Extended Flexible Environment and Vehicle Simulation for an Automated Validation

In FISITA 2010 IPEK (Institute of Product Engineering) introduced the vehicle-in-the-loop platform based on its X-in-the-loop approach (F2010-C-177) (Albers and Düser, Implementation of a vehicle-in-the-loop development and validation platform, FISITA world automotive congress, Budapest, 2010). It offers a methodology for multi domain product development and validation as well focuses on its key hypothesis that validation is the main task in every step of product development process. An open hardware and software platform allows integration of different real components and simulation models as well as the usage of established tools and methods for measurement and validation. The platform is based on a common hardware-in-the-loop System using extended I/O-communication to the vehicle and the test bench. The application is done in C code and Matlab/Simulink so an easy exchange of modular simulation models and test cases is feasible. The architecture of model-, component- and test case implementation simplifies the scalability as well as the modularization. IPEK uses this platform amongst others for its improved fully automated validation environment which allows the optimization of operating time for determination of shifting quality on the chassis dynamometer. The task is to perform several hundred gearshifts under particular reproducible conditions automatically such as engine speed or even battery state of charge, which normally a real driver had to perform on a real test track. Compared to road tests on the rig it is possible to reach time benefits of over 80 % by using a special driver model for acceleration (using gas pedal), deceleration (using dynamometer) and gear shifting (using tip signal at steering wheel). Since the vehicle behaviour on the road is constrained to different environmental conditions it is necessary to reproduce these conditions on the test bench accurately. Different resistances affect the vehicles responses such as shifting strategy, acceleration characteristics or fuel consumption which results in altering test results. State of the art for simulating environmental conditions and vehicle characteristics on the chassis dynamometer is the Road-Load-Simulation (RLS) which uses measured vehicle coast downs to map the static resistances of a real car on a real track onto the test bench. These coast downs have to be redone every single time components of the car or the environment changes. In addition, changing resistances during test like air drag due to headwind and rolling drag due to tire temperature or abrasion can’t be simulated based on that static coast down. This paper shows an approach for simulating all kind of resistances that can appear and vary during the test such as air drag (wind), road gradient, road friction, curve resistance etc. in real-time. It can be used to drive test cases like the determination of characteristic shifting map in a more realistic way to perform better validated results. Central point is a configurable vehicle and environment model which has to be parameterized with data from the real car and track and then calculates the necessary dynamometer responses. Applied with a four roller dynamometer (two or even four driven axles) it offers the possibility to perform complex all-wheel manoeuvres e.g. such as μ-split or cornering with independent wheel behaviour and slip. Besides the advantages of this approach, an analysis of different influencing factors is shown in this paper.