US 3854766 A
A system for automatically holding and/or restoring pressure to log grapple tongs despite shifting of the logs in the tongs.
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Description (OCR text may contain errors)
United States Patent Jordan Dec. 17, 1974  L06 GRAPPLE DEVICE 3,152,706 10/1964 Conrad 294 88 x 3,371,952 3/1968 Hun er 294/88 [761 Invenw Bertram Jmdan, Lewlston, 3,627,351 12/1971 Zimr nerman et al. 294/88 x 27349 3,738,520 6 1973 01111616131. 214/653  Filed: Apr. 13, 1973 Primary Examiner-Even C. Blunk [211 App]' 350878 Assistant Examiner-Johnny D. Cherry Attorney, Agent, or Firm-Fred Philpitt  US. Cl. 294/88  Int. Cl. B66c 3/16  Field of Search 294/86 R, 88, 106, 118;  ABSTRACT 214/147 147 650 656 A system for automatically holding and/0r restoring pressure to log grapple tongs despite shifting of the  References Clted logs in the tongs UNITED STATES PATENTS 2,732,083 l/l956 Smith 294/88 x 2 Clams 6 Drawmg F'gures Oil Tank Main Relief B Accumulator B 5 4| Unlooder A 2O Vulve I g F I .J
I 4 7 Check Valve )1 I losed I enter Pump VOIVE 23 Z l 2 33 32 I I l Tong P1161 43 Llne Ei LCI Pressure I 2 Switch 0 ll PATENTEU HEB! 7 I974 sum 3 o 9 6 EEK lHl LOG GRAPPLE DEVICE BACKGROUND Most of the log grapples in use in the logging industry today are mounted on a boom located at the back end of a skidder, half-track or tractor. Hydraulic circuitry and hydraulic controls permit the operator to raise and lower the grapple, rotate the grapple about its axis of mounting, and to actuate the tongs of the grapple between hold and release positions.
A problem with many log grapples is that although they may initially pick up several logs without difficulty, once the operator begins to drag the logs through a forest, the tongs of the grapple may lose their grip on the logs for one reason or another. For instance, if the logs are wet they may easily slip with respect to each other. The mere weight of the logs and the fact that they are being dragged over very uneven ground nearly always is enough to cause shifting of the logs within the grapple.
Since logs can easily shift enough in the grapple to become loose and fall out, grapple operators have usually tried to avoid loss of logs by continuously applying hydraulic pressure to the tongs of the grapple. Whereas this technique does serve to cause the tongs of the grapple to take up any slack caused by shifting of the logs, it has the disadvantage that the pump in the circuit has to be continuously pumping oil through the system, which leads to overheating of the oil, undue wear of the pump, etc.
THE PRESENT INVENTION The present invention relates to a log grapple having tongs that are actuated by at least one hydraulic cylinder, said at least one hydraulic cylinder being included in a hydraulic circuit that is designed so that the tongs can grasp a group of logs at an initial holding pressure and thereafter automatically maintain the initial holding pressure regardless of any change in the relative positional relationship of the logs within the tongs and regardless of any forces which are applied to the logs in the course of their being moved from one location to another. Basically my hydraulic circuit senses a drop in pressure of the grapple cylinder circuit and automatically restores the desired holding pressure to the grapple cylinder.
My disclosed hydraulic circuit arrangement can be used in its extirety by manufacturers of log grapples, or existing log grapple circuits may be modified so that the resulting circuit conforms with my invention.
My invention will be better understood by referring to the following description taken in conjunction with the attached drawings wherein:
FIG. I shows a log grapple with cylinder actuated tongs;
FIG. 2 is a sketch illustrating one embodiment of my invention;
FIGS. 3 and 4 are sketches illustrating a second em bodiment of my invention;
FIG. 5 is an enlarged view of the unloader valve 59 used in FIGS. 3 and 4 when the pump is in its loaded condition;
FIG. 6 is a simplified hydraulic diagram of an embodiment of my invention using a single tong cylinder.
FIG. 1 illustrates a log grapple containing tongs that are moved relative to each other by hydraulic cylinders.
