A method for assembling a crankshaft for a small aero-piston engine

Abstract

This invention discloses a crankshaft assembly method for small aero-engine piston engines, belonging to the field of aero-engine manufacturing technology. It aims to solve the problems of stress concentration, poor adaptability to high-temperature thermal expansion, easy damage to the conical surface during assembly, and insufficient connection reliability in existing crankshaft tapered surface connections. This method includes a prefabrication process for the connected parts and an assembly process: the prefabrication process uses a segmented fit design with interference fit at the large end and transition fit at the small end for the tapered hole of the connected parts that mates with the long tapered surface of the crankshaft, and hardens the contact end face of the nut; the assembly process employs a step-by-step process of local heating at the large end of the tapered hole, axial pre-assembly with separate tooling, and final assembly verification after cooling. This invention can ensure an effective tapered surface engagement rate of over 85%, reduce assembly stress and tapered surface damage, adapt to wide temperature conditions, and significantly improve the reliability and service life of the crankshaft-load end connection.

Description

Technical Field

[0001] This invention belongs to the field of aircraft generator manufacturing technology, and relates to a crankshaft assembly method for a small aircraft piston engine. Background Technology

[0002] In the general aviation field, small aircraft piston engines are widely used as power plants for various unmanned aerial vehicles and small aircraft due to their compact structure, high power-to-weight ratio, and good economy. As the core component of an aircraft piston engine, the crankshaft is responsible for converting the reciprocating linear motion of the piston into rotational motion and transmitting power to the load end. One end of the crankshaft obtains starting torque and outputs electrical energy through a fixed starter generator, while the other end drives airflow to generate thrust and pull force through a fixed propeller. The reliability of the connection between the crankshaft and the load end directly determines the engine's working stability, safety, and overall service life.

[0003] In small and medium-sized aero-piston power units, the crankshaft will move axially within the bearing clearance range as the working load changes. At the same time, it is limited by the size of the power shaft. Therefore, in order to avoid stress concentration and fracture risks caused by the shoulder structure, the crankshaft and the connected parts (propeller disk, generator rotor, etc.) at the load end generally adopt a tapered surface fit to achieve torque transmission, and use threaded fastening structure to complete the assembly and fixation.

[0004] In the existing technology, relevant optimizations have been carried out on the crankshaft tapered surface connection structure and assembly process. For example, the integrated structural design of the tapered shaft and the threaded shaft is optimized to ensure the strength of the connection base. The spline structure is used to assist in the transmission of torque to reduce axial force constraints. Alternatively, temperature difference assembly and step-by-step pre-tightening methods are used to optimize the assembly effect, which improves the basic reliability of the tapered surface connection to a certain extent.

[0005] However, existing crankshaft tapered surface connection solutions still have many unavoidable technical defects in the actual operating conditions of small aero-piston engines: First, existing conical surface fits mostly adopt a uniform interference fit design with a full conical surface. Although this design can ensure the basic connection strength, it will cause the crankshaft conical surface to bear a large assembly stress and working stress. Since aero-piston engines are under cyclical alternating load conditions, excessive stress during long-term operation can easily lead to fatigue damage to the crankshaft and the connected parts. In severe cases, it can cause cracking of the connecting parts and connection failure, directly threatening the flight safety of the aircraft.

[0006] Secondly, the existing tapered bore structure design does not fully consider its adaptability to high-temperature operating conditions during engine operation. Small aero-piston engines generate significant temperature rises during operation, while crankshafts are mostly made of high-strength alloy steel, and the connected parts are mostly made of aluminum alloy. There is a significant difference in the coefficient of thermal expansion between the two. Under high-temperature conditions, the difference in the expansion of different materials will lead to a significant reduction in the effective contact area of ​​the tapered surface mating, resulting in problems such as loose connection and torque transmission failure, and failing to guarantee connection stability over a wide temperature range.

