A mild hybrid electric vehicle (MHEV) is a vehicle that combines an internal combustion engine (ICE) with a small electric motor and a battery pack.
Compared to full hybrid and plug-in vehicles, mild hybrids are the least electrified hybrids on the current market. For this reason, a mild hybrid cannot propel itself with only an electric motor. The combustion engine remains the main propulsion system.
This leaves the electric motor’s role to mainly support the engine. Typically, it’s directly connected to the engine or transmission. Such an arrangement allows the electric motor to provide a boost to the engine during acceleration or any other manoeuvres that require extra torque.
To save fuel, mild hybrids turn off their petrol engines when the vehicle is decelerating or stopping altogether. Some mild hybrids turn the engine off while coasting and then back on once acceleration is needed.
Starting to move from a dead stop is instantaneous and seamless thanks to the electric motor. Furthermore, the mild hybrid’s auxiliary motor also supports the vehicle’s fuel-thirsty accessories, such as the air conditioning system.
Instead of an external power source, mild hybrid vehicles use a combination of the internal combustion engine and regenerative braking to charge the battery.
In traditional vehicles, the energy produced when the vehicle slows down or brakes is typically lost as heat. However, in the case of mild hybrid vehicles, this kinetic energy is harnessed and transformed into electrical energy through the regenerative braking system. This energy is used to recharge the mild hybrid battery. That being said, their energy capture and storage capabilities are limited compared to full hybrids.
Mild hybrids offer the benefits of lower emissions and improved fuel efficiency, but in comparison with other hybrids, they are not as economical.
The driving experience, apart from the seamless start-stop system, is similar to that of vehicles powered solely by an internal combustion engine. Instead, they serve as a transitional technology towards more electrified vehicles.
- Electric-assist hybrid
- Battery-assisted hybrid vehicle
- Mild hybrid electric vehicle
- Micro hybrid
- Power-assist hybrid