An Analytical Model of an Agricultural Tractor Crossing a Step Obstacle

摘要

Ride and operator comfort are a major concern of off road vehicle design. The aim of this paper is to define, verify and evaluate a simple analytical model of a Case MX110 crossing a step obstacle. The basis of vehicle vibration and the relevant literature on tyre characteristics, tyre modelling and vehicle modelling are briefly reviewed. The vibration behaviour of a simple two-degree of freedom unsuspended vehicle as it rolls over a single input step is modelled using a point contact tyre model. Rolling tyre characteristics were determined from measurements on the tractor, compared with previous measurements and mathematically evaluated. Measured data showed a high level of inaccuracy in the model prediction when the wheel hits the step. A refined vehicle model is proposed where a rigid tread band tyre model replaces the point contact model. Prediction made using the rigid tread band tyre model gives root mean squared (RMS) acceleration within 20% of that measured at the front axle and acceleration within 9% of that measured at the rear axle. The paper gives details of the analytical models and the experimental data collected. Evaluation relates the models and results to comparable published models and data and also considers the limitations and scope of the models.