Freewheel hub with spring made of plastic with cellular structure

Description

[0001] The present invention relates to a freewheel hub for a bicycle, which comprises a hub axle, a hub shell rotatably mounted on the hub axle, a driver rotatably mounted on the hub axle, which driver can be connected to at least one pinion arrangement, and a freewheel device arranged between the hub shell and the driver.

[0002] The freewheel device comprises a first clutch ring that is coupled or can be coupled to the hub sleeve in a torque-transmitting manner, and a second clutch ring that is coupled or can be coupled to the driver in a torque-transmitting manner. The two clutch rings have mutually facing axial toothings. Furthermore, the freewheel device comprises a preloading device that is designed and arranged to axially preload the two clutch rings toward one another. The preloading device comprises a spring arrangement with at least one spring element.

[0003] Such a freewheel is also called an axial freewheel or toothed disc freewheel.

[0004] A generic freewheel hub is known, for example, from the publication

[0005] DE 198 47 73 A1 describes a freewheel hub in which the preloading device is formed by two steel helical compression springs. The publication DE 20 2014 001591 U1 also discloses a freewheel hub of this type.

[0006] However, due to manufacturing limitations in the production of steel springs, particularly with regard to the coil ratio, they can only be used for clutch rings with a limited diameter and consequently a limited number of clutch teeth. For this reason, only relatively large pressure angles, approximately 20° to 15°, are feasible. The forces acting on the clutch teeth are also relatively large due to the limited diameter, leading to rapid wear. Furthermore, the operating noise of freewheels with steel springs is generally very loud.

[0007] As an alternative, freewheel hubs with magnetic preload devices are known, for example from DE 10 2015 009 143 A1.

[0008] However, compared to freewheel hubs with mechanical preload devices, these have a significantly more complex and therefore more cost-intensive design and require high levels of accuracy and tight tolerances.

[0009] In addition, the force exerted by the magnets on the clutch rings is not evenly distributed around the circumference of the hub axle, but acts very selectively. At higher speeds, and especially when the rear wheel compresses rapidly on a full-suspension bike (MTB), the clutch rings begin to wobble, sometimes causing only individual teeth of the axial gears to engage, thus damaging them. With increasing operating time, this can progress to the complete failure of the freewheel.

[0010] Against this background, the object of the present invention is to improve the generic freewheel hub with regard to wear, operating noise and manufacturing costs.

[0011] For this purpose, the invention proposes using a spring element made of a plastic with a cellular structure, in particular based on polyurethane, preferably a mixed-cell polyurethane elastomer, instead of a steel spring.

[0012] For example, a technical foam such as that marketed by BASF under the name Cellasto ® or by Getzner under the name Sylomer ® can be used. Prototypes of the spring according to the invention were manufactured, for example, from Sylomer ® type SR28.

[0013] Polyurethanes are grease and oil resistant, temperature independent and inexpensive to produce and are therefore very suitable for use as springs in axial freewheels.

[0014] Compared to springs made of steel, larger coupling diameters can be realized, resulting in smaller engagement angles and lower forces. Wear is reduced and service life is increased accordingly. The damping properties of the material also reduce noise during operation.

[0015] Compared to the magnetic freewheel, the spring load can be applied more evenly to the flat surface of the clutch ring(s).

[0016] Furthermore, the design of the freewheel according to the invention is very simple, does not require high precision or tight tolerances, and is therefore cost-effective to manufacture. The spring elements, described in more detail below, can be easily manufactured from prefabricated sheet material, for example, using waterjet cutting.

[0017] Compared to the magnetic freewheel, which requires complex machining of the clutch rings and the hub sleeve in order to position the individual magnets appropriately, the overall manufacturing effort of the freewheel is significantly reduced.

[0018] For a uniform distribution of the spring force, it can be provided that the spring arrangement comprises a plurality of, preferably identical, spring elements which are arranged distributed around the circumference of the hub axle, preferably with equal angular distances from one another.

[0019] According to the invention, the spring element or each of the spring elements has an arcuate section, the convex side of which is designed to press in the axial direction against one of the clutch rings in order to preload the two clutch rings towards each other when the spring element is installed in the freewheel hub.

[0020] According to a preferred embodiment, the arcuate section is formed as a strip section with a substantially constant width and thickness. Such structures can be cut particularly easily from a flat foam board, for example, by waterjet cutting. The width direction of the strip section can correspond to the thickness of the board.

[0021] Furthermore, the arcuate section is preferably curved about an axis which runs approximately parallel to the width direction of the strip section or approximately radially in the installed state.

