Top 13: why the fuel consumption deviates from the specifications of the manufacturer
Posted on 18-06-2013 at 12:49 by Wouter – 128 Responses”
For the experts it is not a shock, but for the average consumer, and ill-informed journalists, however: in practice, it is almost impossible to by the manufacturers specified fuel consumption. The highest time for an explanation as to why that is.
The verbruiksverhaal has character, a lot like an open door. We have very recently several times about this issue, which suddenly, in an increasing degree of attention of the Dutch politics (after D66-girl from Veldhoven said state secretary Mansveld is out this week against the NEDC-cycle) message.
Yesterday, normeringsinstituut TNO to the outside with a report on this issue, on the basis of tankpasgegevens of Travelcard. Old wine in new bags so, without further ado, but still went into all the media eagerly on top.
We know this riedel now, therefore, it is high time to dig deep, instead of falling back on a repetition of moves. Below, follows a deepening of the NEDC:
The main reason for the inaccuracy of the NEDC, no one will be satisfied, but it does give more insight into the phenomenon. The history of the test cycle goes back to 1970. A time when CO2 emissions were not on the agenda; we tapped texts on typewriters and the oil seemed not to be able to. Nevertheless, there was also then need to the consumption of cars is more or less objective and repeatable. Thus it came to pass, and the first of the test cycles were designed, but large financial interests were there for the car manufacturers not to fix.
In 1993 there were in Europe the first voluntary guidelines. Car manufacturers would be in 2012 at an average CO2 emission of 120 grams per kilometre have come true. The way to get that was that consumers informed would be about these emissions. Not entirely surprisingly, it was totally not, the CO2 emissions decreased slowly (from 185 grams in 1995 to 160 grams in 2005). At the end of 2007 there came therefore a EU-directive which car manufacturers are required to have in 2015 an average CO2 emission of 120 grams per km, and in 2020 to 95 grams/km.
Since 2007, the playing field is greatly changed, but the test cycle is largely the same. Car manufacturers now have a financial benefit to the CO2 emissions. It is not the CO2-emissions on the road, but the CO2-emissions in the test cycle. This is the time when things go wrong, because the test cycle has quite a few defects which I will explain.
1. The grille and the seams are taped
And so is the air resistance beneficial affected, clearly a favourable influence on the fuel consumption. That this can happen is because the description of the test at this point is not good.
2. Battery is fully charged
The test cycle begins with a fully charged battery, that has a trickle charger hung. Free energy so, because during normal use, it takes the fuel to the battery to charge.
3. Tires with lower rolling resistance
For the test cycle may be tires with lower rolling resistance are used, which are also extremely hard to be inflated.
4. Acceleration gradients to slow
I will not bother with all the details of the cycles, two examples requirements:
the car slowly accelerates to 50 km/h in 26 s
the car cruises at 70 km/h for 50 s (manual: in the 5th gear), then slowly accelerates to 100 km/h in 35 s
If there is accelerated, then it’s done with a velvety touch of the accelerator. That it is not full throttle should be, anyone can understand, but even fully loaded trucks accelerating harder than this.
5. Speed test cycle to low
The entire combined NEDC cycle is 11.023 m long and takes 1.180 seconds. The average speed is 33.6 km/h. Compare that with the average speed that your on-board computer indicates. In any case, there are only 10 seconds up to 120 km/h and therefore meets the test for a total not to consumption on the highway measure.
On top of that there is the use of robots or well-trained test drivers just below the prescribed speeds. It is legal, but by 2 km/h under the speed to stay different the consumption.
6. Rolling resistance
The tests are performed on a chassis dynamometer under controlled conditions. Just as well, because you can each test the same, repeatable way. There is only one problem: the rolling resistance must be determined. For every car there must be, therefore, a test on a test track run. The most commonly used test for this is Idiada in Spain, where there was a very smooth asphalt lane is available, that saves already. I have not been able to verify, but the track seems to be in addition to the two sides 2 degrees. If so, then it is always a special construction, but how is the Idiada track is extremely helpful for the measurement of rolling resistance. The Dutch and Belgian roads are so smooth.
7. Use of higher gears
During the test, made use of by the manufacturers prescribed schakelstrategie. The test writes for some parts specific gears for, but the manufacturer of the transmissions optimize.
8. Options & accessories
Roof rails, the rechterbuitenspiegel and additional lamps may be removed for the test, what air resistance and weight saves. There be anyway bare cars tested, so no nice and packed with instances with electrically adjustable seats, a panoramic roof and hi-fi systems with subwoofers. All in all, this can be tens of kilograms or pounds of car weight care.
9. Battery plug-in hybrid
For cars with a plug that has the NEDC been absolutely insanely good. The low speeds, it is a lot of dwell, and the slow acceleration to ensure that the internal combustion engine during the testing cycle virtually nothing to do. The electric power consumption then count in the overall score, despite the fact that, on average, a minimum of 430 grams of CO2 is emitted to a kwh to generate electricity.
10. Lubricants with low friction
Lower internal resistance means that engines are more efficient, but in practice are driving the consumer, not with the oil in the engine block around.
11. High temperature in test room
A temperature of 29 degrees celsius, ensures that the engine faster to operating temperature. Unfortunately (or fortunately?) the average temperature in Europe is much lower. Especially when you consider that cars are also outside at night or in the arctic circle, cruising in Sweden.
12. Distance from brake pads to brake discs is increased
So gevalletje: all small bits help. Brake pads just against drives to dragging brakes also. To prevent this is for the test cycle that distance fixed increases.
13. The bonus of 4%
As icing on the applesauce manufacturers may, also 4% of the test value subtract.
Now you might think that manufacturers very happy that it is us as consumers so can fool, but nothing is less true. Also they are generally not happy with the current test cycle. Because there are so many tax and other advantages, manufacturers may not unilaterally decide to be braver to do than the rest.
*Editorial note: due to the timeliness, paragraphs 2-4 later added by your blogger of service.