Create a gear transmission (tooth over tooth) that has the variable transmission ratios of a CVT, but without the belt friction that can reach a zero ratio without the need for a clutch. A kind of “holy grail” of transmissions… and which the Italian company Alter Ego is now trying to achieve.
Led by mechanical and automation engineer Edyson Pavilcu, aided by kinematic studies carried out at the Technical University of Milan, they claim to have created such a mechanism: the first CVT transmission with gears, which promises 10% greater efficiency than a CVT with gears. normal strap.
Manual transmission or CVT transmission
Transmissions allow a transmission system (a motor or a pedaling cyclist’s legs) to operate at a speed that delivers efficient torque while adjusting the transmission ratio between the transmission system and the wheels. Let’s analyze the exchange rates they try to combine in Italy:
- manual transmissions: They combine metal gears to deliver between 95 and 98% of the input power to the output. They have a limited number of gears, with gaps in the power delivery where you have to use the clutch (to get out of one gear and go to the next). When it is in gear its ratio is locked so the engine speed has to vary as it accelerates or decelerates. It can be kept close to the ideal engine speed in every condition, but not always.
- CVT shift: They sacrifice transmission efficiency to increase engine efficiency and achieve super smooth shifts. Many operate with a V-shaped friction belt located between two pulleys that can vary in diameter, making one larger while the other is made smaller to maintain tension on the belt. So you can smoothly adjust the gear ratios while driving and the engine speed is exactly where it needs to be for maximum power or efficiency. Mind you, without the metal teeth on metal teeth, most CVTs offer between 70 and 86% efficiency.
Regardless of driving experience, each has its pros and cons, which is why continuously variable transmission with gears is interesting. The RatioZero transmission seeks to achieve this with more gears: the key is that just one gear never drives the output ring gear, but three: each gives it a small push before moving back a few teeth and pushing again.
And how are the transmission ratios modified? Those three internal gears are attached to curved arms and each of them connects to a freely rotating shaft mounted on its own planetary gear: thus, the main input ring gear rotates the three planetary gears, so they always rotate when the input shaft does.
As the planetary gears rotate, these shafts begin to trace circles and the arms begin to move back and forth. The further those shafts travel in the planetary drive gears, the higher the gear ratio and the faster the output gear will rotate per rotation of the input shaft. Something complex, which you can see in this video:
The Alter Ego team has managed to ensure that a constant entry speed leads to a constant exit speed. They have built several functional prototypes. The first, on a bicycle and the next step will be to attach it to a motorcycle combustion engine. But it could be attached to a wind turbine generator, a car, truck, industrial machine…
The company indicates that the main problems they must solve are the “undulations” in the delivery of torque. Also reliability. Because Toyota transmissions, for example, may not be as efficient but they have a five-year warranty and it’s something they should work on too. I hope they pass the laboratory testing phase.
