A bicycle frame down tube five-way assembly and a bicycle frame

Abstract

The application relates to a bicycle frame lower tube five-way pipe assembly and a bicycle frame, and relates to the technical field of bicycle frame manufacturing. The bicycle frame lower tube five-way pipe assembly comprises an integrally formed lower tube part and a five-way pipe part. The lower tube part is a hollow structure and is provided with an integrally formed first pipe assembly opening. The five-way pipe part is internally provided with a penetrating central cavity and is provided with an integrally formed middle tube assembly opening and a lower fork assembly opening. The lower tube part and the five-way pipe part have a dense metal crystal structure formed by a forging process. The application integrally forges the lower tube part and the five-way pipe part to replace the traditional welding connection with a seamless overall structure, eliminates the welding seam and the heat affected zone, and helps to relieve the stress concentration problem, so that the structural strength and the fatigue resistance of the key part of the frame are significantly improved.

Description

Technical Field

[0001] This application relates to the field of bicycle frame manufacturing technology, and in particular to a bicycle frame downtube bottom bracket assembly and a bicycle frame. Background Technology

[0002] In the research and development of high-performance bicycles, the frame, as the core load-bearing component, is designed to achieve extreme lightweighting while maintaining high structural strength. Currently, the mainstream frame manufacturing process in the industry involves welding pre-prepared components such as the downtube, bottom bracket, and seat tube together to form a complete frame structure. This modular manufacturing and subsequent welding approach is widely used.

[0003] However, this traditional welding connection method has inherent technical bottlenecks. The welding process creates weld seams and heat-affected zones at the pipe joints. The metallographic structure of these areas differs from that of the base pipe material, making them prone to stress concentration points under stress. During cycling, the frame repeatedly bears alternating loads from road impacts and pedaling forces. Fatigue cracks will first develop in these stress concentration areas and gradually propagate, potentially leading to structural failure.

[0004] Regarding the aforementioned technologies, there is a problem of stress concentration caused by welding the various pipes, which in turn affects the overall fatigue resistance of the frame. Utility Model Content

[0005] In order to solve the problems of stress concentration and poor fatigue resistance caused by the welding connection between tubes in existing bicycle frames, this application provides a bicycle frame bottom tube assembly and a bicycle frame.

[0006] This application provides a bicycle frame downtube bottom bracket assembly, which adopts the following technical solution: A bicycle frame downtube bottom bracket assembly includes: a downtube section, which is a hollow structure and has a head tube assembly port integrally formed on the downtube section; a bottom bracket section, integrally formed and connected to the downtube section, the bottom bracket section having a through central cavity formed inside, and a center tube assembly port and a fork assembly port integrally formed on the bottom bracket section; wherein, the downtube section and the bottom bracket section have a dense metal crystal structure formed by forging process.

[0007] By adopting the above technical solution, the complexly stressed lower tube section and bottom bracket section of the frame are made into a seamless integral structure. This structure, due to its one-piece molding, eliminates traditional welds, allowing stress to be transferred through continuous metal flow lines. Simultaneously, the dense metal crystal structure formed by the forging process exhibits higher material strength and toughness compared to ordinary castings or welded parts. The combination of these two structural features helps to fundamentally alleviate stress concentration, improving the structural strength and fatigue resistance of the assembly.

[0008] Optionally, the lower tube section has a wall thickness that varies along its axial direction.

[0009] By adopting the above technical solution, differentiated wall thickness designs can be carried out based on the stress analysis of different locations in the lower tube section. This structure can retain a thicker tube wall in critical stress areas to maintain strength, while thinning the material in non-critical areas to achieve weight reduction, which helps to optimize the mechanical properties and weight ratio of the assembly.

[0010] Optionally, in the region of the lower pipe section near the first pipe assembly port and the five-way connector, the pipe wall thickness is greater than the pipe wall thickness in the middle region of the lower pipe section.

[0011] By adopting the above technical solution, a specific structural layout for the aforementioned pipe wall thickness variation is provided. This layout places the thicker pipe wall in the connection area at both ends where the stress is greatest, and the thinner pipe wall in the middle area where the stress is lower. This is an optimized design that conforms to the principles of engineering mechanics and helps to maximize the lightweight effect while ensuring safety and strength.

[0012] Optionally, the axis of the middle tube assembly port intersects the axis of the lower tube at an acute angle.

