bandstra.DeleteThis@gmail.com wrote:
> Hello,
>
> I'm a college student who is planning on developing an aftermarker
> cruise control system as a final project for my bachelor of engineering
> degree.
>
> I'm wondering if there is a way to interface the car's cruise control
> system (to be able to modify the cruise speed). Does anyone have any
> input or ideas?
>
> Thanks,
> Bryan
>
The cruise control speed is incremented and decremented by two switches
in the steering wheel - you can tap into their signals in the harness
under the steering column - keep reading to find out how to use them for
altering the cruise control speed. All cruise control commands are done
thru two wires going thru the clock spring.
The following will be crystal clear if you get the schematics for the
No. 1 Clock Spring out of the FSM - go to a dealer and ask if they'll
let you look at their FSM - they might even photocopy the page for you
if you ask nicely. Or - for the duration of your project, buy a one
year's subscription to
www.alldata.com for $25 ($14 for renewal after
first year) using a valid VIN for your Sebring - that will give you
on-line access to, among other things that may prove valuable, *all* of
the schematics right out of the FSM. Do not go out and buy a Haynes
manual - their schematics are not necesarily for your specific car -
that's why they label them "TYPICAL" - you might as well try to use a
roadmap showing roads between NY City and Pittsburgh to drive from LA to
Seattle.
The clock spring system acts like an A-to-D converter.The PCM forces a
fixed current thru the loop of the two clock spring wires - one of the
wires is a return. The other wire has resistors of the different values
on the distal end (in the steering wheel). The cruise control switches
connect their particular resistor to the return wire. With the fixed
current provided by the PCM, the resistnace value forces a certain
voltage value back to the PCM's A/D converter which it corretcly
interprets as a contact closure of the corresponding switch, and then
takes the appropriate action on the cruise control system.
So - simply unhook the connector under the dash going to the clock
spring, and measure the values of resistance between those two wires
with each switch pressed one at a time, write the resistance values
down, then re-engage the connector for normal operation.
To change the cruise speed using the existing provisions, you simply
would present the resistance value across the two clock spring wires for
speed increment (labeled 'Resume/Accel') and decrement (labeled 'Coast')
- a momentary (pulse) for one increment of speed change (1 mph at a time
decel, 2 mph at a time accel), or hold continuously for change at some
rate change preset into the PCM.
I have made the measurement on my LH car, but it may not be the same as
on the Sebring (though they likely are), so I won't bother publishing
them here.
Here's an idea for a different project - maybe you will change your mind
about your project and do this instead: Use the cruise control switches
to trigger the transmission gear changes thru a custom electronic module
that determines which cruise control switch was pressed, and, depending
on which switch was pressed (Resume/Accel or Coast) send a pulse to the
AutoStick gear incrememnt or decrement wire going to the TCM (or PCM
depending on model year). This would allow changing gears as with
AutoStick with your hands on the steering wheel. A switch on the dash
could be used to set the function of the cruise control swithches to
control the cruise control *or* to control the transmission gears. I
wanted to do this to my non-AutoStick Concordes, but just haven't gotten
around to it. Maybe you can do it as a project and sell me your
resulting custom kit (at a significant discount for giving you all of
this information).
Post back with any questions.
Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')
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