cvt

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roadster
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Saint-Martin (French part)
Re: cvt

Post by roadster » Wed Sep 11, 2019 4:18 am

Here is the direct answer to your question on the assumption that your scenario is actually achievable for your particular vehicle. But note that in many cases it would not be possible to achieve an equilibrium state under the conditions you stipulate.
When you increase the throttle the engine develops more torque this torque creates more tension in the drive belt and how this affects the pulleys depends on the weights on the front pulley which are trying to force it to a larger diameter versus the tension in the belt which is doing the opposite and the counter spring in the back pulley which, in combination with the wormdrive which grips the belt more firmly if there is any tendency for the belt to slip, is also trying to achieve a bigger effective diameter itself.
So you will see that the answer is not simple but it can be summarized by saying that the design parameters for any given scooter are set to match the performance capability of the engine. In general the front pulley effective diameter will become smaller thus allowing the engine to achieve higher rpm provided road speed is well below the scooters practical maximum speed but if the scooter is already travelling at somewhere in the top 25% of its speed range ( unlikely at 3000 rpm ) then the variator is going to stay at maximum effective diameter.
Realistically most scooters in standard form will go up to an almost fixed rpm on any wide throttle opening and then when the front pulley reaches maximum effective diameter the rpm will begin to increase in proportion to road speed. When the throttle is closed rpm will reduce in proportion to road speed and the variator won't start to change ratio until a relatively lower road speed if at all.
Located on UK South Coast
Rides Kymco AK550 previously Kymco Downtown 300i ABS and Triumph Street Twin.

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Drago
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Re: cvt

Post by Drago » Wed Sep 11, 2019 8:36 am

My SYM Joymax tends to stick at 5500rpm (55mph on flat speed). From pulling away at idle - even at WOT it will always stick to this rpm until the speed is at about 50mph, then rpm will increase higher alongside the mph. Even going up a hill in a 30mph to a NSL when throttling up to get to 60mph NSL speed it will always go to 5500rpm and wait for the mph to catch up before revving higher. Which is a bit annoying as peak torque is at 6500rpm (indicated 65mph).
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SYM Joymax Sport 300i 2016-
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MrGrumpy
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Re: cvt

Post by MrGrumpy » Wed Sep 11, 2019 11:00 am

A question......
Are the engines used in CVT-engined scoots specially set up to work most effectively with the CVT? eg to like working at certain rev ranges? Or are they normal engines so that if you somehow fitted a manual box to them it'd work like a 'normal' manual bike??

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roadster
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Saint-Martin (French part)
Re: cvt

Post by roadster » Thu Sep 12, 2019 4:10 am

MrGrumpy wrote:
Wed Sep 11, 2019 11:00 am
A question......
Are the engines used in CVT-engined scoots specially set up to work most effectively with the CVT? eg to like working at certain rev ranges? Or are they normal engines so that if you somehow fitted a manual box to them it'd work like a 'normal' manual bike??
Some of them would definitely not work well with normal transmission. For example my Kymco 300i would pink badly for a few seconds when opening the throttle wide from standstill. So the ignition advance curve was probably not set up for flexibility at low rpm. When tuning for CVT it is useful to concentrate on the working range of rpm which makes it easier to achieve good results than a normal transmission. There is also scope for increasing the rpm in the acceleration range by changing roller weights if you want an engine that revs to peak power every time you use full throttle. But this does significantly damage fuel economy and possibly engine life too.
Located on UK South Coast
Rides Kymco AK550 previously Kymco Downtown 300i ABS and Triumph Street Twin.

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Data
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Re: cvt

Post by Data » Thu Sep 12, 2019 4:36 am

Engines on scooters are generally designed for the actual purpose they are intended, like any engines in any vehicle. Since the engines in a manual bike and CVT bike generally have to do the same job and need similar to identical pulling characteristics, there isn't actually usually any big differences. So rather than making an engine specifically for CVT transmission, the CVT transmissions are made to work with the engine concerned and that's where the real tuning comes in. Not saying some bikes with CVT haven't had the engine characteristics tuned a little, but generally there is no difference. You can see this on cars in particular. Some cars have a manual transmission, while an identical model has the CVT (eg: the Honda Jazz). The engines are identical, same power and delivery of torque, same ecu software etc etc. apart from the transmissions which also usually have their own ecu to control some aspects of the gear ratio changes.

This is often the case with any modern cars with auto tranny too. My own Citroen car has a modern 6spd auto box coupled to a powerful petrol engine. The same car is available with manual transmission with 6 spds and the engines are entirely the same in every way.

So CVT makes no real difference to any bike engine specs in most cases.

XMax400Paul
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Re: cvt

Post by XMax400Paul » Thu Sep 12, 2019 4:47 am

Anyone remember the F1 CVT Prototype that was banned - Williams & David Coultard that was involved in the testing an development...
https://www.auto123.com/en/news/f1-tech ... deo/34642/
https://www.racefans.net/2007/05/03/ban ... ssion-cvt/
https://www.f1technical.net/forum/viewt ... 5&start=10

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smeghead
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Re: cvt

Post by smeghead » Thu Sep 12, 2019 6:25 am

I was watching a program this morning, Henry Cole and Sam Lovegrove had found a 1960's Centaur scooter, USA made, it folded up. The transmission had loads of tiny ball bearings instead of variator rollers. Never seen that before, or the scooter.

XMax400Paul
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Re: cvt

Post by XMax400Paul » Thu Sep 12, 2019 9:48 am

Saw that one... interesting transmission idea...
Can't Stand Henry Cole though... his diction and inflection is so annoying, he should present children's programs!

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smeghead
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Re: cvt

Post by smeghead » Thu Sep 12, 2019 10:19 am

XMax400Paul wrote:
Thu Sep 12, 2019 9:48 am
Saw that one... interesting transmission idea...
Can't Stand Henry Cole though... his diction and inflection is so annoying, he should present children's programs!
I can see your point about Henry, I'm ok with him. I like the other guy, he genuinely seems knowledgeable.

MrGrumpy
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Re: cvt

Post by MrGrumpy » Thu Sep 12, 2019 12:48 pm

smeghead wrote:
Thu Sep 12, 2019 10:19 am
XMax400Paul wrote:
Thu Sep 12, 2019 9:48 am
Saw that one... interesting transmission idea...
Can't Stand Henry Cole though... his diction and inflection is so annoying, he should present children's programs!
I can see your point about Henry, I'm ok with him. I like the other guy, he genuinely seems knowledgeable.
Just to be contrary, I find Henry Cole very slightly irritating, but Sam Lovegrove to be the dullest human on TV - however knowledgible he is!! :lol:


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