Engine maps, throttle maps, turbo updates and more

Discussion in 'Car Information and physics updates' started by Alex Hodgkinson, Dec 16, 2020.

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  1. Alex Hodgkinson

    Alex Hodgkinson Sector3 Developer

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    I'll start by going straight in; when the December update drops, your driveline tuning page will look like this:

    Screenshot 2020-12-16 211218.jpg

    With two new new additions:

    ebr.jpg

    emap.jpg

    Engine Braking Reduction:

    This is something we always had to tinker with behind the scenes. The real power of this became apparent when we started to look at dialling out some tricky behaviours from some of our cars. Namely the off-throttle any-speed unrecoverable spins, also known as instabins. Some of us rarely had any trouble with such behaviour whereas others were very vocal. It turned out those who had little issue with it were naturally keeping a little bit of throttle applied at corner entry to keep the car stable. Those who regularly spun were completely off the accelerator pedal on entry.

    This lead us to realise that some drivers would benefit from a little bit of throttle being applied in order to reduce the engine braking and keep the car stable, even when they were not pressing their actual pedal. We also realised that would not suit everybody as agility is sacrificed. Thus the answer was to make it adjustable and that's when this slider was conceived.

    More clicks/higher values here will decrease the engine braking and make the car more stable when not pressing the accelerator pedal.

    It's worth mentioning that the name engine braking reduction was decided on as the normal English idle adjustment doesn't translate well to other languages, as it intrinsically linked to when the engine is at tickover revs and thus easily confused.

     

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    Last edited: Dec 17, 2020
  2. Alex Hodgkinson

    Alex Hodgkinson Sector3 Developer

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    Turbo code update

    I think we can now admit that behaviour of our turbocharged engines has been somewhat flawed. To the user, the biggest give away of the issues behind the scenes is that pulling away from stationary takes almost full throttle. Then once you are up and moving only the very top end of the accelerator pedal really has any effect.

    Anyone who's ever driven a turbocharged car (probably most of us now) will be aware of different characteristics that a turbocharged engine has, but these were extremely exaggerated. To cut a long story short, our turbo code until now took throttle position in to account not once but twice and thus effectively squaring the user's throttle pedal input. So when giving it 50% power, you were getting 25% power. This starts to explain why our turbo car behaviour has been the way it is.

    On top of that, you couldn't build full turbo pressure unless you were at full throttle, whereas a real turbocharger can build full turbo pressure as long as the revs are rising. How much of that pressure gets used is up to how much the throttle is opened.

    Following a re-write of the code, the turbo pressure now depends much more on engine revs than throttle input. Your throttle inputs also have a much more realistic bearing on how much power is being delivered - you have more range to play with as it's no longer only effective in the upper echelons of it's travel. Seeing as boost pressures can now reach their peak values at part throttle and low revs, race starts and launch behaviour are now much more satisfactory.

    One final thing we did was stop the turbo pressure dropping as it got close to the rev limiter. That's something that does happen with road cars, but race cars go hard all the way to the red line.
     
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    Last edited: Dec 17, 2020
  3. Alex Hodgkinson

    Alex Hodgkinson Sector3 Developer

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    Throttle pedal maps

    This is a really big one. Although we're calling it throttle mapping, I like to refer to it as engine torque response curves. Gone are the entirely linear, perfectly concave or perfectly convex throttle pedal responses. It's now replaced with an entirely customisable system with which we can build bespoke throttle response curves for each and every engine as well as for individual engine maps (which we'll get to later).

    I'll begin by explaining why this is important and what was wrong previously. Firstly we need to understand that an engine is an air pump. When running is actively drawing air in as the suck-squeeze-bang-blow process creates an expansion of gasses which travels out of the exhaust valves and down the exhaust pipe. That creates a void and therefore a vacuum at the inlet side of the engine. It's important to have that understood because it explains that the throttle butterfly valve or slide is not simply a volume control; opening it 25% at idle revs won't simply give us 25% of the power available. It will give us measurably more as the air is being drawn in, and drawn in at a higher speed than if the throttle was wide open at those revs. Thus you can see it's really quite a complicated matter of fluid dynamics and definitely not a volume knob.

    Until now, we've by default a completely linear throttle response in game. Opening the throttle to 50% at any given revs would give you 50% of the power available. That is no longer the case, as we can build response curves which look like this:

    Screenshot 2020-12-17 171010.jpg
    Horizontal axis is throttle input, vertical axis is engine torque response.

    This behaviour is far closer to reality, and entirely tuneable by us behind the scenes.
    You'll notice the black line is very different to the others - that's because this is what throttle response curves looked like before the advent of modern electronic control systems with drive-by-wire throttle systems. All of our pre mid-90s cars will be shipped with this type of throttle response curve.

    Seeing as this is quite a revolution for our throttle behaviour, I'll offer a few words to help;
    • Ensure that your throttle pedal sensitivity is now set to default, which is 50%
    • Initial throttle pickup is much quicker across all of our modern cars (1995-on)
    • From roughly half-throttle onwards you have reduced sensitivity, so you'll find there's more room to play with and the car will be more controllable when you're playing with the power
    • Give yourself some time to get used to it, this is quite a big departure from how a majority of sims have done things for the last 25 years!
    • Some cars which have engine maps have different throttle response curves for each map. Usually higher engine maps give more aggressive throttle response. Have a play with the different maps and you'll surely notice the difference.
     
