The invention relates to a system for controlling the clamp means in a tree harvesting machine, especially grapple harvester, the system comprising means con¬ trolling the flow of pressure medium to actuators which are connected to the clamp means in a power transmitting way, said control means being placed on a line for pressure medium.

This kind of system is disclosed inter alia in US- Patent 4.546.805. The defect in this type of system is that it can not be used in such tree harvesting machines comprising other actuators consuming the output power of pressure medium, especially tree feeding devices. In this case problems arise which are concerned with the adjustment of the clamping pressure to a desired level, its preservation, and the elimination of pressure shocks during the feed.

The object of the invention is to eliminate the above- mentioned drawbacks and disclose a system which is well suitable especially for a grapple harvester. The term grapple harvester denotes a tree harvesting machine comprising clamp means taking hold of a tree, feeding means for feeding the tree between the clamp means as well as a cross-cutting saw for cutting the tree to desired lengths. The grapple harvester is preferably provided also for performing the cutting of the tree for felling. In accordance with the invention the control system for the clamp means in a grapple harvester is characterized by that for adjust¬ ing the clamping pressure, a pressure-reducing valve is placed on the line for pressure medium and it is designed for permitting the flow of pressure medium at a predetermined pressure to the actuator, and further a relief valve is provided on the line after

the pressure-reducing valve. This combination prevents too high a pressure from entering the clamp means and permits the adjustment of the pressure to a desired level therein on one hand, and by means of the pressure relief valve allows to avoid pressure shocks caused by irregularities of a tree during the feed on the other hand.

According to one advantageous embodiment the pressure reducing valve and also the relief valve are connected to a pilot valve, by means of which their operating point can be chosen to a desired value. For ensuring the preservation of the clamp during the feed, the line of pressure medium is connected to a pressure accumulator, according to one advantageous embodiment, and this line branches off to the pressure accumulator preferably before a directional control valve that controls the direction of movement of the actuators. For improving the occupational safety the line to the pressure accumulator can further incorporate a direc¬ tional control valve that is designed for unloading the pressure accumulator after the work. All aforementioned means can be installed in a part that supports the clamp means, such as in a felling head, and all valves present therein can be integrated to a single valve block.

The invention will be described in the following more closely by reference to the accompanying drawings, wherein

Fig. 1 shows the system according to the invention in a schematical view, and

Fig. 2 shows one alternative system for the pilot control valves in a schematical view.

Fig. 1 shows the system according to the invention as a hydraulic scheme. The means shown in the scheme are installed in a part that supports the clamp means in a tree harvesting machine, such as in a felling head in the same valve block, which is surrounded by broken line 10. A line P for pressure medium branches off from a main line P0 situated in the felling head and coming from a pump. Correspondingly, a line T comes from the valve block to enter a main line TO going to a tank. The pair of main lines P0, TO concerned is also connected to means for rotating the feed motors, means for rotating the saw, as well as to other means situated in the felling head, such as to means for felling and lifting and to blade opening means. All the above-mentioned means get their power from the pressure medium lines branching off from the main line P0 of the felling head and they are controlled with control means which are not described more closely herein.

In the pressure medium line P branching off into the valve block 10 there is, as seen in the flow direction of the pressure medium first a pressure-reducing valve 3 which is designed to allow pressure medium at a predetermined pressure to flow to an actuator effecting the pressing of the clamp means, said actuator being denoted by port B8. To the port B8 are connected in parallel those work chambers of the hydraulic cylinders in the felling head which under the pressure passed thereto accomplish the closing of the clamp means and the pressing around the tree. The operation of the pressure reducing valve 3 will be described more closely hereinafter. After the valve on the line there is a check valve 11 which ensures for its part the preservation of the clamping pressure in the line P. After the check valve on the line there is a branching point, at which a line PI branches off to a pressure accumulator 8. After the branching point there is a 4/3 directional control valve 1, by

means of which the direction of action of the clamp means can be chosen with the aid of electric control. The valve is provided for closing the feed of pressure medium along the line P by spring action in the rest position. After the directional control valve 1 the line P branches off to a relief valve 2, which is designed to allow the pressure medium at a predeter¬ mined pressure to flow to the line T passing to the tank. After said point the pressure medium line P passes through the port B8 connected in the above- mentioned manner to the actuators and the line passes further to -the actuators, which are in a power trans¬ mitting relationship to the clamp means.

Clamping means are understood in this context to mean means carrying the tree feeding means, such as feeding rollers, said clamping means clamping the tree there¬ between at the feeding means so that they will be able to feed the tree forward. The clamping means can also be lopping blades and the system according to the invention can also be used for controlling their clamping action. The means carrying the feeding means and the lopping blades can each be controlled by their respective system, but the lopping blades can be connected mechanically to the means carrying the feeding means, in which event both are controlled by a common system.

The above description has made reference to the flow of the pressure medium in a situation where the directional control valve 1 is at its right position, where the line connected to the port B8 after the directional control valve is under pressure and the line coming from the exhaust side of the actuators through the port A8 is connected to the line T passing into the tank.

