Investigation into the vibration characteristics of agricultural wheeled tractor-implement system with hydro-pneumatic suspension on the front axle

Before predicting the vibration characteristics of a tractor/implement system with front axle hydro-pneumatic suspension, it is essential to develop a dynamic model. The nonlinear stiffness and damping calculation equations for hydro-pneumatic suspension are derived and the complete three dimensional multibody dynamic model of the wheeled tractor/implement system is presented in this paper. The construction of the model considers the effect of implement and passive rub cabin suspension as well as front axle hydro-pneumatic suspension together. The vibration responses and the corresponding power spectral densities (PSD) of driver seat, cabin, chassis and implement under different forward speed and field road conditions gathered from the simulation using the models are in good agreement with experimental results, demonstrating the effectiveness of the proposed model. A comparative investigation on the dynamic effects of a passive cabin suspension, implement and front axle hydro-pneumatic suspension under four cases was made. The effects of front axle suspension and the implement on the rollover limit chart for the tractor system were also studied. Simulation results showed that the front axle hydro-pneumatic suspension will deteriorate the ride comfort of drivers but will improve pitch and roll stability. Passive cabin suspension plays a more important role in improving the ride comfort of drivers than the front axle hydro-pneumatic suspension does, while compromising the pitch stability to some extent. The implement will raise the riding comfort of drivers and the pitch stability of tractors, but dramatically worsen the roll stability. The presence of the front axle suspension and the implement improves the minimum slope angle and reduces the maximum slope angle. Furthermore, the effect of the initial nitrogen volume, the pressure of energy accumulators, and the orifice diameter of the small throttle valves on the vibration characteristics of the tractor system with the large throttle valve closed or fully opened is also investigated.