Federal-Mogul Powertrain has developed a simplified transient dynamic simulation model of valve closing action in order to predict dynamic loading on engine valves. By improving the accuracy of calculated deformation and stress under load, the technique enables valve fatigue life to be estimated more reliably and helps to ensure optimum material selection from the early stages of a new engine design.
In the design of intake and exhaust valves for combustion engines, especially those with a high degree of forced induction by supercharging or turbocharging, particular attention is paid to the loading conditions during valve closing.
|Different detail geometry, such as a waisted stem or conical head form, has a major influence on the stress distribution. Source: Federal-Mogul. Click to enlarge.|
The valve drive system is often still under development as the valves are being designed for new engine projects, restricting valve manufacturers to using simplified simulation models which limit valve loading evaluation to the main parameters such as valve closing speed, valve spring return force and the clearance between valve stem and guide.
During the closing event, one side of the valve usually contacts the valve seat first, which can introduce heavy loading of the valve stem. The dynamic simulation model of the closing event, as developed and tested by Federal-Mogul Powertrain, enables precise calculation of these loads that in turn allows components to be configured optimally from the concept stage and life span to be determined more accurately.
As well as fatigue life calculations, the load values associated with valve closing derived from the transient dynamic FE simulation can also be used to evaluate and rank alternative valve designs, according to Dr. Guido Bayard, Director Technology Valves, Federal-Mogul Powertrain.
Different detail geometry, such as a stem undercut or conical underhead, has a major influence on the stress distribution. With our simplified FE simulation, we can quickly draw conclusions on maximum valve loading and likely fatigue failure, and make sound decisions on design and material at an early stage of development.—Dr. Guido Bayard
The results derived using the simulation model have been confirmed by practical testing on a valve test rig developed by Federal-Mogul Powertrain which enables actuation of a single valve and the evaluation of individual closing events. The rig is better suited for the validation of the simulation model than a complete cylinder head for a number of reasons: it provides greater flexibility in the geometry that can be tested; it offers better controllability of the measurements and improved access for the measurement technology.