Haldex?

PA0L0

PA0L0

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Gday, folks I am still looking into the A3 TQS.

I've only really been looking into the quattro's this past week, never really cared about how they worked till I've began to consider buying one.

Was really bored and at the point of sobering up late last night when I stumbled on this link.
Anyway it got me thinking (which granted at that time of the morning wasnt the greatest idea ever), powerloss... the haldex must have a best case and worst case powerloss figure for each car on an individual basis (due to manufacturing differences, wear and tear etc), depending on how the car is being driven and in what conditions, best case slightly more than that of a FWD (during normal driving from a to b) and worst case similar to that of a 4WD/AWD (when pressing on)?

Would I be correct in thinking the above?

Also from the point when the rear wheels do start receiving power, when do they then stop receiving power?

I'm certainly no expert, just trying to get things clear in my own mind, I'm sure there are people on here with a alot of experience and understanding of haldex so I'd really like someone to correct me if I am wrong.

Cheers

Pao
 
Good question, i'd also like to know when the quattro system stops transmitting power to the rear!
 
Would it be fair to say that approximate figures of 18-20% best case (running as FWD) and 30% worst case (haldex engaged) powerloss through drivetrain?
 
i think 30% is a bit to high isnt it?
 
I dont know, thats why I have been asking if anyone has a better idea.

I just noticed... the op in this thread aparently had a loss of about 32% on his nicely uprated s3 between flywheel bhp and wheel bhp measurements
 
yep but on the rollers, because there is no road going under the car it will think the fronts are slipping and put power to the rear. where on road it probably wouldn't, making the 32% loss a worst case @ 50/50 4WD i would think.
 
PA0L0 said:
Would it be fair to say that approximate figures of 18-20% best case (running as FWD) and 30% worst case (haldex engaged) powerloss through drivetrain?
Click to expand...

so looks about right then!
 
i think this would be very difficult to porve as its more a less a matter of opinion.... i suppose you could RR the car with the prop shaft disconnected and then again with it connected...... lot of hassle though
 
Dani_B19 said:
Good question, i'd also like to know when the quattro system stops transmitting power to the rear!
Click to expand...

i believe it stop when there is no difference in rotational rate between input and output shafts to the haldex ie front and back wheels rotating at same speed. think of it as a pump that needs the difference in rotation to pump the clutch closed. thats how i understand it anyway
 
OK guys, my understanding is that the Haldex, out the box at least, works on slip between front and rear axles and throttle position, so in effect, the Haldex only operates under power, so when the throttle is off, then everything if free wheeling. On half throttle lets say, it would use the slip between front and rear axles for it to operate and on full throttle, the Haldex is locked 100%, so 50:50 split power front:rear.
 
jojo said:
OK guys, my understanding is that the Haldex, out the box at least, works on slip between front and rear axles and throttle position, so in effect, the Haldex only operates under power, so when the throttle is off, then everything if free wheeling. On half throttle lets say, it would use the slip between front and rear axles for it to operate and on full throttle, the Haldex is locked 100%, so 50:50 split power front:rear.
Click to expand...

My understanding is that the rear diff/wheels will only kick in 50:50 under extreme loss of traction from the front wheels, think back to the snow we had a month ago. On a normal road at full throttle I would expect the car to be using about 90:10 as the rear wheels just aren't needed. I would have thought that we would be getting loads of threads from people burning out the haldex clutch if it ran 50:50 on full throttle.

Does anyone know whether VAGCOM can be used to log the Haldex activity, that would answer all our queries.
 
Westle said:
I would have thought that we would be getting loads of threads from people burning out the haldex clutch if it ran 50:50 on full throttle.
Click to expand...

How would it get burnt out exactly if it was locked 100% on full throttle? so long as the front and rear wheels are rotating at the same speed, there is nothing to burn right?

Just a thought.
 
it more likley to burn out when its not 50/50 ie the haldex clutch is slipping when not locked at 50/50
 
Thanks for the input guys, its good to hear your ideas and thoughts on how it works.

I appreciate it :thumbsup:
 
jojo said:
How would it get burnt out exactly if it was locked 100% on full throttle? so long as the front and rear wheels are rotating at the same speed, there is nothing to burn right?

Just a thought.
Click to expand...

Sorry I dont think my explanation was very good.

As far as I understand the Haldex system it is a unit containing a clutch that engages when it detects loss of traction to activate the rear wheels. I understand that the clutch components are always spinning so that it is up to speed when it does need to engage the rear axel. I would asume that if this clutch was constantly engaging everytime on full throttle that it would start to wear like a normal clutch?

Basically I thought it only kicked in when detecting loss of traction, so no loss of traction means you're effectively a front wheel drive car!

I've posted a thread in the VAGCOM forum asking if anyone knows if you can log the Haldex activity using VAG as this would answer all our questions :o.k:
 
Hmmm

While i agree with most of what you've said there Wes, the video of the 4 motion system which also uses Haldex doesn't show that. It shows varying rates of power delivered to the rear wheels even on a flat surface, watch the video if you haven't already. The bit where the car overtakes its quite a good representation of what should happen.

G
 
mmm ok. That was just my understanding but that video does show it working all the time.

There used to be a A4 cut in half in the Nurburgring museum to show the Haldex unit working but it was before I had my S3 so I wasn't that interested in it. Now I want to go and see how it works and they've closed the museum down and i'm going in May :keule:
 
It fairly hard to see but the "bars" showing/representing power to each wheel, show that while it's over taking the power is split between the front and rear. I can't quite make out the figures 50% split etc but i'm sure it would be something like that. What i also noticed was it was delivering almost nothing to the rear on the flat surface just before the overtaking maneuver!

Now i'm not saying this video is definative proof, but made by VW Media Services it does kind of say something about the originality of it. I know it's 4 motion but it does say Haldex hydraulic coupling transmission.

It's nice to know that haldex does in fact work and work well. I had a good play around in the snow back in Feb and thought it worked rather well myself. I had no issues with traction where others clearly did.

There are the lovers and haters of the Haldex system here, but what is apparently clear is it does work, otherwise why would Haldex/VAG group etc put so much faith behind it and implement it into their production cars, not to mention the research & development of such a system.

Having the benefits of a 4WD capable system and sometimes not engauging all 4Wheels can only be a good thing. Not only for fuel consumption but wear on components also. I'm not a mechanic and have never professed to be one either but i've a basic understanding of how it works, thanks to the video and litterature on the web.

G
 
Westle said:
As far as I understand the Haldex system it is a unit containing a clutch that engages when it detects loss of traction to activate the rear wheels. I understand that the clutch components are always spinning so that it is up to speed when it does need to engage the rear axel. I would asume that if this clutch was constantly engaging everytime on full throttle that it would start to wear like a normal clutch?

Basically I thought it only kicked in when detecting loss of traction, so no loss of traction means you're effectively a front wheel drive car!
Click to expand...

Yes you are correct in that the Haldex is a closed unit containing a clutch which engages when it detects a loss of traction to the rear wheels. The clutch is a wet type clutch - hence the need for Haldex oil service and filters - which is open and closed hydraulically and controlled electronically(Haldex controller). The idea of the Haldex locking 100% on full throttle is to give you maximum traction when you are giving it, as far as I'm aware, this bypasses the slip part, you would want 50:50 split at maximum throttle wouldn't you? And I guess, to a certain extent, it's to reduce the wear rate of the clutch, as it's already fully engaged, there's no slip... and we all know that clutches wear out when slipping.

What you guys think?
 
I dont know jack anyway so I'm willing to go with what you're saying :friends:

I've done some research on data logging the Haldex with VAGCOM and it doesn't look like it can be done. It would have been great if it could log the bias between front and back while driving.
 
i love these haldex threads, loads of banter and a different overiding conclusion every time:p
 
Lol very very true. Perhaps this is the post to do it though. There is no reason why the information about Haldex and how it truely functions on our cars and others can't be accessed.

Time and effort is all it should take and we'll finally have ammunition to shut all the non believers up! I for one am totally up for that. Oh and of course some ultra friendly banter! :)

G
 
Lol Wes...you'd be right there mate.

I apologised to the ST lads and thats that.....end of story. I've a different view of them and what i did was wrong.

I'm all for proving a point and my point HAS been made. If you don't know what my meaning is on that then...... :):)

I'm not one to start hassles between people regardless of what it might look like to you wes. I stick up for myself and battle to the end if and only IF i think i have just cause to do so.

Unfriendly banter......lol ;)

G
 
Ahem....... lets get back on topic now :blink: lol

VRStu in the VAGCOM forum has checked the Haldex lable file for logging data and it only lets you log the following:

001,0,Brake signals
001,1,Brake Light,Switch -F-,Display range: operated/not operated
001,2,Parking Brake,Switch -F9-,Display range: operated/not operated
002,0,voltage supply and temperature
002,1,Voltage,supply,Specified value: 10...14.5 V
002,2,Oil temperature
050,0,Temperature display
050,1,Oil temperature
051,0,Haldex Clutch Pump
051,1,Haldex Clutch,Pump

I might email ross-tech and ask them if they know of any way to log the front/rear bias with VAG
 
Of course there's no definitive answer, at the end of the day, the Haldex system is a complex bit of kit, how many people do you who can repair it? Answer is always, I think you need a new diff/Haldex controller. It's just cheaper and less stress to get a new part off the shelf. But I am interested in the do' and don't about it, I have a good idea of how it all works in my head, but it's hard to put it all in writing.
 
I've emailed Ross-Tech and they have shown me how to scan a component of the car to create a label file which displays all the things that VAGCOM can log. The label files that come as part of VAGCOM are generic so they only show the basic stuff. I scanned the Haldex and my label file says that it can report "Load" as a percentage. I'm just waiting for Ross-Tech to get back to me as to whether i can log the activity.

I have to say Ross-Tech's support service is excellent and the guy who's been dealing with my email (Andy) has been very fast in his replies. Hopefully I'll have something for you guys later today.
 
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