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Active Air - Small bit of nerd candy

Discussion in 'Model S: Driving Dynamics' started by lolachampcar, Feb 15, 2015.

  1. lolachampcar

    lolachampcar Active Member

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    I was working on my web site the other day and found some data from a suspension lowering module I did for MB's active air. Like Tesla, MB uses Continental springs and potentiometers on all four wheels.

    New Page 1
     
  2. Alipapa

    Alipapa Member

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    thanks for all the great info!

    Is the new air suspension on the D changes the stiffness as suggested on the "order page"? or the stiffness is simply affected by the amount of air as it raise and lower?
     
  3. AmpedRealtor

    AmpedRealtor Active Member

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    Tesla sent following email to lolachampcar, a member of this forum, in response to the same question:

    "Bill,

    Thanks for bringing this up but this statement is actually correct. Air springs by
    their nature automatically adjust stiffness in response to load. This means that the
    ride frequency remains constant even with large loading changes. This is why you now
    often see air springs on the back axles of heavy trucks. The reason for this is that
    in order to maintain ride height, the spring must adjust the air pressure inside the
    spring. This change in pressure also gives a change in spring rate. Since the ride
    frequency is governed by:

    2*pi()*sqrt(K/M)

    Where K = spring rate and M = sprung mass,

    If you change K and M in equal measure, the frequency stays the same. This is one of
    the cool things about air springs.

    The spring will also change stiffness slightly with ride height since the spring is
    now riding on a different portion of the piston which will almost certainly
    correspond to a different stiffness since it is almost impossible to make an air
    spring truly linear.

    Please feel free to pass this along to the other forum participants."
     
  4. Alipapa

    Alipapa Member

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    Oh, thanks for posting again.
     
  5. ra-san

    ra-san Member

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    You know, just as an aside, I really treasure the responses we sometimes get from Tesla that are straightforward and full of information, whether they are a proper technical answer to a technical question, or a straight-talk, no marketing or legal speak straightforward, plainly spoken answer to a policy question, feature discussion, whatever.

    While I see occasional non-answers come out of them, and each of them slightly erodes the bond I feel with them, it's the other type that have thus far characterized my interactions with them, and are what really built the bond in the first place and continue to strengthen it.

    If anyone from Tesla is reading this, I hope you take it to heart and pass it around that that investing in really good answers and carefully cultivating that as a company habit pays real and lasting dividends.

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    Should also add, Lolachamp, I've really appreciated your contribution to the forums and have especially found your suspension, wheel, and tire posts very helpful. Thanks for continuing to contribute.
     
  6. wycolo

    wycolo Active Member

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    Well you should expect engineer-speak from them as opposed to market-hype. What's neat is that they are allowed to speak to us directly.

    @LCC: re those charts: Is there ever a speed where the MS Active Air is fast acting enough to actually level out the ride as the car goes over a 90 degree speed bump, for example? The 1968 Austin America's HydroLastic Suspension was able to do that passively thru tubing and fluid suspension cylinders (rubber bladders).

    Yes, the ride in Very High around the ranch is quite firm with reduced compliance (not the best term perhaps).
    --
     
  7. lolachampcar

    lolachampcar Active Member

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    ra-san,
    I fear that the quality communication will decrease with time as Tesla gets bigger (can not possibly talk with all the customers that want to talk with them) and some of those customers act like children and "bite the hand that feeds them" by bitching or otherwise causing trouble with the information they are given. For my part, I too really appreciate the ability to ask questions and get honest answers. I try not to ask too many for fear I will wear them out :)

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    I think the Tesla system is just like the MB system in that all it can do is pump air into the springs and bleed it off. I believe there is only one speed which is that which you see when you raise and lower your car.
     

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