Hwy vs City HV Efficiency

Discussion in 'Clarity' started by Tacoma Soccer Dad, May 9, 2018.

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  1. Tacoma Soccer Dad

    Tacoma Soccer Dad New Member

    Happy new Clarity owner here! I drive too much to be EV all the time, but after my first trip to the gas station I'm getting 92 mpg.

    I've read some previous threads that suggest (for trips longer than 47 miles) using EV in town and switching to HV on the highway. Ultimately, the goal is to exhaust the battery, but utilize EV in town as much as possible.

    EPA ratings for the clarity are actually better in town than highway (44 city/40 hwy). I think these numbers refer to hybrid driving. So...why not run HV in town and EV on the highway? Is it because EV is most efficient in town and less efficient at high speed?

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  3. Viking79

    Viking79 Well-Known Member

    A couple missing pieces of information. Gas engines have to warm up, so around town they usually just get to their operating temperature by your destination, especially in winter. This means until they are warmed up your efficiency will suffer.

    The Clarity also does much better at low speeds on EV, my wife's was showing an estimated 67 mile EV range yesterday. Around town driving up to 45 mph. Even on gas that would still only be around 40 to 45 mpg after warming up (trips more than 5 miles or so).

    The transmission in the Clarity runs outside the efficient range of the electric motor at higher speed (especially above 60 mph) due to the gearing. This was designed so that the gas engine could operate in a very efficient mode at higher speeds on the highway where you are likely burning gas anyway.

    So yes to your last question, EV is very efficient at mid to low speeds (it can be at high speeds if designed that way, which it isn't in this car, or pretty much any other current car). The EV range of the Clarity might be like 25 at high speed or in the winter and 70 miles cruising along at 40 mph. Rough guesses. The gas mpg range will likely be tighter than that, more like 30 to 50 mpg or something. They compliment each other fairly well (sort of the point of an ideal hybrid, gain efficiency by using strong points of each engine/motor).

    Finally, running on electricity will likely be much cheaper and use less total energy since they don't have as much heat losses as a gas engine. Try to always use all your charge before your charging destination before starting engine. So if you are under your EV range, try to run all EV, if you go over your EV range, use gas where appropriate or let the car decide, but try to end trip with no EV range.

    In my Volt, about the worst I could do on electricity was 48 MPGe in winter with heater on full, which is still better than I could do on gas in most situations (48 MPGe means I am using same amount of energy as a gas car at 48 mpg). Clarity will be similar in that almost every use case electric will use less energy.
    Last edited: May 9, 2018
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  4. M.M.

    M.M. Active Member

    I don't have precise figures, but the delta is not that great. Probably 80% of my driving is at 62-65mph on the freeway with little traffic and only a few hills, and I'm getting at least 40 miles on a charge. It might be worse if you drive 75 or more, but at California freeway speeds, if you're not lead-footing it, you get way more than 25 miles.
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  5. Viking79

    Viking79 Well-Known Member

    When I say 25 at high speed, thinking 75 to 80 mph+, but I haven't had a chance to check that yet, as I am in HV mode if I drive fast for any distance.
  6. jdonalds

    jdonalds Well-Known Member

    One factor is the Atkinson Cycle engine is best at a constant speed where a lot of torque isn't required. They are weak at accelerating so they get assist from the battery. If you've ever driven a Prius with a depleted battery you will experience very slow acceleration. On the other hand the electric motor is superb, providing instant torque, at accelerating.

    I don't plan to exhaust the battery. Around town we are full electric. but when we take trips we go from home to the freeway in ECON/EV mode, then switch to ECON/HV mode when we are on the freeway. That will hold the battery level so we have EV capability when we exit the freeway. If the battery is more than 58% it will bleed off until it drops to 58%
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  8. dstrauss

    dstrauss Well-Known Member

    I've noticed that last part too. Even in HV Mode it slowly drains down to the maximum HV Charge range of 55-60%. What is so magical about that capacity level, and why can you only recharge to that threshold in HV Charge Mode?
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  9. Tacoma Soccer Dad

    Tacoma Soccer Dad New Member

    Thanks for the responses. For longer trips I'll use HV at high speeds and exhaust the battery.

    The info about HV draining the battery to 55-60% is also helpful.
    Johnhaydev likes this.

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