Entry 37000 (Berkeley CSUA MOTD)

Berkeley CSUA MOTD:Entry 37000

WIKI \| FAQ \| Tech FAQ
`http://csua.com/feed/`

2025/05/24 [General] UID:1000 Activity:popular

5/24

2005/3/31-4/1 [Transportation/Car/Hybrid] UID:37000 Activity:nil

3/31    How to get the best MPG out of a Toyota Prius:
        http://www.mixedpower.com/modules.php?name=News&file=article&sid=448
        Look under "Speed, braking, acceleration, and anticipatory driving".
        \_ Reading about the EPA requiring the battery charge to be the
           same at beg. and end of mileage test made me wonder:  Has anyone
           ever investigated any way to charge the battery using solar or
           heat energy?  We all know that cars get baked in the sun during
           the day.  If there were some way to simply charge the battery
           with this energy, you'd have a remarkably low fuel-consumption
           automobile.  Perhaps some process similar to what idealab did
           with the Stirling engine.
           \_ You could charge using solar, but you;d have to install solar
              cells on the car (of course).  Using heat only works if there's
              a heat difference and some sort of Carnot cycle to exploit it,
              such as a Stirling engine.  That's even more of a pain to
              build into a car than solar panels.
              \_ Plus each square meter of solar panel only captures about
                 120-150 wattHour of energy at full sun.  That is not
                 a lot of energy.  I think the Prius has about 70-80
                 kWh of stored energy in the battery.  That'll take a
                 long while to get any meaningful charge into the battery.
                 Probably cost way too much to do it feasibly.
           \_ There is no good way to do what you say, or we'd build power
              plants that way as well as recharge car batteries.
           \_ Put solar cells on the car roof.  But that adds weight, so how
              efficient it is depends on the driving time vs. parking time
              under the sun.  Another way is to put solar cells at the parking
              location.  But then it's no different from ordinary solar cell
              applications, which is not specific to charging vehicles.

2025/05/24 [General] UID:1000 Activity:popular

5/24

You may also be interested in these entries...

2011/12/5-2012/1/10 [Transportation/Car/Hybrid] UID:54250 Activity:nil

12/5    "Eight Ferraris wrecked in million-dollar pileup"
        http://www.csua.org/u/uw3 (autos.yahoo.com)
        "Police and video reports say the wreck began when a 60-year-old
        businessman from Fukushima driving a Ferrari F430 attempted to pass a
        Toyota Prius, but instead hit the guardrail.  That set off a chain
        reaction among the cars driving in a tight formation behind the lead
	...

2010/3/9-30 [Transportation/Car, Transportation/Car/Hybrid] UID:53749 Activity:nil

3/9     "Prius with stuck accelerator glides to safe stop"
        http://news.yahoo.com/s/ap/us_runaway_prius
        "After the car decelerated to about 50 mph, Sikes turned off the
        engine and coasted to a halt."  Hmm, then why didn't he turn off the
        engine when the car was going at 94mph?
	...

2009/11/23-12/2 [Transportation/Car/RoadHogs, Reference/RealEstate] UID:53540 Activity:moderate

 11/23  "Warming's impacts sped up, worsened since Kyoto"
        http://news.yahoo.com/s/ap/sci_climate_09_post_kyoto
        \_ what do you propose we average Joes do about climate warning?
           Oh really? Yeah, exactly.
           \_ Make life choices which reduce your carbon impact.  Communicate
              with your representatives that you consider this an important
	...

Cache (8192 bytes)

