Worldwide Harmonized Light-duty Test Procedures (WLTP)
Being introduced in EU in 2014
One of the agenda at the United Nations World Forum for the Harmonization of Vehicle Regulations (WP29) concerns the uniform test cycles and test methods with regard to the emissions and fuel consumption of vehicles (WLTP: Worldwide Harmonized Light-duty Test Procedures). The test cycles are based on data collected in Japan, US, EU, India and Korea covering vehicle speed-acceleration distributions that are close to the world averages.
The forum plans to adopt the WLTP as part of the UN uniform regulations (UN regulations) in the future and the test procedure will be applied to the emissions and fuel consumption regulations in Japan and EU in and after 2014.
Below is the summary of the Worldwide Harmonized Light-duty Test Procedures (WLTP) and its impact in Japan and EU.
1) Summary of the WLTP regulations being developed by the United Nations
1-1) About WLTP
Pressed with the increasing need to develop emission test cycles and their uniform regulations applicable to small to medium size vehicles that are subject to stringent regulations worldwide, the United Nations World Forum for the Harmonization of Vehicle Regulations (WP29) initiated the necessary work in 2007 called the Worldwide Harmonized Light-duty Test Procedures (WLTP).
Japan proposed the preparation of "worldwide harmonized regulations (gtr) on emission and fuel efficiency tests for passenger cars" to the 143rd session of the WP29 held in November 2007. The forum approved the necessary work be initiated accordingly with the goal of final completion in 2021. It was also agreed that the uniform test cycle, the single most critical issue, be completed by 2013.
Figure 1 Worldwide Harmonized Light-duty Test Procedures (WLTP)
|(Note)||WP29 has drafted world harmonized duty cycles for heavy-duty vehicles and motorcycles and their test procedures (WHDC, WMTC). To realize the mutual recognition of WHDC and WMTC, necessary work is being performed by the Working Party on Pollution and Energy (GRPE) primarily in major countries in EU and Japan to reflect them in the United Nations uniform regulations (UN regulations). Once they are completed, vehicle certification tests will be conducted according to the uniform regulations for mutual approval in Japan, EU, South Africa and other signatory nations to the 1958 Agreement.|
In January 2008, an informal group called "WLTP Informal Group" was organized under GRPE to deal with actual work toward WLTP addressing small and medium size vehicles.
Figure 2 Organization of the WLTP
Targets of development: a) To draft the Worldwide harmonized Light duty driving Test Cycle (WLTC) and b) To update test procedures using the test cycle. In addition, the following was proposed as important agenda: c) Validation of the WLTC and d) Off-cycle tests to regulate emissions during off-cycle driving conditions
The International Organization of Motor Vehicle Manufacturer (OICA) welcomed these activities and expressed intent to participate. OICA proposed that vehicle categories, fuel efficiency test procedure, test conditions, test fuels, on-board diagnosis (OBD) and emission limit thresholds be taken into consideration as well.
Efforts to develop uniform regulations have been led by Japan, US and EU until India became an ardent member while China and Korea started showing interest. One of the most recent progresses is seen with International Energy Agency (IEA) showing expectations.
Figure 3 shows the flow of the test cycle and test procedure development. The test cycle and test procedure in WLTP is subject to approval at WP29 session in March 2014 after which they will be incorporated in European regulations starting the same year.
Figure 3 Schedule during WLTP Phase 1
1-2) Development of harmonized test cycle
The effort for developing the worldwide harmonized light duty driving test cycle (WLTC) started when the first DHC working group met in September 2009. The test cycle is to be built upon in-use data collected in various areas. This requires an objective, reliable method. It was agreed that the test cycle development be performed by Japan Automobile Research Institute (JARI) that has ample experience in test cycle development in Japan.
Figure 4 shows the proposed cycles as of 2012. The draft WLTC (average 46.5 km/h) consists of four parts: Low speed (average 18.9 km/h), Middle speed (average 39.5 km/h), High speed (average 56.6 km/h) and Extra-High speed (average 92.0 km/h) over 1800 seconds. The drive time in each part represents the time proportionate to the world average.
