WLTP homologation cycle: what it is and how it works

WLTP homologation cycle

Over the last period, with the advancement of the marketing of hybrid and electric cars, we have heard more and more often about this infamous WLTP homologation cycle, but what exactly is it and how did we get there?

Let's take a couple of steps back. The current WLTP cycle was only recently introduced, from 1992 until 2017 the NEDC (New European Driving Cycle) cycle was used, which measured the consumption of a car following some specific parameters defined not very accurate in modern times. The test, lasting 11,023 km, forced the driver to maintain an average speed of 34 km / h, with a maximum peak of 120 km / h to be reached only once, and with a maximum use of power calculated in 46 horsepower. To count the "start and stop" variable, the car had to remain stationary for 25% of the travel time.

The NEDC cycle, in addition to the decidedly unrealistic measurement conditions, did not provide for a ban on use some tricks to improve results, even significantly. For example, there was no rule that prohibited inflating the tires more, disconnecting the alternator, using a more fluid oil and so on.

For these reasons in 2017, in order to make the tests more realistic and to have data on more precise consumption, Europe has introduced the Worldwide Harmonized Light Duty Vehicles Test Procedure (WLTP) following a series of studies carried out jointly with China and India. The United States, on the other hand, has maintained the current Epa procedure.

The WLTP cycle is carried out with more realistic cycles and road tests called RDE (Real Driving Emissions) are also planned, to detect the oxides of nitrogen so as to be able to accurately evaluate the real data relating to pollution and counteract any discrepancies.

WLTP approval

The international procedure has therefore replaced the NEDC protocol, forcing manufacturers to pass approval tests, which are decidedly more stringent. In the WLTP cycle, the car must travel a distance of 23 km, with a speed of 46.5 km / h and a peak of 131 km / h. The time dedicated to "start and stop" drops to 13.4%.

The air conditioning must remain off and 0-50 km / h acceleration is covered in 15 seconds flat. In addition, those optional accessories that increase the resistance of a car are also tested, such as the oversized tires, which in the NEDC cycle were replaced with smaller homologated ones. Finally, the WLTP must be performed at a temperature of 23 ° C, while the NEDC cycle prescribed a temperature between 20 and 30 ° C.

For the same vehicle, between a NEDC and a WLTP i values ​​may differ by as much as 30%, as highlighted on several occasions by numerous specialized magazines in the sector.

Hybrid and electric tests

The new cycle includes more stringent tests than to those carried out on traditional endothermic cars, but also between the same categories of low-emission vehicles. As we know, hybrid cars consist of an internal combustion engine combined with an auxiliary electric one or assisted by it. In these cases, the test is doubled: the homologation cycle is in fact carried out both in the "normal" driving mode, therefore with free use of energy, and in the specific one to safeguard the battery reserve.

Why this double test? The reason is simple, in the second case there is a greater expenditure of fuel as the system favors the maintenance of recharging to the detriment of the increase in consumption.

A similar argument can be applied to plug-ins, the rechargeable hybrid variants on tap. The first evaluates the total electric autonomy with the battery at 100% until its complete discharge, while the second measures the emissions of the internal combustion engine when the battery is completely discharged. This is a very interesting situation, as the engine must both move the car and restore energy to the battery, aided only by regenerative braking.

The homologation value, the one shown on the car's technical sheet, is calculated making an average of these two procedures calculated on the ratio between electric and total autonomy.

European homologation cycle vs American cycle

The European homologation test of a car includes a test session 20 minutes while the American one is just over 30 minutes. The longer duration of the test involves a subdivision of the different tests with a more truthful and reliable verification by the bodies in charge. For example, the maximum speed is 57 miles per hour (92 km / h), but it is reached 4 times with different and much more frequent speed variations.

Furthermore, between the two homologation tests there is is another substantial difference: in Europe the surveys are carried out by certified third parties and can be carried out in any EU country, while in the USA they are only carried out by the EPA at the Office of Transportation at Air Quality in Ann Arbor, near Detroit.

WLTP cycle is conservative

The European standard is therefore far from the American one, the differences in this case can also be quite significant. Some tests highlighting, for the same vehicle and version, even a difference of over 30%. Finally, if American customers detect consumption different from those reported on the specifications, they can act legally, which in Europe is practically impossible as it is known that the measurements are not close to the real ones.

Driving styles and the environmental conditions, such as temperature, humidity, altitude variations, are far from a true and authentic use. To give you a more concrete example, a car traveling on the flat at a constant speed on a hot summer day in Spain will hardly have the same fuel consumption and emissions if used in the same way in Sweden.

For these reasons often the WLTP cycle is labeled as “conservative”, precisely by virtue of the fact that the tests performed are far from being evaluated as the only point of reference. In a recent test of ours aboard the Renault Twingo Z.E. we found a range of about 150 km with a mix of urban and extra-urban roads, avoiding sudden accelerations and uncommon driving styles; a result 20% lower than that declared by the WLTP cycle.

The challenge therefore still remains on the plate: to create a homologation standard that is as close as possible to the reality that the customer has to face on the road . Will we ever reach this milestone?