bicycle crank
The use of fluid injection technology with continuous fibers in bicycle cranks addresses the manufacturing challenges of high-performance cranks, achieving a lightweight, stiff, and cost-effective solution through hollow structures and fiber reinforcement.
Patent Information
- Authority / Receiving Office
- DE · DE
- Patent Type
- Utility models
- Current Assignee / Owner
- Filing Date
- 2026-01-14
- Publication Date
- 2026-03-12
AI Technical Summary
Existing bicycle cranks, particularly high-performance ones, are costly and complex to manufacture due to the use of lamination or hydroforming processes, and there is a need for a more efficient and cost-effective method to produce lightweight yet stiff structures.
A bicycle crank is manufactured using fluid injection technology (FIT) with hollow structures and reinforcement by continuous fibers, such as carbon fiber, to achieve high stiffness and low weight, utilizing methods like water injection molding (WIM) and gas injection molding (GIM) to create complex hollow geometries.
The method results in a lightweight, high-stiffness crank arm that is cost-effective to produce, maintaining structural integrity and strength, with the potential for reinforcement using continuous fibers.
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
[0001] The invention relates to a bicycle crank and a bicycle with at least one such bicycle crank.
[0002] A bicycle crank is a central component of a bicycle's drive system and acts as a lever connecting the pedals to the bottom bracket axle. The crank transmits the power applied via the pedals to the chainring and thus to the chain, which ultimately drives the rear wheel.
[0003] Bicycle cranks are typically forged or cast from metal, such as aluminum or steel. Modern high-performance cranks are often made from carbon fiber reinforced plastics. This frequently involves complex and expensive lamination or hydroforming processes to create a hollow, lightweight, and stiff structure.
[0004] Against this background, a bicycle crank with the features of claim 1 and a two-wheeler or bicycle according to claim 14 are presented. Embodiments are described in the dependent claims and in the description.
[0005] The presented bicycle crank has a crank arm which in turn is manufactured using a fluid injection technique and includes at least one cavity or hollow structure.
[0006] The presented bicycle crank is therefore manufactured using a fluid injection technique and comprises at least one cavity or at least one hollow profile, which can also be described as a hollow structure. For example, water injection, gas injection, or projectile injection techniques can be used in its manufacture.
[0007] Fluid injection technology (FIT) is a general term for processes in which cavities are created by injecting a fluid. This method is particularly suitable for achieving high material utilization and high stiffness.
[0008] Fluid injection molding (FIT) can be combined with injection molding, compression molding, or any other suitable process. FIT is particularly useful in conjunction with plastics, especially polymer materials. In addition to the usual design features of plastic parts, this technique / process can be used to create hollow profiles within the components at a low cost. Due to the hollow geometry of the components, FIT parts have higher stiffness while being lightweight and cost-effective to manufacture.
[0009] Reinforcement using continuous fibers is also possible. Composite structures with continuous fibers are materials in which reinforcements with continuous fibers are combined with a matrix material. The dimensions and properties are combined, resulting in a material with high stiffness and strength along the fiber direction.
[0010] The reinforcement can be achieved using fiberglass / carbon fiber, UD tapes and / or organosheets.
[0011] Continuous fibers can also be used with or without matrix material.
[0012] The material for the continuous fibers can be selected from a group that includes: glass, carbon, synthetic aramid fiber, basalt fiber, natural fibers.
[0013] Furthermore, the continuous fibers can be incorporated in the fluid injection step or in a step after the fluid injection step.
[0014] When using continuous fibers, the bicycle crank can have at least one first section in which a cavity or hollow profile is provided, and at least one second section which is reinforced with continuous fibers.
[0015] Processes are known in which hybrid forming is carried out, whereby the forming of an organosheet and injection molding take place simultaneously in the injection mold. Such functional integration and added rib structures result in higher structural strength.
[0016] The cavity provided by means of the injection technique is designed or formed in such a way that it extends over at least part of the length of the crank arm, and in one embodiment over the entire length of the crank arm.
[0017] The bicycle crank or crank arm can be manufactured using a technique selected from a group that includes: water injection technology, gas injection technology, projectile injection technology.
[0018] Furthermore, the crank arm can be made of a carbon fiber reinforced thermoplastic, e.g., a polyamide.
[0019] In another embodiment, the crank arm is manufactured or formed in one piece.
[0020] The shape of the cross-section of the cavity can be circular, elliptical and / or irregular, at least in sections.
[0021] The bicycle crank can have at least one water inlet and at least one water outlet. In principle, it can also have multiple water inlets and / or outlets.
[0022] The fluid injection technique used thus creates hollow structures. All functional integration features of traditional molding processes, such as stiffening structures and attachment points, are also possible with this technique.
