Abstract

Modern urban buses with low floor and considerable over hung design are known to cause poor ride quality and excessive pavement loads. Such performance is partly due to the present status of urban roads and their rapid deterioration. On the other hand, variations in the dynamic tire forces of such vehicles are known to be a cause for acceleration of road damage and are strongly related to vibration modes of the vehicle associated with vertical and pitch motion of the sprung and unsprung masses. The high levels of tire induced road damage has prompted a growing demand for the design of heavy vehicles that are both passenger- and road-friendly. In this investigation, a six degrees-of-freedom pitch plane model of a modern urban bus is developed to study the ride and axle load performance under deterministic as well as measured urban road excitations. The validity of the model is demonstrated by comparing the response characteristics with available measured data. The ride quality of the vehicle is assessed in relation to the proposed guidelines upon applying the recommended frequency-weighting filters. An extensive list of performance measures for dynamic wheel loads and their pavement damage potentials are discussed and used for the assessment of road-friendliness performance. The influence of variations in design and operating variables on the ride performance of the vehicle is investigated through a comprehensive parametric study. The variations in operating conditions include the speed, road roughness, tire inflation pressure and bus load. The parametric study on design variables includes the variations in suspension dampers and springs, geometry of the suspension and wheel base. The results of the study are discussed to highlight the contributions of these parameters on the ride quality and pavement load, and to identify most desirable design and operating conditions