Question on PRIUS Highway MPG

<div class='quotetop'>QUOTE(azguy @ Dec 12 2006, 01:48 PM) [snapback]361006[/snapback]</div>

I coast down hills on the highway, I apply my brakes sometimes on the highway, I have to stop and go sometimes on the highway. I think if you were to drive 55mph on the highway in the Prius you could achieve 51mpg easily. I drove 70-75mph and got 43.5mph according to the MFD.

The electric motor does assist the ICE so that will increase your MPG as well.

Dave

 

<div class='quotetop'>QUOTE(DaveLeePrius @ Dec 12 2006, 02:54 PM) [snapback]361010[/snapback]</div>

Yeah. When driving 80mph I was getting 44 mpg. Driving 65 I got about 55-60. In the city, I get 44.

 

<div class='quotetop'>QUOTE(azguy @ Dec 12 2006, 01:48 PM) [snapback]361006[/snapback]</div>

On the highway none of this applies? Only if roads are perfectly level. Going downhill, the battery does recover some charge. Also, the battery/motor also acts as a sort of supercharger when you need extra power, too, for example, to pass other cars. I don't know how much the weight of the battery adds, but I do know that even at highway speeds, the ICE is not continuously running.

 

<div class='quotetop'>QUOTE(azguy @ Dec 12 2006, 10:48 AM) [snapback]361006[/snapback]</div>

Take a look at the EPA Highway Fuel Economy Driving Schedule [once on that page click on the link for "Appendix I to Part 600—Highway Fuel Economy Driving Schedule (Applicable to 1978 and Later Model Year Automobiles)"]. I doubt that it resembles anything even close to your typical highway driving. The test lasts under 12.5 minutes with a top speed of approximately 60 MPH. Don't forget to take into consideration that the cars are pre-warmed and that air conditioning and other power robbing accessories are off during the test cycle.



On www.fueleconomy.gov the test is described as follows:

 

<div class='quotetop'>QUOTE(azguy @ Dec 12 2006, 01:48 PM) [snapback]361006[/snapback]</div>

I once drove from Saratoga to Fremont (CA), a 20 mile trip (elevation from 50ft to 300ft) maintaining 70-75mpg (very carefully) all the way (night-time, minimum traffic), I got 50+mpg. No lie. If you drive at 65mph or lower, it gets even better. Prius is efficient even on highway because
- when you let go of the gas pedal (downhill or not), the battery is recharged (say to keep distance from the vehicle in front of you) The recharged battery is used by Electric Motor to help maintain highway speed.
- extra weight (hybrid system) is a major factor in acceleration, but less so in maintaining highway speed (wind drag is). Prius has 0.26 Cd. Very minimum drag coeeficient. i.e. you won't see much impact in mpg whether you drive alone or load your prius with 4 persons. The impact is probably about 2mpg. This is assuming you "maintain" the highway speed.
- Atkinson cycle ICE is more efficient in hybrid system than typical Otto ICE of the same displacement.

If you put a regular gas 1.5L engine into the Prius engine bay, you probably would gets 40-45mpg instead of 51mpg on highways. That is the best of my guess.

 

<div class='quotetop'>QUOTE(azguy @ Dec 12 2006, 04:08 PM) [snapback]361019[/snapback]</div>

Well,

Ever taken a look at all the clutches and gears in a regular car with an automatic transmission? The Toyota HSD reduces that complexity dramatically. There is one planteary gear set in the system, with the generator directly bonded to the sun gear, and the motor directly bonded to the ring gear. The engine drives the planet carrier gear. That is it. All the mode switching is done by how the controller tells the power electronics to act.

Rather than having ATF going around in circles in a torque converter, the car has electricty going around in circles from the generator to the motor to do the torque matching.

The losses are similar. And with electronics, the losses will be improved on in time. The physics of hydraulic fluid dynmanics have been well researched for years.

The HSD system seems complicated because its diagramed in a complicated fashion. If the detail in a modern automatic transmission was laid out for you, rather than as its typically drawn a a single block in a diagram, the advantage would be apparent. Its because the motor and generator have multifunctions in the HSD (the meaing of Synergy in Hybrid Synergy Drive), that its diagrammed the way it is, soas to understand what each thing is doing, in each vehicle mode.

Now to your question. Yes, flat and level on a highway, you do not need all the hybrid stuff. Indeed, one really only needs sometihg like a GM Sunracer (the car that went flat and level at 55 mph across Australian desert with no power but the sun). But a GM Sunracer would not be a practical personal car.

The rest of us here live where the roads are not flat and level, and where there is other traffic. Everytime somebody drives a Prius up a hill and down the backside, is a win for the hybrid concept. In a traditional car that energy to climb the hill is lost forever. In the hybrid, some of it is recovered, and some of what is recovered is put to good use.

And a Hybrid that reduces engine size reduces pumping losses as the engine throttle is wider open more of the time, over a gasoline engine vehicle. Cruising on the highway is no different. Although, a 1 liter engine would probably do even beter on the 55 mph flat highway. But then the Prius has the Atkinson engine, which was tested at Argonne National Labs to have about twice the efficiency at 12.5 hp output (55 mph cruising power) than anything else gasoline fueled, of the same displacement. Yes, that is right, that 1.9 liter engine in my old Saturn SL2 is only about 13 percent efficient at 12.5 hp. Which is why I never matched the EPA combined fuel economy in it, but I do in my Prius all summer long (and lord knows I can't drive 55!).

