Why can't gasoline-only vehicles equipped with continuously variable transmissions (CVTs) be made to be as efficient as hybrids?
I thought the main reason that hybrids got better fuel economy was because their electric motor allowed their gasoline engine to be kept at more constant RPMs so that things like valve timing could be better optimized for that range. But can't a CVT keep the engine RPMs just as constant? Or are CVTs way too inefficient over such a wide range of gear ratios?
Hybrids have energy storage. That allows them to take advantage of regenerative braking, which recovers energy that would have been lost as heat in the brakes. Also, a hybrid's engine can be smaller than a vehicle without energy storage, because peak demand can be met by running the engine and the electric motor together, rather than just the engine. Another point in the hybrid's favor is the ability to shut off the engine when the car is stopped, without incurring a delay when you push the gas pedal due to restarting the engine.
Its not just constant RPM, its constant LOAD that increases efficiency. The gas engine in hybrids can be run at a near-constant loading, whereas even with a CVT, the load on the gasoline engine will vary a lot.
Also, hybrids can recover energy during braking, turning the driving motors into generators to put the kinetic energy of the car back into potential energy in the battery to be used on the next acceleration cycle. No CVT can do that.
And, less significantly but not negligible, CVT's aren't notoriously efficient internally. More internal frictional losses than a conventional transmission, which partly cancels out the efficiency gains from a constant engine speed.
"larrymoencurly" wrote
Additional to the previous answers: classic car engines are very inefficient at low load. And this low load is very typical for urban driving.
Pumping air through the cylinders with nearly closed throttle, friction in cylinders, oil, ... There is an advantage for diesel (no throttle) over gas, but fuel cell is still much better.
Thomas
I forgot: best is electric engine, although the batterie takes some efficiency.
Thomas
I disagree, pure electrics are not the best at all. Charging and discharging batteries is much less efficient than most people think. When you're using the battery bank just as a load-levelling power reserve, as in a hybrid, you get the best of both worlds.
Not to mention we already have a *huge* liquid-fuel distribution system infrastructure in place that could easily be converted to whatever future hydrocarbon (methanol, ethanol, etc.) fuels as desired, but the electrical grid can barely keep up with demand as it is now. No way could the electric power distribution system cope with the added load of recharging millions of electric cars at high rates (how would you feel about spending even an hour at a gas station, or owning a car you could only refill at home?), even if the necessary excess generating capacity was there.
The rate of energy transfer when you fill up a liquid hydrocarbon fueled vehicle is most easily measured in megawatts.
|Thomas Schäfer wrote: | |>>There is an advantage for diesel (no throttle) over gas, |>>but fuel cell is still much better. |> |> |> I forgot: best is electric engine, although the batterie |> takes some efficiency. |> |> Thomas | | |I disagree, pure electrics are not the best at all. Charging and |discharging batteries is much less efficient than most people think. |When you're using the battery bank just as a load-levelling power |reserve, as in a hybrid, you get the best of both worlds.
I find it interesting that my 1990 CDX HF has a city/hwy EPA rating virtually identical to the current Civic Hybrid. From what I've read, performance is similar.
Rex in Fort Worth
snipped-for-privacy@my-deja.com (larrymoencurly) wrote in news: snipped-for-privacy@posting.google.com:
On hybrid vehicles, you also have batteries that store energy. The engine doesn't have to run 100% of the time. Energy is also recouped through regerative braking.
Steve wrote in news: snipped-for-privacy@texas.net:
High-efficiency electric motors can approach 97% efficiency. There will still be some loss in the drives controlling the motors, wiring and associated controls, but even if they were 85% efficient overall, it would still be much more than the available gasoline engines.
Frankly, Honda's hybrid implementation is pretty cheesy since the gasoline engine doesn't operate at a constant speed and MUST be running if the car is moving. The Toyota implementation is quite a bit better, but even still their Echo gets practically the same mileage as the Prius. But remember, these are both pretty much first-generationi hybrid vehicles.
Also, I think the automakers started at the wrong end of the market. A hybrid full-size car or Durango-sized SUV would have been ideal, as the efficiency gap between the gasoline and hybrid implementation would have been MUCH bigger.
"Steve" wrote
I disagree. In hybrid cars, electro cars, solar farms etc. a special kind of batteries can be used, with give an efficiency of 70-80% when charging and 90% discharging. Of course these batteries are much more expensive than simple car batteries. But a combustion engine has it's 30-40% efficiency only at high loads in medium revs. Only the case while accelerating or climbing hills. This efficiency can easily drop below 10% in urban stop and go traffic. That's the market for a hybrid, of course not long distance cruising on the highways (->diesel).
Thomas
Not only that, but on the Saturn electric vehicle, the charging "paddle", which they advertise as safe because is contactless, loose about 20% efficiency during charging according to an engineer at Delco who worked in the same building I did at Hughes. It loose efficiency because it is a magnetic coupling instead of direct electrical contact. I can't believe it when I heard about it.
Magnetic coupling is not a new idea. They advertise it as a high tech sophisticated solution to solve all charging problems. How can anyone make such a dumb design decision. As if that was not bad enough, those stupid managers at GM wanted to standardize that charging "paddle" design for all future electric vehicle. Good thing market force took care of their electric car. I can just imagine a million of these electric vehicle loosing 20% efficiency each time they charge up. What would that do to the power grid :(
Ben
True, I'm quite familiar with battery technology (its kinda what I do for a living). That's still a 30-40% loss going in and out of the batteries. Now throw in the fact that you lose *ANOTHER* 30% at the power generating station, and another 10% loss in the transmission grid, and keep adding up all the other losses between the electric motor and the prime energy source.
When you've finished totalling it ALL up, the hybrid wins pretty handily. Fuel cells work well also. Pure electric just aint gonna work.
Ah, but what are the emissions of your 1990 (pre-Clean Air Act) Civic? The hybrid civic is ULEV (manual) and SULEV or AT-PZEV (CVT).
This paper would disagree with your conclusions, particularly about overall efficiency of a pure-electric vehicle:
For example the Zebra battery:
-- Howard Chu Chief Architect, Symas Corp. Director, Highland Sun
So, "if it's in print, it must be true?"
Pffft.
Certainly more credible than a random post on Usenet...
Can you cite reputable published sources that contradict any of the information or references provided in the paper?
From the paper -
"For the following example we will compare the fuel efficiencies of a
1995 Acura 3.2 TL and GM's new electric vehicle: the EV1. See Table 5. Both cost about $34,000 and can accelerate from 0 to 60 mph in 8.5 seconds."They pretended that an Acura TL is a direct competitor for a 2 seat EV1. They ignored the difference in range between an EV1 and almost any car. They didn't mention the 6+ hour recharge time for the EV1. They didn't mention that the EV1's payload capacity was only 440 pounds. If you ignore all the disadvantages of electric cars, they look pretty good.
Ed
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