49mpg for the Plug-in Prius seems low!

Considering it takes 3 hours to charge the pack from 120V, or 1.5 hours to charge from 240V, you can see that the pack will not be recharged by your drive on the highway, fully.

 

The EPA test is one scenario, it never goes over 62 MPH, it never accelerates hard, it HAS to be achievable by all cars to be valid. The PIP has not undergone that test yet, Toyota wisely is not over promising what it will do.

In time we will see a window sticker, until then it is not really a car, it is a promise. You cannot drive a promise.

I was in the computer end of the gold mining business. We always published the most conservative of our estimates, as once you over estimate your gold reserves even once, you have no credibility in the gold business. Sadly that does not seem to be a rule in the car business.

 

Besides the charge time problem that mitch672 is mentioning, I think the OP fails to realize that the non-PHV Prius is EPA rated at 50 mpg combined (or ~60.0475211 miles per Imperial gallon).

From http://priuschat.com/forums/toyota-prius-phv-plug-in/97992-2012-prius-plug-in-product-info-pdf.html, Toyota is claiming 49 mpg (58.85 miles per Imperial gallon in) in hybrid mode. Energy isn't free and the PHV Prius weighs 123 pounds more as well. It seems odd to expect that a heavier car would somehow have "enhancement of mpg after the initial mains charge had been used" given that presumably more energy would/could be sent to the battery during that highway drive than on a regular Prius.

Also, from http://www.fueleconomy.gov/feg/fe_test_schedules.shtml, none of the test cycles are particularly long (back to the charge time problem again). (More info about the EPA tests at http://priuschat.com/forums/other-c...uth-about-epa-city-highway-mpg-estimates.html.)

 

no, but he assumes it will be automagically charged while driving on highway... it wont... just like regular prius wont get full bars until you go down the hill.

 

The difference is most likely in rounding error and YMMV. 123lbs is about the weight of my gf+her purse I'm not sure if I need to estimate the extra weight gasoline difference.

Better regen could give you better city mileage if it was implemented. Likely the number means 48 city/50/highway/49 combined.

 

well, he says he gets regen during highway driving, which isn't that surprising (I've seen this happen on my parents Priuses myself…if the optimal engine RPM provides more power than needed, the excess is sent off to recharge the battery, makes sense to me).

 

It might take a very large MG2 to generate enough voltage and amperage to recharge 100%. Still, if you can't charge the HV battery to at least 50% - 75% while doing a 170 mile drive thats pretty sad. I'm sure there has to be a trade off somewhere though between weight and efficiency.

 

Its a Prius, not a Volt. Even the "Volt" Forced charge mode won't run for long. Its not efficient to charge the battery from burning fuel, and it's not the goal of the PiP either. Quite the opposite, actually.

 

The PIP is heavier, so when it is in hybrid mode, this is likely to be significant in explaining the 2% difference between the PIP and O.P. (original Prius) mileage.

However, Li-Ion charging and discharging efficiency is greater than NiMH efficiency. Since in my everday driving I inevitably recharge the battery through regenerative braking, I should have a greater amount of recaptured energy available simply through this greater efficiency, which should offset gasoline usage.

In addition, occasionally I fill up the O.P. NiMH battery to its 80% SOC limit (my commute is very hilly). Since the Li-Ion batteries are larger, I should in essence be able to fill it up higher and thus reducing gasoline usage.

Finally, the LiON batteries ought to be able to charge and discharge at a much greater power than the NiMH battery. This means that some of the hard braking that engages in the friction brakes in the O.P. ought to instead charge the battery in the PIP.

Altogether I think the final three points that I have describe enable more energy to be recaptured via regenerative braking and enhance mileage greater than 50 mpg for those that can take advantage of it.

Steady-state highway driving ought to favor the O.P. over the PIP.

 

Except that people who use heavy braking a lot are likely not to have been getting EPA mileage. More braking means more acceleration means lower mileage. Hypermilers used to driving without brakes aren't going to see much benefit.

The advantage of lithium will be less about beating the EPA and more about getting closer to it.

It's simple: extra weight means more fuel used during acceleration. Bad thing.

Forget the lithium, more interesting for those seeking higher mileage is the higher true glide speed. Anyone on undulating terrain or doing pulse and glide should be happy to see that.

 

True.

However, there is lots of confusion over the "all-electric range" estimates. Toyota correctly footnotes in at least some of their media materials that the "15 mile" electric range estimate is based on the European test cycle (NEDC). However, many people misleadingly compare this to the published EPA 35 mile electric range of the Volt and the 73 mile range of the Leaf.

The Volt and the Leaf have electric ranges of 52 and 109 miles under the European test cycle. If you correlate these electric range estimates you find the European numbers are both about 48% higher than the EPA numbers.

The Prius Plug-in electric range estimate is actually listed as 23km or 14.3 miles. Assuming the above correlation is valid for the Prius, the resulting equivalent EPA electric range estimate for the Prius Plug-in would be 10 miles.

