From Audi

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What makes an Audi “S” car or SUV worthy of its badge? The easiest
answer is the balance of performance and design. But, Audi’s engineers
often raise the bar a bit further, with one of the latest examples
found in the new Electric-Powered Compressor (EPC) in the 2020 Audi S6
and S7 models.

Brought to the U.S. market for the first time in the Audi S6 and S7,
the 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.”

The EPC takes advantage of our 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 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.

Both the Audi S6 and S7 are rated at 444 horsepower and 443 lb-ft of
torque—37 lb-ft more than their V8 TFSI-powered predecessors. More
importantly than numbers, however, is drivability, control and agile
responsiveness, where the 2.9-liter V6 TFSI with EPC excels. 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.

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