The pressure reducing valve 3 is a cartridge valve which is designed to limit the pressure prevailing in the line P that follows it under a certain level. The construction of the valve is not discussed in more detail in this context, because also other valves performing this type of action can be considered here. However, it can be stated briefly that the valve is a normal valve urged by a spring in an open position so that the bores in its poppet are free to permit the flow of the pressure medium into the line P situated after the valve 3. As the poppet is dis¬ placed, influenced by the pressure prevailing in said line, the holes will close simultaneously and the pressure within the line after the valve 3 adjusts itself automatically to be below a predetermined point of action. The valve is connected to a pilot valve through a pilot line X that branches off from the line situated after the valve. The pilot valve is constituted of relief valves 5 and 6 coupled in parallel to the pilot line X and of a valve 4 coupled in series with one (5) of the valves and being closed at its rest position. When the pressure increases in the line P situated after the valve 3 above a certain value determined by the valves 5 and 6 the pressure prevailing in the pilot line X can be discharged through one of the pilot valves to the tank line T, and the pilot pressure connected to the pilot line X and prevailing on the other side of the poppet that keeps the valve 3 open is also discharged and the valve will be closed. The point of action of the valve 3 is determined according to the pilot valves 5 and 6 coupled in parallel, and they are designed to act at different pressures. The choice can be made with the help of the valve 4. When the valve 4 is in the closed position shown by Fig. 1, the point of action is determined according to the valve 6 operative at the higher pressure, and when the valve 4 is open, the connection from the pilot line to the tank line T

will be opened through the valve 4 operative at the lower pressure and determining the point of action in this case. The valve 4 can be controlled electrically and its position for each working phase can be for example programmed in advance in the program controll¬ ing the work cycle.

The relief valve 2 situated after the directional control valve 1 is also connected to the same pilot valves 5, 6 through a pilot line X which is connected to the pressure medium line P situated after the directional control valve 1. When the pressure in¬ creases in the line P after the directional control valve 1, this pressure will be mediated in the above- described manner through the pilot line X to the parallelly coupled assembly of the pilot valves 5 and 6, and when the pressure increases in the line P above the level determined by the pilot valve 5 or 6, the valve 2 will open as the space situated on the other side of the poppet and connected to the pilot line X is deprived of the pilot pressure tending to close the poppet, thus allowing the passage of the pressure into the tank line T. By the action of the relief valve 2, the pressure rise owing to external factors affecting the position of the clamp means, such as pressure shocks caused by their regularities of the tree to be fed, can be avoided in the line P.

For ensuring a smooth co-operation of the valves 3 and 2 the point of action of the valve 2 is designed to be at a higher pressure than that of the valve 3. In the practice this can be achieved by making the spring of the valve 2 stiffer than that of the valve 3.

The above-described pressure adjustment functions are remarkable for the system shown by Fig. 1 in the sense that within the block 10 the line P under

pressure extending from the valve 3 up to the port P8 is accomplished solely by mean_3 of bores, and conse¬ quently it has no hoses with flexible walls capable of smoothening pressure shocks. The modular technique, however, allows to accomplish a compact structure, the centralization of all operative parts to one single assembly, small volumes of liquid as well as good dynamics, that is, quick action.

The system comprises also a pressure accumulator port. As mentioned above, the pressure line PI for charging the pressure accumulator branches off from the line P after the check valve 11 before the direct¬ ional control valve 1. The location of the point before the directional control valve ensures that the accumulator will be charged also when the directional control valve is closed. The line PI passes to the pressure accumulator 8 through a directional control valve 9, which in its spring-loaded rest position connects the pressure accumulator 8 to a return line Tl, which is connected to the tank line TO for dis¬ charging the pressure of the pressure accumulator. Said operation ensures that the pressure accumulator will be discharged when the felling head is not operated. During the work cycle the valve 9 is electri¬ cally shifted to the work position wherein the line PI gets in communication with the pressure accumulator 8 and the pressure accumulator can be charged and it can perform its general function of smoothening the pressure. In course of pressure decrease within the line P for example during the decrease in the diameter of the tree to be fed in its longitudinal direction, the line PI that is open up to the pressure accumulator guarantees the maintenance of a certain clamp in the clamp means. The pressure can decrease in the line P also owing to the fact that as the tree is fed the feeding motors connected to the main line P0 consume some power. When the work machine is switched off the

valve 9 will automatically return to the position where the pressure accumulator is discharged.

Fig. 2 shows one alternative system regarding pilot valves. Like in Fig. 1, also this alternative provides for the connection of both the valve 3 and the valve 2 to the same pilot valve, each through its own pilot line X. However, the valves 5 and 6 coupled in parallel and the valve 4 for choosing between them are replaced with a proportional valve 7. The pressure of action of this type of relief valve can be adjusted steplessly outside the valve electronically, for example from a driving cabin or by means of program controlling the work cycle and setting the desired pressures during the work cycle.

With the aid of the combination of the pilot valves 5 and 6 or the proportional valve 1 , different pressures can be chosen for the clamp means. When the clamp means engage the tree for a cut for the felling, the point of action of the valve 3 can be set to a higher pressure, that is, the clamping force will thus be greater, and when the tree is fed between the clamp means, the point of action can be at a lower pressure. A suitable clamping pressure on engaging a standing tree can be for example 190 bar and the corresponding pressure during the feed can be for example 130 bar. The choice is made by means of the valve 4 of Fig. 1 or by adjusting correspondingly the proportional valve 7 of Fig. 2.

The invention is not restricted hereinabove only to the embodiment shown by the drawings, but it can be modified within the scope of the invention represented by the claims. The functions of the system can be accomplished also by using analogous parts. Because a compact structure is required in the felling heads suspended from boom ends of tree harvesting machines.

it is preferred that the means that control common means, such as actuators operating the clamp means, are incorporated to the same valve block. In this case it is profitable to integrate the pressure- reducing valve 3, the pilot valves 5, 6 or 7, the directional control valve 1 and the relief valve 2 to the same valve block. It is also profitable to in¬ tegrate the directional control valve 9 for the pressure accumulator into this same block. The fluid volume of the system will consequently remain small. The valves 3 and 2 are preferably accomplished using cartridge technique.

In the system the functions effecting the speed (modular technique) and the functions effecting the elasticity (the valves 3 and 2 and the pressure accumulator 8) are separated from each other, the fact which improves the controllability of the system.