[0022] The resulting spring force is influenced by material-dependent factors, such as the type of plastic and the shape and size of the pores, and by geometry-dependent factors, such as the shape of the arch, the arch radius, and the strip thickness in the case of an arcuate section. By appropriately combining these factors, the desired spring force can be easily adjusted.

[0023] Only relatively low axial restoring forces are required for the freewheel to function. For example, 0.2 to 0.5 N is required for preload, and approximately 1 N is required during freewheel operation.

[0024] It has been found that such low restoring forces can be achieved due to a combination of cellular material and suitable geometry of the spring elements, which also advantageously leads to a reduction in operating noise.

[0025] This is especially true if the spring arrangement is designed such that the spring forces required for freewheeling are primarily generated by the flexural rigidity, rather than by compression of the plastic. In other words, the spring arrangement is preferably designed such that when a contact force of 0.2 N to 0.5 N is applied to the spring arrangement in the axial direction, the spring arrangement bends, but the cellular structure of the plastic is not significantly compressed. Without wishing to be bound by this, it is assumed that the cellular structure of the plastic appropriately reduces the flexural rigidity of the spring elements.

[0026] A particularly flexible use of the spring elements, for example for coupling rings with different diameters, is possible because, according to the invention, the spring arrangement is formed from several, identical and separately designed spring elements.

[0027] Each spring element can be designed as a D-ring or in the shape of an arc with angled longitudinal ends. Other shapes are also conceivable, such as rectangular or angled, as long as they allow for bending or retraction of the installed spring element in the axial direction.

[0028] To determine the installation position of the individual spring elements, it is preferred that they be inserted into corresponding recesses. These recesses are formed in an axial surface, i.e., a surface with an axial normal vector, of the hub sleeve or driver. Other fixing options are also conceivable. For example, the individual spring elements could be inserted into a circumferential groove of the hub sleeve or driver, in which suitable stops are provided, between which the spring elements can be clamped.

[0029] The assembly effort is significantly reduced ,in that according to the invention the plurality of spring elements are connected to one another in one piece and preferably in the form of a continuous strip which forms the spring arrangement.

[0030] Since the plastic material used is sufficiently flexible, the strip with a fixed number of arcuate sections connected to each other by planar sections can first be cut out of a flat plate and then bent, for example by hand, around the hub axis and inserted into a corresponding circular groove provided in an axial surface of the hub shell or driver.

[0031] However, it is important to note that the strip should be inserted in such a way that it does not undergo undesirable deformation during operation. To this end, appropriate structures, such as stops or projections, can be provided in the hub shell or driver.

[0032] Correct installation of the preloading device can be easily ensured or simplified by further providing the preloading device with a retaining ring designed to fix the positions of the individual spring elements relative to one another. The retaining ring is preferably made of a plastic and can be designed for a continuous strip with multiple spring elements or for separate spring elements.

[0033] According to a preferred embodiment, the retaining ring comprises an annular base and a plurality of retaining elements distributed around the circumference of the base and projecting radially therefrom, which retaining elements cover the spring arrangement axially on one side in sections and preferably encompass it radially from the inside and outside.

[0034] This construction is particularly suitable for the strip described above with alternating curved sections and planar sections, which can be inserted into the retaining ring in such a way that the retaining elements cover or encompass the planar sections.

[0035] Additionally, the pretensioning device may further comprise a cover ring that can be mounted on the retaining ring such that the spring assembly is accommodated at least partially, particularly in the area of the planar sections, between the retaining ring and the cover ring and, together with the retaining ring and the cover ring, forms a firmly connected assembly. This prevents the spring assembly from falling out of the retaining ring, and the pretensioning device can be handled particularly easily as a spare part.

[0036] In the following, the present invention is explained using some selected embodiments which are illustrated in the attached figures. Showing:

[0037] Fig. 1 shows a first embodiment of a freewheel hub according to the invention in a longitudinal section, Fig. 2 shows an enlarged detail of the Fig. 1 area marked II, Fig. 3 an exploded view of the pretensioning device of the freewheel hub from Fig. 1 , Fig. 4 a perspective view of the pretensioning device from Fig. 3 in the assembled state, Fig. 5 a side view of the spring arrangement of the pretensioning device from Fig. 3 before it is inserted into the retaining ring, Fig. 6 a plan view of the underside of the object of Fig. 5 , Fig. 7 an enlarged detail of the Fig. 5area designated VII, Fig. 8 is an exploded view of essential components of a second embodiment of a freewheel hub according to the invention, and Fig. 9 is an exploded view of essential components of a third embodiment of a freewheel hub according to the invention.

