ev mode modification ($70)

+1 on what Evan says. The EV mode switch can help get very modest
FE gains… but the slightest misuse is a MPG killer.

I installed one ~3 years ago when there was hot and heavy debate
about its usefulness in getting better MPGs. I couldn't get a sense of
the issues involved, so I jumped right in.

Forget using it for extended EV. Every bit of energy you draw from the
HV battery to drive in EV has to be put back with multiple conversion
losses.

IMHO, its best use is to surpress the ICE coming online. Anytime the
ICE is turning over and you aren't moving is a complete waste of gas.
At this time of year, when warmup time is lengthen due the cold air
temps, the non-EV switch can be useful.

First off, after an overnight cold soak at 30 degF, you can't access the
EV mode because the HV battery is too cold and sluggish in both
providing and accepting power. The HSD uses repeated small charges
and discharges to warm the battery. As part of this strategy the HSD
tries to keep SOC up around 65% as opposed to 60% when the
weather is warm.

Whether or not the HSD will allow EV use, when ICE coolant temps are
below ~110 degF, the ICE runs all the time whether you are moving or
at a stop. The HSD is warming up the ICE and cat-converter to
minimize pollution, actually the primary reason for the whole
Prius-HSD-hybrid concept.

Between ~110 degF and ~145 degF the ICE will shut off at stops if the
heater is off and you push very firmly on the brake pedal. (Sometimes
in this coolant temp range you have to pump the brake pedal very
firmly twice to get ICE OFF.) But, it will come back on randomly. Here,
finally, is where the non-EV switch is useful. By going into EV when the
car is at a stop, ICE ON is surpressed.

But, here too is where you can screw it all up. You must switch out of
EV mode, using either the switch or a quick jab at the accelerator/go-
pedal. If it's a long light, its too easy to forget you're in EV mode and
draw heavily on the HV battery as you accelerate away... all the little
gains are lost.

Above ~145 degF the HSD tends to not run the ICE when the car is
stopped. Once coolant temps are above ~145 degF you can usually get
through a short stop without using the non-EV switch. But beware. If
for whatever reasons, long glides, long stops, extremely cold temps the
coolant temps fall to 145 degF, the ICE will come on to keep the
coolant temps up.

There you have it. I doubt that in the past three years I've recovered
the initial expense... but I'm working on it every cold day. :rockon:

 

i've had one for 7 years, havn't used it in 6.