Tech’splaining: What is Mercedes-Benz EQ Boost?

  • Christian Wardlaw has 25 years of experience serving in automotive editorial leadership roles with Autobytel, Edmunds, J.D. Power, and Tribune Publishing. A married father of four, Chris is based in the Los Angeles suburbs and believes fuel cell electric vehicles will power the future.

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Two years ago, Volvo announced that it would electrify its entire vehicle lineup by 2025. Lots of people misunderstood this announcement, assuming that every Volvo would be an electric vehicle. That’s not the case. Electric and electrified are related, but different, concepts.

Take, for example, the latest Mercedes-AMG 53 models. They’re electrified, employing the automaker’s new EQ Boost technology, but they’re not electric. Combined with enhancements to the AMG 53 models’ turbocharged 3.0-liter inline six-cylinder engine, EQ Boost helps to deliver up to 24 mpg in combined driving and acceleration to 60 mph in as few as 4.3 seconds.

Intrigued? Read on to learn more.

What is EQ Boost?

Mercedes-Benz EQ Boost Integrated Starter Generator
EQ Boost is essentially an integrated starter generator that is mounted between the engine and the transmission, giving the vehicle instantaneous electric motor boost while the turbocharged six-cylinder engine gets revved up. (Christian Wardlaw)

 

Essentially, a Mercedes-Benz equipped with EQ Boost is a mild hybrid, or light-electrified, vehicle. The concept isn’t new but is viewed within the automotive industry as an increasingly viable way to improve efficiency and performance at the same time.

Brian Cotter, Product Manager for Mercedes-AMG, explained that the primary, but not the only, benefit of using EQ Boost in the company’s performance vehicles is to give them instantaneous access to torque. “You’re minimizing the inherent weakness of an internal combustion engine by relying on the strength of an electric motor,” Cotter said.

EQ Boost uses an integrated starter generator, mounted between the engine and the transmission, that combines a starter motor, an alternator, and an electric motor. It serves several functions:

  • Powers an electric auxiliary compressor to virtually eliminate turbo lag, its internal fan spooling to 70,000 revs in a third of a second, supplying eight pounds of boost to either the exhaust-gas-driven turbocharger or directly to the engine
  • Powers a 48-volt electrical system that supplements the standard 12-volt electrical system
  • Supports engine-free sailing (coasting) under specific conditions when the vehicle is driven in Eco mode, improving fuel efficiency in the AMG 53 models to as high as 28 mpg on the highway
  • In the AMG 53 models, adds 21 horsepower and 184 lb-ft of instant torque to maximize acceleration and performance, bringing maximum output to 429 hp and 384 lb-ft of torque
  • Recoups energy, using it to recharge the 0.9 kWh lithium-ion battery that supplies electricity to the 48-volt system
  • Eliminates all pulleys and belts on the engine, giving the inline six-cylinder a more compact size and eliminating parasitic power losses
  • Provides smoother operation of the automatic engine stop/start system

Diving Into the Details

Mercedes-AMG EQ Boost 3.0-liter 6-cylinder Engine
In the Mercedes-AMG 53 models, engineers apply EQ Boost to a 3.0-liter inline six-cylinder engine. Total output is 429 horsepower and 384 lb-ft of torque. (Christian Wardlaw)

 

Cotter said that Mercedes will apply EQ Boost to new models as they’re redesigned. This is because engineers must accommodate the technology when developing the underlying vehicle architecture.

For now, the three EQ Boosted models in the Mercedes lineup include the 2019 AMG CLS 53 and AMG E 53, and the 2020 AMG GLE 53. Each one uses a turbocharged 3.0-liter inline-six, a configuration that Cotter said will run smoother and is inherently better balanced. Refinement, after all, is the name of the game when your brand stands for “the best, or nothing.”

Inline engines also require one less camshaft and one less cylinder head, noted Cotter, reducing weight and complexity. Thanks to EQ Boost, this engine also has no pulleys and no belts, so its overall length is reduced. As an example, Cotter noted that the engine uses an electric water pump instead of a belt-driven water pump. Additionally, the air conditioning compressor and the power steering pump are electric.

Mercedes also employs a Nanoslide cylinder wall coating for this engine in order to reduce friction and improve efficiency. Also, the combustion chambers themselves are shaped for maximum efficiency, and because there is a hot side and a cold side to this engine, AMG can use a plastic intake manifold with an integrated intercooler on the cold side, saving some weight.

Driving the EQ-Boosted AMG 53 Models

Red 2019 Mercedes-AMG CLS 53
Installed in the Mercedes-AMG CLS 53, the EQ Boost powertrain delivers 60 mph in 4.4 seconds and 23 mpg in combined driving. (Christian Wardlaw)

 

At the invitation of Mercedes-AMG, I headed to San Francisco to sample the CLS 53 and the E 53 sedan.

Both cars included the EQ Boost engine, an AMG SpeedShift 9-speed automatic transmission, and an AMG Performance 4Matic all-wheel-drive system. It operates primarily in rear-drive mode, sending up to half of the power to the front wheels when necessary. Torque distribution is fully variable, depending on surface conditions and how the car is driven.

It did not take long for either car to make me a fan of EQ Boost. When you step on the accelerator, the inline-six restarts quickly and almost imperceptibly, and then instantly delivers power without any of the obvious drivetrain activity and hesitation you experience in the latest Audi A6. The Audi also has a light-electrified powertrain combined with the automaker’s Quattro Ultra all-wheel-drive system, and it simply isn’t as refined as Mercedes’ EQ Boost.

With the AMG CLS 53, I averaged 22.9 mpg, just a tick under the official EPA rating of 23 mpg in combined driving. With the AMG E 53 sedan, I got 21.9 mpg, falling short of the EPA rating of 24 mpg. In that car’s defense, however, I frequently drove it with gusto on a route that included spectacular coastal and mountain roads.

If there’s anything to complain about, aside from catching the 9-speed automatic flat-footed on a couple of occasions, I simply wasn’t able to get either car to engage sailing mode. A Mercedes spokesperson said operation is dependent on “a few factors like speed, 48-volt battery charge state, if you abruptly take your foot off the gas,” and others.

Regardless of my trouble with the sailing mode, EQ Boost is the start of things to come. “The industry as a whole is moving this way,” Cotter told me. “The more you can electrify them, the more efficient they are, and (EQ Boost) has broader applications to other powertrains.”


About the Author

  • Christian Wardlaw has 25 years of experience serving in automotive editorial leadership roles with Autobytel, Edmunds, J.D. Power, and Tribune Publishing. A married father of four, Chris is based in the Los Angeles suburbs and believes fuel cell electric vehicles will power the future.

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