| 20110132681 | Steering Control System Combining Electro-Hydraulic And Manually-Actuated Pilot Pressure Control Valves For Safe Operation - A steering control system for directing fluid to steering actuators on a machine include a set of right and left manually-operated pilot pressure fluid control valves and a set of right and left electro-hydraulic (EH) pilot pressure fluid control valves, with both sets being coupled to a main steering control valve for controlling movement of the latter to effect operation of the steering actuators. An electronic control unit (ECU) includes a computer and a memory and receives signals representative of various operating parameters of the control system and of the vehicle ground speed and operates to control the EH pilot pressure control valves and a set of right and left solenoid-operated valves such that only flow from the set of manually-operated valves is connected for operating the main steering control valve to effect a least aggressive steering mode when the vehicle speed is indicative of road travel, and for also actuating the EH pilot pressure control valves for effecting a more aggressive steering mode when the vehicle speed is low indicating off-road travel. EH valve failure results in the control system defaulting to that for effecting the least aggressive steering mode, while failure of one or both of the manually-controlled valves results in the EH control valves being activated to provide that pilot pressure called for by the manually-operated valve. | 06-09-2011 |
