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Audi Electric-Powered Compressor gives 2020 Audi S6 and S7 models a boost; 48V MHEV architecture

Brought to the US market for the first time in the 2020 Audi S6 and S7, Audi’s Electric-Powered Compressor (EPC) comes paired to the 2.9-liter, twin-turbocharged TFSI V6 engine. It consists of an electric motor with a small turbine that helps quickly build turbo boost pressure, sharpening throttle response and reducing any noticeable turbo lag.

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The EPC takes advantage of the latest-generation 48V mild hybrid electrical architecture, supplying electric energy generated during coasting and recuperation to the vehicles’ 9.6 Ah lithium-ion battery. From there, the battery provides the electric motor energy to accelerate the turbine located downstream of the engine’s turbochargers to quickly increase pressure, aiding engine responsiveness and torque delivery.

The entire EPC system adds just 10 kg (22 lbs) to the vehicles’ overall weight and reduces response time to less than 250 milliseconds, faster than an average human’s reaction time.

The compressor is located downstream of the engine’s parallel twin turbochargers and upstream of the air-to-water intercooler, pushing cooler air through the engine’s two throttle bodies and into its cylinders with higher force. At lower engine speeds, the EPC activates at speeds up to 70,000 RPM. This helps the engine operate similar to the smoothness of a naturally aspirated, non-turbocharged, engine.

When the V6 TFSI engine is operating at higher speeds, a valve for the EPC closes, leaving a parallel path for air to move throughout the engine. However, the EPC is always operating, even when idle, ready to respond to the driver’s needs for more power.

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Both the Audi S6 and S7 are rated at 444 horsepower and 443 lb-ft (600 N·m) of torque—37 lb-ft more than their V8 TFSI-powered predecessors. In internal tests that simulate real-world standing starts, the latest powertrain exhibits response characteristics that rival Audi’s torque-rich, turbocharged 4.0-liter TFSI V8. Yet, the 2020 S6 and S7 offer 22% greater EPA-estimated fuel-efficiency with its downsized V6 engine compared to their predecessors without sacrificing performance.

Comments

sd

Last gasp for the high performance IC engine? Seems like it would be better to just add more electric capacity and add power directly to the wheels. Reminds me of the last of the turbo compound aircraft engines in the early 50's (DC-7) or maybe the Pennsylvania Railroad duplex steam engines in the late 40's (T1, Q1 and Q2).

mahonj

It is a pity they couldn't (or wouldn't) apply that type of tech to engines with 1/4 the power, in the A1,2,3,4 for instance.

mahonj

@SD, those are some locomotives - beautiful and mad!

cujet

Quote sd: "Last gasp for the high performance IC engine? ,,. Reminds me of the last of the turbo compound aircraft engines in the early 50's"

And yet, nearly 70 years ago, those turbo compound aircraft engines produced better passenger MPG than all but the best we produce today. Put another way, 70 years ago, we could push unrefined aircraft as far per gallon of fuel. It becomes even more interesting when we realize that Jet-A has more energy per gallon than avgas.

Battery powered electric airliner propulsion remains extremely unlikely, as there is no useful heat, this limits speed. Couple that with the short run times and heavy landing weights, and we have a non starter.

SJC_1

"no useful heat, this limits speed" ?

sd

cujet, I was mostly referring to the complexity of the turbo-compound engines when it was increasing obvious that the future was turbine engines. Just think of changing 224 spark plugs for a 4-engine plane (2 plugs/cylinder x 28 cylinders x 4 engines).

I think that it will difficult to build a battery powered airliner capable of crossing the oceans anytime soon or maybe never. Might get close with lithium air. However, look at https://www.eviation.co/ We are getting close to flying battery powered regional aircraft.

mahonj, The real crime was that all of those "beautiful and mad" steam locomotives were scrapped. Not one was saved for history. Some railroads saved or gave away some of their locomotives to museums, etc. but the Pennsylvania Railroad scrapped just about everything.

gryf

The most efficient turbo-compound was the Napier Nomad and it was a diesel. Even this brilliant engine was never considered by aircraft manufacturers because jet engine aircraft like the Boeing 707 would replace all prop aircraft.
Jet engines were very inefficient and were soon replaced by turbofans. Todays high bypass turbofans produce over 80% of their thrust from the fan not the exhaust. The Pratt & Whitney geared turbofan with a bypass ratio of 12.5:1 is more like a ducted turboprop, so even more thrust is produced by the fan.

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