Slashdot Mirror
Inventor Demonstrates Infinitely Variable Transmission
ElectricSteve writes with this excerpt from Gizmag:
"Ready for a bit of a mental mechanical challenge? Try your hand at understanding how the D-Drive works. Steve Durnin's ingenious new gearbox design is infinitely variable — that is, with your motor running at a constant speed, the D-Drive transmission can smoothly transition from top gear all the way through neutral and into reverse. It doesn't need a clutch, it doesn't use any friction drive components, and the power is always transmitted through strong, reliable gear teeth. In fact, it's a potential revolution in transmission technology."
Fluid friction losses. Recirculating a fluid via a pump in a closed system actually makes a bit of heat, especially when there's a bit of load on it. Works great when something can be built big and doesn't need to go very fast (like the tractor application you mentioned, also used a lot in earth moving equipment and fork-lifts), but when having something that goes fast - not so much. Also if you go too fast, you're either going to have some kind of undesirable hammering or cavitation at a certain point depending on what kind of pump you use to provide hydraulic power.
Some air motors use a tilt-block that does something similar as well in regards to infinite variable speeds, but they're not so much about efficiency as about being able to control speed in industrial environments where electric motors aren't always desired. (Like working around water or in a no-spark environment.)
Actually, the transmission in the Prius is completely different from this. The Prius takes two full power inputs (the engine and the electric motor), and adjusts the power output from the two (balancing them) to achieve the end ratio. This takes a single full power input (and two factional inputs, perhaps a very small fraction if friction losses are small enough), and produces a variable end ratio. Quite a big difference between them. For the Prius transmission to work, both engines need to be of comparable power (A 100 hp gas engine would need somewhere near a 100hp electric motor). This would likely work with a 100hp engine and a pair of 1/2 hp (or less, depending on precision and friction) electric motors.
And FYI, an OTTO cycle engine is not most efficient at 2000 rpm. It's most efficient at its horse power peak RPM, and at full throttle. Anything less than that (RPM or throttle), and you lose volumetric efficiency. And when I say efficient, I'm saying the power/fuel use is the maximum. It's all about the intake and exhaust design (you can tune them for maximum efficiency at a particular RPM for a particular engine design). That's why hybrids typically use smaller engines. So that you can run it closer to its peak power for longer (40hp at full throttle would be plenty to cruise on the highway and still be able to charge the batteries without needing to be throttled back).
If a man isn't willing to take some risk for his opinions, either his opinions are no good or he's no good
It's quite different from the HSD in that it has three inputs, contrary to what GP said - one power input, and two control inputs, both of which ought to require just a fraction of the input power to control the input/output gear ratio.
Real engineers disagree on the "inventor's" website:
http://infinitelyvariabletransmission.com.au/wp-content/uploads/2010/05/dDrive-Transmission-Report.pdf
"The torque provided by the Control shaft will typically be of the same magnitude as the torque provided by the Input shaft."
"The Control shaft (and associated mechanical elements) should be sized to this torque requirement
accordingly – the Input and Control should be considered as parallel power paths rather than as ‘power’
and a ‘control’ elements respectively."
So this whole thing isn't very useful. To add this as a transmission to a power motor, you need
one ore two additional motors of same power with variable speed and enough torque at any speed.