Optimal criteria for durability test of stepped transmissions of agricultural tractors

Tractor manufacturers are constantly trying to reduce the time-to-market and production costs of their products. To achieve these goals, precise knowledge of the service demands, and reliable accelerated tests are necessary. To design an accelerated test, detailed knowledge of the service loads throughout the machine life is demanded. The measurement and the analysis of service loads is a non-trivial task, because loads are influenced by many factors: machine configuration; working conditions; and driver usage. Monitoring loads in all these conditions can be very expensive, especially if carried out with sample of machines equipped with non-embedded sensors. In this paper, a methodology to analyse loads on tractors transmissions acquired with embedded sensors is proposed and an optimal test schedule was calculated. The operating parameters of the transmissions of a fleet of 44 tractors were monitored over a year of usage. From the acquired data, load amplitude and frequency on each transmission component were calculated, and pseudo-damages under different failure modes were computed. Pseudo-damages were then statistically analysed, and a severe-damage profile was estimated. Using an optimisation technique, an accelerated test schedule is determined. The analysis showed that the test schedule should be set to maximise the torque applied to each component. Moreover, not all the gear ratios need necessarily to be tested to test all the gear-wheels in the transmission. The calculation of the test schedule with optimisation solvers permits to quickly design tests for transmissions.