Children's bicycle frame manufactured using plastic injection molding

Abstract

A child's bicycle frame (110) that can be manufactured by injection molding of plastics, comprising at least: - a head tube (118) for receiving a front fork (120) and a handlebar (124); - a seat tube (115) for receiving a seat post (151); - a bottom bracket shell (112); - a pair of seat stays (116) extending from an upper part of the seat tube (115) to a rear wheel shell (114); - a pair of chainstays (113) extending from the bottom bracket shell (112) to the rear wheel shell (114), wherein at least one section of the child's bicycle frame (110) connecting the head tube (118), the seat tube (115) and the bottom bracket shell (112) is hollow and the hollow part of the child's bicycle frame (110) is subdivided into: ◯ a main section (111.1) extending from the head tube (118) extends to a front junction (111.2),◯ an upper tube section (111.3) extending from the front junction (111.2) extends to an upper apex (111.4) at which the seat tube (115) is located. ◯ a down tube section (111.5) which extends as a continuation of the main section (111.1) from the front junction (111.2) to the bottom bracket shell (112). characterized in that, - the child's bicycle frame (110) is formed as a one-piece injection-molded plastic part, wherein the seat stays (116) and the chain stays (113) are not joined to each other at the rear wheel mount (114) and the rear wheel mounts (114) are part of a rear wheel mounting unit (160) separate from the child's bicycle frame (110), - the seat tube (115) has a smaller diameter than the other plastic sections of the child's bicycle frame (110), and - the top tube section (111.3) extends over the area defined by the upper apex. (111.4) seat tube (115) and one in the down tube section (111.5) embedded bottom bracket mount (112) is supported on the down tube section (111.5).

Description

The invention relates to a children's bicycle frame that can be manufactured using plastic injection molding and has the features of the preamble of claim 1. A classic bicycle frame design is known as a diamond frame. This forms a three-dimensional truss structure with two triangles in side view. A front triangle is formed by a down tube and a top tube, extending from a head tube that houses the front fork and handlebars, and connecting to a seat tube that guides the seat post. The seat tube terminates at the bottom of a bottom bracket shell. A second triangle is formed on each side of the rear wheel by the seat tube, a chainstay, and a seatstay. The chainstay extends from the bottom bracket to a rear wheel mount, and the seatstay runs from the upper part of the seat tube to the rear wheel mount. The frame thus comprises seven stays and six joints. This frame design is stable and has proven its worth. If a lower step-through frame is desired, the statically balanced frame design must be abandoned because the top tube, which directly connects the head tube and seat tube, must be eliminated. On women's bicycles, the top tube often runs parallel to the down tube, which can only be seen as a compromise between strength and comfort. The step-through height remains significant. There are also step-through frames for seniors, for example from DE 10 2006 007 862 A1, in which there is no longer a division into top and down tubes, but only one large main tube. It has a continuous curve in the area in front of the bottom bracket and requires a strongly defined joint there. For balance bikes and bicycles for toddlers, the weight load is significantly lower than for adult bicycles. Therefore, this product category typically omits a top tube entirely. Children's balance bikes for toddlers up to about 3 years old, which usually have 12-inch wheels, are designed for a maximum load of 20 kg. Children's bicycles for slightly older children have wheels with a diameter of 14 or 16 inches. Children's balance bikes often feature a frame that extends in an almost linear direction from the head tube to the rear wheel mount, branching into two rear stays in the area of ​​the seat tube. Such a balance bike is known from EP 2 964 514 B1. One disadvantage is that the step-through height in front of the saddle is still relatively high because the main tube of the child's balance bike frame still runs at about three-quarters of its height there – in relation to the total height difference between the head tube and the rear wheel mount. Furthermore, the force distribution is unfavorable because the child's weight acts almost perpendicularly on the balance bike frame via the seat post, specifically at the point where the rear stays attach to the fork. This is structurally unfavorable and hinders lightweight construction. CN 2 03 581 271 U shows and describes a child's balance bike frame. Its central frame component is a very complex part with several internal flow channels and two recessed chambers. The frame component therefore lacks a continuous main tube section and cannot be manufactured as a plastic injection molded part using fluid injection technology. The necessary stability for a hollow plastic body is to be achieved through a large profile height and cutouts reinforced by struts. However, this also makes the frame component very bulky, and