2005 USDM STi yaw sensor answer...

[dustinr]

Dear Mr. Reed:

Thank you for visiting the Subaru Web site and for your interest in
Subaru products! We appreciate you taking the time to contact us.

I've consulted with our Technical Services Department, and they've
advised that the 2005 WRX STi models are equipped with a YAW sensor.
Apparently there is information available about this component in the genuine
Subaru service manual for this model.

I hope this information is helpful to you, but should you have further
questions, please let me know and I'll do my best to assist you
further.

Best Wishes,

Natalie Cox
Subaru of America, Inc.
Customer Dealer Services
E-Contact Group

"So now we know..."

[sperry]

Originally Posted by dustinr

Dear Mr. Reed:

Thank you for visiting the Subaru Web site and for your interest in
Subaru products! We appreciate you taking the time to contact us.

I've consulted with our Technical Services Department, and they've
advised that the 2005 WRX STi models are equipped with a YAW sensor.
Apparently there is information available about this component in the genuine
Subaru service manual for this model.

I hope this information is helpful to you, but should you have further
questions, please let me know and I'll do my best to assist you
further.

Best Wishes,

Natalie Cox
Subaru of America, Inc.
Customer Dealer Services
E-Contact Group

"So now we know..."

Now we know what? What's the yaw sensor for? I don't believe Subaru has any sort of AYC. IIRC, the only use for a yaw sensor would be for helping the DCCD determine when you're turning hard so it will adjust the torque split to the rear.

[MikeSTI]

yah! would suck to have a sensor but no control

just mad because I dont have one

[sperry]

Originally Posted by MikeSTI

yah! would suck to have a sensor but no control

just mad because I dont have one

No, I'm pretty sure all the DCCD car's w/ an "Auto" setting have a yaw sensor. Otherwise the only way it could tell how hard you were turning is by comparing rpms at all 4 tires, which is useless if the tires are spinning.

[dustinr]

Now we know what? What's the yaw sensor for? I don't believe Subaru has any sort of AYC. IIRC, the only use for a yaw sensor would be for helping the DCCD determine when you're turning hard so it will adjust the torque split to the rear.

The STi's haven't had a yaw rate sensor untill this year when the JDM cars got it, but it was never officially stated whether or not the USDM cars got it or not. It's all part of the changes made to the 05's..

http://www.autoweek.com/article.cms?articleId=100446

[sperry]

Originally Posted by dustinr

The STi's haven't had a yaw rate sensor untill this year when the JDM cars got it, but it was never officially stated whether or not the USDM cars got it or not. It's all part of the changes made to the 05's..

http://www.autoweek.com/article.cms?articleId=100446

Well, then I need someone to tell me how the auto mode works on the DCCD.

AFAIK, the car "senses" when the car is in hard turns, and splits the torque bias towards the rear, making the car oversteer instead of understeer like the non-DCCD cars do.

As I said before, you need some sort of yaw or latteral-G sensor, or you need to watch for large discrepancies in wheel rpms (since the wheels on the outside of a turn spin faster than the inside). the problem w/ using wheel rpms is that if the car is sliding or spinning the wheels, that information isn't accurate. Plus in long, fast sweepers, the wheel rpms won't be much different, but a rear torque bias would be very helpful.

Who's got the knowledge to drop on us about DCCD?

[Kevin M]

The Evo uses a yaw sensor as part of the AYC rear diff. Unless Subaru just developed a technology like that without a whisper to the aftermarket community, The '05s don't have that. That means the yaw sensor referred to in that email is actually the lateral G sensor used to tell the DCCD to send torque bias rearward. I can bring my DCCD G sensor to the meet next week asuming I pick up my stuff at S-Squared.

[ScottyS]

Yaw sensor? That's what tells you how much rudder you're holding for the crosswind. I would have thought all WRX's came with those........