Figure 4-1 Present status of drafted WLTC
|WLTC ver.4||Japan||EU/ECE||USA (reference)|
|Low speed||Middle speed||High speed||Extra-high speed||WLTC Total||JC-08||EU/ECE NEDC||"Standard Cycles" FTP75|
|Max Speed (km/h)||56.5||76.6||97.4||131.3||131.3||81.6||120.0||91.2|
|Ave. Speed (km/h)||18.9||39.5||56.6||92.0||46.5||24.4||33.6||34.2|
|Soak||Under considering in DTP Group||Repeated as hot test||N/A||600|
|Gear Shift||Fixed speeds||Fixed speeds||Specific (with evidence)|
(Note) WLTC is currently being evaluated and the figures in the table are subject to change due to frequent minor adjustments.
Figure 4-2 Comparison of test cycles in Japan and EU (US : reference)
Unification was attempted as written below regarding the basic perspective of the test cycle development.
Figure 5 Flow of the test cycle development
1) Uniform speed-acceleration distribution to be calculated for various road types (urban, rural, motorway) and vehicle categories based on in-use data, and a weighting factor matrix be developed for each.
2) The world average uniform speed-acceleration distribution is to be determined based on such data.
3) Vehicle speed change patterns (short trip data) extracted from in-use data to be combined to propose as many test cycles as possible to calculate uniform speed-acceleration distribution for a chi-square test.
4) The chi-square test is used to determine the test cycle having a uniform speed-acceleration distribution closest to the world average, which will be defined as the worldwide harmonized light duty driving test cycle (WLTC).
The working group consisting of Japan, US and EU was later joined by India, China and Korea. Their participation was welcomed as there would be more data available from around the world. However, China could not submit data as planned because of procedural delay and, as a result, work was started to develop test cycle using data collected from Japan, US, EU, India and Korea.
Validation of the test cycle developed in 2011 (Validation 1) was conducted with regard to the drivability and tire slipping during tests on the chassis dynamometer and necessary modification is being performed. Validation 2 is in process in 2012 reflecting acceleration in EU and other countries and followability of the test cycle on roads to increase test reliability.
It has been agreed with regard to low-power vehicles that are found in large numbers in India to apply test cycles that do not include high acceleration mode. This may also apply to many special compact vehicles that are sold in Asia.
Gear shifting methods have been proposed by EU in which the shift point is judged based on the engine output, and by Japan in which gear is shifted at fixed speeds. These proposals are being studied at present.
1-3) Unification of test procedure
Work toward the development of test procedure was initiated in April 2010 by DTP (Development of Test Procedure) working group chaired by US and co-chaired by India. The US stepped down from the chairmanship shortly after work started due to some internal concerns and the group has been chaired by Switzerland since June 2010.
Work is being done by five sub-groups as shown below.
|Internal combustion engine (ICE) sub-group||* To develop harmonized test methods for existing ICE (gasoline, diesel) vehicles. * Vehicles are tested on a chassis dynamometer. Emissions and fuel efficiency may be affected significantly by certain factors as listed below that need to be addressed: a) Vehicle weight setting method, b) tire selection method, c) traction setting method, d) gear-shift setting method, e) definition of low-power vehicles and their test method|
|Electric, hybrid vehicle test procedure (E-Lab) sub-group||* New test procedure for electric vehicles and hybrid vehicles under new test cycles. * Japan leads the world in this area and the sub-group is led by Japan.|
|Particle measurement procedure (PM/PN) sub-group||* Introduction of new regulations for higher accuracy in particle mass (PM) measurement, and proposal of revising the particle number (PN) measurement, to meet tighter regulations on particle emissions from vehicles.|
|Additional pollutant measurement procedure (AP) sub-group||* Working on measurement of additional pollutants in addition to the existing substances (CO, HC, NOx, PM, PN). * Measuring procedure is needed for such substances as NO2 (nitrogen dioxide), N2O (nitrous oxide), NH3 (ammonia) and ethanol.|
|Fuel sub-group||* Formed for the unification of test fuel to be used in certification, but no particular work is being done. * Unification of test fuel will be necessary when the globally harmonized regulatory limits are proposed. * This group faces the most difficult issue which is closely related to the properties of fuels that are commercially available in the market, which fall outside of WP29's work range.|
2) Emissions and fuel efficiency test methods in Japan and EU relative to WLTP
Fuel consumption can be calculated from the exhaust emission test results. For this reason, exhaust emissions and fuel consumption are rated concurrently in a single test over the test cycle.
