Active Torque Vectoring??????
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This is a discussion on Active Torque Vectoring?????? within the STi Technical Forum forums, part of the Tech & Modifying & General Repairs category; I'm curious if anyone has found good solid info they can link to on how the active torque vectoring works ...

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    Active Torque Vectoring??????

    I'm curious if anyone has found good solid info they can link to on how the active torque vectoring works in an STi. I mean we know that both the wrx and STi share this feature and I'm pretty sure I understand how it works in the wrx. However, the STi has an LSD in the front that the WRX does not.. So I would think that when system is braking the inside front wheel, the LSD automatically would send more torque to the outer wheel.. But I like to get more info.
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    zax
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    I've been contemplating the same. What we know:

    1. The ATV system functions by applying the brakes slightly to the inner front wheel in the corner. This serves to rotate the front of the car into the corner and reduce understeer. This is what Mitsubishi managed to do with the AYC, though Subaru is accomplishing the same task using a rearward bias and ATV on the front axle.

    2. The front LSD has the tendency for push understeer. Applying the inner brake should bias torque to the inside tire in the corner, which would seem counterproductive to the purpose of ATV.

    Possibilities for operation:

    1. It is most likely that the ATV only functions off throttle. Off throttle, the power delivery to the axles is either zero or negative. So, applying ATV at this point would not bias torque to the inner tire since the car is not sending any power to the wheels (negative power to the wheels)

    2. Like other Brake-Torque biasing systems, the best explanation is that the electronic throttle control cuts throttle during ATV activation to bring the car back into neutral cornering. After ATV has achieved the desired correction to the car's attitude, the throttle is reapplied.

    I would believe that these two possibilities provide the most logical explanation. From an empirical standpoint, many reviews noted that the car seemed to understeer slightly in the corners on throttle, but even lifting the throttle slightly the car would rotate back into the corner.
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    Quote Originally Posted by zax View Post
    I've been contemplating the same. What we know:

    1. The ATV system functions by applying the brakes slightly to the inner front wheel in the corner. This serves to rotate the front of the car into the corner and reduce understeer. This is what Mitsubishi managed to do with the AYC, though Subaru is accomplishing the same task using a rearward bias and ATV on the front axle.

    2. The front LSD has the tendency for push understeer. Applying the inner brake should bias torque to the inside tire in the corner, which would seem counterproductive to the purpose of ATV.

    Possibilities for operation:

    1. It is most likely that the ATV only functions off throttle. Off throttle, the power delivery to the axles is either zero or negative. So, applying ATV at this point would not bias torque to the inner tire since the car is not sending any power to the wheels (negative power to the wheels)

    2. Like other Brake-Torque biasing systems, the best explanation is that the electronic throttle control cuts throttle during ATV activation to bring the car back into neutral cornering. After ATV has achieved the desired correction to the car's attitude, the throttle is reapplied.

    I would believe that these two possibilities provide the most logical explanation. From an empirical standpoint, many reviews noted that the car seemed to understeer slightly in the corners on throttle, but even lifting the throttle slightly the car would rotate back into the corner.
    That makes sense... Then I have to wonder how significantly different the system works with different levels of nannies engaged. I wish that Subaru had an eloquent explanation out somewhere that I could find.
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    I think that would force Subaru to admit that the idea is a bit of a band-aid to a much deeper issue. IMO, Mitsubishi's AYC implementation is the correct way of solving the problem without having to bias the torque rearward (yes, Mitsu's platform is a 50:50 torque split). The solution does, however, work; this has been demonstrated in detail on the Focus ST and Fiesta ST FWD platforms. FWD is the ultimate example of push/throttle off understeer.

    This is a primary example of marketing strategy. For example, Subaru loves to tout the strengths of symmetrical AWD, without mentioning the technical details of the VCU in the center differential. If Subaru were to explain how the viscous coupling (VCU) operates from a technical perspective, most would begin to realize how inferior the system is compared to nearly every other AWD platform on the market. The same can be said for the ATV system.
    Last edited by zax; 04-21-2014 at 06:31 AM.
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    Quote Originally Posted by zax View Post
    I've been contemplating the same. What we know:

    1. The ATV system functions by applying the brakes slightly to the inner front wheel in the corner. This serves to rotate the front of the car into the corner and reduce understeer. This is what Mitsubishi managed to do with the AYC, though Subaru is accomplishing the same task using a rearward bias and ATV on the front axle.

    2. The front LSD has the tendency for push understeer. Applying the inner brake should bias torque to the inside tire in the corner, which would seem counterproductive to the purpose of ATV.

