Emergency Braking - what's your definition?

[GLK]

When I initially configured my Adaptive Brake Light unit, I looked into what would be considered an emergency braking, or very rapid deceleration, and set the parameters accordingly - at 0.5G threshold.

Now, I have just had an enquiry from a chap, who bought one of my units, expressing dissatisfaction at the fact it didn't flash, when he went from 60mph to a complete stop in exactly 100 yards.

That translates into 0.39G, so the unit didn't react (deceleration of 12.9ft/s2).

I don't know about others, but I wouldn't want my brake lights to flash, when I simply coming to a stop, or slowing down faster, than normal, but still not what I would call 'mash the pedal to the floor' situation?

Even the Highway Code gives that magic 73m stopping distance for 60mph, and that's exactly 0.5G or 4.9m/s2.

What would you consider an emergency braking, when you'd expect your adaptive brake lights to kick in?

 

[PobodY]

To my mind the unit should only flash if it's bordering on uncontrolled stopping. - I'd be annoyed if it was flashing every time I was late and hard on the brakes when I (believe) was under control.

If I have stood on the stop pedal to avoid a child (for example), then that's a situation where flash-a-brake should come on because I'm not paying attention to anything other than stopping before I get a nasty child-shaped dent in my bonnet.

 

[219]

To my mind , and what I suggested to Mercedes-Benz around 30 years ago , is that the brake lights should flash when ABS is brought into operation .

This gives vital extra warning to any non ABS vehicles which might be following , and also helpful to any following drivers .

 

[Deleted member 6183]

To my mind , and what I suggested to Mercedes-Benz around 30 years ago , is that the brake lights should flash when ABS is brought into operation .

This gives vital extra warning to any non ABS vehicles which might be following , and also helpful to any following drivers .

How did Mercedes Benz respond?

 

[PobodY]

Actually that's a damn good point. - What's the threshold on the ABS G-sensor?

 

[markjay]

Actually that's a damn good point. - What's the threshold on the ABS G-sensor?

I am guessing that these days the ABS is controlled by an ECU that relies on input from various sensors, i.e. it is not activated simply by the G value alone...? So the ABS is triggered when certain conditions have been met etc.

 

[190]

0.39 G is hardly an emergency stop. The highway code figure of 0.5 G is reasonable though any modern car should be able to achieve that figure with ease. 0.8 G is more like a real panic stop.

 

[GLK]

0.39 G is hardly an emergency stop. The highway code figure of 0.5 G is reasonable though any modern car should be able to achieve that figure with ease. 0.8 G is more like a real panic stop.

That was pretty much my thinking, and short of hooking up my unit to the ABS (not feasible, due to cost), a reasonable option, I believe.
Besides, it was developed for the older cars, including those without ECU, or even ABS.

 

[John]

Sounds like the guy wants to showboat when he brakes rather than warn others of a genuine braking emergency.

He'll probably buy an Audi next as those are gradually looking more like Christmas trees at the back all the time.

 

[GLK]

Yup, he said he wired a blue LED in parallel to brake light and positioned it next to speedo, to know when it's flashing

 

[John]

Yup, he said he wired a blue LED in parallel to brake light and positioned it next to speedo, to know when it's flashing

Says it all really.

To me, emergency braking is what you do to avoid impact.

Stopping over 100yds from 60 is leisurely in comparison.

 

[219]

How did Mercedes Benz respond?

I got a nice letter back from someone in the R&D department, thanking me for the suggestion, and a nice leather wallet as a token gift .

Where the suggestion went I don’t know , but the feature has appeared on newer cars .

 

[219]

Actually that's a damn good point. - What's the threshold on the ABS G-sensor?

ABS is triggered by differences in wheel rotation beyond specified limits ( using the speed sensors on the front wheels and the diff .
When it is detected that one wheel is locking before the others the braking to that wheel is modulated .
G force is not a parameter because ABS can trigger on ice with minimal deceleration, yet can be not triggered whilst braking very hard on a skid resistant surface such as Shellgrip , as long as the threshold of grip is not exceeded .

 

[190]

G force is not a parameter because ABS can trigger on ice with minimal deceleration, yet can be not triggered whilst braking very hard on a skid resistant surface such as Shellgrip , as long as the threshold of grip is not exceeded .

Agreed, ABS doesn't really come in to it. Over 1 G braking is possible with a high enough level of grip and no ABS.