[0013] By adopting the above technical solution, this specific geometric angle relationship constitutes the basic geometric shape of the main triangular area of ​​the bicycle frame, providing a precise positioning reference for the correct installation of the center tube, and helping to ensure the overall geometric accuracy of the frame.

[0014] Optionally, the lower fork assembly port includes two ports symmetrically arranged with reference to the symmetry center plane of the five-way section.

[0015] By adopting the above technical solution, the symmetrically arranged two-port structure helps to ensure the left and right symmetry of the subsequent connection of the lower fork, ensure the centering of the rear wheel installation and the alignment of the transmission system, and at the same time help to evenly transfer the load from the rear wheel to the bottom bracket.

[0016] Optionally, the middle tube assembly port and the lower fork assembly port are configured as insert-type welding interfaces.

[0017] By adopting the above technical solution and setting up standardized insert welding interfaces, a reliable positioning and matching benchmark is provided for the connection of other tubes such as the center tube and bottom fork, which helps to simplify the subsequent welding and assembly process of the frame and improve assembly accuracy.

[0018] Optionally, the inner wall of the central cavity, the mating surface of the first tube assembly port, the mating surface of the middle tube assembly port, and the mating surface of the lower fork assembly port are all precision-machined surfaces formed by CNC machining.

[0019] By adopting the above technical solution, the precision-machined surface structure of these key mating surfaces achieves extremely high dimensional accuracy and surface finish. This structure helps ensure the tight and precise installation of standard components such as the bottom bracket and headset, reduces abnormal noise and wear, and helps improve transmission efficiency and operational precision.

[0020] To achieve the above objectives, the second aspect of this application provides a bicycle frame with the following technical solution: A bicycle frame includes: a bottom tube assembly, a head tube, a bottom tube, a chainstay, a top tube, and a top fork as described above; the head tube is connected to the head tube mounting port; the bottom tube is connected to the bottom tube mounting port; the chainstay is connected to the chainstay mounting port; the top tube connects the head tube and the bottom tube; and the top fork connects the bottom tube and the chainstay.

[0021] By adopting the above technical solution, the bicycle frame downtube bottom bracket assembly is applied to the construction of the bicycle frame. Since the core stress-bearing area of ​​the frame uses this one-piece molded assembly, compared to frames using traditional welded components, the connection area between the downtube and bottom bracket of this bicycle frame has a better stress distribution, which helps to improve the structural strength and fatigue resistance of the entire frame.

[0022] In summary, this application includes at least one of the following beneficial technical effects: 1. By integrally forming the lower tube section and the bottom bracket section with a dense metal crystal structure formed by forging, the weld between the two is replaced by an integral structure, which helps to alleviate stress concentration and thus helps to improve the fatigue resistance and structural strength of key parts of the frame. 2. By setting a wall thickness that varies along the axial direction on the lower tube section, a lightweight design can be achieved while meeting strength requirements, which helps to optimize the weight-performance ratio of the assembly; 3. By directly molding the head tube assembly port, middle tube assembly port, and lower fork assembly port on the assembly, it helps to simplify the subsequent frame assembly and welding process and improve the efficiency and precision of the whole vehicle manufacturing. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the bicycle frame bottom tube assembly in an embodiment of this application.

[0024] Figure 2 This is a schematic diagram illustrating the application of the bicycle frame bottom tube assembly according to an embodiment of this application in a bicycle frame.

[0025] Figure 3 This is a cross-sectional view of the bicycle frame bottom tube assembly according to an embodiment of this application.

[0026] Figure 4This is a flowchart illustrating the manufacturing method of the bicycle frame bottom tube assembly according to an embodiment of this application.

[0027] Figure 5 This is a schematic diagram of the structure of a casting and forging die for forging according to an embodiment of this application. Figure 6 This is a schematic diagram of the integral part obtained by casting and forging in the embodiments of this application.

[0028] Figure 7 This is a schematic diagram of the integral tube-drawing component obtained after tube-drawing processing in the embodiments of this application.

[0029] Figure 8 This is a schematic diagram illustrating the principle of bending and hydroforming of the integral tube in the embodiments of this application.

[0030] Figure 9 This is a schematic diagram of the integral molded part obtained after water expansion molding in the embodiments of this application.

