HEV, MHEV, DM-i – hybrid car names are utterly bewildering

HEV, MHEV, Super Hybrid, REx, P REEV, DM-i, EM-i... The list of brand-specific names for various hybrid powertrains goes on. Manufacturers can call their cars whatever they like, of course, but the prevailing nomenclature for hybrids is unhelpfully untransparent. Much of it is nonsense as well: 'MHEV' stands for 'mild hybrid electric vehicle' yet is often applied to a petrol or diesel car with a beefy starter motor. The technology may very well be useful to reduce fuel consumption, but mild hybrids are electric vehicles in much the same way that a person wearing roller skates is a train. Given that we have reviewed a couple of novel hybrids lately, it's a good time to take a whistlestop tour of how Autocar sees the hybrid world. An awful lot of new cars are mild hybrids, because the term can mean almost anything. Most common is the integrated starter-generator (ISG), effectively a starter motor that can harvest some energy while slowing, to give the engine a little boost under acceleration and make startup quicker and smoother. Some have a small electric motor in the gearbox. Some have an electric turbocharger. Nothing wrong with any of that, so long as it doesn't get presented as some game-changing technology. What unites them is that they can't drive on electric power alone. For that you want a full hybrid, which is increasingly called a strong hybrid, to contrast with mild hybrids. Toyota coined the term 'self-charging hybrid' when it came up with the Prius. Although that makes clear that they take care of themselves, it also makes them sound like perpetual motion devices. As diesels have fallen out of favour, many manufacturers have been following in Toyota's footsteps to boost fuel economy with cars that can harvest energy while braking, to then drive electrically under light loads. Some do more than others. Stellantis and Audi hybrids have only 25-30 electric BHP, so their capacity for electric running is minimal (but not nothing). On the other hand, Toyota, Renault, Honda and Nissan hybrids can cover impressive distances in town with the engine turned off, which in our testing results in enviable urban fuel economy. On the motorway, they tend to be a bit disappointing, because the motor is often too short-geared to be efficient at high speeds. Each of those manufacturers has its own take on the mechanical layout often to arrive at a similar driving experience. If you're interested in the engineering, it's quite fascinating to learn how they work. Toyota has its planetary gearset that works like a CVT; in Nissan's e-Power cars, the engine only drives a generator while a motor drives the wheels directly; Honda and Renault have come up with novel gearboxes to blend the power sources; Audi, Stellantis and Hyundai and Kia have a motor in or on the gearbox. For the uninterested driver, it generally doesn't matter: they needn't do more than simply put fuel in the tank, select D and let the computer sort things out. Plug-in hybrids are in some ways the most self-explanatory. They're like normal hybrids often mechanically the same, except with a bigger motor and battery that you can charge up from the plug to give it a measurable electric-only range. If you do that consistently and don't use the engine much, you will get incredible MPG figures. If you don't plug it in, you're stuck with a full hybrid that's lugging around an extra 200kg of dead battery and so will get terrible economy. Which brings us to the much-discussed range-extender EV. This was a term that made a lot of sense with the BMW i3 REx and Mazda MX-30 R-EV, which had quite a short electric-only range and a tiny petrol tank and engine to generate some extra juice (noisily and inefficiently) in an emergency. The Leapmotor C10 Hybrid EV that we reviewed last week is similar in that the engine never drives the wheels, you're supposed to plug it in and the electric bits are the primary mode of propulsion, but to most buyers it will be no different to any other plug-in hybrid. Any talk of range-extenders is fundamentally academic. Unless the buyer is particularly interested in their car's mechanicals, all they really need to know is whether it wants plugging in or not. But academic pursuits can be very rewarding, of course, which is why we will continue to bring you explanations of how these things work in our reviews. In a digital world, there's something quite pleasing about cogs interfacing.

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HEV, MHEV, DM-i – hybrid car names are utterly bewildering

From Self-Charging to Mild Hybrid myth - the nomenclature for modern powertrains is unhelpfully opaque

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HEV, MHEV, DM-i – hybrid car names are utterly bewildering

From Self-Charging to Mild Hybrid myth - the nomenclature for modern powertrains is unhelpfully opaque

More from Autocar

Top 10s

Latest car reviews

Top manufacturers

Quick search

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Legal bits

About Autocar