How it works… VW's 48V mild hybrid system

In this article: Electrification is coming and more cost-effective, lower voltage systems are starting the charge

Volkswagen will soon be introducing a new 48V mild hybrid drive system, combined with its 1.5-litre TSI EVO petrol engine. The 48V system joins the conventional 12V vehicle electrical system, and is designed to improve efficiency and reduce tailpipe emissions.

The 48V architecture powers the belt-integrated starter generator (BSG), which is located where the alternator would typically be housed. It has two operating modes: recuperation and boost.

During recuperation (brake energy recovery or regeneration), the BSG acts as an alternator and is able to absorb some of the vehicle’s kinetic energy. The recovered energy is stored in a separate 48V lithium-ion battery. This energy is released in the electric boost mode to power the BSG and support the engine.

Other smart functions allow the BSG to assist the engine during the start-up process, taking on the role of the starter motor. This helps to save fuel and makes the start process easier.

The system also includes an eco-coasting function. This mode allows the vehicle to ‘coast’ with the engine switched off so that no emissions are produced. It can also reduce fuel consumption by 0.4 litres/100km.

The 48V network is linked to the standard vehicle electrical system by a DC/DC converter, which converts the 48V system into the more conventional 12V typically found on vehicles.

Main components:

1. Electronic control unit

The electronic control unit uses CAN and other input data to switch the system to the most appropriate mode, depending on the driving conditions and scenario

2. Lithium-ion battery

The 48V lithium-ion battery pack may also include a capacitor for fast charge and release of energy to improve system performance

3. Internal combustion engine

The internal combustion engine is disconnected and switched off during coasting to improve efficiency, but can be restarted quickly by the BSG

4. Belt-integrated starter generator

The belt-integrated starter generator generates electricity during engine braking and assists the engine under acceleration

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