- Car companies love to say things like
our car has intoxicating form and compelling function.
Yuck.
But if you're an engineer,
you know that's marketing bull poopy.
You can smell it when you see it.
It's not really saying anything about the car.
So what if they said it's got, I don't know,
more agile handling with improve behavior
because of torque vectoring.
Is that more hype, or high tech engineering?
Well, today we're gonna figure out
which torque vectoring systems are the real deal,
and not just clever marketing.
Let's go, dude.
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- Torque is the rotational force
that turns the wheels on your car.
Now torque vectoring varies the amount of torque
being sent to each of the driven wheels.
That relies on multiple sensors, computer controls,
and clever engineering.
But not all torque vectoring is created equal,
and even the most sophisticated systems
build upon equipment already in your car.
So to understand torque vectoring,
we need to start with the diff, AKA the differential.
And we're not talking calculus here.
Oh, calculus joke. (laughs sarcastically)
When your car goes around a corner,
the outside wheel covers a greater distance
than the inside wheel.
If those wheels were locked together
forced to rotate at the same speed,
one would slip or skid losing traction
to compensate for the different distances
that those wheels are traveling.
So to prevent that, your car has a differential in it.
That is a mechanical device
which allows two input shafts to rotate at different speeds
while driven by a single input shaft.
So in a rear wheel drive car, the input is the drive shaft
and the output is the left and right axles.
That differential allows the outside wheel
to rotate faster than the inside wheel
so it can cover a greater distance,
and avoid slipping during ordinary driving.
And most cars use an open differential
containing a set of gears that work together
to send power to the axles,
and also ensure that the wheels
can rotate at different speeds.
At the end of the drive shaft is a pinion gear
that drives a ring gear.
And that ring gear is attached to a case or carrier
holding one or more spider gears.
Ooh, spooky.
As the carrier rotates,
the spider gears drive two side gears attached to the axles.
When both axles turn at the same speed,
that spider gears, they're not rotating,
but they're mounted on bearings so that they can rotate
if there's a difference in speed between the axles.
By rotating, the spider gears
compensate for that difference.
Even if you hold one axle in place,
the other side can still turn because of those spider gears.
That's great for making tight turns, but here's the thing.
There's an issue with it.
Open diffs have problems when there's a large difference
in grip between the driven wheels.
That's because the same rotational force
doesn't always produce the same rotational speed.
Oh.
The common unit of rotational force, or torque,
is the pound foot.
Now one pound foot is equal to one pound of force
applied one foot from the axis of rotation.
And we mess this up a lot.
A lot of times we say foot pounds,
they're technically different.
Don't get mad at me.
It's just the people who invented this system, okay?
Yell at them, not at me.
And to make matters worse,
tool companies actually use foot pounds
on their like, I don't know, torque wrenches.
Speaking of tool shows, click this right here.
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It's called "Tool Party."
It's a lot of fun.
An object isn't necessarily going to rotate
just because torque is applied to it.
If you put one pound foot of torque onto a bolt
that's been tightened to a hundred pound feet,
bolt's not gonna go anywhere.
Now how fast an object rotates depends
on how much torque is being applied to it,
and how much resistance that torque has to overcome.
So in the case of a car's wheel,
some resistance comes from its mass,
but most of it comes from the tires grip
and the proportion of the weight of the car over that wheel.
So the problem with an open differential
is that even though the rotational speed
at each wheel can vary, the torque is shared equally.
And the maximum torque that each wheel can receive,
it's limited to the amount
that will break traction for the wheel
with the least resistance.
That is the traction difference problem.
And in extremely slippery circumstances,
that can leave you stuck.
Insert high low clip here.
- So you can see passenger side tire, all sorts of grip.
But because the driver side tire doesn't have any grip,
all the powers going there
and they're not going anywhere.
- But a more common symptom
of the traction difference problem
is when a slipping wheel is getting too much torque.
That's the one wheel tire fire
that open diffs are known for.
Insert high low clip again
Boom.
- [Man] Yep, That's one tire fire.
- And in performance driving situations,
traction differences occur almost constantly.
I got traction difference problems.
This girl likes me and this one doesn't.
Maybe I should just stop dating girls. (laughs)
During cornering, the car experiences body roll or lean
as its weight transfers to the outside wheels.
That weight shift unloads the inside wheels
reducing their resistance to rotation.
If a car is turning and the unloaded inside tire
can only take 50 pound feet before it breaks traction,
the grippy tire on the other side
will only get a maximum of 50 pound feet too.