FIG. 2 illustrates one embodiment of my invention. Here it will be seen that a pump withdraws oil from a tank of hydraulic oil through line 20 and out through line 21. The fluid then passes through line 22 to point X, where it has the possibility of flowing through line 31 or line 32. Whether the oil will flow through line 31 or line 32 primarily depends upon the pressure of the oil in the system and the position of the tongs. For instance, if the tongs are initially in the open position (as shown) and it is desired to close the tongs, the pump will force the hydraulic fluid through line 32, through the check valve, through lines 33 and 23, through closed center valve F, and then through lines 34, 35 and 36 so as to apply pressure against pistons 39 and 40. Such applied pressure will cause the piston rods to move downwardly so as to close or bring together the tongs around a group of logs. In order to insure that the fluid will flow in this manner the unloaded valve B is maintained in a closed position so that there will not be any flow through line 31. Unloader valve B is preferably a two-way unloader valve. Pressure switch C is designed so that its contacts C and C will remain in the open position (as shown) during the time that the fluid pressure is moving pistons 39 and 40 toward their downward or closing position.
When the fluid pressure has closed the tongs around a group of logs so that the tongs are holding the logs with the desired pressure, it is not desirable for the pump to have to continue to pump fluid thru line 21, and then through the main relief valve and back to the tank through line 41 because this can lead to overheating of the oil and undue wear upon the pump. With my arrangement, when the pressure in the system builds up by virtue of the tongs having exerted their optimum holding pressure on a group of logs, the back pressure developed through lines 35, 36, 34 and 23 will be sensed through pilot line 42 and the piston 43 of the pressure switch is designed to move to the right under such build up pressure. As the piston 43 moves to the right it will close contacts C and C thus energizing the solenoid B and opening the unloader valve B. With unloader valve open the fluid flow from the pump will be through lines 21, 22 and 31 (rather than to line 32).
Now, should the logs shift in the tongs with the result that the pistons 39 and 40 are able to move, then the pressure within the lines 35 and 36 will drop and in turn the pressure in lines 34, 23, 33 and 42 will likewise drop. The drop in pressure in pilot line 42 will cause the force of tension spring 44 to move the piston 43 to the left, which opens contacts C and C The opening of C and C and deenergizes solenoid B,, which in turn closes the unloader valve B so that there will no longer be any flow through line 31. The fluid from the pump will then resume its flow through lines 32, 33, 23, 34, 35 and 36 until the pressure in the system again builds up to the point where the piston 43 will be moved to the right closing contacts C and C FIGS. 3, 4 and 5 illustrate another embodiment of my invention. In FIG. 3 the tongs are shown in the open" or retract" position. Oil is drawn from a reservoir 52 (after passing through filter 53) via line 54 by means of a pump 55 and pumped into line 56 until it reaches open center control valve 57. With open center valve 57 in the position shown the fluid will flow through the line 58 to the inlet 93 of unloading valve 59. The unloader valve 59 is closed by virtue of the fact that spring 80 is exerting sufficient upward pressure against valve stem 82 that it abuts against seat 84, whereby fluid entering through inlet 93 flows around the valve stem 82 and then flows outwardly through outlet 92 and line 92a. A check valve 11 is interposed in the line 92a 92a so as to restrict flow to the right-to-left direction. The fluid passing through line 93a flows into the closed center valve 14, and (with the spool 15 in the position shown) out through line 95 and thence to the rod ends of the tong cylinders. This causes the pistons 39 and 40 to move upwardly, which is the retract postion of the tongs of the grapple. There is an exit flow of hydraulic fluid through lines 35, 36, and 99, then through valve 14, through line 17 and back to the oil reservoir 52.
Now when the operator wishes to activate the tongs so that they will grasp a group of logs he merely moves the spool 15 so that the fluid flow coming through line 93a will pass through valve 14 and into line 99 (rather than into line 95). The fluid going from line 99 to lines 35 and 36 will then push the pistons 39 and 40 down so that thetongs will come toward each other, which achieves the grasp or hold position of the tongs. The fluid below the pistons 39 and 40 will be forced out line 95, through valve 14, through line 17 and back to the oil reservoir 52.