[0031] Explanation of icon numbers: 10. Lower pipe section; 11. First pipe assembly port; 12. Non-uniform pipe wall; 13a. First-order first pipe wall; 13b. First-order second pipe wall; 13c. First transition pipe wall; 14a. Second-order first pipe wall; 14b. Second-order second pipe wall; 14c. Second-order third pipe wall; 14d. Second transition pipe wall; 14e. Third transition pipe wall; 15. Third-order non-uniform pipe wall; 15a. Curved pipe wall; 16. Water injection component of water expansion mold; 16a. Water injection port; 20. Bottom joint; 21. Middle tube assembly port; 22. Lower fork assembly port; 30. First pipe; 40. Top tube; 50. Medium tube; 60. Upper fork; 70. Rear hook claw; 80. Downward fork; 91. Outer mold; 92. Steel core; 93. Injection port; 94. Integral blank. Detailed Implementation

[0032] The following is in conjunction with the appendix Figure 1-9 This application will be described in further detail.

[0033] The technical solutions of this application embodiment relate to the field of metal forming and processing technology, specifically to a bicycle frame bottom tube assembly and a bicycle frame.

[0034] First refer to Figures 1 to 3 , Figure 1This is a schematic diagram of the bicycle frame bottom tube assembly in an embodiment of this application. Figure 2 The application of the bicycle frame bottom tube assembly in a bicycle frame is demonstrated. Figure 3 This is a cross-sectional view of the bicycle frame downtube bottom bracket assembly. As can be seen from the figure, the bicycle frame downtube bottom bracket assembly of this embodiment is an integral structural component, mainly including a downtube portion 10 and a bottom bracket portion 20 integrally connected to the downtube portion 10. To achieve lightweighting while ensuring structural strength, such as... Figure 3 As shown, the lower tube portion 10 has a non-uniform tube wall 12 with varying wall thickness along its length.

[0035] The manufacturing process of the bicycle frame bottom tube assembly can be referred to as follows: Figure 4 As shown, the specific steps include the following: First, step S1 is performed to melt the metal billet into molten metal; then step S2 is performed to pour the molten metal into a casting and forging mold to cast and form an integral part blank 94; then step S3 is performed to forge the integral part blank 94 in the casting and forging mold to form an integral part. These three steps constitute a casting and forging combined forming process, which aims to manufacture the lower tube section and the bottom bracket section into an initial integral part in one go. (Refer to...) Figure 5 The casting and forging mold used includes an outer mold 91 for forming the outer contour and a sprue 93 for injecting molten metal. The casting step facilitates the formation of complex initial shapes, while the subsequent forging step applies high pressure while the integral blank 94 is still in a high-temperature plastic state, causing the internal metal grains to be compressed and refined, resulting in a denser structure. In this embodiment, the casting and forging mold used in step S2 also includes a steel core 92, which is pre-placed in the mold cavity during casting to directly form the hollow structure of the lower tube portion 10. (Refer to...) Figure 6 The integral component obtained after step S3 includes an integrally formed lower tube section 10 and a five-way connector section 20. The lower tube section 10 has an integrally formed head tube assembly port 11, and the five-way connector section 20 has an integrally formed middle tube assembly port 21 and a lower fork assembly port 22. According to the design, the lower tube section 10 is hollow at this time, while the five-way connector section 20 is a solid structure. The solid structure helps to provide sufficient rigid support for subsequent plastic processing steps.

[0036] In some preferred embodiments, to achieve lightweighting and optimize mechanical properties, the manufacturing method may further include subsequent plastic processing of the integral part. This plastic processing may include: step S4, applying a film treatment to the lower tube portion; and step S5, performing a tube-drawing process on the lower tube portion to obtain a tube-drawn integral part. The film treatment in step S4 forms a lubricating protective film on the surface of the lower tube portion 10. This helps reduce the friction between the tube and the mold during the tube-drawing process in step S5, improving surface quality and extending mold life. Specifically, in step S5, the lower tube portion 10 may undergo a tube-drawing and diameter-reducing process. Using specialized tube-drawing equipment, a tensile force is applied to the lower tube portion 10, causing it to pass through one or more molds with gradually decreasing outer diameters, thereby achieving tube wall thinning and length increase. By controlling the parameters of the tube-drawing process, the lower tube portion 10 can form a non-uniform tube wall 12 that varies axially. (Refer to...) Figure 7 By drawing the tube, regions with different tube wall thicknesses are formed, such as first-order first tube wall 13a, first-order second tube wall 13b, or second-order first tube wall 14a, second-order second tube wall 14b, etc., which realizes the optimized design of retaining thicker tube wall in critical stress areas and thinning tube wall in non-critical areas.

