Dynamic modelling and stability analysis of articulated frame steer vehicles

The stability analysis of articulated frame steer vehicle models is presented. To reveal the relationship between the 'oversteer' and 'jack-knife' motion modes based on a 2 degree of freedom (DOF) and 3 DOF vehicle models, respectively, the results derived from these models are investigated and compared. To identify the effects of design variables on the lateral stability of the vehicle, a more realistic model with a hydraulic rotary valve and dynamic tyre models is generated on the basis of the 3 DOF model and the results derived from these models are examined and compared. Similar to traditional articulated vehicles, the jack-knife and 'snaking' modes were identified from practical operations of the articulated frame steer vehicles. Results demonstrate that, with the decrease of the angular spring (representing the hydraulic cylinder between the front and rear sections of the vehicle) stiffness coefficient, the oversteer mode evolves into the jack-knife mode. Compared with the static tyre model, the effects of dynamic transient lateral tyre force degrades the stability of the vehicle over the lower speed range. Results also illustrate that, with the fluid leakage either in the rotary valve or in the hydraulic cylinder, the stability of the oversteer mode dominated motion degrades. On the contrary, in the case of snaking mode dominated motion, the introduction of the fluid leakage will improve the stability of the vehicles.