[ausev] Series hybrids

[Christopher Robison]

On Tue, 2007-12-04 at 09:20 -0500, Charlesvsi at aol.com wrote:
 
> Our ''04 Honda Civic Hybrid is another example of a power assist
> hybrid. The programming does not allow electric only driving, but with
> the CVT (continuously Variable Transmission) the computer controls the
> speed of the gas engine, the ratio of the transmission and amount of
> electric motor boost. Ours 1.4 liter gas engine runs at 3000 rpm most
> of the time, at highest efficient speed providing 44 mpg. When
> climbing hills in cruise control on, the electric drive starts to help
> hold the speed of 73.5 and then the rpm goes up providing more gas
> engine power, transmission is changing ratio to hold the speed. On
> Montana mountains on I 90,  steep incline it still holds 73.5 mph but
> rpm goes up to 4500 while we pass the trucks etc. going over the hill.
> Going down the other side the automatic regenerative braking charges
> the large batteries getting ready for next hill. 

It's not the computer that prevents electric-only driving in the Honda
hybrid powertrain. The electric motor literally replaces the flywheel.
It is bolted to the end of the crankshaft, and so the engine and the
motor must spin at the same speed as they're physically connected. In
this way the Honda system is much less sophisticated than the Toyota
system. While Honda used a true mechanical CVT for those cars that
offered that option, the Toyota 2-motor system with the planetary
linkage allows them to implement the CVT in software.

I understand that Honda is now getting around this by allowing the
valves to close so the pistons draw a vacuum balanced by doing so on all
cylinders, such that the engine can rotate but not fire. Supposedly it
ends up with very little rotating friction, as hard as that may be to
believe. In that way, later models can drive on electric power alone.
I'm not sure what cars if any have been released with this feature.

Something interesting about Honda ditching the flywheel -- they're able
to simulate the effect of a flywheel by literally pulsing power and
regen current through the motor in timing with the engine compression
and combustion strokes, which smooths the vibrations from the engine and
keeps it running smoothly. Pretty cool.


-- 
Christopher Robison
chris at ohmbre.org
http://ohmbre.org          <-- 1999 Isuzu Hombre + Z2K + Warp13!