Understanding that a hybrid car has an engine helped by an electric motor to reduce fuel consumption is easy enough. What can be confusing though, is that there are three different types: full hybrid (also known as a self-charging hybrid), plug-in hybrid electric vehicle (PHEV - a full hybrid with a larger battery you can also plug-in and charge) and mild hybrid electric vehicle (MHEV).
What’s different about an MHEV?
MHEVs are so-called because the electric motor isn’t that powerful compared to the other two. Unlike those “full” hybrids, it cannot be driven for short distances under electric power only.
What it does do is to boost engine power when you accelerate, giving the engine less work to do and saving you fuel. Like EVs and the other two hybrids, an MHEV has regenerative braking which means the electric motor becomes a generator as you slow down, charging the hybrid battery.
The electric motor is usually attached to the outside of the engine and alternatively assists the engine or drives it via a drive belt. An MHEV electric motor is officially called a belt-driven starter generator (BISG). As the name suggests, it also adds another feature to the car, which is stop-start.
Is stop-start easy to use? It seems a bit scary
When you pull up at the traffic lights or in a queue, in fact anywhere for more than a few seconds, the engine will shut down to save fuel. With a manual gearbox car, this is usually when you put the car in neutral.
When you want to move off again, the engine automatically starts again in a heartbeat.
Depending on whether the car is a manual or automatic, that may happen when you de-clutch and select a gear, or simply press the accelerator pedal. Either way, once you’ve acclimatised to your car, it happens so quickly you won’t notice it and there's certainly nothing to worry about.
If the engine is cold or you are using a lot of power (for example, while defrosting the rear window) then the stop-start may automatically decide to keep the engine running. It will all happen automatically though, so you don't need to do anything.