The eighth-generation Volkswagen Golf, due in 2019, will be VW's first passenger car to adopt 48-volt electrical architecture, as revealed by Autocar only last week - and one of its impacts will likely be to redefine what's under the bonnet of the low-emissions BlueMotion model.
Volkswagen's strategy until now has been to fit a low-emissions diesel engine, augmented with low friction transmission oils and tyres, into the Golf BlueMotion as an alternative to economy-minded full hybrid petrol-electric hatchbacks such as the Toyota Prius.
But VW brand chairman Dr Herbert Diess has told Autocar that the advent of 48-volt electrical architecture will make it possible to beat the homologated carbon emissions and fuel economy of a small-capacity diesel Golf using the more powerful energy recovery and electrical assistance solutions that 48-volt technology allows for in a mild hybrid - and to do so in tandem with a small petrol engine and for a similar overall cost of a mild hybrid diesel powertrain.
"We will still offer small capacity diesel engines in the next Golf because they remain important in many markets, and because for customers who do high mileages they will remain the most economical choice," Diess explained. "But 48v allows you to recycle energy more efficiently than 12v and to use it to drive the car with an electric motor of about 10- or 12kW, at a much lower cost than you can with a full hybrid powertrain today. So for those who drive mostly in the city or only cover 6000- to 10,000 miles a year, the new mild hybrid solution should be better."
It would not make business sense for VW to combine such 48v mild hybrid technology with a modern small-capacity diesel engine, however - since doing so would result in a car too costly to appeal at the value end of the Golf model range. "Diesel hybrid is too expensive for this part of the market," Diess explained.
The news will not be welcomed by the likes of Toyota and Honda, which have had the hybrid hatchback market largely to themselves for the last two decades. It's also not yet clear how much benefit could gained from converting the 12v electrical system in a full hybrid car with an existing high-voltage circuit, such as the Prius.
Diess did not expand on what improvement 48-volt tech will deliver for the other hybrid in the Golf range - the more expensive plug-in hybrid Golf GTE - although significant improvement in real-world economy when the car is running in petrol-electric mode is likely, as are modest power & torque gains from the combustion engine.