bbtmn

Another hybrid?

Sunday 4th December 2011

At first glance, electric cars seem to be a good idea. Certainly at current prices, using electricity seems to be a relatively cheap way of fuelling a car. And for many people, who mostly use their car to make short journeys, the range issue isn’t generally a problem.

However, most people also use their car for occasional long trips. For example to visit friends or relatives who don’t live locally. And so although people generally only make short trips, they still need it to be able to make longer journeys on occasion. I think this is probably one of the major barriers preventing wider uptake of electric cars at the moment (price being another big one; a comparable EV typically costs 50-100% more than the alternative conventionally-powered car). Even if you only make short trips 95% of the time, most people don’t want to buy or rent another car for the other 5% of the time.

But perhaps there’s a way to have the best of both worlds. At the moment, certain cars have a “hybrid” system. Here, a traditional internal combustion engine (ICE) provides power in the first instance, and this is supplemented by an electrical system which collects energy which would otherwise be wasted (in braking etc). Seems like a good idea, although I do find it surprising that many of the cars which use this system don’t actually seem to do it very well. For example in the real world, a Prius only seems to be about as efficient as other mid-size cars (e.g. the Ford Mondeo or the BMW 3-series) which use reasonably-sized diesel engines, and are much less efficient than many smaller cars which use small engines with forced-induction. Only the Prius is more harmful to the environment, once you take into account the materials used to manufacture the hybrid system…

I reckon that this might be the wrong way to go about making a hybrid drivetrain. Rather than having a drivetrain that is mostly ICE and partly electric, why not have the balance the other way?

By that I mean, rather than fit an ICE drivetrain with a slimmed-down electric drivetrain, why not fit a small engine to an electric drivetrain? So for short journeys you can run solely from the batteries, which you can then charge as you need. But then if you want to make a longer journey – or if you run out of electricity – you can fill up with petrol or diesel and start the engine.

I can’t see too many downsides to this. It’d be harder to package and would increase the weight slightly, but I guess that this is only the same problem as is faced with the drivetrain on other types of hybrid. But in this solution, the car gets the best of both worlds.

Of course, I’m not a mechanical engineer so there could be problems I haven’t foreseen; perhaps there’s a good reason why no-one uses this drivetrain (if that’s correct. Maybe some cars do, and I just haven’t heard of them). But I really can’t think of many negatives which would outweigh the obvious benefits: EV efficiency for smaller journeys, and ICE range for longer ones.

All this being said, has anyone actually worked out whether EVs really are┬ámore efficient than cars with an ICE? Or does using an electric drivetrain simply move the location at which fuel is consumed away from the vehicle? I actually don’t know the answer to this, although if making a journey using an electric car costs less per mile, I guess that’s a good hint.

Posted at 7:50 pm | Posted In: CarsEngineering Tagged:

3 Comments:

Running with Stethoscopes

Monday 5th December 2011, 6:21 pm

Have you seen the BMW i8 concept car? There is a pure-electric city version too, the i3, but i8 is a hybrid that uses the electronic drive for up to 22 miles, with a 3-cylinder petrol engine on the rear wheels to provide extra kick and range as needed. For short daily commutes, 22 miles is fine (obviously for slightly longer ones you’ll use a bit of petrol but nowhere near the quantity you’d’ve used before) and for long drives you’ve got the petrol backup.

BMW claim 94 miles/gallon for the i8 concept. For a sports car, even a slowish one, that’s not bad at all. The i3 is pure electric but ‘will have the option of a smooth-running petrol engine’ to drive a generator within the car.

Apart from the bonnet, which I hate, the i8 looks pretty good too.

Dickie

Monday 5th December 2011, 7:01 pm

Ooh no, hadn’t seen that. Seems like pretty much what I described; can’t say I’m surprised that BMW thought of it before I did. They’re kinda good at this sorta thing…

I wonder if they’ve actually built anything with that drivetrain (as opposed to just using it in a concept). I’d love to see how well it works.

Running with Stethoscopes

Tuesday 17th January 2012, 8:50 am

I am beginning to wonder if it is a concept car at all. It appeared in the new mission impossible (which incidentally is dreadful) and I suspect that it might actually be a production car, called the i8 concept. Maybe.

Write a comment: