A tractor is vehicle specifically designed to deliver a high tractive effort at slow speeds for carrying out various agriculture operations like ploughing, rotavation etc. using implement. Hydraulic system is a key feature which connects these implements with the tractor. It controls the position and draft of the implement depending upon the type of crop, farming stage, implement type and soil conditions. These variations induces extreme range of load on the hydraulic system, thus making it challenging to design these components. Bell crank assembly is one of the main components of hydraulic system which controls the draft (thus, the loads experienced by tractor) through load sensing mechanism. Often bell crank assembly failures are reported from field due to uneven soil hardness and presence of rocks.
This paper studies one of such bell crank assembly failures in the field. The failure was reported after half life cycle of usage during agriculture Operation. Maximum load and fatigue cycle were identified as the main parameters in predicting the failure. Max loads were calculated based on earlier acquired load data and a fatigue duty cycle was prepared to capture the entire range of agricultural operations, implement types, soil types etc. The bell crank assembly was then analyzed for this duty cycle using CAE analysis. A finite element model was prepared and simulation was done in commercially available software with material and boundary nonlinearities. The simulation results were correlated with the experimental results to fine tune the FE model. Once the failure was captured accurately, design iterations were carried out to reduce the cumulative damage within acceptance limit. The final design was tested in lab for the above duty cycle and strain correlation was done with the simulation results. The test was passed successfully with good correlation between the CAE & lab results.