Mercedes debuts electrically driven exhaust turbocharger on the road

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Mercedes-AMG has finally found a home for its electrified exhaust gas turbocharging technology developed in Formula 1 – the new SL 43 cabriolet.

With the first two iterations of the current generation SL featuring V8s, the latest version is equipped with the company’s potent M139 2.0-litre I4, most commonly found in the A 45. However, rather than being equipped with a standard exhaust driven turbocharger, the SL 43 uses an electronically controlled turbo which sandwiches a 48V electric motor between the turbine and compressor housings, with power provided by the car’s 48V mild hybrid system which incorporates a belt-driven starter/generator.

This technology is apparently directly derived from Mercedes’s F1 program, where the cars have used 1.6-litre V6 engines with exhaust gas energy recovery since 2014. However, in its first road car application, the electric motor is used only to control the speed of the turbocharger, providing on-demand boost at low RPMs, eliminating lag. In F1, the MGU-H as it is called there, is dual use and also feeds power directly to the car’s battery and MGU-K (which directly drives the engine’s crank).

The motor sandwiched between the turbo halves is stated to be just 40mm thick yet can rotate at 170,000rpm as it is directly mounted to the turbo shaft, allowing it to accelerate the compressor, maintaining boost even off throttle and thus increasing throttle response. Notably, the motor, power electronics and turbocharger are all cooled on the same coolant circuit as the main IC engine.

“The electric exhaust gas turbocharger is a fascinating example of the extensive transfer between Formula 1 technology and the development of production vehicles. In implementing this in conjunction with our powerful M139 four-cylinder, we were also able to draw on the enormous wealth of experience of our colleagues at Mercedes-AMG High Performance Powertrains. The technology increases agility and thus driving fun, while at the same time improving the efficiency of the drive system. We are pursuing ambitious goals with a view to our electrified future. Innovative components such as the electric exhaust gas turbocharger help us to achieve this,” commented Jochen Hermann, Mercedes-AMG CTO.

The SL 43 produces a rated output of 381hp at 6,750rpm with maximum torque of 480Nm between 3,250rpm and 5,000 rpm.

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Lawrence has been covering engineering subjects – with a focus on motorsport technology – since 2007 and has edited and contributed to a variety of international titles. Currently he is responsible for content across UKI Media & Events' portfolio of websites while also writing for the company's print titles.

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