Ashen,
My memory is a bit vague, but I heard something like that. It was something to the effect that durability while retaining the capability to tow 7000 lbs was a "problem". At 1st glance, I really didn't understant that; if the vehicle is twice the size(like a 5500 lbs truck relative to a 2900 Prius), just make the components twice as strong,and twice as powerful. On reflection, twice as powerful would work, but since the HSD has to be able to pull 13000 lbs of vehicle and trailer it will have to be a bit more than 4X as strong.The gear teeth will have to have 4X the surface area(and strength). This could mean the HSD it would have to be 4X as long or some combination of increased diameter and length..I don't know what the HH is rated to tow-does anyone know if it is the 3500 lb of the normal HH?.
I suspect it is something other than just putting in bigger gears and bigger motors. I wonder if the offroad pounding that a truck might get has something to do with the problem.
I also a bit puzzled on why the HH doesn't get better FE relative to its non hybrid competition.In Real World city driving the Prius gets 70% better FE than the Corolla or Civic 4 cyl autos. The HH however gets just 33% better FE than the Highlander V6 and maybe just 10-20% better than the Highlander 4 cyl.
Is there some problem in scaling up the Toyota hybrid system that "hurts" FE??
The Camry seems to scale up OK, but I haven't seen CRs 2007 numbers for the CH VS 4 cyl Camry.(I HAVE NOW AND THEY ARE EXACTLY WHAT(28mpg) THEY SHOULD BE RELATIVE TO WT AND CR's 35 mpg Prius mpg.(It beats the HCH2 in city mpg)
Usually in city driving there is a direct relationship between wt and FE-all other things being equal(which they aren't). A V8 Tundra weighs about 5000 lbs and it gets about 13 mpg city.A 2800 Corolla will get about23- 24- mpg city.These numbers are exactly what you would expect if FE (city) is directly pro to wt.
A HH should get and honest 30 mpg city if a Prius gets and honest 45mpg city.
Well,I'm not meaning to take shots at the HH, I'm just thinking out loud. It would certainly be nice to have a 5000 lb pickup that got an honest 24 mpg city.This seems unlikely since the HHs get about that(when driven carefully) and they are lighter,shorter,narrower,smaller tired etc.Thanks.Charlie