BMW simulates valve spring dynamics with DADS

Germany--Increased demands for efficiency and lower emission levels of internal combustion engines require a detailed understanding of engine operations, including the dynamic lift of the valves. For this reason, mechanical engineers at BMW AG in Germany are implementing DADS design simulation software from CADSI (Coralville, IA and Brussels, Belgium) to assist in the analysis of engine-valve behavior.

At high engine-operating speeds, the valve's actual dynamic lift differs significantly from the ideal kinematic behavior. This dynamic behavior, in part, is due to component flexibility, nonlinear cam contact, and valve spring characteristics that change under operating speeds and conditions.

BMW selected DADS for dynamic valve train analysis because of its proven numerical stability, integration with FEA for flexible body simulation, link with controls and hydraulics, and integration with CAD solid modelers.

A recent joint development project between CADSI's mechanical simulation experts and experienced BMW engine designers, as well as Daimler-Benz engine engineers, resulted in the development of a new helical spring element (see photograph) in DADS.

This new spring element combines numerical efficiency and accurate modeling of coil clash and mass effects at high engine speeds. DADS flexible body methods, which combine FEA results with rigid body dynamics, were used to model the spring as a flexible body. Using the new modeling element, engineers confirmed that simulation results and experimental test data correlated.

"DADS provides a detailed simulation of valve spring behavior, which helps meet our goal of building the best engines possible,'' says Dr. Rolf Schlachter, senior engineer at BMW AG. "Ongoing technology transfer between CADSI and BMW AG is resulting in the development of intelligent selection of flexible modes to collect the spring parametric data. The user-friendly interface makes DADS a practical tool for simulation engineers."

And, says BMW, this joint development is also resulting in the expanded use of dynamic simulation throughout its complete engine development process. DADS analysis results help engineers meet requirements for efficiency, low emission levels, shortened development time, and reduced manufacturing costs.