An articulated machine, such as a motor grader, is a versatile apparatus for road work, ditch work, site preparation and other surface contouring and finishing tasks. The versatility of a motor grader is provided in large part by its multiple course setting and course change options. In particular, a motor grader typically includes a steering function implemented via steerable ground engaging wheels while also allowing some degree of course correction or steering via lateral arching or articulation of the machine frame. In this manner, for example, a motor grader may be steered and articulated to follow a curve without driving the rear wheels across the area inside the curve and disturbing the just graded area.
As should be recognized from the above, motor graders, and other articulated machines, are complex pieces of heavy machinery and are operatively complex. Controlling a motor grader includes numerous hand-operated controls to steer the front wheels, position the blade, control articulation, control auxiliary devices such as rippers and plows, and various displays for monitoring machine conditions and/or functions. Control of a motor grader requires highly skilled and focused operators to position the blade while controlling steering.
Automatic articulation control can help relieve an operator of an articulated machine from the moment-to-moment monitoring of articulation while making turns but for reasons including safety, such system may be disengaged under different conditions, such as when the speed of a vehicle exceeds a threshold speed. For example, U.S. Patent Application Publication 2011/0035109 (“Steering System with Automated Articulation Control”) describes a system wherein machine articulation is automatically controlled based on machine steering. The system of the '109 publication adjusts machine articulation to follow steering angles and commands, thereby maintaining tracking between the front and rear wheels of the machine. Automated articulation be automatically disengaged when the ground speed of the machine exceeds a limit.
However, there may be situations in which the automatic disengagement of the automated articulation control function may leave the machine in an undesirable articulated position, such as when increasing speed past the limit or other condition while executing a turn. Sudden reactivation of the automatic articulation control function when the actual and desired steering angle are not aligned may cause a rapid and perhaps unexpected change in articulation angle.