roller chain efficiency 1

[autoguru]

It's generally conceived that roller chain typically have an
efficiency of around 98%. Out of all the different types of losses,
does anyone know which one is the most significant?

There are primarily:

1. Sprocket tooth/chain sliding friction (engagement/disengagement)
loss

2. Chain segment bending loss.

3. Bearing loss.

The joints in the chain are bushings. But is it possible to
substitute it with bearings? It may get larger and heavier, but what
if I need a chain that has the ultimate efficiency, but weight and
size are not as important? Can that be done? With bearings at the
joint, it should have a higher efficiency.

The sprocket tooth sliding friction isn't very big from what I
heard. This is because the chain segment interface is "free to
roll". You can literally touch the tooth interface on the chain and
rotate it with your fingers.

I need a chain that can get an efficiency of 98.5%. Can I replace the bushings in the chain with bearings?

 

[autoguru]

Actually, Magnograil, thanks for bring up the Morse chain. But how come the rocker pin joints are only used for silent chains and not regular roller chains? Is it because of inheritant design limitations or is it cost?

Thanks

 

[Fabrico]

It is something that can only be used on silent chanin. But it is only used on the Hy-Vo chain not typical silent chain. That and the special tooth shaping is what makes the HY-Vo so different from other silent chains.

 

[autoguru]

Thanks.

Got another question.

You know when the roller chain is wrapped around the sprocket, theoretically the load should be shared across all the teeth on the sprocket. Theoretically.

I really doubt that's the case in real life. The chain and the sprocket are not machined to exact specification like gears so it's unlikely that the pitch of the chain will exactly match the pitch of the sprocket. Also, once the chain starts to wear and elongate, things get worse.

Therefore, I think maybe only one or two teeth is bearing the load at any instant. There will be a small "gap" between other teeth and their corresponding chain roller that prevent them to transmit power.

What do you think?

 

[Fabrico]

It would be good if you and others can read up the Hy-Vo design. It's really quite interesting. The development of this particular chain allowed things to be done that were not done before. As this type of chain wears and rides farther out on the sprocket. The teeth literally open up and widen to take up slack and spread the load to several rows of teeth. The "pins" roll only during the transition from straight to bent and visa versa. But it is a constant process and all ads up, especially with so many links. NASCAR type racing only recently discovered the substantial advantages. Many "Super Bikes" are Hy-Vo chain driven. With the need for vehicles to be more efficient, I think you will be hearing more of Hy-Vo chain.

http://www.theautochannel.com/news/press/date/19990602/press024377.html

 

[autoguru]

"As this type of chain wears and rides farther out on the sprocket. The teeth literally open up and widen to take up slack and spread the load to several rows of teeth. The "pins" roll only during the transition from straight to bent and visa versa"

Thanks for the help Fabrico.

But I don't understand why the chain will wear and rides farther out on the sprocket if the joints "rolls" rather than slide. That means there should be essentially no wear or elongation. Or is there? Maybe it's not perfect rolling?

 

[Fabrico]

Perhaps the easiest way to see it is to look at a silent chain laying flat on a table with the teeth facing up. If you set a sprocket on it, the teeth won’t be able to fully engage each other because the teeth of the chain are not lined up but more in a crossed position, making the gaps too small. In operation, the larger the path radius, the more the teeth head toward that position. The chain teeth literally get wider and essentially fill the wider gap between the sprocket teeth.

As far as no wear or elongation, they are close, but nothing is perfect. Roller and needle bearings don’t slide either but they do wear.

 

[autoguru]

I heard the silent chain is about 5 times as expensive as a regular roller chain? What do you think it's the main reason for this price difference? Is it because of the special roller joint? Or do they require more accurate machining of the teeth?

 

[drwebb]

"Therefore, I think maybe only one or two teeth is bearing the load at any instant. There will be a small "gap" between other teeth and their corresponding chain roller that prevent them to transmit power.

What do you think?"

I think that's why MC chain OEM's advise (and experience demands) that the chain & sprockets be replaced as a set- they wear complementarily and spread the load, but are never ideal whether new or old.

What about periodicity? If the chain length and number of sprocket teeth are matched so that the teeth always contact the same rollers is that better or worse for wear?

 

[Fabrico]

"What about periodicity? If the chain length and number of sprocket teeth are matched so that the teeth always contact the same rollers is that better or worse for wear?"

It is highly recommended that a "hunting tooth" ratio be used so the chain does not contact the same teeth.

Hy-VO chains are installed in what might be considered virtually permanent places, such as in the deep center of superbike engines, FWD transaxles, etc. They generally outlast the parts around them. I used some 3" wide 1/2" pitch 10 years ago and it costs $100 per foot.

 

[autoguru]

I wonder if the sprocket tooth profile is formed such that it meshes with the rollers in a way similar to gears? (with very little slippage)?

 

[Fabrico]

There is very little friction and the teeth do "roll" into place.

Magnograil mentioned that Morse is difficult to work with for the little guy and he is right. Ramsey makes what they call the RPV line and claim it to be equivalent and fully interchangable with Morse Hy-Vo.

http://www.ramseychain.com/prod_power_trans.asp