New European Driving Cycle

The New European Driving Cycle (NEDC) is a driving cycle, last updated in 1997, designed to assess the emission levels of car engines and fuel economy in passenger cars (which excludes light trucks and commercial vehicles). It is also referred to as MVEG cycle (Motor Vehicle Emissions Group).

The NEDC, which is supposed to represent the typical usage of a car in Europe, is repeatedly criticised for delivering economy figures which are unachievable in reality. It consists of four repeated ECE-15 urban driving cycles (UDC) and one Extra-Urban driving cycle (EUDC).

The test procedure is defined in UNECE R101[1] and maintained by the UNECE World Forum for Harmonization of Vehicle Regulations (WP.29),[2] which also works in its successor, the Worldwide harmonized Light vehicles Test Procedures (WLTP).

Although originally designed for petrol-based road vehicles, the driving cycle is now also used to estimate the electric power consumption and driving range of hybrid and battery electric vehicles.

Measurements

Several measurements are usually performed along the cycle. The figures made available to the general public are:

The following parameters are also generally measured to validate the compliance to European emission standards:

Test procedure

The cycle must be performed on a cold vehicle at 20–30 °C (typically run at 25 °C). The cycles may be performed on a flat road, in the absence of wind. However, to improve repeatability, they are generally performed on a roller test bench. This type of bench is equipped with an electrical machine to emulate resistance due to aerodynamic drag and vehicle mass (inertia).

For each vehicle configuration, a look-up table is applied: each speed corresponds to a certain value of resistance (reverse torque applied to the drive wheels). This arrangement enables the use of a single physical vehicle to test all vehicle body styles (Sedan, hatchback, MPV etc.) by simply changing the look-up table. A fan is coupled to the roller bench to provide the vehicle air intakes with an airflow matching the current speed. Many more tests can be performed during vehicle development with this arrangement than with conventional road tests.

The test is conducted with all ancillary loads turned off (Air conditioning compressor and fan, lights, heated rear window, etc.)

Urban driving

The NEDC is composed of two parts: ECE-15 (Urban Driving Cycle), repeated 4 times, is plotted from 0 s to 780 s; EUDC cycle is plotted from 780 s to 1180 s

The Urban Driving Cycle ECE-15 (or just UDC) was introduced first in 1970 as part of ECE vehicle regulations; the recent version is defined by ECE R83, R84 and R101.[1][3][4] The cycle has been designed to represent typical driving conditions of busy European cities, and is characterized by low engine load, low exhaust gas temperature, and a maximum speed of 50 km/h.[5]

When the engine starts, the car pauses for 11 s - if equipped with a manual gearbox, 6 s in neutral (with clutch engaged) and 5 s in the 1st gear (with clutch disengaged) - then slowly accelerates to 15 km/h in 4 s, cruises at constant speed for 8 s, brakes to a full stop in 5 s (manual: last 3 s with clutch disengaged), then stops for 21 s (manual: 16 s in neutral, then 5 s in the 1st gear).

At 49 s, the car slowly accelerates to 32 km/h in 12 s (manual: 5 s in 1st gear, 2 s gear change, then 5 s in the 2nd gear), cruises for 24 s, slowly brakes to a full stop in 11 s (manual: last 3 s with clutch disengaged), then pauses for another 21 s (manual: 16 s in neutral, 5 s in the 1st gear).

At 117 s, the car slowly accelerates to 50 km/h in 26 s (manual: 5 s, 9 s and 8 s in the 1st, 2nd and 3rd gears, with additional 2 × 2 s for gear changes), cruises for 12 s, decelerates to 35 km/h in 8 s, cruises for another 13 s, brakes to a full stop in 12 s (manual: 2 s change to the 2nd gear, 7 s in the 2nd gear, last 3 s with clutch disengaged), then pauses for 7 s (manual: in neutral with clutch engaged).

The cycle ends on 195 s after a theoretical distance of 994.03 meters, then it repeats four consecutive times. Total duration is 780 s (13 minutes) over a theoretical distance of 3976.1 meters, with an average speed of 18.35 km/h.

Extra-urban driving

The Extra-Urban Driving Cycle EUDC, introduced by ECE R101 in 1990,[1] has been designed to represent more aggressive, high speed driving modes. The maximum speed of the EUDC cycle is 120 km/h; low-powered vehicles are limited to 90 km/h.[5]

After a 20 s stop - if equipped with manual gearbox, in the 1st gear with clutch disengaged - the car slowly accelerates to 70 km/h in 41 s (manual: 5 s, 9 s, 8 s and 13 s in the 1st, 2nd, 3rd and 4th gears, with additional 3 × 2 s for gear changes), cruises for 50 s (manual: in the 5th gear [sic]), decelerates to 50 km/h in 8 s (manual: 4 s in the 5th and 4 s in the 4th gear [sic]) and cruises for 69 s, then slowly accelerates to 70 km/h in 13 s .

At 201 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 and cruises for 30 s (manual: in the 5th or 6th gear).

Finally, at 316 s the car slowly accelerates to 120 km/h in 20 s, cruises for 10 s, then slowly brakes to a full stop in 34 s (manual: in the 5th or 6th gear, lat 10 s with clutch disengaged), and idles for another 20 s (manual: in neutral).

Total duration is 400 s (6 minutes 40 s econds) and theoretical distance is 6956 meters, with an average speed of 62.6 km/h.

Combined

The combined fuel economy is calculated by a total consumption of urban and extra-urban cycles over the total distance (theoretical 11023 meters). The total test time amounts to 1180 s with an average speed of 33.6 km/h. Sometimes the NEDC is also quoted at 1220 s, which includes the initial 40 s with the vehicle at standstill and combustion engine off.

