Hydraulic circuits for tree-harvesting knuckle booms

#1. Field of the Invention

#This invention relates to achieving more energy-efficient horizontal movement of a tree-working tool being carried on the end of a two-member knuckle boom. The term “tree-working tool” throughout this specification is intended to encompass, for example, saw heads and other devices (such as shear heads, for example), for cutting trees at the stump; tree delimbing heads; tree processing heads; wood-handling grapples for piling or loading trees or logs; and other such tools in the tree-harvesting industry.

#FIGS. 1A and 1B show an example of such a two-member knuckle boom, used in the tree harvesting industry for tree felling with a disc saw. It must often move a tree-harvesting implement in and out about 12 feet while not changing its height above the ground. It comprises a “hoist boom” having a proximal end pivoted to the machine base, and a “stick boom” having a proximal end pivoted to the distal end of the hoist boom. The disc saw is mounted on the distal end of the stick boom.

#The invention will now be described with reference to the accompanying drawings of the preferred and alternative embodiments, by way of example only. In the drawings:

#FIGS. 1A and 1B (both prior art) are side elevation views showing how prior art knuckle boom geometry is typically arranged and how the cylinders must alternately contract and extend to achieve tucking-in to reaching-out action. FIG. 1A shows the knuckle boom retracted, and FIG. 1B shows it extended.

#FIG. 2 (prior art) is a schematic diagram of typical prior art oil flow conduit connections between the major components.

#FIG. 1A shows a typical prior art configuration of a feller buncher for tree harvesting, in a retracted or “close reach” position. FIG. 1B shows it in an extended or “far reach” position. There is a machine base 1 supported above vehicle tracks 2. An operator's cab 3 is mounted on the machine base, and a diesel engine 4 is cantilevered on the back of the machine base. The knuckle boom assembly comprises a hoist boom 6, and a stick boom 7. The hoist boom is pivotally mounted relative to the machine base, for example at a hoist-base pivot pin 8 on a mounting bracket 9 secured to the machine base. The stick boom is pivotally connected to the distal end of the hoist boom at a hoist-stick pivot pin 15. The hoist boom is actuated by at least one hydraulic hoist cylinder 10 connected between the machine base and the hoist boom, at an effective angle relative to the hoist boom. The stick boom is actuated by at least one stick cylinder 11 connected between the hoist boom and the stick boom, at an effective angle relative to the stick boom. A tool, such as a feller-buncher head 12 (not shown in detail), is carried at the distal end of the stick boom. Commonly, the tool must also be kept level, and is therefore pivotally mounted about a horizontal axis at a tool-stick pivot pin 13 at the distal end of the stick boom. A tilt cylinder 14 is connected between the stick boom and the tool to control the angle of the tool relative to the stick boom. In FIGS. 1A and 1B, the tilt cylinder is shown pinned above the boom stick and acting on the head through a crank and link set (to achieve a larger tilt angle range). It is not significant to the invention whether such a crank linkage is used or not, or whether the cylinder is above the stick boom, or below it as shown for example in FIG. 3A.

#The invention generally has or can have the same components as in the prior art, but also has an additional hydraulic cylinder and different connection lines. It is helpful to compare the circuit drawings for the invention with typical prior art circuit drawings, to understand the differences in the hydraulic conduit connections which cause the improvement in operation.

#FIGS. 1A and 1B show how knuckle boom geometry is typically arranged in the prior art, and how the cylinders must alternately contract and extend to achieve reaching and tucking action. FIG. 2 is a schematic diagram of typical oil flow connections in the prior art. Each of the three cylinders has its two ports connected individually by separate hydraulic conduits to the two work ports on respective directional control valves. Thus the hoist cylinder 10 is operated by a hoist control lever 20 through a hoist directional control valve 21. The hydraulic conduit line 101 connects one of the work ports on valve 21 to the rod end port of the hoist cylinder, and conduit 102 connects the other work port of valve 21 to the base end port of the hoist cylinder 10.