Analysis and design of an automatic motion inverter

In this paper, the design of an automatic motion-inverter 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.