[0023] Hollow bodies or hollow profiles can generally be produced using cores or slides in injection molding. By employing water or gas-assisted injection molding technologies, such as water injection molding (WIM), gas injection molding (GIM), or projectile injection molding (PIM), even complex hollow geometries can be created.
[0024] A combination of the aforementioned method and the specific requirements of a heavy-duty, hollow bicycle crank is not known from the prior art.
[0025] This provides a bicycle crank that has an optimized hollow geometry for lower weight while maintaining high stiffness, and which can be manufactured economically, for example, using a water injection molding process.
[0026] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.
[0027] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing. Brief description of the drawing Fig. Figure 1 shows a cross-sectional view of an embodiment of the presented bicycle crank. Fig. Figure 2 shows a possible sequence of the presented procedure in a flowchart. Embodiments of the invention
[0028] The invention is schematically illustrated with reference to embodiments in the drawing and is described in detail below with reference to the drawing.
[0029] Fig. Figure 1 shows a cross-sectional view of an embodiment of the presented bicycle crank, which is generally designated by the reference numeral 10.
[0030] The bicycle crank 10 comprises a crank arm 12, which has an elongated shape, its length being approximately four to six times its height. A first water injection technology (WIT) injector 14 is provided at the upper left end, capable of injecting water into a water inlet 16. A further WIT injector 18 is provided at the upper right end for a water outlet 20. The positions of the water inlet 16 and water outlet 20 channels can be changed. Furthermore, the channels are typically removed later.
[0031] Furthermore, the crank arm 12 has a bottom bracket mount 30 at its left end, which serves to accommodate a bottom bracket. At its right end, the crank arm 12 has a pedal mount 32 for accommodating a pedal. A force applied via the pedal is thus transmitted to the bottom bracket via the crank arm 12.
[0032] By injecting water, a hollow body 34 or a hollow channel is created, which extends almost over the entire length of the crank arm 12. The wall of the crank arm 12 above and below the crank arm is significantly thinner than the height or width of the hollow body 14; in this case, the ratio is approximately 1:4, but other ratios such as 1:3, 1:5, or 1:6, as well as other suitable ratios, are conceivable.
[0033] Furthermore, a method for manufacturing a bicycle crank, as described herein, is presented. A flowchart showing the steps of one embodiment of the presented method is included in Fig. 2 shown.
[0034] In the first step (100), a molten plastic is injected into a mold cavity of an injection mold. Then, in step (102), a fluid, such as water, is injected into the still-plastic molten plastic. This creates a hollow structure. In the final step (104), the bicycle crank is cooled and demolded. A subsequent step (106) for surface treatment of the workpiece may follow.
[0035] The aforementioned polymer melt can consist of a carbon fiber reinforced polyamide.
[0036] Furthermore, the internal pressure of the fluid can align the fibers of the carbon fiber reinforced material along the shape contour, thereby increasing the stiffness of the bicycle crank.
Claims
[1] Bicycle crank comprising a crank arm (12) manufactured by means of a fluid injection technique and comprising at least one cavity (34). [2] Bicycle crank according to claim 1, wherein the cavity (34) extends over at least part of the length of the crank arm (12). [3] Bicycle crank according to claim 1, manufactured using a technique selected from the group comprising: water injection technique, gas injection technique, projectile injection technique. [4] Bicycle crank according to one of claims 1 to 3, wherein the crank arm (12) is made of a carbon fiber reinforced thermoplastic. [5] Bicycle crank according to claim 4, wherein the crank arm (12) is made of a polyamide. [6] Bicycle crank according to one of claims 1 to 5, wherein the crank arm (12) is manufactured in one piece. [7] Bicycle crank according to one of claims 1 to 6, wherein the shape of the cross-section of the cavity (34) is at least partially circular, elliptical or irregular. [8] Bicycle crank according to one of claims 1 to 7, which is reinforced at least in sections by an endless fiber reinforcement. [9] Bicycle crank according to claim 8, wherein the reinforcement is realized by glass fiber / carbon fiber, UD tapes and / or organosheet. [10] Bicycle crank according to claim 8 or 9, in which continuous fibers with or without matrix material are used. [11] Bicycle crank according to one of claims 8 to 10, wherein the material for the continuous fibers is selected from a group comprising: glass, carbon, synthetic aramid fiber, basalt fiber, natural fibers. [12] Bicycle crank according to one of claims 8 to 11, wherein the continuous fibers are incorporated in the fluid injection step or in a step after the fluid injection step. [13] Bicycle crank according to one of claims 1 to 12, which has at least one water inlet and at least one water outlet. [14] Bicycle with at least one bicycle crank (10) according to any one of claims 1 to 13.