It’s been said that the current hybrid power units (and in fact all electric or hybrid
engines) are more ‘torquey’ than previous engines that did not have an electric motor
as part of their power delivery.
In this video we’ll look at what torque actually is, and then see how torque is delivered
to the rear wheels and - crucially - what it means to say an engine is more ‘torquey’
or that it ‘delivers torque instantly’.
Right - what’s torque then?
Torque is a turning force, so we use it for the most part when we referring to forcing
something to rotate.
So it could be the force of turning a wheel around on an axle, pulling open a door on
its hinge or undoing a nut from a screw.
In fact, let’s imagine this nut for a second to better understand torque.
Let’s imagine the nut is on pretty tightly and we’re trying to undo it with a spanner.
Let’s use a really long spanner for reasons we’ll see in a second.
The amount of torque applied is measured by taking the distance from the pivot point at
which you’re applying the force, and multiplying it by how much force you’re putting in.
So let’s think about this in action.
I could push down 15 cm from the pivot point on this spanner with 150 Newtons of force
(a Newton is just a measure of force).
Outside of America we tend to use Newton-metres as units of torque so we just multiply distance
by force here see we’re putting 22.5 Nm of torque into the nut, trying to get it to
turn.
Now, the nut is really tight, so we decide to double the torque.
Now we could do that by pushing down twice as hard, but let’s say that 150 N is the
hardest we can push.
Instead, we can just double the distance, because that will double the torque.
So we push with 150 N of force 30 cm from the pivot and that generates 45 Nm of torque,
causing the nut to come loose.
So anyway - we double the distance, double the torque.
We didn’t have to put more energy in to get more turning force out, which is impressive
and interesting, right?
This is also how the jacks work in pit stops.
One person can lift the entire back of an F1 car because they push the jack REALLY far
from the pivot, which generates a lot of torque in the system.
The lifting pad of the jack is really close to the pivot, though so the force pushing
the car up is magnified as (for constant torque), shrinking the distance multiplies the resultant
force.
Now let’s apply this to an engine.
An engine has a piston, which is forced down by a little explosion in the cylinder.
So it’s applying a force downwards, which is carried through the rod, and this turns
the crankshaft which is just a cylindrical axle beneath the engine.
We see that the piston applies a force to the crankshaft, causing it to spin so it and
the other 5 pistons are collectively generating some torque to spin this crankshaft at incredible
speeds.
If we stick a gear cog on the end of the crankshaft we can measure the force the gear pushes with
at its circumference to work out how much torque the engine is delivering to the crankshaft
at any given time.
Now this torque - the turning force measured at the crankshaft - is the engine torque we
talk about when describing the torque of the engine.
But this is not the torque delivered to the wheels that makes them spin.
To get there, we need to go on a little journey.
And I’m going to describe it in broad terms and illustrate is using models, not the exact
systems you’ll find in an F1 car.
So, the crankshaft connects to the transmission, which drives a drive shaft, which connects
to an axel gear which drives the wheels.
The transmission has gears of different sizes that will connect to the crankshaft depending
on which gear the driver selects.
The different gears are described by their ratios, which just describes how big the gear
is compared to the gear it connects with at the crankshaft.
First gear has the biggest ratio, so it might be 10 times the size of the crankshaft gear.
These ratios get smaller and smaller, until 8th gear which might have a ratio of 0.75:1
with the crankshaft gear.
Why are gear ratios important?
Well because the ratio in size of the two gears directly influences the change in torque
between the crankshaft and the driveshaft.
You should have all the information to figure out why, so let’s step through it.
Let’s keep it super simply and say we’re in first gear and first gear has a gear ratio
of ten, so it’s ten times bigger than the gear at the crankshaft.
Now, when gears connect there is a driving gear (the one with all the power going through
it) and a driven gear (the gear that gains power from the driving gear).
So in this case, the driving gear is the one at the crankshaft and it’s driving our first
gear, here.
The driving gear carries the torque of the crankshaft.
So if the engine is producing 200 Nm of torque, the driving gear of the crankshaft has 200Nm
of torque.
The gears connecting means the teeth of the driving gear are pushing with a force on the
teeth of our first gear.
So the force where two gears meet is the same, obviously ‘cause they are connected via
this force.
But because our first gear is ten times bigger in diameter, the torque delivered to it is
ten times bigger than it is at the crankshaft, because - as we saw - if you apply a force
further away from the pivot, it multiplies the torque you generate.
This goes straight to the driveshaft so we can say the driveshaft has ten times as much
torque as the engine is pulling at the crankshaft.
The gear that converts this turning force to the axle remains constant as is somewhere
around 3:1, so we then multiply the torque by 3 to give a final torque at the wheels
of 6000 Nm.
This is a good 30 times greater than the torque the engine delivers directly to the crankshaft.
This is what a gearbox does: takes the torque of the engine and multiplies it up in different
amounts depending on how much torque the wheels need.
To accelerate from standstill, the wheels need a lot of torque to get going as it’s
a lot harder to get the system moving.
That’s why the ratio of first gear is the biggest, as it has the biggest multiplying
effect.
Once everything’s moving though, you need less and less torque to accelerate and maintain
the wheel rotation speed You’ll also notice when you’re driving
rotation to a larger gear, the gear rotates more slowly.
If the gear ratio is 10:1, as it if with our pretend first gear, you need to rotate the
driving gear 10 times to get the driven gear to turn once.
