on hunkering

Discussion in 'Generation 1 Prius Discussion' started by ChapmanF, Dec 20, 2012.

  1. ChapmanF

    ChapmanF Senior Member

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    The first significant storm in my area, coming on a heavy travel weekend, made me curious to compare a couple ways of hunkering down in a Prius (assuming one may be stuck somewhere for a while but that the car otherwise functions).

    Tested in my driveway, temp about 2 C, wind gusty. Hunkering in READY mode with lights and most accessories off, the on-and-off cycling of the ICE seems to be driven chiefly by coolant temperature loss. The ICE will restart when the coolant drops below 60 C, then usually cycle off after raising the temp to 70 C. While the engine runs for this purpose it seems to consume about 0.25 gallons per hour as reported by the ScanGauge (actually around 0.31 at first, dropping to around 0.25 where it stays for a while, dropping further to around 0.2 for the last several seconds before shutting off, so I'm calling the average 0.25 without using any kind of data recorder to average it for real).

    At that rate, were it possible for the (nominally) 11.9-gallon tank to be completely filled and used, it would be good for something shy of 48 hours of ICE runtime. I'll go with 10 as maximum usable fuel gallons, and say 40 run hours.

    I compared two approaches to hunkering. One is the obvious one: just sit in READY with the heat on AUTO and temperature set to about the minimum. One complete cycle period was 7 minutes 43 seconds, with the ICE on for 4:22, giving a duty cycle of 57%. Nearly 3 days of hunkering might be possible that way.

    Second approach: READY mode, heat OFF, and a 12 volt, 40 watt heated blanket (Trillium Worldwide, bought at Menards). Under these weather conditions this was comfortable, and the cycle period was 13:42 with the ICE on for 2:24, a duty cycle of 18%, which could stretch the full tank to > 9 days (neglecting, of course, food, water, and any other human concerns).

    Of course I'm writing this on 12/20/2012, so either method would be more than adequate to hold out until the Mayan apocalypse....

    -Chap
     
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  2. youngnbald

    youngnbald Junior Member

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    Where I live, we are just getting the edge of the storm. Tonight I travel to Iowa where several inches of snow fell. This is my first snow to drive a Prius in. What are the opinions of others on how this car handles snow and ice?
    For example, I have a GMC Envoy that replaced my Ford Escape. The GMC is not fun in the snow! First problem is the computer refusing to let ME drive the truck. It senses a slide and applies the brakes to straighten out the vehicle! With experience, I knew I needed to give thottle to power out of my situation and the #$#%@ computer said no and even shut off my fuel to the engine, preventing me from putting power to the wheels!!!!!
    My Escape was the best, well balanced vehicle I have ever owned and drove in snow conditions!!! I always knew how the truck was going to handle and how I could control power slides. It was very sure footed and I loved how connected to the road I felt.
    I thought the weight of the Prius front end and battery in rear would give great traction and control. Not much snow fell here so I could not fully test the cars abilities in snow. How do others see this car verses other experiences?

    If I end up stranded in a ditch, your calculations will be going thru my head Chap!
     
  3. ChapmanF

    ChapmanF Senior Member

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    My experience for the most part has been good. It is nice that, with a light enough touch on the go pedal, you can apply as little torque as you want, controllable right down to zero rpm, without having to futz around with feathering the clutch, etc.

    I've had one instance of frustration so far (in 4½ years). I was stopped at an intersection with a slight rise to get onto the cross street, and it was topped in wet, very slippery ice, and there just wasn't any way to make the car move. In that situation the lightest touch was still enough to break traction, and then the spin limiter would cut the power to nothing. (Then it would cycle: spin, nothing, spin, nothing, spin, nothing ... useless.) I was reduced to backing down the slope and taking a running start.

    It's my understanding that the later model Prii replaced the primitive spin limiter on this model with more of a true traction control that is able to brake the slipping wheel, not just cut power. That would be an improvement. On a Gen 1 you just have to be aware of that one limitation. Its spin limiter is really there to make sure you don't overrev MG1, not so much to get you up icy hills.

    -Chap
     
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  4. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Chapman,

    You may have given a way to estimate the heat loss of our NHW11 by using the effect of UPS inverter load on engine cycle times. This may lead to better insights to engine compartment insulation than current processes.

    Bob Wilson
     
  5. ChapmanF

    ChapmanF Senior Member

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    Hey Bob,

    My immediate reaction is to think that so many variables would be confounded in there that I don't see how I've given a way to do that ... but if you do find a way to build on this to tease them apart I'll be a fascinated reader....

    Cheers,
    -Chap
     
  6. NinnJinn

    NinnJinn Member

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    Chap,

    Thanks for going through the trouble of doing all this research! I have often wondered about hunkering myself. I live in Southern Indiana and the Highway department around here doesn't usually get out unless the local distric state police post calls them out.

    I lived in upstate NY for a year and their road conditions at an inch or two an hour snow fall is comparable to our road conditions at 2-3inches of snow fall for the entire night/day

    I believe it was 2yrs ago, we had an awesome white Christmas here, they were closing roads/highways left and right.

    When it starts to hover around freezing, I never let my vehicles get below a half tank. With the prius, (my first full winter with it) and its guess gauge, According to the MDF (mpg and miles driven) I plan to never let it consume more than 4gallons without filling up.
     
  7. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Hi Chapman,

    What happened is you reminded me of these charts:
    [​IMG]
    Notice the no-load cycle time is 20 minutes with a traction battery load of ~0.75 A. But when I put on a 1 kW load, ~5 A, the cycle time goes to 40 minutes for 7 cycles, about 5.71 minutes (~5:43.) Now if the outside temperature is cold enough, I may see engine cycle times driven not just by traction battery SOC but also engine coolant temperature.

