No abstract

No abstract

The United States Army began developing Unmanned Ground Vehicles (UGV) in the early 1900’s. Concurrently, researchers developed and enhanced passenger and commercial ground vehicles. Although significant progress has been made for improving vehicle mobility for all ground vehicles throughout the past century, mobility has lacked a concise mutually agreed definition and analytical standardized criteria. The implementations of improved technologies, such as vehicle traction control, stability control, and torque vectoring systems require researchers to take a step back and reevaluate mobility criteria. UGVs require additional enhancement to include on-line mobility estimation since the vehicle cannot predict nor anticipate terrain conditions on their own prior to the vehicle traversing those conditions. This paper analyzes methodologies researchers have employed for defining and improving vehicle mobility of wheeled vehicles. The analysis is done from a view point of concurrent mobility methodologies’ enhancement and applicability to wheeled UGVs. This analysis is then used to develop off-line and on-line analytical criterion for mobility estimation, and to derive a strategy which can be applied to wheeled vehicles, both manned and unmanned. The on-line mobility estimation enables the UGV to make control changes as the events occur rather than after the event, causing the vehicle to then optimize its reaction to regain control.

For military all-terrain vehicles, there is a need to radically increase tactical and operational mobility through new modalities by fundamentally improving vehicle terrain control. By characterizing the tire relaxation length and time constants for lateral and longitudinal dynamic changes, mobility control can be enhanced to accommodate agile tire dynamics. This paper analyzes the transient period of the tire reaction force development process, which is characterized by the relaxation length, for the purpose of agile tire dynamics control as a pre-emptive, fast and exact response of a tire to dynamic changes of its interaction with terrain. In this regards, a comprehensive literature review was undertaken and the tire relaxation length was analyzed for different types of vehicles and their operational velocities. The time relaxation constants, which are derived from the relaxation length, are determined and analyzed based on the data gathered in technical literature. Based on the analysis, reference magnitudes of the time relaxation constants are proposed to be used in agile tire dynamics control algorithm and hardware developments of military all-terrain vehicles.

No abstract