Quote:
Originally Posted by ps2fixer
Yea, slight improvements in design in each item really adds up in the long run. I'm sure the areo is probably slightly better, the engines on their own probably are slightly better, besides the electronics being better and I'm pretty sure the newer electric motors are higher efficiency too. 1-3% here and there really adds up. I think the biggest gain is the battery tech though. Size doesn't matter an insane amount, it just needs to be big enough for worst case situations and whatever charge/discharge allowance they target for longevity of the battery. Pretty sure Lithium Ion is similar to the NiMh where keeping the charge below 100% and above 0% most likely around 60% is the most ideal for longevity.
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There have definitely been incremental improvements across the board, but I think the EPA's revised MPG labeling and the CAFE credits for A/C efficiency have really helped spur large changes in air conditioning system efficiency. And your Prius is largely responsible!
In 2008 the EPA revised their MPG testing in large part because American drivers weren't getting close to the advertised 60mpg city, 51mpg highway from their gen2 Prii.
Let me step back some and explain the EPA's dynometer mpg tests:
The city mpg test was created in 1972 and was based on rush hour traffic in 1972 Los Angeles. It involves a number of stops and starts with glacial acceleration and generally stays under 30mph except for 2 cycles up to a top speed of 56 mph (the rate of acceleration is equivalent to a 18 second 0-60 time). The overall average speed is 21mph:
The highway test was created in 1975 (1 year after the 55mph national speed limit) and was based on rural highway driving, not interstates. It simulates a 10 mile drive which averages 48mph, again with very slow acceleration (the initial 0-35mph takes about 30 seconds):
Few people drive like that, fewer still do so without air conditioning/heating, in exactly 75F windless weather, and fewer still on premium 93-octane ethanol-free gasoline. So in 1983 or 1984 the EPA crunched the numbers and decided to keep using the same tests (they were mandated for CAFE standards) but to lower the city mpg label by 10% and highway mpg label by 22% to more closely reflect what average drivers - those
not employed by the environmental protection agency - were achieving in the real world in the days of the 55mph speed limit.
These 1970s tests were the very same ones the Prius took in 2003-2004, achieving 66mpg city ("corrected" to 60mpg with the 1980s correction factor) and 62mpg highway (corrected down to 51 mpg with the 1980s correction factor). Many people were irate when they were getting 40-45mpg in the real world and the gen2 Prius was a very hot-seller so it attracted lots of (negative) attention. But the EPA (repeatedly) tested Prii and verified the window sticker. By law Toyota couldn't advertise anything other than the EPA mpg, even if they had wanted to be more conservative.
So for 2008 the EPA added 3 new tests. A high(er) speed test with a bit quicker acceleration:
A 95F outside temperature city test with the AC on, maximum fan (or 72F if equipped with automatic controls), recirculated air:
And finally the original city test, but this time performed in 20F outside temperatures.
In 2016, the EPA added a few new correction factors to try and lower mpg labels a bit more on hybrids to match what average drivers achieve.
Anyway, long story short is that before the 2008 EPA a/c mpg test automakers really didn't pay too much attention to the efficiency of AC systems. Why should they care if their customers used more gas as long as the system was cheap, reliable, and cooled the cabin quickly? But that test, along with the Obama administration's tougher CAFE standards (which offered credits for A/C improvements), helped focus their attention on a/c efficiency.