4 Oct 17

Mild hybrid 48V system will save the combustion engine

Hybrids are an effective way to cut fuel consumption and emissions, but they come at a hefty price. Especially plug-in electrified cars, such as the Toyota Prius Prime, VW Golf GTE, BMW 225xe Active Tourer, Mercedes C350e, Volvo XC60 T8 and so on, hardly make economic sense compared to regular powertrains. Considerable tax incentives and a minimal activation of the internal combustion engine (ICE) are the only way to make the TCO story add up.

But that is about to change, with the arrival of an ‘add-on’ electrification solution based on a 48-Volt architecture. Actually, such a system is already on the market. The Renault Scénic Hybrid Assist is the first model to combine an existing combustion engine, in this case the well-known 1.5 dCi diesel, with a small 10-kW electric motor and a compact lithium-ion battery to feed it. This cost-effective solution saves 0.3 l/100 km and 6 grams of CO2/km compared to the standard dCi model.

Interesting ROI

That equals a gain of 8 percent in efficiency. After 140,000 km, the average mileage of a lease car, this could mean €588 in fuel savings (based on a price of €1.4/litre), plus possibly a more interesting tax band on various levels (BIK, fiscal deductibility, road tax, and so on). Taking into account the €800-odd supplement Renault asks for the Hybrid Assist technology, it makes sense TCO-wise. It stands to reason that the French carmaker carefully calculated how far they could stretch the price to still make an interesting TCO case.

And that is probably what other carmakers will be doing too. VW, Mercedes, PSA, Volvo, JLR: they are all working on 48V systems. When the latter two announced they would go “all electric” by 2019 and 2020, respectively, they really meant that their new models, if not 100 percent electric, will use a combustion engine combined with an electric motor, and in most cases it will be the “mildest” form of hybridisation – indeed, a 48V system. What sounded like a bold statement, is basically an industry-wide reality.

Diesel-like torque and consumption

Renault’s hybridised diesel engine is actually an isolated case – but one that made sense a few years ago, when the development started and diesel wasn’t materia non grata yet. With R&D costs rising and ever fewer units to write off the investment, many OEMs have indicated that diesel is a dead-end street for them. Instead, they firmly believe in the 48V-electrification of existing petrol engines.

In fact, the small electric motor increases torque at low speeds during initial acceleration – when the ICE has to work the hardest and therefore consumes the most fuel. This electric boost means the petrol engine will pick up speed smoother while drinking less. However, contrary to a full hybrid, a mild hybrid cannot drive fully electrically – the battery and the electric motor are too small to be able to do all the work by themselves. Also, a 48V hybrid cannot be plugged in – it is only charged through the recuperation of energy during deceleration, with our without the use of the brake pedal.  

55 percent of all cars by 2025

A 48V system can be added onto existing powertrains fairly easily, limiting production costs. As such, 48V petrol hybrids are cheaper to make than diesels. Consultancy firm Evercore ISI reckons they will outgrow European sales of full hybrids (including PHEVs) by 2020. By 2025, 48V mild hybrids are expected to represent 55 percent of all new car sales. In such numbers, they will help car manufacturers to reach their 95 g/km CO2 target imposed by the EU.

Audi and Mercedes are the next OEMs to launch a 48V hybrid system, in the new A8 an S Class, respectively. The added advantage of a 48V circuit in the premium segment is that it allows the integration of many more electric applications in the comfort, suspension and powertrain area. The VW Golf will have access to the technology in 2019. By that time, PSA, Nissan, Hyundai Motor and other carmakers will also have struck a deal with Continental, Delphi, Bosch or Valeo for the delivery of 48V components.  

Picture copyright: Renault, 2017

Authored by: Dieter Quartier