Abstract:
A tree skidder transport machine and method wherein the machine has a hydraulically operated boom assembly extending rearwardly of a chassis. The boom assembly includes a main boom and a stick boom which cooperate hydraulically to lift the bottom end of a tree, or tree bunch, near the butt, and drag it forwardly over a bogied pair of chassis support wheels. With the further cooperation of a hydraulically actuated heel boom, the tree or tree bunch is then rotated vertically in a counterclockwise direction to lift its top end off the ground and move the tree or tree bunch forwardly a sufficient distance to bring some of the weight of the tree or tree bunch onto the front wheels of the machine.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to timber harvesting machines. It relates particularly to a type of timber harvesting machine commonly referred to as a skidder. 
     BACKGROUND OF THE INVENTION 
     Skidder machines conventionally take the form of articulated frame, rubber-tire tractors. A front section supported by front drive wheels includes the engine and the operators&#39; cab. A rear section supported by rear drive wheels is connected to the front section on a vertical axis pivot so as to be articulatable relative to the front section. The front and rear wheels are driven by conventional drive trains from the engine through a gear box controlled by the operator. Steering is accomplished by varying the angular relationship between the front and rear sections with a hydraulic cylinder steering system 
     Timber Jack, Caterpillar and John Deere &amp; Co., as well as others, manufacture skidder machines of the aforedescribed nature. Caterpillar also manufactures track skidder machines, i.e., machines where continuous drive tracks replace the four wheels. 
     Regardless of whether the skidder machine is wheel or track driven, loggers have found skidders to be the most versatile and cost-effective way to bring in felled trees, terrain and other conditions permitting. A hydraulically controlled boom extending rearwardly from the rear section of the skidder machine grasps a tree or a bunch of trees at a lower end with a grapple or cable loop. The boom is actuated to raise that end of the bundled trees, for example, off the ground and hold them suspended in the air behind the rear wheels of the skidder machine while the machine drags or “skids” the trees out of the forest to waiting transport. 
     Conventional machines which are constructed and operate in the aforedescribed manner are versatile and cost-effective, as has been pointed out. However, because the trees are lifted by the grapple, for example, at their lower ends and carried behind the rear wheels, both the rear wheels and the tops of the bundled trees caused substantial ground disturbance. The weight of the lifted trees at their lower ends and the counter-weight effect of the machines front end cause the rear wheels to rut and shear soil as they exert traction. The tops of the trees dragged along the ground also cause substantial ground disturbance. In addition, the trees frequently suffer damage as they are skidded out of the logging area. 
     BRIEF SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an improved tree transport machine to replace conventional skidders. 
     Another object is to provide a tree transport machine which can transport trees from the logging site with minimal ground disturbance. 
     Still another object is to provide a tree transport machine which requires less tractive effort in transporting trees from a logging site than conventional transport skidders. 
     A further object is to provide a tree transport machine which delivers cleaner trees to their destinations, i.e., trees which have not been damaged by skidding. 
     Still a further object is to provide a tree transport machine wherein the lower ends of the trees are supported significantly ahead of the center line of the rear tires and the tops of the trees are partially or completely off the ground. 
     Yet a further object is to provide an improved method of transporting felled trees from the area where they are felled. 
     The foregoing and other objects are realized with a tree transport machine wherein the rear section of the machine is supported by a pair of wheels on each side. Each pair of wheels is mounted on a bogie which, in turn, is pivotally connected to the rear machine section. 
     In one embodiment of the invention, the wheels on each bogie are rubber-tire wheels. In another embodiment, each bogie may have a continuous track encircling the rubber tires. In either case, the rear machine section is supported on a relatively wide (fore-to-aft) footprint. 
     A hydraulically actuated boom assembly is mounted on the rear machine section. It includes a main boom extending upwardly from, and pivotally mounted on, the rear machine section at the front end of its chassis. A hydraulic actuator cylinder pivotally mounted on the chassis rearwardly of the main boom has its actuator piston pivotally connected to the boom to facilitate pivoting the main boom rearwardly and forwardly under the control of the operator. 
     Extending rearwardly from the main boom, and pivotally connected to its upper end, is a stick boom. The rear end of the stick has a grapple or cable suspended from its free end; the cable or grapple being readily connectable to a felled tree on the ground in a generally conventional manner. A hydraulic actuator cylinder intermediate the ends of the main boom has its actuator piston pivotally connected to the stick boom at a point rearwardly of its connection to the main boom to provide the stick boom with desired lifting force at its grapple or cable end. 
     According to the invention, a heel boom is also pivotally connected to the main boom and extends rearwardly beneath the stick boom. The heel boom is slightly more than one-half as long as the stick boom so that its free end is forward of the free end of the stick boom; about two-fifths of the distance between the stick boom&#39;s free end and the pivot of the stick boom. 
     An actuator cylinder for the heel boom is pivotally connected to the stick boom intermediate its ends. This actuator cylinder has its piston pivotally connected to the free end of the heel boom. Rigidly connected to the free end of the heel boom, and depending therefrom, is a tree-heeling fork. 
