1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

New S3 quattro

Discussion in 'A3/S3/Sportback (8P Chassis)' started by batwad, Jan 17, 2007.

  1. batwad
    Offline

    batwad Member

    Joined:
    Jul 14, 2006
    Messages:
    864
    Likes Received:
    0
    I got some junk mail from Lancaster Audi yesterday that had a little bit about the new S3 in it. The only part that was of any interest was when they said it has "permanent four wheel drive". So does that mean it's not Haldex or have the cretins at Lancaster ballsed up again?
    #1
  2. klauster
    Offline

    klauster Active Member

    Joined:
    Jan 3, 2007
    Messages:
    1,160
    Likes Received:
    112
    its basically the blurb Audi always say about cars with Quattro... although its true (meaning you cant turn it off) we obviously know the car doesnt use 4 wheel drive ALL the time
    #2
  3. Covenant
    Offline

    Covenant Member

    Joined:
    Jul 17, 2006
    Messages:
    246
    Likes Received:
    0
    ...in fact no car at all uses full time 4WD as it would wear the tyres horribly.

    Closest ones iirc are the Unimog, then Land Rover and Jeep with centre diff locked. Though Unimog is stretching it a bit in the definition of a car...
    #3
  4. Dandle
    Offline

    Dandle Member

    Joined:
    Aug 26, 2005
    Messages:
    852
    Likes Received:
    1
    Actually the car does move power aft most of the time the car is moving. The only time the coupling is totally disengaged is when the car is stationary, there is zero throttle while moving or under braking(so as not to much up the abs/ebd). Its a misconception that it only moves power aft if the fronts loose grip.
    #4
  5. PhatPhil
    Offline

    PhatPhil New Member

    Joined:
    Sep 5, 2004
    Messages:
    2
    Likes Received:
    0
    As far as I know both the new S3 and the RS4 split power delivery 60% rear and 40% front by default. Altering the % depending on speed/grip.
    #5
  6. JamS3
    Offline

    JamS3 Active Member

    Joined:
    Jun 17, 2003
    Messages:
    2,257
    Likes Received:
    12
    Batwad

    So I take it the write up was not that interesting then from them? Did they not write it up very well to sell it or was it just brief and not mention much about it?
    #6
  7. johnmv55
    Offline

    johnmv55 Member

    Joined:
    Dec 5, 2004
    Messages:
    247
    Likes Received:
    0
    It also disengages the Haldex unit the moment the brakes are applied, also the handbrake disengages drive to the rear, In normal "cruise" mode there is not much going rearwards, even the after market stand alone controllers for use with Haldex's in other cars can only split to a maximum of 50/50,
    #7
  8. Dandle
    Offline

    Dandle Member

    Joined:
    Aug 26, 2005
    Messages:
    852
    Likes Received:
    1
    No the S3 is front wheel biased and if max power is being transferred aft its still only a 50/50 split(it has to be very slippy to get to that level of power transfer). As john said there isnt much power going aft while cruising but it increases the power aft when accelerating etc.
    #8
  9. batwad
    Offline

    batwad Member

    Joined:
    Jul 14, 2006
    Messages:
    864
    Likes Received:
    0
    @JamS3: it was only marketing blurb trying to tempt me into spending more cash :) Not really a write-up at all.
    #9
  10. southpaw66
    Offline

    southpaw66 Member

    Joined:
    Nov 15, 2006
    Messages:
    166
    Likes Received:
    0
    I beleive the Haldex clutch is fully disengaged during normal driving and only engages when there is 8th/rotation of slip at the front wheels and based on throttle inputs. If you look at the performance upgrades they do engage with zero slip even under braking in race mode, but come with a warning about handling -therefore I doubt the S3 has this type of setting. It may be tuned to react faster though.

    The RS4 is not Haldex (tranverse engines) but Torsen (longitudinal) so can be permanent 60/40 rear bias. The S3 is Haldex so will be 2WD when cruising.
    #10
  11. AL_B
    Offline

    AL_B Active Member

    Joined:
    Jan 6, 2003
    Messages:
    1,572
    Likes Received:
    0
    This haldex operation topic comes up quite often.

    A long time ago, on this site, in its previous incarnation. There was so much discussion about it, one of the lads emailed haldex and got a reply.

