Hello, everyone and welcome in this video we're talking about how Audi is eliminating body role in their SQ7
through the use of two electronic sway bars,
one in the front and one in the rear and an electronic sway bar anti-roll bar acts just like a traditional
anti-roll bar with the difference being you can, vary the stiffness of that roll bar through electronic control.
Which is very cool,
and they're unique advantages to doing that so we're gonna get into that in this video and there are other companies
which have done electronic sway bars this isn't actually anything all that innovative but, what's different, about the audi system
is that they're now
incorporating it into a 48 volt system so it's a bit more powerful and means you've got a bit more range of control
which is pretty cool to have.
So how does this work?
Well let's say you're going around a corner and your center of gravity is up here it's leaning over to the left so the body
of the car, wants to lean left as you're, going around, that corner, well that, means the body of the car
is going to want to come closer it's going to be compressing down on this side of the suspension
and then it's going to be stretching out this side of the
suspension so your anti-roll bar is going to want to counter that so you've got an electric motor which is going to provide a torque
to, actually through a, gear reduction so 200:1
gear ratio that's going to be used there about 200:1. Pretty insane so a huge amount of torque multiplication
with this 48 volt system 1.5 Kilowatt motor they're, saying that they can you know have 1200 newton meters of torque
going through this or about 900 pound feet pretty incredible, which you're going to need a lot
obviously for a big heavy suv as it's going around the corner so you're
going around it's compressing down and because these two are coming closer you, want to push this wheel away
from the body so the body is trying to compress in and then the anti-roll bar is going to be
twisting, that electric motor is going to create you know
try to rotate this downward it's connected to the control arm so the control arms freely pivot but then, the
anti-roll bar is connected to both so it connects those two sides so it's going to try
and press down that side which is going to push it away from the body or the other way
you could think of it is pull up the other side so the other
side of the body is trying to get away and it's trying to push that
wheel up towards the body so it flattens the vehicle out and the vehicle remains flat through that corner
so very simply the car
turns the body rolls and then the motor provides a counter torque to prevent that body from rolling so it's looking at the steering angle
from the drivers input as
well as the vehicle speed it's not using an accelerometer because using an accelerometer would then be reacting
you know too late
basically to the g-forces that the car is feeling and then the roll would have already occurred so it's looking at the
steering input and your vehicle speed and then predicting how
much torque, does it need to provide in order to keep that car flat as you
go through the corner. Now probably the coolest thing about this system, is that you can change the understeer and oversteer
characteristics of the car in real time so whether the front starts to lose traction or the rear starts to lose traction you can
make real-time adjustments to keep the balance of the car very neutral and so how does this work?
Well if you think about a car
let's say this is the front of our car here and it's going around a corner the amount of load transferred to these outside
wheels here is dependent on its center of gravity and its track width
you can't really change how much load transfer you're going to have there but you can
change which tire front to rear gets the majority of that load transfer and partially that's based on how stiff are your anti-roll bars
so for example if you had a front anti-roll bar which was infinitely stiff and then you had a free pivoting rear
axle so it's just simply can rotate about that rear point as
you can imagine as you go around a corner all of that load is
gonna be transferring to that front left tire because it's rigid, so the car wants to lean but it can't lean
even though the rear pivots because the front is completely
rigid so you're
gonna have a lot of load transfer to that front left tire and as a result because you're not evenly
distributing it between the front and the rear and you're sending so much
load transfer to that front left tire it's going to start to understeer because this tire is going to be
overloaded so the front of the car is going to start pushing forward it's going to start to lose grip.
Well if you do the opposite if you have a super
stiff rear axle than a rear anti-roll bar then of course you're
going to overload that rear and the rear is going to want to slide out on you because it's got too much load transfer going
to it so in real time
based on the fact that you can, change the role stiffness of these you know
axles the front and the rear you can, change that rear roll bar
stiffness or the front roll bar stiffness you can
adjust the balance of the vehicle as it's going around a corner so you can, make it want to oversteer you can
make it want to understeer or ideally you can keep it very neutraly
handling so it goes around that corner and it doesn't get squirmy it doesn't you know
become unpredictable it does what you
want it to do and it allows you to go around that you know with the maximum speed possible so the very
basics of it if you have a very stiff front anti-roll bar then you're going to experience understeer if you have a very
stiff rear anti-roll bar then you're going to experience oversteer and you can make adjustments between
each in order to have the ideal handling vehicle from a dynamic standpoint how it behaves going around
that corner. So thank you all for watching and if you have any questions or comments feel free to leave them below.