ACC vs Audi Mag Ride

[morrissey]

Does anybody know how ACC works, and how it differs from Audi's mag ride?

[DavidH]

I have some idea how it works,i'll try to summarise.

ACC uses electromechanical adjustable valves,developed by Ohlins,i've forgotten the name of the system but it's used before by Volvo and other marques.

It's an electromechanical valve,i think it takes about 10ms to make an adjustment,not as fast as the delphi magneride system but the big difference is that while magneride is purely reactive (i think,as it can afford to be because it's so bloody fast-the dampers themselves are capable of 1000 adjustments a second although the true speed is limited by the speed of the processing),the ACC is also predictive in that it takes data from more sensors (body position aswell as wheel position and also driver inputs-steering/throttle/braking),processes all that data through an algorythm and a dedicated computer,and decides the optimum damping for each wheel continuously.i think it's fast enough to adjust the compression and rebound damping seperately up to a decent wheel frequency-not sure though,i'll try to find the article i read about it which gives the frequency.

The delphi,from what i understand just uses wheel position sensors and so is a more reactive system,but it's speed means that it can afford to be.It's also arguably more reliable as it has no extra moving mechanical parts compared to a standard monotube damper,whereas the ACC will need to have motors and moving parts within the valves themselves i assume,which are electromechanical.So ACC is more complicated,there's more moving parts to get stuck/wear out/generally go wrong but i like the idea of it collating all this data and deciding the optimal damping,it sounds cool,like the eurofighter or something ,you know that when you turn in to a corner it's already adjusted the damping in anticipation,even before the suspension has loaded up-i think that's cool anyway.There's a video on VWs site somewhere showing how the system works,i'll find it and post a link.

Magneride essentially is a conventional monotube shock,but makes adjustments by altering the viscosity of the damper fluid (electromagnetically),so the vavle itself doesn't adjust,just the effective viscosity of the fluid.Since it's not mechanical,it can make adjustments very quickly (electricity is quite fast ) and so doesn't need all the additional data input from additional sensors,it can react so fast that it's able to control the damping optimally for each wheel from data just from 4 wheel position sensors.It's fast enough to adjust the compression and rebound damping sperately,from what i can gather,for each cycle/oscillation of the suspension up to a high wheel frequency since it's so fast.

I'll have a hunt for some articles,which can explain it better.

[DavidH]

Here's the little VW videos on how ACC/DCC basically works
http://www.volkswagen.com/vwcms/master_ ... r/dcc.html Cool!

Tenneco CES is the name of the system,so you'll find more info by searching for it under that name.

The Audi sytem is called Delphi magneride,i think they have their own site with more info available.

[morrissey]

Cheers David,

well impressed with that ubertechy explanation.

So as I suspected, ACC is a 'poor man's magride.

I'm not knocking it though - it definitely works and it doesn't cost a prohibitive £1200 premium like the Audi system - everybody who has driven magride thinks it's great but hardly anybody specs it and it has little residual value on trade in.

[DavidH]

I don't know which is the costlier system but i wouldn't assume that because Audi charge more for something that the cost price is much higher,i mean some of the option prices on Audis are pretty ludicrous.VW have developed their own algorythms which i imagine isn't cheap and there's a lot more hardware involved with the extra sensors and stuff.Plus i imagine those dampers are pretty expensive.I'm happy to be getting the ACC anyway,i'm not really fussed either way between that and the magride because the ACC really does seem to work and the main thing will be how the car rides and handles.

Ferarri did chose the Delphi system though,and obvioulsy Audi for the R8 which i gather goes rather well GM have used it in the past.

But who knows all the reasons why they chose to go with one system over another,we'll never know.

The only thing that concerns me slightly is the reliability (how on earth do you know when one of the valves stop working? Is there an error message? or is there a way to test if they're still working at service?) and the replacement cost of those dampers because i have a tendency to go through shocks (and tyres) on my cars,i think probably because of the driving i do and roads i drive on.(i live out in the sticks and driving challenging roads is just daily life-plus i'm an ex-racer so go figure,the chassis/brakes/tyres inevitably work a little harder than most is what i mean).The other thing i was looking at is how vunerable the little auxiallary bits and pieces might be on the rear shocks (for projectiles and because i have to drive a lot of times on the verge to pass oncoming vehicles on the singletrack C-roads and it's hard to judge how deep some of the dips and ditches are when the grass is long-so it's inevitable you catch the underside a little on the odd occasion),there's the brackets and wiring for the sensors aswell as the adjustable part of the shock sticking out at the base of the shock-should be OK though-i think .