    The original thread was called: Haldex and Torsen, and was started by Mutley. Thread ID: #25855 - 15:01 07/07/2003

    MarkR was the chap who contacted Haldex. I know this because I saved the full thread to hard-disk.

    I have done a search for the thread, and it seems to have been lost from this site. I will contact Olly.

    But here is a copy of what was said:

    MarkR's original email ------------------------
    -----------


    Hello.

    As the owner of an Audi S3 I make use of the haldex LSC everyday. I am also
    a member one particular Audi forum (www.audi-sport.net). We have discussed
    the issues of haldex, torque transfer and such like. In particular regard
    comparing to Torsen.

    The haldex LSC solution is often seen as inferior and is often said to be
    "not real 4WD". I disagree and believe it's abilities go beyond that of
    Torsen when used in real driving scenarios.

    I would greatly appreciate it if you could take the time and answer my
    questions. I'll try to be as brief and as clear as possible. Thanks.

    1) haldex claim 100% torque transfer to the rear is possible. Is it? Some
    people dispute this, but I believe it requires 100% slip of the front wheels
    for this to be the case. i.e. In real conditions it would never happen, the
    more realistic split is 50-70% under full load and some slip. I came to this
    conclusion because the front wheels are always driven.

    2) There is much dispute over whether the haldex LSC delivers torque to the
    rear if and only if the front wheels slip. It's my belief that the torque
    transfer can and does occur in response to wide throttle openings, even
    before any slippage occurs. Can you confirm?

    3) With particular regard to the Audi S3 (or TT). Do you know if the
    steering angle is taken into account when deciding whether to increase or
    decrease the torque transfer? i.e. is it purely throttle/slip related or is
    actually much more complex? If possible, some explanation would be useful.
    For example, if there is 10% to the rear and I turn a corner, would it
    increase to 30 or 40% to provide increased stability. If so, would be that
    due to a natural left/right speed difference or a result of steering angle
    change (ESP sensor)?

    4) There is much debate on the "constant speed" torque transfer to the rear.
    i.e. travelling on a road at 30 or 70MPH, how much torque is transferred to
    the rear? Is it speed dependant?

    5) Does the torque transfer under acceleration depend on the current vehicle
    speed? If so, can you provide characteristic details?

    Any further information you can provide would be appreciated, in particular
    how the haldex LSC operates in conjunction with the ESP and whether the ESP
    can affect the transfer of torque.

    The folk on the forums are an enthusiastic bunch who appreciate technical
    explanations to technical problems. If there's anything else you can provide
    beyond the questions I've asked, that would be very welcome. Once again, I
    thank you again for taking the time to read my questions.


    Cheers.

    Mark.

    Reply from Haldex -----------


    Dear Mark,

    I am pleased to see that you like your Audi S3 with the haldex AWD system
    and that you disagree with your Torsen friends when it comes to the
    excellent abilities of the haldex AWD System. It is a fact that the
    electronically controlled haldex AWD system provides a much wider range of
    possibilities over a purely mechanical system. We are also convinced, after
    having delivered 500.000 haldex AWD systems to the market since our start in
    1998, that we also have the best electronically controlled AWD system on the
    market.

    We have put together some answers on your questions that I hope will be
    helpful in your discussions in the Audi forum.



    1. There are situations where near 100% torque transfer to the rear axle
    occur. An example is if the front wheels are on ice and the rear wheels are
    on tarmac. In that case the front wheels have (almost) no grip. In that
    case, the haldex coupling will transfer all torque to the rear axle and
    prevent front wheel spin. On uniform surfaces however, the coupling can not
    transfer all torque to the rear axle. See below.

    2. We need slip over the coupling in order to be able to transfer torque.
    That slip (rotational speed difference between the front and rear axle) is
    created by different tyre rolling radius (front to rear) and drive slip
    between the tyre and road. The rolling raduis difference can be created by
    differently worn tyres (or different dimensions, something that should be
    avoided) and different load. In most cars, the front axle has a greater load
    than the rear axle, which causes the roll radius of the front tire to be
    smaller than the one for the rear tyres (given the same nominal size). This
    gives us the possibility to transfer torque to the rear axle also when no
    slip occurrs on the front tyres.

