Description

Technical Field This application relates to a drive chain system, in particular a drive chain system for a bicycle, comprising a chain with an alternating succession of inner chain links and outer chain links as defined by the preamble of claim 1 . This application further relates to a bicycle comprising a drive chain sys- tem. In this regard, the term bicycles particularly includes conventional bi- cycles driven only by cranks and bicycles driven by a combination of cranks and an electric engine, typically called pedelecs or ebikes.

Background Art Drive chain systems comprising chains with an alternating succession of inner links and outer links are well known in the prior art. One characteristic of such chains is that the distance between opposite outer link plates is much larger than the distance between opposite inner link plates, since the outer link plates are arranged at the outer surfaces of the inner link plates.

CN 2120219 U discloses a drive chain system, wherein the drive inner and outer chain links comprise protrusions in the area between the adjacent link plates. The protrusions comprise a curved surface in order to provide a smoother movement of the chain engaging the teeth of the chainrings. Nev- ertheless, there is a possibility that the teeth engaging the chain have to move into a comparable small gap between the Link plates when engaging the chain links. Said gap is just minimally wider than the width of the teeth. Therefore, the protrusions are insufficient to provide a smooth engagement between chain links and teeth.

Disclosure of Invention

It is an object of the invention to provide a drive chain system with a chain with inner chain links and outer chain links that provides a smooth engage- ment between chain and chainring. The object is attained by the combination of features of the independent claims. The dependent claims provide useful embodiments of the drive chain system described herein.

The drive chain system comprises a chainring with a plurality of teeth and a chain. The chainring is moved by the cranks and/or the electric motor of the bicycle and transmits the motion to the chain. The chain drives the rear wheel of the bicycle via a rear sprocket. The rear sprocket may be part of a rear cassette comprising a multitude of sprockets. The teeth may show generally identical width in the transverse direction and engage alternately with inner chain links and outer chain links. The chain comprises an alternating succession of inner chain links and outer chain links, each inner chain link having a pair of inner link plates contacting the lateral faces of two rollers. Each of the outer chain links has a pair of two outer link plates contacting the inner link plates of adjacent inner chain links. Two outer link plates and two inner link plates and a roller are con- nected by a pin. The inner surfaces of a pair of opposite outer link plates comprise protrusions in the area between the adjacent inner link plates. The protrusions extending from the inner surfaces of outer link plates re- duce the distance between these inner surfaces of outer link plates, so that the lateral clearance between the teeth of a chainring engaging with outer links of the chain is reduced. The chain described herein improves the guid- ance of the teeth between the outer chain link plates on the chainring be- cause it reduces the distance between the inner surfaces and thus the clearance of play between these surfaces and the engaging teeth. The re- duced clearance between teeth engaging between pairs of outer link plates also reduces noise, which usually occurs due to lateral movement of the chain hitting the teeth.

The chainring can have an even number of teeth or an odd number of teeth. The teeth taper laterally towards their respective tip. Therefore, the tips with the reduced thickness can slip into the space between the link plates, and especially the space between the protrusions, more easily than teeth with a constant width. Once introduced into the space between the protrusions, the width of the part of the tooth placed between the protrusions increases while the respective chain link moves into its fully-engaged position on the chainring. During this movement, the clearance between the protrusions and the tooth decreases and the chain is guided by the tooth in lateral di- rection allowing the next tooth to engage the gap between the next pair of link plates. The teeth can comprise a lateral curvature. A lateral curvature allows the tapering of the teeth with a variation of the gradient of the decrease of the teeth width towards the tip of the respective tooth. In praxis, the modulus of the gradient can increase in the direction towards the tip. This allows to provide a rapid increase of lateral guidance of the chain by a respective tooth, shortly after the tip of the tooth has entered the space between the protrusions.

The lateral curvature can have a convex radius of at least 8 mm, particularly at least 10 mm, and/or maximum 14 mm, particularly maximum 12 mm.

Theses values are appropriate to achieve a good lateral guidance of the chain immediately after the tip of a respective tooth entering the space be- tween the protrusions. It is possible that the teeth taper laterally in a section between their respec- tive tip and a section of the respective tooth with parallel lateral surfaces. In this case, the teeth can taper towards their tips in a limited region near the tips and therefore provide a fast increase in lateral guidance of the chain when the tapering region passes the space between the protrusions.