So you’re getting a lot of torque out of this gearing but not actually getting it to
rotate very fast.
With smaller gears, you’re putting as much power in, but need to rotate the wheels much
faster to achieve those high speeds, and you can use these small gears at high speeds cause
you don’t need lots of torque to keep the rotational momentum up.
So, if we ignore normal energy losses for the moment, just note that the power of the
system doesn’t change between the engine and the wheels.
Power is just the rate at which the engine delivers power to the wheels.
If the engine is putting out 500 horsepower of power at the crankshaft, it’s delivering
500 horsepower to the wheels.
Again, ignoring losses due to friction.
The power will go up and down depending on the speed of the engine, i.e. its RPM, but
not with how you gear up the car.
All that changes is the torque and the rotational speeds.
If you up the torque, you sacrifice turning speed at the wheels.
So what’s interesting is that whatever the power at the engine you can deliver as much
or as little torque as you like to the wheels if you’ve play around with the gear ratios
enough.
If won’t give you any more power though.
So what are we talking about when we say ‘ooh Lord, these electric engines have a lot of
torque!’
? Well, firstly we don’t mean “they have
a lot of torque”, that’s a bit of a misunderstanding.
But we can talk about torque delivery or - in a colloquial way - a car being ‘torquey’.
Now we have to look at torque curves.
This means graphs, but I’m gonna make it super simple.
So let’s draw up some axes.
Along the horizontal axis here, we’re going to represent RPM, revs per minute.
So as we move along this axis, the engine does this:
[SOUND EFFECT OF ENGINE REVS INCREASING]
[VROOM VROOM VROOM] Up this axis, we’re going to measure torque,
so the higher up the chart we go, the more turning force the engine is delivering to
the crankshaft.
Not the wheels, the crankshaft.
So we’re talking about pure torque delivery before we’ve used gears to play about with
it.
We’re going to look at the petrol engine part on its own here, just the combustion
engine, not the electric motor.
Now with this engine we don’t get maximum torque straight away.
At low revs, as the engine is building up speed, it’s taking its time to reach maximum
torque.
There’s a few reasons for this: partly, as there are a lot of moving parts right through
the drive train, the engine has to put some of its energy into overcoming the friction
between these parts; partly as the combustion parts of the engine work on sucking fuel and
air into the cylinder, it takes a certain amount of engine speed to bring the optimal
amount of fuel and air into play.
So the torque curve ends up looking like this, with torque getting higher and higher as the
engine gets faster and faster.
It peaks around 12,000 RPM then starts to drop.
It drops because the mechanical resistance of the engine starts to dominate and the cylinder
can’t pull in any more air and fuel fast enough to create more power.
So this is the peak torque of the engine, this sort of area around 10-12,000 RPM.
You can confirm this because you’ll notice after the initial acceleration phase, the
gears are specifically set up such that changing up through the gears keeps the revs in this
peak torque range right through to maximum speeds.
Keep your eye on the telemetry graphics, like the ones here:
[PAUSE] So, looking at this curve we can see that
the torque has a sort of lag, not reaching its maximum until the engine is basically
at its fastest speed.
From in the car, the driver will feel an initial pull of acceleration but this will grow and
grow up to this point.
Not very “torquey”.
Slow to reach its full torque.
Now an electric motor has a very different torque curve.
Unlike the combustion engine, it has very few mechanical parts and it doesn’t rely
on the flow of fuel and air.
In fact, we know from our previous video on the MGUK that it’s just a rotor spinning
in a magnetic field.
Very simple.
So there’s next to no resistance on this motor so the instant you put your foot down,
you’ll pretty much jump straight to maximum torque.
The torque curve looks like this, showing that max torque is delivered from the very
beginning.
That’s why electric cars and hybrid cars feel ‘torquey’ - ‘cos they’re delivering
all this torque right up front, which puts a lot of the engines potential power straight
to the wheels.
In hybrid systems like the ones in F1 cars, the electric motor ‘fills in’ some of
the torque lag at low engine speeds, giving more instant high torque to the wheels that
was missing before.
You’ll see that after a point, the torque drops off dramatically with an electric motor.
And the thing with electric motors is that when putting a rotational spin into the electric
motor, we generate some electromotive force in resistance to the direction of the current.
After a certain RPM it dominates and overpowers the current in the motor, forcing the drop
off of torque delivery.
Now just to reiterate, an engine feeling very torquey doesn’t mean it’s more powerful
(a Formula E car feels more torquey than an F1 car, for example).
But the power delivered by the engine to the wheels ramps up faster the more torque it
being delivered.
We can show, with a bit of mathematical manipulation that Power is just Torque times RPM, so if
there was a constant torque then the Power would just ramp up directly with RPM.
If there’s more torque, the power ramps up more quickly.
If there’s less torque, the power ramps up more slowly.
So a high torque engine isn’t more powerful, but it does help deliver that power to the
engine more quickly.
So hopefully that’s given you a better idea of what torque is.
Engine torque is simply the turning force of the engine that’s then translated down
the drive train, manipulated by the gear box to multiply it up and provide Drive torque
to the rear wheels.
You need maximum torque at low speeds to get the car accelerating and lower torque at high
speeds to keep the wheel spinning faster, which is why higher gears are smaller and
do not crank the torque up as much as low gears.
And Torque does not affect the amount of power in the system, which is just the rate at which
the engine delivers energy.