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ABS signal conditioning??

Discussion in 'Electronic Design' started by Joseph Legris, Aug 19, 2003.

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  1. If I am going to put significantly bigger wheels on the back of a van
    with ABS on all four wheels (for greater load carrying capacity, not
    racing), how can I get the ABS to function happily (and safely)? I have
    considered a digital frequency scaler that simply measures the period of
    the signal coming off the tone ring, multiplies it by a constant and
    then synthesizes the correct frequency. Or maybe a phase-locked loop
    multiplier followed by an appropriate divider.

    My real concern is how the transfer function of a device inserted into
    the feedback loop of the ABS is going to affect its overall stability
    and performance. Does anyone have any advice?
     
  2. Jim Thompson

    Jim Thompson Guest

    Bigger diameter ?? Or wider tread?

    ...Jim Thompson
     
  3. Both.
     
  4. Jim Thompson

    Jim Thompson Guest

    ABS works by comparing wheel distance traveled against a computation
    from an accelerometer and releases the brakes at a certain percentage
    slip (I don't remember the numbers now).

    Changing diameter is certainly going to affect that ratio.

    But my gut guess is that you can't be changing the diameter by very
    much, so it may not be a big deal.

    ...Jim Thompson
     
  5. Many of the cheaper/older systems are much less intelligent than that.
    They don't do anything until they sense that the wheel has actually
    locked (frequency= 0, 100% slip). As a first step, I would take your van
    out and punch the brakes hard while monitoring the signals. Maybe record
    them with one of those laptop sound card programs. If you have the "lock
    sensing" variety, you shouldn't need to make any changes.

    Of course, since this is a safety related issue . . . This advice is
    worth what you paid for it (or maybe less), I am not responsible for
    anything, proceed at your own risk . . . you know the drill. Also be
    aware that because this is a safety related issue, you may get yourself
    into hot water with Transport Canada if you make *any* kind of changes
    to your brake system.
     
  6. Yes.
    You're aware that manipulating security features of your car possibly
    void the insurace coverage.
    You're trying to overload your car too. The brakes are designed for a
    certain mass at a certain speed. By overloading the car you're
    worseing the brake properties. The insurances won't like that either.
    Beside that you risk your and someones else's life.
    Forget it.

    Rene
     
  7. But I've seen this sort of thing done professionally on small buses and
    recreational vehicles where the back is chopped off a van and a larger
    passenger compartment and heavy-duty wheels and suspension are added.

    Does anyone know what they do with the ABS?
     
  8. Just some thoughts...

    How is the wheel distance measured? Is there an optical/hall effect sensor
    counting wheel rotations? Or...? Is there a way to adjust the sensor so that
    it is calibrated correctly to the tire diameter? (gearing, etc.).

    I have heard of companies/individuals who have developed replacement
    firmware (or whatever) for custom engine control, to, say, eliminate the
    upper RPM limit of the engine. Does the same kind of thing exists for ABS
    systems for wheel customizations?

    What does the wheel/vehicle manufacturer say? Do you simply (expensivly?)
    replace the ABS controller with a different model?

    Dana Frank Raymond
     
  9. Andrew Paule

    Andrew Paule Guest

    Depends on the system -

    Most fords run Mecatronic systems (control module is below the master
    cylinder), GM's tend to run TEVES systems, others have other systems.
    The Ford systems that I have had seem to work fine with tire/wheel
    upgrades (16" stock wheel, 215/50 -16 tires to 18" wheels with 215/35
    - 18 tires) on SVT contour, but these also kept tire diameter pretty
    constant. The computer can be reprogrammed if you need other diameter
    tires, and I think that this would be a better solution to you than
    trying to rig something up that would require a serious DVT (if you're
    an engineer, I would assume you would do this before you subject me to
    your bugs and cold solder - don't take offense, I do these things, but
    we try to catch em in a DVT) on something as touchy and serious as
    brakes on a van, lots of time and money. I would bet that a quick call
    to hypertech (www.hypertech-inc.com) could get you what you want.

    Andrew
     
  10. : > > If I am going to put significantly bigger wheels on the back of a van
    : > > with ABS on all four wheels (for greater load carrying capacity, not
    : > > racing), how can I get the ABS to function happily (and safely)? I
    : > > have considered a digital frequency scaler that simply measures the
    : > > period of the signal coming off the tone ring, multiplies it by a
    : > > constant and then synthesizes the correct frequency. Or maybe a
    : > > phase-locked loop multiplier followed by an appropriate divider.
    : > >
    : > > My real concern is how the transfer function of a device inserted into
    : > > the feedback loop of the ABS is going to affect its overall stability
    : > > and performance. Does anyone have any advice?
    : > >
    : > Yes.
    : > You're aware that manipulating security features of your car possibly
    : > void the insurace coverage.
    : > You're trying to overload your car too. The brakes are designed for a
    : > certain mass at a certain speed. By overloading the car you're
    : > worseing the brake properties. The insurances won't like that either.
    : > Beside that you risk your and someones else's life.
    : > Forget it.
    : >
    : > Rene
    :
    : But I've seen this sort of thing done professionally on small buses and
    : recreational vehicles where the back is chopped off a van and a larger
    : passenger compartment and heavy-duty wheels and suspension are added.
    :
    : Does anyone know what they do with the ABS?

    I assume that they do nothing! The ABS is not adapted. I have no idea about
    ABS-Systems used in Non-European-cars. The sensor transmit a sine-wave-signal
    indicating the wheel-speed. The whole slip-calculation takes place in the
    µC located within the ABS. Putting on larger tires does not affect the singalform,
    because only the frequency is relevant for wheel-speed-indication.

    The tire size has a different influence. The computer model is doing all it's
    calculations with a programmed wheel perimeter, this perimeter is not a static
    value within the model but dynamic! The computer model of ABS in modern cars
    calculates the amount of engine-torque to be lessened. Old ABS-systems do not
    affect engine torque hence they do not have a perimeter model. They only compare
    wheel slip.

    As no knows the kind of ABS you use and what is happening inside it is better
    to stay with the legal tire sizes and do no manipulation to the brake system at
    all! The ABS might be less important than the overall vehicle stability, keep
    that in mind. In the US vehicle stability became a big issue for manufacturers,
    mass, tire size etc. are major influence factors. As told in several shows
    "Don't do this at home".

    Regards,
    Taso
     
  11. Andrew Paule

    Andrew Paule Guest

    If this is a GM TEVES system, the on board computers can shut the thing
    down (read no ABS - not the TEVES module itself) if it gets faulty
    inputs - ask my neighbor with the Firebird - little tires in the front.
    I think that the big thing here is that you need to understand your abs
    system a bunch better before you start in on this. The Mechatronic
    systems (Bosch and Ford should be okay here, the honda ABS requires a
    computer reprogram (according to one of my local rice rocketeers - 11
    second civic with ABS), others unknown. Get a manual for your abs
    system before you go this far, and yes, you will probably need a brake
    and suspension upgrade, and modifications like this will require a talk
    with your insurance company (ask me about my insurance - that's why my
    tire diameter remains "stock" - bigger wheels and tires, but kept same
    diameter - they did not like the idea about reprogamming the abs system).

    Andrew
     
  12. Active8

    Active8 Guest

    hmmm... maybe the consumer would like snow tires instead of all seasons.
    not sure if that's a big diff if any at all, but if the computer could
    just figure out the freakin' perimeter from those GPS units they're
    putting in cars these days :) or the accelerometer, nyuk, nyuk... the
    consumer would have more options.

    mike
     
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