MHEV

Mild hybrid electric vehicle (MHEV) refers to a vehicle that combines an internal combustion engine with a small electric motor and a high-voltage electrical system to assist propulsion, without enabling sustained electric-only driving. MHEVs are designed to improve fuel economy and reduce emissions by supporting the engine during acceleration, rather than replacing it.

Operation typically involves a belt-driven starter generator or integrated starter generator that acts as both a motor and a generator. The electric machine can provide torque during acceleration, enable smoother engine starts, and allow idle-stop operation. Regenerative braking captures kinetic energy and stores it in a dedicated 48V battery or capacitor for later use. The system often includes a DC-DC converter to power and charge the 12V electrical system.

Common components of MHEVs include a 48V battery or capacitor, a power electronics unit, a motor/generator integrated with the engine’s belt drive, and sometimes additional cooling and control systems. The 48V architecture is more compact and cost-efficient than higher-voltage hybrid systems, enabling easier integration into a wide range of vehicles.

Benefits of MHEVs include improved fuel efficiency, reduced emissions in urban and stop-and-go driving, smoother engine-off and start behavior, and the ability to operate the engine more efficiently at low speeds. Limitations include the inability to drive solely on electric power for meaningful distances, limited electric torque relative to full hybrids, and added cost and weight from the hybrid components.

MHEVs have been widely adopted by many automakers as a cost-effective step toward greater efficiency, and they commonly sit between conventional combustion vehicles and more advanced hybrids in the evolution of electrified propulsion. Related technologies include full hybrids and plug-in hybrids.