We’ve seen them around.  We know they’re some kind of (some might say) unholy mix between standard internal combustion engines and electric motors. If one lives in cities like Wellington (NZ), you will have noticed a couple of the local taxi companies drive them.


Hybrids: the Prius (top) and Insight (bottom)

And that their dashboards look all space-age and sport interesting-looking graphics with arrows moving back and forward between graphics for fuel pump, engine and battery.

Still, though – what do they actually _do_?  And are they as efficient as they sound?

Note: I’m writing this post as I’ve just spent the last two days driving a Honda Insight from Wellington to Auckland and back again.  Partly as practice for the Mongol Rally, and partly because I’ve never had the opportunity to drive a hybrid before, and was curious. I’ve now learned how hybrids function, and figured I’d share  :)

On to the workings, though!

First, one needs to understand a little about car engines**.  In particular, two important concepts: the flywheel and the transmission.

The flywheel

Flywheels are used in a range of different applications, including vehicle engines.  Their purpose is simple: to store rotational energy.  One stores energy in a flywheel by applying torque -for those people who’re not drivers/mechanically inclined, it’s the ‘vroom!’ factor when one puts one’s foot down.

Flywheels have lots of inertia, meaning that they change their rotational speeds only with quite a bit of persuasion.  Applying torque to them increases their rotational speed, and therefore the amount of energy stored by them.

In car engines, they get used to turn the jagged energy generated by the cylinders/pistons, into the smooth energy which makes the wheels go round, well, smoothly.

In sequence, energy generated by the engine is transferred to the flywheel (which makes ‘smooth’ energy, being all rotational and whatnot), which is then transferred, via the clutch/transmission, to the drive shaft, then diff, then wheels.

The transmission

People who drive cars are probably used to the idea of gears.  Whether driving a manual (where one changes gears, using the clutch, manually) or automatics (where the car, also using the clutch, does this for one, and generally far less well), you’d be familiar with the feeling of changing the engine’s gear ratios depending on how fast you want to go, and how high/low you want the engine’s revs per minute to be.

It’s like a bicycle, but with an engine :)

Electric vehicles, and some hybrids, use CVTs instead.  CVTs, or continuously variable transmissions, do away with the idea of gears.

Which means, for those of us who love driving manuals, no more fun in that respect.

Instead, CVTs can change into what is, effectively, an infinite number of gear ratios, and can do so completely steplessly.  With the result that one doesn’t need a clutch _at all_, although some vehicles do still add them.

Interestingly, Leonardo da Vinci, in 1490, conceptualised one of these.  The first patent for a (toroidal) CVT was filed in 1886.

The hybrid

Hybrids such as the Insight have an electric motor coupled to the combustion engine in the place where the flywheel normally goes, as the motor is able to completely replace the flywheel.  Other hybrids use slightly different solutions***.

The electric motor has a few functions:

  • Capturing otherwise-lost energy using regenerative braking.

Regenerative braking’s the dead clever system (already used on some trains and buses, even here in NZ!) that converts kinetic energy into another form of energy.  So, when one brakes, normally, kinetic (‘moving’) energy is transferred into heat energy, which is why your brakes get hot.  Essentially, it’s wasted. Regenerative braking captures the kinetic energy that’s being lost, and, in the case of hybrid cars, transfers it into electric energy for storage in the battery.

  • Starting the car using less energy.

The car starts using the battery, rather than a starter engine.  Anyone who’s driven a hybrid would know that it’s uncannily quiet on start (I couldn’t actually tell it was on, the first time).  In some cars (such as the one I drove), the internal combustion engine is actually switched off whenever the car comes to a complete halt, for example at traffic lights/intersections — this saves energy which would be lost idling.

  • Helping the engine.

Additionally, the electric motor is also supposed to put energy back into the car when needed, for example on hills or when accelerating.  This means, amongst other things, that the combustion engine can be smaller (less powerful) than it would have to be in similar cars using _only_ a combustion engine.

And what’s the point of all of this? Well, it differs.

Sometimes it’s about providing more power.  Or providing extra power for plugins such as power tools (the mind boggles).  In the hybrids we’d generally see on the street, the idea is that they are supposed to use significantly less fuel than ‘normal’ cars. This is good not only for the bank account but also, more importantly, for emissions.  Hybrids make less of ‘em.

Although the caveat here is, as always, it’s not only what one drives, but _how_ one drives.  Driving efficiently can be done in normal cars too, and takes oodles of concentration in either case.  And, sometimes, makes one very, very unpopular on NZ’s highways.

Hybrids also make scads less noise, which is great for noise pollution, and the batteries, now generally made of nickel metal hydride (NiMH) [oops - I had previously written nickel cadmium, which is of course highly toxic], are considered to be fully recyclable and ‘benign’ toxicity-wise.

And they feel like spaceships.  Which is really, really important if one is driving In The Future :P

Our trip?  We ended up getting 4.3l/100km over the trip.  Not bad :)

More on the trip itself, and our experience driving efficiently, can be found here.


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* Specifically, hybrid electric vehicles, or HEV.  Because there are a number of different types of hybrid engines.

** Which I do not.  I am having to learn.  Very fast.  So the explanations here are pretty simple, and are centred mostly on the one I drove :P

*** Different hybrids really are built differently.  For example a Prius, the most commonly-driven hybrid, is not like the Insight, and neither are like the Porsche hybrid 911. And then there’s the Volt, and the Leaf.  It would be kinda cool to be able to test drive, side by side, all the various permutations…