Automatic diagnosis of engine of agricultural tractors: The BED experiment

The test bed for evaluation and diagnosis (BED) is a simple device designed to perform a quick and automatic diagnosis of the engine of agricultural tractors. It compares the present performance of a tractor to the OECD test. Firstly, a test of the tractor is performed which measures the power take-off speed, the engine torque, the fuel consumption and several environmental variables. The performance curves of the tractor are then plotted against their official reference curves. A rule-based system (Scorpio) compares the present performance to the reference, analyses the differences and suggests which parts may be responsible for the lack of performance. A statistical validation of the expert system was carried out using a database of tests collected over 10 years. The output of the system was compared to the expert decision, which was available for more than a thousand records. This validation of the BED was confirmed by an in situ validation protocol conducted by a tractor repairer. The basic principles of the BED and the results of the validation studies are described.