[SGVLUG] OT: Hybrid efficiency (was:New Linux Lug)
Tom.Emerson at wbconsultant.com
Tue Feb 21 12:03:20 PST 2006
OK, being a hybrid owner, I suppose I should interject my observations...
> -----Original Message-----
> Behalf Of David Lawyer
> On Mon, Feb 20, 2006 at 10:08:47AM -0800, Dustin Laurence wrote:
[hmmm... there is lots of back-and-forth stuff I'll be deleting, and I cannot attrib comments via initials since they are both "DL", so I'll do the best I can and point out the thread should be in the archives...]
> [David:] Charging batteries is only 36% efficient in the Prius II.
While I have the first generation prius, I *suspect* there is an artificial cap placed on charging. I've heard rumors that the system tries to keep the battery at a slightly-less-than-full charge, and I tend to believe those rumors based on what I've seen: the "state of charge" portion of the display typically reads 3/4 charged -almost-all-the-time- for me, and only dips below that for an extended uphill run. When "coasting" down Angeles Crest from the closest "peak" [essentially the vista point/ranger station/vetter (?) approximately 12 (linear) miles from La Canada], I'll get the display to read "100%" about the time I reach the country club (the final set of turns when going downhill). This drops down to 3/4 within 1 mile of "freeway driving" on level ground.
Conversely, it isn't until I reach the second peak & ranger station (near palmdale) that I can actually drop the charge down to 1/4 or even "fully discharged", but this "recovers" back to 3/4 charge within a mile or two of "downhill" driving/coasting.
Long story short, I believe the system *could* recover more energy, but doesn't. Why it doesn't do this is more likely due to political or marketing reasons than technical, but this borders on conspiracy theories...
> > Most of the drag at highway speeds is wind resistance, and the
> > difference there is essentially zero: notice that some cars can be
> > purchased in either configuration. It is the same body
> shape and size, thus the same drag. [...]
> > a hybrid is better there (I suspect less ventilation is needed).
[side note: on the first generation Prius there is a battery exhaust port specifically to ventilate the waste heat generated by the charge/discharge process, but the inlet comes from inside the passengar compartment, so I have no idea how this affects your argument; the Prius II apparently doesn't have this "port", or else it vents to "underneath the vehicle" just to avoid an external blemish -- anyone with the new version around here care to comment?]
> > Which lists the additional weight for a Prius (a fuzzy concept since
> > there is no direct-drive Prius) as 200 lb.
Actually, there is, or at least, there appears to be: the Ford Focus from the same timeframe has a nearly identical exterior size and shape as a Prius I[judged by viewing a Focus that parked next to me one day] There isn't much difference in effective "engine weight" as the electric motor essentially weighs the same as the equivalent portion of the gasoline engine it replaces, however since you're lugging around 6 or 8 extra "batteries", you do have to account for that, and 200 lbs sounds about right for a half a dozen "regular automotive batteries"
> > > But worst of all is the poor efficiency of regenerative braking.
[snipped long treatise on kinetic energy...]
Another observation: near my sister's house there is a good sized "gully" that the road dips down into and back out -- at least a 100' drop or more on each side, with a stop sign at the top. I have, on occasion, started out from a dead stop at the top of one hill, *added* a little energy [from the batteries] and "kicked it into neutral" and coasted to a stop at the top of the second hill. (very tricky to judge "just enough" to add at the start -- usually I'm still going approx 15 mph and have to actually use the brakes) I haven't really tried using "just the energy in creeping" (*) because there is enough traffic on the road that I'll likely get a "suggestion" from another driver on where I would find the gas pedal...
(*) "creeping" -- the prius is specifically designed to mimic "engine creep" as found in a conventional vehicle. Technically, the car shouldn't "add" any energy to the system if you don't have your foot "on the gas", but it does since "people are used to cars doing this" in the first place [I think it even mentions this fact in the handbook...]
Note I said that I "kicked it into neutral" -- if I didn't, the system would automatically attempt to bleed energy from the downhill drop and feed it to the batteries, however the amount "bled" from the system is greater than what it applies as "creep", so I'm nearly certain that the car would indeed "stop" on the way up, and might even start rolling backwards if I were to let it. I don't think it is possible to quantify whether the energy bled from the downhill drop, when stored in the battery and then re-applied to the motor on the way out would be enough to reach the top of the second hill (due to the difficulty in applying "just enough gas" to use the electric motor without the computer automatically starting the gas engine to help push up the hill)
[Dustin, then David]
> > I'd be interested to watch you do an actual test of this
> idea, but you won't be abusing my car to do it.
> You don't abuse cars much by doing this. I've done it and have had to
> do it at times to keep from running out of gas in areas with no gas
> stations open. Cars need to have electric oil pumps that would turn
> on just before starting to avoid the extra wear that happens when one
> starts the engine.
"...electic oil pumps that turn on just before starting..." -- tell me, do these use anti-thiotimoline batteries? :)
[David, then Dustin]
> > > that traffic, signals, and laws were such as to promote coasting,
> > Ever heard of light sequencing?
doesn't work in practice -- "people" are in such a "hurry-up-and-wait" frame of mind that they'll rush to the next light well above the stated speed limit. I'd love to see a roadway designed in such a way that the "friendly reminder sign" at the side of the road would read "speed limit enforced by brick walls" (what I'm thinking of are solid barriers on pistons set up to "drop" to road level if you are travelling at the rated speed, and raise back up after the last car of a group -- while it would effectively prevent speeding, it is, unfortunately, rather impractical)
[David, then Dustin]
> > > I think auto manufacturers should be required to provide
> > > curves for their engines so that drivers can select efficient
> > > operating points.
> > Most drivers can neither select efficient operating points nor
> > understand the efficiency curve.
> > > ...Why not a display on the dash that would show
> > > efficiency?
> > I believe a Prius has this (Tom can tell us for sure).
yes, as does the Honda (but I found the honda to be more annoying and distracting than the toyota, which actually became a deciding factor in my choice) On the Honda, there is a LED bargraph type display that sways back and forth from "charging" to "discharging", and it is placed near the speedometer/odometer; On the Toyota, you have to pull up a seperate screen to show the relation of battery usage: battery usage when the engine isn't running, battery charging due to "coasting", battery charging due to excess engine capacity, battery assisting due to lack of engine capactity, and so on.
As I mentioned earlier, the toyota also has a display that summarizes your "fuel effeciency" over 5-minute periods, and even shows the amount of recovered energy (as "lightbulbs", or something vaguely resembling such -- the screen's resolution isn't all that great...) There is also an instantaneous display.
The truly "geeky" members of the Prius community, however, have gone so far as to install meters showing the actual current draw and have learned to drive "just under" the point at which the "demand" for speed exceeds what the electric motor alone can produce (see the web-based Yahoo discussion group "prius-technical-stuff" for details)
> > Dustin, contemplating the interesting idea of a hybrid
> motorcycle (but where to store the electricity on such a small vehicle)?
it's been done
[google "hybrid motorcycle" results]
[press release for the motorcycle itself:]
[and an article on hybrid bikes being TOO quiet -- they have to add "noise" so pedestrians will get out of the way!]
and how about 180 mpg?
and this odd link found in the search:
regarding using /diesel/ fuel for hybrids...
More information about the SGVLUG