Yoshimura

In the event of a catastrophic failure of the hydraulic brake system, it seems that the electromechanical parking brake can be used as an emergency brake. What is the procedure? Do you have to hold the lever up? Does it modulate the rear brake? How you desactivate it after it have been engaged?

From Audi glossary:

HerrK

You have to hold it up, above a couple mph it won't stay engaged unless held. Our Z4 has a simiar e-brake which activates all 4 brakes, utilizing the ABS system. Hauls it down quickly in a controlled manner. I suspect the Q5 is similar, but I have yet to give it a "brake" test at speed.

MP4.2+6.0

+1 it is using ABS. Try it sometime--on quiet road. Very aggressive stopping.

- B -

Just be careful. Using the brake in an aggressive manner can put bald spots on one's tires.

ex-quattro PETE

If it's using ABS, then the wheels will not lock up, so why would it generate bald spots on tires?

Telate

Yes I tried it once in a parking lot going around 20km/h. It activates full ABS to all 4 wheels and will only stay activated as long as you hold it up.

Bob Petruska

Dynamic emergency stop

If the brake pedal loses its function or becomes blocked, the vehicle can be braked heavily by means of the dynamic emergency stop function.



Activate

By pressing and holding the electromechanical parking brake button, braking of the moving vehicle is carried out at a deceleration rate of approx. 6m/s2.
An acoustic warning signal is triggered and the brake lights are activated.
The dynamic emergency stop function is carried out via hydraulic brake pressure generation at all 4 wheels if the vehicle speed is greater than 7km/h . The
braking manoeuvre is controlled depending on the driving situation by the ABS/ESP function. In this way, stability of the vehicle is assured during braking. If the electromechanical parking brake button is pressed when the vehicle is travelling at less than 7km/h, the parking brake is applied electromechanically (see parking brake function).

Release

If the vehicle speed is greater than 7km/h after a dynamic emergency stop, the brake is released by letting go of the electromechanical parking button or by pressing the accelerator pedal. Once the vehicle has been brought to a halt, the holding brake has to be released as described for the parking brake function.

On actuation of the electromechanical parking brake button, engine torque will be set to idle and the driving assistant functions such as cruise control (CCS), automatic distance control (ADC) or AUTOHOLD will be deactivated.

The emergency stop function is also available when the ignition is switched off.


What Audi is saying that if the hydraulic brake system (ABS) fails, and you are going over 4.2 mph down a hill, the mechanical electronic parking brake won't activate so you better jump!
The old mechanical parking brake lever system gave you a chance........

Redd

In an empty parking lot, try it out.

You have to hold the parking button UP and then the car will take 2-3 seconds to make sure you aren't joking, followed by FULL brake force application.

Unlike a manual parking brake there is no way to apply it immediately, and no way to apply it less than 100% braking effort.

IIRC there's also some beeping going on, just in case you were pulling the button up out of boredom, to let you know the car was going to do a panic stop.

If you have a push-button engine start/stop? Might as well try that too, most of them will kill the engine if you hold that button in for three seconds as well. I should go check my manual to see if the Q5 does too. Of course on many cars, that also locks the steering...I'd better go study in case there's a test.(G)

MP4.2+6.0

...in controlled conditions (empty parking lots, deserted roads, etc.) so you get used to it. In a true emergency, classic training is to have used the equipment and be familiar with how it actually performs. Beyond just book learning.

In situations like the many, many runaway Toyota claims from a few years back or the continuing GM ignition key fiasco, knowing what to do and how the vehicle reacts so the user intervention to overcome the issue (where possible) becomes intuitive is very important. In the true emergency scenario even a second or two can really count. Also true for ABS systems more generally where lots of research showed user's common reaction was to back off the brakes when he/she felt the pulsing; led to the whole next round of automated emergency stopping brake pressure maintenance when triggered by a sudden brake jab.

Redd

At 60mph, one minute takes you a mile down the road. 88 feet in one second. So if your goal is to avoid hitting a car, truck, brick wall, or just a person that's only 10" thick? Two seconds buys you 176' faster stopping. The math can vary...but I'd rather be able to hit the hand brake sooner than later. Since the parking brake is deployed electrically, separately from the service brake, I suppose it might even count as a true emergency brake. (You used to need a Rolls Royce to get that: Service brakes on the wheels, parking brake on the driveshaft, emergency brake on the axle. Three totally separate systems.)

ABS I can also do without. Every survey seems to indicate that while ABS may or may not stop you in the same time as a skilled driver pumping the brakes, ABS drivers in general have more accidents, apparently because they think the ABS system makes them invulnerable. Damned expensive way to compensate for untrained drivers.