WO2001002280A1

WO2001002280A1 - Control system for a boom system in a working machine movable on a terrain

Info

Publication number: WO2001002280A1
Application number: PCT/FI2000/000609
Authority: WO
Inventors: Marko Paakkunainen
Original assignee: Plustech Oy
Priority date: 1999-07-06
Filing date: 2000-07-04
Publication date: 2001-01-11
Also published as: FI991540A; FI111938B; AU5988700A

Abstract

The invention relates to a pressurized medium operated control system for the boom system of a working machine, which boom system comprises at least a first boom part (P1), a second boom part (P2) and a third boom part (P3) fixed to the working machine, and which control system comprises a first cylinder actuator (S1) fixed between the first boom part (P1) and the second boom part (P2), a second cylinder actuator fixed between the second boom part (P2) and the third boom part (P3), first control means (V1) and second control means (V2) connected to a pressure source (P) and a return line (T). In the invention the control system is arranged to be set in an articulation control mode, wherein the first cylinder actuator (S1) is arranged to be independently controlled by means of the first control means (V1), and the second cylinder actuator (S2) is arranged to be controlled independently by means of the second control means (V2), and arranged also to be set in a direct transfer mode, wherein the second boom part (P2) and the third boom part (P3) are arranged to swing simultaneously to opposite directions under the control of the second control means (V2), and wherein the first cylinder actuator (S1) and the second cylinder actuator (S2) are coupled in series.

Description

Control system for a boom system in a working machine movable on a terrain

The invention relates to a pressurized medium operated control system for the boom system of a working machine.

For harvesting, there are known working machines, such as harvesters which move on a terrain, in the end of whose boom system there is a harvesting apparatus, a so-called harvesting head for cutting, felling and sawing a tree trunk growing upright. The sawed tree trunks are collected with another known working machine that is movable on a terrain, i.e. by means of a loading machine, i.e. a forwarder equipped with a grapple, and they are transported in the load space of the same. There are also machine combinations, in which the functions of a harvester and a forwarder are combined together. Thus, the advantage is that the harvesting and the act of collecting the tree trunks can be conducted simultaneously, which reduces the need for several machines in the forest, and decreases the number of machine transfers between the working sites. One example of a combination machine comprising one frame part, a boom system and a load space is disclosed also in the patent publication US 4,984,961.

The above-described working machines comprise a boom system for working purposes, the boom system typically comprising at least three boom parts articulated together with a joint, two of which move on the vertical level. The boom is articulated to the working machine by means of a joint for swinging the boom around a vertical direction. By means of the same joint the cabin can also swing around the same direction, as is presented in the patent publication US 4,984,961. In the free end of the boom, it is possible to fix a suitable tool, such as a harvesting head or a grapple for handling of the load.

In view of the efficiency of the above-presented working machines, it is important that the booms intended for handling, transport and loading of their load can be used logically and the function of the same is reliable and efficient with a good operating efficiency. A combination machine, in particular, has to be capable of performing both the harvesting work and the loading machine work as efficiently as possible. By means of the present invention, this can be attained in an especially efficient manner, wherein for the part of the boom this means that in the harvester work so-called direct transfer properties are available, whereas in the loading machine work so-called independent articulation control properties are available.

The boom systems typically operate under the control of a pressurized medium operated control system that is normally hydraulic, by means of actuators, such as cylinders, and control valves. With reference to

Fig. 1 , one known way to control a boom which is of articulated type is to control each joint of the boom with a separate, articulation-specific control valve and a cylinder actuator in such a manner that the tool at the end of the boom moves to a desired point of location at a desired speed. To actuate the movement, the driver of the working machine takes care of the co-ordination of the control of each joint for example manually by means of valves which a controlled with a lever. The valves can also be controlled automatically by means of an electric computer control of the control unit of the working machine, wherein the driver can use joystick-type actuators for the control.

