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48 volt 'mild hybrid' cars coming soon [Infographic]

Published 18/08/2016

Graphic shows anatomy of a mild hybrid and target carbon dioxide emission levels by country
Graphic shows anatomy of a mild hybrid and target carbon dioxide emission levels by country

New high-voltage “mild hybrids” -- which use 48-volt batteries -- cut both fuel consumption and emissions by boosting acceleration with electric power following Stop/Start and using regenerative braking.

An increasing number of vehicle manufacturers are introducing Stop/Start technology which allows the engine to switch off automatically when it is idling, reducing fuel consumption and emissions.

Manufacturers are now improving Stop/Start, designing so-called “mild”-hybrids that boost engine output and efficiency by building a hybrid powertrain around a second high-voltage battery.

A mild-hybrid system consists of a 48-volt lithium-ion or lead-carbon battery, controllers for the battery and hybrid powertrain, and a DC/DC converter to step down power to 12 volts to power accessories.

An electric motor/generator and an electrically driven supercharger are used to increase the torque of a petrol or diesel engine.

A drive belt connects the electric motor/generator to the crankshaft, boosting the engine with extra torque when it restarts and helping the car accelerate. Once a car is cruising at a constant speed, the motor/generator alone can keep it moving. When the driver brakes, the motor/generator goes into reverse mode, recovering the vehicle’s kinetic energy to recharge the battery.

A 48-volt electronically-controlled supercharger also forces extra air into the engine to boost power when needed. Superchargers could enable a 1-litre engine to achieve the power of a turbocharged 1.5-litre engine. Some car makers say that mild-hybrids could yield 70% of the benefits of a full hybrid at 30% of the cost.

The European market is expected to lead the movement to 48-volts, driven by new emissions requirements that cut carbon dioxide emissions from the current average 130 grammes of CO2 per kilometre to 95g CO2/km by 2021.

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