www.mixedpower.com/modules.php?name=News&file=article&sid=448Save Money on Gas Pollute the Air Less Reduce Foreign Oil Dependency Cool Technology Emit Less Climate-Changing CO2 Coolness Factor Emulate Bill Maher / Other Celebs No Hybrid For Me! General Hybrid News Particularly for those just getting their Prius i n the fall or winter months this must be one of the first questions and most common questions I've seen posted. I think I posted something simil ar myself when I first got my Prius in late Oct. Toyota, rightly, advertises the Prius with the EPA determined gas mileage of 51 highway, 55 combined, and 60 city. I think that as part of the ex citement of getting the car we all anticipate seeing those numbers 'righ t out of the box' when we pick up our car. In this article I'm going to try to clarify the reasons why. I'll also offer some suggestions on how mileage can be improved toward the end. THE EPA NUMBERS When the EPA tests cars and rates their gas mileage they don't actually d rive on a road. They use the exact same pattern of driving that's been used for every tested vehicle for o ver 20 years. And al though there are many stops built in there is nothing like the stop and go driving of a real city. Thus, many people in 'real' cities don't see anything like the city mpg numbers. The highway test portion is equally outdated with an average speed of 48m ph. For those of us who use the interstate transit system in the US and know that posted limits of 70mph are, in reality, minimum speeds with mo st vehicles in the 7580mph range this portion of the EPA test is equally unrealistic. To further exacerbate the issue of innaccuracy with 'real world driving' the EPA tests all the cars in a temperature and climate controlled build ing at 6886 degrees fahrenheit with a vehicle that is already warmed up (highway only, city portion is cold start) and A/C turned off. It measures exhaust CO2 to determine how much fuel was used. See How Vehicles Are Tested in detail at this link, complete with photos. Thus, for those of us with only a 51 0 mile commute we're unlikely to ever get the car into it's most efficie nt operation condition. Due to the battery power and the range of SOC of the battery, particularl y on the city portion of the test, much of the driving may be under batt ery power and a small portion of energy used is never measured by the EP A (as they have no means to do so) thus giving a slight higher MPG ratin g than is really possible. They say that the battery SOC must be at the same level at the beginning and end, but even so there is some innaccura cy in that readout. This becomes most no ticable in a high mpg vehicle like the Prius. The best way to think about this is to consider the Prius compared to ano ther vehicle. hardly even noticable at a fill up since it's only 25mpg less than before. It's the same 10% but it's relatively more due to the lower 'gallonage' of the Prius (that is uses less gas for distance traveled). OTHER FACTORS Especially early in the Prius ownership there are a number of other facto rs that come into play. Break in almost universally people notice an improvement in mileage at ab out the 50006000 mile mark. The first generation Prius owners and a few 2nd generation Prius owners who've passed the 20k mile mark also note a 'secondary break-in' period. It seems that the engine friction, wheel be arings and other moving parts 'loosen up' over that first 5k miles. Also , the High Voltage Nickel Metal Hydride (NiMH or HV) battery becomes mor e efficient over time. Technique/style/learning curve I firmly believe that the Prius driver int uitively or through trial and error improves his/her driving technique o ver time better take advantage of the most efficient modes of driving th eir car. With tim e one learns to accellerate the vehicle in the most efficient manner. He /she learns to anticipate stops and begin coasting or gliding to those s tops without wasting power to get there or putting undue stress on the f riction brakes. particularly in that range of temperatures where A/C use is not necessary but where air temperatures are in a range that is 'comfortable' to the car and HV battery. Almost everyone sees a drama tic improvement in fuel economy in those summer months and reports of ex ceeding the EPA numbers begin to frequently appear on the forums! A/C use there is a significant impact on mileage with A/C use. Unfortunat ely Toyota did not make it easy or intuitive to learn how to get to the 'vent' mode to allow circulation of outside air without engaging the act ual heating/cooling system. In cold weather I either don't use the AC at all since my car stays in the garage at home and usually remains warm e nought (with my coat on) that I don't have to use it, or I turn it on 'A uto A/C' at 65 degrees the lowest setting. That is almost always comfort able when I'm wearing a decent winter coat. If my wife/family are with m e I do need to increase that, but I still try to keep it below 70 degree s Likewise, in the summer, I either just use the 'vent' setting or set the temperture to something b/w 7881 degrees (depends on how much sunlig ht is shining directly into the vehicle as to what is comfortable enough ). Weight in vehicle Although most small articles won't make a major impact you don't wanna be carrying a bunch of unnecessary stuff in the car all the time. If you always have the car full with the spouse and 3 kids and all their necessities of life in the hatch it will impact your mileage. Tire and road rolling resistance The tire rolling resistance of the OEM G oodyear Integrity tires is very low. If under inflated, however, that re sistance increases creating a significant impact on gas mileage. Many of us have decided to use higher tire pressures than Toyota recommends to further improve fuel economy by a small amount and to improve tire wear, handling, and road hazard safety. Some argue that this causes an uncomf ortably rough ride and might be a safety issue. Whatever pressure you ch oose to use always be sure to keep the 2psi higher pressure in the front tires over the rear and to stay within the tire manufacture's maximimum rating (44psi for the Integrity). Other weather related issues Wind speed and direction have an impact, as does rain (see above), humidity, elevation and barometric pressure. Speed, braking, acceleration, and anticipatory driving The MFD's Energy a nd Consumption screens present a degree of feedback unprecedented in any other stock vehicle. It acutely increases our awareness of what is happ ening from moment to moment, every 5 minutes, and over time. This has affected the way I drive dramatically and many other Prius drive rs notice the same. I don' t floor it, but maybe depress the pedal 1/3rd way or so. Once I get over the 2530mph mark I begin trying to 'Deadband' on the energy screen all power is from Engine (ICE) to wheels with no arrows to or from the batte ry. This is the most efficient power phase as there are no losses from c onverting the energy to potential energy in the battery back to kinetic energy for the wheels. I've learned the timin g of the lights on my usual commute and can often see them far ahead and know if I can make it by maintaining my current speed or if it will cha nge before I get there. I watch the other traffic as well trying to anti cipate what they might do I think that kind of anticipation makes for a safer driver in addition to making it possible to drive more fuel effici ently. When I know there is a stop say 1/2 mile ahead but there is traff ic behind me I'll go into a "glide" mode. I take my foot completely off the accelerator for a second (you'll see just green arrows on the energy screen) then I very lightly depress it again to a 'no arrows' condition on the energy screen. That eliminates the 'drag' of the regenerative br aking that occurs with the foot completely off the pedal. If I need to m aintain a little more speed I'll press just enough to get the yellow arr ows of electric only power. Once I see that I must stop then I'll firmly , but not hard, brake to try to use just regenerative braking (no fricti on brakes). When possible I try to avoid coming to a complete stop with this anticipat...