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Hybrid Tips Optimizing mileage

SylviaSylvia Posts: 1,636
edited March 21 in Toyota
Driving tips for getting the most mileage out of each tank of gas.
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Comments

  • motownusamotownusa Posts: 836
    I see complaint from some hybrid owners that they are not getting the advertised MPG from their cars. While others are getting better than the advertised MPG. How do you get the best possible MPG?
  • wwestwwest Posts: 10,706
    Is not the highest, but the best in comparison.

    As anyone can plainly see the Prius hybrid design is not optimized for hwy MPG. The Prius design is optimized for city slow, stop and go driving.

    So the advantage of the design can be primarily shown by comparing city MPG figures with other cars of equivalent weight and loading capability.

    The only real advantage the Prius design has is gained via recharging the batteries during braking or coastdown.

    At a constant cruise speed on a level roadbed the batteries are not really used except to accelerate/(re-)gain speed and generally must be recharged using petro. Using petro to recharge the batteries results in an over-all net loss and therefore the cruise MPG advantage is non-existant.

    If one were willing to disconnect the batteries and forego the "SuperCharging" supplied by the batteries in hwy use I have no doubt the Prius hwy MPG would improve substantially.
  • djasonwdjasonw Posts: 624
    I get 45-50 going 60-70 on the highway. Try doing that with a conventional 4 cyl car! What you say, makes absolutely no sense whatsoever!
  • midnightcowboymidnightcowboy Posts: 1,978
    Djasonw,

    I think you are misreading what Wwest is saying. Wwest is saying that recharging the batteries while crusing is not really needed, because they are not being used normally during cruising. However in the current HSD design even during highway cruising the MG1 generator is contiually turing and contiunally charging batteries, that for the most part are probably alreay fully charge. What Wwest is saying and I very much agree that the continual charging is not needed and that the Prius would get even better highway mileage if it could be disabled. However because of the very nature of the CVT planetary differential transmission design, MG1 can not be disabled.

    I never got the impression that Wwest was criticizing the mileage the Prius obtained or was he comparing it to other cars.

    Let's say you could disable the MG1 and were able to then obtain an EPA rating of 60/55 wouldn't that 4 mpg gain on the highway be better ?

    YMMV,
    MidCow
  • "At a constant cruise speed on a level roadbed the batteries are not really used except to accelerate/(re-)gain speed and generally must be recharged using petro"

    Why does HSD need to recharge if it can route the electricity straight to MG2? The battery is recharged sometimes to power A/C, stereo, etc...

    "If one were willing to disconnect the batteries and forego the "SuperCharging" supplied by the batteries in hwy use I have no doubt the Prius hwy MPG would improve substantially."

    Incorrect premise comes to the wrong conclusion.

    Dennis
  • "However because of the very nature of the CVT planetary differential transmission design, MG1 can not be disabled.

    The question is why would you want to? There is very little instances when MG1 should not be spinning. Most of the time MG1 needs to be spinning foward or backward to adjust optimal ICE output at a given speed. Stopping MG1 would mean ICE has to adjust RPM for a given speed, which would either reduce efficiency or power!

    Dennis
  • tempusvntempusvn Posts: 119
    Exactly.

    The MG spinning is part of the CVT-Like function of the planetary gearset.

    The way this is used to manage engine RPM/Load is one of the most mis-understood nuances of the HSD Design.

    Let me try to give a generic example, with made up numbers.

    The key is that the Atkinson Cycle engine is VERY efficient when it's in the right speed/load band, and less efficient when it's not.

    One of the big reasons for normal ICE inefficiency is the need for the engine to work in a broad RPM band. Using a CVT you can keep the engine in it's sweet spot longer, which is a good thing.

    So, the planetary gearset, using the MG, tries to keep the engine at it's prime speed/load point. That's cool, just like any CVT.

    The real key to the added HSD efficiency is, when the MG is doing this, it can ALSO make use of the extra energy.

    Made Up Example.

    Let's say the ICE is at 27% efficiency at 3000 RPM and 37% efficiency at 4000RPM.

    You could run it at 3000RPM, and get X mileage.

    But, with the MG in the equation, it can let the ICE run at 4000 RPM, and take off the extra energy in the form of generated electricity.