2-1) Test cycle, test conditions and flow of approving test in Japan
Figure 4-2 shows an outline of JC08 mode, the test cycle currently in use in Japan. The test cycle is in the form of a "transient cycle" obtained by simulating actual road drive conditions. This concept is applied in WLTC being developed at the United Nations. The WLTC is being developed using data collected in various regions of the world and in accordance with the cycle development method adopted in Japan. Because of the unique nature of road traffics in Japan, however, a single cycle is used under JC08 without regard to low, medium, high and ultra-high speeds. The maximum vehicle speed is approximately 81.6 km/h with the average speed of 24.4 km/h and test time of 1,204 seconds.
Test is conducted in two ways; cold start test in which exhaust emissions are measured after the engine is left at a constant temperature (soaking), and hot start test with the completely warmed engine. Results from these two tests are added up with a weighting factor to obtain the final rating.
Figure 6 Emission measurement method in Japan
Figure 7 Emission measurement method in EU
2-2) Test cycle, test conditions and flow of approving test in EU
Figure 4-2 shows an outline of the test cycle called NEDC (New European Driving Cycle) currently in use in EU. The straight lines indicate acceleration and low-speed driving. The test cycle consists of combinations of steady acceleration and fixed-speed driving. The maximum vehicle speed is approximately 120 km/h with the average speed of 33.6 km/h and test time of 1,180 seconds.
Test is conducted over a single cycle after the engine is left at a constant temperature (soaking) and only a cold start test is rated.
Figure 7 shows the flow of evaluating the test results in EU. As shown, a vehicle failing the first test may receive a second test so long as the failure does not exceed 10% of the target.
In Japan, vehicles are rated based on the results of a single test that consists of two test modes.
2-3) WLTP introduction plan and its impact in Japan and EU
Completion of the worldwide harmonized light duty driving test cycle (WLTC) and its new test procedure by the fall of 2013 is strongly expected (formal approval at WP29 is slated for March 2014). Once they are approved, necessary work will take place that will lead to the UN Regulation which will have a major impact on the signatory nations to the 1958 Agreement as well.
Figure 8 Introduction plan and impact of the international regulations in Japan and EU
Prior condition: WLTC and test procedure approved at WP29 in March 2014
|Introduction of WLTC||Impact on fuel consumption regulations||Impact on exhaust emission regulations|
|UN harmonized regulations||To be studied by GRPE working group on pollution and energy with a focus on different stance between EU rushing introduction and the less rushing Japan.||UN R101 amendment||UN R83 amendment|
|Japan||Will consider introduction as soon as amendment of UN regulation is foreseeable.||Fuel consumption standard for 2020 is already established. The key issue is the integration among the member countries to the 1958 Agreement.||Preliminary work is needed such as validation of regulatory values under the new cycle.|
|EU||Most proactive about the completion of WLTC and amendment of UN Regulations as introduction of the new cycle is planned in the application of EURO 5/6 EU Regulation.||Same as on the left||Same as on the left|
The European Commission has been demanding that work is completed before the introduction of new European regulation on fuel consumption in 2014 since it has been their basic policy to develop EU regulations based on the United Nations globally harmonized standards with regard to safety and environmental issues as well. The test cycles and methods to be used in European regulations on exhaust emissions and fuel consumption after 2014 owe much to the harmonized standards established by the United Nations.
Japan has already established the policy that its new standard on fuel consumption being introduced in 2020 be based on the JC08 cycle. However, Japan has expressed it would consider WLTC at the earliest opportunity once it is approved at the United Nations.
India has also been quite active and contributed a number of proposals and is likely to adopt WLTC when it is established.
The single most potential impact of the WLTP is measurements of new emission and fuel consumption. Since the new test procedure is associated with new test cycles and average vehicle speed and partial acceleration, the resulting measurements will naturally differ from those that are currently in use in participating countries and regions.
However, the actual change of measurements is not clear as no conclusion has been drawn as to the content of test cycles. Japan and EU will need to wait until about the fall of 2013, when the WLTC and its test procedure will be proposed, before they study its effect on their regulations and determine methods of its introduction according to their respective binding law and procedures.
(It may be said with hesitation that fuel efficiency level will be generally higher if the new test cycle contains shorter extra-low speed drive, at about 10 km/h, or shorter idling time even if the average vehicle speed may increase as a result. See Figure 10 for changes of measurements on electric vehicles.)
Recent industrial efforts to reduce exhaust emissions, from gasoline- and diesel-powered vehicles alike, largely depend on after-treatment using catalysts or other means. Therefore, introduction of a new test cycle will not have intense impact although it will affect exhaust emissions measurement.
Although the exhaust emission regulation is growing stricter, most of the Japanese vehicles have been certified as low-emission vehicles. Therefore, new test cycles should not affect them in maintaining the current regulatory limits.
