General information:
In order to be able to objectively compare various vehicles with each other in terms of consumption and emissions and to be able to reproduce such results, the responsible legislative authorities must define standardized driving cycles. Currently two such methods are in use:
FTP-75 (Federal Test Procedure)
US-American cycle which was also previously used in Switzerland.
New European Driving Cycle (NEDC)
EU cycle, which - because Switzerland has also adopted the EU standards - is also valid in Switzerland.
With the binding introduction of the New European Driving Cycle (NEDC) in line with European Directives 70/220/EEC, 80/1268/EEC and 93/116/EEC on 1st January 1996 , a technical option was created whereby a manufacturer's vehicles could be directly compared with each other and the vehicles from another competitor manufacturer.
For certification purposes the consumption and emission measurements are conducted here on a roller dynamometer, with a stringent, legally regularized process.
The exact driving cycle (NEDC) and the test conditions are described in Directive 70/220/EEC. Here is an overview of the most important criteria:
The vehicle must correspond to the series production standard, there must be no deviations (retrofitting of accessories, custom wheels, roof carriers etc.). Ex-factory special equipment is not to be taken into consideration either.
The test fuel must comply with the CEC reference fuel features (use brand-name fuel).
Ambient temperature to be between 20 °C and 30 °C and air pressure 100 kPa (all emission components are to be normalized at a standard pressure of 100 kPa).
Vehicle temperature (engine oil and coolant fluid) must comply with ambient temperature (2 °C) at start of measurement.
Lights, air conditioning and other electrical consumers to be deactivated.
On manual transmissions the shift points (irrespective of output, torque and gear ratio) are strictly specified.
NEDC consists of a city (approx. 4 km) and an extra-urban driving cycle (approx. 7 km).
The city part of the driving cycle consist of defined idle, acceleration, constant speed and deceleration phases. It lasts for 780 s (13 min..) and an average speed of 19 km/h is reached. The maximum speed in the urban driving cycle is 50 km/h.
The extra-urban driving cycle covers a period of 400 s (6:40 min), at an average speed of 62.6 km/h and a maximum speed of 120 km/h. It primarily consists of constant-speed phases at 50, 70, 100 and 120 km/h.
In the NEDC, the journey on level ground is also simulated. In other words, gradients are not part of the driving profile.
Originally the NEDC was introduced solely as an emission test (for EURO 0 to 6). It was never intended to display "real-life" consumption, but rather it was meant to provide reproducible and comparable emission levels.
Procedure in workshop:
The requirements on the vehicle as well as the test specifications for the fuel consumption certification are extensive. In practice, the actual operating conditions prevalent at the customer's may be different or only roughly oriented on the above-stated legally prescribed criteria (traffic conditions, gradients in route profile). This means that while deviations in the fuel consumption data are imaginable, they can be explained. In direct conversation with the customer, a reference to the test prerequisites should be made and highlighted with regard to the fact that they are a legally prescribed reference basis, which enables products from different manufacturers to be compared with each other. The certified fuel consumption is therefore only partly suited to confirming the consumption data achieved by the customer in his driving profile and under his conditions. If a customer should complain about significant differences in consumption data, it is very important that the customer's consumption data are subjected to a critical analysis and that technical facts are then referred to when clarifying the matter. It is necessary here to ensure that the vehicle has been run-in and that it has covered a distance of at least 3000 km (10000 km would be better because at such a driven distance, significant reductions in consumption can be recorded). If however, the customer is not convinced by the given explanations, it may be necessary in exceptional circumstances to conduct a corresponding measuring drive together with the customer, which should then be geared towards the above-mentioned specifications. The customer however, should be expressly notified before any such measuring drive that the resulting consumption data may still deviate from the given consumption data, because the consumption data is to be determined in accordance with NEDC as based on specific legal specifications on a roller dynamometer with an exactly defined vehicle, etc., and that these circumstances, when taken together, may exert an influence on the consumption.
Preparations for measuring drive in workshop:
1 Check vehicle for standard condition (chip tuning, custom wheels, add-on parts, including ex-factory special equipment). Write down any deviations hereto. Remove any additional load, e.g. in trunk.
2 Check engine and fuel system for external leaktightness.
3 Read out fault memory in engine and transmission control unit to rule out any given faults.
4 On diesel engines with a diesel particulate filter (DPF), carry out manual regeneration of the diesel particulate filter before the measuring drive using XENTRY Diagnostics. (Please make sure that the regeneration process is completely finished before starting the measuring drive.)
5 Set tire pressure to specified values.
6 Precondition the vehicle (drive until engine is warm) over a driving distance of approx. 5 km.
7 Read out the trip computer at the start of the measuring drive, and query, evaluate and document the average speed and consumption data after reset and start. Reset the trip computer "After start".
8 Fill up the vehicle with brand-name fuel until the nozzle switches off for the first time and deactivate all electrical accessories that are not urgently required.
9 Set transmission mode to "C mode" (no "M" or "S mode"), if available: Deactivate the SPORT switch and activate the ECO switch.
Perform the measuring drive:
Start the measuring drive taking the urban driving (1/3) and constant speed 90/120 km/h (2/3) cycles into consideration. During the measuring drive an average speed of 60 km/h should be aimed for. Ensure that the driving style is a foresighted and restrained one. Generally, it should be sufficient to drive a distance of 100 km. When choosing the route, a level route without any gradients is to be aimed for.
Following this measuring drive, the vehicle should be returned to the same gasoline pump as selected before the drive where it should be refueled up to the first time the nozzle switches off.
The refueled fuel quantity and all data from the trip computer are to be documented in the attached test sheet, where they are then to be used as a reference in any discussion with the customer.