[0038] For reasons of clarity, not all features in each figure are provided with reference symbols; instead, only those features necessary to explain the respective figure are indicated. This applies particularly if a figure contains several similar features.

[0039] Identical or corresponding features of the various embodiments are each provided with the same reference numerals, and the second and third embodiments are mainly explained only insofar as they differ from the first embodiment, to the description of which reference is otherwise made.

[0040] Figure 1 shows a longitudinal sectional view of a first embodiment of a freewheel hub 10 according to the invention, whose longitudinal axis M is contained in the sectional plane. The term "axial" in this application, unless otherwise stated, always refers to this longitudinal axis M, which, when installed, coincides with the rear wheel axle of the bicycle.

[0041] The freewheel hub 10 comprises a hub axle 12, which can be fixed to the frame of a bicycle in a known manner. A hub sleeve 14 is rotatably mounted on the hub axle 12 via two roller bearings 11 and 13, and a driver 16 is rotatably mounted via two further roller bearings 15 and 17. In the axial direction, the hub sleeve 14 and driver 16 are attached to the hub axle 12 via locking elements 19 and 21.

[0042] At the longitudinal end of the hub shell 14, which faces the driver 16, the hub shell has a circumferential axial groove 22, which accommodates the freewheel device 18, described in more detail below. Furthermore, the hub shell 14 has two spoke flanges 23 and 25, to which spokes can be attached in a known manner.

[0043] The driver 16 can be connected to a pinion arrangement (not shown here), via which torque can be introduced into the driver 16 and transmitted via this to the hub shell 14 and thus to the rear wheel of the bicycle.

[0044] The freewheel device 18 is arranged in the groove 22 between the hub sleeve 14 and the driver 16 and is sealed to the outside by a further closure element 31.

[0045] The freewheel device 18 is better in the Figure 2It comprises a first coupling ring 24, a second coupling ring 26, and a pretensioning device 28.

[0046] The first coupling ring 24 is coupled to the hub sleeve 14 in a torque-transmitting manner, and the second coupling ring 26 is coupled to the driver 26 in a torque-transmitting manner. The radial external toothings 24a and 16a, respectively, and internal toothings 14i and 26i, respectively, provided on the respective components for this purpose, are best seen in the perspective view in Figure 8 of the second embodiment, but are identical for all embodiments.

[0047] To realize the freewheel, the two coupling rings 24 and 26 further have axial toothings 24z, 26z facing each other in a known manner (cf. Figures 8 and 9 ) with inclined sliding surfaces and are axially preloaded towards each other via the preloading device 28.

[0048] With the exception of the specific design of the preloading device 28, which is described in more detail below, the structure and function of the illustrated freewheel are known. For example, reference is made to the two publications mentioned in the introduction.

[0049] In the first embodiment of the Figures 1 to 7 the pretensioning device 28 is formed from a spring arrangement 30, a retaining ring 40 and a cover ring 46, which in Figure 3 in an exploded view and in Figure 4 are shown in an assembled state in which the three aforementioned components form a firmly connected assembly 48.

[0050] The spring arrangement 30 comprises a plurality of spring elements 32 which, according to the invention, consist of a plastic material with a cellular structure, for example a polyurethane-based foam.

[0051] In the first and second embodiments of the Figures 1 to 8In this case, the five similar spring elements 32 are integrally connected to one another in the form of a continuous strip 34. The strip 34 comprises an alternating arrangement of similar arcuate sections 32b, which form the actual spring elements 32, and similar planar sections 36, which form spacers between the arcuate sections 32b. At the two longitudinal ends, the strip 34 further has planar end sections 37, the length of which is approximately half the length of the remaining planar sections 36 or slightly less.

[0052] The exact shape of the strip 34, which can be cut out of a plate-shaped, sufficiently flexible starting material with a cellular structure, is shown in the Figures 5 to 7 shown in different views. In the example shown, the shape of the strip is mirror-symmetrical with respect to a symmetry plane S. The Figures 5 to 7show the strip in an initial state before it is bent around an axis parallel to the thickness direction D of the strip.

[0053] The width b (cf. Fig. 6 ) of the strip 34 is preferably constant over the length of the strip and can, for example, be between 3 mm and 5 mm. For example, the width b can be determined by the thickness of the plate-shaped starting material.

[0054] The thickness d of the strip is also preferably constant and is preferably between 1.5 mm and 2.5 mm, while its total length I can be approximately 135 mm to 139 mm. The inner arc radius r of the arcuate sections 32b is, for example, between 12 mm and 14 mm, and the length lb of the arcuate sections is, for example, between 18 mm and 20 mm. The distance a1 between the centers of adjacent arcuate sections 32b can be approximately between 26 mm and 29 mm, and the distance a2 between a longitudinal end and the center of the immediately adjacent arcuate section can be approximately between 13 mm and 15 mm.