[0037] To obtain a specific frame geometry or appearance, the manufacturing method may further include: step S6, performing a bending pretreatment on the tube-drawing integral component; step S7, performing a bending treatment on the lower tube portion to obtain a bent integral component. In this embodiment, the pretreatment in step S6 may include annealing and a second coating treatment. For example, annealing can heat the tube-drawing integral component to a specific temperature and then slowly cool it to eliminate the internal stress generated during the tube-drawing process and reduce the material hardness. For example, the Weber hardness can be annealed to below 3 degrees, thereby improving the plasticity of the material. The purpose of step S7 is to give the tube-drawing integral component a preliminary geometric shape, which should be able to be smoothly placed into the cavity of the forming mold used in the subsequent hydroforming process, thereby forming a bent integral component suitable for subsequent hydroforming. This helps to prevent wrinkling or cracking caused by excessive differences between the tube and the mold cavity during the hydroforming process.

[0038] Furthermore, to create more complex tube shapes such as aerodynamic profiles, the manufacturing method may further include: step S8, performing a water-expanding treatment on the bent integral part, specifically, placing the bent integral part in a forming mold with a preset inner cavity contour, and injecting high-pressure liquid into the bent integral part to obtain the formed integral part. (Refer to...) Figure 8During the hydroforming process, the bent integral part is placed in the sealed cavity of the forming mold (not shown in the figure). The inner wall contour of the forming mold constitutes the preset inner cavity contour, which corresponds to the complex curved surface shape that the lower tube 10 is ultimately expected to achieve. The hydroforming mold water injection component 16 is installed at the end of the lower tube 10 away from the five-way connector 20. High-pressure liquid is injected into the interior of the lower tube 10 through the water injection port 16a on the hydroforming mold water injection component 16. The huge internal pressure causes the tube wall of the lower tube 10 to expand outward until it completely conforms to the preset inner cavity contour defined by the inner wall of the forming mold. This process can form complex curved surfaces that are difficult to achieve with traditional machining (such as bending the tube wall 15a). Figure 9 As shown, this also helps to make the stress distribution within the pipe more uniform. Figure 9 As shown, this also helps to make the stress distribution inside the pipe more uniform.

[0039] After all plastic forming processes are completed, step S9 is performed to CNC machine the formed integral part. This step is crucial in determining the final product's precision. Using a high-precision CNC machine tool (e.g., a 5-axis milling machine), the previously solid bottom bracket 20 is drilled and bored to form a central cavity that runs through it for mounting the bottom bracket assembly. Simultaneously, in this embodiment, CNC machining is also used to finish the end faces and mating surfaces of the head tube assembly port 11, the middle tube assembly port 21, and the lower fork assembly port 22. Through precise milling, the middle tube assembly port 21 and the lower fork assembly port 22 are constructed as precisely sized insert-type welding interfaces, providing a reliable positioning reference for the subsequent welding and assembly of the remaining frame components.

[0040] The implementation principle of the bicycle frame downtube bottom bracket assembly in this embodiment is as follows: As a seamless integral component, the internal metal crystal structure of the bicycle frame downtube bottom bracket assembly is continuous. When subjected to external loads, stress can be smoothly transmitted in the continuous material, without stress concentration caused by material discontinuity at traditional welded joints. This is the structural basis for the assembly's improved fatigue resistance. Simultaneously, the non-uniform tube wall 12 structure of the downtube 10 is a direct physical manifestation of optimized engineering mechanics design. Its principle is based on stress distribution diagrams obtained through finite element analysis and other methods. Thicker tube walls are retained in high-stress areas of the frame (such as near the head tube and both ends of the bottom bracket) to maintain strength and rigidity, while thinner tube walls are used in lower-stress areas (such as the middle of the tube) to significantly reduce weight. This helps maximize structural efficiency without sacrificing key performance characteristics.

