, to solve the problem of heat load concentration, aluminum alloy strength decline, cylinder deformation caused by the contact thermal resistance of aluminum alloy cylinder and cylinder cover connection area is too large, in the present application, connecting screw and threaded hole are matched with fine thread to increase contact area, reduce contact thermal resistance and enhance heat conduction performance;Threaded hole counterbore is treated to reduce the amount of residual gas in the hole, reduce the obstruction of gas to heat conduction;Connecting anti-loosening strictly prohibits the use of thread glue, to avoid local temperature rise. And using TC4 titanium alloy screw material, threaded hole circumferential uniform arrangement and enough connection depth and other supporting design, systematically make the heat of connection area conduct and dissipate efficiently, avoid the strength decline caused by heat load concentration, improve the anti-deformation ability of cylinder, ensure that the roundness and cylindricity of cylinder meet the design requirements, the engine performance maintains stable under design condition.

Description

Technical Field

[0001] This invention belongs to the field of aviation piston engine technology, specifically relating to a cylinder block structure and connection method for an air-cooled two-stroke aviation piston engine. Background Technology

[0002] With the booming development of the unmanned industry, low-altitude economy, and general aviation industry, two-stroke air-cooled aero-piston engine technology has been widely used due to its strong adaptability to environmental temperature changes and high reliability, and has now become the mainstream technology supporting industrial development. However, the cylinder block is the main pressure-bearing component of the engine. High speed, high power-to-weight ratio, processing efficiency, and technical stability are the core characteristics of this technology. On the one hand, it needs to ensure a certain degree of rigidity while maintaining the complex pipeline layout of intake, exhaust, and cooling channels. On the other hand, it needs to ensure the requirements of high temperature and high pressure operation while taking into account processing economy and strong adaptability to external temperature changes. Therefore, aluminum alloy cast cylinder blocks have been highly favored in the field of aero-piston engine design and application due to their excellent comprehensive performance.

[0003] As a crucial component of the combustion system, the cylinder block provides a fixed trajectory for the piston's movement. Maintaining its roundness and cylindricity under alternating loads of high temperature and high pressure airflow is key to ensuring stable performance. Due to the high compactness of the aero-piston engine's structural layout, the cylinder block, as part of the combustion chamber, also serves as the mounting base for intake and exhaust ports, sensors, high-voltage coils, and other wiring harnesses. Therefore, its external design is often asymmetrical. When the engine operates under high load for extended periods, the weakest points of the cylinder block exhibit uneven deformation in three-dimensional space along its radial and crankshaft axial directions. Changes in the angle between the cylinder block axis and the crankshaft axis cause the angle between the cylinder block axis and the crankshaft axis of another cylinder to deviate by 90°. Lateral forces occur on the piston and cylinder block along the crankshaft axis, altering the stress conditions in the contact area between the piston rings and the cylinder block. Leakage can occur between the cylinder block and piston, and even cylinder scoring due to accelerated wear.

[0004] Furthermore, in traditional threaded connection assembly, a process clearance is usually left between the bottom hole of the threaded hole and the tail end of the screw. After assembly, this clearance forms a closed or semi-closed gas cavity. The residual air in the cavity becomes a poor medium for heat conduction, further increasing the equivalent thermal resistance of the connection area and exacerbating the risk of concentrated heat load. At the same time, if thread-locking adhesive is used to prevent loosening during assembly, changes in the thread-locking adhesive at high temperatures may cause local temperature increases in the connection area, further deteriorating the thermal environment of the connection area.

[0005] Therefore, how to control the contact thermal resistance of the connection area, increase the effective contact area of ​​the connection area, and reduce the amount of residual gas in the threaded hole so that the heat in the connection area can be efficiently conducted and dissipated, and avoid the decrease in the strength of the aluminum alloy material and the deformation of the cylinder caused by the concentration of heat load in the connection area, is a core technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to solve the above problems and provide a cylinder block structure and connection method for an air-cooled two-stroke aero piston engine.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A cylinder block structure for an air-cooled two-stroke aero piston engine includes a cylinder block, a cylinder head, and connecting bolts connecting the cylinder block and the cylinder head.

[0008] The connecting screws are TC4 titanium alloy screws. The cylinder body has evenly distributed threaded holes along its circumference for mounting these screws. The cylinder head is fixedly connected to the cylinder body via these connecting screws. There are at least eight connecting screws, and the screws are connected to the threaded holes using fine-pitch threads, with an effective connection depth of at least 25mm. This increases the contact area between the screws and the threaded holes, reduces the thermal resistance of the connection area, and enhances the thermal conductivity of the connection area.

[0009] The bottom hole of the connecting threaded hole is countersunk to reduce the amount of residual gas in the connecting threaded hole after assembly, thereby reducing the obstruction of heat conduction in the connecting area by the gas in the threaded hole.

