Originally Posted by
DP-buggyboy
One thing to keep in mind when debating all types of rotary valves is this:
Everyone assumes the valves turn at a constant rate. There is a very easy way to vary the speed of the valve, making it open and close MUCH faster, yet slow down when it's closed.
You can speculate all you want, and even when you can plainly see the valve mechanism, you may not know exactly how it operates.
Gear driven rotary parts can turn slow for half-a revolution and fast for the other half when the gears are offset (not centered) on their shafts.
That is true but still there is a problem. That would result in slow movement for around 180 degrees and fast for the other 180 degrees (not exactly, but just for speculation we will go with it). But this isn't much help. What's needed isn't slow when open, fast when closed but rather to have it open very quickly from the point of first opening until it is open a fair amount (let's say about the first 30 degrees of opening) and slow way down for the next 40 degrees or so to keep the port nice and big for a long time and then speed up again for the last 30 degrees or so until closed. Two off center gears will not accomplish this, though I could see SOME gains being made in this way.
Now, I'm not an expert on off center gears so I will admit that it very well may be possible to design a complex set of multiple off center gears to achieve the desired result. It is making my head hurt just thinking about how to do it right but there are smarter people than me out there that might be able to figure out. I sure would like to see such a system. It would definitely be an engineering masterpiece whether it worked well or not.