
Through the snow as if on rails - clouddrover
https://newsroom.porsche.com/en/2019/technology/porsche-engineering-e-suv-torque-control-software-18800.html
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blunte
Hah. I don't care how good your software and individual wheel control is - if
even in the perfectly optimized situation you exceed the friction limits of
all four wheels, you will slide. And if your software will not allow wheels to
slide, then you will have reduced braking. Either way, you won't stop nearly
as quickly as you want.

What people fail to realize, particularly in slippery conditions, is that it's
often much easier to gain speed than to shed it. Modern traction control
systems make it more (too) easy to gain speed without equally making it easy
to shed speed.

~~~
darksaints
I remember my dad ranting in our 88 oldsmobile about how stupid all of those
4WD SUVs were, running around so fast in the snow. He would always say that
4WD could help you accelerate, but not help you brake. But whenever he bought
tires, he would always get all-seasons. He found out the hard way (by rear
ending an SUV) that a lot of those 4WD vehicles that drive so confidently in
the snow are doing so not because they rely on their 4WD, but because they can
rely on their tires.

Tires matter. A lot. For the past 25 years, snow tires have gotten
continuously better. I recently tried out a set of hakkapeliittas, and the
difference in driving confidence was dramatic. I could actually count on my
car to reasonably stop in a way that I've never felt before, even with chains.

~~~
linsomniac
I had a friend who used to like to say "4WD can help you accelerate but it
can't help you stop". I took him out in my '80 Subaru in the snow one day. It
had a lever to activate 4WD, and I demonstrated how it would slow
significantly faster with 4WD engaged.

The reason is that there was no ABS, and the brake proportioning valve would
send most of the stopping power to the front wheels, since most of your
stopping power comes from them on the dry roads. But in snow, the fronts lock
up before the rears are slowing you down much. With 4WD active, the front
brakes were connected to the back as well as the front and would use their
stopping power as well.

Today is a different world though, with ABS.

You're right, it's all about the tires. I used to drive an Audi S4 which I
would put Blizzaks on in the winter. I would take people out in the snow and
blast around, it was amazingly predictable and controllable.

~~~
windexh8er
In your case the engine braking made up for, what sounds to be, a poorly
calibrated braking system. Yes, front brakes take the majority of braking load
and they are designed that way from a braking distribution standpoint. But you
have zero advantage with engine braking in a 4WD system vs properly calibrated
brakes because on snow it doesn't matter - it simply comes down to the point
where you lose tire tire friction greater than the inertia of the vehicle. ABS
works to prevent a lockup of the wheel which reduces the opportunity to use
friction even friction has been lost.

You are right that some 4WD systems (generally not AWD systems) can have an
advantage of engine braking in wet or snowy conditions by not having to use
brakes as much. Most drivers overcompensate on braking application in snow or
a loss of control situation, which is why ABS works so well against the
natural human response. But if you have a driver that is aware of the vehicle
mass and the road conditions a proper braking system wouldn't lose out to
control of a vehicle being stopped to engine braking in a 4WD system. Most
people don't have the driving skill to know when engine braking would even be
advantageous over wheel braking. And engine braking done too aggressively is
hard to quickly disengage comparative to letting up on too much wheel brake
application which can lead to longer periods of loss of control.

Ultimately what Porsche lays claim to is outlandish in extreme situations.
They can't beat the laws of physics. And unless their car has active tire
studding it wouldn't stand a chance against a quarter mile stretch of wet ice
at 4 degree decline. Doesn't matter what vehicle, tires or software you've
got. That vehicle is sliding to the bottom with no control.

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hcurtiss
Pretty tough to overcome momentum absent friction.

~~~
kempbellt
Easy. Just generate a small, but dense planet-sized mass opposite the
direction of momentum, then terminate its existence once momentum has ceased.
Don't break earth or the space-time continuum in the process though - you
might agitate stockholders.

Seriously though, physics is physics. Software can do _a lot_ , but it can't
do magic.

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alamortsubite
In the '70's, Porsche unabashedly made cars that earned the nickname
"widowmaker."

Now it's bragging that in the near future a driver (user?) will be able to
mash their car's throttle mid-corner with total impunity.

Off the top of my head I can't think of another car company that's had such a
weird trajectory.