As noted previously, when the fluid pressure has closed the tongs around a group of logs so that the tongs are holding the logs with the desired pressure, it is not desirable for the pump to have to continue to pump fluid thru the relief valve because this can lead to overheating of the oil, undue wear on the pump, and other problems. With my arrangement (see FIG. 4) when the pressure in the system builds up by virtue of the tongs having exerted their optimum holding pressure on a group of logs, the back pressure developed through lines 35, 36, 99 and 93a will be sensed through pilot line 100 and the back pressure developed in line 100 will press against pilot piston 21c and move it to the right against the spring 22a (see also FIG. When member 210 is moved to the right'(from the position shown) it will move valve 19 away from valve seat 103,
' which will permit fluid to flow from inlet 93, down through passageway 23a into chamber 101, down through passageway 101a, past valve seat 103, upwardly through the interior of valve stem 82 and out through outlet 95a and line 95b and back to the tank 52. When this happens there will be a pressure drop across valve stem 82 by virtue of fluid flow downwardly through the passageway 2311, this pressure drop allowing the valve stem 82 to move downwardly against the force of the spring 80, and as valve stem 82 moves downwardly fluid flow coming in through inlet 93 will be diverted past valve seat 84, outlet 95a, out line 95b, and then to tank 52 at nearly zero pressure. This unloads the pump. The diversion of flow will continue so long as there is no change in the pressure in chambers 98a and 98b. 4
However, should the pressure in 98a or 98b drop, as for instance because of a shifting of the log within the grasp of the tongs, the pressure of the fluid in pilot line 100 would also be reduced, causing piston member 21c to return toward the ieft, reseating valve 19 on seat 103, thus terminating flow downwardly through passageway 23a, which in turn causes spring 80 to close the valve 82 open valve seat 84. Fluid will come again pass through line 93a, through valve 14, through line 99 and then to chambers 98a and 98b, as discussed previously, and this flow will continue until enough pressure has built up behind the pistons 39 and 40 so that they will exert the desired log holding pressure. Once the desired pressure is once again achieved, then the sequence of pump unloading operations set forth above (relative to diverting the pump flow past valve seat 84 and into line 951)) will start.
The point at which the pump will be unloaded can be controlled by adjusting the force which the spring 22a exerts upon valve 19, for instance by means of a threaded bolt 111.
FIG. 4 shows the position that the closed center valve 14 will be in when the tongs are to be actuated to the closed position, and it will remain in this position after the operator has clamped the tongs around a group of logs. The accumulator makes up for seepage, takes care of pressure surges, etc. For instance, when the grapple operator is dragging a bunch of logs thru the woods, one thing that can happen is that the logs will twist in such a way that a force will be exerted against piston 39 or 40. When this happens the pistons will move to compress the fluid in the cylinder, which will increase its pressure. This increased pressure will be transmitted backwardly through the closed center valve and then into the accumulator where the increased pressure of the fluid will cause the gas in the accumulator to be compressed. The accumulator therefore acts as a cushion against encountering such conditions which might otherwise result in the breakage of lines or valves.
FIG. 6 is a hydraulic flow diagram for the case where only a single tong cylinder would be used and which would otherwise be substantially identical to the arrangement of FIGS. 3, 4 and 5 (and therefore the same numerals have been used) except that a tandem center valve has replaced the open center valve (57).
The closed center valve 14 in FIGS. 3 and '4 may be a single closed center valve or a plurality of closed center valves, each closed center valve being connected to a different hydraulic cylinder. All of the closed center valves could operate at the same time, or each could operate separately or several could operate at the same time. Closed center valves are in parallel.
Whereas FIGS. 3 and 4 show the use of an open center valve 57, I have found that a tandem center valve will serve just as well, and in some cases better.
It is thus seen that l have provided a log grapple that will grasp logs and hold them tightly under all conditions.
A few of the advantages of my log grapple are as follows:
l. A constant holding pressure on the logs that will allow the tongs to tighten automatically around shifting logs and prevent slippage of wet or slick logs.
2. Longer hydraulic pump life due to automatic cycling of the pressure rather than constant loading of the pump by the operator to hold the tongs tight.
3. Ease of operation for the operator because of automatic monitoring and restoration of the holding pressure.
4. Safer log grapple operation between the grapple operator does not have to be looking back to monitor the condition of the logs in the grapple.
In accordance with my invention the main relief valve should always be set to unload at a pressure which is above the unloading pressure of my unloader valves (B or 59) and this can be easily arranged (e.g., by adjustment of the spring 22a). If this is not done then when the pressure builds up in the system the oil will go back to the tank through the main relief valve in preference to going through my unloader valves, which would cause an undesired amount of heat.
What I claim is:
l. A log grapple mounted on a vehicle, said log grapple comprising two tongs that are mounted on said vehicle so as to be movable toward and away from each other, at least one hydraulic cylinder for moving said tongs toward and away from each other, a hydraulic circuit including a hydraulic pump for supplying hydraulic power to said at least one hydraulic cylinder,
6 said hydraulic circuit including:
a. unloader valve means for unloading the hydraulic pump after the tongs have initially obtained a firm grip on a group of logs,
b. means for thereafter sensing any pressure drop in said at least one cylinder that may be due to a slippage or shifting of the logs within the grasp of the grapple,
c. means for automatically and substantially instantaneously restoring the pressure in said at least one hydraulic cylinder to the pressure which existed in said at least one hydraulic cylinder at the time that it attained its initial firm grip on said group of logs.
valve in combination with an unloader valve.