Not long ago, the only info about electric supercharging in these pages was in the classified section next to a male-enhancement ad. Only one of those products actually worked.
-Electric supercharging, long rumored but never fully realized, is finally happening. Audi's upcoming SQ7 TDI pairs an electric supercharger with sequential turbos on the SUV's 4.0-liter diesel V-8. It's a first for a production vehicle.
-As with a conventional centrifugal supercharger, an e-supercharger uses a traditional compressor wheel but drives it with an electric motor rather than a crank-driven belt. E-superchargers draw their power from batteries or capacitors, which can be charged via regenerative braking or, in the case of the SQ7, a beefy generator and a 48-volt sub-system.
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The biggest benefits of e-supercharging are power and response, particularly at low engine speeds. Because an e-supercharger's ability to create boost is not coupled to exhaust energy or engine rpm, it offers flexibility not found in alternatives. Though traditional turbocharging remains a more efficient means of adding power, it has drawbacks such as lag.
-As engines downsize and pressurize, e-supercharging offers the ability to size a compressor for a power target without sacrificing low-rpm drivability. It does so by filling in the torque-less void below the turbo's threshold for creating boost. This is exactly how Audi is using the Valeo-supplied electric supercharger in the SQ7 TDI.
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Electric superchargers won't replace turbos, but they allow for the optimization of turbos and other technologies. For example, deactivated cylinders can remain dormant longer when supported by e-supercharging. And in Miller-cycle engines, which have a longer-than-normal expansion ratio, an electric blower can replace a traditional supercharger to reduce parasitic losses. Valeo describes its e-supercharger as an enabling technology, which gives it at least one thing in common with those male-enhancement products.
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