    The ICE can generate more energy than you need for immediate propulsion for the same fuel expenditure when it's running in the sweet spot, and the MG can recapture that extra efficiency for use later.

    If you couldn't do that, you would be forced to run the engine at a less efficient load.

    If need be, the MG can assist to 'spend' some of the energy it's accumulated then go back to generating.

    It's truely ingenious, and makes the best use of the Atkinson engine characteristics (extreme efficiency, but only in a narrow power band).

    That's one of the reasons it's also ideal for diesels, they have the same sort of power band tendencies that the Atkinson engines do.
  • midnightcowboymidnightcowboy Posts: 1,978
    Why, because the Honda IMA design provides much better highway mileage. The HSD system while giving excellent city mpg, does not do as well as it could on the highway. Every design has it benefits and it determents.

    If the HSD were designed so that the MG1 could be disabled when not needed then highway mpg would improve.

    Think about how the solenoid on a convetional ICE start works. It would be a very easy modification to provide solenod engagement/diengagement of MG1 and get the highway mileage estimate up to 55 mpg A FOUR(4) MPG IMPROVEMENT ;

    But then you would add another failure component to the HSD transmission .

    YMMV,

    MidCow

    P.S. _ I find it very interesting that such statements as "especially for those that don't have engineering and/or automotive educations" come from those that obviously don't have engineering, mathematical or automotive educations.

    P.S.S. - I appreciate your true "engineering" viewpoint.
  • djasonwdjasonw Posts: 624
    Perhaps I am confused but the electric motor is constantly called on during highway driving. If the car was continually charging I'd have FULL green. The last time I got full green was when I had to descend a HUGE hill and had to ride the brake a bit in the sharp turns leading to the bottom. If as he says that the engine is creating a charge that is not needed, I certainly am not seeing that when I look at the display.
  • "Why, because the Honda IMA design provides much better highway mileage."

    Based on what? Smaller and lighter HCH(1.3L) manual tranny has the same 51 MPG EPA highway as Prius(1.5L).

    Ever thought the other way around? Could it be that IMA is inefficient in the city? Could it be because Honda IMA(10kw) can only capture 1/5 regenerative energy of Prius(50KW)? Could it be that HCH does not take much advantage of electric superior efficiency at slow speed?

    "If the HSD were designed so that the MG1 could be disabled when not needed then highway mpg would improve."

    How can it be? What is your explanation? I'll give you a counter example. At 70mph, if you disable/stop MG1, the ICE has to spin 3,000 RPM instead of ICE 1,000 RPM with MG1 -6,500 RPM. You tell me if ICE 1,000 RPM is more efficient or at 3,000 RPM.

    Dennis
  • "At 70mph, if you disable/stop MG1, the ICE has to spin 3,000 RPM instead of ICE 1,000 RPM with MG1 -6,500 RPM. You tell me if ICE 1,000 RPM is more efficient or at 3,000 RPM."

    I didn't mean to contradict Tempusvn's point. Another possible case at 70mph is ICE at 5,000 RPM with MG1 7500 RPM. The point is that, MG1 can adjust to whatever RPM that is the most suitable for the ICE at any given instance. MG1 at 0 RPM(disabled) is just one out of 20,000(-10,000 to +10,000) different possibilities.

    Dennis
  • "Made Up Example.

    Let's say the ICE is at 27% efficiency at 3000 RPM and 37% efficiency at 4000RPM."


    In reality, Atkinson ICE efficient band is very wide, about 80% is near peak efficiency.

    image

    "That's one of the reasons it's also ideal for diesels, they have the same sort of power band tendencies that the Atkinson engines do."

    Diesel engines do have narrow RPM range but their torque curves are not very flat. For Atkinson flat torque, see below. Also, because diesel engines do not have spark plug, shut down/restart of heavier cylinder diesel ICE would be far more difficult. Another reason gasoline and electric synergize more than diesel with electric.

    image

    Dennis
  • "However in the current HSD design even during highway cruising the MG1 generator is contiually turing and contiunally charging batteries, that for the most part are probably alreay fully charge."

