___ |___| |||| ___
| | | \______| |
|___| |___/ |___|
___ |___| ___ |||| ___
| | |__ \________| |
|MG1|/////> __> ________|ICE|
|___| |___/ __ |___|
What was not clear to me was the power flow from the ICE to the wheels. It seemed as if he was saying that the only connection from the ICE to the wheels was indirect, by turning MG1 to generate current that could drive MG2 which drives the wheels. But I don't think that's the case.
I know that if I floor the pedal entering the freeway, the ICE spools up to something like 5000rpm and holds there while the car accelerates. So clearly there is a flexible connection. But is all of that mighty horsepower being transmitted by first being turned into AC in MG1, which flows to MG2, which turns it back into torque? Because that would be rather inefficient I would think.
There's a detailed explanation of all the various modes the gears interact in here: http://prius.ecrostech.com/original/Understanding/WhatsGoing...
The concept is straightforward if you visualize mechanical advantage. A high torque at low RPM is the same power output as a low torque at high RPM. If you picture an asymmetric differential with primary power going into it where one wheel is geared higher than the other, then a weaker motor on one of the wheels could control the torque and RPM of the other wheel.
So we probably could have been using electrically assisted CVTs decades ago where a small fraction of the power could have gone into a generator/motor pair at about 90% conversion efficiency to control the output RPM. I can't help but feeling that most of the gains in things like 6 speed automatic transmissions to increase fuel economy have largely been a waste of time. We could have gotten rid of traditional transmissions and gone with a design like the Prius that are simpler, more efficient and more durable. By now economies of scale probably would have made them less expensive as well.
I’m actually a little curious why this hasn’t happened with supercars.
Furthermore, it would be hard to implement a way of shifting the CVT to a predictable ratio and holding it there while in a tight turn. (Holding the ratio might not be hard, but the driver will probably want a predictable ratio before going into the turn).
Perhaps, perhaps not. Williams had a working CVT in the FW14C F1 car, which was pre-emptively banned at the behest of their competitors. It probably set back CVT research by a couple of decades, and marked the end of F1 as a tech testbed.
Currently it's worth noting the Toyota are running the Lexus 450h in racing, and the Lexus LS600h runs a 327HP/520Nm V8 though a CVT mated to an electric motor running over 200 HP.
Is this more efficient than a gasoline drive system only if the energy to drive the electric motors come from an external source (the power grid, though the batteries)?
The power split device is indeed a brilliant piece of engineering.
The greatest example of hub gearing is the Rohloff Speedhub, which features fourteen ratios with an overall range of 526%. It is a true mechanical marvel, and several examples have done over 100,000km without major servicing.
At any rate the Rohloff hub is really cool, and I'm glad the technology has finally trickled down into popular, attainably priced planetary gear hubs like the Shimano Nexus as well.
I mean: electric motors can rotate at very high speeds. Do it even need a gearset? Or can it just rotate from 0 RPM to say, 15k RPM? Or there is a torque curve or efficiency issues involved?
AC motors (like the ones Tesla use), work by pushing a sinusoidal wave around the "outside" of the stator, while a similar sinusoidal wave (at a retarded phase) is run inside the stator. This creates a magnetic field which is "ahead" of the stator's field (well in forward mode) which "pulls" it toward the field. The torque curve is "constant" and the speed is limited only by how well you can modulate that voltage. (and of course the mechanical construction)