http://www.business2.com/articles/ma...,44383,FF.html

yo check it! lol

i was browsing FARK.com and i found this link on the main page!

pretty cool. assumes the driver is an idiot and shows how the car can respond to the idiot! good read.. i liked it! lol


http://www.business2.com/articles/ma...,44383,FF.html

 

Good article, but where he gets the idea of the heat sensitive pad to start the engine from, I have no idea. Beam me up, Scotty. And, if I was nit-picking, one of the batteries is in the trunk, the second, smaller, start battery is under the hood.

 

ok good, i thought i was the only one that thought something was wrong with that.. thanks and kudos to you for backing me up..

i was thinking in my mind

oh well, the heat sensitive thing does make the car seems more high tech, not that it needs it

 

Yea, we should all do a bit of thinking in our minds!

Regards,

 

Quote......which replaced the mechanical and hydraulic elements of the braking system with a single module employing electronic impulses.....


Please correct me if I'm wrong, but I'd be pretty darned worried if the hydraulic elements of the braking system were redundant!

My understanding is that there is still a split-system hydraulic circuit as backup.

 

brakes? what are brakes? lol

 

Mustard, there's still the dual hydraulic system to actually actuate the brakes. What changes is what triggers the activation of them. The "brake by wire" means that the braking pressure is primarily controlled by measuring what the driver is doing to the brake pedal instead of the brake pedal doing the work directly through a brake servo.

This is just one input and other systems have direct access to the brakes if they need to, for example, the ESP which will selectively brake one or more wheels when required, and the brake assist which pre-applies the brakes when the driver lifts his foot off the throttle and rapidly presses the brake pedal. This is assumed to be an emergency stop so the brakes are applied much faster and more powerfully than the driver's input.

Mercedes research showed that in an emergency braking situation, drivers do not press the pedal hard enough and do not get best benefit from what the brakes can do. They also back off when they feel the ABS pulsing through the pedal. SBC eliminates the pulsing and with brake assist, achieves shorter braking distances. Early (pre-R230) cars with brake assist were too ready to standy on their front wheels, it was a little too enthusiastic.

The pressures in the braking system are boggling - it runs at 160 bar, or nearly 2400 psi and the small container on the left of the SBC control unit is the pressure vessel which provides a reservoir of pressure. In volume terms, it's tiny because the volume of brake fluid moved is very small when you apply the brakes. In effect, the brake control unit moves the pads a very short distance but with incredible force.

The pedal resistance the driver feels is completely artificial and is obtained by a three way compression system. When the pedal is first pressed, the resistance is provided by a simple spring. Then, a second, much stiffer spring comes into play, followed finally by a conical shaped rubber bung which provides a higher and higher spring rate as it is compressed. Taken together, the pedal resistance plotted against pedal movement shows the same rapidly rising curve of a conventional braking system, all to make the driver feel "at home".

There is still a backup hydraulic connection between the pedal and the control unit in case of failure, but this is un-servoed and provides much reduced braking performance.

Sorry, I'm in engineering lecture mode

 

that my friend.. is how u go 60-0! lol

 

Good of you to go into so much detail BlueSL. Makes sense now. The articles I'd read gave the impression the whole system is based on electronic pressure actuators governing the brakes without hydraulics - i.e. the idea of hydraulics was virtually redundant. I assume if the electronics fail the system resorts to normal pressure imputs.

Apart from my own, there's a lot of ignorance about fly-by-wire.

 

BlueSL (and other techno-boffins):

How do you propose the SBC system interprets left-foot braking? Would one get the advantage of the high-speed pre-pressurisation of the system in the case of emergency stops, assuming the brake pedal is already being firmly depressed before the throttle is fully released?

Regards,

 

What they're trying to do I think is to recognise from the pedal inputs the characteristic of a true emergency stop, essentially rapid removal of power and then immediate application of the brake pedal. You can imaging all sorts of borderline grey areas where they have to decide "what is this guy doing?" including pressing both pedals at once.

When the car is at rest, holding the car on the brakes and cranking up the power for a quick getaway is valid, if not particularly kind to your torque converter. If you're travelling at 100 mph and hit the brakes hard with your right foot still on the throttle, that to me would be the sign of a true panic stop so that might be a signal for the car to say "he's braking, forget the throttle"; no point having 14 inch disks fighting against 500 bhp...

 

So you're proposing that by hitting the brakes with left foot @ 100 mph with throttle still depressed will signal to SBC to cut engine power!? You'll agree that the SBC cannot, in this case, do anything about pre-empting the braking action, unless, of course, ESP means something other than Electronic Stability Program.

Regards,

 

It's me speculating, I have no idea whether the power is cut when you brake, I might try it to find out!

 

hey blue.. can i come w/ u to test it? lol

 

Hey, one question. Why would you hit the brakes with your left foot anyways!!!

 

Just a habit. Been doing it since racing Porsches. Find it completely natural, now that I drive mostly autos: 2 pedals - 2 feet....., much quicker reactions. And a lot safer. Try it!

Regards,

 

It's an amazing feeling if you're not used to it. Normally, you never use your left foot when driving an automatic and in a manual, only to press the clutch. You get used to the force required for that, so that when you use the same foot to brake, you tend to brake much harder than you intended - your left foot is not used to the graded force required when applying the brake pedal, more the control used when you release a clutch pedal.

I tried left foot braking on the SL55 yesterday, can't say whether the engine cut out but boy did the car stop quickly! Like standing on its front wheels...

If you're trying this at home, make sure there's nothing behind you.

 

Told you...much quicker reaction!! Especially if you mistake it for the clutch in a high speed change! I also just about flew through the windshield a few times initially, before it became second nature. But a bit off the subject.

Regards,