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CAT RV
Club is a Chapter of Family Motor Coach
Association
There
are two
totally different "let the transmission choose the correct
gear" modes/programs
in the Allison ECU which is the "electronic brain" controlling
shifting and other functions.
In ECONOMY
MODE,
the transmission won't downshift even at
'wide
open throttle' (WOT) until the engine pulls down to peak
torque RPM in
some application and 200 RPM lower than "regular mode" in
others.
In
REGULAR
MODE,
the transmission will
downshift
much earlier (to maintain higher engine RPM). Only
at higher throttle positions is there any difference, so on
flat ground you will not
notice any difference (except accelerating from a stop
if
you are at or close to wide open
throttle).
It
can make a big
difference
in rolling hills. On rolling hills, using regular mode
(particularly in cruise control), it is common for the
transmission to shift down to 5th on the uphill and up to 6th
on the downhill. Repeat this process hundreds of times. In
economy mode, you will stay in 6th gear unless the hill is so
steep or so long that the engine can not pull it without
dropping below peak torque RPM. If you can pull a hill in a
higher gear (lower engine RPM) and
the
engine does not overheat, that is what
Caterpillar recommends for the most economical way to climb a
hill with
a modern in economy mode use the down arrow to drop a gear
(this is what I turbo, after-cooled diesel
engine).
If
you know you will need a lower gear because of the steepness
of the grade and/or engine temperature is rising higher than
temperature
- if driving do), or switch out of economy mode. Be sure to
switch back into economy mode when past the steep section, or
agree to pump extra fuel in the tank.
If
your
engine begins to overheat, your HP/weight ratio is low
or
if it irritates you to loose a few mph on a hill in the name
of saving fuel, in the hills, by all means drive in regular
mode. It confuses me to hear people advocate driving in
economy mode only on flat ground, as there is not 1%
difference in shift RPM's between regular and economy mode on
flat ground, except accelerating from a stop if you use WOT.
Every time you start the coach, the transmission is in regular
mode. This is the default setting. If
you push the mode button, it goes to "economy mode"
and
the light illuminates. There is no "absolute" on how much
difference in fuel economy driving in economy mode will have.
On flat ground where you will be in 6th gear irrespective
of what mode you are in, there will be zero
difference. The most
difference in mileage will be in rolling hills, where in
regular mode, particularly if in cruise control you will start
up a hill in 6th gear, go to WOT in 6th gear, downshift to 5th
gear still at WOT (where
it is using a lot more fuel).
After the hill is crested, the transmission will up-shift to
6th, then likely coast a little in 6th gear (unless you are
driving with the exhaust brake on - if you are the
transmission then applies the exhaust brake and
downshifts toward
the pre-select gear which is generally either 2nd or 4th). And
so on 6-5-6-5-6-5-6-5 . . .
A
modern turbo inter-cooled diesel is much more efficient at low
RPM high throttle settings. This is not
my
opinion. It is stated in those words in the Cat Owner's
Manual! Note:
In either mode, you are free (and welcome) to use the up and
down arrows to proactively
choose the correct gear. You can not screw
anything up - even if you down-arrow to 1st gear at 70 mph,
the transmission knows that you meant "downshift to the next
lower gear as soon as the engine RPM will not exceed the
pre-set amount. Then downshift again when safe . .
."
Also,
you can shift between regular and economy mode as often as you
want with the transmission in any gear when you make the
change.
OPINION:
I drive in economy mode 99% of the time, including in
real
mountains, but use the up and down arrows to choose the proper
gear. I use regular mode only
when I feel "I am willing to throw a lot of fuel away to gain
a little performance." When passing on 2 lane roads,
this
is the
case!  |
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