In many situations, the articulation-specific control has a poor operating efficiency. When the end of the boom is controlled by means of direct transfer, i.e. when it is transferred in the horizontal direction, some of the joints perform so-called positive work against the load, i.e. gravity, and some so-called negative work in the direction of the load. Said control system is, however, well applicable to loading work for example in the handling of tree trunks, in which the load is first lifted up from the ground to the load space of the machine and unloaded later from the load space to a stack. Thus, the load is, to a large degree, transferred from one potential energy level to another, and the work rotation is characterized in that the load and the boom system structure itself is lifted over obstacles, such as the structures of the load space in the working machine. It is advantageous that in addition to the end of the boom, each joint can be controlled separately in a logical manner. The articulated boom according to Fig. 1 is a typical so-called loading machine boom.

In harvesters which fell, delimb and cut the trees, the need for lifting and lowering the load is small when compared to the need for moving the end of the boom and the tool horizontally. To facilitate the use of the boom and to improve the operating efficiency, there are known, mechanically implemented direct transfer booms i.e. parallel booms. In these the direct transfer is often implemented by means of auxiliary beam parts and parallelogram mechanisms, and for example the fastening of the cylinder actuators deviates from the coupling shown in Fig. 1. A problem that often occurs is that the horizontal movement of the end of the boom is linear only at a fixed, predetermined height, and that the auxiliary boom parts increase the weight of the boom and obstruct the view of the driver. It is impractical to use the boom in the loading because the joints cannot be controlled separately.

Fig. 2 shows a known, hydraulically implemented direct transfer boom by means of which the end of the boom actuates an approximate horizontal movement at a fixed, predetermined height. In principle, the presented solution applies the articulated boom construction according to Fig. 1 , but with such a difference that the cylinders are coupled together with a control line, and they are controlled with a common valve. The idea of the solution is that the cylinders moving the joint operate alternately, depending on the horizontal direction of motion of the end of the boom system, in the area of the negative load, at the same time functioning as pumps to move the other joint. Because of this, in different control situations the actual operating pressures of the pressurized medium, generated by means of a pump functioning as a pressure source of the control system, remain on a lower level than those in the embodiment according to Fig. 1 with a corresponding movement. Furthermore, due to the need for only one controllable cylinder actuator, the volume flows also remain on a considerably lower level. This has considerable significance for the power P required by the boom, which can be calculated by means of a dependence P = p ^• Q, in which p is the necessary pressure generated by the pump and Q is the necessary volume flow generated by the pump. However, the use of this boom in the loading is also impractical because the joints cannot be controlled separately.

A control system according to Fig. 2 is disclosed in the patent publication US-3884359, in which each cylinder actuator is also provided with a separate control valve. The control system is, however, connected in such a manner that the control of the valves is conducted by means of three levers, wherein the lowering, lifting and direct transfer of each cylinder have separate levers and valves. The cylinders are also coupled in such a manner that in direct transfer the cylinders move in different directions when compared to the solution of Fig. 2. The problem is that the cylinders cannot be controlled independently at the same time, because their valves are connected to each other, wherein when the control valves of the cylinders are controlled simultaneously, the cylinders are coupled in series. Another problem is caused by various sudden and undesirable movements, which result from the various possible combinations of couplings and positions of the levers.

Furthermore, a practical problem in the system of Fig. 2 is how to conduct reliable oil filling and ventilation of the control line connecting the cylinders. In practice, a connection to the refill oil source and a venting valve are required. Another problem of the system according to Fig. 2 is how to implement the lifting and lowering movements of the end of the boom. As is well known, the height adjustment of the end of the boom is implemented with a separate cylinder, wherein one additional cylinder actuator with its articulations and fixing arrangements is required. This results in problems in reliability and increase in weight due to the complexity of the structure.

There are also known control systems by means of which it is also possible to implement a synchronized movement of the actuators as well as an independent control of the joints. One control system is disclosed in the Japanese patent application JP 57-195904 (Patent Abstracts of Japan, Vol 7, No 47, M-196). To implement the articulated control, each cylinder can be controlled independently with a separate control valve. By means of an auxiliary valve, the cylinders can be coupled in series, wherein the pressurized medium is conveyed from the lower actuator of the boom all the way to the upper actuator. The problem in said control system is the poor operating efficiency especially in the lifting, because the negative loading is utilized only in the lowering, wherein the cylinder space of the lower cylinder of the boom on the side of the piston is affected by the weight of the load, thereby assisting the lifting movement of the upper cylinder. In addition, the system can be applied primarily in situations in which the aim is to keep the load to be supported on a horizontal level by means of a simultaneous movement of the actuators.

