auditron

I have mixed feelings on the electronic parking/emergency brake. It works very well as a parking brake of course but there is no way of coming to a gradual stop in an emergency with this type of system as you could with the older pull up cable or press down foot controlled parking brakes. In the very unlikely event of brake failure, or some kind of computer malfunction that shuts down the engine and disables or slows the normal braking system, please be fully aware the parking brake when engaged will instantly bring you to a stop that duplicates your slamming your brakes on, bringing the car to a very sudden, JOLTING STOP and if anyone might be following closely behind you, they could very likely rear-end you. I returned my 2004 545i BMW to BMW after, on three separate occasions the engine shut-down at 65 MPH and I lost my braking and steering but luckily that car had a pull-up emergency brake that would bring it to a gradual stop. Today's complex computerized cars are not immune to these rare but possible occurrences.
I did my own test on a local empty street and tried to pull the brake up as slowly as possible on my A6 but it was impossible to slow the car down gradually and there was no in-between, the electronic brake engages fully when pulling the lever, bringing the car to a jolting stop no matter how gently you try to apply it. I sure wish the automobile companies would develop an emergency electronic braking system that could be gradually, as well as fully applied when needed. Doesn't sound like an impossible task and would sure be a lot more practical as well as safer.
In addition, raising the lever in error, if for example your jacket cuff or whatever might catch on it, would have this same sudden braking effect. Unlikely yes, but not impossible that it could happen.
Get the feel of this braking system, just to know how to prepare yourself if you are ever in need of using it in an emergency situation. It is a great PARKING BRAKE but in emergency use, take extreme care if ever called upon to apply it.

owdidave

Good discussion point for raising awareness. These are really more of a parking brake vs. a combined parking/emergency brake with older foot or hand systems. I remember reading about it a while back with my "new system to me" A5, and how (it appears) that in a true emergency (i.e., normal brake system failed) it can be applied and will engage the other systems in doing so. Audi talks about it here:

http://www.audiusa.com/us/brand/en/t...l.browser.html

fender4645

This has always scared the bejesus out of me. Years ago, when I was in college, I was driving back to the Bay Area from Yosemite in my old 1995 Nissan pickup. I made the huge mistake of taking Old Priest Grade Road and with a couple of turns left, my breaks went completely out. The only thing that saved me and my girlfriend was the ability to use the emergency brake during those last few turns.

Here's a YT video (not mine) of the grade:

wilfred2k5

I don't know if this helps or hurts your point, but it's truth as best I know.

The parking brake is an electro-mechanical system atop the normal braking system. It does not require that the engine be running (nor do the normal brakes). If the electronics are trashed such that the normal brakes don't work, the parking brake won't work either. Any gradual braking may as well be done via the normal brake pedal since it goes to the same system. The parking brake is simply an "immediate max brake" switch that does not release until told to do so.

If you're having a braking crisis, the parking brake can't do anything the normal brakes won't.

Note that in modern cars, such as your Audi, the brakes, steering and throttle are all fly-by-wire. Don't fool yourself by thinking that ANY of the inputs you provide to the car's brain are more than suggestions. There's a reason why a software upgrade can make the steering not be off-center, why Braking Guard can make it such that the slightest touch of the brakes results in a panic stop, and why the throttle response can be altered through software.

In some Mercedes and BMW's, there isn't even a mechanical backup anymore, with the accelerator and brake pedals leading to nothing more than CAN-bus sensors

DirkM

I don't think that brakes and steering are wire only yet, mainly because US and European laws do not allow such a setup yet.

The steering is electrical asisted but still has a mechanical connection between the steering wheel and steering column. Same for the brakes, it's still a hydraulic system with hydraulic booster and some electronics to control everything. Even with the engine off you can still use the brake pedal but you will need to use more force because the booster is not working anymore due to the engine being off.

http://admin.audionlinetraining.com/...%20A6%20C7.pdf

salvadorik

wow this hella cool thx!

newmoon

Not quite. Google "Audi SSP 997303" and there will be a pdf explaining how the electromechanical parking brake works. There is an electric motor to clamp down the REAR brake pads.

However, the dynamic emergency braking function when you pull the parking brake switch above 5 mph actually uses the ESP to activate ALL FOUR disc brakes.

It can be useful if for example:
- something like a water bottle gets stuck under the brake pedal so you can't press it down.
- the engine is off, or gets stuck at full throttle, such that there is no intake manifold vacuum generated to provide power braking assist to the brake pedal. The ESP has its own hydraulic pump to pump the brake fluid so it will still work.

You can see what the brakes feel like without power assist by pumping the pedal several times with the engine off to use up all the vacuum. Then the pedal will feel very hard. The brakes still work, but you will have to really brace your back in the seat to get just a tiny bit of braking force.

It will NOT work if:
- you cooked and overheated the brakes by riding them down a mountain pass, because this function uses the same brake pads and rotors. Some other cars have small drum brakes inside the hats of the rear disc brakes, used as the parking brake, so these may be used in emergencies like this.

Almost all cars these days use a fly-by-wire throttle, but as far as I know, none have true fly-by-wire braking or steering. The underlying manual systems are still there, but the ESP and electric power steering assist are both powerful enough to override manual input and control the car themselves, such as with braking guard, active lane assist or the self-parking car. This may give the illusion of fly-by-wire control, but strictly speaking, it is not.

wilfred2k5

Audi's TBS (throttle-brake-steering) systems are still partially mechanical, but this is changing quickly. Consider cars like the Tesla (all electric) or a number of hybrids where hydraulic systems simply don't make sense.

My counsel to the OP is, again, don't worry about using the "parking brake" except as a parking brake (to ensure the car just doesn't move when it's parked).

1. If the car's battery is dead, that switch won't activate (or deactivate) anything.
2. If the car's electronics are alive, it's still up to the car what to do and when. For example, I believe you still can't disengage the parking brake unless the brake pedal is pressed/driver's seat belt is on...possibly both.
3. I'm pretty certain that, short of something being stuck underneath the brake pedal, the best thing you can do is brake with the normal pedal. If the brakes aren't responding properly (and the electronics are functioning), the car's software will use whatever means are its disposal to stop (including engine throttle from downshifting and triggering the electromechanical parking brake).

@newmoon
I agree that Audi is not completely fly-by-wire, but Audi has already chosen the AirBus model (where the computer is presumed correct and can overrule the driver). Again, I point out that on electric and certain types of hybrid cars (where the engine is only used to charge the battery, not to provide torque), it's impossible/impractical to have a mechanical system. I would need to check the facts, but it seems unlikely that hitting the brake pedal on a Tesla with a dead battery has any effect. I'm pretty certain that it's impossible to release the emergency brake since a well-known auto reviewer had to be flat-bedded because the battery had died with the emergency brake on.

Also, see http://en.wikipedia.org/wiki/Electronically_Controlled_Brake which implies that the Lexus RX400h, a hybrid, has "almost" complete brake-by-wire.

owdidave

FWIW, pg 76 in the manual also covers how to use for emergency braking.