[0010] The connecting screws are not secured with thread-locking adhesive to avoid localized temperature increases in the connection area caused by the thread-locking adhesive during high-temperature engine operation.

[0011] As a preferred embodiment, the cylinder block is a cast aluminum alloy air-cooled cylinder block, and the outer surface of the cylinder block is provided with heat dissipation fins arranged in a variable cross-section ring rib structure at equal intervals along the cylinder block axis, so as to match the characteristic of decreasing heat load along the cylinder block axis.

[0012] As a further preferred embodiment, the heat dissipation fins are provided with clearance structures for installing wiring harnesses or pipes, and the heat dissipation fins near the cylinder body on the combustion chamber side have at least 3 layers of closed-loop clearance structures with holes or openings.

[0013] As a further preferred embodiment, the nominal diameter of the thread of the connecting screw does not exceed M8.

[0014] As a further preferred option, the anti-loosening method for the connecting screw is to increase the preload or to use a fuse.

[0015] This invention also provides a method for connecting the cylinder block of an air-cooled two-stroke aero-piston engine, comprising the following steps: The cylinder body is evenly arranged with no less than 8 connecting threaded holes along the circumference. The connecting threaded holes adopt a fine thread design, and the bottom hole of each connecting threaded hole is countersunk. TC4 titanium alloy screws are selected as the connecting fasteners. The TC4 titanium alloy screws are matched with the fine thread specification of the connecting threaded hole, and the nominal thread diameter does not exceed M8. Screw the TC4 titanium alloy screws into the connecting threaded holes to fix the cylinder head to the cylinder body. The effective connection depth of each screw is not less than 25mm. Implement anti-loosening measures for all TC4 titanium alloy screws by increasing the preload or using a safety wire; do not use thread-locking adhesive.

[0016] The beneficial effects of this invention are as follows: This invention provides a cylinder block structure and connection method for an air-cooled two-stroke aero-piston engine. With thermal resistance control in the connection area as its core, it achieves the following technical effects through increasing the contact area of ​​the connection region, reducing contact thermal resistance, and decreasing the amount of residual gas in the threaded holes: First, by employing fine-pitch threads for connection, compared to traditional coarse-pitch threads, the smaller pitch and greater number of threads significantly increase the effective contact area within the same thread engagement length. This increased contact area directly reduces the thermal resistance between the connecting screw and the cylinder threaded hole, allowing heat from the connection area to be efficiently conducted to the cylinder cooling fins and dissipated to the external environment through a larger threaded contact surface. The improved thermal conductivity of the connection area effectively reduces the temperature of the aluminum alloy material around the threaded hole, preventing localized strength reduction due to concentrated heat load and maintaining the load-bearing capacity and clamping force stability of the connection area.

[0017] Second, by countersinking the bottom of the threaded hole, the process clearance and enclosed gas cavity at the bottom of the threaded hole after assembly are eliminated. Residual air, as a poor medium for heat conduction, has a much lower thermal conductivity than aluminum alloy and screw metal. Countersinking reduces the amount of residual gas in the threaded hole, thereby reducing the additional thermal resistance of the gas in the hole to the overall heat conduction path of the connection area, further reducing the equivalent thermal resistance of the connection area, and making the heat conduction path smoother. Combined with the high contact area design of the fine thread, the two work synergistically to achieve overall optimization of the thermal resistance of the connection area.

[0018] Third, by strictly prohibiting the use of thread-locking adhesive during the connection and assembly process, the potential for localized temperature rise in the connection area caused by the physical and chemical changes of thread-locking adhesive under the continuous high-temperature operating environment of the engine is eliminated at the source. By prohibiting the use of thread-locking adhesive, combined with increasing the preload or using fuses as alternative anti-loosening methods, the reliability of the connection is ensured while protecting the thermal environment of the connection area from additional adverse effects.

[0019] Fourth, TC4 titanium alloy screws are selected as the connecting fasteners. Their mechanical properties decay less in high-temperature environments than those of conventional steel screws. They can continuously provide stable and reliable clamping force under high-load conditions with cylinder temperatures ≥180℃. This creates a synergistic effect with thermal resistance control measures in the connection area. Thermal resistance control reduces the temperature of the connection area, and the properties of TC4 material ensure the stability of the clamping force within this temperature range.

[0020] 5. By evenly arranging at least 8 threaded holes along the circumference of the cylinder body, the clamping force of the cylinder head on the cylinder body is ensured to be applied uniformly along the circumference, effectively avoiding local stress concentration and uneven deformation of the cylinder body caused by uneven clamping force distribution. Combined with the screw design with an effective connection depth of at least 25mm, sufficient thread bearing length is provided, fully guaranteeing the reliability of the connection and the uniformity of the clamping force.

