What is BMW eBoost?

Automakers spend billions of dollars on research and development in the never-ending quest to make internal combustion engines (ICEs) more useful and efficient. Sometimes that spending results in a giant breakthrough, like the electric self-starter developed more than 100 years ago. But most often, it results in small but significant gains, which is the case with BMW’s eBoost.

2022 BMW M340i xDrive Sedan Black Front Quarter View

Those who follow automotive technology grasp that “e” most often refers to some form of electrification. At the same time, “boost” typically refers to something that momentarily increases performance. For instance, that is the case with the “boost” gained from turbocharging or supercharging. Based on this background, it is not surprising that BMW eBoost refers to a method of improving vehicle performance by adding a relatively short-duration “burst” of horsepower electrically.

To understand BMW eBoost, it is instructive to understand the concept commonly referred to as a “mild hybrid.” In automotive terms, a powertrain with mild-hybrid technology operates in most instances as a conventional gasoline- or diesel-powered vehicle but derives added power in specific instances from a relatively small, low-horsepower electric motor.

Of course, all modern ICEs use an electric motor to get started. That century-old innovation made ICE cars practical for broad use in the first place. Since all ICE vehicles have starter motors, it isn’t too big a leap to use that motor to add power and torque in specific instances.

The first vehicles equipped with mild-hybrid technology used the standard 12-volt electrical system that has been the industry standard since the 1950s and typically employed a somewhat more robust starter motor to add small amounts of horsepower in specific short-term situations like accelerating from stop. This offered some benefits, but the small, 12-volt motor limited the added power (“boost”).

BMW and other European automakers led the way in pioneering 48-volt electrical systems that had the benefit of offering more power. This not only enables them to provide added acceleration but also makes for quicker starting in the almost ubiquitous automatic engine stop/start systems that ICE vehicles use these days.

Two sources send power to the onboard storage battery in the BMW mild-hybrid system. The starter-generator creates some electricity in normal vehicle operation. Regenerative braking captures additional energy when the vehicle brakes (decelerates). A regenerative braking system generates electricity and feeds it into the vehicle’s 48-volt battery.

BMW eBoost

BMW eBoost most often refers to using electric motor power and torque to aid performance and lower fuel consumption and carbon dioxide emissions. The power/torque of the electric starter motor-generator is employed when it is advantageous to add power, such as accelerating from a standstill, gear changes, and hard-throttle acceleration. The last of these might have called for a rapid downshift without the ability to add power from the electric motor. In an engine fitted with a turbocharger, the eBoost can contribute power in what would previously have been a period of “turbo lag.”

The eBoost system is effective because an electric motor provides its maximum torque virtually from zero revolutions per minute (rpm). And it is efficient regenerative braking recaptures much of the electricity—energy that otherwise would be wasted because. Using eBoost also enables the engine stop/start system to shut down the engine more silently and restart it more quickly and easily.

BMW is constantly improving its mild-hybrid technology, even as it puts more and more emphasis on battery-electric vehicles. In fact, the ongoing improvements in battery and electric-motor technology also enable advancements in mild-hybrid tech.

An example of BMW eBoost and mild-hybrid technology in its most advanced form is the current BMW 3 Series. The 3.0-liter inline 6-cylinder engine in the M340i demonstrates the simultaneous optimization of power and efficiency enabled by the tech. The 48-volt starter-generator performs as a second drive unit that assists the gasoline engine in certain situations, allowing it to operate in its most efficient load range. When the driver calls for additional power, the BMW eBoost from the starter generator kicks in to provide it. This could occur when accelerating away from a traffic light or when passing at highway speeds on the autobahn.

Several things enhance efficiency. First, since immediate torque is available from the electric motor, engineers can calibrate the gasoline engine to operate in a more efficient range. At the same time, the 3 Series uses electricity generated by braking and stored in the 48-volt battery to supply the vehicle’s 12-volt electrical system.

In the broadest sense, an automaker could apply eBoost to any situation where it needs to use power from an electric motor to enhance performance or efficiency. Therefore, one could also regard the application of electric power in a more sophisticated hybrid powertrain (like a plug-in hybrid) as eBoost. At times, BMW differentiates between eBoost and something it calls Xtraboost, but the distinctions are nebulous. The critical thing to know is that BMW eBoost enhances both performance and efficiency. And it does so without adding the extreme complication of a more elaborate hybrid system.

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