Good point John, I guess that critical aircraft systems have a fair degree of duplication, but that always comes at a (high) price. I'm just intrigued as to how MB have done it and what is the perceived added value of such a system over traditional mechanical/hydraulic braking (if they've designed in complete redundancy then I guess that a cost saving will not be one of them).
I'm hoping that HJ has the press pack for this announcement and can enlighten us as to its advantages etc...
BTW - Personally speaking, I wouldn't feel comfortable travelling in a fly by wire aircraft that I'd written the software for unless there was an override of some sort.
Rich
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Here's what I wrote before they edited it, warts and all:-
What's 'SBC'?
This is one of the many advanced features of the fabulous new Mercedes Benz SL Series. 'Sensotronic Brake Control' is the world's first brake by wire system fitted to a road car. Instead of a mechanical connection, the brake pedal is connected electrically to the brake master cylinder (removing the need for vacuum servo assistance) and a microprocessor passes the information on to the hydraulically activated brakes using electrical pulses. In order to maintain diver feel, a special simulator uses spring pressure and hydraulics to provide pedal resistance. It works so well that even left-foot braking I could not feel any difference between the brakes of the new SL and the brakes of the other car I was driving that day.
Could be that there is am mechanical connection too, but I can't see the value because most drivers these days are incapable of braking a car without power assistance to the brakes.
HJ
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Why is it considered desireable to replicate the pedal effort
of a conventional system?
It's a shame that the current car "feel" has to be considered as a benchmark, as though what we're used to can't be improved upon.
The first car to come up with brakes where the braking pressure was not generated by the pedal was the Citroën DS way back in the 1950s.
This car braked as well as most of today's saloons - sensationally well for the time - and the pedal felt, and looked, delightfully like a push-button. True, you stood the car on its nose the first couple of times, but you soon learned how to stop gradually as well as rapidly and with no effort at all.
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RM/HJ
Sure electronics have brought about some excellent benefits (ABS, EBD, traction control) and most cars and drivers see great benefits from them.
However, I'm unclear quite what the benefits of this are - it appears to substitute an hydraulic indication of the drivers retardation intentions for an electrical indication, and needs a separate system to provide feedback. It gets rid of vacuum servo assistance, but I'd have thought that's quite feasible without the elctronic link - several cars have electric/hydraulic power steering these days. Some benefit there though - you don't lose servo asistance if the engine has stalled.
The result - the brakes feel exactly like a conventional system. I'd love to know exactly why they chose this route, but I hope this isn't a case of 'they did it because they could'. If you find out, HJ, let us know.
Regards
John S
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HJ wrote....It works so well that even left-foot braking I could not feel any difference between the brakes of the new SL and the brakes of the other car I was driving that day.
Does this imply that your left foot is more sensitive than your right? Why? - I always thought that over time your right foot would be the more sensitive due to the more deft use of the accelerator and brake than your left which is normally reserved for the "clumsy" use of the clutch.
Whenever I've tried braking with my left foot, when driving an auto, I've almost always ended up braking much too hard - I suppose I don't drive autos often enough to get used to it either.
Am I missing some finer driving detail/skill here?
Chad.R
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Chad,
Why use one foot for two pedals? I don't see pedal cyclists doing so. I think you're spot on when you suggest that sensitive left-foot braking is simply a case of getting used to it.
I always left-foot brake in an automatic car and have done so for many years without it getting me into trouble. Not only is it exercising both of my legs but it can also be useful in tricky situations, for example driving along a narrow and winding country road where a sheep might be in the middle of the road just round a bend. By having the left foot hovering over the brake pedal, important reaction time can be saved.
As for 'clumsy' use of the clutch, surely this is not really so? You must have driven in snow or ice, or on a very steep slope, where controlled use of the clutch is vital. Clutch operation is often a very difficult thing for learners to grasp so it must be more refined than some of us everyday drivers realise.
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IIRC, critical systems on aircraft are triplicated.
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"IIRC, critical systems on aircraft are triplicated."
True, I also recall overhearing a commercail pilot radio comm'n as follows.
"Just like to remind the ground crew that our Widget is up the spout. So is the back up, so we're operating on the second backup and we don't have a third back up. It looks as though the original fault was reported on dd/mm/yy ( a date much much earlier!!!)
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