Diesels are the only thing competitive in efficiency. They have almost flat partial power efficiency responses, as there is no throttle on a Diesel engine. Toyota did not pick Diesels, due to the polution issues. The Diesel polution issues may be worked out, but probably at $1500 markup for the Diesel, verus $2000 for the hybrid. And the Hybrid still recovers braking (and do not require frequent brake service consequently) and downhill energies the Diesel does not.

Turbo Diesels in the desert probably are a good idea though. A Turbo Diesel with a manual transmission is hard to beat on a EPA test, which is similar to the 55 mph flat highway. The Turbo Charger recovers what would be wasted exhaust energy. At a constant speed, it has no rotational energy variation, so its efficient. Diesels are torquey, so even though they are made of cast iron, a smaller one can accellerate a car well, weighing in similar to the Prius engine and motors for the same accelleration. I beleive I heard that the latest Turbo Diesels are 40 % efficient, versus the 25 to 35 % efficiency range of the Atkinson engine in the Prius. And, you do not have to worry about the Diesel not starting on a cold morning in the Desert, as it only gets down to about 25 F worse case. But save up some of the fuel savings for the Turbo job between 75 and 100 K miles.

If a Desert climate could support 200 million people spread out in a minimul density hexagonal mesh, man-o-man would VW have something. But, no, the majority of people do not live in the Desert, because of the limited natural resources available. And that means there are hills where the rivers cut through, and where lakes are , and ocean coasts, and mountains. And there are conglomerations of people where there are natural advatanges to people locating. Which means traffic. Which means the Hybrid Car is better where the most of the people are.

 

<div class='quotetop'>QUOTE(azguy @ Dec 12 2006, 10:48 AM) [snapback]361006[/snapback]</div>

What exactly does the 2006 <strike>option</strike> package #9 contain?

 

<div class='quotetop'>QUOTE(ceric @ Dec 12 2006, 06:59 PM) [snapback]361220[/snapback]</div>

I've driven from NC to IN and back, and averaged 47. Given my foot, I was more than delighted. In my day to day commute, with some highway, I see in the low to mid 50s depending on weather.

 

I generally get around 50 mpg on an extended summer highway trip. Sometimes it's a bit higher, but then I generally assume I had a tailwind. This includes trips I've taken to the mountains of British Columbia. My experience is the EPA highway figure is realistic, as long as you're not driving 75 mph.

It's the city EPA figure I seldom match in my real-world driving.

 

<div class='quotetop'>QUOTE(daniel @ Dec 13 2006, 07:00 PM) [snapback]361916[/snapback]</div>

Driving on the Long Island Expressway when traffic is light, cruise set to ~65, I consistantly see the yellow bars marching accross at just above 50 MPG. This is after about a 25 - 30 minute warm-up period. I can see easily getting 55+ MPG at 55MPH ( who would want to drive at 55?)

 

<div class='quotetop'>QUOTE(syclone @ Dec 13 2006, 05:46 PM) [snapback]361966[/snapback]</div>

It's a nice, relaxed, and safe speed. But I generally get around 50 mpg at 65 mph. At 75 it goes down considerably. Wind resistance, and all that.

 

<div class='quotetop'>QUOTE(daniel @ Dec 13 2006, 10:39 PM) [snapback]362023[/snapback]</div>

AMEN to that !!!!

 

<div class='quotetop'>QUOTE(daniel @ Dec 13 2006, 09:00 PM) [snapback]361916[/snapback]</div>

Hi Daniel,

That is my experience as well, in the city mileage. But a funny thing, in the combined I get right at the EPA, maybe a little better in summer weather. And the highway portion of the trip is where worse than 50 mpg happens. So, that means my city portion must be well up there, close to the EPA 61.

Now if I just drive city route, its more like right at 50 mpg for a long trip, and 35 to 50 for shorter trips. Of course, a long city trip is oximoronic, we almost always jump on the highway if we have more than 10 miles to go.

Wierd!

I think it has to do with the warming, and rewarming cycling. With the highway leg, the car stays warm enough during the final 2 miles city portion to get very good mileage. And also, during the city driving at strat up, the engine is being used in pulse and glide while warming up.

So, the "city" and "highway" really is not right. Its "city after highway", versus "city" versus "highway after city" that seems to be concsistant and match the EPA. That is, the "combined" is true to EPA, but not the city only, or the highway only. I believe the EPA test is in a "warmed up" state. That may explain it.

 

<div class='quotetop'>QUOTE(donee @ Dec 15 2006, 02:31 AM) [snapback]362213[/snapback]</div>

The city EPA test is done after cooled down over night, and the highway test is done after warmed up.
http://www.fueleconomy.org/feg/fe_test_schedules.shtml

Ken@Japan

 

[attachmentid=5944][attachmentid=5943][attachmentid=5942]<div class='quotetop'>QUOTE(daniel @ Dec 13 2006, 07:00 PM) [snapback]361916[/snapback]</div>

Daniel,

Is your city driving, heavy stop and go or just non-highway driving, when I drive around town my mileage is quite good especially in the summer, but I live in a small town setting in central Maine, where the "big" city nearby (Bangor) only has a population of about 30-40K. Keep in mind that the "city" EPA figure does not reflect real world city driving like one would see in Boston or New York City (the only two big cities I have driven in), the city test is probably more like small town suburban driving. Pulse and glide, if you have the patience to try it makes a big difference (my MPG went up by about 10 mpg or more in the summer). Note that I started trying the pulse an glide technique around the middle of May 2006, so half of that month is pulse and glide. Compare the mileage of June to Oct 2006 with similar months from 2005 and 2004. See attached chart.

Dennis