As far as Japan is concerned, the weighting factors in cold start and hot start tests may be removed or modified in emission or fuel efficiency rating.
New test conditions may affect test vehicle weight, traction resistance measurement and certain other details. Among them, the vehicle weight setting will have a major impact on test results. There will be no major change in measurement methods of NOx, PM and other pollutants.
3) Application of WLTP to electric vehicles
With an increasing number of electric vehicles and hybrid vehicles being introduced in the market, a recent topic in WLTP working group discussions is the test method of such vehicles using the WLTP cycle. These discussions are led chiefly by the E-Lab sub-group as shown in Figure 2. Introduced below are some of the discussions in which Japan is playing a leading role.
Figure 9 E-Lab sub-group open issues
(Ref: http://www.unece.org/fileadmin/DAM/trans/doc/2012/wp29grpe/WLTP-DTP-08-12e ppt) *) RCB: RESS Charge Balance (=SOC) *) RESS: Rechargeable energy storage system *) AER: All Electric Range *) EAER: Equivalent All Electric Range *) RCDR: Charge Depleting Range *) NEC: Net Energy Change = RCB * nominal voltage of RESS
Figure 9 shows a schematic diagram of a hybrid vehicle test method. The preconditioning of the onboard battery must be maintained to ensure reliability and reproducibility of results from a hybrid vehicle test. Therefore, a number of steps are taken, such as the battery being depleted, the tire pressure confirmed, the vehicle left in a constant temperature (soaking), the vehicle driven under prescribed conditions, the battery charged, etc., before the test starts in a test cycle.
Work is currently under way to determine these pre-conditioning steps. Discussion is being led chiefly by experts from Japan experienced in the topic. Figure 10 shows an example of knowledge about electric vehicles being reflected on the WLTP. The table suggests there is a nearly 20% difference in the range per charge between the current JC08 test mode and the new test cycle (WLTC). The same holds true of the rate of power consumption. While such a difference is due largely to different test cycles, it also results from the difference in the test procedural detail.
Figure 10 Range per charge and rates of power consumption
|WLTC (23.112km)||JC08 (8.172km)|
|Range per charge [km]||101||129|
|Power consumption rate [Wh/km] (power charge from external source)||147 (14.8kWh@AC200V)||115 (14.9kWh@AC200V)|
|WLTC part (drive range: A km)||Low (3.06)||Mid (4.74)||Hi (7.06)||Ex-High (8.25)|
|Power consumption: Y [kWh]||0.29||0.50||0.76||1.11|
|Estimated range per charge: X [km]||137||123||120||97|
Figure 11 shows the effect of the charging voltage as an example of regulation details affecting measurement results. It suggests the range per charge and the rate of power consumption of a vehicle vary by the charging voltage it receives. This leads to need for discussion as to whether these conditions should be defined in detail in the test procedure. The measurement methods for electric vehicles and hybrid vehicles will also be modified in the future, and a change in a test cycle may affect official cruising range of electric vehicles, etc.
If Japanese test procedure is adopted as an international standard, its effect on Japanese regulations should be minimal since work by the E-Lab sub-group is being led by Japan.
Figure 11 Effect of charging voltage (200VAC vs. 100VAC)
The test cycle and test procedure is expected to be completed by the WLTP working group of the United Nations and approved by WP29 by March 2014. The Japanese and European regulations will be modified accordingly.
Work will start at the United Nations to incorporate the proposal in the uniform regulations of the United Nations (UN Regulations) under the 1958 Agreement. The outcome of the WLTP will eventually be reflected in the uniform regulation regarding exhaust emissions (UN R83) and the uniform regulation regarding fuel consumption (UN R101).
These UN Regulations are included in the list of technical requirements of the uniform regulation (UN R0) addressing environmental issues under the United Nations International Whole Vehicle Type Approval (IWVTA) system being introduced in 2016. The signatory countries to the 1958 Agreement will be affected broadly since these changes will apply not only to the certification under individual UN regulations but also reciprocal approval of vehicle certification.
(Note) The US was one of the member countries that presented the original proposal to the WLTP, but failed to sit in meetings due to certain internal concerns. Then, in 2012, the US showed interest in the work and expressed intent to return to activities on the condition that drastic revision be made to the existing work. This demand is causing confusion among the members of the working group. Although such a demand will eventually be tolerated by a political decision by Japan and EU, it will cause a significant delay to the entire schedule.
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