Steering control system for articulated vehicle

Abstract

A steering system for an articulated vehicle has pivotal wheel steering such as front axle wagon-wheel steering, a hydraulic actuator for pivoting the axle with respect to the vehicle, and a pair of hydraulic actuators for causing articulation of the vehicle. The system includes sensors for providing signals dependent on the degree of front wheel pivot relative to the vehicle and the degree of articulation of the vehicle. These signals are detected by a microprocessor controller which in turn controls the sequence of actuation of the axle and articulation hydraulic actuators. The actuators are operated sequentially so that small directional changes of the vehicles are achieved solely through pivoting of the axle. Operation of the axle and articulation actuators is controlled by a manual steering unit having a conventional hydraulic steering valve, with sequencing being provided through manipulation of a hydraulic fluid diverter valve. The timing and duration of the diverter valve actuation is controlled by the controller as a function of various dynamic turning parameters of the vehicle and the response time of the valve. A make-up valve system is also preferably included for automatically returning the articulation cylinders to their home position under certain conditions as the vehicle operates in a pivotable wheel steering mode.