[0055] The individual dimensions such as total length, width, thickness and arc radius of the strip must of course be adapted to the requirements of the individual case, i.e. to the dimensions of the freewheel hub, in particular the coupling rings, the properties of the cellular plastic material used, the desired spring forces and the like.

[0056] In the first embodiment, the strip 34 forming the spring assembly 30 is bent by hand about an axis parallel to the thickness direction D of the strip 34 and inserted into the retaining ring 40.

[0057] The best shown in the exploded view of the Figure 3 The retaining ring 40 comprises an annular base 42 and five retaining elements 44 projecting radially outwards from this.

[0058] The holding elements 44 are each substantially U-shaped, with an outer leg 43, a cover surface 45, and an inner leg 47, which adjoins the base 42 and is integrally connected thereto. The planar sections 36 of the strip 34 are inserted or clamped into the receptacles 44u formed thereby, thereby determining the positions of the spring elements 32 relative to one another.

[0059] One of the holding elements 44 additionally has an inner partition 49, against which the end faces 34s of the strip 34 can be placed, which serves to facilitate assembly. It should also be noted that the cutting plane in Fig. 1 and 2 passes exactly through this partition wall 49, which is located in the lower part of Fig. 2 is clearly visible.

[0060] After inserting the strip 34 into the retaining ring 40, the cover ring 46 can be mounted on the retaining ring 40. For this purpose, in the present embodiment, corresponding projections 46p1 and 46p2 are provided on the cover ring 46, and matching recesses 44r1, 44r2 are provided on the retaining elements 44. For example, press fits, conical fits (as with 46p1 and 44r1), or even snap connections are possible. In the present embodiment, the cover ring 46 is designed as a flat annular disc, which, in addition to the structures for attachment to the retaining ring, also has several rib structures 46r to increase rigidity.

[0061] When the pretensioning device 28 is fully assembled, as shown in Fig. 4As shown, the planar portions 36 of the spring assembly 30 are firmly received between the retaining ring 40 and the cover ring 46, and the preloading device 28 can be easily handled as a spare part. The risk of the strip 34 undesirably bending during assembly on the hub shell 14 is minimized.

[0062] Retaining ring 40 and cover ring 46 may be made of a suitable plastic material, for example by injection molding.

[0063] In the assembled state of the freewheel hub 10, the convex side 32bk of each of the arcuate sections 32 presses axially against the first clutch ring 24 to preload it onto the second clutch ring 26. Due to the relatively large number and even distribution of contact points between the spring assembly 30 and the first clutch ring 24 around the hub axis 12, the spring load can be applied evenly to the clutch rings 24, 26. Preferably, the spring strip is designed such that only the flexural rigidity, not the compression of the plastic, generates the spring forces required for freewheeling, and the cellular structure is not significantly compressed during operation. It is assumed that the cellular structure appropriately reduces the flexural rigidity of the spring assembly.

[0064] It is also possible to omit the cover ring 46, in which case a simpler variant of the retaining ring (not shown) can be used, since the structures for fastening to the cover ring are not necessary in this case.

[0065] It is also possible, although somewhat more demanding in assembly, to insert only the strip 34 as a pre-tensioning device 28 (i.e. without retaining ring and cover ring) into the groove 22 of the hub sleeve 14, as in the second embodiment in Figure 8 is shown.

[0066] For reasons of clarity, in the illustrations of the second and third embodiments in the Figures 8 and 9 in particular to the representation of the closure element 31 (cf. Fig. 1 ) was omitted.

[0067] Instead of a single-piece strip, several separate spring elements 32 can be used, for example in the form of separate D-rings 33, as in the third embodiment in Figure 9 Such D-rings 33 can also be cut out of suitable foam sheets with little effort. Alternatively, individual, separate spring elements could be used, which would look similar to Figure 7 which each comprise a central curved section and flat angled longitudinal ends.

[0068] To prevent the individual spring elements 32 from undesirably slipping against one another during operation of the freewheel hub 10, it can be provided, for example, that corresponding recesses 49 are provided in an axial surface of the hub sleeve 14, into which the spring elements 32 can be inserted or clamped, although this increases the machining effort for the hub sleeve 14. Alternatively, a suitably designed retaining ring can be used for separate spring elements, which fixes the spring elements in their relative position to one another.

