Integrated Hydro-Mechanical Simulation of a Cam-Rocker-Unit Injector System to Address Noise and Vibration Issues 2006-01-0887

Changing and more stringent emissions norms and fuel economy requirements often call for modifications in the fuel injection system of a Diesel engine. There exists a strong interaction between the injection system hydraulics and the dynamics of mechanical components within the unit injector and the camshaft-driven mechanical system used to pressurize it. Hence, accurate predictive analysis of design issues or evaluation of design changes requires highly coupled and integrated hydro-mechanical simulations, combining analysis of fuel injection hydraulics and the dynamics of all mechanical parts, including the cam-drive system.

This paper presents an application of such an integrated model to the study and alleviation of an observed increase in mechanical vibration and related noise levels associated with a proposed design change in unit injectors and valve-train of a 6-cylinder truck diesel engine. The design change was driven by non-mechanical, i.e. combustion and emissions considerations. Increased vibration levels, which occurred across the operating speed range, were thought to be related to the interactions of fuel pressure dynamics and the dynamics of the injector and its drive-train, i.e. the injector rocker arm and the overhead camshaft shared with the valve-train.

Using the coupled, dynamic model of a single unit injector and its drive-train (rigid camshaft segment, cam and rocker arm), first a verification and physical explanation of the observed vibration increase were sought and obtained. The model was shown to match the behavior of the mechanically-driven unit injector and predict high vibration levels across the operating speed range. Once a satisfactory agreement between experimental and simulation results was reached, the model was further exercised in search of solutions to “re-optimize” the overall design, i.e. reduce mechanical vibration levels while preserving the essential elements of the proposed unit injector design. Several such design changes were identified and their contributions to a reduction in vibration levels were individually quantified.