Masters Theses

Junyu Li

Date of Award

8-2001

Degree Type

Thesis

Degree Name

Master of Science

Major

Mechanical Engineering

Major Professor

J. A. M. Boulet

Committee Members

Hamel, Iannelli

Abstract

In this thesis, a new three-dimensional rigid body model for liftoff of the wheels of a heavy commercial truck trailer in steady, circular turning is investigated. For a turn of specified radius, the model predicts two liftoff properties: the speed and roll angle at which liftoff would occur.

Work in this thesis can be divided into two parts. (1) Truck trailer liftoff equations are derived, shown to be internally consistent and used to investigate the importance of several parameters that affect the liftoff properties and roll stability of trailers. Present efforts focus on the modeling of a trailer in a steady maneuver. (2) The model is used on a trailer with one cargo hung from the ceiling of the cargo box. Many factors that influence the liftoff and roll stability of the trailer are discussed. The influence of these parameters on the angular displacement of the cargo itself is also discussed.

The study finds that the influence of trailer weight, path radius, trailer track width, trailer roll stiffness, center of gravity height and lateral location on the liftoff properties and roll stability (resistance to rollover) is high. Also, the influence of roll center height and fore-aft center of gravity location are moderate while the influence of the fifth-wheel height is low. If a change in the system increases either the speed at liftoff or the roll angle of the cargo box at liftoff, we consider that the liftoff properties and roll stability have been improved. The study shows that roll stability and liftoff properties are improved by increasing path radius, trailer track width, roll center height, fifth-wheel height, trailer suspension roll stiffness, or center of gravity longitudinal distance from the fifth-wheel, and by decreasing the center of gravity height or lateral center of gravity offset.

The model can be used to determine the angular displacement of moving cargos in the cargo box and their influence on the liftoff properties and roll stability of the trailer. A simple example of the usage of the model is given in this thesis. When there is one cargo suspended from the ceiling of the cargo box, increasing path radius or longitudinal distance from the fifth-wheel to the suspension point of the cargo, and decreasing the cargo box height or lateral position of the cargo's suspension point can all improve the liftoff properties and roll stability of the trailer. The model also predicts angular displacement of the hanging cargo.

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