[0007] Third, existing assembly processes are prone to causing irreversible damage to the precision of the conical surface fit. During conventional assembly, when preload is applied by rotating the fastening nut, the rotational torque of the nut can easily cause the connected parts to rotate slightly in the circumferential direction relative to the crankshaft conical surface. This not only leads to the conical surface being twisted and deformed, generating assembly internal stress, but also wears down the conical surface mating surface, reduces the effective contact area, and ultimately results in insufficient effective engagement rate of the conical surface fit, failing to meet the high-precision fit requirements of aero-engines.

[0008] Fourth, existing technologies lack protective designs for the stress-bearing end faces of the connected components. During assembly pre-tightening and long-term alternating load operation, the end faces of the connected components in contact with the nut and washer are prone to crushing, wear, and plastic deformation, leading to pre-tightening force attenuation, loosening of the connection, further exacerbating the failure risk of the conical surface connection and shortening the overall service life of the machine.

[0009] In addition, the existing assembly scheme is not well adapted to the control of foreign matter and the step-by-step application of preload during the assembly process. It is easy for foreign matter and improper application of preload in the assembly process to lead to a decrease in the accuracy of the conical surface fit. It cannot take into account both assembly efficiency and fit reliability, and it is difficult to meet the core design requirements of small aero-engines for high power-to-weight ratio, high safety and long service life.

[0010] Therefore, developing a method for assembling small aero-piston engine crankshafts that can adapt to a wide range of operating temperatures, solve stress concentration in conical assembly, ensure effective contact rate of mating surfaces, and improve long-term reliability of connections has become a pressing technical problem in this field. Summary of the Invention

[0011] To address the technical problems of existing crankshaft tapered surface connections in small aero-engines, such as stress concentration, connection failure due to thermal expansion differences under high-temperature conditions, and poor long-term reliability, this invention aims to provide a crankshaft assembly method that is suitable for the wide-temperature operating environment of aero-engines, has high assembly precision, and reasonable stress distribution. Through the synergistic optimization of the tapered hole structure and assembly process, the reliability of the crankshaft connection to the load end, the stability of torque transmission, and the service life of the entire machine are improved.

[0012] To achieve the above objectives, the present invention provides the following technical solution: A crankshaft assembly method for a small aircraft piston engine, wherein the crankshaft is the power transmission shaft of the small aircraft piston engine, and one end of the crankshaft is provided with a long tapered surface for torque transmission through the tapered surface engagement with the load-bearing component. The method is characterized by comprising a pre-assembly component fabrication process and an assembly implementation process. The pre-assembly component fabrication process includes the following steps: Step a: The connected part that mates with the long conical surface of the crankshaft is prepared by processing an aluminum alloy substrate. A conical hole corresponding to the long conical surface is machined on the connected part. The conical hole adopts a segmented fit design: it is divided into an interference fit section near the large end of the conical hole and a transition fit section near the small end of the conical hole. After the connected part is assembled with the crankshaft, the large end of the conical hole forms an interference fit with the long conical surface, and the small end of the conical hole forms a transition fit with the long conical surface. Step b: Perform surface hardening treatment on the end face area of ​​the connected parts that is in contact with the nut washer to increase the surface hardness of the area; The assembly process includes the following steps: Step S1: Before assembly, clean the surface of the parts to be assembled, and locally heat the area corresponding to the large end of the tapered hole of the connected parts to make the area expand due to heat. Step S2: Place the heated connected parts onto the long conical surface of the crankshaft. Using separate tooling nuts and tooling washers, apply preload in stages along the axial direction of the crankshaft to press the connected parts into the preset mating position on the long conical surface, thus completing the pre-assembly. Step S3: After the connected parts have cooled down, remove the tooling nut and tooling washer, clean the threaded surface of the conical end of the crankshaft and apply thread sealant, replace the one-piece nut washer and screw it into the thread of the conical end, complete the final installation according to the preset final preload torque, and check the final installation torque.

[0013] Preferably, in step a, the taper deviation of the interference fit section is controlled to be 0′~-2′, and the taper deviation of the transition fit section is controlled to be ±1′.