A known solution for implementing the horizontal direct transfer and the vertical loading movement is also the one shown in Fig. 3. The height adjustment of the end of the boom is implemented in a manner similar to an articulated boom by controlling the lower actuator by means of a control valve which also functions as a venting valve of the control line connecting the cylinders. Both actuators and the other control valve are still used for the direct transfer i.e. for the horizontal movement, wherein the lower actuator of the boom is coupled to both control valves. In the dimensioning of the overall structure of the control system the loading level of the actuators, especially the pressure level in the connecting line, is taken into account so that the solution would function in a reliable and logical manner. The weakness of the coupling shown in the drawing is, however, the possibility of undesirable movements in the lifting and lowering movements. For example when the lifting movement is conducted within a wide reach of the boom system, an undesirable folding movement of the outer boom part downward around the upper articulation is possible, because the load of the upper actuator and the pressure level caused by the load are higher than the need for pressurized medium caused by the lifting movement in the cylinder space of the lower actuator on the side of the piston.

The above-presented undesirable movement can be prevented for example in such a manner that by means of dimensioning the actuators and the geometry of the boom a situation is attained, in which the pressure level of the lower actuator on the side of the piston is always higher than the pressure level of the cylinder space of the upper actuator on the side of the piston rod. One solution is to provide the line connecting the actuators with a valve, which prevents said undesirable movement of the upper actuator when the lifting movement is performed. A valve suitable for this purpose is for example a so-called load-lowering valve, which for its part is known from the international patent application WO 9716372. A problem reducing the applicability of the solution is, however, that the cylinder actuators and thereby the joints of the boom cannot be controlled irrespective of each other, wherein the control system is only suitable for working machines operating as harvesters.

One aim of the present invention is to eliminate the restrictions of the above-presented solutions and to introduce a control system for a boom system in a working machine with the advantages of an independently controllable articulated boom and direct transfer boom. A working machine, especially said combination machine, in which the control system of the invention is applied to control the boom system, is suitable both for harvesting and loading of trees. To attain this purpose, the control system according to the invention is characterized in what will be presented in the characterizing part of claim 1.

The invention is based on the independent control of cylinder actuators moving the joints of the boom system, and to the implementation of the direct transfer of the same by means of very simple methods. The invention is also based on the idea that to lower the pressures and to improve the operating efficiency, depending on the horizontal direction of motion, each cylinder moving the joint in turn operates in the area of the negative load, at the same time functioning as a pump to move the other joint.

By means of the invention considerable advantages are achieved, such as the simplicity of the structure and thereby also the ease of use and reliability, wherein according to a preferred embodiment of the invention, only two control valves and two cylinder actuators are used. Good operating efficiency is attained in such a manner that both directions of movement are assisted with the load, simultaneously attaining a low volume flow and lower operating pressures. The control system is flexible, and the driver of the working machine can, according to his preferences and habits, also conduct e.g. felling work in the articulation control mode or loading work in the direct transfer mode. In the invention, the aforementioned modes can be selected to facilitate the function of the control and to implement the control only by means of two controllable valves.

The logic valves used in a preferred embodiment of the invention are simple, reliable and inexpensive ready-made components. It is advantageous to place all the logic valves in the same valve block, wherein a reliable structure of small size is attained. If necessary, the same block can also be provided with other valve functions possibly used in the system, such as for example a regenerative function and a function of lowering the load.

In the following, the invention will be described in more detail by using a preferred embodiment of the control system according to the invention as an example, at the same time referring to the appended drawings, in which:

Fig. 1 shows a prior art boom control system and an articulation- specific control in a skeleton diagram,

Fig. 2 shows a prior art boom control system and a control of the direct transfer of the boom in a skeleton diagram,

Fig. 3 shows a prior art boom control system and control of the direct transfer and the vertical movement of the boom in a skeleton diagram, and Fig. 4 shows a boom control system according to a preferred embodiment of the invention and a boom system in which the invention can be applied.