In praxis, the distance between the lateral surfaces of the teeth can be at least 1 ,9 mm and/or maximum 2 mm in the section of the respective tooth with parallel lateral surfaces.

The drive chain system can be configured in such manner that the protru- sions engage a tooth in its section with parallel lateral surfaces, when the chain is fully engaged to this tooth. In this configuration, the tooth provides maximum lateral guidance to the chain when the chain is fully engaged with this tooth.

The section with parallel lateral surfaces may extend by at least 0,5 mm, preferably at least 0,8 mm, towards the tip of the tooth from the point of contact between the protrusion and the tooth nearest to the tip of the tooth, when the chain is fully engaged to this tooth. In this case, the maximum lat eral guidance of the chain provided by the tooth is reached even before the chain is fully engaged with this tooth.

The distance the protrusion protrudes from the link plate towards a tooth can be at least 70%, preferably at least 90%, and/or maximum 130%, pref- erably maximum 1 10% of the distance the parallel lateral surfaces extend towards the tip of the tooth from the point of contact between the protrusion and the tooth nearest to the tip of the tooth, when the chain is fully engaged to this tooth. It turned out that these relations are advantageous regarding the lateral guidance of the chain.

The tips of the teeth can protrude from the chain links when the respective chain link is fully engaged with the respective tooth. This allows an en- gagement between tooth and chain that hinders the chain from jumping of the chain ring if there is an intense movement of the chain, e.g. when the bicycle is used in difficult terrain with high velocities, for example for down- hill mountain biking or the like. Preferably, the tips can protrude at least 1 ,8 mm, preferably at least 2,2 mm from the edge of the respective chain link at its At its narrowest point in height direction.

The circumference and/or diameter of the protrusion can be at least 60% and/or maximum 140% the circumference and/or diameter of the eyes of the outer link plate.

Preferably, the circumference and/or diameter of the protrusion is at least 90% and/or maximum 1 10% of the circumference and/or diameter of the eyes of the outer link plate. It turned out that these measures significantly improve the guidance of the chain on a rear cassette or sprocket.

In praxis, the diameter of the eyes of the outer chain link may be at least 3 mm, preferably at least 3,4 mm, and/or maximum 4 mm, preferably maxi- mum 3,6 mm.

The diameter of the protrusion is at least 3,3 mm, preferably at least 3,5 mm, and/or maximum 3,9 mm, preferably maximum 3,7 mm. This sizes lead to a good guidance. The protrusions can define a generally flat or rounded inner guiding surface. The area of the inner guiding surface may be at least 0,9 mm ² , preferably at least 1 ,1 mm ² , and/or maximum 1 ,5 mm ² , preferably maximum 1 ,3 mm ² . Such an inner guiding surface reduces friction between the teeth and the protrusion.

In Praxis, the smallest distance between the protrusion and the edge of the outer link plate is at least 0,4 mm, preferably at least 0,6 mm, and/or maxi- mum 0,8 mm, preferably maximum 0,7 mm. This allows a combination of a smooth engagement between tooth and chainlink with a good lateral guid- ance of the chain link immediately after engagement with the respective tooth. In one embodiment the thickness of the protrusions corresponds to at least 25 % of the thickness of the inner link plates. The thickness of the protru- sions preferably is at least 70 % and most preferably 100 % of the thickness of the inner link plates. In case of 100 % of the thickness, the inner faces of the protrusions will be in the same lateral plane as the inner faces of the inner link plates so that the lateral guidance for the link plates between the outer link plates is identical to the lateral guidance between the inner link plates. Smaller thicknesses of the protrusions between 25% and 70% of the thickness of the inner link plates still provide improved guidance compared to a chain without protrusions, however not quite as tight as the thickness of 100 % in which case the distance between these protrusions is generally equal to the distance between opposite surfaces of inner link plates. The protrusions may be symmetric to the longitudinal plane of the chain extend- ing in the middle between and parallel two opposite link plates. The guid- ance of the chain on the teeth of a chainring is equal for all chain links. A constant wear of inner and outer link plates as well as of the teeth contact- ing the inner and outer link plates can be achieved.

