The Challenge: New Assessment Process for Pollutant Emissions

Since September 2017, new emission test procedures have been mandatory for the type approval of passenger cars and light commercial vehicles in the European Union. The new test procedures stipulate that emissions must be assessed under real driving conditions. Therefore, Real Driving Emissions (RDE) tests complement conventional tests that are performed under laboratory conditions on chassis dynamometers. 

The Task: Efficiently Frontloading RDE Tests

Factors influencing the driving experience and pollutant emissions.

RDE approval tests are conducted under unpredictable conditions (road, driveability, traffic, environmental conditions, etc.). Due to these parameters and the large number of vehicle variants, a preparation of RDE approval tests that relies entirely on real test drives becomes economically unfeasible. Furthermore, an evaluation that is done solely with prototype vehicles under real driving conditions is unfavorable, because at this point modifications to the system components, such as the exhaust aftertreatment system, entail high costs. To make the development process as efficient as possible, it is recommended to frontload certain tests for RDE approval to suitable earlier phases in the development process. For example, the engine and exhaust controls can be optimized for low emissions very early on. By means of simulation, developers quickly gain important insights into whether the system components that are being developed comply with the current stipulations of emissions regulations.   

The Solution: Simulation-Based Emissions Analysis

Integrating simulation-based RDE tests into the development process.

dSPACE’s seamless tool chain opens up many new possibilities for realistic driving maneuvers with virtual or real engines and exhaust systems in early development phases. The basis for simulation is the tool suite ASM (Automotive Simulation Models), which provides advanced tools for defining and simulating engines, vehicles, roads, and driving maneuvers. The tool suite can be used to simulate RDE tests for a wide range of driving scenarios on rural roads, highways, and in urban areas, including complex surrounding traffic. The combined ASM simulation of the engine, vehicle dynamics, and environment makes it possible to predict the emissions behavior in the virtual driving situations. RDE tests that were defined this way can be reproduced with high precision and can be used to analyze different variants of vehicles, roads, and maneuvers by modifying the parameters. In addition, customer-specific and third-party models can be included in the simulation via the FMI standard. 

With the seamless tool chain, preparatory RDE tests can now be frontloaded to and optimized in different development stages with the well-established development methods of model-, software-, hardware- and engine-in-the-loop simulation (MIL, SIL, HIL, EIL, respectively). 

Seamless Tool Chain for RDE Simulation

RDE tests can be performed seamlessly with the established development methods model-in-the-loop, software-in-the-loop, hardware-in-the-loop, and engine-in-the-loop (MIL, SIL, HIL, EIL).

A simulation-based approach delivers first insights into the emission behavior for the tested driving scenarios already during vehicle development. Therefore, deviations from the stipulated emission limits can be detected early on and eliminated more cost-effectively.

In the early phases of electronic control unit (ECU) development, the offline simulation platform dSPACE VEOS provides efficient means to easily set up and check RDE tests in the form of virtual test drives. For these tests, plant models for combustion engines, exhaust systems, vehicle dynamics, and the environment are executed on the platform together with the controller model or the application software of the engine ECU. Suitable models are available in the ASM simulation tool suite. Depending on the application, customer-specific and third-party models can also be included. The interaction of all components and possible variants in a simulation makes it possible to predict the vehicle’s exhaust behavior very early on.

The real-time simulation platform dSPACE SCALEXIO provides comprehensive means to execute and optimize the RDE tests with a real ECU under real-time conditions. The models, maneuvers and trajectory definitions from the MIL/SIL phase can be reused as is. HIL operation also allows for considering various ECU software and engine variants without having to replace the real combustion engine. This ensures a high level of maturity of the real engine controller and the test environment for the subsequent operation on the engine test bench, saving valuable time on the test bench and thus cutting costs.  

To measure the actual emissions of the real combustion engine during a driving maneuver, a combustion engine is operated on a test bench together with the real-time simulator in a closed-loop system configuration. The real-time simulator emulates the vehicle dynamics model, including the transmission, and an RDE-compliant driving maneuver. The simulation provides torque requests for the combustion engine and engine speed requests for the load machine. During operation, the combustion engine, the load machine, and the vehicle simulation interact by means of torques, which are measured at the engine output. dSPACE’s seamless tool chain makes it possible to reuse RDE tests and the prepared simulation models, which were tested in the preceding development steps, directly on the engine test bench.

Test Bench Coupling

Using a high-performance, synchronized real-time coupling of the vehicle dynamics simulator and the engine test bench ensures that signals between the two systems are exchanged synchronously and with low latency. A standardized interface that is being developed in the ACOSAR research project (ACOSAR = Advanced Co-simulation Open System Architecture) aims at reducing the efforts needed for integration.  

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