An active long-travel, two performance loop control suspension of an open-link locomotion module for off-road applications

An open-link locomotion module (OLLM) is an autonomous energy self-sufficient locomotion setup for designing ground wheeled vehicles of a given configuration that includes drive/driven and steered/non-steered wheels with individual suspension and brake systems. Off-road applications include both trucks and trailers. The paper concentrates on the module's electro-hydraulic suspension design and presents results of analytical and experimental studies of a trailer with four driven (no wheel torque applied) open-link locomotion modules. On highly non-even terrain, the suspension design provides the sprung mass with sufficient vibration protection at low level of normal oscillations, enhanced damping and stabilized angular movements. This is achieved by the introduction of two control loops: (i) a fast-acting loop to control the damping of the normal displacements; and (ii) a slow-acting control loop for varying the pressure and counter-pressure in the suspension system. Thus, two separate but coordinated controls were designed for both loops to act under small (less than ±7 degrees) and big (larger than ±7 degrees) pitch and roll angles of a vehicle designed with a set of the modules. The control actions in both loops of each module are distributed among the trailer's modules through three control channels: one channel to damp normal oscillations of each module and another two channels to stabilize the pitch and roll angles. This paper presents details on the loop controls and the channels and shows the ride efficiency of the suspension system in the 0.5-10 Hz frequency range of the sprung mass vibrations; some details on potential break-down (bottoming) of the suspension prototype are provided based on experimental study of a newly designed trailer with four open-link locomotion modules. Many other suspension design problems (including suspension bandwidth, power requirements, etc.) are not in the scope of the paper.