The distance between two opposite protrusions may be at most 70% larger than the distance between two opposite surfaces of inner link plates. How- ever, preferably the distance between two opposite protrusions is less than 50% larger and most preferably equal to the distance between two opposite inner surfaces of inner link plates.

In practice, the thickness of the outer link plate with the protrusion is gener- ally constant. In this case, the protrusion on the inner surface of the outer link plate corresponds to a recess on the outer surface. The outer surface of the outer link plates may comprise a trough-like recess that produces a bulge forming the protrusion on the inner surface of the outer link plate. Consequently, the protrusion adds no further weight to the outer link plate which would otherwise be necessary if the protrusion was formed as an added surface layer. A trough-like recess and the corresponding bulge have no sharp edges but shows smooth transitions between adjacent faces. This smooth shape re- duces abrasive wear to the teeth of a sprocket or chainring engaging the chain link. In practice, the recess and the corresponding protrusion may be punched into the material of the outer link plates. Punching is a very cheap and easy method for defining a recess on the outer surface and a corresponding bulge or protrusion on the inner surface. The punching of steel link plates generally defines smooth surfaces of the trough-like recess and the bulge with smooth transition radiuses.

The three dimensional deformation of the chain link plate created by the punched protrusions and the trough-like recesses further improve the tor- sional strength of the outer chain links plates. Furthermore, the punching process creates a cold deformation and a cold hardening of the material of the outer link plates further increasing their hardness and stability.

Alternatively, protrusions may be realized by applying additional material to the inner surfaces of the outer link plates. In this case, the outer surface of the outer link plates remains generally flat.

In practice, the protrusions define a generally flat or rounded inner guiding surface in order to provide for a large contact area for the teeth of the chainring and a low friction guidance of the teeth. The guiding surfaces serve provide good lateral guidance for the tooth engaging with the respec- tive outer chain link. In particular, with the guiding surfaces of the protru- sions being are situated in the same lateral plane as the inner surfaces of the inner link plates the guidance of engaging teeth will be identical for all chain links.

In practice, the guiding surfaces of the protrusions may have a length in the longitudinal direction of the chain of at least 10% and preferably at least 50% of the longitudinal distance between two succeeding inner chain links. In this case, a tooth engaging between two opposite protrusions of a pair of outer chain links is guided over the majority of its length in the longitudinal direction. In this context the longitudinal direction corresponds to the direc- tion defined by a line between the two axes of the pins of a chain link.

The guiding can be further improved, if the height of the guiding surface ex- tends over at least 10% of the height of the outer link plate in the area of the protrusion. Preferably the guiding surface extends over at least 15% and more preferably over at least 20% of the height of the outer link plates. In this context the height is measured in a plane parallel to the major plane of the link plate and perpendicular to the longitudinal direction. The height of the guiding surface has to be chosen in order to achieve a good cormpro- mise between a large guiding surface and a smooth shape of the protrusion as well as a strong longitudinal strength of the chain link plate.

The chain of the drive chain system can be manufactured by the method described hereinafter. The method comprises the step of connecting of a pair of inner link plates and a pair of outer link plates to a roller using a pin and repeating this step so as to form an alternating succession of inner chain links and outer chain links. In another step a recess is punched into the outer surface of the outer link plates so as to define a protrusion on the inner surface of the outer link plates. While it may be possible to punch the recession into the outer link place after connecting them to at least one ad- jacent inner link plate, it is preferred to first form the recession and the pro- trusion on the outer link plates and then assemble the chain by fixing them to adjacent rollers and inner link plates. As stated above, punching is a very convenient and well controlled method for forming the protrusions on the inner surfaces of the link plates.