    Possibilities for operation:

    1. It is most likely that the ATV only functions off throttle. Off throttle, the power delivery to the axles is either zero or negative. So, applying ATV at this point would not bias torque to the inner tire since the car is not sending any power to the wheels (negative power to the wheels)

    2. Like other Brake-Torque biasing systems, the best explanation is that the electronic throttle control cuts throttle during ATV activation to bring the car back into neutral cornering. After ATV has achieved the desired correction to the car's attitude, the throttle is reapplied.

    I would believe that these two possibilities provide the most logical explanation. From an empirical standpoint, many reviews noted that the car seemed to understeer slightly in the corners on throttle, but even lifting the throttle slightly the car would rotate back into the corner.



    I just re-watched the "MORE than everything you every wanted to know" video on TFL where they recorded the Subaru presentation from the event at Laguna Seca. Almost right at 14:00 minutes in, the presenter Todd Mills (STi line manager for SOA) specifically says that on the STi, the active torque vectoring system will brake the inside front wheel AND send more torque to the outside wheel. Somehow I missed this before. It is also on the screen.


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    This mostly answered my initial question. However, I'd still at some point like to know more about how the system does all this.
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    He appears to say the same thing for the WRX during the event for that one as well. In this TFL "MORE than everything you ever wanted to know.. WRX" video, when describing the difference between the traditional VDC and the torque vectoring, he actually says "the torque vectoring is for when you're ON throttle..." So... thats interesting. I supposed he could have misspoke but he seems to be not so much ad-libbing.. So I tend to believe him.

    Go to about 3:47 to see/hear him talk about the ATV in the WRX.
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    Jay, but this is opposite to the behavior of an LSD. When the inner wheel is braked, the LSD should attempt to mitigate wheelslip by sending MORE torque to the inner wheel (remember, if the inner wheel is braked the outer wheel is perceived as slipping). I still stand my my statement above.
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    Quote Originally Posted by zax View Post
    Jay, but this is opposite to the behavior of an LSD. When the inner wheel is braked, the LSD should attempt to mitigate wheelslip by sending MORE torque to the inner wheel (remember, if the inner wheel is braked the outer wheel is perceived as slipping). I still stand my my statement above.
    I totally am with you. Which is why I find it interesting that they went our of their way to specifically state this information at two separate events in the technical presentations... So it doesn't seem like they are merely mis-speaking.

    So that means there is most likely more to the explanation of what is actually happening.... Or Subaru intentionally lied in both presentations (less likely).
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    Or the Product Manager didn't understand all the technical details . As a product manger, I can tell you this DOES happen lol
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    Quote Originally Posted by zax View Post
    Or the Product Manager didn't understand all the technical details . As a product manger, I can tell you this DOES happen lol
    I totally believe you.

    But it is an AWFULLY specific technical detail to go out of the way to bullet point it in both visual and in both audio presentations for both cars, for sombody to not at least have thought it to be a known fact based on something other then pure assumption. A detail that if somebody was seemingly unsure of, would be far far easier to simply skip and not mention than make up out of whole cloth.

    I totally get what you are saying about the presumed behavior of an LSD but I still suspect there is more to the story here.
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    Im a little surprised I haven't seen this piece of the puzzle explored more on here or NASIOC or IWSTi. Maybe it has been somewhere but I haven't seen it.
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    So there are now the following traction aids for the STi:

    In 2004:
    - single mode DCCD
    - electronic brake force distribution (EBD)

    In 2008:
    - tri-mode DCCD
    - EBD
    - Electronic Stability Control (ESC)
    -Traction Control

    In 2015:
    - Tri-mode DCCD
    - EBD
    - ESC
    - TC
    - Active Torque Vectoring (ATV)


    It does seem that the electronic nannies are becoming more commonplace and pervasive.
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    Quote Originally Posted by zax View Post
    So there are now the following traction aids for the STi:

    In 2004:
    - single mode DCCD
    - electronic brake force distribution (EBD)

    In 2008:
    - tri-mode DCCD
    - EBD
    - Electronic Stability Control (ESC)
    -Traction Control

    In 2015:
    - Tri-mode DCCD
    - EBD
    - ESC
    - TC
    - Active Torque Vectoring (ATV)


    It does seem that the electronic nannies are becoming more commonplace and pervasive.
    Yeah I'm sure the 15 will be quite an adjustment from my 04.
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    zax
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    Bigger adjustment from my 2003. There are things about my bug that I will miss however. The new STi doesn't have that mechanical feel the bugeye had. The 2015 WRX even less so...
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    Traction mode should turn off the most intrusive stuff at least, no?
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