a low step-through from in front of the saddle is not possible. A bicycle frame disclosed in KR 10 2016 0 064 586 has a top tube section branching off from a main tube, leading to an upper apex. However, the bicycle frame consists of two half-shells. It is therefore not a frame that can be manufactured in one piece using plastic injection molding. A separate seat tube leading to the bottom bracket is not provided. Rather, the seat tube is intended to be integrated into the frame. The children's bicycle shown in US 2016 / 0 375 949 A1 is also neither intended nor suitable to be fitted with a frame formed as a one-piece injection-molded plastic part. From DE 10 2015 008 561 A1, it is generally known to manufacture a bicycle frame using a plastic injection molding process. Cavities within the frame structure are created by injecting water. The frame disclosed in this document is not well suited as a children's bicycle frame due to its geometry. It also has only a single, straight tube between the seat tube and the handlebar tube, which must absorb all bending moments. FR 3 085 662 A1 describes a bicycle frame in the classic diamond shape, manufactured using a plastic injection molding process, so that the frame has the disadvantages of this geometry described above and is not suitable for a children's bicycle. The object of the present invention is therefore to provide a children's bicycle frame that can be manufactured cost-effectively using plastic injection molding and that has a low mass. This problem is solved by a children's bicycle frame having the features of claim 1. The children's bicycle frame according to the invention is optimized for load-bearing capacity and is designed as a lightweight, hollow injection-molded thermoplastic part. The cross-section of the children's bicycle frame has at least one cavity in the area designated as the main tube, between the head tube and the seat tube, and is therefore tubular in this section. This results in a reduction of mass. The use of a thermoplastic material for manufacturing the children's bicycle frame further reduces the mass and enables single-material recycling. Embedded metal parts, particularly for the head tube and seat tube, can be easily separated during recycling. Particular advantages in terms of resource conservation and environmental protection arise from the fact that any type of surface treatment can be dispensed with. While conventional metal running and bicycle frames must be greased during manufacturing, then degreased with solvents, and subsequently painted in several layers, the children's bicycle frame according to the invention can be manufactured directly in the desired color, ready for use, by mixing in a masterbatch containing dyes. Furthermore, a high-gloss finish or a surface with a customized texture can be achieved, depending on the desired effect. Lettering and decorations on the children's bicycle frame can be three-dimensional and therefore have a different visual impact than stickers. According to the invention, the main tube, along its entire length between the head tube and the upper apex of the seat tube, is designed as a hollow profile manufactured using a fluid injection process. The production of this component as an injection-molded plastic part made of a fiber-reinforced thermoplastic, in conjunction with the optimized children's bicycle frame design, offers the advantage that the fibers flow along the walls of the mold during manufacturing and are aligned longitudinally along the wall in the finished part, thus achieving sufficiently high strength with a thin wall. The smooth profile of the children's bicycle frame with continuous transitions is mechanically advantageous. In the children's bicycle frame according to the invention, sharp edges, acute angles, and other areas with high stress concentrations, which lead to stress concentrations, are avoided. Instead, all transitions are generously rounded and continuous.Because the main tube initially drops lower from the head tube than intended for the saddle position, and then rises again from a front, lower apex to an upper apex, a low entry in front of the saddle is possible. The children's bicycle frame has a bottom bracket for pedal drive. The child's weight is transferred into the frame via a seat tube that passes through the top of the frame. The frame is made of thermoplastic injection-molded plastic, and at least in the area of ​​the main tube, it is a single piece with a hollow profile. Since a bottom bracket is required on a children's bicycle, and since additional tensile forces act on the frame via the drive chain or belt, the main tube sloping down from the head tube is extended beyond a front branch point to a bottom bracket shell. From there, two chainstays extend to the rear wheel hub. In a preferred embodiment of the children's bicycle frame according to the invention, the stiffening of the main tube at its upper apex is achieved via the seat tube, which is supported by or connected to the bottom bracket. The bottom bracket and seat tube thus form a T-shaped configuration, preferably made of metallic materials. The seat tube, which passes through a section of the top tube of the children's bicycle frame, has a significantly smaller cross-section