[hou_ge2000]

Can future electric cars benefit from a efficient mechanical CVT?

 

[clett]

The characteristics of electric motor torque are completely different to those of petrol/diesel engines. You need gears and clutches with internal combustion engines because they don't produce power from zero rpm, and once up and running have only a narrow range of rpm where they can produce useful torque.

By contrast, an electric motor makes maximum torque from zero rpm - so, no clutch is needed. Then, as the motor rpms rise, torque falls, such that maximum power remains more or less the same (power = torque x revs). Thus, the characteristics of an electric motor connected directly to the driven wheels with no clutch or gears at all are in some ways already similar to a CVT equiped internal combustion - ie maximum acceleration is always available. Hence, electric vehicles will not benefit from (or even require) CVT gearboxes. In fact, as advancements in efficiency and power density improve motor design, the trend in the future will be to put the motor directly in the wheel hub. A Rasertech motor to fit inside a 15inch wheel, for example, could provide up to 150bhp. Four of these would give a 600bhp 4WD monster and wouldn't cost much more to build than a standard 100bhp runabout! If you doubt the performance potential of single gear EVs, check out the 3.6s 0-60 of AC propulsions T-zero.

:wink:

 

[hou_ge2000]

Then why are so many companies putting so much effort in developing CVTs?

But doesn't electric motor has a most efficient RPM too?

 

[RSnyder]

Who is developing a CVT for strictly electric cars? What do you mean by "so many companies"? It doesn't seem like there are very many even working on strictly electric cars at all.

Like clett said, the fewer gear meshes between an electric motor (correctly sized) and the wheels, the better (zero is best).

 

[hou_ge2000]

All I'm saying is, if electric-drive will soon be the next big thing, then why are there companies like Nissan, Audi, Honda, Luk, Torotrak, and countless Japanese firms developing the CVT.

Will the internal combustion engine still be around for awhile?

Like clett said, the fewer gear meshes between an electric motor (correctly sized) and the wheels, the better (zero is best).

I understand that. But my question was "doesn't motors have a most efficient RPM" too? So that mean it can be more efficient with a CVT. Unless they have a motor with a flat curve.

 

[RSnyder]

Will the internal combustion engine still be around for awhile?

Until you see a sharp drop in oil stock prices, I think it's safe to say the internal combustion engine will be with us.

But my question was "doesn't motors have a most efficient RPM" too? So that mean it can be more efficient with a CVT. Unless they have a motor with a flat curve.

With modern computer controlled, highly efficient, properly sized motors, the difference in efficiency isn't enough to make up for losses through a transmission (CVT or traditional). If you want a really fast car but aren't willing to use high enough voltages, a traditional or CV transmission is a reasonable compromise. But in that case, it's not there for efficiency.

 

[BIF]

Trains and ships, whether diesel or nuclear, already use electric motors for motive power.

It's just shameful that we have taken so long to develop it for personal land transportation purposes.

 

[RSnyder]

Trains and ships, whether diesel or nuclear, already use electric motors for motive power.

It's just shameful that we have taken so long to develop it for personal land transportation purposes.

Shameful??? What problem(s) does/do the electric motors in diesel/nuclear trains/boats solve? I think it's the need for lots of torque at low speed for a long time? Do cars have the same problems? Note that diesel electric trains don't have storage batteries. Gas-electric and diesel-electric hybrid cars do. Sounds to me like a different set of problems being solved. So I wouldn't call it shameful that cars don't use all the same mechanisms as ships and trains. Or do you also think its shameful that we don't have nuclear powered cars?

 

[BIF]

Maybe my use of the word "shameful" was a bit strong. But I think it's valid.

I do think it's shameful that we haven't developed some sort of passenger-vehicle hybrid technology sooner than this. Batteries aren't new. Neither are power-distribution logic circuits. Neither are electric motor/generators that can change their behavior. About the only thing that is new (but maybe not) is that little wonder-device, the PSD. That thing is genius in its simplicity!

Why so long in the making? Shameful? Okay, maybe I was overly dramatic. But it's my answer, and I'm sticking to it. Please remember that it's just my opinion.

 

[RSnyder]

Not even the PSD is new (it's over 1/2 century old). What's new is the ability to get the whole collection of components so efficient that they provide a net gain in efficiency when coupled with a gasoline engine under the highly varying load conditions of a car and demanding expectations of its driver. This is not a problem addressed by the electric motors of trains and ships.

So the automobile industry didn't use all the technology developed for trains and ships. That in itself is not a reason to cast shame (as the nuclear analogy should plainly show).

 

[BIF]

Okay, I'll think about it.

 

[Paul]

I don't own a Prius or EV, but have an "engineering" interest in this stuff. I also have experience with the application of industrial brushless servo systems.

Efficient, cost-effective power conversion electronics are key to making the modern EV car (and the Prius) possible. Availability and dropping cost of rare-earth magnet brushless motors don't hurt either.

These components make ratio changes unnecessary in an EV as large speed ranges are now possible. The losses in any type of transmission, simple or otherwise, cut deeply into overall efficiency that's why direct wheel drive will be the eventual outcome.