wrote in message

On Mon, 19 Dec 2011 11:55:54 -0000
"Recliner" wrote:
You're assuming that it overheated, rather than my guess that the
battery was running low. I presume that they run the engine for
optimum economy, rather than for max power.

I shouldn't make any difference. Once the battery is flat it runs off
the engine just like every hybrid car ever built.

This is a range-extender hybrid, unlike most existing hybrid cars. In
other words, it's more like the Volt, not the Prius (ie, not all hybrid
cars are the same). So the only drive to the axle is from the 174bhp
motor, powered by the battery, with the generator just acting as a
part-time charger, which runs at optimum revs when it runs at all. If
the engine isn't charging the battery as fast as it's discharging, the
bus will have to stop or slow down for long enough for the charge to
accumulate again.

Autocar comments that the engine needed to run most of the time during
its short road test, probably because it wasn't getting much benefit
from regenerative braking, unlike on a normal bus route. This does
suggest that the engine isn't really up to powering the bus for a
sustained run at motorway speeds (unless the engine is pushed hard,
which would destroy the excellent economy and green claims). Wright
claims 11.2mpg for the Boris Bus, compared to 8.6mpg for Wright's Gemini
2 Hybrid (and 4.3mpg for a Citaro G bendy bus). The CO2 figures are also
much better (640g/km, compared to 864 and 1300, respectively).