A working machine for handling and transporting trees, which is intended to be movable in a terrain, typically comprises at least one frame part which is arranged movable for example by means of wheels which are connected to the frame part by means of bogie units. The frame part is also provided with a power source of the working machine, typically a diesel motor, and the working machine is equipped with a mechanical hydrostatic power transmission system. By means of two frame parts the working machine can be arranged to be articulated frame steered. On top of the frame part it is also possible to fix a swivel base, on top of which the driver's cabin is also placed and to which the boom system can also be fixed.

In Figs. 1 to 4, the boom system, the fixtures of the cylinder actuators and the function of the articulation are shown in a reduced diagram. For example the boom parts are shown as straight structures, but it is obvious that a more detailed structure and form of the same can vary a great deal. Furthermore, the articulations are shown by means of simplified hollow circles. In addition, to illustrate the operation, the actuators are fixed to lugs articulated to the boom part by means of a joint, but it is obvious that said joint could in many cases also be placed to the straight boom part.

The boom system according to Fig. 1 comprises a first boom part P1 which comprises a first end P1a which is typically integrated in the working machine, as well as a second end P1b. The attachment of the first end P1a can also be arranged on a base swinging around the vertical axis, wherein the boom system can be turned sideways. The boom part P1 is typically vertical and it is arranged to swing around a vertical axis Z. The boom system comprises a second boom part P2, which comprises a first end P2a which is fixed to the second end P1 b of the first boom part P1 , and a second end P2b. The second end P2b is typically arranged to move in the vertical (plane Z — X) plane, swinging around the joint of the end P2a. The rotation is attained by means of a first cylinder actuator S1 fixed between the first boom part P1 and the second boom part P2. The boom system also comprises a third boom part P3, which comprises a first end P3a which is fixed to the second end P2b of the second boom part P2 by means of a joint, as well as a free second end P3b. The second end P3b is typically arranged to move in the vertical (plane Z — X) plane, swinging around the joint of the end P2b. The rotation is attained by means of a second cylinder actuator S2 fixed between the second boom part P2 and the third boom part P3.

The outermost boom part P3 can also be arranged to function telescopically to widen the reach of the boom system. The free end P3b of the boom system can be provided with a harvesting head known as such, by means of which a growing tree is cut and felled, the tree trunk is delimbed and cut and the tree trunks are loaded in the load space and unloaded therefrom. It is obvious that the end of the boom system can also be provided with a loading apparatus known as such, which is only used for loading of tree trunks, or with a harvesting head which is only used for cutting and felling of a growing tree and for delimbing and cutting of the tree trunk.

With reference to Fig. 1 , the actuator S1 (i.e. the articulation P1b — P2a) is controlled with control means V1 , such as a control valve V1 and control lines L1 , L2. Control means V2, such as a control valve V2 and control lines L3, L4 are used for controlling the actuator S2 (i.e. the articulation P2b — P3a). For example to lengthen the actuator S1 and to lift the second end P2b simultaneously, the line L1 is coupled to a pressure line P, and the line L2 is coupled to a return line T by means of the control valve V1. For example to shorten the actuator S1 and lower the second end P2b simultaneously, the line L2 is coupled to a pressure line P, and the line L1 is coupled to a return line T by means of the control valve V1. The control valves, such as the valves V1 and V2 are connected to the pressure source P of the control system and to the return line T, such as a tank line, the pressure level of which is typically lower than that of the pressure source P. In addition to the pressure source P and the return line T, the control system can also comprise other components known as such, such as tank means for storing the pressurized medium, filter means, pressure control means for setting the pressure level, and pump means functioning as pressure sources to produce pressure and volume flow.

Fig. 2 shows a known solution by means of which the end P3b of the boom according to Fig. 1 implements at least an approximate horizontal direct transfer (arrows X1 and X2) at a given height Z. The cylinder space S1a of the actuator S1 is coupled to the cylinder space S2b of the actuator S2 by means of a connecting control line PK. The other cylinder capacities S1 b and S2a are coupled to the control valve V1 in such a manner that the pressure line P and the return line T can be alternately coupled thereto. When the end P3b is transferred in the direction X1 , the pressure source P is coupled to the space S2a and the actuator S2 functions as a pump, as described above, and the actuator S1 functions as a brake. The volume flow of the pressurized medium, typically hydraulic fluid, is transferred from the space S2b to the space S1a and from the space S1 b to the return line T, coupled by the control valve V1. When the end P3b is transferred in the direction X2, the pressure source P is alternatively coupled to the space S1 b and the actuator S1 functions as a pump and the actuator S2 functions as a brake.

