[Diy_efi] Traction control strategy (solution offered)

[Crescent Kao]

Hmm.. ok. From reading your responses, it looks like the LM339 route is the
way to go using one of two options. Count the number of pulses over a fixed
interval, or determine the time between pulses.

I think Perry's concept of adding the sum of the two wheels will illiminate
any problems due to turning. One thing I think I failed to mention
previously is that our primary usage of the TC would be at the drag strip.
Our integra currently runs 12.80's in full street trim - naturally
aspirated. We run on 22x8x15 M/T's and still get some wheel spin in first.

The TC would basically be used during the first 60' or so... perhaps only up
to about 60mph. Thus, like mentioned previously, the LM2907 wouldn't be a
good candidate for low speed.

Anyways.. Back on topic, about the hardware side of things now... Basically
a single LM339 would suffice since it has 4 inputs. It would give up an
output voltage corrosponding to each zero cross over. (square wave output?)

As suggestioned, the output could then be directly read in from a parallel
port to a PC?

I think at this point in time, I would prefer to take this route - having a
PC run the algorithms - rather than using a PIC or MCU. Main reason being,
is because I am most familiar with this kind of setup. However, if you can
talk me into the other route, then I may decide to venture that way instead.

So, if i have this correct, all that needs to be done is to power up a
simple zero crossing detector circuit with the LM339. Feed the four ABS
signals to the input on the LM339. Then direct the output of the LM339 to
the parallel port.

No Op Amp is required and no A/D is required either.

So do i have this correct? Or am I missing a few components.

As someone also mentioned in a previous post as well, using the serial port
(RS232) may be easier (vs the parallel port). Is this true? If so, what
would be required to take this route?



Onto the software side - using option 1 by counting the number of pulses at
each wheel and comparing them to one another would seem like it would
work... The count the 10 strategy and then rest could work quite well. Count
each pulse for the drive wheels (up to 10) and compare the count to that of
the non-drive wheels. Determine the difference (ratio), and you will get a
percentage of wheel spin. Like bruce mentioned earlier, if the drive wheels
produce 10, and at that same instant, the non drive wheels have only gone 8,
then you know the drive wheels have spun.

Option 2 - in my PC world of programming it wouldn't be that difficult
either. Grab the system time at each pulse and sutract it from the previous
pulse time to determine the pulse width. If the different in pulse width
from the drive wheels vs the non-drive wheels exceed a set percentage, then
there is wheel spin and thus cut power.

Thoughts on these theories?


Crescent Kao
Director of Marketing and Sales
www.c-speedracing.com



-----Original Message-----
From: diy_efi-admin at diy-efi.org [mailto:diy_efi-admin at diy-efi.org]On
Behalf Of Perry Harrington
Sent: Monday, April 29, 2002 6:14 PM
To: diy_efi at diy-efi.org
Subject: [Diy_efi] Traction control strategy (solution offered)


I'm not planning on making any TC devices, but here is how I'd implement it,
I'll give 2 examples.

Example 1:  My 1989 Mustang 5.0 (heh ;).

Since I have SN95 spindles, I'd add the ABS sensor to the front.  For the
rear,
rather than futzing with reluctor rings, I'd just use the VSS, it's
conveniently
mounted to the driveshaft and monitors the exact same thing (driveshaft
speed)
as the Lightning TCS does (they have a reluctor ring on the ring gear in the
diff).

Since I have 3 channels, I'd work it out like this:

LF + RF / 2 = F
R           = R

Slip = F/R

If Slip > 2% (.02) Then engage TCS until Slip < 2% in closed loop

Example 2:

FWD Acura.  Use all 4 ABS sensors in this fashion:

LF + RF = F
LR + RR = R

Slip = R/F

Note that the Slip bias is based on driven wheels.

Apply same TCS strategy as above with 2% slip reg.

Both of these methods allow for cornering and can act on open diffs, closed
diffs, and FWD.

As far as the electrical configuration:

An LM339 configured as a zero crossing detector, each output going to an IRQ
input on an MCU.

The MCU maintains the math internal.

The other option is to use 4 timer input capture trigger inputs and write
code to work around the overflow for sitting still.

The A/D approach is simple, but full of unneccesary hardware and possible
problems.

A direct digital approach like the OEMs is simpler even.

--Perry

--
Perry Harrington             Linux rules all OSes.               APSoft
()
perry at apsoft dot com 			                 Think Blue. /\

Those who would give up essential liberty to purchase a little temporary
safety
deserve neither liberty or safety. Nor, are they likely to end up with
either.
                             -- Benjamin Franklin


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