What is a mild hybrid system?

By David Bonnici, 28 Jul 2017 Car Advice

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What is a mild hybrid system?

While they may not save as much fuel as conventional hybrid systems, mild hybrids are a cheaper way to boost a petrol-driven car’s power and efficiency. Here’s a quick guide to how they work.

A recent decision by Volvo to only build electrified vehicles led to a perception that it was killing petrol and diesel engines entirely.

However, the term “electrified” also includes hybrid vehicles that utilise internal combustion engines, including plug-in hybrid and mild hybrid systems.

You’re probably familiar with hybrid and plug-in hybrid tech through cars like the Toyota Prius and Mitsubishi Outlander, which use a combination of an internal combustion engine and a battery-powered electric motor to increase fuel economy and reduce emissions.

However mild hybrid systems are a relatively lower-tech concept, but one that’s set to become a lot more common as a way to reduce emissions produced by internal combustion engines.

Mild hybrid cars spend most of their time powered by their combustion engine, with a small motor/generator usually taking the place of a conventional alternator – the device that normally charges the battery in a regular combustion-engined car. Unlike a full hybrid system the electric motor of a mild-hybrid system never propels the car on its own, with the motor/generator only delivering drive under heavy acceleration or to give the engine a helping hand from a standing start.

As well as providing a boost to the engine, mild hybrids cut the ignition when engine power isn’t needed such as when stationary, rolling or when braking – a system more commonly known as engine start-stop. Some also capture energy using regenerative braking, which converts the car’s kinetic energy when decelerating and stores it as electrical energy in the batteries.

The motor in the mild-hybrid system also replaces the traditional starter motor and alternator which leads to further efficiencies, weight savings and smoother starting.

While they don’t save as much fuel as conventional hybrids, mild-hybrid systems are claimed to improve efficiency by up to 15 percent and they are much cheaper to manufacture than full hybrids as they’re typically easier to integrate into a conventional car.

Mild hybrids are so far found in a diverse range of vehicles from some Suzuki Swift and Baleno variants, while the Ferrari La Ferrari could also technically be considered a mild hybrid – though its specialised high-output electric motor is very different to what you’d find in a more conventional mild hybrid.