Tuesday, 22 September 2015

a simplified algorithm for car test emission reduction (YMMV)


Since the days of this lovely VW Karmann Ghia, there's been set of statistics produced by car manufacturers about the expected performance from their cars.

The car featured above could accelerate from 0-60 in around 27 seconds, which was at least 3 seconds faster than the regular Volkswagen Beetle and it could get around 30 miles per gallon, although in those days the adverts didn't include performance small print.

Based on my own current car's live readouts, I get about 45 mpg average, yet the description in recent magazine advert small-print shows 53.3 for the combined mpg and up to 67 mpg for the extra-urban. Parker's car guide shows 46 mpg as their estimate, which is very close to my own.

No-one really believes the bigger numbers in the car adverts, and I usually look for the smallest number as the one most likely to be true. In the case of my car its 'urban' which shows 44.8 mpg - close enough to my own estimated 45 mpg - which rises to 50-53mpg on a really long motorway run. I've never seen 60, let alone 67 mpg.

And I don't think I'm a heavy footed driver, I hardly ever engage the 'Sport' mode and will often use the triple radar-assisted intelligent driving mode "Distronic Plus" where the car makes its own decisions about speed.

So there's a general situation which I will refer to as "Your mileage may vary" which is so commonplace it even has its own short form as YMMV.

For example, the American EPA/DOT has a whole screed of small print about YMMV on its printouts.

The 'Golden Vehicles' used for the tests are probably put on thin tyres to lower rolling resistance and presumably tweaked for ideal conditions in what amounts to a wind-resistance free environment.

I notice that a few cars such as some Mini Coopers, the Ford C Max Energi, Lincoln MKZ as well as some Hyundai and Kia cars have all reduced their mpg claims after being randomly tested in the USA.

That brings us to the recent kerfuffle over the diesel emissions logic algorithm. I decided to invent one myself as an experiment because no one in the press seems to have provided one yet.

1) Check if only the powered wheels are turning. (i.e. it's on a test rig)
2) Increase the turbo pressure
3) Allow the temperature to rise beyond the normal upper bound.

That should do it.

The car knows its on a test bed and allows the two factors most likely to burn off emissions to increase beyond their normal upper limit. It wouldn't be wise to leave them at the higher level for too long because of engine wear, but for a 20 minute test, who cares?

It's almost a surprise that more car manufacturers don't do this...Or do they?

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