76 replies to this topic

[Cooperman]

I'm still interested in what the delivered power gain would be in %-age terms to justify this. Presumably it would really only be for competition where a few tenths of a second per lap is important. Not much point, perhaps, on a rally or road car where long life and strength are so important.

 

I'm also interested in how a tensioner could work as the force acting on it with power-off would be high, but with power-on the loading, if tensioned on that side, would be huge and it would be difficult to evolve an automatic tensioner to handle that sort of power.

[M30]

It is an interesting idea, and one i've been reading a bit about, and found this from last year

 

 

How about an idler pulley to take up the tension, maybe on an off centre adjuster like used on some timing belt tensioners?

 

Stu

[Guess-Works.com]

Wasn't there a thread about this not so long ago

 

To do this I suppose you would use what I would call a silent chain or high velocity chain... Kent made a cam drive using this technology a while ago, and everyone slated them for wearing ( however I had one for over a decade now )

 

But what foxes me is usually these systems are run by gears which are fixed to the shaft... with an A series transverse arrangement there is one fixed to a shaft, the broach gear on the gearbox 1st motion, but the other, primary gear, is free floating on the crank with a clutch plate attached to it.

 

Any kind of chain drive will need to be guided, possibly under tension, or it'll flap about like a motorbike chain. If the chain is under tension then it will cause a load on the primary drive which is free floating on the crank, something it's unlikely a phosphor-bronze bush is not going to take lightly so a redesign of how the primary drive is mounted onto the crank will be required, possibly with a redesign of the crank itself ?

 

There's a reason gears are used, they work and they're not complicated.

 

I'm all for innovation, but having my 'practical' head on... lots of development equals lots of time equals lots of money equals high price end product.

[Guess-Works.com]

And as if by magic, something appears while I'm typing...

 

A chain from a Kent HVC timing kit, stuck to two straight cut gears

[stretch tech]

This is extremely interesting, as I have been wanting a chain drive for a very long time. My investigations took me to several manufacturers web sites, and I found that the torque was easily feasible, but the maximum rotational speed was not, because centrifugal force lifts the chain away from the sprocket, and the contact points move too high up on the teeth. So, that is as far as I got.

 

But now we have an expert on the job, so I am hopeful of progress. I think there would be many takers for a conversion kit. Also, the possibility exists of introducing a step up or step down ratio, without the unsatisfactory bodge that is currently used, which compromises correct meshing of the gears.

 

By the way, I wanted  a chain drive just to remove some of the power loss in the drop gears, and solve the reliability problem caused by the helical gears causing the idler to try to tip sideways (yes, I know there is another way of addressing that, by taper roller bearings), without using intolerably noisy straight cut gears. I want driving a Mini to be a pleasant experience!

 

Herringbone gears, which cancel all side thrust and run quietly, were another idea that I looked at, but thin herringbones (limited by the depth of the transfer case) can't be machined in one piece, and I could see immense difficulty in bolting the two halves back to back. The cost would also be considerable.

 

if a suitable set up could be produced, there would be scope to change the ratios fairly easily with different sprocket ratios. One problem i see is that at first, i'd probably try and get the largest pair of sprockets in possible in their to reduce the centrifugal force (well technically there is no such thing as centrifugal forces but that's a different story) acting on the chain and spread the load over more teeth. This might not leave enough room to up size the sprockets accordingly.

 

a correctly spec'd chain drive will be quieter than straight cut transfer gears and hopefully more efficient than both straight and helical gears.

 

herringbone (fish bone, cross/double helical etc) gears was something i thought of also as we are starting to introduce these at work. The theory of the two side loads acting against each other is sound if the gears are ground correctly. As you say though, small cross-helical gears are tricky to machine. 

Yes, in theory you could use two opposing handed gears back to back but alignment would be a headache and would repeatedly need adjusting. This however does lead to the idea of producing backlash free gears - helical or straight cut in fact ! 

 

Backlash is rotational "play" in the gears for anyone who doesn't know. Backlash free gears are split in half (around the diameter) and each "half" of the tooth profile works on apposing flanks of the meshing gear(s). this eliminates the play which improves efficiency by reducing noise produced from the gear train.

 

phew !

