Analysis and design of an automatic motion inverter

In this paper, the design of an automatic motioninverter control system for agricultural tractors has been discussed. The objective of this system is to perform a fully automatic symmetric motion inversion (e.g., from a forward speed of 10 km/h to a reverse speed of -10 km/h). The device used to control the inversion is electro-hydraulic reverser, constituted by two clutches, driven by a proportional electro-hydraulic valve (EVP) and a directional electro-hydraulic valve (EVD). The design of a motion inverter is a nontrivial task, since it is difficult to find a good compromise between speed (the inversion must be completed in a short time) and comfort (bumps and oscillations on the longitudinal speed must be minimized). All the subtasks of the inversion control systems are considered: The design of an inner loop for the control of the EVP current, the open-loop switching strategies, and the design of the outer control loop, which regulates the vehicle speed. The control strategies are experimentally validated, and satisfactory results are obtained.