Prompted by NC's explanation in the Dog thread of self-levelling suspension, I found myself pondering this hypothetical situation.
The Mercedes E I'm about to take on has xenon (sorry, bi-xenon) lights. Being an estate, it also has rear self-levelling. Now, presumably the lights are the same as those fitted to the saloon, which has ordinary rear suspension, so they'll have their own self-levellers to satisfy the regulations. But just suppose those levellers stopped working, would the rear levellers do enough to keep the lights aimed correctly, and so keep the car legal?
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(There will of course be time later for this to degenerate into a slanging match about the merits and/or perceived irresponsibility of HID lighting.)
}:---)
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According to my Haynes manual, Mondeos with xenon headlights take their levelling measurements from both front and rear suspension. The motors in the headlights adjust the beam up and down to compensate for squat and dive, but there is no level detection capability in the headlight units themselves.
If the Mercedes's headlight motor failed in use, the beam would continue to point wherever it was pointing at the moment of failure. The self-levelling suspension would serve to reduce, but not eliminate, squat and dive which means the stuck headlight could still dazzle other road users.
Because the levelling on xenon headlights sets itself to the lowest level before switch-on and raises the beams to the correct level once the beams have stabilised (hence the 1 second or so "bounce" seen when switching them on), I would expect Mercedes have programmed the car to not allow the affected light to illuminate if there was a fault with the motor getting stuck.
I've only ever had 1 headlight levelling system fail on a car - on my 300k mile Skoda the level sensor wore out causing the driver's side light to constantly oscillate up and down between positions 0 and 1.
Last edited by: Dave_TDCi on Wed 25 Apr 12 at 15:59
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Thanks, Dave. Spending a wet afternoon in the library?
};---)
Interesting that the motors come into play every time the lights are used; that hadn't occurred to me. I can hear the 'more to go wrong' bell in my head but the deed is now done and I'm looking forward to what I'm assured will be a better view of the poorly surfaced and marked A-road I drive home every night.
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As Dave says, the lights calibrate themselves every time the car starts up. They will move down all the way, then up and then adjust to the correct level. If you have directional lights then they would also go left and right to calibrate sideways movement too.
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>> If you have directional lights then they would also go left and right to calibrate sideways movement too.
Mine don't, though it'd be really cool if they did.
I've heard of odd cases of the directional lights on older Merc W211s getting stuck and making the car look cross-eyed, like that weird Morgan from a few years ago.
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The adaptive xenons on the '55 plate 5 series touring definitely used to sweep up/down and then left/right, but the ones in the Merc don't do the left/right sweep, or if they do it's imperceptible to me. On the other hand when in use the directional nature of them seems to be more obvious than in the BMW. Conversely the halogen lights in our old 120d used to do the same sweep up on start as xenons...
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>>. Conversely the
>> halogen lights in our old 120d used to do the same sweep up on start
>> as xenons...
My 320d does the same. Down, up, level on every start up.
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>> On the other hand when in use the directional nature of them seems to be more obvious than in the BMW.
Did the Mercedes also have static cornering lights? My VW does and so when the steering is turned enough or indicating at junctions the relevant static cornering light will come on.
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>> >> On the other hand when in use the directional nature of them seems to
>> be more obvious than in the BMW.
>>
>> Did the Mercedes also have static cornering lights? My VW does and so when the
>> steering is turned enough or indicating at junctions the relevant static cornering light will come
>> on.
>>
Not sure TBH. It doesn't have front foglights though, which is what some Merc's and VW/Skodas seem to use for this. The deflection of the dipped beam just seems more pronounced than in the BMW.
The 'Intelligent Lighing System' (!!) is what adapts the length and breadth of the beam and suposedly makes seperate front fog lights redundant - there's not even a front fog light switch. Motorway mode, which is the beam pattern it switches to after a certain length of time above a certain speed (if that makes sense) when travelling in a straightish line is also pretty impressive in terms of the reach of the lights, but has only really been of any use in France so far!!
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Did the Mercedes also have static cornering lights?
My 2007 Roomie had them !
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For belt, braces and half-a-dozen safety pins, you can't beat that late-model Vectra I had on hire some time ago, fitted with GM's Adaptive Forward Lighting system.
That'll be Bi-Xenons that self-level, steer side-to-side and static cornering lights. The latter ratther cleverly being built into the side of the headlamp shell so they illuminated into the side turning, rather than just putting a puddle of light on the floor in front as others do.
Incidently, the Bi-Xenons on that didn't wave around on startup and still managed to self-level and point the right way. It must be a gimmick.
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>> Thanks, Dave. Spending a wet afternoon in the library?
>> };---)
library internet :)
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Xenon lights: how much levelling is enough? - WillDeBeest