[stretch tech]

Dan: that's what i had in mind for the tensioner system - two tensioners inside the chain working in opposite directions to each other.

 

Cooperman: my the aim for this really is for high powered road cars where straight cuts aren't exactly ideal, a correctly set up chain system would be quieter. of course that is if a suitably small system will be strong enough in the first place. I suppose the more efficient transmission would give an advantage on a circuit also.

 

M30: i knew i hadn't imagined it ! I remember seeing this a while ago but couldn't find it. Although i can't help but think that it is a bit of a bodge ? surely the chain pins don't mesh perfectly with a straight cut gear ? i may be wrong however sprockets are the shape they are, tooth wise, for a reason. This is probably the reason for the wear that guess-works describes.

 

Guess-works: The floating gear on the crank is the other big head ache. My knowledge on engines isn't great as i've only built one ! what is the reason for the floating nature of the gear ? would fixing it in place affect the running of the engine ? if not then it wouldn't take much to fix a sprocket to prevent it floating.

No, i'm happy for the constructive criticism, all the issues need to be addressed before a suitable design can be produced 

 

 

keep the comments coming guys 

Rhys

[stretch tech]

Sorry i missed you guys.

 

I think space will make it very difficult to fit in a reliable roller chain as alternative to the drop gears.

 

Might however be worth taking a closer look at the HY-VO toothed driveline chains.

 

yeah that is another possibility, i have a lot of weighing up to do 

 

 

Could you envisage the carnage that occur if the chain failed! Reason enough.

 

a high velocity chain failure is never a good thing but surely you'd just loose drive and the chain would drop to the bottom of the transfer case ? i know this isn't ideal and i suppose the rotating sprockets could chew up the chain and/or themselves doing so   ...

[Mr Joshua]

Not so sir. I have seen chain failure in an enclosed circuit not good luckily there is an asymatry brake fitted to prevent serious damage from occurring.

If it doesn't grab and hang upon the primary gear which would be very bad like you said it would fall to the bottom of the transfer case. You would have to be pretty sharp and knock the car into neutral or serious carnage will ensue.

[Dan]

(well technically there is no such thing as centrifugal forces but that's a different story)

I'm so glad somebody else said that.


The primary gear floats because the clutch drives it and it sits on the crank, if it were fixed there would be no clutch. With the side load the tensioned chain would impose you'd probably have to engineer a bearing for it. The Princess had a conventional clutch and flywheel with the input drive on the extreme end of the whole transmission case and after the clutch which eliminates a lot of issues.

[Carlos W]

 

(well technically there is no such thing as centrifugal forces but that's a different story)

I'm so glad somebody else said that.

 

I was tempted!

 

Seriously I'm following this topic, and it's got some fantastically knowledgeable people commenting!

 

If you can put the power of a hayabusa turbo through a chain, I'm sure you can put 80BHP from a mini through it

[Gremlin]

How about having 2 sprockets on arms that are on free common pivot in a 'V' shape and a spring pushing them apart, so when going from acceleration to overrun or vice versa, the 'V' would just swing over?

[Cooperman]

I really can't see the point on a road car as even if it gave 5% more power, in modern traffic the difference would not be apparent and the Mini would still be slow compared to modern cars. Helical drops have worked well enough over the past 55 years, so why change something that works very well and has good reliability combined with low maintenance and low cost?

However, if it meant that 0.5 seconds per lap could be gained in racing then it would be very welcome indeed.

[mini13]

Guessworks,

 

that dosent look like a HVC chain on a set of SC drops, the teeth look a different profile, and the chain looks much meatier to me.

 

 

 

It is an interesting idea, and one i've been reading a bit about, and found this from last year

 

 

How about an idler pulley to take up the tension, maybe on an off centre adjuster like used on some timing belt tensioners?

 

Stu

[mini13]

more info here...

 

http://mk1-performan...mental_dept.htm

[sledgehammer]

 

seen these used on agricultural machinery , but were spring steel instead of nylon / rubber (don't think reliable enough)

 

also seen two small sprockets twisting against each other to take up the slack

 

in case of chain failure - the housing would be ripped apart , in a fraction of a second - sadly

 

I use ASA60 chain at work v strong - but no good for high speed use