Four Prius Questions

Discussion in 'Gen 2 Prius Technical Discussion' started by duperdo, Sep 13, 2008.

  1. duperdo

    duperdo New Member

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    1) How efficient is the regen function ? If it took 1/100 of an ounce of gas to go from 0 to 60 MPH what percentage of that energy is captured when I coast back down to 0 MPH ? Suppose I slowed to 0 MPH by braking, what percentage of that 1/100th of an ounce of gas was converted into electrical energy ?

    2) How efficient is using cruise control ? Seems cruise accelerates into standing traffic and red lights as well as going way too hard on the gas when I would have been more gentle if I was driving manually ...

    3) When set on the "Energy Monitor" screen, I noticed that I'm leaking electric energy and engaging the electric motor when I'm sitting at a dead stop waiting for a green light. Seems like this happens unless I step hard on the brake pedal. Stopping the Prius is not enough - I gotta stomp on the brake to shut down the system. Is it this way for all of us ?

    4) When night driving I've got a bright bar of reflection from off the top of the dash right in a major portion of the prime viewing area of the windshield. It is coming from the light that illuminates the speedometer cluster. Before I take two of those self-adhesive velcro circles and a strip of black felt and glue 'em on top of the dash, I wanted to ask does anyone else have this problem ? How do you guys solve it ?

    Thanks
     
  2. 9G-man

    9G-man Senior Member

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    It's a conversion of energy, so there are losses, but something is better than nothing right? In fact, It's very efficient, at tuning kinetic energy into stored electrical power in the battery. But its true benefit/efficiency is gained only if it is necessary to slow or stop. The the conversion is no where near as efficient as good driving techniques that don't waste gas by unnecessary braking and having to make that conversion to begin with. Learn to glide. Anticipate stops, slowdowns, etc.

    If steady speed travel (ie: Interstate) is the goal, the CC is quite effective, and efficient. Far better than a person. At moderate speeds, it even exploits the glide and warp stealth capabilities of the the Prius better than only the most adept prius driver could duplicate. 60 MPH = 60 MPG with the CC on. Additionally, the CC in the Prius is smoother and better than any I have experienced. Otherwise, for variable speed routine driving, learn how to manipulate the Prius' fuel saving characteristics with your right foot.

    The prius is designed to simulate a normal cars "creep" when sitting still and you let off the brake. So when you are stopped, simply place just a little more pressure on the brake pedal to inhibit this. No need to stomp. You are really overstating the characteristic.

    Simply turn down the brightness of the speed display. If it's reflecting off your windshield, it's too bright. The rotary switch left of steering wheel will do it. Instrumentation brightness should be turned down to the minimum necessary to read the display when intentionally gazed upon, so as not to cause any pupil dialation, distraction or impairment of overall outside vision. Most people have there displays turned up way too bright in any car.
    Sounds like you really enjoy your new car. Welcome.
     
  3. silver-machine

    silver-machine New Member

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    I'll have a go

    1:its not efficient at all - the energy that is recovered is what would have heated your brake discs up as you braked, actually the enrgy is equivalent to what electricity would have required to heat the brake discs up. Most petrol fuel goes into overcoming the rolling resistance of the tyres and there is no way of getting it back.
    2. The question really is are you more intelligent than a 25pence electronic chip? Of course cruise control is less efficient than a thinking drivr. It just tries to speed the car to set speed assoon as it can.
    3. yep its the same for all. All automatics have a slight forward push when stationary, its just that in the prius the energy monitor shows you, and if you press on the brake harder it stops- which is more efficient than a normal automatic transmission.
    4. yes annoying isnt it.
     
  4. donee

    donee New Member

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    Hi duperdo,

    The regeneration is actually about what an engineer would expect at about 80 percent. This is from the wheels to the battery only.

    Purely electric accelleration efficiency, from battery to the wheels is poor however, only about 60 percent. As the car is a hybrid, not an electric car. In a purely electric car, all the eletrical stuff would be twice the power rating they are in the Prius. So the accelleration efficiency in an electric car , with a lithium battery, this efficiency would be up above 85 percent.

    The overall efficiency of Prius reuse(accellerartion) is down under 50 percent (.80 times .60 ). Check out My 2004 Toyota Prius . On that site there are measurements made by Atilla Vass, with which some data reduction you can arrive at actual values.

    If one uses the regenerated electricity for other than accelleration, the advantage is better. For AC usage, or for stealthing along at the same speed in electric mode, the efficiency of resuse is probably better than 70 percent.
     
  5. donee

    donee New Member

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    Hi again,

    On question 3, yes, you need to hold the brake down securely to cut the electric drive. That is just the way it is.
     
  6. donee

    donee New Member

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    Hi Again,

    On question 4, this has been figured out. The reflection is off the dipping flat surface in front of the speedometer cluster. You can squelch it by placing a vertical piece in front of the spedometer cluster. It should not be so tall as to block vision of the cluster. Its there to prevent light coming out of the cluster from reflection off the dipping portion, and then up to the wind shield, periscope style. I used 1/2 by 3/4 inch by 6 inch piece of black polyurethane foam about 1/4 the eay down the dipping flat section. I glued to the dash with double stick tape. This was foam from a discarded piece of foam floor mat. I used the soft foam so in case it came loose it would not be a hazard.
     
  7. aaf709

    aaf709 Ravenpaw of ThunderClan

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    For me, I've gotten better MPG on the freeway when I have cruise control on. With others it's less. Partly it has to do with the traffic flow and the road (in terms of hills)

    I had the same problem and solved it basically like you described, although I used a thin piece of wood as it won't sag after a time.

    [​IMG]
     
  8. jdenenberg

    jdenenberg EE Professor

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    Actually, the regeneration function in a Prius manages to capture about half of the energy that would have heated up the brakes. This is better than not doing regeneration. Most of the lost 50% is in the relatively inefficient charging of the NiMh battery (a super capacitor would do this a little more efficiently).

    JeffD
     
  9. Dozzer

    Dozzer Prius Noob

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    It's easier to just use your finger and press the "P" button.
     
  10. tedmarshall

    tedmarshall New Member

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    On my '07, if I hold down the break just hard enough to keep the car from moving, it often shows the energy flow from the battery to the motor to the wheels, even though the car isn't moving. Pressing harder kills the flow.

    I assume this is what the OP is referring to and I do assume this is normal.

    I feel no difference in the car (other than the pressure on the break) so I assume that this energy flow is actually non-existent and id just a result of the MFD programming.
     
  11. Dozzer

    Dozzer Prius Noob

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    The energy flow is the result of the "hill hold" function of the automatic gear system... with the brake slightly on it assumes it's on a hill and being "held back" by gravity.. so it applies a little power to prevent roll back.

    It's easier to press "P" and park it.
     
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