Quote:
Originally Posted by MetroMPG
Thanks for the first-hand report, HiFlite!
Curious what you mean by this. I have done a fair amount of urban EV driving, and driving style made a huge impact on range in my experience. (As it does in any ICE car or hybrid.)
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YW! Driving style has a huge impact on efficiency, of course. What I mean by hypermiling is the constant (and irritating to other drivers) cycle of acceleration and coasting used by some in the Prius style hybrid community.
As a game, I've tried multiple driving styles in getting to work. What the Volt has vs most other cars, is 5 distinctly different modes of slowing down:
1) "Normal", that is, shifter in (D)rive. Releasing the gas pedal gives a very light regeneration mode. While it's supposed to simulate the action of a normal ICE automatic transmission car, IMO it's closer to freewheeling than that. Estimated drag on the car ~500 W.
2) "Low", that is, shifter in (L)ow. Releasing the gas pedal gives rather aggressive regeneration, similar say to slowing in a manual transmission in 1st gear from 20 mph. Drag on the car ~10,000 W (depending on speed).
3) "Neutral". This is unique to the Volt AFIK. As soon as one shifts into (N)eutral, the gas pedal has no effect. By computer magic, just enough power is applied to the motor so that there is zero torque on the drive wheels. (I plan on doing some coast down measurements which should give about the purest aero drag measurements one can get from street car.) It's hard to find a perfectly flat street, but from 35 mph in neutral, I can coast about 1 mile.
4) Brake regen. For the first part of the brake pedal travel, the only braking is from the motor. Drag on the car: up to 20,000 W (depending on speed).
5) Friction braking. Push the pedal down hard enough and the normal brakes engage. The battery can only take so much charge rate before damage. Also, for quick stops the rear wheels need to be engaged for stability. Every complete stop, no matter how gentle, will engage friction braking at low speed. E = 1/2 mv^2.
Okay?
Getting there
The thing to remember about regen is that only about 60% of the kinetic energy absorbed by the system can be returned to the wheels. However, coasting, especially in the Volt's Neutral, is nearly 100% efficient. Volt's "Drive" is close.
So the style that's most efficient for me is (D)rive and using the momentum to coast when approaching stoplights, etc.
Why does hypermiling work for a Prius? First, gas engines are most efficient under full load at full throttle. Second, the only way to get power into the battery is through regen. Apparently, cycling the engine artificially lets it run enough more efficiently while accelerating to compensate for the losses caused by aero (at a speed faster than you wish to average) and for the loss in turning that extra kinetic energy into battery power.
In CS (Charge-Sustain) mode, the Volt hypermiles for you! Basically, the engine always runs at full load and full throttle. In situations when that is not possible, it shuts off!
Even under pure battery power, the accel/decal technique doesn't work. At a steady speed ~45+ mph, the small motor/generator engages with the main motor in such a way that its rpm is reduced go be more efficient. Accelerate from there at a significant rate and the small motor detaches from the large, allowing it to spin faster to maximize power. This is less efficient than simply maintaining a steady speed.
Quote:
Originally Posted by rmay635703
The volt doesn't hypermile very well while the gas motor is running, the only way I have found to "hypermile" is to drive 35-55mph DWL with the gasser idling along and then hold 5 miles per KW once the buffer fills and the motor shuts off. Doing this can increase the 40mpg the car gets on its own to around 45mpg, ...
The volt hypermiles easily in EV mode when it is warm out.
Cold its almost better to drive inefficiently because of all the parasitic losses on non-user controllable things such as the battery warmer and erdtt.
(below 24 degrees and I draw 1-3kw with the lights off, heat off and car in neutral)
I have found I can get the parasytic losses to go away for a bit if I accellerate hard at every stop. I am guessing hard accel and regen warm the battery a bit, sadly they only stop it for a relatively short period of time.
Ah well.
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It's possible there's a way to squeeze a little more out of the Volt with hypermiling technique, but I'm skeptical. One problem is that, in both my experience and the gm-volt forum experimenters, the on board energy displays get easily confused when the engine is used. Either a DashDaq or a systematic test is required to get to the real story, IMO.
Correct, cold complicates things. At a stop, car 'on', but HVAC, radio, etc 'off', the Volt draws about 350 W (though the display says 500 W). Full cabin heat is 6 kW and battery heat, when needed, is about 2 kW. When the parasitic load is high, minimizing trip time becomes more important.
Do you park overnight or in a garage? Being from Michigan, I drive in a lot of cold weather, but don't see the battery heat come on very often. However, I usually park overnight (and charge) in my attached garage which is considerably warmer than outside. The battery pack is well-insulated so even though I park in a ramp for 9 hours at work, the pack temperature will imitate the 15 hours it spends at home.
YMMV!