Monday, May 21, 2012

Ecodriving aka Hypermiling

What is EcoDriving?
In a nutshell, ecodriving is driving in the most economical way possible; and is also known as “hypermiling.” It starts with brisk acceleration (trying to use the peak torque of the engine) so you get to "cruising" speed fairly quickly, and then trying to use a minimum of throttle to maintain the speed. Obviously, uphills are your biggest challenge, where it takes throttle just to maintain speed -- if you can, it helps if you let yourself lose a little speed up hills.
There are three possible modes of driving:

1) Accelerating 2) Coasting 3) Decelerating

Accelerating uses energy, depending on the weight of the car, the steepness of the grade, and the rate of acceleration.

Coasting uses no added energy, and it uses the accumulated momentum / kinetic energy gained by the acceleration.  It only loses energy to aerodynamic and rolling drag.

Decelerating loses energy to energy to aerodynamic and rolling drag
and converting kinetic energy to heat in the brakes. Whenever possible, you should downshift to use the engine to brake, as this shuts off the fuel completely.

To be the most efficient, we need to minimize the energy it takes to accelerate and the energy lost through braking, and we need the car to lose a minimum amount of kinetic energy by being as low aerodynamic and rolling drag as possible.

To cover the most distance with the least energy, we need to accelerate up to a speed that will then allow the car to coast as close to the end as possible, and then use the engine to brake to make use of the remaining kinetic energy.  The brakes needs to stay as cool as possible.

Of course, cruising longer distances and/or up hills requires some additional acceleration; either to maintain a constant speed, or to climb a hill / slope.  You can do pulse and glide instead of constant acceleration (using the terrain as possible) and climbing hills well requires what I call "swooping".  This involves accelerating ahead of the uphill slope (when gaining speed takes less energy) and then use this to help carry speed up the hill.  Think how a bicyclist would climb a hill, and you'll understand.

Coasting downhill is a “no-brainer”-- someone dubbed downhills “road candy”!  If you go too fast, then use the engine to slow down, which shuts off the fuel.  And prepare to "swoop" if there is an uphill.
Then use the downhills to ease way off the throttle, or if you need to carry speed, put it in neutral and coast (with the engine idling) -- at 60mph at idle in my xA, I can get well over 300mpg while coasting.
The other common situation is when you can coast, but you need to slow down, or will soon come to a stop -- then you should downshift into a lower gear. When the engine is being pushed by the wheels, in almost all modern fuel injected cars -- will completely shut off the fuel to the engine; yielding "infinite" mileage for the duration of this kind of coasting. I try to only use my brakes at the very end of the coast right before you stop.
So, if you only use just enough throttle to get you where you need to go, and do not waste energy as heat in the brakes; but instead use it to shut off fuel to the engine, and coast to carry speed whenever you can, carrying momentum as far as you can -- then you are most of the way to good ecodriving technique.
There are other things to try, like pulse and glide (when on flat-ish terrain), and minimizing your use of A/C -- and of course if you want to try some simple and reversible mods: like pumping up your tires a bit above the recommended pressure -- but below the maximum listed on the sidewall, or some of the aerodynamic mods on the grill, etc., then all the better.
Let's try this: how far above the EPA combined mileage rating can you average on a tankful?
My Scion xA is rated 27 City/30 Combined/34 Highway by the EPA, so this past summer I was nearly 75% above the Combined, and last winter I was ~43% above – 42mpg was the worst tank average all winter! Here's a (long) thread that I have written about all the aerodynamic modifications I have made on my car:
To sum up the aerodynamic changes I've made: the front grill blocks and fog light covers added ~10-12% to my fuel economy, and the smooth wheel covers added ~6%, and yes the rear wheel skirts are ~3 to maybe 4%. The video mirrors and partial Kamm back also help somewhat. The rest is gained from ecodriving technique. I use a ScanGauge II to help me see how I am driving, and to help me practice and improve my ecodriving.

Not only should you try to combine several trips into one, it helps to drive to the farthest place first, and then drive to the rest of the places on the return. This lets the engine warm up fully as quickly as possible, and so it helps the engine be more efficient overall.

  • Keep track of your fillups and fuel economy, and make use of fuel logs like on
  • Get a Scan Guage II (save $ through, or get an Ultra Gauge for feedback
  • Learn to take advantage of your regular routes, traffic patterns, reduce stress – and save money!

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