EMISSIONS TESTING


difficult enough when just considering the urban, rural and motorway driving elements, but there is another factor which has taken the industry by surprise – climate.


Within the detail of the RDE conditions, a number of new parameters have been set based on external temperature, altitude, speed, driver aggression levels and gradient. “Under the new regime, OEMs will


ultimately need to meet RDE emissions targets from -7°C up to 35°C. Similarly, tests will have to be conducted at altitudes of up to 1300m, higher than Mount Snowdon or Scafell Pike. Clearly, replicating such stringent conditions consistently is a challenge that the


automotive sector has yet to overcome,” said Williams. To put vehicles through their paces in all conditions required for RDE testing, MAHLE Powertrain has developed its Portable Emissions Measurement System (PEMS), apparatus that fits to a test vehicle to measure emissions in different conditions when it’s on the move. However, the company has also produced RDE cycle simulation technology that enables the tests to be performed on a dynamometer or rolling road. Dyno studies can’t replace the RDE cycle, which by definition needs to be performed in real conditions, but it enables crucial development work to be done to ensure the OEMs get everything


❱❱ The migration of the regulatory framework on


emissions during the next few years is complex


right before going through expensive testing of finished products.


NEDC / WLTP DRIVING CYCLES


The NEDC and WLTP driving cycles are similar in profile but have key differences in terms of speed, duration and profile regularity as shown in the image. The NEDC consists of the 780 second Urban Driving Cycle (UDC) with an average speed of 18.35kph and four identical repetitions of speeding up and slowing down. It also has an Extra Urban Driving Cycle of 400 seconds with speeds reaching 120kph. The WLTP has four sections


❱❱ Profile comparison for NEDC and WLTP driving cycles (WLTP class 3 cycle for high power vehicles shown in red)


8 /// Climatic & Vibration Testing 2017


representing low, medium, high and extra high speeds. The cycle used for testing depends on the vehicle power but can last up to 1800 seconds in total and reach speeds of over 130kph.


RDE ON THE DYNAMOMETER When asked about the role of dynamometer simulations, Williams explained that in order to guarantee that the company’s powertrains meet the RDE legislative requirements, MAHLE Powertrain has to ensure that all required RDE conditions are met throughout a multi-year powertrain development programme. The only way to achieve this is to bring RDE back to the chassis dyno. “Using the chassis dyno, we will be able to prove that the powertrain meets the RDE emissions standards across all RDE boundary conditions, including altitude, temperature, gradient, trip dynamics, fuel type and vehicle mass,” he explained. In order to confirm that the company is not just developing powertrains to meet just one RDE cycle, it simulates multiple RDE cycles from a dataset of over 50,000km of real world data, thus ensuring accurate simulation of real world conditions. I asked why this is important, since this is the role of the RDE test performed using the PEMS equipment. “The key point is that by using the chassis dyno, we will be able to test all these conditions in a shorter duration. We won’t run the risk of failing RDE tests due to on road conditions such as traffic or incur the cost of travelling to altitude or hot or cold climatic conditions. Doing this reduces both the development time and the cost,” he said.


Once the powertrain meets RDE requirements on the chassis dyno, on road validation across all RDE conditions will be performed to prove that the vehicle meets the requirements during real world testing. “This process will ensure that the RDE legislation is robustly achieved whilst delivering the powertrain to our customers on time and within budget,” Williams concluded. Similar to many other spheres of engineering, the effort put into simulation and prototyping (both real and virtual), smooths the way to achieving product certification at the final stages of development with reduced risk of failure and subsequent re-engineering work. With something as difficult as varying climatic conditions, it’s hard to imagine any other cost effective way of achieving RDE certification on time and within budget . EE


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