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New Audi R18 e-tron quattro LMP1 racer integrates two hybrid systems, kinetic and thermal
12 December 2013
|Audi R18 e-tron quattro 2014. Click to enlarge.|
Audi has released initial details on its new 2014-generation Audi R18 e-tron quattro LMP1 Le Mans prototype racer. Although the new diesel hybrid sports car appears like a continuous further development of the World Championship winning car and Le Mans winner of the past two years, due to the new LMP1 regulations that will come into effect in 2014, Audi Sport redeveloped every component.
In the new Technical Regulations, a large number of principal definitions, which concern the powertrain, body dimensions, safety and aerodynamics, were re-determined. With the new R18, Audi Sport has opted for a similar concept as in the past—albeit with new detailed solutions and an additional hybrid system. Powertrain elements include:
|Changes in WEC regulations focus on energy consumption|
|The new WEC regulations no longer limit engine output through cubic capacity restrictions, the number of cylinders or the use of air restrictors. Rather, the focus is on the energy consumption of the race car.|
|Until now, the turbo diesel engine of the Audi R18 e-tron quattro was limited to 3.7L of displacement while the permissible maximum size of gasoline engines used by LMP1 race cars was 2L (turbo engines) or 3.4L (normally aspirated engines). As of 2014, displacement no longer numbers among the limiting factors.|
|In the past, the engine was supplied with air through an air flow restrictor (45.1 mm for the case of Audi’s V6 TDI). In the future, gasoline and diesel engines will be allowed to “breathe freely.” While in the past moderate boost pressure restrictions applied to turbocharged engines (diesel: 2.8 bar; gasoline: 2.5 bar), 4 bar is now allowed.|
|In the future, energy charts will define the maximum consumption per lap; manufacturers have to choose one of four energy classes. The chart allows a maximum of recovered hybrid energy, which may be reused in a certain way, in combination with absolute fuel consumption per lap.|
|Flow meters in all the race cars check these consumption levels and transmit the data to the stewards of the meeting on each lap. The same happens with the energy amounts of the hybrid system. This makes a tactical distribution of fuel consumption over the entire race distance impossible.|
|Anytime the prescribed maximum levels are exceeded, the excess consumption must be compensated for within three laps, otherwise penalties may be imposed. Therefore, when it comes to covering the longest distance within a given period of time, the only things that count are the most efficient race car and the corresponding driving style of the driver.|
A further developed V6 TDI mid-engine powers the rear wheels
e-tron quattro hybrid system at the front axle (ERS-K – Energy Recovery System Kinetic, a system to store kinetic energy)
Optimized flywheel energy storage system
Hybrid system with an electric turbocharger in the internal combustion engine (ERS-H – Energy Recovery System Heat, a system that stores energy converted from heat)
The further developed V6 TDI unit of the Audi R18 e-tron quattro makes a crucial contribution to the car’s compliance with the energy specifications of the regulations. The new R18 has to do with up to 30% less fuel than its immediate predecessor.
In addition to the internal combustion engine, the powertrain concept, for the first time, features the integration of two hybrid systems: ERS-K and ERS-H.
ERS-K. As before, during braking events at the front axle a Motor-Generator-Unit (MGU) recovers kinetic energy flows into a flywheel energy storage system.
ERS-H. For the first time, the engine’s turbocharger is linked to an electrical machine, which makes it possible to convert the thermal energy of the exhaust gas flow into electric energy—e.g., when the boost pressure limit has been reached. This energy also flows into the flywheel energy storage system. When the car accelerates, the stored energy can either flow back to the MGU at the front axle or to the innovative electric turbocharger, depending on the operating strategy.
The overall design of these systems and their direct impact on engine and powertrain management require highly complex coordination and tuning work. Audi Sport initially performed theoretical analyses and simulations, followed by rig testing and, since October, by track tests. The options available to the drivers and engineers as a result of the new technology are now more extensive than ever before.
Aerodynamics. The new framework conditions for aerodynamics enable new freedoms, but accompanied by greater restrictions. As an example, the 10 centimeter slimmer body of the new LMP1 sports car means that the front of the R18 becomes mathematically smaller—an advantage. The bodywork accommodates slimmer wheels, which, in turn, reduces aerodynamic drag. This is contrasted by other innovations that do not provide any advantages in aerodynamics.
At 1,050 millimeters, the race car has to be 20 millimeters higher than before, and larger cockpit dimensions are prescribed as well. This leads to less favorable aerodynamics.
The lower overall width of the car results in a slimmer underfloor. In addition, it features a completely different shape in the area of the cutouts for the front wheels. Consequently, the area that can produce downforce becomes smaller.
Instead of a diffusor at the front en, a genuine front wing with a flap may be used for the first time. This promises aerodynamic advantages and lower costs, as this part of the bodywork will lend itself to easier modification to suit the various race tracks. In the past, it was necessary to produce different bodywork assemblies.
On the other hand, greater limits have been imposed on the aerodynamic design freedoms at the rear end. Use of the exhaust gas in the area of the rear diffusor, as in the case of the 2013-generation Audi R18 e-tron quattro, is now prohibited.
Safety. Even in the past, LMP1 sports cars with their closed CFRP cockpit structure were regarded as one of the safest race car categories. The rule-makers have continued to improve the safety of the latest race car generation by imposing numerous discrete requirements.
The new monocoque has to resist higher loads. At the same time, it is reinforced by additional layers of fabric, which are hard to penetrate in the case of a concentrated impact. This reduces the risk of intrusion by pointed objects in accidents.
For the first time, wheel tethers are prescribed. They connect the outer assemblies of the front wheel suspensions with the monocoque and the ones of the rear suspensions with the chassis structure. Each of the two tethers required per wheel can withstand forces of 90 kN, which equates to a weight force of nine metric tons. Another new feature is a CFRP structure behind the transmission—the “crasher”—which absorbs energy in a collision.
This is another example of the considerable challenges faced by the Audi engineers, as all these innovations increase weight, in addition to the second hybrid system. Audi’s previous Le Mans prototype weighed 915 kilograms (2,017 lbs). In the future the car’s weight may be reduced to 870 kilograms (1,918 lbs).
The basic elements of the Audi R18 e-tron quattro’s new configuration were defined back in 2012 and the design of all the single components started at the end of 2012. The new LMP1 sports car was rolled out in the early fall of 2013, followed by track tests of the most recent R18.
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