The Whys And Hows Of (Mild) Hybridisation

We all know what a hybrid is - a fossil fuel-powered vehicle that has some of its go supplemented with an electric motor and a battery pack. The 2 most common types of hybrid vehicles on our roads are your traditional battery-electric hybrid, a la the likes of Toyota Prius, and more recently, the plug-in hybrid (PHEV), which bridges the gap between a pure ICE vehicle and an EV.

These vehicles are significantly more complex than either of their ICE or EV counterparts, as they literally have two different power sources in a single vehicle. As such, maintenance can be more costly, though these would be cheaper to run than your petrol-fuelled daily, and not have the range anxiety that you’d get with something that purely runs on electrons. A small trade-off, for what seems like the best of both worlds, doesn’t it?

We all know that EVs are ruthlessly efficient. Hybrid systems seem to be the Internal Combustion Engine’s saving grace. As carbon emissions regulations globally get ever tighter, and as the masses start shunning fossil fuels for cleaner alternatives, it seems inevitable that petrol will eventually go the way of the dodo. Electrification, especially in the eco-friendly age we live in, will go some ways in prolonging the ICE’s lifespan.

Motorsport has dramatically improved battery and motor technology in recent years. It has always been a testbed for future technology, and a lot of what you have on your modern vehicle was first tested, developed, and used for competition on the racetrack.

Said improvements are definitely dramatic - in 2009, pre-KERS (Kinetic Energy Recovery System), the 2.4 litre Formula One V8s had a thermal efficiency rating of only 29%. This means that only 29% of the energy in the fuel was actually converted into kinetic energy used for propulsion. In 2014, the current 1.6 litre V6 Hybrids were introduced, and further development now sees this figure at 50%. That’s not all; these hybrids made 25% more power whilst being more efficient at the same time!

Mercedes Benz is no stranger to electrifying their vehicles. They’ve proven time and time again that their hybrid systems are superior on the race track, winning both Formula 1 championship titles yearly since 2014. F1 regulations heavily restrict the number of components that can be used in a season, further proving that their electrical propulsion is not only capable of superior performance, but also outstanding reliability.

The technology is slowly trickling down into their road cars. It has also assisted in the development of a third kind of hybrid. These are less involved than your stereotypical hybrids, and obviously have less componentry as well. This also means lower maintenance costs in the long run, but fuel savings will not be as significant as the establishment.

These have been dubbed “Mild Hybrids”, and they lack a dedicated motor and a massive battery pack. What engineers have done is replaced the onboard starter with an integrated starter-generator hooked up to a tiny, shoebox-sized 48V battery. This means that unlike your traditional hybrid, the electric motors in these vehicles cannot directly drive the wheels, nor can you putter around in pure electric mode.

Mercedes Benz aren’t class leaders in just Formula One; a common belief is that the current generation S Class previews what the economy cars two generations down will be equipped with. In simple speak, Mercedes Benz is constantly ahead of the curve, mechanically or otherwise.

Mercedes Benz was the first automaker to use the integrated starter-generator in series production vehicles. The first vehicles out of the factory with the system in 2017. The aforementioned system has your usual “recuperate”, “boost” and “sail” hybrid functions. In their pursuit for luxury, the ISG can also be programmed to rapidly bring the engine up to idling speed, making the starting process even smoother. The restart from coasting is also barely noticeable.

The current EQ Boost branded Mild Hybrids are the second incarnation of the original system. This revision sees the integrated starter-generator shifted into the transmission, which makes adapting it to fit a wider range of power plants a lot easier.
This redesign also sheds some weight and is more efficient.

Mercedes’ new OM 654 M four-cylinder diesel engine is the first diesel to ever be fitted with ISG. The combined power output is rated at 265 hp, with a maximum torque rating of 550 Nm. An additional 15 kW and 180Nms are available for acceleration.
In the course of electrification, the proven OM 654 diesel engine was fundamentally enhanced. A new crankshaft bumps capacity up to 1,993 cm³ from 1,950 cm³. Power adders have also been fitted, and sport variable turbine geometry.

This article is all about Mild Hybrids, but we should also mention the advancements in Turbocharger technology that allows the latest crop of Mercedes Benz vehicles to really maximise their efficiency.

The newly developed four-cylinder M 254 gasoline engine has obviously been fitted with the ISG, but what it also has, is new double scroll turbocharger with variable scroll connection, that first saw use, albeit in a more extreme form, in the Mercedes-AMG W10 that a certain Mr Lewis Hamilton piloted to a Formula One World Title. An electric booster compressor, also from the world of F1, quickly builds up the boost pressure when required for a very dynamic response. The combination of precise control technology and the efficient dual forced induction concept in the M 254 allows the engine output to be safely increased by up to 30 kW (41 hp) for up to 30 seconds.

Whether you like it or not, Hybrids, Mild or otherwise, are here to stay. Advocates for the Internal Combustion Engine will always say that Electric Cars pollute more than their ICE counterparts. That is an argument for another day, but what EVs definitely promise, are cleaner cities, by shifting the carbon emission elsewhere in the energy chain.

What’s also worth noting, is that EVs are extremely efficient. These vehicles have an efficiency rating of up to 86%, which is far higher than even the most frugal of ICE cars. The only drawback with pure EVs, is the lack of charging infrastructure, not just at home, but across the region as well. A road trip up North in an EV would be challenging today, and in most use-cases, an ICE still has its advantages over an EV.

However, once the charging network is mature, that may be a different story altogether.
Once that day rocks about, ICEs will go the way of the Dodo. Hybrids help keep the Internal Combustion Engine relevant, and efficient enough to hang around for just that little bit longer. And as car people, that can only be a good thing.

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Credits: Jek Ray Low