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Thread: Understanding Gen4 Haldex Logging (Mk6 Golf R)

  1. #1
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    Understanding Gen4 Haldex Logging (Mk6 Golf R)

    Hi everyone,

    Not sure if this exactly fits under here, but I am trying to do some initial logging to understand how the Gen4 Haldex system in my Mk6 Golf R works. I will likely consider an upgraded controller/software in the future so I am also looking to have a before and after. In the link below, you'll find some posts I have made on some initial logging of the Haldex operation, and so far I am a bit disappointed in the system acting in an AWD fashion. I am hopeful it will be a bit more lively when on track, but before I jump to too many more conclusions, I want to make sure that I am indeed logging the right values. It is my understanding that there is a valve in the Haldex unit that controls how much oil flows through a certain passage that ultimately controls the pressure plate (paraphrasing here), with 0% being open (i.e. no power to the rear) and 100% being fully closed (i.e. 50% power to the rear), with this essentially being a linear operation (i.e. for every 2% opening in the clutch valve, 1% power goes to the rear). To that end, it appears the values in Module 22 - AWD, measuring block Group 3, Field 2 "Clutch Valve - (N273) Opening (%)" seem to be the ones I am most interested in, and so far my logging seems to show it to be something that moves with what I perceive as power transfer to the rear.

    In short, my question is this: is my understanding of the Haldex system correct and is that the right field to measure to understand power transfer to the rear? Are there other fields I should see or log? Any more knowledge on the Haldex system as a whole would also be great. If anyone else has logs from their cars (Gen4 systems in the Audi TT or S3 would be awesome for comparison too) that would also be cool. Thanks!

    https://forums.vwvortex.com/showthre...#post113904773

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    I have done some measurements to understand how Haldex system works, however it was 5th gen.which means it’s easier to diagnose using VCDS.

    Just a few thoughts of what I learned having VCDS hooked into different vehicles.

    1) Yes, probably the valve opening is the best estimate of torque transfer. However, worth to note that as you go faster transferred torque needed is less thanks to gearing change. Also not to have “overtight coupling/tighter coupling” at higher speeds, the clutch “clamping pressure” should be decreased as speed increases.

    2) Also observed that some vehicles have a “slack (a noticeable speed delta between front and rear axles)” before the Haldex-clutch kicked in. The slack seemed to be different on different gears as well as on different brand/model vehicles. On Skoda Octavia there was no slack on gears 1-3, but then approx. 3km/h and above delta was needed on higher gears for Haldex to kick in. On a Golf Allroad the same but on gears 1-4 no slack. This feature makes them to feel more like front-wheel driven. Both had same engine output 110kW/340Nm. Manual 6-gear transmission.

    3) The third way of operation I observed was a “pre-emptive” approach on high-end VW Transporters. The coupling seems to be driven on driver demand; even slightest push on throttle tightens the clamps of the Haldex-clutch. Seems like it doesn’t allow any speed delta between front and rear axles. It’s actually quite interesting that on snowy surface it won’t even flash traction control light at full throttle even though all 4 wheels are slipping (but equally). Actually I like this behavior a lot.

    4) So I would try plot speed delta between front/rear vs. clutch clamping pressure as a function of vehicle speed to see if that makes any sense.

    Anyways, the target of my measurements was different – to get a misbehaving 4Motion fixed. And eventually it happened – thanks to VCDS! If interested have a look at -> https://www.t6forum.com/threads/4mot...-failure.7157/

    Hope this makes some sense…
    Last edited by VWT6; 01-05-2020 at 03:21 PM. Reason: Information added

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  4. #3
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    Quote Originally Posted by VWT6 View Post
    I have done some measurements to understand how Haldex system works, however it was 5th gen.which means it’s easier to diagnose using VCDS.

    Just a few thoughts of what I learned having VCDS hooked into different vehicles.

    1) Yes, probably the valve opening is the best estimate of torque transfer. However, worth to note that as you go faster transferred torque needed is less thanks to gearing change. Also not to have “overtight coupling/tighter coupling” at higher speeds, the clutch “clamping pressure” should be decreased as speed increases.

    2) Also observed that some vehicles have a “slack (a noticeable speed delta between front and rear axles)” before the Haldex-clutch kicked in. The slack seemed to be different on different gears as well as on different brand/model vehicles. On Skoda Octavia there was no slack on gears 1-3, but then approx. 3km/h and above delta was needed on higher gears for Haldex to kick in. On a Golf Allroad the same but on gears 1-4 no slack. This feature makes them to feel more like front-wheel driven. Both had same engine output 110kW/340Nm. Manual 6-gear transmission.

    3) The third way of operation I observed was a “pre-emptive” approach on high-end VW Transporters. The coupling seems to be driven on driver demand; even slightest push on throttle tightens the clamps of the Haldex-clutch. Seems like it doesn’t allow any speed delta between front and rear axles. It’s actually quite interesting that on snowy surface it won’t even flash traction control light at full throttle even though all 4 wheels are slipping (but equally). Actually I like this behavior a lot.

    4) So I would try plot speed delta between front/rear vs. clutch clamping pressure as a function of vehicle speed to see if that makes any sense.

    Anyways, the target of my measurements was different – to get a misbehaving 4Motion fixed. And eventually it happened – thanks to VCDS! If interested have a look at -> https://www.t6forum.com/threads/4mot...-failure.7157/

    Hope this makes some sense…
    Yeah definitely makes sense, and I see what you are talking about in #1, so I will probably need to look at torque values too. It gives me the option to log estimated torque, but I wonder if that is total estimated engine torque, or just that which is making it to the rear? Even though you are talking about different vehicles and systems, do you know what the values to look for to log axle speed? Not sure if that is in the AWD module or in a different one?

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    Quote Originally Posted by mailman2013 View Post
    Yeah definitely makes sense, and I see what you are talking about in #1, so I will probably need to look at torque values too. It gives me the option to log estimated torque, but I wonder if that is total estimated engine torque, or just that which is making it to the rear? Even though you are talking about different vehicles and systems, do you know what the values to look for to log axle speed? Not sure if that is in the AWD module or in a different one?
    The set of measurement values is pretty limited even on Gen5 - understandably just the internals of the AWD. It took me a while to get grab on what was going/not going on. I would have liked to record engine and gearbox at the same time but that's certainly beyond VCDS's current capabities.

    Anyways, from the AWD I can read speed of the all wheels individually, precalculated axle speed delta and most importantly for me Clutch status - "degree of blockage 0..100%". In addition there are pump current/voltage/PWM depth which just seem to boil down to "degree of blockage". The impressive thing is that VCDS interface HEX-V2 is capable to record at approx 10Hz rate set of 12 freely selectable measurement values.

    The abovementioned capabilities likely would allow to extract more data - as from wheel speed deta acceleration can be extracted, knowing mass of vehicle + accelerations would give us force, etc. Hmmm... fascinating...
    Last edited by VWT6; 01-07-2020 at 12:39 PM. Reason: Clarifications

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