• Apr 27th 2011 at 11:09AM
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Toyota Highlander Hybrid – Click above for high-res image gallery

During the 2011 SAE World Congress, Clark Hochgraf – associate professor of electrical, computer and telecom engineering at the Rochester Institute of Technology – presented a study that examined the powertrain and braking efficiency (PABE) and vehicle limited fuel consumption (VLFC) of light-duty automobiles. The study ranked the most efficient powertrains and the lowest energy consumption chassis based on these criteria outlined by Green Car Congress:
  • VLFC represents the minimum amount of fuel a vehicle consumes to complete a given drive cycle; in computing VLFC, the powertrain is assumed to have 100 percent efficiency and the braking system is considered lossless.
  • PABE characterizes the powertrain for the effect of powertrain energy conversion efficiency and for regenerative braking efficiency. The powertrain and braking efficiency metric characterizes the powertrain system, for both forward propulsion characteristics and for braking characteristics. PABE is affected by hybridization, by engine efficiency, by accessory loads (i.e. air conditioning and lighting) and by powertrain operating strategies including non-hybrid strategies.
The study concluded that the lowest energy consumption chassis of 2010 model year vehicles – computed using the VLFC method – were the Toyota Prius, Suzuki SX4, Toyota Yaris, Honda Civic Hybrid and the Kia Rio.

The most efficient powertrains on the city and highway driving cycle – computed using PABE – were the Toyota Highlander Hybrid, Ford Taurus, Mercury Mariner Hybrid, Ford Escape Hybrid and the Mercury Milan. That's a hodgepodge of vehicles that we've never before seen listed as being equipped with the most efficient powertrains, but when you assume 100 percent efficiency and lossless systems, strange things happen.

*UPDATE: Clark Hochgraf has provided clarification regarding the vehicles with the most efficient powertrains. As it turns out, the most efficient powertrains on the city driving cycle – computed using PABE – were the Toyota Highlander Hybrid, Mercury Milan, Mercury Mariner Hybrid and the Ford Escape Hybrid. Hit the jump for Hochgraf's detailed explanation of why hybrid vehicles dominant the city cycle list.


2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid
  • 2011 Toyota Highlander Hybrid


[Source: Green Car Congress]
In the city cycle, all the top ten powertrains are hybrids. However, that is not the case for the highway, and this makes sense. Part of the reason the hybrid powertrains are more efficient in the city is they can recover substantial braking energy. On the highway cycle, there is very little braking energy to recover. Instead on the highway, a well built manual transmission, or automatic transmission with lockup may couple the engine to the ground more efficiently than the "electric CVT" of a Prius type powertrain.


PABE chart



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    • 1 Second Ago
  • 7 Comments
      harlanx6
      • 4 Years Ago
      The home team scores again! Way to go, FORD
      • 4 Years Ago
      Like they say, there are lies, damn lies, and statistics. You can massage statistics to say anything you want.
      Alterego
      • 4 Years Ago
      This is old news, I read it at least 2 weeks ago. Interesting about the Suzuki chassis. If we could get a smaller engine and some tall gear ratios, it would put up some good mileage numbers.
      Dan Frederiksen
      • 4 Years Ago
      I'm not sure those results are trustworthy. even if we ignore electric cars like the tesla roadster's drivetrain (as apparently they do), how could a prius drivetrain not be more efficient than a 3.5L V6 in a ford taurus... there is no way. either the results are pure nonsense or maybe they used one of those nonsense metrics like mileage per horsepower..
        • 4 Years Ago
        @Dan Frederiksen
        Because it's not measuring what you think it's measuring. The difference is described in the article. The first measure is basically MPGs, and the Prius wins that one just like you'd think it would. The second one is measuring something closer to the Carnot efficiency of the engine (though it's much more comprehensive than that, since it includes braking). How many joules of fuel to you put in to the engine? How many joules do you get out of the wheels? Divide. In this case, it's quite possible for a machine that uses more total energy to have a higher conversion efficiency.
          Dan Frederiksen
          • 4 Years Ago
          that's exactly what I think it is (except for braking). the prius hybrid atkinson is known for it's high efficiency something like 37%. no way the V6 will match it
      Neil Blanchard
      • 4 Years Ago
      The Nissan Leaf has about an 85-90% efficient drivetrain, I think? Neil