So if you match the throttle and send more torque than that,
the inside tire it is just going to break traction and spin.
And once your traction is broken and the tire is slipping,
that reduces its resistance further.
So 50 pound feet is now far more torque than it can use,
and it just keeps spinning until it slows down enough
to regain that lost grip.
Now, throughout all of this, the outside tire,
which has plenty of grip, doesn't get all that torque
that it deserves, and it needs it.
It's like torque me, baby.
Torque me.
And the outside tire that's just ripping and smoking,
it's like, it's my torque.
♪ It's my torque ♪
♪ And I'm just gonna do it forever. ♪
♪ It's my torque ♪
(Jeremiah imitates song riff)
So one way to solve that problem
is to simply back off the accelerator,
but what (beep) fun is that? (laughs)
Not fun at all.
So here is where torque vectoring can help.
Unlike an open differential,
torque vectoring can vary the amount of torque
being sent to each wheel.
Slowing one that's slipping,
and making sure there's enough for one that's gripping.
Now some of you are saying, hold on, hold on, wait a minute.
Limited slip differentials
solve the traction difference problem.
And that is true.
LSDs provide a mechanical solution to the problem
of open differentials, but they're not a perfect solution.
There are several types of LSDs,
and we can't cover how all of them work.
We probably need an entire B2B for that.
If you want it, put a comment down below.
But knowing how a clutch pack LSD works
is gonna be helpful in understanding
how a torque vectoring system works
that we're gonna see later.
Now clutch pack LSDs use alternating friction disc
in steel plates, like the clutch in a motorcycle.
The friction discs rotate with the side gears and axles,
while the steel plates rotate with the ring gear
and differential case.
And under normal conditions, that clutch pack is disengaged.
All those plates just spin past each other,
and the LSD operates like a normal diff.
Transferring power from the ring gear, to the spider gears,
to the side gears, to the axles.
But if the driver presses the accelerator
while the wheels are slipping,
drag causes the pin holding the spider gears
to shift backwards relative to the rest of the differential.
And that movement pushes two spring plates outward,
engaging the clutch packs.
When the clutch plates are pressed together,
the rotation of the differential case
is sent directly to the wheels bypassing the spider gears.
So this locks the wheels together
forcing them to rotate at the same speed.
And this limits how much a wheel
that's lost traction can slip.
It can only rotate as fast as the other wheel,
the one that has grip.
But clutch pack LSDs and every other type of LSDs,
they have a few drawbacks.
Mainly just having a great time.
But for one thing, they require maintenance.
They're also complex and can be expensive.
And because they're solely mechanical, they're a bit dumb.
They can only react to what's already happening.
Torque vectoring on the other hand,
it's like an LSD that can see into the future.
Like me on LSD.
And even though torque vectoring
requires a differential to function,
it can work with any type of diff, open or LSD.
Doing that requires a sophisticated
but very small piece of equipment
that's probably already on your car.
A yaw rate sensor.
Heck yeah y'all, let's get going.
This is my kind of sensor.
If you don't know what yaw is,
yaw is the rotation of the car
around its center access while turning.
Yaw rate is how quickly that rotation happens.
Now you might hear someone say a car feels slow to turn in,
or quick to rotate.
And what they're feeling is changes in yaw rate.
Yaw rate.
I wanna do so many y'all jokes, but I can't.
Automotive journalists freaking love to talk like this.
They salivate at the thought of having to use that word,
but they never seem to measure yaw.
Engineers do though, using a microscopic
electrically conductive gyroscope.
Or euroscope depending on where you live in the world.
That's nothing like the gyroscope you've seen
with spinning concentric discs or circles,
but the principle is still the same.
Gyroscopes can be used to measure
the inertia produced by rotation.
From that, a computer can calculate the rate of yaw,
which makes electronic stability control possible.
And the same process lies at the heart of torque factory.
Electronic stability control, or ESC,
uses sensors in the car's ECU to prevent loss of traction
that can lead to accidents.
So for example, if the ECU detects
a large steering angle but a low yaw rate,
that means that the vehicle isn't turning
as much as the driver is telling it to turn.
It's under steering,
and the car can be headed towards an obstacle
instead of turning to avoid it.
So the ECU will apply breaking force to the inside wheels.
Slowing them in increasing rotation.
The simplest forms of torque vectoring
use that same system to overcome the disadvantage
of an open differential.
Now the most basic form of torque vectoring
is brake based systems,
and they work because the limitation of open differentials
isn't based on the traction at the tire.
