If not the Golf, then who: As one of Volkswagen's bestsellers, the eighth-generation Golf goes into series production with a new electrified drive system. But what advantages does the 48V mHEV drive offer?
The mobility sector is changing rapidly. While customers' demands for comfort and digital networking are increasing, legislators are calling for a sustainable reduction in CO2 fleet emissions to 95 g/km by 2020. Against this background, 48V technology is an attractive option. As early as 2018, Volkswagen announced at the renowned Vienna Motor Symposium that it would make the innovative low-voltage concept accessible to a broad public. Now the Group is delivering on its promise and bringing it into series production this year – in the eighth generation Golf, one of the best-selling vehicles in the world. Initially, the 48V hybrid drive will be available with the EA211 evo family, 1.0 and 1.5l displacement and dual-clutch gearbox (DSG) Golf TSI engines. Volkswagen will then gradually extend the electrification of the drive system to the entire fleet. But what exactly is behind the technology and what are its greatest strengths?
A hybrid with two engines
Compared to current Plug-in Hybrids (PHEV), for example in the Golf GTE and Passat GTE models, the mHEV drive (mild hybrid electric vehicle) equipped with 48V technology offers a reduced range of functions, but is significantly more cost-effective. While the Plug-in Hybrid (PHEV) charges the battery via the mains with a plug, the mHEV does not have a battery that can be recharged via a plug, but is equipped with a 48V belt starter generator. As an electric motor, this supports the combustion engine in order to increase the drive power according to the situation – for example when accelerating. In deceleration phases, the generator converts the vehicle's kinetic energy and charges the battery with energy that would otherwise be lost. This combination offers Volkswagen the opportunity to electrify conventional powertrains without making major changes. Depending on the driving style, the mHEV system can save fuel in the range of 0.4 liters per 100 kilometers.
This is how 48V technology works in detail
In the mHEV vehicles offered in the Golf 8, the Belt-Driven Starter Generator (BSG), an electric motor with 48V operating voltage, acts as a powerful replacement for the generator. When starting up, it also immediately boosts the drive torque via the boost function, thus ensuring greater dynamics and comfort. The starter generator is coupled to the combustion engine. Its power is transmitted to the crankshaft by the belt drive. In addition to the regular 12V on-board battery, the mHEV drive has a 48V lithium-ion battery mounted under the passenger seat. When the driver steps on the brake, the kinetic energy is converted into electrical current. This allows up to 40 percent of the braking energy to be recovered and stored in the battery. A DC/DC converter supplies the conventional 12V grid with voltage.
The 48V mild hybrid offers a number of helpful system functions. In FMA (Freewheel Motor Off) mode, the engine shuts off as soon as the driver takes their foot off the accelerator. The car then continues without consuming fuel. The engine is also hardly noticeable as soon as it is restarted. The engine is switched on and off without delay or loss of comfort, making the Golf 8 considerably more efficient.
To ensure that the driver does not feel any loss in driving comfort, the system also has a Change-of-Mind-enabled Comfort Start function. This means that if the driver presses the accelerator pedal again, the combustion engine starts immediately with low vibration. This is another advantage of the BSG: in contrast to the sprocket starter, the driver experiences a quick and comfortable transition to the drive phase when starting with the BSG. On 48V mild hybrid vehicles, however, the sprocket starter is only used for the first start. In contrast, the driver experiences a comfortable, fast and powerful transition when starting with the BSG – for example from sailing to a subsequent drive phase.
In order to use FMA operation as frequently and efficiently as possible, a predictive assistance function takes into account navigation data such as speed limits or bends in order to reach route points at the optimum speed and thus make the best possible use of the vehicle's kinetic energy.
Innovative technology with perspectives
For the year 2030, Volkswagen expects an electric share of its new vehicles of around 40 percent in Europe and China. The proportion of new vehicles with combustion engines will therefore continue to dominate for a long time to come. However, the efficiency of combustion engines is reaching its physical limits – which is where 48V technology will open new avenues up.
"You cannot afford to write the combustion engine off," said mobility expert Helmut List at the opening of the symposium last year. He warned against pursuing only one technology in order to meet future requirements. According to List, combustion engines, battery electric drives and fuel cells should have a synergy as combined building blocks.