audi at humanspeakers.com
Wed Oct 21 20:01:40 PDT 2009
Brett Dikeman wrote:
> On Wed, Oct 21, 2009 at 8:52 PM, Ed Kellock <ekellock at gmail.com> wrote:
>> An interesting read... it discusses vacuum assisted braking systems and the
>> inability of a car's brake system to stop it at full throttle, regardless of
> Except it's a load of crap; they all have check valves, and brakes are
> MUCH stronger than engines.
Brett, have you ever experimented with vacuum assist brakes with an open
throttle? I have, and you get two or at best three presses of the pedal
before it goes hard.
> Think about the kind of torque you'd need
> to get from 0-60 in 150 feet. That's barely across a large traffic
> intersection. Yet, your brakes can do the opposite handily...
The article mentioned needing 225 pounds IIRC of force on the brake
pedal with no vacuum available to assist it.
> My 'R has vacuum-assisted brakes. I assure you, they work very well,
> including full-throttle-to-hard-braking transitions. Even if the
> engine shuts off, there is an auxiliary vacuum pump which kicks in any
> time the ignition is on and vacuum pressure drops. I was bored one
> evening waiting for someone and played with it- you have to work
> pretty hard to use up the vacuum faster than the pump can replace it
> and exhaust the vacuum reservoir.
Maybe the Lexus didn't have a back-up pump? I don't know what an 'R is,
but I suspect it comes from a more race- or sport-oriented heritage than
> It's also curious why the car, which surely was throttle-by-wire,
> didn't shut off the throttle when the brake was applied. That's very
> common behavior, has been for nearly a decade.
Apparently Toyota is behind the curve on that?
> Why didn't the driver
> attempt to put the car in neutral, switch off the ignition, etc?
Unfamiliar car (in the lead example of the story) that required a 3
second push on the "start" button to turn it off; a complex
manually-shiftable automatic shift lever pattern. Not as easy as
pushing the lever from "D" to "N".
I liked how, just as back in Audi's day in the flames, the floor mats
are cited as a prime culprit.
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