It's based on the resistance, or lack thereof, at the axle.
Basic torque vectoring applies the brakes
to add resistance to the axle of a wheel that's slipping.
This slows the wheel so it can make use
of that torque it's given.
An increasing resistance at a slipping inside wheel
also increases the total torque
that can go to the other wheel.
So it's win-win.
And this type of torque vectoring
can often figure out what to do
simply by comparing differences in wheel speed sensors.
So that's got the same problem as an LSD.
It's purely reactive.
So by incorporating other sensors
like a steering angle for example,
torque vectoring systems like the one used at Porsche
can apply braking to the inside wheel
as soon as a turn begins.
That encourages rotation at corner entry,
and prevents the inside wheel from slipping at all.
Porsche's system also includes
a mechanical limited slip differential
so it doesn't have to rely on the brakes too much.
Fucking Porsche, dude.
German engineering at it's finest.
Systems which don't have an LSD
can sometimes rely on the brakes too much,
causing brake fade when driven at the limit.
We know you like doing that.
But for drivers who don't take their cars to the track,
a solely brake based torque vectoring system
can make a huge difference in how the car drives.
It's less prone to under steer
and with a sharper turning response.
And another cool thing?
They're like stupid cheap to manufacture,
because there's no new equipment needed to make them work.
You just need the right program
in your already established ECU.
Car and Driver even referred to these systems
as dollar store torque vectoring.
I would've said 99 cent store torque vectoring,
but I'm not a journalist.
But that really wasn't a compliment.
Car and Driver and many enthusiasts
think that brake based systems aren't real torque vectoring.
And some of them do sound like marketing hype.
Ford described one of their systems
as applying brake torque to the wheels.
Now braking force can be described as torque,
but it's the torque that's driving the wheels
that most of us are interested in.
And since braking doesn't directly increase
the torque being sent to a wheel, like an LSD can,
these systems can come off as just performance versions
of stability control.
Tricky, tricky, little Ricky.
Unlike Ford, manufacturers like Porsche have shied away
from the term torque vectoring
for solely brake based systems.
Instead referring to a functionally identical system
as an automatic braking differential.
So if you want real torque vectoring,
you may wanna talk to Lexus
'cause in 2014, they debuted the RCF
with a new torque vectoring differential
that uses clutch packs like an LSD,
but the clutches are electronically controlled.
As we saw earlier, with an ordinary clutch pack...
As we saw earlier.
(Jeremiah sips water)
Oh, that beautiful H2O.
Okay.
Now, as we saw earlier with an ordinary clutch pack LSD,
high torque at the input shaft during a loss of traction
causes a reaction in the diff.
Clutch is engaged locking the wheels together.
Lexus's torque vectoring differential
is engaged predictively based on vehicle sensors
and settings chosen by the driver.
So far, that's a bit like the cheaper brake based systems
but because it's got a set of clutch packs,
like a proper mechanical limited slip diff,
it can vary the torque side to side.
Something an open diff cannot do.
One electric motor at each axle rotates a cam
that locks the clutch plates together.
That motor can vary the cam position
to adjust the amount of slip in the clutch plates,
and that means the system can apply
different amounts of locking to each wheel independently.
It also works with the brakes to apply negative torque,
that's what Ford called brake torque,
to the wheels independently to encourage rotation.
So what does this all look like going around a curve?
As the driver turns into a corner entry,
the system applies the brakes to both drive wheels
adding resistance to prevent slip.
As the steering angle increases heading towards the apex,
the braking force is transferred to just the inside wheel
while the clutch pack engages to send more torque
to the outside wheel encouraging rotation.
When the driver unwinds the wheel and steps on the throttle
to power through the corner exit,
the system sends even more torque to the outside wheels,
and monitors the inside wheels applying breaking
if a slip is detected.
And all that's doing it's preventing under steer
that could push the car wide, or reduce your exit speed.
Nothing dollar store about that system.
And it's only a $1,250 option.
That torque vectoring differential decreases lap time,
increases lateral grip, and even reduces
the steering angle necessary to get the car to rotate.
We only had time to scratch the surface of torque vectoring.
We didn't even get time to talk about
the most sophisticated systems yet,
which are all found in all-wheel drive vehicles
because those rely on up to three differentials
to maintain grip.
They also have to vary torque between the front and rear,
as well as side to side.
But look for that in a future episode
about the Audi Quattro.
And maybe we'll do another episode
about how electric cars deal with torque vectoring.
Hmm. You're into that?
Leave a comment down below.
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