     In operation of the transport machine according to the method of the invention, the machine is maneuvered into a position where it is longitudinally aligned with and facing forwardly from the larger lower end of a felled tree or bunch of trees. The main boom and stick boom are moved to their rearwardly most inclined positions so that the grapple or cable can grasp the tree bunch (for example) about six feet from the lower end of the bunch. 
     The actuator cylinders for the main boom and stick boom are then actuated in coordinated fashion by the operator to raise the lower end of the tree bunch and drag it forwardly over the bogied rear section of the machine. When the lower end of the bunch has reached a point just forward of the centerline of the bogies, the actuator cylinder for the heel boom is energized to bring the free end of the tree heeling fork down perpendicular to, and into engagement with, the tree bunch adjacent its lower end. 
     At this point, the actuator cylinders for the main boom and the stick boom are actuated in coordinated fashion to pivot the main boom further forward and the heel boom further downward. The effect, according to the invention, is to pull the tree bunch forward so that its lower end is well forward of the bogied wheels and its top is raised off the ground. The tree bunch can then be moved out of the logging area with the tree tops lifted off the ground and a portion of the weight of the bunch also borne by the front wheels. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, including its construction and method of operation, is illustrated more or less diagrammatically in the drawings in which: 
     FIG. 1 is a side elevational view of a transport machine embodying features of the present invention pictured as it is about to begin to lift a bunch of felled trees into transport position; 
     FIG. 2 is a top plan view of the machine and bunch of trees seen in FIG. 1, in slightly smaller scale and with parts removed; 
     FIG. 3 is a side elevational view, similar to FIG. 1, showing the machine about half-way through its tree bunch lifting operation; 
     FIG. 4 is an enlarged side elevational view of the machine in the position seen in FIG. 3; and 
     FIG. 5 is a side elevational view, similar to FIGS. 1 and 3, showing the machine with the tree bunch lifted into transport position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, a felled tree transport skidder machine embodying features of the present invention is shown generally at  10 . The machine  10  includes a front section  11  supported by two rubber-tire front wheels  12  and a rear section  16  supported by a pair of two-wheel bogies  17 . Each bogy  17  includes two rubber-tire wheels  18 . As shown, it may also include a continuous track  19  which encircles both tires and rotates with the wheels  18 . 
     The front section  11  of the transport machine  10  includes a chassis  20  which contains a conventional engine  21  and an operator&#39;s cab  22 . The front section  11  is joined to the rear section  12  in a conventional manner for articulation about the pivot axis X. 
     The rear section  12  of the machine  10  includes a chassis  30 . Mounted on the chassis  30  is a boom assembly  31 . The boom assembly has a conventional grapple  32  suspended from its free end. In FIGS. 1 and 2, the grapple  32  is shown having just grappled a bunch B of felled trees. 
     The front wheels  12  and rear wheels  18  of the machine  10  are both driven by the engine  21  through a conventional gear box and drive train (not shown). The machine is steered in a conventional fashion by varying the angle between the articulated front section  11  and rear section  16  with hydraulic cylinders (not shown) controlled by the operator. Hydraulic power is supplied by a suitable pump set  35  driven from the engine  21  in a conventional manner. 
     The hydraulic pump set  35  also supplies power to the boom assembly  31 , which is hydraulically actuated in a manner hereinafter discussed. According to the invention, the boom assembly  31  operates in three stages to (1) lift the bottom end of the tree bunch B upwardly, and pull the bunch forwardly until it is over the center line of the bogied wheels  18 , (2) force the bottom end B 1  of the bunch B downwardly about the axis of the grapple  32  to raise the top end B 2  of the bunch off the ground and, simultaneously, (3) pull the tree bunch B forwardly so that the lower end B 1  is well in front of the centerline of the bogied wheels  18  (see FIG.  3 ). 
     Referring now particularly to enlarged FIG. 4, as well as FIGS. 1 and 2, the assembly  31  is seen to include a main boom  41  which is pivotally mounted on the chassis  30  of the rear section  16  at  42 . AS seen in FIG. 2, the main boom  41  comprises parralled boom arms, both of which are pivotally mounted on the chassis  30 . The main boom  41  is mounted for pivotal movement between a forwardmost position about 15° forward of vertical and a rearwardmost position about 75° rearward of vertical (see FIG.  1 ). 
     The travel of the main boom  41  is controlled by a hydraulic cylinder  44  pivotally connected at  45  to the chassis  30  in front of the pivot  42 . The cylinder piston  45  of the cylinder  44  is, in turn, pivotally connected to the main boom  41  at a position  47  displaced from the pivot  42 . 
     Pivotally connected to the free end of the main boom  41  at  48  is a stick boom  49 . As seen in FIG. 2, the stick boom  49  also comprises parralle boom arms, each of which is pivotally connected to a corresponding boom arm in the main boom  41 . The parralle boom arms of the stick boom  49  then converge and meet at a trailing free end. The stick boom  49  is mounted for pivotal movement relative to the main boom  41  from an angle of about 175° to the main boom (see FIG. 1) to an angle of about 60° to the main boom (see FIG.  5 ). 
