A Modular Software-Component Framework for the Development of Distributed Electronic Control Systems for Agricultural Tractors

Modern development of electronic control systems for agricultural tractors relies on model-based design of the control software and extensive virtual testing in simulation environments, before the final field tests on the actual machines. After the definition of requirements and specifications, each step of the typical development and validation flow, which includes model-, software- and hardware-in-the-loop (MIL, SIL, HIL) simulations, addresses different specific levels of detail in the control system while sharing the same top-level requirements in terms of desired machine behavior, thus making toolchain modularity and reusability paramount to optimize the whole development effort. A further level of complexity is added by distributed architectures, where multiple electronic units (ECUs) coordinate their operation via communication over a vehicle network, requiring proper verification of the exchange of signals conveying requests, feedbacks and status information. The present work focuses on a two-unit subsystem controlling the driveline in a class of tractors equipped with a CVT transmission, connected via CAN bus network. Dedicated verification modules have been implemented in the Matlab/Simulink/Stateflow environment, which monitor the relevant physical variables in the system (e.g. clutch pressures) and the message exchange between the two units (e.g. gear request and feedback). The CAN Watcher module internally implements a "reverse control logic", directly derived from the design requirements (i.e. independently of the actual control code implementation, for proper development-validation separation) to check that the overall system behavior be coherent with the maneuver being executed; CVT Performer instead dynamically tests the compliance to performance requirements (e.g. vehicle velocity profile). Each module can seamlessly be deployed as an independent software component in MIL, SIL and HIL environments and on a (dedicated) ECU for on-field online diagnostic.