[0014] Preferably, in step b, the surface hardening treatment is carried out by sulfuric acid hard anodizing, and the surface hardness of the treated rear end area is not less than 500 HV.

[0015] Preferably, the crankshaft is manufactured from high-strength, low-carbon alloy steel, and its long tapered surface has a surface hardness of not less than 55 HRC. The aluminum alloy base material of the connected parts is selected from 2A12 aluminum alloy or 7075 aluminum alloy. The crankshaft uses high-hardness, high-strength alloy steel, while the connected parts use relatively soft aluminum alloy. The two form a soft-hardness adapted mating structure, which can avoid damage to the tapered mating surface due to excessive hardness during assembly, and at the same time adapt to the operating conditions of the engine's cyclic alternating load. Preferably, in step S1, a carburetor cleaner is used to clean the long conical surface of the crankshaft and the inner wall of the conical hole of the connected parts, and then wiped dry with a lint-free cloth to remove excess material from the surface; the temperature of the local heating is controlled at 80℃~100℃ and kept warm until the temperature of the heating area of ​​the connected parts is uniform.

[0016] Preferably, in step S2, the tooling shim has two working surfaces, one of which is surface A, which contacts the tooling nut, and the other of which is surface B, which contacts the connected parts. The surface roughness of surface A is less than that of surface B, and the overall hardness of the tooling shim is lower than that of the end face of the connected parts after hardening treatment, so as to avoid damage to the contact surface of the connected parts during the pre-tightening process of the integrated nut shim.

[0017] Preferably, the tooling gasket is made of 65Mn material, and its surface hardness is controlled at 200HV~300HV; the surface roughness of surface A is controlled at Ra3.2, and the surface roughness of surface B is controlled at Ra6.3.

[0018] Preferably, in step S2, the preload torque applied to the tooling nut during pre-assembly is 50% of the final preload torque; during the process of applying the preload force in stages, tooling shims with a thickness of 2mm, 2.5mm or 3mm are replaced according to the axial pressing position of the connected parts to adapt to the torque application requirements of different axial pressing positions of the connected parts, ensuring that the tooling shims do not deform under high torque preload conditions.

[0019] Preferably, in step S3, the tooling nut and tooling washer are removed after the connected parts have cooled to a surface temperature not exceeding 30°C; after final assembly, the effective contact area between the long conical surface and the conical hole accounts for more than 85% of the total contact conical surface area.

[0020] Preferably, in step S3, the threadlocker is a medium-strength threadlocker.

[0021] The beneficial effects of this invention are as follows: This invention addresses the stress concentration and thermal expansion mismatch issues commonly found in slender conical structures used in aerospace applications. By employing a segmented fit design for the conical holes of the connected components, it overcomes the limitations of traditional uniform interference fits on a full conical surface. This avoids the problems of excessive overall stress in the crankshaft and connected components, and the susceptibility to fatigue damage under long-term alternating loads, which are often associated with full conical interference fits. Furthermore, it is specifically adapted to the wide-temperature operating environment of small aero-engines, effectively mitigating the difference in thermal expansion coefficients between the steel crankshaft and the aluminum alloy connected components. This ensures stable and effective contact throughout the engine's operation, from room temperature assembly to high-temperature operation, preventing loosening and torque transmission failure due to thermal expansion differences. Simultaneously, the flexible and rigid matching design between the steel crankshaft and the aluminum alloy connected components avoids hard wear on the mating surfaces during assembly, further ensuring the accuracy of the conical fit and reducing the risk of fatigue damage.

[0022] The assembly process supporting the present invention eliminates the interference caused by interference fit in the assembly process in advance by locally heating the interference fit area at the large end of the tapered hole, avoiding the wear of the mating surface caused by direct friction of the tapered surface during the press-fitting process. At the same time, a split-type tooling nut and gasket are used for axial pre-assembly, which can ensure that the connected parts only move along the axial direction of the crankshaft during the pre-tightening process, eliminating the problem that the nut rotates to drive the connected parts to rotate circumferentially in traditional assembly, avoiding the generation of assembly internal stress due to the distortion of the tapered surface, and also preventing the reduction of the effective contact area of the tapered surface due to rotational wear, ensuring the mating accuracy of the tapered surface from the source of assembly. At the same time, the design of the split-type tooling can avoid the frictional damage of the traditional integral nut gasket to the end face of the connected parts, protect the stressed end face of the connected parts from the source of assembly, and further ensure the long-term stability of the pre-tightening force.

[0023] The present invention also conducts sulfuric acid hard anodic oxidation treatment on the end face where the connected parts contact the nut gasket, significantly improving the surface hardness and wear resistance of this stressed area, avoiding the problems of end face crushing and plastic deformation during assembly pre-tightening and long-term alternating load operation, effectively preventing the attenuation of the pre-tightening force and the occurrence of connection loosening, and ensuring the long-term use stability of the connection structure. At the same time, a step-by-step assembly process of local heating pre-assembly and cooling final assembly review, combined with hierarchical torque control, can achieve precise positioning of the connected parts, avoid the problem of over-fitting. After final assembly, it can ensure that the proportion of the effective contact area between the long tapered surface of the crankshaft and the tapered hole of the connected parts reaches more than 85%, greatly improving the stability of torque transmission, reducing the risk of fatigue failure of the connecting parts, and fully meeting the core design requirements of small aviation piston engines for high safety and long service life.配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度的影响,进一步保障锥面有效接触率配合装配前的清洁工序,可彻底避免多余物、装配磨损对锥面配合精度影响,进一步保障锥面有效接触率配合装配前配套的装配工艺,通过对锥孔大端过盈区域的局部加热,提前消除装配过程中的过盈干涉,避免压装过程中锥面直接摩擦造成的配合面磨损;同时采用分体式的工装螺母与垫片进行轴向预装,能够在预紧过程中保证被连接件仅沿曲轴轴向运动,杜绝了传统装配中螺母旋转带动被连接件周向转动的问题,避免锥面被扭曲产生装配内应力,也不会因转动磨损导致锥面有效接触面积缩减,从装配源头保障了锥面的配合精度。同时,分体式工装的设计可避免传统一体式螺母垫片对被连接件端面的摩擦损伤,从装配源头保护被连接件的受力端面,进一步保障预紧力的长期稳定性。 Other advantages, objectives and features of the present invention will be described in part in the subsequent specification, and to some extent, will be obvious to those skilled in the art based on the study of the following text, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the following specification. Brief Description of the Drawings

[0024] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in detail preferably with reference to the accompanying drawings, where: Figure 1 is a schematic structural diagram after the assembly of the crankshaft of a small aviation piston engine and the connected parts; Figure 2 is a sectional view of the segmented mating structure of the tapered hole of the connected parts provided by the embodiment of the present invention; Figure 3A flowchart of the prefabrication process of the connected parts before assembly is provided for an embodiment of the present invention; Figure 4 A flowchart of the assembly implementation process provided for an embodiment of the present invention.

[0025] Figure label: 100-Crankshaft; 110-Long conical surface; 120-End of conical surface; 200-Connected part; 210-Conical hole; 211-Large end of conical hole; 212-Small end of conical hole; 300-Integral nut washer. Detailed Implementation

[0026] 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.

[0027] 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.

[0028] 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.

[0029] Please see Figures 1-4 This embodiment discloses a crankshaft assembly method for a small aero-piston engine. This method is used to solve the problem of power torque transmission between the crankshaft and the load-side connected parts, and is adapted to the core usage requirements of small aero-piston engines for high power-to-weight ratio, high reliability, and wide temperature range operation.

