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The purpose of this paper is to present the results of an experiment to determine surface roughness effects, as measured by a response meter, on vehicle suspension. The results suggest that accelerated vehicle suspension fatigue begins to occur on road surfaces with measured road roughnesses less than 2.5 on a Present Serviceability Index (PSI) scale (State of Pennsylvania conversion), and greatly accelerated vehicle suspension fatigue occurs at PSIs less than 1.0.
The basis of vehicle suspension design is to absorb road load inputs to protect the vehicle and driver from variations in the traveled surface. The load input into the suspension depends on the roughness of the surface and the vehicular weight and speed over the surface. Pavement engineers often use PSI to classify pavement wear on the individual roads in their jurisdiction. This paper examines field data from 25 sites ranging in PSI from 0 to 2.5. Using two different instrumented vehicles, load input was measured on each vehicle for eight road load carrying components. The data was analyzed for approximate fatigue response and then compared to the site PSI. The results suggest that for most measured suspension components, fatigue response is affected for PSIs between 2.5 and 1.0 and greatly accelerated for PSIs less than 1.0.
Vehicle manufacturers should be aware of their products' usage in the real world and design their vehicles to be able to accept the appropriate amount of road load input from roads with 2.5 ratings or less. Also, when determining maintenance and resurfacing schedules, road planners should understand at what point the customer may experience significant vehicle damage.
Mays meter, rainflow counting, road load inputs, response-type measuring systems, road roughness, roughness, vehicle fatigue, vehicle response
Senior engineer, Chrysler Corporation, Chelsea, MI
Test and Development engineer, Chrysler Corporation, Chelsea, MI