than the frame itself. This prevents excessive weakening of the plastic frame in the area where the seat tube passes through the top. Furthermore, it prevents material build-up in the plastic for ribs and other structures, because the stiffening between a top tube section and a down tube section is achieved solely by means of the seat tube and is sufficient.The area of ​​the child's bicycle frame between the top tube section and the bottom bracket remains open and is only traversed by the seat tube. Supporting the seat tube directly at the bottom bracket shell is advantageous because in this way the forces introduced via the narrow seat tube are distributed over a large area onto the lower shell of the bottom bracket shell, and the plastic frame is not subjected to a point load at this location. The children's bicycle frame is designed so that the chainstays and seat stays do not join at the rear wheel hub, but are connected there via detachable hub elements. This allows for the easy installation of an endless drive belt or chain without having to open the frame. Furthermore, this design allows the ends of the two stays to form drainage holes, enabling water generated during the manufacturing process (using fluid injection technology) to escape from the frame. One of the advantages of constructing the children's bicycle frame according to the invention as a thermoplastic component lies in its high dimensional accuracy, particularly with regard to angular tolerances. This results in very small angular deviations in the relevant angular relationships, namely between the seat stays and the top tube section, as well as between a main section and the top tube section. Here, the tolerance is only about 1°, whereas with conventionally manufactured frames made of aluminum profiles or steel tubes, only angular tolerances of 3° to 5° can be achieved with reasonable manufacturing effort. The invention is explained in more detail below with reference to the exemplary embodiments shown in the drawings. The figures show, in detail: Fig. 1 a child's balance bike in a side view; Fig. 2A, Fig. 2B each an unclaimed child's balance bike frame in a side view; Fig. 3 the child's balance bike frame in a perspective view from a low angle; Fig. 4 a child's bicycle in a side view; Fig. 5A, Fig. 5B each a child's bicycle frame in a side view; Fig. 6 the child's bicycle frame in a perspective view from a low angle; Fig. 7 the child's bicycle frame in a perspective view from a low angle. Fig. 1 shows a side view of a child's balance bike 200, which is not the subject of the claimed invention. In this embodiment, it has two wheels 230, 240 of different sizes. The front wheel 230 is inserted into a front wheel mount 221 and a front fork 220. This fork is connected to a handlebar 224. The unit consisting of the front fork 220 and the handlebar 224 is guided by a head tube 218, which is embedded in a child's balance bike frame 210. The rear wheel 240 is held between a pair of rear wheel stays 213 and attached to their rear wheel mounts 214. The rear wheel stays 213 extend slightly diagonally backwards from an upper apex of the child's balance bike frame 210. By choosing a front wheel 230 with a larger diameter than the rear wheel 240, the main tube 211 of the child's balance bike frame 210 can descend more steeply from the head tube 218 to a front apex 211.2 and then, within the limited distance between the two wheels 230, 240, rise again to an upper apex than would be the case with wheels of the same size. This step, inserted at the front apex 211.2 in the child's balance bike frame 210, allows for a low step-through in front of a saddle 250. The saddle 250, with its seat post 251, is guided in a seat tube 215. The seat tube 215 passes through the main tube 211 of the balance bike frame 210. To avoid making the junction where the seat tube 215 and the main tube 211 of the balance bike frame 210 are joined too thick, and to prevent material accumulation—in view of the plastic injection molding process—the cross-section of the balance bike frame 210 below the saddle 250 is kept slim. Only a stiffening rib 217 is provided there, extending from the front apex 211.2 to a point behind the seat post 251 where the balance bike frame 210 branches into the two rear stays 213. The stiffening rib 217 surrounds the lower end of the fabric-fitted seat tube 215 on both sides. Fig. 2A shows a side view of the children's balance bike frame 210 without any other parts of the bike. The section between the head tube 218 and the seat tube 215 is designated as the main tube 211. This is designed as a thermoplastic hollow profile, manufactured using fluid injection molding. It is divided into a main section 211.1, which extends from the head tube 218 to the front apex 211.2, and a secondary section 211.3, which extends between the front apex 211.2 and the seat tube 215. The hollow section of the main tube 211 ends shortly behind the seat tube 215. From there, the children's balance bike frame 210 branches into two rear stays 213, each terminating at a rear wheel mount 214. Fig. 2B shows the same view as in Fig. 2A, with the most important angles α, β, γ for the geometry of the children's balance bike frame indicated. The seat tube 215 is inclined, as