Looking at the various options available to Audi to improve performance for next year, the "e-turbo" solution trialled by Audi last winter looks to be one of the most logical evolutions.
But what is the "e-turbo" solution supposed to look like ?
In the
original press release issued on December 12th, 2013, the solution was described as follows:
Quote:
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)
(…)
In addition to the internal combustion engine, the powertrain concept, for the first time, features the integration of two hybrid systems. As in the past, a Motor-Generator-Unit (MGU), during braking events, recovers kinetic energy at the front axle, which flows into a flywheel energy storage system. For the first time, the turbocharger of the internal combustion engine is linked to an electrical machine, which makes it possible to convert the thermal energy of the exhaust gas flow into electric energy – for instance 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.
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As we know, Audi ultimately shelved this solution which did not make it to the actual race car.
It was subsequently claimed by Audi representatives that the e-turbo solution was not intended to be used to recover energy, but mainly as anti-lag system, which statement is in evident contradiction with the original statements in the press release of December 2013. If the electric turbocharger is not supposed to recover energy from the exhaust gases, then why describe it as an ERS-H ? Which statement is true then ?
There is at least concrete evidence that may support the most recent statement, namely the solution embodied in the form of the
Audi RS5 TDI Concept that was presented last June (which presentation was interestingly coinciding with the LM event…).
The engine of the Audi RS5 TDI Concept is equipped with a small electric turbocharger that is used to supplement a conventional turbocharger at low revs in order to reduce turbo-lag. As shown in the following illustration, the electric turbocharger is located in a bypass downstream of the charge air intercooler, i.e. at a location where the e-turbo is unlikely to be much of a benefit in term of energy recovery from the exhaust gases :
This small electric turbocharger is indeed not used to recover energy, but merely as an electrical machine, which is actually powered by energy recovered upon braking and stored in batteries.
What if the e-turbo solution actually trialled by Audi on the R18 was following the same principle ? That would at least be consistent with Audi's latest declarations.
In the affirmative, such an e-turbo solution will not be beneficial in terms of the amount of energy being recovered and Audi would need to find another solution to improve energy recovery, e.g. by adopting a more powerful ERS-K.