Peak engine efficiency curve and hill climbing

Discussion in 'Gen 2 Prius Fuel Economy' started by SFO, Jan 19, 2018.

  1. SFO

    SFO Senior Member

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    We have various grades of different lengths on the west coast, not all of them are a straight shot up and sometimes you need to slow down to take a tight corner or curve and then speed up again.

    Before the start of a hill I usually use cruise control to obtain the safest speed legally possible, once climbing the hill the vehicle will adjust to a higher RPM in an attempt to maintain that set speed and this is where I use the cruise control lever (listen for rpm increase, push CC lever down once, repeat) to slow the set speed down in an attempt to keep the engine from racing into the higher RPM range. This mostly works and depending on the hill doesn't slow the vehicle all that much below the speed limit, and by looking at the live MPG one the MFD there could be some fuel savings happening.

    I've read about tips which may only apply to lower speeds (thanks @ken1784 @ post link) :
    • Best briskly acceleration - No arrow to and from HV battery.
    • Good briskly acceleration - Green arrow to HV battery.
    • Bad briskly acceleration - Yellow arrow from HV battery.
    Awhile back while searching I ran across a thread that talked about some of this RPM stuff in relation to hills, and mentioned a small RPM range, and now I can't find it. Thought this range was around 2400 to 2700 RPM, but have also read about ranges being slightly higher and lower.

    Is there an optimal RPM engine efficiency curve that can be used for hill climbing?
     
  2. valde3

    valde3 Senior Member

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    Here is the brake specific fuel consumption map: File:Toyota 1nzfxe prius bsfc.jpg - EcoModder

    Engine itself is the most efficient between 2200…3500rpm. But as you can see from the diagram if you let the rpms drop to 1700 or go up to redline, there’s only a small difference (from 230 to 235g/kWh).

    So best is just to avoid draining hybrid battery. Unless you know that it will charge back up on downhill in that case, try to drain it enough that it can take all the available energy from downhill.

    Only thing that you can see from the map is that you should avoid those small rpms (below something like 1550rpm) but that won’t be a problem on uphill.
     
    uart, SFO and MickyMatter like this.
  3. SFO

    SFO Senior Member

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    Raytheeagle likes this.
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