    If you have differently worn tyres on the front and rear axles, the new
    tyres should always be on the rear axle. This is true no matter if the car
    is FWD, RWD or AWD, since you otherwise risk heavy and uncontrollable
    oversteer in situations such as aqua planing. In this case, putting the worn
    tyres at the front also helps not to reduce the maximum transferable torque
    (maximum rear axle torque).

    During cruising which a constant velocity, we have the possibility to
    transfer up to 40-45% of the torque to the rear axle, given nominal tyres.
    During acceleration, the weight transfer increase the front tyre slip and
    decreases the rear axle slip, giving us the possibility to achieve more or
    less the same torque distribution as the dynamic weight distribution.
    Generally speaking, depending on the vehicle somewhere around 60-70% is
    possible to achieve during a full acceleration. Note that we are still
    talking about a uniform surface, with no spin on the front wheels.

    When cornering , there is in most cars a tendency for the inner front wheel
    to lift and spin. In that situation, we can increase the torque transfer
    even further.

    So far I have only spoken about what possibilities there is to transfer
    torque. How much is actually transferred depends also on how the haldex
    coupling is controlled. The engine torque and gas pedal position are
    together with the wheel speeds and the engine speed the most important
    signals that are used in the control. Brake, ABS and ESP signals are also
    very important for enabling co-existance between the AWD system and the
    ABS/ESP system. We control the coupling in order to prevent wheel spin as
    well as removing it quicky if it should occur.

    3. Steering angle is not a signal used in the control of the coupling in VW
    group cars. The reason for this is that the steering angle is not available
    in most cars as it is only present when an ESP system is mounted. We do
    however calculate the curve radius from the wheel speeds. We have software
    ready using more signals as the steering angle that we offer to the vehicle
    manufacturers. This enables further optimisation of handling performance.

    4. It may vary a bit with speed (and road surface), but without going into
    details a figure of around 10-15% would be typical. It is enough to help
    stabilising the car while at the same time saving fuel and reducing the
    temperature of certain driveline components. As soon as the driver starts to
    accelerate or decelerate, more torque is transferred.

    5. Yes it does. In general, a higher percentage of the torque is transferred
    to the rear axle in low velicities than in high ones. This is partly due to
    the fact that the total available driveline torque is larger at lower speeds
    (and lower gears), thus causing more weight transfer to the rear axle. In
    order to achieve consequent handling characteristics (as well as optimised
    traction), more torque must then be transferred to the rear axle.

    6. The haldex coupling is completely compatible with ABS and ESP systems.
    In order to optimise the performance of the ABS/ESP system, it is possible
    to open the haldex couplng during ABS braking or a stability control brake
    intervension. The ABS/ESP antispinn and stability control also depend very
    much on being able to calculate the vehicle velocity. That is very easy with
    2WD, but as soon as you have the possibility of four wheels spinning it gets
    very complicated. The haldex coupling and ABS/ESP system interface make it
    easier to obtain a good reference velocity.
    In the cars where the haldex coupling is available today, additional signals
    available with ESP are not used. We do however have software using these
    signals. This enables further optimisation of handling performance and life
    span of driveline components.


    During calibration of the haldex coupling , we try to optimise the traction
    and handling performance of the car. These are however not the only aspects
    that are important. The final calibration is alway a compromise between
    traction, handling, the life span of driveline components, temperatures in
    driveline components, fuel consumption and more. If the car manufacturer
    wants the same calibration to be used in several different cars, a new
    compromise has to be made. Different manufacturers do have different
    strategies about this. Some tend to let many cars share the same calibration
    while others want to optimise each car individually.

    I hope that this answers your questions.

    Best Regards

    Ulf Herlin
    Vice President, Marketing

    ----end----


    AL
    #11
  12. Evotek
    Offline

    Evotek Member

    Joined:
    Jan 4, 2007
    Messages:
    48
    Likes Received:
    0
    #12
  13. Evotek
    Offline

    Evotek Member

    Joined:
    Jan 4, 2007
    Messages:
    48
    Likes Received:
    0
    In the above link press the Swedish flagg after you read the artikel and scroll down to the bottom for a diagram that shows the amount of rearwheel-traction versus original.
    #13

Share This Page