How it Works - The Mild Hybrid Electric Vehicle

What Is a Mild Hybrid (MHEV)?

A mild hybrid electric vehicle (MHEV) is an electrified vehicle with a relatively small electric motor that complements an internal combustion engine (ICE). The least electrified of the hybrid vehicles, the MHEV never operates solely in EV mode because the electric motor is not powerful enough to power the vehicle alone. The electric motor complements the power provided by the combustion engine.

MHEV Batteries and Motor

Like ICE-only vehicles, MHEVs have a conventional vehicle battery in a 12-volt platform to power lights, sensors, etc. However, at the heart of the MHEV system is typically an additional 48-volt lithium-ion battery, relatively small in comparison to other hybrid vehicle types, but big enough to add power to that supplied by the ICE. This battery cannot be charged by external power supply like a plug-in hybrid, but rather stores energy recaptured from braking and other means. The 48-volt battery powers the electric motor, which is connected to the drive train. This electric motor assists the ICE during high-load applications such as during acceleration. It also functions as a generator to charge the battery and as a starter motor capable of starting the ICE.

The Benefits of the MHEV

The relatively small 48-volt battery pack and electric motor of the MHEV have many modest benefits, including improving performance (especially during acceleration) and reducing fuel consumption (especially during coasting on a flat or downward sloping grade when the ICE engine switches off) with a nod to the credo “every little bit counts.” Because they act as an auxiliary power source, MHEV electric motors can augment the performance of smaller and more efficient ICE engines. MHEVs also recover energy that would otherwise be lost during braking and store it for later use. This allows the MHEV to slightly increase fuel efficiency without compromising performance.

MHEV Outlook

Many consumers own mild hybrids and don’t know it because the vehicles are not marketed as such. For example, many carmakers market a proprietary power booster as a feature of their vehicles but do not mention “mild hybrid,” a concept that may have a negative connotation for some consumers. MHEVs are capturing the interest and investment of many carmakers as they face pressure to reduce emissions and boost the efficiency of their vehicles. MHEVs are a relatively easy and inexpensive way to reduce fuel consumption without hurting performance. In fact, some carmakers are adopting the MHEV concept across their formerly ICE-only product lines as a key part of their electrification strategy.

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