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  4. Alex Hodgkinson

    Alex Hodgkinson Sector3 Developer

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    Engine maps & modes

    I'm particularly excited for the introduction of this feature to our simulation.
    Now we can finally unleash the full fury and madness of the ridiculous power outputs of some of our historic content!

    Screenshot 2020-12-18 103715.jpg

    Modern racing cars use fully computer controlled fuel injection, spark timing and throttle inputs which can be infinitely tuned at some point during their development cycle. These allow the engine's behaviour to be moulded in certain ways. Usually the fastest setups here are very aggressive and consume more fuel, whereas a softer engine behaviour is easier to drive as well as being more economical. Our system allows us up to 5 engine maps per car, but some do have fewer.

    Screenshot 2020-12-18 112938.jpg


    Some of our older cars (Group 5, Group C etc) were adjustable in a sense that boost pressures as well as mixture control could be adjusted. In game these still show up under the engine map section and you'll actually find that the setting is much more dramatic as boost pressure offers a wider span of adjustability. Our Nissan R90CK for example now makes less than 600bhp on it's lowest setting, but on the highest it's kicking out over 1000bhp. The implications of fuel usage with such a high boost setting are massive, as well as the increase in turbo lag. One quirk we've applied to our Group C class is lack of in-car adjustability of the engine modes. That is a historical feature, which was something the normally aspirated Jaguar/TWR team lobbied for in 1986 as they argued they couldn't compete with the turbo cars on fuel consumption. They won the world championship in 1987.

    This feature is not simply a modifier of torque and/or power, instead we can tailor the engine's behaviour to individual maps and give them bespoke power curves. For example, map #4 and #5 may be identical on one car except for map #5 uses a more aggressive throttle response as well as delivering more torque close at high revs, at the expense of increased fuel usage. All these factors combined give us subtle but noticeable differences across the engine modes.

    I should also mention at this point that our AI will make use of this new feature. They will use the highest available map during qualifying sessions and are capable of switching maps during races. They will usually use the highest map available that will enable them to finish the race without having to make extra pit stops.

    So what's the trade-off, why wouldn't you use the highest map all the time?
    • Some of the cars with extreme differences across the maps may experience overheating if too long is spent in the highest modes.

    • If you're new to a car, it may be beneficial to turn the engine down a touch while you learn how to drive it. Lower engine modes generally give softer power delivery, especially with older cars.

    • You may be racing in a longer race with pit stops. Careful consideration of engine modes may enable to you extend stint length by several laps.

    • Mid-range maps are geared towards endurance driving with more progressive behaviour. High settings are sprint race orientated.

     
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    Last edited: Dec 18, 2020
  5. Alex Hodgkinson

    Alex Hodgkinson Sector3 Developer

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    Traction control override

    To aid in recovering a car which is facing the wrong direction, we added an assignable button called traction control override.

    Pressing this button will disable traction control as long as it's held down, up to 9m/s or 32.4kph when traction control will be automatically re-enabled.
     
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  6. Alex Hodgkinson

    Alex Hodgkinson Sector3 Developer

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    Energy Recovery Systems

    We currently have two electric racers within RaceRoom; the Volkswagen I.D. R and added more recently the Cupra E-Racer. While both of these cars have very different chassis characteristics, they do have some similarities in their powertrains. Both of these cars receive a few updates to their drivetrain behaviours with this update. However before I cover that I'll begin with a recap of the two driving modes available in both cars:

    D-mode

    This is simply a driving-only mode where the car uses up it's battery charge until empty. There is no recharging of the battery taking place as you drive. Deceleration is handled entirely by the braking system of the car.

    S-mode


    In this mode, the power available is the same as D-mode. However, when lifting off the accelerator the current flow is reversed from the batteries, moving to the batteries instead. This means that the batteries are charged as you decelerate, which has two main effects. The first is that the range you can drive between charges is extended. The second is that the ('engine braking') resistance as you lift of the accelerator pedal is increased in this mode, which affects the feel of the car in braking zones and while entering turns.

    What's new

    Our electric cars will be updated to use the new engine map feature already described above. You'll gain 5 engine modes per car, with increasing levels of power output and energy consumption:

    Screenshot 2020-12-20 201435.jpg

    The energy recovery modes gain adjustability. As mentioned already, the car must be in S-mode for this to be activated. This range is adjustable from 0 (same as D-mode) to 15%. The percentage represents what amount of available acceleration power is available as a charge when decelerating. So at 15%, if a motor produces 200kw at 10,000rpm, then it will charge at a rate of 30kw at 10,000rpm.

    Screenshot 2020-12-20 201458.jpg

    This setting is also available to adjust in-car. Either by an increase/decrease assignment, or by assigning a multi-position switch:

    Screenshot 2020-12-20 201244.jpg
     
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