Opinion: Plug-in hybrids are the vehicles of the future

Quick quiz: What do electric vehicles, hybrid vehicles, plug-in hybrids, mild hybrids and even some mobility scooters have in common? Some sort of electric motor, you suggest? Well, yes, you’re half right, but the correct answer is an electric motor/generator unit.

So just what is an electric motor/generator? Put simply, it’s something that can convert electrical energy to mechanical energy (that’s the motor ‘part’) or alternately, convert mechanical energy to electrical energy (that’s the generator ‘part’). Operating as a motor, it uses electrical energy stored in the battery to produce mechanical energy to propel the vehicle; while as a generator, it can harness the mechanical energy of the vehicle’s momentum to produce electricity, which is then stored back in the battery.

In an EV (or a mobility scooter for that matter) a motor/generator is all you have to power the vehicle. Obviously. All hybrids then combine the motor/generator with an internal-combustion (IC) engine – again, obviously – but vary in the significance of the roles the motor/generator and IC engine play in the vehicle’s operation.

The motor/generator plays the most significant role in a plug-in hybrid, a lesser role in a conventional hybrid (e.g. Toyota Prius) and only a minor role in a so-called mild hybrid like the Land Rover Defender.

Plug-in hybrids, such as Mitsubishi’s Outlander PHEV, have a motor/generator unit that can play a significant role in the vehicle’s operation, simply because the external charging (from the electricity grid or similar) allows it to have a much bigger battery than a conventional hybrid that can only charge its battery via the motor-generator unit. This effectively limits the size of the battery and the overall role the electric side of the powertrain can play in the vehicle’s operation.

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In practice, this means a plug-in hybrid has more scope to be used as an electric-only vehicle without relying on the IC engine at all. The EV-only range afforded by a plug-in hybrid can be anything from 50 to 100km, and with reasonable performance. A recently tested Range Rover Sport PHEV had a 70km EV-mode-only range with easy highway driving, although the IC engine (petrol turbo four-cylinder) would automatically kick in under heavier acceleration or hill-climbing loads.

Conventional hybrids also typically have an EV-only mode, but this is generally very limited in speed (below 40km/h or so) and very limited in range (a few kilometres at best). With a conventional hybrid, the IC engine is still the main game, with the electric motor/generator playing an assisting role primarily with acceleration off the mark and at lower speeds, where the electric motor’s strong low-rpm torque serves it well.

With a mild hybrid, such as the Land Rover Defender P400, the electrical side of the powertrain can’t power the vehicle by itself nor contribute a significant part of the available power. With a mild hybrid, the motor/generator is notably much smaller than it is in a conventional hybrid and serves essentially as the IC engine’s starter motor and to charge the battery.

With the Defender, that’s a significant role, as its electrical system not only has to cope with the usual high electrical demands of a modern 4x4 that has electrical operation for near everything, but it also has to power the engine’s electric supercharger (which supplements its turbocharger) and power the electrically assisted steering.

The motor/generator of the Defender mild hybrid still feeds some mechanical energy back into the drivetrain, but only a very quick assistance just to help the initial transition from standing still to moving. With the Defender’s automatic engine stop-start function, the motor/generator is already engaged with the drivetrain at this point, so it’s a seamless interaction to also help get the car rolling.

Hybrids of all types will become a broader part of the automotive landscape as we transition to seemingly inevitable fully electric vehicles, most likely powered by batteries rather than hydrogen fuel cells due to the relative ease of delivery-infrastructure rollout, but plug-in hybrids are the only ones that point towards the future. Conventional hybrids and mild hybrids are just another way to make a more efficient petrol or diesel burner.