[dustinr]

Originally Posted by BAN SUVS

The Evo uses a yaw sensor as part of the AYC rear diff. Unless Subaru just developed a technology like that without a whisper to the aftermarket community, The '05s don't have that. That means the yaw sensor referred to in that email is actually the lateral G sensor used to tell the DCCD to send torque bias rearward. I can bring my DCCD G sensor to the meet next week asuming I pick up my stuff at S-Squared.

Here's an excerpt from another article...

The new electro-hydraulic system has a yaw-rate sensor, which senses if the car is pivoting and will quickly alter the power sent to each wheel.

The current STi, which already has excellent traction, has a system that's not quite so quick to react. It detects load and slippage of the wheels before redirecting power.

The new system also features a centre differential that can be controlled by the driver, depending on how they like the car to behave. That means the driver can decide which wheels they want more power sent to.

[Kevin M]

That claims that the STi has active front and rear diffs... first I've heard.

The way the DCCD works in Auto mode is it sits at 50/50 torque split until it senses lateral acceleration, which can also be called yaw. The more lateral force, the farther rearward the torque split goes, maxing at 65/35 rear/front.

[sperry]

Originally Posted by BAN SUVS

That claims that the STi has active front and rear diffs... first I've heard.

The way the DCCD works in Auto mode is it sits at 50/50 torque split until it senses lateral acceleration, which can also be called yaw. The more lateral force, the farther rearward the torque split goes, maxing at 65/35 rear/front.

Lateral G and yaw are actually a bit different. Yaw usually preceeds and accompanies lateral G's, but you could potentially get lateral G's w/o yaw, lick if someone bumps you while racing down the straigth away... I wonder if in that situation the DCCD would shift the torque rearwards...

As far as all that talk of active diffs and yaw control, I swear dustin's reading EVO articles, because that's all news to me on an STi... maybe the rally car has that stuff?

[Kevin M]

Originally Posted by sperry

maybe the rally car has that stuff?

You might have nailed it. Prodrive has put all kinds of tasty bits on the WRC cars in recent years.

[dustinr]

Originally Posted by BAN SUVS

That claims that the STi has active front and rear diffs... first I've heard.

The way the DCCD works in Auto mode is it sits at 50/50 torque split until it senses lateral acceleration, which can also be called yaw. The more lateral force, the farther rearward the torque split goes, maxing at 65/35 rear/front.

The owners manual says that in "Auto" the car stays at 35/ 65 (front/ rear) most of the time and then alters that depending on circumstance. I would imagine that when the car senses excessive yaw while comming out of a corner it transfers torque forward which would help pull the car out of the corner instead of transfering it backwards where it could possibly lead to more rear wheel spin/slip.

[sperry]

Originally Posted by dustinr

The owners manual says that in "Auto" the car stays at 35/ 65 (front/ rear) most of the time and then alters that depending on circumstance. I would imagine that when the car senses excessive yaw while comming out of a corner it transfers torque forward which would help pull the car out of the corner instead of transfering it backwards where it could possibly lead to more rear wheel spin/slip.

I remember reading just the opposite... 50/50 until you toss it into a corner where it transfers the torque to the rear so the car will rotate. 'Course, I don't have an STi owners manual.

[Kevin M]

Originally Posted by dustinr

The owners manual says that in "Auto" the car stays at 35/ 65 (front/ rear) most of the time and then alters that depending on circumstance. I would imagine that when the car senses excessive yaw while comming out of a corner it transfers torque forward which would help pull the car out of the corner instead of transfering it backwards where it could possibly lead to more rear wheel spin/slip.

Transferring torque forward while turning in an AWD car is counterproductive. It would create yet more further understeer by increasing the load on the front tires. Anyways, check it again. I'm almost positive that it's 50/50 transferring to 65/35 as needed.

Also, every other manual transmission Subaru currently sold is 50/50 all the time but doesn't have a locking center diff.