    Just needed to address that. It will never happen in Prius or other HSD cars. Overcharging the battery will damage it and shorten the life. As stated before, the electricity can also be routed to another motor and put it to work, instead of the battery.

    Dennis
  • quasar4quasar4 Posts: 110
    --Funny.....14 posts and not a single driving tip on maximizing fuel economy. Sorry to end the streak, but eh...

    --Tip #1: Anticipate!

    a) Redlights: I'll never understand people who race to the next stoplight only to sit there oblivious to the fact that the light has turned green. If you see a red light ahead, try coasting or timing it to keep up your momentum. The Prius coasts rather nicely.

    b) Heavy traffic: If I'm stuck crawling in heavy traffic, I prefer slow & steady as opposed to stop & go. People see a little daylight in the traffic and they punch the gas only to have to hit the brake again seconds later. Studies have shown that this only worsens the bottleneck by creating a lag effect that ripples down the line.

    c) Hills: If you see a hill coming up, accelerate before you get to the hill rather than when you're on the hill. I find this works for bicycles too :)

    d) Other Drivers: Don't tailgate. Otherwise you're letting the guy ahead of you dictate your driving style (not to mention your blood pressure). A buffer zone lets you speed up when it's most efficient for you to do so, or remain coasting at a constant speed while he slows down, makes a turn, fumbles with his cell phone, etc..

    Results...51 mpg on 5200 miles. Love that Prius!
  • djasonwdjasonw Posts: 624
    Great suggestions which I follow as well. What I find is that when allowing a gap (greater than a few car lengths) in between cars causes anger by folks who think you're leaving too much space. What happens? They fill the gap which causes you to have to slow down again. EVERY day I go to work (no kidding) there are three or four cars on the side of the road with a trooper because they had a minor pileup because they were EACH following too closely.
  • motownusamotownusa Posts: 836
    Thanks for the suggestion. Do you do much highway driving with your Prius at say 55 to 75 mph? What kind of mileage do you get on the highway. Seems like a lot of the people's highway MPG is lower than the EPA's estimate of 50 mpg.
  • ft1000ft1000 Posts: 4
    Maybee it's just my car but I do a fair amount of highway milage and I average between 52 and 55 MPG.

    I just got back from a trip to NYC, total round trip of 306 miles with 4 adults in the car. I set the cruise control at 65 and by the time I arrived at NY the display had 54.5 MPG.

    On the return I set the cruise control at 70 and the display at the end of the trip shows 53.2

    I have 8777 miles on the car and my mileage just gets better with every passing month.

    My record is from Harrisburg PA to Philadelphia where I got 57.8 MPG. My speed was between 65 and 70 but I did have some tail wind.

    It's my short trips that bring down my mileage. My average is 8777 miles and 180.9 gallons of gas for lifetime MPG of 48.518.
  • I heard that cruise control helps a lot also. You can practice dead-band acceleration, which is pretty much a proven technique as discussed in yahoo groups. It basically means, when you accelerate, avoid the arrow to and from the battery on the display screen. You want to avoid engine horsepower going into the battery instead of the wheels, especially during acceleration. You would rather charge the battery with regen-braking. Battery in Prius is a good thing but you loose about 17% of the energy when you get it back(83% efficient).

    Using battery as little as possible will also prolong the life of the battery since you are saving the recharge cycles.

    Dennis
  • quasar4quasar4 Posts: 110
    --Yup it's hard to keep a gap without some bonehead squeezing in to jockey for position. It's ironic that the aggressive driver hell-bent on getting to his destination in the least amount of time, actually causes the very traffic jams that slow him and everyone else down.
  • quasar4quasar4 Posts: 110
    --Most of my 5200 miles (guessing about 80%) are at highway speeds. Half of the miles were on a trip from the East Coast to the Midwest. Not sure why other people can't duplicate the 50 mpg number. On that trip I just set the cruise control on 70 and the car got an average of 50.3 mpg over 2000 miles (and that included driving through the Appalachian Mountains of PA). Other than that trip, most of my miles come from short trips to work (8 miles with 6 of them on the interstate). I'm sure my mileage would be much higher if I had a longer commute and more sub-highway speed driving. In those situations, I usually get 55-60 mpg.
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