In Fig. 3, the transfer of the end P3b in the vertical direction (arrow Z), i.e. the movements Z1 and Z2 are implemented by controlling the actuator S1 by means of the control valve V1. Both actuators S1 and S2 and the control valve V2 are used for the direct transfer, i.e. for the horizontal (arrow X) movements X1 , X2.

Fig. 4 shows a first preferred embodiment of the control system according to the invention. In the control system, the swinging of the boom parts is arranged in such a manner that when the actuator S1 lengthens, the end P2b moves upwards, and when it shortens, the end P2b moves downwards, and when the actuator S2 lengthens, the end P3b moves downwards and when it shortens, the end P3b moves upwards.

In a second preferred embodiment of the invention, the coupling of the actuators is such that when the actuator S1 lengthens, the end P2b moves downwards, and when the actuator S2 lengthens, the end P3b moves upwards, wherein also the control line L5, which couples the actuators S1 and S2 in series and which will be described hereinbelow, has to be coupled between the space S1b of the actuator S1 and the space S2a of the actuator S2, wherein the control line L6, which will be described hereinbelow, has to be coupled to the space S1a of the actuator S1. The control line L3 is coupled to the space S2b. A common principle for the first and the second embodiment is that in the direct transfer the cylinder actuator S1 and the cylinder actuator S2 are arranged to move in the same direction, wherein they are either shortened or lengthened.

In a third preferred embodiment of the invention, the coupling of the actuators is such that when the actuator S1 lengthens, the end P2b moves downwards, and when the actuator S2 lengthens, the end P3b moves downward, wherein also the control line L5, which will be described hereinbelow, has to be coupled between the space S1b of the actuator S1 and the space S2b of the actuator S2, wherein the control line L6, which will be described hereinbelow, has to be coupled to the space S1a of the actuator S1. The control line L3 is coupled to the space S2a.

In a fourth preferred embodiment of the invention, the coupling of the actuators is such that when the actuator S1 lengthens, the end P2b moves upwards, and when the actuator S2 lengthens, the end P3b moves upwards, wherein also the control line L5, which will be described hereinbelow, has to be coupled between the space S1a of the actuator S1 and the space S2a of the actuator S2, wherein the control line L6, which will be described hereinbelow, has to be coupled to the space S1b of the actuator S1. The control line L3 is coupled to the space S2b. A common principle for the third and the fourth embodiment is that the cylinder actuator S1 and the cylinder actuator S2 are arranged to move in different directions in the direct transfer mode.

However, a common principle is that in the direct transfer, the boom part P2 and the boom part P3 are arranged to swing to opposite directions simultaneously under the control of the control valve V2.

The control of the movements of the boom system is implemented by means of two control valves V1 and V2. The opening and closing of the control lines is implemented by closing means V3, V4 and V5. According to a preferred embodiment of the invention, the closing means are implemented as such by means of logic valves (Logic Element), which can also comprise a hydraulic pilot control part. Advantageously, the valves are electrically controlled, wherein in the normal position they are either opened or closed and under the electrical control move to another position. The valves are advantageously controlled by means of a control system CTRL of the working machine, comprising for example a control computer. The user informs the control computer for example by means of a switch in which mode the control system has to be at a given time. The closing means V3, V4 and V5 are used for selecting the mode of the boom control, wherein the modes comprise the independent articulation control of the joints of the boom system, as well as the direct transfer, i.e. parallel transfer. With reference to Fig. 4, in the articulation control V3 is open (no control), V4 is closed (no control) and V5 is closed (no control). In the direct transfer V3 is closed (control), V4 is open (control) and V5 is open (control). It is obvious that two or several closing means V3 to V5 can also be arranged in the same valve, such as the electrically controlled two-position directional valve. For the sake of occupational safety, the closing means V3, V4 and V5 are preferably arranged in such a manner that when there is no control, they set the boom control to a mode in which independent articulation control is possible. Thus, the closing means V3, V4 and V5 would be transferred to fixed positions according to Fig. 4 for said mode e.g. by means of spring control. The control may be lacking for example when the electric control is cut off, or in another error situation.