    So I'm thinking:
    • traction battery volts
    • traction battery current (see right-side Y-axis)
    • engine coolant temp
    • mass flow (for fuel consumption)
    • outside air temperature (may have to record manually, will see)
    • SOC
    We are in a cold-snap and a couple of hours after sundown or before sunrise or when directly under the high-pressure system, no wind. All cooling is a combination of radiant and convective and as long as the car is in a no-wind location, this heat loss should be driven by the relative engine coolant and outside air temperatures. Wiki has the non-linear formulas for both radiant and convective loss.

    So my thinking is:
    1. Drive home after sundown on a predicted, no-wind, very cold evening
      1. Remove radiator block (stock configuration)
    2. Instrument the car and begin recording with the inverter ON but no load
    3. After an hour, see if it is cold enough we are getting coolant triggered operation (62C in the past)
    4. Independent variables:
      • Add a measured AC loads to change the rate of engine ON operation
      • With windows down, add heater operation to change the rate of engine cool down and engine ON operation
    Another interesting experiment would be to measure the cool-down rate but it requires putting a charger on the 12V battery. After throughly warming the car, turn it off and put the car back in "IGN" mode. The OBD scanner will see the ECUs but the engine won't run and the 12V DC-to-DC converter will be off. To prevent running down the 12V battery, hook up a battery charger during the test.

    Bob Wilson
     
  8. John H

    John H Senior Member

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    do you carry a tailpipe extension for extended "hunkering" in the snow?
     
  9. 3prongpaul

    3prongpaul Hybrid Shop Owner, worked on 100's of Prius's

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    Last winter I was traveling through Wyoming during a snowstorm in a gen1. The highway patrol closed I-80 and made everyone turn off into a rest area. I had to stay in the car. I just set the climate control at 65, left car on and went to sleep. The gas engine cycled on/off as needed throughout the night and kept me (and the hybrid system) comfortable. Everyone else ran their vehicle pretty much all night to stay warm.

    The next day I noticed a couple MPG less driving with that tank of gas, but not too bad.

    If traveling in winter or major storms, it's wise to fill up when gas tank gets around 1/2 full. You never know when you will have to spend many hours in your car or gas stations will be closed because of power issues like after Sandy.
     
  10. ChapmanF

    ChapmanF Senior Member

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    You have reminded me, I should have mentioned that for my test, my grille curtain was in place.

    -Chap
     
  11. ChapmanF

    ChapmanF Senior Member

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    Good thinking ... that hadn't occurred to me. I guess it wouldn't have to be anything fancy or take up much space; parts stores usually sell some kind of extendible aluminized hose to replace old air-cleaner hot-air intakes.

    What's on other people's checklists for travel when the weather might be threatening? Driving long distances is such a non-problem most of the time that I've grown pretty cavalier about hopping in the car for a 300-mile trip with not much more than the shirt on my back. For the winter I've thrown an old down coat and snow pants in the back seat to just live there until spring. Sometimes I've got something to munch on, and sometimes it occurs to me to include water. I should probably be consistently more provident about that.

    I have at last gotten around to ordering some WAG bags, which I've been meaning to get for several years, ever since a frustrating incident that had nothing to do with weather. Having lived in Michigan and Indiana, I am used to being able to stop in pretty much any filling station or convenience store and find facilities I can use, and I kind of take that for granted, but there might be some state requirement behind it and, if so, Virginia seems not to have that requirement. I was traveling there and was turned away by something like half a dozen filling stations, etc., till I was finally directed to a Wal-Mart about 40 miles past where I really needed to stop. (Once inside the Wal-Mart it was still a hike to find the facilities, which I reached with seconds to spare. A happy ending, but a bad experience overall.)

    -Chap
     
  12. bwilson4web

    bwilson4web BMW i3 and Model 3

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    Just a couple of thoughts:
    • Fill-up on any predicted severe weather - we had 4.25 days without power but I only had half a tank in the NHW11 providing emergency power. Had I filled up, we would have easily covered the whole interval. It only takes a few minutes but having a full tank means you have options.
    • Carry a roll to TP/paper towels - never know when you'll need it. Open passenger side doors and only one side is exposed to view.
    • A bottle of 'cheap' water is always a good idea and a hotel soap - never know when you'll need it.
    • There is a 100-to-1 reduction in carbon monoxide by working catalytic converters and the car raises an error code if it is not work. Mine are working so I don't worry about having a 'hose' (famous last words?)
    Bob Wilson
     
  13. ChapmanF

    ChapmanF Senior Member

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    The wattage of that blanket seems to be in the ballpark also with the figures I've been encountering while looking up heated-seat retrofits, so I assume an ordinary blanket and a heated seat would work about as well, too.

    -Chap
     
  14. ChapmanF

    ChapmanF Senior Member

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    Ok, four winters since I wrote that, the 40 watt blanket lately didn't seem as warm as I remembered. A moment with a seam ripper and flipping it inside out revealed one break in its (single) zigzaggy strand of heat wire, so no heat for me. Disappointing, as I had always tried to handle it pretty gently, roll not fold, etc.

    Won't try to repair, as I never liked the fabric much, anyway. Left blue fuzz all over my Gen 1 upholstery. (My Gen 3 seats aren't cloth and don't attract it as much, but still....)

    Open to suggestions for other 12 volt blankets....

    -Chap