is common practice, at an angle γ of 10° to 15° to the vertical so that, as the child grows taller, not only is the seat height increased, but also the distance to the handlebars. The main section 211.1 and the secondary section 211.2 of the main tube 211 form an angle α of at least 80°. A significantly smaller angle is to be avoided here to prevent stress concentrations. The secondary section 211.3 and the rear stays 213 form an angle β of 110° to 140°. Fig. 3 shows the child's balance bike frame 210 in a perspective view from a low angle. A recess 218.1 is visible on the head tube 218, which can be used to route brake cables or electrical wires, etc. The structure of the stiffening rib 217, which surrounds the seat tube 215, is clearly visible. Fig. 4 shows a side view of a child's bicycle 100 with a child's bicycle frame 110 according to the invention, which in this embodiment has two wheels 130, 140 of different sizes. The front wheel 130 is mounted on a front wheel mount 121 of a front fork 120. This is connected to a handlebar 124. The unit consisting of the front fork 120 and handlebar 124 is guided by a head tube 118, which is embedded in the child's bicycle frame 110. A bottom bracket mount 112 is formed at the bottom of the child's bicycle frame 110. A saddle 150 is guided with its seat post 151 in a seat tube 115, which is embedded in the child's bicycle frame 110. The rear wheel 140 is mounted between the chainstays 113 and the seat stays 116 and attached to rear wheel mounts 114. Fig. 5A shows a side view of the children's bicycle frame 110. A section between the head tube 118, the seat tube 115, and the bottom bracket shell 112 is hollow, formed using fluid injection technology. The hollow part of the children's bicycle frame 110 is divided into: - a main section 111.1, extending from the head tube 118 to a front junction 111.2; - a top tube section 111.3, extending from the front junction 111.2 to the seat tube 115; - a down tube section 111.5, extending as a continuation of the main section 111.1 from the front junction 111.2 to the bottom bracket shell 112. Furthermore, the children's bicycle frame 110, manufactured as a one-piece injection-molded plastic part, has the following molded sections: - a pair of seat stays 116 branching off behind the seat tube 115 and each terminating at a rear wheel mount 114 and - a pair of chainstays 113 extending from an area at or behind the bottom bracket mount 112 to the rear wheel mount 114. By choosing a front wheel 130 with a larger diameter than the rear wheel 140, the main section 111.1 of the main tube 111 can drop steeply from the head tube 118 to the front junction 111.2 and then rise to the upper apex 111.4. This step inserted in the main section 111.1 allows for a low entry point in front of a saddle 150. In particular, the force triangle is important, which consists of: - the top tube section 111.3 between the front junction 111.2 and the seat tube 115; - the down tube section 111.5 between the front junction 111.2 and the bottom bracket mount 112 and - the seat tube 115, which is positively and / or materially connected to the child's bicycle frame 110 at the upper apex 111.4 and which is supported at its lower end on the bottom bracket mount 112 or is firmly connected to it. Fig. 5B shows the child's bicycle frame 110 again from the side, in the same view as Fig. 5A, with the essential angles α', β', γ' indicated. The top tube section 111.3 has a similar profile to that of the child's balance bike frame 210 described above. For the stability of the child's bicycle frame 110 while maintaining low mass, it is advantageous to introduce the child's weight force at the upper apex 111.4, since this results in lower bending stresses acting on the top tube section 111.3 than in conventional geometries according to the prior art, where the seat tube meets the top tube approximately perpendicularly. According to the invention, the seat stays 116 and the top tube section 111.3 form an angle β' of 110° to 140°. The main section 111.1 and the top tube section 111.3 form an angle α' of at least 80°. Fig. 6 is another perspective view of the children's bicycle frame 110. It is clearly visible that the seat tube 115 has a smaller diameter compared to the other sections 111.1, 111.2, and 111.3 of the children's bicycle frame 110, which are made of plastic, and passes through them. A recess 111.6 is formed on the top tube section 111.3, in the region of the upper apex 111.4, to accommodate the portion of the seat tube 115 protruding from the top tube section 111.3. At this point, a positive-locking and / or material-locking connection is provided between the seat tube 115 and the children's bicycle frame 110. Recesses 116.1 for a brake are embedded in the seat stays 116. Fig. 7 shows a perspective view of the child's bicycle frame 110 from a low angle. The sections of the top tube 111.3 and the down tube 111.5, which extend between the seat tube 115 and the point where the tube branches into the seat stays 116 and 117 respectively, are shown. Reinforcing structures 117 and 119 are formed at the chainstay 113. The chainstay 113 and the seat stays 116 each have smooth walls on the sides and top. They are open at the bottom and stiffened by a rib