[0030] In this embodiment, the crankshaft 100 is a core power transmission component of a small aircraft piston engine, used to convert the reciprocating motion of the piston into rotational motion and output power. One end of the crankshaft 100 is provided with a long conical surface 110 for mating connection, and the end of the long conical surface 110 is a conical end 120 with external threads. To ensure the rigidity and fitting accuracy of the conical surface connection, the crankshaft 100 is made of high-strength low-carbon alloy steel, and the surface hardness of its long conical surface 110 is not less than 55HRC.

[0031] This assembly method includes two main parts: the prefabrication process of the connected parts 200 before assembly and the assembly implementation process. The prefabrication process of the connected parts 200 before assembly includes the following steps: Step a: A connecting part 200 is fabricated using an aluminum alloy substrate to mate with the long conical surface 110 of the crankshaft 100. The connecting part 200 is a force transmission component at the load end of the engine, specifically a propeller disk, a starter rotor, etc. A tapered hole 210 corresponding to the long conical surface 110 is machined on the connecting part 200. The tapered hole 210 adopts a segmented fit design: it is divided into an interference fit section near the large end 211 of the tapered hole and a transition fit section near the small end 212 of the tapered hole. After the connecting part 200 is assembled with the crankshaft 100, the large end 211 of the tapered hole forms an interference fit with the long conical surface 110, and the small end 212 of the tapered hole forms a transition fit with the long conical surface 110.

[0032] The taper deviation of the interference fit section is controlled to be 0′~-2′, and the taper deviation of the transition fit section is controlled to be ±1′. This ensures that the large end 211 of the tapered hole has a stable interference amount, guaranteeing the basic strength for torque transmission. The small end 212 of the tapered hole is a transition fit, avoiding the problem of excessive overall stress and fatigue damage under long-term alternating loads caused by full-cone interference. At the same time, the thermal expansion difference between the steel crankshaft 100 and the aluminum alloy connected part 200 under high-temperature conditions during engine operation is fully considered to ensure effective contact of the tapered surface over a wide temperature range and prevent connection loosening and failure at high temperatures. In this step, the aluminum alloy base material of the connected part 200 is selected from 2A12 aluminum alloy or 7075 aluminum alloy. This material is softer than the steel of the crankshaft 100, which can better adapt to the tapered surface fit accuracy and ensure the fit effect after assembly.

[0033] Step b: Surface hardening treatment is performed on the end face area of ​​the connected component 200 that contacts the nut washer. This increases the surface hardness of the area and prevents the end face from being crushed or plastically deformed during assembly pre-tightening and long-term operation, thus preventing the pre-tightening force from weakening. In this step, the surface hardening treatment uses sulfuric acid hard anodizing. After treatment, the surface hardness of the end face area is not less than 500 HV, effectively solving the problem of insufficient hardness in the contact area between the connected component 200 and the nut washer near the small end 212 of the tapered hole, thus improving the long-term stability of the connection structure.

[0034] The assembly process includes the following steps: Step S1: Before assembly, clean the surfaces of the parts to be assembled. Use carburetor cleaner to clean the inner wall of the tapered hole 210 of the connected part 200 and the surface of the long tapered surface 110 of the crankshaft 100. Then wipe them dry with a lint-free cloth to remove excess material and prevent it from embedding into the mating surface, which could reduce the quality of the tapered surface connection and the effective contact area. This process effectively prevents excess material from embedding into the tapered surface mating surface in the early stages of assembly, ensuring the effective contact rate of the tapered surface and preventing a decrease in fitting accuracy. After cleaning, locally heat the area corresponding to the large end 211 of the tapered hole of the connected part 200 to cause thermal expansion, eliminating the assembly interference of the interference fit section. The local heating temperature is controlled at 80℃~100℃ and kept warm until the temperature of the heated area of ​​the connected part 200 is uniform. This ensures that the large end 211 of the tapered hole will not have hard friction with the long tapered surface 110 of the crankshaft 100 during assembly, avoiding wear on the tapered surface and damage to the fitting accuracy during assembly.