It's disappointing the new technology is unlikely to help Porsche users stop
any faster, because the need for them to do so could be a side affect of their
finally feeling secure when turning.

~~~
darksaints
> Now it's bragging that in the near future a driver (user?) will be able to
> mash their car's throttle mid-corner with total impunity.

Funnily enough, that's exactly what you're supposed to do in a Porsche
(assuming it is a rear engine 911). Unlike most cars, 911s will understeer (or
correct an oversteer) when you mash the throttle, and oversteer when you lift
off the throttle. The reason they're called widowmakers is that the
oversteer/understeer dynamics are the _exact opposite_ from what you would
expect. Think you're going too fast into that turn? If you slow down, you're
dead, but if you speed up, you'll survive.

It's also why crazy adrenaline junkies love them so much...in some senses,
they're actually safer when you push them hard than they are when you try to
be careful.

~~~
mcsb4
> Funnily enough, that's exactly what you're supposed to do in a Porsche
> (assuming it is a rear engine 911). Unlike most cars, 911s will understeer
> (or correct an oversteer) when you mash the throttle, and oversteer when you
> lift off the throttle.

That is only true for pre-1994 911s. The 928 never showed that behaviour due
to having a Weissach axle from the very beginning of production in 1977.

~~~
OnlineGladiator
> The 928 never showed that behaviour due to having a Weissach axle from the
> very beginning of production in 1977.

I used to drive a 928. Perfect 50/50 weight distribution, beautiful throaty
engine, and the most god-awful gearbox ever made. I had to rev match to shift
_up!_ in 2nd gear. They had a design flaw where the synchromesh just
fundamentally would not work, and if you fixed it it would just break itself
again.

I had to learn heel-toe shifting just to be able to drive that car at all. I
fucking loved it, and it really got me into cars.

Also that car was great for whipping around a turn, just push on the throttle,
slide around the back, then take off (I realize this is not the fastest way,
but it is the most fun).

I apologize for the tangent, it's just not often people talk about 928s
anymore.

~~~
darksaints
Jeremy Clarkson also is an unabashed fan:

[https://www.youtube.com/watch?v=XiLc7GvmS_A](https://www.youtube.com/watch?v=XiLc7GvmS_A)

A 20 year old 944 was my first sports car. Simultaneously the best and worst
decision I had ever made.

~~~
OnlineGladiator
Don't forget its role in the movie Risky Business:

[https://www.youtube.com/watch?v=8O8_FMhW9dY](https://www.youtube.com/watch?v=8O8_FMhW9dY)

"Porsche. There is no substitute."

I wonder what they paid for that line.

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Animats
It's basically ABS, but with more "vroom".

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bradknowles
Congratulations!

Porsche has discovered the concept of putting an electronic motor into each
wheel, and what that can do for them with regards to stability control.

~~~
bognition
It’s more than that. They’ve implemented a system that’s is capable of
responding in real time.

~~~
CarVac
And without any additional sensors.

This is a control theory problem: creating an observer, a model of the state
of an unmeasurable quantity that you want to control, from limited data
indirectly related to what you want, and using that to make control outputs,
in a stable manner.

~~~
cialowicz
I'm not sure that not adding additional sensors counts as impressive. Cars are
already laden with all sorts of telemetry gathering sensors: ABS/speed at each
individual wheel, steering angle sensor, accelerometers, temp and moisture
sensors, etc.

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kenhwang
I'm curious which company hired Porsche Engineering for this. Porsche wouldn't
hesitate adding more sensors for their own vehicles.

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jonplackett
C’mon! Video please, Porsche.

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ur-whale
Pics or it didn't happen.

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trhway
>There was also an additional challenge: The driving characteristics had to be
optimized exclusively through software. The Porsche engineers could not
install any additional sensors and had to use the existing control devices.
The task, in short, was essentially driving stability by app.

sounds almost like 737 MAX. Though of course it is just a common chewing sound
of "software eating the world".

~~~
blunte
Not at all. The 737 Max added new, larger engines which had to be located more
forward of the wing, leading to very different thrust balance characteristics
compared to the previous models. The new software was made to try to prevent a
pitch up change caused by too much thrust forward of the center of gravity.

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vvanders
Congrats, Porsche has discovered the 3-phase AC VFD. The same technology that
has been used for decades in diesel electric locomotives.

It's well known that it has fantastic anti-slip properties. I'll have to dig
up the source but in the transition from DC->AC in rail engines there was a
massive increase in traction. The inherent principal of a 3-phase motor means
that it will naturally resist overspeed(in the same way EV regen works) unless
the VFD drives it faster.

[edit] I remembered right, the improvement is on the order of 100% over DC[1]

[1] [https://www.republiclocomotive.com/ac-traction-vs-dc-
tractio...](https://www.republiclocomotive.com/ac-traction-vs-dc-
traction.html)

