New used Yeti owner, haldex spin on launch?

[logiclee]

1 hour ago, KenONeill said:

You're most of the way there actually. Haldex is a reactive system with no centre diff, 

 

Gen 1, 2 and 3 were reactive. Gen 4 and 5 are pre-emptive and work with the cars stability systems to pre-empt a loss of traction and move torque rearwards before slip occurs.

 

This can be a high torque demand from launch or launch control activated, input from steering angle, yaw angle sensors and engine torque demand. The parameters are even changed if a trailer is attached as long as it's correctly coded.

 

The post from Muddyboots assumes that haldex is either fully engaged or not engaged. This is not the case. For Gen 4 and Gen 5 the ECU can adjust the pressure on the wet clutch plates which allows slip. This adjusts how much torque is sent to the rear axle and also allows speed differential between the front and rear axle which avoids windup. 

 

For the reactive part of the system Gen 4 and Gen 5 can send 50% of the torque to the rear wheels within 1/8th of a revolution of slip on the front wheels.

 

Have a look at this A3 the rear is squatting on launch before the front looses traction.

 

https://www.youtube.com/watch?v=vbmenMq7jWU

Edited 17 December, 2021 by logiclee

[Ootohere]

Pre-emptive but not Darren Brown / Mind reader, and not using the Ground Temperature, barometer, cameras / radar or GPS.

 

So has no idea that as a driver starts the car they are away to just floor the throttle to move off with a bit of angle on the steering and ditch finder or little better than that tyres.

[logiclee]

18 minutes ago, roottoot said:

Pre-emptive but not Darren Brown / Mind reader, and not using the Ground Temperature, barometer, cameras / radar or GPS.

 

So has no idea that as a driver starts the car they are away to just floor the throttle to move off with a bit of angle on the steering and ditch finder or little better than that tyres.

 

 

Correct.

 

If you are in first and ask for 85% torque with your right foot chances are the Haldex ECU will give you some rear axle assistance before the engine can give you what you've asked for. 

But some steering lock on a wet low grip road, low grip tyres with 25% torque demand and it may well be reacting to that slip.

 

And even with a 50/50 split of torque front / rear torque you may still get some spin on that inside front that the traction control has to try and brake. We are not talking 3 locked differentials here.

 

On the rollers. Gen 5 vs Torsen Quattro 

 

 

 

 

 

 

 

Edited 17 December, 2021 by logiclee

[KenONeill]

1 hour ago, logiclee said:

Gen 1, 2 and 3 were reactive. Gen 4 and 5 are pre-emptive and work with the cars stability systems to pre-empt a loss of traction and move torque rearwards before slip occurs.

That's still a reactive system, faster sure, but it's still reacting to throttle setting and steering angle.

[muddyboots]

24 minutes ago, KenONeill said:

That's still a reactive system, faster sure, but it's still reacting to throttle setting and steering angle.

It's not reactive in the sense it's waiting for wheel slip. Under certain circumstances  (setting off from standstill, or burying the throttle while on the move) it'll engage even if there's no slip.

 

I just remembered a video I made ages ago, one winter when our drive was literally a sheet of ice (so much so I could barely stand up).

Not particularly scientific and you can only see one side, but fun nevertheless...

d

[muddyboots]

1 hour ago, logiclee said:

The post from Muddyboots assumes that haldex is either fully engaged or not engaged. This is not the case. For Gen 4 and Gen 5 the ECU can adjust the pressure on the wet clutch plates which allows slip. This adjusts how much torque is sent to the rear axle and also allows speed differential between the front and rear axle which avoids windup.

Perhaps in this particular circumstance there's a slight mismatch between the level of engagement and the front/rear diff speed difference, such that there's a tiny bit of tension between the two axles ? Just enough for a gentle thump when it disengages.

 

Perhaps this also explains the slight wheelspin when pulling left/right out of a side street - Haldex is not fully engaged (to allow for the front/rear steering difference) - so less drive to the rear than when front wheels are straight, hence a small amount of front spin. It's a lot less spin than you'd get in a front drive car (as I recall).

Edited 17 December, 2021 by muddyboots

[logiclee]

4 hours ago, KenONeill said:

That's still a reactive system, faster sure, but it's still reacting to throttle setting and steering angle.

 

Not in Borg Warners opinion.

 

Moving torque rearwards before slip has occurred using input from sensors and lines of code is classed as pre-emptive.

 

It's not reacting to slipping wheel when traction is already lost.

 

That's no different really to the many different modes in more off road biased 4x4's where torque is distributed depending on mode selected and input from sensors prior to wheel slip.

 

As an Electrical Engineer working daily with code Pre-emptive systems are common place whether you agree with the terminology or not.

 

Definition

 

 

In this case the software Prevents "Forestall" Slip by taking advance action before slip occurs.

 

 

Edited 17 December, 2021 by logiclee