Objective evaluation of gearshift process of agricultural tractors

In the last 20 years, manufacturers have invested in continuously variable transmissions (CVTs) for agricultural tractors, since farmers have demanded more easy-to-use transmissions to increase comfort and driveability. Recently, stepped transmissions have been of interest due to their greater efficiency compared to continuously variable transmissions. To fully compete with CVTs, stepped transmissions must be fully automated and properly handle the operator's comfort during gearshifts. This paper aims to define a test procedure and data analysis method for evaluating the gearshift quality of transmissions for agricultural tractors. The procedure is composed of two tests and aims to reproduce the typical manoeuvres that occur during farming, such as accelerating and shuttling. This method was applied to 14 tractors with different transmissions and engine peak power. On each tractor, an inertial measuring unit and a CAN-Logger were installed to record vehicle and powertrain operating conditions. From the recorded data, a set of metrics was calculated to objectively quantify the impact of gearshift. These metrics were combined to obtain an overall score, which allows for the ranking of tractors in terms of gearshift quality and its dependence on design parameters. Based on our metrics, CVTs outperform stepped transmissions due to their ability to combine high performance with comfort measures. The approach outlined in this study enables manufacturers to quickly spot the weak points of the gearshift behaviour of a tractor so that they can address specific issues and increase operator satisfaction and the overall quality of their tractors.