Application of Three-Port Motors in Hydrostatic Transmission Architectures for 4WD Vehicles

Hydrostatic transmission architectures for the locomotion of 4WD vehicles must provide proper traction capability - i.e. adequate pull force and gradeability - and synchronization, i.e. a set of rotational speed of wheels, adapted to the maneuver being performed. Focusing on a typical machine layout with four motor-wheels, the most common layout is the parallel connection of the four hydraulic motors, which is extremely vulnerable to asymmetrical losses of adherence, unless dedicated control subsystems be added to the transmission. The perfectly opposite solution is the series connection of four motor-wheels, which ensure the synchronization of wheel velocities, but at the cost of a considerably higher working pressure in the circuit, less efficient operation of the first motors in the chain and non-optimal characteristics for cornering maneuvers. A patented mixed series/parallel architecture - based on compound three-port motors and including only hydraulic components - is capable of inherently compensating adherence unbalance, while mitigating the typical drawbacks of a pure series connection. The present work provides a preliminary investigation, through numerical simulation, of this lattermost architecture, which is appealing in all applications where a strong use of electronics is not advisable.