Hydraulic Feed Control System for Log Debarkers

To accommodate the dramatic changes in the logging industry wherein a wider variety of quality and types of logs must be debarked in a total tree harvesting method, a new generation of debarkers has been designed, as described in the above-noted applications. Many of the logs which are now to be debarked are generally of lower quality having greater numbers of sweeps, knots, swelled butts and kinorshums, and of varying lengths and sizes. In the past, a debarker design, as shown for example in U.S. Pat. No. 2,857,945, was used and the spiked feed rolls for feeding the log through the rotating debarking tools of the debarker were mechanically linked and driven so that they would all rotate at the same rate. Thus, when one roll encountered a distortion in the log and was forced to rotate at a different speed than the other rolls, the driving ring gears and pinions would break. This resulted in the log debarker having considerable down time as well as great part replacement and repair expenses. Thus, a new generation of log debarkers as designed by the present inventor has evolved. These are hydraulically driven debarkers and each of the feed rolls has its individual driving means and a sensing means to adjust the individual rate of rotation of each of the rolls to accommodate the uneven log surfaces.

The hydraulic systems of these debarkers have proven to be very successful. However, sometimes sufficient instant power was not available for the hydraulic motors and difficulties were sometimes encountered in feeding a large log smoothly through the debarker. Also, under certain conditions the known systems were sometimes not able to efficiently handle all ranges of feed speeds especially the lower speeds.

Shock loading to log debarkers is caused by any sudden changes in the force required by any one of the hydraulic feeding motors such as when the log strikes the infeed rollers, the debarking tools or the outfeed rollers as might be caused by knots, sweeps, or crooks as when the barking tools drop off the end of a log. It was further desired to have a hydraulic system which could better handle the numerous problems of shock loading encountered with bad logs.

Accordingly, it is the principal object of the present invention to provide a novel design for a log debarker.

Another object of the present invention is to provide a novel design for a hydraulic driving system for log debarkers.

A further object of the present invention is to provide an improved hydraulic driving system which can provide sufficient and greater instant power to each of the feed rolls.

A still further object is to provide a novel hydraulic drive system which can handle any range of speeds especially including the lower speeds.

Another object is to provide a novel hydraulic system which insures that all of the hydraulic motors always have a sufficient supply of oil to prevent cavitation.

A further object is to provide an improved hydraulic drive system which can better handle the problems of shock loading encountered with bad logs.

A still further object is to provide a novel design for hydraulic log debarker drive systems which can be easily assembled on the hydraulic motors.

Another object is to provide an improved hyraulic driving system for log debarkers which has sufficient torque to smoothly feed large logs.

Other objects and advantages of the present invention will become more apparent to those persons having ordinary skill in the art to which the present invention pertains from the foregoing description taken in conjunction with the accompanying drawing.

FIG. 1 is a schematic view of a hydraulic drive circuit for a log debarker of the preferred embodiment of the present invention.

FIG. 2 is an enlarged view of one of the relief systems of the circuit of FIG. 1 illustrated in isolation.

FIG. 1 illustrates the hydraulic drive circuit of the present invention. Referring thereto, it is shown that six hydraulic motors 10a, 10b, 10c, 11a, 11b, and 11c are provided. Each has an upstream port 12a, 12b, 12c, 14a, 14b, and 14c, respectively, and a downstream port 16a, 16b, 16c, 18a, 18b, and 18c, respectively. Each is connected through its drive shaft to a separate log feed roll. Six log feed rolls (not shown) are provided for the debarker and are positioned in a conventional manner in two sets. The first comprises the three infeed rolls and the second set is the three outfeed rolls, each arranged in triangular relationship about the axis of log feed into the debarker. The infeed and outfeed rolls are positioned on opposite sides of the log debarker frame which supports the rotating debarking tools in a conventional manner. Motors 10a, 10b and 10c drive the infeed rolls and motors 11a, 11b and 11c drive the corresponding outfeed rolls. As will become apparent, each of the hydraulic motors can operate at different and differing speeds to accommodate the uneven surfaces of logs.

To obtain the greater desired torque a larger motor than previously used is employed in the subject design. An example of such a motor is the MAE56016 TRW hydraulic motor which has a 49 cubic inch displacement per revolution. This motor develops a torque at its maximum allowable pressure of 1500 psi of 11,850 in-lbs. Although this motor has the combined volume of the MAE24002 and MAE34002 in cubic inches per revolution, it does not have the combined strength. Therefore, because of the potential increase in volume which is directly related to the subject torque and the intensified effects of the positive three-way flow divider (later discussed), a special hydraulic circuit design as shown in the drawing is used to protect each of the hydraulic motors at its respective input motor port. Additionally, as is apparent from the drawing, each infeed hydraulic motor is connected in series with its corresponding outfeed motor. The volume of oil consumed in this series arrangement requires that the downstream or outfeed motor in series must have an additional source of oil to prevent cavitation should its upstream or infeed motor stop rotating.

