Saturday, May 15, 2010
Transmission of the Future?
A clever infinitely variable geared transmission concept makes its debut. Could this be the transmission of the future? With two spinning shafts driving the relative speed of a central and planetary gear the transmission can smoothly go from full forward to full reverse and everywhere in between without disengaging. Like most strikes of genius its simplicity makes one wonder why it hasn't been thought of before.
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It's a planetary. You probably have one in the back of your car.
Such novelty as it may have comes from treating one of the wheel shafts as the "control input", and the other as the drive output.
Think about that for a minute -- to raise the gear ratio, you must apply more torque to the control input than is being output by the transmission to the wheels. And to "go into reverse", you must drive the "control input" backwards, harder and faster than the engine drives the power input.
I don't know if it's still there, but the Exploratorium in San Francisco had an excellent hands-on exhibit in which the differential rear end of a traditional US drivetrain was driven by a fractional-horsepower constant-speed electrical motor, and the car's wheels were replaced with big thick steel drums you could grab securely with the bare hand. If you used your own strength to speed up one of the wheel drums, the other slowed, and could be made to reverse if you worked hard at it. Conversely, if you grabbed hard and stopped one drum, the other would rotate twice as fast -- and if you were strong enough to twist your drum "backwards", the other drum would go even faster.
It could do everything that Steve Durnin's "D-Drive" can do, and for the same reason -- in the demo, the driving engine is so small that a human can overpower it.
Now try scaling that up to automotive engineering.
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