[0021] VI. By designing the cylinder block cooling fins as a variable cross-section ring fin structure with equal spacing along the cylinder block axis, and matching the decreasing heat load distribution along the cylinder block axis, both heat dissipation efficiency and cylinder block structural rigidity are ensured. At least three layers of cooling fins near the combustion chamber employ a closed-loop clearance structure with through holes or openings, balancing the assembly requirements of wiring harnesses with the structural integrity of this high-temperature area, thus providing shape control-level assurance for the overall rigidity of the cylinder block under high-load conditions.

[0022] In summary, this invention uses thermal resistance control in the connection area as the core technical means, supplemented by cylinder block shape and structure optimization, to systematically improve the overall rigidity and deformation resistance of the assembled aluminum alloy cylinder block, achieving an effective balance between lightweight design and high-load performance assurance.

[0023] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1This is a cross-sectional view of the cylinder block in an embodiment of the present invention.

[0025] Figure 2 This is a top view of the cylinder block in an embodiment of the present invention.

[0026] Reference numerals: 1-Cylinder block; 2-Heat dissipation fins; 3-Connecting threaded hole. Detailed Implementation

[0027] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0028] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0029] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0030] Example 1 like Figures 1-2 As shown, this embodiment provides a cylinder block structure for an air-cooled two-stroke aero-piston engine. With thermal resistance control of the connection area as the core, by increasing the contact area of ​​the connection area, reducing the contact thermal resistance, and reducing the amount of residual gas in the threaded hole, the heat in the connection area is efficiently conducted and dissipated. This avoids the heat load concentration in the connection area, which would lead to a decrease in the strength of the aluminum alloy material and cylinder block deformation. It also ensures that the roundness and cylindricity of the cylinder barrel meet the design requirements, and that the engine performance remains stable under the design conditions.

[0031] like Figure 1 As shown, the cylinder block 1 is a cast aluminum alloy air-cooled cylinder block. The outer surface of the cylinder block 1 is provided with heat dissipation fins 2 arranged at equal intervals along the axis of the cylinder block 1. The heat dissipation fins 2 have a variable cross-section ring fin structure to match the decreasing heat load distribution characteristics along the axis of the cylinder block 1, so as to ensure heat dissipation efficiency while taking into account the structural rigidity of the cylinder block 1.

[0032] The cooling fins 2 are provided with clearance structures for installing wiring harnesses or pipes. The cooling fins 2 near the combustion chamber side of the cylinder block 1 have at least three layers of closed-loop clearance structures with holes or openings. This closed-loop design does not damage the annular closed cross section of the cooling fins 2, ensuring the structural integrity and rigidity of this high-temperature area.

[0033] The cylinder body 1 has evenly distributed threaded holes 3 for installing connecting screws along its circumference. These threaded holes 3 feature fine-pitch threads, and the bottom holes are countersunk. TC4 titanium alloy screws are used, matching the fine-pitch thread specifications of the threaded holes 3, with a nominal thread diameter not exceeding M8. At least eight threaded holes 3 are evenly distributed along the top circumference of the cylinder body 1, with an effective connection depth of at least 25mm. The cylinder head is fixedly connected to the cylinder body 1 using TC4 titanium alloy screws. The connecting screws are prevented from loosening by increasing the preload or using a safety wire; threadlocker is not used.

[0034] Example 2 This embodiment describes a connection method for the cylinder block structure in Embodiment 1, including the following steps: Step 1: Machining the connecting threaded holes. At least eight connecting threaded holes 3 are uniformly machined circumferentially on the cylinder body 1. These connecting threaded holes 3 employ a fine-pitch thread design. After machining, the bottom hole of each connecting threaded hole 3 is countersunk. The fine-pitch thread design increases the effective contact area between the threaded pairs, reduces the contact thermal resistance of the connection area, and enhances the thermal conductivity of the connection area. The countersunk treatment eliminates the process clearance between the bottom hole and the screw tail end, reduces the amount of residual gas in the connecting threaded hole 3 after assembly, and reduces the additional thermal resistance of the gas inside the hole to the heat conduction path.

[0035] Step Two: Select Connecting Fasteners. TC4 titanium alloy screws are selected as the connecting fasteners. The TC4 titanium alloy screws are compatible with the fine thread specification of the connecting threaded hole 3, and the nominal thread diameter does not exceed M8. TC4 titanium alloy exhibits less mechanical property degradation at high temperatures compared to conventional steel screws, and can continuously provide stable and reliable clamping force under high-load conditions where the operating temperature of cylinder 1 is not lower than 180℃.