structure. A kickstand mount 113.1 for a bicycle kickstand is provided on at least one of the chainstay 113. Fig. 8 shows a partial section of the children's bicycle frame 110 in a perspective view. The seat tube 115 and bottom bracket shell 112 together form a hammer-like configuration. The seat tube 115 is supported at the top by the dome-shaped recess 111.6; the bottom bracket shell 112 rests at the bottom of the children's bicycle frame 110. Loads are introduced via the seat tube 115, which has a small diameter compared to the width of sections 111.1, 111.3, 111.5 of the children's bicycle frame 110. Forces can thus be directed onto the cylindrical wall of the bottom bracket shell 112 and are therefore distributed over a larger area at the transition to the plastic frame. Behind the mounting point 111.6, a reinforcement structure 119 with reinforcing ribs is formed before the two seat stays 116 branch off. Behind the bottom bracket mounting point 112 and before the branch into the two chainstays 113, the reinforcement structure 117 is provided. Figure 9 shows the area of ​​the rear wheel mounts 114. The chainstay 113 and the seat stay 116 do not meet at this point. Instead, a rear wheel mounting unit 160 is provided. This unit consists of an inner disc 164, an axle guide element 162, an outer disc 163, and a cover cap 161. The axle guide element 162 is made of metal to absorb the high point pressure exerted by the rear axle passing through it and to transfer this pressure into the thermoplastic bicycle frame. It is inserted directly between the chainstay 113 and the seat stay 116 and secured in position by screwing the discs 163 and 164 together. The rear wheel is then attached in the usual way by placing nuts on the axle ends, which are tightened against a shoulder on the axle. The axis guide element 162 also has a projection 162.1, which allows the attachment of a mudguard or a luggage rack. The cover cap 161 covers the other parts of the rear wheel mounting unit 160 and a nut mounted on the rear wheel axle.

Claims

A child's bicycle frame (110) that can be manufactured by injection molding of plastics, comprising at least: - a head tube (118) for receiving a front fork (120) and a handlebar (124); - a seat tube (115) for receiving a seat post (151); - a bottom bracket shell (112); - a pair of seat stays (116) extending from an upper part of the seat tube (115) to a rear wheel shell (114); - a pair of chainstays (113) extending from the bottom bracket shell (112) to the rear wheel shell (114), wherein at least one section of the child's bicycle frame (110) connecting the head tube (118), the seat tube (115) and the bottom bracket shell (112) is hollow and the hollow part of the child's bicycle frame (110) is subdivided into: ◯ a main section (111.1) extending from the head tube (118) extends to a front junction (111.2),◯ an upper tube section (111.3) extending from the front junction (111.2) extends to an upper apex (111.4) at which the seat tube (115) is located. ◯ a down tube section (111.5) which extends as a continuation of the main section (111.1) from the front junction (111.2) to the bottom bracket shell (112). characterized in that, - the child's bicycle frame (110) is formed as a one-piece injection-molded plastic part, wherein the seat stays (116) and the chain stays (113) are not joined to each other at the rear wheel mount (114) and the rear wheel mounts (114) are part of a rear wheel mounting unit (160) separate from the child's bicycle frame (110), - that the seat tube (115) has a smaller diameter than the other plastic sections of the child's bicycle frame (110), and - that the top tube section (111.3) extends over the area defined by the upper apex. (111.4) seat tube (115) and one in the down tube section (111.5) embedded bottom bracket mount (112) is supported on the down tube section (111.5). Children's bicycle frame (110) according to claim 1, characterized in that the head tube (118) and the seat tube (115) are designed as metal profiles which are embedded in the children's bicycle frame (110) in a material-bonded manner. Children's bicycle frame (110) according to one of claims 1 or 2, characterized in that an upper end of the seat tube (115) is positively supported with a receptacle (111.6) formed on the top tube section (111.3) at the upper apex (111.4). Children's bicycle frame (110) according to one of claims 1 to 3, characterized in that the longitudinal axes of the main section (211.1) and the top tube section (111.3) enclose an angle α of 80° to 100° and that the seat stays (116) with the top tube section (111.3) enclose an angle β of 125° to 150°. A child's bicycle (100), comprising at least: - a child's bicycle frame (110) according to any one of the preceding claims 1 to 4; - a front wheel (130) which is inserted into the front fork (120) at a front wheel mount (121) which is connected to the handlebar (124), wherein the unit of front fork (120) and handlebar (124) is guided in the head tube (118); - a rear wheel (140) which is attached to the rear wheel mounts (114). Children's bicycle (100) according to claim 5, characterized in that the front wheel (130) has a larger diameter than the rear wheel (140).

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