Lateral Stability Performance of Articulated Narrow-Track Tractors

Bruno Franceschetti,Enrico Capacci,Valda Rondelli

doi:10.3390/agronomy11122512

Abstract

A tractor losing lateral stability starts to rollover. It is a matter of fact that tractor lateral rollover accidents are one of the most frequent causes of death and injuries for farmers. Consequently, tractors are fitted with a specific protective structure to minimize the consequences for the driver during the rollover (ROPS). The narrow-track tractor, designed to operate in vineyards and orchards, is a tractor category with a very narrow track width and the risk of rollover is higher. The aim of the study was to evaluate the compact narrow-track tractor types commercially available, designed to mount a cantilever engine in the forward position with effects on the Center of Gravity (CoG) because more than 50% of the tractor weight is loaded on the front axle, and, specifically, the articulated narrow-track tractors where the stability is affected by the pivot point connecting the two tractor bodies. As a consequence of the typical tractor design of articulated tractors, during the steering action the line passing through the front and rear tire contact points on the ground changes, influencing the tractor’s stability. The approach of the research was based on reproducing the lateral stability tractor condition by developing a kinematic model, with the goal to virtually simulate the tractor behavior and to calculate the lateral stability angle for articulated tractors. The innovative contribution of this paper was the tractor articulation joint modeling, assuming a virtual pivot point to reproduce two relatives’ rotations between the front and rear bodies of the tractor: vertical (yaw angle) and longitudinal (roll angle) rotations. The lowest value of the stability angle was 39.3°, measured at −35° yaw angle. The model at the tractor design stage will allow adjusting of the tractor parameters to improve the lateral stability performance.

Highlights

The tractor with a fixed chassis is typically a front steering wheel tractor designed with the pivot point located in the mid-point of the front axle and with more than 50% of the tractor’s weight on the rear axle (Figure 1a)
The model was used to examine the behavior of the tractor to variable inputs of the yaw angle to mimic the steering action behavior
The lateral stability angles are theoretically calculated considering the rotation of the tractor with respect to a line passing through the contact points of the tires on the ground

Summary

Introduction

Tractor overturning accidents on slopes have serious consequences for the farmer [1]. Studies indicate that over 80% of tractor accidents are sideways overturns [2]. Studies have been conducted to determine the factors influencing tractor stability on sloped fields [5,6]. The tractor stability issue on slopes was studied for a two-wheel drive tractor [8], concluding that the loss of wheel/ground adhesion, rather than the likelihood of overturning, limits the slopes on which most combinations can safely operate. Grecenko [9] made a state-of-the-art report about the operation on steep slopes, declaring the tire–soil interaction under the effect of a lateral force affects the traction conditions on sloping land with grass cover, and it must be properly analysed to evaluate the respective coefficients of grip. The implement CoG should be behind its axle for better stability [10]

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Conclusion