Automatic Grapple Control System

Technical Field

The invention relates to hydraulic systems for controlling a grapple tong system associated with a work vehicle. More particularly, the invention relates to a hydraulic system for automatically, controllably urging the grapple tongs to a closed position in response to pressures in the hydraulic system.

Background Art

In the use of grapple tongs, it is desirable that pressure be maintained in the hydraulic circuit controlling the closing of the tongs in order to prevent a load carried by the tongs from falling or slipping.

Grapple tong implements are used to grasp and transport loads. These loads sometimes become loose within the grapple, owing to reorientation of the load or leakage of hydraulic fluid from the grapple tong system.

A typical example is the transportation of several logs from a harvesting site to a loading station. This transportation is generally over uneven ground, the logs are of ununiform configuration, and the work vehicle is generally not constructed to isolate the load from impacts during transportation. Shifting of the logs or leakage of hydraulic grapple fluid can cause the logs to fall from the grapple. The resultantly required re¬ loading of the logs in the grapple represents a waste of labor and time. It is, therefore, desirable to provide means for automatically and controllably main¬ taining the grapple in forcible engagement with the load during shifting of the load and/or hydraulic fluid leakage.

Disclosure of Invention

According to the present invention, means is provided for automatically, controllably passing fluid to a first hydraulic line from a second line in response to a preselected pressure in the first line and a higher pressure in the second line.

Brief Description of the Drawing

The drawing is a diagrammatic view of the hydraulic circuit of this invention connected to a grapple of a log transporting vehicle.

Best Mode for Carring Out the Invention

Referring to the drawing, a work vehicle 10 has first and second work systems 12, 14. In the example apparatus shown, the first work system 12 consists of grapple tongs 13 for holding and transporti logs 16 or other items, and the second work system 14 is an elevating system 15 for raising, lowering, and positioning the grapple 13. Opening and closing of the grapple 13 is controlled by a double-acting hydraulic cylinder 18 and the elevating system 15 has a pivotally movable boom 20 that is connected to a double-acting hydraulic cylinder 22 for controlling movement of the grapple 13 to preselected positions.

Such first and second work systems 12, 14 and their controlling hydraulic cylinders 18, 22 are well known in the art.

As is further known in the art, the cylinders 18, 22 each experience the greatest force when the syst is in a condition wherein the grapples are grasping a load and the load has been lifted off the ground. Therefore, the controlling hydraulic portions of each cylinder 18, 22 which will be subjected to the greater

hydraulic fluid pressure are the first or closing chamber 24 of the grapple cylinder 18 and the first or raising chamber 26 of the boom cylinder 22. Each of these first chambers 24, 26 have respective hydraulic lines 28, 30 which are associated with a pressurized fluid source and controlling valve 54.

Each hydraulic cylinder 18, 22 also has a respective opening chamber 25 and lowering chamber 27. A hydraulic line 29 is connected at one end to the opening chamber 25 and at the other end to controlling valve 55. A hydraulic line 31 is connected at one end to the lowering chamber 27 and at the other end to controlling valve 55.

First means 32 is provided for automatically and controllably passing fluid from the second to the first hydraulic lines 30, 28 in response to a pre¬ selected pressure in said first line 28 and a pressure in said second line 30 that is greater than the pressure in said first line 28. A first controlling valve 34 is connected to the first and second hydraulic lines 28, 30. The valve 34 is movable between a first position, shown by broken lines, at which the valve is open and fluid can pass from the second hydraulic line 30 to the first hydraulic line 28, and a second position (shown) at which the valve is closed. The valve 34 is continuously biased toward the second, or closed position and is movable toward the first or open position in response to pressure in the first hydraulic line 28. At a preselected pressure in line 28, the controlling valve 34 is in the first or open position.

As shown in the drawing, the continuous biasing means 40 can be a spring 42 urging the valve 34 toward the closed position. A pilot pressure line 44 is connected at one end to the first hydraulic

line 28 and at the other end to the controlling valve 34. Pressure from the first hydraulic line 28 urges against a spool of the first controlling valve 34 in opposition to force in the spool by the spring 42. By varying the spring force, the controlling valve 34 can be altered to open at different preselected pressures. A suggested opening pressure is greater than about 100 psi. The controlling valve 34 and biasing means 40 are well known in the art. Third means 45 for controlling the passage of fluid in a single direction from the second hydraul line 30, through the first controlling valve 34 and to the first hydraulic line 28 is provided. The third means 45 can be a check valve 48 positioned in a line 46 extending between the second hydraulic line 30 and the controlling valve 34, positioned in line 47 extending between the first controlling valve 34 and the first hydraulic line 28 (shown) or the check valve 48 can be an integral part of the controlling valve 34. Preferably, the check valve 48 is positione between the first controlling valve 34 and the first hydraulic line 28.

It is desirable to provide second means 49 for communicating the third and fourth hydraulic lines 29, 31. As shown in the drawing, second means 49 can be a second controlling valve 34' and check valve 48' which are stabstantially the same as the first controlling valve 34 and check valve 48. The valve 34' is movable between a first or open position and a second or closed position and is continuously biased toward the second or closed position (shown) by spring 42', and is movable toward the first or open position in response to pressure in the first hydraulic line 28. The check valve 48' controls the passage of fluid in a single direction from the third hydraulic line 29 to the fourth hydraulic line 31.

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The second means 4 can be a portion of the controlling valves 5*4,55 of the work vehicle 10. The first and second means 32, 49 can also be of other construction without departing from this invention. However, it is preferred that the first and second means 32, 4 be valves as shown in the drawing. Further, a make-up valve 50, as is known in the art, can be connected to the fourth hydraulic line 31-

Industrial Applicability

In the operation of the grapple tong system, the first and second hydraulic lines 28, 30 are in fluid communication when the first hydraulic line is at or above a preselected pressure and hydraulic fluid and/or pressure is free to pass from the second into the first line 30, 28. Therefore, the tendency of the grapple tongs 13 to loosen due to leakage in the hydraulic circuits or shifting of the load Iβ is substantially overcome. For example, when the grapple tongs are used for transporting logs 16, the first work system 12 is actuated for tightening the grapple tongs 13 about the logs 16. The resultant pressure in the first hy¬ draulic line 28 passes through the pilot pressure line 44, overcomes the spring force, and shifts the first controlling valve 34 from the closed position to the open position. With the load being securely held by the tongs, the second work system 14 is engaged to lift the load from the ground for transportation. Subsequent shifting of the logs within the grapple 13 or loss of hydraulic fluid in the first work system 12 can cause a loosening of the tongs 13 and result in a pressure' drop in the first hydraulic line 28. As the pressure drops, higher pressure in the second hydraulic line 30 is

available to the grapple tongs 13 through the controll valve 34 and check valve 48. The pressure thereafter equalizes in lines 28, 30 with a resultant tightening of the grapple tongs 34 and loss of the load is avoided.

As the grapple tongs 13 tighten, the resulta fluid flow in the third hydraulic line 29 from the opening chamber 18 exhausts to the fourth hydraulic line 31 through the second controlling valve 34' and the second check valve 48'. Any resultant demand for hydraulic fluid in lower chamber 27 caused by automati tightening of the grapple tongs 13 is supplied from the fluid exhausting from the third hydraulic line 29 and/or make-up valve 50. Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.