 

I disagree, even those that try to get good mileage (me for instance) end up using the brakes a lot due to a variety of factors.

If I hit the SOC wall on a long descent, there's nothing that can be done and engine braking will occur, wasting energy that could otherwise be recaptured.

I have multiple hills with red lights at the bottom. The hills are so steep you have to use the friction brakes to maintain a speed of 20-30 mph.

Stupidly designed offramps that force you to brake heavily (multiple along 605, 10, 110, 60 fwys for instance)

For those who use the brakes a lot, even due to bad habit, I say that the PIP will show a significant increase on the mileage that they would achieve in the O.P. (original Prius)

 

The extra battery capacity could be useful for longer glides that slowly drain power. For example, on my work to home commute I have a long downhill section of freeway with 3 humps (the road goes downhill then back up then back down). During this section of road I try to glide as long as possible but inevitability my SOC hits 57% and the engine kicks in and mpg drops from 9999 to between 150 and 330. I would think that the increased battery capacity would allow me to continue gliding for a longer period before the engine kicks in.

 

How high are those hills ? On a 500' descent I get about 250 wh in Leaf. Enough for 1 mile.

BTW, if you charge your battery to full, you won't have much regen until you deplete the battery. So, if the descent is close to your home (like it is for me) - not much regen (if I charge to 100%).

 

I could be wrong, but I do not think there are any hills in the EPA cycle. However much they may help or hurt your real world commutes, they will not aid the PIP in the EPA testing.

 

I descend on the order of 300 feet in a distance of 1/3 of a mile. Then I ascend back up 400 feet, down 300 ft, up 150 ft, down 400 ft before getting to the freeway where I can burn off charge. (these are rough guesses)

Imagine this scenario, which is where a Leaf, Volt or PIP would excel:

Start at 1000 feet, descend to 700 with a red light at the bottom. You're basically regen'ing down to control speed, then you hit the brakes to come to a stop.

Then ascend back up to 1100 feet. The speed limit is 45 mph. It's so steep that it's not feasible to burn off charge because that would limit you to about 20 kW of power in a Prius. At that power you'd be limping up at 10 mph and there are people behind you. Keeping the engine on in eco mode makes you limp up at 20-25 mph. To really get up you have to be in the power band or beyond. In other words, you have to keep your foot down.

Finally you crest the hill at around 40 mph (and people are annoyed you aren't 5 mph faster) and you start to descend to a trough where there is another red light. Basically you have to ride the brakes down to a stop again.

If you repeat this process of regen'ing downhill and burning gasoline uphill, you basically have a recipe to fill up the HV battery.

Sometimes you can glide downhill and swing past lights and crawl slower uphill when no one is around you and you aren't braking as much. If I crest the uphills around 30 mph I can take the downhills around 50-60 mph without using too much brakes and then swing back up again under much reduced ICE loads because I slow down on the way back up.

Where I can't optimize things too much is when a red light is at the bottom, or worse when a light turns red at the bottom just before I can get through the intersection. Also when people are on your tail, you can't burn off charge fast enough.

According to Scanguage, when there is high SOC, the Prius will consume 15-20 amps (3 to 4 kW) from the HV battery when you have the ICE on. That power draw is actually not that much from the battery.

In an EV or Plug-In Hybrid, you have much more power to ascend the hill using the excess charge instead of using gasoline. In the PIP, I'm thinking you could perhaps ascend a mild hill using MG2 alone (though I think in the PIP, the ICE will still have to assist a very steep uphill). Still with much more capacity, in my case it won't really fill up so I don't have the impetus to burn it off in a quick manner.

 

Your assuming the charge depletion stops while the car is using the ICE uphill.

I think what you'll find instead is blended operation where the battery depletes at full rate but its not enough power so the ICE comes on to supplement, not replace it.

The charge will build going down and drain going up but with the losses you'll also lose petrol on the way up. No net gain to SoC unless there is a significant net elevation drop beginning to end.

 

No doubt you are correct (I think I mentioned that somewhere in my post).

In a regular Prius you have a small battery capacity to work with, in a repeated steep uphill and downhill you will charge the battery to its limit unless you work to deplete the battery along the way. When someone is behind you (riding your tail), you can not discharge the battery quickly enough because the Prius only drains it at a rate of 3-4 kW blended with the ICE. To not only ascend but accelerate uphill will require the ICE to be on no matter what.

This is again where an EV would help tremendously.

PS this assumes you have red lights at the bottom of descents.

 

Don't confuse braking regeneration with ordinary recharging from the engine. The former recaptures energy that would otherwise be lost to friction brakes. The later requires the burning of extra fuel, defeating the purpose of pluging in.

When cruising at steady speed on a level highway, there is no braking regeneration, only recharge from the engine.

No it would be worse, due to the extra lossy energy conversions compared to the 2010 Prius.