In the articulation-specific control, the control system functions in a similar manner as the control system according to Fig. 1 , and the function of the valves V1 , V2 in Figs. 1 and 4 correspond to each other. In this mode of the control the control line L6 is closed with the closing means V5, the control line L4 is opened with the closing means V3, and the control line L5 is closed with the closing means V4. In said control the ends P2b and P3b can be controlled independently and with different valves.

In the direct transfer, when the end P3b is transferred in the direction X2, the pressure source P is coupled (by using the control line L6) to the space S1b by means of the valve V2 (closing means V5 open) and to convey the volume flow from the space S1a, it is coupled (by using the control line L5) to the space S2b by means of the closing means V4 (the closing means V3 closed). The volume flow is guided from the space S2a to the return line T by means of the control valve V2. When the end P3b is transferred in the direction X1 , the pressure source P is coupled to the space S2a by means of the valve V2 and to convey the volume flow from the space S2b, it is coupled to the space S1a by means of the closing means V4 (the closing means V3 closed). The volume flow is conveyed from the space S1b to the return line T by means of the control valve V2 (closing means V5 open). In this mode the height adjustment in directions Z1 and Z2 is implemented by means of the valve V1 , wherein to move the end P3b in the direction Z1 , the space S1 b is coupled to the pressure source P and the space S1 b to the return line T, wherein to move the end P3b in the direction Z2, the space S1a is coupled to the pressure source P and the space S1a to the return line T. The control line L6 is coupled to the control line L4, wherein the control valve V2 can be implemented with a three-position four-way valve. The presented valves V1 and V2 comprise a closed middle position to close the lines L1 to L4. Both valves V1 and V2 can also be proportion directional valves implementing the presented operation. Advantageously, the valves are electrically controlled control valves which are connected to the control unit CTRL, and which are controlled by means of joysticks C1 and C2. Said joysticks can also be connected to the control unit CTRL, which controls the control means V1 and V2 on the basis of the position of the controllers.

The invention is not restricted solely to the above-presented solution, but it can be modified within the scope of the appended claims. For example two or several closing means V3 to V5 can also be arranged in the same valve, such as an electrically controlled two-position directional valve. It is also obvious that the control lines L1 to L6 can be implemented with pipes and hoses known as such, and at least partly by arranging the necessary control lines in a control block B, to which said control lines are bored. Advantageously, the borings are also provided with said cartridge-type logic valves V3 to V5. In the description hereinabove, the concept of cylinder space refers to one of the two capacities of the cylinder actuator, i.e. either to the space on the piston side or the space on the piston rod side. The coupling of the two cylinder actuators presented in the four different embodiments of the invention with the boom system varies, and thus, the coupling of the control system is also different, wherein when the first cylinder space refers to the space on the piston side, the second cylinder space of the same actuator refers to the space on the piston rod side. Similarly, when the first cylinder space is the space on the piston rod side, the second cylinder space of the same actuator refers to the space on the piston rod side.

Claims

Claims:

1. Pressurized medium operated control system for the boom system of a working machine, which boom system comprises at least

a first boom part (P1) fixed to the working machine from its first end (P1 a),

- a second boom part (P2) fixed to the first boom part (P1) by means of an articulation, comprising a first end (P1a) and a second end (P1b).

a third boom part (P3) fixed to the second boom part (P2) by means of an articulation, comprising a first end (P3a) and a second end (P3b), and

which control system comprises

- a first cylinder actuator (S1) fixed between the first boom part (P1) and the second boom part (P2), which is arranged for moving the second end (P2b) of the second boom part (P2) on a substantially vertical plane (plane Z — X),

- a second cylinder actuator (S2) fixed between the second boom part (P2) and the third boom part (P3), which is arranged for moving the second end (P3b) of the third boom part (P3) in a substantially vertical plane (plane Z — X),

- first control means (V1) and second control means (V2) connected to the pressure source (P) and the return line (T),

characterized in that

- the control system is arranged to be set in an articulation control mode, wherein the first cylinder actuator (S1) is arranged to be independently controlled by means of the first control means (V1 ), and the second cylinder actuator (S2) is arranged to be controlled independently by means of the second control means (V2),

that the control system is also arranged to be set in a direct transfer mode, wherein the second boom part (P2) and the third boom part (P3) are arranged to swing to opposite directions simultaneously under the control of the second control means (V2), and wherein the first cylinder actuator

(S1) and the second cylinder actuator (S2) are connected in series.