The invention also further relates to a bicycle comprising a drive chain sys- tem comprising the features described above. The bicycle further comprises at least one chainring, wherein the chainring exhibits a plurality of teeth having generally identical widths in the transverse direction and engaging alternately with inner chain links and outer chain links. The chain described above provides better and more uniform guidance of the teeth between the outer chain link plates and reduces the generation of noise. It is most ad- vantageous, if the bicycle comprises a single chainring. The excellent guid- ance of the chain allows the chain engage the chainring in a comparable high angle relative to the chainring and therefore allows to combine a single chainring with a rear cassette comprising a high number of sprockets, for example at least 9, preferably at least 1 1 , sprockets.

Brief Description of Drawings

An embodiment of the drive chain system is described below with reference to the attached drawings.

Figure 1 is a side view of a part of a chainring and an engaging portion of a chain.

Figure 2 is a sectional view according to cutting line A-A in Figure 1 .

Figure 3 is a side view of the part of the chainring of Fig. 1 .

Figure 4 is a sectional view according to cutting line B-B in Figure 3.

Figure 5 is a top view of the chain of Fig. 1 .

Figure 6 is a sectional view according to cutting line C-C in Figure 5. Figure 7 is a perspective view of an outer link plate of the chain of F ig .1 .

Figure 8 is a side view of an outer link plate of the chain of F ig .1 .

Figure 9 is a sectional view according to cutting line D-D in Figure 8.

Description of Embodiments Fig. 1 shows a side view of a portion of a drive chain 10 for a bicycle and a part of a chainring 12 engaging the chain.

The portion of the chain 10 comprises an alternating succession of inner chain links 14 and outer chain links 16. Figures 1 and 5 show inner chain links 14 connected by outer chain links 16. As can be seen in Fig. 5, the in- ner chain links 14 each have a pair of inner link plates 18 and the outer chain links 14 each have a pair of outer link plates 20. The inner link plates 18 comprise inner surfaces 22, facing each other and outer surfaces 24.

The outer link plates 20 also comprise inner surfaces 26 facing each other and outer surfaces 28.

The inner surfaces 22 of a pair of inner link plates 18 contact the lateral faces of two rollers 30 arranged in the end regions of the inner link plates 18. The inner surfaces 26 of the outer link plates 20 each contact the outer surfaces 24 of two adjacent inner link plates 18. The outer link plates 20, the inner link plates 18 and the roller 30 are connected by means of a pin 32 so that the link plates can rotate around said pin 32.

Fig. 1 shows the part of a chainring 12 with three teeth 34a, 34b, 34c, which engage with the chain 10. Fig. 1 shows that the teeth 34a and 34c engage with inner chain links 14 and tooth 34b engages with an outer chain link 16. Of course, the entire chainring 12 comprises further teeth distributed about its circular periphery which are cut away in the representation of Fig. 1 . Fig. 2 shows a detailed sectional view of tooth 34b engaging with a pair of outer link plates 20. The inner surfaces 26 of the opposite outer link plates 20 each comprise a protrusion 36 extending in the lateral (transversal) di- rection towards the tooth 34b between the outer link plates 20 . In the shown embodiment, the thickness of the protrusion 36 measured from the inner surface of the outer link plate 20 where it contacts the outer surface of the inner link plate 18 may be equal to the thickness of the inner link plate 18. Consequently, the distance between two opposite and facing protru- sions 36 on opposite outer link plates 20 may be equal to the distance be- tween the opposite inner surfaces 22 of two inner link plates 18.

The protrusions 36 extend in longitudinal direction of the chain 10 in the ar- ea between the two inner link plates 18 that are located adjacent the re- spective outer link plate 20 and connected to it by means of pins 32. The outer surface 28 of the outer link plates 20 can comprise a trough-like re- cess 38 (also see Fig. 6) corresponding to the protrusion 36. The thickness of the outer link plates 20 can therefore be generally constant. The trough- like recess 38 and/or the corresponding protrusion 36 may extend over the major part of the height of the outer link plate 20.

The recess 38 can be formed by punching and may show no sharp edges lines. The transition between neighboring areas of the trough-like recess 36, such as the bottom 40 of the recess 38 and the side walls 42 of the recess 38 can be realized by radiuses. Also, the transition from the side walls 42 to the outer surface 28 of the outer link plate 20 adjacent to the recess 38 may have a radius.

