Personal computing discussed
Moderators: askfranklin, renee, emkubed, Captain Ned
notfred wrote:But aren't super-capacitors in the required capacity even more expensive than lithium batteries?1) Throw in some super capacitors to capture more of the regenerative braking energy (not rate limited on charging like batteries are).
You want to keep unsprung weight to a minimum, which is why the common fantasy of a motor in every hub is wrong. But a motor at the wheel is a good idea. I've been somewhat surprised that no-one (AFAIK) has done a hybrid AWD implementation with the gas engine running the front wheels and electrics in the rear (which has the nice side-effect of eliminating the driveshaft hump in the cabin). Though of course it would be better to have the electrics running the front wheels all the time, and the gas engine driving the rear wheels only as necessary -- but then you need to put the gas engine in the rear.... hello, Porsche. Too bad batteries are so heavy.2) Electric motor per wheel (either hub or if too heavy inboard on a driveshaft) for crazy 4 wheel drive capability with computerised equivalent to differentials.
UberGerbil wrote:I've been somewhat surprised that no-one (AFAIK) has done a hybrid AWD implementation with the gas engine running the front wheels and electrics in the rear (which has the nice side-effect of eliminating the driveshaft hump in the cabin). Though of course it would be better to have the electrics running the front wheels all the time, and the gas engine driving the rear wheels only as necessary -- but then you need to put the gas engine in the rear.... hello, Porsche. Too bad batteries are so heavy.
UberGerbil wrote:Not a pure super capacitor setup, more a mix of caps and batteries. The current hybrids don't actually recover that much energy from braking as I understand because the batteries have a limited charge rate. If you add a small capacitor bank in addition to the batteries then the braking energy can get dumped in to the bank pretty quickly and then charge the main battery bank more slowly.notfred wrote:But aren't super-capacitors in the required capacity even more expensive than lithium batteries?1) Throw in some super capacitors to capture more of the regenerative braking energy (not rate limited on charging like batteries are).
notfred wrote:Yeah, I understood what you meant: use the supercaps upstream from the batteries to buffer the instantaneous spike during breaking and then dribble it out to the batteries at the rate they can absorb efficiently. But you're still talking about a substantial amount of energy: a 1200kg Prius travelling at highway speeds carries almost exactly half a million joules in kinetic energy. I haven't gone shopping for super/ultracapactiors but I would imagine that something that can absorb 500 KJ at the voltages used in hybrid cars doesn't come cheap. At least, not yet.Not a pure super capacitor setup, more a mix of caps and batteries. The current hybrids don't actually recover that much energy from braking as I understand because the batteries have a limited charge rate. If you add a small capacitor bank in addition to the batteries then the braking energy can get dumped in to the bank pretty quickly and then charge the main battery bank more slowly.
NYTimes wrote:Interestingly, the prototype leaves the factory FWD system intact and adds their own system in the rear, for intermittent AWD (though that would seem to be an artifact of the prototype and not an intended feature.)The ultracapacitors take up about as much space as the lithium ion batteries, although they store a total of less than one kilowatt hour. Mr. Bender described the entire package as looking like an 18-pack of Red Bull cans, shrink-wrapped.
Captain Ned wrote:Last thing I want is to pass a turbine-powered Pious (my pet name for the Prius, and I've yet to see one pass me) when the turbine disk lets go.
ekul wrote:UberGerbil wrote:I've been somewhat surprised that no-one (AFAIK) has done a hybrid AWD implementation with the gas engine running the front wheels and electrics in the rear (which has the nice side-effect of eliminating the driveshaft hump in the cabin). Though of course it would be better to have the electrics running the front wheels all the time, and the gas engine driving the rear wheels only as necessary -- but then you need to put the gas engine in the rear.... hello, Porsche. Too bad batteries are so heavy.
I think Nissan actually did that with the cube in Japan. If you ordered 4 wheel drive you had the gas engine powering the front wheels like normal and a small electric motor in the rear. I don't know if it was that popular.
SpotTheCat wrote:Also: I am all for serial hybrid designs. I won't be touching a parallel hybrid with a 10 foot pole. With serial hybrid/pure electric drive you can get a sharper throttle response than even formula 1 cars.
Voldenuit wrote:SpotTheCat wrote:Also: I am all for serial hybrid designs. I won't be touching a parallel hybrid with a 10 foot pole. With serial hybrid/pure electric drive you can get a sharper throttle response than even formula 1 cars.
The downside of serial hybrids is you need a *lot* more batteries than a parallel hybrid. LOTS more. A prius has an electric driving range of a couple of miles, and even the PHEV version with oodles of batteries stashed in the trunk only has an electric range of 12 miles.
The batteries add weight, you need larger and more powerful motors, and the cost and environmental impact of making and installing more batteries is amplified.
They (serial hybrids) are good in other respects - the drivetrain is simplified and more elegant from an engineering perspective (although the prius transmission system is hella cool), and driving electric-only offsets CO2 production to the local coal, nuclear or hydroelectric plant. Just pointing out that everything has advantages and drawbacks, which is why different players are moving in different directions rather than all doing serial hybrids. For instance, the Prius synergy drive transmission is very complicated, and Toyota didn't simply put the money and effort to design and manufacture it for no reason. They did it because the parallel drive system was more economically feasible - even with the added cost of the transmission - at the time.
As an engineer, my personal passion is for Stirling hybrid engines, but I also know that there are many technical and economic reasons why we don't see them on the market yet (if ever), despite NASA and GRC producing 70mpg stirling powered cars (using petrol-only) for research in the 70s.
SpotTheCat wrote:As far as Stirling engines in cars, I don't see them as practical as they are even less able to cope with power output fluctuates than gas turbines.
notfred wrote:Not a pure super capacitor setup, more a mix of caps and batteries. The current hybrids don't actually recover that much energy from braking as I understand because the batteries have a limited charge rate. If you add a small capacitor bank in addition to the batteries then the braking energy can get dumped in to the bank pretty quickly and then charge the main battery bank more slowly.
Captain Ned wrote:Last thing I want is to pass a turbine-powered Pious (my pet name for the Prius, and I've yet to see one pass me)
SNM wrote:Just because a Prius driver doesn't pass you and your misplaced testosterone doesn't mean they can't.
delsydsoftware wrote:talk about a car ahead of its time.
delsydsoftware wrote:This reminds me a lot of the system used by the Chrysler Patriot:
http://www.allpar.com/model/patriot.html
Talk about a car ahead of its time.