[0036] Step 3: Assembly and Connection. Align the mating surfaces of the cylinder head and cylinder body 1. Screw each TC4 titanium alloy screw through the corresponding mounting holes on the cylinder head and into the threaded holes 3 on the cylinder body 1 to securely connect the cylinder head and cylinder body 1. The effective connection depth of each screw should be no less than 25mm to ensure sufficient thread load-bearing length and heat conduction path length. The threaded holes 3 should be evenly distributed around the circumference of the cylinder body 1, with no fewer than 8 holes, ensuring that the clamping force of the cylinder head on the cylinder body 1 is applied evenly along the circumference.

[0037] Step 4: Anti-loosening treatment. Implement anti-loosening measures for all TC4 titanium alloy screws. Anti-loosening methods include increasing the preload or using a fuse. The use of threadlocker is strictly prohibited. This eliminates the potential for localized temperature rise in the connection area caused by threadlocker under the high-temperature operating environment of the engine, ensuring the overall effectiveness of the thermal resistance control scheme for the connection area.

[0038] This invention employs three measures in synergy: increasing the contact area and reducing contact thermal resistance through fine-pitch threads, reducing residual gas in the holes through countersinking, and eliminating additional heat sources by eliminating the use of threadlocker. These three measures ensure efficient heat dissipation in the connection area, preventing the reduction in the strength of the aluminum alloy material caused by concentrated heat load in the connection area, and fundamentally improving the deformation resistance of the cylinder block 1. Combined with the high-temperature mechanical properties of the TC4 screws, the uniform arrangement of threaded holes, and sufficient connection depth, the system systematically ensures that the roundness and cylindricity of the aluminum alloy cylinder block meet design requirements during operation, that the piston rings effectively perform their sealing function, and that engine performance remains stable under design conditions, while also meeting the stringent lightweight requirements of aerospace products.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A cylinder block structure for an air-cooled two-stroke aero-piston engine, comprising a cylinder block, a cylinder head, and connecting bolts connecting the cylinder block and the cylinder head, characterized in that: The connecting screws are TC4 titanium alloy screws. The cylinder body has threaded holes evenly distributed circumferentially for installing the connecting screws. The cylinder head is fixedly connected to the cylinder body by the connecting screws. The number of connecting screws is no less than 8, and the connecting screws and the threaded holes are connected by fine thread engagement, with an effective connection depth of no less than 25mm, so as to increase the contact area between the connecting screws and the threaded holes, reduce the contact thermal resistance of the connection area, and enhance the thermal conductivity of the connection area. The bottom hole of the connecting threaded hole is countersunk to reduce the amount of residual gas in the connecting threaded hole after assembly, thereby reducing the obstruction of heat conduction in the connecting area by the gas in the threaded hole. The connecting screws are not secured with thread-locking adhesive to avoid localized temperature increases in the connection area caused by the thread-locking adhesive during high-temperature engine operation.

2. The cylinder block structure of the air-cooled two-stroke aero-piston engine according to claim 1, characterized in that, The cylinder block is a cast aluminum alloy air-cooled cylinder block. The outer surface of the cylinder block is provided with heat dissipation fins arranged in a variable cross-section ring rib structure at equal intervals along the cylinder block axis to match the characteristic of decreasing heat load along the cylinder block axis.

3. The cylinder block structure of the air-cooled two-stroke aero-piston engine according to claim 2, characterized in that, The heat dissipation fins are provided with clearance structures for installing wiring harnesses or pipes. The heat dissipation fins near the cylinder body on the combustion chamber side have at least 3 layers of closed-loop clearance structures with holes or openings.

4. The cylinder block structure of the air-cooled two-stroke aero-piston engine according to claim 1, characterized in that, The nominal diameter of the thread of the connecting screw does not exceed M8.

5. The cylinder block structure of the air-cooled two-stroke aero-piston engine according to claim 1, characterized in that, The anti-loosening method for the connecting screw is to increase the preload or to use a fuse.

6. A method for connecting the cylinder block of an air-cooled two-stroke aero-piston engine, characterized in that, Includes the following steps: The cylinder body is evenly arranged with no less than 8 connecting threaded holes along the circumference. The connecting threaded holes adopt a fine thread design, and the bottom hole of each connecting threaded hole is countersunk. TC4 titanium alloy screws are selected as the connecting fasteners. The TC4 titanium alloy screws are matched with the fine thread specification of the connecting threaded hole, and the nominal thread diameter does not exceed M8. Screw the TC4 titanium alloy screws into the connecting threaded holes to fix the cylinder head to the cylinder body. The effective connection depth of each screw is ≥25mm. Implement anti-loosening measures for all TC4 titanium alloy screws by increasing the preload or using a safety wire; do not use thread-locking adhesive.

Images