Claims

1. Freewheel hub (10) for a bicycle, comprising: a hub axle (12), a hub sleeve (14) which is mounted rotatably on the hub axle (12), a driver (16) which is mounted rotatably on the hub axle (12) and can be connected to at least one sprocket arrangement, a freewheel device (18) arranged between the hub sleeve (14) and the driver (16), comprising: a first clutch ring (24), which is coupled or couplable to the hub sleeve (14) in a torque-transmitting manner, a second clutch ring (26), which is coupled or couplable to the driver (16) in a torque-transmitting manner, wherein the two clutch rings (24, 26) have mutually facing axial toothings (24z, 26z), a preload device (28) which is designed and arranged to preload the two clutch rings (24, 26) axially towards one another, wherein the preload device (28) has a spring arrangement (30) with at least one spring element (32), and the spring element (32) consists of a plastic with a cellular structure, characterized in that the spring element (32) or each of the spring elements (32) has an arcuate portion (32b), the convex side (32bk) of which is configured to press against one of the clutch rings (24, 26) in the axial direction, in order to preload the two clutch rings (24, 26) against one another, wherein a plurality of separately formed spring elements (32) of the same type together form the spring arrangement (30).

2. Freewheel hub (10) according to Claim 1, characterized in that the spring element (32) comprises or consists of a polyurethane-based plastic.

3. Freewheel hub (10) according to either of the preceding claims, characterized in that the spring arrangement (30) comprises a plurality of spring elements (32), preferably of the same type, which are arranged distributed around the circumference of the hub axle (12).

4. Freewheel hub (10) according to one of the preceding claims, characterized in that the arcuate portion (32b) is in the form of a strip portion with a substantially constant width (b) and thickness (d).

5. Freewheel hub (10) according to one of the preceding claims, characterized in that the spring arrangement (30) is designed such that, although the spring arrangement (30) is deformed when a contact pressure of 0.2 N to 0.5 N is applied to the spring arrangement (30) in the axial direction, the cellular structure of the plastic is not compressed in the process.

6. Freewheel hub (10) according to one of the preceding claims, characterized in that each spring element (32) is in the form of a D ring (33) or formed in the shape of an arc with angled-away longitudinal ends.

7. Freewheel hub (10) according to one of the preceding claims, wherein the spring elements (32) are inserted into corresponding depressions formed in an axial surface of the hub sleeve (14) or an axial surface of the driver.

8. Freewheel hub (10) for a bicycle, comprising: a hub axle (12), a hub sleeve (14) which is mounted rotatably on the hub axle (12), a driver (16) which is mounted rotatably on the hub axle (12) and can be connected to at least one sprocket arrangement, a freewheel device (18) arranged between the hub sleeve (14) and the driver (16), comprising: a first clutch ring (24), which is coupled or couplable to the hub sleeve (14) in a torque-transmitting manner, a second clutch ring (26), which is coupled or couplable to the driver (16) in a torque-transmitting manner, wherein the two clutch rings (24, 26) have mutually facing axial toothings (24z, 26z), a preload device (28) which is designed and arranged to preload the two clutch rings (24, 26) axially towards one another, wherein the preload device (28) has a spring arrangement (30) with at least one spring element (32), and the spring element (32) consists of a plastic with a cellular structure, characterized in that the spring element (32) or each of the spring elements (32) has an arcuate portion (32b), the convex side (32bk) of which is configured to press against one of the clutch rings (24, 26) in the axial direction, in order to preload the two clutch rings (24, 26) against one another, wherein a plurality of spring elements (32) of the same type, which are connected to one another in one piece and preferably in the form of a cohesive strip (34), form the spring arrangement (30).

9. Freewheel hub (10) according to one of the preceding claims, comprising a plurality of spring elements (32) distributed around the hub axle (12) in the circumferential direction, characterized in that the preload device (28) also has a retaining ring (40), which is designed to fix the positions of the spring elements (32) relative to one another.

10. Freewheel hub according to Claim 8, characterized in that the retaining ring (40) comprises an annular base (42) and a plurality of retaining elements (44) which are distributed around the circumference of the base (42), protrude radially from said base, cover the spring arrangement (30) axially on one side in certain portions and preferably engage around the spring arrangement radially from the inside and outside.

11. Freewheel hub according to Claim 9 or 10, characterized in that the preload device (28) also comprises a cover ring (46), which can be mounted on the retaining ring (40) such that the spring arrangement (30) is received at least in certain portions between the retaining ring (40) and the cover ring (46) and, together with the retaining ring (40) and the cover ring (46), forms a solidly cohesive assembly (48).