Search Results

Coast down testing with full-scale vehicles on level and inclined roads offers an inexpensive approach to road load determination and, in particular, aerodynamic force evaluation, provided that drag component extractions can be accurately achieved under random instrumental disturbances and biased environmental conditions. Wind tunnel testing of large vehicles, especially truck/trailers, to establish their aerodynamic drag is costly and also may produce questionable results when the effects of the moving road, blockage, wake/diffuser interaction, and rotating tires are not properly simulated. On the road, testing is now conveniently and speedily carried out using GPS-based data acquisition and file storage on laptops, allowing instantaneous on-board data processing.

A geometrically accurate, three-dimensional finite element model of a Diesel engine exhaust valve and cylinder head assembly has been developed to analyze the effect of cylinder head interactions on exhaust valve stresses. Results indicate that a multi-lobed stress pattern occurs around the exhaust valve head due to cylinder head deformation, stiffness variations, and thermal asymmetry. Consequently, peak valve bending and hoop stresses from the three-dimensional model are 48% and 40% higher, respectively, than for the two-dimensional, axisymmetric model. These results indicate the degree of model complexity required for more accurate analyses of exhaust valve operating stresses.

Tire rolling resistance, in isolation from vehicle rolling losses including dissipation in the suspension and effects of the road surface, is a weakness in present procedures as they relate to fuel economy and pollution level testing. Work by Funfsinn and Korst, based on coastdown experiments and computer simulation, has shown that substantial and measurable increases in rolling losses occur for rough road surfaces. The present investigation used vehicle axle accelerations to experimentally examine various road surfaces. Correlation with computer simulations allowed the development of a deterministic road roughness model which is used to predict energy dissipation in both the tire and suspension as functions of roughness, tire pressure, and speed. Application of the methodology to coastdown techniques and comparison to the experimental results of Funfsinn results in good agreement and confirms rolling loss increases of up to 20 percent compared to ideal smooth roads.