2. The control system according to claim 1 , in which

said first control means (V1) are arranged for conveying the pressurized medium via a first control line (L1) to the first cylinder space (S1a) of the first cylinder actuator and, alternatively, via a second control line (L2) to the second cylinder space (S1b), and

said second control means (V2) are arranged for conveying the pressurized medium via a third control line (L3) to the first cylinder space (S2a) of the second cylinder actuator and, alternatively, via a fourth control line (L4) to the second cylinder space (S2b), and

which control system also comprises

- a fifth control line (L5) which is arranged for conveying the pressurized medium between the first cylinder space (S1a) of the first cylinder actuator (S1) and the second cylinder space (S2b) of the second cylinder actuator (S2), and

- first closing means (V4) arranged in the fifth control line (L5) for closing and opening said fifth control line (L5), a sixth control line (L6) which is arranged for conveying the pressurized medium between the second control means (V2) and the second cylinder space (S1b) of the first cylinder actuator (S1),

second closing means (V5) arranged in the sixth control line (L6) for closing and opening said sixth control line (L6),

characterized in that

the control system also comprises third closing means (V3) arranged in the fourth control line (L4) for closing and opening said fourth control line (L4),

that in the articulation control mode, when the first closing means (V4) is closed, the second closing means (V5) is closed and the third closing means (V3) is opened, the first cylinder actuator (S1) is arranged to be independently controlled by means of the first control means (V1), and the second cylinder actuator (S2) is arranged to be controlled independently by means of the second control means (V2), and

- that in the direct transfer mode, when the first closing means (V4) is opened, the second closing means (V5) is opened and the third closing means (V3) is closed, the second boom part (P2) and the third boom part (P3) are arranged to swing to opposite directions simultaneously under the control of the second control means (V2).

3. The control system according to claim 2, characterized in that in the direct transfer mode, when the first closing means (V4) is opened, the second closing means (V5) is opened and the third closing means (V3) is closed, the first cylinder actuator (S1) is arranged to be shortened and lengthened by means of the first control means (V1).

4. The control system according to claim 2 or 3, characterized in that the part of said fourth control line (L4), which is located between the second control means (V2) and the third closing means (V3), and said sixth control line (L6) are connected to each other.

5. The control system according to any of the claims 2 to 4, characterized in that the first closing means (V4), the second closing means (V5) and the third closing means (V3) are each formed by means of a 2/2-cartridge valve.

6. The control system according to any of the claims 1 to 5, characterized in that when the first cylinder actuator (S1) is lengthens, it is arranged to move the second end (P2b) of the second boom part (P2) upwards or downwards, and that even when it shortens, the second cylinder actuator (S2) is arranged to move the second end (P3b) of the third boom part (P3) upwards or downwards.

7. The control system according to any of the claims 1 to 6, characterized in that said working machine is a working machine intended movable in a terrain to handle and transport trees, and that a tool functioning as a loader and/or a harvesting head is fixed to the second end (P3b) of the third boom part (P3).

8. The control system according to any of the claims 1 to 7, characterized in that said working machine comprises a computer controlled control unit (CTRL) for setting the control system in the articulation control mode and in the direct transfer mode.

9. The control system according to any of the claims 1 to 8, characterized in that it comprises a first control lever (C1) and a second control lever (C2), wherein in the articulation control mode the first cylinder actuator (S1) is arranged to be controlled by means of the first control lever (C1), and the second cylinder actuator (S2) is arranged to be controlled by means of the second control lever (C2), and wherein in the direct transfer mode both cylinder actuators (S1 , S2) are arranged to be controlled by means of the second control lever (C2) to actuate a horizontal movement (Z1 , Z2), and to be controlled by means of the first control lever (C1) to actuate a vertical movement (X1 , X2).

10. The control system according to any of the claims 1 to 9, characterized in that the first closing means (V1), and the second closing means (V2) are each formed by means of a proportion directional valve.