Difference between revisions of "Tensioner"
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There are a few ways to create tension in a belt or chain drive system. You can increase the distance between the drive and driven sprocket such as in the shimmed or eccentric systems. Another method is to lengthen the path of the chain as in the idler method. | There are a few ways to create tension in a belt or chain drive system. You can increase the distance between the drive and driven sprocket such as in the shimmed or eccentric systems. Another method is to lengthen the path of the chain as in the idler method. | ||
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==Shims== | ==Shims== | ||
Revision as of 10:40, 6 March 2023
A tensioner is a mechanism that necessary to a belt or chain drive to ensure long term proper function. Without correct tension, the drive system may fail catastrophically.
Contents
Tensioning Systems
There are a few ways to create tension in a belt or chain drive system. You can increase the distance between the drive and driven sprocket such as in the shimmed or eccentric systems. Another method is to lengthen the path of the chain as in the idler method.
Shims
Shims are one of the simplest methods of tensioning the chain. A shimmed system only requires a differential mount that has a vertical split that can be bolted together. By inserting shims between the front and rear halves of the differential mount(s), the differential can be moved further away. The shims can be made of any stiff material. Anecdotally these are frowned upon by design judges, but your mileage may vary.
If correctly designed, shims can be the stiffest option for tensioning the chain as the entire system will be held in compression, there are no threads, and no moving parts. The shimmed design also presents an incredibly cheap option.
Guide
Chain guides use a durable low friction material to squeeze the chain into tension. This is most commonly used for timing chains (kept lubricated inside the engine) and sometimes on bicycle[1].
Idler
Another sprocket or pulley is used to add tension to the chain or belt. It does not add any torque to the system and freely spins. A common implementation is the secondary sprocket on a bicycle derailleur.
An idler that is held against the chain by a spring is a passive tensioner and should not need servicing. Due to the passive nature, fine control is difficult. Idlers can also be held in a fixed position with a swing arm held captive in a slot, or pinned to a fixed angle. These will need servicing as the chain lengthens.
Eccentric
An eccentric chain tensioner holds the driven sprocket with a round sheave[2]. The driven sprocket is held off of the neutral axis (eccentrically) such that when the sheave is turned, the driven sprocket is moved closer or farther from the drive sprocket[3]. The sheave may be constrained by friction around the circumference, teeth around the circumference or by shear pins to the larger structure. A frictional retention method allows for infinite adjustability. Teeth or shear pins mean the mount can only be tensioned in discrete steps, but the use of a vernier scale style hole pattern allows shear pins incredibly fine control. The main benefit of the eccentric mount scheme is the ability to tension the chain without removing any parts from the car, or adding new ones.
Eccentric mounts tend to be larger than other mounting schemes and thus may be inherently stiffer. By necessity, they require multiple moving parts which can drive additional complexity and design time.
Footballs
Utilizing "footballs" with eccentric mounting holes allows the sprockets to be moved further away by flipping the football within the mount itself. Unlike a traditional eccentric mount, the chain cannot be tensioned without taking the mount apart and swapping fitting direction, or swapping the fitting for a more or less eccentric version[4].
There is no reason beyond convention that the footballs need to be symmetric, a triangle or polygon of any number of sides could be used to increase the options available per eccentric football.
Turnbuckle
Often implemented on a swing arm type design.
-play
-wear
-packaging
-rigidity[citation needed]
+infinite adjustability
can be done as a differential screw [5][6]
Toothed
- See wollongong 2012
Diagrams
Shimmed
Guide
Idler Sprocket or Pulley
Eccentric
Offset Footballs
need diagram of toothed style chain tensioner
Examples
Curtain University's shimmed chain tensioner in 2012
Tennessee Tech's guide chain tensioner in 2019
Michigan State's eccentric chain tensioner in 2019
Wollongong's toothed chain tensioner in 2012
need example images of football style, idler style
References
- ↑ https://www.specialized.com/us/en/stumpjumper-fsr-comp-evo/p/49715
- ↑ Wiki article on eccentric mechanisms for clarity: https://en.wikipedia.org/wiki/Eccentric_(mechanism)
- ↑ Hansen D. Eccentric Mounting and Adjustment System for Belt Driven Devices https://apps.dtic.mil/sti/pdfs/ADD020388.pdf
- ↑ Scelfo, Tony. Lightweight Torsen Style Limited Slip Differential and Rear Driveline Package for Formula SAE 2006
- ↑ https://en.wikipedia.org/wiki/Differential_screw
- ↑ https://www.halfbakery.com/idea/Differential_20Turnbuckle