Criticism

Inability to represent real-life driving
The NEDC was conceived at a time when European vehicles were lighter and less powerful. The test offers a stylized driving speed pattern with low accelerations, constant speed cruises, and many idling events, however the transient accelerations are much steeper and more dynamic in practice,[6] in part caused by the power surplus of modern engines, as the 0–100 km/h (0–62 mph) average time decreased from 14 seconds in 1981 to 9 seconds in 2007.[7] The UK consumer group Which? criticise the NEDC as being out of date, having been first introduced in the 1970s and not updated since 1997 - before hybrid cars and stop-start technology was generally available. They also criticise it for not replicating real-world driving conditions and having numerous loopholes which mean the test figures are unachievable in practice. Weaknesses noted are: that tests are not necessarily repeatable and comparable, the test cycle does not include sustained motorway driving, test cycles can be performed using optional economy settings which will not typically be selected by drivers, the test cycle is performed with ancillary equipment such a air conditioning and heated windows switched off, the tests can be carried out at 1.2mph below the required speed thus using less fuel, roof rails and passenger door mirror can be removed for the test, tyre pressures for the test can be set above the recommended values thus reducing rolling resistance, no official body polices the tests and the car companies can arbitrarily reduce their results by 4% at the end of the cycle.[8]
Cycle beating
For the emission standards to deliver real emission reductions it is crucial to use a test cycle that reflects real-world driving style. However the fixed speeds, gear shift points and accelerations of the NEDC offer possibilities for manufacturers to engage in what was called 'cycle beating' to optimise engine emission performance to the corresponding operating points of the test cycle, while emissions from typical driving conditions would be much higher than expected, undermining the standards and public health.[6] In one particular instance, research from two German technology institutes found that for diesel cars no 'real' NOx reductions have been achieved after 13 years of stricter standards.[9]

Successors

UNECE WP29 is currently developing a new global harmonized driving cycle, the World Light Test Procedure (WLTP) with participation of experts from the European Union, India, and Japan; it will apply to light duty vehicles (i.e. passenger cars and light commercial vans).[10][11]

The European Commission intends to introduce a type approval procedure to measure the energy efficiency of mobile air conditioning systems in vehicles, as well as its effect on fuel consumption and emissions, and display an efficiency label on the vehicle; the work is being performed by TU Graz (Institute for Internal combustion engines and Thermodynamics), Aristotle University of Thessaloniki (Laboratory of Applied Thermodynamics), TNO and ACEA.[12]

References

  1. ↑ 1.0 1.1 1.2 E/ECE/324/Rev.2/Add.100/Rev.3 or E/ECE/TRANS/505/Rev.2/Add.100/Rev.3 (12 April 2013), "Agreement concerning the adoption of uniform technical prescriptions for wheeled vehicles, equipment and parts which can be fitted and/or be used on wheeled vehicles and the conditions for reciprocal recognition of approvals granted on the basis of these prescriptions", Addendum 100: Regulation No. 101, Uniform provisions concerning the approval of passenger cars powered by an internal combustion engine only, or powered by a hybrid electric power train with regard to the measurement of the emission of carbon dioxide and fuel consumption and/or the measurement of electric energy consumption and electric range, and of categories M1 and N1 vehicles powered by an electric power train only with regard to the measurement of electric energy consumption and electric range.
  2. ↑ "Vehicle Regulations". UNECE Transport Division/World Forum for Harmonization of Vehicle Regulations. Retrieved 30 April 2015.
  3. ↑ E/ECE/324/Rev.1/Add.82/Rev.4 or E/ECE/TRANS/505/Rev.1/Add.82/Rev.4 (26 April 2011), "Agreement concerning the adoption of uniform technical prescriptions for wheeled vehicles, equipment and parts which can be fitted and/or be used on wheeled vehicles and the conditions for reciprocal recognition of approvals granted on the basis of these prescriptions", Addendum 82: Regulation No. 83, Uniform provisions concerning the approval of vehicles with regard to the emission of pollutants according to engine fuel consumption.
  4. ↑ E/ECE/324/Rev.1/Add.83 or E/ECE/TRANS/505/Rev.1/Add.83 (23 August 1991), "Agreement concerning the adoption of uniform conditions of approval and reciprocal recognition of approval for motor vehicle equipment and parts", Addendum 83: Regulation No. 84, Uniform provisions concerning the approval of passenger cars equipped with an internal combustion engine with regard to the measurement of fuel consumption.
  5. ↑ 5.0 5.1 "Emission Test Cycles: ECE 15 + EUDC / NEDC". dieselnet.com. July 2013. Retrieved 30 April 2015.
  6. ↑ 6.0 6.1 Peter Mock, John German, Anup Bandivadekar, Iddo Riemersma (April 2012). "Discrepancies between type-approval and "real-world" fuel consumption and CO2 values" (PDF). International Council on Clean Transportation. Retrieved 27 April 2014.
  7. ↑ Stephen E. Plotkin (December 2007). "Examining Fuel Economy and Carbon Standards for Light Vehicles. Discussion Paper No. 2007-1" (PDF). OECD-ITF Joint Transport Research Centre. Retrieved 27 August 2012.
  8. ↑ "Car Fuel Economy". Which?: 27. May 2015.
  9. ↑ "WHO adds pressure for stricter Euro-5 standards" (PDF). T&E Bulletin, No 146. European Federation for Transport and Environment. March 2006. Retrieved 27 August 2014.
  10. ↑ https://www2.unece.org/wiki/pages/viewpage.action?pageId=2523179
  11. ↑ http://circa.europa.eu/Public/irc/enterprise/wltp-dtp/home
  12. ↑ http://www.ivt.tugraz.at/index.php/en/research/emissions/item/53.html

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