Modeling Dynamic Instability of Off-Highway Mining Dump Trucks

Open Access
Author:
Papavizas, Nicholas Carroll
Graduate Program:
Mechanical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 20, 2017
Committee Members:
  • Christopher Rahn, Thesis Advisor
  • Karen Ann Thole, Committee Member
Keywords:
  • Haul Trucks
  • Off-Highway Vehicles
  • Vibrations
  • Dynamic Instability
  • Mining Trucks
  • Vehicle Dynamics
  • Stability
  • Power Hop
  • OHVs
Abstract:
In this research, a three-degree-of-freedom (3-DOF) mathematical model is developed to predict the onset of unstable pitch/bounce-type vibrations in heavy, off-highway, mining haul trucks. This unstable vibration phenomenon can be described as an instance of “power hop”, a type of dynamic instability also seen in agricultural tractors, wheeled construction vehicles, and other off-highway vehicles (OHVs). A model that can adequately predict dynamic instability is a necessary first step in developing controls solutions that might be able to mitigate or even prevent unstable motion from occurring. The 3-DOF model describes a rear-wheel-drive (RWD) mining haul truck operating on a non-deformable, sloped surface. Analytical stability criteria are derived through closed-form eigenvalue analysis of the equations of motion while neglecting all damping terms. Numerical stability analysis studies parameter sensitivity for a representative haul truck with a 250 ton payload capacity in two payload scenarios: operation at empty vehicle weight (EVW) and operation at 100% payload capacity, or gross vehicle weight (GVW). Results show that the 3-DOF predicts dynamic instability. By utilizing a stability margin, the results further show that there are numerous different operating point configurations that could potentially lead to dynamic instability. Of the 33 million cases tested in each of the two different payload scenarios, 21% are deemed potentially unstable for the empty truck and 38% are deemed potentially unstable for the loaded truck. Furthermore, potentially unstable cases exist over the full range of parameters simulated. The analytical stability criteria derived from the undamped equations of motion do not always correlate with the numerical eigenvalue analysis of the full set of equations of motion that include all damping terms. Instability is shown to be heavily dependent on road grade, tire stiffness and damping properties, the location of the vehicle’s center of gravity, and forward travel speed. The model mainly predicts instability on severe road grades and at high speeds. A result not seen in previous studies of power hop in agricultural tractors is the prediction of dynamic instability when a vehicle travels downhill. While instability on uphill grades primarily occurs when the rear axle is stiffer than the front axle, the opposite is observed on downhill grades. Increased tire damping is shown to reduce the likelihood of instability in both loading scenarios and on all grades. Like tire stiffness, longitudinal center of gravity location also plays a role in whether the truck is more likely to become unstable on positive or negative road grades.