     The travel of the stick boom  49  relative to the main boom  41  is controlled by a hydraulic cylinder  51  pivotally connected to the main boom  41  at  52 . The cylinder piston  53  of the cylinder  51  is, in turn, pivotally connected to the stick boom  49  at a position  54  displaced from the pivot  48 . 
     Suspended from the free end of the stick boom  49 , at  56 , is the conventional grapple  32 . The grapple  32 , or a cable, is used in a well-known manner to grasp the bundle B of felled trees during operation of the machine  10 . 
     Pivotally connected to the free end of the main boom  41 , on the same pivot  48  to which stick boom  49  is connected, is a heel boom  58 . As seen in FIG. 2, the heel boom  58  also comprises parralle boom arms. They are closer together than the parallel boom arms of the stick boom  49  so that the heel boom  58  is pivoted to the end of the main boom  41  between the stick boom  49  arms. The heel boom  58  is about three fourths the length of stick boom. Its position relative to the stick boom  49  is controlled by a hydraulic cylinder  59  pivoted at  61  to the stick boom. The piston  62  for the cylinder  59  is pivotally connected to the free end of the heel boom  58  at  63 . 
     Rigidly connected to the free end of the heel boom  58  is a tree heeling fork  66 . The fork  66  extends downwardly at an angle of approximately 45° to the longitudinal axis of the heel boom  58  so that when this boom is inclined downwardly, as seen in FIG. 5, the fork  66  is inclined forwardly from the vertical at an angle of only 5 °. 
     In operation, the machine  10  is maneuvered into the position shown in FIG.  1 . The boom assembly  31  is normally retracted into the position shown in FIG. 5 for this maneuvering. The cylinder  44  has been actuated to move the main boom  41  into its forwardmost position. The cylinder  51  has been actuated to move the stick boom  49  into a position displaced 60° from the main boom  41 . The position of the stick boom  58  at this point is a matter of choice. 
     With the machine  10  in position, the cylinder  44  is actuated to retract its piston  46  and pivot the boom  41  into the position shown in FIG.  1 . At the same time, the cylinder  51  is actuated to extend its piston  53  and move the stick boom  49  into the position also seen in FIG.  1 . The cylinder  59  is actuated to retract its piston  62  and pivot the heel boom  58  toward the stick boom  49  as far as it will travel. 
     The operator then uses the grapple  32  to grapple the tree bunch B at a location in the lower end B 1  of the bunch, about six feet from that butt end. After the grapple  32  is secured to the bunch B of trees, the cylinder  44  is actuated to drive the piston  46  forwardly and pivot the main boom  41  forwardly. Simultaneously, the cylinder  51  is actuated to retract its piston  53  until the stick boom  49  is positioned at an angle of 175° to the main boom  41 . In this operation, the felled tree bunch B is lifted at its lower end B 1 , and pulled forwardly into the position shown in FIGS. 3 and 4. 
     At this point, the lowermost end of the tree bunch B is over the centerline of the wheel bogies  17 . The top of the tree bunch B is resting on the ground. The heeling fork  66  is positioned over the end B 1 , of the tree bunch, about two feet from the butt of the bunch. The top end B 2  of the felled tree bunch B is resting on the ground. 
     The cylinder  59  for the heel boom  58  is then actuated to bring the heeling fork  66  down into engagement with the tree bunch B immediately adjacent the lower end B 1  and well in front of the point at which the grapple  32  secures the tree. This pivots the auxiliary boom  58  downwardly until it is substantially parallel to the stick boom  49  between the pivot  61  of the cylinder  59  and the pivot  56  where the grapple  32  is connected. 
     The operator then actuates the cylinder  44  to drive the main boom  41  forwardly. Simultaneously, the cylinder  51  is actuated to pull the stick boom  49  downwardly. The effect is to pull the tree bunch B forwardly and, at the same time, press the butt of the bunch B downwardly. 
     As this takes place, the tree bunch B moves forwardly and rotates in a counterclockwise direction about the axis formed by the grapple pivot  56  point. Forward movement and rotation of the tree bunch B continues until the bunch has reached the position shown in FIG. 5, with the bunch disposed approximately parallel to the ground. The machine  10  can then transport the tree bunch B easily out of the logging area. 
     It will be seen, of course, that the top end B 2  of the tree bunch needn&#39;t be lifted completely off the ground to achieve many of the purposes of the invention. Merely relieving a substantial portion of its load bearing effect on the ground serves to improve transport results. 
     For purposes of illustration, the main boom  41  and stick boom  49  are shown in FIG. 2 with single hydraulic actuator cylinders between their respective boom arms. As readily understood by those skilled in the art, however, each boom arm would conventionally have an actuator. 
     While a preferred embodiment of the invention has been described, it should be understood that the invention is not so limited, and modifications may be made without departing from the invention. The scope of the invention is defined by the appended claims, and all devices that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.