Chuck Tomlinson wrote:
> "Larry Bud" > wrote:
> >> The grade sensor doesn't cost much, I'm sure.
> >
> >We in the auto industry try to save *PENNIES* on each piece, because
> >when you multiply that by 15 million units, it adds up to real money.
> >
> >When I was back at Chrysler a few years ago, they had a program that
> >rewarded employees for coming up with cost reduction ideas.
>
> You're right: pennies per vehicle add up fast in high-volume
> models. But a grade sensor is not really necessary to give
> a modern car enough information to detect grades.
>
> The engine controller can calculate the torque delivered to
> the drive wheels, based on airflow, ignition timing, etc.
> With a very simple model of the vehicle's aero drag and
> rolling resistance, and measurements like vehicle speed, an
> engine controller (or trans controller) can calculate a
> force balance on the vehicle. This force balance can be
> used to estimate the current road grade.
>
> The controller doesn't need great accuracy in grade
> measurements to do useful things like downshifting on long
> grades, so moderate errors in the drag model are easily
> tolerated.
>
> That said: software isn't quite free (memory and software
> development cost some money), but it's a lot cheaper and
> more reliable than a sensor in applications like this.
>
> Geek note: the two most variable unknowns in the force
> balance equation are total vehicle mass (e.g., driver only
> vs full load) and road grade. To a very basic grade
> estimation algorithm, a heavy load might look like an uphill
> or downhill grade, depending on whether the vehicle is
> accelerating or decelerating, but with a little more work in
> the algorithm, a useful mass estimate can be created (with
> the assumption that vehicle load doesn't change rapidly
> while the vehicle is moving).
> --
> Chuck Tomlinson

FWIW this seems to have been implemented in some cars; I had the
opportunity to drive my friend's Chrysler Concorde on a long road trip
that involved driving I-68 from Morgantown to I-70. When on cruise
control, the transmission would downshift on a downgrade steep enough
to allow the car's speed to creep up. Kind of nice; but it made me
think about the notorious unreliability of Chrysler 4-speed
automatics...

nate