[dustinr]

Originally Posted by BAN SUVS

Transferring torque forward while turning in an AWD car is counterproductive. It would create yet more further understeer by increasing the load on the front tires. Anyways, check it again. I'm almost positive that it's 50/50 transferring to 65/35 as needed.

Also, every other manual transmission Subaru currently sold is 50/50 all the time but doesn't have a locking center diff.

Not sure for certain how it transfers torque during cornering but I'm 100% certain that it's 35/ 65 normally.

[Kevin M]

Originally Posted by dustinr

Not sure for certain how it transfers torque during cornering but I'm 100% certain that it's 35/ 65 normally.

Gather round, one and all, as the esteemed i-club tech forums moderator eats his words! Dustin, I was wrong about torque split in the STi. It's ALWAYS at 65/35... I had wrong information.

Here's an excerpt from the service manual courtesy of i-club member TreyS:

http://www.phear7imports.net/tech/07...l%20System.pdf

The torque split is always static. It's the locking characteristics that change. Basically, under hard acceleration and cornering, it locks more, and under braking and leisurely driving it locks less.

dustinr 1, BAN SUVS 0.

[MikeSTI]

lol then why do you post 65/35 :? its 35/65

[Nick Koan]

Originally Posted by MikeSTI

lol then why do you post 65/35 :? its 35/65

cause he's a dirty bastard thats posting the rear/front split. Bastard, doesn't he know front/rear > rear/front.

[sperry]

Part of the problem comes from saying "torque split" when that's not really what we mean. I had this conversation with MattR a while back, and we figured it out like this:

The power/torque from the motor is fixed to the wheels (I thought it was 50/50 but I guess it's actually 35/65).

What's varied is the amount of speed difference is necessary before the center diff locks...

When the DCCD is set to full forward mode, the center diff is locked, i.e. the front and rear wheels have to turn at the same speed... so while the rears are getting 65% of the power, they are still locked with the fronts. If you jump on the gas you'll break all 4 loose.

When the DCCD is set to full rear, the center diff requires a much higher speed at the rears before they lock to the fronts. So those rear tires are getting 65% of the power and are free to spin wildly while the fronts grip and pull with their 35% of the power. At full rear, the car behaves more like a RWD car because jumping on the throttle will break the rears loose w/o losing the front traction.

Auto mode uses a lateral G sensor to decide where to set the split. I doubt it will ever go all the way forward, because a locket center diff is only usefull on gravel or snow or in the wet, otherwise the wheels will bind up. My guess is that the diff sits at middle ground normally, but will throw the bias rearward under high latteral G's because having the rears uncoupled lets throttle modulation turn the car... i.e. auto mode helps the car to turn more like a RWD car, but gives you additional traction when driving in a straight line.

Bottom line is this: the DCCD is friggen cool!! Damn I want an STi.

[AtomicLabMonkey]

Originally Posted by sperry

Damn I want an STi.

It's calling your name...

[sperry]

Originally Posted by AtomicLabMonkey

It's calling your name...

I'm constantly sooo tempted. But I also love my car as it is sooo much! If I had $10,000 lying around, I'd be at Subaru tomorrow.

[Nick Koan]

Originally Posted by sperry

I'm constantly sooo tempted. But I also love my car as it is sooo much! If I had $10,000 lying around, I'd be at Subaru tomorrow.

Lies. You hate your car and want to trade it in.

[sperry]

Originally Posted by nKoan

Lies. You hate your car and want to trade it in.

I have to say, I like the way my car looks a 1000 times better than the STi. Plus all the work I've got into it makes it a blast to drive. The only problem is that the drivetrain can't go much further than its current state w/o spending a butt load of cash on it... I think it would be cheaper to just get an STi than to upgrade what I've got. But the kicker, is that an STi means car payments again... and I'm just wrapping up 3 years of that crap, and I'd rather not have new payments again so soon.

[dknv]

Originally Posted by sperry

I'm constantly sooo tempted. But I also love my car as it is sooo much!

I can empathize. Especially with the thought of parking mine for the winter....