[0041] This application also provides a bicycle frame. (See attached image.) Figure 2The bicycle frame structure includes the aforementioned bottom bracket assembly as its core load-bearing component. Specifically, the bicycle frame includes: the bottom bracket assembly; a head tube 30 connected to the bottom tube 10 via a head tube mounting port 11; a bottom tube 50 connected to the bottom bracket 20 via a bottom tube mounting port 21; a top tube 40 connecting the head tube 30 and the bottom tube 50; a chainstay 80, one end of which is connected to the bottom bracket 20 via a chainstay mounting port 22; and a top fork 60 connecting the bottom tube 50 and the other end of the chainstay 80 (e.g., via a dropout 70).

[0042] The implementation principle of the bicycle frame in this embodiment is as follows: by integrating the high-performance bicycle frame downtube bottom bracket assembly into the design of the bicycle frame, it helps to strengthen the "chassis" structure of the entire frame. During bicycle riding, most of the combined torques from pedaling, steering, and road impacts converge at the connection area between the downtube and the bottom bracket. Using this one-piece molded assembly is equivalent to replacing the weakest welded section of a traditional frame with a high-strength, high-fatigue-resistant "structural hub." Therefore, the excellent mechanical properties of the assembly can be transmitted to the entire frame system, helping to improve the overall rigidity, power transmission efficiency, and long-term durability of the frame. Specifically, higher bottom bracket area rigidity means that when the rider pedals forcefully, the elastic deformation of the frame due to force is smaller, thus allowing more pedaling energy to be directly transferred to the drive wheel, reducing energy loss during frame deformation. In short, higher bottom bracket area rigidity means that when the rider pedals forcefully, the elastic deformation of the frame due to force is smaller, thus allowing more pedaling energy to be directly transferred to the drive wheel, improving power transmission efficiency. This provides the bicycle with a more direct power response.

[0043] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A bicycle frame bottom tube bottom bracket assembly, characterized in that, include: The lower tube section (10) is a hollow structure, and the lower tube section (10) has an integrally formed first tube assembly port (11). The five-way section (20) is integrally formed and connected to the lower tube section (10). The five-way section (20) has a through central cavity inside, and the five-way section (20) has an integrally formed central tube assembly port (21) and a lower fork assembly port (22). The lower tube section (10) and the five-way section (20) have a dense metal crystal structure formed by forging process.

2. The bicycle frame bottom tube five-way assembly according to claim 1, characterized in that, The lower tube (10) has a wall thickness that varies along its axial direction.

3. The bicycle frame bottom tube five-way assembly according to claim 2, characterized in that, In the area of ​​the lower pipe section (10) near the first pipe assembly port (11) and the five-way section (20), the pipe wall thickness is greater than the pipe wall thickness in the middle area of ​​the lower pipe section (10).

4. The bicycle frame bottom tube five-way assembly according to claim 1, characterized in that, The axis of the middle tube assembly port (21) intersects the axis of the lower tube (10) at an acute angle.

5. The bicycle frame bottom tube five-way assembly according to claim 1, characterized in that, The lower fork assembly port (22) includes two ports symmetrically arranged with reference to the symmetrical center plane of the five-way section (20).

6. The bicycle frame bottom tube five-way assembly according to claim 1, characterized in that, The middle tube assembly port (21) and the lower fork assembly port (22) are configured as insert-type welding interfaces.

7. The bicycle frame bottom tube five-way assembly according to claim 1, characterized in that, The inner wall of the central cavity, the mating surface of the first tube assembly port (11), the mating surface of the middle tube assembly port (21), and the mating surface of the lower fork assembly port (22) are all precision-machined surfaces formed by CNC machining.

8. A bicycle frame, characterized in that, include: The bicycle frame bottom tube bottom bracket assembly as described in any one of claims 1 to 7; The first tube (30) is connected to the first tube assembly port (11) of the lower tube (10). The middle tube (50) is connected to the middle tube assembly port (21) of the five-way section (20). The lower fork (80) is connected to the lower fork mounting port (22) of the five-way connector (20). Upper pipe (40) connects the first pipe (30) and the middle pipe (50); The upper fork (60) connects the middle tube (50) and the lower fork (80).

9. The bicycle frame according to claim 8, characterized in that, The middle tube (50) and the lower fork (80) are fixed to the middle tube assembly port (21) and the lower fork assembly port (22) respectively by welding.

10. The bicycle frame according to claim 8, characterized in that, The lower pipe section (10) of the assembly has a wall thickness that varies along its axial direction, and the wall thickness of the lower pipe section (10) is thickest in the region near the head pipe (30).

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