Posted by perfb on May 7, 2006, 1:38 pm
excellent description, thanks! Is this tehcnology unique to Toyota,
i.e. patented etc? How does it compare to Honda's or Ford's approach
to the hybrid design?
>From what little I've read, the Honda hybrid system does not seem to
have the same advantages of true motor/generator operation and
simplification of the drivetrain, is that right?
Scott wrote:
> Several others have posted fine links which describe the Prius'
> "eCVT"... thanks to all.
> Let me add my own nutshell description, using a familiar effect many
> folks might have witnessed for themselves, that might illuminate how a
> simple planetary unit can act as a CVT:
> Have you ever seen a conventional car, say a '63 Dodge or some other
> stone-simple vehicle, up on a lift with its engine running? Or
> attempting to accelerate on an icy patch? The engine spins the
> driveshaft, and if traction is equal at both rear wheels, then both
> spin identically. But if one has more "grip" than the other (either
> because it's on a comparatively dry spot, or because the mechanic is
> holding onto one wheel with the car on a lift) then the wheel with the
> lesser grip will do all the spinning.
> That's how a conventional differential channels power from the engine.
> That's also how the Prius' power-split device (aka "electronic CVT")
> works. Kinda/sorta: Imagine the gas engine in place of one wheel and
> an electric motor on the other. The driveshaft, then, becomes the
> output (instead of the input, as in the '63 Dodge). You can now run
> the gas engine at whatever speed you want and still get the desired
> output-shaft rotation rate by varying the speed (and direction) of the
> electric motor, either contributing power or taking it away depending
> on the circumstances. This means you can use an Atkinson/Miller-cycle
> design for your gas engine (or a direct-injection diesel) and take
> advantage of its higher thermodynamic efficiency while accommodating
> the peaky powerbands characteristic of these designs. It also means
> you can dispense with an alternator, since the motor can act as a
> generator. It also means you can eliminate the starter motor, since
> the motor can spin the gas engine if you hold the output shaft steady.
> And, by putting another motor on the output shaft, it ALSO means you
> can drive the car electrically when you want, or capture kinetic energy
> through regenerative braking. Being able to drive the car electrically
> means no reverse mechanism is needed either.
> See how a simple differential lets you eliminate all that stuff you
> used to need? Transmission, clutch or torque converter, alternator,
> starter... and so on. Each elimination means a whole cascade of weight
> savings and loss reduction.
> It's flippin' brilliant, and my real point is that it's a radical
> simplification of conventional automotive design, contrary to the
> picture painted by idiot journalists who wouldn't know a differential
> from a Dove Bar.
> You can also see why I rebel at calling it a "CVT". There's no
> friction belt, for one thing, which is what other CVTs use. (All
> right, so Audi uses a compression belt, so sue me.) I don't trust 'em.
> They wear out, they're touchy about torque, they're stratospherically
> expensive to repair, and they're lossy. The only reason you're seeing
> them in other cars is as a kludge to allow their engines to run at peak
> efficiency, which luckily more than offsets the inefficiency of the
> friction belt. Talk about a technology demonstration! They're
> practically a science-fair project, IMHO. The Prius power-split device
> makes way more sense and is way simpler. Mark my words: there's a good
> likelihood that belt-type CVTs will be a dirty word in five years or
> so, when the first wave of disgruntled owners sees their transmissions
> disintegrate at 80,000 miles. Do the Prius a favor and help me stamp
> out "CVT" as a description of its technology!
Posted by Michelle Steiner on May 7, 2006, 3:24 pm
perfb@yahoo.com wrote:
> excellent description, thanks! Is this tehcnology unique to Toyota,
> i.e. patented etc? How does it compare to Honda's or Ford's
> approach to the hybrid design?
Ford's approach is so similar that they had to license (some of?)
Toyota's patents to avoid infringement. From what I understand, Ford
developed it independently, but there was still the infringement issue.
Honda uses a parallel technology (not parallel to Toyota's, but that's
the kind of technology) in which both the engine and electric motor are
running whenever the car is in motion. (Of course, when the car is
stopped, like at a stop light, the engine is off, just like with the
Toyotas.) The engine is more powerful, and the electric motor is less
powerful. It uses a standard transmission; in fact, you can get the
Civic hybrid with a stick shift.
--
Stop Mad Cowboy Disease: Impeach the son of a Bush.
Posted by alt.google on May 8, 2006, 2:57 am
hmm -
I can see your desire to make a DISTINCTION to call attention to a
significant technological DIFFERENCE.
But, when it comes to naming things, I think that the rule is that the
owner or maker gets to decide - whether children, or dogs, or
transmissions.
You make an excellent point that the Prius eCVT is materially,
qualitatively, and significantly different from the variable pulley
belt drives.
But think about it.
CVT isn't an acronim for
"ComplicatedChainBeltVariableRatioTransmission"
CVT means Continuously Variable Transmission.
Perhaps "second generation CVT" would convey more of the wonder of the
new Prius.
But, it is still a transmission.
And, it is still Continuously Variable.
And if Toyota prefers eCVT to "electric differential CVT" or "second
generation CVT", they make it, and they (not you) get to name it.
Though, I have to say that you have helped others understand the
technology better by your refusal to adopt the given name.
Let's give it a "nick name" (people often do that when they don't like
the given name or it doesn't seem appropriate to the object being
named).
Let's call it eDCVT2 - awfully long, but indicates the second
generation and electronic differential.
I don't really care for the "eD" part either...
Posted by Michael Pardee on May 11, 2006, 6:16 am
> Perhaps "second generation CVT" would convey more of the wonder of the
> new Prius.
> But, it is still a transmission.
Toyota calls it a transmission, and they call the assembly a hybrid
transaxle, but I would argue that in the same way a differential in a
rear-drive axle is a transmission. The similarities are greater than the
differences from a functional point of view. A fundamental difference is the
number of ports: a transmission in a conventional sense has one input port
(connected to the transmission) and one output port (connected to the
differential). A transaxle has three ports: one input and two outputs (for
each drive wheel). A differential has one input and two outputs but lacks
the variable ratio capability. The hybrid transaxle has one input, two
input/output (the motor/generators) and two outputs for the wheels. Nothing
ever changes ratios inside... is that a transmission?
I think your term "electronic differential" captures the operation better.
Mike
Posted by kari on May 12, 2006, 3:17 am
Wouldn't it be more correct to say that the hybrid transaxle has three
input-output ports? After all, MG1 spins up the ICE before fuel ignition.
Kari
>> Perhaps "second generation CVT" would convey more of the wonder of the
>> new Prius.
>> But, it is still a transmission.
>>
> Toyota calls it a transmission, and they call the assembly a hybrid
> transaxle, but I would argue that in the same way a differential in a
> rear-drive axle is a transmission. The similarities are greater than the
> differences from a functional point of view. A fundamental difference is
> the number of ports: a transmission in a conventional sense has one input
> port (connected to the transmission) and one output port (connected to the
> differential). A transaxle has three ports: one input and two outputs (for
> each drive wheel). A differential has one input and two outputs but lacks
> the variable ratio capability. The hybrid transaxle has one input, two
> input/output (the motor/generators) and two outputs for the wheels.
> Nothing ever changes ratios inside... is that a transmission?
> I think your term "electronic differential" captures the operation better.
> Mike
>
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