Roll Angular Velocity and Lateral Overturning Tendency of a Small-Tracked Forestry Tractor Under No-Sideslip Dynamic Driving Conditions

In this study, a driving test was conducted using a small-tracked forestry tractor with a scale of 1/11 in the shape of an actual tractor to assess safety under dynamic conditions. The driving conditions resulting in lateral overturning were derived. Additionally, an angular velocity sensor was used to analyze the variation in roll angular velocity with driving conditions. Driving condition variables comprised obstacle height, ground slope angle, and driving speed. Obstacle height had five levels between 0 and 40 mm in 10 mm intervals, and ground slope angle had 11 levels at 5° intervals from 0° to 50°. Driving speed had three levels: 0.07, 0.11, and 0.13 m/s. The ground slope angle resulting in lateral overturning in the driving scenario was lower than that in non-driving under all conditions. Roll angular velocity increased as obstacle height and tractor driving speed increased. However, ground slope angle did not significantly affect angular velocity. Roll angular velocity at the moment of lateral overturning was about 90 deg/s regardless of driving conditions. A certain critical angular velocity was found to induce lateral overturning, and adjusting the driving method such as reducing driving speed and making turns when the roll angular velocity of the tractor approached the critical value improved safety. However, the quantitative results from the small tractor cannot be directly applied to full-size tractors. Although numerical values may differ, this study focused on capturing the overall trends in lateral overturning considering various driving conditions. Future studies can improve the practical applicability of these findings by determining the critical angular velocity of various full-size tractors.