whats it called

[BrokenBiker]

what is the system called on new cars where the brake lights flicker, and what is it supposed to represent?

I am doing the wiring on the e190 and he wants this system, but we don't know what it is for or why it is used.

any info?

 

[rtbcomp]

Faulty brake light switch?

According to the MOT tester's manual brake lights should emit a steady light.

http://www.motuk.co.uk/manual_120.htm

http://www.customled.com/products/brake_flasher_modulator/brake_flasher_modulator.htm?gclid=CObEm_Wty7kCFcjKtAodhRwAWA

http://www.ebay.co.uk/sch/i.html?_nkw=flashing%20brake%20lights&clk_rvr_id=520750338851&adpos=2o2&MT_ID=10&crlp=15975551077_2113181&tt_encode=raw&geo_id=32241&keyword=flashing+brake+lights&crdt=0

 

[BrokenBiker]

no this is a specifically designed system on new cars.

skip to 45 seconds and watch the veyrons tail lights.

http://www.youtube.com/watch?v=VEL5ABddZ0k

I have also seen this on a ford mondeo estate 2012 model under very heavy braking, and also on a cayenne turbo that flew past me at well over 150 on a drag strip.

 

[BrokenBiker]

right. have had a browse on piston heads too and have found the answer.

the cayenne most likely had a little flasher unit for show, but the mondeo had a system called electronic brake force distribution (ebd) which pretty much means if you stand on the brakes, the car takes over and it can stop you a lot quicker than you could. the flashing is a warning sign to vehicles behind you as they are not likely to be able to stop that quickly.

 

[rtbcomp]

Sounds like a good idea, especially as brake lights can be confused with tail & fog lights.

Maybe the MOT regs haven't caught up, or it may be year specific.

 

[BrokenBiker]

I think it is year specific. Mercedes started it on track cars, then I believe it merged onto merc road cars in late 2010, then onto a few more merc in 2011, and then onto top spec family cars such as the mondeo st and so on in 2012, so pretty much all of the cars with it haven't needed an mot yet. and the few that have needed one, only flash the lights under real panic braking, so testing the brake lights by pressing the pedal will still be normal.

the info above is merely what I have found on a quick google search so it maybe on a lot more cars that I haven't looked at too

 

[Dev]

A lot of newer cars on the continent have this - if you brake harshly it activates the hazard
Gigs to warn drivers behind.

 

[BrokenBiker]

yeah I think I also read somewhere, maybe piston heads, that the bmw cars over here were fitted with led rear lights, with an unused outer ring of led's, because the flashing wasn't authorised here yet, but when it was it simply meant that a small software upgrade was all that was needed to bring the car up to current spec

 

[Fergus]

no this is a specifically designed system on new cars.

skip to 45 seconds and watch the veyrons tail lights.

http://www.youtube.com/watch?v=VEL5ABddZ0k

I have also seen this on a ford mondeo estate 2012 model under very heavy braking, and also on a cayenne turbo that flew past me at well over 150 on a drag strip.

I was under the impression that the effect you are seeing in the video there is due to LED lights being recorded on film.

 

[BrokenBiker]

that may be, and probably is due to the frequency rate of the LED's, but it was merely used to show the effect I was asking about. this is the same thing that happens with ebd under harsh braking.

 

[p0689109]

It is all very well fitting these new systems to cars but if the manufacturers do not tell the general public how the system works and the indications to expect then when Joe Bloggs following one of these cars sees the flashing brake lights or whatever he aint going to know what they are telling him!!!!

 

[BrokenBiker]

this is a good point, but saying that, when I saw the mondeo's lights going, I knew he was braking and I assumed it was to do with the abs and I took action to avoid hitting him.

I have also spoken to a lad with a golf that has seen and done the same thing. it seems tht when people see flashing lights they link it with danger and do what they can to avoid them

 

[AndyStobbs]

Alot of lights are driven by PWM now, they are constantly being turned on or off, faster than the eye can detect - but the camara picks it up. That accounts for 'solid' lights appearing to flash on film.

Different to the original question which is a safety idea as covered already.

 

[seriesonewelder]

Alot of lights are driven by PWM now, they are constantly being turned on or off, faster than the eye can detect - but the camara picks it up. That accounts for 'solid' lights appearing to flash on film.

Is that why headlights on TV flash? - think I've seen it on Top Gear...

 

[AndyStobbs]

Exactly yes

 

[seriesonewelder]

Exactly yes

Cheers

 

[BrokenBiker]

yeah PWM is becoming very common on vehicle applications now. will soon have its place on a 1988 e190 cossie turbo lol

 

[rtbcomp]

What's the idea of using PWM (Pulse Width Modulation) on lights then?

 

[AndyStobbs]

yeah PWM is becoming very common on vehicle applications now. will soon have its place on a 1988 e190 cossie turbo lol

Technically yours is just a flasher, I think the current has to be switched more quickly than the load can change state (for the case of a light from on to off) to be PWM control.


There are various reasons I'm aware of - and probably some I'm not aware of.
Principal one being the BUS systems now in use. There is no longer a direct wire from light switch to lights...

Lets say the driver turns on the lights, the body control module (BCM) picks up on this change, and sends a data signal out across the network to the rear electrical centre (REC) the REC is the only part that is actually wired to the rear lights - receiving a positive feed itself and a data connection.
Some considerable milli seconds after you've turned the switch on the the rear lights actually get turned on - ditto with the front through a different control module up front.

The flickering can come about through the way the BCM reads the switch states, some systems update the 'states' every so many milli seconds, causing a delay and then how the signal is sent out is also a factor:
rather than sending a signal to say
'turn the lights on and leave them on until I say different', the signal is more like
'turn the lights on for a moment' - this signal being constantly re-sent across the network. With periods inbetween where current flow is actually zero.

those abbreviations are GM group but the principal is the same across most makes. Also the turn off can be used to check the function of bulbs, ie. while the current flow is zero, a resistance check can be made on the bulb to verify it is intact.

It gets really quite complex, and only the designers would know the ins and outs of a system fully.

 

[MattF]

So they're basically doing it because they can and to cut down on costs.