_
Border
Go to New-CVT Go to New-CVT
Go to New-CVT
Go to New-CVT
Home Video FAQ Theory Media Source code Contact
Frequently Asked Questions
Transmissions are everywhere, not only cars

Tooth undercutting due to too few teeth? Normally with such very few teeth as the invention uses, tooth undercutting becomes a serious problem (see: Tooth Undercutting of Beveloid Gears, Chia-Chang Liu, Chung-Biau Tsay - Journal of Mechanical Design - DECEMBER 2001, Vol. 123/569.). However, as you can see for yourself in the animations (click to go to the animations page), it is not a problem with the New-CVT. In fact as few as six teeth are possible. The reason is twofold. Firstly, the conical involute gears are created with a pressure angle of 26.6 (=ArcTan(0.5)) at their centre height. And secondly, the conical involute gears intermesh with their shafts parallel to each other. The result of this is that the active pressure angle, of the two gears in the cross-sections, changes in opposite directions. Both these factors together allow for far fewer teeth without the problem of undercutting arising.

Changing gears requires a very quick shift between gears, is this possible? Yes, both electric and pneumatic systems are quick enough. Gear changes will have to be done by computer and the system to change gear will be a major part of the transmission, but it is perfectly feasible and quite compact.

The new-CVT has very many different possible gear ratios, does it need to go through all of them to go from the lowest to the highest gear? No, the system is built around two pinions going up and down a main gear. The combination of all their potential positions is what makes the very high number of gear ratios. So in order to go from the highest to the lowest gear ratio, both pinions will just have to move up the length of the main gear.

During gear changes the gear ratio changes instantly, is this a problem? No. One solution is to disengage drive to the wheels while changing gears just like in a manual transmission. Only a clutch would be required, as the gears are always in sync and in phase as they never disengage. Alternative solutions are also possible (a Fluidampr for example).

How can conical gears be manufactured? The production of conical gears is already well established and quite cheap.

Size / Strength / Fragile? The tops and bottoms (at low teeth numbers the tips are quite sharp though the sharpest bit is never stressed excessively) of the separate gears in the main gear are more fragile than the centre and there is also a tiny little bit of backlash at these points. However, as drive is reduced during gear change, this is not a problem. The teeth curvature at the vertical centres of the gears is less than with normal gears, this leads to a larger contact surface of the flanks, which reduces the pressure accordingly (less Hertzian contact stress). This results in a higher flank load-bearing capacity and thus the system can be made more compact than would have otherwise been possible with normal gears.

Teeth numbers / Gear ratio's? The smallest number of teeth on the first gear the software supports is 6 teeth. So starting at a gear with 6 teeth and with only 7 gears, a gear ratio from 1:1 to 1:9 could be achieved. However, the 6 teeth gear is at the extremes of this new technology (extra backlash, and the Hertzian contact stress at one point is quite high) so it might not be the best option. This is why the default in the software starts at 8 teeth and with 5 gears, resulting in a gear ratio from 1:1 to 1:4. And if the number of gears were to be increased to 9, a gear ratio from 1:1 to 1:9 would be the result, and with an extremely high number of intermediate gear ratios (while still being very compact).

What is the best place to start with this new technology? The blender source code that we used to create the animations on this website contains everything you need to know. Blender is a free software package used by artists from all over the world to create amazing animations (www.blender.org). We choose it because it is powerful and everybody has free access to it. Furthermore, a translation of this source code into dedicated engineering software should be quite easy. Click on the link 'Source code' at the top of this webpage to get the source code.



_