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The stricter fuel consumption and emission regulations put the worldwide carmakers and suppliers under pressure to develop more efficient thermal management systems. High engine efficiency, increased comfort requirements, and stringent emission regulations are examples of the political and public conflicting requirements. The coolant system of current vehicles is already limited on performance due to package and styling constraints. Therefore, any future incremental demands on the coolant system will need to be managed effectively so as to remain within these constraints. Simulation-based design and virtual prototyping can insure greater product performance and quality of both the time and cost required by traditional build-and-test approach for the development of the vehicle thermal management process and the development process in general.

In order to improve the accuracy of vehicle simulation under transient cycle conditions and thus predict performance and fuel consumption, consideration of the complete system engine/drivetrain/vehicle is necessary. The coupling of otherwise independent simulation programs is therefore necessary for the vehicle and engine. The description of thermally transient processes enables the calculation of the heat balance of the engine, which in turn enables the simulation of warming up operation. Through consideration of the engine warming up process, the quality of the prediction of fuel consumption and emissions is improved. The combination of the simulation programs CRUISE and BOOST to determine the engine heat balance has proven to be successful for the analysis of transient drive cycles.

The incorporation of a detailed engine process calculation that takes into account thermal behavior of the engine and exhaust system is essential for a realistic simulation of transient vehicle operation. This is the only possible way to have a precise preliminary calculation of fuel consumption and emissions. Therefore, a comprehensive thermal network of the engine based on the lumped capacity method has been developed. The model allows the computation of component temperatures in steady state operation as well as in transient engine studies, e.g. investigations of engine warm-up. The model is integrated in a co-simulation environment consisting of a detailed vehicle and engine cycle simulation code. The paper describes the procedure of the co-simulation and presents several examples of warm-up simulations.