The hydraulic system accordingly functions as follows. The hydraulic oil is drawn from the tank 20 via a variable volume pressure compensated pump shown generally at 22 and then pumped through line 24 by a valve controlled gauge 26 and by a relief 28. The oil or fluid then flows through a directional valve 30 to a three way positive flow divider shown generally at 32. Three way positive flow divider 32 divides the flow of oil equally in each of its three legs 34a, 34b, 34c. Since the system in each of the three legs is identical only one of the legs will be described.

Thus, one-third of the portion of the oil pumped by pump 22 flows through line or leg 34a through the relief system shown generally at 36a and best shown in FIG. 2 to motor 10a hence to motor 11a. More particularly it flows by the directional check valve 38a and on passed, or through, the relief 40a. Reliefs 40a, 40b, and 40c can comprise any suitable relief such as an adjustable, spring loaded, ball seating type cartridge that is "0" ring seated in a block. The oil then flows on through line 34a to hydraulic motor 10a through its port 12a. After causing motor 10a to rotate, the fluid flows out of hydraulic motor 10a through port 16a. The bulk of the oil passing through motor 10a will do work causing its drive shaft to turn and thus the associated roll (infeed roll) to rotate feeding the log through the debarker. However, each of these motors inherently has some cross port linkage that allows fluid to pass between the ports (12a and 16a) without doing work.

The oil then flows through line 42a through relief system 36a including past (or through) relief 44a. It then continues through line 42a by the directional check valve 46a, and on through line 42a to the outfeed motor port 14a. The oil then passes through the hydraulic motor 11a and out port 18a and through line 48a to the common return line 50 to tank 20.

When the pressure in line 24 from pump 22 exceeds a set pressure, the excess fluid is diverted through relief 28 and to a return oil filter 52 to tank 20. Also, when the fluid pressure differential exceeds that of filter 52, the check valve 54 is popped open and the excess fluid flows directly to tank 20. Further, the remaining fluid from motor 11a passes via line 48a to common return line 50, through directional valve 30 and then through the filter 52 or through springloaded check valve 54 to tank 20.

This system well handles shock load conditions. If, for example, motor 10a encounters a shock load sufficient to break relief 40a and attempts to dump too much of the oil supply back through the line 58 to tank 20, hydraulic motor 11a is still forced to continue to rotate due to the speed of the log passing through the debarker and the fact that the spiked surface of its roll grips the log with no slipping occurring between the log and the roll. Motor 11a would tend to cavitate if it were not for the present design. Hydraulic motor 11a will then, if needed, siphon oil (act as a pump) through directional check valve 46a which communicates with tank 20. This siphoning action occurs because hydraulic motor 11a is still rotating due to the log passing through the debarker and motor 11a requires additional fluid not supplied from motor 10a out of port 16a thereby siphoning oil from the tank through line 58.

When the above hypothesized shock load occurs, directional check valve 38a is sealed by the high pressure in line 34a. Because of the drop in pressure, directional check valve 46a opens supplying oil from line 58 to hydraulic motor 11a. Similarly, if hydraulic motor 11a encounters a shock load condition that is sufficient to break relief 44a, the pressure would also seat directional check valve 46a. The pre-set spring loaded check 56 is set to assist valve 30 to shift under pressure and oil flow.

Thus, the greater torque in these new motors eliminates some of the minor problems encountered with the smaller hydraulic motors. The greater volume of oil consumed by them however necessitates that a relief be installed inside of the motor or at the input port of the motor. The peak torque can and will be reached must faster. Therefore, the pressure control has to be located as close to the motor as possible as is accommodated by the present design. But because of the increased speeds required for this new operation in conjunction with the increased consumption of oil, the motors have been protected by moving the reliefs 36a, 36b, and 36c closer to them. The system is composed of three separate relief modules as opposed to the larger one common module used in the past and each can thus be moved closer to its respective motors. In other words, the relief is formed of three individual self-contained cells, each of which can be easily positioned anywhere on the hydraulic lines.

Motors 10a, 10b, 10c, 11a, 11b, 11c are further protected by the addition of the directional check valves which prevent the possible increased pressure created by motor 10a from passing on to motor 11a but at the same time will open when needed so that either motor that is volume restricted may siphon the needed oil through this open check valve from tank to prevent cavitation. The dual crossover relief with the directional flow controls on both and each supplied with a common return to tank provides a cross motor protection for both of the motors and allows the pressure to build across one motor without affecting the other. It allows the oil from a separate source to reach either motor should it be required to rotate without oil being supplied by its source. The dual crossover relief 36a with directional check valve controls does not allow excess pressure created by one motor to reach the other motor. The pressure intensification created by positive three way flow divider 32 could be very damaging if it were not for the present relief system which does not allow the excess intensified pressure to reach the motors.

From the foregoing detailed description, it will be evident that there are a number of changes, adaptations, and modifications of the present invention which come within the province of those persons having ordinary skill in the art to which the aforementioned invention pertains. However, it is intended that all such variations not departing from the spirit of the invention be considered as within the scope thereof as limited solely by the appended claims.