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Tire pressure alarms

Discussion in 'Electrical Engineering' started by Roby, Mar 19, 2007.

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  1. Roby

    Roby Guest

    The local TV news announced that all new cars sold in US after
    this summer would include built-in devices to warn about low
    tire pressure: more automotive electronics. I found a paper
    by NHTSA that describes the two techniques for accomplishing
    this. Interesting reading. I decided to either buy a new car
    right now, or wait a few years until this stuff is either
    improved or eliminated.

    Have a look for yourself:
    http://www-nrd.nhtsa.dot.gov/vrtc/ca/tpms.htm

    and this report linked there:
    "Examination of Existing Tire Pressure Monitoring Systems"
     
  2. Roby

    Roby Guest

    That's the solution that compares effective radius of tire pairs by
    differencing the wheel pulsetachs (already there for antilock brakes).
    It's appealing because there's no added hardware (except display).
    But it alarms only in response to wheel pair speed differences: it
    would be perfectly happy with all four tire running at 5 psi (or
    totally flat)!

    I got the impression that the industry was leaning toward the other
    scheme: radio telemetry from pressure sensors, either inside each
    tire or screwed onto the existing valve stem. Battery powered, with
    individual codes for each sensor so that the main computer knows which
    tire is low. This also avoids interference from nearby vehicles having
    similar blessings. Sensor replacement (e.g., dead battery) requires
    a visit to dealer who has the special box that tells the main computer
    about the new code. The dealer also has the stuff needed to unmount,
    remount and balance the tire if you have the sensor-inside solution.
    Bring money.

    Oh yes, one reports cautions that these tire pressure monitors are not
    intended to warn about blowouts. I'm glad they told us.
     
  3. Roby

    Roby Guest

    How would the authorities know? In this state at least, many counties
    have no vehicle inspection (it's mandated by EPA air quality). I can't
    imagine the system disabling the car until the sensor is fixed, and
    without some form of enforcement, a lot of broken systems will remain so.
     
  4. Do you think that'll cover their butts in a civil case? There are
    directions in every owners manual that I've ever seen cautioning owners
    to check tire pressures or risk hazardous conditions. Nevertheless,
    someone gets hurt due to a blowout and there's a lawsuit.

    Now, cars are equipped with a 'warning system' that doesn't warn about
    all possible hazardous conditions. Owners think they don't need to worry
    any longer and forget about checking the tires. Now the auto company
    gets sued for lulling divers into a false sense of security.

    One condition that worries me is that the wheel speed sensor technology
    won't catch a condition involving all tires going flat at the same rate.
    Owners STILL have to check pressures manually.
     
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