Auto Diff Control - Caution !

[Brian]

I hearby say that i will no longer be using the AUTO diff control after what happened yesterday.

Ive heard of many stories from members regarding problems with AUTO on the DCC.

Now i have experienced it and it isnt nice.


Ok long straigth road this time !!!

Down to 3rd and floor it, as passing over the Cats eyes in the centre of the road i was side by side the car i was overtaking.
While the nearside wheels were going over the cats eyes still in 3rd gear full throttle.

The car sweerved towards the drivers door of the car i was overtaking !!!

ending up about 2 inches from the drivers door, i then pulled the WR1 back over to the right.

Now this was was the problem

Going over the Cats eyes, on full throttle, the auto control thought i had lost traction so moved power somewhere else, thus giving the swerve toward the side of the car i was overtaking !!

VEry shook up, i took it out of Auto, and into the green manual, and did Exactly the same with the next car in front of me..

No swerving and no problems...

AUTO diff Control !! what a dangerous thing to have.

It will be permantly disconnected from now on. As i know if i take it to the dealers, they will say theres nothing wrong.

As with all the other WR1 Owners who have taken their WR1s back with Auto Diff Problems.

[chris]

$hit, that could have been nasty. I've not had it happen to me (yet) but i may find an empty strech of road to try it on, so i know what to expect.

[stijoy]

glad that you did'nt hit the car, i would have been really shook up if that had happened to me, and then doing the same with dccd off, and totally safe, i hope mike woods see this, because he says leave it in auto the best for driving, but after your experience today, not so sure.

[mr optimax]

i had a simular thing happen,thought it was me not paying enough attention.

[jaycee]

Trade-in for an STI anybody?! No problems like that and it's a proper blue.

Glad you're ok Brian.

[Brian]

what i cant work out is, why it didnt happen when set in manual fully back in the green ?

In auto, it pulled over to the nearside as if it was a front wheel drive car that had just lost traction.

[Kamakarzi]

Thanks for that info Bri!.........Food for thought ah.

[Gee Wr1]

This is what i talked about in other threads when i described it as snatchy. Never liked it for that reason. Don't know if the state of the roads up here (very uneven & bumpy) but quite often found the car veering of line, bit scary at times!!! Always run it full open in the green, only put it in the orange in the snow.

[GalaxiaN]

VEry shook up, i took it out of Auto, and into the green manual, and did Exactly the same with the next car in front of me..

The first near miss would have made me back off a bit.... LOL! Have to admire your determination to check things out throughly
I bet the driver you'd overtaken before was thinking OMFG! Look at that nutter he's doing it again

There are times when you can definately feel the car's power shift between front/rear but I've not experienced anything like you describe. I'm wondering if it could have been something on that patch of road.

[Brian]

it may have been,

it did it while going over the cats eyes.

[johnfelstead]

did you feel the steering pulling to the left when you experienced this?

Looking at the info i have on the MY04 DCCD it does take into acount slip sensed on all 4 wheels independantly, what the info doesnt show is how that affects torque distribution under acceleration when it senses slip on one wheel. Under braking the centre diff is put in an open state if the ABS system activates to free up the diff coupling.

When you go full throttle it is programmed to feed more lock in to distribute more torque to the front wheels, not something i am a big fan of to be honest.

From what you describe i would think Lee is on the right track, i would put this down to the way the front surtrack reacted to a loss of traction whilst you were full throttle and a lot of torque was going to the front diff, rather than the centre diff per se. Having it in Auto mode would make that situation worse due to its increase in front torque transfer under full throttle.

Suretrack diffs are not my favourite devices because of the way they transfer torque which can lead to torque steer issues. This is probably why they have changed the front diff on the MY05 to a helical LSD.

Out of interest, have you ever had the suspension geometries checked? If you have a bit of toe out at the front you will get far more prominant problems when you suffer front torque steer.

[Brian]

Cheers John, from what you are saying also does conclude this, to be loss of grip from the nearside front, while most torque was being sent to the front.

A bit like a front wheel drive car loosing traction, which i experience rather alot in my Tdi Caddy van


The geometry setting were all sorted out last autum as the rear was slightly out.

[Mike Wood]

The thing is though that unless the car yaws and you have considerable differences in axle speeds, the centre diff control will be doing nothing. The reason it didn't do it in manual open is that you may not have got the conditions exactly the same. If the car did drift across it may have been because it was effectively spinning both rear wheels as the DCCD wasn't doing anything anything, although this is very unlikely in a straight line.

99.9% of the time, running the car in Auto gives the same effect as running in manual open, the only real difference is that it will get you out of a tankslapper in Auto where it allows the slip to continue in manual.

A classic example is a pair of corners with a direction change in the middle, like a roundabout with a nice exit although we do this on our track through a sequence of corners. You can provoke the car to create oversteer in the first part but if you aren't sensitive when it comes to turning the other way (or wind too much corrective lock on in panic) the oversteer gets much bigger the other way in manual open, to the point where you may spin. Type R owners may be famililiar with this. In auto, you think you are a driving God and have managed to collect it all up, when what's really happened is that the DCCD has limited the rear wheel slip by locking slightly.

Having said all of that, it could have been the front diff snatching but this is not influenced by the DCCD being set in Auto.

Mike

[johnfelstead]

That's not quite correct though Mike, the centre diff control mapping isnt reliant on axle slip or G input (WR1 doesnt have a yaw sensor) to produe a locking of the diff. If you look at the map profile, even in a straight line the centre diff controller aplies lock based on throttle position, it actually aplies more lock in a straight line than it does when you are experiencing lateral G.

there is a nice illustration of the DCCD-A mapping here where the G axis is lateral G, the 100 axis is throttle position and the LSD axis is % centre diff lock.

[Brian]

Thanks for your Replies Mike and John.

[Mike Wood]

John

It may not have a yaw sensor but it can measure g and in particular responds to rapid changes in direction of g loadings. Try a high speed emergency lane change and recovery with it turned on and off and you will see a marked difference. Note that this should only be done on a test track where there is lots of space to collect it all together!!

Mike

[johnfelstead]

i know Mike. just wanted to clarify that the WR1 doesnt have a yaw rate sensor. The WR1 has a lateral G sensor which isnt capable of outputing a value based on rate of change, where as the MY05 has a lateral G sensor and a yaw rate sensor.

Thats not the main issue with this topic though, the main issue is the way DCCD-A works in a straight line under hard acceleration, and in that scenario the centre diff is being locked, with the diff lock reducing if you come off the throttle or if the car senses lateral G, its not kept in an open state when you are going in a straight line unless you come off the throttle or hit the brakes, where it releases the diff lock to allow the ABS system to control braking traction.

I would say typically people drive in the 15-30% throttle region when driving normally, which is going to give you between 8% and 14% lock. The relationship of lock rate stays pretty linear be it in a straight line or cornering until you get to about 50% throttle, at which point the more lateral load you bring into the equation through cornering, the less the centre diff locks as a percentage of increased throttle. Thats to allow the car to have a power on neutral balance in the corner then as the lateral load drops away as you exit the corner the torque starts shifting to the front to keep that neutral balance.