The nonsense of the NEDC

We have long been interested in what actually lies behind the EEC driving cycles, which is part of the 80 / 1268 / EWG directive and has become known under NEDC fuel consumption measurement.

It was known that the practical relevance is rather limited. Many consumers always come back to the fact that they think their car should not consume (significantly) more than the test results that manufacturers have to provide. One can anticipate that the test values ​​are at best suitable for the mutual comparison of the vehicles with each other. With the actual everyday consumption they often only have something to do away.

Let's take a closer look. We entered the data we found in Excel to graph the history of a test cycle. Horizontal is the time, applied vertically the speed. There are two cycles, one for inner-city, one for extra-urban operation. The inner city cycle lasts 190 seconds. In addition to various downtime, in which times the idle, sometimes the 1. Gear is engaged, and a few sections with constant speed, especially the acceleration sections. We can ignore the delays. As the fuel cutoff switches off the fuel supply anyway.

The accelerations do not exceed 1 m / s². Well, this value really only says a few experts, so an example:

The legendary Citroen DS. We reached 3 m / s² in first gear, 2 m / s² in second gear and 1 m / s² in third gear. After that the DS was at around 50 km / h. So you can see that the accelerations in the test cycle are very low. An older Porsche lets the pointer deflect up to the full scale value of around 6 m / s² in first gear. Much more than 10 m / s² is not possible even with a huge engine power, because the tires can usually no longer transfer the forces.

For accident reconstructions investigations were carried out with which acceleration accelerates the "normal driver". Roughly speaking, it came out that you start with an acceleration of about 2 m / s², quite independent of the maximum acceleration capability of the car. Compared to the normal driver of the first acceleration section is thus already driven with only half the acceleration. If you dig up your old physics book, you can find out that half the acceleration requires only half the energy to reach the same speed (F = m * a, E = F * s = m * a * s). So we have found a substantial reason why the fuel consumption in the tests is so low.

What is also worth mentioning is that the maximum speeds achieved are not very high. The average speed of the test cycle is about 20 km / h. In urban areas one can rather reach an average speed of 30 km / h. Here you have to know that there is a quadratic relationship between energy and velocity. In other words, driving 40 km / h will give you four times more energy than driving 20 km / h. One more reason against the practicability of the cycle values.

Let's take a look at the driving cycle for extra-urban driving:

Here, too, we are primarily dealing with very low accelerations, which in turn fall behind the realistic values. However, one has to admit that with higher speeds actually much lower accelerations are achieved. But what is noticeable? Right, the maximum value of 120 km / h is just kept for 10 seconds, so only for 2,5% of the cycle. In contrast, downtime with 10% is well represented. Especially in this country without general speed limit on motorways, there is also a large discrepancy to the speeds driven in practice.

And last but not least, what is rumored behind closed doors is the so-called cycle recognition. This is a simple and ingenious way to reduce fuel consumption. Because the cycle being traveled is so rigorous, it is no problem for intelligent engine management to detect when such a cycle is being traversed. Now, the injection only has to switch to a particularly lean program and already the engine is running at a reduced power. However, the power is not retrieved in the cycle anyway, so that it is no problem to run the engine particularly "environmentally friendly". And there's another reason why it's so damn hard to ever reach the values ​​the car manufacturer gives us in practice.

The conclusion is simple: 

The NEDC is unworldly and stupid!


Note: The text is from this source and was published here with permission of the author.

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