Project CARS: i segreti dell'Audi R18 E-Tron Quattro

[VELOCIPEDE]

Casey Ringley, Vehicle Lead del progetto Project CARS, ci spiega con l'ausilio del simulatore targato Slightly Mad Studios, tutti i segreti dell'Audi R18 E-Tron Quattro, vettura vincitrice a Le Mans nel 2014.

 

Casey Ringley, Vehicle Lead on Project CARS, gets intimate with Audi’s 2014’s Le Mans winner, the legendary R18, and what he finds might surprise you …
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This was a particularly exciting car to work on after it won Le Mans in 2014. The new hybrid regulations provided some cool engineering challenges, and the real-world teams were, unsurprisingly, reluctant to share data which could reveal relative advantages. That meant loads of work on our side with respect to examining all the available data before doing some reverse engineering to nail down the details. 

Here’s an overview of all the essential areas, and what we discovered about the R18.

 

Suspension
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We received enough points from the CAD to work out steering geometry, anti-dive, and so forth. The general steering feel is clearly a step up from the R10 TDI, and the R18 handles the varying downforce loads far better that the R10. LMP1 cars in 2014 were lighter than previous years (by 30kg—870kg minimum), but the same basic suspension setup works fine from the R10 to the R18 e-tron. Not a big enough difference, anyway, to throw out the basics.

Gearbox
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The R18 features a 7-speed unit, and the on-board telemetry that Audi broadcast during Le Mans and other races during 2014 was enough to give us basic speed-versus-engine RPM analysis. The gear ratios paint a pretty weird-looking setup on paper, but it drives really well since the diesel V6 has stupid levels of torque. The first 4 gears are incredibly tightly spaced; the plan, presumably, was to work in tandem with the flywheel hybrid system. With the odd exception here and there, shifts are executed at 4,500RPM.

Engine
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The 2014 regulations meant no more air restrictors, and a new boost limit set to 4.0 Bar. It’s doubtful Audi went quite that high on the R18 because that would go beyond the fuel-flow limit with a 4.0 litre engine. Best guess is that it was running closer to 3.0 Bar, which lines up neatly with what was used previously with the 3.7 litre version. That’s good for upward of 1,100Nm torque, and is slightly north of Audi’s vague ‘over 800Nm’ claim. But then that was always a no-brainer given the also-claimed 540hp means at least 850Nm@4,500RPM. Extrapolating what we know then from the previous engine, we can safely suggest the R18 was hitting that 540hp power peak early—around 3,500RPM—and then using ECU boost/fuel control to hold it at near constant power all the way up to the shift point. This has two advantages: it saves fuel (540hp is enough, really), and it means that the operating rev’ range pretty much always has maximum power available.

Hybrid
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This is where it gets interesting. Audi’s streaming video/telemetry included a meter for hybrid energy storage. Without any other hard info’, we had to rely on this to get an idea of how the system is working—and that ain’t all bad. We know it was a 2MJ-per-lap system. A closer analysis suggests the R18 was running about 6 full charges of the system per lap around Le Mans. Easy maths, then, to figure that, in Le Mans settings at least, the R18 is maxing-out charge at ~330kJ. Official claims for system storage are over 600kJ, with some even stating up to 1.2MJ, but it doesn’t make much sense to use only 2MJ when you have at least 6 good charging points around the lap. Perhaps Audi used a higher level of storage at shorter tracks for the shorter races, but we don’t have tons of info’ on that, and Le Mans is the main target anyway. Keeping the flywheel at lower speeds would be good for reliability, too, unless harvesting 4MJ per lap is reliably attainable. The race in 2014 also gave us some confirmation on the 330kJ number as Audi have claimed that they doubled their flywheel storage capacity to around 700kJ in their move to the 4MJ class.

Going back to the telemetry, we established that, out of chicanes on the Mulsanne, the R18 was burning through that 330kJ in 5-6s, and was emptied by the time the car hit 230kmh. This suggests an average system output of around 60kW (80hp). Maybe the system can do a full 170kW output as claimed, but that’s only if used at maximum speed (roughly 340kph): below that it is torque-limited in order not to burn through the 2MJ too fast. We’ve got it modeled this way, so 170kW is possible, but not ever really used as it isn’t practical for performance over a whole lap. What you end up with is about the equivalent of an extra 200Nm from the engine accelerating through 5th gear, and that ain’t too shabby.

Aero
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Very little ‘official’ data came our way on aero’, but a lot can be inferred. Audi have made public claims of lift:drag efficiency of 5:1, and we can be sure they are understating that. At top speed, when ride height reduces under downforce load, it’s probably closer to 6:1 (for those who aren’t aero’ nerds, this is seriously efficient). What we also know is that top speeds, without a draft at Le Mans, were typically recorded in the 315-319kmh range. With a draft, that number gets up closer to 340kmh. Not very high in the grand scheme of things, and it works out at something around 420lbf of drag@150mph in Le Mans aero’ spec’. Prototypes can drop 5 percent or more of their total drag compared to static ride height when squatting down under load at top speed. So what we did was: we took that 420lbf drag figure, added about 5 percent when at static ride height, and figured the 5:1 downforce from there. If overall lap time performance is anything to go by, this worked out well.

Audi were also kind enough to run both aero’ packages at Spa in 2014. The Audi number 3 used the ‘LM’ package, while cars number 1 and 2 used the sprint package with high drag/downforce. Car number 3 was good for nearly 300kmh at the end of Kemmel straight, and our ‘LM’ setup matched that exactly. Nice. Move to high downforce, and top speed on Kemmel goes down to 275-279kmh while keeping similar efficiency. That’s downright slow for an LMP1! These new generation cars are getting all of their speed in acceleration and hitting top speeds early on the straights. This is why the higher energy hybrid classes are the way to go, and may have been the key to Porsche’s victory in 2015.

Feel
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What’s it like to drive? Quite a bit different from the 2011-2013-era LMPs. The narrower tyres mean there is a lot less mechanical grip available, and you end up hustling the car more at low speed. At the same time, the new aero/chassis rules mean more downforce on less mass, so high speed corners are an even more intense experience. Cruising to hit a good fuel number and maximize hybrid use is a very different experience and makes for an interesting drive.

 

Fonte Project CARS

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