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minimac 01-08-2016 01:42 PM

bike/scooter cvt
I don't know if this has been posted before, but currently on one of the scooter boards, this is being discussed. I don't understand why a CVT is generally thought to be inefficient for mpg purposes on bikes and scooters, but if it is, could this possibly be a solution? I'm thinking a manually operated solenoid instead of a lever to facilitate changes. I think something like this could help anyone doing a foot forward design. Any thoughts?

PatBox CVT (Continuously Variable Transmission) - Suzuki Burgman Forum

Grant-53 01-08-2016 10:53 PM

Belt drives such as V belts are slightly less efficient mechanically than cut gears or steel roller chain. This is not to say they are not cost efficient in many applications especially at constant speeds. The purpose of any transmission is to best match the engine output to load demands. Cost of manufacture and reliability are always important considerations. Typical load demands tend to follow an exponential curve and gear ratio spacing usually is specified to match.

Detroit1 01-08-2016 10:58 PM

The only advantage I see in that design is that you could manually modify the ratio. But the disadvantages are that now you have even more drag resistance. And when you pull on the lever to force the higher ratio it will cause a lot more drag. The CVT transmission is inefficient because it has a lot of drag, and slippage.

If you want to get the most out of a cvt, I highly recommend you get some flat weights, and new springs. I took a Chinese Tao Tao 50CC scooter and changed the cylinder out to 100cc. With the coil, cylinder head, pistion and cylinder, and 27 carb I was producing enough power to get that little scooter to about 68 mph, even with my 225lb butt on it. Of course thanks to the CVT, I ripped through a dozen v belts until I found the right spring, variator, weight combo.

Now you've got me thinking about my little scooter project, I only put about 30 miles on it after my mods, now it sits in the corner of my garage.

Grant-53 01-08-2016 11:10 PM

Sendler did a fair amount of scooter mods here on an older thread. did an extensive project on a Honda Ruckus. Even if they don't slip belts are more elastic than metal.

sendler 01-09-2016 08:08 AM

The one thing a CVT has going for it is the "constant". Trying to force the belt manually isn't going to help efficiency or performance. They are already load sensitive so you can set it up to cruise at low speeds at the torque peak and yet, rev up to the power peak when you pin the throttle for max accel.
The problems which reduce efficiency versus a chain and trans are belt losses from bending as it goes around the pulleys. And compression as it goes between the pulleys. Also CVT's don't have quite as much range as a 6 speed trans so the highway speed cruise rpm is topped out in ratio and well above the torque peak unless you give up accel from launch with longer final gearing.
Also for hypermilers, on a CVT there is no way to PulseNGlide as you would be able to on a bike with a hand clutch.
But there are some CVT scooters doing some good numbers and the CVT takes the driver gear selection out of the equation. Everyone on a Honda PCX can get a really high fuel efficiency of 94 mpgUS depending on how aero you are on the bike and the average speed. A geared bike like the Honda CBR250R has more variation since many traditionally schooled sport bike riders choose to ride around at 45 mph all the time in a gear that is near the power peak so they can have max accel without shifting to "get out of trouble" and end up with 60 mpgUS. Whereas I can take the same bike and putt around at 45 mph/ 4,000 rpm in competition using pulse and glide with engine off coasting and get 135 mpgUS.

minimac 01-09-2016 08:52 AM

Apparently the idea is go to heavier rollers or sliders, for maximum top end/ mileage and by varying the preload, be able to have infinite "gearing"(for acceleration) up to the maximum that the heavier rollers would provide. Similar to having say, a six speed with out having the clutch and additional weight (and drag)of the gears. As it is now, scooters are stuck with whatever compromises goes with the weight of the rollers/sliders. They can be changed- lighter weight= quicker acceleration, less speed, more noise, higher rpm, or heavier rollers/sliders= slower acceleration ,higher speed at lower rpm, for better mileage.
It shouldn't increase drag by a significant amount because it isn't powering or driving any thing. It is only applying pressure, at varying degrees, to the drive belt to alter it's position. At least that's the way I see it. Besides, I thought the whole idea of the CVT was to keep the vehicle its most efficient mode- or is it different for scooters. I don't see where a belt driven pulley system is less efficient than one that is gear driven, but I'm new to this.
See post#62 maybe that explains it better than I can.
PatBox CVT (Continuously Variable Transmission) - Page 7 - Suzuki Burgman Forum

sendler 01-09-2016 10:11 AM

We will have to get some real world data to find out if adding another belt that is sliding along the first belt, and rolling over two more rollers, gains more from rpm control than it loses in friction.
If you really want to shift, a manual trans and a chain drive will be more efficient but not as simple or maintenance free as a standard CVT.
It looks like Suzuki implements their selectable ratio trim on the factory system for the Burgman 650 by tightening or loosening the tension of the contra spring with motor driven gears. Which eliminates the extra belt and pulleys.

minimac 01-13-2016 12:14 PM

Suzuki changed its CVT with the 2013 model to be a bit more efficient. So now there's a patbox for the 'fly by wire' set up.
I was only thinking of this as it might be easier to package for a recumbent streamliner than dealing with a clutch and forward controls. It looks like it would be a way to "fine tune" a cvt for better economy.

ProDigit 02-25-2017 03:45 AM

I invented an idea a long time ago on scootdawg.proboards of a center based bearing that will press on one side of the center of the variator, to squeeze it together.

The other side of the bearing should have a spring, connected to a cable-based lever (kind of like a choke).

The advantages are:
- installable on nearly all scooters,
- Only needs small amount of space,
- low friction,
- No excessive modifications. Same belt can be used.
- The choke system can help you to choose between performance or eco riding styles.

Cons are:
- Can't accelerate fast in Eco mode, unless the choke-knob is changed to performance.
- Not easy to adjust while riding. (imagine riding a bike with 2 throttles, one the real throttle, the other, a manually steered variable gearing, that also will affect acceleration and speed).

ASV 04-01-2017 10:38 PM

A chain drive is not more efficient than a belt
at least not modern micro v belts that can be as good as 98%
And some of the big cruiser synchronous belts can handle all the power you can give one tire

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