[0035] Step S2: After uniform heating, the connected part 200 is fitted onto the long conical surface 110 of the crankshaft 100. Using a separate tooling nut and tooling washer, preload is applied in stages along the axial direction of the crankshaft 100 to press the connected part 200 into the preset mating position on the long conical surface 110, completing the pre-assembly. In this step, the use of a separate tooling nut and tooling washer completely avoids direct friction between the nut and the end face of the connected part during rotation, preventing scratches and crushing of the end face and ensuring long-term stability of the preload. More preferably, in this step, the preload torque applied to the tooling nut during pre-installation is 50% of the final preload torque to avoid excessive preload causing overfitting between the tapered hole 210 and the long tapered surface 110. During the application of preload in stages, tooling shims with thicknesses of 2mm, 2.5mm, or 3mm are replaced according to the axial pressing position of the connected parts 200 to adapt to the torque application requirements of different axial pressing positions of the connected parts, ensuring that the tooling shims do not deform under high torque preload conditions and ensuring stable transmission of preload.

[0036] The tooling shim has two working surfaces: surface A, which contacts the tooling nut, and surface B, which contacts the connected part 200. The surface roughness of surface A is less than that of surface B, and the overall hardness of the tooling shim is lower than that of the end face of the connected part 200 after hardening treatment.

[0037] Specifically, the tooling gasket is made of 65Mn material, with a surface hardness controlled at 200HV~300HV; the surface roughness of surface A is controlled at Ra3.2, and the surface roughness of surface B is controlled at Ra6.3. This design ensures that the tooling gasket and the tooling nut can slide smoothly relative to each other, while remaining relatively stationary with respect to the connected part 200. During the pre-tightening process of the nut, the connected part 200 will not be driven to rotate circumferentially relative to the long conical surface 110, fundamentally avoiding the problems of assembly internal stress caused by the distortion of the conical surface and the reduction of effective contact area due to wear of the mating surface. At the same time, it can also effectively protect the end face of the connected part 200 from scratches and wear.

[0038] Step S3: After the connected part 200 has cooled naturally, remove the tooling nut and tooling washer. Clean the threaded surface of the conical end 120 of the crankshaft 100, removing oil and impurities, and apply thread-locking adhesive. Then replace the integrated nut washer 300 and screw it into the thread of the conical end 120. Complete the final assembly according to the preset final preload torque. After the final assembly is completed, check the final assembly torque to ensure that the preload meets the design requirements. In this step, the tooling nut and tooling washer should be removed only after the connected part 200 has cooled to a surface temperature not exceeding 30°C to avoid displacement of the connected part 200 due to disassembly at high temperatures. The thread-locking adhesive applied to the threaded surface of the conical end 120 is a medium-strength thread-locking adhesive, which can effectively prevent the threads from loosening, improve the vibration resistance of the connection to adapt to the alternating load conditions of the engine, and facilitate subsequent maintenance and disassembly, preventing the threads from locking up. After final assembly, the effective contact area between the long conical surface 110 and the conical hole 210 accounts for more than 85% of the total contact conical surface area, which fully ensures the stability and reliability of torque transmission.

[0039] The assembly method provided in this embodiment enables rapid, efficient, and precise assembly of the long conical surface of the crankshaft of a small aero-piston engine. It solves the problem of positional deviation between the initial assembly state and the final assembly state of the connected parts. At the same time, through the synergistic optimization of structural design and assembly process, it effectively reduces the damage to the conical surface during assembly, adapts to the operating conditions of the engine in a wide temperature range, significantly improves the reliability of the conical surface fit and the service life of the connected parts, and fully meets the high safety and high stability requirements of small aero-piston engines.

