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Optimally Timing ICE Activation

Discussion in 'Toyota Prius Plug-in' started by iRun26.2, Mar 23, 2012.

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  1. iRun26.2

    iRun26.2 New Member

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    My commute is about 22 miles (each way) and I always fully charge my PiP at home and at work before I leave. I have no choice but to always activate the ICE (switch from EV mode to HV mode) and burn some gas when driving in each direction.

    I do drive at slower city speeds at both ends of my journey (2 miles at each end) so there is more than enough EV reaiming such that I must use a lot of my EV when driving at 55 MPH.

    My question is: For what driving condition/circumstance would it be optimal to initiate my ICE's warm-up cycle (that, once started, can not be stopped until the warm-up period is complete)?

    1) Should it be right before going up a hill or would that not be optimal?
    2) How about turning it on (switching to HV mode) at one of the many stop lights on my journey (to me that would seem to waste the ICE power generated during the warm-up cycle)?

    Certainly there isn't too much to gain here... but I am always interested in finding ways to maximize my fuel efficiency.
  2. 9G-man

    9G-man Active Member

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    I think you need to drive the two miles at each end in EV mode,
    and the remainder in between in blended mode.
    As you are getting on the highway (i assume, or when that first two miles is complete) switch to HV mode to start the ICE warmup and then switch back EV. The hwy. portion will then be blended and use most all remaining EV range in the process.
    Sounds like an ideal situation to get stellar mileage, since you can charge on both ends.

    One of our aftermarket PHV members suggests getting the warmup out of the way early is the best approach. See #55 http://priuschat.com/forums/toyota-...nyone-filled-up-calculated-6.html#post1493761
  3. iRun26.2

    iRun26.2 New Member

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    I thought that blending only took place above 62MPH. That would mean very poor gas mileage (driving at 65 MPh, for example). I am sticking to 55 MPH in EV mode. I want to know when to turn on the ICE. Early doesn't make sense to me because the engine could get cold enough to turn on near the end of my trip when I want it to be in HV mode yet still only using the small bit of EV that is left.
  4. SageBrush

    SageBrush Senior Member

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    Interesting question, that will matter a lot more in cold weather. I can think of a couple related issues.

    1. Warm up the ICE only once
    2. Run the ICE at max efficiency
    3. Use as little petrol as possible during warm-up

    I am unfamiliar with the control logic in HV mode for the PiP, so I can only point to how to figure this out for yourself

    3. Bob Wilson and a few others learned that low ICE load during the warm-up phase was most efficient. Shoot for 1300 rpm on level ground, or warm up on a downhill run.

    2. When the ICE is running and warm, rpm is best at 1500 - 1900 rpm, or MAP (on a ScanGauge) as close to ambient as you can.

    1. The simplest approach is to EV from the start, and let HV kick in when the car says so. That way you are assured of a warm-up only once. If you need battery help to keep the ICE load low when in ICE warm-up, kick into HV a mile before the car does so by itself.

    Have fun, and good luck! :)
    1 person likes this.
  5. 9G-man

    9G-man Active Member

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    OK, then force it on later, but the point is, if YOU make it happen it can be done in a fuel efficient blended mode. If it just happens automatically as total EV range is exausted, it may not be so efficient.
    Blending takes place anytime the ICE is running and in EV mode, regardless of speed. Thus the suggestion to select HV mode (forcing the ICE to start) and immediately return to EV mode. The warmup would be blended. Climate and the need for heat will also play a role in this decision, and cold would dictate an early ICE start also.
    Did you read posts #55 and #59 in the link above?
  6. iRun26.2

    iRun26.2 New Member

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    I turn on the ICE by switching from EV to HV mode. I have not had any trouble (so far) in unintentionally activating the ICE. Since I have more EV than is needed at speeds around 20-30 mph, I choose to drive on EV (55 mph) on the rest of my route. In my normal day to day driving, I do not ever blend (except when my car automatically does it when I choose to be in HV mode).

    Certainly winter will change things but right now it is unusually warm in Minnesota. I will need heat and the EV system may also require heat to function.
  7. iRun26.2

    iRun26.2 New Member

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    Thank you so much for your post. You pretty much answered my question. It sounds like the best time for me to switch over from EV to HV mode (initiating the ICE warm up) is when I won't be demanding a lot of power from the engine. Maybe when I'm driving a constant speed and not expecting any stop lights. I will admit this is sort of counter intuitive (to me, at least) because I know the engine generally is more efficient when you demand a miserate amount of power from it. I guess that warm-up is different.

    One thing I've noticed when switching to HV mode for the first time is that the EV miles drops about 0.4 mile initially (ICE warning up). I think the car realizes that EV power is more efficient than ICE power during warm up. The car does seem to know that the EV miles it 'bowwors' must be returned (and they are eventually, sometimes with interest).

    I like turning on the ICE close to the time when I have 'just enoigh' EV power saved for the final slow section of my journey. This is sometimes not so easy to do! This has the advantage that my ICE will still be warm from the warmup and not turn on immediately when the EV miles hit '0' (I am free to drive slowly for a little bit longer on the full HV battery, as long as I don't accelerate very strongly, I can get an extra mile).

    If you run out of EV miles and the ICE has never been warmed up, your ICE will turn on immediately when EV distance = 0 (a source of anxiety if you hope to have a pure EV drive). With the ICE already warm, you can get just a bit more EV driving for free when EV miles = 0 (and I now exploit this extra battery power, further improving my gas mileage).
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