Ratio Zero gear-driven CVT prototype (Credit: Driving 4 Answers YouTube).
At the moment most scooters have one of three sorts of transmission:
- Classic scooters have manual gears and a manual clutch
- Modern automatic scooters have belt-drive CVT (Continually Variable Transmission)
- Many electric scooters have direct drive without any form of gearbox
(One exception is Honda’s Dual Clutch Transmission system (DCT) as used in various Honda motorcycles and their Forza 750 scooter)
A Vespa drive train, yesterday. Gearboxes don’t come much simpler.
What’s good about gears?
The old system – a top gear and a bottom gear with as many others as you could fit in between – can be as strong as you want it to be, and is very reliable. With care, a gearbox will last the lifetime of a vehicle. A clutch may need to be replaced occasionally due to wear on the friction plates.
What’s bad about gears?
The negative of a manual gearbox is that it must be manually operated; which can be tiring in a city, or rewarding in the countryside. With only a few gears to select from, it is impossible to keep the engine operating at its most efficient all of the time.
A Yamaha T-Max failed CVT drive belt and pulleys. Let that serve as a reminder to service on schedule.
What’s good about V-belt CVT transmission?
The biggest selling point of CVT is that it’s fully automatic; and operated centrifugally. The addition of a centrifugal clutch means that you can literally just ‘twist and go’. Great for ease of use in the city, but slightly ‘beige’ in terms of entertainment out of town. Another good thing about CVT is that it can be tuned to match the performance of any engine. Between the limitation of a ‘top’ and ‘bottom’ gear equivalent are infinite ‘ratios’ allowing the engine to be held at optimum engine rpm throughout an acceleration phase.
What’s bad about V-belt CVT transmission?
Quite a lot to be honest. Firstly it relies entirely on friction between V-belts and pulleys. Friction generates heat and wear, and wastes power. Rubber belt CVTs are inefficient in terms of losses and require regular maintenance. As Vespa GTS riders often know, if you don’t change your drive belt on schedule (or even more often) then belt failure is likely to occur.
Retrospective Scooters electric Vespa conversion with direct-drive rear hub motor.
What’s good about direct drive?
Driving the back wheel without any form of gearbox (single fixed gear) only works well on engines which make extremely strong torque from zero rpm. Luckily electric motors often work that way. Vehicle speed is therefore adjusted solely by adjusting the engine rpm.
This transmission method has extremely low operating losses; especially for hub-drive engines where the motor is housed within the rear wheel.
What’s bad about direct drive?
The problem with direct drive is that the speed range of the vehicle is directly limited by the engine rpm of the motor. Also, the speed at which the engine is most efficient is not necessarily the speed that it will cruise at.
In an ideal world…
You could combine the ease of use and infinite ‘ratios’ of CVT with the robustness and reduced losses of a mechanical gearbox.
That wasn’t really a possibility, until now…
Enter the Ratio Zero mechanical IVT gearbox.
VIDEO: Driving4Answers
You know at SLUK we like to make our own videos to explain things, but on this subject it is impossible to do better than the excellent YouTube channel ‘Driving 4 Answers’. Their explanation of the complex operation of this device cannot be bettered.
This invention, by Edyson Pavilcu of Rovigo Italy, has so far been nine years in the development and patenting process. So far the prototypes have been developed for pedal cycles but Ratio Zero is looking to adapt the system to a Yamaha TMAX (‘King of the maxi scooters’) in place of the belt-drive CVT.
Physically, this should be possible even though the Ratio Zero IVT (Infinitely Variable Transmission) is a good bit bulkier than traditional CVT.
This is the available space for a CVT/IVT in a Yamaha TMAX motor, so I’m expecting the Ratio Zero conversion to stick out a little through the bodywork.
What potential problems are there with Ratio Zero IVT?
While undoubtedly a work of genius, there are no perfect designs. Everything in engineering comes with compromises that are only worth overcoming for specific applications.
Going from the video, I can see a few issues that may prevent rapid adoption of the Ratio Zero design:
1. It looks complicated and therefore expensive to make. By contrast, both CVT and mechanical gearboxes are much simpler and easier to produce.
2. Variation of the ratios is not automatic. At the moment ‘ratio shifting’ of the prototypes is either manual, or electrically driven. This is an added level of cost and complexity compared to centrifugally-operated belt-drive CVT.
3. The sliding elements of the design appear to be vulnerable to wear in use and substitution of worn parts is unlikely to be either cheap or easy.
A T-Max, the day before yesterday.
Will my next scooter use Ratio Zero IVT?
With those compromises in mind, I can’t see this invention ever making it to large-volume, low-profit, small-capacity scooter engines. Try to imagine the additional cost of adding this system to 10,000 scooters, compared to simply manufacturing the same number of tried and tested pulleys and variators.
The fact that modern automatics wear out belts and pulleys is not important to the manufacturers, as service schedules seems to have very little bearing on the buying decision. People will buy a scooter that they like the look of, whether it needs a belt change at 3,000km or 6,000km.
This doesn’t mean that Ratio Zero has no future; it just means that it is more likely to find a home in a high-value scooter, car, boat or other vehicle.
We at SLUK love inventive engineering, and we wish Edyson and his Italian team all the best in raising funds to progress the idea to the next stage.
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