The protrusion 36 may have a flat or rounded guiding surface 44 facing the tooth 34b engaging the outer chain link 16. The guiding surface 44 can be generally located in the center of the protrusion 36 and may extend over about 25% of the height of the protrusion 36 and/or 25% of the length of the protrusion 36 in the longitudinal direction, which corresponds to the line connecting the axes of the two pins 32 connected to each chain link 14, 16. The shape of the guiding surface may vary from the shape shown in the drawings depending on the shape of the punch and the die used in the punching process.

The teeth 34a, 34b and 34c taper laterally towards their respective tip 50. The teeth 34a, 34b, 34c can comprise a lateral curvature 52. The lateral curvature can have a convex radius of at least 8 mm, particularly at least 10 mm, and/or maximum 14 mm, particularly maximum 12 mm.

It is possible that the teeth 34a, 34b, 34c taper laterally in a section 54 be- tween their respective tip 50 and a section 56 of the respective tooth 34a, 34b, 34c with parallel lateral surfaces 64. In this case, the teeth 34a, 34b, 34c can taper towards their tips 50in a limited region near the tips 50 and therefore provide a fast increase in lateral guidance of the chain 10 when the tapering section 54 passes the space between the protrusions 36.

As shown in the embodiment, the distance 66 between the lateral surfaces 64 of the teeth 34 can be at least 1 ,9 mm and/or maximum 2 mm in the sec- tion 56 of the respective tooth 34 with parallel lateral surfaces.

The drive chain system can be configured in such manner that the protru- sions 36 engage a tooth 34 in its section with parallel lateral surfaces, when the chain is fully engaged to this tooth 34. Fig. 1 and Fig. 2 show an outer chain link 16 link fully engaged to the tooth 34b.

The section 56 with parallel lateral surfaces 64 may extend over a distance 48 of at least 0,5 mm, preferably at least 0,8 mm, towards the tip 50 of the tooth 34b from the point of contact between the protrusion 36 and the tooth 34b nearest to the tip 50 of the tooth 34b, when the chain 10 is fully en- gaged to this tooth 34b, as shown in Fig. 2. The distance 70 the protrusion 36 protrudes from the outer link plate 20 to- wards a tooth 34b can be at least 70%, preferably at least 90%, and/or rmax- imum 130%, preferably maximum 1 10% of the distance the parallel lateral surfaces 64 extend towards the tip 50 of the tooth 34b from the point of con- tact between the protrusion 36 and the tooth 34b nearest to the tip 50 of the tooth 34b, when the chain 10 is fully engaged to this tooth 34b.

The tips 50 of the teeth 34 can protrude from the chain links 14, 16 when the respective chain link 14, 16 is fully engaged with the respective tooth 34a, 34b, 34c as shown in the embodiment.

The tips 50 of the teeth 34 can be of a plateau-like shape with a length 75 of the plateau of at least 2,8 mm, in particular at least 3 mm, and/or maxi- mum 3,5 mm, in particular maximum 3,2 mm.

The tips 50 of the teeth 34 can be of a plateau-like shape with a width 76 of the plateau of at least 0,8 mm, in particular at least 0,9 mm, and/or maxi- mum 1 ,2 mm, in particular maximum 1 ,1 mm. The height 77 of the teeth 34 can be at least 7,5 mm, in particular at least 8,5 mm, and/or maximum 9,5 mm, in particular maximum 8,5 mm.

The height 58 of the tapering section 54 can be at least 2,5 mm, in particu- lar at least 3 mm, and/or maximum 4,5 mm, in particular maximum 4 mm.

The height 78 of the section 56 with parallel lateral surfaces 64 can be at least 3 mm, in particular at least 3,5 mm, and/or maximum 5 mm, in particu- lar maximum 4,5 mm. The clearance 80 between a protrusion 36 of an outer chain link 16 and one of the parallel lateral surfaces 64 of a tooth 34b can be at least 0,1 mm, in particular at least 0,13 mm, and/or maximum 2,0 mm, in particular maximum 0,17 mm, when the opposite lateral surface 64 of the same tooth 34b is in contact with the opposite protrusion 36 of the same outer chain link 16 and the outer chain link 16 is fully engaged with the tooth 34b.

