Abstract: An electro hydraulic system for controlling a hydraulic function includes a pump and a reservoir connected to the function through a manually operable, electro-hydraulic control valve. The valve is positionable to either side of a neutral ports blocked position and may be held to one side by the engaging of a spring loaded detent. The detent is disengaged by an electrical signal produced by a comparator when a preset, operator-controlled, limiting signal is equalled by a feed back sensor signal proportional to the output of the function. The system will allow initial activation of the valve to provide continuous operation of the function until the limiting input is reached at which time the function will be stopped. The system further provides manual override of the electrical control system to permit operation of the valve when the feedback signal is greater than the limiting input signal.

Abstract: An articulated, four-wheel drive tree harvesting machine includes a front frame section upon which a felling boom assembly, a delimber assembly, and a feed assembly are mounted. The felling boom assembly is operable for severing a tree and lowering it into a generally horizontal position. The tree is released into the opened knives of the delimber assembly which close to encircle the trunk and into the opened feed rolls of the feed assembly which close to engage the trunk. The feed rolls are then rotatably driven to draw the tree trunk through the knives while the felling boom may be operated to sever and position a second tree. Two solenoid-operated valves control the operation of hydraulic cylinders which respectively open and close the delimber knives and open and close the feed rolls. Two other solenoid operated valves respectively control the operation of a clutch and a transmission to drive the feed rolls in a forward or reverse direction of rotation.