[0040] 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 crankshaft assembly method for a small aircraft piston engine, wherein the crankshaft (100) is the power transmission shaft of the small aircraft piston engine, and one end of the crankshaft (100) is provided with a long tapered surface (110) for torque transmission with the connected part (200) at the load end through the tapered surface engagement, characterized in that: The assembly method includes a prefabrication process for the connected parts before assembly and an assembly implementation process. The prefabrication process for the connected parts before assembly includes the following steps: Step a: A connecting part (200) that mates with the long conical surface (110) of the crankshaft (100) is prepared by processing an aluminum alloy substrate. A conical hole (210) corresponding to the long conical surface (110) is machined on the connecting part (200). The conical hole (210) adopts a segmented fit design: it is divided into an interference fit section near the large end (211) of the conical hole and a transition fit section near the small end (212) of the conical hole. After the connecting part (200) is assembled with the crankshaft (100), the large end (211) of the conical hole forms an interference fit with the long conical surface (110), and the small end (212) of the conical hole forms a transition fit with the long conical surface (110). Step b: Perform surface hardening treatment on the end face area of ​​the connected part (200) that is in contact with the nut washer to increase the surface hardness of the area; The assembly process includes the following steps: Step S1: Before assembly, clean the surface of the parts to be assembled, and locally heat the area corresponding to the large end (211) of the tapered hole of the connected part (200) so that the area expands due to heat. Step S2: The heated connected part (200) is fitted onto the long conical surface (110) of the crankshaft (100). Using a separate tooling nut and tooling washer, pre-tightening force is applied in stages along the axial direction of the crankshaft (100) to press the connected part (200) into the preset mating position of the long conical surface (110) to complete the pre-assembly. Step S3: After the connected parts (200) have cooled down, remove the tooling nut and tooling washer, clean the thread surface of the conical end (120) of the crankshaft (100) and apply thread glue, replace the integrated nut washer (300) and screw it into the thread of the conical end (120), complete the final installation according to the preset final preload torque, and check the final installation torque.

2. The assembly method according to claim 1, characterized in that, In step a, the taper deviation of the interference fit section is controlled to be 0′~-2′, and the taper deviation of the transition fit section is controlled to be ±1′.

3. The assembly method according to claim 1, characterized in that, In step b, the surface hardening treatment is carried out by sulfuric acid hard anodizing, and the surface hardness of the treated rear face area is not less than 500 HV.

4. The assembly method according to claim 1, characterized in that, The crankshaft (100) is made of high-strength low-carbon alloy steel, and the surface hardness of its long conical surface (110) is not less than 55HRC.

5. The assembly method according to claim 1, characterized in that, The aluminum alloy substrate of the connected part (200) is selected from 2A12 aluminum alloy or 7075 aluminum alloy.

6. The assembly method according to claim 1, characterized in that, In step S1, carburetor cleaner is used to clean the long conical surface (110) of the crankshaft (100) and the inner wall of the conical hole (210) of the connected part (200), and wipes them dry with a lint-free cloth to remove excess material from the surface; the temperature of the local heating is controlled at 80℃~100℃ and kept warm until the temperature of the heating area of ​​the connected part (200) is uniform.

7. The assembly method according to claim 1, characterized in that, In step S2, the tooling shim has two working surfaces, one of which is surface A, which contacts the tooling nut, and the other of which is surface B, which contacts the connected part (200). The surface roughness of surface A is less than that of surface B, and the overall hardness of the tooling shim is lower than that of the end face of the connected part (200) after hardening treatment.

8. The assembly method according to claim 7, characterized in that, The tooling gasket (500) is made of 65Mn material, and its surface hardness is controlled at 200HV~300HV; the surface roughness of surface A is controlled at Ra3.2, and the surface roughness of surface B is controlled at Ra6.

3.

9. The assembly method according to claim 1, characterized in that, In step S2, the preload torque applied to the tooling nut during pre-installation is 50% of the final preload torque; during the process of applying the preload force in stages, the tooling shims with a thickness of 2mm, 2.5mm or 3mm are replaced according to the axial pressing position of the connected parts (200).

10. The assembly method according to claim 1, characterized in that, In step S3, after the connected part (200) has cooled to a surface temperature not higher than 30°C, the tooling nut and tooling washer are removed; after final assembly, the effective contact area between the long conical surface (110) and the conical hole (210) accounts for more than 85% of the total contact conical surface area.

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