GREEN SPECIAL: What's a mild hybrid?
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Carmakers have started combining the Internal Combustion Engine (ICE) with electricity in broad strokes and at a very fast pace. In fact, it’s kind of hard to keep up with all the terminology: first we had “hybrids”, then “Plug-in Hybrid Electric Vehicles (PHEVs)” and now there’s much talk of “mild hybrids”.
Eyes glazed over yet? Yes, it can seem overwhelming, but hybrid technology is going to play a major part in motoring from now on. And as with most jargon, the concepts behind the various types of “hybridisation” are actually quite simple.
Any vehicle that relies on two different types of power, like an ICE and electricity, is a hybrid. For that reason a Battery Electric Vehicle (BEV) cannot also be a hybrid because it’s powered purely by electricity. So we’re not talking about Audi e-trons or Teslas.
To most of us, the Toyota Prius is the car that popularised hybrid technology. It has a petrol ICE, a small battery pack and an electric propulsion system. It can be powered by just the ICE, just the battery/motor (but only for very short distances, say a few hundred metres) or both together. Energy that would normally be wasted in deceleration and braking is recovered and used to charge the battery – this is what’s usually called “regeneration”.
A PHEV works exactly the same, except that it has a much bigger battery that can also be recharged by plugging it in; so it can drive quite a long way just on electricity (30-50km is typical) before it reverts to hybrid operation. A PHEV is also technically an Electric Vehicle (EV) because it can be charged from an external source; a hybrid cannot, so it’s just “electrified”.
As the name suggests, a mild hybrid is an even less obvious form of electrification: while it still has extra battery power that assists the ICE powertrain in running power-hungry electrical systems, a mild hybrid does not generally offer electric-only drive. You could be driving a mild hybrid and not really know it.
But that doesn’t mean a mild hybrid is less sophisticated than established hybrid technology. Quite the opposite in some cases.
Manufacturers are using the light and compact nature of mild hybrid systems to dramatically increase efficiency, performance – and ultimately the overall level of technology offered across vehicles.
Audi pioneered the use of mild hybrid tech with a 48-volt power system back in 2017, in the SQ7 SUV. That’s just off the 60v rating that would officially be “high voltage” in a car, but still quadruple the 12v still used in most mainstream vehicles.
The SQ7 system didn’t just power the usual hybridised features: it was also key to an Electric Powered Compressor (EPC) – basically an electric turbocharger to assist the two conventional ones – and a super-fast electronically controlled active suspension system.
Most premium makers have now embraced 48v systems; Audi has developed the technology further in its latest models, including the flagship RS Q8 SUV. Even the latest RS 6 Avant employs 48v mild hybrid technology to provide greater performance, while using less fuel.
But mild hybrid technology isn’t just for high-end cars. It’s likely to become the most common form of electrification in the industry over the next few years - which means most new cars will have it in some form.