Advanced Belt Drive System (ABDS) by Schlumpf Innovations · 2.1 Wrap angle and pretensioning A...

Advanced Belt Drive System (ABDS) by Schlumpf Innovations

schlumpf innovations gmbh · Dorfstrasse 10 · CH-7324 ViltersTel. +41 (0)81 723 80 09 · Fax +41 (0)81 723 83 64 · www.schlumpf.ch

1. Belt-drive systems today

Belt-drive systems for bicycles have only recently become established in the marketplace, and offer a number of benefits in terms of weight, maintenance, etc. But being new, there is still room for improvement.

1.1 Wrap angle and pretensioning

The gear ratios typically used on bikes—roughly 2.5:1—result in an insufficient wrap angle around the rear sprocket. To make up for this low wrap angle and avoid skipping, relatively high pretensioning is used instead.Additionally, the small radius of the contact arc over the rear sprocket necessitates belts with a small 11-mm pitch. The fact that the teeth cannot “bite” deeply into the sprocket is another reason that high pretensioning is needed.

1.2 Belt-width

Expensive manufacturing methods limit drive belts to only a single width (10 mm for 11-mm pitch belts). This barely adequate for high-load situations such as tandems, cargo bikes, or very strong rid-ers. Conversely, it is overkill for low-load situations, such as city bikes, which are typically ridden at low speeds. Moreover, the belt’s stiffness creates unnecessary efficiency losses.

1.3 Belt-line

Chainline has always been important on chain-driven bikes, but on belt-driven bikes it is even moreso, as belts tolerate very little misalignment. While a chain can spread the stress of misalignment over many links, a belt that is laterally misaligned concentrates it at a few points. This can cause breakage,


40

40

40

26

16

40

Fig 1: A ratio of 2.5:1 between the crank sprocket and rear sprocket results in a low wrap angle, requiring high pretensioning.


and rubbing against the flanges causes much greater wear.If the bicycle frame has not been manufactured to extremely close tolerances, it can be very difficult to achieve a proper belt-line. Belt disk manufacturers offer a limited number of belt disks that allow for accurate alignment only for mass-produced bikes designed to use them, but make no allowance for smaller builders or aftermarket sales.

2. The Advanced Belt Drive System (ABDS) from Schlumpf Innovations

With the Advanced Belt Drive System (ABDS), we have tried to overcome the disadvantages of the current state of the art.

2.1 Wrap angle and pretensioning

A bottom-bracket gearing system like the speed-drive allows for a much lower ratio between the crank sprocket and rear sprocket, typically around 1.5:1, as compared to 2.5:1 without a gearing system in the bottom bracket. This means not only a bigger wrap angle at the rear sprocket, but also a bigger rear sprocket. This allows us to use a belt with a bigger pitch, such as the 14-mm industrial standard, instead of the 11-mm size currently being used on bikes.A bigger pitch allows for a closer fit, and eliminates the need for pretensioning. This eliminates bear-ing friction, and reduces bearing losses in general.

40

40

40

26

16

40

Fig 2: A ratio of about 1.5:1 between chainring and rear sprocket (40/26) provides much bigger wrap angle with much closer fit, and eliminates the need for any pretensioning.


2.2 Belt-width and belt-line adaptability

The Advanced Belt Drive System (ABDS) by Schlumpf Innovations uses modular sprockets consisting of the following parts:An adapter disk, with mounting holes for crankset spiders or rear-hub mount around the inside diameter. This adapter has teeth that engage with the belt around the outside diameter.One, two, or more toothed disks that mount to the left or right of the adapter disk, allowing for any desired belt-width or belt-line. This allows for straightforward adjustments by simply moving a toothed disk from one side to the other.Alignment holes on each disk ensure a perfect fit.

Mounting hole for 74-mm bolt-circle diameter (other sizes available) allows the adapter

disk to mount to the rear wheel.

Loaded side of the tooth

Mud-relief scoop

Hole for module-assembly bolt

Fig. 3: Adapter disk

Fig. 4: Toothed disk

Loaded side of the tooth

Mud-relief scoop

Hole for module-assem-bly bolt


2.3 Perfect belt-line

We offer adapter disks for nearly any bolt circle pattern (BCD74, BCD94, BCD110 mm and others), for fixie hubs with 1.37" x 24 tpi thread, for freehubs etc.

You can achieve almost any desired belt-line simply by relocating the toothed disks relative to the adapter disk.

3. Scoops for dirt and mud relief

The asymmetric tooth design includes a deep scoop that allows mud, dirt, snow, or dust to pass through.

Fig 5: Flanges: on one or both sides.

Mud-relief scoop

Hole for module-assem-bly bolt


4. Advantages of ABDS

•Usingonlyafewstandardizedparts,anybeltlinecanbeachieved.

•Anybeltwidthforanytypeofuse(heavy-dutyapplications,light-dutycitybikes)canbesupportedusingthe same standardized parts.

•Abiggerradiusattherearsprocketallowstheuseofindustry-standardbeltswitha14-mmpitch

• Beltswitha14-mmpitchofferabetterfit,andneednopretensioning.

• Thelackofpretensioningincreasesoverallefficiency,andavoidspowerlossesandwearonthebearings.

• Thegreaterfreedomofdesignmakesitpossibletodesigninscoopsformudrelief.


Mud-relief scoop

Module-assembly bolt

Mounting hole for 110-mm bolt-circle diameter (other sizes available) allows

the adapter disk to mount to the speed-drive bottom bracket gearing

system

Sychronizing hole

Fig 6. A set with two flanges, an adapter disk, and two toothed disks


Scoops for dirt and mud relief

Module-assembly bolt

Mounting hole for 110-mm bolt-circle diameter

Synchronizing hole

Fig 7. A set with two flanges, an adapter disk, and two toothed disks


Fig 8. A complete assembly with a 27-tooth sprocket and a fixed-geared hub adapter (1.37” x 24 tpi)


Fig 9. Detail view of an assembly for a 6-mm wide T14 belt (spacing between flanges: 7 mm).

Flange

Adapter disk

Toothed disk

Toothed disk

Flange


Fig. 10: A set with flanges, adapter disk, toothed disks


Fig. 11: speed-drive bottom bracket gearing system with 39t. belt disk

Advanced Belt Drive System (ABDS) by Schlumpf Innovations · 2.1 Wrap angle and pretensioning A...

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