The circumference and/or diameter 72 of the protrusion 36 can be at least 60% and/or maximum 140% the circumference and/or diameter 62 of the eyes 60 of the outer link plate 20.

Preferably, the circumference and/or diameter 72 of the protrusion 36 is at least 90% and/or maximum 110% of the circumference and/or diameter 62 of the eyes 60 of the outer link plate 20.

In the shown embodiment, the diameter 62 of the eyes 60 of the outer chain link 20 may be at least 3 mm, preferably at least 3,4 mm, and/or maximum 4 mm, preferably maximum 3,6 mm.

The diameter 72 of the protrusion 36 may be at least 3,3 mm, preferably at least 3,5 mm, and/or maximum 3,9 mm, preferably maximum 3,7 mm. This sizes lead to a good guidance. The protrusions 36 can define a generally flat or rounded inner guiding sur- face 44. The area of the inner guiding surface 44 may be at least 0,9 mm ² , preferably at least 1 ,1 mm ² , and/or maximum 1 ,5 mm ² , preferably maximum 1 ,3 mm ² . As shown in the embodiment, the smallest distance 74 between the protru- sion 36 and the edge 68 of the outer link plate 20 can be at least 0,4 mm, preferably at least 0,6 mm, and/or maximum 0,8 mm, preferably maximum 0,7 mm. The width 82 of the inner link plates 18 can be at least 0,7 mm, in particular at least 0,75 mm, and/or maximum 1 mm, in particular maximum 0,95 mm. The width 84 of the outer link plates 20 can be at least 0,7 mm, in particular at least 0,75 mm, and/or maximum 1 mm, in particular maximum 0,95 mm.

The distance 86 between the centers of the eyes 60 of the outer link plates 20 can be at least 1 1 ,7 mm, in particular at least 12,2 mm, and/or maximum

13,7 mm, in particular maximum 13,2 mm. Preferably the distance 86 be- tween the centers of the eyes 60 of the outer link plates 20 is 12,7 mm.

The distance 88 between the two rollers 30 of a chain link 14, 16 can be at least 4 mm, in particular at least 4,5 mm, and/or maximum 6 mm, in particu- lar maximum 5,5 mm.

As shown in the embodiment, the smallest distance 90 between the protru- sion 36 and a roller 30 can be at least 0,2 mm, preferably at least 0,75 mm, and/or maximum 0,9 mm, preferably maximum 0,85 mm.

As shown in the embodiment, the smallest distance 92 between the center of the protrusion 36 and an inner link plate 20 can be at least 2,1 mm, pref- erably at least 2,2 mm, and/or maximum 2,9 mm, preferably maximum 2,7mm.

As shown in the embodiment, the smallest distance 94 between the guiding surface 44 and an inner link plate 20 can be at least 1 ,6 mm, preferably at least 1 ,8 mm, and/or maximum 2,4 mm, preferably maximum 2,2 mm.

As shown in the embodiment, the diameter 96 of the rollers 30 can be at least 7 mm, preferably at least 7,5 mm, and/or maximum 8,5 mm, preferably maximum 8 mm. As shown in the embodiment, the width of the rollers 30 can be at least 1 ,7 mm, preferably at least 1 ,9 mm, and/or maximum 2.5 mm, preferably maxi- mum 2,3 mm. Reference numerals

10 chain

12 chainring

14 inner chain link

16 outer chain link

18 inner link plate

20 outer link plate

22 inner surface of inner link plate 24 outer surface of inner link plate

26 inner surface of outer link plate

28 outer surface of outer link plate

30 roller

32 pin

34a, 34b, 34c tooth

36 protrusion

38 recess

40 bottom

42 side wall

44 guiding surface

46 distance

48 distance

50 tip

52 curvature

54 tapering section

58 height tapering section

60 eye

62 diameter

64 lateral surface

66 distance

68 edge

70 distance

72 diameter 74 distance

75 length tip

76 width tip

77 height teeth

78 height

80 clearance

82 width inner link plate

84 width outer link plate

86 distance

88 distance

90 distance

92 distance

94 distance

96 diameter

98 width

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