What is Engine Mapping and how does it affect a car’s behaviour?  | Plus Mini Q&A

What is Engine Mapping and how does it affect a car’s behaviour? | Plus Mini Q&A

Over team radio, throughout a race and in
all the technical after-talk, we hear about engine maps and modes that drivers often change
and fiddle with either independently or at the behest of their engineers.
So what is engine mapping and how does it affect the way the cars perform? Let’s start with the basics. In the way
back when – and I mean way back when – the accelerator pedal was directly, physically
connected to the engine via a mechanical cable. The more you pushed your foot to the pedal,
the more the throttle opened, letting more air and fuel into the engine cylinders, which
drove more power from the engine via increased combustion. It was simple, but limited.
Now the amount of travel in the accelerator pedal is measured electronically and read
by the Electronic Control Unit or ECU The ECU then takes in lots of other inputs
from the car and works out exactly how to manage the combustion part of the engine and
ultimately the power output. It works all this out via engine maps.
Engine maps are essentially a bunch of data tables in which the ECU looks up what’s
going on with the car and driver inputs and finds out what it’s supposed to do with
the engine. To get a feel for this, let’s start with
the Engine Torque Map, which is really more of lay of the land than a series of instruction,
but it all fits into the wider picture, you’ll see.
The Engine Torque Map just describes how much torque the engine delivers as standard at
a given RPM and and amount of throttle. The RPM (the rotational speed of the engine)
and throttle level (basically, how much fuel mixture you’re pumping into the engine)
are your inputs. The torque, (which is strictly how much turning
force the engine is producing) is an output. So if you know your RPM and throttle level,
the map will tell you the engine torque. Let’s imagine a very simple, scaled down
version of this engine map. We can model it to see what would happen at slow, medium and
fast RPMs. And we can also look at narrow, medium and full throttle levels.
This gives us a nice table with 9 possible scenarios – our outputs. So if the engine
is running at low RPM and we’re only squeezing the throttle a little, the map tells us the
engine will be producing a small amount of torque.
Full throttle at high RPM produces a large amount of torque. And so on. We just draw
from the two inputs to find our output torque. You get the idea
Now, obviously, the engine map used in real life is a lot more granular than that, using
more than just our 3 gradations of input but this one looks a lot more daunting at first
glance. So, really, this engine torque map just describes
the engine as it normally behaves – we gather this data but running the engine on a testing
dyno and logging its torque levels under different scenarios. But what if we wanted to create
a map that did make it behave differently to normal?
This is where all the custom, various engine mappings come in. We can create our own versions
of this map so that, when a driver pushes the accelerator pedal at a certain engine
speed, the torques outputted will be different under different maps.
We might want to lower the torque at lower revs, like this. Or we might want to make
the jump from low to high torque more dramatic. The idea behind these maps is that we’re
going to demand from the engine a certain amount of torque or power given certain scenarios.
We’re going to tell the engine – if I’m pushing the throttle half way and you’re
revving at 8000 RPM then you better give me 180 Nm of torque, or whatever.
This engine map is sometimes referred to, aptly, as the Driver Demand Torque Map as
the driver demands a specific output from the engine by applying the throttle pedal.
Let’s just simplify this again by taking engine speed out of the equation for a second
so we can think about what engine maps might mean to the driver.
So, instead, let’s think about the relationship between the accelerator pedal and the torque
out of the engine. So, you’re the driver and when you adjust the pedal with your foot
you’ll have an expectation of what the engine does – what kind of power gets delivered to
the rear wheels. Let’s do a little graph showing how far
the accelerator pedal is pushed down along the bottom and how much torque the engine
is giving you up the side. Now, the rules state that 0% and 100% throttle
must translate to 0% and 100% of the available torque respectively, so that’s here and
here. We could draw a straight line between these
points to create a linear relationship. That would mean 50% throttle produces 50% torque.
27% throttle produces 27% torque and so on. And you might think – cool, that makes sense.
If I’m a driver that would be incredibly intuitive to me; I’d know exactly where
I am with that. But consider this – if you’re accelerating
out of a slow corner you’ve really got to be careful of wheelspin: it slows you down
and wears the tyre. This happens if you whack too much torque into the tyres.
So you might want the pedal to be more delicate at first – each cm of travel in the pedal
producing a smaller change in torque so you can manage more finely a smooth increase in
torque at lower speeds. So the engine map would have a shallower graph
with maybe the first 30% of the pedal travel giving you just 10% of the engine torque.
This is one of many scenarios that feed into the Driver Demand torque map. You’ll probably
have one more suited for wet weather, where again wheel spin is a big problem – even at
high speeds. You might have ones that are more or less power intensive depending on
whether you’re going full beans in qualifying or pacing yourself in the middle of a race.
Your maps will even vary from track to track, with a slow, tight track like Monaco requiring
a very different feel to, say, a high-speed circuit like Spa Francorchamps that requires
far less fiddling about in slow corners and much more control at high speeds and high
revs. A big part of this is about driver feel. What
mapping helps the driver deliver just the power they need in the way they like to use
the accelerator? Two drivers in the same team on the same track might finesse their engine
maps in different ways through practice. If you, the viewer, are a driver you should
understand this – though it may have become subconsciously intuitive by now. When you
use the accelerator pedal you have a sense of how the car is going to behave – you know
how it feels at different RPM and pedal travel. Incidentally, there are limitations on how
you can build your engine maps. You need to submit them to the FIA who check you aren’t
veering too close to traction control or launch control – you can see how the art of managing
errant wheel spin through a computer is a little bit traction-controlly.
So – the Driver Demand torque map takes in the inputs from the pedal and the engine to
deliver torque as requested in whichever map is selected. All the different maps needed
will be available to the driver via the knob on the steering wheel.
But how does the ECU then get the engine to deliver the torque demanded by the driver?
Well it uses a number of other maps to deliver inputs into the actual mechanics of the engine
to deliver the demanded torque – particularly the Ignition Timing Map the Injector Timing
map. These two maps are essentially just tables
that tell the engine when to fire the spark plug and how much fuel to deliver into the
cylinder by looking at the engine speed, or RPM and the amount of torque currently on
the engine. We’re not going into the whole mechanics
of a combustion engine here but essentially, engine power comes from a mixture of air and
fuel being injected into the cylinders and a spark plug igniting to flash-combust that
fuel mix into driving the pistons. In the piston’s cycle of injection, compression,
combustion and exhaustion the exact timing of firing the spark plug – the ignition – the
the amount of fuel delivered – the injection – can have quite the effect on the torque
output of engine. So via the ignition and injection maps, the
ECU looks at the Driver Demand map, it looks at the current state of the engine, it looks
at other inputting factors like temperature and fuel mix and works out the exact combustion
settings to meet the torque demands. It sounds complicated but it all happens incredibly
smoothly. The driver sets an engine mapping they desire.
They demand torque from the engine by pushing the throttle pedal a certain amount. The ECU
sees this demand and takes a look at the engine, making note of its current speed, its loads,
all the inputs it needs. It then takes these inputs and looks them up on the engine map,
which tells the ECU what it needs to do mechanically to the engine to get the result it wants.
Bear in mind, this is a different mechanism to the fuel mix settings, which you may know
from the Codemaster’s game for its Lean, Standard and Rich mix settings. While you
can map engines to work with fuel mixtures and lean into the trade-offs of efficiency,
power and wear, that kettle of fish is for another time. Let’s check in on a few of your questions
“Was the liveries video finished before Ferrari’s cheeky Philip Morris branding?”
– actually, yeah! Well I was in the middle of making it when Ferrari announced a ‘change
in livery’. I was so disappointed that they just stuck a rubbish new logo on the engine
cover and that was that. I assume Mission Winnow is a bottling facility.
What’s my favourite livery this year? My favourite liveries tend to be ones that are
a change on the previous year executed really well. The Sauber livery is really smart, and
I’m really in love with what Toro Rosso have been doing. But I think Renault have
done something really nice this year. And Gianluca asks what would happen is Toro
Rosso didn’t actually get a second driver. Well, if they only turned up with one car
the F1 would class them as having not properly turned up to a race. If the FIA deems you
don’t have the means to take part in the competition your team is disqualified. So
they’ll shove Maldonado in there if they have to.
Til next time!